Vol. 26 No. 2 2024 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 26 No. 2 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Gaikwad V., Chinchanikar S. Investigations on ultrasonic vibration-assisted friction stir welded AA7075 joints: Mechanical properties and fracture analysis........................................................................................................................ 6 Sirota V.V., Zaitsev S.V., Limarenko M.V., Prokhorenkov D.S., Lebedev M.S., Churikov A.S., Dan'shin A.L. Preparation of coatings with high infrared emissivity.......................................................................................................... 23 Babaev A.S., Kozlov V.N., Semenov A.R., Shevchuk A.S., Ovcharenko V.A., Sudarev E.A. Investigation of cutting forces and machinability during milling of corrosion-resistant powder steel produced by laser metal deposition............. 38 Dolgova S.V., Malikov A.G., Golyshev A.A., Nikulina A.A. The eff ect of laser surfacing modes on the geometrical characteristics of the single laser tracks............................................................................................................................... 57 Karlina Y.I., Kononenko R.V., Popov M.A., Deryugin F.F., Byankin V.E. Assessment of welding engineering properties of basic type electrode coatings of diff erent electrode manufacturers for welding of pipe parts and assemblies of heat exchange surfaces of boiler units............................................................................................................................. 71 Yanpolskiy V.V., Ivanova M.V., Nasonova A.A., Yanyushkin A.S. Determination of the rate of electrochemical dissolution of U10A steel under ECM conditions with a stationary cathode-tool............................................................... 95 EQUIPMENT. INSTRUMENTS Zakovorotny V.L., Gvindjiliya V.E. The study of vibration disturbance mapping in the geometry of the surface formed by turning............................................................................................................................................................................. 107 Gasanov B.G., Konko N.A., Baev S.S. Study of the kinetics of forming of spherical sliding bearing parts made of corrosion-resistant steels by die forging of porous blanks............................................................................................... 127 Gvindjiliya V.E., Fominov E.V., Moiseev D.V., Gamaleeva E.I. Infl uence of dynamic characteristics of the turning process on the workpiece surface roughness........................................................................................................................ 143 Lobanov D.V., Skeeba V.Yu., Golyushov I.S., Smirnov V.M., Zverev E.A. Design simulation of modular abrasive tool........................................................................................................................................................................................ 158 MATERIAL SCIENCE EroshenkoA.Yu., Legostaeva E.V., Glukhov I.A., Uvarkin P.V., TolmachevA.I., Sharkeev Yu.P. Thermal stability of extruded Mg-Y-Nd alloy structure.................................................................................................................................. 174 Bazaleeva K.O., Safarova D.E., Ponkratova Yu.Yu., Lugovoi M.E., Tsvetkova E.V., Alekseev A.V., Zhelezni M.V., Logachev I.A., Baskov F.A. The infl uence of technological parameters of the laser engineered net shaping process on the quality of the formed object from titanium alloy VT23......................................................... 186 Efi movich I.A., Zolotukhin I.S. Oxidation temperatures of WC-Co cemented tungsten carbides....................................... 199 Pribytkov G.A., Baranovskiy A.V., Firsina I.A., Akimov K.O., Krivopalov V.P. Study of Fe-matrix composites with carbide strengthening, formed by sintering of iron titanides and carbon mechanically activated mixtures................ 212 EDITORIALMATERIALS 224 FOUNDERS MATERIALS 235 CONTENTS
