Factors affecting die wear

Simple upsetting tests were used to assess the wear of hot forging dies. The influence of forging variables such as die-billet contact time and lubrication is described. A “white” layer is formed at the surface of lubricated dies when die-billet contact times exceed 5 ms. This layer was identified as martensite of increased wear resistance. Lubrication affects the frictional condition at the die-billet interface thus facilitating the relative movement of the billet material over the die surface resulting in the increased wear of flat dies.     

Factors affecting the machining accuracy of a chucked workpiece

A deviation in shape called ‘out-of-roundness’ is commonly observed in machined workpieces held by three-jaw chucks in turning operations. This out-of-roundness is due mainly to the variation in the stiffness of the workpiece-chuck-spindle system; the stiffness being higher when the cutting force is acting against a jaw and lower when acting along a jaw. This variation in stiffness of the workpiece-chuck-spindle system, termed here ‘directional orientation’, also leads to the generation of a type of parametric vibration.An attempt has been made to get rid of this effect of directional orientation by optimizing the contact between the jaw face and workpiece. Cutting tests were conducted on tapered testpeices with full contact between the jaws and the testpiece. Various contact chord lengths and spindle speeds were used. Measurements of out-of-roundness, limiting depth of cut and radial cutting force were made for analysis. Results show that where the deviation in shape of the testpiece has a three-pronged profile, and the peak at the third multiple is significant in the frequency spectrum of the radial cutting force, a contact chord length equal to the radius of the testpiece gives the optimized clamping condition.     

Monitoring tool wear during wood machining with acoustic emission

The purpose of this study was to determine the degree of change in acoustic emission (AE) during cutting as a cutter tool was worn. AE is defined as the stress or pressure waves generated during dynamic processes in materials and is generated during fracture, delamination, deformation and distortion of wood during cutting. Previous work has shown that AE is sensitive to changes in the chip formation process and therefore could be used to monitor continuously the state of the cutting process. For this study a single-point cutting tool was worn by turning a green-white fir (Abies concolor (Gord. and Glend.) Lindl.) log on an engine lathe equipped with an automatic feed. The relationship between the AE output and the amount of wood cut was close to linear in the initial stages of the blade wear. As the blade became severely worn, the AE levels dropped dramatically and an asymptotic relationship between the two variables became evident.     

Reducing electrode wear ratio using cryogenic cooling during electrical discharge machining

In this study, cooling effect of copper electrode on the die-sinking of electrical discharge machining of titanium alloy (Ti-6Al-4V) has been carried out. Investigation on the effect of cooling on electrode wear and surface roughness of the workpiece has been carried out. Design of experiment plan for rotatable central composite design of second order with four variables at five levels each has been employed to carry out the investigation. Current intensity (I), pulse on-time (t _on), pulse off-time (t _off), and gap voltage (v) were considered as the machining parameters, while electrode wear and surface roughness are the responses. Analysis of the influence of cooling on the responses has been carried out and presented in this study. It was possible to reduce electrode wear ratio up to 27% by electrode cooling. Surface roughness was also reduced while machining with electrode cooling.     

Study of wear mechanism of hard-alloy tools during machining of refractory alloys

The work “The Mechanism of Wear Process of Cobalt-Carbide” shows the result of studying cemented carbide when machining refractory alloys based on chromium (X65HBΦT) and nickel (XH77TУP). The conducted research has shown that the machining of chromium-based alloy with a more heat-resistant process of the wear of the carbide inserts with or without a nanoscale coating occurs less intensively than for the tool wear process in the machining of Ni alloy It is established that this effect is connected with different crystal structures, phase contents, and properties of the heat-resistant alloys in question.     

Features of wear of brittle inorganic materials during friction and abrasive machining

Laser confocal microscopy reveals fatigue cracking under the surface of silicate glass upon friction and abrasive machining. Surface cracking is also registered and its maximum depth is determined, indicating that its longitudinal cross section has an irregular profile. The stage of fatigue wear of the glass corresponding to debris nucleation shouldbe visualized. It is established that the mass wear rate and the maximum surface cracking depth are correlated: once a definite sliding velocity is reached, the cracking becomes deeper and the wear rate intensifies in both types of tests. The obtained results prove that several wear mechanism can occur simultaneously during abrasive machining of brittle inorganic materials, namely, brittle chipping, low-cycle fatigue, thermomechanical fracture, and local melting (under critical loading conditions).     

