Influence of welding parameters of battery spot welding machine on welding effect

There are many factors that affect the quality of spot welding of lithium-ion battery pack spot welding machine.

The resistance between the two electrodes, the current shunt during the battery spot welding process, the welding current, the welding time, the electrode pressure and the selection of the welding power source will all have a certain impact on the quality of the spot welding.  

Among these, the welding current, welding time, electrode pressure and welding power source are the biggest factors affecting the quality of spot welding of lithium-ion battery pack spot welding machine.

Welding current

Welding current can affect the heating process of spot welding in the following ways:

The first is to adjust the effective value of the welding current, which can make the internal power source's heat change significantly.

Second, due to the concentrated current shrinkage at the contact point of the two weldments during spot welding, which leads to concentrated heating, first a plastic connection zone appears, forming an uneven heating process during spot welding. In order to change this unfavorable factor, you can choose Different welding current waveforms, changing the shape of the electrode and the size of the end face, etc. can change the shape of the current field and control the current density distribution to achieve the purpose of controlling the shape and position of the nucleus.

As the welding current increases, the resistance heat generated increases, and the corresponding spot welding nuclei and joint shear strength are improved. However, if the welding current is too large, it will cause the base metal to overheat and even increase the electrode end surface loss.

Welding time

During spot welding, the heat generated by the current passing through the two electrodes, part of which is used to heat the welding zone to form a welding spot, is called effective heat. For a certain weldment material and a certain volume of the welding zone metal, this part of the heat is Certainly, it has nothing to do with the length of heating time.

The other part is transferred to the electrode, the cold metal around the welding area and the air while heating, which is called lost heat, which increases with time.

If welding is performed instantaneously, the heat loss will be equal to zero, and the total heat will be equal to the effective heat. So when you want to increase the total heat, you cannot use any method of extending the welding time.

Electrode pressure

First of all, the electrode pressure has a significant effect on the total resistance between the two electrodes, thereby affecting the amount of welding heat during spot welding.

Secondly, the electrode pressure has a great influence on the heat dissipation performance of the welded joint.

When the electrode pressure is too small, the resistance between the two electrodes increases and more welding heat is generated. At this time, the heat dissipation of the welded joint is poor, and it is easy to cause early splashing.

When the electrode pressure is too high, the resistance between the two electrodes is small, the current density is reduced, resulting in insufficient welding heat, and the heat dissipation of the joint is improved, all of which cause the size of the nucleus to become smaller, the penetration rate decreases, and in severe cases, false welding .

When choosing the electrode pressure, you should choose the minimum electrode pressure that does not produce splashes, which saves energy and ensures welding quality.

Welding power

Li-ion battery spot welders are usually composed of three main parts: main welding power source, control device and mechanical device. Among them, the main welding power source is the most important part. Choosing a controllable welding power source that meets the needs is the key to ensuring welding quality.

The AC welding power source uses the principle of voltage transformation to transform the input of the AC 380V grid to obtain a low voltage and large current.

AC welding power source is the most widely used one among all resistance welding power sources. It has strong versatility, economy, easy control, and simple maintenance. It is widely used for spot welding of carbon steel, austenitic stainless steel and other materials with higher resistivity.

However, its power factor is low, only 0.4-0.5; it has a large impact on the power grid, which may affect the normal use of other electrical equipment; its shortest discharge time during welding is 1/2 wave, that is, 0.01s, which cannot be achieved. The precise control of the connection is not suitable for high-standard welding of special materials.

Inverter welding power source, the working principle is to first rectify the input three-phase alternating current into direct current. After filtering, the DC power with small fluctuation is obtained. Then the IGBT inverts the direct current into intermediate frequency alternating current and inputs it to the transformer, and then the step-down rectification The obtained direct current is supplied to the electrode to weld the workpiece.

The inverter welding power source has the following advantages: the inverter system is less affected by the power supply system, the three-phase load is balanced, and the control and measurement accuracy of the welding current have been greatly improved; only 1/3 of the AC welding power source The quality and volume are light and fast; using direct current for welding, there is no zero-crossing phenomenon, the thermal efficiency is greatly improved, and it is more energy-saving. Therefore, inverter welding power sources have been widely used in high-speed automated production.

The secondary rectifier welding power source is improved by adding a rectifier on the basis of the AC welding power source. The temperature rises quickly and the welding quality is more stable. The welding versatility is very strong, and it can be used for welding various metal materials. Better welding effect than AC power supply.

Capacitive energy storage power supply uses the energy storage effect of capacitors to start the capacitor to absorb energy from the grid. When welding the workpiece, the capacitor completes the discharge in a short time, and discharges to the welded workpiece after the transformer is transformed. At present, low-power capacitor energy storage welding machines have been widely used.