A study of regularly spaced shear bands and morphology of serrated chip formation in microcutting process

doi:10.1016/j.scriptamat.2010.03.059

Scripta Materialia

Volume 63, Issue 2, July 2010, Pages 227-230

https://doi.org/10.1016/j.scriptamat.2010.03.059 Get rights and content

Serrated chips with regularly spaced shear bands (RSSBs) are commonly observed in the microcutting of non-ferrous materials with diamond tools. This paper investigates the chip morphology with RSSBs produced in the orthogonal microcutting of cold-rolled brass. The reasons why Merchant’s model and its modified versions fail whenever RSSBs evolve are critically discussed. This paper proposes a generalized model based on the theory of elastic strain induced shear bands where Merchant’s model and its derivatives are construed as special cases.

References (11)

H. Wang et al.
Int. J. Mach. Tools Manuf.
(2010)
W.B. Lee et al.
Scr. Mater.
(1999)
C. Duan et al.
Scr. Mater.
(2005)
M.Q. Jiang et al.
Acta Mater.
(2009)
A. Molinari et al.
Int. J. Mech. Sci.
(2008)

There are more references available in the full text version of this article.

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The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the chip. A pronounced reduction of machining forces and chip thickness was observed with mechanochemical effect during microcutting. Furthermore, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) observations were performed on the chips and shear bands. The result reveals much coarser grains (24.6 μm in size) in the surfactant-affected chip than that in the surfactant-free chip (13.5 μm). Different grain orientations are induced by microcutting. {100}<001> and {110}<112> grain orientations are majority for surfactant-free chip, and {110}<001> and {100}<110> dominate most for all grain orientations for surfactant-affected chip. Additionally, since less localized shear strain and lower temperature are generated inside the shear band with mechanochemical effect, almost no recrystallization phenomena can be observed in this region. TEM analysis shows that fewer subgrains and dislocations could be observed inside the shear band of the surfactant-affected chip in comparison with the surfactant-free chip. Based on the high-resolution transmission electron microscopic (HRTEM) observations, dislocations were observed at the atomic scale. The results show that the main dislocation motion mode in shear bands of surfactant-free and surfactant-affected chips are dislocation climb and dislocation glide, respectively.
A new geometric model of serrated chip formation in high-speed machining
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Then, the specific geometry of serrated chip can be determined by using those geometric characterization parameters. Wang et al. [23] observed shear band and regular distribution in serrated chips. Where, the spacing of shear bands affected the fluctuation of the cutting force, the temperature rise and cutting energy.
The geometry of serrated chip is of paramount importance to the analysis of physical and thermal phenomena in chip formation process, and it can affect tool fatigue life, surface finish and geometric accuracy of the machining part. This paper presents a novel geometry model of serrated chip segment based on chip formation and cutting force in metal cutting by considering the difference between deformation of shear band and primary shear zone. Where, focusing on the high-speed machining, it key points about the geometry of chip segment, shear band angle, secondary shear angle, third shear angle (curvature angle of second shear band), the strain and its rate, and their evolutions in chip formation process are developed, respectively. Finally, the experimental and simulated instances can verify the proposed method. The results can show that this proposed model having a high accuracy can effectively reflect the evolution of chip segment. The shear angle is silent increased with increase of feed rate, while the difference between shear angles is decreasing with increase of feed rate. While the shear strain is increasing with the increasing feed rate and decreasing with increase of cutting depth, the cutting velocity can enlarge the difference. The critical shear strain rate and cutting velocity for the disappear of crack in chip for feed rate of 0.117mm, 0.14mm and 0.187mm are 1.566e⁵1/s and 32.71m/s, 1.486e⁵1/s and 35.98m/s, 1.279e⁵1/s and 39.25m/s, respectively, which decreased with increased of feed rate.
Social network analysis for optimal machining conditions in ultra-precision manufacturing
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Ultra-precision machining (UPM) technology is extensively applied to manufacture top quality products with high precision level and complicated geometry. As complicated machining factors affect the surface quality of machined components in UPM, large numbers of experiments for understanding the influences from particular machining factors are needed, leading overestimate or underestimate of significance of machining factors at certain machining conditions and raising of experimental cost. For these reasons, a crucial approach is urged to adapt for providing a fast track to an optimal machining condition. In this study, social network analysis (SNA) is introduced firstly to develop UPM network, which the network shows the relationship between dominant machining factors in UPM. A complicated UPM network containing interdependencies between each machining factor is generated by SNA. The determinations of network metrics in the UPM network support the selection of optimal machining factors under various machining conditions. Furthermore, the constructed UPM network using SNA provides the complete framework of dependencies in UPM for well predicting the machining outcomes when particular machining factors are adjusted in practical situations. The study contributes to offering a detail guideline for constructing machining strategies or experimental plans to efficiently achieve desired machining outcomes.
