【作者】 王翠英；

【导师】 轧刚；

【作者基本信息】 太原理工大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 许多高应力的零部件比如火车轮轴、齿轮、航空以及汽车发动机用轴类零件等等,它们在工作时往往受到循环载荷的作用,在这种情况下,裂纹扩展速度非常快,迅速缩短了零件的寿命。其后果不仅造成财产损失还会导致人员伤亡,因此提高机械零部件的疲劳强度和寿命具有重要的意义。喷丸作为一种金属表面冷加工技术,主要用于提高金属零部件的疲劳强度,已被广泛应用于航空航天、汽车、电力、核工业等可靠性、安全性要求高的行业。喷丸强化工艺过程是通过小直径高硬度的球形丸粒高速撞击金属材料表面,使金属表面发生塑性变形,同时产生表面晶粒细化、表层局部向外延展和表面材料冷作硬化等现象,通常会在金属零件表层产生120~1000μm的残余压应力层。喷丸所产生的形变强化和组织强化可使零件维氏硬度提高,裂纹扩展阻力增加,使得裂纹扩展的速度大大减慢;此外,喷丸的强化作用以及所引入的高残余压应力,可使表面微观裂纹止裂,并能改善和消除加工工艺过程中零件表层所产生的缺陷,使其可靠性和寿命提高,减缓或防止受循环载荷作用的金属零件的过早失效。超声喷丸可以获得比传统喷丸更深的残余压应力层,同时表面粗糙度也优于传统喷丸强化技术,超声喷丸强化已经被证明能有效地提高零件的疲劳极限。对于目前的超声喷丸强化工艺过程,弹丸的速度还远没有达到能够破坏受喷件安定性的程度,而变幅杆的振幅是影响丸粒喷射速度的重要因素。因此,设计一新型的大振幅变幅杆来提高丸粒的冲击速度成为目前超声喷丸系统研究工作的首要任务。目前,常见的变幅杆类型有:指数形、阶梯形、圆锥形等,各种传统形状的变幅杆各有优点,但都不是最理想的。本文以提高变幅杆的振幅为出发点,应用解析法设计一种新型的级联式变幅杆,并通过有限元ANSYS软件对其进行动力学分析,验证设计所得变幅杆的可靠性;同时对其放大性能进行实验验证。此外,为验证超声喷丸强化能力,设计喷丸装置并进行喷丸强化能力实验。主要研究内容有:1、对级联式变幅杆进行理论探讨,获得级联式变幅杆的放大性能。其振幅放大比为两单节变幅杆的放大比乘积。根据级联式变幅杆的设计理论和单节变幅杆的性能特点,选定级联式变幅杆的推动节和输出节。2、首先,根据传统设计单一变幅杆的理论依据和实际的实验条件,设计符合喷丸实验用的级联式变幅杆,对其性能参数进行分析和理论计算。其次,根据振动理论和有限元方法,借助于有限元软件分别对级联式变幅杆和构成其的两单节变幅杆进行动力学分析,将所获得的变幅杆各性能模态参数与理论计算结果比较,两种方法所得结果很一致。3、加工制造所设计的级联式变幅杆并对其进行振幅放大比的验证实验。在变幅杆输入端和输出端分别安装加速度传感器测量加速度的振幅信号,经电荷放大器将信号放大,由数字示波器采集和记录加速度信号,根据位移与加速度的关系可以计算出位移的大小,从而求得变幅杆的放大比。将其与理论和模拟结果进行比较,所得结论十分接近。4、选购各种不同材质和型号的试验用钢丸。设计超声喷丸强化能力的实验装置,同时建立一套超声喷丸冲击力测量实验系统。钢丸在超声波发生器的激励下进行冲击试验,在喷丸室顶端安装压电式力传感器,测量弹丸的冲击力信号,之后进行冲击力数据处理。结果显示:钢丸的材质对冲击力的影响最大;就不同钢丸材质而言,钢丸直径及其距传感器的距离对冲击力影响最大,其次是超声波发生器的输出功率;而弹丸粒数对冲击力力影响不是很大。5、对不同工艺参数下弹丸冲击力所产生的冲击应力进行计算,分析各工艺参数对弹丸冲击应力的影响,进而分析各工艺参数对喷丸强化能力的影响。所得结论为:随着高度的增加,弹丸的冲击应力降低;而在同一高度时,同直径的铸钢丸产生的冲击应力比不锈钢钢丸要大。更多还原

