Hydrostatic spindles are core components of high precision machine tools, which have been widespread used in mechanical engineering, but the mechanism of rotation error has not been revealed clearly. According to current documents and models, the transient processes of the spindle from an equilibrium position to a dynamical orbit could not be simulated quantitatively. The intrinsic relationship among the disturbance factors, the position, the flow and the oil film force could not be revealed, as resulted in that the mechanism of the rotational error motion of hydrostatic spindle could not be described exactly. The dynamic model of the rotation error motion of hydrostatic spindles is established. Three methods, which are full process moving mesh method, equilibrium position moving mesh method, and equilibrium position simplified formula method, are used to quantitatively calculate the trajectory of a spindle from the concentric position to forming rotational error. The inherent laws among the disturbance factor, total force, the flow and the position are discovered. The rotation error is evaluated by using of the Least squares method. By studying the influence of these three calculation methods on the rotary centre position and rotary error, the reasons that results in calculation difference are found. The method which combines the moving mesh method and the simplified formula to calculate the rotary accuracy of hydrostatic spindle are verified to be efficient and pinpoint.

Study on the Mechanism of Hydrostatic Spindle Rotational Error Motion

Crankshaft is a core part of automobile engine to bear impact load and transmit power. Precision grinding is the most important machining method to achieve high precision of crankshaft main journal. Although many scholars have established various simulation models in the field of cylindrical grinding, it is difficult to carry out effective quantitative simulation for a given crankshaft main journal grinding system. Aiming at the shortcomings of the existing models, a double-rotor dynamic model is proposed, which considers the interaction between the grinding wheel and the main journal, and iterative algorithm is adopted to simulate material removal and roundness change in the grinding process of the main journal. The normal force between grinding wheel and the main journal is defined in detail in the algorithm, which is closer to the actual grinding process. For a given crankshaft grinding system, different grinding strategies of the main journal are quantitatively simulated by using the model. The proposed model and algorithm are validated by experiments, which can provide a basic model for the further study of the crankshaft cylindrical grinding system.

Research on double-rotor dynamic grinding model and simulation algorithm for crankshaft main journal

Cooling and lubrication techniques in grinding: A state-of-the-art review, applications, and sustainability assessment

Research on the consistency model of roundness error in journal cylindrical grinding with random parameters

Regenerative chatter that is the most common type of self-excited vibration is investigated in this paper. The kinetic model of roll grinding process made up of a workpiece and a grinding wheel with the Duffing Oscillator is proposed. The three degrees-of-freedom grinding model system contains two time delays derived from the regenerative chatter of the grindstone and the cylindrical roll. Based on the model, the impact of the width of cut on the regenerative chatter is studied and the stable boundary is plotted in parameter plane. Afterwards, the curves of time history and the bifurcation diagram are used to identify the behavior of dynamic system. The results show that the width of cut has a significant influence on chatter in grinding process. In the end, the velocity feedback is introduced to suppress the regenerative chatter, which has a great effect.

Analysis of Regenerative Chatter in Roll Grinding Process with Duffing Oscillator and Its Suppression

Hydrostatic bearings are the supporting parts of hydrostatic spindles. Hence, the bearing inner bore roundness may affect the spindle shaft equilibrium position and rotation accuracy. Although many scholars have established various models to simulate the internal and external grinding process, the existing models cannot provide precise calculations for choosing an efficient grinding strategy, and the final bore roundness predictions are also insufficient. To achieve precise prediction for grinding process and final bore roundness, the coupling interaction between the grinding wheel spindle system and the workpiece-spindle system during the inner bore grinding process is considered, and then a novel inner bore grinding double rotor model is established. The model adopts iterative algorithm to calculate material removal and the bore roundness forming process. Based on the model, different inner bore grinding strategies are quantitatively simulated for a given grinding system. The material removal and inner bore forming process under different grinding conditions are compared. The final bore roundness roughly matches the experiment results. The proposed double rotor system model and the simulation algorithm could be a new path for further studies of the grinding transition process.

A novel double rotor coupling model for inner bore grinding process

In this work, creep behaviors of dilute Mg-Mn-Zn alloys were investigated in extruded rods (ER) with bimodal grain microstructures and extruded sheets (ES) with homogeneous microstructures. Tensile creep tests were carried out at 423 K along the extrusion direction (ED) and transverse direction (TD). For brevity, the samples were named as ER-ED, ER-TD, ES-ED and ES-TD, respectively. All samples' creep is dominated by dislocation movement, and different types of dislocation slip are seen in the different samples under loading along each direction. For the ER sample, the creep mechanisms of the ER-ED sample were determined to be cross-slip accompanied by pyramidal <c+a> slip. Differently, the creep of the ER-TD sample was dominated by basal slip and accompanied by grain boundary bulging, which induced the worst creep resistance. For the ES alloy, the creep mechanisms were pyramidal <c+a> and cross-slip, but the cross-slip density of the ES-ED sample was higher. Accordingly, the creep test results indicated that the creep resistance was ranked in an order of ES-TD/ED > ER-ED >> ER-TD. Furthermore, bimodal grain microstructure accelerates creep at a similar texture effect level, where grain boundary bulging was clearly observed, as well as the decreased KAM and increased fraction of M/HABs (middle-to-high angle boundaries). These typical softening characteristics might be responsible for weakening the ER-ED sample from the highest room-temperature yield strength to the inferior creep resistance to ES-TD/ED samples, meaning the thermal instability of this strong heterogeneous microstructure. 

Jianhua Chen

Papers

A novel double rotor coupling model for inner bore grinding process

Study on the microstructures and tensile creep behaviors of extruded dilute Mg-Mn-Zn alloys