Definition of crimp point
A harness crimp point is a connection point where more than 2 wires in a harness are hinged.
As shown in the figure below, this crimping point (SP) consists of Wire 1, Wire 2, and Wire 3. The three wires are connected to each other inside the wire harness. The hinged connection point inside the wire harness is the crimping point, also known as the splice point, the wire harness punching point.
Type of crimp point
Automotive wiring harness Splice points, commonly used methods include ultrasonic welding, U-shaped terminal crimping, etc.
ultrasonic welding.
The principle of ultrasonic metal welding is to use the vibration energy of ultrasonic frequency (20-40kHz) to transmit vibration waves to the surfaces of two metal objects to be welded, and under static pressure, the two metal surfaces rub against each other to form a molecular layer. fusion between.
The 50/60 Hz current is converted into 15, 20, 30 or 40 KHz electrical energy by an ultrasonic generator. The converted high-frequency electrical energy is converted into mechanical motion of the same frequency again by the transducer, and then the mechanical motion is transmitted to the welding head through a set of horn devices that can change the amplitude. The welding head transfers the received vibration energy to the joint of the workpiece to be welded, where the vibration energy is converted into heat energy by friction, melting the metal.
Ultrasonic welding can be used to join the same material as well as different materials such as copper and aluminium. Because the metals are soldered directly together, no additional materials such as sleeves, solder or flux are required. In addition, ultrasonic welding produces lower thermal stress on the part (the welding temperature is much lower than the melting point of the part), so the properties of the material to be welded and the properties of the surrounding materials do not change, such as the insulating sleeve remains intact.
Ultrasonic Welding Standard
SAE/USCAR-38, the most authoritative welding standard jointly issued by the American Society of Automotive Engineers and the American Automotive Survey Committee, comprehensively defines the ultrasonic welding process between automotive cables and terminals, providing an important reference for industry specifications.
Advantages and disadvantages of ultrasonic welding
The advantages of this method are that it is fast, energy saving, high fusion strength, good electrical conductivity, no sparks, close to cold processing, no need to use materials, high efficiency, good electrical conductivity, environmental protection and safety, which is the development trend of wiring harness contacts.
The disadvantage is that the welded metal parts should not be too thick (generally less than or equal to 5mm), the welding point should not be too large, and it needs to be pressurized. , Welding equipment prices and maintenance costs are high.
U-Terminal Crimp
Crimping is the process of applying pressure to the contact area of the wire and the terminal to form it and achieve a tight connection. During the crimping process, the conductor is squeezed by the sleeve and deformed in both the longitude and latitude directions, forming a cold weld. The original oxide film on the surface of the conductor and the sleeve is deformed and ruptured, the conductor and the pure metal surface of the terminal sleeve are fully and closely contacted, and the micro-motion during the extrusion deformation process.
Physically crimping the copper wire of the wire evenly through the U-shaped terminal is a contact method that is widely used at present.The USCAR standard is a special connector standard, and USCAR 21 is a terminal crimping performance specification, which comprehensively defines the crimping process of automotive wiring harness terminals and provides an important reference for industry specifications.
Advantages and disadvantages of U-type terminal crimping
The advantages of this method are convenient operation, high efficiency, good electrical conductivity, and cheap crimping equipment and U-shaped terminals;
The disadvantage is that compared with ultrasonic welding, it requires the use of crimping material and increases the weight.
Contact design and selection of location
The location of the crimping point is not only related to the cost of the wire harness, but also to the quality of the wire harness. Unreasonable splice design will not only increase the cost of the wiring harness, but also increase the weight of the wiring harness, and may also cause problems such as assembly difficulties.
The setting of the wiring harness contact position should meet the following points.
● Select a position where the wiring harness layout is relatively stable, and cannot select moving parts and positions with large disturbances.
● Arrange the crimping point near the intersection of each signal line and the trunk, which can effectively reduce wires and save costs.
● The choice of the contact position to avoid the back line, especially in the wet area, there is a back line, which is not conducive to the sealing of the splice point.
● Avoid the common pressure of more than 10 wires at the same crimping point. In other words, once more than 10 wires are under common pressure, a new crimping point needs to be set up.
● For the same crimping point, the wire diameter of the minimum wire diameter cannot be less than 10% of the sum of the wire diameters of all the wires at the crimping point
● The sum of the wire diameters on the left and right sides of the crimping point should be as equal as possible, and the smallest should not be less than 50% of the other side.
● The wire diameter of the wire with the minimum wire diameter of the crimping point should be larger than 16% of the maximum wire diameter of the crimping point as much as possible.
● When a wire connects two crimping points, the distance between the two crimping points is not less than 150mm. As shown in the figure below, the distance between SP1 and SP2 should be greater than 150mm.
● The position of the crimping point and the branch point, the distance of the buckle/tie should be greater than 50mm, and the distance between the contacts should be greater than 50mm (except for the can line), so as to effectively avoid the contact between the contacts.
Protection of crimp points
If the protection of the wiring harness contacts is unreasonable, the insulation at the wiring harness contacts will be punctured, or the contacts will enter into water, resulting in a short circuit fault.
Generally speaking, the distribution of automotive contacts is divided into two categories: dry area and wet area. The contacts in the dry area are protected by special tapes, and the contacts in the wet area need to be treated with glue-containing heat shrinkable tubes or butyl glue. protection to achieve the effect of waterproof sealing.