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Investigation of cutting forces and machinability during milling of corrosion-resistant powder steel produced by laser metal deposition Artem Babaev 1, a, *, Victor Kozlov 2, b, Artem Semenov 1, c, Anton Shevchuk 1, d, Valeriia Ovcharenko2, e, Evgeniy Sudarev 2, f 1 National Research Tomsk State University, 36 Lenin Avenue, Tomsk, 634050, Russian Federation 2 National Research Tomsk Polytechnic University, 30 Lenin Avenue, Tomsk, 634050, Russian Federation a https://orcid.org/0000-0003-2334-1679, temkams@mail.ru; b https://orcid.org/0000-0001-9351-5713, kozlov-viktor@bk.ru; c https://orcid.org/0000-0002-8663-4877, artems2102@yandex.ru; d https://orcid.org/0009-0003-5272-4350, shvpro@yandex.ru; e https://orcid.org/0009-0000-4797-5604, vag14@tpu.ru; f https://orcid.org/0000-0002-5596-4048, sudarev@tpu.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 2 pp. 38–56 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.2-38-56 ART I CLE I NFO Article history: Received: 11 March 2024 Revised: 30 March 2024 Accepted: 09 April 2024 Available online: 15 June 2024 Keywords: Milling Cutting forces Roughness Laser Metal Deposition Cutting modes Funding The work was carried out with financial support from the Russian Science Foundation, project No. 23-79-10166 (ht tps: / / rscf . ru/en/project /23-79- 10166). The authors express their gratitude to the Russian Science Foundation for funding this work. ABSTRACT Introduction. Additive manufacturing technologies for the production of geometrically approximate workpieces require post-processing. This applies to the use of cutting tools in milling operations when machining critical surfaces. The latter are specified strict requirements to accuracy of linear and angular dimensions and quality of the surface layer. An urgent task remains to increase machining productivity when recording cutting forces and surface roughness to develop technological recommendations. Purpose of work: experimental determination of cutting modes providing the highest productivity when milling LMD-workpieces (Laser Metal Deposition) made of steel 0.12-Cr18-Ni10-Ti (AISI 321) by carbide end mill, while maintaining the milling cutter operability and required roughness. The properties and microstructure of the specimens along and across the build direction are investigated. The influence of feed (when the mill moves across and along the build direction), depth and width of milling, speed on the components of the cutting force and roughness of the machined surfaces during counter milling of LMD-workpieces made of steel 0.12-Cr18-Ni10-Ti (AISI 321) with end mill made of H10F carbide with a diameter of 12 mm without wear-resistant coating is established and formalized. The research methods are the dynamic measurement of all three components of the cutting force using a three-component dynamometer and the measurement of roughness with a profilometer. The condition and microgeometry of the cutting edges were monitored before and after milling using scanning optical and scanning electron microscopy. Results and Discussion. The difference in cutting forces depending on the milling pattern (along and across the build direction) was shown. Studies showed that the milling depth and cutting speed have little effect on the lateral and axial components of the cutting force. The feed force increases significantly with increasing depth of cut, especially when feeding across the specimen build direction. It is found that all three components of the cutting force are directly proportional to the value of the minute feed. The equations for calculating all three components of the cutting force with a change in the minute feed are obtained. For citation: Babaev A.S., Kozlov V.N., Semenov A.R., Shevchuk A.S., Ovcharenko V.A., Sudarev E.A. Investigation of cutting forces and machinability during milling of corrosion-resistant powder steel produced by laser metal deposition. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 2, pp. 38–56. DOI: 10.17212/1994-6309-2024- 26.2-38-56. (In Russian). ______ * Corresponding author Babaev Artem S., Ph.D. (Engineering), Senior researcher National Research Tomsk State University, 36 Lenin Avenue, 634050, Tomsk, Russian Federation Тел.: +7 952 805-09-26, e-mail: temkams@mail.ru Introduction The increase in the number of technologies and materials for additive manufacturing of blanks is accompanied by increased requirements for understanding the features of shaping of functional products, patterns and processes of subtractive processing [1]. Regardless of the additive technology used to produce the workpiece, the latter needs post-processing – thermal, chemical or using subtractive methods [2–4].
