1

C«ng nghÖ dËp nguéi

Ch­¬ng­I

C¾t h×nh & ®ét lç

2

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.1.­ChuÈn­bÞ­vËt­liÖu.ChuÈn­bÞ­vËt­liÖu­gåm­c¸c­c«ng­viÖc­sau:-­TÈy­gØ:­Líp­«xit­bªn­ngoµi­®­îc­tÈy­s¹ch­b»ng­c¸c­ph­¬ng­ph¸p­nh­:­tÈy­thñ­c«ng,­phun­c¸t,­phun­bi,­b»ng­tia­n­íc,­dïng­axit,­kiÒm,­…-­Lµm­ph¼ng­vËt­liÖu.

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Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.1.1.­XÕp­h×nh­pha­b¨ng.a.­C¸c­ph­¬ng­ph¸p­xÕp­h×nh.XÕp­h×nh­pha­b¨ng­hîp­lý­ph¶­c¨n­cø­vµo­c¸c­yÕu­tè­sau.

- HiÖu­suÊt­sö­dông­vËt­liÖu­ph¶i­lín­nhÊt.- §¶m­b¶o­chÊt­l­îng­s¶n­phÈm.- ThuËn­lîi­cho­c«ng­ty­thao­t¸c­trªn­khu«n.

- KÕt­cÊu­khu«n­®¬n­gi¶n,­®é­bÒn­cña­khu«n­cao.

- N¨ng­suÊt­lao­®éng­cao,­sè­lÇn­pha­b¨ng­Ýt.

4

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Cã­2­ph­¬ng­ph¸p­xÕp­h×nh­c¬­b¶n­sau:-­XÕp­h×nh­cã­phÕ­theo­toµn­bé­®­êng­bao­cña­vËt­dËp­c¾t.­§¶m­b¶o­®é­chÝnh­x¸c­cao­vÒ­h×nh­d¸ng­vµ­kÝch­th­íc.­Song­l·ng­phÝ­vËt­liÖu­

5

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

-­XÕp­h×nh­kh«ng­cã­phÕ­hoÆc­cã­Ýt:­TiÕt­kiÖm­vËt­liÖu­nh­ng­khã­xÕp,­kÕt­cÊu­khu«n­vµ­®å­g¸­ph¶i­chÝnh­x¸c.

6

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

b.­HiÖu­suÊt­sö­dông­vËt­liÖu.HiÖu­suÊt­sö­dông­vËt­liÖu­®­îc­tÝnh­theo­c«ng­thøc­sau.

­­­­­­Trong­s¶n­xuÊt­ng­êi­ta­cã­thÓ­tÝnh­hiÖu­suÊt­sö­dông­vËt­liÖu­theo­b­íc,­theo­b¨ng­hay­theo­tÊm.

%100.ph

vd

F

F

7

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

VD.­XÕp­h×nh­víi­vËt­trßn.

8

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

VD.­XÕp­h×nh­víi­h×nh­phøc­t¹p.

9

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

c.­TrÞ­sè­m¹ch­nèi­vµ­mÐp­thõa.- M¹ch­nèi:­Lµ­kho¶ng­c¸ch­nhá­nhÊt­gi÷a­c¸c­vËt­trªn­b¨ng­vËt­liÖu.

- MÐp­thõa:­lµ­kho¶ng­c¸ch­nhá­nhÊt­tõ­mÐp­vËt­c¾t­®Õn­mÐp­b¨ng­vËt­liÖu.

TrÞ­sè­m¹ch­nèi­thùc­tÕ­cÇn­®¶m­b¶o­chÊt­l­îng­s¶n­phÈm­cao,­tiÕt­kiÖm­vËt­liÖu,­®é­bÒn­cña­khu«n­cao,­an­toµn­cho­viÖc­®­a­ph«i­vµo.

10

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

TrÞ­sè­m¹ch­nèi­vµ­mÐp­thõa­phô­thuéc­vµo­c¸c­yÕu­tè­sau.

- KÕt­cÊu­h×nh­d¸ng­cña­vËt­c¾t.­KÕt­cÊu­phøc­t¹p,­b¸n­kÝnh­nhá­th×­trÞ­sè­m¹ch­nèi­t¨ng.

