NGHIEN CUTU - TRAO B0\
PHAN TICH ANH Hi/dNG COA VAN T 6 C CAT TREN MAY CAT DAY CNC D^N UNG SUAT D U B^ MAT COA KHUON DAP NGUOI
SCf DUNG NHliU XA TIA X
STUDY ON THE RELATION BETWEEN CUTTING SPEED AND SURFACE LAYER RESIDUAL STRESS OF COLD-FORGING MOLD AFTER CNC WIRE CUTTING MACHINING
USING X-RAY DIFFRACTION
Le Chi CUdng, Dang Thiin Ngon Trudng Dai hpc SU pham Ky thuat TP. Hd Chi Minh.
TOMTAT
tyng sudt dii tdn tai trin bi mat thep SKDl 1 ditng ldm Idiudn ddp ngudi dnh hudng ldn din tuoi thg cda khudn. Khi gia cdng bang mdy cdt ddy CNC, vdn tic cdt cd dnh hiidng ldn din dng sudt dU. Bdi bdo trinh bdy kit qud nghien cdu sU liin quan gida vdn tic cdt vd dng sudt dU sd dung nhiiu xsi X quang.
Kit qud cho thdy van toe ldn hdn 200 xung/ms itng sudt dU co xu hiidng Sn dinh, vd chiiu ddy ldp ddc lai Id nhd nhdt.
TU khoa: tjng sudt dU, mdy cdt ddy CNC, thep SKDl 1, nhieu xa X-quang.
ABSTRACT
Residual stress in the surface layer of cold forging steel SKDU has significant influence to the performance and duration of mold. In the case of fabrication of CNC wire cutting machine, the cutting speed strongly affects to the residual stress. This research studies the relation between cutting speed and the residual stress using X-ray diffraction. This result shows that for the speed of higher than 200pulses/ms, the residual stress tends to remain constant, thus give the minimum thickness of recasting layer.
Keywords: Residual stress, CNC wire cutting machine, steel SKDll, X-ray diffraction.
I . D A T V X N D E tudi thp cua khudn. Mpt trong nhflng nguyen nhan chu ylu cua hiln tUpng ndy Id do flng suat Thep hpp kim SKDll dUpc sfl dpng rdng dU tdn tai trin bl mat cda khudn. Yeu cdu cua rai de ldm khudn dip ngudi do dp bin, dO cdng, khudn dap ngudi la vat U|u khudn phai dUdc dp dai va kha ndng chdng mai mdn tdt sau khi nhilt luyen trUdc dl dat dp cdng khoang td 58 nhi|t luyen II]. Ddi vdi khudn dap loai nay, bong din 60HRC. Do dd, sau khi tdi, bl mat khudn dap nflt trin cdc be mat cac loai khudn dap ngupi Id thudng dUpc gia cdng tinh bang mdy cat ddy dilu mdt dang hU hdng thUdng xudt hi|n, Iam giam khienbangCNCviphUdngphj^ndygiacdngbdngtia'^
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Ifla dien cho ra chilu day vung anh hfldng n h i l t thdp va khdng phu thudc vdo dp cdng cua vdt Ueu [1]. Tuy nhiln, hien nay, hau het cdc c h l dp gia cdng bang may cat day thfldng dUpc xdc dinh vdi muc dich bao ddm tudi thp cua rady, tdng nang sudt va giam chi phi day rad chUa chu trpng d i n chat lupng b l mat cua san pham gia cdng. Do do, vi|c xdc dinh che dp cat bang may cat ddy, ddc bilt Id van tdc cat t^ 11 vdi sd lUpng xung phdt ra trong mdt gidy, lam cd sd cho vi|c toi Uu hda gifla lpi n h u | n kinh te vd chdt lUpng san pham cd y nghia dac bilt quan trpng anh hUdng den flng sudt dU cfla khudn dap.
H i l n nay, tren t h i gidi cd nhieu phUdng phdp xac dinh dng sudt dU tren b l mat chi tilt nhu phUdng phdp: dpc Id, cat Idp, silu am, quang dan hdi, nhieu xa X-quang hoac neutron,... [6, 8]. Trong dd, phfldng phdp nhilu xa X-quang cd nhilu Uu dilm: xac dinh chinh xac flng suat, de dang tu ddng hda,...raa khdng pha hfly chi tilt radu [2,4]. Bai nghien cdu ndy se khdo sdt sU thay ddi cua dng sudt dU t r i n b l mat thep ldm khudn d i p ngudi flng vdi van tdc cat khdc nhau sd dung nhieu xa X quang, td do de xuat van tdc cat tdi Uu.
