Analysis and improvement of water intrusion failure of automobile wiring harness connectors

Analysis and improvement of water intrusion failure of automobile wiring harness connectors

Analysis and Improvement of Water Intake Fault of Wiring Harness Plug-in

The article takes the water intrusion failure of a certain model of automobile wiring harness connector as an example, and uses the fault tree analysis method to analyze and improve the water intrusion failure of the automobile wiring harness connector. The purpose is to eliminate the water intrusion failure of the automobile wiring harness connector and improve the safety of the car. It satisfies users' needs for safe driving and provides a reference for the development of later models and the analysis and improvement of similar faults.

01 Analysis and improvement of water intrusion failure of automobile wiring harness connectors

In the market failure report of a certain model of automobile wiring harness, the fault rate of water intrusion in the wiring harness connector was as high as 47%, and the fault location was mainly concentrated in the nitrogen and oxygen sensor. Water intrusion into the wiring harness connector is the TOP1 fault among the wiring harness failure modes of this model. The following uses "Analysis and Improvement Process of Water Intrusion Failure in the Nitrogen Oxygen Sensor Wiring Harness Connector of This Model" as a case to elaborate on.

After receiving the project task, the company immediately formed a project team, and the company leaders launched the project research. The members of the project team are composed of personnel from suppliers of complete vehicles and wiring harness components who are engaged in cross-disciplinary work such as technology research and development, technology, quality, and production and manufacturing. During the project research process, members of the project team visited markets such as Jiangsu and Zhejiang, conducted on-site investigations on the working conditions of car owners, observed faults on-site, and found that the water ingress was concentrated at the nitrogen and oxygen sensor. The members of the project team and the maintenance technicians from the local maintenance service station worked together to discover, analyze and solve problems at the site of the faulty vehicle, on-site and on-site, and finally formed and implemented a product optimization and improvement plan. The improved product has undergone a large number of experimental verifications and vehicle road tests. The water intrusion failure of the wiring harness connector was finally eliminated, the physical product was switched as scheduled, and the project was successfully completed. During the project development process, the project team members were problem-oriented and aimed at eliminating the water intrusion failure of the nitrogen and oxygen sensor wiring harness connector. They focused on the nitrogen and oxygen sensor wiring harness, compared the product drawings and technical requirements, and used the fault tree analysis method to analyze the problems from people, Systematic discussions and analyzes were carried out on machines, materials, methods, environment, measurement and other aspects, and the reasons for the "water intrusion failure of the nitrogen and oxygen sensor harness connector" were thoroughly searched from the outside to the inside. Through thorough discussion and analysis, three possible reasons were identified:

(1) Process selection issues for wire harness connectors, waterproof plugs, blind plugs, and terminals;

(2) The waterproof bolt is damaged or missing;

(3) Connector design issues.

Further analysis identified two possible reasons for the "process selection problem of wire harness connectors, waterproof plugs, blind plugs, and terminals": one is the problem of wire harness connectors, waterproof plugs, blind plugs, and terminal matching; the second is waterproofing Plug insertion status problem. It was identified that there are two possible reasons for "broken or missing waterproof bolts": one is a problem with employees' standard operations; the other is that the waterproof bolts were damaged during the circulation process. It was identified that there are two possible reasons for the "connector design problem": one is the connector selection problem; the other is the connector assembly position problem.

In summary, through FTA analysis, a total of six potential factors were identified that may cause "water intrusion into the nitrogen and oxygen sensor wiring harness connector", namely: wiring harness connector, waterproof plug, blind plug, terminal matching problem, waterproof plug insertion Status issues, employee standard work issues, waterproof bolts damaged during circulation, connector selection issues, connector assembly location issues. The specific fault tree is shown in the figure below (Figure 1):

►Wire harness connectors, waterproof plugs, blind plugs, and terminal matching issues