- KÝch­th­íc­cña­vËt­c¾t.­KÝch­th­íc­cña­vËt­c¾t­lín­th×­trÞ­sè­m¹ch­nèi­t¨ng.

- ChiÒu­dµy­vËt­liÖu­dËp.­Khi­chiÒu­dµy­t¨ng­th×­trÞ­sè­m¹ch­nèi­t¨ng­(tra­b¶ng).

- TÝnh­chÊt­c¬­häc­cña­vËt­liÖu.­Khi­tÝnh­dÎo­cña­vËt­liÖu­t¨ng­th×­trÞ­sè­m¹ch­nèi­còng­t¨ng.

11

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

-­Ph­¬ng­ph¸p­®­a­b¨ng­vËt­liÖu.- Ph­¬ng­ph¸p­dËp­c¾t.­Khi­qua­nhiÒu­khu«n­th×­tri­sè­m¹ch­nèi­còng­t¨ng­(®Ó bï l¹i ®é cong vªnh cña vËt liÖu). NÕu­vËt­c¾t­cã­söa­tinh­th×­trÞ­sè­m¹ch­nèi­t¨ng­lªn­tõ­20­–­30%

TrÞ­sè­m¹ch­nèi­®­îc­tra­trong­c¸c­b¶ng­trong­sæ­tay­dËp­nguéi­phô­thuéc­vµo­vËt­liÖu,­­chiÒu­dµy,­h×nh­d¹ng,­kÝch­th­íc­vËt­dËp.

Trong thùc tÕ trÞ sè m¹ch nèi kh«ng ®Òu xung quanh vËt dËp, dËp c¾t chØ cã m¹ch nèi ë 1 bªn lµm cho ®é bÒn cña khu«n gi¶m.

12

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

d.­TÝnh­to¸n­chiÒu­réng­b¨ng­vËt­liÖu.

ViÖc­tÝnh­chiÒu­réng­b¨ng­vËt­liÖu­phô­thuéc­vµo­h×nh­d¹ng­cña­vËt­dËp,­kÝch­th­íc­bµn­m¸y,­®é­chÝnh­x¸c­cña­s¶n­phÈm,­…

Tham­kh¶o­trong­sæ­tay­dËp­nguéi.

13

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

14

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

e.­C¾t­(pha)­b¨ng­trªn­tÊm­vËt­liÖu.Yªu­cÇu­khi­c¾t­b¨ng.- HiÖu­suÊt­sö­dông­vËt­liÖu­trªn­toµn­tÊm­lµ­cao­nhÊt.

- Sè­lÇn­c¾t­thµnh­b¨ng­lµ­Ýt­nhÊt.- ThuËn­lîi­cho­thao­t¸c­cña­c«ng­nh©n.- KÕt­cÊu­khu«n­dËp­®¬n­gi¶n.- PhÇn­thõa­cña­tÊm­cßn­sö­dông­®­îc.- Khi­c¾t­b¨ng­®Ó­uèn­cÇn­chó­ý­®­êng­uèn­ph¶i­vu«ng­gãc­víi­thí­cña­kim­lo¹i.

15

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Cã­3­ph­¬ng­ph¸p­c¾t­sau:- C¾t­ngang.- C¾t­däc.

16

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

- C¾t­phèi­hîp.

17

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.1.2.­C¾t­vËt­liÖu­tÊm.a.­C¾t­vËt­liÖu­tÊm­b»ng­dao.Qu¸­tr×nh­c¾t­®øt­vËt­liÖu­tr¶i­qua­3­giai­®o¹n­liªn­tôc.

- Giai­®o¹n­biÕn­d¹ng­®µn­håi.­- Giai­®o¹n­biÕn­d¹ng­dÎo.- Giai­®o¹n­c¾t­®øt.C¸c­lo¹i­m¸y­c¾t­vËt­liÖu­tÊm­bao­gåm.

18

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Lùc­c¾t

19

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*­M¸y­c¾t­l­ìi­b»ng.

­lµ­hÖ­sè­phô­thuéc­vµo­chiÒu­dµy­vµ­®é­cøng­cña­vËt­liÖu.

cSLP .. 1000

.. SPA (kG) (kGm)

20

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*­M¸y­c¾t­l­ìi­nghiªng.

