How Plants in Mexico Evaluate and Approve Suppliers
Onboarding a supplier has six stages, and each one decides something different. This guide explains what gets evaluated at every step, which criteria actually carry weight, when to require PPAP, and what changes when the purchase is a small maintenance lot.
From the buyer's side, approving a new supplier is paperwork with consequences: err on the strict side and it takes months to onboard someone who could have delivered this week; err on the loose side and you introduce a risk into the line that gets paid for in downtime. And it is almost always decided using the least useful piece of information available, which is the quote.
This guide describes the real process stage by stage, says what gets evaluated at each one, and makes clear what changes when the purchase is not series production but a small maintenance lot, where applying the full process does more harm than good.
In Summary
- There are six stages: information and capacity, quotation with scope, initial sample with evidence, second-party audit when risk justifies it, administrative onboarding, and performance measurement.
- The criteria that carry weight are demonstrated quality, delivery, total cost, available capacity, certifications where applicable, communication, and company stability.
- PPAP is requested by level, and the level is set by the customer. Demanding the full package where it does not belong stops repairs instead of protecting them.
- The second-party audit is what confirms the file against the real process, not against a binder.
- And the most expensive error is choosing on unit price. Working with an already audited network of shops resolves stages one through four before your emergency begins.
1. The six stages, and what each one decides
| Stage | What is evaluated | Who decides |
|---|---|---|
| Information and capacity | In-house processes, equipment, free capacity, certifications, references | Purchasing with engineering |
| Quotation with scope | Whether they understood the part, the breakdown, lead time and assumptions | Purchasing with engineering |
| Initial sample | Whether the part conforms, with dimensional evidence: FAI or PPAP as applicable | Quality |
| Second-party audit | Whether the real process supports what the file claims | Supplier quality |
| Administrative and tax onboarding | Legal documentation, commercial terms, insurance | Purchasing and finance |
| Performance | Received quality, on-time delivery, responsiveness | Purchasing with quality |
The stage most often skipped is the third, and it is the most informative: one sample with its dimensional report says more about a supplier than all their marketing material combined.
2. What each stage reveals, used properly
Information and capacity. The catalog does not matter here, free capacity does. Ask about capacity available this week, which processes they subcontract, and who performs metrology.
Quotation. It is no longer just a price: it is a sample of how they work. A line-item breakdown, declared assumptions and questions about the critical callout are worth more than a low number. The full method for making three quotes comparable is in how to choose a CNC machining supplier.
Initial sample. Ask for the part and its evidence. In aerospace the reference is FAI per AS9102; in automotive production, PPAP at the applicable level; everywhere else, a dimensional report on critical callouts plus the material certificate is enough.
Second-party audit. It happens on site and against the process, not against the binder. What is worth seeing: the control plan in use, calibration records, material handling and identification, backward traceability from a finished part, and how the last nonconformance was documented.
Administrative onboarding. It carries the least technical risk and delays everything most often, because it depends on documents nobody asked for in time. Request them in stage one, not stage five.
Performance. Without measurement, onboarding is a decision that never gets revisited.
3. The criteria that actually carry weight
- Demonstrated quality. With evidence from real parts, not a statement of intent.
- Delivery performance. History, not promises. Ask for their on-time percentage and how they measure it.
- Total cost. Price plus freight, plus inspection, plus expected rework, plus your team's time managing the supplier.
- Real available capacity. An excellent, fully loaded supplier is a schedule risk.
- Certifications when the part's destination requires them, verified in a register and with the scope actually read.
- Communication. How fast they respond and whether they raise problems before the delivery date.
- Company stability. Customer concentration, years in operation, ability to sustain a run without full prepayment.
4. PPAP: what it is and when to require each level
PPAP is the production part approval process, the standardized package with which a supplier demonstrates it can manufacture the part to specification using an approved process at the agreed production rate. It consists of a set of documentary elements, and it is submitted by level:
| Level | What is submitted, in general terms |
|---|---|
| 1 | Part submission warrant only, with appearance report where applicable |
| 2 | Warrant, samples and limited data |
| 3 | Warrant, samples and complete documentation |
| 4 | Warrant plus the specific requirements the customer defines |
| 5 | Warrant and samples, with complete documentation available for review at the supplier's site |
Two practical rules. First: the level is set by the customer, based on the part's risk and the supplier's history. Second: PPAP belongs to the world of production and service parts; using it as a universal requirement for any purchase is the most common way to turn a quality process into an administrative obstacle.
