Digraph and matrix method to evaluate the machinability of tungsten carbide composite with wire EDM

Machinability aspect is of considerable importance for efficient process planning in manufacturing. Machinability of an engineering material may be evaluated in terms of the process output variables like material removal rate, processed surface finish, cutting forces, tool life, specific power consumption, etc. In this paper, graph theoretic approach (GTA) is proposed to evaluate the machinability of tungsten carbide composite. Material removal rate is considered as a machinability attribute of tungsten carbide to evaluate the effect of several factors and their subfactors. Factors affecting the machinability and their interactions are analyzed by developing a mathematical model using digraph and matrix method. Permanent function or machinability index is obtained from the matrix model developed from the digraphs. This index value helps in quantifying the influence of considered factors on machinability. In the present illustration, factors affecting machinability of tungsten carbide are grouped into five broad factors namely work material, machine tool, tool electrode, cutting conditions, and geometry to be machined. GTA methodology reveals that the machine tool has highest index value. Therefore, it is the most influencing factor affecting machinability.     

WC–ZrO2 composites: processing and unlubricated tribological properties

In the present work, we report the processing and properties of WC–6 wt.% ZrO₂ composites, densified using the pressureless sintering route. The densification of the WC–ZrO₂ composites was carried out in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y-stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. An important observation is that a transition in friction and wear with load is noted. The dominant mechanisms of material removal appear to be tribochemical wear and spalling of tribolayer.     

Development and study of combined phenol-rubber binders for frictional composites

The paper reports the results of the development of combined phenol-rubber binders for the frictional composites containing resol phenol formaldehyde resin and synthetic butadiene nitrile rubber with various contents of acryl nitrile links. The effect of the method of production of the combined binder on its structure and properties is studied. The results of an investigation of the influence of the binder composition on properties of the frictional composites are presented. The structural transformations that occur during the preparation of the combined binders are studied.     

Compressive quasistatic and dynamic behavior of SiC/ZrO2 aluminum-based nanocomposite

Journal of Mechanical Science and Technology - This research investigated the mechanical properties of aluminum-based nanocomposite. The spark plasma sintering method was adopted to fabricate the...     

Wear and frictional performance of polymeric composites aged in various solutions

The aim of the present work is to investigate the effect of aging process on the wear and frictional characteristics of polyester composites based on oil palm fibres. Prepared samples of treated oil palm fibre reinforced polyester (T-OPRP) composite were immersed in different types of solutions (i.e. water, salt water, diesel, petrol and engine oil) for three years. The samples were then tested on a Pin on disc (POD) machine subjected to a polished stainless steel counterface under dry adhesive wear at different sliding distances (0-6.72 km). Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. Results revealed that aging process has pronounced influence on the adhesive wear and frictional behaviour of the T-OPRP composite. Immersing the samples in water and salt water demonstrated poorest wear performance as compared to the ones immersed in engine oil and diesel. This was mainly due to the higher viscosities of engine oil and diesel solutions as compared to the rest.     

An investigation on the machinability of Al-SiC metal matrix composites using pcd inserts

The paper attempts to study the machinability issues of aluminium-silicon carbide (Al-SiC) metal matrix composites (MMC) in turning using different grades of poly crystalline diamond (PCD) inserts. Al-SiC composite containing 15%wt of SiC was used as work material for turning and PCD inserts of three different grades were used as cutting tools. Experiments were conducted at various cutting speeds, feeds and depth of cuts and parameters, such as surface roughness, specific power consumed, and material removal rate were measured. The worn surface of the insert was examined by scanning electron microscope (SEM). The surface finish observed was found to be much lower than the theoretical surface roughness. The influence of cut was examined for the different grades of PCD inserts. It was observed that the 1600 grade PCD inserts performed well from the surface finish and specific power consumption points of view closely followed by the 1500 grade.     

The crack healing behavior of ZrO2/SiC composite ceramics with TiO2 additive

This paper was carried out to assess the crack-healing behavior of ZrO₂ composite ceramics. The ZrO₂ composite ceramics were made by adding 10 wt.% SiC and TiO₂. The TiO₂ additives were changed to 1, 3 and 5 wt.%. The characteristics of crack-healing behavior were studied as a function of annealing temperature and time. Specimens were mirror polished. The cracks of about 100 ??m were introduced on the specimen surface by Vickers indenter and specimen were heat-treated. The strength of crack-healing was conducted by a three-point bending, and the each specimens was measured by XRD. The results obtained in this study are as follows: The ZST composite ceramics contained crack-healing properties, and the strength of ZST smooth specimens have been shown to be better than ZS specimens. The optimum crack-healing condition of the ZTS3 specimen was 1073 K, 5 hours in the air. Specimens with heat treatment had micro-cracks and large cracks on the surface, but the micro-cracks on the surface did not affect the bending strength. It was found that specimens display phase transformation from tetragonal crystal to monoclinic crystal after heat treatment.     