(KG)(KGm)

tg

SP c..5,0 2

1000

.. tgLPA

21

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*­M¸y­c¾t­dao­®Üa.

­M.­lµ­m«men­quay.­m.­lµ­sè­cÆp­dao­c¾t­®Üa­khi­c¾t­nhiÒu­dao

­.­lµ­gãc­¨n­cña­dao­c¾t­®Üa.­(®é)­k.­lµ­hÖ­sè­kÓ­®Õn­sù­­­­­kh«ng­®ång­®Òu­cña­­­­­vËt­liÖu­k=1,2­–­1,4

(KG)

tg

mSP c ...3,0 2

cDSkM .cos...125.0 2

22

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

b.­C¾t­vËt­dËp­trong­khu«n.­- C¾t­kh«ng­cã­phÕ.­Chñ­yÕu­dïng­®Ó­c¾t­b¨ng­thµnh­ph«i­rêi,­chØ­¸p­dông­®­îc­víi­c¸c­ph«i­h×nh­vu«ng,­ch÷­nhËt,­tam­gi¸c,­…­khi­c¾t­th­êng­chØ­c¾t­1­phÝa­nªn­chÊt­l­îng­s¶n­phÈm­kh«ng­chÝnh­x¸c,­dÔ­cong­vªnh­nhÊt­lµ­khi­c¾t­vËt­liÖu­máng.

- C¾t­cã­phÕ.­Khi­c¾t­cÇn­®Þnh­vÞ­vµ­b­íc­cña­ph«i­chÝnh­x¸c.

ChÊt­l­îng­cña­vËt­c¾t­phô­thuéc­vµo­chiÒu­dµy­cña­ph«i­(th­êng­tõ­cÊp­8­–­10).

23

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.2.­qu¸­tr×nh­c¾t­h×nh­vµ­®ét­lç.Qu¸­tr×nh­c¾t­®ét­chia­lµm­3­giai­®o¹n.

24

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.2.­Khe­hë­gi÷a­chµy­vµ­cèi.Khe­hë­gi÷a­chµy­vµ­cèi­lµ­hiÖu­sè­gi÷a­kÝch­th­íc­lµm­viÖc­cña­cèi­vµ­chµy.

- Khe­hë­hîp­lý­th×­vÕt­nøt­cña­vËt­tõ­chµy­vµ­cèi­sÏ­gÆp­nhau­theo­®­êng­th¼ng.

- NÕu­khe­hë­qu¸­nhá­lµm­cho­vÕt­nøt­kh«ng­trïng­nhau.­Quan­s¸t­thÊy­cã­2­d¶i­s¸ng­ë­trªn­vµ­d­íi,­ë­gi÷a­xï­x×­lín­h×nh­r¨ng­c­a.

- NÕu­khe­hë­qu¸­lín­lµm­cho­vÕt­nøt­kh«ng­trïng­nhau.­Mét­bªn­bÞ­vuèt­dµi­lªn­1­bªn­bÞ­ba­via­xuèng­d­íi

25

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

­­­

26

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

-­TrÞ­sè­khe­hë­phô­thuéc­chñ­yÕu­vµo­b¶n­chÊt­vµ­chiÒu­dµy­cña­vËt­liÖu.­§­îc­x¸c­®Þnh­theo­b¶ng­tra.

- Khi­chÕ­t¹o­chän­Zmin,­khi­lµm­viÖc­®Õn­Zmax­th×­cÇn­kh«i­phôc­l¹i­khu«n­míi­sö­dông­®­îc.

27

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.4.­X¸c­®Þnh­kÝch­th­íc­vµ­dung­sai­chÕ­t¹o­cña­chµy­vµ­cèi.

Môc­®Ých:­§¶m­b¶o­®é­chÝnh­x¸c­cña­s¶n­phÈm,­khe­hë­hîp­lý­vµ­giíi­h¹n­mßn­cho­phÐp.

- Khi­c¾t­h×nh,­kÝch­th­íc­cña­cèi­quyÕt­®Þnh­kÝch­th­íc­cña­s¶n­phÈm,­v×­vËy­lÊy­kÝch­th­íc­cña­cèi­lµm­chuÈn­vµ­thu­hÑp­chµy.

