Ultrasonic welding is a solid-state joining process which uses ultrasonic vibration to join materials at relatively low temperatures. Ultrasonic powder consolidation is a derivative of the ultrasonic additive process which consolidates powder material into a dense solid block without melting. During ultrasonic powder consolidation process, metal powder under a compressive load is subjected to transverse ultrasonic vibrations resulting in a fully-dense consolidated product. While ultrasonic powder consolidation is employed in a wide variety of applications, the effect of critical process parameters on the bonding process of powder particles during consolidation is not clearly understood. This study uses a coupled thermo-mechanical finite element analysis technique to investigate the effect of critical process parameters including vibrational amplitude and base temperature on the stress, strain, and particle temperature distribution during the ultrasonic powder consolidation process. The study finds that during this process, the ultrasonically vibrating tool imparts cyclic vibratory shear stress on the particles. The simulation also revealed that the particle temperature just reaches the recrystallization point. Higher vibration amplitude imparted higher frictional heat on the particles, thereby aiding the consolidation process. The simulation study also showed indications of thermal softening and restricted grain boundary sliding during the ultrasonic powder consolidation process. The outcomes of this study can be used to further the industrial applications of ultrasonic powder consolidation process as well as other ultrasonic welding based processes.

Digital light processing (DLP) three-dimensional (3D) printing is a type of stereolithography (SLA) process that uses a digital projector to selectively cure resin according to a mask image. Each exposure solidifies a planar component of the printed part, allowing full layers to be cured at once. The DLP approach produces better quality parts at a faster rate compared to other 3D printing methods. One of the challenges with DLP printing is the difficulty of incorporating multiple materials within the same part. As the part is cured within a liquid basin, resin switching introduces issues of cross-contamination, layer height variability, and significantly increased print times. In this paper, a novel technique for printing with multiple materials using the DLP method is introduced. The material handling challenges are addressed with the design of a material swapping mechanism, a material tower, and an active part cleaning system. The material tower is a compact design to facilitate the storage and retrieval of different materials during the printing process. A spray mechanism is used for cleaning excess resin from the part between material changes. Challenges encountered within the 3D printing research community are addressed, with a focus on improving the shortcomings of modern multi-material DLP printers.

Shape Memory Alloys are smart materials that tend to remember and return to its original shape when subjected to deformation. These materials find numerous applications in robotics, automotive and biomedical industries. Micromachining of SMAs is often a considerable challenge using conventional machining processes. Micro-Electrical Discharge Machining is a combination of thermal and electrical processes, which can machine any electrically conductive material at micron scale independent of its hardness. It employs dielectric medium such as hydrocarbon oils, deionized water, and kerosene. Using liquid dielectrics has adverse effects on the machined surface causing cracking, white layer deposition, and irregular surface finish. These limitations can be minimized by using a dry dielectric medium such as air or nitrogen gas. This research involves the experimental study of micromachining of Shape Memory Alloys using dry Micro-Electrical Discharge Machining process. The study considers the effect of critical process parameters including discharge voltage and discharge current on the material removal rate and the tool wear rate. A comparison study is performed between the Micro-Electrical Discharge Machining process with using the liquid as well as air as the dielectric medium. In this study, microcavities are successfully machined on shape memory alloys using dry Micro-Electrical Discharge Machining process. The study found that the dry Micro-Electrical Discharge Machining produces a comparatively better surface finish, has lower tool wear and lesser material removal rate compared to the process using the liquid as the dielectric medium. The results of this research could extend the industrial applications of Micro Electrical Discharge Machining processes.

In the present work, Stress corrosion cracking (SCC) and its mechanical behavior are presented. SCC represents complex behavior due to electrochemical and mechanical interaction. Damage models are proposed to predict crack initiation time for stainless steel under constant load using the concept of continuum damage mechanics to show incremental damage accumulation which finally leads to failure of the material. Two damage models applicable to prediction of damage in SCC, Lemaitre damage model and damage driving force model proposed by Kamaya are compared. The comparative study of the results obtained by these damage models shows that in Lemaitre damage law cracks initiate randomly while in damage driving force model the stress concentration occurs around the periphery of damaged element results in increased damage force. The study can be used to estimate the crack initiation time in SCC under corrosive atmosphere.

Laser cladding utilizes a high-powered laser to fuse and solidify the metal powders, which results in a complex change of physical and mechanical properties. Selection of parameters and creative structure design are critical for laser cladding technology. High-speed steel is cladded on the base metal 40Cr by diode laser to investigate the influence of curvature radius, scanning speed, gas flow and laser power. The micro hardness and residue stress are tested while the microstructure is analyzed. According to analysis of the process parameters in orthogonal experiment, the optimal parameters are: curvature radius 100 mm, laser power 1200W, gas flow 1000 L/h, and scanning speed 16 mm/s. Under the optimal parameters, the microstructure and grid is uniform and the grain growth is along the same direction.

