ducnguyen.utc - dung sai lap ghep.pdf

5/22/2018 ducnguyen.utc - Dung sai lap ghep.pdf

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PGS. TS. NGUYN VN YN

BI GING

DUNG SAILP GHP

NNG - 2007

50H7

50n6


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MC LC

Trang

Bi mu1- Gii thiu2- Mt sk hiu thng dng trong Dung sai Lp ghp

Chng 1:Nhng vn cbn trong Dung sai Lp ghp1.1. Kch thc1.2. Lp ghp1.3. Tnh i ln chc nng

Chng 2: Dung sai lp ghp trtrn2.1. Dung sai kch thc

2.1.1. Quy nh vdung sai kch thc

2.1.2. Min dung sai v sai lch cbn2.1.3. Dung sai ca kch thc

2.2. Quy nh lp ghp2.2.1. Hthng l, hthng trc2.2.2. Kiu lp u tin2.2.3. K hiu kiu lp trtrn trn bn v

Chng 3: Dung sai cc yu thnh hc3.1. Sai lch hnh dng v vtr tng i gia cc bmt

3.1.1. Biu din dung sai hnh dng v vtr tng i

3.1.2. Chn dung sai hnh dng v vtr tng i3.2. nhm bmtChng 4: Dung sai cc lp ghp in hnh

4.1. Dung sai lp ghp then bng, then bn nguyt4.2. Dung sai lp ghp then hoa4.3. Dung sai lp ghp ln4.4. Dung sai lp ghp ren4.5. Dung sai truyn ng bnh rng

4.5.1. Sai sgia cng bnh rng4.5.2. chnh xc truyn ng bnh rng

4.5.3. Ghi cp chnh xc v dng khe hmt bnChng 5: Chui kch thc v cch ghi kch thc

5.1. Chui kch thc5.1.1. Cc khi nim cbn5.1.2. Gii bi ton thun5.1.3. Gii bi ton nghch theo i ln chc nng

hon ton5.1.4. Gii bi ton nghch theo i ln chc nng

khng hon ton

34

578

99

91111121213

1515

1718

20202223252525

27

292930

30

31


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5.1.5. Gii bi ton nghch theo phng php tnhxc sut

5.2. Ghi kch thc cho bn vckh5.2.1. Nhng nguyn tc chyu cn m bo khi

ghi kch thc5.2.2. Chn phng n ghi kch thc chiu di cho

bn vchi tit my

3233

33

34


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BI MU

I- Gii thiu

Dung sai - Lp ghp l mn hc cstrong chng trnh o to ksckh. Mn hc trang bcho sinh vin kin thc cbn thit kcc chi titmy, cc mi ghp v thit lp cc bn vckh.

Hc phn Dung sai Lp ghp c 02 n vhc trnh. im hc tp casinh vin c nh gi qua bi kim tra gia hc k, bi thi kt thc hc

phn v im chuyn cn. Hnh thc thi tlun. im chuyn cn c nhgi qua vic hon thnh cc bi tp trong qu trnh hc v thi gian c mttrn lp ca sinh vin.

Gio trnh sdng hc mn hc ny l sch Dung sai v lp ghpca tc giNinh c Tn, do Nh xut bn Gio dc xut bn nm 2006 (Tiliu [1]).

Trc khi hc mn Dung sai Lp ghp, sinh vin cn c trang bcckin thc vVkthut ckh, Ckh i cng, Csthit kmy.

Ni dung ca mn hc Dung sai Lp ghp c trnh by trong 05chng:

Chng1: Nhng vn cbn trong Dung sai Lp ghpTrnh by khi nim sai sgia cng v dung sai. Nhng nguyn nhn

chyu dn n c sai strong qu trnh gia cng ct gt. p dng l thuytXc sut Thng k kho st kch thc gia cng. Trn c s s chnc phng php gia cng hiu qunht, hoc c tha ra phng n iuchnh my hp l hn chphphm.

Trnh by cc khi nim vlp ghp: mi ghp c di, mi ghp ckhe h, kiu lp cht, kiu lp lng, kiu lp trung gian.

Trong chng ny cn cp n vn tnh i ln chc nng ca chitit my.

Chng 2: Dung sai lp ghp trtrnNghin cu dung sai kch thc dng trc v kch thc dng lca chi

tit my. Chn sai lch gii hn trn, sai lch gii hn di ca kch thctrc, kch thc l, m bo mi ghp c c tnh theo yu cu. Cch ghikiu lp trn bn vkthut.

Chng 3: Dung sai cc yu thnh hc ca chi tit myTrnh by cc sai lch vhnh dng: phng ca mt phng; thng

ca ng thng; trn, cn, tr ca mt tr. Cc sai lch v v tr

tng quan: song song, vung gc, ng tm, giao nhau, i


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xng, o mt u, o hng knh. Sai lch cht lng b mt, nhm ca bmt. Hng dn cch chn gi trcho php ca cc sai lch trn,v cch biu din cc sai lch, gi tr cho php ca sai lch trn bn v kthut.

Chng 4: Dung sai cc lp ghp in hnhTp trung nghin cu mi ghp then bng, mi ghp then hoa, mi ghp

ln ln trc v ln bc; mi ghp ren. Hng dn cch chn kiu lp ghp,v biu din kiu lp trn bn v. Trong chng ny cn quan tm n dungsai truyn ng bnh rng. Nguyn nhn dn n cc sai s, cc thng snhgi sai lch trong truyn ng bnh rng, cch chn gi trsai lch cho php,v cch biu din dung sai truyn ng bnh rng trn bn v.

Chng 5: Chui kch thc v cch ghi kch thc

Trnh by cch ghi kch thc trn bn v lp bphn my v bn vchi tit my, m bo thun li cho vic gia cng. Thit lp cc chui kchthc v tnh ton dung sai cho cc khu trong chui kch thc.

II- Mt sk hiu thng dng trong mn hc Dung sai Lp ghp

Ai l kch thc ca khu thi trong chui kch thcd l kch thc ca khu dng trcD l kch thc ca khu dng lei l sai lch di ca kch thc dng trc

es l sai lch trn ca kch thc dng trcEI l sai lch di ca kch thc dng lES l sai lch trn ca kch thc dng lIT l dung sai ca kch thc

N l di ca mi ghpS l khe hca mghpT l sai lch ca kch thc.


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CHNG 1

NHNG VN CBN TRONG DUNG SAI LP GHP

1.1. Kch thc- Kch thc ca chi tit my l khong cch gia hai im, hai ng, hochai mt thuc chi tit my, n vo dng trn bn vckh l mm.

- Kch thc c phn thnh 02 nhm:+ Kch thc nhm trc, khi ct gt thm slmgim kch thc, k hiu l d (Hnh 1.1).+ Kch thc nhm l, khi ct gt thm s lmtng kch thc, k hiu l D (Hnh 1.2).

- Gi trca kch thc c xc nh bng ccho.S dng dng c o chnh xc, phng

php o thch hp, o nhiu ln snhn c kt quo vi chnh xc cao.

- Sai skhi gia cng chi tit my:Khi gia cng khng tht c gi trng nhmong mun, do c

cc nguyn nhn sau:+ My khng chnh xc.+ Dao khng chnh xc.

+ G t khng chnh xc.+ Hthng cng ngh: MGDC bbin dng.+ Rung ng do lc ct thay i.+ Gin nkhng u do nhit thay i.

V d: cn gia cng 100 chi tit trc cng knh 20 mm, ta snhn c cc chi tit ckch thc ng knh dao ng trong khong 20,03 mm n 19,99 mm.

Nhvy lot chi tit c kch thcddn= 20 mm

dmax= 20,03 mm,dmin= 19,99 mm,

dmaxc gi l kch thc gii hn trn.dminl kch thc gii hn di.dmax- dminc gi l khong phn bkch thc(hay sai lch ca kch thc), k hiu l T.ddnl kch thc danh ngha.(dmax+ dmin)/2 l kch thc trung bnh, k hiu ldm.

Sai lch kch thc ln, tc l gia cng cchnh xc thp.