球面上微透镜阵列超精密慢伺服加工精度影响因素的研究

超精密慢伺服车削可加工出高精度的连续和非连续自由曲面,但是在微透镜阵列的加工过程中,不同位置的透镜加工精度也不同,个别子透镜的质量降低可能引起整个功能部件的失效。为了研究曲面上微透镜阵列超精密慢伺服加工精度的影响因素,本文采用实验的方法分析基面几何形状和子透镜位置对球面上微透镜阵列慢伺服车削加工精度的影响,通过在三种不同球径的基面上加工微透镜阵列,并使用Bruker GT-X白光干涉仪测量所加工的基面和微透镜阵列,分析了不同基面上不同位置的子镜表面粗糙度和形状精度的变化趋势。实验结果表明,同一基面上不同位置的子透镜,慢伺服车削加工表面微观形貌不同,表面粗糙度和形状精度也不同;基面的几何形状也会影响子镜的加工精度,当基面球径从50 mm增大至150 mm时,外圈子镜的表面粗糙度从75.78 nm(Ra)变小为69.08 nm(Ra)。在超精密慢伺服加工微透镜阵列过程中,必须考虑基面几何形状和子透镜位置两个因素对加工精度的影响,这将有助于提高微透镜阵列加工精度的一致性并保证微透镜阵列功能的有效性。     

Performance enhancement of cryogenic machining and its effect on tool wear during turning of Al-Ticp composites

The current research is to focus on developing a liquid nitrogen diffusion system to optimize the usage of liquid nitrogen and maximizing cooling and lubrication capability by effective penetration. An atomized liquid nitrogen spray system was developed to diffuse liquid nitrogen effectively at a low flow rate (10–12 L/h) and as a high velocity (8–50 m/s) droplet jet to the machining zone. Using coated carbide tool with varying tool geometry (rake angle, approach angle, and nose radius), an investigation was performed to study the role of atomized liquid nitrogen spray-assisted machining, on performance of tool and surface quality of the machined workpiece during turning of Al-TiCp composite. To analyze the performance of liquid nitrogen spray-assisted machining, various experiments were conducted. The results obtained from the experiments reveal that the effective use of atomized liquid nitrogen spray machining is a feasible alternative to dry, wet, and cryogenically chilled argon gas. This technique significantly reduces heat generation in machining zone. The study also emphasizes the influence of tool geometry on the machinability of Al-TiCp metal matrix composites.     

Cutting force and diamond tool wear in stone machining

Stone machining by diamond tool is a widespread process to manufacture both standard products, such as tiles, slabs, kerbs, and so on, and design shapes. Cutting force and energy may be used to monitor stone machining. Empirical models are required to guide the selection of cutting conditions. In this paper, the effects of cutting conditions on cutting force and cutting energy are related to the shape of the idealized chip thickness. These effects are put into relationship with the diamond tool wear too. The empirical models developed in this paper can be used to predict the variation of the cutting energy. Therefore these models can be used to guide the selection of cutting conditions and to predict when it is needed to change the tool. The chip generation and removal process has been quantified with the intention of assisting both the toolmaker and the stonemason in optimizing the tool composition and cutting process parameters, respectively.     

Dimensional analysis of tool wear in electrical discharge machining

The erosion phenomenon was analysed by dimensional analysis. An empirical equation was obtained which relates the volume of material eroded from the tool electrode to the energy of the pulse, density, thermal conductivity, specific heat and latent heat of vaporization of the electrode material.     

Parametric tool wear estimation solution of HSC appropriate machining

New strategies are used in manufacturing enterprises due to global competition. High-speed cutting offers a very appropriate opportunity to reduce run times since the high cutting speeds and feed rates involved permit the reduction of production times and minimise rework. There are, however, difficulties in judging tool wear [1]. This paper analyses the formation mechanism of tool wear and presents a complete solution to calculate wear using a ball end cutter for high-speed cutting. Chip geometry generated to calculate tool wear is affected by machining conditions such as turning speed, cutting depth and geometries of tool and work piece which in turn determine the key parameters of chip sections such as length of cut and mean chip thickness. An improved algorithm and a knowledge-based decision model developed to calculate effective tool contact are also discussed to help reduce calculation time and improve calculation efficiency. The calculation results include output form and a 3D wear model showing wear data distributed on the tool contour.     

