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High performance cutting of Zr-based bulk metallic glass: a review of chip formation
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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 77 (2018) 421–424 www.elsevier.com/locate/procedia
8th CIRP Conference on High Performance Cutting (HPC 2018)
High performance cutting of Zr-based metallic 28th CIRP Design Conference,bulk May 2018, Nantes,glass: France a review of chip formation A new methodology to analyze the functional and physical architecture of Ding, Chengyong Wang*, Tao Zhang, Lijuan Zheng, Xuguang Zhu existing Feng products for an assembly oriented product family identification aGuangdong University of Technology, No. 100 Waihuan Xi Road Guangzhou Higher Education Mega Center, Guangzhou (510000), China * Corresponding author. Tel.: +86-136-0964-9503; fax: +86 020-39322206. E-mail address: [email protected] a
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Zr-based bulk metallic glass (Zr-based BMG) has a unique amorphous structure, and therefore presents high tensile strength, high elastic limit, low elastic modulus, as well as improved wear and corrosion resistance. For this reason, Zr-based BMG is emerging as a promising material for applications in the aviation, automotive, and healthcare industries. However, Zr-based Abstract BMG is classed as an extremely difficult-to-cut material. At very low cutting speeds, lamellar chips are formed accompanied by frequency cutting more speeds, dazzling light emitted during BMG chip formation and severe the oxidation, Inhigh today’s businessfluctuations. environment,At thehigher trend towards product variety andiscustomization is unbroken. Due to this development, need of crystallization, and melting of the working material and consequently, causingfamilies. premature failure the tool, loss of agile and reconfigurable production systems emerged to copeoccur, with various products and product To design andofoptimize production amorphous properties, andthe poor machining purpose of this paperareis needed. to investigate of Zr-based BMG. systems as well as to choose optimal productaccuracy. matches, The product analysis methods Indeed, chip mostformation of the known methods aim to analyze product or one on the physical level. Different product however, may differ in terms the numberwith and Based aon a survey of product existingfamily works, lamellar chip morphology and itsfamilies, underlying mechanism arelargely reviewed andofcompared nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production crystalline metals. The key factor affecting light emission during chip formation is uncovered. Further, the influence of oxidation, system. A new methodology is proposed to analyze is existing products in view of their functional and physical architecture. The aim is to cluster crystallization, and melting on chip formation investigated. these products in new assembly product foropen the optimization existing lines and the creation of future reconfigurable © 2018 The Authors. Publishedoriented by Elsevier Ltd.families This is an access articleofunder the assembly CC BY-NC-ND license © 2018 The Authors. Published by Elsevier Ltd. the physical structure of the products is analyzed. Functional subassemblies are identified, and assembly systems. Based on Datum Flow Chain, (http://creativecommons.org/licenses/by-nc-nd/3.0/) This is an open access underMoreover, the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) aPeer-review functional analysis is article performed. a hybrid functional and physical architecture graph (HyFPAG) is the output Cutting which depicts under responsibility ofresponsibility the International Scientific Committee of theCommittee 8th CIRP Conference on High Performance (HPC the Selection and peer-review under of the International of the 8th CIRP on HighAn Performance similarity between product families by providing design support to Scientific both, production system planners and Conference product designers. illustrative 2018). Cutting (HPC 2018). example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Prestabulk France is then out to give a first industrial evaluation of the proposed approach. Keywords: cutting; metallic glass;carried chip formation; © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
1. Introduction
(1) Lamellar chips are produced during cutting, which have a denser sawtooth arrangement compared to serrated Over the past three decades, Zr-based bulk metallic glass chips of crystalline metals, which easily lead to fluctuations (Zr-based BMG) has been developed and exhibits a unique and chatter phenomena. amorphous structure. This type of material does not contain (2) Low phase transition temperatures (crystallization 1. Introduction of the product range and characteristics manufactured and/or dislocations, grain boundaries, or other crystal defects, and temperature of ~ 420 ºC and melting temperature of ~710 ºC). assembled in this In this (~4 context, the main challenge in thus, compared to crystalline metals, exhibit high tensile Due to poor heatsystem. conductivity W/m·K), phase transition Due to the fast development in the domain of modelling and analysis is now not only to cope with single strength (> 1400 MPa), high elastic limit (~2 %), low elastic temperatures are easily reached during cutting causing the communication trend ofwear digitization and products, a limitedtoproduct or existing product families, modulus (70-90 and GPa),anas ongoing well as excellent and corrosion working material lose its range amorphous properties. digitalization, manufacturing enterprises are facing important but also to be able to analyze and to compare products to define resistance [1, 2]. This has led to the promising use of Zr-based (3) At relatively high cutting speeds, chip formation in challenges in today’s market environments: a continuing new product families. It can be observed that classical existing BMG in the aviation, automotive, and