This study investigates the critical maximum undeformed equivalent chip thickness for ductile-brittle transition (DBhmax-e) of zirconia ceramics under different lubrication conditions. A DBhmax-e model is developed through geometry and kinematics analyses of ductile-mode grinding. Result shows that DBhmax-e decreases with increasing friction coefficient (μ). An experimental investigation is then conducted to validate the model and determine the effect of dry lubrication, minimum quantity lubrication (MQL), and nanoparticle jet minimum quantity lubrication (NJMQL) conditions on DBhmax-e. According to different formation mechanisms of debris, the grinding behavior of zirconia ceramics is categorized into elastic sliding friction, plastic removal, powder removal, and brittle removal. Grinding forces per unit undeformed chip thickness (Fn/h and Ft/h) are obtained. The lubrication condition affects the normal force and ultimately influences the resultant force on workpiece. In comparison with dry grinding (DBhmax-e = 0.8 μm), MQL and NJMQL grinding processes increase DBhmax-e by 0.99 and 1.79 μm respectively; this finding is similar to model result. The theoretical model is then assessed by different volume fractions of nanofluids under NJMQL condition with an average percentage error of less than 8.6%.

Maximum undeformed equivalent chip thickness for ductile-brittle transition of zirconia ceramics under different lubrication conditions

In this research, the heat transfer model of surface grinding temperature field with nanoparticle jet flow of MQL as well as the proportionality coefficient model of energy input workpiece was esta...

https://journals.sagepub.com/doi/pdf/10.1155/2013/986984

Modeling and Numerical Simulation of the Grinding Temperature Field with Nanoparticle Jet of MQL

In recent years, lots of researches have been launched on nanomaterials for biomedical applications. It has been shown that the performances of many biomaterials used in prosthodontics have been significantly enhanced after their scales were reduced by nanotechnology, from micron-size into nanosize. On the other hand, many nanocomposites composed of nanomaterials and traditional metals, ceramics, resin, or other matrix materials have been widely used in prosthodontics because their properties, such as modulus elasticity, surface hardness, polymerization shrinkage, and filler loading, were significantly increased after the addition of the nanomaterials. In this paper, the latest research progress on the applications of nanometals, nanoceramic materials, nanoresin materials, and other nanomaterials in prosthodontics was reviewed, which not only gives a detailed description of the new related investigations, but also hopefully provides important elicitation for future researches in this field.

/pdf/recent-applications-of-nanomaterials-in-prosthodontics-2jh53b4atg.pdf

Recent applications of nanomaterials in prosthodontics

This study investigates the grinding process of the common grinding wheel under nanoparticle jet flow minimal quantity lubrication. This study establishes a kinematics model, elastic deformation model, and plastic accumulation model of a single grinding wheel, simulates the grain distribution on the surface of the common grinding wheel by using the grain vibration method, and examines the effect of different grinding parameters on the surface topography of the workpiece. Results show that the peaks and valleys on the profile curve of the workpiece surface increase and the corresponding R
 a
 and R
 z
 heights decrease, as the peripheral velocity of the grinding wheel increases. The peaks and valleys on the profile curve of the workpiece surface decrease, and the corresponding R
 a
 and R
 z
 heights increase as the feed speed of the workpiece increases. The number of grinding cracks on the surface of the workpiece decreases, the length of each crack increases, and the bump height on the surface increases slightly as the grinding depth increases. Experiments are conducted to verify the simulation results. The results show that the simulation method can predict the surface roughness of the workpiece, which is a factor in selecting the grinding parameters.

Modeling the operation of a common grinding wheel with nanoparticle jet flow minimal quantity lubrication

This research established a mathematical model of the useful grinding fluid flow rate of a rough grinding wheel. The abrasive distribution matrix of the grinding wheel surface topography was programmed on the MATLAB software platform to obtain the grinding wheel porosity φ at different particle sizes. The grinding fluid flow field was simulated and studied by using the volume of fluid multiphase flow model of FLUENT. Results showed that given a certain circular velocity of the grinding wheel, a larger grinding fluid jet velocity resulted in greater useful grinding fluid flow. When the grinding fluid jet velocity was set, the useful grinding fluid flow increased with increasing circular velocity of the grinding wheel. With the increasing velocity of the grinding wheel, as affected by the airbond layer, the increasing rate of the useful grinding fluid flow decreased, and the flow likewise showed a tendency to decrease. With a certain grinding fluid jet velocity, the useful flow rate of the grinding fluid was positively proportional to the useful flow. When the grinding fluid jet velocity changed and grinding wheel velocity was set, the grinding fluid jet velocity increased as the useful flow rate decreased. When the grinding fluid jet velocity was equivalent to the grinding wheel velocity, the useful flow rate of the grinding fluid was positively proportional to the useful flow. When the minimum clearance of grinding zone h increased, the useful grinding fluid flow and useful flow rate likewise increased. When the grinding fluid jet velocity was equivalent to the grinding wheel velocity, a larger nozzle gap width increased the flow supply for the grinding fluid and the useful grinding fluid flow. However, the increase in the useful flow rate of the grinding fluid was significantly smaller than that of the nozzle flow. This condition decreased the useful flow rate of the grinding fluid.