2. N O I DUNG NGHIEN CCU 2.1 Biln dang t r i n be mat mau thuC
Xet he tpa dp (x,y,z) nhU hinh 2.1, trong dd biln dang va flng sudt dpc theo cac true lan lupt la a^, a^ a^, E^, E^ vd e^. Td ly thuylt dan hdi, ta cd mdi quan he dng suat - biln dang [3,10]:
_^t,w~^o _ l + v
( a - „ c o s ' ^ (2.1)
l + V V ,
+ - ^ ^ 3 3 - - ( O i l +CT- +0-33) + l + V ,
+ - — C<T,3 c o s (P + (723 s m 0 ) s i n 2^^
Hinh 2.1: Hi true tga dd trin bi mat mau.
Trong dd: E va v la md dun dan h6i va he sd Poisson. TrUdng h p p khdng cd y l u cau tinh toan chinh xdc flng sudt theo phUdng phdp tuyln vdi be mat mau, ta coi vdt lieu d trang thai flng suat phang, khdng cd cac thdnh phan thfl 3 tM cdng thflc (2.1) trd thanh:
l + V . 2
T K + O - J (2.2)
Trong do a Id flng suat thanh phdn theo phUdng vi (p, dupe cho bdi:
cr^ = a^ cos^ ^ + cr^ sin Itjf + cr^ sm^ ^ (2.3) Ta cd the vilt Iai, nhU sau:
- ' ' o - ( o - , + o - , ) + d„ (2.4) TU dinh luat Bragg va qua bien ddi tU bifo dang trong mang t m h t h i sang vi tri dinh nhieu xa, ta cd:
•>a-r, 2(1+ v ) t a n g , 180 . ^ E 7t 2vtanfl, 180
(rr, + o - ) + 2ft (2.5) Trong dd, p = 26 la vi tri dmh nhilu xa, 6, la gdc n h i l u xa khi khdng cd dng suat. Do dd, dng suat ddoc xac dinh bing:
= KM (2.6)
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Trong dd M \k dd ddc cua do thi sin2\|/ vk
K la h i n g sd dng suit cua v^t lieu dang hddng, Cng suat dddc xac dinh td do ddc M cua dddc xac dinh bang: dUdng thang ndi suy tuyen tinh vdi m vi tri dinh
trong do thi s i n ^ nhd sau:
K = - E n
2(l + v)tane„ 180 (2.7)
2.2 Xac dinh vi tri dinh n h i l u xa bang p h d d n g phap Gauss
Dinh n h i l u x^ dlidc ndi suy bang phdong phap binh phuong nhd nhat ddi vdi n d i l m dd li$u cildng dd n h i l u x^ (\>Y) nhu sau [5]:
V.-Z^'
"ZsinV, - Z™Vy
(2.10)
/ J d —
(2-8)
Trong dd
x = -Tx„ (/ = 0,4c(n^-4) sm'^/,
Hinh 2.2 Xdc dinh ting sudt bang phUdng phdp sm^i/
2.4 Trinh t d thi n g h i i m
\ l i nghich dao he sd Lorentz-phan cdc vk hap
tiiu. Trddng hop kilu Cl co dinh n khdng cd gidi Thi nghiem ddoc tiln hanh tren thep hjn di?n tich nhieu xsi, ta cd: SKDll (bang 2.1). Mddi mot mau t h i p sfl dung
1^ = 1 - tant|/cot6i (2.9) trong thi nghiem cd kich thddc 12x20x24mm qua phay, mai dat do bdng Rz =l,6\mi vk dddc nhi?t 2.3 Xac dinh d n g sudt td dd thi s i n > luyen.
Bdng 2.1 Thanh phan hoa hoc vd CO tinh ciia thip SKDl 1 [7, 9]
Thanh phan (%)
C d t l n h C 1,4-1,6
Si
<D,6 Gidi hiin b i n (MPa)
2.356
Mn
<0,6 S
<0,03 Md dun d i n hdi E
(MPa) 198
P
<0,03 Cr 11-13 He sd Poisson v
0,3
Ni 0,5
Mo 0,08-0,12 Do cdng (HRC)
58 Mddi m i u thep thi nghiem ddoc gia cdng t r i n may cat day CNC DK7732AZ-3 dat d i n kich thddc 12x20x20mm (hinh 2.3). Hinh 2.4 md t i thdi gian gia cdng tren may cit day bao gdm thdi gian
phdng d i ? n t v i thdi gian ngdng tj. ^
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Di$n tich nhilu Xil Be mitt gia cdng
Bifn
Chuk>'
Thm
Hmh 2.3 Mdu thi nghiim sau idii gia cong. Hmh 2.4 Thdi gian gia cdng trin mdy cat day CNC.
