Experimental investigation of turning AISI 1045 steel using cryogenic carbon dioxide as the cutting fluid

The intensive temperatures in high speed machining not only limit the tool life but also impair the machined surface by inducing tensile residual stresses, microcracks and thermal damage. This problem can be handled largely by reducing the cutting temperature. When the conventional coolant is applied to the cutting zone, it fails to remove the extent of the heat effectively. Hence, a cryogenic coolant is highly recommended for this purpose. In this paper, an attempt has been made to use cryogenic carbon dioxide (CO₂) as the cutting fluid. Experimental investigations are carried out by turning AISI 1045 steel in which the efficiency of cryogenic CO₂ is compared to that of dry and wet machining with respect to cutting temperature, cutting forces, chip disposal and surface roughness. The experimental results show that the application of cryogenic CO₂ as the cutting fluid is an efficient coolant for the turning operation as it reduced the cutting temperature by 5%–22% when compared with conventional machining.It is also observed that the surface finish is improved to an appreciable amount in the finished work piece on the application of cryogenic CO₂. The surface finish is improved by 5%–25% in the cryogenic condition compared with wet machining.     

Machining assessment of nano-crystalline hydroxyapatite bio-ceramic

Hydroxyapatite (HAP) is a widely used bio-ceramic in the fields of orthopedics and dentistry. This study investigates the machinability of nano-crystalline HAP (nHAP) bio-ceramic in end milling operations, using uncoated carbide tool under dry cutting conditions. Efforts are focused on the effects of various machining conditions on surface integrity. A first order surface roughness model for the end milling of nHAP was developed using response surface methodology (RSM), relating surface roughness to the cutting parameters: cutting speed, feed, and depth of cut. Model analysis showed that all three cutting parameters have significant effect on surface roughness. However, the current model has limited statistical predictive power and a higher order model is desired. Furthermore, tool wear and chip morphology was studied. Machined surface analysis showed that the surface integrity was good, and material removal was caused by brittle fracture without plastic flow.     

Laser tempering based turning process for efficient machining of hardened AISI 52100 steel

Cost-effective machining of hardened steel components such as a large wind turbine bearing has traditionally posed a significant challenge. This paper presents an approach to machine hardened steel parts efficiently at higher material removal rates and lower tooling cost. The approach involves a two-step process consisting of laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates with lower cost ceramic tools to efficiently remove the tempered material. The laser scanning parameters that yield the highest depth of tempered layer are obtained from a kinetic phase change model. Machining experiments are performed to demonstrate the possibility of higher material removal rates and improved tool wear behavior compared to the conventional hard turning process. Tool wear performance, cutting forces, and surface finish of Cubic Boron Nitride (CBN) tools as well as low cost ceramic tools are compared in machining of hardened AISI 52100 steel (~63 HRC). In addition, cutting forces and surface finish are compared for the laser tempering based turning and conventional hard turning processes. Experimental results show the potential benefits of the laser tempering based turning process over the conventional hard turning process.     

The effect of spindle speed,feed-rate and machining time to the surface roughness and burr formation of Aluminum Alloy 1100 in micro-milling operation

This paper describes the characteristics and the cutting parameters performance of spindle speeds (n, rpm) and feed-rates (f, mm/s) during three interval ranges of machining times (t, minutes) with respect to the surface roughness and burr formation, by using a miniaturized micro-milling machine. Flat end-mill tools that have two-flutes, made of solid carbide with Mega-T coated, with 0.2 mm in diameter were used to cut Aluminum Alloy AA1100. The causal relationship among spindle speeds, feed-rates, and machining times toward the surface roughness was analyzed using a statistical method ANOVA. It is found that the feed-rate (f) and machining time (t) contribute significantly to the surface roughness. Lower feed-rate would produce better surface roughness. However, when machining time is transformed into total cut length, it is known that a higher feed-rate, that consequently giving more productive machining since produce more cut length, would not degrade surface quality and tool life significantly. Burr occurrence on machined work pieces was analyzed using SEM. The average sizes of top burr for each cutting parameter selection were analyzed to find the relation between the cutting parameters and burr formation. In this research, bottom burr was found. It is formed in a longer machining time compare the formation of top burr, entrance burr and exit burr. Burr formation is significantly affected by the tool condition, which is degrading during the machining process. This knowledge of appropriate cutting parameter selection and actual tool condition would be an important consideration when planning a micro-milling process to produce a product with minimum burr.     

