Operations management

Operations management is an area of management concerned with designing and controlling the process of production and redesigning business operations in the production of goods or services. It involves the responsibility of ensuring that business operations are efficient in terms of using as few resources as needed and effective in meeting customer requirements.
It is concerned with managing an entire production or service system which is the process that converts inputs (in the forms of raw materials, labor, consumers, and energy) into outputs (in the form of goods and/or services for consumers). Operations produce products, manage quality and create services. Operation management covers sectors like banking systems, hospitals, companies, working with suppliers, customers, and using technology. Operations is one of the major functions in an organization along with supply chains, marketing, finance and human resources. The operations function requires management of both the strategic and day-to-day production of goods and services.
In managing manufacturing or service operations several types of decisions are made including operations strategy, product design, process design, quality management, capacity, facilities planning, production planning and inventory control. Each of these requires an ability to analyze the current situation and find better solutions to improve the effectiveness and efficiency of manufacturing or service operations. A modern, integrated vision of the many aspects of operations management may be found in recent textbooks on the subject.
History.
The history of production and operation systems begins around 5000 B.C. when Sumerian priests developed the ancient system of recording inventories, loans, taxes, and business transactions. The next major historical application of operation systems occurred in 4000 B.C. It was during this time that the Egyptians started using planning, organization, and control in large projects such as the construction of the pyramids. By 1100 B.C., labor was being specialized in China; by about 370 B.C., Xenophon described the advantages of dividing the various operations necessary for the production of shoes among different individuals in ancient Greece:
In the Middle Ages, kings and queens ruled over large areas of land. Loyal noblemen maintained large sections of the monarch's territory. This hierarchical organization in which people were divided into classes based on social position and wealth became known as the feudal system. In the feudal system, vassals and serfs produced for themselves and people of higher classes by using the ruler's land and resources. Although a large part of labor was employed in agriculture, artisans contributed to economic output and formed guilds. The guild system, operating mainly between 1100 and 1500, consisted of two types: merchant guilds, who bought and sold goods, and craft guilds, which made goods. Although guilds were regulated as to the quality of work performed, the resulting system was rather rigid, shoemakers, for example, were prohibited from tanning hides.
Services were also performed in the Middle Ages by servants. They provided service to the nobility in the form of cooking, cleaning and providing entertainment. Court jesters were considered service providers. The medieval army could also be considered a service since they defended the nobility.
The industrial revolution was facilitated by two elements: interchangeability of parts and division of labor. Division of labor has been a feature from the beginning of civilization, the extent to which the division is carried out varied considerably depending on period and location. Compared to the Middle Ages, the Renaissance and the Age of Discovery were characterized by a greater specialization in labor, which was a characteristic of the growing cities and trade networks of Europe. An important leap in manufacturing efficiency came in the late eighteenth century as Eli Whitney popularized the concept of interchangeability of parts when he manufactured 10,000 muskets. Up to this point in the history of manufacturing, each product (e.g. each musket) was considered a special order, meaning that parts of a given musket were fitted only for that particular musket and could not be used in other muskets. Interchangeability of parts allowed the mass production of parts independent of the final products in which they would be used. An entire new market to fill the need for the sale and manufacturing of muskets began at this time.
In 1883, Frederick Winslow Taylor introduced the stopwatch method for accurately measuring the time to perform each single task of a complicated job. He developed the scientific study of productivity and identifying how to coordinate different tasks to eliminate wasting of time and increase the quality of work. The next generation of scientific study occurred with the development of work sampling and predetermined motion time systems (PMTS). Work sampling is used to measure the random variable associated with the time of each task. PMTS allows the use of standard predetermined tables of the smallest body movements (e.g. turning the left wrist by 90°), and integrating them to predict the time needed to perform a simple task. PMTS has gained substantial importance due to the fact that it can predict work measurements without observing the actual work. The foundation of PMTS was laid out by the research and development of Frank B. and Lillian M. Gilbreth around 1912. The Gilbreths took advantage of taking motion pictures at known time intervals while operators were performing the given task.
Service Industries: At the turn of the twentieth century, the services industries were already developed, but largely fragmented. In 1900 the U.S. service industry consisted of banks, professional services, schools, general stores, railroads and telegraph. Services were largely local in nature (except for railroads and telegraph) and owned by entrepreneurs and families. The U.S. in 1900 had 31% employment in services, 31% in manufacturing and 38% in agriculture.
The idea of the production line has been used multiple times in history prior to Henry Ford: the Venetian Arsenal (1104); Smith's pin manufacturing, in the Wealth of Nations (1776) or Brunel's Portsmouth Block Mills (1802). Ransom Olds was the first to manufacture cars using the assembly line system, but Henry Ford developed the first auto assembly system where a car chassis was moved through the assembly line by a conveyor belt while workers added components to it until the car was completed. During World War II, the growth of computing power led to further development of efficient manufacturing methods and the use of advanced mathematical and statistical tools. This was supported by the development of academic programs in industrial and systems engineering disciplines, as well as fields of operations research and management science (as multi-disciplinary fields of problem solving). While systems engineering concentrated on the broad characteristics of the relationships between inputs and outputs of generic systems, operations researchers concentrated on solving specific and focused problems. The synergy of operations research and systems engineering allowed for the realization of solving large scale and complex problems in the modern era. Recently, the development of faster and smaller computers, intelligent systems, and the World Wide Web has opened new opportunities for operations, manufacturing, production, and service systems.
Industrial Revolution.
Before the First industrial revolution work was mainly done through two systems: domestic system and craft guilds. In the domestic system merchants took materials to homes where artisans performed the necessary work, craft guilds on the other hand were associations of artisans which passed work from one shop to another, for example: leather was tanned by a tanner, passed to curriers, and finally arrived at shoemakers and saddlers.
The beginning of the industrial revolution is usually associated with the eighteenth-century English textile industry, with the invention of the flying shuttle by John Kay in 1733, the spinning jenny by James Hargreaves in 1765, the water frame by Richard Arkwright in 1769 and the steam engine by James Watt in 1765. In 1851 at the Crystal Palace Exhibition the term American system of manufacturing was used to describe the new approach that was evolving in the United States of America which was based on two central features: interchangeable parts and extensive use of mechanization to produce them.
Second Industrial Revolution and post-industrial society.
Henry Ford was 39 years old when he founded the Ford Motor Company in 1903, with $28,000 capital from twelve investors. The model T car was introduced in 1908, however it was not until Ford implemented the assembly line concept, that his vision of making a popular car affordable by every middle-class American citizen would be realized. The first factory in which Henry Ford used the concept of the assembly line was Highland Park (1913), he characterized the system as follows:
This became one of the central ideas that led to mass production, one of the main elements of the Second Industrial Revolution, along with emergence of the electrical industry and petroleum industry.
The post-industrial economy was noted in 1973 by Daniel Bell. He stated that the future economy would provide more GDP and employment from services than from manufacturing and have a great effect on society. Since all sectors are highly interconnected, this did not reflect less importance for manufacturing, agriculture, and mining but just a shift in the type of economic activity.
Operations management.
Although productivity benefited considerably from technological inventions and division of labor, the problem of systematic measurement of performances and the calculation of these by the use of formulas remained somewhat unexplored until Frederick Taylor, whose early work focused on developing what he called a "differential piece-rate system" and a series of experiments, measurements and formulas dealing with cutting metals and manual labor. The differential piece-rate system consisted in offering two different pay rates for doing a job: a higher rate for workers with high productivity (efficiency) and who produced high quality goods (effectiveness) and a lower rate for those who fail to achieve the standard. One of the problems Taylor believed could be solved with this system, was the problem of soldiering: faster workers reducing their production rate to that of the slowest worker.
In 1911 Taylor published his "The Principles of Scientific Management", in which he characterized scientific management (also known as Taylorism) as:
Taylor is also credited for developing stopwatch time study, this combined with Frank and Lillian Gilbreth motion study gave way to time and motion study which is centered on the concepts of standard method and standard time. Frank Gilbreth is also responsible for introducing the flow process chart in 1921. Other contemporaries of Taylor worth remembering are Morris Cooke (rural electrification in the 1920s and implementer of Taylor's principles of scientific management in the Philadelphia's Department of Public Works), Carl Barth (speed-and-feed-calculating slide rules ) and Henry Gantt (Gantt chart). Also in 1910 Hugo Diemer published the first industrial engineering book: Factory Organization and Administration.
In 1913 Ford Whitman Harris published his "How many parts to make at once" in which he presented the idea of the economic order quantity model. He described the problem as follows:
This paper inspired a large body of mathematical literature focusing on the problem of production planning and inventory control.
In 1924 Walter Shewhart introduced the control chart through a technical memorandum while working at Bell Labs, central to his method was the distinction between common cause and special cause of variation. In 1931 Shewhart published his Economic Control of Quality of Manufactured Product, the first systematic treatment of the subject of Statistical Process Control (SPC). He defined control:
In the 1940s methods-time measurement (MTM) was developed by H.B. Maynard, J.L. Schwab and G.J. Stegemerten. MTM was the first of a series of predetermined motion time systems, predetermined in the sense that estimates of time are not determined in loco but are derived from an industry standard. This was explained by its originators in a book they published in 1948 called "Method-Time Measurement".
Up to this point in history, optimization techniques were known for a very long time, from the simple methods employed by F.W.Harris to the more elaborate techniques of the calculus of variations developed by Euler in 1733 or the multipliers employed by Lagrange in 1811, and computers were slowly being developed, first as analog computers by Sir William Thomson (1872) and James Thomson (1876) moving to the electromechanical computers of Konrad Zuse (1939 and 1941). During World War II however, the development of mathematical optimization went through a major boost with the development of the Colossus computer, the first electronic digital computer that was all programmable, and the possibility to computationally solve large linear programming problems, first by Kantorovich in 1939 working for the Soviet government and latter on in 1947 with the simplex method of Dantzig. These methods are known today as belonging to the field of operations research.
From this point on a curious development took place: while in the United States the possibility of applying the computer to business operations led to the development of management software architecture such as MRP and successive modifications, and ever more sophisticated optimization techniques and manufacturing simulation software, in post-war Japan a series of events at Toyota Motor led to the development of the Toyota Production System (TPS) and Lean Manufacturing.
In 1943, in Japan, Taiichi Ohno arrived at Toyota Motor company. Toyota evolved a unique manufacturing system centered on two complementary notions: just in time (produce only what is needed) and autonomation (automation with a human touch). Regarding JIT, Ohno was inspired by American supermarkets: workstations functioned like a supermarket shelf where the customer can get products they need, at the time they need and in the amount needed, the workstation (shelf) is then restocked. Autonomation was developed by Toyoda Sakichi in Toyoda Spinning and Weaving: an automatically activated loom that was also foolproof, that is automatically detected problems. In 1983 J.N Edwards published his "MRP and Kanban-American style" in which he described JIT goals in terms of seven zeros: zero defects, zero (excess) lot size, zero setups, zero breakdowns, zero handling, zero lead time and zero surging. This period also marks the spread of Total Quality Management (TQM) in Japan, ideas initially developed by American authors such as Deming, Juran and Armand V. Feigenbaum. TQM is a strategy for implementing and managing quality improvement on an organizational basis, this includes: participation, work culture, customer focus, supplier quality improvement and integration of the quality system with business goals. Schnonberger identified seven fundamentals principles essential to the Japanese approach:
Meanwhile, in the sixties, a different approach was developed by George W. Plossl and Oliver W. Wight, this approach was continued by Joseph Orlicky as a response to the TOYOTA Manufacturing Program which led to Material Requirements Planning (MRP) at IBM, latter gaining momentum in 1972 when the American Production and Inventory Control Society launched the "MRP Crusade". One of the key insights of this management system was the distinction between dependent demand and independent demand. Independent demand is demand which originates outside of the production system, therefore not directly controllable, and dependent demand is demand for components of final products, therefore subject to being directly controllable by management through the bill of materials, via product design. Orlicky wrote "Materials Requirement Planning" in 1975, the first hard cover book on the subject. MRP II was developed by Gene Thomas at IBM, and expanded the original MRP software to include additional production functions. Enterprise resource planning (ERP) is the modern software architecture, which addresses, besides production operations, distribution, accounting, human resources and procurement.
Dramatic changes were occurring in the service industries, as well. Beginning in 1955 McDonald's provided one of the first innovations in service operations. McDonald's is founded on the idea of the production-line approach to service. This requires a standard and limited menu, an assembly-line type of production process in the back-room, high customer service in the front-room with cleanliness, courtesy and fast service. While modeled after manufacturing in the production of the food in the back-room, the service in the front-room was defined and oriented to the customer. It was the McDonald's operations system of both production and service that made the difference. McDonald's also pioneered the idea of franchising this operation system to rapidly spread the business around the country and later the world.
FedEx in 1971 provided the first overnight delivery of packages in the U.S. This was based on the innovative idea of flying all packages into the single airport in Memphis Tenn by midnight each day, resorting the packages for delivery to destinations and then flying them back out the next morning for delivery to numerous locations. This concept of a fast package delivery system created a whole new industry, and eventually allowed fast delivery of online orders by Amazon and other retailers.
Walmart provided the first example of very low cost retailing through design of their stores and efficient management of their entire supply chain. Starting with a single store in Roger's Arkansas in 1962, Walmart has now become the world's largest company. This was accomplished by adhering to their system of delivering the goods and the service to the customers at the lowest possible cost. The operations system included careful selection of merchandise, low cost sourcing, ownership of transportation, cross-docking, efficient location of stores and friendly home-town service to the customer.
