Essential Tips for Designing a Part for Injection Molding


Every manufacturer knows that before starting to draw up the design for a new part to be produced with injection molding it’s necessary to take many design essentials into consideration.

There are certain design essentials which have to be taken into account so that you can expedite the process as much as possible and avoid problems once your project reaches production. Let’s take a look at a few things that need to be considered when producing a design for an injection molding project.

Radii and Draft

Radii are necessary to properly fill a mold and ensure structural strength. These intersecting points smooth corners and allow material to flow and fill minute cavities, reducing the risk of stressors eroding or cracking a part’s features. Draft angles anticipate shrinkage during the cooling process. When a part is being released from the mold draft angles reduce friction between the walls of the part and the mold making a clean release possible.

This will prevent a part from being damaged by surface tension as it leaves the mold, something which is a common occurrence with poorly designed parts. The amount of draft necessary will be determined by your part design and material selection. Your draft needs should be determined early in your design in order to avoid possibly costly issues once your project reaches production.

Wall Thickness

The thickness of the walls of a part is a very crucial detail when it comes to designing it for optimal manufacturability. Wall thickness will also help manage the cosmetic aspects of parts, as well as their strength, weight, and cost.

The type of resin being used can determine the acceptable amount of thickness. If you are unsure of the appropriate correlations between wall thickness and resin type, the link below offers an official chart that details suggested wall thicknesses for a variety of materials.

**Recommended Wall Thickness by Resin Type Chart

Ribbing and Coring

A part that is designed to be structurally sound requires more than thick walls, in fact, thick walls can make a part weaker. After coring out a part, implementing support ribs and gussets are essential designing strategies that will structurally and cosmetically benefit your piece.

Coring out a thick piece will not only reduce a parts manufacturing costs but also improve its look and performance without influencing other important dimensions. Ribbing helps thick sections cool at similar rates to thin sections and reduces stressors that could ultimately warp and sink walls.

While a parts thickness is not always uniform, properly coring-out and ribbing a wall can help maintain the original design’s integrity and prevent cosmetic damages such as warps, sinks, and voids.


A core-cavity approach is a design technique that can decrease manufacturing costs, time consumption, and improve the overall cosmetics of a part. The core and the cavity represent the separate halves of a mold. In this design approach, the halves outer and inner walls are drafted parallel to each other as opposed to drafting one half with a deep-ridge approach. Not only does this drafting technique ease ejection and improve strength, it will also help maintain wall thickness and save on manufacturing costs.

Ejection and Gating

In injection molding, the gate is required for the injection of plastic into a mold’s cavity. It’s the feature on your mold that allows the resin to flow into it. Ejector pins are necessary as well so that parts can be easily removed from the mold without creating damage.

There are a few different types of gates such as tab gates, sub-gates, hot tip gates, and direct sprue gates. These all have specific benefits for different types of designs, but direct sprue gates tend to be the least used because they feature a large diameter which adds an additional operation to remove excess material.

When it comes to designing a part for injection molding there are many design essentials which need to be taken into consideration in order to optimize both the speed and the accuracy with which parts are produced.

Planning for things like DFM, wall thickness, gating, ejection, ribbing, coring out, core-cavity, radii, and draft will make it possible to avoid complications during the production process. With an excellent design for molding, it is possible to increase project profitability while reducing manufacturing time and complexity which is always a win.

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