Testing and inspecting the final sand casting
Making sure the final part meets specification and required tolerances.
Casting inspection and validation
Inspection and validation is a vital part of the sand casting process- determining or demonstrating compliance, identifying any defects in the casting and generating inspection reports.
ADVANCED CASTING INSPECTION METHODS
Visual inspection (sometimes including endoscope inspection) and tactile measurement can be used as a first pass when looking to establish part conformity or characterisation.
More advanced technology such as CT scanning, X-ray, and GOM are used as non-destructive testing methods
What other inspection and validation methods for sand castings are there?
Other inspection methods include:
mechanical property testing
All of these methods help ensure castings achieve optimal part function, meeting specifications for tolerance, surface finish, quality and dimensional accuracy.
The results of the inspection can also be used to balance the casting, which is a process needed before machining to ensure the casting 'cleans up'.
Considering accepting criteria in the inspection process
All processes have a capability, within which certain tolerances can be met with a high degree of probability (measured by Cpk). If you specify dimensions or properties tighter than this capability, then more parts will be out of specification (defects).
These will require rework, concession or scrap. There are so many factors that affect process capability that it is important to discuss this early on in the design process - especially for critical features.
understanding specified acceptance criteria to reduce unnecessary cost
Some features on drawings have tolerances inherited from earlier designs or are perceived 'rules of thumb' and not necessarily deliberate choices made by the designer. This is worth checking carefully.
Over-toleranced features can cause the designer to build-in unnecessary cost which can be significant. If not challenged then unexpectedly high scrap rates could jeopardise production capacity.
Read more: CNC machining a sand casting
ensuring sand casting integrity with high detection sensitivity with CT scanning
CT is an X-ray machine with the ability to generate a 3D Grayscale model. The 3D pixels are called voxels. With detection sensitivities around 2% of section thickness, a defect of 0.2mm is detectable in a plate of 10mm thickness. The limit of resolution is 1 voxel- around 0.1mm