Machining Of Ceramics Research Articles

Precision Grinding Technology of Silicon Carbide (SiC) Ceramics by Longitudinal Torsional Ultrasonic Vibrations.

Silicon carbide (SiC) ceramic material has become the most promising third-generation semiconductor material for its excellent mechanical properties at room temperature and high temperature. However, SiC ceramic machining has serious tool wear, low machining efficiency, poor machining quality and other disadvantages due to its high hardness and high wear resistance, which limits the promotion and application of such materials. In this paper, comparison experiments of longitudinal torsional ultrasonic vibration grinding (LTUVG) and common grinding (CG) of SiC ceramics were conducted, and the longitudinal torsional ultrasonic vibration grinding SiC ceramics cutting force model was developed. In addition, the effects of ultrasonic machining parameters on cutting forces, machining quality and subsurface cracking were investigated, and the main factors and optimal parameters affecting the cutting force improvement rate were obtained by orthogonal tests. The results showed that the maximum improvement of cutting force, surface roughness and subsurface crack fracture depth by longitudinal torsional ultrasonic vibrations were 82.59%, 22.78% and 30.75%, respectively. A longitudinal torsional ultrasonic vibrations cutting force prediction model containing the parameters of tool, material properties and ultrasound was established by the removal characteristics of SiC ceramic material, ultrasonic grinding principle and brittle fracture theory. And the predicted results were in good agreement with the experimental results, and the maximum error was less than 15%. The optimum process parameters for cutting force reduction were a spindle speed of 22,000 rpm, a feed rate of 600 mm/min and a depth of cut of 0.011 mm.

Laser-Based Manufacturing of Ceramics: A Review.

Ceramics are widely used in microelectronics, semiconductor manufacturing, medical devices, aerospace, and aviation, cutting tools, precision optics, MEMS and NEMS devices, insulating components, and ceramic molds. But the fabrication and machining of the ceramic-based materials by conventional processes are always difficult due to their higher hardness and mechanical properties. Therefore, advanced manufacturing techniques are being preferred for these advanced materials, and out of that, laser-based processes are widely used. The benefits of laser fabrication and machining of ceramics include high precision, reduced thermal damage, non-contact processing, and the ability to work with complex geometries. Laser technology continues to advance, enabling even more intricate and diverse applications for ceramics in a wide range of industries. This paper explains various laser based ceramic processing techniques, such as selective laser sintering and melting, and laser machining techniques, such as laser drilling, etc. Identifying and optimizing the process parameters that influence the output quality of laser processed parts is the key technique to improving the quality, which is also focused on in this paper. It aims to facilitate the researchers by providing knowledge on laser-based manufacturing of ceramics and their composites to establish the field further.

ANALSYS OF DEFECT LAYER IN ELECTRICAL DISCHARGE MACHINING OF NON-CONDUCTIVE CERAMIC

The aim of the research is to describe a new approach for processing non-conductive ceramics. A method of electrical discharge machining with an assisting electrode is presented, which allows the machining of zirconium ceramics. An analysis of the defective layer, i.e., the recast layer and the heat-affected zone, was performed. Two parameters, discharge current and pulse duration, were chosen to study the effects on the thickness of the defect layer. The test results show that increasing the discharge current and pulse duration increases the thickness of the defect layer. This is due to the increase of discharge energy, which causes more heat in the machining zone. Future research can be directed to the analysis of a larger number of test points to see a better dependence between the machining parameters and the thickness of the defect layer.

Study on the unstable crack propagation mechanism in turning machinable ceramics based on the energy conversion principle and the fracture mechanics theory

Study on the unstable crack propagation mechanism in turning machinable ceramics based on the energy conversion principle and the fracture mechanics theory

Impact of Green Ceramic Hybrid Machining (GCHM) on Reliability and Repeatability of the Properties of Sintered Yttrium-Tetragonal Zirconia Polycrystal Parts

