Analysis of wiring harness failure mode in vehicle assembly

The normal operation of the vehicle wiring harness is the prerequisite for the realization of various functions of the vehicle. Frequent wiring harness failure in vehicle assembly has a great impact on vehicle manufacturing efficiency and product quality. Based on the systematic analysis of the wiring harness failure modes in the whole vehicle assembly process, the wiring harness failure modes are emphatically classified, and corresponding solutions are proposed for the similar failure modes. This paper can provide help for the wiring harness design and the solution of wiring harness failure in the whole vehicle assembly process.


As the "nervous system" of the car, the wiring harness is responsible for the transmission of data such as voltage and signal between various parts of the car. Similarly, the wiring harness is as complex and fragile as the "nervous system", which is prone to numerous problems in the whole vehicle manufacturing process. The analysis and solution of wiring harness failure mode in the whole vehicle assembly becomes an important part to guarantee the safety of the vehicle. Especially in today's automotive electronic system to the integration, functional, intelligent development, wiring harness failure will directly lead to the vehicle "paralysis", automotive wiring harness failure mode is causing great concern. In this paper, the wiring harness failure modes in the whole vehicle assembly process are sorted out and analyzed, and the corresponding solutions are put forward, which provides guidance for the automotive wiring harness design and assembly.


1 Introduction to automotive wiring harness
The function of automotive wiring harness is to transfer the electric energy generated by the battery or power generation system to the electrical equipment, and at the same time to serve as the vehicle signal and other data transmission role. Automotive wiring harnesses consist of conductors, terminals, cladding, connectors and other components. The conductor consists of a wire core and an insulating layer. Because of the stringent installation space and conditions of the vehicle, the conductor requires high flexibility. In order to increase flexibility, the conductor core is drawn into multiple strands, and the thinning of the wires increases the degree of freedom and the risk of being cut off. Insulation layer and cladding act similarly to provide protection and isolation for wires, and their choice affects the safety of wires. Connectors are used to connect wires and electrical appliances, wires and wires, and are composed of a male end and a female end. The compatibility of the male end and the female end with each other and the terminal butt joint affect the circuit conduction function. Other parts, such as studs and muffles, affect the direction of wiring harness and waterproof of the vehicle. All components of the wiring harness jointly complete the transmission of the vehicle voltage, signal and other data. Failure of any part will affect the normal operation of the vehicle.


