Determination of material removal rate in wire electro-discharge machining of metal matrix composites using dimensional analysis

Wire electro-discharge machining (WEDM) is a vital process in manufacturing intricate shapes. The present work proposes a semi-empirical model for material removal rate in WEDM based on thermo-physical properties of the work piece and machining parameters such as pulse on-time and average gap voltage. The model is developed by using dimensional analysis and non-linear estimation technique such as quasi-Newton and simplex. Predictability of the proposed model is more than 99% for all work materials studied. The work materials were silicon carbide particulate reinforced aluminium matrix composites. The experiments and model prediction show significant role of coefficient of thermal expansion in WEDM of these materials. In addition, an empirical model, based on response surface method, has also been developed. The comparison of these models shows significant agreement in the predictions.     

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.     

Multi response optimization of machining parameters of drilling Al/SiC metal matrix composite using grey relational analysis in the Taguchi method

This paper presents a new approach for the optimization of drilling parameters on drilling Al/SiC metal matrix composite with multiple responses based on orthogonal array with grey relational analysis. Experiments are conducted on LM25-based aluminium alloy reinforced with green bonded silicon carbide of size 25 μm (10% volume fraction). Drilling tests are carried out using TiN coated HSS twist drills of 10 mm diameter under dry condition. In this study, drilling parameters namely cutting speed, feed and point angle are optimized with the considerations of multi responses such as surface roughness, cutting force and torque. A grey relational grade is obtained from the grey analysis. Based on the grey relational grade, optimum levels of parameters have been identified and significant contribution of parameters is determined by ANOVA. Confirmation test is conducted to validate the test result. Experimental results have shown that the responses in drilling process can be improved effectively through the new approach.     

Application of the central composite design in optimization of machining parameters in drilling hybrid metal matrix composites

In this study, the application of response surface methodology (RSM) and central composite design (CCD) for modeling, optimization, and an analysis of the influences of dominant machining parameters on thrust force, surface roughness and burr height in the drilling of hybrid metal matrix composites produced through stir casting route. Experiments are carried out using Al 356-aluminum alloy reinforced with silicon carbide of size 25 μm and Mica of size 45 μm. Drilling test is carried out using carbide drill of 6 mm diameter. The design of experiment concept has been used to optimize the experimental conditions. The experimental data are collected based on a three-factor-three-level full central composite design. The multiple regression analysis using RSM is used to establish the input–output relationships of the process. The mathematical models are developed and tested for adequacy using analysis of variance and other adequacy measures using the developed models. The main and interaction effect of the input variables on the predicted responses are investigated. The predicted values and measured values are fairly close, which indicate that the developed models can be effectively used to predict the responses in the drilling of hybrid metal matrix composites. The optimized drilling process parameters have been obtained by numerical optimization using RSM by ensuring the minimum thrust force of 84 N, surface roughness of 1.67 μm, and the burr height of 0.16 mm. After the drilling experiments, a scanning electron microscope (SEM) is used to investigate the machined surface and tool wear.     

On wire breakage and microstructure in WEDC of SiCp/6061 aluminum metal matrix composites

Unconventional machining like wire electric discharge machining/cutting (WEDM/WEDC) seems to be a better choice for machining/cutting the metal matrix composites (MMCs) because it offers easy control and has the capability of machining intricate complex shapes. But wire breakage in the WEDM/WEDC process decreases the machining accuracy and the quality of the machined surface. This paper describes the effect of four input process parameters (i.e., servo voltage, pulse-on time, pulse-off time, and wire feed rate) on wire breakage frequency and the microstructure of the cut surface during WEDC of SiC_p/6061 Al MMC. An optimum range of input parameters has been bracketed as the outcome of this work for determining the effects of input process parameters on the average cutting speed, material removal rate, and surface roughness during WEDC of SiC_p/6061 Al MMC. This range of input parameters can also be used for carrying out further research to develop the models for WEDC of SiC_p/6061 Al MMC and to optimize the WEDC parameters for smooth cutting.     

