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Due to the low rigidity of the boring bar with a large length-to-diameter ratio, chatter easily occurs during deep hole boring. In this paper, an ultrasonic vibration boring bar with a length-to-diameter ratio greater than 10 is designed to suppress the chatter during the boring operation of deep holes. First, the dynamic model of the boring operation is built to guide the design of the ultrasonic vibration boring bar. Then, the optimal design of structure parameter of the ultrasonic vibration boring bar is performed by the finite element method, and then the optimized boring bar is manufactured. Finally, the vibration performance test and cutting experiments are carried out to verify the machining capability of the bar. The experimental results show that the ultrasonic vibration boring bar can reduce the cutting force by about 35%, improve the system stability, and increase the quality of the relative machined surface by about 43%, which demonstrate the feasibility of chatter suppression of the developed ultrasonic vibration boring bar. [ABSTRACT FROM AUTHOR]

Burnishing is a way to realize surface strengthening by plastic deformation behavior. How to characterize the severe plastic deformation in subsequent burnishing process and how to make the severe plastic deformation more reasonable and effective for the improvement of machined surface integrity have become key problems. This work studied the relationships among plastic deformation behaviors, strain energy, and improved surface integrity ratio in subsequent burnishing with different initial surface conditions. To achieve this purpose, a numerical strain energy model was first established and then utilized to analyze the material flow behaviors and plastic deformation mechanism. The results indicated that the strain energy density decreases first and then increases, while the strain energy and corresponding energy efficiency gradually increases with the increase of turning feed, i.e., surface residue. As a result, the plastic deformation in subsequent burnishing first increases and then decreases with the increase of surface residue and reached the severest when the turning feed is 0.35 mm/r. Even though the turning-induced surface integrity can be further improved by the subsequent burnishing, the improved surface integrity ratio showed a downward trend with the increase of the turning feed, which ever increased the machining efficiency for the process chain. It is expected to improve both the energy efficiency ratio and improved surface integrity ratio, so as to improve the sustainability of the subsequent burnishing process. [ABSTRACT FROM AUTHOR]

Coated carbide tools are widely used in the processing of nickel-based superalloys due to their excellent wear resistance, high strength, and good hardness at high temperatures. In this paper, the high-speed milling experiments and finite element simulation of Inconel 718 are carried out by using PVD TiAlN-coated carbide tools. Simulations of tool temperature, cutting force, and chip morphology were performed to analyze the effect of cutting speed on the degree of sawtooth chip formation and the effect of sawtooth chip formation on the cutting force and tool wear. The results show that the cutting temperature mainly focuses on the rake face, and with the cutting speed increasing from 60 to 120 m/min, the maximum temperature of the rake face increases from 580 to 660 ℃. The maximum temperature region (MTR) on the rake face gradually approaches the tool nose with a decrease in the cutting speed. The generation of sawtooth chips leads to fluctuations in the cutting force component. As the cutting speed increases, the degree of chip sawing increases. The effect of the sawtooth chip on the fluctuation of the cutting force will also increase, thus increasing the degree of tool wear. [ABSTRACT FROM AUTHOR]

Ultrasonic elliptical vibration cutting (UEVC) has been successfully applied to precision machining of difficult-to-machine materials with its advantages of low machined surface roughness and low tool wear. In this study, an eccentric cone UEVC tool is proposed based on the mechanical vibration theory, with the idea of combining longitudinal vibration and bending vibration. The preliminary dimensions of the UEVC tool are obtained by theoretical calculations. Then, the dimensions of the tool are optimized through finite element analysis (FEA) to meet the requirements of vibration modes and resonant frequencies. Finally, a prototype of the eccentric cone UEVC tool is developed, and the vibration performance tests and cutting experiments are conducted on the designed tool to verify its cutting trajectory and cutting performance. According to the results, the new developed eccentric cone UEVC tool can achieve the elliptical vibration trajectory at the tool tip; the resonant frequency of the tool is 28019 Hz; and the longitudinal and the bending amplitude are 6.2 μm and 4.9 μm, respectively. The new developed eccentric cone UEVC tool can obtain workpieces with the surface roughness about 0.337 μm and reduced the tool wear. [ABSTRACT FROM AUTHOR]

