Choosing an injection molding partner is one of the highest-leverage decisions in product development. The right supplier prevents defects you never see, suggests design changes that save tooling money, and scales with you from prototype to production. The wrong one delivers late, drifts on quality, and holds your tooling hostage.

Yet most selection processes reduce to comparing piece prices on a spreadsheet — the least informative data point in the entire RFQ. This guide gives you fifteen questions that actually predict success, grouped into the five areas that matter: technical capability, quality systems, tooling and IP, commercial terms, and communication.

Why Partner Selection Matters More Than Price

A molded part is not a commodity purchase. It is a program that spans months or years and involves tooling, process development, quality validation, and logistics. The cost of a supplier failure is not the piece price difference — it is:

• Re-tooling and re-validation ($10,000–$100,000+)
• Launch delays measured in weeks or months
• Scrap, rework, and field failures
• Engineering time diverted to supplier management

A supplier charging 15% more per part that delivers first-article approval on the first trial is almost always the cheaper choice.

Technical Capability

Q1. Do you make the molds in-house, or outsource them?

In-house custom mold making is the strongest predictor of program control. When the tool builder and the molder are the same organization, DFM feedback arrives faster, design changes are cheaper, and there is no finger-pointing when a part does not fill. Outsourced tooling is workable but adds a layer between you and the people cutting steel.

Q2. What press sizes and capabilities do you operate?

Match the supplier's equipment to your part. Ask about tonnage range, shot size, and whether they run hot runner systems, two-shot molding, insert molding, or gas assist. A shop whose largest press is 200 tons cannot mold your 800-ton automotive panel — and a shop that only runs 800-ton machines will overcharge for your small enclosure.

Q3. Do you provide DFM feedback before quoting?

This is the single best free signal of engineering competence. A capable partner returns comments on wall thickness, draft, rib ratios, gate location, and tolerance — not just a number. If a supplier quotes your drawing without asking a single question, they will build exactly what you drew, including the problems.

Q4. Can you support the full volume curve?

Confirm they can take you from rapid prototyping through bridge tooling to hardened production steel. Transitioning suppliers between stages costs time and loses accumulated process knowledge.

Quality Systems

Q5. What certifications do you hold, and what is the scope?

Ask for current certificates and check the scope statement. ISO 9001 is the baseline. Automotive programs require IATF 16949 — verify through the IATF Global Oversight scheme. Medical device programs require ISO 13485. A certificate for "trading of plastic products" is not the same as one for "manufacture of injection molded components."

Q6. What inspection equipment do you have?

Look for CMM, optical comparators, vision systems, and calibrated gauges. Ask whether they perform first-article inspection (FAI) and can provide full dimensional reports. A supplier with no metrology capability cannot prove conformity — they can only assert it.

Q7. Do you run process monitoring?

Mature molders use cavity pressure sensing, statistical process control (SPC), and documented process parameters. Ask what happens when a dimension drifts: is there a defined reaction plan, or do they simply adjust until parts look right?

Q8. Can you share process capability data?

For critical dimensions, request Cpk or Ppk values from a comparable program. A supplier who tracks capability can tell you whether your tolerance is achievable before you pay for the tool. Material and testing references from bodies such as ASTM International support specification and validation.

Tooling, IP, and Ownership

Q9. Who owns the mold?

This is the question most buyers forget until it is expensive. Standard practice: you paid for it, you own it. Get it in writing, along with the right to have the tool released and shipped. Some suppliers quote low piece prices precisely because they retain the tool and lock you in.

Q10. What is the expected tool life, in shots?

Tool life depends on steel grade, part geometry, and material. A hardened steel mold should run 500,000 to over 1,000,000 shots; aluminum bridge tooling runs 10,000–100,000. Ask what steel grade they propose (e.g., H13, S136, 2316) and what life that corresponds to.

Q11. How do you protect my IP?

Discuss NDAs, whether your tooling will be used for other customers, and where molds are stored. Reputable exporters will sign enforceable agreements and segregate customer tooling. If a supplier is vague here, treat it as a serious warning.

Commercial Terms

Q12. What is included in the quoted price?

Piece price alone means little. Confirm what is bundled: tooling, secondary operations, packaging, inspection, and freight terms (Incoterms). A low piece price that excludes assembly and packaging is not comparable to a higher all-in price.

Q13. What are the payment terms and MOQ?

Understand the tooling deposit schedule (commonly 50% upfront, 50% on first-article approval), minimum order quantities, and price validity. Ask how price scales with volume and what happens if your forecast changes significantly.

Communication and Support

Q14. Who is my point of contact, and what is the response time?

Ask for a named account or project engineer, not a generic sales inbox. Clarify time-zone overlap, typical response windows, and how technical questions are escalated. Ambiguity costs more than distance — you want a partner who answers questions with specifics.

Q15. What happens when something goes wrong?

