NGHIEN CUfU-TRAO DOI
DANH GIA K H A NANG CAT CUA DA MAI CO BE MAT LAM VIEC GIAN DOAN THONG QUA DAI LU'ONG HIEU SUAT MAI
KHI M A I T H E P 45 NHIET LUYEN
EVALUATION OF THE CUTTING CAPABILITY OF WORK SEGMENTED GRINDING WHEEL BY THE PRODUCTIVITY OF HARDENED C45 STEEL
GRINDING PROCESS
Nguyen Tien Dong*, Nguyen Thi PhUdng Giang', Trinh Van CUdng^ Nguyin Thi PhUdng' 'Vien Co khi, TrUdng Dai hpc Bach Khoa Ha Npi
-TrUdng Dai hpc Sao Dd 'Tong cue Hau can, Bd Cdng an
TOM TAT
Dd mdi xe ranh dUdc nghien cdu vd phdt trien gan day tai Viet Nam dUa tren nguyen ly gia cong gian doan dUdc sii dung nham muc dich nang cao hieu qua gia cong cua hat mdi. Hien tUdngphoi mdi chiem vd bdm dinh vao khoang khonggiUa cdc hat mdi, khien dd bi "cun", dUdc giam di. Trong bdi bdo nay, mot tieu chi danh gid dd mdi cd be mat lam viec gian doan dUdc dUa tren hieu sudt gia cong }x, dUdc dinh nghia Id ty le giUa lUdng kim loai hdt di thUc te Q^^ vd lUdng kim loai hdt di theo ly thuyet Q,^ trong mot ddn vi thdi gian, doi vdi loai thep C45 dd nhiet luyen. Nam vien dd mdi xe ranh co so ranh lan lUdt la 12,18, 20, 22, 24 vd mot vien dd mdi thong thiidng khong xe ranh, dUdc sii dung de mdi thep C45 da nhiet luyen. Ket qua cho thay lUdng kim loai Q^^ dUdc hdt di trong mot giay khi mdi thep C45 nhiet luyen vdi phUdngphap mdi phang sii dung vien dd mdi co so ranh 18 Idn hdn nhieu so vdidd mdi lien tuc thong thudng. Hieu sudt mdi doi vdi loai da mdi co so ranh ndy cho hieu sudt cao nhat.
Tii khoa: Thep nhiet luyen C45; Dd mdi gian doan; Hat mdi.
ABSTRACT
Recently developed in Vietnam segmented grinding wheels base on the fundamental of discontinuous machining is used to enhance the grindability of abrasive grains. The phenomenon of grinding chips adhesived to space between grains, that make the wheels became "dull", was reduce. In this paper, the evalution of segmented grinding wheel is based on the cutting performance ^, is defined as the ratio between the real volume of removed material Q and the theory volume of removed material Q^^ in unit time, in machining hardened C45 steel. There are five segmented grinding wheels with number of segment is 12, 18, 20, 22, 24 alternately, and a conventional grinding wheel. Results showed that when grinding hardened C45 steel by segmented wheel with 18 segments is considerably higher than the result of conventional wheels. The 18 segments wheel provides the highest processing performance comparing to the other wheels.
Keywords: Hardened C45 steel; Segmented grinding wheel. Abrasive grain. ~^
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I . G I O I THIEU CHUNG
Mai la qua trinh xuat hien sU tach mdt Idp vat lieu ra khdi vat gia cdng d dang phoi. Dung cu mai cd nhflng tinh chat dae trUng nhat dinh nhU:
Vat lieu hat mai, dd hat, dp cUng, dd rong, chat dinh ket... Kich thude va hinh dang hat mai lai bi thay doi trong sudt qua trinh mai. SU thay doi nay lam thay doi kha nang cat cua nd, thay ddi tinh chat ban dau cua da mai gay ra sU mdn dung cu.
Khai niem "kha nang gia cdng" dupe nhieu nha nghien euus quan tam. De xac dinh dupe kha nang cat cua da mai phai dUa tren dac diem dac trUng cua qua trinh mai, tfle la vat lieu dupc tach ra bIng mdt lUpng Idn cac hat mai dUOc bo tri ngau nhien tren be mat da vdi cac thdng sd hinh hpc khdng xac djnh.
