MANUFACTURING / JAPAN SOURCING
Welded assemblies: in what condition should dimensions be accepted?
A frame can fit its welding fixture and still need a separate check in its delivered condition. Agree the fabrication stage, support/restraint, datum and measurement method before comparing dimensional reports.
A result in the fixture describes that condition
A buyer receives a dimensional report for a welded mounting frame. The report was taken with the frame clamped in its welding fixture; receiving inspection checks it after release on different supports. A difference between the reports is worth investigating, but “measured after welding” does not make their conditions equivalent.
TWI explains that restraint holds components during welding and that movement can occur when it is removed.[1] Ask whether the order requires a free-state check, a defined restrained check, or both, and have the responsible designer specify the applicable condition. Do not assume free state is always the acceptance state for every assembly.
- 1Restrained: identify the fixture and clamping condition
- 2Released: identify support locations and the part state
- 3Acceptance: retain datum, measured features and report conditions
Two front-view sketches of one hypothetical frame. Curvature is exaggerated only to show a possible state difference, not a predicted deformation. Neither support nor clamp layout is a fabrication instruction.
Separate in-process checks from the final requirement
Define which checks concern individual members, fit-up/tack assembly, the completed weldment, and any subsequent machining or finish. A pre-weld location check can prevent a problem, but is not a report on the final machined mounting faces. FARO describes verification earlier in fabrication and assembly as a distinct QA opportunity.[2]
For this frame, identify the delivered stage and any process steps remaining after each report. If machining establishes the final mounting faces, make its allowance, datum and inspection stage visible. If a coating affects a fit requirement, agree the state in which that feature is inspected.
| Record | Specify before manufacture | Keep with the result |
|---|---|---|
| Stage | Specify before manufactureMember, tack assembly, weldment, machined or finished item | Keep with the resultActual completed operations and part/drawing revision |
| Restraint | Specify before manufactureRequired free or restrained state; fixture and clamp definition | Keep with the resultWhat was fitted, clamped or released |
| Support and datum | Specify before manufactureSupport/contact locations and datum references | Keep with the resultSetup identity and alignment used |
| Conditions | Specify before manufactureRequired temperature/settling and measurement method | Keep with the resultActual conditions, instrument and relevant limitations |
| Features and decision | Specify before manufactureLocations, tolerances, report scope and acceptance owner | Keep with the resultResults, deviations and disposition record |
Make two reports comparable before judging a difference
Use the same feature definitions and datum references, and record support, clamping and the relevant temperature condition. Ask how the method and setup can measure the required features with suitable capability. A different alignment or support arrangement may answer a different dimensional question.
Where the reports disagree, compare the setup records and repeat the agreed measurement if necessary. Do not average unlike results into a pass, force the frame into an unspecified fixture, or silently redefine the datum after seeing a deviation. Retain uncertainty or method limitations for the quality team to assess.
Keep dimensional acceptance separate from weld acceptance
A dimensional pass does not establish weld quality, strength or procedure compliance. Keep the applicable welding and weld-inspection requirements under their responsible engineering review. This guide does not choose a weld sequence, heat treatment, straightening method or general distortion allowance.
If a feature is outside the agreed requirement, identify the deviation and obtain a disposition from the authorized party before repair or acceptance. Record any approved rework and the required reinspection state. That gives the next supplier and receiving team the same reference, rather than a bare “within tolerance” statement.
Questions to send your supplier
Open supplier questions
Product: welded mounting frame Drawing revision, delivered stage and remaining processing: Which dimensions apply before/after welding, machining and finish? Required free/defined restrained state, fixture and clamp definition: Support/contact locations and datum references: Temperature/settling and measurement method/capability requirements: Please retain actual setup, part identity and conditions with each result. Separate dimensional acceptance from welding/weld inspection requirements. Who disposes of deviations, authorizes rework and defines reinspection? Quantity, destination and timing:
Sources
- TWI — Distortion: prevention by pre-setting, pre-bending or use of restraint
Sections on restraint and jigs explain movement after release and stresses. Not used to prescribe welding, restraint, preheat or stress-relief procedures.
- FARO — Guided assembly and QA validation for fabrication, metalforming and welding
Public description distinguishes earlier in-process verification from later QA. No device accuracy, universal tolerance or guaranteed savings adopted.