Machined Workpiece Surface Research Articles

An Investigation of Lateral Surface Hardness and Related Cutting Forces in One-Directional Ultrasonic-Vibration Assisted Turning

The experimental investigation of UAT shows that the movement of cutting tool edge relative to the workpiece results from the cutting speed, feed speed and tools vibration in tangential direction affects the lateral machined surface of workpiece and leaves a repeating pattern of toothed regions on it. In UAT process, because of constant feed rate of tool toward workpiece, the cutting tool never separates from workpiece, though the tool rake face may separate periodically from chip in every cycle of vibration. This results in an increase in the surface hardness of the lateral machined surface in comparison with conventional turning (CT). The results of the present study confirm the advantage of UAT as far as the lower cutting force is concerned compared with CT. The higher surface hardness of the lateral surface observed in UAT causes the maximum cutting force to increase but the average force decreases with respect to CT.

Modelling cutting force including thrust and tangential damping in peripheral milling process

This paper presents an analytical model to predict cutting force components, including the cutting process damping in peripheral milling. The cutting process damping is associated to the interference mechanism between the tool flank and the machined workpiece surface. It creates two components (thrust and tangential) of a dynamic cutting force. The total force model including the process damping effect is obtained through numerical integration of the local forces. The effects of cutting and tool parameters on process damping and cutting force distributions are discussed. It is shown that the average value of the process damping and the amplitude of the cutting force increase with increasing feed rate, axial and radial depth of cut, and tool diameter; but decrease with increasing cutting speed. Besides, when the tool helix angle increases, the process damping increases, and the cutting force decreases. The number of tool’s teeth does not affect the variation of the damping process and cutting forces. However, it affects the number of cycles of the periodic cutting process.

Fast Cutter Workpiece Engagement Estimation Method for Prediction Of Instantaneous Cutting Force in Continuous Multi-Axis Controlled Machining

This study proposes a new efficient methodology to estimate an engagement between cutter of endmill and machined workpiece surface in continuous multi axis controlled machining process. In order to shorten calculation time for the engagement domain and realize real-time prediction of instantaneous cutting force, a new concept adapting ultra-parallel processing technology is proposed. In the proposed concept, the engagement domain is divided into a large number of estimation point. Then, inclusion estimation process between the estimation point and the machined workpiece volume is decomposed into simple estimation processes about tool swept volume. The developed prototype system shows good performance for complicate NC programs generated by commercial CAM system.

An Investigation of Lateral Surface Hardness and Related Cutting Forces in One-Directional Ultrasonic-Vibration Assisted Turning

The experimental investigation of UAT shows that the movement of cutting tool edge relative to the workpiece results from the cutting speed, feed speed and tools vibration in tangential direction affects the lateral machined surface of workpiece and leaves a repeating pattern of toothed regions on it. In UAT process, because of constant feed rate of tool toward workpiece, the cutting tool never separates from workpiece, though the tool rake face may separate periodically from chip in every cycle of vibration. This results in an increase in the surface hardness of the lateral machined surface in comparison with conventional turning (CT). The results of the present study confirm the advantage of UAT as far as the lower cutting force is concerned compared with CT. The higher surface hardness of the lateral surface observed in UAT causes the maximum cutting force to increase but the average force decreases with respect to CT.

Monitoring of Vibrations in the Technology of AWJ

Vibrations of cutting head act as co-factor causing striation of machined work-piece surface, deteriorating its surface quality. In this paper, measurement and evaluation of vibrations generated during the AWJ machining is performed using specialized diagnostic systems. In conclusion, means to minimize influence of cutting-head vibrations on the machined work-piece surface quality are discussed.

