Guidelines for Controlling Winding Parameters in Filament Winding Process

 

 

This article will take you into the intricate world of filament winding, uncovering all aspects of this critical technology for the composites industry. Here is a quick summary to get you up to speed on the content of this article:

 

Understanding Filament Winding:

Take a deep dive into the basic spiral horizontal filament winding machine and explore its economic and weight advantages.

 

Addressing the Challenges:

Address issues such as fiber slippage and large diameter winding, providing insights into mitigation strategies.

 

Creels and Mandrels:

Explore these basic components and understand their roles, design considerations, and drag factors.

 

Flat Winders:

Take a deep dive into the design and functional simplicity of flat filament winding machines.

 

Fiber Spreading Technology:

Understand the nuances of “S” winding and analyze the effects of path length and back tension on winding width.

 

Applications and Case Studies:

Witness the versatility of filament winding across various industries through a number of applications and real-world examples.

 

Conclusion:

Summarize key insights and discuss potential areas for further research and development in filament winding.

 

Understanding Filament Winding

 

Introduction to Filament Winding Process

 

The filament winding process has become a key technology in the composites industry, especially for the manufacture of composite preforms. The process has been used for more than 50 years and has been significantly modernized in the past decade.

 

The filament winding process, especially in its early stages, was very manual and involved steps such as manually loading the mandrel, mixing the resin, tying the fibers onto the mandrel, changing the fiber type, cutting the roving after winding, and unloading the wet wound mandrel into the oven.

 

The modern filament winding process has undergone a revolution, incorporating automation and advanced technologies such as robotic or handling equipment assisted loading/unloading of the mandrel and automatic resin mixing systems.

 

 

 

Basic Spiral Horizontal Filament Winding Machine System

 

Explore the Basic Spiral Horizontal Filament Winding Machine

The basic spiral horizontal filament winding machine system is a basic tool in the filament winding process. In the early days of filament winding, the machine was mechanically controlled, utilizing a gearbox to determine the winding angle and a chain to determine the length of the part to be wound. Adjustment of the winding angle and part length was manual, requiring an understanding of the relationships within the gearbox and how these relationships relate to the resulting winding angle on the manufactured part.

 

Highlighting the Economic and Weight Advantages of Filament Winding

Filament winding offers significant economic and weight advantages, especially when compared to metal products. The process is recognized for its ability to obtain excellent mechanical properties from continuously aligned fibers, especially when manufacturing axisymmetric bodies. The main limiting factors of the winding process include geometric constraints and the necessity for a single programming of the fiber air path (which can be repeated to provide a fiber layer that completely covers the mandrel).

 

However, the method has proven to be cost-effective and efficient, especially in applications where the mechanical properties of the aligned fibers can be fully utilized.

 

Addressing Challenges in the Filament Winding Process

 

Identifying and Mitigating Fiber Slippage Issues

 

 

 

Schematic diagram of fiber bridgingFiber slip is a widespread problem in filament winding, especially in large diameter windings.

 

Due to the low viscosity of the resin, the fibers may slip off the mandrel during the curing process. Friction and anti-slip properties can originate from various physical mechanisms other than pure mechanical friction. For example, when winding with viscous tow impregnated materials (resin pre-impregnated tow), there is some physical adhesion between the applied fibers and the mandrel.

 

Also, during wet winding processes where fiber tension is high, the new fibers tend to compress into the already laid material, resulting in a degree of mechanical interlocking. Advanced software systems used to program filament winding machines must include some concept of friction, and the user must be able to specify limits (i.e., anti-slip values) for the material used.

 

Meeting the Challenges of Large Diameter Winding

 

 

 

 

SpaceX Carbon Fiber Fuel Tank

 

Large diameter windings present their own set of challenges in filament winding. Fibers, especially those with larger diameters, can slip uncontrollably. Winding processes for axisymmetric shapes such as cylinders, tapered shafts, spheres, and cones are common, with fluid conveying pipes or closed-end cylinders (usually spherical, ellipsoidal, or quasi-spherical) being the most manufactured components in pressure vessels or storage vessels. Filament winding offers several advantages over other manufacturing processes, including the fact that it is one of the few automated processes for producing composite preforms.

