ANSWER: You need to look at all elements of the project in order to pinpoint the problem. We suggest looking at the molded parts for warpage, heat sinks and cavity-to-cavity variations. Look at the joint design to make sure you have the right joint for the material and the part configuration. For example, using an energy director on a nylon part is a bad match.
Next, check out the elements of the welding system itself. Does the horn match the contours of the part? Or maybe the horn has a small, hairline crack.
Check the fixture to make sure it isn't allowing the part to move around or is in some other way dissipating energy.
Check the booster. Is it providing the right amount of amplitude for the resin and the part design?
The fastest way to diagnose all these problems is with iQ Explorer II advance user software. You can analyze distance, energy level, peak power, force, pressure--any relevant variable-- Along with detailed graphs of the weld process. It's worth the investment.
Call Dukane. They'll come in and do a full diagnostic test using their own iQ Servo welders with patented Melt-Match® technology, and the price is right--it's free!