Power density is one of the most critical parameters in laser processing. Using a higher power density, in the microsecond time range, the surface can be heated to the boiling point, resulting in a large number of vaporization. Therefore, the high power density for material removal processing, such as drilling, cutting, sculpting favorable. For lower power densities, the surface temperature reaches the boiling point needs to go through a few milliseconds, before the surface vaporization, the bottom to reach the melting point, easy to form a good fusion welding. Therefore, in the conduction type brightest laser pointer welding, the power density in the range of 104 ~ 106W / cm2. Laser pulse waveform in laser welding is an important problem, especially for sheet welding is more important. When the high-intensity laser beam to the surface of the material, the metal surface will be 60 ~ 98% of the high power laser pointer energy reflected and lost, and the reflectivity with the surface temperature. During a laser pulse, the metal reflectivity changes greatly. Pulse width is one of the important parameters of pulse laser welding. It is not only an important parameter different from material removal and material melting, but also a key parameter to determine the cost and volume of processing equipment. Effect of defocusing on welding quality. Laser welding usually requires a certain degree of defocus, because the laser focal spot at the center of the power density is too high, easy to evaporate into holes. The power density distribution is relatively uniform across the planes away from the laser focus. There are two defocus modes: positive defocus and negative defocus. Focal plane is located above the workpiece is positive from the focus, otherwise negative out of focus. According to the theory of geometric optics, when positive and negative do an article equal, the corresponding power density on the plane is approximately the same, but in fact the shape of the pool is different. In the case of negative defocusing, a greater penetration depth is obtained, which is related to the formation of the bath. Experiments show that the burning laser pointer heating 50 ~ 200us material began to melt, the formation of liquid metal and the emergence of sub-vaporization, the formation of municipal pressure steam, and high speed jet, emitting dazzling white. At the same time, the high concentration vapor moves the liquid metal to the edge of the molten pool, forming a depression in the center of the bath. When the negative focus, the internal power density of the material is higher than the surface, easy to form a stronger melting, vaporization, so that the light energy to the deeper transmission material. Therefore, in practical applications, when the required depth of penetration is large, the use of negative out of focus; welding thin material, it is appropriate to use is out of focus. Laser welding process: between the chip and the chip welding, including butt welding, welding, welding penetration through the center, the center perforation melting welding four kinds of methods; wire and wire welding, including wire and wire butt welding, cross welding , Parallel lap welding, T-type welding and other four kinds of technology; wire and block components of the welding, the use of 2000mw laser pointer welding can be successfully achieved wire and block-like components of the connection, the size of the block can be arbitrary, Should pay attention to the geometric size of filament components; different metal welding, welding different types of metal to solve the weldability and weldability parameters range. Laser welding between different materials is only possible with certain combinations of materials. Laser brazing some components of the connection should not be laser welding, but can use the laser as a heat source, the implementation of brazing and brazing, the same laser welding has the advantage. There are many ways to use brazing, in which 5000mw laser pointer soldering is mainly used for printed circuit board welding, especially for chip components assembly technology. Advantages of using laser soldering compared with other methods: As the local heating, the component is not easy to produce thermal damage, heat affected zone is small, so the implementation of the soldering in the vicinity of thermal components; with non-contact heating, melting bandwidth, Need any auxiliary tools, double-sided printed circuit board in the double-sided components after processing equipment; repeat the operation of good stability. The laser beam is easy to realize the spectrophotometry, and can be divided into time and space by optical elements such as half mirror, mirror, prism, scanning mirror, etc. The laser beam is easy to be divided into two parts: the laser beam is easy to be controlled, Can be multi-point simultaneous symmetrical welding; 1000mw laser pointer brazing multi-purpose wavelength of 1.06um laser as a heat source can be used optical fiber transmission, it can be welded in the conventional way difficult to deal with parts of the processing, flexibility is good; focus, and easy to achieve multi-station device Of automation.