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Heat treatment methods (annealing, normalization, etc.) allow to provide phase transformations in the metal structure, and also significantly affect the physical and mechanical characteristics of the workpiece material, and, as a result, the resistance to cutting [5–9]. In order to give the final shape, maintain geometric accuracy and surface roughness, the additive workpiece is subjected to subtractive processing, i.e. machining with the removal of material. The latter can include the processes of blade and abrasive cutting. At the same time, it is important to understand that the removal of “excess” material (overlap or allowance) is accompanied by a range of specific phenomena – chip formation, the occurrence and dynamic change of cutting forces, temperature changes in the cutting zone, the gradual formation of wear on the working surfaces of the cutting tool, etc. [10–21]. Special attention is paid to the peculiarities of the interaction of the “tool material-machined material” pair. Observation and study of these phenomena contribute to the development of scientifically based recommendations on the choice and assigning of edge cutting machining modes, especially when it comes to machining new materials or workpiece obtained by additive methods – it becomes possible to indirectly estimate the economic costs of producing a fully functional product [4]. Significant progress has been made in the synthesis of stainless steels by various additive methods, which makes it possible to use the resulting workpiece of stable quality for further heat treatment, as well as to give the required structural design, roughness, shape and size accuracy by removing the allowance [22– 25]. In [26], a team of researchers studied the impact of additive manufacturing on the development of the space industry. The authors concluded that the repeatability and consistency of the mechanical properties of finished parts of additive manufacturing have not yet been fully studied, and special attention should be paid to the development of standards, certificates and inspection protocols. Scientific papers [15, 27–29] are devoted to the anisotropy of the properties of additive metallic materials. In the review work [29], the main factors that cause microstructural features and heterogeneity of mechanical properties are highlighted: grain morphology; crystallographic texture; defects in the absence of merger; phase transformations; heterogeneous recrystallization; banding of layers and microstructural coarsening. As a result, the anisotropy of the properties affects the resistance of the material to cutting. It is necessary to know the distribution of contact stresses on the rake surface and on the wear chamfer of the flank and back surface to calculate the milling teeth for strength, in addition to the cutting forces Pz, Py and Px acting on the milling tooth. The authors of [30] have developed a technique for constructing of a contact stresses diagram on the rake surface of the cutting wedge when turning steel, but it is also applicable in milling. The length of the chip contact with the rake surface of the milling cutter tooth at the largest cut thickness, i.e. for counter milling, this occurs at the moment preceding the tooth exhaust from contact with the workpiece should be known to do this. This contact length c can not only be measured, but also determined by graphs с = f (ai,g) [30], knowing the uncut chip thickness a (mm) at the end of the tooth contact with the workpiece: amax ≈ sz×2×(t/d) 1/2, where s z is the feed to the tooth, mm/tooth; t is the milling depth, mm; d is the diameter of the cutter, mm; γ is the rake angle of the cutting wedge. Designations (Nometclature) Plaser is the laser radiation power, W; Dialaser is the laser spot diameter, mm; xwidth is the width offset of the rollers, mm; hwidth is the height offset of the rollers, mm; VLMD is the LMD speed, mm/s; Qpowder is the powder consumption, g/min; s0.2 is the yield strength, MPa; sUTS is the ultimate tensile strength, MPa; d5 is the relative elongation, %; KCU is the impact strength, J/cm2;
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Ra is the arithmetic mean deviation of the roughness profile, μm; d is the milling cutter diameter, mm; d1 is the diameter of the milling cutter shank, mm; l is the length of the working part of the milling cutter, mm; L is the full length of the milling cutter, mm; a is the clearance(rear) angle, degree; g is the rake angle, degree; ω is the angle of inclination of the chip groove, degree; z is the number of teeth, pcs; r is the radius of rounding (sharpness) of the cutting edge, μm; Ra (r) is the arithmetic mean deviation of the roughness profile on the cutting edge, μm; b is the wedge angle, degree; t is the milling depth, mm; B is the milling width, mm; V is the cutting speed, m/min; n is the rotation speed, rpm; fmin is the feed per minute, mm/min; Q