Stability charts with large curve-flute end-mills for thin-walled workpieces

The development of advanced performance materials by foundrymen allows new designs of components with similar mechanical resistance but lower thicknesses. This accentuates the well-known problems in machining cutting systems (static form errors, forced vibrations, and chatter), which appear increasingly early. These problems are particularly severe in the case of rotating parts in the field of aeronautics. Currently, the machining time for impellers and blisks can be improved so that new cutting tools with innovative features are continually developed. Barrel type or curved end mills will have a significant impact on the manufacturing of aircraft components during incoming years. In this paper, a time domain method is proposed for the first time to predict stability in milling operations when using these tools. The dynamic cutting forces are first obtained and then used to plot stability contour maps. Key aspects, such as tool orientation angles, several dynamic modes, and runout were also considered. Finally, chatter tests were performed for a low-stiffness mechanical system to validate the model. The presented maps indicate chatter severity and may be used for chatter prediction and productivity improvement.     

Optimization of machining parameters using genetic algorithm and experimental validation for end-milling operations

Optimization of cutting parameters is valuable in terms of providing high precision and efficient machining. Optimization of machining parameters for milling is an important step to minimize the machining time and cutting force, increase productivity and tool life and obtain better surface finish. In this work a mathematical model has been developed based on both the material behavior and the machine dynamics to determine cutting force for milling operations. The system used for optimization is based on powerful artificial intelligence called genetic algorithms (GA). The machining time is considered as the objective function and constraints are tool life, limits of feed rate, depth of cut, cutting speed, surface roughness, cutting force and amplitude of vibrations while maintaining a constant material removal rate. The result of the work shows how a complex optimization problem is handled by a genetic algorithm and converges very quickly. Experimental end milling tests have been performed on mild steel to measure surface roughness, cutting force using milling tool dynamometer and vibration using a FFT (fast Fourier transform) analyzer for the optimized cutting parameters in a Universal milling machine using an HSS cutter. From the estimated surface roughness value of 0.71 μm, the optimal cutting parameters that have given a maximum material removal rate of 6.0×10³ mm³/min with less amplitude of vibration at the work piece support 1.66 μm maximum displacement. The good agreement between the GA cutting forces and measured cutting forces clearly demonstrates the accuracy and effectiveness of the model presented and program developed. The obtained results indicate that the optimized parameters are capable of machining the work piece more efficiently with better surface finish.     

A MACHINING PERFORMANCE STUDY IN DRY CONTOUR TURNING OF ALUMINUM ALLOYS WITH FLAT-FACED AND GROOVED DIAMOND TOOLS

This paper presents the results from an experimental study of dry contour turning operations on aluminum alloys (6061B and 2011-T3) using PCD flat-faced and diamond coated grooved tools. The machining performance is assessed on the basis of cutting forces, chip flow, chip-form and surface roughness observed during contour turning operations. The constantly varying cutting conditions (especially effective depth of cut due to varying geometry of the contour surface) and effective tool geometry cause a wide fluctuation in cutting forces and the ensuing chip flow. The chip flow angle is measured along the contour geometry using high-speed filming techniques and these results are compared with predicted chip flow values from the measured experimental cutting forces (which are measured along the entire contour geometry). The resultant surface roughness at different locations along the contour profile is measured and correlated with the chip flow and chip-form variations. Machining performance issues specifically relevant to dry contour turning of aluminum (such as problems due to poor chip flow and the resultant poor surface roughness) are studied and the effectiveness of selective work-tool (both tool material and tool geometry) pairs is illustrated.     

