Showing papers in "Machining Science and Technology in 2011"

3d finite element modelling of chip formation process for machining inconel 718: comparison of fe software predictions

Abstract: Many efforts have been focused on the development of Finite Element (FE) machining models due to growing interest in solving practical machining problems in a computational environment in industry. Most of the current models are developed under 2D orthogonal plane strain assumptions, or make use of either arbitrary damage criterion or remeshing techniques for obtaining the chip. A complete understanding of the material removal process together with its effects on the machined parts and wear behaviour of the cutting tools requires accurate 3D computational models to analyze the entire physical phenomenon in materials undergoing large elastic-plastic deformations and large temperature changes as well as high strain rates. This work presents a comparison of 3D machining models developed using commercially available FE softwares ABAQUS/Explicit© and DEFORM™3D Machining. The work material is chosen as Inconel 718, a difficult-to-cut nickel-based alloy material. Computational results of temperature, strain and ...

An analysis of surface integrity when drilling inconel 718 using palm oil and synthetic ester under mql condition

Abstract: The components being manufactured in the aerospace industry must be capable of being utilized for long periods without failure. Thus, the functional behavior of these machined components is greatly dependent upon their surface integrity. The present work compares the performance of palm oil and synthetic ester on surface integrity during drilling of Inconel 718. The results indicate the substantial benefit of the minimum quantity of lubrication (MQL) by palm oil on microhardness, surface roughness, surface defects and sub-surface deformation.

Parametric influence and optimization of wire edm of hot die steel

Abstract: Wire-cut Electro Discharge Machining (WEDM) is a special form of conventional EDM process in which the electrode is a continuously moving conductive wire. The present study aims at determining parametric influence and optimum process parameters of Wire-EDM using Taguchi's technique and a Genetic algorithm. The variation of the performance parameters with machining parameters was mathematically modeled by Regression analysis method. The objective functions are defined as Dimensional Error (DE), Surface Roughness (SR) and Volumetric Material Removal Rate (VMRR). Experiments were designed as per Taguchi's L16 Orthogonal Array (OA) wherein Pulse-on duration, Current, Pulse-off duration, Bed-speed and Flushing rate have been considered as the important input parameters. The matrix experiments were conducted for the material Hot Die Steel (HDS) having the thickness of 40 mm. The Heat Affected Zone (HAZ) characteristics of the eroded materials were assessed by Scanning Electron Microscope (SEM) and the microhard...

Mechanism of chip formation in high-speed turning of inconel 718

Abstract: The mechanism of serrated chip formation during high-speed turning of Inconel 718 using PCBN cutting tools has been investigated with the aid of scanning electron microscopy and optical microscopy. A conceptual model of chip formation has been developed knowing the chip morphology. It is followed by the analysis of chip segmentation frequency and the chip forms. Further, the chip segment forms and geometry were quantitatively characterized as a function of machining parameters and the cutting edge geometry using statistical methods. The chip morphology has been correlated with the cutting forces, specific shearing energy and the resultant roughness of the machined surfaces.

Evaluation and comparison of lubricant properties in minimum quantity lubrication machining

Abstract: Minimum Quantity Lubrication (MQL) machining involves the application of a minute amount of an oil-based lubricant to the machining process in an attempt to replace the conventional flood coolant system. Understanding the correlations between fluid properties and MQL performance can help in selecting lubricants from a variety of choices without going through extensive machining tests. This study compared nine different MQL fluids in terms of their physical properties, wettability, tribological properties (lubricity and extreme pressure (EP) properties), mist characteristics and machinability to determine the correlation of measured properties and MQL drilling and reaming performance. Results show that low fluid viscosity, high mist concentration, large mist droplet diameter and high wettability were best correlated with good machinability. Although it is difficult to draw strong relationships, the optimal machining in a mild cutting condition was found with the low viscosity fluids, which may also have th...

