Application of Reliability Technology in Coupler Sockets　

Abstract: This paper mainly discusses the failure mode of coupler sockets and the analytical ideas for improving product reliability. Starting from the core link of quality management - quality control, a reliability quality improvement model is created that can improve product quality without increasing product production costs. Through summary analysis, the main problems in product use are found, and in-depth analysis is conducted to find out the root causes of the problems. The coupler socket structure is optimized and changed from the perspective of product reliability. It makes it more suitable for after-sales use environment and achieves the purpose of significantly reducing product failure rate. At the same time, the safety of the product is also improved.

0 Introduction

The coupler socket is a special socket for the power supply of the air conditioner cabinet of Company A. It is safer and can be operated by a knob. When the plug is screwed into the socket and locked, the power is turned on. When the plug is unlocked and screwed out of the socket, the power is turned off. It is different from the common plug-in socket. It has great advantages in terms of power safety and protection against electric shock. Therefore, it is of great significance to further improve the reliability of the coupler socket.

This project analyzes a large number of after-sales faulty parts to identify the core failure points that affect product quality, and combines them with user experimental usage conditions to avoid quality problems from the design source.

1 Reliability Development Planning

As consumers have higher and higher requirements for the quality of home appliances, products with high reliability are favored. How to improve product quality and safety depends on the long life and high reliability of individual components. The study of coupler sockets is based on this starting point. Starting from the reliability research of a single product, a complete set of reliability analysis methods is established, promoted and applied, so as to improve the overall reliability of the product.

Coupler socket reliability research fully utilizes reliability technology to ensure the applicability and durability of the design. During the project process, the overall design of the project is carried out in accordance with reliability planning, reliability analysis, and reliability review, and fault tree analysis, fault simulation, improvement effect evaluation and other analysis methods are used to ensure the reliability of the design project.

In the reliability planning stage, the purpose of the project is mainly to confirm the definition of reliability and the reliability indicators that need to be achieved, and to clarify the reliability requirements. In the reliability analysis stage, data collection and analysis are first carried out, and the causes are determined by using fault tree analysis. Combined with key factors and design-related elements, relevant numerical simulations are carried out and verified, and finally the reliability of the structural design is confirmed [1]. Based on the design test results, the optimization plan is continuously updated, and the final rectification effect is compared and evaluated. The design plan is modified or confirmed by long-term use of data tracking and other evaluation methods. The design implementation flow chart is shown in Figure 1.

2 Summary and analysis of user problems

2.1 Using Fault Tree Analysis to Analyze Failure Categories

2.1.1 Data Statistical Classification

Coupler socket failure not only affects the reliability of air conditioners, but also directly affects the safety of electricity use by users. Improving its reliability is urgent and important. The collection of relevant data provides support for successful data analysis and product quality evaluation. The causes of after-sales failures of the coupler socket over a period of time are summarized and analyzed, and they are distinguished according to the fault category as shown in Figure 2.

The top two faults are burnt out due to improper insertion (accounting for 36.8%) and deformed socket (22.2%), accounting for 59% of the total faults; followed by improper installation and use, accounting for 11.5% of the total faults; bouncing and burning, accounting for 10.5%; and poor wiring, accounting for 9.1% of the total faults.

2.2 Fault Tree Analysis

Before using the fault tree for analysis, it is necessary to sort out the failure mode and find the terminal factors of the problem. Combined with the characteristics of the use of the coupler socket, we divide the failure mode into two categories for sorting and research: one is that the plug cannot be assembled and cannot be rotated into place; the other is that the power supply ignites and burns out. Through refinement and summary, the coupler socket failure fault tree is shown in Figure 3.

Through the fault tree analysis, it can be seen that the main factors leading to the failure of the coupler socket are: material structure defects (base structure, spring structure, sleeve material, slider temperature resistance), user use, installation and maintenance.

