I received this question today from a blogger…
How should I proceed, when I want to adjust the process on an older pressure-controlled machine (not velocity controlled)?
Although each of these older machines have their own specific limitations… there is a basic strategy to use with open-loop pressure-limited injection molding machines:
1) Fill and pack using first stage pressure – The mold should be completely full with small sinks near the gate area
2) Transfer using time – Using second stage hold to eliminate any sinks at the gate area.
Many of these molding machines have really accurate limit switches on the injection unit. Unfortunately, the variability in mold filling as a result of viscosity changes can often cause a process to bounce between shorts and flash.