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Oxide Formation In Metal Injection Molding Of 316L Stainless Steel

Jang J. M., Lee W., Ko S.-H., Han C., Choi H.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1281--1285

EN

The effects of sintering condition and powder size on the microstructure of MIMed parts were investigated using water-atomized 316L stainless steel powder. The 316L stainless steel feedstock was injected into micro mold with micro features of various shapes and dimensions. The green parts were debound and pre-sintered at 800°C in hydrogen atmosphere and then sintered at 1300°C and 1350°C in argon atmosphere of 5torr and 760torr, respectively. The oxide particles were formed and distributed homogeneously inside the sample except for the outermost region regardless of sintering condition and powder size. The width of layer without oxide particles are increased with decrease of sintering atmosphere pressure and powder size. The fine oxides act as the obstacle on grain growth and the high sintering temperature causes severe grain growth in micro features due to larger amount of heat gain than that in macro ones.

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Powder injection moulding of micro parts

Biało D., Skalski A.

Journal of Automation Mobile Robotics and Intelligent Systems

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2009

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Vol. 3, No. 4

87-90

EN

This paper presents and discusses individual phases of forming micro parts using the injection moulding method. Tests involving the preparing of feedstock for the process of injection micro moulding were conducted. The rheological properties for binder-powder compositions were also defined. Tests were conducted for 316L stainless steel and iron metal powders and Al2O3 ceramics with granularity ranging from 0.135 žm to 16 žm. Binders consisted of polyethylene, paraffin and wax. Technological parameters of the process of injection micro moulding are presented, including the impact of individual factors on the filling of the mould cavities. Moreover, results of tests with respect to the shrinking of the micro parts as well as of the structure of the material following sintering are presented.

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Specyfika procesu formowania wtryskowego mikroelementów z proszków metali

Biało D., Skalski A., Paszkowski L.

Rudy i Metale Nieżelazne

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2008

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R. 53, nr 4

241-245

PL

Przedstawiono oryginalną metodę oceny przebiegu napełniania mikrokanałów, ważnego problemu przy formowaniu wtryskowym mikroelementów z proszków metali. W takim procesie wtryskiwaniu poddawana jest masa złożona z mikroproszku i specjalnego, wieloskładnikowego, termoplastycznego lepiszcza. Potem lepiszcze jest usuwane a kształtka spiekana. Do badań zastosowano specjalną wkładkę formującą z wieloma mikrokanałami o szerokości od 50 do 500 mim. Badano masy z proszkiem żelaza o ziarnistości 1 i 4 mim i z lepiszczem złożonym z polietylenu, wosku i parafiny. Wykazano, że najważniejszym parametrem decydującym o przebiegu napełniania mikrokanałów jest temperatura formy i dla badanych mas powinna przekraczać 70 stopni Celsjusza. Im większy jest stopień napełnienia masy proszkiem Vp i im drobniejsze są cząstki proszku, tym trudniej przebiega wpływanie masy do mikrokanałów. Ma to ścisły związek ze wzrostem lepkości masy.

EN

Micro metal injection moulding (miMIM) is the process which allows to manufacture very small elements (micro parts) with dimensions below 1mm in large - scale production cycle, complex shape, wide range of materials and in economic way. In miMIM very fine powders are mixed with special, complex binder with thermoplastic properties. Obtained mass (feedstock for injection) is injected to the micro mould. Next the binder is removed and shapes undergo sintering. Selected problems of micro injection moulding of micro parts is presented in this paper. It deals with first step of the micro forming process. The metal powder used in this study was carbonyl iron powder with particles of 1 and 4 mim. The binder system was based on wax, polyethylene and paraffin. Powder / binder feedstock was prepared in 2Z type mixer with heating system at temperature of 125 degrees of Celsius in 1 hour. Volume fraction of powder in the feedstock Vp was 50 and 60 %. Rheological properties of the feedstock was determined on cylinder - cylinder type rheometer in the function of shear rate and temperature. For the purpose of micro injection, special micro form was designed. Micro form was equipped in heating - cooling system and insert having 6 micro channel with cross - section ranged from 2 to 210 mim2. The following injection parameters were used: feedstock temperature of 115 degrees of Celsius, pressure of 60 MPa and mould temperature of 25 to 80 degrees of Celsius. The way of channel feeling i.e. the distance L on which the feedstock flow - in to the channel was taken as the indicator of feedstock behaviour during injection. The research has shown that the principal parameter influenced on distance L is temperature of the mould T/f. The higher is T/f, the longer is L. It is worth to note that characteristic threshold value of temperature above witch feeling of channel is possible occurs. For the feedstock tested it was above 70 degrees of Celsius. The following conclusion which may be drown from the presented research is that the higher is volume fraction of the powder in the feedstock and the smaller is the micro powder the more difficult is micro channel feeling. It has strong connection with higher viscosity of the feedstock.

