1985 Hou Ws Scraping

8/4/2019 1985 Hou Ws Scraping

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Ef f ec t o f su r f ace t o p o g r ap h y o fsc r ap ed m ach i n e t o o l g u i d ew ayson the i r t r ibo log ica l behaviour*Hou Yuk eng, Chen Darong and Zheng LinqingtTr ibologica l behaviour of two k inds of scraped surface topogra phy o fmachine too l gu ideways - the convent ional form named 'nar row-deep"scraping and an improv ed form terme d 'w ide-s hallow ' scraping - is descr ibed.Behaviour is compared und er the fo. llowing co ndit io ns: average pressurep = 0 .13 5-0 .67 5 kg f cm -2 and s liding ve loc i t y V = 1 5-6 00 mm min -1 .In comparison with narrow-deep scraping of sl ideways, wide-shallow scrap-ing may reduce the f r i c t ion coe f f i c ien t by abou t 5 0-9 0% , rel ieve the pheno-menon of st ick-s l ip , and increase the am oun t of tab le f loat ing. Consequent ly,the p osi t ion ing accuracy o f the machine too l feed dr ive system and the weardu rab i l i ty o f gu ideways can be expected to be improved great ly. The am oun tof scraping work migh t be decreased to less than . An at tem pt is mad e toexp la in the above resu lts f rom the v iewpo in t o f hydrodyn amic lub r ica t ionand to summ arize the character ist ics of th e two kind s of scraped surfaceme ntion ed above. Based upo n a series of exper iments, the a uthors proposeth at in evaluat ing th e performance of guideway surfaces, the concepts o foi l - f i lm- forming abi l i ty and o i l - f i lm- reta in ing abi l i ty are helpfu l .Keyword=:sl ideways, surface texture, oi l f i lmsGuideways a re impo r t an t comp onen t s o f mach ine too l s , t oa l a rge ex t en t de t e rmin ing the w ork ing accuracy , ope ra t ingpe r fo rmance , and w ork ing l if e t ime o f t he mach ines . Ma nygu ideways su f fer f rom one o r more o f t he fo l lowing de fec t s :'heavy hand-fee l ing ' , s t ick-slipping, low pos i t ioning accuracyin micro-feeding, and po or w ear resistance . Al l of theseproblems are concerned wi th the i r t r ibologica l behaviour .Now adays, there are severa l me tho ds for improv ing thet r ibologica l charac ter istics of mac hine tool g uideways -ease harden ing, chemical t rea tme nts, use of a l loy cast i ronor var ious plast ic layers on gu idew ay surfaces, hyd rosta t icsystems, rol l ing guidew ays, semi- l i f t ing guidew ays, andthe use o f gu ideway o i l s con ta in ing d i f f e ren t add it i ve s .These are a l l va luable in di f feren t way s, but in mo st casesthe autho rs a lso reco mm end the so-ca l led "wide-shallow'scraping m eth od to improve pla in guideway s even fur ther .The a t t r ac t ions a re ev iden t : l ow expense and ex t raord ina rye f fec ts . Th i s k ind o f p l a in gu ideway was deve loped by theShoud u Mach ine Works i n 1965 . S ince then i t ha s beenappl ied to la thes, gr inders, mi l l ing machines, jig bor ingmach ines and dr i l l ing machines. Goo d resul ts have beenob ta ined : In t he o rd ina ry r ange o f ope ra ting speed , f ri c t i on coe f f i-c i en ts have been reduced by 5 0-9 0% St i ck - s li p phenom enon have been a l l ev i a ted , wi th t hecr i t ica l speed for s tick-slip dropping by an order o fmagni tude ; a t t he same t ime the mic ro - feed pos i ti on ingaccuracy has been improved f rom t ens o f m ic rome t re sto several microm etres*.4 vers ion o f this paper w as pub l ished in t he Chinese journa lLub rication Engineering, 1982 , No. 2. The pap er has been revisedfo r this publication.?~Fstnghua University, Belting, The People's Republic of China

