NGHIEN CUTU-TRAO DOI
y P H l / a N G PHAP DO NHIET BANG BLTC XA KHONG TIEP XUC KHI GIA CONG TOC DO CAO
MEASUREMENT TEMPERATURE BY NONCONTACT RADIOMETRIC METHOD WHEN HIGH SPEED MACHINNING
Nguyen Tien Nga
Trudng Cao dSng Ky thuat Cdng nghiep (Bac Giang)
TOM TAT
Nhiet cat vd nhiet do phdn bo doc theo phdn tiep xiic giua dung cu cat vdi chi tiet gia cong trong qud trinh cat Id nhan td co bdn trong nghien ciru qud trinh gia cong kim loai bdi vi no dnh hudng den chat luong be mat, tuoi ben cua dung cu, do chinh xdc gia cong, trgng thdi kim loai vd tdc do bdc tdch phoi Da cd mot so phuong phdp dua ra each do nhiet do trong qud trinh cat nhu phuong phdp P^
thuat cap nhiet dien, dnh nhiet hdng ngoai vd cdc phuong phdp thuc nghiem cat kim loai. Mdi phuong phdp cd nhimg uu diem vd nhirng han che rieng. Trong bdi bdo nay. tdc gid dua ra phucmg phdp do nhiet cd su dung mot he do nhiet dong phat sinh trong qud trinh cat bao gdm mot day cdc cam bien quang nhiet HgTeCd, cd the do duoc cdc tin hieu thoi gian phat nhiet sap si 250 nano giay vd cung cdp du do chinh xdc de thu duoc nhiet do trong sudt qud trinh gia cdng. Cdc thuc nghiem do viing nhiet phat sinh trong qud trinh gia cdng hop kim nhdm cd che do cat la chieu cat 0,5 mm, gdc cat a = 5,5°, van tdc cat 30 m/s vd su dung mdnh dao hop kim cd viing mon vd dao sac.
Tir khoa: Phucmg phdp do nhiet cat; Do nhiet khdng tiep xiic; Do nhiet do bdng hdng ngoai.
ABSTRACT
The cutting temperature and temperature distribution along the rake face of cutting tool and work piece is an essential factor in study of machining processes due to its effect on surface quality, tool life, tolerances, metallurgical behavior and chip-removing rate. Several methods have been introduced to measure temperature during machining, such as the thermocouple technique, infrared camera and metallurgical methods. Each of these methods has some advantages and limitations. In this article, a dynamic temperaturedynamic temperature system using a linear array ofphotoconductive HgTeCd detectors has been used to record the signal real time of approximately 250 ns and provides sufficent resolution to capture transient temperature for during high speed machining (HSM). The experimental measures of the temperate fiels generated during machining Aluminum Alloy for cutting with a 0,5 mm depth of cut and 5,5" rake angle at 30m/s velocity using tools has a wear -land and sharp tool.
Keywords: Temperature measurement; Non-Contact Temperature Measurement, infrared temperature measurement.
NGHIEN CUfU - TRAO OOl
1. DAT VAN DE
Thyc nghiem da ehiing td rang, trong qua trinh cat ggt kim loai gan nhu tat ca cac cdng can thiet trong qua trinh eat ddu bidn thanh nhiet.
Phan Idn nhiet nay da dugc vao phoi cit nhung mpt phan nhiet khdng nhd dupe truyen sang dung eu cat va ehi tiet gia edng.
Viec xac dinh nhiet dp ciia qua trinh gia cdng la het sue quan trpng dac biet la trong bdi eanh hien nay khi ma nganh Cdng nghe ehe tao may cdng cu, vat lieu dung cu cat rat phat trien va da dat dugc nhieu thanh tuu, thi yeu cau ciia nganh gia cdng eat ggt la lam sao de tang tde dp eat, nang cao nang suat gia cdng gdp phan giam chi phi gia cdng la het siic biic thiet. Do dd, trong gia cdng cao tde, dat ra cho chiing ta la lam the nao de dinh dugc nhiet do trong dung eu cat, tren ehi tiet gia cdng. Day la mot van de kho khan nhung rat quan trgng trong thiet ke, ehe tao va sii dung dung cu, bdi vi nhiet do va sy phan bd nhiet do trong dung cu ed quan he mat thiet vdi qua trinh suy giam do ciing cua vat lieu dung eu cat d vimg ludi cat ciing nhu ca ehe mdn va tde dp mdn xay ra d dd, lam thay ddi eac thdng sd hinh hoc cua dung cu, giam tudi ben ciing nhu kha nang lam vice cua dung cu, mdn con anh hudng tryc tidp ddn chat lugng va dp chinh xac ciia be mat gia cdng. Ngoai ra, nhiet truyen sang chi tiet gia cdng lam thay ddi tinh chat ca - ly Idp be mat, gay ling suSt du cd the gay sai sd gia edng ciing nhu pha huy ehi tiet.
