Manufacturing of high-precision surface micro-structures on stainless steel by ultrasonic impact peening

Ultrasonic impact peening (UIP) is not only a mature technique of surface treatment, but also a promising method of surface texturing for promoting performance and functionalities of components and devices. In the present work, we demonstrate the feasibility of applying UIP in the manufacturing of high precision surface micro-structures on 316L stainless steel using a YG6 cemented carbide tool. Specifically, analytical investigation of the material deformation map under UIP is carried out, which is validated by corresponding finite element simulations based on a combined nonlinear isotropic/kinematic hardening model, as well as experiments performed on home-made UIP apparatus. Finally, surface micro-structures of aligned grooves with a depth of 2 µm and a periodicity of 240 µm are fabricated by using UIP, and are subsequently subjected to linear reciprocating ball-disk sliding tests. Corresponding experimental results show that the micro-structures fabricated by UIP possess comparable accuracy of groove morphology and frictional properties with that fabricated by using ultrasonic elliptical vibration cutting using a single crystal diamond tool. The present work sheds lights on the low-cost fabrication of high precision surface micro-structures on ferrous metals by mature UIP technique.

Prediction of tool wear constants for diamond turn machining of CuBe

While several studies in diamond turning of homogeneous materials like Cu, Al, and Si are well published, there is a lack of understanding about tool wear in case of heterogeneous materials like CuBe. Severity of the tool wear can be understood from the magnitude of the wear coefficients, and the magnitude of these coefficients is influenced by the wear mechanism. Hence, this study is aimed to calculate the wear coefficients from a known tool wear model in diamond turn machining of CuBe. Molecular dynamics simulation (MDS) results show that stress and temperature are responsible for increasing rate of tool wear. From the experimental results, change in the tool cutting edge radius due to wear was obtained and the temperature and stress for various a/r were found out using MDS. With these data, the wear coefficients, A & B, from a wear model for diamond turning were calculated. This methodology of using MDS to obtain stress and temperature for various a/ r wherein, values of r are obtained from a single machining trial on actual material, will be useful for calculating the wear coefficients for the combination of single crystal diamond tool with various work piece materials and their activation energies.

Machining of Smooth Optical Surfaces by Ultraprecision Milling with Compensated Feeding Mechanisms

Waviness tends to be generated on cut surfaces even when an ultraprecision milling machine with a single-crystal diamond tool is used. The present study deals with the reduction of waviness by controlling the feeding mechanisms of the milling machine. A machining experiment on a spherical surface of a mirror element in a mirror array showed that the machined surface exhibited periodic waviness with a height of 30 nm and a wavelength of 300 μm. To investigate the reason for such waviness, a slope was machined under simultaneous multiaxis motion control of the feeding mechanisms of the milling machine. This proved that the interpolation errors of the encoders used in the milling machine produce the waviness on the machined surface when machining is carried out under simultaneous multiaxis motion control. To reduce such interpolation errors, the positioning accuracy of the machine stages was measured using a laser interferometer. On the basis of the measured results, the feeding mechanisms were compensated such that the positioning errors including the interpolation errors were corrected. Using the machine with the compensated feeding system, a mirror element was shaped. Consequently, waviness was reduced and the surface smoothness was less than 10 nm, demonstrating that such compensation can produce superior optical surfaces.