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Review Article

J. Manuf. Sci. Eng. 2019;141(4):040801-040801-14. doi:10.1115/1.4042789.

This paper presents a comprehensive review on the sources of model inaccuracy and parameter uncertainty in metal laser powder bed fusion (L-PBF) process. Metal additive manufacturing (AM) involves multiple physical phenomena and parameters that potentially affect the quality of the final part. To capture the dynamics and complexity of heat and phase transformations that exist in the metal L-PBF process, computational models and simulations ranging from low to high fidelity have been developed. Since it is difficult to incorporate all the physical phenomena encountered in the L-PBF process, computational models rely on assumptions that may neglect or simplify some physics of the process. Modeling assumptions and uncertainty play significant role in the predictive accuracy of such L-PBF models. In this study, sources of modeling inaccuracy at different stages of the process from powder bed formation to melting and solidification are reviewed. The sources of parameter uncertainty related to material properties and process parameters are also reviewed. The aim of this review is to support the development of an approach to quantify these sources of uncertainty in L-PBF models in the future. The quantification of uncertainty sources is necessary for understanding the tradeoffs in model fidelity and guiding the selection of a model suitable for its intended purpose.

Commentary by Dr. Valentin Fuster

Research Papers

J. Manuf. Sci. Eng. 2019;141(4):041001-041001-9. doi:10.1115/1.4042578.

This paper deals with the detailed analysis of the lateral process forces in rolling-cut shearing of heavy steel plates and their impact on edge defects. Rolling-cut shearing is still the most common method of heavy-plate side trimming. However, this method can entail edge defects like uneven longitudinal shape as well as burr and fractures in the area of the cut-changeover (beginning and end of the periodical cuts). In the existing literature, neither the root cause of these edge defects nor their nexus with the upper blade trajectory (blade drive-kinematics) has been analyzed in detail. In this work, these issues will be explored based on the finite element method (FEM) simulations and measurements from an industrial plant. The complex interrelation between drive-kinematics, varying lateral force, unintended lateral motion of the upper blade, unintended variation of the blade clearance, and quality defects is analyzed. The variation of the lateral force is identified as the root cause of such quality defects and a physical explanation for variations of the lateral force is given. The detailed understanding of the shearing process serves as a solid basis for an optimization and re-design of the drive-kinematics in a future work. Measurements from an industrial plant and simulation results show good agreement and thus confirm the theory. The results are transferable to other rolling-cut trimming shears.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041002-041002-10. doi:10.1115/1.4042581.

3D printing offers the opportunity to design and make replacement parts to exacting specifications when needed. This is particularly helpful for space applications where stand-alone replacement mechanisms are required. Samples of 3D-printed polylactic acid (PLA) were subjected with up to 200 kGy of gamma radiation from a Cobalt-60 irradiator. The mechanical responses to destructive testing were successfully modeled with a combination of linear and exponential functions and may be understood given the underlying chemical changes due to said radiation exposures. We find that for doses up to 50 kGy, the performance of 3D-printed PLA is largely unaffected, which is beneficial for applications in space and in medicine. At larger doses, it appears that decomposition processes win out over cross-linking, which may aid in the degradation of PLA in waste streams.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041003-041003-8. doi:10.1115/1.4042583.

Die casting is a type of metal casting in which a liquid metal is solidified in a reusable die. In such a complex process, measuring and controlling the process parameters are difficult. Conventional deterministic simulations are insufficient to completely estimate the effect of stochastic variation in the process parameters on product quality. In this research, a framework to simulate the effect of stochastic variation together with verification, validation, and uncertainty quantification (UQ) is proposed. This framework includes high-speed numerical simulations of solidification, microstructure, and mechanical properties prediction models along with experimental inputs for calibration and validation. Both experimental data and stochastic variation in process parameters with numerical modeling are employed, thus enhancing the utility of traditional numerical simulations used in die casting to have a better prediction of product quality. Although the framework is being developed and applied to die casting, it can be generalized to any manufacturing process or other engineering problems as well.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041004-041004-16. doi:10.1115/1.4042606.

