Speeds and feeds

The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often considered as a pair because of their combined effect on the cutting process. Each, however, can also be considered and analyzed in its own right.
"Cutting speed" (also called "surface speed" or simply "speed") is the speed difference (relative velocity) between the cutting tool and the surface of the workpiece it is operating on. It is expressed in units of distance across the workpiece surface per unit of time, typically surface feet per minute (sfm) or meters per minute (m/min). "Feed rate" (also often styled as a solid compound, "feedrate", or called simply "feed") is the relative velocity at which the cutter is advanced along the workpiece; its vector is perpendicular to the vector of cutting speed. Feed rate units depend on the motion of the tool and workpiece; when the workpiece rotates ("e.g.", in turning and boring), the units are almost always distance per spindle revolution (inches per revolution [in/rev or ipr] or millimeters per revolution [mm/rev]). When the workpiece does not rotate ("e.g.", in milling), the units are typically distance per time (inches per minute [in/min or ipm] or millimeters per minute [mm/min]), although distance per revolution or per cutter tooth are also sometimes used.
If variables such as cutter geometry and the rigidity of the machine tool and its tooling setup could be ideally maximized (and reduced to negligible constants), then only a lack of power (that is, kilowatts or horsepower) available to the spindle would prevent the use of the maximum possible speeds and feeds for any given workpiece material and cutter material. Of course, in reality those other variables are dynamic and not negligible, but there is still a correlation between power available and feeds and speeds employed. In practice, lack of rigidity is usually the limiting constraint.
The phrases "speeds and feeds" or "feeds and speeds" have sometimes been used metaphorically to refer to the execution details of a plan, which only skilled technicians (as opposed to designers or managers) would know.
Cutting speed.
Cutting speed may be defined as the rate at the workpiece surface, irrespective of the machining operation used. A cutting speed for mild steel of 100 ft/min is the same whether it is the speed of the cutter passing over the workpiece, such as in a turning operation, or the speed of the cutter moving past a workpiece, such as in a milling operation. The cutting conditions will affect the value of this surface speed for mild steel.
Schematically, speed at the workpiece surface can be thought of as the tangential speed at the tool-cutter interface, that is, how fast the material moves past the cutting edge of the tool, although "which surface to focus on" is a topic with several valid answers. In drilling and milling, the outside diameter of the tool is the widely agreed surface. In turning and boring, the surface can be defined on either side of the depth of cut, that is, either the starting surface or the ending surface, with neither definition being "wrong" as long as the people involved understand the difference. An experienced machinist summed this up succinctly as "the diameter I am turning from" versus "the diameter I am turning to." He uses the "from", not the "to", and explains why, while acknowledging that some others do not. The logic of focusing on the largest diameter involved (OD of drill or end mill, starting diameter of turned workpiece) is that this is where the highest tangential speed is, with the most heat generation, which is the main driver of tool wear.
There will be an optimum cutting speed for each material and set of machining conditions, and the spindle speed (RPM) can be calculated from this speed. Factors affecting the calculation of cutting speed are:
Cutting speeds are calculated on the assumption that optimum cutting conditions exist. These include:
The cutting "speed" is given as a set of constants that are available from the material manufacturer or supplier. The most common materials are available in reference books or charts, but will always be subject to adjustment depending on the cutting conditions. The following table gives the cutting speeds for a selection of common materials under one set of conditions. The conditions are a tool life of 1 hour, dry cutting (no coolant), and at medium feeds, so they may appear to be incorrect depending on circumstances. These cutting speeds may change if, for instance, adequate coolant is available or an improved grade of HSS is used (such as one that includes [cobalt]).
Machinability rating.
The machinability rating of a material attempts to quantify the machinability of various materials. It is expressed as a percentage or a normalized value. The American Iron and Steel Institute (AISI) determined machinability ratings for a wide variety of materials by running turning tests at 180 surface feet per minute (sfpm). It then arbitrarily assigned 160 Brinell B1112 steel a machinability rating of 100%. The machinability rating is determined by measuring the weighed averages of the normal cutting speed, surface finish, and tool life for each material. Note that a material with a machinability rating less than 100% would be more difficult to machine than B1112 and material and a value more than 100% would be easier.
Machinability ratings can be used in conjunction with the Taylor tool life equation, in order to determine cutting speeds or tool life. It is known that B1112 has a tool life of 60 minutes at a cutting speed of 100 sfpm. If a material has a machinability rating of 70%, it can be determined, with the above knowns, that in order to maintain the same tool life (60 minutes), the cutting speed must be 70 sfpm (assuming the same tooling is used).
When calculating for copper alloys, the machine rating is arrived at by assuming the 100 rating of 600 SFM. For example, phosphorus bronze (grades A–D) has a machinability rating of 20. This means that phosphor bronze runs at 20% the speed of 600 SFM or 120 SFM. However, 165 SFM is generally accepted as the basic 100% rating for "grading steels".
Formula
Cutting Speed (V)= [πDN]/1000 m/min
Where
D=Diameter of Workpiece in meter or millimeter
N=Spindle Speed in rpm
Spindle speed.
The spindle speed is the rotational frequency of the spindle of the machine, measured in revolutions per minute (RPM). The preferred speed is determined by working backward from the desired surface speed (sfm or m/min) and incorporating the diameter (of workpiece or cutter).
The spindle may hold the:
Excessive spindle speed will cause premature tool wear, breakages, and can cause tool chatter, all of which can lead to potentially dangerous conditions. Using the correct spindle speed for the material and tools will greatly enhance tool life and the quality of the surface finish.
For a given machining operation, the cutting speed will remain constant for most situations; therefore the spindle speed will also remain constant. However, facing, forming, parting off, and recess operations on a lathe or screw machine involve the machining of a constantly changing diameter. Ideally, this means changing the spindle speed as the cut advances across the face of the workpiece, producing constant surface speed (CSS). Mechanical arrangements to effect CSS have existed for centuries, but they were never applied commonly to machine tool control. In the pre-CNC era, the ideal of CSS was ignored for most work. For unusual work that demanded it, special pains were taken to achieve it. The introduction of CNC-controlled lathes has provided a practical, everyday solution via automated CSS Machining Process Monitoring and Control. By means of the machine's software and variable speed electric motors, the lathe can increase the RPM of the spindle as the cutter gets closer to the center of the part.
Grinding wheels are designed to be run at a maximum safe speed, the spindle speed of the grinding machine may be variable but this should only be changed with due attention to the safe working speed of the wheel. As a wheel wears it will decrease in diameter, and its effective cutting speed will be reduced. Some grinders have the provision to increase the spindle speed, which corrects for this loss of cutting ability; however, increasing the speed beyond the wheels rating will destroy the wheel and create a serious hazard to life and limb.
Generally speaking, spindle speeds and feed rates are less critical in woodworking than metalworking. Most woodworking machines including power saws such as circular saws and band saws, jointers, Thickness planers rotate at a fixed RPM. In those machines, cutting speed is regulated through the feed rate. The required feed rate can be extremely variable depending on the power of the motor, the hardness of the wood or other material being machined, and the sharpness of the cutting tool.
In woodworking, the ideal feed rate is one that is slow enough not to bog down the motor, yet fast enough to avoid burning the material. Certain woods, such as black cherry and maple are more prone to burning than others. The right feed rate is usually obtained by "feel" if the material is hand fed, or by trial and error if a power feeder is used. In thicknessers (planers), the wood is usually fed automatically through rubber or corrugated steel rollers. Some of these machines allow varying the feed rate, usually by changing pulleys. A slower feed rate usually results in a finer surface as more cuts are made for any length of wood.