The innovative Green Ceramic Hybrid Machining (GCHM) process sequentially combines milling with a cutting tool (GCM, Green Ceramic Machining) and laser beam machining (GCLBM) of a ceramic material (black Y-TZP in this study) at the green stage mainly to increase productivity, avoid taper angle limitations of laser beam machining, and obtain micro-features. The study focuses on the reliability and the repeatability of the properties of sintered parts obtained by three manufacturing processes (GCM, GCLBM, GCHM) to assess the performance of hybridisation. It turns out that GCHM is a compromise of both milling and laser beam processes; it increases the repeatability of the surface quality and it slightly reduces (less than 7%) the flexural strength by comparison to milling for a similar reliability. The study also highlights that the surface quality of GCLBM processed parts relies on of the surface generated by the previous operation. Milling that surface at the previous step is therefore recommended, corresponding to the sequence adopted by GCHM.

Performance prediction and parameter optimization of alumina-titanium carbide ceramic micro-EDM hole machining process based on XGBoost

Aiming at the difficulties in setting process parameters and the low accuracy of process performance prediction in electrical discharge machining (EDM) hole machining of alumina ceramics, a novel EDM process performance prediction method based on eXtreme Gradient Boosting (XGBoost) is proposed in this study. The independent variables selected include processing polarity (P), interelectrode voltage (V), peak current (I), pulse frequency (F), pulse width (T), and tool electrode and workpiece electrode gap (W), while the dependent variables are tool electrode length loss (ELW), tool electrode volume loss (EVW), and material removal rate (MRR). An L18 (21 × 35) orthogonal test is designed to obtain training samples for model development. The accuracy of the prediction results for ELW, EVW, and MRR by the XGBoost model is found to be 1.7%, 2.5%, and 9.4%, respectively. These results show a significant improvement compared to the linear regression model, with an improvement of 41.7%, 62.5%, and 19.4%, respectively. Furthermore, when compared to the support vector regression (SVR) model, the XGBoost model also shows improvement of 23.6%, 5.9%, and 12.0% for ELW, EVW, and MRR prediction accuracy, respectively. These findings suggest that the proposed XGBoost-based method is effective and accurate in predicting the performance of alumina ceramic EDM processes. In addition, the third generation nondominated sorting genetic algorithm (NSGA-III) is utilized to optimize the process parameters with both single objective and multi-objective approaches. The optimal parameters for ELW, EVW, and MRR, including the selection of machining polarity, interelectrode voltage, peak current, pulse frequency, pulse width, and tool electrode and workpiece electrode gap are obtained through the Pareto frontier of the three comprehensive optima. The average relative errors between the experimental results and the optimized results are found to be 6.46%, 10.45%, and 9.58% for ELW, EVW, and MRR, respectively, indicating the accuracy and effectiveness of the optimized results.

Local optimization of low power laser machining of MgO at the green state enables cost- and energy-efficient benchtop fabrication

Laser machining of ceramics at the green state offers a low-cost route to the near-net fabrication of ceramics. A matrix of laser machining (i.e., laser cutting and scanning) parameters were tested on 5 mm-thick green bodies of magnesium oxide (MgO) using a CO2 laser with a maximum power capacity of 130 W. The input parameters were feed rate and power; we scanned the feed rate of 3–14 mm/s and power of 23–31 W for laser cutting, and 10–60 mm/s and 16–27 W for laser scanning. The quality of the laser-cut and -scanned surfaces was tracked through SEM. Thermal damage along the laser path was assessed to optimize laser cutting. High laser power and/or long dwell time resulted in partial sintering. At both cutting and scanning operations, low feed rates induced thermal damage, while high feed rates provided better edge retention and surface smoothness. However, very high feed rates failed to generate complete cuts and through-holes due to insufficient transfer of the excitation energy. Various combinations of the feed rate and power produced completely cut 5 mm cubes with smooth surfaces via laser cutting in a single pass. The most energy-efficient combination of 12 mm/s and 28 W rendered the highest surface quality with minimum thermal damage. This parameterization set provides a practical roadmap for choosing process parameters for the laser machining of MgO at the green state.

