Electrically-assisted forming (EAF) has been increasingly utilized as an effective auxiliary processing technology to improve the formability of hard-to-deform metals. Previous works have revealed that the phase transformation of titanium alloys subjected to electropulsing treatment (EPT) can occur at a lower temperature and in a remarkably shorter time compared with those subjected to the traditional heating treatment (THT). However, an in-depth experimental verification and further analysis is still missing so far. Therefore, to characterize the specific effects of EPT on α→β transformation process, both EPT and THT experiments were conducted on Ti-6Al-4V sheet specimens. After that, a calculation method based on the analysis of optical microscopic (OM) metallographs was developed to characterize the amount of phase transformation in EPT and THT. According to the results, it was found that the pulse current can significantly reduce the phase transus temperature and accelerate the transformation process in EPT comparing to THT. Furthermore, the specific effects of EPT on transus temperature and phase transformation rate were investigated in detail. Based on that, the transformation kinetics of the electropulsing-induced α→β phase transformation was also analyzed by utilizing the JMA model. It is revealed that the activation energies of both nucleation and growth of phase transformation are reduced by electric current. Hence the phase transformation can start at a lower temperature with a higher rate in EPT. The mechanism behind the effects was also discussed in detail in the present work.

Despite the rapid growth and widespread recognition of Additive Manufacturing (AM) technologies, the geometrical inaccuracy of the manufactured products remains a challenging issue and effective prediction of the geometric deviations in AM is critical for the solution of this issue. The layerwise characteristic of the AM process has motivated the investigation of deviation from in-plane and out-of-plane perspectives, the latter of which has been seldom studied and will be the focus of this paper. In this paper, an out-of-plane deviation modeling method will be proposed based on statistical modal analysis. Owing to the convenience in data acquisition, AM simulation is conducted to obtain the layer-level out-of-plane deviation on parts manufactured by the Selective Laser Melting process. Discrete Cosine Transform is adopted to identify the major deviation modes from the data. The statistical relationship between mode coefficients and related part and process parameters is studied based on the Gaussian Process model. To gain data for model training, experimental design is conducted to sample parameter combinations as simulation input. A case study is presented to demonstrate the proposed method and the effectiveness is validated on test data. The method can be applied in multiple domains of AM, such as quality control and tolerancing, to provide high-fidelity prediction of geometric deviations.

The corrosion resistance of resistance spot welded (RSW) Al-steel couples of varying combinations of 6016-T4 aluminum alloys and steel substrates, including with and without adhesive at the faying interface have been successfully evaluated, and compared to corresponding self-pierce riveted (SPR) couples. The corrosion resistance of resistance spot welded Al-steel couples has performed well in cyclic corrosion testing (GMW 17026) and the results are comparable to or better than that of self-pierce riveted couples. SPR couples are more susceptible to galvanic corrosion than resistance spot-welded couples based upon experimentally measured electrochemical potentials from actual joints. The presence of adhesive acts significantly to reduce galvanic corrosion between aluminum alloy and steel substrates, and moreover tensile lap-shear strength significantly increased with structural adhesive for both RSW and SPR joining systems. However, despite the presence of adhesive the lap-shear strength was reduced by more than 50% after cyclic corrosion testing to strength levels comparable to the lap-shear strength of couples having no adhesive and tested in ambient conditions.

The growing flexibility of modern production systems complicates the quality assurance and process safety of mechanical processing. As an import component of milling machines, the workpiece clamping systems plays a quality-determining role within every milling process. Thus, a sensory workpiece clamping system which utilizes sensory swing clamps was developed in former research work in order to provide monitoring capabilities. This contribution deals with the experimental analysis of the multiple integrated sensors of the sensory swing clamp and the characterization of their measuring capability towards different measurands. By means of the stepwise linear regression method, different models were developed that enable the determination of the clamping force, hydraulic pressure and the piston position. The results verify that the multi-sensor evaluation significantly increases the measuring accuracy of a sensory swing clamp. Thus, the measuring accuracy is measurable with a standard deviation of 0.05 MPa for the hydraulic pressure, 101 N for the clamping force and 0.62 mm for the piston position. Furthermore, the practicability and flexible use at varying boundary conditions is proved.

