Geometrical variation is one of the sources of quality issues in a product. Spot welding is an operation that impacts the final geometrical variation of a sheet metal assembly considerably. Evaluating the outcome of the assembly, considering the existing geometrical variation between the components, can be achieved using the method of influence coefficients (MICs), based on the finite element method (FEM). The sequence with which the spot welding operation is performed influences the final geometrical deformations of the assembly. Finding the optimal sequence that results in the minimum geometrical deformation is a combinatorial problem that is experimentally and computationally expensive. Traditionally, spot welding sequence optimization strategies have been to simulate the geometrical variation of the spot-welded assembly after the assembly has been positioned in an inspection fixture. In this approach, the calculation of deformation after springback is one of the most time-consuming steps. In this paper, a method is proposed where the springback calculation in the inspection fixture is bypassed during the sequence evaluation. The results show a significant correlation between the proposed method of weld relative displacements evaluation in the assembly fixture and the assembly deformation in the inspection fixture. Evaluating the relative weld displacement makes each assembly simulation less time-consuming, and thereby, sequence optimization time can be reduced by up to 30%, compared to the traditional approach.

Deformation machining (DM) is a hybrid process which combines two emerging manufacturing processes, machining of thin structures and single-point incremental forming (SPIF). This hybrid process enables the creation of structures that have geometries that would be difficult or impossible to create using any either process alone. A comprehensive study of DM bending mode components has been carried out in this paper by studying their dimensional repeatability and fatigue life and comparing these with similar components fabricated with sheet metal. Experimental studies have been performed for part features created by the DM “bending mode” process, in which a thin vertical wall is machined on the part, and then incrementally bent with a single-point forming tool. The dimensional repeatability of DM components is compared with sheet metal components made by single-point incremental forming and conventional bending in a press brake [Agrawal et al., 2010, “Comparison of Dimensional Repeatability of Deformation Machined Components With Sheet Metal Components,” North American Manufacturing Research Conference, NAMRC 38, Transactions of NAMRI/SME, Vol. 38, pp. 571–576]. The results of this study indicate that the DM process is not capable of holding tolerances as tight as a standard milling process. This may be due to local variations in material properties that influence the yield strength and resulting springback. However, thin components created by DM are more repeatable than similar components created from sheet metal using SPIF, but less repeatable than components created by conventional bending of sheet metal. The second objective of the present work is to investigate whether components fabricated using the DM process can be considered for fatigue critical applications [Megahed et al., 1996, “Low-Cycle Fatigue in Rotating Cantilever Under Bending I: Theoretical Analysis,” Int. J. Fatigue, 18(6), pp. 401–412; Khalid et al., 2007, “Bending Fatigue Behavior of Hybrid Aluminum/Composite Drive Shafts,” Mater. Des., 28, pp. 329–334]. Studies were performed to experimentally compare the fatigue life of components fabricated by DM process with sheet metal components made by single-point incremental forming and conventional bending. Results of the study indicate that sheet metal SPIF components under the present loading conditions have significantly longer fatigue life of approximately 3900–5500 cycles, compared to DM and sheet metal conventionally bent components with approximately equal fatigue life of 2200–3900 cycles.

Single point incremental forming (SPIF) is plagued by an unavoidable and unintended bending in the region of the sheet between the current tool position and the fixture. The effect is a deformation of the region of the sheet in between the formed area and the fixture as well as deformation of the already formed portion of the wall, leading to significant geometric inaccuracy in SPIF. Double sided incremental forming (DSIF) uses two tools, one on each side of the sheet to form the sheet into the desired shape. This work explores the capabilities of DSIF in terms of improving the geometric accuracy as compared to SPIF by using a novel toolpath strategy in which the sheet is locally squeezed between the two tools. Experiments and simulations are performed to show that this strategy can improve the geometric accuracy of the component significantly by causing the deformation to be stabilized into a local region around the contact point of the forming tool. At the same time an examination of the forming forces indicates that after a certain amount of deformation by using this strategy a loss of contact occurs between the bottom tool and the sheet. The effects of this loss of contact of the bottom tool on the geometric accuracy and potential strategies, in order to avoid this loss of contact, are also discussed.

