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Abstract
Research was conducted on additive technology to manufacture large parts with complex
internal passage ways. The research uncovered novel control systems that have the potential to
additively manufacture large parts with internal complex passageways. These control systems that
are mentioned in this paper are Layer-to-Layer Temperature Control and Layer-to-Layer Height
Control. These controls systems come from an additive methodthat is knownas LMD (Laser Metal
Deposition). The control systems were analyzed on how will there potentials can lead the way for
large parts with complex internal passageways to be made. The potential of combining the
methodologies were discussed on how they could lead to improvements. One concern that was
mentioned was the material property effects of the methodologies. The concern was analyzed by
using Ni-Ti phase diagram and discussing how the methodologies could elevate the concerns.
Finally in two to three decades these novel control systems can be seen in the LMD process.

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Intro
The purpose of the research is to find additive manufacturing that is being researched and
developed that could manufacture the combustor of the jet engine. The most efficient way to
additively manufacture large parts is the LMD process (Laser Metal Deposition). Another
method that is similar to the LMD process is EBAM (Electron Beam Additive Manufacturing).
Instead of a laser this method uses an Electron beam and wire feed system. These Technologies
are available and used in industry. These methods have limitations that affect almost every
aspects of the part that comes from them.
These limitations are variations with the size of track and layers; non-consistent cooling
rates that lead to inconstancies of grain size; limits on the materials that could be used in the process
due to phase properties. They mean the grain sizes and track and layer are not the same through
out the part. Affects the material property of the part from the strength to temperature resistance
and various properties. The material that could be only be used can limit performance of the part.
What makes them significance is when there is a part that calls for complex passageways like a
combustor for the jet engine the variations in size of the track and layers could affect the flow of
air and fuel. Since the combustor is also a structural component and a thermal barrier it has to
withstand thermal and structural loading. The overall weight to performance ratio could be affected
to due to the constraints of materials used. Which make these technologies impractical to
manufacture a combustion section of the jet engine in one part. Besides being impractical to deal
with complex passageways there are researched improvements to potentially have those large parts
to be made with these additive methods.
The methods that allow for the possibilities of large parts with complex internal
passageways are, melt pool temperature control, and layer to height control. Melt pool temperature
control works by controlling the melt pool temperature in each layer. This results in reduced width
variation while shrinking the size of the grain; improving strength. The other method only controls
height of the layer but not the grain size of the material. The only improvement is dimensional
precision improved due to reduced variation of height. If these improvements where to be
combined width and height variations could improve. The description of these improvements will
explain by their inner workings, to how their inner workings result in improvements.

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Melt Pool temperature Control:
Melt Pool Temperature Control operates by adjusting the laser power profile between
layers based on temperature reference. The process to achieve this is by first measuring the height
profile between different layers. Then the melt pool temperature is measured by using a
temperature sensor. (As shown in Figure 1) The measured height profile and temperature is used
to identify the model parameters based on particle swarm optimization (PSO). Lastly the laser
power profile is generated with respects to the reference melt pool temperature of the next layer.
With these inner workings there will be improvements in the width in the vertical and horizontal
axis in the track.
Figure 1; LMD process using melt pool temperature control (Melt Pool Temperature Control
for Laser Metal Deposition Processes—Part II: Layer-to-Layer Temperature Control) [Landers
09]
The way this researched improvement will lead to improvements in precision is the use of
PSO algorithm. The PSO algorithm is used to approximate convection coefficient and powder
catchment efficiency. By being able to approximate convection coefficient and powder catchment
efficiency from the recorded temperature and height measurements. The ILC algorithm will be
able to construct a laser profile for the next layer. With these processes, as the next set of layers
are formed, the tracks become more uniform. Due to the uniformity of the tracks, the exterior
surface can potentially require little to no machining. The potential for large parts with complex
internal passageways to made using the LMD process grows.

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Layer to Height Control:
Layer to Height Control adjust the mass flow rate of the powder layer by layer. The process
to adjust the mass flow rate for height starts with the measurement of temperature and height of
the layers. (As shown in Figure 2) The layers are measured by laser displacement, temperature
measured from a sensor. They are then used as inputs for the PSO algorithm to estimate model
parameters for heat loss. The process was done because track geometry is dependent on
temperature and powder flow rate. With the inputs from the PSO, the ILC would be able to set the
mass flow rate for the next layer. According to Dr. Landers, the methodology only improves track
width variation in the vertical direction.
Figure 2: LMD process using Layer to Height Methodology (Layer-to-Layer Height Control
for Laser Metal Deposition Process) [Landers09]
The way this methodology will improve the width variation in a single axis with in the
inner workings starts with inputs from the laser displacement censor and temperature sensor and
previous powder flow rate. With these inputs an evolutionary algorithm PSO will be able to
estimate the heat loss in the track. With evolutionary algorithm the approximations for the heat
loss will have a high fidelity. With the high Fidelity of the heat loss the ILC would be able
efficiently set the powder flow rate for the layer. With these elements, there will be improvements
in making the layers and track more uniform.

