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Use of Powder Metallurgical High Speed Steel in Gear Hobbing and Gear Shaping
Use of Powder Metallurgical High Speed Steel in Gear Hobbing and Gear Shaping K.-D. Bouzakis, Aristoteles University Thessaloniki/Greece; W . Konig ( l ) , K. Vossen, Laboratoriurn fur Werkzeugmaschinen und Betriebslehre, RWTH Aachen/Germany A r e l a t i v e new d e v e l o p m e n t on t h e a r e a of
h i q h - s p e e d - s t e e l s a r e t h e powder m e t a l l u r g i c a l high--Tfed-steels Based (PY-HSS). On a c c o u n t of t t e m a n u f a c t u r i n a method a n e a r l y homogeneous s t r u c t u r e c a n be o b t a i n e d . on p r a c t i c a l knowledge, improved c u t t i n g p r o p e r t i e s , an i n c r e a s e d g r i n d a b i l i t y and an i n S e n s i t i v b e h a v i m In t h i s paper, t h e a 9 p l i c a t i o n of sane d i f f e r e n t l y a l l o y e d d u r i n g t h e h e a t t r e a t m e n t c a n be e x p e c t e d . P M - s t e e l s a t t h e t w o main methods o f g e a r m a n u f a c t u r i n g , g e a r hobbing and q e a r s h a p i n a , i s s y s t e m a t i c a l l y examined and w i t h r e g a r d t o t h e economy compared among t h e m s e l v e s and w i t h c o n v e n t i o n a l l y m a n u f a c t u r e d h i g h - s p e e d - s t e e 1s.
1 . INTRODUCTION The a d v a n t a q e o f h i g h s p e e d s t e e l p r o d u c e d by ~ p x . ~ I c r n b = t a l l u r g y compared t o c o n v e n t i o n a l l y p r o d u c e d highSpE€d s t e e l s i S t h e f i n e - g r a i n e d s t r u c t u r e arid f r e e d a n from S e g r e g a t i o n , which d o e s n o t c a u s e any banded s t r u c t u r e during f i n a l h o t forming i n t o t h e d e s i r e d f i n i s h e d d i mensions. The p o s i t i v e i n f l u e n c e o f t h e p o w d e r m e t a l l u r g y t y p e o f m a n u f a c t u r e on t h e s t r u c t u r e h a s a l r e a d y beconfirme d i n s e v e r a l s t u d i e s /1 t o 4 / , w h e r e a s d i f f e r i n g a n d , t o some e x t e n t , c o n t r a d i c t o r y o p i n i o n s a r e found w i t h For i n r e s p e c t t o t h e e f f e c t on c u t t i n g p e r f o r m a n c e . d u s t r y however, and p a r t i c u l a r l y f o r g e a r m a n u f a c t u r e which d e p e n d s On v e r y e x p e n s i v e tools of h i g h s p d s t e e l , c u t t i n g p e r f o r m a n c e i s a d e c i s i v e f a c t o r i n t h e economy o f t h e g e a r p r o d u c t i o n p r o c e s s . The s t u d y c o v e r s t h e a p p l i c a t i o n of t h e PM c u t t i n g mat e r i a l s ASP 23, 3 0 and 6 0 ( F i q u r e 1 ) i n t h e c u t t i n g o f c a s e - h a r d e n e d 16MnCr5 N and h e a t t r e a t a b l e steel 4ZYM04 V. Based on t h e wear p e r f o r m a n c e d e t e r m i n e d f o r t h e v a r i o u s PM c u t t i n g m a t e r i a l s , an economic c o m p a r i s o n is p e r f o r m e a amongst o t h e r a s p e c t s , i n which t h e most f a v o u r a b l e c u t t i n g c o n d i t i o n s w i t h r e s p e c t t o t i m e and c o s t s a r e determined.
M2C i n t h e c o n v e n t i o n a l p r o d u c t i o n o f h i g h s p e e d Steels; t h e s e c a r b i d e s a r e d i f f i c u l t t o r e l e a s e . AS a r e s u l t o f t h e powder m e t a l l u r g i c a l p r o d u c t i o n , t h e f o r m a t i o n of l a r g e M2Ccarbidescanbeextensively a v o i d e d , even w i t h h i g h c a r b o n c o n t e n t s , t h u s a c h i e v i n g a n improvement i n wear r e s i s t a n c e . On a c c o u n t o f i t s c o m p o s i t i o n and t h e t y p e o f p r o d u c t i o n , s t e e l P.SP 60 p o s s e s s e s higher high-temperature s t r e n g t h , r e t e n t i o n of hardn e s s and h i g h e r wear r e s i s t a n c e t h a n t h e o t h e r h i g h s p e e d s t e e l s examined.
The h e a t t r e a t m e n t d a t a , which a r e s p e c i f i e d f o r e a c h c u t t i n g m a t e r i a l , c o r r e s p o n d t o t h e d a t a recommended by t h e s t e e l m a n u f a c t u r e r s and which have p r o v e d t o b e a n optimum w i t h r e s p e c t t o h a r d n e s s and s t r e n g t h , a f t e r A conspicuous a p p r o p r i a t e t r i a l s on t h e steels / 2 / . a s p e c t i s t h a t a l l PM s t e e l s e x h i b i t a lower a u s t e n i t i z i n g temperature than t h e conventional high speed s t e e l s S 6-5-2-5 and S 6-5-3; t h i s i s t h e r e s u l t of u n i f o r m s t r u c t u r e and t h e l a c k of s e g r a g a t i o n . S i n c e a n overproprtional d r o p i n b e n d i n g s t r e n g t h o c c u r s on PM s t e e l s a t a u s t e n i t i z i n g t e m p e r a t u r e s o f g r e a t e r t h a n 1190oC,an upper l i m i t i s s p e c i f i e d f o r t h e a u s t e n i t i z i n g t e m p e r a t u r e s / 2 / . I n o r d e r t o examine t h e a u s t e n i t i z i n g t e m p e r a t u r e r a n q e i m m e d i a t e l y below t h e critic a l t e m p e r a t u r e l i m i t , PM s t e e l ASP 30 was a p p l i e d i n t h e h e a t t r e a t m e n t s l i s t e d under numbers 2 t o 4 . On h i g h s p e e d s t e e l s , a n i n c r e a s e i n s u l p h u r c o n t e n t r e s u l t s i n improved m a c h i n a b i l i t y i n t h e m a n u f a c t u r e o f t001S. t h u s a l l o w i n g t h e t o o l c o s t s t o b e r e d u c e d . I n conventional manufacture, a sulphur a d d i t i v e leads t o s e c o n d a r y phenomena s u c h a s s e q r e q a t i o n , r e d u c t i o n i n e d g e and b e n d i n g s t r e n a t h ; t h i s h a s a n e g a t i v e e f f e c t on t h e wear p e r f o r m a n c e o f t h e h i q h s p e e d s t e e l s . With t h e PM steels, a s a r e s u l t of t h e t y p e of manuf a c t u r e , i t i s p o s s i b l e to s u p p r e s s t h e s e n e g a t i v e characteristics. For t h i s r e a s o n , 0 . 1 2 % s u l p h u r was added t o PM s t e e l ASP 30 which i s n o r m a l l y s u l p h u r - f r e e , i n o r d e r t o s t u d y t h e i n f l u e n c e o f t h e s u l p h u r on t h e wear p e r f o r m a n c e o f h i g h s p e e d s t e e l s m a n u f a c t u r e d by p d e r metallurgy. The c u t t i n g c o n d i t i o n s s e l e c t e d w e r e c h o s e n a c c o r d i n a t o t h e a s p e c t s o c c u r r i n g i n p r a c t i c e , because theywere t h e b a s i s f o r a s u b s e q u e n t economic s t u d y . R e f e r e n c e was made t o e x t e n s i v e e x a m i n a t i o n s o f t h e c u t t i n q p r o cess /7. 5 , 21/ and t h e r e q u i r e d d a t a w e r e d e t e r m i n e d from t h e s e . 3 . U T I L I Z A T I O N OFPM-TOOL .UTERIALS I N GEAR SHAPING
F i g u r e 1 : T e c h n o l o g i c a l Data of Used T o o l M a t e r i a l s .
3.1 E f f e c t s o f t h e q e n e r a t i n q f e e d and c u t t i n q s p e e d on tool l i f e
2. CHEMICAL COMPOSITION AND CHARACTERISTICS OF THE CUTTING MATERIALS APPLIED The most i m p o r t a n t t e c h n o l o g i c a l d a t a and p i c t u r e s of s t r u c t u r e s of t h e c u t t i n g m a t e r i a l s examined a r e comp i l e d i n F i g u r e 1 . High s p e e d s t e e l s ASP 23, 30 and 6 0 a r e PM c u t t i n g m a t e r i a l s . High s p e e d s t e e l s S 6 - 5 -2-5 (EM0 5CO 5 1 and S 6-5-3 (EM0 5 V 3 ) w e r e i n c l u d e d i n t h e e x a m i n a t i o n s on a c c o u n t of t h e i r c h e m i c a l comp o s i t i o n which i s c o m p a r a b l e t o t h a t o f s t e e l s ASP 30 and ASP 23. Thus i t was i n t e n d e d t o s t u d y t h e i n f l u e n c e o f t h e t y p e o f m a n u f a c t u r e on t h e c u t t i n g c h a r a c t e r i s t i c s of a t o o l .
F i a u r e 2 provides an overview of t h e t o o l l i v e s obtaine d d u r i n g s h a p i n g o f 4 2 C r M o 4 and 16MnCr 5 N a s f u n c t i o n s o f c u t t i n g s p e e d and q e n e r a t i n a f e e d . The d e v e lopment of t h e t o o l l i f e curves drawn a s a f u n c t i o n o f c u t t i n g s p e e d c a n be e x p l a i n e d by t h e f o r m a t i o n o f b u i l t -up e d g e s / 5 , 9 , l o / . A s e x p e c t e d , l o n a e r t o o l l i v e s w e r e a c h i e v e d w i t h s t e e l ASP 60 a t h i q h g e n e r a t i n q f e e d s and c u t t i n q s p e e d s , o n a c c o u n t o f i t s b e t t e r c u t ting characteristics. Particularly a t high cuttinq speeds it e f f e c t s a g r e a t i n c r e a s e i n tool l i f e i n c a n p a r i s o n with t h a t of t h e o t h e r h i g h speed s t e e l s e m p l q r e d . Q u a l i t a t i v e l y similarobservationsresultfrom a m p a r i s o n between steels ASP 30 md S 6-5-2-5 (J3-bSCOj). Powder m e t a l l u r g i c a l m a n u f a c t u r e a s w e l l a s t h e h i q h er c a r b o n and c o b a l t c o n t e n t s l e d t o c o m p a r a t i v e l y h i g h e r t o o l l i v e s f o r t h e ASP 3 0 . The lowest t o o l l i v e s were o b t a i n e d w i t h s t e e l ASP 23. The p i c t u r e i n d i c a t e s , however, t h a t t h e d i f f e r e n c e s i n tool l i f e a r e low a t s l o w c u t t i n g s p e e d s , b o t h f o r t h e h e a t - t r e a t a b l e and for the n o r m a l i z e d s t e e l . T h i s i s c h i e f l y the r e s u l t
I n c o n t r a s t t o a l l t h e o t h e r steels examined, ASP 23 and S 6-5-3 c o n t a i n no c o b a l t . S t e e l ASP 60 e x h i b i t s t h e h i g h e s t c a r b o n c o n t e n t i n c o m p a r i s o n w i t h t h e 0t h e r h i g h s p e e d steels examined. Although h i g h c a r bon c o n t e n t s r e s u l t i n improved t o o l wear performance, t h e y promote t h e f o r m a t i o n of l o n g c a r b i d e s of t y p e
Annals of the CIRP Vol. 31/1/1982
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F i g u r e 3 : Tool L i f e o f ASP 30 f o r D i f f e r e n t C u t t i n q C o n d l t i o n s i n Shaping F i q u r e 2 : T o o l L i f e o f D i f f e r e n t Tool M a t e r i a l s i n Shaping with D i f f e r e n t C u t t i n g C o n d iti ons and Work M a t e r i a l s .
