Boss thickness for Injection-Molded parts

[MecEngineer]

I am new to injection-molded parts. I have read some online available guide sources on injection-molding process. All guide sources recommends using Boss thickness from 60-80% of the Wall thickness i.e. if Wall thickness is 4mm then 2.4 to 3.2mm for the Boss thickness.

I am not able to decide that if Boss thickness of the 6mm is used for a Wall thickness of 4mm: Is injection-molded process feasible for the part? Any recommendation on this topic would be appreciated.

Thanks

 

[dgowans]

If you are asking if you can have a boss w/ 6mm thickness coming off a wall of 4mm thickness, the answer is "Yes, but it is not recommended." Look up sink marks in your online guides...

 

[patprimmer]

Look up sink marks and contraction voids.

You can have thicker bosses if you isolate them from the thinner wall by a thin rib.

Regards

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[mcgyvr]

Some general guidlines
Wall thickness around a boss design feature should be 60% of the nominal part thickness if the part is less than 1/8” thick.
If the nominal part thickness is greater than 1/8”, the boss wall thickness should be 40% of the nominal wall thickness.
The height of the boss should be no more than 2 ½ x’s the diameter of the hole in the boss to avoid sink marks and surface imperfections.

Google "injection molding design guide" and you should get tons of information. Even the manufacturers of the plastics you intend to use have product specific recommendations.

 

[dwightdixon]

Thick bosses cause sink problems because of the shrinkage of the volume of the boss. low shrink materials will have less problem with boss caused sinks that low shrink polymers. Bosses can also cause dead zone or blind corner fills and resultant burns, if not properly vented. Fiber filled material will also have orientation problems around bosses due to the disruptions in flow. Talk to the tech service folks at you material supplier and have them review your design.