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Qu1)1)School of Materials Science and Engineering,University of Science and Technology Beijing,Beijing 100083,China 2)School of Mechanical and Electrical Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China (Received:16 February 2012;revised:12 April 2012;accepted:25 April 2012)Abstract:Micro powder injection molding( μ PIM)was investigated for possible mass production of micro-components at relatively low cost.However,scaling down to such a level produces challenges in injection molding and debinding.Micro gears were fabricated byμPIM from in-house feedstock.The effect of injection speed and injection pressure on the replication of the micro gear cavity was investigated.Solvent debinding and thermal debinding processes were discussed.The results show that microgears can be successfully fabricated under the injection pressure of 70 MPa and the 60%injection speed.Either too low or too high injection speed can cause incomplete filling of micro gears.The same is the case with too low injection pressure.Too high injection pressure can bring cracks.Solvent debinding of micro gears was performed in a mixture of petroleum ether and ethanol.
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Subsequently,micro gears were successfully debound by a multistep heating schedule.Keywords:gear manufacture;micro gears;injection molding;debinding;zirconia
1.Introduction
Over the past ten years,there has been an increasing
demand for micro components or micro structures,
which are applied in microelectronic systems,microfluidics,
and medical tools[1-3].One such promising
process is the micro powder injection molding(μPIM)
technology,which is a near net shape production of
complex micro components on a large scale[4-6].
Evolved from powder injection molding(PIM),the
four major processing steps ofμPIM are feedstock
preparation,injection molding,debinding,and sintering
[7-8].
In theμPIM process,injection molding is a crucial
step that has significant influence on mold filling and
demolding.During injection,melting feedstock flows
through the runner,enters the gates and fills into the
mold cavity to form the desired part.Inappropriate
molding parameters will lead to such defects as short
shot,fracture and powder-binder separation,which
usually act during the debinding and sintering stages
[9-10].Krug et al.[11]revealed that the pressure history during solidification of large injection moldings
has remarkable effects on cracks that appear after
binder removal.Tsai et al.[12]found that the surface
quality of lenses can be improved with higher melting
temperature,injection pressure,packing pressure,and
mold temperature.Chen et al.[13]found that the dimensional
accuracy of micro-channels increased with
increasing injection speed,packing pressure,and melting
temperature.TheμPIM technology imposes different
requirements for the molding process compared
to the conventional PIM technology.For example,a
lower ejecting speed is required during demolding to
avoid failure or sticking[14-15].
InμPIM,the removal of the binder from the
molded part,so-called debinding,is an important step.
High risk of sample distortion and long duration are
major problems for the economic success ofμPIM.In
general,the widely used debinding method is a combination
of solvent debinding and thermal debinding.
Through the solvent debinding step,part of bindercomponents can be
removed and pore channels appear,
which will help to remove the remaining componentsin the following thermal debinding[16].The debinding
process without introducing any defects is of great significance
forμPIM because the defects cannot be
eliminated during the following sintering[17].
In this paper,two process parameters,injection
speed and injection pressure,were used to study the