20

100

Hnh 1.1: Cc kchthc dng trc

15

22

Hnh 1.2: Cc kchthc dng l

dmin

ddn

dm

dmax

Hnh 1.3: Sai lch ca kch

thc gia cng


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- Ngoi ra, kch thc cn c phn thnh nhng loi sau:+ Kch thc thc,+ Kch thc o c,+ Kch thc thc theo k thut (kch thc o c + dung sai ca

dng co.+ Kch thc danh ngha,+ Kch thc gii hn,

- Biu din kch thc v sai lch kch thc trn s(Hnh 1.3).

nh gi mc chnh xc gia cngchi tit my, ngi tatin hnh gia cng mtlot N chi tit (slng

N khng t hn 60chic), sau o, xcnh cc kch thcgii hn, xc nh tnsut xut hin cc gitrkch thc, vngcong phn b tn sut,v ng cong phn bmt xc sut.

- ng cong phn btn sut Hnh 1.4.Trong dil gi trkch thc nm trong khong dmindmax), di/N l tn sutxut hin kch thc thi (Khi N ln c thxem y l xc sut p ca kchthc thi).

- ng cong phn bmtxc sut ca kch thcgia cng, phn b chun

Gauss (Hnh 1.5). Trong x = di- dm ,y = dp/dx,

l sai lch bnh phngtrung bnh

2= NxN

i

i /1

2=

Theo l thuyt xc sut, c99,73% kch thc calot chi tit nm trongkhong xmax- xmin= 6.

dm dmax

Hnh 1.4: Sphn btn sut kch thc

Tn sut di/N

Kch thc

dminMin phn bkchthc

dm6

Hnh 1.5: Sphn bmt xc sut kch thc

Trung tm phn by

x


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Khi thit k, m bo cho chi tit my c kh nng lm vic,ngi thit kphi xc nh sai lch cho php ca kch thc d (cn gi ldung sai, k hiu l IT), n nh kch thc ln nht v nhnht c thchpnhn:

dmax= d + esdmin= d + eiIT = es - ei

es gi l gi trsai lch trn cho phpei l gi trsai lch di cho php

Nu ta chn phng php gia cng khng hp l, min phn b 6khng nm trong min dung sai IT, sc phphm. Nu min phn b6qunhhn IT, c ngha l chng ta gia cng chnh xc cao hn so vi yucu, lm tng gi thnh ca chi tit. Phng php gia cng hp l nht (m

bo khng c phphm, v gi gia cng r), khi m 6= IT v min phn bkch thc trng vi min dung sai.

Dng xc sut kho st sai sgia cng kch thc chc thsdngtrong trng hp sn xut hng lot. Sau khi kho st lot chi tit gia cng utin, ta c th chn c phng php gia cng thch hp hn, hoc iuchnh my loi bcc chi tit phphm.

1.2. Lp ghp

- Mi ghp: Lp chi tit trc vo chitit bc sc mt mi ghp. Trnhnh 1.6 biu din mi ghp trtrn.

+ Mi ghp c di gi lmi ghp cht. di k hiul N, N = d - D.+ Mi ghp c khe h gi lmi ghp lng. Khe hk hiul S, S = D - d

- Kiu lp: Khi xem xt cc mi ghp ghp ca lot chi tit bc A vi lot chi

tit trc B, ngi ta phn bit:+ Kiu lp cht: Tt ccc mi ghp ca lot chi tit lp ghp vi nhauu c di. Ly bt cchi tit bc no lp vi chi tit trc u cmi ghp cht.+ Kiu lp lng: Tt ccc mi ghp ca lot chi tit lp ghp vi nhauu c khe h.+ Kiu lp trung gian: Mt smi ghp trong lot c di, skhc ckhe h. Ly mt chi tit bc lp vi mt trc bt ksc mi ghpc thcht, cng c thlng.

d

D

Hnh 1.6: Mi ghp trtrn


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Biu din kiu lp, min dung sai ca kch thc trc, ca kch thc ltrn Hnh 1.7. Kch thc trc, lc sai lch, nn di v khe hcng c sailch.

Sai lch ca di v khe h:Nmax= dmax- Dmin= es - EINmin= dmim- Dmax= ei - ESSmax= Dmax- dmin= ES - eiSmin= Dmim- dmax= EI - es

Cn c vo yu cu lm vic cami ghp, khi thit kchng ta phi chncc gi tr cho php [Nmax], [Nmin] hoc[Smax], [Smin]. Mi ghp t yu cu, khi

di hoc khe h nm trong gii hncho php.

1.3. Tnh i ln chc nng

- Yu cu ca kiu lp: khe hnm trong khong t [Smax] n [Smin]. Nulot chi tit trc B lp vi lot chi tit lA c Smax[Smax] v Smin[Smin]. Cngha l ta ly bt cchi tit trc no trong lot A lp vi mt chi tit tronglot B u c mi ghp thomn yu cu. Ta ni cc chi tit my trong lotA v B c tnh i ln chc nng hon ton. Chng c ththay thcho nhau,

m vn m bo chc nng lm vic.- Nu Smax> [Smax] hoc Smin< [Smin], lc cc chi tit trong lot A v Bkhng c tnh i ln chc nng. Tc l mt mi ghp ang thomn yu cu,nu thay thmt chi tit trc khc lp vo bc ang c, c thnhn c mtmi ghp khng t yu cu.

- Khi thit k, ngi ta cgng chn dung sai kch thc ca chi tit my mtcch hp l, chi tit my thomn tnh i ln chc nng.

- Trong sn xut hng lot, nu mi chi tit ca lot u t tnh i ln chcnng th lot chi tit t tnh i ln chc nng hon ton. Nu c mt hocmt schi tit trong lot khng t tnh i ln chc nng, th lot chi tit t tnh i ln chc nng khng hon ton.

Hnh 1.7: Min dung sai ca kchthc trc, kch thc l

Sai lch cakch thc l

Sai lch cakch thc truc

Kchthc

danhngha

es

ei ES

EI


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CHNG 2

DUNG SAI LP GHP TRTRN

2.1. Dung sai kch thc

2.1.1. Quy nh vdung sai kch thc

Dung sai ca kch thc c chn tuthuc vo chnh xc yu cuv ln ca kch thc

T = ai

Trong i l n vdung sai. n vdung sai c thtnh theo cng thc:

i = 0,45 3 d+ 0,001d i vi kch thc t1 dn 500 mm

i = 0,004d + 2,1 i vi kch thc trn 500 n 3150 mm

Tuy nhin, n gii cho vic lp tiu chun, TCVN quy nh gi tric thcho cc khong kch thc. Kch thc t1 n 500 mm c thphnthnh 13 25 khong, tutheo c tnh ca tng loi lp ghp.

a: l hsphthuc vo yu cu mc chnh xc ca kch thc.

TCVN 2244-1999 c quy nh 20 cp chnh xc kch thc: cp 01 ; 0 ;1 ; 2 ; 3 ; .... ; 18. Trong cp 01 chnh xc cao nht, cp 18 t chnh xc

nht. Cp 5 n cp 11 c dng trong thit kcc my thng dng. Gi trca a c thchn nhsau:

Cp chnh xc 4 5 6 7 8 9 10 11 12Gi trca a 5 7 10 16 25 40 64 100 160

Dung sai kch thc do TCVN quy nh c k hiu l IT. Gi tr ca ITc chn theo Bng 4.2 trang 24 ti liu [1]. Theo Bng 4.2, ng vi mi cpchnh xc v tng khong kch thc, kch thc cng ln, chnh xc cngthp, th dung sai cng ln.

2.1.2. Min dung sai v sai lch cbn

V d, to mi ghp tr trn t chitit trc v bc (Hnh 2.1) c kch thc danhngha d = D = 60 mm, chnh xc cp 7. Tra

bng 4.2 ta c

ITd= ITD= 30m = 0,03mm.

Mun c mi ghp cht ta phi b tr mindung sai ca trc mn pha trn min dung

60

Hnh 2.1: Mi ghp trtrn


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sai ca l(Hnh 2.2). Mun c mi ghp lng ta phi btr min dung sai catrc nm pha di min dung sai ca l(Hnh 2.3).

TCVN quy nh 27 cch btr min dung sai (so vi kch thc danhngha) cho kch trc, v 27 min dung sai cho kch thc l.

