Qualifying a supplier is the highest-leverage activity in procurement
Industry data consistently shows that 60–70% of manufactured-part quality issues trace back to supplier selection, not to design errors. A single quality escape on a medical device or aerospace component can cost $10K–$100K+ per event when you factor in investigation, containment, corrective action, and customer impact. The 20–40 hours you invest in qualifying a new manufacturing partner typically pays back on the first production order. This guide walks through the complete process — from initial screening to ongoing performance tracking.
Why Supplier Qualification Matters
The cost of a wrong supplier is never the unit price delta. It shows up downstream as rework, scrap, missed ship dates, and quality escapes that erode your team's credibility.
Rework & scrap costs compound
CNC rework rates at unqualified shops typically run 8–15% vs. 1–3% at qualified suppliers. At $50–$150/hr loaded shop rate, reworking a batch of 50 parts can add $2,500–$7,500 per order — before accounting for the schedule slip.
Quality escapes are expensive
A nonconforming part that reaches your assembly line costs 10× more to address than one caught at incoming inspection. A nonconforming part that reaches your customer costs 100×. For regulated industries (medical, aerospace), a field escape can trigger FDA or FAA investigations.
Schedule risk is hidden cost
When a supplier misses a delivery, the cost is not just the expedite fee. It cascades: your assembly line idles, your test schedule shifts, your product launch slips. Compressed development timelines (58% of teams report shorter cycles) leave no buffer for supplier-caused delays.
Qualification investment is modest
A thorough qualification takes 20–40 engineering hours and 4–8 weeks. The cost of not qualifying — a production lot rejection, a customer return, or a regulatory finding — typically exceeds the qualification cost by 10–50×.
Pro Tip
Track the total cost of quality (CoQ) per supplier, not just unit price. CoQ = unit price + incoming inspection labor + rework/scrap + expedite fees + engineering time spent resolving issues. The supplier with the lowest quote frequently has the highest CoQ.
Pre-Qualification Screening
Before sending a drawing, verify basic alignment on process capability, equipment, tolerances, materials, and capacity. A 30-minute screening call eliminates 60–70% of mismatched suppliers.
Process capability match
Confirm the supplier runs the exact process you need. "CNC machining" is not one thing — a 3-axis shop quoting 5-axis work will either sub it out (losing control) or attempt it on inadequate equipment. Ask: What machines do you run? What axis count? What is your maximum travel envelope?
What to ask: Request an equipment list with make, model, axis count, and work envelope. For CNC: confirm whether they have 5-axis simultaneous or 3+2 positioning — the distinction matters for complex contoured surfaces.
Tolerance capability
Every shop has a standard tolerance band and a precision tolerance band. Verify that your critical tolerances fall within their standard band — not their heroic one-off capability. A shop whose standard tolerance is ±0.005″ (±0.13 mm) can likely hold ±0.001″ (±0.025 mm), but at significantly higher cost and reject rate.
What to ask: Ask: What is your standard holding tolerance for CNC-machined features in 6061-T6 aluminum? If the answer is vague ("we can hold whatever you need"), that is a yellow flag — qualified shops know their process capability quantitatively.
Material and finish capability
Confirm the supplier has experience with your specific alloy/grade and finish. A shop that routinely machines 6061-T6 aluminum may struggle with Inconel 718 or titanium Ti-6Al-4V due to different tool wear, cutting speeds, and coolant requirements.
What to ask: Ask for 2–3 examples of parts they have produced in your target material. If they cannot provide examples, the learning curve will be on your dime.
Capacity and lead time
A shop that quotes 3-week lead time but is running at 90% capacity will slip. Ask about current capacity utilization, shift patterns (single vs. double), and how they handle demand spikes. For production orders, confirm they can sustain your required delivery cadence.
What to ask: Ask: What is your typical lead time for a first-run order of 25–50 CNC parts? What is your current shop load? How many shifts do you run? Can you scale to 2 shifts if my volume increases?
Inspection equipment
The supplier's inspection capability must match your drawing requirements. If you call out GD&T per ASME Y14.5, they need a CMM — not just calipers and micrometers. If you require surface finish verification, they need a profilometer (not a visual comparator).
What to ask: Ask for the make/model of their CMM and the date of last calibration. Calibration intervals should be 6–12 months per ISO 10012. If they sub-contract inspection, understand the turnaround time impact on your lead time.
Geographic and communication fit
Timezone overlap affects responsiveness. A 12-hour offset means every question takes a full business day to answer. Language barriers compound this — technical miscommunication on a drawing revision can result in an entire lot of wrong parts.
What to ask: Evaluate response time during the quoting phase as a proxy for production communication. If they take 5+ days to return a quote, expect similar delays on RFIs during production.
Pro Tip
Create a one-page capability questionnaire and send it before requesting quotes. Suppliers that refuse to complete it or provide vague answers are self-selecting out of your qualification process, saving you time.
Quality System Assessment
Not all quality certifications are equal. Match the supplier's quality system to your industry's regulatory and contractual requirements.
