## Water Sensor

Water in Fuel Sensor or WiF sensor indicates the presence of water in the fuel. It is installed in the fuel filter and when the water level in the water separator reaches the warning level, the Wif sends an electrical signal to the ECU or to dashboard (lamp). The WiF is used especially in the Common Rail engines to avoid the Fuel injector damage.The WiF sensor uses the difference of electric conductivity through water and diesel fuel by 2 electrodes.

First generation WiF sensors use a potting resin to isolate the electronic circuit, while the latest generation of Wif sensors (the WS3 sensor in Surface-mount technology) are made totally without leakage using an innovative co-moulding process.

The latest generation of WiF sensors have a high resistance to vibrations and to thermal excursion cycles.

The main automotive WiF designer and producer is SMP Poland.
A level sensing device is designed to measure the level of flow substances including liquids, slurries and granular materials. Ther are also continuous level sensors; however, these sensing modules can only detect the level of flow of a substance with a specific range.

A water sensor is a device used in the detection of the water level for various applications. Water sensors are of several types that include ultrasonic sensors, pressure transducers, bubblers, and float sensors.

### Working Method

Ultrasonic sensors operate by transmitting sound waves that reflect from the liquid surface and are obtained by the sensor. The sensor measures the time interval between the transmitted and received signals, which is then converted into distance measurement with the help of electronic circuits within the sensor thereby measuring the level of the liquid.

Float sensors work based on the change in resistance of a potentiometer within the sensor by the turning of a pulley or a spring-loaded shaft.

Bubbler sensors, on the other hand, measure water level by detecting the pressure of air-filled tubes with an open, submerged bottom end. The static pressure at the end of the tubes is more when the water level is high, and therefore more air pressure is required to fill the tube.

### Applications

Water sensors find applications in nuclear power plants, automobiles for measuring the amount of gasoline left in the fuel tank, engine oil, cooling water, and brake/power steering fluid.
Industrial applications of water level sensors include water level sensing in transport and storage tanks and water treatment tanks. Wess Global Inc. manufacture different types of level instruments for their use in municipal areas and also in the food and beverage industry.

## Turbocharged direct injection

Turbocharged direct injection or TDI is a design of turbodiesel engines featuring turbocharging and cylinder-direct fuel injection that was developed and produced by the Volkswagen Group (VW AG). These TDI engines are widely used in all mainstream Volkswagen Group marquesof passenger cars and light commercial vehicles made by the company (particularly those sold in Europe). They are also used as marine enginesin Volkswagen Marine and Volkswagen Industrial Motor applications.
Some TDI engines installed in 2009 to 2015 model year Volkswagen Group cars sold through 18 September 2015 had an emissions defeat device, which activated emissions controls only during emissions testing. The emissions controls were suppressed otherwise, allowing the TDI engines to exceed legal limits on emissions. VW has admitted to using the illegal device in its TDI diesel cars.
In many countries, TDI is a registered trademark of Volkswagen AG.
The TDI designation has also been used on vehicles powered by Land Rover-designed diesel engines. These are unrelated to Volkswagen Group engines.
Overview
The TDI engine uses direct injection, where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder, rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine also uses forced induction by way of a turbocharger to increase the amount of air which is able to enter the engine cylinders, and most TDI engines also feature an intercooler to lower the temperature (and therefore increase the density) of the 'charged', or compressed air from the turbo, thereby increasing the amount of fuel that can be injected and combusted. These, in combination, allow for greater engine efficiency, and therefore greater power outputs (from a more complete combustion process compared to indirect injection), while also decreasing emissions and providing more torque than the non-turbo and non-direct injection petrol engined counterpart from VAG.
Similar technology has been used by other automotive companies, but "TDI" specifically refers to these Volkswagen Group engines. Naturally aspirated direct-injection diesel engines (those without a turbocharger) made by Volkswagen Group use the Suction Diesel Injection(SDI) label.
Because these engines are relatively low displacement and quite compact, they have a low surface area. The resulting reduced surface area of the direct injection diesel engine reduces heat losses, and thereby increases engine efficiency, at the expense of slightly increased combustion noise. A direct injection engine is also easier to start when cold, because of more efficient placing and usage of glowplugs.
Direct injection turbodiesel engines are frequent winners of various prizes in the International Engine of the Year Awards. In 1999 in particular, six out of twelve categories were won by direct injection engines: three were Volkswagen, two were BMW, and one Audi. Notably that year, the Volkswagen Group 1.2 TDI 3 L beat the Toyota Prius to win "Best Fuel Economy" in its class. The TDI engine has won "Green Car of the Year" award in the years 2009 (Volkswagen Jetta 2.0-litre common-rail TDI clean diesel) and 2010 (Audi A3 TDI clean diesel) beating other various electric cars.

