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Nickel-based superalloy GH4169 is widely demanded in the aerospace industry due to its superior properties. However, there are some problems such as serious tool wear and poor surface quality in the cutting process of GH4169. In this study, in order to improve the machinability of GH4169, GnP-ZrO2 hybrid nanofluids (NFs) were prepared and applied to cutting machining. Thermophysical properties of the prepared hybrid NFs such as dynamic viscosity, thermal conductivity, and contact angle were tested. Meanwhile, a series of wear tests and turning processes of GH4169 under Dry, MQL, GnPNMQL (GNMQL), GnP-ZrO2 hybrid NMQL (GZNMQL) conditions were conducted to evaluate the performance of NFs. The results showed that the thermophysical property of NFs was improved and the coefficient of friction was significantly reduced with the addition of GnP and ZrO2 hybrid nanoparticles. The machined surface roughness and cutting temperatures under the GZNMQL cooling condition were reduced by 53.53% and 54.06% compared to those under the Dry condition, respectively. Additionally, the tool life was significantly improved. The "flake-spheres-flake" structure of the GnP and ZrO2 improved the lubricity, cooling effect, and friction properties of the cutting fluids, which resulted in a better performance in terms of machined surface roughness, cutting temperatures, and further improved tool life. [ABSTRACT FROM AUTHOR]

Fully sintered zirconia ceramic material (ZrO2) is widely used because of its excellent properties of high strength, high hardness, and excessive temperature resistance. However, machining high quality small holes in ZrO2 workpiece is an ongoing challenge. In this study, the helical milling process using PCD tools is investigated to fabricate high quality small holes in ZrO2. A three-factor and three-level response surface method experiment is designed taking the crack area at the hole entrance (Δw), inner hole surface roughness (Ra) and crack area at the hole exit (Δe) as response values. The influences of spindle speed (n), feed per tooth (fz), and axial depth of cut (ap) on each response value and their interacting relationships are investigated. Then, the regression models of each response value are established. The optimal sets of parameters for helical milling have been obtained by optimizing each independent variable. Furthermore, the accuracy of the constructed regression models has been evaluated. The results demonstrate that Δw, Ra and Δe values are reduced by 73.94%, 82.18%, and 59.08% respectively using the optimized helical milling process and parameters compared with the results before optimization. Two strategies are proposed to further reduce Δe, and the final results demonstrate that Δe can be further decreased by up to 49.56%. Analysis of the cutting edge by SEM shows that the main wear mechanism is stripping wear. The EDS analysis of the cutting edge shows that there is no significant change in the cutting edge material. [ABSTRACT FROM AUTHOR]

The problems of tool wear and machining economy are prominent in hard cutting process. Clean cutting technology can effectively improve the cutting environment. The cutting performance of coated tools and PCBN tools is investigated in clean hard cutting of H13 steel (55 ± 1 HRC) under dry, cold air, and cryogenic liquid nitrogen conditions. The machining economics are also analyzed to investigate the feasibility of improving tool life through clean cutting technology. From the perspective of machining economy, the machining cost of cold air cutting is lower than that of dry cutting and liquid nitrogen cutting. The coated tool is suitable for cutting under cryogenic liquid nitrogen condition. Compared with dry cutting, the coated tool life is increased by 55.6% at cryogenic liquid nitrogen condition. PCBN tools are prone to chipping at cryogenic temperature, resulting in early failure. PCBN tools achieve the longest tool life in cold air cutting. [ABSTRACT FROM AUTHOR]

High-aspect-ratio vortex curved thin wall is widely used in electronics, precision instruments, aerospace, and other fields. It is a typical flexible geometrical structure with varying curvature making it very difficult to be fabricated with high quality due to burrs, dimensional errors, tool marks, and other defects in the machining process. In order to improve the machining quality of vortex curved thin walls, a new micromilling process with large cutting depth and slow feed is proposed. Firstly, through the single factor finite element simulation and micromilling experiment, the influences of radial depth of cut ae and feed per tooth fz on milling forces are analyzed under the condition of large axial depth of cut ap. Then, under the guidance from the results of single-factor experiments, the orthogonal experiments are conducted selecting surface roughness Ra, dimensional error △w, and burr height h as the evaluation indexes of machining quality. The influences of key milling parameters (feed per tooth fz, axial depth of cut ap, radial depth of cut ae, and spindle speed n) on machining quality are explored. By comprehensively analyzing the key milling parameters and their effects, an optimum combination of cutting parameters is identified. Finally, the new micromilling process is validated for the fabrication of high quality vortex curved thin walls. [ABSTRACT FROM AUTHOR]

