Ligfa (clhi(0)]ni dhie (do c a t Iklhui plhiay amw §k(d
IL ^
B)diWg k y tlhiiu[(fiit b e m a t clhil t i e u
(*) NGUYEN VAN DU"
(**) PHAN THI HLTONG
TOM TAT
Bai bao nay trinh bay mot each thiic xac dinh che dp cat da muc tieu l<hi phay tinh thep lam l<hudn SKD 61 (AISIHIS) bang phuang phap be mat chi tieu (Response Surface Methodology-RSM). Ky thuat leo doc Box-Wilson, thie't ke t h i nghiem toan phan va phan tich phUdng sai da dUdc sCr dung de l<hao sat cac mau SKD 61 dugc phay tinh sau l<hi tdi ciing 45-48 HRC. Ke't qua cho tha'y, cd the phay ciing SKD 61 dat do nham Ra tdi 0,2 mieromet vdi nang sua't cat 0,45 gam/phut. Quy trinh gia cong l<hudn mau hien dang sir dung tai nhieu ca sd san xua't, cd the loai bd nguyen cdng danh bdng tiep sau nhd ke't qua nghien ciJu nay.
1. DAT VAN DE
Phay cirng (Hard milling) la ten ggi thudng dugc dimg de chi qua trinh phay vat lieu cd dp cirng 35 - 70 HRC [1- 3]. Dac biet, trong che tao khudn mau vdi nhirng loai vat lieu cd dp cirng va do ben cao, xu the gia cdng tinh bang cat ggt sau nhiet luyen thay cho mai dang trd nen phd bien [4,5,10]. Nhieu nghien ciru da khang dinh, nham be mat [4-11] va nang suat gia cdng [4,10] la cac ehi tieu quan trgng cua qua trinh gia cdng tinh bang phay cirng. Nghien ciru thuc nghiem bang ky thuat be mat chi tieu (Response Surface Methodology - RSM) [12] duge sir dung phd bien cho bai toan nay
[4,5,7-10].
0 Viet Nam, phay cirng khudn mau lam bang SKD 61 (AISI H13 [4]) thay cho mai ciing dang dugc thuc hien d nhieu ca sd san xuat. Tuy nhien, tdc do true chinh may gia cdng chi khoang 3.000-4.000 vdng/phut, thugc nhdm tdc do quay trung binh. Ci mdt sd ca sd, khudn mau thudng dugc nhiet luyen dat do rin 45-48 HRC, phay tinh, sau dd danh bdng va tham Ni-to. Khao sat thuc te cho thay, vdi che do cat chgn theo kinh nghiem, do nham thudng chi dat dugc trong khoang 0,6 den 1,5 mm. Den nay, van de nang cao do nham gia cdng tinh
(*) Truong Dai hoc Ky tluiat Cong nghiep Thai Nguyen (**) Truong Cao dang Cong nghiep Viet-Du'c, Thai Nguyen
bang phay cirng vat lieu SKD 61, dac biet trong pham vi tdc do cua cac may CNC, dang dugc sir dung pho bien d Viet Nam (vai ngan vdng/ phut), van chua dugc de cap den.
Bai bao nay trinh bay mgt giai phap cho van de tren.
Bang each ap dung ky thuat tdi uu hda theo phuong phap be mat chi tieu (RSM), mgt loat eac thi nghiem da dugc thiet ke va trien khai nham xac dinh vimg che dp cat thda man ddng thdi hai chi tieu nham be mat va nang suat cat. Cach tiep can nay cd the dugc phat trien cho cac cap do cirng hay cac vat lieu khac va tren cac trung tam gia cdng khac nhau.
