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Review Article

J. Manuf. Sci. Eng. 2018;140(12):120801-120801-19. doi:10.1115/1.4041325.

This review paper presents a comprehensive analysis of period-n (i.e., motion that repeats every n tooth periods) bifurcations in milling. Although period-n bifurcations in milling were only first reported experimentally in 1998, multiple researchers have since used both simulation and experiment to study their unique behavior in milling. To complement this work, the authors of this paper completed a three year study to answer the fundamental question “Is all chatter bad?”, where time-domain simulation and experiments were combined to: predict and verify the presence of period-2 to period-15 bifurcations; apply subharmonic (periodic) sampling strategies to the automated identification of bifurcation type; establish the sensitivity of bifurcation behavior to the system dynamics, including natural frequency and damping; and predict and verify surface location error (SLE) and surface roughness under both stable and period-2 bifurcation conditions. These results are summarized. To aid in parameter selection that yields period-n behavior, graphical tools including Poincaré maps, bifurcation diagrams, and stability maps are presented.

Commentary by Dr. Valentin Fuster

Research Papers

J. Manuf. Sci. Eng. 2018;140(12):121001-121001-7. doi:10.1115/1.4041245.

Grain depth-of-cut, which is the predominant factor determining the surface morphology, grinding force, and subsurface damage, has a significant impact on the surface quality of the finished part made of hard and brittle materials. When the existing analytical models are used to predict the gain depth-of-cut in ultra-precision grinding process of silicon wafer, the results obtained become unreasonable due to an extremely shallow grain depth-of-cut, which is inconsistent with the theory of the contact mechanics. In this study, an improved model for analyzing the grain depth-of-cut in ultra-fine rotational grinding is proposed, in which the minimum grain depth-of-cut for chip formation, the equivalent grain cutting tip radius, elastic recovery deformation in cutting process, and the actual number of effective grains are considered in the prediction of the ultrafine rotational grinding of brittle materials. The improved model is validated experimentally and shows higher accuracy than the existing model. Furthermore, the sensitivity of the grain depth-of-cut to three introduced factors is analyzed, presenting the necessity of the consideration of these factors during the prediction of grain depth-of-cut in ultrafine grinding.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121002-121002-7. doi:10.1115/1.4041247.

Impact welding is a material processing technology that enables metallurgical bonding in the solid state using a high-speed oblique collision. In this study, the effects of thickness of the flier and collision angle on weld interface morphology were investigated through the vaporizing foil actuator welding (VFAW) of AA1100-O to AISI 1018 Steel. The weld interfaces at various controlled conditions show wavelength increasing with the flier thickness and collision angle. The AA1100-O flier sheets ranged in thickness from 0.127 to 1.016 mm. The velocity of the fliers was directly measured by in situ photon Doppler velocimetry (PDV) and kept nearly constant at 670 m/s. The collision angles were controlled by a customized steel target with a set of various collision angles ranging from 8 deg to 28 deg. A numerical solid mechanics model was optimized for mesh sizes and provided to confirm the wavelength variation. Temperature estimates from the model were also performed to predict local melting and its complex spatial distribution near the weld interface and to compare that prediction to experiments.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121003-121003-11. doi:10.1115/1.4041248.

Although the effectiveness of spindle speed variation (SSV) method in chatter suppression has been extensively reported, the determination of optimal SSV parameters remains a challenge owing to the difficulties in obtaining accurate modal parameters especially under varying cutting conditions. This paper proposes a closed-loop SSV cutting system to suppress chatter in turning. The dimensionless SSV amplitude is adaptively adjusted with a model-free controller to accommodate change of the chatter level. The wavelet packet entropy (WPE) is computed online to evaluate quantitatively the machining state, and a predetermined chatter threshold is used to calculate the controller input. Energy-based analysis of SSV parameters effect on chatter shows that the amplitude is the more dominant parameter than the frequency. Then we introduce the scheme of the proposed chatter suppression system, where the Bootstrap method is adopted to determine the threshold value. Next, the feasibility of the proposed method for chatter suppression is tested by simulations with different cutting depths. Finally, comparisons of experimental results verify the conclusion of theoretical analysis about the effect of SSV parameters, and two cutting tests with diverse activating strategies are performed to validate the effectiveness of the proposed system for chatter suppression in turning.

Topics: Machining , Chatter , Cutting
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121004-121004-19. doi:10.1115/1.4041250.

