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The direct application of an electric current to a metallic workpiece during a manufacturing process, more commonly known as electrically-assisted manufacturing (EAM), produces many beneficial effects. During forming, significant flow stress reductions can be achieved. While there is much literature characterizing the effects of an electric current on the mechanical properties of materials during deformation, few feasible control systems for use in industrial processing have been developed. One such method is developed and tested herein using tensile testing in which electric current is triggered once a user-defined stress level is reached. The current then remains on until the stress reaches a desired minimum level. This cycle repeats until fracture occurs. The influence of several process parameters is discussed and an empirical formulation for determining the pulse frequency and the required energy per pulse is developed. This control method was found to be successful for forming metals while not exceeding a desired stress level. Furthermore, its application towards industrial use is also discussed.

Multimaterial joining has become necessary to continue to reduce vehicle mass in order to further improve fuel economy. Novel processes continue to be developed which are capable of joining various materials. Friction element welding (FEW) is one such process used to join aluminum and steel sheets. This process is well known for its rapid process times, typically less than two seconds, and its extraordinary robustness. FEW is also capable of joining aluminum sheets to the strongest steels used in automotive bodies. A derivative of the FEW process was explored, termed friction element riveting (FER). This process is used to perform aluminum to aluminum joining and shares many of the same benefits as FEW. For example, there remains no need for pre-hole drilling, a distinct advantage of the FEW process. Several strength metrics and the influence of process parameters are defined herein. It was determined that FER is a viable process for use in industrial applications. Through parameter optimization of the welding step, the joint resulted in a cross tension strength and transverse shear strength of 7.37±0.31 kN and 21.4±1.21 kN, respectively, which makes it a competitive technology for similar joining methods.

Multimaterial use in automotive body structures has become essential for continuing vehicle mass reduction. This has created challenges in joining of these materials. Friction element welding (FEW) is a joining process capable of joining aluminum to high strength steels. In this process, the element is driven through the aluminum sheet and friction welded to the steel, securing the aluminum under the head of the fastener. The flow of aluminum during the FEW process is a critical parameter. Poor aluminum flow conditions can result in the protrusions of aluminum chips from the underhead of the fastener. These chips can accelerate corrosion and generate contamination. The flow of aluminum material was observed experimentally and modeled in order to better understand the FEW process and guide parameter selection. Two aluminum alloys, 6061 and 7075, were selected for this study due to their differences in ductility and strength and for their widespread use in the automotive industry. Various experimental methods were explored for revealing the flow of aluminum during processing and validating simulations. The results of this testing reveal that there is minimal radial and vertical mixing within the aluminum substrate. It was also found that the 6061 material exhibits much greater upwards flow of aluminum, while the 7075 alloy experiences more outward flow.

The electroplastic effect (EPE) encompasses the known reduction in flow stress and increase in ductility in a metal resulting from the application of an electric current concurrently with deformation, a phenomenon which cannot be accounted due solely to resistive heating. While several theories have been postulated, the mechanism responsible for the electroplastic effect is still in debate after nearly 60 years of scientific research. A significant amount of research has been conducted on the anomalous effects observed when performing research on the EPE. Particular behaviors which remain elusive are the transient effect of electric current application and the difference between constant and pulsed current applications. Throughout literature, the type of power supply used in electric current application appears to be ignorantly selected and output signals improperly or incompletely documented. It was found herein that the type of power supply used in electrically assisted tensile testing can have a significant effect on the resulting transient mechanical behavior for pulsed current testing within the parameters explored in this research.

Increasing the productivity and efficiency of milling practices is of high importance with the rapidly changing global economy. To this end researchers have turned to alternative milling toolpaths, such as trochoidal milling, which has been shown to increase tool life with a corresponding reduction in machining time for some applications. To better understand the trochoidal milling process and optimize it for manufacturing scenarios, the modeling of cutting forces must be investigated; semi-mechanistic methods are the focus of this work. The basis for this type of force modeling lies in uncut chip thickness modeling combined with cutting force coefficients and edge force coefficients. With a novel uncut chip thickness model proposed by the authors in a previous work, this investigation looks to understand the dependence of the model coefficients as they relate to trochoidal path parameters along with machining outputs such as maximum cutting force and tool wear. Furthermore, the machining parameters are investigated as to how they relate to the improvement of tool life and cutting force utilizing the Taguchi method, where optimal parameters are found for minimum tool wear and cutting forces. The effects of the trochoidal path on the subsurface of the machined samples as they relate to the machining affected zone, are also investigated in both the radial and axial directions. It is found that tool wear increases the depth of the machining affected zone as does increasing chip thickness.

Electrically assisted manufacturing is the direct application of an electric current or field to a workpiece during a manufacturing operation. In addition to resistive heating, various anomalous effects have been observed experimentally. Since its conception in the 1950s, scientists continue to debate the existence of these so called electroplastic effects (EPEs) due to conflicted results shown throughout literature. A popular theory of electroplasticity is the electron wind, which postulates that there is a transfer of momentum between electrons and dislocations, which assists their motion during deformation. Though refuted both mathematically and experimentally in other types of tests, the electron wind theory, and therefore the existence of electroplasticity, is interestingly supported by the existence of polarity effects in wire drawing. A detailed review of the literature that has shown polarity effects in wire drawing is conducted. While the authors of these publications failed to fully disclose all test parameters, requiring several assumptions to be made, it appears that no mathematical/logical trends could be established. It is hypothesized herein that the velocity of the wire in a wire drawing application can influence the drift velocity of electrons, thereby increasing or decreasing current flow explicitly through the moving section of the wire. In order to test this hypothesis, a fixture was constructed which is capable of passing a current through a moving wire at common wire drawing speeds. Modern sensing equipment was used to measure various electrical parameters during testing. The wire speed effect hypothesis was refuted by experimental testing. While the results of experimental testing thus far indicate the existence of electroplasticity, further testing that includes drawing and force measurements must be conducted in order to fully conclude its existence in the wire drawing application.

