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metalcasting 101 M


Exploring Permanent Molding Cast Metals Institute, Schaumburg, Illinois


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ermanent mold casting is a manufacturing process using a metal or graphite mold in- stead of sand, ceramics


or other media that can be broken up to remove the solidified part. The mold halves, or dies, are closed when molten metal is introduced to create a casting and opened to remove the casting. The molds are themselves cast to shape and machine finished or cut entirely from billet. Permanent mold castings typi-


cally are poured in one of four ways. Static pouring involves hand pour- ing the metal into an opening at the center of the mold. Test bars and chemistry slugs often are poured this way, along with simple shape castings. Molds also can be poured horizontally and then hydraulically tilted to a vertical position. This “tilt-pour” method utilizes a pouring cup and engineered system to intro- duce metal into the mold in a more controlled, calm manner. Preventing metal splashing in the mold cavity increases the casting’s mechani- cal properties. The third method involves using low pressure to slowly fill the mold and reduce turbulence even further. Finally, high pressure diecasting involves forcing molten metal into the mold cavity quickly using a hydraulic mechanism. Alu- minum alloys are well suited to the permanent mold casting process, particularly diecasting. T e thickness of the mold area af-


fects the molten metal’s solidifi cation rate. Due to the mold’s high thermal conductivity, molds can be heated to prevent premature solidifi cation. Specifi c areas of the mold also can be coated to insulate the molten metal, as well as protect the mold surface. Another method of controlling solidi- fi cation is implementing cooled metal pieces, or inserts, in the mold. Due to the complete lack of permeability of a permanent mold, vents must be consid-


The tilt-pour process allows metal to be introduced into the mold with little turbulence.


Diecasting uses high pressure to blast metal into the mold cavity in a single shot.


ered during the engineering phase and machined into the dies. Sand cores can be used to produce complex castings in the permanent mold process. Despite the size and shape limitations


of the process, permanent mold castings off er good repeatability, good surface fi n- ish and fi ne grain structure. T e process is best when used for medium to high volume production runs. 


Mar/Apr 2012 | METAL CASTING DESIGN & PURCHASING | 51


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