I recently attended a conference in Boston on simulating plastic injection molding. Outside the cab window, the countryside looked a lot quainter than that of my hometown Cleveland. I especially like the antique homes, which are probably at least a hundred years old, or more. The conference took place at the National Plastics Center & Museum, a beautiful old brick building. Moldflow Corp. of Framingham, Mass., hosted the event, part of its Better Injection Molding Tour.

Peter Kennedy in R&D at the company gave an interesting presentation. He says the kinds of questions that mold simulation can answer today include:

-- Will the mold fill?
-- Where is the location of weld line?
-- What is the cooling time?
-- What kind of machine (e.g. clamp tonnage) is required?

However, he says, questions that cannot be answered include:

-- Will the finished part break?
-- What happens if the part color is changed? (With plastics, this means you have to change the material.)
-- Will the weld line be visible on the finished part?
-- Say, for example, the finished part is a drill. When will the bits fall out? (The mechanism holding them in wears out.)
-- What is the surface finish?
-- What happens if the part is left in the sun? (Warpage as a function of time)

To answer these questions, he says, it's necessary to understand material properties, characterize materials, and predict their properties during and after processing. One difficulty is polymers as a class of materials are different than, say, metals. For example, it's easy to snap a long, skinny rectangular part about 1/4-in. thick into two pieces with your hands. But squeeze the same part between two metal rollers to reduce its thickness and the part now easily ties into knots.

Kennedy says material properties that mold simulation requires include viscosity, conductivity, pvT, specific heat, modulus, and the thermal expansion coefficient. But an intrinsic inaccuracy is these properties are measured under conditions that are different than when the material is actually being processed. To get more exact results the company has various research programs underway to study shrinkage, morphology, and properties. It also partners with nuclear labs to use synchrotron radiation to probe the structure of materials and study their crystallization and molecular orientation.

This message has been edited. Last edited by: Leslie Gordon,