As a difficult problem in the automotive wiring harness industry, the problem of terminal pin withdrawal has been plaguing wiring harness designers, wiring harness craftsmen, quality personnel and manufacturing personnel
With the increasing number of automotive electrical functions , it becomes more and more obvious whether the vehicle electrical appliances are normal or not that users can experience. As a bridge that connects various electrical components in the vehicle in series, the wiring harness realizes the normal connection of various electrical circuits, and more and more content needs to be controlled. There has always been a saying in the industry that the most problematic parts of automobiles are electrical appliances, and the most problematic component in electrical appliances is the wiring harness. Therefore, it is important to improve the reliability of wire harness design and manufacturing.
Regarding the many failure modes of automotive wiring harness products, connector withdrawal has always been the most unacceptable and extremely difficult to control problem. Because it not only intuitively reflects the manufacturing defects of the product, but also directly leads to vehicle functional failure. At the same time, because there are many factors affecting terminal withdrawal, covering all aspects of design, parts production, wire harness manufacturing, logistics, etc., it is difficult to control. It is very necessary to systematically analyze and control the problem of connector withdrawal.
?1. Type of terminal withdrawal. When analyzing the terminal withdrawal problem in the wire harness, compared with the terminal withdrawal problem in the wire harness shown in the figure below, it will first be judged whether the terminal is withdrawn before testing or whether it is tested. When the right accessory or probe holder is inserted, it will be ejected. The way to judge is to observe whether the terminal locking structure in the connector sheath is damaged. If the lock is intact, the terminal can be re-inserted. The terminal can maintain a good locking state and does not withdraw. It can be judged that the reason for withdrawing the terminal is that the product was not assembled in place during production. If the lock is damaged, it can be judged that there is external force. Push out the terminal or pull out a single terminal under force: different judgment directions determine different terminal withdrawal control methods.
Generally speaking, the terminal withdrawal problems found from the user's perspective can be divided into two categories based on the path they occur:
① The terminal is not assembled in place in the sheath Cause withdrawal; ② When the terminals are plugged in, they are pushed out or are pulled out due to tension.
Another problem is that there is a problem with the supplier’s incoming materials, and the needles are withdrawn due to stuck points and lack of materials.
The first category focuses on the manufacturing angle of wire harness products, the second category focuses more on the design matching issues of wire harnesses and connectors, and the third category focuses on issues with supplier incoming materials. By clarifying the type of terminal withdrawal, the control range of the withdrawal terminal can be narrowed, the influencing factors can be reduced, and the source of failure can be easily identified, and control measures can be formulated more accurately.
2 Control method for withdrawing terminals 2.1 The terminals are not assembled in place in the sheath, resulting in pin withdrawal
Intuitively speaking, the terminals are not assembled in place in the sheath because of operator error, resulting in incorrect operation. Qualified products flow out. In the current wire harness manufacturing industry, terminal insertion into connectors is basically done manually. In the wire harness industry, the commonly recognized terminal insertion method is "one insertion, two listening, and three pulling back." The most important thing is "three pulling back." The effectiveness of the pulling back action determines the first pass rate of terminal withdrawal. of high or low. The employee's operational proficiency determines the effectiveness of the pullback action. The method to improve the operating proficiency of employees in the industry is: before employees produce every day, they first perform the pull-back operation to establish the pull-back feel, and conduct production practice based on this feel. The effectiveness of the execution of a pullback operation is entirely evaluated by the employee's perception, and its effectiveness will certainly be greatly compromised. Considering that a worker can insert approximately 2,000 terminals every day, approximately one million terminals are assembled and inserted into the sheath manually in a manufacturing plant every day. Therefore, it is difficult to avoid the problem of terminal withdrawal from flowing out to the OEM by relying solely on manual operation and inspection.
