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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

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

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