Die cast failure possibilities include:
1. Porosity
Porosity is when air bubbles get caught in the part during the die casting process. A few tiny voids are often inevitable, but too many small voids or a few larger ones can greatly weaken the integrity of the final part and allow it to collapse under stress.
Quality assurance professionals usually test for porosity using X-ray techniques or destructive testing. Proper casting techniques should prevent catastrophic porosity, so it is important to make every possible effort to avoid excessive porosity by utilizing good process controls while die casting. However, testing the finished product for failures helps assure the highest quality product possible.
2. Incorrect Appearance
It is very important that there are visual criteria established for the surface appearance of the casting. This is usually done in the early stages of product development with the customer prior to the mold design. There are a number of reasons why a piece may not look right visually. The most obvious is usually a need for retooling or poor casting process controls.
The only real way to know if a piece doesn’t look the way it is supposed to is by comparing the actual casting surface to the visual standard established by the customer. If a casting is highly cosmetic it is imperative that the die caster knows what the customer needs for surface finish, then create a written cosmetic standard that will be used in production by the quality team.
3. Dimensional Problems
Some parts may not conform to expected dimensions because of wear in the die or shifting between die halves. These dimensional issues may be too small to detect with the naked eye, but they can still cause problems later. Critical dimensions must be noted on the part print and reviewed with the die caster during product development to assure the die caster can meet the dimensional tolerances. Critical dimensions always need to be measured during the casting process by the quality team. Measurements can be simple or sometimes they will need special gages built for very special dimensions on the die casting.
If you are experiencing frequent dimensional problems or lack of repeatability, you probably need to consider repairing the mold or retooling.
4. Omitted Painting or Assembly Steps
As with appearance issues, the only real way to tell if you have left something out in your finishing or assembly is by looking at the workpiece. These types of problems are nearly always the result of an incorrect procedure. Having clear processes and checklists written out can help to avoid this issue. A good die caster will have a system to trace the parts during production throughout the plant and also very explicit inspection criteria for each station of the process.
5. Leaking castings
Castings can leak for a variety of reasons, including porosity and worn dies. To test for leaking castings, you would commonly use an air decay leak tester. Another method to inspect for leaks is to submerge the part underwater for a specified time and pressure. This method needs to be defined by the customer during the product launch and prior to the mold design.
6. Trimming Issues
If you are leaving excess material on your part, this is a problem of poor die cast maintenance, poor design or a poor trimming process. It is usually quite easy to see if you have a trimming issue, although you can also use in-line gaging or poke yoke methods to test for more subtle trim problems.
Product testing for quality assurance can be effective if you take the time to do it properly. It is extremely important because it helps you avoid sending defective parts to customers. Defective parts can cause customer production delays, excess costs, property damage and personal injury, and they can also tarnish your reputation.
Quality assurance also helps you identify areas in your process you can streamline and improve to consistently produce a better product. We at Premier Die Casting believe strongly in the importance of good quality control.
