Micro-textures applied to cutting tool surfaces provide certain advantages such as reducing tool forces, stresses, and temperature hence overall friction between the tool-chip contact and improving chip adherence and associated tool wear. This study explores the effect of micro-texture geometry parameters fabricated on the rake face of tungsten carbide inserts that were tested in dry turning titanium alloy Ti-6Al-4V. The effects of micro-texture geometry on the cutting forces, tool stresses, tool temperatures, tool wear rate and variable friction coefficient were studied with 3D finite element (FE) simulations. The simulation model was validated comparing cutting forces predicted and measured. The results indicated some effects of micro-textured tool geometry parameters being significant and others are not as significant. The experiments reveal that the effects of micro-groove width, depth, and distance from cutting edge are found to be significant on cutting forces, but the spacing is not as much. The effect of increasing feed rate on cutting force and tool wear was significant and suppressed the advantages offered by micro-grooved texture tool geometry. The simulation results indicate that the effect of micro-texture parameters such as groove depth and distance from cutting edge are significant on tool temperature and wear rate. The variable nature of friction coefficient was emphasized and represented as functions of state variables such as normal stress and local temperature as well as micro-texture parameters.

Metals such as Cu, Al, Ni, Ta, and stainless steels, despite their softness and ductility, are considered difficult to machine. This is due to large cutting forces and corresponding formation of a very thick chip during cutting, and hence, these metals are referred to as “gummy.” Their poor machinability of these materials arises because of an unsteady and highly redundant mode of plastic deformation referred to as sinuous flow. The prevailing plastic deformation mode during machining can be overcome by the application of certain coatings and chemical media on the undeformed free surface of the workpiece ahead of the cutting process. Using in situ imaging and concurrent force measurements, we present two different mechanochemical routes through which these media can improve machinability. The first route, which requires chemicals that adhere to the metal surface, such as glues and inks, improves cutting by inducing a change in the local plastic deformation mode—from sinuous flow to one characterized by periodic fracture or segmented flow. The second route, which requires chemicals that can react with the workpiece to form a low-friction layer, changes the sinuous flow mode to a smooth, laminar one. Both routes decrease cutting forces by more than 50% with order of magnitude improvement in surface texture as characterized by measured roughness and defect density. The results suggest a broad range of opportunities for improving the performance of machining processes for many difficult-to-cut gummy metals.

Tailored blanks characterized by variable thickness were friction stir welded (FSWed) with the aim to obtain constant joint properties along the weld seam, regardless of the thickness change. To pursue this goal, the heat input was kept constant by in-process control of tool rotation. A dedicated numerical model of the process was used to determine the tool rotation values as a function of the sheet thickness. The mechanical properties and the microstructure of the FSWed joints, produced with varying process parameters, were studied. It was found that the proposed approach can produce joints with uniform properties along the weld line in terms of stress–strain curve shape, joint strength, elongation at failure, and microstructure.

Prediction of temperature in the tool, chip, and workpiece surface is important to study tool wear, residual stresses in the machined part, and to design cutting tool substrates and coating. This paper presents a finite difference method-based prediction of temperature distribution in the tool, chip, and workpiece surface for transient conditions. The model allows inclusion of anisotropic materials such as coating or different material properties. The energy is created in the primary shear zone where the metal is sheared, the secondary deformation zone where the chip moves on the tool rake face with friction, and the tertiary zone where the flank face of the tool rubs against the finished part surface. The model allows both sticking and sliding friction contact of the moving chip on the rake face of the tool. The distribution of temperature is evaluated by meshing chip, workpiece surface zone, and tool into small discrete elements. The heat transfer among the elements is modeled, and the temperature is predicted at the center of each element. The heat transfer to the tool, workpiece, and chip is iteratively evaluated. The predicted temperature values are compared against the experimental measurements collected with coated tools in turning.