healthcare industries. cutting of Zr-based BMG is accompanied by light emission tendency towards of product times and product families are regrouped of clients or features. Casting is the reduction most commonly useddevelopment method for producing phenomena. Often, extremelyin function high flash temperatures far shortened product lifecycles. In addition, there is an increasing However, assembly oriented product families are hardly to find. Zr-based BMG components, while cutting operations such as exceed the tolerance of the tool material resulting in tool demand customization, being thethe same time in a global On the product family level, products differ mainly in two turning, of milling and drilling, areatstill main methods used damage. competition with competitors all over the world. This trend, main the number of easily components andbecome (ii) the to achieve accuracy and high-quality surface finishing of (4)characteristics: Chips at high (i) temperature can melt and which is inducing the development from macro to micro type of components (e.g. mechanical, electrical, electronical). BMG parts. However, Zr-based BMG is classified as a welded to the tool tip, which leads to adhesive wear of the markets, resultsmaterial in diminished due to augmenting Classical methodologies considering mainly single products difficult-to-cut owing tolot thesizes following factors [3-6]: product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 The optimization Authors. Publishedpotentials by Elsevier Ltd. open access causes article under the CC BY-NC-ND license an efficient definition and identify in This theis an existing difficulties regarding (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Keywords: Assembly; Design method; Family identification
Peer-review of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting (HPC 2018).. 2212-8271 ©under 2018responsibility The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection © and peer-review under responsibility of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting 2212-8271 2017 The Authors. Published by Elsevier B.V. (HPC 2018). Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.294
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cutting tool and consequently, galling, smearing, and chipping of the machined surface. (5) Machined surfaces are susceptible to damage due to high temperatures and machining accuracy is difficult to guarantee. Chip formation is an important aspect in evaluating the machinability of Zr-based BMG. Unlike the serrated chips of most crystalline metals, lamellar chips of Zr-based BMG generate much higher frequency cyclic cutting forces, which augment the cutting fluctuation and chatter. Moreover, crystallization, melting, and light emission phenomena during chip formation accelerate tool wear and failure, and cause flaws in the machined surface. In this review, attention is mainly focused on chip formation during cutting of Zr-based BMG. Chip morphology and the underlying formation mechanism are investigated. Light emission is analyzed, as well as factors affected by light and temperature. Furthermore, oxidation, crystallization, and melting, as well as their association with chip formation, are reviewed.
were observed when using the WC-PVD tool compared to PCD tool with the same cutting parameters, as shown in Fig. 2. This may be attributed to lower thermal conductivity of the WC-PVD tool. Higher temperatures, as a result of machining, accelerate the accumulation of free volume and decrease the viscosity of the work material, thus generating voids and viscous flow in the chip.
Fig. 1 Chip morphology of Zr-based BMG produced at cutting speed of 4.2 m/min, feed rate of 0.025 mm/r and cutting depth of 0.1 mm [7].
2. Chip formation without light emission 2.1. Chip morphology Fig. 1 illustrates lamellar chips formed at a cutting speed of 4.2 m/min, feed rate of 0.025 mm/r, and cutting depth of 0.1 mm [7]. Macroscopically, although a typical continuous curled shape is presented. A large number of shear bands form at the primary shear zone (PSZ) and create a periodic arrangement with constant spacing. The formation of periodic shear bands causes the chip to display a laminated structure. This illustrates that Zr-based BMG chips are not perfectly continuous, however, like serrated chips of crystalline metals, they can be depicted as a stacked structure tilted towards the free surface through periodical shear movement, as shown in Fig. 2 [7]. However, compared to serrated chips, the back surface of BMG lamellar chips is more homogeneous, flat and featureless, apart from a few shear bands. In the top surface view, the lamellar chip is shown to have much smaller shear band spacing δc (Fig. 2 a), smaller shear displacement ψ (Fig. 2 b) and in addition to primary shear bands in the PSZ, many secondary shear bands can be observed on the top surface. In fact, Zr-based BMG undergoes plastic strain during plastic deformation, mainly through shear localization. Thus, a large number of local shear bands are formed to avoid immediate fracture of the work material upon being subjected to cutting forces, even at very low cutting speeds, which are extremely low compared to titanium alloys (~9 m/min) [8] and steels (~100 m/min) [9]. Fig. 3 shows the chip morphology of Zr-based BMG produced at a cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [4]. It is clear that serrated chips with sharp edges and large shear band spacing appear at higher cutting speeds, feed rates and cutting depth. Qin also found that the shear band spacing increases with increasing depth of cut, causing less plastic shear deformation, and shifting the lamellar chip to a serrated chip [10]. Furthermore, in BMG cutting, rougher fracture surfaces and void formation
Fig. 2 Two-dimensional schematic of (a) lamellar chip in BMG (b) serrated chip in crystalline metal [7].
Fig. 3 Chip morphology of Zr-based BMG produced at cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [4]: (a) WC-PVD tool; (b) PCD tool.
