November 2010
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Thermoplastics | design feature
Jac Gofers of Promolding describes the challenges that were met in the design, development and manufacturing of an innovative full polymer aircraft catering trolley
Plastic makes its mark in aircraft catering The project
later advances targeted on weight saving led to the use
Airlines are
The design of the traditional aluminium panel aircraft
of aluminium sandwich panels. The focus was on
expected to
trolley had remained unchanged for more than 50 years,
making the aluminium stronger so that the panels
increasingly
despite airlines’ requests for trolleys with less weight
could be constructed of thinner walled sheets. This
switch from
and less maintenance. In 2006, Helm and Lambrecht
reduced the weight to 22–23 kg per cart. Compared with
metal to
illustrated the importance of weight saving. They
the previous weight of 35 kg, this was a good result, but
thermoplastics
calculated that 100 kg less weight saves 4.5 million
not the limit of what can be achieved.
litres of fuel and 1 million tonnes of CO2 over the
To decrease the mass yet more, there are basically
lifetime of an aircraft. Product development and
two options: make the walls even thinner or change the
plastics processing company, Promolding then
materials. Both approaches were tried. Making walls
undertook a complete redesign; its concept was an
thinner resulted in lighter trolleys, but they were no
innovative thermoplastic polymer trolley that would
longer robust. It is easy to dent the thin-walled panels
save weight and avoid extensive maintenance. Three
and once dented, the trolleys are less appealing or, even
years later, the product was enthusiastically received in
worse, no longer usable. There is a limit to how far you
the market. This article charts the design and manufac-
can go with thinning the sheets, and foil was not doing
turing journey to this successful outcome.
the job.
From massive aluminium to aluminium-foil panels
Trials for plastic
The establishment of the commercial aircraft industry
combining aluminium with thermoset sandwich panels.
created an opportunity for specialised companies to
The aluminium panels were exchanged for thermoset
design a standardised trolley that would serve meals
panels without modifying the design. This resulted in
and beverages onboard in a convenient way. The
lighter, more expensive trolleys, but the drawback was
development of these trolleys stabilised with carts
that the panels were hard to repair.
1
typically made from thick-walled aluminium panels,
In other cases, companies made hybrid trolleys,
Another issue occurred when those trolleys under-
which meant that each cart weighs approximately 35 kg.
went certification tests. Because the design had not
Although some airlines still use these heavy trolleys,
changed, the door locking mechanism still functioned on
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November 2010 | injection world
19
design feature | Thermoplastics
The complete design of
ance and toughness. PEI performs better for stiffness
the thermoplastic
and strength. The designers chose PPSU (Radel R7700)
trolley
made by Solvay Advanced Polymers rather than PEI (Ultem) because l modulus and yield stress are not significantly different l the stiffness and strength of the product can be improved by a clever design l the durability and image of the polymer trolley must under no circumstances be limited by the possibility of fracture due to impact or a lack of chemical resistance l improvements in chemical resistance and impact properties cannot be reached by modifications to the design. Once the material was selected, the company started to design the trolley based on the properties of PPSU. The task was divided into body design and door design; both projects ran in parallel and both ended in a patentable design. For the body, the extremely high loads and test demands led to a double-walled rectangular extruded tube with inner ribs in a configuration determined using finite element analysis. In this way, the tray and drawer holders could be extruded in the same process in one part. For the door, the main challenge was the innovation l dimensions are according ATLAS standard
of the locking mechanism. Instead of the existing
l inner space is to have a minimum of seven standard
construction of three interconnecting points where the
drawers
local tensions would make the plastic fail, it was
l the maximum allowable load is 100 kg, which
necessary to spread the load over more points. This
includes the weight of the trolley.
ended up in a multiple 14-point interconnecting slider
Authorities bound:
that is operated through an ergonomically located grip
l the trolley is to meet all air safety regulations,
handle on the left top of the door front.
particularly those regarding strength B flammability,
After the design of those two important components,
smoke, toxicity and heat release and fire containment.
the focus turned to the hinge of the door; the door-
Manufacturing bound:
frame, which has to interface with the extruded body;
l the trolley is to be recyclable, cradle-to-cradle
and the assembly of all parts and components. This
l be mass producible
ended in the completed design that is shown above.
