NGHIEN cuu-TRAO eOl
A ' 4 . . V
Tmh toon che do hon plcismo coc lien ket giap moi vat mep mot piiia tuf hofp kim nliom
(*) TS BUI VAN HANH
1. Dat van de
Khi ban cac lien ket giap mdi vat mep mdt phia mdi ban Idt cd \ ai ttd rat Idn trong \ ice dam bao chat luong toan bd lien ket ban. Do cac dieu kien \ e hinh thanh mdi ban khdng thuan Igi nen mdi ban Idt thudng rat khd thue hien, neu thira nhiet thi rat de hi chay thiing hoac sut be mat mdi ban. neu thieu nhiet thi de hi khdng ngau. Van de nay dac biet quan trgng khi ban hgp kun nhdm \ i tinh dan nhiet cua hgp kim nhdm cao va tten be mat cua chiing thudng xuyen tdn tai ldp dxyt nhdm can ttd sir hinh thanh mdi ban. Mat khac, khi ban cac lien ket giap mdi cd vat mep su phan bd nhiet khdng tuan theo cac quy luat da duge nghien cim.
Khi dd tai chd vat mep cac dudng dang nhiet bi gay khue.
lugng nhiet thoat ra mdi trudng xung quanh nhieu hon la lam nung ndng kim loai eo ban. Trong trudng hgp nay neu ap dung thuan tiiy ly thuyet ve ngudn nhiet diem, dudng, khdi de tuih toan qua trinh nhiet la ehua thoa dang. Cdng trinh nay nghien cim ve sir phan bd nhiet khi ban cac lien ket giap mdi cd \ at mep mot phia tir hgp kim nhdm. tten co' sd dd dua ra dugc phuong phap tinh toan che do ban mdi ban Idt va kiem nghiem ket qua tinh toan bang thue nghiem ban plasma tten hgp kim nhdm AMD3.
2. Tinh toan che do han
Lien ket ban thudng gap khi ban hgp kim nhdm cd ehieu day trung binh va Idn la lien ket giap mdi \ at mep chir V mdt phia, phan khdng vat mep C hgp ly la bang 40%
chieu day chi tiet (hinh 3). Cac ldp han dugc thue hien tir hai phia, ldp ban Idt duge thuc hien tii phia khdng vat mep, eae ldp ban cdn lai (nhieu hay it tviy thudc vao ehieu day chi tiet) dugc thuc hien tir phia cd vat mep. Thdng thudng phia ldp han Idt la mat ttong cua ket can va yeu cau be mat mdi han phang nhu kim loai co ban de ttanh tap tiimg iing suat va giam cac dieu kien ga\- an mdn ben ttong ket cau (noi tiep xiic true tiep vdi eae dung mdi, hda chat gay an mdn chiia ttong ket cau) hoac be mat ldp ban Idt cd su chuyen tiep tton tm tdi kim loai co ban. Trong cdng trinh nay tac gia dua ra cac tieu chi danh gia miic do dat yeu cau cua mdi ban lot la chieu sau ngau, chieu rdng mdi ban va be mat mdi
(*) Trudng Dai hgc Bach khoa Ha Ndi
ban phang nhu kun loai co ban.
De tinh toan su dung ngudn nhiet diem ed edng suat Q„. Gia su ngudn nhiet dang d vi tri (x,y,z). Nhiet do T tai mdt diem bat k\' (4,ri,0 tren vat ban tai thdi diem / duge tinh theo edng thirc sau:
( 1 ) T{x.v.z,l) = ^——-exp c.p(4Ti.aJ)'
( x - c ) - + 0 - r i ) ' + ( z - C ) ' 4a.l
d day:
- c la nhiet dung rieng cua kim loai co ban, J/(kg.K) - p la trong lugng rieng eua kim loai co ban, g/mm^
- a la he sd truyen nhiet do cua kim loai co ban, mmVs Khi dat den thdi gian tdi ban, nhiet do tai mdt diem bat ky thudc vat ban khdng phu thudc vao yen td thdi gian. Lue dd lugng nhiet do ngudn nhiet ban cung cap can bang \di lugng nhiet lam kim loai co ban ndng len den nhiet do can bang \a lugng nhiet tda ra mdi trudng xung quanh. Phuong ttinh (1) ed the viet dudi dang:
a)n,„.,=,.,.f,»p(^)...(^i,,(.,.-),
Trong dd:
F,{r7) = 1 + 2 ^ cos 1 , • - K,.-l K. V-r
"' la '''
la ham ke den
do sai lech eiia ngudn nhiet tuyen tinh cdng suat q phan bd ddng deu theo toan bd chieu day tam phang.
