NKFI FK 124361

Suppression of self-excited vibration in manufacturing processes

In this project, the dynamical modelling of heavy-duty manufacturing processes is carried out considering forced and self-excited vibrations and their limiting phenomena, as well as the effect of digital control mechanisms. Subtractive and deforming manufacturing processes, namely, milling and axles rolling are investigated in this framework, which both are important to produce large, high-valued and fatigue resistant parts for automotive, energy, avionic and rail industries. From process point of view, the modelling of limiting piecewise smooth threshold phenomena, in milling the fly-over and in axles rolling the elastic-plastic relay are of importance, in order to know more accurately the dynamic behaviour of the corresponding manufacturing processes. In milling, the fly-over effect, when the cutting edge abruptly leaves the surface, has great influence on the efficiency of today’s semi-active and active vibration attenuation techniques. Also, in axles rolling the elastic-plastic deformation and its stiffening behaviour are greatly important to model helping to set on effective hydraulic control methodology of this cold forming manufacturing process. In both controlled processes, the effect of actuator saturation and sampling need to be modelled accurately to select appropriate equipment for the machine tools in the design stage. The project is about to deliver the mechanical models for such controlled manufacturing processes, as well as, the necessary numerical techniques to perform time domain simulations and stability calculations. Moreover, by the help of the international industrial partners the validations of these developed models will be carried out.

The main research question is how to model such heavy-duty manufacturing processes that are subjected to self-excited regenerative effects and influenced by non-smooth limiting threshold phenomena. The regeneration, when the past vibration pattern left on the surface excites the machine tool, can be described mathematically by delayed differential equations. These infinite dimensional mathematical systems are effected by the non-smooth phenomena, when the tool leaves the surface in milling or when deformation switches between elastic & plastic state in axles rolling. By modelling sampling and actuator saturation the mechanical model becomes enormous challenge to solve, which is confronted by the proposed project. Beside the complex modelling of the controlled combined mechatronic, hydraulic and mechanic system their solution techniques are only partly developed. The project is about to develop also, numerical techniques to perform continuations taking into account non-smooth invariant torus solution, which is important to predict the resultant behaviour of the manufacturing processes under unstable stationary circumstances. In axles rolling, the behaviour of the elastic-plastic stiffening deforming force is completely unknown. In order to develop a model for it, numerical nonlinear finite element calculations and test rig measurements are performed. For both selected regenerative milling and rolling processes the developed models are tested and validated in industrial environment by the international industrial partners. It is important how to set the digital control mechanism to attenuate vibration in the most effective manner keeping or increasing the productivity.

From the beginning of the new millennium, the size and prices of electric systems are reduced and their speed were continuously increased. These electronic systems have leaked into our daily life connecting users and computers through internet. The experts expect a new 4th industrial revolution also in manufacturing, based on embedded systems and internet of things (IoT). This tendency increases automation and machine tools are able to self-characterize and self-act to control the quality of the just produced products. In this manner, the automatic elimination of harmful vibrations is a must. Moreover, the application of these embedded cyber physical systems (CPS) changes the entire dynamics introducing actuators with their saturations, and global sampling of the usually cascade realisation of the control mechanisms. An effective CPS machine tool compatible with the EU roadmap Industry 4.0 has to be prepared with equipment and methodologies to attenuate forced and self-excited vibrations as much as it is possible. In process-wise the fly-over mechanisms in milling and the elastic-plastic relay in axles rolling have not effectively modelled yet, although their effect on semi-active and active damping techniques are not a question. Moreover, the deployed control has its own limitations, which needs to be modelled related to its saturation limit. Also, it has of importance to choose the right sampling frequency to have an effective control mechanism. The PI of the proposed project believes the solution of the explained modelling issues will help for the industry to set up more automatic machine tools that are completely fitting to 21st century requirements. Indirectly, this helps to keep the competitive level of EU companies introducing more automation. Since the machine tool industry is quite conservative there is no any actively effective controlling mechanism mounted in commercial machine tools yet, but the push of the demand is enormous nowadays. Both milling and axles rolling machines are for large scale productions, where companies tries to decrease expensive expert interactions by demanding CPS machine tools.

Preliminary Works

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