Advanced Materials Research Vols. 264-265

Abstract: Titanium alloys are being widely used in the aerospace, biomedical and automotive industries because of their good strength-to-weight ratio and superior corrosion resistance. Surface roughness is one of the most important requirements in machining of Titanium alloys. This paper describes mathematically the effect of cutting parameters on Surface roughness in end milling of Ti6Al4V. The mathematical model for the surface roughness has been developed in terms of cutting speed, feed rate, and axial depth of cut using design of experiments and the response surface methodology (RSM). Central composite design was employed in developing the surface roughness models in relation to primary cutting parameters. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated. The developed RSM is coupled as a fitness function with genetic algorithm to predict the optimum cutting conditions leading to the least surface roughness value. MATLAB 7.0 toolbox for GA is used to develop GA program. The predicted results are in good agreement with the experimental one and hence the model can be efficiently used to achieve the minimum surface roughness value.

Abstract: Dynamic change in cutting force is one of the major causes of chatter formation in metal cutting which affect machining accuracy. Thus, accurate modeling of cutting force is necessary for the prediction of machining performance and determination of the mechanisms and machining parameters that affect the stability of machining operations. The present paper discusses the development of a mathematical model for predicting the tangential cutting force produced in endmilling operation of Ti6Al4V. The mathematical model for cutting force prediction has been developed in terms of the input cutting parameters cutting speed, feed rate, and axial depth of cut using response surface methodology (RSM). Effects of all the individual cutting parameters on cutting force as well as their interactions are investigated in this study. Central composite design was employed in developing the cutting force model in relation to the primary cutting parameters. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated.

Abstract: High Speed Machining is applicable for producing parts that require little or no grinding / polishing operations within the required machining tolerances. For achieving required level of quality, selection of cutting tools and parameters in high speed machining is very important. In this study, small diameter flat end milling tool was used to achieve high rpm to facilitate the application of low values of feed and depth of cut to achieve better surface roughness. Machining was performed on a Vertical Machining Centre (VMC) with a high speed milling attachment (HES 510), using cutting speed, depth of cut, and feed as machining variables. Statistical prediction model of average surface roughness was developed using three-level full factorial design of experiments. It was observed that depth of cut is the most dominating factor followed by cutting speed and feed. The developed model was used for optimization by desirability function approach to obtain minimum Ra. Maximum desirability of 95.63% was obtained.

Abstract: Chatter is an unwanted but sometimes unavoidable phenomenon in machining. The term defines the self-excited violent relative dynamic motion between the cutting tool and work-piece. Chatter is undesirable due to its adverse effects on the product quality, operation cost, machining accuracy, tool life, machine-tool bearings, and machine-tool life. It is also responsible for reducing output. This paper includes the findings of an experimental study on instabilities of the chip formation process during end milling of Ti6Al4V alloy at different cutting conditions with two different two holders and its influencing factors on chatter formation. The instabilities of chip formation process are expressed as primary or secondary serrated frequency. The chip formed at different cutting conditions is analyzed and its frequency was calculated. It is observed that the primary serrated frequency is more prominent in end milling of Ti6Al4V alloy and its chip serration frequency has significant interaction effect with the with the prominent natural mode frequency of the system components. The vibration signals in frequency domain (FFT) have been analyzed to identify the chatter frequencies which have been compared with the chip serration frequencies in different cutting conditions for two different tool holders. It has been fairly concluded from the experimental findings that chatter is the outcome of resonance, in between the frequency of primary or secondary serrated frequency with the „prominent natural frequency‟ modes of the system components.

Abstract: Electrical discharge machining (EDM) process is a manufacturing method for shaping hard metals and formation of deep and complex shaped hole by spark erosion in electrical conductive materials such as metals, metallic alloys, ceramics etc. EDM process is achieved by a series of recurring electrical discharges between the electrode and workpiece in the presence of dielectric fluid. EDM unique feature of using thermal energy to machine conductive materials irrespective of material hardness has been its major advantage in the manufacture of aerospace, surgical, mould, die, automotive and as well as sport components. The effectiveness of EDM process depends among other factors on the thermal properties of the electrode material. The objective of this study is to study the influence of electrode cooling on recast layers and micro crack in EDM of titanium. The machining parameters investigated in the present study are current intensity (I), pulse on-time (Ton), pulse off-time (Toff) and gap voltage (V), which are of great interest for EDM researchers. The copper electrode is used to EDM titanium workpiece at room temperature and at sub-zero temperature using liquid nitrogen. The influence of cooling of copper electrode on recast layers and micro crack on titanium were investigated using scanning electron microscope (SEM) and has been reported in this study.

