Chuong 2 + 3 CNCTM Bkhn

Chng 2. Cht lng b mt gia cng

I. Khi nim

nh gi cht lng ch to chi tit my, ngi ta dng 4 yu t c bn:

chnh xc v kch thc cc b mt

chnh xc v hnh dng cc b mt

chnh xc v tr tng quan gia cc b mt

Cht lng b mt.

TS. Trng c Phc

B mn Cng ngh Ch to my Vin C kh BKHN

I. Khi nim

Cht lng b mt g/c c nh gi bng 2 yu t c trng:

Tnh cht c l ca lp kim loi b mt (mc bin cng, chiu su bin cng v ng sut d)

nhm b mt

TS. Trng c Phc


II. Cc dng b mt gia cng

1 - sng v nhm

2 - sng v nhm va phi

3 - B mt phng, nhm cao

4 - B mt phng v nhm thp

TS. Trng c Phc


Tnh cht hnh hc ca b mt gia cng c nh gi bng nhm b mt v sng b mt.

Trong qu trnh ct, li ct ca dng c ct s trt trn b mt phi ht i 1 lng phoi, s tip xc ma st s to ra nhng vt xc cc nh trn b mt gia cng, tc b mt gia cng s c nhm.

III. nhm dc v nhm ngang

a) nhm dc: trng vi phng tc ct

b) nhm ngang: vung gc vi phng tc ct

TS. Trng c Phc


nhm dc xut hin khi c lc ct bin i gy ra rung ng. Ngoi ra, nhm dc cn xut hin do hin tng lo dao.

Hin tng lo dao

TS. Trng c Phc


Hin tng lo dao l hin tng mt phn nh vt liu trong qu trnh bin dng do b nng chy cc b di p sut v nhit ln thot khi phi, do truyn nhit ra cc thnh phn xung quanh nn nhit gim t ngt khin cho vt liu b ng cng, t ti cng bm cht vo mt trc ca dao ( phn st cnh li ct ), n to nn mt mng hay lp bo v c tc dng nh mt ci nm lm thay i cc thng s ca dao, iu ny lm gim sc ca li ct dn n lm gim nhn b mt gia cng hoc dn n mt kh nng ct gt ca dng c v lm hng li ct.

(Lo dao)

(Phoi)

(Phi)

IV. Cc yu t nh hng CL b mt

Tnh cht ca vt liu gia cng

PP gia cng (tin, bo, phay, mi)

Ch ct (S,V,t)

cng vng ca h thng cng ngh

Thng s hnh hc ca dao

Dung dch trn ngui

TS. Trng c Phc


V. nhm b mt (1)

nhm b mt ( nhp nh t vi) l tp hp tt c nhng b li, lm vi bc cc nh

nh gi nhm ta v ng trung bnh. ng trung bnh c v sao cho tng din tch (phn gch ng) t hai pha bng nhau

Chiu di chun l l chiu di dng nh gi cc thng s ca nhm

Ra sai lch bnh phng trung bnh cng ca cc gi tr chiu cao h tnh t ng trung bnh trong phm vi chiu di chun l

TS. Trng c Phc


V. nhm b mt (3)

TS. Trng c Phc


V. nhm b mt (2)

Ra c xc nh:

l- chiu di chun, h- tung profin o c t ng trung bnh, n l s tung ca profin c o

Rz l chiu cao nhp nh, bng gi tr trung bnh gia nm nh cao nht v nm nh thp nht) o trong chiu di chun l c xc nh theo cng thc:

Rz = [(H1+H3+H5+H7+H9) - (H2+H4+H6+H8+H10)]/5

n

l i

1a

0

h1

R hdll n

TS. Trng c Phc


V. nhm b mt (2)

Sm- bc nhp nh theo ng trung bnh (gi tr trung bnh cng ca cc bc nhp nh)

Sm = (Smi)/n

n l bc nhp nh theo ng trung bnh trong phm vi chiu di chun l

S bc nhp nh theo nh (gi tr trung bnh cng ca cc bc nhp nh theo nh) trong phm vi chiu di chun l

Sm = (Si)/n

n l bc nhp nh theo nh trong phm vi chiu di chun l

TS. Trng c Phc


VI. ng cong ca phn vt liu

TS. Trng c Phc


Chiu di ca phn vt liu v tr no l tng chiu di ca phn kim loi i qua cc im ca nhm

ng cong a cho php xp nh gi tr ca phn vt liu cc cao khc nhau ca profin b mt. ng cong a ca phn vt liu c trng cho kh nng chu ti ca b mt.

