Threading (manufacturing)

In manufacturing, threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods (many kinds of thread cutting and grinding, as detailed below); deformative or transformative methods (rolling and forming; molding and casting); additive methods (such as 3D printing); or combinations thereof.
Overview of methods (comparison, selection, etc.).
There are various methods for generating screw threads. The method for any one application is chosen based on constraints—time, money, degree of precision needed (or not needed), what equipment is already available, what equipment purchases could be justified based on resulting unit price of the threaded part (which depends on how many parts are planned), etc.
In general, certain thread-generating processes tend to fall along certain portions of the spectrum from toolroom-made parts to mass-produced parts, although there can be considerable overlap. For example, thread lapping following thread grinding would fall only on the extreme toolroom end of the spectrum, while thread rolling is a large and diverse area of practice that is used for everything from microlathe leadscrews (somewhat pricey and very precise) to the cheapest deck screws (very affordable and with precision to spare).
Threads of metal fasteners are usually created on a thread rolling machine. They may also be cut with a lathe, tap or die. Rolled threads are stronger than cut threads, with increases of 10% to 20% in tensile strength and possibly more in fatigue resistance and wear resistance.
Thread Milling has a better thread quality than tapping as it offers better chip evacuation. Tapping uses a tool the same size as the thread, forcing the chip through the thread for evacuation.
Subtractive methods.
Thread cutting.
Thread cutting, as compared to thread forming and rolling, is used when full thread depth is required, when the quantity is small, when the blank is not very accurate, when threading up to a shoulder is required, when threading a tapered thread, or when the material is brittle.
Taps and dies.
A common method of threading is cutting with taps and dies. Unlike drill bits, hand taps do not automatically remove the chips they create. A hand tap cannot cut its threads in a single rotation because it creates long chips which quickly jam the tap (an effect known as "crowding"), possibly breaking it. Therefore, in manual thread cutting, normal wrench usage is to cut the threads 1/2 to 2/3 of a turn (180 to 240 degree rotation), then reverse the tap for about 1/6 of a turn (60 degrees) until the chips are broken by the back edges of the cutters. It may be necessary to periodically remove the tap from the hole to clear the chips, especially when a blind hole is threaded.
For continuous tapping operations (i.e., power tapping) specialized spiral point or "gun" taps are used to eject the chips and prevent crowding.
Single-point threading.
Single-point threading, also colloquially called single-pointing (or just thread cutting when the context is implicit), is an operation that uses a single-point tool to produce a thread form on a cylinder or cone. The tool moves linearly while the precise rotation of the workpiece determines the lead of the thread. The process can be done to create external or internal threads (male or female). In external thread cutting, the piece can either be held in a chuck or mounted between two centers. With internal thread cutting, the piece is held in a chuck. The tool moves across the piece linearly, taking chips off the workpiece with each pass. Usually 5 to 7 light cuts create the correct depth of the thread.
The coordination of various machine elements including leadscrew, slide rest, and change gears was the technological advance that allowed the invention of the screw-cutting lathe, which was the origin of single-point threading as we know it today.
Today engine lathes and CNC lathes are the commonly used machines for single-point threading. On CNC machines, the process is quick and easy (relative to manual control) due to the machine's ability to constantly track the relationship of the tool position and spindle position (called "spindle synchronization"). CNC software includes "canned cycles", that is, preprogrammed subroutines, that obviate the manual programming of a single-point threading cycle. Parameters are entered (e.g., thread size, tool offset, length of thread), and the machine does the rest.
All threading could feasibly be done using a single-point tool, but because of the high speed and thus low unit cost of other methods (e.g., tapping, die threading, and thread rolling and forming), single-point threading is usually only used when other factors of the manufacturing process happen to favor it (e.g., if only a few threads need to be made, if an unusual or unique thread is required, or if there is a need for very high concentricity with other part features machined during the same setup.)
Thread milling.
Threads may be milled with a rotating milling cutter if the correct helical toolpath can be arranged. This was formerly arranged mechanically, and it was suitable for mass-production work although uncommon in job-shop work. With the widespread dissemination of affordable, fast, precise CNC, it became much more common, and today internal and external threads are often milled even on work where they would formerly have been cut with taps, die heads, or single-pointing. Some advantages of thread milling, as compared to single-point cutting or taps and dies, are faster cycle times, less tool breakage, and that a left- or right-hand thread can be created with the same tool. Additionally, for large, awkward workpieces (such as a fire hydrant casting), it is simply easier to let the workpiece sit stationary on a table while all needed machining operations are performed on it with rotating tools, as opposed to rigging it up for rotation around the axis of each set of threads (that is, for the "arms" and "mouth" of the hydrant).
There are various types of thread milling, including several variants of "form-milling" and a combination of drilling and threading with one cutter, called "thrilling".
One main advantage against tapping, is that tapping only starts making a complete thread profile on the third thread, whereas thread milling will produce a complete thread profile from the top to the bottom.
Form-milling uses either a single- or multiple-form cutter. In one variant of form-milling, the single-form cutter is tilted to the helix angle of the thread and then fed radially into the blank. The blank is then slowly rotated as the cutter is precisely moved along the axis of the blank, which cuts the thread into the blank. This can be done in one pass, if the cutter is fed to the full thread depth, or in two passes, with the first not being to the full thread depth. This process is mainly used on threads larger than . It is commonly used to cut large-lead or multiple-lead threads. A similar variant using a multiple-form cutter exists, in which the process completes the thread in one revolution around the blank. The cutter must be longer than the desired thread length. Using a multiple-form cutter is faster than using a single-form cutter but it is limited to threads with a helix angle less than 3°. It is also limited to blanks of a substantial diameter and no longer than .
Another variant of form-milling involves holding the cutter's axis orthogonally (no canting to the thread's helix angle) and feeding the cutter in a toolpath that will generate the thread. The part is usually a stationary workpiece, such as a boss on a valve body (in external thread milling) or a hole in a plate or block (in internal thread milling). This type of thread milling uses essentially the same concept as contouring with an endmill or ball-nose mill, but the cutter and toolpath are arranged specifically to define the "contour" of a thread. The toolpath is achieved either using helical interpolation (which is circular interpolation in one plane [typically XY] with simultaneous linear interpolation along a third axis [typically Z]; the CNC control model must be one that supports using the third axis) or a simulation of it using extremely small increments of 3-axes linear interpolation (which is not practical to program manually but can be programmed easily with CAD/CAM software). The cutter geometry reflects the thread pitch but not its lead; the lead (thread helix angle) is determined by the toolpath. Tapered threads can be cut either with a tapered multiple-form cutter that completes the thread in one revolution using helical interpolation, or with a straight or tapered cutter (of single- or multiple-form) whose toolpath is one or more revolutions but cannot use helical interpolation and must use CAD/CAM software to generate a contour-like simulation of helical interpolation.
The tooling used for thread milling can be solid or indexable. For internal threads, solid cutters are generally limited to holes larger than , and indexable internal thread cutting tools are limited to holes larger than . The advantage is that when the insert wears out it is easily and more cost effectively replaced. The disadvantage is the cycle time is generally longer than solid tools. Note that solid multiple-form thread cutting tools look similar to taps, but they differ in that the cutting tool does not have a backtaper and there is not a lead-in chamfer. This lack of a lead-in chamfer allows the threads to be formed within one pitch length of the bottom of a blind hole.
Thrilling.
Thrilling is the process of threading and drilling (accomplished in the reverse order) internal threads using a specialized cutting tool on a CNC mill. The cutting tool tip is shaped like a drill or center-cutting endmill, while the body has a thread-shaped form with a countersink cutter form near the shank. The cutter first plunges to drill the hole. Then the thread is circularly interpolated just like the multiple-form cutter described above. This tool drills, chamfers, and threads a hole all in one compact cycle. The advantage is this process eliminates a tool, tool-holder, and tool change. The disadvantage is that the process is limited to hole depth no greater than three times the diameter of the tool.
Helical broaching (Punch Tap).
A method of helical broaching was developed in the 2010s that shortens the toolpath of tapping. To a casual observer (without slow motion), it looks rather similar to traditional tapping but with faster movement into and out of the hole. It uses a specific tool geometry and toolpath to position rapidly, broach the thread in a single half-turn, and then retract rapidly, shortening the cycle time and consuming less energy. It reduces the cost of threading for any holes that can safely allow the two small fast-helix grooves that it leaves behind along with the thread, which could be true in many applications.
Thread grinding.
Thread grinding is done on a grinding machine using specially dressed grinding wheels matching the shape of the threads. The process is usually used to produce accurate threads or threads in hard materials; a common application is ball screw mechanisms. There are three types: "center-type grinding with axial feed", "center-type infeed thread grinding" and "centerless thread grinding". Center-type grinding with an axial feed is the most common of the three. It is similar to cutting a thread on a lathe with a single-point cutting tool, except the cutting tool is replaced with a grinding wheel. Usually a single ribbed wheel is used, although multiple ribbed wheels are also available. To complete the thread multiple passes are commonly required. Center-type infeed thread grinding use a grinding wheel with multiple ribs that is longer than the length of the desired thread. First, the grinding wheel is fed into the blank to the full thread depth. Then the blank is slowly rotated through approximately 1.5 turns while axially advancing through one pitch per revolution. Finally, the centerless thread grinding process is used to make head-less set screws in a similar method as centerless grinding. The blanks are hopper-fed to the grinding wheels, where the thread is fully formed. Common centerless thread grinding production rates are 60 to 70 pieces per minute for a long set screw.
