Study On Cold Work Hardening Influencing Mechanism On Forming Quality Of High Speed Cold Rolling

High-speed cold roll-beating forming technology is a plastic forming technology which is efficient, green and high precision; it has become one of the main processing methods of some key parts, widely used in automotive, aerospace, machine tool and other industries. High-speed cold roll-beating forming is a complicated forming process which involves multi-disciplinary, multi-factor impact makes its research more difficult. Current research on High-speed cold roll-beating are mainly in kinematics, dynamics and the design of roll-beating wheel, few in the surface quality of forming parts, and among the factors about surface quality, hardening has a great influence on the strength and anti-impact resistance performance and so on. In this paper, a method of theoretical study, numerical simulation combine with experimental study, was used to research on the mechanism of work hardening in high-speed cold roll-beating forming, to control the degree of surface hardening and improve the performance of parts. The main contents are as follows:Researching relationships of flowing stress and dislocation density, dislocation density and hardening index, it can be obtained that the degree of hardening is closely related to the flowing stress of the workpiece material. Analyzing cold roll-beating forming thermal-mechanical coupling mechanism, it can be known that the heat and the force play dual roles in hardening producing process, and get thermal-mechanical coupling mechanism of hardening.The finite element model based on the thermal-mechanical coupling has been built. The whole movement process of a struck in cold roll-beating forming (including idle stage, beat-into stage and beat-out stage) is analyzed, and found the rotation angle that that the roll-beating wheel relative to the initial position at the beat-into the deepest moment and wheel left from the workpiece moment, providing theoretical basis for subsequent analysis. The influence of the beat force and the forming heat to work hardening is analyzed, got the strengthen result of beat force and the weaken result of heat. The influence rule of the roll-beating wheel rotational speed, shape of roll-beating wheel, friction coefficient and beating times on medium effect force field, distribution of hardness on tooth profile, and tooth profile shape in cold roll-beating forming process has been studied. It can be obtained that the effect that forming heat on hardening process is very obvious. It is necessary to take appropriate lubrication conditions to reduce the heat in forming process, to control the degree of strain hardening. High-speed cold roll-beating parameters have certain influence on the degree of work hardening. There is a set of optimal forming parameters that can control the degree of strain hardening parts within a reasonable range, improve the forming quality and their performance, and prolong the service life of rolling wheel.Work hardening related experiments are carried out, and research on the hardening degree of parts on addendum, dividing circle, tooth root are done. It can be obtained that the depth of hardening layer of the root is the largest, the micro-hardness of the dividing circle is the largest and the addendum is minimized. To view the metal structure of different parts, found that the metal structure is refined and the result of the tooth root parts is the most obvious. Contrast analysis spline tooth root and dividing circle part of the surface hardness and depth of hardening layer under different roll-beating wheel speed of2000r/min and3000r/min. The simulation results were compared with the experimental results; the reliability of simulation results is validated.