How that package is assembled, with APQP and SPC around it, is detailed in the three quality pillars for an automotive Tier 1 supplier.
5. What changes on small lots and MRO
This is where the corporate process collides with plant reality. A spare part that has a line down cannot wait eight weeks of supplier onboarding, and applying the series-production package does not make it safer: it makes it impossible.
What works in that scenario:
- A fast lane defined in advance, with proportional requirements: verified ISO 9001, a dimensional report on the functional callout, a material certificate, and a purchase order with written acceptance criteria.
- Pre-qualified suppliers before the emergency. Onboarding happens cold, when nobody is under pressure, and sits ready for the day it is needed.
- Value and risk limits on that lane, so it does not get used where it should not.
- Later review. If the fast-lane supplier becomes recurring, they enter the full process.
The four operational filters that let you qualify a maintenance and tooling supplier cold, without standing up an entire program, are in how to qualify a tooling and MRO supplier.
6. Performance measurement after onboarding
Few indicators, always the same ones, on a fixed cadence:
- Quality of what was received, as conforming parts over parts delivered.
- On-time delivery, against the originally committed date rather than the renegotiated one.
- Response time to quote requests and to nonconformances.
- Documentary accuracy, because a report arriving late or incomplete costs internal work.
Supplier quality manuals typically classify suppliers into categories based on these indicators, and provide for removing a supplier that stays in the lowest category across several consecutive periods. It is worth having that consequence written down from onboarding: a supplier who knows how they are measured has a reason to improve before the problem escalates.
7. The most expensive error in the process
Choosing on unit price. It is the only criterion that compares with no effort, which is why it wins arguments it should not win.
The three costs that never appear in that column: rework and rejection when the evidence was weak; line downtime when the lead time was not real; and your own team's time managing a supplier who needs constant follow-up. Once all three are estimated, even roughly, the decision frequently changes.
Frequently Asked Questions
What are the stages for onboarding a manufacturing supplier?
Six: information request and capacity verification, quotation with defined scope, initial sample with its dimensional evidence, second-party audit when risk justifies it, administrative and tax onboarding, and performance measurement once they start supplying. Skipping the sample or the audit is what produces the problems later blamed on price.
Which criteria carry the most weight when evaluating a supplier?
Demonstrated quality backed by evidence, delivery performance, total cost, real available capacity, certifications when the part's destination requires them, communication, and company stability. Unit price is one criterion, not the criterion: it is the only one comparable on a single sheet, which is why it dominates the decisions that go wrong.
What is a second-party audit?
It is the one the customer performs at the supplier's facilities, as opposed to a third-party audit performed by a certification body. It verifies against the real process what the file claims: process control, metrology and calibration, material handling, traceability and nonconformance handling.
When should PPAP be required, and at what level?
PPAP is the production part approval process and it applies to production and service parts in automotive chains. Levels run from 1, with only the submission warrant, to 5, with full documentation available for review at the supplier's site, and the level is set by the customer based on risk. For a small maintenance lot, requiring the full package usually delays the repair without adding safety.
How is a supplier measured after onboarding?
With few indicators on a fixed cadence: quality of what was received, on-time delivery, response time to requests and to nonconformances, and documentary accuracy. Supplier quality manuals typically classify suppliers into categories and provide for removing one that stays in the lowest category across several consecutive periods.
Conclusion: the process works when it is proportional to risk
A good approval process is not the strictest one, it is the one that applies rigor where the risk is and opens a fast lane where risk is low and urgency is real. Plants that run it this way onboard faster and get fewer surprises, because the rigor sits where it matters.
If what you need is fewer onboardings, working with an already audited network of shops resolves the first four stages before your project starts, with a single onboarding covering several processes: the full scope is on our manufacturing services page. Upload a part at app.radii.com.mx and the quote arrives with the process, the executing shop identified and the quality documentation inside the scope.