Many overseas buyers source plastic parts from China. Prices are competitive and capacity is large. But the wrong supplier costs more than you save on unit price.
We are a mold factory in China. We see these mistakes every month. Here is what to check before you commit.
1. Verify Real Manufacturing Capability
Many buyers pick a supplier from a nice website. Then they learn the “factory” is a trading desk. Ask how many machines run on the floor. Ask the tonnage range.
A supplier running presses from around 80T to 800T can cover most plastic parts. Ask whether they build molds in-house. A real toolroom has CNC centers, EDM, and wire cutting. Shops without one outsource your mold. Then nobody controls the schedule.
Ask for a live video walk of the shop floor. Stock photos prove nothing. A handful of presses is a small shop. Rows of them is a mid-size factory. Match the size to your order. Check what they already make. A shop full of auto connectors may struggle with your cosmetic housing.
2. Demand DFM Support
Most mold rework starts with a bad design. Thick walls sink. Sharp corners crack. Missing draft locks the part in the steel. Thick-to-thin transitions are the classic sink mark cause. DFM catches them before steel is cut.
DFM means Design for Manufacturability. A good supplier reviews your 3D files before quoting the mold. They flag thick sections, zero-draft walls, and undercuts. Fixing these on paper costs almost nothing. Fixing them in steel costs thousands.
Ask for the DFM report before you approve the mold design. No report, no order.
3. Clarify Mold Ownership and IP Terms
Buyers forget the mold question until they want to leave. Then the supplier names a “storage fee.” Your mold is your asset. State it in writing before you pay.
Spell out who owns the mold, who keeps the design files, and how you take the mold elsewhere. A straight supplier confirms you own the mold once paid in full. Get that in one sentence in the contract.
Sign an NDA before sending drawings. Ask where your files live and who can open them. Keep a copy of the mold design files yourself. If the relationship ends, you still have them.
4. Inspect Quality Control
One bad shipment can stall your line for a week. Ask how they stop it. Good shops check incoming resin. Operators measure parts during the run, not just at the end.
Calipers and micrometers are the minimum. A CMM shows a higher level of control. Ask how often they calibrate. A CMM past its calibration date is decoration. Ask for a real inspection report. It should show measured values against your tolerances. A rubber “PASS” stamp tells you nothing.
Also ask who pays for sorting and rework when parts fail. Settle this before the first shipment, not after.
5. Test Communication Early
Reply speed during quoting predicts reply speed during a crisis. Write one technical question about your drawing. See if the answer is direct or evasive.
Ask to speak with an engineer, not only the salesperson. Engineers spot problems salespeople miss. A supplier who asks sharp questions about your part is usually the safer bet.
Watch for “no problem” to every question. It often means they did not read the drawing. Time zones matter. A big gap means one exchange per day. Plan for it.
6. Always Run a Trial First
T1 samples reveal what drawings hide. Warpage, fit issues, and color drift all appear here first. Measure critical dimensions against your drawing. Test assembly and function.
Send written feedback and require corrected samples before approval. Vague approvals cause disputes later. Note the delivery date too. A supplier who misses T1 dates will miss production dates. Keep the T1 samples. They are your reference when production parts drift.
7. Sign a Clear Contract
A clear contract slows the start by a few days. It saves months of argument later. Cover part price, mold price, and payment terms. Add tooling lead time, production lead time, and quality standards.
State mold ownership and file ownership. State how defective parts are handled and who pays. A common split is deposit to start the mold, balance after sample approval, and T/T for production orders. Be wary of 100% upfront with no milestones. Milestones keep both sides honest. Put a late-delivery clause in writing. Without one, your urgent order waits behind bigger customers.
Injection molding and die casting are different processes. One shapes plastic. The other shapes metal. A supplier who mixes them up is waving a red flag.
Leave a Reply