Search

As an important transmission component, the spur gear has been widely used in automobiles and various mechanical equipment. However, spur gears are usually produced by the hobbing and shaving, which inevitably reduces the service strength and service life of the gear. In this paper, the one-step punching forming process of spur gear is presented. Compared with the traditional gear machining process, the process not only avoids the destruction of the metal flow line but significantly decreases the material cost. The effect of tooth filling and equivalent strain accumulation on gear forming quality was investigated by finite element simulation. The effects of upper die punching speed, lower die preheating temperature, and friction coefficient on lower die wear during forming were studied by response surface method. The optimum process parameters of punching of spur gear were a lower die preheating temperature of 280 ℃, friction coefficient of 0.27, and upper die feed speed of 8.3 mm/s, respectively. It is predicted that about 110,000 gears can be produced before the wear failure of the lower die. On the basis of the finite element simulation results, the gear punching experiment is performed. The experimental results are in good agreement with the simulation results, and the metal flow line at the tooth is uniform and continuous, which verifies the reliability of the one-step punching process. [ABSTRACT FROM AUTHOR]

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]

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]

In cutting, the mechanical impact caused by material mechanics, geometric discontinuity, and intermittent cutting process is the main factor that induces cutting tool fracture. Impact fracture and fatigue failure of cutting tools are sudden, which can be harmful to safe production and quality control. In this paper, the effect mechanism of shim stiffness on the impact fracture performance of a tool in a mechanically clamped cutting tool system is studied. Furthermore, the vibration model of the tool-shim system is established to analyze the impact loading response characteristics of the tool-shim system under different stiffness shims. Meanwhile, the effect of shim stiffness on the loading rate, peak value, high-level fluctuation, unloading rate, and elastic energy release of shim elastic reaction force is explored. Apart from that, theoretical analysis of the stress field change near the tool crack tip is carried out. Finally, intermittent turning experiments are performed, including carbide inserts with four shims of N8 aluminum alloy, TC4 titanium alloy, 08 steel, and YT14 cemented carbide. Moreover, the analysis of each stage of the vibration response is verified. According to the results, the stiffness of the shim affects both the impact fracture of the tool basal body and the coating peeling. Besides, appropriately weakening the shim stiffness can reduce the load peak value of the shim elastic reaction force on the tool, the high load fluctuation amplitude, the unloading rate, and the dynamic stress intensity factor (DSIF), which can be conductive to improving the impact damage resistance of the tool. [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]

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]

Burnishing has been proved to be a faster, lower-cost, and more effective strengthening process to improve surface integrity especially for alloy components when compared with heat treatment. It has been suggested that smaller static force is necessary to the required deformation when vibration excitation is superimposed to the static force, and this kind of material softening phenomenon resulting from external excited vibration is called acoustoplastic effect. This work is to investigate the influence of vibration excitation on the material under deformation in terms of stress condition. A 3D finite element model has been developed and validated by the experimental data. The effect of vibration frequency of 0–28 kHz on the total contact force as well as the distribution of residual stress and plastic strain fields was comprehensively analyzed. The vibrations at different frequencies studied in this work caused the increase of the maximum contact force. Overall, vibrations at 0 kHz, 0.1 kHz, 1.3 kHz, and 14 kHz led to the increases of the maximum residual stress and equivalent plastic strain while not exerting pronounced effect on the distribution of stress and strain fields of treated samples. However, in case of a very high frequency vibration at 28 kHz, pulse hammering contact force produced between the rolling ball and being treated surface, resulting in a significant change of the distribution of stress and strain fields. The observations at high vibration frequency can be interpreted as that pulse hammering contact force produced at some high frequency coupled with other process parameters caused the formation and continuous propagation of dynamic oscillatory stress wave traveling long distance inside the material. [ABSTRACT FROM AUTHOR]

Saw tooth chip is a typical characteristic encountered in high-speed machining. It consists of nearly undeformed segments and highly sheared concentrated shear bands. However, no consensus on the formation of the concentrated shear band has been reached though several saw tooth chip formation models have been built. In this paper, the concentrated shear band formation procedure is analyzed based on a new proposed saw tooth chip formation model. Cutting experiments have been conducted to validate the proposed mode. It shows that the plastic side flow and elastic compression of the uncut chip are crucial for the concentrated shear band formation. The localized shear at the inner end (tool tip side) of the primary shear plane firstly takes place under the indentation of cutting tool. Then, the second localized shear is produced at the outer end (free surface side) of the primary shear plane due to stress concentration there, after which the whole concentrated shear band forms. The stress transition at the outer end of the primary shear plane makes the second localized shear easier evolve into cracks. Influences of material brittleness and cutting speed on initiation and propagation of the concentrated shear band are also analyzed. [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]