Pistons are key components of air compressors and have been widely used in the air compressor industry as the primary actuator for air compression. The working strength, stiffness and reliability of the piston are related to the operating life of the whole machine. Once the design deviation occurs, the piston will be broken, strained and other failure modes, and the whole machine will be scrapped.
This paper takes V0.17/7 air compressor as an example, makes full use of UG design system, adopts parametric design of piston parts, and analyzes the reliability and safety of piston through UG/CAE module. The above design method will shorten the traditional design cycle and effectively improve the design quality.
1 piston working principle and structure The air compression mechanism of the whole machine adopts a crank slider mechanism. The pulley transmits the kinetic energy of the motor to the crankshaft. The crankshaft rotates and drives the connecting rod to work. The reciprocating motion of the connecting rod forces the piston edge at the execution end of the air compression mechanism. The cylinder wall makes a reciprocating linear motion. Since the movement of the piston will cause a change in the volume of air in the cylinder, a strong pressure will be generated when the volume of the air is compressed. The specific mechanism principle is as shown.
There are three basic structural forms of the piston: a disc shape, a cylindrical shape, and a cylindrical shape. The V0.17/7 air compressor in this paper adopts a cylindrical structure with a flat top at the top. There are three slots in the head of the piston. The top two channels are air ring grooves. The bottom channel is an oil ring groove. The oil ring groove surface is drilled with a plurality of radial holes for returning the oil scraped on the cylinder wall. The specific structure is as shown.
Piston working principle diagram Piston parts piston finite element analysis 2.1 Piston modeling and pre-processing UG is used to construct the piston 3D geometric model. Considering that part of the characteristic structure of the plug body has little effect on the overall analysis results, and in order to improve the meshing quality and computational efficiency, the related features are suppressed. The optimized model is shown.
2.2 Material Attribute Setting and Meshing Fund Project: Yanzhou College Hospital Fund (KZY1207); Cangzhou Science and Technology Bureau Project (20121048) 2.3 Boundary Condition Setting and Solution When the crankshaft runs to the equilibrium position, the piston rises to the highest point. At this time, the gas volume is compressed to a minimum, and the pressure on the piston is the largest, so the piston load should take this value. According to the compressor design formula, the maximum pressure of the piston is 0.8 MPa. Under the balance state of the crankshaft, the piston and the piston pin have no relative rotation, and the piston is fixed on the piston pin. Therefore, the contact surface between the piston and the pin can be set in the constraint condition. To fix the constraint, to define the degree of freedom here.
The set conditions are post-processed by the NASTRAN solver to obtain the corresponding stress-strain diagram. As shown. It can be seen from the figure that the maximum stress of the piston is 27.28Mpa and the maximum displacement is 0.00716mm. The maximum stress is concentrated at the corner of the inner rib of the piston, and the maximum displacement occurs at the center of the top of the piston.
Finite element displacement. 4 Strength check and structure optimization ZL104 yield strength after T6 process is 276Mpa after test, taking safety factor 11=2, then the allowable stress of material=s/n=276/2=138Mpa. The maximum stress = 27.28Mpa, which is much smaller than the required stress, so the piston strength fully meets the design requirements. The maximum displacement of the piston is 0.00716mm, and the deformation is much lower than the allowable deformation of 0.0125mm, so the stiffness also meets the design requirements.
Through the finite element analysis calculation, the right angle over-design for the piston rib can be trimmed to an excessive arc to reduce excessive stress concentration. The single reinforced rib is a cross-shaped rib, which can effectively reduce the deformation of the top of the piston and improve the strength and rigidity of the top of the piston.
3 Conclusions 1) Based on the finite element method, the parametric design of the piston is more flexible, and the modification is extremely simple.
Physical and chemical, reliability provides a new way. The use of the finite element analysis module greatly saves design, check time and reduces production costs.
3) For the weak parts of the finite element analysis, the designer can quickly and effectively propose improvements to ensure the reliability of the parts. At present, the piston has been put into production of this V0.17/7 type air compressor equipment, and the operation effect is good.
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