Grinding Of Ceramic Materials Research Articles

A Time-Frequency Acoustic Emission-Based Technique to Assess Workpiece Surface Quality in Ceramic Grinding with PZT Transducer.

Innovative monitoring systems based on sensor signals have emerged in recent years in view of their potential for diagnosing machining process conditions. In this context, preliminary applications of fast-response and low-cost piezoelectric diaphragms (PZT) have recently emerged in the grinding monitoring field. However, there is a lack of application regarding the grinding of ceramic materials. Thus, this work presents an analysis of the feasibility of using the acoustic emission signals obtained through the PZT diaphragm, together with digital signal processing in the time–frequency domain, in the monitoring of the surface quality of ceramic components during the surface grinding process. For comparative purpose, an acoustic emission (AE) sensor, commonly used in industry, was used as a baseline. The results obtained by the PZT diaphragm were similar to the results obtained using the AE sensor. The time–frequency analysis allowed to identify irregularities throughout the monitored process.

Research on surface quality of Si3N4 ceramics by internal grinding

The machined surface quality of hard and brittle materials was studied based on the analysis of the material removal mechanism of ceramics. According to the geometrical relationship of the internal grinding, the equivalent diameter of grinding wheel was deduced. In the internal grinding, the models of undeformed chip thickness, peak-valley surface roughness and arithmetic mean surface roughness were established with the assistance of planar grinding. The proposed models were verified utilizing the orthogonal test of internal grinding Si3N4 ceramics. The trend of experimental results was consistent with the theoretical model. The scientific validity of the proposed models was supported by the experimental results, and the investigation provides a theoretical reference and experimental basis for further study on the grinding of ceramic materials.

Force Controlled Grinding of Ceramic Materials

Brittle materials like ceramics or glass can be machined by cutting with negative rake angles and by abrasive machining processes. Especially grinding allows for low surface roughness and high shape accuracy. Conventional path-controlled grinding processes may damage functional surfaces if brittle fracture occurs and may thus lead to lateral, radial and axial cracks. High grinding forces can be a reason for brittle fracture when grinding ceramic materials. A solution for this effect may be the application of force controlled grinding processes. In this paper adapted control algorithms were implemented for force controlled grinding and verified in grinding experiments. As an example, cylindrical grooves were ground with an injection moulded spherical grinding tool in alumina and zirconia ceramics. After grinding surface roughness, shape accuracy and process forces are analysed and discussed.

Model siły skrawania w procesie szlifowania obwodowego ceramiki inżynierskiej ze wspomaganiem ultradźwiękowym

Model siły skrawania w procesie szlifowania obwodowego ceramiki inżynierskiej ze wspomaganiem ultradźwiękowym

Predictive Modeling of Surface Roughness in Grinding of Ceramics

The surface roughness represents the quality of ground surface since irregularities on the surface may form nucleation for cracks or corrosion and thus degrade the mechanical properties of the component. The surface generation mechanism in grinding of ceramic materials could behave as a mixture of plastic flow and brittle fracture, while the extent of the mixture hinges upon certain process parameters and material properties. The resulting surface profile can be distinctively different from these two mechanisms. In this article, a physics-based model is proposed to predict the surface roughness in grinding of ceramic materials considering the combined effect of brittle and ductile material removal. The random distribution of cutting edges is first described by a Rayleigh probability function. Afterwards, surface profile generated by brittle mode grinding is characterized via indentation mechanics approach. Last, the surface roughness is modeled through a probabilistic analysis of ductile and brittle generated surface profile. The model expresses the surface finish as a function of the wheel microstructure, the process conditions, and the material properties. The predictions are compared with experimental results from grinding of silicon carbide and silicon nitride workpieces (SiC and Si3N4, respectively) using a diamond wheel.

Acoustic emission testing of surface roughness and wear caused by grinding of ceramic materials

The current manufacturing trend mainly involves automation precisely to offer better productivity and improved quality. In this context, on-line monitoring of tools becomes essential. Acoustic emission is the most recognized technique used for condition monitoring of machine tools. Grinding is a material removal and surface generation process employed to shape and finish components made of metals and other materials. The research work deals with machining of CUMITUFF WR-90 alumina ceramics by employing two different grinding wheels made of aluminum oxide and silicon carbide under varying depth of cut. Surface roughness of the machined component and wear of both grinding wheels were analyzed using acoustic emission technique. For a constant depth, the quality of machining has been improved for the material grinded using silicon carbide wheel, which is inferred from low surface roughness value compared to material grinded using aluminum oxide wheel.