Wear ra tes have been grea t ly reduce d The num ber of man -hours for scraping has decreased.On the ba se o f t he expe r i ence ga ined a t S houdu M ach ineWorks, a ser ies of experiments has been perfor med . Someessent ia l explan at ion is given in this p aper .Exper imenta l r igShoudu Mach ine Works ' gu ideway r ig (F igs 1 and 2 ) .Sample sizes were as show n in Fig 3. The t rad i t ionalscraped surface is the so-ca l led 'narrow -deep ' scraped( N - D ) s u rf a ce . W i t h th i s m e t h o d t h e n u m b e r o f l a p pi n gcon tac t spo t s on the gu ideway i s abou t 20 -2 2 pe r squareinch, and o n the sl ider is about 16 per square inch. Scrapingdep th i s abou t 10-2 0 gm (Figs 4 and 13(a )) .The othe r kind of scraped surface i s the 'wide-shal low'scraped (W -S ) surface . Here the scraping mark size i s abo ut15 x 5 mm 2 and the sc rap ing dep th i s abou t 1 - 2 ban

F i g I T h e S h o u d u M a c h i n e W o r k s g u i d e w a y r i g

TRIBOLOGY internationa l 0 3 0 1 - 6 7 9 X / 8 5 / 0 2 0 1 2 5 - 0 5 $ 0 3 .0 0 1 9 8 5 B u t t e r w o r th & C o (P u b li sh e rs ) L t d 125


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Hou. Chen and Zheng - t r ibo logy o f mach ine too l s lidewaysl I nd u ct an c e ~ ~ _ [ F o r c e - m e a s u r i n ginstrument X-Y recorder St rain meter [ r ing

/ /Dial i n d i ca t o r'he

P ick-ups l i d e r

Fig 2 Basic components o f the guideway rigEEo

3 7 0 mm

/ S c re w

Fromsteplessspeedregu la t ionmotor

E- - 0r~

OJ

J 6 2- I mm~Fig 3 Test piece dimensions

Fig 4 A 'narrow-deep' scraped surface

Fig 5 A ~vide-shallow" scraped surface( F i gs 5 and 13( b ) ) . T he su r f aces o f gu i dew ay and t he s l ide ra r e t he s ame .F i ve l ub r i can t s w e r e used - s ee T ab l e 1 f o r v i s cos i ti e s -n o n e o f w h i c h c o n t a i n e d v i i m p r o v e r o r e p a d d i ti v e s. T e s t sw e r e p e r f o r m e d a t a v e r ag e p r e s s u re s o f p = 0 . 1 3 5 , 0 . 2 7 0 ,0 . 4 0 5 , 0 . 5 4 0 a n d 0 . 6 7 5 k g f c m - 2 , a n d a t s li d in g s p e e d s o fV = 1 5 , 7 5 , 3 0 0 , 4 5 0 a n d 6 0 0 m m / m i n .

R e s u I t sT h e f r i c t i o n c o e f f i c i e n tT he f r i c t i on f o r ce w as de t e r mi ne d us i ng a d ia l i nd i ca t o r( F i g 2 ) . A t yp i ca l r e su l t i s show n i n F i g 6 . I t w as f oun dt ha t i n t he usua l r ange o f sl id i ng speed o f mos t m ach i net o o ls , i e 0 - 6 0 0 m m / m i n , t h e f - V c u r ve o f W - S g u i d ew a y sT a b l e 1 . L u b r i c a n t v i s c o s it i esO i l V i s c o s i t y , Usec S t

1 0 1 011 111 5 1 53 0 3 0

1 5 0 1 5 00 . 2 5

,,- 0.20Ea}_o 0 158u= o . I 0u . 0 0 5 'W-S ', O i l iS , P = 04 55

I I I I 10 15 7 5 1 5 0 3 0 0 4 5 0 6 0 0Sl id ing speed V, ram/rain

Fig 6 Typical fric tion coeffic ient values0 . 4 0

o.2o~_ 0 1 0

0 7 5 1 50 2 2 5 3 0 0Sl id ing speed V, ram/rainF i g 7 f - v curves fo r unlubricated scraped surfaces

o.2o ~ i T u rb i n e o i ,(V S O =2 2 )o Cot tonseed oi l containing0 15 sulphide (WSO 20 )

c._e x 50 15 0 mixture of the. 0 two oi ls'$ o. 0g

0 0 5

0 5 0 I 0 0 1 5 0 200 2 5 0 300Sl id ing speed V, ram/rain

Fig 8 Effect o f additives on f - v c u r v e for W -S guideway

1 2 6 A p r i l 1 9 8 5 V o l 1 8 N o 2


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0 . 2 0P : 0 13 5 k gf

0 . 1 5

' l \"6~ o.~o I

0 0 5

crn-2

O i l I 0Io 15 75 15o 3OO 45q 600S l i d i n g s p e e d V , m m /m i n

F i g 9 E f f e c t o f o i l vi s c os i ty o n f -v c u r ve f o r W - S g u i d e w a y0 . 2 0

