Research process and methods of laser plastic welding technology

Since the emergence of laser plastic welding technology, people have been studying how to use lasers as a material processing tool. In the 1970s, the automotive industry began to experiment with using lasers to process materials. In 1998, Marquardt used semiconductor lasers to mass-produce electronic car keys, welding black polymer (PA) key covers to the same black but laser-transparent PA key shells.

According to molecular structure, they can be divided into three categories: thermoplastics, thermosetting materials, and synthetic rubbers. Laser welding of thermoplastic materials has been widely studied and applied. This article briefly describes the process of laser welding of thermoplastic materials and its research progress from three aspects.

Laser welding process and method:

Laser welding of thermoplastic materials mainly adopts laser transmission welding. This method has certain requirements on the welding performance of both materials, that is, the upper thermoplastic layer is transparent to the laser wavelength, and the lower thermoplastic layer can absorb the laser energy. The laser beam passes through the transparent upper material to reach the lower material, and the surface of the material melts due to the absorption of laser energy. At this time, the molecular connection welds the two materials together under a certain pressure. Because the laser is in mechanical contact, it is focused on the surface of the bottom material, and the thermal effect generated is local, so this method can effectively prevent mechanical and thermal damage to the welding material. At present, about 20% of thermoplastic materials are made by laser welding. For different welding tasks and operating requirements, it is roughly as follows:

Arc laser welding is currently the most widely used simple welding method. During the welding process, the laser passes through the optical system and the vibrating mirror to make the laser beam or laser beam stationary. The time of action between the welding target and the laser depends on the focusing size and movement speed of the beam, which in turn affects the welding time and welding effect. It is a very flexible welding method that can complete complex three-dimensional welding and has a wide range of applications in the packaging industry.

Mask laser welding is a process based on contour welding or synchronous welding, and its principle is similar to the photolithography technology in chip manufacturing. This process is mainly used for complex geometric welding patterns with a minimum seam width of more than 100 microns. The mask is usually made of thin sheets or metallic glass. However, the mask method is more complicated to make, and the design of the mask is only for the welding geometry, so the flexibility of mask welding is low and it is suitable for large-scale welding processing.

Quasi-synchronous laser welding is an organic combination of contour laser welding and synchronous welding. Using a speed of up to 10m/s, the laser beam quickly passes through the weld and scans repeatedly, so that the entire weld area is melted at the same time, and the effect is similar to synchronous welding. Using the synchronous fusion process, the quasi-synchronous method and the synchronous method are also suitable for bridging welding of two adjacent large gaps.

Synchronous laser welding uses a laser beam to irradiate the welding area, which greatly shortens the welding process time and enables adjacent parts with large gaps to be used for bridging welding. Compared with contour welding, synchronous welding welds more reliable parts due to the long laser action time.

Second, welding plastic color

Based on the principle of laser transmission welding, the color matching problem of laser plastic welding is determined, which is one of the research topics of laser plastic welding. The following chart illustrates the welding difficulties caused by different material colors. First, the laser welding of transparent black materials was successfully realized. In addition, the welding of black materials is also widely adopted.

In laser welding, CO2 lasers are used for laser welding, mainly because their absorption band is generally located in the ultraviolet region. Mixing and adding pigments can greatly change the optical absorption characteristics of plastics, greatly improving the absorption of plastics to visible and near-infrared materials. The original laser transparent material is transformed into a laser absorbing material, realizing the traditional Nd:YAG solid laser (1064nm and frequency-doubled 532nm); high-power Gaas semiconductor lasers (800-1000nm) and new fiber lasers can be used for welding. The addition of colorants also changes the characteristics and parameters of the original plastic welding, making it more suitable for special purposes.

3. Solder Matching

When studying the matching of welding materials, try to match the color of the material. The material that TPTP welding is widely used in industry is thermoplastic TPTP welding. Because laser transmission welding is full contact, these thermoplastic materials can also be welded with other materials. For example, synthetic rubber with the same thermoplasticity has the elasticity and scalability of thermoplastic materials, and the parameters such as welding processing temperature and cooling time are very similar to those of thermoplastic materials. It is easy to achieve TPTPE welding using laser transmission technology. Because TPE has a good feel and friction, TPTPE was first used in the automotive industry to produce car steering wheels. In addition, laser transmission welding can also weld TPE and TPE to form TPETPE welding.

Laser welding of plastics, metals, and ceramic materials is one of the latest research directions. For example, plastic is indirectly heated by laser, the contact surface melts, and then it is wrapped by metal to form a strong connection with the metal.