How do I source custom plastic parts?

Let's start with custom plastic parts.  This is where most of the head-scratching occurs in a small-lot run (say, 2000 parts).

Let’s say you have a design of moderate complexity, with something like 10-20 custom plastic parts. How do you make the plastic parts?  3D printing is not viable.  First, the surface finish is not there. Second, the structural strength is often not there due to the limitations in materials and processes.  Lastly, if your product needs to pass regulatory approval for sale in Europe – i.e. you need the CE mark – plastic parts must have flame retardants built in, and that is very hard to find in RP parts.  Cast urethane parts come closer in surface finish and structural strength but the per-part cost is still prohibitive.  This leaves molding and forming as the viable processes.

Injection molding is by far the most practical way to make small to medium sized plastic parts. The cost, once you invest in molds, can be a few cents per part at quantity and less than $1 per part at lots of 2000.  The problem is that you must invest in molds.  There are a few choices.

  • Use a service like Protomold – 4-6 week turn, prototype level molds, good for a relatively smaller quantity of parts for the lifetime of the molds. The molds will cost significantly less than traditional high volume molds. The per-part cost will be significantly higher than traditional processes.
  • Engage an injection molding supplier – 3 month turn, production ready molds, good for up to 100,000 – 500,000 parts per mold.  The molds will cost a lot more.  For example, the molds that were involved in the original Zeo Sleep Manager (one of my old products) was made in China and the molds cost around $100,000 all in (and this was a very simple board-in-box product).

Generally speaking, injection molded plastic parts will cost less if made in China than if made in the USA.  Making your plastic parts in the USA has the obvious benefit of proximity between R&D and manufacturing. It is much easier to have your engineering team live there for a couple of weeks to tweak all the molds so everything fits correctly.  However it is significantly cheaper to do it in China, and the minimum order quantity for plastic parts in China can be quite low in the beginning (500-1000 range is not uncommon) provided that the product team can convince the supplier that there is long term upside.  The “right-shoring” decision is up to the product team and the unique needs of the project again.  I is usually faster to do things in the USA the first go-around, and sometimes this is worth the price premium.


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