The AISI P20 tool steel is widely used for manufacturing the plastic mold components, while surface defects problem often arises during ball-end milling process, which can deteriorate the fatigue life of the plastic molds. Therefore, it is vital to reveal the formation mechanism of the surface defects. First, a surface topology predictive model is conducted which is verified by experimental results; in addition, according to the simulation and experimental results, tool wear, surface topology, and surface profile are analyzed. Secondly, the origin of the surface defects is analyzed on the basis of the scanning electron microscope (SEM) images, and the relationship between the chip and surface defects is also discussed. Based on the investigation, the cutting friction and heating rather than the carbide particles are the main reason for surface defects in milling AISI P20 steel. This research is beneficial for the understanding of surface topology and surface defect formation mechanism. Meanwhile, the results could provide a technical base for selecting cutting parameters in five-axis ball-end milling of AISI P20 steel.

Compared with the traditional technological process, hard milling of hot work tool steel (AISI H13) can significantly improve the physical/mechanical performances of machined components. A three dimensional (3D) finite element (FE) simulation model was built in this research to investigate the complex nonlinear process. First, the geometric model of workpiece was established considering the previous machined surface profile in actual milling process. Secondly, the prediction validation of the simulation model about hard milling process was verified by comparing the simulated cutting forces with the experiment results. Finally, the effect of cutting speed and feed rate on cutting forces and cutting temperature were researched by using the FE simulation model. The results indicate that cutting forces increase with the increase of feed rate, while cutting temperature increases with the increase of cutting speed. The effects of cutting speed on cutting forces and feed rate on cutting temperature are not significant. The simulated temperature is much lower than the austenitizing temperature of AISI H13 steel which means white layer is unlikely to be formed under the cutting conditions used in this study. The research can contribute to the fundamental understanding of mechanism and optimization of cutting parameters in hard milling.

Brush plating is one of the remanufacturing technologies which have been widely used in engine remanufacturing. In this paper, α-Al2O3/Ni composite coatings were prepared on the inner hole face of the big end of connecting rod by a self-made automatic plating machine. To investigate the effects of process parameters on residual stresses of α-Al2O3/Ni composite coating, a L16(44) orthogonal experiment was designed and operated in which four process parameters (voltage, concentration of α-Al2O3 particles, speed, and distance between anode and workpiece) were selected as factors. ANOVA (analysis of variance) were employed to determine the effects of process parameters on the residual stresses of composite coatings. It was found that speed was the most significant factor for the residual stresses. The optimal process parameters for the desirable residual stresses were obtained, which was proved to be valid by the verification experiments. In addition, single factor experiments were employed to study the main effects of sprocess parameters on composite coatings.

•The sliding asperity interaction is studied by semi-analytical and finite element methods.•The asperity profiles are assumed as parabolas.•The asperities are assumed as the power-law hardening materials.•The effects of hardening exponents on contact parameters are studied.The study of the sliding process between asperities on rough surfaces can improve the understanding of wear mechanisms. The sliding interaction between asperities is analyzed in this paper using both a semi-analytical model and a finite element model. Power-law hardening materials are considered, and the asperity profiles are assumed to be a parabolic approximation to the cylinder. The effects of strain hardening exponents on some contact parameters are explored with the finite element model. Results show that the faster semi-analytical model agrees well with the finite element model for materials with larger hardening exponents, while for materials with smaller exponents, the errors would preclude its use. As the exponent decreases, the dragging effect in sliding becomes more notable and influences the contact parameters more significantly. Friction shows a significant effect in the sliding process after preliminary consideration, which should be explored in detail further.

•An analytical asperity interaction model was built for power-law hardening materials.•A numerical contact model was built to account for the contact between a rigid flat and a rough surface.•The rough surface was reconstructed by wavelet transform with actual topography.•The effects of power-law hardening material properties on asperity interaction were studied.In the present work, an analytical interaction model of multi-asperity contact for the power-law hardening materials is proposed. The real surface topography including the asperity locations, heights and radii of summit is considered. Meantime, a numerical model is built based on the finite element method, to study the contact of a rigid flat and a deformable rough surface which is simplified and reconstructed with the measured original surface using the wavelet transform. The analytical results are close to the numerical results. Finally, the effect of the power-law hardening material properties on the asperity interaction is studied.

•Mixed mode fracture mechanics experiments were conducted on zirconia/veneer interface.•A modified sandwich test configuration was proposed and used in the tests.•Crack initiation and propagation were predicted by three fracture criteria based on interface fracture mechanics.Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive stresses in the veneer.