of t h e l o w c u t t i n g t e m p e r a t u r e s h e r e , a t which t h c h i g h r e t e n t i o n of h a r d n e s s and h i g h t e m p e r a t u r e a r e not s t r e n g t h of steels ASP 3 0 , G O and EMo5Co5 exploited. The c l e a r t r e n d i n d i c a t e d by t h e r e s u l t s i n F i g u r e 2 i s t h a t t o o l l i f e becomesextended o v e r a w i d e r a n g e of c u t t i n g s p e e d s w i t h i n c r e a s i n g g e n e r a t i n g f e e d . T h i s wear p e r f o r m a n c e was a l s o e s t a b l i s h e d d u r i n g s h a p i n g of o t h e r t o o t h i n g g e o m e t r i e s / 5 . 9, 1 0 / and i s b a s e d on t h e f a c t t h a t t h e number o f o p e r a t i n g s t r o k e s per tooth space decreases a t higher feeds. I n F i g u r e 3, f o r ASP 30 f o r example, t h e t o t a l number of o p e r a t i n g s t r o k e s u n t i l VB=O.8mmis r e a c h e d , i s i n d i c a t e d f o r e a c h m e a s u r i n g p o i n t and a d d i t i o n a l l y marked b y b a r s o f d i f f e r e n t s i z e s f o r p u r p o s e s Of c o m p a r i s o n . I t c a n c l e a r l y b e s e e n t h a t t h e number o f o p e r a t i n g s t r o k e s of t h e s h a p e r c u t t e r u n t i l tool f a i l u r e is c o n s i d e r a b l y lower a t f = 0 . 9 1 m / D H t h a n a t f = =0.31 mm/DH. T h i s f a c t i s e x p l a i n e d by t h e g r e a t e r c h i p c r o s s - s e c t i o n s and r e s u l t a n t , h i g h e r c u t t i n a l d s . The increase i n t o o l l i f e which is nevertheless obtained i s gov e r n e d by t h e d e c r e a s i n g number of s t r o k e s p e r t o o t h space. F i n a l l y , i t c a n be e s t a b l i s h e d t h a t steels ASP 30 and ASP 60 l e a d t o c l e a r g a i n s i n t o o l l i f e a t h i g h cutting s p e e d s and g e n e r a t i n g f e e d s i n c o m p a r i s o n w i t h o t h e r h i g h s p e e d s t e e l s m a n u f a c t u r e d by powder m e t a l l u r g y and c o n v e n t i o n a l l y . I f i t i s n e c e s s a r y t o work a t l o w c u t t i n g s p e e d s and g e n e r a t i n g f e e d s on a c c o u n t o f p e r m i s s i b l e l o a d r e s t r i c t i o n s on s h a p i n g m a c h i n e s , t h e ut i l i z a t i o n of a higher-performance c u t t i n g m a t e r i a l p r o v i d e s no g a i n s w i t h r e s p e c t t o t o o l l i f e .
3.2 D e t e r m i n i n g t h e c u t t i n g c o n d i t i o n s f o r optimum t i m e s and costs F i g u r e 4 p r o v i d e s a s a summary a n o v e r v i e w o f minimum m a n u f a c t u r i n g c o s t s , t o o l l i f e and optimum-cost c u t t i n g s p e e d f o r t h e c u t t i n g m a t e r i a l s and w o r k p i e c e mat e r i a l s examined. The m a n u f a c t u r i n g c o s t s and tool l i f e f o r t h e i n d i v i d u a l workpiece m a t e r i a l s a r e repres e n t e d by t h e optimum-cost c u t t i n g s p e e d which i s marke d by b l a c k t r i a n g l e s i n t h e l o w e r p a r t o f t h e p i c t u r e . Minimum m a n u f a c t u r i n g c o s t s and t h e g r e a t e s t t o o l l i v e s a r e o b t a i n e d d u r i n g s h a p i n g w i t h t h e PM h i g h speedsteel ASP 60. The c u t t i n g s p e e d t o b e a d j u s t e d i s h i g h e r t h a n f o r a l l o t h e r c u t t i n s m a t e r i a l s examined. The p o o r e s t economy i s t h e r e s u l t of u t i l i z i n g ASP 23, bec a u s e t h e l a t t e r e x h i b i t s t h e lowest optimum-cost cutt i n g s p e e d o f a l l t h e s t e e l s examined. Although APS 30 and S 6-5-2-5 h a v e comparably h i g h t o o l l i v e s , t h e m a n u f a c t u r i n g costs w i t h ASP 30 a r e somewhat lower t h a n w i t h S 6-5-2-5 on a c c o u n t o f t h e h i a h e r o p t i m u m cost c u t t i n g s p e e d . A c o m p a r i s o n between minimum m a n u f a c t u r i n g c o s t s d u r i n g s h a p i n g of c a s e - h a r d e n e d s t e e l 16MnCr5N shows t h a t t h e r e a r e o n l y s l i g h t d i f f e r e n c e s between a l l c u t t i n g m a t e r i a l s examined. I n a d d i t i o n t o t h e manuf a c t u r i n g c o s t s , however, t h e c u t t i n g s p e e d and hence m a n u f a c t u r i n g t i m e a t which t h e minimum c o s t s o c c u r i s s i g n i f i c a n t w i t h r e s p e c t t o economy. T h i s i s marke d i n t h e l o w e r s e c t i o n o f t h e p i c t u r e by a b l a c k t r i a n g l e i n e a c h c a s e . PM s t e e l ASP 60 i s t h e b e s t steel ~-
26
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E r a t h c economic a s p e c t i n t h i s s t u d y on a c c o u n t o f i t s l o w e s t costs, t o g e t h e r w i t h h i g h e s t optimum-cost c u t t i n g T e e d . A r e s t r i c t i o n , however, i s t h c f a c t t h a t w i t h ASP 6 0 p r o b l e m s o c c u r d u r i n q m a n u f a c t u r e of
t h e t o o l s b e c a u s e of t h e v e r y h i g h c a r b o n and vanadium c o n t e n t s ( 2 . 3 % and 6 . 5 % r e s p e c t i v e l y ) . The b a r s i n t h e lower d i a g r a m s d e m a r c a t e a c u t t i n g s p e e d r a n g e a t which an i n c r e a s e of 5 % i n minimum man u f a c t u r i n q costs o c c u r s . With t h i s s l i q h t i n c r e a s e in c o s t s , t h e r e i s t h u s a p o s s i b i l i t y of i n c r e a s i n q t h e c u t t i n s speed bv a p p r o x i m a t e l v 101 i n o r d e r t o a r r i v e c l o s e ; t b an o+i&m manufacturing t i m e . In ind u s t r y t h i s means t h a t i n t h e e v e n t of p r o d u c t i o n b o t t l e n e c k s , f r e s h c a p a c i t y c a n be a c h i e v e d w i t h o u t s i q n i f i c a n t i n c r e a s e i n costs.
F i g u r e 4 : P r o d u c t i o n Costs i n S h a p i n g o f D i f f e r e n t M a t e r i a l s w i t h D i E f e r e n t Tool M a t e r i a l s 3.3 w E fi tf he cASP t o f 30 a u s t e n i t i z i n g t e m p e r a t u r e on t o o l l i f e
The v a r i a t i o n i n a u s t e n i t i z i n g t e m p e r a t u r c was included i n t h i s s e r i e s of t r i a l s , t o e s t a b l i s h whether i t is n e c e s s a r y to m a i n t a i n t h e s p e c i f i e d a u s t e n i t i z i n g t e m p c r a t u r c p r c c l s e l y . The a u s t e n i t i z i n g t e m p e r a t u r e i s p r o v i d e d w i t h a n u p p e r l i m i t by t h c ~ r a p i dd r o p i n b e n d i n g and e d g e s t r e n g t h from 1190°C o n w a r d s ; i n t h e l o w e r r e g i o n a s l o w d e c r e a s e i n h a r d n e s s becomes not i c e a b l e . According t o / 2 / a r e d u c t i o n i n a u s t e n i t i z i n g t e m p e r a t u r e f r o m 118O',C t o 115OuC w i t h ASP30should r e s u l t i n a d r o p i n h a r d n e s s o f 0.5-1 HRc w i t h a s i m u l t a n e o u s i n c r e a s e i n b e n d i n g s t r e n g t h ; t h i s was a l s o
From tile r e s u l t s i:? r i q u-re 5 i t c a n h c sccc t h a t p r a c t i c a l i ; . no c h a i i g e i n %ear G e r f o r m a n c e o c c u r e d i n mac h i n i n < ? 42Cr?!o4 .:\ ?:)is t r e i i d , whic!i x a s cllso c o n f i r m e d d u r i y q sl!api;:y o f 1 6 XnCr 5 N, shows :!:at a f i u c t u n t i o n i n a u s t c n i t i z i n q t c n p c r d t u r c o v e r t:ie r a n g e 1 1 5 C ' < t o 1130. C h a s :>o s i g n i f i c a n t c E f r c t o n t l i ? 'iirar p e r f o r m a n c e of P:l s t e e l ASP 30.
4.1
i.ffcct
o f c u t t i n g s p e c d on t o o l l l f r
T i y u r e 7 p r o v i d c s a n o v c r v i e w of w e a r p e r f o r m a n c c of tt:c PY s t e e l s c x a m i n e d , d u r i n g g c a r h o b b i n g on v a r i o i i s m a t c r ; a l s . S t e e l ASP 6 0 e x h i b i t s t h c h i g h e s t tool l i ' I P S i r i t h a l l m a t e r i a l s a n d c?.ittinc, s p c e d s . i n t h e u p p e r d l a g r a n i t can a l s o b e s e e n t h a t w i t h 16 YnCr5 s t h e r i s e i n w e a r is l a r q e l y i d e n t i c a l f o r ,111 c u t t i n r j m a t e r i a l s , up to a 'width of f l a n k wear x h i c h i s d c p c n d e c t o n c u t t i n g s p e c d a n d u n d e r t h e rel e v a n t m a c h i n i n g c o n d i t i o n s . rron t h l s f a c t i t c a n b e c o n c l u d e d ?!>at t h e d i f f c r c n t t e c h n o l o q l c a l c h a r a c t c r i s t i c s o f t h e h i g h s p e e d stccls o n l y becomeeffcctive a f t c r a c e r t a i n b l u n t l n g of t h c c u t t i n g e d g e , b e c a u s c with a b l u n t c u t t i n g edge t h e temperature a t t h e Cutt i n g p o i n t rises a s a r e s u l t o f q r c a t e r f r i c t i o n and t h c r e t e n t i o n of h a r d n c s s o f t h e h i g h s p e e d s t e e l is exceeded. This p o i n t dcpends on t h e c u t t i n q s p c e d d a x i a l fced, because t h e c u t t i n g temperature a l s o r i s e s (iith incrcasing c u t t i n q loads.
,\t a c u t t i n q s p e e d o f " = a 0 m / m i n , a l l s t e e l s e x h i b i t t h e same r i s e i n w c a r u p t o a w i d t h of f l a n k w e a r o f 'JB~O.Smn1, w i l s t a t t h c c u t t i n q s p e e d 0: v=120 m / m i n d i f f e r e n c e s a l r e a d y a p p e a r a t a w i d t h o f f l a n k wear q f , VA-0.3mm.
i t s low h i g h - t e m p c r a t u r c s t r e n g t h and r c t e n t i o n o f h a r d n e s s , c o b a l t - f r e e s t e e l ASP 2 3 i s t h e f i r s : ta r e a c h t h c c r i t i c a l p o i n t a t w h i c h t h c rise i n w e a r b e g i n s t o i n c r e a s e s e v e r e l y . By l i m i t i n g t h e maximum p e r m i s s i b l e w i d t h o f f l a n k w e a r t o t h c s c v a l u e s , s t c c l ASP 23 c o u l d be s u p c r i o r t o t h e o t h e r s t c c l s from t h e e c o n o m i c a s p e c t , o n a c c o u n t o f i t s lower p r o c u r e m e n t c o s t s . T h e l o n g e r n o n - p r o d u c t i v e times r e s u l t i n g f r o m rnorc E r c q u e n t t o o l c h a n g e s m u n t c r dct d r e d u c t i o n i n m a n u f a c t u r i n g costs. AS a r e s u l t o f
0.91
r i g u r c 5: Wcdr B e h a v i o u r 0 : ASP 3 0 w i t h D i f f e r c n t Iteat Treatment i n Shasing 3.4
E f f c c t of the sulphur c o n t c n t on tool l i f c with
ASP 3 0 The c u t t i n ? n a t e r i a l ASP 30 S u t i l i z e d i n t h i s s c r i e s o f t r i a l s h a s n , , r e c i s c ? l y dcPj.ncd s u l p h u r c o n t c n t of 0 . 1 2 . , iihilst t h c s u l p h u r c o n t c n t of ASP 30 i s less t h a n 0 .02'.
