TRNG AI HOC S PHAM KY THUAT TP. HO CH MINHKHOA C KH CHE TAO MAY

BO MON CONG NGHE CHE TAO MAY

THANH PHO HO CH MINH NAM 2004

LI NOI AU

Khoi kien thc thuoc nhom cong nghe che tao may c phan chia thanh hai giao trnh chnh, o la:

1 - C S CONG NGHE CHE TAO MAY la mon hoc c s cho tat ca cac nganh c kh nh: CKM, KCN, TKM, CKT, CK, CT, CT Noi dung cung cap cac kien thc c ban nh nguyen ly tao hnh be mat, cac chuyen ong cat got, nguyen ly cat got kim loai, dung cu cat cung vi cac phng phap cat got.

e co the che tao ra cac chi tiet may (oi tng nghien cu cua Cong nghe che tao may) at chat lng cao can phai nam vng cac kien thc c ban ve nguyen ly cat got, chat lng be mat va o chnh xac gia cong chi tiet may, khai niem ve chuan cong nghe va cach chon chuan trong qua trnh cong nghe, cung nh nhng hieu biet c ban ve dung cu cat got va cac phng phap gia cong cat got.

2 CONG NGHE CHE TAO MAY la mon hoc chuyen nganh cho nganh CKM. Noi dung cua giao trnh nay gom cac phan chnh nh: Thiet ke qua trnh cong nghe, thiet ke o ga, cong nghe gia cong cac chi tiet ien hnh, cong nghe lap rap cac san pham c kh.

Phan nay giup cho sinh vien chuyen nganh i sau vao lanh vc thiet ke quI trnh cong nghe va cac trang thiet b cong nghe nh o ga e nh v va kep chat phoi, chi tiet hoac dao cat tren cac may cong cu. Ngoai ra, cung cap mot so kien thc c ban ve cong nghe lap rap cac chi tiet may thanh cac san pham c kh.

e hoan thanh tap giao trnh nay ngoai s co gang cua cac tac gia con co s gop y cua ong nghiep sao cho phu hp vi muc tieu ao tao cua trng ai hoc S Pham Ky Thuat.

Ngoai giao trnh nay ra, trong qua trnh hoc tap sinh vien co the tham khao cac giao trnh Cong nghe Che tao may cua trng ai hoc Bach khoa TP HCM va ai hoc Bach khoa Ha noi.

Cac tac gia rat mong s ong gop tan tnh cua cac thay co ong nghiep va sinh vien.

TP.Ho Ch Minh, ngay 30 thang 8 nam 2003.

CAC TAC GIA

CHNG 1

NHNG KHAI NIEM C BAN 1.1 Khai niem ve qua trnh hnh thanh san pham c kh

1.1.1 Khai niem ve san pham c kh

Trong qua trnh san xuat kinh doanh va dch vu cac mat hang c kh, san pham c kh co the la nhng chi tiet kim loai thuan tuy hoac mot cum may c lap ghep t nhng chi tiet kim loai va phi kim loai hay mot may hoan chnh e ap ng mot nhu cau s dung nao o.

V du: Nha may san xuat phu tung may no, san pham c kh ay co the la Piston, xec mang, thanh truyen v.v hay nha may san xuat o bi th san pham c kh la o bi c lap ghep t cac chi tiet kim loai nh vong bi, vien bi v.v Con bo phan phi kim loai ay co the la vong cach c che tao t nha v.v

San pham c kh co the la may moc thiet b hoan chnh. V du: Nha may san xuat may cong cu (may tien, may phay v.v)

Cung nh bat ky san pham nao khac, san pham c kh c san xuat nham ap ng nhu cau nao o ma xa hoi va th trng yeu cau.

1.1.2 Mo hnh hnh thanh san pham c kh

Qua trnh hnh thanh san pham c kh c nhan thc ro qua viec phan tch moi quan he mo ta di ay:

SX CBSX & TCSX

T - THXH - TT SP

NC - PT CT

Ghi chu:

SP: San pham XH TT: Xa hoi Th trng T TH: Tiep th NC PH: Nghien cu Phat trien CT: Che th CBSX va TCSX: Chuan b san xuat va to chc san xuat. SX: San xuat

Tiep th: la bo phan rat quan trong, au moi giao te gia cung va cau, co cac nhiem vu:

- Chao va ban hang.

- Nam bat th hieu cua khach hang oi vi san pham cong ty, x nghiep ang san xuat.

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- D bao ve nhu cau phat trien ve so lng, chat lng va nhng yeu cau khac.

- Kch thch tao ra nhu cau chnh ang mi, qua o tao th trng mi. ay mot van e can quan tam la nhu cau khong phai co san ma phai qua quang cao, dung th.

Hien nay e chiem lnh th trung rat nhieu cong ty a khong ngng phat trien manh ve quang cao tiep th, ac biet la cac cong ty lien doanh, san pham co the la mi hoac truyen thong.

Nghien cu Phat trien: la mot khau rat quan trong co sc manh khoa hoc cong nghe u hoan thanh cac cong viec:

- Nghien cu cai tien san pham ang san xuat.

- Nghien cu san xuat nhng san pham mi do th trng yeu cau.

- Nghien cu cac cong nghe mi ang ng dung vao lnh vc san xuat cua cac x nghiep.

Bo phan nghien cu phat trien luon gan lien vi khau tiep th va che th e t o cai tien khong ngng san pham cua mnh ve moi mat: chat lng va mau ma e ngay cang chiem lnh c th trng trong nc va xuat khau .

nhng hang hoac cong ty ln, ty le au t cho bo phan nghien cu phat trien rat ln, nhat la au t ve lc lng ky thuat, trang thiet b v.v Chnh t bo phan nay, nhng thanh tu mi ve cong nghe a c nghien cu va ng dung, gop phan phat trien hang va gop phan phat trien khoa hoc cong nghe cho tng giai oan phat trien cua xa hoi.

Che th: Bat c cong ty, x nghiep san xuat nao muon phat trien va cai tien mat hang cua mnh eu phai co bo phan che th. Bo phan nay muc ch kiem nghiem ve mat nguyen ly, ket cau va chat lng lam viec cua thiet b. T thc te lam viec cua thiet b che th chung ta se tien hanh nhng thay oi ve cac mat nh nguyen ly, ket cau, vat lieu v.v e thoa man ieu kien toi u. Bo phan che th can thiet c trang b ay u may moc cung nh cac phng tien kiem tra, anh gia chat lng. Can bo ky thuat cung nh cong nhan phai co kien thc thc te va tay nghe cao. Co u nang lc e thc hien nhanh chong nhng san pham mi do bo phan nghien cu phat trien yeu cau.

Chuan b san xuat va to chc san xuat: ay la cong oan quan trong nhat cua qua trnh san xuat san pham. Chuan b san xuat bao gom: chuan b ve thiet ke va chuan b ve cong nghe.

- Chuan b ve thiet ke: Cong viec nay thng thuoc bo phan NC PT. Can c vao yeu cau s dung, thiet ke ra nguyen ly cua thiet b, t nguyen ly thiet ke ra ke cau thc sau o a ra bo phan che th kiem nghiem ket cau va sa oi hoan chnh roi mi a sang chuan b san xuat.

- Chuan b ve cong nghe:Nha cong nghe che tao can c vao ket cau a c thiet ke e chuan b nhng tai lieu cong nghe hng dan qua trnh san xuat va to chc san xuat. Giai oan chuan b cong nghe can phai tien hanh nhanh chong, ngay nay nh trang b ky thuat hien ai nh s dung cac thiet b vi tnh vi phan mem manh a giup cho cac nha

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cong nghe hoan thanh nhanh chong cong viec nay vi thi gian can thiet e nhanh chong a vao san xuat hang loat. Co nh vay san pham mi khong b lac hau va chiem lnh th trng nh kha nang oc quyen cua mat hang.

T ban ve thiet ke ket cau en luc ra san pham cu the la mot qua trnh phc tap, chu tac ong cua nhieu yeu to khach quan va chu quan lam cho san phan c kh sau khi che tao co sai lech so vi ban thiet ke ket cau. Nh vay khi chuan b cong nghe che tao can chu y khong che sai lech o trong pham vi cho phep.

Cong nghe che tao may la mot lnh vc khoa hoc ky thuat co nhiem vu nghien cu, thiet ke va to chc thc hien qua trnh che tao san pham c kh at cac chi tieu kinh te ky thuat nhat nh trong ieu kien quy mo san xuat cu the. Mot mat cong nghe che tao may ly thuyet phuc vu cho cong viec chuan b ve cong nghe co hieu qua nhat. Mat khac no nghien cu cac qua trnh hnh thanh cac be mat chi tiet va lap rap chung thanh san pham.

1.2 Qua trnh san xuat va qua trnh cong nghe 1.2.1 Qua trnh san xuat

Qua trnh san xuat la qua trnh con ngi tac ong vao tai nguyen thien nhien e bien no thanh san pham phuc vu cho li ch cua con ngi.

Qua trnh san xuat trong nha may c kh la tap hp cac hoat ong co ch e bien nguyen vat lieu hay ban thanh pham thanh san pham. V du, san pham c kh th phai qua khai thac quang, luyen kim, che tao phoi, gia cong c kh, gia cong nhiet hoa, kiem tra, lap rap va hanh loat cac qua trnh phu nh: van chuyen, che tao dung cu, bao quan, sa cha thiet b, chay th, ieu chnh, sn, bao b ong goi .v.v

1.2.2 Qua trnh cong nghe

Qua trnh cong nghe la mot phan cua qua trnh san xuat trc tiep lam thay oi hnh dang kch thc, tnh chat ly hoa cua ban than chi tiet va v tr tng quan gia cac chi tiet trong san pham.

Qua trnh cong nghe gia cong c la qua trnh cat got phoi e lam thay oi hnh dang va kch thc cua no.

Qua trnh cong nghe nhiet luyen la qua trnh lam thay oi tnh chat ly hoa cua vat lieu chi tiet.

Qua trnh cong nghe lap rap la qua trnh tao thanh nhng quan he tng quan gia cac chi tiet thong qua cac loai lien ket moi lap ghep.

Xac nh qua trnh cong nghe hp ly roi ghi thanh van kien cong nghe th cac van kien cong nghe o goi la quy trnh cong nghe.

1.2.3 Cac thanh phan cua qui trnh cong nghe

a) Nguyen cong

La mot phan cua qua trnh cong nghe, c hoan thanh lien tuc, tai mot cho lam viec va do mot hay mot nhom cong nhan cung thc hien.

Neu thay oi mot trong cac ieu kien: tnh lien tuc, hoac cho lam viec th ta a chuyen sang mot nguyen cong khac.

V du: Tien mot truc bac nh hnh 1.1, co the co 3 phng an gia cong nh sau:

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- Phng an 1: Tien au B xong roi tr au tien C ngay, o la mot nguyen cong.

- Phng an 2: Tien au B cho ca loat, xong mi tien au C cung cho ca loat tren may o, nh vay ta a chia thanh 2 nguyen cong v tnh lien tuc khong bao am.

l1 l2 l3

AB C

Hnh 1-1 Tien truc bac

D

- Phng an 3: Tien au B tren may so 1; tien au C tren may so 2; Nh vay cung la 2 nguyen cong v cho lam viec a thay oi mac du tnh lien tuc van bao am.

Con thc hien nguyen cong tien xong, phay ranh then A, D mot may khac, o cung la 2 nguyen cong.

Nguyen cong la n v c ban cua qua trnh cong nghe e hoach toan kinh te va to chc san xuat. Phan chia qua trnh cong nghe ra thanh cac nguyen cong co y ngha ky thuat va kinh te.

* Y ngha ky thuat la cho khong the va tien va phay hay va tien va mai mot chi tiet tren cung mot may, nen phai chia thanh 2 nguyen cong (khai niem nay ung khi khong co may van nang to hp).

* Y ngha kinh te la cho viec phan chia thanh t hay nhieu nguyen cong con tuy thuoc ieu kien thiet b va san lng hang nam. Hoac tren mot may chnh xac khong nen lam ca cong viec tho lan cong viec tinh ma phai chia thanh hai nguyen cong tho va tinh cho hai may, may gia cong tho va may gia cong chnh xac (v may gia cong chnh xac at tien hn may gia cong tho).

b) Ga

La mot phan cua nguyen cong c hoan thanh trong mot lan ga at chi tiet (mot lan kep chat). Mot nguyen cong co the co mot hay nhieu lan ga.

V du: Tien mot au roi tr au kia (hnh 1.1) e tien la hai lan ga.

c) V tr

La mot phan cua nguyen cong, c xac nh bi mot v tr tng quan gia chi tiet gia cong vi may hoac dung cu cat.

Cung hnh 1.1 neu dung u phan o e ga at chi tiet khi phay ranh then, th se co hai co v tr khi phay hai ranh A, D. Nh vay mot lan ga co the co mot hoac nhieu v tr.

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d) Bc

La mot phan cua nguyen cong c ac trng bi :

- Gia cong mot be mat hoac nhieu be mat cung luc;

- S dung mot dao hoac mot nhom dao ghep;

- Cung mot che o cat.

Thay oi mot trong ba yeu to tren la ta a chuyen qua bc khac.

V du : Tren hnh 1.1, khi ta s dung phng an mot e gia cong th nguyen cong tien co hai bc khac nhau v a thay oi be mat gia cong, ngha la tien au B la bc mot, tien au C la bc hai.

e) ng chuyen dao

La mot phan cua bc e ht i mot lp kim loai, s dung cung mot dao va mot che o cat.

V du: Khi tien au B cua truc, do lng d qua ln ta phai cat hai lan vi n, s, t nh nhau, o la hai ng chuyen dao trong cung mot bc. Neu lan cat th hai ta s dung che o cat khac th o la hai bc ch khong phai hai ng chuyen dao.

f) ong tac

La mot hanh ong cua cong nhan e ieu khien may thc hien viec gia cong hay lap rap. V du: nhan nut, quay u dao, xiet mam cap

1.3 Hnh thc to chc san xuat va dang san xuat 1.3.1 Cac hnh thc to chc san xuat

To chc san xuat theo day chuyen: moi nguyen cong hoan thanh tai mot a iem nhat nh nhng co quan he vi nhau ve mat thi gian va khong gian. Ta con goi la tuan thu nhp gia cong T (phut) va bc van chuyen L (met). So lng nguyen cong phai c tnh toan thong qua nhp san xuat va o tin cay cua tng nguyen cong. Phng phap to chc san xuat theo day chuyen luon luon mang lai hieu qua kinh te cao.

To chc san xuat khong theo day chuyen: Moi nguyen cong c thc hien mot cach oc lap, khong co lien quan ve khong gian va thi gian vi cac nguyen cong khac. Hieu qua kinh te phng phap nay thap. Viec bo tr thiet b thng theo nhom may: Tien, phay, bao, mai Phng phap nay phu hp vi san xuat nho, sa cha, che tao phu tung thay the v.v

1.3.2 Dang san xuat

Dang san xuat la mot khai niem cho ta hnh dung ve qui mo san xuat mot san pham nao o. No giup cho viec nh hng hp ly cach to chc ky thuat cong nghe cung nh to chc toan bo qua trnh san xuat. Cac yeu to ac trng cho dang san xuat la:

- San lng tnh bang n v san pham hoac trong lng;

- Tnh on nh ve so lng va chung loai san pham;

- Tnh lap lai cua qua trnh san xuat;

- Mc o chuyen mon hoa trong san xuat.

San lng chi tiet can che tao trong mot nam cua nha may c tnh nh sau:

)100

1).(100

1.(.0 ++= mNN

trong o: N0 - So san pham trong mot nam theo ke hoach;

m So lng chi tiet nh nhau trong mot san pham;

- So phan tram goi au ke hoach (10 20 %); - So phan tram phe pham cho phep ( 3%)

Tuy thuoc cac dang ac trng a neu, ngi ta chia ra cac dang san xuat nh sau:

a) Dang san xuat n chiec

San lng t, thng t 1 en vai chuc chiec, chung loai nhieu, tnh lap lai khong biet trc. oi vi dang san xuat nay ta phai to chc ky thuat cong nghe nh sau:

- Thiet b van nang ap ng tnh a dang cua san pham. May moc c bo tr theo loai may, thanh tng bo phan san xuat khac nhau.

- Trnh o th a nang co the thc hien c nhieu cong viec khac nhau.

- Tai lieu hng dan cong nghe ch la net c ban, qui trnh cong nghe ch the hien di dang tien trnh.

b) Dang san xuat hang loat

San lng khong t, san pham c che tao tng loat theo chu ky xac nh va co tnh tng oi on nh.

Tuy theo san lng va mc o on nh san pham ma ta chia ra loat nho, loat va va loat ln.

Dang san xuat loat nho gan vi san xuat n chiec, con san xuat loat ln thng dung nhieu thiet b chuyen dung, qui trnh cong nghe c thanh lap mot cach kha t m.

c) Dang san xuat hang khoi.

Co san lng ln, san pham on nh, trnh o chuyen mon hoa san xuat cao, trang thiet b, dung cu, cong nghe thng chuyen dung, qui trnh cong nghe c thiet ke va tnh toan chnh xac va c ghi thanh cac tai lieu cong nghe co noi dung rat chi tiet va t m. Viec bo tr thiet b theo th t nguyen cong cua qui tnh cong nghe va tao thanh day chuyen san xuat. Trnh o th ng may khong can cao nhng phai co th ieu chnh may gioi.

Dang san xuat hang khoi cho phep ta ng dung cac phng phap cong nghe tien tien, tao ieu kien c kh hoa va t ong hoa san xuat.

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Khi san xuat theo kieu day chuyen ta phai tnh toan so lng may va nang suat lam viec tng nguyen cong sao cho qua trnh san xuat am bao ong bo tien o gia cong, tuan theo nhp san xuat cua day chuyen. Nhp san xuat la khoang thi gian lap lai chu ky gia cong hoac lap rap, trong khoang thi gian o oi tng san xuat c hoan thien va c chuyen ra khoi day chuyen san xuat.

NTtn /= : nhp san xuat cua day chuyen. nt

: khoang thi gian lam viec (phut). T

: so lng san pham c hoan thanh trong thi gian T . N

e am bao tnh ong bo cua day chuyen san suat va am bao so lng san pham theo ke hoach can phai thoa man ieu kien:

ni KtTnc =Trong o :

: thi gian nguyen cong th i cua qui trnh cong nghe. iTnc

K : so nguyen. Tuy thuoc K = 1, 2, 3 ma ta can chon so may sao cho khong b ong san pham.

S phat trien cua nen kinh te xa hoi trong vai thap ky gan ay a xuat hien nhu cau oi hoi phai co san pham a dang, mau ma luon thay oi, vi so lng nho hoac ln theo nhu cau tng luc, tng ni, tng oi tng khach hang. Do vay ac trng cua to chc ky thuat cong nghe va cha ng nhng ac trng cua san xuat n chiec va bao gom cac yeu to cua san xuat hang loat ln va hang khoi. e ap ng yeu cau nay nhieu ky thuat cong nghe mi a c ng dung. V du gia cong bang CNC (Computer numerical control), vi loai thiet b nay se ap ng c:

- Gia cong vi chat lng va nang suat cao va san pham on nh.

- Co kha nang thay oi cac hoat ong chc nang mot cach de dang nh x ly phan mem chng trnh.

- Qua trnh chuan b c thc hien nhanh chong nh s dung cac ky thuat tnh toan hien ai.

Ngay nay nh ng dung cac thanh tu ve ien t tin hoc, x ly ien toan va ky thuat ieu khien t ong, cong nghe cua qua trnh san xuat c thc hien bi cac may c ieu khien t ong nh may tnh ien t, co kha nang lap trnh a dang e thch nghi vi san pham mi.

Dang san xuat nh vay c goi la san xuat linh hoat cung la dang san xuat ac trng va ngay cang pho cap trong xa hoi.

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CHNG 2

C S LY THUYET CAT GOT KIM LOAI

2.1 Khai niem chung

Hien nay co rat nhieu phng phap e gia cong kim loai: uc, ren, can, han ... song cac phng phap nay c ban la tao phoi hoac cac san pham tho s, thng o chnh xac va o bong khong cao.

e nang cao o bong va o chnh xac cua cac chi tiet theo yeu cau ky thuat th phai tien hanh gia cong bang cat got kim loai.

Gia cong kim loai bang cat got (con goi gia cong c co phoi) tc la boc i lp kim loai tha e tao nen hnh dang chi tiet phu hp vi yeu cau ky thuat cua chi tiet.

Hien nay tuy a xuat hien nhieu phng phap gia cong mi nhng cac phng phap: tien, phay, bao, khoan, khoet, doa, chuot, mai ... van la cac phng phap c ban e cat got kim loai.

He thong thiet b dung e hoan thanh nhiem vu cat got c goi la he thong cong nghe, bao gom: May o ga Dao Chi tiet. V du trong hnh 2.1:

- May co nhiem vu cung cap nang lng can thiet cho qua trnh cat got.

- o ga co nhiem vu xac nh va gi v tr tng quan chnh xac gia dao, may va chi tiet gia cong trong suot qua trnh gia cong chi tiet.

- Dao co nhiem vu trc tiep cat bo lp kim loai tha ra khoi chi tiet nh nang lng cua may cung cap thong qua cac chuyen ong tng oi.

- Chi tiet gia cong la oi tng cua qua trnh cat got. Moi ket qua cua qua trnh cat eu c phan anh len chi tiet gia cong.

Moi phng phap gia cong eu dung may, dao va cac chuyen ong cua chung khac nhau, nen tao ra cac quy ao chuyen ong tng oi khac nhau va ket qua hnh thanh cac be mat chi tiet khac nhau.

May

Dao

Phoi

Ga

Hnh 2-1. He thong M-G-D-P

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2.1.1 Cac be mat thng gap trong chi tiet may

Trong gia cong c kh, cac be mat chi tiet gia cong thng gap co the chia ba dang chnh:

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a)

b)

c)

Hnh 2.2 Cac be mat

thng gap trong gia cong.

- Dang be mat tron xoay: mat tru, mat con, mat ren, mat nh hnh (hnh 2.2a);

- Dang mat phang hoac profil tao nen bi cac mat phang (hnh 2.2b);

- Dang mat ac biet: cam a ... (hnh 2.2c).

2.1.2 Cac chuyen ong tao hnh be mat

Chuyen ong tao hnh bao gom moi chuyen tng oi gia dao va phoi, trc tiep tao ra be mat gia cong.

e tao ra cac be mat gia cong, may phai truyen cho cac c cau chap hanh cua may cac chuyen ong tng oi. Chuyen ong tng oi nay phu thuoc vao be mat gia cong. V vay can nghien cu cac chuyen ong tng oi e tao ra be mat, da vao o e thiet ke ra dao va may. So chuyen ong tao hnh co the 1 (nh chuot: hnh 2.3a), 2 (nh tien, bao, xoc: hnh 2.3b, phay: hnh 2.3c), 3 (nh lan rang: hnh 2.3d). Cac chuyen ong nay (du phc tap) eu co the quy ve nhng chuyen ong (n gian) cua mot vai c cau nguyen thuy co chuyen ong quay tron va tnh tien.

Trong cat got kim loai, cac chuyen ong chia thanh cac chuyen ong sau:

- Chuyen ong cat chnh: La chuyen ong c ban e tao ra phoi cat, chuyen ong tieu hao nang lng cat ln nhat (chuyen ong 1 Hnh 2.3). Chuyen ong cat chnh co the tnh tien, nhng cung co the quay.

- Chuyen ong chay dao: La chuyen ong can thiet e tiep tuc tao ra phoi cat (chuyen ong 2 Hnh 2.3). Chuyen ong chay dao co the tnh tien, nhng cung co the quay.

- Chuyen ong phu: Bao gom cac chuyen ong nh a dao vao, lui dao ra, chay dao ve cat lan hai ...

V du:

- Khi chuot (hnh 2.3a) chuyen ong cat chnh la chuyen ong tnh tien (1) cua dao, khong co chuyen ong chay dao.

- Khi tien (hnh 2.3b) chuyen ong cat chnh la chuyen ong quay tron (1) cua chi tiet, chuyen ong chay dao la chuyen ong tnh tien (2) cua dao. Khi bao va xoc (hnh 2.3b) chuyen ong cat chnh la chuyen ong tnh tien kh hoi (1) cua dao, chuyen ong chay dao la chuyen ong tnh tien (2) cua ban may mang chi tiet.

- Khi phay (hnh 2.3c) chuyen ong cat chnh la chuyen ong quay tron (1) cua dao, chuyen ong chay dao la chuyen ong tnh tien (2) cua ban may mang chi tiet.

- Khi phay banh rang (hnh 2.3d) ngoai chuyen ong cat chnh (1) chuyen ong quay cua dao, chuyen ong chay dao (2) chuyen ong tnh tien cua dao, con chuyen ong chay dao (3) chuyen ong quay cua phoi (theo nguyen ly bao hnh).

a) Chuyen ong cat chnh va van toc cat

e ac trng cho chuyen ong chnh, ta s dung hai ai lng:

- Van toc cat v (tai mot iem) hay con goi toc o cat: La lng dch chuyen tng oi gia li cat va chi tiet gia cong trong mot n v thi gian.

- So vong quay n (hoac so hanh trnh kep) trong n v thi gian. oi vi tien, toc o cat la toc o tong hp cua toc o vong cua chi tiet gia cong va toc

o cua chuyen ong chay dao. Tuy nhien trong thc te v toc o cua chuyen ong chay dao thng rat be so vi toc o vong cua chi tiet gia cong nen thng bo qua.

VsVnV +=Trong o: - toc o vong cua chi tiet gia cong. Vn

- toc o cua chuyen ong chay dao. VsV nho so vi rat nhieu nen trong tnh toan co the bo qua.

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Vay cong thc gan ung e tnh van toc nh sau:

)/(1000

phmnDV = Trong o D : ng knh chi tiet gia cong (mm).

n : so vong quay cua chi tiet gia cong trong mot phut (vg/phut).

Neu chuyen ong chnh la chuyen ong tnh tien, th gia van toc cat (m/phut), so hanh trnh kep n (htk/phut) va chieu dai hanh trnh L (mm) co quan he sau:

Vs Vn

)/(10002 phmnLV =

1

2

1

2

1

2

b)

Chi tiet gia cong

-13-

1

a)

1

2

c)

d)

Hnh 2.3 Cac chuyen ong tao hnh.

b) Chuyen ong chay dao va lng chay dao

e ac trng cho chuyen ong chay dao, ta s dung lng chay dao. Lng chay dao co the la lng chay dao vong, lng chay dao phut V du:

- Lng chay dao khi tien la khoang dch chuyen cua dao theo phng chuyen ong chay dao sau mot vong quay cua chi tiet gia cong: S (mm/vong).

- Lng chay dao khi bao, xoc: la lng dch chuyen tng oi cua ban may mang chi tiet sau mot hanh trnh kep cua dao: Sk ( mm/htk).

- oi vi phng phap phay, tr so dch chuyen tng oi cua ban may trong mot phut goi la lng chay dao phut: Sph = S. n (mm/ph); trong o S la lng chay dao vong, lng dch chuyen cua ban may khi dao quay c mot vong (mm/vong); n la so vong quay cua dao trong mot phut (vong/ph). Ngoai ra con co khai niem lng chay dao rang, la lng dch chuyen cua ban may khi dao quay c mot goc rang : Sz = S/z (mm/rang); trong o z la so rang cua dao phay.

Tuy theo phng cua chuyen ong chay dao co lng chay dao doc, lng chay dao ngang, lng chay dao thang, lng chay dao vong

c) Chuyen ong phu va chieu sau cat

Chieu sau cat t (mm) la khoang cach gia be mat a gia cong va be mat cha gia cong, hoac la chieu sau lp kim loai cat i sau mot lan cat o theo phng thang goc vi be mat a gia cong.

V du khi tien chieu sau cat c tnh theo cong thc:

)(2

mmdDt = D : ng knh chi tiet trc khi gia cong (mm).

d: ng knh chi tiet sau khi gia cong (mm ).

Tap hp cac yeu to: t, s, v - goi la che o cat.

2.1.3 Cac phng phap cat got kim loai

Yeu cau be mat gia cong rat a dang, v vay phai co nhieu phng phap cat got e thoa man nhng yeu cau a dang o.

Co nhieu cach phan loai cac phng phap cat got, xuat phat t muc ch nghien cu va s dung khac nhau:

- Xuat phat t nguyen ly tao hnh be mat: Phng phap gia cong nh hnh (nh hnh dang dao len be mat chi tiet gia cong hnh 2.4a); Phng phap gia cong chep hnh (chep lai hnh dang chi tiet mau hnh 2.4b); Phng phap gia cong theo vet (phng phap quy tch) nh tien, phay, bao ...; Phng phap bao hnh (be mat tao hnh se la ng bao cua profil dao cat khi chung chuyen ong bao hnh vi nhau hnh 2.4c) nh phay lan rang.

- Xuat phat t may cat kim loai: Phng phap cat got nh tien, bao, xoc (hnh 2.3b), phay (hnh 2.3c), mai, khoan, khoet, doa, chuot (hnh 2.3a).

- Xuat phat t yeu cau chat lng chi tiet gia cong: Gia cong tho, gia cong ban tinh, gia cong tinh, gia cong sieu tinh.

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- Xuat phat t be mat chi tiet gia cong: Gia cong mat phang (hnh 2.2b), gia cong mat tron xoay (hnh 2.2a) ...

-15-

Mau

Chi tietDao

b)

Chi tiet Dao

2.1.4 Khai niem ve cac be mat hnh thanh khi gia cong chi tiet

Tren chi tiet khi ang gia cong ta phan biet (hnh 2.5):

- Mat cha gia cong 1 la be mat chi tiet se c cat i mot lp kim loai d. Lp kim loai d tach ra khoi chi tiet goi la phoi.

- Mat ang gia cong 2 la be mat chi tiet noi tiep gia mat cha gia cong va mat a gia cong. Trong qua trnh cat, mat ang gia cong luon tiep xuc vi li cat chnh cua dao.

- Mat a gia cong 3 la be mat chi tiet c tao thanh sau khi cat i mot lp kim loai.

a)

Dao

Hnh 2.4 Cac phng phap cat got kim loai.

Chi tiet c)

phoiphoi

a) b)

Hnh 2.5 Cac be mat hnh thanh khi

gia cong chi tiet.

2.1.5 Khai niem c ban ve dung cu cat

Muon cat c kim loai, ngoai yeu cau ve o cng, o ben, o chu nhiet, dao can phai co hnh dang phan cat hp ly. Co rat nhieu loai dao (nh dao tien, phay, mui khoan, khoet, doa ...) dung tren cac may khac nhau nhng xet cho cung, du chung co phc tap en au, phan cat cua chung eu co cau tao ve c ban giong nh dao tien ngoai (hnh2.6).

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Dao tienngoai a) b) c)

Hnh 2.6 Cau thanh cac

dung cu cat c ban n. t dao tie

Do o chu yeu ta se nghien cu ket cau va cac thong so hnh hoc cua dao tien ngoai va sau o m rong cho cac loai dao khac. Cac nh ngha ve thong so hnh hoc va hien tng xay ra trong qua trnh tien eu co the ap dung oi vi cac phng phap gia cong khac.

Sau ay, chung ta nghien cu ket cau cua dao tien ngoai. Tren hnh 2.7 la dao tien ngoai au thang co ket cau n gian, gom hai phan chnh:

- Phan lam viec (phan cat) trc tiep lam nhiem vu cat.

1

2

3

4

5

6

B

H

L

Phan cat

Phan than

Phng chay dao

Hnh 2.7 Ket cau cua dao tien ngoai

- Phan than dung e ga dao vao ban dao hoac truc chnh.

Tren phan cat cua dao co cac mat sau ay:

- Mat trc (1) la mat ma phoi se tiep xuc va theo o thoat ra trong qua trnh cat.

- Mat sau chnh (2) la mat dao oi dien vi mat chi tiet ang gia cong.

- Mat sau phu (3) la mat dao oi dien vi mat chi tiet a gia cong.

Cac mat nay co the la mat phang hoac cong. Giao tuyen cua chung tao thanh cac li cat cua dao. Tren phan cat gom cac li cat sau:

- Li cat chnh (5) la giao tuyen cua mat trc va mat sau chnh, gi nhiem vu trc tiep cat got ra phoi trong qua trnh cat.

- Li cat phu (6) la giao tuyen cua mat trc va mat sau phu, trong qua trnh cat mot phan li cat phu cung tham gia cat (rat nho, khoang .S). Dao co the co mot mat sau phu hay nhieu mat sau phu va do o co mot hay nhieu li cat phu.

Phan noi tiep gia cac li cat goi la mui dao (4); mui dao co the nhon hoac co ban knh r (r 0,12mm).

Chieu dai phan cat cua dao la khoang cach t mui dao en giao tuyen gia mat trc va than dao. Phan than dao co the co tiet dien hnh tron hay hnh ch nhat, hnh vuong.

2.1.6 Cac mat toa o e nghien cu dung cu cat

V tr tng oi gia cac be mat tren phan lam viec cua dao so vicac be mat tren chi tiet gia cong co anh hng ln ti qua trnh cat got. V tr cac be mat va li cat c xac nh bi nhng goc o tren phan lam viec cua dao.

Noi en goc o tren phan lam viec cua dao ngha la noi en v tr tng quan gia cac be mat va li cat so vi he toa o nao o c chon lam chuan. He toa o nay goi la he toa o xac nh.

Trong nghien cu dung cu cat, he toa o xac nh c thanh lap tren c s cua ba chuyen ong cat ( vts ,, ). Tong quat hn, phng cua ba chuyen ong cat ( vts ,, ) tng ng cac phng cua he toa o e cac (x, y, z). Nh vay bao gom ba mat phang c ban sau: (hnh 2.8)

Hnh 2.8 Cac mat phang tao o cua dung

cu cat.

C

-17-

- Mat c ban 1 (x-x) c tao bi vec t toc o cat v va vec t chay dao s .

- Mat c ban 2 (y-y) c tao bi vec t toc o cat v va vec t chieu sau cat t .

- Mat c ban 3 (con goi la mat ay ky hieu ) c tao bi vec t chay dao s va vec t chieu sau cat t .

Ngoai ba mat c ban tren, ta can s dung them cac mat phang va tiet dien phu tr:

- Mat cat (ky hieu C) i qua mot iem nao o tren li cat chnh: la mot mat phang qua iem o, tiep tuyen vi mat ang gia cong va cha vec t van toc cat v (neu li cat chnh thang th mat cat cha li cat chnh).

Toc o cat ay la toc o dch chuyen tng oi gia li cat va chi tiet gia cong. trang thai thiet ke (tnh) hng cua vect van toc cat ngc vi hng quay cua chi tiet (thc chat khi thiet ke chi tiet khong chuyen ong nen vect van toc cat ay hoan toan quy c va hng quay cua chi tiet tng tng nh khi chi tiet se quay khi cat got). Con khi xet trang thai lam viec (ong), toc o cat la tong hp toc o chuyen ong quay cua chi tiet va toc o chuyen ong chay dao.

- Tiet dien chnh la mat phang thang goc vi hnh chieu cua li cat chnh tren mat ay (ky hieu N-N).

- Tiet dien phu la mat phang thang goc vi hnh chieu cua li cat phu tren mat ay (ky hieu N1-N1).

2.1.7 Thong so hnh hoc phan cat dao tien khi thiet ke (trang thai tnh)

Hnh 2.9 Thong so hnh hoc

dao tien. N

N

N-N

N1

N1

N1-N1

> 0

K

Chieu K

-18-

Qua trnh thiet ke, thong so hnh hoc cua dao uc xet trong hai tiet dien chnh N-N va tiet dien phu N1-N1, v phoi thng c thoat ra theo cac phng cua tiet dien o, keo theo cac hien tng vat ly xay ra trong qua trnh cat.

Trong tiet dien chnh ta co cac goc chnh, trong tiet dien phu ta co cac goc phu. Tren hnh 2.9, xet tai mot iem M tren li cat chnh va mot iem M1 tren li cat phu ta co:

- Goc trc chnh : la goc gia mat trc va mat ay o trong tiet dien chnh. Goc trc co tr so dng khi mat trc thap hn mat ay, tr so am khi ngc lai va bang 0 khi mat trc trung mat ay (hnh 2.10). Goc co anh hng en qua trnh thoat phoi khi cat.

Hnh 2.10 Goc trc chnh .

- Goc sau chnh : la goc gia mat sau chnh va mat cat o trong tiet dien chnh. Goc luon luon dng va co anh hng en van e ma sat khi cat.

Trong o goc va goc la hai goc oc lap c chon trc tuy theo yeu cau gia cong (vat lieu, chat lng be mat gia cong ), con hai goc va la hai goc phu thuoc vao goc va .

- Goc sac chnh : la goc gia mat trc va mat sau chnh o trong tiet dien chnh. + + = 90O

- Goc cat chnh : la goc gia mat trc va mat cat o trong tiet dien chnh. - Goc trc phu 1: la goc gia mat trc va mat ay o trong tiet dien phu. Goc 1

cung co the am, dng hoac bang khong tng t nh . - Goc sau phu 1: la goc gia mat sau phu va mat phang hp bi li cat phu va truc

Z tai M1 , o trong tiet dien phu. Goc 1 cung luon luon dng. - Goc sac phu 1 : la goc gia mat trc va mat sau phu o trong tiet dien phu. - Goc cat phu 1 : la goc gia mat trc va mat phang hp bi li cat phu va truc Z

tai M1 , o trong tiet dien phu.

1 + 1 + 1 = 90O - Goc nghieng chnh : la goc gia hnh chieu cua li cat chnh tren mat ay va

phng chay dao.

- Goc nghieng phu 1: la goc gia hnh chieu cua li cat phu tren mat ay va phng chay dao.

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- Goc mui dao : la goc gia hnh chieu cua li cat chnh va li cat phu tren mat ay.

+ + 1 = 1800- Goc nang : Khi li cat chnh thang th la goc o gia li cat chnh va hnh

chieu cua no tren mat phang ay (hnh 2.11a). Khi li cat chnh cong, la goc o gia tiep tuyen tai mot iem bat ky tren li cat chnh va hnh chieu cua no tren mat phang ay (hnh 2.11b).

Goc co the dng, am hay bang 0 va co anh hng en phng thoat phoi; dng khi mui dao la iem thap nhat cua li cat, am khi mui dao la iem cao nhat, con khi li cat song song vi mat ay th = 0 (hnh 2.12).

Hnh 2.11- Goc nang a) Li cat chnh thang b) Li cat chnh cong

a) b)

Hnh 2.12 - Cac gia tr goc nang .

2.1.8 Anh hng ga at dao va cac chuyen ong cat en goc o dao

Trong qua trnh cat (trang thai ong), goc o cua dao co the thay oi do cac nguyen nhan c ban sau:

- Khi ga, hng dao khong am bao v tr tng quan vi chi tiet hoac mui dao ga khong ngang tam may.

- Do anh hng cua cac chuyen ong chay dao.

- Ngoai ra con co mot so nguyen nhan khac nh : tr so goc nang cua li cat chnh , hien tng leo dao cung anh hng en goc o cua dao.

-20-

Ta se lan lt xet anh hng cua ba nguyen nhan tren:

1/ Khi ga hng dao khong am bao v tr tng quan vi chi tiet

Sau khi mai sac dao co cac goc nghieng chnh va goc nghieng phu 1. Trng hp ga dao ung nh khi thiet ke, truc dao vuong goc vi truc chi tiet gia

cong th va 1 khong oi (hnh 2.13a).

-21-

Neu truc dao c ga khong vuong goc vi truc chi tiet gia cong ma xoay i mot goc so vi truc chi tiet th va 1 se bien oi nh sau: - Ga nghieng phai : (hnh 2.13b)

= + 1 = 1 -

Trong o:

, 1 : goc nghieng chnh, goc nghieng phu khi thiet ke; , : goc nghieng chnh, goc nghieng phu sau khi ga dao;

Hnh 2.13a Trng hp ga dao ung

x,y - Toa o khi thiet ke dao X, Y - Toa o khi cat

1

S

nx X

yY

- Ga nghieng trai : (hnh 2.13c)

= - 1 = 1 +

Trong o:

, 1 : goc nghieng chnh, goc nghieng phu khi thiet ke; , : goc nghieng chnh, goc nghieng phu sau khi ga dao;

2/ Khi ga mui dao thap hn hay cao hn ng tam cua chi tiet

Khi tien ngoai neu mui dao ga cao hn ng tam cua may (hnh 2.14a) th goc trc tang len con goc sau giam xuong. Ngc lai neu mui dao ga thap hn ng tam may th goc trc se giam i con goc sau se tang len (hnh 2.14b).

Khi tien trong neu mui dao c ga cao hoac thap hn ng tam cua may th s bien oi cua cac goc dao cua dao se ngc vi trng hp tien ngoai. Trong trng hp tren, cac goc cua dao se bien oi mot lng bang .

Hnh 2.14 a) Ga mui dao cao hn tam may b) Ga mui dao thap hn tam may

- Khi mui dao cao hn tam may:

c = + c = -

- Khi dao thap hn tam may:

c = - c = +

Trong o : Rh=sin

h: o cao cua mui dao so vi tam may.

R: ban knh chi tiet gia cong.

3/ Do anh hng cua chuyen ong chay dao.

Khi tien co chuyen ong chay dao doc hoac ngang nen mat cat va mat ay thay oi v tr a en goc , cung thay oi.

V du: Khi tien cat t, do phoi hp hai chuyen ong quay tron cua chi tiet (chuyen ong chnh) va tnh tien vuong goc vi chi tiet (chuyen ong chay dao ngang), quy ao chuyen ong cat tng oi la ng Acsimet, hng vect toc o cat trong qua trnh cat thay oi, dan en mat cat thay oi lam thay oi goc o cua dao (hnh 2.15).

-22-

Thc te khi cat t hay xen mat au thng tr so Sn be nen goc be, goc sau cua dao giam khong ang ke. Nhng khi dao chay cang gan vao tam, ng knh cua chi tiet D cang giam lam goc cang tang. Neu c th c se am hoac bang khong, luc o dao khong cat c ma mat sau chnh cua dao se ma sat vao be mat chi tiet ang gia cong gay ra lc ln e gay chi tiet hoac gay dao. Do o phai chon goc ln hn ieu kien cat bnh thng.

Trong nhng trng hp can s dung lng chay dao ln (khi chay dao doc) nen chu y en s thay oi cua cac goc.

2.1.9 Thong so hnh hoc tiet dien phoi cat

Cac yeu to cua che o cat chu yeu ac trng cho qua trnh cat ve mat nang suat, cha giai thch ay u ban chat vat ly cua qua trnh cat.

e co the hieu c ay u hn ve ban chat cua qua trnh cat, can co khai niem ve thong so hnh hoc cua lp kim loai b cat (tiet dien phoi cat) khi cat got.

Quy c o tiet dien phoi cat trong mat ay i qua mui dao trong mot lan chay dao s (hnh 2.16).

Hnh 2.16 Tiet dien va thong so hnh hoc lp cat.

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Khi li cat chnh thang va tao mot goc vi phng chay dao, tiet dien lp cat la mot hnh bnh hanh co ay la lng chay dao (s) va chieu cao la chieu sau cat (t). Thong so hnh hoc cua lp cat bao gom chieu rong cat (b) va chieu day cat (a). Nh vay o ln cua tiet dien lp cat c ac trng bi hai cap kch thc: a, b va t, s.

Thong so hnh hoc cua lp cat c nh ngha nh sau:

- Chieu rong cat b (mm): la khoang cach gia be mat a gia cong va be mat cha gia cong o doc theo li cat (hay chieu dai li cat tham gia cat got).

- Chieu day cat a (mm): la khoang cach gia hai v tr lien tiep cua li cat.

Tren hnh 2.16 ta co:

)(sin

)(sin

mmSa

mmtb

==

oi vi li cat chnh cong chieu day cat a la khoang cach gia hai tiep tuyen cua hai v tr lien tiep cua li cat. Tr so cua a thay oi tai moi v tr cua li cat.

oi vi li cat chnh thang chieu day doc theo li cat khong oi.

Hnh 2.17 Chieu cao lp cat con sot lai tren be mat.

a) Li cat chnh thang. b) Li cat chnh cong.

H

A

H

r

a)

b)

Dien tch cua lp cat F (mm2) c tnh:

F = a.b = s.t (mm2).

Thc chat khi cat tren be mat gia cong con d lai nhng vet nhap nho do dao khong cat het, chieu cao cua cac vet nhap nho la H (hnh 2.17 a,b ) se la mot ai lng ac trng cho chat lng be mat gia cong. Co hai trng hp sau:

- Mui dao nhon ban knh mui dao r = 0 (hnh 2.17a):

H = CD

AD = CD.ctg 1DB = CD. ctg AD+DB = S = CD. (ctg 1+ ctg ).

1

1

ctgctg

ctgctg

+=+==

SH

SHCD

-24-

- Mui dao co ban knh r 0 (hnh 2.17b): H = AC = OA OC = r OC = r - r. cos = r. ( 1 cos) = r. 2 sin2/2.

Trong o: sin = S/2r. S/2r. /2 S/4r.

sin2/2 S2/16r2. Suy ra:

rSH.8

2

=

Khi ban knh mui dao r = 0, lng chay dao S tang th chieu cao nhap nho tang, goc nghieng chnh va goc nghieng 1 tang, ctg va ctg1 giam th H tang.

Khi ban knh mui dao r 0, lng chay dao S tang th chieu cao nhap nho H tang, ban knh mui dao r tang th chieu cao nhap nho H giam.

Trong thc te, chieu cao H ln hn so vi tr so tnh toan v trong qua trnh cat, be mat chi tiet gia cong con chu anh hng rat nhieu cua cac bien dang nh: bien dang deo, bien dang an hoi, rung ong vv

2.2 Vat lieu che tao dung cu cat 2.2.1 Nhng yeu cau oi vi vat lieu lam dung cu cat

Vat lieu lam dung cu cat la mot trong nhng yeu to quan trong quyet nh nang suat cua qua trnh cat got kim loai. Nang suat cong tac cua moi loai dung cu cat phu thuoc rat nhieu vao kha nang gi c tnh cat trong mot khoang thi gian dai cua vat lieu lam dao. Khi cat, dung cu phai chu ap lc, nhiet o cao, rung ong, mai mon khien cho tnh cat cua vat lieu lam dao chong b giam thap.

Do o muon lam viec c, vat lieu lam dung cu cat phai am bao nhng yeu cau c ban sau:

a) o cng: e cat c kim loai, vat lieu lam dao can co o cng cao hn vat lieu gia cong, thong thng co o cng t 62 65HRC. e gia cong cac loai thep cng (thep khong r, thep chu nong), o cng cua dung cu cat got phai tren 65 HRC.

b) o ben c hoc: Trong qua trnh cat, dao thng chu nhng lc c hoc ln (mat trc cua dao chu ap lc rat ln, nen rat de v, me). Ngoai ra con chu rung ong do he thong cong nghe khong u cng vng, lam cho lc cat khong on nh, de gay va hong dao. Muon lam viec lau dai, dao can phai co o be c hoc cao nh sc ben va o deo cao.

c) o chu nhiet la tnh nang rat quan trong cua vat lieu lam dung cu cat got.Vat lieu khi b nung nong th o cng cua no b giam i, tuy nhien neu trong qua trnh nung nong o vat lieu khong b bien oi ve to chc th sau khi lam nguoi, o cng cua vat lieu se c phuc hoi. o chu nhiet la kha nang gi c o cng cao va cac tnh chat khac nhiet o

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cao (khong co chuyen bien ve to chc) trong mot thi gian dai. Cung vi o chu nhiet, vat lieu lam dao co tnh dan ien cang cao cang tot, v nh vay se giam nhiet o sinh ra khu vc cat lam cho dao lau b mon.

d) o chu mai mon: Trong qua trnh cat, tren mat trc cua dao chu ma sat cua phoi khi thoat ra, con mat sau tiep xuc vi mat ang gia cong, nen dao chong mon. Ngoai ra nguyen nhan chu yeu lam cho dao chong mon la do hien tng chay dnh gia vat lieu gia cong va vat lieu lam dao. Tnh dnh c ac trng bang nhiet o chay dnh gi hai vat lieu tiep xuc nhau. Do o yeu cau vat lieu che tao dung cu cat got phai co nhiet o chay dnh cao.

e) Tnh cong nghe: Vat lieu lam dung cu cat phai de ren, de dap, de cat got, hay noi cach khac chung phai c tao dang mot cach de dang, e thuan tien cho cong viec che tao va phuc hoi tnh nang cua dung cu cat trong san xuat.

f) Tnh kinh te: Gia ca phai phu hp, chung loai phai a dang

Ngoai nhng yeu cau c ban tren, vat lieu che tao dung cu cat can co nhng tnh nang hp ly khac nh o dan ien, dan nhiet va phu thuoc vao yeu cau san xuat.

2.2.2 Cac loai vat lieu che tao dung cu cat

Vat lieu dung cu cat thng c che tao t nhng nhom vat lieu sau ay:

- Thep cacbon dung cu.

- Thep hp kim dung cu.

- Thep gio.

- Hp kim cng.

- Vat lieu s.

- Vat lieu mai va cac vat lieu to hp khac.

1/ Thep cacbon dung cu (tcvn 1822-76 )

Thanh phan hoa hoc:

- Cac bon t: 0,7 1,5%. - Cac thanh phan hp kim (Mn, Si, P, Cr, Ni) khong vt qua 0,1 0,3%.

o cng trang thai toi: 60 62 HRC. Song v o tham toi thap do o loi co o deo nhat nh, thch hp cho viec che tao mot so dung cu cat nh uc, dua

o ben nhiet thap, ch thch hp vi nhiet o 200oC250oC do o cung ch lam viec toc o cat thap ( 4 5 m/ph). Mac thep cacbon: CD70, CD80, CD80Mn, CD100

CD70A, CD80A, CD80MnA. vi chat lng cao.

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2/ Thep hp kim dung cu (tcvn 1823-76)

Thep hp kim dung cu la thep cacbon dung cu co ham lng mot so nguyen to hp kim vao khoang 0,5 5%. e tang tnh chu nong phai dung mot lng cac hp kim ac biet nh: Crom, Vonfram; tang o tham toi: Vanadi; tang o cng: Crom; tang o chu nhiet va o mai mon: Vonfram

Thep hp kim dung cu co the toi 820oC850oC trong dau hoac nc, sau khi toi at c tnh chat sau:

o cng trang thai toi: en 62 HRC.

o be nhiet vao khoang: 350 400oC. Toc o cat tang 20% so vi thep cacbon dung cu.

Thng dung che tao cac dung cu cat bang tay nh li ca, mui ot dau, ban ren, taro, dao cao nguoi.

Mac thep hp kim thong dung: 70CrV, 80CrV, 110Cr, 40Cr5W2Vsi

3/ Thep gio (cha co tieu chuan Viet Nam)

Thep gio cung la loai thep hp kim dung cu nhng ham lng hp kim Vonfram cao t 5 20%, nen tnh nang cua no ac biet va tnh chu mon va tnh chu nhiet tang cao. Thep gio c s dung rong rai v toc o cat co the nang cao gap 2 4 lan, tuoi ben nang cao t 8 15 lan so vi thep cacbon va thep hp kim dung cu. Ngi ta con them Vanadi va Coban e nang cao o chu nhiet va dung gia cong cac loai thep hp kim co o cng cao.

o cng trang thai toi: 60 70 HRC. Thep gio co the cat toc o: t 25 35 m/phut. o be nhiet: 400 600oC. Mac thep gio tieu chuan Nga (roct 19265-73): P9, P18, P95.P9K5, P9K10, P10K55. Mac thep gio theo tiau chuan My (He thong ky hieu AISI): M1, M2, M3(Thep gio Molipden): T1, T2, T4,(Thep gio Vonfram).

Mac thep gio theo tieu chuan c: S12-1-4-5, S10-4-3-10,(hay HS12-1-4-5)

Mac thep gio theo tieu chuan Nhat (JIS G4403-83): SKH2, SKH3,

4/ Hp kim cng

La loai vat lieu lam dao c dung rong rai nhat va co hieu qua kinh te cao. Vat lieu nay c che tao bang phng phap luyen kim bot, luyen kim khong phai qua nau chay ma van trang thai ran. Hp kim cng (HKC) c che tao bang cach ep va thieu ket, do o ve cau truc cung nh tnh chat c ly co nhng khac biet so vi thep gio.

Thanh phan chu yeu la cac Cac-bt Vonfram (WC), Cac-bt Titan (TiC). Cac-bt Tantan (TaC), dang hat mn, tron vi Coban (Co) sau o em ep va thieu ket nhiet o,

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ap suat cao. Do lng Cacbit chiem t le rat ln (> 90%) nen tnh chat cua HKC phu thuoc vao tnh chat cua cac Cacbit co mat trong no.

o cng cua HKC 70HRC. HKC co the lam viec nhiet o 800 1000oC vi toc o cat len en 400m/phut. Ngi ta chia HKC ra lam 3 nhom:

- Nhom 1 Cacbit:

To chc: WC + Co

Ky hieu: BK (con so sau ch K ch lng Coban con lai la lng WC).

V du: BK8 (co 8%Co: 92%WC)

Nhom BK deo hn ca nen chu va ap tot hn, chu nhiet thap nen thng dung gia cong gang, cac loai thep cng (thep a toi, thep khong r, thep chu nong) va kim loai mau.

- Nhom 2 Cacbit:

To chc: WC + TiC +Co

Ky hieu: TK (con so sau ch T ch lng TiC, con so sau ch K ch

lng Coban, con lai la lng WC).

V du: T15K6 (co 15% TiC, 6% Co, 79%WC).

Nhom TK co o cng va tnh chu nhiet tot hn, ong thi nhiet o cao th he so ma sat giam. Thng dung gia cong thep.

- Nhom 3 Cacbit:

To chc: WC + TiC + TaC + Co

Ky hieu: TTK (con so sau ch TT ch lng TiC+TaC, con so sau ch

K ch lng Coban, con lai la lng WC).

V du: TT7K12 (co7% TiC+TaC, 12%Co, 81%WC).

Nhom TTK dung gia cong vat lieu co o cng va o be cao.

e tiet kiem, HKC thng c che tao thanh cac manh co kch thc nhat nh sau o gan len than dao bang phng phap han hoac ghep c kh. Loai lap ghep co u viet la thuan li thay oi li cat khi b mon.

Khuyet iem chnh cua hp kim cng la sc ben uon kem nen khi lam viec co va ap de b me.

S phat trien gan ay trong tm kiem dung cu cat tot hn la trang phu hoac tham nitride titan cho dung cu cat HKC. Cac manh hp kim co lp tham noi chung co tuoi ben dai hn, nang suat cao hn va phoi thoat de dang hn. Lp trang phu tac ong nh mot chat boi trn lau dai lam giam ro ret cac lc cat, nhiet phat sinh va s mai mon. ieu nay cho phep s dung cat toc cat cao hn khi gia cong, ac biet khi can co o bong cao. Tnh boi

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trn va cac ac tnh chong dnh cua lp trang phu lam giam manh nhiet lng va ng suat phat sinh khi cat got.

Viec s dung cac lp tham trang phu bang carbide, nitride va oxide cho cac manh HKC co tac dung cai thien ro ret hieu suat cua dung cu HKC. Cac manh HKC vi to hp 2 hoac 3 vat lieu trong lp trang phu co tnh chat ac biet: carbide titan chong mai mon cao tao ra lp trong cung; lp tiep theo bang lp oxide nhom day va la tang o dai va ap, tnh chong va ap cao, tnh on nh hoa hoc nhiet o cao; lp th 3 rat mong cha nitrade titan lam giam ma sat.

6/ Vat lieu s

La loai vat lieu re tien, co tnh nang cat got tot, chu nong, chu mai mon cao. Thanh phan hoa hoc chu yeu la xuyt nhom (Al2O3). Vat lieu s chnh la at set ky thuat c nung nong nhiet o cao khoang 1400 1600oC. San pham thu c em nghien nho at kch thc khoang 1m, sau o em ep thanh cac manh dao co kch thc thch hp va mang i thieu ket.

S co o cng 92 93 HRC va co o chu nhiet t 1100oC 1200oC. Tuoi ben dao s gap 2 3 lan dao hp kim cng. Dao s co the cat en toc o

600m/phut. Co the gia cong c cac vat lieu a nhiet luyen en o cng 66HRC. Dung cu s chu c s mai mon cua cat va tap chat co trong cac vat uc.

Khuyet iem chu yeu cua s la gion, gii han be uon thap, khong chu c va ap, rung ong va rat kho mai sac. Hien nay, mot trong nhng phng hng nghien cu la tm cach tang sc ben uon len.

7/ Kim cng

Kim cng gom hai loai: t nhien va nhan tao. Kim cng nhan tao tong hp t graphit trong ieu kien ap suat va nhiet o ac biet. Kim cng nhan tao c s dung nhieu e tao ra a mai, dung mai sac dung cu va gia cong cac loai cac loai vat lieu kho gia cong. Ngoai ra dung lam dao tien e gia cong hp kim cng, hp kim mau va vat lieu phi kim loai toc o cat cao.

Kim cng co o cng cao hn hp kim cng t 5 6 lan, tnh dan nhiet cao hn t 1,5 2,5 lan. o chu nhiet thap, t 800 1000oC. Toc o cat co the len ti hang ngan m/phut.

Nhc iem cua kim cng cng la de gion, de v.

Trong cong nghiep a s dung cac dung cu cat kim cng trong nhieu nam e gia cong cac loai vat lieu khong co sat va mai nhng vat lieu rat cng. Vao nhng nam 1980, ngi ta a bat au ngh en viec trang phu kim cng day vai micromet tren dung cu cat bang hp kim cng va thep gio. Tuoi ben cua dung cu cat co trang phu kim cng co the gap 60 lan dung cu cat bang hp kim cng va 240 lan bang thep gio khi gia cong cac vat lieu rat cng, o mai mon cao, khong cha sat hoac phi kim loai.

Hien nay kim cng chu yeu dung che tao a mai e mai sac va mai bong dung cu cat.

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8/ Nitrit Bo lap phng (con goi la el-bo)

La loai vat lieu tong hp co nhieu tnh nang u viet nh kim cng. ac biet el-bo co tnh chu nhiet len ti 2000oC.

Hien nay el-bo chu yeu c dung lam hat mai trong cac dung cu mai.

9/ Vat lieu mai

Dung che tao cac loai a mai, thanh mai, thoi mai cho cac nguyen cong mai tron, mai phang va lam giay nham. Ngoai ra no con dung lam bot nhao cho cac nguyen cong mai nghien.

Vat lieu dung lam hat mai co hai loai chu yeu la loai thien nhien va loai nhan tao.

Vat lieu thien nhien: Kim cng, oxuyt nhom (Al2O3), thach anh ga thanh cao, t s dung.

Vat lieu nhan tao: Kim cng nhan tao, oxuyt nhom ien (thu t lo ien t quang Boxt), cacbt silic (SiC), cacbt Bo (B4C).

Oxuyt nhom ien ( con goi la Corun ien ) c chia lam hai loai:

- Oxuyt nhon ien thng: 92% 95% Al2O3, c dung pho bien. Co sc be cao, c dung e mai tho, mai ban tinh va tinh cac vat lieu co sc ben cao nh thep, gang deo va mai sac dung cu cat.

- Oxuyt nhom ien trang: 97% 98% Al2O3, co o cng cao hn oxuyt nhom ien thng, c dung chu yeu e mai nh hnh va mai lang.

Cacbit silic (SiC) c chia lam hai loai:

- Cacbit silic en: 97% 98% SiC, sc ben cao nhng o cng hi thap. Dung e mai vat lieu co gii han ben thap nh: gang trang, gang xam, ong thanh, ong thau, nhom va cac loai vat lieu phi kim loai.

- Cacbit silic xanh: 98% 99% SiC, co o cng ch thua kim cng va cacbt bo nhung sc ben thap. Dung mai cac loai vat lieu dai, de nt nh HKC va mai sac dung cu cat hp kim cng va s.

Cacbit Bo gom 70% 92% B4C, rat cng nhng ron hn cacbit silic. Dung mai bong HKC hoac cac vat lieu rat cng.

Cacbit Bo Silic khac vi cacbit bo cho khong co tap chat graphit nen co tnh nang on nh, ben va ga thanh re hn. Thng chung c dung nguyen cong anh bong va cho nang suat cao hn cacbit bo t 30% 40%. Cac loai vat lieu nhan tao hien nay c s dung rong rat pho bien v tnh u viet va gia thanh phu hp.

2.3 C s vat ly cua qua trnh cat kim loai

Qua trnh cat got kim loai la qua trnh phc tap co nhieu hien tng vat ly kem theo nh bien dang, toa nhiet, bien cng, ... Tm hieu ban chat cua cac hien tng vat ly co mot y ngha rat quan trong ve mat kinh te. T o co the ieu khien qua trnh cat got e at nang suat cao, chat lng tot nhat sau khi gia cong.

2.3.1 Qua trnh tao phoi va hien tng co rut phoi

a) S bien dang cua kim loai

Bien dang la qua trnh lam thay oi hnh dang cua kim loai do tac dung cua tai trong ben ngoai hay cua cac hien tng vat ly.

Khi tac dung tai trong ben ngoai len kim loai, tuy theo mc o, kim loai co the b bien dang an hoi, bien dang deo hoac b pha huy.

Hnh 2.18 Bieu o keo kim loai

Tren bieu o hnh 2.18 bien dang an hoi ng vi oan OP. Khi tac dung tai trong nho hn Pp mau kim loai b keo dai ra mot oan nao o ty le thuan vi tai trong nhng khi bo tai trong th mau kim loai tr ve v tr ban au.

Khi tai trong ln hn Pp (v du Pa) th khi bo tai trong kim loai khong tr ve theo ng bien dang ban au OP ma theo ng aa song song vi OP. Ket qua mau b keo dai them mot oan Oa(bien dang deo).

Khi tai trong tac dung at ti Pb mau b hnh thanh co that, luc nay lc giam i nhng co that van phat trien dai ra cho en khi t (b pha huy).

b) Qua trnh tao phoi

Quan sat thc te qua trnh cat ta nhan thay rang :

- Phoi c tach ra khoi chi tiet khi cat khong theo phng van toc cat v (tc la phng lc tac dung) va b xep lp (hnh 2.19 a).

- Phoi khi cat ra b uon cong ve pha mat t do, kch thc cua phoi b thay oi so vi lp cat khi con tren phoi (hnh 2.19b).

Quan sat phoi tren hnh 2.19a ta thay phoi b xep lp, cac lp nghieng mot goc so vi phng tac dung lc, hn na phoi b cong ve pha mat t do, tc la mat oi dien vi mat trc dao. Quan sat hnh 2.19b ta lai thay phoi ngan hn nhng day hn so vi lp kim loai tren phoi, ngha la quang ng chay dao L ln hn chieu dai phoi Lf va chieu day

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phoi af ln hn chieu day lp cat a. Viec thay oi kch thc phoi nh vay goi la hien tng co rut phoi.

a) b)

Hnh 2.19 Qua trnh tao phoi

Dao

Phoi

Phoi

Lf

af

a

e giai thch nhng ieu nhan thay tren ta tien hanh cac th nghiem sau:

- Th nghiem nen va cat mau kim loai: th nghiem nen mau, th nghiem cat mau vi dao co = 0.

Khi quan sat th nghiem nen mau (hnh 2.20 a), ngi ta thay rang: cac phan t kim loai di sc ep cua au nen b bien dang, phng bien dang la phng AB va CD tao vi phng cua ngoai lc tac dung P mot goc xac nh oi vi tng loai vat lieu (vi thep = 45 ).

ieu tng t o cung xay ra oi vi mau cat (hnh 2.20 b), nhng phng CD th cac phan to kim loai a b phan kim loai tren mau chan lai. Do o phng bien dang ch con la AB.

Ket qua tren a cho ta ket luan quan trong la: thc chat qua trnh tach phoi ra khoi chi tiet la qua trnh bien dang cua cac phan t kim loai di sc ep cua au dao.

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a)

b)

Hnh 2.20 Th nghiem nen va cat

- Th nghiem quan sat s dch chuyen cac phan t khi cat: e tiep tuc lam ro ban chat cua qua trnh cat kim loai, ngi ta tien hanh mot th nghiem khac. th nghiem nay, cac phan t kim loai tren mat ben cua mau c anh dau. Khi cat ta quan sat s dch chuyen cua cac phan t kim loai a c anh dau.

V du tren hnh 2.21 mo ta qua trnh dch chuyen cua phan t kim loai P khi cat. T P en 1 phan t kim loai dch chuyen gan nh song song vi phng van toc cat V. Qua khoi iem 1, ang le phan t kim loai chuyen en iem 2 , nhng thc te th no dch chuyen en iem 2. oan 22 goi la lng trt cua phan t kim loai P tai thi iem 2. iem 1 la iem bat au trt cua phan t P khi cat. Tng t nh vay thi iem 3 lng trt la 33. Tiep tuc cat, sau khi qua khoi iem 3 phan t P di chuyen en iem 4. oan ng 34 song song vi mat trc cua dao. ieu o co nghia la en thi iem 3 th qua trnh trt cua phan t kim loai P a ket thuc va no a chuyen thanh phoi cat. iem 3 c goi la iem ket thuc trt cua phan t P khi cat. Bang cach anh dau nh vay ta xay dng c ng dch chuyen cua phan t kim loai P khi cat la P1234P. Trong o oan 4P la mot cung cong ve pha mat t do cua phoi co ban knh Rp . iem 4 c xac nh bang cach : t iem tach ri gia phoi va mat trc dao E ta ke EF vuong goc vi mat trc dao (EF OE). EF se cat ng P1234P tai iem 4 .

Hnh 2.21 Quan sat phoi trt

Vung gii han bi mat bat au trt OA va mat ket thuc trt OC goi la mien bien dang (mien tao phoi) hay con goi la vung trt. Th nghiem tren c tien hanh vi van toc cat v = 0,002 m/ph. Trong thc te van toc cat ln hn nhieu do vay toc o bien dang cung rat ln, hai mat trt OA va OC gan nh trung nhau, ch cach nhau khoang 0,03 0,2 mm. e n gian ta coi hai mat nay trung nhau va goi la mat trt - nam nghieng so vi phng van toc cat V mot goc 1 = 30o40o. Ben trong moi phan t cung dien ra s xe dch gia cac tinh the di mot goc 2 = 60o 65o (hay la goc tach phoi) (hnh 2.19a).

Qua hai th nghiem neu tren, ta co the ket luan rang : qua trnh hnh thanh phoi cat la qua trnh bien dang trt cua cac phan t kim loai theo cac mat trt cua chung.

c) Cac dang phoi

Nghien cu cac dang phoi cat co y ngha rat thc te v tuy tng loai vat lieu gia cong, hnh dang hnh hoc cua dao, che o cat, ta se thu c hnh dang phoi cat khac nhau. Do o can c vao phoi cat ta co the anh gia dung cu cat tot hay xau, s tieu hao nang lng nhieu hay t, be mat gia cong co bong hay khong.

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Co the chia phoi ra cac loai sau: phoi vun (hnh 2.22 e), phoi xep (hnh 2.22a, b), phoi day (hnh 2.22c, d).

Phoi vun thng gap khi gia cong vat lieu don nh gang, ong thau cng S d nh vay v cac vat lieu nay t bien dang deo, ng suat at ngay ti gii han t nen vat lieu vun ra. Trong trng hp nay, lc cat va nhiet o tap trung mui dao, dao chong b mon, s hnh thanh phoi cat khong lien tuc nen lc cat bien oi gay rung ong, o bong be mat gia cong khong cao.

Phoi xep thng gap khi gia cong vat lieu deo nh thep, ong thau mem toc o cat thap, chieu day cat ln va goc cat cua dao co gia tr tng oi ln. Phoi co dang tng manh xep lp len nhau. Mat phoi ke mat trc cua dao bong, mat kia co nhng gn ne. Khi cat ra phoi nay, lc thay oi t hn, do o rung ong t hn, be mat gia cong bong hn trng hp nhan c phoi vun.

Phoi day thng gap khi gia cong vat lieu deo toc o cat cao, chieu day cat be. Phoi dai lien tuc, ke mat trc cua dao rat bong, mat oi dien hi b gn. Mc o bien dang deo khi tao phoi day t hn so vi khi tao phoi xep. Khi tao phoi day, lc cat n v be va t bien oi, o bong be mat se cao hn khi tao phoi xep.

Khi hnh thanh phoi xep va phoi day, s tiep xuc gia phoi va mat trc cua dao cach mui dao mot oan, ieu o tao kha nang cai thien ieu kien lam viec cua mui dao.

d) Hien tng co rut phoi

Co rut phoi la ac tnh tieu bieu nhat noi len mc o bien dang cua kim loai khi cat va la ket qua cua s bien dang cua kim loai ve mat so lng. Nghien cu s co rut phoi co the phan oan viec cat kho hay de, nang lng tieu hao nhieu hay t.

phan tren ta a xet qua trnh hnh thanh phoi. Moi phan t cua phoi b ep lai di tac dung cua lc t pha mat trc cua dao, ket qua la phoi luon luon co chieu dai nho hn chieu dai cua be mat ma t o phoi c cat ra. Hay noi cach khac kch thc cua phoi tach ra khong giong cac kch thc lp cat tng ng khi no con nam trong chi tiet: L > Lf , af > a, bf = b (hnh 2.19b).

Hien tng o goi la hien tng co rut phoi va c ac trng bi he so co rut phoi:

K = L / Lf = af / a > 1

Trong o :

L, Lf - chieu dai lp cat va chieu dai cua phoi.

af, a - chieu day phoi va chieu day lp cat.

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bf, b - chieu rong phoi va chieu rong lp cat.

Thc nghiem cho thay K = 1,1 10. Nhan to anh hng en he so co rut phoi

He so K cang ln th phoi bien dang cang nhieu va ngc lai. Cac nhan to co lien quan en bien dang va ma sat trong qua trnh cat t nhieu eu anh hng en s bien dang cua phoi. Bang cach ieu chnh cac nhan to o co the lam tang hay giam bt s bien dang cua kim loai. Mat khac bien dang co quan he trc tiep en nang lng tieu hao. Khi cat, bien dang cang nhieu, nang lng tieu hao cang ln. Do o viec nghien cu s co rut phoi co mot y ngha rat thc te.

Di ay la mot so nhan to chnh anh hng en he so co rut phoi:

- Anh hng cua vat lieu gia cong va vat lieu lam dao:

+ Tnh chat cua vat lieu gia cong co anh hng ln en he so co rut phoi. Trong eu kien cat nh nhau, vat lieu cang deo th bien dang cang ln.

+ Moi loai vat lieu lam dao co he so ma sat vi vat lieu gia cong khac nhau, ma sat cang ln th bien dang cang nhieu va ngc lai.

- Anh hng cua che o cat:

+ Chieu day cat a tang th bien dang cua kim loai giam nen K giam.

+ Chieu sau cat t khong anh hng ang ke en s co rut phoi.

+ Toc o cat V anh hng nhieu nhat en s co rut phoi. Qua thc nghiem ta co quan he gia K va V, quan he gia he so ma sat va V nh hnh 2.23.

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Giai thch:

Tang t V1 en V2 ma sat tang, nen bien dang tang, nhng do nhng toc o nay thng de sinh ra leo dao lam goc trc tang nen bien dang giam. Anh hng leo dao nhieu hn nen ket qua K giam.

Tiep tuc tang t V2 en V3, ma sat tang va leo dao giam lam bien dang tang nen ket qua la K giam.

Hnh 2.23 a) Quan he gia he so co rut phoi va van toc cat. b) Quan he gia he so ma sat va van toc cat.

V tiep tuc tang vt qua V3, khong co leo dao va ma sat giam nhanh. Mat khac do V cao thi toc o bien dang giam nen K giam (khi V 200 m/phut th s co rut phoi hau nh khong oi)

- Anh hng cua thong so hnh hoc cua dao:

+ Goc trc cang ln phoi thoat cang de, bien dang giam. + Goc nghieng chnh tang vi ban knh mui dao r = 0 th chieu day cat se tang

(a = S. sin) do o phoi cang day cang kho bien dang. Vi ban knh mui dao r 0, khi thay oi, s thay oi cua K phc tap hn. Luc au,

khi tang do chieu day cat a tang nen K giam. Khi vt qua 60o 70o th K tang v chieu dai phan cong cua li cat tham gia lam viec tang len.

+ Ban knh mui dao r tang, chieu dai phan cong cua li cat tham gia lam viec tang len nen K tang.

- Dung dch trn nguoi: lam giam ma sat do o lam giam bien dang.

2.3.2 Qua trnh hnh thanh be mat gia cong va hien tng cng nguoi.

Khao sat qua trnh hnh thanh be mat gia cong (hnh 2.24a) ta nhan thay e cat mot lp kim loai co chieu day cat la a va be mat hnh thanh se la DE. Khi bat au cat, do li cat cua dao khong nhon ly tng ma luon luon co mot ban knh , s tiep xuc cua dao va chi tiet bat au t iem A. Dao cang i sau vao chi tiet, iem co ng suat ln nhat cang ha thap va khi qua trnh cat a on nh th chiem v tr B (nam ngay tren mat trt) do o ch co mot lp kim loai co chieu day cat a nam tren ng BC la c cat thanh phoi. Lp kim loai nam di ng BC khong c cat ma b nen, do o chu bien dang an hoi, bien dang deo va sau gia cong no b cng nguoi (hoa cng).

Sau khi mui dao i qua, lp be mat do s an hoi c nang len mot chieu cao h, do o gay nen mot ap lc phap tuyen va ma sat vi mat sau cua dao. Ket qua lp mong be mat lai chu bien dang them. Neu ban knh cong cua dao cang ln, ma sat cang ln va mc o bien dang be mat cang tang.

e giai thch ro hn qua trnh hnh thanh be mat gia cong (hnh 2.24b) ta hay khao sat kha nang dch chuyen cua ba phan t kim loai O1, O2, O3 trong qua trnh cat. Ta nhan xet:

h

A

a

B

D E C

a

Hnh 2.24a Khao sat be mat hnh thanh khi gia cong

- Phng trt cua hat kim loai tao vi ap lc phap tuyen len phan t kim loai o mot goc .

- Phan t kim loai tai O1 co phng trt hng ve pha phoi, do o co kha nang trt e thanh phoi.

- Phan t kim loai tai O2 co phng trt song song vi phng van toc cat.

- Phan t kim loai tai O3 co phng trt hng ve pha phoi, do o co kha nang trt b chan lai, khong the thanh phoi cat.

T nhan xet tren ta rut ra ket luan: -36-

Khi cat, nhng phan t kim loai (tren lp cat co chieu day a) nam tren mat O2C se b trt va tao thanh phoi; nhng phan t nam di co chieu day H se b au dao nen ep e tao thanh be mat gia cong.

S bien dang cua lp kim loai H xay ra ca bien dang deo va bien dang an hoi. Do bien dang an hoi nen sau khi ra khoi mat sau dao, mot phan cua lp kim loai c phuc hoi mot lng h < H. S phuc hoi nay xay ra ot ngot t trang thai b chen ep sang trang thai t do nen de phat sinh ra cac vet nt te vi.

Ket qua cua bien dang deo la sau khi gia cong mot lp mong tren be mat chi tiet thay oi tnh chat ban au cua no va o cng tang len, tc la tinh the kim loai b nat vun khien cho lp be mat tr nen ben va cng hn. Hien tng o la hien tng cng nguoi. Ngoai ra be mat gia cong con co nhng tnh chat nh ng suat d, cac vet nt te vi va do sinh nhiet (bien dang va ma sat) lam suy yeu be mat.

Ap lc phap tuyen:

Thong so ac trng cho cng nguoi

- Mc o cng nguoi:

%100=Ht

HtHsH

Trong o:

Hs - o cng lp be mat sau khi bien dang deo.

Ht - o cng lp be mat trc khi bien dang deo (vat lieu ban au).

-37-

- Chieu sau lp cng nguoi: V du khi gia cong phoi uc bang khuon kim loai, trong ieu kien bnh thng, chieu sau lp cng nguoi nh sau:

Sau gia cong tho bang dao tien: 0,04 0,05 mm Sau gia cong tinh bang dao tien: 0,02 0,03 mm Sau mai tinh: 0,015 mm

Nhan to anh hng en cng nguoi co cung quy luat vi nhan to anh hng en co rut phoi. V du vai nhan to anh hng chnh:

- Nhng vat lieu gia cong co o deo cang cao th hien tng cng nguoi xay ra vi mc o cang cao.

- Goc trc cua dao cang nho th mc o cng nguoi cang tang.

- Cat got co dung dch trn nguoi th mc o cng nguoi giam.

Tac dung cua cng nguoi

- Tac dung tot: Bao ve be mat, tang gii han ben moi cua chi tiet sau gia cong;

- Tac dung xau:

+ Neu tren be mat chi tiet sau gia cong co vet nt, ne th cng nguoi se lam giam gii han ben moi.

+ Lp cng nguoi se gay kho khan cho cac nguyen cong gia cong tinh.

+ Khi gia cong tho, cng nguoi de gay cong venh cho nhng chi tiet yeu cng vng.

2.3.3 Hien tng leo dao (phoi bam)

a) Hien tng va ieu kien hnh thanh leo dao

Hien tng leo dao va quan he gia chieu cao leo dao va toc

o cat

Toc o cat v, m/phut

-38-

Khi cat kim loai, tren mat trc cua dao ke ngay li cat, thng xuat hien lp kim loai co cau truc kim tng khac han vi vat lieu gia cong va vat lieu lam dao. Neu lp kim loai nay bam chac vao li cat cua dao th c goi la leo dao hay phoi bam.

Nguyen nhan la trong qua trnh cat co hien tng chay cham. Khi phoi thoat theo mat trc cua dao th lp kim loai sat mat trc do chu ap lc ln va nhiet o cao nen lc ma sat ln lam cho toc o dch chuyen cham. Vi ieu kien lc lien ket trong noi bo kim loai be hn lc ma sat gia mat trc cua dao va phoi, mot lp kim loai gan mat trc se tach khoi phoi va nam lai tren mat trc e hnh thanh leo dao (hnh 2.25 a).

Leo dao khong ton tai lau tren dao, no nh ky b be gay roi ri vao gia li cat va phoi (hnh 2.25b), khi o cac mau phoi nho se gay nen cac vet lom (xc) tren be mat gia cong, lam cho be mat gia cong khong trn nhan.

b) Nhan to anh hng en leo dao

- Van toc cat (hnh 2.25 c): toc o cat thap (V < 5 m/phut), lc lien ket trong noi bo kim loai ln, tuy rang he so ma sat ben ngoai cung ln nhng cha chiem u the nen thng khong co leo dao.

Khi toc o cat tang len cao (V > 80 m/phut), lc lien ket trong noi bo kim loai giam dan, ong thi he so ma sat cung giam nhanh. Mat khac, lp kim loai gan mat trc cua dao di nhiet o cao gan nh chay long, co tac dung lam nhn nen khong co leo dao.

- Chieu day cat: Chieu day cat a cang ln, toc o hnh thanh leo dao cang thap va chieu cao leo dao cang cao (hnh 2.26). Quan he gia chieu day cat

va chieu cao leo dao

Hnh 2.27 Quan he gia vat lieu gia cong

va chieu cao leo dao

Hnh 2.28 Quan he gia goc trc va

chieu cao leo dao

-39-

- Vat lieu gia cong deo khi cat de hnh thanh leo dao hn vat lieu don, vat lieu B deo hn vat lieu A (hnh 2.27).

- Goc trc cang ln th toc o hnh thanh leo dao cang cao va chieu cao leo dao cang be (hnh 2.28).

c) Tac dung cua leo dao

- Tac dung tot:

+ o cng cua cac khoi leo dao cao hn nhieu so vi ban than vat lieu chi tiet (gap 2,5 3,5 lan) nen co the thay the li cat.

+ Khi gia cong tho, leo dao co li v no tang goc trc cua dao khien cho qua trnh tao phoi de dang va bao ve li cat khoi b mon.

- Tac dung xau: Khi gia cong tinh, leo dao co hai v no lam giam o chnh xac va o trn nhan cua be mat gia cong.

Khac phuc hien tng leo dao va nang cao chat lng cua be mat gia cong bang cac bien phap sau:

- Gia cong vi toc o cat hp ly, nen trach vung toc o cat thng gay ra leo dao V=7 80 m/phut (hnh 2.25c).

- Mai bong mat trc cua dao.

- Dung dung dch ti nguoi.

2.3.4 Hien tng nhiet

Hien tng nhiet va s truyen nhiet trong qua trnh cat rat quan trong v nhiet o sinh ra trong qua trnh cat va s phan bo nhiet o lam thay oi tnh chat c ly cua vat lieu gia cong anh hng en tuoi tho cua dao, lam giam nang suat va o chnh xac gia cong.

a) Nguon nhiet.

Trong qua trnh cat cong tieu hao c chuyen hoa thanh nhiet. Neu goi Q la nhiet lng sinh ra trong qua trnh cat th no la ket qua cua:

- Cong ma sat trong gia cac phan t vat lieu gia cong trong qua trnh bien dang Q1

- Cong ma sat ngoai gia phoi va mat trc dao Q . 2

- Cong ma sat gia be mat chi tiet gia cong va mat sau dao Q . 3

- Cong cat t phoi Q . 4

Phng trnh can bang nhiet c viet:

-40-

Q = Q + Q + Q + Q1 2 3 4

Neu cho rang toan bo cong c hoc khi cat bien thanh nhiet th:

427VPz

EVPz

ERQ ===

Trong o: Q Lng nhiet (Kcal/phut).

R Cong cat (KGm/phut).

E Tng ng gia nhiet va cong (E = 427 KGm/Kcal).

Pz Lc cat (KG).

V Van toc cat (m/phut).

Trong thc te khong phai toan bo cong tieu hao chuyen thanh nhiet. Mot phan cong c tieu hao e lam thay oi the nang cua mang tinh the. Tuy nhien tieu ton o rat t, nen trong tnh toan co the bo qua.

Hnh 2.29 Khu vc phat sinh nhiet khi cat

Khi cat co ba khu vc phat sinh nhiet chnh (hnh 2.29):

- Khu vc tiep xuc gia dao va phoi mat trc (1).

- Khu vc tiep xuc gia mat sau cua dao vi chi tiet gia cong (2).

- mat t phoi (3).

b) S truyen nhiet

Muon ieu khien c qua trnh cat, ieu quan trong khong ch la biet c lng nhiet sinh ra ma la nhiet o thc s dao, phoi va chi tiet. ang chu y nhat la nhiet o dao v no co the lam cho dao mat o cng va b mai mon nhanh.

Nhiet sinh ra trong qua trnh cat c truyen qua dao, chi tiet, phoi va khong kh.

Q + Q + Q + Q = Q + Q

-41-

1 2 3 4 dao chi tiet + Qphoi + Qkk

V du qua th nghiem lng nhiet phan bo khi gia cong thep 40Cr phan bo nh sau:

V (m/phut) Phoi Chi tiet Dao Khong kh

25 50 45% 50% 2,5% 1 2,5% 100350 75% 22% 1,5% 1 1,5%

Nh vay qua th nghiem, khi cat vi toc o cao lng nhiet truyen vao phoi ln nhat, roi en chi tiet, sau cung mi la dao. ieu nay giai thch nh sau: phoi chu hai nguon sinh nhiet (1 va 3) nen lng nhiet vao phoi ln hn ca; Lng nhiet dao t v tnh dan nhiet cua dao kem; Lng nhiet chi tiet ln hn v tnh dan nhiet cua chi tiet tot hn.

Van toc cat cang ln, bien dang va masat chu yeu nam trong phoi do thi gian tiep xuc vi dao va chi tiet t nen nhiet truyen t i, v vay nhiet o truyen vao chi tiet va dao cang giam.

Qua nghien cu chng to nhiet o cao nhat nam gia khu vc tiep xuc gia dao va phoi, ngha la tai iem cach li cat vao khoang (0,3 0,5)l ; trong o l la khoang cach chieu dai tiep xuc cua phoi va mat trc cua dao. Nhiet o o quy c la nhiet o cat.

c) Nhng nhan to anh hng en nhiet cat

Tat ca nhan to anh hng en bien dang eu anh hng en nhiet o cat, di ay la mot vai nhan to anh hng chnh:

- Che o cat: V, s, t tang nhiet o cat tang, nhng khong ty le thuan (hnh 2.30).

Hnh 2.30 Quan he gia nhiet o cat va che o cat

- Thong so hnh hoc cua dao:

+ Goc trc tang, bien dang giam nen nhiet o cat giam. Song goc trc tang, kha nang truyen nhiet kem i, ket qua nhiet o cat giam t.

+ Goc nghieng chnh tang, a tang (a= S sin ) a en K giam, ieu kien truyen nhiet xau, ket qua nhiet o cat tang.

- Vat lieu gia cong don, bien dang t, nhiet o cat thap so vi vat lieu deo.

- Vat lieu lam dao nao co he so ma sat cang ln va tnh truyen nhiet cang be th nhiet o tren dao cang cao.

- Khi cat co ti dung dch trn nguoi th ma sat va nhiet o tren dao giam.

2.3.5 Hien tng rung ong

Trong qua trnh cat kim loai, he thong cong nghe thng xay ra rung ong do yeu cng vng. Rung ong lam anh hng en chat lng chi tiet gia cong, en nang suat cung nh sc khoe ngi th.

e co the nang cao nang suat, ac biet la nang cao toc o, van e rung ong cang c ac biet chu trong.

Tuy nhien van e rung ong la mot van e het sc phc tap, ac biet la rung ong trong qua trnh cat, ma ban chat cua no cho en nay tiep tuc c nghien cu.

Hien nay co the noi mot cach khang nh rang trong qua trnh cat co hai loai rung ong: rung ong cng bc va rung ong t rung.

-42-

-43-

Rung ong cng bc (do cac nguyen nhan ngoai) trong qua trnh cat c gay ra do nhng nguyen nhan sau ay:

- Do s khong can bang cua cac bo phan may - dao - chi tiet - o ga.

- Do he thong truyen ong cua may co s va ap tuan hoan.

- Do vat cat khong tron, lng d gia cong khong eu.

- Do dao chuyen ong khong can bang.

Nhng nguyen nhan tren de thay do o de tm bien phap khac phuc.

T rung ong la do lc gay ra va duy tr no trong qua trnh cat. Co nhieu cach giai thch ve nhng nguyen nhan gay ra t rung:

- Do s thay oi cua lc ma sat mat trc va sau cua dao trong qua trnh cat.

- Do s thay oi tnh deo cua vat lieu gia cong trong qua trnh cat khien cho lc cat thay oi.

- Do s phat sinh va mat i cua leo dao.

- Do s bien dang an hoi cua dao chi tiet.

Cac nhan to anh hng en rung ong:

- Tang toc o cat th bien o dao ong tang (trong vung de sinh leo dao), sau khi bien o dao ong at c mot gia tr cc ai nao o th toc o cat cang tang, bien o dao ong cang giam.

- Khi chieu sau cat tang th bien o dao ong tang v lc cat tang anh hng en he thong cong nghe.

- Anh hng cua thong so hnh hoc, ang ke nhat la goc , goc cang tang rung ong giam, (lc Py = PN.cos, la lc cat anh hng en rung ong nhieu nhat).

- Khi gia cong gang, cat ra phoi vun, lc cat bien oi nhieu nen rung ong tang. Con cat vat lieu deo, khi ieu kien hnh thanh leo dao ln th rung ong cang tang.

Ngoai ra s rung ong con chu anh hng rat ln cua he thong cong nghe. Neu he thong nay cang cng vng th rung ong cang giam.

Trong thc te, can chon che o cat hp ly, ong thi tang o cng vng cua he thong may dao chi tiet va dung mot so dung cu giam rung chuyen dung khac.

2.3.6 Hien tng mai mon dao cat va van e tuoi ben dao

a) Hien tng va quy luat mai mon dao

Khi cat got mat trc cua dao luon tiep xuc va co chuyen ong tng oi vi phoi, mat sau cua dao luon tiep xuc va co chuyen ong tng i vi mat gia cong, mui dao va li dao tiep xuc va co chuyen ong tng oi vi mat ang gia cong cua chi tiet, v the qua trnh cat dao b mai mon.

S mai mon cua dao giong s mai mon cua cac chi tiet chuyen ong tng oi vi nhau nhng ieu kien co nang ne hn, v vay quy luat mai mon dao cung giong nh quy luat mai mon gia cac chi tiet. S mai mon cua dao theo thi gian c chia lam 3 giai oan nh sau (hnh 2.31):

Giai oan I : Mai mon khoc liet do tren mat dao con vet nhap nho;

-44-

Giai oan II : Mai mon on nh;

Giai oan III : Mai mon pha huy, giai oan nay nhiet o tang cao, o cng giam nen s mai mon xay ra rat nhanh.

Khi lam viec neu dao b mon gan en cuoi giai oan II phai mai dao lai.

Tm hieu c che mai mon dao la mot cong viec het sc quan trong trong viec nghien cu qua trnh cat got.

o mon

III III

0

BA

C

Thi gian

Hnh 2.31 Quan he gia mai mon dao va thi gian

b) Nguyen nhan gay ra mai mon dao

- toc o cat thap, s mai mon chu yeu do ma sat gia mat trc cua dung cu cat vi phoi va gia chi tiet vi mat sau cua dao, o la mai mon c hoc.

- Khi toc o cat tng oi cao, nhiet o sinh ra cao at mot gia tr nao o, lp be mat cua dao thay oi cau truc nen dao chong mon hn, s mai mon chu yeu v nhiet.

- Khi toc o cat cao, nhiet o cao, lp be mat chi tiet b oxy hoa, tr nen rat don, de b pha huy. ong thi vi ap suat cao, nhiet o cao con co s mai mon v dnh. Khi o phoi cat thoat ra dnh vao mat trc cua dao, khi chuyen ong phoi se keo theo tng mang nho vat lieu mat trc cua dao lam cho dao b mon. Ngoai ra con co mai mon v khuyech tan, do khi cat cac loai thep va hp kim chu nong bang dao hp kim cng toc o cao. Khi nhiet o cat t 900 o oC 1000 C th co hien tng khuyech tan thanh phan cua vat lieu dao vao lp be mat chi tiet gia cong, ket qua dao b mon rat nhanh.

c) Cac dang mai mon dao

a) b) c)

d) e)

Hnh 2.32

Cac dang mai mon dao

Tuy theo ieu kien cat got, tnh chat vat lieu gia cong va vat lieu lam dao, dung cu cat got co cac dang mai mon sau:

- Mai mon mat sau (hnh 2.32a), thng xay ra khi gia cong vi chieu day cat nho (a < 0,1 mm) va ac biet khi gia cong cac vat lieu don nh gang.

- Mai mon mat trc (hnh 2.32b) va mai mon li liem (hnh 2.32c)., thng xay

ra khi gia cong vat lieu deo co chieu day cat a > 0,5 mm.

- Mai mon ong thi ca mat trc va mat sau xay ra khi cat kim loai deo co chieu day cat a = 0,1 0.5.

- Mai mon mui dao (hnh 2.32d) va cun li cat (hnh 2.32e), thng xay ra khi gia cong tinh cac vat lieu co tnh dan nhiet. Khi o di anh hng cua nhiet o cao, li cat nhanh chong b mem va cun.

Mai mon mat sau la dang chu yeu va de o nhat. Do o thng dung lam tieu chuan mai mon (hoac o mai mon cho phep). Khi gia cong tinh o mai mon cho phep tuy thuoc vao o bong va o chnh xac gia cong.

d) Tuoi ben dao.

Thi gian lam viec lien tuc gia 2 lan mai dao goi la tuoi ben cua dao, ky hieu la T (phut).

Tuoi ben cua dao phu thuoc vao nhieu yeu to: vat lieu lam dao, vat lieu gia cong, thong so hnh hoc cua dao, che o cat, dung dch trn nguoi v.v...

Anh hng nhieu nhat en tuoi ben cua dao la toc o cat. Toc o cat cang cao, nang lng tieu hao trong qua trnh cat cang ln, nhiet toa ra cang nhieu, qua trnh mon nhiet va mai mon dien ra cang manh dan en tuoi ben cua dao cang giam.

Toc o cat la mot trong nhng nhan to quan trong anh hng nhieu en chat lng be mat gia cong, nang suat va gia thanh san pham. Khi tang toc o cat lam tang nang suat gia cong nhng ong thi lam dao chong mon, hao ph thi gian thay dao va mai lai, khi o se lam giam nang suat va tang gia thanh san pham. Do o viec xac nh mot toc o cat hp ly la can thiet. Toc o cat hp ly la toc o va am bao nang suat cao nhat, va am bao gia thanh ha nhat.

Thc te trong ieu kien cat cu the, ngi ta a xac nh trc tuoi ben hp ly cua dao, nhiem vu cat got la phai ieu chnh may e co toc o phu hp nham am bao tuoi ben dao a chon.

Ngoai toc o cat, con rat nhieu nhan to anh hng en tuoi ben dao nh lng chay dao, chieu sau cat, thong so hnh hoc cua dao, vat lieu gia cong, vat lieu dao

Di ay ta xet mot vai nhan to chnh anh hng en tuoi ben dao:

- Toc o cat cang cao, nhiet o cat cang ln, tnh chat c ly cua dao thay oi nen dao chong mon.

Ta co quan he gia tuoi ben dao va toc o cat qua thc nghiem nh sau:

mTAv =

Trong o:

T : tuoi ben dao ( phut);

V : toc o cat ( m/phut);

-45-

A : hang so phu thuoc vao vat lieu gia cong;

m : gia tr ac trng cho mc o anh hng cua tuoi ben dao en toc o cat

oi vi dao thep gio m = 0,125

oi vi dao hp kim cng m = 0,2

oi vi dao bang s m = 0,5

T quan he tren ta thay: neu tang V th T giam. Do o muon gi cho tuoi ben cua dao cao th phai chon toc o cat hp ly.

- Khi cat, neu tang chieu sau cat t va lng chay dao s th lc cat va nhiet cat cung tang len dao chong mai mon, anh hng en tuoi ben dao. Do o muon gi tuoi ben T cua dao khong oi th can phai giam toc o cat.

- Thong so hnh hoc dao co anh hng rat ln en tuoi ben dao. V vay tuy theo tng tnh chat gia cong, vat lieu gia cong ma ta co the chon dao (vat lieu lam dao, hnh dang hnh hoc, thong so hnh hoc) sao cho hp ly e at c nang suat cao nhat, va chat lng cao nhat.

+ Anh hng cua goc trc : neu goc trc tang th ma sat, lc cat, nhiet cat giam nhng neu goc trc tang qua ln se lam goc sac giam, ieu kien truyen nhiet kem, dao b chong mai mon. Neu muon gi tuoi ben T cua dao khong oi th can phai giam toc o cat. V vay can chon goc trc hp ly e co toc o cao nhat (hnh 2.33a).

+ Anh hng cua goc sau : neu goc sau tang th se lam giam ma sat gia mat sau va mat gia cong. Tuy nhien neu goc sau tang qua ln th se lam giam goc sac, giam ieu kien truyen nhiet gay nen dao chong mai mon. Neu muon gi tuoi ben T cua dao khong oi th can phai giam toc o cat. V vay can chon goc sau hp ly e co toc o cao nhat (hnh 2.33b).

a) b)

Hnh 2.33 Quan he gia van toc cat va goc trc, goc sau cua dao.

+ Anh hng cua ban knh mui dao: neu ban knh mui dao ln th chieu dai li cat tham gia cat ln, truyen nhiet tot nen co the tang toc o cat.

+ Anh hng cua tiet dien than dao: Than dao cang ln ieu kien truyen nhiet cang tot, nen co kha nang tang toc o cat.

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- Anh hng cua dung dch trn nguoi: Dung dch trn nguoi lam cho s hnh thanh phoi de dang, ma sat giam, nhiet cat giam. V vay khi cat co dung dch trn nguoi cho phep nang cao toc o cat, tang tuoi ben cua dao.

Tong hp cac nhan to tren ngi ta a ra cac cong thc thc nghiem tnh toan van toc cat nh sau:

vyxmv KstT

CVvv=

..

Trong o:

T: Tuoi ben dao (phut).

t: Chieu sau cat (mm).

s: lng chay dao (mm/vong).

C , m, x , yv v v: phu thuoc vao ieu kien gia cong, tra trong so tay che o cat khi gia cong c.

Kv: He so ieu chnh, tra trong so tay che o cat khi gia cong c.

......... KKKKKKKK runmV =

Trong o:

Km: He so hieu chnh xet en vat lieu gia cong. K : He so hieu chnh xet en trang thai phoi. nKu: He so hieu chnh xet en anh hng cua vat lieu lam dao.

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Kr ; K ; K ; K : He so hieu chnh xet en anh hng cua thong so hnh hoc dao.

2.3.7 Hien tng lc cat

a) Lc cat

Muon cat kim loai can phai tac dung vao dao mot lc e thang c lc lien ket trong noi bo kim loai. Nghien cu lc cat co mot tam quan trong rat ln v biet lc cat mi tnh c cong suat tieu thu cua may, mi tnh c lc kep chi tiet e tren c s thiet ke o ga v.v... Lc cat ln hay nho anh hng en tuoi ben cua dao va chat lng be mat gia cong.

Trong cat got kim loai, ngi ta goi lc sinh ra trong qua trnh cat tac ong len dao la lc cat; Lc co cung o ln, cung phng nhng ngc chieu vi lc cat goi la phan lc cat.

Khi cat, tren mat trc cua dao do phoi ap vao nen co lc phap tuyen N1 (hnh 2.34), ong thi do phoi chuyen ong nen co lc ma sat F1, ta co:

111 NFQ +=

R

Q2 Q1

N1 N2 F2

F1

Hnh 2.34 Lc tac dung len dao

Hnh 2.35 Cac phng lc cat

Tren mat sau cua dao do bien dang an hoi va chuyen ong nen co ap lc N2 va ma sat F2 ; ta co:

222 NFQ += Nhng cac lc tac dung len mat sau khong tham gia qua trnh tao phoi ma gay ra

nhng tai trong vo ch co anh hng ln en rung ong va mai mon. Tong hp cac lc tren ta c lc cat R:

21 QQR += e nghien cu lc cat ngi ta phan lc cat thanh cac thanh phan theo cac phng

can thiet. Khi tien, cac thanh phan lc cat co phng trung vi phng cua cac chuyen ong cat got (hnh 2.35):

Pz - lc tiep tuyen, trung vi phng van toc V, co gia tr ln nhat. Dung e kiem nghiem cong suat tieu thu cua may.

Py - lc hng knh, co phng trung vi phng chieu sau cat t. Lc nay gay rung ong trong mat phang ngang, anh hng en o chnh xac va o bong be mat gia cong.

Px - lc chay dao, co phng trung vi phng chay dao s. Lc nay tac dung len c cau chay dao. C cau chay dao phai khac phuc lc nay cung vi lc ma sat tren song trt cua may.

Luc nay ta co hp lc la :

xyZ PPPR ++= hay co the viet lai:

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2x2y

2Z PPPR ++=

ay la phng phap phan tch lc pho bien nhat, bi v phng cac chuyen ong cat la hoan toan xac nh, do vay viec o cac thanh phan lc cat c tien hanh de dang.

b) Nhan to anh hng en lc cat

Nhan to anh hng en lc cat cung quy luat nh anh hng en bien dang cua phoi. V du:

- Tnh chat c ly cua vat lieu gia cong anh hng ln en lc cat. Khi gia cong vat lieu don, lc cat nho hn so vi vat lieu deo. Kim loai co o hat cang nho, o cng cang cao, lc cat cang ln.

- Chieu sau cat t va lng chay dao s tang, lc cat tang, nhng anh hng cua t ln hn s. Van toc cat v anh hng en lc cat cung tng t nh anh hng cua no en bien dang cua phoi (hnh 2.23). Khi v tang en v2 (15 20 m/phut) lc giam; Tiep tuc tang en v3 (40 50 m/phut) lc tang; Tiep tuc tang na lc giam, cho en v 200 m/phut th lc hau nh khong thay oi. Hien nay, xu hng cat vi van toc cat cao (v> 50 m/phut) nen coi quan he gia v va lc cat nh sau: v tang lc cat giam.

- Goc va goc tang lc cat giam ... - Moi loai vat lieu lam dao khac nhau co he so ma sat khac nhau nen lc cat cung

thay oi.

- Mat sau dao cang mon th dien tch tiep xuc gia dao va mat gia cong cang ln nen lc cat cang tang.

- Khi cat got co ti dung dch trn nguoi, nhiet cat giam, ma sat giam ... nen lc cat giam.

Tong hp cac nhan to anh hng tren vao cong thc tnh lc cat, ta co cong thc thc nghiem nh sau:

Pz = Cpz txpz sypz vnpz Kpz

Py = Cpy txpy sypy vnpy Kpy

Px = Cpx txpx sypx vnpx Kpx

Trong o: Cpz , Cpy , Cpx - Hang so phu thuoc nhom vat lieu gia cong.

xpz , ypz , npz - So mu ch mc o anh hng cua t, s, v en lc Pz.

xpy, ypy, npy - So mu ch mc o anh hng cua t, s, v en lc Py.

xpx, ypx, ypx - So mu ch mc o anh hng cua t, s, v en lc Px.

Kpz, Kpy, Kpx - Cac he so ieu chnh tnh en anh hng cua cac thong so con lai nh thong so hnh hoc cua dao (vat lieu dao, goc o dao ...).

Cac tr so tren c tra trong so tay cong nghe hoac so tay che o cat khi gia cong c.

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Ngoai ra tr so lc cat con co the tnh theo cac cong thc khac nh tnh theo lc cat n v (la tr so lc cat khi cat mot dien tch phoi 1 mm2 ) va dien tch lp cat hoac bang cach o trc tiep vi dung cu o lc cat.

e o lc cat, trong thc te thng dung cac loai lc ke khac nhau, cac lc ke nay eu da tren nguyen tac bien dang an hoi cua mot phan t lam viec chu tac dung cua lc cat. Phan t nay co the la xa an hoi lc ke c kh, co the la lo xo ong cac lc ke thuy lc, hay cac mang kim loai trong cac lc ke ien.

Theo nguyen ly tac dung co the chia lc ke ra lam 3 nhom: lc ke c kh, lc ke thuy lc va lc ke ien. Tuy vao yeu cau o va phng phap gia cong ma dung cac loai lc ke cho phu hp.

c) Cong suat cat

Cong suat tieu hao khi cat phu thuoc vao lc Pz va Px (Py khong sinh ra cong v theo phng Py khong co chuyen v).

Cong suat co ch khi cat c tnh theo cong thc :

)(

102.60. KWvPN zc =

Cong suat co ch khi chay dao :

)(102.10.60..

3 KWsnP

N xcd = Trong o:

Pz, Px: la cac lc cat thanh phan (KG).

n : la so vong quay cua chi tiet gia cong (vong/phut).

s : lng chay dao(mm/vong).

v : toc o cat ( m/phut).

1KW = 102 -1 KG.m/s

Cong suat cat toan phan c tnh nh sau:

CdCCtp NNN +=V thng NCd rat be nen khi tnh toan cong suat gan ung co the bo qua. Cong suat

can thiet cua ong c ien c xac nh:

)(KWN

N Cc =

Trong o: - hieu suat hu ch cua may ( = 0,7 0,75)

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2.4 La chon hnh dang mat trc va thong so hnh hoc hp ly cua dao Cac yeu to hnh hoc phan cat cua dao co anh hng rat ln en lc cat, toc o cat, o

mon dao, chat lng be mat gia cong.

Do o chon cac yeu to nay hp ly la ieu kien can thiet trc khi chon che o cat. Chon cac yeu to nay hp ly se tao kha nang a cao nang suat khi gia cong.

Tuy vao tng loai vat lieu dao, ieu kien cat, che o cat, vat lieu gia cong ma ta chon hnh dang hnh hoc hp ly cua dao khac nhau.

a) Chon dang mat trc cua dao

- oi vi dao thep gio

Dao lam bang thep co u iem la chu uon tot song chu nhiet va chu mai mon kem hn HKC . Thng co cac dang mat trc nh sau (hnh 2.36):

2.36

- Mat trc phang khong co canh vat (hnh 2.36 a): dung cho cac dao gia cong vat lieu don (gang, ong thanh), gia cong thep vi lng chay dao s < 0,2mm/vong.

- Mat trc phang co canh vat (hnh 2.36b): dung cho cac loai dao gia cong thep co o cng trung bnh (b = 700-900 N/mm2) vi s > 0,2 mm/vong. Canh vat f lam tang sc ben cua li cat; f = 0,2 1mm. Lng chay dao ln th chon f ln.

- Mat trc cong khong co canh vat (hnh 2.36c): dung cho cac loai dao gia cong thep co o cng thap va o deo cao (b < 700 N/mm2); vi s 0,2 mm/vong. Phoi de cuon va de t.

- Mat trc cong co canh vat (hnh 2.36d): Thng dung cho cac loai dao tien (tr dao tien nh hnh) gia cong thep co o cng trung bnh (b 700 900 N/mm2) vi s > 0,2 mm/vong. u iem chnh la cuon phoi, be phoi tot hn va lc cat giam.

- oi vi hp kim cng

Hp kim cng co ac iem la don, chu uon kem song chu mon va chu nhiet tot, thng c lam theo cac dang sau (hnh 2.37):

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2.37

=4

- Mat truc phang co canh vat am (hnh 2.37a): Dung cat thep co gii han ben b 800 N/mm2, cung co the dung cat gang xam va gang ren, goc trc cua canh vat thng lay v = 0 -5o, chieu rong f = (1 2) a, (a la chieu day cat).

- Mat trc cong co canh vat am (hnh 2.37b): Dung cat thep co b 800 N/nm2 vi t= 15nm, s = 0,3mm/vong, mat trc cong phoi de cuon va de gay.

- Mat truc phang co goc trc am kep (hnh 2.37c): Dung cat thep co b>800 N/nm2 khi lng d khong eu va phoi cng vng.

- Mat truc phang co goc trc am n (hnh 2.37d): Dung cat thep co b> 800 N/nm2 va toc o cat cao, nhng o cng vng cua he thong gia cong phai tot.

e tiet kiem a mai va giam thi gian mai cac dao tien co li cat bang hp kim cng thng tao them goc sau e thoat a khi mai.

b) Chon cac goc o dao hp ly

- Chon goc trc

Goc trc tang th bien dang va ma sat giam, song neu tang nhieu qua th