High temperature, short welding time, and low relative motion generate high bond quality in ultrasonic metal welding (USMW). Friction is considered to be the main heat source during USMW. Hence, a comprehensive and accurate understanding of friction heating has become particularly valuable for designing USMW processes and devices. However, stick, slip, and separation states may appear alternately in the welding zone between superimposed workpieces during USMW vibrations; hence, a strong nonlinear process is created. Furthermore, the structural dynamics and the heat transfer are highly coupled because material properties depend on temperature. In this research, we propose a fast and accurate numerical methodology to calculate the friction heating through a multiphysical approach integrating a nonlinear contact model, a nonlinear structural dynamics model, and a thermal model. The harmonic balance method and the finite element method are utilized to accelerate the simulation. Several experiments were performed with aluminum and copper workpieces under different clamping forces and vibration amplitudes to confirm the presented numerical method, resulting in a good match.

AA7xxx series aluminum alloys have great potentials in mass saving of vehicle bodies due to pretty high specific strength. However, the use of these high strength materials poses significant challenges to the traditional self-piercing riveting (SPR) process. To address this issue, a novel process, friction self-piercing riveting (F-SPR), was applied to join aluminum alloy AA7075-T6 sheets. The effects of the spindle speed and rivet feed rate on F-SPR joint cross section geometry evolution, riveting force, and energy input were investigated systematically. It was found that the rivet shank deformation, especially the buckling of the shank tip before penetrating through the top sheet, has significant influence on geometry and lap shear failure mode of the final joint. A medium rivet feed rate combined with a high spindle speed was prone to produce a defect-free joint with sound mechanical interlocking. F-SPR joints with the failure mode of rivet shear fracture were observed to have superior lap shear peak load and energy absorption over the joints with mechanical interlock failure. The optimized F-SPR joint in this study exhibited 67.6% and 13.9% greater lap shear peak load compared with SPR and refill friction stir spot welding joints, respectively, of the same sheets. This research provides a valuable reference for further understanding the F-SPR process.

This paper aims at providing a state-of-the-art review of an increasingly important class of joining technologies called solid-state (SS) welding, as compared to more conventional fusion welding. Among many other advantages such as low heat input, SS processes are particularly suitable for dissimilar materials joining. In this paper, major SS joining technologies such as the linear and rotary friction welding (RFW), friction stir welding (FSW), ultrasonic welding, impact welding, are reviewed, as well as diffusion and roll bonding (RB). For each technology, the joining process is first depicted, followed by the process characterization, modeling and simulation, monitoring/diagnostics/ nondestructive evaluation (NDE), and ended with concluding remarks. A discussion section is provided after reviewing all the technologies on the common critical factors that affect the SS processes. Finally, the future outlook is presented.

As energy efficiency increases in importance, researchers have identified manufacturing processes as opportunities where energy consumption can be reduced. Drawing is one widely employed, energy intensive manufacturing process, which could benefit by analysis of energy consumption during operation. To optimize the energy consumption of the drawing process, this paper developed an explicit model to quantify the process energy for the cylindrical drawing process by analyzing the dynamic punch force during the process. In this analysis, the evolution of the stress and strain was analyzed in the drawn part by considering all the structure parameters of the drawn part. The stress and strain analyses were integrated into an overall process energy model, and the behavior of the model was classified into three categories, based on their physical mechanisms, i.e., deformation energy, bending energy, and friction energy. The model was validated using numerical experiments designed by the Taguchi method where two different kinds of materials were tested over 18 runs. The results from the numerical experiments were compared with those from the model, and show that the maximum variation of the process energy predicted by this model is less than 10% for a given part. Sensitivity analysis was performed on the model to understand the contributions of the process parameters on the process energy to guide process optimization for lower energy consumption. The established model can assist in the rapid design of drawn parts with lower embodied energy.

