Time Required for Process Stabilization…

This question highlights a common point of disagreement within the molding industry…

How long does process stabilization take, from set-up to first good parts?
My Response
With the explosion of SMED, Single Minute Exchange of Dies, there are many companies who have successfully reduced their changeover time to a matter of minutes or even seconds. Unfortunately, the startup time is not always as fast.
Generally speaking, most processes take around 5-10 minutes to stabilize. This typically occurs when the flow length and the ability to fill the mold is not significantly affected by the temperature of specific mold components. You can still shorten this time to stabilization by taking steps like the following:
  • Pre-conditioning the tool temperature before installing it into the machine
  • Pre-heat the hot runner system before installing it into the machine
  • Use insulation between the mold and the machine platens
  • Purge regularly when the machine is idle to help stabilize the melt temperature
High speed molding, and thin wall molding processes where you are processing with a much tighter window, stabilization can take up to 2 hours. When such a situation takes place, it is important to document the variations that take place and develop a time schedule to adjust for this. For example, if the cores take an hour to stabilize, then you might be have to use one 2nd stage packing pressure and 1st stage speed for the first 15 minutes, and then drop them down each 15 minutes until the process stabilizes.
Additional Thoughts
Always document the process using the process outputs. This will help you better determine when the process achieves stabilization.
For more on this, I recommend: Process Inputs vs. Process Outputs

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