Increasing awareness of global warming and strict government regulations have required the automotive industry to pursue lightweighting as an avenue towards increased vehicle efficiency. Lightweight designs typically rely heavily on multi-material use, which enables selective strengthening of critical areas without additional, unnecessary mass. Joining these materials during manufacturing has proven to be a challenging endeavor. Friction element welding (FEW) is one process that is capable of joining aluminum to steel. This two-sided joining technique utilizes a fastener to secure the aluminum sheet by creating a friction weld with the steel sheet. While this process is extremely robust for most materials, the FEW process can result in the extrusion of material from underneath the head of the fastener, termed chipping, which leads to corrosion and aesthetic issues. This behavior is typically seen in high strength aluminum alloys, such as 7075. A solution to chipping is implemented herein, which utilizes a modified downholder to conductively heat the aluminum sheet prior to the FEW process. This heating method was explored experimentally and through various numerical analyses. This method was found to be a viable option for relieving chipping. While the process time was only increased by a maximum of 2.5 seconds, faster, more localized heating should be targeted for future work.

The use of multiple material in the structural components of a vehicle allows for significant weight reduction. Friction element welding (FEW) is a novel method that allows the joining of two or more dissimilar material sheets. A limitation of this process is the chip formation in high strength aluminum alloys, which is observed as the protrusion of thin aluminum segments from under the head of the fastener. Chipping can degrade the joint’s strength over time due to accelerated crevice corrosion. A novel method is proposed to eliminate chip formation using thermal assistance. A grading scheme is developed to quantify the severity of chip formation. The effect of thermal assistance on chipping is analyzed. An investigation is also carried out to validate that the thermal assistance does not negatively affect the process time, energy, and joint strength. Thermal assistance is proposed to be a novel method of overcoming this limitation to allow more widespread use of the FEW process for higher-strength aluminum alloys. Future work will include the development of feasible, rapid methods of heating and measurement of energy utilization for implementation in the industrial environment.

Electrically-assisted manufacturing refers to the direct application of electrical current to a workpiece during a manufacturing process. This assistance results in several benefits such as flow stress reduction, increased elongation, reduced springback, increased diffusion, and increased precipitation control. These effects are also associated with traditional thermal assistance. However, for over half a decade it has been argued whether or not these observed effects are due to electroplasticity, a term which describes effects that cannot be fully explained through resistive heating. Several theories have been proposed as to the mechanism responsible for these purported athermal effects. Conflicting results within literature have enabled this debate over electroplasticity since its discovery in the mid 20th century. While the effects of electrically-assisted manufacturing are clearly characterized throughout literature, there is a lack of research related to control systems which may be used to take advantage of its effects. Typically, control systems are developed using an empirical approach, requiring extensive testing in order to fully characterize the stress-strain behavior at all conditions. Additionally, current research has primarily focused on reducing flow stresses during electrically-assisted processes without regard for the strength of the material subsequent to forming. Therefore, there is a strong need for a control system which can quickly be deployed for new materials and does not significantly reduce the subsequent strength of the material. Herein, a novel control approach is developed in which electrical pulses are triggered by a predetermined stress level. This stress value would be set according to the manufacturer’s stamping die strength. Once the material reaches this stress value, current is deployed until a minimum stress level is reached. At that point, the electricity is turned off and the material allowed to cool; at that stage the stress begins to elevate and the cycle continues. This approach does not require extensive pre-testing and is robust to a range of strain rate. This type of implementation can also be adapted to different levels of capability. For example, since the current is controlled by force and not by time, a low-current power supply will stay on for each pulse longer than a power supply with higher capabilities; however, each will achieve a similar effect. This study investigates the effect of several different minimum stress levels and strain rates. The strain rates chosen are relatively similar to common stamping process. This system was experimentally tested using 1018 CR steel. This control approach was found to be a successful method of maintaining a desired stress level.

