End mill

An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most milling bits can cut in the radial direction. Not all mills can cut axially; those designed to cut axially are known as end mills.
End mills are used in milling applications such as profile milling, tracer milling, face milling, and plunging.
Types.
Several broad categories of end- and face-milling tools exist, such as center-cutting versus non-center-cutting (whether the mill can take plunging cuts); and categorization by number of flutes; by helix angle; by material; and by coating material. Each category may be further divided by specific application and special geometry.
A very popular helix angle, especially for general cutting of metal materials, is 30°. For finishing end mills, it is common to see more tight spiral, with helix angles 45° or 60°. Straight flute end mills (helix angle 0°) are used in special applications, like milling plastics or composites of epoxy and glass. Straight flute end mills were also used historically for metal cutting before invention of helical flute end mill by Carl A. Bergstrom of Weldon Tool Company in 1918.
There exist end mills with variable flute helix or pseudo-random helix angle, and discontinuous flute geometries, to help break material into smaller pieces while cutting (improving chip evacuation and reducing risk of jamming) and reduce tool engagement on big cuts. Some modern designs also include small features like the corner chamfer and chipbreaker. While more expensive, due to more complex design and manufacturing process, such end mills can last longer due to less wear and improve productivity in high speed machining (HSM) applications.
It is becoming increasingly common for traditional solid end mills to be replaced by more cost-effective inserted cutting tools (which, though more expensive initially, reduce tool-change times and allow for the easy replacement of worn or broken cutting edges rather than the entire tool). Another advantage of indexable end mills(another term for tools with inserts) is their ability to be flexible with what materials they can work on, rather than being specialized for a certain material type like more traditional end mills. For the time being however, this only generally applies to larger diameter end mills, at or above 3/4 of an inch. These end mills are generally used for roughing operation, whereas traditional end mills are still used for finishing and work where a smaller diameter, or a tighter tolerance, are required; modular tooling introduces additional margins of error that can compound with each new component, whereas a solid tool can provide a smaller tolerance range for the same price level.
End mills are sold in both imperial and metric shank and cutting diameters. In the USA, metric is readily available, but it is only used in some machine shops and not others; in Canada, due to the country's proximity to the US, much the same is true. In Asia and Europe, metric diameters are standard.
Geometry.
A variety of grooves, slots, and pockets in the work-piece may be produced from a variety of tool bits. Common tool bit types are: square end cutters, ball end cutters, t-slot cutters, and shell mills. Square end cutters can mill square slots, pockets, and edges. Ball end cutters mill radiused slots or fillets. T-slot cutters mill exactly that: T-shaped slots. Shell end cutters are used for large flat surfaces and for angle cuts. There are variations of these tool types as well.
There are four critical angles of each cutting tool: end cutting edge angle, axial relief angle, radial relief angle, and radial rake angle.
Depending on the material being milled, and what task should be performed, different tool types and geometry may be used. For instance, when milling a material like aluminum, it may be advantageous to use a tool with very deep, polished flutes, a very sharp cutting edge and high rake angles. When machining a tough material such as stainless steel, however, shallow flutes and a squared-off cutting edge will optimize material removal and tool life.
A wide variety of materials are used to produce the cutting tools. Carbide inserts are the most common because they are good for high production milling. High speed steel is commonly used when a special tool shape is needed, not usually used for high production processes. Ceramics inserts are typically used in high speed machining with high production. Diamond inserts are typically used on products that require tight tolerances, typically consisting of high surface qualities (nonferrous or non-metallic materials).
In the early 90s, use of coatings became more common. Coatings can provide various benefits including wear resistance, reduction of friction to assist with chip evacuation, and increased heat resistance. Most of these coatings are referred to by their chemical composition.
Though PCD veins is not a coating, some end mills are manufactured with a 'vein' of polycrystalline diamond. The vein is formed in a high temperature-high pressure environment. The vein is formed in a blank and then the material is ground out along the vein to form the cutting edge. Although the tools can be very costly, they can last many times longer than other tooling.
Advances in end mill coatings are being made, however, with coatings such as Amorphous Diamond and nanocomposite PVD coatings beginning to be seen at high-end shops (as of 2004).
Although coatings have a typical color, manufacturers may modify the coating process or add additives to change the appearance without affecting the performance as part of their branding. Bright blues, reds and turquoise are among the "unnatural" colors.
End mills are typically made on CNC (computer numeric controlled) tool and cutter grinder machines under high-pressure lubricants such as water, water-soluble oil, and high-flashpoint oil. Grinding inside the machine is accomplished with abrasive wheels mounted on a spindle (and in some cases, multiple spindles). Depending on what material is being ground, these wheels are made with industrial diamond (when grinding tungsten carbide), cubic boron nitride (when grinding cobalt steel), and other materials (when grinding, for instance, ceramics), set in a bond (sometimes copper).
Flute types.
Single: Is used to remove lots of material at a very fast rate. Traditionally used in a roughing operation.
2 Flute: Allows for more chips to be removed from the part. Primarily used in slotting and pocketing operations in non-ferrous materials.
3 Flute: Similar to the 2 Flute end mill but can be used to cut ferrous and non-ferrous materials
4+ Flute: Designed to run at faster feed rates but due to having more flutes it causes issues with chip removal.
Operations.
Roughing: the purpose is to remove a big chunk of material from workpieces, sometimes to get rid of excess material in order to get closer to the final shape. It attempts to get really close to the finalized shape. Traditionally it's the first major operation in the machining process.
Contouring/Profiling: this is a process used to mill different surfaces such as flat or irregular ones. This type of process can be done during the roughing or finishing phase of the overall operation.
Facing: is an operation used to face the part down to specified dimension. Facing can be done using end mills or a special face mill.
Pocketing/Slotting: this is a process to make a pocket on the inside of the part. A pocket can be shallow or deep, depending on specs.


Thickness planer

A thickness planer (also known in the UK and Australia as a thicknesser or in North America as a planer) is a woodworking machine to trim boards to a consistent thickness throughout their length.
This machine transcribes the desired thickness using the downside as a reference / index. So, to produce a completely straight planed board requires that the down surface is straight before planing. Obtaining the first flat side requires either face planing with a jointer or face planing using a planer and jointer sled.
Function.
A thickness planer is a woodworking machine to trim boards to a consistent thickness throughout their length and flat on both surfaces.
It is different from a surface planer, or jointer, where the cutter head is set into the bed surface. A surface planer has slight advantages for producing the first flat surface and may be able to do so in a single pass. However the thicknesser has more important advantages in that it can produce a board with a consistent thickness, avoids producing a tapered board, and by making passes on each side and turning the board, may also be used for the initial preparation of an unplaned board.
Design.
A thickness planer consists of three elements: a cutter head which contains the cutting knives; a set of rollers which draw the board through the machine; and a table which is adjustable relative to the cutter head to control the resultant thickness of the board. Some portable thickness planers differ slightly in that the table is fixed and the cutter head/feed roller assembly is adjusted.
Industrial thickness planers are capable of accepting very wide boards and removing large amounts of material in a single pass. These machines are driven by powerful motors and are of very heavy construction. In recent times, a range of lightweight portable thickness planers have become available which use the cheaper, but noisy, universal motors rather than induction motors and are much less expensive than industrial versions.
In Europe, the functions of the jointer and thickness planer are often combined into a single combination machine, a jointer-planer. In the U.K. this is called a "planer–thicknesser" or "over–and–under".
Operation.
In operation, the table is set to the desired height and then the machine is switched on. The board is fed into the machine until it makes contact with the in-feed roller which grips the board and draws it into the machine and past the rotating cutter head. The knives remove material on the way through and the out-feed roller pulls the board through and ejects it from the machine at the end of the pass.
To finish a board that is flat and of uniform thickness along its length, it is necessary to start with a board that has at least one perfectly flat reference face. The board is fed with this reference face flat on the table and the cutter head removes an amount of material from the opposite face so that it is made parallel to the reference face. The reference face is often created by first passing the board over a jointer. If the lower face is not flat, the feed roller pressure pressing the board against the table will deform the board, which will then spring back as it leaves the machine, resulting in a non-flat upper surface.
One problem often encountered when using a thickness planer is snipe. This manifests as a deeper cut on a short section of the board at either end and is caused by incorrect feeding or misalignment of the in-feed or out-feed tables, or an unnecessarily high setting of the rollers recessed in the surface of the in-feed table. It can be accommodated by keeping the board overlong to allow later trimming.


Conformal cooling channel

Conformal cooling channel is a cooling passageway which follows the shape or profile of the mould core or cavity to perform rapid uniform cooling process for injection moulding or blow moulding processes.


Direct clustering algorithm

Direct clustering algorithm (DCA) is a methodology for identification of cellular manufacturing structure within an existing manufacturing shop. The DCA was introduced in 1982 by H.M. Chan and D.A. Milner The algorithm restructures the existing machine / component (product) matrix of a shop by switching the rows and columns in such a way that a resulting matrix shows component families (groups) with corresponding machine groups. See Group technology. The algorithm is executable in manual way but was already suitable for computer use of the time.
Procedure.
The cellular manufacturing structure consists of several machine groups (production cells) where corresponding product groups (products with similar technology) are being exclusively manufactured. In aim of identification of possible cellular manufacturing structure within an existing manufacturing shop the DCA methodology roughly provides following procedure:
The experience.
The DCA methodology would give a perfect result in an ideal case where there are no overlapping machines or products between the groups. The overlapping in most real cases represents further challenge for the methodology users. The "Formation of Machine Cells/ Part Families in Cellular Manufacturing Systems Using an ART-Modified Single Linkage Clustering Approach – A Comparative Study" by M. Murugan and V. Selladurai shows the comparison of DCA to some other methodologies of the same purpose.


