Fundamental investigations on micro single-lip deep hole drilling of challenging drilling situations

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In order to stabilize the tool at the beginning of the drilling process, deep hole drilling tools require a drill guide in the form of pilot holes or drill bushes. The conventional process chain for deep hole drilling in complex drilling situations, consisting of face milling, mechanical pilot hole drilling and subsequent deep hole drilling, can be significantly shortened by substituting face milling and mechanical pilot hole drilling with the laser pilot hole drilling process. In addition to increasing productivity, laser processing also enables the wear-free drilling of pilot holes in case hardened components. The research project applied for follows on from the DFG last project, within the framework of which extensive investigations were carried out on the generation of laser pilot holes using single laser pulses and on the process combination of laser pilot hole drilling and single-lip deep hole drilling in demanding drilling situations. Based on the results, the aim of this project is to extend the flexibility of the laser drilling process, which has so far been limited by the single pulse with regard to the feasible bore hole diameters, by the use of laser helical drilling. By distributing the material ablation over a large number of laser pulses, the roundness deviation of the laser bore is also to be reduced. The identification of suitable laser parameters for the processing of the materials X2CrNiMo17-12-2 and 20MnCr5 is followed by investigations on tool life and bore hole quality when using the process combination. Due to the solidification of the melt at the bore hole wall, laser drillings show a lower bore hole quality compared to mechanically produced bore holes. Therefore, a further aim of this project is to use a step drill to machine the entire bore hole surface through the second step of the step drill thus significantly increasing the bore hole quality. For the machining of case hardened components with the step drill, a local heat treatment is required to reduce the hardness of the material in the contact area of the cutting edges. A thermal simulation will be used to identify suitable laser parameters for the realization of the required temperature window. Due to the increasing use of innovative additive methods like selective laser melting, the proportion of components with complex surface contours and thus demanding drilling situations is increasing. A further goal of this research project is the fundamental investigation of deep hole drilling in demanding drilling situations using additive manufactured pilot holes. The focus of the investigations is on the influence of the high roughness of the additive holes on tool wear and the guidance of the tool.