An Introduction to the Manufacturing Methods and Key Technologies of HXN5 Locomotive Wire Harnesses by Anbofu

Overview of wire harness manufacturing process

The HXN5 locomotive has about thirty wire harnesses, among which the largest wire harness is composed of about one thousand wires of different lengths and specifications. The handling of this wire harness requires lifting by a crane. The manufacturing process of wire harnesses should include: preparation of wire harness materials (including wire 2, terminals, connectors, binding straps, wire number labels, insulation tape, heat shrink tubing, etc.), preparation of production tooling tools (crimping machines, heat shrink machines, scissors, testing equipment, etc.), stripping of wires, setting wire numbers, terminal crimping, connector assembly, wiring binding, wire harness testing, wire harness sorting and storage

Key processes

2.1 Terminal crimping

Terminals are the connections between wires and instrument equipment. Power and signals from wires flow into or out of the instrument equipment through the terminals. The quality of terminal crimping and whether it meets relevant standard requirements directly affect the normal operation of the instrument equipment. A terminal should be composed of two main parts: the insertion area, transition area, and crimping area. The situation where crimping quality problems occur is as follows:

3.1.1 The crimping height is too high or too low

The crimping height refers to the cross-sectional height of the conductor crimping area after crimping, and it is the most important feature of good crimping. Excessive crimping height cannot effectively compress the wire core, which can cause ineffective gaps in the crimping area. Due to insufficient metal contact between the wire and terminal metal, the contact resistance increases, leading to heating and burning of the terminal. A too small crimping height reduces the pulling force and rated current of the cable, which can break the wire core or the crimping area of the terminal, causing the wire connection to break and causing a circuit break. Use specialized measuring tools such as micrometers to inspect the quality of crimping, and regularly verify the crimping pliers and crimping equipment to ensure the quality of terminal crimping

2.1.2 Insulation crimping area too small or too large

Due to the variety of wire specifications and terminal types, there is no unified regulation, and it can only be obtained through accumulated experience in practical operation. Insulation crimping provides stress relief for the conductor crimping area, so that when the cable is played with, the conductor crimping area will not break due to the buffering of the insulation crimping area. Therefore, good insulation layer crimping plays an important role in protecting the conductor crimping. Too small insulation layer crimping can cause excessive metal stress in the insulation crimping area, weakening its stress release function. However, too large insulation layer crimping cannot effectively buffer the stress release in the wire crimping area. By observing with the naked eye and gently shaking the wire with your hand, the insulation crimping area should not shake

2.1.3 Loose wires in the wire crimping area

Loose wire crimping is one of the most common quality issues that occur during terminal crimping, and it is a major cause of crimping failure. All wire cores are not completely enclosed in the conductor crimping area, and the strength and current load capacity of the crimping components will be significantly reduced. Simply rewind the cables into bundles and insert them into the terminals for crimping. Peeling off the insulation layer from the cable is a separate operation process. During handling or bundling, the wire core may be accidentally separated. When using a recording wire clamp to strip the wire and maintain the removal of an appropriate length of insulation layer without causing it to fall off, the insulation sleeve may not be completely removed from the cable until it is ready to be crimped onto the cable with terminals. This will help minimize the problem of loose wire cores

2.1.4 The stripping length is too short

When stripping wires, it is necessary to ensure that the stripping length is appropriate. If the stripping length is too short, the wire cannot be fully inserted into the conductor crimping area during terminal crimping, and the crimping force between terminals and wires cannot meet the requirements of the tensile test, which can easily cause the wire to fall off due to vibration during locomotive operation. Due to the decrease in metal contact between the wires and terminals, there will be severe heating here, which may cause a circuit breaker. Strict measures should be taken to ensure sufficient wire stripping length, and during crimping, the wire should be inserted into the crimping area as much as possible.

2.1.5 Cable insertion too deep

Contrary to 3.1.4, if the wire is inserted too much to enter the transition zone. Due to excessively long wire cores, the pins may not be properly inserted, resulting in poor wire contact between the two connectors and signal interruption. Another type of malfunction that often occurs is due to the insertion of wires that are too long, resulting in a short circuit between the two lines. This situation has led to multiple engine damage accidents in the connector of the locomotive traction motor speed sensor. The method to eliminate such quality problems is to strictly require that the stripping length cannot be too long, and to maintain an appropriate amount of wire insertion when crimping wires.

2.2 Connector assembly

The assembly of connectors should focus on the following key steps:

2.2.1 There are various types of connectors for locomotives, many of which have similar appearances but completely different internal structures. When assembling, materials are strictly taken according to the material rack code. After receiving the materials, they are strictly compared with the operation manual

3.2.2 When inserting the terminal into the connector socket, hold a moderate amount of force. When a "creak" sound is heard, the terminal should not be inserted properly, and no further force should be applied at this time. Multiple quality issues occurred on site due to the operator's judgment of inserting the product in place solely based on its appearance

2.2.3 After assembling the connector, it should be protected. Connectors are mostly used for locomotive signal lines and control lines. Dust and air moisture in the production site can invade the interior of the connectors, causing short circuits between adjacent lines, seriously affecting the normal control of signals for locomotives and vehicles. Use the connector's built-in protective cover to cover the entire connector and tighten it to ensure organizational quality

2.3 Wiring binding: The wiring harness is a neural network that connects different parts of locomotive equipment, so the manufactured wiring harness should be able to perfectly connect to the instruments and equipment on the locomotive. When wiring, follow the route specified on the wiring board and strictly tie the wires. Only one tie tape can be used for cross binding at the intersection, avoiding the use of multiple ties. This can effectively prevent the wiring harness from loosening.