Tool Design

For production volumes a dedicated press tool is required for manufacture of BREMAG magnets.

Compared to injection moulding tooling compression bonding tooling is simpler and usually cheaper.

Although we do not manufacture our own tooling in house, our engineers have considerable experience in the design of tooling and are often involved in the design with the tool manufacturers. This means during the development stages of a product we can advise customers of any practical limitations on the size or shape of magnet they are designing or features that would be beneficial for production.

Compression Moulding

A standard compression moulding tool consists of a dye with a one or more cavities into which the powder is loaded and a punch that compresses the powder. If a hole is required in the part, as in the case of a ring magnet a core rod inside the die is used. Although in principle any 2D shape that can be extruded in the direction of pressing can be pressed as a bonded magnet, it advisable to keeping the shape as simple as possible, avoiding undercuts or anything that will key the product into the press tool. The pressed part needs a straight clear route that can be ejected out through the die cavity. Example a top hat shape can be pressed and ejected provided it is made upside down.

When considering manufacture by the compression bonding it is advisable to avoid chamfers or radii on edges where possible, as they add cost to the tooling and greatly reduce the running life between re-faces. It is standard practice to rework the faces of the punches and core rods throughout the life of a tool to keep edges sharp in order to maintain tolerances. A point to bear in mind is that bonded neodymium does not chip easily like some sintered magnets and burrs never form on internal or external diameters. Features such as keyways and slots, holes on a P.C.D. array are all possible as are counter bores and countersinks.

With existing equipment Bunting Magnetics can press parts up to a depth of 40mm depending on the top surface area. The maximum pressing area is 33cm which a ring of up to 200mm diameter can be pressed provided the inside diameter is no less than 190mm.