Principle of bonding welding.
Bonding welding is also called ultrasonic aluminum wire welding. The principle is to use an ultrasonic generator to generate energy. The magnetostrictive transducer rapidly expands and contracts under the induction of a high-frequency magnetic field to generate elastic vibration, so that the corresponding vibration of the wedge is simultaneously applied to the wedge Under a certain pressure, under the combined action of these two forces, the wedge drives the aluminum wire to rub quickly on the surface of the metal oxide layer (such as aluminum film) in the welded area, causing plastic deformation on the surface of the aluminum wire and aluminum film. This deformation It also destroys the oxide layer at the interface of the aluminum layer, so that the two pure metal surfaces are in close contact to achieve interatomic bonding, thereby forming a weld. During welding, the ultrasonic energy is transferred to the welding area through the welding head. Because the welding area, that is, the interface between two weldings, will generate local high temperature, and due to the poor thermal conductivity of the workpiece, the heat cannot be dissipated in time and concentrated in the welding area , So that the molecules on the contact surface of the two workpieces quickly penetrate and diffuse each other, so that they can be integrated into one. When the ultrasonic stops, continue to maintain a certain pressure to solidify and form a solid molecular chain to achieve the purpose of welding. The welding strength can be close to the strength of the raw material body.
At present, the bonding welding of lithium-ion batteries is mainly used on nickel, aluminum and other materials. Usually, each polarity (positive or negative) of the battery is welded with one aluminum wire or aluminum strip, and each aluminum wire or aluminum has two welds. point.
Bonding welding classification.
According to the shape of aluminum wire, bonding welding can be divided into aluminum wire welding and aluminum strip welding.
① Aluminum wire welding.
a. The diameter of the aluminum wire commonly used in the aluminum wire welding of lithium-ion batteries is 200-500um;
b. The adjustment range of aluminum wire welding pressure is 50 ~ 1500g:
c. Transducer welded by aluminum wire: ORTHODYNE ultrasonic generator, working frequency 60kHz;
d. Ultrasonic generator power for aluminum wire welding: 60w
The above parameters are for reference only and can be adjusted accordingly according to the actual application.
② Aluminum strip welding.
a. The diameter of the aluminum strip usually used in the welding of lithium-ion battery aluminum strip is 20×4 ~ 80x12mil;
b. The adjustment range of the welding pressure of aluminum strip is 100 ~ 5000g;
c. Transducer welded by aluminum strip: ORTHODYNE ultrasonic generator, working frequency 60kHz;
d. Ultrasonic generator power for aluminum strip welding: 150W.
The above parameters are for reference only, and can be adjusted accordingly according to the actual application.
Aluminum wire welding rules.
Aluminum wire welding is not only used for connection, but also plays another important role: overcurrent protection, that is, the fuse effect, different specifications of aluminum wire have different overcurrent values.
Method for judging the strength of solder joints.
① Pull force judgment method.
The bonding equipment has an automatic tensile force detection device, and the tensile force test is completed during the welding process, which is also called an on-line detection method. This detection method is a non-destructive tensile test. After each solder joint is welded, the equipment automatically detects and judges the tensile force according to the set value.
② Solder joint strength standard.
Different sizes of aluminum wire will have different tensile strength standards.
Precautions for bonding and welding process.
The following aspects need to be paid attention to during the bonding and welding process:
①The object to be welded (cells, bus bars) must be securely fixed to prevent unstable welding due to shaking during bonding and welding, and aluminum wire or ribbon breakage due to vibration after welding. It is recommended that the cell end be fixed by UV , Fasten the fixing screws of the busbar;
②The whole thing to be welded must be fixed firmly to prevent abnormal welding caused by shaking during welding; clean it;
③It is necessary to ensure that the welding surface of the object to be welded (bus bar, lithium battery pack) is clean, and laser cleaning measures are recommended.
④Aluminum wire and aluminum strip welding method cannot exist at the same time in the same lithium-ion battery pack;
⑤The welding surface of each lithium ion battery is the same as the welding height of the busbar;
⑥For product quality, it is recommended to turn on the tension detection function, but this function will reduce the productivity after activation. According to the actual application calculation: the total working hours of bonding welding + tension detection is 1.2-1.5s for a solder joint.
Note: The above parameters are for reference only.
⑦Follow the maximum arc distance of bonding wire: 40mm;
⑧Follow the minimum bonding wire distance detection: 2mm;
⑨ The equipment must be maintained in accordance with the equipment maintenance cycle and methods.