l M ! M i l ! l « M c 6 N CQNGJSIGHE
NANG CAO NANG SUAT VA CHAT Ll/ONG BE MAT GIA CONG CUA PHUONG PHAP GIA CONG BANG TIA LUfA DIEN
ENHANCING MACHINING EFFICIENCY AND SURFACE QUALITY OF ELECTRICAL DISCHARGE MACHINING
Banh Tien Long, Ngo Cudng, Nguyen HuTu Phan, Pham Viet Hiing
T 6 m t J i t
Gia cdng bSng tia Ida dien (EDM) la phUdng phap gia cdng khong truyen thdng dddc sd dung rdng rai nhit trong nganh che tao khudn mSu. Vi vay, nhiitig nghien cdu nang cao nang suit va chat Idong cda phuong phap nay cd # nghTa thifc tien to Idn. Bal bao nay gidi thieu hudng nghien cdu mdi nhSm nang cao ndng suat va chat iKcmg be mat gia cdng cda EDM vdi bSt kim loai ducre trgn trong dung dich dien mdi (PMEDM). Bdttitan dUoc sddung va sucdi thien hieu quti gia cdng ddoc danh gl^ qua cac thong sd: ning suSt bde tach vat lieu (MRR), lUong mdn dien circ (TWR) va nham be mat gia cong (R^), Thep lam khudn dap ndng SKD61 va dien cdc ddng da ddoc sddung trong nghien cdu. V^ kit qu^ nghien cdu da eho thay:
TWR vaR^ giam, MRR tang.
TCf khda: PMEDM, EDM, MRR, TWR, thep SKD61.
Abstract
Elearlcal Discharge Machining (EDM) Is a non traditional method that is widely used to produce dies and molds. Therefore, many researches focused to improve efficiency and quality of the EDM process have been carried out This paper presents a new research woilt to improve performance of the conventional EDM when using powder-mixed dielectric. A titanium powder is used and the improvement is assessed through material removal rate (MRR), tool wearrate (TWR) andsur^ce roughness {SR).The hot work steel SKD61 and eledrode made from copperare used in this experimental research. The results show that MRR is enhanced, TWR and R^ are decreased.
Keywords: EDM, PMEDM, MRR, TWR, SR, SKD61,
GSTSKHBanh^MiLong ~' ~ ~ TnrJRigDai hoc Bach khoa Hi Noi
TS. Ngfi Ciittig, ThS. Nguyf n HOu Phan, KS. Pham Viet Hdng Tm*ng Cao dSng Kinli \i • ^ thu|it, Dai hpc Thai Nguyen Email: phanktcmigmaiLcom
I . O A T V A N D i
Gia cong bang tia ICfa dien (EDM) la mot trong nhCing phifong phap gia cong tien tien dong vai tro rat quan trong trong linh vifc cong nghe che tao may. Trong phiicfng phap nay, nguon nang laang nhiet rat Idn sinh ra bdi cac
Ngaynhanbai: 03/11/2014 Ngiydiffp nhan dang: 15/12/2014
tia iLfa dien di/oc sCr dung de tao hinh be mat can gia cong. Do do, EDM co the gia cdng cac loai vat lieu dan dien co dp ben va do cCrng bat ki, cac loai khuon mau va dyng cu phiJc tap, chi tiet sCt dung trong nganh hang khong, thiet bj t u dong.... Tuy nhien, phUcJng phap nay
cung ton tai mot so nhUOc diem nhU:
nang suat boc tach vat lieu thap, dd nhan be mat sau gia cong khong caova dien cUc bj mon lien tuc khi gia cong.
Dieu nay cung da va dang la moi quan tam chinh cua rat nhieu cac nghien cdu [3],[6],[8^10]. Cac ket qu5 nghien cdu da cho thay ra rang, nang suat va chat lUdng be mat gia cong bSng EDM ttUOe cai thien dang ke khi trpn bot kim loai hoac hop kim vao trong dung dich dien moi.