Selection of optimal process parameters in WEDM while machining Al7075/SiCp metal matrix composites

Aluminium metal matrix composites (MMCs) reinforced with silicon carbide particulate (SiCp) find several applications due to their improved mechanical properties over the conventional metals for a wide variety of aerospace and automotive applications. However, the presence of discontinuously distributed hard ceramic in the MMCs made them as difficult-to-cut materials for conventional machining methods. The wire electrical discharge machining (WEDM), as a widely adopted non-traditional machining method for difficult-to-cut precision components, found an appropriate metal removal process for MMCs to enhance quality of cut within the stipulated cost. While machining the advanced materials like MMCs, a clear understanding into the machining performance of the process for its control variables could make the process uncomplicated and economical. In light of the growing industrial need of making high performance-low cost components, the investigation aimed to explore the machining performance characteristics of SiCp reinforced Al7075 matrix composites (Al7075/SiCp) during WEDM. While conducting the machining experiments, surface roughness, metal removal rate, and wire wear ratio are considered the responses to evaluate the WEDM performance. Response surface methodology is used to develop the empirical models for these WEDM responses. SiC particulate size and volume percentages are considered the process variables along with pulse-on time, pulse-off time, and wire tension. Analysis of variance (ANOVA) is used to check the adequacy of the developed models. Since the machining responses are conflicting in nature, the problem is formulated as a multi-objective optimization problem and is solved using the Non-dominated Sorting Genetic Algorithm-II to obtain the set of Pareto-optimal solutions. The derived optimal process responses are confirmed by the experimental validation tests, and the results are analyzed by SEM.     

Microstructure and wear properties of in situ TiC/FeCrBSi composite coating prepared by gas tungsten arc welding

Using a gas tungsten arc welding (GTAW) process, in situ synthesis TiC particles reinforced Fe-based alloy composite coating has been produced by preplaced FeCrBSi alloy, graphite and ferrotitanium powders. The microstructure and wear properties of the composite coatings were studied by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD) and wear test. The effects of thickness of the pre-placed powder layer on the microstructure, hardness and wear resistance of the composite coatings were also investigated. The results indicated that TiC particles were produced by direct metallurgical reaction between ferrotitanium and graphite during the GTAW process. TiC particles with sizes in the range of 3–5 μm were dispersed in the matrix. The volume fraction of TiC particles and microhardness gradually increased from the bottom to the top of the composite coatings. The TiC-reinforced composite coatings enhance the hardness and wear resistance. The highest wear resistance of the composite coating with a 1.2 mm layer was obtained.     

Microstructure and wear properties of in situ TiC/FeCrBSi composite coating prepared by gas tungsten arc welding

Using a gas tungsten arc welding (GTAW) process, in situ synthesis TiC particles reinforced Fe-based alloy composite coating has been produced by pre-coated FeCrBSi alloy, graphite and ferrotitanium powders on the substrate. The microstructure and wear properties of the composite coatings were studied by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD) and wear test. The effects of thickness of the pre-coated powder layer on the microstructure, hardness and wear resistance of the composite coatings were also investigated. The results indicated that TiC particles were produced by direct metallurgical reaction between ferrotitanium and graphite during the GTAW process. TiC particles with sizes in the range of 3–5 μm were dispersed in the matrix. The volume fraction of TiC particles and microhardness gradually increased from the bottom to the top of the composite coatings. The TiC-reinforced composite coatings enhance the hardness and wear resistance. The highest wear resistance of the composite coating with a 1.2 mm layer was obtained.     

Modeling and analysis of performances in drilling hybrid metal matrix composites using D-optimal design

The present paper deals with the modeling and analysis of machining responses such as the thrust force, surface roughness, burr height, and tool wear in the drilling of hybrid metal matrix composites using carbide, coated carbide, and polycrystalline diamond drills. Experiments are conducted on Al 356 aluminum alloy reinforced with silicon carbide of size 25 μm and mica of size 45 μm. Machining parameters such as spindle speed, feed rate, and weight percent of silicon carbide are chosen as the numerical factors; the drill material is considered as the categorical factor. An experimental plan of a four-factor (three numerical plus one categorical) D-optimal design based on the response surface methodology is employed to carry out the experimental study. The results indicated that the predicted values through the developed model are well in agreement with the experimental results. The results also indicated that the method used is effectively applied for the modeling and analysis of drilling parameters in drilling hybrid metal matrix composites.     

Statistical analysis of process parameters in drilling of AL/SICP metal matrix composite

Four micro-holes were made using micro-EDM on rake face of the cemented carbide (WC/TiC/Co) tools. MoS₂, CaF₂, and graphite solid lubricants were respectively embedded into the four micro-holes to form self-lubricated tools (SLT-1, SLT-2, and SLT-3). Dry machining tests on hardened steel were carried out with these self-lubricated tools and conventional tools (SLT-4). The cutting forces, average friction coefficient between tool and chip, and tool wear were measured and compared. It was shown that the cutting forces and tool wear of self-lubricated tools were clearly reduced compared with those of the SLT-4 conventional tool. The SLT-1 self-lubricated tool embedded with MoS₂ just exhibited lower friction coefficient between tool and chip in cutting speed of less than 100?m/min; the SLT-2 self-lubricated tool embedded with CaF₂ possessed lower friction coefficient in cutting speed of more than 100?m/min; and the SLT-3 self-lubricated tool embedded with graphite accomplished good lubricating behaviors steadily under the test conditions. It is indicated that cemented carbide inserts with four micro-holes on rake face embedded with appropriate solid lubricants on rake face is an effective way to reduce cutting forces and rake wear.     

