Search

The actual vibration amplitude (AVA) during ultrasonic vibration-assisted face grinding (UVAFG) is an essential parameter that affects grinding force and surface quality. However, an effective method for the real-time measurement of AVA during grinding remains unavailable, hindering research on UVAFG. In this study, an experimental setup for measuring AVA is firstly established using an eddy current sensor. Ultrasonic amplitude curves under the condition of tool rotation without load are measured and analysed. Then, amplitude attenuation with different grinding forces is evaluated during the UVAFG of silicon carbide (SiC) ceramics. The influences of AVA on grinding force and surface quality are investigated through comparative experiments of the UVAFG and conventional grinding (CG) of SiC ceramics. Finally, experimental results indicate that AVA exhibits a negative correlation with grinding force. Compared with CG, UAVFG has lower grinding force when grinding SiC ceramics. AVA is the key factor that affects surface roughness during UVAFG, the AVA of UVAFG is less than 4.3 μm; thus, surface roughness during UAVFG will be less than that during CG. Moreover, vibration can reduce the scratches made by the tools on the grinding surface. [ABSTRACT FROM AUTHOR]

Abstract A finite element model (FEM) of single-grain surface grinding of SiC has been established to understand the effects of the cutting-edge radius and grinding wheel speed on SiC chip formation. Based on the mechanic deformation behavior of SiC, the critical chip formation thickness and critical ductile-brittle transition thickness were found. Results obtained show that critical ductile-brittle transition thickness has a peak value at R c = 1.25 µm and v s = 80 m/s respectively. Normal grinding force increased firstly with the increasing cutting edge radius and then declined. The critical cutting edge radius R c = 1.25 µm and grinding wheel speed v s = 80 m/s were determined depending on the variation of critical chip formation thickness, critical ductile-brittle transition thickness, grinding force, ground surface quality. Finally, the simulation results were verified experimentally by an indirect single diamond grain scratching SiC ceramics test. [ABSTRACT FROM AUTHOR]

Highlights • The tension-shear coupled fracture criterion was proposed to simulate the brittle-ductile transition phenomenon in the brittle materials machining process. • Tension-shear coupled fracture criterion is more suitable than the equivalent plastic strain fracture criterion for the simulation of brittle materials precision machining. • The equivalent plastic strain parameter could be used to distinguish the materials removed in ductile mode or brittle mode. • Even though the materials removed in brittle mode, the plastic deformation may happen and residual stress may be left on the machined surface or subsurface. Abstract Despite great efforts have been made to understand the machining mechanism of brittle materials, few numerical models are available to describe the brittle-ductile transition (BDT) in engineering ceramic grinding due to the fracture mechanism difference in brittle and ductile removal modes. This paper introduces the tension-shear coupled (TSC) fracture criterion for the finite element method (FEM) analysis of the brittle material machining that is capable of describing BDT. With TSC fracture criterion, simulation results of single diamond grain grinding of silicon carbide (SiC) ceramic, including the ground surface/subsurface morphology, grinding forces, and equivalent plastic strain, were compared with those under effective plastic strain (EPS) fracture criterion, the one widely adopted by commercial finite element software. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion. Graphical abstract Image, graphical abstract Up to now, few numerical models are available to predict the brittle-ductile transition phenomenon of materials removal mode in engineering ceramics grinding process due to different fracture mechanisms of brittle removal mode and ductile removal mode. To that problem, a new fracture criterion (tension-shear coupled (TSC) fracture criterion) was proposed in the present work to simulate the brittle materials machining process with finite element method. The simulation results (e.g. ground surface/subsurface morphologies, grinding force and equivalent plastic strain) with TSC fracture criterion were compared with those of effective plastic strain (EPS) fracture criterion, which was widely implemented into the commercial finite element software, e.g. ABAQUS, Ls-Dyna etc. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion. [ABSTRACT FROM AUTHOR]

A single grain grinding experiment with fixed speed ratio v s / v w was designed to decouple the effect of grinding speed and undeformed chip thickness (UCT) on the SiC material removal mechanism during elevating the grinding wheel speed. Ground surface and subsurface topography, grinding forces, and specific energy were measured with grinding speed ranging from 20 to 160 m/s and maximum UCT a gmax from 0.02 to 3 μm. The results demonstrated the grinding force and specific grinding energy show an evident decreased tendency with the increasing of grinding speed, despite the a gmax value was kept at 0.03, 1 μm. However, at a gmax = 0.3 μm, the grinding force has a peak value with the increment of grinding wheel speed. The subsurface has the same trend. Based on the subsurface morphologies, grinding forces, grinding energy, the critical grinding wheel speeds v s = 100, 80, 80 m/s were determined at the a gmax = 0.03, 0.3, 1 μm, respectively. Besides, grinding forces show different growth rates with the gradually increasing a gmax at three stages under typical grinding speeds due to the transition of material removal mechanism. The critical a gmax values for ductile-brittle transition and beginning of brittle regime grinding are determined as 0.3 and 1 μm by surface and subsurface morphologies, grinding forces, grinding energy, respectively. [ABSTRACT FROM AUTHOR]

Rotary longitudinal–torsional coupled ultrasonic vibration-assisted grinding (LTUAG) is a new manufacturing method that can improve the grinding ability of silicon carbide ceramics. However, compared with longitudinal ultrasonic vibration-assisted grinding (LUAG), the role of torsional vibration in the grinding process is unclear. In this study, an effective method for measuring longitudinal–torsional coupled ultrasonic vibration amplitude and an experimental setup for measuring actual amplitude during grinding are proposed. The trajectory of the abrasive grains under the same grinding parameters and the same longitudinal amplitude during LTUAG and LUAG are analysed. Ultrasonic amplitude curves under the condition of tool rotation are then measured and analysed. Finally, the effect of torsional vibration on grinding force and surface roughness under the same grinding conditions is explained. Experimental analysis shows that the introduction of torsional vibration has little effect on the trajectory length and does not change the number of interference overlaps between abrasive grain tracks. Torsional vibration will only increase the cutting speed during grinding and reduce the undeformed chip thickness, which will reduce the grinding force and improve the surface roughness of LTUAG. [ABSTRACT FROM AUTHOR]