INCREASING THE WORKING EFFICIENCY OF ABRASIVE GRAINS IN MACHINING SKD11 STEEL BY USING NEWLY DEVELOPED INCLINED SEGMENTED GRINDING WHEEL

HỘI NGHỊ KHCN TỒN QUỐC VỀ CƠ KHÍ - ĐỘNG LỰC NĂM 2017 Ngày 14 tháng 10 năm 2017 Trường ĐH Bách Khoa - ĐHQG TP HCM INCREASING THE WORKING EFFICIENCY OF ABRASIVE GRAINS IN MACHINING SKD11 STEEL BY USING NEWLY DEVELOPED INCLINED SEGMENTED GRINDING WHEEL Tien Dong Nguyen* Hanoi University of Science and Technology, No 1, Dai Co Viet, Hai Ba Trung, Hanoi, Viet Nam ABSTRACT: In this paper, newly developed inclined segmented grinding wheel (ISGW), which have segments on the working surface; angle between these segments and a shaft of grinding machine β=15º, were used to grind SKD11 steel which is popular material in mold making technology The percentage of discontinue on wheel surface symbolized by η, is defined as the ratio between the area does not containing abrasive grains and the total area of wheel surface Four ISGWs, with different percentage of discontinue η (16.37, 18.19, 20.01 and 21.83%) and a conventional wheel with η = 0% were used in experimental process The number of abrasive grain in contact with sample surface per unit area per second , was calculated to evaluate the efficiency of abrasive grains by wheel rotation speed, feeding speed and percentage of discontinue η Surface roughness of ground sample was employed When the number of abrasive grain increase or the feeding speed S decrease, the surface roughness of surface ground by conventional grinding wheel decrease, but it obtained the same values by using ISGWs It seems that the surface roughness does not depend on number of abrasive grain participate in the grinding process In other word, the working efficiency of abrasive grains can increase up to 20% as increasing of the feeding speed from 12 m/min to 15 m/mm using inclined segmented grinding wheels Keywords: inclined segmented grinding wheel (ISGW), SDK11 steel, roughness, abrasive grains INTRODUCTION In the last few years, grinding process is a strategic process for machining new materials with tough characteristics, such as hard and brittle materials, ceramics, etc, which required a good accuracy and a high quality of surface roughness Grinding process can be used to combine high removal rate with high accuracy [1] Alternatively, grinding can be employed with moderate removal rates to produce high accuracy parts in large volumes In manufacturing mold plate, spherical grinding plays an important role because it is the simplest and least expensive process for machining materials which is popular in mold making technology To increase the productivity and quality of grinding process, researchers not only spend time to optimize the parameters on machine, apply new materials but also present new design of wheels to reduce average force and temperature to have better surface roughness, such as cup-type diamond-grindingwheels with hexagonal pattern were used to grind ceramic material shows advantage of increasing effective working abrasive grains in comparison with conventional grinding wheels [2] According to the previous researches, smoother surface can be obtained by decreasing speed rate or decreasing cutting depth [3-14], but speed rate or cutting depth have the limit depending on ground samples or grinding machines In this work, newly developed inclined segmented grinding wheels - ISGW with different number of segments on the wheel surface are used to grind SKD11 steel, which is applied widely in manufacturing mold plate and base The effects of abrasive grains and surface roughness of ground sample are evaluated This paper reveals a new mechanism of grinding process by the proposed ISGWs Trang 145 HỘI NGHỊ KHCN TỒN QUỐC VỀ CƠ KHÍ - ĐỘNG LỰC NĂM 2017 Ngày 14 tháng 10 năm 2017 Trường ĐH Bách Khoa - ĐHQG TP HCM EXPERIMENTAL Newly developed grinding wheel inclined segmented experiment, grinding wheels were dressed by industrial diamond grinding stone with grinding conditions of 0.1 mm cutting depth, 450 rpm wheel rotation speed in order to obtain flatness on the wheel surface Figure Inclined segmented grinding wheel which has outside diameter D = 350 mm, inner diameter d = 127 mm, wide of segment w = 10 mm, height of segment h = 15 mm, thickness B = 40 mm and inclined angle β=15 These wheels are characterized by number of segment Z, and inclined angle of segment β=15º All the wheels have outside diameter of 350 mm, inner diameter of 127 mm, wide and height of segment are 10 mm and 15 mm respectively Percentage of discontinue η, is defined as the ratio between the area does not containing abrasive grains and the total area of wheels Four inclined segmented grinding wheels with different η (16.37, 18.19, 20.01 and 21.83%) and a conventional wheel with η = 0% were used