Mc in y kim loi cng cao th tnh chng mn cng cao v kn kht b mt lp ghp cng cao.

VII. Cp nhm (1)

Tiu chun nh nc qui nh: nhm chia ra 14 cp. Cp 1 c nhm cao nht, cp 14 c nhm thp nht (Ra = 0,01um, Rz = 0,05 um)

Tr s Ra c cho khi yu cu nhm b mt t cp 6 n cp 12 (Ra = 2,5 ~ 0,04 um)

Tr s RZ c ghi trn bn v nu yu cu nhm trong phm vi t cp 1 n cp 5 hoc cp 13 v 14 (RZ = 0,08~0,05 m)

TS. Trng c Phc


VII.Cp nhm (2)

TS. Trng c Phc


VIII. /hng ca /nhm n TCSD ca c/tit

nhm c nh hng n:

1. mn U ca chi tit

2. Qu trnh n mn ha hc trn b mt

TS. Trng c Phc


1. /hng ca Ra n /mn U ca chi tit (1)

Ma st v mn ca chi tit my ph thuc v chiu cao v hnh dng ca nhm b mt v phng ca vt g/c

Cc im 01 v 02 ng vi mn ban u nh nht ca cc b mt tip xc

Ta thy: trong iu kin lm vic nng ng cong 2 dch chuyn v pha trn v bn phi ng vi nhm ti u (02) c gi tr ln hn.

ng cong 1: iu kin lm vic nh

TS. Trng c Phc


U

1. /hng ca Ra n /mn U ca chi tit (2)

mn ban u c th san phng 70% chiu cao nhm

nhm c chn trn c s dung sai :

Khi ng knh lp ghp >50mm:

RZ = (0,1~0,15)

Khi ng knh lp ghp trong khong 18~50mm: RZ = (0,15~0,2)

Khi ng knh lp ghp

2. Qu trnh n mn ha hc trn b/mt

Tng nhn b mt s nng cao bn mi ca chi tit.

nhm nh hng ln n tnh chng n mn ha hc ca b mt chi tit

Cc ch lm cha cc tp cht nh axit, muiCc tp cht n mn b mt theo sn dc ca nhp nh v to thnh nhp nh mi. Nh vy, b mt c nhm cng cao th qu trnh n mn cng nhanh

TS. Trng c Phc


X. /hng ca bin cng n TCSD

B mt bin cng tng bn mi ca chi tit ln khong 20%, tng chng mn ln 2~3 ln (hn ch kh nng gy ra cc vt nt ph hng chi tit)

B mt qu cng lm gim bn mi ca chi tit

TS. Trng c Phc


XI. /hng ca ng sut d n TCSD

ng sut d nn trn b mt tng bn mi ca chi tit, cn ng sut ko gim bn mi ca chi tit

V d: b mt chi tit thp c ng sut d nn tng bn mi ln 50% v c ng sut d ko s gim bn mi 30%

TS. Trng c Phc


XII. Cc y/t /hng n /nhm b/mt

1. Thng s hnh hc ca dao

2. nh hng ca tc ct

3. nh hng ca lng chy dao

4. nh hng ca chiu su ct

5. nh hng ca vt liu gia cng

6. nh hng ca rung ng

TS. Trng c Phc


1. Thng s hnh hc ca dao

a) v b): S1>S2 ta c RZ trn hnh

b nh hn RZ trn hnh a

c) v d): hnh dng nhm thay i theo bn knh mi dao

e) bn knh mi dao r2 tng s lm gim nhm b mt

g) cc gc chnh v gc ph 1 c nh hng n nhm

Thng s hnh hc ca dao nh hng n nhm

TS. Trng c Phc


2. nh hng ca tc ct

Khi V nh, bin dng t, nhit ct khng cao, do RZ thp. Nu V tng gn 20m/ph th nhit ct tng ln hng nghn nn sinh ra lo dao, lo dao lm thay i hnh dng mi dao lm tng RZ . Nu tng V ln na (100 m/ph), lo dao bin mt v RZ gim