Thread lapping.
Rarely, thread cutting or grinding (usually the latter) will be followed by thread lapping in order to achieve the highest precision and surface finish achievable. This is a toolroom practice when the highest precision is required, rarely employed except for the leadscrews or ballscrews of high-end machine tools.
Threading with EDM.
Internal threads can be electrical discharge machined (EDM) into hard materials using a sinker style machine.
Deformative or transformative methods.
Thread forming and rolling.
Thread forming and thread rolling are processes for forming, rather than cutting, screw threads, with the former referring to creating internal threads and the latter external threads. In both of these processes threads are formed into a blank by pressing a shaped tool, commonly called a 'thread rolling die' against the blank, in a process similar to knurling. These processes are used for large production runs because typical production rates are around one piece per second. Forming and rolling produce no swarf and less material is required because the blank size starts smaller than a blank required for cutting threads; there is typically a 15 to 20% material savings in the blank, by weight. A rolled thread can be easily recognized on fasteners that were formed from an unstopped blank because the thread has a larger diameter than the blank rod from which it has been made; however, necks and undercuts can be cut or rolled onto blanks with threads that are not rolled, and some fasteners are made from blanks with a reduced shank in the region to be rolled to maintain a constant major diameter from thread to unthreaded shank. Unless faced off, the end threads of a rolled fastener have a cupped end, as the surplus material in the tapering down final threads collapses uniformly over the end of the blank.
Materials are limited to ductile materials because the threads are cold formed. However, this increases the thread's yield strength, surface finish, hardness, wear resistance, and fatigue strength due to conformance of the grain with the thread profile. Also, materials with good deformation characteristics are necessary for rolling; these materials include softer (more ductile) metals and exclude brittle materials, such as cast iron. Tolerances are typically ±0.001 in. (±0.025 mm), but tolerances as tight as ±0.0006 in (±0.015 mm) are achievable. Surface finishes range from 6 to 32 micro-inches.
There are four main types of thread rolling, named after the configuration of the dies: "flat dies", "two-die cylindrical", "three-die cylindrical", and "planetary dies". The flat die system has two flat dies. The bottom one is held stationary and the other slides. The blank is placed on one end of the stationary die and then the moving die slides over the blank, which causes the blank to roll between the two dies forming the threads. Before the moving die reaches the end of its stroke the blank rolls off the stationary die in a finished form. The two-die cylindrical process is used to produce threads up to in diameter and in length. There are two types of three-die processes; the first has the three dies move radially out from the center to let the blank enter the dies and then closes and rotates to roll the threads. This type of process is commonly employed on turret lathes and screw machines. The second type takes the form of a self-opening die head. This type is more common than the former, but is limited by not being able form the last 1.5 to 2 threads against shoulders. Planetary dies are used to mass-produce threads up to in diameter.
Thread forming is performed using a ', or ', which closely resembles a cutting tap without the flutes. There are "lobes" periodically spaced around the tap that actually do the thread forming as the tap is advanced into a properly sized hole. Since the tap does not produce chips, there is no need to periodically back out the tap to clear away chips, which, in a cutting tap, can jam and break the tap. Thus thread forming is particularly suited to tapping blind holes, which are tougher to tap with a cutting tap due to the chip build-up in the hole. Note that the tap drill size differs from that used for a cutting tap and that an accurate hole size is required because a slightly undersized hole can break the tap. Proper lubrication is essential because of the frictional forces involved, therefore a lubricating oil is used instead of cutting oil.
When considering the blank diameter tolerance, a change in blank diameter will affect the major diameter by an approximate ratio of 3 to 1. Production rates are usually three to five times faster than thread cutting.
Thread casting and molding.
In casting and molding the threads are directly formed by the geometry of the mold cavity in the mold or die. When the material freezes in the mold, it retains the shape after the mold is removed. The material is heated to a liquid, or mixed with a liquid that will either dry or cure (such as plaster or cement). Alternatively, the material may be forced into a mold as a powder and compressed into a solid, as with graphite.
Although the first thoughts that come to mind for most machinists regarding threading are of thread "cutting" processes (such as tapping, single-pointing, or helical milling), Smid points out that, when plastic bottles for food, beverages, personal care products, and other consumer products are considered, it is actually plastic molding that is the principal method (by sheer volume) of thread generation in manufacturing today. Of course, this fact highlights the importance of the moldmakers getting the mold just right (in preparation for millions of cycles, usually at high speed).
Cast threads in metal parts may be finished by machining, or may be left in the as-cast state. (The same can be said of cast gear teeth.) Whether or not to bother with the additional expense of a machining operation depends on the application. For parts where the extra precision and surface finish is not strictly necessary, the machining is forgone in order to achieve a lower cost. With sand casting parts this means a rather rough finish; but with molded plastic or die-cast metal, the threads can be very nice indeed straight from the mold or die. A common example of molded plastic threads is on soda (pop) bottles. A common example of die-cast threads is on cable glands (connectors/fittings).
Additive methods.
Many, perhaps most, threaded parts have "potential" to be generated via additive manufacturing (3D printing), of which there are many variants, including fused deposition modeling, selective laser sintering, direct metal laser sintering, selective laser melting, electron beam melting, layered object manufacturing, and stereolithography. For most additive technologies, it has not been long since they emerged from the laboratory end of their historical development, but further commercialization is picking up speed. To date, most additive methods tend to produce a rough surface finish and tend to be restricted in the material properties that they can produce, and thus their earliest commercial victories have been in parts for which those restrictions were acceptable. However, the capabilities are continually growing.
Good examples of threaded parts produced with additive manufacturing are found in the dental implant and bone screw fields, where selective laser sintering and selective laser melting have produced threaded titanium implants.
Combinations of subtractive, additive, deformative, or transformative methods.
Often subtractive, additive, deformative, or transformative methods are combined in whatever ways are advantageous. Such multidisciplinary manufacturing falls under classifications including rapid prototyping, desktop manufacturing, direct manufacturing, direct digital manufacturing, digital fabrication, instant manufacturing, or on-demand manufacturing.
Inspection.
Inspection of the finished screw threads can be achieved in various ways, with the expense of the method tailored to the requirements of the product application. Shop-floor inspection of a thread is often as simple as running a nut onto it (for male threads) or a bolt into it (for female threads). This is plenty good enough for many applications (e.g., MRO or hobbyist work), although it is not good enough for most commercial manufacturing. Higher-precision methods are discussed below.
Commercial-grade inspection of screw threads can involve most of the same inspection methods and tools used to inspect other manufactured products, such as micrometers; vernier or dial calipers; surface plates and height gauges; gauge blocks; optical comparators; white light scanners; and coordinate-measuring machines (CMMs). Even industrial radiography (including industrial CT scanning) can be used, for example, to inspect internal thread geometry in the way that an optical comparator can inspect external thread geometry.
Conical micrometer anvils, specifically suited to resting on the sides of the thread, are made for various thread angles, with 60° being the most common. Mics with such anvils are usually called "thread mics" or "pitch mics" (because they directly measure the pitch diameter). Users who lack thread mics rely instead on the "3-wire method", which involves placing 3 short pieces of wire (or gauge pins) of known diameter into the valleys of the thread and then measuring from wire to wire with standard (flat) anvils. A conversion factor (produced by a straightforward trigonometric calculation) is then multiplied with the measured value to infer a measurement of the thread's pitch diameter. Tables of these conversion factors were established many decades ago for all standard thread sizes, so today a user need only take the measurement and then perform the table lookup (as opposed to recalculating each time). The 3-wire method is also used when high precision is needed to inspect a specific diameter, commonly the pitch diameter, or on specialty threads such as multi-start or when the thread angle is not 60°. Ball-shaped micrometer anvils can be used in similar fashion (same trigonometric relationship, less cumbersome to use). Digital calipers and micrometers can send each measurement (data point) as it occurs to storage or software through an interface (such as USB or RS-232), in which case the table lookup is done in an automated way, and quality assurance and quality control can be achieved using statistical process control.
History.
Each method of thread generation has its own detailed history. Therefore, a comprehensive discussion is beyond the scope of this article; but much historical information is available in related articles, including:
Cold-rolling.
The first patent for the cold rolling of screw threads was issued in 1836 to William Keane of Monroe, N.Y. However, the dies for rolling the threads onto the screw blanks were made of cast iron, which is brittle, so the machine was not successful.
The process languished until 1867, when Harvey J. Harwood of Utica, New York filed a patent for the cold-rolling of threads on wood screws. Further efforts to cold-roll threads on screws followed, but none seemed to meet with much success until Hayward Augustus Harvey (1824-1893) of Orange, N.J. filed his patents of 1880 and 1881. Charles D. Rogers of the American Screw Co. of Providence, Rhode Island made further refinements to the process of rolling threads onto screws.