Surface texture after grinding of ceramic materials and its influence on the friction

Ceramic materials are used as construction materials for components which are exposed to the extreme loading conditions. There is a question of properties like high strength, hardness, chemical resistance and heat resistance at high temperature. Ceramic materials are produced usually by sintering. Very important technology of the last years is the technology of coating ceramic materials by thermal spraying. The coated surface is ground and the texture of such a surface differs from the sintered one. Also functional properties are another. In the contribution there are introduced the grinding results of ceramic materials coated by thermal spraying, that is, the cutting forces, surface roughness when using different wheels (SiC, CBN and DIA).

Subsurface structure of alumina associated with single-point scratching

The mechanisms of macroscopic ductile deformation of brittle ceramics during grinding operations are still unclear although the microcracking-free processes of grinding have been used widely in industry. This paper analyses the dislocation structure in the plastic zones of scratched alumina. It is shown that there exist three independent slip systems (two basal and one prism) and two twin systems even far below the critical onset temperatures of these systems that is usually expected. This new finding explains the formation mechanism of the macroscopic deformation induced by scratching and indicates that it is the stress field around the cutting edge which plays an important role in the activation of the slip systems. The present study offers a new insight into the mechanism understanding of material removal in ductile-regime grinding of ceramic materials.

Effect of machining residual stresses on the repetitive impact behavior of silicon nitride

Silicon nitride is a candidate valve material for internal combustion engines. Its low density and attractive mechanical properties relative to conventional metallic alloys portend significant improvements in valve performance. The production of valves involves a significant amount of machining, especially grinding. Grinding of ceramic materials may result in surface and subsurface damage in the form of fracture or residual stresses which may affect impact behavior and, consequently, the behavior of silicon nitride ceramic materials as valves. The effects of residual stresses due to grinding on the impact wear behavior of one silicon nitride composition ground under various conditions have been investigated.

A Fracture Mechanics Approach to Modeling Strength Degradation in Ceramic Grinding Processes

Strength degradation of the finished part due to surface and sub-surface damage is a critical issue in grinding of ceramic materials. In this paper, the chip formation process is modeled as a two-dimensional system of radial and lateral cracks, and an integral equation approach is developed to investigate the interactions of these radial and lateral cracks with various distributions of planar microcracks. The effects in the vicinity of the free surface are modeled explicitly. The amplification and shielding effects on stress intensity factors due to various microcrack distributions are studied in detail. Numerical results are presented for crack systems representing single-grit as well as multi-grit grinding, and the implications of crack interactions on strength degradation of finished products are discussed. Effective elastic properties for workpieces containing microcrack distributions are obtained and their ramifications on the grinding process are investigated. Some benevolent microcrack distributions that will facilitate chip formation as well as suppress surface and subsurface damage evolution are also presented.

Fine grinding of ceramic materials (review)

Fine grinding of ceramic materials (review)

Development of a Simplified Electrochemical Dressing Method with Twin Electrodes

The paper deals with a newly developed method for electrochemical dressing of metal bonded superabrasive wheels. In this method, alternating current derived from a wall outlet via an inexpensive transformer is supplied to a wheel through twin electrodes, hence a troublesome brush and an expensive DC power source are unnecessary. The preprocess dressing of a wheel (d 3 = 200 mm) was accomplished within a few minutes. Inprocess dressing of a wheel resulted in lower grinding force, longer wheel life and higher grinding efficiency in grinding of ceramic materials and hard metals.

Consideration to Chip Generation in Grinding of Ceramic Materials

In an attempt to improve both grinding efficiency and accuracy, silicon carbide, alumina and zirconia ceramics were ground under various grinding conditions using diamond grinding wheels of several grain sizes, and chip generation was discussed from the view point of grinding force acting on the cutting edge. In zirconia ceramics, the plastic deformation induced by grinding causes chip generation just as in metals, and the brittle fracture becomes dominant in alumina, more pronounced with silicon carbide.

Optimum regime for wet fine grinding of ceramic materials

Optimum regime for wet fine grinding of ceramic materials

The grinding of ceramic materials with bonded abrasives

The grinding of ceramic materials with bonded abrasives

The grinding of ceramic materials with free abrasives

The grinding of ceramic materials with free abrasives