How To Correctly Use Gas In Laser Welding

In laser welding, the shielding gas will affect the weld forming, weld quality, weld depth and weld width. In most cases, blowing protective gas will have a positive effect on the weld, but it may also have an adverse effect.

1. The correct blowing into the protective gas will effectively protect the weld pool to reduce or even avoid oxidation.

2. The correct blowing of the protective gas can effectively reduce the splash generated during the welding process.

3. The correct blowing of the protective gas can promote the uniform spread of the weld pool during solidification, so that the weld forming is uniform and beautiful.

4. The correct blowing of the protective gas can effectively reduce the shielding effect of the metal vapor plume or plasma cloud on the laser, and increase the effective utilization rate of the laser.

5. The correct blowing of the protective gas can effectively reduce the porosity of the weld.

As long as the gas type, gas flow rate, and injection method are selected correctly, the ideal effect can be achieved.

However, incorrect use of shielding gas can also have adverse effects on welding.

However, incorrect use of shielding gas can also have adverse effects on welding.

1. Incorrect blowing of shielding gas may cause the weld to deteriorate.

2. Choosing the wrong gas type may cause cracks in the weld, and may also lead to a reduction in the mechanical properties of the weld.

3. Choosing the wrong gas to blow in The flow rate may cause more serious oxidation of the weld (whether the flow rate is too large or too small), and may also cause the weld pool metal to be seriously disturbed by external forces, resulting in weld collapse or uneven formation.

4. Choose the wrong gas injection method It will cause the weld to have no protective effect or even basically no protective effect or have a negative impact on the weld shape.

5. Blowing in the shielding gas will have a certain impact on the weld penetration, especially when welding thin plates, it will reduce the welding depth. Deep seam penetration.

Commonly used laser welding protective gases mainly include N2, Ar, and He. Their physical and chemical properties are different, and therefore their effects on the welds are also different.

1. Nitrogen(N2)

The ionization energy of N2 is moderate, higher than that of Ar and lower than that of He. The degree of ionization under the action of laser is average, which can better reduce the formation of plasma cloud, thereby increasing the effective utilization of the laser.Nitrogen can chemically react with aluminum alloys and carbon steel at a certain temperature to produce nitrides, which will increase the brittleness of the weld and reduce the toughness, which will have a greater adverse impact on the mechanical properties of the weld joint. , so it is not recommended to use nitrogen to protect aluminum alloy and carbon steel welds.

The nitride produced by the chemical reaction between nitrogen and stainless steel can improve the strength of the weld joint and will help improve the mechanical properties of the weld. Therefore, nitrogen can be used as a protective gas when welding stainless steel.

2. Argon

Ar has a relatively low ionization energy and a high degree of ionization under the action of laser, which is not conducive to controlling the formation of plasma clouds and will have a certain impact on the effective utilization of the laser. However, Ar activity is very low and it is difficult to chemically react with common metals. reaction, and the cost of Ar is not high. In addition, the density of Ar is relatively large, which is conducive to sinking to the top of the weld pool and can better protect the weld pool, so it can be used as a conventional shielding gas.

3.  Helium

He has the highest ionization energy, and the degree of ionization under the action of laser is very low. It can well control the formation of plasma clouds. The laser can act well on metals. WeChat public account: micro welder, and He activity is very low and basically not harmful. It reacts chemically with metal and is a good weld protective gas. However, the cost of He is too high, and this gas is generally not used in mass-produced products. He is generally used for scientific research or products with very high added value.

There are currently two main ways of blowing protective gas: One is side-axis blowing protective gas. The other is coaxial protective gas.

The specific choice between the two blowing methods depends on comprehensive considerations. Generally, it is recommended to use the side blowing protective gas method.

First of all, it needs to be made clear that the so-called "oxidation" of the weld is just a common name. Theoretically, it refers to the chemical reaction between the weld and harmful components in the air, resulting in the deterioration of the quality of the weld. Commonly, the weld metal is oxidized at a certain temperature. Chemically reacts with oxygen, nitrogen, hydrogen, etc. in the air.

To prevent the weld from being "oxidized" is to reduce or avoid the contact of such harmful components with the weld metal at a high temperature, which is not only the molten pool metal, but the entire time period from the time the weld metal is melted until the molten pool metal is solidified and its temperature is reduced below a certain temperature.

For example, titanium alloy welding, when the temperature above 300 ° C can quickly absorb hydrogen, above 450 ° C can quickly absorb oxygen, above 600 ° C can quickly absorb nitrogen, so titanium alloy weld after solidification and the temperature is reduced to below 300 ° C this stage need to be effective protection, otherwise it will be "oxidized".

It is not difficult to understand from the above description that the blown protective gas not only needs to timely protect the weld pool, but also needs to protect the just-solidified area that has been welded. Therefore, the side-blown protective gas shown in Figure 1 is generally adopted, because the protection of this way is wider than that of the coaxial protection in Figure 2. In particular, it has better protection for the area where the weld has just solidified.

Side-shaft side blowing For engineering applications, not all products can use side-shaft side blowing protective gas. For some specific products, only coaxial protective gas can be used. The specific requirements need to be determined from the product structure and joint form. Targeted selection.

1. line welding

The shape of the weld seam of the product is linear, and the joint form can be a butt joint, a lap joint, an internal angle joint or a lap welding joint. For this type of product, it is better to use side-axis side-blown protective gas.

2. Flat closed pattern weld

The weld shape of the product is a closed shape such as a flat circular shape, a flat polygonal shape, a flat multi-segment linear shape, etc. The joint forms can be butt joints, lap joints, overlap welding joints, etc. This type of products are all used as shown in Figure 2 The coaxial protective gas method is better.

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