Cd thd noi rang, cho den nay, ly thuyet trao ddi nhiet chua thd md ta chinh xae trudng nhiet do khi cat dd dinh lugng dugc nhiet dp tai cac dikm cu thd tren dung eu cat. Tuy vay, viec nghien eiiu ly thuydt rat cd y nghia khi dieu kien do true tidp gap kho khan, khdng chinh xae hoac khdng thk tidn hanh dugc. De nghien ciiu ye trudng nhiet do xuat hien trong dung cu khi cat, gan day ngudi ta hay su dyng phucmg phap phan tu hiiu han dd xac dinh trudng nhiet dp. Phuang phap phan tu h&u han la phuang phap sd dimg de giai cac bai toan dugc md ta bdi cac phuang trinh
vi phan rieng phan cimg vdi eac dieu kien bien cu the. Co sd ciia phuong phap nay la lam rdi rac hoa cac mien lien tuc phiic tap cua bai toan.
Cac mien lien tuc dugc chia thanh nhieu mien con (phan tir). Cae mien nay dugc lien ket vdi nhau tai cac diem mit. Tren mien con nay, dang bi6n phan tuong duong vdi bai toan dugc giai xap xi dya tren cae ham xap xi tren timg phan tir, thoa man dieu kien tren bien eiing vdi su can bang va hen tuc giiia eae phan tir. Tuy nhien, phuong phap nay da sir dung eae phep toan gia djnh, thuc te khdng phai hoan toan nhu vay va cae kdt qua duge tinh toan cd sir dung phep tinh xap xi cho nen ket qua cd phan sai lech.
Ngoai ra, ed rat nhieu phuang phap khae xac dinh nhiet cat nhu xac dinh nhiet eat bang phuang trinh thuc nghiem thdng qua viee xac dinh anh hudng eua mot sd yeu td nhu vat lieu gia edng, vat lieu lam dao, tdc dp eat, chieu day, rong ciia lap eat, cae thdng sd hinh hgc eiia dao,... ta cd the thiet lap dugc phuong trinh kinh nghiem tinh toan nhiet cat.
2. NOI DUNG NGHIEN ClTU
Qua cac nghien eiiu va tir thye te cat ggt ta thay rang nhiet cat cd anh hudng rat Idn den qua trinh cat, do vay, can phai xac dinh dugc do Idn ciia chiing trong nhung trudng hop cat gpt cu the.
Tuy thude vao muc dich nghien ciiu ma ta cd the xac dinh nhiet eat tren dao, tren chi tiet, tren phoi hoac d mdi trudng chung quanh. Sy phan tieh ly thuyet ve sy thu nhan nhiet ciia qua trinh cat cho kha nang danh gia duge anh hugng eua cac thdng so CO ban cd lien quan den qua trinh cat den sy xuat hien va su dan nhiet khi eat, tuy nhien, viee xac dinh su thu nhan nhiet bang tinh toan la r4t khd va khdng chinh xac nen chi thudng dupe ap dung khi viec do dac nhiet dp tryc tidp khd khan hoac khdng the tien hanh dugc.
Ngay nay, vdi sy phat trien ciia cac nganh khoa hpc, ky thuat do nhiet ndi chung va do nhiet cat ndi rieng ngay cang hoan hao. Do vay, viec xac dinh nhiet cat bang caeh do la phd biSn. Hien nay, ^
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NGHIEN CUfU-TRAO D C I
phuang phap tdt nhat de do nhiet ly cat trong qua trinh gia cdng true giao la phuang phap do biic xa khdng tiep xiic. Day la phuang phap cung cap each do trudng nhiet dp thuan tien nhimg be mat phdi ma khdng can thiep vdi qua trinh cat. Cae tien bd gan day trong cac thiet bi dd hdng ngoai eho phep do nhiet dp tai mpi thdi diem, ket qua trong ca hai khdng gian va thdi gian cua ITnh vuc dpng nhiet hgc. Cd rat nhieu he thdng do khac nhau da dugc thiet ke va su dung trong cac nd luc de do nhiet dp xung quanh vimg ludi cat (miii dao). Vi du nhu phuang phap cap nhiet dien; Phim nhay eam nhiet hoac la cac thiet bi quet nhiet. Tuy nhien, he thdng do nhiet dugc trinh bay sau day cd mpt sd Igi the so vdi cac he thdng do khac.