Effect of crystallographic orientation on cutting forces and surface finish in ductile cutting of kdp crystals

Abstract: In order to investigate the influence of material anisotropy in ductile cutting of Potassium Dihydrogen Phosphate (KDP) crystals, experiments of face cutting of (001) plane of KDP crystals are carried out by using an ultra-precision lathe with a single point diamond tool. The cutting forces, surface finish, and surface roughness in all crystallographic orientations of the machined surface are measured, and a power spectrum analysis method is used to reveal the cutting force patterns. The experimental results show that the cutting forces and surface roughness vary greatly with different crystallographic orientations of KDP crystal, and that amplitude variation of cutting forces and surface finish is closely related with the cutting parameter of the maximum undeformed chip thickness. With the maximum undeformed chip thickness below 30 nm, the amplitude variation of cutting force and surface finish is minimized, and a super-smooth surface with consistent surface finish in all the crystallographic orientation...

Suppression of period doubling chatter in high-speed milling by spindle speed variation

Abstract: Spindle speed variation is a well known technique to suppress regenerative machine tool vibrations, but it is usually considered to be effective only for low spindle speeds. In the current paper, spindle speed variation is applied to the high speed milling process, at the spindle speeds where the constant speed cutting results in period doubling chatter. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. It is shown that the milling process can be stabilized by increasing the amplitude of the spindle speed variation, while the frequency of the variation has no significant effect on the dynamic behaviour. The results are validated by experiments. Based on the analysis of the machined workpieces, it is shown that the surface roughness can also be decreased by the spindle speed variation technique.

An analytical model of oblique cutting with application to end milling

Abstract: A new analytical cutting force model is presented for oblique cutting. Orthogonal cutting theory based on unequal division shear zone is extended to oblique cutting using equivalent plane approach. The equivalent plane angle is defined to determine the orientation of the equivalent plane. The governing equations of chip flow through the primary shear zone are established by introducing a piecewise power law distribution assumption of shear strain rate. The flow stress is calculated from Johnson-cook material constitutive equation. The predictions were compared with test data from the available literature and showed good correlation. The proposed model of oblique cutting was applied to predict the cutting forces in end milling. The helical flutes are decomposed into a set of differential oblique cutting edges. To every engaged tooth element, the differential cutting forces are obtained from oblique cutting process. Experiments on machining AISI 1045 steel under different cutting conditions were conducted t...

Modeling and optimization of process parameters for delamination in drilling glass fiber reinforced plastic (gfrp) composites

Abstract: Glass fiber-reinforced composite materials are used in varieties of applications due to their excellent properties. Drilling is an indispensable process for this kind of materials. Delamination due to drilling is an important concern and is to be reduced. In the present work, drilling tests were carried out on computer numeric control (CNC) drilling machine. The parameters considered for the drilling investigations were spindle speed, feed rate and diameter of the drill bits. Multiple regression analysis is used for the modeling of process parameters in drilling of GFRP composites. Taguchi's S/N ratio analysis and desirability-based approach are used for the optimization of process parameters for studying the delamination in drilling of GFRP composites. The results revealed that the factor feed rate and drill diameter are the most influential parameters which affects the delamination in drilling of GFRP composites. The interaction between the parameters also affects the delamination in drilling of GFRP co...

Machining of cortical bone: simulations of chip formation mechanics using metal machining models

Abstract: 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.

Ductile regime single point diamond turning of quartz resulting in an improved and damage-free surface

Abstract: Quartz (fused silica) is one of the advanced engineered ceramic materials designed to operate in extreme environments. The mechanics of material removal in glass (Quartz) can be classified into two categories; brittle fracture and ductile plastic deformation. Good optical quality surfaces can be achieved by removing the material in a ductile manner. The strength, hardness and fracture toughness of the workpiece material are the governing factors that control the extent of brittle fracture. The main goal of the subject research is to improve the surface quality of Quartz to be used as an optic device (mirrors and windows) via single point diamond turning (SPDT). Sub-surface damage analysis was carried out on the machined sample using Scanning Acoustic Microscopy (SAcM). Surface roughness (Ra) values of less than 45 nm without sub surface damage were obtained. Tool wear was also investigated.

