Filament winding of complex components

Filament winding of complex components

S PECIAL FEATURE Filament winding of complex components F i l a m e n t w i n d i n g o f non-axisymmetric s h a p e s is fact n o t f i c t i o n s...

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Filament winding of complex components F i l a m e n t w i n d i n g o f non-axisymmetric s h a p e s is fact n o t f i c t i o n say A n d r e w Priestley and V. Middleton. CAD t e c h n i q u e s e n a b l e e n g i n e e r s to have a high degree o f c o n t r o l over their c o m p o s i t e structures. Where a u t o m a t e d p r o d u c t i o n p r o c e s s e s s u c h as f i l a m e n t w i n d i n g are u s e d t h e p r o c e s s must be given full c o n s i d e r a t i o n during design. CADFIL II from C r e s c e n t C o n s u l t a n t s Ltd offers a CAD route for f i l a m e n t w i n d i n g design.

i l a m e n t w i n d i n g is a p r o d u c t i o n process whereby resin impregnated fibres are dispensed from a moving head and wound onto a rotating former or mandrel. It is a fully a u t o m a t e d production process t h a t produces continuous fibres c o m p o s i t e s with high specific strength. Materials used in filament winding include

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FIGURE 1: The design cycle.

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glass, aramid and carbon fibres, reinforcing a polyester, epoxy, vinyl ester or thermoplastic matrix. Traditionally, components have been axisymmetric (rotationally symmetric) and programming techniques for these types of component are relatively simple. Commercial packages are available and most machine manufacturers provide some software systems for parts made up of simple geometric shapes such as cylinders, cones and spheres. For complex components, such as pipe bends, T joints and wind turbine blades, as well as a vast range of other non-axisymmetric components, the only previous program generation technique was 'teach-in'. This method involves the program being manually generated moving each axis separately to the next position. The teach-in method is slow, consuming days of production time on expensive capital equipment. It does not easily lend itself to producing quality laminates, and does not integrate into an engineering design strategy. The laminate is 'designed' to cover a shape by the machine's operator. To investigate if the component is fit for the intended purpose it needs to be inspected to either create data for detailed stress analysis, or mechanically tested to failure. Such inspection and testing extend the prototype phase of development, and are often very expensive. Use of the CADFIL software leads to g r e a t e r speed of p r o d u c t d e v e l o p m e n t , concept to customer time is dramatically reduced, winding machine development time is minimized, and higher quality laminates are produced. The system integrates into a total engineering design strategy, and allows more design variants to be studied by a design engineer remote from the winding machine. Filament winding machine technology has advanced enormously in the last ten years, fast, accurate, multi-axis, computer numerically controlled (CNC) machines are now available. The use of computer aided design (CAD) software allows the full potential of such machines to be realized allowing a

0034-3617/92/$3.50 © 1992, Elsevier Science Publishers Ltd.

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m u c h l a r g e r r a n g e of p r o d u c t s to b e m a n u factured.

Design procedure E n g i n e e r i n g design is an i t e r a t i v e process. The c o m p o n e n t g e o m e t r y is i n f l u e n c e d by its f u n c t i o n a n d by t h e l o a d i n g a p p l i e d to it. F o r p r o d u c t i o n by f i l a m e n t w i n d i n g t h e r e a r e g e o m e t r i c a l c o n s t r a i n t s d i c t a t e d by t h e p r o cess. Fibre p a t h s on t h e m a n d r e l s u r f a c e m u s t n o t slip or b r i d g e o v e r c o n c a v e a r e a s d u r i n g w i n d i n g a n d t h e fibres n e e d to be t u r n e d a r o u n d at t h e c o m p o n e n t s ' ends. This influe n c e s t h e r a n g e of fibre angles t h a t c a n be a c h i e v e d on t h e m a n d r e l s u r f a c e w h i c h in t u r n d i c t a t e s t h e l o a d b e a r i n g c a p a c i t y of t h e structure. A f i l a m e n t w i n d i n g CAD s y s t e m m u s t e n a b l e t h e f i b r e p a t h p o s s i b i l i t i e s to b e e v a l u a t e d a n d d e c i s i o n s r e l a t i n g to c o m p o n e n t g e o m e t r i c m o d i f i c a t i o n to be m a d e . A flow c h a r t s h o w i n g t h e a s p e c t s of d e s i g n i t e r a t i o n c a n be s e e n in Figure 1. The b a s i c a s p e c t s of a f i l a m e n t w i n d i n g CAD s y s t e m are m a n d r e l s u r f a c e modelling, fibre p a t h a n d l a m i n a t e d e v e l o p m e n t , g e n e r a tion of i n t e r f a c e d a t a for s t r e s s analysis a n d finally g e n e r a t i o n of CNC c o n t r o l d a t a t h a t can be directly t r a n s f e r r e d to t h e w i n d i n g m a c h i n e for c o m p o n e n t m a n u f a c t u r e . The mandrel surface definition of the CADFIL s y s t e m c a n be g e n e r a t e d m a k i n g u s e of t h e v a s t r a n g e of d r a w i n g p a c k a g e s t h a t are available. T h e m a n d r e l d a t a can t h e n b e i m p o r t e d into t h e s y s t e m a n d t h e s u r f a c e m e s h g e n e r a t e d , i n d e p e n d e n t of a n y specific s u r f a c e modeller. T e m p l a t e fibre p a t h s c a n be g e n e r a t e d on t h e i n p u t m a n d r e l s u r f a c e b a s e d on geodesic p r i n c i p a l s . The t r a j e c t o r i e s m a y be m o d i f i e d slightly by t h e u s e of t h e friction t h a t e x i s t s between fibre and mandrel surface. The t e m p l a t e p a t h s are g e n e r a t e d to o b t a i n t h e f i b r e a n g l e s t h a t t h e d e s i g n e r w i s h e s to achieve, given t h e l o a d s on t h e c o m p o n e n t a n d given d u e r e s p e c t to t h e c o m p o n e n t geometry. At this s t a g e t h e u s e r m a y wish to rea p p r a i s e t h e c o m p o n e n t g e o m e t r y to m a k e it m o r e a m e n a b l e to winding. Having p r o d u c e d a set of a c c e p t a b l e t e m p l a t e fibre t r a c k s t h e s e

