Chng 21: Nguyn l gia cng kim loiREVIEW QUESTIONS21.1. Ba loi c bn ca qu trnh bc tch vt liu l g?Ba loi c bn ca qu trnh bc tch vt liu l:1. Cc qu trnh gia cng thng thng.2. Qu trnh mi mn.3. Gia cng phi truyn thng.21.2. iu g phn bit qu trnh gia cng bc tch vt liu v cc qu trnh gia cng khc?Trong gia cng bc tch, vt liu b loi b khi chi tit thu c chi tit c hnh dng v kch thc mong mun.21.3. Xc nh nhng l do ti sao tnh thng mi v cng ngh trong gia cng c vai tr quan trng.Nhng l do bao gm:1. C th p dng cho hu ht cc vt liu.2. C th to ra nhiu hnh dng theo tng phn ca chi tit.3. C th t c dung sai nh hn cc phng php gia cng khc.4. Kt thc qu trnh gia cng c th to ra b mt cht lng tt.21.4. Ba qu trnh gia cng ph bin l g?Ba qu trnh gia cng ph bin l: tin, khoan, phay.21.5. Hai loi dng c ct c bn l g? Cho v d phng php gia cng dng loi dng c ny.Hai loi dng c ct c bn l:1. Dng c c li ct n, dng trong phng php tin v doa.2. Dng c nhiu li ct, dng trong phng php phay v khoan.21.6. Thng s trong hot ng gia cng, bao gm iu kin ct l g?iu kin khi gia cng bao gm: tc ct v, lng tin dao, chiu su ct v dung dch trn ngui lm mt (nu dng).21.7. Gii thch im khc nhau gia gia cng th v gia cng tinh. Gia cng th c dng loi b nhanh chng mt lng ln vt liu, to ra hnh dng v kch thc gn ging vi mong mun. Gia cng th l cng on gia cng kim loi ban u vi lng ct ln, sau khi gia cng ta cn cha khong d tin hnh gia cng tinh. Gia cng tinh l cng on gia cng cui cng cho ra chi tit hon chnh, m bo yu cu v kch thc, dung sai, nhm b mt Gia cng th c lng chy dao v chiu su ct ln hn gia cng tinh nhng tc ct ca gia cng th li nh hn khi gia cng tinh. 21.8. My cng c l g?My cng c c nh ngha nh mt thit b chy bng nng lng in m v tr v tc dng c lin quan n vic thc hin gia cng hoc cc phng php to hnh khc.21.9. Ct trc giao l g?Ct trc giao l phng php ct s dng dng c ct hnh nm trong li ct vung gc vi hng vn tc ct.21.10. Ti sao m hnh ct trc giao li hu ch trong vic phn tch qu trnh gia cng ct gt kim loi?Bi v m hnh ct trc giao: l m hnh hnh hc n gin nhng vn m t c ch gia cng tng i chnh xc. V dng c ct trong m hnh trc giao ch c 2 thng s l gc trc v gc sau.21.11. K tn v m t ngn gn 4 loi phoi trong qu trnh ct gt kim loi?1. Phoi vn (phoi khng lin tc): cc phoi thng to thnh cc on ring bit.2. Phoi dy (phoi lin tc): l mt loi phoi lin tc, cc phn t phoi lin kt nhau thnh chui lin tc, hnh thnh si hoc dy d un..3. Phoi lo dao (phoi lin tc c mp un) : khi ct to ra phoi dy hoc phoi lin tc th thng xy ra hin trng: cc phn t kim loi ca chi tit gia cng b tch ra dnh trn mt trc, mt sau dao; dnh trn mt ang v gia cng ca chi tit. Cc khi kim loi dnh nh vy c gi l khi lo dao.4. Phoi xp(phoi rng ca): cc phn t phoi to ra s khng b gy thnh cc ht vn, m chng to thnh cc mnh phoi c lin kt v chng xp ln nhau thnh hnh rng ca, xy ra vi kim loi mu.21.12. Xc nh 4 lc tc dng ln phoi trong m hnh ct gt kim loi trc giao m cc lc ny khng th o c trc tip?Bn lc l: lc ma st F, p lc ma st N, lc trt Fs v p lc trt Fn.F = Fc sin + Ft cos N = Fc cosFt sin Fs = Fc cos Ft sin Fn = Fc sin + Ft cos 21.13. Xc nh hai lc c th o c trong m hnh ct kim loi trc giao?1. Lc ct Fc:

c xc nh bng cng thc: 2. Lc y Ft:

c xc nh bng cng thc: 21.14. Mi quan h gia h s ma st v gc ma st trong cc trc giao ct m hnh?