### Emissions testing falsification

On 18 September 2015 the US EPA and California Air Resources Board served notice to VW that approximately 480,000 VW and Audi automobiles equipped with 2.0 TDI engines sold in the US between 2009 and 2015 had an emissions compliance defeat device installed. The defeat device, in the form of specially crafted engine management unitfirmware, detects emissions testing conditions, and in such conditions will cause the vehicle to comply with emissions regulations by properly activating all emissions controls. However, under normal driving conditions, the emissions controls are suppressed, allowing the engine to produce more torque and get better fuel economy, at the expense of emitting up to 40 times more nitrogen oxides than allowed by law. Such NOx emission levels are not in compliance with US regulations. VW has since admitted to these allegations, and said that the illegal software was in use in its diesel cars worldwide, affecting some 11 million vehicles.

## Fuel

The fuels required for TDI engines include diesel fuel (also known as petrodiesel), or B5, B20, or B99 biodiesel, depending on emissions equipment, location dependent.
A 2007 Volkswagen Jetta Mk5 with a 1.9 TDI engine and a five-speed manual transmission achieves 5.2 litres per 100 kilometres (54 mpg‑imp; 45 mpg‑US) on the European combined-cycle test (an US EPA test of the same vehicle would achieve around 34 MPG), while a six-speed direct-shift gearbox (DSG) automatic version reaches 5.9 litres per 100 kilometres (48 mpg‑imp; 40 mpg‑US).
Newer TDI engines, with higher injection pressures, are less forgiving about poor-quality fuel than their 1980s ancestors. Volkswagen Group's warranty does not cover damage due to bad fuel (diesel or bio), and has in the past recommended that only mixtures up to 5% biodiesel (B5) be used. Volkswagen Group has recently permitted mixes up to B20, and has recommended B5 be used in place of 100% petroleum-based diesel because of biodiesel's improved lubricating properties.
In North America, No. 2 diesel fuel is recommended, since it has a higher cetane number than No. 1 fuel, and has lower viscosity (better ability to flow) than heavier fuel oils. Some owners in North America, where cetane levels are generally poor (as low as 40), use additives, or premium diesel, to get cetane numbers closer to the standard levels found in the European market (at least 51) where the engine is designed. Improved cetane reduces emissions while improving performance, and may increase fuel economy.
New ultra low-sulphur petroleum-only diesels are known to cause some seals to shrink, and may cause fuel pump failures in TDI engines used in 2006 to 2009 models. TDI engines from 2009 on and before 2006 are designed to use ULSD exclusively; biodiesel blends are reported to prevent that failure

## Unit Pump System

The Unit Pump system is a modular high-pressure diesel injection system,  the system is closely related to the Unit Injector system UI, this system is mainly developed for use in commercial vehicle diesel engines.
The systems use a separate injection pump placed on the engine mountings for each cylinder so it is primarily designed for OHV or "cam in the block" engines. The fuel pumps are driven by an extra camshaft lobe where each pump unit is connected to the injector via a short precise length high-pressure fuel line as opposed to Unit Injector systems which combines both a pump and an injector element in a compact unit.
Both systems feature electronically controlled fuel solenoids for precise timing and the injection of fuel quantity is variably adjusted for each cylinder.
The high-pressure pump is driven directly by the engine camshaft. The pump’s high delivery rate ensures a continuous rise in pressure during the entire duration of the injection.
The injection valves meter the fuel with the help of high-speed solenoid valves. These are triggered by the electronic engine control unit. With variable injection start, variable injection duration, great latitude in adapting to the engine’s operating conditions as well as cylinder-specific correction capabilities, UPS contributes toward environmentally-friendly and fuel-saving engine operation.
The Unit Pump System is used for commercial-vehicle engines with performances of up to 80 kW per cylinder and up to eight cylinders. The electronic control unit can trigger a system comprising a maximum of eight cylinders. A second control unit allows the system to be extended to 16 cylinders.
Benefits
• Economical fuel consumption
• Low emissions
• Easy conversion from fuel-injection systems with in-line or distributor pumps
• Simple and fast customer service as the pumps can be exchanged easily
• no need to redesign the cylinder head