Every program hits problems. Ask for a concrete example: a time a part did not mold as expected, and how it was resolved. Suppliers with real experience will describe root-cause analysis and corrective action. Suppliers with a perfect track record story are usually telling you they have not run enough programs.

How to Prepare an RFQ That Gets Useful Quotes

The quality of the quotes you receive is directly proportional to the quality of the RFQ you send. An incomplete package forces suppliers to guess — and they will guess conservatively, padding the price or quietly assuming the cheapest interpretation.

A complete RFQ package includes:

• 3D CAD file — STEP or IGES, in the correct units and scale, with the final revision
• 2D drawing with GD&T — critical dimensions, tolerances, datum structure, and surface finish callouts
• Material specification — exact grade, color (with a Pantone or RAL reference or a physical sample), and any flame-retardant or food/medical compliance requirement
• Annual volume and order pattern — total yearly quantity, typical order size, and expected ramp
• Target timeline — when you need prototypes, first articles, and production
• Cosmetic requirements — define the A-surface, specify texture (or provide a texture sample number), gloss level, and acceptable gate and ejector mark locations
• Secondary operations — painting, plating, printing, assembly, welding, or insert installation
• Packaging and shipping — protection level, labeling, and Incoterms
• Quality documentation required — FAIR, material certs, RoHS/REACH declarations, inspection level

Optional but useful: a target price. Some buyers avoid sharing one, but a realistic target tells suppliers whether the program is viable for them before either side invests weeks in the exercise. It also surfaces unrealistic expectations early, which is valuable information in itself.

What a good RFQ response looks like. Beyond price, expect: DFM comments, confirmation of material availability, a proposed tooling approach and steel grade, an estimated tool life, lead times for tooling and production, and questions. Lots of questions is a good sign — it means someone read your package properly.

Vendor Evaluation Checklist

Red Flags to Watch For

• Significantly lowest quote. A price 30–40% below the pack usually means different steel, fewer cavities, skipped inspection, or a bait-and-switch on volume.
• No questions about your drawing. Silence is not efficiency; it is lack of engineering engagement.
• Reluctance to share certificates, audits, or references. Legitimate exporters expect due diligence.
• No physical facility. Some "manufacturers" are trading companies. Ask for a video audit or third-party inspection report.
• Pressure to skip prototyping. A supplier pushing you straight to hardened steel may be optimizing for their tooling revenue, not your risk.

How to Run a Trial Order

The trial order is where a supplier's claims meet reality — and it is the highest-value few thousand dollars you will spend in the selection process. Run it deliberately.

What to include in the trial

• Give the supplier the real production geometry, not a simplified test part. Their ability to mold your actual part is what matters.
• Specify the actual production material and grade, including any FR or filled variant.
• Ask for a full first-article inspection report with dimensional data on every CTQ dimension, plus material certification.
• Request process parameter documentation — the recorded melt temperature, pressures, and cycle time they actually ran.

What to measure

• Dimensional conformance — do all CTQ dimensions fall inside tolerance, and by what margin?
• Cosmetic quality — check A-surfaces for sink, flow lines, weld lines, flash, and gate vestige.
• Consistency across the run — request samples from the start, middle, and end of the run, not just hand-picked good parts.
• Packaging and protection — parts that arrive scratched tell you how the supplier handles product.
• Communication quality — how quickly did they respond to questions, and were the answers specific?

How to evaluate

Score the trial on the same five dimensions used for selection. A supplier whose parts are dimensionally perfect but who took a week to answer each email is giving you important information about the next three years.

Treat the trial as a rehearsal. If the supplier treats it as a formality, that is your answer.

Understanding Total Cost of Ownership

Piece price is the number everyone compares and the number that matters least in isolation. What you actually pay is total cost of ownership.

How to compare quotes properly. Normalize every quote to the same scope before comparing: same Incoterms, same volume, same secondary operations, same packaging, same inspection level. Only then is the piece-price comparison meaningful. A quote that looks 20% cheaper because it excludes assembly and inspection is not cheaper — it is differently scoped.

The failure cost is the biggest line item. Re-tooling, re-qualification, and launch delay typically dwarf the annual piece-price difference between two competent suppliers. This is why the evaluation weighting earlier puts technical capability and quality systems ahead of commercial terms.

Making the Decision

Score candidates across the five areas rather than on price alone. A practical weighting:

• Technical capability — 25%
• Quality systems — 25%
• Tooling and IP terms — 20%
• Commercial terms — 15%
• Communication — 15%

Then run a paid prototype or bridge tooling trial with your top one or two candidates before committing to production tooling. The trial reveals more than any questionnaire: how they communicate, how they handle a problem, and whether the parts match the promise.

Evaluate Us Against These 15 Questions

We welcome this list — it is exactly how a serious OEM molding supplier should be assessed. Our team provides in-house custom mold making, rapid prototyping, DFM review with every quote, and full dimensional reporting. We also support die casting and metal stamping when your assembly needs mixed processes.

Send us your RFQ and ask all fifteen questions. Learn more about our company and capabilities.