2.2. Chip formation mechanism Lamellar chip formation in Zr-based BMG cutting is similar to the formation of serrated chips in crystalline metal cutting. Both are formed via repeated shear band formation in the PSZ due to interplay between the tool and work material. The occurrence of serrated chips is generally explained by two prevailing theories: thermoplastic instability and periodic initiation and propagation of cracks inside the PSZ. The thermoplastic shear mechanism reasonably interprets serrated chip deformation in cutting of titanium alloys and steels [8, 9]. Bakkal suggests the chip formation mechanism in cutting Zrbased BMG under high strain rates is similar to the formation mechanism of serrated chips in crystalline metal. Cutting heat in the PSZ cannot be spread in a short time due to low thermal conductivity thus adiabatic shear bands are formed due to thermal instability of the work material [4]. Evidence suggests that high temperatures produced during BMG deformation
Feng Ding et al. / Procedia CIRP 77 (2018) 421–424 Author name / Procedia CIRP 00 (2018) 000–000
using high strain rates cause melting of the fracture surface [11]. However, the shear band thickness of BMG is in the order of ~10 nm [12], which is much thinner than that of conventional adiabatic shear bands in crystalline metals (~10100 μm). Considering the thermal diffusion length √2𝛼𝛼𝛼𝛼 (α ≈ 3×10-6 m2/s), heat transfer time within shear bands must be in the order of picoseconds to ensure the shear process is completely adiabatic, which is far less than that in cutting.
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slip when stress reaches a maximum value [13], which is similar to the result of Jiang’s prediction. Chen proposed that the PSZ of BMG suffers the most severe plastic deformation due to shear force [14]. When plastic deformation reaches the limit, the material is forced to separate from the workpiece and become a chip. This theory falls within the views of traditional plastic metal cutting principles. Both Fujita and Chen explain the formation of chips in BMG for their respective cutting operations, however, only on a qualitative level. Comprehensive and quantitative understanding of chip formation is still lacking. 3. Chip formation with light emission In machining of Zr-based BMG, by using higher cutting speed, smaller cutting rake angle, and tool material with lower thermal conductivity, the cutting region emits bright light and light emission decays along the chip length beyond the toolworkpiece contact region, as shown in Fig. 5. This demonstrates that light emission in BMG cutting is always associated with high temperature.
Fig. 4 Dimensionless shear stress τ, free volume concentration ξ, and temperature T based on a nonlinear dynamic model [7]: (a)-(c): calculation results for different heat flow coefficients; (d): trajectories (τ, ξ, T) converging towards stable limit points.
Jiang considered the balance of temperature and free volume in the PSZ during the BMG cutting process and proposed a nonlinear dynamic model to predict the relationship between shear stress, temperature, and free volume in the PSZ during lamellar chip formation [7]. Results are illustrated in Fig. 4 and it can be seen that shear stress increases linearly in the initial elastic deformation stage of the BMG and reaches a peak value as the tool cuts into the work material. The source of free volume concentration would exceed its flow as the stress increases. In turn, the net increase in free volume resulted in a catastrophic drop in shear stress, seen as chips breaking along the shear plane. Moreover, plastic work is converted into heat during the chip fracture process, resulting in an instantaneous increase in temperature. This cyclic balance of free volume, temperature and stress leads to the formation of lamellar chips in BMG cutting. Thus, different from the serrated chip of crystalline alloy caused by thermal instability, the onset of lamellar chip formation in BMG is caused by symmetry breaking of free volume flow and source, whereas thermal instability only affects chip morphology. Although the model reasonably interprets the relationship between shear stress and free volume and temperature at a very low cutting speeds, it does not explain the occurrence of crystallization and molten chips at higher cutting speeds. This is because the predicted temperature is clearly lower than the phase transition temperature of the work material. In the model, however, stress-driven free volume instability, not a concern in conventional metal cutting, is proposed and combined with thermal instability to analyze lamellar chips and may provide a new horizon for studying chip formation in BMG. Fujita argued that the formation of lamellar chips follows the maximum stress theory, that is, the chip undergoes shear
Fig. 5 Light emission phenomena in machining of BMG: (a) turning [3]; (b) drilling [5]; (c) milling [15].
Fig. 6 Chip morphology with light emission using WC-CVD tool at cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [3].
Bakkal suggests that light emission is activated by exothermic oxidation of Zr elements due to high cutting temperature [3]. High temperature causes light emission phenomena due to the oxidation of BMG chips, which in turn, creates a higher flash temperature during cutting, which can reach the order of 2400 ºC [3]. This far exceeds the crystallization and melting temperatures of BMG. Fig. 6 shows a typical chip morphology with light emission in BMG cutting [3]. The original lamellar structure is lost and the shape is seriously distorted due to partial melting of the work material. Shear bands of the chips are still observed among the twisted and tangled lamellae surrounded by regions of viscous-like molten and solidified work material. Fig. 7 shows the cross-section of the chips of Fig. 6 after corrosion [5]. Differing from the cross-sectional morphology of the corroded serrated chips of crystalline metals, shear high-strain features are not observed in BMG chips. Large areas of dendritic phase (marked as E in Fig.7) and leafshaped phase (marked as G in Fig.7) are distributed throughout the chip cross-section. The patterns demonstrate crystallization of the machined chips that occurs during cutting. It should be noted that even when the same cutting parameters are used, oxidation and crystallization of chips
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may be uneven due to the uneven distribution of cutting temperature. For partially crystalline chips at relatively low temperature (Fig. 7a), less heat is transferred to the chip interior, therefore, the temperature of the innermost layer is below the crystallization temperature and an amorphous structure is still observed (marked as A in Fig.7). The entire chip section depicts a region of mixed crystalline-amorphous structure. For fully crystalline chips at high temperature, as shown in Fig. 7b, more heat is transferred into the chip, and no amorphous regions are observed on the outside or inside. Particularly in drilling, oxidation and crystallization cause the chip to become brittle and powder-like chips to occur, as shown in Fig. 8 [6]. Coral-like grains of ZrO2 are present on the chip surface, moreover, brittle fracture of the surface is evident. In addition to a thick oxidized layer on the surface, the chip interior is also filled with dendrites, similar to the fully crystalline chip of Fig. 7.