Linear tool path segments of computer numerical control (CNC) machine tools need to be smoothed and interpolated in order to guarantee continuous and steady machining. However, because of the highly nonlinear relation between arc lengths and spline parameters, it is difficult to develop algorithms to simultaneously achieve real-time corner smoothing and interpolation with high-order continuity, although it is important to guarantee both high calculation efficiency and good dynamic performance of high-speed CNC machining. This paper develops a computationally efficient real-time corner smoothing and interpolation algorithm with C3 continuous feature. The corners at the junction of linear segments are smoothed by inserting Pythagorean-hodograph (PH) splines under the constraints of user-defined tolerance limits. Analytical solutions of the arc length and curvature of the smoothed tool path are obtained by evaluating a polynomial function of the spline parameter. The smoothed tool path is interpolated in real time with continuous and peak-constrained jerk. Simulations and experimental results show that the proposed tool path smoothing and interpolation algorithm can be executed in real time with 0.5 ms control period. Acceleration and jerk continuity of each axis are achieved along the tool path. Comparisons with existing corner smoothing algorithms show that the proposed method has lower jerk than existing C2 algorithms and the real-time interpolation algorithms based on the Taylor series expansion.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041005-041005-11. doi:10.1115/1.4042568.

AA7xxx series aluminum alloys have great potentials in mass saving of vehicle bodies due to pretty high specific strength. However, the use of these high strength materials poses significant challenges to the traditional self-piercing riveting (SPR) process. To address this issue, a novel process, friction self-piercing riveting (F-SPR), was applied to join aluminum alloy AA7075-T6 sheets. The effects of the spindle speed and rivet feed rate on F-SPR joint cross section geometry evolution, riveting force, and energy input were investigated systematically. It was found that the rivet shank deformation, especially the buckling of the shank tip before penetrating through the top sheet, has significant influence on geometry and lap shear failure mode of the final joint. A medium rivet feed rate combined with a high spindle speed was prone to produce a defect-free joint with sound mechanical interlocking. F-SPR joints with the failure mode of rivet shear fracture were observed to have superior lap shear peak load and energy absorption over the joints with mechanical interlock failure. The optimized F-SPR joint in this study exhibited 67.6% and 13.9% greater lap shear peak load compared with SPR and refill friction stir spot welding joints, respectively, of the same sheets. This research provides a valuable reference for further understanding the F-SPR process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041006-041006-7. doi:10.1115/1.4042787.

In recent years, cutting tool manufacturers are moving toward improving the robustness of the positioning of an insert in the tool body interface. Increasing the robustness of the interface involves designs with both chamfered and serrated surfaces. These designs have a tendency to overdetermine the positioning and cause instabilities in the interface. Cutting forces generated from the machining process will also plastically deform the interface, consequently, altering the positioning of the insert. Current methodologies within positioning and variation simulation use point-based contacts and assume linear material behavior. In this paper, a first-order reliability-based design optimization framework that allows robust positioning of surface-to-surface-based contacts is presented. Results show that the contact variation over the interface can be limited to predefined contact zones, consequently allowing successful positioning of inserts in early design phases of cutting tool designs.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041007-041007-8. doi:10.1115/1.4042580.

The significant advance in the boosted fabrication speed and printing resolution of additive manufacturing (AM) technology has considerably increased the capability of achieving product designs with high geometric complexity and provided tremendous potential for mass customization. However, it is also because of geometric complexity and large quantity of mass-customized products that the prefabrication (layer slicing, path planning, and support generation) is becoming the bottleneck of the AM process due to the ever-increasing computational cost. In this paper, the authors devise an integrated computational framework by synthesizing the parametric level set-based topology optimization method with the stereolithography (SLA)-based AM process for intelligent design and manufacturing of multiscale structures. The topology of the design is optimized with a distance-regularized parametric level set method considering the prefabrication computation. With the proposed framework, the structural topology optimization not only can create single material structure designs but also can generate multiscale, multimaterial structures, offering the flexibility and robustness of the structural design that the conventional methods could not provide. The output of the framework is a set of mask images that can be directly used in the AM process. The proposed approach seamlessly integrates the rational design and manufacturing to reduce the numerical complexity of the computationally expensive prefabrication process. More specifically, the prefabrication-friendly design and optimization procedure are devised to drastically eliminate the redundant computations in the traditional framework. Two test examples, including a free-form 3D cantilever beam and a multiscale meta-structure, are utilized to demonstrate the performance of the proposed approach. Both the simulation and experimental results verified that the new rational design could significantly reduce the prefabrication computation cost without affecting the original design intent or sacrificing the original functionality.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041008-041008-10. doi:10.1115/1.4042790.

