About the Injecting Method of Protective Atmosphere When Doing Laser Welding

  • By:Iris Liang
  • Date:2021/12/01

There are currently two main ways to inject in the protective atmosphere: one is to blow the protective atmosphere on the side shaft side, and the other is the coaxial protective atmosphere.

How to choose the two blowing methods should be considered in many ways. In most cases, it is recommended to use side blowing protective atmosphere.

The principle of choosing the method of blowing protective atmosphere

The first thing that needs to be clear is that the so-called "oxidized" of the weld is only an easy-to-understand term. Theoretically, some components in the weld and the components in the air react chemically to cause the quality of the weld to deteriorate. The most common is that the more active metal components of the weld chemically react with oxygen, nitrogen, and hydrogen in the air at a certain temperature.

To prevent the weld from being "oxidized" is to reduce or prevent such active components from contacting the metal components in the weld at high temperatures. As we all know, high temperature can make molecular activities more active. This high temperature state is not only the molten pool metal, but also includes the entire time period from when the weld metal is melted to when the molten pool metal solidifies and its temperature drops to a certain temperature.

For example, when welding titanium alloy, when the temperature reaches 300℃ or higher, titanium alloy can quickly absorb hydrogen in the air; when it is above 450℃, it will quickly absorb oxygen in the air; when it reaches 600℃ or above, it can quickly absorb air In the nitrogen. Therefore, after the titanium alloy welds are solidified and the temperature is reduced to at least 300 ℃, they need to be effectively protected to isolate the complex air from contacting the welds, otherwise the welds will be "oxidized." It even affects the degree of bonding between the molten pool and the base metal.

In order to better ensure the quality of the weld during the time the weld is cooled to a specific temperature, Hangao Tech (SEKO Machinery) has innovatively added a protective atmosphere box in the welding section of the high standard welding pipe manufacturing machinery. When the welding torch is working, a protective atmosphere is automatically injected into the box to maintain a certain concentration at a certain flow rate to achieve the purpose of driving out the air. A protective atmosphere tunnel with a length of about 30 cm is also added to prevent the residual temperature from oxidizing the weld.

From the above description, we can know that injecting protective atmosphere not only needs to protect the weld pool, but also requires protection of the area that has not solidified after the welding is completed, so most of them will use side-shaft side blowing protective atmosphere. Because compared with the coaxial protection method, this method has a wider protection range, especially for the area where the weld has just solidified.

However, for engineering applications, not all products can be welded with side-shaft side blowing protective gas. For some special products, only the method of coaxial blowing of shielding gas can be used, and the joint form of the product structure needs to be selected in a targeted manner.

Selection of specific protective atmosphere blowing method

1) Straight weld

If the weld shape of the product is straight, it can be a butt joint, lap joint, internal corner joint or overlap weld joint. This type of product is more appropriate to use side-blow protective atmosphere.

2) Plane closed graphic weld

If the weld shape of the product presents a closed shape such as a flat circle, a flat polygon, and a flat polyline, and it is a joint form such as a butt joint, a lap joint, and a overlap weld joint. This type of product adopts the coaxial shielding gas method, and the welding effect will be better.

The type of protective atmosphere and the choice of delivery method directly affect the quality, efficiency and cost of welding production. However, considering the diversity of welding materials, in actual operation, the selection of welding gas types and delivery methods is also more complicated, and various influencing factors need to be considered comprehensively, such as: product material, welding process method, welding seam position, and welding effect. It is recommended to conduct a welding test first and choose a more suitable delivery method and welding gas to achieve a more ideal welding result.

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