Influence of Cutting Parameters on Surface Characteristics for Milling Powder Metallurgy Nickel-Based Superalloy

Powder metallurgy (PM) nickel-based superalloy is regarded as one of the most important aerospace industry materials, which has been widely used for engine components. As the demands of the service performance increase, the surface characteristics are becoming more and more important. However, the machined surface of PM nickel-based superalloy is easily damaged due to its poor machinability. A series of milling experiments in a wide range of speeds were carried out to investigate the effects of dry milling parameters on the surface characteristics of PM nickel-based superalloy. The machined surface is evaluated in terms of surface roughness and work hardening. The results show that, milled surface characteristics of PM nickel-based superalloy are sensitivity to the cutting speeds. The machined surface roughness increases with increase of the cutting speed, but with further increase of cutting speed between 70 to 90 m/min and 150 to 170 m/min two decreases in surface roughness appear. For work hardening, it can be seen that the machined workpiece surface hardens seriously.

Research of Tool Wear Condition Recognition Diagnosis System Based on the Machined Workpiece Surface Texture Image

Aiming at the machined workpiece surface texture images,some technology about image pre-processing and the texture feature extraction based on gray level co-occurrence matrix are researched. Then it is time for the analysis of the texture characteristic parameters based on BP neural network and the identification and diagnosis of tool wear state, Finally the recognition diagnosis system interface is designed by Matlab-GUI.System simulation shows that the interface fusion of image processing and neural network is a good way to ensure the realization of tool wear condition recognition,what’more, the identification diagnosis rate is profect.

Influence of cutting speed on surface integrity for powder metallurgy nickel-based superalloy FGH95

Powder metallurgy (PM) nickel-based superalloy FGH95 has been widely used for components, which requires the greatest service performance. The surface integrity is becoming more and more important in order to satisfy the increasing service demands. However, the machined surface of FGH95 is easily damaged due to its poor machinability. The purpose of this paper is to investigate the effects of dry milling process parameters on the surface integrity of FGH95. Experiments were conducted on a CNC machining center under different cutting speeds. The machined surface is evaluated in terms of surface roughness, microhardness and white layer. Experiments results show milled surface integrity of FGH95 is sensitivity to the cutting speeds. The machined surface roughness decreases with increase of the cutting speed, but with further increase of cutting speed between 80 m/min to 100 m/min an increase in surface roughness appears. For microhardness, it can be seen that the machined workpiece surface hardens seriously. It can also draw the conclusion that cutting speed has the marginal effect on the white layer thickness generated in the machined subsurface.

A New Experimental Approach for Determination the Effect of Tool Flank Wear Length on Cutting Temperature Distributions

This paper gives a new experimental approach for determination the effect of tool flank wear length on workpiece surface cutting temperature distributions. Three different tool flank wear lengths 0.3, 0.5, 1mm were given by wire cutting, which were much more useful to study the effect of tool flank wear lengths on machined workpiece surface. VarioCAM high resolution head was used to measure the cutting zone temperature distribution, and for protecting the camera lens two pieces of silicon with a thickness of 0.5 mm were put ahead of the camera.

Development of a New BCB ELID Lapping Process

In this paper, the mechanism of Electrolysis In-process Dressing (ELID) lapping process using new BCB (bamboo charcoal bonded) abrasive wheel is researched. Some experiments of machining for silicon wafers were carried out for exploring the effect of some machining process parameters on material removal rate and surface roughness. Experiments show that: Material removal rate and machined workpiece surface roughness are increased with increase of the lapping wheel’s rotation speed and processing loading; The machined workpiece surface quality is affected with the lapping wheel surface condition, due to the abrasives are trued by electrolysis dressing in the lapping process, therefore the BCB lapping wheel always keeps better machining condition to obtain excellent machined workpiece surface quality efficiently.

High-Production Lathe-Turning with Ra ≤ 1μm

At classical machining with a tool having defined tip radius, the shape of tip is copied onto the machined surface of workpiece. Among the highest height of profile unevenness Rz, shift f and tip radius, the analitical relation is valid, by which increasing of f strongly increases Rz. This is the main obstacle in increasing machining productivity. The solution is in increasing the tip radius of tool. Within enourmous increase of re even by roughing, the medium arithmetic height of unevenness of machined profile Ra less than 1μm can be obtained. This contribution analyses this option.