2. VAT LIEU VA PHlTONG PHAP THI NGHIEM 2.1. Dung cu thi nghiem
Cac thi nghiem dugc tien hanh khi phay mat phang cd be rgng 6 mm, chieu sau cat 0.1mm, tren eac man lam bang vat lieu SKD 61, tdi va ram dat do cung 45-48 HRC. Qua trinh gia cdng dugc thuc hien tren may phay CNC Ctek KM80/100D tai trudng Cao dang cdng nghiep Viet Dire - Thai Nguyen. May thugc Model KM - 80D, do Dai Loan san xuat nam 2005, cd dai toe do tmc chinh tir 0 den 6.000 vdng/
phut; pham vi toe do chay dao ddng tir 10 den 8000 mm/phut. Thanh phan hda hgc cua vat lieu dugc kiem dinh bing may ARL 4360 va duge trinh bay, trong bang 1.
TAP C H i c a KHi VIET NAM V So 09-Tiiang 9 nam 2010
Bang 1: Thanh phan ca ban vat lieu SKD 61 Nguyen to
Ham lugng (%) trong SKD 61 chuan Ham lugng (%) trong mau thi nghiem
C 0 . 3 2 - 0 . 4 2
0.39
Si 0 . 8 0 - 1 . 2
0.97
Mn
<0.50 0.41
Cl 4 . 5 - 5 . 5
5.44
Mo 1 - 1 . 5
1.25
V 0 . 8 - 1 . 2
0.83 Dung cu gia cdng la dao phay ngdn SPSED4A, phu
PVD - TiAIN, dudng kinh 10 mm ciia hang Okazaki - Nhat Ban. Nham be mat sau gia cdng dugc do bang may Mitutoyo - SJ 201P do Nhat Ban san xuat.
2.2. Thiet ke thi nghiem
Tien trinh thi nghiem dugc thiet ke theo phuong phap be mat chi tieu [12], bao gdm 3 budc sau:
Budc 1: Tien hanh cac thi nghiem toan phan, 2 yeu td la lugng chay dao S (mm/ph) va tdc dp true chinh n (v/ph). Muc dich la xac dinh md hinh quan he don gian giiia nham be mat va 2 yeu td dau vao. Phuong trinh hdi quy bac nhat cd dugc tir ket qua thi nghiem se dugc dung lam ca sd cho budc 2.
Budc 2: Dua vao phuong trinh hdi quy bac nhat, xac dinh budc va hudng leo ddc theo phuong phap Box- Wilson. Muc dich la tien nhanh den vung cd nham be mat nhd nhat, khao sat cac diem trong pham vi toe do va lugng chay dao ciia may.
Budc 3: Thiet ke va trien khai thi nghiem dang quy hoach hgp-tam xoay CCD (Central Composite Design) de xay dimg md hinh quan he giiia cac ham chi tieu la nham be mat va nang suat cat vdi cae thdng so che do cat. Ky thuat tdi uu hda bang phuang phap xep chong dudng mire (Overlaid contours) dugc sii dung de xac dinh -vimg che do eat tdi uu da muc tieu.
3. KET QUA VA THAO LUAN
Budc 1: Trudc het, cac thi nghiem so bd dang T da dugc tien hanh vdi cac thdng so dugc thiet lap nhu
trong bang 2. De loai bd cac sai sd ngau nhien, moi cap gia tri dau vao dugc thi nghiem 2 lan.
Bang 2: Cac thiSt lap thi nghiem sa bo Thong so
Gia tri ma hda Tdc dp cat n (v/p) Lugng chay dao S
(mm/p)
Muc thap -1 2900
200
Miic cao +1 3500
450
Bien thf nghiem
N/A
^ 1
^^2
Cac mau sau khi gia cdng dugc do dp nham, moi be mat dupe do 3 lan va lay trung binh de giam sai sd do.' Cac ket qua thi nghiem dugc trinh bay trong bang 3.
Bang 3. Ket qua thi nghiem so bo STT
1 2
2
4 5 6 7 8
n (v/ph) 3500 2900 3500 2900 2900 3500 3500 2900
S (mm/ph) 200 450 450 450 200 450 200 200
Ra (mm) 0,27 0,40 0,38 0,42 0,37 0,39 0,27 0,37 Ket qua nay dugc su dung de xac dinh phuong trinh hdi quy dang da thirc bac nhat cho quan he giiia nham be mat (Ra) vdi cac thdng sd dau vao la toe dp true chinh (n) va lugng chay dao (S). Hinh 1 trinh bay ket qua phan tich md hinh hdi quy dudi dang ma hda.