TS. Trng c Phc


3. nh hng ca lng chy dao

Nhn chung, khi tng lng chy dao S th nhm tng v bin dng do, bin dng n hi v rung ng. Nu S>0,15 th nhm tng nhanh (do bin dng n hi)

TS. Trng c Phc


4. nh hng ca chiu su ct

Chiu su ct nhn chung khng c nh hng ng k n nhm b mt g/c

Tuy nhin, nu chiu su ct qu ln th rung ng ca qu trnh ct ln s lm tng nhm

Nu chiu su ct qu nh s gy ra hin tng trt dao trn b mt g/c nn nhm tng. Hin tng trt dao xy ra khi t < 0,02~0,03 mm)

TS. Trng c Phc


5. nh hng ca vt liu gia cng

Vt liu do v dai (thp t cacbon) d bin dng, do nhm tng

Vt liu cng v gin (t bin dng), do nhm gim

Gim tnh do ca b mt gia cng bng bin cng cng lm gim nhm

TS. Trng c Phc


6. nh hng ca rung ng

Rung ng lm thay i iu kin ma st, gy nn sng v nhm trn b mt gia cng

Rung ng sinh ra do nhiu nguyn nhn:

Tnh trng ca my

cng vng ca dao, chi tit v g

Gia cng vi ch ct khng hp l

Gia cng khng c dung dch trn ngui

Vt liu gia cng c tnh do cao

TS. Trng c Phc


XIII. P/php t bng b mt (1)

TS. Trng c Phc


XIII. P/php t bng b mt (2)

TS. Trng c Phc


XIV. P/php t cng b mt (1)

TS. Trng c Phc


XIV. P/php t cng b mt (2)

TS. Trng c Phc


XV. P/php t ng sut d b mt

Tng tc ct V hoc lng chy dao S cng c th tng hoc gim ng sut d

Lng chy dao S tng lm tng chiu su c ng sut d

Gc trc c tr s m gy ra ng sut d nn

Gia cng vt liu gin bng dng c ct c li to ra ng sut d nn, cn gia cng vt liu do thng gy ra ng sut d ko

Gia cng bng mi thng gy ra ng sut d ko, cn gia cng bng ai mi thng to ra ng sut d nn

TS. Trng c Phc


XVI. P/php nh gi nhm b mt

Phng php quang hc (dng knh hin vi)

Phng php o nhm bng my o profile

Phng php so snh bng mt (trong cc phn xng SX ngi ta mang vt mu so snh vi b mt gia cng v kt lun xem thuc cp bng no)

TS. Trng c Phc


XVII. P/php nh gi bin cng

Dng my o cng (tc dng ln b mt mt lc P, sau xc nh din tch S ca b mt do u kim cng n xung)

Cng thc tnh bin cng H:

H = P/S

H bin cng (N/mm2), P- lc tc dng ca u kim cng (N), S- din tch do u kim cng n xung (mm2)

chiu su bin cng dng u kim cng tc ng ln lt xung b mt mu t ngoi vo trong, sau mi ln tc ng ta o din tch b ln S n khi S khng thay i th dng li v o c chiu su b/c

TS. Trng c Phc


XVIII. P/php nh gi ng sut d

Phng php tia Rnghen (dng tia Rnghen kch thch ln b mt mu mt lp dy 5~10 m v sau mi ln kch thch ta chp nh th Rnghen. Phng php ny cho php o c c chiu su bin cng. Tuy nhin, phng php phc tp v tn thi gian cho iu chnh th Rnghen (10 gi cho mt ln o)

Phng php tnh ton lng bin dng (sau khi ht tng lp mng kim loi bng PP ha hc v in c kh ta tnh lng bin dng ca chi tit mu. Da vo lng bin dng ta xc nh c ng sut d.

