Solving Warpage ProblemsWith Autodesk Moldflow

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Why does warpage occur in injection molded parts?

● Variation in internal stresses across the part

● Caused by non-uniform part shrinkage

Webinar – Warp in Plastic Parts

Our example family mold exhibits excessivewarpage of two critical components.

Webinar – Warp in Plastic Parts

Case

Cover

Material: 30% GR Nylon Excessive warp of Case and Cover

What are the root causes for non-uniform shrinkage?

● Part Design

● Material Selection

● Mold Design

● Process Settings

Using Moldflow we can explore each of these areas in depthTo determine the underlying cause of warpage in our parts.

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Webinar – Warp in Plastic Parts

Three components to warpage

● Warpage from Differential Cooling

● Warpage from Differential Shrinkage

● Warpage from Material Orientation

With Moldflow we can isolate and determine which affect causes our problem

Webinar – Warp in Plastic Parts

Non-Uniform Cooling

● To control warp all surfaces of the mold are a uniform temperature

● All surfaces of the part must cool at the same rate

When out of balance the cool side of the mold cools fasterand shrinks less.The hot side shrinks more from increased crystallinity which causes the part to warp toward the hot side.

Mold Temperature Results

Cavity Temperature Uniformity

Temperature differences in mold should not exceed 10°F

Differential Cooling Effects

Results: Shrink from non-uniform cooling

In this case, Moldflow indicates warp is minimal as a result of differential cooling

Webinar – Warp in Plastic Parts

Differential Shrinkage

● To control warp the cavity pressure should be uniform after packing

● Maintain recommended part wall section and mold temperature to assure proper crystallinity and shrinkage

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Moldflow indicates that warp from differential shrinkage is significant

Differential Shrinkage

● To control warp the cavity pressure should be uniform after packing

● Maintain recommended part wall section and mold temperature to assure proper crystallinity and shrinkage

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Differential Shrinkage

● Variations in shrinkage across the part are minimized by proper packing and influenced by gate location

Moldflow shrinkage results after pack

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Material Orientation Effects

● Orientation gives a variation in shrinkage in directions parallel and perpendicular to the flow direction

● Crystalline and fiber filled materials exhibit the greatest variation in shrink rates longitudinal to transverse

Moldflow results indicate Material Orientation has greatest affect

Material Orientation Effects

● Orientation gives a variation in shrinkage in directions parallel and perpendicular to the flow direction

● Crystalline and fiber filled materials exhibit the greatest variation in shrink rates longitudinal to transverse

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Quickly Study Alternate Gating

● Alternate gating was investigated but shown little improvement in total warpage of the critical parts

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

A material change to an unfilled amorphous material solves the warp problem on the critical sealing surface

Quickly Study Alternate Materials

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Summary of Warp IssuesProcess Settings Inadequate injection pressure or time Inadequate Barrel residence time Barrel Temperature too low Nozzle temperature too low Inadequate Packing Injection pressure too high

Mold Design Gates too small Gate location (Uniform flow distance) Number of gates Differential Shrinkage (Low at gates, high at extremities) Family tooling (Imbalanced runners) Ejection System

Cooling System Uneven cooling Wrong mold temperature

Material Issues Improper flow rate Differential Shrinkage (Crystalline, Fiber Filled, Molecular Orientation) Varying crystallinity (difference in cooling rate) Material orientation affects

Part Design Thickness variations Part Geometry (Flat plate with many ribs one side) Part thickness

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts

Webinar – Warp in Plastic PartsWebinar – Warp in Plastic Parts