AN EXPERIMENTAL STUDY OF ORTHOGONAL MACHINING OF GLASS

An experimental study of machining glass with a geometrically defined cutting tool is presented. Orthogonal cutting conditions are employed to permit a focus on the fundamental modes of chip and surface formation. Analysis of the machined surfaces under an optical microscope identifies four regimes that are distinctly different with respect to either chip formation or surface formation. For a very small target uncut chip thickness, one on the order of the cutting edge radius, pure rubbing of the edge with no chip formation is observed. Edge rubbing imparts light scuffmarks on the machined surface giving it a frosted appearance. At a larger uncut chip thickness, ductile-mode chip formation occurs ahead of the cutting edge and a scuffed surface remains after the subsequent rubbing of the edge across the freshly machined surface. A further increase in uncut chip thickness maintains a ductile-mode of chip formation, but surface damage initiates in the form of surface cracks that grow down into the machined surface and ahead of the tool. The transition to this machining mode is highly dependent on rake angle. Increasing the uncut chip thickness further causes brittle spalling of chips leaving half-clamshell shaped divots on the surface. This experimental identification of the machining modes and their dependence on uncut chip thickness and rake angle supports the use of geometrically defined cutting tools to machine glass in a rough-semi-finish-finish machining strategy as is traditionally employed for machining metals.     

AN EXPERIMENTAL STUDY OF ORTHOGONAL MACHINING OF GLASS

Abstract

An experimental study of machining glass with a geometrically defined cutting tool is presented. Orthogonal cutting conditions are employed to permit a focus on the fundamental modes of chip and surface formation. Analysis of the machined surfaces under an optical microscope identifies four regimes that are distinctly different with respect to either chip formation or surface formation. For a very small target uncut chip thickness, one on the order of the cutting edge radius, pure rubbing of the edge with no chip formation is observed. Edge rubbing imparts light scuffmarks on the machined surface giving it a frosted appearance. At a larger uncut chip thickness, ductile-mode chip formation occurs ahead of the cutting edge and a scuffed surface remains after the subsequent rubbing of the edge across the freshly machined surface. A further increase in uncut chip thickness maintains a ductile-mode of chip formation, but surface damage initiates in the form of surface cracks that grow down into the machined surface and ahead of the tool. The transition to this machining mode is highly dependent on rake angle. Increasing the uncut chip thickness further causes brittle spalling of chips leaving half-clamshell shaped divots on the surface. This experimental identification of the machining modes and their dependence on uncut chip thickness and rake angle supports the use of geometrically defined cutting tools to machine glass in a rough-semi-finish-finish machining strategy as is traditionally employed for machining metals.     

A study on the effect of tool-edge radius on critical machining characteristics in ultra-precision milling of tungsten carbide

A crack-free surface can be finished on brittle materials by a specialized but traditional machining technique known as ductile-mode machining. In ductile-mode machining of brittle material, crack propagation is suppressed by selecting a suitable combination of tool and machining parameters leading to the removal of material through plastic deformation enabled by dislocation motion. In ductile-mode machining, the tool–workpiece interaction is of critical significance for the capability of the cutting process to finish a crack-free surface on a brittle material. This interaction is largely dictated by the cutting-edge radius of the tool when the undeformed chip thickness is comparable to the edge radius as is the case of ductile-mode machining. This paper presents the experimental results of ductile-mode milling of tungsten carbide to investigate the effect of cutting-edge radius on certain critical machining characteristics associated with the ductile–brittle transition specific to milling process of brittle material. The experimental results have established that an increase in the cutting-edge radius within a certain range increases the critical feed per edge leading to the improvement of material removal rate in ductile-mode milling. An increasingly negative effective rake angle is desired during milling with larger edge-radiused tool to suppress the crack propagation in the cutting zone to achieve ductile-mode machining. The results also identify the effect of the edge radius on certain other parameters such as critical specific cutting energy, plowing effect and subsurface damage depth to comprehend the ductile–brittle transition phenomenon in ductile-mode milling.     

