Triage the leak before changing the process
A leaking sand-cast aluminium part is a symptom, not a diagnosis. Before a conversion to squeeze casting can be approved, the buyer and the foundry have to agree on which mechanism is failing, because the new process only removes the mechanisms it can actually influence. Most rejected sand-cast parts trace back to one of a few mechanisms.
- Shrinkage porosity. Solidification contraction concentrated in a hot spot the sand mould cannot feed. On a radiograph it reads as irregular, often intergranular voids close to a thermal centre.
- Gas porosity. Rounder, smoother-walled voids from dissolved hydrogen or entrapped air, usually spread through the section instead of clustered at one hot spot.
- Oxide films and inclusions. Turbulence during filling folds the surface oxide back into the melt stream. The result is a crack-like discontinuity that can open a leak path even when the film area looks tolerable on a single view.
- Machining into porosity. The casting was sound enough, but the cut removed the dense skin and exposed subsurface pores on a sealing face, a thread root or an O-ring groove.
The distinction drives the approval, not just the fix. If the leak comes from machining into porosity, higher casting integrity helps, but the real countermeasure may belong in the machining stock allowance or in the seal design. If the leak is an oxide film from a turbulent sand pour, the process change is the countermeasure. The conversion file should therefore open with evidence rather than with a quotation: a sectioned part, a radiograph of the leaking region, and a record of exactly where on the part the leak was detected.
The conversion approval workflow, step by step
The sequence below is one a buyer's engineering and quality functions can audit. Each step produces a document the next step depends on, so skipping ahead leaves a gap in the approval trail rather than saving work.
- Engineering change request. Record the part number, drawing revision, leak location, current process route, the containment already in place, and the acceptance criteria the new part must meet. The ECR also names the signatory for each later gate.
- Leak root-cause dossier. Sectioning, radiography of the failed region, and pressure-tightness testing where the buyer specifies it. CEX has X-ray inspection equipment for internal soundness and helium leak testing equipment for parts that require pressure tightness, both applied against acceptance criteria agreed in advance.
- Alloy substitution approval. Sand-cast alloys and squeeze-cast A356 / A356.2 are not interchangeable on paper alone; a material change alters strength, elongation, weldability and heat-treat response. Published CEX reference values for A356.2-T6 are 260–320 MPa tensile strength and 220–260 MPa yield strength (company-reported reference values, not acceptance criteria) — the drawing still decides acceptance. Work through the alloy equivalent substitution approval checklist and confirm the temper in the A356-T6 casting specification before the substitution is signed.
- DFM review. Gate and feeding concept, machining stock, datum scheme and ejection. Squeeze casting at CEX covers parts of 50 g to 20 kg (company-reported) with an envelope up to 1.2 × 0.8 m (company-reported) and an as-cast blank tolerance of ±0.2 mm (company-reported), so the review must confirm the geometry fits the process before tooling is released.
- Tooling. Tool approval drawing, cavity layout, thermal plan and ejection, built in-house by CEX and signed off by the buyer before steel is cut.
- First article inspection and radiographic acceptance. The FAI is dimensional and documented to the drawing. Radiographic acceptance references ASTM E155 for aluminium casting reference radiographs and ASTM E505 for aluminium die castings, with image quality to ISO 19232. The severity level that is acceptable is set on the buyer's drawing; the foundry grades to it and does not choose it.
- Leak test method and rate. The buyer specifies the method, the test medium, the pressure, the stabilisation approach and the sampling rate. The foundry demonstrates that its fixture and process can hold that specification.
- PPAP / FAI submission and production release. Where the buyer's supplier quality agreement calls for a PPAP, it is built on the FAI, the process flow, the control plan and the leak test validation. Release is the buyer's signature, not the foundry's.
Mapping evidence to the approver
Approval stalls when a document arrives without a named owner. The split below is workable for a conversion project; adjust titles to the buyer's organisation, but keep one signatory per gate.
| Approval gate | Evidence package | Signed by |
|---|---|---|
| Engineering change request | Revised drawing, leak location, failure photographs, current process route, containment record | Buyer engineering and buyer quality |
| Leak root-cause dossier | Sectioned part, radiograph of the failed region, pressure-tightness result where specified | Foundry quality, accepted by buyer SQE |
| Alloy substitution | Old and new alloy designation, temper, mechanical reference values, weldability note | Buyer engineering |
| DFM review | Gate and feeding concept, machining stock, datum scheme, blank tolerance | Buyer engineering |
| Tooling | Tool approval drawing, cavity layout, ejection and thermal plan | Buyer engineering |
| First article inspection | Full dimensional report to drawing, material certificate, heat-treat record | Buyer quality |
| Radiographic acceptance | Films or digital images graded to ASTM E155 / ASTM E505, image quality to ISO 19232, graded against the severity on the drawing | Buyer quality |
| Leak test validation | Method, fixture, medium and reject rate as specified by the buyer, plus a capability run on the production fixture | Buyer quality |
| PPAP / production release | FAI, process flow, control plan, PFMEA, MSA and capability study where the buyer's agreement requires them | Buyer SQA |
The confirmed case: a trailer bracket
CEX publishes a conversion example that matches this workflow directly. A trailer bracket previously produced as a sand casting was converted to a squeeze casting in A356.2-T6. The published result is a part that is weldable and shows about 50% higher strength than the sand-cast original (company-reported). The bracket is a useful reference because it exercises the gates that most often delay approval: the alloy and temper change, and the acceptance criteria for internal soundness on a part that is subsequently welded.
A second published example, a trailer connector squeeze cast in A356.2-T6 that replaced a steel casting with at least 54% weight reduction (company-reported), shows the same pattern from a different starting point. Neither example replaces the buyer's own drawing; they show what the approval trail looks like when it is complete.
What the buyer owns and the foundry cannot approve
The items that stay on the buyer's side of the table in every conversion are the radiographic severity acceptable for each zone of the part, the leak test method and reject rate, the alloy and temper designation on the drawing, and the sampling frequency in the control plan. A foundry that proposes values for these is guessing at the buyer's risk appetite. The practical way to close the loop is to issue them in the RFQ package so they appear in the quotation, the DFM response and the FAI report without a further round of questions — the casting RFQ checklist lists the items that belong in that package.
Who would run the conversion
CEX Casting is a combined factory and trading company. The manufacturing entity is Qingdao Dechengxin Metal Products Co., Ltd., which holds the quality certificates — including ISO 9001:2015 and IATF 16949:2016 — in its own name; the trading company is Qingdao Chengenxin, under the same owner. Operations are in Jimo District, Qingdao, Shandong, China, across three manufacturing bases (company-reported). CEX has been casting aluminium since 1995 (company-reported). Squeeze casting has been developed in-house since 2015 (company-reported) on machines from 300 to 1,100 tonnes (company-reported), alongside aluminium die casting from 160 to 1,100 tonnes (company-reported). Tooling, T6 heat treatment and 25 CNC machining machines (company-reported) are in-house, and X-ray plus helium leak testing support the acceptance gates described above.
Related: gravity and LPDC to squeeze casting