An optimization method of the machining parameters in high-speed machining of stainless steel using coated carbide tool for best surface finish

High-speed machining (HSM) has emerged as a key technology in rapid tooling and manufacturing applications. Compared with traditional machining, the cutting speed, feed rate has been great progress, and the cutting mechanism is not the same. HSM with coated carbide cutting tools used in high-speed, high temperature situations and cutting more efficient and provided a lower surface roughness. However, the demand for high quality focuses extensive attention to the analysis and prediction of surface roughness and cutting force as the level of surface roughness and the cutting force partially determine the quality of the cutting process. This paper presents an optimization method of the machining parameters in high-speed machining of stainless steel using coated carbide tool to achieve minimum cutting forces and better surface roughness. Taguchi optimization method is the most effective method to optimize the machining parameters, in which a response variable can be identified. The standard orthogonal array of L₉ (3⁴) was employed in this research work and the results were analyzed for the optimization process using signal to noise (S/N) ratio response analysis and Pareto analysis of variance (ANOVA) to identify the most significant parameters affecting the cutting forces and surface roughness. For such application, several machining parameters are considered to be significantly affecting cutting forces and surface roughness. These parameters include the lubrication modes, feed rate, cutting speed, and depth of cut. Finally, conformation tests were carried out to investigate the improvement of the optimization. The result showed a reduction of 25.5% in the cutting forces and 41.3% improvement on the surface roughness performance.     

PERFORMANCE PREDICTION MODELS FOR TURNING WITH ROUNDED CORNER PLANE FACED LATHE TOOLS. II. VERIFICATION OF MODELS

Extensive numerical simulation and experimental verification of the predictive force and surface roughness models for turning operations have been carried out encompassing the domain of cutting conditions recommended in practice. It has been shown that the three force models predicted very similar qualitative and plausible trends in the tangential, feed and radial force components as well as chip flow angle with changes in the many operation variables. The experimental testing involved about 500 turning cuts over a wide range of inclination angles, normal rake angles, major cutting edge angles, corner radius, feed and depth of cut. All the qualitative trends in the forces and chip flow angle noted in the simulation studies have been experimentally confirmed for all the three force models for both TiN coated and uncoated tools. The first two force models predictions correlated very well with the experimental results while only reasonable correlation was found with the third (approximate) model. The surface roughness predictive models were found to be adequate for turning with TiN coated HSS tools only while empirical equations were still necessary for reliable estimates of surface roughness for turning with the uncoated HSS tools. This investigation has shown that comprehensive and quantitatively reliable predictive models for the forces, power, chip flow angle and surface roughness can be established from fundamental cutting the- ory and analysis. In particular, the findings of this investigation provide further evidence in support of the generic nature of the 'unified mechanics of cutting approach' to technological performance prediction and the potential of the predictive surface roughness models for machining with coated tools.     

Elliptical vibration cutting of hardened die steel with coated carbide tools

Elliptical vibration cutting of hardened die steel with coated carbide tools is examined in this research in order to achieve low-cost high-precision machining. Diamond coated tools are applied because of superior hardness of their polycrystalline diamond coating and its low manufacturing cost. TiN coated tools are also tested, since they are widely used for conventional machining of steels. Machinability of hardened die steel by the elliptical vibration cutting with coated carbide tools is discussed in three aspects in this study, i.e. transferability of cutting edge profile to cut surface, cutting force, and tool life. The transferability is evaluated quantitatively by calculating correlation coefficients of measured roughness profiles. It is clarified that the diamond coated tools have high transferability which leads to diffraction of light on the surface machined at micro-scale pick feed. Total cutting forces including ploughing components are measured at various feed rates, and then shearing components and ploughing components are separated utilizing linear regression. The measured results indicate, for example, that the all forces become considerably smaller only when elliptical vibration is applied to the TiN coated tool without cutting fluid. It is also found that this considerable reduction of forces interestingly corresponds to higher friction coefficient, which is identified from the ploughing components. Tool life tests are carried out by various machining methods, i.e. elliptical vibration/ordinary wet/dry cutting with diamond/TiN coated tools. The result shows, for example, that the flank wear is smallest in the wet elliptical vibration cutting with the diamond coated tool.     

SIMULATION CONCEPT FOR PREDICTING WORKPIECE VIBRATIONS IN FIVE-AXIS MILLING

The characteristic discontinuous cut of the milling process influences the whole machining process by an increased susceptibility to vibrations of the machine-tool-workpiece system. This can result in undesirable effects on the workpiece surface or in a shorter lifetime of the tool and the spindle. Especially with regard to the machining of thin-walled components, such as turbine blades and thin profiles, the dynamic behavior of the workpiece is of particular interest. In this paper a simulation concept for predicting regenerative workpiece vibrations during the five-axis milling process is presented. This concept combines an accurate and fast simulation of the five-axis machining process including material removal and force calculation with an implemented finite element model for computing workpiece displacements. The simulation results are compared with data from experiments, which were conducted using a milling tool with high stiffness in order to minimize the influence of the milling tool dynamics.     

