Plastic Molding Principles for Your Project

We’ve been getting more and more requests to do “full turn-key” projects here at NexPCB. You may be asking yourself what does the full mean? As the name would imply, this includes everything that is needed to deliver a complete product to end users. This includes the typical PCB, SMT and PCBA, but will also include elements such as plastic casings, various fittings (metal or plastic), printing, packaging and any other process that is required to get a product out-the-door.

One of the areas where we have seen the most misunderstanding, confusion and downright disbelief is around the costs of plastics and the molding process. The prevalent notion is something to the affect of “it’s just a plastic box!” and it is shattered forthwith when the myriad of complexities are introduced. In this article, I want to discuss some of the elements that will add to the overall cost and complexity of the project around plastics.

Before we begin, I recommend taking a look a couple of videos as a primer for some of the terms that we’ll be using. The first is from “The Engineer Guy” and is an outstanding overall discussion of how all of this works :



The second is specific to creating molds. This part is vitally important to understanding the main driver of cost in a plastics project.



Finally, if you’re feeling really geeky, you can check out the Wikipedia article dedicated to discussing Injection Molding here :

So, now that we have that out of the way, let’s get into the nitty gritty.

There are quite a few variables that go into the mix to get a satisfactory results and good price/performance.

We’re going to discuss this in direct relation to the China market and what is common here. Other parts of the world will have some different variations, but they should generally hold. I’m also going to discuss prices in multipliers from a base as much of our pricing data is confidential with our suppliers.


This one (rightfully) starts at the top. The simplicity or complexity level of your molding design will directly impact its cost and manufacturability. Intricacies will increase the cost and complexity tremendously. It’s nice to have a cool shape or effect in the plastics. However, that can directly impact the way the mold tooling will be created, drive higher costs and, potentially, decrease yield levels to a point where it’s not economical to produce the product. Simplicity is the name of the game here.

A side note about design and impact on assembly. We find that the final assembly can be very challenging if the designs have not been adequately tested in the lab. We recommend a good 3D print of your components before sending for manufacturing. It’s much less costly to spot assembly issues early with a good 3D printed version, so take the time to take advantage of being in second decade of the 21st century and print up some cases!

Mold Base

There are two types of mold base with different types of materials. There are “standard mold bases” that are, just like they sound, the ones that conform to a set of standards. They are generally a similar size and are not always the best option if you either have a very large or very small part to mold. There are also custom mold bases. The main driver of cost is where they are sourced from as well as the materials used. Locally sourced Steel #45 mold bases are the least expensive. The most dominant maker of premium mold bases in East Asia is LKM (Lung Kee) and these are generally about 2-3x more expensive than the locally sourced mold bases.

Custom mold bases will vary wildly in price since they are not common, but there are some reasons why these may be a better idea. When the parts are smaller, for example, a custom mold base may be better. In this case, it is possible that a custom mold base may be a more economical way to go since the amount of materials needed may be less than a standard mold. It pays to find a professional that can help to guide this decision process.

Mold Insert

This is where the most variation comes into play. The cost of the mold inserts will be directly related to the materials used and the size of the parts that will be molded. Molds are priced per kilogram. The main difference with the materials is the lifespan of the mold. The stronger the materials, the longer the mold insert will last. In the Chinese market, there is also a significant difference between imported materials versus domestic materials. In general, the imported mold insert materials come from Japan, Germany and Korea with Japan being the most common source. We’ve put together a handy table below to compare the materials (below). Steel #45 is used as the baseline.

Materials Domestic Pricing (per kg) Imported Pricing (per kg) Lifespan (# of shots)
Steel#45/#50 1-2x N/A 50,000-100,000
P20 3x-5x N/A 300,000-500,000
718 Steel 5x-7x 15x >500,000
738 Steel 8x-10x 15x >500,000
NAK80 15x-18x 23x >800,000

As you can see, the variation in price is huge. However, since the insert costs are one of the highest costs in this process, it’s good to make sure that you know how many of these parts are going to be made. Also worth noting is that it’s not common to use steel #45 for these inserts because the resulting plastic tends to be rough. There may be a temptation to “go cheap” with a lower quality material, but this is where planning ahead can save a lot of money in the long run.


