I
I I
PAPER Nr. : 72
Advances in composite manufacturing
of heli components
-Impacts on factory installations and
methods-by
Dr. Dierk Minke
M 8 8
Helicopter and Military AircraftFIFTEENTH EUROPEAN ROTORCRAFT FORUM
Advances in
compos[~manufacturing
II
Helicopter and Military Aircraft _,~--- · • I I . - ' ' -(. -,,, .,._ .. _,· .- 1
In the past, airframe manufacturers and subcontractors through-out the world have spent considerable time and financial
resources on developing advanced manufacturing facilities and techniques for composite structures. An extensive selection of technologies is avai1able today, and the approaches even within my own company differ widely according to the field of application as well as to load and performance specifications.
(Fig, 1) fig. 1 F111mawor1< and/or lrun conatruellon ~---···
_
... . ·---· Annuallll-11!11$- 2
-Encouraged by the successful introduction of advanced composites in the production of rotor blades more than 25 years ago, the evolution of airframes followed the path towards lightweight fuselages in composite design.
Today it is known that one can best save on specific weight in the case of highly loaded structures with only a few load intro-duction areas and insert bridges by using a sandwich design made of advanced composites. For medium loaded structures or fuselages with many load introduction areas, hand holes, edges etc. the box-type construction may be the more efficient composite solution. Both solutions are normally highly integrated and
sometimes even manufactured in one shot, that is to say, with a minimum of process cycles.
This brings me to a basic question on future manufacturing technology, Who or what is going to be the future workmate in the composite shop ? CFig. 2)
The future of composites manufacturing ?
3
Will it be a robot or maybe a workmate in protective clothing or just a normal craftsman ?
To answer this question, we have to analyse the manufacturing process in two aspects:
The first aspect is The second aspect is
Health impairment Cost effiency
In Planning a lay-out for a composite plant we have to be
thoroughlY aware of potential health risks involved in storing, handling and processing composite materials. (Fig. 3)
fig. 3
Health aspects of composite manufacturing ... ... .,
.. Hazardous operations & compounds:
1 Batch mixing : I Machining
&
trimming & c:::: .. I Lay - up ,~ Curing
cutting L ______ I ____ \
- - -
-I Vola lila ! Skin Reaction
l/1 compounds
~ penetrating
! ' products,
I of resins, resin & solvent , I fumes etc.
I solvents etc. I compounds I
Fine dust
11 & fibre particles
I
.. Industrial consequences:
• Consequent renunciation a. substitution of hazardous compounds
• Continuous Impairment tests & health qualification programs( i.e. new materials) • Substitution at hazardous manual operations biJ robots/machines
• Local separation of hazardous areas & individual clean-air shop installations • Consequent pushing of passive personal protective means (i.e. protective gloves)
. - - - --~--- - - '
4
Although the chemical industry strictly bans and replaces any known hazardous compound out of its mfr. program, there will still remain a considerable risk that existing or future
compounds may be declared to be health impairing, or even worse, carcinogenic.
This is partly due to the diversitY of materials with low purchase quantities in the airframe industry and to the less comprehensive impairing tests of advanced materials compared for example to the automobile industry. Once a material in
aerospace industrY has been qualified and established in a program, a complete substitution will last at least 3 years. (Fig, 4)
Impacts of advanced composites
Production rate High > 1000/ year Low < 100 I year
Lowlec:h eompoalloa
X
INon-directional f1bres Inner furnishing
I 10-50% and low performance matrix ! Advflne•d composites
~
---
I Dnectronal trbres>50%X
(glass,I<EVLAR.carbonl I low shrinking matrixAdfsnced composlln Short llbres long llbros
e.g. Epoxid-resin
In airframe mfr. + drao~bl!?lnansiOito~ble> + conhr.uoos proc""~'~
fig, 4 Therrno . . t lhtriX
9 7\ Stat• ol art:
+creep res1~tance -~~ \:o s..-~· ... ·~·~
~
+ proce$~ expenence
,~~
+rei low m~tprtce
Cowlings etc. / ' ' ~
+low c~nng tempera\. ,ill ... ,_
Thermoplut Matrix ,/ \ + unlimited stornble + non-pollutrng / I
+ reprocessable Structural parts Dynamic parts
'-0-'"""'"'d""'""' '""'"''"''""'"''
+ weld11ble "'-""'"""'"_,.,.,, .. , ... ""~c·•»•••><•-• "•
-N4 Expl!r!montal Shop. Oltobrunn 05.30.1989
The introduction of long fibre composites and epoxy based adhesives in the production of helicopters changed the
mechanical manufacturing process into a chemical and physical manufacturing process with considerable shop floor investments. These investments were to ban any remaining health risk contained
in handling advanced composites based on thermoset resin systems. Modern composites Plants usuallY consist of dislocated mfr. areas with specific clean-air or suction systems for all kinds of
5
Within the processing industrY we have learned to take the so-called •subacute• exposure to resin systems. solvents. fine dust particles etc. as serious.
