How do you source a plastic injection mold maker in China?

I’ve been working with tool makers in China for over 10 years. They run the gamut from making *awful* quality molds that used repurposed screw driver bits as alignment pins, all the way up to $100k finely crafted, high quality European steel. It’s not hard to find tool makers. In fact, if you go to a particular industrial park in Dongguan, Guangdong, there are at least 20 of them in just that part of town. The hard part is finding one that actually makes good molds at a fair price. I choose to use a middle man who is excellent at part design, and who reps for a couple factories. If you find a good factory, that is not necessary, but it works for me.

The best thing, as another poster suggested, is to go to a trade show and talk to them. If that’s not in the budget, or time does not allow, then search for companies that claim ISO9001 compliance (even if your company isn’t ISO9001). The company should have been in business for over a decade to have the experience necessary to design and build molds. When you ask for references, they should readily provide them. You can search online and see if they have shipments into the US (the customs data is online). I looked, and the tool maker I use showed 19 shipments to the US last year.

A larger company like my employer would send a representative to the factory, to vet them. During the visit, we make them fill out a questionnaire, check compliance with local laws, bank account, credit check, etc. We have a non-disclosure agreement and a waiver that makes it clear that they will waive their rights to any designs that they assisted you to draw and mold. That’s important if you are seeking a patent. I got into a situation where a mold maker improved a design I made, but then he wouldn’t sign away his rights to to the patent I wanted. During a tour, an old building is not something to focus on (in fact, you could argue it’s a strong point). They should have a variety of molding presses, to conduct mold trials. They should have presses that are equipped with dryers. They should have modern CNC equipment, EDMs, CMMs, etc. They should have a gallery of parts that they’ve molded (and be very proud of!). They should observe safety and environmental rules. They should not have doors padlocked or any obvious stuff like that.

They should provide you with a list of their suppliers of the mold bases and mold steel, components like hot sprues, textures, etc. The better mold makers use Swedish or German steel and DME components, but can also offer Chinese equivalents at a discount. The Chinese steel can be just fine, when used in the right application. They should have a mold design staff in-house that can not only design the mold, but also assist you in part design. That part is critical! Their software should be up to date. A lower tier molder will do things like use pirated software, use another shell company to design the molds and do CAD and CAM work, use yet another company to sell the molds, change names often, etc.

If they passed those steps, then you want to review their communication. Is their rep able to speak and write good English, but also understand molding? Countless times, the person coordinating the job does not understand molding. This makes things 10 times harder (and makes my job miserable at times). The factory should be asking questions about you as well. What presses do you have? What procedures and requirements do you have? A good molder will assume nothing and check every conceivable detail. They will also not let you talk them into making a junk mold by using the wrong steel, wrong gate design, etc. etc.

When they quote, they should give you the following:

Price, lead time, shot size, number of cavities, mold outside dimensions, steel specification (especially hardness) and manufacturer for each part of the mold, cycle time estimate, sprue/gating style and manufacturer (if applicable), surface finish/texture spec, required press tonnage, etc. and payment terms. Good molders will agree to a minimum expected tool life, and offer a guarantee if something goes wrong. They will also quote you longer to machine the mold than cheaper molders, because cheap steel is easier to machine. Be wary of 28 day lead times. That’s what all my low quality junk mold factories quote. A large mold with high hardness steel takes a solid 6–8 weeks between the order and the first sample (the T1 sample). Never pay more than half up front, and never pay the remainder until you have received a good part that you can approve. You also need to understand how the mold will be packed, crated, and shipped to the port for its voyage to the US. Molds are typically sprayed down with protectant to make sure the mold won’t rust in the high humidity sea container.

At this point, if you want to order the mold, it is standard for them to require a purchase order before assisting you with design for manufacturing (DFM). It is reasonable for them to ask for a design fee for DFM if you are not ready to place an order. You can stipulate that the design fee be waived, if and when you buy the mold. Unless you have a plastics engineer with mold flow software in your office, you’re relying on them to fine tune your design to get the optimal part. This is the point where the best tool makers separate themselves. A good tooling engineer is worth the extra cost up front. They will thoroughly analyze the wall thickness, draft angles, gate design, etc. to reduce material, reduce warping or other issues, and reduce cycle time. They can find innovative approaches to handle undercuts. My bad mold makers will just take the part design I sent them, add draft angles, and call it a day. They’ll also claim they can’t handle an undercut situation, but after you argue with them, suddenly they figure it out. Often the bad ones will agree to make a part as designed, but then take liberties on their own after you place the PO. I’ve also seen bad ones send me drawings with obvious issues, like missing draft angles, thin areas that are not really mold-able, etc. and then ask me to approve. A more recent development in China is rapid prototyping. They should have a relationship with a rapid prototyper to make a sample, if that’s what you need.

They should provide you with revised 3d drawings of your part, and also drawings of the mold you are agreeing to buy. You will need those later if there is a repair or re-texturing. Refusing to provide that is a big red flag that I see all the time. What happens is cheaper mold makers put work into the quote, but don’t get the business, and so they are reluctant to cough up the drawings until they get paid. So now they hold your files hostage. Another thing that can happen is that they use your mold to make parts for someone else. I’ve seen that too.

Once you approve the samples, the factory should provide you the optimal press parameters to obtain the best part. Good molders will give you spare parts like lifters, the EDM electrodes, etc. as part of the price, so that you don’t have to scramble if one fails.

Finally, educate yourself on Chinese business culture. It is part of the business culture to never say “No” and always make promises that they are capable of something. To say that they can’t do something would be “losing face” and would bring them shame. So instead, they just quote you an exorbitant price and hope that you say no. It is also Chinese business culture to quote a low RFQ price, then nickel and dime you for engineering changes and other unexpected upcharges later. Learn to identify these tactics early on.