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Casting processes - Gravity Die The process is capable of producing castings in cast iron, copper base alloys, aluminium alloys and others including zinc. It is used for medium to long runs of castings with weight ranges typically from ½ kg to 50kg. It can be automated to a certain extent on the closing and pouring side. Much of the production involves manual labour. Most of the output is aluminium castings.
Brief description
The gravity diecasting process may be simply defined as follows:
The production of castings from a reusable mould or die having two or more parts each located in relation to other parts. The die contains an impression of the casting together with its running, feeding and venting systems. Provision is made for the removal of the casting by some means. The die can readily be cleared of debris such as hot metal splashes and sand so that the casting's accuracy is maintained. The die is capable of a regular cycle and of (quickly) dissipating the heat of the metal poured into it.
The gravity diecasting process has had a long history and will continue to supply both simple and complex quality castings well into the foreseeable future. It lacks the obvious attraction of sophisticated machines used by pressure diecasters and to the outsider may seem archaic. The gravity process can handle heat treatment high strength aluminium alloys that pressure diecasting still cannot.
The process is a viable route for castings with complex intricate coring and for castings with small volumes uneconomic for pressure casting production. The UK has traditionally produced a greater tonnage gravity diecastings than pressure castings. The combined tonnage of gravity and low-pressure diecasting is still greater than the tonnage of pressure diecastings made in the UK today.
The process has had very little research funding and there are few opportunities world wide for adequately training an aspiring gravity diecasting technician. Thereafter a long period of production, gravity diecasting toolmaking and die design experience is necessary before a good (imaginative) gravity die designer is produced. There are few such people. As a result many diecasting plants perform well below the achievable. The exceptions are memorably impressive. It is a class process that is rarely pushed to its limits.
In spite of this, the process's flexibility plays well in a market place demanding quality castings. There is much more to gravity diecasting than an impression in a block.
Courtesy of the Institute of Cast Metals Engineers.
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