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Wibrostabilność skrawania wieloostrzowymi narzędziami obrotowymi

Pajor M.

Prace Naukowe Politechniki Szczecińskiej. Instytut Technologii Mechanicznej

2006

Nr 597 (19)

3-190

Pierwszym i głównym celem pracy jest stworzenie uniwersalnej metodyki modelowania procesu skrawania narzędziami wieloostrzowymi z zastosowaniem techniki NURBS, możliwej do wykorzystania w przypadku szerokiej klasy narzędzi wieloostrzowych pracujących w różnorodnych konfiguracjach technologicznych, a w szczególności podczas obróbki w pięciu osiach.

The present monograph gives the reader a summary of the author's earlier research into modeling cutting process with rotational multi-edge tools in order to analyze the vibrostability of machine tool-cutting process (MT-CP) system. Vibrostability, i.e. the resistance of a system to self-excited vibrations, is one of the basic dynamic properties of machine tool. Self-excited vibrations heavily affect the process of machining, the quality of machined surface and the tool and machine's life. Following the recent quick development of machine building and control techniques a modern type of CNC (computer numerical control) machine tools, which can be controlled in five axes, as well as machine tools with parallel kinematics (also called hexapods) came into use. These types of machine tools can perform many complex operations of the machine tool versus the work piece and consequently they enable to machine surfaces with complex topology. In this case, using standard models of the machine cutting process to predict the vibrostability of MT-CP (machine tool-cutting process) system proved to be inadequate. Therefore, there was a need to further develop these models using new techniques of geometric modeling applied in advanced CAD systems. The precision of vibrostability forecasting depends on the precision of both numerical models of mass-damping-spring (MDS) system and models of processes taking place in the machine tool. The work presents a concise description of the ways of MDS modeling using the finite (rigid, deformable and hybrid) element method, modal method and the methods of describing the kinematics of a system by means of homogeneous transformations. The basic operation of a machine tool is machine cutting. Two aspects of machine cutting process can be singled out: a model describing the geometry of the machined layer's cross- section and the so-called elementary model of the machine cutting process. The monograph presents a simplified method of describing the geometry of the machined layer's cross-section applied to modeling the machining of planes and holes, in which the machine tool performs a rectilinear advance movement. If this is the case, the cross-section of the machined layer is fixed and can be given using simple geometrical relations. The machining of complex spatial surfaces on five-axis machine tools using modern tools such as toroidal and spherical cutters is an example of a process, which is difficult to model using simple geometrical relations. The present work suggests an original method of describing the geometry of the cross-section to be machined using NURBS technique (rational B-spline curves and surfaces). The method seems to be very universal and also it makes it possible to apply a uniform mathematical method to build geometrical models of the cutting process. Moreover, the method can be used with a majority of rotational multi-edge tools (such as face milling cutters, spherical and toroidal cutters, drills, reamers, boring bars, etc.). These kinds of models can also be well applied to model five-axis machining. The monograph also contains a synthetic review of elementary models of the machine cutting process, which describe dynamic phenomena taking place at the cutting zone and directly at the cutter. These models, combined with a geometrical model, are used to describe the dynamics of cutting with a rotational, multi-edge tool as well as to analyze the vibrostability of MT-CP (machine tool-cutting process) system. There are many models of the machine cutting process and methods of forecasting the vibrostability that significantly differ one from the other. Their usefulness depends to a large degree on the aim, the constructor - designer has in mind. The work lists the main guidelines used in the selection process of choosing a geometrical model of the cutting layer, an elementary model of the cutting process and criteria of assessing vibrostability. Theoretical reasoning presented in the monograph is illustrated with many examples of practical applications and it is also experimentally verified. The work contains many results of simulations, measurements of real cutting forces, forecasting and experiments on vibrostability of both conventional and parallel kinematics machine tools. The results of experiments and tests are in good agreement with the results of numerical simulations and therefore confirm the usefulness of the presented computational methods. In the summary, the author suggests some future directions of further research in the fields of modeling of the process of cutting with rotational, multi-edge tools and in forecasting vibrostability of MT-CP system.