Single point incremental forming (SPIF) is a dieless forming process which uses local deformations to form complex geometries. This is achieved through the use of a typically hemispherical tipped forming tool. Several variations of SPIF have been developed to improve the performance of this process. This includes the use of a partial die which is placed on the back-side of the material. The forming tool is then able to press the material into this partial die. Another method is to utilize a clamping fixture with a periphery that closely matches that of the desired geometry. While both of these methods improve the performance of SPIF, they also require dedicated fixturing. While these modifications still present an advantage over traditional stamping, it is desirable to avoid the use of any geometry-specific equipment. Springback is a significant issue when performing traditional SPIF. Springback can occur in two different ways: local and global. Local springback results from the elastic deformations created outside the region located directly beneath the forming tool. This causes poor accuracy as a result. Compensation methods have been developed to overcome this type of springback but are faced with certain limitations. Global springback refers to the springback experienced once the material is removed from its clamping fixture. This springback is a result of all residual stresses produced during forming. This springback is much more difficult to reduce and often requires annealing the workpiece subsequent to forming. A toolpath approach is explored herein as a method to reduce springback without the use of geometry-specific equipment. The toolpath developed begins at the edge of the clamping fixture, regardless of the geometry shape, and forms the flashing material prior to the desired geometry. By starting the toolpath along the edge of the fixture, elastic deformations are minimized. Additionally, the work hardening produced during this forming acts as a stiffener for the desired geometry, which behaves as a frame which matches the periphery of the desired geometry. This method was experimentally tested for its accuracy improvements when forming a truncated pyramid from 5052 aluminum. The angle of this stiffener, the step size of the stiffener, and the size of the desired geometry were varied. The fixture dimensions were held constant. This method was found to reduce the overall springback of the part and increase the accuracy of the resulting geometry. Furthermore, it was found that a large step size can be used to form the stiffener section of the part. By using a large step size, the time it takes to form this sacrificial region is minimized.

Wire connection sub-assemblies in automobiles can cause installers to awkwardly position themselves to complete the connection during the manufacturing of the vehicle. This decreases the likelihood of a successful connection which in turn causes malfunction in the vehicle after the vehicle has left the plant. A potential solution to this problem is a wearable device that detects the amount of force being used while connecting wire sub-assemblies. Our approach to this wearable device is a hand glove that can detect the amount of normal and shear force applied to the hand when a load is applied. The challenge with this is differentiating between shear and normal forces. In this paper we aim to tackle this challenge by exploring capacitance and resistive approaches to measuring forces using flexible materials and parallel plate capacitors as well as contact resistive approaches. The flexible material will favor deformation in a specific direction which will allow us to differentiate between when a shear load has been applied, and when a normal load has been applied. Using this flexible sensor will allow us to characterize the amount of normal and shear loading required for a successful connection and improve the rate at which successful connections are made.

Productivity and profitability in machining operations are known to be affected by three different interconnected aspects: state of health of the tool, state of health of the workpiece, and state of health of the machine. The interconnection of these factors is vital since there is high dependence between them. Due to the high strength, material strengthening mechanisms under loading, and low thermal conductivity of nickel-based alloys, cutting tool health has significant influence on the quality of the machined part. The objective of this work is to study the underlying effects of tool flank wear on surface integrity metrics of Inconel 718 (IN718) nickel-based alloys in a turning operation. Three parameters are taken together to represent the workpiece state of health: surface roughness, dimensional integrity and residual stress; and the tool wear effect on each is investigated. It is shown that unlike the common belief of the detrimental effects of wear on surface roughness, tool flank wear does not necessarily have a significant effect on the roughness profile evolution of the workpiece. To study the effect of wear on dimensional integrity, the geometrical relationship of the tool-tip and flank wear width is derived, and the estimated results of tool wear from the previous work of the authors in the use of a probabilistic Extended Kalman Filter are utilized for classification of dimensional deviation. The results are also compared with naive Bayes and Support Vector Machine (SVM) classification strategies, and it is shown that probabilistic-based methods outperform the deterministic classifier. For studying the wear effect on machining-induced residual stresses, a 3D finite element model is developed. The results of the finite element model for the sharp tool are first validated with the experimental results, with good agreement. Next, the sharp tool geometry is updated to represent a wear land and found to have deviation from the validation tests in the compression zone; the sources of error in the finite element numerical model are discussed. The combination of this work on monitoring state of workpiece health alongside the proposed wear estimation strategy for monitoring state of cutting tool health provides a complete platform for in-process monitoring of machining health in cutting hard-to-machine alloys.

Single point incremental forming (SPIF) is a dieless forming process for sheet materials. This process forms materials with a hemispherical forming tool which locally deforms the sheet at incremental depths. The freeform nature of this process promises significant efficiency improvements within small and medium volume industries where stamping is traditionally used. However, several drawbacks currently inhibit its widespread use. One of these drawbacks is springback or elastic recovery resulting in reduced geometrical accuracy. An existing approach to counter this involves using a dedicated backing die, increasing the cost of the forming apparatus and the overall energy input per part. Other springback reduction methods involve the direct addition of energy to the workpiece through electrical or heat input. This study investigates the use of sacrificial steel blanks as backing dies for incremental forming of polycarbonate sheets, to overcome the loss in geometrical accuracy affiliated with forming geometries with a relatively large distance between the geometry periphery and the clamped edge. The blanks were not bound to each other, but rather clamped along their edges. In this study, polycarbonate blanks were tested using a three-factorial design of experiments, with relative plate thicknesses of 0.4, 0.5, and 0.6, and wall angles of 15°, 30°, 45°, and 60° as independent factors. The test geometry used was a straight walled pyramid with a square base. Using the backing sheet, a reduction in the springback was observed, demonstrating the effectiveness of sacrificial backing blanks. Particularly, the ‘pillow effect’ at the base of the geometry was reduced. This is attributed to the higher stiffness of the steel plates, increasing the plastic strain on the polycarbonate. However, the formability is found to decrease for higher values of the backing plate thickness due to premature steel failure. In future studies, this work will be expanded to include additional thickness ratios, geometries, toolpath types, step sizes and materials to form a more complete trend.

