Design Of Variable Pitch Separable Type Cathode Working Tooth And Study Of Drag-reduction

The variable pitch helix processed was broaden and inclined by the traditional cathode of Electrochemical machining processing equal pitch helix,in which the working teeth and cathode body is an integral whole,because the rigid working tooth can not be altered with the angle according to helix equation, in particular,the variable pitch helix with the helix angle altering from 0°could scarcely processed. In order to solve this problem, a new separable type cathode was presented, the work part of which were divided in a number of certain thickness section perpendicular to and along the axial direction of cathode, each section is made from the working tooth around cathode body.which was called the wheel plate. While the cathode moves as helix equation,each wheel plate driven by the micro-motor embedded in the cathode body rotate around the body to keep the angle of the envelop line of working tooth consistent with the angle of the helix processed as the blueprint. But there are steps between adjacent working tooth sections,arising cavitations, separation and vortex in machining gap flow field around steps,which effect machining accuracy of variable pitch helix.For the sake of the even gap flow field,two sorts of cathodes with equal thickness section working teeth and variable thickness section working teeth were put forward in this paper. And eight schemes for optimization of tooth section shape were proposed and the gap flow field for each scheme was simulated by COMSOL Multiphysics to compare the streamline distribution, velocity distribution and pressure distribution in gap flow field.Combining the simulation for each scheme with calculation on the time-averaged drag coefficient CD value,the result shows that the gap flow field of the eighth option is best,in which we have half of every piece thick tooth cut off,the steps spiraled of the thick tooth on this side cut into rounded angle,of which radius no more than 0.3mm,and the lower right corner of the thin tooth on the other side cut no more than 0.4mm.It is effective to reduce the influence on gap flow field from steps adjacent working tooth section by variable thicknes section designed in the light of different position from steps.Based on the best scheme the working teeth with different size riblet surface were designed in terms of the theory of Drag-reduction of riblet surface to optimize teeth shape and the gap flow field further. The gap flow field were simulated based on the COMSOL Multiphysics, the influence of the shape parameter of riblet surface upon the velocity,turbulence parameter and shear rate were discussed, which had proved that the riblet surface size likes s=0.2mm,h=0.05mm of the working tooth not only can reduce the friction, but also stabilize the gap flow field.