structure disappears and the chip interior become dominated by the crystallized phase. Melted chips can easily become welded to the tool tip. Furthermore, high flash temperatures brought on by light emission are much higher than the temperature tolerance of coated tools and may result in premature tool failure; therefore, to avoid this phenomenon effective cooling and other related techniques must be applied in BMG cutting operations. Finally, it should be noted that lamellar chips formed at low cutting temperatures may generate greater fluctuations and chatter during the cutting process, easily leading to tool tipping, which brings about a great challenge to cutting tools. Acknowledgments Financial support from the Key Program of the National Natural Science Foundation of China (Grant No.51735003) is appreciated. References
Fig. 7 Cross-sectional morphology of chip with light emission [5]: (a) partially crystalline chip; (b) fully crystalline chip.
Fig. 8 Seriously oxidized and crystallized chip: (a) surface morphology; (b) cross-sectional morphology [6].
4. Conclusions Although Zr-based BMG is emerging as a new class of advanced material, research on chip formation mechanisms in cutting Zr-based BMG is still lacking. A survey of existing literature suggests lamellar chips are produced due to shear localization, even at very low cutting speeds. Interpretations of the lamellar chip formation mechanism can be divided into two views: thermal instability and free volume instability. Free volume instability does not explain the crystallization and melting phenomena of work material at high cutting speed particularly well, therefore, based on traditional strain, strain rate, and temperature effects, free volume has been introduced as an influencing factor. Thus, the relationship between shear stress, free volume, and temperature in chip formation can be defined. In conventional cutting, we are more concerned with thermal instability, however, in BMG cutting, free volume instability also merits consideration. High temperature is the key factor affecting light emission, and initiates a series of oxidation, crystallization, and melting events in cutting of BMG. Under high temperature conditions, chips are severely distorted, moreover, the original laminar
[1] Wang WH. The elastic properties, elastic models and elastic perspectives of metallic glasses. Progress in Materials Science, 2012, 57(3):487-656. [2] Sun BA, Wang WH. The fracture of bulk metallic glasses. Progress in Materials Science, 2015, 74:211-307. [3] Bakkal M, Shih AJ, Scattergood RO, Liu CT. Machining of a Zr–Ti–Al– Cu–Ni metallic glass. Scripta Materialia 2004;50(5):583-588. [4] Bakkal M, Shih AJ, Scattergood RO. Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass. International Journal of Machine Tools & Manufacture 2004;44(9):915-925. [5] Bakkal M, Liu CT, Watkins TR, Scattergood RO, Shih AJ. Oxidation and crystallization of Zr-based bulk metallic glass due to machining. Intermetallics 2004;12(2):195-204. [6] Bakkal M, Shih AJ, Mcspadden SB, Liu CT, Scattergood RO. Light emission, chip morphology, and burr formation in drilling the bulk metallic glass. International Journal of Machine Tools & Manufacture 2005;45(7):741-752. [7] Jiang MQ, Dai LH. Formation mechanism of lamellar chips during machining of bulk metallic glass. Acta Materialia 2009;57(9):2730-2738. [8] Gao Y, Wang G, Liu B. Chip formation characteristics in the machining of titanium alloys: A review. International Journal of Machining & Machinability of Materials 2016;18(1/2):155. [9] Wang CY, Xie YX, Zheng LJ, Qin Z, Tang DW, Song YX. Research on the chip formation mechanism during the high-speed milling of hardened steel. International Journal of Machine Tools & Manufacture 2014;79(4):31-48. [10] Qin MY, Liu YJ, Xu LY, Luo YS. Experimental study of chip formation and cutting force during machining Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass. Hydromechatronics Engineering 2014;42(12):50-53. [11] Yoon S, Lee C, Choi H, Kim H, Bae J. Impacting behavior of bulk metallic glass powder at an abnormally high strain rate during kinetic spraying. Materials Science & Engineering A 2007;449-451(449):911915. [12] Greer AL, Cheng YQ, Ma E. Shear bands in metallic glasses. Materials Science & Engineering R Report 2013;74(4):71-132. [13] Fujita K, Morishita Y, Nishiyama N, Kimura H, Inoue A. Cutting characteristics of bulk metallic glass. Materials Transactions 2005;46(12):2856-2863. [14] Chen X, Xiao J, Zhu Y, Tian RJ, Shu XW, Xu JF. Micro-machinability of bulk metallic glass in ultra-precision cutting. Materials & Design 2017;136:1-12. [15] Xie B, Kumar MN, Yan DP, Jin XL. Material Behavior in Micro Milling of Zirconium Based Bulk Metallic Glass. TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. Springer International Publishing, 2017.