Machining of complex geometries is conventionally accomplished through the use of a ball-end mill and a helical toolpath which follows along the contours of the geometry at incremental depths. While effective for the majority of geometries, this method produces scallops which result from the ball-end mill radius and the step size of the toolpath. The size of these scallops, which degrades the surface finish, can be minimized by utilizing a relatively small step size. However, this results in increased machining time. A novel method of scallop removal is simulated and experimentally tested herein on 6061-T6511 aluminum. This method applies a friction stir processing effect to the workpiece by rotating a ball-end mill tool in reverse over the surface of the material subsequent to ball-end mill cutting passes. Additionally, the path constructed for scallop removal was a self-intersecting epicycloid which plastically deforms the scallops in order to reduce the surface roughness and impart favorable compressive surface stress. In this study, the surface variability produced from this process is reported for several different tool paths, determined experimentally and through simulation. Future studies will investigate the microstructural effects of this process, as well as the resulting microhardness and residual stress profile.

Nickel-based alloys are a class of hard-to-machine materials that exhibit a unique combination of high strength at high temperature. While they are widely used in industry, the high tool wear rate of these materials makes machining them a challenging task. Furthermore, machining tolerances, residual stresses, and tool runout impose uncertainty in tracking tool wear. In this work, the current view on tracking progressive tool wear is shifted from deterministic domains into the stochastic domain to study the probability distribution of the tool wear during the process. To do so, Bayesian-based estimation was used for accurate model inference and the result was fed into the Kalman filter for tracking tool wear in end-milling Rene-108 Ni-based alloy. To improve the accuracy, a direct laser measuring system for capturing tool length change was fused with the indirect power measurement. The results show a significant improvement in accuracy over the indirect method, with less than 8 µm root mean square error. This measuring strategy improved the accuracy, while preserving the automated platform for monitoring the tool’s health.

An extended Kalman filter (EKF) is employed in this work for tracking tool flank wear area in wet-turning of Inconel 718 (IN718) nickel-based alloy in variable feed condition. The tool wear area evolution is modeled with a 3rd order polynomial empirical function and an analytical solution for discrete state space system is derived. The state uncertainty was found to decrease up to a critical range of 200–250 μm of average flank wear length, and then increase abruptly with an increase in tool wear. Therefore, the tool wear uncertainty was modeled with failure probability density, i.e. the bathtub function, while a constant uncertainty was considered for the measurement signal (spindle power). To demonstrate the significance of using this method, the root mean square error (RMSE) and the mean absolute error (MAE) were calculated and compared with deterministic method in estimation of the tool wear area. It was shown that the proposed estimation based on stochastic filter EKF increased the accuracy of estimation by maximum of 60%. Results for estimation of the rate of tool wear area indicate additional possible effects or transitions of effects at higher wear conditions.

The electroplastic effect can be predicted and modeled as a 100% bulk heating/softening phenomenon in the quasi-steady-state; however, these same models do not accurately predict flow stress in transient cases. In this work, heterogeneous Joule heating is examined as the possible cause for the transient stress drop during quasi-static pulsed tension of 7075-T6 aluminum. A multiscale finite element model is constructed where heterogeneous thermal softening is explored through the representation of grains, grain boundaries, and precipitates. Electrical resistivity is modeled as a function of temperature and dislocation density. In order to drive the model to predict the observed stress drop, the bulk temperature of the specimen exceeds experiment, while the dislocation density and grain boundary electrical resistivity exceed published values, thereby suggesting that microscale heterogeneous heating theory is not the full explanation for the transient electroplastic effect. A new theory for explaining the electroplastic effect based on dissolution of bonds is proposed called the Electron Stagnation Theory.

To improve the fuel economy, the automobile industry is vigorously shifting towards using a mix of lightweight materials which offers high strength-to-weight ratio. Dissimilar material joining is of critical importance in this area. Friction element welding (FEW) has been proposed for dissimilar materials, with the capability of joining high strength materials of varying thickness in minimal time with low input energy. A coupled thermal-mechanical finite element model is developed in this work to better understand the physical mechanisms involved in the process and predict the evolution of parameters such as temperature, stress, material flow, and weld quality. The Coupled Eulerian-Lagrangian (CEL) approach is adopted to capture the severe plastic deformation of both the tool and the workpiece. The material deformation and temperature evolution are analyzed at different steps, and good agreement are shown between the simulation results and the experimental data.

To increase the fuel economy of their fleets, automotive OEMs are turning to lightweighting their vehicles through multi-material bodies. This involves forming and joining of materials with high strength to weight ratios such as aluminum and advanced high strength steels. These metals come with the downside of decreased formability and increased springback compared to conventional automotive steels. Electrical augmentation has been shown to decrease springback and increase formability in sheet forming and represents a potential solution to the use of new lightweight metals. Applied electricity is traditionally measured as a current density, however this measure struggles to represent elevated strain rate manufacturing processes. This paper examines other predictors of electrically assisted process performance such as electrical energy and power through comparison of nominally equivalent waveforms. It is found that energy is a better predictor of process performance than current density, but is dependent on the ability to predict process temperature. The leading predictive electrically assisted temperature model is examined in depth through testing of 13 different parameter sets. It is found that the model is unable to predict the correct temperature at a high current density and that the transient stress drop cannot predicted for any of the electrical cases.

