Selection of Contact Protection Materials in Automobile Wire Harness

The insulating wrapping material, wires and connectors constitute the automotive Wiring Harness, and the traditional automotive wire harness is mostly connected by connectors. In recent years, due to the gradual decline of automobile prices, the connection mode of automotive wiring loom has gradually changed into high-frequency welding connection and U-card connection. The rapid increase of Wire Harness contacts puts forward higher requirements for the protective materials of the contacts. Whether the automotive wiring harness is safe and reliable largely depends on the protection of the contacts. Because of the great difference in the position of automobile harness, there are also great differences in the protective materials of harness contacts.

PVC tape, namely PVC tape, is the most commonly used in the protection of wiring harness contacts. Blue PVC tape and black PVC tape are common PVC insulation tapes. 20m in length, 40mm in width and 0.2mm in thickness are common specifications of blue PVC insulating tape, while the commonly used black PVC insulating tape is 20m in length, 0.2mm in thickness and 38mm in width. As the car design and vehicle safety performance of most domestic manufacturers are gradually in line with the international standards, the harness manufacturers have reduced the use of PVC insulation tape for automotive wiring harness contacts.

Before using the blue PVC insulating tape, it is necessary to fix the tape near the wrapping machine, put the tape head into the cutter slot, connect the power supply, and press the contacts in the wrapping machine for wrapping. The raw material price of blue PVC insulating tape is low, and the machine wrapping method improves the convenience and efficiency of wrapping work. However, the blue PVC tape has many layers, poor overall aesthetics, takes a long time, and is difficult to waterproof. The difference between black PVC insulating tape and blue PVC tape is mainly reflected in the thickness and glue content of the tape, and its application method is basically the same as that of blue PVC insulating tape.

The cutting and peeling machine for the covering of Desha masking tape does not need manual operation, and its main function is to output the covering materials of nodes. According to the area of the contact wire, choose the length of the contact wrapping material, and set the length of the tape wrapping. The shearing and stripping machine will output the tape according to the set length. Good abrasion resistance, high working efficiency, good insulation effect and strong viscosity are the obvious advantages of Desha masking tape, but the price of Desha masking tape is higher. Therefore, Desha masking tape is often used in the contacts of car door lines, car bodies and instruments.

The wiring harness should not be set in the following areas: the branch point, the sub-branch point, the big curvature area, the running water storage area, the sports area and the unprotected position. The choice of the location of the automotive wiring harness contact directly affects the cost and quality of the wiring harness. Once the contact position is unreasonable, the thickness and width of the automotive wiring harness are increased, the quality of the wire harness is reduced, and the raw material cost of the enterprise is increased. Unreasonable contact position will also make the subsequent harness design more difficult and affect the installation and use of the subsequent harness. Branch-and-intersection method is a common method to select the contact position. According to the main content of the branch intersection method, if the contact is closer to the branch intersection, the number of wires consumed is less. As the automotive wiring harness contact cannot be set at the branch, the contact position should be as close as possible to the branch. The different hinge modes and contact positions have great influence on the wire diameter, installation and use of automotive wiring harness.

In actual installation, technicians should give priority to single-point articulation. Too many contacts in automotive wiring harness will affect the safety of electric power. Generally, 70 sets of contact wires are the best. Double-point hinge is suitable for the situation that more wires can be saved and the contact wire diameter is larger. Reasonable contact position can greatly reduce the cost of raw materials, which is helpful to reduce the cost and improve the assembly.

Ultrasonic welding, solder spot welding, short circuit breaker replacement and U-shaped card connection are common design methods in automotive wiring harness. The development trend of wire harness industry in China is ultrasonic welding, and ultrasonic welding is the best design method recognized by the international community. After the metal surface is pressurized, the metal surface will have a large friction, thus promoting the welding between molecular layers. Ultrasonic welding is widely praised for its high efficiency and low energy consumption. However, the welding equipment of this design method is expensive and the maintenance cost is high. U-card connection is a widely used contact method in Kable-X. After the copper wire is extruded with the U-shaped terminal, the friction between the copper wires can effectively connect the U-shaped terminal. U-shaped card connection has the advantages of easy operation, good conductivity, low material price and low cost.

Watertightness test is mainly to test and analyze the performance and protection effect of automotive wiring harness in humid environment, so as to avoid contact short-circuit fault as much as possible. First, one side of the megohmmeter is connected with the contact wire, and the other connection electrode is placed in water. When the display data of the megohmmeter is close to positive infinity, the insulation of the contact is good; On the contrary, the contact may cause water leakage or even short circuit. Second, use multimeter to check the contact current. The current of the contact is large, which indicates that the contact has been leaking and its waterproof performance is poor. The heat shrinkable tube used in the test shall conform to the requirements of water tightness, that is, no bubbles and no damage. The main component of the heat shrinkable tube is waterproof hot melt adhesive, and the waterproof hot melt adhesive has strong viscosity. The waterproof effect, anti-corrosion effect and insulation effect of the joints are greatly improved by using heat-shrinkable tubes, but the raw material cost of heat-shrinkable tubes is high, and high-quality heat-shrinkable tubes need to be used, which leads to many processes and takes a long time.

Automobile manufacturers pay more and more attention to the contact protection of automotive wiring harness. Unscientific contact protection will damage the insulation protection tape at the contact, and then short circuit will occur. The oxidation of the contact will also reduce the electrical performance of the circuit. Therefore, professionals should constantly refine the protection of contacts. Generally, the high-temperature wet area is mostly the front cabin area of the automobile, while the low-temperature dry area refers to the cab and trunk. The contacts in the wet area must be equipped with contact protection devices to achieve the purpose of sealing and waterproofing the contacts. Covered tape can meet the protection requirements of dry area contacts, and Desha masking tape is used to cover the dry area, which can not only improve the waterproof performance of the interface, but also have high cost performance. However, for the protection of wet area contacts, heat shrinkable tubes should be installed, and the heat shrinkable tubes should be pre-glued. The bumper harness also needs to have a certain waterproof effect, which can be lower than that of the engine harness under certain conditions.

To sum up, enterprises pay more and more attention to the management of automobile production cost, and people gradually begin to pay attention to the design and protection of automobile contact wire harness contacts. Automotive wiring harness joints can not only reduce the production cost of automobiles, but also greatly improve the quality of automotive wiring harness.