Abstracts:The adhesive bonding process is widely used in the automobile industry because of sealing, insulation and good mechanical properties. In this study, the effects of surface treatments and joint parameters on shear strength and failure mode were investigated. Four different sandpaper treatments, overlap length and adhesive thickness were selected to carry out quasi-static shear test. The failure behaviour of aluminium alloy single-lap adhesive joints was analysed and a dimensionless parameters δ was introduced to quantitatively evaluate the effect of overlap length on joint strength. Results showed that the joint strength was enhanced by sandpaper grinding due to the change of surface roughness. The specimens with 90°/0° grinding direction using P360 sandpaper had the best performance rather than an excessively rough surface. The joint shear strength decreased with the increase of adhesive thickness but the effect of overlap length on joint strength was limited. The adhesive thickness had little impact on joint shear strength when the overlap length over 40 mm. In addition, the joint strength could be improved by increasing overlap length until δ below 0.95. However, with the decrease of δ, there was almost no effect on joint strength because of high peeling stress at the both ends of the long joints.

Abstracts:Al–Mg–Si alloys with different heat treatment states were used as base metals (BMs) in investigating the effect of BM state on the microstructure and mechanical properties of Al–Mg–Si alloy friction stir-welded (FSW) joints. The Al grains and insoluble phases of the FSW joints were not affected by BM state, but the compositions of the precipitated phases in the heat-affected zones (HAZs) and nugget zones (NZs) depended on the phase compositions of the BMs. The FSW joint that was welded using the BM with water quenching (WQ) and artificial aging state exhibited the greatest hardness among the joints at the same zones because of the high densities of the β″ phases in the BM, the fine and high densities of the β′ phases in the HAZ, the high number of solution atoms, and the formation of Guinier–Preston zones in the NZ. Moreover, the joint exhibited the highest yield strength because of the high hardness of its HAZ, which is the fracture location in FSW joints. The FSW joint that was welded using the BM with WQ and natural aging state exhibited the highest ultimate tensile strength and tensile elongation because of its high structural uniformity.

Abstracts:One of the most important parameters making the production of precision tubes a challenging process, is the inhomogeneity of mass flow in the pre-stage of processing leading to eccentricity, heterogeneity of residual stresses and crystallographic texture. This paper presents a multiscale modeling framework linking four disparate length scales for studying eccentricity and texture evolution in the tube drawing process with standard as well as tilted dies. The main aim of using this methodology was to comprise the anisotropic elastic and plastic behavior of the material and the crystallographic orientations in the FEM model. This multiscale modeling framework starts with electronic scale calculations using the density functional theory approach to calculate the energy variation as a function of lattice parameters as well as the generalized stacking fault energy for copper. The calculated parameters are bridged to the next simulation scale, the atomic scale calculation. Where molecular dynamics simulations are performed to generate mobilities for dislocations and drag coefficients. The dislocation dynamics approach in the microscale then utilized the mobility values to compute the hardening parameters using the Palm-Voce hardening equation. The use of UMAT subroutine allowed to combine the crystal plasticity theory with the FEM model and calculated elastic and plastic parameters. These last ones were imported to the FEM simulations created for a two-step tube drawing process, performed with standard as well as tilted dies. The simulation results were validated using the measured eccentricity, texture, and mechanical properties: they were in a good agreement with the experimental results.

Abstracts:In this paper, the thermal behavior and process optimization for polyamide 6 during the selective laser sintering process were systematically investigated via numerical simulations and experimental testing. The effects of laser power and scanning speed were studied, and the simulation results showed that the increasing laser power and decreasing scanning speed led to the increase of the maximum temperature and the three-dimensional size of molten pool. Then, the single-layer experiments under different process parameters were carried out to verify the accuracy of the model. In addition, the energy density was applied to evaluate the combined effect of laser power and scanning speed on the thermal behavior. A process map for parameter optimization was obtained based on the predicted results, and the optimized parameters were in the region that the powder can be remelt resulting in an enough depth of molten pool, while the maximum temperature was below the decomposition temperature. Meanwhile, the specimen selected in the remelting region showed the highest tensile strength.

