Vauxhall's New Technique in Making Dies
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ItilANY components on commercial /V.I. ;vehicles are die-stampings, in which the metal used is forced into shape in metal dies. The process is quick, and the results excellent, as little or no machining is called for after the component has left the die-stamping machine.
The cost of the dies, however, is usually high. Furthermore, essential modifications in a component are often delayed as long as possible, because of the cost of new dies and the fear of production being interfered with as a result of the time factor in making the dies.
Dies, too, have been known to fail during a run on the presses, and so that there should be no undue hold-up it is general practice to have on hand a duplicate set which can be substituted for those which have failed.
Vauxhall Motors, Ltd., Luton, is now adopting an entirely new method. which virtually revolutionizes die production. Dies are now cast, instead of being shaped out of solid blocks of steel.
Normal Preliminaries ' Known as the Kirksite system—the name being derived from that of the man who evolved the metal used—the preliminaries are the same as with the normal procedure. First, the component —say, a valve rocker cover—is designed and a wood pattern made. Thereafter, however, the proceedings are entirely different.
The pattern is taken and placed inside a strong wood case—known as a flask—and moulding sand is packed tightly around it. The flask is then fitted with a lid, turned upside down, and the pattern removed. The metal
is poured into the space left by the pattern, and when the metal has cooled the flask is removed, the sand knocked away, and the die is formed, completing the operation.
It is sometimes possible to dispense with the making of a female pattern by using the male casting. This is coated with a special preparation. placed in the flask, and molten metal poured over it. This results in the production of a female die which exactly matches the male—an achievement which is almost impossible when both male and female have to be cut from solid metal.
The metal used is a zinc-base alloy having an ultimate tensile strength of 37,800 lb. per sq. in., a Brinell hardness of 100—which can be increased to 130 by cold quenching—a compression strength of 60,000-75,000 lb. per sq. in., a melting point of 717 degrees F., and a solidification shrinkage of only. 0.14 in. per ft.
Some idea of the sensitiveness of the metal may be gauged from the fact that even a pencil mark on the pattern will reproduce on the die.
The first " pour " was made in the new foundry at Luton on August 26, and when the foundry is in full swing it will have a capacity for casting 25 tons of metal daily. This new process illustrates the progressive outlook of the Vauxhall concern.