The regenerative milling chatter is usually regarded as some kind of bifurcation or chaos behaviors of the machining system. Although several chatter patterns such as the secondary Hopf, the period doubling, and the cyclic fold bifurcations were once reported, their relationships with cutting conditions remain undiscovered. This paper aims to uncover the dynamic mechanism of distinct chatter behaviors in general milling scenarios. First, two complementary methods, i.e., the generalized Runge–Kutta method and the time-domain simulation technique, are presented to jointly study the distribution rule of chatter patterns in stability lobe diagrams for milling processes with general flute-spacing tools considering runout. The theoretical predictions are validated by one published example and two cutting experiments under three different cutting conditions. Furthermore, the cutting signal characteristics and cutting surface topography of distinct chatter patterns are analyzed and compared in detail. On this basis, this paper studies the joint influences of cutting parameters, tool geometries, and runout on regenerative chatter behaviors with the proposed methods.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121005-121005-9. doi:10.1115/1.4041181.

Direct thermal imprinting of nanostructures on glass substrates is reliable when manufacturing net-shaped glass devices with various surface functions. However, several problems are recognized, including a long thermal cycle, tedious optimization, difficulties in ensuring high level replication fidelity, and unnecessary thermal deformation of the glass substrate. Here, we describe a more sustainable and energy efficient method for direct thermal imprinting of nanostructures onto glass substrates; we use silicon mold transparent to infrared between 2.5 and 25 μm in wavelength combined with CO2 laser scanning irradiation. The glass strongly absorbed the 10.6 μm wavelength irradiation, triggering substantial heating of a thin layer on the glass surface, which significantly enhanced the filling of pressed glass material into nanostructured silicon mold cavities. For comparison, we conducted conventional direct glass thermal imprinting experiments, further emphasizing the advantages of our new method, which outperformed conventional methods. The thermal mass cycle was shorter and the imprint pattern quality and yield, higher. Our method is sustainable, allowing more rapid scalable fabrication of glass nanostructures using less energy without sacrificing the quality and productivity of the fabricated devices.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121006-121006-12. doi:10.1115/1.4041179.

Computational models for simulating physical phenomena during laser-based powder bed fusion additive manufacturing (L-PBF AM) processes are essential for enhancing our understanding of these phenomena, enable process optimization, and accelerate qualification and certification of AM materials and parts. It is a well-known fact that such models typically involve multiple sources of uncertainty that originate from different sources such as model parameters uncertainty, or model/code inadequacy, among many others. Uncertainty quantification (UQ) is a broad field that focuses on characterizing such uncertainties in order to maximize the benefit of these models. Although UQ has been a center theme in computational models associated with diverse fields such as computational fluid dynamics and macro-economics, it has not yet been fully exploited with computational models for advanced manufacturing. The current study presents one among the first efforts to conduct uncertainty propagation (UP) analysis in the context of L-PBF AM. More specifically, we present a generalized polynomial chaos expansions (gPCE) framework to assess the distributions of melt pool dimensions due to uncertainty in input model parameters. We develop the methodology and then employ it to validate model predictions, both through benchmarking them against Monte Carlo (MC) methods and against experimental data acquired from an experimental testbed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121007-121007-9. doi:10.1115/1.4041480.

A three-dimensional (3D) inner surface inspection system is developed in this research based on circle-structured light, which is an improved laser triangulation method. A conical reflector is used to reflect the laser and generate radial laser plane that is called circle-structured light, and a CCD camera is used to capture the light stripe on the inner surface. Then, the 3D coordinates of points on the light stripe are calculated through laser triangulation algorithm. Compared with existing inner surface measurement systems, this research takes assembly errors and refraction distortion into consideration and proposes a laser plane mathematical model with four degrees-of-freedom along with corresponding flexible laser plane calibration technique based on binocular vision that is easy to operate. The proposed inspection system calibrated by proposed algorithm performs well in diameter measurement experiment, in which the absolute error is superior to 3 μm, and defect detecting experiment, in which the defect resolution is superior to 0.02 mm. Moreover, the system also performs well in straightness and roundness evaluation. Experiments indicate that this system is applicable in inner surface measurement and inspection, and the calibration method is accurate and easy to operate.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121008-121008-10. doi:10.1115/1.4041478.

Ball-end milling is widely used in five-axis high-speed machining. The abrupt change of tool orientations or rotary axes movements will scrap the workpiece. This research presents a smoothing method of rotary axes movements within the feasible domains of the rotary-axes space. Most existing smoothing methods of tool orientation or rotary axes movements employ the Dijkstra's shortest path algorithm. However, this algorithm requires extensive computations if the number of the cutter locations is large or the sampling resolution in the feasible regions is high. Moreover, jumps in the results obtained with the Dijkstra's shortest path algorithm may occur, because the optimization problem has to be converted from a continuous problem into a discrete problem when using this algorithm. The progressive iterative approximation (PIA) method incorporating smoothness terms is established as a gradient-based optimization method to smooth the rotary axes movements in this research. Then a gradient-based differential evolution (DE) algorithm, combining the global exploration feature of the DE algorithm and the local searching ability of the gradient-based optimization method, is developed to solve the smoothing model. The validity and effectiveness of the proposed approach are confirmed by numerical examples.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121009-121009-12. doi:10.1115/1.4041420.

