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Friction stir welding (FSW) of galvanized steel offers unique advantages as it can avoid the extensive metallurgical problems associated with fusion welding. However, conventional FSW still leads to a higher temperature in the stir zone, which deteriorates the microstructure. To obtain a satisfactory weld, the welded joints of galvanized steel were created by FSW with different cooling rates employing a W–Re rotary tool with a large-diameter needle. The correlation between the microstructure evolution and mechanical behavior of joints at different cooling rates was systematically studied. The results demonstrate that the rapid cooling rate favors the refinement of ferrite and diffuse distribution of Fe3C. In addition, weakening of the texture and dispersion of dislocations were also observed after fast cooling FSW. It can be concluded that the microstructural evolution mechanism of the stirring zone (SZ) is continuous dynamic recrystallization at a slow cooling rate, while the microstructure has discontinuous dynamic recrystallization as the primary evolution mechanism at a fast cooling rate. Based on these advantages, the tensile specimens with fast cooling FSW obtained a synergistic improvement in strength-ductility, even surpassing the base material. This work provides new ideas for welding galvanized steel. [ABSTRACT FROM AUTHOR]

In this paper, a novel friction stir welding tool with large diameter disc at the tip of the pin was developed to solve the problems in aluminum/magnesium friction stir lap welding. Based on the structural design of the shoulder at the tip of the pin, the temperature difference in the thickness direction of the joint was coordinated, and the aluminum-magnesium dissimilar lap joint was successfully prepared in two kinds of lap configuration. Taking AZ31B magnesium alloy and 6061 aluminum alloy as the research object, the defects and microstructure of weld joint were observed and analyzed by optical microscope and scanning electron microscope. Additionally, their mechanical properties were also evaluated. The results show that an excellent metallurgical bonding was formed between aluminum and magnesium. With the increase of the effective plate thickness and the decrease of the effective lap width, the unique hook defect shape of lap welding joint was optimized, which also promoted the improvement of the mechanical properties of the weld. In the tensile-shear test, it was found that the tensile shear strength was improved, and the joint fractured in a mixed mode of toughness and brittleness due to the change of the shape of the hook defect, and it is a mixed fracture of toughness and brittleness. [ABSTRACT FROM AUTHOR]

This paper proposes an error allocation method based on sensitivity analysis and optimized genetic algorithm, which allocates the errors of the five-axis ultra-precision machine tool. Firstly, a geometric error model of the five-axis ultra-precision machine tool is established. Then, the sensitivity indices of the errors are calculated, and the error boundaries and cost boundaries for error allocation are set according to the indices. Finally, the error allocation is carried out by using optimized genetic algorithm, and the results of the error allocation are verified by an error synthesis model. It is proved that the error allocation of five-axis ultra-precision machine tools can be quickly and accurately achieved with the method proposed in this paper. [ABSTRACT FROM AUTHOR]

While the lower machinability of SiCp/Al poses a strong barrier to their widespread application, discovering the undeformed chip thickness (UCT) for its brittle-to-ductile cutting mode transition is crucial to achieve ultra-smooth machined surfaces of SiCp/Al. In this paper, a specific cutting energy-based mathematical model that predicts the critical UCT for cutting mode transition for SiCp/Al is developed, which takes into account comprehensive parameters of particle volume fraction, particle size, particle strengthening, cutting temperature and machining parameters. Meanwhile, groove cutting experiment of SiCp/Al with continuously varied UCT reveals significant differences in cutting force and machined surface morphology under small and large UCTs, indicating the presence of a cutting mode transition. Finally, the physical properties of SiCp/Al and machining parameters used in the experiment are substituted into the mathematical model established, and the predicted result of critical UCT for cutting mode transition is compared with experimental data, which verifies the accuracy of the established mathematical model. This study establishes a theoretical foundation for understanding the energy consumption in SiCp/Al cutting, as well as provides guidance for rationally selecting parameters to achieve the ultra-smooth machined surface of SiCp/Al. [ABSTRACT FROM AUTHOR]

