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There are numerous manufacturing processes to transform raw material into designed products:
Simplified, the system is a two electrode system separated by a dielectric medium. The wire is one electrode and the workpiece
being machined is the other. EDM machining utilizes a voltage across these two electrodes which is greater than the breakdown
voltage across the gap between the workpiece and the wire. This breakdown voltage is a function of the distance between the wire
and workpiece, the insulating properties of the dielectric (fluid separating the electrodes), and the degree of pollution of the
gap.
Sheet metal forming is a grouping of many complementary processes that are used to form sheet metal parts. One or more of these
processes is used to take a flat sheet of ductile metal, and mechanically apply deformation forces that alter the shape of the
materia. Before deciding on the process(es), one should determine whether a particular sheet metal can be formed into the desired
shape without failure.
The various sheet metal forming processes are:
| Process | Characteristics |
| Roll forming | - long parts with constant complex cross-sections;
- good surface finish;
- high production rates;
- high tooling costs.
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| Stretch forming | - large parts with shallow contours;
- suitable for low-quantity production;
- high labor costs;
- tooling and equipment costs.
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| Drawing | - shallow or deep parts with relatively simple shapes;
- high production rates;
- high tooling and equipment costs.
|
| Stamping | - includes a variety of operations, such as punching, embossing, bending, flanging, and coining;
- simple or complex shapes formed at high production rates;
- tooling and equipment costs can be high, but labor cost is low.
|
| Rubber forming | - drawing and embossing of simple or complex shapes;
- sheet surface protected by rubber membranes;
- flexibility of operation;
- low tooling costs.
|
| Spinning | - small or large axisymmetric parts;
- good surface finish; low tooling costs, but labor costs can be high unless operations are automated.
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| Superplastic forming | - complex shapes, fine detail and close tolerances;
- forming times are long, hence production rates are low;
- parts not suitable for high-temperature use.
|
| Peen forming | - shallow contours on large sheets;
- flexibility of operation;
- equipment costs can be high;
- process is also used for straightening parts.
|
| Explosive forming | - very large sheets with relatively complex shapes, although usually axisymmetric;
- low tooling costs, but high labor cost;
- suitable for low-quantity production;
- long cycle times.
|
| Magnetic-pulse forming | - shallow forming, bulging, and embossing operations on relatively low-strength sheets;
- most suitable for tubular shapes;
- high production rates;
- requires special tooling.
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Molten metal is forced into the die cavity at pressures ranging from 0.7 to 700 MPa. When the metal solidifies the die halves
open and the casting is ejected.
Metal mold makes wax or plastic replica of the piece to be cast. These replica are spruced, then surrounded with investment
material, baked out, and metal is poured in the resultant cavity. Molds are broken to remove the castings.
Tempered sand is packed onto wood or metal pattern halves, removed from the pattern, and assembled with or without cores, and
metal is poured into resultant cavities. Various core materials can be used. Molds are broken to remove castings. Specialized
binders now in use can improve tolerances and surface finish.
Resin-coated sand is poured onto hot metal patterns, curing into shell-like mold halves. These are removed from the
pattern and assembled with or without cores. Metal is poured into resultant cavities. Molds are broken to remove castings.
In slip casting - sometimes called drain casting - a plaster of paris mold is filled with a slip. Slip is a liquid containing a
ceramic material in a water suspension. As the mold absorbs water, the ceramic suspension solidifies uniformly on the walls of
the mold. Once the desired wall thickness is reached, the remaining slip is drained, the mold is separated or broken, and the part
is removed. The part, now in a powder compact or green stage, is then sintered in an oven.
In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3000 rpm) as the molten metal is
poured. The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is
usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical
situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.
Extrusion is a process that forces metal to flow through a shape-forming die. The metal is plastically deformed under compression
in the die cavity. Extrusion processes can be carried on hot or cold. Extrusion differs from drawing in that the metal is pushed,
rather than pulled under tension.
Forging denotes a family of processes by which plastic deformation of the workpiece is carried out by compressive forces, at room
temperature, or at elevated temperatures, hence the terms cold and hot forging. Simple forging can be made with a heavy hammer and
an anvil using techniques that have been available for centuries. However, usually a set of dies and a press are required.
Milling is one of the most versatile processes. Milling uses a multitooth cutter that rotates along various axes with respect to
the workpiece. Milling includes a number of versatile machining operations, which are capable of producing a variety of
configurations using a milling cutter.
Turning is one of the oldest and the most fundamental manufacturing processes. It is the machining of a round workpiece; the
profile of the workpiece can be straight, conical, curved, or grooves, like shafts, spindles, pins, handles, and various machine
components. In turning, the work piece is rotated and the cutting tool is stationary; this is different from another very old and
traditional machining process, milling, where the cutting tool rotates and the workpiece moves in transition only.
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