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Revision as of 15:34, 6 September 2007

When manufacturing shapes that are too complex or costly to simply cut, a casting process can be used. Casting is the process whereby a solid is obtained from a molten material, such as metal or plastic, poured into a mold.

Problems

Castings will often shrink when they cool due to solidification and temperature differences. Different materials have different shrinkage rates. Shrinkage can sometimes cause problems because it weakens the cast by leaving cavities. One way of dealing with this problem is to oversize the pattern by 1-6%. Another solution is to include risers, often called feeders, are included in the cast. Risers pump additional material into the cast as it solidifies.

Types

http://www.pyrotek-inc.com/item_files/section_large/Sand-Casting-pic.jpg

http://www.pyrotek-inc.com/section.asp?id=150

http://www.codesmiths.com/shed/things/smithing/casting/halloween_foam.jpg

[Investment Casting:] http://www.railway-technology.com/contractor_images/pickersgill/pk5.jpg One of the oldest processes for metal forming is Investment Casting. This process uses a wax as the mold for the hot metal. This process is primarily concerned with the production of the wax mold. This rather complicated process can most easily be described as a series of dipping and coating a positive of the metal, until a sufficiently thick shell remains to be used as the mold.

http://samkwangprecision.en.ec21.com/co/s/samkwangprecision/upimg/mold.jp

Vacuum Casting: http://abbess.com/vac/images-castingsystem/DSCF0017.JPG Vacuum casting utilizes vacuum pressure to force the heated and liquified material into the mold. It can be used to make small and detailed metal parts. Various gasses can also be introduced into the process to improve the process to remove pores and prevent oxidation during the casting.

Centrifugal Casting: http://www.spincast.co.nz/unzipped/img/index.jpg Similar to vacuum casting, centrifugal casting is ideal for casting small and detailed parts. However, instead of using a vacuum force to draw the metal into the mold, molten metal is forced into the mold by centrifugal force. Apart from forcing the molten metal into a fixed mold, this process can also be used to create symmetrical objects such as metal wheels or cymbals.

Continuous Casting: http://www.agcarbon.com/images/content/specgraph_razlivka1.jpg A casting process used when high-volume constant cross-sectional pieces are needed. For example, stock products, such as angled-aluminum are made using a continuous casting process. In this process the material being used is heated to a molten state. It is forced through a mold by gravity, typically no bigger than 0.5m. The metal is then shaped and continues to slide downward (sometimes curved to horizontal) while being cooled. This process is non-stop and pieces are simply cut off while moving to the correct length.

Billet: The thing that the bar is called http://www.industry.siemens.com/metals/en/VAI/Continuous_Casting_VAIPOMINI-Billet.htm