Due to the enclosed chip evacuation space in deep hole drilling process, chips are accumulated in drill flutes as drilling depth increases, resulting in the increase of drilling torque and lead to drill breakage. Peck drilling is a widely used method to periodically alleviate the drilling torque caused by chip evacuation; the drilling depth in each step directly determines both drill life and machining efficiency. The existing drilling depth optimization methods face problems including low accuracy of the prediction model, the hysteresis of signal diagnosis, and onerous experiments. To overcome these problems, a novel drilling depth optimization method for peck drilling based on the iterative learning optimization is proposed. First, the chip evacuation torque coefficients (CETCs) are introduced into the chip evacuation torque model to simplify the model for learning. Then, the effect of chip removal process in peck drilling on drilling depth is analyzed. The extended depth coefficient by chip removal (EDCbCR) is introduced to develop the relationship between the extended depth in each drilling step and drilling depth. On the foundation of the modeling above, an iterative learning method for drilling depth optimization in peck drilling is developed, in which a modified Newton's method is proposed to maximize machining efficiency and avoid drill breakage. In experiments with different cutting parameters, the effectiveness of the proposed method is validated by comparing the optimized and measured results. The results show that the presented learning method is able to obtain the maximum drilling depth accurately with the error less than 10%.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121010-121010-12. doi:10.1115/1.4041496.

An accurate analytical method is normally the preferred choice in engineering practice since this approach usually does not require additional software and can be applied for different situations. A number of analytical methods have been proposed for the air bending process, however, none of them has the capacity to deal with large radius bending. Large radius bending is characterized by a high ratio of the punch radius to the die opening and it is often applied for high-strength steels because of their limited bendability. This bending mode is used to fulfill the imposed level of maximum strain during the forming process. This contribution develops an analytical solution based on the assumption that the bent plate profile can be represented by two straight lines and a circular segment. Three different hardening laws—linear, Swift, and Aerens—are used for the bending moment calculation. Unit moment measurements are used in order to avoid extrapolation of hardening curves obtained by tensile testing. The model is compared with a wide range of experiments using the coefficient of determination, relative and absolute average errors, in addition to the mean standard error. The analytical prediction based on the circular approximation is found to be an accurate and robust tool for the calculation of the major bending characteristics for large radius air bending of high-strength steels.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121011-121011-15. doi:10.1115/1.4041327.

Owing to its outstanding physical and mechanical properties, polycrystalline diamond (PCD) is ideal for cutting titanium alloys. However, the high temperature and stress caused by the interaction of tool surface and chip flow lead to different types of wear. This paper investigates the wear mechanisms of PCD tools in three different tribological regions: sticking zone, transition zone, and sliding zone, when machining titanium alloy Ti6Al4V. The tribological behavior of PCD tools in the wear processes were analyzed through both experiments and theoretical calculations. Analytical models of stresses and temperature distribution were developed and validated by turning experiments. PCD tools, consisting of diamond grains of different sizes: CTB002 (2 μm), CTB010 (10 μm), and CTM302 (2–30 μm), were used to cut Ti6Al4V at the normal cutting speed of 160 m/min and high cutting speed 240 m/min. It was found that adhesion, abrasion and diffusion dominated the wear process of PCD tools in different worn regions. Microscopic characters showed that the wear mechanisms were different in the three tribological regions, which was affected by the distribution of stresses and temperature. “Sticking” of workpiece material was obvious on the cutting edge, abrasion was severe in the transition zone, and adhesion was significant in the sliding zone. The shapes and morphological characters in different worn regions were affected by the stresses distribution and the types of PCD materials.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121012-121012-8. doi:10.1115/1.4041328.

The dimensional accuracy of fused deposition modeling (FDM) machines is dependent on errors caused by processing parameters and machine motions. In this study, an integrated error model combining these effects is developed. Extruder temperature, layer thickness, and infill density are selected as parameters of this study for three FDM machines, namely, Flashforge Finder, Ultimaker 2 go, and XYZ da Vinci 2.0 Duo. Experiments have been conducted using Taguchi method and the interactions between processing parameters are analyzed. Based on the dimensional deviations between fabricated parts and the computer aided design (CAD) geometry, a set of coefficients for the integrated error model are calculated to characterize each machine. Based on the results of the integrated error model, the original CAD geometry is optimized for fabrication accuracy on each machine. New parts are fabricated using the optimized CAD geometries. Through comparing the dimensional deviations of parts fabricated before and after optimization, the effectiveness of the integrated error model is analyzed and demonstrated for the three FDM machines.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121013-121013-14. doi:10.1115/1.4041329.

