Light-Alloy Foundry Technique
The Manufacture and Use of Metal Patterns: Cores and Moulds
One of the important results of the influence of the aircraft industry has been the demand for accurate high-quality light alloy castings in large quantities; also, foundry standards have been raised to a level that a few years ago would have been considered impossible. To a large extent, output requirements have been met by plant mechanization and the wider use of machine moulding, as described in past issues of this journal, whilst accuracy and quality have been improved by the introduction of new techniques.
The development of metal patterns for machine moulding is one such advance which has played an important part in improving dimensional accuracy and the quality of surface finish of light alloy castings, and in this article we describe the manufacture and use of such equipment by Magnal Products, Ltd., who are specialists in this technique.
This article first appeared in the Volume 6, Number 64 (February, 1944) issue of Aircraft Production magazine, and is presented here through the kind permission of Flight International. Thanks also to Bruce Vander Mark for furnishing volumes of Aircraft Production for scanning.
One of the innovations forced upon light alloy foundries during the past few years has been the extended use of metal patterns for machine moulding in preference to the wood type traditionally associated with sand casting. It is true, of course, that metal equipment is only an economic proposition when sufficiently large numbers of castings are required, but the resultant castings are so superior in many respects that attempts are made to apply the technique whenever possible.
The chief advantage of metal layouts is that it enables the application of standardization to foundry work, assisting in giving detailed processes that, for accuracy, are akin to modern machine shop production practice, i.e. their use enables production engineering methods to be applied in the sand foundry. Apart from the obvious advantage of easier production, moulds made by this method are extremely accurate, and such faults as crushes on the parting line and variations in wall thickness are eliminated. The production of high-quality aircraft castings, however, depends upon much more than a suitable mould for the metal. For example, the speed at which the metal enters the mould is a very important factor; here, the use of metal patterns ensures running channels and risers of constant shape and size, thus avoiding the inaccuracies and scrap often caused by hand-cut channels or risers of uncertain volume. These conditions apply also to the design of core boxes, and, indeed, by taking thought, core-making may be reduced to a minimum.
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