Laser machining of silicon carbide: Experimental analysis and multiobjective optimization

This work investigates the feasibility of laser engraving of silicon carbide by adopting a Q-Switched fiber laser. To study the effect of the laser parameters on the laser-material interaction, a 3³ full factorial plan was developed and tested. During the tests, the following laser parameters were varied: scanning speed, pulse frequency, which affects the pulse power, and the number of repetitions, i.e., the number of times the laser beam passes on the same line. After the tests, digital microscopy was used to measure the depth of the engraved pocket, and a 3D laser profilometer was used to acquire the pocket surface and morphology and to calculate the main roughness parameters. The analysis of variance (ANOVA) was carried out in order to detect how the process parameters affect laser machining. The Response Surface Methodology (RSM) was additionally performed to obtain the regression model and finally, the Multi-Response Optimization (MRO) was implemented to identify the optimal process conditions. The results show that it is possible to machine pockets with low roughness (Ra <1 μm) at high material removal rates (MRR> 0.1 mg/s).     

Synthesis of nanophase tungsten carbide by electrical discharge machining

Tungsten carbide nanopowders were synthesized successfully by electric discharge machining followed by annealing under a nitrogen atmosphere. The tungsten workpieces were initially melted and evaporated on the working surface during the electric discharge machining process, and then the tungsten powders were reacted with the carbon electrode and the working medium of kerosene to form the nanocrystalline WC_1−x powders. The powders produced were characterized by XRD, SEM, and TEM. When annealing the powders under an N₂ atmosphere, the cubic phases of WC_1−x gradually changed to hexagonal W₂C and then were transformed fully to nanocrystalline hexagonal WC at 1200 °C, with the nanocrystalline tungsten carbide encapsulated in a carbon shell. On the other hand, under an H₂ atmosphere, the WC_1−x phase changed via a W₂C phase to reduced powders of pure tungsten at 1000 °C or were reduced directly from WC_1−x to elemental W.     

Understanding surface discharge activity with epoxy silicon carbide nanocomposites

Surface discharge inception voltage (SDIV) with epoxy silicon carbide nanocomposite material in LN₂ medium is about three times higher than that in air. Under AC voltage that SDIV increases with increase in wt% of silicon carbide (SIC) material in epoxy nanocomposites. Dielectric measurements indicates an increase in temperature of the specimen and the weight percentage of SIC filler in epoxy resin increases the permittivity of the material. Also, irrespective of percentage of SiC in epoxy resin, the tan(δ) reduces with increase in frequency and the converse at room temperature. The UHF signal measured during surface discharge activity in air/LN₂ medium has frequency content in the range of 0.5–1.5 GHz. The charge decay characteristics of epoxy SiC nanocomposites indicate the deposited charge is less and the charge decay time reduces with increase in wt% of SiC in epoxy resin. The surface roughness caused due to surface discharge activity is high under negative DC voltage compared with positive DC/AC voltage. The phase resolved partial discharge (PRPD) analysis indicates discharges occur at the near peak of the AC voltage on inception of surface discharge and at higher stress it appears at the rising portion of AC voltage. POLYM. ENG. SCI., 57:1349–1355, 2017. © 2017 Society of Plastics Engineers     

电火花加工技术的发展历程

电火花加工技术作为特种加工领域的重要技术之一，最早应用于二战时期折断丝锥取出时的加工。随着人类进入信息化时代，电加工技术取得了突飞猛进的发展，可控性更高，数字化程度更好：     

基于BP神经元网络优化电火花加工参数

基于BP神经网络模型对用电极(铜Cu)-材料(模具钢NAK80)电火花加工系统的一组参数进行了优化.计算结果表明,减少输入层神经元的数量可以加快收敛速度,但计算精度将受到影响.若保持隐层结构,仅由不同训练函数的学习结果改变权系数(映射)实现网络结构优化,则可能较好地预言加工效果.     

Trough of polycrystalline silicon carbide for electric soaking pits

Conclusions The results of laboratory investigations and tests under industrial conditions demonstrated that in principle it is possible to use MPC as material for trough sections for electrically heated soaking pits.Translated from Ogneupory, No. 1, pp. 31–36, January, 1975.     

A comprehensive review of electric discharge machining of advanced ceramics

Advanced ceramics are widely used in high temperature and wear related situations due to their unique physical and chemical characteristics. With the increasing demand for ceramics, the machining techniques of ceramics become a hot and tough issue because ceramics are extremely fragile and difficult to process. Traditional mechanical machining techniques like milling, turning, and drilling are subjected to large cutting forces and heat leading to extensive tool wear and poor machining performance. Electric discharge machining (EDM) has an outstanding ability of no-contact machining brittle and hardness materials with complex shapes via generating extreme high-temperature plasma channel to melt and vaporize materials. Therefore, in this paper, the research trends of latest EDM technologies for advanced ceramic materials were comprehensively reviewed. Firstly, according to the electrical conductivity of advanced ceramics, different EDM processes were introduced in details. Secondly, the existing physical models and material removal mechanisms of EDM process of ceramics were compared and analyzed. Then the machining performance indicators, such as MRR, Ra, TWR, surface topography, and micro-structures, were respectively investigated. Additionally, the new hybrid machining techniques of EDM were presented to provide some potential for efficiently machining advanced ceramics. Eventually, this paper also discussed the challenges associated with electrical discharge machining of advanced ceramic materials, and suggested some related research areas which possibly attract significant research attentions in the future.     

