Chuong 4 CHUẨN- Công nghệ chế tạo máy

BI GING CNG NGH CH TO MY

H ni, 1/2015

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B mn Cng ngh ch to my

Vin C kh - HBKHN

T1

Cng ngh Ch to my

Chng 4. Chun

I. Khi nim

Khi gia cng chi tit cn c mt v tr xc nh so vi my hoc g. Chi tit c cc b mt:

B mt nh v: 1,2

B mt kp cht: 3

B mt gia cng: 4,5

B mt t do: 6,7,8

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B mn Cng ngh Ch to my Vin C kh BKHN

II. nh ngha

Chun l tp hp nhng b mt, nhng ng, nhng im m ngi ta cn c vo xc nh v tr ca cc b mt, ng hoc im khc ca bn thn chi tit hoc ca chi tit khc

Nh vy, chun c th l b mt, ng hoc im

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III. Phn loi chun

1. Chun thit k

2. Chun cng ngh

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1. Chun thit k

L nhng b mt, ng hoc im c dng thit k chi tit

Chun thit k c th l: chun thc hoc chun o

Chun thc (mt A) Chun o (im O)

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2. Chun cng ngh

Chun cng ngh chia ra:

Chun gia cng

Chun lp rp

Chun o lng (chun kim tra)

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2.1. Chun gia cng

Nu g t t ng t kch thc H th mt A lm hai nhim v: mt t v mt nh v (a)

Nu g chi tit theo ng vch du B th mt A lm nhim v mt t (b), cn chun nh v l ng vch du B

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2.1.1. Chun th

L chun cha c gia cng

Chun th cn phi bng phng, khng c g gh, khng c h hng

Ch trong trng hp phi a vo xng dng gia cng s b th chun th mi l nhng b mt qua gia cng. Nhng trng hp ny thng gp trong ch to my hng nng. , cc chi tit rn ln chuyn n qua tin th vi mc ch pht hin ph phm khi to phi, vn chuyn v gia cng d dng.

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2.1.2. Chun tinh

L chun qua gia cng. Chun tinh chia ra:

Chun tinh chnh (chun dng khi gia cng v lp rp-l A trn hnh a)

Chun tinh ph (chun chi c dng khi gia cng m khng dng khi lp rp- mt 1 v l 2 trn hnh b, mt l tm trn hnh c)

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(a) (b)

(c)

2.2. Chun lp rp

L chun c dng xc nh v tr tng quan ca cc chi tit khc nhau ca mt b phn my trong qu trnh lp rp

Cc bnh rng, bcchun lp rp l l v mt u

Chun lp rp c th trng vi mt t lp rp cng c khi khng

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2.3. Chun o lng

Chun o lng (chun kim tra) l chun cn c vo o hay kim tra kch thc, hnh dng hnh hc hoc v tr tng quan

Trong thc t c khi chun thit k, chun gia cng, chun lp rp v chun o lng trng nhau hoc khng trng nhau

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VD: khi kim tra ng tm ca cc bc trc, thng dng 2 l tm lm chun, chun ny l chun kim tra

IV. Qu trnh g t chi tit

Mc ch ca qu trnh g t???

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IV. Qu trnh g t chi tit

1. Qu trnh nh v

2. Qu trnh kp cht

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1. Qu trnh nh v

Xc nh v tr chnh xc ca chi tit: hnh a: chi tit c nh v bng mt B t kch thc H, gc KT l bn my hoc b mt nh v. G t trn mm cp 3 chu t nh tm: sau khi a chi tit ln mm cp, vn cho cc chu tin vo, sao cho tm chi tit trng vi tm my. Lc ny qu trnh nh v kt thc.

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B

2. Qu trnh kp cht

L qu trnh c nh v tr ca chi tit sau khi nh v chng li tc dng ca ngoi lc (ch yu l lc ct) trong qu trnh gia cng lm x dch chi tit sau khi nh v

Qu trnh kp cht xy ra sau qu trnh nh . v, ch khi no qu trnh nh v kt thc th mi bt u qu trnh kp cht. Khng bao gi lm ngc li.

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V. Cc phng php g t chi tit

1. Phng php r g

2. Phng php t ng t kch thc

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1. Phng php r g

C hai PP r g: r trc tip trn my v r theo ng vch du. Theo PP ny th cng nhn dng mt vi dng c nh bn r, mi r, ng h so hoc ng knh quang hc (trn my doa ta ) xc nh v tr ca chi tit so vi my v dng c ct

PP r g c dng trong SX nh hay n chic hoc trong nhng trng hp mt phi qu th khng th dng g c

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1a. u im ca PP r g

C th t CX cao (dng ng h chnh xc v tay ngh cng nhn)

