Showing papers on "Machining published in 2008"

Laser beam machining—A review

Abstract: Laser beam machining (LBM) is one of the most widely used thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. Laser beam is focussed for melting and vaporizing the unwanted material from the parent material. It is suitable for geometrically complex profile cutting and making miniature holes in sheetmetal. Among various type of lasers used for machining in industries, CO2 and Nd:YAG lasers are most established. In recent years, researchers have explored a number of ways to improve the LBM process performance by analysing the different factors that affect the quality characteristics. The experimental and theoretical studies show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters. This paper reviews the research work carried out so far in the area of LBM of different materials and shapes. It reports about the experimental and theoretical studies of LBM to improve the process performance. Several modelling and optimization techniques for the determination of optimum laser beam cutting condition have been critically examined. The last part of this paper discusses the LBM developments and outlines the trend for future research.

Review of vibration-assisted machining

Abstract: Vibration-assisted machining (VAM) combines precision machining with small-amplitude tool vibration to improve the fabrication process. It has been applied to a number of processes from turning to drilling to grinding [9] , [36] . The emphasis on this literature review is the turning process where VAM has been applied to difficult applications such as diamond turning of ferrous and brittle materials, creating microstructures with complex geometries for products like molds and optical elements, or economically producing precision macro-scale components in hard alloys such as Inconel or titanium. This review paper presents the basic kinematic relationships for 1D (linear vibratory tool path) and 2D VAM (circular/elliptical tool path). Typical hardware systems used to achieve these vibratory motions are described. The periodic separation between the tool rake face and uncut material, characteristic of VAM, is related to observed reductions in machining forces and chip thickness, with distinct explanations offered for 1D and 2D modes. The reduced tool forces in turn are related to improvements in surface finish and extended tool life. Additional consideration is given to the intermittent cutting mechanism and how it reduces the effect of thermo-chemical mechanisms believed responsible for rapid wear of diamond tools when machining ferrous materials. The ability of VAM to machine brittle materials in the ductile regime at increased depth of cut is also described.

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti–6Al–4V

Abstract: A new material constitutive law is implemented in a 2D finite element model to analyse the chip formation and shear localisation when machining titanium alloys. The numerical simulations use a commercial finite element software (FORGE 2005®) able to solve complex thermo-mechanical problems. One of the main machining characteristics of titanium alloys is to produce segmented chips for a wide range of cutting speeds and feeds. The present study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. The new developed model takes into account the influence of strain, strain rate and temperature on the flow stress and also introduces a strain softening effect. The tool chip friction is managed by a combined Coulomb–Tresca friction law. The influence of two different strain softening levels and machining parameters on the cutting forces and chip morphology has been studied. Chip morphology, cutting and feed forces predicted by numerical simulations are compared with experimental results.

Machining of Polymer Composites

Abstract: to Polymer Composites.- Conventional Machining Operations.- Mechanics of Chip Formation.- Tool Materials and Tool Wear.- Conventional Machining of FRPs.- Nontraditional Machining of FRPs.- Health and Safety Aspects in Machining FRPs.

Laser Fabrication and Machining of Materials

Abstract: Fundamentals of Laser Processing.- Basics of Lasers.- Laser Materials Interactions.- Laser Machining.- Manufacturing Processes: An Overview.- Laser Drilling.- Laser Cutting.- Three-Dimensional Laser Machining.- Laser Micromachining.- Laser Fabrication.- Laser Forming.- Laser-Based Rapid Prototyping Processes.- Laser Welding.- Special Topics in Laser Processing.- Laser Interference Processing.- Laser Shock Processing.- Laser Dressing of Grinding Wheels.- Lasers Processing in Medicine and Surgery.

A review of cryogenic cooling in machining processes

Abstract: The cooling applications in machining operations play a very important role and many operations cannot be carried out efficiently without cooling. Application of a coolant in a cutting process can increase tool life and dimensional accuracy, decrease cutting temperatures, surface roughness and the amount of power consumed in a metal cutting process and thus improve the productivity. In this review, liquid nitrogen, as a cryogenic coolant, was investigated in detail in terms of application methods in material removal operations and its effects on cutting tool and workpiece material properties, cutting temperature, tool wear/life, surface roughness and dimensional deviation, friction and cutting forces. As a result, cryogenic cooling has been determined as one of the most favourable method for material cutting operations due to being capable of considerable improvement in tool life and surface finish through reduction in tool wear through control of machining temperature desirably at the cutting zone.

Industrial applications of superhard nanocomposite coatings

Abstract: Recent progress in the development and industrialization of superhard and tough nanocomposite coatings, which consist of hard transition metal nitride nanocrystals “glued together” by about 1 monolayer of silicon nitride, is summarized and documented by selected illustrative examples. It is shown that already the presently available superhard nanocomposites applied on machining, stamping and forming tools significantly increase their lifetime and the cutting speed, and consequently also the overall productivity of the machining operations. Further improvement of the presently available and newly developed nanocomposite coatings will push the machining technology towards new horizons. Besides of the superhard nanocomposites, also medium hard, but very tough thick coatings with low internal stress applied to forming tools increase their lifetime by at least one order of magnitude.

