Research Of The Mechanism Of Ultrasonic Shot Peening

With the development of modern industry technology, people's requirements of safety and reliability on machine equipments become more and more rigid. In machine equipments like airplanes, armored cars, ships, locomotives, automobiles, internal-combustion engines, steamships, metallurgy machine equipments, petroleum machine equipments and mine machine equipments etc., their important bearing parts that endure cycle loading may cause fatigue rupture suddenly, it will not only lead to function loss, but also engender casualty, therefore to improve the fatigue strength and the life-span of the machine parts is significance. Shot peening strengthen technology can produce surface hardening and residual compress stress through cold extruding workpiece surface, currently it has been proved to be able to enhance the fatigue resistance ability and the stress corrosion resistance ability remarkably, and to extend the use life-span of a part. Nowadays, shot peening strengthen technology has become indispensable in modern part manufacture it is also one of the symbols to evaluate a country's level of machine manufacture technology.Due to some unavoidable disadvantages of traditional shot peening processes, new shot peening technologies begin to come forth. Utilizing ultrasonic power to conduct shot peening displays many advantages, for example, there is almost no shot broken and dust pollution during shot peening process; the shot particles can be used several times; the equipment has small volume with less energy consuming, it even could be made into portable type, which can be either integrated into production line or perform site work. The simple equipment can be used to deal with various shape parts such as the parts with complex inside cavity.In the paper, based on the aim to validate ultrasonic shot peening ability and investigate the mechanism of ultrasonic shot peening, an experimental equipment of ultrasonic shot peening was designed and manufactured; and the experiment on evaluated ultrasonic shot peening ability was carried out; the mechanism of ultrasonic shot peening was discussed theoretically; and the shot peening process was simulated through ANSYS/LS-DYNA FEM software, the main contents include as follow:1. According to elastic-plastic mechanics, contact mechanics and dynamic plastic mechanics, the mechanism of ultrasonic shot peening is discussed. The residual compression stress distribution in a sample was derived under the condition of fixed shot peening parameter. The stress distribution obtained from theory calculation results has same trend with practical condition, and the both has close numerical value.2. The ultrasonic shot-peening process is simplified as the models of 1, 2, 9 and 13 shots projected on a sample at same time, and is simulated based on ANASYS/LS-DYNA software. It seemed that with the increase of shot diameter or shot density, the layer depth and maximum value of residual stress will increase. The results also show that when the central distance between two shots is less than the shot diameter, the interaction of two adjacent projected regions cannot be neglected. The coverage ratio of shot peening has great influence on strengthening effect. When the coverage ratio is lower than 100%, tensile stress will be engendered in certain direction, which will reduce the strengthening effect.3. A horn is designed by applying horn design theory and according to two end face diameters of the horn. According to vibration theory and finite element method, mode analysis and harmonious analysis are carried out by ANSYS FEM software. At the same time, the other structures of ultrasonic shot-peening experimental equipment are designed as well.4. A measuring system for the impact force of ultrasonic shot peening is established, its main components are the ultrasonic generator, transducer, horn and peening room. A piezoelectricity force sensor is installed in the workpiece hold close to the work end-face of the horn to measure the shot impact force; the signals are amplified by charge amplifier, collected and recorded by numerical oscillograph. Comparing the theory calculation result, the finite element analysis and the experimental measuring result, three results are much close.5. Ultrasonic shot peening experiments were performed on the experimental device, the surface residual compression stress, the value of surface roughness and surface configuration of shot peened samples were measured. The results show that ultrasonic shot peening process can increase the residual compression stress on metal sample surface greatly with little increase of surface roughness value.