Tn dng mt s phi khng chnh xc phn b u lng d

Loi tr nh hng ca mn dao

Khng cn g phc tp

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1b. Nhc im ca PP r g

Tn thi gian cho r g

Bc th phi cao

Khi r theo ng vch du s c sai s v ng vch du c kch thc

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2. Phng php t ng t kch thc

Theo phng php ny th dng c ct c v tr tng quan c nh so vi chi tit (v tr iu chnh). V tr ny nh cc c cu nh v ca g m bo

Khi gia cng theo phng php T t kch thc th my v dao c iu chnh trc

Phng php c s dng trong SX ln

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2a. /im ca PP t ng t k/thc

m bo CX gia cng, t ph thuc vo tay ngh ca cng nhn

Sau khi g, ct mt ln l t kch thc

Nng sut gia cng cao

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2b. N/im ca PP T t kch thc

Chi ph tin v thi gian cho vic iu chnh

Chi ph cho vic ch to phi chnh xc

Chi ph cho vic ch to g

Nu dao mn nhanh s nh hng n kch thc gia cng

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VI. Nguyn tc 6 im khi nh v chi tit

Mt vt rn trong khng gian c 6 bc t do khi ta t vo h ta -cc (h ta khng gian 3 chiu). 6 bc t do l: 3 bc xoay xung quanh 0X, 0Y v 0Z; 3 bc t do tnh tin dc trc 0X, 0Y v 0Z

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VI. Nguyn tc 6 im khi nh v chi tit

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1. Mt s qui nh v s bc t do

Mt mt phng hn ch 3 bc t do

Khi V di hn ch 4 bc t do

Khi V ngn hn ch 2 bc t do

Cht tr di hn ch 4 bc t do

Cht tr ngn hn ch 2 bc t do

Cht trm hn ch 1 bc t do

Hai mi tm hn ch 5 bc t do (g trn my tin hoc my mi)

Mm cp 3 chu t nh tm hn ch 4 hoc 2 bc t do ty tng trng hp

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1. Mt s qui nh v s bc t do

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2. Siu nh v

Trong trng hp mt bc t do c hn ch qu mt ln th s sinh ra siu nh v

a) Mt phng v cht tr di (3+4=7). Nh vy l siu nh v

b) Nu ta c tnh cho mt phng tip xc vi mt t thi cht nh v s b b cong

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VII. Nguyn tc chn chun

Mc ch chn chun:

m bo cht lng gia cng

Nng cao nng sut v h gi thnh

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1. Chn chun cho chi tit dng hp

-Trng hp c c ta ly A lm chun gia cng l 0, sau ly 0 lm chun gia cng A, cui cng ly A lm chun gia cng B

-Trng hp l c rng: ly l lm chun gia cng A ri sau ly A lm chun gia cng B v 0

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2. Chn chun cho v ng c in

Khi g/c v ng c in phi m bo dy ca thnh u n. Nu ly l A lm chun th g/c mt y C, sau ly C lm chun g/c l A s m bo ng tm gia l A v mt B. Khi khng c g th ly du l A m bo thnh l gia A v B c b dy u n. Lm nh vy chnh l ly l A lm chun nh v

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3. Nguyn tc chn chun th (1)

Nu chi tit c mt b mt khng g/c th chn b mt lm chun th. V d: Hnh a: ly A lm chun th g/c cc b mt B,C,D. Hnh b: ly mt trong khng cn g/c lm chun th g/c mt ngoi, nh vy m bo ng tm gia mt ngoi v mt trong

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Nu chi tit c mt s b mt khng cn g/c th ly b mt khng g/c no c yu cu CX cao v v tr tng quan i vi b mt g/c lm chun th. V d: Cc mt A v B u khng cn gia cng. ta chn mt A lm chun th g/c l. Nh vy, s m bo ng tm gia l v mt ngoi

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Chi tit c nhiu b mt cn g/c thi chn b mt no c lng d u v nh lm chun th. V d: g/c bng my tin: ly B lm chun g/c mt A, sau ly A lm chun g/c mt B v B khi c nm na khun di nn c lng d u v nh hn.


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Chun th phi tng i bng phng, khng c g gh, u rt, u ngt

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Chun th chi c dng mt ln. V d: khi gia cng trc bc, nu ly mt 2 lm chun th g/c mt 3, sau li ly mt 2 lm chun g/c mt 1, nh vy s khng m bo ng tm gia 1 v 3

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4. Nguyn tc chn chun tinh (1)

Nn chn chun tinh l chun tinh chnh cho v tr ca chi tit khi gia cng v khi lp rp trng nhau. V d: i vi bnh rng tr ta chn l A lm chun tinh chnh v khi g/c v lp rp u dng l A

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Chn chun nh v trng vi gc kch thc cho sai s chun bng 0

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Chn chun sao cho khi g/c chi tit khng b bin dng do lc ct v lc kep. Mt chun phi c din tch nh v

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Chn chun sao cho kt cu ca g n gin v thun tin khi s dng

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C gng chn chun tinh thng nht (chun c dng nhiu ln trong qu trnh gia cng)