The project team inspected the models and wire diameters of the wiring harness connectors, waterproof plugs, blind plugs, and wiring harness terminals at the nitrogen and oxygen sensor locations. At the production site, 50 physical products were randomly selected for testing. Among them, connectors, waterproof plugs, blind plugs, and wiring harness terminals are all parts specified by the vehicle manufacturer. Their sizes and models comply with the requirements of the technical drawings. Wiring harness connectors, waterproof plugs, Blind plugging and terminal plug-in matching are good. Carry out airtightness test and watertightness waterproofing test on nitrogen and oxygen sensor sheaths, waterproof plugs, blind plugs, etc. in accordance with the definitions in Part 1 of QC/T 417.1-2001, test methods and general performance requirements (automotive part) 4.9 waterproof performance requirements, and observe There was no airflow during the test, and there were no visible traces of water inside the connector. The test results proved that the actual product complied with the technical requirements of 4.9 waterproof performance in QC/T 417.1-2001 Part 1, Test Methods and General Performance Requirements (Automotive Part).

Therefore, "wire harness connectors, waterproof plugs, blind plugs, and terminal matching issues" are not the key factors affecting the water ingress of the nitrogen and oxygen sensor wire harness connectors.

►Problems with the insertion status of waterproof bolts

The project team organized design, process, quality and other relevant personnel to jointly conduct process discipline inspections at the production and manufacturing site. The operating standards for the crimping station, waterproof plug assembly station and interpolation station at the manufacturing site are complete and effective. The operator operates the fully automatic offline crimping equipment to crimp the terminals, and the semi-automatic waterproof plug equipment inserts the waterproof plug. The production equipment is operating in good and stable condition, and on-site equipment maintenance records are complete. The insertion status of 100 waterproof bolts was tested on site. The insertion position of the waterproof bolts was stable. The quality of the waterproof bolts after insertion met the technical standards.

Therefore, "the insertion status of the waterproof plug is not the key factor affecting the water ingress of the nitrogen and oxygen sensor harness connector.

►Employee standard operating issues

At the manufacturing site, wire harness terminals are crimped using special molds. The mold is regularly maintained and maintained in good and stable condition. The wire harness terminal crimping height, pullout force and other dimensions and performance meet the requirements of technical standards, and the terminal crimping condition is in good condition. A random inspection of the process inspection records of the workshop inspector found that on a certain day the inspector randomly inspected 120 nitrogen and oxygen sensor wire harnesses, and 8 blind bolts were missing. The solution was to rework. Carefully look at the inspector's process inspection record sheet, which shows that a different number of nitrogen and oxygen sensor blind bolts are missing every month. In order to further find out the reason for the missing installation of blind bolts, the project team went to the formwork insertion station of the workshop to conduct an investigation. There is a work standard instruction book on the template inserting and planting station, and the work standard instruction book clearly stipulates that blind bolts must be assembled. During the inspection, it was found that there were multiple operators at the template insertion and planting station at the same time, but the personnel who assembled the blind bolts were not fixed, and the operators installed them by themselves, which easily caused the blind bolts to be missed.

Therefore, "employee standard work issues" are the key factors affecting the water ingress of the nitrogen and oxygen sensor wiring harness connector.

Improvement measures: In order to prevent employees from missing the blind bolt installation, the project team optimized the process and adjusted the blind bolt assembly from the template insertion station to the previous process: the batching station. That is, after the batching personnel assemble the blind bolts, the product flows into the next process: the template insertion station. The planting personnel will check and confirm that the blind bolts in the previous process are in place. In this way, the upper and lower processes perform self-inspections and mutual inspections to prevent missing installation of blind bolts. The project team promptly solidified the optimized process into FMEA, operating standard instructions and other relevant technical documents, and organized training and evaluation of relevant employees on knowledge and skills. Employees who pass the evaluation will be put on the job. After process optimization, project team members tracked the quality of the nitrogen and oxygen sensor wiring harness at the manufacturing site and found no missing blind bolts. They tracked and inspected the inspection records of the workshop process inspector for a month and found no missing blind bolts. Process improvement The results are obvious.