Burr (cutter)

Burrs or burs (sometimes called rotary files) are small cutting tools; not to be confused with small pieces of metal formed from cutting metal, used in die grinders, rotary tools, or dental drills. The name may be considered appropriate when their small-sized head (3 mm diameter shaft) is compared to a bur (fruit seed with hooks) or their teeth are compared to a metal burr.
Description.
Burrs are a rotary analog to files that cut linearly (hence their alternate name, rotary files). They are also in many ways comparable to endmills and router bits; a distinction is that the latter usually have their toolpath controlled by the machine, whereas burrs are often used freehand. However, there is substantial overlap in the use and toolpath control of these various classes of cutters, and e outcomes accomplished with them. For example, endmills can be used in routers, and burrs can be used like endmills in milling by CNC or manual machine tools. These are often used in CNC machining centers for removing burrs (the small flakes of metal) after a machining process.
Burrs are spun quickly to maintain the ideal surface speed and cutting conditions (thousands or tens of thousands of RPM; often the top speed available on a given spindle). Because they are constructed of tungsten carbide, the cutters in the image can operate at higher speeds than comparable "HSS" cutters while still maintaining their cutting edges.
Because the cutting edges of burrs are so small, they can often be touched when spinning by a finger without cutting the skin, which flexes out of the way, although it would not be safe to pinch or grip them from two sides. Hard metal or ceramic workpieces cannot flex beyond the cutting edges, so the tools remove material from them. This characteristic makes burrs suitable for use in dentistry, as the tool will grind the hard enamel of teeth, yet leaves soft mouth tissues unharmed if the tool should unintentionally touch them.


Embedded wafer level ball grid array

Embedded wafer level ball grid array (eWLB) is a packaging technology for integrated circuits. The package interconnects are applied on an artificial wafer made of silicon chips and a casting compound.
eWLB is a further development of the classical wafer level ball grid array technology (WLB or WLP: wafer level package). The main driving force behind the eWLB technology was to allow fanout and more space for interconnect routing.
All process steps for the generation of the package are performed on the wafer. This allows, in comparison to classical packaging technologies (e. g. ball grid array), the generation of very small and flat packages with excellent electrical and thermal performance at lowest cost. It is common for all WLB technologies, which are built on a silicon wafer, that the interconnects (typically solder balls) fit on the chip (so called fan-in design). Therefore only chips with a restricted number of interconnects can be packaged.
The eWLB technology allows the realization of chips with a high number of interconnects. The package is not created on a silicon wafer as for the classical wafer level package, but on an artificial wafer. Therefore a front-end-processed wafer is diced and the singulated chips are placed on a carrier. The distance between the chips can be chosen freely, but it is typically larger than on the silicon wafer. The gaps and the edges around the chips are now filled with a casting compound to form a wafer. After curing an artificial wafer containing a mold frame around the dies for carrying additional interconnect elements is created. After the build of the artificial wafer (the so-called "reconstitution") the electrical connections from the chip pads to the interconnects are made in thin-film technology, as for any other classical wafer level package.
With this technology any number of additional interconnects can be realized on the package in an arbitrary distance (fan-out design). Therefore, this wafer level packaging technology can also be used for space sensitive applications, where the chip area wouldn’t be sufficient to place the required number of interconnects at a suitable distance. The eWLB technology was developed by Infineon, STMicroelectronics and STATS ChipPAC Ltd. First components were brought into market mid of 2009 (mobile phone).


STEP-NC

STEP-NC is a machine tool control language that extends the ISO 10303 STEP standards with the machining model in ISO 14649, adding geometric dimension and tolerance data for inspection, and the STEP PDM model for integration into the wider enterprise. The combined result has been standardized as ISO 10303-238 (also known as AP238).
STEP-NC was designed to replace ISO 6983/RS274D G-codes with a modern, associative communications protocol that connects computer numerical controlled (CNC) process data to a product description of the part being machined.
A STEP-NC program can use the full range of geometric constructs from the STEP standard to communicate device-independent toolpaths to the CNC. It can provide CAM operational descriptions and STEP CAD geometry to the CNC so workpieces, stock, fixtures and cutting tool shapes can be visualized and analyzed in the context of the toolpaths. STEP GD&T information can also be added to enable quality measurement on the control, and CAM-independent volume removal features may be added to facilitate regeneration and modification of the toolpaths before or during machining for closed loop manufacturing.
Motivation.
Input to a CNC in the ISO 6983/RS274D G-code control language is often machine-specific and limited to axis motion commands. The machine tool is given little or no information about the desired result of the machining.
STEP-NC allows more information about the machining process to be sent to the machine control and adds new information about the product being machined. This "Smart Data for Smart Machining" enables applications such as the following:
Capabilities.
STEP-NC can communicate a complete machining process description to a machine tool control or between manufacturing software applications. The information handled by STEP-NC can be divided into the following general categories. The standard handles technology-specific parameters for milling and turning, and extensions for other technologies under development (see Future work).
STEP-NC can exchange the explicit toolpath descriptions in use today, and add part, stock, and fixture geometry, a description of the tools, geometric dimensions and tolerances, and PDM information. A STEP-NC file is difficult to edit by hand because it contains geometry descriptions but for large programs the file size can be smaller because STEP-NC uses a compressed XML format instead of ASCII codes.
History.
STEP-NC is not the first attempt at providing better quality information to a CNC. The EIA 494 Basic Control Language (BCL) defined a control language that was portable and had toolpaths independent of machine geometry, but did not contain any of the other product model information found in STEP-NC.
The core of STEP-NC is the ISO 14649 model for CNC control developed
by European ESPRIT and IMS STEP-NC projects begun in 1999. These were led by Siemens with contributions from RWTH Aachen University and the University of Stuttgart in Germany, Komatsu and FANUC in Japan, Heidenhain in Switzerland, and the Pohang University of Science and Technology in Korea. Models for the control of CNC milling and turning machines were published in 2005, and draft models exist for EDM and contour cutting.
Integration of the CNC model into STEP to produce ISO 10303-238 was done in the United States, under the NIST ATP Model Driven Intelligent Control of Manufacturing project, led by STEP Tools, Inc. with an industrial review board (IRB) consisting of Fortune 500 companies, CAD and CAM software developers, machine tool manufacturers, job shops and industry experts. STEP-NC AP238 was published in 2007.
In 2005 the OMAC STEP-NC Working Group hosted an AP238 testing forum in Orlando to demonstrate 5-axis parts machined using AP238 CC1 machine independent toolpaths. Four CAD/CAM systems produced AP238 machining programs for milling a 5-axis test part (an NAS 979 circle/diamond/square with an inverted NAS 979 cone test in the center). Each run on a pair of CNCs configured for completely different machine geometries (AB tool tilt vs. BC table tilt). In addition, Boeing cut parts on a variety of machines at their Tulsa facility and a machine at NIST in Gaithersburg.
In June 2006, a live 5-axis STEP-NC machining demonstration was hosted by Airbus at the Université Paul Sabatier Laboratoire de Génie mécanique in Toulouse. Further machining and measurement demonstrations were conducted in Ibusuki Japan in 2007.
On March 10–12, 2008, the STEP Manufacturing team (ISO TC184 SC4 WG3 T24) met in Sandviken and Stockholm, Sweden to demonstrate use of STEP-NC for feed and speed optimization, high-speed machining, tolerance-driven tool compensation and traceability. The participants in the demonstrations included Airbus/Univ. Bordeaux, Boeing, Eurostep, KTH Royal Institute of Technology, NIST, Sandvik Coromant, Scania, STEP Tools, and Univ. of Vigo.
On October 1–2, 2008, the STEP Manufacturing team met at the Connecticut Center for Advanced Technology, in Hartford, Connecticut to demonstrate closed-loop machining, feed optimization, and measurement using STEP-NC. The highlight of the meeting was the live 5-axis machining of a titanium impeller. Participants in the machining demonstration and other activities included Boeing, Connecticut Center for Advanced Technology, Concepts NRec, DMG, KTH Royal Institute of Technology, Mitutoyo, NIST, Sandvik Coromant, Scania, Siemens, and STEP Tools.
These participants and others continue to hold STEP-NC international implementation and testing events on a roughly six-month cycle. The demonstrations in 2009 focused on machining a Mold part at multiple sites from the same AP238 data including one part machined on a FANUC-developed STEP-NC control. At a meeting in Seattle the parts were then measured for accuracy using a CMM probe and a laser scanner.
In the first half of 2010, the testing activity focused on tool wear management and machining a part in multiple setups with multiple alternate machining plans for 3, 4 and 5-axis machining. The new test part was a gear box that must be machined on all six sides. The tool wear and consequent machine loads were predicted from the STEP-NC data and verified using a dynamometer. In the second half of 2010, the testing forum applied STEP-NC to set up compensation with on-machine measurement of part and fixture datums using a FaroArm portable measurement device.
In 2012, the testing focused on machine tool accuracy calculations, culminating in a demonstration in June at the KTH production engineering labs in Stockholm. The test case milled a forged blank for a Crown Wheel Gear on an older Mazak VQC 20. Accuracy data from the machine was combined with tool engagement information from the STEP-NC to predict the deflections, which were tested against actual machining results.
In 2014, CAM data exchange using STEP-NC was shown at IMTS 2014 with daily machining demonstrations hosted by Okuma. A base machining process for a mold part was created by Boeing and then sent to Sandvik and ISCAR for optimization, producing a STEP-NC description containing all three process options. All machining was done in titanium and a range of CAM software was used, with all results captured as STEP-NC.
At IMTS 2018, a team consisting of Airbus, Boeing, DMG MORI, Hyundai WIA, Renishaw, and Mitutoyo demonstrated Digital Twin manufacturing by combining STEP-NC model and process data with MTConnect machine tool status and Quality Information Format (QIF) metrology results.
A second edition of AP238 was published in 2020, followed by a third edition in 2022 for model-based integrated manufacturing, with geometry, tolerance, and kinematics improvements first introduced by AP242.
Future work.
Work continues within the ISO standard committees to extend STEP-NC to new technologies and to incorporate refinements discovered during use. Process models for new technologies are usually produced by the ISO TC184/SC1/WG7 committee. Models for Wire & Sink EDM and contour cutting of wood or stone are under investigation.
Work on extending and integrating STEP-NC with the manufacturing enterprise takes place in the ISO TC184/SC4/WG3/T24 STEP Manufacturing Team. This group also works on extensions and refinements discovered during testing. A series of traceability extensions have been proposed for linking STEP-NC machining programs with sensor feedback and machine state information during execution.
The National Shipbuilding Research Program (NSRP) has also hosted work to implement a prototype that connects a shipyard design system to a plate cutting using STEP-NC. This work involved extending STEP-NC to steel plate cutting and marking using lasers and plasma torches.