Microgrooving on electroless nickel plated materials using a single crystal diamond tool

Diamond tools are used in ultra precision machining for their outstanding hardness and crystalline structure, which enable the fabrication of very sharp cutting edges. Single crystal diamond tools are thus extremely useful to machine electroless nickel-plated dies which are generally used for making molds for optical components. This paper deals with the objective to evaluate the performance and suitability of a single crystal diamond tool during microgrooving on electroless nickel plated workpieces. Effects of different machining parameters on overall machining performance were also investigated. The experimental results revealed that long distance (50 km) machining of microgrooves on electroless nickel is possible with a single crystal diamond tool without any significant tool wear. Some groove wear on the rake face were found after machining 28.5 km. No evidence of chipping or wear had been observed on the flank face during the total machining length. The surface roughness range of the machined workpieces was found to be 4–6 nm. Both thrust and cutting components of the machining forces showed an increasing trend with increasing machining distance, though magnitude of the thrust forces were found to increase more than the cutting forces.     

ROTARY ULTRASONIC MACHINING OF CARBON FIBER-REINFORCED POLYMER: FEASIBILITY STUDY

Carbon fiber-reinforced polymer (CFRP) has been widely used in aircraft components, automotive parts, and sporting goods. Hole machining is the most frequently employed operation of secondary machining for fiber-reinforced composites. However, challenges (delamination, splintering, burr, short tool life, low machining precision, and low surface quality) still remain for their widespread applications. Rotary ultrasonic machining (RUM) is a non-conventional machining process that has been used to drill holes in composite materials. However, it has not been used to drill this type of CFRP. In this article, RUM is introduced into drilling holes in this type of CFRP for the first time. The feasibility to machine carbon fiber-reinforced epoxy using RUM is investigated experimentally. Chips, edge chipping, surface roughness, tool wear, and thrust force were measured. Effects of RUM process variables (rotation speed, vibration amplitude, and feedrate) on thrust force and surface roughness were studied. Results showed that RUM could be used to drill holes in CFRP with high productivity and low tool wear. A better surface was produced by higher rotation speed and lower feed rate.     

Effect of machining parameters on the milling process of 2.5D C/SiC ceramic matrix composites

Abstract

The C/SiC ceramic matrix composites are widely used for high-value components in the nuclear, aerospace and aircraft industries. The cutting mechanism of machining C/SiC ceramic matrix composites is one of the most challenging problems in composites application. Therefore, the effects of machining parameters on the machinability of milling 2.5D C/SiC ceramic matrix composites is are investigated in this article. The related milling experiments has been carried out based on the C/SiC ceramic matrix composites fixed in two different machining directions. For two different machining directions, the influences of spindle speed, feed rate and depth of cut on cutting forces and surface roughness are studied, and the chip formation mechanism is discussed further. It can be seen from the experiment results that the measured cutting forces of the machining direction B are greater than those of the in machining direction A under the same machining conditions. The machining parameters, which include spindle speed, feed rate, depth of cut and machining direction, have an important influence on the cutting force and surface roughness. This research provides an important guidance for improving the machining efficiency, controlling and optimizing the machined surface quality of C/SiC ceramic matrix composites in the milling process.     

Development of a programmable vibration cutting tool for diamond turning of hardened mold steels

