Filling small molds that include three inserts with a hard-to-flow material can be trouble for molders such as CG TEC in France. To help with the problem, the company acquired Moldflow software from Moldflow Corp., Framingham, Mass. (moldflow.com) to evaluate shear rates, pressures, volumetric shrinkage, and warp. This helped the company determine whether or not the inserts can be over-molded without moving or damaging them. That's because inserts alter a resin's flow and shrinkage, making it difficult to anticipate the effect on the flow. The software is detailed enough to consider the mechanical characteristics of the inserts and analyzes the overall part deflection for a more accurate evaluations.

“The software let us anticipate the required fine tuning the product would need,” says CG-TEC engineer Michelle Bossi. “It also lets us show the customer how injection points and possible adjustments change the product. Because the analysis helps us understand warpage, we optimized the design before building the mold.”

“The first flow analysis showed it was impossible to inject this part in one shot,” says Bossi. “Too much shear pressure on the plastic and pressure on the metal inserts would damage them.” Bossi and the customer decided to make the part in two injection stages. The first stage let them position inserts and avoid the effects of pressure. The second stage filled the mold.

“A second flow analysis let us suggest alterations that would lower material temperature and shear rate, so the material would flow better. Then warp analysis, which included the inserts, predicted overall part deflection.”

This two-week study took about forty iterations before finding an acceptable result. “Before using the program, molds had to be remachined if they didn't meet all points of complex specs,” he says.