By controlling the workers' operating methods to control the terminals in the sheath without withdrawal, from a practical point of view, it can only reduce the terminal withdrawal rate in the short term, but it cannot completely solve the problem, and the mobility of workers makes this problem The effect of the rectification creates great uncertainty, so it is necessary to seek effective inspection methods to identify whether the terminals have exited, and ensure that any terminals that are not assembled in place can be effectively identified. The push-type probe on the conduction equipment came into being under such demand.
Push-type probes are also called switch needles or powerful probes. Compared with traditional conduction probes, push-type probes consist of a push module with an upper part in contact with the terminal and a lower part with the conductor. It consists of a detection module connected to the device. During detection, the device can detect the line loop only after the terminal squeezes the probe push module onto the detection module (Figure 2).
At the same time, the compression force of the probe is larger than the traditional probe compression force of not more than 1.5N, but generally does not exceed 15N, depending on the stop force value of the terminal when it is not assembled in place. Therefore, when the terminal is not assembled in place in the sheath, and the terminal does not have enough stop force to squeeze the push module onto the detection module, the terminal and the device cannot form a detection loop, and the continuity test fails, so it can be effectively discovered. Whether the terminal has exited.
When using push-type probes, you need to pay attention to two issues: ① The contact position between the probe and the terminal should be selected correctly (the edge of the terminal or the bent part of the terminal should be selected for contact). If the probe is inserted For in-terminal detection, modules with push-type probes cannot be used, as this may easily cause the terminal to expand; ② During use of the push-type probe, its pushing force will gradually decrease, and routine maintenance of the probe compression force should be carried out to avoid compression. The force is too small to achieve the detection function.
With the application of push-type probes, it is easier to ensure that the terminals do not exit at the manufacturing level, because the probe on the conduction equipment can 100% detect whether the terminals are in place, making it possible to solve the problems that occur during the manufacturing process. The problem of terminals not being assembled in place can be effectively solved. We no longer have to worry about the hidden dangers of terminals not being assembled in place due to problems such as difficulty in terminal insertion, the ability to insert both front and back terminals, flying wires during wire crimping, and the inability to effectively avoid and implement terminal crimping.
Based on the application of the push probe and the characteristics of the sheath (with and without secondary locking), the control measures for terminal assembly in the sheath without exit are refined into the following controls Path, see Figure 3. The following path can be used to ensure that the terminal is assembled in the sheath without exit.
? It should be noted that the sheath with secondary locking mentioned here refers to the accessory (TPA) with secondary locking terminals, rather than the accessory where the sheath serves as a limiter. (CPA). Because for the secondary locking connector, because the terminal is locked by the primary locking of the sheath and the TPA lock, and the dual structure locking, the possibility of backlash is almost non-existent, but this conclusion is based on the secondary locking It is a premise that it has the function of secondary locking terminal. Because the design of the connector is not absolutely perfect in the actual process, the size design of the secondary lock is often unreasonable, resulting in the inability to lock the terminal. Therefore, before applying a certain plug connector, if the plug connector has secondary locking, its locking effect needs to be evaluated.
Regarding the assembly problem of secondary locking, the assembly detection of secondary locking on the conduction stage has been used very maturely in the industry. However, in practical applications, some manufacturers often assemble a secondary lock after conduction for the convenience of conduction inspection and repair. Such an assembly process is risky, because the terminal is not assembled in place, which does not mean that the secondary lock is The secondary lock must not be assembled in place, and without a continuity check after assembling the secondary lock, it is impossible to identify whether the terminal is in the correct assembly position. Therefore, any assembly with a connection function should be performed before continuity testing.
2.2 Terminals are not ejected when plugged together
There are relatively many control points involved in preventing terminals from being ejected when plugged in. Such faults often occur in concentrated locations. There is also more regularity, and some even have terminal withdrawals in batches. This type of fault is subdivided into two main categories: insufficient terminal retention force and misalignment of terminals when plugged in. There are different control methods for different types, as shown in Figure 4.
