Ultrasonic Troubles?

Plastic ultrasonic welding is a fast and efficient method of joining thermoplastic parts using high-frequency vibrations. However, like any other process, it can encounter some problems that affect the quality and strength of the weld. In this blog post, we will discuss some of the common problems in plastic ultrasonic welding and how to troubleshoot them.

Problem 1: Weak or inconsistent welds

One of the most common problems in plastic ultrasonic welding is weak or inconsistent welds. This can be caused by several factors, such as:

• Incorrect welding parameters: The welding parameters, such as amplitude, pressure, time, and trigger force, need to be adjusted according to the material, geometry, and design of the parts. If the parameters are too low or too high, the weld may not form properly or may overheat and damage the parts. To troubleshoot this problem, you need to experiment with different settings and find the optimal ones for your application. You can also use a closed loop systems to measure and control the welding parameters in real-time.
• Poor part fit or alignment: The parts to be welded need to fit together well and align with the ultrasonic horn (sonotrode – the welding tool). If the parts are loose, warped, or misaligned, the vibrations may not be transmitted evenly and the weld may not form or may be uneven. To troubleshoot this problem, you need to check the quality and accuracy of the parts and the fixture. You may need to modify the parts or the fixture to improve the fit and alignment. You can also use a knurled or textured horn to increase the friction and grip between the parts. This option depends greatly on the part being welded.
• Incompatible materials: Not all thermoplastics are suitable for ultrasonic welding. Some materials may have poor weldability, low melting point, high viscosity, or high hygroscopicity (absorption of moisture). These factors can affect the heat generation and flow of the plastic during the welding process. To troubleshoot this problem, you need to check the compatibility of the materials and choose the ones that have similar properties and good weldability. You can also use a compatibility chart or a weldability test to determine the best materials for your application.

Problem 2: Flash or excessive material around the weld

Another common problem in plastic ultrasonic welding is flash or excessive material around the weld. This can be caused by several factors, such as:

• Excessive welding parameters: If the welding parameters are too high, the plastic may melt too much and squeeze out of the joint area, forming flash or excess material around the weld. This can affect the appearance and functionality of the parts. To troubleshoot this problem, you need to reduce the welding parameters, such as amplitude, pressure, time, and trigger force, to the minimum required for a good weld. You can also use a closed loop system to measure and control the welding parameters in real-time.
• Poor joint design: The joint design, such as the shape, size, and location of the energy director (the raised ridge that concentrates the vibrations and heat), plays a crucial role in the welding process. If the joint design is not suitable for the material, geometry, or function of the parts, the plastic may not melt and flow properly, resulting in flash or excess material around the weld. To troubleshoot this problem, you need to optimize the joint design according to the best practices and guidelines for ultrasonic welding. You may need to change the shape, size, or location of the energy director, or use a different joint type, such as a step joint, a tongue-and-groove joint, or a shear joint.
• Contamination or additives in the material: The material used for ultrasonic welding needs to be clean and free of any contamination or additives that may affect the melting and flow of the plastic. Contamination or additives, such as mold release agents, lubricants, plasticizers, fillers, flame retardants, regrind, colorants, or resin grade, can alter the properties and behavior of the material during the welding process, resulting in flash or excess material around the weld. To troubleshoot this problem, you need to check the quality and purity of the material and avoid any contamination or additives that may interfere with the welding process. You may need to use a different material or a different source of material for your application.

Conclusion

Plastic ultrasonic welding is a reliable and efficient method of joining thermoplastic parts, but it can also encounter some problems that affect the quality and strength of the weld. By following the troubleshooting steps and tips discussed in this blog post, you can solve some of the common problems in plastic ultrasonic welding and improve your welding performance and results. If you need more help or advice on plastic ultrasonic welding, you can contact us. We will be happy to assist you with your welding needs and challenges.