## Pantograph

pantograph (Greek roots παντ- "all, every" and γραφ- "to write", from their original use for copying writing) is a mechanical linkageconnected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line drawing is traced by the first point, an identical, enlarged, or miniaturized copy will be drawn by a pen fixed to the other. Using the same principle, different kinds of pantographs are used for other forms of duplication in areas such as sculpture, minting, engraving and milling.
Because of the shape of the original device, a pantograph also refers to a kind of structure that can compress or extend like an accordion, forming a characteristic rhomboidal pattern. This can be found in extension arms for wall-mounted mirrors, temporary fences, scissor lifts, and other scissor mechanisms such as the pantograph used on electric locomotives and trams.History
The first pantograph was constructed in 1603 by Christoph Scheiner, who used the device to copy and scale diagrams, but he wrote about the invention over 27 years later, in "Pantographice" (Rome 1631). One arm of the pantograph contained a small pointer, while the other held a drawing implement, and by moving the pointer over a diagram, a copy of the diagram was drawn on another piece of paper. By changing the positions of the arms in the linkage between the pointer arm and drawing arm, the scale of the image produced can be changed.In 1821, Professor William Wallace (1768–1843) invented the eidograph to improve upon the practical utility of the pantograph. The eidograph relocates the fixed point to the center of the parallelogram and uses a narrow parallelogram to provide improved mechanical advantages.

## Uses

### Drafting

The original use of the pantograph was for copying and scaling line drawings. Modern versions are sold as toys.

### Sculpture and minting

In sculpture, a three-dimensional version of the pantograph was used, usually a large boom connected to a fixed point at one end, bearing two rotating pointing needles at arbitrary points along this boom. By adjusting the needles different enlargement or reduction ratios can be achieved. This device, now largely overtaken by computer guided router systems that scan a model and can produce it in a variety of materials and in any desired size, was invented by inventor and steam pioneer James Watt (1736–1819) and perfected by Benjamin Cheverton (1796–1876) in 1836. Cheverton's machine was fitted with a rotating cutting bit to carve reduced versions of well-known sculptures Of course a three-dimensional pantograph can also be used to enlarge sculpture by interchanging the position of the model and the copy.
Another version is still very much in use to reduce the size of large relief designs for coins down to the required size of the coin.

### Acoustic cylinder duplication

One advantage of phonograph and gramophone discs over cylinders in the 1890s—before electronic amplification was available—was that large numbers of discs could be stamped quickly and cheaply. In 1890, the only ways of manufacturing copies of a master cylinder were to mold the cylinders (which was slow and, early on, produced very poor copies), to record cylinders by the "round", over and over again, or to acoustically copy the sound by placing the horns of two phonographs together or to hook the two together with a rubber tube (one phonograph recording and the other playing the cylinder back). Edison, Bettini, Leon Douglass and others solved this problem (partly) by mechanically linking a cutting stylus and a playback stylus together and copying the "hill-and-dale" grooves of the cylinder mechanically. When molding improved somewhat, molded cylinders were used as pantograph masters. This was employed by Edison and Columbia in 1898, and was used until about January 1902 (Columbia brown waxes after this were molded). Some companies like the United States Phonograph Co. of Newark, New Jersey, supplied cylinder masters for smaller companies so that they could duplicate them, sometimes pantographically. Pantographs could turn out about 30 records per day and produce up to about 150 records per master. In theory, pantograph masters could be used for 200 or 300 duplicates if the master and the duplicate were running in reverse and the record would be duplicated in reverse. This, in theory, could extend the usability of a pantograph master by using the unworn/lesser worn part of the recording for duplication. Pathé employed this system with mastering their vertically-cut records until 1923; a 5-inch-diameter (130 mm), 4-or-6-inch-long (100 or 150 mm) master cylinder, rotating at a high speed, would be recorded on. This was done as the resulting cylinder was considerably loud and of very high fidelity. Then, the cylinder would be placed on the mandrel of a duplicating pantograph that would be played with a stylus on the end of a lever, which would transfer the sound to a wax disc master, which would be electroplated and be used to stamp copies out. This system resulted in some fidelity reduction and rumble, but relatively high quality sound. Edison Diamond Disc Records were made by recording directly onto the wax master disc.