ASP 30 w i t h i t s somewhat h i g h e r a l l o y o n l y r e a c h e s i t s c r i t i c a l p o i n t s a t q r c a t e r widths of f l a n k wear. A t t h e s e w i d t h s o f f l a n k w e a r , ASP 30 a n d ASP G O a l r e a d y c x h i b i t c l e a r g a i n s i n tool l i f c compared t o ASP 23, v h i c h w i l l dlso b e r e f l e c t e d i n t h c m a n u f a c t u r i n g c o s t s . A f u r t h c r i n c r e a s e i n p e r m i s s i b l e w i d t h of E l a n k w e a r i s o n l y u s e f u l w i t h ASP 6 0 , s i n c e clear q a i n s in tool l i f c can s t i l l bc achieved h e r e . In machining h e a t - t r e a t a b l e
steel 42CrMo4Vsuch p r o -
?he r e s u l t s c f t h e s e w c a r c x a r n i n a t i o n s are c o m p i l e d F i g u r c 6. T h e s h a p e r c u t t e r s o f ASP 3 0 a n d o f ASP 30 S r e s u l t e d i n a l m o s t e q u a l l y h i g h wear v a l u e s u n d e r t h e same c u t t i n g c o n d i t i o n s . O n l y a t t h e h i g h c u t t i n q s p e c d a n d h i g h g e n e r a t i n q f e e d was i t p o s s i b l c t o e s tablish a v e r y s l i g h t d e t e r i o r a t i o n i n wear p e r f o r m a n c e f o r s t e e l ASP 3 0 s o v e r a w i d t h o f f l a n k wear o f VB=0.6 mni. T h e s e r e s u l t s c l e a r l y i n d i c a t e t h a t steel ASP 30 S c a n be u t i l i z c d i n s t e a d of s teel A S P 3 0 w i t h o u t s a c r i f i c j n 9 tool l i f c . I m p r o v e d m a c h i n i n g is t h u s a c h i e v e d d u r i n g m a n u f a c t u r e cf tile tmls, a l l w i r q a r e d u c t i o n t o b c made i n tool m a n u f a c t u r i n g costs. The rcs u l t s presented i n t h i s f i g u r e f o r machining of heatt r c a t a b l c steel 42Cr4104 V were c o n f i r m e d by t h c applic a t i o n of 16MnCr5 N.
,
F i g u r e 7:
Wear B e h a v i o u r of P X - T o o l M a t e r i a l s i n Gear F o b b i n g of D i f f e r e n t Work M a t e r i a l s with Different Cutting Conditions
0.91
minent p o i n t s c a n no l o n g e r be e s t a b l i s h e d , o n a c c o u n t of t h c h i g h s t r e n g t h o f t h e r e s u l t a n t , h i g h c u t t i n g load. Finally, with respect t o t h i s figure it can be said t h a t t h e e f f e c t of c u t t i n g s p e e d o n t o o l l i f e t c n d s t o b e t h e same f o r a l l t h e c u t t i n g m a t e r i a l s a n d workp i e c e m a t e r i a l s examined, a l t h o u g h t h e r e a r e q u a n t i t a t i v e l y g r e a t d i f f e r e n c c s . I t h a s b e e n shown t h a t PI3 s t e e l ASP 60 w i t h i t s h i g h alloy p r o v i d e s t h e b e s t r e s u l t s over a w i d e r a n g e o f c u t t i n g s p e e d s .
4.2. F i g u r e 6: Wear B e h a v i o u r of ASP 3 0 w i t h D i f f e r e n t Cont e n t of S u l 9 h u r i n S h a p i n q
_Determining t h e c u t t i n g c o n d i t i o n s for optimum t i m e s a n d costs
'The m a n u f a c t u r i n g costs f o r t h e m a c h i n i n g o f 1 6 h C r 5 N are entered as a function o f c u t t i n g speed i n t h e l e f t of F i g u r e 8. r t i s a p p a r e n t t h a t a l l c u t -
up?er
27
i n
number
m - d m m , n.23'.
of cuts
R - Z U O r e . z11z2=Y1M. " - 9 , 42CrMD4V. Rm-9ZQNlmm2
vc * 3 ml min, 1, = 4 mml WU. counter directional climb habbing
F i g u r e 8:
P r o d u c t i o n Costs a n d 'rimes p e r t i e a r i n Hobb i n g w i t h O i f f e r e n t T o o l Materials
t i n g m a t e r i a l s e x h i b i t minimum cost a t a c u t t i n q s p e e d o f a p p r o x i m a t e l y 8 0 m/min, w i t h t h e r a t e of i n c r e a s e b e c o m i n g v e r y s t e e p a t v=lOOm/min. The r e a s o n f o r t h i s response is t h a t t o o l l i v e s d r o p s e v e r e l y w i t h i n c r e a s i n g c u t t i n g s p e e d s (see F i q u r e 7 ) , r e s u l t i n g i n d n i n c r e a s e i n t h e number o f r c q u i r c d h o b s a n d i n nonp r o d u c t i v e t i m e s . T h e costs t h e r e f o r e r i s e , a l t h o u g h t h e p r o d u c t i v e t i m e d e c r e a s e s on d c c o u n t . o f h i g h e r c u t t i n g s p e e d . A t c u t t i n g s p e e d s o f l e s s t h a n bOm/min, t h e c o s t s a l s o i n c r e a s e b e c a u s c no f u r t h e r i m p r o v e m e n t i n tool l i f e o c c u r s , b u t p r o d u c t i v e times c o n t i n u e t o g r o w . T h u s t h e c u r v e - a l r e a d y known f r o m s h a p i n g / 3 , 5 , 9/ i s p r o d u c e d w i t h a minimum a t a c u t t i n g speed o f 80 m i m i n . T h c h i q h - a l l o y s t e e l ASP G O w h i c h h a s a l s o r e a c h e d t h e h i g h e s t l e v e l s o f t o o l l i f e (see F i g u r e 7 ) , h a s t h e lowest m a n u f a c t u r i n g costs o v e r t h e e n t i r e r a n g e of c u t t i n g s p e e d . ASP 30 h a s o n l y s l i g h t l y h i g h e r c o s t s , w h i l s t ASP 23 e x h i b i t s a c o n s i d e r a b l e i n c r e a s e i n c o s t s ( a p p r o x i m a t e l y 20E,).
-
L n t e r e d i n t h e lower ] . e f t p a r t of F i g u r e 8 I S t h e man u f a c t u r i n g t i m e a s a f u n c t i o n o f c u t t i n g s p e e d . €'or t h e same r e a s o n s a s w i t h m a n u f a c t u r i n q c o s t s , a c u r v e w i t h a minimum m a n u f a c t u r i n g t i m e a l s o a p p e a r s h e r e . The m a n u f a c t u r i n g t i m e f o r a l l t h e c u t t i n g materials e x a m i n e d i s i d e n t i c a l , u p t o a c u t t i n 9 s p e e d of v = 1 0 0 m/min. From t h e r e s u l t s p r e s e n t e d i n F i g u r e 8 i t c a n b e c o n c l u d e d t h a t ASP 6 0 represents t h e m o s t economical sol u t i o n amongst t h e c u t t i n g m a t c r i a l s examined h e r e , both w i t h r e s p e c t to cost and t i m e o p t i m i z a t i o n . B a s e d o n t h e d e p e n d e n c e s d e s c r i b e d i n F i g u r e 7 it w a s e s t a b l i s h e d t h a t t h e rise i n wear i s i d e n t i c a l f o r a l l c u t t i n g materials, up t o a p a r t i c u l a r w i d t h o f f l a n k wear which is dependent on c u t t i n g speed. For t h i s r e a s o n , a t t h e m i n i m u m - c o s t c u t t i n g s p e e d o f v=80m/min a f u r t h e r e x a m i n a t i o n w a s implemented t o i l l u s t r a t e t h e e f f e c t o f t h e p e r m i s s i b l e w i d t h o f f l a n k wear o n manuf a c t u r i n g costs ( F i g u r e 8 , r i g h t ) . I t i s a p p a r e n t h e r e t h a t a t t h e maximum p e r m i s s i b l e w i d t h o f f l a n k wear o f less t h a n 0 . 5 mm ASP 23 i s more c o s t - e f f e c t i v e t h a n ASP 6 0 , b u t t h e a b s o l u t e v a l u e o f costs is c o n s i d e r a b l y h i g h e r t h a n w i t h a w i d t h o f f l a n k wear o f 0 . 6 mm, o n a c c o u n t of t h e g r e a t n o n - p r o d u c t i v e times r e s u l t i n g from f r e q u e n t t o o l c h a n g e s . I n m n t r a s t and a p p l y i n g 0 . 6 mm a s t o o l l i f e c r i t e r i o n , ASP 6 0 e x h i b i t s t h e lowest m a n u f a c t u r i n g c o s t s . A r e d u c t i o n i n p e r m i s s i b l e w i d t h o f f l a n k wear is t h e r e f o r e n o t a d v i s a b l e f o r economic r e a s o n s .
4.3.
Shown i n t h e f i g u r e a r e b o t h t h e l e a d i n q flank (E) a n d t h e t r a i l i n g f l a n k ( A ) i n o r d e r to e x a m i n e t h e e f f e c t a t h i g h e r a n d lower l o a d s ( l e a d i n q f l a n k and t r a i l i n a flank resppcctively). I t can be seen t h a t , apart f r o m s l i g h t s c a t t e r c a u s e d by t h e t r i a l o r measurcm e n t m e t h o d s , t h e same s e a r d e v e l o p m e n t i s p r e s e n t a t a l l three austenitizing temperatures, both on t h c leadino f l a n k a n d o n t h e t r a i l i n g f l a n k . T h u s bet w e e n t h e l i m i t s 1150'C t o 1 1 9 O ' C , t h e r e is a p p a r e n t l y no d i r e c t e f f e c t o f a u s t e n i t i z i n q t e m p e r a t u r e on t h e s t r u c t u r e a n d wear d e v e l o p m e n t . 4 . 4 E f f e c t o f s u l p h u r c o n t e n t ork the tool l i f e o f ASP-?
S u i p h u r i s p r e s e n t i n t h e f o r m of m a n g a n e s e s u l p h i d e i n a l l t y p e s of steel a n d i n d i f f e r i n g q u a n t i t i e s . With e x c e s s i v e l y h i g h a l l o y i n g c o n s t i t u e n t s , t h e s u l pnur impairs t h e t e c h n o l o g i c a l c h a r a c t e r i s t i c s o f t h e s t e e l s w i t h t h e e x c e p t i o n o f m a c h i n a b i l i t y , w h i c h is improved. 'Thus, w i t h a f e w e x c e p t i o n s Ie.q. f r e e - c u t ting steels), there a r e l i m i t s to the s u l p h u r c o n t e n t w h i c h m u s t be m a i n t a i n e d w i t h o u t f a i l . I n powder m e t a l l u r g y t h e n e g a t i v e s e c o n d a r y phenomend c a n b e better c o n t r o l l e d ; t h e r e a s o n is t h a t t h e r i s k o f s e g r e g a t i o n c a n be e x t e n s i v e l y e l i m i n a t e d b y t h e m a n u f a c t u r e o f v e r y f i n e p a r t i c l e s o f powder. An i n crease i n s u l p h u r c o n t e n t t o 0 . 1 2 1 s h o u l d e n a b l e c o s t s a v i n g s t o b e made i n t h e m a n u f a c t u r e o f h o b s . d e p e n d ing on t h e a p p l i c a t i o n . 'The q u e s t i o n o f w h e t h e r t h i s s . i l p h u r c o n t e n t l e a d s to a n e f f e c t o n c u t t i n g p e r f o r m a n c e I S a n s w e r e d by t h e r e s u l t s i n F i g u r e 1 0 .
masuring mint
mm
--. . -
i
--
E f f e c t of a u s t e n i t i z i n g t e m p e r a t u r e o n t o o l l i f e w i t h ASP 30
I n o r d e r t o e x a m i n e t h e e f f e c t of t h e a u s t e n i t i z i n g t e m p e r a t u r e o n wear p e r f o r m a n c e , p o w d e r - m e t a l l u r g i c a l l y m a n u f a c t u r e d h i g h s p e e d s t e e l ASP 3 0 w a s h a r d e n e d a t t h r e e d i f f e r e n t t e m p e r a t u r e s (see F i g u r e 1 ) . T h e f i n d i n g s o b t a i n e d i n s h a p i n g were t a k e n i n t o a c c o u n t (sec S e c t i o n 3 . 3 ) . F i g u r e 9 i s i n t e n d e d t o d i s p l a y t h e e f f e c t s of d i f f e r e n t a u s t e n i t i z i n g t e m p e r a t u r e s o n t h e wear p e r f o r m a n c e o f ASP 3 0 d u r i n g m a c h i n i n g o f 4 2 C r - v. A u s t e n i t i z i n g t e m p e r a t u r e s 1 1 5O"C, 1 1 8 0 ' C a n d 1 1 90 'C , d e m a r c a t e a r a n g e which i s u s u a l l y c o v e r e d i n t h e h a r d e n i n g o f PM s t e e l s / 2 / . As a l r e a d y e x p l a i n e d , b e n d i n g and edge s t r e n g t h d r o p s a t h i g h e r t c m p e r a t u r e s : a t l o w er t e m p e r a t u r e s , o n t h e o t h e r h a n d , b o t h h a r d n e s s a n d wear r e s i s t a n c e a r e n o l o n g e r a d q u a t e .