From the terminal factors analyzed above, it can be seen that the defects in product structure have a greater impact on product reliability: ① It is not very versatile and is prone to problems when used with some power cords, such as hard copper wires, aluminum wires, etc.; ② Operability. The socket is a power plug that rotates with the socket to connect the power. However, when the user uses it, if it is not rotated into place and the power is already connected, it will cause sparks due to the small contact area. The structure needs to be optimized to increase operability; ③ After-sales installation and maintenance, which is caused by the after-sales staff's technical skills and carelessness at work. This part can only be reduced by strengthening personnel management to reduce the occurrence of failures.

In summary, in order to improve the reliability of the product itself, the structural design needs to be optimized to fundamentally prevent the occurrence of problems.

3 Reliability Improvement Plan

3.1 A lower shell structure of a limit sleeve

3.1.1 Failure Cause Analysis

After conducting statistics on regions that reported faults over a period of time, it was found that the failure rates were higher in Anhui, Henan, Hebei, Shandong and other places. After investigating the power cords installed and used in sockets in various places, it was found that Henan, Anhui, Hebei and other places mostly used single-strand hard copper wires, while Guangdong mostly used multi-strand copper wires.

Field investigation shows that the wires used for installing coupler sockets in most areas of Anhui are single-core hard copper wires of 2.5 mm2-3 mm2. For easy installation, the power cord is usually reserved longer. After wiring, the wires will be bent and coiled in the wall hole behind the socket, as shown in Figure 4. Combining the above two regional differences, it is found that the after-sales failure rate in areas using single-strand hard copper wires is generally higher.

The deformation of the socket is mainly due to the fact that during after-sales installation, the customer's home uses single-strand wire. The material of the single-strand wire is hard, and the back of the socket is subjected to force during wiring, which pulls on the socket and causes the socket to deform. After mating with the power cord plug, the pin slides out of the socket when it rotates and impacts the spring, causing deformation, as shown in Figure 5.

Connect the coupler socket to a single-core hard copper wire to simulate the installation of the coupler socket, bend and press the copper wire down. When the bending angle of the copper wire is large, press the copper wire down and the position of the socket will shift (Figure 6). At this time, the plug cannot be inserted. Release the copper wire and restore it to its original state (Figure 7), as shown in Figure 7.

Checking the coupler structure, there is a large gap between the socket and the lower shell on both sides (Figure 8), and the socket cannot be fixed. When the copper wire is stressed, it will drive the socket to move forward and backward, and the socket position will change, making it impossible to insert the plug.

3.1.2 Reliability Improvement Plan

To improve product reliability by preventing the sleeve from moving, the structure of the lower shell is optimized, and bumps are added around the sleeve to limit the sleeve's range of movement. Before the rectification, there were no injection molded parts on both sides of the sleeve, and the movable space was large (as shown in Figure 9, left). After the rectification, each electrode sleeve has an injection molded part limiter (as shown in Figure 9, right).

3.1.3 Confirmation of reliability rectification effect

Connect the rectified product to a single-core hard copper wire. After bending and pulling the copper wire, the rectified product will move slightly, but it will not affect the screwing in of the plug. Limits are set at each socket position to prevent the socket from loosening, thus solving the problems of socket deformation, socket opening size and inability to rotate during installation.

3.2 No-in, no-out plug-in mode

3.2.1 Failure Cause Analysis

Among the coupler failures, the failures caused by the plug not being properly inserted accounted for 36.8% of all the defects. The main reason for this is that the plug was not rotated into place when the customer used it, resulting in point contact or partial contact, and the temperature was too high after long-term use, causing the plastic part to melt or burn (Figure 10). Due to the complex user group of air conditioners, in addition to training the user on the operating methods during the installation of the air conditioner, this type of problem can only be eliminated by optimizing the product structure itself. After analyzing the faulty parts, the above problems can only be avoided by keeping the connection between the plug and the socket in the two states of on and off, that is, there is no critical state in Figure 10.