H s ma st c xc nh bi cng thc:

Gc ma st c xc nh bi cng thc: 21.15. ngha ca phng trnh Merchant?

ng sut ct c th c tnh theo cng thc: Phng trnh Merchant biu th mi quan h gia gc trt vi gc trt v gc ma st:

Trong cc lc Fc, Ft, v cc kch thc ,w u o c.Trong :

: Gc trt;: Gc trc;: Gc ma stPhng trnh Merchant ni rng gc mt phng ct tng khi gc trc tng v gc ma st gim.21.16. S lin quan gia cng sut vi lc ct?Lc ct kim loi c th t n 1000N.Tc ct t n vi trm mt trn pht (m/min).Nng lng cn thit trong mt hot ng ct bng lc ct nhn vi vn tc ct.Cng sut my ct cn m bo Pc = Fc.v (Nm/min)Pc : nng lng yu cu; n v: N-m/s or W (ft-lb/min)Fc : lc ct; n v: N (lb)V : vn tc ct; n v: m/s (ft/min)Khi theo chun M (horsepower)

Cng sut ca my cn ln hn cng sut tnh ton v trong thc t my ct kim loi c hiu sut khong 90%. Ty vo tng loi my s c hiu sut E, do cng sut thc ca my:

Cng sut ct trn mt n v khi lng vt ct (unit power)

Unit power cho bit cng sut cn thit ct ri mt n v kim loi nguyn cht. T tnh ton c cng sut ct i vi vt liu l hp kim.21.17. Nng lng ring trong gia cng kim loi?Nng lng ring bng cng n v:

Nng lng ring l lng nng lng cn thit loi b mt n v th tch ca kim loi ra khi chi tit. Chiu dy phoi trc khi ct nh hng n khi lng ring. 21.18. Kch thc gii hn c tc dng g trong qu trnh ct kim loi?

Tc dng ca cc kch thc n qu trnh ct kim loi th hiu vic tng nng lng ring khi din tch mt ct ngang ca phoi ( trong m hnh trc giao v trong phng php tin) gim.21.19. Cp nhit in dng c - phoi l g?Cp nhit in ny bao gm cc dng c v phoi khi hai kim loi khc nhau to thnh ng cp nhit in ni lin nhau. Bng cch kt ni ng dng in dn n dng c v b mt lm vic (c kt ni vi cc phoi), in p c to ra ti b mt phn cch gia dng c v phoi trong qu trnh ct c th c theo di bng mt my o in th hoc thit b thu thp d liu thch hp khc. in p ng ra ca cp nhit ngu (o bng mV) c th c chuyn i thnh cc gi tr nhit tng ng bng phng trnh chun cho s kt hp cng c lm vic c th. Cp nhit ngu c s dng bi cc nh nghin cu nghin cu mi quan h gia nhit v iu kin ct nh tc ct v cp phi.

23.8/ Nu 3 tnh cht quan trng ca vt liu dng c ct ?3 tnh cht quan trng ca vt liu dng c ct: dai ( bn) : kh nng ca mt vt liu hp th nng lng m khng b ph hy, chu c lc va p sinh ra khi gia cng. cng nng: kh nng ca mt loi vt liu gi cng nhit cao. S chng mi mn. cng l c tnh quan trng nht cn thit chng li s mi mn. Tt c cc vt liu dng c ct phi cng vng.23.9 / Thnh phn hp kim quan trng trong thp tc cao gm nhng g ?Thnh phn hp kim quan trng trong thp tc cao gm: Vonfram hoc s kt hp ca vonfram v molypden. crom (Cr). vanadi (V). Cacbon (C). Coban (Co) : tng cng cng nng ca thp ct tc cao.23.10/ S khc nhau trong thnh phn gia loi thp ct v thp khng ct ca hp kim cng l g?- Loi thp khng ct ch bao gm WC v Co.- Loi thp ct vi s kt hp ca TiC v TaC bn cnh WC-Co23.11/ Xc nh mt s hp cht chung ca dng lp ph mng trn b mt ca vt liu c lp ph.- Titanium-Nitride (TiN) : c mu vng thng c ph ln thp tc cao hoc carbide. TiN c cng cao, h s ma st nh, gim ddwwocj mi mn v dnh trong qu trnh gia cng.- Titanium-carbide (TiC)- Aluminum oxide (Al2O3)23.12/ Nu tn ca 7 thng s hnh hc ca dng c ct n im.7 thng s hnh hc ca dng c ct n im: Gc trc li chnhGc trc li ph Gc sauGc sau cnh Gc bnGc vo ca li dao Bn knh mi dao23.13) Ti sao cc cng c ct gm thng c thit k vi cc gc trc m?V gm s c ct thp v bn ko nhng cng chu nn tt. Trong sut qu trnh ct, s kt hp ca cc thuc tnh l tt nht c khai thc bng cch cho cng c mt gc trc m c xu hng ti cng c trong iu kin nn.23.14) Xc nh cc cch thc khc nhau m mt cng c ct c t chc ti ch trong qu trnh gia cng?C 3 cch chnh: Chn vng chc, trong ct cnh l mt phn khng th thiu ca dao, mt v d l tc cao. Chn brazed, c s dng cho mt s hp kim cng. Chn kp c hc, c s dng cho hu ht cc vt liu cng c cng bao gm hp kim cng v hp kim cng ph, gm s, gm kim loi, SPD, v CBN.23.15) K tn hai loi chnh ca dung dch ct theo chc nng?Hai loi chc nng dung dch ct l: cht lm ngui v cht bi trn.23.16) K tn ba loi chnh ca dung dch ct theo ha hc?Ba loi dung dch ct l: du ct, du nh ha v cht lng ha hc bn ha hc.23.17) C ch bi trn ch yu cho cng vic dung dch ct l g?C hai c ch bi trn c cho l c hiu qu trong ct kim loi: Bi trn ranh gii, trong bao gm s hnh thnh ca mt lp cht lng mng gip phn bit v bo v cc b mt tip xc. Bi trn p lc cc oan, trong mt lp rn mng ca mui nh st sunfua c hnh thnh trn b mt cng c cung cp du bi trn.23.18. What are the methods by which cutting fluids are applied in a machining operation?Phng php ph bin nht l flooding, dng n nh ca cht lng quyt nh n hot ng. Ngoi ra cn c: ng dng hi nc, gia cng kh, ng dng lm bng tay.23.19. Why are cutting fluid filter systems becoming more common and what are their advantages?H thng dung dch ct ang tr nn ph bin hn do Lut Bo v mi trng v s cn thit phi ko di tui th ca dung dch trc khi x l. u im ca h thng lc bao gm: tui th cht lng di lu, gim chi ph x l, v sinh tt hn, bo tr my cng c thp hn, v tui th cng c ct ko di hn.23.20. Dry machining is being considered by machine shops because of certain problems inherent in theuse of cutting fluids.(a) What are those problems associated with the use of cutting fluids? (b) What are some of the new problems introduced by machining dry?a) Dung dch ct b nhim theo thi gian vi mt lot cc cht gy nhim, bao gm c du trn, rc thi, khun mu, nm v vi khun. Ngoi gy mi hi v mi nguy him sc khe, cht lng ct nhim khng thc hin chc nng bi trn ca n cng nh khi chng c ti v sch s.b) Vn vi gia cng kh bao gm: (1) cng c qu nng, (2) hot ng tc ct thp v t l sn xut ko di tui th cng c, v (3) khng c li ch loi b phoi trong nghin v phay.23.21. What are some of the new problems introduced by machining dry?Trnh cc vn v nhim cht lng ct, x l, v lc nhng c th dn n vn ring ca n

