A meta-model framework for grinding simulation

When considering the mechanics of grinding, several physical phenomena have to be modeled, each one having effect on the resulting grinding forces, wheel and workpiece geometry. Depending on the analyzed problem, some dependencies can be neglected to privilege some aspects instead of others. Nevertheless, all models essentially start considering wheel-workpiece engagement and the corresponding material removal (both wheel and workpiece side), deriving the forces by means of energy balances and/or shear mechanics. The meta-model proposed in this paper represents a general framework conceived for providing a time-domain simulation engine based on a dexel representation of wheel and workpiece, capable to “host” all the semi-empirical models existing in literature, where the overall grinding force is the result of the integration of the force contributions associated to the local removal along wheel-workpiece engagement arc. A cascade approach is adopted to solve for forces and displacements the DAEs set describing the dynamic interactions between wheel and workpiece, whereas all the algebraic relationships pertaining to the various specific models are solved in a pre-processing phase, yielding a set of response surfaces that are queried during time integration. Finally, the meta-model framework is instantiated for a model of traverse roll grinding with force-dependent wheel wear

A model-based approach for online estimation of surface waviness in roll grinding

Vibrations onset represents a paramount issue in all grinding processes. The related surface defects appear in the form of micrometric waviness that decreases the finishing quality and in some cases the functionality of the ground workpieces: sometimes, these defects can be also marked on the grinding wheel surface. This paper presents an online model-based approach to identify and quantify the level of waviness starting from multiple acceleration measurements, allowing a continuous monitoring of wheel and/or workpiece defects. The identification algorithm, that exploits a linear model of machine and process dynamics, is based on the application of Least Squares method in the frequency domain. Experiments confirm the good performance of the algorithm that, hence, can be exploited for developing advanced control schemes of the grinding process

Non-Regenerative Dynamic Instability In Surface Grinding

n this paper a particular type of non-regenerative instability in surface grinding is studied. Clear evidences have been collected suggesting that vibrations can occur suddenly even during the first wheel pass and just after wheel dressing, circumstances that exclude workpiece and wheel surface regeneration as instability origin, whereas both surfaces have to be considered ideal. Therefore, the stability of the dynamic system constituted by an oscillating ideal wheel immerged in a positional and velocity-dependent process force field has been studied, demonstrating that in some circumstances the force field itself exhibits an unstable behaviour. The instability occurrence is strictly related to the oscillation direction of the wheel centre according to the mode shape associated to the dominant resonance, with respect to the direction of the grinding force (identified by the ratio between tangential and normal components). Then, the analysis leads to the identification of a simple necessary condition for instability occurrence. The analytical results are confirmed by proper time domain grinding simulations and compared with experimental evidences

Model-Based identification of Chatter Marks during cylindrical grinding

The following paper presents an online model-based monitoring algorithm that identifies and quantifies the level of waviness caused by grinding chatter exploiting accelerations measured on the machine. A Weighted Least Squares method has been applied in the frequency domain that leads to a clear interpretation of the forcing effect caused by the waviness at particular frequency components exciting the machine structure. A sensitivity analysis has been carried out in order to define the limits of applicability and the precision of the approach in relation to the adopted analytical models. The development has been supported by simulations produced by an integrated model implemented in Matlab/Simulink® environment. Finally, experiments on the real machine confirmed the good estimation performance of the algorithm

Force-field instability in surface grinding

In this paper, a particular kind of non-regenerative instability in surface grinding is studied. Clear evidences have been collected suggesting that vibrations can occur suddenly even during the first grinding pass, just after wheel dressing. These circumstances exclude workpiece and wheel surface regeneration as instability origin, whereas both surfaces have to be considered initially smooth. On these bases, the stability of the dynamic system constituted by an oscillating ideal wheel (namely without waviness on the surface) immerged in a positional and velocity-dependent process force field has been studied, demonstrating that, under particular conditions, the force field generates an unstable behaviour. The instability occurrence is strictly related to the oscillation direction of the wheel centre, according to the mode shape associated to the dominant resonance, with respect to the direction of the grinding force (identified by the ratio between its tangential and normal components). The analysis leads to the identification of a simple necessary condition for instability occurrence. The analytical results are confirmed by time-domain grinding simulations and compared with experimental evidences

A Time-Domain Surface Grinding Model for Dynamic Simulation

The quality of a workpiece resulting from a grinding process is strongly influenced by the static and dynamic behavior of the mechanical system, composed by machine tool, wheel, fixture and workpiece. In particular, the dynamic compliance may cause vibrations leading to poor surface quality. In order to evaluate in advance the process performance in terms of surface quality, a simulation model for surface grinding has been developed, based on workpiece discretization by means of a z-buffer approach. The volume engaged by the wheel is associated to the grinding force by means of a variable specific energy that is a function of the equivalent chip thickness. The model is able to provide static and dynamic grinding force components taking into account the following aspects: nonlinearity of the grinding force with respect to cutting parameters, grinding damping effect, contact stiffness, machine-workpiece dynamics in all the relevant degrees of freedom (radial and tangential both for wheel and workpiece). The implementation in Matlab/Simulink™ environment allows an easy connection with any given mechatronic models of the grinding machine. Stable surface grinding tests with force measurements have been performed on a commercial CNC grinding machine for identifying the model parameters; then, the validation was extended to the dynamic case by introducing an artificial wheel unbalance