Cac loai bgt co kich thi/dcva vat lieu khac nhau da duoc trpn vao dung djch dien moi nham lam giam d6 ben cda no, tang so luong tia ICra dien va khehd phong dien va tao ra qua trinh gia cong on dinh tCf do nang cao nang suat,chal luong be mat gia cong cCia EDM [11, [2]. Viec tron bdt Si vao dung djch dier moi da MRR tang manh so vdi v6i EDM khong bot khi gia thep AISI D2[31.Khi nghien cdu anh hudng cua cac loai bgt Al, Cr, Cu va SIC trpn vao dung djch didn moi da chi ra ring: kich thUdc, nong dp, dp dan dien va dan nhiet cCia bdt CO anh hudng rat Idn den hi^u quSgia cong cua EDM, Hinh 1 [4]. BptGraphit CO kich thudc nano khi trpn vao dung djch da tao ra be mat c6 dp b6ng rat cao, tuy nhien mot Idp b6t m6ng bj dong dudi d^y binh thi nghiem la van de can dUOc quan tam nghien ciJu[5!.
4 TapdiiKHOAHOC&CONGNGHE. S o 2 5 . 2 0 1 4
SCIENCETECHNOLOGYl
Khi tron bot graphit vao dung dich dien moi vdi nong do 4g/l da lam khe hd phong dien tang trong khi dien ap phong dien lai giam, dp on dinh cua qua trinh gia cong dupc nang cao va nang suat bde tach vat lieu tang 60%, luong mdn dien cUc giam 28%, Hinh 2 [6]. Iron bgt Si vao dung dich dien moi de gia cong thep SKD61 da nang cao dupe chat lupng be mat gia cong [7].
Anh hudng cua viec sd dung bdt kim loai trong cdng nghe EDM den chat lupng be mat gia cdng con phu thupc vao loai vat lieu gia cong: trpn bdt Al cd kich thudc trung binh vao dung djch dien mdi khi gia cdng thep SKH-51 da cho dp bdng be mat cao nhung khi gia cdng thep 5KH-54 lai nhan dupe do bong be mat thap [8]. Tri so nhap nhd be mat gia cdng con phu thudc vao dien tich va thdi gian gia cdng: R^ thay doi t u 0,09 um den 0,57 |jm khi dien tich gia cdng thay doi tU 1 cm^ den 64 cm=[9].
Hinh 1. Anh hUdng eua bdt den MRR [4]
Hinh 2. Anh hirdng cua bdt graphit den TWR, MRR va he sd mon dien cuc(WR}[6]
NhUng ket qua nghien cUu tren cho thay rang day la hudng nghien cufu khS thi rat can dupe quan tam va tiep
tuc nghien cUu. Hau het cae ket qua nghien cUu ve PMEDM da cho thay:
ndng do bot la thdng sd cdng nghe co anh hudng tich cue den nang suat va chat tuong qua trinh gia cong [2], [6]
[9-^10]. Trong nghien cUu nay, sU thay doi ndng dp cua bdt Titan trong dung dich dien mdi la dau nham nang eao hieu qua gia cong cua phuong phap EDM vdi dien cue dupe phan cUc thuan.
Cac thong sd: nang suat bde tach vat lieu, luong mon dien eUc va trj so nhap nhd be mat duac sU dung de danh gia cho muc dich nghien cUu.
Z.THlfTKETHfNGHIEIVl Bang 1, Cac thong sd cdng nghe gsa cdng
IT 1 2 3 5 6 7 8
Thong so Circing do dong dien xung (A) Thdi gian xung (us) Thdi gian ngimg xung (ps) Phan cdc Thdi gian gia cong {ph) Bienap(V) Nong dd hot (g/l)
Tri so 15 50 85 15 150 0,5,10,
15,20
Hinh3,He thong thi nghiem a. Sadd thi nghiem b Binh thinghiem Bang 2, Ket qua MRR
S o d o t h i n g h i e m d u p e t r i n h b a y d h i n h 3, q u a t r i n h p h a n c u e k h i g i a c d n g la p h a n cUc t h u a n . T h i n g h i e m t r e n m a y x u n g d i e n C N C - A G 4 0 L ( H a n g S o d i c k , I n c . USA) c u a T r u n g t a m t h i n g h i e m T r u d n g D a l h p c Ky t h u a t C d n g n g h i e p T h a i N g u y e n . V a t l i e u m a u t h i n g h i e m ta t h e p S K D 6 1 (TC JIS - N h a t Ban) n h i e t l u y e n d a t d p c d n g HRC ^ ( 4 8 ^ 5 2 ) , m a u c d k i c h t h u d c 4 5 x 2 7 x 5 m m . V a t l i e u d i e n c u e la d d n g C 1 1 0 0 ( 9 9 , 9 % ) c d d U d n g k i n h 2 5 m m . B o t t i t a n c d k i c h t h U d c c d h a t 4 5 p m d u o c l u a c h p n d e t r p n t r o n g d u n g d i c h d i e n m d i . D u n g d i c h d i e n m o i la d a u H D - 1 c u a H a n g ELECTROL.
