Introduction of Wire harness Pressure Welding Technology

There are diffusion welding, high-frequency welding, cold pressure welding and ultrasonic welding.

1. Diffusion welding

The welding method of bonding the welded parts tightly and keeping them at a certain temperature and pressure for a period of time, so that atoms between the contact surfaces can diffuse to form a joint. The main factors affecting diffusion welding process and joint quality are temperatures, pressure, diffusion time and surface roughness. The higher the welding temperature is, the faster the atomic diffusion is. The welding temperature is generally 0.5-0.8 times of the melting point of the material. According to the material type and the quality requirement of the joint, diffusion welding can be carried out in vacuum, protective gas or solvent, among which vacuum diffusion welding is the most widely used. In order to speed up the welding process, reduce the requirement of welded surface roughness or prevent harmful structures from appearing in the joints, the intermediate sandwich material with a specific composition is often added between the welded surfaces, and its thickness is about 0.01 mm. Diffusion welding pressure is small, the workpiece does not produce macro plastic deformation, suitable for precision parts that are no longer processed after welding. Diffusion welding can be combined with other thermal processes, such as heat consumption-diffusion welding, powder sintering-diffusion welding, and superplastic forming-diffusion welding. These combined processes can not only greatly improve productivity, but also solve problems that can not be solved by a single process. For example, all kinds of titanium alloy components on supersonic aircraft are diffusion welded joints made by superplastic forming-diffusion welding, which have the same properties as base metal. They are especially suitable for welding non-metallic materials such as dissimilar metal materials, graphite and ceramics, high-temperature alloys with dispersion strengthening, metal matrix composites and porous sintered materials. Diffusion welding has been widely used in the manufacture of reactor fuel elements, honeycomb structural plates, electrostatic accelerator tubes, various blades, impellers, dies, filter tubes and electronic components.

Diffusion welding is to contact the welding surface of the material to be welded at a certain temperature and pressure, expand the physical contact of the surface to be welded by micro-plastic deformation or by generating micro-liquid phase on the welding surface, so that the distance is within (1-5) x 10-8 cm (so that the gravity between atoms can play a role, then metal bonds can be formed), and then through the continuous diffusion of atoms for a long time, to each other. Permeation is a welding method to achieve metallurgical bonding. Obviously, diffusion welding is too expensive for ordinary wire harness welding.

2. High-Frequency Welding

High-frequency welding is based on solid resistance heat. During welding, the resistance heat generated by high-frequency current in the workpiece is used to heat the surface of the workpiece's welding zone to melting or near plastic state, and then the forging force is applied (or not applied) and the real metal is combined. Therefore, it is a solid phase resistance welding method. High-frequency welding can be divided into contact high-frequency welding and induction high-frequency welding according to the way that high-frequency current generates heat in the workpiece. When contacting high-frequency welding, high-frequency current is transmitted to the workpiece through mechanical contact with the workpiece. In induction high-frequency welding, the high-frequency current generates the induction current in the workpiece through the coupling effect of the induction coil outside the workpiece. High-frequency welding is a highly specialized welding method, which should be equipped with special equipment according to the products. High productivity, welding speed up to 30 m/min. It is mainly used for welding longitudinal seam or spiral seam in pipe manufacturing. Obviously, high-frequency welding is not suitable for small wire harness.

3. Cold Press Welding

When the workpiece is deformed under pressure, the oxide film on the workpiece's contact surface is destroyed and extruded, which can purify the welded joint. The compressive force is generally higher than the yield strength of the material to produce 60-90% of the deformation. Pressure can be slowly extruded, rolled or impacted, or it can be applied several times to achieve the required deformation.

Cold press welding is easy to operate and automate because it does not need heating and filler, and the main welding parameters are determined by the size of the die. The welding quality is stable, the productivity is high and the cost is low. Without flux, the joint will not cause corrosion. The joint temperature does not rise and the crystalline state of the material remains unchanged during welding, which is especially suitable for the one that can not be achieved by dissimilar metals and thermal welding. Welding of some metal materials and products. Cold pressure welding has become one of the most important limited welding methods in the electric industry, aluminum products industry and space welding field.

The working surface of cold press welding machine and its die may accumulate metal debris, which must be removed regularly. If compressed air is available, the debris can be blown off with compressed air. If debris is to be removed thoroughly, the die can be removed from the welding machine, four modules of the die can be dismantled, and each module can be carefully removed with a magnifying glass to ensure that all the micro-debris on the surface of the module is removed. Care must be taken when removing the mold, especially when small springs are easily lost. The surface of the die is not clean, which will cause the wiring to slip easily in the die, so that the welding failure. Note that no grease is allowed on the working surface of the repaired die.

Cold press welding requires simple equipment, simple process and good working conditions. However, the extrusion force required by cold press welding is large, the welding equipment of large cross-section workpiece is huge, and the surface of overlap welded workpiece has deep pressure pits, which limits its application to a certain extent. Therefore, cold press welding is not a perfect choice for wire harness welding.