The Main Process Parameters Of Deep Welding Of Laser Welding Machine

- Oct 31, 2017 -

(1) laser power. Laser welding there is a laser energy density threshold, below this value, the depth is very shallow, once reached or exceeded this value, the penetration will be greatly improved. Only when the laser power density on the workpiece exceeds the threshold (related to the material), the plasma will be generated, which marks the progress of the stable deep welding. If the laser power is below this threshold, the workpiece is only surface melted, that is, welding to stabilize the heat conduction type. And when the laser power density is in the vicinity of the critical conditions for the formation of small holes, welding machine the deep welding and conducting welding alternately become unstable welding process, resulting in large fluctuations in penetration depth. Laser deep welding, the laser power while controlling the penetration depth and welding speed. The weld penetration is directly related to the beam power density and is a function of the incident beam power and the beam focal spot. In general, for a certain diameter of the laser beam, the penetration depth increases as the beam power increases.

(2) beam focal spot. The beam spot size is one of the most important variables of laser welding because it determines the power density. But for high-power lasers, the measurement of it is a problem, welding machine although there are already a lot of indirect measurement techniques.

The beam spot diffraction limit spot size can be calculated according to the theory of light diffraction, but the actual spot is larger than the calculated value due to the presence of the focusing lens aberration. The simplest method of measurement is the isothermal contour method, that is, with thick paper charred and penetrate the polypropylene plate to measure the focal spot and perforation diameter. This method through the measurement practice, master the laser power size and beam action time.

(3) material absorption value. The absorption of the material depends on some important properties of the material, such as absorbency, reflectivity, thermal conductivity, melting temperature, evaporation temperature, etc., of which the most important is the absorption rate.

The factors that affect the absorptivity of the material to the laser beam include two aspects: the first is the resistance coefficient of the material. After absorbing the absorbance of the material, it is found that the absorptivity of the material is proportional to the square root of the resistance coefficient and the resistance coefficient And then the surface state (or finish) of the material has a more important effect on the absorption rate of the beam, welding machine which has a significant effect on the welding effect.

(4) welding speed. Welding speed on the depth of penetration, increase the speed will make the depth of shallow, but the speed is too low will lead to excessive melting of materials, workpiece welding wear. Therefore, for a certain laser power and a certain thickness of a particular material has a suitable welding speed range, and in which the corresponding speed value can get the maximum depth of penetration.

(5) to protect the gas. Laser welding process often use inert gas to protect the molten pool, when some of the material does not care about the surface oxidation can also not consider the protection, but for most applications are often used helium, argon, welding machine nitrogen and other gases for protection, so that the workpiece in the The process of welding from oxidation.

Helium is not easy to ionize (ionization energy is high), allowing the laser to pass smoothly, the beam energy is unimpeded to the workpiece surface. This is the most effective shielding gas used in laser welding, but the price is more expensive.

Argon is relatively cheap, the density is large, so the protection effect is better. But it is susceptible to high-temperature metal ionization, the results shield some of the beam shot to the workpiece, welding machine reducing the welding of the effective laser power, but also damage the welding speed and penetration. The surface of the weldment protected by argon is smoother than when using helium.

Nitrogen is the cheapest as a protective gas, but is not suitable for certain types of stainless steel welding, mainly due to metallurgical problems such as absorption, and sometimes in the overlap area to produce pores.

The second effect of using a protective gas is to protect the focusing lens from metal vapor contamination and sputtering of liquid droplets. Especially in the high-power laser welding, because of its spray becomes very strong, then the protection of the lens is more necessary. In the case of

The third role of the protective gas is to disperse the plasma shields produced by high power laser welding. The metal vapor absorbs the laser beam into a plasma cloud, and the protective gas around the metal vapor is ionized by heat. welding machine If the plasma is present too much, the laser beam is consumed to some extent by the plasma. The plasma is present as a second energy on the working surface, making the depth of penetration shallow and the surface of the weld pool is widened. The electron recombination rate is increased by increasing the collision of electrons with ions and neutral atoms to reduce the electron density in the plasma. The higher the neutral atom, the higher the collision frequency, the higher the recombination rate; on the other hand, only the protective gas with high ionization energy will not increase the electron density due to the ionization of the gas itself. In the case of