Ti-6Al-4 V alloy is growing used in the fields of aerospace, automobile and medical industries, and the requirement for machining accuracy of those parts is also increasing. However, it is difficult to achieve ultra-precision cutting of titanium alloy with traditional manufacture techniques. The ultrasonic elliptical vibration assisted cutting (UEVC) is considered the promising manufacture strategy for ultra-precision cutting of Ti-6Al-4 V alloy. Remarkably, under the ultra-precision cutting scale, the detrimental effect of vibration texture caused by UEVC process on surface roughness should not be ignored. In this paper, the theoretical analysis and experimental studies on the influence of process parameters on the surface roughness were carried out for suppressing the adverse effects of vibration texture and improving the machined surface quality. The influence of vibration amplitudes in cutting and cutting depth directions, tool edge radius, cutting speed, and feed rate on the surface roughness was clarified. An ultra-precision machined surface of Ti-6Al-4 V alloy (Ra < 30 nm) was obtained, when the optimal process parameters were adopted. The research results indicated that the use of optimal process parameters can suppress the adverse effect of vibration texture on surface roughness and simultaneously retain the technical advantages of UEVC process. [ABSTRACT FROM AUTHOR]

To solve the problem of geometric error measurement for five-axis ultra-precision machine tools in interpolated five-axis motion, a measurement method based on the double ballbar (DBB) is proposed in this paper. The method proposed in this research can measure the geometric errors of five-axis ultra-precision machine tool through only one-time installation, and the new method is less limited by the layout of machine tools. The motion trajectory is designed, and the length of the DBB remains constant during the measurement process to achieve the measurement of the geometric errors. Furthermore, the measured results are compared with the theoretical results of the error model. It is found that the trend and the amplitude of the measurement results are in agreement with the theoretical results. It is proved that the method can measure the geometric errors of five-axis ultra-precision machine tool effectively. [ABSTRACT FROM AUTHOR]

Swing friction stir spot welding (SFSSW) technology which is mainly consisted of two steps is applied to join AA5083 Al alloy to AZ31B Mg alloy in the present investigation. In addition, AA5083/AZ31B joints produced by conventional FSSW were obtained. Optical microscope, scanning electron microscope equipped with energy-dispersive X-ray spectroscope, and X-ray diffraction pattern were used to analyze the morphology and microstructure of different joints. Lap-shear tensile testing and microhardness measurements were conducted to evaluate the joint performance. Results show that the bonding area and the material mixing of the spot welds fabricated by SFSSW technology were both promoted in comparison with that made by conventional FSSW. The thickness of intermetallic compounds (IMCs) at the interface around the filled original keyhole was larger owing to more heat input. The bonding interface of SFSSWed joints was irregular, and the IMCs along the annular interface were thinner than that produced by conventional FSSW. The IMC structure in the interface layer of SFSSWed joints is spherical, which is different from the dendritic structure by conventional FSSW. Finally, IMCs were found in the weld zone through phase analysis by XRD and microhardness measurements of SFSSWed joints. The fracture modes and morphologies were different to two joints, and the lap-shear tensile load of SFSSWed joint was 72.95% larger than the conventional FSSWed joint. [ABSTRACT FROM AUTHOR]

Ultrasonic impact peening (UIP) is not only a mature technique of surface treatment, but also a promising method of surface texturing for promoting performance and functionalities of components and devices. In the present work, we demonstrate the feasibility of applying UIP in the manufacturing of high precision surface micro-structures on 316L stainless steel using a YG6 cemented carbide tool. Specifically, analytical investigation of material deformation map under UIP is carried out, which is validated by corresponding finite element simulations based on a combined nonlinear isotropic/kinematic hardening model, as well as experiments performed on home-made UIP apparatus. Finally, surface micro-structures of aligned grooves with a depth of 2 μm and a periodicity of 240 μm are fabricated by using UIP, and are subsequently subjected to linear reciprocating ball-disk sliding tests. Corresponding experimental results show that the micro-structures fabricated by UIP possess comparable accuracy of groove morphology and frictional properties with that fabricated by using ultrasonic elliptical vibration cutting using a single crystal diamond tool. The present work sheds lights on the fabrication of high precision surface micro-structures on ferrous metals by mature UIP technique. [ABSTRACT FROM AUTHOR]

The improvement of ultra-precision machining technology has significantly boosted the demand for the surface quality and surface accuracy of the workpieces to be machined. However, the geometric shapes of workpiece surfaces cannot be adequately manufactured with simple plane, cylindrical, or spherical surfaces because of their different applications in various fields. In this research, a method was proposed to generate tool paths for the machining of complex spherical surfaces based on an ultra-precise five-axis turning and milling machine with a C-Y-Z-X-B structure. Through the proposed tool path generation method, ultra-precise complex spherical surface machining was achieved. First, the complex spherical surface model was modeled and calculated, and then it was combined with the designed model to generate the tool path. Then the tool paths were generated with a numerically controlled (NC) program. Based on an ultra-precision three-coordinate measuring instrument and a white light interferometer, the machining accuracy of a workpiece surface was characterized, and the effectiveness of the tool path generation method was verified. The surface roughness of the machined workpiece was less than 90 nm. Furthermore, the surface roughness within the spherical region appeared to be less than 30 nm. The presented tool path generation method in this research produced ultra-precision spherical complex surfaces. The method could be applied to complex spherical surfaces with other characteristics. [ABSTRACT FROM AUTHOR]