 

However, geometric constraints and the need for single-shot programming of the fiber air path (repeatable to provide a complete coverage of the mandrel with fiber layers) are major limiting factors in the winding process.

 

Creels and Mandrels: Integral Components in the Filament Winding Process

 

Define and Understand the Role of Creels

 

 

Fixed Creel

The creel plays a key role in the fiber winding process and is a device that holds the necessary number of roving balls or supply packages in position for unwinding onto the mandrel during the fiber winding process. The creel ensures that the fiber can be pulled from the core of the bundle without tension, but it will twist, which has its own consequences and considerations during the winding process.

 

Explore the different types of creels and their applications

 

 

 

Rotating Fiber Package Creels

There are many types of creels used in the fiber winding process, each with specific applications and functions:

• Fixed creel:

This type of creel is essentially a rack that allows the fiber to be pulled from the center of the bundle without tension, but with twist.

 

• Rotating creel:

Allows the fiber package to rotate, reducing fiber twist during the unwinding process.

 

• Braking creel:

Provides tension control by applying a braking force to the fiber package during the unwinding process.

 

• Combinations:

Creels can also be designed with a combination of the above features to meet specific winding requirements.

Discussion of twist considerations in fiber removal

 

 

 

Twist Considerations

When fibers (also called tow or roving) are removed from the roll, they are not twisted in the roll. The fiber removal process, especially from the first yarn guide, is best performed on the horizontal centerline of the roll to prevent the roll edge from falling off and to minimize wear.

 

If the first yarn guide in the roll is moved to either side of the centerline, the departure angle becomes more acute, causing it to slide laterally as it unwinds, thereby abrading the underlying fibers. All redirections must have a large radius or bevel to minimize friction and prevent fiber damage. Excessive tension should be avoided to prevent increased self-wear on the roller surface and in the yarn guide, possible tow breakage, and the tendency for the tow to embed into the layers below.

 

Mandrels in Filament Winding

 

Explore Mandrel Materials and Design Considerations

 

Mandrels play a key role in fiber winding as a tool that provides the internal surface and shape to form the wound product. Various types of mandrels are used in the manufacturing process, including those made from materials ranging from cardboard to stainless steel. The basic requirement is that they can be removed from the wound component or left in the component as a liner in some applications such as pressure vessels. Some alternative approaches to mandrel design and use are presented in the book.

 

For example, a filament-wound container with fibers at ±54.75° will expand in both directions under internal pressure, maintaining the winding angle. Filament-wound mandrels take advantage of this fact to simplify the extraction of the filament-wound tube wound onto it. Mandrels are made by overwinding the ends of a dissolvable mandrel or a compressible foam mandrel and using a center mandrel with end-compression connections.

 

 

Filament-Wound Composite Fuselage

 

Discuss Drag Factors: Winding Tension, Curing Heat, and Deformation

 

Mandrels must be designed to resist various factors, such as winding tension, curing heat, and deformation caused by the weight of the product and the mandrel itself. They must be manufactured to the necessary tolerances and have sufficient durability. When considering drag factors, it is important to explore how the mandrel interacts with the winding process and how it withstands the various stresses and strains introduced during manufacturing.

 

For example, if the package has a spring, washer, and nut arrangement mounted on the shaft (for tension control), the package should be rotated in the direction of loosening the nut to prevent sticking.

 

Explore the Planar Filament Winding Machine

 

Introduction to the Planar Filament Winding Machine

 

 

Planar Fiber Winding Machine

A planar fiber winding machine is a unique fiber winding machine that works by rotating the mandrel while the fiber delivery carriage moves around the mandrel, but not along the shortest distance from one end to the other on the cylindrical surface. Instead, this movement places the fiber on a polar path, meaning it is not a direct path from one end to the other on the cylindrical surface. The mechanism is shown in the figure, which visually demonstrates its method of operation. In this case, the fiber is not directly subjected to the maximum internal stress, which is an important aspect to consider in the winding process.

 

Analyzing its Design and Functional Simplicity

The design of a planar fiber winding machine is essentially to ensure that the fiber is placed on a specific path, which is not the shortest, but is carefully calculated to achieve the desired winding results. The movement of the fiber delivery carriage relative to the rotating mandrel is carefully designed to facilitate the polar path of the fiber, which has its own set of advantages and considerations in the fiber winding process. The design and functional simplicity of the planar winding machine are critical to ensuring that the fiber is wound in a manner that is conducive to the structural and functional integrity of the final product.

