Ultrasonic Welding Technology Can Reliably Weld Large Square High-Voltage Wire Harness Terminals to Help Electric Vehicles Charge Quickly

As we all know, long battery charging time is one of the key factors limiting the growth of electric vehicle market. Usually, electric vehicles need several hours of charging time to get the cruising range, while traditional fuel vehicles or trucks can be filled with gasoline or diesel in a short time to ensure the cruising range.

In order to shorten the charging time of electric vehicle batteries, electric vehicle manufacturers need to improve the ability of the circuits in the charging system to carry high voltage and high current, which depends on the cable with large current carrying capacity. Therefore, the wire harness with large cross-sectional area is widely used to circulate higher current, and it also has good heat dissipation capacity, which is an effective method to improve the charging efficiency of electric vehicle batteries.

In the future, the current carrying capacity of the high-voltage wiring harness for electric vehicles will be four to five times that of the existing ordinary electric vehicle cables. In terms of wiring loom size, if copper is selected as the conductor material, the cross-sectional area of the cable harness used will be increased from 50mm² to 200mm², or even higher.

How to connect these cables with larger cross-sectional area reliably?

However, how to reliably connect these cables with larger cross-sectional areas is a major technical challenge for automobile manufacturers. At the same time, the rapid update and iteration of electric vehicles have also brought about the exploration of technical points such as how to arrange and accommodate these cables, cable length and low internal resistance connection technology. Ideally, the shorter the cable length, the better, so as to achieve the performance of low internal resistance and low temperature rise. However, in actual electric vehicles, the cable length can't be shortened, so the cable diameter needs to be increased correspondingly to ensure low internal resistance and good heat dissipation. As more and more battery modules are arranged under the vehicle, larger cross-sectional wire harnesses or conductors need to be installed and arranged around and under the passenger compartment. Therefore, the body structure must not only be insulated from cables and conductors, but also safely dissipate the temperature rise generated by the wiring harness during rapid charging.

Returning to the technical challenges of the connection process, ultrasonic metal welding process, as an efficient solid-phase connection process, has many advantages, such as short welding time, low internal resistance of joints, high mechanical strength, etc., and is especially suitable for welding key wire harnesses and wire harnesses and terminals in high-voltage connector systems. However, ultrasonic welding of high-voltage wire harness with large cross-sectional area (≥ 50m²) requires the use of very high-power equipment, and at the same time, the mechanical strength of the welded wire harness and connectors in use should be ensured. For the wire harness with cross-sectional area over 50mm², the conventional ultrasonic metal welding equipment is difficult to achieve the ideal welding effect. When welding high-voltage wire harnesses, it is necessary to exert a great welding pressure. As the conventional welding equipment is mostly of cantilever structure design, the bending phenomenon of the actuator will occur, resulting in low welding energy conversion efficiency. In order to compensate for the loss of energy, the welding amplitude is usually increased. However, this not only fails to improve this problem, but also causes more serious problems. For example, a large amplitude will increase the stress of the internal wire core and may damage the wiring harness, thus failing to meet the welding quality requirements required by automobile manufacturers.

Here, the following problems caused by simply increasing welding amplitude and equipment power in this application are emphasized:

(1) The deformation and stress generated by the wire core inside the wire harness will increase, which will lead to the decrease of the fatigue life of the wire harness and the potential mechanical failure.

(2) With the increase of the relative movement distance between the welding head and the wire harness, the frictional heat energy will exceed the reasonable energy range required for welding the wire harness, thus causing excessive heat to not spread to other areas in time, resulting in low utilization rate of ultrasonic welding energy and decreased welding efficiency.

(3) The reliability and efficiency of the welding head are reduced, and excessive amplitude and power will cause the softening of the wire harness. However, the softening in the welding process will easily cause the welding head to slip abnormally on the wire harness, which will aggravate the wear of the welding head and increase the life cost of the welding head.

For the above problems caused by simply increasing welding amplitude and equipment power, welding stability and energy conversion efficiency can also be improved by increasing welding pressure. However, the test results show that the pressure of the traditional cantilever ultrasonic metal welding machine exceeds its mechanical design limit when welding a wire harness with a length of more than 50mm².

In order to meet the technical challenges of high-voltage wire harness welding, a new welding structure is needed to achieve higher energy conversion efficiency. Here, we will focus on the direct pressure ultrasonic welding technology and equipment of Branson.

In order to solve the shortcomings of cantilever welding frame, Emerson Branson developed a new generation of "direct pressure" ultrasonic welding equipment, the representative product of which is Branson GMX-20DP. By directly pressurizing the welding spot position, the welding pressure is fully applied between the welding head and the workpiece, which improves the efficiency of converting ultrasonic vibration energy into friction heat energy applied to the workpiece, and is conducive to giving full play to the ability of high-power equipment when it is applied to high-voltage line welding.

The equipment has two characteristics:

(1) Higher welding pressure, which can reach 6100N, acts vertically on the wire harness to be welded;

(2) Lower welding amplitude can improve welding slippage with high energy, and the damage of large amplitude to the surface of wire harness.

Compared with the conventional cantilever welding equipment, Branson GMX-20DP can easily cope with the welding application of high-voltage wire harness connectors and achieve excellent welding quality.

At the same time, GMX-20DP is equipped with higher precision pressure sensor and displacement sensor, which can detect and control the welding process more accurately. For the monitoring of welding quality, the equipment can be connected with customer MES system, so that the whole process parameters can be recorded and traced. High-voltage wiring harness terminal welding workstation, equipped with specially designed welding terminal clamping fixture, can firmly fix the weldment, ensure the stability of the welding process, and finally provide customers with efficient and reliable high-voltage wiring harness welding scheme.