Plastic Welding, Explained
Plastic welding involves creating a molecular bond between two compatible thermoplastics. This bond is much stronger than other plastic joining processes — like adhesives and riveting. As such, it’s a common manufacturing process used throughout a variety of industries. Here, we’ll break down the specifics of plastic welding and help you determine if it’s right for your business.
Most Common Types of Plastic Welding
One of the most common types of plastic welding, ultrasonic welding uses mechanical vibrations with high frequency and low amplitude to join two plastics. The vibrations cause frictional heat, which melts the material together, creating a molecular bond.
Ultrasonic welding is fast, cost-effective, easily automated, and well-suited for mass production, making it one of the most popular plastic welding choices. With production rates of up to 60 parts per minute, this is likely the best choice for your operation.
However, you should consider a few limitations of ultrasonic welding before choosing this process. It’s not suitable for thermoplastics with high moisture content and hard/strong thermoplastics like polypropylene. It’s also only best to create joints that overlap each other with this process. Corner, butt, tee, and edge joints likely won’t work well.
As the name suggests, laser welding uses a laser beam to melt the plastic — keeping it below the evaporation temperature. Pressure is then applied to weld the two pieces together. It’s an extremely fast process and has a variety of options to choose from: contour, simultaneous, and hybrid.
Contour laser welding is similar to traditional welding; the laser makes a single pass over the joint. During this pass, the plastic softens, melts, and fuses together. Because it’s limited to heating one single point along the weld line, it takes longer than some other methods.
Simultaneous laser welding heats the entire joint at the same time, making it faster than contour laser welding. It often makes use of multiple lasers to speed up the process.
Hybrid laser welding is similar to contour welding. It adds a high-powered halogen lamp to help the laser make a faster, more efficient cycle. The heat from the lamp helps improve laser travel speed and helps alleviate stress on the material. This process is typically used for large, free-form parts.
Overall, laser welding allows for high-quality welds and fast throughput. However, it requires extremely tight tolerance parts to execute a great weld. Because the spot size after laser focusing is small and the weld is narrow, it’s susceptible to welding defects when the workpiece assembly or beam positioning is off.
This process does not use heat; rather, it involves applying external pressure on both plastic materials by moving and rotating them against each other. Then, pressure is applied until a permanent join forms.
Friction welding is great for joining dissimilar materials, including plastics, composites, and even metals. It’s also a fast manufacturing process and can be automated, which makes it ideal for mass production.
While friction welding does produce strong joints, it’s not without disadvantages. It’s typically only suitable for round bars with the same cross-section and angular and flat butt joints.
High Frequency Welding
High frequency welding uses an electromagnetic field to generate heat inside the material. Pressure is then applied until a permanent joint forms. It’s the most suitable plastic welding process for dissimilar plastic materials. However, it’s only compatible with a few materials, like polyvinyl chloride, EVA, and some PET materials.
Vibration welding involves rubbing the plastic part at a certain frequency and amplitude, creating heat and — ultimately — a weld.
This sounds similar to ultrasonic welding, but the two processes are unique. The vibration welding process vibrates one component against the other in a linear side-to-side motion. Conversely, the ultrasonic welding process vibrates one component perpendicularly to another.
Vibration welding and ultrasonic welding also use different frequencies when joining plastic. The vibration welding process uses 120-240 Hz, and will depend on the size of the parts being welded. Ultrasonic welding uses much higher frequencies, typically 20,000-40,000 Hz (20kHz). The amplitude of the two processes is also different. Vibration welding typically uses between 0.4mm and 4.0mm, while ultrasonic welding uses between 0.025 or 0.125mm.
Lastly, the welding time for each of these processes is slightly different. Vibration welding has a typical cycle time within the five to 10 second range, while ultrasonic welding is completed between one and three seconds.
Work with SEA-LECT Plastics for Your Plastic Welding Needs
When you need an experienced company to complete plastic welding services, turn to SEA-LECT Plastics. Founded in 1987, we have decades of experience completing high-quality ultrasonic welding projects, along with providing injection molding services, and serving other needs for a wide range of industries.
Our 36,000-square-foot, state-of-the-art facility has a dedicated engineering team, an ISO 9001:2015 certification, and round-the-clock operations, making us the perfect partner for your engineered resin needs. No matter your need, we’ll help create the right solution for your business.
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