Nanometric ductile cutting characteristics of silicon wafer using single crystal diamond tools

In current wafer fabrication, most machining processes, such as slicing, edge grinding, finishing, lapping, polishing, back thinning, and dicing, are based on grinding or abrasive process, which always generated microcracks and subsurface damage. In this article, theoretical analysis on ductile mode cutting of silicon wafer showed that the machined silicon surface with free of fracture and nanometer scale surface roughness can be achieved when dislocation dominated the chip formation rather than crack propagation. Nanometric cutting on silicon wafers using an ultraprecision lathe with a single crystal diamond tool has been carried out to verify ductile cutting performance of silicon wafer. The machined workpiece surfaces and diamond tools used were examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The experimental results are found to well substantiate the analytical findings, and nanometric ductile mode cutting of silicon wafer has been successfully achieved under the critical cutting conditions.

Surface characterisation-based tool wear monitoring in peripheral milling

In the last decade, the progress of surface metrology has led to improved 3D characterisation of surfaces, offering the possibility of monitoring manufacturing operations and providing highly detailed information regarding the machine tool condition. This paper presents a case study where areal surface characterisation is used to monitor tool wear in peripheral milling. Due to the fact that tool wear has a direct effect on the machined workpiece surface, the machined surface topography contains much information concerning the machining conditions, including the tool wear state. By analysing the often subtle changes in the surface topography, one can highlight the tool wear state. This paper utilises areal surface characterization, areal auto-correlation function (AACF) and pattern analysis to illustrate the effect of tool wear on the workpiece surface. The result shows the following: (1) tool wear, previously difficult to detect, will influence almost all of the areal surface parameters; (2) the pattern features of AACF spectrum can reflect the subtle surface texture variation with increasing tool wear. The authors consider that, combined analysis of the surface roughness and its AACF spectrum are a good choice for monitoring the tool wear state especially with the latest developments in on-machine surface metrology.

Mechanisms of Al/SiC Composite Machining with Diamond Whiskers

The objective of this study is to experimentally investigate the mechanisms in machining of aluminum/silicon carbide (SiC) composite with two types of diamond whiskers. These whiskers are prepared from polycrystalline diamond compacts (PDC) and chemical vapor deposition (CVD) diamond plates which are cut into dimensions of 10×0.3×0.6 mm with an Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser. In order to obtain sharp and consistent cutting edges, the diamond whiskers are polished with diamond powders of the average grain sizes of 10 µm, 2.5 µm and 1 µm, respectively. A precision grinder is used to conduct machining of the aluminum/SiC composite at a depth of cut smaller than that in the conventional milling but larger than the individual grit depth of cut in grinding. Scanning electron microscopy (SEM) is utilized for observing the machined workpiece surfaces, the whisker cutting edges, and a surface profilometer for inspecting surface roughness and verifying the actual depth of cut in the machined workpiece. The study discusses the mechanisms of workpiece material removal and diamond whisker wear in machining of the aluminum/SiC composite.

The influence of tool flank wear on residual stresses induced by milling aluminum alloy

The machining processes could induce residual stresses that enhance or impair greatly the performance of the machined component. Machining residual stresses correlate very closely with the cutting parameters and the tool geometries. In this paper, the effect of the tool flank wear on residual stresses profiles in milling of aluminum alloy 7050-T7451 was investigated. In the experiments, the residual stresses on the surface of the workpiece and in-depth were measured by using X-ray diffraction technique in combination with electro-polishing technique. In order to correlate the residual stresses with the thermal and mechanical phenomena developed during milling, the orthogonal components of the cutting forces were measured using a Kistler 9257A type three-component piezoelectric dynamometer. The temperature field of the machined workpiece surface was obtained with the combination of infrared thermal imaging system and finite element method. The results show that the tool flank wear has a significant effect on residual stresses profiles, especially superficial residual stress. As the tool flank wear length increases, the residual stress on the machined surface shifts obviously to tensile range, the residual compressive stress beneath the machined surface increases and the thickness of the residual stresses layer also increases. The magnitude and distributions of the residual stresses are closely correlated with cutting forces and temperature field. The three orthogonal components of the peak cutting forces increase and the highest temperature of the machined workpiece surface also increases significantly with an increase in the flank wear. The results reveal that the thermal load plays a significant role in the formation of the superficial residual stress, while the dominative factor that affects thickness of residual stresses layer is the mechanical load in high-speed milling aluminum alloy using worn tool.