2. Wiring harness failure mode in vehicle assembly
In order to improve production efficiency and facilitate maintenance, the vehicle equipment process will adopt the strategy of breaking up assembly steps and assigning them to each station. The installation of wiring harness is the same. This "break up into parts" assembly strategy significantly improves the manufacturing speed of the vehicle. However, due to the scattered assembly, wiring harness interfaces and positioning parts are numerous, which often increases the probability of wiring harness failure. Wiring harness assembly runs through the whole vehicle manufacturing process, which is mainly distributed in the interior decoration and door line section. Meanwhile, the chassis section also has the butt joint of some connectors.
The whole vehicle wiring harness assembly span is large, the procedure is many, the wiring harness failure is also correspondingly many. The wiring harness failure modes in vehicle assembly are mainly divided into interference failure, man-machine failure, design failure, matching failure, function failure and abnormal sound failure.
2.1 Interference failure
Interference failure of wire harness refers to the problem or risk caused by too small clearance between wire harness and surrounding components. The causes of interference failure can be divided into design problems, assembly manufacturing problems, quality problems and potential problems. The design problem is caused by the fact that the gap between the wiring harness and the surrounding environment is not considered in the design phase. The non-conformance terms can be found and changed through the 3D simulation review in the design phase, especially the gap in the limit state. Assembly manufacturing will also cause interference failure. The high degree of freedom of the wire harness itself makes it difficult to fix the attitude. State changes will occur in the process of manufacturing, transportation and assembly.
Interference failures caused by assembly manufacturing can be avoided by standardizing the operating flow or process changes for manufacturing, transportation and installation. The interference failure caused by quality problem can be solved by the supplier quality management engineer to strengthen the control of material quality. When a potential problem occurs when the engineering team is unable to determine whether a risk exists, the data of the durable and test vehicles becomes an important basis for the definition of interference failure.
2.2 Man-Machine failure
The man-machine failure in the whole vehicle assembly process is caused by the violation of man-machine engineering. Ergonomics is the interaction between human and machine and the environment. The purpose of ergonomics research is to improve the efficiency, safety and employees' comfort and health. The man-machine failure of wiring harness in the whole vehicle assembly process mainly includes the following three kinds: high wiring harness installation force, improper assembly gesture and posture, and lack of feedback. Excellent wiring harness is the main reason of large installation force, ergonomics has a strict definition of the force of each part of the staff; Small assembly space, large local stress and high frequency strain also have important influence on the assembly of wire harness. Visual or auditory feedback of assembly not only affects the efficiency of wiring harness installation, but also has great significance to vehicle quality and personnel safety. For the man-machine failure of wiring harness, the virtual evaluation in the design and development stage is particularly important. At the same time, each department carries out high frequency joint fitting to avoid man-machine failure in the design stage.
2.3 Design failure
Wiring harness design failure often occurs in the early stage of vehicle assembly. In the first stage of the factory test of a project, the number of label paper of wiring harness parts was not correct, and wiring harness connectors did not have docking parts, etc. Harness design failures occur only after the first build or engineering change, and harness release problems can be quickly identified and resolved. In order to avoid or reduce design failure problems, the parts list and sample status should be checked carefully before the design is released.
2.4 Matching failure
Wiring harness matching failure also occurs in the whole vehicle assembly process, this kind of failure mainly occurs in the pin and connector. The wiring harness clamp has the requirement of matching degree and plug and pull force, and the male and female ends of the connector also need to meet the requirements of matching degree and plug and pull force. In addition, the installation of wire harness and connectors is closely related to the assembly space. During the building stage of a project, the position of body sheet metal hole changed, but the position of wire harness clamp failed to match with the changed position, so the wire harness clamp could not be installed.
In case of such matching failure, the R&D personnel should intervene in the design stage of the digital model in advance and carry out matching related inspection on the digital model. Meanwhile, in the later stage of engineering changes, they should timely inform the corresponding engineers of the surrounding parts and coordinate with them to make changes after communication to ensure the matching of wiring harness changes.
2.5 Functional failure
The wiring harness is responsible for transmitting electrical energy, voltage and other signals on the vehicle. The failure of wiring harness often causes the function failure of the vehicle. The wiring harness function failure in the whole vehicle assembly process is various, automobile electronics related engineer through SPY3 and other tools to determine the problem area, wiring harness engineer combined with circuit schematic diagram and wiring harness assembly drawing to confirm the specific part of the problem. The failure of wiring harness function in the whole vehicle assembly process is mainly caused by the improper docking of connectors, bent needles and the failure of the secondary lock. In addition, the vehicle wiring harness assembly not in accordance with the statutory requirements will also cause functional failure. For example, the power supply of the whole vehicle should be cut off urgently, the regulations require emergency cut off wiring harness needs to be in the area that can be easily cut off, in order to cut off in the first time in the vehicle major accident, rescue people inside.
2.6 Abnormal sound failure
There are several main reasons for the abnormal sound failure of the wire harness, including the collision between the wire harness and surrounding parts, the installation of the wire harness clips is not tight and the wire harness connectors are not fixed. The main difficulty in solving the abnormal sound failure lies in finding the abnormal sound source. General replacement method and auscultation equipment can find the abnormal sound source of the abnormal sound failure of the wire harness. The abnormal sound failure of the wire harness can be solved by corresponding adjustment of the state of the wire harness according to the reason of the abnormal sound failure. At the same time, the possibility of abnormal sound failure can be identified in advance through envelope analysis at the design stage, and the abnormal sound failure caused by excessively long wire harness can be solved by using sponge tape.
2.7 Other failures
There are also other failure modes in the whole vehicle assembly process, such as the unattractive color of the wire harness cladding, the inability to switch the changed parts of the wire harness, etc. This kind of complex failure needs to be modified in combination with the evaluation opinions of various parties, and market research is particularly important. However, the failure problem of material switching is often not solved by one person. Strictly following the material switching process can largely avoid this kind of problem.

3 conclusion
With the increasing demand of automobile function, the wiring harness will be more and more complex. Correspondingly, more and more wiring harness failures occur in the whole vehicle assembly process. Firstly, the wiring harness is briefly introduced, and then the wiring harness failure in the whole vehicle assembly process is systematically classified, and the solutions are proposed according to the characteristics of various failure modes. That is, carefully check the list of parts in the design stage and strictly simulate the state, carry out multi-party trial installation after the sample is produced, consider surrounding parts when changing, and strictly implement the installation process during the installation. The accumulation of these solutions has a certain guiding significance for wiring harness failure treatment.