l'article presente les avances de la technologie du moulage par injection de poudres metalliques pour la realisation de composants structures et de micro-composants mono et bi matieres par la technologie du moulage par injection de poudres. les essais de melanges, d'injection, de deliantage et de densification conduisent a l'obtention de composants et de micro-composants sans defauts possedant d'excellente propriete fonctionnelle et structural

BARRIERE, Thierry

GELIN, Jean-Claude

KONG X.

I-Revues

20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  1 
Manufacturing of micro-components by powder injection 
moulding process 
X. Kong
a
, T. Barriere
a
, J-C. Gelin
a
 
a. FEMTO-ST Institute, 24 Épitaphe Avenue, BESANCON (France) 
Abstract: 
The powder injection moulding (PIM) process satisfies the increasing demand to manufacture smaller parts 
with complex shapes. The related researches in this area have been carried out at FEMTO-ST Institute since 
a few years. An injectable feedstock formulation composed of polymers and metallic powders has been tested. 
Micro injection and bi-material injection tests have been carried out. During the bi-material injection test 
with a three-plate mould configuration, the interface between the two different feedstocks has been well 
defined. After thermal debinding stage, the correctly debinded components are sintered with different 
sintering cycles, the resulted components have been successfully realized. 
Keywords: powder injection moulding, bi-material injection, 316L stainless steel, feedstock 
1 Introduction  
Powder-injection moulding (PIM) is a process based on technologies issued from powder metallurgy for 
producing near-net-shape components. PIM has the ability to process advanced metallic or ceramic powders 
into complex-shaped parts [1]. In recent years, to satisfy the increasing demands for microparts in different 
applications fields, micro powder injection moulding (micro-PIM) already represents one of the key 
technologies to obtain micro-components or to realize micro-structured surfaces [2]. This is related to the 
high efficiency and the near-net-shape capability to manufacture complex shaped parts of the PIM process. 
Four similar stages to the ones in PIM process have been included in micro-PIM process: mixing of very fine 
metallic powders and thermoplastic binders to get feedstock, injection of powder/binder mixtures in the 
mould micro-cavity, thermal/catalytic or solvent debinding and finally sintering by solid state diffusion. 
2 Feedstock formulation 
2.1 Powder 
In the last recent years, 316L stainless steel powders are the common one employed in injection molded 
alloys, either gas atomized or water atomized. It results from the fact that these powders offer interesting 
capabilities to be sintered to high density and its corrosion resistance [3]. Due to the superior strength of the 
material produced using pre-alloyed powder compared to the master alloyed prepared material [3], two 316L 
stainless steel powders have been chosen in our tests to perform the proposed analysis.  
The density of both powders is 7.9 g.cm
-3
. The mean particle sizes is equal to 5 µm and 16 µm, the powder 
particle size distributions are mentioned in table 1, and the SEM photos of these two powders are given in 
figure 1 as well. 
Table 1. Powder particle size distributions of the two 316 L stainless steel powders used in the present study 
Powder D10 [µm] D50 [µm] D90 [µm] 
316L stainless steel (5 µm) 1.8  3.4  6.0  
316L stainless steel (16 µm) 4.1  10.5 21.9  
 
20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  2 
        
FIG 1. SEM of spherical 316L stainless steel powders used in the proposed investigations 
In addition, a copper powder (figure 2) with D50 equals 6.34 µm has been used to realize the bi-material-
injection experiments, the density is 8.93 g.cm
-3
. 
 
FIG 2. Copper powder (D50=6.34 µm) used in the proposed investigations for bi-material-injection moulding 
2.2 Binder 
The main role of the binders is to transport the metallic powder particles in the mold cavity during the 
injection stage, and hold the required shape of the components during the ejection, debinding stage and the 
beginning of the sintering stage by solid state diffusion. 
At present, there are many options for the choice of the binder that is very important in the PIM process. In 
this investigation, polypropylene (PP), paraffin wax (PW) and stearic acid (SA) has been retained to 
compose the binder system, due to the fact that the feedstocks prepared according to this feedstock 
formulation leads to the adapted mixing torque and shear viscosity [4].The descriptions and characterizations 
of the different binders used to elaborate the feedstocks are related in table 2. Meanwhile, the primary binder 
PP is used to keep the component shape after injection molding and debinding. The main effect of the 
secondary binder PW is to decrease the feedstock viscosity and increase the replication ability of the 
feedstock. The surfactant SA is used to facilitate powder wetting [5]. 
Table 2. Characteristics and contents of the proposed binder system 
Binder Melting  temperature [°C] Density [g.cm
-3
] Linear Formula Comments 
PP 140  0.90 [CH2CH(CH3)]n 
Mw≈304940 
Mn≈46832 
PW 58~60  0.91 (CnH2n+2)m 
Mw≈754 
Mn≈721 
SA 70.1 0.86 CH3(CH2)16COOH 
Mw≈484 
Mn≈475 
Note: Mw: the weight average molecular weight; Mn: the number average molecular weight. 
 