Application of Taguchi method to selection of optimal lubrication and cutting conditions in face milling of AlMg3

This paper outlines the Taguchi optimization methodology, which is applied to optimize the cutting parameters in face milling when machining AlMg₃ (EN AW 5754) with HSS (high speed steel) tool under semi-finishing conditions in order to get the best surface roughness and the minimum power consumption. Beside the conventional flood lubrication, the investigations include the minimal quantity lubrication and the dry milling. These environment-friendly cutting techniques are considered two practical ways to the cleaner manufacturing in the context of the sustainable production. The parameters evaluated are the cutting speed, the depth of cut, the feed rate and the cooling lubrication techniques (cutting fluid flow). The appropriate orthogonal array, signal to noise (S/N) ratio and Pareto analysis of variance (ANOVA) are employed to analyze the effect of the mentioned parameters on the good surface finish (surface roughness). This paper illustrates the application of the techniques for single performance characteristics optimization, which employs the weighting factors to each of the S/N ration of the responses to obtain a multi-response S/N ratio for each trial of the orthogonal array and, finally, a single optimal process parameters setting. Using Taguchi method for the design of experiments (DOE), it is investigated the significant influence and the parameters interaction effect with minimum number of trials as compared with a full factorial design.     

Comparison between numerical simulations and experiments for single-point diamond turning of single-crystal silicon carbide

Single-point diamond turning (SPDT) experiments conducted on single-crystal 6-H silicon carbide (SiC) have shown chip formation similar to that seen in the machining of metals. The ductile nature of SiC is believed to be the result of a high-pressure phase transformation (HPPT), which generates a plastic zone of material that behaves in a metallic manner. This metallic behavior is the basis for using AdvantEdge, a metal machining simulation software, for comparison to experimental results.Simulations (2D) were carried out by matching the SPDT experimental conditions, which were conducted at nanometer (nm) depths of cut and varying tool rake angles. The experiments were performed by machining the circumference of the single-crystal wafer, thereby conforming to a 2D orthogonal cut (plunge cuts, or an infeed, achieved the depth of cut, and no cross feed was incorporated).The cutting and thrust forces generated from the experiments under ductile cutting conditions compared favorably with the simulation. As the depth of cut is decreased (250 nm, 100 nm, and 50 nm), the experimental conditions transition from a brittle to ductile behavior, with the 50 nm cuts being dominated by the ductile regime. Thus, the forces from the experiment and the simulations are in much better agreement for the smaller depths of cut, that is, below the critical depth of cut that establishes the ductile-to-brittle transition, as ductile conditions exist in both the simulation and experiments. The differences in the results that do arise are assumed to be primarily due to a springback of the material leading to increased rubbing on the flank face.     

Cryogenic Machining of Tantalum

A new approach for the machining of tantalum is presented. The new approach is a combination of traditional turning and cryogenically enhanced machining (CEM). In the tests, CEM was used to reduce the temperature at the cutting tool/workpiece interface, and thus reduce the temperature-dependent tool wear to prolong cutting tool life. The new method resulted in a reduction of surface roughness of the tantalum workpiece by 200% and a decrease of cutting forces by approximately 60% in experiments. Moreover, cutting tool life was extended up to 300% over that in the conventional machining.     

Analytical modelling of residual stresses in orthogonal machining of AISI4340 steel

Residual stress profile in a component is often considered as the critical characteristic as it directly affects the fatigue life of a machined component. This work presents an analytical model for the prediction of residual stresses in orthogonal machining of AISI4340 steel. The novelty of the model lies in the physics-based approach focusing on the nature of contact stresses in various machining zones and the effect of machining temperature. The model incorporates: (i) stresses in three contact regions viz. shear, tool-nose-work piece and tool flank and machined surface, (ii) machining temperature, (iii) strain, strain rate and temperature dependent work material properties, (iv) plastic stresses evaluation by two algorithms, S-J and hybrid, (v) relaxation procedure and (iv) cutting conditions. The model benchmarking shows (86–88%) agreement between the experimental and predicted residual stresses in the X- and Y-directions. On the machined surface, the tensile residual stresses decrease with an increase the edge radius and increase with an increase the cutting speed. However, below the surface, the compressive residual stresses increase with an increase the depth of cut. Further, it is observed that the proposed model with hybrid algorithm gives better results at a lower feed rate, whereas with the S-J algorithm, at a higher feed rate.     

Performance-Based Predictive Models and Optimization Methods for Turning Operations and Applications: Part 3—Optimum Cutting Conditions and Selection of Cutting Tools

This paper presents a summary of recent developments in developing performance-based machining optimization methodologies for turning operations. Four major machining performance measures (cutting force, tool wear/tool life, chip form/chip breakability, and surface roughness) are considered in the present work, which involves the development and integration of hybrid models for single and multi-pass turning operations with and without the effects of progressive tool wear. Nonlinear programming techniques were used for single-pass operations, while a genetic algorithms approach was adopted for multi-pass operations. This methodology offers the selection of optimum cutting conditions and cutting tools for turning with complex grooved tools.     

