Analysis of Viewpoints and Countermeasures for Quality Inspection of Automobile Wiring Harness

The automotive wiring harness is an important part of modern cars. It is the network body of the automotive circuit, directing the current to the various electrical components in the car, and plays a major role in realizing the intentions of the people in the car. If the human body is used as an example, the engine is equivalent to the heart of the human body, and the wiring harness is like the blood vessels or nervous system of the human body.

 

Among various automobile failure problems, the adverse effects caused by the wiring harness account for a considerable proportion. If the wires, rubbers, hoses, etc. in the wiring harness are damaged, causing the wires to short-circuit or break, it will damage the transmission function. This will not only cause various equipment to fail to operate, but also cause major problems such as smoke, fire, inability to drive, turn, and brake, depending on the degree.

 

Since the wiring harness occupies such an important position in the whole vehicle, as a quality management personnel in the automobile production factory, it is necessary to focus on the quality control and strict management of the wiring harness. In order to enable customers to ride in the car with confidence and comfort, it is necessary to verify the quality of the wiring harness through a work based on a systematic and professional point of view. This method is the wire harness certification, also called W.P.T certification, and this view is also the view of wire harness certification.

 

This article discusses the inspection viewpoints of wire harness inspection work that quality management personnel need to apply during the wire harness inspection process.

 

1 Overview of wire harness inspection

Wire harness inspection is called W.P.T inspection. W.P.T is the initials of WIRE, PIPE, and TUBE. It generally refers to wire harnesses, cables, hoses, rubber tubes, etc. Checking whether they are damaged is W.ET inspection.

During the development and trial production stage of Dongfeng Honda's new models, factory quality personnel need to complete wire harness inspection at specific stages, and the wire harness inspection at each stage is different.

Although the wire harness inspection at each stage is different in content and form, the inspection viewpoints based on each wire harness inspection are the same. With these viewpoints, problems can be effectively discovered and solved, thereby improving quality and preventing defective products from flowing into the next process.

 

2 Harness Verification Viewpoints

Common harness problems include: interference, bite, insufficient CL, difficult installation, inability to install, misassembly, pulling, stretching, etc. For these problems, harness verification personnel will use corresponding viewpoints to find and solve problems.

For the convenience of explanation, the following is a classification of various problems that occur in harness verification to explore the viewpoints that need to be upheld during harness verification.

 

2.1 Interference

After a vehicle is assembled, the harness and the surrounding parts (sheet metal, trim, functional parts, etc.) are in sharp contact and there is force interaction, which means that the harness interferes with the object part. Interference is the easiest and most common problem in harness verification (see Figure 2).

Considering the possibility of interference between the harness and the blue control box, the length of CLIP1, CLIP2 points ~ Upoint b can be calculated. If the sum is less than the length of the harness at the MAX tolerance, interference will occur. If it is greater than the length of the harness at the MAX tolerance, no interference will occur.

By calculation, the distance from CLIP1 to point b is: l01 mm

The distance from CLIP2 to point b is: 200.5 mm

When the trunk line is up to 305 m, 305>101+200.5, interference between the harness and the control box will occur.

By extension, if the values ​​of A, B, and D3 data change (C=A+B), how will the judgment of harness interference change? It can be seen that the judgment of whether the harness and the control box interfere can be obtained by calculating the distance between the two nearest fixed points of the possible interference part of the harness and the possible interference point of the part. In the early stage when there is only a surface but no finished car, the possible interference part can be found based on this, as the focus of attention.

 

2.2 Cutting

The harness cutting is a more obvious manifestation of the interference between the harness and the surrounding parts, which more directly reflects the consequences of harness interference. The harness cutting will cause the wire to break and the copper wire to be exposed or the wire to be cut, causing a short circuit or open circuit. Its external manifestation is that the relevant functions do not work, and in more serious cases, the car will burn.

In the whole vehicle, due to the spatial structure, the design of the wiring harness inevitably passes through some compact areas. A perfect non-interference layout is impossible to appear in the actual completed car. At this time, it is necessary to consider whether there is a hidden danger of the wiring harness being cut in the area where the wiring harness must contact the surrounding parts. So in the wiring harness inspection, how to determine whether there is a risk of cutting in the interference part, there are several factors to consider.

 

2.2.1 Protection form of wiring harness

Wire harnesses have the following forms of protective outer coverings: TwiStTube, Corr Tube, PVC Tube, PVC Tape, Urethane Foam, CushionTape.

Each outer covering has different models, but the basic physical and chemical properties of the same outer covering between different models are roughly the same. You can choose a suitable protective outer covering for the wiring harness according to its characteristics.

As for the hidden danger of wire harness cutting, the wear resistance of the outer coating is mainly aimed at. The above outer coatings can be simply ranked from strong to weak: Twist Tube>CorrTube>CUSHION Tape>PVC Tube>URETHANE FOAM>PVC Tape.

 

2.2.2 Drawing properties of wire harness

Compare with the 2D drawing to determine the line length, outer coating and model between the two fixed points of the wire harness at the interference part. Consider the tolerance of the line length. Under the extreme MAx or MIN state, what is the interference degree of the wire harness? What kind of outer coating is used for the wire harness, what is the model, and whether it has the protective effect in the current environment: sometimes the outer surface of the corrugated tube (Corr Tube) is not wrapped with PVC tape. If the corrugated tube model used is not suitable, the wire may jump out of the opening of the corrugated tube. In this case, we should pay attention to the possibility of interference around.

 

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. Generally, it is assumed that the sharp edge of sheet metal cannot interfere with the wire harness that is not wrapped by a corrugated tube (CorrTube) or a twist tube (TwistTube). There are solder joints at the welding parts of sheet metal. If there is a long burr at the solder joint, and the wire harness is close to the burr, the burr may penetrate into the wire harness, pierce the wire, and cause the wire harness to be cut.

 

2.2.4 Contact Part Form

The wire harness protected by the corrugated tube (Corr Tube) contacts the sharp edge of sheet metal. Although it is protected by the corrugated tube, if the relative position of the corrugated tube and the sharp edge is in a state of being perpendicular to each other, it may also cause the wire harness to be cut.

 

2.3 Bite

The occurrence of bite phenomenon is basically because the direction of the wire harness (which may be the design direction or the direction fluctuation caused by tolerance fluctuation) is exactly located at the assembly position of the surrounding parts, causing the wire harness to be squeezed between the two mating parts.

During the wire harness inspection process, sometimes the wire harness is found to be stuck between parts. Sometimes it may be because the wire harness naturally sags due to gravity, and sometimes it may be because the tolerance fluctuation causes the wire harness to be too long or too short, resulting in bite.

The wire harness is mainly composed of wires and their protective outer coverings. The purpose of wire harness inspection is to ensure that the wires in the wire harness are not damaged by external forces and affect the function. Therefore, slight deformation of the protective outer covering can be accepted by quality personnel under the condition that 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 wire harness, it can be considered that the wire harness here is fine.

 

3 Conclusion

As an important part of electrical work, wire harness inspection requires quality management personnel to combine the inspection performance of various models, continuously improve their professional knowledge, and accumulate experience. The above views on wire harness inspection hope to be able to form a complete and mature view of wire harness inspection.

In the future, if the design viewpoints of designers can be combined to evaluate the wiring harness of the whole vehicle from the perspective of designers, quality managers and assemblers, the wiring harness inspection work can be promoted more comprehensively, and customers can also be ensured to get the most comfortable user experience.