GIO TRNH:

C KH I CNG

1

CHNG 1

CC KHI NIM C BN V SN XUT C KH1.1. CC KHI NIM V QU TRNH SN XUT1.1.1. S QU TRNH SN XUT C KH K thut c kh l mn hc gii thiu mt cch khi qut qu trnh sn xut c kh v phng php cng ngh gia cng kim loi v hp kim ch to cc chi tit my hoc kt cu my. Qu trnh sn xut v ch to bao gm nhiu giai on khc nhau c tm tt nh sau:Ti nguyn thin nhin Qung, nhin liu, cht tr dung

Phi kim

Ch to vt liu

Luyn kim

Thp, gang, ng, nhm, hp kim

Ch to phi Ph phm v ph liu Gia cng ct gt Ph phm v ph liu X l v bo v

c, cn, rn dp, hn...

Tin, phay, bo, khoan, mi...

Nhit luyn, ho nhit luyn, m, sn...

Chi tit my

H.1.1.S qu trnh sn xut c kh

1.1.2. QU TRNH THIT K L qu trnh khi tho, tnh ton, thit k ra mt dng sn phm th hin trn bn v k thut, thuyt minh, tnh ton, cng trnh v.v... l qu trnh tch lu kinh nghim, s dng nhng thnh tu khoa hc k thut sng to ra nhng sn phm mi ngy cng hon thin. Bn thit k l c s thc hin qu trnh sn xut, l c s php l kim tra, o lng, thc hin cc hp ng. v.v...

GIO TRNH:

C KH I CNG

2

1.1.3. QU TRNH SN XUT: Qu trnh sn xut l qu trnh tc ng trc tip ca con ngi thng qua cng c sn xut nhm bin i ti nguyn thin nhin hoc bn thnh phm thnh sn phm c th p ng yu cu ca x hi. Qu trnh sn xut thng bao gm nhiu giai on. Mi giai on tng ng vi mt cng on, mt phn xng hay mt b phn....lm nhng nhim v chuyn mn khc nhau. Qu trnh sn xut c chia ra cc cng on nh, theo mt qu trnh cng ngh. 1.1.4. QUI TRNH CNG NGH QTCN l mt phn ca qu trnh sn xut nhm trc tip lm thay i trng thi ca i tng sn xut theo mt th t cht ch, bng mt cng ngh nht nh. V d: QTCN nhit luyn nhm lm thay i tnh cht vt l ca vt liu chi tit nh cng, bn.v.v...Cc thnh phn ca quy trnh cng ngh bao gm: a/ Nguyn cng: l mt phn ca qu trnh cng ngh do mt hoc mt nhm cng nhn thc hin lin tc ti mt ch lm vic gia cng chi tit (hay mt nhm chi tit cng gia cng mt ln). b/ Bc: l mt phn ca nguyn cng trc tip lm thay i trng thi hnh dng k thut ca sn phm bng mt hay mt tp hp dng c vi ch lm vic khng i. Khi thay i dng c, thay i b mt, thay i ch ...ta chuyn sang mt bc mi. c/ ng tc: l tp hp cc hot ng, thao tc ca cng nhn thc hin nhim v ca bc hoc nguyn cng. 1.1.5. DNG SN XUT Tu theo quy m sn xut, c trng v t chc, trang b k thut v quy trnh cng ngh m c cc dng sn xut sau: a/ Sn xut n chic: l dng sn xut m sn phm c sn xut ra vi s lng t v thng t lp li v khng theo mt quy lut no. Chng loi mt hng rt a dng, s lng mi loi rt t v th phn xng, nh my thng s dng cc dng c, thit b vn nng. y l dng sn xut thng dng trong sa cha, thay th... b/ Sn xut hng lot: l dng sn xut m sn phm c ch to theo l (lot) c lp i lp li thng xuyn sau mt khong thi gian nht nh vi s lng trong lot tng i nhiu (vi trm n hng nghn) nh sn phm ca my bm, ng c in.v.v...Tu theo khi lng, kch thc, mc phc tp v s lng m phn ra dng sn xut hng lot nh, va v ln. Trong sn xut hng lot cc dng c, thit b s dng l cc loi chuyn mn ho c km c loi vn nng hp. c/ Sn xut hng khi: hay sn xut ng lot l dng sn xut trong sn phm c sn xut lin tc trong mt thi gian di vi s lng rt ln. Dng sn xut ny rt d c kh ho v t ng ho nh x nghip sn xut ng h, xe my, t, xe p.v.v... 1.1.6. KHI NIM V SN PHM V PHI a/ Sn phm: l mt danh t quy c ch mt vt phm c to ra giai on cui cng ca mt qu trnh sn xut, ti mt c s sn xut. Sn phm c th l my mc hon chnh hay mt b phn, cm my, chi tit...dng lp rp hay thay th. b/ Chi tit my: l n v nh nht v hon chnh v mt k thut ca my nh bnh rng, trc c, bi v.v...

GIO TRNH:

C KH I CNG

3

c/ Phi: cn gi l bn thnh phm l danh t k thut c quy c ch vt phm c to ra t mt qu trnh sn xut ny chuyn sang mt qu trnh sn xut khc. V d: sn phm c c th l chi tit c (nu em dng ngay) c th l phi c nu n cn gia cng thm (ct gt, nhit luyn, rn dp...) trc khi dng. Cc phn xng ch to phi l c, rn, dp, hn, g, ct kim loi v.v.. 1.1.7. KHI NIM V C CU MY V B PHN MY a/ B phn my: y l mt phn ca my, bao gm 2 hay nhiu chi tit my c lin kt vi nhau theo nhng nguyn l my nht nh (lin kt ng hay lin kt c nh) nh hp tc , may xe p v.v... b/ C cu my: y l mt phn ca my hoc b phn my c nhin v nht nh trong my. V d: a, xch, lp ca xe p to thnh c cu chuyn ng xch trong xe p. 1.2. KHI NIM V CHT LNG B MT CA SN PHM Cht lng b mt ca cc chi tit my ng mt vi tr rt quan trng cho cc my mc thit b c kh nng lm vic chnh xc chu ti trng, tc cao, p lc ln, nhit .v.v... N c nh gi bi nhn b mt v tnh cht c l ca lp kim loi b mt. 1.2.1. NHN B MT (NHM) B mt chi tit sau khi gia cng khng bng phng mt cch l tng nh trn bn v m c nhp nh. Nhng nhp nh ny l do vt dao li, ca rung ng trong qu trnh ct.v.v... L bng b mt l nhp nh t vi ca lp y Rmax ng nh b mt (H.1.2) gm li lm, sng, bng y1 h3 h5 h1 h9 x h10 (nhm). nh gi nhp nh b mt sau khi gia 0 cng ngi ta dng hai ch tiu l Ra v Rz (m). h6 h4 yn h2 TCVN 2511- 95 cng nh ISO quy nh 14 ng y cp nhm c k hiu km theo cc tr s. H.1.2. nhm b mt chi tit - Ra l sai lch trung bnh s hc cc khong cch t nhng im ca profil o c n ng trung bnh ox o theo phng vung gc vi ng trung bnh ca nhp nh t vi trn chiu di chun L. Ta c th tnh:

1 1 1 n Ra = ydx Ra = ( y1 + y 2 + y 3 + ... + y n ) = y i . L0 n n i =1- Rz l chiu cao nhp nh t vi trn chiu di chun L vi gi tr trung bnh ca tng cc gi tr tuyt i ca chiu cao 5 nh cao nht h1, h3, h5, h7, h9 v chiu su ca 5 y thp nht h2, h4, h6, h8, h10 ca profin trong khong chiu di chun.5 T cp 6 12, ch yu dng Ra, cn i vi cc cp 1 5 v 13 14 dng Rz. khi ghi trn bn v bng c th hin nh H.1.3. Trong thc t sn xut, tu theo cc phng php gia cng khc nhau ta c cc cp bng khc nhau. V d: Rz =

L

(h

1

+ h2 + L + h9 ) ( h2 + h4 + L + h102,5a/

)

.Rz20b/ H.1.3. K hiu bng

a/ K hiu bng theo Ra b/ K hiu bng theo RZ

GIO TRNH:

C KH I CNG

4

B mt rt th, th t cp 1 3 (Rz = 320 40): c, rn Gia cng na tinh v tinh t cp 46 (Rz = 4010, Ra = 2,5): tin, phay, khoan. Gia cng tinh t cp 6 8 (Ra = 2,5 0,32): khot, doa, mi.

Cc gi tr thng s nhm b mt (TCVN 2511 - 78) Cp nhm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Tr s nhm (m) Ra Rz 2,5-1,25 1,25-0,63 0,63-0,32 0,32-0,16 0,16-0,08 0,08-0,04 0,04-0,02 320 - 160 160 - 80 80 - 40 40 - 20 20 - 10 0,1 - 0,05 0,05 - 0,025 Chiu di chun L(mm) 8 8 8 2,5 2,5 2,5 0,8 0,8 0,8 0,25 0,25 0,25 0,08 0,08 Phng php gia cng Tin th, ca, da, khoan ... Tin tinh, da tinh, phay... Doa, mi, nh bng v.v... Mi tinh mng, nghin, r, gia cng c bit, ph. php khc Cc b mt khng tip xc, khng quan trng: gi , chn my v.v... B mt tip xc tnh, ng, trc vt, b. rng ... B mt tip xc ng: mt rng, mt pittng, xi lanh, cht v.v... B mt mt, van, bi, con ln, dng c o, cn mu v.v... B mt lm vic chi tit chnh xc, dng c o ng dng

1.2.2. TNH CHT C L CA LP B MT SN PHM Tnh cht c l ca lp b mt gm cu trc t vi b mt, cng t vi, tr s v du ca ng sut d b mt. Chng nh hng nhiu n tui th ca chi tit my. Cu trc t vi v tnh cht c l ca lp b mt chi tit sau gia cng c gii thiu trn H.1.4: a/ Mt ngoi b ph hu (1) do chu lc p v ma st khi ct gt, nhit tng cao. Ngoi cng l mng kh hp th dy khong 23 ngstron (1 = 10-8cm), n hnh thnh khi tip xc vi khng kh v mt i khi b nung nng. Sau l lp b xy ho dy khong (40 80). b/ Lp cng ngui (2) l lp kim loi b bin dng do c chiu dy khong 50.000, vi cng cao thay i gim dn t ngoi vo, lm tnh cht c l thay i. Kim loi c bn t vng (3) tr vo.1 2 3 HB 1- Mt ngoi b ph hu 2- Lp cng ngui 3- Kim loi c bn h- Chiu su kim loi HB- cng

h H.1.4. Tnh cht c l lp b mt

1.3. KHI NIM V CHNH XC GIA CNG C KH

GIO TRNH:

C KH I CNG

5

1.3.1. KHI NIM V CHNH XC GIA CNG chnh xc gia cng ca chi tit my l c tnh quan trng ca ngnh c kh nhm p ng yu cu ca my mc thit b cn c kh nng lm vic chnh xc chu ti trng, tc cao, p lc ln, nhit v.v... chnh xc gia cng l mc chnh xc t c khi gia cng so vi yu cu thit k. Trong thc t chnh xc gia cng c biu th bng cc sai s v kch thc, sai lch v hnh dng hnh hc, sai lch v v tr tng i gia cc yu t hnh hc ca chi tit c biu th bng dung sai. chnh xc gia cng cn phn no c th hin hnh dng hnh hc lp t vi b mt. l bng hay nhn b mt, cn gi l nhm. 1.3.2. DUNG SAI a/ Khi nim: Khi ch to mt sn phm, khng th thc hin kch thc, hnh dng, v tr chnh xc mt cch tuyt i c sn phm ging ht nh mong mun v ging nhau hng lot, v vic gia cng ph thuc vo nhiu yu t khch quan nh chnh xc ca dng c, thit b gia cng, dng c o, trnh tay ngh ca cng nhn v.v...Do mi sn phm khi thit k cn tnh n mt sai s cho php sao cho m bo tt cc yu cu k thut, chc nng lm vic v gi thnh hp l. Dung sai c trng cho chnh xc yu cu ca kch thc hay cn gi l chnh xc thit k v c ghi km vi kch thc danh ngha trn bn v k thut. Tr s dung sai kch thc (IT- m) D (d) >3 >6 > 10 Cp 3 chnh xc 6 10 18 4 6 8 8 5 6 8 9 11 6 10 12 15 18 7 14 18 22 27 8 25 30 36 43 9 40 48 58 70 10 60 75 90 110 11 100 120 150 180 12 > 18 30 9 13 21 33 52 84 130 210 > 30 50 11 16 25 39 62 100 160 250 > 50 80 13 19 30 46 74 120 190 300 > 80 120 15 22 35 54 87 140 220 350 > 120 180 18 25 40 63 100 160 250 400 >180 250 20 29 46 72 115 185 290 460

D (d) - Kch thc danh ngha ca chi tit. b/ Dung sai kch thc: Dung sai kch thc l sai s cho php gia kch thc t c sau khi gia cng v kch thc danh ngha. l hiu gia kch thc gii hn ln nht v nh nht hoc hiu i s gia sai lch trn v sai lch di. Theo TCVN 2244 - 99 cng nh ISO k hiu ch in hoa dng cho l, k hiu ch thng dng cho trc. Trong : D (d): Kch thc danh ngha, s dng theo kch thc trong dy u tin ca TCVN 192 - 66.

GIO TRNH:

C KH I CNG

6

E EI Dmin Dmax D

es ei dmin dmax d

ITl

ITt

a/ Dung sai kch thc l

b/ Dung sai kch thc trc

H.1.5. Dung sai kch thc trc v l

- Dmax, dmax: kch thc gii hn ln nht. - Dmin, dmin: kch thc gii hn nh nht. - ES = Dmax - D, es = dmax - d : sai lch trn. - EI = Dmin - D, ei = dmin - d : sai lch di. - ITl = Dmax - Dmin = D = ES - EJ : khong dung sai ca l. - ITt = dmax - dmin = d = es - ei : khong dung sai ca trc. Dung sai lp ghp l tng dung sai ca l v trc. c/ Min dung sai L l tn gi c dng k hiu cc b mt tr trong cc chi tit. Theo ISO v TCVN min dung sai ca l c k hiu bng mt ch in hoa A, B, C..., ZA, ZB, ZC (k hiu sai lch c bn) v mt s (k hiu cp chnh xc), trong c l c s c sai lch c bn H vi EI = 0 (Dmin= D), cp chnh xc JS c cc sai lch i xng ( ES = EI ). Trc l tn gi c dng k hiu cc b mt tr ngoi b bao ca chi tit. Min dung sai ca trc c k hiu bng ch thng a, b, c..., za, zb, zc; trong trc c bn c cp chnh xc h vi ei = 0 (dmax= d), cp chnh xc js c cc sai lch i xng ( es = ei ). Tri s

Min dung sai trc f fg g h d e ef j km zb y z za p r s t u v x

zc

Kch thc danh ngha

c b a

cd

A + Sai lch B C C DE Min dung sai l K MN P R S T U V X Y Z ZA ZB ZC J JS

H.1.6. V tr cc min dung sai ca Trc v L dung sai v sai lch c bn xc nh min dung sai. Mi kch thc c ghi gm 2 phn: kch thc danh ngha v min dung sai. Trn bn v ch to ghi kch thc danh ngha v gi tr cc sai lch. V d: trn bn thit k ghi 20H7,

40g6 cn trn bn v ch to ghi kch thc tng ng (tra bng): 20+0,021, 40 0,,009 ... 0 025 d/ Sai s hnh dng v v tr: Sai s hnh dng hnh hc l nhng sai lch v hnh dng hnh hc ca sn phm thc so vi hnh dng hnh hc khi thit k nh thng, phng, cn...

Kch thc danh ngha

EF F FG G H

GIO TRNH:

C KH I CNG

7

Sai s hnh dng hnh hc TT Tn gi 1 Dung sai thng 2 Dung sai phng 3 Dung sai trn 4 Dung sai tr K hiu

Sai s v tr tng i cc b mt TT 1 2 3 4 5 6 7 Tn gi Dung sai song song Dung sai vung gc Dung sai ng tm Dung sai i xng Dung sai giao nhau D. sai o mt u D. sai o hng knh K hiu

Sai lch v tr tng i l s sai lch v tr thc ca phn t c kho st so vi v tr danh ngha nh khng song song, khng vung gc, khng ng tm, o v.v...Cc k hiu v v d cch ghi cc sai lch ny trn bng trn. / Cp chnh xc: Cp chnh xc c qui nh theo tr s t nh n ln theo mc chnh xc kch thc. TCVN v ISO chia ra 20 cp chnh xc nh s theo th t chnh xc gim dn l 01, 0, 1, 2, ...15, 16, 17, 18. Trong : - Cp 01 cp 1 l cc cp siu chnh xc. - Cp 1 cp 5 l cc cp chnh xc cao, cho cc chi tit chnh xc, dng c o. - Cp 6 cp 11 l cc cp chnh xc thng, p dng cho cc mi lp ghp. - Cp 12 cp 18 l cc cp chnh xc thp, dng cho cc kch thc t do (khng lp ghp). 1.3.3. LP GHP V PHNG PHP LP GHP a/ H thng lp ghp - H thng l: l h thng lp ghp ly l lm chun, ta chn trc c cc kiu lp khc nhau; min dung sai k hiu bng ch in hoa; ti min dung sai l c bn H c ES > 0, cn EI = 0. H thng l thng c s dng nhiu hn h thng trc. - H thng trc: l h thng lp ghp ly trc lm chun, ta chn l c cc kiu lp khc nhau; min dung sai k hiu bng ch thng; min dung sai trc c bn h c es = 0, cn ei < 0. b/ Phng php lp ghp - Lp lng: l phng php lp ghp m kch thc trc lun lun nh hn kch thc ca l, gia 2 chi tit lp ghp c h, chng c th chuyn ng tng i vi nhau nn dng cc mi lp ghp c truyn chuyn ng quay hay trt. Dng lp ghp ny, theo TCVN l c min dung sai A, B, ...G, H hoc cc trc c min dung sai a, b, ...g, h. - Lp cht: l phng php lp ghp m kch thc trc lun lun ln hn kch thc l. Khi lp ghp gia 2 chi tit c di nn cn c lc p cht hoc gia cng nhit cho l (hoc trc), thng dng cho cc mi lp ghp c truyn lc. Dng lp ghp ny, theo TCVN l c min dung sai P, R, ..., ZC hoc cc trc c min dung sai p, r, ..., zc.

GIO TRNH:

C KH I CNG

8

- Lp trung gian: l loi lp ghp m tu theo kch thc ca l v kch thc trc mi lp c th c h hoc di. Gia 2 chi tit lp ghp c th c h rt nh hoc di rt nh. Khi lp c th p nh c mi lp. Dng lp ghp ny, theo TCVN l c min dung sai JS, K, M, N hoc cc trc c min dung sai js, k, m, n. 1.3.4. PHNG PHP O V DNG C O

25

H7 e8b/

+ 0,021 25 + 0,028 + 0,015

a/

H.1.7. S v cch ghi k hiu lp ghp a/ Cch ghi k hiu trn bn v thit k b/ Cch ghi k hiu trn bn v lp

a/ Phng php o: tu theo nguyn l lm vic ca dng c o, cch xc nh gi tr o, ta c cc phng php o sau: - o trc tip: l phng php o m gi tr ca i lng o c xc nh trc tip theo ch s hoc s o trn dng c o: o trc tip tuyt i dng o trc tip kch thc cn o v gi tr o c nhn trc tip trn vch ch th ca dng c. o trc tip so snh dng xc nh tr s sai lch ca kch thc so vi mu chun. Gi tr sai s c xc nh bng php cng i s kch thc mu chun vi tr s sai lch . - o gin tip: dng xc nh kch thc gin tip qua cc kt qu o cc i lng c lin quan n i lng o. - o phn tch (tng phn): dng xc nh cc thng s ca chi tit mt cch ring bit, khng ph thuc vo nhau. b/ Dng c o: Cc loi dng c o thng gp l cc loi thc: thc thng, thc cun, thc dy, thc l, thc cp, thc o gc, compa, panme, ng h so, calp, cn mu...Cc loi thit b o tin tin thng dng nh: u o kh nn, u o bng siu m hoc laze, thit b quang hc, thit b o bng in hoc in t v.v... - Thc l: c vch chia n 0,5 hoc 1mm c chnh xc thp khong 0,5mm. - Thc cp: l dng c o vn nng o cc kch thc c gii hn v ngn nh chiu di, chiu su, khong cch, ng knh l v.v... vi chnh xc khong (0,020,05)mm. - Panme: thng dng o ng knh ngoi, l, rnh...vi chnh xc cao, c th t (0,0050,01)mm. Panme ch o c kch thc gii hn. V d panme ghi 0 - 25 ch o c kch thc 25mm. - Calp - cn mu: l loi dng c kim tra dng trong sn xut hng lot, hng khi kim tra kch thc gii hn cc sn phm t yu cu hay khng. - ng h so: c chnh xc n 0,01mm, dng kim tra sai s o so vi kch thc chun bng bn r, bn g chun nn c th kim tra c nhiu dng b mt. Dng ng h so c th xc nh c khng song song, khng vung gc, ng tm, trn, phng, thng, o v.v... - Dng: ch dng kim tra mt kch thc hoc hnh dng.

GIO TRNH:

C KH I CNG

9

CHNG 2

VT LIU DNG TRONG C KH2.1. TNH CHT CHUNG CA KIM LOI V HP KIMKim loi v hp kim c s dng rng ri trong cng nghip ch to cc chi tit my. Mi loi chi tit my phi c nhng tnh nng k thut khc nhau ph hp vi iu kin lm vic. Mun vy phi nm c cc tnh cht c bn ca chng sau y: 2.1.1. C TNH C tnh l c trng c hc biu th kh nng ca kim loi hay hp kim khi chu tc dng ca cc ti trng. Chng c trng bi: a/ bn: l kh nng ca vt liu chu tc dng ca ngoi lc m khng b ph hu. bn c k hiu . Tu theo cc dng khc nhau ca ngoi lc ta c cc loi bn: bn ko (k); bn un (u); bn nn (n). Gi tr bn ko tnh theo cng thc : F0 P P(N) P(N) (N/mm2). k = F0H.2.1.S mu o bn

Ti thi im khi P t n gi tr no lm cho thanh kim loi c F0 b t s ng vi gii hn bn ko ca vt liu . Tng t ta s c gii hn bn un v bn nn. b/ cng: l kh nng chng ln ca vt liu khi chu tc dng ca ngoi lc. Nu cng mt gi tr lc nn, lm bin dng trn mu o cng ln, cng su th cng ca mu o cng km. cng c o bng cch dng ti trng n vin bi bng thp cng hoc mi cn kim cng hoc mi chp kim cng ln b mt ca vt liu mun th, ng thi xc nh kch thc vt lm in trn b mt vt liu o. C cc loi cng Brinen; cng Rcoen; cng Vicke. - cng Brinen: dng ti trng P (i vi thp v gang P = 30D2) n vin bi bng thp nhit luyn, c ng knh D (D = 10; 5; 0,25 mm) ln b mt vt liu mun th (H.2.2.a). cng Brinen c tnh theo cng thc: P (kG/mm2). y, F - din tch mt cu ca vt lm (mm2). HB = F cng Brinen dng o vt liu c cng thp (< 4500 N/mm2)D P P P

h a/

d b/

d d c/

H.2.2. S th nghim o cng

- cng Rcoen: (H.2.2.b) c xc nh bng cch dng ti trng P n vin bi bng thp nhit luyn, c ng knh D = 1,587 mm tc l 1/16 (thang B) hoc mi cn bng kim cng c gc nh 1200 (thang C hoc A) ln b mt vt liu th. Trong khi th, s cng c ch trc tip ngay bng kim ng h. cng Rcoen c k hiu HRB khi dng bi thp

GIO TRNH:

C KH I CNG

10

th vt liu t cng; HRC v HRA khi dng mi cn kim cng th vt liu c cng cao (>4500 N/mm2). Chn thang o cng Brinen - Rcoen cng Thang o Mi th Ti trng Brinen Rcoen chnh P (N) HB (mu) B () Vin bi thp 1000 60230 C (en) Vin bi thp 1500 230700 A (en) Mi kim cng 600 > 700 K hiu Gii hn cho php cng Rcoen thang Rcoen HRB HRC HRA 25100 2067 > 70

- cng Vicke (HV) dng mi o 1 (hnh chp gc vt = 1360) bng kim cng (H.2.2.c) dng o cho vt liu mm, vt liu cng v vt liu c cng nh lp mng ca b mt c thm than, thm nit.v.v... P HV = 1,8544 2 . Trong d - ng cho ca vt lm (mm); P- ti trng (kg). d c/ Tnh do: l kh nng bin dng vnh cu ca kim loi v hp kim khi chu tc dng ca ngoi lc. Khi th mu n c th hin qua dn di tng i (%) l t l tnh theo phn trm gia lng dn di sau khi ko v chiu di ban u: l l = 1 0 * 100% . Trong l1 v l2 - di mu trc v sau khi ko (mm). Vt l0 liu c (%) cng ln th cng do v ngc li. d/ dai va chm (ak): C nhng chi tit my lm vic thng chu cc ti trng tc dng t ngt (ti trng va p). Kh nng chu ng cc ti trng m khng b ph hu ca vt liu gi l dai va chm. A (J/mm2). Trong : A - cng sinh ra khi va p lm gy mu (J); F - din ak = F tch tit din mu (mm2). 2.1.2. L TNH L tnh l nhng tnh cht ca kim loi th hin qua cc hin tng vt l khi thnh phn ho hc ca kim loi khng b thay i. N c c trng bi: khi lng ring, nhit nng chy, tnh dn n, tnh dn nhit, tnh dn in v t tnh... 2.1.3. HO TNH Ho tnh l bn ca kim loi i vi nhng tc dng ho hc ca cc cht khc nh xy, nc, axt v.v... m khng b ph hu. a/ Tnh chu n mn: l bn ca kim loi i vi s n mn cc mi trng xung quanh. b/ Tnh chu nhit: l bn ca kim loi i vi s n mn ca xy trong khng kh nhit cao. c/ Tnh chu axt: l bn ca kim loi i vi s n mn ca axt.

GIO TRNH:

C KH I CNG

11

2.1.4. TNH CNG NGH Tnh cng ngh l kh nng ca kim loi v hp kim cho php gia cng theo phng php no l hp l. Chng c c trng bi: a/ Tnh c: c c trng bi chy long, co, ho tan kh v tnh thin tch. chy long cng cao th cng d c; co, ho tan kh v tnh thin tch cng ln th kh c. b/ Tnh rn: l kh nng bin dng vnh cu ca kim loi khi chu tc dng ca ngoi lc to thnh hnh dng ca chi tit m khng b ph hu. Thp d rn v c tnh do cao, gang khng rn c v dn; ng, ch rt d rn. c/ Tnh hn: l kh nng to s lin kt gia cc chi tit hn. Thp d hn, gang, nhm, ng kh hn.

2.2. THP2.2.1. THP CCBONA/ KHI NIM CHUNG V THP CCBON

Thp ccbon l hp cht ca Fe-C vi hm lng ccbon nh hn 2,14%. Ngoi ra trong thp ccbon cn cha mt lng tp cht nh Si, Mn, S, P ...Cng vi s tng hm lng ccbon, cng v bn tng ln cn do v dai li gim xung. Si, Mn l nhng tp cht c li cn S v P th c hi v gy nn dn nng v dn ngui nn cn hn ch < 0,03%. Thp ccbon c c tnh tng hp khng cao, ch dng trong xy dng, ch to cc chi tit chu ti trng nh v va trong iu kin p sut v nhit thp.B/ PHN LOI THP CCBON

a/ Phn loi theo hm lng ccbon - Thp ccbon thp C < 0,25%. - Thp ccbon trung bnh C = 0,250,5%. - Thp ccbon cao C > 0,50%. b/ Phn loi theo cng dng - Thp ccbon cht lng thng: loi ny c tnh khng cao, ch dng ch to cc chi tit my, cc kt cu chu ti trng nh. Thng dng trong ngnh xy dng, giao thng. Nhm thp thng dng ny hin chim ti 80% khi lng thp dng trong thc t, thng c cung cp dng qua cn nng (tm, thanh, dy, ng, thp hnh: ch U, I, thp gc, ...). Nhm thp ny c cc mc thp sau: Mc thp LXCT0 CT1 CT2 CT3 CT4 CT5 CT6

Mc thp VNCT31 CT33 CT34 CT38 CT42 CT51 CT61

k (kG/mm2) 31 3242 3444 3849 4254 5064 60

0,2 (kG/mm2)20 21 24 26 30

(%)20 31 29 23 21 17 12

Theo TCVN 1765-75 nhm thp ny c k hiu bng ch CT vi con s tip theo ch gii hn bn ko ti thiu.

GIO TRNH:

C KH I CNG

12

- Thp ccbon kt cu: l loi thp c hm lng tp cht S, P rt nh, c th: S 0,04%, P 0,035%, tnh nng l ho tt thun tin, hm lng ccbon chnh xc v ch tiu c tnh r rng. Theo TCVN 1766-75, nhm thp ny c k hiu bng ch C vi con s ch lng ccbon trung bnh theo phn vn. V d: thp C40 l thp ccbon kt cu vi lng ccbon trung bnh l 0,40%. Thp ccbon kt cu dng ch to cc chi tit my chu lc cao nh cc loi trc, bnh rng, l xo v.v... Loi ny thng c cung cp di dng bn thnh phm vi cc mc thp sau: C08, C10, C15, C20, C30, C35, C40, C45, C50, C55, C60 C65, C70, C80, C85. - Thp ccbon dng c: l loi thp c hm lng ccbon cao (0,701,3%), c hm lng tp cht P v S thp (< 0,025%). Thp ccbon dng c tuy c cng cao sau khi nhit luyn nhng chu nhit thp nn ch dng lamf cc dng c nh c, da hay cc loi khun dp, cc chi tit cn cng cao. Theo TCVN 1822-76, nhm thp ny c k hiu bng ch CD vi con s ch lng ccbon trung bnh theo phn vn. V d: CD70 l thp ccbon dng c vi 0,70% C. Loi thp ny gm cc mc thp: CD70, CD80, CD90, ...CD130 tng ng vi thp Lin x l: Y7, Y8, Y9, ...Y13. - Thp ccbon c cng dng ring: Thp ng ray cn c bn v kh nng chu mi mn cao l loi thp ccbon cht lng cao c hm lng C v Mn cao (0,500,8% C, 0,61,0% Mn). Ray hng c th dng ch to cc chi tit v dng c nh c, dao, nhp, dng c gia cng g,...Dy thp cc loi: dy thp ccbon cao v c bin dng ln khi ko ngui (d = 0,1 mm), gii hn bn ko c th t n 400450 kG/mm2. Dy thp ccbon thp thng c m km hoc thic dng lm dy in thoi v trong sinh hot. Dy thp c thnh phn 0,50,7% C dng cun thnh cc l xo trn. Trong k thut cn dng cc loi dy cp c bn cao c bn t cc si dy thp nh. Thp l dp ngui: c hm lng ccbon v Si nh (0,050,2% C v 0,070,17% Si). tng kh nng chng n mn trong kh quyn, cc tm thp l mng c th ng trng Sn (gi l st ty) hoc trng Zn (gi l tn trng km). 2.2.2.THP HP KIMA/ KHI NIM V THP HP KIM

Thp hp kim l loi thp m ngoi st, ccbon v cc tp cht ra, ngi ta cn c a vo cc nguyn t c bit vi mt lng nht nh lm thay i t chc v tnh cht ca thp hp vi yu cu s dng. Cc nguyn t a vo gi l nguyn t hp kim thng gp l: Cr, Ni, Mn, Si, W, V, Mo, Ti, Nb, Cu,...vi hm lng nh sau: Mn: 0,8 - 1,0%; Si: 0,5 - 0,8%; Cr: 0,2 - 0,8%; Ni: 0,2 - 0,6%; W: 0,1 - 0,6%; Mo: 0,05 - 0,2; Ti, V, Nb, Cu > 0,1%; B > 0,002%. Trong thp hp kim, lng cha cc tp cht c hi nh S, P v cc kh xy, hyr, nit l rt thp so vi thp ccbon. V c tnh thp hp kim c bn cao hn hn so vi thp ccbon dc bit l sau khi nhit luyn. V tnh chu nhit: Thp hp kim gi c cng cao v tnh chng do ti 6000C (trong khi thp ccbon ch n 2000C), tnh chng xy ho ti 800-10000C. V cc tnh cht vt l v ho hc c bit: thp ccbon b g trong khng kh, b n mn mnh trong cc mi trng axit, baz v mui,...Nh hp kim ho m c th to ra thp khng g, thp c tnh gin n v n hi c bit, thp c t tnh cao v thp khng c t tnh, ...

GIO TRNH:

C KH I CNG

13

B/ PHN LOI THP HP KIM

a/ Thp hp kim kt cu: Trn c s l thp ccbon kt cu cho thm cc nguyn t hp kim. Thp hp kim kt cu c hm lng ccbon khong 0,10,85% v lng phn trm nguyn t hp kim thp. Thp ny phi qua thm than ri nhit luyn c tnh mi cao. Loi thp ny c dng ch to cc chi tit chu ti trng cao, cn cng, chu mi mn, hoc cn tnh n hi cao v.v...Cc mc thp hp kim kt cu thng gp: 15Cr, 20Cr, 40Cr, 20CrNi, 12Cr2Ni4, 35CrMnSi; cc loi c hm lng ccbon cao dng lm thp l xo nh 50Si2, 60Si2CrA v.v... K hiu mc thp biu th ch s u l hm lng ccbon tnh theo phn vn, cc ch s t sau nguyn t hp kim l hm lng ca nguyn t , ch A l loi tt. V d: thp 12Cr2Ni4A trong c 0,12% C, 2% Cr, 4% Ni v l thp tt. b/ Thp hp kim dng c: L loi thp dng ch to cc loi dng c gia cng kim loi v cc loi vt liu khc nh g, cht do v.v...Thp hp kim dng c cn cng cao sau khi nhit luyn, chu nhit v chu mi mn cao. Hm lng ccbon trong thp hp kim dng c cao t 0,71,4%; cc nguyn t hp kim cho vo l Cr, W, Si v Mn. Thp hp kim dng c sau khi nhit luyn c cng t 6062 HRC. C mt s mc thp chuyn dng nh sau: - Thp dao ct: dng ch to cc loi dao ct nh dao tin, dao bo, dao phay, mi khoan v.v...nh 90CrSi, 140CrW5, 100CrWMn, hoc mt s thp gi nh 80W18Cr4VMo, 90W9V2, 75W18V cc loi thp gi c cng cao, bn, chu mi mn v chu nhit n 6500C. - Thp lm khun dp: i vi khun dp ngui thng dng 100CrWMn, 160Cr12Mo, 40CrSi. i vi khun dp nng hay dng cc mc thp: 50CrNiMo, 30Cr2W8V, 40Cr5W2VSi. - Thp ln: l loi thp dng ch to cc loi bi hay a l loi thp chuyn dng nh OL100Cr2, OL100Cr2SiMn. Cc ln lm vic trong mi trng nc bin phi dng thp khng g nh 90Cr18 v lm vic trong iu kin nhit cao phi dng thp gi loi 90W9Cr4V2Mo. Cc k hiu ca thp hp kim dng c cng c biu th nh cc loi thp hp kim khc tr thp ln l c thm ch OL ban u. c/ Thp hp kim c bit: Trong cng nghip cn thit phi c nhng loi thp c bit p ng yu cu ca cng vic. C cc loi thp: - Thp khng g: l loi thp c kh nng chng li mi trng n mn. Thng dng cc mc thp: 12Cr13, 20Cr13, 30Cr13, 12Cr18Ni9, 12Cr18Ni9Ti,... - Thp bn nng: l loi thp lm vic nhit cao m bn khng gim, khng b xy ho b mt. V d 12CrMo, 04Cr9Si2 chu c nhit 3005000C; loi bn nng 10Cr18Ni12, 04Cr14Ni14W2Mo chu c nhit 5007000C; hoc l thp NiCrm chuyn ch to dy in tr 10Cr150Ni60. - Thp t tnh: l loi thp c nhim t cao. Thp hp kim t cng thng dng cc thp Cr, Cr-W, Cr-Co hoc dng hp kim h Fe-Ni-Al, Fe-Ni-Al-Co ch to cc loi nam chm vnh cu bng phng php c v qua mt qu trnh nhit luyn c bit trong t trng. Thp v hp kim t mm c lc kh t nh t thm ln dng lm li my bin p, stato my in, nam chm in cc loi,...Thng dng: st ty nguyn cht k thut ( 10mm) nn cn gi l dp ngui. Vt liu dng trong dp tm: Thp ccbon, thp hp kim mm, ng v hp kim ng, nhm v hp kim nhm, niken, thic, ch vv...v vt liu phi kim nh: giy cctng, bnt, fp, aming, da, vv... b/ c im: Nng sut lao ng cao do d t ng ho v c kh ho. Chuyn ng ca thit b n gin, cng nhn khng cn trnh cao, m bo chnh xc cao. C th dp c nhng chi tit phc tp v p, c bn cao..v.v... c/ Cng dng: Dp tm c dng rng ri trong cc ngnh cng nghip c bit ngnh ch to my bay, nng nghip, t, thit b in, dn dng v.v... 4.7.2. CNG NGH DP TM Cng ngh dp tm c c trng bi 2 nhm nguyn cng chnh: nguyn cng ct v nguyn cng to hnh.A/ NHM NGUYN CNG CT

Ct phi l nguyn cng tch mt phn ca phi khi phn kim loi chung. Nguyn cng ny c 3 loi: ct t, ct phi, t l. a/ Ct t: L nguyn cng ct phi thnh tng ming theo ng ct h, dng ct thnh tng di c chiu rng cn thit, ct thnh ming nh t nhng phi thp tm ln. C cc loi my ct t sau: My ct li dao song song: - Gc trc =230 + + + + - Ct c cc tm rng B 3200 mm, B S chiu dy S n 60 mm. - Ch ct c ng thng, chiu rng H.4.23.My ct li dao song song tm ct phi nh hn chiu di dao. - ng ct thng, p, hnh trnh dao nh; Lc ct tng i ln: P = 1,3.B.S. c (N). B - chiu rng ct ca phi (mm); S - chiu dy phi ct (mm). c - Gii hn bn ct ca phi c = (0,60,8)b (N/mm2). My ct dao nghing: + + + + - Li dao di nm ngang, li dao trn nghing mt gc = 260. S - Gc ct = 75850; gc sau = 230. - h gia 2 dao Z = 0,05 0,2mm Z H.4.24.My ct li dao nghing - Lc ct khng ln, ct c cc tm dy; Ct c cc ng cong; ng ct khng thng v nhn. Hnh trnh ca dao ln:

GIO TRNH:

C KH I CNG

41

0,5. S 2 . c P = 1,3 tg

(N)

My ct chn ng: My c 2 li dao nghing to thnh mt gc = 24300; gc trc = 670, khi ct li ct trn ln xung rt nhanh (20003000 ln/pht) v vi hnh trnh ngn 23 mm. Ct c tm c S 10 mm. My ct dao a mt cp dao:D S h B a/ Dao a c tm trc song song B D S

H.4.25. My ct chn ngD h B Z

b/ My ct dao di nghing

c/ Hai dao nghing

H.5.26. My ct dao a mt cp daoB My ct nhiu dao a. - Li ct l 2 a trn quay ngc chiu nhau; my D c th c hai hoc nhiu cp a ct. - Gc ct 900; Z = (0,1 0,2)S - ng knh dao a: D =(40 125)S (mm). - Chiu dy dao: B = 15 30 (mm) Z - Vn tc ct: v = 1 5 m/s H.5.26. My ct dao a mt cp dao - Vt liu lm dao: 5XBC My ny dng ct cc ng thng v ng cong chiu di tu mng < 10 mm.

b/ Dp ct v t l: y l nguyn cng ct m ng ct l mt chu vi kn. V nguyn l dp ct v t l ging nhau ch khc nhau v cng dng. t l l qu trnh to nn l rng trn phi, phn vt liu tch khi phi gi l ph liu, phn cn li l phi i qua nguyn cng to hnh. i vi dp ct th phn ct ri l phi phn cn li l Cc loi u chy ph liu. Mt s thng s k thut cn lu : - Chy v ci phi c cnh sc to thnh li ct, gia chy v ci c khong h Z = (5% 10%)S. - Khi t mun c kch thc l t cho th kch thc ca P z chy chn bng kch thc ca l, cn kch thc ca ci ln hn 2Z. Chy vt lm pha trong to thnh rnh ct. - Khi ct phi c kch thc cho th kch thc ca ci bng kch thc ca phi cn ca chy nh thua 2Z. H.4.27. S dp ct v t l - Lc ct hoc t P

GIO TRNH:

C KH I CNG

42

+ Khi ng ct trn: P = 1,25.d.s.cp (N); + Khi ng ct bt k: P = 1,25L.s.cp (N). s - chiu dy phi (mm); d - ng knh phi hoc l t (mm). L - chu vi ng ct (mm); cp- gii hn bn ct (N/mm2). B/ NHM NGUYN CNG TO HNH L nhng nguyn cng dch chuyn mt phn ca phi i vi phn khc m phi khng b ph hu. Chy a/ Nguyn cng un: L nguyn cng lm thay i Lp trung ho hng ca trc phi. Trong qu trnh un cong lp kim loi S pha trn b nn, lp kim loi pha ngoi b ko, lp kim loi r gia khng b ko nn gi l lp trung ho. Khi bn knh x.S un cong cng b th mc nn v ko cng ln c th lm Ci cho vt un cong b nt n. Lc ny lp trung ho c xu hng dch v pha un cong. V tr v kch thc lp trung ho c xc nh bi bn knh lp trung ho: H.4.28. Nguyn cng un r = + . . S . (r - bn knh un trong; S - chiu dy phi (mm); - bn knh lp trung ho) S 2 b/ Nguyn cng dp vut: Dp vut l nguyn cng ch to cc chi tit rng c hnh dng bt k t phi phng v c tin hnh trn cc khun dp vut. Khi dp vut c th lm mng thnh hoc khng lm mng thnh. - Dp vut khng lm mng thnh + Chn hnh dng v kch thc phi: Nu chi tit l hnh hp y ch nht th phi c dng hnh bu dc hay elp, cn nu chi tit l hnh hp y vung hoc hnh tr y trn th phi l ming ct trn. Nu S < 0,5 mm th din tch phi bng din tch mt trong hoc din tch mt ngoi ca chi tit, cn nu S > 0,5mm th ly bng din tch lp trung ho ca chi tit (k c y). + Xc nh s ln dp vut: Khi dp vut tu theo tnh do dct ca vt liu mi ln dp cho php dp thnh chi tit c ng d3 knh nht nh. H s dp cho php c tnh nh sau: d2 d ct d m= = 0,550,95 ; Nh vy: m1 = 1 d1 = m1.D; D ph D d1 tng t ta c: d2 = m2.d1 = m1.m2.D; dn = m1.m2.m3...mn.D. Ly gi tr trung bnh: mtb = n1 m2 . m3 ...mn S ln dp n ca phi c dng knh D thnh chi tit c lg d n lg(m1 . D) ng knh dn: n = 1 + lg mtb + Qu trnh dp vut: Nhng chi tit c phi l tm dy th tin hnh trn khun khng cn vnh p, nhng nu phi l tm mng s xy ra hin tng nhn xp thnh sn phm nn dng thm vnh p.D

1 Q 4 P Q 3 2 d1 D H.4.29. Qu trnh dp vut1. chy p; 2. khun p, 3. phi k.loi; 4. vnh p

GIO TRNH:

C KH I CNG

43

- Dp vut lm mng thnh: c thc hin khi h gia chy v khun nh hn chiu dy phi. ng knh gim t, chiu su tng nhiu v gim chiu dy thnh phi. rt ngn s ln dp gin, mt s ln dp u khng lm mng thnh, sau mi dp gin lm mng thnh.

S0 S rch S0 P

z =( 0,3-0,8)S

H.4.30. Dp vut khng lm mng thnh

c/ Un vnh: L phng php ch to cc chi tit c g, ng knh D chiu cao H, y chi tit rng. Phi un vnh phi t l vi d trc, sau dng chy v khun to vnh. d - Bn knh ln ca chy v khun R = (510)S. - Khe h gia chy v ci Z = (810)S. S H R - L b dng chy u hnh cu hoc hnh chp. D - khng xy ra nt mp vng l t th phi D1 c h s un vnh hp l: Ku = d/D = 0,620,78 H.4. 31. S un vnhd d/ Tp ming: L nguyn cng lm cho ming ca phi rng (thng l hnh tr) thu nh li. Phn tp nh li c th l hnh cn, cn v tr, na hnh cu v.v...Khun di lm nhim v nh v chi tit, khun trn c l hnh cn ng knh gim dn, phn cui ca khun trn l hnh tr. trnh xy ra hin tng xp ming tp th: d d0 K = 0 = 1,2 1,3 d Khi cn tp n chi tit c ng knh nh hn gii hn cho php th phi qua mt s ln tp.

e/ Mit Mit l phng php ch to cc chi tit trn xoay mng. c bit mit c dng ch to nhng chi tit c ng knh ming thu nh vo v thn phnh ra nh bi ng, l hoa...k tip sau nguyn cng dp vut.

Khun

Phi

Ta

Cn p

H.4.32. S mit