Chuong 3a Ban Ve Chi Tiet 6682 7299

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CHNG 3 : BN V CHI TIT

MC CH - YU CU

Sau khi hc xong phn ny, sinh vin c kh nng: - Xc nh c cc ni dung ca bn v chi tit.- La chn c hnh chiu chnh v cc hnh biu din thch hp khc din

t hnh dng v cu to ca chi tit.- c, hiu cc bn v chi tit.- V c cc hnh chiu ca chi tit v ghi y kch thc theo quy nh.

NI DUNG ( 6 tit ) 3.1. Cng dng v ni dung ca bn v chi tit3.2. Trnh t v phc chi tit3.3. La chn hnh biu din cho chi tit

3.3.1. Hnh chiu chnh3.3.2. Cc hnh biu din khc3.3.3. Biu din quy c v n gin ha3.3.4. Cch c bn v chi tit

3.4. Ghi kch thc chi tit3.4.1. Chun kch thc3.4.2. Quy tc ghi kch thc

3.5. Ghi dung sai kch thc3.5.1. n v o3.5.2. Cch ghi kch thc trn bn v chi tit3.5.3. Cch ghi dung sai kch thc trn bn v lp

3.6. Ghi dung sai hnh hc3.6.1. K hiu sai lch hnh dng hnh hc3.6.2. Ch dn trn bn v

3.7. Ghi nhm b mt3.7.1. Khi nim v nhm b mt3.7.2. Cch ghi k hiu nhm b mt

3.8. Cu hi v bi tp

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CHNG 3 :BN V CHI TIT

3.1. CNG DNG V NI DUNG CA BN V CHI TITBn v chi tit (cn c gi l bn v ch to chi tit) l ti liu k thut quan

trng dng t chc sn xut. Bn v chi tit c cc ni dung sau :- Cc hnh biu din: (hnh chiu, hnh ct, mt ct, hnh v quy c) din t

chnh xc, y , r rng hnh dng v cu to cc b phn ca chi tit my .- Cc kch thc: th hin chnh xc, hon chnh, hp l ln cc b phn

ca chi tit my cn thit cho vic ch to v kim tra .- Cc yu cu k: thut gm cc k hiu v nhn b mt, dung sai kch

thc, dung sai hnh hc, cc yu cu v nhit luyn, nhng ch dn v gia cng, kim tra, iu chnh

- Khung tn: (khung tiu ), gm cc ni dung lin quan n vic qun l bn v, qun l sn phm nh tn gi chi tit, vt liu, s lng, k hiu bn v, tn h, ch k, ngy thc hin ca nhng ngi c trch nhim i vi bn v.

Hnh 3.1 l bn v chi tit Ci gt. Trong chng ny, ta ch trng n Cc hnh biu din v Cc kch thc

ca bn v chi tit.

Hnh 3.1

85

3.2. TRNH T V PHC CHI TIT

Bn v phc l bn v c tnh cht tm thi dng trong thit k v sn xut. N l ti liu u tin lp cc bn v khc.

Bn v phc c v bng tay, thng khng dng dng c v v khng cn theo t l mt cch chnh xc. Cc kch thc c c lng bng mt, nhng phi gi c s cn i v t l gia cc kch thc. Bn v phc thng v trn giy k vung, giy k li hoc giy thng.

Bn v phc khng phi l bn v nhp m l mt ti liu k thut , phi c y hnh biu din, kch thc, k hiu v nhn b mt, sai lch hnh dng v ccyu cu k thut khc.

Khi lp bn v phc chi tit, trc ht phi nghin cu k chi tit, phn tch hnh dng v cu to ca chi tit , hiu r chc nng ca chi tit v phng php ch to chi tit; trn c s chn phng n biu din, chn chun kch thc. Sau chn kh giy v v theo trnh t nht nh :

Bc 1: B tr cc hnh biu din bng cc ng trc, ng tm ca cc hnh biu din.

Bc 2: V m, ln lt v tng phn ca chi tit, v cc ng bao ngoi, cc kt cu bn trong.

Bc 3: T m, dng bt ch cng k cc ng gch gch ca mt ct v ca hnh ct; dng bt ch mm t m cc ng bao. K cc ng dng v ng ghi kch thc.

Bc 4: hon thin, ghi cc ch s kch thc, cc k hiu nhm, dung sai hnh dng v v tr, vit cc yu cu k thut v cc ni dung trong khung tn. Cui cng kim tra v sa cha bn v.

V d 1: V phc chi tit ( Hnh 3.2 a, b, c)

Hnh 3.2 a : B tr hnh biu din

86

Hnh 3.2 b: V m, t m

Hnh 3.2 c : Hon thin bn v

V d 2 : V phc thn bm (hnh 3.3).

87

Hnh 3.3. Thn bm

Hnh 3.4. Bc 1: B tr cc hnh biu din

88

Hnh 3.5. Bc 2: V m

Hnh 3.6. Bc 3: T m

89

Hnh 3.7. Bc 4 : o v ghi kch thc

3.3. LA CHN HNH BIU DIN CHO CHI TIT

Hnh biu din ca chi tit gm c hnh chiu, hnh ct, mt ct, hnh trch v.v... quy nh trong TCVN 8:2002.

Ty theo c im hnh dng v cu to ca tng chi tit, ngi v s chn cc loi hnh biu din thch hp sao cho vi s lng hnh biu din t nht m th hin y hnh dng v cu to ca chi tit, ng thi c li cho vic b tr bn v.

3.3.1. Hnh chiu chnh

Trong bn v c kh, hnh biu din v tr hnh chiu ng l hnh chiu chnh ca bn v, n phi th hin c c trng v hnh dng ca chi tit v phn nh c v tr lm vic hay v tr gia cng ca chi tit.

Mun v hnh chiu chnh , phi da trn hai quy tc v cch t chi tit xc nh v tr ca chi tit i vi mt phng hnh chiu.

a. t chi tit theo v tr lm vic

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V tr lm vic ca chi tit l v tr ca chi tit trong my . t chi tit theo v tr lm vic ngi c bn v d hnh dung.

V d v tr ca mc cu trong my cn trc l dc, v tr ca sau my tin l nm ngang, u hng v bn tri (hnh 3.8).

Nhng mt s chi tit chuyn ng khng c v tr lm vic nht nh nh thanh truyn, tay quay, v.v... hoc c mt s chi tit, tuy c v tr lm vic c nh, song n nghing so vi mt bng; i vi nhng chi tit k trn, nn t theo v tr gia cng hoc v tr t nhin

Hnh 3.8. V tr ca mc cn trc v sau my tin

b. t chi tit theo v tr gia cng V tr gia cng ca chi tit l v tr ca chi tit t trn my cng c khi gia

cng . i vi chi tit c dng trn xoay nh trc, bc v.v..., thng c gia cng trn my tin, khi v hnh chiu chnh ca chng, nn t theo v tr gia cng , ngha l t sao cho trc quay ca chi tit nm ngang.

ng thi vi vic xc nh v tr ca chi tit, cn xc nh hng chiu cho hnh chiu ng th hin c c trng hnh dng ca chi tit v c li cho vic b tr cc hnh biu din khc(sao cho cc hnh biu din t nt khut nht v s dngkh giy mt cch hp l.

3.3.2. Cc hnh biu din khcNgoi hnh chiu chnh, mun biu din chi tit cn phi c mt s hnh biu

din nht nh khc (vi s lng t nht) th hin y nht, r rng nht cu to ca chi tit .

Hnh 3.9

91

V d : biu din mt trc c ren ( Hnh 3.9 ), ch cn mt hnh chiu c bn lm hnh chiu chnh v mt mt ct th hin pht vt trn hnh tr . Trng hp ny khng cn v hnh chiu bng hoc hnh chiu cnh. 3.3.3. Biu din quy c v n gin ho

Ngoi cc hnh hnh biu din : Hnh chiu, hnh ct, mt ct, hnh trch, trn cc bn v k thut cn dng mt s cch biu din quy c v n gin ho.

Sau y l mt s quy tc v biu din quy nh trong TCVN 8-34: 2002 (ISO 128-34: 2001) :

Nu hnh chiu, hnh ct v mt ct l i xng th cho php ch v mt na ( gii hn bng nt chm gch mnh ( Hnh 3.10 ) hoc v qu mt na ( gii hn bng nt ln sng.

Hnh 3.10 Nu c mt s phn t ging nhau v phn b u nh l ca mt bch, rng ca bnh rng v.vth ch v vi phn t, cc phn t cn li c v n gin hay v theo quy c. (Hnh 3.11).

Hnh 3.11 Hnh 3.12

Khi khng i hi v chnh xc ,cho php v n gin giao tuyn ca cc mt : c th thay ng cong bng cung trn hay on thng (Hnh 3.12, 3.13). Giao tuyn thc thy c v bng nt lin m (Hnh 3.12, 3.13). Giao tuyn tng tng ti cc gc ln (ng chuyn tip) v bng nt lin mnh v khng v chm vo ng bao (Hnh 3.14).

92

ng chuyen tiep

Hnh 3.13

Hnh 3.14 ng biu din phn chuyn tip gia hai mt c th v theo quy c

bng nt mnh (Hnh 3.14; hnh 3.15; 3.16a) hoc khng v nu chng khng th hin r rt (Hnh 3.16 b).

a) Hnh 3.15 b)

a) b)Hnh 3.16

93

Cho php v tng thm cn v dc, nu chng qu nh. Trn hnh biu din, ch cn v mt ng tng ng vi kch thc nh ca cn hoc dc ( Hnh 3.17 ).

Khi cn phn bit phn mt phng vi phn mt cong ca b mt, cho php k hai ng cho bng nt mnh trn phn mt phng ( Hnh 3.18) .

Hnh 3.18

Hnh 3.17

Cc chi tit hay phn t di c mt ct ngang khng i hay thay i u n nh trc, thp hnh v.vth cho php ct i phn gia (ct la), song kch thc chiu di vn l kch thc chiu di ton b ( Hnh 3.19 ).

Hnh 3.19

i vi chi tit c chm tr, kha nhm cho php ch v n gin mt phn kt cu ( Hnh 3.20).

Biu din l ca moay , rnh then bng ng bao ca chng (Hnh 3.21).

Hnh 3.20 Hnh 3.21

Khi thiu hnh biu din th kch thc dy v chiu di ca chi tit c ghi bng k hiu S v L (Hnh 3.22).

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Hnh 3.22V d : Biu din quy c v n gin ha (hnh 3.23, 3.24)

Hnh 3.23

Hnh 3.24

- Dng mt hnh chiu v cc du hiu , , M, dy S... cho cc chi tit c dng trn xoay hay chi tit c dng n gin nh hnh 3.23.

- Dng mt hnh chiu chnh v mt vi mt ct ri hay hnh chiu ring phn, hnh ct ring phn cho cc dng trn nhng cn thm cc l, rnh nh hnh 3.24.

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3.3.4. Cch c bn v chi tit

3.3.4.1. Cc yu cu

c bn v k thut l mt yu cu quan trng i vi nhn vin k thut, n i hi ngi c phi hiu mt cch chnh xc v y cc ni dung ca bn v.

- Hiu r tn gi, cng dng ca chi tit, vt liu v tnh cht ca vt liu ch to chi tit, s lng v khi lng chi tit..

- T cc hnh biu din hnh dung c hnh dng v cu to ca chi tit.- Hiu r ngha ca cc kch thc v cch o, cc k hiu nhm b mt

v phng php gia cng, cc yu cu k thut v phng php m bo cc yu cu

- Hiu r c ni dung cc k hiu, cc yu cu k thut ghi trn bn v.

3.3.4.2. Trnh t c bn v chi tit

a) c khung tn ca bn v bit c tn gi chi tit, vt liu, khi lng, s lng chi tit, t l ca

bn vb) c cc hnh biu dinBit c tn gi cc hnh biu din, s lin quan h gia chng. Phn tch

hnh dng v kt cu tng phn i n hnh dung c hnh dng v kt cu ca chi tit.

c) c cc kch thc- Bit c ln ca chi tit thng qua cc kch thc v chiu di, chiu

rng, chiu cao...(Kch thc khun kh)- Bit c chun kch thc ta c th suy ra phng php gia cng khi cn

thit v bit cch o..(Kch thc nh v)- Bit c hnh dng ca chi tit t cc k hiu , R, cu, - Kch thc lp ghp...

d) c yu cu k thut- c cc sai lch kch thc.- c sai lch hnh dng v v tr b mt, hiu cc dng sai lch v tr s sai

lch.- c nhm b mt- c v hiu cc yu cu k thut khc nh :mp vt, gc c, lp ph,

cng v cc yu cu khc ghi trong bn v. Nhng b mt cn li ca chi tit khng ghi nhm th c chung nhm ghi gc trn bn phi bn v.

e) Tng ktSau khi c bn v, ngi c phi hiu r cc ni dung sau :- Hiu r tn gi, cng dng, vt liu ch to chi tit, khi lng, s lng chi

tit, t l.- Hnh dung ton b cu to bn trong v bn ngoi chi tit.- Bit cch o cc kch thc khi gia cng v kim tra chi tit.- Pht hin sai st v nhng iu cha r trn bn v.

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1

1

L1

L2

L3

3

L1

L2

L3

1

2

2

1

2

3

Hnh 3.26

3.4. GHI KCH THC CHI TIT3.4.1. Chun kch thc

Chun l tp hp cc yu t hnh hc (im, ng, mt) ca chi tit, c dng lm c s xc nh cc kch thc ca chi tit, c chia lm 3 loi:

a) Mt chun: Thng ly cc mt gia cng ch yu, mt tip xc quan trng hay mt i xng ca chi tit lm mt chun.

V d : Mt chun II l mt chun xc nh v tr ca trc i vi mt (chiu cao ca ng trc).

Hnh 3.25

a) b)

c) d)

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b) ng chun: Thng ly trc quay ca khi trn xoay lm ng chun xc nh kch thc ng knh hay cc kch thc nh v ca trc quay.

V d : Trn hnh trc quay ca trc bc l ng chun, n xc nh cc ng knh 1, 2, 3 ca trc (hnh 3.26).

c) im chun: V d thng ly tm ca hnh lm im chun xc nh khong cch t n cc im khc.

* Cc hnh thc ghi kch thc:a) Ghi theo to : Cc kch thc u xut pht t mt gc chung (hnh 3.26

a).b) Ghi theo xch: Cc kch thc ni tip nhau (hnh 3.27). V d:

Hnh 3.27

c) Ghi kt hp: Cc kch thc ghi theo c hai hnh thc trn. Cch ghi ny c dng nhiu nht (hnh 3.25).

Nh vy, trc khi ghi kch thc ca mt chi tit, ta phi chn chun sao cho ph hp vi yu cu thit k v yu cu cng ngh. Cch chn chun v hnh thc ghi kch thc c lin quan cht ch n trnh t gia cng chi tit.

3.4.2 . Quy tc ghi kch thc

Hnh 3.28 Hnh 3.29

- Kch thc ca mp vt 450 c ghi nh hnh 3.28, kch thc ca mp vt khc 450 th ghi theo nguyn tc chung v ghi kch thc.

- Khi ghi kch thc ca mt lot phn t ging nhau th ch ghi kch thc mt phn t c km theo s lng phn t (hnh 3.29).

5x45 4 lo 10

98

- Cc kch thc c ghi ni tip nhau trn 1 ng thng, nhng khng to thnh 1 chui khp kn ( Hnh 3.27)

- Nu c mt lot cc kch thc lin tip nhau th c th dng cch ghi theo chun 0 (hnh 3.30).

Hnh 3.30

- Trong mt s trng hp, dng cch ghi theo bng (Hnh 3.31)

Hnh 3.31

- Ghi kch thc cc phn t ging nhau v phn b u (Hnh 3. 31).-

- Ghi kch thc mt s l theo qui c n gin ( TCVN- 4368 086 ) : Bng 3.1.

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Bng 3.1

100

3.5. GHI DUNG SAI KCH THC

TCVN 5706 :1993 qui nh cch ghi dung sai kch thc di v kch thc gc trn cc bn v k thut , ph hp vi tiu chun quc t ISO 406: 1987.

3.5.1. n v o Cc sai lch kch thc c cng n v o vi kch thc danh ngha.

3.5.2. Cch ghi kch thc trn bn v chi tit

3.5.2.1. Phn b vng dung saiTa thy vi hai chi tit trc v l c ch to vi cng mt kch thc danh

ngha, nhng dung sai v cp chnh xc khc nhau c th phi hp to nn cc kiu lp ghp khc nhau ta gi l dung sai lp ghp vi cc ch lp ghp khc nhau. Phn b v tr ca vng dung sai so vi kch thc danh ngha c TCVN chia lm 26 min dung sai nh s t A n Z ty thuc vo trc hay l v cp chnh xc. Bng 3.2 gii thiu s phn b min dung sai ca trc v l cp chnh xc 8. Min dung sai l c quy nh vit bng ch in A, B, ... Z, min dung sai trc c quy nh vit bng ch thng a, b, c ... z. Con s k bn l cp chnh xc.

Bng 3.2 Phn b min dung sai ca h trc(trc c s: ch thng) v h l (l c s: ch in)

3.5.2.2. H thng l v h thng trcTiu chun v dung sai lp rp hnh tr trn ca TCVN c thay i nhiu qua

tng thi k. Hin nay, TCVN da trn tiu chun quc t ISO. d dng to ch lp rp gia trc v l, ta cn chn mt trong hai yu t trc hoc l lm chun, thay i dung sai ca yu t kia ta c th t c ch lp rp mong mun. C hai h thng:

1- H thng lThng c dng v chim n 90%- 95% cc mi lp trong c kh v l l mt

tr trong, kh ch to chnh xc v t bng cao nh trc nn khi chn l lm chun, ta c th thay i dung sai trc d dng t ch lp rp mong mun. Trong h thng ny, min dung sai ca l lun l H c sai lch gii hn di bng 0 sai lch

101

gii hn trn lun dng v ph thuc cp chnh xc. V d, vi kch thc 100H8 th kch thc l chun l 100+0,15. L tiu chun d dng thc hin nh doa ( li doa Php: Alsoir, Anh: Reamer) dc tiu chun ha t lu.

2- H thng trct c dng hn v ch chim khong 5%- 10% cc mi lp trong c kh v l

do nu trn. Trong h thng ny ta chn trc lm chun, thay i dung sai l t ch lp rp mong mun.

H thng trc ch c dng khi mt trc ng thi lp vi hai chi tit l vi cc ch lp khc nhau.

V d : Mi lp gi then bng v rnh trn trc v trn l cng theo h trc v l do ni trn. Vi knh thc danh ngha b rng then l 12 th then lp ghp trt chnh xc (lp lng) trn rnh trc vi kiu dung sai nh sau:

7

810

h

Hv lp ghp cht nh

(lp cht) vi rnh trn l theo kiu 6

710

h

K. Ta thy iu ny ph hp vi thc t v

trc ( b ngang B ca then) c ch to d dng vi cng mt kiu dung sai 10h7 trn my mi phng. Nu dng h thng l th khng th ch to mt kch thc then 10 vi hai vng dung sai khc nhau.

Trong h thng ny, min dung sai ca trc lun l h c sai lch gii hn di m, sai lch gii hn trn bng 0 v ph thuc cp chnh xc. V d, vi kch thc 100h6 th kch thc trc chun l 0 022,0100 . Hnh 3.2, mi lp then bng 108 gia trc v then vi rnh trn l v rnh trn trc theo h trc.

Hnh 3.2 Mi lp then bng 108 gia trc v thenvi rnh trn l v rnh trn trc theo h trc. kch thc 38 em ra ngoi trc

c v nm ngang theo TVVN c hay ISO xem p v d c.

3.5.2.3. Cc ch ghp hnh tr trnDo yu cu s dng trong thc t m c ba kiu lp ghp hnh tr trn vi cc

mc phn b ca cc vng dung sai khc nhau gia trc v l .1- Lp cht (lp c di)Khi ng knh trc ln hn ng knh l:- Trong h thng l vi min dung sai l chun l H (l c s) th khi lp cht

min dung sai ca trc s l k, l, m, n...z

102

- Trong h thng trc vi min dung sai trc chun l h (trc c s) th khi lp cht min dung sai ca l s l K, L, M, N...Z

2- Lp trung gian Khi kch thc trc v l gn tng ng nhau:

- Trong h thng l vi min dung sai l chun l H (l c s) th khi lp trung gian min dung sai ca trc s l g, h, i, j.

- Trong h thng trc vi min dung sai trc chun l h (trc c s)th khi lp trung gian min dung sai ca l s l G, H, I, J.

3- Lp lng Khi ng knh trc nh hn ng knh l:

- Trong h thng l vi min dung sai l chun l H (l c s) th vi ch lp lng min dung sai ca trc s l a, b, c, d, e, f.

- Trong h thng trc vi min dung sai trc chun l h (trc c s) th vi ch lp lng min dung sai ca l s l A, B, C, D, E, F.

3.5.2.4. Cch ghi dung sai kch thc trn bn v chi tit

- Mt kch thc c dung sai gm cc thnh phn sau :+ Kch thc danh ngha

+ K hiu dung sai V d : 30f7 Nu bn cnh kch thc danh ngha v k hiu dung sai cn ghi tr s sai lch gii hn th phi ghi trong ngoc n V d : 30f7 -0.020 - 0,041

- Mt kch thc c tr s dung sai c th , gm cc thnh phn sau :+ Kch thc danh ngha + Tr s cc sai lch gii hn

V d : 32 + 0,1 - 0,2

- Nu dung sai i xng th ln ca ch s sai lch gii hn bng ln ca ch s kch thc danh ngha , ng sau kch thc danh ngha v du V d : 32 0,1

- Cho php khng ghi tr s sai lch bng 0 V d : 35 - 0,02 hoc 40 + 0,02

- Da vo kiu dung sai ghi trn bn v lp ta tra s tay k thut dung sai lp rp hay theo bng dung sai 3.7, 3.8 phn cui chng ny xc nh dung sai c th ca kch thc ny ca trc hoc l ghi trn bn v chi tit.

V d: 6725

kH l kiu dung sai ghi trn bn v lp th trn hai bn v ch to

trc v l ta phi:- Trong bn v l: tra dung sai 25H7 trong bng dung sai 3.7 cho l v ghi kch

thc c th l 021,025 cho l.

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- Trong bn v trc: tra dung sai 25k6 trong bng dung sai cho trc v ghi kch thc c th l 015,0 002,025 cho trc.

Hnh 3.32, trnh by kch thc trong bn v ch to ca ca trc v l ca mi lp tr

6740

kH v rnh then B= 12 trn l v trc nh sau:

Hnh 3.32. Trnh by kch thc trong bn v ch toca trc v l ca mi lp tr

6740

kH v then. Ch theo TCVN mi kch thc 40

em ra ngoi t nghing theo ng kch thc th khng c p v kh c.Khi ghi dung sai vo kch thc bn v ch to, ta t i t n v m cho trn

bng thnh mm.Mt im cn ch l cng ngh ti nc ta hin nay chnh xc ch mi t

n 0,01mm tc l trn 10m. Nn cc gi tr dung sai cho di gi tr ny hoc ghi n l phn ngn c tnh cht tham kho. chnh xc gia cng ti nc ta trong vng 50 nm qua khng tng ln ng k nn thi im hin nay, mc d c nhiu trung tm cng ngh cao nhng cha pht huy c nhn lc, cng ngh v thit b.

3.5.3 . Cch ghi dung sai kch thc trn bn v lp

Trong bn v lp ch nhng kch thc lp rp gia hai b phn mi c ct ring phn biu din kch thc v ghi kiu dung sai.

Kch thc c kiu dung sai lp ghp trong bn v lp gm ba phn: Kch thc danh ngha chung ca hai thnh phn lp rp, k tip l mt phn s m t s ch vng phn b dung sai ca l (ch in), theo sau l cp chnh xc ca l cn mu s ch vng phn b dung sai ca trc (ch thng) theo sau l cp chnh xc ca trc. Ta cn ch n mt s c im sau:

- Vng dung sai l lun t s v ghi bng ch in.- Vng dung sai l lun mu s v ghi bng ch thng.- Thng vng no c min dung sai H l thuc h thng (H in trn t s: h

l, h thng di mu s: h trc). Phn ln theo h l nn c H in trn t s.- Nu dung sai l (t s) khc H m dung sai trc mu s l h thng th chc

chn kiu lp theo h trc.

104

- Khi c hai vng u c k hiu H v h c th phi xem xt cc kch thc lin quan v dng kinh nghim cng ngh xt xem l h trc hay h l m 90% trng hp l h l.

- Cp chnh xc ca l trn t s lun thp hn cp chnh xc ca trc di mu s mt n v v l kh ch to t chnh xc cao bng trc nn ta phi h xung mt cp. V d:

7840

kH l mi lp cht va vi kch thc danh ngha 40 trong h l, cp

chnh xc trc l 7 cao hn cp chnh xc l l 8 mt n v.

7840

fH l mi lp lng va vi kch thc danh ngha 40 trong h l, cp

chnh xc trc l 7 cao hn cp chnh xc l l 8 mt n v.

7

825

h

M l mi lp cht vi kch thc danh ngha 25 trong h trc, cp chnh xc trc l 7 cao hn cp chnh xc l l 8 mt n v.

- Hnh 3.33 trnh by kch thc ca mi ghp c dung sai gm cc thnh phn sau :

+ Kch thc danh ngha ca l v ca trc + K hiu dung sai ca l + K hiu dung sai ca trc - Ghi sai lch gii hn thay cho k hiu dung sai v lp ghp (hnh 3.34)- Nu ng thi ghi k hiu dung sai v ghi tr s sai lch gii hn th ghi tr s

sai lch gii hn trong ngoc n.

a) b)

Hnh 3.33 Hnh 3.34

105

3.6. GHI DUNG SAI HNH HC 3.6.1. K hiu sai lch hnh dng hnh hc (Bng 3.3)

Bng 3.3

3.6.2. Ch dn trn bn v-Nhng ch dn v dung sai v v tr c ghi trong khung ch nht, gm 2 hay

nhiu : + th nht : Ghi k hiu dung sai theo bng 3.3+ th hai : Tr s dung sai + th ba : Ch ci l k hiu chun, trong trng hp cn thit

V d :

Hnh 3.35- Bng 3.4 nu ln cc v d v ch dn dung sai hnh dng v v tr trn bn v.

106

Bng 3.4

107

108

3.7. GHI NHM B MT 3.7.1. Khi nim v nhm b mt

Nhm b mt l tp hp nhng mp m c bc tng i nh trn b mt thc ca chi tit c xt trong phm vi chiu di chun.

Hnh 3.36 l hnh v phng to prfin ca b mt chi tit trong gii hn chiu di chun l.

Nhm b mt c nh gi theo mt trong hai ch tiu sau :a) Sai lch s hc trung bnh ca prfin (Ra) : l tr s s hc trung bnh ca

cc gi tr tuyt i ca sai lch prfin trong khong chiu di chun :

109

Ra =

n

iiYn 1

1

Hnh 3.36

b) Chiu cao mp m ca prfin theo 10 im (Rz) : l tr s trung bnh ca cc gi tr rtuyt i ca chiu cao nm nh cao nht v chiu su nm y thp nht ca prfin trong khong chiu di chun :

Rz =

5

1

5

1

minmax5

1

i iii HH

Nhm b mt c th hin bng nhm b mt . TCVN 2511:1995 qui nh 14 cp nhm v tr s ca cc thng s Ra, Rz ( bng 3.5) . Tr s cng b th b mt cng nhn.

Bng 3.6 trnh by cp nhm b mt v phng php gia cng.

3.7.2. Cch ghi k hiu nhm b mt

a. K hiu

- Du hoc ghi nhm b mt nu ngi thit k khng ch r phng php gia cng (hnh 3.37a).

- Du nu b mt c gia cng bng ct gt (hnh 3.37b).

- Du hoc nu b mt khng b ly i lp vt liu hay gi nguyn nh c (hnh 3.37c).

b. Quy tc ghi k hiu nhm - K hiu nhm c ghi trc tip trn ng bao b mt hoc trn ng ko

di ca ng bao (Hnh 3.38a ).V tr , ch s v k hiu nhm ghi nh hnh (Hnh 3.38b,c) ;

110

- Nu tt c cc b mt ca chi tit c cng 1 cp nhm th khng ghi trn hnh biu din m ghi chung gc trn, bn phi bn v ( Hnh 3.39) ;

- Mt vi mt c nhm khc nhau th ghi trc tip , cn a s cc b mt c cng nhm th gc trn, bn phi bn v km theo k hiu t trong ngoc n (hnh 3.40, hnh 3.41).

Bng 3.5. nhm b mt

111

Bng 3.6. Cp nhn v cc phng php gia cng

Hnh 3.37

112

a) b)

Hnh 3.38

Hnh 3.39

113

Hnh 3.40

Hnh 3.41

- Tr s nhm ca lp ph b mt c ghi trn ng chm gch m biu din lp ph . Nhm trc khi ph c ghi trn ng bao (Hnh 3.42).

Hnh 3.42

3.8. CU HI V BI TP

3.8.1. Cc v d

V d 1 : Lp bn v phc chi tit Gi trc (hnh 3.43)

114

Hnh 3.43. Gi trc

Bc 1 : B tr hnh biu din (hnh 3.44)

Hnh 3.44

115

Bc 2 : V m (hnh 3.45)

Bc 3 : T m (hnh 3.46)

Hnh 3.46Bc 4 : Ghi kch thc v cc ghi ch (hnh 3.47)

116

Hnh 3.47V d 2: c bn v chi tit np (hnh 3.48)

117

Bn v chi tit npa. c khung tn :- Tn gi chi tit : Np.- Vt liu : Gang xm GX 15 32.- T l : 1: 2 (Chi tit ln gp i hnh v).- S lng : 1b. c hnh biu din : Hai hnh biu din- Hnh ct ng l hnh ct xoay A A th hin l ren hnh cn, l bc gia,

l lp vt v l lp boulon. - Hnh chiu cnh ch yu th hin v tr su l lp boulon v ba l lp vt.- L ren ng cn R (ng knh danh ngha inches), chiu di on ren l

17mm ni vi l khuu 90o c kch thc 10.- Ba l lp vt M10 (Ren h mt bc ln, ng knh d = 10).c. c cc kch thc :- Kch thc khun kh : 37 90- Kch thc nh v : 5 l kch thc xc nh khong cch t mt u ca np

n mt lp ghp np v thn my, 20 l kch thc xc nh chiu dy ca np (phng nm ngang); 20 (phng thng ng) l kch thc xc nh v tr ca l 10 i vi tm ca np; 5 l kch thc xc nh dy ca g np bn phi; 10 l kch thc xc nh dy ca g np bn tri (10 + 1); 42 l kch thc xc nh v tr ca 3 l lp vt; 71 l kch thc xc nh v tr ca 6 l lp bulng.

- Kch thc lp ghp :+ Cc l 32H8 v 16H7 c chnh xc cao nn c ghi cc k hiu

lp ghp v dung sai hnh dng v v tr b mt.32H8 : L c ng knh danh ngha l 32mm, sai lch c bn H, cp

chnh xc 8.16H7 : L c ng knh danh ngha l 16mm sai lch c bn H, cp

chnh xc 7.+ G phi ca np c kch thc 55g6 : trc c ng knh danh ngha

l 55mm, sai lch c bn g, cp chnh xc 6.+ Su l lp boulon 7/15.

- Kch thc nh hnh :+ G tri c dng ng 52, vt cnh 145o.+ G phi c gc ln R2, kch thc hc l 35.

d. c yu cu k thut :- c nhm b mt :

+ L 32H8, l 16H7, g phi 55g6, mt lp ghp pha phi c nhm b mt l Ra1,6.

+ L 35 khng gia cng ( th).+ Cc b mt cn li c nhm Ra6,3.

- c dung sai hnh dng :+ Dung sai ng tm ca cc b mt l 16H7 v b mt tr 55g6

khng ln hn 0,025mm.+ Dung sai vung gc gia mt lp ghp pha phi v b mt l

16H7 khng ln hn 0,025mm.

118

V d 3 : c bn v chi tit ng lt (hnh 3.49).

Hnh 3.49. Bn v chi tit ng lt ng

a. c khung tn :- Tn gi chi tit : ng lt ng.- Vt liu : Thp C45.- T l : 1: 2 (Chi tit ln gp i hnh v).- S lng : 1b. c hnh biu din : Nm hnh biu dinHnh 3.49 l bn v ng lt ca ng my tin.- Hnh biu din chnh l hnh ct dc, chi tit c t theo v tr gia cng

cng l v tr lm vic ca ng lt trong ng, phn u c hnh cn hng sang tri lp mi nh tm.

- Hnh chiu cnh th hin hnh dng mt u pha tri ca ng lt v v tr lp bng khc du milimet.

- Hai mt ct u l mt ct ri, mt ct bn tri th hin l sut 8 v chiu rng ca rnh di; mt ct bn phi th hin hai l ren M8.

- Hnh chiu ring phn B ch cc du khc milimt mt ngoi u bn tri ng lt.

- Cc kch thc ng knh ly ng trc lm chun v kch thc chiu di ly mt mt bn phi lm chun. Cc l c nh v bng kch thc ghi dn tm l.

119

- Rnh then l kt cu tiu chun ha, y then c xc nh bng kch thc 50,5 o n mt tr.

- Ba l lp vt M8-6H (Ren h mt bc ln, ng knh d = 8, cp chnh xc 6, kiu lp h l H).

c. c cc kch thc :- Kch thc khun kh : 260 55 0,01- Kch thc nh v : 20 l kch thc xc nh khong cch t mt u ca

ng lt n l 5; 54 l kch thc xc nh chiu di ca rnh b2h1; 42 l kch thc xc nh v tr ca rnh thot dao gia hai b mt l 36 v 26; 90 l kch thc xc nh di ca phn cn lp mi nh tm; 148 l kch thc xc nh v tr ca l sut 8; 160 l kch thc xc nh chiu di ca rnh di, 45o l kch thc xc nh v tr lp bng khc du milimet so vi phng thng ng.

- Kch thc lp ghp :+ 31,269 ; cn moc s 4 + 55 0,01

- Kch thc nh hnh :+ u tri c dng ng 55 0,01; vt cnh l cn 0,545o, mt ngoi

v trn bn knh R1.+ u phi vt cnh 245o l 36 v mt tr ngoi.

d. c yu cu k thut :- c nhm b mt :

+ L 36, mt lp ghp then mt bn c nhm b mt l Ra6,3.+ L cn 31,269 v mt ngoi ca ng lt c nhm b mt l

Ra1,6.+ Hai mt u ca ng lt v y then rnh di c nhm b mt l

Ra12,5.+ Cc b mt cn li c nhm Ra25.

- c dung sai hnh dng :Cc sai lch hnh dng v o ghi trong cc khung dung sai hnh hc vi

mt chun A (b mt tr ngoi 55 0,01 ). + Dung sai o hng tm ca b mt l 36 i vi b mt tr

ngoi 55 0,01 khng ln hn 0,02mm.+ Dung sai o hng tm ca b mt l cn 31,269 i vi b mt

tr ngoi 55 0,01 khng ln hn 0,01mm.+ Dung sai trn ca mt tr ngoi 55 0,01 khng ln hn

0,01mm.+ Dung sai tr ca mt tr ngoi 55 0,01 khng ln hn 0,01mm.Ngoi cc b mt c nhm ghi trn hnh biu din, cc mt cn li c

nhm nh nhau c ghi chung gc trn bn phi bn v l Ra25.- Cc yu cu k thut ghi phn trn khung tn :

+ ng lt c ti cng t cng HRC 22+ Mt cn moc ti t cng HRC 40.

3.8.2. Cu hi v bi tp1. Trnh by ngha ca bn v k thut i vi thit k v ch to sn phm.

120

2. Th no l bn v chi tit? Bn v chi tit dng lm g? 3. Trnh by mt s qui tc v hnh biu din thng dng ttrn bn v chi tit.4.Th no l chun kch thc? Cc yu t hnh hc no thng c chn lm

chun kch thc?5. Nu trnh t c bn v chi tit.6. c bn v chi tit cn gt (hnh 3.50).

Hnh 3.50. Bn v chi tit cn gtHng dn :Hnh 3.50 l bn v cn gt, gm hai hnh chiu c bn v hai hnh biu din

b sung. - Hnh chiu ng th hin phn ng bn tri c rnh then lp trc, thn

cong c mt ct ri hnh elip v phn hnh tr lp tay quay.Hnh ct cc b th hin l ren, v tr hai l ren v kt cu phn ny c th

hin trn hnh chiu ring phn A.- Hnh chiu bng c hai hnh ct cc b th hin l c rnh then v l lp trc

20. Phn hnh chiu th hin l lp boulon 18.- Hnh chiu ph A biu din phn ph ng ca cn gt gm c hai l ren

M12-7H (ng knh danh ngha 12, ren phi, cp chnh xc 7, kiu lp h l H).

121

Ngoi cc b mt c nhm ghi trn hnh biu din, cc mt cn li c nhm nh nhau c ghi chung gc trn bn phi bn v l Ra12,5.

7. c bn v chi tit hp (hnh 3.51).

Hnh 3.51. Bn v chi tit hp

122

2 lo

R20

8. V chi tit gi nghing (hnh 3.52) bng cc hnh biu din sau y :- Hnh ct ng qua rnh 10, l 16 v l 12.- Hnh chiu bng.- Hnh chiu cnh.- Ghi cc kch thc xc nh chi tit.Thc hin bi tp trn giy A4.

Hnh 3.52. Gi nghing.

9. V chi tit gi nh v (hnh 3.53) bng cc hnh biu din sau y :- Hnh chiu ng.- Hnh chiu bng vi hnh ct cc b l 16.- Hnh chiu cnh.- Ghi cc kch thc xc nh chi tit.Thc hin bi tp trn giy A4.

10. V chi tit thn my (hnh 3.54) bng cc hnh biu din sau y :- Hnh chiu ng.- Hnh chiu bng.

123

- Hnh chiu cnh.- Ghi cc kch thc xc nh chi titThc hin bi tp trn giy A4.

Hnh 3.52. Gi nh v.

Hnh 3.53. Thn my.

124

suot

11. V chi tit gi xoay (hnh 3.54) bng cc hnh biu din sau y :- Hnh chiu ng.- Hnh chiu bng.- Hnh ct cnh.- Ghi cc kch thc xc nh chi titThc hin bi tp trn giy A4.

Hnh 3.54. Gi xoay.

12. c bn v chi tit thn (hnh 3.55), bnh vt (hnh 3.56), thn (hnh 3.57), gi (hnh 3.58), .trc (hnh 3.59), trc vt (hnh 3.60), hp (hnh 3.61), tay quay (hnh 3.62), thn van (hnh 3.63) theo cc yu cu sau :

a) Bn v gm cc hnh biu din no? Gii thch cc hnh ct th hin nhng phn no ca chi tit?

b) Phn tch hnh dng tng phn ca chi tit. Mi phn c xc nh bng cc kch thc no ? ng v mt no lm chun kch thc? Kch thc no l kch thc nh v?

c) Kch thc no c chnh xc cao nht? Mt no c nhm nh nht? Hy gii thch?

d) Gii thch ngha cc k hiu lp ghp v dung sai hnh dng ghi trn bn v.

e) Gii thch ngha cc k hiu ren ghi trn bn v.

125

Hnh 3.55. Thn .

126

Hnh 3.56. Bnh vt.

127

Hnh 3.57. Thn

128

Hnh 3.58. Gi .

129

Hnh 3.59. Trc.

130

Hnh 3.60. Trc vt.

131

Hnh 3.61. Hp.

132

Hnh 3.62. Tay quay.

133

Hnh 3.63. Thn van.

134