D u y t r i sU d d n g d e u v a k h d n g b i l a n g d o n g eua b d t t i t a n t r o n g d u n g d i c h d i e n m d i b a n g ca c a u k h u a y g d m : d d n g CO k h i n e n c o t d c d o q u a y 5 0 0 v d n g / p h u t , c a n h q u a t k h u a y c d d U d n g k i n h 1 0 5 m m , D u n g m d i d u p e c u n g c a p v a o v u n g g i a c d n g b a n g b O m A 3 0 3 c u a T r u n g Q u o c c d c d n g s u i t 6 0 0 l i t / g i d , d u d n g k i n h v d i p h u n 0 8 m m . Cac t h d n g s d duoc l u a c h o n d e n g h i e n c U u ( b a n g 1) d U a t r e n ca s d m d t s d n g h i e n eUu t u t r U d c .
O o k h d i l u p n g c u a p h d i t r U d c v a s a u k h i g i a c d n g b a n g c a n d i e n t d AJ 2 0 3 ( H a n g S h i n k o D e n s h i C o . LTD - J a p a n ) , k h o i l u p n g I d n n h a t m a c a n c d t h e c a n duac la 2 0 0 g , d p c h i n h x a c 0 , 0 0 1 g . Tri s d n h a m b e m a t g i a c d n g ( R J duac d o b a n g m a y d o b i e n d a n g k i e u d a u d o t i e p x u c SJ-301 ( H a n g M I T U T O Y O - J A P A N ) , c h i e u d a i c h u a n d o la 5 m m , t h u c h i e n 3 Ian d o t r e n m d i m a u t h i n g h i e m v a k e t q u a d p n h a m la g i a t r i t r u n g b i n h c u a m o i Ian d o .
3 . K ^ T Q U A V A T H A O L U A N 3 . 1 . A n h h i / d n g d e n M R R
TN 1 2 3 4 5
MRR (mm^/min)
0,716 0,634 0,746 1,037 1,208
me,
(mmVmin) 0,597 0,834 0,927 0,859 1,400
MRR (iTi[tf/min}
0,657 0,734 0,837 0,948 1,304
Ndngddbdt(g/I) No 5 10 15 20
S o 2 5 . 2 0 1 4 •TapdiiKHOAHOC&CONGNGHE !2!
^s^ssm CONG NGHE
Bang 3. Ket qua TWR
Hinh 4. Anh hifong ciia nong do bot den MRR MRR d U d c x a c d i n h b d i t y s o glUa h i e u k h o i l U p n g v a t l i e u p h d i t r U d c v a sau g i a c d n g v d i t h d i g i a n g i a c d n g :
W - W ,
MRR = —! '-A 0 0 0 m m ' / p h u t p.t ^ (1) T r o n g d d :
W^ la k h d i l u o n g m a u t r u d c g i a c d n g (g).
W j la k h d i l u o n g m a u s a u g i a c o n g (g).
t la t h d i g i a n g i a c o n g c h o m d i I a n chaythU{t=15phut),
p la khoi lupng rieng cua vat lieu mau ( p - 7 , 8 1 g/cm').
MRR la dai lUpng lien quan trUe tiep den thdi gian che tao sin pham, tang MRR se giup rut ngan dUpc thdi gian gia cdng chi tiet. Xac dinh gia trj MRR cho 5 thi nghiem, moi thi nghiem lap 2 tan. Ket qua (bang 2 va hinh 4} eho thay viec trpn bot titan trong dung dich dien mdi da lam tang MRR so vdi gia cdng khong cd bdt. Nguyen nhan tang MRR CO the giai thich nhUsau:
- Khi bot titan xuat hien trong dung dich dien mdi da tao them rat nhieu cau noi phdng tia Ida dien lam tang mat dp tia Ida dien cung tham gia cat,
- Tdng nang lUdng cua cac tia Ida dien sU dung de gia cong vat lieu tang khi cd bdt trgn trong dung dich dien moi. Nguyen nhan la do: bdt titan cd kha nang dan dien tot duoc trdn vao dung dich dien mdi se lam giam do ben each dien cua dung dich dien mdi tU do lam giam tieu hao nang luong danh thCing dien mdi.
- Khi ndng dp bdt thay doi t d (0 IN
1 2 3 4 5
IWR (mrrf/mm) TWR 1,316 0,871 0,816 0,658 0,441
i m , 1,279 0,934 0,735 0,587 0,483
T W R (mmVmin)
1,298 0,903 0,776 0,623 0.462
Nong do b5t (9/i)
No
5 1
10 15 20^15)g/l ta cd MRR tang kha giong nhau nhung cang ve sau MRR tang cang manh va khi nong dp bdt Idn nhat 20g/l thi MRR cao nhat MRRmdx
^ 1,304mmVphLit {tang 98,47% so vdi khdng cd bdt). Khi ndng dp bdt tang se dan den so luong cae hat bdt xuat hien trong khe hd phdng tia Ida dien tang lam sd luong tia Ida dien smh ra trong mot Ian phat xung cung tang len va dp ben each dien cua dung djch dien mdi bj giam di nen nang luong dung cho danh thung dung dich dien mdi cung giam theo. Tuy nhien khi nong dd bdt qua cao cd the xly ra hien tUOng ngan mach xuat hien trong qua trinh gia cong gay tieu hao nang lupng gia cdng.
3.2. Anh hudng den TWR TWR la dai lupng duoc xac dinh bdi ty sd gida hieu khdi lUpng vat lieu dien cUc trudc va sau gia cdng vdi thdi gian gia cdng:
T W R - ^ ^ ^ . l O O O m m V phut
pT-t (2) Trong dd:
T la khdi lupng ban dau eua dien cue (g).
Tf la Khdi lupng dien cue sau gia cdng (g).
t la thdi gian gia cdng cho moi Ian chaythd(t=15phut),
p^ la khdi lupng rieng cua vat lieu dien cue (p^ = 8,94 g/cm'),
Mdn dien cue xay ra trong suot qua trinh gia cdng lam anh hudng den dp chinh xac thdng sd hinh hpc cua chi tiet gia cong, TWR tang edn lam tang chi phi san xuat do phai thay the dien cue bj mdn.
Hinh 5. Anh hu6ng ciia nong do bot (len TWR K e t q u a x a c d j n h l U p n g m o n dien cue ( b a n g 3 v a h i n h 5) c h o t h a y :
- Khi gia cdng khdng co bot tron trong dung mdi lam TWR Idn nhal Nguyen nhan la cac ion dUpc hinh thanh trong qua trinh ion hda chatdltr mdi cd ddng lUpng cao va nang lu'ong se tac dung len be mat dien cUc gayu xdi mdn dien cue Idn.
- Bdt titan trpn vao trong dung djcli dien mdi lam TWR giam. Dd la do cac hat bdt di vao vung khe hd phong tia Ida dien cat ngang dUdng di chuyen cua cac ion ve phia be mat dien ciJc Oieu nay lam giam ddng luong ciia cat ion, cac ion cd nang luong thap hon tac dung len be mat dien cue lam dienciJt it bi xdi mdn hon.
