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It is known that a remarkable difference from sintering and
posttreatment processes will result from different powder
materials used in SLS process. Unlike the pretext investiga-
tions, polymer powder mixed composite elemental metal
powders were used for forming materials in this work, which
had been proven to be flexible and convenient in literature [6].
This work is concerned mainly on how the green part was
formed with polymer powder mixed with composite elemental
metal powders, the influences fromheat transmission when the
powders were heated by laser beam, the removal of redundant
loose powders from the cooling channels, the detailed
infiltration method, the microstructure of infiltrated materials,
and the injection plastic part generated by the final mold.
2 Experimental
2.1 Materials
Epoxy powders mixed with composite elemental metal
powders presented in literature [6] were chosen as SLS-
forming powders in this work. The content of epoxy in the
mixed powders was 4%. The composite elemental metal
powders were composed of iron, copper, nickel, and carbon
as shown in Table 1. Bronze powders were chosen for
infiltrating materials in the posttreatment process.2.2 Experiment path
Elemental metal powders and epoxy powders weremixed in a
three-dimensional motional blending machine initially. Then
the composite powders were sintered in an SLS system
developed by Huazhong University of Science and Technol-
ogy. According to dimensional and structural characteristics
of the insert, forming path and process parameters were
designed to guarantee the precision and strength of the SLS
green insert. Two cubic green parts (120 mm×20 mm×
15mm)werealsoformedtobeemployedascomparative
specimens with the inserts. The green inserts and the cubic
parts were both heated at 80°C/1 h for strength enhancement
in a furnace. Then, they were infiltrated by bronze melt under
the protection of H2 in a graphite cabin after they had been
debinded and sintered at 1,000°C/1 h. The infiltrating
temperature was set at 1,080°C and then, the infiltrated
inserts were cooled naturally in the furnace. Debinding
process followed what was expressed in literature 6. The
infiltrated inserts and one of the cubic parts were treated
following the process listed in Table 2, and then, two groups
of tensile test samples (Fig. 1) made from the cubic parts
before and after thermal treatment were processed. There
were five tensile test samples in each group, and the final test
results were the mean value of five samples in each group.
SEM samples made of the cubic parts before and after
thermal treatment were also produced to analyze the
variation of alloys microstructures.Polymer powders are heated by laser beam in the composite
powders, and they turn into viscous liquid to adhere other
hard powders around them together. It is possible for the
powders which do not belong to scanning cross-sections to
be softened owing to the heat accumulation and transmis-
sion within the powders during sintering process. There-
fore, loose powders inside of the cooling channels are liable
to be heated to stick to the channels' wall. This will trouble
the removal of powder and further affect the precision of
the green inserts under such conditions. Thermal accumu-
lations and transmissions are affected by the positionrelationship between the channel structure and the laser
beam, which is decided by the forming path.
Figure 3 shows the heat transmission between the
successive layers. qSG in Fig. 3 is heat flux density of
convection and qSS is heat flux density of conduction. T1 is
the temperature after laser energy has been absorbed by a