Surface textures have various applications, such as friction/wear reduction and light absorbing enhancement. Deformation-based surface texturing has the potential of economically creating micro-scale surface textures over a large surface area. A novel desktop surface texturing system is proposed for efficiently and economically fabricating microchannels on the surface of thin sheet material for microfluid and friction/wear reduction applications. Both the experimental and numerical studies were employed to analyze the problems of the flatness of the textured sheet, the uniform of the channel depth and pile-ups built up during the surface texturing process. The results demonstrated a clear relationship between relative velocity of the upper and lower rolls and the flatness of the textured sheet and the final profile of the microchannels.

For deep cylindrical cups with a large height-diameter ratio, it is difficult to be hydroformed in one stroke. Reverse deep drawing is necessary after deep drawing. Deformation optimization was performed to achieve a large drawing ratio and uniform thickness. An inconel718 superalloy deep cup was investigated numerically and experimentally. For a larger total drawing ratio 3.1, different deformations were analyzed for hydromechanical deep drawing and reverse hydromechanical deep drawing under the condition of different loading paths. Effects of deformations were discussed on the thickness. Typical defects were analyzed for different deformation. Optimal deformation was determined for hydromechanical deep drawing and reverse hydromechanical deep drawing. The results show that a superalloy cup with a total drawing ratio 3.1 could be successfully hydroformed, and the minimum thickness is 0.65 mm.

The effects of different prestrain levels, paths, and subsequent annealing on the postannealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were prestrained in uniaxial, plane strain, and equibiaxial tension to several equivalent strain levels, annealed at 350 °C for short (10 s) and long (20 min) durations and then tested for postannealing mechanical properties, including tensile properties, anisotropy, and forming limits. The tensile properties, R-values at 0, 45, and 90 deg relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies on prestrain and annealing history. The importance of the process variables and their effects were identified via designed experiments and analysis of variance. Three-dimensional digital image correlation, which captured the onset of local necking, was employed in the FLD development. Texture in the as-received and deformed sheets was investigated with electron backscatter diffraction and provided a means for linking prestrain and static recovery or recrystallization with microstructure. This guided the understanding of the mechanical property changes observed after preforming and annealing. Ultimately, the expanded forming limit curve demonstrated the advantage of annealing in extending the formability of strained AA5182-O.

The combination of thin metal cases or tubes with a filling made of metal foams is interesting and promising for many applications in mechanical engineering. Components made of an outer hollow thin compact metal structure and a cellular lightweight core are especially suited to energy absorption applications. In order to allow for an efficient product/process design with a concurrent engineering approach, reliable and computationally affordable finite element method (FEM) calculations are required by both product and process engineers. The structural performance of these complex composite parts must be numerically predicted, in order to find the optimal combination of outer structure and metal foam properties. While FEM simulation at large deformations of bending, crushing, etc. of thin sheets and tubes is state of the art, the accurate FEM simulation of the mechanical behavior of metal foams cannot be considered fully established. In this paper the three most common methods for FEM simulation of metal foam materials are discussed: (a) homogenization approach, (b) realistic reconstruction of tomographic data, and (c) repetition of standard unit cells. A new effective approach is proposed, suited for simulation of composite, metal foam filled, structures of realistic dimensions. The approach is based on meshing the metal foam by replicating a unit cell made of 32 triangular shell elements, and then by randomizing the nodal position in order to emulate the intrinsic homogeneity of foam morphology. The method is validated by means of different experimental tests. The results show that the proposed method correctly predicts the behavior of foam structures in axial compression. The method slightly overestimated the actual load registered in three point bending tests. Several improvements are described and discussed in the paper, such as randomization of nodal positions of the mesh, in order to reduce the overestimation of forces. An FEM approach for the simulation of large deformations of metal foam filled metal structure (e.g., tubes) suited for the design of realistic large dimensions structural components has been presented. The proposed method shows some innovative features with respect to the available scientific literature, such as a configuration based on octahedral unit cells with low number of triangular shell elements. Randomization of nodal positions of each unit cell has been implemented as a method for better representing the intrinsic variability of metal foams and for reducing the stiffness of the simulated structure.

