Case Study 2.2: Clamping of Thin-Walled Curved Workpieces

Abstract

Thin-walled curved workpieces are typical for structural parts of airplanes. The issue in the workpiece clamping and subsequent machining is the changeable workpiece stiffness during material removal. The fixture forces and the cutting forces deform the workpiece with dependence on the part decreasing static stiffness that causes large local surface location errors of the part. As a result, the workpiece wall thickness is out of tolerance and consequently the part’s weight is also out of tolerance. The proposed solution is based on new fixtures with integrated support and clamping function. The workpiece is clamped using a vacuum. A suitable thickness measurement sensor was integrated into the machine tool. The new fixture elements are autonomous and plug-and-produce ready, with integrated safety by monitoring the minimal workpiece clamping force. The fixture control enables fully automated operation using the specific control software. The machining process was optimized in terms of tool path strategy and cutting conditions to avoid chatter during machining and shorten the production time. The proposed manufacturing process leads to a shortening of the production time with the requested surface quality. The presented manufacturing procedure is beneficial from the productivity and cost point of view. A group of fixtures, including the necessary harness and control, offers a universal possibility for replacing a set of six specific fixtures designed as a mould with part negative shape.