2-4-6-2

A 2-4-6-2 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a two-wheel leading truck, one set of four driving wheels, one set of six driving wheels, and a two-wheel trailing truck.
Other equivalent classifications are:
UIC classification: 1BC1 (also known as German classification and Italian classification)
French classification: 1231
This most unusual wheel arrangement was only ever used on a duplex locomotive type.


Saki Corporation

 is a Japanese company established in 1994 that manufactures high-speed automated optical inspection (AOI) and solder paste inspection (SPI) systems for the electronics assembly markets. Saki Corporation has headquarters in Tokyo, Japan with offices and sales and support centers on the world.
Saki Corporation has Quality Management System JIS Q 9001:2008 and certifications. The company's CEO is Koike Norihiro.
AOI.
References


Z-pinning

Z-pinning is a technique to insert reinforcing fibres (also called Z-pins or Z-fibres) along the Z-direction of continuous fibre-reinforced plastics. Z-pins can be made of metal or precured unidirectional composite fibres. It is designed for use within pre-preg technology; there is extensive experimental evidence that Z-pinning dramatically improves the resistance of the composite structure to delamination. The figure on the right shows a Z-pin inserted in between the fibres of the material.  The pin spreads the fibres and creates an oval shaped gap that is filled with resin. The Z-pin prevents the composite from delamination.  When a load is applied the cracks will typically form along the line of the opening.
Benefits.
Z-pinning is a versatile technique that can be applied to many materials that will benefit from added strength and durability. They are especially effective when used in materials that are subject to delamination, because the Z-pins can counteract this problem. Z-pinning has been used in aircraft manufacturing to add strength.  By Z-pinning the materials on an aircraft, such as the wings, it can have a much higher resistance to damage during flight.  Also, if the aircraft does suffer from a minor crack, the Z-pinning will prevent it from catastrophic failure.  Z-pins can also be used for automotive applications. The pins can be inserted into carbon fibre parts to increase the strength of them.  If the front splitter of a car was constructed with Z-pins, it would be able to withstand significantly more impacts because the Z-pins would hold it together even with a minor crack. This allows the carbon fibre parts to remain light while still being strong. Testing of different size Z-pins has indicated that larger pins lead to an increase in strength. A 1% increase in the size of the Z-pin increases toughness by up to 6 to 25 times. However, too large of a pin can disrupts the fibres of the material more leading to it fracturing.
Z-Pin production.
There are many methods of creating Z-pins.  Typically, Z-pins are pre-cured and then inserted into composites. One process consists of pulling a continuous-fibre tow through a bath of liquid resin using a pultrusion machine.  The fibre is then pulled out of the bath through the die which creates the shape and size of the pin.  The pin is next sandwiched in a vertical orientation in foam to finish the process.  The pin may be coated or treated as an additional step depending on the application. This process is one of the more efficient and cost effective ways of producing Z-pins because it can be easily adapted to different pin sizes.
Manufacturing with Z-Pins.
Z-pins have many ways of being inserted into the material of choice. The most common method is a process using an ultrasonic hammer.  The hammer compresses the foam that encases the pins and pushes the pins into the material. The hammer induces high frequency vibrations to the pin as it compresses. The vibrating chamfered tip of the Z-pins locally heats up and softens the resin allowing the Z-fibre to penetrate the preform with minimal disruption of the long fibres. The remaining pin and laminate above the surface are removed to create a smooth and even surface The surface can be finished with a coating to seal the Z-pins inside the material. A hand-held ultrasonic gun can also be used to insert Z-pins on a small scale production. This is ideal for testing materials containing Z-pins because they can be easily inserted into any location on the material.


Velostat

Velostat, also known as Linqstat, is a packaging material made of a polymeric foil (polyolefins) impregnated with carbon black to make it somewhat electrically conductive. It is used for the protection of items or devices that are susceptible to damage from electrostatic discharge. It was developed by Custom Materials, now part of 3M. Velostat is a U.S. registered trademark (4,964,564) of Desco Industries Inc. Desco Industries purchased the assets of the 3M Static Control business on January 2, 2015.
Velostat is piezoresistive; its resistance changes with flexing or pressure. For instance, 25 mm² of fresh Velostat sandwiched between two electrodes measures around 9 kΩ without any force applied. But with 3 Newtons of force applied, its resistance drops to 1 kΩ. For material that has been used, those resistances are roughly halved.
Velostat's low cost and piezoresistive properties have made it popular for making inexpensive flex or pressure sensors for microcontrollers. One example is shoes which light up when the wearer steps. Since Velostat's resistance is reduced when pressure is applied, a voltage divider measuring that resistance can indicate when weight is applied or removed from the shoes.