Factorial Fit: Ra (Mm) versus n (v/p). S (mm/p)
Estimated Effects and Coefficients for Ra (Mm) (coded units) Term
Constant n (v/p) S (mm/p)
n ( v / p ) * s (mm/p)
E f f e c t - 0 . 0 6 2 5 0 0 . 0 7 7 5 0 0 . 0 3 7 5 0
0 - 0 0 0
Coef . 3 5 8 7 5 03125 03875 01875
SE Coef 0 . 0 0 2 7 9 5 0 . 0 0 2 7 9 5 0 . 0 0 2 7 9 5 0 . 0 0 2 7 9 5
128 - 1 1 13 6
T .35 .18 86 71
0 0 0 0
P 000 000 000 003
S = 0.00790569 R-Sq = 98.91%
PRESS = 0 . 0 0 1
R - S q ( p r e d ) = 9 5 . 6 3 % R - S q ( a d j ) = 9 8 . 0 9 % Hinh 1. Ket qua phan tich mo hinh h6i quy hac 1
TAP C H i c a KHf VIET NAM *> So 09-Thang 9 nam 2010
Phan tich ket qua tren hinh I, cd the thay, cac he so cua phuong trinh hdi quy deu cd gia tri p-value rat nhd, hon muc y nghia xac xuat (a-level) thdng dung (thdng thudng a=0,05). Do vay, cd the ket luan rang, cac gia tri cua cac he sd phuong trinh hdi quy la chap nhan dugc.
Theo ket qua nay, phuang trinh hdi quy bac nhat bieu dien quan he cua nham be mat dugc viet dudi dang;
(1) R^ = 0.3875 - 0,03125 n + 0,03875 S
Budc 2: Vdi muc tieu tien nhanh den vung cac thdng sd cho ra gia tri Ra nhd nhat, su dung ky thuat leo ddc Box-Wilson.
Hudng tien va do dai mdi budc gia sd thi nghiem dupe xac dinh nhu dudi day:
Trudc het, vi muc tieu la giam Ra, cac gia sd tdc dp quay true chinh Dn va gia sd lugng tien dao DS se dugc lay ngugc ddu vdi cac he sd trong phuang trinh hdi quy (1). Tire la, cac thi nghiem xudng ddc vdi xu the tang tdc dp quay n va giam lupng chay dao S se dupc trien khai. Thii hai, gia tri dp dai cac budc tien dupc xac dinh theo phuang phap gradient [9], tire la can theo ty le:
Bang 4; K6t qua thi nghiem leo doc.
(2) A5; ^ 0.03875 ^ A/7 0.03125 1.24
Nghia la, cir tang n len 1 don vi ma hda thi can giam S di 1.24 don vi ma hoa.
Tdc dp vdng quay n cd hai gia tri la 2900 va 3500 (v/p), tuong irng vdi hai mire ma hda la -1 va +1, do vay mdi don vi ma hda se cd dd Idn thuc la:
3 5 0 0 - 2 9 0 0
300{v/p)
Cling tuong tir, lupng chay dao S cd hai gia tri 200 va 450 (mm/ph) nen khi ma hoa, mdi don vi ma hda ciia S se cd gia tri thuc la:
4 5 0 - 2 0 0 , ^ , ,
= 62.5 {mm I p)
De khao sat chi tiet trong pham vi dai tdc dp true chinh ciia may, chpn gia sd budc thay ddi tdc dp cit bang 1/3 don vi, tire la bang 100 vdng/phut. Khi nay, gia sd budc thay ddi lupng chay dao se dupc tinh:
AS = ^^'^'''^"^ = 25,8 - 26{mmlph)
Tien hanh cac thi nghiem vdi tdc dp quay true chinh va lupng chay dao dupc thay ddi theo cac xac lap neu tren. Ket qua dugc trinh bay trong bang 4 dudi day:
Budc 1 2
4 5 6 7 8
n (v/p) 3500 3600 3700 3800 3900 4000 4100 4200
S (mm/p) 200
174 148 122 96 70 44 18
Ra (mm) 0.31 0.28 0.32 0.27 0.23 0.19 0.14 0.12 Qua bang 4, cd the nhan thay, gia tri do nham giam khi tang tdc do true chinh n va giam lupng chay dao S.
