Soldering

Soldering  is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.
Soldering is commonly used in the electronics industry for the manufacture and repair of printed circuit boards (PCBs) and other electronic components. It is also used in plumbing and metalwork, as well as in the manufacture of jewelry and other decorative items.
The solder used in the process can vary in composition, with different alloys used for different applications. Common solder alloys include tin-lead, tin-silver, and tin-copper, among others. Lead-free solder has also become more widely used in recent years due to health and environmental concerns associated with the use of lead.
In addition to the type of solder used, the temperature and method of heating also play a crucial role in the soldering process. Different types of solder require different temperatures to melt, and heating must be carefully controlled to avoid damaging the materials being joined or creating weak joints.
There are several methods of heating used in soldering, including soldering irons, torches, and hot air guns. Each method has its own advantages and disadvantages, and the choice of method depends on the application and the materials being joined.
Soldering is an important skill for many industries and hobbies, and it requires a combination of technical knowledge and practical experience to achieve good results.
Origins.
There is evidence that soldering was employed as early as 5,000 years ago in Mesopotamia. Soldering and brazing are thought to have originated very early in the history of metal-working, probably before 4000 BC. Sumerian swords from were assembled using hard soldering.
Soldering was historically used to make jewelry, cookware and cooking tools, assembling stained glass, as well as other uses.
Applications.
Soldering is used in plumbing, electronics, and metalwork from flashing to jewelry and musical instruments.
Soldering provides reasonably permanent but reversible connections between copper pipes in plumbing systems as well as joints in sheet metal objects such as food cans, roof flashing, rain gutters and automobile radiators.
Jewelry components, machine tools and some refrigeration and plumbing components are often assembled and repaired by the higher temperature silver soldering process. Small mechanical parts are often soldered or brazed as well. Soldering is also used to join lead came and copper foil in stained glass work.
Electronic soldering connects electrical wiring to devices, and electronic components to printed circuit boards. Electronic connections may be hand-soldered with a soldering iron. Automated methods such as wave soldering or use of ovens can make many joints on a complex circuit board in one operation, vastly reducing production cost of electronic devices.
Musical instruments, especially brass and woodwind instruments, use a combination of soldering and brazing in their assembly. Brass bodies are often soldered together, while keywork and braces are most often brazed.
Solderability.
The solderability of a substrate is a measure of the ease with which a soldered joint can be made to that material.
Some metals are easier to solder than others. Copper, zinc, brass, silver and gold are easy. Iron, mild steel and nickel are next in difficulty. Because of their thin, strong oxide films, stainless steel and some aluminium alloys are even more difficult to solder. Titanium, magnesium, cast irons, some high-carbon steels, ceramics, and graphite can be soldered but it involves a process similar to joining carbides: they are first plated with a suitable metallic element that induces interfacial bonding.
Solders.
Soldering filler materials are available in many different alloys for differing applications. In electronics assembly, the eutectic alloy with 63% tin and 37% lead (or 60/40, which is almost identical in melting point) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications. Some examples of soft-solder are tin-lead for general purposes, tin-zinc for joining aluminium, lead-silver for strength at higher than room temperature, cadmium-silver for strength at high temperatures, zinc-aluminium for aluminium and corrosion resistance, and tin-silver and tin-bismuth for electronics.
A eutectic formulation has advantages when applied to soldering: the liquidus and solidus temperatures are the same, so there is no plastic phase, and it has the lowest possible melting point. Having the lowest possible melting point minimizes heat stress on electronic components during soldering. And, having no plastic phase allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures. Any movement during the plastic phase may result in cracks, resulting in an unreliable joint.
Common solder formulations based on tin and lead are listed below. The fraction represent percentage of tin first, then lead, totaling 100%:
For environmental reasons and the introduction of regulations such as the European RoHS (Restriction of Hazardous Substances Directive), lead-free solders are becoming more widely used. They are also suggested anywhere young children may come into contact with (since young children are likely to place things into their mouths), or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Unfortunately, common lead-free solders are not eutectic formulations, melting at around , making it more difficult to create reliable joints with them.
Other common solders include low-temperature formulations (often containing bismuth), which are often used to join previously soldered assemblies without unsoldering earlier connections, and high-temperature formulations (usually containing silver) which are used for high-temperature operation or for first assembly of items which must not become unsoldered during subsequent operations. Alloying silver with other metals changes the melting point, adhesion and wetting characteristics, and tensile strength. Of all the brazing alloys, silver solders have the greatest strength and the broadest applications. Specialty alloys are available with properties such as higher strength, the ability to solder aluminum, better electrical conductivity, and higher corrosion resistance.
Soldering vs. brazing.
There are three forms of soldering, each requiring progressively higher temperatures and producing an increasingly stronger joint strength:
The alloy of the filler metal for each type of soldering can be adjusted to modify the melting temperature of the filler. Soldering differs from gluing significantly in that the filler metals directly bond with the surfaces of the workpieces at the junction to form a bond that is both electrically conductive and gas- and liquid-tight.
Soft soldering is characterized by having a melting point of the filler metal below approximately , whereas silver soldering and brazing use higher temperatures, typically requiring a flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys (often containing lead) that have liquidus temperatures below .
In this soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in a surface alloying process called wetting. In stranded wire, the solder is drawn up into the wire between the strands by capillary action in a process called 'wicking'. Capillary action also takes place when the workpieces are very close together or touching. The joint's tensile strength is dependent on the filler metal used; in electrical soldering little tensile strength comes from the added solder which is why it is advised that wires be twisted or folded together before soldering to provide some mechanical strength for a joint. A good solder joint produces an electrically conductive, water- and gas-tight join.
Each type of solder offers advantages and disadvantages. Soft solder is so called because of the soft lead that is its primary ingredient. Soft soldering uses the lowest temperatures (and so thermally stresses components the least) but does not make a strong joint and is unsuitable for mechanical load-bearing applications. It is also unsuitable for high-temperature applications as it loses strength, and eventually melts. Silver soldering, as used by jewelers, machinists and in some plumbing applications, requires the use of a torch or other high-temperature source, and is much stronger than soft soldering. Brazing provides the strongest of the non-welded joints but also requires the hottest temperatures to melt the filler metal, requiring a torch or other high temperature source and darkened goggles to protect the eyes from the bright light produced by the white-hot work. It is often used to repair cast-iron objects, wrought-iron furniture, etc.
Soldering operations can be performed with hand tools, one joint at a time, or "en masse" on a production line. Hand soldering is typically performed with a soldering iron, soldering gun, or a torch, or occasionally a hot-air pencil. Sheetmetal work was traditionally done with "soldering coppers" directly heated by a flame, with sufficient stored heat in the mass of the soldering copper to complete a joint; gas torches (e.g. butane or propane) or electrically heated soldering irons are more convenient. All soldered joints require the same elements of cleaning of the metal parts to be joined, fitting up the joint, heating the parts, applying flux, applying the filler, removing heat and holding the assembly still until the filler metal has completely solidified. Depending on the nature of flux material used and the application, cleaning of the joint may be required after it has cooled.
Each solder alloy has characteristics that work best for certain applications, notably strength and conductivity, and each type of solder and alloy has different melting temperatures. The term "silver solder" denotes the type of solder that is used. Some soft solders are "silver-bearing" alloys used to solder silver-plated items. Lead-based solders should not be used on precious metals because the lead dissolves the metal and disfigures it.
The distinction between soldering and brazing is based on the melting temperature of the filler alloy. A temperature of 450 °C is usually used as a practical demarcation between soldering and brazing. Soft soldering can be done with a heated iron whereas the other methods typically require a higher temperature torch or a furnace to melt the filler metal.
Different equipment is usually required since a soldering iron cannot achieve high enough temperatures for hard soldering or brazing. Brazing filler metal is stronger than silver solder, which is stronger than lead-based soft solder. Brazing solders are formulated primarily for strength, silver solder is used by jewelers to protect the precious metal and by machinists and refrigeration technicians for its tensile strength but lower melting temperature than brazing, and the primary benefit of soft solder is the low temperature used (to prevent heat damage to electronic components and insulation).
Since the joint is produced using a metal with a lower melting temperature than the workpiece, the joint will weaken as the ambient temperature approaches the melting point of the filler metal. For that reason, the higher temperature processes produce joints which are effective at higher temperatures. Brazed connections can be as strong or nearly as strong as the parts they connect, even at elevated temperatures.
Silver soldering.
"Hard soldering" or "silver soldering" is used to join precious and semi-precious metals such as gold, silver, brass, and copper. The solder is usually described as easy, medium, or hard in reference to its melting temperature, not the strength of the joint. Extra-easy solder contains 56% silver and has a melting point of . Extra-hard solder has 80% silver and melts at . If multiple joints are needed, then the jeweler will start with hard or extra-hard solder and switch to lower-temperature solders for later joints.
Silver solder is somewhat absorbed by the surrounding metal, resulting in a joint that is actually stronger than the metal being joined. The metal being joined must be perfectly flush, as silver solder cannot normally be used as a filler and will not fill gaps.
Another difference between brazing and soldering is how the solder is applied. In brazing, one generally uses rods that are touched to the joint while being heated. With silver soldering, small pieces of solder wire are placed onto the metal prior to heating. A flux, often made of boric acid and denatured alcohol, is used to keep the metal and solder clean and to prevent the solder from moving before it melts.
When silver solder melts, it tends to flow towards the area of greatest heat. Jewelers can somewhat control the direction the solder moves by leading it with a torch; it will even sometimes run straight up along a seam.
Mechanical and aluminium soldering.
A number of solder materials, primarily zinc alloys, are used for soldering aluminium metal and alloys and to a lesser extent steel and zinc. This mechanical soldering is similar to a low temperature brazing operation, in that the mechanical characteristics of the joint are reasonably good and it can be used for structural repairs of those materials.
The American Welding Society defines brazing as using filler metals with melting points over — or, by the traditional definition in the United States, above . Aluminium soldering alloys generally have melting temperatures around . This soldering / brazing operation can use a propane torch heat source.
These materials are often advertised as "aluminium welding", but the process does not involve melting the base metal, and therefore is not properly a weld.
United States Military Standard or MIL-SPEC specification MIL-R-4208 defines one standard for these zinc-based brazing/soldering alloys. A number of products meet this specification. or very similar performance standards.
Flux.
The purpose of flux is to facilitate the soldering process. One of the obstacles to a successful solder joint is an impurity at the site of the joint; for example, dirt, oil or oxidation. The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece. One of the earliest forms of flux was charcoal, which acts as a reducing agent and helps prevent oxidation during the soldering process. Some fluxes go beyond the simple prevention of oxidation and also provide some form of chemical cleaning (corrosion). Many fluxes also act as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to flow and wet the workpieces more easily.
For many years, the most common type of flux used in electronics (soft soldering) was rosin-based, using the rosin from selected pine trees. It was nearly ideal in that it was non-corrosive and non-conductive at normal temperatures but became mildly reactive (corrosive) at elevated soldering temperatures. Plumbing and automotive applications, among others, typically use an acid-based (hydrochloric acid) flux which provides rather aggressive cleaning of the joint. These fluxes cannot be used in electronics because their residues are conductive leading to unintended electrical connections, and because they will eventually dissolve small diameter wires. Citric acid is an excellent water-soluble acid-type flux for copper and electronics but must be washed off afterwards.
Fluxes for soft solder are currently available in three basic formulations:
Flux performance must be carefully evaluated for best results; a very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for more variable hand-soldering operations.
