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Step-by-Step Guide for Optimizing Automated Thermoplastic Fiber Placement

Updated: Apr 17, 2023


In this comprehensive blog, we delve into the automated fiber placement process, a crucial technique for manufacturing high-performance composite components. We discuss the importance of optimizing process parameters to ensure the highest quality of the final product and examine the factors that affect its quality, including raw material characteristics, mandrel factors, compaction roller dimensions, and heat source variables.

We then explore how Design of Experiments (DOE) can be used to analyze and optimize these parameters, leading to improved voids, crystallinity, and mechanical properties of the composite material. By applying the optimized parameters in production, we can achieve consistent material properties and bond strength, while effectively monitoring and maintaining temperature, pressure, and time.

The blog also covers advancements in process optimization and adaptation, such as the use of digital twin software for continuous product quality monitoring, AI models for data-driven adaptation of process parameters, and the development of more accurate physics-informed AI models to eliminate trial and error.

Lastly, we provide resources for further exploration, including relevant literature, expert consultations, industry forums for knowledge sharing, and training resources for staff involved in the automated fiber placement process.

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1. Introduction

The manufacturing industry is constantly seeking innovative methods to improve the production of high-quality composite materials. One such technique, which has gained significant traction in recent years, is the Automated Fiber Placement (AFP) process. This process involves utilizing unidirectional carbon fiber-reinforced thermoplastic tapes to create high-performance composite components, which are increasingly finding applications in various industrial sectors. In this blog, we will explore the AFP process and discuss the importance of optimizing the process parameters for manufacturing composite parts.

1.1 Understanding the Automated Fiber Placement Process

The Automated Fiber Placement (AFP) process involves using a robotic system to place unidirectional pre-impregnated fiber tapes onto a substrate or mandrel. The tapes are laid along pre-defined paths, allowing for a high degree of freedom in designing the final product. The AFP process is enhanced by incorporating a heat source, which melts the thermoplastic matrix during fiber placement. This enables in situ consolidation of the fiber, eliminating the need for post-processing and curing steps.

The AFP process offers several advantages, including higher productivity, better quality composites, reduced waste material, less labor, shorter production time, improved accuracy and repeatability of the product, and software solutions to streamline the process.

1.2 Importance of Optimizing Process Parameters for Manufacturing

The quality of the final composite part is dependent on various factors, such as void-free and well-consolidated structure, and controlled crystallinity. These factors are influenced by the parameters involved in the AFP process. Therefore, it is crucial to optimize these parameters to achieve the desired outcome.

In this blog, we will discuss some of the key process parameters include: raw material quality, mandrel factors, compaction roller dimensions, heat source variables, and process parameters like heat transfer coefficient, placement rate, and substrate temperature. A thorough understanding and optimization of these parameters can lead to the production of high-quality composite parts that are reliable for use in various structures.

2. Assessing factors affecting the quality of the final product

2.1 Evaluating raw material (UD tape) characteristics

  1. Checking tape impregnation quality: Ensuring that the fiber has good impregnation quality will lead to better final product performance.

  2. Measuring tape thickness: A consistent fiber thickness is important for achieving uniform properties across the final product.

  3. Assessing fiber surface roughness: A smoother fiber surface can improve the bonding between layers and reduce voids in the final product.

  4. Monitoring tape tension: Maintaining proper fiber tension during the process ensures consistent fiber placement and prevents defects.

2.2 Considering mandrel factors

  1. Assessing mandrel curvature: The shape of the mandrel affects the laying path and the heat source angle, which in turn impact the final product quality.

  2. Controlling mandrel temperature: Maintaining an optimal mandrel temperature (10-30°C above the glass transition temperature) can reduce stresses and improve the crystallinity of the final product.

  3. Selecting mandrel with appropriate thermal conductivity: Choosing a mandrel with the right thermal conductivity can help achieve the desired temperature distribution and improve bonding between layers.

2.3 Analyzing compaction roller dimensions

  1. Adjusting compaction force: Applying the right amount of force ensures intimate contact between layers and better consolidation.

