Electromagnetic crimping is a solid state, high-speed, and high strain-rate joining process. Finite element analysis, as well as experimental study, was carried out on three types of field shapers, namely, tapered, taper-stepped, and stepped. In all three field shapers, the effective length, outer diameter, inner diameter, total length, and 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, and uniformity in crimping among the three types of field shapers.

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.

The study is to investigate the electropolishing characteristics of 316L stainless steel in a sulfuric acid-free electrolyte of phosphoric acid and glycerol and to explore the possibility of using this eco-friendly electrolyte instead of the widely used sulfuric acid-based electrolyte. The influences of process parameters on polishing effects and the corrosion resistance of electropolished samples are investigated. The experimental results show that the electropolishing temperature and acid concentration are directly related to the mass transport mechanism in the limiting current plateau region. The grain boundaries of workpiece were electrochemically dissolved faster than the grain themselves at the beginning of the electropolishing process because they are more reactive than grains. Moreover, the conventional sulfuric—phosphoric acid electrolyte was also used to electropolish the 316L stainless steel, and the electropolished surfaces were compared with the sulfuric acid-free electrolyte proposed in this study. When the sulfuric acid-free electrolyte was used to electropolish the 316L stainless steel, the X-ray photoelectron spectroscopy (XPS) analysis shows that atomic Cr/Fe ratio of 316L stainless steel was increased from 0.802 to 1.909 after electropolishing process in the sulfuric acid-free electrolyte of phosphoric acid and glycerol. The corrosion resistance of the electropolished 316L stainless steel is studied using electrochemical analysis, and the results are verified experimentally.

Self-piercing riveting has been widely used in vehicle body manufacturing to join aluminum alloys or aluminum to steel. However, it is difficult to rivet ultrahigh strength steel (UHSS) because of its resistance to piercing of the rivet. In this paper, a thermally assisted self-piercing riveting (TA-SPR) process was proposed to improve riveting of the UHSS, through locally preheating the UHSS sheet using an induction coil prior to the traditional self-piercing riveting (SPR) process. An experimental system consisting of inductive heating apparatus, conventional self-piercing riveting equipment, and coupon transfer mechanism was established and the steps, e.g., preheating, coupons transfer, and riveting, were automatically conducted at preset schedules. Based on experiments with this system, the effects of heating current, heating time, and coil heating distance on riveting of AA6061-T6 and DP980 were examined systematically by metallurgical analyses and mechanical tests. It was found that an appropriate combination of heating current and heating time, e.g., 0.5 s at 600 A, could produce crack-free joints having 77.8% higher undercut and 24% higher lap-shear strength, compared with results obtained using a conventional SPR process.

A great challenge of metal cutting modeling is the ability of the material constitutive model to describe the mechanical behavior of the work material under the deformation conditions that characterizes this process. In particular, metal cutting generates a large range of state of stresses, as well as strains and strain rates higher than those generated by conventional mechanical tests, including the Split-Hopkinson pressure bar tests. A new hybrid analytical–experimental methodology to identify the material constitutive model coefficients is proposed. This methodology is based on an in situ high-resolution imaging and digital image correlation (DIC) technique, coupled with an analytical model of orthogonal cutting. This methodology is particularly suitable for the identification of the constitutive model coefficients at strains and strain rates higher than those found in mechanical tests. Orthogonal cutting tests of nickel aluminum bronze alloy are performed to obtain the strains and strain rates fields in the cutting zone, using DIC technique. Shear forces derived from stress integrations are matched to the measured ones. Then, the constitutive model coefficients can be determined, which is performed by solving a sequential optimization problem. Verifications are made by comparing the strain, strain rate, and temperature fields of cutting zone from experiments against those obtained by finite element simulations using the identified material constitutive model coefficients as input.

