Orthogonal machining of single-crystal and coarse-grained aluminum

Orthogonal machining of single-crystal and coarse-grained (i.e., grain size considerably larger than the uncut chip thickness) materials has been a subject to many studies in the literature. The first part of this paper presents background on machining single-crystal materials, including experimental and modeling attempts. The second part briefly describes more recent modeling results from the authors, and presents new experimental results on planing and plunge-turning of single-crystal and coarse-grained aluminum using diamond tools. The experiments indicate that (1) cutting across grains of a coarse-grained aluminum workpiece produces distinctly varying forces and surface roughness from one grain to another, (2) plunge-turning and planing of single crystal aluminum provide equivalent force data for large rake angles, (3) forces alter between two distinct levels while cutting single crystals with small rake angles, and (4) with small rake angles, subsurface damage on single-crystal aluminum is extensive, reaching depths comparable to the uncut chip thickness.     

Evaluation of vegetable based cutting fluids with extreme pressure and cutting parameters in turning of AISI 304L by Taguchi method

Many problems such as health and environment issues are identified with the use of cutting fluids (CFs). There has been a high demand for developing new environmentally friendly CFs such as vegetable based cutting fluids (VBCFs) to reduce these harmful effects. In this study, performances of six CFs, four different VBCFs from sunflower and canola oils with different ratios of extreme pressure (EP) additives, and two commercial types of CFs (semi-synthetic and mineral) are evaluated for reducing of surface roughness, and cutting and feed forces during turning of AISI 304L austenitic stainless steel with carbide insert tool. Taguchi’s mixed level parameter design (L₁₈) is used for the experimental design. Cutting fluid, spindle speed, feed rate and depth of cut are considered as machining parameters. Regression analyses are applied to predict surface roughness, and cutting and feed forces. ANOVA is used to determine effects of the machining parameters and CFs on surface roughness, cutting and feed forces. In turning of AISI 304L, effects of feed rate and depth of cut are found to be more effective than CFs and spindle speed on reducing forces and improving the surface finish. Performances of VBCFs and commercial CFs are also compared and results generally show that sunflower and canola based CFs perform better than the others.     

Ball end milling mechanistic model based on a voxel-based geometric representation and a ray casting technique

Prediction of machining forces involved in complex geometry can be valuable information for machine shops. This paper presents a mechanistic cutting force simulation model for ball end milling processes, using ray casting and voxel representation methods used in 3D computer graphics field. Using this method, instantaneous uncut chip cross sectional areas can be extracted, which can be used in cutting pressure coefficient extraction and machining simulation including machining forces and geometry of the workpiece. The major advantage of the proposed scheme is that it can simulate milling processes with arbitrary cutting tool geometry on a workpiece with complex geometry, using an algorithm with constant time complexity. A series of cutting experiments were carried out to validate the model.     

An Approach to Theoretical Modeling and Simulation of Face Milling Forces

A new approach to theoretical modeling and simulation of face milling forces is presented. The present approach is based on a predictive machining theory in which machining characteristic factors in continuous cutting with a single-point cutting tool can be predicted from the workpiece material properties, tool geometry, and cutting conditions. The action of a milling cutter is considered as the simultaneous work of a number of single-point cutting tools, and the milling forces are predicted from input data of workpiece material properties, cutter parameters and tooth geometry, cutting condition, cutter and workpiece vibration structure parameters, and types of milling. A predictive force model for face milling is developed using this approach. In the model, the workpiece material properties are considered as functions of strain, strain rate, and temperature. The ratio of cutter tooth engagement over milling is taken into account for the determination of temperature in the cutting region. Cutter runout is included in the modeling for the chip load. The relative displacement between the cutter and workpiece due to the cutter and workpiece vibration is also included in the modeling to consider the effect on the undeformed chip thickness. A milling force simulation system has been developed using the model, and face milling experimental tests have been conducted to verify the simulation system. It is shown that the simulation results agree well with experimental results.     

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.     

Distinct element modeling of laser assisted milling of silicon nitride ceramics

Laser assisted milling (LAMill) of ceramics shows some complicated characteristics such as discontinuous chips, crack formation, propagation and coalescence. In this paper, numerical simulation is conducted to explore the machining mechanism of LAMill. The distinct element method (or discrete element method, DEM) is applied to model the microstructure of a β-type silicon nitride ceramic. Clusters are used to simulate the real grain shape of the silicon nitride ceramic and parallel bonds are employed to represent the connections between intergranular glass phase and grains. Numerical tests (compression, bending and fracture toughness tests) are performed to evaluate the macroproperties of the synthetic material, thus matching the corresponding physical properties of the real silicon nitride. Moreover, a temperature-dependent synthetic DEM specimen is created and then used in simulations of LAMill. The DEM model is validated through comparing the simulation results with the experimental ones in terms of the cutting forces and subsurface damage under different depths of cut. It is shown that the model can successfully predict the subsurface damage in LAMill.     

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.     

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.     

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.     

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.     

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.     

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.     

Application of FEM simulation of chip formation to stability analysis in orthogonal cutting process

Models for chatter prediction in machining often use a mechanistic force model that calculate the force as the product of a material dependent cutting constant and chip area. However, in reality, the forces are the result of complex interaction between the tool and the chip, and are affected by many factors. The effects of these complex, and often nonlinear, factors on the machining dynamics may only be included in chatter prediction if the chip formation process is simulated concurrently with simulation of the machining dynamics. In this paper, finite element simulation of the chip formation process is combined with simulation of chatter dynamics and the inter-relationship between the chip formation process and the chatter phenomenon is investigated. Mesh adaptation technique is used to simulate the chip formation within an FEM elastoplastic analysis with dynamic effects and frictional contact. The combined modeling predicts the occurrence of process damping at low cutting speeds, which other models are generally unable to predict.     