Dynamic properties for modeling and simulation of machining: effect of pearlite to austenite phase transition on flow stress in aisi 1075 steel

Abstract: The Pulse-Heated Kolsky Bar Laboratory at the National Institute of Standards and Technology (NIST) has been developed for the measurement of dynamic properties of metals. With this system, a small sample can be pre-heated from room temperature to several hundred degrees C in less than a second, prior to rapid loading in compression at strain rates up to the order of 104 per second. A major focus of this research program has been on investigating the influence of the heating rate and time at temperature on the flow stress of carbon steels, for application to the modeling and simulation of high-speed machining operations. The unique pulse heating capability of the NIST Kolsky bar system enables flow stress measurements to be obtained under conditions that differ significantly from those in which the test specimens have been pre-heated to a high temperature more slowly, because there is less time for thermally activated microstructural processes such as dislocation annealing, grain growth, and solid state p...

Energy deposition and non-thermal ablation in femtosecond laser grooving of silicon

Abstract: Ultra-short pulsed laser ablation of crystalline silicon is characterized by a complicated heat diffusion and material removal process. In this research, a computational investigation is undertaken to understand the temperature distribution and heat effect in femtosecond laser grooving of silicon. Energy accumulation and threshold fluence of silicon ablation by femtosecond lasers are estimated through solving coupled energy balance equations. Thermal and optical properties of the material are considered in the calculations. The possible non-thermal ablation process and ablation geometry are analyzed for the case of succession of laser pulses. Thermal-mechanical response induced by temperature gradient is discussed around the laser ablation region. The agreement between the model calculations and experimental results show that this research provides an efficient thermal analysis method of the explosive laser-silicon interaction process, and a feasible way to optimize process parameters with minimum thermal...

Prediction and experimental analysis of cutting forces during machining of precision external threads

Abstract: External thread cutting is a complex 3-D process in which the cutting conditions vary over the thread cutter profile. It is accepted as a mature; however, heavily experience based technology and there are few academic work published. Determining the cutting forces during machining is crucial to explain formation of the surface layer, residual stresses, selection of the most appropriate machine tool and optimizing the process. This investigation is an attempt to predict thread cutting forces by dividing the thread chip into three parts, one thread root and two side faces. Variation of the cutting parameters including the shear angle, mean cutting temperature and friction force on the flank face of the tool along the thread tool root and sides are determined. In the thread root and sides, chip compression ratios for the V-shaped single piece and separately cut chip zones are measured and cutting forces are calculated and compared for precision metric thread cutting on a SAE 4340 steel bar.

CUTTING PERFORMANCE AND WEAR MECHANISM OF Si3N4-BASED NANOCOMPOSITE CERAMIC CUTTING TOOL IN MACHINING OF CAST IRON

Abstract: A type of Si3N4-based nanocomposites ceramic cutting tool material was prepared by the addition of nano-scale Si3N4W whisker and nano-scale TiN particle. Cutting performance of the Si3N4/Si3N4W/TiN nanocomposite ceramic tool in machining of cast iron was investigated in comparison with a commercial sialon ceramic tool, and the tool wear mechanism was studied. The two types of cutting tools have similar cutting performance at relatively low cutting parameters, while Si3N4/Si3N4W/TiN nanocomposite tool exhibits a better wear resistance than sialon tool at the relatively high cutting parameters. The wear of sialon ceramic cutting tool is dominated by the plastic deformation, abrasive action, microcracking, pullout of grains and chemical action at the higher cutting parameters. The higher mechanical properties, and the refined matrix grains, intragranular TiN grains and dislocation in the microstructure improve the resistances to plastic deformation, microcracking, and pullout of grains for Si3N4/Si3N4W/TiN n...