Modeling and simulation of useful fluid flow rate in grinding

A heat transfer model for the precision grinding process on nano-zirconia ceramics has been investigated. Based on the analysis of the processing properties of nano-zirconia ceramic materials, a theoretical model for the temperature field in the grinding of nano-zirconia ceramics was established. The model was then simulated and analysed under different grinding conditions. The effect of temperature dependent thermal properties and heat flux profile on temperature distribution in the workpiece has also been investigated. Parametric studies were carried out to study the effect of different input parameters such as the depth of cut, work feed rate and grinding speed on temperature distribution in the contact zone and in the workpiece across the grinding width and along the direction of movement. The results showed that, as the grinding wheel cut into the workpiece, the workpiece temperature rose sharply, and then levelled-off, with a high temperature gradient on the surface of workpiece. As the grinding depth of cut increased, a local high temperature took place in the grinding contact zone.

Investigation into temperature field of nano-zirconia ceramics precision grinding

The conventional method of delivering grinding fluid with a high supply of pressure and hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect. In the present paper, theoretical hydrodynamic pressure modelling was applied to induce a flow of coolant fluid through the grinding zone during flood delivery grinding. The simulation results show that hydrodynamic pressure was proportional to grinding wheel velocity, and inversely proportional to the minimum gap between the wheel and workpiece surface. The maximum pressure value was generated in the minimum gap region where higher fluid pressure gradient occurred. Moreover, the hydrodynamic pressure at the wedge-shaped zone was also measured through experiments. The results suggest that the proposed model agrees with the theoretical model and it can accurately forecast changes in the hydrodynamic pressure at the contact zone between the grinding wheel and the workpiece.

Analytical and experimental investigation of grinding fluid hydrodynamic pressure at wedge-shaped zone

Structural parameters are important factors that affect the dynamic performance of the electrical spindle of high-speed grinder. In this study, the influences of the electric spindle's major structural parameters on its dynamic characteristics are investigated. Based on the transfer-matrix method and taking into consideration the gyroscopic couple, the shear, the variable cross-section, and other influential factors, a dynamic model is established for the multidisk rotor of the rotor-bearing system of the electric spindle. The critical speeds of first three orders, the modes of variation, and other dynamic characteristic parameters of the electric spindle are programmed and calculated. The influences of the axial pre-tightening force of the bearing, the span of the fulcrum bearing as well as the changes in the front and rear overhangs on the critical speed of the rotor-bearing system on the electric spindle and their pattern of changes are analyzed. The results show that the span of the fulcrum bearing and the overhang have significant influences on the critical speed within a certain range, and the study provide the basis and guidance for the structural design and performance optimization of the electric spindle.

An analysis of the electric spindle's dynamic characteristics of high-speed grinder

Based on the transfer-matrix method and taking into consideration the gyroscopic couple, the shear, the variable cross-section and other influential factors, a critical speed model was established for the multi-disk rotor of the rotor-bearing system of the grinder spindle. The critical speeds of first three orders, the modes of variation and other dynamic characteristic parameters of the grinder spindle were numerical investigated and calculated. The influences of the axial pre-tightening force of the bearing, the span of the fulcrum bearing as well as the changes in the front and rear overhangs on the critical speed of the rotor-bearing system on the grinder spindle and their pattern of changes were analyzed. The results showed that the working speed of the spindle system is much lower than the primary critical speed and can therefore stay away the resonance range effectively. Furthermore, the span of the fulcrum bearing and the overhang had significant influences on the critical speed within a certain range, and the study provided the basis and guidance for the structural design and performance optimization of the grinder spindle.

Numerical Study on Critical Speed Modeling of Ultra-High Speed Grinder Spindle

This study was aimed at the theoretical analysis and experimental investigation on the critical conditions for the brittle-ductile removal transition in nano-ZrO2 dental ceramic grinding. The K-P36 numerical-control precision surface grinder was employed for the grinding test on 3Y-TZP nano-ZrO2 dental ceramics. The experimental results indicated that the maximal thickness of the undeformed chipping smaller than 1.9 μm corresponded to the ductile removal mode; the brittle-fracture removal induced by side cracks appeared when the maximal thickness of undeformed chipping was between 1.9 μm and 2.1 μm, and the removal mode was brittle-ductile mixed removal; when the maximal thickness of undeformed chipping was 5.23 μm, large-scale brittle fracture appeared at the grinding surface, and a large number of pits induced by the brittle fracture in half-coin shape remained on the surface. It was deduced that the maximal thickness of undeformed chipping was the decisive factor that determined the brittle-ductile rem...

Y.C. Ding

Papers

Investigation into temperature field of nano-zirconia ceramics precision grinding

Analytical and experimental investigation of grinding fluid hydrodynamic pressure at wedge-shaped zone

An analysis of the electric spindle's dynamic characteristics of high-speed grinder

Numerical Study on Critical Speed Modeling of Ultra-High Speed Grinder Spindle

Critical conditions for brittle-ductile removal transition in nano-ZrO2 dental ceramic grinding