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8 tips for cost-effective injection molding

Injection molding is a manufacturing process that uses a pressurized nozzle to inject molten material into a durable metal mold, eject the part once it has set, and refill the mold in quick succession. This enables the economic production of identical parts with repeatable tolerances in high volume, including products like plastic bottle components, medical devices, electronics housings, and automotive parts.

A highly adaptable process, injection molding is compatible with a wide range of materials and allows for good design flexibility in terms of part geometry. But how much does injection molding cost? It can be quite an expensive method of production, due to the investment of time and funds required to properly tool and test the hardened steel molds — as such, product teams can benefit from finding a few effective ways to reduce costs throughout the product development process. Here are a few places to start.

1. Avoid undercuts

Undercuts are overhanging design features (such as snap-fit tabs) that prevent a part from being ejected from the mold without damage. In many cases, undercuts can be avoided by orienting the part’s features so that they are parallel to the line of pull when the mold is open. However, if undercuts are unavoidable, incorporating side actions will prove beneficial in the long run but will add to injection molding costs.

2. Design parts (and molds) efficiently

The goal of efficient injection molding designs should be to achieve predefined requirements while minimizing material use, and without sacrificing on quality. Removing unnecessary custom injection molding features such as branding, textured surfaces, and part numbers from mold designs is key to keeping costs low.

Incorporating additional material into part design can actually damage a part’s structural integrity. This is because large parts and thick sections not only are prone to warping and sinkage, but also drive up material costs and cooling times. Additionally, optimizing part orientation within a mold can improve fill rates, minimize scrap material, and reduce costs.

3. Use multi-cavity molds

If material and geometry allow, including additional part cavities in a mold design is a fairly straightforward way of increasing production efficiency. While the additional cavities will increase the cost of cutting individual molds, they are far more economical to produce than separate molds and tooling for each part. Multi-cavity molds increase the speed of production and help to significantly lower the per-unit production cost over time, as well.

4. Consolidate similar parts into the same mold

If part families or multiple plastic injection molding projects involve components that use the same material and are approximately the same size, it’s possible they can be consolidated into a single mold, another way of reducing tooling expenses. This is called a “family mold.”

Joining part components with a living hinge or self-mating features is another way of eliminating post-processing steps (though these may limit viable material options to those such polypropylene, which offers both good durability and flexibility).

5. Optimize part tolerances

While a degree of variation is unavoidable in manufacturing, tolerances — or the acceptable range of variation between components and runs — allow product teams to ensure that viable parts are of consistent size, shape, and quality.

Tighter tolerances require better mold definition, and the CNC machining costs associated with tight-tolerance tooling rise quickly. If there’s room for flexibility in a part’s tolerance, product teams can potentially reduce tooling expenses by specifying only critical tolerances.

6. Modify molds instead of tooling new ones

If a part goes through several iterations before a workable design is finalized, product teams may be able to cut costs by modifying their existing molds rather than tooling new ones. Designing tool inserts or re-machining a mold in stages to include additional features eliminates the need for multiple rounds of tooling. Doing so often reduces development costs dramatically.

7. Take advantage of mold-fill analysis tools

Injection molding tools like mold-fill simulation software can prove instrumental in refining mold design before tooling begins. Digital mold prototypes allow teams to improve cooling efficiency,  optimize cycle times, and test for issues like uneven fill rates, air pockets, and warpage. Properly implemented, these tools contribute to higher-quality molds and prevent costly revisions.

8. Monitor cycle time

Faster cycle times reduce the per-unit cost of production. In general, the injection molding cycle time outpaces that of other manufacturing methods, enabling the rapid and cost-effective production of parts in large volumes.

Part material, part geometry, and mold composition all affect how quickly the thermoplastic resin cools — which is one of the primary drivers of cycle time. Aluminum offers better thermal transfer rates than advanced high-strength steels — enabling faster cycle times — but is also far less durable and therefore cannot produce as many parts.

Hardened steel molds take longer to tool, but are less likely to be damaged by intricate component geometries or difficult materials. Molds that require heating and cooling should be outfitted with water circuits to improve cycle time.

Start improving cost efficiency today

Operational efficiency is key to reducing injection molding production costs, and can be achieved through a combination of steps including streamlining part design for optimal cycle times, limiting expensive tooling time, and adding multiple, similar parts to the same mold. Finally, one of the most reliably effective ways to keep costs down is to partner with an expert manufacturer like Fast Radius.

Fast Radius provides highly flexible and efficient on-demand manufacturing solutions, from injection molding and urethane casting to industrial-grade additive manufacturing services. Our team specializes in optimizing end-to-end processes to make product development, production, and fulfillment more efficient and cost-effective. Contact us today to learn more.

Visit the Fast Radius learning center to read more about injection molding, including our guides to common thermoplastics and material additives.

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