In metal cutting processes, the use of cutting fluids shows significant effects on workpiece surface quality by reducing thermomechanical loads on cutting tool and workpiece. Many efforts are made to model these thermomechanical processes, however without considering detailed heat transfer between cutting fluid, tool, and workpiece. To account for heat transfer effects, a coupling approach is developed, which combines computational fluid dynamics (CFD) and finite element method (FEM) chip formation simulation. Prior to the simulation, experimental investigations in orthogonal cutting in dry and wet cutting conditions with two different workpiece materials (AISI 1045 and DA 718) are conducted. To measure the tool temperature in dry as well as in wet cutting conditions, a two color pyrometer is placed inside an electrical discharge machining (EDM) drilled cutting tool hole. Besides tool temperature, the cutting force is recorded during the experiments and later used to calculate heat source terms for the CFD simulation. After the experiments, FEM chip formation simulations are performed and provide the chip forms for the CFD mesh generation. In general, CFD simulation and experiment are in reasonable agreement, as for each workpiece setup the measured temperature data are located between the simulation results from the two different tool geometries. Furthermore, numerical and experimental results both show a decrease of tool temperature in wet cutting conditions, however revealing a more significant cooling effect in a AISI 1045 workpiece setup. The results suggest that the placement of drilling holes has a major influence on the local tool temperature distribution, as the drilling hole equals a thermal resistance and hence leads to elevated temperatures at the tool front.

The objective of this work is to fabricate thermocouples directly on the rake face of a commercially available tungsten carbide cutting insert for accurately measuring the tool–chip interface temperature during metal cutting. The thermocouples are sputtered onto the cutting insert using micromachined stencils, are electrically isolated with layers of Al 2 O 3 , and receive a top coating of AlTiN for durability. The result is a nonsacrificial thermocouple junction that is approximately 1.3 µm below the rake face of the tool and 30 µm from the cutting edge. Experimental and numerical characterization of the temperature measurement accuracy and response time are presented. The instrumented cutting tool can capture the tool–chip interface temperature transients at frequencies of up to 1 MHz, which enables the observation of serrated chip formation and adiabatic shear events. Temperature measurements from oblique machining of 4140 steel are presented and compared with three-dimensional, transient numerical simulations using finite element analysis, where cutting speed and feed are varied. This method of measuring the tool–chip interface temperature shows promise for future research and smart manufacturing applications.

This paper studies how to control boundary slope of optimized parts in density-based topology optimization for additive manufacturing (AM). Boundary slope of a part affects the amount of support structure required during its fabrication by additive processes. Boundary slope also has a direct relation with the resulting surface roughness from the AM processes, which in turn affects the heat transfer efficiency. By constraining the minimal boundary slope, support structures can be eliminated or reduced for AM, and thus, material and postprocessing costs are reduced; by constraining the maximal boundary slope, high-surface roughness can be attained, and thus, the heat transfer efficiency is increased. In this paper, the boundary slope is controlled through a constraint between the density gradient and the given build direction. This allows us to explicitly control the boundary slope through density gradient in the density-based topology optimization approach. We control the boundary slope through two single global constraints. An adaptive scheme is also proposed to select the thresholds of these two boundary slope constraints. Numerical examples of linear elastic problem, heat conduction problem, and thermoelastic problems demonstrate the effectiveness and efficiency of the proposed formulation in controlling boundary slopes for additive manufacturing. Experimental results from metal 3D printed parts confirm that our boundary slope-based formulation is effective for controlling part self-support during printing and for affecting surface roughness of the printed parts.

Additive manufacturing (AM) is a novel fabrication technique capable of producing highly complex parts. Nevertheless, a major challenge is the quality assurance of the AM fabricated parts. While there are several ways of approaching this problem, how to develop informative process signatures to detect part anomalies for quality control is still an open question. The objective of this study is to build a new layer-wise process signature model to characterize the thermal-defect relationship. Based on melt pool images, we propose novel layer-wise key process signatures, which are calculated using multilinear principal component analysis (MPCA) and are directly correlated with the layer-wise quality of the part. The resultant layer-wise quality features can be used to predict the overall defect distribution of a fabricated layer during the build. The proposed model is validated through a case study based on a direct laser deposition experiment, where the layer-wise quality of the part is predicted on the fly. The accuracy of prediction is calculated using three measures (i.e., recall, precision, and F-score), showing reasonable success of the proposed methodology in predicting layer-wise quality. The proposed quality prediction methodology enables online process correction to eliminate anomalies and to ultimately improve the quality of the fabricated parts.

