Special Design Considerations for Insert Molding:

• Inserts should have no sharp corners  

• They should be round and have rounded knurling  

• An undercut should be provided for pullout strength

• The insert should protrude at least 0.016 inches into the mold cavity 

• The boss diameter should be 1.5 times the insert diameter - except for inserts with a diameter greater than .5 inches.  For these diameters - the boss wall should be created with the total part thickness and specific grade of material in mind 

• Keep the metal insert small relative to the plastic surrounding it    

• The thickness of the material beneath it should be equal to at least one-sixth of the diameter of the insert to minimize sink marks

The toughened grades of the various resins should be evaluated. These grades offer higher elongation than standard grades, with a greater resistance to cracking. Most engineering plastics can be used in insert molding.  Lower shrinkage rates for some materials, however, give them an advantage in the insert molding application. 

Because glass and mineral reinforced resins have the advantage of even lower mold shrinkages than their base resins, they too have been used successfully for insert molding applications.