Material behavior of AA5754 was investigated under different forming process conditions, including two loading conditions (uniaxial tensile and biaxial bulge), several strain rates (constant strain rates at 0.0013 and 0.013/s, and variable strain rate profiles: increasing and decreasing profiles), and several temperature levels (ambient up to 260 °C). Additional warm hydroforming experiments were conducted using a closed-die set up to understand the forming limits of AA5754. The results from tensile and hydraulic bulge tests as well as closed-die hydroforming experiments suggested that, in general, formability of AA5754 can be significantly improved with slow forming rates (<0.02/s), high forming temperature (>200 °C), and biaxial loading (hydroforming) that can delay strain localization (necking). However, the effect of forming rate did not reveal any significant gain in formability for temperatures below 200 °C. The effect of variable strain rate control was found to be significant only at elevated temperatures (>200 °C), where increasing strain rate resulted in lower formability and decreasing strain rate improved the maximum attainable dome height at temperatures above 200 °C. Finally, the material flow curves obtained from the tensile and bulge tests were shown to provide reasonably accurate predictions for cavity filling ratios (∼ 3–15% error) in finite element analyses.

To explore the effects of cutting speed, feed rate and rake angle on chip morphology transition, a thermomechanical coupled orthogonal (2-D) finite element (FE) model is developed, and to determine the effects of tool nose radius and lead angle on hard turning process, an oblique (3-D) FE model is further proposed. Three one-factor simulations are conducted to determine the evolution of chip morphology with feed rate, rake angle, and cutting speed, respectively. The chip morphology evolution from continuous to saw-tooth chip is described by means of the variations of chip dimensional values, saw-tooth chip segmental degree and frequency. The results suggest that chip morphology transits from continuous to saw-tooth chip with increasing feed rate and cutting speed, and changing a tool’s positive rake angle to negative rake angle. There exists a critical cutting speed at which the chip morphology transfers from continuous to saw-tooth chip. The saw-tooth chip segmental frequency decreases as the feed rate and the tool negative rake angle value increases; however, it increases almost linearly with the cutting speed. The larger negative rake angle, the larger feed rate and higher cutting speed dominate saw-tooth chip morphology while positive rake angle, small feed rate and low cutting speed combine to determine continuous chip morphology. The 3-D FE model considers tool nose radii of 0.4 mm and 0.8 mm, respectively, with tool lead angels of 0 deg and 7 deg. The model successfully simulates 3-D saw-tooth chip morphology generated by periodic adiabatic shear and demonstrates the continuous and saw-tooth chip morphology, chip characteristic line and the material flow direction between chip-tool interfaces. The predicted chip morphology, cutting temperature, plastic strain distribution, and cutting forces agree well with the experimental data. The oblique cutting process simulation reveals that a bigger lead angle results in a severer chip deformation, the maximum temperature on the chip-tool interface reaches 1289 deg, close to the measured average temperature of 1100 deg; the predicted average tangential force is 150N, with 7% difference from the experimental data. When the cutting tool nose radius increases to 0.8 mm, the chip’s temperature and strain becomes relatively higher, and average tangential force increases 10N. This paper also discusses reasons for discrepancies between the experimental measured cutting force and that predicted by finite element simulation.

In this paper, plane strain extrusion through arbitrarily curved dies is investigated analytically, numerically, and experimentally. Two kinematically admissible velocity fields based on assuming proportional angles, angular velocity field, and proportional distances from the midline in the deformation zone, sine velocity field, are developed for use in upper bound models. The relative average extrusion pressures for the two velocity fields are compared to each other and also with the velocity field of a reference for extrusion through a curved die. The results demonstrate that the angular velocity field is the best. Then, by using the developed analytical model, optimum die lengths which minimize the extrusion loads are determined for a streamlined die and also for a wedge shaped die. The corresponding results for those two die shapes are also determined by using the finite element code and by doing some experiments and are compared with upper bound results. These comparisons show a good agreement.

This paper documents a recent R&D effort conducted by the Air Force Research Laboratory, Space Vehicles Directorate, to assess the feasibility of fabricating large composite launch vehicle fairings without the use of autoclaves. Two composite manufacturing approaches were demonstrated: vacuum-bag compaction with oven cure and vacuum assisted resin transfer molding with oven cure. For this project, a 2.8-m diameter fairing was developed for the Minotaur IV launch system. The prototype fairing was instrumented and tested up to qualification test loads. No damage or permanent deformations were observed. Measured strain and displacement data were compared to model predictions; trends and amplitudes were generally in agreement.