Thii nhat, he thdng khdng thay ddi dang ke mien bien dang, thii 2 la he thdng khdng thay ddi dang ke mien nhiet, thii 3 la he thdng do dugc day du mien nhiet va thir 4 la he thdng cd kha nang dap ling thdi gian nhanh.
Trong he thdng ghi nhiet dp khi gia cdng cao tdc sir dung mpt day cac cam bien quang dan HgCdTe, day nay bao gom 15 thiet bi kich thudc 80 X 80 |im vdi khoang each tir tam cac cam bien la lOO^m va cd tdng chieu dai dat cam bien la 1,48 mm. Day cac cam bien dat d dang sau eira shaphire trong mot binh Dewar chua Nita Idng.
Dieu nay cho phep cac bd dd dupe lam lanh tdi 77 K de giam thieu nhieu dien va tdi da hoa sy nhay.
He thdng do nhiet cd tin hieu trong khoang thdi gian xap xi 250 ns va eung cap dp phan giai du de bat tin hieu nhiet ehuyen tiep cho tdc dp cat cao.
De cac phep do dugc thyc hien, day cac bd dd dupe tap trung tren be mat dudi cua mau, tren dudng thSng vudng gdc vdi hudng eat va nam khoang giiia cac vat mau. Hinh 1 la he quang hgc dugc su dyng do nhiet do khi gia cdng cao tdc. He thdng bao gom: Guong 1dm duge phu mot Idp nhdm va hai guong phang trong dd cd mpt guong phang dupe phu Idp vang. Lap phii de tang eudng cac phan xa birc xa hong ngoai. Sy phdng dai cua he thdng quang hpc cd the dupe thay doi nhung da dugc chgn mpt gia tri. Chii y cSn chinh he thdng quan hpc sao cho luon duge tap tnmg tren bg mat dudi cua phdi va diing vi tri dau cua
Bdi vi rat khd khan dd dua ra mpt each chinh xae mdi quan he giai tieh giiia diSn ap va nhiet do cho he thdng do nhu the nay, vi v4y, hau hdt cac nha nghien eiiu dS thir nghiem m6t thi nghiem chuan cung cap mgt mdi quan he tnrc ti8p giua nhiet do tren be mat cua phdi va dien ap ra eua he thdng do nhiet dd gia cdng cao toe.
Rd rang cac dieu kien ciia mot thi nghiem thyc tS cd the dugc thiet lap khi ma thuc hien mpt hieu chinh. Trong thi nghiem tren, mdi mpt bd dd dugc hieu chinh can than bang each su dung phuong phap dan gian cua cac nha nghien cim trudc day [2, 3, 4, 7]. Hinh 2 chi ra dang dudng cong nhiet chuan khi gia cong cao tdc hgp kim nhdm.
Hinh I: He thdng quang hoc do nhiet
Hinh 2: Dudng cong nhiet chudn khi gia cong hop kim nhdm 6061-T6
Da thire thii 2 dugc su dyng nhu chiic nang chuydn ddi dien ap ra sang nhiSt dp. Bdi vi cae thidt bi dd hdng ngoai khdng xae dinh dugc nhiet dp thuc nhimg sy khac nhau trong nhiet dp, nd can thidt phai kd den nhidt dd phdng trong qua trinh thi nghiem.
NGHIEN CaU-TRAODOl
Chu y rang, do nham b^ mat cua hgp kim nhiet do trong dung cu cat khdng phai la hinh anh nhdm cd thd thay doi dang kd trong sudt qua trinh va nhiet dp Idn nhit xudt hien tren bg mat tidp xiic bien dang. Anh hudng ciia do nham be mat len dung eu/phoi. Hon ntia true y la true xac dinh vi cac chi sd trong he thdng da dugc trinh bay bdi tri ciia bd dd thi d mpt ty le khac vdi true x, vi tri cae nha nghien ciiu [4, 6]. Mason [5] da chi ra dgc theo dudng din cat.rang sy phu thudc cua cae bd dd hdng ngoai.
