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J. Manuf. Sci. Eng. 2019;141(9):091001-091001-15. doi:10.1115/1.4043978.

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

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091002-091002-14. doi:10.1115/1.4043982.

Studies have indicated that reducing the process energy demand is as important as improving the energy conversion efficiency to make manufacturing equipment more energy efficient. However, little work has been done to understand the energy demand characteristics of the widely employed drawing process. In this paper, the energy demand of the cylindrical drawing process under a range of operating parameters was measured and analyzed. Since any energy saving efforts should not have negative effects on the product quality, the forming quality of the drawn part indicated by the maximum thinning and thickening ratios and variation of thickness was also considered. To identify the main contributors to energy demand and forming quality, two sets of experiments were designed based on the Taguchi method. The first set of experiments include three parameters (i.e., punch velocity, blank holder force, and drawn depth) at three levels, while the second set of experiments only include two factors (i.e., punch velocity and blank holder force) at three levels due to their impacts on the forming quality. Analysis of variance (ANOVA) and analysis of means (ANOM) were then used to analyze the experimental results. Finally, grey relational analysis (GRA) was used to reveal the correlation between the forming quality and the process energy. Results show that the mean thickness variation has the strongest relational grading with the process energy, which suggests that the process energy can be used as an effective indicator to predict mean thickness variation of the drawn part. The identified characteristics of the process energy and the forming quality can be used to select process parameters for reduced energy demands of drawing processes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091003-091003-12. doi:10.1115/1.4043979.

Laser micromachining has several advantages such as the capability of flexibly producing very small features in both conductive and nonconductive materials. However, it may often suffer from induced defects, such as debris deposition on workpieces. To improve laser micromachining, a novel machining process, called “ultrasound-assisted water-confined laser micromachining” (UWLM), was proposed by the corresponding author. The ultrasound during UWLM can be applied through different approaches, such as an ultrasonic horn or a high-intensity focused ultrasound (HIFU) transducer, which can be called horn- and HIFU-based UWLM, respectively. This is the first paper (to the authors’ best knowledge) reporting experimental studies on microhole drilling using the novel HIFU-based UWLM process. In this study, drilled workpieces have been characterized; and in situ time-resolved shadowgraph imaging and pressure measurement during the UWLM process have been performed. Under the investigated conditions, it has been found that the microholes drilled by HIFU-based UWLM under suitable conditions appear reasonably clean without significant debris depositions often seen for a nanosecond (ns) laser ablation in air. The UWLM process can produce much larger average ablation depths per pulse than laser ablation in water without ultrasound (e.g., for copper, the former depth can be up to more than six times the latter). The study has revealed one important mechanism for the enhanced ablation depth, which is introduced in more details in the paper.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091004-091004-7. doi:10.1115/1.4044101.

In this paper, the impact of recycling and remanufacturing on the behavior of low-density polyethylene/multi-walled carbon nanotube (LDPE/MWCNT) composites is investigated. LDPE/MWCNT composites with 0.1–5 wt%, previously manufactured by injection molding, were mechanically recycled and remanufactured by injection molding and 3D filament extrusion, and the rheological, electrical, and mechanical properties were analyzed and compared with those of virgin composites under the same conditions. Experimental results demonstrate that the recycled LDPE/MWCNT composites have similar rheological, electrical, and mechanical properties as that of virgin composites, if not better. Therefore, the recycled LDPE/MWCNT composites have a great potential for being used in engineering applications, while reducing the environmental impact.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091005-091005-16. doi:10.1115/1.4044105.

Recent efforts in smart manufacturing (SM) have proven quite effective at elucidating system behavior using sensing systems, communications, and computational platforms, along with statistical methods to collect and analyze the real-time performance data. However, how do you effectively select where and when to implement these technology solutions within manufacturing operations? Furthermore, how do you account for the human-driven activities in manufacturing when inserting new technologies? Due to a reliance on human problem-solving skills, today’s maintenance operations are largely manual processes without wide-spread automation. The current state-of-the-art maintenance management systems and out-of-the-box solutions do not directly provide necessary synergy between human and technology, and many paradigms ultimately keep the human and digital knowledge systems separate. Decision makers are using one or the other on a case-by-case basis, causing both human and machine to cannibalize each other’s function, leaving both disadvantaged despite ultimately having common goals. A new paradigm can be achieved through a hybridized system approach—where human intelligence is effectively augmented with sensing technology and decision support tools, including analytics, diagnostics, or prognostic tools. While these tools promise more efficient, cost-effective maintenance decisions and improved system productivity, their use is hindered when it is unclear what core organizational or cultural problems they are being implemented to solve. To explicitly frame our discussion about implementation of new technologies in maintenance management around these problems, we adopt well-established error mitigation frameworks from human factors experts—who have promoted human–system integration for decades—to maintenance in manufacturing. Our resulting tiered mitigation strategy guides where and how to insert SM technologies into a human-dominated maintenance management process.