is the volume of the material to be removed (cutting capacity), mm3/min. Experiment technique Specimen (shape, properties, structure) The workpiece (after its final preparation – the specimen) for testing was obtained using direct laser deposition technology (LMD – Laser Metal Deposition) from powder raw materials of the Fe-Cr-Ni-Ti system. Changes in the irradiation parameters (laser power, irradiation rate and the distance between layers) affect the size of the melt bath and the porosity of the structure of the resulting material, and, consequently, the mechanical properties of additively manufactured workpieces [31]. Therefore, the workpieces were obtained in the spent modes under the same conditions from the powder of the same delivery batch sequentially in the same modes (Table 1) and along the same deposition trajectory (Fig. 1). The specimens were obtained by successive unidirectional filling vectors: feeding along the specimen at a VLMD velocity, then feeding across the specimen by y = 1.67 mm, and so on until the first layer was obtained. Then by moving to the thickness of one layer (hwidth = 0.8 mm), moving to the starting point of synthesis of the first layer, filling along the long side of the sample, etc. All workpieces were obtained from a powder mixture, the passport and certified composition of which is given (Table 2). The resulting workpieces after growing had dimensions of 190×100×14 mm. The crust on workpieces was removed by electroerosion cutting. The latter made it possible to eliminate the appearance of distortion of internal stresses on the machined surfaces. Specimens for physical and mechanical tests were cut out of several workpieces. In order to avoid the spread of values caused by the location of the specimens relative to the workpiece, a check was carried Ta b l e 1 LMD modes for steel 0.12-Cr18-Ni10-Ti (AISI 321) products manufacturing Steel Plaser, W Dialaser, mm xwidth, mm hwidth, mm VLMD, mm/s Qpowder, mm3/min 0.12-Cr18-Ni10-Ti (AISI 321) 2,400 2.7 1.67 0.8 25 16
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Fig. 1. Scheme of the filling strategy for growing specimens from steel 0.12-Cr18-Ni10-Ti (AISI 321) Ta b l e 2 Chemical composition of the powder Chemical element, mass % Fe Cr Ni Mn Si Ti Cu V Mo C Bal. 18.19 10.67 1.14 0.54 0.51 0.18 0.10 0.17 0.06 out – the location of the test specimens was determined and cut out randomly. The specimens were certified at room temperature using various research equipment. As a result, data on thermophysical and physical and mechanical properties were obtained (Table 3). The mechanical properties of steel 0.12-Cr18-Ni10-Ti (AISI 321) in its initial state and after heat treatment correspond to OST 95-29-72 “Workpieces made of corrosion-resistant steels”. Blanks with a size of 160×80×8 mm were used directly for milling. The thermophysical properties of steel 0.12-Cr18-Ni10-Ti (AISI 321) were determined at a temperature of 20 °C. The following values were obtained: density 7.91 g/cm3; thermal conductivity coefficient 14 W/ m∙°C; specific heat capacity 473 J/kg∙°C. Figure 2 shows the microstructure of the specimen in the ZY plane and in the ZX plane. The study of the microstructure showed the two-phase nature of additive specimens: an austenitic matrix based on γ-Fe with a face-centered cubic lattice (FCC) and high-temperature rack and vermicular δ-ferrite with a body-centered cubic lattice (BCC), which is also confirmed by a diffractogram of the specimens (Fig. 3). Mainlyδ-ferrite is formed at the fusion boundaries. Titanium carbides TiC are present in the specimens. Ta b l e 3 Mechanical properties of steel 0.12-Cr18-Ni10-Ti (AISI 321) Condition Sampling direction (see Fig. 1) Hardness, HB σ0.2, MPa UTS (σUTS), MPa δ5, % KCU, J/cm2 Plate (OST 95-29-72) – ≈180–190 246 520 37 215–372 LMD X axis 193–205 412±20 627±34 48.2±1.5 271±18 Z axis 387±16 606±28 51.2±2 286±21
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology a b Fig. 2. Microstructure of the specimen in the ZY plane (a), in the ZX plane (b) The cutting tool and its geometry Carbide end mills with universal geometry were used as cutting tools for machining steels from group P (Fig. 4) and (Table 4). The cemented carbide of the H10F brand had the following characteristics: ≈ 89.4 wt. % of tungsten carbide; up to 0.6 wt. % of mixed carbides and about 10.0 wt. % of cobalt as a binder. The grain size of the carbide phase is 0.5– 0.6 μm, the bending strength is ≈ 3,200 MPa, and the hardness is 92 HRA. In total, 5 milling cutters were sequentially manufactured on a tool and cutter grinding machine without readjustment. The cemented carbide blanks for manufacturing were taken from one shipment. This made it possible to avoid the appearance of an undesirable factor — the influence of heterogeneity in the quality of the tool material. In order to avoid the effect of wear on the flank or back surface on the data obtained, milling cutters were used that worked to a wear chamfer length no more than 0.10–0.12 mm on the flank or back surface. It is known that the parameters of microgeometry have a stable effect on the mechanics and dynamics of the cutting process, while changing the conditions of friction and wear of the cutting edge [21]. In order to avoid the appearance of this factor on the results of this work, the state of the microgeometry of the cutting edges were estimated. The Edge Master X device, manufactured by Alicona (Switzerland), was used to a b Fig. 3.Typical microstructure of LMD steel 0.12-Cr18-Ni10-Ti (AISI 321)
