Hoe een spuitgietleverancier te auditen: fabriek, kwaliteit en risicochecklist

Choosing the wrong leverancier spuitgieten can cost you months of delays, thousands in scrapped parts, and a product launch that falls flat. We have seen it happen — companies that skip the audit step end up with molds that wear out after 5,000 shots, parts with chronic sink marks, and suppliers who stop replying when quality problems surface.

This guide gives you a practical, field-tested checklist for auditing an injection molding supplier. Whether you are evaluating a new vendor for a critical project or re-qualifying an existing one, these are the questions, measurements, and red flags that actually matter — drawn from 20+ years of running production in Shanghai.

What Should You Check Before Visiting an Injection Molding Factory

A pre-visit desk audit is essential before committing time and money to a factory tour. Request their equipment list, quality certifications, recent FAI reports, and verify their business registration online. If they hesitate or send generic brochures instead of actual data, that is your first warning sign. Cross-reference their claimed machine count and tonnage range against their production photos and facility size.

Cross-reference their claimed machine count and tonnage range against their production photos and facility size. If they say they have 50 machines but their factory floor photos show 10, something does not add up. Review their client list carefully. Suppliers who only list vague descriptions like ‘Fortune 500 companies’ without naming any specific industries or part types may be inflating their track record. Look for suppliers who can describe relevant projects similar to yours — same material family, comparable part complexity, and similar production volumes. This pre-screening step typically eliminates 60-70% of candidates before you invest time in a factory visit.

For a deeper understanding of the overall injection molding process and what capabilities matter, our spuitgieten guide covers the fundamentals that inform every audit decision.

How Do You Evaluate a Factory Equipment and Capacity

The most critical evaluation is matching the supplier’s machine fleet to your part requirements. Check tonnage range, machine count, and auxiliary equipment. A factory running machines from 90T to 1850T can handle everything from tiny precision connectors to large automotive panels. If your parts require 500T clamping force but the supplier’s largest machine is 300T, you have a fundamental mismatch.

Count the actual operational machines, not the nameplate capacity. Ask to see prototype samples and parts on display from recent projects — this tells you what the factory actually produces versus what it claims. We have seen factories claim 60 machines when half are mothballed or cannibalized for parts. Check their auxiliary equipment too. Dryers, mold temperature controllers, robots for part removal, and automated material handling systems tell you whether the factory is set up for consistent production or manual improvisation.

In our Shanghai factory, we run 47 injection molding machines spanning 90T to 1850T, giving us the flexibility to produce parts from micro-molded medical components to large industrial housings without subcontracting to unknown third parties.

What Quality Systems Must a Reliable Supplier Have

The minimum requirement is ISO 9001¹ certification combined with a documented quality workflow covering IQC through OQC. Quality systems separate professional manufacturers from garage operations. Ask to see their most recent audit report, not just the certificate. Non-conformances and corrective actions tell you more about a supplier’s quality culture than a clean certificate ever will.

A factory working under ISO 9001, ISO 13485², ISO 14001, and ISO 45001 has invested heavily in process discipline — that investment directly translates to more consistent part quality for you. Look beyond the certificates to the actual workflow. A robust quality process includes incoming material inspection (IQC), in-process checks during molding, first-article inspection for each new setup, and final outgoing quality control (OQC). Ask to see a real inspection report from a recent production run. Check whether they record dimensional data with actual measurements, not just pass/fail checkmarks.

A supplier who measures critical dimensions on 100% of first articles and samples during production runs is fundamentally different from one who only inspects the first piece and hopes for the best. Our quality workflow follows a 6-step process: IQC, sample checking, process inspection, packaging and assembly inspection, FQC, and OQC — each step has defined acceptance criteria and documented records. With 10+ QC specialists dedicated to these checkpoints, we catch issues before they REACH³ the customer.

How Do You Assess Mold Tooling Capabilities

Mold quality determines part quality — this is not negotiable. When auditing a supplier, the single most important question about tooling is whether they build molds in-house or outsource to a third-party mold shop. In-house tooling means direct control over design iterations, faster modifications, and accountability when problems arise. Outsourced tooling introduces a middleman, longer lead times for changes, and finger-pointing when dimensions drift. Walk the mold shop floor if possible. Look for CNC machining centers, EDM machines (both wire and sinker), precision grinding equipment, and CMM (coordinate measuring machine) inspection capability. The number of mold sets they produce per month tells you about their throughput and experience level.

A facility capable of producing 100+ mold sets per month has the scale and repeatable processes to handle your project efficiently. Ask about their mold design process. Do they run mold flow analysis before cutting steel? Can they show you examples of complex mold features like lifters, slide cores, or multi-cavity layouts? These are the details that separate a competent mold builder from a basic shop. Our guide on spuitgietvorm design covers the fundamentals every buyer should understand. Also verify their mold maintenance program. Molds are precision tools that require regular cleaning, component replacement, and dimensional verification.

