Review Article

J. Manuf. Sci. Eng. 2018;140(6):060801-060801-13. doi:10.1115/1.4038644.

Hybrid additive manufacturing (hybrid-AM) has described hybrid processes and machines as well as multimaterial, multistructural, and multifunctional printing. The capabilities afforded by hybrid-AM are rewriting the design rules for materials and adding a new dimension in the design for additive manufacturing (AM) paradigm. This work primarily focuses on defining hybrid-AM in relation to hybrid manufacturing (HM) and classifying hybrid-AM processes. Hybrid-AM machines, materials, structures, and function are also discussed. Hybrid-AM processes are defined as the use of AM with one or more secondary processes or energy sources that are fully coupled and synergistically affect part quality, functionality, and/or process performance. Historically, defining HM processes centered on process improvement rather than improvements to part quality or performance; however, the primary goal for the majority of hybrid-AM processes is to improve part quality and part performance rather than improve processing. Hybrid-AM processes are typically a cyclic process chain and are distinguished from postprocessing operations that do not meet the fully coupled criterion. Secondary processes and energy sources include subtractive and transformative manufacturing technologies, such as machining, remelting, peening, rolling, and friction stir processing (FSP). As interest in hybrid-AM grows, new economic and sustainability tools are needed as well as sensing technologies that better facilitate hybrid processing. Hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way goods are manufactured.

Commentary by Dr. Valentin Fuster

Research Papers

J. Manuf. Sci. Eng. 2018;140(6):061001-061001-10. doi:10.1115/1.4039199.

High-resolution spatial data are essential for characterizing and monitoring surface quality in manufacturing. However, the measurement of high-resolution spatial data is generally expensive and time-consuming. Interpolation based on spatial models is a typical approach to cost-effectively acquire high-resolution data. Conventional modeling methods fail to adequately model the spatial correlation induced by periodicity, and thus their interpolation precision is limited. In this paper, we propose using a Bessel additive periodic variogram model to capture such spatial correlation. When combined with kriging, a geostatistical interpolation method, accurate interpolation performance can be achieved for common periodic surfaces. In addition, parameters of the proposed model provide valuable insights for the characterization and monitoring of spatial processes in manufacturing. Both simulated and real-world case studies are presented to demonstrate the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061002-061002-9. doi:10.1115/1.4039109.

Ultrasonic-assisted machining, which is the application of ultrasonic vibrations to standard or “conventional” machine tools for processes such as drilling, milling, and turning, is a rapidly developing technology aimed at increasing the productivity of machining processes. While a solid foundation is being established through laboratory-based research studies, typically these processes have not yet progressed to fulfill the demanding requirements of the factory floor. The objective of the current work is to transition the ultrasonic-assisted drilling (UAD) process from the laboratory to a production system compatible with automated machining systems. This work details the design and development of an ultrasonic drilling module that has sufficient strength, stiffness, and accuracy for production demands, while maintaining powerful levels of ultrasonic vibrations that result in lowered drilling forces and faster feed rates. In addition, this work will review prior work in UAD, including the development of a module based on a vibration-isolating case using a standard tool holder. Performance of the system is shown to provide thrust force reductions, while maintaining or improving surface finish and drilling accuracy. The results from drilling several materials are presented.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061003-061003-11. doi:10.1115/1.4038570.

This paper formulates the generalized dynamics and stability of thread turning operations with custom multipoint inserts. The closed-loop chip regeneration mechanism is modeled by evaluating the effect of the current vibrations and the vibration marks left from the previous tooth. Using the developed chip discretization method, the dynamic cutting and process damping forces are obtained at each point along the cutting edge by projecting the three-dimensional (3D) vibrations of the tool and workpiece in the direction of local chip thickness. The equation of motion is derived in both physical and modal spaces, and stability is analyzed in frequency domain using Nyquist criterion. An iterative process optimization algorithm has been developed to maximize productivity while respecting machine tool's torque and power limits. Extension of the model to thin-walled workpieces along with the validating experiments on real-scale oil pipes is presented in Part II of this paper.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061004-061004-11. doi:10.1115/1.4039063.

One of the key barriers to widespread adoption of additive manufacturing (AM) for metal parts is the build-up of residual stresses. In the laser-based powder bed fusion process, a laser selectively fuses metal powder layer by layer, generating significant temperature gradients that cause residual stress within the part. This can lead to parts exceeding tolerances and experiencing severe deformations. In order to develop strategies to reduce the adverse effects of these stresses, the stresses first need to be quantified. Cylindrical Nickel Alloy 625 samples were designed with varied outer diameters, inner diameters, and heights. Neutron diffraction was used to characterize the three-dimensional (3D) stress state throughout the parts. The stress state of the parts was generally comprised of tensile exteriors and compressive interiors. Regardless of part height, only the topmost scan height of each part experienced large reductions in axial and hoop stress. Improved understanding of the residual stress trends will aid in model development and validation leading to techniques to reduce negative effects of the residual stress.