Bing 2.2 l i dilu kien gia cdng bang may cat day, trong dd m i u 0 la m i u t h i p tdi khdng gia cdng;
cac mau 1 d i n 10 ddoc gia cdng vdi tan sd td 333 d i n 83 chu kj'/giay, tddng dng thdi gian phdng difn td 20 den llOiis va nang suat gia cdng ttt 29 den 48mm'/min. Dien i p , cddng dd ddng diei, vjn tdc tang ddoc gifl nguyen.
Bdng 2.2 Che do cdt trin mdy cat ddy CNC cila cdc mm sau khi nhiit luyin
\ Thong
\ so Mlu \
0 1 2 3 4 5 6 7 8 9 10
Van toe true tang (m/s)
DUdng kinh day
(mm)
Dien ap
(vj
00 Khoang each xung t,lfis)
Thdi gian gia cong t ( / i s )
Van tdc cit (chu ley/
ms)
Nang suat gia cong (mm7 min
-
7 0.15 80 5 10
20 30 40 50 60 70 80 90 100
333 250 200 167 143 125 111 100 91 83
29 31 34 36 38 41 43 45 47 48 ' : Dilu kiln do b i n g nhieu xa X quang dUpc
cho trong bang 2.3. Phan m i m tinh todn OriginPro 8 dupe sd dpng de tinh toan vi tri dinh n h i l u xa vd ndi suy dd thi sin^|/. D l tinh dUpc gid tri chinh xdc cua vi tri dinh n h i l u xa, cUdng dd nhieu xa dupe hilu chinh vdi h i sd Lorentz, phan cUc va hap thu. Vi tri dinh cua dUdng nhieu xa dUpc xdc dinh tfl phUdng phdp ndi suy dudng cong Gauss.
Bdng 2.3 Dieu kien do bdng nhieu xa X quang Phuang phip do
DJc tinh tia X vi budcsdng M$t nhilu x$
T ^ l o c Thdi gian do Budc gdc nhilu x$
D i ^ i p Cudng dO ddng di$n
Kiiu Ci cidinhi) Cu-Ka, /.= 1,S04SA'
(222) Ni
5giSy 0.04' 45kV 40mA
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2.5 K i t qua vd khao sdt Bang 2.5 trinh bay k i t qua do flng sudt dU cua 10 mau sau gia cdng (mau 0 khdng gia cdng).
Hhih 2.5 Id dudng nhieu xa tai cac gdc i|/ Kit qua cho thay, flng suat dU nen se tang mang dupe npi suy bdng dudng cong Gauss de xdc dinh khi van tdc gia cdng tdr^.
vi tri dinh nhieu x?. Bang 2.4 Id vi tri dinh n h i l u
xa cung vdi khodng each mat nguyin tfl d. Sdng 2.5 Ifng sudt du cua cdc mdu sau gia cong (MPa)
Hinh 2.5 Dudng nhiiu xa cda mdu s610 dUdc ndi suy dudng cong Gauss.
Bdng 2.4 Dinh nhiiu xa vd khodng cdch mat nguyin til cda mdu so 10
s i n ^ 28(40)
ci(A') 0 136.685 0.82875
0.1 136.702 0.82870
0.2 136.752 0.82855
0.4 136.952 0.82799
M i u s d 0 1 2 3 4 5
tfngsuit dd
M a u s d Cng suat dd -351 (khdng gia cong) -403
-416 -427 -469 -522
6 7 8 9 10
-658 -699 -741 -781 -789
Hinh 2.6 Id dd thi sin^)/ cua mau sd 10.
Ung sudt du dupe xdc dinh tfl dp ddc cfla dudng thang nOi suy t r i n dd thi s i n ^ theo nhU cdng thflc (2.10).