 
Table 3. Constituents and related contents used for the three proposed feedstock formulations 
Type 316L stainless steel  PP PW  SA  
Volume, % 60 16 22 2.0 
Weight, % 92.9 2.8 3.9 0.4 
Volume, % 62 15.2 20.9 1.9 
Weight, % 93.4 2.7 3.6 0.3 
Volume, % 64 14.4 19.8 1.8 
Weight, % 93.9 2.5 3.3 0.3 
5 µm 5 µm 
316L stainless steel powder of 5 µm 316L stainless steel powder of 16 µm 
a) b) 
50 µm 10 µm b) a) 
20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  3 
Table 3 summarizes the binder system details according to the proposed formulation; one can notice that the 
ratio of PP/PW/SA is always 8/11/1. The feedstock (powder volume loading of 60% is taken as an example) 
related to the proposed formulation has been tested using a twin-screw mixer, according to the following 
conditions: mixing temperature 160 °C, mixing time 30 min and mixing rotation speed 30 rpm. The mixing 
torques measured during the tests are illustrated in figure 3 a), on can observe that the final mixing torque 
corresponding to formulation 2 is about 0.3 N.m. Besides, the viscosity of the feedstock (powder volume 
loading of 60%) has been measured from capillary rheometer at 200 °C with the length/die diameter 
(16mm/1mm) ratio always equals 16 and related in figure 3 b). Based on both measurements, the feedstock 
prepared according to the retained formulation (PP+PW+SA) could be injected. 
  
FIG 3. Characterisation of the employed feedstock formulation (powder volume loading of 60%), a) mixing 
torque vs. mixing time, measured at 160 °C; b) shear viscosity vs. shear rate (100 s
-1
 to 10000 s
-1
) 
3 Injection molding tests of selected feedstock 
As the injection tests, both mono-material injection with one single feedstock and bi-material injection 
combining two different feedstocks have been tried by using a Battenfeld
®
 Microsystem micro-injection 
equipment. 
3.1 Mono-injection with micro mould 
Four types of specimen have been assembled in a micro mould, the micro die cavity of this two-plate mold is 
related in figure 4 a), the 316L stainless steel feedstock (powder volume loading of 62%) above prepared is 
injected and the resulted components are shown in figure 4 b), the thickness of these specimens is 0.5 mm.  
 
FIG 4. a) Die cavity of the micro mould for mono-injection tests, b) injected micro-components from mono-
injection with micro mould (injection temperature: 210 °C, injection volume: 45 mm
3
; injection velocity: 10 
m.min
-1
; injection pressure: 35 bar) 
3.2 Bi-material injection with two-plate mould 
Bi-material components could be produced by using co-powder injection molding technique. This process 
requires a well adapted bi-unit injection molding equipment. 
During the first bi-material injection moulding test, the 316L stainless steel feedstock (D50=3.4 µm, 
according to formulation F3) with different powder loadings of 60% and 64% have been injected into the die 
cavity of a two-plate mould through two separate sets of sprue and rectangular runner (figure 5 a)) using a 
Battenfeld Microsystem
©
 50.  
Observing the photo taken under macroscope (figure 5 b)), it is clearly shown that the interface between 
a) b) 
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30
Time [min]
M
ix
in
g
 T
o
rq
u
e
 [
N
.m
] PP+PW+SA 
1
10
100
100 1000 10000
Shear rate [s
-1
]
S
h
e
a
r 
v
is
c
o
s
it
y
 [
P
a
.s
]
PP+PW+SA
5 mm 
a) b) 
20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  4 
the two feedstocks is not straight, and its position varies with the injection parameters, this is related to the 
fact that the die cavities for both feedstocks are not separated, and they are injected simultaneously, so the 
front flows of both different feedstock flows meet together to form the interface, but this irregular joining of 
the feedstocks is not able to be repeated uniformly. However, the injected components (figure 5 c)) have 
been successfully obtained without external defects, and the size and weight of the specimens are uniform. 
 
