Quality Control in Investment Casting
Investment casting is ideal for producing parts that will be highly loaded, subjected to high temperatures and pressures, or require precise geometry that minimizes secondary operations. This is especially true when the alloys used are expensive and hard to machine.
In many applications quality is more important than cost. Tolerances are often tight and deviations from design limits must be minimized. Alloys must meet specifications and defects like cracks and inclusions are to be avoided.
Impro meets and exceeds expectations for the quality of investment castings through rigorous QA and QC procedures. These are applied both during product and process development and after the product enters series production. The particular inspections needed depend on part design and function as well as customer requirements, but can include:
- Visual inspection
- Material verification
- Measurement of geometry
- Surface inspection
- Subsurface/internal inspection
Wax patterns and investment cast parts are both subjected to close visual inspection. This is to detect defects like nonfills or pattern assembly errors that could affect clean up during machining and performance in service.
Our NADCAP-certified Materials Testing Laboratory is equipped to perform a wide range of testing on both raw materials and cast parts. Capabilities include both chemical and metallographic analysis to ensure the alloy is of the expected composition and that the casting process is producing the desired metallurgical structure.
Measurement of Geometry
We use sophisticated equipment like CMMs and laser scanners to measure patterns and cores thoroughly during tooling development and again during production.
During process development cast parts undergo thorough dimensional checks, some of which include sectioning to reach internal features. Where surface finish is an important characteristic, this is measured by a profilometer.
Once the tooling and process are proven, destructive inspections are avoided as far as possible to reduce waste.
Shrinkage can cause cracking at changes of section in the cast part. During development magnetic particle and liquid penetrant testing are used to find any such defects. This work is carried out by certified NDT Level 2 and Level 3 technicians.
These inspections can also be used once the part is in production, although careful development should result in a robust part design and a process where cracking has been designed-out.
During development it’s possible to find internal flaws like cracks by sectioning, but this isn’t possible or practical during production. Other types of flaws, like alloy inclusions or porosity, are hidden beneath the surface. To detect these defects we have ultrasound and X-ray nondestructive testing and hydrostatic pressure testing.
Performed by certified NDT Level 2 and Level 3 technicians working to ASTM standards, these checks will find internal defects that could otherwise cause in-service failure. As with the surface defect detection efforts, these technologies are used extensively during development and at a frequency agreed with the customer once the part has entered production.
Agreeing QC Requirements With Customers
Quality Control checks are part of the process used to develop a new part, and for subsequently ensuring the part meets expectations after it has entered production. For parts made by investment casting QC takes on added importance, due to the type of applications they will go into. These inspections are determined by or in consultation with our customers.
As part of our commitment to quality, we have invested in an extensive range of QC capabilities. This relates to the people and facilities used as well as to the equipment installed in our laboratories and inspection areas. Contact us to learn more about our QC capabilities and certifications, or to discuss your specific inspection requirements.