The high strength-to-weight ratio of magnesium alloys makes them attractive for automotive applications. These materials have been used for the engine cradle, seat frame, and shock tower applications to reduce vehicle weight. Despite these advantages, there are limiting factors to the application of magnesium alloys. One of these factors is the joining of magnesium alloys. Although there are various joining processes available, self-piercing riveting (SPR) is particularly promising. It provides not only the speed but also the necessary structural strength. However, because of the large amount of deformation associated with the process and the limited formability of magnesium at room temperature, SPR often results in part cracking of the riveted magnesium alloys, which reduces the part quality. In this study, a method of preheating the magnesium alloy before riveting was adopted to improve the joint quality. The fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Zener–Hollomon parameter was employed. Experiments were conducted to validate the proposed preheat temperature. Magnesium alloy AZ31 with a thickness of 2 mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections, and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180–200°C largely eliminated the discrepancies in SPR 2 mm thick magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200°C. The strength increase is attributed to the reduction in joint discrepancies and an increase in mechanical interlock between the rivet and work pieces. The current findings on the development of a method can be used to determine the preheat temperature for self-piercing riveting of magnesium castings.

In a free state, flexible parts may have different shapes compared to their computer-aided design (CAD) model. Such parts may likewise undergo large deformations depending on their space orientation. These conditions severely restrict the feasibility of inspecting flexible parts without restricting the deformations of the part and therefore require dedicated and expensive tools such as a conformation jig or a fixture to maintain the integrity of the part. To address these challenges, this paper proposes a new inspection method, the iterative displacement inspection (IDI) algorithm, that evaluates profile variations without the need for specialized fixtures. This study examines 32 models of simulated manufactured parts to show that the IDI algorithm can iteratively deform the meshed CAD model until it resembles the scanned manufactured part, which enables their comparison. The method deforms the mesh in such a manner so as to ensure its smoothness. This way, neither surface defects nor the measurement noise of the scanned parts are concealed during the matching process. As a result, the case studies illustrate that the method’s error essentially only represents the scanned part’s measurement noise. The inspection results, therefore, solely reflect the effect of variations from the manufacturing process itself and not the deformation of the part.

A die face morphing concept was recently introduced for quick die design for evolutionary products from their prior generations. Based on this concept, this paper proposes a strain increment method for early formability assessment by predicting strain distribution directly from the part-to-part mapping process. This method consists of mapping the finite element mesh to the part geometry, solving a part-to-part mapping function with smoothness and strain gradient penalties, and extracting strain increment from geometric morphing. It is shown, through a case study, that the strain field estimated by the proposed strain increment method compares well with that from the direct finite element analysis. Since this method does not require the knowledge on new die surface, such formability assessment can serve as a tool for early manufacturing feasibility analysis on the new part design.

The microscale laser dynamic forming (LDF) process is a high strain rate microfabrication technique, which uses a pulse laser to generate high pressure by vaporizing and ionizing an ablative coating, and thus produces complex 3D microstructures in thin foils. One of the most important features of this technique is ultrahigh strain rate (typically 10 6 – 7 s − 1 ), which is theoretically favorable for increasing formability. However, due to the lack of measurement techniques in microscale and submicroscale, the formability of workpieces in LDF is hardly studied. In this article, experiments were carried out on aluminum foils to study the forming limits and fracture of thin films in LDF. The deformation depth was measured by an optical profilometer and the formed feature was observed using a focused ion beam and a scanning electron microscope. Meanwhile, a finite element model based on a modified Johnson–Cook constitutive model and a Johnson–Cook failure model was developed to simulate the mechanical and fracture behaviors of materials in LDF. Experimental results were used to verify the model. The verified model was used to predict the forming limit diagram of aluminum foil in LDF. The forming limit diagrams show a significant increase in formability compared with other metal forming processes.