as shown in Table Figure Grinding machine AMADA WASINO SE63 Figure Surface roughness Mitutoyo SJ-301 Table Number of segment Z and % discontinue η of grinding wheels Z η Z=0 Z = 18 Z = 20 Z = 22 Z = 24 0% 16,37% 18,19% 20,01% 21,83% Experiment procedures Samples are SKD11 steel with dimensions of Length x Wide x Height = 60x30x10 mm A sample was placed at the center of machine table so that long edge was perpendicular to the shaft of machine Conventional and inclined segmented grinding wheels (Cn46 MV2 350x40x127-35m/s) were used Before each Trang 146 Grinding wheel rotation speed 450 rpm for the whole experiment process On each grinding wheel, experiment was carried out on different cutting conditions with cutting depth was 0.02 mm per pass, feeding speed were 12, 15 and 20 m/min alternatively The wheels were redressed before each grinding experiment The coolant water was sprayed into the contact zone between grinding wheel and sample during grinding process Grinding conditions are listed in Table The surface roughness, was measured using roughness tester Mitutoyo SJ-301 HỘI NGHỊ KHCN TỒN QUỐC VỀ CƠ KHÍ - ĐỘNG LỰC NĂM 2017 Ngày 14 tháng 10 năm 2017 Trường ĐH Bách Khoa - ĐHQG TP HCM Table Specifications of grinding wheels, grinding conditions and sample Grinding wheels Inner diameter: 127 mm Outside diameter: 350 mm Thickness: 40mm Segment wide: 10 mm Segment height: 15 mm Inclined angle: 15º Cn: Corundum abrasive 46: Size of abrasive grain MV2: Hardness Grinding condition Rotation speed: 450 rpm Cutting depth: 0.02mm and 0.05mm Feeding speed: 12, 15 and 20 m/min Sample Material: SKD11 Length: 60mm Wide: 30mm Height: 10mm RESUTS AND DISCUSSION Figure and show surface roughness Ra as function of number of segment Z for different feeding speed S = 12 and S = 15 m/min respectively The same trend of the surface roughness on sample ground by ISGW with different feeding speeds can be observe Discussion With small change in number of segment Z, depth of cut a or feeding speed S It is difficult to recognize the differences of input parameter between different cutting conditions Number of abrasive grain participate in grinding process is possible choice in this situation Figure Peripheral surface of conventional grinding wheel Number of abrasive grain in contact with sample surface per unit area per second on conventional grinding wheel: ∙ = (grain) (1) Where grinding wheel revolution to complete the grinding process along the length of workpiece in the experiment; is a number of abrasive on working surface of grinding wheel, in the conventional wheel used in the experiment = 109900 grains Figure Sample surface roughness Ra as function of number of segment Z at S = 12 m/min, a = 0.02 mm on SKD11  = 12 m/min = 200 mm/s Time need to complete the grinding process along the length of workpiece: = = = 0.3 (s) (2) Grinding wheel revolution to complete the grinding process along the length of workpiece: ∙ V = 0.3 ∙ 24.17 = 7.251 (rev) = (3) Number of abrasive grain in contact with sample surface per unit area per second by conventional grinding wheel: = Figure Sample surface roughness Ra as function of number of segment Z at S = 15 m/min, a = 0.02 mm on SKD11 ∙ = ∙ = 332 (grains) (4)  = 15 m/min = 250 mm/s Time need to complete the grinding process along the length of workpiece: Trang 147 HỘI NGHỊ KHCN TOÀN QUỐC VỀ CƠ KHÍ - ĐỘNG LỰC NĂM 2017 Ngày 14 tháng 10 năm 2017 Trường ĐH Bách Khoa - ĐHQG TP HCM = = = 0.24 (s) (5) Grinding wheel revolution to complete the grinding process along the length of workpiece: = (6) ∙ V = 0.24 ∙ 24.17 = 5.801 (rev) Number of abrasive grain in contact with sample surface per unit area per second by conventional grinding wheel: ∙ = = 5.801 ∙ = 266 (grains) (7) The number of abrasive grain in contact with sample surface per unit area per second on ISGW can be calculated due to percentage of discontinue η on table Table Number of abrasive grain in contact with sample surface per unit area per second on each grinding wheels at S = 12 m/min and S = 15 m/min TT Z % discontinu eη Number of abrasive grain Z=0 332 266 Z = 18 16,37% 278 222 Z = 20 18,19% 272 218 Z = 22 20,01% 266 213 Z = 24 21,83% 260 208 Figure 7, illustrate the relation between number of abrasive grain in contact with surface sample per unit area per second XS and surface roughness Ra On conventional grinding wheel, the surface roughness Ra decrease when the number of abrasive grain in contact with sample surface per unit area per second increase or the feeding speed S decrease This result is in accord with metal cutting theory, which has been published in many researches about grinding operation, there are clear differences in surface roughness among different number of abrasive grain [4-6] However, on ISGW, the desired surface roughness