Heating methods.
Different types of soldering tools are made for specific applications. The required heat can be generated from burning fuel or from an electrically operated heating element or by passing an electric current through the item to be soldered. Another method for soldering is to place solder and flux at the locations of joints in the object to be soldered, then heat the entire object in an oven to melt the solder; toaster ovens and hand-held infrared lights have been used by hobbyists to replicate production soldering processes on a much smaller scale. A third method of soldering is to use a solder pot where the part (with flux) is dipped in a small heated iron cup of liquid solder, or a pump in a bath of liquid solder produces an elevated "wave" of solder which the part is quickly passed through. Wave soldering uses surface tension to keep solder from bridging the insulating gaps between the copper lines of flux-coated printed wiring boards/printed circuit boards.
The electric soldering iron is widely used for hand-soldering, consisting of a heating element in contact with the "iron" (a larger mass of metal, usually copper) which is in contact with the working tip made of copper. Usually, soldering irons can be fitted with a variety of tips, ranging from blunt, to very fine, to chisel heads for hot-cutting plastics rather than soldering. Plain copper tips are subject to errosion/dissolution in hot solder, and may be plated with pure iron to prevent that. The simplest irons do not have temperature regulation. Small irons rapidly cool when used to solder to, say, a metal chassis, while large irons have tips too cumbersome for working on printed circuit boards (PCBs) and similar fine work. A 25-watt iron will not provide enough heat for large electrical connectors, joining copper roof flashing, or large stained-glass lead came. On the other hand, a 100-watt iron may provide too much heat for PCBs. Temperature-controlled irons have a reserve of power and can maintain temperature over a wide range of work.
A soldering gun heats a small cross-section copper tip very quickly by conducting a large AC current through it using a large cross-section one-turn transformer; the copper tip then conducts the heat to the part like other soldering irons. A soldering gun will be larger and heavier than a heating-element soldering iron of the same power rating because of the built-in transformer.
Gas-powered irons using a catalytic tip to heat a bit, without flame, are used for portable applications. Hot-air guns and pencils allow rework of component packages (such as surface mount devices) which cannot easily be performed with electric irons and guns.
For non-electronic applications, soldering torches use a flame rather than a soldering tip to heat solder. Soldering torches are often powered by butane and are available in sizes ranging from very small butane/oxygen units suitable for very fine but high-temperature jewelry work, to full-size oxy-fuel torches suitable for much larger work such as copper piping. Common multipurpose propane torches, the same kind used for heat-stripping paint and thawing pipes, can be used for soldering pipes and other fairly large objects either with or without a soldering tip attachment; pipes are generally soldered with a torch by directly applying the open flame.
A soldering copper is a tool with a large copper head and a long handle which is heated with a small direct flame and used to apply heat to sheet metal such as tin plated steel for soldering. Typical soldering coppers have heads weighing between one and four pounds. The head provides a large thermal mass to store enough heat for soldering large areas before needing re-heating in the fire; the larger the head, the longer the working time. The copper surface of the tool must be constantly cleaned and re-tinned during use. Historically, soldering coppers were standard tools used in auto bodywork, although body solder has been mostly superseded by spot welding for mechanical connection, and non-metallic fillers for contouring.
During WW2 and for some time afterwards SOE forces used small pyrotechnic self-soldering joints to make connections for the remote detonation of demolition and sabotage explosives. These consisted of a small copper tube partially filled with solder and a slow-burning pyrotechnic composition wrapped around the tube. The wires to be joined would be inserted into the tube and a small blob of ignition compound allowed the device to be struck like a match to ignite the pyrotechnic and heat the tube for long enough to melt the solder and make the joint.
Laser soldering.
"Laser soldering" is a technique where a 30–50 W laser is used to melt and solder an electrical connection joint. Diode laser systems based on semiconductor junctions are used for this purpose. Suzanne Jenniches patented laser soldering in 1980.
Wavelengths are typically 808 nm through 980 nm. The beam is delivered via an optical fiber to the workpiece, with fiber diameters 800 µm and smaller. Since the beam out of the end of the fiber diverges rapidly, lenses are used to create a suitable spot size on the workpiece at a suitable working distance. A wire feeder is used to supply solder.
Both lead-tin and silver-tin material can be soldered. Process recipes will differ depending on the alloy composition. For soldering 44-pin chip carriers to a board using soldering preforms, power levels were on the order of 10 watts and solder times approximately 1 second. Low power levels can lead to incomplete wetting and the formation of voids, both of which can weaken the joint.
Photonic soldering.
Photonic soldering is a relatively new process that uses broadband light from rapidly pulsing flashlamps to solder components to a circuit board. Energy consumption is approximately 85% less than that of a reflow oven, while the throughput is higher, and the footprint is smaller. It is similar to photonic curing, in that the components to be soldered are heated while the substrate remains relatively cool. This enables the use of high-temperature solders, such as SAC305, even on thermally fragile substrates such as PET, cellulose, and fabrics. An entire circuit board can be processed in a few seconds. In some cases, masks are used, but it can also be performed without registration, enabling very high processing rates.
Induction soldering.
Induction soldering uses induction heating by high-frequency alternating current in a surrounding copper coil. This induces currents in the part being soldered, which generates heat because of the higher resistance of a joint versus its surrounding metal (resistive heating). These copper coils can be shaped to fit the joint more precisely. A filler metal (solder) is placed between the facing surfaces, and this solder melts at a fairly low temperature. Fluxes are commonly used in induction soldering. This technique is particularly suited to continuously soldering, in which case these coils wrap around a cylinder or a pipe that needs to be soldered.
Fiber focus infrared soldering.
Fiber focus infrared soldering is technique where many infrared sources are led through fibers, then focused onto a single spot at which the connection is soldered.
Resistance soldering.
Resistance soldering is soldering in which the heat required to melt the solder is created by passing an electric current through the parts to be soldered. When electric current is conducted through any metal, heat is generated; when that current is confined to a smaller cross-sectional area, the heat produced in the entire circuit is concentrated in the portion with the reduced cross-sectional area. The current doing the heating is applied by electrodes or tips energized from a low (open-circuit) voltage source, typically 2-7 volts. They can be tweezer-like for general connections or specially-shaped to make contact with parts located closely together.
Resistance soldering is unlike using a conduction iron, where heat is produced within an element and then passed through a thermally conductive tip into the joint area. A cold soldering iron requires time to reach working temperature and must be kept hot between solder joints. Thermal transfer may be inhibited if the tip is not kept properly wetted during use. With resistance soldering an intense heat can be rapidly developed directly within the joint area and in a tightly controlled manner. This allows a faster ramp up to the required solder melt temperature and minimizes thermal travel away from the solder joint, which helps to minimize the potential for thermal damage to materials or components in the surrounding area. Heat is only produced while each joint is being made, making resistance soldering more energy efficient. Because of these advantages, resistance soldering is common in industries which solder in small spaces such as connectors and wire terminals, and where high power is required, such as desoldering automotive parts.
Resistance soldering equipment, unlike conduction irons, can be used for difficult soldering and brazing applications where significantly higher temperatures may be required. This makes resistance comparable to flame soldering in some situations, but the resistance heat is more localized because of direct contact, whereas the flame might heat a larger area.
Active soldering.
Flux-less soldering with aid of conventional soldering iron, ultrasonic soldering iron or specialized solder pot and active solder that contains an active element, most often titanium, zirconium or chromium. The active elements, owing to mechanical activation, react with the surface of the materials generally considered difficult to solder without premetallization. The active solders can be protected against excessive oxidation of their active element by addition of rare-earth elements with higher affinity to oxygen (typically cerium or lanthanum). Another common additive is gallium – usually introduced as a wetting promoter. Mechanical activation, needed for active soldering, can be performed by brushing (for example with use of stainless wire brush or steel spatula) or ultrasonic vibration (20–60 kHz). Active soldering has been shown to effectively bond ceramics, aluminium, titanium, silicon, graphite and carbon nanotube based structures at temperatures lower than 450 °C or use of protective atmosphere.
Pipe soldering.
Copper pipe, or 'tube', is commonly joined by soldering. When applied in a plumbing trade context in the United States, soldering is often referred to as "sweating", and a tubing connection so made is referred to as a "sweated joint".
Outside the United States, "sweating" refers to the joining of flat metallic surfaces by a two step process by which solder is first applied to one surface, then this first piece is placed in position against the second surface and both are re-heated to achieve the desired joint.
Copper tubing conducts heat away much faster than a conventional hand-held soldering iron or gun can provide, so a propane torch is most commonly used to deliver the necessary power; for large tubing sizes and fittings a MAPP-fueled, acetylene-fueled, or propylene-fueled torch is used with atmospheric air as the oxidizer; MAPP/oxygen or acetylene/oxygen are rarely used because the flame temperature is much higher than the melting point of copper. Too much heat destroys the temper of hard-tempered copper tubing, and can burn the flux out of a joint before the solder is added, resulting in a faulty joint. For larger tubing sizes, a torch fitted with various sizes of interchangeable "swirl tips" is employed to deliver the needed heating power. In the hands of a skilled tradesman, the hotter flame of acetylene, MAPP, or propylene allows more joints to be completed per hour without damage to copper tempering.
However, it is possible to use an electrical tool to solder joints in copper pipe sized from . For example, the Antex Pipemaster is recommended for use in tight spaces, when open flames are hazardous, or by do-it-yourself users. The pliers-like tool uses heated fitted jaws that completely encircle the pipe, allowing a joint to be melted in as little as 10 seconds.
Solder fittings, also known as 'capillary fittings', are usually used for copper joints. These fittings are short sections of smooth pipe designed to slide over the outside of the mating tube. Commonly used fittings include for straight connectors, reducers, bends, and tees. There are two types of solder fittings: 'end feed fittings' which contain no solder, and 'solder ring fittings' (also known as Yorkshire fittings), in which there is a ring of solder in a small circular recess inside the fitting.
As with all solder joints, all parts to be joined must be clean and oxide free. Internal and external wire brushes are available for the common pipe and fitting sizes; emery cloth and wire-wool are frequently used as well, although metal wool products are discouraged, as they can contain oil, which would contaminate the joint.
Because of the size of the parts involved, and the high activity and contaminating tendency of the flame, plumbing fluxes are typically much more chemically active, and often more acidic, than electronic fluxes. Because plumbing joints may be done at any angle, even upside down, plumbing fluxes are generally formulated as pastes which stay in place better than liquids. Flux is applied to all surfaces of the joint, inside and out. Flux residues are removed after the joint is complete to prevent erosion and failure of the joint.
Many plumbing solder formulations are available, with different characteristics, such as higher or lower melting temperature, depending on the specific requirements of the job. Building codes currently almost universally require the use of lead-free solder for drinking water piping (and also flux must be approved for drinking water applications), though traditional tin-lead solder is still available. Studies have shown that lead-soldered plumbing pipes can result in elevated levels of lead in drinking water.
Since copper pipe quickly conducts heat away from a joint, great care must be taken to ensure that the joint is properly heated through to obtain a good bond. After the joint is properly cleaned, fluxed and fitted, the torch flame is applied to the thickest part of the joint, typically the fitting with the pipe inside it, with the solder applied at the gap between the tube and the fitting. When all the parts are heated through, the solder will melt and flow into the joint by capillary action. The torch may need to be moved around the joint to ensure all areas are wetted out. However, the installer must take care to not overheat the areas being soldered. If the tube begins to discolor it means that the tube has been over-heated and is beginning to oxidize, stopping the flow of the solder and causing the soldered joint not to seal properly. Before oxidation the molten solder will follow the heat of the torch around the joint. When the joint is properly wetted out, the solder and then the heat are removed, and while the joint is still very hot, it is usually wiped with a dry rag. This removes excess solder as well as flux residue before it cools down and hardens. With a solder ring joint, the joint is heated until a ring of molten solder is visible around the edge of the fitting and allowed to cool.
Of the three methods of connecting copper tubing, solder connections require the most skill, but soldering copper is a very reliable process, provided some basic conditions are met:
Copper is only one material that is joined in this manner. Brass fittings are often used for valves or as a connection fitting between copper and other metals. Brass piping is soldered in this manner in the making of brass instruments and some woodwind (saxophone and flute) musical instruments
Wire brush, wire wool and emery cloth are commonly used to prepare plumbing joints for connection. Bristle brushes are usually used to apply plumbing paste flux. A heavy rag is usually used to remove flux from a plumbing joint before it cools and hardens. A fiberglass brush can also be used.
When soldering pipes closely connected to valves such as in refrigeration systems it may be necessary to protect the valve from heat that could damage rubber or plastic components within, in this case a wet cloth wrapped around the valve can often sink sufficient heat through the boiling of the water to protect the valve.
Copper tube soldering defects.
In the joining of copper tube, failure to properly heat and fill a joint may lead to a 'void' being formed. This is usually a result of improper placement of the flame. If the heat of the flame is not directed at the back of the fitting cup, and the solder wire applied degrees opposite the flame, then solder will quickly fill the opening of the fitting, trapping some flux inside the joint. This bubble of trapped flux is the void; an area inside a soldered joint where solder is unable to completely fill the fittings' cup, because flux has become sealed inside the joint, preventing solder from occupying that space.
Stained glass soldering.
Historically, stained glass soldering tips were copper, heated by being placed in a charcoal-burning brazier. Multiple tips were used; when one tip cooled down from use, it was placed back in the brazier of charcoal and the next tip was used.
More recently, electrically heated soldering irons are used. These are heated by a coil or ceramic heating element inside the tip of the iron. Different power ratings are available, and temperature can be controlled electronically. These characteristics allow longer beads to be run without interrupting the work to change tips. Soldering irons designed for electronic use are often effective though they are sometimes underpowered for the heavy copper and lead came used in stained glass work.
Oleic acid is the classic flux material that has been used to improve solderability.
Tiffany-type stained glass is made by gluing copper foil around the edges of the pieces of glass and then soldering them together. This method makes it possible to create three-dimensional stained glass pieces.
Electronics soldering.
Hand soldering.
For attachment of electronic components to a PCB, proper selection and use of flux helps prevent oxidation during soldering; it is essential for good wetting and heat transfer. The soldering iron tip must be clean and pre-tinned with solder to ensure rapid heat transfer.
Electronic joints are usually made between surfaces that have been tinned and rarely require mechanical cleaning, though tarnished component leads and copper traces with a dark layer of oxide passivation (due to aging), as on a new prototyping board that has been on the shelf for about a year or more, may need to be mechanically cleaned.
To simplify soldering, beginners are usually advised to apply the soldering iron and the solder separately to the joint, rather than the solder being applied directly to the iron. When sufficient solder is applied, the solder wire is removed. When the surfaces are adequately heated, the solder will flow around the workpieces. The iron is then removed from the joint.
If all metal surfaces have not been properly cleaned ("fluxed") or brought entirely above the melting temperature of the solder used, the result will be an unreliable ("cold solder") joint, even though its appearance may suggest otherwise.
Excess solder, unconsumed flux and residue is sometimes wiped from the soldering iron tip between joints. The tip of the bit (commonly iron plated to reduce erosion) is kept wetted with solder ("tinned") when hot to assist soldering, and to minimize oxidation and corrosion of the tip itself.
After inserting a through-hole mounted component, the excess lead is cut off, leaving a length of about the radius of the pad.
Hand-soldering techniques require a great deal of skill for the fine-pitch soldering of surface-mount chip packages. In particular ball grid array (BGA) devices are notoriously difficult, if not impossible, to rework by hand.
Defects.
Cold joints.
Various problems may arise in the soldering process which lead to joints which are nonfunctional either immediately or after a period of use.
The most common defect when hand-soldering results from the parts being joined not exceeding the solder's liquidus temperature, resulting in a "cold solder" joint. This is usually the result of the soldering iron being used to heat the solder directly, rather than the parts themselves. Properly done, the iron heats the parts to be connected, which in turn melt the solder, guaranteeing adequate heat in the joined parts for thorough wetting. If using solder wire with an embedded flux core, heating the solder first may cause the flux to evaporate before it cleans the surfaces being soldered.
A cold-soldered joint may not conduct at all, or may conduct only intermittently. Cold-soldered joints also happen in mass production, and are a common cause of equipment which passes testing, but malfunctions after sometimes years of operation.
Dry joints.
A "dry joint" occurs when the cooling solder is moved. Since non-eutectic solder alloys have a small plastic range, the joint must not be moved until the solder has cooled down through both the liquidus and solidus temperatures. Dry joints often occur because the joint moves when the soldering iron is removed from the joint. They are weak mechanically and poor conductors electrically.
Avoiding overheating of components.
For hand soldering, the heat source tool is selected to provide adequate heat for the size of joint to be completed. A 100-watt soldering iron may provide too much heat for printed circuit boards (PCBs), while a 25-watt iron will not provide enough heat for large electrical connectors.
Using a tool with too high a temperature can damage sensitive components, but protracted heating by a tool that is too cool or under powered can also cause heat damage. Excessive heating of a PCB may result in delamination — the copper traces may actually lift off the substrate, particularly on single sided PCBs without through hole plating.
While hand-soldering, a heat sink, such as a crocodile clip, may be used on the leads of heat-sensitive components to reduce heat transfer to the components and avoid damaging them. This is especially applicable to germanium parts.
The heat sink limits the temperature of the component body by absorbing and dissipating heat, by reducing the thermal resistance between the component and the air. Meanwhile, the thermal resistance of the leads maintains the temperature difference between the part of the leads being soldered and the component body. Thus, the leads become hot enough to melt the solder while the component body remains cooler. The heat sink will mean the use of more heat to complete the joint, since heat taken up by the heat sink will not heat the work pieces.
Components which dissipate large amounts of heat during operation are sometimes elevated above the PCB to avoid PCB overheating. Plastic or metal mounting clips or holders may be used with large devices to aid heat dissipation and reduce joint stresses.
Visual inspection of joints.
When visually inspected, a good solder joint will appear smooth, bright and shiny, with the outline of the soldered wire clearly visible. In general a good-looking soldered joint is a good joint.
A matte gray surface is a good indicator of a joint that was moved during soldering. A dry joint has a characteristically dull or grainy appearance immediately after the joint is made. This appearance is caused by crystallization of the liquid solder. Too little solder will result in a dry and unreliable joint.
Cold solder joints are dull and sometimes cracked or pock-marked. If the joint has lumps or balls of otherwise shiny solder, the metal has not wetted properly. Too much solder (the familiar 'solder blob' to beginners) is not necessarily unsound, but tends to mean poor wetting.
A concave fillet is ideal. The boundary between the solder and the workpiece in a good joint will have a low angle. This indicates good wetting and minimal use of solder, and therefore minimal heating of heat sensitive components. A joint may be good, but if a large amount of unnecessary solder is used, then excess heating was obviously required.
Lead-free solder formulations may cool to a dull surface even if the joint is good. The solder looks shiny while molten, and suddenly hazes over as it solidifies even though it has not been disturbed during cooling.
Flux use and residue.
An improperly selected or applied flux can cause joint failure. Without flux the joint may not be clean, or may be oxidized, resulting in an unsound joint.
For electronic work, flux-core solder wire is generally used, but additional flux may be used from a flux pen or dispensed from a small bottle with a syringe-like needle.
Some fluxes are designed to be stable and inactive when cool and do not need to be cleaned off, though they can if desired. If such fluxes are used, cleaning may merely be a matter of aesthetics or to make visual inspection of joints easier in specialised 'mission critical' applications such as medical devices, military and aerospace. For satellites, this will also reduce weight, slightly but usefully. In high humidity, since even non-corrosive flux might remain slightly active, the flux may be removed to reduce corrosion over time.
Some fluxes are corrosive and flux residue must be removed after soldering. If not properly cleaned, the flux may corrode the joint or the PCB. Water, alcohol, acetone, or other solvents compatible with the flux and the parts involved are commonly used with cotton swabs or bristle brushes.
In some applications, the PCB might also be coated in some form of protective material such as a lacquer to protect it and exposed solder joints from the environment.
Desoldering and resoldering.
Used solder contains some of the dissolved base metals and is unsuitable for reuse in making new joints. Once the solder's capacity for the base metal has been reached, it will no longer properly bond with the base metal, usually resulting in a brittle cold solder joint with a crystalline appearance.
It is good practice to remove solder from a joint prior to resoldering — desoldering braids (or wicks) or vacuum desoldering equipment (solder suckers) can be used. Desoldering wicks contain plenty of flux which will remove the oxidation from the copper trace and any device leads that are present. This will leave a bright, shiny, clean junction to be resoldered.
The lower melting point of solder means it can be melted away from the base metal, leaving it mostly intact, though the outer layer will be "tinned" with solder. Flux will remain which can easily be removed by abrasive or chemical processes. This tinned layer will allow solder to flow onto a new joint, resulting in a new joint, as well as making the new solder flow very quickly and easily.
Wave soldering and reflow soldering.
Currently, mass-production printed circuit boards (PCBs) are mostly wave soldered or reflow soldered, though hand soldering of production electronics is also still widely used.
In wave soldering, components are prepped (trimmed or modified) and installed on the PCB. Sometimes, to prevent movement they are temporarily kept in place with small dabs of adhesive or secured with a fixture, then the assembly is passed over flowing solder in a bulk container. This solder flow is forced to produce a standing wave so the whole PCB is not submerged in solder, but rather just touched. The result is that solder stays on pins and pads, but not on the PCB itself.
Reflow soldering is a process in which a solder paste (a mixture of prealloyed solder powder and a flux-vehicle that has a peanut butter-like consistency) is used to stick the components to their attachment pads, after which the assembly is heated by an infrared lamp, a hot air pencil, or, more commonly, by passing it through a carefully controlled oven.
Since different components can be best assembled by different techniques, it is common to use two or more processes for a given PCB. For example, surface mounted parts may be reflow soldered first, with a wave soldering process for the through-hole mounted components coming next, and bulkier parts hand-soldered last.
Hot-bar reflow.
"Hot-bar reflow" is a selective soldering process where two pre-fluxed, solder coated parts are heated with a heating element (called a thermode) to a temperature sufficient to melt the solder.
Pressure is applied through the entire process (usually 15 seconds) to ensure that components stay in place during cooling. The heating element is heated and cooled for each connection. Up to 4000 W can be used in the heating element, allowing fast soldering, good results with connections requiring high energy.
Environmental regulation and RoHS.
Environmental legislation in many countries has led to a change in formulation of both solders and fluxes.
The RoHS directives in the European Community required many new electronic circuit boards to be lead-free by 1 July 2006, mostly in the consumer goods industry, but in some others as well. In Japan, lead was phased out prior to legislation by manufacturers, due to the additional expense in recycling products containing lead.
Water-soluble non-rosin-based fluxes have been increasingly used since the 1980s so that soldered boards can be cleaned with water or water-based cleaners. This eliminates hazardous solvents from the production environment, and from factory effluents.
Even without the presence of lead, soldering can release fumes that are harmful and/or toxic to humans. It is highly recommended to use a device that can remove the fumes from the work area either by ventilating outside or filtering the air.
Lead-free.
Lead free soldering requires higher soldering temperatures than lead/tin soldering. SnPb 63/37 eutectic solder melts at . SAC lead-free solder melts at .
Nevertheless, many new technical challenges have arisen with this endeavor. To reduce the melting point of tin-based solder alloys, various new alloys have had to be researched, with additives of copper, silver, bismuth as typical minor additives to reduce the melting point and control other properties. Additionally, tin is a more corrosive metal, and can eventually lead to the failure of solder baths.
Lead-free construction has also extended to components, pins, and connectors. Most of these pins used copper frames, and either lead, tin, gold or other finishes. Tin finishes are the most popular of lead-free finishes. Nevertheless, this brings up the issue of how to deal with tin whiskers. The current movement brings the electronics industry back to the problems solved in the 1960s by adding lead. JEDEC has created a classification system to help lead-free electronic manufacturers decide what provisions to take against whiskers, depending upon their application.