TS. Trng c Phc


Cng ngh Ch to my

Chng 3. chnh xc gia cng

1. Khi nim

chnh xc gia cng ca chi tit my l mc ging nhau v kch thc, hnh dng hnh hc v v tr tng quan ca chi tit gia cng v chi tit thit k

trn bn v

chnh xc c nh gi theo cc yu t:

CX kch thc (di, rng, cao)

CX hnh dng hnh hc ( cn, ovan, tang trng, a cnh)

CX v tr tng quan ( song song, vung gc, ng tm)

TS. Trng c Phc


2. CX kinh t & CX c th t ti

CX kinh t l CX t c trong iu kin SX bnh thng vi gi thnh h nht (my, dao, g, dng c o bnh thng, cng nhn c tay ngh bnh thng)

CX c th t ti l CX t c trong iu kin SX c bit, khng tnh n gi thnh (my chnh xc, g tt, dng c o chuyn dng tt, cng nhn c tay ngh cao)

TS. Trng c Phc


3. Quan h gia CX (sai s) gia cng v gi thnh (1)

TS. Trng c Phc


3. Quan h gia CX (sai s) gia cng v gi thnh (2)

1- tin th, 2- tin tinh,

3- mi

Vng I: CX c th t ti (chn PP mi v c C min

Vng II: CX kinh t (PP tin tinh v c C min)

Vng III: CX m bo (chn PP tin th v c C min)

TS. Trng c Phc


4. Tnh cht ca sai s gia cng

Sai s h thng c nh

Sai s h thng thay i (theo thi gian gia cng)

Sai s ngu nhin

TS. Trng c Phc


4.1. N/nhn gy ra sai s HT c nh

Sai s l thuyt ca phng php ct

Sai s ch to my, dao, g

Bin dng nhit ca chi tit gia cng

TS. Trng c Phc


4.2. N/nhn gy ra sai s HT thay i

Dng c b mn theo thi gian

Bin dng nhit ca my, dao v g

TS. Trng c Phc


4.3. N/nhn gy ra sai s ngu nhin

cng ca vt liu khng u

Lng d gia cng khng u

V tr ca phi trong g khng c nh

Thay i ca ng sut d

G dao nhiu ln

Mi dao nhiu ln

Thay i nhiu my gia cng

Dao ng nhit ca qu trnh ct

Cc loi rung ng trong qu trnh ct

TS. Trng c Phc


5. Cc p/php t CX gia cng

5.1. Phng php ct th

5.2. Phng php t ng t kch thc

TS. Trng c Phc


5.1. Phng php ct th

Bn cht: sau khi g phi, ngi cng nhn ct tng lp nht nh, sau dng my kim tra chi tit, nu cha t th tip tc thc hin cng vic cho n khi t c KT yu cu

u im ca PP: my khng CX vn t c CX cao nh tay ngh CN; khng cn g t tin

Nhc im: ngi th lm vic cng thng nn d mt, gy ra sai s g/c; nng sut thp do ct nhiu ln; gi thnh cao; khng th ct vi b dy nh hn 0,05mm, do khng m bo c CX kch thc nh hn b dy . PP ch c s/d trong SX nh

TS. Trng c Phc


5.2. Phng php T t kch thc (1)

Bn cht: chi tit c g trn g, dao c iu chnh c v tr tng quan so vi chi tit g/c

u im: m bo CX gia cng, CX khng ph thuc vo tay ngh ca CN; ct mt ln l t kch thc; s dng hp l tay ngh CN; nng sut cao; hiu qu KT cao

Nhc im: chi ph ch to g; chi ph ch to phi chnh xc; nu dng c mn nhanh s nh hng ln n kch thc gia cng. PP ch c s dng trong SX ln

TS. Trng c Phc


5.2. Phng php T t kch thc (2)

a) a) 1- t, 2- chi tit gia cng, 3- dao phay

b) 1- g, 2- chi tit gia cng, 3- dao phay, 4- chi tit t

TS. Trng c Phc


6. Cc n/nhn gy ra sai s g/cng (1)

1. cng vng ca HTCN (H thng CN)