 

Fiber Spreading Technology

 

 

 

Filament Winding (FW) Mandrels

 

Understanding “S” Wraps and Static Rods

“S” wraps consist of two static rods stacked on top of each other and have proven to be an effective method for spreading fibers during filament winding. The pair of static rods can rotate as a unit to minimize or increase fiber contact or provide tension in the fiber. The longer the fiber is in contact with the static rod surface (dwell time), the greater the spread width.

 

Interestingly, run speed has little effect on spread width. If multiple “S” wraps or static rods are used, path length affects spread width, with a 2 to 4 foot (0.6 to 1.2 meter) path being a good working range. Beyond this range, the fibers tend to rope or re-aggregate, which is especially important for resin-wetted fibers.

 

Analyzing the Effects of Path Length and Back Tension on Spread Width

Path length and back tension are key factors in fiber spread. Longer path lengths, especially those outside the optimal working range, can cause fiber curling or re-aggregation, especially for resin-wetted fibers. The higher the back tension on the fiber, the more critical the sweep angle during unwinding.

 

If the package is mounted with a spring, washer and nut arrangement on the shaft (for tension control), the package should rotate in the direction that loosens the nut. Otherwise, it tightens the nut until the package gets stuck, making the winding process challenging.

 

Applications of Filament Winding

 

Showcasing various applications in different industries

Filament winding is a key technology in the composites industry, providing a versatile method for producing strong, high-strength structures across industries. From aerospace to civil engineering, filament winding helps to manufacture a variety of components and structures, proving its wide applicability and effectiveness.

 

 

Filament Wound Ribs

 

Explore Case Studies and Real-life Examples

 

• Backing and Filament Wound Surface Finishes:

Backing technology enhances the external finish and consolidation of filament wound products. The approach uses internal and external backing plates to ensure that the composite components are pushed outward and compressed during pre-cure pressurization, optimizing the surface finish and structural integrity of the final product.

• Clay Pipe Flanges:

In response to the frequent damage of integral flanges on large clay pipes, filament winding technology has been used to create durable composite flanges on common clay pipes. This application significantly reduces damage incidents and saves factory costs and installation expenses.

 

 

Filament Wound Disc Shock Absorbers

• Filament Wound Boat:

A lightweight filament wound boat demonstrates the use of this technology in the marine industry. Made primarily of filament wound materials, the boat demonstrates the durability and resilience of such structures, even in challenging conditions such as crossing a rocky stream.

• Filament Wound Aircraft Fuselage:

Filament winding technology has also found its way into the aerospace industry, with successful aircraft fuselages. This application is recognized for its significant reduction in weight and lifecycle costs of filament wound structures.

• Filament Wound Ribs on Filament Wound Underground Pipes:

For large filament wound pipelines underground, especially those under roadways, stiffening ribs are wound at intervals along the length of the pipeline. This application ensures the structural integrity of the pipeline, providing it with the necessary strength and durability.

• Other Case Studies:

Various other case studies such as filament wound shock absorbers, vehicle springs, and small diameter long pipes further illustrate the versatility and applicability of this technology in different industries and applications.

 

Conclusion

As mentioned earlier, filament winding is a versatile and efficient technology in the composites industry that can be used to create strong, high-strength structures in a variety of applications. We have explored the complex world of filament winding by understanding the basic process, overcoming challenges, exploring various machines such as flat winders, and delving into the intricacies of components such as creels and mandrels. The technology not only offers economic and weight advantages, but also provides solutions to large diameter winding and fiber slippage issues.

 

While filament winding has numerous advantages and applications across various industries, it is not without its challenges. Fiber slippage, challenges of large diameter winding, and considerations in fiber spreading techniques are issues that practitioners and researchers in the field are working to address.

 

The exploration of new materials, innovative design approaches for creels and mandrels, and advancements in machinery such as flat winders provide open areas for research and development. Furthermore, delving into the applications and case studies of filament winding across various industries can pave the way for innovative applications and solutions to existing challenges.