The present research aims to study the influence of equal channel angular extrusion (ECAE) parameters (die channel angle, die corner angle, and friction coefficient) on cracking and fracture tendency. For this type of analysis, a MATLAB code integrated with finite element Abaqus/Explicit model was developed and used. A parametric study is done to investigate how the damage tendency varies with changes of ECAE parameters. The distribution of the damage factor based on Cockcroft–Latham equation for different channel angles, corner angles, and friction coefficients is depicted. It is observed that the appearance of cracks on the upper surface is more likely to occur than on the lower surface. The reduction in friction coefficient does not guarantee minimum damage tendency. Finally, the optimum parameters for reducing the fracture tendency in ECAE are presented.

In this study, the friction stir welding (FSW) of aluminum alloy 6061-T6511 to TRIP 780 steel is analyzed under various process conditions. Two FSW tools with different sizes are used. To understand the underlying joining mechanisms and material flow behavior, nano-computed tomography (nano-CT) is applied for a 3D visualization of material distribution in the weld. With insufficient heat input, steel fragments are generally scattered in the weld zone in large pieces. This is observed in a combined condition of big tool, small tool offset, and low rotating speed or a small tool with low rotating speed. Higher heat input improves the material flowability and generates a continuous strip of steel. The remaining steel fragments are much finer. When the volume fraction of steel involved in the stirring nugget is small, this steel strip can be in a flat shape near the bottom, which generally corresponds to a better joint quality and the joint would fracture in the base aluminum side. Otherwise, a hook structure is formed and reduces the joint strength. The joint would fail with a combined brittle behavior on the steel hook and a ductile behavior in the surrounding aluminum matrix.

A hybrid friction stir resistance spot welding (RSW) process is applied for joining aluminum alloy 6061 to TRIP 780 steel. Compared with conventional RSW, the applied current density is lower and the welding process remains in the solid state. Compared with conventional friction stir spot welding (FSSW) process, the welding force is reduced and the dissimilar material joint strength is increased. The electrical current is applied in both a pulsed and direct form. With the equal amount of energy input, the approximately same force reduction indicates that the electro-plastic material softening effect is insignificant during FSSW process. The welding force is reduced mainly due to the resistance heating induced thermal softening of materials. With the application of electrical current, a wider aluminum flow pattern is observed in the thermo-mechanically affected zone (TMAZ) of weld cross sections and a more uniform hook is formed at the Fe/Al interface. This implies that the aluminum material flow is enhanced. Moreover, the Al composition in the Al–Fe interfacial layer is higher, which means the atomic diffusion is accelerated.

Friction stir scribe (FSS) welding as a recent derivative of friction stir welding (FSW) has been successfully used to fabricate a linear joint between automotive Al and steel sheets. It has been established that FSS welding generates a hook-like structure at the bimaterial interface. Beyond the hook-like structure, there is a lack of fundamental understanding on the bond formation mechanism during this newly developed FSS welding process. In this paper, the microstructures and phases at the joint interface of FSS welded Al to ultra-high-strength steel were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that both mechanical interlocking and interfacial bonding occurred simultaneously during the FSS welding process. Based on SEM observations, a higher diffusion driving force in the advancing side was found compared to the retreating side and the scribe swept zone, and thermally activated diffusion was the primary driving force for the interfacial bond formation in the scribe swept region. The TEM energy-dispersive X-ray spectroscopy (EDXS) revealed that a thin intermetallic compound (IMC) layer was formed through the interface, where the thickness of this layer gradually decreased from the advancing side to the retreating side owing to different material plastic deformation and heat generations. In addition, the diffraction pattern (or one-dimensional fast Fourier transform (FFT) pattern) revealed that the IMC layer was composed of Fe 2 Al 5 or Fe 4 Al 13 with a Fe/Al solid solution depending on the weld regions.

Expanding performance of friction power in material processing techniques, considerably improves the process efficiency while decreases required load and increases imposed strain by the localized material softening. This paper proposes friction-assisted tube forming (FATF) and friction-assisted tube extrusion (FATE) to deform cylindrical tubes for desirable radius and thickness. These methods were successfully examined on commercially pure copper tubes. Finite element (FE) analyses were executed to simulate heat generation, temperature, and strain fields. Using friction power in the presented methods significantly reduced processing force and enhanced imposed strain. Therefore, FATF and FATE show a great capability to forming and extrusion of the cylindrical tubes with minimum processing power. Mechanical properties of the processed tubes showed considerable changes in which yield strength and ultimate tensile strength increased 4.6 and 1.6 times greater than those from the initial values. Dynamically recrystallized fine grains with mean size of 8.3 μ m were obtained compared with 60 μ m for the annealed sample.