- Khi­®ét­lç,­kÝch­th­íc­cña­chµy­quyÕt­®Þnh­kÝch­th­íc­cña­s¶n­phÈm,­v×­vËy­lÊy­kÝch­th­íc­cña­chµy­lµm­chuÈn­vµ­më­réng­cèi.

28

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.4.1.­Chày, cối cắt hình và đột lỗ tròn

a.­Ph­¬ng­ph¸p­chÕ­t¹o­riªng.­Sö­dông­khi­chÕ­t¹o­hµng­lo¹t­chµy,­cèi­cã­tÝnh­l¾p­lÇn­cao.

*.­C¾t­h×nh.Trong­tr­êng­hîp­nµy­kÝch­th­íc­danh­nghÜa­cña­cèi­®­îc­lÊy­b»ng­kÝch­th­íc­giíi­h¹n­nhá­nhÊt­cña­s¶n­phÈm.

29

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

30

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

KÝch­th­íc­cña­cèi:­KÝch­th­íc­cña­chµy:Trong­®ã:­­­-­lµ­dung­sai­chÕ­t¹o­cèi­­­-­lµ­dung­sai­chÕ­t¹o­chµy­Zmin­-­lµ­khe­hë­2­phÝa­nhá­nhÊt­gi÷a­chµy­vµ­cèi

DDdc

)(DDc

)( minZDDch

31

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­§ét­lç.­­Trong­tr­êng­hîp­nµy­kÝch­th­íc­danh­nghÜa­cña­chµy­®­îc­lÊy­b»ng­kÝch­th­íc­(lç)­giíi­h¹n­lín­nhÊt­cña­s¶n­phÈm.

KÝch­th­íc­chµy.kÝch­th­íc­cèi.

dDdch

)(dDc

)( minZdDc

)(dDc

)( minZdDc

)(dDc

32

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

33

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Chó­ý:­- Tæng dung sai chÕ t¹o chµy vµ cèi

kh«ng ® îc v ît qu¸ hiÖu sè khe hë lín nhÊt vµ nhá nhÊt

- Gi¸ trÞ tuyÖt ®èi cña dung sai chÕ t¹o chµy hoÆc cèi ph¶i nhá h¬n hoÆc b»ng 1/4 dung sai chÕ t¹o s¶n phÈm.

minmax ZZ

4;

4

minmax ZZ

4;

4

34

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

b.­Ph­¬ng­ph¸p­chÕ­t¹o­phèi­hîp.Ph­¬ng­ph¸p­nµy­sö­dông­trong­s¶n­xuÊt­®¬n­chiÕc­hay­khu«n­cã­®é­chÝnh­x¸c­cao.

Ph­¬ng­ph¸p­nµy­sau­khi­chÕ­t¹o­xong­chµy­(cèi)­th×­lÊy­®ã­lµm­chuÈn­®Ó­gia­c«ng­cèi­(chµy).

35

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­Khi­c¾t­h×nh,­kÝch­th­íc­s¶n­phÈm­do­cèi­quyÕt­®Þnh­cho­nªn­lÊy­kÝch­th­íc­cèi­lµm­chuÈn.

Cèi­Víi­­Cèi­chÕ­t¹o­víi­chµy­sao­cho­khe­hë­n»m­trong­giíi­h¹n­

)(DDc

4

maxmin ZZ

36

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­Khi­®ét­lç,­kÝch­th­íc­s¶n­phÈm­do­chµy­­quyÕt­®Þnh­cho­nªn­lÊy­kÝch­th­íc­chµy­­lµm­chuÈn.