Mim dung sai ca kch thc trc c k hiu bng chin thng:

a, b, c, cd, d, e, ef, f, g, h, j, js, k, m, n, p, r, s, t, u, v, x, y, z, za, zb, zc

Min dung sai ca kch thc lc k hiu bng chin hoa:

A, B, C, CD, D, E, EF, F, G, H, J, JS, K, M, N, P, R, S, T, U, V, X, Y,Z, ZA, ZB, ZC

Vtr ca min dung sai c xc nh bi sai lch cbn (Hnh 2.4).

ITd

ITD

ddn

Hnh 2.2: Mi ghp cht

ITd

ITD

ddn

Hnh 2.3: Mi ghp lng

Rh

HF

TD

Ddn,ddn

Hnh 2.4: Hthng sai lch cbn theo TCVN

A

TD

B

TDTD

TD

JS

Td

jsTd

Td

a

fTdb

Td

TD

Td

r

Td

zc

ZC

TD


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Trsca cc sai lch cbn ca trc c cho trong Bng 4.3 trang27; trsca cc sai lch cbn ca lc cho trong Bng 4.4 trang 29 tiliu [1].

2.1.3. Dung sai ca kch thcKch thc trc, kch thc lv dung sai ca nc ghi trn bn vnhsau (Hnh 2.5):

- Ghi kch thc danh ngha, sai lch cbn v chnh xc kch thc

V d: 50n7 ; 150K7; 230h8 ; 130JS7

- Ghi kch thc danh ngha, km theo sai lch trnv sai lch di

V d: 042,0 017,050++ ; 012,0 028,0150+ ; 230-0,072; 02,0130

Nu sai lch trn, hoc sai lch di bng 0 th khng ghi s0; nu sai lchtrn v sai lch di c gi trtuyt i bng nhau, th ghi ln pha trn cngvi du .

- Hoc ghi csai lch cbn, cp chnh xc v sai lch trn, sai lch di

)(750 042,0 017,0++ n ; 230h8 (-0,072)

Trssai lch gii hn ca kch thc lc cho trong Bng 1 trang

133 ti liu [1]. Tr s sai lch gii hn ca kch thc trc c cho trongBng 2 trang 138 ti liu [1].

Trc khi ghi dung sai kch thc ln bn v, ngi thit kphi tnhton, hoc la chn cp chnh xc cho kch thc, dng sai lch cbn, hoccc sai lch gii hn ca kch thc. Cc sai lch gii hn c thnhn cthng qua bi ton gii chui kch thc, hoc xut pht tyu cu ca mighp, hoc ly theo kinh nghim c thng k trong cc bng tra. Khichn cp chnh xc gia cng cc kch thc cng cn n khnng tc chnh xc gia cng ca my, ca cc nguyn cng gia cng trn my.

2.2. Quy nh lp ghp:

p ng yu cu sn xut, ngi ta phi quy nh cc kiu lp vinhng c tnh khc nhau. Yu cu tt ccc mi ghp phi c di (chnkiu lp cht), yu cu tt ccc mi ghp c khe (chn kiu lp lng); hocyu cu mi ghp c di cng c m c khe hnh cng c (chnkiu lp trung gian).

50n7

1300,02

Hnh 2.5: Ghi dung sai


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2.2.1. Hthng l, hthng trc

Khi lp nhiu trc trn mtchi tit bc, ngi ta dng hthnglcbn. Min dung sai ca lcnh, c sai lch cbn kiu H. c c tnh khc nhau ca cc mighp, ta thay i min dung sai cakch thc trc (Hnh 2.6).

Khi lp nhiu bc trn mt chitit trc, ngi ta dng h thngtrc cbn. Min dung sai ca trcc nh, c sai lch c bn kiu h.

c c tnh khc nhau ca ccmi ghp, ta thay i min dung saica kch thc l(Hnh 2.7).

2.2.2. Kiu lp tiu chun,kiu lp u tin

Khi thit k mt mi ghpvi c tnh cho trc, chng ta cthchn mt min dung sai ca trckt hp vi mt min dung sai cal c di, hoc khe hngtheo yu cu. Song thun tincho vic gia cng, o kim tra kchthc ca chi tit trc v l, chngta nn chn cc kiu lp tiu chun c TCVN quy nh. Cc kiu lp tiuchun theo hthng lc cho trn Bng4.5 trang 32 ti liu [1]. Cc kiu lp tiuchun theo h thng trc c cho trn

Bng 4.6 trang 33 ti liu [1]. Cc kiu lptrong khung bi en l kiu lp u tin.

Nhvy,vi cc gi trgii hn cakhe h, hoc di cho trc, chng ta lachn cc kiu lp u tin trc; nu khngtm c kiu lp thomn c tnh choca mi ghp th chn cc kiu lp khngkhng u tin trong tiu chun; nu cngkhng tho mn c tnh cho ca mi

ghp, ta c thdng kiu lp kt hp gia h thng lv h thng trc theo

Td

TD1

TD2

TD3

d

dn

Hnh 2.7: Lp theo hthng trc cbn

Hnh 2.8: Ghi mi ghp trtrn

608

7

e

H

TD

Td1

Td2

Td3

Ddn

Hnh 2.6: Lp theo hthng lcbn


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Bng 2- 1: i chiu tiu chun TCVN 2245-77 vi tiu chun lp ghp cMim dung sai ca trccho kch thc t1 mm n 500 mm

TCVNc

TCVN2245-77

TCVNc

TCVN2245-77

TCVNc

TCVN2245-77

TCVN c TCVN2245-77

T41T31T21T11

L11= B1L21L31T4T3

n5m5k5

jS5h5g5f6n6m6

T2T1

L1 = BL2L3L4L5L6T43

k6jS6h6g6f7e8d8c8n7

T33T23T13

L13= B3L33

L14= B4L34L54

L15= B5

m7k7

jS7h7f8

h8, h9f9, e9

d9jS10

L16= B6L36L46L56

L17= B7L37

L18= B8L19= B9L110=B10

h11d11

b11, c11a11, b11

h12b12h14h15h16

tiu chun; nu vn khng tm c kiu lp thomn c tnh cho ca mighp, lc ta c thkt hp min dung sai bt kca trc v lc mighp c c tnh ng theo yu cu.

2.2.3. Ghi k hiu kiu lp trtrn trn bn vSau khi xc nh c tnh ca mi ghp, chn chnh xc cho kch

thc trc, kch thc l, chn hthng lp ghp, chn dng sai lch cbn(hay min phn bdung sai) cho kch thc trc, kch thc l, chng ta ghikiu lp ln bn v.

Kiu lp bao gm kch thc danh ngha, sai lch cbn v cp chnhxc ca kch thc lghi trn ts, sai lch cbn v chnh xc ca trcghi di mu s(Hnh 2.8).

Trong nhiu ti liu thit k, cng nhtrong cc tp bn vchi tit my,cc kiu lp c ghi theo tiu chun TCVN ban hnh nm 1963 (TCVN c).V d:

- Kiu lp cht C1, C2, C3, C4,

- Kiu lp trung gian T1, T2, T33, T41,

- Kiu lp lng L1, L2, L3, L4, L5, L6.

n nay cc tiu chun ny c thay th bng TCVN 2245-77,trong tiu chun mi, cch ghi kiu lp c quy nh khc vi tiu chun c.

ngi thit ktin sdng cc ti liu ctrong vic thit lp cc bn v,trn Bng 2-1 v Bng 2-2 ghi schuyn i ttiu chun csang tiu chunmi ca mt skiu lp thng dng.


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V d:

- Kiu lp ghi theo kiu c2T

A , c thay thbng kiu ghi mi6

7

k

H ,

- Kiu lpB

L2 , c thay thbng kiu ghi mi6

7

h

G ,

Bng 2-2: i chiu tiu chun TCVN 2245-77 vi tiu chun lp ghp cMim dung sai ca lcho kch thc t1 mm n 500 mm

TCVNc

TCVN2245-77

TCVNc

TCVN2245-77

TCVNc

TCVN2245-77

TCVNc

TCVN2245-77

T41T31T21

T11L11= A1L21L31T4T3

N6M6K6

JS6H6G6F7

N7M7

T2T1

L1 = A

L2L3L4L5T43T33

K7JS7H7

G7F7, F8E8D8N8M8

T23T13

L13= A3

L14= A4L34L54

L15= A5L16= A6

L36

K8JS8H8

H8, H9F9, E9D9, F10

H10H11D11

L46L56

L17= A7

L37A8A9A10

B11, C11A11, B11

H12

B12H14H15H16


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15

CHNG 3

DUNG SAI CC YU THNH HC

3.1. Sai lch hnh dng v vtr tng i ca cc bmt

Trong qu trnh gia cng c, khng nhng kch thc ca chi tit myc sai s, m hnh dng hnh hc ca bmt, vtr tng quan gia cc bmtcng c sai lch so vi l thuyt.