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VIII. Cch tnh sai s g t

Sai s g t l tng vc-t ca 3 thnh phn:

Sai s chun

Sai s kp cht

Sai s g

Gi tr ca sai s g t:

_

gd dgc k

2 2 2

gd c k dg

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1. Sai s chun (1)

Sai s chun c: l lng bin ng ca kch thc thit k theo phng kch thc thc hin. Sai s chun xut hin khi chun nh v khng trng vi gc kch thc

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1. Sai s chun (2)

a) Gia cng mt N: chun nh v l K, kch thc A c gc l K v vy c(A) = 0 (Hnh a)

b) Sai s chun ca kch thc B: c(B) = H (Hnh b)

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1. Sai s chun khi /v trn khi V (3)

Tnh sai s chun ca H1,H2,H3:

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1. Sai s chun ca H1 (4)

Sai s chun ca H1:

Sau khi bin i ta c:

1max max min min

1 1C H

D D D DBB CB CB (C0 0B)

2 22sin 2sin

2 2

1C H

1( 1)

2sin

2

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Sai s chun ca H2:

Sau khi bin i ta c:

2 1 1 1 1C H

max max min min

AA CA CA (CO 0A) (C0 0 A )

D D D D

2 22sin 21sin

2 2

2C H

1( 1)

2sin

2

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Sai s chun ca H3:

Vy:

3max min

1 1C H

D D00 C0 C0

2sin 2sin2 2

3C H

2sin2

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Chi tit c nh v trn hai mi tm

C(a)=0 v kch thc A c nh c iu chnh sn. Sai s chun C(b) 0 v kch thc b khng c nh. C l kch thc t mt gia cng ti mi tm (C=constant). Sai s chun C(D) 0 v c th ly bng 0,25D (D khng chu nh hng ca hai l tm, nhng nu hai l tm lch nhau s gy ra sai s chun)

Hnh b: Sai s chun ca cc kch thc a v b u bng 0 v dng mi tm ty ng (mm)

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Sai s chun ca kch thc b c tnh nh sau:

max min max minC

d d d d(b) ( )tg(90 ) ( )ctg

2 2 2 2

Do sai s chun ca kch thc b:

d dC(b) tg(90 ) ct g

2 2 2 2

d- dung sai ca

kch thc l tm

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1. Tnh s/s chun bng lp chui KT (9)

PP lp chui kch thc tnh sai s chun (PP cc i-cc tiu): chui kch thc xut pht t b mt g/c qua cc khu c nh, bin i ri li quay v b mt gia cng. Nh vy, s hnh thnh chui kch thc khp kn

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1. Tnh s/s chun H1 bng lp CKT(10)

Ta c phng trnh sau:

a b + c - d = 0

d = a b + c

d = a D/(2sin/2) + D/2

Vi phn 2 v ta c:

1

,,

,

c(H )

D D D 11

2 22sin sin

2 2

11

2sin

2

d

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Ta c:

m n p + q = 0

q = m n p =

= m D/(2sin/2) D/2. Sau khi bin i ta c:

2C H

1( 1)

2sin

2

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Ta c phng trnh:

x = z + y = D/(2sin/2)+z

z = x - D/(2sin/2)+z

Vi phn z ta c:

c(H3) = /2sin/2

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2. Sai s kp cht k (1)

Sai s kp cht k l lng bin ng ca kch thc do lc kp gy ra

k = (ymax ymin).cos

ymax , ymin bin dng ln nht v nh nht do lc kp gy ra; - gc gia phng ca kch thc v phng ca lc kp

Sai s kp cht bng 0 khi lc kp vung gc vi kch thc

Sai s kp cht ln nht khi lc kp v kch thc // vi nhau (trng phng)

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3. Sai s g dg

Sai s g bao gm:

Sai s ch to g ct

Sai s mn g m

Sai s iu chnh g dc

m = 0,18 . .Vi N- s c/tit g trn /g

dc = 5~10 m

Sai s ch to: ct

Ta cn xc nh sai s ch to ct t yu cu k thut ca g

N

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4. Sai s g t gd

Sai s g t:

T :

Ghi ch: tr s di cn phi > 0. Trong trng hp khng c ta tm cch gim cc thnh phn v th 2 trong ngoc n. Chn sai s g t g=(1/3~1/5)nc

2 2 2 2 2 2 2 2

gd c k dg c k ct m dc

2 2 2 2 2ct gd c k m dc

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5. iu kin k thut ca g

Khi c sai s ch to ct ta cn c vo gi tr ca n t yu cu k thut ca g

V d: ct = 0,03mm. Khi ta ghi cc iu kin k thut ca g nh sau:

khng song song gia b mt phin t v y g 0,03mm

khng vung gc gia tm bc dn v y g 0,03mm

khng trng tm gia hai khi V 0,03mm

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Chuong 4 CHUẨN- Công nghệ chế tạo máy