UNIVERSITI MALAYSIA PAHANG
BMM3643 (SEM II_2012-13)
1. a) What metals are frequently cast into products?
b) What materials are used to produce the expendable patterns for investment casting?
c) Explain why a casting may have to be subjected to various heat treatments.
a) Cast parts can range in size from a fraction of an inch and a fraction of an ounce to over 30 feet and many tons. Moreover, casting can incorporate complex shapes, hollow sections or internal cavities, and irregular curved surfaces.
b) In investment casting a pattern is formed from a low melting temperature, low vaporization temperature material, often wax. The mold is produced by surrounding the pattern with the mold material. The mold cavity is produced when the pattern is removed by melting/vaporizing the pattern. In early process development with porous mold materials the melted wax from the pattern would migrate into the mold material and be lost.
c) Heat treatments (described in Chapter 4) such as quenching and tempering, among others, are carried out to optimize the grain structure of metal castings, thereby controlling and enhancing mechanical properties. Heat treating can control microporosity, which is a main reason that castings are weak in tension.
2. a) What are some of the attractive features of die casting compared to alternative casting methods? b) For the cast metal wheel illustrated in Figure below, show how (a) riser placement, (b) core placement, and (c) chills may be used to help feed molten metal and eliminate porosity in the isolated hub boss.
c) What are some of the general defects encountered in casting processes? Name and briefly describe three. (8 marks)
a) Die casting is characterized by extremely smooth surface finishes, excellent dimensional accuracy, and high production rates. A single set of dies can produce many