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Voids and Shrinkage
  • Shrinkage is caused by intersecting walls of non-uniform wall thickness. Examples of these are ribs, bosses, and other projections of the nominal wall. If these projections have greater wall thicknesses, they will solidify slower. The region where they are attached to the nominal wall will shrink along with the projection, resulting in a sink in the nominal wall.

  • Shrink can be minimized by maintaining rib thicknesses to 50 to 60% of the walls they are attached to.
  • Bosses located at corners can result in very thick walls causing sinks. Bosses can be isolated using the techniques illustrated.