Computational modelling and simulation are employed to study a rotating susceptor vertical impinging Chemical Vapor Deposition (CVD) reactor to predict GaN film deposition. Many metal organic chemical vapor deposition reactor manufacturers use prior experience to design and fabricate CVD reactors without a fundamental basis for the process and information on the optimal conditions for the deposition. Through trial and error, they fine tune the gas flow parameters, heater temperatures, chamber pressure, and concentration of species gases for optimal growth. However, expensive raw precursor gas and time are wasted through this method. A computational model is an important step in CVD reactor design and GaN growth prediction. It can be used to model and optimize the reactor to yield favorable operating conditions. In this paper, a simple geometry consisting of a rotating susceptor and flow guide is considered. The focus is on gallium nitride (GaN) thin films. The study shows how the computational model can benefit reactor design. It also presents comparisons between model prediction results and experimental data from a physical, practical, system. Commercially available software is used, with appropriate modifications, and the results obtained are discussed in detail.

An additive manufacturing-enabled bi-continuous piezocomposite architecture is presented to achieve mechanical flexibility and piezoelectricity simultaneously in piezoelectric materials. This architecture is comprised of an active ferroelectric ceramic phase and a passive flexible polymer phase, which are separated by a tailorable phase interface. Triply periodic minimal surfaces were used to define the phase interface, due to their excellent elastic properties and load transfer efficiency. A suspension-enclosing projection-stereolithography process was used to additively manufacture this material. Post processes including polymer infiltration, electroding and poling are introduced. Piezoelectric properties of the piezocomposites are numerically and experimentally studied. The results highlight the role of tailorable triply periodic phase interfaces in promoting mechanical flexibility and piezoelectricity of bi-continuous piezocomposites.

In this study, the conditions for wall thickness reduction in hollow sinking were obtained by tube drawing experiments in which the drawing speed ratio was controlled under three conditions (1.09, 1.11, and 1.14). These conditions have not been found in the history of hollow sinking. The results of the experiment and the theoretical formulas indicate that the geometric condition is obtained from the figure of the ratio of inner diameter to outer diameter after drawing against that ratio before drawing. Furthermore, the ratio of the inner diameter to the outer diameter after drawing must be above the constant wall thickness line derived from the cross-sectional change. To satisfy this geometric condition, the drawing speed ratio must be larger than threshold value, which is obtained from the ratio of the inner diameter to the outer diameter before drawing, and the reduction of the die. However, the value of the back stress approaches that of the strength of the tube when the drawing speed ratio increases. A simple dynamical model shows that parameters other than the drawing speed ratio do not significantly decrease the back stress during drawing. Therefore, the drawing speed ratio should be set such that the tube does not break.

Due to their superior machining quality, efficiency, and availability, five-axis machine tools are important for the manufacturing of complicated parts of freeform surfaces. In this study, a new type of five-axis machine tool was designed that is composed of four rotary axes as well as one translational axis. Given the structure of the proposed machine tool, an inverse kinematics analysis was conducted analytically, and a set of methods was then proposed to address the issues in the kinematic analysis, e.g., the singularity and multi-solution problems. Compared with traditional five-axis machine tools, which are typically composed of three linear axes and two rotary axes, the proposed machine tool exhibited better kinematic performance with machining parts with hub features, such as impellers, which was validated by simulations and real cuttings.

The novel sheet metal bending process is designed to change the load path in order to control the damage evolution. The process superposes targeted radial stresses during bending and is therefore called radial stress superposed (RSS) bending. As material damage is strongly dependent on the load path, the setting of this property becomes possible in this process. Hence, the process principle, its features, and the tool setup are presented. Furthermore, numerical simulations are carried out with the aim to investigate the occurring deformation zone and the resulting radial stress superposition. Scanning electron micrographs prove that the evolution of voids is delayed. With the acquired knowledge to change the stress state during the bending process, the property “damage” can be controlled and finally reduced. This enhances the microstructure and lifetime performance of the bent product. The improved product performance is shown by a newly designed specimen for impact testing of bent products.