### Milling machines

Before the advent of control technologies such as numerical control (NC and CNC) and programmable logic control (PLC), duplicate parts being milled on a milling machine could not have their contours mapped out by moving the milling cutter in a "connect-the-dots" ("by-the-numbers") fashion. The only ways to control the movement of the cutting tool were to dial the positions by hand using dexterous skill (with natural limits on a human's accuracy and precision) or to trace a cam, template, or model in some way, and have the cutter mimic the movement of the tracing stylus. If the milling head was mounted on a pantograph, a duplicate part could be cut (and at various scales of magnification besides 1:1) simply by tracing a template. (The template itself was usually made by a tool and die maker using toolroommethods, including milling via dialing followed by hand sculpting with files and/or die grinder points.) This was essentially the same concept as reproducing documents with a pen-equipped pantograph, but applied to the machining of hard materials such as metal, wood, or plastic. Pantograph routing, which is conceptually identical to pantograph milling, also exists (as does CNC routing). The Blanchard lathe, a copying lathe developed by Thomas Blanchard, used the same essential concept.
The development and dissemination throughout industry of NC, CNC, PLC, and other control technologies provided a new way to control the movement of the milling cutter: via feeding information from a program to actuators (servos, selsyns, leadscrews, machine slides, spindles, and so on) that would move the cutter as the information directed. Today most commercial machining is done via such programmable, computerized methods. Home machinists are likely to work via manual control, but computerized control has reached the home-shop level as well (it's just not yet as pervasive as its commercial counterparts). Thus pantograph milling machines are largely a thing of the past. They are still in commercial use, but at a greatly reduced and ever-dwindling level. They are no longer built new by machine tool builders, but a small market for used machines still exists. As for the magnification-and-reduction feature of a pantograph (with the scale determined by the adjustable arm lengths), it is achieved in CNC via mathematic calculations that the computer applies to the program information practically instantaneously. Scaling functions (as well as mirroring functions) are built into languages such as G-code.

### Other uses

Perhaps the pantograph that is most familiar to the general public is the extension arm of an adjustable wall-mounted mirror.
In another application similar to drafting, the pantograph is incorporated into a pantograph engraving machine with a revolving cutter instead of a pen, and a tray at the pointer end to fix precut lettered plates (referred to as 'copy'), which the pointer follows and thus the cutter, via the pantograph, reproduces the 'copy' at a ratio to which the pantograph arms have been set. The typical range of ratio is Maximum 1:1 Minimum 50:1 (reduction) In this way machinists can neatly and accurately engrave numbers and letters onto a part. Pantographs are no longer commonly used in modern engraving, with computerized laser and rotary engraving taking favor.
The device which maintains electrical contact with the contact wire and transfers power from the wire to the traction unit, used in electric locomotives and trams, is also called a "pantograph".
Some types of trains on the New York City Subway use end pantograph gates (which, to avoid interference, compress under spring pressure around curves while the train is en route) to prevent passengers on station platforms from falling into or riding in the gaps between the cars.
Old-style 'baby gates' used a 2-dimensional pantograph mechanism (in a similar style to pantograph gates on subway cars) as a means of keeping toddlers away from stairways. The openings in these gates are too large to meet modern baby gate safety standards.
Herman Hollerith's "Keyboard punch" used for the 1890 U.S. Census was a pantograph design and sometimes referred to as "The Pantograph Punch".
An early 19th-century device employing this mechanism is the polygraph, which produces a duplicate of a letter as the original is written.
Longarm quilting machine operators may trace a pantograph, paper pattern, with a laser pointer to stitch a custom pattern onto the quilt. Digitized pantographs are followed by computerized machines.
Linn Boyd Benton invented a pantographic engraving machine for type design, which was capable not only of scaling a single font design pattern to a variety of sizes, but could also condense, extend, and slant the design (mathematically, these are cases of affine transformation, which is the fundamental geometric operation of most systems of digital typography today, including PostScript).
Pantographs are also used as guide frames in heavy-duty applications including scissor lifts, material handling equipment, stage lifts and specialty hinges (such as for panel doors on boats and airplanes).
Richard Feynman used the analogy of a pantograph as a way of scaling down tools to the nanometer scale in his talk There's Plenty of Room at the Bottom.
Numerous trade-show displays use 3-dimensional pantograph mechanisms to support backdrops for exhibit booths. The framework expands in 2 directions (vertical and horizontal) from a bundle of connected rods into a self-supporting structure on which a fabric backdrop is hung

## Thermoacoustic heat engine

 thermo-acoustic engine image sourse

## Operation

### Overview of device

A thermoacoustic device basically consists of heat exchangers, a resonator, and a stack (on standing wave devices) or regenerator (on travelling wave devices). Depending on the type of engine a driver or loudspeaker might be used as well to generate sound waves.
Consider a tube closed at both ends. Interference can occur between two waves traveling in opposite directions at certain frequencies. The interference causes resonance creating a standing wave. Resonance only occurs at certain frequencies called resonance frequencies, and these are mainly determined by the length of the resonator.
The stack is a part consisting of small parallel channels. When the stack is placed at a certain location in the resonator, while having a standing wave in the resonator, a temperature difference can be measured across the stack. By placing heat exchangers at each side of the stack, heat can be moved. The opposite is possible as well, by creating a temperature difference across the stack, a sound wave can be induced. The first example is a simple heat pump, while the second is a prime mover.

