Troubleshooting

PROBLEM PROBABLE CAUSES SOLUTIONS
Non-uniform
weld around
the joint
(continued)
Inconsistent energy director height.
Wall flexure.
Knock-out pin location in joint area.
Improper alignment.
Non-uniform horn contact.
Part tolerance.
Mold release.
Accumulation of fillers in one area.
Moisture in joint area.
Correct mold to ensure uniform energy director height.
Check molding conditions.
Add internal ribs to part.
Increase wall thickness.
Modify fixture to prevent outward flexure.
Move knock-out pin location from joint area.
Make sure knock-out pin marks are flush with surface.
Check for part shifting during welding.
Check alignment features in mating parts.
Check for parallelism of horn, part, and/or fixture.
Check fit of part to horn.
Check part fit with horn using carbon paper.
Check for sinks.
Check for proper support in fixture.
Tighten part tolerances.
Check molding conditions.
Clean mating surfaces.
If mold release is required, use a paintable/printable grade.
Check molding conditions.
Reduce the amount of filler.
Use only short fiber fillers
Dry parts as required.
Inconsistent
weld results
part-to-part
Mold release.
Part tolerances.
Cavity-to-cavity variations.
Regrind/degraded plastic.
Clean mating surfaces.
If mold release is required, use a paintable/printable grade.
Tighten part tolerances.
Check part dimensions.
Check molding conditions.
Run statistical study to see if a pattern develops with
certain cavity combinations.
Check part tolerances/dimensions.
Check for cavity wear.
Check molding conditions.
Centralize gate location.
Check with molder for percentage of regrind
Check molding conditions.
Reduce percentage of regrind (maintain below 10%).
Improve quality of regrind.