28
Wear B e h a v i o u r o f D i f f e r e n t T'cmpered ASP 30 i n Gear iiobbinq
r i y u r e 9:
numbtr d cuts
m.4nm
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~.o.z1~z1-~/r).n,-12
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F i g u r c 10:
Wear B e h a v i o u r i n G c o r H o b b i n g w r t h Tool Materials of D i f f e r e n t S u l p h u r C o n t e n t
T h e t r i a l s were p e r f o r m e d w l t h PM s t e e l ASP 3 O w h o s c s u l p h u r c o n t e n t i s less t h a n 0 , 0 2 8 a c c o r d l n g t o t h e m a n u f a c t u r e r ' s s p e c l f i c a t l o n s . As a c o m p a r i s o n . 0 . 1 2 6 s u l p h u r was a d d e d t o ASP 3 0 a n d t h l s e x p e r m e n t a l C u t t i n g m a t e r i d l i s d e s i g n a t e d a s ASP 3 0 s h e r e . Themar c u r v e s c l e a r l y i n d i c a t e t h a t no d i f f e r e n c e i n i n c r e a s i n wear c a n b c f o u n d a t v = 8 0 m / m l n . A t t h e h i g h e r c u t t i n g s p e e d s , o n t h e o t h e r h a n d , s u l p h u r o u s ASP 30 S
e x h i b i t s s l i g h t d e t e r i o r a t i o n i n tool l i f e . I n s p i t e of t h e PM manufacture, i t can t h e r e f o r e be assumed t h a t t h e r e is a n impairment t o t h e t e c h n o l o g i c a l characteristics which o n l y becomes s i g n i f i c a n t , however, a t h i g h c u t t i n g l o a d s . When t h e p e r m i s s i b l e width of f l a n k wear is l i m i t e d t o VB=O.Smm (v=IOOm/min) o r VB= = 0 . 3 nun (v=120 m/min), this disadvantage c a n be e l i m i nated as is c l e a r l y shown by t h e wear curves. These r e s u l t s w e r e also confirmed i n shaping and i n d i c a t e t h a t a h i g h e r s u l p h u r c o n t e n t is p e r m i s s i b l e with a view to improved m a c h i n a b i l i t y i n t o o l manufacture. 4.5 E f f e c t of t h e t y p e o f manufacture on tool l i f e In o r d e r t o o b t a i n a comparison between powder and smelt-mshllurgically manufactured high speed steels, t h e following steels which a r e similar w i t h r e s p e c t to chemical composition were d i r e c t l y compared: S 65-3 (EM05 V 3 ) and ASP 23, S 6-5-2-5 (EM05Co 5) and ASP 30. The m e t a l l o g r a p h i c s t u d i e s o f s e c t i o n 4 have shown t h a t w i t h respect t o s t r u c t u r e , t h e conventiona l steels were s i g n i f i c a n t l y p o o r e r than t h e PM steels which e x h i b i t a n almost i d e a l s t r u c t u r e on account of t h e method of manufacture. It w a s n o t p o s s i b l e to confirm t h e expected, improved wear performance o f t h e PM steels i n t h e d i r e c t comparison between ASP 23 and EM0 5 V 3 ( F i u r e 11 a s w e l l as ASP 30 and S 6-5-2-5 ( F i g u r e 12-dicated by wear diagrams of t h e leadinaandtrailiny f l a n k s , t h e rise i n wear o f t h e c u t t i n g materials concerned is almost t h e same. The d i f f e r e n t c u t t i n g f i g u r e s i n t h e two diaqrams area t h e r e s u l t of t h e greater q u a n t i t y of a l l o y i n g elements and t h e admixture o f c o b a l t t o ASP30 and S 6-5-2-5. With t h e s e two c u t t i n g materials i t c a n a l s o t e t h a t a t h i g h e r c u t t i n g l o a d s , d i f f e r e n c e s i n wear performance w i l l appear because ASP 30 h a s somewhat h i g h e r carbon, vanadium and cobalt c o n t e n t s . The f i n d i n g s o b t a i n e d h e r e are a c o n t r a d i c t i o n t o those p r e s e n t e d i n S e c t i o n 3.2 f o r shaping. The s u p p s i t i o n t h a t t h e d i f f e r e n t d i r e c t i o n of t h e c a r b i d e banded s t r u c t u r e s on hobs and on shaper c u t t e r s o f S 6-5-2-5 is t h e r e a s o n f o r t h i s performance w a s n o t confirmed i n subsequent s t u d i e s . The cause must ther e f o r e be t h e d i f f e r e n t c u t t i n g kinematics of t h e two g e a r manufacuring methods, which r e s u l t i n d i f f e r e n t c o n t a c t c o n d i t i o n s and c u t t i n g geometries amongst ot h e r a s p e c t s /5, 7, 8 , 11, 12, 1 3 , 16/. F i n a l l y , it can be e s t a b l i s h e d t h a t t h e d i f f e r e n t ty-
numrdc&
m - 4 m m . n-itP. p -0,
y 2 -ni~-12 ~ .
16mCr5N. R m * 5 a W a m , 1,4mn!W. (I&-
P i q u r e 12: Vear Behavior i n G e a r €Sobbing with D i f f e r e n t Tool M a t e r i a l s P a r i s o n to be made between t h e t w o t y p e s of panufactu r e , s m e l t - r r e t a l l u r q i c a l l y wanufactured hiqh spec? steels w e r e i n c o r p o r a t e d i n t h e examination. For one PH v a r i a n t t h e e f f e c t of a u s t e n i t i z i n g t e r p e r a t u r e and sulphur c o n t e n t on t h e s t r u c t u r e and on wear perfom-ance were a d d i t i o n a l l y i n v e s t i g a t e d . 6. REFERENCES I. Haberlitg, E. : Cicensct.aften -Jon p u l v c r n e r a l i u r ~ i r hLerzestsllt+m 3 c t n + l l a r b * i ? s s t a h l . ?+a51 ?in3 Z3ssn .35 11975) Xr. 17. : Y h b + h a n d l u n $ vin y l v e r o r . t a l l u r q 3 s c h '.-rees t e l l t e n AS?-Schnellarbsitsstghl+n. B e r k h t 33ber d l n i6. 3Brt.rr r i t r c h n i s c 5 s Fachtagmg ?. 16-14. X.rmmhsr ;???.
2 . RrllIMrtn, ?.
3. Bouzakis, F. : Einsatz vnn ~ulv~rmetallurgin~:hherqestnlltc?n ; - h n e l l a r b e i t s s t ~ h l c n bsim XZlzfr8sen m d USlzetmsen. ZahnrEdund " e t r i r h u n t e r s u c h u n g . 3oricht iiber l i c i I. ,!rhcr;'ts?spnq 413 2.1. .in3 22. Xaf I983 .:n Aachen.
P. : Hochf.rste pulverr.etel:urgiacke S c h n e l i a r h i [email protected]$nr ;W { 2 9 W i ) , ?h-. 2 3 . ?. in-19.
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K. : Erhzhung der i i i r t s f h a f t l i c h k s i t h i m %lzstotsen durch 3ptimierung des LerspanIJmzessss an3 3er ilnrkwugaus5. huzatis,
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Bouz&is, K. : S c h n e i d s m f f e u s m h l 3ein Yilhstorsnn .I~.dustr3eAna-iqer 103 f 1 9 7 5 ) N r . 5 5 , ?. 13-17.
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aouzakis, K . : 3ptiuiwrunq d e r S c k z e i d r a d e u s l o ~ n gh i m WSlzstossen u t t e r Jsriicksichtigung d e r jpanbildung. In&isris-An%-iger 33 (1377) )(r. 14, ?. >909-:wq. 7.
3. KSnig, ?I. Bouzakia, , K. : Chip Tornation 3al5 3f the 'XPP 'Jol. 25/2/1377. ?. :7-20.
:n
ihapinq. An-
: r)ptimieruni: der Schnitthdlng'Jngen h i m Xkilztossen. wt-Zclts?hrift fijr i n d u x r r i e i l e i * r t i z u n g 58 (14781, P.
'3. %uzalr.is, K. 7w-755.
10. ' i p i t z , H . , KSnig, FT., Sulzsr, G., Bouzakis, F. : 'JWS2hleiS3sr:cht ;untersuchungen t e i n XZlztossm =mn %radv*rzahnunZen. 4es Landcs Nor3Fhei.n-XnsTfslsn X r . 2 W 1 , 1374, li. Bouzakis, K. : Konzept 2nd technologiscte Grundlagen zur aut o m a t i a i e r t e n Erstellung o p t l n a l r r Bearbeitungsbedingunungen Ssim .dalzfrZsen. H a b l l i t a t i o n s s c h r i f t IH Aa&en, 1.990 'iS1-2'erlaq. ?or?schr.-f)sr. 73IZ-l(eihc 2, Nr. 4 2 .
.
F i g u r e 11: Wear Behaviour i n Gear Hobbing with Diff e r e n t Tool M a t e r i a l s . p e o f manufacture i n g e a r hobbing a p p a r e n t l y h a s no eff e c t o n t h e wear Ferfomnnce o f hiqh speed steels, a l though t h e e f f e c t o n t h e s t r u c t u r e is g r e a t . However, a non-uniform c a r b i d e d i s t r i b u t i o n c a n l e a d t o consid e r a b l e scatter i n t h e d e v e l o p l e n t o f wear, whichwould n o t o c c u r w i t h Pblmanufacture. Thus i n mass production a r e p r o d u c i b i l i t y o f rise i n wear can be ensured,which c a n n o t b e achieved to t h i s e x t e n t i n s m e l t - n e t a l l u r g b a1 n a n u f a c t u r e o f t h e tools. 5. SUM'ARY The a a j o r i t y o f i n d u s t r i a l l y produces s t r a i c h t o r helically-toothed c y l i n d r i c a l g e a r s are manufactured by hobbing or shapinq. The a p p l i c a t i o n o f powder-netall u r g i c a l l y manufactured high SFeed steels could r e p r e s e n t a p o s s i b i l i t y o f i n c r e a s i n q performance. Advant a c e s can p a r t i c u l a r l y be expected with tools which are d i f f i c u l t t o g r i n d , i n c l u d i n c hobsand shaprcutters. Within t h e scope o f t h i s r e p o r t , t h e r e f o r e , it was i n tended t o examine some PN steels with d i f f e r i n q alloyi n g l e v e l s , w i t h r e s p e c t to wear p e r f o m a n c e i n q e a r hobbin? and s h a r i n g . I n o r d e r to a l l o w a l i r o c t COF-
2 . h l e r r , 5 . : Leistungsstaiqerunt bei der Z71indcrradh4rst"l;xng durch geneun Zrfas+*inX 3er ZsrspanLinsmstit Diw.er?a?
.
:3. Joppa. K. i e i s t u n g s s t e i g a r u n g beia Wtilzfrlsen tit SChnella r b e i t s s t a h l durch Analyse , Beurteilung und Meir.f:ussung deS Zerspanprozesses. 3 i s s s r t a t i o n ?R Aachsn, 1377.