Vi vay, kha nang eat cua da mai la kha nang tao phoi tU vat lieu gia cdng tren co sd mdt nang lUpng tieu bao nhat dinh va vdi lupng hao mdn cho phep cua da [ 1,2,3].
2. M O T S O C O S 6 D A N H GIA KHA NANG CAT CUA DA MAI
De danh gia kha nang cat cua da, ed the sfl dung mdt hay mdt sd chi tieu vdi dieu kien gia cdng da dinh, dd la ty le giUa: LUpng bdc vat lieu va lUpng mdn cUa da, hay gifla cdng suat mai va Iflc cat khi mai, dp nhap nhd be mat sau khi mai...Da mai ed kha nang cat tot khi ed lUc eat nhd, cdng suat mai nhd, lUpng mdn cua da mai it nhUng cd kha nang duy tri kha nang bdc vat Heu va chat lUpng be mat chi tiet gia cdng eao.
Nhieu tac gia da quan tam den kha nang cat cua da va dUa ra phUpng phap danh gia khae nhau. Cach danh gia cd the tien hanh tren co sd cua mdt sd hien tUpng co, ly thich hpp dupe chpn nhU: Mat dp Idp vat lieu gia cdng, dp Idn cua lUc, sdng va chat lUpng be mat gia cdng [2,4,5], Mot vai tieu chuan khac lien quan den thdng sd co ban cua cdng nghe mai: Tudi ben da, tdc dp mai, tdc dp chi tiet, tdc dp tien dao, phUPng phap mai va
dp cflng vUng cua he thong cdng nghe...Tac gia Armarego [6] da de xuat mot tieu chuan mdi ve kha nang eat cua da xuat phat tfl viec danh gia giai doan phat tia Ifla cua qua trinh mai.
3. DANH GlA KHA N A N G CAT CUA DA M A I THONG QUA HIEU SUAT M A I
Tac gia R.Snoes, J.Peters [6,7] da ehi ra tich so: h.VydO.Vj, dUpc trinh bay nhU hinh 1, la dai lupng cd quan he vdi hau het cac dai lUpng khac trong qua trinh mai. Dai lUpng nay dUpe gpi la chieu day edt tUOng dUOng, heq, y nghia ciia dai lupng nay cho rang the tich Idp vat lieu dupe bdc ra bdi da mai d toe dp Vd bang vdi the tich Idp vat lieu dupc bdc ra khdi vat gia cdng sau mot don vi thdi gian.
• C/ip,\,^,-l~:r'^—^—r-—
-'i t h , , v^i I'l
r
Hinh 1: Chieu day cat tUdng duong khi mai phang.
Tren nguyen tic bao toan lugng vat lieu di vao va di ra khoi vung cat ta co:
t.b.V, =h,,.b.V|
Trong do:
(1) (2)
b: Chieu rong tiep xiic giiia da va chi tiet;
V,: Toe do chi tiet;
V^: Toe dp da (m/s);
t: La chieu sau cat (mm).
The tich vat lieu hoc ra trong mot ddn vi thdi gian theo ly thuyet: Q„ = b.t.V ^ (3)
The tich vat lieu dupc hoc ra trong mot don vi thdi gian doi vdi 1 don vi chieu rpng lam viec cua da mai la: Q^ = t.V ^ = h^ .V^. (4)
S
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HieusuatmaidUpcMaxiop[8]danhgiabang va thdng sd cua cac vien da mai gian doan dupe ty le ^1 = Q,, /Qj^ <1. (5) trinh bay trong cac Bang 1 va 2.
Trong do:
Qj^: Lupng kim loai thfle te trong mdt don vi thdi gian;
Qi^: Lupng kim loai theo ly thuyet trong mot don vi thdi gian.
Ty sd nay, cho thay nang suat bdc vat lieu thUc te khi mai ludn nhd hpn so vdi ly thuyet dUpc xac dinh bdi che dp gia cdng da cho. Ty sd nay dac trUng cho hieu qua cua qua trinh mai thfle te [5,6,7]. Dai luong nay phu thudc vao rat yeu to nhU; Lflc phap tuyen, dp cUng vflng cua he thdng cdng nghe, chieu day Idp vat lieu dUpc bdc, nang suat rieng, tudi ben eiia da mai, thdi gian sfla da...