There are two drawbacks in the performance of the resonant vibration cutting tools currently available. One is that the vibration frequency cannot be changed arbitrarily and the other is that the cutting force is low. It is impossible to turn mirror plates with many kinds of materials using these resonant vibration cutting tools because they cannot match the desirable turning speeds that correspond to the machined materials and the vibration frequency needs to be increased or decreased to obtain the desired surface roughness. Resonant vibration cutting tools do not allow the vibration frequency to be set arbitrarily. The small cutting force of these tools also causes some difficulties in diamond turning of metals other than soft metals such as aluminum and copper. In this research, we developed a vibration cutting tool that can generate two-dimensional vibration shapes without distortion by placing two piezoelectric actuators at right angles. This tool can machine the many kinds of mirror plates with different materials to the desired surface roughness. It is also possible to machine hard materials such as mold steels because the amplitudes of the vibrations do not decrease, even when large cutting forces are required. In this paper, we describe the design of the nonresonant vibration cutting tool, and show by the diamond turning of oxygen-free copper and aluminum that our nonresonant vibration cutting tool can machine desired shapes. Finally, it is verified by actual machining experiments that the proposed vibration cutting tool can machine hardened mold steels such as STAVAX with HRC 54.     

CVD金刚石薄膜涂层刀具精密切削表面质量的研究

CVD金刚石薄膜刀具的表面粗糙度及加工过程中的切削用量是影响加工工件表面质量的关键因素。为改进CVD沉积工艺 ,减小金刚石薄膜表面粗糙度 ,提出了合理控制沉积气压的新工艺方法 ,并通过切削试验研究了不同沉积工艺下制备的CVD薄膜涂层刀具和加工过程中不同切削用量对精密切削表面质量的影响。     

金刚石刀具精密切削钛合金薄壁件试验研究

为满足航空发动机的减重、提高零部件的加工质量和对性能的要求,采用试验的方法,对航空用钛合金薄壁件进行精密切削加工研究,主要以表面加工质量为研究对象,并以其为约束,以提高效率为目的对切削参数进行优化,得到了较为可行的加工参数,并对表面粗糙度的变化规律进行分析研究,同时分析了金刚石刀具在精密切削钛合金薄壁件加工中,刀具磨损初期、中期和后期的磨损形式和成因,研究为实际型号钛合金薄壁零件的加工提供了一种改进加工工艺技术的方法。     

CVD金刚石薄膜涂层刀具精密切削表面质量的研究

CVD金刚石薄膜刀具的表面粗糙度和加工过程中的切削用量是影响加工工件表面质量的关键因素.为改进CVD沉积工艺,减小金刚石薄膜表面粗糙度,提出了合理控制沉积气压的新工艺方法,并通过切削试验研究了不同沉积工艺下制备的CVD薄膜涂层刀具和加工过程中不同切削用量对精密切削表面质量的影响.     

Surface roughness and cutting forces modeling for optimization of machining condition in finish hard turning of AISI 52100 steel

An experimental investigation was conducted to analyze the effect of cutting parameters (cutting speed, feed rate and depth of cut) and workpiece hardness on surface roughness and cutting force components. The finish hard turning of AISI 52100 steel with coated Al₂O₃ + TiC mixed ceramic cutting tools was studied. The planning of experiment were based on Taguchi’s L₂₇ orthogonal array. The response table and analysis of variance (ANOVA) have allowed to check the validity of linear regression model and to determine the significant parameters affecting the surface roughness and cutting forces. The statistical analysis reveals that the feed rate, workpiece hardness and cutting speed have significant effects in reducing the surface roughness; whereas the depth of cut, workpiece hardness and feed rate are observed to have a statistically significant impact on the cutting force components than the cutting speed. Consequently, empirical models were developed to correlate the cutting parameters and workpiece hardness with surface roughness and cutting forces. The optimum machining conditions to produce the lowest surface roughness with minimal cutting force components under these experimental conditions were searched using desirability function approach for multiple response factors optimization. Finally, confirmation experiments were performed to verify the pertinence of the developed empirical models.     

Optimization of machining parameters in rotary EDM process by using the Taguchi method

Electrical discharge machining (EDM) is one of the advanced methods of machining. Most publications on the EDM process are directed towards non-rotational tools. But rotation of the tool provides a good flushing in the machining zone. In this study, the optimal setting of the process parameters on rotary EDM was determined. A total of three variables of peak current, pulse on time, and rotational speed of the tool with three types of electrode were considered as machining parameters. Then some experiments have been performed by using Taguchi's method to evaluate the effects of input parameters on material removal rate, electrode wear rate, surface roughness, and overcut. Moreover, the optimal setting of the parameters was determined through experiments planned, conducted, and analyzed using the Taguchi method. Results indicate that the model has an acceptable performance to optimize the rotary EDM process.     

