Feng Jiao

Study on Ultrasonic Vibration Grinding Character of Nano ZrO2 Ceramics

Nano ceramics possessed ascendant mechanical property and physical characteristics contrast with engineering ceramics, so it has extensive application prospect in various industries. On the basis of applying the indentation fracture mechanics to analyze the removal mechanics of ceramic material, this paper analyzed the critical ductile grinding depth of the nano ZrO2 ceramics. Adopting ultrasonic composite processing we describe the influence of different processing parameters and grain size of diamond wheel on the grinding forces and surface roughness. Based on the grinding forces and surface roughness the grinding process with and without vibration is analyzed. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics are also discussed. The paper supplied the theoretical and experimental basis for the grinding of the large-sized ultraprecision plate structure of nano ZrO2 ceramics (nm).

Study on Motion Model of Abrasive Particle and Surface Formation Mechanics under Two Dimensional Ultrasonic Grinding

This paper worked on two dimensional ultrasonic grinding system with workpiece adhered to ultrasonic vibration. It analyzed the working locus of abrasive particle under two dimensional ultrasonic grinding (TDUG), and emulated the working course, and gave the key parameters affecting grinding efficiency and grinding locus’s characteristic under different grinding parameters, and brought forward the cutting course between abrasive particle and workpiece under TDUG belongs to an new rotating dynamic contact cutting model. At the same time, it put forward the theoretically critical speed condition under TDUG to obtain the optimum grinding effect, and verified good micro-feature of finished surface under TDUG by the means of grinding tests of nano ZrO2 ceramics.

Experimental Research on Surface Integrity of Ceramic Nanocomposites in Two-Dimensional Ultrasonic Vibration Grinding

The grain cutting trace of elliptical spiral in workpiece two-dimensional ultrasonic vibration grinding(WTDUVG) is defined, the reason of machining accuracy improvement by applying two-dimensional ultrasonic vibration is discussed. Adopting two-dimensional ultrasonic composite processing, the influences of grinding depth, worktable velocity, wheel granularity on the surface roughness of Al2O3/ZrO2 ceramic nanocomposites were described. Experimental results of AFM microstructure show that the material removal model in WTDUVG is dominated by ductile flow of material, some crystal refinement, the crush powder and grain pull-out are visible and there is almost no fracture. Furthermore, the surface roughness in WTDUVG with coarse grit is about 30 40% less than that in CG under identical grinding condition; the qualitative analysis of X-diffraction results indicated that the surface phases are composed of α-Al2O3, t-ZrO2 and small quality m-ZrO2, there are amorphous phase in the surface both with and without vibration grinding. M-zirconia phase transitions rule in vibration and conventional grinding was found. Under definitive grinding conditions, the material removal mechanism of inelastic deformation is the principal removal mechanism of Al2O3/ZrO2 ceramic nanocomposites, the grit size of diamond wheel and vibration grinding mode have important influence on material removal mechanism of ceramic nanocomposites.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Research on Relationships Between Surface Fracture States and Surface Roughness Dispersion Range in Ultrasonic Grinding ZrO2

On the basis of the relationship between machined surface roughness and cutting parameters of hard-brittle materials, experiments of common and ultrasonic honing ZrO2 engineering ceramics were carried out using coarse diamond grits to discuss the relationship between surface roughness and its dispersion range and surface fracture states. Experimental results show that the machined surface roughness value of hard-brittle materials and the characteristics of its dispersion range can be considered as the criteria of cutting state. Therefore, as the machined surface roughness value and its dispersion range are both rather small, the cutting goes in the ductile cutting state, whilst the machined surface roughness value and its dispersion range are both rather large, the cutting goes in the crack cutting state. When the machined surface roughness value is rather small and its dispersion range is rather large the cutting is in the transition cutting state. Introduction At present with combination to the special machining technology such as ultrasonic, the traditional ultra-precision machining technology for hard-brittle materials has developed a new way to obtain the ductile surface effectively. In 1993, Professor D. Prabhakar put forward a theoretical model of material removal rate for rotating ultrasonic machining engineering ceramics [1] to discuss the theoretical relationship between material removal rate and amplitude, rotating velocity, grit size and machining pressure, and proved that the rotating ultrasonic machining has a relatively lower cutting force and higher material removal rate with the same conditions as common grinding. In 1994, H. Frei and G. Grathwohl studied the microstructure and intensity of advanced ceramics after ultrasonic machining [2], and found out in the process of machining engineering ceramics such as Al2O3, ZrO2 and N4Si3, the material removal process includes both crack and mini-plastic deformation, and the later resulted in higher surface compressive stress and flexural strength. In the same year, Professor X. Ai and D.M. Kim studied the ultrasonic drilling of engineering ceramics [3] and found that ultrasonic machining has smaller cutting force, lower cutting temperature and better surface quality than common way. In 1995, Z.J. Pei investigated the material removal rate of rotating ultrasonic milling MgO and ZrO2 engineering ceramics, and forecasted the relation between removal rate and cutting parameters [4]. A.R Jones worked over the press distributing model of ultrasonic polishing using stamping die [5]. Z.Y. Wang put forward the dynamic model of material removal rate in ultrasonic machining metal accessories [6]. H. Dam studied the productivity, surface quality and dimension tolerance of ultrasonic machining ceramics [7]. In the 48th CIRP annual meeting, B. Varghese and S. Malkin gave a progress report of radial ultrasonic vibration machining, and the results shew contact press, loaded area, working cycle time, ultrasonic vibration and its direction, and slotted wheel have effort on the material removal rate of ZrO2 and Si3N4 [8]. E. Uhlman and G. Spur discussed the surface figuration mechanism of slow-feed grinding advanced ceramics assisted by ultrasonic, reviewed the cut-in mechanism of single grit imposed ultrasonic vibration in the normal direction of workpiece, and forecasted that the axial vibration could get a better machining effect [9]. Obviously these researches focused on the Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 239-243 doi:10.4028/www.scientific.net/KEM.259-260.239