FIG 5. a) Two-plate die cavity mould for bi-material injection test; b) enlargement of the interface region 
between the two 316L stainless steel (D50=3.4 µm) feedstocks with different powder volume loadings (60% 
and 64%); c) bi-material injected tensile test specimen (injection temperature: 220 °C, injection volume for 
both injection units: 30 mm
3
, injection pressure: 40 bar) 
3.3 Bi-material injection with three-plate mould 
In order to solve the joining problem associated to different feedstocks during bi-material injection, another 
mould (figure 6 a)) specially designed with two separated injection chambers is developed for the bi-material 
injection test to integrate the 316L stainless steel (16 µm) feedstock (powder volume loading of 60%) and 
copper feedstock (powder volume loading of 60%) which are prepared according to the proposed 
formulation. 
 
FIG 6. a) Three-plate mould for bi-material injection moulding dedicated to the injection of feedstocks based 
on 316L stainless steel (16 µm) and copper powder, b) sizes of the injected bi-material component  
During the injection tests, the ring has been firstly injected with copper feedstock while a cylinder like pin 
was inserted into the cylinder die cavity of 316L stainless steel feedstock. And then it was removed to let in 
the 316L stainless steel feedstock. The interval between both injections is about 0.2 second corresponding to 
the exit of the internal pin. Thus, the interface has been well controlled. The main injection parameters are 
the same for both injection units: injection temperature equal 220 °C, injection pressure equal 40 bar, except 
for the injection volumes equal 45 mm
3
 associated to the 316L stainless steel feedstock and 60 mm
3
 
associated to the Cu feedstock. However, there are still some flashes in edge region (figure 6 b)). The reason 
of the phenomena is related the loose fits between the moveable and the fixed parts of the mold or over 
pressurization during mould filling.  
4 Debinding tests 
During the injection stage, the binder is used to transport out the powder particles to fill out the mould 
cavities, so it has to be eliminated in the debinding stage. In the present study, thermal debinding process has 
been set up for the sake of simplicity, safety and environment respect.  
A standard thermal debinding cycle has been applied in nitrogen atmosphere. The injected compacts have 
been firstly heated with a heating rate equal 55 °C/hour from the 20 °C to 130 °C (lower than the beginning 
temperature of the decomposition of paraffin wax and stearic acid) to vaporize the water vapor absorbed in 
Micro die 
cavity  
a) 
Flash 
b) 
a) b) 
Runner B Runner A 
Sprue B Sprue A 
Micro cavity 
c) 
11 mm 
Powder volume 
loading of 60% Powder volume 
loading of 64% 
20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  5 
the injected components. Then the temperature is increased up to 220 °C with a very slow heating rate equal 
4.5 °C/hour to eliminate the paraffin wax and stearic acid, without removing the polypropylene which serves 
as the backbone of the debinded porous components. Finally, the components are cooled during 120 min to 
reach ambient temperature. During this stage, a porous structure is formed because nearly 75% of the binders 
are removed. As shown in figure 7, the debinded components corresponding to both mono-injection with 
micro mould and bi-material injection with two-plate mould after this cycle are free of defects such as 
uneven binder removal, creating residual stress, etc, and the initial shape of the injected components are well 
kept. 
5 Sintering tests by solid state diffusion 
The purpose of sintering stage is to bond the particles together to form a homogenous structure when full 
densification is achieved [6]. In order to eliminate the pores between powder particles in the debinded 
components, the porous parts are heated to a temperature slightly lower than the melting temperature of the 
material used in the process, and then the powder particles bond together under capillary forces.  
During the sintering tests for the specimens injected with two 316L stainless steel feedstocks (powder 
volume loading of 60% and 64%), the temperature has been heated up to 1360 °C to activate fast sintering 
mechanisms, slightly lower than 1371~1398 °C corresponding to the melting point of 316L stainless steel 
powders [7]. The related sintering ramps are indicated in table 4, and figure 7 a) show the components after 
injection, debinding and sintering stage, respectively. The components are correctly sintered with no obvious 
defects appearing and no cracks near the interface between both different feedstocks, even along the 
interface zone. In length direction, the sintered bi-material components (feedstock with powder volume 
loading of 60% and 64%) exhibit over 10.94% shrinkage. 
Table 4. Sintering ramps for specimens from bi-material injection 
 Ramp 1 Ramp 2 Ramp 3 
Heating rate [°C/min] 10 20 -10 
Temperature [°C] 600 1360 20 
Holding time [min] 30 120 End 
 