Ti-6Al-4V (grade 5 titanium alloy) is one of the most widely used materials in aerospace applications including turbine blades for aerospace engines. Due to the difficulty of machining titanium alloys using conventional machining processes, wire-electro-discharge machining (wire-EDM) is used extensively for cutting titanium parts with complex geometries and profiles. The objective of this study is to investigate the effect of two important non-electrical parameters in wire-EDM, i.e. wire feed rate and wire tension, on the geometric corner and profile accuracies of the Ti-6Al-4V parts machined by wire EDM. A complex profile was designed for machining in two different thicknesses of titanium alloy using each set of experimental parameters. The complex part includes corners with 45°, 90° and 112.5°, as well as thin wall section for measuring the kerf accuracy. It was found that with the increase of wire tension, the corner accuracies at almost all the angles improved. however, too high wire tension caused inaccuracies by providing larger angles than the target values. The effect of wire tension was dependent on the thickness of the machined part. For thinner workpiece the results of the angles generated barely followed a trend, whereas for thicker part, the measured angles followed an excellent trend. The kerf accuracies were found to improve with the increase of wire tension for thin part, whereas for thick part the results of kerf width accuracies were inconsistent. In case of wire feed rate, it was found that comparatively lower settings of wire feed rates were favorable for machining thinner parts with enhanced corner accuracies. On the other hand, slightly higher wire feed rates provided better corner accuracies for thick part. Besides corner inaccuracy, profile undercuts and deviations from the machining paths were observed for lower wire tensions. Finally, it can be concluded that comparatively lower wire feed rate and higher wire tension provides improved corner and profile accuracies. however, for machining thinner sections using wire-EDM, the trends are not obvious.

A new analytical model is proposed to predict the residual stress in the milling process of Inconel 718 based upon the mechanics analysis of microstructural evolutions. The model proposes to quantify the effects of dynamic recrystallization process on the material flow stress under combined thermal-mechanical loadings in machining. Physics-based mechanistic model is applied to predict the percentage of dynamic recrystallization and the grain size as functions of the milling process parameters and materials constative attributes. The variation of grain size is expected to alter the yield stress, and such dependency relationship is applied to predict the flow stress, which is also dependent on strain, strain rate, and temperature. The time-varying trajectory of residual stress is then predicted at each milling rotation angle through the transformation from milling to equivalent orthogonal cutting, the calculation of stress distribution in loading process, and the stress change during relaxation. The results of analytical model are validated through numerical prediction. The residual stress profile predicted by proposed analytical model matches better with results from numerical model comparing with model without consideration of dynamic recrystallization, especially within subsurface area, with improved accuracy of peak compressive residual stress prediction.

Microsphere Photolithography (MPL) uses a self-assembled array of transparent microspheres to focus incident ultraviolet radiation and produce an array of photonic jets in photoresist. Typically, the microspheres are self-assembled directly on the photoresist layer and are removed after exposure during development. Reusing the microsphere array reduces the expense of the process. A mask is formed by transferring the self-assembled microsphere array to a transparent tape. This can be used for multiple exposures when pressed into contact with the photoresist. This paper demonstrates the use of this process to pattern infrared metasurface absorbers and discusses the effects of the mask-based MPL process on the metasurface performance.

The present study provides detailed investigation on the effect of various laser processing parameters and scan strategy during laser forming of thin open-celled aluminium foam. Previous research on laser bending showed that metal foams can be formed by laser processing, but it is very difficult to form the metal foams mechanically owing to their brittle nature. The 2D Laser forming operation was carried out using 2 kW fiber laser with laser power and scanning speed as input process parameters while bending angle was calculated as an output parameter. The effect of laser power, scan speed, number of scans and scan distance from the edge on bending angle of the foam were analyzed and presented. It was observed that the laser processing showed a decrease in bending angle with an increase in scan speed except for 1750 W power, where after 12500 mm/min the bending angle did not follow the trend. The bending angle decreased with increase in number of scans probably due to strain hardening effect. The effect of scan distance from the edge was different for lower process parameter combinations {600 W, 2500 mm/min} and {1000 W, 4000 mm/min}, where the bending angle was maximum for a distance of 20 mm from edge in 1400 W, 7500 mm/min scan speed. For 1750W, 11000 mm/min bending angle was maximum for 80 mm distance from edge. The SEM analysis showed that the major concern associated with laser forming of open-celled Aluminium foam is foam melting. EDS and XRD analysis showed that formation of different oxides and compounds of Aluminium increases with increases in laser power and scan speed. Micro-Computed Tomography (micro-CT) analysis confirmed the absence of crack during laser forming and the pore density variation during laser forming was clearly visible between laser processed zone and the parent material zone.

