Developments in the non-traditional machining of particle reinforced metal matrix composites

The non-traditional machining of particulate reinforced metal matrix composites is relatively new. However, researchers seem to pay more attention in this field recently as the traditional machining of particulate reinforced metal matrix composites is very complex. This research investigates different non-traditional machining, such as electro-discharge, laser beam, abrasive water jet, electro-chemical and electro-chemical discharge machining of this composite materials. The machining mechanism, material removal rate/machining speed and surface finish have been analysed for every machining process. This analysis clearly shows that vaporisation, melting, chemical dissolution and mechanical erosion are the main material removal mechanisms during non-traditional machining. The thermal degradation and the presence of reinforcement particles mainly damage the machined surface. The understanding of electro-discharge, laser beam and abrasive water jet machining is more developed than that of electro-chemical and electro-chemical discharge machining for particulate reinforced MMC

Electrical Discharge Machining of MMCs Reinforced with Very Small Particles

This paper investigates material removal rate (MRR), kerf width, surface finish, and electrode wire wear for different pule-on-times as well as wire tensions during EDM of 6061 aluminum alloy reinforced with 10 vol % 700 nm SiCp MMC. Effects of pulse-on-time on output variables at lower and higher wire tensions were investigated. Similarly, effects of the wire tensions on output variables at shorter and longer pulse-on-times were also investigated. Longer pule-on-time increases the MRR though the higher wire tension reduces the MMR. The effect of wire tension on MRR is much more significant at longer pule-on-time compare to that at shorter pule-on-time. There is an optimum pule-on-time for which best surface finish is achieved. The surface finish deteriorates when the pulse-on-time is higher or lower than the optimum pule-on-time. With the rise of tension in wire, the surface roughness increases and decreases at shorter and longer pule-on-times, respectively. The machined surface contains solidified molten material, splash of materials, and blisters. Generation of the tapered slot with higher kerf width at the top indicates the wear of wire electrode. Significant variation of the electrode wire diameter was due to coating of the matrix, wear, and clogging of small reinforced particles in the electrode gap

Wire EDM Mechanism of MMCs with the Variation of Reinforced Particle Size

The size of reinforced particles notably affects the electro-discharge machining (EDM) of metal matrix composites (MMCs). This paper explores the mechanism of wire EDM of MMCs with different sizes of reinforced particles as well as the corresponding unreinforced matrix material. The mechanisms of material removal, surface generation, and taper kerf formation were investigated. This study shows that the particles’ ability to protect matrix materials from the intense heat of electric arc controls the material removal rate, surface generation, and taper of kerf. The low melting point matrix material is removed very easily, but the heat resistance reinforced particles delay the removal of material and facilitate the transfer of the workpiece material to wire electrode and vice versa. Thus, the material stays longer in touch with intense heat and affects the surface generation, wire electrode wear, and width of the kerf

Sustainability in wire electrical discharge machining of titanium alloy: Understanding wire rupture

To reduce the machining time and energy, it is important to have uninterrupted machining to make the process sustainable. Understanding the factors and mechanism that affect the wire failure is vital to reduce machining time to preserve resources and improve sustainability. Therefore, the mechanism of wire electrode rupture during electrical discharge machining (EDM) of Ti-6Al-4V alloy has been investigated in this study. To aid the analysis, electrolyte flushing pressure (7, 10, 15, 18 MPa), wire tension (800, 1100, 1400 and 1700 gf) and pulse-on-time (4, 6, 8 and 10 µsec) were varied to understand the effects of these parameters on wire rupture. The incidents of wire rupture are high at lower flushing pressure and higher wire tension. The influence of pulse-on-time depends on the interaction ns between wire tension and flushing pressure. The wire rupture occurs at instantaneous high temperature due to generation of unwanted arcs when the EDM debris/wastes are not flushed away properly. Higher wire tension may break the wire even at lower temperature in the machining zone. The wire rupture might be very sudden and/or gradual decrease of cross-section of the wire, however, the tips of the broken wire experience necking before fracture which is contributed to associated wire tension and softening by high temperature. The coating of the wire was disrupted and wear-off around the tips of broken wire. Workpiece material was not detected on the tips, however, trace of oxides islands was detected that formed due to high temperature oxidation of wire materials around the broken tips

