Bubbles in plastic parts is one of the most common defects and it can be tricky to solve.
These are the steps we recommend at The Tool Hub.
- Find out what type of bubble you are dealing with. (Is it trapped gas or is it a vacuum void)
Different Bubbles need different solutions
This can be done by carefully heating up the part with a heat gun
The bubble expands after heating = trapped gas
The bubble collapses after heating = vacuum void
- If we find that we are dealing with trapped gas
Start by examining your injection parameters.
The first step in the procedure is to take off hold / second stage by adjusting the hold pressure down to a very low number and see if the bubbles are still there.
Assuming you still see bubbles, the next check is to learn the filling pattern to determine if the gas is air trapped upon filling the part.
Analyze where the bubbles form and look at the flow pattern to see if there are any hesitations that might form the bubble
Make sure you maintain a proper temperature profile.
Make sure your injection speeds are not too high.
Try increasing the back pressure.
Make sure you vent at least 30% of the perimeter.
Thin out thick sections / features that might cause hesitations.
Add dynamic rheological control inserts to alter the flow pattern within the cavity.
(see our article on evaluating gate balance)
Ensure that you have the correct drying conditions
- If we find that we are dealing with vacuum voids
- This defect is caused by insufficient packing or thick sections that form voids during material cooling.
Try a slower fill rate.
Increase the back pressure.
Reduce the melt temperature.
Open up the gates slightly to allow a longer hold time.
Change the gate position to fill the problematic section sooner
Core out eventual thick sections.
For any help with these issues, please contact us at The Tool Hub