Insufficient terminal retention force is mainly reflected in defects in the locking structure of the terminal. Some people damage the locking structure due to manual repairs. There are also situations where the size and material of the locking structure lead to defects in the locking terminal. Such problems are easier to trace in the factory's repair records and incoming material records, and the cause of the problem can be quickly identified and controlled accordingly. However, the number of problems after they occur is often large, especially after the material of the sheath locking structure is changed, which is often not easy to detect. Therefore, the retention force of the terminal in the sheath should be reflected in the factory acceptance as part of the incoming material inspection. Avoid batch issues.
The problem of misalignment of terminals during plugging occurs frequently in actual cases. The causes of such problems are not easy to find. For the mismatch in the position design of male and female terminals, simple size verification can solve the problem. Problems can be found and the cost of design verification is low, but if they are not found, the cost of later mold repair and rectification will be higher. Therefore, before selecting a plug-in connector, especially before opening the mold on the public end of the component, it is necessary to design the contact design position of the male and female ends. Check to reduce the risk of terminal withdrawal.
As for terminal skew, there are many fault factors involved. Crimping, assembly, and transportation may cause the terminal to bend and deform. However, it is easy to break if the bend exceeds a certain range. It must be straightened manually before use, and it needs to be scrapped! The following focuses on the control method of terminal skew.
According to the study of actual cases, terminal skew is divided into three categories: skew during transfer, crimping and bending, and wire pulling on the terminal (single force).
? 1) The transfer process is divided into the transfer process when the wire harness factory is manufacturing it and the transfer process when the wire harness factory sends it to the OEM. For these two different transfer stages, different controls are applied. Method to control the prevention of terminal skew. During the manufacturing process of the wire harness factory, the skew that occurs during the transfer process is inspected and corrected through the anti-skew correction fixture on the conduction table (Figure 5). When the wire harness assembly is delivered to the OEM for assembly, a protective cover should be added to prevent the terminal from skewing (Figure 6). This plastic protective cover is not only cheap, but can also be recycled and reused.
2) Crimping bending failure, as the name suggests, comes from the upturned, sagging, and twisted terminals caused by crimping. Crimping bending itself belongs to the control category of crimping quality. You can refer to other crimping management materials for corresponding control methods. Here is a brief explanation. Through actual production comparison, there are molds designed with terminal fixation structures (in layman terms, press the terminals first and then crimp them), which has a significant effect on eliminating terminal crimping bending faults.
3) The problem of the wires pulling on the terminals is due to the excessive stress on the wires at the end of the connector during the design or production of the wire harness, which transfers the stress on the wires at the end of the connector to the terminals, causing The terminal is displaced from its normal mated position in the housing. The core of the control should be how to reduce the stress on the tail wire of the connector. In general, it is to "untie" the tail wire. The control method is from the perspective of the wire harness direction design. The location of the wire harness branch point should be selected to ensure smooth insertion of the tail wires of the connector. The wire harness branch point of the connector should be above the connector mating plane (Figure 7).
? Another way to "untie" the tail wires of the connector is to control the distance of the tape wrapping of the tail wires of the connector to avoid the tape being wrapped too tightly and causing stress on the wires: generally as shown in Figure 8 Distance requirements are required for the manufacturing of wire harness products.
?3 Conclusion There are many reasons for the withdrawal of terminals from plug-in connectors. In practical applications, corresponding analysis and control should be carried out according to specific problems. According to the control method described in this article, practical solutions can be solved quickly and efficiently. Question) Based on the fact that the industry generally considers whether the "pull back" execution in terminal assembly is in place as a regular control content. 2. How to ensure that the pull back operation is more effective? In practice, we have explored the following two methods: ① The terminal insertion method has been changed from "one plug, two listens, and three pulls" to "one plug, two listens, three releases (hands), and four pulls"; ② Terminal insertion Pulling back needs to be done with the elbow joint as the fulcrum. The starting point of the above two methods is to decompose and quantify employee operation actions to facilitate standardized execution and standardized inspection of employee operations. They can quickly reduce the one-time assembly failure rate of withdrawn terminals, reduce the ratio of withdrawn terminals, and improve the overall reliability of wire harness products.