A widespread use of lasers in additive manufacturing is to induce a given temperature and a phase transformation in materials deposited onto a substrate. For a laser to induce a phase transformation in the material, the power intensity must be sufficiently high to induce melting and, in all cases, stay below a vaporization or burn-off temperature of the target material. Oftentimes, there is variability in the laser input to the target zone. For a process designer, a central question is to determine the uncertainty of the resulting target state, i.e., temperature and state (solid or melted), due to uncertainty in the energy (laser) input. This motivates the present work, which integrates relatively fundamental heat transfer models that describe the thermal effects due to (a) laser irradiation, (b) heat conduction into the surface of deposition, (c) infrared radiation outwards into the surroundings, (d) convection due to an exhaust apparatus to control the cooling of the system, and (e) phase transformations, for a dry Nylon 6 powder as a sample material. One key advantage of this framework is that it is amenable to a sensitivity and uncertainty analysis with respect to any of its parameter inputs. Accordingly, uncertainty quantification studies are also undertaken to ascertain the relationship between variation in laser input to variation in the processed material state. Examples will be presented to illustrate the thermal behavior of the numerical model. Due to its simplicity, this framework is designed to be computationally implemented in a straightforward fashion. The model allows for rapid computation and sensitivity analyses, which are provided as numerical examples. Extensions are also given to include mass transport (losses) due to ablation of the target material.

This study investigates the prediction of maraging steel C250 microgrinding forces by incorporating phase transformation effects with the manufacturing process mechanics. The results could consequently increase the accuracy of the prediction and better understand the influence of phase evolution on the materials processing. Based on a detailed analysis of microgrinding mechanics and thermodynamics, an iterative blending scheme integrating phase transformation kinetics and material genome analysis is developed. The physical-based formulation, experimental validation, and computational configuration are presented herein for the microgrinding forces, quantifying phase transformation effects. According to the results, the implementation of the iterative blending scheme can help achieve a higher prediction accuracy of microgrinding forces. Besides, the iterative blending would enable the consideration of the interactive relation between process mechanics and microstructure evolution through materials genome analysis.

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.

In this research, we propose a coupled thermomechanical modeling method for predicting grinding residual stress based on randomly distributed grains. In order to deal with the problem that the nominal grinding force is too small to generate the plastic deformation, we hold the opinion that grinding residual stress is totally derived from three factors: thermal stress, the nominal grinding force (pressure) over the entire grinding zone, and the equivalent plowing force just under the bottom of the abrasive wheel. Finite element model (FEM) simulation of the single-grain grinding (SGG) is conducted to obtain the critical plowing depth and the SGG force at an arbitrary cutting depth. Based on the randomly distributed abrasive grains, the equivalent grinding heat source model, the equivalent SGG plowing force model, and the equivalent nominal pressure model are all established. A 2D coupled thermomechanical model is established to simulate the grinding process for temperature fields and grinding residual stress fields. In addition, verification tests are conducted to validate the model. It turns out that the coupled model can accurately predict the multiphysical fields on both temperature and residual stress. Based on the simulation results of the model, the generation mechanism of grinding residual stress is quantitatively studied. This research provides a promising pathway to residual stress control of grinding.

A new adaptive disturbance feedforward control strategy of the strip thickness in a hot strip rolling mill with online parameter estimation is proposed. The feedforward control strategy makes use of the measured strip temperature and strip entry thickness. To avoid that these disturbances cause a nonuniform strip exit thickness, the Sims’ roll gap model and a linear mill stand deflection model are used to compute control inputs, which compensate for these disturbances. By minimizing the difference between the expected roll force from the model and the measured roll force, uncertain parameters of the model and also errors of the strip tracking are estimated in real time. The estimated parameters are immediately used in the adaptive feedforward controller. Experimental results of the proposed control approach obtained from an industrial hot strip rolling mill show a significant improvement of the strip thickness accuracy compared to the existing standard controllers. The proposed adaptive feedforward control strategy is now in permanent operation at the considered rolling mill.

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.