  2. Determining compaction area: A suitable compaction area can help achieve uniform pressure distribution and improve bonding.

  3. Controlling roller interface temperature: Optimizing the roller interface temperature will impact the viscosity of the matrix and the development of intimate contact.

  4. Choosing roller diameter: The roller diameter affects the pressure distribution and contact between layers.

  5. Identifying roller thermal conductivity: The thermal conductivity of the roller influences the heat transfer between the roller and the fiber, which affects the final product quality.

2.4 Evaluating heat source variables

  1. Setting heat source intensity: The power of the heat source should be customized based on the material and processing speed.

  2. Adjusting heat source profile: Ensuring heat source homogeneity will result in uniform heating across the target area.

  3. Selecting heat source size and shape: A compact heating system allows for a more maneuverable AFP head, which can handle intricate structures.

  4. Configuring heat source angle: The angle of the heat source impacts the reflection, absorption, and transmission of the heat, ultimately affecting the heating efficiency.

  5. Determining incoming fiber angle: The incoming fiber angle can influence the reflection of the heat source and the effectiveness of heating.

2.5 Understanding process parameters

  1. Estimating heat transfer coefficient: The heat transfer coefficient affects the temperature distribution and the final product quality.

  2. Setting placement rate: Optimizing the placement rate ensures proper bonding between layers and improves the quality of the final product.

  3. Controlling substrate temperature: A suitable substrate temperature is crucial for achieving the desired crystallinity and bonding performance.

  4. Monitoring fiber temperature: Maintaining optimal fiber temperature is important for achieving better bonding and reducing voids in the final product.

3. Implementing optimization techniques

3.1 Applying Design of Experiments (DOE) for process parameter optimization

Design of Experiments (DOE) is an approach to systematically design experiments that vary relevant factors to identify optimal conditions. In the context of AFP processes, DOE helps manufacturers analyze and optimize the input parameters to achieve the desired output parameters

3.2 Analyzing output parameters: voids, crystallinity, and mechanical properties

Three main output parameters are evaluated after each experiment with DOE: voids, crystallinity, and mechanical properties.

  1. Voids: Voids are categorized into two types - intralaminar and interlaminar. Intralaminar voids occur during the fiber impregnation process, while interlaminar voids result from the fiber laying process. These voids can affect the overall performance of the final product.

  2. Crystallinity: Crystallinity influences the mechanical properties of the final product and is dependent on the thermal cycle and cooling rate of the thermoplastic. The degree of crystallinity ranges from 20 to 35% in most HAFP/AFP applications. Higher crystallinity increases strength and rigidity, while lower crystallinity improves impact resistance and breaking strength.

  3. Mechanical properties: Mechanical tests such as 3-point bending test (3PBT) and interlaminar shear strength (ILSS) are commonly performed to determine the bonding quality between interlayers. These tests provide valuable insight into the effect of input parameters on the final product's performance.

3.3 Identifying optimal conditions through DOE analysis

By analyzing the output parameters, manufacturers can determine the ideal combination of input parameters to optimize the AFP process. For instance, it has been observed that the degree of crystallinity and the size of the crystals are higher for samples cooled by higher melting temperatures. Additionally, similar degrees of crystallinity have been obtained in other studies, indicating that PEEK is not sensitive to the cooling rates involved in the AFP process.

In conclusion, implementing optimization techniques like DOE can help manufacturers identify optimal conditions for the AFP process. Analyzing output parameters such as voids, crystallinity, and mechanical properties enables manufacturers to fine-tune their processes to achieve superior product quality and performance.

4. Applying the Optimized Parameters in Production

With the optimal conditions identified through DOE analysis, manufacturers can now proceed to apply these parameters in the production of composite materials using the AFP process. This section will discuss how to adjust the process parameters based on the DOE results, ensure consistency in material properties and bond strength, and monitor and maintain temperature, pressure, and time throughout the process.