Air bearing

Air bearings (also known as aerostatic or aerodynamic bearings) are bearings that use a thin film of pressurized gas to provide a low friction load-bearing interface between surfaces. The two surfaces do not touch, thus avoiding the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer distinct advantages in precision positioning, such as lacking backlash and static friction, as well as in high-speed applications. Space craft simulators now most often use air bearings and 3-D printers are now used to make air-bearing-based attitude simulators for CubeSat satellites.
A differentiation is made between aerodynamic bearings, which establish the air cushion through the relative motion between static and moving parts, and aerostatic bearings, in which the pressure is being externally inserted.
Gas bearings are mainly used in precision machinery tools (measuring and processing machines) and high-speed machines (spindle, small-scale turbomachinery, precision gyroscopes).
Gas bearing types.
Gas-lubricated bearings are classified in two groups, depending on the source of pressurization of the gas film providing the load-carrying capacity:
Hybrid bearings combining the two families also exist. In such cases, a bearing is typically fed with externally-compressed gas at low speed and then relies partially or entirely on the self-pressurizing effect at higher speeds.
Among these two technological categories, gas bearings are classified depending on the kind of linkage they realize:
The main air bearing types fall under the following categories:
Aerostatic bearings.
Pressurized gas acts as a lubricant in the gap between bearing moving parts. The gas cushion carries the load without any contact between the moving parts. Normally, the compressed gas is supplied by a compressor. A key goal of supplying the gas pressure in the gap is that the stiffness and damping of the gas cushion reaches the highest possible level. In addition, gas consumption and uniformity of gas supply into the gap are crucial for the behaviors of aerostatic bearings.
Delivery of gas to the gap.
Supplying gas to the interface between moving elements of an aerostatic bearing can be achieved in a few different methods:
There is no single best approach to feeding the film. All methods have their advantages and disadvantages specific to each application.
Dead volume.
Dead volumes refer in particular to chambers and canals existing in conventional aerostatic bearings in order to distribute the gas and increase the compressed pressure within the gap. The cavity inside porous (sintered) gas bearings are also attributed to dead volume.
Conventional aerostatic bearings.
With conventional single nozzle aerostatic bearings, the compressed air flows through a few relatively large nozzles (diameter 0.1 – 0.5 mm) into the bearing gap. The gas consumption thus allows only some flexibility such that the bearing's features (force, moments, bearing surface, bearing gap height, damping) can be adjusted only insufficiently. However, in order to allow a uniform gas pressure even with only some nozzles, aerostatic bearing manufacturers take constructive techniques. In doing so, these bearings cause dead volumes (non-compressible and thus weak air volume). In effect, this dead volume is very harmful for the gas bearing's dynamic and causes self-excited vibrations.
Single-nozzle aerostatic bearings.
The pre-pressured chamber consists of a chamber around the centralized nozzle. Usually, this chamber's ratio is between 3% and 20% of the bearing's surface. Even with a chamber depth of 1/100 mm, the dead volume is very high. In the worst cases, these air bearings consist of a concave bearing surface instead of a chamber. Disadvantages of these air bearings include a very poor tilt stiffness.
Gas bearings with channels and chambers.
Typically, conventional aerostatic bearings are implemented with chambers and canals. This design assumes that with a limited amount of nozzles, the dead volume should decrease while distributing the gas within the gap uniformly. Most constructive ideas refer to special canal structures. Since the late 1980s, aerostatic bearings with micro canal structures without chambers are manufactured. However, this technique also has to manage problems with dead volume. With an increasing gap height, the micro canal's load and stiffness decreases. As in the case of high-speed linear drives or high-frequency spindles, this may cause serious disadvantages.
Laser drilled Micro-nozzle aerostatic bearings.
Laser-drilled micro nozzle aerostatic bearings make use of computerized manufacturing and design techniques to optimize performance and efficiency. This technology allows manufacturers more flexibility in manufacturing. In turn this allows a larger design envelope in which to optimize their designs for a given application. In many cases engineers can create air bearings that approach the theoretical limit of performance.
Rather than a few large nozzles, aerostatic bearings with many micro nozzles avoid dynamically disadvantageous dead volumes. Dead volumes refer to all cavities in which gas cannot be compressed during decrease of the gap. These appear as weak gas pressure stimulates vibration. Examples of the benefits are: linear drives with accelerations of more than 1,000 m/s² (100 g), or impact drives with even more than 100,000 m/s² (10,000 g) due to high damping in combination with dynamic stiffness; sub-nanometer movements due to lowest noise-induced errors; and seal-free transmission of gas or vacuum for rotary and linear drives via the gap due to guided air supply.
Micro-nozzle aerostatic bearings achieve an effective, nearly perfect pressure distribution within the gap with a large number of micro nozzles. Their typical diameter is between 0.02 mm and 0.06 mm. The narrowest cross-section of these nozzles lies exactly at the bearing's surface. Thereby the technology avoids a dead volume on the supporting air bearing's surface and within the area of the air supplying nozzles.
The micro nozzles are automatically drilled with a laser beam that provides top-quality and repeatability. The physical behaviors of the air bearings prove to have a low variation for large as well as for small production volumes. In contrast to conventional bearings, with this technique the air bearings require no manual or costly manufacturing.
The advantages of the micro-nozzle air bearing technology include:
Some of these advantages, such as the high flexibility, the excellent static and dynamic properties in combination, and a low noise excitation, prove to be unique among all other aerostatic bearings.
Various designs.
Standard air bearings are offered with various mountings to link them in a system:
Theoretical modeling.
Gas-lubricated bearings are usually modeled using the Reynolds equation to describe the evolution of pressure in the thin film domain. Unlike liquid-lubricated bearings, the gas lubricant has to be considered as compressible, leading to a non-linear differential equation to be solved.
Numerical methods such as Finite difference method or Finite element method are common for the discretization and the resolution of the equation, accounting for the boundary conditions associated to each bearing geometry (linear-motion, journal and thrust bearings). In most cases, the gas film can be considered as isothermal and respecting the ideal gas law, leading to a simplification of the Reynolds equation.
Examples.
Automotive technology.
Even for movements which cause damage due to disruptive wear with roller bearings, lifetimes of the drive systems are unlimited.
In order to provide confidence and for the first investigations, an initial conversion from a conventional oil-guided turbo charger into air-guided was done. For a real future version, the use of results obtained from high-temperature solutions, mass products (proved production costs) and high-frequency spindles (know-how of dynamic background) will be very helpful.
Semiconductor technology.
In terms of the measurement of wafers and flat panels, it is very important to place the sensor chip precisely and without any contact along the surface. Therefore, the chip is integrated directly into the bearing's surface. The maximum distance tolerance to the surface which refers to the gap variation of the air bearing, is smaller than 0.5 μm. When placing the air bearing with the sensor chip, they must not touch the wafer surface being measured. As for the up-and-down movement, a pneumatic piston is used which is, for repeatability reasons, also air-guided. The preload of the air bearing and thus the gap height are also adjusted with this piston.
For the electrical testing of wafers the chuck can be lifted stick-slip-free up to 3 mm. The needed contact force for the probe is adjustable and independent from stroke. The lift drive is based on a voice coil motor; the guidance is air-guided. An air-guided pneumatic piston between the chuck and the drive limits the contact force.
Linear drives.
The filigree structure enables through light measurements for the 300 nm chip production with the utmost precision of less than 1 nm. In particular, the air bearings are designed for lowest air consumption with the highest stiffness.
The High-accelerated Doppler drive supports and guides a carbon fiber mirror (surface 500 mm x 250 mm) with an acceleration of up to 300 m/s² and a flexible movement profile with high precision. The solution consists of an air-guided drive: The beam (length 900 mm), which is fixed at the mirror, is manufactured of carbon fibre and carries the magnets of the linear motors. Cables/tubes (motor, air bearing, measurement system) do not move in order to avoid breakages due to high load cycles. The air-bearings are absolutely insensitive against geometric fluctuation as a result of a temperature change.
Beside the performance, the reliability is extremely important for a production machine. The air-guided solution is designed to be statically determined. The iron-core linear motor and piston bearings achieve the preload for the air bearings. Thereby, the drive is easy to assemble and insensitive against geometric variations, for instance through temperature influences or the disposition of the machines.
Medical technology.
Fat- and oil-free drives for respirators, stick-slip-free movements of scanners or a high rotary speed of large rotors have all been achieved with air bearings.
High rotary speed (> 5.5 Hz / 330 rpm), low operation costs, no noise, large inner rotor diameter (> 1 m), small weight of rotor and frame, tilt possibility of the rotor as well as a high reliability. Besides a direct drive, a belt drive is also possible.
Production technology.
Primarily, stick-slip-free movements and/or smallest forces are required. The air bearing technology is predestinated for fat/oil-free high-dynamic movements with short strokes.
With air-guided units, optical components can be arranged to have the same diameter on a rotary table. The air bearing with vacuum preload and a constant bearing gap height floats contact-less on top of the rotary table.
The linear slider, which is air-guided and statically determined, guarantees a high-precision positioning of the optical component before grinding. The self-aligning process is done without friction or force. When clamped the component retains its position for further manufacturing in the sub-micrometer-range.
Space technology.
When transporting solar panels for satellites in a launching rocket, these must be folded. After reaching orbit, they unfold via a spring mechanism, weightlessly and without friction. This process requires prior testing on Earth due to reliability reasons. During the testing design, the solar panels are hung on magnetic preloaded air-bearings that compensate for gravity. In doing so, the unfolding movement process is carried out with a minimum friction impact which means that the solar panels are tested at close to reality. Moreover, the design offers absolutely maintenance-free handling with equal sequential movements.
The air-bearing components (diameter 34 mm) with integrated magnets are so small such that they are able to glide contact-free along conventional rolled sheet plates smoothly and with a bearing gap height of about 25 μm. The holding force of an air bearing for one solar panel averages 600 N. This force is achieved by an equal distribution of the load on 16 single air bearing elements. The unfolding process of the solar panels has been developed for an area of 21 m x 2.5 m.
The permanent magnetic preloaded air-bearing guidance system may be used for many types of hanging transportation movements as well as for many other applications, such as for instance for the stick-slip-free positioning of components during assembly.


Ras Al Khor Industrial Area

Ras Al Khor Industrial Area  is a locality in Dubai, the United Arab Emirates. Literally meaning "Cape of the Creek", Ras Al Khor is part of several industrial areas (such as Al Aweer) located in the suburban areas of Dubai. The Ras Al Khor Industrial Area comprises three sub-localities:
This area has automobile spare parts sales shops, Automobile service centers, Car wash/clinic, and vehicle repair. There are no more business or companies in the Ras Al Khor industrial Areas. All companies are related to the Auto mobile service/clinic/workshop/spare parts. This industrial area has a few warehouses.


Die forming (plastics)

