In laser welding, the shielding gas affects the shape of the weld, the quality of the weld, the depth and width of the weld, and in most cases, blowing in the shielding gas will have a positive effect on the weld, but it may also have a negative effect.
Positive effects:
1. The correct blowing of shielding gas will effectively protect the weld pool from oxidation;
2. The correct blowing of shielding gas can effectively reduce the spatter generated during the welding process;
3. The correct blowing into the protective gas can be prompted to weld the molten pool solidified evenly spread, making the weld molding uniform and beautiful;
4. The correct blowing into the protective gas can effectively reduce the metal vapor plume or plasma cloud on the laser shielding effect, increase the effective utilization of laser;
5. The correct blowing into the protective gas can effectively reduce the weld porosity.
As long as the gas type, gas flow rate and blowing method are correctly selected, ideal results can be obtained.
However, incorrect use of shielding gas can also bring adverse effects to the welding.
The unfavorable effects are as follows:
1. Incorrect blowing in of shielding gas may lead to deterioration of the weld:
2. Selection of the wrong type of gas may lead to cracks in the weld and may also lead to a reduction in the mechanical properties of the weld;
3. Choose the wrong gas blowing into the flow may lead to more serious oxidation of the weld (whether the flow is too large or too small), may also lead to the weld molten pool of metal by external interference serious cause of weld collapse or molding uneven;
4. Choose the wrong gas blowing method will lead to the weld can not achieve the protective effect or even basically no protective effect or negative impact on the weld molding;
5. Blowing into the shielding gas will have a certain impact on the weld depth, especially when thin plate welding, will reduce the weld depth.
Types of shielding gas
Commonly used laser welding shielding gas is mainly N2, Ar, He, its physical and chemical properties are different, and therefore the effect on the weld is also different.
1. Nitrogen N2
N2 ionization energy moderate, higher than Ar, lower than He, in the laser action of ionization degree is general, can be better to reduce the formation of plasma cloud, thus increasing the effective utilization of laser.
Nitrogen at a certain temperature can be chemical reaction with aluminum alloy, carbon steel, produce nitride, will improve the weld brittleness, toughness reduction, the mechanical properties of welded joints will have a greater adverse effect, so do not recommend the use of nitrogen on aluminum alloy and carbon steel weld protection.
Nitrogen and stainless steel chemical reaction produces nitride can improve the strength of the weld joint, will be conducive to the mechanical properties of the weld to improve, so you can use nitrogen as a protective gas when welding stainless steel.
2. Argon Ar
Ar's ionization energy is relatively the lowest, under the action of the laser ionization degree is high, is not conducive to controlling the formation of the plasma cloud, will have a certain impact on the effective utilization of the laser, but the Ar activity is very low, it is difficult to have a chemical reaction with the common metal, and Ar cost is not high;
In addition, Ar's density is large, conducive to sinking to the weld pool above the weld pool, can better protect the weld pool, so it can be used as a conventional protective gas.
3. Helium He
He of the highest ionization energy, ionization under the action of the laser is very low, can be very good control of the formation of plasma clouds, the laser can be very good role in the metal, and He activity is very low, basically do not have a chemical reaction with the metal, is a very good weld protection gas.
However, the cost of He is too high, generally mass production type products will not use the gas, He is generally used for scientific research or very high value-added products.
How to choose the two blowing methods is a comprehensive consideration of various aspects, and generally it is recommended to use the side blowing of protective gas.
Protective gas blowing method selection principles
First of all, it should be clear that the so-called weld is "oxidized" is only a common name, theoretically refers to the weld and the harmful components in the air chemical reaction leads to poor quality of the weld, commonly weld metal at a certain temperature and the oxygen, nitrogen, hydrogen and other chemical reactions in the air.
Preventing the weld from being "oxidized" means reducing or avoiding the contact of such hazardous components with the weld metal at a high temperature, which is not just the molten pool metal, but the entire time period from the time the weld metal is melted until the pool metal is solidified and its temperature is reduced to below a certain temperature.
Example
For example, titanium alloy welding, when the temperature is above 300 ℃ can quickly absorb hydrogen, 450 ℃ can quickly absorb oxygen, 600 ℃ can quickly absorb nitrogen, so titanium alloy weld in the solidification and the temperature is lowered to below 300 ℃ in this stage need to be effective protection effect, otherwise it will be "oxidized".
From the above description is not difficult to understand, blowing into the protective gas not only need to timely protection of the weld pool, but also need to have been welded just solidified area for protection, so the general use of Figure 1 shown in the side of the axial side of the blowing protective gas, because of this way of protection relative to the coaxial protection in Figure 2 in the protection of a wider range of protection, especially for the weld just solidified area has a better protection.
Side shaft side blowing for engineering applications, not all products can be used for side shaft side blowing protective gas way, for some specific products, can only be used coaxial protective gas, specific needs from the product structure and the form of joints for targeted selection.
