6 Main Factors Affecting Laser Deep Penetration Welding

  • By:Iris Liang
  • Date:2021/12/17

Laser welding: It is an efficient and precise welding method that uses a high-energy density laser beam as a heat source. Laser welding is one of the important aspects of the application of laser material processing technology in laser welding pipe production line. As one of the two basic modes of laser welding (the other is heat conduction welding), laser deep penetration welding is more and more widely used.

    

Deep penetration, or deep penetration welding. It is usually used for welding thicker materials with high laser power. In deep penetration welding, the lasers are focused together to create a very high power density on the workpiece. In fact, the extremely high temperature at the location where the laser beam is focused will vaporize the metal, causing a blind hole (that is, a deep penetration hole) to appear in the molten metal pool. The metal vapor pressure will block the surrounding molten metal, so that the blind hole is always open during the welding process. The laser power is mainly absorbed by the melt at the boundary between the vapor and the melt and the wall of the deep penetration hole. The focused laser beam and the deep penetration hole continue to move along the welding track. The welding material melts in front of the deep penetration hole and resolidifies at the back to form a weld.

   

The factors that affect the effect of laser deep penetration welding are:

1. Laser power density

The prerequisite for deep penetration welding is to focus the laser spot so that it has a sufficiently high power density, so the laser power density has a decisive influence on the weld formation. The laser power controls the penetration depth and welding speed at the same time. For a laser beam with a certain diameter, when the laser power is increased, the penetration deepens and the welding speed increases.

  

There is generally a critical value for the laser power to reach a certain welding penetration. When this critical value is reached, the molten pool will boil violently. However, after exceeding the critical value, the penetration will decrease sharply. In addition, due to the presence of metal vapor, small holes are formed in the molten pool. The small hole is the key to achieve deep penetration welding. It should be noted that the focal spot power density is not only proportional to the laser power, but also related to the laser beam and focusing optical path parameters.

  

2. Welding speed

In the deep penetration welding process, the welding speed is inversely proportional to the penetration depth. In the case of keeping the laser power constant, increasing the welding speed will reduce the heat input and the penetration depth. Therefore, appropriately reducing the welding speed can increase the penetration depth. But be careful: too low a speed will cause the material to melt too much, and the material will be welded through. Therefore, when the production line needs to change molds to produce welded pipes of other specifications, we have to spend a lot of time and energy to re-adjust the data of the production line to obtain optimal efficiency. How to formulate the production process to help users reduce costs is one of the directions Hangao Tech (SEKO Machinery) has been committed to researching. Therefore, we recommend that customers better equip each industrial stainless steel welded pipe production line tube mill machine with an intelligent control system. It can not only make the operation of the production line more intelligent, but also track and store production data. Various production data will be stored in the database for up to one year, which is convenient for users to deploy at any time.

  

3. Focus position

When performing deep penetration welding, in order to maintain sufficient power density, the focus position is very important. The change of the relative position of the focus and the surface of the workpiece directly affects the width and depth of the weld. Only when the focal point is located at a suitable position on the surface of the workpiece, the resulting weld can form a parallel section and obtain the maximum penetration depth.

   

4. Shielding gas

The role of shielding gas has two points: 1) Exclude the air in the welding local area, and protect the working surface from oxidation; 2) Prevent the generation of plasma cloud during high-power laser welding.

    

5. Butt gap between strip edges

The gap in the butt joint of the strip edge, this gap is directly related to the penetration depth and the width of the weld. In deep penetration welding, if the joint gap exceeds the spot size, it cannot be welded; if the joint gap is too small, sometimes the process will produce undesirable effects such as overlapping of strip edges and difficulty in fusion; if the joint gap is too large, it is easy to cause weld penetration Condition: Slow welding can make up for some weld defects caused by excessive gaps, while high-speed welding will narrow the welds, which makes assembly requirements more stringent.

  

6. Material nature

The absorption of laser by strip steel material determines the efficiency of laser welding. There are two factors that affect the material's absorption rate of laser light:

 

1) Material resistivity. After measuring the absorptivity of the polished surface of different materials, it is found that the absorptivity of the material to the laser is proportional to the square root of the resistivity. The resistivity will change with temperature, the higher the temperature, the greater the resistance.

 

2) The surface state of the material has an important influence on the beam absorption rate, and therefore has a significant effect on the welding effect.

   

Nowadays, the development of the laser industry is more and more extensive, and more and more people know about laser welding. Laser welding has advantages over traditional welding. However, when using it, we still need to choose the most suitable welding method based on our actual situation, such as whether the material is suitable for laser welding, economic conditions, etc.

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