Machining characteristics of complex surfaces using fast tool servo system

Abstract: Optical components with complex surfaces are more and more widely applied, but it is very difficult to manufacture these components by using traditional mechanical fabricating methods. Fast tool servo system can manufacture these complex surfaces or microstructures efficiently and accurately. The relative position between the tool and workpiece surface will vary continuously in the fast tool servo machining process, owing to the height change of workpiece profile in the same circle, and this will worsen the cutting conditions and debase the machining accuracy. In this paper, the cutting characteristics are studied in the fast tool servo machining process of complex workpiece, including the varying rule of cutting angle, and its influences on the rake angle and back angle, and the choice of machining parameters. Furthermore, the conditions for identifying tool interference are given. On the basis of the above work, two kinds of typical complex workpieces are manufactured by using fast tool servo system, in...

Surface finish and tool wear characterization in hard turning using a mathematical cutting tool representation

Abstract: The development of a general 3D model for a corner-radiused, chamfered, edge-honed cutting worn tool is elaborated. The surface of the cutting tool was constructed using one angular scalar specifying location on the corner radius and leading/trailing edges and another non-dimensional scalar for specifying location on the relief, edge-hone, chamfer and tool-top. Then, for given geometric parameters and cutting conditions, the angular extremities of contact on the corner radius and leading/trailing edges was obtained and validated. The kinematic surface finish on the workpiece surface including the Brammertz and sideflow effects was then simulated in typical hard turning. The model was expanded to allow wiper edges and flank wear. A simplified crater wear model was adopted for continuous hard turning to allow virtual cross-sectioning. Accurate estimation of flank and crater wear volume was also enabled. The model results for the fresh tool agreed with well-known trends from 2D modeling. Preliminary results ...

A threshold model for laser cleaning of larger silicon wafers

Abstract: High cleaning quality for silicon wafers without damage is a challenge in laser cleaning technologies. Laser cleaning of Al2O3 micro-particles, which are the main contaminants of silicon wafer lapping and polishing solutions used in industry, from silicon wafers was studied for determining laser energy for high efficient particle removal while not causing damage to the wafers. As the cleaning force is generated from laser-energy absorption and conduction of the wafer, heat-conduction model on silicon wafer was developed during laser irradiation using a finer finite element method, from which cleaning force exerting on the particles greater than the adhesion force between the particle and the substrate, but less than the wafer damage energy of laser input was determined. Calculations of the laser energy threshold values for both particle cleaning and wafer damage were conducted for silicon wafers of 200 mm in diameter and 0.2 mm in thickness, and they were found to be about 60 mJ/cm2 and 320 mJ/cm2, respec...

Optimization of cutting conditions in drilling operations with plane rake faced twist drills

Abstract: Optimization analyses and strategies for drilling operations on CNC machine tools with plane rake faced (PRF) twist drills are presented using a deterministic optimization approach. The optimization is based on criteria typified by maximum production rate while allowing for a range of practical constraints. The optimization analyses result in a deeper understanding of the effect of the constraints and a clearly defined optimization strategy that guarantees the global optimum solution. A numerical study is finally carried out to assess the optimization model and demonstrate the economic benefits of using this model over handbook recommendations in selecting the drilling parameters.

Influence of clamping strategies on roundness deviations of turned rings

Abstract: During turning of rings, shape deviations occur due to clamping. These deviations can be minimized by using optimized clamping fixtures. However, for small batch production with varying ring diamet...

Analysis of cutting characteristic of polycarbonate sheet subjected to wedge indentation by knife edge and grooved plate

Abstract: Asymmetric plunge cutting by using a grooved knife edge plate was proposed for advanced die cutting of a polycarbonate (PC) sheet. By varying the tip angle αU and the tip thickness w U of knife edge in the counter plate, and combining a standard steel cutting rule of 42° center bevel blade, a cutting load response of PC sheet was experimentally investigated, and the deformation was also observed by a CCD camera. Furthermore, an FEM simulation was carried out by varying the lower tip thickness for revealing the effect of interference of lower grooved counter plate. Through this work, the following were found: 1) there were two deformation modes of sheared profile; 2) the lower tip thickness w U was a primary factor, compared to the lower tip angle of αU; 3) the equivalent wedge angle effect was revealed with respect to the upper/lower angles α and αU, while the PC sheet was bent up by the lower knife indentation.