The necking behavior of sheet metals under stretch-bending process is a challenge for the forming limit prediction. State-of-the-art forming limit curves (FLCs) allow the prediction under the in-plane stretching but fall short in the case under out-of-plane loading condition. To account for the bending and straightening deformation when sheet metal enters a die cavity or slide along a radius, anisotropic hardening model is essential to reflect the nonproportional loading effect on stress evolution. This paper aims to revisit the M-K analysis under the stretch-bending condition and extend it to accommodate both distortionless and distortional anisotropic hardening behavior. Furthermore, hardening models are calibrated based on the same material response. Then the detailed comparison is proposed for providing better insight into the numerical prediction and necking behavior. Finally, the evolution of the yield surface and stress transition states is examined. It is found that the forming limit prediction under stretch-bending condition through the M-K analysis strongly depends on the employed anisotropic hardening model.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121014-121014-10. doi:10.1115/1.4041479.

The present research aims to study the influence of equal channel angular extrusion (ECAE) parameters (die channel angle, die corner angle, and friction coefficient) on cracking and fracture tendency. For this type of analysis, a MATLAB code integrated with finite element Abaqus/Explicit model was developed and used. A parametric study is done to investigate how the damage tendency varies with changes of ECAE parameters. The distribution of the damage factor based on Cockcroft–Latham equation for different channel angles, corner angles, and friction coefficients is depicted. It is observed that the appearance of cracks on the upper surface is more likely to occur than on the lower surface. The reduction in friction coefficient does not guarantee minimum damage tendency. Finally, the optimum parameters for reducing the fracture tendency in ECAE are presented.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):121015-121015-16. doi:10.1115/1.4041426.

The traditional stability analysis by only considering cutting depth-spindle speed lobe diagram is appropriate for parameters optimization and efficiency improvement of the five-axis ball-end milling. However due to the complicated cutter-workpiece engagement (CWE) of bull-nose end cutter in five-axis milling, the maximal cutting depth may not produce the maximal material removal rate (MRR). Thus, the traditional stability analysis is not suitable for the five-axis bull-nose end milling in parameters optimization, and this paper presents a new stability analysis method to analyze the effect of tool orientation on machining efficiency for five-axis bull-nose end milling. In the establishing of stability prediction model, coordinate transformation and vector projection method are adopted to identify the CWE and dynamic cutting thickness, and the geometrical relationship of frequency response function (FRF) coordinate system and cutting force coordinate system with variable tool orientation is derived to establish the conversion of FRF and cutting force in stability equation. Based on the CWE sweeping, the cutting area along the feed direction is calculated to realize the critical MRR analysis in the stability model. Based on the established stability prediction model, the effects of tool orientation on critical cutting depth and MRR considering the chatter constraint are analyzed and validated by the cutting experiments, respectively. The lead-tilt diagram, which not only gives the boundary of stability region but also describes the contour line for MRR, is proposed for the further tool orientation optimization.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Manuf. Sci. Eng. 2018;140(12):124501-124501-8. doi:10.1115/1.4041243.

Rail grinding has been widely recognized as an essential measure in routine maintenance of railway network in the world. Compared with other technologies, the emerging abrasive belt grinding process for direct rail maintenance rather than limited polishing finish has shown the convincing potential to improve metal removal rate and surface quality. However, the influencing mechanism of the rubber wheel on contact pressure and metal removal for the corrugated rails is yet unknown. This paper develops a contact pressure model to obtain the boundary curve and the stress distribution of the contact zone between the rubber wheel with concave peripheral surface and the rail surface with corrugation. Based on this, the metal removal model is subsequently established through the abrasive processing theory. Finite element (FE) simulations and grinding tests are finally implemented. Results confirm the above-mentioned theoretical models of contact pressure and metal removal and show the significant influences of the rubber wheel's feature on contact pressure and metal removal.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2018;140(12):124502-124502-7. doi:10.1115/1.4041477.

It is environmentally friendly to use water-based emulsion instead of the oil when cold drawing Al alloy production. In this research, adopting specially prepared water-based emulsion, contact angles and tribological properties of as-selected multilayer diamond films are clarified. The contact angle on diamond film is much smaller than that on WC-Co with the same surface roughness, and tribological behaviors of the diamond film are much better. The effects of surface roughness Ra of the film, lubrication, and water content in the emulsion W are studied, indicating that the contact angle increases with W or Ra. For the diamond film, lower Ra is beneficial for reducing the coefficient of friction (COF), Al alloy ball wear and oxidation, while lower W contributes to the reduction of the COF, ball oxidation, and coated disk wear. Finally, high-speed drawing of high-quality 6021 Al alloy wires (AWs) is accomplished, proving that using coated drawing dies, the water-based emulsion (W < 80 vol %) can totally replace oil, and coated dies under the water-based emulsion lubrication present much elongated lifetime and can guarantee the production quality, compared to uncoated ones under the oil lubrication, in spite of slightly severer wire oxidation.

Commentary by Dr. Valentin Fuster

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