In this paper an inverse method is presented to evaluate the inner workpiece temperature distribution during cryogenic turning of metastable austenitic steel AISI 347 utilizing a FE representation of the process. Temperature data during the experiments is provided by thermocouples and a commercial thermo-graphy system. A constant cutting speed at two varying feeds are investigated. Inverse parameter verification by aligning simulated and experimental data in a least squares sense is achieved. A heat flux from tool to workpiece as well as heat transfer coefficients for forced convection by air and by carbon dioxide as cryogenic coolant are identified for each set of cutting parameters. Rigid body rotation in the model is considered applying convective time derivatives of the temperature field. Unphysical oscillations occurring in regions of high Péclet numbers are suppressed utilizing a streamline-upwind/Petrov-Galerkin scheme.

Tube forming is one of the main manufacturing techniques for processing of tubular components. This process is subdivided depending on the processing i.e., tube end forming either to expand or reduce the section. One of these tube end forming techniques is a flaring process. Most applications for flaring tube ends, utilizes a conical tool for flaring the tube either till a particular deformation to achieve a desired shape or till failure to characterize the material properties. The relationship between the flaring behavior during the process based on the outer diameter and thickness of the tube was experimentally characterized in this paper for variety of tube sizes. Further flaring limits were analyzed in these considered tube sizes. For this four outer diameter to thickness ratio were experimented and results were analyzed. Further numerical simulations were performed to match the results. A closer look on the required force-displacement curve is presented and unique regions were identified. Based on the data an empirical equation is proposed. This equation provides a concept based on material or process stiffness. It is believed that once an equation is established and variables are linked to the parameter a more better prediction can be carried out for flaring the tubes.

In this paper, a 2D milling stability analysis is reduced to a 1D problem by performing a modal analysis on an oriented transfer function matrix under a given feed direction. The oriented frequency response function (FRF) of the oriented transfer matrix are obtained as explicit functions of the radial immersion and feed direction. At different feed directions in most of the lower immersion range, the process is demonstrated to be the least stable when the modal direction of the directional matrix is oriented at 45° and 225° and in the −45° and 135°, yielding a local minimum critical depth of cut, regardless of up or down cuts. At higher immersion, the worst critical depth of cut is dominated by the lower frequency mode, and becomes a constant, independent of the feed direction at full cut. When the modal direction is oriented along the x or y axes, the process has a local maximum critical depth of cut.

Dendritic electrolytic copper powder was sintered using a newly developed friction sintering process. Green copper pellets of 14 mm height and 16 mm diameter were prepared at room temperature with 5-ton load and 60 seconds holding time. The pellets were sintered using a newly developed rapid, cost-effective, energy efficient, green friction sintering process that allows for easy and quick removal of sintered products. An aluminum plate of 14 mm thickness and 16.1 mm diameter through hole was used to hold green pellets during sintering. Frictional heat and pressure were applied on a top plate through a rotating 18 mm diameter, flat shoulder, WC tool. Sintering was performed at 12 kN axial load and 800 rpm tool rotational speed. Sintering temperatures were measured using K-type thermocouples. SEM (scanning electron microscope) images of fractured surfaces for sintered pellets show neck formation between copper particles. The neck formation is approximately uniform throughout the depth. This is in-line with hardness results along the thickness of the pellet. The process holds promise particularly for solid-state sintering of metal based powders.

Carbon fiber reinforced plastic (CFRP) composites have many excellent properties, which make them be widely used in many applications. After demolding processes, CFRP composites still need additional machining processes to achieve final shape with desired tolerances. Edge trimming is the first machining process performed on composites after their molding processes. Because of carbon fibers’ abrasive properties as well as CFRPs’ properties of inhomogeneity and anisotropy, CFRPs are regarded as the difficult-to-cut materials. Many problems are generated in traditional machining processes. To reduce and solve the problems, edge trimming using rotary ultrasonic machining (RUM) is reported in this manuscript. This paper, for the first time, makes the comparisons on machining performance (cutting forces, torque, and surface roughness) between edge trimming processes with and without ultrasonic vibration assistance. To better understand effects of ultrasonic vibration on such a process, machining mechanisms are also obtained and analyzed. This paper will provide guides for RUM edge trimming of CFRP composites.

On-machine scanning measurement of workpiece geometry has a strong advantage in its efficiency, compared to conventional discrete measurement using a touch-trigger probe. When a workpiece is rotated and tilted, position and orientation errors in workpiece setup with respect to the machine’s rotary axes can be a significant contributor to the measurement error. The machine’s geometric errors also influence the measurement error. To establish the traceability of on-machine laser scanning measurement with workpiece rotation, this paper kinematically formulates their contribution to measured profiles. As a practical application example, this paper studies the sensitivity of work-piece setup errors and rotary axis geometric errors on the error in laser scanning measurement of an axis-symmetric part.

