Tool Nose Region Research Articles

Investigation of the Machining Behavior of Ti6Al4V/TiC Composites During Conventional and Laser-Assisted Machining

Conventional machining of Ti6Al4V/TiC composites is a very difficult process, which exhibits a peculiar cutting force pattern where the thrust forces are higher than the tangential forces. This behavior results in rapid tool wear and consequently very short tool life. This study is concerned with describing the reasons for the attendant behavior using experimentally validated 3D finite element simulations and alleviating this behavior via laser assisted machining (LAM). Simulations were conducted using an equivalent homogeneous model (EHM) and a multiscale heterogeneous model (MHM) of the Ti6Al4V/TiC composite. Results showed a good agreement between the tangential forces obtained from experiments, EHM, and MHM for conventional machining and LAM. However, only the MHM was able to successfully predict the unusual high thrust forces. The MHM simulation results showed that the tool/particle interaction along the tool nose region presented the highest resistance due to the high resistance against pushing the TiC particles by the tool into the machined surface. This resistance results from the efficient load transfer capability between the particles and the matrix below the machined surface. When using LAM, the stated resistance was decreased by the reduction in load transfer capability of the Ti6Al4V/TiC workpiece such that the thrust and tangential forces were reduced by 78% and 37%, respectively, according to the MHM simulation. The experimental results showed that the tool wear was improved by 68% by LAM. All the results demonstrated that the MHM successfully captured the underlying machining mechanism of the Ti6Al4V/TiC composites.

Effect of wedge angle on surface roughness in finish turning: analytical and experimental study

Most of the theoretical models for surface roughness in finish turning assume that the work piece surface profile is formed by the rounded tip of the tool nose. The effect of the straight flank section in the tool nose region on the surface roughness is usually neglected. In this work, the straight flank section is taken into account in order to predict the arithmetic average roughness R a and root-mean-square roughness R q more accurately. The analytical models for R a and R q are developed as a function of three parameters, namely feed rate, nose radius, and wedge angle. These models were verified using digital simulation method. The surface roughness determined using the new three-parameter models were compared with the existing two-parameter models that consider only the feed rate and nose radius. Decreasing wedge angle was found to lower the surface roughness significantly. An experiment was conducted to test the validity of the three-parameter model at different feed rates in real machining operation. The experimental results agreed more closely with the proposed three-parameter models compared to the two-parameter models.

Assessment of flank wear and nose radius wear from workpiece roughness profile in turning operation using machine vision

Although literature on the measurement of flank wear and crater wear in single-point turning tools using machine vision is well documented, the study on the effect of nose radius wear on the roughness profile and dimensional changes of workpiece is less explored. The measurement of flank wear using the 2-D profile of the tool nose region or the roughness profile of the workpiece has also not been attempted in the past. In this work, the nose radius wear of cutting tools and roughness profile of turned parts in a lathe operation were measured using the machine vision method. The flank wear width VBC in the nose area was determined from the nose radius wear using the tool setup and machining geometry. The nose radius wear was also determined from the roughness profile of the workpiece and used in calculating the flank wear width. Comparison between the maximum flank wear width VBCmax determined from the roughness profile and that obtained using a toolmaker’s microscope showed a mean deviation of 5.5%. This result indicates that flank wear can be determined fairly accurately from the workpiece roughness profile if the tool and machining geometry are known.

A New Approach of Formulating the Transfer Function for Dynamic Cutting Processes

The dynamics of a cutting process are very complex in nature. It involves not only the changes of plastic state in the intensive deformation zone but also the elastic behavior of work material surrounding the deformation zone, especially in the vicinity of the tool nose region. These changes are induced by the inner and outer modulations of the uncut chip thickness during the process and at the same time govern the variation of the cutting force. Based on these causal relationships, the transfer function between the vibration variables and the dynamic force components for a single degree-of-freedom machining system has been developed. The characterization of the mechanics of the cutting process by the new model provides more insight into the physics of the cutting dynamics. The model has been tested through computer simulation for both orthogonal wave-generating and wave-removing processes. By reference to existing experimental evidence, the theoretical predictions show a very good agreement with the test results.