An experimental approach to study the capability of end-milling for microcutting of glass

Glass is a hard and brittle material. It is finding mounting quantum of applications in semiconductor, opto-electronics, and mold manufacturing sectors. However, glass is not amenable to machining because of its low fracture toughness. If machined with conventional approach, the mechanism of material removal in machining of glass is fracture based that results into poor quality of the machined surface and imparts subsurface damage. In order to achieve superior surface finish, glass must be machined in ductile mode. Ductile-mode machining is now a well-established technique but most of the work has been performed with single-point cutting processes. To assess the capability of ductile-mode machining with multipoint cutting process, fundamental studies are highly desired. This paper reports the results of an experimental investigation into ductile-mode machining of glass by milling process. Side-milling tests have been performed on the glass workpiece to identify the key parameters governing the ductile-brittle transition mechanism. Experimental results demonstrate that fracture-free surface can be machined on glass by milling process. Cutting forces were analyzed to comprehend the dynamic behavior of the cutting process in ductile mode.     

Specific cutting force, tool wear and chip morphology characteristics during dry drilling of austempered ductile iron (ADI)

Dry machining is being recognized as ecological machining due to its less environmental impact and manufacturing cost. However, the choice of dry machining is mainly influenced by the workpiece material properties, machining operation and cutting conditions. The recent emergence of austempered ductile iron (ADI) can be considered a significant economic advantage to the increasing industrial demand for cost- and weight-efficient materials. However, due to its microstructure-induced inherent properties, ADI is considered hard-to-machine material. Thus, the dry drilling of ADI is investigated in this paper. The ADI material used in the present study is produced using an innovative process route for near net shape casting production. Drilling experiments are conducted on a DMU80P Deckel Maho five-axis machining centre using PVD-coated carbide tools under dry cutting environment. The dry drilling of ADI under different cutting conditions is evaluated in terms of specific cutting force and tool wear analysis. The influence of cutting conditions on chip morphology and surface roughness is also investigated. The experimental results revealed that the combination of the low feed rate and higher cutting speed leads to the higher mechanical and thermal loads on the tool's cutting edge, resulting in higher specific cutting force values. This behaviour is further supported by the chip morphology analysis, which revealed the formation of segmented chips at higher cutting speed with segment spacing increase with an increase in feed rate. Depending upon the cutting parameters, different modes of tool failures including crater wear, flank wear, chipping, breakage and built-up edge were observed. Surface roughness analysis revealed the influence of tool wear and chip morphology on the machined surface finish.     

Measurement and analysis of thrust force in drilling of particle board (PB) composite panels

Particleboard is a wood based composite extensively used in wood working. Drilling is the most commonly used machining process in furniture industries. The surface characteristics and the damage free drilling are significantly influenced by the machining parameters. The thrust force developed during drilling play a major role in gaining the surface quality and minimizing the delamination tendency. The objective of this study is to measure and analyze the cutting conditions which influences the thrust force in drilling of particle board panels. The parameters considered are spindle speed, feed rate and point angle. The drilling experiments are performed based on Taguchi’s design of experiments and a response surface methodology (RSM) based mathematical model is developed to predict the influence of cutting parameters on thrust force. The results showed that high spindle speed with low feed rate combination minimizes the thrust force in drilling of pre-laminated particle board (PB) panels.     

Understanding and Characterizing the Drilling of Recycled Plastics

Recycled plastics are increasingly being used to manufacture planks used in large-volume applications, including decks, garden, and cloakroom chairs. These products, although manufactured near-to-net shape, often require drilling for assembly purposes. There are very limited data on the machining of plastic material. Manufacturers often rely on data and models established for metals. The machining of plastics, although limited to assembly purposes, or to the removal of excess materials, requires an understanding of the behavior of these materials during the machining in order to obtain better quality parts. It is even more important for recycled plastics, which are inhomogeneous, contain pores, and most often, are made with more than one type of product. This work analyzes the machining of recycled plastics in order to establish and compare their machining models with those traditionally used for metals, and to better understand the behavior of the plastics during machining. The workpiece is drilled at different process conditions and at different temperatures. The process performance indicators such as cutting forces, chip formation, and chip form are analyzed. The originality of this work resides in its study of chip formation and the effects of the preset workpiece temperature on the drilling mechanisms. It is found that there is a range of critical temperatures of transition for plastics similar to the Charpy impact ductile-brittle temperature separating the domain of low cutting force and long and spiral chip from that of high cutting force corresponding to the accordion-type of chip. A parameter describing this phenomenon is defined. It is also found that for low- to moderate-speed operations, the cutting speed has very little effect on the cutting forces, which depend mainly on the feed rate and the workpiece temperature. The relationship between the drilling forces and the feed rate established for metals remain valid, but the exponent of the feed rate for the thrust force is lower. The thrust force and the tangential force are proportional to the feed rate exponent 0.4 compared to 0.8 for metals when drilling workpiece at room temperature or below.     