Chµy­­Víi­­Cèi­chÕ­t¹o­víi­chµy­sao­cho­khe­hë­n»m­trong­giíi­h¹n­

)(dDch

4

maxmin ZZ

37

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.4.2.­Chày, cối cắt hình và đột lỗ kh«ng tròn

a. C¾t­h×nh.KÝch­th­íc­vµ­dung­sai­cña­s¶n­phÈm­

c¾t­h×nh­lµ­c¬­së­®Ó­thµnh­lËp­vßng­lµm­viÖc­cña­cèi.­Chµy­lÊy­theo­cèi­sao­cho­khe­hë­n»m­trong­kho¶ng

(TrÞ sè khe hë 1 phÝa lÊy theo sæ tay)­TÊt­c¶­c¸c­kÝch­th­íc­vßng­lµm­viÖc­cña­

cèi­chia­lµm­3­d¹ng:­t¨ng,­gi¶m­vµ­kh«ng­thay­®æi.

maxmin ZZ

38

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­C¸c­kÝch­th­íc­t¨ng.­kÝch­th­íc­danh­nghÜa­cña­cèi­b»ng­kÝch­th­íc­nhá­nhÊt­cña­s¶n­phÈm,­dung­sai­lÊy­dÊu­céng­vµ­b»ng­1/4­dung­sai­cña­s¶n­phÈm­(L lµ chu vi ph«i)

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­víi­ minLLt

c 4

minLLt

c 4

39

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­C¸c­kÝch­th­íc­gi¶m.­kÝch­th­íc­danh­nghÜa­cña­cèi­b»ng­kÝch­th­íc­lín­nhÊt­cña­s¶n­phÈm,­dung­sai­lÊy­dÊu­trõ­vµ­b»ng­1/4­dung­sai­cña­s¶n­phÈm

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­víi­+.­C¸c­kÝch­th­íc­kh«ng­thay­®æi,­

víi­

maxLLgc 4

)

2( minLLkd

c

4

40

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

b.­§ét­lç.KÝch­th­íc­vµ­dung­sai­cña­lç­®ét­lµ­

c¬­së­®Ó­thµnh­lËp­vßng­lµm­viÖc­cña­chµy.­Cèi­lÊy­theo­chµy­sao­cho­khe­hë­n»m­trong­kho¶ng

(TrÞ sè khe hë 1 phÝa lÊy theo sæ tay)­

TÊt­c¶­c¸c­kÝch­th­íc­vßng­lµm­viÖc­cña­chµy­chia­lµm­3­d¹ng:­t¨ng,­gi¶m­vµ­kh«ng­thay­®æi.

maxmin ZZ

41

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­C¸c­kÝch­th­íc­t¨ng.­kÝch­th­íc­danh­nghÜa­cña­chµy­b»ng­kÝch­th­íc­nhá­nhÊt­cña­lç,­dung­sai­lÊy­dÊu­céng­vµ­b»ng­1/4­dung­sai­cña­s¶n­phÈm­(L lµ chu vi lç)

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­víi­­ minLLt

ch4

42

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­C¸c­kÝch­th­íc­gi¶m.­kÝch­th­íc­danh­nghÜa­cña­chµy­b»ng­kÝch­th­íc­lín­nhÊt­cña­lç­®ét,­dung­sai­lÊy­dÊu­trõ­vµ­b»ng­1/4­dung­sai­cña­s¶n­phÈm

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­víi­+.­C¸c­kÝch­th­íc­kh«ng­thay­®æi,­

víi­

maxLLgch 4

4

)

2( minLLkd

ch

43

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.5.­Lùc­c¾t­h×nh­vµ­®ét­lç.1.5.1.­X¸c­®Þnh­lùc­c¾t­h×nh­vµ­

®ét­lç.Lùc­c¾t­h×nh­hay­®ét­lç­phô­thuéc­vµo­kÝch­th­íc­h×nh­hay­lç,­chiÒu­dµy­tÊm,­c¬­tÝnh­cña­vËt­liÖu,­khe­hë­gi÷a­chµy­vµ­cèi,­h×nh­d¸ng­vµ­tr¹ng­th¸i­mÐp­c¾t­cña­chµy­vµ­cèi.

Lùc­dËp­®­îc­tÝnh­theo­c«ng­thøc­sau:­

44

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Trong­®ã.K=­1,1­-1,3­-­lµ­hÖ­sè­kÓ­®Õn­sù­kh«ng­®ång­®Òu­vÒ­chiÒu­dµy­vµ­tÝnh­chÊt­cña­vËt­liÖu,­mÐp­c¾t­bÞ­mßn,­chÕ­t¹o­vµ­l¾p­ghÐp­kh«ng­chÝnh­x¸c.