Application of a comprehensive dynamic cutting force model to orthogonal wave-generating processes

The dynamics of a cutting process are very complex in nature. They involve not only the changes of plastic state in the intensive shear zone of the chip formation process but also the elastic behaviour of work material surrounding the plastic deformation zone, especially in the vicinity of the tool nose region. As an extension to the previous developments in formulating the shear angle oscillation in dynamic cutting (D. W. Wu, Development of dynamic shear angle model for wave-generating processes based on work-hardening slip-line field theory. Int. J. Mech. Sci. 29, 407–424, 1987; D. W. Wu, Governing equations of the shear angle oscillation in dynamic orthogonal cutting. Trans. ASME J. of Engng for Indust. 108, 280, 1986), a comprehensive dynamic cutting force model has been developed from the mechanics of the cutting process by taking into account the equilibrium of forces in the primary and secondary plastic deformation zones and the redistribution of the contact stress inside the workpiece in the vicinity of the tool nose region. The model has been tested through a computer simulation for orthogonal wave-generating processes. By reference to existing experimental evidence, the theoretical predictions show generally good agreement with the test results.

Surface characteristics of machined Inconel-718 nickel-base superalloy using natural and controlled contact length tools

The surface characteristics of machined Inconel-718 nickel-base superalloy were investigated using natural and controlled contact length tools, at various cutting speeds, and under both dry and lubricated conditions. Surface damage in the form of cavities and holes, fractured areas, and long and short straight grooves parallel to the direction of cutting was produced when machining was carried out at low cutting speeds and with tools having natural or controlled contact length, and at high cutting speeds with tools having natural contact lengths. The intensity of surface damage and total area affected decreased as the cutting speed was increased. The quality of the machined surface was drastically improved at high cutting speeds, when tools having controlled contact lengths were used. The application of lubricants was less effective for improving the surface quality. The results were interpreted in terms of the mechanics of chip formation, the interaction between the tool-nose region and freshly machined surface, and the tool forces resulting from the machining process.

An Analytical Model of Cutting Dynamics. Part 2: Verification

The dynamic force model developed in the preceding paper [1] is further examined. The analysis shows a successful prediction of the forms of stability boundary over a wide range of cutting speed. It reveals that the cutting force acting on tool rake face controls the high-speed stability, while the ploughing force acting on tool nose region dominates the low-speed stability. A series of cutting tests were carried out to examine the validity of the model. The result shows a fairly good agreement between the theoretical prediction of stability limit and the experimental determination of critical width of cut when the cutting conditions are properly chosen to avoid the presence of built-up-edge on tool tip.

Surface Integrity in Machining Solution-Treated and Aged 2024-Aluminum Alloy, Using Natural and Controlled Contact Length Tools. Part I—Unlubricated Conditions

The effects of cutting speed, chip-tool contact length and tool surface finish on the surface integrity of a solution-treated and aged 2024-Aluminum alloy, that is machined under dry, orthogonal conditions are investigated. The surface region of machined workpieces is examined using a wide variety of diagnostic techniques. In addition, tool forces are measured and both the cutting geometry and cutting temperatures are calculated. The results of the investigation show that a wide variety of geometrical surface features are generated that contribute to the natural surface roughness. The results also show that a plastically deformed surface region is generated that contains variations in hardness, microstructure and residual strain. The results of the investigation are interpreted in terms of the type of chip produced, formation of the built-up edge, the mechanics and thermodynamics of the cutting process and the interaction between the tool nose region and freshly machined workpiece surface.

State of the subsurface region in machining-solution-treated and aged 18% Ni maraging steel

The effect of cutting speed and tool wear land length on the mechanical and metallurgical state of the subsurface region of solution-treated and aged 18% Ni maraging steel machined under unlubricated and lubricated orthogonal conditions was determined. The surface region of machined test pieces was examined using optical microscopy, X-ray microprobe analysis, plastic strain analysis and microhardness measurements. Tool forces were measured. The results of the investigation show that when machining under unlubricated conditions, a very narrow (damaged) surface region is produced that is different from the bulk of the material. At low cutting speeds the damage consists of hardening associated with plastic deformation whereas at high cutting speeds the damage consists of thermal softening associated with overaging. When machining under lubricated conditions, very little surface region damage is produced. The results are interpreted in terms of the interaction between the tool nose region and freshly machined workpiece surface.

Surface damage during machining of solution treated and aged 18% nickel maraging steel I — Unlubricated conditions

The effect of cutting speed and tool wear land length on the surface damage produced during the machining of solution treated and aged 18% nickel maraging steel under dry unlubricated conditions was determined. Machined workpieces were examined with a scanning electron microscope and an optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that steady state machining can be carried out only over a very restricted range of experimental conditions where the surfaces generated show evidence only of fine scale surface damage. It is suggested that the fine scale surface damage is associated with the phenomena of continuous chip formation and of interaction between the tool nose region and freshly machined workpiece surface.

