Buyer note: confirm assumptions before quoting
Lead time, MOQ, yield, leak-test scope, machining scope, and landed cost depend on the drawing, alloy, inspection plan, annual volume, and destination market. For current supplier facts, review the supplier capability sheet or send an RFQ package.
# Heat Treatment Distortion and Machining Datums for Aluminum Castings: RFQ Checklist for T6 Movement, Fixtures, CMM, and Approval
Heat treatment can make an aluminum casting stronger, but it can also move the part enough to change machining allowance, bearing-seat alignment, gasket-face flatness, bore position, and CMM results. This is especially important for A356, A356-T6, ZL114-equivalent, pump housings, valve bodies, gearbox housings, reducer housings, and EV motor housings with precision-machined interfaces.
This checklist helps buyers turn "T6 required" into a quote-ready RFQ instead of a vague material note.
Useful Bohua routes:
- •A356 Material Page
- •Gearbox Housing OEM Quote
- •EV Motor Housing OEM Quote
- •Quality Documentation RFQ
- •Structured RFQ upload
1) State why heat treatment is required
Do not write "T6" only because it appeared on an old drawing. Explain the engineering reason:
- •strength or hardness target
- •pressure or leak-risk requirement
- •fatigue, vibration, or structural concern
- •bearing-seat stability after machining
- •customer material standard
- •legacy part approval requirement
If the buyer is open to alternatives, say so. If A356-T6 is fixed by drawing or customer specification, say that too. A supplier cannot quote the right route unless the RFQ separates required properties from preferred assumptions.
2) Define the inspection state for dimensions
Distortion discussions become confused when buyers and suppliers inspect different states. A casting can be checked:
- •as cast
- •after heat treatment
- •after straightening, if allowed
- •after rough machining
- •after finish machining
- •after coating, impregnation, or final cleaning
For quote comparison, state which dimensions must be proven at each state. A raw casting CMM report does not prove a final bearing bore. A final machining CMM report may not show how much heat treatment moved the casting before machining.
3) Protect datum strategy before tooling and fixtures are quoted
Machining datums should not be an afterthought. Heat treatment movement can change how the part sits in a fixture, how much stock remains, and whether critical faces clean up.
Mark these features in the RFQ:
- •primary, secondary, and tertiary datums
- •bearing seats, seal bores, gasket faces, and O-ring grooves
- •machined mounting faces and bolt patterns
- •areas with thin walls, ribs, or large flat surfaces
- •surfaces that must clean up after heat treatment
- •any datum shift concern from an existing supplier or previous sample
If the current drawing has unclear datums, attach a marked-up PDF and ask the supplier to confirm the machining datum plan before final quotation.
4) Quote machining allowance and fixture plan together
RFQ CTA
Have a casting project? Upload your drawing for a fast, structured quote review.
Send the drawing, target alloy, finishing scope, MOQ, and delivery timing. Bohua will review it like a real sourcing project, not a generic contact request.
Heat-treatment distortion is not only a heat-treatment issue. It affects casting tooling, machining stock, roughing sequence, clamping, and inspection. Ask suppliers to state:
- •proposed machining allowance on critical faces and bores
- •whether rough machining before heat treatment is needed or not allowed
- •whether the fixture references cast surfaces or pre-machined datums
- •whether straightening is allowed by the buyer
- •whether a trial sample should be measured before finalizing fixtures
- •whether CMM programming is included in the quote
Do not compare unit prices if one supplier included fixture validation and another quoted only finish machining.
5) Ask for records that match the risk
The record package should fit the part. For a simple bracket, heat-treatment records may be enough. For a gearbox housing or EV motor housing, the buyer may need a stronger inspection package.
Consider asking for:
- •heat-treatment batch record
- •hardness or mechanical-property record if drawing-defined
- •pre-machining dimensional check for distortion-sensitive castings
- •final CMM report tied to the drawing datums
- •flatness, runout, concentricity, or bore gauge record
- •FAI or PPAP-style approval record when required
- •material certificate linked to the heat-treatment lot
Avoid generic promises such as "distortion controlled." Ask what the supplier will measure, at which stage, and how the record will be delivered.
6) Use application risk to choose the right RFQ path
Different castings need different emphasis:
| Part family | Main distortion / datum risk |
|---|---|
| Gearbox or reducer housing | bearing-seat alignment, shaft center distance, gasket-face flatness |
| EV motor housing or end bell | bearing bore concentricity, seal face, mounting datum stack |
| Pump housing | seal bore, bearing seat, gasket face, leak-test after machining |
| Valve body | port position, sealing face, thread alignment, burr and cleanliness risk |
| Structural bracket | hole pattern, mounting flatness, load path, PPAP or FAI evidence |
Use the specific product-family quote route when the buyer has a part-family risk, and use the quality-documentation route when the blocker is the record package.
Copy-paste RFQ starter
> Heat treatment distortion and machining datum RFQ (copy-paste)
> Files: 2D PDF rev __ ; STEP rev __
> Alloy and temper: A356 / A356-T6 / ZL114 / buyer-defined __
> Reason for heat treatment: strength / hardness / pressure / customer spec / legacy approval __
> Inspection state required: as-cast __ ; post-heat-treatment __ ; rough-machined __ ; final-machined __
> Critical datums: primary __ ; secondary __ ; tertiary __
> Critical features: bearing seats __ ; seal bores __ ; gasket faces __ ; bolt patterns __ ; O-ring grooves __
> Machining allowance concern: faces __ ; bores __ ; thin walls __
> Records requested: heat-treatment record __ ; hardness/mechanical record __ ; CMM __ ; flatness/runout/bore gauge __ ; FAI/PPAP if required __
> Annual volume and destination: __ ; Incoterm __
Submit the heat-treatment and datum scope before price comparison
Use this route when T6 movement, fixture strategy, machining stock, or final CMM approval could change the supplier's quote. Send the drawing, STEP file, datum plan, heat-treatment requirement, inspection state, and approval records before comparing price.
Buyer questions before RFQ
What should buyers send for an A356-T6 heat-treatment distortion and datum RFQ?
Send 2D and STEP files, alloy and temper requirement, why heat treatment is required, inspection state, primary and secondary datums, bearing seats, seal bores, gasket faces, machining allowance concerns, fixture strategy questions, heat-treatment record needs, CMM stage, annual volume, destination, and Incoterm.
Why should post-heat-treatment and final-machining inspection states be separated?
Heat treatment can move the raw casting before machining, while final machining determines the approved functional surfaces. Separating the states helps buyers compare machining allowance, fixture assumptions, final CMM scope, and whether the supplier included enough validation in the quote.
Which Bohua route fits heat treatment and datum risk?
Use the A356 material route for alloy and temper questions, gearbox or EV motor housing routes for bearing-seat and datum-stack risks, and the quality-documentation route when the buyer needs heat-treatment records, final CMM, FAI, or PPAP-style approval evidence.
Project CTA
Need Quality Documentation With Your RFQ?
Send your drawing for a structured DFM review, quote scope, and project-specific timing discussion.