02-02-2013, 12:41 PM
Casting Processes
Casting Processes.ppt (Size: 1.25 MB / Downloads: 95)
Shell Molding
It is a process in which, the sand mixed with thermosetting resin is allowed to come in contact with the heated metallic pattern plate, so that a thin and strong shell of mould is formed around the pattern, Then the shell is removed from the pattern and the cope and drag are removed together and kept in a flask with necessary back up material and then the molten metal is poured.
Applications
-Crankshaft fabrication
-Steel casting parts, fittings
-Molded tubing fabrication
-Hydraulic control housing fabrication
-Automotive castings (cylinder head and ribbed cylinder fabrication).
Precision Investment Castings through Lost Wax Process
Investment Casting uses a mold that has been produced by surrounding an expendable pattern with a refractory slurry that sets at room temperature. The pattern (usually of wax) is then melted or burned out, leaving the mold cavity.
Investment casting is also known as the "lost-wax process" and as "precision casting".
In Investment casting, a metal pattern die is used to produce the patterns, which, in turn, are used to produce ceramic molds. Both the pattern and molds are expendable. Ceramic cores are used, as required, and these also are expendable.
Precision Investment Castings
Investment casting is the most flexible of all the precision casting process with respect to attainable intricacy, precision and the variety of alloys that may be cast within its inherent size limitations.
Many exaggerated claims were made regarding the "precision" casting process.
Many technical articles purported to establish the dimensional tolerances for production castings to limits as extreme as 0.0001 in.
In reality, however, liner tolerances of 0.002-0.005 in. per inch where difficult to obtain
Advantages of precision casting
Complex shapes can be made as there is no need to withdraw the pattern
Very fine details and thin sections can be obtained
Reasonably close tolerances and good finish can be achieved
Castings require little or no machining
Since there is no parting line the dimensions across will not vary