Studies on wear behavior of nano-intermetallic reinforced Al-base amorphous/nanocrystalline matrix in situ composite

Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on fretting wear behavior of in situ nano-Al₃Ti reinforced Al–Ti–Si amorphous/nanocrystalline matrix composite, processed by high pressure (8 GPa) sintering at room temperature, 350, 400 or 450 °C. The wear experiments were carried out in gross slip fretting regime to investigate the performance of this composite against Al₂O₃ at ambient temperature (22–25 °C) and humidity (50–55%). The highest resistance to fretting wear has been observed in the composites sintered at 400 °C. The fretting wear involves oxidation of Al₃Ti particles in the composite. A continuous, smooth and protective tribolayer is formed on the worn surface of the composite sintered at 400 °C, while fragmentation and spallation leads to a rougher surface and greater wear in the composite sintered at 450 °C.     

Microstructural origins of corrosion in a 20% SiCp/2124 aluminium alloy metal matrix composite

The microstructure of a metal matrix composite (MMC) consisting of 20 wt% 3 μm SiC particles in a 2124 Al alloy matrix has been examined and the relationship to corrosion pitting processes investigated. Standard bulk corrosion tests show that the MMC forms a higher density of pits than the unreinforced alloy, although the overall performance is similar as the pits are shallower. In a new addition to conventional characterization techniques, transmission electron microscopy samples have been directly subjected to ‘flash’ corrosion treatment and subsequently examined. This technique is shown to be effective in studying the initiation of pits. The SiC particles and the widespread 9 intermetallic precipitates are shown to play little, if any, role. A sparse population of features introduced during powder processing and consolidation procedures, probably linked with strong magnesium segregation, is suggested to be responsible for pit initiation.     

A theoretical and experimental investigation of surface generation in diamond turning of an Al6061/SiCp metal matrix composite

In this paper, the surface generation in ultra-precision diamond turning of Al6061/15SiC_p metal-matrix composites was investigated based on different analytical approaches which include parametric analysis, cutting mechanic analysis, finite element method (FEM) analysis and power spectrum analysis. Parametric analysis was performed to explore the in situ inter-relationships between the process parameters and the surface roughness. The surface properties of the diamond turned surface were extracted and analyzed by the power spectrum analysis of the surface roughness profiles. Different surface generation mechanisms were deduced based on the cutting mechanics and FEM analysis. The results of the theoretical analyses were verified through a series of cutting tests conducted under various cutting conditions and a good correlation between the theoretical and experimental results was obtained.     

Application of response surface methodology for determining cutting force model in turning of LM6/SiCP metal matrix composite

In the present investigation an attempt is made to evaluate the effect of certain cutting variables on cutting forces in straight turning of aluminum metal matrix composites under dry cutting condition. Cutting speed, depth of cut and weight percentage of SiC_P are selected as the influencing parameters. The application of response surface methodology and face centered composite design for modeling, optimization, and an analysis of the influences of dominant cutting parameters on tangential cutting force, axial cutting force and radial cutting force of aluminum metal matrix composites produced through stir casting route. Experiments are carried out using aluminum (LM6) alloy reinforced with silicon carbide particles. The mathematical models are developed and tested for adequacy using analysis of variance and other adequacy measures using the developed models. The predicted values and measured values are fairly close, which indicate that the developed models can be effectively used to predict the responses in the turning of aluminum metal matrix composites. The contour plots of the process parameters revel that the low cutting forces are associated with the lowest level of depth of cut and the highest level of cutting speed and the sensitivity analysis revealed that cutting speed is most significant factor influencing the response variables investigated.     

Measurement of changes in surface profile due to wear using a 147Pm β particle backscatter technique II: Application to the simulated wear of dental composite resin and amalgam restorations

A ¹⁴⁷Pm β particle backscatter instrument has been developed and its applications to the measurement of changes in the surface profiles, due to wear, of dental restorations is described. The response of the β particle backscatter instrument to small changes in surface profile are adequately described by a model based on the known behaviour of backscattered electrons. The simulated wear of dental amalgam restorations, composite resin restorations and metal-coated replicas has been studied using this technique. The β particle backscatter instrument is capable of detecting changes of the order of 15 μm in the profile of irregularly shaped surfaces.