Thermoplastic processing basic troubleshooting

Define the Problem:

Focus effort on defining the exact problem, not the result of the problem.
Example: Although short shots present a problem, they are really the result of not enough material in the mold.
Example: Although flash presents a problem, it is really the result of poor tooling, weak clamp, improper transfer from fill to pack or a combination.

Quantify with Numbers:

The more precisely you can quantify the numbers, the better off you will be.
Hot? How hot — 100, 200, 450? F? or C? scale?
Melt temperature? — the actual temperature of the plastic.
Mold temperature? — the actual temperature of the surface of the mold cavity.
Fast? Slow? Injection time — the time from the start of injection until transfer to pack. • Shot to machine capacity? — the weight of parts and runner vs. the maximum machine shot.
Cycle time? • Part weight achieved during fill time?
Final part weights after pack and (or) holding pressures are applied?

Process Parameters:

Understand the process. - What is supposed to happen?
Process from the plastics point of view
Avoid temperature adjustments because they take too long to reach equilibrium
Make machine adjustments only to repeat proven plastic conditions. - Once a set of plastic conditions produce the desired parts, they will continue to do so.
Understand when melt and or mold temperature adjustments need to be made. - Rarely and only to repeat proven plastic conditions .
Many machines will not develop a consistent pressure or flow until the hydraulic oil reaches an ideal operating temperature range. Action Plan: • Develop a clear written plan.
Change only one condition at a time.
Allow sufficient stabilization time after each change. Record:
Know where you started.
Keep an accurate record of each change.
Note the results for cause-and-effect analysis.

Plastic Troubleshooting