N~c= =8

0 . 1 5

0 . 1 0

O il 1 5 0

0 0 5

P = O . 6 7 50 15 7 5 1 5 0 3 0 t 4 5 0 6 0 0

S l i d i n g s p e e d V , r n r n / m i nF i g 1 0 E f f e c t o f p r e s s u r e o n f -v curve f o r W - S g u i d ew a y

appears as the Striebeck's curve, initially dropping rapidlyand then rising slowly. This demonstrates that there ismixed lubrication at low speeds and hydrodynamic lubri-cation at higher speeds, and that there is a critical point(ie the lowest point) between these two kinds of lubrica-tion condition. For the N- D guideways, there is generallyonly one lubrication conditon - mixed lubrication.T h e f - V curves of the two kinds o f guideway are different,however, only when they are lubricated; otherwise, theyagree closely with each other (Fig 7) and fi s alwaysindependent to V. Summarizing then, it is clear that themain difference between the two kinds of scraped surfaceis that of hydrodynamic effect, caused by the differencesin surface topography.Although different oils and different pressures were used,the f - V curves of N-D guideway remain similar, and allin the shadowed region in Fig 6, showing once more thatthe hydrodynamic effect with the N-D guideway is weak.Fig 8 shows that the kinematic coefficient of friction isalmost independent of any additives in off; only the stick-slip phenomenon (shown by shadowed region) is affected.in Fig 9, it is shown that f is about 0.02 at the criticalpoint. To the left of the critical point, the higher the oilviscosity thenthe lower is f; to the right, the higher the oilviscosity then the higher the value of f.Fig 10 shows that , for W-S guideways, f decreases when pincreases. This is true both in the region of mixed lubrica-tion and in the region of hydrodynamic lubrication. But,for N- D guideways, as mentioned above ,f is almostindependent ofp (F ig 6 ) . This ident i f i es again that W-S

Hou, Chen and Zheng - t r ibology of machine tool s lidewaysguideways exhibit more hydrodynamic effect, and N-Dguideways exhibit more boundary effect.From experiments, the comparison of f is as follows: At very low speeds (about several mm/min), fi s approxi-mately the same for both methods At normal speeds (V < 200 mm/ min ), ffo r the W-Sguideway is between 2 and 10 times smaller than that

of the N-D surface. At higher speeds (V = 200-600 mm/min), the W-Sguideway has a friction coefficient 2-5 times smallerthan that of N-D scraped surfaces.G u i d e w a y - s l i d e r s e p a r a ~ m .To verify the hydrodynamic effect of W-S guidewaydirectly, the separation of slider and guideway when inmotion was also measured. Measurements were made withan inductance instrument which had a sensitivity of about0.1/an. Typical results are shown in Fig 11; these havebeen shown to coincide with theoretical calculations.Comparing Fig 11 with Figs 6,9 and 10, it can be seenthat hydrodynamic lubrication is already dominant whenh ~. 1/am. Fig 11 shows hat the W-S guideway canundoubtedly form a ~onsiderable thickness of oil film.In contrast, N-D guideways cannot form an effective oilfilm, because h is too small to separate two rough surfaces(Fig 13). For N-D guideways, h is many times smaller thanfor a W-S guideway.It is evident then why W-S guideways have so much betterfriction properties. Fig 11 contains two h - V curves for

7 . 0 0

6 . 0 0 ~ - ~ W - S[ - - . D N - D

5 . 0 0E=k

.a:._oEB.

4 . 0 0

s , o o l - / /

2.00

I , OO

~ 1 -- ~ -- -- _ 7 ~ - - - - u - - ; ~ - - - ~0 1 5 7 5 1 50 5 0 0 4 5 0 6 0 0

S l i d i n g s p e e d V , m m / m i nF i g 1 1 G u i d e w a y - s l i d e r s e p a r a t i o n ( K e y : A - o i l 1 5 0 ,p = 0 . 1 3 5 ; B - o i l 1 5 , p = 0 . 1 3 5 ; C - o i l 1 1 , p = 0 . 1 3 5 ;D - o i l 3 0 , p = 0 . 1 3 5 ; E - o i l 1 0, p = 0 . 1 3 5 ; F - o i l 3 0 ,p = 0 . 4 0 5 ; G - o i 1 3 0 , p = 0 . 6 7 5 )