Today we all know that the careless exposure to these
materials. for instance by prepreg lay-up without protective gloves. may cause allergic reactions. eczemas or even worse acute itching rash.
Such symptoms normally subside when the correct use of pro-tective measures both for the exposed operators as well as for the working areas is re-established. Special attention has to be paid to providing the operators in the composite shop with comprehensive health information and education on the correct and safe use of thermoset materials. CFig, 5)
fig' 5
Thermoplastic composites o PEEK yarns & fabrics
Carbon flbro ro-onforcod thormoplast
N5
• Stiff & non-drapable at room temperature I • (hot forming >250'C)
""'"""'""""
...
.,. ...• Commingled yarns & fabrics o Powder prepregs
Carbon IIbras
wovon with thormopl~&Hillros
• Drapable I flexible material
• No solvents • Broad goods • Preforming
= Multilayer
= Near net shape
Soorce· =MOO-Til ZTT':l 0316i
6
Although today the use of fibre reinforced thermoplasts in the helicopter industry is still in the stage of feasibility studies, we should closely observe the development of Price and performance of these nonpolluting new composites. Safer thermo-plastic materials with sufficient lay-up characteristics at room temperature may soon be available for manufacturing, The prepregs on the right side of this figure already fulfill the drapabilitY specification at room temperature and may be a promising approach to health safety in composite manufacturing.
(Fig. 6)
fig. 6
Added value shares in composite manufacturing
--
.. .,.,, .. .,,nMfr. depth I Composite structures I "' • Finished parts I Raw parts I Raw composites ' Material cultlngs Prepared materials Row materials ....
..
' ~..
.s= "..
:I «i > .., " .., .., ..: Aerospace Industry --~::::~.t 4fiir-·l -~ Streamlined lay-up • Raw parts i I • Deep-drawing , / ? /.
/ / / ...-Consolidated aoml-producta • profiles I " ' " ' : , - , prepre~gs ! I
~~~
I Aotoolm Fibre ~atorlal rosm -Composites Industry I I 2000 -·---=_j
1960 1980Exp11rlm11nlml Shop, Oltobrunn 05.30.1969
With respect to the high cost imPlications of qualification programs for advanced materials, cooperation between partners in international airframe programs as well as in the composites industry has to be as close as possible.
Both the chemistry and aerospace industries have to be aware of the increasing cost risks involved, depending on the degree of their engagement in advanced materials.
- 7
-Expensive material qualification programs as well as con-siderable plant investments for health and environment pro-tection have been the admission charge to a new technology, Now we have to make sure that this financial burden will be paid back by a cost-effective and streamlined production line. Comparing recurring costs in the aerospace industry, we must carefullY analyse the variety of materials and existing
structural design solutions in composite production. (Fig, 7)
Variety of composite materials
fig. 7
N?
··"""'''''"
& ... ,, .. , ... ,
Today, we are able to handle and process nearly any combination of different materials such as fibres, resins, prepregs, foams, honeycombs etc. Prices, however, differ up to a factor of 30 even within one material group, as does for example the group of unidirectional carbon-prepregs which is mainly dependend upon the young's modulus ! Lot size, amount of scrap material, expiration date etc. are further factors that make it difficult to compare material costs.
- 8
-Concerning mfr. costs and manhours, the complexitY and variety of design solutions in the aerospace industry make it even more difficult to judge according to a general yard stick. (Fig, 8)
Variety of composite structures
fig' 8
E!>!perlm.,nl~l Shop. Otlobrunn 05.30.1989
This figure should give a slight impression of the nearly unlimited possibilities in design and functional performances one can achieve by using advanced composites. Calculations of mfr. costs, however, depend upon the individual process chain of these components and cannot normallY be compared to each other. (Fig. 9)
fig, 9
- 9
-Cost potentials in composite manufacturing
CFC use saves min. 20% In weight lor approx. 14% more money mainly due to material costs !