►The waterproof bolt was damaged during circulation

At the manufacturing site, the wire harness terminals after crimping are equipped with plastic protective cups for protection, and the terminal protection effect is good. The wiring harness was hung on a special work station equipment trolley and circulated within the workshop. During the circulation process, no damage or missing waterproof plug of the nitrogen and oxygen sensor was found.

Therefore, "the waterproof plug is damaged during the circulation process" is not the key factor affecting the water ingress of the nitrogen and oxygen sensor wiring harness connector.

►Connector selection issues

There are two types of nitrogen and oxygen sensor wiring harness connectors for this model, namely Part A and Part B. After sorting out the market failure reports, it was found that the faulty connector models were all Part A. However, for vehicles equipped with Part B, there was no water intrusion into the connectors on the market. In order to further identify the cause, the project team dissected the faulty parts and found that the oxidation direction of the wires was from the connector to the wiring harness branch. Then they picked out the terminals and found that the oxidation was from the terminal head to the wires. These phenomena indicate that water enters between the two plug-ins. Comparative analysis of the two connectors, Part A and Part B (Figure 2), shows that the terminals of Part A are exposed to the outside without protection; while Part B has restrictors that completely cover the terminals, resulting in better sealing and higher waterproofing effect.

Therefore, the "connector selection problem" is a key factor affecting the water ingress of the nitrogen and oxygen sensor wiring harness connector.

Improvement measures: The connector B was subjected to a watertight and waterproof test, and the test results were qualified and in line with the technical requirements of 4.9 waterproof performance in QC/T417.1-2001 Part 1 Definition, Test Methods and General Performance Requirements (Automotive Part). The project team optimized the product design and switched the nitrogen and oxygen sensor wire harness end connector from Part A to Part B. At the same time, it modified relevant technical documents such as FMEA, product drawings and technical standards, and organized training for relevant employees to form organizational memory and prevent Similar design selection problems occurred again.

►Connector assembly position problem

Members of the project team conducted air-tight and waterproof tests on 10 nitrogen and oxygen sensor wire harness connectors returned from the market. The test verification results were all qualified and in line with the definitions, test methods and general performance requirements (automotive part) of QC/T 417.1-2001 Part 1 4.9 Technical requirements for waterproof performance. Place the connector in the vehicle system for analysis. The nitrogen and oxygen sensor is installed above the fuel tank and exhaust pipe. The assembly position here is lower. The temperature is higher when the vehicle is driving. The impact of water pressure here on rainy days. The waterproof level of the wiring harness connector cannot meet the requirements of the vehicle layout environment. A small amount of water vapor will enter the sensor along the sensor wiring harness, causing damage to the nitrogen and oxygen sensor.

Therefore, "connector assembly position problem" is a key factor affecting the water ingress of the nitrogen and oxygen sensor wiring harness connector.

Improvement measures: Adjust the assembly position of the nitrogen and oxygen sensor on the vehicle from the original position of the fuel tank and exhaust pipe to the position inside the chassis frame of the car. At the same time, add dripping points to avoid water accumulation in the nitrogen and oxygen sensor wiring harness connector caused by high temperature and high pressure. According to the improvement plan, five vehicles were installed and tested on the road. There was no water intrusion into the nitrogen and oxygen sensor wiring harness connector, and the improvement measures were effective. The project team modified product drawings, technical standards, technical requirements and related process documents and operating standard instructions, and organized timely training to form organizational memory and prevent similar design problems from happening again.

02 Conclusion

In summary, through fault tree analysis, the three key factors causing water intrusion into the nitrogen and oxygen sensor harness connector were identified: employee standard work issues, connector selection issues, and connector assembly location issues. Based on these three key factors, a product improvement plan was proposed and implemented. The improved vehicle did not have water intrusion into the nitrogen and oxygen sensor wiring harness connector. The project team solidifies and standardizes the product improvement results in a timely manner to form organizational memory. Through the project research, the water intrusion fault of the nitrogen and oxygen sensor wiring harness connector has been eliminated, the safety of the car has been improved, and the users' needs for safe driving have been met for a better life. At the same time, it has provided a reference for the development of later models and provided information for the analysis and improvement of similar faults. Learn from.