How to Prevent Common Failure Modes in Injection Molding?

Release time: 2024-12-14

I. Preventing common failure modes (e.g., air bubbles, deformation, warpage, short shots, etc.) in the injection molding process is key to ensuring product quality and productivity.

Here are some points to detect to prevent common failure modes.

1. air bubbles 2. short shots 3. deformation and warpage 4. silver streaks (air marks) 5. shrink marks 6. raw edges 7. scorching

II. Some of the failure modes that companies tend to fall into.

Screw and barrel

Properly inspecting screws and barrels is paramount to controlling a validated process. Screws should be pulled every six months to measure flights, barrel inner diameter, and the screw shank, especially in the compression/transition zone.

Clamp performance

Poorly maintained clamps can also be detrimental to maintaining consistent processes. Clamp components such as bushings, pancake sensors, linear transducers, and self-lube systems and lines should be inspected monthly for wear and proper operation. Clamp parallelism should be checked every six months, or sooner if abnormal flash events occur during a validated process. Signs that might show poor clamp performance may include the inability to reach or maintain clamp force/tonnage setpoints, hold pressure during a tonnage event, or maintain consistent mold open times.

Temperature performance

There are three primary contributors to poor temperature performance in a molding process — barrel temperature, mold temperature, and the hot runner. Key inspection factors for each, as well as process monitoring data that should be reviewed for troubleshooting purposes, are as follows:

Barrel temperatures that vary more than 2°F show signs of poor calibration or failing heater bands. In addition, if a zone heats much slower at startup than other zones, this might point to heater band failure. In most cases, barrel temperature actuals should reflect no more than a 1°F variance from setpoint.

Mold temperature fluctuations greater than 3°F should be considered suspect. Mold temperatures and actuals should generally stay constant with no significant differences between actual vs. setpoint. Variations often point to a burnt heater, or a valve sticking open or closed. Regarding process monitoring, gallons per minute (GPM) and process to/from pressures should also be monitored.

Hot runner set points should match actuals. Changing temperature controls from PID to manual should only occur when production needs require it for a short-term basis. Large swings in actual temperatures reveal potential calibration or failing heater issues. It is important to remember that, in most cases, the hot runner is merely an extension of the nozzle into the mold cavity. These temperatures should generally be equal to each other.

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