Extending the possibilities of cryogenic assisted grinding
Final Report Abstract
Cooling lubricants are essential in grinding as they help to prevent heat-related problems such as surface cracks, grinding burn, and tensile residual stresses. An alternative method is cryogenic cooling, which involves using cryogens like LN2 or CO2 at extremely low temperatures. In this project various cryogenic cooling strategies such as pre-cooling of the workpiece, partial pre-cooling and in-process cooling with LN2 and CO2 were investigated. It has been found that the most important factor for a successful application of the precooling for surface grinding is the clamping strategy. Unlike cylindrical plunge grinding the the thermal conduction at the interface of workpiece and clamping device dominates the heating of the cryogenic pre-cooled workpiece rather than the thermal convection with the surrounding air. It could be shown that by using insulated clamping covers (e.g. glassreinforced plastic or polyurethane) the cold could be kept in the workpiece during grinding. However, it was found that the pre-cooling method is not ideal for grinding with low depths of cut, because of the high workpiece temperature differences over time leading to an expansion of the workpiece. The different cooling strategies resulted in varying surface roughness, residual stress, microstructure and -hardness in the ground workpiece due to the different thermomechanical loads during grinding. While previous research from the literature on cryogenic grinding has shown improved grindability, in this project it was found that using a conventional oil-based cooling lubricant still resulted in a superior surface finish due to lower machining forces and temperatures. The CO2 in-process cooling yielded promising results in terms of achieved surface quality, which was comparable to that of conventional cooling despite higher forces and temperatures prevailing. Partial pre-cooling and pre-cooling led to similar results as dry grinding. However, there is room for improvement, particularly in shortening the time between cooling of the workpiece and the grinding. The LN2 in-process cooling strategy performed poorly with the given set-up. This could be attributed to the formation of a vapor cushion at the workpiece surface, the presence of a gaseous phase, and icing of the nozzle outlet. The experiments were supplemented by dynamic 3D finite element method (FEM) heat transfer simulations to map the temperature development temporally and locally in the workpiece. The approach is characterized by simplifying the cryogenic grinding process to a moving heat and cooling source. Therefore, the heat transfer coefficient hcryo between the workpiece and the cryogenic, as well as the length of cooling source lcryo were determined first using the inverse method. The simulation models were validated for various cryogenic cooling strategies for surface and cylindrical plunge grinding.
Publications
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3D-FEM-Wärmeübertragungssimulation des Schleifens. Zeitschrift für wirtschaftlichen Fabrikbetrieb, 117(7-8), 484-488.
Weber, Daniel; Kirsch, Benjamin; Silva, Eraldo J. da & Aurich, Jan C.
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3D FEM heat transfer simulation of surface grinding of cryogenic pre-cooled parts. Procedia CIRP, 117, 205-210.
Weber, D.; Kirsch, B.; Silva, J.S.; da Silva, E.J. & Aurich, J.C.
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MODELING AND SIMULATION OF THERMAL EFFECTS IN CYLINDRICAL PLUNGE DRY GRINDING WITH PRECOOLING. Proceedings of the 27th International Congress of Mechanical Engineering. ABCM.
Carvalho, de Santana Ézio; Jannone, da Silva Eraldo & Urbano, Gabriel
