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From Drawing to First Article: The Sample Approval Sequence OEM Buyers Should Run on New Castings
2026-09-16
A T1 Photograph, and 5,000 Parts With a Boss 3.8 mm Out
A pump manufacturer in Coimbatore released a new volute housing on the strength of a T1 sample photograph. The photo looked clean, the price was right, and the tooling was already cut. Six weeks later 5,000 castings arrived with a boss 3.8 mm off datum, and every part sat wrong in the CNC fixture.
The scrap bill ran to 41,000 euro, the machining line stopped for nine days, and the customer programme slipped a quarter. Nobody had measured the sample against the datum structure. Approve a measured layout report, never a photograph.
Freeze the Drawing Before Anyone Cuts Steel
A frozen drawing is a document, not a file name. It must carry the datum structure per ISO 5459 or ASME Y14.5, with features A, B and C matching how the part is machined. Add GD&T to ISO 1101 on every functional face, not plus-or-minus dimensions alone.
Then specify the casting-specific items buyers forget:
- machining allowance 1.0 to 1.5 mm on die cast faces, 2 to 3 mm on gravity faces over 100 mm
- draft 1 to 2 degrees external, 2 to 3 internal
- parting line shift limit 0.3 mm
- gate and ejector mark zones marked, at 0.5 mm raised and 0.3 mm deep
Geometry of this kind is what a controlled aluminum alloy gravity casting process can hold.
Review Flow and Solidification Before Tooling
Require a casting simulation before the tool is cut, not after the first shot. Ask for fill time, fill sequence, and a solidification plot; on aluminium the fill time for a medium housing is typically 0.05 to 0.15 seconds in high pressure work and 3 to 8 seconds in gravity.
Read the plot for one thing: directional solidification toward the feeder. Any isolated hot spot above 0.5 cubic centimetres in a machined zone is a future claim. Make the supplier submit the model file and the gating revision with the quote, and treat gating changes as drawing changes.
T1 Layout: Measure to the Datum, Not With Calipers
The first article report is the gate, and it has to be complete. Require a full dimensional layout on three to five pieces, measured on a CMM aligned to the drawing datums, with every ballooned dimension listed as nominal, tolerance, actual and deviation. A caliper spot check on five favourite dimensions is not a layout.
Then demand capability, not just conformance. Set Cpk of 1.33 or better on every critical characteristic, and require 30 pieces measured for those features. Where a part is a zinc high pressure die casting, the same rule applies to as-cast datums.
Material Certificate, Test Bars and the Furnace Chart
A material certificate for the ingot is not a certificate for the casting. Require separately cast test bars poured from the same ladle, tested to ISO 6892 for tensile and ISO 6506 for Brinell, with elongation reported, not just strength.
Use hard acceptance numbers. For A356 in T6 expect 260 to 310 MPa ultimate, 180 to 240 MPa yield, 3 to 7 per cent elongation and 80 to 95 HBW. For ADC12 as-cast, expect about 310 MPa with 1 to 3 per cent elongation. For every T6 batch take the furnace chart with thermocouple calibration, solution at 535 degrees for 6 to 10 hours, quench, then artificial ageing at 155 degrees for 3 to 5 hours. Programmes built on an aluminum alloy low pressure casting should hold the same standard.
Machine Real Parts on Real Fixtures
Dimensional approval on a bare casting proves nothing about the machined part. Run a machining trial of 30 to 50 pieces on the production fixtures, at production speeds, before signing off. Record three numbers: cycle time against target, inserts consumed per 100 parts, and scrap and rework rate.
A casting that meets drawing but adds 40 seconds of cycle time or doubles insert consumption is a cost increase disguised as a pass. Put the cycle time number in the approval document so it can be enforced later.
The Deviation Log and Who Pays for Tooling Changes
Every sample round produces deviations, and unmanaged deviations become production reality. Run a single numbered log with deviation, root cause, containment, permanent fix, owner and date. Each tooling modification gets a revision letter and a re-approval trigger.
Settle payment before the first deviation. The rule that works: the foundry pays when the part misses the frozen drawing, and the buyer pays when the drawing changes. Cap the foundry's exposure at tooling value, and require written approval before any tool modification.
FAI Level, Retention Samples and the Sign-Off Gate
Smaller buyers do not need full PPAP, but they do need a defined pack. Ask for a twelve-item FAI-lite: frozen drawing, layout report, material certificate, heat treat chart, process flow, control plan, gauge list, capability study on critical features, visual standard, packaging specification, deviation log and three sealed retention samples.
Keep those samples for three years or programme life plus one year, signed and dated by both parties. Then enforce the gate: no production release without a written first article approval signed by buyer quality and engineering, and any tooling change restarts the sequence at T1. That rule separates a controlled aluminum alloy high pressure die casting programme from a costly one.
The Bottom Line
Speed comes from sequence, not from skipping steps. Freeze the drawing with datums, GD&T, allowance and draft, review solidification before tooling, and approve a CMM layout report, never a photograph. Demand ladle-poured test bars with furnace charts, run 30 to 50 parts on real fixtures, log every deviation, and hold retention samples. Release production only on a written first article approval, and the 3.8 millimetre surprise never reaches your machining line.