* Do nhiet cat trong qua trinh gia cdng:
Hinh 3 dai dien cho mot linh vyc nhiet khi qua trinh cat dugc thuc hien vdi tdc do eat v ^ 30 m/s, chieu sau cat t = 0,5 mm, gdc cat a ^ 5,5", su dung manh hgp kim vonfram H13A, day hdng ngoai dugc tap trung ben trdn miii dao dd nhan duac nhiet dp Idn nhat, thudng xuat hien tren mat nghieng mpt khoang tir miii dao. Vi tri eiia miii dao thudng duge udc lugng la x =^ 0,50 mm, y ^ 0,36 mm. Nhiet dp Idn nhat nhan dugc trong cac thi nghiem la 23S°C va dugc ghi lai d vi tri x = 0,38 mm, y = 1,25 mm.
Hinh 4 dua ra mpt mien nhiet dp qua trinh c5t vdi cat v = 30 m/s, chieu sau cat la t = 0,5 mm va gdc cat a ^ -5,5", sii dung manh hgp kim von&am H13A. Vi tri cua mui dao dugc udc lugng X ^ 0,5 mm, y = -0,56 mm. Nhiet dp Idn nhat nhan dugc trong thi nghiem nay la 336"C va d vi tri X - 0,69 mm, y ^ 0,94 mm. Dir lieu thi nghiem da khdng thay ddi khdng ke mau nao deu cd nhiet do tap trung d nhirng kgt qua tren. Dudng cong nhiet dp chuan (H2) da dugc sii dung de xac dinh tuong quan dien ap ra tir eac bd dd HgCdTe va nhiet dd cat.
Hinh 4: Nhiet do phdn bd vdi dung cu cdl cd goc cdt a = 5.5° vd chieu sdu cat t = 0,5 mm
Gia tri nhiet dp cat Idn nhat eho tdt ca 12 lan thi nghiem dupe cho trong bang dudi day, nd cho thay rang su khac nhau giiia nhiet dp Idn nhat khi sir dung manh dao cat HI 3 A va D2 khdng Idn va nhd hon 10% gia trj nhiet do Idn nhdt. Han nira, gia tri ciia nhiet dp cat Idn nhat tang Ign vdi sy giam gdc cat. Tuy nhien, cd mpt budc nhay Idn vg gia tri Idn nhat ciia nhiet do khi thay ddi gia trj gdc cat a tir 0'' den - 5,5" so vdi khi thay ddi gdc cdt a tir 5,5" tdi 0°. Ngoai ra, cd su tang nhiet dp cat Idn nhat cimg vdi khi tang chieu sau cat.
Nhiet do do duoc khi khi thay ddi diAng cu cdt. gdc cdt, chieu sdu cdt
Goc cit cua dao
5.5"
0"
-5,5"
Dao gan manh hcrp kim H13A Chieu sau cat t (nun)
0,25 201"
222"
282"
0,5 238"
271"
336"
Dao lam bang vat lieu D2 Chieu sau cat t (mm)
0,25 223"
242"
296"
0,5 258"
275"
321"
* Do nhiet dp viing mdn.
Nhiet do tap trung nhan dugc tir nghien cihi nay chi ra rang dp Idn cua nhiet phat sinh trong phdi trong vimg lan can bg mat gia cdng lan Chii y rdng trong tit ca cac con sd ehi cudi thi nhd hem nhidu so vdi nhiet cdt Idn nhat. Mpt "^
Hinh 3: Nhiet do phdn bd vdi dung cu cdt cd gdc cdt (J. = 5,5" vd chieu sdu cat t = 0.5 mm
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NGHIEN CUfU-TRAO DOI
each lam tang do Idn cua nhiet trong phdi gia dung dao cd viing mdn va dao sac, hildng cat til cdng la dua vao dao cdt mot lugng mdn (Hmh 6), trai sang phai. Cac biic anh nay rd rang chi ra co no se lam giam gdc cat a va lam phat sinh ma sat, cac Idp bien ciing tren b^ mat cua san pham sil digu nay tac ddng viirig phat sinh nhiet ttong phdi dung manh dao cd viing mdn.
va dan ra mot ung suat du trgn bg mat san pham.