When postforming machining operations are required on high-strength structural components, tool life becomes a costly issue, often requiring external softening via techniques such as laser assistance for press-hardened steel components. Electrically assisted manufacturing (EAM) uses electricity during material removal processes to reduce cutting loads through thermal softening. This paper evaluates the effect of electric current on a drilling process, termed electroplastic drilling, through the metrics of axial force, and workpiece temperature when machining mild low carbon steel (1008CR steel) and an advanced high strength press hardened steel. A design of experiment (DoE) is conducted on 1008CR steel to determine primary process parameter effects; it is found that electricity can reduce cutting loads at the cost of an increased workpiece temperature. The knowledge generated from the DoE is applied to the advanced high strength steel to evaluate cutting force reduction, process time savings, and tool life improvement at elevated feedrates. It is found that force can be reduced by 50% in high feedrates without observing catastrophic tool failure for up to ten cuts, while tool failure occurs in only a single cut for the no-current condition. Finally, the limitations of the developed model in electroplastic drilling are discussed along with future suggestions for industrialization of the method.

γ′-strengthened nickel-based superalloys are developed for high-performance systems such as jet engines, internal combustion engines, and gas turbines. Their excellent properties are given by specifically designed microstructure. Unfortunately, the structure is deformed during machining. Too much deformation generated results in components with low mechanical integrity and reduced in-service life. Experimental investigations indicated that the machining affected zone or subsurface damage formation for nickel-based superalloys is an atypical phenomenon; its dependence on the process parameters is fundamentally different from the conventional materials. This research investigates subsurface damage formation in orthogonal cutting tests performed on nickel-based superalloys, followed by empirical and numerical modeling. The simulations are used to estimate the depth of the subsurface damage and are compared with the experimental results. The knowledge can then be applied to select optimum cutting parameters for an acceptable depth of subsurface damage.

Nickel-based superalloys constitute a significant portion of the materials used in important industries such as aerospace, energy production, automotive, and biomedical industries. Due to their superior properties that make them appealing for these industries such as their high strength at elevated operating temperatures, manufacturing these alloys to end product specifications has been a difficult task. Despite the several recent studies that unearth various methods to tackle different aspects of this challenge, machining of nickel-based superalloys continues to be a mostly unknown territory. Researchers have mostly worked on finding optimal machining parameters that provide milder operating conditions, lower cost of tooling, or better end-product dimensional accuracy and surface quality; however, the tool material and type are generally constant in these studies. Therefore, it is difficult to apply the information gathered from these studies when there is a change in the machine tool that has been used, as it frequently happens when tool manufacturers produce new tools that perform better. In this study, an alternative glance at the bigger picture is presented, providing an insight toward a generalized model that directly addresses the industrial concern of process cost. Solid carbide and ceramic tools, which are known to be heavily utilized in manufacturing gas turbine components, are investigated by their performance as well as the relative cost they induce during end milling the gamma-prime strengthened nickel-based superalloy. First, the performance of solid carbide tools with no coating are compared to those with coatings of different material and cost, through a set of tool life experiments at industrially applicable machining conditions. Then, the performances of solid ceramic tools are investigated using machining conditions taken directly from gas turbine component production. Finally, a cost-based model is introduced to compare the performance of the solid carbide and ceramic tools.

Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.

The requirement of increased fuel economy standards has forced automakers to incorporate multi-materials into their current steel dominant vehicles in order to lightweight their fleets. Technologies such as Self Piercing Rivets and Flow Drill Screws are currently implemented for joining aluminum to high-strength steels but only one-technology is viable for joining aluminum to ultra-high-strength steels without pre-holes, namely Friction Element Welding. This study is aimed at investigating how variations in the cleaning and welding steps of the Friction Element Welding process influence joint quality. A design of experiment was conducted to understand the influence of key process parameters (endload, spindle RPM, and relative distance) during these steps on the pre-defined joint quality metrics of head height, weld zone diameter, under-head fill area, temperature, and microhardness. It is found that cleaning step parameters have the greatest influence on process time and energy consumption, while welding step parameters greatly influence maximum torque on the element, head height, and underhead fill, with both cleaning force and weld force influencing weld diameter, all parameters influence temperature.

Increasing governmental fuel economy requirements drives automakers to increase the fuel economy of their fleets. One of the methods for improving fuel economy is lightweighting vehicles through the use of materials with high strength to weight ratios. Some of these new metals entering the automotive sector are difficult to machine and cause drastically reduced tool life and increase machining cost. It has been shown that electricity has the ability to reduce cutting force during orthogonal cutting and turning. In this research, a design of experiments study on an electrically assisted drilling operation is conducted to determine the impact and interaction between the following input parameters: applied electric current, feedrate, spindle speed, and number of holes cut. These variables used to determine impact and interaction on the following output variables: flank wear, axial cutting force, and temperature evolution. A 2D finite volume method model is used to predict drilling temperature during the process, and is used to aid in predicting axial force. It is found that electric current can reduce cutting force by 10% for 1008 steel at the cost of increased temperature, however, arcing at initial contact causes increased tool wear at higher current inputs.

With the increasing demands in the automotive industry for passenger safety and higher structural strength and stiffness, the automotive industry is using more advanced high strength steels. The ability to reduce tool wear and drilling forces in post forming drilling of high strength steel parts is of high importance to the automotive industry. Electrically assisted drilling is a process in which electric current is passed through the drill bit to the workpiece resulting in local softening, and allowing for a reduction in cutting forces and potential increase in tool life. In this paper, tungsten carbide (WC)-tipped drill bits are used to study the effect of varying electrical current on 1500 Usibor® steel work pieces. The effects of current on the drilling process of high strength steel are investigated in this research by studying the maximum temperature during drilling, the dependence of chip formation, tool wear and the axial force during the drilling operation. It was found that the magnitude of current passed through the workpiece directly influences the axial force that the tool experiences, and thus the tool wear. This effect is modeled through Joule heating, leading to elevated temperature and thermal softening.