The role of various dielectrics used in EDM process and their environmental, health, and safety issues

Electrical discharge machining (EDM) is one of the well-known newer machining processes which are used to machine ceramics, alloys, composites, and hard metals. Besides being a process with lower material removal rate (MRR), it also releases toxic vapors & fumes, and aerosols due to the thermal decomposition of the dielectrics. Moreover, disposal of these toxic and non-biodegradable dielectric wastes also poses a major challenge to the environment. This article discusses the issue of noxious fumes that are released during machining, as well as the use of alternative dielectric mediums that can be utilized in place of traditional EDM oils.

Laser Drilling in Alumina Ceramics Using a Combination of Laser Pulses in the Free-Running and Q-Switched Modes.

The possibility of using a two-pulse laser action consisting of a pulse of the free-running pulse followed by the Q-switched pulse in the processes of laser drilling in alumina ceramics is considered. A diagram of a laser machine for implementing the proposed processing method and the method for determining the energy required to form the through hole and the drilling time are presented. For thermal exposure, pulsed radiation of Nd:YAG of the laser operating in the free-running mode (pulse duration 0.5 ms, energy up to 0.3 J) was used. The Q-switched pulse was generated using a second Nd:YAG laser (pulse duration 25-30 ns, energy up to 0.03 J). The laser radiation was focused on the surface of the material at one point. The time between the start of generation of the first and second lasers varied in the range of 0-1000 μs. The optimal delay time for the start of the generation of the second laser relative to the first was determined experimentally. The obtained results showed that the combination of the free-running pulse and the Q-switched pulse can significantly increase the efficiency of laser machining of ceramics and improve the hole quality. This scheme turned out to be promising for optimizing parameters of the process of laser drilling in thin-sheet alumina ceramics. The obtained results obtained have great potential in the field of precision laser machining of ceramics.

Machining of aluminium nitride ceramic with a hAJM process using SiC abrasives: Experiments and simulation

Extreme hardness makes aluminium nitride (AlN) ceramic machining costly. Hot abrasive jet machining (hAJM) erodes a target profile by indentation of an air-hot abrasive stream comprising fine hot SiC grains for cutting AlN ceramic materials without thermal deformation. This study is intended to analyze the material removal rate (MRR) in the hAJM process of AlN ceramic. The Box-Behnken design of experiments was used to test 15 sets of machining limitations (abrasive temperature, compressed air pressure, and nozzle angle) (BBDOE). Computational fluid dynamics (CFD) modeling was used to establish a relationship between machined profile shape and erosive flow. Hot abrasives in hAJM improved material removal efficiency. SEM investigation of the machined surface indicated fracture initiation, propagation, and erodent particle embedment. Depending on the percentage concentration and mesh size of the abrasive grains, they are dispersed randomly throughout the medium. The predicted results from simulation and those obtained from experimental observation are compared to describe the relative importance of hAJM constraints. Moreover, the analysis revealed that abrasive temperature, nozzle angle, and air pressure significantly influenced the machined surface profile and material erosion. Improved hole quality, material erosion, and impact collision of abrasives were obtained under machining with the vertically positioned nozzle.

Influence of cutting damage on the bending strength of Ti<sub>2</sub>AlC MAX phase machinable ceramics

Ti2AlC MAX phase ceramics are excellent candidates for high-temperature heat resistant materials. In addition, they are machinable using cemented carbide tools. However, heavy machining induces many surface cracks, reducing the mechanical strength and reliability of ceramic parts. Herein, we investigated the influence of the machining process on the bending strength and microstructure of Ti2AlC ceramics. Nearly fully dense Ti2AlC ceramics with elongated grains were machined using a carbide end mill in brittle mode, producing numerous cracks; however, the roughness of the ceramic was similar to that of tool steel cut in ductile mode. Despite its rough surface, the bending strength of the machined Ti2AlC was only slightly lower than that of polished Ti2AlC. The cracks in the machined Ti2AlC ceramics were induced with a kinking structure; however, they stopped at a length equivalent to one grain. The minimum strength of the machined Ti2AlC ceramics with a fracture toughness of 6.9 MPa·m1/2 was estimated by assuming a machining through-crack shape that was as deep as the maximum grain size. Cutting damage was limited to a single grain; thus, the bending strength of the machined Ti2AlC was not significantly reduced.