Friction self-piercing riveting (F-SPR) process has shown advantages over fusion welding, solid state welding, and traditional mechanical joining processes in joining dissimilar materials. Because of the thermo-mechanical nature of F-SPR process, formation of the joint is determined by both riveting force and softening degree of materials to be joined. However, it is still not clear that how exactly the riveting force and generated frictional heat jointly influence mechanical interlocking formation and crack inhibition during F-SPR process. To address these issues, F-SPR process was applied to join 2.2 mm-thick aluminum alloy AA6061-T6 to 2.0 mm-thick magnesium alloy AZ31B. The correlation of riveting force, torque responses, and energy input with joint quality was investigated systematically under a wide range of process parameter combinations. It was found that a relatively greater final peak force and higher energy input were favorable to produce sound joints. Based on that, a two-stage F-SPR method was proposed to better control the energy input and riveting force for improved joint quality. The joints produced by the two-stage method exhibited significantly improved lap-shear strength, i.e., 70% higher than traditional self-piercing riveting (SPR) joints and 30% higher than previous one-stage F-SPR joints. This research provides a valuable reference for further understanding the F-SPR joint formation mechanism and conducting process optimization.

This paper presents investigation findings on additive manufacturing (AM) aspects of Ti6Al4V by microplasma transferred arc powder deposition ( μ -PTAPD) process in continuous and dwell-time mode. Pilot experiments were conducted to identify feasible values of six important parameters of μ -PTAPD process for single-layer deposition followed by 27 main experiments varying three parameters. Energy consumption aspects were used to identify optimum values of parameters varied during main experiments for multilayer deposition. It revealed that higher values of flow rate of powder and travel speed of deposition head result in smaller values of power consumption per unit flow rate of powder and energy consumption per unit traverse length. Continuous and dwell-time modes were used to study deposition characteristics, microstructure, lamellae widths, wear characteristics, tensile properties, fractography of tensile specimen, wear mechanism, and microhardness of multilayer depositions. Dwell-time deposition yielded higher effective wall width (EWW), deposition efficiency (DE), yield strength, ultimate strength, microhardness, surface straightness, lower strain, wear volume and friction coefficient, and smaller lamellar width. It had good deposition quality with fine partial martensite and basket-weave microstructure. Fractography analysis exhibited fine dimple rupture for dwell-time multilayer deposition and occurrence of elongated regions for continuous multilayer deposition. Wear of dwell-time multilayer deposition occurred by microploughing and microcutting resulting in smaller wear debris. Comparison of Ti6Al4V depositions by different processes revealed that dwell-time μ -PTAPD process is cost-effective than laser-based processes and energy efficient than pulsed plasma arc process.

Fiber waviness is one of the most significant defects that occurs in composites due to the severe knockdown in mechanical properties that it causes. This paper investigates the mechanisms for the generation of fiber path defects during processing of composites prepreg materials and proposes new predictive numerical models. A key focus of the work was on thick sections, where consolidation of the ply stack leads to out of plane ply movement. This deformation can either directly lead to fiber waviness or can cause excess fiber length in a ply that in turn leads to the formation of wrinkles. The novel predictive model, built on extensive characterization of prepregs in small-scale compaction tests, was implemented in the finite element software abaqus as a bespoke user-defined material. A number of industrially relevant case studies were investigated to demonstrate the formation of defects in typical component features. The validated numerical model was used to extend the understanding gained from manufacturing trials to isolate the influence of various material, geometric, and process parameters on defect formation.

