Design for Casting Manufacture Part 1

Die castings have a number of part design requirements in order to ensure castability.  Beyond that, many quality problems are designed into, or can be designed out of a casting product.

 

There are many concerns that must be addressed when designing a die casting.  Since parts are made from a permanent die casting die, the design of a part is difficult to change once a tool is built.  Parts made from this tool will be very similar to each other, so problems put into the part design will repeat.  For this reason, it is important that the design of a successful die casting take into account the potential problems and needs of the die casting process.

We will review some of the concerns that designers should be aware of in multiple parts.  These issues include:

  1. Draft Concerns
  2. Trimming Issues
  3. Dimensional Repeatability
  4. Porosity and Leakage Concerns
  5. Design for Assembly

 

Draft Concerns

The primary requirement for the manufacture of a die casting is draft.  As a die opens up after metal has been injected and solidified, the die steel must come apart from the casting.  If this does not, or cannot happen, the casting will be damaged upon die opening.

To take a step back, its important to understand that all die casting dies have two halves, a cover and an ejector.  The draft on the part must be set up with the parting line of these two halves in mind.  On one side of the parting line, draft must be set to pull away from that side of the die.  On the other side of the parting line, draft must be reversed.  In general, for a wall or boss parallel to the movement of the cover and ejector, the draft must be set such that the thickest section is right at the parting line.  The wall or boss will then get smaller as it goes into the cover or ejector.  This angle is typically 2 degrees.

Beyond simple cover and ejector parting line pulls, a die casting die can have moving steel components, referred to as slides, on the perimeter of the die.  These slides can allow you to create a part with draft angles going in different directions and angles from the cover and ejector.  Within the slide area, all draft must be set parallel to the movement of that particular slide.

Slides add to the cost of the die casting die and the part itself.  They also add variability to the dimensions of the final casting.  The use of slides is frequently necessary in part design, but should be done with caution.

In part 2 of this discussion, we will discussing the needs for flash and excess material removal, or die trim, in a die casting part and also dimensional concerns.

Mark Fischer, Engineering and Quality Manager