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Friday 8 November 2013

Extrusion

Extrusion is the process by which long straight metal parts can be produced. The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes. Tubes and many other different types. Extrusion is done by squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press.
Extrusion produces compressive and shear forces in the stock. No tensile is produced, which makes high deformation possible without tearing the metal. The cavity in which the raw material is contained is lined with a wear resistant material. This can withstand the high radial loads that are created when the material is pushed the die.
Extrusions, often minimize the need for secondary machining, but are not of the same dimensional accuracy or surface finish as machined parts. Surface finish for steel is 3 µm; (125 µ in), and Aluminum and Magnesium is 0.8 µm (30 µ in). However, this process can produce a wide variety of cross-sections that are hard to produce cost-effectively using other methods. Minimum thickness of steel is about 3 mm (0.120 in), whereas Aluminum and Magnesium is about 1mm (0.040 in). Minimum cross sections are 250 mm² (0.4 in²) for steel and less than that for Aluminum and Magnesium. Minimum corner and fillet radii are 0.4 mm (0.015 in) for Aluminum and Magnesium, and for steel, the minimum corner radius is 0.8mm(0.030 in) and 4 mm (0.120 in) fillet radius.

Tuesday 29 October 2013

Green Sand Molding

The most common method used to make metal castings is green sand molding. In this process, granular refractory sand is coated with a mixture of bentonite clay, water and, in some cases, other additives. The additives help to harden and hold the mold shape to withstand the pressures of the molten metal.
The green sand mixture is compacted through mechanical force or by hand around a pattern to create a mold. The mechanical force can be induced by slinging, jolting, squeezing or by impact/impulse.
The following points should be taken into account when considering the green sand molding process:

for many metal applications, green sand processes are the most cost-effective of all metal forming operations;
these processes readily lend themselves to automated systems for high-volume work as well as short runs and prototype work;
in the case of slinging, manual jolt or squeeze molding to form the mold, wood or plastic pattern materials can be used. High-pressure, high-density molding methods almost always require metal pattern equipment;
high-pressure, high-density molding normally produces a well-compacted mold, which yields better surface finishes, casting dimensions and tolerances;
the properties of green sand are adjustable within a wide range, making it possible to use this process with all types of green sand molding equipment and for a majority of alloys poured.

Wednesday 23 October 2013

METAL CASTING PROCESSES

•Sand Casting

•Other Expendable Mold Casting Processes

•Permanent Mold Casting Processes

•Foundry Practice

•Casting Quality

•Metals for Casting

•Product Design Considerations

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