Anhai Li

Cutting forces and tool failure in high-speed milling of titanium alloy TC21 with coated carbide tools

TC21 alloy is a new alpha–beta damage tolerance titanium alloy with high strength and high toughness. Little work has been done in the field of machinability analysis since this alloy was developed. The cutting forces and tool wear in high-speed milling of TC21 alloy with physical vapor deposition ((Ti, Al)N-TiN)-coated carbide tools under different cutting conditions were investigated in this article. The results showed that the cutting force component F x was more dominant of the three components, and the cutting forces presented an increasing trend with the tool wear progress, which in turn deteriorated the cutting condition and accelerated the tool failure progress. The major tool wear modes in high-speed side-milling TC21 alloy with coated carbide were adhesion and chipping on the rake face along with chipping and transverse crack on the flank face. Moreover, there was obvious nose depression from both the rake face and the flank face. Chipping along the flank and rake faces was identified as the main factor responsible for the failure of the coated carbide tools during the milling of titanium alloy TC21.

Experimental Study on Cutting Forces and Surface Integrity in High-Speed Side Milling of Ti-6Al-4V Titanium Alloy

This article is concerned with the cutting forces and surface integrity in high-speed side milling of Ti-6Al-4V titanium alloy. The experiments were conducted with coated carbide cutting tools under dry cutting conditions. The effects of cutting parameters on the cutting forces, tool wear and surface integrity (including surface roughness, microhardness and microstructure beneath the machined surface) were investigated. The velocity effects are focused on in the present study. The experimental results show that the cutting forces in three directions increase with cutting speed, feed per tooth and depth of cut (DoC). The widths of flank wear VB increases rapidly with the increasing cutting speed. The surface roughness initially decreases and presents a minimum value at the cutting speed 200 m/min, and then increases with the cutting speed. The microstructure beneath the machined surfaces had minimal or no obvious plastic deformation under the present milling conditions. Work hardening leads to an increment in micro-hardness on the top surface. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. The results indicated that the cutting speed 200 m/min could be considered as a critical value at which both relatively low cutting forces and improved surface quality can be obtained.

Research on the machined surface integrity under combination of various inclination angles in multi-axis ball end milling:

It is well known that the multi-axis machining technology has been developed into a key technique applied in the manufacturing field. The machined surface integrity is one of the most important factors influencing the performance of the produced components. Hence, this research concentrated on the machined surface integrity induced by the multi-axis milling operation with different inclination angle combinations. In this research work, the cutting conditions of the conventional or up-milling process with tool orientations were divided into eight different types, and the machining characteristics corresponding to different cutting strategies were discussed. The varying conditions of surface topography, texture and other machining features induced in machining process which corresponds to different inclination angle combinations were analyzed by geometrical analysis, and the surface roughness and linear profile along specific directions on the machined surface were also investigated. There is a special corresponding relationship between the rotation angle and tool tilt and lead angles. Better surface roughness could be achieved when rotation angles are 0° (positive lead), 60° (combination of positive tilt and positive lead), 90° (positive tilt) and 330° (combination of negative tilt and positive lead). Then, the samples used for study of the metamorphic layer were produced by lapping and polishing process, and the macro hardness (HL) and micro-hardness (HV) of the top machined surface were investigated. According to the measured results of both Leeb hardness and micro-hardness, higher surface hardness could be obtained under rotation angles of 60° (combination of positive tilt and positive lead), 120° (combination of positive tilt and negative lead) and 210° (negative tilt and negative lead). Moreover, the variations of the micro-hardness along the depth direction of the samples were studied. Finally, discussions on the machined surface residual stresses in both feed and cross-feed direction were carried out. Compressive surface residual stress in both feed and cross-feed direction could be generated when rotation angles are 210° (combination of negative tilt angle with smaller value and negative lead angle with larger value) and 330° (combination of negative tilt angle with smaller value and positive lead angle with larger value). Generally, the evaluation indicators of surface integrity are not all very satisfying under one special cutting condition with a certain inclination angle combination, and the optimal cutting parameters should be selected based on the specific application requirements. Finally, the optimal tool orientations and related cutting parameters were recommended, and further studies of the related topics were also presented.

A comparison between whisker-reinforced alumina and SiAlON ceramic tools in high-speed face milling of Inconel 718

This study makes a comparison between whisker-reinforced alumina and SiAlON ceramic tools in high-speed face milling of Inconel 718. A series of tests have been conducted, and the cutting forces, tool wear morphologies and tool failure mechanisms are discussed with regard to a wide range of cutting speeds (500–3000 m/min). Results show that the resultant cutting force of SiAlON ceramic tool KY1540 is much bigger than that of whisker-reinforced alumina ceramic tool KY4300 at the same cutting condition. For both kinds of tools, under relatively lower cutting speed, nose notch wear is the predominant failure mode affecting the tool life, while further increase in the cutting speed, notch wear at the depth of cut becomes the determining factor. KY1540 shows a better notch wear and thermal shock resistance than KY4300. The tool failure mechanisms involve notching, microcracks, chipping, flaking, adhesion and oxidation wear. Better surface quality can be got using KY4300 ceramic tools.

