Warp In Crystalline
IMM 04/02

We mold automotive parts from crystalline materials and have warped parts. Does anyone have a good method to predict warp in parts using specific materials? How should the tool be modified for warped parts? Do you reverse the amount the part warps and hope the part come out flat?

Assuming a well-designed and -gated part and mold, warpage is usually caused by one of four things:

• Over-packing. When something is compressed it springs back when the pressure is released.

• Parts sticking / dragging on ejection. Caused by cavity metal problem, ejector placement, or over-packing.

• Uneven cavity / part temperature. Cooling lines clogged.

• Uneven heat transfers through the cavity steel to the cooling source. Areas of the molding surface are at varying distances from the cooling channels or water flow rates are different.

The higher heat transfer allows you to mold at the same cycle with higher mold / water temperature because more heat transfers more easily through the cavity block. The higher mold temperature permits lower injection pressure, which reduces stress / warp. The hard surface and low friction allow for easier release / drag. This process can even allow for the elimination of all internal water channels in a cavity block and can be retrofitted to many existing cavities. - R. Lewis, P.R. Lewis Consulting, Dorado, PR, (787) 270-4418, lewispr@earthlink.net.