l be low maintenance. This POD placed extremely high demands on the
During the design phase, Promolding realised that the
and choice of materials. The company’s research and
equipment required to extrude and inject these large
development department intensively researched
parts with thin walls (10 mm) was not available within
materials applicable for these applications. It reached
the company. After a search for outside manufacturing
the conclusion that basically only two types of polymer
expertise, it partnered with Bemis Contracts Group
would be candidates: PEI (Ultem 9075/9085) and PPSU
(Sheboygan Falls, Wisconsin, USA), which had the
(Radel R7700). The choice between PEI and PPSU was
facilities and the courage to take on such a demanding
based on four factors:
task. When entering into discussions about the work
l elastic modulus (stiffness)
with the Bemis engineers, it became clear that
l strength (yield stress)
extrusion of the body as one part (a rectangular tube)
l chemical resistance
was too risky. Promolding had to redesign this part into
l toughness/impact properties.
two identical C-shaped parts that were to connect on
PPSU performs better in terms of chemical resist22
Production is the hard part
construction and therefore on production technology
injection world | November 2010
bottom and top. In that way, manufacture was challengwww.injectionworld.com
design feature | Thermoplastics
Fill time = 5.128(s)
Last but not least In the aerospace industry, an important step is to certify the product with the regulations and this is a time consuming, complex and costly process. It took more than one year to fulfil all tests and obtain feedback from the authorities, but the result was the first thermoplastic aircraft trolley in the world that complies with the most rigorous tests in the regulations. It is capable of carrying 135 kg of contents and withstanding all forces. This certification proves that the design and the production technology delivered a robust product that meets requirements for l lightweight l cradle-to-cradle recyclability
Scale (10 in)
Using 10 drop gates, the flow is fairly balanced
l high impact resistance (not sensitive to denting) l ergonomics l low maintenance. In addition, this plastic trolley can carry radio frequency identification (RFID) tags, which an alumini-
ing, but less risky. The other parts for extrusion, that is,
um trolley cannot. This feature was not a design
the top tray, door filler panel and connecting H-profile
parameter, but during the design and pre-production
were not difficult and did not need any modifications.
phase it became an increasingly important attribute.
Making the extrusion die proved challenging. An
Airlines want to improve their catering logistics and
extrusion die for PPSU RADEL R7700 [for these dimen-
control their assets and RFID is indispensable for this.
sions (90 cm wide, legs of 14 cm legs, double walls with
Moreover, because it is possible with RFID to track and
wall thickness of 1 mm and inner ribs of 0.5 mm) had
trace the trolleys all over the world (assuming that the
never been made. It presented Bemis and the mould
necessary infrastructure is installed), leasing compa-
maker with an extremely challenging job, which they
nies are interested in leasing these plastic trolleys to
completed with a new mould concept in due time. The
the airlines, which offers airlines an option to exchange
surprises came only when the mould was fired for the
capital expenses with operating costs.
first time. Although the melt came out flowing in a well
The design and manufacture of a thermoplastic
divided and balanced way, the material set so fast, that
aircraft catering trolley was not an easy project. The
the calibrator had to be placed extremely close to the die,
whole team ran into technical challenges that were not
in fact, a mere half an inch away. After the first runs, it
foreseen. The undertaking shows unique co-operation
took the team more than one year to finalise the set-up
between developer, manufacturer, raw material supplier
for reproducible and stable processing conditions with
and market players. With a joint effort the project
this extremely difficult to process material. Thanks to
succeeded in bringing innovation to a conservative
help from Solvay, the process of subsequential runs was
market.
taken to the final result: an extruded PPSU part to design specification. For the door, the locking mechanism, the hinge and
We dare to say that this will be the turning point for airlines, which will increasingly move from metal to thermoplastics. The first proof of this is the development
the interfacing to the body, Promolding designed two
of an innovative new galley that Airbus has created,
injection moulded parts. Although these seemed to
known as SPICE. Promolding has been asked to develop
cause less trouble than the extrusion parts, there were
the plastic boxes that are to be applied in this concept.
still some interesting challenges. Because of the long
http://videos.airbus.com/video/iLyROoaf89yy.html
flow length at wall thicknesses of less than 1 mm at
Jac W.C.A. Gofers is managing director of Promolding, based in The Netherlands, â?™ www.promolding.nl
some spots, the company found in the mould flow simulations that it had to take care of a considerable amount of runners and gates (Figure 6). There were shorts in filling, air traps, burning spots and too many
24
Reference
visible weld lines, which eventually led to the number of
1. H. Helm H. and U. Lambrecht, The Potential Contribution of
gates, as shown. Assistance from Solvay and Bemis
Light Weighting to Reduce Transport Energy Consumption,
resulted in control of the injection moulding process.
International Journal of Lifecycle Assessment (2006).
injection world | November 2010
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