FIGURE 2: Pipe T joint. a r e t h e n r e p l i c a t e d to p r o d u c e a c o m p o s i t e , a p r o c e s s r e f e r r e d to as l a m i n a t i o n . L a m i n a t i o n m a y be p e r f o r m e d in a n u m b e r of ways, t h e t e m p l a t e fibre t r a c k s m a y be replicated such that adjacent paths have a c o n s t a n t s e p a r a t i o n or b a n d width. In s o m e c a s e s it is b e t t e r to allow a d j a c e n t b a n d s to p r o g r e s s i v e l y o v e r l a p as t h e m a n d r e l ' s se(' t i o n a l p e r i m e t e r decreases. A t h i r d m e t h o d allows high a n g l e c o n s t a n t p i t c h w i n d i n g s to be m a d e . Having p r o d u c e d a l a m i n a t e t h a t covers the c o m p o n e n t a n d by i n t r o d u c i n g m a t e r i a l p a r a meters a laminate description incorporating fibre d i r e c t i o n s a n d p a r t t h i c k n e s s e s can be g e n e r a t e d . This i n f o r m a t i o n i n t e r f a c e s directly to a n y f i n i t e e l e m e n t s y s t e m . T h u s t h e s t r u c t u r a l design e v a l u a t i o n can be m a d e before a n y test: w i n d i n g is u n d e r t a k e n , a n d f u r t h e r i t e r a t i o n s to p r o d u c e m o r e a c c e p t a b l e p a t h s c a n be g e n e r a t e d if required. The final s t a g e of a n y CAD s y s t e m is to be able to g e n e r a t e t h e CNC c o n t r o l i n f o r m a t i o n r e q u i r e d to wind t h e d e s i g n e d l a m i n a t e on t h e f i l a m e n t w i n d i n g m a c h i n e . The c o n t r o l s t r a t egy m u s t t a k e into a c c o u n t t h e m a t e r i a l s t h a t are b e i n g used, t h e m a c h i n e h e a d configuration a n d t h e n u m b e r of i n d e p e n d e n t m a c h i n e a x e s t h a t a r e available. C r e s c e n t h a s prove:n s y s t e m s t h a t w o r k for two to six a x e s c,f m a c h i n e control. The p r o d u c t i o n of c o n t r o l d a t a / ' o r a specific w i n d i n g m a c h i n e is u n d e r t a k e n by t h e p o s t p r o c e s s o r . Post p r o c e s s o r s for all m a c h i n e c o n f i g u r a t i o n a n d m a c h i n e

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FIGURE 3: Prototype windings for wind turbine blade.

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control types are available. The control d a t a can t he n be directly loaded onto the winding machine and c o m p o n e n t s can be manufactured. To d e m o n s t r a t e the possibilities of the p r o c e s s for c o m p l e x geometries, several applications are now discussed, these shapes are not the limit, but serve as a guide to w ha t could be achieved given the imagination of the engineer.

FIGURE 4: Doubly curved duct for marine radar support arm.

REINFORCED PLASTICS JULY 1992

Applications o f CADFIL II CADFIL software has been applied to a variety of n o n - a x i s y m m e t r i c a p p l i c a t i o n s some of which are briefly discussed. The pipe T joint shown in Figure 2 is manufact u r e d for use within the chemical industry. These composite Ts are highly corrosion resistant, lightweight, and do not suffer from t h e r m a l shock. In t h e dry w o u n d e x a m p l e shown, som e of t h e series of 'bandsets' t h a t make up the full laminate can be seen. The pin fittings at the mandrel ends are re-usable and are cut free after resin cure. The pin fittings give total flexibility in the fibre entry and exit positions, along with fibre angles at the mandrel ends, their use eliminating a potential design constraint. A multi-part extractable steel mandrel is used, to produce this hollow component. Figure 3 shows prototype windings for a wind turbine blade. The design concept is for a foam core with longitudinal stiffening struts on the u p p e r and lower surfaces. The winding is t hen generated to give fibres at both + 45 ° and -45 ° to the main part of the aerofoil, imparting high torsional rigidity. There is a steel insert at the blade root which bonds, and effectively 'taper locks', into the composite. The p h o t o g r a p h shows the basic fibre p a t h s with a single t ow for clarity. In product i on the p a r t would be wound with 12 individual rovings making up a wider band. The pat hs shown provide a full layer with only j ust eight machine cycles along the component. The use of filament winding offers an interesting alternative to the hand lay-up m et hods currently employed, especially when quality control is an issue. The doubly curved duct shown in Figure 4 is for use as a marine r a d a r s u p p o r t arm. It is a multi angle lay-up with near axial, 'hoop and intermediate fibre angles. The final layer is a hoop wind to provide consolidation of the composite. As with the o t h e r c o m p o n e n t s the laminate description and the CNC d a t a have been fully generated using the CADFIL software. The CADFIL II s o f t w a r e is c u r r e n t l y available on engineering workstations with versions based on st andard IBM personal c o m p u t e r s being s h o r t l y available. The system is fully graphical and is m e n u driven for ease of use. W

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