A "die" in polymer processing is a metal restrictor or channel capable of providing a constant cross sectional profile to a stream of liquid polymer. This allows for continuous processing of shapes such as sheets, films, pipes, rods, and other more complex profiles. This is a continuous process, allowing for constant production (assuming constant supply of polymer melt), as opposed to a sequential (non-constant) process such as injection molding.
Process.
Die forming typically occurs immediately after polymer melt has exited an extruder. The most basic process involves guiding the stream of molten polymer under pressure through a die, which three distinct regions: manifold, approach, and lip. The 'manifold' serves to channel the polymer melt from its initial extrusion point to a near-net-shape of the final product. The 'approach' region further guides the melt into the final shape, and begins to correct for any non-uniform flow. Finally, the 'lip' forms the melt into the final desired cross section and compensates for any remaining flow asymmetry. After exiting the lip of the die, the polymer melt will undergo die swell before curing. Die swell is an expansion of the melt as the pressure is released, and is dependent on polymer chemistry and die design. After curing, the solid, continuous part is drawn onto a take-up roller or cut into transportable lengths, depending on the type of part. This process may vary significantly depending on the type of die and extrusion process.
Sheet/film extrusion.
There are two major types of dies used in flat sheet extrusion: T-shaped and coat-hanger. A T-shaped die consists of two arms extending at right angles from the initial extrusion channel; these arms have a small slit along their length to allow the polymer melt to flow through. The melt is then further thinned by a short, flat approach before being pushed through the lips of the die. This setup can cause non-uniform flow across the width of the extruded sheet, with the melt at the center flowing faster than the melt at the edges of the die, resulting in buckling and other defects after exiting the die.
A more modern design is the coat-hanger die. This die differs from the T-shaped die in that the arms are not at right angles to the input direction; instead, the arms are at a shallower angle and are often curved. The arms also have a variable diameter, tapering down to a smaller radius further from the input channel. The approach portion of coat-hanger dies are longer than their T-shaped counterparts, further reducing any flow nonuniformity. Finally, the melt is extruded through lips as in the T-shaped die.
For products such as plastic sheets or films, cooling is achieved by pulling through a set of cooling rolls (also known as calender or chill rolls), usually 3 or 4 in number. In sheet extrusion, these rolls not only deliver the necessary cooling but also help determine sheet thickness and surface texture (in case of structured rolls; i.e. smooth, levant, haircell, etc.). A common processing defect known as nerve may occur when contact time between the rollers and extrudate is too brief, resulting in insufficient cooling time.
Coextrusion is common in sheet and film extrusion, allowing for speedy production of multi-layered parts. This is accomplished by joining multiple polymer melts in either the manifold or approach stage. Layers of different thicknesses may be formed by introducing melts at different flow rates or different manifold sizes.
Blown film extrusion.
The manufacture of plastic film for products such as shopping bags and continuous sheeting is achieved using a blown film line. Polymer melt from an extruder is fed through an upright die with an annular opening. There are several types of dies that can be used, depending on final requirements of film quality and characteristics of the polymer melt: spider, crosshead, and spiral dies.
A spider die consists of an internal mandrel connected to the outer die wall by several "legs", and is a moderately complex design. The resulting film will feature weld lines wherever legs were present. These weld lines are weaker than the surrounding polymer, and may also have different optical characteristics, such as haze. This weakness is caused by incomplete healing of the polymer molecular matrix. Furthermore, a pressure gradient produced by the spider legs will cause nonuniform die swell, resulting in nonuniform film thickness.
A crosshead die splits the melt flow in two at the manifold inlet, recombining them at the opposite side of a cylindrical center mandrel. This relatively simple design results in non-symmetrical flow, as molecules take longer to reach the opposite side than the close side of the mandrel. As such, the resulting film will not be of uniform thickness. To reduce this nonuniformity, inlet diameters can be varied, and various inserts can be added to minimize stagnant regions.
A spiral die is the most complex of the three major blown film die types. The polymer melt is evenly distributed into several feed tubes, which wind around a central mandrel. Each of these feed tubes is connected to the space between the mandrel and outer die walls; the feed tubes gradually diminish in diameter as they spiral around the mandrel. At the same time, the space between the mandrel and outer die walls is increased. This allows the polymer melt to layer and blend, resulting in a uniform melt profile free of weld lines. This die design produces the most uniform films, but is also the most expensive.
Air pressure is introduced through the extrusion die so that after the polymer melt leaves the lip of the die, it expands in circumference. The tubing is also drawn along its length faster than it is being extruded. This leads to thinning of the film as it is expanded in both the draw (or machine) direction, and in the transverse (or hoop) direction. The ratio of the blown diameter to the extruded diameter is known as the blow-up ratio, and affects the resulting physical properties of the film, such as stiffness and strength. Film thickness and blow-up ratio can be varied by altering the take-up rate of the rollers, the internal pressure in the blown tube, and the melt extrusion rate.
As the film is drawn upwards, it is cooled by a ring of air blowers so that the melt first becomes an amorphous viscoelastic solid, and then a semicrystalline solid, at what is known as the frost line. After solidification, the blown film tube continues to be cooled as it is pulled up by several sets of rollers, deflating the film to form lay-flat tubing. The flat film is then wound on a spool before further processing or shipping. The height of the film line is often 10 times the diameter of the blown tube or more; film lines in excess of 30 meters are possible.
Once the film tube is completely cooled, it is taken up by several nip rollers. The width of the resulting doubled-over flat film is equal to half of the blown tube's circumference. The film is then either spooled as a flattened tube, or immediately split into two separate pieces. At this point, the film is ready for further processing, such as printing or cutting into final shape.
Overjacketing extrusion.
Overjacketing extrusion is a coating process, in which individual bare wires or bundles of pre-coated wires are coated with a layer of insulating polymer. A wide variety of materials may be used, depending on the specific application. For many applications, such as insulated cables, the polymer should be a good insulator, flexible, and wear resistant.
In this process, a wire (or bundle of wires) is preheated to above the glass transition or melting temperature of the polymer coating that is to be applied. This is to ensure adhesion of the new coating. Next, this preheated bare wire is pulled through a die which places a thin coating of polymer around the wire. Due to the geometry of the dies used, relatively high extrusion rates are possible while still avoiding melt fracture. The newly coated wire is then drawn through an air or gas flame to smooth the surface of the coating, and finally a water bath to fully cool the coated wire. Coated wires are now spooled to prepare for further processing, if desired.
There are two major types of dies used in overjacketing extrusion, both based on an overall crosshead design. Regardless of die type used, the polymer melt is often extruded at a rate less than the speed of the bare wire that is drawn through the die, typically on the order of 1-4 times the speed of the melt. This causes the polymer jacket to extend, thin, and tighten around the central wire, increasing adhesion of the new layer.
The first dye type is an annular, or tubing/jacketing, die that extrudes a tube of polymer that is initially "not" touching the bare wire. A vacuum is then applied to the still-molten polymer tube, causing it to be drawn onto and bond to the surface of the bare wire. This type of die is typically used to coat very thin wires with polymer jacketing that is highly viscous.
The second die type, known as a pressure type die, relies on contact between the jacketing polymer and bare wire inside the die. In this die type, a ring of polymer melt under pressure is forced around the bare wire. Due to the applied pressure of the melt, the opening around the inlet for the bare wire must be very small, on the order of 0.05 mm. The size of the exit opening controls the thickness of the resulting coating. This type of die results in more intimate contact between the outer coating and the bare wire than the jacketing die.
Fiber drawing (polymers).
Fiber drawing is a hybrid process, in which gravity or another force is used to geometrically and mechanically alter the extruded fibers. This process not only reduces the cross section of the polymer fiber, but also increases the strength of the fibers by aligning the individual polymer molecules.
Before drawing, polymer melt is pushed through a die with a large number of small holes, known as a spinneret. Typically, the fibers are air cooled without any need for curing. If curing is needed, two methods are available: dry and wet spinning. In wet spinning, the polymer is dissolved and extruded through a spinneret into a chemical bath. In dry spinning, a solvent is allowed to evaporate as the fibers are cooled.
Typically, fiber drawing occurs immediately after spinning. Application of an external force, either from gravity or take up rollers, causes the fibers to contract laterally and lengthen. This orients the individual polymer molecules along the length of the fiber, increasing strength. The radius of the fibers have been shown to decrease hyperbolically as they lengthen. Once the fibers solidify, they may begin to crystallize, with each grain initially randomly oriented. Further drawing will cause the crystal grains to elongate and reorient in the direction of the tensile axis, further strengthening the fibers.
Spinning stability.
In practice, not all polymers are suitable for fiber spinning or drawing. This is particularly an issue in extensional-thinning polymers, where capillary failure or necking can cause separation of the melt before solidification.
Draw resonance is the most common issue that can occur during drawing of the polymer melt, regardless of polymer suitability. Resonance occurs when the rate of mass flow is not constant between the spinneret and fiber take up roller, despite being constant at each of those individual components. When the mass flow rate is not constant, the diameter of the fiber will vary to accommodate the variation. Once started, this resonance may not correct itself, requiring a complete shutdown of the extrusion line.
It has been shown that draw resonance occurs once a critical drawdown ratio is exceeded; this ratio is dependent on the flow behavior (i.e. Newtonian, shear thinning) and viscoelastic behavior of the fluid. Draw resonance has not been found to be a function of the flow rate, however. A polymer melt approaching a Newtonian fluid such as PET can have a drawdown ratio of around 20, whereas highly shear thinning and viscoelastic polymer melts such as polyethylene, polystyrene, and polypropylene may have critical drawdown ratios as low as 3.
Tube forming.
Tube forming dies allow for continuous extrusion of thick walled (relative to blown film extrusion) tubes and pipes. The dies themselves are almost identical to those used in blown film extrusion; the only major difference is the gap between the inner mandrel and outer die wall. Once the polymer melt is extruded from the die, it is pulled away by take-up rollers. Cooling is accomplished through the use of water baths, or a large number of cooling fans. After cooling, the tube is either wound onto large spools (if flexible), or cut into pre-set lengths and stacked (if stiff).
Tubing with multiple lumens (holes) must be made for specialty applications. For these applications, the tooling is made by placing more than one mandrel in the center of the die, to produce the number of lumens necessary. In most cases, these mandrels are supplied with air pressure from different sources. In this way, the individual lumen sizes can be adjusted by adjusting the pressure to the individual mandrels.
Profile extrusion.
Profile extrusion, the extrusion of complex shapes such as rain gutters, structural supports, and other components, brings with it some of the most complex die designs of any extrusion process. This difficulty is due to two primary concerns: producing the initial, still molten profile, and then controlling for asymmetrical shrinkage and die swell due to varying wall thicknesses.
Unlike in blown film, pipe, and sheet extrusion, the dies used in profile extrusion are rarely round or completely flat. Whereas a round (or flat) profile has uniform flow rates along all edges, this is not the case for more complex shapes. Take, for instance, the example of a simple, solid, square profile. The velocity of the melt is highest at the center of the die, and slowest at the edges and corners due to friction between the melt and die walls. When moving from the center of the die to the midpoint of one of the edges, the velocity gradient is high, especially near the outer die wall. However, when moving from the center to one of the corners, the velocity gradient is more gradual. As a result, the extruded square profile will experience more die swell at the edges than the corners, causing the once square profile to become more circular. This can be compensated for by bowing in the sides of the die so it approximates the shape of a four-pointed star; the sides of the polymer melt will now swell to the intended dimensions.
As the desired profile becomes more complex, the die in turn becomes more complex. Care must be taken to minimize weld lines, as well as ensuring complete filling of the die to prevent bubbles and other defects in the finished extruded profile. After the initial extrusion is complete, the molten polymer profile is cooled slightly before being run through a sizing die. This die ensures that the extruded profile meets specifications, and can correct the shape to fit those specifications. After sizing is complete, the profile is cooled before any further processing.
Coextrusion.
In practice, many films, sheets, and other extruded parts are multilayered; this allows for optimization of a wide range of properties, such as oxygen permeability, strength, and stiffness. The primary difficulty of coextrusion is bridging the gap in properties between each layer. Adding a thin "compatibility" layer is a common solution to alleviating viscosity or stiffness incompatibilities.
There are two major die types for coextrusion: single manifold and multi manifold. Both types rely on a separate extruder for each polymer chemistry. In multi manifold dies, each layer is extruded separately and only combined just before the die lips. This die type is expensive due to the complex tooling required, but can alleviate vast differences in rheological behavior between the various layers. Single manifold dies form the multiple layers into a single layer, allowing contact between the polymer layers for a longer period of time. This ensures optimal bonding, but comes at the consequence of needing higher compatibility polymers.
There are two types of processing defects that can occur during coextrusion. The first defect is interface instability, causing unintended interface shapes. This can cause "encapsulation" of the higher viscosity melt by the lower viscosity melt, leading to poor final performance of the extruded part. The severity of this type of defect is proportional to the difference in viscosities between the two polymer melts. The other type of defect forms from oscillations in the melt flow, causing small wavelike patterns on the surface of the melt and reducing optical transparency.


