What are the advantages and difficulties of laser welding process for power battery?

Advantages of laser welding process

1. Concentrated energy, high welding efficiency, high processing precision, and large weld depth to width ratio. The laser beam is easy to focus, align and be guided by optical instruments, and can be placed at an appropriate distance from the workpiece, and can be redirected between fixtures or obstacles around the workpiece.battery pilot line Due to the space constraints mentioned above, other welding rules do not work.

2. Small heat input, small heat-affected zone, small residual stress and deformation of the workpiece; welding energy can be accurately controlled, welding effect is stable, welding appearance is good; non-contact welding, fiber optic transmission, accessibility, high degree of automation. When welding thinner materials or wires with finer diameters, there will be no remelting trouble like arc welding. Because the battery cells used in power batteries follow the principle of "lightweight", they are usually made of lighter aluminum and need to be made thinner. The general requirements of the shell, cover, bottom of 1.0 mm or less, the current mainstream manufacturers of the base material thickness of about 0.8 mm.

3. Can provide high-strength welding for a variety of material combinations, especially suitable for welding between copper and aluminum.laser welding machine for lithium ion batteries It is also the only technology that can weld electroplated nickel to copper.

Difficulties of the laser welding process

Currently, aluminum alloy battery cases account for more than 90% of the total development of power car batteries. Its welding difficulties mainly lies in the aluminum alloy on the laser reflectivity is very high, welding work process produces high sensitivity to porosity, welding can not be avoided for some problems will appear for the existence of defects,ESS lithium battery machine one of the most important is the porosity, thermal cracks and blowing fire.

1. Aluminum alloy laser welding there are two kinds of porosity: hydrogen porosity and bubble rupture porosity. The hydrogen porosity problem is exacerbated by the fast cooling rate of laser welding, and a new type of porosity appears in laser welding due to the collapse of the porosity.

2. The problem of thermal cocrystal. Aluminum alloy is a typical eutectic alloy, which is prone to thermal cracking in the welding process, including weld crystallization cracks and Haz liquefaction cracks. Under stress, liquefaction cracks will be produced at the grain boundaries, which will reduce the performance of welded joints.

3. The problem of explosive fires (also known as spatter). Many factors, such as the cleanliness of the material, the purity of the material itself, and the properties of the material itself, play a decisive role in the stability of the laser. The surface of the housing is bulging with air holes and bubbles inside. The main reason is that the fiber core diameter is too small or the laser energy setting is too high. Unlike some laser equipment suppliers who advertise "better beam quality and better welding results", good beam quality is suitable for stack welding with greater penetration depth. The key to solving this problem is to find the right process parameters.

4.Other Difficulties

Flexible package lug welding, the welding tooling design requirements are high, the lugs must be pressed firmly to ensure that the enterprise welding gap. S-shaped, spiral and other complex trajectories can be realized high-speed welding, increasing the weld combined with the building area at the same time by strengthening the strength of the welded structure.

Cylindrical core welding technology can be mainly used for positive pole welding, due to the negative part of the shell is thin, very easy to weld through. Such as the current existence of some manufacturers through the use of the negative pole free welding construction process, the positive pole used for laser welding.

Welding square battery packs, pole posts or connections are contaminated thicker, welding connections, pollutants decomposition, easy to form welding explosion point, resulting in holes; easy to weld through. The electrode is smaller, but it is also easy to weld deviation, so that the plastic burns, forming a burst point. Do not use multi-layer connectors, there are holes between layers, not easy to weld firmly.

The most important process in the welding of square batteries is the encapsulation of the shell cover, which is divided into the welding of the top cover and the bottom cover depending on the location. Some battery manufacturers due to the production of small battery size, the use of "deep stamping" process to manufacture battery shell, only the welding of the top cover.

Square battery welding methods are mainly divided into side welding and top welding, of which the main advantage of the side welding is the core body of the internal impact is small, spatter is not easy to enter the internal shell. The side welding process requires stability of the laser and cleanliness of the material, as it may lead to post-weld bulging, which has little effect on the assembly of subsequent processes. Since the top welding process is a single-sided welding, it requires less integration of welding equipment and is simple to produce, but there are two drawbacks. First, a small amount of spatter may enter the core during the welding process, and second, the machining requirements for the front end of the shell can lead to high cost issues.