What Should Buyers Put in an Aluminum Sand Casting Tolerance RFQ?
An aluminum sand casting tolerance RFQ should include the controlled drawing and model, alloy or material standard, casting route, part condition, datum scheme, as-cast limits, machined interfaces, core features, surface zones, quantity, inspection method, and acceptance records. Buyers should identify which dimensions are functional and which are only envelope or appearance requirements. A supplier cannot price a tolerance responsibly when the request mixes raw-casting dimensions with final machined dimensions.
Start by naming the delivery state. State whether the quote covers raw casting, trimming, cleaning, machining, coating, leak testing, or assembly. The sand-casting service scope should then be matched to the drawing and the features that control the product. This creates a comparable quote and prevents a later dispute over whether a tight interface was included.
Mark Critical Dimensions and Datums
Mark gasket lands, bearing seats, bores, mounting pads, bolt patterns, wall minimums, clearance features, and cosmetic faces. For each, identify the datum and the condition in which it is checked. A rough casting may use a fixture or a defined cast surface; a finished part may use a machined datum. If a dimension is measured from a core, identify the section and axis rather than relying on a general hole callout.
State whether a tolerance applies to size, position, flatness, profile, wall, or a relationship between features. If the part will be machined, show the stock allowance and final remaining wall. A large generic tolerance zone may not protect a seal or bearing, while a tight limit on a nonfunctional surface only increases cost.
RFQ input | Why it affects the quote | What to attach |
|---|---|---|
Alloy and process | Changes flow, solidification, machining, and inspection assumptions | Material designation and route requirement |
Datum scheme | Determines setup, fixture, and comparable measurements | Drawing datums, fixture concept, and part state |
Core and wall map | Shows shift, stock, and internal access risk | Sections, minimum walls, passages, and core prints |
Machining scope | Separates cast envelope from finished interface | Faces, bores, stock, fixtures, tools, and final checks |
Acceptance evidence | Controls inspection labor and release responsibility | Reports, samples, visual zones, and functional tests |
Define the Inspection Condition
Write whether inspection occurs after shakeout, trimming, blasting, cleaning, machining, coating, or assembly. Cleaning and trimming can remove flash and change an edge used for measurement. Machining can establish a datum and alter the final wall. Coating can change fit without changing the underlying cast geometry. The report should state the exact condition so supplier results can be compared.
For a hidden core, identify how the feature will be reached. A sectioned sample, coordinate measurement, internal gauge, scanning method, or functional test answers different questions. Choose the method with the design owner and state the locations, sample plan, and disposition rule. A leak test can show boundary performance, but it does not by itself locate a core or prove every wall thickness.
Separate Design Tolerance From Process Target
The design tolerance is the permitted product variation. The process target is the condition the supplier uses to keep the result inside that limit. Buyers should ask how the pattern, core, mold closing, machining, and fixture control support the requirement, but should not turn an internal process target into an unsupported capability promise. The quotation should say which records demonstrate the process for the actual part.
If the supplier recommends a design change, such as a larger transition, a different core print, or a machined datum, record the reason and the effect on cost, tooling, weight, and function. A change that helps casting may affect assembly or appearance. Approval belongs to the drawing owner.
State Commercial Boundaries
List tooling, pattern or core work, casting, trimming, cleaning, machining, inspection, coating, packaging, and sample approval as separate scope items. Include the model revision, annual and lot quantity, packaging constraints, and change-control expectations. Ask which reports are included and which tests require separate quotation.
A good RFQ makes aluminum sand casting tolerances specific to a feature, datum, condition, and evidence method. Include post-machining when a finished interface is required. This gives purchasing a like-for-like comparison and gives engineering a clear route to approve the cast blank and the final part.
Before release, ask for an assumption list that names any open input: alloy condition, pattern direction, core method, machining fixture, coating state, or functional test. Closing those assumptions early is usually more useful than asking for a tighter number without a process basis.
Ask the supplier to identify the first inspection gate for each high-risk feature. For example, a cored bore may need a rough-blank wall check before boring, while a gasket land may need a final flatness and leak review after machining. Naming the gate prevents a final report from hiding a problem that could have been corrected earlier in the process.
Also define the change path. State who approves a pattern adjustment, core-print repair, fixture change, alloy substitution, or machining-sequence revision. A tolerance RFQ is stronger when it explains how the parties will recheck an affected feature. That protects the drawing owner and gives purchasing a clear basis for comparing corrective-action costs.
