Thermoplastic Tube Production Explained

Laser-assisted tape winding, a revolutionary technique in composite manufacturing, has a rich history spanning nearly three decades. Despite its long-standing existence, this innovative process has only been available for industrial applications for less than 15 years. As a result, it remains a relatively obscure technology in the broader manufacturing landscape. This comprehensive article aims to shed light on this cutting-edge process and provide you with the essential knowledge required for a successful configuration of laser-assisted tape winding systems.

Before delving into the intricacies of the configurator, it is crucial to establish a solid foundation by defining the key terminology associated with this Automated Fiber Placement (AFP) process. Familiarizing yourself with these terms will greatly enhance your understanding of the subsequent sections and enable you to make informed decisions when configuring your system:

CFR TP - Continuous Fiber Reinforced ThermoPlastic: This advanced material combines continuous fibers with a thermoplastic matrix, offering superior strength-to-weight ratios and the ability to be reshaped or recycled.
Mandrel – A critical component in the winding process, the mandrel is a rotational body that serves as the foundation upon which the composite material is wound. Once the winding process is complete, the mandrel is carefully extracted, leaving behind the finished composite structure.
Track – In the context of tape winding, a track refers to a single strip of tape that is meticulously wound around the mandrel. The angle at which the track is applied relative to the rotational axis is a crucial factor in determining the final properties of the composite structure.
Layer – A layer is comprised of a collection of tracks that work in harmony to fully enclose the mandrel's perimeter. The key characteristic of a well-designed layer is the absence of gaps or overlaps, ensuring uniform coverage and structural integrity.
Winding Type / Strategy - This term refers to the fundamental approach taken in the winding process. The two primary strategies are angle winding and cross winding, each with its own set of advantages and considerations. A more detailed explanation of these strategies will be provided in subsequent sections of this article.
Waste length – An inherent aspect of the winding process, waste length refers to the portions at both ends of the tube where the process is inherently unstable. This length is influenced by several factors, including the winding angle, tape width, and mandrel diameter. It is important to note that this waste length is dynamically calculated and is always removed before the final product is shipped to ensure optimal quality.
Good length / component – This term denotes the specified length of a part that will be delivered to the customer. It is the usable portion of the wound structure after the waste length has been removed.
Winding – A winding represents a complete cycle of preparing the mandrel, tape, and machine to produce a single part. Depending on the configuration, one winding may yield a single part or a mother tube containing multiple components.
Mother tube – In scenarios where multiple components are required, a mother tube refers to a single winding that encompasses multiple components within one extended length. This approach can often lead to improved efficiency and cost-effectiveness in production.
Steps – In the context of the winding process, steps refer to a collection of layers that share the same winding strategy. This grouping allows for more efficient production and can be tailored to achieve specific structural properties in the final product.
Effective Winding Angle - This crucial parameter is determined by a complex interplay of factors, including the target winding angle, mandrel diameter, and tape width. The effective winding angle represents the angle closest to the target that allows for a layer to be completely closed without gaps or overlaps, ensuring optimal structural integrity.
Component Quality - This multifaceted term encompasses various aspects that contribute to the overall performance of a part for a given application. Key factors include consolidation quality, porosity levels, fiber-matrix adhesion strength, and dimensional accuracy. Each of these elements plays a crucial role in determining the final properties and reliability of the composite structure.
Production Quality - While component quality focuses on the end product, production quality refers to the capability and stability of the manufacturing process itself. In laser-assisted tape winding, this is primarily governed by the sophistication and precision of the laser control system, which plays a pivotal role in ensuring consistent and high-quality output.
Production Certificate - This comprehensive document serves as a quality assurance record, detailing crucial parameters of the production process. It includes information such as the actual winding angle achieved, the consolidation pressure applied, and the winding speed for each layer. Additionally, it provides traceability by recording tape material batch information and production data. The certificate also confirms compliance with internal process limits established for a given polymer, ensuring that the final product meets stringent quality standards.

To better understand the structure of a winding operation, it is helpful to consider the hierarchical relationship between its components. The following list outlines this hierarchy in ascending order of complexity:

Track - The most basic unit, representing a single strip of tape applied to the mandrel.
Layer - A complete enclosure of the mandrel, composed of multiple tracks.
Step - A collection of layers sharing the same winding strategy.
Part - The finished component, which may consist of multiple steps.
Winding - The complete process of creating one or more parts in a single operation.
Order - The highest level, potentially comprising multiple windings to fulfill a customer's requirements.

Optimize Price Per Part

When designing components for laser-assisted tape winding, there is often some flexibility in the specifications. If the primary goal is to optimize the price per part, two key factors stand out as having the most significant impact on cost-effectiveness:

Tape width - The choice of tape width can dramatically affect production speed and material utilization.
Part length - The length of individual parts influences the efficiency of the winding process and material usage.

Tape Width

Unidirectional (UD) thermoplastic prepreg tape, the primary material used in this process, typically comes in a range of dimensions. The thickness generally falls between 0.15-0.25 mm (0.006-0.01 inches), while the width can vary from 6 to 50 mm (approximately 0.25-2 inches). In Alformet's web shop, the standard tapes offered adhere to this thickness range and are categorized into two width groups: narrow (10-15 mm, including 1/2 inch) and wide (20-26 mm, including 1 inch).

