Plastic design guidelines is a very important topic, as there are many differences in design consideration based on plastic manufacturing processes. Each manufacturer manufactures a plastic part based on past experiences. Designers also design plastic parts based on past errors and rulebooks. There is no standard way to define how a plastic part can be produced, it is just a collaborative effort of the designer and manufacturer. These basic guidelines are captured based on general principles. One can modify certain techniques based on his experience.

Here are few plastic design guidelines

Uniform wall thickness

  • Irregular wall thickness is a major factor contributing to warpage in plastic part.
  • Maximum or minimum thickness of plastic part should be decided based on material properties.
  • Proper rounds on edges are also essential to avoid sink marks. 
defects of irregular wall thickness

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radius to plastic parts

Rib designing factors

Ribs are major part while designing any plastic body, as it serves in strengthening of the part. Improper designing may lead to failure of ribs, which will lead to failure of part. Proper design with proper draft and radius as well as adequate spacing in between ribs is important for rib designing. Too many ribs may complicate the part manufacturing process and less ribs may lead to part failure. Hence proper designing of ribs is very important.

Minimum radius to rib is also important. Providing radius at bottom and top serves in better part ejection

ribs designing for plastic parts

Designing of Boss

Boss designing is a very critical part as it acts as a locating or mounting feature. Mostly, partial or complete load of plastic part is handled by the boss. So, proper boss design with controlled height and depth of hole is important. Adequate ribs for supporting the boss is also important. Hole present in the boss should not be too deep, which will cause manufacturing issues. 

Boss designing


Drafts in plastic part are most important, as they serve in removal of plastic parts from dies. Proper part ejection is key factor while considering draft angles. Parting line, pulling direction, material shrinkage, wall depth, etc play key role while selecting draft for your feature. Generally 1 degree draft if preferable, but in some cases 2 to 5 degree is also used.

Draft vs No draft
Pulling direction for draft

One must remember that part design should be according to easy manufacturing process. Complicated tooling results in high cost as well as defects in parts. Proper part ejection with minimum tooling is the basic criteria in plastic design.

All above mentioned  plastic design guidelines are meant to design parts with standard procedures. One can modify certain principles based on designing factors and your past experience.