Overview:-
One of most important and basic design principle for plastic parts design is thickness (wall thickness/ Nominal thickness).
When designer starts work on plastic then its a most important point which must be considered as per size and shape of part to create economical and easily produced plastic part.
Thickness of part:-
In ideal practice, Plastic part must having uniform part thickness because uniform thickness allow the mold parts (Core and cavity) to fill more easily. If part don't have uniform thickness then thin section cools first then as thick section cools which can generate defects in part.
For cost savings and high rate of production, plastic parts have a minimum wall thickness because thick parts take more time to fill in molds part and take more time to cool which can increase cycle time and chance of defects also.
On average, the wall thickness of an injection mold parts ranges comes-in between 2mm to 4mm.
But most part can be designed in range of 0.75mm to 5mm thickness.
Ex-
ABS-> 0.75mm-3.18mm
Polycarbonate-> 1mm- 9.53mm
PVC (Rigid) -> 1mm - 9.53mm
Nylon-> 0.38mm-3.18mm
Polypropylene-> 0.64mm-7.60mm
In Above Image, there is no uniform thickness rule implemented so it have this area weak where stress concentration can be.
Thickness Transition:-
In plastic part design, uniform thickness is important but on some places we have change part thickness then we never change it abrupt transition and gradually change but we change it as smooth transition.
Ref- Here we have smooth transition from nominal part thickness to required part thickness.
For change, thickness can be dropped only 25% or less of part thickness.
For best design, there is no change of thickness.
For smooth transition, change of thickness must be in 3X.
X= Required part thickness
Some Video Tutorials:-
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