Modelling and analysis of micro scale milling considering size effect, micro cutter edge radius and minimum chip thickness

Abstract: This paper presents mechanisms studies of micro scale milling operation focusing on its characteristics, size effect, micro cutter edge radius and minimum chip thickness. Firstly, a modified Johnson–Cook constitutive equation is formulated to model the material strengthening behaviours at micron level using strain gradient plasticity. A finite element model for micro scale orthogonal machining process is developed considering the material strengthening behaviours, micro cutter edge radius and fracture behaviour of the work material. Then, an analytical micro scale milling force model is developed based on the FE simulations using the cutting principles and the slip-line theory. Extensive experiments of OFHC copper micro scale milling using 0.1 mm diameter micro tool were performed with miniaturized machine tool, and good agreements were achieved between the predicted and the experimental results. Finally, chip formation and size effect of micro scale milling are investigated using the proposed model, and the effects of material strengthening behaviours and minimum chip thickness are discussed as well. Some research findings can be drawn: (1) from the chip formation studies, minimum chip thickness is proposed to be 0.25 times of cutter edge radius for OFHC copper when rake angle is 10° and the cutting edge radius is 2 μm; (2) material strengthening behaviours are found to be the main cause of the size effect of micro scale machining, and the proposed constitutive equation can be used to explain it accurately. (3) That the specific shear energy increases greatly when the uncut chip thickness is smaller than minimum chip thickness is due to the ploughing phenomenon and the accumulation of the actual chip thickness.

Effect of machining parameters and cutting edge geometry on surface integrity of high-speed turned Inconel 718

Abstract: Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. This paper extends the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone (MAZ). The residual stress analysis, microhardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles.

Multi response optimization of machining parameters of drilling Al/SiC metal matrix composite using grey relational analysis in the Taguchi method.

Abstract: This paper presents a new approach for the optimization of drilling parameters on drilling Al/SiC metal matrix composite with multiple responses based on orthogonal array with grey relational analysis. Experiments are conducted on LM25-based aluminium alloy reinforced with green bonded silicon carbide of size 25 μm (10% volume fraction). Drilling tests are carried out using TiN coated HSS twist drills of 10 mm diameter under dry condition. In this study, drilling parameters namely cutting speed, feed and point angle are optimized with the considerations of multi responses such as surface roughness, cutting force and torque. A grey relational grade is obtained from the grey analysis. Based on the grey relational grade, optimum levels of parameters have been identified and significant contribution of parameters is determined by ANOVA. Confirmation test is conducted to validate the test result. Experimental results have shown that the responses in drilling process can be improved effectively through the new approach.

Effect of machining parameters in ultrasonic vibration cutting

Abstract: The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool–workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings.

Effects of high speed in the drilling of glass fibre reinforced plastic: Evaluation of the delamination factor

Abstract: High speed machining (HSM) is an outstanding technology capable of improving productivity and lowering production costs in manufacturing companies. Drilling is probably the machining process most widely applied to composite materials; nevertheless, the damage induced by this operation may reduce drastically the component performance. This work employs HSM to realize high performance drilling of glass fibre reinforced plastics (GFRP) with reduced damage. In order to establish the damage level, digital analysis is used to assess delamination. A comparison between the conventional (Fd) and adjusted (Fda) delamination factor is presented. The experimental results indicate that the use of HSM is suitable for drilling GFRP ensuring low damage levels.

Experimental investigation of surface/subsurface damage formation and material removal mechanisms in SiC grinding

Abstract: The difficulty and cost involved in the abrasive machining of hard and brittle ceramics are among the major impediments to the widespread use of advanced ceramics in industries these days. It is often desired to increase the machining rate while maintaining the desired surface integrity. The success of this approach, however, relies in the understanding of mechanism of material removal on the microstructural scale and the relationship between the grinding characteristics and formation of surface/subsurface machining-induced damage. In this paper, grinding characteristics, surface integrity and material removal mechanisms of SiC ground with diamond wheel on surface grinding machine have been investigated. The surface and subsurface damages have been studied with scanning electron microscope (SEM). The effects of grinding conditions on surface/subsurface damage have been discussed. This research links the surface roughness, surface and subsurface damages to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grinding-induced damage on grinding conditions.

Chatter stability of milling in frequency and discrete time domain

Abstract: Chatter stability of milling operations has been gaining significant attention with a view to improving the material removal rates in high speed machining of aluminum alloys and low speed milling of difficult to cut, thermal resistant alloys. This paper presents frequency and discrete time domain chatter stability laws for milling operations in a unified manner. The time periodic dynamics of the milling process are modelled. By averaging time varying directional factors at cutter pitch intervals, the stability lobes are solved directly and analytically. When the process is highly intermittent, which occurs at high speeds and low radial depth of cuts, the stability lobes are more accurately solved either by taking higher harmonics of directional factors in frequency domain, or by using semi-discretization method. This paper compares the stability solutions against the numerical solutions and experiments, and provides comprehensive mathematical details of both fundamental stability solutions.