Once all of the tooling is done, then there is the question of plastics. There are many different types of plastics out there. There are general, industrial and medical grade plastics (among others). There are various vendors for each with wildly varying prices. However, compared to the tooling costs, the plastics tend to drive less cost than other parts of the process. In China, the most common plastics come from Kingfa (domestic) and Chimei (Taiwan). The pricing is competitive. There are also foreign manufacturers such as Bayer/Covestro that are readily available. A word of caution, however. There are lots of problems with counterfeiting when it comes to “branded” plastics. It pays huge dividends to make sure you have a trusted supplier, manufacturing partner and/or EMS partner. NexPCB maintains good relationships with many of these trusted suppliers to ensure we get the proper materials.

There is one more element that gets precious little airtime with plastics: colors. Many new products will offer a variety of colors for their customers to select from. Be careful, here. Plastic colors can be made one of two ways. The first way is to buy a pre-colored plastic that is either a standard or a custom color. The second way is to mix colorant in at production to produce a color. The first way is very precise and the second way can be highly variable from one run to the next. Why would you not choose the first option you may ask? MOQ’s…

For colored plastics, the MOQ’s can be very high. Some companies want MOQ’s as high as 750kg or more for each color. Plastics are light, so some quick math on a product that only needs 50g of plastic per shot tells you that this is a LOT for smaller projects. If you offer 5 colors, then you’re looking at a minimum outlay of 3750 kg of plastics. For some projects, this isn’t a big deal. But, for makers that are just starting out, and extra $30k in cost just for plastics may blow a hole in their budget.

That leaves mixing. This is a fairly economical route since the price for colorant beads isn’t too high and the MOQ’s are generally a 10kg bag or two. The challenge is precision. If you’re planning to ramp up production and want the colors to match from one batch to the next, it will be a challenge. The colors will generally be close, but they won’t exactly match. This may bother some people, but others don’t sweat it. Just keep the caveat in mind when you tell your Kickstarter campaign that they can have a rainbow of colors to choose from…

Mold Production, Assembly Test and Loading

Different production processes will vary the cost and the amount of time needed for each part. This depends on the design abilities and the facilities of the factory. Some plants specialize in automotive plastics while other focus more on industrial plastics. If you ask a plant that specializes in something that doesn’t fit the profile of the product you want to produce, it’s likely that you’ll get an answer that is overpriced. This is generally because the plants will add an extra risk premium in when producing projects that are outside of their core competence. It’s best to choose plastics factories that are aligned with what the project requires (as much as that’s possible).

Speaking of risk, the matter of testing also comes up regularly. The pricing for a production run will vary based on the number of tests that the factory will run to confirm that the final product is correct. Some some factories (in China) support molding tests up to three times whereas others do not specify how many times they will test. There is different risk levels to the supplier, so they may run more tests for verification. We generally recommend a minimum of two tests to be run per production.


Obviously, since we’re talking about manufacturing, the minimum order and lead time can drastically impact the cost of the production. Higher values for both (respectively) lead to lower costs. There are some specific topics that we’ve found are the easiest to overlook when it comes to MOQ’s. These generally are:

    • Colors (discussed earlier)
    • Factory imposed MOQ’s(some factories will do small runs in between larger ones, so this affects lead-times)
    • Plastic material selections (some plastics require higher purchase amounts than others, so make sure to ask)

Whew.. That was a lot.. Now you can understand why I get so nervous when a customer talks about their plastics work like it’s just a box to cover their stuff. It’s not quite so easy. There are a lot of variables to keep in mind.

If you’re confused by all of this, NexPCB would be happy to help you out. We have relationships with many trusted suppliers in China that can help you with the plastics part of your turnkey project. We’re always happy to help customers that need a fully assembled solution. Feel free to reach out to and one of our friendly folks will help to demystify these challenges for you!

If you have a project that you'd like NexPCB to assist with, you can fill out our handy project request form here and we'll review your technical details as well as give you a competitive price.

Posted by Chris Howes

Chris Howes

Having had a long career at IBM, Chris joined NexPCB to bring pragmatic solutions to companies that are starting a new hardware adventure. Chris was also a maker before there was even such a term.