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Your Guide To Designing Perfect Plastic Parts

Jan 21, 2019

While we always stand by our "your design, no compromises" promise, there are instances when part features can be manipulated to make manufacturing more efficient without sacrificing the intent of the designed part. Follow these tips for designing parts that will transition flawlessly into production. 

prototype mold with ejector pins

Add draft to your CAD model.

Draft refers to the angles incorporated into your part design that aids in the ejection process from the mold. The amount of draft required for your part will vary depending on material thickness and texture. Consider the shrink properties of the material as it hardens. By tapering the sides of a mold to a recommended draft angle, the part will be easier to remove.

Here are a few general draft guidelines to follow when designing your next part:

  • Always use as much draft as possible: 1-5 deg on your part
  • Draft your part in the direction of pull
  • Consider more draft with texture: 2-3 deg or 3-5 deg with deep texture

Eliminate undercuts as much as possible.

An undercut is any back drafted area that prohibits the ejection of a part from a mold and adds complexity to the build. Reducing the number of undercuts or eliminating them altogether will simplify the tooling process. Experienced design engineers can assist with providing modification solutions to decrease or eliminate undercuts from a part design – which will likely result in a better design, a more efficient molding process and reduced costs.

When possible, avoid sharp corners.

Sharp corners are an important feature to avoid during the prototype design process because they can greatly increase the stress concentration and lead to part failure. It is imperative to avoid part stress because it can cause warp, sink marks, cracking, premature failure and more. While some stress in a part is expected, designers should always keep the stress factor in mind to ensure the integrity of the part.

Try to reduce thick areas. 

Material thickness is one of the most critical factors in part design. Thickness plays a role in a number of factors including performance, appearance, moldability, cost and more. Thinner material walls will reduce the amount of material, and cycle time. While minimizing material use should be on the mind of a designer, achieving an ideal wall thickness can be a balance between the strength of the material and weight which are important factors to the part’s overall durability and cost. Here are some general material thickness guidelines to consider:


0.045 - 0.140


0.030 - 0.120


0.025 - 0.500

Liquid crystal polymer

0.030 - 0.120

Long-fiber reinforced plastics

0.075 - 1.000


0.030 - 0.115


0.040 - 0.150


0.025 - 0.125


0.030 - 0.200

Polyphenylene sulfide

0.020 - 0.180


0.025 - 0.150


0.035 - 0.150


0.080 - 0.750

Rigid PVC


Soft PVC


If ribs are necessary, keep them 50% of the adjoining wall thickness. 

In part design, ribs provide strength, stiffness and minimize warp without having to increase the material thickness. Ribs should be approximately 50% of the joining wall thickness to avoid sink marks. If strength is critical to the functionality of the part, using cross-hatched rip patterns can increase strength and avoid sink. Thin ribs may be hard to fill, making it important for designers to consider the material in the design phase.

We hope this helps with your future designs. Feel free to leave questions for our engineers in the comments section below.

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