Laser Welding Technology in Automotive Lamp Field

With the rapid development of the automotive industry. The production technology of auto parts is also constantly innovating. As the important lighting exterior fittings of the vehicle, the car headlights affect the commerciality of the car in terms of function. In order to comply with consumers' pursuit of quality and beauty, laser welding technology has been widely used in the field of vehicle lights. However, at the same time as the introduction of new technology and complex processes, there are potential hidden dangers that affect the quality of the products, resulting in poor lamp performance and even the possibility of traffic accidents. The article combines the ideas of FMEA (design potential failure mode) to provide several Analytical methods for ensuring product quality during the design phase, as well as common methods for managing quality after trial and mass production. In recent years, with the expansion of the global automotive market demand, while the automotive intelligentization process is accelerating, the advanced manufacturing technology represented by laser technology is also constantly promoting the upgrading of the automobile manufacturing industry, combining advanced laser manufacturing technology with automobile production. It is already the trend of the times.

The object of laser welding in the field of vehicle lamp is resin, and other principles are the same as body welding. It is a technology that melts two or more resin parts to be welded and binds them completely by the heat energy generated by laser, so as to realize the good sealing of the lamp. The steps are as follows: fixing the two parts to be welded by fixture. The upper and lower fixtures are closed, the parts are clamped together, and then the NIR laser (wavelength 810-1064 nm) transmits through the first part, which is absorbed by the second part. The absorbed NIR laser is converted into heat energy, and the contact surface of the two parts is melted to form a welding zone. Apply pressure to make the welding zone firm.

Advantages: concentrated energy, minimal energy consumption. The molten resin is small in volume, resulting in less excess resin chips. Because it is not a contact welding process, the wear and tear of the machine can be minimized. The laser path can be controlled by a simple optical refraction principle and is therefore suitable for products of all shapes. The laser beam can be focused in a small area and can be welded to small, closely spaced components. The range of weldable materials is large, and various heterogeneous materials can be joined to each other. Easy to automate high speed welding, digital or computer controlled. The switching device can share the laser source on multiple devices.

Disadvantages: The position of the weldment needs to be very precise and must be within the focus of the laser beam. When using a fixture with a weldment, it must be ensured that the final position of the weldment is within tolerance. The color of the resin material has an effect on the weldability. The equipment is expensive. It can be seen that under the premise of satisfying the sealing performance of the lamp, the laser welding has advantages in many aspects such as appearance, energy saving and environmental protection, and wide application. However, due to the high precision, the corresponding products and fixtures are required to have strict dimensional tolerance requirements.

Production conditions are high. Laser welding technology has many requirements for dimensional accuracy. Firstly, the laser path of the whole part of the welded part should be simulated. Combined with the shape of the welded part, the allowable positional deviation can be calculated. In actual production, not only the deformation of the product itself, but also the dimensions and tolerances that may cause positional deviations such as the use of a jig. At the same time, the parameter setting of the laser device and the pressurizing device is also complicated. The usage conditions vary greatly. Nowadays, the application of laser welding technology in the lamp industry has matured, but due to the different shape of the lamp, the connection with the car body is different, etc., different regions and different use conditions. Therefore, a series of methods are needed before mass production to evaluate whether the product meets the conditions for mass production.

The lights and the body are generally bolted, and the lights will not be released during installation, resulting in long-term stress in the lights. This stress acts on the welded portion and may cause separation of the welded portion. Therefore, in the product design stage, the simulation software should be used to simulate the stress that may be generated during the installation of the luminaire. If the stress is below the safe value, it is judged as qualified.

Laser welding engineering needs to consider various problems that may lead to poor welding in the actual production process. Common problems to be considered are: working size, laser incident angle, laser refraction angle, light source position, pressurization angle, pressure, fixture Dimensional tolerances, operator safety, etc. The dimensional tolerance of the jig is small, but it cannot be ignored. It is closely related to whether the laser can effectively enter the welding part. The product should be designed in consideration of the extreme position deviation state, whether the laser can ensure that the laser can enter the welded part effectively all the time without energy loss or even reflection.

As the most common means of transportation, consumers must ensure that the performance of the lamps meets the standards under the harsh conditions of high-speed driving on bumpy roads. Therefore, even if the airtight inspection is passed, it is necessary to evaluate and analyze the tensile strength of the welded portion. The evaluation method is: cutting the welded portion of the lamp, fixing the side, and forcibly pulling the welded member away from the welded portion by using a tensile force meter. Determine if the force is above a safe value. The parameter setting of the laser welding equipment is complicated, and the time, pressure and displacement will affect the welding quality. The displacement can be measured by cutting the section, and the relationship between the amount of pressing and the tensile strength can be intuitively determined. The method comprises the steps of cutting the welding zone into several sections, and grinding the section to clearly distinguish the state of the two material boundary lines, and measuring whether the pressing amount of the melted component is higher than a safe value.

After all the qualities of laser welding meet the requirements, the product enters the stage of mass production, but the changes of product shape and production site occur from time to time. Because the precision of laser welding and every minor change have the possibility of affecting the welding quality, the welding quality should be continuously evaluated after the product enters the stage of mass production. The commonly used evaluation methods are: air tightness inspection method, blow-off test method, damage test method and so on. The method of air tightness inspection is to place the laser welded parts on the fixture, pressurize the opening, observe whether the barometer reading has changed, and judge whether the barometer is qualified by keeping the barometer unchanged. This method is suitable for all kinds of welding processes, and the whole product is generally inspected.