Protomold Design Tip - July 2008

Protomold: Rapid Injection Molding
July Design Tip

You've Got to Check This!

"Flaps 10 degrees………check, cabin air intake………check, landing light………check."

Ever dream about being a pilot running through your preflight checklist with your co-pilot? Well, now as a designer, you can have almost as much fun when you design plastic parts using the Protomold Plastic Part Design Checklist. You too can be confident you won't miss a single aspect of parts design when you use this handy resource tool.

Like a pilot's preflight routine, our checklist below is a handy reminder of some of the considerations to keep in mind when you're designing injection molded plastic parts.

And, in addition to our checklist, we've cataloged dozens of tips that can aid in making your parts easier to manufacture, lighter, stronger and offer improved performance. Each tip is chock full of great manufacturability pointers, including coring out, preventing sink, drafting for easy ejection, adding text, and more. Some of these useful design tips are referenced in the designer checklist; or you can download our complete Design Tip compilation volumes here.

Also, you can access ProtoQuote® automated design analyses, which can help to identify potential design problems once a 3D CAD model has been submitted. These free services allow you to quickly see issues that are easy to overlook. Our suggestions and recommended design modifications are returned to you within one day of submitting your part.

Try our Checklist! It's a practical tool that allows you, the designer, to spot potential issues and correct them beforehand.

Designing with Protomold in mind

Fig. 1

Design Considerations

Are the cores and holes drafted towards the ejector pin side (low cosmetic side) of my part?

Check YES

Does my part design include sufficient draft for part removal from mold?

Check YES — We strongly advise using at least 0.5 degrees on all "vertical" faces. Learn more.

Do I need to add draft to my design?

Check MAYBE — For aluminum molds, increments of .5 degrees (shallow features) to 3 degrees (deep features) should be added. A good rule of thumb is 1 degree per inch depth including cam/side pull cores.

Fig. 2

Does my part have a wall thickness that is greater than .040" and under .180"?

Check YES

Check NO — Parts under .040" may produce a part that has shorts, voids, weak knit lines; parts over .180" may have excessive sink, internal voids, warp, poor texture pick-up.

Learn more — recommended uniform all thickness for Protomold


What do I need to consider when selecting a material that is best for my design?

  • Selection of the proper material is crucial to part production. Designers should consider the mechanical characteristics, molding properties, and cost of the resin used.
    Learn more about material selection.


Does my part have two dimensions that are larger than .25" and less than one of the following? (Dimensions (in mold) = X x Y x Z (depth of part))

  • 30.5" X 13.5" X .25"
  • 28.5" X 11.5" X 1"
  • 26.5" X 9.5" X 2"
  • 24.5" X 7.5" X 3"

Check YES — proceed to Volume

Check NO — My part is over 3".

My part is over 3" deep, is my parting line in the middle of the part?

Check YES Learn more.

Check NO — Protomold may not be able to mold your part


Does my part have a volume greater than .005 in 3 ?

Check YES — proceed

Check NO — Protomold may not be able to mold your part

Does my part have a volume less than 59 in 3 ?

Check YES — proceed

Check NO — Protomold may not be able to mold your part

Surface Area

Does my part have a surface area of less than 175 square inches?

Check YES — proceed

Check NO — Protomold may not be able to mold your part


Is it a straight pull mold?

Check YES — proceed

Check NO — Off angle geometry may need to be modified or cams/side actions need to be applied

Check I DON’T KNOW learn more.


Are the undercuts located towards the outside of my part?

Check YES — Proceed to next question, Protomold may be able to use cams/side actions to mold the undercut

Check NO — Pass through cores or filling in the undercut geometry will be required. Protomold can certainly mold your prototype parts, however may not be able to mold your production parts. You could cut the undercut geometry with a secondary operation for testing or low volume production.

Is the undercut on my part less than one 8.419" X 2.377" X 2.900"? (Dimensions (in mold) = Horizontal x Vertical x Depth of cam pull)

Check YES — Protomold will use cam/side action to mold the feature
Learn more.

Check NO — Can you use sliding shut offs?

Read past Protomold Design Tips on Sliding Shut Offs:
October 2006
September 2007

Interactive Quotes


ProtoQuote is new and improved! Try it out today:

Upload your 3D CAD model and we will e-mail you an informative quote.

ProtoFlow  Analysis

ProtoFlow ® Analysis
Select ProtoQuotes include a ProtoFlow analysis to predict potential mold fill issues.
Watch a video demo.

Design Guidelines

As always, you can visit the Protomold Design Guide for helpful Rapid Injection Molding design information.

Design Tips Volumes

Design  Tips  Compilation  Volumes

Download Design Tips compilation volumes and catch up on what you've missed.

Plastics Trivia Question

Intelimer ® polymers:

A. can change their viscosity, permeability, and volume in response to relatively small changes in ambient temperature

B. can be used to keep meat fresh without refrigeration

C. can change their optical properties in response to light in the UV waveband

D. will bend through an arc of up to 180° in response to electrical stimulation

E. are selectively permeable to higher-energy molecules but impermeable to lower-energy molecules

(Honor System: No Googling, Yahooing, or Dogpiling until after you've submitted your guess.)

Last month's question/results:
Speaking of glass fiber, what item did Edward Drummond Libbey exhibit at the 1893 World's Columbian Exposition?:

A. glass reinforced concrete

B. woven glass fiber rope

C. a glass reinforced adhesive

D. a glass fiber dress

E. glass fiber jewelry

The correct answer is
D. a glass fiber dress.

The responses are represented in the following chart:

Last  Month's  Results

Upcoming Tradeshows

Want to talk in person? Stop by to discuss your design.

MD&M Minneapolis
October 22-23, 2008
Minneapolis Convention Center
Minneapolis, MN

For more information, visit our web site at

Get  a  ProtoQuote


Please e-mail suggested topics for future Design Tips, questions for future Designer Surveys, and obscure bits of Plastics Trivia to


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