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?
- 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.