Page 130 - Injection Molding Advanced Troubleshooting Guide
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13.1 Cavity Pressure Technology 117
Process problems are easy to detect with process monitoring equipment. Fig-
ure 13.5 shows a process where the screw run time increased due to a poor mate-
rial pickup. The next shot was back to normal other than a change in end-of-cavity
pressure. Alarm bands can be established to automatically reject parts that fall
outside the established process window. Note also in Figure 13.5 that there are
three cavity pressure transducers: two near the end of cavity and one just inside
the gate.
Figure 13.5 Process monitoring showing process change
Process changes are easily detected with process monitoring. In Figure 13.6 a
velocity change was made and is visible on all of the curves. This change would be
easy to detect on the machine as well but with process monitoring it is possible to
detect the impact on the cavity pressure as well as having clear documentation of
exactly when the change occurred (helps reduce the “I don’t know who made that
change” excuse). This is another situation where alarm settings could be used to
automatically reject the parts produced with the alternate process.