Translucency, Microhardness and Fracture Toughness of Two Machinable Ceramics as Affected by Two Acidic Beverages

Translucency, Microhardness and Fracture Toughness of Two Machinable Ceramics as Affected by Two Acidic Beverages

Characterization of surface topography during multi-pass WEDM of MWCNT alumina composites

The thermal spalling action of material removal associated with electrical discharge machining of ceramics results in severe surface debris, cracks, pores, etc. This led to a rough machined surface, ultimately rendering the machined component not susceptible for direct applications. Such a behavior points towards the need to further process the machined surface so as to reduce the net severity of the machined surface. The current work utilizes multi-pass wire electrical discharge machining to enhance the machined surface characteristics of alumina composites. Detailed comparison of the surface characteristics with regards to amplitude, spatial, hybrid and functional volume parameters depicted a superior and homogenous machined surface post multi-pass process. The recast layer severity was minimal as well by incorporation of multi-pass. Furthermore, a detailed analysis of the structural fingerprints of the surface elements depicts actual breakage and subsequent burn-out of the filler material.

Study on the surface damage of green ZrO2 ceramics in dry cutting based on discrete element method

AbstractDiscrete element simulation model and cutting tests are conducted to investigate the surface damage during the machining of green ZrO2 ceramics. The discrete element simulation model (DEM) is developed based on the macroscopic physical and mechanical properties of the isostatically pressed green ZrO2 ceramics. The validity of the simulation model is verified by cutting tests on green ZrO2 ceramics. The results show that the physical and mechanical properties of the DEM model established by the PFC2D software are consistent with the macroscopic physical and mechanical properties of the green ZrO2 ceramics. The depth of cut, the cutting speed, and the tool rake angles have a large effect on surface/subsurface cracks. The tool rear angle has large effect on the distribution of the peak residual stresses. When the cutting force increases suddenly, the number of cracks produced increases sharply. Smaller cutting force can reduce the number of cracks and surface damage.

A numerical investigation on material removal mechanism of electro discharge machining of non-conductive ceramics

A numerical investigation on material removal mechanism of electro discharge machining of non-conductive ceramics

The mechanism and machinability of laser-assisted machining zirconia ceramics

Laser-assisted machining (LAM) is regarded as a useful technique which can process ceramic materials without damage and efficiently. This work reported a study on the mechanism by which LAM technology can improve the machinability of zirconia ceramic. The absorptivity of zirconia ceramic to fiber laser energy was obtained through the combination of experiment and simulation. The temperature-dependent mechanical property of zirconia ceramic was studied by nanoindentation experiments. Meanwhile, scratch tests were used to investigate the plastic-brittle transition and damage mechanism under various high-temperature conditions. The results showed that the absorptivity of zirconia ceramic to fiber laser energy is 0.52. The hardness and elasticity modulus are decreasing as the temperature increases. The functions that relate them to temperature are fitted. Moreover, the increase in temperature can enhance the plastic-brittle transition depth of ceramic and suppress median cracks and chipping. Furthermore, the shape of the chips is changed from discontinuous lumpy chips to continuous coiled chips. These evidence and research can clearly explain the mechanism by which LAM technology can improve the machinability of zirconia ceramics. They can also provide guidance and theory for the industrialization of LAM technology.

Marginal gap distance and cyclic fatigue loading for different all-ceramic endocrowns.

