Complete Solution To Spot Welding Process

01.Spot welding process

Spot welding, as the name suggests, is a process of locally heating and melting two metal plates, and then applying pressure to recrystallize the melted parts, ultimately achieving a firm connection between the metal plates. In industrial production, spot welding is mainly used for splicing, reinforcing, and connecting metal sheets.

Spot welding is mainly applied in the following areas:

1. Automotive manufacturing: can be used for welding body components, chassis, engine hood, door panels, and frame structures. Especially in the overlapping and fixing of body sheet metal stamping parts, spot welding technology plays an important role

2. Lithium battery manufacturing: used for welding the positive and negative electrodes of batteries to ensure their safety performance and service life.

3. Aerospace: widely used for welding key components such as aircraft fuselage, wings, engines, etc.

4. Home appliance manufacturing: mainly used for welding and fixing thin plate structures. Products such as air conditioners, refrigerators, washing machines, etc

5. Electronic and electrical components industry: Spot welding technology is used in the welding of silver contacts on various switches and electronic components.

6. Other industrial manufacturing fields: In addition to the above-mentioned fields, spot welding technology is also widely used in metal structure welding in industries such as pipelines, construction, ships, railways, and petrochemicals.

02.Characteristic

During spot welding, the welded parts form a lap joint and are compressed between two electrodes. Its main characteristics are as follows:

1. Fast welding speed: Due to the fact that spot welding only heats the local connection area and has a short heating time, the welding speed is fast and the production efficiency is high.

2. Stable and reliable quality: During spot welding, the heating time for the connection area is very short, and the welding speed is fast, so the heat affected zone is small, the deformation of the welded part is small, and it is not easy to crack. Meanwhile, due to the fact that spot welding only consumes electrical energy and does not require filling materials, flux, gas, etc., the welding quality is stable and reliable.

3. High degree of mechanization and automation: The spot welding machine adopts an automated control system, which can achieve continuous and automated production and improve production efficiency. At the same time, spot welding machines use electrode pressure for welding, which can avoid errors caused by manual operation and ensure the stability and consistency of welding quality.

4. Low labor intensity: Spot welding machines are easy to operate and have a high degree of mechanization and automation, resulting in lower labor intensity for workers.

5. High equipment cost: Due to the high current and pressure required for welding with spot welding machines, the power of the equipment is relatively high and the cost is high. Meanwhile, due to the use of electrodes for welding in spot welding machines, the cost of consumables for electrodes is also relatively high.

6. It is difficult to perform non-destructive testing on welding points: due to the short heating time and fast welding speed of spot welding, non-destructive testing of welding points is difficult.

03.Operation process

Before welding, the surface of the workpiece should be cleaned thoroughly. The commonly used cleaning method is acid washing, which involves first pickling in heated sulfuric acid with a concentration of 10%, and then rinsing in hot water. The specific welding process is as follows:

(1) Insert the workpiece joint between the upper and lower electrodes of the spot welding machine and clamp it tightly;

(2) Electricity is applied to heat the contact surface between two workpieces, causing local melting and forming a molten core;

(3) Maintain pressure after power outage, allowing the molten core to cool and solidify under pressure, forming solder joints;

(4) Remove the pressure and take out the workpiece.

04.Influence factor

The main influencing factors of welding quality include welding current and energization time, electrode pressure, and current diversion.

1. Welding current and energization time

Spot welding can be divided into two types: hard specification and soft specification, based on the magnitude of welding current and the length of electrification time. The specification of passing high current in a short period of time is called a hard specification, which has the advantages of high productivity, long electrode life, and small deformation of the welded parts, and is suitable for welding metals with good thermal conductivity. A specification that uses a smaller current for a longer period of time is called a soft specification, which has lower productivity and is suitable for welding metals with a tendency towards quenching and hardening.

2. Electrode pressure

When spot welding, the pressure applied to the workpiece through the electrode is called electrode pressure. Appropriate electrode pressure can ensure good contact between the metal in the welding area, promote heat transfer and metal fusion. When the pressure is high, it can eliminate the shrinkage and porosity that may occur during the solidification of the weld core. However, the decrease in resistance and current density during the welding process leads to insufficient heating of the workpiece, a reduction in the diameter of the weld core, and a decrease in the strength of the weld joint. The magnitude of electrode pressure can be selected based on the following factors:

(1) The material of the welded component. The higher the high-temperature strength of the material, the greater the required electrode pressure. Therefore, when welding stainless steel and heat-resistant steel, a higher electrode pressure should be used than when welding low carbon steel.

(2) Welding parameters. The harder the welding specification, the greater the electrode pressure.

3. Diversion

When spot welding, the current flowing outside the main welding circuit is called shunt. The diversion reduces the current flowing through the welding area, resulting in insufficient heating and a significant decrease in the strength of the welding point, which affects the welding quality. The factors that affect the degree of diversion mainly include the following aspects:

(1) Welding thickness and spacing between welding points. As the distance between solder joints increases, the shunt resistance increases and the degree of shunt decreases. When using a conventional point spacing of 30-50mm, the shunt current accounts for 25% to 40% of the total current, and the degree of shunt decreases as the thickness of the weldment decreases.

(2) Surface condition of welded components. When there are oxides or dirt on the surface of the welded parts, the contact resistance between the two welded parts increases, and the current passing through the welding area decreases, that is, the degree of diversion increases. The workpiece can be pickled, sandblasted or polished.

05.Safety precautions

(1) The foot switch of the welding machine should have a sturdy protective cover to prevent accidental operation.

(2) The homework site should be equipped with a baffle to prevent sparks from splashing.

(3) Welders should wear flat light protective goggles, gloves, work clothes, etc. during welding

(4) The place where the welding machine is placed should be kept dry, and the ground should be covered with anti slip plates.

(5) After the welding work is completed, the power should be cut off, and the cooling water switch should be extended for 10 seconds before being turned off. When the temperature is low, the accumulated water in the waterway should also be drained to prevent freezing.