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Possible Issues with Ultrasonic Plastic Welding in Assembly

The performance of plastic parts often depends on the staking method applied during the manufacturing process. Ultrasonic plastic welding is a popular option among manufacturers, but product designers and process engineers need to keep in mind there may be some issues with the technology.

With ultrasonic welding, the production cycles are fast, doesn’t need any additional consumables, and works well in a variety of different applications. When deciding to use ultrasonic technology for the welds and joints, you should consider possible issues that can arise during the design stages. The product layout needs to cater to ultrasonic welding to prevent poor quality connections and joints forming within the assemblies.

Here are some of the main manufacturing issues with ultrasonic plastic welding.

1. Device Calibration and Accuracy

Ultrasonic welding uses vibrations to generate heat in the area where the weld is required. As the devices operate between 15 and 70 kHz, it is essential that the device should remain calibrated for maximum accuracy. If you don’t regularly inspect the device, it can create lower quality welds that won’t operate correctly or according to the design pressures.

Another issue could arise from variable heat generated in the process due to energy or component failures in the device. A faulty power supply or converter will influence the quality, producing inconsistent welds during the manufacturing process. It may be possible that two similarly configured devices produce different results. Usually, this points to a faulty component within the machine.

2. Process Complexity

Application engineers need to configure the devices for the thermoplastic materials used in the design. The different amplitudes used will produce different strength welds depending on the materials, requiring exact control during the process. As there is mechanical loading on the parts during the vibration and weld, the accuracy of the controller and the viability of the design is of paramount importance.

Common design considerations include:

  • Material composition changes requiring different process parameters and configurations.
  • Suitable equipment types for the different applications.
  • Part geometry for consistent quality of the ultrasonic welds.

If you do not properly address any of the above during the design and manufacturing process, it can create problems with the individual products produced. Either an incorrectly configured device or any unknown changes in both the parameters and material used can compromise the structural integrity of the assembly.

3. Part Damage and Surface Marking

The application of vibration energy could create surface markings or cause damage to the components during the welding process. The most common surface markings include part gouging, texture marring, degating, and surface burning. Troubleshooting any of these issues with ultrasonic welding requires experts who understand both the design suitability and the equipment’s process parameters and the material properties. Other part damages are related to the vibration causing cold solder joints, stress cracks and component failures on electrical components and circuitry.

4. Contamination in Medical Devices

The process of welding the plastics with ultrasonic is a very fast and violent process that causes the plastics to melt very fast. This weld process produces contaminants from the plastic materials and causes outgassing.  This can cause measurable and unacceptable contaminant particles levels in the medical device or assembly that can be a cause rejection in the test and measurement phase of the assembly process. Engineers and Scientists must determine if the nature of the product or device requires a high level of cleanliness and the PPM requirements to ensure the process is the most effective assembly solution.

Using Thermal Press for Heat Staking

Opposed to ultrasonic welding, heat staking and heat sealing offers more consistent and reliable joining of plastics, films, foils and filter within a product. The machines are automatable, offer greater flexibility with more components, and produces higher pull strength on the joints. For the best plastic assembly techniques and designing products with manufacturing in mind, contact Thermal Press today.

Originally posted at

device calibration, medical device assembly, plastic contamination, ultrasonic welding

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