Spindle speed becomes important in the operation of routers, spindle moulders or shapers, and drills. Older and smaller routers often rotate at a fixed spindle speed, usually between 20,000 and 25,000 rpm. While these speeds are fine for small router bits, using larger bits, say more than or 25 millimeters in diameter, can be dangerous and can lead to chatter. Larger routers now have variable speeds and larger bits require slower speed. Drilling wood generally uses higher spindle speeds than metal, and the speed is not as critical. However, larger diameter drill bits do require slower speeds to avoid burning.
Cutting feeds and speeds, and the spindle speeds that are derived from them, are the "ideal" cutting conditions for a tool. If the conditions are less than ideal then adjustments are made to the spindle's speed, this adjustment is usually a reduction in RPM to the closest available speed, or one that is deemed (through knowledge and experience) to be correct.
Some materials, such as machinable wax, can be cut at a wide variety of spindle speeds, while others, such as stainless steel require much more careful control as the cutting speed is critical, to avoid overheating both the cutter and workpiece. Stainless steel is one material that hardens very easily under cold working, therefore insufficient feed rate or incorrect spindle speed can lead to less than ideal cutting conditions as the work piece will quickly harden and resist the tool's cutting action. The liberal application of cutting fluid can improve these cutting conditions; however, the correct selection of speeds is the critical factor.
Spindle speed calculations.
Most metalworking books have nomograms or tables of spindle speeds and feed rates for different cutters and workpiece materials; similar tables are also likely available from the manufacturer of the cutter used.
The spindle speeds may be calculated for all machining operations once the SFM or MPM is known. In most cases, we are dealing with a cylindrical object such as a milling cutter or a workpiece turning in a lathe so we need to determine the speed at the periphery of this round object. This speed at the periphery (of a point on the circumference, moving past a stationary point) will depend on the rotational speed (RPM) and diameter of the object.
One analogy would be a skateboard rider and a bicycle rider travelling side by side along the road. For a given surface speed (the speed of this pair along the road) the rotational speed (RPM) of their wheels (large for the skater and small for the bicycle rider) will be different. This rotational speed (RPM) is what we are calculating, given a fixed surface speed (speed along the road) and known values for their wheel sizes (cutter or workpiece).
The following formulae may be used to estimate this value.
Approximation.
The exact RPM is not always needed, a close approximation will work (using 3 for the value of formula_1).
e.g. for a cutting speed of 100 ft/min (a plain HSS steel cutter on mild steel) and diameter of 10 inches (the cutter or the work piece)
and, for an example using metric values, where the cutting speed is 30 m/min and a diameter of 10 mm (0.01 m),
Accuracy.
However, for more accurate calculations, and at the expense of simplicity, this formula can be used:
and using the same example
and using the same example as above
where:
Feed rate.
Feed rate is the velocity at which the cutter is fed, that is, advanced against the workpiece. It is expressed in units of distance per revolution for turning and boring (typically "inches per revolution" ["ipr"] or "millimeters per revolution"). It can be expressed thus for milling also, but it is often expressed in units of distance per time for milling (typically "inches per minute" ["ipm"] or "millimeters per minute"), with considerations of how many teeth (or flutes) the cutter has then determined what that means for each tooth.
Feed rate is dependent on the:
When deciding what feed rate to use for a certain cutting operation, the calculation is fairly straightforward for single-point cutting tools, because all of the cutting work is done at one point (done by "one tooth", as it were). With a milling machine or jointer, where multi-tipped/multi-fluted cutting tools are involved, then the desired feed rate becomes dependent on the number of teeth on the cutter, as well as the desired amount of material per tooth to cut (expressed as chip load). The greater the number of cutting edges, the higher the feed rate permissible: for a cutting edge to work efficiently it must remove sufficient material to cut rather than rub; it also must do its fair share of work.
The ratio of the spindle speed and the feed rate controls how aggressive the cut is, and the nature of the swarf formed.
Formula to determine feed rate.
This formula can be used to figure out the feed rate that the cutter travels into or around the work. This would apply to cutters on a milling machine, drill press and a number of other machine tools. This is not to be used on the lathe for turning operations, as the feed rate on a lathe is given as "feed per revolution."
formula_8
Where:
Depth of cut.
Cutting speed and feed rate come together with "depth of cut" to determine the "material removal rate", which is the volume of workpiece material (metal, wood, plastic, etc.) that can be removed per time unit.
Interrelationship of theory and practice.
Speed-and-feed selection is analogous to other examples of applied science, such as meteorology or pharmacology, in that the theoretical modeling is necessary and useful but can never fully predict the reality of specific cases because of the massively multivariate environment. Just as weather forecasts or drug dosages can be modeled with fair accuracy, but never with complete certainty, machinists can predict with charts and formulas the approximate speed and feed values that will work best on a particular job, but cannot know the exact optimal values until running the job. In CNC machining, usually the programmer programs speeds and feedrates that are as maximally tuned as calculations and general guidelines can supply. The operator then fine-tunes the values while running the machine, based on sights, sounds, smells, temperatures, tolerance holding, and tool tip lifespan. Under proper management, the revised values are captured for future use, so that when a program is run again later, this work need not be duplicated.
As with meteorology and pharmacology, however, the interrelationship of theory and practice has been developing over decades as the theory part of the balance becomes more advanced thanks to information technology. For example, an effort called the Machine Tool Genome Project is working toward providing the computer modeling (simulation) needed to predict optimal speed-and-feed combinations for particular setups in any internet-connected shop with less local experimentation and testing. Instead of the only option being the measuring and testing of the behavior of its own equipment, it will benefit from others' experience and simulation; in a sense, rather than 'reinventing a wheel', it will be able to 'make better use of existing wheels already developed by others in remote locations'.
Academic research examples.
Speeds and feeds have been studied scientifically since at least the 1890s. The work is typically done in engineering laboratories, with the funding coming from three basic roots: corporations, governments (including their militaries), and universities. All three types of institution have invested large amounts of money in the cause, often in collaborative partnerships. Examples of such work are highlighted below.
In the 1890s through 1910s, Frederick Winslow Taylor performed turning experiments that became famous (and seminal). He developed Taylor's Equation for Tool Life Expectancy.
Scientific study by Holz and De Leeuw of the Cincinnati Milling Machine Company did for milling cutters what F. W. Taylor had done for single-point cutters.
"Following World War II, many new alloys were developed. New standards were needed to increase [U.S.] American productivity. Metcut Research Associates, with technical support from the Air Force Materials Laboratory and the Army Science and Technology Laboratory, published the first Machining Data Handbook in 1966. The recommended speeds and feeds provided in this book were the result of extensive testing to determine optimum tool life under controlled conditions for every material of the day, operation and hardness."
A study on the effect of the variation of cutting parameters in the surface integrity in turning of an AISI 304 stainless steel revealed that the feed rate has the greatest impairing effect on the quality of the surface, and that besides the achievement of the desired roughness profile, it is necessary to analyze the effect of speed and feed on the creation of micropits and microdefects on the machined surface. Moreover, they found that the conventional empirical relation that relates feed rate to roughness value does not fit adequately for low cutting speeds.