L­-­lµ­chu­vi­vËt­c¾t­hay­®ét­lç.S­-­lµ­chiÒu­dµy­vËt­dËp.c­–­øng­suÊt­c¾t­cña­vËt­liÖu.­kG/mm2.

cSLkP ... )(kG

45

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

C«ng­dïng­®Ó­c¾t­h×nh­vµ­®ét­lç­®­îc­x¸c­®Þnh­theo­c«ng­thøc.

­­­­­­­­­­­­­­­­­­­­­A=a.S.P (kGm)Trong­®ã.a­–­lµ­hÖ­sè­phô­thuéc­vµo­chiÒu­dµy­vµ­®é­cøng­cña­vËt­liÖu,­a­=­0,4–­0,7­(tØ lÖ nghÞch)

S­–­lµ­chiÒu­dµy­vËt­liÖu,­mm­ P­–­lµ­lùc­c¾t­hay­®ét­lç.

46

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.5.2.­C¸c­biÖn­ph¸p­gi¶m­lùc­c¾t­-­®ét

Gi¶m­lùc­c¾t­lµm­t¨ng­®é­bÒn­cña­chµy,­cèi,­t¨ng­kh¶­n¨ng­c«ng­nghÖ­cña­thiÕt­bÞ.

+.­Nung­vËt­liÖu.­Khi­nhiÖt­®é­t¨ng­lµm­gi¶m­øng­suÊt­c¾t­do­®ã­lùc­c¾t­gi¶m­®i.

Chó ý: BÒ mÆt s¶n phÈm xÊu, chi nªn dïng khi S ≥ 3 mm, s¶n phÈm co kho¶ng (0,6 – 0,8)%, víi thÐp cacbon cao vµ thÐp hîp kim ph¶i ñ ®Ó khö øng suÊt.

47

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­Dïng­chµy,­cèi­cã­mÆt­l­în­sãng.Th­êng­dïng­víi­s¶n­phÈm­lín,­s¶n­phÈm­trung­b×nh­chØ­nªn­dïng­mÆt­chÐo­

Chó ý. Khi c¾t hay ®ét lç xong ph¶i lµm ph¼ng s¶n phÈm.

48

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

+.­Khu«n­c¾t­®ét­cã­nhiÒu­chµy­th×­bè­trÝ­thµnh­nhiÒu­bËc.

49

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.6.­x¸c­®Þnh­t©m­¸p­lùcT©m­¸p­¸p­lùc­cña­khu«n­lµ­®iÓm­®Æt­cña­tæng­c¸c­lùc­c¾t­h×nh­vµ­®ét­lç­cña­khu«n.­Träng­t©m­khu«n­ph¶i­trïng­víi­t©m­l¾p­lç­c¸n­khu«n­trong­khèi­tr­ît­cña­m¸y­Ðp.­

- §èi­víi­c¸c­vßng­c¾t­cã­2­trôc­®èi­xøng­th×­t©m­¸p­lùc­n»m­ë­giao­®iÓm­cña­2­trôc­®ã.

- ­§èi­víi­c¸c­vßng­c¾t­cã­1­trôc­®èi­xøng­th×­t©m­¸p­lùc­n»m­ë­trªn­trôc­®ã.

- T©m­¸p­lùc­cña­khu«n­®­îc­x¸c­®Þnh­theo­2­ph­¬ng­ph¸p:­Gi¶i­thÝch­vµ­biÓu­®å.

50

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.6.1.­Ph­¬ng­ph¸p­gi¶i­tÝch.C¬­së­cña­ph­¬ng­ph¸p­nµy­dùa­trªn­®Þnh­luËt:­“Tæng­m«men­cña­c¸c­lùc­thµnh­phÇn­®èi­víi­1­trôc­nµo­®ã­b»ng­m«men­cña­tæng­hîp­lùc­®ã­®èi­víi­trôc­®ã”

51

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­§èi­víi­khu«n­c¾t­h×nh­d¹ng­phøc­t¹p.- §Æt­1­hÖ­to¹­®é­xoy­bªn­ngoµi­h×nh­c¾t.

- Chia­vßng­c¾t­thµnh­nh÷ng­®o¹n­th¼ng­vµ­h×nh­cong­®¬n­gi¶n,­x¸c­®Þnh­trong­t©m­cña­­chóng­vµ­kho¶ng­c¸ch.

