OEM Supplier Audit Checklist for Casting and Machined Parts

Overview

Selecting a casting or CNC machining supplier for an automotive or industrial program is a risk decision, not a price decision. A structured on-site audit before award and at periodic intervals protects launch timing, part conformity, and downstream warranty cost. This checklist separates the Quality System Audit (QSA) from the Quality Process Audit (QPA), then drills into the capabilities that most often determine whether a supplier can hold critical characteristics on aluminium castings and their machined features.

Use this page alongside your sourcing process. For the controlled-quality planning that follows award, see APQP and PPAP and the IATF 16949 overview.

Audit Structure: QSA vs QPA

QSA (Quality System Audit) — Evaluate the management system against IATF 16949 / ISO 9001. Why: confirms documented, repeatable processes rather than reactive firefighting. How: review procedures, management review minutes, internal audit records, and objective evidence of deployment.
QPA (Process / Product Audit) — Evaluate the actual production line, tooling, and part conformity at the workstation. Why: a strong QMS on paper can still ship non-conforming parts. How: observe a live run, pull first-article and SPC records, and physically inspect parts and gauges.

A passing QSA with a failing QPA should block production-part approval until the process gaps are closed.

Quality Certifications

Valid IATF 16949 certificate issued by an accredited certification body. Why: baseline expectation for automotive casting and machining supply. How: check the certificate number and accreditation logo; verify scope and expiry.
ISO 9001 for non-automotive or standalone secondary operations. Note: not a substitute for IATF 16949 on automotive programs.
Certificate scope matches the audited site — the casting and machining processes at the visited plant must be in scope, not a sister facility. Why: a group certificate covering only a different plant gives no assurance for your parts.

Equipment and Clamp Tonnage

Machine clamp tonnage covers the required projected area. Why: required clamp force ≈ projected area × specific cavity pressure (roughly 40–90 MPa for aluminium high-pressure die casting). Undersized machines cause flash, short fills, and dimensional drift. How: compute required force from part envelope and compare to the machine’s rated lock.
Tonnage class matches the part type. Note: general HPDC spans ~150–3500 t; structural and mega-castings require 2000–6000 t class machines.
Machine condition and maintenance — tie-bar stretch calibration, platen parallelism logs, and documented preventive maintenance. Why: worn platens distort the die parting line and wreck repeatability.

In-House vs Outsourced Operations

CNC machining capability in-house. Why: in-house machining shortens lead time and tightens process control and traceability versus sub-contracted finishing. How: confirm number and control of machines, and that critical features are not silently outsourced.
Surface treatment / plating. Note: if outsourced, require sub-supplier approval and flow-down of the control plan, plus valid environmental permits.
Leak testing (for housings). Why: pressure-decay or helium leak testing is decisive for enclosures. Confirm the method, acceptance limit, and test frequency are in the control plan.
X-ray / CT (NDT). Why: porosity and homogeneity verification for structural castings. Confirm NDT level, equipment, and inspection frequency, in-house or contracted.

Measurement and Inspection Capability

CMM and probing with calibrated equipment and an ISO/IEC 17025 accredited laboratory for material and mechanical testing. Why: ensures reported Cpk and tensile/elongation results are trustworthy.
Active SPC on critical characteristics with Cpk ≥ 1.33 for critical and ≥ 1.67 for safety characteristics. Note: ask for live control charts and recent studies, not just a policy statement.
Calibration system — gauges calibrated on schedule and traceable to national standards; gauge R&R performed on key features. Why: undetected gauge error masks real process shifts.

Problem Solving and CAPA Maturity

8D discipline maturity. Why: immature containment predicts repeat escapes. How: review three recent 8D reports for structured root cause (5 Why / Ishikawa) and verified effectiveness.
CAPA closure rate and on-time delivery of corrective actions. Note: chronic overdue actions signal weak management commitment.
Lessons-learned linkage to PFMEA and control plan updates. Why: a closed loop prevents recurrence across programs.

Site, Safety, and Financial Health

5S and housekeeping on the shop floor. Why: a disorganized cell correlates with mixed parts and calibration lapses.
Molten-metal safety — PPE, melt-house guarding, pyrotechnic/explosion controls, and furnace venting. Why: casting plants carry inherent thermal and chemical risk that affects continuity.
Financial health — years in business, customer concentration, and capacity utilization. Why: a low-quote supplier that fails mid-program is far more expensive than a stable one.
Business continuity plan covering melt disruption, key-machine breakdown, and logistics.

Audit Summary Table

Area	Pass criterion
QSA	IATF 16949 valid; scope matches audited site
QPA	Cpk ≥ 1.33 critical / ≥ 1.67 safety; live SPC
Equipment	Lock tonnage ≥ required clamp force; maintained
In-house ops	Machining/leak-test in control; sub-suppliers approved
Inspection	ISO 17025 lab; calibrated CMM; gauge R&R
CAPA	8D with verified root cause; on-time closure
Site/safety	5S; molten-metal controls; BCP present

References

IATF 16949:2016 — Automotive Quality Management System Standard
ISO 9001:2015 — Quality Management Systems — Requirements
ISO/IEC 17025:2017 — General Requirements for the Competence of Testing and Calibration Laboratories
AIAG CQI-27 — Special Process: Casting System Assessment
AIAG — Advanced Product Quality Planning (APQP) and Production Part Approval Process (PPAP) Reference Manuals