Determination of key workpiece product characteristics in a machining fixture using uncertainty analysis and loss cost function implementation

The study of fixture related errors is playing an increasingly important role in the improvement of machined part quality. In this work, the locator variability of machining fixtures is analyzed following an uncertainty approach, allowing us to estimate the effect of fixture related geometrical errors on key product characteristics of machined workpieces. Monte Carlo simulation was implemented to generate sufficient variability to determine the expected value of the measuring points of the machined workpiece surface and its related key product characteristic. The results from the Monte Carlo simulation allow sufficient range of values to construct a mathematical relationship between fixture related errors and machined workpiece key product characteristics. Furthermore, the Taguchi loss function is used to investigate the loss cost incurred by a given fixturing uncertainty scheme. An example problem of a prismatic workpiece is presented, where the locating error due to the fixturing system is evaluated in order to know its influence on the workpiece flatness and its associated uncertainty.

Numerical and experimental study of dry cutting for an aeronautic aluminium alloy (A2024-T351)

In the present contribution, numerical and experimental methodologies concerning orthogonal cutting are proposed in order to study the dry cutting of an aeronautic aluminium alloy (A2024-T351). The global aim concerns the comprehension of physical phenomena accompanying chip formation according to cutting velocity variation. For the numerical model, material behaviour and its failure criterion are based on the Johnson–Cook law. The model proposes a coupling between material damage evolution and its fracture energy. A high-speed camera was used to capture the chip formation sequences. The numerical results show that the chip–workpiece contact and the tool advancement induce bending loads on the chip. Consequently, a fragmentation phenomenon takes place above the rake face when the chip begins to curl up. The computed results corroborate with experimental ones. The numerical results predict the residual stress distribution and show high values, along the cutting direction, on the machined workpiece surface.

A Tool Path Modification Approach to Cutting Engagement Regulation for the Improvement of Machining Accuracy in 2D Milling With a Straight End Mill

In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.

Characteristics of ductile mode chip formation in nanoscale cutting of brittle materials

In this paper, a comprehensive study of the machining characteristics of nanoscale ductile mode cutting of brittle materials is presented, covering the critical cutting conditions for the ductile mode of chip formation, cutting conditions for crack initiation in the chip formation zone, effect of the cutting edge radius, machined workpiece surface and subsurface damage, effect of ultrasonic vibration assistance, mechanism of nanoscale ductile mode chip formation, cutting forces, tool wear and dynamic hard particles in the chip formation zone. Systematic experiments for nanoscale cutting of a number of brittle materials, including tungsten carbide, silicon and glass, are conducted and Molecular Dynamics (MD) modelling and simulation for nanoscale cutting of monocrystalline silicon are carried out. The results are shown in detail in the paper.

Characteristics of ultrasonic vibration-assisted ductile mode cutting of tungsten carbide

In this study, investigations were carried out to evaluate the characteristics of ultrasonic vibration-assisted cutting of tungsten carbide material using a CNC lathe with CBN tool inserts. The cutting forces were measured using a three-component dynamometer, and the machined workpiece surfaces and chip formation were examined using a SEM. The experimental results showed that the radial force F x was much larger than the tangential force F z and axial force F y . The SEM observations on the machined workpiece surfaces and chip formation indicated that the critical condition for ductile mode cutting of tungsten carbide was mainly the maximum undeformed chip thickness when the tool cutting edge radius was fixed, that is, the ductile mode cutting can be achieved when the maximum undeformed chip thickness was smaller than a critical value. Corresponding to the chip formation mode (ductile or brittle), three types of the machined workpiece surfaces were obtained: fracture free surface, semi-fractured surface and fractured surface. It was also found that the cutting speed has no significant effect on the ductile chip formation mode.