The invisible and intangible "gas", which cannot be ignored in laser welding, refers to the shielding gas. Its selection directly affects the quality, efficiency and cost of welding production. Today, Hangao Tech will talk with you about shielding gas related knowledge.
1. The role of protective atmosphere
In laser welding, shielding gas will affect the weld shape, weld quality, weld penetration and penetration width. In most cases, blowing shielding gas will have a positive effect on the weld, but it may also bring come to an adverse effect.
Positive effects
1) The correct insufflation of shielding gas will effectively protect the weld pool to reduce or even avoid oxidation;
2) The correct blowing of shielding gas can effectively reduce the spatter generated during the welding process;
3) The correct insufflation of protective gas can promote the uniform spreading of the weld pool when it solidifies, making the weld shape uniform and beautiful;
4) Correct blowing of protective gas can effectively reduce the shielding effect of metal vapor plume or plasma cloud on laser, and increase the effective utilization rate of laser;
5) Correct blowing of shielding gas can effectively reduce weld porosity.
As long as the gas type, gas flow rate, and insufflation method are selected correctly, the ideal effect can be obtained. However, incorrect use of shielding gas can also have adverse effects on welding.
Negative Effects
1) Improper insufflation of shielding gas may result in poor weld seams;
2) Choosing the wrong type of gas may cause cracks in the weld, and may also lead to a decrease in the mechanical properties of the weld;
3) Choosing the wrong gas blowing flow rate may lead to more serious weld oxidation (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 forming;
4) Choosing the wrong gas injection method will result in the weld not reaching the protective effect or even basically no protective effect or negatively affecting the weld formation;
5) Insufflation of protective gas will have a certain impact on the weld penetration, especially when welding thin plates, it will reduce the weld penetration.
2. Types of protective gas
Commonly used shielding gases for laser welding mainly include nitrogen, argon, and helium, and their physical and chemical properties are different, so the effect on the weld is also different.
1) Nitrogen
The ionization energy of nitrogen is moderate, higher than that of argon, lower than that of helium, and 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 rate of laser. Nitrogen can chemically react with aluminum alloy and carbon steel at a certain temperature to produce nitrides, which will increase the brittleness of the weld, reduce the toughness, and have a greater adverse effect on the mechanical properties of the weld joint, so it is not recommended to use nitrogen for Aluminum alloy and carbon steel welds for protection.
The nitrogen produced by the chemical reaction between nitrogen and stainless steel can increase the strength of the weld joint, which will help improve the mechanical properties of the weld, so nitrogen can be used as a shielding gas when welding stainless steel.
2) Argon
The ionization energy of argon is relatively the lowest, and the ionization degree is high 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 laser. However, argon has very low activity and is difficult to combine with common metals. A chemical reaction occurs, and the cost of argon is not high. In addition, the density of argon is high, which is conducive to sinking to the top of the weld pool, which can better protect the weld pool, so it can be used as a conventional shielding gas use.
3) Helium
The ionization energy of helium is the highest, and the ionization degree is very low under the action of laser, which can well control the formation of plasma cloud. The laser can act on metals well, and the activity of helium is very low, and it basically does not chemically react with metals. , is a very good welding seam shielding gas, but the cost of helium is too high, and generally mass-produced products do not use this gas. Helium is generally used for scientific research or products with very high added value.
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