Modeling Study On Grinding Force Of Hard And Brittle Materials In Ultrasonic Vibration Assisted Micro End Grinding

Micro-grinding provides a competitive edge for machining 3D micro components and structure of hard and brittle material, because of its especial capable for processing hard and brittle material. However, there exist several disadvantages in present micro-grinding technology, such as low efficiency, high heat generation and rapid micro wheel wear, etc. Previous researches indicate that several significant advantages can be achieved in vibration assisted machining, such as decrease of machining force and heat, and relieving of wheel obstruction, etc. So a processing method ultrasonic vibration assisted micro end grinding UAMEG, adding small-amplitude ultrasonic vibration to work-piece in micro end grinding, is investigated in this work to improve the present micro-grinding technology. Grinding force is one of the most important parameters which can synthetically reflect the grinding process. So, the grinding force in UAMEG is studied by modeling and experiments in this work, which is of much theoretical and experimental significance.Basing on analysis of the micro topography of grinding surface, the micro end grinding zone is divided into three grinding region: main grinding region, ploughing grinding region, sliding grinding region. Basing on kinematic analysis on adjacent two abrasives, the critical conditions of intermittent grinding and brittle-ductile transition in UAMEG are studied. Single grain force model were developed under different material removal mode: basing on Brinell hardness test, force model under ploughing effect and sliding effect are developed; basing on plastic-shearing theory and improved Janson-Cook material constitutive model, force model under the plastic-shearing effect is established; basing on fracture mechanics and scratch test, force model under crack generation is developed. From the point of material strain gradient theory, Taylor dislocation model and plowing and sliding effect point, the size effect on the grinding force is considered into force modeling. Basing on micro topography analysis of diamond grinding wheel end surface, statistical principle and discrete integral method, grinding force model of the whole grinding wheel are finally established.The experimental UAMEG machine tool is designed and set up for experiments. The predicted results matched well with the measured reults of grinding force. The results show that: When the frequency coefficient K is not an integer and the feed-amplitude ratio is less than 2, intermittent grinding can be achieved in UAMEG; In UAMEG, the normal grinding force, the feed direction grinding force and the tangential grinding force are respectively decreased by 65.6%, 47.7%, and 42.2%. In addition, the surface quality is improved significantly in UAMEG. With the wheel rotating speed increasing, and grinding depth and feed speed decreasing, the grinding forces decrease, and the machined surface quality is improved.