Trong qua trinh mai thUc te, do anh hUdng cua cac yen td ke tren nen nang suat cua qua trinh mai ludn thap.
Da mai xe ranh, thUc te se ed it sd hat mai d tren be mat da hon so vdi da mai hen tuc, vi vay the tich Idp vat lieu dupe hdt di theo ly thuyet cua da xe ranh se it hpn so vdi da mai lien tuc. Bai bao nay xem xet kha nang cat ciia da mai xe ranh thdng qua dai lUpng hieu suat mai khi gia cdng thep 45 da nhiet luyen.
• Da mai gian doan:
Trong thi nghiem nay, mdt vien da mai thdng thflcfng va nam vien da mai gian doan da dflpc sfl dung. Cac vien da mai cd cung dudng kinh, dp rpng, cung chat dinh ket va che dp sfla da, kich thudc hat, do hat va dp cUng, cung nha san xuat (Cdng ty Da mai Hai Dflong). Vien da mai thdng thUdng cd be mat lam viec lien tuc (ty le gian doan = 0%) trong khi cac vien da mai gian doan dupe xe cae ranh each deu nhau quanh ehu vi d^' cd cac ty le gian doan khac nhau.
Hinh 2 la anh chup mdt trong sd cae vien da mai gian doan. Tlidng sd chung cua da mai
Bang 1. Thdng so chung cua dd mdi 1. Ky hieu da: Cn46 MV2 350x40xl27-35m/s 2. Dudng kinh ngoai cua da: 350 (mm) 3. Dudng kinh trong cua da: 127 (mm) 4. Be rpng cua da: 40 (mm) 5. Van tdc da: 35 (m/s) 6. Hat mai: Cn46 GV6 MV2 7. Chat ket dinh: Gom
Bang 2. Thong so cua dd mdi gian doan Vien da
Vien so 1 Vien sd 2 Vien sd 3 Vien sd 4 Vien sd 5
So ranh d a z
12 18 20 22 24
Goc gifia 2 ranh da lien tiep a (do)
30 20 18 16.36
15
Ty le gian doan (%)
10.91 16.37 18.19 20.01 21.83
HJnh 2: Thdng so hinh hoc cua dd mdi xe ranh vdi goc a, chieu rdng ranh w vd chieu sau ranh b 4. QUA TRINH THI NGHIEM
Qua trinh mai dUpc thUc hien bdi may mai phang OKAMATO san xuat tai Nhat Ban cd cae thdng sd ky thuat cua may mai dupe Met ke trong Bang 3. Hinh 3 chup anh da mai da dUoc ga tren may.
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Bdng3. Thong so'ky thuat cua may mdi
Thdng so ky thuat 1. Kich thudc mav 2. Kich thudc ban may 3. Hanh trinh lam viec cua ban may
Dai (mm) 4.280 2.150 1.200
Rong (mm) 1.850 800 520
Cao (mm) 2.190 350 4. Cdng suat cua dpng co true chinh: IIKW
Hinh 3: Gd da len mdy mdi
Phdi thep sfl dung cho qua trinh thi nghiem la thep C45 da qua nhiet luyen dat dp cflng 42-43HRC, san xuat bdi Cdng ty TNHH Van Xuan, cd kich thUde axbxc = 100x35x40mm.
Hinh 3 la anh chup mdt m i u phdi sfl dung trong thi nghiem.
Hinh 4: Phdi thep C45 nhiet luyen cd kich thUdc 100x35x40mm, dat dd cdng 42-43 HRC.
Ddi vdi tat ca eac thi nghiem, van tdc cat V va Iflpng chay dao s dflpc gifl ed dinh d cac gia tri v=35m/s, s=12m/ph, trong khi chieu sau cat t
dupc thay doi lan lUpt la 0,015mm; 0,025mm va 0,05mm. Moi lan cat dupe thUc hien vdi 10 hanh trinh kep. Viec do chieu sau eua Idp kim loai thUc te dupe hdt di sau 10 hanh trinh kep dUpc thUc hien bdi mdt thUde cap dien tfl Mitsubishi.