Topics: Stress
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061005-061005-10. doi:10.1115/1.4037438.

This paper discusses the investigation of residual stresses developed as a result of mechanical and laser forming processes in commercially pure grade 2 titanium alloy plates as well as the concept of total fatigue stress (TFS). The intention of the study was to bend the plates using the respective processes to a final radius of 120 mm using both processes. The hole drilling method was used to measure residual strains in all the plates. High stress gradients were witnessed in the current research and possible cases analyzed and investigated. The effects of processing speeds and powers used also played a significant role in the residual stress distribution in all the formed plates. A change in laser power resulted in changes to residual stress distribution in the plates evaluated. This study also dwells into how the loads that are not normally incorporated in fatigue testing influence fatigue life of commercially pure grade 2 titanium alloy plates. Also, the parent material was used to benchmark the performance of the two forming processes in terms of stresses developed. Residual stresses developed from the two forming processes and those obtained from the parent material were used. The residual stress values were then added to the mean stress and the alternating stress from the fatigue machine to develop the concept of TFS. This exercise indicated the effect of these stresses on the fatigue life of the parent material, laser and mechanically formed plate samples. A strong link between these stresses was obtained and formulae explaining the relationship were formulated. A comparison between theory and practical application shown by test results is found to be satisfactory in explaining concerns that may arise. The laser forming process is more influential in the development of residual stress, compared to the mechanical forming process. With each parameter change in laser forming, there is a change in residual stress arrangement. Under the influence of laser forming, the stress is more tensile in nature making the laser formed plate specimens more susceptible to early fatigue failure. The laser and mechanical forming processes involve bending of the plate samples and most of these samples experienced a two-dimensional defect, which is a dislocation. The dislocation is the defect responsible for the phenomenon of slip by which most metals deform plastically. Also, the high temperatures experienced in laser forming were one of the major driving factors in bending.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061007-061007-11. doi:10.1115/1.4039118.

Aluminum alloys have been increasingly adopted in the fabrication of automotive body structures as an integral component of mass savings strategy. However, mixed use of dissimilar aluminum alloys, such as sheet metals, castings, and extrusions, poses significant challenges to the existing joining technologies, especially in regard to single-sided joint access. To address this issue, the current study applied the friction stir blind riveting (FSBR) process to join 1.2 mm-thick AA6022-T4 aluminum alloy to 3 mm-thick Aural-2 cast aluminum. A newly developed, robot mounted, servo-driven, FSBR equipment and the procedure using it to make FSBR joints were introduced systematically. The effect of rivet feed rate and spindle speed on joint formation and cross section geometry was investigated, and it was found that a high spindle speed and a low rivet feed rate, i.e., high heat input, are prone to produce good joints, and that low heat input can cause severe problems related to insufficient softening of the sheets. The rivet deformation, especially the notch location on the mandrel relative to the shank has significant influence on lap-shear strength and fracture mode of the final joints. A rivet pull-out fracture mode was observed at higher rivet feed rates and lower spindle speeds and exhibited significantly improved energy absorption capability, i.e., 62% higher compared to traditional blind riveted (BR) joints.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061008-061008-11. doi:10.1115/1.4039197.

Manufacturers consume about 27% of the total electricity in the U.S. and are among the main contributors in the rising electricity demand. End-user electricity demand response is an effective demand side management tool that can help energy suppliers reduce electricity generation expenditures while providing opportunities for manufacturers to decrease operating costs. Several studies on demand response for manufacturers have been conducted. However, there lacks a unified production model that balances production capability degradation, maintenance requirements, and time-of-use (TOU) electricity prices simultaneously such that the interaction between production, maintenance, and electricity costs is considered. In this paper, a cost-effective production and maintenance scheduling model considering TOU electricity demand response is presented. Additionally, an aggregate cost model is formulated, which considers production, maintenance, and demand response parameters in the same function. The proposed models provide manufacturers with tools for implementing feasible and cost-effective demand response while meeting production targets and efficiently allocating maintenance resources. A case study is performed and illustrates that 19% in cost savings can be achieved when using the proposed model compared to solely minimizing the electricity billing cost. In addition, 14% in cost savings can be achieved when using the proposed model compared to a strategy where only the maintenance cost is minimized. Finally, the benefits of demand response driven production and maintenance scheduling under different cost and parameter settings are investigated; where the rated power, production rate, and initial machine production capability show to have the largest impact on the cost effectiveness of implementing demand response.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061009-061009-9. doi:10.1115/1.4038890.

