Ultrasonic welding is fast and stable, but defects can occur when parameters or tooling don't match the job. Here are the three most common defects and how to address them.
1. Weak welds (insufficient strength)
Symptoms: joints break apart easily or fail pull tests. Common causes: insufficient weld energy, low pressure, or poor contact between horn and part. Increase weld time or amplitude gradually, check air pressure stability, and make sure the horn face sits parallel to the part surface. Moisture in the material also causes weak welds — hygroscopic materials like nylon should be dried before welding.
2. Excessive flash
Symptoms: too much molten plastic squeezed out around the joint, hurting appearance. Usually caused by excessive energy or pressure forcing material out of the weld zone. Reduce amplitude, shorten weld time, and review the energy director design — a proper energy director keeps molten material inside the joint.
3. Part cracking
Symptoms: cracks appear after welding, mostly on thin-walled parts or areas far from the horn. Caused by excessive amplitude or stress concentrations in the part design. Lower the amplitude, shorten weld time, and consider adding ribs or avoiding sharp corners at the mold design stage.
Troubleshooting advice
When defects appear, check in this order: material — horn — parameters — fixture. First confirm the material isn't damp or changed; then inspect the horn for cracks and face wear; then fine-tune one parameter at a time; finally verify fixture support. Systematic troubleshooting beats blind parameter tweaking.