From the table we can see that the size of the plasma cloud and the use of different shielding gases change, helium minimum, followed by nitrogen, the use of argon when the largest. The larger the plasma size, the deeper the penetration. The reason for this difference is due to the fact that the degree of ionization of the gas molecules is different, and the difference in diffusion of metal vapor due to the different density of the shielding gas. In the case of

Helium ionization is minimal and the density is minimal, and it can quickly get rid of the rising metal vapor from the metal bath. welding machine So helium for the protection of gas, can maximize the inhibition of plasma, thereby increasing the penetration depth, improve the welding speed; due to light and can escape, not easy to cause stomata. Of course, from the actual effect of our welding, with the effect of argon protection is also good.

The effect of plasma cloud on the penetration depth is most pronounced in the low welding velocity zone. When the welding speed increases, its impact will be weakened.

The protective gas is injected through the nozzle mouth at a certain pressure to reach the surface of the workpiece, the nozzle of the hydrodynamic shape and the size of the export diameter is very important. It must be large enough to drive the sprayed gas to cover the welding surface, but in order to effectively protect the lens, to prevent metal vapor contamination or metal splash damage to the lens, the nozzle size should be limited. The flow should be controlled, otherwise the protective layer of the laminar flow into turbulence, the atmosphere involved in the pool, the final formation of stomata.

In order to improve the protective effect, it is also possible to use an additional lateral blowing method, that is, through a smaller diameter nozzle to the protective gas at a certain angle directly into the deep welding of small holes. welding machine The shielding gas not only suppresses the plasma cloud on the surface of the workpiece, but also exerts an influence on the formation of the plasma and the pores in the hole, and the penetration depth is further increased to obtain the ideal weld. However, this method requires precise control of air flow size, direction, or prone to turbulence and damage the pool, resulting in the welding process is difficult to stabilize.

(6) lens focal length. Welding is usually used to focus on the convergence of laser, the general use of 63 ~ 254mm (2.5 "~ 10") focal length lens. Focus spot size and focal length is proportional to the shorter focal length, the smaller the spot. But the length of the focal length also affect the depth of focus, that is, the depth of focus increases with the focal length, so short focal length can increase the power density, but the focus is small, you must accurately maintain the lens and workpiece spacing, and the depth is not large. Due to the splash and laser modes produced during the welding process, the actual focal length of the actual welding is more than the focal length of 126mm (5 "). When the joints are large or need to increase the spot size to increase the weld A lens with a focal length of 254 mm (10 ") is selected. In this case, a higher laser output power (power density) is required in order to achieve a deep hole effect.

When the laser power exceeds 2kW, especially for 10.6μm CO2 laser beam, the use of special optical materials constitute the optical system, welding machine in order to avoid the risk of optical damage to the lens, often use reflective focus method, the general use of polished copper mirror as a mirror The Due to its efficient cooling, it is often recommended for high power laser beam focusing.

(7) focus position. When welding, in order to maintain a sufficient power density, the focus position is essential. The change of the relative position between the focal point and the workpiece surface directly affects the width and depth of the weld.

In most laser welding applications, the position of the focus is usually set at about 1/4 of the depth of penetration required beneath the surface of the workpiece.

(8) laser beam position. For laser welding of different materials, the laser beam position controls the final quality of the weld, especially in the case of butt joints. For example, when the quenched steel gear is welded to a low carbon steel drum, proper control of the laser beam position will facilitate the generation of welds consisting mainly of low carbon components, which have good crack resistance. In some applications, the geometrical shape of the workpiece to be welded requires an angle of deflection of the laser beam. When the deflection angle between the beam axis and the joint plane is within 100 degrees, the absorption of laser energy by the workpiece is not affected.

(9) welding start, the termination of the laser power gradually, gradually down control. Laser deep welding, regardless of the depth of the weld, welding machine hole phenomenon is always there. When the welding process is terminated and the power switch is turned off, the pit will appear at the end of the weld. In addition, when the laser welding layer covers the original weld, there will be excessive absorption of the laser beam, resulting in overheating or produce pores.

In order to prevent the above phenomenon, the power start and stop point preparation procedures, so that the power start and termination time becomes adjustable, that is, the starting power of electronic methods in a short time from zero to set the power value, welding machine and adjust the welding Time, and finally the power at the end of the welding from the set power gradually reduced to zero.

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