Micro dimple milling on cylinder surfaces

The paper presents a micro dimple machining on a cylinder surface with a two-flutes ball end mill. When the cutter axis is inclined and the depth of cut is less than the tool radius, non-cutting time, during which neither of the two cutting edges contacts the workpiece, appears in a rotation of the cutter. The rotation of the workpiece and the feed of the tool are controlled so that the cutting areas do not overlap each other. In order to incline the tool with respect to the tangential direction on the cylinder surface, the tool is located at a position oriented at 45° from the top of the cylinder. An analytical model is presented to control the shapes of the dimples with the cutting parameters. The presented machining is verified in cutting tests with measuring the shape and the profile of the dimples. Pre-machining operations are conducted to have a high cylindricity of the workpiece in longitudinal turning and polishing. The cutter runout of the tool is also eliminated by adjusting the orientation and the position of the tool in the collet chuck with measuring the cutting force. The micro dimples are machined accurately as they are simulated.     

Rotary ultrasonic machining of potassium dihydrogen phosphate (KDP) crystal: An experimental investigation on surface roughness

Potassium dihydrogen phosphate (KDP) crystal, widely used for important electro-optic parts, is a typical hard-to-machine material because of its soft, brittle, and anisotropic properties. High quality is usually required for machined surfaces on KDP parts. Reported machining methods for KDP crystal include diamond turning, grinding, magnetorheological finishing, and polishing. Each of these methods has its limitations. Therefore, it is desirable to develop new machining methods for KDP crystal. This paper presents an experimental investigation on surface roughness in rotary ultrasonic machining (RUM) of KDP. It was found that the surface roughness obtained when using a tool with a chamfered corner was lower than that obtained using tools with right-angle corners. Other process variables (spindle speed, feedrate, and ultrasonic power) also affected the surface roughness obtained.     

Machining Performance and Health Effects of Cutting Fluid Application in Drilling of A390.0 Cast Aluminum Alloy

Environmental issues in machining have led to a push to curtail the use of cutting fluids. However, cutting fluid effects on part quality, process planning, and operator exposure to aerosols need to be first studied. The effects of cutting fluid application on hole accuracy and mist generation have been studied for blind-hole drilling of A390.0 aluminum alloy. Different cutting fluid types and application modes were tested under varying conditions of cutting speed, feed, and hole depth. The cooling and chip-transporting ability of cutting fluids was found to have the maximum effect on dimensional accuracy. Dry cutting yielded holes with the least accuracy, while mist lubrication was found to give superior dimensional accuracy to dry cutting but had the worst aerosol concentration. Flooding with synthetic cutting fluid gave the best overall results.     

Intelligent monitoring and identification of cutting states of chips and chatter on CNC turning machine

To realize an intelligent machine tool, which can autonomously determine the cutting states and can change them automatically as required due to changes in the environmental conditions, a method has been developed to monitor and identify the states of cutting for CNC turning based on a pattern recognition technique. The method proposed introduces three parameters to classify the cutting states of continuous chip formation, broken chip formation, and chatter. Among the states of cutting, the broken chip formation is required for the stable and reliable machining process. The three parameters are calculated and obtained by taking the ratio of the average variances of the dynamic components of three cutting forces. The algorithm was developed to calculate the values of three parameters during the process to obtain the reference feature spaces and determine the proper threshold values for classification of the cutting states. A tool dynamometer is developed, and implemented to the CNC turning machine to monitor the turning process.It is proved by a series of cutting experiments that the states of cutting are well identified by the method developed and proposed regardless of the cutting conditions. The algorithm is proposed to obtain the broken chips by changing the cutting conditions during the process.     

Effect of fluid concentration in titanium machining with an atomization-based cutting fluid (ACF) spray system

The aim of this work is to investigate the effect of metal-working fluid (MWF) concentration on the machining responses including tool life and wear, cutting force, friction coefficient, chip morphology, and surface roughness during the machining of titanium with the use of the ACF spray system. Five different concentrations from 5 to 15% of a water-soluble metalworking fluid (MWF) were applied during turning of a titanium alloy, Ti–6Al–4V. The thermo-physical properties such as viscosity, surface tension and thermal conductivity of these concentrations were also measured. The test results demonstrate that the tool life first extends with the increase in MWF concentration and then drops with further increase. At low concentration (e.g., 5%), a lack of the lubrication effect causes to increase in a higher friction at the tool–chip interface resulting in severe chipping and tool nose/flank wear within a short machining time. On the other hand, at high concentration, the cooling effect is less. This increases cutting temperature and a faster thermal softening/chipping/notching of the tool material and higher friction at the tool–chip–workpiece interaction zones resulting in early tool failure. A good balance between the cooling and the lubrication effects seems to be found at the 10% MWF concentration as it offers the best machining performance. However, machining with flood coolant is observed to perform the best in the range of 5–7%.     