In this paper, numerical investigation of the effects of cutting conditions in slot up milling of Ti-6Al-4V is conducted using Finite Element Method (FEM). Experiments are conducted to validate the FEM models. The validated models are then used to predict the cutting force components when different cutting conditions are applied. It is found that cutting speed, feed rate, and depth of cut have strong influence on cutting force components and tool temperature. This research provides insightful guidance for selecting optimal cutting conditions for slot milling of Ti-6Al-4V.

Low frequency vibration assisted drilling (LFVAD) is regarded as one of the most promising process in CFRP/Ti stacks drilling. This work carries the investigation of the difference between conventional drilling and LFVAD based on kinematic model. The experiments are conducted under varied vibration amplitude to a specific feed rate, also under varying spindle speeds, feed rates when the ratio of amplitude to feed rate is fixed. Then the hole quality of CFRP is evaluated based on the analysis of drilling force, chip morphology, chip extraction. The results show that there is rarely no difference between conventional drilling and LFVAD in drilling mechanism when the drilling diameter is over 1 mm. Because the impact effect caused by drill vibration is already weak. It is found that the severe mechanical damage of the CFRP holes surface could be significantly reduced due to the fragmented chips obtained in vibration drilling. The maximum instantaneous feed rate combined with feed rate and amplitude plays a significant role in CFRP hole quality. Lower maximum instantaneous feed rate results in better hole wall quality and less entry delamination. Spindle speed has no visible influence on entry delamination, while higher spindle speed improves the hole surface quality due to the resin coating phenomenon.

In this paper, a Coupled Eulerian Lagrangian (CEL) finite element model (FEM) was developed to simulate the friction stir spot welding (FSSW) of commercial pure copper. Through simulations results, the paper presents and discusses the effect of FSSW process parameters; namely rotational speed, plunging rate and dwell time, on the developed temperatures and their distribution within the workpiece as well as material flow and deformation. Model validation showed a good agreement between predicted temperature history and the experiment one, with a maximum error of 6%. Furthermore, the predicted formation of flash was also found in good agreement with the experiment with an error of only 7%. Simulation results predicted peak temperature and plastic strain among all studied welding conditions were 920 K and 3.5 respectively at 1200 rpm rotational speed, 20 mm/min plunging rate and 4 seconds dwell time, which is approximately 70% of the melting point of pure copper.

Laser shock peening (LSP) is an advanced surface treatment technique that can extend fatigue life in metallic components by inducing near-surface compressive residual stresses. In this study, LSP was implemented to induce compressive residual stresses and modify material properties of selective laser melted (SLM) aluminum A357 specimens. An initial hypothesis on the effect of LSP during tension testing was formulated and tested using finite element simulation. The hypothesis was that, due to the LSP-induced tensile residual stress field in the middle of the specimen cross sections, yielding was expected to initiate in this region. True stress-strain curves of two as-built (AB) and two laser shock peened samples were obtained through transverse tensile tests. The single explicit analysis using time dependent damping (SEATD) technique was used to simulate LSP process utilizing Johnson-Cook (J-C) constitutive parameters. J-C parameters for the cast A357 alloy were used for preliminary study. This was followed by the simulation of the transverse tensile test. J-C parameters for SLM A357 alloy were then empirically estimated, and simulations were repeated accordingly. It was found that the specific LSP pattern induced tensile residual stresses along the edges as well as the middle of the test specimen’s cross-section. Axial residual stress and yield strength profiles along three different paths on specimen’s cross-section were compared and yield regions were investigated. This supported the initial hypothesis, but also provided for a more detailed understanding of actual tensile test failure in the specific SLM A357 specimens for the given LSP treatment. In addition, the same LSP treatment on SLM A357 alloy resulted in lower magnitude of compressive residual stress than for cast A357 aluminum alloy.

Laser surface hardening of most of the industrial components require depth of surface modification in the range of 100–150 micron. Conventional laser surface hardening uses laser as a heat source to modify a particular area of the surface without melting in an inert gas environment. However, the hardened profile in this case shows peak hardness value at a certain depth from the top surface. Also, hardening the top surface to get relatively much higher hardness near the top surface in case of thin sheets becomes difficult due to accumulation of heat below the surface of the specimen which in turn lowers the cooling rate. Hence, self-quenching becomes inadequate. In the present study, an in-house fabricated laser processing head with coaxial water nozzle has been used to flow a laminar water-jet during the laser surface hardening process to induce forced convection at the top surface. Thus, heat gets carried away by the water-jet from the top surface and by the water from the bottom surface as well. Results show that with judicious selection of process parameters, it is possible to get higher hardness (800 HV) to that of conventional laser surface hardening (500 HV) at the top surface using this process. Present process can be used for those cases where high hardness values are required near the top surface specially for thin sheets and thermally sensitive materials.