It is indispensable to explore the appropriate level of surface residual stress to enhance the wear resistance of coated tools. TiAlSiN-coated carbide tools with dissimilar surface residual compressive stresses (− 300 ~ − 600 MPa) are acquired via micro-sandblasting, which are used in the high-speed sliding friction experiments and turning experiments. The influence of residual stress on the sliding wear and cutting wear performance of TiAlSiN coated tools is investigated. The results show that with the improvement of surface residual compressive stress (absolute value), the friction coefficient and wear rate are reduced. The sliding wear resistance of the coated tool is enhanced. In addition, the cutting performance of the tool is also improved with the increase of residual compressive stress (absolute value). However, the excessive surface residual compressive stresses (absolute value) can lead to severe coating peeling, which in turn impairs the capability of wear resistance. The TiAlSiN-coated carbide tool with the stress of − 500 MPa presents the best wear resistance in the high-speed sliding wear and cutting wear process. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP) is widely used in various fields due to its excellent properties. However, machining defects such as delamination and burr are still the key issues constraining high-quality hole making on CFRP. This research takes the helical milling process to make holes on CFRP and two kinds of cutting conditions (dry cutting and jet cold air-assisted cutting) are explored. Tool wear, cutting force, delamination, and surface morphology are taken as the main indices to be analyzed. The influences of key cutting parameters (spindle speed n, axial feed per tooth fza, and pitch ap) on cutting force and delamination are investigated and optimized. It turns out that the jet cold air condition is more suitable for helical milling of holes on CFRP with better qualities. The holes with smaller delamination factor and smoother surface are successfully fabricated based on the optimized cutting parameters. [ABSTRACT FROM AUTHOR]

In order to further reduce the machining errors of microstraight thin walls caused by the elastic deformation in micromilling process, the deformation mechanism has been studied, and a compensation method is proposed to reduce the machining errors. Firstly, conventional micromilling experiments have been conducted. It shows that large dimensional errors exist in finished thin walls. Second, a mathematical model is established to calculate the thin wall deformation based on Rayleigh–Ritz theory. The deformation values are determined by calculating the selected discrete measurement points. Based on the deformation of measurement points, the thin wall deformation of any position can be calculated by numerical method. Finally, the thin wall dimensional errors are reduced by compensating the deformation according to the analysis based on the introduced mathematical model. The high machining quality of the thin wall is realized. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the deformation compensation. The average relative dimensional errors have been reduced from 6.86 to 1.11 ~ 2.69%. Also, the fabricated thin walls keep good shape accuracy. The experimental results show that the introduced device and the compensation method can effectively improve micromilling quality of thin walls. [ABSTRACT FROM AUTHOR]

Due to the high-efficiency, environmental protection, the low-cost, micro sandblasting technology is used in the surface treatment of the coated tools. The simulation and application of the coated tool micro sandblasting are carried out to reveal the surface treatment mechanism and analyze the influence of sandblasting parameters on the tool surface integrity. The flow field erosion simulation model of abrasive water–air three-phase flow is established. Moreover, the cutting experiments are conducted to verify the effect of micro sandblasting. The results show that the maximum velocity and pressure are obtained at the center of jet flow. The pressure distribution on the target surface has little correlation with the distance to the nozzle. The surface morphology of the AlTiN-coated tool changes obviously after micro sandblasting. Moreover, the low surface roughness Ra of the blasted tool can be obtained at the small sandblasting pressure and time. Additionally, the residual compressive stress on the surface of the AlTiN-coated tool is enhanced after micro sandblasting. The longer cutting time of the AlTiN-coated tool can be obtained at the sandblasting pressure of 0.3 MPa and sandblasting time of 3 s. This work has practical significance for optimizing micro sandblasting process and improving the surface integrity of coated tools. [ABSTRACT FROM AUTHOR]

In order to further improve the dimensional accuracy of micromilled thin walls with high aspect ratios, the machining process should be actively controlled. A device for active cutting force measurement and cutting parameter compensation is developed to realize the real-time measurement of radial cutting forces and compensation of radial cutting parameters in thin wall cutting process. Firstly, a mathematical model is established to calculate the deformation and cutting force of thin walls based on the cantilever beam deformation theory. The thin wall deformation in the cutting process is estimated by measuring the cutting force. Then, the obtained incremental thin wall deformation is to be compared with the compensation threshold, which is set at 0.5 μm. If the value of the incremental deformation is less than 0.5 μm, compensation will not be processed. Otherwise, the incremental deformation is used as the compensation value for iterative compensation, until the incremental deformation of the thin wall is less than 0.5 μm. At last, a contrast experiment is carried out. The experimental results show that the introduced device and compensation method are feasible. Machining quality of the thin wall has been obviously improved in dimension precision after the cutting parameter compensations. [ABSTRACT FROM AUTHOR]

