Cold Chamber Die Casting

by Sudarsan Chakraborty

The cold chamber die casting is a process that uses the investment mold method and which makes use of solidifying from both sides to make the casting cooling faster. The main working principles are as followed: when the centrifugal force exists in the liquid metal, it will spin in one direction along with the liquid metal rotating under gravity; at this moment, the molten metal flow will be occurred outwards via expansion and contraction channels on two opposite surfaces; finally, two surfaces become parabola spouts.

The cold chamber die casting investment process consists of mold preparation, wax model making and molding wax forming (lost pattern method), injection of molten metal into a block made by steel plates called “investment”, before being cooled slowly which takes about 30 minutes or so at room temperature; then pressurized air blows away the investment from around the casting via water steam explosion, after which the casting is further slowly cooled via air blowing. There are two types of cold chamber die casting, one is the “closed type” which has air circulation from both sides of the cooling block; it just takes about 5 to 10 minutes for cooling after blowing away investment. The other one is “open type”, using a water steam explosion to blow away the investment, that then uses compressed air as a pressurized, therefore taking about half an hour for cooling.

1. The closed type die casting: Once investment around the mold blocks have been blown off by hot water and steam, they are covered up by cold-chamber covers.
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Both water and steam enter from inlet pipes located on top cover of each chamber and flow outwards through outlet pipes located on bottom cover of each chamber.
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2. The open type die casting: A liquid metal bath (a tank which is used to store molten metal and will be connected with the die casting machine later) is located under the cooling block, usually a porous plate; after the insulation has been removed, it is filled up with cold water in order to cool down the mold blocks more conveniently. After blowing off investment by hot water and steam from around both covers, compressed air blows over them; meanwhile cold water runs through pipes made out of stainless steel. The top cover can be moved horizontally towards right or left while being vertical along an axis. There are two pairs of vertically installed rolling wheels at both ends of top cover for moving purposes. The top cover takes advantage of the pair of wheels to roll over an outer side mobile frame, thus rolling outwards and going in. There is an evacuation gear for releasing pressure on the cooling block at both ends of bottom covers; when temperature gets lower, this gear will move downwards then close up tightly to make a hermetic seal once again.

The cold chamber die casting process uses water spray and air blowing to remove investment from around the mold blocks. 30 minutes have passed by after blowing off investment then they are removed from inside the machine; however, it needs another 1 hour or more for them to cool further before workers can remove those parts which are called “casting rings”.

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