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Ocena wpływu warunków wtryskiwania na przebieg napełniania mikrokanałów termoplastycznym materiałem z proszkami

Skalski A., Biało D., Wiśniewski W.

Kompozyty

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2008

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R. 8, nr 4

322-326

PL

Praca przedstawia problemy związane z formowaniem mikroelementów z materiałów proszkowych i obejmuje pierwszy etap - wtryskiwanie do gniazd formujących i napełnianie mikrokanałów. Wtryskiwano materiał stanowiący kompozycję złożoną ze specjalnego termoplastycznego lepiszcza i proszku metalowego. Do badań zastosowano proszki żelaza karbonylowego o ziarnistości 1 i 4 žm oraz proszek stali kwasoodpornej o ziarnistości 16 žm. Składnikami lepiszcza były: wosk, polietylen i parafina. Mieszaninę proszku z lepiszczem przygotowano w mieszalniku typu 2Z w temperaturze 125°C przez 1 godzinę, co zapewniało uzyskanie masy homogenicznej. Udział proszku w przygotowywanych masach wynosił Vp = 60% obj. Wtryskiwanie przeprowadzono na specjalnej mikrowtryskarce własnej konstrukcji, umożliwiającej wtryskiwanie porcji materiału (masy) w zakresie od 1 do 200 mm2. Do przeprowadzenia badań w tym zakresie została wykonana specjalna wkładka formująca, zawierająca mikrokanały o szerokości od 50 do 500 m. Stosowano następujące parametry wtrysku: temperatura masy (Tw) 115 i 125° C, ciśnienie (p) 60 MPa, temperatura formy (Tf) od 25 do 80°C. Przedstawiono badania dotyczące wpływu parametrów wtryskiwania: temperatury formy, temperatury materiału oraz składu materiału na jakość wypełniania przez materiał mikroformy. Jako wskaźnik zachowania masy podczas wtryskiwania przyjęto drogę L wpływania masy do mikrokanałów i do gniazd mikroform. Wykazano, że najważniejszym parametrem decydującym o przebiegu napełniania mikrokanałów jest temperatura formy i dla badanych mas nie powinna być niższa niż 70°C. Uzyskane informacje wykorzystano w próbach wtryskiwania kształtek do prób na zginanie i rozciąganie oraz koła zębatego.

EN

In the last few years micro system technology has gained increasing development and new method of fabrication of micro components are needed. Micro metal injection moulding (žMIM) is the process which allows to manufacture very small elements (micro parts) with dimensions below 1 mm in large - scale production cycle, complex shape, wide range of materials and in economic way. In žMIM very fine powders are mixed with special, complex binder with thermoplastic properties. Obtained mass (feedstock for injection) is injected to the micro mould. Next the binder is removed and shapes undergo sintering. Selected problems of micro injection moulding of micro parts is presented in this paper. It deals with first step of the micro forming process. The metal powder used in this study was carbonyl iron powder with particles of 1, 4 žm and stainless steel powder with particles of 16 žm. The binder system was based on wax, polyethylene and paraffin. Powder / binder feedstock was prepared in 2Z type mixer with heating system at temperature of 125°C in 1 hour. Volume fraction of powder in the feedstock Vp was 60%. For the purpose of micro injection, special micro form was designed. Micro form was equipped in heating - cooling system and insert having 6 micro channel with cross - section ranged from 2 to 210 žm2. The following injection parameters were used: feedstock temperature of 115 and 125°C, pressure of 60 MPa and mould temperature of 25 to 80 C. The way of channel feeling i.e. the distance L on which the feedstock flow - in to the channel was taken as the indicator of feedstock behavior during injection. The research has shown that the principal parameter influenced on distance L is temperature of the mould Tf. The higher is Tf, the longer is L. It is worth to note that characteristic threshold value of temperature above which feeling of channel is possible occurs. For the feedstock tested it was above 70°C. The following conclusion which may be drown from the presented research is that the higher is volume fraction of the powder in the feedstock the more difficult is micro channel feeling. It has strong connection with higher viscosity of the feedstock.