Nguyn nhn c cc sai lch trn cng do h thng cng nghMDGCbin dng, do my khng chnh xc, lc ct khng n nh, nhit thay i,dng cct khng chnh xc.

Cc sai lch hnh dng thng gp:

- phng ca mt phng

- thng ca ng thng

- trca mt tr

- trn ca mt tr

- cn (lm, trng) ca mt tr

Cc sai lch vtr tng i thng gp:

- song song ca hai bmt- vung gc ca bmt

- ng tm gia hai mt tr

- i xng ga hai bmt

- giao nhau gia hai ng

- o hng knh ca mt trso vi ng tm

- o mt u so vi ng tm

3.1.1. Biu din dung sai hnh dng v vtr tng i trn bn v

Dung sai hnh dng v vtr tng i ca cc bmt chi tit my cghi trn bn vnhHnh 3.1.

Dung sai hnh dng c biu din trong hai hnh ch nht. thnht ghi k hiu dng sai lch, thhai ghi gi trsai lch ln nht cho php:

- Dung sai thng, c tnh theo mt on thng no , v c khiu l " ", gi trsai lch ghi trn bn vc n vl mm.- Dung sai phng, tnh cho mt phng c gii hn bi mt ng

bao, c k hiu l " ", gi trsai lch c ghi trn bn vl mm.


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16

Hnh 3.1: Sai lch hnh dng v vtr tng quan ca cc bmt

A

0,06 AB

B

0,030,05 0,03 C

0,05 C

C

0,05

0,02

0,1/100 A

A

0,05

0,06 B

B

0,06 A

0,2 B

BA

- Dung sai trn, tnh cho mt ng trn, k hiu l " ", gi trsailch ghi trn bn vc n vl mm.- Dung sai cn ( lm, trng) c tnh trn mt mt ct dctrc ca mt tr, c k hiu l " ", gi trsai lch ghi trn bn vc

n vl mm.- Dung sai tr, tnh cho mt trc di nht nh, c k hiu l" ", gi trca sai lch ghi trn bn vl mm.

Dung sai vtr tng i c biu din trong ba hnh chnht. thnht ghi k hiu dng sai lch, thhai ghi gi trsai lch ln nht cho php, thba ghi mt hoc ng chun dng so snh. Cc dung sai vtr tngi gm c:

- Dung sai song song, quy nh song song gia 2 mt phng,

ng tm vi mt phng, gia 2 ng tm vi nhau, c k hiu l"// ", gi trsai lch song song ghi trn bn vc n vl mm.


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17

- Dung sai vung gc, quy nh vung gc gia hai mt phngvi nhau, gia hai ng tm vi nhau, gia ng tm vi mt phng,trn bn vk hiu l " ", gi trvung gc ghi trn bn vc nvl mm.

- Dung sai ng tm, quy nh slch ng tm cho php ca haimt tr theo l thuyt c chung ng tm, k hiu l " ", gi trng tm ghi trn bn vc n vl mm.- Dung sai i xng, quy nh sai lch cho php ca hai mt ixng thc ca hai phn tc chung mt i xng, k hiu l " ", gitrghi trn bn vc n vl mm.- Dung sai ct nhau, quy nh khong cch nhau cho php gia haing tm ca hai mt tr, theo danh ngha n phi ct nhau, k hiu l" ", gi trghi trn bn vl mm.

- Dung sai o hng knh - cn gi l o hng tm - ca mtmt tr i vi ng tm danh ngha hoc ng tm ca mt trchun no , c o trn mt mt ct ngang; k hiu l " ", gi trghi trn bn vc n vl mm.- Dung sai o mt u - cn gi l o mt mt - i vi ngtm danh ngha hoc ng tm ca mt trchun no , c o trnng bin ca mt u; k hiu l " ", gi trghi trn bn vc nvl mm.

3.1.2. Chn gi trdung sai hnh dng v vtr tng i

Trc khi ghi dung sai hnh dng v vtr tng quan ln bn v, chngta phi chn gi trdung sai hp l cho cc bmt v vtr tng i gia cc

bmt.

Dung sai hnh dng v v tr tng i ca cc bmt c chn tuthuc vo chnh xc yu cu ca chi tit my, m bo chi tit my c khnng lm vic. ng thi cng phi m bo c thddng gia cng chto chi tit my.

Tiu chun Vit Nam TCVN 384-1993 quy nh 16 cp chnh xc cho

yu thnh dng v vtr tng i ca bmt. Cp chnh xc ca yu thnhdng c chn tng ng vi cp chnh xc kch thc ca chi tit my, theoBng 5.2 trang 76 ti liu [1]. Cp chnh xc ca yu thnh dng v v trtng quan tng ng vi cc nguyn cng ct gt c cho trong Bng 5.5trang 80 ti liu [1].

Sai lch gii hn ca cc yu thnh dng v v tr tng quan cchn theo Bng 8 n Bng 11 Phlc 2 trang 147 ti liu [1].


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18

3.2. nhm bmt

Bmt chi tit

my sau khigia cngkhng bng

phng mtcch ltng, mc nhngmp m(Hnh 3.2).

Nhng mp m ny l do lp bmt bbin dng do khi ct gt, l donh hng ca cc chn ng khi ct, l vt ca li ct li trn bmt giacng, vv..

Theo tiu chun c ca Vit Nam (v tiuchun OCT ca Lin X c) nhm bmt cchia lm 14 cp (cp 1 n cp 14), cp 1 l nhmnht v cp 14 l bng nht. Trn bn v nhmc k hiu 1 n 14 - hoa 1 n hoa 14 (Hnh3.3).

Theo quy nh mi ca Vit Nam TCVN2511-1995, nhm trn b mt chi tit my cnh gi bng mt trong hai thng s Ra hoc Rz(Hnh 3.4). Nhng sc km chRzl gi trca Rz,nhng skhng km ch l gi trca Ra, n v lm.

- Sai lch trung bnh shc ca prfil Ra, co bng m. L trung bnh shc cc gi trtuyt ica prfil (hi) trong khong chiu di chun (L). Chtiu Rathng dng nh gi nhm bmt cp6 n cp 12.

- Chiu cao trung bnh ca prfil Rz, m. L trstrung bnh ca tngcc gi trtuyt i ca chiu cao 5 nh cao nht (ti) v chiu su ca 5 ythp nht (ki) ca prfil trong khong chiu di chun (L). Chtiu Rzthngdng nh gi nhm bmt cp 1 n cp 5 v cp 13, 14.

tin sdng cc ti liu thit kc xut bn trc y, trn Bng3-1 ghi gi trca Rav Rztng ng vi 14 cp nhm.

65

Hnh 3.3: Ghi nhmtheo quy nh c

2,1Rz15

Hnh 3.4: Ghi nhm

theo quy nh mi

L

ki

hi

Hnh 3.2: Bin dng ca bmt chi tit

ti


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Cp nhm ca bmt chi tit my cng c chn tng ng vicp chnh xc kch thc, cp chnh xc hnh dng ca chi tit my. ng thicng phi tng ng vi khnng gia cng ca cc nguyn cng gia cng c.

Gi trRav Rzca cc bmt c chn theo Bng 5.5 trang 80 vBng 5.6 trang 82 ti liu [1].

Cp nhm Ra, m Rz, m

12

3456789

1011121314

T80,0 40,0di 40 20

di 20 10di 10 5di 5 2,5di 2,5 1,25di 1,25 0,63di 0,63 0,32di 0,32 0,16di 0,16 0,08di 0,08 0,04

di 0,04 0,02di 0,02 0,01di 0,01 0,005

T320 160di 160 80

di 80 40di 40 20di 20 10di 10 6,3di 6,3 3,2di 3,2 1,6di 1,6 0,8di 0,8 0,4di 0,4 0,2

di 0,2 0,1di 0,1 0,05di 0,05 0,025

Bng 3.1: nhm bmt chi tit my


21/36

20

CHNG 4

DUNG SAI CC LP GHP IN HNH

4.1. Dung sai lp ghp then bng, then bn nguyt

Mi ghp then bng, then bn nguyt thng c dng lp bnhrng, bnh vt, bnh ai, a xch, khp ni trn trc.

Then l mt thanh hnh trc tit din chnht (i vi then bng) vhnh bn nguyt (i vi then bn nguyt). Trn trc v trn bc c lm ccrnh hnh trc tit din tng ng vi tit din ca then.

Mi ghp then bng trn trc bao gm hai mi ghp trtrn: Mi ghpgia then vi rnh trn trc v mi ghp gia then vi rnh trn bc (Hnh4.1).

Min dung sai ca kch thc b cathen, ca rnh then trn trc v trn bc cchn theo Bng 4.11 trang 39 ti liu [1].Dung sai chiu rng b ca then dng kiu h9.Dung sai chiu rng b ca rnh trn trcthng dng kiu H9, N9, P9. Dung sai chiurng b ca rnh trn bc thng dng kiuD10, JS9, P9.

Kiu lp ca mi ghp then c thchnnhsau:- Trong sn xut hng lot ln, then lp vi trc theo kiu N9/h9, v lp vi

bc theo kiu JS9/h9.- Trong sn xut n chic v lot nh, then lp trn trc v trn bc theo kiuP9/h9.- Khi chiu di then ln (l > 2d), then nn lp vi bc theo kiu D10/h9.- i vi then dn hng, cn di trt chi tit bc dc trc, then lp trn trctheo kiu N9/h9 v lp vi bc theo kiu D10/h9.

Sai lch gii hn ca cc kch thc trong mi ghp c thtra Bng 1,Bng 2 Phlc 1 trang 133, 138 ti liu [1].

4.2. Dung sai lp ghp then hoa

Mi ghp trc then hoa vi bc then hoa thc hin lp ghp theo haitrong ba kch thc: Chiu rng b, ng knh ngoi D, v ng knh trong d(Hnh 4.2).

Lp ghp then hoa c ththc hin nhsau:- Lp ghp theo yu tkch thc D v b khi lm ng tm theo D.

b

Hnh 4.1: Mi ghp then bng


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- Lp theo yu tkch thc d v b khi lm ng tm theo d.- Lp theo yu tkch thc b khi lm ngtm theo b.

Min dung sai kch thc ca trcthen hoa v bc then hoa c quy nhtrong TCVN 2324-1978. Khi thit k mighp c thchn min dung sai theo chdntrn Bng 4.12 v Bng 4.13 trang 41 tiliu [1].

Kiu lp ca mi ghp then hoa cthchn nhsau:

- Khi nh tm theo kch thc D

+ Lp ghp theo kch thc D c thchn kiu H7/f7 hoc H7/js6+ Lp ghp theo kch thc b c thchn kiu F8/f7 hoc F8/js7

- Khi nh tm theo kch thc d+ Lp ghp theo kch thc d c thchn kiu H7/f7 hoc H7/g6+ Lp ghp theo kch thc b c thchn kiu D9/h9 hoc D9/js7

Ghi k hiu lp ghp then hoa trn bn v:- C thghi ring tng mi ghp theo ba kch thc trn bn v.- Cng c th

ghi chung thnhmt dy s(Hnh 4.3).Trong d biuthnh tm theo

bmt trngknh d. S 8 chra c 8 then trntrc. Tip theo lkch thc v

kiu lp cang knh d,kch thc vkiu lp cang knh D,kch thc vkiu lp ca chiu rng b.

Hnh 4.3: Ghi kiu lp cho mi ghp then hoa

d-83677

f

H 401112

a

H 799

h

D

D

d

d1

Hnh 4.2: Mi ghp then hoa

b


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Sai lch caD, cp chnhxc 0, m

Sai lch ca D,cp chnh xc6, m

Sai lch ca d,cp chnh xc0, m

Sai lch ca d,cp chnh xc6, m

ng knhdanh nghaca : d, mm

es ei es ei ES EI ES EIn 18trn 18 30

trn 30 50trn 50 80trn 80 120trn 120150trn 150180trn 180250trn 250315trn 315400trn 400500

00

000000000

-8-9

-11-13-15-18-25-30-35-40-45

00

000000000

-7-8

-9-11-13-15-18-21-25-28-33

00

000000000

-8-10

-12-15-20-22-25-30-35-40-45

00

000000000

-7-8

-10-12-14-16-18-21-25-30-35

Bng 4.1: Sai lch gii hn ca kch thc ln

4.3. Dung sai lp ghp ln

Mi ghp ln c biu din trn Hnh 4.4. ln l chi tit my ctiu chun ha cao, c ch to trong nh my chuyn mn ha. Dung sai

ca ln c quy nh trong tiu chun v ln, nh my ch to ln gia cng ng theo tiu chun.

Khi thit kchng ta chtnh chn kiu , cln v cp chnh xc ca, khng cn quy nh dung sai cho .

Tiu chun quy nh 5 cp chnh xc ca ln: cp 0, cp 6, cp 5, cp4 v cp 2. Trong cp 0 l cp chnh xc bnh thng, cp 2 l chnh xccao nht.

Cc ln thng dng trong hp gim tcc cp chnh xc 0, trng hp svng quay catrc qu ln hoc yu cu chnh xc ng tmca trc cao, c thdng ln cp chnh xc 6.Bit k hiu ca ln chng ta s bit dung saica , do khng cn ghi k hiu dung sai ca ln trn bn vlp.

V d: ghi kiu lp gia bi vi trc v gi(Hnh 4.4):

K hiu 40k6 biu th:

ng knh trc l 40mm,

Hnh 4.4: Ghi kiu lpcho ln

40k6

68G7


24/36

23

pr

d1 =D1

d2 =D2

d = D

ai c

bu ln

Hnh 4.5: Kch thc cami ghp ren

Mim dung sai ca trc l k6,ng knh lvng trong ca d=40mm, min dung sai ca kchthc d do nh my chto quy nh.

K hiu 68G7 biu th:

ng knh lca gi l 68mm,Mim dung sai ca ll G7,ng knh vng ngoi ca D=68mm, min dung sai ca kch thcD do nh my chto quy nh.

Tuy nhin, khi lp ghp ln vi trc v gi , thng mt trong haivng lp c di. di slm cho vng bin dng c thdn n kt. tnh ton dn nca cc vng , kim tra hhng tm sau khilp ghp ln, chng ta cn bit dung sai kch thc ng knh ngoi D,

ng knh trong d ca . Gi trdung sai kch thc D, v d c ghi trnBng 4.1.

Kiu lp ghp ln vi trc v vhp c chn tuthuc vo kt cuca , iu kin sdng , c tnh tc dng ca ti trng v dng ti trngca cc vng ln.

C ba dng ti trng tc dng ln ln: Ti trng cc b, ti trng chukv ti trng dao ng.

i vi vng chu ti trng cc bv dao ng, thng chn kiu lp

c h di tc dng ca va p vchn ng, vng bx dch, thay i imchu lc, lc ln tng c tui bn.

i vi vng chu ti chu k,thng chn kiu lp c di duy trtnh trng chu lc ng u cu .

Tham kho Bng 4.7 v Bng 4.8trang 37 ti liu [1] chn kiu lp hp lcho vng trong v vng ngoi ca .

4.4. Dung sai lp ghp ren

Mi ghp ren gm c chi tit bu lngghp vi chi tit ai c. Bu lng c renngoi, ai c c ren trong. y chng tachquan tm n mi ghp ren hMt, ctit din ren tam gic.

Tu theo yu cu sdng, mi ghp

ren cng c thit k theo kiu lp cht,


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kiu lp lp lng, hoc kiu lp trung gian.

Cc kch thc chyu ca mi ghp ren c trnh by trn Hnh 4.5.

Mt ren l bmt xon vt, chnh xc to hnh ca n do ba thng s

(ng knh trung bnh d2= D2, bc ren pr, v gc nh ren ) quyt nh.Tuy nhin vic o kim tra kch thc prv tng i kh khn,

ngi ta thng quy nh dung sai cho cc kch thc d, d2, D2, D1m bo chnh xc ca mi ghp ren.

Cp chnh xc ca cc kch thc chyu ca mi ghp ren cchn theo Bng 7.1 trang 91 ti liu [1].

Sai lch cbn, min dung sai ca mi ghp ren theo kiu lp lngc chn theo Bng 7.2 v Bng 7.3 trang 91 ti liu [1].

Sai lch c bn, min dung sai ca mi ghp ren theo kiu lptrung gian c chn theo Bng 7.4 v Bng 7.5 trang 92 ti liu [1].

Sai lch cbn, min dung sai ca mi ghp ren theo kiu lp chtc chn theo Bng 7.6 v Bng 7.7 trang 93 ti liu [1].

Dung sai kch thc v sai lch gii hn ca cc kch thc trongmi ghp ren c chn trong Bng 15 n Bng 21 Phlc 4 trang 152ti liu [1].

Biu din mi ghp ren trn bnv, v dnhtrn Hnh 4.6. Trong :- M20 biu th ren tam gic h Mt, cng knh thn bu lng d = 20mm,- S1,5 biu thdng ren bc nhpr=1,5mm (nu dng bc ren ln th khng cnghi),- K hiu 2(Pl) chren 2 u mi (nu ren1 u mi th khng cn ghi,- ChLH chren tri (nu ren xon phi thkhng cn ghi),- K hiu 4H6H l mim dung sai ca lai c, ng knh trung bnh D2ccp chnh xc 4 sai lch cbn kiu H; ng knh trong ca ai c D1c cpchnh xc 6 sai lch cbn kiu H (nu kch thc D2v D1cng min dungsai th chghi mt ln).- K hiu 4j6g biu thmin dung sai ng knh trung bnh d2ca bu lng,cp chnh xc 4 sai lch cbn kiu j, (d2= (d+d1) / 2); ng knh ngoi ca

bu lng d c cp chnh xc 6 sai lch cbn kiu g. Nu kch thc d2v dcng cp chnh xc v min dung sai th chghi mt ln.

Hnh 4.6: Ghi kiu lp mi ghp renM20 1,5 2(Pl) LH - 4H6H /4j6g

d1

d


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4.5. Dung sai truyn ng bnh rng

4.5.1. Sai sgia cng bnh rng

B truyn bnh rng c gia cng v lp t chnh xc s thc hin

chuyn chuyn ng m, s vng quay n2 ca trc b dn khng dao ng,trong qu trnh n khp cc mt rng tip xc tt vi nhau, khng xy ra chnp nhau. Thc tkhi gia cng bnh rng, c nhiu yu t lm sai lch hnhdng v kch thc ca rng, ca bnh rng, dn n btruyn lm vic khngtt.

Cc sai skhi gia cng bnh rng c chia thnh bn loi:

- Sai s hng tm, gy ra s dch chuyn bin dng rng theo hngknh, bin dng thc tgn tm quay hoc xa tm quay hn so vi vtrl thuyt.

- Sai shng tip tuyn, lm cho bin dng rng dch chuyn qua li sovi vtr l thuyt theo phng tip tuyn ca vng trn chia.

- Sai shng trc, lm cho bin dng rng dch chuyn sai vi vtr lthuyt theo hng dc trc.

- Sai shnh dng bin dng rng, lm cho bin dng rng khng ngvi ng thn khai ca vng trn.

Cc sai sgia cng bnh rng cng c chia lm hai nhm:- Sai s tn s thp, l sai sxut hin mt ln sau mi vng quay ca

bnh rng. Cc sai sny gn lin vi phi v bn my mang phi ch

to bnh rng. Sai stn sthp c k hiu bng chF.- Sai s tn scao, l sai sxut hin nhiu ln sau mi vng quay ca

bnh rng. Cc sai sny thng gn lin vi dao v bn my mangdao gia cng bnh rng. Sai stn scao c k hiu bng chf.

4.5.2. chnh xc truyn ng bnh rng

chnh xc ca truyn ng bnh rng c nh gi thng qua bnchnh xc thnh phn:

- chnh xc ng hc, l mc dao ng ca svng quay trn trcbdn.- chnh xc n khp m, l mc gy nn rung ng, va p, tingn trong qu trnh btruyn lm vic.

- chnh xc tip xc, l khnng tip xc nhiu hay t ca i rng nkhp trong qu trnh chu ti trng.

- chnh xc khe hmt bn ca i rng, l khnng khng gy chnp gia cc rng trong qu trnh n khp.

chnh xc ng hc ca btruyn bnh rng c phn chia thnh12 cp, cp 1 c mc chnh xc cao nht, cp 12 c mc chnh xc thp nht.

chnh xc ng hc c nh gi qua cc thng s:


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- o hng tm ca vnh rng Fr, l s thay i ln nht khongcch ttm quay n ng chia ca rng, sau mt vng quay.

- Sai sng hc ca bnh rng Fi, l sai lch ln nht vgc quay cabnh rng sau mt vng quay, khi n n khp vi bnh rng mu chnh

xc.- dao ng khong cch tm o sau mt vng Fi, l sthay i ln

nht ca khong cch tm gia bnh rng c sai s (bnh rng o) vbnh rng mu chnh xc n khp kht vi nhau, khi quay bnh rng oi mt vng.

- Sai stch lubc rng FP, l hiu i sln nht ca cc gi trsai stch luk bc rng, vi tt ccc gi trk t2 n z/2 (z l srng ca

bnh rng).- Sai s ln rng Fc, l sai s ln nht vgc quay gia bnh rng gia

cng v d

ng cct rng (dao phay r

ng).

- Dao ng khong php tuyn chung Fvw, l sdch chuyn bin dngrng theo hng tip tuyn trong phm vi mt vng quay ca bnhrng.

chnh xc lm vic m cng c chia lm 12 cp . Mc chnhxc cao hay thp, tuthuc vo gi trca cc thng ssau:

- Sai sng hc cc b fi, l sai lch ln nht vgc quay ca bnhrng sau khi quay i mt rng, khi n n khp vi bnh rng mu chnhxc.

-

Sai lch khong cch tm o sau mt rng fi

,

l sthay i ln nht cakhong cch tm gia bnh rng c sai s(bnh rng o) v bnh rngmu chnh xc n khp kht vi nhau, khi quay bnh rng o i mtrng.

- Sai s bin dng rng ff, l khong cch ln nht gia hai bin dngdanh ngha p vi bin dng thc.

- Sai lch bc rng fpt, l hiu ca sai lch trn v sai lch di ca bcrng pt.

- Sai lch bc csfpb, l hiu gia bc csthc v danh ngha.chnh xc tip xc cng c 12 cp . nh gi mc chnh xctip xc thng qua cc thng s:

- Vt tip xc, quan st c khi ta bi sn ln rng ca mt bnh rngv cho n khp vi bnh rng khc, c ti trng. T sgia din tchca vt tip xc v din tch bmt lm vic ca rng cng ln, th chnh xc cng cao.

- Sai shng rng F, l khong cch ln nht gia ng thng hocng xon p vi mt rng v ng l thuyt.

- Sai shnh dng v v tr ng tip xc Fk, l khong cch gia haing thng p vi mt rng thc, song song vi ng tip xc ca

i rng.


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Mc hmt bn c nh gi qua hmt bn Jn. Jnc o trnng php tuyn vi bin dng rng. Jndao ng nhiu th chnh xc thpv ngc li.

i vi cp bnh rng khng iu chnh c vtr tm bnh rng, thhmt bn c dnh gi thng qua sai lch khong cch tm fa.

i vi bnh rng iu chnh c v tr tm, th hmt bn cnh gi thng qua dch chuyn phnhnht ca bin dng gc EH.

kim tra mc chnh xc chto bnh rng ta dng mt bthngsbao gm nhng thng sv nhng cp thng snh gi mc chnh xcng hc, n khp m, tip xc v hmt bn (xem Bngg 8.1 trang 102ti liu [1]). Vic chn b thng sno l tu thuc vo cp chnh xc ca

bnh rng v iu kin sn xut, kim tra ca c s sn xut. B thng s

c chn cn kt hp sao cho vic kim tra l n gin nht, sdng csdng l t nht. V d, khi chn thng snh gi chnh xc ng hc lFi

, th sdng ngay thng sfinh gi chnh xc n khp m.

Tiu chun Vit Nam TCVN 1067-84 quy nh 12 cp chnh xc cho chnh xc ng hc, n khp m, tip xc, vi cp 1 l chnh xc cao nht.TCVN 1067-84 cng quy nh 6 dng khe h mt bn: A, B, C, D, E, H.Trong dng A c sai lch cbn ln nht v dng H c sai lch c bn

bng khng (Jnmin = 0). Tiu chun cng quy nh 8 cp chnh xc ca hmt bn ca rng, k hiu x, y, z, a, b, c, d, h. Trong cp x c dung sai lnnht v cp h c dung sai nhnht.

Chn cp chnh xc cho truyn ng bnh rng, phi da vo iu kinlm vic cthca btruyn, v nhng yu cu vtruyn ng. Xc nh cpchnh xc c thbng tnh ton hoc da theo kinh nghim, theo cc bng chdn (Bng 8.2. trang 105 ti liu [1]). Cc chnh xc ca truyn ng bnhrng c th chn cc cp khc nhau. Theo kinh nghim: cp chnh xc nkhp m cao hn khng qu 2 cp v thp hn khng qu 1 cp so vi cpchnh xc ng hc, cp chnh xc tip xc c thcao hn hoc thp hn 1cp so vi cp chnh xc n khp m.

4.5.3. Ghi k hiu cp chnh xc v dng khe hmt bn trn bn v

Cp chnh xc v dng khe hmt bn ca b truyn bnh rng cghi bng dy sv ch.

V d: 8-7-6 Ba TCVN 1067-1984. Trong chsu tin chcp chnhxc ca chnh xc ng hc, sthhai chcp ca chnh xc n khpm, sthba chcp ca chnh xc tip xc, chin hoa chdng khe hcnh rng, chin thng chchnh xc ca dng khe h.


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Trng hp c bit, nu cp chnh xc ca ba chnh xc nhnhau,th chcn ghi mt chs(v d8 Ba TCVN 1067-1984). Nu cp chnh xcca dng khe h cnh bn trng vi dng khe h th khng phi ghi ch inthng km theo (v d8-7-6 B TCVN 1067-1984).


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CHNG 5

CHUI KCH THC V CCH GHI KCH THC

5.1. Chui kch thc5.1.1. Cc khi nim cbn

- nh ngha:Chui kch thc l tp hp cc kch

thc c lin quan vi nhau v to thnh mtvng kn (Hnh 5.1).

Cc kch thc tham gia trong chui gil cc khu.

- Phn loi:+ Chui kch thc chi tit: Tt c cc khutrong chui thuc mt chi tit.+ Chui kch thc lp ghp: Cc khutrong chui thuc cc chi tit khc nhautrong mi ghp.+ Chui ng thng: Cc khu trongchui song song vi nhau.+ Chui mt phng: Cc khu trong chui

khng song vi nhau, nhng nm trongcng mt mt phng (Hnh 5.2).+ Chui khng gian: Cc khu trong chuikhng song vi nhau, v nm trong cc mt phng khc nhau.+ Khu thnh phn: Kch thc ca khu thnh phn do qu trnh gia cngquyt nh v khng phthuc vo cc khu khc. Cc khu thnh phn ck hiu l Ai, vi i = 1 n+m.+ Khu khp kn (hay khu tng): Kch thc ca n hon ton phthuc vocc khu thnh phn. Trong mi chui chc mt khu khp kn, c k hiul A.

+ Khu tng: Khi tng kch thc ca khu tng, th kch thc ca khu khpkn cng tng v ngc li. Slng khu tng trong chui c k hiu l m.Khu tng c tnh cht ging nhkch thc l, nn sai lch gii hn trn cakhu tng k hiu l ES, sai lch gii hn di l EI.+ Khu gim: Khi tng kch thc ca khu gim, th kch thc ca khukhp kn gim v ngc li. S lng khu gim trong chui k hiu l n.Khu gim c tnh cht nhkch thc dng trc, nn sai lch gii hn cakhu gim k hiu l es v ei.

- Cc bi ton gii chui kch thc, c hai bi ton:

Hnh 5.1: Chui kch

A1

A2

A3A

2

A2A3

Hnh 5.2: Chui mt phng

A1

A


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+ Bi ton thun: Cho kch thc v sai lch gii hn ca cc khu thnhphn, tnh kch thc v sai lch gii hn ca khu khp kn.+ Bi ton nghch: Cho kch thc ca cc khu trong chui, cho sai lch giihn ca khu tng, tnh sai lch gii hn ca cc khu thnh phn.

5.1.2. Gii bi ton thun

Xt chui kch thc mt phng c n khu gim v m khu tng. Dungsai ca khu thnh phn thi l Ti. Sai lch trn ca khu tng l ESi, sai lchdi l EIi(i=1m). Sai lch ca khu gim l esjv eij, vi j=1n. Cc n sca bi ton c xc nh nhsau:- Kch thc ca khu tng c tnh theo cng thc:

A= +

=

mn

i

iiA1

Trong il hsnh hng ca khu thnh phn n khu tng.i vi khu tng i= cosi, i vi khu gim i= -cosi. Vi il gc lmbi phng ca khu i v phng ca khu tng.- Dung sai ca khu khp kn bng tng dung sai ca cc khu thnh phn:

T= imn

i

i T+

=1

- Sai lch trn ca khu khp kn c tnh theo cng thc:

ES= = =

m

i

n

j

jji eiE1 1

iS

- Sai lch di ca khu khp kn c tnh theo cng thc:

EI= = =

m

i

n

j

jji esE1 1

iI

- Sai lch trung bnh ca khu khp kin k hiu l Em, sai lch trung bnh cakhu khp kn bng tng sai lch trung bnh ca khu tng tri tng sai lchtrung bnh ca khu gim:

Em= = =

m

i

n

j

mjji eE1 1

mi

5.1.3. Gii bi ton nghch theo i ln chc nng hon ton

n gin ta xt chui ng, c m+n khu thnh phn, v mt khutng. bit kch thc ca cc khu, bit sai lch trn v sai lch di cakhu tng. Tnh sai lch trn v sai lch di ca cc khu thnh phn. Biton c 2(n+m) n s l ESiv EIivi i = 1 m+n. Bi ton c gii nhsau:

- Giscc khu thnh phn c cng chnh xc, tc l cc khu c cng hschnh xc am.

- Xc nh hskch thc i ca cc khu thnh phn, dng Bng 9.1 trang114 ti liu [1].

(5.1)

(5.2)

(5.3)

(5.4)

(5.5)


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- Tnh am: Tcng thc T= +

=

nm

i

iT1

= +

=

nm

j

jmia1

= amij, suy ra

am= T/ij

- Xc nh chnh xc ca cc khu: Dng Bng 4.1 trang 24 ti liu [1] xc nh chnh xc ca cc khu thnh phn. Nu am trng vi gi tr atrong bng, ta ly chnh xc ca cc khu l nhnhau. Nu amnm gia haigi tra trong bng 4.1, ta ly mt skhu c chnh xc cao hn am, mt skhu c chnh xc thp so vi am.

- Chn mt khu k li lm khu b, sai lch ca khu ny c tnh ton.

- Tra sai lch gii hn ca cc khu tng theo sai lch cbn kiu H, sai lchgii hn ca cc khu gim theo sai lch cbn kiu h. Ta stm c m+n-1sai lch gii hn trn v m+n-1 sai lch gii hn di.