The coated tool is one of the most widely used cutters in the processing of titanium alloy. The wear of the coated tool is influenced by its surface integrity which can be improved by surface treatment, such as micro-blasting. The experiment of high-speed dry turning of titanium alloy Ti6Al4V (TC4) is carried out by the PVD-TiAlN coated carbide tools which are untreated and micro-blasted. For the coated tool, the evolution of the tool surface integrity, including tool surface roughness, tool surface topography, tool surface hardness, and tool surface residual stress, is studied at different wear stages. Moreover, the evolution of tool wear is analyzed at different wear stages. Then, the influence of tool surface integrity on tool wear is investigated. It is suggested that the tool surface integrity and wear resistance of the treated tool is improved. The change of tool wear is consistent with the change of coating surface integrity. That is to say, the better tool surface integrity is, the less tool wear will be. In addition, the main tool wear mechanisms are adhesive wear and oxidative wear. In the end, the stable wear stage of treated tools is prolonged, and the tool life is increased by more than 40%. [ABSTRACT FROM AUTHOR]

To solve the problem of the poor machining quality of the leading and trailing edge surface of the aircraft engine blade, a tool path generation method based on smooth machine rotary angle and tilt angle in five-axis surface machining with torus cutters was proposed. In terms of a specified type of five-axis machine tool, a relationship equation between design variables of tool position and machine rotary angles was firstly derived. A new tool orientation smoothing approach was then put forward. On this foundation, a tool path generation method based on a smooth machine rotary angle and tilt angle was presented. Finally, an aircraft engine blade was used as an example. The angular variation, angular velocity, and acceleration of the machine rotary axes produced by the Sturz method and the proposed method were compared and analyzed. Also, cutting trials were performed on the specified 5-axis machine tool. Experimental and comparison results proved that the proposed method can shorten the actual machining time, avoid the abrupt change of machine rotary axes, make the movement of machine axes more stable and smoother, and obtain better machining quality. [ABSTRACT FROM AUTHOR]

Accurate energy consumption prediction before actual turning is helpful for operators to select optimal processing parameters to improve energy efficiency. Tool wear is very fast in hard-to-process materials turning, which leads to the increase of cutting force, cutting temperature, and cutting power of machine tool. However, most existing prediction models do not consider the impact of tool wear on machine tool energy consumption. A new prediction model of machine tool energy consumption based on tool wear, spindle speed, and material removal rate in hard-to-process materials turning is developed, and verified with 06Cr19Ni10 stainless steel turning experiments. The experimental results show that the proposed model has higher prediction accuracy, and the maximum relative error between predicted value and true value is 2.9%. Furthermore, the influence of processing parameters and tool wear on machine tool energy consumption is studied. The machine tool energy consumption is proportional to the material removal volume, and linearly related to tool wear and spindle speed. The machine tool energy consumption decreases with the increase of material removal rate. The research results are helpful to formulate energy-saving turning scheme in hard-to-process materials turning. [ABSTRACT FROM AUTHOR]

Stainless steel is a well-known difficult-to-machine material with high toughness, low thermal conductivity, and high work hardening characteristics. Burrs generated in micromilling of the stainless steel seriously affect the performances of the fabricated high-accuracy miniaturized geometrical features. Aiming at reasonable control of burrs in micromilling of the 304 austenitic stainless steel, single-factor analyses, multi-factor optimization, and further post processing procedures are introduced in the paper. First, the axial depth of cut ap, feed per tooth fz, spindle speed n, and radial depth of cut ae are investigated by single-factor micromilling experiments. It shows that burrs generated in up milling are smaller than that in down milling. The minimum burr widths of 171.93 μm can be achieved, and the overall trend of micromilling force is in accordance with the burr widths. Then, multi-factor orthogonal experiments have been carried out to optimize micromilling parameters based on the Taguchi method. It shows that the significance sequence of key parameters for burr widths from large to small is ap, n, ae, and fz. The optimized minimum burr width is 83.69 μm with micromilling parameters ap of 45 μm, fz of 1.0 μm/z, n of 48,000 min−1, and ae of 200 μm. To further reduce the burrs, ap of 0 is set for post processing experiments. It shows that the radial depth of cut affects burr sizes greatly. The optimized radial depth of cut is 500 μm, and burr widths have been finally reduced to 14.3 μm. The study provides an effective method to reduce burr sizes in micromilling of very ductile materials. [ABSTRACT FROM AUTHOR]

