Definition of Post-cast Dimensional Stability
The movement is small (often within a few hundredths of a millimeter), but it is enough to open a flatness callout on a sealing face or shift a bore out of position on a thin-walled housing. It can appear immediately after machining, over days in storage, or after the part sees heat in service.
Thin sections, large flat faces and heavy wall transitions are the geometries most affected. Where a part is sensitive, suppliers manage it through casting design, a stress relief step before finish machining, or by splitting machining into roughing and finishing passes. JoinCast addresses stability at the tooling stage in Taichung, since wall balance designed into the mold does more for stability than any correction made later.
Why This Matters for Your Business
If your part has a flatness or position requirement on a large machined face, raise stability during the quotation rather than after the first rejection. Ask whether the supplier plans a stress relief step, whether it measures samples after a delay rather than straight off the machine, and how it validated the process at sample stage.
The cost of managing stability is modest when it is designed in and considerable when it is discovered later. A wall thickness change in the tool costs one mold modification. A stress relief operation added to a running job costs a process step on every part for the life of the project.
FAQ
Can aluminum die castings shift dimensionally after CNC machining, and how is post-cast dimensional stability managed?
Post-cast dimensional stability is a real risk on aluminum die castings, and yes, parts can move after machining. Residual stress from rapid solidification is redistributed when machining removes material, and the casting settles into a slightly different shape. Movement of two or three hundredths of a millimeter is common on thin or asymmetric sections.Suppliers manage it by balancing wall sections in the tool, adding a stress relief step before finish machining, and separating roughing from finishing so that most material comes off before the final cut. Our die casting production process at JoinCast covers how casting parameters are set to limit stress in the first place.
How can I verify post-cast dimensional stability before approving a supplier's samples?
Verifying post-cast dimensional stability takes more than measuring the samples on arrival. Ask the supplier to measure parts straight off the machine and again after a week, and to send you both sets of readings. If your part sees heat in service, ask for measurements after a thermal cycle that approximates the application.Three or four samples from different shots tell you more than ten from one, since stability varies with cavity and shot conditions. Where the requirement is tight, run your own measurement after the parts have sat in your plant for two weeks. Our quality inspection process at JoinCast describes the measurement stages we apply to sample and production parts.
Which part geometries are most at risk from poor post-cast dimensional stability?
Post-cast dimensional stability is hardest to hold on parts with large flat machined faces, thin walls, asymmetric material distribution, or sudden changes between heavy and light sections. A cover plate with a wide sealing face and a thin body is a common example, as is a housing with a heavy boss on one side and a thin wall opposite.Long parts with a machined bore running through them are also sensitive, since a small bow translates into a position error at each end. If your drawing carries flatness or true position under 0.05 mm on such a geometry, raise it early. Our mold engineering capabilities at JoinCast explain how wall balance is addressed in tool design.