After machining nickel-based superalloys, tensile surface residual stresses can cause end-product issues such as fatigue failure. Modeling the residual stress profile is currently tedious and inaccurate. This study introduces a new method of understanding the residual stress profile in terms of quantifiable key measures: peak tensile stress at the surface, magnitude and depth of peak compressive stress, and depth at which residual stress becomes near-zero. Experiments in turning IN-100 and milling GTD-111 have been conducted and subsequent X-ray Diffraction measurements have been utilized to obtain residual stress profiles. Using a sinusoidal decay function fitted to measured residual stress profiles, these four key profile measures are extracted and then the effects of process parameters such as cutting speed, feed, cutting edge radius, and tool coating on these measures are investigated.

Recent research by the authors has resulted in the conception of several methods of accounting for direct electrical effects during an electrically assisted manufacturing process, where electricity is applied to a conductive workpiece to enhance its formability characteristics. This modeling and analysis strategy accounts for both mechanical effects and heat transfer effects due to the applied electrical power. This study presents a sensitivity analysis and explanation of several key material and process inputs during an electrically assisted forming test on Stainless Steel 304 and Titanium Grades 2 and 5 specimens. First, the effect that the specific heat ( Cp) value has on the model will be discussed and compared with another lightweight material. Second, the significance of all three heat transfer modes (conduction, convection, and radiation) will be noted, and any possible simplifications to the existing heat transfer model will be highlighted. Third, the general electroplastic effect coefficient profile shape for the Stainless Steel 304 material will be compared to that of titanium alloys. Fourth, a frequency analysis will be done on the data taken during the experiments, by way of a Fast Fourier Transform, and the variation of frequency response with the electric input is studied. Overall, this study provides insight into several factors affecting a material’s electroplastic effect coefficient profile and also compares resulting electroplastic effect coefficient profiles of various materials.

A polyacrylonitrile (PAN)-based carbon fiber (CF) manufacturing cost estimation model driven by mass is presented in this study. One of the biggest limiting factors in the large-scale use of carbon fiber (CF) in manufacturing is its high cost. The costs involved in manufacturing the carbon fiber have been formalized into a cost model in order to facilitate the understanding of these factors. This can play a key role in manufacturing CF in a cost-effective method. This cost model accounts for the fixed and variable costs involved in all the stages of manufacturing, in addition to accounting for price elasticity.

7075-T6 aluminum suffers from limited elongation during tensile forming; electrically assisted forming (EAF), which uses direct current to improve formability, is a viable candidate process to improve this effect. In past electrical tension testing by various authors, two types of waveforms have been examined: continuous current and square waveforms. For tension, it was shown that the applying current using square waveforms was able to extend formability beyond what continuous current could do, due to reducing the overheating in the necking region. The goal of this paper is to model the temperature and flow stress effects of saw tooth waves by modifying an existing square wave temperature prediction model and combining it with a theoretical flow stress model. Nondecaying and linearly globally decaying saw tooth waveforms are used in an attempt to control the temperature of the necking zone to allow for increased strain at fracture. Comparisons between saw tooth waveforms and square waveforms are exhibited, and it is found that the saw tooth waveforms are inferior to square waves for increasing strain at fracture for 7075-T6.

It has been shown that electrically assisted machining has the ability to reduce cutting force, change chip type, and improve surface finish. However, the effect of electricity on tungsten carbide has not been examined, a material often used to create cutting tools used in electrically assisted machining. During machining processes, depending on the type of cut, a small amount of the tool may be in contact with the workpiece. This will lead to an increased current density at that point on the tool which could lead to undesired effects with respect to tool wear and life. This paper conducts electrically assisted compression tests on uncoated tungsten carbide rod to examine the effect of electricity on the material and determine if there are any current densities that cause large magnitude weakening of the tungsten carbide. It is concluded that there is a maximum current density that can be passed through tungsten carbide before thermal softening becomes a problem. At a current density lower than this threshold, electricity has little effect on the strength of the carbide. This work is related to past electrically assisted turning experimentation.Copyright © 2016 by ASME

Driven by the automotive industry’s drive towards lightweighting, electrically assisted forming (EAF) is one of the most rapidly growing research fields in bulk deformation, and is classified under the general term “Electrically-Assisted Manufacturing (EAM)”. In EAF electric current (continuous or intermittent) is applied to a metallic sheet during the forming process, leading to numerous advantageous effects that have been studied and proven by several research groups and for different structural metals, such as reduced forming load and flow stress, increased formability, and reduction (or even elimination) of springback. Electrically-assisted bending (EAB) is a recent evolution of EAF technique, with the aim of capitalizing on the aforementioned advantages of EAF technique. In this work the effects of the EAB process on the final springback in an air bending test are identified, with the metal sheet being bent under different electrical field conditions. In addition, a comparison between the effects of applying the current during forming versus post forming are investigated. It was found that in general, higher current density (amount of current through cross sectional area of specimen (A/mm2), more frequent pulse period, and longer pulse duration all resulted in a greater degree of springback reduction. A microstructural evaluation showed no change in grain size in the presence of electric current.