can be achieved at the cutting conditions with less number of abrasive grain To put it differently, on ISGW, surface roughness does not depend on number of abrasive grain participate in the grinding process As shown in Figure 8, Curve (I) for feeding speed S = 12 m/min and Curve (II) for feeding speed S = 15 m/min in figure By multiplying 0.75 to the value of for the feeding speed S = 12 m/min, Curve (I) of feeding speed S = 12 m/min superposes on Curve (II) for feeding speed S = 15 m/min as shown in Figure In other words, working efficiency of abrasive grain on ISGW can increase by 25% by increasing the feeding speed from 12 m/min to 15 m/min Figure Surface roughness, versus number of abrasive grains XS Curve (I) for feeding speed S = 12 m/min and Curve (II) for feeding speed S = 15 m/min Figure Number of abrasive grain in contact with sample surface per unit area per second as function of surface roughness Ra at a=0.02m/min Trang 148 HỘI NGHỊ KHCN TỒN QUỐC VỀ CƠ KHÍ - ĐỘNG LỰC NĂM 2017 Ngày 14 tháng 10 năm 2017 Trường ĐH Bách Khoa - ĐHQG TP HCM Figure Surface roughness, Ra versus number of abrasive grains XS Curve (I) of feeding speed S = 12 m/min is superposed on Curve (II) of feeding speed S = 15 m/min by multiplying 0.75 to the value of XS of feeding speed S = 12 m/min [3] S Malkin, Grinding Technology Theory and Applications Machining with Abrasives, Chichester, England: Ellis Horwood Limited Publication, 1989 [4] M C Shaw, Principles of Processing, USA: Oxford Publications, 1996 [5] J E Mayer and G P Fang, "Effects of Grinding Parameters on Surface Finishing of Ground Ceramics", Annals of the CIRP, vol 44, 1995 [6] G Warnecke and U Rosenberger, "Basic of Process Parameter Selection in Grinding of Advanced Ceramics", Annals of the CIRP, vol 44, 1995 [7] J Pe´rez, S Hoyas, D.L Skuratov, Yu.L Ratis, I.A Selezneva, P Ferna´ndez de Co´rdoba, J.F Urchueguı´a eHeat “Transfer analysis of intermittent grinding processes”, International Journal of Heat and Mass Transfer 51 (2008) 4132–4138 [8] Taghi Tawakoli, Bahman Azarhoushang* (2011) “Intermittent grinding of ceramic matrix composites (CMCS) utilizing a developed segmented whell” [9] Xiarui Fan, Michele Miller, Force analysis for segmental grinding, chining Science and Technology, 10 (2006), 435-455 CONCLUSIONS In this work, samples made by SKD11 steel are ground by a conventional and newly developed ISGWs The abrasive grain efficiency and surface roughness were evaluated The following can be concluded:    Surface roughness of sample ground by conventional wheel decrease as the number of abrasive grain increase On ISGWs, surface roughness obtained the same values when feeding speed S are changed from 12 m/min to 15 m/mm alternately In other words, surface roughness does not depend on number of abrasive grain participate in the grinding process It is possible to increase the working efficiency of abrasive grain on ISGW by 25% by increasing the feeding speed from 12m/min to 15m/min REFERENCES [1] W B Rowe, Principles of Modern Grinding Technology, Massachusetts: Elsevier, 2013 [2] Tien Dong NGUYEN, Koji MATSUMARU, Masakazu TAKATSU and Kozo ISHIZAKI, "Abrasive Grain Efficiency And Surface Roughness For Machining Ceramics By Newly developed Cup-Type DiamondGrindings-Wheels," Advantage in Technology of Material and Material Processing, vol 10, pp 77-84, 2008 Abrasive Science [10] Agarwal S, Venkateswara Rao P, “A new surface roughness prediction model for ceramic grinding”, Proc Inst Mech Eng, B J Eng Manuf, 219 (11) (2005) 811–821 [11] Young HT, Liao HT, Huang HY, “Surface integrity of silicon wafers in ultra precision machining”, Int J Adv Manuf Technol, 29(3–4) (2006) 372–378 [12] W H Tuan, J C Kuo, “Effects of grinding parameters on the reliability of alumina”, Materials Chemistry and Physics, 52 (1998) 41-45 [13] R Gupta, K S Shishodia, G.S Sekhon, “Optimization of grinding process parameters using enumeration method”, Journal of Material Processing Technology, 112 (2001) 63-67 [14] G F Li, L S Wang, L B Yang, “Multi- parameter optimization and control of the cylindrical grinding process”, Journal of Material Processing Technology, 129 (2002) 232-236 Trang 149 ... EXPERIMENTAL Newly developed grinding wheel inclined segmented experiment, grinding wheels were dressed by industrial diamond grinding stone with grinding conditions of 0.1 mm cutting depth, 450 rpm wheel. .. of abrasive grain participate in the grinding process It is possible to increase the working efficiency of abrasive grain on ISGW by 25% by increasing the feeding speed from 12m/min to 15m/min... conventional grinding wheel: ∙ = (grain) (1) Where grinding wheel revolution to complete the grinding process along the length of workpiece in the experiment; is a number of abrasive on working surface of