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.     

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.     

Experimental investigation,intelligent modeling and multi-characteristics optimization of dry WEDM process of Al–SiC metal matrix composite

Dry wire electrical discharge machining (WEDM) is an environmentally friendly modification of the oil WEDM process in which liquid dielectric is replaced by a gaseous medium. In the present work, parametric analysis has been fulfilled while dry WEDM of Al–SiC metal matrix composite. Experiments were designed and conducted based on L₂₇ Taguchi's orthogonal array to study the effect of pulse on time, pulse off time, gap voltage, discharge current, wire tension and wire feed on cutting velocity (CV) and surface roughness (SR). Firstly, a series of exploratory experiments has been conducted to identify appropriate gas and wire material based on the values of cutting velocity. After selection of best gas and best wire, they were used for later stage of experiments. Analysis of variances (ANOVA) has been performed to identify significant factors. In order to correlate relationship between process inputs and responses, an adaptive neuro-fuzzy inference system (ANFIS) has been employed to predict the process characteristics based on experimental observation. At the end, an artificial bee colony (ABC) algorithm has been associated with ANFIS models to maximize CV and minimize SR, simultaneously. Then the optimal solutions that obtained through ANFIS-ABC technique have been compared with numbers of confirmatory experiments. Results indicated that oxygen gas and brass wire guarantee superior cutting velocity. Also, according to ANOVA, pulse on time and discharge current were found to have significant effect on CV and SR. In modeling of CV and SR by ANFIS, it was resulted that the proposed method has superiority in prediction of them in the ranges of factors beyond the training condition. Also, association of ANFIS with ABC can find the optimal combination of process parameters accurately according to the confirmatory experiments.     

Modulation-assisted high speed machining of compacted graphite iron (CGI)

The application of controlled, low-frequency modulation (～100 Hz) superimposed onto the cutting process in the feed-direction – modulation-assisted machining (MAM) – is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500 m/min). The tool life is at least 20 times greater than in conventional machining. This significant reduction in wear is a consequence of the multiple effects realized by MAM, including periodic disruption of the tool–workpiece contact, formation of discrete chips, enhanced fluid action and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The tool wear in MAM is also found to be smaller at the higher cutting speeds (730 m/min) tested. The feed-direction MAM appears feasible for implementation in industrial machining applications involving high speeds.     

Measurement of tool internal temperatures in the tool–chip contact region by embedded micro thin film thermocouples

Sensors capable of providing fast and reliable feedback signals for monitoring and control of existing and emerging machining processes are an important research topic, that has quickly gained academic and industrial interest in recent years. Generally, high-precision machining processes are very sensitive to variation in local machining conditions at the tool–workpiece interface and lack a thorough understanding of fundamental thermomechanical phenomena. Existing sensors to monitor the machining conditions are not suitable for robust in-process control as they are either destructively embedded and/or do not possess the necessary spatial and temporal resolution to monitor local tool internal temperatures during machining at the cutting tip/edge effectively. This paper presents a novel approach for assessing transient tool internal temperature fields in the close vicinity of less than 300 μm of the tool cutting edge. A revised array layout of 10 micro thin film micro thermocouples, fabricated using adapted semiconductor microfabrication methods, has been embedded into polycrystalline cubic boron nitride (PCBN) cutting inserts by means of a modified diffusion bonding technique. Scanning electron microscopy was used to examine material interactions at the bonding interface and to determine optimal bonding parameters. Sensor performance was statically and dynamically characterized. They show good linearity, sensitivity and very fast response time. Initial machining tests on aluminum alloys are described herein. The tests have been performed to demonstrate the functionality and reliability of tool embedded thin film sensors, and are part of a feasibility study with the ultimate goal of applying the instrumented insert in hard machining operations. The microsensor array was used for the acquisition of tool internal temperature profiles very close to the cutting tip. The influence of varying cutting parameters on transient tool internal temperature profiles was measured and discussed. With further study, the described instrumented cutting inserts could provide more valuable insight into the process physics and could improve various aspects of machining processes, e.g. reliability, tool life, and workpiece quality.     

Investigation of chipping and wear of silicon wafer dicing

Wafer dicing chipping and blade wear processes in transient and steady stages were investigated. Dicing blades with two different diamond grit sizes were used to cut wafers. In the cutting experiments, the dicing blades with two different diamond grit sizes were used to cut wafers and for a given type of wafer, the cooling water temperature, cutting feed speed, and rotational speed were fixed. The chipping size, blade surface wear area and surface roughness of the wafer were measured at cutting distances of 50, 150, 300, 975, 1350, and 1900 m, respectively. Cutting debris of cutting distances of 300 m and 1900 m was collected and analyzed. The correlation between blade surface properties and chipping size was investigated. Based on this experimental system, attention is to pay to examine the correlation between blade surface properties and chipping size for transient stage and steady stage. In transient stage, the roughness of dicing blade increases rapidly. This will rapidly increase the chipping size. In steady stage, the chipping size decreases slowly with the decreasing roughness of blade surface. This concludes that blade surface condition is an important factor that affects the chipping size. Moreover, in transient stage, diamond grits that are salient or less bonded to the blade detach leave caves on the blade surface which increases surface roughness of the blade and the chipping size. In steady stage, the heights of grits become even and the chipping size decreases accordingly.