Non-circular gear

A non-circular gear (NCG) is a special gear design with special characteristics and purpose. While a regular gear is optimized to transmit torque to another engaged member with minimum noise and wear and with maximum efficiency, a non-circular gear's main objective might be ratio variations, axle displacement oscillations and more. Common applications include textile machines, potentiometers, CVTs (continuously variable transmissions), window shade panel drives, mechanical presses and high torque hydraulic engines.
A regular gear pair can be represented as two circles rolling together without slip. In the case of non-circular gears, those circles are replaced with anything different from a circle. For this reason NCGs in most cases are not round, but round NCGs looking like regular gears are also possible (small ratio variations result from meshing area modifications).
Generally NCG should meet all the requirements of regular gearing, but in some cases, for example variable axle distance, could prove impossible to support and such gears require very tight manufacturing tolerances and assembling problems arise. Because of complicated geometry, NCGs are most likely spur gears and molding or electrical discharge machining technology is used instead of generation.
Mathematical description.
Ignoring the gear teeth for the moment (i.e. assuming the gear teeth are very small), let formula_1 be the radius of the first gear wheel as a function of angle from the axis of rotation formula_2, and let formula_3 be the radius of the second gear wheel as a function of angle from its axis of rotation formula_4. If the axles remain fixed, the distance between the axles is also fixed:
Assuming that the point of contact lies on the line connecting the axles, in order for the gears to touch without slipping, the velocity of each wheel must be equal at the point of contact and perpendicular to the line connecting the axles, which implies that:
Each wheel must be cyclic in its angular coordinates. If the shape of the first wheel is known, the shape of the second can often be found using the above equations. If the relationship between the angles is specified, the shapes of both wheels can often be determined analytically as well.
It is more convenient to use the circular variable formula_7 when analyzing this problem. Assuming the radius of the first gear wheel is known as a function of "z", and using the relationship formula_8, the above two equations can be combined to yield the differential equation:
where formula_10 and formula_11 describe the rotation of the first and second gears respectively. This equation can be formally solved as:
where formula_13 is a constant of integration.