Reaction-bonded silicon carbide (RB-SiC) possesses a low machinability due to its hard-brittle characteristics, as well as the poor synergetic deformation behavior between different phases. In the present work, we perform finite element simulations to explore ultrasonic elliptical vibration cutting (UEVC) of RB-SiC using single crystalline diamond tool, with an emphasis on its dependence on utilized vibration parameters. Corresponding UEVC experiments using the same machining and material parameters with the simulations are also carried out to verify the prediction results. Simulation and experimental results reveal individual tool-particle interactions, as well as their correlations with machining force and machined surface quality. It is found that the frequency and amplitude of the two-dimensional vibrations have important influences on the cutting processes. And optimized values of vibration frequency and vibration amplitudes along both cutting direction and depth of cut direction for achieving rationalized cutting performance of RB-SiC by applying the UEVC are found. [ABSTRACT FROM AUTHOR]

Submerged friction stir welding on magnesium (Mg) alloy is investigated with limits in the past. ME20M is an important lightweight Mg alloy with enhanced yield strength and heat resistance that merits further research. In this paper, submerged friction stir welding of ME20M Mg alloy was carried out in different temperatures of cooling water. Three-dimensional numerical was employed to analyze the thermal field under the same weld conditions, and the numerical predictions were compared with the experimental results. The macrostructure, microstructure, tensile properties, and hardness are tested. The results show that the numerical results and the experimental results exhibits the same trends. By increasing the cooling water temperature, the grain size of the weld nugget increased, the tensile strength of the joint decreased, and the microhardness of the weld joint decreased. The largest tensile strength was 170.5 MPa, which was ~ 71.04% of the base metal. The highest and the lowest hardness values of the weld joint were obtained at the cooling water temperature of 15 °C and 75 °C, respectively, in the weld nugget and heat-affected zones. [ABSTRACT FROM AUTHOR]

Brittle-to-ductile transition plays a crucial role in ultra-precision machining of hard-brittle materials. In the present work, we investigate the brittle-to-ductile transition in diamond grooving of monocrystalline silicon by finite element modeling and simulation based on Drucker-Prager constitutive model. The brittle-to-ductile transition behavior is distinguished by analyzing evolutions of chip profile and cutting force. Corresponding diamond grooving experiment using the same machining configuration with the finite element simulation is also carried out to derive the critical depth of cut for the brittle-to-ductile transition. The comparison of experimental value of the critical depth of cut and predicted one by the finite element simulation demonstrates the high accuracy of as-established finite element model. Subsequent finite element simulations are performed to investigate the influence of rake angle of cutting tool on both diamond grooving and conventional diamond cutting with a constant depth of cut, which demonstrates a prominent dependence of brittle-to-ductile transition of silicon on the rake angle ranging from − 60° to 0°. And a critical rake angle for the most pronounced ductile machinability of silicon is found. [ABSTRACT FROM AUTHOR]

In the application of the 13.5-nm extreme ultraviolet (EUV) collector optics of the discharge produced plasma (DPP) source, the Wolter-I structure based on the X-ray grazing incidence optical design is usually adopted. The requirement of the surface roughness of this collector optics is demanding, which should reach to several nanometers. Currently, the mandrel replication is the main fabrication technology of this collector optics. Obviously, the requirement of the surface roughness of the mandrel used for the replication process should reach to the same level of the collector optics. However, the fabrication of the Wolter-I mandrel with high surface quality requirement still faces great challenge. In this paper, we propose a method that applies an elastic spherical tool to polish the surface of the Wolter-I mandrel, in which the shape of the elastic sphere can be changed relatively easily to accommodate the aspherical surface of the Wolter-I mandrel. A mathematical model regarding the movement trace of the polishing tool was established. Based on this model, the contact force between the polishing sphere and the aspherical surface can be controlled to point from the center of the polishing sphere in the normal direction to the polishing point. The influence of the polishing parameters on the material removal thicknesses is simulated and analyzed. The polishing experiments of ellipsoid and hyperboloid are carried out considering the difference of the diameter of each radial section on the Wolter-I mandrel surface. The proposed method is proved to reduce the surface roughness of the mandrel coated with chemically deposited nickel-phosphorous (NiP) alloy after diamond turning effectively. The root mean square (RMS) roughness of the mandrel surface after polishing can be reduced to 1.56 nm. It indicates that this method is suitable for further polishing of nickel-plated Wolter-I mandrel after ultra-precision turning. As a result, the manufacturing precision and efficiency of the Wolter-I mandrels can be improved by using the proposed polishing approach in this study, and the manufacturing cost can be reduced accordingly. [ABSTRACT FROM AUTHOR]