The white layer formed in machining has significant impacts on the friction property, fatigue resistance, and service life of products. This paper presents an analytical model for white layer prediction in orthogonal cutting based on phase transformation mechanism. The effects of stress, elastic, and plastic strain on phase transformation temperature are taken into consideration. A function related to cutting temperature and phase transformation temperature is defined to determine the white layer thickness. The theoretical model is validated by machining AerMet100 steel under different cutting conditions. Optical microscope and X-ray diffraction (XRD) are employed to analyze the microstructures of the white layer. A phase transformation is detected in the white layer region, and the predicted white layer thicknesses are in good agreement with the measured values. In addition, the plastic strain is found to be the major factor that causes a reduction in phase transformation temperature. This work can be further applied to optimize cutting conditions to improve machined surface integrity.

The quantification of the heat flow distribution in the metal cutting process depending on the cut material and the process parameters is a research area with a long history. However, a quantification of the heat flow distribution between chip, tool, and workpiece is still a not fully solved problem and remains a necessary input value for the further modeling of temperature fields and subsequent tool wear and thermal induced surface alterations, which may impair the workpiece functionality. Thus, the following publication shows the results of orthogonal cutting in order to investigate the heat flow distribution between the chip and workpiece. Therefore, the heat partitions in the cutting process were calculated by a thermodynamic methodology. This methodology considers the temperature rise in the workpiece and the chip, measured by thermography and pyrometry, as the effect of the cutting work dissipated into sensible heat. Four metals, Inconel 718, AISI 1045, Ti6Al4V, and AlMgSi0.5, were cut at varying undeformed chip thicknesses and cutting velocities. By formulating a dimensionless number for the cutting process, the Péclet number, the thermal diffusivity was included as an evaluation criterion of heat partitioning between the chip and workpiece across material properties and process settings. In this way, the validity of the Péclet number as an evaluation criterion for heat partitions in cutting and as a valuable heuristic for process design was confirmed. Another goal was to extend the state of the art approach of empirical process analysis by orthogonal cuts with regard to specific cutting forces into the thermal domain in order to provide the basis for further temperature modeling in cutting processes. The usage of the empirical data basis was finally demonstrated for the analytical modeling of temperature fields in the workpiece during milling. Therefore, the specific heat inputs into the workpiece measured in the orthogonal cuts were transferred to the milling process kinematics in order to model the heat flow into the workpiece during milling. This heat flow was used as input for an existing analytical model in order to predict stationary temperature fields in the milling process for the two-dimensional case.

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.

The morphology of microchannels machined by multiple ultrafast laser pulses with 500 fs and 8 ps durations on fused silica plate is predicted by a two-step model with experimental validation in present work. A spike structure at crater boundary with different scales in 500 fs and 8 ps pulse ablation is found in the numerical investigation, which could be attributed to diffraction and attenuation of light intensity in both cases. To analyze the evolution of crater morphology and damaged area with an increasing number of pulses, the distribution of light intensity, lattice temperature, and self-trapped excitons density during certain pulses are studied. The results showed that 500 fs pulses lead to smoother crater boundary, smaller heat affected zone, and larger electrical damage area with respect to 8 ps pulses.

Prediction of residual stresses induced by any additive layer manufacturing process greatly helps in preventing thermal cracking and distortion formed in the substrate and deposition material. This paper presents the development of a model for the prediction of residual stresses using three-dimensional finite element simulation (3D-FES) and their experimental validation in a single-track and double-track deposition of Ti-6Al-4V powder on AISI 4130 substrate by the microplasma transferred arc (µ-PTA) powder deposition process. It involved 3D-FES of the temperature distribution and thermal cycles that were validated experimentally using three K-type thermocouples mounted along the deposition direction. Temperature distribution, thermal cycles, and residual stresses are predicted in terms of the µ-PTA process parameters and temperature-dependent properties of substrate and deposition materials. Influence of a number of deposition tracks on the residual stresses is also studied. Results reveal that (i) tensile residual stress is higher at the bonding between the deposition and substrate and attains a minimum value at the midpoint of a deposition track; (ii) maximum tensile residual stress occurs in the substrate material at its interface with deposition track. This primarily causes distortion and thermal cracks; (iii) maximum compressive residual stress occurs approximately at mid-height of the substrate material; and (iv) deposition of a subsequent track relieves tensile residual stress induced by the previously deposited track.