Recording Process Changes and Monitoring Actuals
Plastic injection processing long ago made the transition from art to a science of replication
as technology and understanding evolved, the industry came to recognize the importance
of historical data and replicating key parameters. RJG, Paulson and John Bozzelli all helped
to provide keen insight into methods of replicating process. This article addresses the need
for process monitoring, as well as how and what changes made to a process should be recorded.
Understanding these fundamental principles are paramount to global production facilities, and
will greatly reduce waste of motion as well as improve scrap rates and improve efficiencies.
We must first assess what variables should be monitored. Fill time and peak pressure (the measurement
of actual pressure reached during the cut-off transition from filling to pack pressure) are definitely
important to process replication and should be regularly monitored and recorded for the purpose of
analyzing historical data. Melt temperatures and shot weight are also critical elements that must be
regularly checked and repeated. A couple of questions that are common on the shop floor are
"what data should we record?" and "Why is recording process actuals important?". Answers to these
questions are simple...we should record any and all data that is available for the purpose of
"photographing" an optimized and efficient operation. And why?..because efficient and profitable
operations simply mirror their process, press set up and operation over and over.
Here is a list of key recordable actuals:
*Fill Time
Actual Back Pressure
*Peak Pressure
Running Melt Temperature
*Cycle Time
Actual barrel temperatures
*Screw Recovery Time
Running Cavitation Temperature
*Shot Weight (full shot, runner, shot without runner)
Pressure To and From Thermolator
Actual Thermolator Temp
Individual circuit pressures(mold-GPM)
*Area Set Up
*Screw RPM actual
Cushion
*cut-off actual
hot runner actuals
*Press setpoints
material: moisture content
Do most companies retain all of this information? Not usually...it is time consuming to collect and
monitor all of this data. In fact, note that the categories above that are asterisked (*) are crucial
and a process has proven itself as efficient and profitable (low scrap/ high efficiency) over an 8 hour
run, all of this data should be recorded for future referencing when a job becomes troublesome. By
retaining all of this information, it will provide you with the ability to identify what has changed
and oftentimes help pinpoint causes (man/mold/material).
Lastly, when setpoint changes are made it is important to note what change was made to the process and why.
Not only does this allow processors a means of repeating successful setpoint changes to recurring
problems, it also helps to quickly identify and correct a change that has caused an adverse affect.
It is also a great training tool for new or weak processors.. not only are they exposed to methods
of resolving scrap-related problems, changes that they record that are not a suitable approach can be
addressed and proper approach to scrap resolutions can be taught.
Long ago, color photography surpassed black and white.. with color, the mind had better depth perception,
and scenes were brought to very vivid new plane. By recording as much data available when a job runs well,
you are taking a snapshot of the overall process. Using these tools will improve your overall operations
and eliminate many of the headaches that come with fighting scrap.
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