Operational behaviour of micro-structured cutting tools with integrated lubricant supply

• Applicant: Professor Dr.-Ing. Eckart Uhlmann
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317539900

During the first investigation period of the research project, knowledge of the micro-texture depended chip formation as a result of various geometric variations as well as a correlation between the simulative calculated pressure distribution and the empirically resulting adhesion area was attained. A relation between the induced cracks and the maximum principal stresses was also apparent. Consequently, it is assumed that the thermo-mechanical loading during machining exceeds the permitted positive principal stress of the CVD diamond thick film and leads to fracture of the cutting material. The specific properties are correlated with the manufacturing process, growth rate and coating thickness. Depending on the coating thickness, there is also an adversative relationship between thermal conductivity and permissible principal stress. However, the permissible tensile strength is also adversely affected. Thus, a compromise between high heat conduction and high tensile strength is necessary to enable increased process reliability. The second investigation period of the research project deals with the classification of defined CVD specifications for the cutting process of Ti 6Al 4V and the development of micro textures considering the specific material properties of CVD diamond. To identify the performance limits and thus the mechanical load capacity, analyses are executed with regard to the maximum principal stress. These are performed both with and without the use of micro textured surfaces, whereby a micro-texture-dependent displacement of the specific principal stress can be measured. With the use of the Finite Element Method (FEM), the process limits and tool limits for an effective chip formation as well as the associated compressive loads per micro-texture element will be defined. The empirical results and numerical calculations are used to predict the micro-texture- and process-dependent pressure distribution of the micro-texture elements. Based on this pressure distribution prediction, an analytical load model is developed and interpolated within an FE-model so that sensitivity analyses can follow. Thus, an effective dimensioning of the micro-texture geometry parameters can be realized considering the mechanical properties of the cutting material. Depending on the respective CVD specification, this results in an individual micro texture combination which will have a positive influence both on the existing tool stresses and on chip formation. This allows, for the first time, a reduction of the sudden tool failure as well as the potential crack induction of brittle materials under consideration of the maximum permissible positive principal stresses by the use micro textures. As a result, an improved understanding of the interaction between chip flow, temperature, microstructure and tool load with regard to the titanium alloy Ti-6Al-4V and depending on various cutting material specifications is available.

• DFG Programme: Research Grants