Conventional single-point incremental forming (SPIF) is already in use for small batch prototyping and fabrication of customized parts from thin sheet metal blanks by inducing plastic deformation with a rigid round-tip tool. The major advantages of the SPIF process are its high flexibility and die-free nature. In lieu of employing a rigid tool to incrementally form the sheet metal, a high-speed water jet as an alternative was proposed as the forming tool. Since there is no tool-workpiece contact in this process, unlike in the traditional SPIF process, no lubricant and rotational motion of the tool are required to reduce friction. However, the geometry of the part formed by water jet incremental microforming (WJIMF) will no longer be controlled by the motion of the rigid tool. On the contrary, process parameters such as water jet pressure, stage motion speed, water jet diameter, blank thickness, and tool path design will determine the final shape of the workpiece. This paper experimentally studies the influence of the above-mentioned key process parameters on the geometry of a truncated cone shape and on the corresponding surface quality. A numerical model is proposed to predict the shape of the truncated cone part after WJIMF with given input process parameters. The results prove that the formed part's geometric properties predicted by the numerical model are in excellent agreement with the actually measured ones. Arrays of miniature dots, channels, two-level truncated cones, and letters were also successfully fabricated on stainless-steel foils to demonstrate WJIMF capabilities.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041009-041009-8. doi:10.1115/1.4042611.

In this work, a mechano-chemical surface modification to improve cutting tool performance is proposed. We applied this surface modification via shot peening the rake faces of high-speed steel tools with a blend of Al2O3 and Cu2S particles that serve as a plastic deformation medium and a chemical precursor, respectively. Orthogonal cutting experiments under base oil lubrication demonstrated that the proposed treatment results in a reduction of cutting and thrust forces, as well as in a reduction of built-up edge formation. These effects are explained by favorable changes in the lubricity and roughness of the rake face, and they suggest that this method has the potential to increase cutting tool life, lower energy consumption, and improve the dimensional accuracy and surface quality of a machined workpiece.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041010-041010-15. doi:10.1115/1.4042582.

Calibration is an important way to improve and guarantee the accuracy of machine tools. This paper presents a systematic approach for position independent geometric errors (PIGEs) calibration of five-axis machine tools based on the product of exponentials (POE) formula. Instead of using 4 × 4 homogeneous transformation matrices (HTMs), it establishes the error model by transforming the 6 × 1 error vectors of rigid bodies between different frames resorting to 6 × 6 adjoint transformation matrices. A stable and efficient error model for the iterative identification of PIGEs should satisfy the requirements of completeness, continuity, and minimality. Since the POE-based error models for five-axis machine tools calibration are naturally complete and continuous, the key issue is to ensure the minimality by eliminating the redundant parameters. Three kinds of redundant parameters, which are caused by joint symmetry information, tool-workpiece metrology, and incomplete measuring data, are illustrated and explained in a geometrically intuitive way. Hence, a straightforward process is presented to select the complete and minimal set of PIGEs for five-axis machine tools. Based on the established unified and compact error Jacobian matrices, observability analyses which quantitatively describe the identification efficiency are conducted and compared for different kinds of tool tip deviations obtained from several commonly used measuring devices, including the laser tracker, R-test, and double ball-bar. Simulations are conducted on a five-axis machine tool to illustrate the application of the calibration model. The effectiveness of the model is also verified by experiments on a five-axis machine tool by using a double ball-bar.

Topics: Machine tools , Errors
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041011-041011-10. doi:10.1115/1.4042786.

Additive manufacturing (AM) is based on layer-by-layer addition of materials. It gives design flexibility and potential to decrease costs and manufacturing lead time. Because the AM process involves incremental deposition of materials, it provides unique opportunities to investigate the material quality as it is deposited. Development of in situ monitoring methodologies is a vital part of the assessment of process performance and understanding of defects formation. In situ process monitoring provides the capability for early detection of process faults and defects. Due to the sensitivity of AM processes to different factors such as laser and material properties, any changes in aspects of the process can potentially have an impact on the part quality. As a result, in-process monitoring of AM is crucial to assure the quality, integrity, and safety of AM parts. There are various sensors and techniques that have been used for in situ process monitoring. In this work, acoustic signatures were used for in situ monitoring of the metal direct energy deposition (DED) AM process operating under different process conditions. Correlations were demonstrated between metrics and various process conditions. Demonstrated correlation between the acoustic signatures and the manufacturing process conditions shows the capability of acoustic technique for in situ monitoring of the additive manufacturing process. To identify the different process conditions, a new approach of K-means statistical clustering algorithm is used for the classification of different process conditions, and quantitative evaluation of the classification performance in terms of cohesion and isolation of the clusters. The identified acoustic signatures, quantitative clustering approach, and the achieved classification efficiency demonstrate potential for use in in situ acoustic monitoring and quality control for the additive manufacturing process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041012-041012-9. doi:10.1115/1.4042605.

