Die Casting Supplier Audit: A Checklist That Produces Decisions, Not Photographs

Most supplier audits are a plant tour with a clipboard. Two people walk the floor, the supplier shows the newest machine, everyone agrees the place looks tidy, and the report says “approved” with three minor observations. Six months later the supplier ships 4,000 parts with porosity and the auditor’s notes say nothing useful.

A useful audit answers one question: if this supplier’s process moves, will they know before the parts reach me? Everything below is built around that. It covers the document request, the walk sequence, what to look for in each area with concrete acceptance signals, the interview questions that separate real control from paperwork, the red flags that should end the discussion, a scoring method that produces a go or no-go, and how to write corrective actions that actually close.

What an audit is for: decide what you are verifying

Before you book the flight, write down the three things that can go wrong with this specific part. A structural housing with a pressure test requirement and a decorative zinc handle with a chrome finish are two completely different audits. For a housing you are verifying melting practice, vacuum or shot control, and impregnation policy. For the handle you are verifying surface handling, plating subcontract control and packing.

Decide also what outcome you will accept:

• Approved for production with a defined control plan.
• Conditionally approved, with named corrective actions, a defined interim containment, and a re-audit date.
• Not approved, with the specific gap stated.

If you cannot say which gaps would cause a “not approved” before you arrive, you will not be able to say it afterwards either.

Pre-audit document request list

Send this 10 working days ahead and say that the audit starts with a document review, not a floor walk. Which documents come back, and how fast and how complete they are, is itself a result.

• Quality manual and certificate scope, plus the current ISO 9001 or IATF 16949 certificate with the actual site address and the excluded clauses.
• Process flow diagram for the part family in question, with control plan and PFMEA.
• Material certificates for the last three months of ingot purchases, by alloy and heat lot, plus the incoming inspection procedure for ingot.
• Furnace and holding temperature records, and degassing or rotary treatment records for aluminium.
• Die list: die ID, part number, cavity count, build date, accumulated shots, and the last preventive maintenance date and findings.
• Shot monitoring or machine parameter records: the last 30 days for one machine running your part or a comparable part.
• Calibration certificates and the gauge list: gauge ID, type, range, last calibration, next due, and location.
• Operator qualification records and the training matrix for casting, trim and inspection.
• Scrap and rework data for the last six months, by defect code, with the top five Pareto and the actions taken.
• Customer complaint log for 12 months with 8D or equivalent reports, including closure dates.
• Subcontractor list, specifically plating, heat treatment, impregnation and machining.
• Control plan for finishing: media type, cycle, abrasive specification, and how cosmetic class is defined and inspected.
• Packaging specification, and the last drop test or transit test report.
• Nonconforming material procedure, including how product on hold is physically segregated.

Ask for the records in their working format, screenshots or exports are fine. A supplier that can only produce a printed summary with no raw data is telling you something important about traceability.

The plant walk sequence

Walk the process in production order, and walk it backwards from the shipping door at least once. Allocate time and stick to it; the casting cell always tries to consume the whole visit.

What to look for in each area

Melting and metal handling

• Ask for the melt log and then read the furnace controller on the spot. They should agree within the stated tolerance, typically ±10 C for holding.
• Check the degassing rotor: is it in the furnace, is it turning, and is there a record of the last treatment with duration and gas flow?
• Look at dross handling. Large accumulations of dross next to the furnace and a wet floor are both safety and process signals.
• Check whether returns, gates and runners are remelted. If yes, ask what proportion, how they are segregated by alloy, and whether they are cleaned and dried. Uncontrolled returns are a regular source of inclusion and iron pick-up.
• For aluminium, ask for the last spectrographic analysis and the frequency. Weekly at minimum for a plant running multiple alloys.
• Unlabelled ingots, mixed alloy pallets, or rusted steel crucibles in contact with aluminium are immediate findings.

Casting cell

• Stand at the machine for ten shots and watch the operator. Do they do the same thing every cycle? Is spray time consistent? Is the part removed the same way?
• Look at the shot monitoring display. Is it live? Are limits set? Ask the operator what happens when an alarm fires and what they do. If the answer is “we call the technician”, ask for the alarm log and see how often it fires and what reasons are recorded.
• Check whether the shot counter increments and whether it can be reset. Ask the maintenance technician for the die’s accumulated shot count and compare it with the die maintenance record.
• Look at the die: parting line condition, flash level, evidence of soldering, cooling lines connected and labelled, water temperature or flow visible.
• Ask for the startup procedure and the number of warm-up shots discarded. A plant that knows its process discards a defined number and can tell you why.
• Check the die spray and lubricant: is the dilution prepared centrally or does the operator guess from a tap? Ask for the mixing ratio and the concentration check method.
• Look for a defined scrap bin at the machine, physically separated from returns for remelting.

