Achieving high surface integrity when polishing hard and brittle materials requires precise control over the material removal mechanism. This study introduces an active control method that utilizes a magnetorheological elastomer (MRE) tool with a magnetically tunable elastic modulus. A multiscale model was developed to correlate the applied magnetic field and the elastic modulus of the tool with the resulting contact stress at the tool-workpiece interface. The model predicted a controllable transition from ductile to brittle material removal mode, which was subsequently verified through polishing experiments on BK7 optical glass. The experimental results were in excellent agreement with the model predictions, demonstrating that optimal magnetic field of 0.3 T reduced the surface roughness to Ra = 0.093 μm, corresponding to a 67.25% reduction compared with the polishing condition at 0 T. Although higher magnetic fields increased the material removal rate, they also induced brittle fracture and macroscopic waviness, thereby degrading the surface quality. This work establishes a deterministic, model-based framework for controlling the ductile-to-brittle transition during polishing, offering a new approach to the high-quality finishing of brittle optical components.
Particle-reinforced titanium matrix composites (PTMCs) are advanced aerospace materials with low density, high hardness and strength, and excellent creep, fatigue, and high-temperature performance. However, their intrinsic properties cause severe machinability problems, including dimensional inaccuracy, poor surface reproducibility, excessive tool wear, and low processing efficiency. Firstly, to address the lack of theoretical modeling, a four-component grinding force model incorporating friction, chip formation, interfacial adhesion, and TiC particle fracture is developed. Secondly, a 3D FE (finite element) model with randomly distributed TiC particles is established in ABAQUS to reveal the material removal mechanism. Furtherly, single-factor grinding experiments are conducted to validate the model and to investigate the effects of grinding depth (ap), wheel speed (vs), and feed speed (vw) on grinding force, surface morphology, and roughness. Finally, the machining performance of electroplated and resin-bonded diamond wheels is compared. The proposed model agrees well with the experiments, with errors below 15%. The material removal process proceeds through matrix plastic deformation, TiC particle fracture and debonding, and subsequent matrix removal. Both grinding force and surface roughness increase with increasing ap and vw, but decrease with increasing vs. The resin-bonded diamond wheel produces lower grinding forces and better surface quality, proving more suitable for precision grinding of PTMCs. These findings provide a theoretical and simulation-based framework for optimizing the precision grinding of PTMCs.
Aiming at the performance requirements of low surface roughness, high residual compressive stress and its depth for the inner raceway of aero-engine bearing rings, the cross spindle barrel finishing process is proposed. Taking the installation angle as a variable, considering the single particle collision kinetic energy, the update and replacement rate, and the difficulty of flowing through the workpiece, the surface strengthening model was constructed. The optimal installation angle was theoretically derived to be 42.61°. By using discrete element simulation method, it is found that with the increase of installation angle, the normal force increases from 0.232 N to 0.272 N, but the number of granular media flowing through the workpiece decreases by 21.56%, and the number of collisions decreases by 30.45%. Increasing normal force is not equivalent to the improvement of the strengthening effect. At low installation angle, the processing mechanism is dominated by high frequency scratching and collision. At high installation angle, granular media accumulate at the ring leading edge, which weakens the strengthening effect. Through finishing experiment, the residual compressive stress of the inner raceway was increased from −334.3 MPa to −425.45 MPa, an increase of 27.27%. The optimal installation angle obtained through simulation and experimentation is 40°. The depth of the residual compressive stress increased from 37.5 μm to 73 μm, an increase of 94.67%. The study reveals the mechanism of the installation angle on the surface integrity and provides a theoretical basis and process plan for the strengthening of aero-engine bearings.
Existing six-degree-of-freedom (6-DOF) magnetic levitation planar motors (MLPMs) commonly suffer from limited tilt ranges, excessive coil heating, and complex sensing schemes. To address these challenges, we developed a compact 6-DOF MLPM that combines stacked multi-turn flexible printed circuits (FPCs) and Hall-sensor-array-based pose feedback enhanced by a neural network. The stacked FPC winding enables a compact multi-turn stator within the thickness-constrained air gap. In a controlled equal-ampere-turn coupon test using matched board thickness, copper thickness, and common cooling boundaries, the multi-turn FPC coil exhibits lower estimated copper loss and temperature rise than the single-turn PCB coil, supporting improved thermally sustainable continuous force and power capability. The neural estimator maps the nonlinear relation between Hall measurements and mover pose, while a coil–Hall compensation method suppresses current-induced magnetic disturbances. Absolute position accuracy was validated along the x and z axes against an interferometer reference. The prototype demonstrated closed-loop translational motions within 30 mm × 30 mm × 6 mm and rotations within 6°×6°× 10°, illustrating the feasibility of compact 6-DOF feedback-controlled motion.
Precision control is a critical requirement for piezoelectric-driven compliant grippers, particularly in grasping tasks that demand accurate position tracking and stable force regulation in the presence of nonlinearities and external disturbances. To address the conflicting requirements of fast dynamic response and chattering suppression in conventional sliding mode control (SMC), this paper proposes an adaptive composite SMC strategy that integrates exponential and variable-rate reaching laws. An adaptive mechanism is introduced to dynamically regulate the convergence gain, enabling an effective trade-off between response speed and steady-state accuracy under varying operating conditions. To accommodate the sequential operation of the compliant gripper, the proposed control strategy is further combined with a position/force switching control scheme, allowing decoupled regulation of position and contact force during free motion and grasping stages, respectively. Compared with conventional SMC methods, the proposed approach can achieve faster convergence to the sliding surface while significantly reducing chattering without compromising steady-state precision. Stability and convergence analyses are provided, and experimental validation is conducted on a piezoelectric-driven compliant gripper. The experimental results demonstrate that the proposed controller outperforms the conventional PID controller in both position and force tracking.