Titanium alloy Ti-5Al-5V-3Cr-0.5Fe (Ti-5553) is a new generation of near-beta titanium alloy that is commonly used in the aerospace industry. Machining is one of the manufacturing methods to produce parts that are made of this near-beta alloy. This study presents the machining performance of new generation near-beta alloys, namely, Ti-5553, by focusing on a high-speed cutting process under cryogenic cooling conditions and dry machining. The machining experiments were conducted under a wide range of cutting speeds, including high speeds that used liquid nitrogen (LN2) and carbon dioxide (CO2) as cryogenic coolants. The experimental data on the cutting temperature, tool wear, force components, chip breakability, dimensional accuracy, and surface integrity characteristics are presented and were analyzed to evaluate the machining process of this alloy and resulting surface characteristics. This study shows that cryogenic machining improved the machining performance of the Ti-5553 alloy by substantially reducing the tool wear, cutting temperature, and dimensional deviation of the machined parts. The cryogenic machining also produced shorter chips as compared to dry machining.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041013-041013-7. doi:10.1115/1.4042604.

Hydraulic deep drawing presses are manifold machines that can be used for a number of use cases. The general need for the reduction of the energy consumption of industrial machines forces press manufacturers and owners to optimize their machines and processes. This article presents methods for the analysis and optimization of the drive systems of a hydraulic deep drawing press with four-point die cushion. For the slide drive, two alternatives of control methods for speed variable displacement pumps are compared to the conventionally used displacement pump with a constant speed. For the drive of the die cushion, two displacement control drive systems are compared to a conventional valve drive system.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041014-041014-10. doi:10.1115/1.4042610.

Conformally integrating conductive circuits with rigid 3D surfaces is a key need for smart materials and structures. This paper investigates sequential thermoforming and flash light sintering (FLS) of conductive silver (Ag) nanowire (NW) interconnects printed on planar polymer sheets. The resulting interconnect–polymer assemblies are thus preshaped to the desired 3D geometry and can be robustly attached to the surface. This conformal circuit integration approach avoids interconnect delamination in manual conformation of planar flexible electronics, eliminates heating of the 3D object in direct conformal printing, and enables easy circuit replacement. The interconnect resistance increases after thermoforming, but critically, is reduced significantly by subsequent FLS. The resistance depends nonlinearly on the forming strain, interconnect thickness, and FLS fluence. The underlying physics behind these observations are uncovered by understanding interconnect morphology and temperature evolution during the process. With the optimal parameters found here, this process achieves interconnect resistance of <10 Ω/cm within 90.8 s at 100% maximum strain over a 1 square inch forming area. The application of this process for complex surfaces is demonstrated via a simple conformal LED-lighting circuit. The potential of this approach to enable surface size and material insensitivity, robust integration, and easy replaceability for conformal circuit fabrication is discussed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041015-041015-8. doi:10.1115/1.4042603.

This study investigated the grinding force in rotational atherectomy, a clinical procedure that uses a high-speed grinding wheel to remove hardened, calcified plaque inside the human arteries. The grinding force, wheel motion, and ground surface were measured based on a ring-shape bovine bone surrogate for the calcified plaque. At 135,000, 155,000, and 175,000 rpm wheel rotational speed, the grinding forces were 1.84, 1.92, and 2.22 N and the wheel orbital speeds were 6060, 6840, and 7800 rpm, respectively. The grinding wheel was observed to bounce on the wall of the bone surrogate, leaving discrete grinding marks. Based on this observation, we modeled the grinding force in two components: impact and cutting forces. The impact force between the grinding wheel and the bone surrogate was calculated by the Hertz contact model. A multigrain smoothed particle hydrodynamics (SPH) model was established to simulate the cutting force. The grinding wheel model was built according to the wheel surface topography scanned by a laser confocal microscope. The workpiece was modeled by kinematic-geometrical cutting. The simulation predicted a cutting force of 41, 51, and 99 mN at the three investigated wheel rotational speeds. The resultant grinding forces, combining the impact and cutting forces modeled by the Hertz contact and SPH simulation, matched with the experimental measurements with relative errors less than 10%.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041016-041016-7. doi:10.1115/1.4042831.

