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

As a new technology in manufacturing, turn-milling broadens the application ranges of mechanical processing, wherein both cutting tool and workpiece are given a rotary motion simultaneously. The objective of the present work is to study workpiece surface topography during orthogonal turn-milling process. This study begins with two mathematical models, which describe theoretical surface roughness and topography of rotationally symmetrical workpiece. The models are built with the establishment of locus function according to orthogonal turn-milling principle. Then based on these models, the influence law of surface topography affected by various cutting parameters is found by some simulation methods. The law also matches with orthogonal turn-milling surface roughness and topography experiments. By analyzing the experimental results, some parameter selection criteria during orthogonal turn-milling processing are also proposed qualitatively and quantitatively. The comparison between the simulation and experimental results shows that a better surface quality and tiny oil storage structure can be obtained if the cutting parameters are chosen in reason. This conclusion provides a theoretical foundation and reference for the orthogonal turn-milling mechanism research.

Research on rotary surface topography by orthogonal turn-milling

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

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

This study was focused on the experimental investigations about mechanical characteristics and tribological mechanisms of nanometric zirconia dental ceramics. A universal mechanical testing machine was used to test the three- point flexural strength and the fracture toughness. A microhardness tester was used to test the Vickers hardness of the test specimens. An MRH-3 digital-display high-speed ring-on-block tribometer was used for frictional wear experiments. A PGI800 coarseness profiling instrument was used to test the width and the length of the grinding defects on specimen surfaces. An S-3500N SEM was employed in the microscopic observation of the surface morphology after the abrasion. Results indicates that the flexural strength of the test specimens � 890MPa, the fracture toughness � 6Mpa.m 1/2 , the Vickers hardness � 1240MPa, the linear contraction � 21%, and the apparent porosity � 0.32%. Moreover, the frictional factor and the wear rate of nanometric ZrO2 ceramics decreased significantly under identical working and frictional conditions compared with ZrO2. The wear mechanism of nanometric ZrO2 ceramics was micromachining and plastic deformation while the wearing mechanism of ZrO2 ceramics was brittle fracture and abrasive wear.

/pdf/experimental-investigations-of-mechanical-characteristics-1xr3zfaefq.pdf

Experimental Investigations of Mechanical Characteristics and Tribological Mechanisms of Nanometric Zirconia Dental Ceramics

The invention belongs to a method and a device for mechanical grinding, namely a process and equipment for grinding nanometer fluid. The nanometer fluid grinding process comprises that nanometer-grade solid containing powder is supplied to a grinding area as a cooling lubrication medium in a grinding process. The equipment is characterized in that: the equipment comprises a lubricant storage tank, a water storage tank, a nanometer-grade powder storage tank and a high pressure air pump, which are arranged on a machine frame; and various mediums are mixed with the high pressure air, the mixtureenters an atomizing chamber for mixing atomization and is conveyed to the grinding processing area by a hose and a spray head. Because the coefficient of thermal conductivity of the nanometer powder is high, the nanometer fluid can bring away a large amount of grinding heat when passing the high-temperature area, so that the cooling property of the grinding medium is enhanced, and the defect of the poor cooling effect of the micro lubrication is overcome; and simultaneously, because the weight of the nanometer powder is light, the characteristics and the advantages of the micro lubrication are maintained, the active effects of high processing quality, low cost and no pollution are achieved, and the method becomes the fourth generation lubrication cooling grinding process after wet processing, dry processing and micro lubrication.

Process for grinding nanometer fluid

The utility model relates to grinding equipment, in particular to a nanometer powder minimal quantity lubricating, cooling and grinding device. The device is characterized in that the device is provided with a lubricating oil storage tank 2, a water storage tank 3 and a nanometer powder storage tank 4, wherein a flow control valve and a power supply device are connected below each storage tank. When in work, high pressure air, lubricating oil, water and nanometer powder are transported to a mixing zone 17 for atomization, so as to form nanoparticle and water-in-oil grinding fluid which are transported to a grinding and processing area through a flexible pipe 19 and a sprayer 20. The consumption of the grinding fluid is low, and the consumption of general lubricating oil is no more than 50 ml/h, which accounts for twentieth to fiftieth of that in the traditional processing method. The consumption of the nanometer powder is no more than 100 g/h, compressed air also takes chip removing and cooling effects, workpiece cleaning procedures are simplified, the service life of the cleaning agent is greatly prolonged, a cooling circulatory system is omitted, and the energy consumption is greatly reduced. Frictions between a small tool and workpieces and between a tool and cuttings are effectively reduced, the service lives of the tools are long, the processing quality is improved, and various disadvantages caused by use of a great amount of grinding fluid in the conventional pouring process can be avoided. Not only is the work efficiency improved, but also the environmental pollution is avoided.

Nanometer powder minimal quantity lubricating, cooling and grinding device

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...

Zhanrui Liu

Papers

Investigation into temperature field of nano-zirconia ceramics precision grinding

Experimental Investigations of Mechanical Characteristics and Tribological Mechanisms of Nanometric Zirconia Dental Ceramics

Process for grinding nanometer fluid

Nanometer powder minimal quantity lubricating, cooling and grinding device

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