The effect of substrate surface preheating on part distortion in laser cladding is investigated through the experimental results of laser deposited Ti–6Al–4V. In situ temperature and distortion measurements were used to monitor the behavior of the substrates before, during, and after deposition. The resulting trends were analyzed, and it was determined that substrate preheating reduces the amount of distortion accumulated in thin substrates but increases the amount of distortion accumulated in thick substrates. Additionally, substrate preheating was found to cause additional distortion of thick substrates during cool-down after processing had finished. The in situ measurements suggest that the stress relaxation of Ti–6Al–4V at elevated temperatures increases the distortion observed in thick substrates, but has minimal effect on distortion in thin substrates.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061010-061010-18. doi:10.1115/1.4038074.

Dramatic advancements and adoption of computing capabilities, communication technologies, and advanced, pervasive sensing have impacted every aspect of modern manufacturing. Furthermore, as society explores the Fourth Industrial Revolution characterized by access to and leveraging of knowledge in the manufacturing enterprise, the very character of manufacturing is rapidly evolving, with new, more complex processes, and radically, new products appearing in both the industries and academe. As for traditional manufacturing processes, they are also undergoing transformations in the sense that they face ever-increasing requirements in terms of quality, reliability, and productivity, needs that are being addressed in the knowledge domain. Finally, across all manufacturing we see the need to understand and control interactions between various stages of any given process, as well as interactions between multiple products produced in a manufacturing system. All these factors have motivated tremendous advancements in methodologies and applications of control theory in all aspects of manufacturing: at process and equipment level, manufacturing systems level, and operations level. Motivated by these factors, the purpose of this paper is to give a high-level overview of latest progress in process and operations control in modern manufacturing. Such a review of relevant work at various scales of manufacturing is aimed not only to offer interested readers information about state-of-the art in control methods and applications in manufacturing, but also to give researchers and practitioners a vision about where the direction of future research may be, especially in light of opportunities that lay as one concurrently looks at the process, system and operation levels of manufacturing.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061011-061011-9. doi:10.1115/1.4039440.

Oxygen inhibition has been proved capable of reducing the separation force and enabling successful prints in constrained surface vat photopolymerization (CSVP) based three-dimensional (3D) printing processes. It has also been demonstrated as a key factor that determines the feasibility of the newly developed CSVP-based continuous 3D printing systems, such as the continuous liquid interface production. Despite its well-known importance, it is still largely unknown regarding how to control and enhance the oxygen inhibition in CSVP. To close this knowledge gap, this paper investigates the constrained surface design, which allows for continuous and sufficient air permeation to enhance the oxygen inhibition in CSVP systems. In this paper, a novel constrained surface with air-diffusion-channel is proposed. The influences of the air-diffusion-channel design parameters on the robustness of the constrained surface, the light transmission rate, and light intensity uniformity are studied. The thickness of the oxygen inhibition layer associated with the proposed constrained surface is studied analytically and experimentally. Experimental results show that the proposed air-diffusion-channel design is effective in maintaining and enhancing the oxygen-inhibition effect, and thus can increase the solid cross section size of printable parts.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061012-061012-11. doi:10.1115/1.4039441.

Laser engineered net shaping (LENS) has become a promising technology in direct manufacturing or repairing of high-performance metal parts. Investigations on LENS manufacturing of Inconel 718 (IN718) parts have been conducted for potential applications in the aircraft turbine component manufacturing or repairing. Fabrication defects, such as pores and heterogeneous microstructures, are inevitably induced in the parts, affecting part qualities and mechanical properties. Therefore, it is necessary to investigate a high-efficiency LENS process for the high-quality IN718 part fabrication. Ultrasonic vibration has been implemented into various melting material solidification processes for part performance improvements. However, there is a lack of studies on the utilization of ultrasonic vibration in LENS process for IN718 part manufacturing. In this paper, ultrasonic vibration-assisted (UV-A) LENS process is, thus, proposed to fabricate IN718 parts for the potential reduction of fabrication defects. Experimental investigations are conducted to study the effects of ultrasonic vibration on microstructures and mechanical properties of LENS-fabricated parts under two levels of laser power. The results showed that ultrasonic vibration could reduce the mean porosity to 0.1%, refine the microstructure with an average grain size of 5 μm, and fragment the detrimental Laves precipitated phase into small particles in a uniform distribution, thus enhancing yield strength, ultimate tensile strength (UTS), microhardness, and wear resistance of the fabricated IN718 parts.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061013-061013-8. doi:10.1115/1.4039382.