N. Tondorf, 1. : W G h u n ~d e r F'ertigungsgenauigkeit beirn W S Z f r a s r n durch vptsmatischc?rjemei
29
h i q h - s p e e d - s t e e l s a r e t h e powder m e t a l l u r g i c a l high--Tfed-steels Based (PY-HSS). On a c c o u n t of t t e m a n u f a c t u r i n a method a n e a r l y homogeneous s t r u c t u r e c a n be o b t a i n e d . on p r a c t i c a l knowledge, improved c u t t i n g p r o p e r t i e s , an i n c r e a s e d g r i n d a b i l i t y and an i n S e n s i t i v b e h a v i m In t h i s paper, t h e a 9 p l i c a t i o n of sane d i f f e r e n t l y a l l o y e d d u r i n g t h e h e a t t r e a t m e n t c a n be e x p e c t e d . P M - s t e e l s a t t h e t w o main methods o f g e a r m a n u f a c t u r i n g , g e a r hobbing and q e a r s h a p i n a , i s s y s t e m a t i c a l l y examined and w i t h r e g a r d t o t h e economy compared among t h e m s e l v e s and w i t h c o n v e n t i o n a l l y m a n u f a c t u r e d h i g h - s p e e d - s t e e 1s.
1 . INTRODUCTION The a d v a n t a q e o f h i g h s p e e d s t e e l p r o d u c e d by ~ p x . ~ I c r n b = t a l l u r g y compared t o c o n v e n t i o n a l l y p r o d u c e d highSpE€d s t e e l s i S t h e f i n e - g r a i n e d s t r u c t u r e arid f r e e d a n from S e g r e g a t i o n , which d o e s n o t c a u s e any banded s t r u c t u r e during f i n a l h o t forming i n t o t h e d e s i r e d f i n i s h e d d i mensions. The p o s i t i v e i n f l u e n c e o f t h e p o w d e r m e t a l l u r g y t y p e o f m a n u f a c t u r e on t h e s t r u c t u r e h a s a l r e a d y beconfirme d i n s e v e r a l s t u d i e s /1 t o 4 / , w h e r e a s d i f f e r i n g a n d , t o some e x t e n t , c o n t r a d i c t o r y o p i n i o n s a r e found w i t h For i n r e s p e c t t o t h e e f f e c t on c u t t i n g p e r f o r m a n c e . d u s t r y however, and p a r t i c u l a r l y f o r g e a r m a n u f a c t u r e which d e p e n d s On v e r y e x p e n s i v e tools of h i g h s p d s t e e l , c u t t i n g p e r f o r m a n c e i s a d e c i s i v e f a c t o r i n t h e economy o f t h e g e a r p r o d u c t i o n p r o c e s s . The s t u d y c o v e r s t h e a p p l i c a t i o n of t h e PM c u t t i n g mat e r i a l s ASP 23, 3 0 and 6 0 ( F i q u r e 1 ) i n t h e c u t t i n g o f c a s e - h a r d e n e d 16MnCr5 N and h e a t t r e a t a b l e steel 4ZYM04 V. Based on t h e wear p e r f o r m a n c e d e t e r m i n e d f o r t h e v a r i o u s PM c u t t i n g m a t e r i a l s , an economic c o m p a r i s o n is p e r f o r m e a amongst o t h e r a s p e c t s , i n which t h e most f a v o u r a b l e c u t t i n g c o n d i t i o n s w i t h r e s p e c t t o t i m e and c o s t s a r e determined.
M2C i n t h e c o n v e n t i o n a l p r o d u c t i o n o f h i g h s p e e d Steels; t h e s e c a r b i d e s a r e d i f f i c u l t t o r e l e a s e . AS a r e s u l t o f t h e powder m e t a l l u r g i c a l p r o d u c t i o n , t h e f o r m a t i o n of l a r g e M2Ccarbidescanbeextensively a v o i d e d , even w i t h h i g h c a r b o n c o n t e n t s , t h u s a c h i e v i n g a n improvement i n wear r e s i s t a n c e . On a c c o u n t o f i t s c o m p o s i t i o n and t h e t y p e o f p r o d u c t i o n , s t e e l P.SP 60 p o s s e s s e s higher high-temperature s t r e n g t h , r e t e n t i o n of hardn e s s and h i g h e r wear r e s i s t a n c e t h a n t h e o t h e r h i g h s p e e d s t e e l s examined.
The h e a t t r e a t m e n t d a t a , which a r e s p e c i f i e d f o r e a c h c u t t i n g m a t e r i a l , c o r r e s p o n d t o t h e d a t a recommended by t h e s t e e l m a n u f a c t u r e r s and which have p r o v e d t o b e a n optimum w i t h r e s p e c t t o h a r d n e s s and s t r e n g t h , a f t e r A conspicuous a p p r o p r i a t e t r i a l s on t h e steels / 2 / . a s p e c t i s t h a t a l l PM s t e e l s e x h i b i t a lower a u s t e n i t i z i n g temperature than t h e conventional high speed s t e e l s S 6-5-2-5 and S 6-5-3; t h i s i s t h e r e s u l t of u n i f o r m s t r u c t u r e and t h e l a c k of s e g r a g a t i o n . S i n c e a n overproprtional d r o p i n b e n d i n g s t r e n g t h o c c u r s on PM s t e e l s a t a u s t e n i t i z i n g t e m p e r a t u r e s o f g r e a t e r t h a n 1190oC,an upper l i m i t i s s p e c i f i e d f o r t h e a u s t e n i t i z i n g t e m p e r a t u r e s / 2 / . I n o r d e r t o examine t h e a u s t e n i t i z i n g t e m p e r a t u r e r a n q e i m m e d i a t e l y below t h e critic a l t e m p e r a t u r e l i m i t , PM s t e e l ASP 30 was a p p l i e d i n t h e h e a t t r e a t m e n t s l i s t e d under numbers 2 t o 4 . On h i g h s p e e d s t e e l s , a n i n c r e a s e i n s u l p h u r c o n t e n t r e s u l t s i n improved m a c h i n a b i l i t y i n t h e m a n u f a c t u r e o f t001S. t h u s a l l o w i n g t h e t o o l c o s t s t o b e r e d u c e d . I n conventional manufacture, a sulphur a d d i t i v e leads t o s e c o n d a r y phenomena s u c h a s s e q r e q a t i o n , r e d u c t i o n i n e d g e and b e n d i n g s t r e n a t h ; t h i s h a s a n e g a t i v e e f f e c t on t h e wear p e r f o r m a n c e o f t h e h i q h s p e e d s t e e l s . With t h e PM steels, a s a r e s u l t of t h e t y p e of manuf a c t u r e , i t i s p o s s i b l e to s u p p r e s s t h e s e n e g a t i v e characteristics. For t h i s r e a s o n , 0 . 1 2 % s u l p h u r was added t o PM s t e e l ASP 30 which i s n o r m a l l y s u l p h u r - f r e e , i n o r d e r t o s t u d y t h e i n f l u e n c e o f t h e s u l p h u r on t h e wear p e r f o r m a n c e o f h i g h s p e e d s t e e l s m a n u f a c t u r e d by p d e r metallurgy. The c u t t i n g c o n d i t i o n s s e l e c t e d w e r e c h o s e n a c c o r d i n a t o t h e a s p e c t s o c c u r r i n g i n p r a c t i c e , because theywere t h e b a s i s f o r a s u b s e q u e n t economic s t u d y . R e f e r e n c e was made t o e x t e n s i v e e x a m i n a t i o n s o f t h e c u t t i n q p r o cess /7. 5 , 21/ and t h e r e q u i r e d d a t a w e r e d e t e r m i n e d from t h e s e . 3 . U T I L I Z A T I O N OFPM-TOOL .UTERIALS I N GEAR SHAPING
F i g u r e 1 : T e c h n o l o g i c a l Data of Used T o o l M a t e r i a l s .
3.1 E f f e c t s o f t h e q e n e r a t i n q f e e d and c u t t i n q s p e e d on tool l i f e
2. CHEMICAL COMPOSITION AND CHARACTERISTICS OF THE CUTTING MATERIALS APPLIED The most i m p o r t a n t t e c h n o l o g i c a l d a t a and p i c t u r e s of s t r u c t u r e s of t h e c u t t i n g m a t e r i a l s examined a r e comp i l e d i n F i g u r e 1 . High s p e e d s t e e l s ASP 23, 30 and 6 0 a r e PM c u t t i n g m a t e r i a l s . High s p e e d s t e e l s S 6 - 5 -2-5 (EM0 5CO 5 1 and S 6-5-3 (EM0 5 V 3 ) w e r e i n c l u d e d i n t h e e x a m i n a t i o n s on a c c o u n t of t h e i r c h e m i c a l comp o s i t i o n which i s c o m p a r a b l e t o t h a t o f s t e e l s ASP 30 and ASP 23. Thus i t was i n t e n d e d t o s t u d y t h e i n f l u e n c e o f t h e t y p e o f m a n u f a c t u r e on t h e c u t t i n g c h a r a c t e r i s t i c s of a t o o l .
F i a u r e 2 provides an overview of t h e t o o l l i v e s obtaine d d u r i n g s h a p i n g o f 4 2 C r M o 4 and 16MnCr 5 N a s f u n c t i o n s o f c u t t i n g s p e e d and q e n e r a t i n a f e e d . The d e v e lopment of t h e t o o l l i f e curves drawn a s a f u n c t i o n o f c u t t i n g s p e e d c a n be e x p l a i n e d by t h e f o r m a t i o n o f b u i l t -up e d g e s / 5 , 9 , l o / . A s e x p e c t e d , l o n a e r t o o l l i v e s w e r e a c h i e v e d w i t h s t e e l ASP 60 a t h i q h g e n e r a t i n q f e e d s and c u t t i n q s p e e d s , o n a c c o u n t o f i t s b e t t e r c u t ting characteristics. Particularly a t high cuttinq speeds it e f f e c t s a g r e a t i n c r e a s e i n tool l i f e i n c a n p a r i s o n with t h a t of t h e o t h e r h i g h speed s t e e l s e m p l q r e d . Q u a l i t a t i v e l y similarobservationsresultfrom a m p a r i s o n between steels ASP 30 md S 6-5-2-5 (J3-bSCOj). Powder m e t a l l u r g i c a l m a n u f a c t u r e a s w e l l a s t h e h i q h er c a r b o n and c o b a l t c o n t e n t s l e d t o c o m p a r a t i v e l y h i g h e r t o o l l i v e s f o r t h e ASP 3 0 . The lowest t o o l l i v e s were o b t a i n e d w i t h s t e e l ASP 23. The p i c t u r e i n d i c a t e s , however, t h a t t h e d i f f e r e n c e s i n tool l i f e a r e low a t s l o w c u t t i n g s p e e d s , b o t h f o r t h e h e a t - t r e a t a b l e and for the n o r m a l i z e d s t e e l . T h i s i s c h i e f l y the r e s u l t
I n c o n t r a s t t o a l l t h e o t h e r steels examined, ASP 23 and S 6-5-3 c o n t a i n no c o b a l t . S t e e l ASP 60 e x h i b i t s t h e h i g h e s t c a r b o n c o n t e n t i n c o m p a r i s o n w i t h t h e 0t h e r h i g h s p e e d steels examined. Although h i g h c a r bon c o n t e n t s r e s u l t i n improved t o o l wear performance, t h e y promote t h e f o r m a t i o n of l o n g c a r b i d e s of t y p e
Annals of the CIRP Vol. 31/1/1982
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F i g u r e 3 : Tool L i f e o f ASP 30 f o r D i f f e r e n t C u t t i n q C o n d l t i o n s i n Shaping F i q u r e 2 : T o o l L i f e o f D i f f e r e n t Tool M a t e r i a l s i n Shaping with D i f f e r e n t C u t t i n g C o n d iti ons and Work M a t e r i a l s .
of t h e l o w c u t t i n g t e m p e r a t u r e s h e r e , a t which t h c h i g h r e t e n t i o n of h a r d n e s s and h i g h t e m p e r a t u r e a r e not s t r e n g t h of steels ASP 3 0 , G O and EMo5Co5 exploited. The c l e a r t r e n d i n d i c a t e d by t h e r e s u l t s i n F i g u r e 2 i s t h a t t o o l l i f e becomesextended o v e r a w i d e r a n g e of c u t t i n g s p e e d s w i t h i n c r e a s i n g g e n e r a t i n g f e e d . T h i s wear p e r f o r m a n c e was a l s o e s t a b l i s h e d d u r i n g s h a p i n g of o t h e r t o o t h i n g g e o m e t r i e s / 5 . 9, 1 0 / and i s b a s e d on t h e f a c t t h a t t h e number o f o p e r a t i n g s t r o k e s per tooth space decreases a t higher feeds. I n F i g u r e 3, f o r ASP 30 f o r example, t h e t o t a l number of o p e r a t i n g s t r o k e s u n t i l VB=O.8mmis r e a c h e d , i s i n d i c a t e d f o r e a c h m e a s u r i n g p o i n t and a d d i t i o n a l l y marked b y b a r s o f d i f f e r e n t s i z e s f o r p u r p o s e s Of c o m p a r i s o n . I t c a n c l e a r l y b e s e e n t h a t t h e number o f o p e r a t i n g s t r o k e s of t h e s h a p e r c u t t e r u n t i l tool f a i l u r e is c o n s i d e r a b l y lower a t f = 0 . 9 1 m / D H t h a n a t f = =0.31 mm/DH. T h i s f a c t i s e x p l a i n e d by t h e g r e a t e r c h i p c r o s s - s e c t i o n s and r e s u l t a n t , h i g h e r c u t t i n a l d s . The increase i n t o o l l i f e which is nevertheless obtained i s gov e r n e d by t h e d e c r e a s i n g number of s t r o k e s p e r t o o t h space. F i n a l l y , i t c a n be e s t a b l i s h e d t h a t steels ASP 30 and ASP 60 l e a d t o c l e a r g a i n s i n t o o l l i f e a t h i g h cutting s p e e d s and g e n e r a t i n g f e e d s i n c o m p a r i s o n w i t h o t h e r h i g h s p e e d s t e e l s m a n u f a c t u r e d by powder m e t a l l u r g y and c o n v e n t i o n a l l y . I f i t i s n e c e s s a r y t o work a t l o w c u t t i n g s p e e d s and g e n e r a t i n g f e e d s on a c c o u n t o f p e r m i s s i b l e l o a d r e s t r i c t i o n s on s h a p i n g m a c h i n e s , t h e ut i l i z a t i o n of a higher-performance c u t t i n g m a t e r i a l p r o v i d e s no g a i n s w i t h r e s p e c t t o t o o l l i f e .
3.2 D e t e r m i n i n g t h e c u t t i n g c o n d i t i o n s f o r optimum t i m e s and costs F i g u r e 4 p r o v i d e s a s a summary a n o v e r v i e w o f minimum m a n u f a c t u r i n g c o s t s , t o o l l i f e and optimum-cost c u t t i n g s p e e d f o r t h e c u t t i n g m a t e r i a l s and w o r k p i e c e mat e r i a l s examined. The m a n u f a c t u r i n g c o s t s and tool l i f e f o r t h e i n d i v i d u a l workpiece m a t e r i a l s a r e repres e n t e d by t h e optimum-cost c u t t i n g s p e e d which i s marke d by b l a c k t r i a n g l e s i n t h e l o w e r p a r t o f t h e p i c t u r e . Minimum m a n u f a c t u r i n g c o s t s and t h e g r e a t e s t t o o l l i v e s a r e o b t a i n e d d u r i n g s h a p i n g w i t h t h e PM h i g h speedsteel ASP 60. The c u t t i n g s p e e d t o b e a d j u s t e d i s h i g h e r t h a n f o r a l l o t h e r c u t t i n s m a t e r i a l s examined. The p o o r e s t economy i s t h e r e s u l t of u t i l i z i n g ASP 23, bec a u s e t h e l a t t e r e x h i b i t s t h e lowest optimum-cost cutt i n g s p e e d o f a l l t h e s t e e l s examined. Although APS 30 and S 6-5-2-5 h a v e comparably h i g h t o o l l i v e s , t h e m a n u f a c t u r i n g costs w i t h ASP 30 a r e somewhat lower t h a n w i t h S 6-5-2-5 on a c c o u n t o f t h e h i a h e r o p t i m u m cost c u t t i n g s p e e d . A c o m p a r i s o n between minimum m a n u f a c t u r i n g c o s t s d u r i n g s h a p i n g of c a s e - h a r d e n e d s t e e l 16MnCr5N shows t h a t t h e r e a r e o n l y s l i g h t d i f f e r e n c e s between a l l c u t t i n g m a t e r i a l s examined. I n a d d i t i o n t o t h e manuf a c t u r i n g c o s t s , however, t h e c u t t i n g s p e e d and hence m a n u f a c t u r i n g t i m e a t which t h e minimum c o s t s o c c u r i s s i g n i f i c a n t w i t h r e s p e c t t o economy. T h i s i s marke d i n t h e l o w e r s e c t i o n o f t h e p i c t u r e by a b l a c k t r i a n g l e i n e a c h c a s e . PM s t e e l ASP 60 i s t h e b e s t steel ~-
26
~
E r a t h c economic a s p e c t i n t h i s s t u d y on a c c o u n t o f i t s l o w e s t costs, t o g e t h e r w i t h h i g h e s t optimum-cost c u t t i n g T e e d . A r e s t r i c t i o n , however, i s t h c f a c t t h a t w i t h ASP 6 0 p r o b l e m s o c c u r d u r i n q m a n u f a c t u r e of
t h e t o o l s b e c a u s e of t h e v e r y h i g h c a r b o n and vanadium c o n t e n t s ( 2 . 3 % and 6 . 5 % r e s p e c t i v e l y ) . The b a r s i n t h e lower d i a g r a m s d e m a r c a t e a c u t t i n g s p e e d r a n g e a t which an i n c r e a s e of 5 % i n minimum man u f a c t u r i n q costs o c c u r s . With t h i s s l i q h t i n c r e a s e in c o s t s , t h e r e i s t h u s a p o s s i b i l i t y of i n c r e a s i n q t h e c u t t i n s speed bv a p p r o x i m a t e l v 101 i n o r d e r t o a r r i v e c l o s e ; t b an o+i&m manufacturing t i m e . In ind u s t r y t h i s means t h a t i n t h e e v e n t of p r o d u c t i o n b o t t l e n e c k s , f r e s h c a p a c i t y c a n be a c h i e v e d w i t h o u t s i q n i f i c a n t i n c r e a s e i n costs.
F i g u r e 4 : P r o d u c t i o n Costs i n S h a p i n g o f D i f f e r e n t M a t e r i a l s w i t h D i E f e r e n t Tool M a t e r i a l s 3.3 w E fi tf he cASP t o f 30 a u s t e n i t i z i n g t e m p e r a t u r e on t o o l l i f e
The v a r i a t i o n i n a u s t e n i t i z i n g t e m p e r a t u r c was included i n t h i s s e r i e s of t r i a l s , t o e s t a b l i s h whether i t is n e c e s s a r y to m a i n t a i n t h e s p e c i f i e d a u s t e n i t i z i n g t e m p c r a t u r c p r c c l s e l y . The a u s t e n i t i z i n g t e m p e r a t u r e i s p r o v i d e d w i t h a n u p p e r l i m i t by t h c ~ r a p i dd r o p i n b e n d i n g and e d g e s t r e n g t h from 1190°C o n w a r d s ; i n t h e l o w e r r e g i o n a s l o w d e c r e a s e i n h a r d n e s s becomes not i c e a b l e . According t o / 2 / a r e d u c t i o n i n a u s t e n i t i z i n g t e m p e r a t u r e f r o m 118O',C t o 115OuC w i t h ASP30should r e s u l t i n a d r o p i n h a r d n e s s o f 0.5-1 HRc w i t h a s i m u l t a n e o u s i n c r e a s e i n b e n d i n g s t r e n g t h ; t h i s was a l s o
From tile r e s u l t s i:? r i q u-re 5 i t c a n h c sccc t h a t p r a c t i c a l i ; . no c h a i i g e i n %ear G e r f o r m a n c e o c c u r e d i n mac h i n i n < ? 42Cr?!o4 .:\ ?:)is t r e i i d , whic!i x a s cllso c o n f i r m e d d u r i y q sl!api;:y o f 1 6 XnCr 5 N, shows :!:at a f i u c t u n t i o n i n a u s t c n i t i z i n q t c n p c r d t u r c o v e r t:ie r a n g e 1 1 5 C ' < t o 1130. C h a s :>o s i g n i f i c a n t c E f r c t o n t l i ? 'iirar p e r f o r m a n c e of P:l s t e e l ASP 30.
4.1
i.ffcct
o f c u t t i n g s p e c d on t o o l l l f r
T i y u r e 7 p r o v i d c s a n o v c r v i e w of w e a r p e r f o r m a n c c of tt:c PY s t e e l s c x a m i n e d , d u r i n g g c a r h o b b i n g on v a r i o i i s m a t c r ; a l s . S t e e l ASP 6 0 e x h i b i t s t h c h i g h e s t tool l i ' I P S i r i t h a l l m a t e r i a l s a n d c?.ittinc, s p c e d s . i n t h e u p p e r d l a g r a n i t can a l s o b e s e e n t h a t w i t h 16 YnCr5 s t h e r i s e i n w e a r is l a r q e l y i d e n t i c a l f o r ,111 c u t t i n r j m a t e r i a l s , up to a 'width of f l a n k wear x h i c h i s d c p c n d e c t o n c u t t i n g s p e c d a n d u n d e r t h e rel e v a n t m a c h i n i n g c o n d i t i o n s . rron t h l s f a c t i t c a n b e c o n c l u d e d ?!>at t h e d i f f c r c n t t e c h n o l o q l c a l c h a r a c t c r i s t i c s o f t h e h i g h s p e e d stccls o n l y becomeeffcctive a f t c r a c e r t a i n b l u n t l n g of t h c c u t t i n g e d g e , b e c a u s c with a b l u n t c u t t i n g edge t h e temperature a t t h e Cutt i n g p o i n t rises a s a r e s u l t o f q r c a t e r f r i c t i o n and t h c r e t e n t i o n of h a r d n c s s o f t h e h i g h s p e e d s t e e l is exceeded. This p o i n t dcpends on t h e c u t t i n q s p c e d d a x i a l fced, because t h e c u t t i n g temperature a l s o r i s e s (iith incrcasing c u t t i n q loads.
,\t a c u t t i n q s p e e d o f " = a 0 m / m i n , a l l s t e e l s e x h i b i t t h e same r i s e i n w c a r u p t o a w i d t h of f l a n k w e a r o f 'JB~O.Smn1, w i l s t a t t h c c u t t i n q s p e e d 0: v=120 m / m i n d i f f e r e n c e s a l r e a d y a p p e a r a t a w i d t h o f f l a n k wear q f , VA-0.3mm.
i t s low h i g h - t e m p c r a t u r c s t r e n g t h and r c t e n t i o n o f h a r d n e s s , c o b a l t - f r e e s t e e l ASP 2 3 i s t h e f i r s : ta r e a c h t h c c r i t i c a l p o i n t a t w h i c h t h c rise i n w e a r b e g i n s t o i n c r e a s e s e v e r e l y . By l i m i t i n g t h e maximum p e r m i s s i b l e w i d t h o f f l a n k w e a r t o t h c s c v a l u e s , s t c c l ASP 23 c o u l d be s u p c r i o r t o t h e o t h e r s t c c l s from t h e e c o n o m i c a s p e c t , o n a c c o u n t o f i t s lower p r o c u r e m e n t c o s t s . T h e l o n g e r n o n - p r o d u c t i v e times r e s u l t i n g f r o m rnorc E r c q u e n t t o o l c h a n g e s m u n t c r dct d r e d u c t i o n i n m a n u f a c t u r i n g costs. AS a r e s u l t o f
0.91
r i g u r c 5: Wcdr B e h a v i o u r 0 : ASP 3 0 w i t h D i f f e r c n t Iteat Treatment i n Shasing 3.4
E f f c c t of the sulphur c o n t c n t on tool l i f c with
ASP 3 0 The c u t t i n ? n a t e r i a l ASP 30 S u t i l i z e d i n t h i s s c r i e s o f t r i a l s h a s n , , r e c i s c ? l y dcPj.ncd s u l p h u r c o n t c n t of 0 . 1 2 . , iihilst t h c s u l p h u r c o n t c n t of ASP 30 i s less t h a n 0 .02'.