Tuy nhien, giam lugng chay dao S ddng nghia vdi giam nang suat, tiic la tang thdi gian gia cdng, mgt chi tieu quan trgng khi phay tinh. De dap ung ddng thdi cac yeu cau giiia do nham dat dugc va nang suat cat, quy hoach thi nghiem hgp-tam xoay ket hgp vdi tdi uu hda da muc tieu da dugc tien hanh va dugc trinh bay dudi day.
Budc 3: Quy hoach hgp va tdi uu hda da muc tieu.
Quy hoach thi nghiem 2 nhan td cd cac diem dgc true a
= ± 1.4142 dugc tien hanh tai lan can diem cd Ra » 0,2 (hang sd 6 ciia bang 4). Gia tri tdc do quay 4000 vdng/
phut va lugng chay dao 70 mm/ph la cac gia tri nam trong pham vi thdng dung ciia cac may CNC. Cac mire gia tri thi nghiem dugc trinh bay trong bang 5.
Md hinh hdi quy: Mgt sd tac gia sir dung md hinh bieu dien quan he giira nham be mat vdi cac thdng so cat dudi dang loga [5], mdt sd khac lai bieu dien quan he nay dudi dang ham da thirc bac 1 hoac bac 2 [7,9-
11]. Md hinh da thirc dugc sir dung trong nghien cim nay do tinh tien dung trong tinh toan, ddng thdi van co the phan anh dimg dan eac mdi quan he trong pham vi khao sat.
Bang 5. Cac mire ciia thdng so thi nghiem CCD Thong so
n (v/p) S (nun/p)
Gidi han dudi
(-a) 3858
33
Miic thap (-1) 3900
44
Mijc trung binh
(0) 4000
70
Muc cao (+1) 4100 96
Gidi faan tren (+a) 4142 107 Thiet ke cac thi nghiem dang CCD va tien hanh gia cdng, do nham be mat va tinh nang suat cat, thu dugc ket qua nhu bang 6 dudi day.
TAP CHica KHI VIET NAM V S6 09 - Thang 9 nam 2010
Bang 6. Kk qua thuc hien cac thi ngliiem CCD n (v/p)
4000 3900 4100 3900 4000 4000 4142
S(mm/p) 70 96 44 44 70 70 70
R ( m m ) 0.21 0.23 0.11 0.17 0.22 0.22 0.19
R,(mm) 1.2 1.5 1.02 1.42 1.25 1.2 1.4
Q(g/ph) 0.33 0.45 0.21 0.21 0.33 0.33 0.33
3858 4000 4100 4000 4000 4000
70 33 96 107 70 70
0.3 0.13 0.15 0.24 0.17 0.2
1.6 0.96 1.4 1.49 1.22 1.32
0.33 0.16 0.45 0.5 0.33 0.33 Phan tich md hinh hdi quy (xem hinh 2) cho thay, cac gia tri p (p-value) ciia he sd bac cao n-; S-; n*S lan lugt la 0.527; 0.116; 0.764, Idn hon nhieu so vdi muc a thdng thudng (0,05).