Ultrasonic Dressing of Grinding Wheel and Its Influence on Grinding Quality

Being a key step in grinding process, dressing of grinding wheel influences the whole grinding results, especially grinding quality. Because of its good dressing effect, a new dressing method assisted by ultrasonic vibration attracted researchers’ attention. In this paper, on the basis of the researches on dressing with single-point diamond dresser, physical model of ultrasonic dressing of grinding wheel were established. According to the physical model and the SEM photos of grinding wheel’s surface topography, the mechanism of ultrasonic dressing was brought to light. Through contrast experiments, based on roughness and micro-feature of the ground surface, the influence of ultrasonic dressing on grinding quality was researched.

Influences of Ultrasonic Assistance in High Speed Lapping of Nano ZTA Engineering Ceramic on the Surface Machining Quality

Ultrasonic aided high speed lapping with solid abrasive material was put forward aimed at the precision finishing of nano ZTA engineering ceramic. Through theoretical analysis and contrast lapping experiments, the influences of ultrasonic assistance on the surface machining quality were clarified. Research results show that the maximum undeformed chip thickness in ultrasonic aided lapping is smaller than that in conventional lapping under the same conditions; ultrasonic assistance is beneficial to enlarging the range of ductile lapping regime and improving the surface quality of nano ZTA ceramic; with the application of ultrasonic vibration, smaller surface roughness and more regular surface profile can be obtained.

Study on Residual Stress of GCr15 Bearing Steel under Ultrasonic Vibration Turning

The effects of the cutting parameters on residual stresss were investigated in common and ultrasonic vibration hard turning bearing steel GCr15 with PCBN. The residual stresses under the machined surface were measured by X-ray diffraction technique. The results obtained in this study show that residual compressive stress is produced both in common and ultrasonic turning of GCr15 bearing steel. Under the same turning condition the residual compressive produced by the ultrasonic turning is smaller than that by the common turning. Residual compressive stress can improve the fatigue performance and life of workpiece, so the cutting parameters should be optimized to get the best residual compressive stress in ultrasonic turning.

Research on the Mechanism and the Superficial Microstructure of the Nano-Composited Ceramics under Ultrasonic Polishing

The polishing experiment of the ZrO2 toughed Al2O3 nano-ceramics is carried on by the ultrasonic installment manufactured according to the local resonance theory. Using the white light interferometer, SEM and so on to observe the superficial microstructure of nano-ceramics after polishing under the same parameter and component condition, the surface layer occurred mainly in material powdering and crystal grain fragmentation. The subsurface layer deformed also plastically operated by crystal lattice distortion and the crystal boundary slipping. The microscopic distortion is operated by the coordinated mechanism, including intragranular dislocation in crystal strengthened structures. The nano-particles along the grain boundaries reduce expanding of cracks, which led the materials favorable finished surface.

Research on Micro Characteristics of Surface and Subsurface Layer in Two-Dimensional Ultrasonic Grinding Nano-Composite Ceramics

This work mainly studied the deterioration layer structure, crystal grain size, crystal lattice distortion of ground surface in two-dimensional ultrasonic vibration grinding nano-composite ceramics. The research indicated that under a certain grinding condition the ductile deformation layer on the ground surface of nano-composite ceramics in two-dimensional ultrasonic vibration grinding is formed by the ways of material powdering, crystal grain fragmentation, materials extrusion, the crystal grain pull-off and so on. The transition layer between the surface layer and the base body is plastic deformation layer by the primarily ways of crystal lattice distortion and the crystal boundary slipping. The removed material in brittleness fracture mode is extremely few. In this work, the structural model of deterioration layer on ground surface in two-dimensional ultrasonic grinding nano-composite ceramics is put forward. The microscopic deformation mechanism of nano materials is inner grain dislocation of inner-grain-structure strengthened phase. Its deformation coordination mechanism is the the grain-boundary sliding of matrix grain and the coordinated deformation of intercrystalline second-phase. The TEM and SEM observation discovers that the nano particles dispersed in grain boundary stops crack from expanding in nano materials, which causes the materials to appear in transcrystalline fracture behavior. And this fracture behavior gives materials favorable finished surface. The plastic deformation is the dominant removal mechanism of the nano materials in two-dimensional ultrasonic vibration grinding.