Design away die-casting difficulties

Design for Manufacturing (DFM) is one of those “best practices” that engineers routinely claim to follow. The reality, though, is that manufacturing often takes a back seat to functionality during the design process. With die-cast parts, ignoring manufacturability can be a particularly expensive mistake.

Parts designed without regard for die-casting’s DFM guidelines are more likely to require expensive secondary operations, such as finish machining or extra assembly steps. They may suffer from lower yields and quality problems, driving up scrap rates. In the worst cases, parts may even be impossible to cast and require an expensive redesign.

All these factors add dramatically to the part and life-cycle costs of diecast components. Consider that secondary operations alone can represent as much as 80% of a cast-part’s cost. Low yields likewise drive up manufacturing expenses. Poor quality can trigger immediate and longterm cost increases, too, not just from lower yields but also as premature failures in the field. And those trips back to the drawing board to rework unsatisfactory designs can delay product introduction and drive up development costs.

Fortunately, designing with the die-casting process in mind helps avoid all these pitfalls. Dynacast engineers, for example, use a Design for Die Casting (DFDC) methodology that optimizes casting manufacturability while preserving functionality. The gains from DFDC vary with each job, depending on whether the initial design is casting-friendly or not. But our engineers routinely manage to cut total costs by 30% or more. Here’s a look at the three key strategies behind DFDC.

Improve the geometry
Engineers must follow part-design guidelines for most manufacturing processes, and die casting is no exception. Its design-for-manufacturing guidelines cover geometry, wall thickness, draft angles, and more.

Much of this information is readily available from qualified manufacturers. Dynacast’s Web site for example, includes interactive tools that can guide engineers through important part-geometry decisions. The North American Die Casting Assn.’s Web site is also a good source of information, including detailed die-casting specifications with design recommendations.

These guidelines go a long way toward improving the die-casting process as well as the quality of the parts themselves. It’s important to keep in mind, however, that published design guides are best regarded as the basics. Pushing the envelope with die casting sometimes requires that engineers bend or even break the basic design rules.

And that’s where the skill of the die caster comes into play. Those with advanced machines, process controls, tooling, and engineering know-how can offer more design freedom than the basic rules typically permit.

Consider the wall thickness of zinc die castings, for example. Traditional design rules specify uniform walls at least 1.1-mm thick, without any abrupt thickto- thin transitions. But engineers increasingly want thinner parts or localized thinwall sections to reduce mass or part size, or to save on materials. Dynacast regularly produces parts significantly thinner than traditional guidelines recommend. The thinnest of these parts have nominal walls down to 0.3 mm with localized transitions down to 0.2 mm.