­­­­­­­­­­­­­­­­­­­­x1,­x2,­x3,­…­­®Õn­trôc­y

­­­­­­­­­­­­­­vµ­­­y1,­y2,­y3,­…­­®Õn­trôc­x-­Lùc­c¾t­®­îc­xem­lµ­ph©n­bè­®ång­®Òu­theo­chiÒu­dµi­c¸c­®o¹n­th¼ng­l1,­l2,­l3,­…­cho­nªn­®iÓm­®Æt­cña­nã­®­îc­xem­nh­­®Æt­ë­träng­t©m­cña­c¸c­®o¹n­®ã.

52

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

y

xA

B

CD

E G

HK

o

53

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

Lùc­c¾t­®­îc­tÝnh­nh­­sau:P1­=­l1.S.cP2­=­l2.S.cP3­=­l3.S.c

54

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

- Lùc­c¾t­tæng­hîp­P­=­P1­+­P2­+­P3­+­…

- §iÓm­®Æt­cña­hîp­lùc­P­®­îc­x¸c­®Þnh­theo­c«ng­thøc­sau:

n

nn

n

nno lll

xlxlxl

PPP

xPxPxPx

...

...

...

...

21

2211

21

2211

n

nn

n

nno lll

ylylyl

PPP

yPyPyPy

...

...

...

...

21

2211

21

2211

55

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­§èi­víi­khu«n­c¾t­-­®ét­bè­trÝ­nhiÒu­chµy.

- §Æt­hÖ­to¹­®é­xoy­ngoµi­h×nh­c¾t.

56

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

- X¸c­®Þnh­c¸c­kho¶ng­c¸ch­cña­c¸c­träng­t©m­®Õn­trôc­to¹­®é.­x1,­x2,­x3,­…;­y1,­y2,­y3,..

- TÝnh­chu­vi­c¸c­vßng­c¾t­L1,­L2,­L3,­…

n

nno LLL

xLxLxLx

...

...

21

2211

n

nno LLL

yLyLyLy

...

...

21

2211

57

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.6.2.­Ph­¬ng­ph¸p­biÓu­®å.Ph­¬ng­ph¸p­nµy­sö­dông­c¸c­vÐct¬­lùc­®Ó­x¸c­®Þnh,­tÝnh­to¸n­qua­nhiÒu­b­íc,­ph­¬ng­ph¸p­nµy­cho­®é­chÝnh­x¸c­kh«ng­cao,­nh­ng­dÔ­thùc­hiÖn.

a.­§èi­víi­khu«n­c¾t­-­®ét­phøc­t¹p.Thø­tù­lËp­biÓu­®å­nh­­sau:*­Theo­c¹nh­cña­khu«n­x©y­dùng­hÖ­trôc­to¹­®é­XOY.

*­Chia­vßng­c¾t­thµnh­nh÷ng­phÇn­®¬n­gi¶n­vµ­x¸c­®Þnh­träng­t©m­cña­chóng.

58

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*­Tõ­c¸c­träng­t©m­kέc¸c­®­êng­song­song­víi­trôc­X­vµ­Y,­trªn­®ã­®Æt­c¸c­vect¬­lùc­thµnh­phÇn­t­¬ng­øng­theo­1­tû­lÖ­xÝnh­nhÊt­®Þnh­(Px1­=­Py1­=­L1).

­­­­­­Px1,­Px2,­Px3,­…­

­­­­­­Py1,­Py2,­Py3,­…

*­Kέ1­®­êng­th¼ng­song­song­bÊt­kú­víi­trôc­Y,­®Æt­liªn­tiÕp­c¸c­vÐct¬­Py1,­Py2,­Py3,­…­lªn­trªn­®ã­vµ­nèi­®Õn­1­®iÓm­O­bÊt­kú­b»ng­c¸c­tia­1,­2,­3,­…

59

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*­Kέ®­êng­1’­//­1­c¾t­qua­®­êng­giãng­cña­vect¬­Py1,­tõ­giao­®iÓm­kέ2’­//­2­c¾t­qua­®­êng­giãng­cña­vect¬­Py2,­kέt­¬ng­tù­víi­c¸c­®­êng­cßn­l¹i.

