I was recently asked a few questions via email, this is one part of that email….
Are these still correct with Injection Compression?
– Relative viscosity fairly constant during even with low fill speed
– Fill volume 95-98%
Basically, you are correct, the first stage fill should use velocity control, but you may need profiling to maintain a low shear rate through the mold cavity. Additionally, the mold should be short shot, but the degree of short shot will be greatly affected by the amount of compression used during the packing phase.
The primary purpose of this process is to reduce the polymer chain orientation within the mold by increasing the effective thickness of the mold during injection. By applying some packing pressure through compression rather than through the gate, chain alignment should not be increased during second stage.