Nghiên cứu ảnh hưởng của môi trường nhiệt ẩm đến tuổi thọ và độ tin cậy của vít me đai ốc bi

NGHIEN ClifU - TRAO OOl /b r z NGHIEN CLTU ANH HlTdNG CUA MOI TRlTOfNG NHIET AM D £ N T U O I T H O V A D O TIN CAY CUA VIT ME - DAI C BI STUDYING ON EFFECT OF TROPICAL ENVIRONMENT TO LIFE TIME AND RELIABILITY OF BALL SCREW Trin Diic Toan', Phgm Van HCing^ ^Khoa Cong nghe Ca khi, Truong Dai hpc Dien lire -Vien Co khi, Truong Dai hpc Bach Khoa Ha Npi TOM TAT Bdi bdo trinh bdy kit qud nghiin curu quan he giiia mon dpc true cua vit me - dai 6c bi (VMDB) cdc hi ca dien tic, dgc biit Id mdy cong cu CNC v&i mpt so thong so dnh hu&ng cua tdi trpng, toe dp, mdi tru&ng nhiet dm Viet Nam (TCVN7699-2-30) Kit qud nghiin cicu la ca s& de ddnh gid tuoi thp vd dp tin cay cua VMDB, dong th&i kit hgp v&i ddnh gid cua ISO di cd thi sic dung hieu qud han VMDB dieu kien Viet Nam Tur khoa: Moi tru&ng nhiet dm; Vit me - dai 6c bi; Mon; Tudi thp; Dp tin cay ABSTRACT This paper present the relationship between axial wearing of ball screw in mechatronic systems, especially in CNC machines with parameters such as load, speed, and the Vietnam tropical environment (TCVN 7699-2-30) The result would be basis parameters to evaluate the life time and reliability of ball screws On the other hand, combining this result with related ISO announcements can use ball screws in Vietnam conditions more efficiency Keywords: TCVN7699-2-30; Environment; Ball screw; Wear; Life; Reliability ISSN 0866-7056 TAP CHi CO KHi VIET NAM S6 1+2 nam 2015 www.cokhivietnam.vn NGHIEN C U T U - T R A O D O I DAT VAN DE Hien nay, may cdng cu CNC duoc sir dung rat rpng rai a Viet Nam Theo khuyin cao cua cac nha san xuat va thdng ke tai Viet Nam thi may cdng eu CNC thuong hu hong bp phSn truyin dpng la VMDB, din din nhanh dat din giai han tuoi thp quy dinh truoe, nho han tudi thp va dp tin cay cdng bo Mdt nhiing nguyen nhan ehinh la Iam viec moi trucmg Viet Nam dupe dac trung bing mdi huong TCVN 7699-2-30, la mdi truong dien hinh cho hau nhiet im bien ddi eua Viet Nam (nhit la d miln Bic) Vi vay, viec xac dinh he sd tudi thg bo sung eua VMDB theo tieu chuan ISO lam viec mdi truong theo TCVN7699-2-30 ciing voi cac miie tin cay khac la cap thiet Do do, viec tinh tudi thg du kien se chinh xac hon, co ca sd du bao su suy giam cap chinh xac may va co ke hoach sii dung, bao dudtig, sira chua hoac thay the phu hop NQI DUNG NGHIEN ClTU Theo [1], md hinh vat ly va md hinh dp Cling tuong duong ciia he VMDB dugc thi hien tren hinh I He VMDB gdm bi chan " " truc vit "5" - dai 6c va hi "8" dugc md hinh hda nhu he ba 16 xo ghep ndi tiep de tinh toan Cling, bien dang va chuyen vi, chuyen vi dgc true cua dai de la tdng hgp chuyen vi ciia he ba 16 xo Tai dgc true tac ddng len true vit me ciing la tai dpc true tac dgng len dai 6c va bing tong tai dgc true