Piezo-based parallel kinematics for tool positioning

Parts with a functional micro contour or a micro structure are needed in a large number of applications. Manufacturing process with a geometrically defined cutting edge are usually rare for such applications. Reasons for this are limited dynamics and accuracy of the existing machine tools. An example of use is the compensation of elastic deformations in cylinder crankcases due to fastening of cylinder head bolts during theirs assembly and general operating conditions. Under unoptimized conditions this results in non-circular cylinder bores, also sometimes called a four-leafed clover owing to its similarity. In the state of the art, torque plates are used during the honing operation to compensate the deformations or a novel method - called form honing - is applied. The Fraunhofer IWU developed a piezo-based spindle support for high dynamic positioning of the cutting edge. Thereby it's possible to manufacture non-circular cylinder holes in one of the very first machining operations. This enables a decrease in processing time of cylinder crankcases and in manufacturing more complex and more precise cylinder contours. The spindle support consists of eight high volt piezo actuators in a differential arrangement around a flexure, in whom the spindle is fastened. The flexure itself allows three degrees of freedom (jx, jy, z) for displacement of the HSC-spindle. Depending on tool length, displacements of the tool center point up to ±60 ìm were achieved and four-leafed clover shaped cylinder bores were manufactured at speeds up to 6000 rpm.