AN EXPERIMENTAL AND FEM STUDY ON DRY TURNING OF ROTOR STEEL 26NiCrMoV145 USING MULTILAYER COATED CEMENTED CARBIDE TOOL

Abstract: Rotor steel 26NiCrMoV145 has been widely employed in aerospace and power industry because of its unique properties. As to this new material that is used widely in important places, it is worth studying its machinability. An experiment and finite element (FE) simulation has been carried out to study the cutting forces, cutting temperature and tool wear mechanism during high speed dry turning of 26NiCrMoV145 using multilayer TiCN + Al2O3 coated carbide inserts. The orthogonal test was chosen and cutting forces were measured to validate the FE simulations. SEM analysis has been carried out on worn tools to determine the tool wear mechanism. Crater wear and coating peeling could be found at every cutting speed. Flank face wear appears smooth when cutting speed increases. Analyses of tool stress and temperature distribution during simulated cutting process were also taken out to help in understanding tool wear mechanism. At last, an optimization of the cutting conditions was suggested when considering material...

Grade of stability in fuzzy chatter stability lobe model in milling

Abstract: The machining productivity and part quality are typically limited by the regenerative chatter induced by the dynamic interactions of spindle-holder-tool combination system. The conventional chatter stability model predicts the permissible stable axial depth of cut versus spindle speed by plotting the stability lobe diagram which represents two independent regions as absolutely stable zone and instable zone divided by the critical lobe curve. In fact, it is more reasonable to be a transition stage between the stable and instable zone. This paper introduced the grade of stability (GOS) to improve the conventional chatter stability model and study the transition zone in the stability lobe diagram. The variation of transition zone width with the stability sensibilities for different order lobe curve in milling system was analyzed. Sigmoid function was used as the membership function to develop the fuzzy stability lobe model. Then, the fuzzy stability lobe diagram with an adjustable slope coefficient was imple...

Investigation of the tool wear and surface finish in low-speed milling of stainless steel under flood and mist lubrication

Abstract: This paper examines the performance of AlN/TiN coated carbide tool during milling of STAVAX® (modified AISI 420 stainless steel) at a low speed of 50 m/min under conventional flood and mist lubrication. Abrasion, chipping, fracture resulting in the formation of crater and catastrophic failure are the wear mechanisms encountered during machining under flood lubrication. The flank wear, and the likeliness of the cutting tool to fracture, chip and fail prematurely increased with an increase in the hardness of the workpiece and a reduction in the helix angle of the tool. Small quantity of mineral oil sprayed in mist form was effective in reducing the flank wear and severity of abrasion wear, and preventing the formation of crater and the occurrence of catastrophic failure. In milling 35 and 55 HRC-STAVAX® using a feed rate of 0.4 mm/tooth and a depth of cut of 0.2 mm under mist lubrication, the cutting edge of the 25° and 40° helix angle tools only suffered small-scale edge chipping and abrasive wear througho...

Assessing the possibility of machining of the self-reinforced bioresorbable polymer p(l/dl)la 70:30

Abstract: This new study has sought to assess the machining possibility of the self-reinforced bioresorbable polymer P(L/DL)LA 70:30, used in healthcare. To verify the viability of machining of the components and, consequently, the influence of the cutting parameters on the surface quality of the machined samples, experiments were performed with different values for speed, feed, applications of cutting fluid, material and tool geometry. After machining, the roughness was measured and the generated surfaces were analyzed qualitatively. The interaction of the machining parameters and the surface quality were particularly analyzed on the search for surfaces with the characteristics used in the area of implants that interact with bone tissue, to decide on the viability of machining. With these results, it was determined that the material properties have played a decisive role in the resoluteness of the surface quality of the machined samples. To achieve the necessary characteristics for an implant, the machining parame...