In today’s society, electric welding technology is widely used, not only in construction projects but also in industrial production. It has facilitated the optimization and upgrading of various types of welding machines.
As a result, the study of electric welding technology is given great importance, and it is a core focus in the field of future production.
I. Arc Welding
Arc welding is one of the most popular welding technologies in today’s society, playing a vital role. It primarily uses arc welding machines as the main welding equipment, utilizing low voltage to ignite and melt the welding rod and burning piece, solidifying them at the target welding position.
Some key aspects of the common arc welding process include:
Concept of Arc Welding
Arc welding, also known as stick electrode welding, is the most widely used welding method in today’s industry.
It works by generating heat through electric arc discharge to melt the welding rod and the target and solidify them into a weld seam, creating a sturdy welding joint, thus ensuring the integrity of the construction.
Working Principle of Arc Welding
In the arc welding process, the arc is directly supplied by the power source. It is controlled through the discharge phenomenon between industrial devices and the welding rod. It is managed via ionization of gas and the emission of cathode electrons.
Currently, stick electrode welding is mainly used for manual welding operations, primarily flat welding and vertical welding.
Scope of Arc Welding
Arc welding is primarily used for manually operable welding workpieces. It includes various working methods such as vertical welding, flat welding, and overhead welding.
Furthermore, due to the lightweight and flexible handling characteristics of stick electrode welding equipment, it can be widely applied in any welding work with a power source. It also has the advantage of using a wide range of materials and unrestricted structural shapes.
General Provisions of Arc Welding
Firstly, we must analyze the structural component’s level, diameter, shape, and joint form in advance, choose a reasonable welding rod to ensure the normal progress of the welding work, and also analyze the welding process and welding parameters in advance.
Secondly, during welding, arc initiation should be controlled on backing plates, stay strips, and weld seams, and the main reinforcement should not be burnt to prevent structural deformation.
Lastly, the ground wire must be tightly connected to the rebar and other metal structures during welding to ensure safe operation.
Considerations in the Selection of Arc Welding Process
In today’s engineering projects, if arc welding is chosen for construction, we must strictly control the following to ensure the smooth progress of the work.
Firstly, electric shock accidents can occur due to differences in welding standards and welding processes, requiring frequent changes of welding rods and welding currents/voltages.
Therefore, protective gear must meet standards, workers’ technical skills must be standardized, and violations of operation procedures must be avoided.
Secondly, to prevent fire accidents, as sparks and arcs may ignite during arc welding, even raising the air temperature, adequate fire prevention and control measures must be put in place.
II. Resistance Welding Process Analysis
Resistance welding refers to a modern welding process where pressure is generated after the workpiece is connected to the power source, and the resistance heat generated when current passes through the joint and neighboring areas is used for welding.
This welding technique is also common in current work, heating the workpiece’s contact surface and neighboring areas to a molten or plastic state through the resistive heat effect of the current flowing through it, forming a metallic bond.
1. Spot Welding
Spot welding is a resistance welding method where the workpieces are assembled into a lap joint and clamped between two cylindrical electrodes. The parent metal is melted using resistive heat, forming a weld spot.
Spot welding is mainly used for thin plate welding.
The spot welding process includes:
Firstly, pre-compression to ensure good contact between the workpieces.
Secondly, the application of electricity to form a molten core and plastic ring at the welding site.
Lastly, cooling under continued pressure after power is cut off, forming a dense, crack-free, and pore-free weld spot.
2. Seam Welding
Seam welding is similar to spot welding.
However, it replaces cylindrical electrodes with rotating disc-shaped roller electrodes. The workpieces are assembled into a lap or butt joint and placed between the two roller electrodes.
As the rollers exert pressure on the workpieces and rotate, continuous or intermittent current is applied to form a continuous weld seam.
Seam welding is primarily used for welding structures that require regular seams and sealing, with a thickness generally under 3mm.
With the development of aerospace, electronics, automotive, and household appliance industries, resistance welding has gained increasing attention. Higher quality requirements have been placed on resistance welding.
Fortunately, the development of microelectronics technology in China and the production of high-powered silicon-controlled rectifiers and rectifiers provide conditions for the improvement of resistance welding technology.
China has already produced high-performance secondary rectifier welding machines. Control boxes composed of integrated circuits and microcomputers have been used in the matching of new welding machines and the renovation of old ones.
Advanced closed-loop monitoring technologies like constant current, dynamic resistance, and thermal expansion have started to be promoted and applied in production.
III. Lap Welding and Overlap Welding
Prior to welding, the assembly and positioning of the rebar should meet the following requirements.
(1) When using lap welding, the gap between the two main rebar ends should be between 2 to 5mm.
(2) When using overlap welding, the bending and installation of the rebar should ensure that the axes of the two rebars are in a straight line.
(3) For lap welding, the lap bar and the main rebar should be fixed by welding at four points; for overlap welding, they should be fixed at two points. The positioning weld should be at least 20mm away from the lap bar or the overlap end.
Under the conditions of field prefabricated component installation, when the rebars at the joints are overlap welded, if it is genuinely difficult to bend the rebar in advance, it doesn’t have to be bent.
During welding, the arc should start at one end of the lap bar or overlapping rebar, and the arc should end at the head of the lap bar or overlapping rebar, with the crater filled.
In multi-layer welding, the first weld should have sufficient depth, and the main weld and the positioning weld, especially during the period and at the end of the positioning weld, should be well fused.
IV. Electroslag Pressure Welding
The welding process includes arc ignition, arc stabilization, electroslag, and upsetting.
Before welding, the rust within about 120mm of the rebar end should be removed. The clamp should be securely clamped on the lower rebar, and the upper rebar should be straightened and securely clamped in the moving electrode. The flux box should be filled with flux.
When manually performing electroslag pressure welding, the direct arc ignition method can be used.
First, the upper and lower rebars should touch. After the welding power source is turned on, the upper rebar should be immediately lifted by 2 to 4mm to ignite the arc.
Then, the rebar should be gently lifted by a few millimeters. After the arc burns stably, it should be gradually fed down as the rebar melts, transitioning to the electroslag process.
After the rebar has melted to a certain degree, the welding power source should be cut off and rapid upsetting should be performed.
After cooling for 1 to 3 minutes, the flux box can be opened, the flux can be collected, the clamp can be removed, and the slag can be knocked off. The lifting and feeding of the rebar should be appropriate to prevent open circuit or short circuit.
Welding technology and techniques are widely used in modern engineering construction today, and various welding techniques and construction processes are constantly innovating and developing. Using different welding equipment according to actual conditions can more efficiently and high-quality meet construction requirements.
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