Laser laser welding - rapid development of laser welding

Rapidly developing laser welding technology
The basic principle of laser welding plastic is to superimpose two workpieces by pressing the clamp, and then inject laser into the upper workpiece so that the laser can penetrate the workpiece and be absorbed by the workpiece below. The absorbed laser light energy is converted into heat energy, which in turn causes the contact faces of the two workpieces to melt, eventually forming a weld zone. However, it is true that the application of laser welding techniques to solder thermoplastic materials has gone through considerable lengths. In an era of new materials, new equipment and new technologies, current producers must not only understand the characteristics, advantages and requirements of laser welding, but also recognize the many innovations and future trends in this field, so as to grasp the trend of technology. Always at the forefront of technology, Radial Laser Welding offers.

Material development
In order to better adapt to laser welding technology, material suppliers have made some significant progress in thermoplastic materials. About three years ago, almost all single natural materials achieved good laser welding quality after adding carbon black, but at that time the color of the absorbent could only be black. Now, there has been a lot of progress in this area. Producers can design almost any color, and can meet the requirements of laser welding at the same time, and ensure the stability of the process.
In addition to color, innovations in materials technology have also broken some of the limitations of laser welding. For example, the flame retardants originally used in thermoplastic materials are all phosphating flame retardants, and laser welding thereof often leads to insufficient light transmittance of the material to near-infrared light. Nowadays, many material suppliers have developed a new type of chlorine-free flame retardant, which solves this problem well and successfully meets the requirements of laser welding.

Process and equipment technology
In the early years, laser welding technology required a large machine, even a small electronic component, and required a complicated external cooling system, which required a large factory space, which would undoubtedly lead to higher investment costs. And the welding equipment at that time used to use Nd:YAG solid-state lasers. Although the successful application of diode lasers has gradually replaced this solid-state laser, these diode lasers usually have a warranty time of less than 3000h and still cannot compete with solid-state lasers. With the successful development of new diode lasers, they are almost maintenance-free and have a life expectancy of up to 20,000 h, making it the first choice for manufacturers to successfully replace solid-state lasers. The current laser welding system is compact and compact, and the standard system can handle workpieces up to 240 mm x 240 mm with a focusing diameter of less than 1.5 mm. In addition, a variety of process monitoring methods are also available.

Seeing the huge application potential and broad application prospects of diode laser technology, suppliers continue to increase research and development, and many new technologies have emerged. For example, diode laser fiber coupling technology and laser welding using industrial robots, etc., diode laser fiber coupling technology can ensure the uniformity of the laser beam even after replacing the laser source.

As technology advances, laser welding can easily take advantage of processes and equipment to bridge the gap between equipment and conventional methods in terms of equipment cost. Therefore, cost factors are no longer the main reason for limiting the widespread use of laser welding technology.

As a leader in laser welding applications, the tremendous growth of the automotive industry has once again proven the advantages of laser welding technology. Taking the sensor housing as an example (as shown in Figure 1), laser welding technology has been used in the automotive field for several years. Currently, the design of any new module has been designed from the beginning to accommodate its changes. In the case of sensitive electronic packaging, the use of conventional welding methods often produces significant mechanical stress and high temperature effects on electronic components, while laser welding can control and adjust the welding energy as needed, thus ensuring the fine and accurate welding quality. In addition, the economics of laser welding have also eased the extreme pressure on the automotive industry to reduce costs. The successful application of laser welding technology in the automotive industry is a testament to this.

Future trend
Regarding device size, there are two opposite trends in the market: on the one hand, the device is getting smaller and smaller, and the weld is complex; on the other hand, the device is larger and three-dimensional. The continuous development of laser welding equipment can meet both requirements.

At present, medical diagnostic products continue to develop toward miniaturization, which requires welding technology to simultaneously integrate several functional devices in a minimum space. It is very difficult or impossible to solder capillary microfluidic structures (as shown in Figure 2) by other methods, and now, even today's inexpensive SEM scanning laser systems can solder such products. Previously, people chose Nd:YAG lasers that were easy to focus on, but the technology was very expensive and the technology was not flexible enough. In contrast, fiber laser or fiber-coupled diode laser welding technology can not only meet the weld width of 0.1mm, but also is not limited by the shape of the weld and the size of the chamber.
If the inner diameter of the fiber is reduced, the SEM scanning laser system can also weld smaller welds or larger weld areas while achieving high speed welding. In order to adapt to the changing trend of device size, LPKF (Lopco Optoelectronics Co., Ltd.) has developed an SEM scanning welding system suitable for three-dimensional welding (as shown in Figure 3), which has a focal depth variation of up to 80 mm. The laser can enlarge the welding area of the welded workpiece to 370 mm × 370 mm and the weld width is less than 2 mm. Currently, this technology has been applied to large three-dimensional automotive parts such as welding engine compartments or automotive interiors.
However, the application processing of the SEM scanning system has certain limitations. Complex three-dimensional components such as automobile taillights may obstruct the laser irradiation due to the concave or reverse beam angle, so the contour welding method must be selected. Contour welding has very strict requirements on the workpiece, and the welding cycle is long, which limits its application in this respect.

LPKF has invented a hybrid welding method that compensates for many of the shortcomings of contour welding and has great advantages when welding three-dimensional large parts. The method uses a flexible, flexible robot to guide the laser, while the pressure required by the fixture comes from the weld head. The rollers used generate a lot of pressure without indentation of the workpiece and it is not sensitive to dirt. More importantly, the technology uses a laser with a chlorine lamp with a wider spectrum. The chlorine lamp directly heats the upper workpiece while absorbing heat from the underlying workpiece to form an integral heating of the workpiece. Compared with the conventional welding method, the heat transfer of the workpiece welding surface is more uniform, and the hardness of the upper workpiece is reduced. If there is a gap error, it can be processed earlier, thereby ensuring a higher and more stable welding quality, and at the same time shortening. Welding time. The addition of a chlorine lamp effectively reduces the power of the laser required and correspondingly reduces the cost. In addition, when the composite welding is applied, the inherent residual stress of the workpiece is small, and the subsequent tempering treatment can be greatly simplified or even unnecessary, which is of great benefit to the amorphous thermoplastic material.

In addition to innovations in device welds, a number of new material combinations have emerged, and laser welding techniques are no longer limited to combinations of hard/hard materials. New laser welding materials are emerging, including thermoplastic fabrics, thermoplastic elastomers, and sheet materials for packaging and medical catheters, expanding the range of applications for laser welding. Now, even laser cleaners or coatings can be used to achieve clean welding of amorphous plastics, which is simple and reliable. The emergence of other laser sources, such as CO2 lasers, provides a new opportunity for laser welding technology because its long-wavelength light can be absorbed by any transparent plastic.
From an economic point of view, innovations in diode lasers and process technologies ensure efficient laser welding, and the reduction in laser costs also means lower investment costs. More importantly, the machine's working time is further improved by continuously extending the maintenance interval and the service life of the equipment.

in conclusion
Although laser hybrid welding technology is relatively new, it has unique advantages and can even replace conventional welding technology in some aspects. At the same time, the development trend of device miniaturization and complex three-dimensionality also shows that laser hybrid welding technology has great potential for future application development.