Surface damage during machining of solution treated and aged 18% nickel maraging steel II — Lubricated conditions

The effect of cutting speed and tool wear land length on the surface damage produced during machining of solution treated and aged 18% nickel maraging steel under lubricated orthogonal conditions was determined. Machined test pieces were examined with a scanning electron microscope and an optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that steady state machining can be carried out only over a restricted range of experimental conditions, where the surfaces generated show evidence only of fine scale surface damage. It is suggested that the fine scale surface damage is associated with the phenomenon of continuous chip formation and interaction between the tool nose region and the freshly machined workpiece surface. Comparisons are made between the characteristics of surfaces machined under lubricated and unlubricated conditions and few differences are found.

Surface damage during machining of annealed 18% nickel maraging steel Part 2 — Lubricated conditions

The effect of cutting speed and tool wear land length on the surface damage produced during the machining of annealed 18% nickel maraging steel under lubricated conditions was determined. Machined test pieces were examined with a scanning electron microscope and an optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that during machining fine scale surface damage in a variety of forms is produced over the range of cutting conditions used. It is suggested that the fine scale surface damage is associated with the phenomena of continuous chip formation and interaction between the tool nose region and freshly machined workpiece surface. Comparisons are made between the characteristics of surfaces machined under lubricated and unlubricated conditions. The differences are interpreted in terms of the changes produced in the frictional conditions and stress distributions at the contact surfaces between the chip, tool and workpiece by application of a lubricant. It is shown that scanning electron microscopy is more indicative of the true condition of the surface than surface roughness measurements.

Surface damage during machining of annealed 18% nickel maraging steel Part 1 — Unlubricated conditions

The effect of cutting speed and tool wear land length on the surface damage produced during the machining of annealed 18% nickel maraging steel under dry orthogonal conditions was determined. Machined test pieces were examined with a scanning electron microscope and an optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that during machining a wide variety of different forms of surface damage is generated. The machined surfaces show extended regions where both coarse and fine scale surface damage have occurred at cutting speeds up to 0.1 m s −1, whereas at cutting speeds greater than 0.1 m s −1 the surfaces show evidence only of fine scale surface damage. It is suggested that the regions of coarse scale surface damage are associated with the phenomenon of partially discontinuous chip formation and the nucleation of cracks in the vicinity of the tool nose region. Several mechanisms of crack nucleation and propagation, which are thought to account for the occurrence of many aspects of the surface topography observed, are presented and discussed. It is suggested also that the regions of fine scale surface damage are associated with the phenomenon of continuous chip formation and interaction between the tool nose region and the freshly machined workpiece surface. It is shown that scanning electron microscopy is more indicative of the true condition of the surface than surface roughness measurements.

Surface Integrity in Machining AISI 4340 Steel

The effect of cutting speed and tool wear land length on the surface integrity of quenched and tempered AISI 4340 steel machined under dry, unlubricated orthogonal conditions is determined. The surface region of machined test pieces is examined using optical microscopy, scanning electron microscopy, X-ray microprobe analysis, microhardness measurements, and profilometry. In addition, tool forces are measured and tool temperatures calculated. The results of the investigation show that during machining a damaged surface region is produced which is quite different from the bulk of the material. It is found when cutting at low speeds with sharp cutting tools that the damage is restricted to a variety of geometrical defects associated with the surface. It is found when cutting at high speeds or with tools having large artificially controlled wear lands that considerable subsurface damage involving changes in metallurgical structure and hardness is produced. The results are interpreted in terms of the type of chip produced during machining, the temperatures generated during machining, and the interaction between the tool nose region and workpiece. It is suggested that observations based on scanning electron microscopy are more indicative of the true surface condition than surface roughness measurements.

On surface damage during machining of AISI 4340 STEEL

The effect of cutting speed and wear land length on the surface damage produced during machining of quenched and tempered AISI 4340 steel under dry, orthogonal conditions was determined. Machined test pieces were examined with a scanning electron and optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that during machining considerable surface damage is produced; the intensity of which decreases with an increase in cutting speed and wear land length. It was found that the surface damage existed in a wide variety of forms which included chatter marks perpendicular to the direction of relative work-tool motion, long straight grooves parallel to the direction of work-tool motion, large cavities, workpiece debris, tool debris, plastic deformation, cracks, microcracks and voids. The results are interpreted in terms of the type of chip produced during machining and the interaction between the tool nose region and work piece. It is shown that scanning electron microscopy is more indicative of the true condition of the surface than surface roughness measurements.