Simulation of the Vibratory Peening Process

Vibratory peening is a finishing process that combines two processes in one. It has the same effect as shot peening that increases fatigue life by inducing compressive residual stresses while polishing the treated part, which is usually done by vibratory finishing. This process is also believed to improve the industrial productivity since it combines the shot peening and the vibratory finishing processes into one single process. This study is part of a more general project that aims to explain the befenits of advanced surface treatment technologies on aerospace materials. Polytechnique Montréal collaborated with Safran France and Centre Technologique en Aérospatiale (CTA). This work concentrates on realizing a preliminary study of discrete elements simulations to assess velocity fields inside the vibratory peening machine during operation. It also involves an experimental study to intrument the vibratory peening machine to determine its 3D motion. The literature review reveals that the amplitude and the frequency of the vibratory peening machine were the most relevant parameters to characterize the effects of the process. The first part of the literature survey presents the vibratory peening process and the parameters that characterize it such as coverage and Almen intensity. The studies show that both shot peening and vibratory peening can reach a range of Almen intensities of 0.12 mmA to 0.25 mmA. The second part focuses on the ways of monitoring a vibratory peening machine. The kinematic modelling of the machine shows that the motion of a vibratory peening machine is vertical. This part also shows the common technologies able to measure vibrations at low frequencies. The third part of the literature review presents the ways of modelling granular flow. It shows that the discrete element method is the most relevant method to predict velocity fields inside a vibratory peening machine. The studies produced with the discrete element method show that normal forces between shot and the workpiece contributed to the peening effect while tangential forces contributed to the polishing effect. The experiments show that our vibratory peening machine has mainly vertical modes of vibrations. The amplitude of the vibratory peening machine at imposed shaft frequencies ranging from 17.5 Hz to 30 Hz varies from 1.7 mm to 2.6 mm. For specific shaft frequencies, second mode of vibration influences the displacement and velocity fields of media inside the vibratory peening machine. The second mode of vibration is a typical frequency of 3 Hz for 22.5 Hz and 30 Hz shaft frequencies. The amplitude is respectively of 5.3 mm and 8.5 mm at 22.5 Hz and 30 Hz. The simulations based on the measured motion of the vibratory peening machine show that the normal impact velocity of shot on the workpiece varies linearly with the shaft frequency of the vibratory peening machine. The impact velocity reaches 0.6 m/s at 17.5 Hz and 0.95 m/s at 30 Hz. Moreover, a linear correlation has been found between Almen intensity and impact velocity. Finally, this preliminary study permits to conclude that the discrete element method was appropriate to have a better understanding of the vibratory peening process and guide the next research about the interaction between media and workpiece with the vibratory peening process.