Optimizing machining parameters of silicon carbide ceramics with ED milling and mechanical grinding combined process

A novel combined process of machining silicon carbide (SiC) ceramics with electrical discharge milling and mechanical grinding is presented. The process is able to effectively machine a large surface area on SiC ceramics with a good surface quality. The effect of tool polarity on the process performance has been investigated. The effects of peak current, peak voltage, pulse on-time and pulse off-time on the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR) have been investigated with Taguchi experimental design. The mathematical models for the MRR, EWR, and SR have been established with the stepwise regression method. The experiment results show that the MRR, EWR, and SR can reach 46.2543 mm³/min, 20.7176%, and 0.0340 µm, respectively, with each optimal combination level of machining parameters.     

Influence of dielectric and machining parameters on the process performance for electric discharge milling of SiC ceramic

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD).     

Experimental research on machining characteristics of SiC ceramic with end electric discharge milling

Silicon carbide (SiC) ceramic has been widely used in modern industry. However, the beneficial properties of SiC ceramic make machining difficult and costly by conventional machining methods. This paper proposes a new process of machining SiC ceramic using end electric discharge (ED) milling. The process is able to effectively machine a large surface area on SiC ceramic at low cost and no environmental pollution. The effects of emulsion concentration, emulsion flux, milling depth, copper electrode number, and copper electrode diameter on the process performance such as the material removal rate, electrode wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope, and the material removal mechanism of SiC ceramic during end ED milling is obtained.     

Experimental investigations while hard machining of DIEVAR tool steel (50 HRC)

This paper describes hard machining which offers many potential benefits over traditional manufacturing techniques. In this work, investigations were carried out on end milling of hardened tool steel DIEVAR (hardness 50 HRC), a newly developed tool steel material used by tool- and die-making industries. The objective of the present investigation was to study the performance characteristics of machining parameters such as cutting speed, feed, depth of cut and width of cut with due consideration to multiple responses, i.e. volume of material removed, tool wear, tool life and surface finish. Performance evaluation of physical vapour deposition-coated carbide inserts, ball end mill cutter and polycrystalline cubic boron nitride inserts (PCBN) was done for rough and finish machining on the basis of flank wear, tool life, volume of material removed, surface roughness and chip formation. It has been observed from investigations that chipping, diffusion and adhesion were active tool wear mechanisms and saw-toothed chips were formed whilst machining DIEVAR hard steel. PCBN inserts give an excellent performance in terms of tool life and surface finish in comparison with carbide-coated inserts. End milling technique using PCBN inserts could be a viable alternative to grinding in comparison to ball end mill cutter in terms of surface finish and tool life.     

Characteristic investigation of pipe cutting technology based on electro-discharge machining

Pipe cutting technology plays an important role in the process of offshore platforms decommissioning, as many devices such as tubing, drill pipe, and casing need to be decommissioned. In this study, a novel cutting pipe technology based on electro-discharge machining (EDM) is proposed, and a cutting pipe mechanism is developed to cut the pipes for decommissioning offshore platforms. The machining principles and characteristics of the technique are described. The effects of machining parameters, including tool polarity, dielectric fluid, electrode material and width, pulse on-time, pulse off-time, peak voltage, and electrode rotation speed to machining performance, are investigated. The material removal rate (MRR) of the machined casing and tool electrode wear ratio (EWR) is obtained based on the calculation of the percentage of mass loss per machining time. The experimental results show that a better cutting performance can be obtained with negative tool polarity at the conditions of dielectric fluid of emulsion, pulse on-time of 500 μs, pulse off-time of 200 μs, peak voltage of 70 V, copper electrode width of 28 mm, and electrode rotation speed of 250 rpm is a better choice. Additionally, the cutting slots surface has been investigated by the means of SEM. The cutting slots machined by the rotary EDM are clean and smooth.     

Slotted-electrical discharge diamond cut-off grinding of Al/SiC/B4C hybrid metal matrix composite

Advanced manufacturing industries need materials with high strength and low weight in the fields of advanced engineering, such as automobiles and aeronautics. Metal matrix composites (MMCs) are one of the advanced engineering materials that meet the above requirements. To enhance the properties of MMCs, researchers added an additional phase of reinforcements into single reinforced MMCs; such developed MMCs are known as hybrid MMCs. The additional phase of reinforcements enhances the properties of MMCs, but simultaneously leads to rapid tool wear and poor machinability. This study developed an innovative hybrid machining process (HMP) consisting of electrical discharge grinding and diamond grinding in such a way that both the processes occur alternately with equal intervals due to the rotation of a slotted abrasive grinding wheel. The performance of the hybrid process was tested on an Al/SiC_p/B₄C_p work-piece in cut-off grinding mode. The experiments were conducted on an electrical discharge machining machine, which consists of a separate attachment on a vertical column to rotate the wheel. Pulse current, pulse on-time, pulse off-time, wheel RPM, and abrasive grit number were taken as input parameters while material removal rate (MRR) and average surface roughness were taken as output parameters. Result were shown that the HMP gives higher MRR with better surface finish as compared to the constituent processes. Pulse current ranging from 3 A to 21 A, pulse on-time ranging from 30 μs to 200 μs, and pulse off-time ranging from 15 μs to 90 μs were also found to be more suitable for higher MRR, and a wheel RPM at 1300 RPM was more suitable for higher MRR with better surface finish.     