+ , K„: Ham Bessel I, VS ' "
A = U i ( 0 - c o s P ^ U / i ; la ham tich phan theo chieu day tam cua phan hi ngudn nhiet diem q (Q
TAP CHI c a KHI VIET NAM V Sd 05-Tliang 5 nam 2010
NGHIEN cuu-TRAODO!
Ddi vdi trudng hgp ban plasma eae hen kdt gmp moi cd vat mep mdt phia nhu da chgn mdt each gan diing ed the coi q,(Q phan bd theo dudng thang (hinh 2), khi dd:
n -I V J y Vrt •/ •Boos K-iC •B - X: he sd dan nhiet, J/(mm.s.K)
- S: chieu day chi tiet ban, mm
- C: chieu cao chan (phan khdng vat mep), mm - V: toe do di chuyen ciia ngudn nhiet, mm/s (tdc do ban) - q: Cdng suat nhiet hieu dung cua hd quang, q=r|.
u„i,.w
- r: ban kinh tinh theo tga do tru, r^=x-+y^, Thay F|(r,z) vao phuong trinh (2) ta cd:
mm
(3)n.,,,„,.g.„,fc').«.t£
Tvr (1) va (3) suy ra:
l + 2 ^ c o s | - ^ K„.-l
< >
(4) ^(q,V,r,x)
ln-K-S-Ky--^\T{x,r,z,^)-2Y^K,,l, exp V-r
' la
-? = 0 ,
Khi chuyen sang he tga do tru, phuong trinh (3) cd dang: y = F(x,V,q,...).
De tinh toan trong mdi mat phang z=const ta ebon diem A ed toa dd (x=0, y= y , z). Khi dd ddi vdi mdi dudng dang nhiet ndng chay T^^ toa do cua diem A se la x=0, yjy^^ d day y^^ la gia tri Idn nhat ciia dudng dang nhiet T^^ ttong mat phang z. Khi z=0 diem A(x,y,z) se nam ngay tten be mat chi tiet ban, tiic la ttong mat phang z=0 gia tri y chinh la chieu rdng b eiia mdi han.
Suv ra:
cy(x) ax
= 0 tai diem x=x =0 y=y
Dieu nay cd nghia la tai diem y cd gia tri Idn nhat tten dudng dang nhiet T_^^, tiie la tai diem A(x=0,y=y__^^^) dao ham rieng eiia y theo x cd gia tri bang 0, tire la tai dd tiep tuyen cua dudng cong y = F(x,V,q,...) song song \ di true Ox (hinh 1). Ta cd he phuong trinh:
(5) (D(q,V,r,x)=0 dy{x)
C'X
• 0 tai x=0 y=b
De dam bao chieu rdng mdi ban b va chieu sau ndng chay h theo tieu chuan nham dam bao mdi han du chieu rdng va chieu sau ngau. ta chgn hai diem A, mdt d tten be mat mdi ban, tiic la mat phang z=0 (luc dd y=4.5mm) va mot o chan mdi ban, tiie la tren mat phang z=h (liie dd y=0) de giai he phuong trinh (5). Thay cac gia tri x,y,z tuong img o timg mat phang z \ a cac gia tn a, cp, S, T=T^^
vao he phuong trinh (5) ta tim duge bd thdng sd V,^ tuong irng vdi q. Do q la mdt ham phu thudc vao \ nen ta se nhan dugc bd thdng sd V^^ irng \ di 1^.