Superplastic forming

Superplastic forming is an industrial process used for creating precise and complex components out of superplastic materials.
Process.
The material is first heated up to promote superplasticity. For titanium alloys e.g. Ti 6Al 4V and some stainless steels this is around and for aluminium alloys e.g. AA5083 it is between 450 and 520 °C. In this state the material becomes soft so processes that are usually used on plastics can be applied, such as: thermoforming, blow forming, and vacuum forming. Inert gas pressure is applied on the superplastic sheet forcing it into a female die.
Advantages and disadvantages.
The major advantage of this process is that it can form large and complex workpieces in one operation. The finished product has excellent precision and a fine surface finish. It also does not suffer from springback or residual stresses. Products can also be made larger to eliminate assemblies or reduce weight, which is critical in aerospace applications. Lower strength required and less tooling costs. McDonnell Douglas utilized SPF design and production technology into the F-15 in the 1980s, while in Europe an example of application can be found in some Eurofighter Typhoon assemblies (e.g. engine bays panels, foreplanes, slats).
The largest disadvantage of the process is its slow forming rate. Cycle times vary from two minutes to two hours, therefore it is usually used in low volume production applications. Another disadvantage is the non-uniformity of the produced part thickness. Several methods are used to improve the thickness uniformity of SPF parts. One is to apply a designed varying gas pressure profile instead of a constant pressure. Another approach is to tailor the contact friction between the die surface and the superplastic sheet.


Edwin Ruud

Edwin Ruud (9 June 1854 – 9 December 1932) was a Norwegian-American mechanical engineer and inventor who immigrated to the United States where he designed, sold, and popularized the tankless water heater. He was the founder and President of Ruud Manufacturing Company, now a division of Rheem Manufacturing Company.
Biography.
Early life.
Edwin Ruud was born in the parish of Askim in Østfold, Norway. He was educated in engineering at the Horten Technical School ("Horten tekniske skole") in Vestfold, Norway.
The Fuel Gas And Manufacturing Company.
In the 1880s, Ruud began working for George Westinghouse at the Fuel Gas and Manufacturing Company in Pittsburgh, Pennsylvania. Eight years after filing his first US patent, Ruud filed the first of five patents he would assign to Westinghouse's Fuel Gas and Manufacturing company.
In 1889, Ruud engineered a design for an automatic storage tank-type gas water heater that used a bottom gas heater and temperature controlled gas-valve. He later patented the design in 1890. In October 1890, he expanded on his first water heater design, under the Fuel Gas and Manufacturing Company.
Ruud Manufacturing Company.
On January 22, 1897, Ruud filed a patent separate from the Fuel Gas and Manufacturing Company for an Automatic Water Heater. His new design consisted of a cast iron shell, enclosing burners, heating surfaces (a coil of copper tubing through which water flows), and thermostat controlling gas-valves. The object of the design improvement was, "to maintain the supply of water at the desired temperature at all times."
With this new design, Ruud left the Fuel Gas and Manufacturing Company to start Ruud Manufacturing, his own engineering and manufacturing shop where he began to manufacture and popularize in home, as well as commercial and industrial water heaters.
Ruud was issued his patent for the coiled tube Automatic Water Heater on September 6, 1898.
Ruud's business expanded as he popularized and improved on his instant water heater design. In 1908, Ruud Manufacturing acquired two local heating and plumbing firms. James Hay of the James Hay Company, heating and plumbing engineers, closed his business in order to operate as president of the Ruud Manufacturing Company in 1908. and J.H. Folsom of Folsom-Webster Co., heating and plumbing contracting firm, dissolved his partnership in Folsom-Webster Company in 1908 to serve as chief of the Cincinnati branch of the Ruud Manufacturing Company. By 1915, the Ruud Manufacturing Company had offices in Pittsburgh, Pennsylvania; Kalamazoo, Michigan; Toronto, Canada; and Hamburg, Germany.
The Ruud Instantaneous Automatic Water Heater.
The Thermal Valve Model, Type F, of the Ruud Instantaneous Automatic Water Heater is a design that allows the user to instantaneously heat water for on demand applications while not heating, thus saving fuel, when not in use. The Type F was able to use LP gas, natural gas, and gasoline, requiring only a change of burner spud orifices, and was manufactured in two variations, the "Standard Pressure Heaters," designed to operate in conditions where pressure was at least twenty-five pounds per square inch (1.7 bar), and "Low Pressure Heaters," where operational water pressure could be as low as four pounds per square inch (0.3 bar). Thermal Valve Model, Type F heaters were manufactured in four residential sizes reflective of their output in gallons per minute: 3, 4, 6, 8.
In 1915, there were approximately one-hundred-thousand of the Type F installed throughout The United States and Canada.
Ruud Heating and Air Conditioning Equipment.
Edwin Ruud died in 1932 and his widow, Minna Kaufmann Ruud died in 1953. In 1959, the water heater arm of the Ruud Manufacturing Company was purchased by Rheem Manufacturing Company and continued operation as a division of Rheem.