Helical milling as an eco-friendly hole-making process has various advantages comparing to conventional drilling process and has been widely studied. But micro helical milling for small holes was not investigated. This paper focuses on preliminary studies on micro helical milling of small holes with flat micro end mills. The cutting phenomena of the radial and axial cutting edges are considered and discussed separately. Based on the size effect existing in microcutting processes, the minimum undeformed chip thicknesses (hmin) for both radial and axial cutting edges are identified for work material copper C26000 by finite element method and micro helical milling experiments. Since burrs are noticed during experimental studies, burrs at the hole entrance are analyzed elementarily and it shows that the burr size has a relation with the critical conditions in micro helical milling. The study turns out that the ratio of hmin to cutting edge radius in micro helical milling is from 0.6 to 0.68 and is larger than that of conventional microcutting processes for various materials, which is usually in the range from 0.14 to 0.43. It is a good sign for micro helical milling of small holes with higher productivities since the ratio of hmin to tool cutting edge radius is larger than that of conventional microcutting processes. [ABSTRACT FROM AUTHOR]

Avoiding significant fluctuations of tool orientation is an important problem in five-axis machining. The dramatic change of tool orientation may greatly increase the angular acceleration of machine rotary axes, produce larger nonlinear machining errors and gouging, reduce the feed rate of machine rotary axes, etc. In this paper, we propose a tool orientation smoothing method based on machine rotary axes for five-axis machining with ball end cutters to reduce fluctuations of tool orientation in the machine coordinate system (MCS). The core idea of the proposed method is to directly smooth machine rotary angles in the machine coordinate system for the smooth variation of tool orientation. First of all, we establish the relationship between the design variables of tool position and machine rotary angles. Then, we define an objective function of tool orientation smoothing based on machine rotary angles. In order to solve the above objective function, we also develop a simplified algorithm to obtain the minimum sum of squares of compound angular accelerations. Finally, a blade surface is used as a test example, and tool paths are generated by the Sturz and proposed methods, respectively. Comparison and analysis results show that the proposed method can improve the kinematics performance of five-axis machine tool, as well as surface machining quality and efficiency. [ABSTRACT FROM AUTHOR]

The sliding friction and wear tests were performed with a pin-on-disc system. The time series values of the friction forces were collected. The fractal characterization of the friction forces of the graded ceramic tool material and Inconel 718 pair was investigated in the sliding wear process, according to the calculation method of correlation dimension. The worn surfaces of the friction pairs were characterized by a scanning electron microscopy (SEM) with an energy-dispersive X-ray spectrometer (EDS). And the sliding wear mechanisms of the graded material and Inconel 718 were also analyzed. The results showed that the time series values of the friction forces had an apparent fractal characteristic. The fractal dimension of the friction forces decreased gradually in the sliding wear process. The sliding wear mechanisms of the ceramic disc in the sliding wear tests were adhesive wear, abrasive wear, and chipping, while those of the Inconel 718 pin were plastic deformation, abrasive wear and adhesive wear, as a result of the combined effect of high temperature and high stress in the contact surface. [ABSTRACT FROM AUTHOR]

The cutting performance, failure types, and mechanisms of the graded nano-composite ceramic tools were investigated during dry face milling of Inconel 718. In these tests, round ceramic inserts were used at cutting speeds ranging from 500 to 1,100 m/min. The structures of the chips, cutting forces, and surface roughness were also examined. Failure surfaces of the tools were characterized by scanning electron microscopy. The results showed that the graded tool possessed a self-sharpening characteristic and exhibited higher cutting performance compared with the homogeneous ones, as a result of its enhanced mechanical properties, higher abrasive wear, and fracture resistance. The failure mechanisms of the tools involved chipping, flaking, notch wear, abrasive wear, and adhesive wear. The mechanisms responsible for the higher cutting performance of the graded tools were inferred to be the formation of compressive residual stress in the surface layer induced by the graded compositional structure. [ABSTRACT FROM AUTHOR]

Sialon-SiN graded nano-composite ceramic tool materials were fabricated by using hot-pressing technique. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The cutting performance and wear mechanisms of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The surface roughness of the finish hard turning of Inconel 718 and the microstructures of the chips were also examined. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that graded structure in Sialon-SiN graded ceramic tool materials can induce residual compressive stresses in the surface layer during fabrication process. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual stress in the surface layer of the graded tools, which led to an increase in the resistance to fracture. [ABSTRACT FROM AUTHOR]