PROBLEMS21.1.

Trong m hnh ct trc giao, dng c ct c gc trc . Chiu su ct v phoi sau khi ct c dy . Tnh:a) Gc trt.b) Bin dng trt.Bi gii:a) H s co rt phoi:

Khi , theo cng thc 21.3

b) Bin dng trt:

Trong bi 21.1, thay i gc trc . Gi s rng gc ma st vn gi nguyn, xc nh:a) Gc trt. dy phoi.Bin dng trt.Bi gii:a) Theo bi 21.1 ta c , khi theo cng thc Merchant:

Theo bi 21.2 ta c: , bng trng hp 21.

b) dy phoi:

c) Bin dng trt:

21.4. Trong phng php tin, trc chnh quay cung cp tc ct 1.8m/s. Lng tin dao v chiu su ct ln lt 0.3mm v 2.6mm. Dng c ct c gc trc 8o. Sau khi ct, dy phoi o c l 0.49mm. Xc nh:a) Gc trt.b) Bin dng trt.c) H s bc tch vt liu.Bi gii:a) H s co rt phoi:

Theo cng thc 21.3 ta c b) Bin dng trt:

c) H s bc tch vt liu:

21.19. Trong qu trnh gia cng tin trn thp khng g vi cng 200 HB, tc ct 200m /pht, lng n dao 0.25mm/ vng, chiu su ct 7.5mm. Hi nng lng thc hin qu trnh gia cng ny l bao nhiu nu hiu sut c hc l 90%. S dng bng 21.2 c c cc gi tr nng lng thch hp.Bi gii:Tra bng 21.2 vi vt liu thp khng g v cng 200HB ta c nng lng Pu = 2.8 Nm/mm3.H s bc tch kim loi:

Cng sut ct cn thit:

Cng sut thc ca my:

21.21. Trong hot ng tin nhm, tc ct 900ft/min, lng tin dao 0.02in/rev v chiu su ct 0.25in. Cng sut tnh theo m lc cn thit trn ng c bng bao nhiu, nu bit hiu sut ca my l 87%.Bi gii:

Tra bng 21.2 ta c

Tra th 21.14 ta c h s iu chnh Khi :

21.33. Ct trc giao c thc hin trn kim loi c nhit dung ring khi lng = 1.0J/g.C, mt 2.9g/cm3 v h s khuch tn nhit k= 0.8 cm2/s. Tc ct 4.5m/s, dy phoi trc khi ct l 0.25 mm, v chiu rng ct l 2.2 mm. Lc ct o c 1170 N. S dng phng trnh Cook, xc nh nhit ct nu nhit mi trng = 22C.Bi gii:Ta c:

Theo cng thc 21.22 ta c

T