Abstract: Inconel 718 is widely used in the aviation, space, navigation and shipping industries because of its outstanding properties. The very mechanical characteristics that give this alloy the highly valued properties also make it one of the most difficult-to-machine aerospace materials. Due to the hardness of nickel-based super-alloys, such as Inconel 718, advanced tools like ceramics have been recommended to machine them. But ceramics are low conductive materials, and the heat generated during the machining of Inconel 718 transfers very slowly through them. The accumulation of generated heat on the cutting edges of ceramic tools causes many problems and sometime leads to premature tool failure. Hence in this study the effectiveness of PVD TiAlN coated carbide insert has been investigated. One approach to overcome the difficulties in machining of Inconel 718 is to use an external heat source to soften the work material surface layer to be removed in order to decrease its tensile strength. A new approach of preheating using inducting heating as an economical alternative to Laser Assisted Machining for end milling of Inconel 718 is presented in this paper. The machinability of Inconel 718 under varying conditions is evaluated by examining tool wear, surface roughness and chip morphology. With increasing work-piece preheating temperature, from room temperature to 420 °C, the advantages of Induction heating is demonstrated by an extended tool life and better surface finish due to more stable chip formation and elimination of micro and macro failure of the tool.

Abstract: Surface finish and dimensional accuracy is one of the most important requirements in machining process. Inconel 718 has been widely used in the aerospace industries. High speed machining (HSM) is capable of producing parts that require little or no grinding/lapping operations within the required machining tolerances. In this study small diameter tools are used to achieve high rpm to facilitate the application of low values of feed and depths of cut to investigate better surface finish in high speed machining of Inconel 718. This paper describes mathematically the effect of cutting parameters on Surface roughness in high speed end milling of Inconel 718. The mathematical model for the surface roughness has been developed in terms of cutting speed, feed rate, and axial depth of cut using design of experiments and the response surface methodology (RSM). Central composite design was employed in developing the surface roughness models in relation to primary cutting parameters. Machining were performed using CNC Vertical Machining Center (VMC) with a HES510 high speed machining attachment in which using a 4mm solid carbide fluted flat end mill tool. Wyko NT1100 optical profiler was used to measure the definite machined surface for obtaining the surface roughness data. The predicted results are in good agreement with the experimental one and hence the model can be efficiently used to predict the surface roughness value with in the specified cutting conditions limit.

Abstract: Electrical discharge machining (EDM) is widely used in the machining of electrically conductive hard metals for the production of dies and moulds. This paper describes an investigation of the effect of electrode cooling on the amount of elements migration from the electrode to the workpiece surface and from the workpiece to the electrode surface. In the present study EDM has been performed with electrodes cooled by liquid nitrogen as well as with electrodes without cooling. Current, pulse-on time, pulse-off time and voltage were taken as the variables during conducting the experiments. The analysis on material migration during EDM was carried out by SEM and EDX. It was observed that EDM with liquid nitrogen reduces material migration and minimizes the surface contamination of both the electrodes.

Abstract: Electric discharge machining (EDM) is an effective manufacturing technique that enables the production of parts made of hard materials with complicated geometry that are difficult to produce by conventional machining processes. EDM is a process of eroding material by transient action of electric sparks on electrically conductive materials, one being the workpiece the other being the electrode immersed in a dielectric fluid and separated by a spark gap. The EDM ability to control the process parameters to achieve the required dimensional accuracy and surface finish has placed this machining operation in a prominent position in industrial applications. This work reports on the different electrode profiles on the machinability factors of surface roughness (Ra) and material removal rate (MRR). The machining factors used in this study are the current (I), on-time and off-time. Based on the experimental results influence of the electrode profile on the responses were made and reported in this study.

Abstract: This paper focuses on the influence of cutting tool edge geometry, cutting speed and feed rate on the tool performance and workpiece’s surface integrity in dry turning of Ti-6Al-4V alloy using PCBN inserts. The parameters evaluated are tool life, wear rate, wear mechanisms, surface roughness and subsurface microstructure alterations. The rate of wear growth of the insert was assessed by progressive flank wear using optical microscope by taking photographs after certain length of cut. The wear mechanism at the end of tool life was investigated in detail using scanning electron microscope (SEM) and EDAX analysis. The results show, by increasing the cutting speed and feed rate resulted in tool life reduction. Cutting with honed edge insert at cutting speed of 180 m/min has shown very little wear, even after 20 min of cutting. The honed insert proved less sensitive to increases in feed rate than the chamfered insert. In general the honed insert showed a significant improvement in tool life. All inserts failed due to attrition wear and adhesion. No flank notch wear was observed, but some crater wear occurred at the chamfer land. Microstructure alteration was not found when machining using the different edge geometry. In these trials, the subsurface micro structural deformations in the direction of cutting were deformed grain boundaries and elongation of grains. Chip smearing and debris on the surface was also found.