- Tnh sai lch ca khu Aktm hai n scn li:Dung sai ca khu Akc tnh theo cng thc:

Tk= T- +

=

1

1

nm

i

iT

Trng hp Akl khu tng

Emk=

==

+ mm

i

mi

n

j

mj EEe1

11

ESk = Emk+ Tk/2EIk= Emk- Tk/2

Trng hp Akl khu gimemk=

==

mn

j

mj

m

i

mj EE1

11

E

esk= emk+ Tk/2eik= emk- Tk/2

Gii chui theo phng php i ln chc nng hon ton sthun licho vic tchc sn xut, lp rp my, c bit thun li cho vic sa chathay thcc chi tit my bhng. Nhng trong trng hp dung sai ca khu

tng nh, s lng khu thnh phn ln, lm cho dung sai ca khu thnhphn qu nh, kh khn cho vic gia cng, tng gi thnh gia cng. Lc ngi ta phi gii chui theo phng php i ln chc nng khng hon ton.

5.1.4. Gii bi ton nghch theo i ln chc nng khng hon ton

Thc cht ca phng php ny l mrng dung sai ca cc khu thnhphn cho dgia cng, hgi thnh sn phm. Chng ta c thdng mt trongbn cch sau y:

- Phng php tnh xc sut: Chp nhn c mt s lng nh ph phm(khng m bo yu cu ca khu tng) ln trong sn phm. S lng ph

(5.6)


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phm thng c khng chdi 5%. Lng dung sai mrng thm ctnh theo xc sut.

- Phng php lp sa: Chng ta chn ra mt khu Akc thddng ct gt,co sa trong khi lp (Akc gi l khu b, hay khu bi thng). Dung saica cc khu thnh phn cn li sc chn theo chnh xc v khnnggia cng kch thc thun li nht. c tnh ca khu khp kn c m bo

bng cch co sa khu Ak trong qu trnh lp ghp. Dung sai ca cc khuthnh phn phi m bo cho khu Akc lng dln co sa. Phng

php ny tn rt nhiu thi gian cho qu trnh lp ghp. c bit kh khn, khicn phi thay thchi tit my bhng.

- Phng php lp iu chnh: Chng ta chn ra mt khu Aklm khu iuchnh, c thiu chnh c kch thc ca khu ny trong qu trnh lp rp.Dung sai ca cc khu thnh phn khc c chn theo chnh xc v khnng gia cng kch thc. c tnh ca khu khp kn c m bo bngcch iu chnh khu Ak trong qu trnh lp ghp. Dung sai ca cc khuthnh phn phi m bo cho khu Akc khong iu chnh khng qu ln.Phng php ny tn t thi gian hn phng php lp sa, nhng kt cumy phc tp.

- Phng php lp chn: Mrng dung sai ca mi khu thnh phn ln hai,ba hoc bn ln. Sau mi khu c chia thnh cc nhm tng ng vi sln tng dung sai. V dtng 3 ln, thi ta chia lm 3 nhm. Khi lp ghp, phily chi tit ca cc nhm tng ng lp vi nhau. V dnhm 1 lp vi 1,

nhm 2 lp vi 2. Nh vy s m bo c c tnh ca khu khp kn.Phng php ny mt thi gian phn nhm, phin phc trong lp ghp v boqun cc nhm.

5.1.5. Gii bi ton nghch theo phng php tnh xc sut

Khi gii theo yng php i ln chc nng hon ton, ta thy khukhp kn Ac gi trln nht khi tt ccc khu tng c gi trln nht vcc khu gim c gi trb nht, v ngc li. Song xc sut kch thc nhnht v kch thc ln nht ca mi khu thnh phn l qu b, nn xc sut

kch thc nhnht v kch thc ln nht ca khu tng, c thcoi nhbngkhng. Vi l lun nhvy, ta c thmrng dung sai ca mi khu thnhphn ln mt lng, th xc sut cc kch thc ca khu tng nm ngoi mindung sai cng tng ln khng ng k, c thchp nhn c.

p dng nh l ca xc sut cho chui kch thc ta c:

+

=

=nm

i

i

1

22

Nu ly Ti= 6i v T= 6, , thay vo cng thc (5.7), ta c

+

= =

nm

i

iTT1

22 hay

(5.7)


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+

=

=nm

i

iTT1

2

Chn cp chnh xc ca cc khu thnh phn nhnhau, Ti= amii, ta c:

+

= =

nm

i

im iaT1

2 suy ra

am= T/ +

=

nm

i

ii1

2

Gi trca amtnh theo cng thc (5.9) ln hn nhiu so vi tnh theocng thc (5.6). C ngha l chnh xc ca kch thc gim i, dung saikch thc c tng ln.

C c gi th amchng ta tip tc thc hin cc bc gii bi tontng tnhgii bi ton theo phng php i ln chc nng hon ton.

5.2. Ghi kch thc cho bn vckh

Sau khi tnh ton kch thc ca cc chi tit my theo cc iu kin bn,iu kin cng. Ta thit lp bn vlp cc bphn my, vtch ring tng chitit my. Tin hnh ghi kch thc cho bn vlp bphn my, bn vchi titmy.

Ghi kch thc cho bn vlp mt cch hp l, sthun li cho vic lp rp,ddng m bo cht lng ca my, thun li cho vic gii chui kch thcxc nh dung sai kch thc ca cc khu.

Ghi kch thc cho bn vchi tit my mt cch hp l, chn ng chun kchthc, chn ng khu khp kn, sm bo cho chi tit my c khnnglm vic v ddng cho qu trnh gia cng chto chi tit my.

Kch thc trn bn v c ba loi: Kch thc chiu di, kch thc ngknh v kch thc gc.

a s cc kch thc chiu di tham gia vo chui kch thc, chng ta squan tm nhiu hn n loi kch thc ny.

5.2.1. Nhng nguyn tc chyu cn m bo khi ghi kch thcKhi ghi kch thc cho bn v lp, bn vchi tt my cn m bo mt snguyn tc sau:

- Kch thc ca mi phn t trn bn vphi c xc nh mt cch duynht. Hoc c trc tip trn bn v, hoc c tnh ton qua cc kch thccc khu thnh phn ca chui.

- Khng ghi kch thc cho khu khp kn trong chui kch thc. Nu ghi thphi c du hiu chr l khu khp kn.

- Trn bn vmi kch thc chc ghi mt ln.

(5.9)

(5.8)


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- Tt ccc kch thc u phi c sai lch trn v sai lch di cho php.

- Skhu trong mt chui cng t, cng tt.

- Mt kch thc c ththam gia nhiu chui kch thc. Schui kch thc,

mt khu tham gia, cng t cng tt.- Mi kch thc c mt chun xc nh (mc tnh). Ngi lp quy trnhcng nghc thdng chun khc vi ngi thit k. Cgng dng cng tchun cng tt. Chun thit knn trng vi chun cng ngh.

5.2.2. Chn phng n ghi kch thc chiu di cho bn vchi tit my

Kch thc chiu di ca chi tit my c thghi theo nhiu phng nkhc nhau. Cc phng n u thhin y kch thc mi phn tthucchi tit my. Song chng ta phi chn ra phng n tt nht, ph hp vi

phng php gia cng v quy m sn xut chi tit my.C ba cch ghi kch thc chiu di:

- Ghi kch thc thnh mt chui, cc kch thc ni tip nhau (Hnh 5.3).Mi kch thcdng mtchun khcnhau. Mi khuthnh phn cdung sai nh,

nhng dung saica khu khpkn rt ln.Phng phpny ph hp vi dng sn xut nh, thc hin trn cc my vn nng.

- Ghi kch thc theo mt chun thng nht (Hnh 5.4). S chui kchthc nhiu,khu khp knnhiu. Dung sai

ca mt skhukhp kn c thvt qu gi tryu cu. Kiuny thngdng trong snxut hng lot,dng nhiu daogia cng trongmt nguyncng.

Hnh 5.3: Ghi lin tip cc kch thc thnh mt chui

A1 A2 A3 A4 A5

Hnh 5.3: Ghi kch thc theo chun thng nht

A1A2

A3A4

A5


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Hnh 5.3: Ghi kch thc kt hp chai cch

A1

A2

A3

A4

A5

- Dng phi hp hai cch trn (Hnh 5.5). Dng chun thng nht gimskhu. Trong khi nhng kch thc cn chnh xc cao, c dung sainh, khng dng lm khu khp kn trong chui kch thc. Phng phpny c dng nhiu trong thc tsn xut.

ducnguyen.utc - dung sai lap ghep.pdf

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