3D metal moulding

3D metal moulding, also referred to as metal injection moulding or (MIM), is used to manufacture components with complex geometries. The process uses a mixture of metal powders and polymer binders – also known as "feedstock" – which are then injection-moulded.
After moulding, the parts are thermally processed in order to remove the binding agent. They are then sintered to a high-density metal component which has mechanical properties comparable to wrought materials.
3D metal moulding is mainly used to achieve intricate and complex shapes that are very difficult or expensive to produce using conventional manufacturing methods.
Applications.
3D metal molding is used in aerospace, medical and other industries. Its popularity is due to its strength in the form of a custom shape or part. More commonly found as a 3D mold are thermoplastic and thermosetting polymers. Both of these processes are used in the following industries:
3D metal printing.
3D metal printing builds components by delivering the powdered metal and binder in alternative layers through a nozzle controlled by a computer system, working to a CAD drawing. The initial process does not achieve the required strength so parts must go through a secondary process which involves fusing another type of metal into the shape.
There are multiple methods used in 3D metal printing. Selective laser sintering, or SLS, uses heat from a powerful laser to fuse tiny ceramic, glass or plastic particles together, forming a 3D part. Carl Deckard and Joe Beaman of the University of Texas developed and patented the process in the 1980s.
Direct metal laser sintering, or DMLS, uses a laser to sinter powdered metal into a solid object in gradual layers built upon each other. Cooling channels can be printed to any shape in this process, which lessens time and waste and improves quality.
Selective laser melting, or SLM, completely melts the powder to form a homogeneous part. This process can only be used for single materials, so is not suitable for alloys.


Pentalobular screw thread

A pentalobular screw thread is a form of self-forming thread used for screws. Self-forming screws are used in ductile materials, such as aluminium and plastics.
Self-tapping screws are widely used for driving into sheet metal or plastics and forming their own thread. They may be either self-drilling, forming their own hole through unbroken material, or fitted into a pre-pierced hole. Self-drilling screws have some ability to cut a thread, as for a tap. Others work not by cutting, but rather by roll-forming the thread, pushing excess material out of the way by plastic deformation. This is one reason why ductile host materials, rather than brittle, are needed.
To form a close-fitting thread that will not be loose afterwards, roll-forming requires a lobed tool rather than a constant diameter cylindrical tool. This is particularly the case when the tool and the fastener are the same, such as for a screw. A lobed or polygonal form allows residual compressive stresses from the forming parts of the thread to be relieved in the undercut clearance between the lobes.
This lobular thread has other advantages too. It allows the screw to be turned with lower torque, which also increases the 'strip-to-drive ratio' between the torques needed to drive the screw in or to damagingly strip the threads out. The proportions of the lobular thread can also change over the length of the screw, so that the tip of the screw can use greater lobulation to form the thread more aggressively and also provide a centring effect.
In conjunction with a thread profile with sharp arrises, a three-lobed thread of this form is the basis of the well-known Taptite screws.
The optimum number of lobes is five. Their number should be prime, to avoid the usual harmonic effects between lobes. As is already widely recognised with tapered reamers, five has better stability than three in imperfectly circular holes. More lobes than this, such as seven, would reduce the spacing for clearance between the lobes. A patent has been applied for about a thread with such an optimised pentalobular form.
Such thread forms are not a new innovation. A patent for machinery to roll-form the threads of the screws was granted in 1975.


Operation chart

The operation chart is a graphical and symbolic representation of the manufacturing operations used to produce a product. The operation chart illustrates only the value-adding activities in the manufacturing process; therefore, material handling and storage are not illustrated in this chart. operation chart records the overall picture of process and sequencewise steps of operations.
Operations and their symbols in the operation chart.
The operations described in the operation chart are:


Instrumentation and control engineering

Instrumentation and control engineering (ICE) is a branch of engineering that studies the measurement and control of process variables, and the design and implementation of systems that incorporate them. Process variables include pressure, temperature, humidity, flow, pH, force and speed.
ICE combines two branches of engineering. Instrumentation engineering is the science of the measurement and control of process variables within a production or manufacturing area. Meanwhile, control engineering, also called control systems engineering, is the engineering discipline that applies control theory to design systems with desired behaviors.
Control engineers are responsible for the research, design, and development of control devices and systems, typically in manufacturing facilities and process plants. Control methods employ sensors to measure the output variable of the device and provide feedback to the controller so that it can make corrections toward desired performance. Automatic control manages a device without the need of human inputs for correction, such as cruise control for regulating a car's speed.
Control systems engineering activities are multi-disciplinary in nature. They focus on the implementation of control systems, mainly derived by mathematical modeling. Because instrumentation and control play a significant role in gathering information from a system and changing its parameters, they are a key part of control loops.
As profession.
High demand for engineering professionals is found in fields associated with process automation. Specializations include industrial instrumentation, system dynamics, process control, and control systems. Additionally, technological knowledge, particularly in computer systems, is essential to the job of an instrumentation and control engineer; important technology-related topics include human–computer interaction, programmable logic controllers, and SCADA. The tasks center around designing, developing, maintaining and managing control systems.
The goals of the work of an instrumentation and control engineer are to maximize:
As academic discipline.
Many universities teach instrumentation and control engineering as an academic courses at the graduate and postgraduate levels. It is possible to approach this field coming from many standard engineering backgrounds, being the most common among them Electrical and Mechanical Engineering, since these branches cover strong foundational subjects in control systems, system dynamics, electro-mechanical machines and devices, as well as electric circuits.


The Association for Manufacturing Technology (AMT) is a trade association based in McLean, Virginia, in the United States. It was founded as the National Machine Tool Builders' Association (NMTBA) in 1902. It represents and promotes the interests of American providers of manufacturing machinery and equipment.
As machine tools advanced, NMTBA launched the first National Machine Tool Builders’ Exposition in 1927, which would later be rebranded IMTS- International Manufacturing Technology Show.
The AMT’s most visible activity is its management of the International Manufacturing Technology Show (IMTS), which is held on even-numbered years at McCormick Place in Chicago, Illinois.
Examples of activities fostered by the AMT include:
AMT also supports their membership with technology centers and representative offices in China, India, Poland, Mexico and Brazil.
Other AMT Events.
AMT puts on a number of events throughout the year. While IMTS takes place in every even year, AMT also hosts the MFG Meeting and MTForecast Conference every year.


Spur gear

Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with teeth projecting radially. Viewing the gear at 90 degrees from the shaft length (side on) the tooth faces are straight and aligned parallel to the axis of rotation. Looking down the length of the shaft, a tooth's cross section is usually not triangular. Instead of being straight (as in a triangle) the sides of the cross section have a curved form (usually involute and less commonly cycloidal) to achieve a constant drive ratio. Spur gears mesh together correctly only if fitted to parallel shafts. No axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but tend to be noisy at high speeds.
Spur gear can be classified into two pressure angles, 20° being the current industry standard and 14½° being the former (often found in older equipment). Spur gear teeth are manufactured as either involute profile or cycloidal profile. When two gears are in mesh it is possible that an involute portion of one will contact a non-involute portion of the other gear. This phenomenon is known as "interference" and occurs when the number of teeth on the smaller of the two meshing gears is less than a required minimum. Undercutting (cutting the tooth narrower closer to its base) is sometimes used to avoid interference but is usually not suitable because the decreased thickness leaves the tooth weaker at its base. In this situation, corrected gears are used. In corrected gears the cutter rack is shifted upwards or downwards.
Spur gears can be classified into two main categories: External and Internal. Gears with teeth on the outside of the cylinder are known as "external gears". Gears with teeth on the internal side of the cylinder are known as "internal gears". An external gear can mesh with an external gear or an internal gear. When two external gears mesh together they rotate in the opposite directions. An internal gear can only mesh with an external gear and the gears rotate in the same direction. Due to the close positioning of shafts, internal gear assemblies are more compact than external gear assemblies.
PCD and MOD.
In the case of Module (MOD) 4.0 spur gears:
There are two types of corrected gears:


Airwolf 3D

Airwolf 3D is a Costa Mesa, California-based company that produces 3D printers.
History.
Airwolf was founded in May 2012 by Erick Wolf, a garage mechanic and patent attorney with a mechanical engineering degree, and his wife Eva. The inspiration for the company came from a 3D printer that Erick bought just before Christmas 2011. After encountering difficulty with his goal of getting the printer to print replacement parts for itself, he spent several days working on the printer before determining that it wasn't able to complete the task. The printer was eventually scrapped for parts, and Erick instead began building his own printer, which was named the Airwolf 3D.
The original Airwolf printer (v.4) was derived from the Prusa Mendel and Mecano Air designs, hence the name "Airwolf."
The company started shipping fully assembled 3D printers in June 2012 from their garage in Newport Beach, California. The first printer was sold to Lars Brubaker and Kevin Pope of MatterHackers. MatterHackers went on to develop MatterControl, 3D printing software that works with many 3D printers and is offered in a customized version for Airwolf 3D.
Airwolf's customer base includes Boeing, John Deere, Raytheon, Saleen Automotive and Honeywell — as well as schools and home hobbyists.
Products.
AW3D 5.5.
The AW3D 5.5 was introduced in late 2012 and superseded the v.4 and v.5.
AW3D XL.
The AW3D XL was introduced in January 2013. The maximum printing surface is approximately 12"x 8"x 7". It operates on a RAMBo board made by Ultimachine which offers options for expandability, such as a dual extruder, multiple fans, and several other features including direct heatbed control. The XL 3D printer plays an integral part in “STEAM” academic curricula in Orange Unified School District.
AW3D HD.
The AW3D HD was introduced in November 2013 at the 3D Print Show in Paris, France. It featured a print area of approximately 12"x8"x12." The AW3D HD featured a print volume of 12" x 8" x 12" (1150in³) and had a layer-to-layer resolution of .06mm (.002"). The HD was equipped with a single print head that came standard with a .5mm nozzle or a .35mm nozzle as an option.
AW3D HDL.
The AW3D HDL was the Airwolf 3D base model 3D printer which could be upgraded depending on the user's needs. It was equipped with an un-heated print bed and a single print head capable of sustained temperatures of 260°C (500°F). The AW3D had a print resolution of .08mm with a maximum print speed of 150mm/s. The AW3D had a build volume of 12" x 8" x 11" (1056in³) and came standard with .5mm print nozzle or a .35mm nozzle optional.
AW3D HDx.
The AW3D HDx was introduced in May 2014. It is a 3D printer can build prototypes out of engineering-grade materials like polycarbonate, bridge nylon and nylon 645. The HDx uses the company's JRx hot end and can continuously hold temperatures of up to 599°F, which allows 3D printing in more durable materials. The HDx was selected as Editor's Pick of the Week by Desktop Engineering. The HDX had a print volume of 12" x 8" x 12" (1150in³) and had a layer-to-layer resolution of .06mm (.002"). The HDX came was equipped with the proprietary JRx high-temperature print head and came standard with a .5mm nozzle or an optional .35mm nozzle.
AW3D HD2x.
The AW3D HD2x was a dual-head 3D printer that was introduced in 2014. The HD2x featured a dual print head capable of sustained temperatures of 315 °C(599 °F). The original HD2x was designed for traditional hard-wired printing and slicing functionality; however, wireless capability was later provided by Airwolf 3D's Wolfbox™ wireless controller. The HD2x was capable of printing in two different colors or two different materials simultaneously provided that the two materials had similar extruding temperatures. The HD2x had a print volume of 11" X 8" x 12" (1056in³) and offered a layer-to-layer resolution as fine as .06mm (.002").
AW3D HD-R.
The AW3D HD-R was introduced at the 2015 Consumer Electronics Show. The HD-R was the first Airwolf 3D model to offer integrated WiFi and cloud based slicing, file storage, and file management based on the AstroPrint® platform by 3DaGoGo®. The HD-R could be interfaced via a traditional PC connection or a mobile device. By default an 8” tablet was supplied with the each unit for wireless interface. The HD-R came equipped with dual print heads each capable of sustained temperatures of 315°C (599°F). The dual print head configuration allowed the user to print with two different colors or two different types of filament provided that the filaments had similar extruding temperatures. The HD-R was built with an improved aluminum backbone for rigidity and had a maximum build envelope of 11”x 8”x 12” (1056 in³). The HD-R had a print resolution of .06mm (.002") and came standard with a .5mm nozzle or an optional .35mm nozzle.
AXIOM.
The first in the AXIOM line is made from extruded aluminum and injection molded polycarbonate parts. It has a large build volume of 12.5”x8”x10”, can print layers as fine as 40 microns, and its heated bed, along with the company's proprietary hot end, allow the AXIOM to print in a wide variety of materials, from PLA to Nylon and polycarbonate. And, with the integration of cloud printer management system AstroPrint, the AXIOM can be controlled via the web, as well as USB, micro SD card, or Ethernet.
Wolfbite.
Wolfbite is a 3D printing adhesive to facilitate the bonding and removal of nylon and nylon blend prints from glass and ceramic build plates. The product was formulated to solve the problems of warping and adhesion that are inherent when 3D printing with nylon.
Specifications.
Many components are fabricated using acrylonitrile butadiene styrene (ABS), a common thermoplastic.


Uttara Export Processing Zone

Uttara Export Processing Zone (UEPZ) , also known as Uttara EPZ or Nilphamari EPZ, is the seventh of the eight export processing zone in Bangladesh located at Nilphamari. It's the only export processing zone of Rangpur division/ north Bengal. It was established in September 2001on about 213,66 acres of lands in Sangloshi area in Nilphamari town.
Industrial plot.
There are more than 180 industrial plots in this EPZ. Allocation of 138 plots has been completed. 12 plots are running. 33 plots undeveloped and 09 plots are empty.
Company.
1. Evergreen Products Factory (BD) Ltd.
2. Ventura Leatherware MFY (BD) Ltd.
3. Sonic (Bangladesh) Ltd.
4. Mazen (Bangladesh) Industries Ltd.
5. Kord (BD) Ltd 6. Dong Jin Industrial (BD) Company Ltd.
7. EPF Printing Ltd
8. Oasis Transformation Ltd.
9. EPF Cartoon Ltd.
10. DESHBANDHU TEXTILES MILLS LTD
11. EXPO LINK IND. LTD
12. NILPHAMARI PACKAGING LTD
13. Section Seven International Limited
14. Uttara Sweater Manufacturing Company Limited
15. Viyellatex Apparels Ltd.
16. Independent Export (BD) Ltd.
17. Glorious Export BD Ltd.
18. SKY Star IND. LTD.
19. Fardin Accessories Limited
20. Quest Accessories (BD) Ltd.
21. TN Accessories Ltd.
22. Padma Spining & Composite


Microthermoforming

Microthermoforming is the abbreviation for microscopic or microscale thermoforming, or, more precisely, for thermoforming of microproducts or microstructure products. Microstructure products means products that have structures in the micrometre range and have their technical function provided by the shape of the microstructure [1]. Thermoforming [2] in turn means shaping of heated and therefore softened semi finished products in the form of thermoplastic polymer films or plates with their edges fixed by three-dimensional stretching. Shaping is carried out mainly by forming the films or plates into female moulds (negative forming) or over male moulds (positive forming). While the other polymer microreplication processes such as micro injection moulding or (vacuum) hot embossing are primary forming processes where forming occurs already in a molten, liquid phase of the heated polymer material, microthermoforming is a secondary forming process where forming occurs in a strongly softened, but still solid phase of the heated polymer.
Moulds for polymer microreplication in general and in particular for microthermoforming can be fabricated by various methods such as mechanical micromachining, lithographic based methods in combination with electroplating (see also the so-called 'LIGA' process) and wet or dry etching. And they can be fabricated of various materials such as metal, silicon and glass.
State of the art.
For several years now, at Karlsruhe Institute of Technology (KIT), a pressure or high pressure (thermo)forming process is used to fabricate film microchips for capillary electrophoresis (CE) [3–5] and for three-dimensional cell cultivation [6–8]. The process is derived from the macroscopic trapped sheet forming process [2]. This is a simple variation of vacuum or pressure forming without prestretching, i.e. a single stage forming, into a female mould with heating of the plastic sheet using a contact heating plate inside the forming station. The forming air is supplied via through holes in the heating plate. Still in a laboratory scale process, diverse thermoplastic films also from biodegradable polymers such as polycaprolactone (PCL) with thicknesses typically between 20 and 100 μm are thermoformed. This is performed with gas pressures up to 5 MPa into mechanically micromachined cavities of plate shaped micromoulds from brass.
First examples of processes coming near to something that could be called 'microthermoforming' originate from the second half of the nineties. So, in 1993, dome shaped polymer microstructures for use in electrical membrane switches were fabricated [9]. This was done between a mating upper and lower metal emboss die with a concave and a convex detail, respectively, first in a hot, then in a second cold press. And in 1999, corrugated sheet like polymer microstructures for use e.g. in electrostatic actuators were fabricated [10]. This was also done between heated tools and counter tools, namely in discontinuous processes between stamps or in continuous processes between rollers. Partly, the counter tool was a soft one in the form of a thicker, unpatterned film or plate made from an easily deformable, e.g. elastomeric material which is able to assume the shape of the hard, metallic tool. In 2006, at the School of Polymer, Textile and Fiber Engineering (PTFE) of the Georgia Institute of Technology (GIT), the same technology approach was used to fabricate similar corrugated sheet like structures in a so-called 'rubber-assisted hot embossing process' [11].
Features and applications.
The microthermoforming process including its products can have all the advantageous properties of the powerful macroscopic production process. Moreover, the thermoformed microparts have additional, specific properties appearing only in microscale dimensions and resulting from their unusual morphology. Thermoformed e.g. microfluidic structures have free standing microcavities such as channels and reservoirs and they are thin walled partly in the range of a few micrometers. Specific properties of thermoformed microparts are, amongst others, their high flexibility, their small volume and mass, their low thermal resistance and heat capacity, and their low light absorbance and background fluorescence. Morphology and properties of these microparts now can result in improved or even new, so far unthought of applications.
Compared to the other microreplication processes, in microthermoforming, modifications of the film to be formed remain preserved beyond the forming step due to the already mentioned material coherence during this secondary forming process. This enables surface and bulk modification and functionalisation of the three-dimensionally formed films or membranes, namely as highly resolved micro- and nanopatterns, and all side, i.e. on hardly accessible side walls and even behind undercuts. Thus, e.g. thermoformed chips for three-dimensional cell cultivation can be provided with pores, cell adhesion patterns [6–8], surface topologies and electrodes [12].
Future application fields for microthermoforming are expected to be