Mitre box

A mitre box or miter box (American English) is a wood working appliance used to guide a hand saw for making precise cuts, usually 45° mitre cuts. Traditional mitre boxes are simple in construction and made of wood, while adjustable mitre boxes are made of metal and can be adjusted for cutting any angle from 45° to 90°.
In many workshops and jobsites mitre boxes have been superseded by the powered mitre saw, however advocates for mitre boxes argue that they are more accurate, safer, quieter, cheaper, and take up less space than a powered mitre saw.
Description.
Basic mitre box.
The most common and simplest form of a mitre box is a U-shaped block made from wood, plastic or aluminium, which is open at the top and the ends. The box is made wide enough to accommodate the width of the workpieces to be cut. Slots are cut in the walls of the box at the precise angle at which the cut is to be made. These slots provide the guide for the saw to follow. Most commonly, the slots in the mitre box are cut at 45° and 90° angles.
While wooden mitre boxes are mass produced, being simple in construction they are often made by woodworkers themselves from three pieces of wood screwed or glued together. The slots are then cut using the same saw that will be used with the box.
Wooden mitre boxes have a limited lifespan, as over time the saw wears away the sides and bottoms of the slots, reducing the accuracy of cuts. Some mitre boxes are fitted with guides across the top of the box to reduce wear on the slots and to provide rigidity to the box.
Mitre boxes can also be purpose-made by the woodworker for cutting angles other than 45° or for cutting compound (sloped) angles, or they can be designed for securing a particular size of workpiece.
Adjustable mitre box.
An adjustable mitre box is designed for cutting any angle from 45° to 90° degrees. Made of metal, they consist of a base, a fence, and a mechanism for supporting a backsaw at the set angle. The workpiece is held against the fence while the saw is used. Historically a "mitre saw" is a type of backsaw with a wide blade designed for use with an adjustable mitre box, however the term is now more commonly used to refer to a powered mitre saw, which is a successor of the adjustable mitre box.
Use.
As well as pieces of wood for use in joinery, the mitre box also sees common use in workshops and on jobsites for cutting various types of moulding. For precise work, a workpiece cut in a mitre box might then be further refined using a hand plane and shooting board.
Basic mitre box.
The workpiece is placed in the box and the point at which the board is to be cut is lined up with the appropriate slot in the sides of the mitre box. The workpiece is then held or clamped in place. Backsaws are the most common hand saw used with mitre boxes, but other types of hand saw are also used. The saw is placed between the slots before sawing.
Adjustable mitre box.
The workpiece is aligned with the saw and held or clamped against the fence. Depending on the mitre box design, the cut is then made with either a dedicated mitre saw, or another suitable saw that can fit between the guides.


Cycloidal drive

A cycloidal drive or cycloidal speed reducer is a mechanism for reducing the speed of an input shaft by a certain ratio. Cycloidal speed reducers are capable of relatively high ratios in compact sizes with very low backlash.
The input shaft drives an eccentric bearing that in turn drives the cycloidal disc in an eccentric, cycloidal motion. The perimeter of this disc is geared to a stationary ring gear and has a series of output shaft pins or rollers placed through the face of the disc. These output shaft pins directly drive the output shaft as the cycloidal disc rotates. The radial motion of the disc is not translated to the output shaft.
Theory of operation.
The input shaft is mounted eccentrically to a rolling-element bearing (typically a cylindrical roller bearing), causing the cycloidal disc to wobble in a circle. The cycloidal disc will independently rotate around the bearing as it is pushed against the ring gear. This is similar to planetary gearing. The direction of rotation of the disc and output is opposite to that of the input shaft.
The number of pins on the ring gear is larger than the number of pins on the cycloidal disc. This causes the cycloidal disc to rotate around the bearing faster than the input shaft is moving it around, giving an overall rotation in the direction opposing the rotation of the input shaft.
The cycloidal disc has holes that are larger (by an amount equal to the eccentricity of the input shaft) than the output roller pins that go inside them. The output pins will move around in the holes to achieve steady rotation of the output shaft from the wobbling movement of the cycloidal disc.
The reduction rate of the cycloidal drive is obtained from the following formula, where P means the number of the ring gear pins and L is the number of lobes on the cycloidal disc.
Single-stage efficiency approaches 93% and double-stage approaches 86%. Single stage reductions are available commercially up to 119:1 and double stage up to 7,569:1.
The cycloid disc is usually designed with a "shortened cycloid" in order to minimize the eccentricity of the disc and the associated unbalance forces at high speeds. For this reason, two cycloid discs are often mounted offset by 180°.
Many modern precision drives provide the eccentric motion through multiple shafts that also transmit the output force, typically 2 to 5 shafts arranged in the same circular pattern as the output rollers of the most basic design. The shafts are driven through planetary-like gears by a central input shaft. Since these shafts are always aligned by the input gears this allows the output to be transmitted through roller bearings rather than intermittent surface contact. Due to the planetary input this is effectively a two-stage drive and may be designed to be directly driven by a high speed brushless motor. This type is often used in robot actuators.
Disadvantages.
Due to the eccentric nature of the drive, if the cycloidal disk is not balanced by a second disk or a counterweight, it will generate vibrations which propagate through the driven shafts and the body. This increases wear on the exterior teeth of the cycloidal disk and the component bearings. With two discs the static imbalance is corrected but a small dynamic imbalance remains. This is generally considered acceptable for most applications. To reduce vibration, high-speed drives use three or more discs to correct the imbalance; the outer discs move in unison, in opposition to the middle one, which is twice as massive.
Advantages.
Cycloidal drives can feature zero backlash and high torque capacity while being compact in size, unlike Involute gearboxes. They are useful in situations where low speed with high torque is required. Cycloidal drives may be designed with significantly higher contact areas for their size than any gear-based transmission such as epicyclic gearing. They apply force through many of the teeth at once, allowing very high torque output relative to size at the cost of requiring sliding contact.


2018 Copa Sudamericana final stages

The 2018 Copa Sudamericana final stages were played from 21 August to 12 December 2018. A total of 16 teams competed in the final stages to decide the champions of the 2018 Copa Sudamericana.
Qualified teams.
The 16 winners of the second stage advanced to the round of 16.
Seeding.

Starting from the round of 16, the teams were seeded according to the second stage draw, with each team assigned a "seed" 1–16 corresponding to the tie they win (O1–O16) (Regulations Article 22.c).
Format.

Starting from the round of 16, the teams played a single-elimination tournament with the following rules:
Bracket.
The bracket starting from the round of 16 was determined as follows:

The bracket was decided based on the second stage draw, which was held on 4 June 2018.

Round of 16.
The first legs were played on 21–22 August, 18–20 and 26 September, and the second legs were played on 19, 25, 27 September, and 2–4 October 2018.

Match A.
"Tied 0–0 on aggregate, Santa Fe won on penalties and advanced to the quarterfinals (Match S1)."
Match B.
"Tied 3–3 on aggregate, Bahia won on penalties and advanced to the quarterfinals (Match S2)."
Match C.
"Tied 3–3 on aggregate, Nacional won on away goals and advanced to the quarterfinals (Match S3)."
Match D.
"Junior won 2–1 on aggregate and advanced to the quarterfinals (Match S4)."
Match E.
"Defensa y Justicia won 2–0 on aggregate and advanced to the quarterfinals (Match S4)."
Match F.
"Fluminense won 4–0 on aggregate and advanced to the quarterfinals (Match S3)."
Match G.
"Atlético Paranaense won 4–1 on aggregate and advanced to the quarterfinals (Match S2)."
Match H.
"Tied 1–1 on aggregate, Deportivo Cali won on penalties and advanced to the quarterfinals (Match S1)."
Quarterfinals.
The first legs were played on 23–25 October, and the second legs were played on 30–31 October and 1 November 2018.

Match S1.
"Santa Fe won 3–2 on aggregate and advanced to the semifinals (Match F1)."
Match S2.
"Tied 1–1 on aggregate, Atlético Paranaense won on penalties and advanced to the semifinals (Match F2)."
Match S3.
"Fluminense won 2–1 on aggregate and advanced to the semifinals (Match F2)."
Match S4.
"Tied 3–3 on aggregate, Junior won on away goals and advanced to the semifinals (Match F1)."
Semifinals.
The first legs were played on 7–8 November, and the second legs were played on 28–29 November 2018.

Match F1.
"Junior won 3–0 on aggregate and advanced to the finals."
Match F2.
"Atlético Paranaense won 4–0 on aggregate and advanced to the finals."
Finals.
In the finals, if tied on aggregate, the away goals rule would not be used, and 30 minutes of extra time would be played. If still tied after extra time, the penalty shoot-out would be used to determine the winner (Regulations Article 28).
The first leg was played on 5 December, and the second leg was played on 12 December 2018.

"Tied 2–2 on aggregate, Atlético Paranaense won on penalties."