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Fig. 4. Schematic representation of a mill with indication of the main geometric characteristics Ta b l e 4 Values of the main geometric characteristics of the H10F carbide mill d, mm d1, mm l, mm L, mm α, degree γ, degree ω, degree z, pcs 12 12h6 26 84 +10 +8 40 4 carry out measurements to understand the state of the microgeometry of the cutting edges. Measurements were made on all working edges located on the screw surface, while retreating from the end by 2–3 mm (Fig. 5). Test bench and work plan The tests were carried out on the milling machining center of the DMU 50 model, manufactured by DMG (Germany). According to the passport data and production experience, the machine has a sufficiently high rigidity for roughing steel in modes with accelerated material removal. The maximum spindle speed nmax is 10,000 min –1, and the feed rate is up to 30,000 mm/min. The specimen was fixed in a special device mounted within the bearing surface of the dynamometer (Fig. 6). Preliminary modeling of the grip conditions was carried out in order to prevent collisions during Fig. 5. Measuring circuit and example presentation of cutting edge microgeometry parameters
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology a b Fig. 6. Model (a) and appearance (b) of the experimental stand with an installed dynamometer, a specimen and a mill testing. The Kistler dynamometer mod. 9257BA for measuring cutting forces was mounted directly on the table of the milling machine. The specimens were milled both along and across the build direction (see Fig. 1). In this case, it is important to track the influence of the specimen build direction on the change in cutting forces and the roughness of the have machined surface. Milling was carried out without the use of a coolant to minimize the influence of the cooling factor and lubrication of the cutting zone. The cutting modes were adopted according to Table 5 in order to experimentally determine the highest possible feed according to the strength of the cutter and its teeth, that is, for the increased volume of the chip being cut Q. Attempts to increase the cutting speed and feed above the table values inevitably led to the failure of the mill after the first seconds of operation (Fig. 7). During the tests, conventional or up milling was used according to the scheme shown in Fig. 8. Adistinctive feature of conventional or up milling (counter milling) from climb or down milling (passing milling) is that during conventional milling, the uncut chip thickness ai increases from zero to the maximum value at the moment the tooth leaves contact with the workpiece. This allows for a short period of time to ensure smooth loading of the cutting edge, unlike in climbmilling, when there is an abrupt load in the first moments of cutting, often leading to premature destruction of the cutting edges. Ta b l e 5 Milling modes Experiment No. n, rev/min V, m/min Fmin, mm/min t, mm B, mm Q, mm3/min 1 2.000 75 120 1 7 840 2 240 1.680 3 480 3.360 4 850 5.950 5 2 11.900 6 2.5 14.875 7 2.500 94 8 3 17.850 9 1.050 22.050
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Fig. 7. Appearance of a mill prematurely removed from testing and a fragment of the cutting-edge wear Fig. 8. Schematic representation of milling modes The components of the cutting force were measured using a threecomponent dynamometer model 9257BA Kistler (Switzerland) (Fig. 9). The duration of the data collection cycle was 5 seconds from the moment of steady cutting, that is, after all the teeth of the milling cutter had already taken part in machining the specimen. The registration of forces was carried out with a frequency of 10 kHz signal reception. The rotation of the milling cutter was always performed clockwise. In the built-in software of the Kistler dynamometer, the symbols Fz (tangential component of the cutting force, i.e. acting vertically downwards for conventional turning), Fx (axial component of the cutting force, i.e. acting in a horizontal plane along the axis of rotation of the lathe spindle from left to right for conventional turning), Fy (radial component of the cutting force, i.e. acting in a horizontal plane and perpendicular to the axis of rotation of the spindle of the lathe towards the operator for conventional turning)which indicate the direction of forces characteristic of classical turning. These symbols are indicated on the graphs of changes in these components on the dynamometer monitor. In Fig. 9, it is indicated by the Fig. 9. Flow pattern of cutting forces on the mill relative to the coordinate system of the dynamometer