The stability prediction is an effective approach to suppress the unstable milling process caused by the regenerative chatter. Through updating a numerical solution scheme (NSS), a fast prediction method is proposed in this paper. Firstly, a NSS is constructed by combining the Lagrange polynomial and Euler's method. Then, the solution of the differential equations described the milling process is transformed into the initial-value problem of the equation which is expressed by the built NSS over each small discrete time interval. Subsequently, the state transition matrix over one tooth passing period is established to predict the stability lobe diagram (SLD) via the Floquet theory. Finally, the computational performances of the proposed method are verified by the single and two DOF dynamic models. Compared with the complete discretization scheme, the computational accuracy and efficiency of the proposed method are increased by 2.69 times and 2.01 times, respectively. The proposed method reduces the computational accuracy by 2.16 times in comparison to the first-order full-discretization method, but it increases the computational efficiency by 2.2 times. [ABSTRACT FROM AUTHOR]

The stability prediction is usually used to avoid the unstable machining in milling process. According to the Lagrange-Simpson hybrid interpolation scheme, this paper improves a numerical integration method (NIM) to perform the milling chatter prediction accurately and efficiently. Firstly, the higher-order numerical integral formulas (NIFs) are constructed based on the Lagrange polynomial. Thus, the third-order and fourth-order NIMs are built and investigated respectively. Then, to improve the calculated performance of the NIMs, the Simpson scheme is introduced to decrease the local discretization error. Finally, the comparisons among the built NIMs and the existing discretization methods are carried out by calculating the convergence rate and the stability boundaries. Compared to the third-order NIM and the third-order full-discretization method, the proposed second-order Lagrange-Simpson NIM shows the better computational performance. [ABSTRACT FROM AUTHOR]

Three-axis computer numerical control machining centers are commonly used in machining due to their simple operations. When machining curved surfaces, the 3-axis CNC machining centers use interpolation line segment to fit the curved surfaces. The quality of the machined surface is affected by the length of the interpolation line segment. Sharp corners are formed at the junction of straight segments. The appearance of sharp corners will lead to increased stress concentration. To study the relationship between machined surface quality and interpolation straight line, this paper establishes the mathematical model of surface topography in ball-end milling multi-curved surfaces by a 3-axis milling center with considering the acceleration and deceleration controls. Based on the surface topography model, the stress concentration factor is analyzed in machining curved surfaces with different lengths of interpolation lines. The results show that the stress concentration factor decreases with the increase of the central angle when the length of interpolation lines and the radius of curvature are kept in constant, while decreases with the increase of the radius of curvature when the length of the interpolation lines and the central angle are held on. Moreover, the stress concentration factor increases as the length of the interpolation lines increases when the radius of curvature and the central angle are kept in constant. A method for selecting proper length of interpolation lines based on the stress concentration is proposed. In addition, the quality of the machined surfaces can be improved through the optimization of the tool path. [ABSTRACT FROM AUTHOR]

DLC has been applied as coating material in the machining of difficult-to-cut materials, and shows a good cutting performance. In this study, Cr/W-DLC/DLC-coated tools were compared with other three kinds of coated tools (TiC-, TiAlN-, Al2O3-) to investigate the cutting performance in the machining of Al–Si alloy. The influence of Cr/W-DLC/DLC-coated tools on the cutting performance under different cutting speeds was studied. Cutting force, cutting temperature, heat partition coefficient, cutting deformation rate, plastic deformation of machined surface, the interface temperature, and stress were investigated numerically with the aid of finite element method (FEM). Actual cutting experiments were carried out to verify the FEM models by means of the cutting force and cutting temperature measurement. The investigation results show that Cr/W-DLC/DLC-coated tool had the best cutting performance among these four kinds of coated tools. With the increasing of cutting speeds, cutting force and cutting temperature showed an increase trend, while the plastic deformation depth of machined surface and heat partition into cutting tool all showed a decrease trend during the machining with Cr/W-DLC/DLC-coated tool. This investigation can provide the theory basis or technical guidance for the cutting practice with Cr/W-DLC/DLC-coated tools. [ABSTRACT FROM AUTHOR]

The coating effect on the cutting temperature has long been a hot topic in understanding heat transfer mechanism in machining coated tools, and especially the multi-layer coated tools. For multi-layer coated tools, the coating structure, coating thickness, and coating material will affect the cutting temperature of the tools. This paper is devoted to the cutting temperature in dry turning of H13 hardened steel with multi-layer coatings. New analytical models for estimating coating temperature and coating–substrate interface temperature were proposed. The multi-layer coating can be equivalent to mono-layer composite coating, which applies equivalent coating layer approach, and was developed to estimate the cutting temperature in turning by heat transfer model of mono-layer coated tool. The analyzed results were compared with appropriate experimental process data using thermocouples and FEM simulated data. The models can accurately reflect the cutting temperature of two multi-layer coated tools under the same cutting condition. [ABSTRACT FROM AUTHOR]

