Hesitation is an unintended slowing down of the flow front. When a flow front slows down too much, it gets too cold and in severe cases can freeze off. This is what has happened in the top example in Figure 9. Hesitation will occur when there is a large variation in wall thickness in the part. In this case, the rib is much thinner than the nominal wall. Having a fast injection time can minimize hesitation. This increases shear heating and provides less time for the material to hesitate. Another way to reduce hesitation is to gate as far as possible from thinner areas, as was done in the bottom example.
Jay Shoemaker has held several positions within Moldflow, including Design Engineer, Customer Services Engineer, and Senior Technical Instructor and Designer, his current role. Jay's primary responsibility is to develop technical training material and deliver training classes for Moldflow Plastics Insight (MPI) products. Learn more.