Current understanding of surface effects in microcutting
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The phenomenon reflected differences in the stress-strain curves where shear testing displayed indications of the approaching failure point and tensile testing abruptly ended without warning. This perspective of shearing can be applied to the shearing process during chip formation [115] to explain the continuity in material flow under external pressures instead of submission to brittle failure. It is good to note that the hydrostatic pressure has a large influence on the mechanical properties on various types of engineering materials such as plastics [116,117] and metals [118,119].
Machining processes have made technological leaps in achieving ultraprecision material removal and surface finishing at the submicrometric scale. At this level of precision, size effects have dominated machining investigations while surface effects have often been overlooked. The majority of micromachining research works are ignorant of the potential implications that these phenomena bring as the characteristic length approaches the ultraprecision machining level. In this review, physicochemical and physical surface effects are discussed by examining the theoretical developments and applications of each phenomenon in machining. These effects include the Rehbinder effect, solid coatings, and extrusion-cutting. Substantial mesoscopic analyses have been performed on metals with the Rehbinder effect and extrusion-cutting but the inherently different material deformation characteristics in microcutting invite further investigations. While solid coating effects have been reported at the microscale, its discovery questions the influence of other inevitably formed surface coatings (i.e. oxide layers). To these ends, key areas for future research in the microcutting of engineering metals and brittle materials are proposed in addition to the integration with unavoidable size effects. As machining technology and material characterization techniques progress into the nanometric scale, there is a need to rally efforts towards the embrace of surface phenomena in microcutting.
Investigation on the microstructure and machinability of ASTM A131 steel manufactured by directed energy deposition
2020, Journal of Materials Processing Technology
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When the stress in the shear band exceeds the limit of elastic deformation, the relative movement between the chip and workpiece happens and the serrated chips are produced. A theoretical model has been developed in our previous works by Wang et al. (2010a) and Wang et al. (2010b). Grain size is one of the influencing factors on the location of relative movement.
This paper investigates the microstructure and machinability of ASTM A131 steel parts manufactured by directed energy deposition (DED). The surface finish of A131 steel parts is improved by a combination of additive manufacturing (AM) and subtractive manufacturing technologies. Microstructures of the DED and hot-rolled (HR) samples are studied. A large amount of acicular martensite appears on the top face (DED-top) and side face (DED-side) of the DED samples which are substantially different as compared to the ferrite + pearlite microstructure commonly observed in HR samples. The measured microhardness on the DED-top face is over 30% higher than that of the HR samples. As a major post-processing method for AM, milling operation was conducted at varying cutting speeds. Cutting force, tool wear, chip formation, surface roughness, and microhardness before/after milling were investigated to evaluate the machinability of additively manufactured parts. It is evident that the microhardness of both DED-top and DED-side samples change slightly after milling. The surface roughness (Ra) can be greatly modified from >20 μm to <1 μm by the post-processing. The DED-side sample yields the highest cutting forces due to the interference between the cutting tool and a large number of melt-pool boundaries that restrict material flow. Tool wear tends to escalate in the machining of the DED samples. Moreover, the DED samples present a lower chip curvature than HR samples with much less burr formation. In addition, the chip morphology analysis indicates that DED samples have shorter chip serration spacing and continuous chip formation. Comprehensive analysis indicates that DED enhances the machinability of the work material ASTM A131 steel.
Crystal plasticity finite element modeling and simulation of diamond cutting of polycrystalline copper
2019, Journal of Manufacturing Processes
Microstructural-related deformation behavior leads to anisotropic machining characteristics of polycrystalline materials. In the present work, we develop a crystal plasticity finite element model of ultra-precision diamond cutting of polycrystalline copper, aiming to evaluate the influence of grain boundaries on the correlation between microscopic deformation behavior of the material and macroscopic machining results. The crystal plasticity dealing with the anisotropy of polycrystalline copper is implemented in a user subroutine (UMAT), and an efficient element deletion technique based on the Johnson-Cook damage model is adopted to describe material removal and chip formation. The effectiveness of as-established crystal plasticity finite element model is verified by experiments of nanoindentation, nanoscratching and in-situ diamond microcutting. Subsequent crystal plasticity finite element simulation of diamond cutting across a high angle grain boundary demonstrates significant anisotropic machining characteristics in terms of machined surface quality, chip profile and cutting force, due to heterogeneous plastic deformation behavior in the grain level.

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A study of regularly spaced shear bands and morphology of serrated chip formation in microcutting process

Int. J. Mach. Tools Manuf.

Scr. Mater.

Scr. Mater.

Acta Mater.

Int. J. Mech. Sci.