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Top 5 Product Design Rules You Must Obey to Ensure Problem Free Plastic Injection Molded Parts


Today the standard vehicle has more than 331 lbs. of plastics encased in the form of seats, dashboards, bumpers, and engine components. A Boeing 787 on the other hand has 50% carbon fibre-reinforced plastic and other composites in its airframe.

Plastics offer beneficial mechanical properties and are quite lighter than metal; this makes our products more efficient and able to stand the test of time. In the last few decades, use of lightweight alternatives such as plastics and composites has dramatically increased, however, it is important that designers consider certain physical and mechanical properties of plastics.

The most common manufacturing process is Plastic Injection Molding, however due to its complexities product creators need to make sufficient design considerations to guarantee that the part design focuses on maximizing molding performance and reduce the tooling cost.  These two factors highly afflict the reputation of plastic injection molding industry.
With proper part design features plastic part performance and cost can be significantly improved. Consider the following plastic injection molding design considerations before you design your plastic parts.

  1. Radius
  • A design with corners always needs to accommodate large radii.
  • Sharp corners spell stress thereby affecting the manufacturability of parts.
  • Corners between bosses and surfaces which are often overlooked require scrutiny.
  • The radius should always be with regards to the part thickness thereby eliminating the prospects of high-stress concentration and resulting in the breakage of the plastic part.
  • General guideline suggest that the thickness at the corner should be in the range of 0.9 times the nominal thicknessto 2 times the nominal thickness of the part.
  1. Wall Thickness
  • Plastic parts should always have walls with uniform thickness.
    • Swerving away from the recommended would give rise to unfavorable results such as shrinkage and warpage.
  • Uniform wall thickness gives the assurance of minimum manufacturing cost.
  • Uniform wall thickness ensures quick cooling which in turn lets one produce more parts in a short span of time and optimum utilization
  • General guidelines suggest that wall thicknesses for reinforced plastic materials should be between the range of 0.75 mm to 3 mm and those for unfilled materials should be 0.5 mm to 5 mm.
  1. Determine an apt location for gate
  • Proper gate location will decide the success of the part.
  • Experts recommend designs with the gate at a location at which the melt enter the thickest section of the cavity only to flow out of a narrower region.
  1. Draft
  • Plastic heavily relies on mold draft in the course of its removal from the mold.
  • The lack of an appropriate draft would make the removal of plastic parts almost impossible.
  • A design with sufficient draft is always considered to be a good practice.
  • 5 degrees for a depth of 0.25mm is usually recommended by design experts. General guidelines suggests that a draft angle of 0.5 degrees is recommended for core and 1.0 degrees for cavity
  1. Ribs
  • A known aspect of plastic is its stiff nature.
  • The inclusion of ribs in a design is often recommended which adds to the bending stiffness.
  • Ribs are pocket-friendly and a convenient option, the end result of which is often well received by both the designer and the manufacturer.
  • Thick and deep ribs can cause sink marks and filling problems respectively.
  • Rib thickness of a part should never exceed the wall thickness.
  • General guidelines suggests that rib thickness at its base should be around 0.6 times nominal wall thickness of the part. Failing to include a proper rib would eventually lead to the distortion of the plastic part.

For 70 years, our customers have trusted PM Plastics to provide plastic injection moldings and customer service that is flexible and reliable with innovative solutions. Our company’s portfolio includes Target, L’Oreal, Walgreens, Alluma Tech, Almay, Black Opal, Cedar Creek, Central Aquatics, Covergirl, DCI Marketing, Duane Reade, E.L.F. Cosmetics, EWI Worldwide, Genlyte Thomas Group LLC, Harbor Industries, Kimberly Clark, Mabelinne, Neutrogena, Olay, No. 7, Process Retail Group, Procter & Gamble, Revlon, Rexnord, Rimmel, Sally Hansen, Vaportek, Velvac and Wet N Wild.

Founded in 1946, by the Ford Brothers, PM Plastics Company was created through the belief of serving others. Motivated by our customers our company has played a pivotal role in the plastics injection molding industry for over 70 years. For more information, visit