2. mm do ca HTCN

3. Bin dng ca dao

4. nh hng ca sai s ca phi

5. Xc nh cng vng tnh

6. Quan h gia lc P v bin dng y

7. Xc nh cng vng ng

8. Cc p/php nng cao cng vng

9. nh hng ca chnh xc ca my

TS. Trng c Phc



10. Sng trt ca my khng thng

11. Hai mi tm khng trng nhau

12. Chi tit c gia cng trong hai ln g

13. Trc chnh my khng v/gc vi bn my

14. Sng trt ca my b mn

15. nh hng ca sai s g

16. nh hng ca sai s ca dng c ct

17. Quan h gia mn U v chiu di ct L

18. nh hng ca bin dng nhit ca my

TS. Trng c Phc



19. Bin php gim bin dng nhit

20. nh hng ca bin dng nhit ca dao

21. /hng ca g/cng g/on n b/d nhit

22. /hng ca bin dng nhit ca chi tit

23. Bin php gim bin dng nhit ca c/tit

24. Rung ng cng bc

25. Bin php gim rung ng cng bc

26. T rung ng

27. Bin php gim t rung

TS. Trng c Phc



28. nh hng ca phng php g t

29. nh hng ca dng c o v p/php o

TS. Trng c Phc


TS. Trng c Phc


6.1. nh hng ca bin dng n hi ca h thng CN

H thng cng ngh (My, dao, g, chi tit) khng phi l h thng tuyt i cng vng. Khi chu tc dng ca ngoi lc th n s b bin dng n hi vo bin dng tip xc.

Trong qu trnh ct gt cc bin dng ny s gy ra sai s kch thc, sai s hnh dng hnh hc v v tr tng quan gia cc b mt ca chi tit gia cng.

TS. Trng c Phc


Lc ct trong qu trnh gia cng tin

Phi

Hng tin dao

Chiu su ct

P

Py

Px

Pz Pz P

Py

Lc ct P c tch thnh: Px : Lc ct dc trc Py : Lc ct hng knh Pz: Lc ct tip tuyn

TS. Trng c Phc


Lc ct trong qu trnh gia cng tin Phi

Hng tin dao

Chiu su ct

P

Py

Px

Pz Pz P

Py

Lc ct P gy ra lng dch chuyn tng i gia dao v chi tit gia cng . Lng dch chuyn c chia thnh 3 thnh phn theo 3 trc X, Y v Z.

TS. Trng c Phc


i vi dao mt li ct, chuyn v theo phng y c nh hng ti kch thc gia cng nhiu nht. Cn chuyn v theo phng x v z khng nh hng nhiu n kch thc gia cng.

Bn knh ca chi tit gia cng khi c sai s do dch chuyn

TS. Trng c Phc


i vi dao nhiu li ct hoc giao nh hnh th c trng hp 3 chuyn v theo phng x, y, v z u nh hng n chnh xc gia cng. xc nh nh hng ny th ngi ta dng phng php thc nghim. o lc ct v bin dng ca h thng cng ngh theo 3 phng.

TS. Trng c Phc


Trong tnh ton, ngi ta thng quan tm n lc php tuyn Py v b qua nh hng ca Px v Pz.

Py l thnh phn lc php tuyn thng gc vi mt gia cng v y l lng chuyn v tng i gia dao v chi tit gia cng theo phng php tuyn. Khi , t s Py/y gi l cng vng ca h thng cng ngh.

cng vng ca h thng cng ngh: l kh nng chng li bin dng ca n khi c ngoi lc tc dng vo

mm do l kh nng bin dng di tc dng ca ngoi lc:

= y/Py

mm do (m/kN hay mm/kG)

Py lc tc dng (kN hoc kG)

y - lng dch chuyn ca mi dao theo phng tc dng lc (mm)

Nh vy, mm do :

= 1/J

TS. Trng c Phc


TS. Trng c Phc


Lng chuyn v ca HTCN bao gm chuyn v ca c h thng gm nhiu chi tit lp ghp vi nhau. Da trn nguyn l cng c lp tc dng:

Mt khc:

Do :

H thng cng nhiu thnh phn th cng km cng vng.

