The principle and type of laser welding technology for power battery

The reasonable choice of welding methods and processes in the power battery manufacturing process will directly affect the cost, quality, safety and consistency of the battery. Next I organize the content of power battery welding.

1 Laser welding principle

Laser technology welding is the use of laser beam excellent directionality and high power density and other characteristics can be managed, through the use of optical information systems will focus the laser beam in a very small area, in a very short period of time so that the place to be welded to form their own an important energy needs to be highly concentrated in the heat source area,battery pilot line so that the welded material melting and the formation of a more solid weld and weld seam.

2 Types of laser welding

Heat conduction welding and deep melting welding

In heat conduction welding, the laser beam melts the surface of the workpiece in concert along the weld seam, and the melted material comes together and solidifies to form the weld seam.laser welding machine for lithium ion batteries It is mainly used for thinner materials, the maximum welding depth is limited by its thermal conductivity, the weld width is always greater than the welding depth.

Deep penetration welding, high-power laser focusing on the metal surface, the heat is too late to emit, the welding depth will be sharply deepened. This welding technique is deep fusion welding.ESS lithium battery machine Because the deep fusion welding technique is extremely fast, the heat-affected zone is small, and the distortion is minimized, this technique can be used for deep fusion welding or welding several layers of data together.

The main difference between heat conduction welding and deep fusion welding is the different power densities applied to the metal surface per unit of time and the different critical values for different metals.

Penetration and seam welding

By welding, the joints do not need to be punched and are relatively simple to process. Penetration welding requires a high-power laser welder. The depth of penetration welding is lower than that of seam welding, which makes it less reliable.

Seam welding requires a less powerful laser welder than penetration welding. The melting depth of seam welding is higher than that of penetration welding, and the reliability study is relatively good. However, the connecting piece needs to be punched and the processing technology is relatively difficult.

Pulse welding and continuous welding

Pulse mode welding

Laser welding, should choose the appropriate welding waveform, commonly used pulse waveforms are square wave, spike wave, double-peak wave, etc., the metal surface due to the reflection of the energy loss caused by the laser energy loss accounted for 60% -98%, the reflectivity with the change in surface temperature and change. In general welding aluminum alloy, the best choice is the spike wave and double peak wave. The pulse width of the deceleration part after the welding wave is larger, which can effectively reduce the formation of porosity and cracks.

Since aluminum alloys have a high reflectivity to laser light, the welding head is usually deflected at a certain angle when welding in order to prevent the vertical reflection of the laser beam from damaging the laser focusing lens. The diameter of the weld joint and the effective bonding surface increases with the laser tilt angle. When the laser tilt angle of 40 °, the maximum weld joint, the effective bonding surface is the largest. Weld depth and effective depth of fusion decrease with the increase of laser tilt angle, and the effective depth of fusion decreases to zero when the laser tilt angle is greater than 60°. Therefore, tilting the welding head to a certain angle can appropriately increase the weld depth and width.

In addition, 65% of the partial cover and 35% of the shell need to be welded with the weld seam as the boundary, which can effectively reduce the explosion fire caused by the cover problem.

Continuous Mode Welding

Since the heating process of continuous laser welding is not like pulsed machine quenching and sudden heating, cracking tendency is not obvious. In order to improve the quality of the weld, continuous laser welding is used, and the surface of the weld is smooth and uniform, without spatter and defects, and the weld is free of cracks. In the welding of aluminum alloy, continuous laser has obvious advantages, compared with the traditional welding method, high production efficiency, no need to fill the wire; compared with pulsed laser welding, it can solve the defects such as cracks, pores, spatter and so on after welding. And ensure the good mechanical properties of aluminum alloy after welding; no dent after welding, the amount of post-welding polishing is reduced, saving the production cost. However, due to the relatively small spot of continuous laser, the assembly precision of the workpiece is required to be high.

In the power battery welding process, welding process information technology management personnel will be based on the customer's battery material, shape, thickness, tension requirements, such as selecting a suitable laser and welding process parameters, including welding speed, waveform, peak, welding head tilt angle, etc. to set up a scientific and reasonable welding process parameters to ensure that our final welding results can meet the requirements of the spirit of power battery manufacturers. .