A supplier without a documented mold maintenance schedule will let your tool degrade silently — until you start seeing flash, dimensional shifts, or surface defects that should never appear. With our in-house mold manufacturing facility producing 100+ mold sets per month, we control the entire tooling lifecycle from design through production maintenance.

What Red Flags Should You Watch for During a Factory Audit

The biggest red flags are showroom-only tours, missing inspection data, bins of scrap parts, and workers making undocumented manual adjustments. We have learned to spot these warning signs over two decades of evaluating injection molding suppliers. If your factory tour never reaches the actual production floor, something is wrong.

Either way, it is a risk. In practice, a well-run factory has these documents organized and accessible — they know auditors ask for them. Third, excessive rework and scrap visible on the floor. A few rejected parts are normal in any molding operation, but bins overflowing with scrap or a rework area larger than the quality lab indicates systemic process control problems. Fourth, workers making manual adjustments without documented procedures. If you see operators tweaking cycle parameters by feel rather than following standardized process sheets, the factory is relying on individual skill rather than engineered processes. This works until that experienced operator leaves or takes a vacation. Fifth, check their material handling.

Fifth, check their material handling and clean room facilities. Are hygroscopic materials like nylon and polycarbonate stored in sealed containers with desiccant? Are they using hopper dryers with documented temperature settings? If the factory has clean room capability for medical or sensitive parts, verify the classification and maintenance records. Proper material drying is fundamental — a supplier who neglects it will deliver parts with bubbles, splay marks, and degraded mechanical properties.

How Do You Verify Material Handling and Compliance

Material handling is a core capability that directly determines part consistency and defect rates. A supplier working with 400+ materials should have documented procedures for material identification, storage, drying, and changeover between production runs. Walk their warehouse and check whether materials are labeled clearly with grade, lot number, and date received. Are they stored on pallets away from walls and moisture? Is there a first-in-first-out (FIFO) system to prevent aged material from being used inadvertently? Pay special attention to how they handle material changeovers — cross-contamination between different resins can cause cosmetic defects and mechanical failures.

Ask about their material testing capability too. Do they have a moisture analyzer for hygroscopic resins? Can they perform MFI (melt flow index) testing on incoming material to verify it meets specifications before it enters the production line? These are basic quality tools for any serious molding operation, yet many smaller shops skip them entirely and rely on supplier certificates of conformance instead of independent verification. Compliance also extends to environmental and safety regulations — RoHS, REACH, and FDA food-contact regulations impose specific material restrictions that a competent supplier must track and enforce across their entire inventory.

For regulated industries, material traceability is critical and non-negotiable. Your supplier should be able to trace every production lot back to the raw material batch, including the material supplier’s certificate of analysis. This traceability chain must be documented and retrievable — not just promised verbally during a sales call. If you are sourcing for automotive, medical, or aerospace applications, this is not optional; it is a regulatory requirement that auditors will verify during compliance assessments. Ask to see a sample traceability record from a recent production run to confirm the system actually works in daily practice, not just on paper.

If they cannot produce a REACH or RoHS declaration for a material they claim to stock regularly, that is a significant gap.

What Questions Should You Ask a Supplier Before Signing

The final evaluation stage is a structured technical conversation that separates true manufacturing partners from order-takers. Here are the questions that cut through the sales pitch:

Can you describe a recent project similar to mine that had quality challenges, and how you resolved them? This question forces the supplier to demonstrate real problem-solving capability. Suppliers who can only share success stories may be hiding recurring issues or lack experience with genuine production challenges. What is your mold warranty policy, and what happens if the tool fails prematurely? A supplier confident in their mold quality will offer a clear warranty — typically measured in shots or years.

Vague warranties or deflections about tool life expectancy suggest they are not standing behind their work. How do you handle design changes after mold construction begins? The answer reveals their engineering maturity. Good suppliers have a documented engineering change process with cost and timeline impact analysis. Suppliers who say changes are easy without discussing trade-offs are either inexperienced or being dishonest. What is your on-time delivery rate for the past 12 months, and can you share the data? Production performance speaks louder than promises. Look for delivery rates above 95% with transparent tracking. For more on selecting and evaluating suppliers systematically, our sourcing guide provides a comprehensive framework.

Who will be my dedicated project manager, and what is their English proficiency? Communication failures cause more project delays than technical problems. A supplier with 30+ English-speaking project managers has invested in the communication infrastructure that international projects demand. Ask to meet your assigned PM before signing — a five-minute conversation tells you more than any language certificate.