Machining

Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The methods that have this common theme are collectively called subtractive manufacturing, which utilizes machine tools, in contrast to "additive manufacturing" (3D printing), which uses controlled addition of material.
Machining is a part of the manufacture of many metal products, but it can also be used on other materials such as wood, plastic, ceramic, and composite material. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Much of modern-day machining is carried out by computer numerical control (CNC), in which computers are used to control the movement and operation of mills, lathes, and other cutting machines. This increases efficiency, as the CNC machine runs unmanned, reducing labor costs for machine shops.
History and terminology.
The precise meaning of the term "machining" has evolved over the past one and a half centuries as technology has advanced. In the 18th century, the word "machinist" meant a person who built or repaired machines. This person's work was primarily done by hand, using processes such as the carving of wood and the writing-forging and hand-filing of metal. At the time, millwrights and builders of new kinds of "engines" (meaning, more or less, machines of any kind), such as James Watt or John Wilkinson, would fit the definition. The noun "machine tool" and the verb "to machine" ("machined, machining") did not yet exist.
Around the middle of the 20th century, the latter words were coined as the concepts they described evolved into widespread existence. Therefore, during the Machine Age, "machining" referred to (what we today might call) the "traditional" machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planing, abrasive cutting, reaming, and tapping. In these "traditional" or "conventional" machining processes, machine tools, such as lathes, milling machines, drill presses, or others, are used with a sharp cutting tool to remove material to achieve a desired geometry.
Since the advent of new technologies in the post–World War II era, such as electrical discharge machining, electrochemical machining, electron beam machining, photochemical machining, and ultrasonic machining, the retronym "conventional machining" can be used to differentiate those classic technologies from the newer ones. Currently, "machining" without qualification usually implies the traditional machining processes.
In the decades of the 2000s and 2010s, as additive manufacturing (AM) evolved beyond its earlier laboratory and rapid prototyping contexts and began to become standard throughout all phases of manufacturing, the term "subtractive manufacturing" became common retronymously in logical contrast with AM, covering essentially any removal processes also previously covered by the term "machining". The two terms are effectively synonymous, although the long-established usage of the term "machining" continues. This is comparable to the idea that evolved because of the proliferation of ways to contact someone (telephone, email, IM, SMS, and so on) but did not entirely replace the earlier terms such as "call", "talk to", or "write to".
Machining operations.
The three principal machining processes are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planing, boring, broaching, and sawing.
An unfinished workpiece requiring machining must have some material cut away to create a finished product. A finished product would be a workpiece that meets the specifications set out for that workpiece by engineering drawings or blueprints. For example, a workpiece may require a specific outside diameter. A lathe is a machine tool that can create that diameter by rotating a metal workpiece so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can remove the metal in the shape of a cylindrical hole. Other tools that may be used for metal removal are milling machines, saws, and grinding machines. Many of these same techniques are used in woodworking.
As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing primary machine tools. Although a machine shop can be a stand-alone operation, many businesses maintain internal machine shops that support the business's specialized needs.
Machining requires attention to many details for a workpiece to meet the specifications in the engineering drawings or blueprints. Besides the obvious problems related to correct dimensions, there is the problem of achieving the right finish or surface smoothness on the workpiece. The inferior finish found on the machined surface of a workpiece may be caused by incorrect clamping, a dull tool, or inappropriate presentation of a device. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish and waves on the machined surfaces of the workpiece.
Overview of machining technology.
Machining is any process in which a cutting tool removes small chips of material from the workpiece (the workpiece is often called the "work"). Relative motion is required between the device and the work to perform the operation. This relative motion is achieved in most machining operations using a primary activity called "cutting speed" and a secondary movement called "feed". The shape of the tool and its penetration into the work surface, combined with these motions, produce the desired shape of the resulting work surface.
Machining operations.
There are many kinds of machining operations, each of which is capable of generating a specific part geometry and surface texture.
In turning, a cutting tool with a single cutting edge removes material from a rotating workpiece to generate a cylindrical shape. The primary motion is provided by rotating the workpiece, and the feed motion is achieved by moving the cutting tool slowly in a direction parallel to the workpiece's rotation axis.
Drilling is used to create a round hole. It is accomplished by a rotating tool that typically has two or four helical cutting edges. The device is fed in a direction parallel to its axis of rotation into the workpiece to form the round hole.
In boring, a tool with a single bent pointed tip is advanced into a roughly made hole in a spinning workpiece to enlarge the gap and improve its accuracy slightly. It is a fine-finishing operation used in the final stages of product manufacture.
Reaming is one of the sizing operations that removes a small amount of metal from a drilled hole.
In milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or straight surface. The direction of the feed motion is perpendicular to the tool's axis of rotation. The rotating milling cutter provides speed motion. The two primary forms of milling are:
Other conventional machining operations include shaping, planing, broaching, and sawing. Also, grinding and similar abrasive operations are often included within the category of machining.
Cutting tool.
A cutting tool has one or more sharp cutting edges and is made of a harder material than the work material. The cutting edge serves to separate the chip from the parent work material. Connected to the cutting edge are the two surfaces of the tool:
The rake face, which directs the flow of the newly formed chip, is oriented at a certain angle and is called the rake angle "α." It is measured relative to the plane perpendicular to the work surface. The rake angle can be positive or negative. The flank of the tool provides a clearance between the tool and the newly formed work surface, thus protecting the surface from abrasion, which would degrade the finish. This angle between the work and flank surfaces is called the relief angle. There are two basic types of cutting tools:
A single-point tool has one cutting edge for turning, boring, and planning. During machining, the device's point penetrates below the work part's original work surface. The fact is sometimes rounded to a certain radius, called the nose radius.
Multiple cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the work part by rotating. Drilling and milling use turning multiple-cutting-edge tools. Although the shapes of these tools are different from a single-point device, many elements of tool geometry are similar.
Cutting conditions.
Relative motion is required between the tool and work to perform a machining operation. The primary action is at a specific cutting speed. In addition, the device must be moved laterally across the work. This is a much slower motion called the feed. The remaining dimension of the cut is the penetration of the cutting tool below the original work surface, reaching the cut's depth. Speed, feed, and depth of cut are called the cutting conditions. They form the three dimensions of the machining process, and for certain operations, their product can be used to obtain the material removal rate for the process:
where
Stages in metal cutting.
Machining operations usually divide into two categories, distinguished by purpose and cutting conditions:
Roughing cuts are used to remove a large amount of material from the starting work part as rapidly as possible, i.e., with a significant Material Removal Rate (MRR), to produce a shape close to the desired form but leaving some material on the piece for a subsequent finishing operation.
Finishing cuts complete the part and achieve the final dimension, tolerances, and surface finish. In production machining jobs, one or more roughing cuts are usually performed on the work, followed by one or two finishing cuts. Roughing operations are done at high feeds and depths – feeds of 0.4–1.25  mm/rev (0.015–0.050 in/rev) and depths of 2.5–20 mm (0.100–0.750 in) are typical, but actual values depend on the workpiece materials. Finishing operations are carried out at low feeds and depths – dinners of 0.0125–0.04  mm/rev (0.0005–0.0015 in/rev) and depths of 0.75–2.0 mm (0.030–0.075 in) are typical. Cutting speeds are lower in roughing than in finishing.
A cutting fluid is often applied to the machining operation to cool and lubricate the cutting tool. Determining whether a cutting fluid should be used and, if so, choosing the proper cutting fluid is usually included within the scope of the cutting condition.
Today other forms of metal cutting are becoming increasingly popular. An example of this is water jet cutting. Water jet cutting involves pressurized water over 620 MPa (90 000 psi) and can cut metal and have a finished product. This process is called cold cutting, which eliminates the damage caused by a heat-affected zone, as opposed to laser and plasma cutting.
Relationship of subtractive and additive techniques.
With the recent proliferation of additive manufacturing technologies, conventional machining has been retronymously classified, in thought and language, as a subtractive manufacturing method. In narrow contexts, additive and subtractive methods may compete with each other. In the broad context of entire industries, their Relationship is complementary. Each method has its advantages over the other. While additive manufacturing methods can produce very intricate prototype designs impossible to replicate by machining, strength and material selection may be limited.


List of CAx companies

This is a list of computer-aided technologies (CAx) companies and their software products. Software using computer-aided technologies (CAx) has been produced since the 1970s for a variety of computer platforms. This software may include applications for computer-aided design (CAD), computer-aided engineering (CAE), computer-aided manufacturing (CAM) and product data management (PDM).
The list is far from complete or representative as the CAD business landscape is very dynamic: almost every month new companies appear, old companies go out of business, and companies split and merge. Sometimes some names disappear and reappear again.
Past CAD Brands.
Acquired, orphaned, failed or rebranded.
In-house CAD software.
Developed by companies for their own use. Some are no longer used as the organizations are now using commercial systems.


Spindle (tool)

In machine tools, a spindle is a rotating axis of the machine, which often has a shaft at its heart. The shaft itself is called a spindle, but also, in shop-floor practice, the word often is used metonymically to refer to the entire rotary unit, including not only the shaft itself, but its bearings and anything attached to it (chuck, etc.). Spindles are electrically or pneumatically powered and come in various sizes. They are versatile in terms of material it can work with. Materials that spindles work with include embroidery, foam, glass, wood, and etc.
A machine tool may have several spindles, such as the headstock and tailstock spindles on a bench lathe. The main spindle is usually the biggest one. References to "the spindle" without further qualification imply the main spindle. Some machine tools that specialize in high-volume mass production have a group of 4, 6, or even more main spindles. These are called multispindle machines. For example, gang drills and many screw machines are multispindle machines. Although a bench lathe has more than one spindle (counting the tailstock), it is not called a multispindle machine; it has one main spindle.
Examples of spindles include
High speed spindle.
High speed spindles are used strictly in machines, like CNC mills, designed for metal work. There are two types of high speed spindles, each with different designs:
Belt-driven spindle.
Consisting of spindle and bearing shafts held within the spindle housing, the belt-driven spindle is powered by an external motor connected via a belt-pulley system.
Integral motor spindle.
A main component of this spindle is the motor, stored internally.
Both types, the belt-driven and the integral motor spindles, have advantages and disadvantages according to their design. Which one is more desirable depends on the purpose of the machine and product(s) being produced.
CNC machines used with spindles.
The type of CNC machine being used with your spindle will vary. Common CNC machines used are:
Being that there are a variety of CNC machines available, it is important to choose the right one that fits your specifities.


