Most ultrasonic welding defects are straightforward to diagnose and fix. Use this guide to identify problems and solutions quickly.
1. Underwelding
Underwelding occurs when the weld doesn’t cover the entire intended area, leaving gaps and weak joints.
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Common Causes: Too little energy reaching the part, weld time too short, amplitude too low, or energy being lost into a soft fixture. It can also be caused by contaminants like mold release or moisture.
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Solutions: Ensure parts are clean. Increase pressure, trigger force, or down speed to increase energy applied to the part. If energy is being lost, switch to a rigid fixture like aluminum or stainless steel.
2. Overweld
The opposite of underwelding, this occurs when excess energy spreads beyond the intended area, affecting dimensions and finish.
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Common Causes: Excess energy application, weld time is too long, or the "Collapse" (melt down distance) and absolute distance settings are too high.
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Solutions: Reduce pressure and weld time. Adjust parameters one at a time—try 20–30% changes to clearly see the effect.
3. Flash
Flash is the excess plastic forced out of the joint, ruining the part's appearance and functionality.
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Common Causes: Excessive energy application, an oversized energy director, or inconsistent joint design.
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Solutions: Reduce weld time and applied pressure. Verify your fixture setup to ensure the part is held firmly without being crushed.
4. Marking & Surface Damage
Marking is aesthetic damage to the surface finish, often problematic for consumer-facing products.
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Common Causes: Misalignment between the horn, fixture, and part, or the ultrasonic horn heating up excessively.
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Solutions: Check alignment of the horn and fixture. If the horn is overheating, it may require professional tuning or repair. Marking is often a side effect of overwelding.
5. Inconsistent Results (Part-to-Part)
When welds vary across a single batch, it leads to high scrap rates and batch rejections.
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Common Causes: Maintenance issues, fluctuations in air-line pressure, or equipment calibration drift over time.
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Solutions: Verify air-line supply capacity. Ensure all parts are cleaned consistently to eliminate moisture. If the welder produces inconsistent results despite steady air pressure, it likely requires professional service.
6. Internal Component Damage
Internal electronics or mechanisms can be damaged or accidentally welded during the process.
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Common Causes: Too much energy or vibration duration, or improper internal mounting.
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Solutions: Reduce amplitude, pressure, or down speed. If you cannot reduce energy further without causing an underweld, the equipment likely needs professional recalibration.
7. Diaphragming (Oil-Canning)
This is a "bubble" or outward distortion of a part wall, damaging both aesthetics and seal integrity.
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Common Causes: Excessive welding energy or using the wrong horn for the specific geometry of the part.
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Solutions: Reduce weld time or amplitude. Reposition the horn or consult with an expert about proper horn selection.
Achieving the perfect ultrasonic weld is a delicate balance of physics, material science, and mechanical precision. As this guide shows, a minor shift in pressure or a slight misalignment can be the difference between a high-quality product and a costly bin full of scrap. When DIY adjustments to your amplitude or weld time stop yielding results, you need a partner who understands the nuances of the equipment and the processes involved.
Contact Rochester Industrial Services for Dukane or Branson Ultrasonic Equipment Repairs or review our error code guides for more knowledge on how to identify issues.
Branson Error Codes Dukane Troubleshooting
At Rochester Industrial Services, we are the leading experts in diagnosing and resolving the most complex ultrasonic welding defects. Our expert technicians rebuild the equipment and know it inside and out. Whether you are struggling with inconsistent joint strength, surface marking on consumer-facing parts, or internal component damage, our team has the technical mastery to optimize your process. Don't let poor part quality or high scrap rates stall your production; contact Rochester Industrial Services today and let us restore your welding operation to peak efficiency.