In 1987 the International Organization for Standardization (ISO), recognizing the growing importance of quality, issued the ISO 9000, a family of standards related to quality management systems. There standards apply to both manufacturing and service organizations. There has been some controversy regarding the proper procedures to follow and the amount of paperwork involved, but much of that has improved in current ISO 9000 revisions.
With the coming of the Internet, in 1994 Amazon devised a service system of on-line retailing and distribution. With this innovative system customers were able to search for products they might like to buy, enter the order for the product, pay online, and track delivery of the product to their location, all in two days. This required not only very large computer operations, but dispersed warehouses, and an efficient transportation system. Service to customers including a high merchandise assortment, return services of purchases, and fast delivery is at the forefront of this business. It is the customer being in the system during the production and delivery of the service that distinguishes all services from manufacturing.
Recent trends in the field revolve around concepts such as:
Topics.
Production systems.
A production system comprises both the technological elements (machines and tools) and organizational behavior (division of labor and information flow). An individual production system is usually analyzed in the literature referring to a single business, therefore it's usually improper to include in a given production system the operations necessary to process goods that are obtained by purchasing or the operations carried by the customer on the sold products, the reason being simply that since businesses need to design their own production systems this then becomes the focus of analysis, modeling and decision making (also called "configuring" a production system).
A first possible distinction in production systems (technological classification) is between continuous process production and discrete part production (manufacturing).
Another possible classification is one based on Lead Time (manufacturing lead time vs delivery lead time): engineer to order (ETO), purchase to order (PTO), make to order (MTO), assemble to order (ATO) and make to stock (MTS). According to this classification different kinds of systems will have different customer order decoupling points (CODP), meaning that work in progress (WIP) cycle stock levels are practically nonexistent regarding operations located after the CODP (except for WIP due to queues). (See Order fulfillment)
The concept of production systems can be expanded to the service sector world keeping in mind that services have some fundamental differences in respect to material goods: intangibility, client always present during transformation processes, no stocks for "finished goods". Services can be classified according to a service process matrix: degree of labor intensity (volume) vs degree of customization (variety). With a high degree of labor intensity there are Mass Services (e.g., commercial banking bill payments and state schools) and Professional Services (e.g., personal physicians and lawyers), while with a low degree of labor intensity there are Service Factories (e.g., airlines and hotels) and Service Shops (e.g., hospitals and auto mechanics).
The systems described above are ideal types: real systems may present themselves as hybrids of those categories. Consider, for example, that the production of jeans involves initially carding, spinning, dyeing and weaving, then cutting the fabric in different shapes and assembling the parts in pants or jackets by combining the fabric with thread, zippers and buttons, finally finishing and distressing the pants/jackets before being shipped to stores. The beginning can be seen as process production, the middle as part production and the end again as process production: it's unlikely that a single company will keep all the stages of production under a single roof, therefore the problem of vertical integration and outsourcing arises. Most products require, "from a supply chain perspective", both process production and part production.
Metrics: efficiency and effectiveness.
Operations strategy concerns policies and plans of use of the firm productive resources with the aim of supporting long term competitive strategy. Metrics in operations management can be broadly classified into efficiency metrics and effectiveness metrics. Effectiveness metrics involve:
A more recent approach, introduced by Terry Hill, involves distinguishing competitive variables in order winner and order qualifiers when defining operations strategy. Order winners are variables which permit differentiating the company from competitors, while order qualifiers are prerequisites for engaging in a transaction. This view can be seen as a unifying approach between operations management and marketing (see segmentation and positioning).
Productivity is a standard efficiency metric for evaluation of production systems, broadly speaking a ratio between outputs and inputs, and can assume many specific forms, for example: machine productivity, workforce productivity, raw material productivity, warehouse productivity (=inventory turnover). It is also useful to break up productivity in use U (productive percentage of total time) and yield η (ratio between produced volume and productive time) to better evaluate production systems performances. Cycle times can be modeled through manufacturing engineering if the individual operations are heavily automated, if the manual component is the prevalent one, methods used include: time and motion study, predetermined motion time systems and work sampling.
ABC analysis is a method for analyzing inventory based on Pareto distribution, it posits that since revenue from items on inventory will be power law distributed then it makes sense to manage items differently based on their position on a revenue-inventory level matrix, 3 classes are constructed (A, B and C) from cumulative item revenues, so in a matrix each item will have a letter (A, B or C) assigned for revenue and inventory. This method posits that items away from the diagonal should be managed differently: items in the upper part are subject to risk of obsolescence, items in the lower part are subject to risk of stockout.
Throughput is a variable which quantifies the number of parts produced in the unit of time. Although estimating throughput for a single process maybe fairly simple, doing so for an entire production system involves an additional difficulty due to the presence of queues which can come from: machine breakdowns, processing time variability, scraps, setups, maintenance time, lack of orders, lack of materials, strikes, bad coordination between resources, mix variability, plus all these inefficiencies tend to compound depending on the nature of the production system. One important example of how system throughput is tied to system design are bottlenecks: in job shops bottlenecks are typically dynamic and dependent on scheduling while on transfer lines it makes sense to speak of "the bottleneck" since it can be univocally associated with a specific station on the line. This leads to the problem of how to define capacity measures, that is an estimation of the maximum output of a given production system, and capacity utilization.
Overall equipment effectiveness (OEE) is defined as the product between system availability, cycle time efficiency and quality rate. OEE is typically used as key performance indicator (KPI) in conjunction with the lean manufacturing approach.
Configuration and management.
Designing the "configuration of production systems" involves both technological and organizational variables. Choices in production technology involve: dimensioning capacity, fractioning capacity, capacity location, outsourcing processes, process technology, automation of operations, trade-off between volume and variety (see Hayes-Wheelwright matrix). Choices in the organizational area involve: defining worker skills and responsibilities, team coordination, worker incentives and information flow.
In "production planning", there is a basic distinction between the push approach and the pull approach, with the later including the singular approach of just in time. Pull means that the production system authorizes production based on inventory level; push means that production occurs based on demand (forecasted or present, that is purchase orders). An individual production system can be both push and pull; for example activities before the CODP may work under a pull system, while activities after the CODP may work under a push system.
The traditional pull approach to inventory control, a number of techniques have been developed based on the work of Ford W. Harris (1913), which came to be known as the economic order quantity (EOQ) model. This model marks the beginning of inventory theory, which includes the Wagner-Within procedure, the newsvendor model, base stock model and the fixed time period model. These models usually involve the calculation of cycle stocks and buffer stocks, the latter usually modeled as a function of demand variability. The economic production quantity (EPQ) differs from the EOQ model only in that it assumes a constant fill rate for the part being produced, instead of the instantaneous refilling of the EOQ model.
Joseph Orlickly and others at IBM developed a push approach to inventory control and production planning, now known as material requirements planning (MRP), which takes as input both the master production schedule (MPS) and the bill of materials (BOM) and gives as output a schedule for the materials (components) needed in the production process. MRP therefore is a planning tool to manage purchase orders and production orders (also called jobs).
The MPS can be seen as a kind of aggregate planning for production coming in two fundamentally opposing varieties: plans which try to chase demand and level plans which try to keep uniform capacity utilization. Many models have been proposed to solve MPS problems:
MRP can be briefly described as a 3s procedure: sum (different orders), split (in lots), shift (in time according to item lead time). To avoid an "explosion" of data processing in MRP (number of BOMs required in input) planning bills (such as family bills or super bills) can be useful since they allow a rationalization of input data into common codes.
MRP had some notorious problems such as infinite capacity and fixed lead times, which influenced successive modifications of the original software architecture in the form of MRP II, enterprise resource planning (ERP) and advanced planning and scheduling (APS).
In this context problems of scheduling (sequencing of production), loading (tools to use), part type selection (parts to work on) and applications of operations research have a significant role to play.
Lean manufacturing is an approach to production which arose in Toyota between the end of World War II and the seventies. It comes mainly from the ideas of Taiichi Ohno and Toyoda Sakichi which are centered on the complementary notions of just in time and autonomation (jidoka), all aimed at reducing waste (usually applied in PDCA style). Some additional elements are also fundamental: production smoothing (Heijunka), capacity buffers, setup reduction, cross-training and plant layout.
A series of tools have been developed mainly with the objective of replicating Toyota success: a very common implementation involves small cards known as kanbans; these also come in some varieties: reorder kanbans, alarm kanbans, triangular kanbans, etc. In the classic kanban procedure with one card:
The two-card kanban procedure differs a bit:
Since the number of kanbans in the production system is set by managers as a constant number, the kanban procedure works as WIP controlling device, which for a given arrival rate, per Little's law, works as a lead time controlling device.
In Toyota the TPS represented more of a philosophy of production than a set of specific lean tools, the latter would include:
Seen more broadly, JIT can include methods such as: product standardization and modularity, group technology, total productive maintenance, job enlargement, job enrichment, flat organization and vendor rating (JIT production is very sensitive to replenishment conditions).
In heavily automated production systems production planning and information gathering may be executed via the control system, attention should be paid however to avoid problems such as deadlocks, as these can lead to productivity losses.
Project Production Management (PPM) applies the concepts of operations management to the execution of delivery of capital projects by viewing the sequence of activities in a project as a production system. Operations managements principles of variability reduction and management are applied by buffering through a combination of capacity, time and inventory.
Service operations.
Service industries are a major part of economic activity and employment in all industrialized countries comprising 80 percent of employment and GDP in the U.S. Operations management of these services, as distinct from manufacturing, has been developing since the 1970s through publication of unique practices and academic research. Please note that this section does not particularly include "Professional Services Firms" and the professional services practiced from this expertise (specialized training and education within).
According to Fitzsimmons, Fitzsimmons and Bordoloi (2014) differences between manufactured goods and services are as follows:
These four comparisons indicate how management of service operations are quite different from manufacturing regarding such issues as capacity requirements (highly variable), quality assurance (hard to quantify), location of facilities (dispersed), and interaction with the customer during delivery of the service (product and process design).
While there are differences there are also many similarities. For example, quality management approaches used in manufacturing such as the Baldrige Award, and Six Sigma have been widely applied to services. Likewise, lean service principles and practices have also been applied in service operations. The important difference being the customer is in the system while the service is being provided and needs to be considered when applying these practices.
One important difference is service recovery. When an error occurs in service delivery, the recovery must be delivered on the spot by the service provider. If a waiter in a restaurant spills soup on the customer's lap, then the recovery could include a free meal and a promise of free dry cleaning. Another difference is in planning capacity. Since the product cannot be stored, the service facility must be managed to peak demand which requires more flexibility than manufacturing. Location of facilities must be near the customers and scale economics can be lacking. Scheduling must consider the customer can be waiting in line. Queuing theory has been devised to assist in design of service facilities waiting lines. Revenue management is important for service operations, since empty seats on an airplane are lost revenue when the plane departs and cannot be stored for future use.
Mathematical modeling.
There are also fields of mathematical theory which have found applications in the field of operations management such as operations research: mainly mathematical optimization problems and queue theory. Queue theory is employed in modelling queue and processing times in production systems while mathematical optimization draws heavily from multivariate calculus and linear algebra. Queue theory is based on Markov chains and stochastic processes. Computations of safety stocks are usually based on modeling demand as a normal distribution and MRP and some inventory problems can be formulated using optimal control.
When analytical models are not enough, managers may resort to using simulation. Simulation has been traditionally done through the discrete event simulation paradigm, where the simulation model possesses a state which can only change when a discrete event happens, which consists of a clock and list of events. The more recent transaction-level modeling paradigm consists of a set of resources and a set of transactions: transactions move through a network of resources (nodes) according to a code, called a process.
Since real production processes are always affected by disturbances in both inputs and outputs, many companies implement some form of quality management or quality control. The Seven Basic Tools of Quality designation provides a summary of commonly used tools:
These are used in approaches like total quality management and Six Sigma. Keeping quality under control is relevant to both increasing customer satisfaction and reducing processing waste.
Operations management textbooks usually cover demand forecasting, even though it is not strictly speaking an operations problem, because demand is related to some production systems variables. For example, a classic approach in dimensioning safety stocks requires calculating the standard deviation of forecast errors. Demand forecasting is also a critical part of push systems, since order releases have to be planned ahead of actual clients’ orders. Also, any serious discussion of capacity planning involves adjusting company outputs with market demands.
Safety, risk and maintenance.
Other important management problems involve maintenance policies (see also reliability engineering and maintenance philosophy), safety management systems (see also safety engineering and Risk management), facility management and supply chain integration.
Organizations.
The following organizations support and promote operations management:
Journals.
The following high-ranked academic journals are concerned with operations management issues:


Apple Dot Matrix Printer

The Apple Dot Matrix Printer (often shortened to Apple DMP) is a printer manufactured by C. Itoh and sold under the Apple Computer, Inc. label in 1982 for the Apple II series, Lisa, and the Apple III. It was succeeded by the ImageWriter in 1984.
The Apple DMP is the last parallel port printer sold under the Apple label; all subsequent Apple printers (ImageWriter, ImageWriter II, Scribe, LaserWriter, etc.) were serial port printers.


Computer-aided production engineering

Computer-aided production engineering (CAPE) is a relatively new and significant branch of engineering. Global manufacturing has changed the environment in which goods are produced. Meanwhile, the rapid development of electronics and communication technologies has required design and manufacturing to keep pace.
Description of CAPE.
CAPE is seen as a new type of computer-aided engineering environment which will improve the productivity of manufacturing/industrial engineers. This environment would be used by engineers to design and implement future manufacturing systems and subsystems. Work is currently underway at the United States National Institute of Standards and Technology (NIST) on CAPE systems. The NIST project is aimed at advancing the development of software environments and tools for the design and engineering of manufacturing systems.
CAPE and the Future of Manufacturing.
The future of manufacturing will be determined by the efficiency with which it can incorporate new technologies. The current process in engineering manufacturing systems is often ad hoc, with computerized tools being used on a limited basis. Given the costs and resources involved in the construction and operation of manufacturing systems, the engineering process must be made more efficient. New computing environments for engineering manufacturing systems could help achieve that objective.
Why is CAPE important? In much the same way that product designers need computer-aided design systems, manufacturing and industrial engineers need sophisticated computing capabilities to solve complex problems and manage the vast data associated with the design of a manufacturing system.
In order to solve these complex problems and manage design data, computerized tools must be used in the application of scientific and engineering methods to the problem of the
design and implementation of manufacturing systems. Engineers must address the entire factory as a system and the interactions of that system with its surrounding environment.
Components of a factory system include:
CAPE must not only be concerned with the initial design and engineering of the factory, it must also address enhancements over time. CAPE should support standard engineering methods and problem-solving techniques, automate mundane tasks, and provide reference data to support the decision-making process.
The environment should be designed to help engineers become more productive and effective in their work. This would be implemented on personal computers or engineering workstations which have been configured with appropriate peripheral devices. Engineering tool developers will have to integrate the functions and data used by a number of different disciplines, for example:
Many of the methods, formulas, and data associated with these technical areas currently exist only in engineering handbooks. Although some computerized tools are available, they are often very specialized, difficult to use, and do not share information or work together. Engineering tools built by different vendors must be made compatible through open systems architectures and interface standards.
What CAPE will look like.
CAPE will be based upon computer systems providing an integrated set of design and engineering tools. These software tools will be used by a company's manufacturing engineers to continuously improve its production systems. They will maintain information about manufacturing resources, enhance production capabilities, and develop new facilities and systems. Engineers working on different workstations will share information through a common database.
Using CAPE, an engineering team will prepare detailed plans and working models for an entire factory in a matter of days. Alternative solutions to production problems could be quickly developed and evaluated. This would be a significant improvement over current manual methods which may require weeks or months of intensive activity.
To achieve this goal, a new set of engineering tools are needed. Examples of functions which should be supported include:
The tools implementing these functions must be highly automated and integrated; and will need to provide quick access to a wide range of data. This data must be maintained in a format that is accessible and usable by the engineering tools. Some examples of the information that might be contained in these electronic libraries include:
These on-line libraries would allow engineers to quickly develop solutions based upon the work of others.
Another critical aspect of this engineering environment is affordability, which
can best be achieved by designing an environment that can be constructed from low cost "off-the-shelf" commercial products, rather than custombuilt computer hardware and software. The basic engineering environment must be affordable. For both cost and technical reasons, it must be designed to be able to support incremental upgrades. Incremental upgrades would allow companies to add capabilities as they are needed. Commercial software products must be easy to install and integrate with other software already in use. These capabilities exist to a limited extent in some general purpose commercial software today, e.g., word processors, databases, spreadsheets.
Technical Concerns.
Many technical issues must be considered in the design and development of new engineering tools for CAPE. These issues include:
There are three critical elements to be addressed: creating a common manufacturing systems information model; using an engineering life cycle approach; and developing a software tool integration framework.
Resolution of these elements will help ensure that independently developed systems will be able to work together. The common information model should identify the elements of the manufacturing system and their relationships to each other; the functions or processes performed by each element; the tools, materials, and information required to perform those functions; and measures of effectiveness for the model and its component elements.
There have been many efforts over the years to develop information models for different
aspects of manufacturing, but no known existing model fully meets the needs of a CAPE ernviroment. Therefore, a life cycle approach is needed to identify the different processes that a CAPE environment must support, and must define all phases of a manufacturing system or subsystem's existence. Some of the major phases which may be included in a system life cycle approach are, requirements identification; system design specification; vendor selection; system development and upgrades; installation, testing, and training; and benchmarking of production operations.
Management, coordination, and administration functions need to be performed during each phase of the life cycle. Phases may be repeated over time as a system is upgraded or re-engineered to meet changing needs or incorporate new technologies.
A software tool integration framework should specify how the tools could be independently designed and developed. The framework would define how CAPE tools would deal with common services, interact with each other and coordinate problem solving activities. Although some existing software products and standards currently address the common services issue, the problem of tool interaction remains largely unsolved. The problem of tool interaction is not limited to the domain of computer-aided manufacturing systems engineering—it is pervasive across the software industry.
CAPE's current state.
An initial CAPE environment has been established from commercial off-the-shelf (COTS) software packages. This new environment is being used to demonstrate commercially available tools to perform CAPE functions, to develop a better understanding and define functional requirements for individual engineering tools and the overall environment, and to identify the integration issues which must be addressed to implement compatible environments in the future.
Several engineering demonstrations using COTS tools are under development. These demonstrations are designed to illustrate the various types of functions that must be performed in engineering a manufacturing system.
Functions supported by the current COTS environment include: system specification/diagramming,
process flowcharting, information modeling, computer-aided design of products, plant layout, material flow analysis, ergonomic workplace design, mathematical modeling, statistical analysis, line balancing, manufacturing simulation, investment analysis, project management, knowledge-based system development, spreadsheets, document preparation, user interface development, document illustration, forms and database management.