This paper presents a novel application of intensity-based volume registration to manufacturing using voxel-based computer-aided manufacturing (CAM) models. The introduced techniques are presented in the the context of machining irregularly shaped materials by integrating volumetric imaging feedback to computer numerical control (CNC) machine tools. This requires a comparison and alignment to be performed in the software to geometrically “fit” the source design model inside a rendered starting material. The requirements differ from many typical registration applications in that the workpiece will necessarily be larger (i.e., greater in volume) than the desired final computer-aided design (CAD) file. Therefore, models need to be aligned for toolpath generation to workpiece counterparts that have been either volumetrically offset or contain additional material/volume. Intensity-based registrations are unique in that they consider only the voxel values over the entire volume. Although advancements in medical imaging have produced efficient, robust voxel registration algorithms, these techniques have not yet been applied to manufacturing. This research introduces the use of maximization of mutual information (MMI) for voxel-based CAM to drive an alignment registration for systems integrating imaging technology. A simple but novel method, which the authors have named minimization of distance variance (MDV), is also introduced. This minimizes the variance between voxel intensities to demonstrate the design of a similarity metric for a simple case in machining rough castings.

Micromilling can fabricate complex features in a wide range of engineering materials with excellent finish but the limited flexural stiffness of the micro-end mill can result in catastrophic tool failure. This issue can be overcome by using high rotational speeds. Note that the combination of high rotational speeds and low flexural stiffness can induce process instability which is aggravated by the accelerated wear of the microtools at high speeds, specifically, for Ti-alloys. The effect of progressive tool wear on the stability has been investigated in micromilling of Ti6Al4V. For incorporating tool wear, the cutting force coefficients are modeled as a function of instantaneous cutting edge radius (CER). These coefficients also depend on feed/flute and the initial CER of the micro-tool (due to inherent variability in grinding process). A significant increase (85%-114%) in the instantaneous CER is observed with an increase in the length of cut. At high rotational speeds, a zero-order approximation frequency domain model may not be accurate. Therefore, a 2-DOF time domain model based on semidiscretization method has been used to characterize the evolution of stability limits with an increase in the length of cut. The frequency spectra of velocity and surface topography have been analyzed for the model validation. The progressive tool wear affects the stability limits along with the initial CER and the feed/flute. At higher speeds (90,000-110000 rpm), the effect of progressive tool wear is pronounced and the stability limits reduce by ~30% in that range.

Face milling is widely used in machining processes, aimed at providing workpieces with high surface quality. The chatter generated in face milling could lead to tremendous damage to machine tools, poor machined surface quality, and loss of processing efficiency. Most related researches have been focused on the modeling of spindle dynamics and discretization algorithms for chatter prediction. However, few published articles have taken the geometric characteristics of workpieces into consideration, especially for workpieces with discontinuous surfaces in face milling, which leads to poor accuracy of chatter prediction as well as the waste of processing efficiency. To overcome this shortage, a novel dynamic model for the face milling process is built in this paper, considering the cutting insert engagement based on the geometric characteristics of the workpieces and the tool path. The stability lobe diagrams (SLDs) applicable to workpieces with discontinuous surfaces are constructed. A process parameter optimization model is developed to maximize the chatter-free processing efficiency of the face milling process. The sensitivity analysis is utilized to simplify the objective function, and the genetic algorithm is employed to solve the optimization model. The proposed approach is validated by an experimental case study of an engine block, improving the chatter-free material removal rate by 53.3% in comparison to the classic approach.

This study compares two processing routes, selective laser melting (SLM) and flame spray (FS) to fabricate an Al/MWCNT composite layer over an aluminum alloy 6013 (AA6013) substrate. The final surface and cross section morphologies were evaluated by scanning electron microscopy (SEM) and optical microscopy (OM). The effect of these processing routes on the multiwall carbon nanotubes (MWCNT) was evaluated by X-ray diffraction (XRD) and Raman spectroscopy (RS). Finally, the mechanical properties were evaluated by Vickers microhardness. The Raman bands corresponding to carbon were identified in the spectrum of both samples processed by SLM and FS. However, the Al4C3 formation was also identified in the latter. The Vickers microhardness results show an increase in the hardness values of the FS and SLM processed coatings of 44% and 9%, respectively, when compared with the AA6013 substrate.