Quality Management System Comparison
| Standard | Industry | Key Requirements Beyond ISO 9001 | When to Require |
|---|---|---|---|
| ISO 9001:2015 | General commercial | Baseline QMS: document control, corrective action, management review, internal audits, process approach | Commercial CNC, sheet metal, or 3D printing parts without industry-specific regulatory requirements |
| AS9100D | Aerospace & defense | Configuration management, risk management (per SAE J1739 or equivalent), FAI per AS9102, FOD prevention, counterfeit-part prevention, key characteristic management, OASIS registration | Flight-critical or defense components, or any part flowing down FAR/DFARS clauses |
| ISO 13485:2016 | Medical devices | Design controls (if applicable), full traceability (lot/serial), validated processes, complaint handling, biocompatibility documentation, risk management per ISO 14971, cleanroom controls (if required) | Class I/II/III medical device components, surgical instruments, diagnostic housings, or any parts requiring FDA 21 CFR 820 compliance |
| IATF 16949:2016 | Automotive | APQP (advanced product quality planning), PPAP (production part approval), SPC (statistical process control), MSA (measurement system analysis), control plans, FMEA | Automotive OEM or Tier 1/Tier 2 supply chain parts with PPAP requirements |
NADCAP for special processes
If your parts require heat treatment, chemical processing (anodizing, plating, passivation), welding, or NDT (non-destructive testing), verify whether the supplier or their sub-tier holds NADCAP accreditation for that process. NADCAP is not a QMS — it is a process-specific accreditation administered by PRI (Performance Review Institute). Aerospace primes (Boeing, Lockheed Martin, Raytheon) typically require NADCAP for all special processes.
Verify, don't trust
Always verify certifications independently. ISO 9001 and AS9100 certificates can be checked on the IAF CertSearch database. IATF 16949 certificates can be verified through the IATF database. NADCAP accreditations are public on the eAuditNet portal. Expired or suspended certifications are more common than you would expect — verify before you qualify.
Pro Tip
A certification tells you the supplier has a quality system. It does not tell you they make good parts. Always combine certification verification with a trial order (Section 4) to validate actual output quality.
Trial Order Strategy
A controlled trial order with first article inspection (FAI) is the most reliable way to validate a new supplier's actual capability — not their quoted capability.
Design the trial order
Order 3–5 identical parts, not just one. A single part can be babied through the shop on a manual machine by the most experienced operator. Multiple parts force the supplier to set up a repeatable process — which is what you are actually qualifying.
Recommendation: Choose a part that represents your typical complexity, tolerance range, and material. If you have a simple bracket and a tight-tolerance housing, order both as part of the trial.
Require a balloon drawing and full dimensional report
A balloon drawing numbers every dimension and tolerance on the engineering drawing. The FAI report maps every balloon number to a measured value, stated tolerance, and pass/fail status. This is the AS9102 standard, but it is good practice for any industry.
Recommendation: Provide the supplier with your balloon drawing template or use the AS9102 Form 3 (Characteristic Accountability, Verification, and Compatibility) format. Specify whether you want CMM data, caliper/micrometer measurements, or both.
Define accept/reject criteria in advance
Before the trial order ships, define what "pass" looks like. Typical criteria: 100% of critical dimensions in tolerance, ≥95% of non-critical dimensions in tolerance, all material certifications (mill certs) provided, surface finish within spec on inspected surfaces.
Recommendation: Document your accept/reject criteria in the PO or a separate quality requirements document. This prevents after-the-fact negotiation when some dimensions are out of spec.
Inspect independently
Do not rely solely on the supplier's self-inspection report. Perform your own incoming inspection on the trial parts — or use an independent third-party inspection house. Compare your measurements to theirs. Discrepancies reveal measurement system issues that will cause problems in production.
Recommendation: If you do not have a CMM, budget $200–$500 for third-party CMM inspection of your trial parts. The cost is trivial compared to the cost of qualifying a supplier who cannot actually hold your tolerances.
Pro Tip
Pay attention to how the supplier handles the FAI process itself — not just the results. A supplier who pushes back on providing inspection data, delivers it late, or provides sloppy reports is telling you how they will behave on production orders.
Ongoing Performance Metrics
Qualification is not a one-time gate. Track these five metrics quarterly to detect degradation before it becomes a quality escape or a missed shipment.
Supplier Scorecard Metrics
| Metric | Target | Action Trigger | How to Measure |
|---|---|---|---|
| On-Time Delivery (OTD) | ≥95% | <90% for 2 consecutive months | Ship date vs. PO required date. Count early deliveries as on-time only if approved. |
| Defect Rate (PPM) | <1,000 PPM | >2,500 PPM on any single lot | Nonconforming parts ÷ total parts received × 1,000,000. Track at incoming inspection. |
| First-Pass Yield | ≥97% | <95% on any order | Parts accepted at incoming inspection ÷ total parts received. Reworked parts count as failures. |
| CAPA Response Time | ≤5 business days to root cause | >10 business days or no root cause | Days from NCR issuance to documented root cause analysis from supplier. |
| Quote Turnaround | ≤3 business days | >5 business days consistently | Business days from RFQ sent to quote received. Track median, not average. |
Pro Tip
Share the scorecard with your supplier quarterly. Suppliers who see their metrics improve when given visibility. Those who do not improve after two review cycles are unlikely to improve at all — start qualifying a replacement.