Inkjet technology

Inkjet technology originally was invented for depositing aqueous inks on paper in 'selective' positions based on the ink properties only. Inkjet nozzles and inks were designed together and the inkjet performance was based on a design. It was used as a data recorder in the early 1950s, later in the 1950s co-solvent-based inks in the publishing industry were seen for text and images, then solvent-based inks appeared in industrial marking on specialized surfaces and in the1990's phase change or hot-melt ink has become a popular with images and digital fabrication of electronic and mechanical devices, especially jewelry. Although the terms "jetting", "inkjet technology" and "inkjet printing", are commonly used interchangeably, inkjet printing usually refers to the publishing industry, used for printing graphical content, while industrial jetting usually refers to general purpose fabrication via material particle deposition.
Many companies have worked with inkjet over the years. Many patents have been issued and the technology has been used in a number of products. The basic form of the inkjet was a single nozzle with either fluid forced through under pressure, pulled from it by electrical potential or pushed out with the help of a piezo. Single nozzle inkjets will be discussed first in this introduction. Inkjet technology was pioneered by Teletype Corporation in the 1960s which introduced the "electronic pull", high voltage drop extraction from a nozzle, Inktronic Teleprinter in 1965 printing at 120 characters per second (cps) from a row of 40 inkjets using the Charles R. Winston patent, Method and Apparatus for Transferring Inks, 1962, US3,060,429. Teletype experimented with "hot-melt" wax inks as described in a Teletype patent by Johannes F. Gottwald, Liquid Metal Recorder, 1971, US 3,596,285, that outputs a fabricated metal symbol (Stock exchange symbols and quotes) able to be removed from the conveyor carrier and the Bismuth metal alloy reused if desired. The use of Hot-melt inks with a newer Drop-On-Demand inkjet technology(invented by Zoltan in 1972) with these inks would not be seen again until 1984 at Howtek and Exxon.
Howtek was started as R.H Research in 1982 by Robert Howard after successfully growing Centronics, the first dot-matrix solenoid-driven wire ribbon impact printer company in 1968. Howard calculated his solenoid matrix printer was 10-20 times faster than Teletype. Howard had tested making dots on paper by using ultrasonic sound in the late 1960s but did not advance the idea until some 20 years later in 1984 with Howtek when he hired 6 key employees from Exxon to develop his hot-melt color inkjet printer idea..
Exxon Office Systems(EOS), Brookfield, Ct plunged into the non-impact printer business in the late 1970s and invested as much as $2 billion. Patent records show a lengthy list of printing background employees at the EOS, Exxon Enterprises, Danbury Systems Division starting in 1978 including Ken Bower who was recruited by Exxon to found the engineering department at Exxon Enterprises. Ken's first job out of college in 1963 was at AT&T's Teletype, Division in Skokie, IL where his job was to transition an electro-mechanical stock exchange ticker (inkjet printer) into production. On his first day of work he smelled wax and was shown a 42 jet printer with heated printheads that was under development. Ken went on to work at UARCO business forms and made associations with developers of On-Demand inkjet, including Steve Zoltan at Gould and Silonics under Ed Kyser and Stephen Sears. Steve Zoltan was using the cylindrical piezoelectric tube with cylindrical compression and Ed Keyser was using a flat piezoelectric diaphragm that squirted ink like an oil can.
Two employees hired at Exxon (EOS) with no experience in printing were James McMahon and Kathy Olson. McMahon was hired to install the first Zoltan style single-nozzle inkjet, code name "Alpha Jet" to a fax printer and Olson was hired to build the "Alpha" jets for fax printer production. McMahon and Olson (married name McMahon) were two of the six employees hired by Robert Howard to design and build on-demand inkjets for the Pixelmaster color printer. Within 6 months of joining R.H Research(name changed to Howtek) the Alpha jet print samples with hot-melt ink were being shown at COMDEX, in Las Vegas. J. McMahon is credited with an Improved Inkjet System using the Zoltan technology at EOS and K. McMahon is credited with nozzle manufacturing techniques at Howtek. J. McMahon went on to work at Sanders Prototype(Solidscape) 3D printer manufacturer and is now employed at Layer Grown Model Technology supporting On-demand single-nozzle inkjets and claims to be the godfather of 3D Inkjet single-nozzle technology as a historian who worked in the field since 1978 with Steve Zoltan and Ken Bower at Exxon. 3D Inkjet single-nozzle printing has a direct path from Teletype hot-melt inks (Wax and metal alloy) to Steve Zoltan's single-nozzle jetting technology that never developed at Exxon with glass nozzles but became reality at Howtek with Teflon molded nozzles and heated printheads in 1984. An ex-Howtek employee, Richard Helinski is credited for the patent using two materials to produce particle deposition articles in 3D using Howtek style inkjets and thermoplastic inks. These same Howtek inkjets and materials were used in the Ballistic Particle Manufacturing, Personal Modeler and the Visual Impact Corporation, Sculptor 3D printer businesses that have since closed. These printers and original Howtek style inkjets and materials can be seen at the 3D Inkjet Collection in New Hampshire, the only historical collection of Zoltan style inkjets and 3D printers. Single nozzle jets are still in use today in Solidscape 3D printers and are considered to produce a very high quality model.
Applications.
Some inks must have high conductivity, high oxidation resistance and low sintering temperature while others are for other applications.
Drop formation.
Various drop formation technologies exist, and can be classified into two main types: continuous inkjet (CIJ) and drop-on-demand (DOD).
While CIJ has a straightforward drop creation and sophisticated drop trajectory manipulation, DOD has sophisticated drop creation and 'some' trajectory manipulation and alternate nozzle designs are possible. This single-nozzle inkjet technology is still in its early stages for those who want to investigate.
A Howtek inkjet nozzle uses a tubular thin wall piezo that produces a sound wave in the fluid chamber reflecting off both ends of the nozzle. The leading edge of a square wave signal triggers it and the lagging edge of the square wave signal in coincidence with the pressure wave expels the drop. This DOD single jet is acoustic. The 120C Tefzel nozzle is not rigid and does not squeeze. Drop formation is controlled by the fluid properties and nozzle geometry. Drive pulse amplitude and timing play a major role in drop volume and formation. Generally, DOD technology can be very complicated to understand and use.
Drop-on-demand (DOD).
In this method, drops of ink are released individually, on demand, by a voltage signal. Released drops either fall vertically without any trajectory manipulation or require special fire timing when projected horizontally from a rotary printhead spinning at 121 RPM to form characters (Howtek color printer 1986). Commercial printheads can have a single nozzle (Solidscape) or thousands of nozzles (HP) and many other variations in between. Arrayed Inkjet Apparatus (John G Martner patent 4468680, 1984 Exxon Research and Engineering Co) was invented after testing a Piezo DOD epoxied on the end of a piano wire 30 inches long and inserted into an ink fluid chamber leading to a nozzle. The tiny piezo either was pulling the wire in and out of the fluid chamber or transmitting a sound wave through the wire to impart acoustic energy into the fluid to fire a drop. The object of the invention was to build a printhead to reduce crosstalk (sound or any energy into closely placed nozzles for text printing).
The two leading technologies for forcing ink out of a nozzle on demand are thermal DOD and piezoelectric DOD. Notice the DOD may use a "Fill before firing a drop" or "Fire before fill" and Thermal DOD just "fires before fill". Drops must be precisely controlled with Piezo DOD or Thermal DOD. A standard Piezo DOD can fire drops at 9 feet per second drop velocity. Piezo DOD drop target positioning is very accurate with every drop fired horizontally or vertically.
Additional technologies include electrospray, acoustic discharge, electrostatic membrane and thermal bimorph.
Piezoelectric DOD.
Piezoelectric Drop-On-Demand (DOD) was invented in the 1970s. One disadvantage of the piezoelectric-DOD method is that jettable inks must have viscosity and surface tension within a relatively strict range to expel smaller drops without spray or satellite drops. One big advantage is DOD piezoelectric jets can be designed to work with high temperature Thermoplastics and other hot-melt inks in the temperature range of 100-130C. This allows for three-dimensional droplets to be printed on substrates and makes investment casting and 3D modelling possible. The Richard Helinski 3D patent US5136515A started a new era in inkjet printing. Helinski's experience at Howtek, Inc from 1984 -1989 and his many other patents including subtractive color (layering colored drops) with suggestions from a fellow inventor/employee, Alan Hock, about investment casting encouraged this patent. The patent is focused on printing complex solid 3D objects printed with a clean burning material when placed in an investment casting process primarily in the jewelry industry but also favored by electronics, automotive and medical industries in the early 1990s. Howtek style inkjets and Thermoplastic materials were created to print documents and images and later Braille characters.
There are many patents and methods to expel drops with piezoelectric devices. A piezo changes shape when voltage is applied. The amount of dimensional change is extremely small. A Piezo also be made in many different sizes. The smaller the piezo the smaller the shape displacement. The use of a DOD piezo to print a text character (the size of these letters) requires the piezo to be placed side by side in a housing. Drops must be smaller than .005 inches and be placed precisely in lines to form letters. A Piezo placed side by side at frequencies high enough to print a full sheet of paper vibrate loudly and effect the drops nearby. Drop-On-Demand (DOD) printheads have manufacturing limits with single nozzles. Multi-jet DOD printing is most common with inkjet printers for this reason.