Recent development of electrically assisted manufacturing processes proved the advantages of using the electric current, mainly related with the decrease in the mechanical forming load, and improvement in the formability when electrically assisted forming of metals. The reduction of forming load was formulated previously assuming that a part of the electrical energy input is dissipated into heat, thus producing thermal softening of the material, while the remaining component directly aids the plastic deformation. The fraction of electrical energy applied, which assists the deformation process compared to the total amount of electrical energy, is given by the electroplastic effect coefficient. The objective of the current research is to investigate the complex effect of the electricity applied during deformation, and to establish a methodology for quantifying the electroplastic effect coefficient. Temperature behavior is observed for varying levels of deformation and previous cold work. Results are used to refine the understanding of the electroplastic effect coefficient, and a new relationship, in the form of a power law, is derived. This model is validated under independent experiments in Grade 2 (commercially pure) and Grade 5 (Ti–6Al–4V) titanium.

The automobile and aerospace sectors are increasingly turning their attention to the opportunities created by the use of lightweight alloys with large strength-to-weight ratios, such as aluminium, magnesium, stainless steel, and titanium alloys. However, when using conventional forming processes, these light materials create processing challenges: low formability and high yield strength. Electrically assisted forming (EAF) is a method that can overcome these limitations. Specifically, EAF is a novel forming process where electricity is applied to the metallic workpiece during deformation. Previous investigations have shown that EAF creates a reduction in flow stress, an increase in formability, an ability to reduce/eliminate springback, and an improved precision. This study investigates the influence of electricity on lubricant performance and identifies lubricant candidates for EAF. When electricity is applied, besides the changes due to surface expansion at the interface that occur in conventional processes, the lubricant is exposed to high localized temperatures and current fields. Electrically assisted ring compression tests are conducted and the performance characteristics of three lubricants are evaluated. By combining the experiments and finite element simulation results, friction coefficients can be estimated, and the effect of electric current flow on friction characteristics quantified.

The suitability of various polymer-powder spraying technologies for coating of metal-stampings used in polymer metal hybrid (PMH) load-bearing automotive-component applications is considered. The suitability of the spraying technologies is assessed with respect to a need for metal-stamping surface preparation/treatment, their ability to deposit the polymeric material without significant material degradation, the ability to selectively overcoat the metal-stamping, the resulting magnitude of the polymer-to-metal adhesion strength, durability of the polymer/metal bond with respect to prolonged exposure to high-temperature/high-humidity and mechanical/thermal fatigue service conditions, and compatibility with the automotive body-in-white (BIW) manufacturing process chain. The analysis revealed that while each of the spraying technologies has some limitations, the cold-gas dynamic-spray process appears to be the leading candidate technology for the indicated applications.

Despite their increasing use in leading industries, manufacture of alloys with superior mechanical properties have been a big challenge in the recent years. Researchers have been working on using assisted or augmented processes to overcome this challenge, with methods such as ultrasonically assisted, thermally assisted, vibration-assisted, magnetic field-assisted, and laser-assisted machining. Utilizing electrical assistance in manufacturing has not caught much attention due to its difficult-to-apply nature. However, it is possible to increase the ductility and machinability (through reduced flow stress) of certain metallic materials through the use of electricity. In this method, the electrical current resistively heats the material while aiding in deforming the material through the electroplastic effect. The limited amount of work in this topic is mainly focused on exploring the forming characteristics of relatively softer materials. Application of this augmentation to alloys with superior mechanical properties at elevated temperatures, on the other hand, has not been explored. This study aims to fill in that void through an investigation of applying different currents through the tool concentrated on the tool-workpiece contact zone. Both the titanium alloy Ti-6Al-4V and the nickel-based superalloy IN-738 were investigated, and the results showed that for both materials, there are two separate thresholds that need to be considered in any analysis. The first threshold is where the material starts to get deformed, below which no significant divergence from the baseline (no current) tests was observed. After exceeding this value, machining forces start decreasing with increasing current up to a certain point (second threshold) where the effect of electric current is reversed. If the second threshold is surpassed, the machining forces increase rapidly. Findings of this study can be used in assisting the machining of such materials.

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti–6Al–4V. To capture the tool response, controlled milling experiments are conducted at suitable corner points of the recommended feed-speed design space, for constant stock material removal volumes. For each case, the tool material volume worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients, is quantified—these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW) which is a measure of the cutting tool efficiency, are related to the MRR—these provide a tool-life based optimal MRR for profitability. This work not only elevates tool wear from a 1D to 3D concept, but helps in assessing machining economics from a stock material-removal-efficiency perspective as well.

The objective of this paper is to analyze the effect of different carbide grain sizes on the tool material volume worn away from straight tungsten–carbide–cobalt (WC–Co) turning inserts. A previously developed metrology method for assessing the tool material volume worn away from milling inserts is adapted for quantifying the volumetric tool wear (VTW) of turning inserts. Controlled turning experiments are conducted at suitable points in the feed-speed design space for two sets of uncoated inserts having different carbide grain sizes. Three levels of Ti–6Al–4V stock removal volumes (10-cm3 each) are analyzed. For each insert, the tool material volume worn away (in mm3) as well as the three-dimensional (3D) wear profile evolution is quantified after each run. Further, the specific volumetric wear rate and the M-ratio (volume of stock removed to VTW) are related to the material removal rate (MRR). The effect of carbide grain size on VTW is examined using scanning electron microscopy and elemental analysis. Finally, the inverse dependence of the M-ratio on MRR enables the definition of actual usable tool life in terms of its efficiency in removing stock, rather than being based on a tool geometry related metric.