Percentages
100%
AI AI-Li
ContlnuoU$ $\rGamllnlng ol mfr. procossas anumod &. roductlon of mahnlal prlcos expoctGd in futuro I +14% CFC Advanced materials
-"~
...
...
"'" Rei. cost Wetght-N9 E:.:porlmental Sllop. O!lobn.mn 05.30.1989
After this introduction, I would like to compare the production-cost calculation of identical structures both in metal <here: Aluminium alloy) and carbon fibre reinforced plastic.
According to this calculation, we have to assume that a light-weight structure made with carbon fibres is still more expensive today, mainlY due to the high material prices.
We expect, however, that the price for advanced composites will become more competitive in the next decade, partly due to the higher purchase quantities of the cooperating airframe
industries. Furthermore we may assume that material waste will be minimized bY means of better nesting programs for computer-controlled cutting machines, batch manufacturing of cuttings, modular cutting, structured Mylar films etc.
There is still the question of the portion of the recurring cost, which is a challenge for the mfr. engineer. BY this I mean the cost potentials in the composite shop or the manhour potentials.
fig, 10
10
Lay-up of composite structures - " " ' " " ' "
-""""'
...~
Single curved Double curved
- Natural path - - Wrinkles,
folds-__ ,
--~~, ... ~~.
\---;,.\"•~ e;)~ o 20-&/or 30-layups in general done by hand
e
.
'~ o Parallel mfr. tests close to structure design o lt&ratlv& culting & layup specification o Prepreg prices depend upon libra material o Layup & curing process depend upon resin type100\0 , - - - . . 0 0 . Prod<~<:l!on N1D
I
I:::::;~.:-~=l'
D~ cool Inc,... . .Structure Preparations Structure
design & Tooling fabrication
Comparo:
1
01 manufa~turrng.-·:~·.
·"
I e.g. NC-Mi!ling /
--' '
Expurlmont11l Shop, Oltobrunn 05.30.1989
The core operation of composites manufacturing is very similar to an assembly process, where different parts have to be
positioned and fixed in a given orientation.
As you probably remember, this lay-up of fabric-cuttings cannot be completelY simulated on drawing boards or design screens if the loft or surface of the composite parts is curved.
Furthermore, the draping of a flat cutting on a curved surface Will follow a natural path and will eventuallY fall in folds. Two consequences may be derived from this complex operation:
1) Cutting and lay-up drawings for composite mfr. can only be optimized by parallel mfr. tests
in a nearby experimental shop. This is also valid in spite of improved 3D-computer aided design tools. 2) Even with optimal design data, the lay-up process
of broadgood cuttings on double curved surfaces or along restricted corners will not be completely mastered by usual automatization approaches in series production. Unfortunately this lay-up work might have to be primarilY performed by hand in the near future !
fig, 11
- 11
Fibre placement In series production Sch~mat•c represental•o~ of baMC melhC>ds an.d types
1 COHT"'UO\I$ "OTATINCI .. .t.Nl>"!C
\CI\QUII<I~ .... I\ ... 1
~
I. IIIAI"-""'-""'HD("
.
--
--S'i~IG<.' :;Pl M~ndbOO~ <:>I T~tchnoloqy & ErnJ of R~·Enlor~ed PI-;IK:';I(ompo~•l~
tlf nn. D 24~
'---~---
~~-~--~--This figure shows well known methods and types of mechanical fibre Placement in composites manufacturing. What all these kinematic solutions have in common is that we have a continous
lay-up process with endless ravings or tapes and that they can be profitablY used to manufacture flat or convex parts with closed surfaces.
The support of machines, however, for the fabrication of concave lay-ups in negative-moulds, double curved structures full
of corners as well as highly integrated sandwich structures is extremely limited.