Subtractive machining is required for laser cladded coatings to improve surface quality. However, cutting force performs distinctively due to the coarse profile and structural properties of the laser cladded coatings. The coarse profile of the laser cladded coatings resulted in variable depth of cut in rough turning, while the vibration caused the fluctuations of cutting force in finish turning. In this research, the cutting force characteristics in remanufacturing turning of the laser cladded coatings are investigated. Firstly, cutting force model was established by considering the coarse profile as well as cutting vibration. The experimental results further confirmed that the presented model could predict the cutting forces in remanufacturing processes. Secondly, the effects of the coarse profile and cutting vibration on cutting forces were analyzed based on the presented model. The rough profile is prone to cause tool breakage in rough turning, while the cutting vibration generated great influence on radial force component in finish turning. The results suggested that the rough turning needed to be divided into multiple passes for peeling-off, and the stiffness should be enhanced to reduce cutting vibration in finish turning. [ABSTRACT FROM AUTHOR]

This paper presents a study of the relationship between cutting force and tool crater wear of solid carbide tool during milling Ti6Al4V. The cutting force model in milling considering tool crater wear is discussed, which shows that for given the cutting conditions, tool geometries, and workpiece material, cutting force under the tool crater wear effect could be predicted easily and conveniently. The tool wear condition in milling Ti6Al4V is obtained by finite element simulation method. In addition, the experimental work of end milling Ti6Al4V with solid carbide tool is developed. Comparisons among experiment results, mathematical model results, and finite element simulation model results, including cutting force and tool wear, are discussed. The results show that the proposed mathematical model could predict cutting force under the tool crater wear effect with higher accuracy. [ABSTRACT FROM AUTHOR]

Since Dr. Carl Salomon proposed the well-known hypothesis on cutting temperatures in 1931, the debate on the hypothesis has never stopped. It shows that evolutions of temperatures with the increase of cutting speed measured at different points are different. From the tool wear and surface integrity point of view, this paper focuses on the evolutions of chip temperature (Chip temp.), tool-chip contact temperature (T-C temp.), and tool-workpiece contact temperature (T-W temp.) with the increase of cutting speed from low (100 m/min) to very high (7000 m/min). First, the cutting heat generation and the temperature increment in machining are theoretically analyzed. Then the influences of chip shape and mechanical property variations with the increase of cutting speed on the temperatures are analyzed. Finally, the cutting temperatures are semiquantitatively derived from chip colors and other heat characteristics in the chip and cutting tool obtained in cutting experiments: evolutions of Chip temp., T-C temp., and T-W temp. with the increase of cutting speed are presented based on the experiment results. The influence of chip shape and temperature variation on tool wear are also discussed. [ABSTRACT FROM AUTHOR]

Diamond-like carbon (DLC)-coated tools are suitable for the machining of various aluminum alloys, graphite, and other non-ferrous metals. The shortcomings of DLC-coated tools such as high internal residual stress, low toughness, and poor adhesion strength limit their application. In order to reveal the mechanical and cutting performance of DLC-coated tools, a DLC monolayer coating, Cr/CrN/DLC composite coating, and Cr/W-DLC/DLC composite coating had been prepared on the cemented carbide cutting tools. The influences of transition interlayer on the microstructure and mechanical properties of DLC coatings were analyzed. Tool lives, wear mechanism, and machined surface roughness obtained with uncoated cemented carbide tool, DLC monolayer–coated tool, and Cr/x/DLC-coated tool during the machining of Al-Si alloys were investigated. Compared with DLC monolayer coating, the strength ratio (ID/IG) of the DLC composite coatings with Cr/x transition structure was improved, while the sp3 covalent bond contents was decreased. The results show that the adhesion strength and toughness of the Cr/x/DLC composite coating were enhanced, and the residual stress was greatly reduced. The cutting tests further indicate that the DLC coating significantly improved the tool life. Based on comprehensive evaluation, the Cr/W-DLC/DLC composite coating has the highest adhesion, highest toughness, the lowest residual stress, and the longest tool life, and it is suitable for the machining of non-ferrous metal. [ABSTRACT FROM AUTHOR]