In the traditional metal forming product development paradigm, product design is generally based on heuristic know-how and experience, which are basically acquired through many years of practice. This kind of product design paradigm is of more trial-and-error than in-depth scientific calculation and analysis. Product defect prediction and quality assurance is, thus, a nontrivial issue in this product development paradigm. With the aid of finite element (FE) simulation, deformation-related defects can be predicted and analyzed. In this paper, flow-induced folding defect in forging of axially symmetrical flanged components is systematically investigated. A FE model to study the root-cause of the defect based on the material flow behavior is developed and a defect formation mechanism is revealed. The variation of material flow behavior with the changes of part geometry parameters is investigated extensively. Based on the simulation results, the parameter variation characteristics and the sensitivity of each parameter to folding defect avoidance are identified. Using industrial components as case studies, the efficiency of the proposed defect avoidance approach is verified. The approach is further proven to be able to provide practical guidelines for the design of defect-free axially symmetrical flanged components.

Alternative manufacturing processes such as hot working and electrical-assisted forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable effects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes, and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore, the dislocation density, related in part by the grain size, appears to be a factor in the EAF process.

In order to study the deformation mechanisms during ultrahigh strain rate deformation of face centered cubic metals, laser shock peening of a 304L stainless steel is systematically investigated. Two deformation modes—microtwins and microbands—and their interrelationship during high strain rate deformation are discussed in detail. Transmission electron microscopy and selected area electron diffraction are employed to study the deformation modes. It is found that twinning takes place even when the shock pressure is much less than the critical twinning stress in stainless steels. Theoretical critical twinning stress is not the only criteria to decide the deformation modes of twinning or slip. The formation of twinning and slip can be affected by the factors such as loading profile, loading stress/strain rate, stacking fault energy, grain sizes, and cell substructures. Factors that influence twin-slip transition in shock loading are discussed. The formation of dislocation structure is compared with those predicted using 3D dislocation dynamic simulation.

Microscale laser dynamic forming ( μ LDF ) is a novel microfabrication technique to introduce complex 3D profiles in thin films. This process utilizes pulse laser to generate plasma to induce shockwave pressure into the thin film, which is placed above a microsized mold. The strain rate in μ LDF reaches 10 6 – 10 7 S − 1 . Under these ultrahigh strain rates in microscale, deformation behaviors of materials are very complicated and almost impossible to be measured in situ experimentally. In this paper, a finite element method model is built to simulate the μ LDF process. An improved Johnson–Cook model was used to calculate the flow stress, and the Johnson–Cook failure criterion was employed to simulate failure during μ LDF . The simulation results are validated by experiments, in which the deformation of Cu thin foils after μ LDF experiments are characterized by scanning electron microscopy and compared with simulation results. With the verified model, the ultrafast μ LDF process is generally discussed first. A series of numerical simulations are conducted to investigate the effects of critical parameters on deformation behaviors. These critical parameters include the ratio of the fillet radius to film thickness, the aspect ratio of mold, as well as laser intensities. The relationship of laser pulse energy and the deformation depth is also verified by a series of μ LDF experiments.

Recent research studying the deformation of various metals in compression, while running an electric current through the material, has been quite promising. A problem occurs when trying to identify the specific mechanisms that cause the changes in the mechanical properties, however, since the flow of electricity produces resistive heating, which also affects the mechanical properties of metals. However, previous research has proven that not all of the effects on the properties can be explained through resistive heating, implying that the electron flow through the metal also causes changes to the mechanical properties. Therefore, this work develops a model capable of differentiating between the effects of resistive heating and the effects of the electron flow when deforming 6061-T6511 aluminum in compression. To accomplish this, a detailed finite element simulation has been developed using ANSYS ® with two models in symbiosis. The first model predicts the temperature of the specimen and compression fixtures due to the applied electrical current. The resulting thermal data are then input into a deformation model to observe how the temperature change affects the deformation characteristics of the material. From this model, temperature profiles for the specimen are developed along with true stress versus strain plots. These theoretical data are then compared with experimentally determined data collected for 6061-T6511 aluminum in compression. By knowing the exact effects of resistive heating, as obtained through the finite element analysis (FEA) model, the effects of the electron flow are isolated by subtracting out the effects of resistive heating from the data obtained experimentally. Future work will use these results to develop a new material behavior model that will incorporate both the resistive and flow effects from the electricity.