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology first symbols in order Fz, Fx, Fy. When milling, it is impossible to measure (isolate) with a dynamometer the tangential Pz and radial Py cutting forces acting on the tooth of the cutter and, accordingly, from the tooth of the cutter to the dynamometer, due to the turn (rotation) of the cutter (Fig. 10). Fig. 10. Scheme of decomposition of cutting forces in a plane perpendicular to the axis of rotation of the mill During milling, only the forces acting from the cutter on the dynamometer can be measured: the feed force Ph acting along the feed direction of the table, and the lateral force Pv acting perpendicular to the feed direction. In this case, the long side of the dynamometer must be installed strictly perpendicular regarding the direction of the table feed, as shown in Fig. 9 and 10, or strictly parallel to the table feed. The designation of these components depends on the direction of the table feed. When mounting the dynamometer with the long side strictly perpendicular to the longitudinal feed of the table (see Fig. 9 and 10), these components of the cutting force have the following designation (indicated by the second symbols in order): Fz = Px, Fx = Ph, Fy = Pv. With a small cutting depth t = 1 mm and a significantly large mill diameter d = 12 mm (t/d ratio < 0.1) and the direction of the minute table feed fmin across the long side of the dynamometer, these directions correspond to another system of forces acting on the specimen (workpiece) from the side of the milling cutter tooth (indicated by the third symbols in order) at the moment when the milling cutter tooth is embedding in the workpiece: Fz = Px = Px, Fx = Ph ≈ Pz, Fy = Pv ≈ Py. The same colors (Fz – purple, Fx – blue, Fy – red) these forces and graphs of its changes are indicated on the monitor. Turning to the system of forces acting on the specimen (workpiece) from the side of the milling cutter tooth, the following approximations will be used: Px = Fz, Py ≈ Fy, Pz ≈ Fx. Thus, you need to understand that in the interface of the Kistler DynoWare software, at the moment when the cutter tooth is embedding in the workpiece, Fz means that in fact it is Px; Fy means that in fact it is Py; Fx means that in fact it is Pz. The surface roughness of the machined specimens was measured using a profilometer model SJ-210 from Mitutoyo (Japan) (Fig. 11). Measurements were performed on five arbitrary sections on the initial workpiece before milling and after removing a layer with a thickness equal to the width of milling B
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Fig. 11. Process flow diagram of measuring the surface roughness of a specimen after milling (see Fig. 8). For measurements and data processing of the initial roughness profile, the technique according to EN ISO 4288 was used. The data obtained during the registration process were processed using the classical provisions of mathematical statistics and experimental planning, and STATISTICA software was used to automate calculations. Results and discussion Below are the results of a study of milling machining of a steel 0.12-Cr18-Ni10-Ti (AISI 321). Measurements of the roughness parameter Ra depending on the milling modes and the specimens build direction are shown in Table 6. The milling width was assumed to be B = const = 7 mm with a plate thickness of h = 8.5 mm, i.e. the teeth of the mill at its end were always involved in machining. The minute feed of fmin varied under other identical cutting conditions (machining modes). The least squares method was used to plot graphs based on empirical data. All figures took into account the changes in the largest magnitude of these forces (see Fig. 12–14). Graphs of the change in the feed force Ph (the direction of the force Ph acts along the feed direction vector) and the lateral force Pv (the direction of the force Pv is perpendicular to the direction of the feed vector) with a change in the feed per minute fmin are shown in Fig. 12, and Fig. 13 shows graphs of the change in the axial force Px (acts along the axis of the mill, i.e. at the end milling – vertically), and for comparison, a graph of the change in the lateral force Pv is also placed on this field. In Fig. 13, the Px max along graph has an inflection when feed fmin = 240 mm/min. We believe that it is possible to simplify the nature of this graph and draw a straight line through all four points (line 4 in Fig. 13), taking into account the insignificance of the error under this assumption. The study of the influence of the milling depth t on the cutting forces showed a direct proportionality of the forces Ph from the milling depth (Fig. 15).