Lots of heat generated in the cutting deformation zone can cause the temperature rising of cutting tool and workpiece during the cutting process. Tool temperature is mainly depended on the heat energy entering into tool in the secondary deformation zone. Higher working temperature can weaken the cutting tool strength and then deteriorate the tool wear. Advanced coating layer deposited on the tool substrate can change the tool-chip friction and affect the heat partition in the tool-chip interface. In order to reveal the mechanism of heat conduction in the secondary deformation zone, the model of heat partition into cutting tool was built. With the aid of finite element method (FEM), the relative parameters which were necessary for the solving of heat partition model were quantified. Actual cutting experiments were carried out to the verification of the FEM models by means of the cutting force and temperature measurement. Influences of coatings (i.e., coating materials, coating thickness) and cutting speeds on the heat partition were analyzed. And then, rake face temperatures obtained at four kinds of coated tools were compared. The investigation results showed that TiC coating appears as the maximum value and Al2O3 coating appears as the minimum value of heat partition coefficient into cutting tool among these four kinds of coatings (i.e., TiC, TiN, TiAlN, Al2O3). With the increasing of coating thickness and cutting speeds, heat partition into cutting tool all showed a decrease trend. Al2O3-coated tool had the maximum rake face temperature among these four kinds of coated tools; however, the location of peak temperature on the rake face of Al2O3-coated tool was the shortest distance from the tool tip. [ABSTRACT FROM AUTHOR]

Coated cutting tools have been widely employed in metal cutting operations owing to its excellent abrasion resistance and heat transfer performances. Rake face temperature is the primary factor that determines the temperature distribution in the cutting tool body. Based on the heat source theory, a new prediction model is proposed in this paper to forecast the temperature distribution on the rake face. Infrared image is used to develop a new turning experimental apparatus to measure the rake face temperature of coated tool during the cutting process. Rake face temperature measurement results are used to verify the proposed model prediction results of temperature distribution. Several cutting tests are carried out with monolayer coated tools in the machining of H13 hardened steel. The rake face temperature in monolayer coated tool for machining H13 shows an increase trend as the cutting speed increases. The influence parameters including thermo-physical properties and tool/workpiece frictional coefficient of coating material on temperature distribution in coated tools are discussed and illustrated. The research results presented in this paper can help to access the potential of coated tools used in the hardened steel machining. [ABSTRACT FROM AUTHOR]

FGH95 is one kind of powder metallurgy (PM) superalloy which has excellent mechanical properties at high temperature. It has been developed for turbine disc applications to improve aeroengine efficiency under higher operating temperatures. However, this kind of superalloy is very difficult to machine because of its poor thermal diffusivity and work-hardening properties during the machining process. The machining process can lead to damage of the machined surface and subsurface. Thus, the purpose of this paper was to investigate damage of the machined surface and subsurface in hard machining of FGH95 PM superalloy. Orthogonal milling experiments using coated carbide inserts were carried out on a CNC machining center. The machined surface was observed and recorded using an optical microscope, white light interferometer, and scanning electron microscope. Machined surface defects were recorded and analyzed. The effects of cutting speed on machined surface roughness, white layer thickness, plastic deformation, and microhardness were investigated. The research results show that better surface roughness can be generated at higher cutting speeds, while several defects appeared on the FGH95 machined surface. White layer thickness and machined surface microhardness increase with the cutting speed. Also, plastic shear strain in the machined surface layer increases with cutting speed. The depth of plastic deformation decreases with the increase of cutting speed. These investigation results are essential for the evaluation of PM superalloy surface integrity and are significant for the prediction of PM superalloy service life. [ABSTRACT FROM AUTHOR]

High-speed machining is being recognized as one of the key manufacturing technologies for getting higher productivity and better surface integrity. FGH95 powder metallurgy superalloy is a kind of nickel-based superalloy which is produced by near-net-shape technology. With increasing demands for high precision and high performance of FGH95 components in aerospace industry, it is essential to recognize that the machined surface integrity may determine machined part service performance and reliability. Then, little is known about the machined surface integrity of this superalloy. Thus, the surface integrity in high-speed machining of FGH95 is investigated in this paper. Experiments are conducted on a CNC milling center with coated carbide tools under dry cutting conditions. The surface integrity is evaluated in terms of surface roughness, microhardness, and white layer. The influence of cutting speed on chip morphology is also investigated. Experiment results show that surface integrity and chip morphology of FGH95 are very sensitive to the cutting speed. When cutting speeds are below 2,400 m/min, the values of surface roughness have little variation, while when cutting speeds are in the range of 2,800-3,600 m/min, the values of surface roughness are higher than that of other cutting speeds. Severe work hardening is observed resulting from high-speed machining of FGH95 superalloy. The higher the cutting speed, the higher the surface hardness. When cutting speeds are in the range of 2,800-3,600 m/min, the white layer thickness is slightly higher than that of other cutting speeds. In high-speed machining of FGH95, the chip is segmented and has a typical sawtooth shape. The degree of serrated chip increases with the cutting speed. When the cutting speeds exceed 2,400 m/min, serrated chips change into fragment chips. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]