Experimentally validated calculation of the cutting edge temperature during dry milling of Ti6Al4V

摘要

In service, milling tools have to cope with severe levels of thermal and mechanical load. Especially temperature influences the damage behavior of a tool's cutting edge by influencing material properties and thermally induced stresses. It is therefore of relevance to gain quantitative information on the thermal tool load situation. Information on temperatures in milling tools is not readily available today. Therefore, extensive experimental effort was necessary to determine temperatures in-situ during milling in the axial center of a rotating end mill and in a Ti6Al4V workpiece near the milled surface. The used end mill was a WC-Co hard metal tool protected by a TiAlN coating. Since the damage-relevant cutting edge temperature is not directly accessible by experimental means, a simulation was employed. The transient temperature field in the tool was calculated by an iterative and synergetic use of two-dimensional finite element cutting models, three-dimensional finite element end mill models and two-dimensional workpiece models. The simulation allows for the description of the time-dependent temperature distribution from the chip formation site at the cutting edge to the axial tool center and into the workpiece, where thermocouples were placed in experiments. Validation of the calculated cutting edge temperatures was performed for 5000 individual consecutive cuts via comparison of results for tool core temperature in experiment and simulation. The model yields a very pronounced concentration of the thermal load maximum of T > 650 degrees C near the cutting edges in a very small volume of only 1 ppm of the tool's volume. In particular, the model's spatial discretization is able to resolve the gradient of temperature in the hard coating towards the coating/substrate interface, showing temperature shielding effects of the hard coating.