As the main link for current and signal transmission in automotive wiring harnesses, the reliability of transmission between connectors directly determines the effectiveness of current and signal transmission. This article will start with several forms of connector failure, classify and introduce common types of connector failure, as precautions when selecting connectors.
1 Background
With the rapid development of the automotive industry, people's requirements for the safety and reliability of various functions of automobiles are constantly increasing. The safety and reliability of automotive connectors, as the link connecting vehicle body harnesses, have also attracted increasing attention. In this context, combined with the tracking feedback during the use of connectors, this article summarizes and classifies the common types of connector failures, and elaborates on the main causes of problems, which facilitates people's understanding of common forms of connector failures and can also serve as a reference for analyzing the failure modes of automotive connectors.
2 Failure types
After years of data investigation and analysis of feedback on the connector market, it has been found that the common types of failure in automotive connectors on the market can be roughly divided into: sheath fracture, terminal displacement, sealing failure, and terminal spring failure. The above failure modes will have an impact on the functionality of the connector, even leading to loss of function, and belong to high severity failure modes. Below, we will classify and analyze the above types of failures.
2.1 Sheath breakage
The sheath is a part of the connector, and its components are mostly made of polymer engineering plastics. Commonly used materials include nylon, polypropylene, and polybutylene terephthalate (PBT). The main function of the sheath is to provide fixed support and insulation protection for the terminals. Therefore, the sheath itself should have sufficient strength to support and protect, as well as sufficient toughness to meet the needs of connector installation and disassembly. The molecular chains of polymer materials are generally sensitive to the influence of the external environment. For example, nylon materials have a significant decrease in strength and a significant increase in toughness in humid and hot environments, which can easily lead to inadequate retention of terminals in the sheath; In a dry and cold environment, the strength will significantly increase, but the toughness will significantly decrease, making it prone to fracture problems. The main form of connector fracture is brittle fracture at the bending part of the connector, such as the common fracture of the sleeve hinge during the folding process. The main factors that cause fracture generally include the following.
1) The moisture content of the sheath material exceeds the standard. Polymer materials have strict requirements for moisture content, so standardized drying operations are generally carried out before injection molding production. The purpose is to ensure that the material meets certain moisture content requirements. If the moisture content is low, it will change the toughness of the material and increase the probability of fracture.
2) The injection temperature is not suitable. Excessive injection temperature can cause the molecular chains of polymer materials to break and recombine, changing the original characteristics of the material and affecting its toughness, exacerbating the occurrence of product fracture.
3) The injection molding machine model (displacement) does not match the product. The production of small-sized products by injection molding machines with excessive displacement can cause the material to melt too long in the injection molding equipment, leading to the degradation of material molecular chains, changing the characteristics of the material, and reducing its performance.
4) For hinge products, the ratio of the length of the hinge to the thickness of the hinge is too small. During the hinge folding process, fracture may also occur due to excessive stress at the hinge bending point.
5) The low toughness of raw materials themselves can also exacerbate the risk of fracture. For example, PBT materials are more prone to fracture defects due to their low material toughness. Therefore, when selecting materials for connector design in the early stage, it is necessary to fully consider the product's usage environment and choose appropriate materials.Therefore, in the production process of connectors, it is necessary to strictly follow the established production process operations, and not arbitrarily change production processes and equipment. At the same time, it is necessary to ensure a reasonable product structure, and then select appropriate materials according to the product usage environment to reduce the occurrence of fractures.
2.2 Terminal displacement
The displacement of connector terminals can directly cause interruption of connector current or signal transmission, leading to loss of function, and is a highly severe failure mode. There are generally several reasons that can cause connector terminals to fall out.
1) Reason for assembly process. The occurrence of this type of failure is mostly due to the terminals not being installed properly, and there is no effective connection between the terminals and the sheath. At this time, the terminals are in a virtual hanging state, which makes it easy for the terminals to detach from the sheath when subjected to force. This situation is usually caused by the assembly workers not strictly adhering to the requirements of "one plug, two listen, and three pull" when assembling the terminals, resulting in the occurrence of defects.
