Volumes of production

In order to justify the setup and tooling costs, high-volume production is needed—a minimum of 10,000 units.

Unit price vs. capital investment

High capital investment but a very low unit price.

Speed

The actual injection of material is similar to that of standard injection molding in plastics (see p.196), but the sintering and the removal of the binder add time and expense to the process.

Surface

The process gives an excellent surface finish on components and has the ability to produce fine detail.

Types/complexity of shape

Highly complex shapes similar to those obtainable through standard plastic injection molding. These can also be enhanced by the use of multicavity tooling.

Scale

MIM is currently capable of producing only small parts for use in larger products.

Tolerances

The MIM process can achieve a general tolerance of ±1/250 inch.

Relevant materials

MIM is economical for producing large numbers of complex components with a range of surface finishes. It can be applied to a range of metals: bronze, stainless steel, low-alloy steels, tool steels, magnetic alloys, and alloys of low thermal expansion.

Typical products

Surgical and dental tools, computer components, automotive parts, casings for electronics and consumer products (cell phones, laptops, PDAs).

Similar methods

Although die-casting in metal (p.219) is possibly the closest to MIM in terms of production quantities and complexity of shape achievable, the key difference between the processes is in the ability of MIM to work with metals with high melting points, such as low-alloy steels and stainless steel.

Sustainability issues

The additional processing and heating cycles significantly increase energy consumption in comparison with traditional plastic injection molding. Compared to casting or metal machining, there is practically no excess or scrap material, which helps to reduce waste and energy use from secondary processing. The high-temperature nature of the materials means they are less likely to feed into the recycling stream.

Further information

www.mimparts.com

www.pi-castings.co.uk

www.mpif.org

High-Pressure Die-Casting

Product	Matchbox Lotus Europa
Materials	zinc
Manufacturer	Matchbox
Country	UK
Date	1969

Die-cast metal toys are part of many people’s childhood memories. The ability of die-casting to create fine, complex details is well illustrated by the clearly legible text on the underside of my son’s toy car.

High-pressure die-casting is one of the most economical methods of producing metal components with complex shapes. It is the process to use if you want to produce high volumes of intricate components. In this sense, it is similar to metal injection molding (MIM) (see p.216), but its main advantage over MIM is that it is suitable for metals with low melting points where no sintering is required.

The process involves molten metal being poured into a reservoir, where a plunger forces the liquid, under high pressure, into a die cavity. The pressure is maintained until the metal solidifies, at which point small ejector pins push the components out of the die. Just as in injection molding (see p.196), die-casting molding dies are made in two halves.

–  Ideal for complex shapes.

–  Excellent surface finish.

–  Good dimensional accuracy.

–  Can allow for small sections and thin walls.

–  Excellent consistency between parts.

–  A fast process that requires minimal post-machining work.

–  The tooling is expensive, so the process is only suited to very high production volumes.

–  Produces parts where flash is present.

–  Parts are not guaranteed to have high structural strength.