In my opinion, the lay-up work will continue to be performed by hand for most of these parts unless we succeed in developing reproducible forming processes for flat lay-ups such as hot-forming, bag moulding etc. CFig. 12)
fig, 12 - 12 -Heat forming ===;;::;;=· -.=·,::•r< -\ : Heat mandrel : ~:-,-- -.,_ ____ :.: \li'• ~ ~\;lt1~ ' \ "--·~.,-·--.--- "--·~.,-·--.---"--·~.,-·--.---==l J ~----~ .. -···~~ r~~r•l·l' ---·-__ , _____ ... -.,,,,. . :• ,\\
In contrast to forming and deep-drawing processes used on
(isotropic-) sheet metal, tne nature of remoulding flat composite lay-ups is based on a fibre-displacement process in the softened matrix. This explains why short fibre lay-ups can easilY be deep-drawn into complex surface shapes. It also explains why remoul-ding of long-fibre reinforced thermoset lay-ups is generally
limited to a preforming operation used to gain a rough formed, bi-stage part.
Endshape forming and final curing still need the autoclave process or solid mouldings with complex pressure tools.
I am afraid that this process chain will stay the usual tech-nology for the reproducible manufacturing of composite struc-tures based on long-fibre reinforced thermosets.
But even for this conventional process chain we can streamline our shop organization with respect to the many provisioning and distribution operations involved or in general in respect to indirect times. CFig. 13)
13
Build line for sandwich structures
l /Turn- \l i
' \ !(Jb!es ! '
- '-.
fig, 13 Material cycle
-· ---.- ··- . .
Cullinq & r;\oml.Jc t, dillhibulion
'll?
""'""'""'""""'
...
, ... ~ ...Curing area
..JII.-tmr;.
trimming
Here a schematic representation of a build-line for sandwich structures is shown, which allows a high division of labor and sufficient flexibilitY in the case of frequentlY changing batches. Cutting and preforming honeycombs and prepregs
is done in batches in specific mfr. areas, which are then stored, readY to be available on order call.
The next figure shows some plant photos with details of the tooling circle and material distribution area next to the cold-storage depot of prepreg cuttings. (Fig. 14)
- 14
-Build-line facilities for series production of composites
fig, 14
I should emphasize that this kind of investment only pays off if a reasonable series production of composites components is taken as a basis. New shoP lay-outs, however, can be planned according to the expected logistical demands.
The last cost potential I would like to mention here concerns the aspect of standardization or specification of part families as well as functional modules. CFig. 15)
fig, 15
- 15
-Modular techniques in composite manufacturing
--...
-
...E.g. CFC fabrication of AIRBUS vertical stabilizer
Muter model Ftoxtble NC mould
~
CuUIMQ•
•
\curod Module Sholl
\ \
\ \
\
"" Exp!trlm~tnlal Shop. Otlobnmn 05.30.1989
I assume that we all know the modular or unit construction principle very well from manY designs of structures and equipment both in aerospace products as well as in tooling. Regarding the variety of composite structures and toolings, however, I feel that this ide a shou I d be taken up again by the production engineers.
A consistent translation of this Principle into a composites structure is, for instance, the carbon fibre structure of the Airbus vertical stabilizer.
In this case, the frame-stringer structure was divided into modular structural boxes, which can be manufactured separately and then bonded together in one shot. The economic benefits are mainly due to the limitation of cutting shapes, tool-modules, shop operations etc. while the production lead-time can be reduced by the high degree of parallel pre-fabrication of structural modules.
- 16
-Before I run out of time, I.et me briefly come back to the opening question of the future employee in the composite
shop. Advanced composite materials represent nearly unlimited possibilities in the design of lightweight structures.
The variety and complexitY of today's aerospace structures is a reflection of the many degrees of freedom in design that the airframe engineers have been offered by these materials.
Even the hard-line advocates of standardization won't argue about the benefits of individual lightweight and functional designs. They may, however, suggest that, if possible, a minor cut in performance or weight can be profitable for the series production in the sense that the limitation to 90 % of the technical optimum may eventuallY save 20 up 25% of the manufacturing cost.
In any case, in the near future, composites shop work will remain a skilled manual-craft, at least in the core operation, that is to say, the lay-up of broadgood cuttings.
The peripheral areas, however, ranging from cutting to non-destructive testing, will be consistently streamlined and
automated. Hopefully, new materials will allow us to throw away the protective gloves and substitute manual draping with forming processes based on flat lay-ups, or even with consolidated
profiles and semi products. ·
Dr. D. Minke
Experimental Shop MBB - Ottobrunn