ASP 30 w i t h i t s somewhat h i g h e r a l l o y o n l y r e a c h e s i t s c r i t i c a l p o i n t s a t q r c a t e r widths of f l a n k wear. A t t h e s e w i d t h s o f f l a n k w e a r , ASP 30 a n d ASP G O a l r e a d y c x h i b i t c l e a r g a i n s i n tool l i f c compared t o ASP 23, v h i c h w i l l dlso b e r e f l e c t e d i n t h c m a n u f a c t u r i n g c o s t s . A f u r t h c r i n c r e a s e i n p e r m i s s i b l e w i d t h of E l a n k w e a r i s o n l y u s e f u l w i t h ASP 6 0 , s i n c e clear q a i n s in tool l i f c can s t i l l bc achieved h e r e . In machining h e a t - t r e a t a b l e
steel 42CrMo4Vsuch p r o -
?he r e s u l t s c f t h e s e w c a r c x a r n i n a t i o n s are c o m p i l e d F i g u r c 6. T h e s h a p e r c u t t e r s o f ASP 3 0 a n d o f ASP 30 S r e s u l t e d i n a l m o s t e q u a l l y h i g h wear v a l u e s u n d e r t h e same c u t t i n g c o n d i t i o n s . O n l y a t t h e h i g h c u t t i n q s p e c d a n d h i g h g e n e r a t i n q f e e d was i t p o s s i b l c t o e s tablish a v e r y s l i g h t d e t e r i o r a t i o n i n wear p e r f o r m a n c e f o r s t e e l ASP 3 0 s o v e r a w i d t h o f f l a n k wear o f VB=0.6 mni. T h e s e r e s u l t s c l e a r l y i n d i c a t e t h a t steel ASP 30 S c a n be u t i l i z c d i n s t e a d of s teel A S P 3 0 w i t h o u t s a c r i f i c j n 9 tool l i f c . I m p r o v e d m a c h i n i n g is t h u s a c h i e v e d d u r i n g m a n u f a c t u r e cf tile tmls, a l l w i r q a r e d u c t i o n t o b c made i n tool m a n u f a c t u r i n g costs. The rcs u l t s presented i n t h i s f i g u r e f o r machining of heatt r c a t a b l c steel 42Cr4104 V were c o n f i r m e d by t h c applic a t i o n of 16MnCr5 N.
,
F i g u r e 7:
Wear B e h a v i o u r of P X - T o o l M a t e r i a l s i n Gear F o b b i n g of D i f f e r e n t Work M a t e r i a l s with Different Cutting Conditions
0.91
minent p o i n t s c a n no l o n g e r be e s t a b l i s h e d , o n a c c o u n t of t h c h i g h s t r e n g t h o f t h e r e s u l t a n t , h i g h c u t t i n g load. Finally, with respect t o t h i s figure it can be said t h a t t h e e f f e c t of c u t t i n g s p e e d o n t o o l l i f e t c n d s t o b e t h e same f o r a l l t h e c u t t i n g m a t e r i a l s a n d workp i e c e m a t e r i a l s examined, a l t h o u g h t h e r e a r e q u a n t i t a t i v e l y g r e a t d i f f e r e n c c s . I t h a s b e e n shown t h a t PI3 s t e e l ASP 60 w i t h i t s h i g h alloy p r o v i d e s t h e b e s t r e s u l t s over a w i d e r a n g e o f c u t t i n g s p e e d s .
4.2. F i g u r e 6: Wear B e h a v i o u r of ASP 3 0 w i t h D i f f e r e n t Cont e n t of S u l 9 h u r i n S h a p i n q
_Determining t h e c u t t i n g c o n d i t i o n s for optimum t i m e s a n d costs
'The m a n u f a c t u r i n g costs f o r t h e m a c h i n i n g o f 1 6 h C r 5 N are entered as a function o f c u t t i n g speed i n t h e l e f t of F i g u r e 8. r t i s a p p a r e n t t h a t a l l c u t -
up?er
27
i n
number
m - d m m , n.23'.
of cuts
R - Z U O r e . z11z2=Y1M. " - 9 , 42CrMD4V. Rm-9ZQNlmm2
vc * 3 ml min, 1, = 4 mml WU. counter directional climb habbing
F i g u r e 8:
P r o d u c t i o n Costs a n d 'rimes p e r t i e a r i n Hobb i n g w i t h O i f f e r e n t T o o l Materials
t i n g m a t e r i a l s e x h i b i t minimum cost a t a c u t t i n q s p e e d o f a p p r o x i m a t e l y 8 0 m/min, w i t h t h e r a t e of i n c r e a s e b e c o m i n g v e r y s t e e p a t v=lOOm/min. The r e a s o n f o r t h i s response is t h a t t o o l l i v e s d r o p s e v e r e l y w i t h i n c r e a s i n g c u t t i n g s p e e d s (see F i q u r e 7 ) , r e s u l t i n g i n d n i n c r e a s e i n t h e number o f r c q u i r c d h o b s a n d i n nonp r o d u c t i v e t i m e s . T h e costs t h e r e f o r e r i s e , a l t h o u g h t h e p r o d u c t i v e t i m e d e c r e a s e s on d c c o u n t . o f h i g h e r c u t t i n g s p e e d . A t c u t t i n g s p e e d s o f l e s s t h a n bOm/min, t h e c o s t s a l s o i n c r e a s e b e c a u s c no f u r t h e r i m p r o v e m e n t i n tool l i f e o c c u r s , b u t p r o d u c t i v e times c o n t i n u e t o g r o w . T h u s t h e c u r v e - a l r e a d y known f r o m s h a p i n g / 3 , 5 , 9/ i s p r o d u c e d w i t h a minimum a t a c u t t i n g speed o f 80 m i m i n . T h c h i q h - a l l o y s t e e l ASP G O w h i c h h a s a l s o r e a c h e d t h e h i g h e s t l e v e l s o f t o o l l i f e (see F i g u r e 7 ) , h a s t h e lowest m a n u f a c t u r i n g costs o v e r t h e e n t i r e r a n g e of c u t t i n g s p e e d . ASP 30 h a s o n l y s l i g h t l y h i g h e r c o s t s , w h i l s t ASP 23 e x h i b i t s a c o n s i d e r a b l e i n c r e a s e i n c o s t s ( a p p r o x i m a t e l y 20E,).
-
L n t e r e d i n t h e lower ] . e f t p a r t of F i g u r e 8 I S t h e man u f a c t u r i n g t i m e a s a f u n c t i o n o f c u t t i n g s p e e d . €'or t h e same r e a s o n s a s w i t h m a n u f a c t u r i n q c o s t s , a c u r v e w i t h a minimum m a n u f a c t u r i n g t i m e a l s o a p p e a r s h e r e . The m a n u f a c t u r i n g t i m e f o r a l l t h e c u t t i n g materials e x a m i n e d i s i d e n t i c a l , u p t o a c u t t i n 9 s p e e d of v = 1 0 0 m/min. From t h e r e s u l t s p r e s e n t e d i n F i g u r e 8 i t c a n b e c o n c l u d e d t h a t ASP 6 0 represents t h e m o s t economical sol u t i o n amongst t h e c u t t i n g m a t c r i a l s examined h e r e , both w i t h r e s p e c t to cost and t i m e o p t i m i z a t i o n . B a s e d o n t h e d e p e n d e n c e s d e s c r i b e d i n F i g u r e 7 it w a s e s t a b l i s h e d t h a t t h e rise i n wear i s i d e n t i c a l f o r a l l c u t t i n g materials, up t o a p a r t i c u l a r w i d t h o f f l a n k wear which is dependent on c u t t i n g speed. For t h i s r e a s o n , a t t h e m i n i m u m - c o s t c u t t i n g s p e e d o f v=80m/min a f u r t h e r e x a m i n a t i o n w a s implemented t o i l l u s t r a t e t h e e f f e c t o f t h e p e r m i s s i b l e w i d t h o f f l a n k wear o n manuf a c t u r i n g costs ( F i g u r e 8 , r i g h t ) . I t i s a p p a r e n t h e r e t h a t a t t h e maximum p e r m i s s i b l e w i d t h o f f l a n k wear o f less t h a n 0 . 5 mm ASP 23 i s more c o s t - e f f e c t i v e t h a n ASP 6 0 , b u t t h e a b s o l u t e v a l u e o f costs is c o n s i d e r a b l y h i g h e r t h a n w i t h a w i d t h o f f l a n k wear o f 0 . 6 mm, o n a c c o u n t of t h e g r e a t n o n - p r o d u c t i v e times r e s u l t i n g from f r e q u e n t t o o l c h a n g e s . I n m n t r a s t and a p p l y i n g 0 . 6 mm a s t o o l l i f e c r i t e r i o n , ASP 6 0 e x h i b i t s t h e lowest m a n u f a c t u r i n g c o s t s . A r e d u c t i o n i n p e r m i s s i b l e w i d t h o f f l a n k wear is t h e r e f o r e n o t a d v i s a b l e f o r economic r e a s o n s .
4.3.
Shown i n t h e f i g u r e a r e b o t h t h e l e a d i n q flank (E) a n d t h e t r a i l i n g f l a n k ( A ) i n o r d e r to e x a m i n e t h e e f f e c t a t h i g h e r a n d lower l o a d s ( l e a d i n q f l a n k and t r a i l i n a flank resppcctively). I t can be seen t h a t , apart f r o m s l i g h t s c a t t e r c a u s e d by t h e t r i a l o r measurcm e n t m e t h o d s , t h e same s e a r d e v e l o p m e n t i s p r e s e n t a t a l l three austenitizing temperatures, both on t h c leadino f l a n k a n d o n t h e t r a i l i n g f l a n k . T h u s bet w e e n t h e l i m i t s 1150'C t o 1 1 9 O ' C , t h e r e is a p p a r e n t l y no d i r e c t e f f e c t o f a u s t e n i t i z i n q t e m p e r a t u r e on t h e s t r u c t u r e a n d wear d e v e l o p m e n t . 4 . 4 E f f e c t o f s u l p h u r c o n t e n t ork the tool l i f e o f ASP-?
S u i p h u r i s p r e s e n t i n t h e f o r m of m a n g a n e s e s u l p h i d e i n a l l t y p e s of steel a n d i n d i f f e r i n g q u a n t i t i e s . With e x c e s s i v e l y h i g h a l l o y i n g c o n s t i t u e n t s , t h e s u l pnur impairs t h e t e c h n o l o g i c a l c h a r a c t e r i s t i c s o f t h e s t e e l s w i t h t h e e x c e p t i o n o f m a c h i n a b i l i t y , w h i c h is improved. 'Thus, w i t h a f e w e x c e p t i o n s Ie.q. f r e e - c u t ting steels), there a r e l i m i t s to the s u l p h u r c o n t e n t w h i c h m u s t be m a i n t a i n e d w i t h o u t f a i l . I n powder m e t a l l u r g y t h e n e g a t i v e s e c o n d a r y phenomend c a n b e better c o n t r o l l e d ; t h e r e a s o n is t h a t t h e r i s k o f s e g r e g a t i o n c a n be e x t e n s i v e l y e l i m i n a t e d b y t h e m a n u f a c t u r e o f v e r y f i n e p a r t i c l e s o f powder. An i n crease i n s u l p h u r c o n t e n t t o 0 . 1 2 1 s h o u l d e n a b l e c o s t s a v i n g s t o b e made i n t h e m a n u f a c t u r e o f h o b s . d e p e n d ing on t h e a p p l i c a t i o n . 'The q u e s t i o n o f w h e t h e r t h i s s . i l p h u r c o n t e n t l e a d s to a n e f f e c t o n c u t t i n g p e r f o r m a n c e I S a n s w e r e d by t h e r e s u l t s i n F i g u r e 1 0 .
masuring mint
mm
--. . -
i
--
E f f e c t of a u s t e n i t i z i n g t e m p e r a t u r e o n t o o l l i f e w i t h ASP 30
I n o r d e r t o e x a m i n e t h e e f f e c t of t h e a u s t e n i t i z i n g t e m p e r a t u r e o n wear p e r f o r m a n c e , p o w d e r - m e t a l l u r g i c a l l y m a n u f a c t u r e d h i g h s p e e d s t e e l ASP 3 0 w a s h a r d e n e d a t t h r e e d i f f e r e n t t e m p e r a t u r e s (see F i g u r e 1 ) . T h e f i n d i n g s o b t a i n e d i n s h a p i n g were t a k e n i n t o a c c o u n t (sec S e c t i o n 3 . 3 ) . F i g u r e 9 i s i n t e n d e d t o d i s p l a y t h e e f f e c t s of d i f f e r e n t a u s t e n i t i z i n g t e m p e r a t u r e s o n t h e wear p e r f o r m a n c e o f ASP 3 0 d u r i n g m a c h i n i n g o f 4 2 C r - v. A u s t e n i t i z i n g t e m p e r a t u r e s 1 1 5O"C, 1 1 8 0 ' C a n d 1 1 90 'C , d e m a r c a t e a r a n g e which i s u s u a l l y c o v e r e d i n t h e h a r d e n i n g o f PM s t e e l s / 2 / . As a l r e a d y e x p l a i n e d , b e n d i n g and edge s t r e n g t h d r o p s a t h i g h e r t c m p e r a t u r e s : a t l o w er t e m p e r a t u r e s , o n t h e o t h e r h a n d , b o t h h a r d n e s s a n d wear r e s i s t a n c e a r e n o l o n g e r a d q u a t e .