Three-dimensional finite element modeling of high-speed end milling operations of Ti-6Al-4V

This article presents the development of a three-dimensional finite element model to simulate the high-speed end milling of Ti-6Al-4V titanium alloy based on the commercial finite element package Abaqus/Explicit. The Johnson–Cook material constitutive model was employed to model the flow stress behavior of the workpiece. Zorev’s friction model was used to determine the frictional behavior of the tool–chip interface, and Johnson–Cook shear failure criterion was used to realize chip separation. Based on the three-dimensional finite element model, cutting forces in three directions were predicted under different cutting conditions, and chip evolution and morphologies of different cutting parameters were also analyzed. Corresponding high-speed end milling tests were conducted, and cutting forces were measured using a piezoelectric dynamometer in order to validate the finite element model. The simulation results demonstrate an acceptable agreement with experimental results in both the chip morphologies and cutting forces in the range of cutting speed and feed rates considered.

SURFACE INTEGRITY OF HIGH-SPEED FACE MILLED Ti-6Al-4V ALLOY WITH PCD TOOLS

This study is focused on the machined surface integrity of Ti-6Al-4V alloy using polycrystalline diamond (PCD) tools under wet milling condition. The surface integrity in terms of surface roughness, surface topography, microhardness, microstructure, and metallurgical alternations is investigated. The observations and conclusions are primarily focused on the effect of cutting speed (250–2,000 m/min) on the surface and subsurface of the machined Ti-6Al-4V. Experimental results show that machined surface integrity of Ti-6Al-4V alloy is sensitive to the variation of cutting speeds. Obvious machining (feed) marks can be found on the machined surfaces. Micro hardness examinations showed 5–20% hardening of the top machined surfaces than the bulk material. The analyses of microstructure and metallurgical alternations reveal that slight subsurface microstructure alteration such as plastic deformation on the subsurface and no phase transformation were observed. The evolution of crystallographic texture induced by the intense plastic deformation of the machined surface should be responsible for the modifications of the peak intensity radios in XRD patterns as well as higher peak broadening crystal structures.

Effect of cutting speed on chip formation and wear mechanisms of coated carbide tools when ultra-high-speed face milling titanium alloy Ti-6Al-4V:

Chip morphology and its formation mechanisms, cutting force, cutting power, specific cutting energy, tool wear, and tool wear mechanisms at different cutting speeds of 100–3000 m/min during dry face milling of Ti-6Al-4V alloy using physical vapor deposition-(Ti,Al)N-TiN-coated cemented carbide tools were investigated. The cutting speed was linked to the chip formation process and tool failure mechanisms of the coated cemented cutting tools. Results revealed that the machined chips exhibited clear saw-tooth profile and were almost segmented at high cutting speeds, and apparent degree of saw-tooth chip morphology occurred as cutting speed increased. Abrasion in the flank face, the adhered chips on the wear surface, and even melt chips were the most typical wear forms. Complex and synergistic interactions among abrasive wear, coating delamination, adhesive wear, oxidation wear, and thermal mechanical–mechanical impacts were the main wear or failure mechanisms. As the cutting speed was very high (>2000 m/min), discontinuous or fragment chips and even melt chips were produced, but few chips can be collected because the chips easily burned under the extremely high cutting temperature. Large area flaking, extreme abrasion, and serious adhesion dominated the wear patterns, and the tool wear mechanisms were the interaction of thermal wear and mechanical wear or failure under the ultra-high frequency and strong impact thermo-mechanical loads.

Wear Mechanism Analysis of Coated Carbide Tools in High-Speed Milling of Ti-6Al-4V Alloy via Cross-Section Characterization of Worn Cutting Edge

Tool wear analysis is essential in high speed machining, especially in the intermittent cutting and milling processes. Analyses of tool wear mechanisms will be beneficial for proposing the suggestions in the tool design process how to enhance the tool material properties to improve the cutting performance and eventually tool life. Wear mechanisms of coated carbide tools in high-speed dry milling of Ti-6A1-4V were assessed by characterization of the cross-section of worn tool cutting edge utilizing scanning electron microscopy, and the element distribution of the worn tool surface was detected by using energy dispersive spectroscopy. Results show that flank wear, chipping and flaking of tool material on the rake face and/or at the nose of tools were the dominant failure modes. And synergistic interaction among coating delamination, erosion wear, adhesion, dissolution-diffusion wear, and thermal-mechanical fatigue wear were the main wear mechanisms analyzed from cross-sectional worn cutting edge. Erosion wear was identified in high speed milling of Titanium alloy and introduced into the wear mechanisms of metal cutting tools. The hydromechanics characteristic of the chips produced in high-speed machining should be responsible for erosion wear of cuttings tools.Copyright

Machined surface roughness and chip morphology in high speed side milling of inconel 718

Nickel-based Superalloy Inconel 718 is a difficult-to-machine material wide used in hot sections of gas turbine engines in aerospace industry. In this study, machined surface roughness of the machined surface in high speed side milling of Inconel 718 using a solid carbide end mill was investigated experimentally for a wide range of cutting conditions, and chip morphology during dry milling of Inconel 718 has been examined under different cutting speeds using scanning electron microscope (SEM). The experimental results have shown that the milled surface shows good surface quality with the range of surface roughness values in the feed directions from 0.05 to 0.3μm. Surface roughness value decreases with the increase of cutting speed in the range of 40–100 m/min, but has much less variation in the feed and depth-of-cut (DoC) range. In addition, the degree of chip serration increased with the increase in cutting speed.