Wear behaviour of alumina based ceramic cutting tools on machining steels

The advanced ceramic cutting tools have very good wear resistance, high refractoriness, good mechanical strength and hot hardness. Alumina based ceramic cutting tools have very high abrasion resistance and hot hardness. Chemically they are more stable than high-speed steels and carbides, thus having less tendency to adhere to metals during machining and less tendency to form built-up edge. This results in good surface finish and dimensional accuracy in machining steels. In this paper wear behaviour of alumina based ceramic cutting tools is investigated. The machining tests were conducted using SiC whisker reinforced alumina ceramic cutting tool and Ti[C,N] mixed alumina ceramic cutting tool on martensitic stainless steel-grade 410 and EN 24 steel work pieces. Flank wear in Ti[C,N] mixed alumina ceramic cutting tool is lower than that of the SiC whisker reinforced alumina cutting tool. SiC whisker reinforced alumina cutting tool exhibits poor crater wear resistance while machining. Notch wear in SiC whisker reinforced alumina cutting tool is lower than that of the Ti[C,N] mixed alumina ceramic cutting tool. The flank wear, crater wear and notch wear are higher on machining martensitic stainless steel than on machining hardened steel. In summary Ti[C,N] mixed alumina cutting tool performs better than SiC whisker reinforced alumina cutting tool on machining martensitic stainless steel.     

Influence of machining parameters on surface roughness in finish cut of WEDM

Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.     

An experimental research on a kind of distributed-flushing ED milling

In order to reduce the electrode wear and increase the material removal, this paper proposed a kind of distributed-flushing ED milling. A rotating electrode with some distributed holes was used during the machining process. The distributed flushing developed the machining environment and increased the adhesion of debris on the electrode, thus decreasing the electrode wear rate. Compared with the material removal rate of conventional ED milling, the relative electrode wear ratio decreased by 10.7 %. Furthermore, the material removal rate of the new method increased by 21.1 %. The effects of rotating speed, peak current, pulse duration, pulse interval, and tool electrode polarity on machining performance, including material removal rate, relative electrode wear ratio, and surface roughness were researched to determine the characteristics of the new process.

     

ELECTRIC DISCHARGE MILLING AND MECHANICAL GRINDING COMPOUND MACHINING OF SILICON CARBIDE CERAMIC

Silicon carbide (SiC) ceramics have been widely used in modern industry. However, the manufacture of SiC ceramics is not an efficient process. This paper proposes a new technology of machining SiC ceramics with electrical discharge milling and mechanical grinding compound method. The compound process employs the pulse generator used in electrical discharge machining, and uses a water-based emulsion as the machining fluid. It is able to effectively machine a large surface area on SiC ceramics with a good surface quality. In this paper, the effects of pulse duration, pulse interval, peak voltage, peak current and feed rate of the workpiece on the process performance parameters, such as material removal rate, relative electrode wear ratio and surface roughness, have been investigated. A L₂₅ orthogonal array based on Taguchi method is adopted, and the experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the process performance are obtained. In addition, the workpiece surface microstructure is examined with a scanning electron microscope and an energy dispersive spectrometer.     

Diamond face grinding of WC-Co composite with spark assistance: Experimental study and parameter optimization

Electro-discharge machining (EDM) characteristics of tungsten carbide-cobalt composite are accompanied by a number of problems such as the presence of resolidified layer, large tool wear rate and thermal cracks. Use of combination of conventional grinding and EDM (a new hybrid feature) has potential to overcome these problems. This article presents the face grinding of tungsten carbide-cobalt composite (WC-Co) with electrical spark discharge incorporated within face of wheel and flat surface of cylindrical workpiece. A face grinding setup for electro- discharge diamond grinding (EDDG) process is developed. The effect of input parameters such as wheel speed, current, pulse on-time and duty factor on output parameters such as material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (ASR), are investigated. The present study shows that MRR increases with increase in current and wheel speed while it decreases with increase in pulse on-time for higher pulse on-time (above 100 μs). The most significant factor has been found as wheel speed affecting the robustness of electro- discharge diamond face grinding (EDDFG) process.     

