Related Sponsors

Vocabulary and Lingo

Home » Manufacturing » Injection Molding » Vocabulary and Lingo

1) Design Details

Part design includes draft features – angled surfaces – to facilitate removal from the mold. Surface length draft angles down to half a degree are reasonable. Typical draft angles down to half a degree are reasonable. Dimensional tolerance specification will govern the part cost and manufacturability. If a small region of the part needs higher tolerances, say the location of a critical feature used for alignment – do not specify tight tolerance. Instead design and plan for post molding processes such as machining using “assembly intent” fixturing.

2) Wall Thickness

Wall thickness for thin parts such as a soda bottle or pall point pen ink inserts are quite possible and economical. This wall sections are possible as well. Uneven wall thickness present challenges in the plastic molder manufacturer. Designing your part with uniform walls and cross section will simplify manufacturing and costing. At wall intersection or “tees” sinking will occur. Thick walls cool slower and greater shrinking will occur. Thin walls cool faster as thus, less shrinkage.

3) Radii and Corners

Maintain uniform wall thickness at corners. External and internal radius should share the same center point. External radii = internal radii + wall thickness. The minimum radii should not be less than ¼ minimum wall thickness. Design for radii to be ½ to ¾ of the nominal wall thickness. When significant stress is present, design is larger radius as larger radius distributes stress uniformly.

4) Ribs

Ribs should be ½ to 2/3 of the nominal wall thickness and less than three times thickness in height. Taper of one degree is typical. Extra thickness promotes shrinkage. Excess rib height combined with taper will produce thin sections requiring extra fill time at the mold.

Sources

http://www.engineersedge.com/injection_molding,.htm

http://www.big-builders.com/construction/cad.html

http://en.wikipedia.org/wiki/Computer-aided_design#Capabilities

http://www.collegegrad.com/careers/proft17.shtml

http://www.bls.gov/oco/ocos027.htm#outlook

Next Page: CNC Overview

Related Injection Molding Articles