Regression modeling and optimization of machinability behavior of glass-coir-polyester hybrid composite using factorial design methodology

Polymer-based composite materials posses superior properties such as high strength-to-weight ratio, stiffness-to-weight ratio, and good corrosive resistance and therefore, are preferred for high-performance applications such as in the aerospace, defense, and sport goods industries. Drilling is one of the indispensable methods for building products with composite panels. In this present work, an investigation has been carried out to evaluate mechanical and machinability characteristics of hybrid composites, E-glass, and natural coir fiber abundantly available in India. A regression model is developed for correlating the interactions of some drilling parameters such as drill bit diameter, spindle speed and feed rate, and their effects on responses such as thrust force, torque, and tool wear during drilling of glass-coir fiber reinforced hybrid composites by Design of Experiment techniques. Results indicated that feed rate is playing major role on the responses than other two variables.     

The frictional behavior of mild steel under horizontal vibration

The present paper investigates experimentally the effect of external horizontal vibration on friction property of mild steel. To do so, a pin-on-disc apparatus having facility of vibrating the test samples in horizontal direction was designed and fabricated. Horizontal vibration is created along the sliding direction of vibration and perpendicular to the direction of vibration. The experimental setup has the facility to vary the amplitudes and frequencies of vibration while velocity of vibration is kept constant. During the experiment, the frequency and amplitude of vibration were varied from 0 to 500 Hz and 0 to 200 μm, respectively. Results show that the friction coefficient increases with the increase in amplitude and frequency of vibration for mild steel. The horizontal vibration can be of two types: one along the direction of sliding (longitudinal direction) and the other along the perpendicular direction of sliding (transverse direction). For both the cases, test sample slides horizontally. It is found that the magnitude of friction coefficient for longitudinal vibration is less than that for under transverse vibration. These results are analyzed by dimensional analysis to correlate the friction coefficient with sliding velocity, frequency and amplitude of vibration. The experimental results are also compared with those available in literature and simple physical explanations are provided.     

Tribological behavior of frictional seismic dampers of pendulum type

Frictional pendulum bearings have universal properties that can meet various requirements at service of buildings, bridges, and industrial constructions. The formulas for the average dimensionless wear rate and friction coefficient of the bearings are obtained. The use of the bearings as seismic dampers of shell drilling rigs is described and characteristics of the frictional pendulum bearings are given.     

Reciprocative sliding friction and wear properties of electrical discharge machined ZrO2‐based composites

Hot‐pressed, laboratory‐made, ZrO₂‐based composites with 40 vol. % WC, TiCN or TiN were surface finished by electrical discharge machining in order to compare their reciprocating sliding friction and wear response against WC–6wt%Co cemented carbide in unlubricated conditions. Sliding experiments were performed using a Plint TE77 pin‐on‐flat wear test rig, revealing a strong impact of the secondary phase on the tribological behaviour of the ZrO₂‐based composites. The worn surfaces and wear debris were characterised by scanning electron microscopy, energy dispersive X‐ray analysis and surface topography scanning, pointing out abrasion, polishing and adhesion as main wear mechanisms. The most favourable friction and wear characteristics were encountered with ZrO₂–WC composites compared to the other grades with equal amount of volumetric secondary phase. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of strain-hardening on frictional behavior in tip test

In previous investigation of the tip test using aluminum alloy AL6061-O, it was found that the distance of radial tip from the external side surface of the workpiece deformed has a linear relationship with the maximum forming load measured at a certain punch stroke. In this study, further experiments with aluminum alloys AL2024-O, AL5083-O, AL6061-O, AL7075-O, annealed carbon steel AISI 1010 and pure copper C12100 were carried out to investigate the effect of material properties on frictional behavior by the tip test for the materials commonly used in bulk metal forming. To characterize the relationships among radial tip distance, maximum forming load and shear friction factor, finite element analyses were employed. It was observed that the linear relationships among these three were maintained for the various tested materials. Also, it was found that the friction condition at the punch was always higher than that at the lower die interface such that the ratio of shear friction factors at the die and punch interfaces should be less than one. By examining the material properties currently tested, it was determined that this ratio could be estimated from a logarithmic equation from the value of strain-hardening exponent, depending on the material used.     

Tribological behavior of polytetrafluoroethylene-silica composites

The effect of finely dispersed silica on the structure and mechanical and tribological characteristics of polytetrafluoroethylene-silica composites is studied. It is shown that the introduction of a small amount of filler (0.5%) results in qualitative and quantitative changes in the supermolecular structure of the polymer matrix, which entail variations in the friction coefficient and wear rate of the composites. During friction, dispersion of the filler and its accumulation in the composite’s surface occur. Within a narrow range of the filling degree, this causes a considerable rise of the abrasiveness of the composite accompanied with high wear resistance, which may be attributed to an increase in the adhesion of transfer films. The maximal wear resistance of polytetrafluoroethylene-silica composites is found when the filler is present in a small quantity, providing for a combination of high strength characteristics, low friction coefficient, and moderate abrasiveness.     