Machining of titanium alloy (Ti-6Al-4V) - theory to application

This paper correlates laboratory based understanding in machining of titanium alloys with theindustry based outputs and find possible solutions to improve machining efficiency oftitanium alloy Ti-6Al-4V. The machining outputs are explained based on different aspects ofchip formation mechanism and practical issues faced by industries during titaniummachining. This study also analyzed and linked the methods that effectively improve themachinability of titanium alloys. It is found that the deformation mechanism duringmachining of titanium alloys is complex and causes basic challenges, such as saw-toothchips, high temperature, high stress on cutting tool, high tool wear and undercut parts. Thesechallenges are correlated and affected by each other. Saw tooth-chips cause variation incutting forces which results in high cyclic stress on cutting tools. On the other hand, lowthermal conductivity of titanium alloy causes high temperature. These cause a favorableenvironment for high tool wear. Thus, improvements in machining titanium alloy dependmainly on overcoming the complexities associated with the inherent properties of this alloy.Vibration analysis kit, high pressure coolant, cryogenic cooling, thermally enhancedmachining, hybrid machining and, use of high conductive cutting tool and tool holdersimprove the machinability of titanium alloy

Degradation of wire electrode during electrical discharge machining of metal matrix composites

This paper investigated the degradation of wire electrode during electrical discharge machining of SiC reinforced Al-based metal matrix composites (MMCs). MMCs with different size of reinforcements (0.7, 3 and 13. µm) as well as corresponding matrix material were machined under similar machining conditions to understand the effect of reinforcement size on the degradation of wire. In addition, pulse-on-time and wire tension were varied to understand the effect of machining parameters and interaction between machining parameters and size of the reinforcements. It was found that initial circular shaped wire deformed during the machining process as curved front and rear edges and two straight side edges irrespective of cutting conditions and workpiece materials. The curved edge at the front and straight side edges take part in material removal and experience sever degradations. The final cross-sectional area of the wire after the machining process is decided by balancing two mechanisms: (i) downward flow of highly malleable soft wire material due to high temperature which increases the diameter of wire electrode and (ii) vaporisation of the wire material at higher temperature which reduces the diameter of wire electrode. These complex processes are affected by machining conditions as well as workpiece materials

Ultra-precision machining of electroless-nickel plated die material

Master'sMASTER OF ENGINEERIN

Prediction of cutting forces in machining of Metal Matrix Composites

This paper presents a mechanics model for predicting the forces of cutting aluminium-based SiC/Al2O3 particle reinforced MMCs. The force generation mechanism was considered to be due to three factors: (a) the chip formation force, (b) the ploughing force, and (c) the particle fracture force. The chip formation force was obtained by using Merchant’s analysis but those due to matrix ploughing deformation and particle fracture were formulated, respectively, with the aid of the slip line field theory of plasticity and the Griffith theory of fracture. A comparison of the model predictions with the authors’ experimental results and those published in the literature showed that the theoretical model developed has captured the major material removal/deformation mechanisms in MMCs and describes very well the experimental measurements

Duplex surface treatment of steels by nitriding and chromizing

Duplex surface treatment, that is, chromizing and plasma nitriding (PN) of steels have attracted interest from industrial sectors because of its attractive properties and ability to apply on different types of steels. This paper aims to investigate duplex treatment on different types of steels at different treatment conditions. The improvements of the treated surfaces in terms of morphology and thickness, composition, surface hardness and roughness, as well as wear and friction of the engineered layer have been analysed. It was found that several layers of different thickness are formed due to duplex treatment which depends on the specimen’s carbon content and treatment temperature. Mainly carbides and nitrides of chromium and iron are formed, where the amount and composition of them are controlled by duplex treatment process parameters. These compounds enhance the hardness and wear resistance of the treated surface. The CrxN phase is the main contributor towards high microhardness of duplex-treated layers. In addition to high hardness, it also provides excellent wear resistance properties. The PN process reduces the coefficient of friction of chromized steels due to the lower friction coefficient of chromium nitride. However, the surface roughness of the treated surface increases due to the intrinsic properties of formed phases

Machining of metal matrix composites: effect of ceramic particles on residual stress, surface roughness and chip formation

Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes