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ASSIGNMENT # 3
AEAS 6173: Aerospace Materials Processing and Performance
30 September 2020
QUESTION 1:
What is the difference between rapid prototype and additive manufacturing? What are the key aspects
of rapid prototyping and explain the need for rapid prototyping? Explain with suitable example.
ANSWER:
1.
Rapid prototyping refers in fact to the fast manufacture of prototypes for different purposes
including ergonomic and visual trials, assessment of functional performance, supporting parts to other
processes. In many cases, such rapid prototypes are also obtained by means of high-speed computer
numerical control machining or using rapid form copying processes, after obtaining initial models.
Additive manufacture makes reference to any manufacturing technology using layer-by-layer or dropby-drop processes. In many cases, these AMTs are used for obtaining prototypes, as they are not
normally oriented towards production of large series. However, in recent years, more and more AMTs
are being used for final parts, especially when the geometries are complex or for the incorporation of
special functionalities.
a.
the one difference is the perspective on the process: Basically, the way the part is
generated can be the same, using the same technology and machine in both cases, however,
rapid prototyping as an older term is focused on producing a part that is not meant for service
application, but as a prototype. As such, it may or may not have all the properties and thus
performance characteristics of the final part of which it is a model. Additive manufacturing on
the other hand underlines the use of such methods as actual production processes, i.e. the parts
generated are meant for a true product life cycle.
b.
Additive manufacturing is a more general term than rapid prototyping, as it describes
any technology that generates parts or merely structures by adding, drop by drop or layer by
layer, material. Hence for example stereolithography again would seem to fit both in the
additive manufacturing and the rapid prototyping category. Inkjet printing of strain gauges, on
the other hand, is clearly additive manufacturing.
2.
Some key aspects of Rapid Prototyping are described below:
a.
The most important benefit of rapid prototyping is it allows to thoroughly test the
products early on. One can create multiple prototypes in one go, detect some design flaws in
the designs, and create more refined ones in a short amount of time. Detecting functional and
design flaws early in the product can prevent huge costs later on if flaws are identified during
final production. Nowadays with 3D printing, one can also replicate inner mechanical parts of
the product with finer details. This helps to work on both the product’s aesthetics and
functionality.
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b.
3D printing has been there since the 1980s. However, due to its huge cost and heavy
machinery, it was only affordable for big companies back then. But that’s not the case today.
Due to the rapid advancement in technology, 3D printers have become much affordable and
sport a compact design. Buying a 3D printer has become so convenient that many tech
enthusiasts own one in their home. For a business, 3D printers come with a variety of functions
to suit different requirements of products such as aesthetics, complexity, and mechanics. Also,
unlike CNC machines which require special expertise to operate it, 3D printing can be done by
following simple instructions. If one has a decent knowledge of CAD and product designing,
operating 3D printers is quite easy.
c.
Rapid prototyping tools simplify the process of generating new product ideas by
allowing frequent creation of visual replicas. Having a solid 3-dimensional replica in front helps
exploring new ideas and rework on them with ease. One can work on the product step-by-step
by creating the initial prototype and add the changes until one is satisfied with the end results.
d.
Although prototyping is an important process in product design, it is considered as a
bottleneck. It takes a lot of time and effort to come up with a brand-new product idea and turn
it into reality. The most tedious part of product designing is working on the visuals and intricate
details of the product. This is where rapid prototyping shines. It significantly reduces the time
taken during prototyping and redesigning phase of product design. Also, tweaking the product
to perfection early on speed up the final manufacturing process.
QUESTION 2:
Discuss the evolution of RP systems indicating the history and their growth rate in the Aircraft industry.
What is the most dominant surface effect caused by RP processes? Outline how can this effect be
minimized?
ANSWER:
1.
Due to the pressure of international competition and market globalization in the 21 st century,
there continues to be strong driving forces in the aircraft industry to compete effectively by reducing
manufacturing times and cost while assuming high quality product and service however convectional
machining methods is characterized by long lead time and high cost. It cannot meet the demand for
rapid product development.
For the last 10 years, the aerospace industry has been one of the top sectors leading the RP market (Figs.
2.1 and 2.2). Today, 18.2% of the revenue in the RP industry is received from the aerospace industry.
The aerospace sector is also the fastest growing sector, showing an annual increase of 1.6% in 2016,
followed by motor vehicles with a growth of 1.0%. The revenues from the RP are estimated at $2.7
billion in 2016 (growth of 12.9% with respect to 2015) and are expected to surpass $100 billion within
the next two decades, mostly in the aerospace industry.
[Source: A. Wohlers, Wohlers Report 2016, 3D Printing and Additive Manufacturing State of the
Industry, Annual Worldwide Progress Report, Associates Wohlers, 2016]
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The history of the rapid prototyping in aircraft industry can be summarized below:
a.
The market for RP parts in aerospace can be divided into metallic and nonmetallic
(mostly polymer) components, which are generally related to critical and noncritical aircraft
parts, respectively. Boeing and Bell Helicopter started using polymer AM parts for
nonstructural components in the mid-1990s. In March 2015, Boeing fabricated more than 200
unique parts for 10 different aircraft using RP technologies. By that time, more than 20,000
nonmetallic RP parts were installed in airplanes. [Caujolle et al. 2017]
b.
Today, Boeing has installed tens of thousands of AM parts on 16 commercial and
military aircraft. In 2017, Boeing started using at least four AM titanium-alloy parts to produce
its 787 Dreamliner aircraft with near-future plans to manufacture almost 1000 parts via AM to
save $2 million to $3 million per airplane. [Mearian et al. 2017]
c.