Spot welding

Spot welding (or resistance spot welding) is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current.
The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the thickness range. Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is that a large amount of energy can be delivered to the spot in a very short time (approximately 10–100 milliseconds). This permits the welding to occur without excessive heating of the remainder of the sheet.
The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current. The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes. Applying too little energy will not melt the metal or will make a poor weld. Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld. Another feature of spot welding is that the energy delivered to the spot can be controlled to produce reliable welds.
Process and equipment.
Spot welding involves three stages; the first of which involves the electrodes being brought to the surface of the metal and applying a slight amount of pressure. The current from the electrodes is then applied briefly after which the current is removed but the electrodes remain in place for the material to cool. Weld times range from 0.01 sec to 0.63 sec depending on the thickness of the metal, the electrode force and the diameter of the electrodes themselves.
The equipment used in the spot welding process consists of tool holders and electrodes. The tool holders function as a mechanism to hold the electrodes firmly in place and also support optional water hoses that cool the electrodes during welding. Tool holding methods include a paddle-type, light duty, universal, and regular offset. The electrodes generally are made of a low resistance alloy, usually copper, and are designed in many different shapes and sizes depending on the application needed.
The two materials being welded together are known as the workpieces and must conduct electricity. The width of the workpieces is limited by the throat length of the welding apparatus and ranges typically from . Workpiece thickness can range from .
After the current is removed from the workpiece, it is cooled via the coolant holes in the center of the electrodes. Both water and a brine solution may be used as coolants in spot welding mechanisms.
In the case of resistance spot welding, there are two main parts of the tooling system, the features of which fundamentally influence the whole process: the gun and its type, and the size and shape of the electrode. In such application, where the gun layout should be as rigid as possible due to the high applying forces (e.g. welding of thick materials), the C-type gun is widely used. As well as the high resulting rigidity, this arrangement leads to a high tooling flexibility, as the motion of the electrodes is collinear. Unlike the C-type, the so-called X-type arrangement provides less rigidity, although the reachable workspace is far larger than with the C-type, thus this layout is very common, where thin and flat objects are being processed (e.g. manufacturing of floor pan or roof panel). However, it offers less flexibility in terms of tooling, because the paths of the moving electrodes are not collinear (like the tips of a scissor), so a dome-shaped electrode tip should be used.
Electrodes used in spot welding can vary greatly with different applications. Each tool style has a different purpose. Radius style electrodes are used for high heat applications, electrodes with a truncated tip for high pressure, eccentric electrodes for welding corners, offset eccentric tips for reaching into corners and small spaces, and finally offset truncated for reaching into the workpiece itself.
Characteristics.
The spot welding process tends to harden the material, causing it to warp. This reduces the material's fatigue strength, and may stretch the material as well as anneal it. The physical effects of spot welding include internal cracking, surface cracks and a bad appearance. The crack around the weld nugget will be extended under an external load or fatigue to produce a different type of failure. The chemical properties affected include the metal's internal resistance and its corrosive properties.
Welding times are often very short, which can cause problems with the electrodes—they cannot move fast enough to keep the material clamped. Welding controllers will use a double pulse to get around this problem. During the first pulse, the electrode contact may not be able to make a good weld. The first pulse will soften the metal. During the pause between the two pulses, the electrodes will come closer and make better contact.
During spot welding, the large electric current induces a large magnetic field, and the electric current and magnetic field interact with each other to produce a large magnetic force field too, which drives the melted metal to move very fast at a velocity up to 0.5 m/s. As such, the heat energy distribution in spot welding could be dramatically changed by the fast motion of the melted metal. The fast motion in spot welding can be observed with high-speed photography.
The basic spot welder consists of a power supply, an energy storage unit (e.g., a capacitor bank), a switch, a welding transformer, and the welding electrodes. The energy storage element allows the welder to deliver high instantaneous power levels. If the power demands are not high, then the energy storage element isn't needed. The switch causes the stored energy to be dumped into the welding transformer. The welding transformer steps down the voltage and steps up the current. An important feature of the transformer is it reduces the current level that the switch must handle. The welding electrodes are part of the transformer's secondary circuit. There is also a control box that manages the switch and may monitor the welding electrode voltage or current.
The resistance presented to the welder is complicated. There is the resistance of secondary winding, the cables, and the welding electrodes. There is also the contact resistance between the welding electrodes and the workpiece. There is the resistance of the workpieces, and the contact resistance between the workpieces.
At the beginning of the weld, the contact resistances are usually high, so most of the initial energy will be dissipated there. That heat and the clamping force will soften and smooth out the material at the electrode-material interface and make better contact (that is, lower the contact resistance). Consequently, more electrical energy will go into the workpiece and the junction resistance of the two workpieces. As electrical energy is delivered to the weld and causes the temperature to rise, the electrodes and the workpiece are conducting that heat away. The goal is to apply enough energy so that a portion of material within the spot melts without having the entire spot melt. The perimeter of the spot will conduct away much heat and keep the perimeter at a lower temperature. The interior of the spot has less heat conducted away, so it melts first. If the welding current is applied too long, the entire spot melts, the material runs out or otherwise fails, and the "weld" becomes a hole.
The voltage needed for welding depends on the resistance of the material to be welded, the sheet thickness and desired size of the nugget. When welding a common combination like 1.0 + 1.0 mm sheet steel, the voltage between the electrodes is only about 1.5 V at the start of the weld but can fall as low as 1 V at the end of the weld. This decrease in voltage results from the reduction in resistance caused by the workpiece melting. The open circuit voltage from the transformer is higher than this, typically in the 5 to 22 volt range.
The resistance of the weld spot changes as it flows and liquefies. Modern welding equipment can monitor and adjust the weld in real time to ensure a consistent weld. The equipment may seek to control different variables during the weld, such as current, voltage, power, or energy.
Welder sizes range from 5 to 500 kVA. Micro spot welders, used in a variety of industries, can go down to 1.5 kVA or less for precision welding needs.
It is common for a spray of molten metal droplets (sparks) to be ejected from the area of the weld during the process.
Resistance spot welding generates no bright arc, so UV protection is not required. OSHA requires transparent face shields or goggles for splatter protection, but does not require any filter lens.
Applications.
Spot welding is typically used when welding particular types of sheet metal, welded wire mesh or wire mesh. Thicker stock is more difficult to spot weld because the heat flows into the surrounding metal more easily. Spot welding can be easily identified on many sheet metal goods, such as metal buckets. Aluminium alloys can be spot welded, but their much higher thermal conductivity and electrical conductivity requires higher welding currents. This requires larger, more powerful, and more expensive welding transformers.
Perhaps the most common application of spot welding is in the automobile manufacturing industry, where it is used almost universally to weld the sheet metal to form a car. Spot welders can also be completely automated, and many of the industrial robots found on assembly lines are spot welders (the other major use for robots being painting).
Spot welding is also used in the orthodontist's clinic, where small-scale spot welding equipment is used when resizing metal "molar bands" used in orthodontics.
Another application is spot welding straps to nickel–cadmium, nickel–metal hydride or Lithium-ion battery cells to make batteries. The cells are joined by spot welding thin nickel straps to the battery terminals. Spot welding can keep the battery from getting too hot, as might happen if conventional soldering were done.
Good design practice must always allow for adequate accessibility. Connecting surfaces should be free of contaminants such as scale, oil, and dirt, to ensure quality welds. Metal thickness is generally not a factor in determining good welds.
Modifications.
"Projection welding" is a modification of spot welding in which the weld is localized by means of raised sections, or projections, on one or both of the workpieces to be joined. Heat is concentrated at the projections, which permits the welding of heavier sections or the closer spacing of welds. The projections can also serve as a means of positioning the workpieces. Projection welding is often used to weld studs, nuts, and other threaded machine parts to metal plate. It is also frequently used to join crossed wires and bars. This is another high-production process, and multiple projection welds can be arranged by suitable designing and jigging.