Thermal inkjet (TIJ) DOD.
Thermal DOD was introduced in the 1980s by Canon and Hewlett-Packard. Thermal printing does not use high-temperature inks.
One disadvantage of this method is that the variety of inks compatible with TIJ is essentially limited, because this method is compatible with inks that have high vapour pressure, low boiling point and high kogation stability. Water's being such a solvent limited the popularity of this method for non-industrial photo printing only, where water-based inks are used.
Continuous inkjet (CIJ).
In this method, a stream of ink is released continuously from the nozzle. A garden hose jet stream is a good example of a continuous flow from a nozzle except CIJ nozzles are tiny (less than .005 inch or about 1/10 millimeter). The ink stream naturally breaks into separate drops due to Plateau–Rayleigh flow instability. Fluid streams can be broken into different size drops with vibration from a piezoelectric device. The use of a piezoelectric device should not be confused with Drop-On-Demand Inkjet which uses the piezo to generate sound waves in nozzles or expand the fluid chamber size to push single drops from a nozzle. The CIJ formed ink drops are either deflected by an electric field towards the desired location on the substrate or collected for reuse. CIJ printheads can be either have a single jet (nozzle) or multiple jets. CIJ is popular in industry and publishing but not typically seen in retail printers for home use.
One disadvantage of the CIJ method is the need for solvent monitoring. Since only a small fraction of the ink is being used for actual printing, solvent must be continually added to the recycled ink to compensate the evaporation that takes place during flight of the recycled drops.
Another disadvantage is the need for ink additives. Since this method is based on electrostatic deflection, ink additives, such as potassium thiocyanate, may deteriorate the performance of the printed devices.
CIJ can be directed through a magnetic field using low-temperature metal alloy ink as described in Johannes F Gottwald's Liquid Metal Recorder patent US3596285A, issued on July 27, 1971. The .003-inch aperture glass nozzle printed stock market quote symbols on a moving metal substrate belt and dropped on the table to be used as signage or reused in the recorder to print other symbols. This was possibly the earliest example of printing "fabricated objects" with an inkjet.
Printhead.
The printhead must have heating capability to print any material influenced by viscosity changes. Oil-based inks are sensitive to temperature. Waxes and hot-melt materials are solids at room temperature. Water-based inks may not need heat. It is also possible to print with metallic alloys such as lead, tin, indium, zinc and aluminum. The process of printing of low-melting point metals is called "direct melt printing" and was introduced in 1971 by Johannes F Gottwald patent, US3596285, "Liquid Metal Recording" with a Continuous inkjet (CIJ) long before any form of 3D Printing was ever considered. Thermoplastic DOD inkjets print at or above the piezoelectric Curie temperature and must be continuously poled to work. Piezo D33 displacement had to be optimized to lower drive voltages. See "Piezo-response force microscopy" for relevant theory. Prior research in 1980 by James McMahon about the six piezo physical poling states and tests to maximize piezo resonant and anti-resonant frequencies sped up the development time. Howtek manufactured these state of the art inkjets in 1985 before 3D printing with inkjets was invented on 8/4/1992.
Original DOD inkjet printheads were made of glass in 1972 by Steve Zoltan. These early single nozzle inkjet printheads printed with water-based inks. Later a housing was needed to surround the inkjet with a stable thermal mass. Glass inkjet nozzles were hard to duplicate and the molded nozzles were introduced by Howtek, Inc. Howtek glass nozzles had to be made with heat by a torch and drawn glass tubes, then cut to size and polished to produce a flat nozzle orifice surface. Glass nozzle technology was better understood by one inventor, Laszlo Halasz in the 1980s and he could form different nozzle shapes by using heated oil to melt glass capillaries. Howtek introduced single-tubular Tefzel molded nozzles using a stainless steel core pin – blind molded and then sliced with a razor to expose the orifice in perfect shape. Howtek produced its own full-color thermoplastic- ink material printing letterhead sheets in the rotary-head Pixelmaster printer in 1986 with 32 single nozzles (eight for each primary color). The Tefzel nozzle material operating at 125C allowed only the voltage pulse energy to trigger an acoustical pressure wave in the fluid without coupling the high-frequency vibrations from the piezo that cause spray and fluid vibration as the drops are ejected. The ideas for the design came from a book discovered by Jim McMahon in 1972, Harry F Olson's "Music, Physics and Engineering". Earlier inkjet designs with glass nozzles were also resonance sources and when packed with vibration dampening material could never eliminate spray. The object of the design was to have clean spray-free drops ejected over the frequency range of the nozzle length. The Howtek jets run nicely from 1 to 16,000 Hertz. No other company has produced printheads with this design to this day. The Tefzel nozzle with a long tapered front fluid chamber absorbed unwanted harmonics and allowed only the hydraulic fluid surge from the individual piezo drive pulse to eject a drop. One drive pulse equaled one drop at all frequencies up to the fluid resonance for the tube length. The square wave pulse leading edge triggered a sound wave in the fluid that reflected off the tail end of the nozzle tube and was reinforced when the lagging edge of the drive pulse was passing under the center of the piezo to boost the fluid pressure sufficiently to expel one single drop. The speed of sound for each of the two inks (wax and Thermoplastic) differs resulting in two maximum resonance frequencies for the same inkjet nozzle structure. Thus one Howtek printhead design works for two different inks. The Howtek inkjet nozzle is unique in so many ways. The design requires a strict assembly sequence and manufacturing process.
One 3D printer in use in 2021 (Solidscape) still has a Howtek style nozzle as it was manufactured in 1986. It originally had a hex-shaped metal nozzle-end structure with an offset-nozzle orifice that allowed the jet drops to be (aimed) directed toward a target to align properly for the best print quality when it was previously installed in the Howtek Pixelmaster. Over 1500 Howtek style inkjets were acquired by early Sanders Prototype, Inc when production of the Modelmaker 6 Pro was first started in 1994. The Modelmaker 6 pro uses two inkjets per machine. The inkjets are installed in a special printhead directing the drops straight downward for 3D printing. The original prototype 3D printer, the Sculptor by Visual Impact Corporation, using Howtek nozzles, printed horizontally in 1989. The Pixelmaster also projected the drops horizontally from a 121 rpm rotating printhead to print 2D characters or images on paper. A Braille character printer was introduced by Howtek and only sold a few machines in 1990–1991 with raised-font printed on plain paper using Howtek inkjets. This required four layers of drops to stack up for each Braille character. This was an early example of how three-dimensional (ink) material printing (not called 3D printing in 1984) got started and now-a-days Additive Manufacturing (AM) does not reference historical jetting of hot-melt material properties used in 3D printing. 3D printing (printing with raised surface inks) was inkjet printing in the 1960–1980s with wax, liquid metal and thermoplastic hot-melt fluids.
Fabrication approaches.
The printed material is rarely only one step in the process, which may include direct material deposition followed by a mechanical roller or a controlled surface milling step. It may be a deposition of a precursor followed by a catalyst, sintering, photonic curing, electroless plating etc., to give the final result. See Ballistic Particle Manufacturing(BPM)which uses a Solid ink single nozzle, heated to 125C and a 5 axis printing technique that required no other process for fabrication.
Inkjet fluid materials.
The ink must be liquid, but may also contain small solids if they do not cause clogging. The solid particles should be smaller than 1/10 of the nozzle diameter to avoid clogging and be smaller than 2 microns to reduce satellite drop spray. Fine detail inkjet printing has material filtered by 1 micron filters to prevent spray and fluid lines protected by 15 micron filters to prevent clogging.
Drop formation is governed by two main physical properties: surface tension and viscosity. The surface tension forms ejected drops into spheres, in accordance with Plateau–Rayleigh instability. The viscosity can be optimized at jet time by using an appropriate printhead temperature. Drop volume is controlled by drive pulse timing width and drive voltage amplitude. Each inkjet assembly will have a slight variation in drop size and maintaining all material and jet parameters is necessary for optimum performance. Drop formation and volume varies with drop frequency and jet orifice meniscus position. The liquid is positioned in the nozzle aperture by gravity (fluid storage tank must be slightly lower in height to the nozzle). The fluid surface tension also holds the fluid at the edge of the nozzle orifice (hole). The action of expelling a drop alters this natural steady fluid position condition. This condition is commonly called the meniscus of the fluid. The meniscus acts like a barrier and most be overcome to allow drop ejection. The meniscus also exerts strong forces when stretched. The lower the storage tank height the higher the force required to expel a drop. The meniscus spring action timing alters the drop size, drop velocity and drive voltage in drops formation. Firing drops more frequently means the characteristics of the drop change constantly because of meniscus position. Each jettable material has different physical properties and requires different printer parameters and tank height settings. Materials can not just be switched. The temperature of the inkjet must be more closely controlled to maintain surface tension and viscosity in a DOD system than in a CIJ system.
Generally, lower viscosity allows better droplet formation and in practice only liquids with viscosity of 2-50 mPa s can be printed. More precisely, liquids whose Ohnesorge number is larger than 0.1 and smaller than 1 are jettable.