Due to the decrease in size (especially the thickness) for the micro-injected components from the micro-
injection with fine powder, there is no need for the sintering temperature to be so high (like 1360 °C which 
has been used in our previous sintering for the bi-material injected specimens). As a temperature about 
1250 °C [2] has been proposed in literature, so 1200 °C has been set as the maximal temperature for the 
micro-mono-injected specimens.  
Table 4 gives the details of this sintering cycle and the sintered components issued from this cycle are shown 
in figure 7 b). As the results, the sintered components obtained are free of obvious defects and 9.6% has been 
revealed as the mean shrinkage in length direction by the micro-components related to the 316L stainless 
steel feedstock loaded at 62%. 
Table 4. Sintering cycles for specimens from micro-mono-injection 
 Ramp 1 Ramp 2 Ramp 3 
Heating rate [°C/min] 5 10 -10 
Temperature [°C] 600 1200 20 
Holding time [min] 30 120 End 
 
In addition, the density after sintering stage of the micro components have been measured by the water 
displacement method (Archimede’s method), a value of 7.51 g.cm-3 has been reported as the density, so the 
relative density has reached to 95.1%. 
Besides of the shrinkages and densities of the sintered micro components, Vickers hardness tests have been 
also used to evaluate the resulting mechanical properties, an average value of HV/160 (before post-treatment 
like quenching, etc) has been observed. 
 
20ème Congrès Français de Mécanique                                                                  Besançon, 29 août au 2 septembre 2011 
  6 
 
FIG 7. a) Micro-mono-injection specimens, b) bi-material-injection specimens 
6 Conclusions 
This paper demonstrates a way to manufacture components and microparts by powder injection molding 
process. By using the proposed feedstock formulation, the feedstocks based on 316L stainless steel powder 
(5 µm and 16 µm) and copper powder have been obtained, and then injected to realize the micro injection 
and bi-material injection. During the first bi-material injection test, two 316L stainless steel feedstock with 
different powder volume loading have been injected using a two-plate mould. In the bi-material injection 
with the three-plate mould, a 316L stainless steel feedstock and a copper feedstock have been combined, and 
the interface between the two feedstocks has been well controlled. After thermal debinding stage, the 
components have been correctly sintered in a furnace and significant shrinkage has been obtained in the 
sintering stage. The bi-material components injected with two different feedstocks based on 316L stainless 
steel fine powder (5 µm) have been successfully tested from PIM process.  
REFERENCES 
 
[1] D. Checot-Moinard, C. Rigollet and P. Lourdin, Powder injection moulding PIM of feedstock based on 
hydrosoluble binder and submicronic powder to manufacture parts having micro-details, Powder Technology, 
Volume 208, Issue 2, 25 March 2011, Pages 472-479. 
[2] R.M. German and A. Bose, Injection molding of metals and ceramics, 1997, Princeton, New Jersey, USA, 
MPIF. 
[3] D.F. Heaney, T.J. Mueller and P A. Davies, Mechanical properties of metal injection moulded 316l 
stainless steel using both prealloy and master alloy techniques, Powder Metallurgy, Volume 47, Number 4, 
2004, pp. 367-373. 
[4] X. Kong, T. Barriere and J. C. Gelin, Investigations on sintering of 316L stainless steel powders and 
identification of physical parameters from coupling experiments and finite element simulations, International 
Journal of Powder Metallurgy, May/June, 2010, pp. 61-72. 
[5] L. Liu, N.H. Loh, B.Y. Tay, S.B. Tor, Y. Murakoshi and R. Maeda, “Mixing and characterisation of 
316L stainless steel feedstock for micro powder injection molding”, Materials Characterization, 54: 230-238, 
2005. 
[6] R.M. German, Sintering theory and practice, 1996, J. Wiley and Sons, New York. 
[7] C. Quinard, T. Barriere and J.C. Gelin, Development and property identification of 316L stainless steel 
feedstock for PIM and µPIM, Powder Technology, Volume 190, Issues 1-2, 5 March 2009, Pages 123-128. 
Debinded Debinded 
Sintered Injected Sintered Injected 
a) b) 
11 mm 
9.7 mm 
Debinded Sintered Injected 


Manufacturing of micro-components by powder injection moulding process

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Manufacturing of micro-components by powder injection moulding process

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