Wall thickness could be measured by parts cross section. Depending on part design, a single part could have many different wall thicknesses. For injection molding part, there are some suggestion regarding wall thickness for a better surface finish and easier production.
- Wall thickness shall be same at every cross section of parts. (it is difficult to achieve since the nowadays parts are becoming more and more complicated)
- If the part needs different wall thickness, the area shall change gradually.
- If there is corner in part design, the corner shall have radius.
- Too much wall thickness is not suggested. If there is strength concern, please add ribs (see B-4)
- Gate shall be at the thickest area, in order to reduce pressure-drop during injection molding process.
Too much wall thickness
Plastic expends when temperature goes up and shrinks when temperature goes down (see B-7). If the part has too much wall thickness, it could lead to unexpected shrinkage and remaining stress inside part.
Black area has more wall thickness than white area, it means black area preserve more heat during injection molding process. After ejection, the part starts cool down and shrink by itself (without mold profile). Black area will keep cool down/shrinks after white finish cooling. Then the polymer molecular starts move differently, it creates unnecessary stress inside parts. At the meantime, more shrinkage area will generate unnecessary shrink mark, See illustration in Pic.-1.
If the part with very big wall thickness difference, other than the phenomenon mentioned above, the part may deform or have holes inside. See illustration in Pic.-2.
Too thin/sharp wall thickness
It leads to injection molding difficulty and weak mold design. See illustration in Pic.-3
Suggest wall thickness change
Here is an example regarding wall thickness change, see below 3 pictures for same purpose part with different design.
- The wall thickness change area has no radius, wall thickness change rapidly.
- The area changes with taper, it is a better wall thickness change design.
- The area changes gradually and reduce unnecessary wall thickness. The part wall thickness becoming more even than design 1 and 2, design 3 is the best design in wall thickness perspective.