Trim, secondary and finishing

• Measure burr height on five parts straight off trim. Compare it with the stated limit. A trim die at the end of its life produces a burr that no finishing process handles cheaply.
• Look at the trim die maintenance record: sharpening interval in shots, and how the decision is made.
• In finishing, look for written parameters: belt or media grade, speed, force or feed, cycle time, change interval. A cell with no posted parameters is running on operator memory.
• Check whether cosmetic parts touch each other at any point between the last polish and the pack. If they do, the reject rate is a function of luck.
• Ask how abrasive life is managed: by time, by count, or by operator judgement. Time or count with a recorded value is acceptable; judgement alone is not.
• Look at dust extraction and housekeeping in grinding. Heavy settled aluminium dust is both a quality problem and a safety finding.

Inspection

• Pick five gauges at random from the floor and check the calibration label against the gauge list. One out-of-date gauge out of five is a systemic finding, not a minor one.
• Ask for the gauge R and R result on the customer’s key characteristic. If they have never run one, that is the finding.
• Ask how often the CMM or vision system is qualified, and ask to see the last check with a known standard.
• Look at the inspection records for the last week. Are they filled in with real values, or with ticks? Ticks mean the measurement is not happening.
• Check the nonconforming material area. Is it physically separated, labelled, and does it contain material older than the stated disposition time?
• Ask what happens when an inspector and a production supervisor disagree. The answer tells you more about the quality culture than any certificate.

Packing and shipping

• Open one finished carton at random and check against the packaging specification: layer count, separation, orientation, labelling.
• Trace one carton ID back to a shot or batch. Time it. If it takes more than 15 minutes, traceability is theoretical.
• Look at the pallet: column stack or brick, wrap layers, corner protection, overhang.
• Check the packing area environment. Packing under a grinding bay contaminates the pack with dust.

Interview questions that expose real control

Ask the same question of a supervisor and an operator and compare the answers. Divergence is the finding.

• “What are the three defects you scrap most, and what did you change last month because of them?” A controlled plant answers immediately from memory.
• “If a shot alarm fires, what do you do, and who decides?” Listen for a defined action and a reason code.
• “How many shots on this die since the last service, and what triggers the next one?” Compare with the record.
• “Show me the last time you changed a parameter, who authorised it, and how you verified the result.”
• “Which of these measurements does the customer care about most, and what is the capability?” Ask for the Cpk value, not a pass/fail.
• “What is your cosmetic acceptance standard, at what distance, under what light, for how long?” If they look at you blankly, cosmetic disputes are coming.
• “If you found out this morning that yesterday’s parts were bad, which ones could you identify and where are they now?” The answer should name a range, not a shift.
• “Which process do you subcontract, and how do you control it?” Uncontrolled plating subcontractors cause more cosmetic escapes than any casting defect.
• “What did you do differently this year than last year?” A plant doing nothing new is either perfect or static; ask which.

Red flags that end the conversation

Some findings are not negotiable. Each of these indicates that the controls you were shown cannot be trusted:

• Shot counters disabled, reset at will, or no relationship between the displayed count and the die maintenance record.
• No die maintenance records at all, or records created after the audit was announced.
• Gauges without calibration labels, or a calibration certificate covering a gauge that does not exist on the floor.
• Unlabelled or mixed alloy material in the melt area.
• Scrap records that are implausibly good, for example under 0.3 percent on a complex structural casting, with no impregnation step and no reject bins visible.
• An inspection record book that is filled in for the next day already.
• Material in the nonconforming area with no identification and no disposition date.
• Refusal to show raw data, only summaries.
• A plating or heat treatment subcontractor they will not name or allow you to audit.

One of these is a conditional approval with containment and a 60-day re-audit. Two or more is a no-go until they are closed, regardless of price.

A scoring method that produces a decision

Score each area 0 to 3, and weight the areas that matter for your part. Do not average an unweighted score; weighting is what makes the number meaningful.