Wire bonding

Wire bonding is the method of making interconnections between an integrated circuit (IC) or other semiconductor device and its packaging during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one printed circuit board (PCB) to another. Wire bonding is generally considered the most cost-effective and flexible interconnect technology and is used to assemble the vast majority of semiconductor packages. Wire bonding can be used at frequencies above 100 GHz.
Materials.
Bondwires usually consist of one of the following materials:
Wire diameters start from under 10 μm and can be up to several hundred micrometres for high-powered applications.
The wire bonding industry is transitioning from gold to copper. This change has been instigated by the rising cost of gold and the comparatively stable, and much lower, cost of copper. While possessing higher thermal and electrical conductivity than gold, copper had previously been seen as less reliable due to its hardness and susceptibility to corrosion. By 2015, it is expected that more than a third of all wire bonding machines in use will be set up for copper.
Copper wire has become one of the preferred materials for wire bonding interconnects in many semiconductor and microelectronic applications. Copper is used for fine wire ball bonding in sizes from up to . Copper wire has the ability of being used at smaller diameters providing the same performance as gold without the high material cost.
Copper wire up to can be successfully wedge bonded. Large diameter copper wire can and does replace aluminium wire where high current carrying capacity is needed or where there are problems with complex geometry. Annealing and process steps used by manufacturers enhance the ability to use large diameter copper wire to wedge bond to silicon without damage occurring to the die.
Copper wire does pose some challenges in that it is harder than both gold and aluminium, so bonding parameters must be kept under tight control. The formation of oxides is inherent with this material, so storage and shelf life are issues that must be considered. Special packaging is required in order to protect copper wire and achieve a longer shelf life. Palladium coated copper wire is a common alternative which has shown significant resistance to corrosion, albeit at a higher hardness than pure copper and a greater price, though still less than gold. During the fabrication of wire bonds, copper wire, as well as its plated varieties, must be worked in the presence of forming gas [95% nitrogen and 5% hydrogen] or a similar anoxic gas in order to prevent corrosion. A method for coping with copper's relative hardness is the use of high purity [5N+] varieties.
Long-term corrosion effects (Cu2Si) and other stability topics led to increased quality requirements when used in automotive applications
Pure gold wire doped with controlled amounts of beryllium and other elements is normally used for ball bonding. This process brings together the two materials that are to be bonded using heat, pressure and ultrasonic energy referred to as thermosonic bonding. The most common approach in thermosonic bonding is to ball-bond to the chip, then stitch-bond to the substrate. Very tight controls during processing enhance looping characteristics and eliminate sagging.
Junction size, bond strength and conductivity requirements typically determine the most suitable wire size for a specific wire bonding application. Typical manufacturers make gold wire in diameters from and larger. Production tolerance on gold wire diameter is +/-3%.
Alloyed aluminium wires are generally preferred to pure aluminium wire except in high-current devices because of greater drawing ease to fine sizes and higher pull-test strengths in finished devices. Pure aluminium and 0.5% magnesium-aluminium are most commonly used in sizes larger than .
All-aluminium systems in semiconductor fabrication eliminate the "purple plague" (brittle gold-aluminium intermetallic compound) sometimes associated with pure gold bonding wire. Aluminuim is particularly suitable for thermosonic bonding.
In order to assure that high quality bonds can be obtained at high production speeds, special controls are used in the manufacture of 1% silicon-aluminium wire. One of the most important characteristics of high grade bonding wire of this type is homogeneity of the alloy system. Homogeneity is given special attention during the manufacturing process. Microscopic checks of the alloy structure of finished lots of 1% silicon-aluminium wire are performed routinely. Processing also is carried out under conditions which yield the ultimate in surface cleanliness and smooth finish and permits entirely snag-free de-reeling.
Attachment techniques.
The main classes of wire bonding:
Ball bonding usually is restricted to gold and copper wire and usually requires heat. For wedge bonding, only gold wire requires heat. Wedge bonding can use large diameter wires or wire ribbons for power electronics application. Ball bonding is limited to small diameter wires, suitable for interconnect application.
In either type of wire bonding, the wire is attached at both ends using a combination of downward pressure, ultrasonic energy, and in some cases heat, to make a weld. Heat is used to make the metal softer. The correct combination of temperature and ultrasonic energy is used in order to maximize the reliability and strength of a wire bond. If heat and ultrasonic energy is used, the process is called thermosonic bonding.
In wedge bonding, the wire must be drawn in a straight line according to the first bond. This slows down the process due to time needed for tool alignment. Ball bonding, however, creates its first bond in a ball shape with the wire sticking out at the top, having no directional preference. Thus, the wire can be drawn in any direction, making it a faster process.
Compliant bonding transmits heat and pressure through a compliant or indentable aluminium tape and therefore is applicable in bonding gold wires and the beam leads that have been electroformed to the silicon integrated circuit (known as the beam leaded integrated circuit).
Manufacturing and reliability challenges.
There are multiple challenges when it comes to wire bond manufacturing and reliability. These challenges tend of be a function of several parameters such as the material systems, bonding parameters, and use environment. Different wire bond-bond pad metal systems such as Aluminium-Aluminium (Al-Al), Gold-Aluminium (Au-Al), and Copper-Aluminium (Cu-Al) require different manufacturing parameters and behave differently under the same use environments.
Wire bond manufacturing.
Much work has been done to characterize various metal systems, review critical manufacturing parameters, and identify typical reliability issues that occur in wire bonding. When it comes to material selection, the application and use environment will dictate the metal system. Often the electrical properties, mechanical properties, and cost are taken into account when making a decision. For example, a high current device for a space application might require a large diameter aluminium wire bond in a hermetically sealed ceramic package. If cost is a large constraint, then avoiding gold wire bonds may be a necessity. Some recent work has been done to look at copper wire bonds in automotive applications. This is only a small sampling, as there is a vast body of work reviewing and testing what material systems work best in different applications.
From a manufacturing perspective, the bonding parameters play a critical role in bond formation and bond quality. Parameters such bond force, ultrasonic energy, temperature, and loop geometry, to name a few, can have a significant effect on bond quality. There are various wire bonding techniques (thermosonic bonding, ultrasonic bonding, thermocompression bonding) and types of wire bonds (ball bonding, wedge bonding) that affect susceptibility to manufacturing defects and reliability issues. Certain materials and wire diameters are more practical for fine pitch or complex layouts. The bond pad also plays an important role as the metallization and barrier layer(s) stackup will impact the bond formation.
Typical failure modes that result from poor bond quality and manufacturing defects include: fracture at the ball bond neck, heel cracking (wedge bonds), pad liftoff, pad peel, overcompression, and improper intermetallic formation. A combination of wire bond pull/shear testing, nondestructive testing, and destructive physical analysis (DPA) can be used to screen manufacturing and quality issues.
Wire bond reliability.
While wirebond manufacturing tends to focus on bond quality, it often does not account for wearout mechanisms related to wire bond reliability. In this case, an understanding of the application and use environment can help prevent reliability issues. Common examples of environments that lead to wire bond failures include elevated temperature, humidity, and temperature cycling.
Under elevated temperatures, excessive intermetallics (IMC) growth can create brittle points of fracture. Much work that has been done to characterize the intermetallic formation and aging for various metal systems. This not a problem in metal systems where the wire bond and bond pad are the same material such as Al-Al. This does become a concern in dissimilar metal systems. One of the most well known examples is the brittle intermetallics formed in gold-aluminium IMCs such as purple plague. Additionally, diffusion related issues, such as Kirkendall voiding and Horsting voiding, can also lead to wire bond failures.
Under elevated temperature and humidity environments, corrosion can be a concern. This is most common in Au-Al metal systems and is driven by galvanic corrosion. The presence of halides such as chlorine can accelerate this behavior. This Au-Al corrosion is often characterized with Peck's law for temperature and humidity. This is not as common in other metal systems.
Under temperature cycling, thermomechanical stress is generated in the wire bond as a result of coefficient of thermal expansion (CTE) mismatch between the epoxy molding compound (EMC), the leadframe, the die, the die adhesive, and the wire bond. This leads to low cycle fatigue due to shear or tensile stresses in the wire bond. Various fatigue models have been used to predict the fatigue life of wire bonds under such conditions.
Proper understanding of the use environment and metal systems are often the most important factors for increasing wire bond reliability.
Testing.
While there are some wire bond pull and shear testing techniques, these tend to be applicable for manufacturing quality rather than reliability. They are often monotonic overstress techniques, where peak force and fracture location are the critical outputs. In this case the damage is plasticity dominated, and does not reflect some wearout mechanisms that might be seen under environmental conditions.
Wire pull testing applies an upward force under the wire, effectively pulling it away from the substrate or die. The purpose of the test is as MIL-STD-883 2011.9 describes it: "To measure bond strengths, evaluate bond strength distributions, or determine compliance with specified bond strength requirements". A wire can be pulled to destruction, but there are also non-destructive variants whereby one tests whether the wire can withstand a certain force. Non-destructive test methods are typically used for 100% testing of safety critical, high quality and high cost products, avoiding damage to the acceptable wired bonds tested.
The term wire pull usually refers to the act of pulling a wire with a hook mounted on a pull sensor on a bond tester. However, to promote certain failure modes, wires can be cut and then pulled by tweezers, also mounted on a pull sensor on a bond tester. Usually wires up to 75 μm diameter (3 mil) are classified as thin wire. Beyond that size, we speak about thick wire testing.