Microvia

Microvias are used as the interconnects between layers in high density interconnect (HDI) substrates and printed circuit boards (PCBs) to accommodate the high input/output (I/O) density of advanced packages. Driven by portability and wireless communications, the electronics industry strives to produce affordable, light, and reliable products with increased functionality. At the electronic component level, this translates to components with increased I/Os with smaller footprint areas (e.g. flip-chip packages, chip-scale packages, and direct chip attachments), and on the printed circuit board and package substrate level, to the use of high density interconnects (HDIs) (e.g. finer lines and spaces, and smaller vias).
Overview.
IPC standards revised the definition of a microvia in 2013 to a hole with depth to diameter aspect ratio of 1:1 or less, and the hole depth not to exceed 0.25mm. Previously, microvia was any hole less than or equal to 0.15 mm in diameter
With the advent of smartphones and hand-held electronic devices, microvias have evolved from single-level to stacked microvias that cross over multiple HDI layers. Sequential build-up (SBU) technology is used to fabricate HDI boards. The HDI layers are usually built up from a traditionally manufactured double-sided core board or multilayer PCB. The HDI layers are built on both sides of the traditional PCB one by one with microvias. The SBU process consists of several steps: layer lamination, via formation, via metallization, and via filling. There are multiple choices of materials and/or technologies for each step.
Microvias can be filled with different materials and processes:
Buried microvias are required to be filled, while blind microvias on the external layers usually do not have any fill requirements. A stacked microvia is usually filled with electroplated copper to make electrical interconnections between multiple HDI layers and provide structural support for the outer level(s) of the microvia or for a component mounted on the outermost copper pad.
Microvia reliability.
The reliability of HDI structure is one of the major constraints for its successful widespread implementation in the PCB industry. Good thermo-mechanical reliability of microvias is an essential part of HDI reliability. Many researchers and professionals have studied the reliability of microvias in HDI PCBs. The reliability of microvias depends on many factors such as microvia geometry parameters, dielectric material properties, and processing parameters.
Microvia reliability research has focused on experimental assessment of the reliability of single-level unfilled microvias, as well as finite element analysis on stress/strain distributions in single-level microvias and microvia fatigue life estimation. Microvia failures identified from the research include interfacial separation (separation between the base of the microvia and the target pad), barrel cracks, corner/knee cracks, and target pad cracks (also referred to as microvia pull out). These failures result from the thermomechanical stresses caused by coefficient of thermal expansion (CTE) mismatch, in the PCB thickness direction, between the metallization in a microvia structure and the dielectric materials surrounding the metal. The following paragraph highlights some of the microvia reliability research.
Ogunjimi et al. looked at the effect of manufacturing and design process variables on the fatigue life of microvias, including trace (conductor) thickness, layer or layers of the dielectric around the trace and in the microvia, via geometry, via wall angle, ductility coefficient of the conductor material, and strain concentration factor. Finite element models were created with different geometries, and ANOVA method was used to determine the significance of the different process variables. The ANOVA results showed that the strain concentration factor was the most important variable, followed with the ductility factor, metallization thickness, and via wall angle. Prabhu et al. conducted a finite element analysis (FEA) on an HDI microvia structure to determine the effect of accelerated temperature cycling and thermal shock. Liu et al. and Ramakrishna et al. conducted liquid-to-liquid and air-to-air thermal shock testing, respectively, to studied the effect of dielectric material properties and microvia geometry parameters, such as microvia diameter, wall angle and plating thickness, on microvia reliability. Andrews et al. investigated single-level microvia reliability using IST (interconnect stress test), and considered the effect of reflow cycles of lead-free solder. Wang and Lai investigated the potential failure sites of microvias using finite element modeling. They found that filled microvias have a lower stress than unfilled microvias. Choi and Dasgupta introduced microvia non-destructive inspection method in their work.
Although most microvia reliability research focuses on single-level microvias, Birch tested multiple-level stacked and staggered microvias using IST test. Weibull analysis on the test data showed that single- and 2-level stacked microvias last longer than 3- and 4-level microvias (e. g. 2-level stacked microvias experienced about 20 times more cycles to failure than 4-level stacked microvias).
Microvia voiding.
One challenge for high density interconnect board development, is to fabricate reliable microvias, especially for stacked microvias, without resulting in incomplete filling, dimples, or voids in the copper plating process. The authors of have been investigating the risk of microvias in terms of voids and other defects using both experimental testing and finite element analysis. They found that incomplete copper filling increases the stress levels in microvias and hence decreases microvia fatigue life.
As for voids, different voiding conditions, such as different void sizes, shapes, and locations result in different effects on microvia reliability. Small voids of a spherical shape lightly increase the microvia fatigue life, but extreme voiding conditions greatly reduce the duration of microvias.


Kearney and Trecker

Kearney and Trecker founded in 1898 by Edward J. Kearney and Theodore Trecker was a machine manufacturer based in West Allis, Wisconsin. It became one of the largest machine tool suppliers in the world.
History.
The company was founded in 1898 and their first location was above a small shop. They soon became known for created milling machines and precision machine tools. By 1943 they were one of three largest milling machine manufacturers in the United States.
In 1965 the company was a leading automated tool maker, and had sales of more than 47 million dollars. They manufactured more than 100 different boring and milling machines. They merged with the Rockwell Standard corporation in 1965.
By 1955 the company had grown to become one of the largest machine tool suppliers in the world. The factories of Kearney & Trecker covered a 95-acre compound. In 1955 they had 2,250 employees.
In 1979 Kearney & Trecker merged with the Cross Company and became the Cross & Trecker, and just 12 years later, it was purchased by Giddings & Lewis, Inc.


2016 Copa Libertadores final stages

The 2016 Copa Libertadores final stages were played from 26 April to 27 July 2016. A total of 16 teams competed in the final stages to decide the champions of the 2016 Copa Libertadores. Atlético Nacional won the title by defeating Independiente del Valle in the finals.
Qualified teams.

The winners and runners-up of each of the eight groups in the second stage qualified for the final stages.

Seeding.

The qualified teams were seeded in the final stages according to their results in the second stage, with the group winners seeded 1–8, and the group runners-up seeded 9–16.

Format.

In the final stages, the 16 teams played a single-elimination tournament, with the following rules:
Bracket.

Round of 16.
The first legs were played on 26–28 April, and the second legs were played on 3–5 May 2016.

Match A.
"Atlético Nacional won 4–2 on aggregate and advanced to the quarterfinals (Match S1)."
Match B.
"UNAM won 2–1 on aggregate and advanced to the quarterfinals (Match S2)."
Match C.
"Tied 2–2 on aggregate, Nacional won on away goals and advanced to the quarterfinals (Match S3)."
Match D.
"Atlético Mineiro won 2–1 on aggregate and advanced to the quarterfinals (Match S4)."
Match E.
"São Paulo won 5–3 on aggregate and advanced to the quarterfinals (Match S4)."
Match F.
"Boca Juniors won 5–2 on aggregate and advanced to the quarterfinals (Match S3)."
Match G.
"Independiente del Valle won 2–1 on aggregate and advanced to the quarterfinals (Match S2)."
Match H.
"Rosario Central won 4–0 on aggregate and advanced to the quarterfinals (Match S1)."
Quarterfinals.
The first legs were played on 11–12 and 17 May, and the second legs were played on 18–19 and 24 May 2016.

Match S1.
"Atlético Nacional won 3–2 on aggregate and advanced to the semifinals (Match F1)."
Match S2.
"Tied 3–3 on aggregate, Independiente del Valle won on penalties and advanced to the semifinals (Match F2)."
Match S3.
"Tied 2–2 on aggregate, Boca Juniors won on penalties and advanced to the semifinals (Match F2)."
Match S4.
"Tied 2–2 on aggregate, São Paulo won on away goals and advanced to the semifinals (Match F1)."
Semifinals.
The first legs were played on 6–7 July, and the second legs were played on 13–14 July 2016.

Match F1.
"Atlético Nacional won 4–1 on aggregate and advanced to the finals."
Match F2.
"Independiente del Valle won 5–3 on aggregate and advanced to the finals."
Finals.
The first leg was played on 20 July, and the second leg was played on 27 July 2016.

"Atlético Nacional won 2–1 on aggregate."


ION LMD

ION LMD system is one of the laser microdissection systems and a name of device that follows Gravity-Assisted Microdissection method, also known as GAM method. This non-contact laser microdissection system makes cell isolation for further genetic analysis possible. It is the first developed laser microdissection system in Asia.
History.
At first, proto type of ION LMD system was developed in 2004.
The first generation of ION LMD was developed in 2005 and then the second generation(so-called G2) was developed in 2008. At last, the third generation(so-called ION LMD Pro) was developed in 2012.
Manufacturer.
JungWoo F&B was founded in 1994, and offers various factory automation products for clients in semiconductor, consumer electronics, LCD, automotive manufacturing and ship-building industries. In 2003, the company entered the bio-mechanics business for the medical laboratory market and developed an ION LMD system which is utilized in cancer research.
Awards.
This ION LMD system has got some reliable awards.


