What is the best welding process for automotive wiring harnesses?

What is the wiring harness?

A wiring harness is a component that connects the various electrical devices in a circuit. It consists of an insulating sheath, terminals, wires and insulating wrapping material. In contrast to cable assemblies, wire harnesses have multiple branches and multiple terminals on each branch. Wire harnesses are usually used in a variety of sophisticated electronic devices, such as automotive circuits, computer motherboard circuits, home appliance circuits, etc.

What is wiring harness welding?

Wiring harness welding refers to the action of welding the metal of the wires with any required terminals. Wiring harnesses in the cars are prone to damage due to normal uses, human factors during assembly and maintenance, electrical equipment failure, etc. Therefore, wiring harness welding technology is most commonly applied to in automotive wiring harness welding. The common ultrasonic wire harness welding machine is called the automotive wire harness welding machine.

The automotive wiring harness is called the “blood vessel” of a car and is often recognized as “the central nervous system “of a vehicle because it connects the on-board computer to relevant functioning components on the vehicle. The quality of the weld of the wiring harness in the vehicle is becoming an important indicator for evaluating the performance of the vehicle. The quality of the wiring harness welding is very important to vehicles. And the quality of the automotive wiring harness welding is directly influenced by the welding technique.

Quality requirements for automotive wiring harness welding

Automotive wiring harness welding standards:

The ratio of the weld width to the weld height should be between 1:1 and 2:1;

No discoloration on the wires;

The weld length should not be too short or too long.

The surface of the weld should be smooth without any defects like roughness and slag.

The outline of the strands is recognizable on the pressed side whereas the strands should not be loose.

Automotive wiring harness welding standards

Wire harness crimping should not break the conductor.

The crimped terminals should not interfere with the mutual mating of the connectors.

Waterproofing and dielectric strength testing should be carried out after welding.

Automotive wire harness welding techniques

Automotive wire harness welding techniques mainly include pressure welding, fusion welding, brazing, ultrasonic welding.

Comparison of the four techniques:

Welding processWelding principlesAdvantagesDisadvantages
Pressure weldingAlso known as solid state welding, the two workpieces are bonded interatomically in the solid state under great pressure. The commonly used pressure welding process is resistance butt welding. When the current passes through the joint end of the two workpieces, the temperature right there rises due to the high resistance. When heated to a plastic state, two workpieces joint together under axial pressure.No filler is needed. No melting process. Fast crimping process. production. Light equipment.There is a risk of metal stamping backlash and the risk of oxidation and rusting in harsh working conditions, all of which can lead to poor contact.
Fusion weldingThe workpiece interface is heated to a melt and the weld is completed without pressure.Able to weld different metals together. The weld tumor on the joint of the wiring harness is highly resistant, which greatly reduces the service life of the harness. Defects such as porosity, slag and cracks easily formed in the weld, will deteriorate the quality and performance of the weld.
BrazingUse a metal with a lower melting point than the workpiece as the filler material. The filler material is heated to a temperature between the melting point of the workpiece and the filler material. Then, the filler becomes liquid and fills the interface gap and achieves inter-atomic diffusion with the workpiece to form the weld.Less distortion and precise dimension. Able to weld different metals together. The joint is of low strength. The quality of the weld is affected by the welding filler materials. Overheating, embrittlement, hardening or softening may occur in the weld and heat-affected zone after welding, degrading the performance of the weld.
Ultrasonic weldingThe physical effect created by the ultrasonic vibrations instantly melts the workpiece molecules and binds the wires together.Good welding results and low welding costs. Avoid the risks associated with pressure welding. The electric resistance of the weld is extremely low, close to zero.The ultrasonic welding equipment is relatively more expensive. 

What we learn from the comparison is that the first 3 welding methods have their own limitations, hence fail to be widely used. Only ultrasonic welding is much simpler and of low cost thus it has become the most common method of wiring harness welding.

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