JOURNAL OF SCIENCE & TECHNOLOGY No 94-2013 THE GRAIN SIZE EFFICIENCY ON SURFACE ROUGHNESS IN ROUGH MACHINING THE HARDENED C45 STEEL USING BROWN AL2O3 GRINDING WHEELS ANH HLTCNG CtiA KICH THlTdC HAT MAI CORUNDOM AL2O3 DEN DO N H A M BE MAT CHI TIET GIA CONG KHI GIA CONG THO VAT LIEU THEP 45 NHIET LUYET Nguyen Tien Dong, Nguyen Thi Phuong Giang Hanoi University of Science and Technology Received January 30, 2013; accepted March 29, 2013 ABSTRACT Surface roughness in rough machining affects the quality and processing capacity of finis process The smaller grain Size obtains the smoother surface In this paper, the recently dev brown A/jOa grinding wheels in Vietnam, which can machine up to speed of45m/s, has been ob There are four gnnding wheels with different of grain sizes #36, 46, 60 and 90 were used to m hardened C45 steel in order to evaluate ghndabality of grain sizes The results showed that sm surface could be obtained in shorter time by coarse grains, e.g., the surface roughness of 34 could be obtained by #36 grinding wheel In 14 gnnding times, while grinding time of #46, 60 a were 15, 19 and 27 grinding times, respectively On the other hand, the bigger grain size I.e shows advantage In rough machining to obtain smoother surface than that of fine grains Keywords: brown AI203 grain, grinding wiieel, surface roughness, hardened steel 045 TOM TAT Bpnhim bS mit chi tiet gia cong tho anh hifdng den chit lupng vi nang suit cua qui tr jgia cdng lin cudi bing hat mil Thong thirimg gia cong bing hat mii, kich thiiOc hat cing nho nhim bi mat cing nho Trong bai bio niy di cap din viec khio sit vi ning gia cong cua d mii mii duvc nghien cuu gin diy a Viet nam s& dung hat mii corundum nau AI2O3 co thi gia c din vin too 45m/s C6 bin viin di mii diiijc sit dung vol kich thutao hat Miic ii #36, 46, SO duvc 5i> dung di gia cdng vat liiu thip C45 nhiet luytn nhim dinh gii nang gia cdng cua mii Kit qui cho thiy di d^t cung gii tri nhim bi mit yiu ciu gia cing thi di mil hat c6 kich ithiriic hat mii l&n cin so lin hinh trinh gia cong It han C(/ thi, dp nhim Ra 0,34pm dat duvc bai d mii cd hat #36 sau 14 hinh trinh gia cong, vai hat mii cd id hat #46, 60 vi 80 thi so Ctrinh cin thiit di dat duvc cimg gia tri dd nhim trin lin luat li 15 19vi27 hinh trinh Ndi cich khic : • kich thuac hat mii ldn hon thi hidn tinh uu viet tmng gia cdng tho han cic hat mil cd kich thudc han Introduction : Abrasive machining ,s usually used as the finishing process Thrs process affects the surface roughness and the accuracy of * , machining parts Recently, due to the demand of high speed cutting grinding wheels for machining the hard and brittle materials, some researchers in Vietnam have developed a new high speed cutting grinding wheels, which can ^^^^.^^^ ^^ ^^^ ^^^.^^ ^^^^ ^^^^^^ ^^.^^^ ,^^ ^^^^^ ^^^^^^^ ^1^^^ ^^^^^.^^ ^^^^ ^^^ ^^ j „ • r n ceramic as bonding material [1] Normally, there are many ways to evaluate the cutting ability of grinding wheels JOURNAL OF SCIENCE & TECHNOLOGY • No 94 - 2013 such as: cutting forces [2, 8], thermal of cutting [2], or thewear of grinding wheel and the workpiece The abrasive is characterized by dimensions the length, the width and the thickness; the width of grains is used for evaluate the wear of grinding wheel in some research [1.8] The wear of grinding wheels results in the sharpening decreases as well as damaged machining surface, thus leading lo the unstability of grinding process, and changing the real cutting edge on grinding wheel surface determine the efficiency and the quality of the grinding process The wheel life relates to the volume of removed material as well as the wear of grinding wheel 18,2] Qs- In this paper, the surface roughness of the workpiece and its relationship with the wear of grinding wheel, e.g grinding wheel life, was researched Experiments: Workpiece was made from hardened C45 steel with the hardness of 44-48 HRC; the sample diameter (d^) of 45mm and the length of 100 mm Grinding machine was model 3151 (made in Soviet Union) Four grinding wheels use the brown corundun Al203as abrasive grain, with different grain sizes I.e., #36, 46, 60 and 80, respectively The parameter of the wheel is given in Table l.The grinding wheels were in the process of truing and dressing before each experiment (1) Where: Q„ the volume of removed materials in unit time (mm'/s),a, the real cutting depth (mm), d^ths diameter of the workpiece (mm), Vf the feed rate, b^ the width of the grinding wheel (mm), d., the diameter of the grinding wheel (mm) The equation (I) can be written as follows: _ _ (3) Grinding is a very complex machining process, thus in order to research the phenomenons of this machining, it is usually evaluated under specific grinding conditions The grinding wheel life therefore can be estimated as the relation with the removed material in unit time and the wear of grinding wheels The wear of the grinding wheel is not constant during the machining process due to many reasons such as heat and mechanical impact of grinding process The phenomenon of the wear of the grinding wheel can be defined In many ways In this paper, the phenomenon that the grinding chips were adhered to the space between two abrasive grains on the grinding wheel surface, thus the grinding wheel became dull and lost the cutting ability, was called "the wear of grinding wheel" The wear of grinding wheel occurs through periods, the Initial wear period, the normally working period and the intensively wear period [2] The wear of grinding wheel, Q„, is a ftmction of time t (s) and the volume of removed materials in unit time (mmVs) The volume of removed materials can be calculated as follows [8] Qm = bw.ac.tP^^ n.d, Where Q, the wear of grinding wheel, d,ik diameter of the grinding wheel, b„the width of the grinding wheel (mm), u,,., the wear of grinding wheel after a transverse (mm) The cutting parametes are set a> following: workpiece velocity Vc = 20 mm/min, the cutting depth t = 0.02mm Coolant used 20 litters/ The hardness of grinding wheels and the workpiece were tested on the hardness testing machine Rockwell - Japan, the surface roughness of the workpiece was measured on the automatic roughness testing Surffest by^,.n.d^^Vf (2) The grinding wheel life represents not only the mechanical ability of the grinding wheel but also plays an important role to 96 JOURNAL OF SCIENCE & TECHNOLOGY * No 94 - 2013 SJ-201P by Mitutoyo, Japan seconds In order to meet the requirement of surface roughness Ra 0.32 |im, the transverse of machining process k, was counted during machining process, then the grinding wheel life can be estimated as: Tablel Parameter of the grinding wheel use the brown corundum AI2O3 abrasive with the ceramic bond T = k.- (4) Where k is number of double transverse, /Mthe grinding time of the workpiece has a length of 100mm, in this case ii,n got the value of 85 _ ^ I No Cn36 Cn46 Cn60 Cn8Q Grinding wheels Grain size Hardness #36(p=400-430nm) J #46(p-310-340Mm) J #60(p=250-300^m) J #80(p=i60-24Q|im) J Pa 1036 [