• 0 – No system, or the system exists only on paper and the floor contradicts it.
• 1 – System exists, partially implemented, no evidence of effectiveness.
• 2 – Implemented with records, minor gaps, evidence of review and action.
• 3 – Implemented, effective, with trend data showing improvement.

Suggested weighting for a structural aluminium part: melting 15 percent, casting 30 percent, trim and finishing 15 percent, inspection 25 percent, packing and traceability 10 percent, management system 5 percent.

Decision rules:

• Any area scored 0 in melting, casting or inspection: conditional at best, with containment.
• Weighted score below 60 percent: not approved.
• Between 60 and 80 percent: conditional, with a corrective action plan and a re-audit within 90 days.
• Above 80 percent with no red flags: approved, with an annual surveillance audit and a defined data review cadence.

Send the scoring sheet to the supplier with the report. It removes the argument about whether the audit was fair.

Writing corrective actions that get closed

A corrective action that says “improve die maintenance” will never close. Write each one so that a stranger could verify it.

Every corrective action needs:

• Finding, stated as an observed fact with a location and evidence: “Die D-114 had no maintenance record after 71,000 shots; the shot counter display showed 12,400.”
• Requirement, stated as a measurable outcome: “Accumulated shot count per die maintained and reconciled monthly; preventive maintenance performed at 50,000 shots ±5,000 with the findings recorded.”
• Root cause, not a symptom. “No one owned the log” is a cause. “Operator error” is not.
• Action, with an owner by name and a date.
• Verification method: what you will look at, and when. “Upload the die maintenance log and a photo of the counter for die D-114 by 30 November; verifier reviews the next two PM records in the February data review.”
• Containment until the action is complete: what protects you in the meantime, for example 100 percent pressure testing or a third-party inspection at the supplier’s cost.

Cap the plan at eight actions. A twenty-item plan means nothing gets done. Put the top three in a 30-day window, the rest at 90 days, and schedule a 30-minute call at the halfway point. Ask for evidence as documents, not as a presentation; a presentation is a summary written to look good, and you asked for data.

Audit report, follow-up cadence and the one-page checklist

Issue the report within five working days, while the details are fresh, and include the photographs with captions stating what each shows. State the decision, the conditions, and the re-audit date in the first page.

Follow-up cadence after approval:

• Monthly: scrap and complaint data exchange, top three defects, and any parameter or material change notification.
• Quarterly: capability data review on the key characteristics, and a check that corrective actions remain closed.
• Annually: on-site surveillance audit, half a day, focused on the areas that scored lowest last time.

The purpose of the rhythm is to catch drift while it is still a number moving and not a container of bad parts. If you are selecting between suppliers rather than auditing one, how to choose a zinc die casting manufacturer and sourcing aluminium die casting from China cover the commercial and technical screening that should happen before you get on a plane. And when the audit turns up a dimensional question, aluminium die casting tolerances is the reference for what you can reasonably ask a supplier to hold.

Finally, the sheet to carry in your pocket:

• Documents received in advance, complete, in raw form.
• Walk in production order, time-boxed, no detours to the showroom machine.
• Every gauge checked has a valid calibration label.
• Die shot counters verified against maintenance records.
• Shot parameters read live and compared with the control plan.
• Burr height measured off trim, five pieces.
• Finishing parameters posted and recorded.
• Cosmetic standard agreed: distance, light, time.
• One carton traced back to a shot range, under 15 minutes.
• Nonconforming area: identified, segregated, dated.
• Three interviews: operator, supervisor, quality lead.
• Red flags recorded verbatim with evidence.
• Score sheet completed and shared before you leave the site.
• Corrective actions written on site with owners and dates.
• Report issued within five working days.

One last note on scoring: finishing deserves its own line, because that is where variance becomes visible.

Finishing is where a weak supplier’s process variance becomes visible scrap, and it is the area we get called into most often after an audit. DZ Machinery builds robotic deburring, grinding and polishing cells with force-controlled floating spindles, automatic tool change, multi-station turntables and fixtures designed around part families, together with dust extraction and cycle time and yield calculations, so the finishing stage has a defined process window and a defined record. If your audit found cosmetic or deburring instability, send us the part drawings, alloy, burr condition off the trim die and annual volume, and our engineering team will come back with a cell concept, station layout and cycle time you can hold us to.