Automobile Connecting cables Quality Inspection

Automotive wiring harness is an important part of modern automobiles and the network main body of automobile circuits. Directing current to various electrical components in the car plays a significant role in realizing the intentions of the people in the car. Using the human body as a representation, the engine is equivalent to the human heart, and the wiring harness is like the human body’s blood vessels or nervous system.
Among various automobile failure problems, the adverse effects caused by wiring harnesses account for a considerable proportion. If the wires, rubber, hoses, etc. in the wiring harness are damaged, causing short circuit or open circuit in the wire, it will damage the transmission function. This will not only cause various equipment to stop moving, but depending on the degree, it may also cause smoke, fire, inability to walk, turn, brake and other major problems.
Since the wiring harness occupies such an important position in the entire automobile, as a quality manager in the automobile production factory, it is necessary to focus on control and strict management of the quality issues of the wiring harness. In order for customers to ride in their cars with confidence and comfort, the quality of the wiring harness must be verified through a systematic and professional approach. This method is the wiring harness certificate, also called W.P.T inspection. This point of view is also the point of view of wire harness verification.
This article discusses the inspection perspectives of wire harness inspection work that need to be applied as quality managers during the wire harness inspection process.

Wiring harness quality inspection

1 – Overview of Wiring Harness Certification
Wiring harness inspection is called W.P.T inspection. W.P.T is the acronym for WIRE, PIPE, and TUBE. Generally refers to parts such as wire harnesses, cables, hoses and rubber tubes. Checking whether there is any damage is W.ET inspection.
During the development and trial production stages of Dongfeng Honda’s new models, factory quality personnel need to complete wire harness inspections at specific stages. And the wiring harness inspection at each stage is different (see Figure 1).

Figure 1 Wiring harness inspection during the development and trial production stages of Dongfeng Honda’s new models
Although the content and form of wire harness inspection at each stage are different, the inspection point of view based on each wire harness inspection is the same. With these perspectives, problems can be effectively discovered and solved, thereby improving quality and preventing defective products from flowing to the next process.

2 – Wire Harness Verification Perspective
Common wiring harness problems include: interference, bite, insufficient CL, installation difficulty, installation failure, misassembly, pulling, stretching, etc. In response to these problems, wire harness inspection personnel will use corresponding viewpoints to find and solve problems.
For the convenience of explanation, the problems that arise in various wire harness inspections are classified below to discuss the perspectives that need to be adhered to during the wire harness inspection process.

Common wiring harness interference

2.1 Interference
After the assembly of a complete vehicle is completed, if the sharp edges of the wiring harness come into contact with the peripheral parts of the wiring harness (sheet metal, trim panels, functional parts, etc.) and there is force interaction, it means that the wiring harness and the object interfere with each other. Interference problems are the easiest and most common problems in wire harness verification (see Figure 2).
Figure 2 Common wiring harness interference
Considering the possibility of interference between the wire harness and the blue control box, you can calculate CLIP1, CLIP2 points ~ the length of Upoint b. If the sum is less than the length of the harness at the MAX tolerance, interference will occur. If the length is greater than the MAX tolerance of the wire harness, interference will not occur.
Through calculation, the distance from CLIP1 to point b: l01 mm
Distance from CLIP2 to Point b: 200.5 mm
When the trunk line length is up to 305 m, 305>101+200.5, interference between the wiring harness and the control box will occur.
By extension, if the three data values of A, B, and D change (C=A+B), how will the determination of wire harness interference change? Determining whether the wire harness interferes with the control box can be calculated by calculating the distance between the two closest fixed points of the possible interference part of the wire harness and the possible interference points of the component. In the early stage, when there is only a wiring harness but no completed car, you can use this to find possible areas of interference as key locations.

