Page 77 - Injection Molding Advanced Troubleshooting Guide

8 Machine Performance

The methods discussed in this chapter all reference to an ANTEC paper written by
John Bozzelli, Rodney Groleau, and Norm Ward “The Machine Audit: A Systematic
Evaluation of Injection Molding Machines: How To Tell a Good Machine—Old or
New” [1].
The simplest thing to keep in mind is that a machine must do what we want when
we want it. If a machine is set to produce 700 psi hydraulic hold pressure it should
provide 700 psi every shot day after day. Many times, it will be said that a given
mold does not run well in a given press but is fine in another identical press. When
running into this type of problem the root cause of the machine difference must be
determined. If the machines are not producing the same results then something is
wrong. If the performance of the machine is not measured a processor is relying on
hoping a press is doing what is needed. A good rule of thumb is not to process
around machine issues, because this only narrows the process window and will
eventually cause part problems.
Walking up to a machine and giving a look over does not tell how well a machine
will perform. See Figure 8.1; is this a quality machine capable of providing repeat-
able processes? It is not possible to know unless a systematic approach to machine
evaluation is used.
The example shown in Figure 8.2 of a machine testing report card that documents
the various tests is one easy-to-use format. Using a simple green and red rating
with an overall A–E grade is a simple and visual way to grade and compare all the
machines in the shop.