Meaning
Process deviations are measured by comparing the highest pressure reached during each injection cycle over a production run. A high peak pressure variance indicates that the moulding process is unstable, which can lead to inconsistencies in part weight and dimensions. This instability often stems from variations in resin viscosity or fluctuations in the barrel temperature.
Batch Consistency
Maintaining the same force for every cycle is necessary for producing uniform parts. When the peak pressure variance is low, the machine is successfully overcoming the resistance of the mould and the material in a repeatable way. Excessive variation suggests that either the material is inconsistent or the machine hydraulics are not performing as expected.
Cavity Pressure
Sensors inside the tool provide the most accurate reading of the conditions where the part is formed. Monitoring the peak pressure variance from a cavity sensor is more reliable than using hydraulic pressure because it ignores the friction losses in the injection unit. This data allows for the automatic rejection of parts that do not meet the pressure target.
Modern controllers can use this information to adjust the packing pressure on the fly for the next cycle.
Injection Consistency
Evaluating the health of a production run involves looking at the spread of these maximum values. A stable process will show a peak pressure variance that is within a small range relative to the mean.