This paper describes some fundamental principles, specific features, and the technological capabilities of a new method of quenching steel surface by turning without separation of chips. The underlying process of this method is a deformational cutting (DC), which is based on the undercutting and deformation of surface layers that remain attached to the workpiece. The energy released in the area of DC is used to heat the undercut layer up to the temperatures of structural and phase transformation of workpiece material. This type of process results into a hardened structure formed at the surface which consists of inclined thin undercut layers tightly packed and stuck together and form a single solid body. The resulting hardened structures achieved in steels workpieces are presented in the paper. The samples hardened by DC showed a higher wear resistance compared to samples with traditional quenching. This paper also describes an estimation of the thermo-physical parameters of the DC process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061014-061014-10. doi:10.1115/1.4039115.

Steel SUS420J1, which is the key material of turbine blade, is generally treated by heat to improve the strength prior to use. And the austenization process at different heating rates would determine the depth and width of heat treatment. In this paper, the austenization temperatures in heat treatment with the heat from induction wire, infrared lamp, and laser are measured, respectively. The effect of heating rate on the austenization temperature has been investigated. The research results show that the measured austenization temperature increases with the heating rate. And this trend is specially enlarged in the heat treatment method with larger gradient of temperature distribution, e.g., laser. The calculated phase transformation threshold shows that negative linear relationship exists between the logarithmic heating rate and the logarithmic austenization threshold for both induction heating and infrared heating, while abnormal relationship exists for laser heating. Thermal finite element analysis (FEA) models are then developed to calculate the temperature distributions in these three heating methods, and the calculated results show that the nonuniform temperature distribution leads to the gap between the measured austenization temperature and that of the material, which also leads to the abnormal variation law of austenization threshold in laser heating. The measured austenization temperature in induction heating method is thought to be the closest to the actual austenization temperature of the material among these three methods. This paper provides a guide for choosing the proper parameters to heat the steel SUS420J1 in hardening.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061015-061015-18. doi:10.1115/1.4039442.

Finish boring is a machining process to achieve the cylinder bore dimensional and geometrical accuracy. The bore cylindricity error sources, including the workpiece thermal expansion and deformation due to cutting and clamping forces, and spindle radial error motion, in finish boring were identified using combined experimental and finite element method (FEM) analysis. Experiments were conducted to measure the workpiece temperature, cutting and clamping forces, spindle error, and bore shape. FEM analysis of the workpiece temperature, thermal expansion, and deformation due to cutting and clamping forces was performed. The coordinate measurement machine (CMM) measurements of the bore after finish boring showed the 5.6 μm cylindricity and a broad spectrum from the second to tenth harmonics. The FEM revealed the effects of workpiece thermal expansion (1.7 μm cylindricity), deformation due to cutting force (0.8 μm cylindricity), and clamping force (1.9 μm cylindricity) on the finished bore and the dominance by the first to third harmonics using the three-jaw fixture. The spindle synchronous radial error motion (3.2 μm cylindricity) was dominated by the fourth and higher order harmonics and matched well with the high (above the fourth) harmonics in CMM measurements (2.9 μm cylindricity). The spindle error was the dominant error source for bore cylindricity in this finish boring study, contributing to about half of the total cylindricity error.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061016-061016-8. doi:10.1115/1.4039493.

Bipolar tissue hemostasis is a medical procedure where high frequency alternating current is applied to biological tissue for wound closing and blood vessel sealing through heating. The process is often performed with a set of laparoscopic forceps in a minimal invasive surgery to achieve less bleeding and shorter recovery time. However, problems such as tissue sticking, thermal damage, and seal failure often occur and need to be solved before the process can be reliably used in more surgical procedures. In this study, experiments were conducted to examine process parameters and the dynamic behavior of bipolar heating process through electrical impedance measurements. The effects of electrode compression level, heating power, and time are analyzed. Heating energy and bio-impedance are evaluated for quality prediction. Tissue sticking levels were correlated to the size of denatured tissue zone. It is found that tissue denaturation starts from the center of the heated region. Dynamic impedance reveals the stages of tissue hemostasis process. However, it is strongly affected by the compression level and heating power. Existing criteria for quality prediction and control using the heating energy and minimal impedance are not reliable. The size of denatured tissue zone can be predicted with the heating energy; however, the prediction is strongly dependent on the compression level. To avoid sticking, a low power and low compression level should be used for the same denatured tissue zone size.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(6):061017-061017-14. doi:10.1115/1.4039648.

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.

Commentary by Dr. Valentin Fuster

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