Discussion on ways to reduce the design cost of air compressor
Reduce the friction between the end face of the crankshaft and the end face of the crankcase
On the direct-coupled air compressor, the front end of the crankshaft adopts gear transmission, and the gears are divided into straight and helical teeth. When adopting helical gear transmission, an axial force will be generated in the axial direction. In order to ensure that the designed product can be For long-term normal and reliable operation, usually a thrust washer is designed at the position where the crankshaft and crankcase are in contact with friction to reduce the friction between the end face of the crankshaft and the end face of the crankcase. Figure 1 is a partial assembly diagram of an air compressor case body with a thrust washer and a structural diagram of the thrust washer used.
This is a completely correct design, and there is no need to discuss it. But if we all think about it, adding one part will increase the cost. Is there any other structure to replace the thrust washer design?
The sliding friction coefficient of materials is introduced in the first volume of the "Machine Design Manual": the sliding friction coefficient between steel and bronze without lubricant is 0.15, and the sliding friction coefficient with lubricant is 0.1～0.15; steel and bronze The coefficient of sliding friction between cast irons when there is no lubricant is 0.18, and when there is lubricant, the coefficient of sliding friction is 0.05 to 0.15. It can be seen from the above data that in the presence of lubricant, the friction pair between steel and cast iron is better than the friction pair between steel and bronze. In the design, there is forced lubrication, which provides a strong theoretical basis for improving the design. Figure 2 is a partial assembly diagram of the air compressor case body without a thrust washer and a structural diagram without a thrust washer.
Now look at the structure of the thrust retaining ring. In order to lubricate it, two square grooves are opened for lubrication. You can refer to this principle in the design of the crankcase to cast the end surface that is rubbing against the crankshaft by casting. The lubricating oil groove of 4mm and the height of 2mm has the same function as the square groove on the thrust retaining ring and can achieve the same lubrication effect.
The costs that can be reduced after such an improvement include: (1) saving a thrust retaining ring at a price of 2.52 yuan; (2) reducing two processes (installing the thrust retaining ring hole and drilling a half hole) during crankcase processing; ( 3) The amount of cast iron in the shaft sleeve hole is reduced.
maintainability issues
With the development of the times, the concept of designers should also change. In the past, due to the poor economic strength of users, designers had to consider the maintainability of the product when designing. Now the user's economic strength has increased. When there is a problem in the use of the air compressor, instead of replacing individual parts, the air compressor is replaced as a whole for maintenance. For this reason, the designer can design according to the actual situation without considering the maintainability of the product, which can significantly reduce the cost of the product.
The structure diagram before the improvement is shown in Figure 3a: In order to meet the design requirements, we use the combination of crankcase, O-ring, bolts and gaskets, back cover, oil return joint, and copper sealing gasket to achieve the function of oil intake and return. , And the purpose of design is to ensure the smooth flow of oil in and return. At the same time, because the functions are completed by combination, there may be hidden quality risks of oil leakage due to improper assembly.
Look at the improved structure diagram as shown in Figure 3b: Combining the above parts together by casting reduces the number of parts and reduces the processing procedures. At the same time, because the crankcase is subjected to a pressure test during the production process, oil leakage can be fundamentally eliminated. However, the modified crankcase does not increase the processing difficulty in processing.
The cost savings of the above improvements are indeed considerable: (1) The oil return joint is 2.8 yuan; (2) The copper sealing gasket is 0.66 yuan; (3) The back end cover is 3.4 yuan; (4) O-ring is 0.5 Yuan; (5) 4 M8x20 bolts are 0.68 Yuan; (6) 4 spring washers are 0.06 Yuan. The total value of the above parts is 8.1 yuan.
Bolt connection structure design
In product design, the unused hole surface is often designed with a gasket and cover plate connected by bolts.
Analyze the rear end structure before improvement as shown in Figure 4a: It can be seen that in order to seal the rear end face, a total of four parts including a rear gasket, a rear cover, a φ8 flat washer, and a M8×20 bolt are needed to complete its design function. Due to the threaded assembly relationship of this structure, looseness and leakage problems may occur under certain vibration conditions.
Change the design method and look at the improved rear end structure as shown in Figure 4b: The new structure only uses an interference assembly between the rear cover and the crankcase to achieve our design intent, and there is no leakage risk due to loose threads. . On the other hand, it can also reduce production costs.
The cost savings of the above improvements are indeed considerable. The parts value of the original structure: (1) the back cover pad is 0.41 yuan; (2) the back cover is 3 yuan; (3) 4 φ8 flat washers are 0.07 yuan; (4) 4 M8×20 bolts are 0.68 yuan. The total value of the above parts is 4.16 yuan. The new structure of the rear cover is 0.6 yuan, and the value of the two parts only saves 3.56 yuan.
From the processing point of view, the modified structure has a simple processing technology and reduced processing costs, and the reduction in materials used at the rear end of the crankcase also reduces product costs. The above structure has been used in the design of normal products and has produced considerable economic and social benefits.
Conclusion
Improving design by changing ideas can significantly reduce product costs, improve product market competitiveness, and help companies achieve considerable economic benefits.
