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Catalytic gas phase erosion for the rapid debinding of metal injection moulded (MIM) green parts
METAL I N J E C T I O N MOULDING ( M I M ) - P R O C E S S E C O N O M I C S AND FUTURE PROSPECTS N.V. Nallicheri, (IBIS Associaties Inc, USA). T h e a d v a n t a g e s of MIM a n d s o m e applications for MIM p a r t s were outlined a n d a n account given of t h e growth of MIM since its inception with a projection to t h e year 1993. The obstacles to t h e future d e v e l o p m e n t of MIM were s t a t e d to be t h e need to reduce raw material costs a n d d e v e l o p m e n t of a n o n - d i s t o r t i n g a n d easily removed binder. Consistent s t a n d a r d s were said to be needed. An a s s e s s m e n t was given of t h e c o m p e t i t i v e p o s i t i o n o f MIM compared with other processes and a c o m p u t e r i z e d cost m o d e l was u s e d to assist in t h e review of process economics.
IMPROVEMENT OF PROFITABILITY IN THE METAL I N J E C T I O N MOULDING ( M I M ) INDUSTRY K.M. Kulkarni, ( A d v a n c e d Metalworking Practices Inc, Carmel, Indiana, USA). The factors which will d e t e r m i n e t h e long t e r m d e v e l o p m e n t a n d profitability of t h e MIM i n d u s t r y were discussed. The need for t i g h t control of process costs a n d strict process control was emphasized. Possible i m p a c t of t r e n d s in raw material prices a n d new technology was considered. ROLE OF A T M O S P H E R E IN THERMAL P R O C E S S I N G OF I N J E C T I O N M O U L D E D STEEL E.L. Stretcher et al, (L'Air Liquide, Paris, France). Studies of t h e t h e r m a l d e b i n d i n g of i n j e c t i o n m o u l d e d 2%Ni s t e e l w e r e reported. The objective was to optimize gas composition a n d t h e t h e r m a l cycle for t h e process. The b i n d e r used c o n t a i n e d paraffin and carnuba waxes and polypropylene. The relationships between t h e gases a n d t h e r m o g r a v i m e t r i c b e h a v i o u r of t h e b i n d e r were defined. Effects of debinding temperature on density, hardness, carbon content and microstructures were evaluated. CATALYTIC GAS PHASE E R O S I O N FOR THE RAPID D E B I N D I N G OF METAL INJECTION MOULDED (MIM) GREEN PARTS J.S. E b e n h o c h et al, (BASF AG, Ludwigshafen, Germany). A new m e t h o d for t h e rapid d e b i n d i n g of MIM p a r t s , c a t a l y t i c gas erosion, w a s described. The b i n d e r is a t h e r m o p l a s t i c polymer which is stable at t h e moulding t e m p e r a t u r e b u t is decomposed in a gas flow below t h e melting point. The gas does not penetrate the binder and decomposition occurs only a t t h e interface with gas e x c h a n g e occurring only in t h e d e b o u n d region of t h e p a r t so t h a t t h e r e is
58 MPR October 1991
no build up of pressure. The process is carried o u t in a steel lined, gas tight, furnace at c o n s t a n t t e m p e r a t u r e a n d is n o t affected by small variations in process conditions.
CHANGES IN WICKING CHARACTERISTICS OF WICKING POWDER WITH R E P E A T E D USE T. Ohsako et al, ( S u m i t o m o Metal Mining Co Ltd, Tokyo, J a p a n ) . Research into t h e wicking properties of t h e s u b s t r a t e with regard to d e b i n d i n g rate a n d surface defects was reported. Compacts m a d e from Fe carbonyl powder with a w a x / p o l y e t h y l e n e b i n d e r w e r e d e b o u n d by wicking on A1203 powder. Changes in t h e ability of t h e wicking p o w d e r to d e b i n d t h e compacts with r e p e a t e d use were studied with regard to t h e effects of particle size, porosity and residual binder content. Debinding times a n d compact defects were discussed.
METAL I N J E C T I O N MOULDING ( M I M ) A N D REACTIVE S I N T E R I N G ( R S ) OF NICKEL ALUMINIDE W.Z. Mosiolek et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). An investigation into t h e fabrication of Ni 3 b y MIM a n d RS w a s d e s c r i b e d . Elemental powders were mixed with b i n d e r a n d moulded. Debinding was by combination of s o l v e n t v a p o u r a n d t h e r m a l m e a n s a n d reactive sintering was carried o u t in dry H a n d vacuum. Severe distortion during sintering was n o t e d a n d this was shown to be due to the t h e r m a l d e b i n d i n g cycle a n d t e m p e r a t u r e gradients d u r i n g sintering. Densities of m a t e r i a l s sintered in H were 70% a n d were higher w h e n t h e sintering was in vacuum.
STRUCTURAL D E V E L O P M E N T DURING S I N T E R I N G OF METAL I N J E C T I O N M O U L D E D ( M I M ) 2% NICKEL STEEL H. Zhang a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Densification, properties, microstructural changes and homogenization of Ni c o n t e n t in injection moulded 2%Ni steel were investigated. The powder was m i x e d with a polymer/wax b i n d e r a n d m o u l d e d into tensile test bars. Dilatometry was used to d e t e r m i n e t h e relationship between dimensional changes during sintering a n d temperature. It was reported that the most extensive densification occurred below 1000 °. Above 1000 ° t h e r e was little change in density b u t extensive change in structure and properties. Pore elimination, grain growth, pearlite coarsening a n d Ni homogenization were n o t e d a n d t h e r e was an increase in tensile s t r e n g t h a n d a reduction in ductility.
CONTROL OF CARBON C O N T E N T DURING P R O C E S S I N G OF I N J E C T I O N M O U L D E D STEEL D.R. Bankovic a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Control of %C in injection m o u l d e d steel was studied using a 2%Ni steel which was d e b o u n d a n d s i n t e r e d in a n a t m o s p h e r e of known c a r b o n p o t e n t i a l in o r d e r to a t t a i n a p r e d e t e r m i n e d %C. The C p o t e n t i a l of a n atmosphere was found to vary with t e m p e r a t u r e a n d t h e composition of t h e gas was varied to give a c o n s t a n t value. The gas m i x t u r e c o n t a i n e d CO, C02, H2 a n d H20. The effectiveness of this a p p r o a c h was verified by bulk C analysis of t h e steel, microstructure a n d sintered density. RECENT D E V E L O P M E N T S IN IRON MICROPOWDERS FOR METAL I N J E C T I O N MOULDING ( M I M ) J.E. J a p k a a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Studies of t h e use of carbonyl Fe powder for MIM w e r e d e s c r i b e d . The p o w d e r p r o p e r t i e s a n d t h e MIM p r o c e s s were discussed. Development of modified p o w d e r s to give i m p r o v e d a s - s i n t e r e d properties was considered. Suitable materials were characterized by scanning electron microscopy and mechanical properties were measured. E F F E C T S OF POWDER SHAPES, VOLUME FRACTIONS OF B I N D E R S AND B I N D E R TYPES IN METAL I N J E C T I O N MOULDING OF IRON BASED POWDERS I~F. Hens et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). A detailed study of injection moulded Fe powders was reported. Effects of particle shape, p a r t geometry, b i n d e r formulation a n d volume fraction were investigated using a n i n s t r u m e n t e d MIM machine. Process p r o b l e m s were described, The i m p o r t a n c e of optimization of all process variables was emphasized. Bebinding p r o c e d u r e s were discussed in relation to binder formulation. Continuous and batch furnaces for sintering were evaluated. IMPROVED WAX BASED BINDER FORMULATIONS B.O. Rhee et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). A t t e n t i o n was d r a w n to t h e tendency of some w a x / p o l y m e r b i n d e r s to s e p a r a t e from t h e m e t a l powder during injection moulding due to t h e high pressures used. Various w a x b a s e d b i n d e r s c o n t a i n i n g different polymers were used to c o m p a r e t h e effects of variation in miscibility on t h e moulding process. It was found t h a t t h e binders containing polymers with greater a d h e s i o n to t h e m e t a l or greater misciblility in t h e wax h a d less t e n d e n c y to separate. Polymers with higher softening points gave
IMPROVEMENT OF PROFITABILITY IN THE METAL I N J E C T I O N MOULDING ( M I M ) INDUSTRY K.M. Kulkarni, ( A d v a n c e d Metalworking Practices Inc, Carmel, Indiana, USA). The factors which will d e t e r m i n e t h e long t e r m d e v e l o p m e n t a n d profitability of t h e MIM i n d u s t r y were discussed. The need for t i g h t control of process costs a n d strict process control was emphasized. Possible i m p a c t of t r e n d s in raw material prices a n d new technology was considered. ROLE OF A T M O S P H E R E IN THERMAL P R O C E S S I N G OF I N J E C T I O N M O U L D E D STEEL E.L. Stretcher et al, (L'Air Liquide, Paris, France). Studies of t h e t h e r m a l d e b i n d i n g of i n j e c t i o n m o u l d e d 2%Ni s t e e l w e r e reported. The objective was to optimize gas composition a n d t h e t h e r m a l cycle for t h e process. The b i n d e r used c o n t a i n e d paraffin and carnuba waxes and polypropylene. The relationships between t h e gases a n d t h e r m o g r a v i m e t r i c b e h a v i o u r of t h e b i n d e r were defined. Effects of debinding temperature on density, hardness, carbon content and microstructures were evaluated. CATALYTIC GAS PHASE E R O S I O N FOR THE RAPID D E B I N D I N G OF METAL INJECTION MOULDED (MIM) GREEN PARTS J.S. E b e n h o c h et al, (BASF AG, Ludwigshafen, Germany). A new m e t h o d for t h e rapid d e b i n d i n g of MIM p a r t s , c a t a l y t i c gas erosion, w a s described. The b i n d e r is a t h e r m o p l a s t i c polymer which is stable at t h e moulding t e m p e r a t u r e b u t is decomposed in a gas flow below t h e melting point. The gas does not penetrate the binder and decomposition occurs only a t t h e interface with gas e x c h a n g e occurring only in t h e d e b o u n d region of t h e p a r t so t h a t t h e r e is
58 MPR October 1991
no build up of pressure. The process is carried o u t in a steel lined, gas tight, furnace at c o n s t a n t t e m p e r a t u r e a n d is n o t affected by small variations in process conditions.
CHANGES IN WICKING CHARACTERISTICS OF WICKING POWDER WITH R E P E A T E D USE T. Ohsako et al, ( S u m i t o m o Metal Mining Co Ltd, Tokyo, J a p a n ) . Research into t h e wicking properties of t h e s u b s t r a t e with regard to d e b i n d i n g rate a n d surface defects was reported. Compacts m a d e from Fe carbonyl powder with a w a x / p o l y e t h y l e n e b i n d e r w e r e d e b o u n d by wicking on A1203 powder. Changes in t h e ability of t h e wicking p o w d e r to d e b i n d t h e compacts with r e p e a t e d use were studied with regard to t h e effects of particle size, porosity and residual binder content. Debinding times a n d compact defects were discussed.
METAL I N J E C T I O N MOULDING ( M I M ) A N D REACTIVE S I N T E R I N G ( R S ) OF NICKEL ALUMINIDE W.Z. Mosiolek et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). An investigation into t h e fabrication of Ni 3 b y MIM a n d RS w a s d e s c r i b e d . Elemental powders were mixed with b i n d e r a n d moulded. Debinding was by combination of s o l v e n t v a p o u r a n d t h e r m a l m e a n s a n d reactive sintering was carried o u t in dry H a n d vacuum. Severe distortion during sintering was n o t e d a n d this was shown to be due to the t h e r m a l d e b i n d i n g cycle a n d t e m p e r a t u r e gradients d u r i n g sintering. Densities of m a t e r i a l s sintered in H were 70% a n d were higher w h e n t h e sintering was in vacuum.