In order for the electroplastic effect to take place, the applied electricity must be able to flow from the dies and through the workpiece. Because of this, the interfaces between the dies/workpiece are critical.

This chapter describes the fundamentals behind electroplasticity in metals. Specifically, it focuses on electrical current flow, previous electroplastic theories, and an overall explanation of the electroplastic effect on metals. This overall theory will be supported with experimental results, and electroplastic conclusions will be drawn at the end of the chapter.

Within this book, a modeling strategy for the EAF technique is explained for both compression and tension. Both strategies separate the thermal softening effects from the direct electrical effects and thus produce temperature and force profiles for their respective processes. However, in the real world, manufacturing processes are rarely exclusively compression or tension. Therefore, within this chapter, manufacturing processes that can be applicable to EAF will be explained. These include bending, stretch forming, machining, friction stir welding, and miscellaneous other EAF-industrialization research by researchers other than the authors. In addition, this chapter will include experimental EAF findings for compression, tension, channel formation, springback, and various types of forming.

Electrically assisted forming (EAF) is a recently introduced metal-forming technique capable of enhancing a metal’s formability during deformation and reducing springback after deformation.

For successful implementation of EAF in manufacturing industries, one area that needs to be addressed is the predictability or material response at a bulk level. This chapter introduces the modeling strategy for the electroplastic effect at the macroscale, which are used for compressive modeling (Chap. 5) and tensile modeling (Chap. 6). For macro-level modeling of EAF in Chaps. 5 and 6, the models use a coupled thermo-mechanical approach based on energy and displacement continuity. Additional laws utilized in Chaps. 5 and 6 include: the first law of thermodynamics, Joule’s first law for heat generation, Fourier’s law for conduction, and Newton’s law of cooling.

In this chapter, several control approaches are described for forming a metal under an electrical current field. In addition, the approaches are demonstrated and potential applications for these control schemes are discussed. The specific examples where closed-loop control is used to determine the process output are for constant force forming, constant stress forming, and constant current density (CCD) forming. Last, the feasibility toward model-based control (MBC) is discussed for the models developed in Chaps. 4– 6.

The overall goal of this chapter is to develop a model for an electrically assisted forging process and then use this model to highlight specific sensitivities and relationships within the EAF process. A modeling strategy will be defined, based on existing conventional forging equations. These equations will then be modified to account for the electroplastic effect in an EAF process.

This chapter contains modeling work for sheet metal subject to an applied direct electrical current in uniaxial tension. The modeling is divided into a thermal and mechanical approach which is combined to a thermo-mechanical model to predict the deformation behavior during EAF.

Research regarding tool wear in the machining of difficult materials is important because it is a significant indicator of process failure in terms of degradation of part quality, and the resulting high cost and increased process time. Prior researchers have investigated the effects of cutting parameters on tool wear and as a result, tool life has seen significant improvement. However, these studies are not concerned with tool flank wear during machining; they instead focus on tool flank wear after a certain amount of cutting distance. This study proposes a new method of predicting tool flank wear during machining that has the capability of suggesting tool failure without directly measuring the tool. For this purpose, a detailed set of experiments on end milling of titanium alloy Ti-6Al-4V was conducted and analyzed. Then, the resultant force output, which can be monitored during machining, was used to establish a predictive algorithm for tool flank wear. Using the increase in the resultant force as well as the total energy spent on the workpiece, it was shown that tool flank wear can be effectively predicted during machining and this can decrease the time spent on tool failure inspection and early tool change, increasing the throughput of the process.Copyright © 2014 by ASME

Nickel-based superalloys are designed for use in extreme environments and are getting progressively better for these environments, therefore much harder to machine. They play a crucial role in elevated temperature applications where high strength, high resistance to corrosion and creep resistance are required. Machinability suffers as a result of these properties and harsh machining conditions occur, resulting in high cutting forces and tool wear. To combat the difficulties in the machining of nickel-based superalloys, such as poor thermal diffusivity and high levels of abrasive wear, trochoidal milling was introduced as an alternative method of milling. This method of milling combines linear motion with uniform circular motion, reducing chip load in exchange for increased machining time. Industry is averse to its widespread adoption due to increasing cycle times when compared to conventional milling methods, however it has been shown that overall productivity can be improved due to less tool wear with a more predictable behavior. This work characterizes the effects of trochoidal milling and provides a comparison of trochoidal milling with a traditional milling technique, end milling, for the machining of Inconel 738. In order to compare the trochoidal and conventional machining approaches directly, metrics of productivity normalized to tool wear are introduced. The normalized metrics introduced in this study aim to provide a more representative comparison of productivity and efficiency characteristics: volumetric material removal per unit tool wear (MR/VB) and the material removal rate per unit tool wear (MRR/VB). It was found that significantly higher volumetric material removal is possible using trochoidal milling, and fewer tools are needed; material removal rates that competitive with end milling can be achieved. When the amount of time spent on tool change for the same volume of material removal is considered, material removal rate of trochoidal milling can even be higher than end milling, indicating that better productivity and efficiency of the process is possible at reduced tooling costs.Copyright © 2014 by ASME