简体中文
From the perspective of use, the function that the wiring terminal should achieve is: the contact area that should be conductive must be conductive, and the contact should be reliable. The parts of the insulation that should not be conductive must be insulated reliably. There are three common forms of fatal faults in wiring terminals:
1. Poor contact
The metal conductor inside the terminal is the core component of the terminal, which transmits voltage, current, or signals from external wires or cables to the corresponding contacts of the corresponding connectors. Therefore, the contact parts must have excellent structure, stable and reliable contact retention force, and good conductivity. Due to the unreasonable design of the contact structure, incorrect material selection, unstable mold, oversized machining, rough surface, unreasonable surface treatment processes such as heat treatment and electroplating, improper assembly, harsh storage and use environment, and improper operation, poor contact can be caused at the contact and mating parts of the contact.
2. Poor insulation
The function of an insulator is to maintain the correct alignment of the contacts and to insulate them from each other, as well as from the shell. Therefore, insulation components must have excellent electrical, mechanical, and process forming properties. Especially with the widespread use of high-density and miniaturized terminal blocks, the effective wall thickness of insulators is becoming thinner and thinner. This puts forward stricter requirements for insulation materials, injection mold accuracy, and molding process. Due to the presence of metal residues, surface dust, solder contamination, moisture, organic material precipitates, and harmful gas adsorption films on the surface or inside of the insulator, they fuse with the surface water film to form ionic conductive channels, absorb moisture, mold, and aging insulation materials, all of which can cause insulation defects such as short circuits, leakage, breakdown, and low insulation resistance.
3. Poor fixation
Insulators not only serve as insulation, but also provide precise alignment and protection for extended contacts. They also have the function of installation positioning, locking and fixing on the equipment. Poor fixation may affect the reliability of contact, resulting in instant power outage. The most serious issue is product disassembly. Disassembly refers to the abnormal separation between plugs and sockets, as well as between pins and sockets, caused by unreliable structure due to material, design, process, and other reasons when the wiring terminal is in the plug-in state, which will cause serious consequences such as power transmission and signal control interruption in the control system. Due to unreliable design, incorrect material selection, improper selection of forming process, poor quality of heat treatment, mold, assembly, fusion and other processes, and inadequate assembly, poor fixation can all be caused.
In addition, poor appearance caused by peeling, corrosion, bruises, plastic shell flash, breakage, rough processing of contact parts, deformation, and other reasons of the coating, as well as poor interchangeability caused by oversized positioning and locking fit size, poor processing quality consistency, and excessive total separation force, are also common and frequently occurring diseases. These types of faults can generally be detected and eliminated in a timely manner during inspection and use.
Reliability screening test for failure prevention
To ensure the quality and reliability of wiring terminals and prevent the occurrence of fatal faults mentioned above, it is recommended to study and develop corresponding screening technical requirements according to the technical conditions of the product, and carry out the following targeted reliability tests for preventing failures.
1. Prevention of poor contact
1) Conduction detection
At present, there is no acceptance test for the products of general terminal manufacturers, and users generally need to conduct conductivity testing after installation. Therefore, it is recommended that manufacturers add 100% point by point conduction testing to some key models of products.
2) Instantaneous break detection
Some wiring terminals are used in dynamic vibration environments. The experiment proves that only checking whether the static contact resistance is qualified cannot guarantee reliable contact in dynamic environments. Because connectors with qualified contact resistance often experience momentary power outages during vibration, impact, and other simulated environmental tests, it is best to conduct dynamic vibration tests on 100% of high reliability terminal blocks to assess their contact reliability.
3) Single hole separation force detection
Single hole separation force refers to the separation force that changes the contact part in the insertion state from static to moving, used to indicate that the pin and socket are in contact. Experiments have shown that if the separation force of a single hole is too small, it may cause signal transient interruption when subjected to vibration and impact loads. The method of measuring the separation force of a single hole to check contact reliability is more effective than measuring contact resistance. The inspection found that the contact resistance of the socket with a single hole separation force exceeding the tolerance is often still qualified when measured. Therefore, in addition to developing a new generation of flexible, stable and reliable contact parts, the production plant should not use automatic insertion and extraction force testing machines for multi-point simultaneous testing of key models. The finished product should undergo 100% point by point single hole separation force inspection to prevent signal instantaneous interruption caused by individual socket looseness.
2. Prevention of poor insulation
1) Insulation material inspection
The quality of raw materials has a significant impact on the insulation performance of insulators. Therefore, the selection of raw material manufacturers is particularly important. We should not blindly reduce costs and lose material quality. We should choose reputable large factory materials, and carefully check and inspect important information such as batch numbers and material certificates for each batch of incoming materials. We should also provide traceability information for material use
2) Insulation resistance inspection of insulators
At present, some production factories require electrical performance testing after assembly into finished products, but due to the insulation resistance of the insulator itself being unqualified, the entire batch of finished products has to be scrapped. The reasonable process should be 100% process screening in the state of the insulator parts to ensure qualified electrical performance.
3. Prevention of poor fixation
1) Interchangeability check
Interchangeability check is a dynamic check. It requires plugs and sockets of the same series to be able to be inserted and connected to each other. It is found whether there are any reasons such as the size of insulators, contacts, and other parts being out of tolerance, missing or not assembled in place that prevent them from being inserted, positioned, and locked, or even causing disassembly under rotating force. Another function of interchangeability inspection is to detect in a timely manner whether there are metal residues that affect insulation performance through plug and pull connections such as threads and bayonets. Therefore, 100% inspection should be conducted on some important terminal blocks to avoid such major fatal failure accidents.
2) Torque resistance inspection
Torque resistance inspection is a very effective inspection method for assessing the reliability of terminal structure. According to the US military standard MIL-L-39012, samples should be sampled from each batch for torque resistance inspection to detect problems in a timely manner
3) Connection testing of crimped wires
During electrical installation, it is often found that individual core crimping wires cannot be delivered in place or cannot be locked after being delivered, resulting in unreliable contact. The reason for the analysis is that there are burrs or dirt stuck at the screw teeth of individual installation holes. Especially when using the last few installation holes that have already been installed into a plug socket by the factory, if the defect is found, the wires that have already been installed in other holes must be removed one by one and the plug socket must be replaced. In addition, due to improper matching of wire diameter and crimping aperture, or due to incorrect crimping process operation, it can also cause accidents of unstable crimping ends. For this reason, the production factory needs to conduct a test on all installation holes of the delivered plug (socket) samples before the finished product leaves the factory, that is, use loading and unloading tools to simulate the wires with crimped pins or sockets and send them in place to check whether they can be locked. According to the product technical specifications, check the pulling force of each crimped wire.
Without reliable wiring terminals, there is no reliable system engineering. Failure and reliability are two aspects of a contradictory entity that correspond and are interrelated. By screening the reliability of wiring terminals, various failure modes and mechanisms can be identified, which can lead to a large number of lessons learned and eliminate various hidden dangers, providing scientific basis for improving design, process, inspection, and use. It is also an important basis for revising and formulating the technical conditions of wiring terminals. The ultimate goal of failure analysis is to find measures to prevent failure and achieve the transformation from failure to reliability.