STRUCTURAL D E V E L O P M E N T DURING S I N T E R I N G OF METAL I N J E C T I O N M O U L D E D ( M I M ) 2% NICKEL STEEL H. Zhang a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Densification, properties, microstructural changes and homogenization of Ni c o n t e n t in injection moulded 2%Ni steel were investigated. The powder was m i x e d with a polymer/wax b i n d e r a n d m o u l d e d into tensile test bars. Dilatometry was used to d e t e r m i n e t h e relationship between dimensional changes during sintering a n d temperature. It was reported that the most extensive densification occurred below 1000 °. Above 1000 ° t h e r e was little change in density b u t extensive change in structure and properties. Pore elimination, grain growth, pearlite coarsening a n d Ni homogenization were n o t e d a n d t h e r e was an increase in tensile s t r e n g t h a n d a reduction in ductility.
CONTROL OF CARBON C O N T E N T DURING P R O C E S S I N G OF I N J E C T I O N M O U L D E D STEEL D.R. Bankovic a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Control of %C in injection m o u l d e d steel was studied using a 2%Ni steel which was d e b o u n d a n d s i n t e r e d in a n a t m o s p h e r e of known c a r b o n p o t e n t i a l in o r d e r to a t t a i n a p r e d e t e r m i n e d %C. The C p o t e n t i a l of a n atmosphere was found to vary with t e m p e r a t u r e a n d t h e composition of t h e gas was varied to give a c o n s t a n t value. The gas m i x t u r e c o n t a i n e d CO, C02, H2 a n d H20. The effectiveness of this a p p r o a c h was verified by bulk C analysis of t h e steel, microstructure a n d sintered density. RECENT D E V E L O P M E N T S IN IRON MICROPOWDERS FOR METAL I N J E C T I O N MOULDING ( M I M ) J.E. J a p k a a n d R.M. German, (Rensselaer Polytechnic Inst, Troy, New York, USA). Studies of t h e use of carbonyl Fe powder for MIM w e r e d e s c r i b e d . The p o w d e r p r o p e r t i e s a n d t h e MIM p r o c e s s were discussed. Development of modified p o w d e r s to give i m p r o v e d a s - s i n t e r e d properties was considered. Suitable materials were characterized by scanning electron microscopy and mechanical properties were measured. E F F E C T S OF POWDER SHAPES, VOLUME FRACTIONS OF B I N D E R S AND B I N D E R TYPES IN METAL I N J E C T I O N MOULDING OF IRON BASED POWDERS I~F. Hens et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). A detailed study of injection moulded Fe powders was reported. Effects of particle shape, p a r t geometry, b i n d e r formulation a n d volume fraction were investigated using a n i n s t r u m e n t e d MIM machine. Process p r o b l e m s were described, The i m p o r t a n c e of optimization of all process variables was emphasized. Bebinding p r o c e d u r e s were discussed in relation to binder formulation. Continuous and batch furnaces for sintering were evaluated. IMPROVED WAX BASED BINDER FORMULATIONS B.O. Rhee et al, (Rensselaer Polytechnic Inst, Troy, New York, USA). A t t e n t i o n was d r a w n to t h e tendency of some w a x / p o l y m e r b i n d e r s to s e p a r a t e from t h e m e t a l powder during injection moulding due to t h e high pressures used. Various w a x b a s e d b i n d e r s c o n t a i n i n g different polymers were used to c o m p a r e t h e effects of variation in miscibility on t h e moulding process. It was found t h a t t h e binders containing polymers with greater a d h e s i o n to t h e m e t a l or greater misciblility in t h e wax h a d less t e n d e n c y to separate. Polymers with higher softening points gave