The aim of the study was to evaluate the effect of the fabrication techniques of two types of glass ceramics on the marginal gap distance and the fracture resistance of endocrown restorations after cyclic loading. Forty extracted mandibular first molars were root canal treated. Decoronation was done for all the endodontically treated teeth 2 mm above the cemento-enamel junction. The teeth were individually fixed vertically into epoxy resin mounting cylinders. All teeth were prepared to receive endocrown restorations. The prepared teeth were randomly divided into four equal groups (n=10) according to the all-ceramic materials and technique used for endocrown construction as follows: Group I (n=10): Pressable lithium disilicate glass ceramics (IPS e-max Press), Group II (n=10): Pressable zirconia-reinforced lithium disilicate glass ceramics (Celtra Press), Group III (n=10): Machinable lithium disilicate glass ceramics (IPS e-max CAD), Group IV (n=10): Machinable zirconia-reinforced lithium disilicate glass ceramics (Celtra Duo). The endocrowns were cemented using dual-cure resin cement. All endocrowns were subjected to fatigue loading. The cycles were repeated 120,000 times to clinically simulate one year chewing condition. Marginal gap distance of all endocrowns was measured directly using a digital microscope with x100 magnification. The load required to failure was recorded in Newton. Data were collected, tabulated, and statistically analyzed. Fracture resistance testing of all-ceramic crowns revealed a statistically significant difference between all different ceramic materials used in this study (p-value <0.001). On the other hand, there was a statistically significant difference between all the four ceramic crowns for the marginal gap distance either before or after fatigue cyclic loading. After considering the limitation of the current study, the following conclusions were given: endocrowns are considered one of the promising minimally invasive restorations for root canal treated molars. CAD/CAM technology revealed better results than heat press technology regarding the fracture resistance of glass ceramics. Heat Press technology revealed better results than CAD/CAM technology regarding the marginal accuracy of glass ceramics.

Processing and properties of reactively densified TiB2-AlN-hBN conductive ceramics with tunable compositions

Reactive sintering has been widely utilized to densify ceramics. Although the technology has numerous advantages, the composition of as-sintered ceramics is hard to be adjusted unless additional products are added. In this work, a novel solid-state route based on the reactions among TiN, Al and B were proposed to consolidate TiB2-AlN-hBN ceramics (TAB) with tunable compositions (hBN ≤ 42 vol%, AlN ≤ 45 vol%). Dense TAB with high relative density, refined grain size and homogeneous microstructure were obtained via spark plasma sintering at 1800 °C and 60 MPa. It was found that exothermic reactions between the reactants could be ignited during heating, and the order of temperature at which the combustion process occurred was just opposite to the sequence of adiabatic temperature for individual reactions. Effects of hBN and AlN amounts on the densification, microstructure, mechanical properties, machinability and electrical resistivity of as-sintered ceramics were comprehensively investigated. Compared to AlN, hBN content played a more obvious role on those properties. As hBN contents increased from 0 to 42 vol%, the flexural strength, fracture toughness, Vickers hardness and modulus of TAB continuously decreased. TAB with hBN amounts ≥ 13 vol% exhibited better machinability with surface roughness lower than 2.9 µm after machining. Nevertheless, their electrical resistivity values at room temperature fluctuated in a narrow range between 43 μΩ·cm and 83 μΩ·cm, irrelevant with the hBN amounts.

The effect of acrylate on the properties and machinability of alumina ceramics

Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improve green alumina compacts machinability. Properties of green compacts and their corresponding sintered samples prepared with and without MMA were compared. Investigation of green and sintered properties was performed on samples compacted at applied pressures up to 150 MPa. After pressing, samples with MMA were thermally treated at 115oC. The intention was to enhance the polymerization of MMA at a temperature a little higher than the glass transition temperature (Tg = 103oC) of poly (methyl methacrylate). Green compacts with MMA had higher green density values than those without MMA. Sintered samples with MMA had lower values of sintered density and higher values of total porosity; after sintering, relative linear shrinkage was around 15 % for the whole range of applied pressures. The possibility of easily machining the green compacts with MMA produces great possibilities for application in many fields

Non-invasive improvement of machining by reversible electrochemical doping: A proof of principle with computational modeling on the example of lithiation of TiO2

We show in a combined density functional theory – molecular dynamics computational study that a small amount of lithium intercalated in TiO2, which preserves the host structure and can be introduced reversibly, in particular, by electrochemical doping, leads to a lowering of the strength of work materials and the cutting force. This is in spite of the fact that modifications of the elastic constants at room temperature are small, i.e. the effect is mostly on plastic properties. This approach is expected to be applicable to a class of ceramics exhibiting similar mechanisms of host-dopant interactions and presents a reversible and non-destructive way of modifying mechanical properties and improving machinability of hard ceramics.