The Design and Attention of Wire Harness Pressure Contact and Wire Punch Point

The design of crimping point of Wiring Harness, some of which are called punch point, contact point, splice point and crimping point, has a great influence on the stability of the electrical function of the whole vehicle and the cost of wiring harness. This paper discusses the design of crimping point, focusing on the design and location selection of crimping point.

Wire Harness crimping point refers to the connection point where more than two wires in the wire harness are hinged.

Press contact (SP) is composed of Wire 1, Wire 2 and Wire 3. The three wires are interconnected inside the harness, and the hinged connection points of the three wires inside the harness are press contact points, also called splice points, and the punch-in points of the harness.

Automotive wiring harness Splice point, commonly used methods are ultrasonic welding, U-shaped terminal crimping, etc.

The principle of ultrasonic welding is that the vibration energy with ultrasonic frequency (20-40kHz) is used to transmit the vibration wave to the surfaces of two metal objects to be welded, and under the static pressure, the two metal surfaces rub against each other, thus forming the fusion between molecular layers.

The 50/60 Hz current is converted into 15, 20, 30 or 40 KHz electric energy by an ultrasonic generator. The converted high-frequency electric energy is converted into mechanical motion with the same frequency again through the transducer, and then the mechanical motion is transmitted to the welding head through a set of amplitude-changeable horn device. The welding head transmits the received vibration energy to the joint of the workpiece to be welded, and in this area, the vibration energy is converted into heat energy by friction, melting the metal.

Ultrasonic welding can be used to join the same material or different materials, such as copper and aluminum. Because the metals are directly welded together, no additional materials such as bushing, solder or flux are needed. In addition, ultrasonic welding produces low thermal stress on the parts (the welding temperature is much lower than the melting point of the parts), so the properties of the welded materials and the surrounding materials do not change, such as the insulation sleeve remains intact.

SAE/USCAR-38, the most authoritative welding standard jointly issued by American Society of Automotive Engineers and American Automobile Investigation Committee, comprehensively defines the ultrasonic welding process between automobile cables and terminals, which provides an important reference for industry standards.

This method has the advantages of high speed, energy saving, high fusion strength, good conductivity, no spark, close to cold processing, no need of materials, high efficiency, good conductivity, environmental protection and safety, which is the development trend of wiring harness contacts.

The disadvantages are that the welded metal parts should not be too thick (generally less than or equal to 5mm), the welding spot should not be too large, and it needs to be pressurized. The welding equipment price and maintenance cost are high.

Bonding is the process of applying pressure to the contact area between the wire and the terminal to shape it and realize the tight connection. During the welding process, the conductor is squeezed by the sleeve, and it deforms in both longitude and latitude directions, forming cold welding. The original oxide film on the surface of the conductor sleeve deforms and ruptures, and the conductor and the pure metal surface of the terminal sleeve fully and closely contact, resulting in micro-motion in the process of extrusion deformation.

At present, it is a widely used contact method to press the copper wires of electric wires evenly and physically through U-shaped terminals.

The USCAR standard is a special Connector standard, and the USCAR 21 is a terminal crimping performance specification, which comprehensively defines the terminal crimping process in automotive wiring harness and provides an important reference for the industry specification.

This method has the advantages of convenient operation, high efficiency, good electrical conductivity, and cheaper crimping equipment and U-shaped terminals.

The disadvantage is that compared with ultrasonic welding, it needs to use crimping materials, which increases the weight.

The position of the contact is not only related to the cost of the wire harness, but also related to the quality of the wiring harness. Unreasonable splice design will not only increase the cost of cable harness, but also increase the weight of wiring harness, and may cause problems such as assembly difficulties.

The setting of the contact position of the harness of our company, Kable-X, should meet the following points.

1. Choose the position where the wiring harness layout is relatively stable, but not the moving position and the position with large disturbance.

2. The crimping point is arranged near the intersection of each signal line and the trunk, which can effectively reduce the number of wires and save the cost.

3. Choose the contact position to avoid the back line, especially in the wet area, which is not conducive to splice point sealing.

4. For the same crimping point, avoid voltage sharing by more than 10 wires. In other words, once more than 10 wires are voltage sharing, a new crimping point needs to be additionally set.

5. For the same crimping point, the wire diameter of the smallest wire diameter shall not be less than 10% of the sum of the wire diameters of all wires in the crimping point.

6. The sum of the wire diameters of the left and right sides of the crimping point should be equal as far as possible, and the smallest should not be less than 50% of the other side.

7. The wire diameter of the conductor with the minimum wire diameter of the crimp contact shall be as large as 16% of the maximum wire diameter of the crimp contact.

8. When a wire connects two crimping points, the distance between the two crimping points is not less than 150mm. The distance between SP1 and SP2 in the figure below is greater than 150mm.

9. The distance between the position of the pressure contact and the branch point, buckle/tie should be greater than 50mm, and the distance between the contacts should also be greater than 50mm (except CAN line), so as to effectively avoid the contact between the contacts.

If the protection of the harness contact is unreasonable, the insulation at the harness contact will be punctured or the contact will be flooded, resulting in a short circuit fault.

Generally speaking, the distribution of automobile contact points can be divided into two categories: dry area and wet area. The contact points in the dry area are protected by special adhesive tape, while the contact points in the wet area need to be protected by rubber-containing heat shrinkable tube or butyl rubber to achieve waterproof and sealing effect.

The part below the wading line is called wet area, and the rest outside the dehumidifying area is dry area.

This paper systematically introduces the definition, classification, location selection and protection of crimping point. It is necessary to pay attention to crimping point when making layout design and principle design.