Magnetic pulse welding (MPW) has attracted widespread attention due to its advantages on joining dissimilar metals. This paper mainly focused on the effect of surface treatment on the weldability and mechanical properties of Al-Fe joints. Two kinds of surface grinding directions, including parallel to welding direction (P2W) and vertical to welding direction (V2W), were designed to prepare MPW joints. Mechanical properties and interface microstructures were systematically analyzed to establish the corresponding relationship between the two. Results showed V2W welded joints presented a wavy-shape interface and had better mechanical properties. The P2W specimens only showed a straight interface, and the element diffusion in the zone of the wave interface was better than that in the zone of the straight interface. The discharge energies affected mechanical properties by changing the interfacial morphology. In addition, the formed jets could be trapped and led to the formation of interfacial waves when the scratch direction did not coincide with the welding direction, contributing to the formation mechanism of wave interface. [ABSTRACT FROM AUTHOR]

This paper presents a new ultrasonic elliptical vibration cutting (UEVC) device based on a sandwiched and symmetrical structure. The proposed UEVC device is able to work with the third resonant mode of longitudinal vibration and the sixth resonant mode of bending vibration. Also, the vibration nodes of the two resonant modes were completely superposed at the center of the flange. Therefore, the single-node fixed method was employed, which was practical and had no interference to the resonance mode of the UEVC device. The modal analysis of the designed UEVC device was performed by using finite element method (FEM). The results revealed that the modal degeneration can be realized by optimizing design parameters. Based on the optimized results, a prototype UEVC device was manufactured, and its vibration characteristics were evaluated by an impedance analyzer and a laser displacement sensor. The measurement results indicated that the resonant frequencies were close to the simulation frequencies and an elliptical trajectory was generated at the tool tip. Finally, the proposed UEVC device was integrated into an ultra-precision machine tool to confirm the feasibility of the designed UEVC in the practical application. [ABSTRACT FROM AUTHOR]

It continues to be a challenge in machining the optical mandrel with high steepness axisymmetric aspheric surface due to the high machining cost. In this study, a novel approach which uses the arc-edged diamond cutter tangent to workpiece's meridian profile curve at the interpolation points in 'XZ' 2-axis machine tool is proposed. The mathematical model is established and the maximum of rough interpolation error that is generated using this method is also calculated. The number of rough interpolation segments and coordinates of the cutter center motion trajectory are determined when the maximum rough interpolation error is less than the allowable value of the given error. It analyzes the interpolation trajectory and interpolation error to determine the position and numerical value with the maximum rough interpolation error, as well as the correlation between the interpolation error and the number of interpolation points. The experimental results show that this method could generate smaller dimensional and form error compared to traditional 2-axis contouring approach method. In addition, compared to using multi-axis ultraprecision computer numerically controlled (CNC) lathe with the B-axis, processing of high steepness aspheric in 'XZ' 2-axis lathe greatly reduces the cost. This method can thus be used for precision turning of Wolter type-I extreme ultraviolet (EUV) replication mandrel with high steepness aspheric surface. [ABSTRACT FROM AUTHOR]

It is of great interest to determine which of the numerous sources of error in an ultra-precision diamond turning machine has the greatest influence on the machining inaccuracy. Global sensitivity analysis is a well-known mathematical technique that is able to quantify the contribution of each error source to the machining inaccuracy. The present study employs a variance-based sensitivity analysis method to comprehensively investigate the influence of each error source in a three-axis diamond turning machine on the machining inaccuracy. The procedure for establishing a volumetric error model based on multi-body system theory in conjunction with a homogeneous transformation matrix is first described in detail. The basic working principle and relevant estimation process of the Sobol method is then explained, and the Sobol method is employed to quantify the sensitivity index of each error source based on the volumetric error model. Finally, simulation testing is conducted to comprehensively investigate the main geometric error sources contributing to machining errors along the X, Y, and Z directions, and with respect to comprehensive volumetric errors. After the main geometric error sources are identified, some measures are taken to improve the identified error sources, and a flat surface cutting experiment is conducted to verify the effectiveness of the proposed sensitivity method. The results show that the proposed sensitivity method is effective for identifying the most crucial geometric errors, the form error of flat surface is improved by approximately 50% after modifying parts of these errors, and these errors should then be the subjects of careful scrutiny in the precision design, error compensation, and precision processing stages. The method is of significant guidance for on-machine and real-time online error compensation. [ABSTRACT FROM AUTHOR]