*­Qua­giao­®iÓm­cña­®­êng­1’­vµ­9’­kέ®­êng­nn’­//­OY.

*­T­¬ng­tù­kέmm’­//­OX.*­Giao­®iÓm­nn’­vµ­mm’­lµ­t©m­¸p­lùc­cña­khu«n.

60

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

61

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

b.­§èi­víi­khu«n­c¾t­-­®ét­nhiÒu­chµy.C¸c­b­íc­gåm:- §Æt­hÖ­trôc­to¹­®é­XOY.- TÝnh­chu­vi­c¸c­h×nh­c¾t­-­®ét.- X¸c­®Þnh­trong­t©m­c¸c­h×nh­vµ­qua­®ã­kέc¸c­®­êng­th¼ng­//­víi­trôc­X­vµ­trôc­Y.

- §Æt­trªn­®ã­c¸c­vect¬­lùc­t­¬ng­øng­víi­chiÒu­dµi­c¾t­theo­1­tû­lÖ­xÝch­chän­tr­íc.

- TiÕp­theo­nh­­b­íc­trªn.

62

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

63

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.7.­lùc­th¸o­vËt­c¾t­vµ­phÕ­liÖu.-­Sau­khi­®ét,­c¾t­do­tÝnh­®µn­håi­cña­vËt­liÖu­mµ­vËt­c¾t­hay­phÕ­liÖu­dÝnh­trong­cèi­hay­trªn­chµy.

-­Lùc­®Ó­th¸o­vËt­liÖu­ra­khái­chµy­vµ­vËt­c¾t­ra­khái­cèi­phô­thuéc­vµo­chiÒu­dµy­vµ­tÝnh­chÊt­vËt­liÖu,­kÝch­th­íc­vµ­chÕ­®é­b«i­tr¬n.

64

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.7.1.­Lùc­th¸o­phÕ­liÖu.Lùc­th¸o­phÕ­liÖu­ra­khái­chµy­®­îc­tÝnh­theo­c«ng­thøc.

­­­­­­­­­­­­­­­­­Qt = Kt.P

P­–­lµ­lùc­c¾t­hay­®ét­lç.Kt­–­lµ­hÖ­sè­phô­thuéc­vµo­vËt­liÖu­vµ­s¬­®å­c¾t.

65

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.7.2.­Lùc­®Èy­vËt­c¾t.­­­­­Lùc­dïng­®Ó­®Èy­vËt­c¾t­tõ­trong­lßng­cèi­h×nh­trô­ra­ngoµi­ra­khái­cèi­h×nh­trô­®­îc­tÝnh­theo­c«ng­thøc.

­­­­­­­Qd = K®. n. P

P­–­lµ­lùc­c¾t­hay­®ét­lç.Kt­–­lµ­hÖ­sè­phô­thuéc­vµo­vËt­liÖu­vµ­s¬­®å­c¾t.

n­–­Sè­vËt­dËp­trong­lßng­cèi­h×nh­trô

66

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.8.­KÕt­cÊu­khu«n­c¾t­h×nh­®ét­lç.

1.8.1.­KÕt­cÊu­cña­chµy­cèi.*­Chµy­c¾t­h×nh­vµ­®ét­lç.-­Chµy­ghÐp:­Sö­dông­khi­c¾t­h×nh­vµ­®ét­lç­lín.

67

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

-­Chµy­nguyªn­víi­h×nh­d¸ng­mÐp­c¾t­kh¸c­nhau.

68

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

-­Chµy­cã­vßng­c¾t­phøc­t¹p,­phÇn­l¾p­ghÐp­®­îc­lµm­trßn­hay­h×nh­ch÷­nhËt.

69

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­Cèi­c¾t­h×nh­vµ­®ét­lç.

70

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

1.8.2.­KÕt­cÊu­cña­khu«n­c¾t­h×nh­vµ­®ét­lç.

*.­Khu«n­c¾t­-­®ét­kh«ng­cã­dÉn­h­íng­cì­nhá­vµ­trung­b×nh.

71

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç

*.­Khu«n­c¾t­h×nh­cì­lín.

72

Ch­¬ng­I.­c¾t­h×nh­&­§ét­lç