Do phuong trinh (4) la mot ham sieu viet, viec lay dao ham rieng cua y theo x khd thuc hien nen viec giai he phuong ttinh (5) thuan tien nhat la sir dung phuong phap sd, so dd thuat toan giai duge dua ra tten hinh 4. De don gian cho viec giai ta chuyen sang he toa do tru:
x=r.cos(9) y=r.sin((0)
Khi tinh tich phan L cae he sd A, B dugc xac dinh tvr dien tich ndng chay:
F, {A + B)-C 2
1
Y
c
'
i-i \
> . M \
f \
/ / \ / / / J r \ q n 2 ) - A i U . z /
z y
Hinh 1: Hinh dang vting han
Hinh 2: So do phan bo cong suat nguon nhiet khi han lien ket co vat mep
Nhan thay rang cdng suat nhiet hiru ich q bang dien tich ndng chay F tiic la:
TAP CHI c a KHI VIET NAM V Sd 05-Thang 5 nam 2010
NGHIEN cuu-TRAO001
{A + B)>C q=
2 o day: q=ri,.U,,.l,^
U =30+0.033 I,
- Han plasma ttong khi bao ve aigon cd T|^=0.5-0.6, lay ri^=0.5. Vung kich tliudc cho phep cua tiet dien ngang mdi ban la\ theo COST 14-806-80, theo dd chieu rdng mdi ban cho phep nam trong khoang 8-14imn. chieu sau ngau tu- 5.2-7.6mm.
chieu rdng phan chan mdi ban tir 1.0-3.6mm (Hmh 3).
A(4.5,0)
Hinh 3: Viing kich thudc cho phep ciia mat cat ngang moi han khi S=12mm,C=40%S
Chuong trinh tinh toan duge viet bang ngdn ngii C, cac sai sd SjVa e, lay bang 0.01, thdi gian tinh toan khdng qua 2 phut. Ket qua tinh toan dua ra ttong bang 1.
Bang 1: Ket qua tinh toan ddng dien va tdc do ban (S=12mm, C=40%S=4.8mm).
TT 1 2 3 4 5 6
>„ (mm) 4.5 0.02
4.5 0.02
4.5 0.02
4.5 0.02
4.5 0.02
4.5 0.02
z„ (mm) 0.0 6.5 0.0 6.5 0.0 6.5 0.0 6.5 0.0 6.5 0.0 6.5
q (W) 2621 3446 3660 3878 4099 4436
(A) 150 190 200 210 220 235
VJm/h)
9.5 21.6 24.5 29.3 33.1 39.6
3. Thirc nghiem kiem chirng
De kiem chirng ket qua tinh toan o tren, cae thuc nghiem dugc tien hanh ddi vdi hgp kim nhdm AMD3.
Che do ban la> theo ket qua tinh toan o bang 1, tuc la cimg mdt hinh dang \ a kich thudc hen ket thuc hien 6 diem thvrc nghiem nham danh gia tinh chinh xac cua phuong phap tinh toan che do ban nhu de xuat dua tten cac tieu chi ^ e chieu sau ngau, chieu rdng mdi han \ a dang chuyen tiep tir kim loai mdi ban den kim loai eo ban (bang 2).
Khi bao \ e su dung khi argon, dudng kinh dau plasma
la 3.6mm. Sau khi dang gia theo ba tieu chi tten cac mau dugc kiem tra bang phuong phap chup anh thd dai va thu CO tinh. Anh chup thd dai cac man dugc dua ra tren hinh 5 \a ket qua thu co tuih tren hinh 6.
Tren bang 2 ta thay rang su sai lech Idn nhat ve kich thudc thuc chieu rdng mdi ban va chieu sau ngau so \ai tinh toan la 0.3mm, sai lech nay la chap nhan duge.