The investigation of mechanism of serrated chip formation under different cutting speeds

Chip type is determined by the coupled effects of workpiece material property, cutting speed, uncut chip thickness, feed rate, and tool edge geometry. The understanding of chip formation plays a critical role in studying surface integrity and optimization of machining process variables. Serrated chip, one of the major important chip type, is usually formed in hard cutting at high speed. In this study, a new analytical model has been proposed to better understand the formation of serrated chip, and the simulations have been acquired using ABAQUS/Explicit in machining AISI 1045 during different speeds (from 60 to 6000 m/min). The workpiece material property is modeled with the Johnson-Cook model, and the experiments have been conducted with AISI 1045 during speeds from 60 to 1200 m/min. It has been shown that flow stress is influenced simultaneously by the strain rate hardening and temperature softening. When the speed reaches very high, the temperature softening will fail, and the strain rate hardening will play a more important role. Also, it can be found that the hardening ratio increases when the cutting speed rises. The results of the simulations and experiments correlated well. The cutting force and thrust force both decrease as the cutting speed increases, and the difference between them will shrink when the machining speed reaches a high level.     

MACHINING OF CORTICAL BONE: SIMULATIONS OF CHIP FORMATION MECHANICS USING METAL MACHINING MODELS

This paper investigates chip formation in the machining of cortical bone and the application of isotropic elastic-plastic material models with a pressure dependent yield stress and a strain path dependent failure strain law to finite element calculations to predict observed behaviour. It is shown that a range of models can be created that result in segmented chip formations and a range of specific cutting forces similar to those observed experimentally. Results from the simulations provide an explanation for differences in the ratio of thrust to cutting forces observed between previous experimental studies, namely that the cutting tools used may have had different edge sharpness or degree of damage induced by the material removal process. Measurements of edge profiles from one of these studies support that explanation and emphasize the importance of tool toughness in maintaining efficient cutting of bone.     

THE ELECTRICAL DISCHARGE MACHINING (EDM) HANDBOOK

Abstract

Recycled plastics are increasingly being used to manufacture planks used in large-volume applications, including decks, garden, and cloakroom chairs. These products, although manufactured near-to-net shape, often require drilling for assembly purposes. There are very limited data on the machining of plastic material. Manufacturers often rely on data and models established for metals. The machining of plastics, although limited to assembly purposes, or to the removal of excess materials, requires an understanding of the behavior of these materials during the machining in order to obtain better quality parts. It is even more important for recycled plastics, which are inhomogeneous, contain pores, and most often, are made with more than one type of product. This work analyzes the machining of recycled plastics in order to establish and compare their machining models with those traditionally used for metals, and to better understand the behavior of the plastics during machining. The workpiece is drilled at different process conditions and at different temperatures. The process performance indicators such as cutting forces, chip formation, and chip form are analyzed. The originality of this work resides in its study of chip formation and the effects of the preset workpiece temperature on the drilling mechanisms. It is found that there is a range of critical temperatures of transition for plastics similar to the Charpy impact ductile-brittle temperature separating the domain of low cutting force and long and spiral chip from that of high cutting force corresponding to the accordion-type of chip. A parameter describing this phenomenon is defined. It is also found that for low- to moderate-speed operations, the cutting speed has very little effect on the cutting forces, which depend mainly on the feed rate and the workpiece temperature. The relationship between the drilling forces and the feed rate established for metals remain valid, but the exponent of the feed rate for the thrust force is lower. The thrust force and the tangential force are proportional to the feed rate exponent 0.4 compared to 0.8 for metals when drilling workpiece at room temperature or below.     

