Scientific problems and development of surface strengthening of high strength automobile gears

1. Numerical simulation and scientific problems of gear surface strengthening

In the field of scientific research and engineering technology, numerical simulation is a basic research method that pays equal attention to theoretical analysis and experimental test. The development of numerical simulation technology provides a platform for the optimization design of gear surface strengthening technology.

In the field of mechanical numerical simulation of gear peening process, scholars at home and abroad have done some research and application, including using the one-dimensional analytical method of elastic-plastic model to predict the residual stress of peening, considering the factors of peening intensity to simulate the two-dimensional peening process, using the three-dimensional finite element model to study the numerical simulation of micro crack growth and gear surface morphology[ 51] etc. However, for the study of the mechanical properties of shot peening materials at nano scale, the quantitative relationship between shot peening parameters and the improvement of gear performance, and the simulation of multiple continuous impact of different materials and diameters of shot still need further study.

Based on the surface structure optimization to improve the friction and wear lubrication performance of the gear pair surface, the research in this field has been a long-term focus in the academic and engineering circles. The influence of different machining and surface strengthening treatment on the geometry and roughness of gear surface is directly related to the lubrication state of gear [52]. Therefore, it is necessary to study the mixed EHL characteristics of different tooth surfaces, to solve the elastic deformation, surface temperature rise and contact flash temperature of the tooth surfaces, to analyze the pyrolysis of different coating surfaces and the quantitative laws of surface morphology and gear friction and wear under different lubrication conditions, and to study the failure mechanism of the tooth surfaces and optimize the design of gear strength.

Because the internal and external excitation and non-linear factors of gear drive are rich, and the working environment is complex and changeable, the dynamic analysis of gear drive is very complex. Factors such as manufacturing, processing, error, wear, lubrication and operation environment will lead to the uncertainty of the excitation parameters of gear system. Multiple uncertainties exist at the same time, resulting in the high dimension of gear system problems, which makes the gear failure It is difficult to study the mechanism and strengthening mechanism. Therefore, to study the dynamics of gear system, it is necessary to consider the uncertainty optimization design method and sensitivity analysis method.

2. Development of gear surface strengthening technology

The gear transmission system under various complex working conditions makes the technology of gear surface strengthening appear new problems. For example, the light weight of the automobile transmission system and the high speed and high torque of the transmission of new energy vehicles put forward higher requirements for the strength of the automobile gear. The transmission condition of new energy electric vehicles rises from the maximum speed of the traditional automobile engine 6500 R / min to 14000 R / min, the torque increases by about 30%, and the fatigue life of the gear increases by more than 40%. The single surface strengthening technology can not meet the requirements of gear with high comprehensive performance. The surface strengthening technology with multiple composite surface strengthening technologies will be applied in the field of high-strength gear.

The development of surface strengthening technology needs to meet the multi-objective requirements of high strength, high precision, high fatigue life and low noise. The non independence and contradiction between the objectives make the composite surface strengthening technology not the superposition of single strengthening technology. The multi-objective optimization method of gear surface composite strengthening should be established for the technology of gear surface composite strengthening. Based on the theory of multi-objective optimization design [53], the relationship between the strengthening mechanism of gear surface heat treatment, shot peening strengthening technology, surface conversion coating and the scientific theory of gear surface integrity should be systematically studied. The future research focus of gear surface heat treatment includes: Mastering the basic parameters and strength characteristics of the material through the genetic analysis and basic performance experiment of gear material, predicting the numerical simulation and control technology research of gear heat treatment deformation, research and development of new gear steel and new heat treatment technology; research on gear peening strengthening technology, combining with material mechanics and modern mechanics, participating in peening The relationship between number and gear surface integrity (residual stress field, roughness, nano scale mechanical properties, etc.); the Tribological Study of various coatings on the gear surface is one of the important issues in gear research. Based on the actual working condition, transient temperature field and lubrication conditions of the gear, in-depth study on the influence of gear surface integrity on contact fatigue life is carried out. Another key point is to control the grain size, distribution and grain boundary size in the coating structure, so that the coating has higher hardness and toughness. How to further control the grain size has become an important part of the study.

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