Burr Formation and Removal at Profile Grinding of Riblet Structures

Compared to smooth surfaces, ideal riblet structures have proven to reduce skin friction and wall shear stresses in turbulent flow by up to 10%. Investigations in the wind tunnel show that the tip radius of the riblets has a significant influence on the reduction of the skin friction. One promising process for the production of riblets on large surfaces is profile grinding. In the first experiments conducted only a minimum tip radius of 8 μm was reached. Micrograph sections of the workpiece show that the radius results from a rolled burr. The contact area between the grinding wheel and the workpiece is simulated in order to identify the mechanisms of the burr formation. It is observed that the contact area is asymmetric. Thus the removed material mainly flows to one side of the groove and forms a burr. In the following, the influence of the grinding strategy, the grinding wheel specifications and the grinding parameters on the size of the burr is investigated. The experiments have shown that the burr formation in up grinding process is quite unsteady in comparison to down grinding. The cutting speed and the feed rate as well as the grinding wheel specifications have no significant influence on the burr size. However, the burr size develops linear to the depth of cut, i.e. an increase in the depth of cut leads to an increase in the burr size. The burr can be removed by a spark-out process after the grinding process. Furthermore, the burr size decreases with an increasing feed rate during the spark-out process. Thus a riblet tip radius below 2 μm is achieved.