### Heat pumping

To be able to create or move heat, work must be done, and the acoustic power provides this work. When a stack is placed inside a resonator a pressure drop occurs. Interference between the incoming and reflected wave is now imperfect since there is a difference in amplitude causing the standing wave to travel little, giving the wave acoustic power.
In the acoustic wave, parcels of gas adiabatically compress and expand. Pressure and temperature change simultaneously; when pressure reaches a maximum or minimum, so does the temperature. Heat pumping along a stack in a standing wave device can now be described using the Brayton cycle.
Below is the counter-clockwise Brayton cycle consisting of four processes for a refrigerator when a parcel of gas is followed between two plates of a stack.
1. Adiabatic compression of the gas. When a parcel of gas is displaced from its rightmost position to its leftmost position, the parcel is adiabatic compressed and thus the temperature increases. At the leftmost position the parcel now has a higher temperature than the warm plate.
2. Isobaric heat transfer. The parcel's temperature is higher than that of the plate causing it to transfer heat to the plate at constant pressure losing temperature.
3. Adiabatic expansion of the gas. The gas is displaced back from the leftmost position to the rightmost position and due to adiabatic expansion the gas is cooled to a temperature lower than that of the cold plate.
4. Isobaric heat transfer. The parcel's temperature is now lower than that of the plate causing heat to be transferred from the cold plate to the gas at a constant pressure, increasing the parcel's temperature back to its original value.
Travelling wave devices can be described using the Stirling cycle.

An engine and heat pump both typically use a stack and heat exchangers. The boundary between a prime mover and heat pump is given by the temperature gradient operator, which is the mean temperature gradient divided by the critical temperature gradient.
${\displaystyle \mathrm {I} ={\frac {\nabla T_{m}}{\nabla T_{crit}}}}$
The mean temperature gradient is the temperature difference across the stack divided by the length of the stack.
${\displaystyle \nabla T_{m}={\frac {\Delta T_{m}}{\Delta x_{stack}}}}$
The critical temperature gradient is a value depending on certain characteristics of the device like frequency, cross-sectional area and gas properties.
If the temperature gradient operator exceeds one, the mean temperature gradient is larger than the critical temperature gradient and the stack operates as a prime mover. If the temperature gradient operator is less than one, the mean temperature gradient is smaller than the critical gradient and the stack operates as a heat pump.

### Theoretical efficiency

In thermodynamics the highest achievable efficiency is the Carnot efficiency. The efficiency of thermoacoustic engines can be compared to Carnot efficiency using the temperature gradient operator.
The efficiency of a thermoacoustic engine is given by
${\displaystyle \eta ={\frac {\eta _{c}}{\mathrm {I} }}}$
The coefficient of performance of a thermoacoustic heat pump is given by
${\displaystyle COP=\mathrm {I} \cdot COP_{c}}$

## Derivations

Using the Navier-Stokes equations for fluids, Rott was able to derive equations specific for thermoacoustics.[2] Swift continued with these equations, deriving expressions for the acoustic power in thermoacoustic devices.[3]

## Efficiency in practice

The most efficient thermoacoustic devices built to date have an efficiency approaching 40% of the Carnot limit, or about 20% to 30% overall (depending on the heat enginetemperatures).
Higher hot-end temperatures may be possible with thermoacoustic devices because there are no moving parts, thus allowing the Carnot efficiency to be higher. This may partially offset their lower efficiency, compared to conventional heat engines, as a percentage of Carnot.
The ideal Stirling cycle, approximated by traveling wave devices, is inherently more efficient than the ideal Brayton cycle, approximated by standing wave devices. However, the narrower pores required to give good thermal contact in a travelling wave regenerator, as compared to a standing wave stack which requires deliberately imperfect thermal contact, also gives rise to greater frictional losses, reducing the efficiency of a practical engine. The toroidal geometry often used in traveling wave devices, but not required for standing wave devices, can also give rise to losses due to Gedeon streaming around the loop.