Sheet metal

Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes.
Thicknesses can vary significantly; extremely thin sheets are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate, such as plate steel, a class of structural steel.
Sheet metal is available in flat pieces or coiled strips. The coils are formed by running a continuous sheet of metal through a roll slitter.
In most of the world, sheet metal thickness is consistently specified in millimeters. In the U.S., the thickness of sheet metal is commonly specified by a traditional, non-linear measure known as its gauge. The larger the gauge number, the thinner the metal. Commonly used steel sheet metal ranges from 30 gauge to about 7 gauge. Gauge differs between ferrous (iron-based) metals and nonferrous metals such as aluminum or copper. Copper thickness, for example, is measured in ounces, representing the weight of copper contained in an area of one square foot. Parts manufactured from sheet metal must maintain a uniform thickness for ideal results.
There are many different metals that can be made into sheet metal, such as aluminium, brass, copper, steel, tin, nickel and titanium. For decorative uses, some important sheet metals include silver, gold, and platinum (platinum sheet metal is also utilized as a catalyst).
Sheet metal is used in automobile and truck (lorry) bodies, major appliances, airplane fuselages and wings, tinplate for tin cans, roofing for buildings (architecture), and many other applications. Sheet metal of iron and other materials with high magnetic permeability, also known as laminated steel cores, has applications in transformers and electric machines. Historically, an important use of sheet metal was in plate armor worn by cavalry, and sheet metal continues to have many decorative uses, including in horse tack. Sheet metal workers are also known as "tin bashers" (or "tin knockers"), a name derived from the hammering of panel seams when installing tin roofs.
History.
Hand-hammered metal sheets have been used since ancient times for architectural purposes. Water-powered rolling mills replaced the manual process in the late 17th century. The process of flattening metal sheets required large rotating iron cylinders which pressed metal pieces into sheets. The metals suited for this were lead, copper, zinc, iron and later steel. Tin was often used to coat iron and steel sheets to prevent it from rusting. This tin-coated sheet metal was called "tinplate." Sheet metals appeared in the United States in the 1870s, being used for shingle roofing, stamped ornamental ceilings, and exterior façades. Sheet metal ceilings were only popularly known as "tin ceilings" later as manufacturers of the period did not use the term. The popularity of both shingles and ceilings encouraged widespread production. With further advances of steel sheet metal production in the 1890s, the promise of being cheap, durable, easy to install, lightweight and fireproof gave the middle-class a significant appetite for sheet metal products. It was not until the 1930s and WWII that metals became scarce and the sheet metal industry began to collapse. However, some American companies, such as the W.F. Norman Corporation, were able to stay in business by making other products until Historic preservation projects aided the revival of ornamental sheet metal.
Materials.
Stainless steel.
Grade 304 is the most common of the three grades. It offers good corrosion resistance while maintaining formability and weldability. Available finishes are #2B, #3, and #4. Grade 303 is not available in sheet form.
Grade 316 possesses more corrosion resistance and strength at elevated temperatures than 304. It is commonly used for pumps, valves, chemical equipment, and marine applications. Available finishes are #2B, #3, and #4.
Grade 410 is a heat treatable stainless steel, but it has a lower corrosion resistance than the other grades. It is commonly used in cutlery. The only available finish is dull.
Grade 430 is a popular grade, low-cost alternative to series 300's grades. This is used when high corrosion resistance is not a primary criterion. Common grade for appliance products, often with a brushed finish.
Aluminum.
Aluminum, or aluminium in British English, is also a popular metal used in sheet metal due to its flexibility, wide range of options, cost effectiveness, and other properties. The four most common aluminium grades available as sheet metal are 1100-H14, 3003-H14, 5052-H32, and 6061-T6.
Grade 1100-H14 is commercially pure aluminium, highly chemical and weather resistant. It is ductile enough for deep drawing and weldable, but has low strength. It is commonly used in chemical processing equipment, light reflectors, and jewelry.
Grade 3003-H14 is stronger than 1100, while maintaining the same formability and low cost. It is corrosion resistant and weldable. It is often used in stampings, spun and drawn parts, mail boxes, cabinets, tanks, and fan blades.
Grade 5052-H32 is much stronger than 3003 while still maintaining good formability. It maintains high corrosion resistance and weldability. Common applications include electronic chassis, tanks, and pressure vessels.
Grade 6061-T6 is a common heat-treated structural aluminium alloy. It is weldable, corrosion resistant, and stronger than 5052, but not as formable. It loses some of its strength when welded. It is used in modern aircraft structures.
Brass.
Brass is an alloy of copper, which is widely used as a sheet metal. It has more strength, corrosion resistance and formability when compared to copper while retaining its conductivity.
In sheet hydroforming, variation in incoming sheet coil properties is a common problem for forming process, especially with materials for automotive applications. Even though incoming sheet coil may meet tensile test specifications, high rejection rate is often observed in production due to inconsistent material behavior. Thus there is a strong need for a discriminating method for testing incoming sheet material formability. The hydraulic sheet bulge test emulates biaxial deformation conditions commonly seen in production operations.
For forming limit curves of materials aluminium, mild steel and brass. Theoretical analysis is carried out by deriving governing equations for determining of equivalent stress and equivalent strain based on the bulging to be spherical and Tresca's yield criterion with the associated flow rule. For experimentation circular grid analysis is one of the most effective methods.
Gauge.
Use of gauge numbers to designate sheet metal thickness is discouraged by numerous international standards organizations. For example, ASTM states in specification ASTM A480-10a: "The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning."
Manufacturers' Standard Gauge for Sheet Steel is based on an average density of 41.82 lb per square foot per inch thick, equivalent to . Gauge is defined differently for ferrous (iron-based) and non-ferrous metals (e.g. aluminium and brass).
The gauge thicknesses shown in column 2 (U.S. standard sheet and plate iron and steel decimal inch (mm)) seem somewhat arbitrary. The progression of thicknesses is clear in column 3 (U.S. standard for sheet and plate iron and steel 64ths inch (delta)). The thicknesses vary first by inch in higher thicknesses and then step down to increments of inch, then inch, with the final increments at decimal fractions of inch.
Some steel tubes are manufactured by folding a single steel sheet into a square/circle and welding the seam together. Their wall thickness has a similar (but distinct) gauge to the thickness of steel sheets.
Tolerances.
During the rolling process the rollers bow slightly, which results in the sheets being thinner on the edges. The tolerances in the table and attachments reflect current manufacturing practices and commercial standards and are not representative of the Manufacturer's Standard Gauge, which has no inherent tolerances.
Forming processes.
Bending.
The equation for estimating the maximum bending force is,
formula_1,
where "k" is a factor taking into account several parameters including friction. "T" is the ultimate tensile strength of the metal. "L" and "t" are the length and thickness of the sheet metal, respectively. The variable "W" is the open width of a V-die or wiping die.
Curling.
The curling process is used to form an edge on a ring. This process is used to remove sharp edges. It also increases the moment of inertia near the curled end.
The flare/burr should be turned away from the die. It is used to curl a material of specific thickness. Tool steel is generally used due to the amount of wear done by operation.
Decambering.
It is a metal working process of removing camber, the horizontal bend, from a strip shaped material. It may be done to a finite length section or coils. It resembles flattening of leveling process, but on a deformed edge.
Deep drawing.
Drawing is a forming process in which the metal is stretched over a form or die. In deep drawing the depth of the part being made is more than half its diameter. Deep drawing is used for making automotive fuel tanks, kitchen sinks, two-piece aluminum cans, etc. Deep drawing is generally done in multiple steps called draw reductions. The greater the depth, the more reductions are required. Deep drawing may also be accomplished with fewer reductions by heating the workpiece, for example in sink manufacture.
In many cases, material is rolled at the mill in both directions to aid in deep drawing. This leads to a more uniform grain structure which limits tearing and is referred to as "draw quality" material.
Expanding.
Expanding is a process of cutting or stamping slits in alternating pattern much like the stretcher bond in brickwork and then stretching the sheet open in accordion-like fashion. It is used in applications where air and water flow are desired as well as when light weight is desired at cost of a solid flat surface. A similar process is used in other materials such as paper to create a low cost packing paper with better supportive properties than flat paper alone.
Hemming and seaming.
Hemming is a process of folding the edge of sheet metal onto itself to reinforce that edge. Seaming is a process of folding two sheets of metal together to form a joint.
Hydroforming.
Hydroforming is a process that is analogous to deep drawing, in that the part is formed by stretching the blank over a stationary die. The force required is generated by the direct application of extremely high hydrostatic pressure to the workpiece or to a bladder that is in contact with the workpiece, rather than by the movable part of a die in a mechanical or hydraulic press. Unlike deep drawing, hydroforming usually does not involve draw reductions—the piece is formed in a single step.
Incremental sheet forming.
Incremental sheet forming or ISF forming process is basically sheet metal working or sheet metal forming process. In this case, sheet is formed into final shape by a series of processes in which small incremental deformation can be done in each series.
Ironing.
Ironing is a sheet metal working or sheet metal forming process. It uniformly thins the workpiece in a specific area. This is a very useful process. It is used to produce a uniform wall thickness part with a high height-to-diameter ratio.
It is used in making aluminium beverage cans.
Laser cutting.
Sheet metal can be cut in various ways, from hand tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting. Many sheet metal cutting operations are based on computer numerically controlled (CNC) laser cutting or multi-tool CNC punch press.
CNC laser involves moving a lens assembly carrying a beam of laser light over the surface of the metal. Oxygen, nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth and a precision of around can be obtained. Cutting speeds on thin sheet can be as high as per minute. Most laser cutting systems use a based laser source with a wavelength of around 10 µm; some more recent systems use a YAG based laser with a wavelength of around 1 µm.
Photochemical machining.
Photochemical machining, also known as photo etching, is a tightly controlled corrosion process which is used to produce complex metal parts from sheet metal with very fine detail. The photo etching process involves photo sensitive polymer being applied to a raw metal sheet. Using CAD designed photo-tools as stencils, the metal is exposed to UV light to leave a design pattern, which is developed and etched from the metal sheet.
Perforating.
Perforating is a cutting process that punches multiple small holes close together in a flat workpiece. Perforated sheet metal is used to make a wide variety of surface cutting tools, such as the surform.
Press brake forming.
This is a form of bending used to produce long, thin sheet metal parts. The machine that bends the metal is called a press brake. The lower part of the press contains a V-shaped groove called the die. The upper part of the press contains a punch that presses the sheet metal down into the v-shaped die, causing it to bend. There are several techniques used, but the most common modern method is "air bending". Here, the die has a sharper angle than the required bend (typically 85 degrees for a 90 degree bend) and the upper tool is precisely controlled in its stroke to push the metal down the required amount to bend it through 90 degrees. Typically, a general purpose machine has an available bending force of around 25 tons per meter of length. The opening width of the lower die is typically 8 to 10 times the thickness of the metal to be bent (for example, 5 mm material could be bent in a 40 mm die). The inner radius of the bend formed in the metal is determined not by the radius of the upper tool, but by the lower die width. Typically, the inner radius is equal to 1/6 of the V-width used in the forming process.
The press usually has some sort of back gauge to position depth of the bend along the workpiece. The backgauge can be computer controlled to allow the operator to make a series of bends in a component to a high degree of accuracy. Simple machines control only the backstop, more advanced machines control the position and angle of the stop, its height and the position of the two reference pegs used to locate the material. The machine can also record the exact position and pressure required for each bending operation to allow the operator to achieve a perfect 90 degree bend across a variety of operations on the part.
Punching.
Punching is performed by placing the sheet of metal stock between a punch and a die mounted in a press. The punch and die are made of hardened steel and are the same shape. The punch is sized to be a very close fit in the die. The press pushes the punch against and into the die with enough force to cut a hole in the stock. In some cases the punch and die "nest" together to create a depression in the stock. In progressive stamping, a coil of stock is fed into a long die/punch set with many stages. Multiple simple shaped holes may be produced in one stage, but complex holes are created in multiple stages. In the final stage, the part is punched free from the "web".
A typical CNC turret punch has a choice of up to 60 tools in a "turret" that can be rotated to bring any tool to the punching position. A simple shape (e.g. a square, circle, or hexagon) is cut directly from the sheet. A complex shape can be cut out by making many square or rounded cuts around the perimeter. A punch is less flexible than a laser for cutting compound shapes, but faster for repetitive shapes (for example, the grille of an air-conditioning unit). A CNC punch can achieve 600 strokes per minute.
A typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under 15 seconds by either a press or a laser CNC machine.
Roll forming.
A continuous bending operation for producing open profiles or welded tubes with long lengths or in large quantities.
Rolling.
Rolling is metal working or metal forming process. In this method, stock passes through one or more pair of rolls to reduce thickness. It is used to make thickness uniform. It is classified according to its temperature of rolling:
Spinning.
Spinning is used to make tubular (axis-symmetric) parts by fixing a piece of sheet stock to a rotating form (mandrel). Rollers or rigid tools press the stock against the form, stretching it until the stock takes the shape of the form. Spinning is used to make rocket motor casings, missile nose cones, satellite dishes and metal kitchen funnels.
Stamping.
Stamping includes a variety of operations such as punching, blanking, embossing, bending, flanging, and coining; simple or complex shapes can be formed at high production rates; tooling and equipment costs can be high, but labor costs are low.
Alternatively, the related techniques repoussé and chasing have low tooling and equipment costs, but high labor costs.
Water jet cutting.
A water jet cutter, also known as a waterjet, is a tool capable of a controlled erosion into metal or other materials using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance.
Wheeling.
The process of using an English wheel is called wheeling. It is basically a metal working or metal forming process. An English wheel is used by a craftsperson to form compound curves from a flat sheet of metal of aluminium or steel. It is costly, as highly skilled labour is required. It can produce different panels by the same method. A stamping press is used for high numbers in production.
Fasteners.
Fasteners that are commonly used on sheet metal include: clecos, rivets, and sheet metal screws.