Gpi Q^^" la the tich kim loai thUc te dflpc hdt di trong 10 hanh trinh kep, la thdi gian thfle hien mot hanh trinh kep cua ban may (tinh bang giay). Ta xac dinh dUpc the tich kim loai thUc te dupc hdt di trong 1 hanh trinh kep trong thdi gian 1 giay theo edng thfle:
~ lO.r " 10.L Vdi:
a
— {mm^/s) (6)- S |,^,=axb (mm^): Dien tich be mat phoi;
- : Chieu sau Icfp kim loai thUc te dupc hcit di sau 10 hanh trinh kep (mm);
- L: Quang dUdng di chuyen cua ban may trong 1 hanh trinh kep L=2.300=600(mm);
- V^^: van toe ciia ban may, V^^=12m/ph
=200mm/s."
Cac gia tri Q|| thu dupc trong qua trinh thi nghiem dupc xil ly va bieu diSn tren do thi bang phan mem Sigma Plot cho phep so sanh va danh gia ket qua.
5. KET QUA THi NGHIEM VA THAO LUAN Moi quan he giiJa the tich kim loai thUc te dupc hdt di Q^^ vdi so ranh z cua da mai tuang ling vdi chieu sau cit t thay doi dupc bieu dien tren hinh 5.
Co the thay ring, d che dp cit vdi chieu sau cat t| = 0,15mm, khi tang so ranh da thi gia tri Qjj tang nhanh den mot gia tri cao nhat, sau dd dupc giii kliong doi khi tiep tuc tang so ranh da. Tang chieu sau cat len t, = 0,025mm, va t, = 0,05mm thi quy luat nay cang dupc t h i hi^n ro rang, tdc la Q^^ tang nhanh den gia tri a l e dai sau do giam dan. Gia tri Q^^ cao nhat dat diipc doi vdi vien da CO z = 18 va cao hpn so vdi vien da mai lien tuc thong thUdng. Dieu nay cd the giai thich tren cac phupng dien sau day.
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Hmh 5: The tich kim loai thUc te'Q^diidc boc ra trong mdt ddn vi thdi gian khi chieu sau cat t thay doi
Ddi vdi da mai lien tuc thdng thUdng, sU gia cong dflpc thfle hien Hen tuc tren be mat da, sd luong ludi cat tham gia qua trinh cat Idn nen sd lupng phoi mai tao ra trong qua trinh cat eiing Idn. Cac phoi mai khdng dUpc day ra ngoai vung eat se tich tu lai nhanh chdng tai cac 16 trdng gifla cac hat mai. SU tiep can cua dung dich tron ngupi khi mai vdi da mai lien tue gan nhu chi thUe hien d dau vung mai, sfl tac ddng trUc tiep vao khu vUc mai d£ lam sach be mat va cuon phoi mai ra ngoai la khd khan. Dieu nay, cang lam tang sfl tich tu cua phoi, dan den phoi mai se dien day va chiem khdng gian tai eac lo xdp tren be mat da mai. Cac hat mai khi do gan nhfl bi "bit" lai bdi cac dam phoi va mat di kha nang tfl mai sic. Ket qua la dan den hien tUpng "cun", "bet da". Day la nguyen nhan khien cho eac hat mai mat di kha nang cat gpt, giam hieu qua bdc tach vat Heu.
