Experimental study on step drill geometry and pecking drilling with variable parameters processing method as drilling of CFRP and Ti stacks

Integrated drilling of CFRP and Ti stacks is a challenging task due to the disparate machining property. Choosing proper tool structure and processing method are effective ways to obtain high -quality holes. In this paper, drilling experiments are carried out to research the performance of step drills and variable processing method in drilling of CFRP/Ti stacks. The effect of ratio of primary cutting edge diameter, point angle of primary cutting edge and secondary cutting edge and the location of variable processing on the burr of Ti layer, delamination and thermal damage are analyzed. Decrease the primary cutting edge can restrain the thermal damage and delamination. The point angle of secondary cutting edge has the influence on the final holes directly, and as drilling from Ti to CFRP, the point angle of secondary cutting edge is 110 degrees, by contrast, as drilling from CFRP to Ti, the point angle of secondary cutting edge is 130 degrees. Pecking drilling with variable parameter can reduce the drilling damage. As the pecking drilling feed rate increase from 2f to continuously drilling, thermal damage increases by 176.4 %. Variable parameter processing method can reduce the thermal damage as drilling of Ti layer with low spindle speed.