4.1 Adjusting Process Parameters Based on DOE Results

The DOE results provide invaluable insights into the ideal combination of input parameters for achieving optimal output parameters. Manufacturers should adjust their process parameters accordingly, ensuring that the fiber placement process is carried out under optimal conditions. Some of the adjustments may include changes to the heat source power, fiber placement speed, compaction roller pressure, and substrate temperature.

4.2 Ensuring Consistency of Material Properties and Bond Strength

Applying the optimized parameters in production is crucial to ensure consistency in material properties and bond strength across the final composite parts. This involves maintaining the ideal degree of crystallinity, minimizing voids, and ensuring strong interlayer bonding. To achieve this, manufacturers should focus on quality control measures throughout the production process. Regular inspection and testing of the produced parts can help identify any deviations from the desired properties and allow for prompt corrective action.

4.3 Monitoring and Maintaining Temperature, Pressure, and Time

The HAFP/AFP process relies on precise control of temperature, pressure, and time to ensure proper consolidation and bonding of the composite layers. Manufacturers must continuously monitor these parameters during production to maintain consistency and achieve the desired output parameters. Advanced sensors and control systems can be employed to measure and maintain these parameters within the specified range. Any deviations from the set parameters should be promptly addressed to prevent negative impacts on the final product's quality and performance.

5. Advancements in Process Optimization and Adaptation

As the industry continues to evolve, it is essential to focus on ongoing improvements and adaptation to ensure that the AFP process remains efficient and effective in producing high-quality composite parts. In this section, we will explore the use of digital twin software for continuous monitoring of product quality, building AI models to adapt process parameters for different parts, and developing more accurate physics-informed AI models to minimize the need for trial and error.

5.1 Continuously Monitoring Product Quality Using Digital Twin Software

Digital twin technology allows manufacturers to create a virtual replica of the production process and monitor the product quality in real-time. By utilizing digital twin software, manufacturers can identify any deviations from the desired parameters and make necessary adjustments to the process. This ensures that the final composite parts meet the required quality standards and reduces the risk of defects or inconsistencies.

5.2 Building an AI Model for Data to Adapt Process Parameters

Artificial intelligence (AI) models can be employed to analyze the data collected during the AFP process and adapt the process parameters for composite parts of different sizes and shapes. By feeding the AI model with historical data and process parameters, it can identify patterns and trends that may impact the final product's quality. This allows manufacturers to make informed decisions on the process parameters for different parts without relying on trial and error, improving efficiency and reducing waste.

5.3 Building More Accurate Physics-Informed AI Models to Eliminate the Need for Trial and Error

Developing more accurate physics-informed AI models can further enhance the AFP process by minimizing the need for trial and error. These models integrate the underlying physics of the process, such as heat transfer and material properties, with AI-driven algorithms to provide a more accurate representation of the process. By leveraging these models, manufacturers can gain insights into the optimal process parameters for different composite parts and make necessary adjustments without the need for extensive experimentation.

6. Resources

6.1 Relevant literature and research on process optimization

In this ever-evolving field, it is crucial to stay up-to-date with the latest research and advancements in process optimization for the automated tape placement process.

Listen to our recent webinar on the subject

6.2 Expert consultations and industry forums for knowledge sharing

Building a network of industry professionals and experts can be highly beneficial for exchanging knowledge, experiences, and best practices in the field of automated tape placement. We recommend participating in industry forums, conferences, and webinars that bring together experts and professionals from around the globe. By engaging in such events, you can gain insights into the latest trends, technological advancements, and practical solutions to address challenges in your manufacturing processes.

6.3 Training resources for staff involved in the automated tape placement process

Investing in continuous learning and skill development is essential to ensure that your staff can effectively implement and optimize the automated tape placement process. In this section, we will provide updated information on available training programs, workshops, and online courses that cater to various levels of expertise, from beginner to advanced. These resources will cover topics such as process optimization, material selection, and advanced manufacturing techniques, equipping your team with the necessary knowledge and skills to excel in their roles and contribute to the success of your manufacturing operations.

*Note: This section will be regularly updated with new resources, research, and opportunities to help you stay at the forefront of the industry. Stay tuned for the latest updates and developments in process optimization and adaptation for the automated tape placement process.

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