When a Forging-to-Squeeze-Casting Conversion Is Worth Reviewing
A forged aluminum bracket, connector or housing is usually a mature part on a mature drawing. Nobody reopens the process without a reason. In practice the trigger is one of a short list: the forging tooling is at end of life and re-tooling is quoted against a shrinking volume; the part carries machining operations that casting could take out; a design change adds a boss, rib, port or mounting pad that a forging cannot form without a secondary operation; or the programme needs a pressure-tight or weldable section that the current route struggles to hold.
Squeeze casting enters that review because it sits between forging and conventional high-pressure die casting in the way it fills and feeds a die. CEX has developed its aluminum squeeze casting process in-house since 2015 (company-reported) and casts A356 and A356.2 with T6 heat treatment to a casting blank tolerance of ±0.2 mm (company-reported). Squeeze-cast part weight runs from 50 g to 20 kg with envelopes up to 1.2 x 0.8 m (company-reported); fit is confirmed per part at drawing review. Published A356-T6 reference values of 260-320 MPa tensile and 220-260 MPa yield (company-reported; reference values, not acceptance criteria) tell you the alloy family is in the right range. They do not tell you the part will pass, which is what the validation plan below is for. See the A356-T6 casting specification for how to turn a reference value into a purchase requirement.
The engineering review that has to happen first is short but non-negotiable: draft angles, minimum wall, machining stock distribution, datum scheme, and the load path the forging was designed around. If the alloy changes to A356, treat that as a substitution rather than a copy-across: use the alloy equivalent substitution approval checklist and have the design authority sign the change, not only the buyer.
First-Article and PPAP-Style Validation Checklist
The first article is where a conversion either becomes a supply relationship or becomes a story about how the samples looked good. Treat the following as the minimum submission package.
- Drawing and revision control. Confirm the drawing used to build tooling is revision-identical to the drawing used for inspection, and list every accepted deviation together with who accepted it.
- Material and chemistry certificate. Heat and lot traceability plus spectrographic chemistry against the specified alloy, taken from the casting supplier's own records rather than the melt-stock supplier's.
- Full dimensional layout. Every characteristic, not only the drawing-marked ones, with the datum scheme recorded as fixtured. Castings move on datums, and a layout that hides that returns later as a CMM argument.
- X-ray of agreed zones. Zone the part before the first shot: critical, structural, non-critical. Cite radiographic acceptance by standard name, such as ASTM E505, with the zone map defining where it applies. CEX uses X-ray inspection against agreed acceptance criteria (company-reported).
- Mechanical test specimen location. State on the drawing whether the tensile specimen is a cast-on coupon or cut from a designated part region, and whether that region represents the loaded section. Both routes are legitimate; an unstated one is not.
- Heat treatment record. Furnace load identity, cycle and chart for the T6 treatment applied to the first-article parts, filed with the dimensional report. CEX performs T6 heat treatment in-house (company-reported).
- Pressure-tightness and finishing evidence. Leak test results where the drawing calls for tightness (CEX has helium leak testing equipment for parts that require pressure tightness, company-reported), plus machining and surface finish reports taken after all operations.
Acceptance Sampling for Mechanical Properties
Mechanical property sampling is where forging conversions most often go wrong, because the forging habit is to test the material while the casting habit is to test the process.
Who defines the lot
The buyer should, in the purchase order, not the supplier in the control plan. A workable definition is castings from the same die, alloy heat and heat-treatment furnace load. Whatever basis is chosen, it must be unambiguous before the first shipment, because lot definition drives the sampling table.
Cast-on coupon or cut from the part
Cast-on coupons are repeatable, traceable and cheap, but they solidify differently from a heavy section and can flatter the result. Cut-from-part specimens reflect what the customer receives but destroy the part and depend on section thickness. A defensible compromise is coupons for routine release plus cut-from-part specimens at first article and at an agreed requalification point.
Test and sampling standards, by name
Tensile testing to ASTM B557; attribute sampling plans to ISO 2859-1 or ANSI Z1.4, with the inspection level and AQL agreed in writing between buyer and supplier rather than inherited from an unrelated programme.
| Element | Buyer decides | Supplier records |
|---|---|---|
| Lot definition | Die, alloy heat, furnace load basis | Heat numbers and furnace load identity |
| Specimen type | Cast-on, cut-from-part, or both and when | Specimen location on the layout |
| Test method | ASTM B557 | Test report and machine calibration status |
| Sampling plan | ISO 2859-1 or ANSI Z1.4, inspection level, AQL | Lot quantity, sample quantity, results |
| Nonconformance route | Who may concession and who may not | Deviation, X-ray review, disposition |
Volume Break-Even Framework
Break-even between a forged part and a converted squeeze casting is not a piece-price comparison. It is a landed-cost-per-good-part comparison over the remaining life of the programme, and it includes money already sunk in the forging route only where that money is genuinely recoverable.
Framework: landed cost per part = (tooling + validation + first-article cost) ÷ lifetime volume + (piece price + machining + heat treatment + inspection) ÷ first-pass yield + logistics and inventory carrying cost.
| Cost element | Where it moves | Watch for |
|---|---|---|
| Tooling and die life | Higher upfront on the casting route | Die life quoted against a different alloy |
| First article and validation | Higher on the casting route | Validation cost left out of the comparison |
| Machining content | Usually lower after conversion | Fixtures and CNC capacity not re-costed |
| Heat treatment | New line item for T6 | In-house versus outsourced cycle control |
| Inspection | X-ray and leak test added | Sampling frequency assumed, not agreed |
| Scrap and rework | Learning curve early in the programme | Yield assumed steady from the first lot |
| Logistics and inventory | Shifts with sourcing region | Freight and carrying cost omitted |
The crossover is where the tooling and validation investment divided by volume falls below the per-part savings in machining, weight and assembly. Because those terms are known to different accuracies, run the comparison as a range and stress the volume assumption hardest: it moves the answer most, and it is the figure procurement is most often optimistic about.
When to Keep the Forging
- The section is fatigue-critical with a known, validated grain-flow direction and no equivalent casting validation exists.
- Section thickness changes are extreme and the forging route is the reason the part works.
- Volume is low enough that tooling and validation never amortise.
- The programme is late in life and the existing forging tool still has useful life.
- The end-product certification is written around the forging specification, so changing it reopens a safety case.
CEX Scope on Conversion Projects
CEX is a combined factory and trading company. The factory is Qingdao Dechengxin Metal Products Co., Ltd., which holds the ISO 9001:2015, IATF 16949:2016, ISO 14001:2015 and ISO 45001:2018 certificates in its own name (company-reported), and the trading company is Qingdao Chengenxin, under the same owner. Casting has run since 1995 (company-reported) from three manufacturing bases in Jimo District, Qingdao, serving industrial customers mainly in North America and Europe. Tooling is made in-house (company-reported), 25 CNC machining machines run in-house (company-reported), and squeeze casting machines range from 300 to 1,100 tonnes alongside aluminum die casting machines from 160 to 1,100 tonnes (company-reported).
Before sending a drawing, work through the casting RFQ checklist so the enquiry carries the alloy, the heat treatment, the critical zones and the inspection basis rather than only a model file.
Related: forging to casting conversion