Selective laser heat treatment allows local modification of material properties and can have a wide range of applications within the automotive industry. Enhanced formability and strength are possible to achieve. As the process involves selective heating, positioning of the heat treatment pattern in local areas is vital. Pattern positioning is often suggested based on the part design and forming aspects of the material to avoid failures during manufacturing. Along with improving material properties in desired local areas, the process also produces unwanted distortion in the material. Such effects on variation should be considered and minimized. In this paper, the heat treatment pattern is offset from its original position and its effect on geometrical variation is investigated. Boron steel blanks are selectively laser heat treated with a specific heat treatment pattern and then cold formed to the desired shape. Two heat treatment pattern dimensions are examined. Geometrical variation at the blank level and after cold forming, and springback after cold forming are observed. Results show that pattern offsetting increases the effect on geometrical variation. Therefore, correct positioning of the heat treatment pattern is important to minimize its effect on geometrical variation along with enhancement in the material properties. Knowledge from this study will contribute to various stages of the geometry assurance process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):041017-041017-11. doi:10.1115/1.4042788.

Titanium alloy Ti-6Al-4V, an alpha-beta alloy, possesses ductile deformation behavior and offers advantageous properties, light weight but high strength, good resilience, and resistance to corrosion, becoming highly suitable for aerospace and biomedical applications. However, its machinability is still considered a limiting factor in improving productivity. This paper presents a finite element modeling methodology for orthogonal cutting titanium alloy Ti-6Al-4V by considering material constitutive modeling together with material ductile failure in combination with damage initiation and cumulative damage-based evolution to simulate not only ductile material separation from workpiece to form chips but also chip serration mechanism by applying an elastic–viscoplastic formulation. The finite element model is further verified with orthogonal cutting experiments (using both uncoated and TiAlN-coated carbide tools) by comparing simulated and acquired forces and simulated and captured chip images at high cutting speeds. The effects of cutting speed, feed, tool rake angle, and tool coating on the degree of chip serration are studied through the simulation results. The cutting temperature and strain distributions are obtained to study the chip serration mechanism under different cutting conditions. It is confirmed that the material failure, crack initiation, and damage evolution are of great significance in the chip serration in cutting titanium alloy Ti-6Al-4V.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Manuf. Sci. Eng. 2019;141(4):044501-044501-7. doi:10.1115/1.4042579.

The modern manufacturing industry faces increasing demands to customize products according to personal needs, thereby leading to the proliferation of complex designs. To cope with design complexity, manufacturing systems are increasingly equipped with advanced sensing and imaging capabilities. However, traditional statistical process control methods are not concerned with the stream of in-process imaging data. Also, very little has been done to investigate nonlinearity, irregularity, and inhomogeneity in the image stream collected from manufacturing processes. This paper presents the joint multifractal and lacunarity analysis to characterize irregular and inhomogeneous patterns of image profiles, as well as detect the hidden dynamics in the manufacturing process. Experimental studies show that the proposed method not only effectively characterizes surface finishes for quality control of ultraprecision machining but also provides an effective model to link process parameters with fractal characteristics of in-process images acquired from additive manufacturing. This, in turn, will allow a swift response to processes changes and consequently reduce the number of defective products. The proposed multifractal method shows strong potentials to be applied for process monitoring and control in a variety of domains such as ultraprecision machining and additive manufacturing.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(4):044502-044502-7. doi:10.1115/1.4042842.

Reliable and robust tab joints in pouch cells are key to the functional reliability and durability of lithium-ion batteries. In this study, a novel solder-reinforced adhesive (SRA) bonding technology is applied to lithium-ion battery tab joining, and its feasibility is explored by the application of simplified specimens. The three main components involved in the implementation of the SRA process are the substrate, solder ball, and adhesive system. The application of flux to the solder balls and the size of the adhesive application area are the two main process variables. Results showed that both the flux and adhesive area have positive correlation with the mechanical performance due to the formation of a robust connection of the solder and the substrate. In addition, the SRA joints have a relatively lower resistivity than joints fabricated by conventional ultrasonic welding (USW) technology. Thus, there is significant potential for this process to be applied for joining of battery tabs.

Commentary by Dr. Valentin Fuster

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