Response Surface Regression: Ra(Mm) versus n (v/p), S(mm/p)
The a n a l y s i s was done u s i n g codeci u n i t s . Estimated R e g r e s s i o n C o e f f i c i e n t s f o r Ra (Mm) Term
C o n s t a n t n ( v / p ) S (mm/p) n ( v / p ) * n S ( m m / p ) * S ( n ( v / p ) * S (
( v / p ) mm/p) mm/p)
0 - 0 0 0 - 0 - 0
C o e f 2 0 3 7 9 3 0 3 6 8 7 4 0 3 1 8 6 7 0 0 8 0 2 4 0 2 1 5 8 4 0 0 5 0 0 0
SE C o e f 0 . 0 1 4 3 1 0 . 0 1 1 2 9 0 . 0 1 1 2 8 0 . 0 1 2 0 6 0 . 0 1 2 0 2 0 . 0 1 6 0 0
1 4 - 3 2 0 - 1 - 0
T 2 4 4 2 6 7 8 2 6 6 6 5 7 9 6 3 1 3
0 0 0 0 0 0
P 0 0 0 0 1 4 0 2 6 5 2 7 1 1 6 7 6 4 Hmh 2. Phan tich mo hinh hoi quy hac 2
Do vay, su cd mat ciia cac thanh phan nay trong phuang trinh hdi quy la khdng cd y nghia.
Loai dan cac he sd cd p-value Idn han 0,05, cudi ciing thu dugc md hinh dugc phan tich phuang sai nhu tren hinh :
Response Surface Regression: Ra(Mm) versus n (v/p), S(mm/p)
The a n a l y s i s was done u s i n g coded u n i t s . E s t i m a t e d R e g r e s s i o n C o e f f i c i e n t s f o r Ra(Mm) Term
Constant n (v/p) S (inin/p)
0 -0 0
Coef 19538 03687 03187
SE Coef 0.009375 0.011926 0.011914
20 - 3 2
T 841 092 675
0 0 0
P 000 Oil 023 S = 0.0338023 PRESS = 0.0230629
R-Sq = 62.57% R-Sq(pred) = 24.44't R-Sq(adj) = 55.08%
Analysis of Variance for Ra(t<tn)
Source DF Seq SS Adj SS Adj MS F P Regression 2 0.019097 0.019097 0.009549 8.36 0.007
Linear 2 0.019097 0.019097 0.009549 8.36 0.007 Residual Error 10 0.011426 0.011425 0.001143
|Lack-of-Fit 6 0.009706 0.009706 0.001618 3.76 0.110|
Pure Error 4 0.001720 0.001720 0.000430 Total 12 0.030523
Hinh 3. Phan tich phuang sai cho mo hinli hoi quy cuoi ciing
TAP C H i c a KHf VIET NAM •*• S6 09-Thang 9 nam 2010
Phan tich ket qua: Nhin vao hinh 3 (cac viing dugc ddng khung), nhan thay;
(1) Cac he sd ciia phuang trinh hdi quy deu cd gia tri p-value nhd han 0,05
(2) p-value cua "mire do khdng khdp ciia md hinh"
(Lack-of-fit) la Idn hon 0,05. Tii' dd, tuong ung cd the ket luan: (1) cac he sd ciia phuong trinh hdi quy la cd nghia va (2) md hinh hdi quy tim dugc la phii hgp.
Gia sir nha san xuat mudn lua chgn che do cat thda man ddng thdi hai chi tieu ve nham be mat R^
va nang suat cat Q. Giai phap cho van de nay dugc thuc hien bang each, tinh toan them cac gia tri nang suat cat tuang irng vdi cac che do cat da thi nghiem, sau dd sir dung cdng cu xep chdng dudng mire va tdi uu hda ciia cac phan mem thiet ke thi nghiem de xac dinh vung cac thdng sd dau vao. Hinh 4 trinh bay mdt ket qua xac dinh che do cat bang phan mem thiet ke thi nghiem Minitab® cho cac gia tri Ra nam trong khoang [0,11-0,2], cdn Q nam trong khoang [0,21- 0,45], tire la:
(3) fO,l 1 < i?„ < 0,2 (3a) I 0 , 2 1 < g < 0 , 4 5 {3b)
Tren hinh 4, tap hgp cac gia tri lugng chay dao S va tdc do quay true chinh n d viing sd 1 la vimg thda man he (3), viing sd 2 chi thda man phuong trinh (3b), viing sd 3 khdng thda man ca hai phuong trinh (3), cdn viing sd (4) chi thda man phuong trinh (3 a).