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Height Control and melt pool temperature control:
Combining the two methodologies may not have been tested before; however there could
be possibilities for better results for the layers and track. The methodology of controlling the melt
pool temperature does make the tracks in the LMD process more uniform, if layer height
methodology where to be introduced then there might me a possibility that the track geometry
could become more controlled. With the track geometry controlled the outer surface of the part
will need little to no machining in the post process. The reason for the possibilities comes from the
facts of the researched methodologies.
According to Dr. Landers Layer height control provided slight improvement in the width
in the vertical direction. The reason for this improvement was due to the mass flow rate of the
powder being controlled. If the mass flow rate and laser power where be controlled at the same
time the results will be is the layer and track geometry can be controlled more easily. The other
factor for the more controlled track geometry is, according to Dr. Landers the melt pool
temperature control methodology results in uniform width both the vertical and horizontal. Due
the fact of that element being observed, combining the methodologies could result in more
controlled track geometry.
Materiel Property effects from the methods:
Despite these cutting edge control methodologies, materiel properties are just as important,
due to the fact that the researched methodologies used H13 tool steel powder material to
experiment with. In this report, titanium nickel alloys will be used as an example. According to a
phase diagram found in Murray, NI-Ti Phase Diagrams of Binary Nickel Alloys in figure 3, for high
temperature applications a weight percent less than 5% is needed. That shows the margin of error
has to be pretty small in order to obtain high temperature performance of the alloy. In order for the
researched methods to result in materiel for high temp application, materiel is alloyed and then
grinded down to powder. By doing that process, when melted by the laser then cooled down, the
materiel will still be able to maintain high temperature capabilities. Besides high temperature
properties the combustor of the jet engine is also a structural component, the materiel also has to
be able to take structural loads.

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Figure 3 Phase diagrams of Nickel-Titanium alloys (NI-Ti Phase Diagrams of Binary Nickel
Alloys, 1991, Fig 1)
One major thing that decides the structural strength, is the crystal structure of the metal
material. What is possible is that the metal alloy would possess high temperature capabilities
except; the structural strength could be poor. Given these methodologies, questions arise if they
can yield materiel that can have high temperature abilities and retain structural strength at the same
time. According to figure 3 for the best high temperature application the alloy on the alpha to beta
phase would be one the best choices. According to a Progress in Materiel Science article, titanium
nickel alloys are known to change from martensitic to austenitic depending on the temperature.
That means this alloy could be used in the combustor of the jet engine only if the size of its crystal
grains where to be fine. Given the process of melt pool temperature control, the crystal structure
of the materiel would be finer due to lower melt pool temperature. Without this methodology the
grain size and mechanical properties may not be the same throughout the whole part. In the end
melt pool temperature control could ensure the mechanical properties of a component.

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Conclusions:
The methodologies to help make large parts with complex internal passageways like the
combustor of the jet engine are still in development. They may not be seen in industry for two to
three decades down the line. The reason why, is the learning algorithms may not be practical in
additive manufacturing due to limitations in computing power and the economics of computing
power. Also the conducted research on these novel control systems does not account for most
industrial conditions and have yet to be researched. Given these limitations there would not be
additively manufactured combustors in single piece for the next couple decades. The only parts of
the combustor that are currently additively manufactured are fuel injectors for the LEAP engine.
The LMD process was not used; instead powder bed additive manufacturing was used. At the end
of day parts with complex internal passageways that are large in volume could be possibly be made
by additive manufacturing.

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Reference
1. Landers. Melt Pool Temperature Control for Laser Metal Deposition Processes—Part II:
Layer-to-Layer Temperature Control (2009).
2. Landers. Layer-to-Layer Height Control for Laser Metal Deposition Process (2009).
3. NI-Ti Phase Diagrams of Binary Nickel Alloys, Murry, 1991, p 342-353
4. K.Otsuka, X.Ren. Physical metallurgy of Ti–Ni-based shape memory alloys (2004).
5. Figure 1
Layer-to-layer temperature controller structure
6. Figure 2
Laser metal deposition height controller structure
7. Figure 3
Assessed Ti-Ni Phase Diagram