Overview Of Laser Welding Process And Principle For Lithium-Ion Battery Processing
From the production of lithium-ion battery cells to battery pack assembly, welding stands as a critical manufacturing process. The conductivity, strength, airtightness, metal fatigue, and corrosion resistance of lithium-ion batteries serve as crucial quality evaluation standards for battery welding.
Over the years of evolution in the lithium battery industry, spot welding equipment has undergone continuous advancements, progressing from the initial AC pulse spot welder to the energy storage spot welder, intermediate frequency spot welder, transistor spot welder, and eventually to the laser spot welder. This ongoing development has led to a consistent enhancement in the quality of spot welding equipment.
New design lithium battery laser welding machine
AC Pulse Spot Welder
The AC pulse spot welder operates by having the thyristor controlled by a single-chip microcomputer intercept the AC pulse voltage to the primary coil of the welding transformer. The transformer then converts the high-voltage pulse into a low-voltage large current, which is outputted to the spot welding needle for discharge spot welding.
The advantages of the AC pulse spot welding machine include its low cost and low failure rate. However, a notable disadvantage is that once the thyristor is triggered and turned on, it must wait until the AC zero-crossing point before turning off. This results in prolonged welding time, which is detrimental to the welding effect. Prolonged welding time increases the temperature of the solder joints, leading to reduced power, virtual welding, frying welding, tin melting, and other issues. This phenomenon is commonly observed in the spot welding of nickel sheets on protective plates, particularly due to the high spot welding temperature of the AC pulse. When spot welding the negative electrode of the aluminum shell or the positive electrode of the steel shell, the small area of the rivets makes heat dissipation challenging, often resulting in the melting of the sealing ring.
Energy Storage Spot Welding Machine
The energy storage spot welding machine delivers concentrated discharge energy, resulting in a short welding time and relatively low costs, making it highly suitable for battery spot welding applications. However, it is associated with large welding sparks and a higher failure rate. The performance of the welding machine can decline due to the capacity attenuation of the energy storage capacitor. In recent years, with the increasing trend of welding automation, the charging time of the energy storage capacitor has posed limitations, preventing the quick and stable output of welding energy. Consequently, it is best suited for manual spot welding applications.
Intermediate Frequency Welding Power Source
The frequency and control method of an inverter welding machine serve as crucial indicators for assessing its performance. Generally, an inverter frequency ranging from 1-10KHz is collectively referred to as intermediate frequency, while frequencies above 10KHz are termed high frequency. In terms of control mode, the primary side constant current is considered an ideal control method. The primary side constant current involves closed-loop control, allowing for the adjustment of high-frequency pulse width based on the actual output current. In less optimal cases, fixed pulse width modulation is adopted, falling under open-loop control.
During spot welding, the spot welding needle and the weldment itself significantly influence the welding process, resulting in relatively poor stability. The preferred frequency for an intermediate frequency welding power supply typically falls within the range of 4-5KHz. This frequency range ensures the attainment of a stable welding waveform at the output end and facilitates effective feedback and control of a large discharge current. It's noteworthy that transformers have a specific response time, and excessively high frequencies may not contribute significantly to the current.
Transistor Welding Power Source
The most optimal resistance welding power source eliminates the need for a welding transformer, enabling rapid current rise and direct high-frequency output of the current waveform. It offers flexibility in selecting control modes, including constant current, constant voltage, or a combination of constant current and constant voltage. However, it comes with the drawback of being relatively expensive.
Laser Spot Welding Machine
The laser spot welding machine comprises components such as a crystal, xenon lamp, condensing cavity, optical resonant cavity, cooling filter, and laser power supply. Widely utilized in the battery industry, it finds application in the welding of steel shells and aluminum shell cover plates, with recent advancements extending to the spot welding of polymer PACK protective plates. In comparison to resistance welding, the laser welding machine offers several advantages, including the elimination of the need for spot welding needle grinding, firm and uniform welding, and a reduced likelihood of false welding.
From the production of lithium-ion battery cells to battery pack assembly, welding stands as a critical manufacturing process. The conductivity, strength, airtightness, metal fatigue, and corrosion resistance of lithium-ion batteries serve as crucial quality evaluation standards for battery welding. The choice of welding methods and processes directly impacts the cost, quality, safety, and consistency of lithium-ion batteries.
Among various welding methods, laser welding stands out for lithium-ion battery processing due to the following advantages: Firstly, laser welding offers high energy density, resulting in minimal welding deformation and a small heat-affected zone. This effectively enhances part accuracy, providing smooth, impurity-free, uniform, and dense weld seams without the need for additional grinding work. Secondly, laser welding allows for precise control, featuring a small focus spot and high-precision positioning. It is easily automated with a mechanical arm, leading to improved welding efficiency, reduced man-hours, and cost savings. Additionally, when laser welding thin plates or small diameter wires, it is less susceptible to meltback compared to arc welding.