28
Wear B e h a v i o u r o f D i f f e r e n t T'cmpered ASP 30 i n Gear iiobbinq
r i y u r e 9:
numbtr d cuts
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F i g u r c 10:
Wear B e h a v i o u r i n G c o r H o b b i n g w r t h Tool Materials of D i f f e r e n t S u l p h u r C o n t e n t
T h e t r i a l s were p e r f o r m e d w l t h PM s t e e l ASP 3 O w h o s c s u l p h u r c o n t e n t i s less t h a n 0 , 0 2 8 a c c o r d l n g t o t h e m a n u f a c t u r e r ' s s p e c l f i c a t l o n s . As a c o m p a r i s o n . 0 . 1 2 6 s u l p h u r was a d d e d t o ASP 3 0 a n d t h l s e x p e r m e n t a l C u t t i n g m a t e r i d l i s d e s i g n a t e d a s ASP 3 0 s h e r e . Themar c u r v e s c l e a r l y i n d i c a t e t h a t no d i f f e r e n c e i n i n c r e a s i n wear c a n b c f o u n d a t v = 8 0 m / m l n . A t t h e h i g h e r c u t t i n g s p e e d s , o n t h e o t h e r h a n d , s u l p h u r o u s ASP 30 S
e x h i b i t s s l i g h t d e t e r i o r a t i o n i n tool l i f e . I n s p i t e of t h e PM manufacture, i t can t h e r e f o r e be assumed t h a t t h e r e is a n impairment t o t h e t e c h n o l o g i c a l characteristics which o n l y becomes s i g n i f i c a n t , however, a t h i g h c u t t i n g l o a d s . When t h e p e r m i s s i b l e width of f l a n k wear is l i m i t e d t o VB=O.Smm (v=IOOm/min) o r VB= = 0 . 3 nun (v=120 m/min), this disadvantage c a n be e l i m i nated as is c l e a r l y shown by t h e wear curves. These r e s u l t s w e r e also confirmed i n shaping and i n d i c a t e t h a t a h i g h e r s u l p h u r c o n t e n t is p e r m i s s i b l e with a view to improved m a c h i n a b i l i t y i n t o o l manufacture. 4.5 E f f e c t of t h e t y p e o f manufacture on tool l i f e In o r d e r t o o b t a i n a comparison between powder and smelt-mshllurgically manufactured high speed steels, t h e following steels which a r e similar w i t h r e s p e c t to chemical composition were d i r e c t l y compared: S 65-3 (EM05 V 3 ) and ASP 23, S 6-5-2-5 (EM05Co 5) and ASP 30. The m e t a l l o g r a p h i c s t u d i e s o f s e c t i o n 4 have shown t h a t w i t h respect t o s t r u c t u r e , t h e conventiona l steels were s i g n i f i c a n t l y p o o r e r than t h e PM steels which e x h i b i t a n almost i d e a l s t r u c t u r e on account of t h e method of manufacture. It w a s n o t p o s s i b l e to confirm t h e expected, improved wear performance o f t h e PM steels i n t h e d i r e c t comparison between ASP 23 and EM0 5 V 3 ( F i u r e 11 a s w e l l as ASP 30 and S 6-5-2-5 ( F i g u r e 12-dicated by wear diagrams of t h e leadinaandtrailiny f l a n k s , t h e rise i n wear o f t h e c u t t i n g materials concerned is almost t h e same. The d i f f e r e n t c u t t i n g f i g u r e s i n t h e two diaqrams area t h e r e s u l t of t h e greater q u a n t i t y of a l l o y i n g elements and t h e admixture o f c o b a l t t o ASP30 and S 6-5-2-5. With t h e s e two c u t t i n g materials i t c a n a l s o t e t h a t a t h i g h e r c u t t i n g l o a d s , d i f f e r e n c e s i n wear performance w i l l appear because ASP 30 h a s somewhat h i g h e r carbon, vanadium and cobalt c o n t e n t s . The f i n d i n g s o b t a i n e d h e r e are a c o n t r a d i c t i o n t o those p r e s e n t e d i n S e c t i o n 3.2 f o r shaping. The s u p p s i t i o n t h a t t h e d i f f e r e n t d i r e c t i o n of t h e c a r b i d e banded s t r u c t u r e s on hobs and on shaper c u t t e r s o f S 6-5-2-5 is t h e r e a s o n f o r t h i s performance w a s n o t confirmed i n subsequent s t u d i e s . The cause must ther e f o r e be t h e d i f f e r e n t c u t t i n g kinematics of t h e two g e a r manufacuring methods, which r e s u l t i n d i f f e r e n t c o n t a c t c o n d i t i o n s and c u t t i n g geometries amongst ot h e r a s p e c t s /5, 7, 8 , 11, 12, 1 3 , 16/. F i n a l l y , it can be e s t a b l i s h e d t h a t t h e d i f f e r e n t ty-
numrdc&
m - 4 m m . n-itP. p -0,
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P i q u r e 12: Vear Behavior i n G e a r €Sobbing with D i f f e r e n t Tool M a t e r i a l s P a r i s o n to be made between t h e t w o t y p e s of panufactu r e , s m e l t - r r e t a l l u r q i c a l l y wanufactured hiqh spec? steels w e r e i n c o r p o r a t e d i n t h e examination. For one PH v a r i a n t t h e e f f e c t of a u s t e n i t i z i n g t e r p e r a t u r e and sulphur c o n t e n t on t h e s t r u c t u r e and on wear perfom-ance were a d d i t i o n a l l y i n v e s t i g a t e d . 6. REFERENCES I. Haberlitg, E. : Cicensct.aften -Jon p u l v c r n e r a l i u r ~ i r hLerzestsllt+m 3 c t n + l l a r b * i ? s s t a h l . ?+a51 ?in3 Z3ssn .35 11975) Xr. 17. : Y h b + h a n d l u n $ vin y l v e r o r . t a l l u r q 3 s c h '.-rees t e l l t e n AS?-Schnellarbsitsstghl+n. B e r k h t 33ber d l n i6. 3Brt.rr r i t r c h n i s c 5 s Fachtagmg ?. 16-14. X.rmmhsr ;???.
2 . RrllIMrtn, ?.
3. Bouzakis, F. : Einsatz vnn ~ulv~rmetallurgin~:hherqestnlltc?n ; - h n e l l a r b e i t s s t ~ h l c n bsim XZlzfr8sen m d USlzetmsen. ZahnrEdund " e t r i r h u n t e r s u c h u n g . 3oricht iiber l i c i I. ,!rhcr;'ts?spnq 413 2.1. .in3 22. Xaf I983 .:n Aachen.
P. : Hochf.rste pulverr.etel:urgiacke S c h n e l i a r h i [email protected]$nr ;W { 2 9 W i ) , ?h-. 2 3 . ?. in-19.
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;?able.
K. : Erhzhung der i i i r t s f h a f t l i c h k s i t h i m %lzstotsen durch 3ptimierung des LerspanIJmzessss an3 3er ilnrkwugaus5. huzatis,
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X s s s r t a t i m f H Aachsn, 1975.
Bouz&is, K. : S c h n e i d s m f f e u s m h l 3ein Yilhstorsnn .I~.dustr3eAna-iqer 103 f 1 9 7 5 ) N r . 5 5 , ?. 13-17.
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aouzakis, K . : 3ptiuiwrunq d e r S c k z e i d r a d e u s l o ~ n gh i m WSlzstossen u t t e r Jsriicksichtigung d e r jpanbildung. In&isris-An%-iger 33 (1377) )(r. 14, ?. >909-:wq. 7.
3. KSnig, ?I. Bouzakia, , K. : Chip Tornation 3al5 3f the 'XPP 'Jol. 25/2/1377. ?. :7-20.
:n
ihapinq. An-
: r)ptimieruni: der Schnitthdlng'Jngen h i m Xkilztossen. wt-Zclts?hrift fijr i n d u x r r i e i l e i * r t i z u n g 58 (14781, P.
'3. %uzalr.is, K. 7w-755.
10. ' i p i t z , H . , KSnig, FT., Sulzsr, G., Bouzakis, F. : 'JWS2hleiS3sr:cht ;untersuchungen t e i n XZlztossm =mn %radv*rzahnunZen. 4es Landcs Nor3Fhei.n-XnsTfslsn X r . 2 W 1 , 1374, li. Bouzakis, K. : Konzept 2nd technologiscte Grundlagen zur aut o m a t i a i e r t e n Erstellung o p t l n a l r r Bearbeitungsbedingunungen Ssim .dalzfrZsen. H a b l l i t a t i o n s s c h r i f t IH Aa&en, 1.990 'iS1-2'erlaq. ?or?schr.-f)sr. 73IZ-l(eihc 2, Nr. 4 2 .
.
F i g u r e 11: Wear Behaviour i n Gear Hobbing with Diff e r e n t Tool M a t e r i a l s . p e o f manufacture i n g e a r hobbing a p p a r e n t l y h a s no eff e c t o n t h e wear Ferfomnnce o f hiqh speed steels, a l though t h e e f f e c t o n t h e s t r u c t u r e is g r e a t . However, a non-uniform c a r b i d e d i s t r i b u t i o n c a n l e a d t o consid e r a b l e scatter i n t h e d e v e l o p l e n t o f wear, whichwould n o t o c c u r w i t h Pblmanufacture. Thus i n mass production a r e p r o d u c i b i l i t y o f rise i n wear can be ensured,which c a n n o t b e achieved to t h i s e x t e n t i n s m e l t - n e t a l l u r g b a1 n a n u f a c t u r e o f t h e tools. 5. SUM'ARY The a a j o r i t y o f i n d u s t r i a l l y produces s t r a i c h t o r helically-toothed c y l i n d r i c a l g e a r s are manufactured by hobbing or shapinq. The a p p l i c a t i o n o f powder-netall u r g i c a l l y manufactured high SFeed steels could r e p r e s e n t a p o s s i b i l i t y o f i n c r e a s i n q performance. Advant a c e s can p a r t i c u l a r l y be expected with tools which are d i f f i c u l t t o g r i n d , i n c l u d i n c hobsand shaprcutters. Within t h e scope o f t h i s r e p o r t , t h e r e f o r e , it was i n tended t o examine some PN steels with d i f f e r i n q alloyi n g l e v e l s , w i t h r e s p e c t to wear p e r f o m a n c e i n q e a r hobbin? and s h a r i n g . I n o r d e r to a l l o w a l i r o c t COF-
2 . h l e r r , 5 . : Leistungsstaiqerunt bei der Z71indcrradh4rst"l;xng durch geneun Zrfas+*inX 3er ZsrspanLinsmstit Diw.er?a?
.
:3. Joppa. K. i e i s t u n g s s t e i g a r u n g beia Wtilzfrlsen tit SChnella r b e i t s s t a h l durch Analyse , Beurteilung und Meir.f:ussung deS Zerspanprozesses. 3 i s s s r t a t i o n ?R Aachsn, 1377.
N. Tondorf, 1. : W G h u n ~d e r F'ertigungsgenauigkeit beirn W S Z f r a s r n durch vptsmatischc?rjemei
29