Abstracts:When minimum cutting depth is down to a single atomic layer, two portions of the cutting tool, namely, cutting edge and lowest atoms of the cutting tool, are involved in the cutting-induced material removal. Correspondingly, there are different critical rake angles for those two portions of the tool, different from the nominal rake angle in conventional cutting and edge radius-induced effective rake angle in nanocutting. Both they should be considered in atomic and close-to-atomic cutting to obtain the defect-free processed surface with an ideal crystalline structure. Molecular dynamics modelling is carried out to investigate the critical rake angles to enable single atomic layer removal on monocrystalline Cu (1 1 1) surface. The analysis results clearly indicate that the critical rake angles of nanometric cutting edge and the lowest tool atoms for single atomic layer removal are among the range of (–70°, –65°) and (–17°, –14°), respectively. To achieve single atomic layer removal, the tool edge radius is suggested to be not greater than 2 nm. The research findings would provide theoretical guidelines to the cutting tool design for the application of mechanical cutting of high-performance atomic scale devices.

Abstracts:Hybrid laser-arc welding of aluminum alloys has been receiving more and more attention in academic and industrial communities. The outstanding mechanical and fatigue properties of laser-arc welded joints with similar Al alloys have been demonstrated in literatures. Very few studies, however, reported the microstructures and properties of laser-arc welded joints with dissimilar Al alloys, while they are increasingly applied in modern engineering structures. Here, we study laser-arc welding of two dissimilar Al alloys, AA5083 and AA7N01. Their weldability, microstructures and properties are particularly investigated. Results show that sound welded joints of dissimilar Al alloys can be obtained via adjusting welding parameters. Microstructural characterization via SEM, EBSD and TEM reveals that microstructure in the fusion zone (FZ) is featured by large precipitates, low dislocation density, and coarsened grains with an average size of 66 ± 57 μm. The tensile strength of FZ of coarsened microstructure is degenerated to 230 MPa, which is the lowest among the three zones. The fatigue strength of the joints is 110 MPa, about 40% of their tensile strength. Pores and inclusions are the main sources for the deterioration of fatigue strength, as evidenced from SEM observations. In addition, a strength model is successfully built and utilized to simulate the yield strength, strain rate hardening and work hardening behavior of fusion zone.

Abstracts:Wire Arc Additive Manufacturing (WAAM) is an effective metal additive manufacturing process. In this research, 347 Austenitic Stainless Steel (ASS) walls were manufactured with ER347 consumable material. The microstructure of the WAAM processed 347 plate is entirely heterogeneous with changing grain morphology along the building direction and this is attributed to the complex cyclic thermal history during WAAM process. The microstructure is composed of columnar, cellular and equiaxed structures at various regions. The hardness decreased gradually from bottom to top along the building direction. The volume fraction of ferrite ranged from 0.5% to 4.2% at various regions and the presence of niobium carbide (NbC) was confirmed. The aim of the current work is to provide an outline of the WAAM processed 347 steel under dry sliding conditions at elevated temperatures. The elevated temperature wear mechanism has mild oxidative wear characteristic due to the formation of tribo-oxides on the wearing and sliding surfaces. However, the average coefficient of friction (COF) is lower for the WAAM processed 347 compared to 347 substrate. In all cases after initial running-in, the wear debris from the wearing and sliding surface forms mechanically mixed composite layer of tribo-oxides (Fe2O3, Fe3O4 and Al2O3). The worn surface at 200 °C presents different wear behavior compared to the samples at 400 °C and 600 °C. The wear at 200 °C is a typical adhesive wear, while the wear at 400−600 °C is mild oxidative wear. The increase in the percentage of Fe3O4 helps to heal the wear surface by forming a mechanically mixed composite layer. The characteristics of mild oxidative wear were elucidated.