tac dung len eae bi Trong dd, mdi quan he giira tai phap tuyen tac ddng len bi va tai tac dung len bi theo phuang dgc true dugc the hien qua cdng thiic [2]: (1) ,=1 Trong do: n - Sd bi bd truyen vit me - dai dc bi; Fa - Tai tac dung theo phucmg dgc true; Pj -Tai phap tuyen tac dung len bi thii j ; a -Goc tiep xiic giiia bi va ranh true vit, ranh dai 6c; y -Goc nang ren 2.1 Xac dinh mon dgc true vit me - dai 6c bi I) Dpng ca: 2) Kh&p noi; 3) bi chdn; 4) Encoder gdc; 5) True vit me; 6) Thdn thu&c thdng; 7) Con chgy thu&c thang; 8) Dai dc bi; 9) bi da Hinh I Mo hinh hda vit me - dai 6c bi [1] Hinh 2: Phdn bo tdi trpng vit me - dai dc bi [2] Hinh 2, the hien mdi quan he hinh hpc giiia tai phap tuyen Pj va tai dgc true Fa "^ ISSN 0866 - 7056 TAP CHi CO KHi VIET NAM, S6 1+2 nam 2015 www.cokhivietnam.vn NGHIEN cufu-TRAOD6| Gpi U la m6n tong cpng (mdn phap Iam viec den lugng mdn dpc true cua nd tuyen); Uc la mon theo phucmg doe true (mon (lugng tang sai I^ch dpc true) diing bang hieu dpc true), nhu vay: gidi han tren va gidi han dudi sai lech dgc true cho phep duac xae dinh theo cap chinh xac ciia VMDB U - U^ Sm a Cos (2) Tren thuc te, "Sin a Cos y" dupe coi Vdi bg truyen VMDB co ma hieu nhu mpt hang sd, it thay ddi qua trinh Iam IS()3408-I6x5x220-T7R4 cip chinh xac co viec, dd ty le giu'a mon dpc true va mon t6ng chieu dai doan ren lam viec Lu = 180 mm, xac cpng la tuyen tinh vdi gia tri khong thay ddi dinh dugc sai lech dpc true cho phep cua bd truyen [3]: Theo danh nghTa, lupng tinh tien "t^"cua - ^ L" dai dc ty le vdi gdc quay cua true vit me vdi (3) he so ty le chinh bang budc vit me; t^ = n (n: sd vdng quay true vit me; t: budc vit me} Trong dd: Tuy nhien, thuc te lupng tinh tien ciia dai dc (tac ddng tryc tiep den dp ehinh xae gia c6ng) e Dp chinh xac dpc true eho phep (phuang thudmg khong theo diing ty le tren, n6 chm phap khdng tai, ISO 230-2) anh hudng ciia nhieu yeu t6 khac nhu:,Sai s6 ^3oop ~ -^^^ ^i"^ ^^^° ^^P chinh xac Vdi T7 thi budc vit; Bien dang dan h6i; Bien dang nhiet; %op^52^im Rung dpng; Mdn Khi xet den anh huong ciia cac nguyen nhan tren den lugng tinh tien tong Do do, tinh dugc e = 31,2 jim —* hgp ciia dai 6c thi chi c6 mdn la nguyen nhan sai lech dpc true cho phep theo ca hai chilu chinh va dan tdi sir gia tang sai lech lupng tinh (VMDB lam viec hai chilu) la [UJ - 31,2 x tien dpc true ciia dai 6c theo thdi gian Noi each = 62,4 |im khac, lugng tang sai lech cua chuyin dpng tinh tien theo thdi gian chinh la ket qua ciia mdn Vi vay, luang mdn doc true cua VMDB (ISO3408-16x5x220-T7R4J dat tdi gidi Tdng hgp cac phan tich, danh gia neu han tudi thp la 62,4 pm tren va theo cac tai lieu [1,2] cho thay "Lugng tang sai lech chuyen dpng tinh tien dpc true ciia 2.3 Xac djnh he so tuoi tho va d6 tin e$y dai 6c theo thdi gian chinh la lugng mon dpc true theo thdi