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Available online atonline www.sciencedirect.com Available at www.sciencedirect.com
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Procedia CIRP 00 (2018) 000–000
www.elsevier.com/locate/procedia
Procedia CIRP 00 (2017) 000–000 Procedia CIRP 77 (2018) 421–424 www.elsevier.com/locate/procedia
8th CIRP Conference on High Performance Cutting (HPC 2018)
High performance cutting of Zr-based metallic 28th CIRP Design Conference,bulk May 2018, Nantes,glass: France a review of chip formation A new methodology to analyze the functional and physical architecture of Ding, Chengyong Wang*, Tao Zhang, Lijuan Zheng, Xuguang Zhu existing Feng products for an assembly oriented product family identification aGuangdong University of Technology, No. 100 Waihuan Xi Road Guangzhou Higher Education Mega Center, Guangzhou (510000), China * Corresponding author. Tel.: +86-136-0964-9503; fax: +86 020-39322206. E-mail address: [email protected] a
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Zr-based bulk metallic glass (Zr-based BMG) has a unique amorphous structure, and therefore presents high tensile strength, high elastic limit, low elastic modulus, as well as improved wear and corrosion resistance. For this reason, Zr-based BMG is emerging as a promising material for applications in the aviation, automotive, and healthcare industries. However, Zr-based Abstract BMG is classed as an extremely difficult-to-cut material. At very low cutting speeds, lamellar chips are formed accompanied by frequency cutting more speeds, dazzling light emitted during BMG chip formation and severe the oxidation, Inhigh today’s businessfluctuations. environment,At thehigher trend towards product variety andiscustomization is unbroken. Due to this development, need of crystallization, and melting of the working material and consequently, causingfamilies. premature failure the tool, loss of agile and reconfigurable production systems emerged to copeoccur, with various products and product To design andofoptimize production amorphous properties, andthe poor machining purpose of this paperareis needed. to investigate of Zr-based BMG. systems as well as to choose optimal productaccuracy. matches, The product analysis methods Indeed, chip mostformation of the known methods aim to analyze product or one on the physical level. Different product however, may differ in terms the numberwith and Based aon a survey of product existingfamily works, lamellar chip morphology and itsfamilies, underlying mechanism arelargely reviewed andofcompared nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production crystalline metals. The key factor affecting light emission during chip formation is uncovered. Further, the influence of oxidation, system. A new methodology is proposed to analyze is existing products in view of their functional and physical architecture. The aim is to cluster crystallization, and melting on chip formation investigated. these products in new assembly product foropen the optimization existing lines and the creation of future reconfigurable © 2018 The Authors. Publishedoriented by Elsevier Ltd.families This is an access articleofunder the assembly CC BY-NC-ND license © 2018 The Authors. Published by Elsevier Ltd. the physical structure of the products is analyzed. Functional subassemblies are identified, and assembly systems. Based on Datum Flow Chain, (http://creativecommons.org/licenses/by-nc-nd/3.0/) This is an open access underMoreover, the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) aPeer-review functional analysis is article performed. a hybrid functional and physical architecture graph (HyFPAG) is the output Cutting which depicts under responsibility ofresponsibility the International Scientific Committee of theCommittee 8th CIRP Conference on High Performance (HPC the Selection and peer-review under of the International of the 8th CIRP on HighAn Performance similarity between product families by providing design support to Scientific both, production system planners and Conference product designers. illustrative 2018). Cutting (HPC 2018). example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Prestabulk France is then out to give a first industrial evaluation of the proposed approach. Keywords: cutting; metallic glass;carried chip formation; © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
1. Introduction
(1) Lamellar chips are produced during cutting, which have a denser sawtooth arrangement compared to serrated Over the past three decades, Zr-based bulk metallic glass chips of crystalline metals, which easily lead to fluctuations (Zr-based BMG) has been developed and exhibits a unique and chatter phenomena. amorphous structure. This type of material does not contain (2) Low phase transition temperatures (crystallization 1. Introduction of the product range and characteristics manufactured and/or dislocations, grain boundaries, or other crystal defects, and temperature of ~ 420 ºC and melting temperature of ~710 ºC). assembled in this In this (~4 context, the main challenge in thus, compared to crystalline metals, exhibit high tensile Due to poor heatsystem. conductivity W/m·K), phase transition Due to the fast development in the domain of modelling and analysis is now not only to cope with single strength (> 1400 MPa), high elastic limit (~2 %), low elastic temperatures are easily reached during cutting causing the communication trend ofwear digitization and products, a limitedtoproduct or existing product families, modulus (70-90 and GPa),anas ongoing well as excellent and corrosion working material lose its range amorphous properties. digitalization, manufacturing enterprises are facing important but also to be able to analyze and to compare products to define resistance [1, 2]. This has led to the promising use of Zr-based (3) At relatively high cutting speeds, chip formation in challenges in today’s market environments: a continuing new product families. It can be observed that classical existing BMG in the aviation, automotive, and healthcare industries. cutting