In the automobile industry, plastics are used more and more. Similarly, the integration of materials and components means that the welding method of plastics is becoming a key technology.
The existing technologies, such as ultrasonic welding, thermal welding and bonding, all have their own advantages, but they all have many limitations, such as limited weldable materials, high cost or the need to use special tools in the processing. However, in view of the limitations of these technologies, a new technology has emerged: laser welding technology. The commercialization of high-power diode laser and the development of transmission welding technology have fundamentally improved the ability of plastic welding, and have developed to the point where laser welding may become the key processing technology of plastic processing.
Warwick Laser System Company developed a plastic laser welding equipment and commercialized it. A series of suitability evaluations of thermoplastics have determined the welding conditions of many materials, including colored materials, polypropylene, polyethylene, acrylic resin, polycarbonate, glass filler and film materials.
As a non-connection technology, laser welding avoids tool pollution and product placement problems related to other traditional technologies. The beam emitted by diode laser system is highly controllable, the output is stable and preset, and continuous welding is allowed. The laser has high power and wide beam, and can be used for large-area welding. In fact, there is no limit to the size and structure of the module. And if necessary, the high controllability of the light beam and the accuracy of the light beam transmission can also ensure a very accurate welding operation.
Laser transmission welding technology has been well applied in food packaging, medical equipment and mechanical equipment, and the automobile industry is still the most important application field of this technology. Recently, the plastic company in Burberry, England (Liversidge, West Yorkshire) manufactured a new type of electronically controlled throttle (ETC) pedal for motor vehicles by laser transmission welding technology. Made of glass fiber filled nylon material, it is widely used in automobile industry.
Figure 1. Only by combining laser welding with automation device can its real advantages be brought into play.
The new ETC pedal is characterized by using integrated sensors instead of bolt sensors, which makes it integrated, economical and not easy to be damaged compared with other pedals. When the driver steps on the pedal, the demand signal is transmitted to the engine control system. Compared with the ignition chart, it can add fuel to the engine more accurately and maintain a high combustion efficiency, thus achieving the purposes of economy, performance optimization and less exhaust emissions.
The most important thing to integrate the sensor into the pedal is to weld the potentiometer in the correct position accurately. Because the potentiometer needs accurate placement and zero adjustment, it is unrealistic to weld between two different plastic components by vibration welding technology. In addition, because the potentiometer and pedal used are filled with two different grades of glass fiber nylon, and their melting points are different, it is impossible to connect the two parts by thermal technology or ultrasonic welding technology.
After many successful experiments, the development center of Warwick Laser System Company directly incorporated the diode laser welding system into the automatic assembly, welding and testing production line specially established by Burberry Company to weld two glass fiber filled nylon components in the electronic accelerator pedal components. The system creates a seam 3 mm wide and seals the potentiometer on the pedal.
In this case, the laser is installed on the robot hand in KUKA, Germany, and no special tools are needed. The advantage of using manipulator to operate this part is to realize the flexibility of the system. Because both sides of the assembly need to be welded, in this case, the manipulator is the most effective choice.
If there are duplicate components, it is necessary to use fixtures and make changes to the program. The program of the manipulator can be stored, thus reducing the downtime.
The power meter can regularly monitor the output power of the laser. Because of the large working area of the manipulator, the power meter can be installed in any convenient place. Through a simple program, the measurement can be carried out after a large number of parts are produced.
Our plan to build a material testing platform is in progress, which can be placed in any area between 90- 180 outside the work area. The advantage is that the cost of laser, manipulator and safety has been calculated. In this way, only the fixing fixture and manipulator program need to be considered.
Another application example of this technology is to weld the permanently sealed fuel filter housing for the British Pall Automobile Department. The shell is made of polyoxymethylene with a wall thickness of 2mm. In fact, the shell is circular and cylindrical, so it needs to be butt welded from the outer edge and the inner edge. Before welding, the filter medium in the shell is compressed in the box. Because of the damping effect, vibration welding technology cannot be used. The minimum blasting pressure of the shell is 12 bar, and the safe working pressure is 6 bar.
Although it has successfully passed the automobile industry test specification, the bursting pressure of the filter is considered as the decisive test of welding strength, because it is the final failure mode of the weld. The manual hydraulic cylinder is used to pressurize the filter, and the pressure sensor is used to measure the pressure. The filter is filled with oil and sealed. Continue to pressurize the hydraulic cylinder until the working pressure of the filter reaches 12 bar. Hold this pressure for a few seconds, and any pressure drop may indicate a crack. Then continue to pressurize until the filter finally breaks. Standard value of bursting pressure >: 30 bar.
As a means of bonding and welding plastics, high-power diode laser transmission welding technology is rapidly becoming a feasible alternative to traditional technology. Its advantages meet the needs of automobile industry, and in some gluing applications, this technology is often the only choice.