TS. Trng c Phc


Xt trng hp tin trc trn, chi tit g trn 2 mi tm, vi tr tng i gia dao v chi tit ph thuc vo v tr tng i ca trc, sau v bn dao. Kho st chuyn v ca tng b phn ni trn, tng hp li ta s c chuyn v ca c HTCN, t xc nh c sai s gia cng.

6.1.1. nh hng ca cng vng ca HTCN

(1) Sai s do chuyn v ca 2 mi tm

TS. Trng c Phc



(1) Sai s do chuyn v ca 2 mi tm

Xt v tr dao cch mi tm sau 1 khong x

TS. Trng c Phc



Gi L l chiu di trc cn gia cng.

Phng trnh cn bng mmen:

TS. Trng c Phc



Phng trnh cn bng lc:

TS. Trng c Phc



Lng chuyn v ca mi tm sau theo phng tc dng lc Py:

TS. Trng c Phc



Lng chuyn v ca mi tm trc theo phng tc dng lc Py:

TS. Trng c Phc



V tr tng i ca mi dao so vi tm quay ca chi tit s dch chuyn i 2 khong t C n C:

TS. Trng c Phc



Nh vy, nu cha k n bin dng ca chi tit gia cng, th CC chnh l lng tng bn knh ca chi tit gia cng ti mt ang xt:

Khi ct ht chiu di, lng tng bn knh r1 l 1 ng cong parabol.

TS. Trng c Phc


(2) Sai s bin dng ca chi tit gia cng


TS. Trng c Phc



TS. Trng c Phc


(3) Sai s bin dng ca dao v g dao


Dao ct v g dao khi tc dng ca ngoi lc cng b bin dng n hi v lm cho bn knh chi tit gia cng tng thm 1 lng r3

cng vng Jd v g dao l hng s. dao mang dao ct chuyn ng dc trc ca chi tit ct ht chiu di. Vi ch ct khng thay i (Py l hng s), do vy r3 cng l hng s.

TS. Trng c Phc


(2) Sai s bin dng ca chi tit gia cng


Phi c hnh dng van, sau khi gia cng ta nhn c chi tit cng c hnh dng van nhng c sai s nh hn

K = ct/ph

K- h s in dp

ct- sai s ca chi tit (hiu gia cc ng knh max v min ca chi tit)

ph- sai s ca phi (hiu gia cc ng knh max v min ca phi)

TS. Trng c Phc


(4) nh hng do sai s ca phi


7. Xc nh cng vng tnh

Trng ti P c tng dn v dng ng h 2 xc nh lng bin dng n hi ca trc chnh 1. Lc P tng dn t 0 n mt gi tr cc i no (ph thuc vo loi my). Sau khi lc P t gi tr max th P gim dn v ng h 2 xc nh lng bin dng tng ng

TS. Trng c Phc


8. Quan h gia lc P v bin dng y

Ta thy: hai ng cong khi tng v gim lc P khng trng nhau

Gii thch: ngoi bin dng n hi ca HTCN cn c bin dng tip xc v ma st cc b mt lp ghp

Nu ti mt im no trn cc ng cong ta v ng tip tuyn (TT) th tg l cng vng ca b phn my

tg- gc gia ng TT v trc y

TS. Trng c Phc


9. Cc PP nng cao cng vng

Tng CV ca tng khu trong HTCN

Tng CV tip xc bng cch gim nhm b mt v gim khe h lp ghp

Gim s khu trong HTCN v mm do ca HT l tng mm do ca cc khu

S dng cc c cu lm tng CV nh dng cc cht t, luy-nt iu chnh hoc trc iu chnh

10. nh hng ca CX ca my

o hng knh ca trc chnh

o ca l cn trc chnh

o mt u ca trc chnh

Cc sai s ca sng trt, bn my

Chi tit c sai s hnh cn khi trc chnh khng song song vi sng trt

TS. Trng c Phc


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Chuong 2 + 3 CNCTM Bkhn