Understanding these distinctions is critical for making informed sourcing decisions. Many buyers conflate certifications with capability, or assume that a large factory floor automatically means better results. In practice, the most reliable suppliers combine systematic quality processes with hands-on engineering expertise — they can explain not just what they do, but why each step matters for your specific part geometry and material requirements. The difference becomes apparent when you ask detailed technical questions and evaluate whether their answers reflect genuine manufacturing knowledge or rehearsed sales talking points.

Veelgestelde vragen

What are the most important things to check when auditing an injection molding supplier?

When auditing an injection molding supplier, the most critical areas to evaluate are their equipment capability, quality management systems, mold tooling infrastructure, material handling procedures, and communication reliability. Start by verifying their machine tonnage range matches your part requirements, then examine their ISO certifications and actual inspection workflow on the production floor. Check whether they build molds in-house or outsource to third parties, as this directly impacts lead times and accountability. Request real inspection reports with actual dimensional data, not just pass or fail checkmarks. Walk the factory floor to confirm that what you observe matches what they claim in their marketing materials and documentation.

Should I Audit a Supplier In Person or Is a Video Tour Sufficient?

An in-person audit is always more revealing than a video tour because you can observe things the camera intentionally avoids: the condition of auxiliary equipment, housekeeping standards, scrap levels on the production floor, and how workers actually handle materials and molds. Video tours are useful for initial screening but should never replace a physical visit before signing a significant production contract. For smaller orders, a well-structured video audit with live question and answer sessions can be acceptable if you independently verify documentation such as ISO certificates, inspection records, and material compliance declarations through third-party sources.

How Many ISO Certifications Should a Good Injection Molding Supplier Have?

At minimum, a good injection molding supplier should hold ISO 9001 certification for quality management. For medical device parts, ISO 13485 is essential and non-negotiable. ISO 14001 for environmental management and ISO 45001 for occupational health and safety indicate a mature operation that takes systematic management seriously. More certifications do not automatically mean better quality parts, but they do indicate a factory that invests in disciplined processes and continuous improvement. Always verify that certifications are current through the issuing body and ask to see recent audit reports with documented corrective actions rather than just the certificate itself.

What Does a Mold Warranty Typically Cover?

Most reputable injection molding suppliers warranty molds for a specific number of shots or a defined time period, typically ranging from 100,000 to 500,000 shots or one to three years of production use. The warranty should cover dimensional accuracy, surface finish integrity, and structural soundness under normal operating conditions. Before signing any agreement, clarify what constitutes normal wear versus a manufacturing defect, who bears the cost of shipping for warranty repairs, and how quickly warranty issues will be resolved. A supplier confident in their tooling quality will offer clear warranty terms without excessive exclusions or conditions that effectively void the coverage.

Can I Trust a Supplier Who Outsources Their Mold Building?

Whether you can trust a supplier who outsources mold building depends on the specific arrangement and your risk tolerance for the project. If the supplier has a long-standing partnership with a vetted mold shop and takes full contractual responsibility for mold quality and performance, it can work for simpler tooling. However, outsourced tooling adds communication layers between you and the mold builder, extends lead times for design modifications, and creates accountability gaps when dimensional or surface quality problems arise. For complex molds with tight tolerances, multi-cavity layouts, or aggressive project timelines, in-house tooling is strongly preferable because the supplier controls every step from initial design through production sampling.

How Do I Verify a Supplier’s Claims About Their Production Capabilities?

To verify a supplier claims about production capabilities, cross-reference every assertion with verifiable evidence. If they claim to operate 50 machines, physically count them during your factory visit and note how many are actually running production. If they hold ISO certifications, verify them directly through the issuing certification body database rather than accepting framed certificates on the wall. Ask for production records showing actual cycle times, scrap rates, and on-time delivery percentages over the past six to twelve months. A trustworthy supplier provides this data readily and transparently, while one who makes excuses, delays responses, or offers only aggregate statistics should raise legitimate concerns about the accuracy of all their representations.

Ready to Evaluate Your Next Injection Molding Supplier

Finding the right supplier means verifying equipment, quality systems, and tooling capability match your requirements. The real test is always what you see on the factory floor, not what appears in a sales presentation.

Get a Free Quote and let us show you why serious buyers choose to partner with us for their injection molding projects.

1. ISO 9001: ISO 9001 refers to 2015 Quality Management Systems Requirements ↩

2. ISO 13485: ISO 13485 refers to the international standard for medical device quality management systems ↩

3. REACH: REACH refers to eU REACH Regulation EC 1907/2006 on Registration Evaluation Authorisation and Restriction of Chemicals ↩