Benefits of diecast prototyping

Traditionally diecast prototype moulds have been created by spin casting or machining due to the perceived expense and impracticality of diecasting prototypes. However, in recent years it’s become apparent that one of the most effective ways to create a prototype mould for diecasting, is to diecast it.

Spin casting and machining, although great for creating prototypes, can’t perfectly duplicate the mechanical properties of the cast in the same way diecasting can. The reason why is down to the part’s final microstructure which is greatly affected by the result of the tooling, process conditions and the part’s surface shape. Although in many cases these different types of prototyping can employ very similar metal alloys, the parts they produce have a grain structure and density which differ greatly from one another. Diecasting the prototype helps to eliminate any variables in production, which wouldn’t get picked up by casting the mould in any other way.

3 Problems with using spin cast or machined prototypes for diecast parts

When a spin cast or machined tool is used as a prototype for production, this doesn’t offer an accurate representation of what the final part will be like if the parts will be diecast. There are three main differences which make the process problematic.

1. Added strength

The strength of a part is most noticeable on the surface and diecast components obtain a substantial amount of tensile strength and durability from the top layer or “skin” that forms on the surface of the part as a result of molten metal filling the die and rapidly cooling. This process creates a non-porous ‘skin’ on the surface which is around 0.5mm thick which strengthens the part. Prototypes which haven’t been diecast don’t have the benefit of this ‘skin’ which, whether diecasting zinc or aluminium, adds strength and size to the part. As diecasting adds around 0.5mm to a design, this would need to be accounted for when the parts are put into production.

2. Part geometry

The surface shape and structure of a part influences not only how the part fills and cools but also its permeability and grain structure. The surface structure also determines the part’s internal stress states and this impacts on areas which can potentially reduce a part’s strength, such as sharp corners. When parts have been designed with diecasting in mind, and therefore account for filling, cooling and ejection, they have microstructures which differ significantly when compared to machined or spin cast parts. The problem with not diecasting a prototype for a diecast production is that the grain structure (and therefore the parts’ strength) will differ.

3. Process Conditions

The diecasting process involves extremely high temperatures, which are combined with high-pressures and rapid cooling. This process produces parts which will have very different grain structures when compared to processes like spin casting or machining which involve low-pressure and low-temperatures. This difference in processes is another reason why spin casting and machining provide such an imbalance of strength in the final parts when compared to the diecasting process.