The world’s first laser machine was born 40 years ago.with the rapid development of the laser technology, combined with many interdisciplinary information of multiple application technologies, such as information optoelectronic technology, laser medicine and biology photon, laser processing technology, laser detection and measurement technology, laser holography, laser spectroscopy, laser chemistry, laser radar, laser-guidance, laser isotope separation, laser controlled nuclear fusion, laser weapons, which greatly promoted the development of traditional industries and emerging industries.  Monochrome laser which has good energy density, has been widely used in various manufacturing and processing areas because of the advantages in its controllability of space and time and other factors. With the use of plastics in in various industries such as aerospace, electronics, chemical, automotive, packaging and medical equipment, there has been a widespread use and expansion of laser application technology and laser processing technology began to enter the field of secondary processing of plastics.

The technology of plastic laser processing utilizes the laser beam interaction with the organic polymer material properties of the plastic for cutting, welding, surface treatment, drilling and micro-processing which is a new processing technology.  Laser processing technology is an integrated technology which incorporates the use of light, machine, electricity, materials and testing and many other factors.   Laser processing which is a non-contact processing, high speed, and no noise, enables high-precision machining for the purpose of creating complex shapes, without the usual sense of the "Tool "wearing out and without the need to replace the "head".  Laser combined with computer control technology allows the combination of laser processing technology to achieve full automation in industrial production, which has the incomparable advantage over more common processing technology.

1 .   Laser welding of plastics

1.1 Applications and features of Laser Welding of plastics

Currently used mainly in hot-melt plastic welding, high frequency welding, friction welding and ultrasonic vibration welding. Plastics laser welding technology has been developed in Europe and the United States in a variety of degree of application. Our own technology in this area is still off stage.

Plastic laser welding technology can replace general welding technology which is difficult to adapt to plastic products such as high-density circuit board, plastic parts and complex shapes.   And strict cleanliness requirements of the plastic products (such as medical devices, electronic sensors, etc.) can be achieved through the use of Laser Welding Technology.  Laser can easily be computer controlled and the use of fiber optics can output laser beams which can reach small flexible parts which other welding methods cannot easily weld to the tight  region.  Traditional welding techniques in the welding of profiled plastic can also have the opportunity to be a good weld, such as the laser may be able to Near-infrared laser through the polycarbonate (PC) and 30% glass fiber reinforced black poly butylene terephthalate ketone (PBT) welded together.  The traditional welding methods will encounter two kinds of problems that makes it impossible to weld in these structures: (a) softening point and (b) the reinforcing material used so that the different polymers can be connected.   But these two problems will not be encountered using Laser Welding Technology.

Laser welding technology as used in the high end applications on Bumper cars has the advantages of lower heat input,  good appearance and looks and can achieve high weld strength.  Most bumper materials are made of  polypropylene (PP), ethylene propylene copolymer (EPDM) and 10% talcum powder blends, and polycarbonate (PC), polybutylene terephthalate (PBT).  Before stopping distance using ultrasonic welding to weld the sensor adapter to have Shanghao paint bumper, but the strength and appearance of the damage is difficult to achieve that would co-exist with the United States Standards. But using laser transmission welding in bumper sensor adapters produces very little melt, there is no melt overflow and the weld is in a good strength.   At the same time, beautiful looks and appearance is very close to station, but I take that the initial part of the investment costs of laser welding is still relatively high, and will only be reasonable when the high demands of bumpers whose structural design in future trends  requires material thickness to be smaller, which is very particularly suitable for using laser technology. In addition to new materials and processing requirements, the use of laser technology will give more freedom to weld in different shapes and position.  Welding strength of the general result of the unit up to 60MPa, and the installation space more narrow, so the application of laser welding creates better opportunities.

Plastics laser welding technology compared to traditional plastic welding technology, these are the following features:

(1)  Easy to control and good adaptability for achieving automated production.

(2)   More precise solid welding and welding sealing.

(3)  The thermal history of welding short pieces, welding stress is  relatively small with less degradation of welding resin and almost no debris

(4)   Small size or shape can be welded even in a structure of complex parts, and even some complex parts can be "through welding”.

(5)   More different materials can be welded together.

1.2  The principles and method of the plastic laser welding

1.2.1     The basic principles of the laser welding plastic

Two low-pressure plastic are clamped together, the laser goes through a product and then absorbed by another product, the product will absorb laser light energy into heat and melt the plastic contact surface to form a weld zone.

 Plastic laser welding is required to improve the material associated with these new requirements are usually difficult to accomplish.  The so-called requirements of laser transmission welding using laser radiation through parts, on the other hand, requires a strong absorption performance of the parts most importantly to avoid cracks to the two parts during the laser welding process, the absorbent part and partial melting temperature, the energy transfer by heat conduction to the light transmission parts. in the external pressure 2 parts together. laser welding technology was attractive because only a few pieces of the heat input structure, it will only have a controlled amount of the minimum melting. The result is available to high welding strength, and because of melting material spill or vaporization rarely obtained impeccable visual quality. in a small area on the welding of high strength can be obtained, this method makes this technique is limited space in the operating conditions of access technology than the station superior.

1.2.2   Commonly used method of laser welding

(1)  Quick scan of the laser beam along the weld, to achieve the purpose of welding;

(2)  Through the use of laser beam to shape optical elements, while the heat is being generated in the weld;

(3)   Irradiation mask welding, laser beam heating products on not only covered part of the mask, you can quickly weld complicated seams;

(4)   Laser beam fixed, plastic piece placed under program control of the multi-dimensional movable bench.

1.3   Adpatability of Laser welding of plastic materials

Laser welding of plastic material must absorb the laser, otherwise it can’t achieve the laser welding . Most of the true color plastic and color translucent plastic can use the laser welding, such as polystyrene (PC),polyvinyl chloride (PVC), polypropylene (PP) and so on.

To increase the absorption rate of thermoplastics, first select the type of laser; second is the addition of laser sensitizing agents (such as carbon black, etc.), which can greatly improve the plastic’s absorption of near infrared laser. Studies made on the reflectance and transmittance of laser through a variety of plastic materials,  laser welding of plastics materials and so on can be resolved.