Tools and Strategies for Grinding of Riblets on Freeformed Compressor Blades

A major goal in the design of turbomachinery is the increase of efficiency. To attain this increase, the flow losses must be reduced. A substantial proportion of the losses is generated by skin friction between compressor blades and working fluid. With respect to smooth surfaces, micropatterns (riblet-structures) reduce skin friction in turbulent flow by up to 10%. Grinding with multiprofiled wheels is an effective method for the manufacturing of riblet-structures on large plane surfaces. However, the grinding wheel wear affects the accuracy of the riblet geometry and the efficiency of the manufacturing process. Therefore, this paper shows the potential of different grinding wheel types for the manufacturing of riblet structures on an industrial scale with regard to tool wear. The results show that vitrified bonded tools are not suitable for the structuring of compressor blades. Here, axial forces lead to high profile wear. In contrast, grinding wheels with a metal bond are more wear resistant. However, the dressing process of metal bonded tools is time-consuming and causes 80% of the total machining time. As a consequence, just one blade can be structured per day. To increase the efficiency, a new grinding wheel was developed, which is bionically inspired by beaver teeth. The tool is constructed of alternating layers consisting of metal bonded diamonds and pure resin respectively. With this layer-by-layer setup, the tool does not have to be dressed and enables structuring of up to 50 compressor blades per day.BMBF/03V047