•Composite coatings are prepared by means of brush plating at different PH.•Morphologies of composite coatings vary with the change of zeta potential.•The content of α-Al2O3 in coatings is varied with electrolyte pH.•The hardness and wear resistance are promoted by the increase of α-Al2O3 particle.•Different zeta potentials lead to different co-deposition processes.Zeta potential of α-Al2O3 particles in electrolytes was measured and used to describe the electrical properties of nano-particles. α-Al2O3 reinforced composite coatings were prepared from electrolytes respectively from pH 5, 6, 7, 8, 9 and 10 by electro-brush plating. Morphologies of the six coatings were observed in a scanning electron microscope (SEM). Some bright dots were found in the coatings prepared at pH 5, 6 and 7, while no dots were found in the coatings prepared at pH 8, 9 and 10. To investigate the differences, energy dispersive spectroscopy (EDS) was performed to determine the composition of bright dots in the coatings. And it was found that the bright dots were α-Al2O3 depositing in the coatings. The result indicated that α-Al2O3 particles with positive zeta potentials deposit in a different way from particles with negative zeta potentials. A new co-deposition process of nano-particles and metallic ions was introduced from the perspective of nano-particle electrical behaviors. In general, the higher the absolute value of zeta potential is, the more the nano-particles will deposit in the coatings, and the better performance the coatings will have in micro-hardness and wear resistance because of the lower size of grains. But more negative zeta potential will prevent nano-particles from depositing.

Chip formation and its morphology are important features of metal cutting, and they can yield much more important information on the cutting operations. Meantime, the cutting forces are the most commonly used on-line indicators to monitor the cutting process. In this research, the formation of the saw-tooth chips has been investigated in association with the fluctuation of the cutting force components under different cutting parameters in turning of Inconel 718 with (Ti, Al)N/TiN coated cutting tools under dry cutting condition. By means of the optical microscopy and the scanning electron microscopy (SEM), the saw-tooth chips are observed at high cutting speeds, which directly cause the cutting force components to fluctuate. Based on the frequency analysis, the segmentation frequencies of the saw-tooth chips and the fluctuation frequency of the cutting forces are very close to each other. It indicates that the formation of the saw-tooth chips is one of the important factors leading to the periodical fluctuation of the cutting force components, even though the cutting parameters all keep constant in turning of Inconel 718.

In the present study, an experimental investigation was conducted to determine the effects of surface texture, cutting parameters and phase transformation on the surface and in-depth residual stress distributions induced by hard milling of AISI H13 steel (50 ± 1HRc) with the coated carbide tools. The results show that the surface residual stress distribution between two adjacent machined lays has the same periodic variational regularity as the surface profiles, which means that the surface residual stress distribution has a high correlation with the machined surface texture. Surface residual stresses in the pick direction are much more compressive than that in the feed direction; at the same time, radial depth of cut and feed are the main cutting parameters affecting surface residual stresses. Very thin white layer forms or even no obvious microstructural alteration appears in the subsurface. Phase transformations of the subsurface material deeply affect the in-depth residual stress distribution, a ‘hook’ shaped residual stress profile beneath the machined surface is generated in which the maximum compressive stresses occur at the depth of 3–18 μm below the surface.

Ti-6Al-4V alloy is an attractive material in many industries due to its unique and excellent combination of strength to weight ratio and their resistance to corrosion. However, because of its low thermal conductivity and high chemical reactivity, Ti-6Al-4V alloy is generally classified as a difficult-to-cut material that can be characterized by low productivity and rapid tool wear rate even at conventional cutting speeds. It is well known that tool wear has a strong relationship with the cutting forces and a sound knowledge about correlation between cutting forces variation and tool wear propagation is vital to monitor and optimize the automatic manufacturing process. In the present study, high-speed end-milling of Ti-6Al-4V alloy with uncoated cemented tungsten carbide tools under dry cutting conditions is experimentally investigated. The main objective of this work is to analyze the tool wear and the cutting forces variation during high-speed end-milling Ti-6Al-4V alloy. The experimental results show that the major tool wear mechanisms in high-speed end-milling Ti-6Al-4V alloy with uncoated cemented tungsten carbide tools are adhesion and diffusion at the crater wear along with adhesion and abrasion at the flank wear. The cutting force component in the negative y-direction is more dominant of the three components and displays significantly higher magnitudes than that of the other two components in x- and z-directions. The variation of cutting force component Fy has a positive correlation with the tool wear propagation, which can be used as a tool wear indicator during automatic manufacturing process.

