Comprehensive introduction to TIG welding machines
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1. What is tig welder
TIG welding (Tungsten Inert Gas Welding), also known as non-melting extremely inert gas shielded arc welding. Whether it is manual welding or automatic welding of 0.5 to 4.0mm thick stainless steel, TIG welding is the most commonly used welding method. TIG welding with filler wire is often used for bottom welding of pressure vessels because the air tightness of TIG welding is better and can reduce the pores in the weld seam during pressure vessel welding. The heat source of TIG welding is a DC arc, the working voltage is 10 to 95 volts, but the current can reach 600 amps. The correct connection method of the welding machine is that the workpiece is connected to the positive electrode of the power supply, and the tungsten electrode in the welding torch is used as the negative electrode. The inert gas is usually argon.
2. How tig weld
The inert gas is fed through the welding torch to form a shield around the arc and the welding pool. To increase heat input, 5% hydrogen is generally added to the argon. However, when welding ferritic stainless steel, hydrogen cannot be added in argon. Gas consumption is about 3 to 8 liters per minute. During the welding process, in addition to blowing inert gas from the welding torch, it is also best to blow in gas to protect the back of the weld from under the weld.
If necessary, the weld pool can be filled with welding wire having the same composition as the austenitic material to be welded. When welding ferritic stainless steel, type 316 filler is usually used.
3. TIG welding classification
Tungsten argon arc welding is divided into three categories: manual welding, semi-automatic welding and automatic welding according to the operation mode. In manual tungsten argon arc welding, the movement of the welding gun and the addition of filler wire are completely manual operations; in semi-automatic tungsten argon arc welding, the movement of the welding gun is manually operated, but the filler wire is automatically fed by the wire feeding mechanism; in automatic tungsten argon arc welding, the filling wire is automatically fed by the wire feeding mechanism. During arc welding, if the workpiece has a fixed arc movement, the welding gun is installed on the welding trolley, and the traveling and filling wire of the trolley can be added with cold wire or hot wire. Hot wire refers to increasing the deposition speed. In some cases, such as thin plate welding or primer passes, it is sometimes not necessary to add filler wire.
Among the above three welding methods, manual tungsten arc welding is the most widely used, while semi-automatic tungsten arc welding is rarely used.
4. Welding power supply
During TIG welding, due to the small current density used and the low thermal conductivity of argon, the arc is basically not compressed and the static characteristics of the arc are horizontal. According to the requirements for the external characteristics of the power supply based on the static characteristics of the arc, whether AC power or DC is used The power supply should use a power supply with reduced external characteristics. Since small changes in arc length will cause large fluctuations in the welding power supply during TIG welding, the most ideal power supply for TIG welding is to use a power supply with vertical steep drop characteristics (such as a magnetic amplifier silicon arc welding rectifier), which can Eliminates current fluctuations caused by changes in arc length.
AC power is generally used when TIG welding aluminum, magnesium and their alloys.
5. How to tig weld aluminum
(1) Welding principle
TIG welding uses the arc formed between the tungsten electrode and the workpiece to generate a large amount of heat to melt the area to be welded, and at the same time, a filler wire is added to obtain a strong welding joint. Since oxide films are easy to form on the surface of aluminum alloys, when using TIG welding, the “cathode atomization” characteristic of AC welding can effectively remove the oxide film and ensure welding quality.
(2) Equipment and material preparation
Welding equipment:
TIG welder (AC power supply recommended)
Argon protection device
welding nozzle
Welding materials:
Tungsten electrode (commonly used tungsten electrode materials include pure tungsten, thoriated tungsten and cerium tungsten)
Aluminum welding wire (select the appropriate welding wire according to the type of aluminum alloy welded)
Protective gas (pure argon, flow rate is generally 5~15L/min)
(3)Tig welding aluminum settings
Nozzle aperture and protective gas flow rate:
Nozzle hole diameter: 5 ~ 22 mm
Protective gas flow: 5～15L/min
The extension length of the tungsten electrode and the distance from the nozzle to the workpiece:
Tungsten electrode extension length: 5 to 6 mm for butt welds, 7 to 8 mm for fillet welds
Distance from nozzle to workpiece: about 10 mm
Welding current and voltage:
Current type: AC power
When welding aluminum alloys with a thickness less than 6 mm, the maximum welding current can be determined according to the formula I = (60~65)d, where d is the electrode diameter (mm)
The arc voltage is determined by the arc length, which is usually equal to the tungsten electrode diameter.
Welding speed:
Manual TIG welding: adjust the welding speed at any time according to the size of the molten pool, the shape of the molten pool and the fusion situation on both sides, generally 8 ~ 12m/h
Automatic TIG welding: the welding speed generally remains unchanged after setting
Welding wire diameter:
Welding wire diameter should be determined based on plate thickness and welding current
(4) Welding process
Preparation:
Clean the welding area to ensure it is free of oil and oxides
Select the appropriate tungsten electrode and sharpen the end of the tungsten electrode to stabilize the arc
Pilot arc:
Use arc starting plate and arc extinguishing plate to prevent crack defects at the arc starting and arc ending places.
After the tungsten tip is heated to a certain temperature, the arc is moved into the welding zone
Welding operations:
Maintain an appropriate arc length, usually equal to the tungsten electrode diameter, to obtain adequate penetration and prevent excessive weld bead width and undercutting
During manual TIG welding, the welding speed should be adjusted at any time according to the size and shape of the molten pool to ensure uniform welding.
When pulsed TIG welding is used, high pulses provide large current values to ensure penetration, and low pulses cool the molten pool to prevent burn-through.
Weld seam forming:
Use faster welding speeds to reduce distortion
The scouring of the protective gas flow accelerates joint cooling and improves the joint structure and performance.
(5) Post-weld treatment
Check weld quality:
Check the surface brightness and flatness of the weld seam
Detect whether there are cracks, pores and other defects inside the weld
Clean welds:
Clean the residue in the welding area to ensure the cleanliness and anti-corrosion performance of the welded joints