Abstracts:Ni-based superalloy Inconel 625, despite its extensive applications (in aerospace, oil and gas, marine, chemical processing and alike industry) is categorized as difficult-to-cut material due to distinct thermal and physical characteristics. Incidentally, the use of novel multi radii insert (wiper) geometry, that is reported to provide extended machining capabilities for different materials and machining scenarios has not been found to be reported for this alloy. This work employs PVD coated carbide inserts with novel wiper edge geometry for face milling of Inconel 625 under dry cutting conditions. Cutting speed, feed per tooth and axial depth of cut have been taken as input variables and machining performance is evaluated in terms of tool life, tool wear analysis, material removed and surface integrity aspects (namely roughness and microhardness). Taguchi L8 array has been employed for experimentation phase followed by post experimental analysis. It is found that for tool life, axial depth of cut is the most significant factor with contribution of 45.43%. Maximum tool life of 42.8 min was achieved when machining was done employing lower values of feed (0.08 mm/tooth) and axial depth of cut (0.25 mm) with higher value of cutting speed (45 m/min). For the case of surface roughness, feed/tooth is found to be the most contributing factor (PCR 46.25%). Results are found to be correlating well with the cutting temperatures generated during the process. Experiments with minimum axial depth of cuts resulted in lesser temperatures and better output parameters in general. Review of the wear pattern via SEM analysis indicate adhesion, BUE, attrition and chipping to be the main wear mechanism in general except where higher axial depth of cut (0.5 mm) was employed that culminated in fracture. For the conditions where maximum tool life was obtained, a work-hardened layer was observed beneath the machined surface extending up to ∼400 μm depth. An indirect comparison of the results with other literature reported face milling scenarios of Inconel 625 (where other tool types are employed), seems to indicate the effectiveness of wiper inserts employed herein. The results are well explained and supported by the physical phenomenon involved.

Abstracts:The trend toward the miniaturizing of commercial and engineering products is inevitable. Micromilling is the most versatile process to shape microcomponents subtractively. One of the main areas that benefit from micromilling is medical, with titanium and titanium alloy being its most frequently used materials. The popular Ti-6Al-4V alloy has excellent combination of strength and toughness, combined with a great resistance to corrosion and oxidation. This particular alloy dominates other Ti alloys and is used in 50% of all titanium applications. Taking into consideration that this alloy is considered a difficult to cut material, this study investigates the machinability of Ti-6Al-4V in micromilling operations. The wear of micro tools (152.4 μm diameter) coated with TiAlN and diamond-like carbon coating (DLC) are investigated and compared against uncoated tools. The tests are performed on a four-axis CNC milling system with a 60,000 min−1 maximum spindle speed. The tools are tested under dry conditions and wet conditions using the minimum quantity of lubrication. It is used cutting speed of 9.6 m/min, feed rate of 0.1 μm/tooth and axial depth of cut of 10 μm. The test consisted of machining slots 4.2 mm long until the end of the tool life. The results show that edge radius rounding and flank wear are the main wear types. The wear is predominant on the secondary clearance face of the microtool when applying cutting fluid. The lowest tool wear is obtained with the DLC coated microtools under dry conditions, presenting a wear reduction of 640% and 267% when compared to TiAlN coated and the uncoated microtool, respectively.

Abstracts:The burr influences the surface quality and the performance of the part. Nowadays, vibration-assisted drilling (VAD) is used to decrease the exit burr size. However, further analysis of the VAD burr formation mechanism is required. A mathematical burr prediction model of low-frequency VAD is proposed for the aluminum 7075-T6 alloy cutting. This model includes material deformation mechanisms, multi-region thrust force, and VAD kinematic characteristics. In the material deformation process of VAD, the Johnson-Cook model and fracture model are considered. The results indicate that the experimental burr height is consistent with the model prediction values, and the deviation is less than 8%. The average burr height of VAD decreases by 49.5 %–52.6 % compared with conventional drilling (CD). The parameter analysis shows that the vibration amplitude had the highest sensitivity to the burr height. In the Multivariate regression analysis (MRA), the regression coefficient sum of vibration-related parameters’ absolute values (0.676) approximates the sum of other parameters’ absolute values (0.817).