Electron-beam additive manufacturing

Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material (metal powder or wire) is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.
Metal powder-based systems.
Metal powders can be consolidated into a solid mass using an electron beam as the heat source. Parts are manufactured by melting metal powder, layer by layer, with an electron beam in a high vacuum.
This powder bed method produces fully dense metal parts directly from metal powder with characteristics of the target material. The EBM machine reads data from a 3D CAD model and lays down successive layers of powdered material. These layers are melted together utilizing a computer-controlled electron beam. In this way it builds up the parts. The process takes place under vacuum, which makes it suited to manufacture parts in reactive materials with a high affinity for oxygen, e.g. titanium. The process is known to operate at higher temperatures (up to 1000 °C), which can lead to differences in phase formation though solidification and solid-state phase transformation.
The powder feedstock is typically pre-alloyed, as opposed to a mixture. That aspect allows classification of EBM with selective laser melting (SLM), where competing technologies like SLS and DMLS require thermal treatment after fabrication. Compared to SLM and DMLS, EBM has a generally superior build rate because of its higher energy density and scanning method.
Research developments.
Recent work has been published by ORNL, demonstrating the use of EBM technology to control local crystallographic grain orientations in Inconel. After testing in the transmission electron microscope by the state-of-the-art in-situ technique, the EBM Inconel alloy has been proved to exhibit similar mechanical property comparing to a wrought Inconel alloy. Other notable developments have focused on the development of process parameters to produce parts out of alloys such as copper, niobium, Al 2024, bulk metallic glass, stainless steel, and titanium aluminide. Currently commercial materials for EBM include commercially pure Titanium, Ti-6Al-4V, CoCr, Inconel 718, and Inconel 625.
Metal wire-based systems.
Another approach is to use an electron beam to melt welding wire onto a surface to build up a part. This is similar to the common 3D printing process of fused deposition modeling, but with metal, rather than plastics. With this process, an electron-beam gun provides the energy source used for melting metallic feedstock, which is typically wire. The electron beam is a highly efficient power source that can be both precisely focused and deflected using electromagnetic coils at rates well into thousands of hertz. Typical electron-beam welding systems have high power availability, with 30- and 42-kilowatt systems being most common. A major advantage of using metallic components with electron beams is that the process is conducted within a high-vacuum environment of 1 Torr or greater, providing a contamination-free work zone that does not require the use of additional inert gases commonly used with laser and arc-based processes. With EBDM, the feedstock material is fed into a molten pool created by the electron beam. Through the use of computer numeric controls (CNC), the molten pool is moved about on a substrate plate, adding material just where it is needed to produce the near net shape. This process is repeated in a layer-by-layer fashion until the desired 3D shape is produced.
Depending on the part being manufactured, deposition rates can range up to per hour. With a light alloy, such as titanium, this translates to a real-time deposition rate of per hour. A wide range of engineering alloys are compatible with the EBDM process and are readily available in the form of welding wire from an existing supply base. These include, but are not limited to, stainless steels, cobalt alloys, nickel alloys, copper nickel alloys, tantalum, titanium alloys, as well as many other high-value materials.
Market.
Titanium alloys are widely used with this technology, which makes it a suitable choice for the medical implant market.
CE-certified acetabular cups are in series production with EBM since 2007 by two European orthopedic implant manufacturers, Adler Ortho and Lima Corporate.
The U.S. implant manufacturer Exactech has also received FDA clearance for an acetabular cup manufactured with the EBM technology.
Aerospace and other highly demanding mechanical applications are also targeted, see Rutherford rocket engine.
The EBM process has been developed for manufacturing parts in gamma titanium aluminide and is currently being developed by Avio S.p.A. and General Electric Aviation for the production of turbine blades in γ-TiAl for gas-turbine engines.
The first EBM machine in the United States is housed by the Department of Industrial and Systems Engineering at North Carolina State University.


Laser-hybrid welding

Laser-hybrid welding is a type of welding process that combines the principles of laser beam welding and arc welding.
The combination of laser light and an electrical arc into an amalgamated welding process has existed since the 1970s, but has only recently been used in industrial applications. There are three main types of hybrid welding process, depending on the arc used: TIG, plasma arc or MIG augmented laser welding. While TIG-augmented laser welding was the first to be researched, MIG is the first to go into industry and is commonly known as hybrid laser welding.
Whereas in the early days laser sources still had to prove their suitability for industrial use, today they are standard equipment in many manufacturing enterprises.
The combination of laser welding with another weld process is called a "hybrid welding process". This means that a laser beam and an electrical arc act simultaneously in one welding zone, influencing and supporting each other.
Laser.
Laser welding not only requires high laser power but also a high quality beam to obtain the desired "deep-weld effect". The resulting higher quality of beam can be exploited either to obtain a smaller focus diameter or a larger focal distance. A variety of laser types are used for this process, in particular where the laser light can be transmitted via a water-cooled glass fiber. The beam is projected onto the workpiece by collimating and focusing optics. Carbon dioxide laser can also be used where the beam is transmitted via lens or mirrors.
Laser-hybrid process.
For welding metallic objects, the laser beam is focused to obtain intensities of more than 1 MW/cm2. When the laser beam hits the surface of the material, this spot is heated up to vaporization temperature, and a vapor cavity is formed in the weld metal due to the escaping metal vapor. This is known as a keyhole. The extraordinary feature of the weld seam is its high depth-to-width ratio. The energy-flow density of the freely burning arc is slightly more than 100 kW/cm2. Unlike a dual process where two separate weld processes act in succession, hybrid welding may be viewed as a combination of both weld processes acting simultaneously in one and the same process zone. Depending on the kind of arc or laser process used, and depending on the process parameters, the two systems will influence each other in different ways.
The combination of the laser process and the arc process results in an increase in both weld penetration depth and welding speed (as compared to each process alone). The metal vapor escaping from the vapor cavity acts upon the arc plasma. Absorption of the laser radiation in the processing plasma remains negligible. Depending on the ratio of the two power inputs, the character of the overall process may be mainly determined either by the laser or by the arc.
Absorption of the laser radiation is substantially influenced by the temperature of the workpiece surface. Before the laser welding process can start, the initial reflectance must be overcome, especially on aluminum surfaces. This can be achieved by preheating the material. In the hybrid process, the arc heats the metal, helping the laser beam to couple in. After the vaporisation temperature has been reached, the vapor cavity is formed, and nearly all radiation energy can be put into the workpiece. The energy required for this is thus determined by the temperature-dependent absorption and by the amount of energy lost by conduction into the rest of the workpiece. In laser-hybrid welding, using MIG, vaporisation takes place not only from the surface of the workpiece but also from the filler wire, so that more metal vapor is available to facilitate the absorption of the laser radiation.
Fatigue behavior.
Over the years a great deal of research has been done to understand fatigue behavior, particularly for new techniques like laser-hybrid welding, but knowledge is still limited. Laser-hybrid welding is an advanced welding technology that creates narrow deep welds and offers greater freedom to control the weld surface geometry. Therefore, fatigue analysis and life prediction of hybrid weld joints has become more important and is the subject of ongoing research.


Changeover

In manufacturing, changeover is the process of converting a line or machine from running one product to another. Changeover times can last from a few minutes to as much as several weeks in the case of automobile manufacturers retooling for new models. Reducing changeover times became a popular way to reduce waste in Lean manufacturing after Taiichi Ohno and Shingo Shigeo popularized the SMED (Single Minute Die Exchange) method in the, now famous, Toyota Production System (TPS). The terms "set-up" and "changeover" are sometimes used interchangeably however this usage is incorrect. Set-up is only one component of changeover. Example: A soft drink bottler may run 16oz glass bottles one day, perform a changeover on the line and then run 20oz plastic bottles the next day.
The 3 Ups.
Changeover can be divided into the 3 Ups:
Clean-up.
"Clean-up product, materials and components from the line. It may range from minor, if only the label of a package is being changed (for example from an English to a Spanish label) to major, requiring complete disassembly of the equipment, cleaning and sterilizing of the line components in the case of an injectable pharmaceutical product.
Set-up.
"Set-up" is the process of actually converting the equipment. This may be achieved by adjusting the equipment to correspond to the next product or by changing non-adjustable "change parts" to accommodate the product. Typically it will be a combination of both.
Start-up.
"Start-up" is the time spent fine tuning the equipment after it has been restarted. It is characterized by frequent stoppages, jams, quality rejects and other problems. It is generally caused by variability in the clean-up and set-up or by variability in the product or its components.


