Process and tool development of single lip drills due to an optimisation of the circumferential shape and surface topography

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The former fundamental project, the production and influencing of the circumferential surface topography of single-lip drills, was analysed using three different preparation methods. The resulting improvement of the bore quality offers the possibility of increasing the process quality for numerous applications. These include, for example, the medical industry for the production of boreholes in bone nails, the tool and mold making for heating/cooling bores, the usage in the offshore industry and the automotive industry for injection components. For the automotive industry, especially for the production of high and low pressure bores in commonrail injection systems of commercial vehicles (CV), is the increase of the bore quality a main target. This is necessary because current tools cannot meet the requirements for the maximum roughness depth Rmax < 10 microns. Therefore, the aim of the approach is a modification of the circumferential tool shape in combination with a surface topography improvement by grinding with an elastic bonding. In addition, it is necessary to consider the mentioned aspects with an optimized coating process to achieve a minimization of the maximum depth of the grooves. The results of the fundamental project show that due to a tool preparation of the circumferential shape, an improvement of the run-in behaviour of Rmax = 8.5 microns to Rmax = 2.6 microns and of the bore quality over the tool life of lc = 3 m Rmax = 4 microns to Rmax = 2,2 microns is possible. This is achieved by changing the circumferential tool shape as well as by improving the surface quality of the guiding strips from Rz = 1 microns to Rz = 0.7 microns in the uncoated state. For the prototypical implementation of the findings on industrial processes, it is necessary to transfer the knowledge of optimizing the single-lip drills by a suitable process chain and to avoid post-treatments by an adapted coating process.