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Ta b l e 6 Roughness values Ra depending on the milling direction and cutting modes Experiment No. V, m/min fmin, mm/ min t, mm B, mm Ra, μm (milling along) Ra, μm (milling across) 1 75 120 1 7 0.817±0,15 2.013±0.24 2 240 1.589±0.15 3 480 1.203±0.20 4 850 0.775±0.24 5 2 0.566±0.20 0.699±0.11 6 2.5 0.496±0.18 0.566±0.10 7 94 0.438±0.23 0.510±0.15 8 3 1.495±0.32 0.922±0.32 9 1,050 1.220±0.22 1.979±0.34 Fig. 12. Graph of changes in the highest values of cutting forces Ph и Pv (N) depending on the feed fmin (mm/min) (B = 7 mm, V = 75 m/min, t = 1 mm) Fig. 13. Graph of changes in the highest values of cutting forces Ph и Px (N) depending on the feed fmin (mm/min) (B = 7 mm, V = 75 m/min, t = 1 mm)
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 Fig. 14. Example of a graph of changes in the force components from the cutting time in the milling process along the build direction (B = 7 mm, V = 75 m/min, t = 1 mm, fmin = 120 mm/min) Fig. 15. Components of the cutting force Ph, Pv and Px (N) when milling in different modes depending on the cutting depth t (mm) when B = 7 mm
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology It should be noted that the force Pv is directed away from the operator, i.e. in the opposite direction of the OY axis, i.e. the milling cutter tooth pushes the workpiece away from the operator, because when measured, it is displayed on the dynamometer monitor with a minus sign (–). In Fig. 12, the force Pv is indicated on the positive axis so as not to draw another axis. Despite the negative magnitude of the forces Pv and Px, its absolute value is taken into account – the greater it is, the greater the force. The sign of the force Ph is positive, i.e. the direction of the force coincides with the direction of the OX axis (see Fig. 9). The sign of the force Px is negative (–), this indicates that it is directed in the opposite direction from the direction of the OZ axis, i.e. the milling cutter tooth pulls the workpiece up (see Fig. 9) due to the positive angle of inclination of the screw groove ω (see Table 4). Direct proportionality of graphs Phmax = f(fmin), Pvmax = f(fmin) from the value of the feed per minute fmin (see Fig. 12) allows for t = 1 mm and the specified other cutting modes to use equations described by a linear relationship: Phmax across = 266.4+0.556∙fmin; (1) Phmax along = 200 + 0.545∙fmin; (2) Pvmax across = 100.4 + 0.899∙fmin; (3) Pvmax along = 46.2+0.135∙fmin. (4) Direct proportionality of graphs Pxmax = f(fmin) depending on the value of the feed per minute (see Fig. 13) allows for t = 1 mm and the specified other cutting modes to use the equations: Pxmax across = 10.8+ 0.162∙fmin; (5) Pxmax along = 3.97+0.128∙fmin. (6) In all the considered cases, the magnitude of the forces Phmax, Pvmax and Pxmax in the feed direction along the feed direction during the synthesis of specimens (workpieces) is slightly less than in the perpendicular feed direction (see Fig. 12 and 13). The analysis of Fig. 14 shows, despite the fact that at a cutting depth of t = 1 mm, a four-teeth milling cutter should have contact with the specimen of only one tooth and therefore the forces should decrease to zero, but this does not happen. This is most clearly seen in the graphs of changes in the feed force Ph (blue color of the graph). As the feed increases, the minimum Ph value increases. In all cases, four peaks and troughs (valleys) are clearly visible, which indicates the operation of four teeth. The different magnitude of these peaks indicates the presence of a small radial runout of the teeth. For the milling cutter used, any two adjacent teeth have the same distance from the axis of rotation of the milling cutter, as indicated by the same magnitude of the greatest Ph force. This indicates that there is a slightly different distance of the cutting edge of the teeth relative to the axis of rotation of the spindle, and not the displacement of the axis of the cutter when it is fixed in the collet chuck. I.e., the observed error appeared during the manufacture of the milling cutter, and not when it is installed in the chuck. The steepness of the rise and fall of the force Ph graph, as the most characteristic, clearly visible and important, is approximately the same (see Fig. 12, 13), although it was expected that the decrease should occur more quickly, because during conventional milling, the tooth exit has a very short exit period (the uncut chip thickness ai decreases more quickly before the tooth completely leaves contact with the specimen) compared to the period of increasing the uncut chip thickness. We explain this phenomenon by changing the direction of the force Pz as the main force when removing the allowance. Before the tooth leaves the contact, the force Pz rotates along the rotation of the cutter and increases the force Pv to a greater extent, rather than the Ph (see Fig. 12). Therefore, the decrease in the