2.2 Cut
Wire harness cutting is the most obvious manifestation of interference between the wire harness and surrounding components, and it more directly reflects the consequences of wire harness interference. Cutting the wire harness will cause the broken copper wires of the wires to be exposed or the wires to be cut, causing a short circuit or open circuit. Its external manifestation is that the relevant functions do not operate, and in more serious cases, the car may burn.
In the entire vehicle, due to the spatial structure, the routing design of the wiring harness inevitably passes through some compact areas. A perfect hands-off layout is impossible to achieve in an actual finished car. At this time, it is necessary to consider whether there may be a hidden danger of cutting the wire harness in the area where the wire harness must be in contact with surrounding components. So in wire harness inspection, how to determine the risk of cutting at the interference part, there are the following factors to consider.

2.2.1 Protection form of wire harness
The wiring harness has the following forms of protective exterior: TwiStTube, Corr Tube, PVC Tube, PVC Tape, Urethane Foam, CushionTape.
Each type of exterior has different models, but the basic physical and chemical properties of the same exterior among different models are roughly the same. Appropriate protective outer covering can be selected for the wiring harness according to its characteristics.
As far as the hidden danger of wire harness cutting is concerned, mainly based on the wear-resistant strength of the exterior, the above exteriors can be simply sorted. From strong to weak: Twist Tube>CorrTube>CUSHION Tape>PVC Tube>URETHANE FOAM>PVC Tape.

2.2.2 Drawing properties of wire harness
Refer to the 2D drawing to determine the line length, exterior decoration and model between the two fixed points of the interference part. Considering the tolerance of the wire length, what is the degree of wire harness interference in the extreme MAx or MIN state? What kind of wire harness exterior is used, what is the model, and whether it has the protective effect in the current environment: Sometimes corrugated pipe (Corr Tube) is not wrapped with PVC tape around the outside. If the type of corrugated pipe used is inappropriate, the wires may jump out of the opening of the corrugated pipe. In this case, you need to pay attention to the possibility of interference from the surrounding area.

2.2.3 Material of contact parts
If there is relative movement and friction between the contact parts, it may cause the wire harness to be cut. By default, sheet metal sharp edges cannot interfere with wire harnesses that are not wrapped with corrugated tubes (CorrTube) or Twist Tubes (Twist Tube). There are welding spots in the sheet metal welding parts. If there are long burrs at the solder joints and the wire harness is close to the burrs, the burrs may penetrate deep into the wire harness and pierce the wires, causing the wire harness to be cut.

2.2.4 Contact part shape
The wire harness protected by the corrugated tube comes into contact with the sharp edge of the sheet metal. Although it is protected by the corrugated tube, if the relative positions of the corrugated tube and the sharp edge are perpendicular to each other, the wire harness may be cut.

2.3 Occlusion
The occurrence of the bite phenomenon is basically due to the fact that the wiring harness direction (may be the design direction, or may be the direction fluctuation caused by tolerance fluctuation) is exactly located at the assembly position of the surrounding components. As a result, the wiring harness is squeezed between the two mating parts.
During the wire harness inspection process, it is sometimes found that the wire harness is stuck between parts. Sometimes it may be because the wire harness naturally sag due to gravity, and sometimes it may be due to tolerance fluctuations where the wire harness is too long or too short, causing bites.
The wiring harness mainly consists of wires and their protective outer coverings. Wiring harness inspection is to ensure that the wires in the wiring harness are not damaged by external forces and affect their functions. Therefore, slight deformation of the protective exterior can be accepted by quality personnel as long as it does not cause damage to the wires. In other words, as long as the degree of bite does not affect the wires in the wiring harness, it can be considered that there is no problem with the wiring harness here.

3-Conclusion
As an important part of electrical installation work, wire harness inspection requires quality management personnel to continuously improve their professional knowledge and accumulate experience based on the inspection results of various models. I hope that the above views on wire harness inspection can serve as inspiration and form a complete and mature view on wire harness inspection.
In the future, if the entire vehicle wiring harness can be evaluated from the perspective of the designer, quality manager, and assembler combined with the designer’s design perspective, then the wiring harness verification work can be advanced more comprehensively. It also ensures that customers get the most comfortable user experience.