Composite Materials Technology Lecture: A Detailed Understanding of the Characteristics, Types, Advantages and Disadvantages of Filament Winding Technology

 

Filament winding is a process used primarily to manufacture hollow, round or prismatic parts such as pipes and tanks. It is achieved by winding a continuous fiber bundle onto a rotating mandrel using a specialized winder. Filament wound parts are commonly used in the aerospace, energy and consumer goods industries.

 

 

Common Filament Wound Structural Parts

Filament Winding Process

Continuous fiber bundles are fed to the filament winding machine through a fiber delivery system, where they are wound onto the mandrel in a predetermined repeating geometric pattern. The position of the tow is guided by a fiber delivery head, which is attached to a movable bracket on the filament winding machine.

 

The relative angle of the tow to the mandrel (called the winding angle) can be adjusted to provide strength and stiffness in the desired direction. When enough tow layers are used, the resulting laminate is cured on the mandrel. The overall size and shape of the finished part are determined by the mandrel shape and the thickness of the laminate.

 

The winding angle will determine the mechanical properties of the composite part, such as strength, stiffness and weight. The density of the laminate is controlled by the tow tension during the winding process. Composite parts manufactured by these methods generally have good strength-to-weight ratio characteristics.

 

The Main Material Systems in the Winding Process Include:

Resin: usually thermosetting resins such as epoxy resin, polyester, vinyl ester, phenolic resin;

Fiber: carbon fiber, glass fiber, etc.; The fiber is used directly from the creel instead of being woven or stitched into a fabric form.

 

Main Types of Filament Winding Processes

There are two different forms of filament winding: wet winding and dry winding.

 

Wet winding: In wet winding, the fibers are unwound from the roving and passed through a bath of resin mixture (i.e. impregnated) and then wound on a mandrel in a prescribed orientation. The placement pattern is controlled by the rotation rate of the mandrel and the feed or metering mechanism.

 

Dry winding: The dry process uses the fibers in a pre-impregnated form. When the correct layer thickness is achieved, the component is cured in an oven. After curing, the mandrel can be removed or used as part of the finished part. During the curing process, cross-linking occurs, resulting in a 3D network of fibers.

 

Filament Winding Angles

 

Clairault Relations:

Axisymmetric objects have other interesting properties, as discovered by the famous French mathematician Alexis Claude de Clairault. The Clairault relation is a formula from classical differential geometry. This relationship applies to any point on a geodesic path on an arbitrary surface of revolution:

 

r.sin(α) = constant

Where r is the radial distance between any point on the geodesic path and the axis of rotation, and α is the angle between the tangent vector and the latitude circle, or, for the non-mathematicians out there, the winding angle.

 

BandwidthFor simple axisymmetric cases like a pipe, the number of loops required to cover the pipe is determined by considering the fiber band of true width B at the winding (helix) angle α. By applying some simple trigonometry, the band width in the circumferential direction is B/cos(α), and dividing this by the pipe circumference, the number of loops (N) required to cover a pipe of diameter D is given by:

 

N=πDCos(α)/B

The number of cycles is always an integer; with a given mandrel diameter D and bandwidth B, the bandwidth B is defined by e. A better way to get the possible winding angles, taking into account all the other variables, is

 

α=Cos-1(N.B/Pi.D)

From the above equation, N can now be varied to get the closest fiber orientation that matches the FEM simulation.

 

 

 

Advantages and Disadvantages

 

Main Advantages:

It is a very fast and economical method of laying down materials.

Resin content can be controlled by metering resin onto each fiber bundle through a roller gap or die.

Fiber costs are minimized because there is no secondary process to convert the fibers into fabric before use.

The structural properties of the laminate are very good because straight fibers can be laid in complex patterns to match the applied loads

 

Main Disadvantages:

Process is limited to convex parts.

Fibers cannot be laid completely along the length of the component.

Mandrel costs can be high for large parts.

The outer surface of the part is not formed

Mechanical, health and safety properties are lower when low viscosity resins are generally used.