Auto-tracking single point diamond cutting on non-planar brittle material substrates by a high-rigidity force controlled fast tool servo

This paper presents auto-tracking single point diamond cutting, which can conduct precision cutting on non-planar brittle material substrates without prior knowledge of their surface forms, by utilizing a force controlled fast tool servo (FTS). Differing from traditional force feedback control machining based on a cantilever mechanism such as an atomic force microscope (AFM) that suffers from low-rigidity and limited machining area, the force controlled FTS utilizes a highly-rigid piezoelectric-type force sensor integrated with a tool holder of the FTS system to provide sufficient stiffness and robustness for force-controlled cutting of brittle materials. It is also possible for the system to be integrated with machine tools to deal with the difficulties in the cutting of large area non-planar brittle materials, which requires not only high machining efficiency but also a high stiffness. Experimental setup is developed by integrating the force controlled FTS to a four-axis ultra-precision diamond turning machine. For the verification of the feasibility and effectiveness of the proposed cutting strategy and system, auto-tracking diamond cutting of micro-grooves is conducted on an inclined silicon substrate and a convex BK7 glass lens, while realizing constant depths of cuts under controlled thrust forces.     

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.     

Prediction of cutting forces and machining error in ball end milling of curved surfaces -I theoretical analysis

This paper presents a theoretical model by which cutting forces and machining error in ball end milling of curved surfaces can be predicted. The actual trochoidal paths of the cutting edges are considered in the evaluation of the chip geometry. The cutting forces are evaluated based on the theory of oblique cutting. The machining errors resulting from force induced tool deflections are calculated at various parts of the machined surface. The influences of various cutting conditions, cutting styles and cutting modes on cutting forces and machining error are investigated. The results of this study show that in contouring, the cutting force component which influences the machining error decreases with increase in milling position angle; while in ramping, the two force components which influence machining error are hardly affected by the milling position angle. It is further seen that in contouring, down cross-feed yields higher accuracy than up cross-feed, while in ramping, right cross-feed yields higher accuracy than left cross-feed. The machining error generally decreases with increase in milling position angle.     

Effect of Chilled Air on Machining Performance in End Milling

Flood coolant is customarily used to increase tool life and to improve workpiece surface finish in machining. It is also responsible for some adverse effects on the environment and users’ health, and hence the interest in chilled air assisted machining as an alternative to flood coolant. The effect of chilled air on machining performance was carried out using an end-milling operation on ASSAB 718HH mould steel using uncoated tungsten carbide inserts at different depths of cut, feedrates and cutting speeds under three different lubrication modes, i.e. chilled air, conventional coolant, and dry cutting. The relative performance of these modes is evaluated in terms of tool wear, surface finish, cutting force, and quality of the chips. Lower tool wear was observed using chilled air compared to that for the conventional flood coolant at a lower depth of cut, lower feedrate and lower cutting speed. The surface roughness was found to reduce at higher depths of cut, higher feedrates and higher cutting speeds for chilled air as compared to dry cutting and flood coolant. It is also observed that the cutting force experienced with chilled air is comparable and, in many cases, lower than that when using flood coolant. Stress lines on the chip surfaces show that the chips experienced the highest shear stress in dry cutting, followed by cutting with chilled air and lastly, with flood coolant.     

高速铣削淬硬钢时切削载荷平稳化研究

和传统的铣削加工相比,高速铣削淬硬钢更需要稳定的切削载荷,以尽可能减少刀具碎裂和过度磨损。本研究借助三向压电石英测力仪,使用TiAlN涂层球形端铣刀,在13500 r/min的转速下,对淬火45#钢(47HRC~48HRC)进行了高速铣削试验,建立了高速铣削下的多项式切削力试验模型,模拟了以恒定切削力为目标、优化进给率的加工实例。结果显示,稳定的切削载荷能有效地提高加工效率,避免刀具剧烈磨损。     

Study on mechanism of chip formation during high-speed milling of alloy cast iron

By adopting an equivalent geometry model of chip, a finite element model was developed to study the mechanism of chip formation during high-speed milling of alloy cast iron. Several key technologies such as material constitutive model, friction model, chip separation criteria, chip damage criteria, heat dissipation, and transfer were implemented to improve the accuracy of finite element simulation. Saw-tooth chip of alloy cast iron was observed. The chip shape and cutting force agreed well with experimental results. The simulation results show that the maximum cutting temperature produced with appearance of saw-tooth chip crack, and it is located on the chip-tool contact surface. The saw-tooth chip is caused by double actions of thermoplastic instability and plastic instability. The chip saw-tooth degree decreases when increasing the rotating speed, while it increases when increasing the feed speed. This work provides a useful understanding for chip formation process and helps to optimize machining parameters and process of high-speed milling of alloy cast iron.     