The choice of tape width has significant implications for both production efficiency and part quality. Wider tapes allow for a higher placement rate, which translates to faster production times and, consequently, lower part costs. However, it's important to note that there's a trade-off between tape width and production quality, particularly as the mandrel diameter decreases. For this reason, narrow tapes are the preferred choice when working with smaller mandrel diameters, as they allow for better control and higher quality in these more challenging configurations.

Part Length:

In the context of high mix-low volume production, a significant portion of the overall cost is attributed to the secondary time required for pre- and post-production activities. As a result, single pieces that necessitate individual winding tend to be the most expensive to produce. The maximum achievable winding length is constrained by the length of the available winding tool. In situations where your single piece exceeds the capacity of the available tooling, it is advisable to consult with our experts for guidance on potential options and solutions.

When it comes to optimizing the part price for components where multiple units can be accommodated in a single winding, a key principle to remember is that increasing the number of pieces per winding allows for better distribution of waste and secondary time costs. This more efficient allocation of resources typically results in a lower price per part, improving overall cost-effectiveness.

IMPORTANT: It's crucial to note that in certain scenarios, counter-intuitively, increasing the number of parts may actually lead to a higher price per part. These "price jumps" occur when the total quantity of parts necessitates multiple windings, but the length of the winding mandrel is not optimally utilized. To illustrate this concept, consider the following example: If 10 components of a given length can be accommodated on a specific mandrel, the optimal part price will be achieved for an order of 10 components. However, if the quantity increases to 11, the price per part will experience a significant increase compared to the 10-part scenario. This is because two separate windings are now required to fulfill the order, effectively doubling the setup and processing time while only marginally increasing the output. As you continue to increase the quantity beyond this point, the part price will gradually decrease until the next optimum is reached at 20 parts, where both winding cycles are fully utilized. Understanding these dynamics is crucial for making informed decisions about order quantities and optimizing production efficiency.

Winding Strategy

In the realm of laser-assisted tape winding, two primary strategies have emerged for winding unidirectional (UD) tapes onto a mandrel: angle winding and cross winding. Each of these approaches offers distinct advantages and considerations, making them suitable for different applications and production requirements.

Angle winding is characterized by its methodical approach to enclosing a single layer with a carefully calculated number of tracks. The process unfolds as follows: A single track of tape is automatically fed forward and precisely attached to the substrate using an innovative "add-on-the-fly" function. The tape then winds along the entire length of the part, with the laser system ensuring proper consolidation throughout. Upon reaching the end of the part, the "cut-on-the-fly" function is employed to cleanly terminate the track. The final step in this cycle involves an empty run back to the starting point of the part, where the entire process is reinitiated for the next track or layer.

Cross winding, in contrast, adopts a more continuous approach that eliminates the "dead time" associated with the return run in angle winding. In this strategy, the material is fed continuously, running back and forth along the length of the mandrel using specially designed "turning zones." This technique results in the creation of equivalent positive and negative angles that interweave with each other, producing a pattern reminiscent of braiding. While this method offers certain efficiency advantages, it's important to note that at the cross-points where the two layers intersect, there can be fiber undulations and generally a wider variance in wall thickness compared to angle winding.

When deciding between these two strategies, the primary considerations typically revolve around cost and quality. Cross winding generally offers a more cost-effective solution due to its continuous nature and the absence of dead time in the process. However, angle winding often produces higher quality results, as each layer is meticulously finished individually, allowing for greater control over the final structure. Another important factor to consider is that cross layers can only be laid in pairs, which results in a larger wall-thickness tolerance of plus or minus two tape thicknesses. This characteristic may be advantageous or disadvantageous depending on the specific requirements of your application. It's worth noting that both strategies can be implemented in your component using the step functions, allowing for a hybrid approach that capitalizes on the strengths of each method where appropriate.

Tolerances

Understanding and managing tolerances is crucial in laser-assisted tape winding to ensure the production of high-quality, consistent parts that meet specific dimensional requirements. Two key areas where tolerances play a significant role are the inner diameter and the wall thickness (or outer diameter) of the wound component.

The inner diameter of the wound component is primarily determined by the winding tool, also known as the mandrel. These tools are manufactured to extremely tight specifications, typically adhering to an h7 fitting tolerance. This high level of precision ensures consistency in the inner diameter across multiple productions. However, it's important to note that for larger mandrels, the coefficient of thermal expansion (CTE) of the steel used in the mandrel construction can play a minor role in the final dimensions. The extent of this effect is largely dependent on how the mandrel is pre-heated prior to the winding process, highlighting the importance of careful temperature control in achieving precise inner diameters.

The wall thickness (and consequently, the outer diameter) tolerance is influenced by two main factors: the discrete application of tape layers and the inherent thickness variations within the tape itself. For parts ordered through Alformet's web shop, production adheres strictly to the number of layers specified in the configuration. This approach ensures consistency but may result in slight variations in the final outer diameter. In cases where a specific outer diameter is crucial for the component's function or fit, customers have the option to specify this requirement in the configuration's comment section. When doing so, it's important to clearly define whether you require a plus tolerance, minus tolerance, or an "as close as possible" tolerance. To set realistic expectations, it's worth noting that the tolerance range for wall thickness is typically defined by one tape thickness for angle winding, or two tape thicknesses for cross winding, due to the nature of these processes.

Armed with this in-depth knowledge of laser-assisted tape winding processes, tolerances, and strategies, you are now well-equipped to begin the exciting process of designing your custom tube. We encourage you to explore the various options available and to reach out to our expert team if you have any questions or require further guidance. Enjoy the process of bringing your unique composite design to life!