gian" Thyc tl, VMDB (ISO3408 - 16x5 x 220 - T7R4), dam bao cac tieu chuan co ban va 2.2 Moi quan he mon va tu6i th^ vit me - lam viec giai doan dn dinh Khi tdc dp dai 6c bi mdn C dugc tinh theo cdng thiic [4, 5]: Khai niem tu6i thp may va chi tiet may dugc xac dinh theo muc dich va yeu ciu sir dung Vdi cac nudc c6 nen cdng nghiep phat trien thi dat tdi gidi han tudi thg, may se khdng dam bao chinh xac Iam viec (do chinh xac dugc xac dinh theo cip chinh xac) Theo ISO 230-2 "Xac dinh dp chinh xac va kha nang lap lai dinh vj ciia true dilu khiln sd" da quy dinh cac phep dugc thuc hien khdng tai Nhu vay, tudi thg cua VMDB chinh la thdi gian tie t W (4) Trong do: Uc - T6c dp mon dpc true; t - Thdi gian thyc nghiem; [U ] - Lugng mon dpc true gidi h ^ ; L^j - Tudi thp lam viee mdi trudng thi nghiem ISSN 0866 - 7056 TAP CHI CO KHi VIET NAM, Sd 1+2 nam 2015 www.cokhivietnam.vn NGHIEN CtfU - TRAO OOl Tuoi thp VMDB theo thuc nghiem duac 30 Quy hoach thyc nghiem [7, 8] nhu sau: tinh bang cong thiic - DSu vao tai "F"; [UJ (5) "• F^„ = 3500N; FO = 3000N; F ,^ = 2500N Nen he so tuoi thp c6 yeu to moi truong dupe xac dinh theo nghiem: - Dau vao toe quay true vit me "n": (6) MSO !„„ = 100 vg/ph; n^ = 89 vg/ph; n^_„ = 78 vg/ph Trong do: USD - Tu6i thp tinh ISO [6]: MSO = CC,a/F)'3 ;10I'6.1/(60 nJCh Ham muc tieu he so tuoi thp "m" (7) (m = ^ ) xac dinh theo phuong trinh hai quy thuc nghiem vdi thoi gian thu nghiem 4Bh, chu KET QUA VA THAO LUAlN ky 24 gid, lay 12 dilm [9, 10]: Thuc nghiem xac dinh L^^ theo cae "f = a^ + a, F + a^ n + aj F u (8) thdng sd vao co ban la tai doc true "F" va tdc dp quay true vit me "n" dugc thuc hien Lupng mdn dpc true Uc cac thi mdi trudng dae thii Viet Nam TCVN 7699-2- nghiem dugc het ke d bang I Bdng 1: Bdng Hit ke lugng mdn dpc true U^ (fim) cdc thi nghiem Ten tiif nghiem Ch^ l^m viec TNI TN2 TN3 TN4 TN5 TN6 F_,_ F„„ Fo no •' • F„_ •'du Fo no / ko boi tron 1(0 boi tron ko boi tron ko boi trim ko b&i trtfn boi tron TCVN 7699-2-30 TCVN 7699-2-30 TCVN 7699-2-30 TCVN 7699-2-30 TCVN 7699-2-30 TCVN 7699-2-30 40.000 6,9 4,7 3,4 2,4 2,0 2,1 42.500 6,9 4,5 3,3 2,3 45.000 6,8 4,7 3,5 2,4 1,9 2,0 2,0 47.500 6,8 4,5 3,6 2,4 1,9 2,2 50.000 6,7 4,7 3.4 2,3 1,8 2,1 52.500 7,1 5,0 3,5 2,5 1,9 2,0 55.000 6,9 4,9 3,6 2,4 1,8 2,0 57.500 7,1 4,8 3,5 2,5 1,8 2,1 60.000 7,1 4,6 3,4 2,5 1.8 2,1 62.500 7,2 4,6 3.4 2,3 1.9 2,1 65.000 6,9 4,5 3,4 2,4 2,0 2,0 67.500 7,0 4,9 3,4 2,4 Trung binh 6,9S 4,70 S,4S 2,40 1,9 1,S9 2,05 / / / Mon dilm dicli ISSN 0866 - 7056 TAP CHi CO KHi V I £ T NAM, Sd l+2nam20I5 www.cokhivietnam.vn 2,0 1,9 NGHIEN cufu - TRAO DOI Xii ly s5 lieu thuc nghiem [7, 8], tim dugc ham h6i quy he sd tuoi thp mk vit me Iam viec mdi trudng TCVN7699-2-30 va khdng bdi tron nhu sau: Lmt =m.Ljso (12) - Khi kh6ng bdi tran: L'^t (13) " H - - 1,57 10-=+6,42 10^F+1,78 10-^ Ket