Optimization of wire electrical discharge machining parameters for cutting electrically conductive boron carbide

In this work, Pure boron carbide (B₄C) was consolidated using spark plasma sintering (SPS) at 2050 °C with a dwell of 10 min under 50 MPa uniaxial pressure in Argon atmosphere. The sintered specimen was >99% dense and offered characteristic Vickers hardness and fracture toughness of 31.4 GPa and 4.21 MPa-m^0.5, respectively, at 4.9 N indentation load. The specimen showed satisfactory wire electrical discharge machining (WEDM) performance because of its good electrical conductivity. The design of experiment (DOE) was arranged by L32 orthogonal array (OA) between the machining input parameters namely pulse on-time, pulse off-time, pulse peak current, dielectric fluid pressure and servo feed rate and the output responses like machining speed and surface roughness (R_a). Regression models were employed to establish the numerical correlation between the machining parameters and output responses. Experimental observations were utilized to formulate the first-order regression models to predict responses of WEDM. The optimized input parameters were 27 μs pulse on time, 48 μs pulse off time, 180 A pulse peak current, 7 kg/cm² water pressure and 2200 mm/min servo feed rate for the WEDM performance to produce an optimum machining speed and R_a.     

Improved additive manufacturing of silicon carbide parts via pressureless electric field-assisted sintering

High solids loading silicon carbide (SiC)-based aqueous slurries containing only .5 wt. % organic additives were utilized to create specimens of various geometries via an extrusion-based additive manufacturing (AM) technique. Pressureless electric field-assisted sintering was performed to densify each specimen without deformation. The combination of these techniques produced parts with >98% relative density despite containing only 5 wt.% oxide sintering additives. After sintering, specimens contained only the α-SiC and yttrium aluminum perovskite phases. This suggests the evolution of a nonequilibrium yttrium aluminate phase, as well as transformation from β-SiC to α-SiC. The fabrication method presented in this work has advantages over other AM techniques commonly used with SiC, because it does not require significant organic additives nor additional postprocessing steps such as chemical vapor infiltration or polymer impregnation and pyrolysis.     

Joining of silicon carbide ceramics using a silicon carbide tape

This paper reports the joining of liquid-phase sintered SiC ceramics using a thin SiC tape with the same composition as base SiC material. The base SiC ceramics were fabricated by hot pressing of submicron SiC powders with 4 wt% Al₂O₃–Y₂O₃–MgO additives. The base SiC ceramics were joined by hot-pressing at 1800-1900°C under a pressure of 10 or 20 MPa in an argon atmosphere. The effects of sintering temperature and pressure were examined carefully in terms of microstructure and strength of the joined samples. The flexural strength of the SiC ceramic which was joined at 1850°C under 20 MPa, was 343 ± 53 MPa, higher than the SiC material (289 ± 53 MPa). The joined SiC ceramics showed no residual stress built up near the joining layer, which was evidenced by indentation cracks with almost the same lengths in four directions.     

电石冶炼混合炉料电阻率实验研究

采用"电导池法"研究了电石生产所用混合炉料电阻率与粒径、配炭量、无烟煤与焦炭的置换比之间的关系。通过实验研究得出,混合炉料电阻率随粒径的增加呈幂函数关系缩小,变化趋势与纯焦炭堆积电阻相似;随着配炭量增加,混合炉料电阻率下降,二者在一定范围内呈线性关系;在炭素原料中配入无烟煤可增加混合炉料的电阻率,且电阻率与煤焦比呈线性关系。     

Evaporation-condensation derived silicon carbide membrane from silicon carbide particles with different sizes

Silicon carbide ceramic is a promising membrane material because of the high corrosive and high temperature resistance, and the excellent hydrophility. Here, a silicon carbide ceramic membrane with both substrate layer and separate layer composed of pure silicon carbide phase was successfully prepared. The effect of particle size on the microstructure and properties was investigated. The substrates were prepared from three silicon carbide particles at 2200 ℃. With the content increase of fine particle, the average pore size increased from 5.6 μm to 14.1 μm; meanwhile, the flexural strength of the substrate increased from 14.1 MPa to 24.6 MPa. The separation layers were made from particles of 3.0 μm and 0.5 μm. When sintered at 1900 ℃, the separation layer formed pore network with homogeneous structure. Such silicon ceramic membrane can be used in harsh conditions, including high temperature wastewater and strongly corrosive wastewater.     

Optimizing machining parameters to combine high productivity with high surface integrity in grinding silicon carbide ceramics

Advanced ceramics such as silicon carbide offer many desirable characteristics for industrial and commercial use in terms of their high temperature tolerance, wear and abrasive resistance, and corrosion resistance. However, the machining of ceramics into practical forms presents a challenge because of the difficulty and cost involved in the material removal process due to their high hardness and high brittleness. In this work, experiments were conducted to study the effect of various parameters such as depth of cut, table feed, size and density of grit on the metal removal rate, surface roughness, surface and subsurface damages. Mathematical models were developed using the data obtained experimentally considering the significant parameters only. Finally, a genetic algorithm (GA) code has been developed to optimize the ceramic grinding process with multiple objectives. The manufacturer׳s constraints on the basis of functional requirements of the component were also considered in the GA code. The study demonstrates that the grinding process parameters can be varied to achieve better metal removal rate, good surface finish and lower surface and subsurface damages simultaneously.     

Sialon-containing silicon carbide refractories

Conclusions We worked out the technology of sialon-containing silicon carbide refractories for lining the shafts of blast furnaces. It was shown that addition of MgO in combination with the waste products of the oxides of the rare-earth elements improves the strength and the other properties of the products fired at 1550°C in nitrogen atmosphere.The sialon-containing silicon carbide refractories exhibit a high resistance to the action of slags and are recommended for lining the lower portion of the shaft and the bosh of blast furnaces.Translated from Ogneupory, No. 5, pp. 6–8, May, 1992.