Laser plastic welding is a broader term that encompasses four major types of laser welding processes.
Although these processes all employ the same principles, it is important to understand that they are all quite different and one method may be excellent for one application and not for another.
This article will outline the differences between the laser plastic welding methods and lay out some pros and cons of each.
Contour Laser Welding
When you first think of welding it is likely you are visualizing contour welding. Similar to traditional metal welding, contour laser plastic welding is where the laser makes a single pass over the joint. The plastic will soften, melt, fuse and cool in this one single pass.
Contour welding is very flexible geometrically. It is well suited for large parts with complex curves and height changes. The process is also capable of high process and quality controls.
Slower welding time, compared to the other laser welding methods, is the major drawback of contour welding.
Simultaneous Laser Welding
Where contour welding is heating a single point along the weld line, simultaneous welding heats and welds the entire joint at the same time. Making use of multiple lasers, often formed into arrays using multiple fiber optic cables, the “beam” is shaped into the pattern of the weld joint.
The major advantage of simultaneous welding is cycle time. The entire joint is being heated simultaneously making the total weld time very short, often times under 10 seconds.
Because of the customized and often very complicated beam forming tools needed to focus the laser into the pattern of a weld joint, and also the fact that simultaneous welding may require multiple laser sources, simultaneous weld tooling can be very expensive. Also, because the tooling is specific to each individual weld pattern new tooling would be required for each application. This makes for higher ongoing tooling costs, down time for switching tooling and very limited flexibility.
Quasi-simultaneous Welding (Scanner-based Welding)
Quasi-simultaneous welding makes use of high-precision, high-accuracy galvo-scanning mirrors. A single laser beam is fed into the mirror system and the laser traces the entire weld seam multiple times rapidly. Because of the high travel speed of the laser the entire joint is essentially being heated “simultaneously,” hence the term quasi-simultaneous.
This welding method is widely used and has quite a few advantages. The most notable advantage is the flexibility of the method. The scanning mirror system is controlled by software allowing for contour/pattern changes to take place instantly. This is massively important for prototyping, situations where multiple applications run through the same line or frequently changing applications.
A secondary advantage is the quick cycle times. Although, not quite as fast as simultaneous welding the cycle times are comparable.
This method is mainly used for two-dimensional parts, minor z-axis changes can take place, but the majority of applications have flat upper surfaces.
Hybrid Laser Welding
Hybrid welding is an extension of contour welding. Technically it is contour welding with an additional feature, halogen radiation. Hybrid welding adds a high-powered halogen lamp to assist the laser. Typically hybrid welding is used with exterior automotive lighting or other large, free-form parts.
The benefits of adding halogen radiation to a contour welding application can result in excellent process improvements. For starters the added heat from the lamp helps improve laser travel speed as the plastic is essentially being pre-heated by the larger halogen radiation zone. Furthermore, the poly-chromatic heat from the lamp will heat both pieces of plastic alleviating stress and allowing for better gap bridging (better fit) between the two pieces.
In automotive lighting applications a time-consuming, post-weld annealing process is required by other welding technologies (ultrasonic, vibration or hot-plate welding), however, the halogen radiation from hybrid laser welding allows for the annealing process to take place during the weld.
- Radial welding – radial welding is essentially contour welding of a cylindrical shape, however, most often the part is indexed and the laser is fixed.
- Laser Staking – utilizes laser welding technology to heat stake and mount circuit boards into plastic housings,
Laser plastic welding has ushered in some great advantages as a new and quickly growing welding technology and each method has its own set of nuances.
No one method of laser plastic welding is better than the next. Each method brings its own advantages and drawbacks to the table. Determining which method is right for your application is not typically a difficult process. What you need to consider when determining your laser plastic welding method are your priorities (cycle-time, capital investment, flexibility) and your part geometries.
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