How to make your injection molding run more cost effective

Nicola Brittain

Expert guide to reducing costs on smaller plastic print runs.

Injection molding, the process of creating a component by injecting melted material into a mold until it solidifies, is a traditionally expensive practice. The high set-up costs, normally between US$10,000 and US$100,000, mean that to benefit from a return on investment manufacturers normally need to print at high volumes with the result that the practice is usually only adopted by big plants producing runs of thousands or sometimes millions of components.

But what if a smaller plant wants to produce a much lower volume run? This article from on-demand digital manufacturing platform, Hubs, provides tips on how to make this economically viable.

Tooling costs

The primary cost for an injection molding project is around tooling – encompassing the design and machining of the mold, and material.

Tooling has the greatest impact for small batches (roughly 50-70% of the total cost) meaning planning a project in advance is essential.

The straight pull mold

To cut costs, operators should consider redesigning the injection molded part to avoid undercuts (the part that prevents ejection from the mould). These add to costs and complicate things, so it’s worth eliminating them where possible.

Smaller parts

Smaller parts can be molded faster resulting in a higher production output, reducing the cost per part. Smaller parts also result in lower material costs and reduce the price of the mold.

Many parts in one

Using a single mold for multiple parts is standard practice. Typically, one mold comprises six to eight small identical parts cutting down production time significantly. You can also place parts with varying shapes into the same mold, much like model airplane kits. Sometimes, two assembly parts share the same main body. With a touch of inventive design, you can craft interlock points or hinges at symmetrical spots, essentially creating a mirrored part. This lets you use one mold for both parts, halving your tooling expenses.

Avoid small details

Manufacturing a mold with fine details takes longer owing to extended machining and finishing times. Text serves as a prime example, often demanding specialised techniques like electrical discharge machining (EDM), which can drive up costs.

Use lower grade finishes

Part designers may use textures for a variety of aesthetic purposes. A smooth or matte surface texture improves its appearance and gives it a polished aspect but such finishes to molds can be pricey, especially if they are high grade. If your part isn’t meant for cosmetic purposes, it’s best to skip the expensive finish.

Reduce wall thickness

Reducing the wall thickness of your part will cut costs since thinner walls allow the mold to fill faster, thereby speeding up production. Cutting thickness from 3mm to 2mm can slash the cycle time by 50% to 75%. In addition smaller parts set more rapidly.





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