Chris McMahon (academic)

Christopher Alan McMahon is a British mechanical engineer, academic and a researcher. He is a retired professor of engineering design and serves as senior research fellow and senior associate teacher at the University of Bristol.
McMahon has published two editions of a textbook on computer-aided design and manufacture, and authored a number of research papers focusing on engineering design and computer-aided design, especially concerning the application of computers to the management of information and uncertainty in design and design automation.
Education and early career.
McMahon graduated in mechanical engineering from the University of Bristol in 1978; prior to working in the railway and then automotive industries.
Academic career.
McMahon joined the University of Bristol as a lecturer in 1984, and worked there until 2002, when he joined the University of Bath. He was promoted to professor of engineering design in 2005, becoming director of Bath's Integrated Design and Manufacturing Research Centre. In 2012 he returned to the University of Bristol as professor of engineering design. In 2017 and 2018 he worked in the Department of Mechanical Engineering of the Technical University of Denmark.
Research.
McMahon's research interests include engineering design and computer-aided design, focusing on the application of computers to the management of information and uncertainty in design and design automation. He has carried out research in knowledge and information management for complex long-lived engineering products and systems, in information requirements of engineering designers and in systems to support their information organization and access. He has also researched in annotation in design, risk and uncertainty management in design, in component durability and reliability, and in eco-design and design for remanufacturing. The majority of his work has been carried out in conjunction with industry.
His research on computer aided design and manufacture (CADCAM) includes the introduction of a general purpose ontology-driven annotation approach for recording view-point dependent information in CAD, and work on the use of parametric and associative CAD systems to support the complex and lengthy design activities in the automotive industry.
He and his colleagues conducted in order to examine the barriers to improving information management in engineering companies, and to develop a set of core issues to inform their long term planning of information systems strategy. In a 2006 paper, hen proposed an information accessing framework using computational classification technologies. He also presented the use of multiple document structure views using decomposition schemes. His proposed framework combines automatic fragment extraction, markup technologies, document structure study and faceted classification for retrieving specific document fragment.
McMahon has made a number of observations on the diversity of design research, applying his experience in information management to the categorization of design research activities. He has also published influential review papers on knowledge management in engineering design, noting the broad division between personalisation and codification approaches, and on informatics in engineering design.
Professional activities.
McMahon is associated as an editorial board member with various journals including "Research in Engineering Design", "Journal of Engineering Design", "Advanced Engineering Informatics", "International Journal of PLM", "AIEDAM" and "She Ji: Journal of Design", "Economics and Innovation". In 2005, he joined the Board of Management of the Design Society and served as its president from 2011 to 2013. He is a Fellow of the Institution of Mechanical Engineers.
Together with Jimmie Browne of the National University of Ireland, Galway, in 1992 McMahon published a textbook on computer-aided design and manufacture "CADCAM From Principles to Practice ("second edition, 1998)
In 2020, McMahon published a translation of Philippe Bihouix's book, "The Age of Low Tech: Towards a Technologically Sustainable Civilization".


Mitsubishi Logisnext

Mitsubishi Forklift Trucks is the brand name used for a range of materials handling products manufactured and distributed by Mitsubishi Heavy Industries (MHI) and several of its Mitsubishi Caterpillar Forklifts subsidiaries: MCFE Mitsubishi Caterpillar Forklift Europe, MCFA Mitsubishi Caterpillar Forklift America, MLAP Mitsubishi Logisnext Asia Pacific, and MCFC Mitsubishi Caterpillar Forklift (Shanghai).
History.
The Mitsubishi Forklift Trucks brand was formed in 1992 when MHI entered a joint venture with Caterpillar Inc.
In February 2013, Mitsubishi Forklift Trucks has signed an agreement with the Japanese company Nichiyu to create Mitsubishi Nichiyu Forklift Co., Ltd.
As of 2018, Mitsubishi Forklift Trucks operates as a subsidiary of Mitsubishi Logisnext.
Products.
Mitsubishi Forklift Trucks products cover a range of counterbalance forklift trucks and warehouse equipment, including:
• IC engine counterbalance trucks (diesel and LPG)
• Electric counterbalance trucks
• Powered pallet trucks
• Stackers
• Order pickers
• Reach and multi-way trucks
Although many of the designs and components are common to all regions, there are some differences in the product ranges across continents.
Production facilities.
Worldwide headquarters:
Manufacturing centres:


Piezoresistive effect

The piezoresistive effect is a change in the electrical resistivity of a semiconductor or metal when mechanical strain is applied. In contrast to the piezoelectric effect, the piezoresistive effect causes a change only in electrical resistance, not in electric potential.
History.
The change of electrical resistance in metal devices due to an applied mechanical load was first discovered in 1856 by Lord Kelvin. With single crystal silicon becoming the material of choice for the design of analog and digital circuits, the large piezoresistive effect in silicon and germanium was first discovered in 1954 (Smith 1954).
Mechanism.
In conducting and semi-conducting materials, changes in inter-atomic spacing resulting from strain affect the bandgaps, making it easier (or harder depending on the material and strain) for electrons to be raised into the conduction band. This results in a change in resistivity of the material. Within a certain range of strain this relationship is linear, so that the piezoresistive coefficient
where
is constant.
Piezoresistivity in metals.
Usually the resistance change in metals is mostly due to the change of geometry resulting from applied mechanical stress. However, even though the piezoresistive effect is small in those cases it is often not negligible. In cases where it is, it can be calculated using the simple resistance equation derived from Ohm's law;
where
Some metals display piezoresistivity that is much larger than the resistance change due to geometry. In platinum alloys, for instance, piezoresistivity is more than a factor of two larger, combining with the geometry effects to give a strain gauge sensitivity of up to more than three times as large than due to geometry effects alone. Pure nickel's piezoresistivity is -13 times larger, completely dwarfing and even reversing the sign of the geometry-induced resistance change.
Piezoresistive effect in bulk semiconductors.
The piezoresistive effect of semiconductor materials can be several orders of magnitudes larger than the geometrical effect and is present in materials like germanium, polycrystalline silicon, amorphous silicon, silicon carbide, and single crystal silicon. Hence, semiconductor strain gauges with a very high coefficient of sensitivity can be built. For precision measurements they are more difficult to handle than metal strain gauges, because semiconductor strain gauges are generally sensitive to environmental conditions (especially temperature).
For silicon, gauge factors can be two orders of magnitudes larger than those observed in most metals (Smith 1954). The resistance of n-conducting silicon mainly changes due to a shift of the three different conducting valley pairs. The shifting causes a redistribution of the carriers between valleys with different mobilities. This results in varying mobilities dependent on the direction of current flow. A minor effect is due to the effective mass change related to changing shapes of the valleys. In p-conducting silicon the phenomena are more complex and also result in mass changes and hole transfer.
Giant piezoresistance in metal-silicon hybrid structures.
A giant piezoresistive effect – where the piezoresistive coefficient exceeds the bulk value – was reported for a microfabricated silicon-aluminium hybrid structure. The effect has been applied to silicon-based sensor technologies.
Giant piezoresistive effect in silicon nanostructures.
The longitudinal piezoresistive coefficient of top-down fabricated silicon nanowires was measured to be 60% larger than in bulk silicon.
In 2006, giant piezoresistance was reported in bottom-up fabricated silicon nanowires – a >30 increase in the longitudinal piezoresistive coefficient compared to bulk silicon was reported. The suggestion of a giant piezoresistance in nanostructures has since stimulated much effort into a physical understanding of the effect not only in silicon but also in other functional materials.
Piezoresistive silicon devices.
The piezoresistive effect of semiconductors has been used for sensor devices employing all kinds of semiconductor materials such as germanium, polycrystalline silicon, amorphous silicon, and single crystal silicon. Since silicon is today the material of choice for integrated digital and analog circuits the use of piezoresistive silicon devices has been of great interest. It enables the easy integration of stress sensors with Bipolar and CMOS circuits.
This has enabled a wide range of products using the piezoresistive effect. Many commercial devices such as pressure sensors and acceleration sensors employ the piezoresistive effect in silicon. But due to its magnitude the piezoresistive effect in silicon has also attracted the attention of research and development for all other devices using single crystal silicon. Semiconductor Hall sensors, for example, were capable of achieving their current precision only after employing methods which eliminate signal contributions due to applied mechanical stress.
Piezoresistors.
Piezoresistors are resistors made from a piezoresistive material and are usually used for measurement of mechanical
stress. They are the simplest form of piezoresistive devices.
Fabrication.
Piezoresistors can be fabricated using wide variety of piezoresistive materials. The simplest form of piezoresistive silicon sensors are diffused resistors. Piezoresistors consist of a simple two contact diffused n- or p-wells within a p- or n-substrate. As the typical square resistances of these devices are in the range of several hundred ohms, additional p+ or n+ plus diffusions are a potential method to facilitate ohmic contacts to the device.
"Schematic cross-section of the basic elements of a silicon n-well piezoresistor."
Physics of operation.
For typical stress values in the MPa range the stress dependent voltage drop along the resistor Vr, can be considered to be linear. A piezoresistor aligned with the x-axis as shown in the figure may be described by
where formula_5, "I", formula_6, formula_7, and formula_8 denote the stress free resistance, the applied current, the transverse and longitudinal piezoresistive coefficients, and the three tensile stress components, respectively. The piezoresistive coefficients vary significantly with the sensor orientation with respect to the crystallographic axes and with the doping profile. Despite the fairly large stress sensitivity of simple resistors, they are preferably used in more complex configurations eliminating certain cross sensitivities and drawbacks. Piezoresistors have the disadvantage of being highly sensitive to temperature changes while featuring comparatively small relative stress dependent signal amplitude changes.
Other piezoresistive devices.
In silicon the piezoresistive effect is used in piezoresistors, transducers, piezo-FETS, solid state accelerometers and bipolar transistors.
The electrically-conductive packaging material Velostat is used by hobbyists to make pressure sensors due to is piezoresistive properties and low cost.