Aluminum alloys have been increasingly adopted in the fabrication of automotive body structures as an integral component of mass savings strategy. However, mixed use of dissimilar aluminum alloys, such as sheet metals, castings, and extrusions, poses significant challenges to the existing joining technologies, especially in regard to single-sided joint access. To address this issue, the current study applied the friction stir blind riveting (FSBR) process to join 1.2 mm-thick AA6022-T4 aluminum alloy to 3 mm-thick Aural-2 cast aluminum. A newly developed, robot mounted, servo-driven, FSBR equipment and the procedure using it to make FSBR joints were introduced systematically. The effect of rivet feed rate and spindle speed on joint formation and cross section geometry was investigated, and it was found that a high spindle speed and a low rivet feed rate, i.e., high heat input, are prone to produce good joints, and that low heat input can cause severe problems related to insufficient softening of the sheets. The rivet deformation, especially the notch location on the mandrel relative to the shank has significant influence on lap-shear strength and fracture mode of the final joints. A rivet pull-out fracture mode was observed at higher rivet feed rates and lower spindle speeds and exhibited significantly improved energy absorption capability, i.e., 62% higher compared to traditional blind riveted (BR) joints.

Thermal history and residual stresses in dissimilar friction stir welding (FSW) of AA2024 and AZ31 were studied under different tool offsets using a coupled Eulerian–Lagrangian (CEL) finite element model and a mechanical model. Welding experiments and residual stresses' measurements were conducted to validate the models. Comparisons between the experimental and numerical results indicated good agreement. The maximum temperature in the welded zone was predicted to be slightly lower than 400 °C, regardless of offset, and that its location shifted with tool offset from the advancing side (AS) to the retreating side (RS). Longitudinal residual stresses changed from tensile under the tool shoulder to compressive beyond this region and it appeared to be the dominant stress component. The transverse stresses were tensile and of lower magnitude. Both the longitudinal and transverse residual stresses have their maximum values within the weld zone near the end of the weld length. For both peak temperatures and residual stresses, higher values were obtained at the AS with no tool offset and 1 mm offset to the AS, and at the RS with 1 mm offset to the RS. Lower residual stresses and better weld quality were obtained with tool offset to the aluminum side.

Friction stir blind riveting (FSBR) process offers the ability to create highly efficient joints for lightweight metal alloys. During the process, a distinctive gradient microstructure can be generated for the work material near the rivet hole surface due to high-gradient plastic deformation and friction. In this work, discontinuous dynamic recrystallization (dDRX) is found to be the major recrystallization mechanism of aluminum alloy 6111 undergoing FSBR. A cellular automaton (CA) model is developed for the first time to simulate the evolution of microstructure of workpiece material during the dynamic FSBR process by incorporating main microstructure evolution mechanisms, including dislocation dynamics during severe plastic deformation, dynamic recovery, dDRX, and subsequent grain growth. Complex thermomechanical loading conditions during FSBR are obtained using a mesh-free Lagrangian particle-based smooth particle hydrodynamics (SPH) method, and are applied in the CA model to predict the microstructure evolution near the rivet hole. The simulation results in grain structure agree well with the experiments, which indicates that the important characteristics of microstructure evolution during the FSBR process are well captured by the CA model. This study presents a novel numerical approach to model and simulate microstructure evolution undergoing severe plastic deformation processes.

The stamping of fiber metal laminates (FMLs) at thermoforming temperature of the thermoplastic matrix is investigated. The studied FML types consist of a unidirectional carbon fiber-reinforced core that is attached to metal cover layers either made of a steel or magnesium alloy. An analytical model is established in order to predict the process forces during forming, which are the blankholder force required to make the metal covers yield plastically, the punch force, and the corresponding load distribution on the individual layers (outer layer, core layer, and inner layer). The global forces are primarily verified through experimental force measurements, while numerical simulations are mainly performed to assess the resulting load distribution with the help of strain distributions in the cover layers. The results show that the introduced model can be applied successfully if the stamp-forming process is dominated by friction-induced tensional loading rather than by bending.