Bang 2: Ket qua thue nghiem
TT 1 2 3 4 5 6
Chieu day tam
S,mm 12 12 12 12 12 12
I,.. A 150 190 200 210 220 235
m/h 9.5 21.6 24.3 29.3 33.1 39.6
Chieu rdng mdi
han,mm 9.0 9.1 9.2 9.2 9.3 9.3
Chieu sau ngau,
mm 6.2 6.2 6.3 6.4 6.5 6.6
Dang chuyen tiep
KLMH- KLCB Phang Phang Phang Phang Phang Phang
/ B a i f t u V
H 5=5 I
I E
3:
a=0,1 b=L
a:
I O O + b u o e o ] |Fa=F») F I ^ = F I M | F a F l x O
I FaFb^O I / kc(a.b) /
C KFT THUC^
Huih 4: Sa do khoi thuat toan tmh che dp han cac lien ket giap moi vat mep mot phia
J TAP CHI c a KHI VIET NAM V Sd 05 - Thang 5 nam 2010
NGHIEN CUU • TRAO DOI
M6i han lot dat yeu cau
a)
Khong ngau, nirt
b)
c)
Hinh 5: Anh chup tho dai mat cat ngang cac moi han thu nghiem a) moi han dat yeu cau
b) moi han khong ngau c) moi han bi sut be mat
Hinh 6: Ket qua thir nghiem ca tinh cac mau han: a) mau keo, b) mau uon
Tren hinh 5a dua ra anh td chiic thd dai cua lien ket ban giap hai phia mdi cd vat mep. Mdi ban Idt d phia thir nhat dam bao ngau bet phan \at mep \ a su chuyen tiep phang til' kun loai mdi ban den kim loai co ban. Mdi ban a phia thu hai ngau het phan chan cua mdi ban Idt. Rd rang khi mdi han Idt dat chat lugng thi chat lugng eua loan bd lien ket ban dugc dam bao. Khi che do han khdng duge tinh toan chinh xac thi mdi ban se khdng ngau (hinh 5b) hoac bi sut be mat (hinh 5c). Cac ket qua thu co tinh hen ket ban tten hinh 6 cho thay lien ket bi pha huy a phan kim loai co ban, gdc udn cac mau dat duge la hoan loan thoa man.
4. Ket luan
- Su dung phuong phap phan tich \ e trudng nhiet do de tinh toan che do ban trong trudng hgp ngudn nhiet cd su phan bd phiic tap khdng tuan theo quy luat phan bd eua eae ngudn nhiet co ban tren tam phang la rat hieu qua. Cac ket qua tinh toan cd sai lech so \di gia tri thuc do dugc.
tu>- nhien sai sd la hoan toan chap nhan dugc.
- Neu ddng dien \a tdc do han dugc lua chgn phii hgp
\ di nhau thi chieu sau ngau \ a chieu rdng mdi ban hoan toan cd the dam bao dugc. Tuy nhien de su chuyen tiep giira kim loai mdi ban va kim loai co ban ddng deu hon thi nen chgn ddng dien ban la 210A\a tdc do ban la 29.3m/h ddi vdi tam cd chieu day 12mm.
- Phuong phap tinh toan nay hoan toan ed the ap dung cho tat ca cac kim loai \ a hgp kim chi can dua \ ao tinh chat \ at ly cua chiing khi giai phuong trinh rang budc giiia nhiet do viing ban, tinh chat ly nhiet \ a cae thdng sd che do ban.
- Khi ban eae lien ket giap mdi cd vat mep, hoan toan cd the nhan dugc be mat mdi ban Idt cd su chuyen tiep tron tru den kim loai co ban, tham chi la phang neu chgn che do ban hgp ly. •
a)
Tai lieu tham khao:
[1] Thennal analysis of welds, N.T, Nguyen. WIT Press. Soulhhamton, 2004, [2] AWS Welding Handbook, 8th Edition. 1996,Pages 17-119 (AI), [3] Aluminium Welding. N,R, MandaL Alpha Science International Ltd, Pangbourne. 2002,
[4] -Numencai methods - Department of Mathematics - HongKong Baptist University.
TAP CHI c a KHI VIET NAM V So 0 5 - T l i a n g 5 nam 2010