Electrical discharge when machining medium-density fibreboard and tool wear

Electrical potentials between the workpiece and cutting tool have been shown to be generated when cutting green and dry wood. The voltages have been reported as relatively constant. A series of turning tests on medium-density fibreboard (MDF) were undertaken to characterize the electrical potentials in wood machining. The results indicated numerous discharges generally from the MDF-workpiece (cathode) to the tool (anode). However, both voltage and current reversals or discharges occurred from the tool to the MDF-workpiece. The reversals occurred simultaneously with electrostatic discharges within the MDF-workpiece. The possibility of an electric discharge machining effect on tool wear is also discussed. These electrical discharge characteristics from wood machining could provide insight for the wear mechanisms for dry wood and wood products as well as for other dielectric materials.     

Experimental investigation of tool wear and machining rate in rotary ultrasonic machining of nickel alloy

Nickel alloys possess the excellent potential at high temperature and resistance to oxidation/corrosion owing to its high nickel content. These materials necessitate non-traditional machining methods. The rotary ultrasonic machining (RUM) process comes into existence as a superior alternative to the conventional machining of nickel alloys. The processing of these alloys using RUM needs attention. This article details the multi-response optimization in RUM of nickel alloy using the desirability concept. The present work is carried out with two shapes of the tool: (i) Plain tool and (ii) lateral slotted tool. During RUM, the process parameters—power rating tool rotation, abrasive diamond grit size and feed rate are varied. Compared with the plain tool, the lateral slotted tool shows the more efficient machining rate (MR) with less tool wear (TW). The micro-graphs disclose the mechanism of MR and TW during RUM.     

Tool wear and tool thermal expansion during micro-machining by spark assisted chemical engraving

Gravity-feed micro-hole machining using spark assisted chemical engraving (SACE) has achieved repeatable hole drilling up to few hundred microns in depth. However, the tool wear and tool thermal expansion were not included in these measurements. In this paper, quantitative results are presented for the tool wear and tool expansion for three tool electrode materials: tungsten, steel and stainless steel. A simplified lumped thermal model predicting tool expansion and its dynamics is presented. It is as well demonstrated how the tool electrode temperature can be controlled by pulsed voltage supply. These results will enable higher measurement accuracy and therefore more precise micro-machining by SACE.     

Modelling the effect of flank wear on machining thrust stability

This paper discusses an analytical assessment of the effect of cutting tool flank wear on machining stability along the thrust direction in a turning operation based on an analysis of frequency band root-mean-square (RMS) level of the accelerometer signals. The energy content of machining at the tool-tip/workpiece interface along the flank is represented by the RMS signal level, in comparison to the random vibration of the cantilever portion of the tool holder. The RMS signals measured from a tool-post accelerometer in stable machining with tool wear effect are calculated using the frequency band RMS method at the first natural frequency of the cantilever portion of the tool holder. Increasing flank wear results in increasing stability and decreasing RMS in the thrust direction in machining. For model validation, a series of machining experiments were performed under the condition of various flank wear/land widths, while the RMS signals from a tool-post accelerometer were collected and studied. It was found that theoretical predictions were shown to be in agreement with experimental results.     

Influence of thermal conductivity on wear when machining titanium alloys

We study failure of coated carbide tools due to thermal loading. The study emphasizes the role of thermo-physical properties of the tool material in enhancing wear resistance of the tool. We show that heat conduction in the tool active zone is a function of the so called thermodynamic forces. Due to coupling between thermal and mechanical states within the active volume of the tool material, three distinct thermal zones evolve. The first, which is located on the rake face close to the primary shear zone, exhibits a severe drop in its ability of thermal conduction. The second zone, located at the tool tip is characterized by a predominant thermo mechanically induced conduction anisotropy. The anisotropic behaviour, forces heat to partially flow toward the thermally dead zone whence contributing to the intense thermal energy accumulation within the affected material volume. The third zone is one where the thermally triggered degradation of conduction takes place. Heat flow, in light of the existence of these zones, evolves such that, the tip of the tool will be almost thermally congested. The congestion is thought to be the mechanism that renders the energy needed to activate wear mechanisms available.