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 force Ph does not occur so quickly, because this decrease begins earlier, even before the tooth approaches the exit point of the main cutting edge from the contact. In addition, the cutter has a slope of the cutting edge with an angle of ω (in some foreign sources this angle is indicated by the symbol β), which makes it impossible for the entire cutting edge to come out of contact with the workpiece at the same time. And the larger the milling width B and the larger the angle ω, the smoother the reduction of all forces will be. The rotation of the force vectors Pz and Py during the rotation of the milling cutter with a simultaneous increase in the uncut chip thickness ai during conventional milling leads to a slight discrepancy in the phases of changes in the forces Ph and Pv (see Fig. 14). When the cutting speed is increased from 75 to 94 m/min with the same feed fmin feed force Phmax along and Phmax across is less (see Fig. 15, compare graphs 1 and 5; 2 and 6). An increase in the milling depth t at V = 75 m/min leads to a less significant increase in the forcePvmax across (see Fig. 15, graph 3), and the force Pvmax along at V = 75 m/min even decreases slightly (see Fig. 15, graph 4), although theforcesPvmax alongand Pvmax across at different speeds differ alittle from each other (see Fig. 15, compare graphs 4 and 6; 3 and 7). At a cutting speed of V = 94 m/min, the force Pv during milling in the transverse direction relative to the feed direction during AT synthesis (Pvmax across) does not change with increasing milling depth t (see Fig. 15, graph 7). In the longitudinal feed direction, the force Pvmax along does not practically change with increasing cutting depth t and slightly depends on the cutting speed (see Fig. 15, graphs 4 and 8). This lack of influence of the milling depth t is explained by an increase in the force Pv already towards the operator at the last stage of cutting when turning the milling cutter, i.e. the tooth of the cutter begins to pull the workpiece towards the operator, and not push it away as in the initial stage. Only the force Phmax across decreases significantly with increasing cutting speed V (see Fig. 15, graphs 1 and 5), and the force Phmax along decreases slightly (see Fig. 15, graphs 2 and 6), and the remaining components of Pvmax along and Pvmax across (see Fig. 15, graphs 4 and 8, 3 and 7), Pxmax along and Pxmax across (graphs are not presented due to the absence of changes in the magnitude of these forces with increasing cutting speed) do not change. It is possible that with a significantly higher cutting speed (more than 130 m/min), the forces will decrease, as is observed when turning in the absence of an built-up edge due to an increase in the deformation rate in the zone of primary plastic deformation and a decrease in plasticity as opposed to an increase in the plasticity of the machined metal due to an increase in temperature [30]. An increase in the deformation rate leads to a decrease in the ductility of the metal and, as a result, to a decrease in the zone of primary plastic deformation, which causes a decrease in the cutting force. Conclusion During the preparation and during the execution of this study, it was possible to minimize the influence of third-party factors on the results due to a comprehensive study of both the parameters of the specimen and the tool, and the conditions of the technological environment for milling. Based on the performed research, the following conclusions are made: 1. The limiting milling modes have been determined, which ensure the absence of destruction of carbide cutters in the process of edge cutting (subtractive) machining of LMD steel 0.12-Cr18-Ni10-Ti (AISI 321), both along and across the growing direction. 2. When studying the cutting forces, it was found that an increase in the feed fmin in the range from 120 to 850 mm/min leads to a directly proportional increase in the forces Phmax, Pvmax and Pxmax described by linear equations. 3. An increase in the milling depth t by 2.5 times leads to a significant increase in the feed force Phmax, especially Phmax across up to 1,580 N, but at the same time the milling depth does not significantly affect the change in lateral and axial forces. 4. The roughness Ra of the machined surface depends on the direction of growing the additive specimen (workpiece), and when milling in modes (see Table 5) it depends more on the feed and cutting speed. At the same time, the lowest values of Ra = 0.438±0.23 μm (when milling along) and Ra = 0.510 ±0.15 μm (when milling across) are observed in the modes V = 94 m/min; fmin = 850 mm/min; t = 2.5 mm; B = 7 mm.
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