Helmz

Helmz (stylized as HELMS) is a sports bicycle from Bridgestone Cycle Co., Ltd. jointly developed with fashion brand narifuri.
Overview.
Bridgestone Cycle's 60th anniversary model was developed as "bicycle to be a part of fashion" with narifuri taking charge in frame design and concept establishment. It is made with an "approach to create focus on design ". The model was announced in 2009 and was sold starting in 2010.
The name HELMZ was taken from the English term "helm."
Custom-designed original parts were made for HELMZ, by Japanese cycle part brands such as NITTO, MKS Pedal, and Sugino. Japanese oriented brand parts were selected carefully to minimize the use of Shimano parts.
These original parts of HELMZ are sold as aftermarket cycle products. The entire sales plan, including the package design of selling boxes and POP, was awarded the Minister of Economy Award and Planning Award in 42nd JPM Creative Design Show in 2012. SR1 received Good Design award in 2014.
Technical features.
Air pressure formed aluminum frame.
The frame was based on a Top tube, sloped, low-front design from narifuri and was manufactured using superplastic forming) which molds the frame by inflating high air pressure in the 7005 aluminum pipe. Bridgestone cycle usually used this manufacturing method to improve riding performance, but in HELMZ it was necessary to realize the design.
Wheels.
The texture and rim height differ in front and rear wheels. The front wheel is silver with 35mm rim height. The rear wheel is black with 38 mm rim height. Models with high-performance sports wheels were launched afterward.
Thumb shifter.
For models with gear shifts, the Thumb shifter was selected. This shifter is operated with the thumb unlike the typical modern sports bicycle push bar mechanical shift.
Original aftermarket parts.
Hlmz original aftermarket parts were released on 2012. Stem, handle bar, saddle, wheels, gear cranks, and most other original parts were sold on market as aftermarket parts.
Belt drive.
The belt drive equipped models, SR1 and S10, were introduced in 2013. These models were an update of Bridegestone's belt drive experience from 1980, "SSSD" (Selectable SS Solld Drive). The new belt drives were made out of carbon instead of kevlar making the belts lighter and more flexible.
Models.
Frame shape and concepts have not been changed since its first announcement except for the new sizes being set.
Collaboration.
Star Wars.
Collaborating with Star Wars, Helmz released two 5 year anniversary models in different colors. The Galactic Empire model is black based with blue, while the Rebel Alliance model is Silver based with red. The bikes were hand painted at the Bridgestone Cycle headquarter factory.
Awards.
2013 Planning: JPM Minister of Economy Award in 42nd JPM Creative Design Show for Year 2012
2014 SR1: Good Design award 2014
2016 SR1: selected as "JAPANESE DESIGN TODAY 100" in Singapore


Pulau Indah Industrial Park

Pulau Indah Industrial Park (PIIP) located in Klang District, Selangor, Malaysia is 3,500 acres industrial area which are occupied by business like manufacturing, logistics and warehousing.


Punching machine

A punching machine is a machine tool for punching and embossing flat sheet-materials to produce form-features needed as mechanical element and/or to extend static stability of a sheet section.
CNC punching.
Punch presses are developed for high flexibility and efficient processing of metal stampings. The main areas of application are for small and medium runs. Those machines are typically equipped with a linear die carrier (tool carrier) and quick change tools. Today the method is used where the application of lasers are inefficient or technically impractical. CNC is the abbreviation of Computer Numerically Controlled.
Principle of operation.
After programming the work pieces and entering length of bars the control automatically calculates the maximum number of pieces to be punched (for example, 18 pieces of a bar of 6000 mm). Once the desired number of work pieces is entered, the bar is pushed toward the stop. The machine is fully automated once the production process is launched.
The third CNC axis always moves the cylinder exactly over the tool, which keeps the wear on the bearings and tools to a minimum. All pieces are sent down a slat conveyor and are pushed sideways on a table. Any scrap is carried to the end of the conveyor and dropped into a bin. Different workpieces can be produced within one work cycle to optimize production.
Programming.
Programming is done on a PC equipped with appropriate software that can be part of the machine or a connected external workstation. For generating a new program engineering data can be imported or pasted per mouse and keyboard. Through a graphic and menu-driven user interface previous CNC programming skills are not required. All the punches in a work piece are shown on the screen making programming mistakes easily detected. Ideally each program is stored in one database, so it is easy to recover them by search and sort functions. When selecting a new piece, all the necessary tooling changes are displayed. Before transferring it to the control unit the software scans each program for possible collisions. This eliminates most handling errors.
Tool change system.
The linear tool carrier (y-axis) has several stations that hold the punching tools and one cutting tool. Especially for flexibility and efficient processing are set up times a crucial cost factor. Downtimes should be reduced to a minimum. Therefore, recent tool systems are designed for fast and convenient change of punches and dies. They are equipped with a special plug-in system for a quick and easy change of tools.
There is no need to screw anything together. The punch and die plate are adjusted to each other automatically Punches and dies can be changed rapidly meaning less machine downtime.
Networking with the whole production line.
A lot of organizational effort and interface management is saved, if the CNC punch press is connected to the previous and subsequent process. For a connection to other machines and external workstations corporate interfaces have to be established.
Integration of further production steps.
Besides punching, machines of the high end class can be equipped with special functions. For example:


Stencil printing

Stencil printing is the process of depositing solder paste on the printed wiring boards (PWBs) to establish electrical connections. It is immediately followed by the component placement stage. The equipment and materials used in this stage are a stencil, solder paste, and a printer.
The stencil printing function is achieved through a single material namely solder paste which consists of solder metal and flux. Paste also acts as an adhesive during component placement and solder reflow. The tackiness of the paste enables the components to stay in place. A good solder joint is one where the solder paste has melted well and flowed and wetted the lead or termination on the component and the pad on the board.
In order to achieve this kind of a solder joint, the component needs to be in the right place, the right volume of solder paste needs to be applied, the paste needs to wet well on the board and component, and there needs to be a residue that is either safe to leave on the board or one that can easily be cleaned.
The solder volume is a function of the stencil, the printing process and equipment, solder powder, and rheology or the physical properties of the paste. Good solder wetting is a function of the flux.
Inputs.
Inputs to the process can be classified as design input, material input and process parameter input. The output of the process is a printed wiring board that meets the process specification limits. These specifications usually are consistent solder paste volume and height, and printed solder paste aligned on the PWB pads. This determines the process yield.
In electronic design automation, the solder paste mask and thus the stencil is typically defined in a layer named codice_1/codice_2 aka codice_3/codice_4, codice_5/codice_6, codice_7/codice_8, or codice_9/codice_10 (EAGLE), codice_11/codice_12 (KiCad), codice_13/codice_14 (TARGET), codice_15/codice_16 (OrCAD), codice_17/codice_18 (PADS), codice_19/codice_20 (WEdirekt), codice_21/codice_22 (Gerber and many others). Some (less common) EDA software does not treat the solder paste mask as a regular part of a PCB's layer stack, in which case the paste mask must be derived from the solder stop mask.
For improved accuracy, stencils traditionally were often mounted in proprietary aluminum frames of various kinds. Today, the usage of quick mount systems is more common at least for low volume batches, mounting the stencil pneumatically or mechanically. For this the stencil needs additional perforations for alignment following one of several mount system standards including QuattroFlex, ZelFlex, ESSEMTEC, PAGGEN, Metz, DEK VectorGuard, Mechatronic Systems and others.
Printing process.
The process begins with loading the board into the printer. The internal vision system aligns the stencil to the board, after which the squeegee prints the solder paste. The stencil and board are then separated and unloaded. The bottom of the stencil is wiped about every ten prints to remove excess solder paste remaining on the stencil.
A typical printing operation has a speed of around 15 to 45 seconds per board. Print head speed is typically 1 to 8 inches per second. The printing process must be carefully controlled. Misalignment of motion from the reference results in several defects, hence the board must be secured correctly before the process begins. A snugger and vacuum holders are used to secure the X and Y axes of the board. Vacuum holders must be carefully used, as they may affect the pin-in-paste printing process if not secured properly.
The longest process is the printing operation, followed by the separation process. Post print inspection is crucial and is usually performed with special 2D vision systems on the printer or separate 3D systems.
Printed wiring boards.
Design.
Vision systems in the stencil printing machines use global fiducial marks for aligning the PWB. Without these fiducials the printer would not print the solder paste in exact alignment with the pads. The PWB should have close dimensional tolerances so that it mates to the stencil. This is necessary to achieve the required alignment of solder blocks on the pads.
Masking.
The required accuracy in alignment can also be achieved by controlling the flow of solder on the PWB during reflow soldering. For this purpose, the space between the pads is often coated with a solder mask. The solder mask materials have no affinity to the molten solder and hence, no positive bonding is formed between them as the solder solidifies. This process is often referred to as "Solder masking". The mask must be centered correctly. The mask protects the PWB against oxidation, and prevents unintended solder bridges from forming between closely spaced solder pads.
Also the height of the solder mask should be lower than the pad height to avoid gasketing problems. If the height of the solder mask is greater than that of the pad, then some of the solder paste would settle in the empty space between the mask and the pad. This is what is referred to as gasketing. It is a seal that fills the space between two surfaces to prevent leakages. Gasketing is a problem as the excess solder paste around the pad may be more than a nuisance factor for circuits having very small line spacing.
Finishing.
The pads on the PWB are made of copper and are susceptible to oxidization. Surface oxidization on the copper will inhibit the ability of the solder to form a reliable joint. To avoid this unwanted effect, all exposed copper is protected with a surface finish.
Aperture fill and release.
The core of a well printed PWB lies in the fill and release of solder paste into the aperture. When the stencil is in contact with the PWB, solder paste is applied over the top surface of the stencil using a squeegee. This causes the aperture to fill with solder paste. The PWB is then lowered from the stencil. The amount of solder paste which is released from the stencil apertures and transferred to the PWB pads, determines whether or not the print is good. Ideally, all volumes of solder paste should be equal to the volume of the corresponding stencil aperture. In reality however, this is never the case. Hence, a print is considered to be good if a certain fraction of the paste is released. One way of quantifying print performance is to calculate the "transfer efficiency". This is mathematically stated as:
In the above expression, the theoretical maximum volume is simply the open volume of the stencil aperture. Ideally, a transfer efficiency of 1 is desired. In reality however, greater the transfer efficiency, better is the print.
Now in order to get the aperture full of paste requires sufficient flow rate and sufficient fill time. Apertures which are not completely filled will not release paste onto the board, which results in clogged stencils and defective solder joints.
Solder paste release is determined by the separation speed of the board from the stencil. The adhesion of the paste to the board has to provide the shearing force to overcome the adhesion of the paste to the stencil walls. This hydrodynamic shearing force depends on the separation speed.
Stencils.
Stencils are used to print solder paste on the PCB. They are often made of stainless steel or nickel and are manufactured by different processes described below.
Manufacturing processes.
Laser cutting.
The use of laser technology allows having tighter tolerances and greater accuracy.
The aperture walls can be smoothed through electro-polishing and/or nickel plating. The laser cutting process results in trapezoidal apertures that can create better solder paste release characteristics.
The repeatability of dimensions in laser-cut stencils is generally better than that of chemical etching. With laser cutting, there are no photo films requiring precise alignment or protection from moisture.
E-FAB stencil.
This stencil is formed by the process of electroforming nickel, hence the name E-FAB. The nickel has better wear characteristics than steel and electroforming creates smooth tapered aperture walls. The process also creates a ridge along the bottom of the stencil that can improve stencil-to-board gasketing and result in more consistent solder paste release.
Stencil design.
Due to the need for fine pitch components, as the size of the aperture becomes smaller and smaller, they become “tall-narrow” apertures. In such cases, the apertures may be filled with solder paste but not completely released, or sometimes not even completely filled and hence get no deposits. In order to counter this problem, aperture walls are made as smooth as possible. Also, molecular layer nano coatings are put on the stencil walls so that the solder paste does not stick.
Consistent fill and release is the most important output of stencil printing. When the stencil is down on the board, paste is filling the aperture and it's in contact with the pad and walls of the stencil. The contact is judged by taking the ratio of these areas i.e. the ratio of the area of the pad to the area of the walls. This is called "area ratio".
The information about the standards for stencil design is available at IPC Specification 7525 and other standards. In general, including stencils with tall and narrow apertures, an area ratio greater than 0.66 is recommended.
Illustrations of the various dimensions:
For fine pitch stencils (smaller 20 mils pitch, 10 mils aperture), even with a 5 mils stencil, which is the most commonly used stencil thickness, the area ratio is below 1.5. This necessitates the use of a thinner stencil.
For BGA/CSP and other very small apertures, the area ratio is used. It should be greater than 0.66, as this ensures a high probability of good fill and release. An area ratio below 0.66 would mean a much less reliable process.
Examples of area ratios for BGAs:
Aperture size should be smaller than the pad size to avoid the excess solder paste or production of solder balls. A 10 to 20% reduction in aperture size as compared to the pad size is typical to minimize solder balls. Solder balls can result in malfunctioning of the electric circuit.
Other considerations.
Step down stencils.
A PCB may need varying amounts of solder paste to be applied depending upon the design and size of components. Applying a uniform maximum level of solder may not be a good solution in this case, as these stencils often find use when "pin and paste" technology (i.e., printing solder paste into through-holes to avoid wave soldering) and components of significantly different pitch are used in the same PWB. For this purpose, to achieve a varying solder amount, step down stencils are used.
Solder paste stencil life.
Ideally, a solder paste should have, at minimum, a 4-hour stencil life. The stencil life is defined as a time period in which there will be no significant change in the solder paste material characteristics. A solder paste with a longer stencil life will be more robust in the printing process. Actual stencil life for a paste should be determined from the manufacturers' specifications and on-site verification.
Handling and storage of stencils.
To improve the life and performance of stencils, they must be cleaned after use by removing any solder paste on them or within the apertures. The cleaned stencils are stored away in a protective area. Before usage, stencils are inspected for wear or damage.
Stencils are typically identified by job numbers to reduce the risk of mishandling or misplacing.
Squeegee.
Squeegees are used to spread solder over the stencil and to fill all apertures consistently. Squeegees come in two different types based either on metal or polyurethane. Metal squeegees are preferred over polyurethane. They produce very consistent solder volumes and are resistant to scooping the solder paste out of the apertures when printing. In addition, they have better wear characteristics, leading to longer life.
Common difficulties.
Insufficient solder paste.
Insufficient solder paste may cause poor bonds and contact between components and the board. The common causes of insufficient solder paste are poor gasketing, clogged stencil apertures, insufficient solder paste bead size, paste/stencil being used beyond recommended life span, stencil not wiped clean, or low squeegee pressure.
Smudging/bridging.
The main causes of smudging/bridging are excessive squeegee pressure, inadequate stencil wiping, poor contact between the board and stencil, high temperature or humidity, or low solder paste viscosity.
Misalignment print.
A typical misalignment print is usually caused by the vision system not spotting fiducials, PWB or stencil stretch, poor contact between the board and the stencil, or weak board support.
Bow and twist.
A PCB board not fixed properly during solder paste printing gives poor results and increases soldering related issues. Normally, solder paste printing equipment can handle warpage of 1.0 to 3.0 mm but beyond this limit needs some special jigs or fixtures to hold the PCB. It may be difficult to tackle thick and small boards compared to thin and bigger size boards.
Statistical process control.
More than 50% of defects in electronics assembly are due to solder paste printing problems. There are many parameters involved in this process, making it difficult to find the specific problem and to optimize the process. A careful statistical study of the process may be used to improve output significantly. The number of opportunities for a defect characterizes defects, not the actual number of defective parts.
Example:
Hence, there are 69 opportunities for defects to produce one defective component. Counting the defect opportunities is the most valid process monitor. Processes are typically rated in terms of number of defects per million opportunities (DPM). As an example, a process resulting in 100 defects when given 1 million defect opportunities would have a rating of 100 DPM. World class printing processes have defect levels around 20 DPM.
A low DPM printing process may be achieved by employing statistical techniques to determine the effects of individual parameters or interactions between different parameters. Important process parameters can then be optimized using design of experiments (DOE) techniques. These optimized parameters can then be implemented and process bench marking can begin. Statistical process control can then be used to continuously monitor and improve printing DPM levels.


Wide-format printer

Wide format printers (large format printers) are generally accepted to be any computer-controlled printing machines (printers) that support a maximum print roll width of between . Printers with capacities over 100 in wide are considered "super-wide" or "grand" format. Wide-format printers are used to print banners, posters, trade show graphics, wallpaper, murals, backlit film (duratrans), vehicle image wraps, electronic circuit schematics, architectural drawings, construction plans, backdrops for theatrical and media sets, and any other large format artwork or signage. Wide-format printers usually employ some variant of inkjet or toner-based technology to produce the printed image; and are more economical than other print methods such as screen printing for most short-run (low quantity) print projects, depending on print size, run length (quantity of prints per single original), and the type of substrate or print medium. Wide-format printers are usually designed for printing onto a roll of print media that feeds incrementally during the print process, rather than onto individual sheets.
Technologies.
Wide-format printers can be categorized by the type of ink transfer process they employ:


Stochastic hill climbing

Stochastic hill climbing is a variant of the basic hill climbing method. While basic hill climbing always chooses the steepest uphill move, "stochastic hill climbing chooses at random from among the uphill moves; the probability of selection can vary with the steepness of the uphill move."