2) Product structure reasons. Due to structural or material reasons, the strength of the terminal or sheath connection structure is insufficient (the retention force of the terminal in the sheath does not meet the standard requirements). When the terminal is subjected to the tension of the tail crimping wire, it may be pulled out. There are generally two situations where this defect occurs: one is that the hanging spring of the terminal has insufficient strength and is pulled and damaged; Another type is that the tongue strength of the sheath is insufficient and is damaged by tension.
3) Connector alignment center offset. There are generally several reasons for this situation: ① Inconsistent center to center distance dimensions of connectors, interference between plug terminals and socket terminals or socket sheaths during matching, resulting in terminals being pushed out; ② The clearance between connectors is too large, causing the center of the connector to shift during the insertion process, resulting in defects; ③ The clearance between the plug terminal and the plug sheath cavity is too large, or the plug terminal lacks a reliable positioning structure in the sheath, causing the terminal head to shift, thereby affecting the normal insertion of the connector; ④ The deformation of the plug terminal after crimping causes the terminal to shift after assembly, leading to the occurrence of defects.So, to avoid the problem of connector misalignment, it is necessary to first require the connector to have sufficient retention force, then establish reasonable terminal assembly specifications, and then cooperate with the specified connector clearance to meet the above conditions, and the problem of terminal misalignment can basically be avoided.
2.3 Sealing Failure
Waterproofness is an essential performance requirement for wire harness connectors used in wet areas of automobiles, such as the engine compartment. The waterproof components of connectors are mainly divided into two types: sealing rings and sealing plugs. Sealing rings are used to seal the connectors, while sealing plugs are used to seal the wires and connector inlet ends. Sealing rings are further divided into axial seals and end face seals, while sealing plugs are further divided into individual sealing plugs and integral sealing plugs. The main manifestations of sealing component failure are: there is a gap defect in the sealing rib used for sealing on the sealing component; There are injection defects such as seams, burrs, and insufficient injection in the sealing area of the sheath that matches the sealing components; Insufficient effective sealing interference of sealing components; The irreversible plastic deformation of sealing components after high-temperature aging can all lead to sealing failure. Therefore, in the production control stage, it is necessary to ensure the smoothness and flatness of the sealing ring and sheath sealing area, and select sealing ring materials that can meet the requirements of high-temperature aging. There is a special form of failure for integral sealing plugs: integral sealing generally adopts the form of terminal installation after passing through the sealing plug. During the assembly process of the terminal, it is easy to cause tearing of the sealing area of the inner ring of the sealing plug, leading to sealing failure. Therefore, the integral sealing plug requires that the terminal head that is compatible must be smooth and free of appearance defects such as edges and burrs, in order to avoid the occurrence of such defects.
2.4 Terminal spring failure
The most direct function of terminal shrapnel is to provide reliable positive pressure F for effective contact between plug terminals and socket terminals, meeting the reliability of current and signal transmission. The failure of terminal shrapnel is generally caused by the following reasons: ① The shrapnel gap size L is too large during the production process of the terminal, causing the shrapnel to be unable to contact the plug terminal, and thus unable to provide reliable positive pressure F for the plug terminal, resulting in contact failure; ② During the electrical inspection process after installing the protective sheath on the terminal, if the probe of the electrical inspection is stuck and does not rebound, the spring will not rebound due to excessive compression of the spring; ③ Improper operation during rework and repair, excessive compression of terminal shrapnel causing terminal shrapnel to not rebound; ④ The bending arc R at the root of the terminal spring is too small, resulting in stress concentration. During the deformation process, the spring produces plastic deformation at the root of the bending arc. Therefore, the solution to the failure of terminal shrapnel requires strict control of the gap between shrapnel and the size of the arc root during the production process, as well as regular inspection of electrical inspection fixtures and standardized rework and repair stations, in order to minimize the occurrence of shrapnel failure.
3 Summary
In summary, the forms of connector failure include breakage, terminal misalignment issues, sealing issues, and terminal spring failure. Therefore, in the design and selection of connectors, it is necessary to determine the performance testing items of connectors in a targeted manner based on their usage environment. At the same time, it is necessary to strictly follow the connector operation specifications to avoid defects caused by improper operation.