Timeline of intelligent design

This timeline of intelligent design outlines the major events in the development of intelligent design as presented and promoted by the intelligent design movement.


Varian, Inc.

Varian, Inc. was one of the largest manufacturers of scientific instruments for the scientific industry. They had offerings over a broad range of chemical analysis equipment, with a particular focus on Information Rich Detection and Vacuum technology. Varian was spun off from Varian Associates in 1999 and was purchased by Agilent Technologies in May 2010 for $1.5 billion, or $52 per share.
Varian Inc. had its corporate headquarters in Palo Alto, California, and offices in Australia, the Benelux countries, Brazil, Canada, China, Germany, France, Italy, Japan, Korea, Russia, Sweden, Taiwan, the United Kingdom, and the United States.
Manufacturing plants.
Varian Inc. contained the following manufacturing plants:
History.
In October 1967, Techtron Pty Ltd merged with Varian Associates. Techtron is a manufacturer of Atomic Absorption Spectrometers and Spectral lamps.
In 1982 Varian transferred the Cary UV-Visible product line to Australia.
In 1997 Varian bought Chemagnetics, a Colorado-based manufacturer of solid-state NMR spectrometers.
In 2002 Varian bought Ansys Technologies, Inc., a California-based manufacturer of In-Vitro Medical Devices.
In 2004 Varian Inc bought Magnex Scientific, an Oxford-based manufacturer of high-field magnets.
In 2005 Varian bought Polymer Laboratories, a speciality polymer analysis and manufacturing company.
In 2006 Varian bought Ion Spec, an FTMS (Fourier Transform Mass Spectrometry) manufacturing company.
In 2007, Varian, Inc. bought Analogix, Inc., a company specializing in flash chromatography.
In 2008, Varian bought Oxford Diffraction, a British company specializing in X-ray diffraction equipment.
On 27 July 2009 Agilent Technologies announced it would buy Varian Inc, for $1.5 Billion.
On 14 October 2014 Agilent made the strategic decision to close its NMR business. Agilent entered the NMR business in 2010, with the acquisition of Varian.


Production leveling

Production leveling, also known as production smoothing or – by its Japanese original term – , is a technique for reducing the mura (unevenness) which in turn reduces muda (waste). It was vital to the development of production efficiency in the Toyota Production System and lean manufacturing. The goal is to produce intermediate goods at a constant rate so that further processing may also be carried out at a constant and predictable rate.
Where demand is constant, production leveling is easy, but where customer demand fluctuates, two approaches have been adopted: 1) "demand leveling" and 2) "production leveling" through flexible production.
To prevent fluctuations in production, even in outside affiliates, it is important to minimize fluctuation in the final assembly line. Toyota's final assembly line never assembles the same automobile model in a batch. Instead, they level production by assembling a mix of models in each batch and the batches are made as small as possible.
Production leveling by volume or by product type or mix.
Production leveling can refer to leveling by volume, or leveling by product type or mix, although the two are closely related.
Leveling by volume.
If for a family of products that use the same production process there is a demand that varies between 800 and 1,200 units then it might seem a good idea to produce the amount ordered. Toyota's view is that production systems that vary in the required output suffer from mura and muri with capacity being 'forced' in some periods. So their approach is to manufacture at the long-term average demand and carry an inventory proportional to the variability of demand, stability of the production process and the frequency of shipments. So for our case of 800–1,200 units, if the production process were 100% reliable and the shipments once a week, then the production would be with minimum standard inventory of 200 at the start of the week and 1,200 at the point of shipment. The advantage of carrying this inventory is that it can smooth production throughout the plant and therefore reduce process inventories and simplify operations which reduces costs.
Leveling by product.
Most value streams produce a mix of products and therefore face a choice of production mix and sequence. It is here that the discussions on economic order quantities take place and have been dominated by changeover times and the inventory this requires. Toyota's approach resulted in a different discussion where it reduced the time and cost of changeovers so that smaller and smaller batches were not prohibitive and lost production time and quality costs were not significant. This meant that the demand for components could be leveled for the upstream sub-processes and therefore lead time and total inventories reduced along the entire value stream. To simplify leveling of products with different demand levels a related visual scheduling board known as a heijunka box is often used in achieving these heijunka style efficiencies. Other production leveling techniques based on this thinking have also been developed. Once leveling by product is achieved then there is one more leveling phase, that of "Just in Sequence" where leveling occurs at the lowest level of product production.
The use of production leveling as well as broader lean production techniques helped Toyota massively reduce vehicle production times as well as inventory levels during the 1980s.
Implementation.
Even Toyota hasn't reached the final stage in this journey, single-piece flows, across all of their processes; indeed they recommend following their journey rather than trying to jump into an intermediate stage. The reason Toyota advocates this is that each production stage is accompanied by adjustments and adaptations to support services to production; if those services are not given these adaptation steps then major issues can arise.
Demand leveling.
Demand leveling is the deliberate influencing of demand itself or the demand processes to deliver a more predictable pattern of customer demand. Some of this influencing is by manipulating the product offering, some by influencing the ordering process and some by revealing the demand amplification induced variability of ordering patterns. Demand levelling does not include influencing activities designed to clear existing stock.
Historically demand leveling evolved as subset of production levelling and has been approached in a variety of ways:
Implementation.
If it is accepted that a large part of demand variability in high volume products can be substantially caused by sales and ordering process artifacts then analysis and leveling can be attempted.
The use of long delay supply chains to reduce manufacturing costs often means that production orders are placed long before customer demand can be realistically estimated. The much later arrival of forecast product demand volumes makes demand leveling irrelevant since the issue has now switched to disposal at best price possible products that are already created and possibly paid for. Demand leveling has only proven possible where build times have been made relatively low and production has been made relatively reliable and flexible. Examples of these are fast airborne supply chains (e.g. Apple iPod) or direct to customer selling through web sites allowing late customisation (e.g. NIKEiD custom shoes) or local manufacture (e.g. Timbuk2 custom courier bags).
Where actual build-delivery times can be brought within the same scale as customer time horizons then effort to modify impulse buying and make it somewhat planned can be successful. Reliable, flexible manufacturing will then mean that low stock levels (if any) do not interfere with customer satisfaction and that incentives to sell what has been produced eliminated.
Where demand follows a predictable pattern, e.g. flat, then regular deliveries of constant amounts can be agreed with variances in actual demand ignored unless it exceeds some agreed trigger level. Where this cannot be agreed then it can be simulated and the benefits gained through frequent deliveries and a market location.
The predictable pattern does not have to be flat and may, for example, be an annual pattern with higher volumes at particular periods. Here again the deliveries can be agreed to follow a simplified but similar pattern, perhaps one delivery volume for six months of the year and another for the other six months.


