Tool path prediction in virtual manufacturing for high speed milling (HSM)

One of the most important problem for the optimization of high speed machining, with spindle rotation up to 40000 rpm and linear displacements with velocity up to 40 m/min, is the interaction between the mechanical structure and the control system. This is a very important aspect which become fundamental especially in early stage of the conception of a new machining centre. During the last decade a lot of efforts have been conducted from many authors[1],[2],[3]. The development of a “virtual machining centre” allows to verify the effectiveness of alternative project solutions aimed at making both the bandwidth of each control loop and the natural frequencies of the structure as high as possible. In this work an integrated modeling technique for a machining centre is proposed. In particular a virtual model of a five axis controlled for high speed milling manufactured from Breton S.p.A. is presented. The virtual model, developed by means Simulink® environment and I-DEAS® FEM, is based on: a simplified model of the CNC, which is Sinumerik 840-D from Siemens. a proportional controller for the position loop and two proportional-integral controllers for the velocity and current loops [4],[5],[6] 4 equations for the electrical equilibrium of the motor armature circuit. 15 differential equations obtained with the Craig & Bampton method reduction starting from the finite element model (FEM) of the whole machining centre with about 73000 d.o.f. The “virtual machine”, completed also with the friction model, allows to realize a real time simulation, for example, of the tool path due to a commanded trajectory coming from the CNC. 2-D trajectory like ball bar test and 3-D path can be simulated and also the dynamic interaction between the axis are taken into account. The developped System is now in usein Breton’s project Dept, both to improve the performances of the current machines and for design optimisation of new machine tools.