V/P changeover and holding setup: which values to start the machine with?

When a new mold is mounted on the machine, the first question is: which values should I start with? The sequence below describes starting from an estimate and then confirming it during the trial run.

1. Filling: speed-controlled

You fill the cavity speed-controlled: the machine produces whatever pressure is needed to reach the set speed. The goal at this stage is for the melt to advance through the cavity stably and quickly.

• Speed profile: Slow at the gate (right after entry), fast in the middle region, slow again near the end. This reduces the risk of jetting, burn marks and flash. A good starting point is a profile that begins at 70% of the main speed and rises to 130%; the final values are set during the trial.
• Pressure limit: Set it slightly above the hydraulic pressure needed for filling; leave it too high and you lose mold protection, too low and speed drops.

2. V/P (velocity to pressure) changeover

The V/P changeover is the switch point from speed control to pressure control. It's usually done when the cavity is above 90% full (often 95–99%). Important: V/P is not triggered by a pressure value but by a trigger such as screw position, time, or cavity pressure.

• Switch too early and the cavity underfills (short shot).
• Switch too late and you get a pressure spike and flash.

During the trial it's safe to set the changeover so the part is 98–99% full, then complete filling with holding pressure.

3. Holding pressure

This is the pressure that completes the cavity and compensates for shrinkage. Start with a value roughly half to two-thirds of the fill pressure, then adjust using sink marks and dimensional checks. High pressure causes flash and internal stress, low pressure causes sink marks and dimensional deviation.

4. Holding time: the gate-freeze study

Don't pick the holding time by guessing; measure it:

1. Keep the cooling time constant.
2. Increase the holding time starting from 0, weighing the part each time.
3. Once the part weight stops increasing, the gate has frozen; holding beyond this point is useless.
4. Choose a holding time slightly (e.g. 0.3–0.5 s) beyond this point.

Excessively long holding extends the cycle unnecessarily; too little holding causes sink marks and volume loss.

5. Cooling

Cooling time is the period from the end of holding to part ejection. Find the shortest time the part can be ejected without warping or deforming using an ejection test.

Note: The values given by the tool below are a starting point; fine-tuning from the machine screen during the trial is expected.

The calculation tool gives these values for your machine and part in the "Machine setup starting values" table and saves them to your company account.