T R I B O L O G Y i nt er n at io n al 1 2 7


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Hou, Chen and Zheng - tr ibolog y of machine too l dideways

~ r zE

iZ

70 I \ I ~ ~ II 0 2 0 3 0 4 0 5 0

P = 0.135 kgf cm 2. . . . W -S. . . . . N - D

T ime, sF ig "12 R ed uc t io n in s epara t ion h w i th s tand ing t im e

Table 2 . Cr i t ica l t ravel ve loci t ies for avoid ing =t ick -s l ipwi th the two sur face topographiesL u b r i c a n t L o a d , p C r i t i c a l s p e e d , Vcr

k g f c m ' 2 W - S N - DO i l 1 0 0 . 1 3 5 7 5 1 7 5

0 . 2 7 0 1 1 3 3 7 5O i l 3 0 0 . 1 3 5 2 . 5 2 2 5

0 . 2 7 0 7 3 3 7 5O i l 1 1 0 . ] 3 5 < 0 . 0 3 6 2 5

0 . 2 7 0 0 . 2 5 > 8 0 0

T h e crit ical speed of =tick-=lip (Vet)Resistance wire st ra in gauges, a s t ra inom eter , and an X-Yrecorder were used to observe the st ick-sl ip pheno me non .The cr i t ica l speeds Vcr of the tw o kinds o f guideway surfaceare given in Table 2 . Because the st i f fness of the experi .men ta l system is mu ch smal ler than tha t of a prac t ica lma chin e, the values of Vet given in Table 2 are muc hlarger than w ould be experienced in an ac tual mach ine .Nevertheless, i t is evident tha t th e W -S guidew ay hasmu ch be t t e r s ti ck -s li p r e s is t ance than the N -D gu ideway .Mo reover , the higher the o i l viscosi ty , the grea ter thea d v an t ag e o f W - S o v er N - D .Experim ents have indica ted tha t the off-f ilm re ta iningabi l i ty i s an im por tant qua l i ty for resist ing stick-slippheno men on wi th s li ding gu ideways . I f gu ideways havegood oi l - fi lm forming abi l i ty only, th ey wi ll s t i ll not resiststick-slip at all unless the y also have goo d oil-fi lm retainin gabi l i ty . This i s because machine tools are a lways op era tedwi th a ' s top-move -s top ' pa t t e rn . The d rop o f t he coe f f i c i en to f f r i c t i on in W -S gu ideways i s even la rge r t han tha t i nN -D gu ideways a t t he mom ent o f s t a r t ing and a t ve ry lowtravel speeds.The off-fi lm re ta ining abi l i ty of the two kinds o f scrapedguide way can be com pared in the sinkage curves shown inFig 12. Moreover , the di f ference of oi l - fi lm re ta ining abi l i tybe tween the tw o gu ideways cou ld be g rea t ly i ncrea sedwh en the separa t ion h decreases to the o rdina ry value .When the W -S gu ideway is we l l p repa red an d the o i l i swel l se lec ted, i t is not di f f icul t to re ta in h = 1 -2 /z m forseveral hours.To pograp hy of wide-shal low scraped guideway

oi l 150; one from experim enta l resul ts , the oth er theore- In the f ina l analysis , surface topo grap hy is the source oft ica l. Together these dem onstra te the di f f icu l ty in f i ll ing the perform ance di fference of guidew ay surfaces. This i sup the smal l gap wi th a high-viscosi ty oi l . a problem w ort hy of fur th er s tud y. Figs 4 and 5 are the

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i 5 0 - E l ' i i ! I J . ~ A ' : I i !, ~ - : : : : ! i - - - ;

. . " t' i I : [ i i i: i i i I ' : = = i 3 :

! ! ! l ! " [ : : : ~ - - - i - - [ I ' i i i i i ] :

- -b i l l ; : l : i ~ i i I i ' [ [ : i i i3 0 O 0 0 0 0 0 0 0 O O 0 0 0 O O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O 0 0 O O O O O 0 0 O U O 0 0 O O O O O 0 0 O O 0 0 1 ] O 0 a ll i~ l R A N K TA Y L OR H OB S ON L E I C ES TE R 9 1 81 R A N K TA Y L OR H OB S ON L EF ig 13 Ta ly s ur f t races o f (a a 'nar r ow-deep ' s cr aped mr[acean d ( b ) a ~vide- shal low ' scraped mr[ace

1 2 8 A p r il 1 9 8 5 V o l 1 8 N o 2


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1985 Hou Ws Scraping

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