Page 24 - Injection Molding Advanced Troubleshooting Guide

1.4 Troubleshooting Methodology 5

it is much easier to troubleshoot with a systematic approach. By considering which
of the 4M’s could contribute and working through one category at a time a list of
potential root causes can quickly be gathered.
All of the defects discussed in this book will use the 4M method for description of
potential causes. Utilize the possible causes to systematically work through resolv-
ing the problem. Keep asking which of the 4M’s could be contributing to the defect
and why. Always try to drive deeper to get to the root cause of the problem. An
example of using the 4M’s is when troubleshooting sink: the natural place to start
is with second-stage pressure; however, if the pressure is raised to compensate for
a machine problem, was the true issue resolved or are you processing around an-
other issue? The goal of the 4M method is to avoid processing around issues. Often
times molders are left trying to work “process magic” to get good parts when a
tooling improvement should have been implemented. Using the 4M method helps
to keep process windows as wide as possible and will lead to less scrap, waste, and
PPM (defective parts per million) in the long run.
Most people are familiar with the “5 Why” approach that was developed at Toyota.
This approach is a tool that systematically drives toward asking questions about
the root cause. In this approach, the goal is to get to the true root cause by asking
why after every answer when problem solving. Many people find this technique
useful.
One key to a systematic approach to troubleshooting is to review what has possibly
changed in the mold, molding process, material, or machine. Frequently people
will work on trying to fix a problem but not address what had actually changed
that originally led to the problem. In other words, sometimes technicians are
struggling to solve the wrong problem. A common example of this is someone
slowing first-stage velocity to fix a burn that was actually caused by dirty mold
vents. Using a systematic approach will help to focus on the true root cause of the
problem and not to process around an issue.
The mentality to keep when troubleshooting should be to try to remove one poten-
tial root cause at a time. Until an issue has been proven to have no effect it remains
a potential root cause. Using a systematic approach allows a troubleshooter to re-
move one cause at a time, focusing initially on the most likely causes and working
from there. Always remember though that data is key to proving a root cause.
Change one thing at a time and determine the impact. If a troubleshooter changes
multiple things at a time it is impossible to determine what the root cause was.
After making a change, always give the molding machine time to stabilize before
evaluating the impact of the change. If the process change shows no impact on the
defect, it can be reset to the original documented process.
It is also vital to make changes that are large enough to have a potential impact.
Frequently processors will make an adjustment to a process and when they do not