On-machine measurement (OMM) involves the interruption of the machining process and the subsequent measurement of the workpiece without its removal from the machining tool. Chromatic confocal sensing is a well-known measurement technique that is able to evaluate the position of a point on an object surface along the optical axis of the system with high accuracy. The present study integrates a chromatic confocal measurement probe with an ultra-precision diamond turning machine to achieve the non-contact OMM of machined components. The procedure for establishing the position of the rotary axis of the spindle based on dual standard spheres is first described in detail, and the relevant OMM procedure for machined components of different surface topographies is explained. Then, a 50-μm quartz step height standard is employed to investigate the linear measurement accuracy of the chromatic confocal probe. Finally, the measurement accuracy of the proposed OMM method is compared experimentally with that of the stylus method. The results show that the estimated form error value of the OMM method agrees well with the value obtained by the stylus method. The proposed OMM method feasibly achieves non-contact OMM with a nanometer-level accuracy for an ultra-precision turning machine and is capable of reconstructing the 3D surface topography of flat, spherical, and aspheric surfaces. After integrating the OMM method, the ultra-precision turning machine can realize the function of processing-measurement integration. [ABSTRACT FROM AUTHOR]

Ultra-precision machining has been widely used in the manufacturing of optical components. Volumetric error analysis and error compensation are essential issues that must be considered to improve the accuracy of the machining process. However, analysis of the effects of kinematics errors on surface generation by ultra-precision machining using a swing arm ultra-precision diamond turning machine (SA-UDTM) and the alignment methods required have received little research attention to date. This paper presents the development of a kinematics error model of the SA-UDTM that accounts for geometric errors by simplifying the machining system and considering it as a rigid multi-body system. Then, the main error contributions to the processing precision can be derived from sensitivity analysis of error components. Finally, an alignment method is developed to reduce or eliminate the corresponding positioning errors of the mechanical system and thus improves the form accuracy of processed surface. To verify the theoretical kinematics model and the proposed alignment method, a series of contrast machining experiments have been performed, and the experimental results indicate that the proposed method is effective. [ABSTRACT FROM AUTHOR]

Damage-tolerant titanium alloy, TC21, is widely used for the important components of the new-generation aircraft with high strength and durability requirements, many of which are machined by plunge milling. For optimizing the plunge milling parameters and improving machining efficiency, a number of experiments were carried out to study the machinability of plunge milling TC21. The effects of plunge milling parameters on cutting forces, the cutting temperature, and the tool life were investigated and analyzed. The process of the tool failure and the mechanism of tool wear were explored. Results showed that the cutting temperature had more influence than cutting force under the same parameters, and higher cutting heat was the main reason of the tool failure. In addition, this study showed that a large fracture of insert corner was the form of final tool failure. Furthermore, the results indicated that TiAlN-coating tool was more suitable for plunge milling TC21 than TiN-coating tool, and abrasive wear and adhesive wear were the main reasons of tool wear. Finally, reasonable parameters of plunge milling TC21 were recommended. Thus, a cutting tool with proper plunge milling parameters and tool materials should be carefully chosen to satisfy the tool life in real production. [ABSTRACT FROM AUTHOR]

In mechanical lapping, diamond exhibits a highly anisotropic tribological behavior. The dependency of wear rate on crystal orientation has long been noticed by diamond polishers. However, in the diamond manufacturing, the surface quality is another side in need of attention. In this paper, the relationship between surface morphology and crystallographic orientation under a certain lapping condition was examined. It is found that a fine surface can still be obtained at the directions that deviate a lot from the 'soft' directions (near <001> crystal direction for {110} surface). But, with respect to the 'hard' directions (near <110> crystal direction for {110} surface), a bad surface finish with a fracture appears. This result comes down to two aspects. First, on {110} surface, as the lapping direction from the <001> (soft direction) approaches <110> (hard direction) the phase change of diamond carbon atoms gets more difficult, which causes the depth of the amorphization layer becomes thinner. Second, the energy required by diamond amorphization is lower than that by surface fracture around the soft direction, while near the hard direction, the contrary is the case. Our work provides a further understanding of the diamond tribological properties. [ABSTRACT FROM AUTHOR]