Topics: Maintenance , Errors
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091006-091006-8. doi:10.1115/1.4044104.

For the scalable production of commercial products based on vertically aligned carbon nanotubes (VACNTs), referred to as CNT forests, key manufacturing challenges must be overcome. In this work, we describe some of the main challenges currently facing CNT forest manufacturing, along with how we address these challenges with our custom-built rapid thermal processing chemical vapor deposition (CVD) reactor. First, the complexity of the multistep processes and reaction pathways involved in CNT growth by CVD limits the control on CNT population growth dynamics. Importantly, gas-phase decomposition of hydrocarbons, formation of catalyst nanoparticles, and catalytic growth of CNTs are typically coupled. Here, we demonstrated a decoupled recipe with independent control of each step. Second, significant run-to-run variations plague CNT growth by CVD. To improve growth consistency, we designed various measures to remove oxygen-containing molecules from the reactor, including air baking between runs, dynamic pumping down cycles, and low-pressure baking before growth. Third, real-time measurements during growth are needed for process monitoring. We implement in situ height kinetics via videography. The combination of approaches presented here has the potential to transform lab-scale CNT synthesis to robust manufacturing processes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091007-091007-14. doi:10.1115/1.4044007.

In industrial production, the roller trace design is still based on the trial-and-error method that is more like an art than science. In this paper, we establish the mathematical model of the involute curve roller trace and adopted the forming clearance compensation in the attaching-mandrel process. The backward pass roller trace is optimized to avoid the roller interference due to blank springback. The spinning simulation model of seven forming passes is set up and verified by the experiments with superalloy GH3030. The wall thickness, the strain distribution, and the tool forces are analyzed. The results show that the forming clearance compensation can greatly shorten the forming time and enhance the production efficiency and saving energy. The metal accumulates at the edge of the blank, and the maximum thinning zone appeared near the edge and is prone to crack. In the straightening pass, the tool forces of both the roller and the mandrel are larger than those in the other passes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091008-091008-9. doi:10.1115/1.4044035.

The objective of this work is to fabricate thermocouples directly on the rake face of a commercially available tungsten carbide cutting insert for accurately measuring the tool–chip interface temperature during metal cutting. The thermocouples are sputtered onto the cutting insert using micromachined stencils, are electrically isolated with layers of Al2O3, and receive a top coating of AlTiN for durability. The result is a nonsacrificial thermocouple junction that is approximately 1.3 µm below the rake face of the tool and 30 µm from the cutting edge. Experimental and numerical characterization of the temperature measurement accuracy and response time are presented. The instrumented cutting tool can capture the tool–chip interface temperature transients at frequencies of up to 1 MHz, which enables the observation of serrated chip formation and adiabatic shear events. Temperature measurements from oblique machining of 4140 steel are presented and compared with three-dimensional, transient numerical simulations using finite element analysis, where cutting speed and feed are varied. This method of measuring the tool–chip interface temperature shows promise for future research and smart manufacturing applications.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2019;141(9):091009-091009-15. doi:10.1115/1.4044098.

Advanced high strength steels (AHSS) and ultra-high strength steels (UHSS) have been increasingly implemented by the automotive industry for better crashworthiness and fuel economy. However, these steels are often sensitive to the trimmed edge cracking. The objective of the present paper is to study the sheared edge of ultra-high strength dual-phase steel, DP980, in mechanical trimming and hole punching by sheared edge quality assessment, stretchability, and hole expansion tests as well as finite element analysis. Furthermore, the mechanism of fracture propagation in trimming and hole punching processes of DP980 was discussed. Rather a unique fracture mechanism was observed for trimming of DP980 steel leading to the burr removal at the final stage of the trimming process. Finite element analysis revealed that, under very large clearances, a secondary crack initiates from the edge of the lower tool, and the primary propagated crack turns toward it simultaneously. Intersecting of these two cracks leads to the total separation and leaves the edge of the trimmed part with a broken burr. Fracture observation of trimmed specimens revealed that crack initiation sites under tension moved from the middle of the trimmed surface toward the burr tip with increasing the clearance. This study demonstrates the importance of stretchability tests for designing the stamping dies as well as a reliable finite element simulation for characterizing the material behavior during the shearing process.

Commentary by Dr. Valentin Fuster

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