Airbus is also a main player in AM. It has installed AM metal brackets and bleed pipes
on the Airbus A320neo and the A350 XWB test aircraft. It also has a multiyear cooperative
research agreement with Arconic to produce large-scale AM airframe components (1 m in
length). NASA, the European Space Agency, and SpaceX are exploring the use of AM igniters,
injectors, and combustion chambers on their rocket engines. Honeywell Aerospace, Lockheed
Martin, and Northrop Grumman are also important users of AM. [BusinessWire 2017]
[Source:
L. Mearian, Boeing Turns to 3D-Printed Parts to Save Millions on its 787 Dreamliner. April 11, 2017.
Available from: ,https://www.computerworld.com/article/3188899/3dprinting/boeing-turns-to-3dprinted-parts-to-save-millions-on-its-787-dreamliner.html..
M. Caujolle, First Titanium 3D-Printed Part Installed Into Serial Production Aircraft. Newsroom 2017,
September
13,
2017.
Available
from:
,http://www.airbus.com/
newsroom/pressreleases/en/2017/09/first-titanium-3d-printed-part-installed-into-serialproduction-.html..
BusinessWire, in: BusinessWire (Ed.), Arconic, Airbus to Advance 3D Printing for Aerospace Under
Multi-Year Cooperative Research Agreement To Produce, Qualify Large-Scale 3D Printed Airbus
Airframe Components, BusinessWire, New York and Frankfurt, 2017]
2.
The most dominant surface effect caused by RP processes is called Stair stepping process.
a.
The slicing process produces a set of horizontal cross sections and, in a horizontal
plane, each of these sections conforms to the geometry of the original Computer Aided Design
(CAD) model to a degree of accuracy which is really significant to the entire process. However,
each layer is of continuous cross section through its thickness (i.e. in the Z-direction), and
therefore parts cannot accurately conform to the CAD geometry in the vertical plane.
b.
Suppose a cylinder has been built with its circular cross section parallel to the slice
axis, i.e. perpendicular to the layers. If any single part layer is considered it can be seen that the
slicing software has produced a layer, the top surface of which conforms precisely to the CAD
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geometry. However, because the layer is rectangular in cross section it cannot conform to the
curve surface across its entire thickness, the largest deviation at its bottom surface. This result
in the stepped effect shown which has been termed the ``stair-stepping phenomenon''.
c.
Researchers seek to create a method to 3D print nonplanar layers on top of planar layers
in any object. The team achieved its goal by adjusting open-source slicing software Slic3r.
Adding the ability to print nonplanar surfaces to an open-source slicer increase the usability
and provides a general-purpose approach. The algorithm in the study is specifically developed
for the Ultimaker 2. Because of the new algorithm, the areas that should be printed with
nonplanar are detected automatically. The algorithm also checks for possible collisions while
printing. Collision prevention sees to it that the printhead does not crash into previously printed
structures while printing nonplanar layers.
QUESTION 3:
Which part of an aircraft can most benefit from structural health monitoring (SHM) system? Is it the
fuselage, wings, landing gear, flaps, rudder, elevator, vertical stabilizer or another component? Why is
this component the prime candidate? Explain briefly.?
ANSWER:
1.
Structural maintenance of civil aviation aircraft is currently based on scheduled maintenance,
where the maintenance interval is determined based on safety and reliability. However, the current
practice of scheduled maintenance is expensive for airlines. The inspection and maintenance cost
accounts for more than 27% of the total lifecycle cost of an aircraft. There are ongoing research efforts
to reduce the maintenance cost by utilizing condition-based maintenance (CBM) where the health status
of the system is continuously monitored and maintenance is requested when the safety of the system is
threatened. The condition of the structure is monitored using structural health monitoring (SHM)
techniques.
2.
The SHM system is used to detect damage and to determine the size and location of damage.
Since the SHM system use installed sensors, it is unnecessary to remove internal surrounding structures
for inspection. In addition to detecting damage, the SHM can be used to predict the future behavior of
detected damage based on damage data at past inspections, which is called prognostics. This makes it
possible to predict when the existing damage threaten the safety of the system and repair them before
that. Therefore, the scheduled maintenance is often referred to as preventive maintenance, while CBM
as predictive maintenance. With prognostics information, it is possible that airlines and MRO
(maintenance, repair and overhaul) can schedule and prepare for maintenance in advance..
3.
Parts that are easy to access can't lower maintenance costs as much as difficult to
reach structures. Since we are trying to lower the cost without compromising safety of the procedures,
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the logical step is to put a monitor on the parts expected to show signs of fatigue first and for which
fatigue is well understood. We want agreement with the model, proving that we can design the sensor,
not that the sensor happened to find or not find crack growth.
Based on these considerations, I think fuselage is the prime candidate that can benefit from structural
health monitoring (SHM) system.
The fuselage is a semi-monocoque structure made up of skin to carry cabin pressure (tension) and shear
loads, longitudinal stringers or longerons to carry the longitudinal tension and compression loads,
circumferential frames to maintain the fuselage shape and redistribute loads into the skin, and bulkheads
to carry concentrated loads. In high-performance military aircraft, thick bulkheads are used rather than
frames. The fuselage can be divided into three areas: crown, sides and bottom. Predominant loads during
flight are tension in the crown, shear in the sides and compression in the bottom. These loads are caused
by bending of the fuselage due to loading of the wings during flight and by cabin pressure. Taxiing
causes compression in the top and tension in the bottom, however these stresses are less than the inflight stresses. Strength, Young’s modulus, fatigue initiation, fatigue crack growth, fracture toughness
and corrosion are all important, but fracture toughness is often the limiting design consideration. In the
fuselage, the Compression cycles are a different fatigue mechanism than time spent in the air, requiring
modelling and checks. For that SHM can play a big role in case of fuselage.