The most commonly used welding method for stainless steel is manual welding (MMA), followed by metal arc welding (MIG/MAG) and tungsten inert gas welding (TIG).

Preparation before welding: The thickness of less than 4mm does not need to be broken, weld directly, and one side is welded through at one time. Butt welds with a thickness of 4 to 6 mm can be welded on both sides without opening the joint. Above 6 mm, generally open V or U, X-shaped groove.

Secondly: remove oil and scale from welding parts and filler wires. to ensure welding quality.

Welding parameters: including welding current, tungsten electrode diameter, arc length, arc voltage, welding speed, protective air flow, nozzle diameter, etc.

(1) Welding current is a key factor in determining the shape of the weld. It is usually determined based on the weldment material, thickness, and groove shape.

(2) The diameter of the welding electrode is determined by the size of the welding current. The greater the current, the greater the diameter.

(3) Welding arc and arc film, the arc length range is about 0.5 to 3mm, and the corresponding arc voltage is 8~10V.

(4) Welding speed: The current size, sensitivity of the weldment material, welding position and operation method should be taken into consideration when selecting.

1 Manual welding (MMA):

Manual welding is a very common and easy-to-use welding method. The length of the arc is adjusted by human hands and is determined by the size of the gap between the welding rod and the workpiece. At the same time, when used as an arc carrier, the welding rod is also a weld filling material.

This welding method is very simple and can be used to weld almost all materials. For outdoor use, it has good adaptability and is no problem even when used underwater. In electrode welding, the arc length is determined by the human hand: when you change the gap between the electrode and the workpiece, you also change the length of the arc. In most cases, welding uses direct current, and the electrode serves as both an arc carrier and a Weld filler material. The electrode is composed of an alloy or non-alloy metal core wire and a welding rod coating. This coating protects the weld from air and stabilizes the arc. It also causes the formation of a slag layer, protecting the weld and shaping it. Welding rods can be either titanium or alkaline, depending on the thickness and composition of the coating. Titanium welding rods are easy to weld, the welds are flat and beautiful, and the welding slag is easy to remove. If the electrode is stored for a long time, it must be rebaked because moisture from the air will quickly accumulate in the electrode.

Key points and precautions for stainless steel flux-cored wire welding:

(1) Use a flat characteristic welding power source, and use reverse polarity during DC welding. You can use an ordinary CO2 welder to weld, but please loosen the pressure on the wire feed wheel slightly.

(2) The protective gas is generally carbon dioxide gas, and the gas flow rate is 20~25L/min.

(3) The appropriate distance between the welding tip and the workpiece is 15~25mm.

(4) Dry elongation: The general welding current is about 15mm when the welding current is below 250A, and about 20~25mm when the welding current is above 250A.

2 MIG/MAG welding:

This is an automatic gas shielded arc welding method. In this method, the arc generates steady heat between the current carrier wire and the workpiece under a protective gas shield. The wire fed by the machine acts as a welding rod and melts under its own arc. Due to the versatility and specificity of the MIG/MAG welding method, it is still the most widely used welding method in the world and is suitable for steel, non-alloy steel, low alloy steel and high alloy-based materials. This makes it an ideal welding method for production and repair. When welding steel, MAG can meet the requirements of thin gauge steel plates with only 0.6mm thickness. The protective gas used here is reactive gas, such as carbon dioxide or mixed gas.

Key points and precautions for MIG welding of stainless steel:

(1) Use a flat characteristic welding power source, and use reverse polarity for DC (welding wire connected to the positive electrode).

(2) Generally, pure argon (99.99% purity) or Ar+2%O2 is used, and the flow rate is preferably 20~25L/min.

(3) Arc length: MIG welding of stainless steel is generally performed under spray transition conditions, and the voltage should be adjusted to an arc length of 4 to 6 mm.

(4) Wind protection: MIG welding is easily affected by wind, and sometimes breeze can cause pores. Therefore, wind protection measures should be taken wherever the wind speed is above 0.5m/sec.

(5) Moisture-proof: When welding outdoors, the workpiece must be protected from moisture to maintain the protective effect of the gas.

3 TIG welding:

The arc is generated between the refractory tungsten welding wire and the workpiece. The generally used protective gas is pure argon, and the fed welding wire is not charged. It can be fed by hand or mechanically. There are also some specific uses where welding wire does not need to be fed. The material to be welded determines whether to use direct current or alternating current: when using direct current, the tungsten welding wire is set to the negative electrode, because it has deep welding penetration ability, which is very suitable for different types of steel, but for the weld pool There is no "cleaning effect" whatsoever.

The main advantage of the TIG welding method is that it can weld a wide range of materials, including workpieces with a thickness of 0.6mm and above. The materials include alloy steel, aluminum, magnesium, copper and its alloys, gray cast iron, Common dry, various bronzes, nickel, silver, titanium and lead. The main areas of application are the welding of thin and medium-thick workpieces and the use as a root pass on thicker sections.

Key points and precautions for stainless steel TIG welding:

(1) Use a power source with vertical external characteristics, and use positive polarity for DC (the welding wire is connected to the negative electrode).

(2) Generally suitable for welding thin plates below 6mm, with the characteristics of beautiful welding seam shape and small welding deformation.

(3) The protective gas is argon with a purity of 99.99%. When the welding current is 50~150A, the argon gas flow is 8~10L/min; when the current is 150~250A, the argon gas flow is 12~15L/min.

(4) The length of the tungsten electrode protruding from the gas nozzle is preferably 4 to 5 mm. In places with poor shielding such as fillet welds, it is 2 to 3 mm. In places with deep grooves, it is 5 to 6 mm. The distance from the nozzle to the workpiece generally does not exceed 15mm.

(5) In order to prevent the occurrence of welding pores, any rust, oil stains, etc. on the welding part must be cleaned up.

(6) The welding arc length is preferably 2~4mm when welding ordinary steel, and 1~3mm when welding stainless steel. If it is too long, the protection effect will be poor.

(7) During butt bonding, in order to prevent the back side of the underlying weld bead from being oxidized, the back side also needs to be protected by gas.

(8) In order to make the argon gas protect the welding pool well and facilitate the welding operation, the center line of the tungsten electrode and the workpiece at the welding location should generally maintain an angle of 80~85°, and the filler wire and the surface of the workpiece should generally maintain an angle of 80~85°. The angle should be as small as possible, generally around 10°.

(9) Wind protection and ventilation. In windy areas, be sure to take measures to block nets, and take appropriate ventilation measures indoors.