qua kiem tra miic dp tuong hgp cua Khi vit me lam viec moi truong thue nghiem bang tieu chuan Fisher [8] cho TCVN 7699-2-30 va cd bdi tran, he s6 hi6i thp thay thuc nghiem thda man miic y nghia 0,05 ^ duoc xac dinh: (dp tin c^y 95%) Qua thue nghiem cho thiy dp tin cay eiia tuoi thp VMDB Iam viec (10) mdi truomg TCVN 7699-2-30 la tich ciia dO tin m =(nu/L)/( cay tinh theo ISO vdi dp tin cay thuc nghiem Trong do: \|/ - Dugc xac dinh theo ty so giiia lugng m6n co bdi tran va kh6ng Sii dung cac gia tri Ky vpng va Phuang bdi tran cac thi nghiem tam quy hoach sai ciia "m^" de tim khoang gia tri ciia "m^" ling vai dp tin cay thuc nghiem 95% Theo [7], (= Ui(C boi tron)/Ui(C ko boi tron) = 1,68 (11) khoang gia tri ciia "m^" duoc tinh theo: Dd thi su phu thupc he sd tudi thp " " 7±a^.zi, = Tn^±l,63.lO-^ theo tai dpc true "F" va t6c dp quay "n" VMDB Iam viec m6i trudfng TCVN Trong dd: 7699-2-30 dugc thi hien tren hinh (14) ^ =1,68, xac dinh dupe gia tri he so tuoi thp c6 boi tron "m" moi truong TCVN 7699-2-30 Bang thi hien khoang gia tri m iing vdi cac dp tin cay Bdng 3: Khodng gid tri m ung v&i cdc dp tin cay STT So till cay tliirc te 85,50 90,25 91,20 92,15 93,10 94,05 V 1,68 He so tuoi tho "in = ini(.l|l" l.OO.C" = 2.74.10"= ) 0,62.C'": 2.74.10"=) 0,53.(>"= 2.74.10-') 0,44.('"r-.74.10-') 0,33.('"± 2,74.10"') 0,21.(™ = 2.74.10"') Nhu vay, tudi thp thuc te ma VMDB chiu anh hudng cua moi trudng TCVN 7699-2-30 theo TCVN 7699-2-30 van duge tinh theo hai thdng sd ca ban la " F " va "n", nhung can bd sung them he s6 tu6i thp m cd bdi tran va mk khong b6i tron, m dugc tinh theo c6ng thiic thuc nghiem (14) vdi gia tri m^, va^m dugc xac dinh tir thuc nghiem Trong trudng hgp theo yeu cau thuc te phai dam bao dp tin cay ciia tudi thp van giu d gia tri 90%, mac dii lam vide moi trudng cd dac trung theo TCVN 7699-2-30 thi dp tin cay tinh toan theo ISO phai dugc xac dinh d miic xap xi 95% Ndi each khac, tudi thp thuc te se nhd hon tudi thp tinh toan theo ISO cd cimg miic tm cay ^ ISSN 0866 - 7056 TAP CHi CO KHi VIET NAM, S6 1+2 nam 2015 www.cokhivietnam.vn > ' ' -V C NGHIEN CIJU - TRAO DOI KET LUAN - Kit qua ciia nghien ciiu budc dau md ta mdi quan he giua mdn phu thupc tai "F", toe dp quay "n" cua VMDB ma hieu ISO3408-I6x5x220-T7R4 hoat dpng moi truong nhiet im ciia Viet Nam c6 dac trung theo TCVN 7699-2-30 - TIT kit qua thuc nghiem mdi trudng theo TCVN 7699-2-30 da xac dinh dupe tuoi thp thuc tl ciia VMDB theo c6ng thucLmt = m.Liso Gia tri he s6 m da dugc xac djnh theo cac dp tin cay tuong iing - Dp tm cay cua tu6i thp VMDB thuc te se bi giam khoang 5% so vai dp tin cay theo ISO, dd mudn tri tin cay thuc te la 90% thi dp tm eay xae dinh theo ISO phai nang len 95% - Ket qua ciia nghien ciiu ed the tham khao tinh toan, danh gia dp tin cay va tudi thp ddi vdi mdt sd VMDB khae ciia may cdng cu.