Through-hole technology

In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, either by manual assembly (hand placement) or by the use of automated insertion mount machines.
History.
Through-hole technology almost completely replaced earlier electronics assembly techniques such as point-to-point construction. From the second generation of computers in the 1950s until surface-mount technology (SMT) became popular in the mid 1980s, every component on a typical PCB was a through-hole component. PCBs initially had tracks printed on one side only, later both sides, then multi-layer boards were in use. Through holes became plated-through holes (PTH) in order for the components to make contact with the required conductive layers. Plated-through holes are no longer required with SMT boards for making the component connections, but are still used for making interconnections between the layers and in this role are more usually called vias.
Leads.
Axial and radial leads.
Components with wire leads are generally used on through-hole boards. Axial leads protrude from each end of a typically cylindrical or elongated box-shaped component, on the geometrical axis of symmetry. Axial-leaded components resemble wire jumpers in shape, and can be used to span short distances on a board, or even otherwise unsupported through an open space in point-to-point wiring. Axial components do not protrude much above the surface of a board, producing a low-profile or flat configuration when placed "lying down" or parallel to the board.
Radial leads project more or less in parallel from the same surface or aspect of a component package, rather than from opposite ends of the package. Originally, radial leads were defined as more-or-less following a radius of a cylindrical component (such as a ceramic disk capacitor). Over time, this definition was generalized in contrast to axial leads, and took on its current form. When placed on a board, radial components "stand up" perpendicular, occupying a smaller footprint on sometimes-scarce "board real estate", making them useful in many high-density designs. The parallel leads projecting from a single mounting surface gives radial components an overall "plugin nature", facilitating their use in high-speed automated component insertion ("board-stuffing") machines.
When needed, an axial component can be effectively converted into a radial component, by bending one of its leads into a "U" shape so that it ends up close to and parallel with the other lead. Extra insulation with heat-shrink tubing may be used to prevent shorting out on nearby components. Conversely, a radial component can be pressed into service as an axial component by separating its leads as far as possible, and extending them into an overall length-spanning shape. These improvisations are often seen in breadboard or prototype construction, but are deprecated for mass production designs. This is because of difficulties in use with automated component placement machinery, and poorer reliability because of reduced vibration and mechanical shock resistance in the completed assembly.
Multiple lead devices.
For electronic components with two or more leads, for example, diodes, transistors, ICs, or resistor packs, a range of standard-sized semiconductor packages are used, either directly onto the PCB or via a socket.
Characteristics.
While through-hole mounting provides strong mechanical bonds when compared to SMT techniques, the additional drilling required makes the boards more expensive to produce. They also limit the available routing area for signal traces on layers immediately below the top layer on multilayer boards since the holes must pass through all layers to the opposite side. To that end, through-hole mounting techniques are now usually reserved for bulkier or heavier components such as electrolytic capacitors or semiconductors in larger packages such as the TO-220 that require the additional mounting strength, or for components such as plug connectors or electromechanical relays that require great strength in support.
Design engineers often prefer the larger through-hole rather than surface mount parts when prototyping, because they can be easily used with breadboard sockets. However, high-speed or high-frequency designs may require SMT technology to minimize stray inductance and capacitance in wire leads, which would impair circuit function. Ultra-compact designs may also dictate SMT construction, even in the prototype phase of design.
Through-hole components are ideal for prototyping circuits with breadboards using microprocessors such as Arduino or PICAXE. These components are large enough to be easy to use and solder by hand.


Rautaruukki

Rautaruukki Oyj, using the marketing name Ruukki, is a Finnish company, headquartered in Helsinki, which manufactures and supplies metal-based components and systems to the construction and engineering industries. In 2014 Swedish SSAB bought Ruukki.
The company was founded in 1960 by the Finnish Government to provide the steel supply needed by the nation's heavy industries. Since part-privatization in 1994, the state has gradually decreased its holding in Rautaruukki.The firm consists of three business areas: construction, engineering and metals. Rautaruukki produces a range of products for clients in various industries, including cabins and chassis for heavy vehicles, hot rolled steel plates and coils, roofing sheets and building and bridge structures.
Ownership.
On 31 December 2011the principal shareholders were:


Engineering design process

The engineering design process, also known as the engineering method, is a common series of steps that engineers use in creating functional products and processes. The process is highly iterative - parts of the process often need to be repeated many times before another can be entered - though the part(s) that get iterated and the number of such cycles in any given project may vary.
It is a decision making process (often iterative) in which the basic sciences, mathematics, and engineering sciences are applied to convert resources optimally to meet a stated objective. Among the fundamental elements of the design process are the establishment of objectives and criteria, synthesis, analysis, construction, testing and evaluation.
Common stages of the engineering design process.
It's important to understand that there are various framings/articulations of the engineering design process. Different terminology employed may have varying degrees of overlap, which affects what steps get stated explicitly or deemed "high level" versus subordinate in any given model. This, of course, applies as much to any particular example steps/sequences given here.
One example framing of the engineering design process delineates the following stages: "research, conceptualization, feasibility assessment, establishing design requirements, preliminary design, detailed design, production planning and tool design, and production". Others, noting that "different authors (in both research literature and in textbooks) define different phases of the design process with varying activities occurring within them," have suggested more simplified/generalized models - such as "problem definition, conceptual design, preliminary design, detailed design, and design communication". Another summary of the process, from European engineering design literature, includes "clarification of the task, conceptual design, embodiment design, detail design". (NOTE: In these examples, other key aspects - such as concept evaluation and prototyping - are subsets and/or extensions of one or more of the listed steps.)
Research.
Various stages of the design process (and even earlier) can involve a significant amount of time spent on locating information and research. Consideration should be given to the existing applicable literature, problems and successes associated with existing solutions, costs, and marketplace needs.
The source of information should be relevant. Reverse engineering can be an effective technique if other solutions are available on the market. Other sources of information include the Internet, local libraries, available government documents, personal organizations, trade journals, vendor catalogs and individual experts available.
Design requirements.
Establishing design requirements and conducting requirement analysis, sometimes termed problem definition (or deemed a related activity), is one of the most important elements in the design process, and this task is often performed at the same time as a feasibility analysis. The design requirements control the design of the product or process being developed, throughout the engineering design process. These include basic things like the functions, attributes, and specifications - determined after assessing user needs. Some design requirements include hardware and software parameters, maintainability, availability, and testability.
Feasibility.
In some cases, a feasibility study is carried out after which schedules, resource plans and estimates for the next phase are developed. The feasibility study is an evaluation and analysis of the potential of a proposed project to support the process of decision making. It outlines and analyses alternatives or methods of achieving the desired outcome. The feasibility study helps to narrow the scope of the project to identify the best scenario.
A feasibility report is generated following which Post Feasibility Review is performed.
The purpose of a feasibility assessment is to determine whether the engineer's project can proceed into the design phase. This is based on two criteria: the project needs to be based on an achievable idea, and it needs to be within cost constraints. It is important to have engineers with experience and good judgment to be involved in this portion of the feasibility study.
Concept Generation.
A concept study (conceptualization, conceptual design) is often a phase of project planning that includes producing ideas and taking into account the pros and cons of implementing those ideas. This stage of a project is done to minimize the likelihood of error, manage costs, assess risks, and evaluate the potential success of the intended project. In any event, once an engineering issue or problem is defined, potential solutions must be identified. These solutions can be found by using ideation, the mental process by which ideas are generated. In fact, this step is often termed Ideation or "Concept Generation." The following are widely used techniques:
Various generated ideas must then undergo a concept evaluation step, which utilizes various tools to compare and contrast the relative strengths and weakness of possible alternatives.
Preliminary design.
The preliminary design, or high-level design includes (also called FEED or Basic design), often bridges a gap between design conception and detailed design, particularly in cases where the level of conceptualization achieved during ideation is not sufficient for full evaluation. So in this task, the overall system configuration is defined, and schematics, diagrams, and layouts of the project may provide early project configuration. (This notably varies a lot by field, industry, and product.) During detailed design and optimization, the parameters of the part being created will change, but the preliminary design focuses on creating the general framework to build the project on.
S. Blanchard and J. Fabrycky describe it as:
“The ‘whats’ initiating conceptual design produce ‘hows’ from the conceptual design evaluation effort applied to feasible conceptual design concepts. Next, the ‘hows’ are taken into preliminary design through the means of allocated requirements. There they become ‘whats’ and drive preliminary design to address ‘hows’ at this lower level.”
Detailed design.
Following FEED is the Detailed Design (Detailed Engineering) phase, which may consist of procurement of materials as well.
This phase further elaborates each aspect of the project/product by complete description through solid modeling, drawings as well as specifications.
Computer-aided design (CAD) programs have made the detailed design phase more efficient. For example, a CAD program can provide optimization to reduce volume without hindering a part's quality. It can also calculate stress and displacement using the finite element method to determine stresses throughout the part.
Production planning.
The production planning and tool design consists of planning how to mass-produce the product and which tools should be used in the manufacturing process. Tasks to complete in this step include selecting materials, selection of the production processes, determination of the sequence of operations, and selection of tools such as jigs, fixtures, metal cutting and metal or plastics forming tools. This task also involves additional prototype testing iterations to ensure the mass-produced version meets qualification testing standards.
Comparison with the scientific method.
Engineering is formulating a problem that can be solved through design. Science is formulating a question that can be solved through investigation.
The engineering design process bears some similarity to the scientific method. Both processes begin with existing knowledge, and gradually become more specific in the search for "knowledge" (in the case of "pure" or basic science) or a "solution" (in the case of "applied" science, such as engineering). The key difference between the engineering process and the scientific process is that the engineering process focuses on design, creativity and innovation while the scientific process emphasizes Discovery (observation).
Degree Programs.
Methods are being taught and developed in Universities including:


Tin Can Alley

Tin Can Alley is an inexpensive electronic shooting game for children. It uses infrared technology embedded inside a small plastic pistol or rifle. The objective is to aim at a mark below a selection of small tin cans perched upon a plastic wall. Successfully aiming at the marks below each of the cans causes the can to "pop off".
The game is based on a popular UK carnival game of the same name, which involves throwing bean bags at tin cans to knock them down. Both the electronic and carnival game are named for Tin Pan Alley, a name for a collection of New York City songwriters and music publishers, as well as the name of the Manhattan location where many of the songwriters and publishers worked.


Research-based design

The research-based design process is a research process proposed by Teemu Leinonen, inspired by several design theories. It is strongly oriented towards the building of prototypes and it emphasizes creative solutions, exploration of various ideas and design concepts, continuous testing and redesign of the design solutions.
The method is firmly influenced by the Scandinavian participatory design approach. Therefore, most of the activities take place in a close dialogue with the community that is expected to use the tools or services designed.
Phases.
The process can be divided into four major phases, although they all happen concurrently and side by side. At different times of the research, researchers are asked to put more effort into different phases. The continuous iteration, however, asks researchers to keep all the phases alive all the time: contextual inquiry, participatory design, product design, prototype as hypothesis.
Contextual inquiry.
Contextual inquiry refers to the exploration of the socio-cultural context of the design. The aim is to understand the environment, situation, and culture where the design takes place. The results of the contextual inquiry are better understanding of the context by recognizing in it possible challenges and design opportunities. In this phase, design researchers use rapid ethnographic methods, such as participatory observation, note-taking, sketching, informal conversations, and interviews. At the same time as the field work, the design researchers are doing a focused review of the literature, benchmarking existing solutions, and analyzing trends in the area in order to understand and recognise design challenges.
Participatory design.
Throughout the contextual inquiry design researchers start to develop some preliminary design ideas, which would be developed during the next stage—participatory design—in workshops with different stakeholders. The participatory design sessions tend to take place with small groups of 4 to 6 participants. A common practice is to present the results as scenarios made by the design researchers containing challenges and design opportunities. In the workshop, the participants are invited to come up with design solutions to the challenges and to bring to the discussion new challenges and solutions.
Since one of the main features of the research-based design is its participatory nature, the user's involvement is an integral part of the process. In this regard, participatory design workshops are organized during the different stages in order to validate initial ideas and discuss the prototypes at different stage of development.
Product design.
The results of the participatory design are analysed in a design studio by the design researchers who use the materials from the contextual inquiry and participatory design sessions to redefine the design problems and redesign the prototypes. By keeping a distance from the stakeholders, in the product design phase the design researchers will get a chance to analyse the results of the participatory design, categorize them, use specific design language related to implementation of the prototypes, and finally make design decisions.
Prototype as hypothesis.
Ultimately, the prototypes are developed to be functional on a level that they can be tested with real people in their everyday situations. The prototypes are still considered to be a hypothesis, prototypes as hypothesis, because they are expected to be part of the solutions for the challenges defined and redefined during the research. It remains to the stakeholders to decide whether they support the assertions made by the design researchers. Therefore the first prototypes brought to the use of the real people can be considered to be also minimum viable products.
Research-based design is not to be confused with design-based research or educational design research. In research-based design, which builds on art and design tradition, the focus is on the artifacts, the end-results of the design. The way the artifacts are, the affordances and features they have or do not have, form an important part of the research argumentation. As such, research-based design as a methodological approach includes research, design, and design interventions that are all intertwined.


Sherline

Sherline is a machine tool builder founded in Australia and currently headquartered in Vista, California, USA. It builds miniature machine tools (microlathes and micromills) and a wide range of tooling to be used on them. Within the miniature segment of the machine tool industry, Sherline is one of the most widely known brands. According to Sherline, their line of OEM accessories (chucks, vises, rotary tables, and so on) is more comprehensive than that of any other builder of machine tools, regardless of machine size.
Sherline tools are often used by hobbyists for making nearly any kind of part that can be machined, as long as it fits within a miniature machine tool's limits of slide travel. Sherline's products are also used by industry. They provide an inexpensive way to build custom tooling using modular components (XY tables, machine slides, etc.).
Sherline's sales are global. Its product line helps to put machine tools in places where traditionally they would be unlikely to go by lowering the threshold for market entry. Its turnkey CNC systems are some of the least expensive CNC machine tools on the market, making it possible for individual hobbyists to enter a market that in past decades was almost entirely industrial.


Straight-line mechanism

A straight-line mechanism is a mechanism that converts any type of rotary or angular motion to perfect or near-perfect straight-line motion, or "vice versa". Straight-line motion is linear motion of definite length or "stroke", every forward stroke being followed by a return stroke, giving reciprocating motion.
The first such mechanism, patented in 1784 by James Watt, produced approximate straight-line motion, referred to by Watt as parallel motion.
Straight-line mechanisms are used in a variety of applications, such as engines, vehicle suspensions, walking robots, and rover wheels.
History.
In the late eighteenth century, before the development of the planer and the milling machine, it was extremely difficult to machine straight, flat surfaces. During that era, much thought was given to the problem of attaining a straight-line motion, as this would allow the flat surfaces to be machined. To find a solution to the problem, the first straight line mechanism was developed by James Watt, for guiding the piston of early steam engines. Although it does not generate an exact straight line, a good approximation is achieved over a considerable distance of travel.
Perfect straight line linkages were later discovered in the nineteenth century, but they weren't as needed, as by then other techniques for machining had been developed.
List of linkages.
Approximate straight line linkages.
These mechanisms often utilize four bar linkages as they require very few pieces. These four-bar linkages have coupler curves that have one or more regions of approximately perfect straight line motion. The exception in this list is Watt's parallel motion, which combines Watt's linkage with another four-bar linkage – the pantograph – to amplify the existing approximate straight line movement.
It is not possible to create perfectly straight line motion using a four-bar linkage, without using a prismatic joint.
Perfect straight line linkages.
Eventually, perfect straight line motion would be achieved.
The Sarrus linkage was the first perfect linear linkage, made in 1853. However, it is a spatial linkage rather than a planar linkage. The first planar linkage would not be made until 1864.
Currently, all planar linkages which produce perfect linear motion utilize the inversion around a circle to produce a hypothetical circle of infinite radius, which is a line. This is why they are called inversors or inversor cells.
The simplest solutions are Hart's W-frame – which use 6-bars – and the Quadruplanar inversors – Sylvester-Kempe and Kumara-Kampling, which also use 6-bars.
The Scott Russell linkage (1803) translates linear motion through a right angle, but is not a straight line mechanism in itself. The Grasshopper beam/Evans linkage, an approximate straight line linkage, and the Bricard linkage, an exact straight line linkage, share similarities with the Scott Russell linkage and the Trammel of Archimedes.
Compound eccentric mechanisms with elliptical motion.
These mechanisms use the principle of a rolling curve instead of a coupler curve and can convert continuous, rather than just limited, rotary motion to reciprocating motion and "vice versa" via elliptical motion. The straight-line sinusoidal motion produces no second-order inertial forces, which simplifies balancing in high-speed machines.
Gallery.
Approximate straight line linkages.
Parts/links of the same color are the same dimensions.
Perfect straight line linkages.
Parts/links of the same color are the same dimensions.