Thuc hien lam thi nghiem nghien ciiu anh hudng cua vimg mdn len sy phat sinh nhiet tren be mat phdi gia cdng. Hinh 6 dua ra mien tap trung nhiet img vdi che do sau (1): Chieu sau cat t ^ 0,5 mm, gdc cat a = 5,5°, v ^ 30 m/s va sir dung manh dao cae bit vontram co viing mdn. Nhiet dp Ion nhat thu dupe tren be mat gia cdng la 106"C.
Hinh 6. Nhiet do phdn bo trong sudt qud trinh gia cdng cao tdc vdi che do cdt (I) Hinh 7, thg hien mien tap trung nhiet ling vdi chg do cat (11): chigu sau cdt t = 0,5 mm, gdc cat a ^ 5,5", V = 30 m/s va sir dung manh cac bit vonfram sac. Ket qua thay ring vimg nhiet khong phat trien nhigu ben dudi miii dao va dp Idn eiia viing phat nhiet tren phdi khdng nhigu.
Hinh 7 Nhiet do phdn bo trong sudt qud trinh gia cdng cao tdc vdi che do cdt (II) Hinh 8, 9 the hien be mat san pham si£
Hinh 8: Be mat gia cong sit dung dao co viing mdn
Hmh 9: Be mat gia cong sii dung dao Co viing mon
3. KET LUAN
Nhiet dp phan bo duoc dua ra td nghita ciJu cua Vernaza Pena et al [19] va cac kft qua do dUdc cua thi nghiem tren thay rang nhiet tren be mat gia cong lan cuoi nho hon nhieu so vdi nhiet dp 16n nhat. Mpt each de lam tang nhiet dp truyfa sang phpi la s\i dung dao co vung mon. Dao co vung mon (hinh 6) la dang chung ciia diong cat khi bi mpn, no lam cho gpc cat bi giam va lam tang ma sat trong qua trinh gia cong lan cuoi.
Dieu nay, lam tang vimg phat sinh nhiet trong phoi va do do lam phat sinh ijfng suat tren be mat san pham. Do dd anh hudng cua viing mon da dupe tim ra. Nghien cUu linh vUc nhiet phat sinh trong qua trinh gia cong cao toe vdi mot dung cu cat CO mpt vung mon chi ra rang viing mon la mpt ngudn nhiet dang ke.
NGHIEN CUfU-TRAO OOl
Nhiet cdt do dugc trong qua trinh gia cdng cao tdc chi ra rang nhiet cat tang khi giam gdc cdt va tang chieu sau cdt. Vdi trudng hgp dao cd vung mdn la 0,75nim khi eat vdi chidu sau cdt t ^ 0,5 mm va gdc cdt la 5,5", van tdc cdt 30 m/s, sir dung manh eae bit HlSAthi nhiet cdt trong phdi la 106"C, nd bang khoang 4 5 % nhiet do Idn nhdt phat sinh trong qiia trinh edt. •
Ngay nhan bai: 12/4/2014 Ngay phan bien: 20/5/2014
Tai li^u tham kh^o:
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Ha Noi.
[2]. Duffy J, Campbell JD, Hawley RH (1971) On the use of torsional spUt-hopkinson bar to study rate effects in 1100-0 aluminum. J Appl Mech 93:83-91.
[3]. Duffy J, Chi YC (1992) On the measurement of local strainand temperature during the formation of adiabatic shear bands. Mater Sci EngA157:195-210.
[4]. Hartley KA, Duffy J, Hawley RH (1987) Measurement of the temperature profile during shear band formation in steels deforming at high strain rates. J Mech Phys Solids 35(3): 283-301.
[5]. Mason JJ, Rosakis AJ, Ravichandran G (1993) Use of high- speed infrared detectors for dynamic deformation and failure. Experimental techniques in the dynamics of deformable solids. ASME-AMD 165:11-24.
[6]. Mason JJ, Rosakis AJ, Ravichandran G (1994) On the strain and strain rate dependence of the fraction of plastic work converted to heat: an experimental study using high speed infrared detectors and the kolsky bar.
Mech Mater 17: 135-145.
[7]. Zehnder AT, Rosakis AJ (1991) On the temperamre distribution at the vicinity of dynamic propagating cracks in 4340 steel. J Mech Phys Solids 39(3):385^15.
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