of Zr-based BMG is accompanied by light emission tendency towards of product times and product families are regrouped of clients or features. Casting is the reduction most commonly useddevelopment method for producing phenomena. Often, extremelyin function high flash temperatures far shortened product lifecycles. In addition, there is an increasing However, assembly oriented product families are hardly to find. Zr-based BMG components, while cutting operations such as exceed the tolerance of the tool material resulting in tool demand customization, being thethe same time in a global On the product family level, products differ mainly in two turning, of milling and drilling, areatstill main methods used damage. competition with competitors all over the world. This trend, main the number of easily components andbecome (ii) the to achieve accuracy and high-quality surface finishing of (4)characteristics: Chips at high (i) temperature can melt and which is inducing the development from macro to micro type of components (e.g. mechanical, electrical, electronical). BMG parts. However, Zr-based BMG is classified as a welded to the tool tip, which leads to adhesive wear of the markets, resultsmaterial in diminished due to augmenting Classical methodologies considering mainly single products difficult-to-cut owing tolot thesizes following factors [3-6]: product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 The optimization Authors. Publishedpotentials by Elsevier Ltd. open access causes article under the CC BY-NC-ND license an efficient definition and identify in This theis an existing difficulties regarding (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Keywords: Assembly; Design method; Family identification
Peer-review of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting (HPC 2018).. 2212-8271 ©under 2018responsibility The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection © and peer-review under responsibility of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting 2212-8271 2017 The Authors. Published by Elsevier B.V. (HPC 2018). Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.294
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Feng Ding et al. / Procedia CIRP 77 (2018) 421–424 Author name / Procedia CIRP 00 (2018) 000–000
cutting tool and consequently, galling, smearing, and chipping of the machined surface. (5) Machined surfaces are susceptible to damage due to high temperatures and machining accuracy is difficult to guarantee. Chip formation is an important aspect in evaluating the machinability of Zr-based BMG. Unlike the serrated chips of most crystalline metals, lamellar chips of Zr-based BMG generate much higher frequency cyclic cutting forces, which augment the cutting fluctuation and chatter. Moreover, crystallization, melting, and light emission phenomena during chip formation accelerate tool wear and failure, and cause flaws in the machined surface. In this review, attention is mainly focused on chip formation during cutting of Zr-based BMG. Chip morphology and the underlying formation mechanism are investigated. Light emission is analyzed, as well as factors affected by light and temperature. Furthermore, oxidation, crystallization, and melting, as well as their association with chip formation, are reviewed.
were observed when using the WC-PVD tool compared to PCD tool with the same cutting parameters, as shown in Fig. 2. This may be attributed to lower thermal conductivity of the WC-PVD tool. Higher temperatures, as a result of machining, accelerate the accumulation of free volume and decrease the viscosity of the work material, thus generating voids and viscous flow in the chip.
Fig. 1 Chip morphology of Zr-based BMG produced at cutting speed of 4.2 m/min, feed rate of 0.025 mm/r and cutting depth of 0.1 mm [7].
2. Chip formation without light emission 2.1. Chip morphology Fig. 1 illustrates lamellar chips formed at a cutting speed of 4.2 m/min, feed rate of 0.025 mm/r, and cutting depth of 0.1 mm [7]. Macroscopically, although a typical continuous curled shape is presented. A large number of shear bands form at the primary shear zone (PSZ) and create a periodic arrangement with constant spacing. The formation of periodic shear bands causes the chip to display a laminated structure. This illustrates that Zr-based BMG chips are not perfectly continuous, however, like serrated chips of crystalline metals, they can be depicted as a stacked structure tilted towards the free surface through periodical shear movement, as shown in Fig. 2 [7]. However, compared to serrated chips, the back surface of BMG lamellar chips is more homogeneous, flat and featureless, apart from a few shear bands. In the top surface view, the lamellar chip is shown to have much smaller shear band spacing δc (Fig. 2 a), smaller shear displacement ψ (Fig. 2 b) and in addition to primary shear bands in the PSZ, many secondary shear bands can be observed on the top surface. In fact, Zr-based BMG undergoes plastic strain during plastic deformation, mainly through shear localization. Thus, a large number of local shear bands are formed to avoid immediate fracture of the work material upon being subjected to cutting forces, even at very low cutting speeds, which are extremely low compared to titanium alloys (~9 m/min) [8] and steels (~100 m/min) [9]. Fig. 3 shows the chip morphology of Zr-based BMG produced at a cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [4]. It is clear that serrated chips with sharp edges and large shear band spacing appear at higher cutting speeds, feed rates and cutting depth. Qin also found that the shear band spacing increases with increasing depth of cut, causing less plastic shear deformation, and shifting the lamellar chip to a serrated chip [10]. Furthermore, in BMG cutting, rougher fracture surfaces and void formation
Fig. 2 Two-dimensional schematic of (a) lamellar chip in BMG (b) serrated chip in crystalline metal [7].
Fig. 3 Chip morphology of Zr-based BMG produced at cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [4]: (a) WC-PVD tool; (b) PCD tool.