Investigation of adhesive and frictional behavior of GeSbTe films with AFM/FFM

Frictional force microscope (FFM) was used to investigate the nanoscale frictional behavior of GeSbTe films deposited by magnetron sputtering. The effects of relative humidity, scanning velocity and surface roughness on friction were taken into account. Besides, the frictional behavior of GeSbTe films with different compositions was analyzed. Experimental results show that the coefficient of friction of GeSbTe films is almost independent of scanning velocity, while the frictional force decreases with increasing velocity. Both the relationship of friction vs. normal load and that of friction vs. RMS keep relatively linear, and the coefficient of friction increases with the increase in RMS. The influence of humidity on adhesion between the tip and the GeSb₂Te₄ film is more significant than that between the tip and the Ge₂Sb₂Te₅ film.     

Sensitivity study of frictional behavior by dimensional analysis in cold forging

In metal forming operations, material flow and quality of the product depend on the conditions at the billet/tools interface friction, lubrication, and surface finish. Of these parameters, friction is the most difficult to characterize and its influence is often difficult to predict because of its dependency on a variety of factors. Recently, through a number of investigations conducted, a linear relationship among shear friction factor, dimensionless load and tip distance was obtained. The aim of the present study is to see whether the linear relationship obtained in the previous works was fortuitous or genuine by applying a dimensional analysis introducing processing parameters such as contact pressure, ram velocity, viscosity of the lubricant, load, surface roughness and shear friction factor. From the dimensional analysis based on Buckingham π theorem and the data obtained from the tip test experiment, the present theoretical work derives dimensionless parameters and analysis of variance determines any correlation between the dimensionless parameters obtained. This work reconfirms the theoretical background of the previous experimental findings in the literature.     

Development of cutting tools with microscale and nanoscale textures to improve frictional behavior

We developed novel cutting tools that had either microscale or nanoscale textures on their surfaces. Texturing microscale or nanoscale features on a solid surface allowed us to control the tribological characteristics of the tool. The textures, which had pitches and depths ranging from several hundreds of nanometers to several tens of micrometers, were fabricated utilizing the ablation and interference phenomena of a femtosecond laser. The effect of the texture shape on the machinability of an aluminum alloy was investigated with a turning experiment applying the minimum quantity lubrication method. The texture decreased the cutting force due to the corresponding reduction in the friction on the rake face. This effect strongly depended on the direction of the texture; lower cutting forces were achieved when the texture was perpendicular to the chip flow direction rather than parallel. This effect was only observed at high cutting speeds over 420 m/min. These results indicate that the developed tools effectively improved the machinability of the alloy.     

The effect of process parameters on machining of magnesium nano alumina composites through EDM

The effects of electrical discharge machining (EDM) parameters on drilled-hole quality such as taper and surface finish are evaluated. Microwave-sintered magnesium nano composites (reinforced with 0.8 and 1.2 wt.% of nano alumina) are used as work materials. Experiments were conducted using Taguchi methodology to ascertain the effects of EDM process parameter. The process parameters such as pulse-on time, pulse-off time, voltage gap, and servo speed were optimized to get better surface finish and reduced taper. ANOVA analyses were carried out to identify the significant factors that affect the hole accuracy and the surface roughness. Confirmation tests were performed on the predicted optimum process parameters. Pulse-on time and the servo speed are identified as major response variables. Micro structural changes and the effects of nano particle reinforcement in the drilled hole were studied through SEM micrographs.     

ZrO2对激光烧结Al2O3/SiO2/ZrO2显微组织和显微硬度的影响

在Nd:YAG激光器低功率烧结的条件下,基于选择性激光烧结工艺（SLS）成形复相陶瓷Al2O3/SiO2/ZrO2材料,利用扫描电子显微镜（SEM）、X射线衍射分析仪（XRD）和显微硬度计分别对激光烧结层加入ZrO2前后的表面形貌和断口形貌、表面物相、表面显微硬度进行了分析。结果表明,部分四方相ZrO2(t-ZrO2)相变成单斜相ZrO2(m-ZrO2),应力诱导微裂纹增韧作用和Al2O3弥散强化共同作用在某种程度上提高了烧结试样的断裂韧性,对于改善零件整体寿命和可靠性有着重要的意义。     

Effect of microwave heat treating processing on frictional behaviour of aluminium alloy 2900 composites

The sliding wear behaviour of microwave processed, SiC_p and Al₂O_3p reinforced aluminium alloy 2900 and 2024 metal matrix composites prepared by powder metallurgy method was investigated in a pin on disc system. The objective is to determine the effects of novel alloying elements of AA 2900, ceramic addition and microwave aging process on the strength to tribological properties. This composite is evaluated to be an effective replacement for conventionally available AA 2024 composites in brake applications. Compared to conventional heat treating processes, microwave processing used for heat treating the samples is observed to be novel method in improving the strength–microstructural–tribological properties. AA 2900 with 6 wt-% Al₂O₃ exhibited good strength to microstructure relationship with excellent wear characteristics compared to AA 2024 composites which are governed by alloying elements in AA 2900. 2 H aged AA 2900 with 6 wt-% Al₂O₃ sample exhibited good frictional coefficient values with good density and strength characteristics. Hence, it is observed that alloying elements in AA 2900 and microwave processing have enhanced the strength to tribological behaviour where the property enhancement is achieved only through ceramic reinforcements.