Travers Tool

Travers Tool is a distributor of metalworking tools and industrial supplies. The company is based in Flushing, New York, and has distribution branches in or near New York City, Los Angeles, and Duncan, South Carolina.
Travers offers high speed steel cutting tools, solid carbide cutting tools, carbide indexable cutting tools, blades, abrasives, deburring tools, files, machinery, machine tools, machine tool accessories, measuring tools, inspection instruments, hand tools, power tools, pneumatic tools, welding equipment, fasteners, tooling components, stock materials, Maintenance, Repair and Operations (MRO) products, safety products and equipment, material handling equipment and reference books and software.
History.
Travers Tool Co., Inc. was started in 1924 by David Trevas. An aspiring young entrepreneur, David borrowed $1000 and asked a New York tool distributor to let him place a telephone on one of the empty desks at the office. After gaining some measure of success, David opened his first metalworking tool distribution office at 5 Court Square in Long Island City, New York. Because many of his customers did not pronounce his last name correctly, David Trevas named his company Travers Tool Co., Inc.
Seymour Trevas started working for his father in the 1930s. In the 1940s, Travers Tool was honored by receiving the coveted Navy E Award (for excellence) as a navy subcontractor. In the 1950s, Travers Tool relocated to 10-23 Jackson Avenue in Long Island City. In 1967, under the leadership of Barry Zolot, Seymour's son-in-law, the first Travers Tool mail order Master Catalog was created. This move served as a catalyst for significant growth for the company. In 1974, Travers Tool purchased and moved into a , 2-story facility at 25-26 50th Street in Woodside, New York.
As business grew throughout the 1980s, Travers Tool moved into a larger facility at 128-15 26th Avenue, Flushing, New York and built a warehouse in Duncan, South Carolina.
Racing sponsor.
In 1994, Travers Tool Company went into sponsoring race cars, first, in the NHRA, when they sponsored Blaine Johnson for his entire career, which lasted from the 1994 Winter Nationals, to the 1996 U.S. Nationals, where Johnson was killed during qualifying, Travers Tool Company has not sponsored a driver since.