Some studies into wire electro-discharge machining of alumina particulate-reinforced aluminum matrix composites

Non-traditional process like wire electro-discharge machining is found to show a promise for machining metal matrix composites. However, the machining information for the difficult-to-machine particle-reinforced material is inadequate. This paper is focused on experimental investigation to examine the effect of electrical as well as non-electrical machining parameters on performance in wire electro-discharge machining of metal matrix composites (Al/Al₂O₃p). Taguchi orthogonal array was used to study the effect of combination of reinforcement, current, pulse on-time, off-time, servo reference voltage, maximum feed speed, wire speed, flushing pressure and wire tension on cutting speed, surface finish, and kerf width. Reinforcement percentage, current, and on-time was found to have significant effect on cutting rate, surface finish, and kerf width. The optimum machining parameter combinations were obtained for surface finish, cutting speed, and kerf width separately. Wire breakages were found to pose limitations on the cutting speed in machining of these materials. Wire shifting was found to deteriorate the machined surfaces.     

Micromechanical machining of soda lime glass

Micromechanical machining, which is the mechanical removal of materials using miniature cutting tools, is one of the fabrication methods in the microrealm that has recently attracted a great deal of attention because it has the advantage of being able to machine complex shapes from brittle materials. The most challenging problem in the mechanical machining of brittle material is the fabrication of fracture-free surfaces. To avoid brittle fractures, a thorough investigation is required to find the machining parameters in the ductile cutting regime, which is characterized by plastic deformation of the material when the chip thickness is smaller than the critical value. In this study, cutting forces and surface characteristics of soda lime glass are examined in detail. Conical scratch tests are performed to identify the critical chip thickness, and the cutting forces in the ductile regime are modeled. In addition, coated ball end mill cutters were used to perform machining on inclined soda lime glass to investigate the feed rate effects, up and down milling, and depth of cuts on the surface finish and to examine tool wear.     

Analysis model of parameters affecting cutting performance in high-speed machining

Further progress in green cutting applications depends on the innovativeness of machine tools, advances in tool development, and, especially, more complex tool and cutting technologies. Therefore, this study analyzes the factors influencing high-speed cutting performance. Grey relational analysis and the Taguchi method are then incorporated in the experimental plan with high-speed milling of AISI H13 tool steel. Experimental results indicate that the contributions of tool grinding precision, geometric angle, and cutting conditions to the multiple quality characteristics of high-speed milling for AISI H13 tool steel are 11.75, 9.80, and 73.11 %, respectively. For rough machining, tool life and metal removal volume are the primary evaluation indicators and cutting parameters should be prioritized, especially cutting speed and feed per tooth. In finish machining, workpiece surface roughness is the primary evaluation indicator. Besides the selection of cutting parameters, the design and grinding of endmill are critical factors, especially the design and grinding of relief angles.     

Effect of machining parameters on the milling process of 2.5D C/SiC ceramic matrix composites

Abstract

The C/SiC ceramic matrix composites are widely used for high-value components in the nuclear, aerospace and aircraft industries. The cutting mechanism of machining C/SiC ceramic matrix composites is one of the most challenging problems in composites application. Therefore, the effects of machining parameters on the machinability of milling 2.5D C/SiC ceramic matrix composites is are investigated in this article. The related milling experiments has been carried out based on the C/SiC ceramic matrix composites fixed in two different machining directions. For two different machining directions, the influences of spindle speed, feed rate and depth of cut on cutting forces and surface roughness are studied, and the chip formation mechanism is discussed further. It can be seen from the experiment results that the measured cutting forces of the machining direction B are greater than those of the in machining direction A under the same machining conditions. The machining parameters, which include spindle speed, feed rate, depth of cut and machining direction, have an important influence on the cutting force and surface roughness. This research provides an important guidance for improving the machining efficiency, controlling and optimizing the machined surface quality of C/SiC ceramic matrix composites in the milling process.     

Optimization of machining parameters using genetic algorithm and experimental validation for end-milling operations

Optimization of cutting parameters is valuable in terms of providing high precision and efficient machining. Optimization of machining parameters for milling is an important step to minimize the machining time and cutting force, increase productivity and tool life and obtain better surface finish. In this work a mathematical model has been developed based on both the material behavior and the machine dynamics to determine cutting force for milling operations. The system used for optimization is based on powerful artificial intelligence called genetic algorithms (GA). The machining time is considered as the objective function and constraints are tool life, limits of feed rate, depth of cut, cutting speed, surface roughness, cutting force and amplitude of vibrations while maintaining a constant material removal rate. The result of the work shows how a complex optimization problem is handled by a genetic algorithm and converges very quickly. Experimental end milling tests have been performed on mild steel to measure surface roughness, cutting force using milling tool dynamometer and vibration using a FFT (fast Fourier transform) analyzer for the optimized cutting parameters in a Universal milling machine using an HSS cutter. From the estimated surface roughness value of 0.71 μm, the optimal cutting parameters that have given a maximum material removal rate of 6.0×10³ mm³/min with less amplitude of vibration at the work piece support 1.66 μm maximum displacement. The good agreement between the GA cutting forces and measured cutting forces clearly demonstrates the accuracy and effectiveness of the model presented and program developed. The obtained results indicate that the optimized parameters are capable of machining the work piece more efficiently with better surface finish.     