Red Flags & Deal-Breakers
These warning signs during evaluation almost always predict problems in production. It is far less expensive to walk away during qualification than to recover from a failed production lot.
Refuses to sign an NDA
If a supplier will not sign a mutual NDA before reviewing your drawings, they either lack a legal process or do not respect IP protection. Both are disqualifying for any proprietary design.
Cannot produce inspection reports
If the supplier cannot provide a sample dimensional inspection report from a previous job (redacted for confidentiality), they likely do not perform in-process or final inspection systematically. Your parts will not be inspected either.
No material certifications
Mill certifications (certs of conformance) trace raw material back to the producing mill and verify alloy composition, heat number, and mechanical properties. A supplier who cannot provide mill certs is either not requesting them from their material distributor or not maintaining traceability — both are disqualifying for regulated industries.
Pricing does not separate NRE from recurring
If the quote lumps tooling, fixturing, programming (NRE) into the per-part price, you cannot evaluate the true unit cost. It also means you will pay for tooling again on every reorder. Qualified suppliers always separate NRE from recurring cost.
No revision control process
Ask: "If I send you a rev B drawing, how do you ensure rev A is removed from the shop floor?" If the answer is vague or involves verbal communication only, expect wrong-revision parts. Drawing control is fundamental to any functional QMS.
Quotes tolerances they cannot hold
A shop that quotes ±0.0005″ (±0.013 mm) on every feature without questioning it is either not reading your drawing or plans to charge you for rejects. Qualified suppliers ask clarifying questions about tight tolerances — they know what costs more and want to help you avoid it.
Pro Tip
The quoting phase is a free audit. A supplier's responsiveness, attention to detail, and willingness to ask questions during quoting predicts their behavior during production. If the quote experience is painful, production will be worse.
Supplier Qualification Checklist
Use this checklist as-is or adapt it to your company's supplier qualification procedure. Each item maps to a section above.
| # | Check | Phase | Critical? |
|---|---|---|---|
| 1 | NDA signed and executed | Pre-screening | Yes |
| 2 | Capability questionnaire completed | Pre-screening | Yes |
| 3 | Equipment list reviewed (machines, CMM, profilometer) | Pre-screening | Yes |
| 4 | Quality certification verified (ISO/AS/IATF/13485) | Quality review | Industry-dependent |
| 5 | Certification checked on IAF CertSearch / OASIS / IATF DB | Quality review | Yes |
| 6 | NADCAP accreditation verified (if special processes) | Quality review | Aerospace: Yes |
| 7 | Sample inspection report reviewed | Quality review | Yes |
| 8 | Trial order placed (3–5 parts) | Trial order | Yes |
| 9 | Balloon drawing provided to supplier | Trial order | Yes |
| 10 | FAI report received and reviewed | Trial order | Yes |
| 11 | Independent incoming inspection performed | Trial order | Recommended |
| 12 | Accept/reject criteria met | Trial order | Yes |
| 13 | Material certifications (mill certs) received | Trial order | Yes |
| 14 | Scorecard metrics baselined (OTD, PPM, CAPA) | Ongoing | Yes |
| 15 | Quarterly review cadence established | Ongoing | Recommended |
Pro Tip
Start with items #1–#7 (pre-screening and quality review) before committing to a trial order. This front-loaded screening eliminates unqualified suppliers before you spend money on trial parts.
Conclusion
Supplier qualification is not bureaucracy — it is the highest-leverage activity in your procurement process. The 20–40 hours you invest in screening, quality-system review, and a controlled trial order prevent the 200–400 hours you would spend managing quality escapes, rework cycles, and delivery failures from an unqualified source.
Start Here
Send a capability questionnaire, verify certifications on public databases, and evaluate quoting responsiveness. This 2–4 hour investment eliminates 60–70% of mismatched suppliers.
Validate
Order 3–5 parts with full FAI. Inspect independently. A $500–$2,000 trial order is the most reliable predictor of production quality.
Sustain
Track OTD, PPM, first-pass yield, and CAPA responsiveness quarterly. Share results with the supplier. Replace underperformers before they cause a field escape.
Frequently Asked Questions
What certifications should a CNC machining supplier have?
How many suppliers should I qualify for each process?
What is a first article inspection (FAI)?
How long does supplier qualification typically take?
When should I re-qualify a supplier?
What is the difference between a supplier audit and a supplier assessment?
Should I require ISO certification for prototype orders?
Related Resources
Ready to Work with a Qualified Partner?
MakerStage provides full inspection reports, material certifications, and transparent pricing on every order. Upload your drawings and see for yourself.
Get Free Quote Fast