Hinh 2.7 cho thay sfl biln thiin cfla flng suat du vdi van tdc cat, dUpc bilu h i | n thdng qua tan so phdng diln. Mau sau khi tdi khdng gia cdng cd gid tri flng suat dU nen nhd nhat. Id khodng 370MPa. Nhin chung, flng suat dU (nin) tdng khi vdn tdc cat tang (tdn sd phdng diln gidm). TVong khoang van tdc cat tang tfl 333xung/ms len d i n khoang 200xung/ms (nang sudt gia cdng tang tfl 29 len 34 mmVmin), flng sudt dU nen tang c h i m tfl khoang 400MPa d i n khodng 450MPa. Sau dd khi v ^ tdc cat tang tilp d i n 83xung/ms (nang suat gia cdng tang lln d i n 48mm^/min), flng sudt dfl nen tang manh v l gia tri Un d i n gan 800MPa.
..
... 1
...
• • • s
V (lun.'nn)
-^ ^ 2 ~
» ,..
. 0
_."
Hinh 2.7 Su thay doi itng sudt dii v6i vdn tdc cdt ,"„', "' Dilu n i y la kit qua ttt cic y l u td sau:
Hinh 2.6 B6 thi sin'f cia miu so 10. - Sau khi nhiet luyen, b l m j t mau cd d n g ' '
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NGHIEN CUlU - TRAO D O I
suit dd nen. 3. KET LUAN
Vin tdc cat (nang suit gia cdng) ty le
thuan vdi nhilt cat p h i t smh. ve:
Khi van tdc cat tang thi thdi gian phdng dien trong mot chu ky tang, nhiet do v i keo theo la chilu siu anh hddng nhiet (chilu s i u ldp due lai) tang lln, dan d i n gia tang ttng suit dd n i n .
N h d vay, ddi vdi thep khudn d i p ngupi SKDl 1 sau khi tdi, van toe cat tot nhat n i n trong khoing 200-250 xung/ms phat sinh ra ttng suat dd khdng qua ldn. Tang van tdc qua gia tri n i y ttng suit du tang manh l i m be mat d l bong trdc.
Bai b i o trinh b i y cic k i t q u i nghiin ciJu
Tinh toan dng suit dd cda thep lim khudn dap ngudi SKDl 1 bang nhieu xa X quang.
Khao sat moi liln h i gida van tdc eat (nang suit cat) vdi dng suit dtt b l mat xuit hien trong q u i trinh gia cdng b i n g may cat d i y CNC.
Ket q u i cho t h i y van tdc cat c i n g tang thi ttng suit dtt nen tang v i manh nhat la khi gia eong d v i n tdc cao hon 200 xung/ms. Do dd, van tdc cat tdi d u cua khudn d i p ngudi S K D l l n i n chpn trong khoang l i 200-250 xung/ms. •!•
Ngiy n h i n bai: 05/5/2013 Ngiy phan bien: 08/6/2013
Ngddi phan bien: PGS, TS. Tniong Ngpc Thuc, Trddng Cao dang Viin Ddng.
Tii lilu tham khio;
[1]. Vu Hoai An (2005), Gia cdng tia Ha diin CNC, NXB. Khoa hpc vk Ky flluSt, pp. 25-40.
[2]. Li Cdng DUdng (1984), Ky thuitphdn tich can triic bang tia Rdnghen, NXB. Khoa hpc vk Ky thult, pp. 122- 141.
[3]. Nguyin TrUdng Thanh (2000), Gido trinh Ly thuyet bien dang, NXB. Dai hpc Quoe gia TE HCM, pp. 33-55.
[4]. Cullity B. D. (2003), Elements of X-ray Diffraction, Prentice Hall Upper Saddle River, NJ 07458, pp.97-118.
[5]. Cuong, L. C and M. Kurita (2003). Absorption Factor and Influence of LPA on Stress and Diffraction IM Width in X- Ray Stress Measurement, JSME, Vol. 1, pp.7-14
[6]. Hauk V. (1997), Structural and Residual Stress Analysis by Nondestructive Methods, Elsevier, pp. 82-115.
[7]. Hauk v., Hougardy H., Macherauch E. (2005), Residual Stresses Measurement, Calculation, Evaluatifln, Informationsgesellschaft, pp. 112-117.
[8]. James M., Lu J., Roy G. (1996), Handbook of Measurement of Residual Stress: Englewood Cliffs, Prentice Hall, p p 29-50.
[9]. John E. B (2004), Handbook of Comparative World Steel Standards (ASTM DS67B) - Third Edition, ASTM International.
[10]. Noyan 1. C , Cohen J. B. (1987), Residual Stress Measurement by Diffraction and Interpretation, New Yoric Springer-Verlag, pp. 40-47.
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