Single step of binder thermal debinding and sintering of injection moulded 316L stainless steel Indra Putra Almanar 1,a , Zuhailawati Hussain 2,b and Mohd Afian Omar 3,c 1 School of Mechanical Engineering, 2 School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia 3 Advanced Materials Research Centre, Sirim Berhad, Lot 34, Jalan Hi-Tech 2/3, Kulim Hi-Tech Park, 09000 Kedah, Malaysia a [email protected], b [email protected], c [email protected]Keywords: Metal injection moulding, stainless steel, sintering Abstract. Metal injection moulding was performed with gas atomized 316L stainless steel powders. Feedstocks were prepared using a paraffin wax/polyethylene/stearic acid binder system and subsequen tly molded into tensile bar specime ns. Solvent extraction done at 80 ○ C has shortened the debinding process to 30 minute. Single step of thermal binder debinding and sintering was done in a vacuum furnace. Sintering at 1380 ○ C has reduced the porosity and associated with grain growth that result in an increase in ultimate tensile strength to 444 MPa while the elongation increased to 29% before fracture.Introduction Injection moulding using stainless steels powder has significant utilisation in the manufacturing of relatively small, complex shaped parts requiring high strength and good corrosion resistance. The debinding in PIM is a critical processing step and has been identified as that part of the technique, which had p rimarily to be improv ed. Long debind ing times or altern atively high risk of sample distortion have been a major obstacle for the economic success of PIM. Thermal, solvent, and vacuum debinding processes have been widely adopted by the powder injection molding (PIM) industry [1,2]. A more recent developed vacuum debinding process combines debinding and sintering cycles into a single step and minimizes damage caused by the handling of fragile debound parts [3,4]. In this process, a high vacuum is employed at low temperatures to enhance the thermal debinding rate of low temperature binder components such as paraffin wax. At high temperatures, low vacuum is used to remove the remaining major binders. After debinding, the parts are sintered in the same furnace. This combination of debinding and sintering cycles is made possible by using a special pumping system which avoids the build up of condensed binder vapours in the pipings. The present work deals with metal injection moulding of 316L stainless steel using two steps of debinding process whic h are solvent debinding followed by thermal deb inding. The relationship betwe en the sintering temperature and mechanical properties of the sintered products are discussed. Methodology In this study, gas atomized 316L stainless steel powder supplied by Anval, Sweden with 15 µm median particle size was used. 55 wt. % of paraffin wax, 35 wt. % of polyethylene and 10 wt. % ofstearic acid were used as binder system. Tensile bar specimen was produced using MCP HEK-
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Single Step of Binder Thermal Debinding and Sintering of Injection Moulded 316L Stainless Steel
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8/8/2019 Single Step of Binder Thermal Debinding and Sintering of Injection Moulded 316L Stainless Steel
Keywords: Metal injection moulding, stainless steel, sintering
Abstract. Metal injection moulding was performed with gas atomized 316L stainless steel powders.
Feedstocks were prepared using a paraffin wax/polyethylene/stearic acid binder system and
subsequently molded into tensile bar specimens. Solvent extraction done at 80○
C has shortened the
debinding process to 30 minute. Single step of thermal binder debinding and sintering was done in a
vacuum furnace. Sintering at 1380○C has reduced the porosity and associated with grain growth that
result in an increase in ultimate tensile strength to 444 MPa while the elongation increased to 29%
before fracture.
Introduction
Injection moulding using stainless steels powder has significant utilisation in the manufacturing
of relatively small, complex shaped parts requiring high strength and good corrosion resistance. The
debinding in PIM is a critical processing step and has been identified as that part of the technique,
which had primarily to be improved. Long debinding times or alternatively high risk of sample
distortion have been a major obstacle for the economic success of PIM. Thermal, solvent, and
vacuum debinding processes have been widely adopted by the powder injection molding (PIM)
industry [1,2].
A more recent developed vacuum debinding process combines debinding and sintering cycles
into a single step and minimizes damage caused by the handling of fragile debound parts [3,4]. In
this process, a high vacuum is employed at low temperatures to enhance the thermal debinding rateof low temperature binder components such as paraffin wax. At high temperatures, low vacuum is
used to remove the remaining major binders. After debinding, the parts are sintered in the same
furnace. This combination of debinding and sintering cycles is made possible by using a special
pumping system which avoids the build up of condensed binder vapours in the pipings. The present
work deals with metal injection moulding of 316L stainless steel using two steps of debinding
process which are solvent debinding followed by thermal debinding. The relationship between the
sintering temperature and mechanical properties of the sintered products are discussed.
Methodology
In this study, gas atomized 316L stainless steel powder supplied by Anval, Sweden with 15 µm
median particle size was used. 55 wt. % of paraffin wax, 35 wt. % of polyethylene and 10 wt. % of
stearic acid were used as binder system. Tensile bar specimen was produced using MCP HEK-
the specimens. The ultimate tensile strength increased from 327 to 444 MPa when the sintering
temperature was increased from 1300○
C to 1380○
C while the elongation increased from 19% to 29 %
before fracture.
Conclusions
In this study, solvent extraction debinding process coupled with the thermal removal of theremaining binder phase during sintering has been applied on injection molding part of 316L
stainless steel. The rate of extraction of paraffin wax from the green body increased with increasing
solvent extraction temperature. As the time increased, the weight loss increased and the pores
channels enlarged. The pores present in the sintered part generally very fine, closed and uniformly
distributed (at 1360○
C and 1380○
C). Low porosity in the sample sintered at higher temperature
exhibited good ultimate tensile strength and elongation.
Acknowledgement
Financial support provided by Universiti Sains Malaysia under the schemes of TPLN and Research
University Grant are acknowledged. Acknowledgement is also extended to Ms. Yew Sin Lin for her
assistance in experimental work.
References
[1] R. Seidel, F. Petzoldt, G. Veltl, and H.-D. Kunze: Met. Powder Rep. Vol. 47 (1992), p. 56
[2] M.Y. Cao, J.W. O’Connor and C.I. Chung: A New Water Soluble Solid Polymer Solution
Binder For Powder Injection Moulding, PIM Symposium Proceedings, San Francisco (1992).
[3] K.S. Hwang, K.H. Lin and S.C. Lee: Mater. Manuf. Processes Vol. 12 (1997), p. 593
[4] M.A. Omar, R. Ibrahim, M.I. Sidik, M. Mustapha and M. Mohamad, J. Mater. Process.