Backflush accounting

Backflush accounting is a subset of management accounting focused on types of "postproduction issuing;" It is a product costing approach, used in a Just-In-Time (JIT) operating environment, in which costing is delayed until goods are finished. Backflush accounting delays the recording of costs until after the events have taken place, then standard costs are used to work backwards to 'flush' out the manufacturing costs. The result is that detailed tracking of costs is eliminated. Journal entries to inventory accounts may be delayed until the time of product completion or even the time of sale, and standard costs are used to assign costs to units when journal entries are made. Backflushing transaction has two steps: one step of the transaction reports the produced part which serves to increase the quantity on-hand of the produced part and a second step which relieves the inventory of all the component parts. Component part numbers and quantities-per are taken from the standard bill of material (BOM). This represents a huge saving over the traditional method of a) issuing component parts one at a time, usually to a discrete work order, b) receiving the finished parts into inventory, and c) returning any unused components, one at a time, back into inventory.
It can be argued that backflush accounting simplifies costing since it ignores both labor variances and work-in-process. Backflush accounting is employed where the overall business cycle time is relatively short and inventory levels are low.
Backflush accounting is inappropriate when production process is long, and this has been attributed as a major flaw in the design of the concept. It may also be inappropriate if the bill of materials contains not only piece goods but also many parts with more or less variable consumption. If the parts with variable consumption are just a few, like grease or the ink used to print product-labels, the consumed quantities can be assigned to product-independent cost centers at the withdrawal from stores (preproduction issuing) and can eventually be broken down afterwards to specific products or product groups, just like any other indirect or overhead expense. Difficulties maintaining correct inventories on shop floor may also appear if it is usual practice to use alternative materials and/or quantities without needing derogation.
Therefore, in case of a more complex production system, it is a better approach to use a Manufacturing Execution System (MES) which gathers real production data and is able to deliver exact data to the accounting software or Enterprise resource planning-system where the goods issue is recorded. Thus, variances in consumption, in comparison to the standard bill of materials, are taken into account and assigned to the correct product, production order and workplace. Another advantage of using a MES is that it implements also the Production Track & Trace and the status of work in progress is also known in real time. A disadvantage of MES is that it is not suitable for small series or prototype production. Such type of production should be segregated from the series production and mass production.
Meaning of backflushing.
From a financial accounting perspective, backflushing is a technique of the perpetual inventory system. Small businesses which have a low variety of items in their inventory still use periodic inventory management.
A periodic inventory system does not require day-to-day tracking of physical inventory. Purchases, cost of goods sold, and inventory on hand cannot be tracked until the end of the accounting time period when a physical inventory is performed and ending inventory is compared against the sum of beginning inventory and purchases. Cost of ending inventory can be calculated by using the LIFO or FIFO inventory accounting methods, or other less common methods. The end of the accounting period is considered usually the end of each month because otherwise some taxes like the VAT (value added tax) cannot be charged. The monthly stock-taking is the main disadvantage of the periodic inventory system. Another disadvantage is that it requires also monthly a reconciliation between the records of the management accounting and the financial accounting.
The main difference between the periodic inventory and the perpetual inventory is that the perpetual inventory does not keep the inventory-balance by using the inventory accounts, instead the entire input is booked immediately on the expense accounts. The principle is the following:
output= initial inventory + input - final inventory
At the end of the accounting period the inventory is assessed through stock-taking:
inventory asset account = expense account
At the beginning of the accounting period the stock is canceled using the opposite booking:
expense account = inventory asset account
During the accounting period any input is booked directly to the expense account. For example, if we buy materials the bookings are:
material account = supplier account
material expense account = material account
At the end of the accounting period, at the stock-taking the booking will be material account = material expenses account
Development of more sophisticated computer scanning of inventory has allowed regular use of perpetual inventory systems by companies. According to the generally accepted accounting principles (GAAP), companies can use either perpetual inventory systems or periodic inventory systems. Perpetual inventory management is a system where store balances of inventory are recorded after every transaction. It eliminates the need for the store to close down constantly for inventory stock-taking as perpetual inventory systems allow for continuous stock-taking. Perpetual inventory systems keep a running account of the company's inventory. Perpetual inventory systems involve more record-keeping than periodic inventory systems. Every inventory item is kept on a separate ledger. These inventory ledgers contain information on cost of goods sold, purchases, and inventory on hand. Perpetual inventory management systems allow for a high degree of control of the company's inventory by management. Perpetual inventory management is generally used by companies who have the ability to scan the inventory items.
In the context of perpetual inventory, backflushing is automatic accounting of material consumed for production, at the time of confirmation of the production, e.g., when a 4-wheeler automobile is rolled out from assembly line, 4 wheels and tires are deemed to be consumed and issued to production order automatically by way of back flushing by the system. Typically, the assembly line has its own limited stock of materials as work in process. This stock is replenished by transferring materials from a warehouse (store) into the assembly lines own designated location, e.g., a supermarket. At goods receipt the consumed materials are posted automatically from the location designated to the issuing production line. In other words, back flushing refers only to materials which are already withdrawn from the inventory of the warehouse (store) and were delivered to the shop floor. Parts are issued from stores to Work-In-Process inventory, but not based on a job order or for a specific production order. They are issued in quantities estimated to cover requirements of individual work centers and production lines. The issuing may be used to cover a period of time or to fill a fixed—size container. But unlike the traditional approach, also known as "preproduction issuing," where the costs are assigned to the product order at the withdrawal of materials from the stores and after completion of production any excess material is given back to the stores, backflushing delays that until the goods receipt of the finished product or assembly is issued. The remaining quantity of unused material left on the shops is still held in the system as floor stock and so material will not be ordered incorrectly through the Manufacturing resource planning (MRP). By eliminating work-in-process accounts, backflush costing simplifies the accounting process. However, this simplification and other deviations from traditional costing systems mean that backflush costing may not always conform to generally accepted accounting principles (GAAP). Another drawback of this system is the lack of a sequential audit trail. The main advantage of postproduction issuing, not necessarily of backflushing, is that there is no need to update the store balances of inventory at the withdrawal of the materials from stores and recording the excess material through reverse posting (storno). This is especially useful in series or mass production where it is no need to give back excess material to the stores because it is used for the next production order. Even if excess material is given back to stores it does not involve any update to the inventory balance in the financial accounting (stock accounts). It involves only a stock transfer in the inventory management or warehouse management. Only the materials reported as consumed through the method of backflushing or by the MES imply an update to the inventory balance:
material account = material expenses account
Back flush is used for materials which are required for the product and have a fixed relationship with it. Depending on how backflushing is implemented in the accounting software being used and depending on organizational rules, the back flushing may create error records which need to be analyzed by someone in charge for the cost accounting. One possible reason for the creation of these error records can be that there is no sufficient book inventory available in the designated back flushing location (shop floor). By simply deleting the error record, without working it out, could mean that the costs are not assigned correctly to products and/or even that the expenses in the financial accounting (inventory accounts) are not being recorded. The error record as such, is not a specific consequence of using back flushing. It may exist also when a MES system is being used when no back flushing is needed. The reason for this is that any error in transmitting and/or interpreting the data being sent by the MES system to the ERP system is consigned and needs to be worked out. When using back flushing, any scrap, material usage variance (using more or less than specified in the BOM) or substitution must be reported separately in order to maintain acceptable inventory accuracy. These are typically implemented as unplanned transactions. The downside of unplanned transactions is that they are prone to error. Unplanned inventory transactions must be eliminated and replaced creatively with planned transactions because even a very low percentage of misreported transactions will take inventory accuracy quickly to an unacceptable level. That is why the usage of backflushing is recommended only if 2 conditions are met: low I/O Variation and low Production Lead Times. Without low part I/O variation through low scrap, non-standard usage, and substitution, system inventory levels become unreliable. The exception transactions just cannot come through quickly or accurately enough to tame the beast. Loss of trust in the system occurs. Without short manufacturing lead times, components get moved into production but don't get relieved right away from the ERP inventory. This leads to confusion. Evident discrepancies between physical and system inventory counts cause frustration and lack of trust in the system. Without accurate and timely inventory levels, internal production plans and external purchase orders cannot be scheduled effectively, leading to inventory shortages and excess inventory. Inventory shortages cause disruptions to the manufacturing schedule, forcing additional setups, forced substitutions, overtime, premium freight charges, missed shipments and lost capacity. Excess inventory increases obsolescence and consumes precious cash flow and shelf space. Both excess inventory and shortages can indirectly lead to poor quality. A plant cannot cycle-count its way to accurate inventories. Cycle counting is not timely enough to be of benefit. And cycle counts are more likely to introduce errors than to correct them.
Alternatives to backflushing.
If the nature of a manufacturing process is such that component usage variation is natural and unavoidable, and/or production lead times are long, an ERP implementation design that entails a different methodology than backflushing from the shop-floor stock is required. There are two strategies used to deliver materials to the shop floor: Push and Pull, see Push–pull strategy. Depending on which strategy is being used and depending on how it is implemented, backflushing can be eliminated.
Alternatives to Backflushing when using the Push-strategy
The traditional way of issuing consumed materials is by using dual issues and returns against work orders. Components are counted when issued to a production order from Stores when the production order is opened. Produced parts and leftover components are counted when returned to stores when the work order is closed. In conjunction with a tightly controlled material Stores with discrete storage places, this can deliver very high inventory accuracy without the need for additional transactions to report scrap, material substitution, and non-standard usage separately. This obviously requires more transactions than backflushing. But these can be automated in a variety of ways, especially since most transactions take place in a limited area (Stores) and not throughout the plant. Accountability for component usage and operator time/efficiency at the work-order level by operator/shift/cell is greatly increased in this method over backflushing. Work orders also deliver higher lot-control quality measurement potential, substitution management (through a modified work-order BOM) and higher part and customer container bar-coding accuracy. The shop-floor stock in this case uses a discrete storage bin, identical to the number of the production order but no backflushing is required when the produced parts are counted. Leftover components are returned to the store and all the components from the discrete shop-floor storage bin are issued against that production order (postproduction issuing), in a similar way like backflushing, but not based on the bill of materials (BOM) but on the real stock which was consumed (transferred from the stores) for that particular production order.
