JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013 - 55

Fig. 7: Comparison of Windform® XT to PA6 BG-35 injection-moulded plastic

structure (Figure 6).
Studies also showed that Windform®
XT performs in a predictable manner.
The material was compared to injection-moulded production materials to
determine how it would react when
exposed to extended temperature
cycling. Having a predictable material
is important when examining possible
failure modes for design studies.
The chart in Figure 7, which compares the evolution of tensile strength
between Windform XT and PA6 BG35, shows that Windform® XT is a good
candidate for additive manufacturing
for the CubeSat application.

Construction of the bus
and propulsion modules
Windform® XT is used to build parts
using the laser sintering process. This
process comprises several steps, described in Figure 8.
Laser sintering is a powder-based additive manufacturing method that consists

Fig. 8: Illustration of the LS process

in building up a part with each layer of
powder being sintered separately by a
laser. As each layer is sintered, it slowly
constructs the part step by step. Various
material grades are used, each with their
own characteristics, but all are used the
same way in the LS machine.
The LS machine basically consists of
three powder beds and a laser. Two of
the powder beds hold the feed powder
and the third one holds the part. The
part bed is in the middle of the beds
with the laser acting directly perpendicular to this bed. A roller is used to push
the layers of powder over the part bed
and all three beds have their own heater
source. The process itself is very simple
and repeatable.
The part building process is a repeatable
three-step process:
- Step 1: A roller is positioned beside
one of the feed beds. This feed bed then
raises a set amount of powder (usually <
0.1 mm) and the roller pushes the raised
powder across, covering the part bed

Main advantages of Windform® XT
- Passes outgas screening (ASTM E-595).
- Produced in a manner that makes it dense.
- Can be easily machined using conventional methods.
- Good heat deflection temperature (HDT) relative to other RP materials (above 170°C).
- The base polyamide material has been proven to meet performance needs of other aerospace applications.
- Material batches are quality controlled, each coming with a certificate of conformance (COC).
- Build volume of SLS system fits well with CubeSat
applications= 381 x 330 x 457 mm.
- Can be plated without the need for sealing agents.

with a powder layer.
- Step 2: With the layer of powder present,
the laser starts to trace out the desired
shape of the part in the powder, melting the
powder as it contacts the surface.
- Step 3: Once this is done, the part bed
drops down enough for the set amount of
powder and the process continues from the
opposite side, with the other feed bed raising the powder and the roller distributing
another layer of it over the part bed, and
the laser again traces the shape (Figure 9).

Fig. 9: Steps of the LS process

The part is built up in slices, with each layer
of powder representing a single slice. As the
laser melts the powder, the layers fuse together to grow a solid part. Since the part is
made up in layers, very complex shapes and
design can be manufactured that would
otherwise be impossible by conventional
means. Windform® XT uses microfibres
as a reinforcing system and is similar to
carbon lay-up techniques in that it is nonisotropic. Similar design rules are applied
when building parts to take advantage of
the increased strength in one direction over
the other resulting from the build process.
In the case of the RAMPART bus, the decision was made to produce the part with the

No78 January - February 2013

/ jec composites magazine 55

JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013