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    Discussion in 'Plastic moulding' started by hello bowen, Oct 5, 2014.

    1. hello bowen

      hello bowen Member

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      2.Product design
      I am not a product designer, so i am not proficient in terms of product designing. But here are some advice to get a lower shrinkage part.

      Wall thickness: Keep thickness as thin and uniform as possible, in this way, even filling of the mold and anticipated shrinkage through the molding can be obtained in the best way. Internal stresses can be reduced. Where varying wall thicknesses are unavoidable for reasons of design, there should be a gradual transition.

      Corners: an important principle is to avoid sharp internal corners,usually the cooling at the outside is better than the cooling at the inside, as a result the material at the inside shows more shrinkage and so the corner tends to deflect.
      PS: For some product designer, sometime the product has some small fillet, like 0.1mm—0.2mm,and many fillet bind together, when mold designer want to add draft(sometimes the product has no draft, mold designer should add draft by themselves), they need remove fillet first, and then add draft. But those small fillet will kill them, especially for bind together fillet. Actually, when we manufactured the mold, there always has fillet about 0.1-0.2mm,we called natural fillet. But if you want get a straight corner or sharp corner, the mould should make with the insert.

      Ribs:
      For Crystallized plastic : PP,PE,PA,POM...
      the thickness of a rib must not exceed about 35 percent of the wall. For example PP:if the wall thickness is 2.5mm, the ribs should not exceed 0.8mm when you don’t want to have sink marks. But if the ribs was under the cambered surface or under the corners, that will not easily have a sink marks, even the ribs is as thickness as the wall.
      TIPS: flat surface will easily cause sink marks than cambered surface.and 35 percent was empirical data.
      For non-crystallized plastic: ABS,PC,PMMA...
      the thickness of a rib must not exceed about 60 percent of the wall.

      (If someone found some mistakes, pls do not hesitate to correct me, Feedback is a gift. Especially the sentence’s grammar or structure. TKS)

      And next time, i will talk about the mold design. Gate, ejector, cooling... I really hope more people can join it, share your ideas. TKS
      i am not 100% fluent, but at least i am improving.
       
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