2.2. Chip formation mechanism Lamellar chip formation in Zr-based BMG cutting is similar to the formation of serrated chips in crystalline metal cutting. Both are formed via repeated shear band formation in the PSZ due to interplay between the tool and work material. The occurrence of serrated chips is generally explained by two prevailing theories: thermoplastic instability and periodic initiation and propagation of cracks inside the PSZ. The thermoplastic shear mechanism reasonably interprets serrated chip deformation in cutting of titanium alloys and steels [8, 9]. Bakkal suggests the chip formation mechanism in cutting Zrbased BMG under high strain rates is similar to the formation mechanism of serrated chips in crystalline metal. Cutting heat in the PSZ cannot be spread in a short time due to low thermal conductivity thus adiabatic shear bands are formed due to thermal instability of the work material [4]. Evidence suggests that high temperatures produced during BMG deformation
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using high strain rates cause melting of the fracture surface [11]. However, the shear band thickness of BMG is in the order of ~10 nm [12], which is much thinner than that of conventional adiabatic shear bands in crystalline metals (~10100 μm). Considering the thermal diffusion length √2𝛼𝛼𝛼𝛼 (α ≈ 3×10-6 m2/s), heat transfer time within shear bands must be in the order of picoseconds to ensure the shear process is completely adiabatic, which is far less than that in cutting.
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slip when stress reaches a maximum value [13], which is similar to the result of Jiang’s prediction. Chen proposed that the PSZ of BMG suffers the most severe plastic deformation due to shear force [14]. When plastic deformation reaches the limit, the material is forced to separate from the workpiece and become a chip. This theory falls within the views of traditional plastic metal cutting principles. Both Fujita and Chen explain the formation of chips in BMG for their respective cutting operations, however, only on a qualitative level. Comprehensive and quantitative understanding of chip formation is still lacking. 3. Chip formation with light emission In machining of Zr-based BMG, by using higher cutting speed, smaller cutting rake angle, and tool material with lower thermal conductivity, the cutting region emits bright light and light emission decays along the chip length beyond the toolworkpiece contact region, as shown in Fig. 5. This demonstrates that light emission in BMG cutting is always associated with high temperature.
Fig. 4 Dimensionless shear stress τ, free volume concentration ξ, and temperature T based on a nonlinear dynamic model [7]: (a)-(c): calculation results for different heat flow coefficients; (d): trajectories (τ, ξ, T) converging towards stable limit points.
Jiang considered the balance of temperature and free volume in the PSZ during the BMG cutting process and proposed a nonlinear dynamic model to predict the relationship between shear stress, temperature, and free volume in the PSZ during lamellar chip formation [7]. Results are illustrated in Fig. 4 and it can be seen that shear stress increases linearly in the initial elastic deformation stage of the BMG and reaches a peak value as the tool cuts into the work material. The source of free volume concentration would exceed its flow as the stress increases. In turn, the net increase in free volume resulted in a catastrophic drop in shear stress, seen as chips breaking along the shear plane. Moreover, plastic work is converted into heat during the chip fracture process, resulting in an instantaneous increase in temperature. This cyclic balance of free volume, temperature and stress leads to the formation of lamellar chips in BMG cutting. Thus, different from the serrated chip of crystalline alloy caused by thermal instability, the onset of lamellar chip formation in BMG is caused by symmetry breaking of free volume flow and source, whereas thermal instability only affects chip morphology. Although the model reasonably interprets the relationship between shear stress and free volume and temperature at a very low cutting speeds, it does not explain the occurrence of crystallization and molten chips at higher cutting speeds. This is because the predicted temperature is clearly lower than the phase transition temperature of the work material. In the model, however, stress-driven free volume instability, not a concern in conventional metal cutting, is proposed and combined with thermal instability to analyze lamellar chips and may provide a new horizon for studying chip formation in BMG. Fujita argued that the formation of lamellar chips follows the maximum stress theory, that is, the chip undergoes shear
Fig. 5 Light emission phenomena in machining of BMG: (a) turning [3]; (b) drilling [5]; (c) milling [15].
Fig. 6 Chip morphology with light emission using WC-CVD tool at cutting speed of 91.2 m/min, feed rate of 0.05 mm/r, and cutting depth of 0.5 mm [3].
Bakkal suggests that light emission is activated by exothermic oxidation of Zr elements due to high cutting temperature [3]. High temperature causes light emission phenomena due to the oxidation of BMG chips, which in turn, creates a higher flash temperature during cutting, which can reach the order of 2400 ºC [3]. This far exceeds the crystallization and melting temperatures of BMG. Fig. 6 shows a typical chip morphology with light emission in BMG cutting [3]. The original lamellar structure is lost and the shape is seriously distorted due to partial melting of the work material. Shear bands of the chips are still observed among the twisted and tangled lamellae surrounded by regions of viscous-like molten and solidified work material. Fig. 7 shows the cross-section of the chips of Fig. 6 after corrosion [5]. Differing from the cross-sectional morphology of the corroded serrated chips of crystalline metals, shear high-strain features are not observed in BMG chips. Large areas of dendritic phase (marked as E in Fig.7) and leafshaped phase (marked as G in Fig.7) are distributed throughout the chip cross-section. The patterns demonstrate crystallization of the machined chips that occurs during cutting. It should be noted that even when the same cutting parameters are used, oxidation and crystallization of chips
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may be uneven due to the uneven distribution of cutting temperature. For partially crystalline chips at relatively low temperature (Fig. 7a), less heat is transferred to the chip interior, therefore, the temperature of the innermost layer is below the crystallization temperature and an amorphous structure is still observed (marked as A in Fig.7). The entire chip section depicts a region of mixed crystalline-amorphous structure. For fully crystalline chips at high temperature, as shown in Fig. 7b, more heat is transferred into the chip, and no amorphous regions are observed on the outside or inside. Particularly in drilling, oxidation and crystallization cause the chip to become brittle and powder-like chips to occur, as shown in Fig. 8 [6]. Coral-like grains of ZrO2 are present on the chip surface, moreover, brittle fracture of the surface is evident. In addition to a thick oxidized layer on the surface, the chip interior is also filled with dendrites, similar to the fully crystalline chip of Fig. 7.