Sherlock Automated Design Analysis

Sherlock Automated Design Analysis is a software tool developed by DfR Solutions for analyzing, grading, and certifying the expected reliability of products at the circuit card assembly level. Based on the science of Physics of Failure, Sherlock predicts failure mechanism-specific failure rates over time using a combination of finite element method and material properties to capture stress values and first order analytical equations to evaluate damage evolution. The software is designed for use by design and reliability engineers and managers in the electronics industry. DfR Solutions is based in Beltsville, Maryland, USA, and was acquired by ANSYS, Inc. in May 2019.
Approach.
Users upload either a complete design package, like ODB++ or IPC-2581, or individual data packets, such as Gerber, Bill of Materials, and Pick and Place files.
Sherlock incorporates stresses from a variety of environments into its physics-based prediction algorithms, including elevated temperature, thermal cycling, vibrations (random and harmonic), mechanical shock and electrical stresses (voltage, current, power). Sherlock then performs several different types of reliability analysis and provides the useful (constant failure rate) and wear out (increasing failure rate) portions of the life curve for each mechanism-component combination. The specific mechanisms that are evaluated and predicted include low-cycle solder fatigue due to thermal cycling, high-cycle solder fatigue due to vibration, solder cracking/component cracking/pad cratering due to mechanical shock or excessive flexure, lead fatigue, wire bond fatigue, via fatigue, electromigration, time dependent dielectric breakdown, hot-carrier injection, and negative bias temperature instability. Published research has indicated that the physics of failure-based predictions are highly accurate and are now used to validate other techniques.
These individual life curves are then summed to provide a physics-based reliability curve for the overall product. Sherlock also provides design rule checks (DRC) for board-level design (schematic and layout) and an overall reliability score. The reliability scoring, which is provided for the overall products – as well as individual scores and commentary for each area of analysis is used when physics-based quantitative predictions are not possible. The analysis is delivered both in PDF and HTML format. Depending on the types of analysis run and the data entered to create the analysis, reports can run between 20 and over 200 pages in length.
The semiconductor module is in compliance with SAE ARP 6338 and is being considered as a replacement to traditional empirical reliability prediction methods (MIL-HDBK-217, Telcordia SR-332, FIDES, and Siemens SN29500) in predicting the reliability of semiconductor devices.
A graphical interface allows users to examine results, make iterations, and pre-perform analyses as necessary. The software does not allow the user to make permanent changes to the electronic design. This activity takes place within the original EDA or CAD software. Sherlock is compatible with Abaqus, Ansys, and Siemens NX.
Outputs.
Sherlock Automated Design Analysis produces the following outputs:
Version History.
Sherlock Automated Design Analysis was launched in April 2011. Subsequent releases include
Market Acceptance.
A company has reported requiring suppliers use Sherlock to reduce risk and help accelerate design validation and product verification.


Ball transfer unit

Ball transfer units are omnidirectional load-bearing spherical balls mounted inside a restraining fixture. They are identical in principle to a computer trackball (pointing device). Typically the design involves a single large ball supported by smaller ball bearings.
They are commonly used in an inverted ball up position where objects are quickly moved across an array of units, known as a ball transfer table, a type of conveyor system. This permits manual transfer to and from machines and between different sections of another conveyor system. They are used in airports for luggage delivery, or in industry as part of manufacturing systems. Prior to the invention of the ball transfer unit, first patented by Autoset Production Ltd in 1958, these applications were solved by the use of inverted casters. However, casters recognise a trail, meaning that the wheels had to align before directional change could be achieved.
Ball transfer units can also be used in a non-inverted ball down position as a type of caster, however this use is restricted by load-bearing limitations and the type of floor. Manufacturers have addressed this problem with ball transfer units incorporating recirculating ball principles, however the inverted position is still the most common application and the least problematic.


Toyota Motors Tohoku

Toyota Motors Tohoku was an auto parts manufacturing subcontractor under the Toyota Group. The company was created in July 1997 in Taiwa, Miyagi, Japan.
On July 1, 2012, three Toyota subcontractors Central Motors, Toyota Motors Tohoku, and Kanto Auto Works assumed operations as a combined company, with all manufacturing facilities and assets of the three former companies to now be known as Toyota Motor East Japan, Inc.


Wetting current

In electrical and electronics engineering, wetting current is the minimum electric current needing to flow through a contact to break through the surface film resistance at a contact. It is typically far below the contact's nominal maximum current rating.
A thin film of oxidation, or an otherwise passivated layer, tends to form in most environments, particularly those with high humidity, and, along with surface roughness, contributes to the contact resistance at an interface. Providing a sufficient amount of wetting current is a crucial step in designing systems that use delicate switches with small contact pressure as sensor inputs. Failing to do this might result in switches remaining electrically "open" when pressed, due to contact oxidation.
Capacitor discharge solution.
In some low voltage applications, where switching current is below the manufacturer's wetting current specification, a capacitor discharge method may be employed by placing a small capacitor across the switch contacts to boost the current through contact surface upon contact closure.
Sealing current.
A related term sealing current (aka wetting current or fritting current) is widely used in the telecommunication industry describing a small constant DC current (typically 1-20 mA) in copper wire loops in order to avoid contact oxidation of contacts and splices. It is defined in ITU-T G.992.3 for "all digital mode ADSL" as a current flowing from the ATU-C (ADSL Linecard) via the phone lines to the ATU-R (CPE). Carbon brushes develop high resistance glaze when they're used without current flow for an extended period. A special circuit is utilized for turbines and generators to introduce current through the brushes into the shaft to prevent this contact fritting.
Contact cleaner.
Contact cleaner can be applied to the contact surfaces to inhibit the formation of resistive surface films and/or to ameliorate existing films.


Drawing (manufacturing)

Drawing is a metalworking process that uses tensile forces to elongate metal, glass, or plastic. As the material is drawn (pulled), it stretches and becomes thinner, achieving a desired shape and thickness. Drawing is classified into two types: sheet metal drawing and wire, bar, and tube drawing. Sheet metal drawing is defined as a plastic deformation over a curved axis. For wire, bar, and tube drawing, the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually performed at room temperature, thus classified as a cold working process; however, drawing may also be performed at higher temperatures to hot work large wires, rods, or hollow tubes in order to reduce forces.
Drawing differs from rolling in that pressure is not applied by the turning action of a mill but instead depends on force applied locally near the area of compression. This means the maximal drawing force is limited by the tensile strength of the material, a fact particularly evident when drawing thin wires.
The starting point of cold drawing is hot-rolled stock of a suitable size.
Metal.
Successful drawing depends on the flow and stretch of the material. Steels, copper alloys, and aluminium alloys are commonly drawn metals.
In sheet metal drawing, as a die forms a shape from a flat sheet of metal (the "blank"), the material is forced to move and conform to the die. The flow of material is controlled through pressure applied to the blank and lubrication applied to the die or the blank. If the form moves too easily, wrinkles will occur in the part. To correct this, more pressure or less lubrication is applied to the blank to limit the flow of material and cause the material to stretch or set thin. If too much pressure is applied, the part will become too thin and break. Drawing metal requires finding the correct balance between wrinkles and breaking to achieve a successful part.
Sheet metal drawing becomes deep drawing when the workpiece is longer than its diameter. It is common that the workpiece is also processed using other forming processes, such as piercing, ironing, necking, rolling, and beading. In shallow drawing, the depth of drawing is less than the smallest dimension of the hole.
Bar, tube, and wire drawing all work upon the same principle: the starting stock is drawn through a die to reduce its diameter and increase its length. Usually, the die is mounted on a draw bench. The starting end of the workpiece is narrowed or pointed to get the end through the die. The end is then placed in grips which pull the rest of the workpiece through the die.
Drawing can also be used to cold form a shaped cross-section. Cold drawn cross-sections are more precise and have a better surface finish than hot extruded parts. Inexpensive materials can be used instead of expensive alloys for strength requirements, due to work hardening. Bars or rods that are drawn cannot be coiled; therefore, straight-pull draw benches are used. Chain drives are used to draw workpieces up to . Hydraulic cylinders are used for shorter length workpieces. The reduction in area is usually restricted to between 20% and 50%, because greater reductions would exceed the tensile strength of the material, depending on its ductility. To achieve a certain size or shape, multiple passes through progressively smaller dies and intermediate anneals may be required. Tube drawing is very similar to bar drawing, except the beginning stock is a tube. It is used to decrease the diameter, improve surface finish, and improve dimensional accuracy. A mandrel may or may not be used depending on the specific process used. A floating plug may also be inserted into the inside diameter of the tube to control the wall thickness. Wire drawing has long been used to produce flexible metal wire by drawing the material through a series of dies of decreasing size. These dies are manufactured from a number of materials, the most common being tungsten carbide and diamond.
The cold drawing process for steel bars and wire is as follows:
Glass.
Similar drawing processes are applied in glassblowing and in making glass and plastic optical fiber.
Plastics.
Plastic drawing, sometimes referred to as "cold drawing", is the same process as used on metal bars, applied to plastics. Plastic drawing is primarily used in manufacturing plastic fibers. The process was discovered by Julian W. Hill in 1930 while trying to make fibers from an early polyester.
It is performed after the material has been "spun" into filaments; by extruding the polymer melt through pores of a spinneret. During this process, the individual polymer chains tend to somewhat align because of viscous flow. These filaments still have an amorphous structure, so they are drawn to align the fibers further, thus increasing crystallinity, tensile strength, and stiffness. This is done on a draw twister machine. For nylon, the fiber is stretched to four times its spun length. The crystals formed during drawing are held together by hydrogen bonds between the amide hydrogens of one chain and the carbonyl oxygens of another chain. Polyethylene terephthalate (PET) sheet is drawn in two dimensions to make BoPET (biaxially-oriented polyethylene terephthalate) with improved mechanical properties.