## Research in thermoacoustics

Modern research and development of thermoacoustic systems is largely based upon the work of Rott (1980) and later Greg Swift (1988),in which linear thermoacoustic models were developed to form a basic quantitative understanding, and numeric models for computation. Commercial interest has resulted in niche applications such as small to medium scale cryogenic applications.

## Autocollimator

An autocollimator is an optical instrument for non-contact measurement of angles. They are typically used to align components and measure deflections in optical or mechanical systems. An autocollimator works by projecting an image onto a target mirror and measuring the deflection of the returned image against a scale, either visually or by means of an electronic detector. A visual autocollimator can measure angles as small as 0.5 arcminute (0.15 mrad), while an electronic autocollimator can have up to 100 times more resolution.
 autocollimator (image source)

Visual autocollimators are often used for lining up laser rod ends and checking the face parallelism of optical windows and wedges. Electronic and digital autocollimators are used as angle measurement standards, for monitoring angular movement over long periods of time and for checking angular position repeatability in mechanical systems. Servo autocollimators are specialized compact forms of electronic autocollimators that are used in high-speed servo-feedback loops for stable-platform applications. An electronic autocollimator is typically calibrated to read the actual mirror angle.

## Types Of Dies In Sheet Metal, Die Construction, Tool Making And Tool Engineering

Hi friends in the previous post we have discussed types of tool die operations. This post is about types of dies used in the manufacturing industry for sheet metal components. In which the function of dies and differences between these dies are mentioned.

### Sheet Metal Stamping Dies

Stamping dies are used to produce the high volume production by stamping process. The die will have the ability to provide appropriate stamping force to perform the required operation. In the die there will be two parts, upper half and the lower half. These part can also be referred as male part and female part. Male or female parts can take either the upper position or the lower position.

#### Construction of dies

In a tool, the punches of respective operations like blanking and punching is at the ram or at the bed of the plate. The ram will bolted with the bed of the machine.
For example, the figure of bending tool is given. The tool will rest on the bed of tool. And ram part will press the sheet metal component to produce a bend.

 Bending press tool

### Types Of Dies

The different types of dies are given below. The difference between them is important to understand.

#### Simple Dies

Dies which can perform only one operation in one stroke by press are known as simple dies. This operation can be either cutting operation or forming operation.

#### Combination Die

These dies are also able to perform more than one operation at one machine station. Since compound die can perform only cutting operation, this die can perform bending or drawing operation along with cutting operations. Because of these properties in the die it is called combination die. For example, to produce a cup shaped component the combination die can be used for blanking punching and drawing simultaneously.

#### Compound Die

Compound dies are those in which more than one operations can be performed by one stroke of press at a single station. Basically these types of dies are cutting tools. In such dies only cutting operations can be performed. For example a washer can be pressed out by performing blanking and piercing operation at the same station. These type of dies are very accurate than dies of single operation. Mass production by these dies is more economical than single operation die.

#### Progressive Dies or follow Dies

Die which can perform series of operations is called progressive or follow die. The operation is performed at each station on a work piece during a stroke of press. The work piece is transferred to the next station between the strokes. In every stroke a finished work is completed. For example, if piercing is done on a part in one stroke, the blanking punch tool cut a blank in the metal in which the previous hole is pierced at previous station. That is why after the first stroke, when thw hole will be punched, the finished product will be produced by each stroke of press.

#### Transfer Dies

In the transfer dies, the metal work piece do not fed progressively from one to another work station, as in the progressive dies. But in these type of dies the already blanked out work-piece is fed mechanically from one station to another station.

#### Multiple Dies Or Gang Dies

Multiple dies are those which has the ability to produce more than one work pieces in a single stoke of the press. This is also called Gang Dies.  In this die the number of simple dies and punches are combined or ganged together so that it can produced more than one parts at each stroke of the press.

#### Inverted Dies

In other dies, the punching tool is held in the punch holder plate which is fastened to the ram. On the other side, the die is fitted with die holder which is fastened at the bed of press. In the inverted dies there is a difference. The places of punch and die are interchanged. In this the punch if fastened at the bed of press and die is attached with the ram.

#### Difference between progressive die, combination die and compound die

Compound die performs one or more operation simultaneously while progressive die performs series of operations and combination die performs two or more operations at one station. Compound die only performs cutting operations and combination dies can perform other operations like bending, drawing etc.