- Khi ndng dp bdt 5g/l trong dung dich dien mdi da lam TWR gilm rat manh, tiep tuc tang ndng dp bptTV/B giam vdi mot lupng nhd hOn. TWR*
-0,462pm khi ndng dd bdt la 2 0 g A ^ nay dupc g i l i thich la do; cac hat bot*
ngan c i n s u d i chuyen cua cac ion la IA nhat nen cac ion se cd nang lUOng nW nhat khi tac dung len be mat dien CL(C
3.3. Anh hudng den do nham b mat gia cdng
26|TapdiiKH0AHOC&C0NGNGHC« S o 2 5 . 2 0 1 4
SCIENCETECHNOLOGYl
K e t q u i d b a n g 4 v a h i n h 6 e h o t h a y , Ho n h a m b e m a t g i a c d n g g i a m l i e n t u c
<ha m a n h k h i t r o n b d t t i t a n v a o t r o n g d u n g d i c h d i e n m d i ( d o t h i c d d p d o c J e u v a I d n k h i t a n g n d n g d p b d t ) . C d
h e g i a i t h i c h n g u y e n n h a n n h U s a u : Bang 4. Ket qua dp nham be mat gia cong
™
1 2 3 4 5
R.
(pm) 4,22 3,74 3,15 2,97 2,54
Nong dd bdt (g/l)
No 5 10 15 20
N d n g d o b^T titm(£/1) Hinh 6. Anh hudng cOa nong dp hot den R^
- Khi bdt xuat hi&n trong dung djch tien mdi da lam tang kich thudc va md dng vung phdng tia Ida dien va tao fieu kien thuan Ipi cho qua trinh van huyen phoi ra khdi vung gia cdng.
:!ac hat bot t o n tai trong khe hd phdng tien lam tia Ida dien bi phan chia thanh ihieu tia Ida dien cd nang lupng nhd ion nhieu khi tham gia gia cdng. Dieu lay da tao ra cac vet Idm tren be mat jia cdng cd dUdng kinh va chieu sau i h d hdn dan den dp nham giam.
- Ndng dp bdt titan tang thi sd uong hat bdt ton tai trong vung khe i d phdng tia Ida dien cung tang len,
;d lupng cac tia Ida dien dUOc tao ra rong mdt Ian phat xung cung tang len am cho nang lupng cua mdi tia giam ludng nen tri nhap nhd be mat cung ji3m theo. Od nham R^^,^ = 2,54pm khi long dp bdt titan la 20g/l, neu tiep tuc ang ndng dp bdt thi hien tupng ng^n nach cd the se xuat hien nhieu hon am cho qua trinh gia cdng khdng on
djnh va do nham be mat gia cdng cd the lai tang.
4. K^T LUAN
Td cac ket qua nghien cdu khao sat tren, cac tac gia dUa ra mdt sd ket luan va dexuat mdi sau:
- Ndng dp bdt titan trong dung dich dien mdi la thdng sd cdng nghe cd anh hudng kha Idn den nang suat va chat luong be mat gia cdng cua EDM. MRR tang, TWR va R^ deu giam khi tang ndng dd bdt titan. Ndng dp bdt tang tU 0 len 20g/l thi MRR tang 98,47%, TWR giam 96,961 % va R^ giam 65,40%.
- T r p n b d t t i t a n t r o n g d u n g d i c h d i e n m d i d a n a n g c a o d a n g k e h i e u q u a g i a c d n g e u a E D M . T u y n h i e n , cac v a n d e n h U : d p c h i n h x a c g i a c d n g , t h a n h p h a n h o a h p c v a c a u t r u e I d p b e m a t , d p c d n g t e v i v a p r o f i n c u a b e m a t s a u g i a c d n g vhn c h U a duac d e c a p . V i v a y c a n c d t h e m n h d n g n g h i e n c d u t h e o h u d n g n a y d d i v d i b d t t i t a n . N g o a l ra, d p d d n g d e u c u a b d t t r o n g d u n g d i c h d i e n m d i v a l u u l u p n g c u n g c a p d u n g m d i v a o v u n g g i a c d n g la t h d n g sd q u a n t r o n g c u n g c a n q u a n t a m k h i n g h i e n c U u .
PhAn bien khoa tioc: PGS.TS. Hoang Van fitft
T A I L I I U THAM KHAO
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