Fixed repeating schedule

Fixed repeating schedule is a key element of the Toyota Production System and lean manufacturing. As its name suggests it is a production schedule which is 'unchanging' and repeated perhaps daily or over a longer period such as two weeks or month. If it can be implemented, economies of repetition start to become evident and suppliers and customers can be assured in their own activity scheduling. What impedes this being implemented is the uncertainty of demand and supply. Therefore whilst the scheduling becomes simple, the activities to make the scheduling possible become more complex. Thus the planning to move to FRS reveals issues which, if managed correctly, will reduce complexity overall and improve customer service.
History.
Fixed repeating schedules have been invented all over the place by many organisations as local solutions. Perhaps Ford's early production technique was a trivial example since by ensuring only one product, the black model T, the scheduling became simple as well.
The first widely publicised example with a systematic development was in the Toyota Production System where an FRS smooths flow in the factory and therefore reduces the waste of unevenness (or mura).
Implementation.
Step 1: red stream/green stream.
Since in all but the trivial example of constant demand there will actually be fluctuations in required production, FRS is only part of a scheduling solution. The challenge in the early steps of implementation is to isolate the maximum part of production that can be fixed from the part of production that cannot. This isolation, at least in the early stages, should extend to the supporting services as well as the value adding process or gemba itself. Thus procurement, stock keeping, deliveries and so on should be run separately for the fixed and non-fixed schedules. For example, this means two procurement 'contracts'; one for fixed deliveries of fixed amounts at regular intervals and one for deliveries as otherwise requested. If this disciple in not complete then the uncertainties in the unfixed side will 'leak' back into the fixed side which will then become unfixed for lack of resources.
To enforce this separation some factories have actually split the factory into two different parts with each part being represented and painted a different colour. This separation went as far as painting forklift trucks, tools, floor areas and stock containers in their corresponding colour as well as selecting staff based upon their temperament to work on one side or the other. The German factory director believed it was as close as he could come to actually running two factories, one FRS and the other flexible.
The benefit of this work was the significant cost decreases that occurred in the FRS 'factory' which far outweighed the slight increase in costs in the flexible 'factory'. In the FRS 'factory' all costs and activities will be repeated which allows significant process simplifications and time and cost reductions to occur across all functions. This is because the 'exceptions' to the standard process will no longer occur and schedules will always be achieved so that process failure 'safety net' processes and equipment and staff can be eliminated or re-deployed.
These benefits only accrue whilst the green stream/FRS products or services remain predictable in demand. Therefore it is critical to ensure appropriate frequency reviews of product demand to ensure promotion of stable products from the red stream and demotion of now less stable demand products to the red stream. This may follow product maturity curves where, after initial introduction, when demand stabilises products move into the FRS and then later, when purchase enthusiasm wanes, they are removed again. Seasonality can be built into FRS by having, for example, a summer and a winter fixed schedule.
Step 2: speed up the FRS.
The implementation of step 1 will have allowed people in the 'FRS' factory to run simpler processes and to establish routines that were not possible in the schedule, reschedule, reschedule world that existed before, and may still exist in the 'non-FRS factory'. This will make the work more manageable and simplify the communications in the 'factory' that are so critical to performance. Because of this it will become much clearer what sub-processes are limiting production capability and therefore which operations can be simplified and improved. It is often the case that large stock levels pre-existed, or were built to make FRS 'possible', the actual causes of these stocks can now be addressed by operational improvements to reduce lot sizes and improve reliability. Once these have been done and supporting services have also adjusted then the aim is to shorten the period of the repeat in 'FRS'. This planning and then action will surface new issues along the lines of the earlier phase which should in their turn be managed as a priority. The shortening of the cycle will allow the reduction of finished goods and WIP stocks as well whilst maintaining availability of stocks for customers. This cycle should be repeated until management nerve breaks.
For Toyota the implementation of a fixed repeating schedule is one of the early steps in achieving production levelling which follows further steps to achieve lower lot sizes gain the lower costs and flexibility this makes possible.


Cylindrical grinder

The cylindrical grinder is a type of grinding machine used to shape the outside of an object. The cylindrical grinder can work on a variety of shapes, however the object must have a central axis of rotation. This includes but is not limited to such shapes as a cylinder, an ellipse, a cam, or a crankshaft.
Cylindrical grinding is defined as having four essential actions:
While the majority of cylindrical grinders employ all four movements, there are grinders that only employ three of the four actions.
History.
The origins of the cylindrical grinder, as with all other modern machine tools, stem from the experimentation and invention of John Wilkinson and later Henry Maudslay who built the first horizontal boring machine and the first engine lathe, respectively. The cylindrical grinder owes much of its development from the onset of the Industrial Revolution, particularly to the advent of reliable, inexpensive steel production and later the improvement of the grinding wheel. The basis for the modern day cylindrical grinder was first built in the 1830s by two men working independently, Jonathan Bridges and James Wheaton . It is unclear as to which man had first produced the machine but both are closely tied to the first historical appearance of the modern day tool. It took another 40 years before further improvement and refinement of the tool occurred.
The Brown & Sharpe company in Providence, RI was one of the first builders of the Willcox & Gibbs Sewing Machine, one of the first piece of precision machinery to be used in a residential setting. Joseph Brown believed that the shaft and needle bars of the sewing machine must be crafted from hardened tool steel. It was this desire that led to their experimentation with building a cylindrical grinder. The first attempt was simply a small lathe with a grinding wheel mounted to it. Subsequent attempts led to the cylindrical grinder displayed at the 1876 Centennial Exposition and the subsequent patent.
It is important to note that Brown & Sharpe cannot be given sole credit of pioneering advances in cylindrical grinding. A man in Waltham, Massachusetts, Ambrose Webster had created a small grinding machine in 1860 that contained all of the improvements Brown & Sharpe claimed to be their own original invention. Even more so, the emphasis on precision, accuracy, and reliability was championed by Charles Norton.
Norton was an employee of Brown & Sharpe who quit the company with the desire to further pursue his belief that the cylindrical grinder is not merely a finishing tool but could be a staple of the machine shop. He founded the Norton Grinding Company, where he continued improving the cylindrical grinder to use faster rpm values and more precise grinding tolerances. He was acknowledged for his work on April 18, 1925 when he won The John Scott Medal and Premium for his invention of "accurate grinding devices of high power". These standards developed by Norton were the status quo until about the middle of the 20th century.
The remainder of technological innovation applicable to the cylindrical grinder is almost identical and entangled in a sense, to the rest of machine tools. The innovation of the last 70 years can be characterized by three waves of change. The first wave was the creation of numerical control by John T. Parsons in the 1940s. The U.S. Air Force, looking for a faster, cheaper, and more efficient means of part and tool production for airplanes, played a large role in developing NC both politically and financially. The first implementation of NC in machine tools occurred in the 1950s and continued through the 1960s. The second wave of innovation, occurring during the 1970s and 1980s, is marked by the massive demand for microcomputers to be used to direct NC. The joining of computers marked the birth of Computer Numerical Control which once again revolutionized the ability of the cylindrical grinder. Now the machine was able to receive instruction from a computer which would give it precise directions on every imaginable dimension and measurement needed to produce the desired product. This was a completely different work environment in comparison to mid-century production where a worker had to direct the machine at every point on how to manipulate the work. The third wave of change came in the 1990s with the advent of the Personal Computer. Integrating CNC and the PC into one dynamic system allowed for even further control of the manufacturing process that required little to no human supervision.
Methods.
There are five different types of cylindrical grinding: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding.
Outside diameter grinding.
OD grinding is grinding occurring on external surface of an object between the centers. The centers are end units with a point that allow the object to be rotated. The grinding wheel is also being rotated in the same direction when it comes in contact with the object. This effectively means the two surfaces will be moving opposite directions when contact is made which allows for a smoother operation and less chance of a jam up.
Inside diameter grinding.
ID grinding is grinding occurring on the inside of an object. The grinding wheel is always smaller than the width of the hole being ground. The object is held in place by a collet, which also rotates the object in place. Just as with OD grinding, the grinding wheel and the object rotated in opposite directions giving reversed direction contact of the two surfaces where the grinding occurs.
See also ID Grinding.
Plunge grinding.
A form of OD grinding, however the major difference is that the grinding wheel makes continuous contact with a single point of the object instead of traversing the object.
Creep feed grinding.
Creep Feed is a form of grinding where a full depth of cut is removed in a single pass of the wheel. Successful operation of this technique can reduce manufacturing time by 50%, but often the grinding machine being used must be designed specifically for this purpose. This form occurs in both cylindrical and surface grinding.
Centerless grinding.
Centerless grinding is a form of grinding where there is no collet or pair of centers holding the object in place. Instead, there is a regulating wheel positioned on the opposite side of the object to the grinding wheel. A work rest keeps the object at the appropriate height but has no bearing on its rotary speed. The workblade is angled slightly towards the regulating wheel, with the workpiece centerline above the centerlines of the regulating and grinding wheel; this means that high spots do not tend to generate corresponding opposite low spots, and hence the roundness of parts can be improved. Centerless grinding is much easier to combine with automatic loading procedures than centered grinding; through feed grinding, where the regulating wheel is held at a slight angle to the part so that there is a force feeding the part through the grinder, is particularly efficient.
Control methods.
There are three basics ways in which an operator can interact with a cylindrical grinder. Either manual manipulation of the machine, Numerical Control with a punched card system or using Computer Numerical Control using a pre existing interface designed for that machine or by using a PC as an interface to communicate with the grinder. The first two options are rarely if ever used today. CNC operated cylindrical grinders are the most technologically advanced, efficient, reliable systems in the manufacturing industry.
Applications.
The cylindrical grinder is responsible for a plethora of innovations and inventions in the progression of science and technology. Any situation in which extremely precise metalworking is required, the cylindrical grinder is able to provide a high level of precision. From the automotive industry to military applications, the benefits of the cylindrical grinder are numerous.