钛合金旋转超声辅助钻削的钻削力和切屑研究

针对难加工材料钛合金在采用普通麻花钻传统钻削过程中存在钻削力和扭矩较大使得钻孔困难,刀具使用寿命低,连续长切屑易缠绕刀具、划伤孔加工表面、增大刀具-切屑-工件孔壁之间的摩擦以及排屑差引起堵屑和卡刀具的问题,引入一种新刃型刀具（即八面钻）,并结合超声振动钻削技术,进行了钛合金旋转超声辅助钻削试验。分析了旋转超声辅助钻削和普通钻削中切屑形成原理,采用文中所设计的旋转超声振动钻削主轴结合BV100立式加工中心平台、测力系统和非接触激光测量系统进行了无冷却条件下基于八面钻的钛合金旋转超声辅助钻削和普通钻削试验以及钻削力、扭矩和切屑形态的研究。试验结果表明：相比于普通钻削,超声钻削明显降低钻削力和扭矩分别为19.07%~20.09%和31.66%~34.3%,明显增强了钻头横刃和主切削刃的切削能力,获得了良好的断屑和排屑效果,提高了切削过程的稳定性,能够极大改善钛合金钻孔过程钻削困难、刀具使用寿命低和孔加工质量差的问题。     

MOLECULAR DYNAMICS SIMULATION OF NANOMETRIC CUTTING

Molecular Dynamics (MD) simulations of nanometric cutting of single-crystal copper were conducted to predict cutting forces and investigate the mechanism of chip formation at the nano-level. The MD simulations were conducted at a conventional cutting speed of 5 m/s and different depths of cut (0.724–2.172 nm), and cutting forces and shear angle were predicted. The effect of tool rake angles and depths of cut on the mechanism of chip formation was investigated. Tools with different rake angles, namely 0°, 5°, 10°, 15°, 30°, and 45°, were used. It was found that the cutting force, thrust force, and the ratio of the thrust force to cutting force decrease with increasing rake angle. However, the ratio of the thrust force to the cutting force is found to be independent of the depth of cut. In addition, the chip thickness was found to decrease with an increase in rake angle. As a consequence, the cutting ratio and the shear angle increase as the rake angle increases. The dislocation and subsurface deformation in the workpiece material were observed in the cutting region near the tool rake face. The adhesion of copper atoms to the diamond tool was clearly seen. The same approach can be used to simulate micromachining by significantly increasing the number of atoms in the MD model to represent cutting depths in the order of microns.     

EFFECT OF PROCESS PARAMETERS AND TOOL SHAPE ON THE MACHINABILITY OF A PARTICULATE FILLED-POLYMER COMPOSITE MATERIAL FOR RAPID TOOLING

This paper presents the results of an experimental study on the effects of machining parameters (cutting speed, feed, depth of cut) and tool shape on chip formation, surface topography, resultant cutting force and surface roughness produced in flat and ball end milling of the Ren Shape-Express 2000™ aluminum particulate filled-polymer composite material. This material is shown to exhibit a brittle-to-ductile transition in chip formation with decreasing cutting speed. The transition is explained by the strain-rate sensitivity of the polymer matrix and is found to correlate well with a corresponding change in the surface roughness. The absence of clear feed marks on the milled surface explains why molds made from the composite material require less hand polishing than machined metal molds. The influence of cutting conditions and tool shape (flat end vs. ball-nose) on the cutting force, surface roughness, and workpiece breakout are discussed and relevant comparisons with conventional metal and polymer machining are made.     

液氮低温切削钛合金实验研究

针对钛合金难加工特点,将液氮作为冷却介质直接喷向切削区进行钛合金TC4低温车削加工,测量其切削力、表面粗糙度和刀具磨损,并与干切削在相同实验条件下对比,分析低温切削对钛合金的影响。实验结果表明:低温切削钛合金,主切削力有所增大,但进给方向力减小,刀具磨损状况与表面质量得到改善,断屑相对容易。