Experimental Evaluation of Cutter Orientation When Ball Nose End Milling Inconel 718™

High-speed machining (HSM), specifically end milling and ball end cutting, is attracting interest in the aerospace industry for the machining of complex 3D aerofoil surfaces in titanium alloys and nickel-based superalloys. Following a brief introduction on HSM and related aerospace work, the paper reviews published data on the effect of cutter/workpiece orientation, also known as engagement or tilt angle, on tool performance. Such angles are defined as ±β_fN and ±β_f.Experimental work is detailed on the effect of cutter orientation on tool life, cutting forces, chip formation, specific force, and workpiece surface roughness when high-speed ball end milling Inconel 718™. Dry cutting was performed using 8 mm diameter PVD-coated solid carbide cutters with the workpiece mounted at an angle of 45° from the cutter axis.A horizontal downward (-β_fN) cutting orientation provided the best tool life with cut lengths ∼50% longer than for all other directions (+β_fN, +β_f, and –β_f). Evaluation of cutting forces and associated spectrum analysis of results indicated that cutters employed in a horizontal downward direction produced the least vibration. This contributed to improved workpiece surface roughness, with typical mean values of ∼0.4 μm Ra as opposed to ∼1.25 μm Ra when machining in the vertical downward (–β_f) direction.     

Feasibility of lignin as additive in metalworking fluids for micro-milling

The conventional additives in metalworking fluids (MWFs) have effects in improving the machining conditions. However, many additives can lead to environmental contamination and health problems. In this paper, lignin obtained from wood is considered as a new “green” additive in MWFs. Lignin has been used as additives in other areas like pasted lead electrodes and polypropylene/coir composites but has never been applied in cutting fluids. In this paper, lignin is dissolved in 5% conventional MWF aqueous solutions in 8 different concentrations through injection and atomization methods. Then, experiments are conducted to evaluate the effectiveness of lignin containing MWFs in micro-milling operations. The performance is compared with that of 5% conventional cutting fluid in terms of machining forces, tool wears, and burr formations. The results show that the concentration of 0.015% lignin leads to the least cutting forces, tool wear and burrs. The results also show that an appropriate concentration of lignin in MWFs can help to improve the cooling and lubrication performances during machining. The results of this paper thus indicate that lignin has a potential to be used as an additive in metalworking fluids.     

Analytical process damping stability prediction

This paper describes an analytical solution for turning and milling stability that includes process damping effects. Comparisons between the new analytical solution, time-domain simulation, and experiment are provided. The velocity-dependent process damping model applied in the analysis relies on a single coefficient similar to the specific cutting force approach to modeling cutting force. The process damping coefficient is identified experimentally using a flexure-based machining setup for a selected tool-workpiece pair (carbide insert-AISI 1018 steel). The effects of tool wear and cutting edge relief angle are also evaluated. It is shown that a smaller relief angle or higher wear results in increased process damping and improved stability at low spindle speeds.     

3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.     

AFM probe based nano mechanical scribing of soda-lime glass

In recent years, demands for miniature components have increased due to their reduced size, weight and energy consumption. In particular, brittle materials such as glass can provide high stiffness, hardness, corrosion resistance and high-temperature strength for various biomedical and high-temperature applications. In this study, cutting properties and the effects of machining parameters on the ductile cutting of soda-lime glass are investigated through the nano-scale scratching process. In order to understand the fundamentals of the material removal mechanism at the atomic scale, such as machined surface quality, cutting forces and the apparent friction, theoretical investigation along with experimental study are needed. Scribing tests have been performed using a single crystal diamond atomic force microscope (AFM) probe as the scratching tool, in order to find the cutting mechanism of soda-lime glass in the nano-scale. The extended lateral force calibration method is proposed to acquire accurate lateral forces. The experimental thrust and cutting forces are obtained and apparent friction coefficients are deduced. The effects of feed rates and the ploughing to shearing transition of soda-lime glass have been investigated.     

铣削工艺参数对锡铋合金表面粗糙度特征影响及试验分析

目的对锡铋合金表面粗糙度特征进行研究分析,提高表面加工质量。方法采用正交试验设计方法,以最小表面粗糙度作为优化指标,以主轴转速、铣削深度、进给速度、铣削宽度作为影响因素,进行精密铣削试验研究。结果利用方差分析确定了进给速度是锡铋合金铣削表面粗糙度最重要的影响因素,并基于田口方法优化分析得到了锡铋合金铣削加工工艺最优组合。结论采用田口法对锡铋合金铣削工艺参数优化,有效地减少了加工表面粗糙度,提高了工件表面质量。