Meaning
Injection stroke transition defines the physical location of the screw where the machine switches from velocity-controlled filling to pressure-controlled packing. This transition point is the switchover position, and it is usually set to occur when the cavity is ninety-five percent full. Correct setting prevents flash and mould damage while ensuring complete part filling.
It is one of the most critical settings in establishing a stable process.
Overpacking Prevention
Switching to pressure control too late during the stroke can cause high pressure spikes that flash the mould. The switchover position must be set before the cavity is completely filled to allow the remaining volume to be filled under managed packing pressure. Early switchover prevents tool damage and reduces part weight variation.
Short Shot Risk
Transitioning to pressure control too early in the stroke can result in incomplete part filling. If the switchover position is too far back, the machine may not have enough volume in the velocity stage to push the melt through thin sections. Incomplete filling leads to short shots or poor surface finish in distant regions.
Process Control
Monitoring the injection pressure at the transition point provides a clear measure of melt viscosity consistency. A stable switchover position ensures that the transition occurs at the same fill volume each cycle, reducing shot-to-shot variation. Process consistency is essential for maintaining tight dimensional tolerances on high-precision components.