MACHINING OF CORTICAL BONE: SURFACE TEXTURE,SURFACE INTEGRITY AND CUTTING FORCES

Cutting, drilling and reaming of human bone are conducted in total joint replacement procedures and the placement of dental implants. In the current study orthogonal machining of cortical bone was performed and the cutting and thrust forces, as well as the machined surface quality, were evaluated over a range of osteon orientations and cutting conditions. Results showed that cutting perpendicular to the osteons resulted in the highest machining forces, largest surface roughness and extensive sub-surface damage for some parametric conditions. The average surface roughness of the machined bone ranged from 1 μm to over 70 μm, was largest for positive rake angle tools and increased with the depth of cut. There was no correlation between the cutting forces and machined surface quality. While negative rake angle tools resulted in the largest cutting forces, they provided the lowest surface roughness and highest apparent surface quality. Overall, the results show that orthogonal cutting of bone can result in near-surface damage that reduces the degree of contact between bone and implanted devices and is potentially detrimental to the post-surgical recovery rate.     

MACHINING OF CORTICAL BONE: SURFACE TEXTURE, SURFACE INTEGRITY AND CUTTING FORCES

Cutting, drilling and reaming of human bone are conducted in total joint replacement procedures and the placement of dental implants. In the current study orthogonal machining of cortical bone was performed and the cutting and thrust forces, as well as the machined surface quality, were evaluated over a range of osteon orientations and cutting conditions. Results showed that cutting perpendicular to the osteons resulted in the highest machining forces, largest surface roughness and extensive sub-surface damage for some parametric conditions. The average surface roughness of the machined bone ranged from 1 μm to over 70 μm, was largest for positive rake angle tools and increased with the depth of cut. There was no correlation between the cutting forces and machined surface quality. While negative rake angle tools resulted in the largest cutting forces, they provided the lowest surface roughness and highest apparent surface quality. Overall, the results show that orthogonal cutting of bone can result in near-surface damage that reduces the degree of contact between bone and implanted devices and is potentially detrimental to the post-surgical recovery rate.     

<Emphasis Type="Bold">Prediction of Surface Topomorphy and Roughness in Ball-End Milling</Emphasis>

Milling is today the most effective, productive and flexible-manufacturing method for machining complicated or sculptured surfaces. Ball-end tools are used for machining 3D freeform surfaces for dies, moulds, and various parts, such as aerospace components, etc. Milling data, such as surface topomorphy, surface roughness, non-deformed chip dimensions, cutting force components and dynamic cutting behaviour, are very helpful, especially if they can be accurately produced by means of a simulation program. This paper presents a novel simulation model, the so-called MSN-Milling Software Needle program, which is able to determine the surface produced and the resulting surface roughness, for ball-end milling. The model simulates precisely the tool kinematics and considers the effect of the cutting geometry on the resulting roughness. The accuracy of the simulation model has been thoroughly verified, with the aid of a wide variety of cutting experiments. Many roughness measurements were carried out on workpieces, which were cut using a 5-axis machining centre. The calculated roughness levels were found to be in agreement with the experimental ones. The proposed model has proved to be suitable for determining optimal cutting conditions, when finishing complex surfaces. The software can be easily integrated into various CAD-CAM systems.     

The role of viscous deformation in the machining of polymers

This study aims to evaluate the machinability of typical thermoplastic and thermosetting polymers and understand the effect of their viscous properties on surface integrity, chip formation and machining forces. The interaction between the strain rate and temperature during machining was particularly addressed. It was found that the viscous deformation of a polymer plays a decisive role in determining the quality of a machined surface. To minimize the surface roughness, for instance, the machining conditions must be selected in such a way that the material removal deformation falls in the regime without visco-plastic scaling/tearing and brittle cracking. The optimal machining condition must be based on the polymer properties, such as the glass transition temperature, fracture toughness and molecular mobility. The shear stress in the shear plane of chipping is a good measure of the coupled effect of strain rate and temperature rise. In addition, the study discovered two new types of chips whose deformation and curling were in close relation to the surface integrity of the machined components.