Application of Taguchi and response surface methodologies for surface roughness in machining glass fiber reinforced plastics by PCD tooling

Abstract: This paper discusses the use of Taguchi and response surface methodologies for minimizing the surface roughness in machining glass fiber reinforced (GFRP) plastics with a polycrystalline diamond (PCD) tool. The experiments have been conducted using Taguchi’s experimental design technique. The cutting parameters used are cutting speed, feed and depth of cut. The effect of cutting parameters on surface roughness is evaluated and the optimum cutting condition for minimizing the surface roughness is determined. A second-order model has been established between the cutting parameters and surface roughness using response surface methodology. The experimental results reveal that the most significant machining parameter for surface roughness is feed followed by cutting speed. The predicted values and measured values are fairly close, which indicates that the developed model can be effectively used to predict the surface roughness in the machining of GFRP composites. The predicted values are confirmed by using validation experiments.

Machining : fundamentals and recent advances

Abstract: Metal Cutting Mechanics, Finite Element Modelling Tools (Geometry and Material) and Tool Wear Workpiece Surface Integrity Machining of Hard Materials Machining of Particulate-reinforced Metal Matrix Composites Drilling Polymeric Matrix Composites Ecological Machining: Near Dry Machining Sculptured Surface Machining Grinding Technology and New Grinding Wheels Micro and Nanomachining Advanced (Non-traditional) Machining Processes Intelligent Machining: Computational Methods and Optimization

Feed optimization for five-axis CNC machine tools with drive constraints

Abstract: Real time control of five-axis machine tools requires smooth generation of feed, acceleration and jerk in CNC systems without violating the physical limits of the drives. This paper presents a feed scheduling algorithm for CNC systems to minimize the machining time for five-axis contour machining of sculptured surfaces. The variation of the feed along the five-axis tool-path is expressed in a cubic B-spline form. The velocity, acceleration and jerk limits of the five axes are considered in finding the most optimal feed along the tool-path in order to ensure smooth and linear operation of the servo drives with minimal tracking error. The time optimal feed motion is obtained by iteratively modulating the feed control points of the B-spline to maximize the feed along the tool-path without violating the programmed feed and the drives’ physical limits. Long tool-paths are handled efficiently by applying a moving window technique. The improvement in the productivity and linear operation of the five drives is demonstrated with five-axis simulations and experiments on a CNC machine tool.

Investigations on the thermal effect caused by laser cutting with respect to static strength of CFRP

Abstract: To increase production volume and efficiency in the area of CFRP (carbon fiber-reinforced plastics) component production, fast, flexible and cost-efficient technologies are needed. One process that is necessary during CFRP component production is trimming and cutting. Although laser cutting in principle meets these requirements, it is often not used for component trimming and contour cutting, due to insufficient knowledge about the influences of thermal machining on the material behavior. It is a common argument that lasers, as a thermally acting tool, may damage the CFRP, thus reducing its strength properties. This, however, has never been proven or disproven. Therefore, this paper presents investigations on the influence of laser cutting on the static strength of a CFRP laminate. The material is cut using three different high-power laser sources: a pulsed Nd:YAG laser, a disk laser and a CO2 laser. Appropriate cutting parameters have been found, and the results in cut quality and heat-affected zone are discussed. With these parameter sets, specimens for tensile strength and bending tests have been prepared. These specimens have been tested under static tensile and bending conditions, and the results have been compared to conventional milling as well as abrasive water-jet cut samples. Though a clear dependency of the static strength values on the heat-affected zone was detected, all strengths were found to be far above the material values given by the producer of the laminate.

A study of delamination on graphite/epoxy composites in abrasive waterjet machining

Abstract: Delamination is a major component defect when machining composites or layered materials. This study aims to explore the mechanism of delamination in graphite/epoxy composites under abrasive waterjet (AWJ) machining. It is found that crack tips are generated by the shock wave impact of the waterjet at the initial cutting stage, while delamination is a result of water penetration into the crack tips that promotes water-wedging and abrasive embedment. Based on an energy conservation approach, a semi-analytical model is developed to predict the maximum delamination length generated by an AWJ. The model prediction is found in good agreement with the experimental data and can be used as a practical guide for process planning to minimise or eliminate the delamination defects on the components in AWJ machining of graphite/epoxy composites.

Machining of metal matrix composites: effect of ceramic particles on residual stress, surface roughness and chip formation

Abstract: Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes.

Use of the grey relational analysis to determine optimum laser cutting parameters with multi-performance characteristics

Abstract: This paper presents an effective approach for the optimization of laser cutting process of St-37 steel with multiple performance characteristics based on the grey relational analysis. Sixteen experimental runs based on the Taguchi method of orthogonal arrays were performed to determine the best factor level condition. The response table and response graph for each level of the machining parameters were obtained from the grey relational grade. In this study, the laser cutting parameters such as laser power and cutting speed are optimized with consideration of multiple-performance characteristics, such as workpiece surface roughness, top kerf width and width of heat affected zone (HAZ). By analyzing the grey relational grade, it is observed that the laser power has more effect on responses rather than cutting speed. It is clearly shown that the above performance characteristics in laser cutting process can be improved effectively through this approach.