Dip mould tooling overview

The tooling for dip moulding is usually cast and/or machined aluminium although other metals including steel and brass are also used. The former is of the male type and so is easily produced in even the most basic of machine shops. However, where more complex shapes are required it makes economic sense to have the tooling cast and machine finished. Sand casting is predominantly used and the dip mould former shares many of the requirements of the patterns used for sand casting where draught angles and radii are concerned.

Basic tool requirements

The one most important fact to be born in mind with dip moulding tooling is that the moulding material is a thick liquid that gels once it comes into contact with a heat source. To offer a flat surface, a hole or undercut to the material surface can trap air and produce holes or depressions in the moulding. However, air entrapment can be used positively for producing openings in the moulding that would otherwise have to be produced as a post moulding operation.

The control of air entrapment can also be governed by tool temperature as a cooler than normal dip will allow the material to flow more easily in and out of depressions or valleys, such as in the case of some bellows tooling where the material will flow over the convolutions and trap air rather than flow up and down, The speed of the dip also has its influence as too slow a speed coupled with high temperature can cause "creep" lines that in severe cases will cause small pin holes to form. By the same token too fast a dip speed may well cause air to be trapped.

Products as formers

There are applications where the item that is to be fitted with a dip moulding can be used as tooling saving a considerable amount of expense compared with tooling from scratch. Consider a tubular "U" shaped frame that has the ends flattened. There may well be a requirement for a cap to be fitted over the flattened ends of the piece so as to offer protection to either the surface the frame comes into contact with or the end of the piece itself. In such a case the frame, or sections from it, could be used as the tooling. The fit of the mouldings produced from such tooling will be aided by the fact that such work is usually finished in a paint or a plastic coating which of course would not be applied to the tooling made from the same item.