The downside of this method is that it may not be suited for a more complex and repetitive production because it requires perfect contention of the WIP (raw materials and assemblies) on the shop floor: the materials issued to a production order shouldn't interfere with another production order or the next production order of the same kind. This can be done only if all work-steps required to complete the production order are limited more or less to a single workplace. That is why this kind of approach can be implemented for complex products only by using the push strategy. Push strategy means that a complex finished product is divided into many smaller assemblies and even assemblies may contain smaller assemblies and so on. All these assemblies will receive their own production order. These production orders are usually created automatically by the MRP\ERP - system. The ERP system uses Manufacturing resource planning (MRP) for the planning of production orders. Usually only the production planning for the finished product is done manually by the production planner, the assemblies are planned automatically based on backward scheduling. This is especially useful if the assemblies are being produced in another production line, workshop or plant. The downside of MRP and Push strategy is that it usually leads to larger stocks in the supply chain. That is why Push is regarded as the opposite of lean production because lean production involves the Pull strategy which means that any part should only be produced if there is a certain demand for it and therefore WIP will be small. Push strategy is when MRP is used also to schedule production orders for semi-finished products (assemblies) based on the forecasted demand of the finished product. These assemblies are put into stores without any reference to a certain production order of the finished product. The finished product may not even have had production orders released at the time the assembly was delivered to the store. That is why using MRP to schedule the execution of production orders is by definition a push system because releases are made according to a master production schedule without regard to system status. Hence, no "a priori" WIP limit exists. However MRP can be designed in such a way that it has an explicit WIP constraint. That means that assemblies are not produced further if a certain level of inventory is reached. MRP with a WIP constraint can be regarded as a pull system. However, even if a WIP constraint is implemented, Push-strategy generally means that the time, needed from the first operation or assembly until the finished good is obtained, is much longer as opposed to pull-strategy. This is due to the lead-times needed for each assembly and can be analyzed by using a technique called Value stream mapping. There is usually also much more handling: putting the assemblies into the stores, picking the assemblies from stores to the next production step (order) which uses the assembly to make another assembly or finished product. In reality, most firms use both strategies. For example: you could use MRP (push) without WIP constraint to schedule assemblies that are produced in another workshop, plant or external supplier and Kanban (pull) in your own plant. You can also use Kanban to schedule the assemblies in another workshop or plant, but it is usually not done when these assemblies are produced on large machines because with MRP the demand of several days can be comprised in bigger lot sizes of production orders of similar type in such a way that the workshops own scheduling system (MES) is then able to use the available machine-capacity better by bringing the production orders into an optimal sequence using suitable algorithms. This is usually the case when the machines are expensive, their number is relatively small and they have big output-capacities and setup time is expensive. Implementing Kanban in such a case would require to use a bigger number of smaller\cheaper machines, dedicated to certain production lines, in order to react more flexibly to the demand. Another requirement would be that the frequency of transports from\to that plant to be higher and the distance to that plant to be relatively small. These requirements however, cannot be accomplished in each case. On the other side, the workshop (supplier) which manufactures the assemblies may very well use a push strategy or a pull-strategy for delivering the needed materials to each of its own machines.
As described above, this alternative to backflushing has a self-correcting property: the shop-floor stock is always related to a certain production order, onto which all the consumed materials were actually issued. On the other hand, backflushing by its very definition can never be self-correcting and should only be used when corrections are rarely needed. An objection can be made with the above described alternative that scrap is not reported with a reason code, or broken out separately from other forms of non-standard usage. But how accurate is scrap reporting in an environment without inventory accuracy? Better to settle for inventory accuracy and worry about scrap later as a separate issue. Option: implement a separate scrap analysis protocol unrelated to inventory transactions. Scrapped parts are segregated for subsequent inspection, quality data recording and possible rework. In both cases, scrapped parts are already removed from inventory at the end of the manufacturing cycle (presumably by returning fewer components to stores). Therefore, an inventory transaction is only needed when parts are deemed acceptable upon inspection, or after a rework operation is performed. Scrap reporting can also be done by using data from the Process control system and/or Manufacturing Execution System. Usually such a system exists to some degree in any firm, even if it is not called PCS or MES and even if it is used eventually only for keeping data regarding personnel performance and piecework, as a basis for calculating the salary of the workers. Such a system could be extended so that each worker reports also the scrapped parts.
More technical requirements like Production Track & Trace, Overall Equipment Efficiency, Production Performance analysis or displaying production progress of a production order in real time should always be implemented as part of an MES. It is a bad approach to implement such systems more or less just for the sake of inventory accuracy. Inventory accuracy should be attained through much simpler means, as described above and should not depend for example on the quality of the scrap reporting. The same is true the other way around: for example if you need Production Track & Trace (which components belonging to which lots were incorporated into a product with a given serial number) you shouldn't rely solely on the components issued as consumed for a specific production order, especially when using backflushing that would be a bad idea.
The same is true for production scheduling: an ERP\MRP can be used to schedule production orders (to establish deadlines for their delivery) as well as to schedule goods receipts from the suppliers. It is also a very useful tool to offer data for internal usage about medium to long-term demand and\or planning or a forecast for external suppliers based on BOM explosion. But ERP\MRP is usually not very useful for scheduling operations on the shop-floor. A production planner using ERP may oversee total gross-capacity demand for all or for a certain type of operation but may not see bottlenecks on individual machines or workplaces. It is the job of the scheduling system (MES) to dispatch the production orders received from the ERP to individual machines\work places. When lean production is used (Pull), see next chapter, the production order received from the ERP usually refers to a finished product or to a more complex assembly. In this case, the scheduling system is even more important because it has to dispatch parts of the production order to individual work-places.
Alternatives to Back flushing when using the Pull-strategy
Pull strategy means that work centers request the materials needed for a specific production order from the store or from an upstream workplace (demand driven). Usually this means that semi-finished products are produced for a specific production order of the finished product and therefore stocks held in the supply chain are better managed (usually smaller). This can be accomplished by using Kanban. Kanban is essentially a production scheduling system. It can be used together with a Process control system to make a Manufacturing Execution System. A Process control system gathers data from the work places where the production order is executed. It receives the individual workloads assigned by the scheduling system to individual work places. The purpose of the scheduling system is to optimize the usage of resources. For scheduling the production of individual workplaces, Kanban can be used solely or a more complex optimization software is necessary. Usually a scheduling system based on an optimization software is necessary if the production is executed on machines and it is non-trivial to decide on which machine a specific production order should be executed in order to use resources optimally. Such a type of scheduling problem is known as Job shop scheduling or Flow shop scheduling. Job shop scheduling means that each production order needs to be executed only on one machine for completion and the problem is to get the optimal sequence of orders for a specific machine and, in case that we have several machines that are able to execute the same order, to assign the order to the machine that has available resources. Flow shop scheduling means that a production order has to pass several types of work-centers (machines) in a predefined order. This is a more complex problem than "job shop scheduling" because after completion of one work-step, the system has to assign an available machine for the next type of operation until all operations for a given production order are completed. Regardless of the type of scheduling problem the algorithm needed to accomplish this task has n! complexity (n factorial). There is a well known similar type of problem called the Travelling salesman problem. Only very small problems of this kind can be solved using Brute-force search. A simple example: Let's assume that we have only one machine and 20 production orders. Due dates have no importance. We want to put these 20 production orders in the optimal sequence so that the overall setup time is minimal. All setup times needed to switch from one order to the other are known and may be different: setting the machine up from order1 to order2 may need 1 minute, but from order 2 to order1 the time may be different from 1 minute. So we have permutations of size 2 for 20 objects which equals 320 distinct pairs of setup costs. But there are 20!= 2,432 * 10^18 distinct possibilities for putting the 20 orders in a sequence. Enumerating each possibility is not feasible because there are 2,432 * 10^18 possibilities. Therefore, Heuristic algorithms are used for solving problems of this kind. These algorithms do not guarantee to find the optimal solution, but they usually find a solution in the vicinity of the optimal solution in a reasonably short period of time. So the meaning of a MES is to be able to use such heuristic algorithms in order to fulfill the business policy. The business policy defines how the antagonistic restrictions are weighted, which of them are more important. These antagonistic restrictions are: delivery deadlines, machine setup time and machine usage. The scheduling system knows everything about the capabilities of the machines, the available tools and so on, and it can therefore make an optimal decision, which work-place (machine) should execute which part of the production order and when. Of course the operator should be able to refuse the order if something unpredictable has happened (a tool is missing or not operational etc.) and the system should be able to reschedule the order automatically or with the aid of a production planner or supervisor. A MES has to be a dynamic system which can react to the real and unpredictable events.
In such an environment, where the production order received form the ERP\MRP software is scheduled using a MES or Kanban and the materials are assigned to the shop floor at the withdrawal from stores, there is no need for using backflushing. The materials are usually issued from the stores to a supermarket on the shop floor without being related to a specific production order but in the amount needed to cover the demand of the already released production orders. This amount is dynamic, and we call it "Kanban-quantity." It should be calculated in real-time by the MES. The supermarket itself can be regarded as a derogation from the principles of lean production, especially from those of the "One Piece Flow" concept, because it represents work in progress, WIP, which is not yet assigned to a specific production order being executed or which has been already released for production. The stock in the supermarket is already issued to the shop floor stock. The usage of a supermarket is usually necessary when not all of the individual work steps which are needed for the completion of the production order have the same execution time and therefore a small buffer is needed to avoid that one workplace is waiting for an upstream workplace to complete work. This buffer is usually maintained using 2 containers in the supermarket in which such kind of assemblies are stored. If none of the containers is empty, no further assemblies are being produced. If one of the container is empty, the remaining container is swapped with the empty one (FIFO) and production of the assembly is resumed according to the kanban-quantity computed by the MES. Another purpose of the supermarket is that it enables a quick replenishment of the workplaces with the needed raw-materials without the necessity for taking these materials from the store for each production order as opposed to the above described push-strategy where every material has to be issued to every production order at the withdrawal from stores. In other words, the quantity of any assembly or raw-material being stored in the supermarket is strictly limited, there is an explicit WIP constraint. Usually the supermarket is placed in the proximity of the work-places, so that the work-places have quick access to the needed materials. Every material has its own storage location in the supermarket (coordinates) so that it can be easily located when needed. The materials to be consumed are assigned by each workplace to the production order either by scanning them at the withdrawal from the supermarket (preproduction issuing) or by reporting them through the MES and Process control system (postproduction issuing).
Usually the first approach (scanning at the withdrawal) is used for materials which are piece goods. If the materials are not piece goods (bulk material, yard ware), then the workplace has to report the consumed quantities after it has finished its job on a particular production order. If a process control system is being used then the process control system will report the consumed materials directly to the ERP\MRP- System or to the MES and then the MES reports to the ERP. If no process control system is used, usually the case when manual work is being done, the consumed quantities have to be reported manually from every workplace by using a terminal (scanner, PC, etc.). Usually, when using bulk materials, the workplace reports the consumed quantity on the level of the handling unit (HU). A handling unit is a number assigned to the carton, pallet or any other kind of unitized packaging. So the handling unit is assigned to the workplace, the consumed quantity from that HU is issued and the HU, if no longer needed is put back to the supermarket. As a direct consequence a partial withdrawal from that handling unit is issued as consumed also in the ERP\MRP system. Any physically empty HU is reported using a distinct transaction. That means that any residual book inventory quantity that may exist in the ERP system, assigned to the shop floor and to that specific HU is reported as consumed and issued to a distinct cost center. Inversely, should a workplace report a consumption from a HU that has no book inventory in the shop-floor stock (is already empty in the ERP system), an error is generated as a backlog in issuing the consumed materials, see chapter "Meaning of backflushing." What kind of unplanned transactions are used to handle this error is a question of internal policy of every firm.
The reason why residual book inventory may exist in the MRP/ERP system may have multiple causes. A few of them are:
- the quantity in the original packaging was not completely exact (e.g. the supplier indicated a quantity of 10000 meters per coil, but some coils had only 9500 meters);
- the workplace has consumed some materials for adjusting the machine without being able to report that quantity exactly;
- the operator has omitted to assign a new handling unit to the workplace or has assigned the false handling unit. Such errors can be avoided if the system has a good data validation. For example, the machine does not start processing the job until all handling units required for that job are assigned to the work place or machine.
It is very important to design the interface between the MES and the MRP\ERP properly: the reporting of the consumed quantities has to be processed consistently, in the right order, in other words all the recorded/reported consumptions from a handling unit should be issued in the ERP before issuing the handling unit as empty. Otherwise a large number of false errors would get into the error-backlog because the book inventory is already zero as a consequence of issuing the handling unit as being empty before issuing all the consumption which refer to that specific handling unit.
These two alternatives to backflushing based on the pull-strategy (preproduction issuing/postproduction issuing) have also a self-correcting property: real quantities are reported from each workplace (not based on the bill of materials) and each unitized packaging (handling unit), when empty, is reported as empty and any residual book-inventory on the shopfloor is discarded.