Alloy wheel

In the automotive industry, alloy wheels are wheels that are made from an alloy of aluminium or magnesium. Alloys are mixtures of a metal and other elements. They generally provide greater strength over pure metals, which are usually much softer and more ductile. Alloys of aluminium or magnesium are typically lighter for the same strength, provide better heat conduction, and often produce improved cosmetic appearance over steel wheels. Although steel, the most common material used in wheel production, is an alloy of iron and carbon, the term "alloy wheel" is usually reserved for wheels made from nonferrous alloys.
The earliest light-alloy wheels were made of magnesium alloys. Although they lost favor on common vehicles, they remained popular through the 1960s, albeit in very limited numbers. In the mid-to-late 1960s, aluminium-casting refinements allowed the manufacture of safer wheels that were not as brittle. Until this time, most aluminium wheels suffered from low ductility, usually ranging from 2-3% elongation. Because light-alloy wheels at the time were often made of magnesium (often referred to as "mags"), these early wheel failures were later attributed to magnesium's low ductility, when in many instances these wheels were poorly cast aluminium alloy wheels. Once these aluminium casting improvements were more widely adopted, the aluminium wheel took the place of magnesium as low cost, high-performance wheels for motorsports.
Characteristics.
Lighter wheels can improve handling by reducing unsprung mass, allowing suspension to follow the terrain more closely and thus improve grip, however not all alloy wheels are lighter than their steel equivalents. Reduction in overall vehicle mass can also help to reduce fuel consumption.
Better heat conduction and a more open wheel design can help dissipate heat from the brakes, which improves braking performance in more demanding driving conditions and reduces the chance of diminished brake performance or even failure due to overheating.
Alloy wheels are also purchased for cosmetic purposes although the cheaper alloys used are usually not corrosion-resistant. Alloys allow the use of attractive bare-metal finishes, but these need to be sealed with paint or wheel covers. Even if so protected the wheels in use will eventually start to corrode after 3 to 5 years but refurbishment is now widely available at a cost. The manufacturing processes also allow intricate, bold designs. In contrast, steel wheels are usually pressed from sheet metal, and then welded together (often leaving unsightly bumps) and must be painted to avoid corrosion and/or hidden with wheel covers/hub caps.
Alloy wheels are prone to galvanic corrosion, which can cause the tires to leak air if appropriate preventive measures are not taken. Also, alloy wheels are more difficult to repair than steel wheels when bent, but their higher price usually makes repairs cheaper than replacement.
Alloy wheels are more expensive to produce than standard steel wheels, and thus are often not included as standard equipment, instead being marketed as optional add-ons or as part of a more expensive trim package. However, alloy wheels have become considerably more common since 2000, now being offered on economy and subcompact cars, compared to a decade earlier where alloy wheels were often not factory options on inexpensive vehicles. Alloy wheels have long been included as standard equipment on higher-priced luxury or sports cars, with larger-sized or "exclusive" alloy wheels being options. The high cost of alloy wheels makes them attractive to thieves; to counter this, automakers and dealers often use locking lug nuts or bolts which require a special key to remove.
Most alloy wheels are manufactured using casting, but some are forged. Forged wheels are usually lighter, stronger, but much more expensive than cast wheels. There are two types of forged wheels: one piece and modular. Modular forged wheels may feature two- or three-piece design. Typical multi-piece wheels consist of the inner rim base, outer rim lip and wheel center piece with openings for lug nuts. All parts of a modular wheel are held with bolts. BBS RS is one of the most famous three-piece modular forged wheels.
Aftermarket wheels.
A sizable selection of alloy wheels are available to automobile owners who want lighter, more visually appealing, rarer, and/or larger wheels on their cars, going from 14 and 15 inch standard wheels up to 16, 17, 18, 19, 20, 21, 22, 24, 26, 28 and 30 inch wheel sizes. With the larger alloy wheels came Tru-Spinner Wheels and spinner wheel add-on spinners that would free-spin and continue to free-spin after the alloy wheel itself came to rest. American inventor James JD Gragg of International and American Tru-Spinners were the original ones and were leaders in the industry. Another function of Tru-Spinners was they could also spin backward as the alloy wheel was rolling forward. Although replacing standard steel wheel and tire combinations with lighter alloy wheels and potentially lower profile tires can result in increased performance and handling, this doesn't necessarily hold when increasingly large wheels are employed. Research by "Car and Driver" conducted using a selection of differently sized alloy wheels from all outfitted with the same make and model of tires showed that both acceleration and fuel economy suffered with larger wheels. They also noted that ride comfort and noise were negatively affected by the larger wheels.
Magnesium alloy wheels.
Magnesium alloy wheels were the first die-cast wheels produced, and were often referred to as simply "mag wheels." Magnesium wheels were originally used for racing, but their popularity during the 1960s led to the development of other die-cast wheels, particularly of aluminium alloys. The term "mag wheels" became synonymous with die-cast wheels made from any material, from modern aluminium alloy wheels to plastic and composite wheels used on items like bicycles, wheelchairs, and skateboards.
However, pure magnesium wheels are no longer produced, being found only on classic cars. Pure magnesium suffers from many problems. Vintage magnesium rims were very susceptible to pitting, cracking and corrosion. Magnesium in bulk is hard to ignite but pure magnesium wheels can be ignited by a burning tire or by prolonged scraping of the wheel on the road surface following a puncture. Alloys of magnesium were later developed to alleviate most of these problems. In fact, US Federal Aviation Administration has conducted wide-ranging tests over the past decade, and has reached a conclusion that potential flammability of magnesium is no longer deemed to be a concern. Modern surface treatment technologies provide protection from corrosion and significantly extend the average lifecycle of magnesium rims.
Production methods.
Forging.
Forging can be done by a one or multistep process forging from various magnesium alloys, most commonly AZ80, ZK60 (MA14 in Russia). Wheels produced by this method are usually of higher toughness and ductility than aluminium wheels, although the costs are much higher. Forging is a complicated process that involves such processes, as heating, rolling, applying high pressure, hammering and/or combination of these. As a result, the crystal structure of the alloy changes, and as a result the material becomes stronger and more lightweight.
Assembly.
There are one- two- and three-piece forged wheels. Every piece is originally an alloy billet, which is further transformed into a wheel, in cases of one-piece forged wheels, or into a wheel part in cases of multi-piece wheels.
High pressure die casting.
This process uses a die arranged in a large machine that has high closing force to clamp the die closed. The molten magnesium is poured into a filler tube called a shot sleeve. A piston pushes the metal into the die with high speed and pressure, the magnesium solidifies, and the die is opened, and the wheel is released. Wheels produced by this method can offer reductions in price and improvements in corrosion resistance, but they are less ductile and of lower strength due to the nature of high pressure die casting.
Low pressure die casting.
This process usually employs a steel die, it is arranged above the crucible filled with molten magnesium. Most commonly, the crucible is sealed against the die and pressurized air/cover gas mix is used to force the molten metal up a straw-like filler tube into the die.
When processed using best practice methods, low pressure die casting wheels can offer improvements in ductility over magnesium wheels and any cast aluminium wheels, they remain less ductile than forged magnesium.
Gravity casting.
Gravity-cast magnesium wheels have been in production since the early 1920s and provide good ductility, and relative properties above what can be made with aluminium casting. Tooling costs for gravity-cast wheels are among the cheapest of any process. This has allowed small batch production, flexibility in design and short development time.


Undercut (manufacturing)

In manufacturing, an undercut is a special type of recessed surface that is inaccessible using a straight tool. In turning, it refers to a recess in a diameter generally on the inside diameter of the part. In milling, it refers to a feature which is not visible when the part is viewed from the spindle. In molding, it refers to a feature that cannot be molded using only a single pull mold. In printed circuit board construction, it refers to the portion of the copper that is etched away under the photoresist.
Turning.
On turned parts an undercut is also known as a "neck" or "relief groove". They are often used at the end of the threaded portion of a shaft or screw to provide clearance for the cutting tool.
Molding.
Undercut - Any indentation or protrusion in a shape that will prevent its withdrawal from a one-piece mold.
Milling.
In milling the spindle is where a cutting tool is mounted. In some situations material must be cut from a direction where the feature can not be seen from the perspective of the spindle and requires special tooling to reach behind the visible material.
The corners may be undercut to remove the radius that is usually left by the milling cutter this is commonly referred to as a relief.
Etching.
Undercuts from etching (microfabrication) are a side effect, not an intentional feature.