Khi da mai dflpc xe ranh, chinh nhflng khoang gian doan tren be mat lam viec cua da giup de dang cuon cac phoi mai ra khdi khu vfle cat va cung cap dich trOn ngupi de ngan ngfla hien tUpng leo dao d dau cac hat mai dang lam viec. Di^'u nay rat quan trpng vdi hat mai min cd khoang trong 16 xop qua nhd. Nd giup day phoi va ngan ngfla sfl dinh phoi trong Id xop cua be mat da mai. SU bd tri cua cac ranh da cung tao ra sU tiep can cua dimg dich tron ngupi vao vimg gia cdng triet de hon (hinh 7). Chinh dieu nay lam cho hien t ' o n g tac nghen khoang trong gifla cac hat m^> 1 ' 'S ^^y ^^ ^^ ^ ° ^^ ^^° ^^ ^ ^ nang bdc tach vat iieu cua da mai gian doan tot hon da mai
Hinh 6: Hieu sudt mdi p doi vdi dd mdi co so ranh khdc nhau khi chieu sau cat thay doi Hen tuc thdng thudnj
Hinh 7: Hinh gidi thich sU khdc nhau ciia dung dich trdn ngudi tiep xuc vdo vung gia cdng khi sii dung dd
mdi lien tuc vd dd mdi gian doan TU ket qua thi nghiem cho thay gia tri Q^^
ddi vdi vien da z = 18 dat cao nhat khi cat vdi ca 3 chieu sau cat t^, t,, t^, tUOng flng vdi the tich boc la hieu suat cua qua trinh mai doi vdi loai da nay cung la eao nhat. Vien da ed z = 18 ed the xem la lUa chpn tdi flu de cho Q^^ cao hon so vdi da mai thdng thfldng vdi che dp cat dflpc xac dinh la v = 35m/s, s = 12m/p, t^ = 0.015mm.
Khi dudng kinh da thay ddi, sd thdng sd dac trUng cua viec gian doan (sd lUpng ranh, khoang each ranh...) cung thay doi theo, vi vay, sd ranh z-18 the hien Uu diem ve gia tri Q^^ flng vdi dudng kinh da xac dinh la 350 mm. Tuy nhien, dUa tren ket qua nghien eflu nay se tim ra dUpe quy luat cua bd thdng so phu hop cho cac che dp gia cdng khac nhau khi thay doi dUdng kinh da,
sd ranh, vat lieu gia cdng... '^
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6. KET LUAN
Viec xe ranh da mai tao ra cac khoang gian doan tren b^ mat da, giup hinh thanh cac khoang trdng de thoat phoi va lam cho sU tiep can cua dung dich trpn ngudi vao vung gia cdng triet de hon.
Nd giup cho cae phoi sinh ra trong qua trinh mai thoat ra khdi vung gia cdng de dang, ngan ngfla sfl tich tu phoi mai tai eac Id xdp tren be mat da, lam giam hi6n tflpng cun, bet da va do dd lam tang kha nang eat gpt cung nhU hieu qua gia cdng cua da mai gian doan.
Da mai gian doan cho thay tinh Uu viet hon so vdi da mai thdng thUdng trong kha nang bdc tach vat lieu, nang cao hieu qua gia edng, hieu suat mai tang eao hon so vdi da mai thdng thUdng. • Ngay nhan bai: 02/4/2014
Ngay phan bien: 04/4/2014
Tai lieu tham khao:
[1]. Banh Tien Long, Tran Sy Tuy, Tran The Luc, Nguyen ly gia cong vat lieu, NXB. Khoa hoc va Ky thuat. Ha Npi (2001).
[2]. Kristek-EObrobitelnost matepialu Praha. 200102. Page 173-181.
[3]. Nakayama,K.,Takagi,J.,andNakano,T„ Peculiarity m the Grinding of Hardened Steel, Annals of the CIRP, 23(1): 89-90 (1974).
[4]. Komanduri,R., Lucca, D.A., and tani,Y., Technological Advances in Fine Abrasive Process, Annals of the CIRP, 46 (2) : 545-596 (1997).
[5]. Michele H. Miller (1) and Xiaorui Fan (2) "Wheel wear during intermittent grinding" Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University (1) —Houghton, Ml American Showa, Inc. Sunbury, OH (2).
[6]. Chandrasekaran,T.,Natara]an,K.A., and Knshore, Influence of microstructure on the wear of grinding Media, Wear, 147(2): 267-274 (1991).
[7]. Buckley, D.H., Importance and definition of materials in tribology - Status of understanding, tribologyin the 80s, (W.R. Loomis.ed.) pp.18-42, Noyes PubL.NJ (1985).
[8]. Nguyen Tien Dong, Nguyen Thi Phuong Giang, TrUdng DHBK Ha Npi "Khd ndnggidm lUc cat khi gia cong vat lieu ceramics sd dung dd mdicd he mat lam viec gian doan", Tap chi Khoa hoc va Congnghe - So 81.
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