Experimental research on electrical discharge machining characteristics of engineering ceramics with different electrical resistivities

Electrical discharge machining (EDM) is the extensively used nonconventional material removal process for machining engineering ceramics provided they are electrically conductive. However, the electrical resistivity of the popular engineering ceramics is higher, and there has been no research on the relationship between the EDM parameters and the electrical resistivity of the engineering ceramics that can be machined effectively by EDM. This paper investigates the effects of the electrical resistivity and the EDM parameters on the EDM performance of ZnO/Al₂O₃ ceramic in terms of the machining efficiency and the quality. The experimental results showed that the electrical resistivity and the EDM parameters such as pulse on-time, pulse off-time, and peak current had the great influence on the machining efficiency and the quality during electrical discharge machining of ZnO/Al₂O₃ ceramic. Moreover, the electrical resistivity of the ZnO/Al₂O₃ ceramic, which could be effectively machined by EDM, increased with increasing the pulse on-time and peak current and with decreasing the pulse off-time, respectively. Furthermore, the ZnO/Al₂O₃ ceramic with the electrical resistivity up to 3,410 Ω cm could be effectively machined by EDM with the appropriate machining condition.     

Soft computing models based prediction of cutting speed and surface roughness in wire electro-discharge machining of tungsten carbide cobalt composite

This paper reports on an experimental investigation of small deep hole drilling of Inconel 718 using the EDM process. The parameters such as peak current, pulse on-time, duty factor and electrode speed were chosen to study the machining characteristics. An electrolytic copper tube of 3 mm diameter was selected as a tool electrode. The experiments were planned using central composite design (CCD) procedure. The output responses measured were material removal rate (MRR) and depth averaged surface roughness (DASR). Mathematical models were derived for the above responses using response surface methodology (RSM). The results revealed that MRR is more influenced by peak current, duty factor and electrode rotation, whereas DASR is strongly influenced by peak current and pulse on-time. Finally, the parameters were optimized for maximum MRR with the desired surface roughness value using desirability function approach.     

Improvement of machinability of Waspaloy via laser-assisted machining

Waspaloy is a heat-resistant alloy primarily used in aircraft turbine engines, as forged turbine and compressor disk, which is difficult to machine at room temperature due to excessive tool wear and poor surface finish. Laser-assisted machining (LAM) offers the ability to machine such superalloys more efficiently by locally heating and softening the workpiece material prior to material removal and machining with a conventional single-point cutting tool. A transient, three-dimensional heat transfer model is used for modeling LAM of Waspaloy. The thermal model is validated by comparing the temperature predictions and the surface temperature measurements using an infrared camera. The machinability of Waspaloy under varying conditions is evaluated by examining tool wear, cutting forces, and surface finish. With increasing material removal temperature from room temperature to 300–400°C, the benefit of LAM is demonstrated by a 20% decrease in specific cutting energy, a two- to three-fold improvement in surface roughness, and a 50% increase in ceramic tool life over conventional machining.     

Study of engineering ceramic machining with a new design of ripple controlled microdetonation of electrode arc striking

Based on the principle of strong shock wave generating transient dynamic high-pressure, physical theory of vacuum discharge, and high-power pulse technology, this study developed a new machining system of ripple controlled microdetonation of electrode arc striking (MDEAS), which was specially used to machine hard and crisp materials, such as ceramic. The topographies such as hole, ladder plane, column surface, and abnomity plane is machined successfully with the system on Si₃N₄ ceramic. Test results show that there is one deteriorative layer with thickness of 0.25?～?0.45 mm on the test piece surface after MDEAS machining. The deteriorative layer is composed of amorphous phases and crystalloid Si, can be machined and removed with ceramic tools or common grinding wheel. There are obvious transverse cracks near the interface of the degenerative layer and the matrix, but the cracks along the depth direction are not found. Furthermore, the optimal machining parameters for Si₃N₄ ceramic are obtained through orthogonal experimental. The analysis on the machining mechanism proves that one negative pressure zone will form in the spherical space below the concave due to the action of negative peak overpressure when the detonation pressure attenuates to the negative peak overpressure, which has closure effect for the original microcracks on the material surface and subsurface, so the residual stress will not be produced on the deep layer inside the work piece material to cause the reduction of material strength. Compared with other machining technologies, because Si₃N₄ ceramic is disposed by the compositive way of detonation and gasification machined with the MDEAS technology, the technology has many outstanding merits such as low machining cost, well parameter controllability, and machining stability. So, it has an important applied value.