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Product Design Tips For Injection Molding

by Luke Lawson

Many companies that specialize in injection molding have in-house teams that can help you design an injection-molded product, but it's helpful to know some basic design principles before you begin actually working with a designer. Keep these product design tips in mind when you first begin to think about a product that will eventually be made via injection molding.

Maintain Uniform Thickness When Possible

The thickness of your part's various walls and bars should be as uniform as possible. This will help ensure that the plastic flows evenly throughout the mold, and an even flow is crucial to creating consistently high-quality products. If the fluid plastic is prone to flow at uneven rates, the final thickness of walls and bars can vary as a result and weak points can form in the product.

Importantly, this doesn't mean that the thickness of every wall and bar must be the same as the thickness of every other component. Instead, the principle of uniform thickness means that each wall and bar should have a consistent thickness throughout that particular piece.

Move From Thicker to Thinner If Necessary

While even thickness is always preferable, it's not always achievable. In situations where you must alter the thickness within an individual wall or bar, the best method is to design the product so that the plastic will flow from the thickest to the thinnest section.

With a direction of flow that goes from the thickest section to the thinnest, the plastic will still fill the entire component and flow relatively well (if a little slower than normal). In contrast, a thin-to-thick flow direction will result in plastic being bottlenecked when it first enters the component, and the plastic might not reach all of the thicker section.

Use Soft Bends At Turns

Plastic will have a harder time flowing around sharp bends than it will around soft, and the corner of a sharp bend can be especially problematic. Depending on the exact direction and rate of flow, plastic might not seep into the entire corner, resulting in uneven and possibly weak spots. There are a couple of ways to make bends less harsh.

First, curved corners are better than sharp ones. Plastic can flow more easily around curves and will fill in the entire curve as it flows.

Second, slightly obtuse angles will allow the plastic to flow more easily during the plastic injection molding process than right angles will.