structure disappears and the chip interior become dominated by the crystallized phase. Melted chips can easily become welded to the tool tip. Furthermore, high flash temperatures brought on by light emission are much higher than the temperature tolerance of coated tools and may result in premature tool failure; therefore, to avoid this phenomenon effective cooling and other related techniques must be applied in BMG cutting operations. Finally, it should be noted that lamellar chips formed at low cutting temperatures may generate greater fluctuations and chatter during the cutting process, easily leading to tool tipping, which brings about a great challenge to cutting tools. Acknowledgments Financial support from the Key Program of the National Natural Science Foundation of China (Grant No.51735003) is appreciated. References
Fig. 7 Cross-sectional morphology of chip with light emission [5]: (a) partially crystalline chip; (b) fully crystalline chip.
Fig. 8 Seriously oxidized and crystallized chip: (a) surface morphology; (b) cross-sectional morphology [6].
4. Conclusions Although Zr-based BMG is emerging as a new class of advanced material, research on chip formation mechanisms in cutting Zr-based BMG is still lacking. A survey of existing literature suggests lamellar chips are produced due to shear localization, even at very low cutting speeds. Interpretations of the lamellar chip formation mechanism can be divided into two views: thermal instability and free volume instability. Free volume instability does not explain the crystallization and melting phenomena of work material at high cutting speed particularly well, therefore, based on traditional strain, strain rate, and temperature effects, free volume has been introduced as an influencing factor. Thus, the relationship between shear stress, free volume, and temperature in chip formation can be defined. In conventional cutting, we are more concerned with thermal instability, however, in BMG cutting, free volume instability also merits consideration. High temperature is the key factor affecting light emission, and initiates a series of oxidation, crystallization, and melting events in cutting of BMG. Under high temperature conditions, chips are severely distorted, moreover, the original laminar
[1] Wang WH. The elastic properties, elastic models and elastic perspectives of metallic glasses. Progress in Materials Science, 2012, 57(3):487-656. [2] Sun BA, Wang WH. The fracture of bulk metallic glasses. Progress in Materials Science, 2015, 74:211-307. [3] Bakkal M, Shih AJ, Scattergood RO, Liu CT. Machining of a Zr–Ti–Al– Cu–Ni metallic glass. Scripta Materialia 2004;50(5):583-588. [4] Bakkal M, Shih AJ, Scattergood RO. Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass. International Journal of Machine Tools & Manufacture 2004;44(9):915-925. [5] Bakkal M, Liu CT, Watkins TR, Scattergood RO, Shih AJ. Oxidation and crystallization of Zr-based bulk metallic glass due to machining. Intermetallics 2004;12(2):195-204. [6] Bakkal M, Shih AJ, Mcspadden SB, Liu CT, Scattergood RO. Light emission, chip morphology, and burr formation in drilling the bulk metallic glass. International Journal of Machine Tools & Manufacture 2005;45(7):741-752. [7] Jiang MQ, Dai LH. Formation mechanism of lamellar chips during machining of bulk metallic glass. Acta Materialia 2009;57(9):2730-2738. [8] Gao Y, Wang G, Liu B. Chip formation characteristics in the machining of titanium alloys: A review. International Journal of Machining & Machinability of Materials 2016;18(1/2):155. [9] Wang CY, Xie YX, Zheng LJ, Qin Z, Tang DW, Song YX. Research on the chip formation mechanism during the high-speed milling of hardened steel. International Journal of Machine Tools & Manufacture 2014;79(4):31-48. [10] Qin MY, Liu YJ, Xu LY, Luo YS. Experimental study of chip formation and cutting force during machining Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass. Hydromechatronics Engineering 2014;42(12):50-53. [11] Yoon S, Lee C, Choi H, Kim H, Bae J. Impacting behavior of bulk metallic glass powder at an abnormally high strain rate during kinetic spraying. Materials Science & Engineering A 2007;449-451(449):911915. [12] Greer AL, Cheng YQ, Ma E. Shear bands in metallic glasses. Materials Science & Engineering R Report 2013;74(4):71-132. [13] Fujita K, Morishita Y, Nishiyama N, Kimura H, Inoue A. Cutting characteristics of bulk metallic glass. Materials Transactions 2005;46(12):2856-2863. [14] Chen X, Xiao J, Zhu Y, Tian RJ, Shu XW, Xu JF. Micro-machinability of bulk metallic glass in ultra-precision cutting. Materials & Design 2017;136:1-12. [15] Xie B, Kumar MN, Yan DP, Jin XL. Material Behavior in Micro Milling of Zirconium Based Bulk Metallic Glass. TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. Springer International Publishing, 2017.