Researches and constructive solution to enhancing the stiffness of the gantry type milling machines

Abstract

For machining of large size work pieces, CNC milling machines with moving bridge (known as Gantry Type milling machines) that have a large distance between the bridge columns, i.e. 4 to 7 meters are frequently required. This leads to a difficult guiding, driving and stiffening of the moving bridge. At the same time, the moving bridge is required during the cutting process by a number of forces, some of them fixed, others variable. The manufacturers of such machine tools sort out this problem by a “suitable” sizing of the moving bridge that involves large overall dimensions of the bridge, with major implications on its guiding. This work presents an innovative solution concerning the increase of the stiffness of the Gantry type bridge, so that the geometrical accuracy of the machine is preserved regardless the force variations in the guiding system of the moving bridge. This work sets out an interdependent connection between the variation of the requiring forces generated at a high extent by the location of the moving elements on the cross rail and the compensating forces in the guiding of the two columns of the bridge.