Residual stress (RS) is a major processing issue for selective laser melting (SLM) of metal alloys. Postprocessing by way of heat treatment or hot isostatic pressing is usually required for acceptable mechanical properties. In this work, laser shock peening (LSP) treatment on both SLM and cast aluminum A357 alloys are compared with regard to the development of beneficial near-surface compressive RS. Experiments are conducted using high energy nanosecond pulsed laser, together with a fast photodetector connected to a high-resolution oscilloscope and high-speed camera to identify detailed temporal and spatial laser pulse profiles to improve numerical predictions. Constitutive modeling for SLM A357 alloy is performed using finite element simulation and data obtained from X-ray diffraction (XRD) measurements. Since XRD-RS measurements are accompanied with significant machine-reported error, an effective method is introduced to quantify the material constitutive model uncertainty in terms of a joint probability mass function. Conventionally, most constitutive behavior research for LSP involves deterministic material modeling. Predicted RS using deterministic approaches fail to reflect real-world variations in the materials, laser treatment, or RS measurements. A discretized Bayesian inference is used to quantify the rate-dependent plasticity material model parameters as a joint probability function. RS are then characterized as random fields, which provides far greater insight into the practical ability to attain desired residual stresses. Moreover, for identical LSP treatments, it is determined that the material models are significantly different for the SLM and the conventional cast A357 aluminum alloys, resulting in much lower magnitude of compressive RS in the SLM alloy.

A silicon wafer is important for the electronic and computer industries. However, subsurface damage (SSD), which is detrimental to the performance and lifetime of a silicon chip, is easily induced in a silicon wafer during a grinding process since silicon is typically a hard and brittle material. Therefore, it is necessary to detect and remove SSD in the subsequent processes. In this study, a polarized laser scattering (PLS) system is installed to detect the SSD in a ground wafer. It is found that not only the subsurface crack but also the residual stress leads to depolarization of an incident light. The effects of residual stress on depolarization are studied. The residual stress results in the photoelasticity, which causes the depolarization of the incident light in the PLS system. The depolarization caused by the residual stress is determined by the directions and the difference of the principal stresses. When the polarization direction of the incident light is aligned with one of the principal stresses, the effects of the residual stress can be minimized; therefore, the subsurface crack can be quantitatively estimated by PLS.

X-ray computed tomography (XCT) is a promising non-destructive evaluation technique for additively manufactured (AM) parts with complex shapes. Industrial XCT scanning is a relatively new development, and XCT has several acquisition parameters a user can change for a scan whose effects are not fully understood. An artifact incorporating simulated defects of different sizes was produced using laser powder bed fusion (LPBF) AM. The influence of six XCT acquisition parameters was investigated experimentally based on a fractional factorial designed experiment. Twenty experimental runs were performed. The noise level of the XCT images was affected by the acquisition parameters, and the importance of the acquisition parameters was ranked. The measurement results were further analyzed to understand the probability of detection (POD) of the simulated defects. The POD determination process is detailed, including estimation of the POD confidence limit curve using a bootstrap method. The results are interpreted in the context of the AM process and XCT acquisition parameters.

Electromagnetic crimping is a solid state, high-speed, and high strain-rate materials joining process. In this process, the flyer tube is deformed over the base rod plastically to produce the joint. In this work, variation in the geometry of the field shaper was analyzed to concentrate the electromagnetic pressure at the specified location to produce a joint having better mechanical strength. Finite element analysis in LS-Dyna package, as well as experimental study, was carried out on three types of field shaper namely tapered, taper-stepped and stepped. In all three field shapers the effective length, outer diameter, inner diameter, total length, materials properties were constant. These field shapers were kept inside the same multi-turn solenoid coil for all the experiments. It was found that the taper-stepped field shaper results better regarding impact velocity, Lorentz force, temperature generation, less heating, uniformity in crimping among the three types of field shaper. The efficiency of the taper-stepped field shaper was found to be higher compared to stepped field shaper than that of tapered field shaper.

In micro-milling process, the minimization of tool chatter is critical for good surface finish quality. The analysis of chatter requires an understanding of the milling tool as well as the dynamics of milling system structure. Frequency response function (FRF) at micro-milling tool point reflects dynamic behavior of the whole micro-milling machine-spindle-tool system. However, the tool point FRF of micro-milling does not come directly from hammering test. In order to solve the problem, this paper gets the FRF of the spindle system based on the rotating Timoshenko beam theory and receptance coupling substructure analysis (RCSA), and the bearing characteristics are added into the spindle model through structural modification. Then the centrifugal force and gyroscopic effect caused by the high-speed rotation of the micro-milling spindle are taken into account to better simulate the real scenario and increase the accuracy of modal parameters. The method has general usage and is adaptive for different micro-milling tool under which only the spindle dimension, bearing characteristics and contact parameters need to be changed.