Incremental micro-forming for surface finishing with piezoelectrically actuated hammering tool with coupling unit

Machine hammer peening can be referred as an incremental mechanical surface treatment procedure, which can be realized by using various tools being based on various actuator principles. For the purpose of high productivity, a high-performance drive for generating vibrations in the tool of a high frequency is desired. Therefore, this paper presents a new hammer peening tool with a piezoelectric actuator. In order to facilitate this actuator principle for practical applications, a coupling unit is necessary being installed between the tool and the machine. This coupling unit insulates the process vibration at the machine (e.g. a machine tool or an industrial robot) and changes the operating mode of the hammer peening process from position controlled to force controlled. In such way, the accuracy of the positioning movement as well as the accuracy of the workpiece are not the issue anymore and the piezoelectrically actuated tool with a low stroke of 120 µm can be deployed for practical applications. This tool together with the coupling unit can reach hammering frequencies in the range from 800 to 1300 Hz. These frequencies enable higher feed rates and productivity of the hammer peening process than tools with pneumatic or electromagnetic actuators being available on the market. For the purpose of demonstration of the tool potential, some experimental tests are presented in this paper. Here, workpiece being milled like in die making were treated by the hammer peening process with the new tool. The surface were smoothed from Ra 1.18 μm to Ra 0.10 μm.