Cac gia tri gidi han ciia cac ham muc tieu ndi tren cd the thiet dat de dang trong phan mem. Do vay, nha tu van cd the nhanh chdng chi ra cac •viing che do cat thda man cac mire muc tieu khac, dap irng yen can ciia san xuat.
Contour Plot of Ra(Mm), Q(g/ph) icn
90 80 70-
60- 50- 40-
.0.
/© o
/
W~7\
MMm) 0.11 Oi Q(g/ph)
- o.« 021
3900 3950 4000 4050 410O n ( v / p )
Hinh 4. Xep chong cac duang miic nham be mat va nang suit cit
4. KET LUAN > y.:,:v-
Van de xac dinh che do cit dap irng dong thdi hai chi tieu thudng dugc quan tam nhat khi gia cdng tinh bing phay cirng khudn man SKD 61 da dugc giai quyet.
Phuang phap thiet ke thi nghiem b§ng ky thuat be mat chi tieu cho ra ket qua nhanh va don gian. Ky thuat nay cd the ap dung cho cac qua trinh gia cdng khac, vdi cac ham muc tieu khac nhau. •>
Tai lieu tham khao:
[1]. Iqbala A., Ning H., Khana L, Liang L., Naeem Ullah Dara N.U., Modelmg the effects of cutting parameters in. MQL-employed finish hard-milling process using D-optiraal method, Joumal of materials processing technology 199 (2008), pp. 379-390;
[2]. Iqbal A.,Ning H., DarN.U., Liang L., Comparison of fuzzy expert system based strategies of offline and online estimation of flank wear in hard milling process. Expert Systems with Apphcations 33(2007)61-66;
[3], ChandrasekaranH., SaoubiR. M , Improved machinabUity in hard milling and strategies for steel development, CIRP Annals - Manufacturing Technology, Volume 55/1,2006, pp. 93-96;
[4]. ColdweU H., Woods R., Paul M., Koshy R, Dewes R.;
Rapid machining of hardened AISI HI 3 and D2 moulds, dies and press tools; Materials Processing, 135 (2003), p.p. 301-311;
[5]. Vivancos J., Optimal machining parameters selection in high speed milling of hardened steels for injection moulds, Joumal of Materials Processing Technology 155-156 (2004) pp.
1505-1512,
[6]. Reddy N.S.K., Rao RY, A Genetic Algorithmic approach for optimization of surface roughness prediction model in dry milling. Machining Science and Technology 9 (1) (2005), pp. 63-84.
[7]. Sahin Y, Motorcu A.R., Surface roughness model for machining mild steel with coated carbide tool. Material & Design 26 (4) (2005), pp. 321-326.
[8]. Mansour A., Abdalla H., Surface roughness model for end millmg: a semi-free cuttmg carbon casehardening steel (EN32) in dry condition, Joumal of Materials Processing Technology, 124 (2002), 183-191.
[9]. Ktema H. O., Erzurumlu T, Kurtaran H., Application of response surface methodology in the optimization of cutting conditions for surface roughness, Joumal of Materials Processing Technology 170 (2005), pp. 11-16;
[10]. Lopez L.N, Larrukiza A., Sancheza J.A., Arana J.L., Improving the surface fimsh in high speed milling of stamping dies, Joumal of Matenals Processuig Technology 123 (2002) 292-302;
[11]. Zhang I Z., Chenb J.C, Kirby D.E., Surface roughness optimization m an end-milling operation usmg the Taguchi design method; Joumal of Materials Processing Technology 184 (2007) 233-239.
[12]. MyersR.H.,MontgomeryD.C. and Anderson-Cook CM., Response Surface Methodology: Process and Product Optimization Using Designed Experiments, Third Edition, 2009 John Wiley &
Sons, Inc.
TAP CHI c a KHI VIET NAM V So 09-Thang 9 nam2010