【Abstract】 Many high-stress components, such as axles of trains, gears, shafts of cars and aircrafts, etc, are often subjected to the cyclic load at work. In this case, the speed of the crack propagation is very fast, which rapidly shortens the life of parts. It will not only lead to property lost, but also engender casualties, therefore to improve the fatigue strength and the life-span of the machine parts is significant. Shot peening, as a cold processing technique of metal surface, is mainly used to enhance the fatigue strength of metal parts and has been widely used in such demanding industries on reliability and security as aerospace, automotive, electric power and nuclear industry. Shot peening strengthen process leads metal surface to engender plastic deformation, grain refinement, local extension outward and work hardening by using small and high hardness pellets to impact the metal surface of parts at high speed, and then metal surface will generate residual compressive stress layer of 120~1000μm. Deformation strengthening and structure strengthening of shot peening can increase HV hardness of parts, hinder crack propagation and slow down the speed of crack propagation. Shot peening strengthen and higher residual compressive stress are able to stop surface micro-crack, eliminate defects of parts appeared in process and improve the reliability and the life-span of parts, which can slow or prevent the premature failure of metal parts under cycle load.Ultrasonic shot peening can get deeper compressive stress layer than the traditional shot peening, and the surface roughness is also superior to the traditional shot peening strengthen technique. Ultrasonic shot peening has been proved to be able to enhance the fatigue resistance ability. For the current ultrasonic shot penning process, the speed of shot is so small that can’t damage the stability of parts. Therefore, enhancing the speed of shot namely improving the magnification factor of the horn is the primary mission under the current development of ultrasonic shot peening equipment. At present, the common horns are exponential horn, conical horn, stepped horn and etc. Different kinds of horns have its own advantages, but none of them is perfect.In this paper, to enhance the amplitude magnification ratio of horn is the fundamental purpose. The design of composite horn is based on analytical method, and finite element software ANSYS is used for the dynamic analysis of the ultrasonic horn to verify reliability of it, while experiment is designed to verify amplitude ability. In addition, shot peening equipment and experiment are designed to bear out the ability of ultrasonic shot peening. The main contents are as follows:1.After discussing theoretically the amplification performance of composite horn, it is known that the amplitude ratio of composite horn is amplification ratio product of two single-horns. The driven horn section and output horn section of composite horn are selected according to the design theory of composite horn and the performance characteristics of single horn.2.Firstly the composite horn, used in experiments of ultrasonic shot peening, is designed according to the theory of single horn and conditions of experiments, and its the parameters are analyzed and calculated. Secondly, according to vibration theory and finite element method, modal analysis for three kinds of horns is carried through by using the finite element software ANSYS11.0. Comparing the modal dynamic parameters and the theory calculation result, it can be concluded that the both results are consistant.3.After the composite horn produced, a set of apparatus for experimental measurements of amplitude ratio is built. Two piezoelectric accelerometers, which are sticked to both ends of the measured composite horn, are used to measure the amplitudes of accelerations in both ends of the composite horn; the signals are amplified by a charge amplifier, then collected and recorded by digital oscillograph. Based on the values of accelerations, the amplitudes of displacement are easily calculated and the amplification factor of the composite horn can be obtained. Comparing the theory calculation result, the finite element analysis and the experimental measuring results, it can be elicited that the finite element analysis and the experimental measuring results both are close.4.Purchase experiment shots of different materials and models, and design experiment device for ultrasonic shot peening. Then the measuring system of ultrasonic shot peening impact force is established. The piezoelectricity force transducer is mounted on the center surface of the metal part to be used to measure the shot impact force, and then dates of impact force are analyzed. The result shows that the effect of shot material on impact force is largest; when the shot material is different, the effect of shot diameter and its distance to sensor is largest, while the effect of output power of ultrasonic generator is lager; the effect of quantity of shots is not great.5.The contact stress of shot peening impact force under different parameters is calculated and the effect of different parameters on contact stress and shot peening strengthen ability is analyzed. The conclusions are as follows: as the height increases, the contact stress of pellet reduces; while in same height, the contact stress of cast steel shots, whose diameter is the same as stainless steel shot, is lager than that of stainless steel shot.更多还原