In the present research, an attempt has been made to experimentally investigate the effects of cutting parameters on cutting forces and surface roughness in hard milling of AISI H13 steel with coated carbide tools. Based on Taguchi’s method, four-factor (cutting speed, feed, radial depth of cut, and axial depth of cut) four-level orthogonal experiments were employed. Three cutting force components and roughness of machined surface were measured, and then range analysis and analysis of variance (ANOVA) are performed. It is found that the axial depth of cut and the feed are the two dominant factors affecting the cutting forces. The optimal cutting parameters for minimal cutting forces and surface roughness in the range of this experiment under these experimental conditions are searched. Two empirical models for cutting forces and surface roughness are established, and ANOVA indicates that a linear model best fits the variation of cutting forces while a quadratic model best describes the variation of surface roughness. Surface roughness under some cutting parameters is less than 0.25 μm, which shows that finish hard milling is an alternative to grinding process in die and mold industry.

The objective of the present research is to investigate the relationship among tool wear, surface topography, and surface roughness when high-speed end milling Ti-6Al-4V alloy, and also to define an optimal flank wear criterion for the cutting tool to integrate tool life and the surface roughness requirements of the finish milling process. An annealed Ti-6Al-4V alloy was selected as the workpiece material, undergoing end milling with uncoated carbide inserts. The flank wear of the insert was observed and measured with the toolmaker’s microscope. To examine machined surfaces, 3D surface topography was provided by the white light interferometer, and the arithmetical mean roughness (Ra) was calculated with the WYKO Vision32 software. The flank wear increases with cutting time, and the maximal flank wear is set as the flank wear criterion. As the cutting process progresses, tool wear is the predominant factor affecting the variation of surface roughness. According to the plots for the tool wear propagation and surface roughness variation, an optimal flank wear criterion can be defined which integrates the tool life and the surface roughness requirements for the finish milling process.

During high-speed machining Ti-6Al-4V alloy, high-temperature at the tool–chip interface and the concentration gradient of chemical species between tool material and workpiece material support the activation of diffusion process, and therefore the crater wear forms on the rake surface of the cutting tool at a short distance from the cutting edge. In this paper, the diffusion analysis was theoretically proposed. The constituent diffusion at the contact interface between tool material and Ti-6Al-4V alloy at high-temperature environment, the crater wear on the rake surface of the tool, and the chips collected from high-speed milling Ti-6Al-4V alloy with straight tungsten carbide tools were analyzed by the scanning electron microscope with energy dispersive X-ray spectroscopy. The constituents inside the tool could diffuse into the workpiece and the diffusion layer was very thin and close to the interface. Compared with the diffusion of tungsten and carbon atoms, the pulling out and removing of the tungsten carbide (WC) particles due to cobalt diffusion dominated the crater wear mechanism on the rake surface of the cutting tool.

Statement of problemChipping of veneering porcelain and delamination of a zirconia-veneer interface are 2 common clinical failure modes for zirconia-based restorations and may be partially due to weak interface bonding. The effect of liner on the bond strength of the interface has not been clearly identified.PurposeThe purpose of the research was to evaluate the interface toughness between the zirconia core and veneering porcelain by means of a fracture mechanics test and to assess the effect of liner on the bond strength of the interface.Material and methodsThirty bilayered beam-shape specimens were prepared and divided into 2 groups according to liner application. The specimens in each group were subdivided into 3 subgroups in accordance with 3 different veneer thicknesses. A fracture mechanics test was used on each specimen, and the energy release rate, G, and phase angle, ψ, were calculated according to the experimental results. A video microscope was used to monitor the crack propagation, and a scanning electron microscope was used to identify the fracture mode after testing. Two-way ANOVA and the Tukey honestly significant difference test were performed to analyze the experimental data (α=.05) .ResultsAt each phase angle, the interfaces without a liner had higher mean G values than the interfaces with a liner. Both of the interfaces showed mixed failure mode with thin layers of a veneer or a liner that remained on the zirconia surfaces.ConclusionsLiner application before veneering reduced the interface toughness between zirconia and veneer.

The use of flood cutting fluids in machining processes has been questioned lately due to the several negative effects on environment and health. Considerable attention has been given to reduce or completely omit the cutting fluids, and meet the demands for environment-friendly cutting processes. The low cooling capacity of the air limits the application of minimum quantity lubrication (MQL) in machining Inconel 718. The minimum quantity cooling lubrication (MQCL) system which combines the advantages of the cryogenic air and MQL, can improve the machinability of Inconel 718. In this work, dry cutting and MQCL cutting with biodegradable vegetable oil are associated to study tool wear and cutting forces during end milling Inconel 718 with coated cutting tools. Meantime, the relationship between tool wear propagation and the cutting force variations under different cutting conditions is also explored. The experimental results have shown that MQCL cutting with biodegradable vegetable oil can effectively improve the machinability of Inconel 718, such as extension of tool life and reduction of cutting forces. From an environmental point of view, MQCL cutting with biodegradable vegetable oil meet the increasing demands for cleaner manufacturing of Inconel 718, and is an alternative of MQL cutting and dry cutting.