Additive Manufacturing of High-performance Polymers: Processing Parameters and Mechanical Properties

Naohara Nakajima^*
*Correspondence: Naohara Nakajima, Department of Mechanical Engineering, Chiba Keizai University, Japan, Email:

Introduction

Additive manufacturing, commonly known as 3D printing, has emerged as a transformative technology in various industries, enabling the rapid production of complex geometries with minimal waste. The advent of high-performance polymers in AM has further expanded the potential of this technology, particularly in sectors such as aerospace, automotive, and medical devices, where material performance and durability are critical. This paper reviews the state-of-the-art in additive manufacturing of high-performance polymers, focusing on the processing parameters that influence the properties of the final product. Key factors such as temperature, printing speed, layer height, and post-processing methods are discussed in the context of mechanical properties including tensile strength, modulus, impact resistance, and fatigue performance. The paper also highlights the challenges and future directions in optimizing AM of high-performance polymers for industrial applications.

Additive manufacturing has revolutionized the way products are designed and produced, offering unprecedented flexibility in creating geometrically complex structures. Traditionally, polymers used in AM were limited to lowcost, low-performance materials, but recent advances in the development of high-performance polymers have opened new frontiers in manufacturing. These materials, such as polyether ether ketone, polyimide, and Ultem, offer superior mechanical properties, chemical resistance, and thermal stability, making them ideal candidates for demanding applications in industries like aerospace, automotive, and medical.

High-performance polymers are characterized by their ability to withstand extreme conditions, including high temperatures, aggressive chemicals, and mechanical stresses, without significant degradation. When integrated into additive manufacturing processes, these polymers enable the creation of parts that are both lightweight and durable, offering cost-effective alternatives to traditional manufacturing methods like injection molding or machining. However, achieving the desired mechanical properties in 3D-printed parts made from these materials requires a careful understanding of the relationship between processing parameters and material behavior.

This article explores the factors that influence the mechanical properties of high-performance polymers in AM, reviewing the processing parameters that affect the quality and performance of the final printed parts. High-performance polymers, due to their excellent thermal, mechanical, and chemical properties, have a wide range of applications in industries requiring high reliability and longevity of components. Known for its high-temperature resistance, low friction, and wear resistance, PEEK is widely used in aerospace, automotive, and medical applications. PEEK parts exhibit high tensile strength, modulus, and chemical resistance, making them suitable for functional prototypes and end-use parts. Polyimides, such as Kapton, are known for their outstanding thermal stability and dielectric properties, making them ideal for electronics and aerospace applications. PI offers excellent resistance to high temperatures and aggressive chemicals, though it is typically more challenging to process due to its high viscosity and tendency to degrade at certain temperatures.

Description

Ultem is a thermoplastic polymer with high mechanical strength and thermal stability. It is widely used in automotive and medical industries due to its excellent dimensional stability, high tensile strength, and resistance to chemicals. TPE materials combine the characteristics of elastomers with the processability of thermoplastics. These materials are often used in applications that require flexibility, such as in medical devices and consumer goods.

Each of these materials has distinct advantages and processing challenges in the context of additive manufacturing, requiring specific conditions to optimize their performance [1-3]. FDM is one of the most widely used AM techniques for thermoplastic materials. It involves extruding heated filament through a nozzle, layer by layer, to build up a part. FDM is particularly popular for polymers such as PEEK, Ultem, and PEI, as it allows for relatively easy processing with the ability to print large parts. SLS uses a laser to selectively sinter powdered materials, layer by layer, to form a solid part. SLS is commonly used for high-performance polymers like PA12, PA6, and PEEK. The key advantage of SLS is its ability to produce complex geometries without the need for support structures, making it particularly useful for parts with intricate designs.

SLA uses a laser or UV light to cure a photopolymer resin, layer by layer, to build up a part. SLA is generally used for materials like resins and photopolymers, but recent advances in the development of high-temperature photopolymers are making it a viable option for high-performance applications. In MJ, droplets of material are deposited and cured layer by layer. This method is gaining traction for high-performance polymers due to its ability to produce high-resolution, fine-featured parts, often used for rapid prototyping and medical applications. DIW is an extrusion-based additive manufacturing technique where a highly viscous ink is deposited layer by layer. While primarily used in the research and development of composite materials, DIW is increasingly being considered for high-performance polymer applications.

The mechanical properties of parts made from high-performance polymers in additive manufacturing are significantly influenced by a range of processing parameters. These parameters dictate the final microstructure and characteristics of the printed part, affecting properties such as tensile strength, modulus, impact resistance, and fatigue performance.Temperature is one of the most critical factors influencing the properties of highperformance polymers in AM. Both the extrusion temperature (for FDM and DIW) and the bed temperature (for FDM, SLS, and SLA) play an important role in determining the flow characteristics of the material, adhesion between layers, and crystallinity.

A higher extrusion temperature can improve material flow and layer bonding, but it can also increase the likelihood of thermal degradation. For materials like PEEK, precise temperature control is necessary to avoid loss of mechanical strength due to overheating. The bed temperature must be optimized to prevent warping and ensure good adhesion to the substrate [4,5]. For materials with high thermal stability like Ultem, a heated bed can promote better layer bonding and reduce the chances of delamination. Print speed and layer height directly affect the resolution and density of the printed part. Faster print speeds typically result in reduced resolution and may lead to defects such as poor layer bonding or voids within the material. In contrast, a slower print speed can result in improved bonding between layers and better surface quality. The layer height determines the resolution of the printed part. Smaller layer heights provide finer details but require longer printing times. The optimal layer height is a balance between resolution, print speed, and material properties. For high-performance polymers, a smaller layer height can improve the mechanical properties by enhancing the interlayer bonding.

The cooling rate affects the crystallization and polymer orientation in the printed part. Rapid cooling can lead to uneven crystallinity and internal stresses, potentially reducing the mechanical performance of the part. For high-performance polymers, controlled cooling is necessary to achieve the desired microstructure and mechanical properties. Post-processing treatments, such as annealing or chemical vapor smoothing, can significantly improve the mechanical properties of AM parts. Annealing, for example, can promote the crystallization of polymers like PEEK, enhancing their thermal and mechanical properties.

Post-processing annealing treatments help reduce residual stresses and improve the overall mechanical properties, such as tensile strength and impact resistance. For polymers like PEEK, annealing at elevated temperatures can also improve crystallinity, leading to higher strength and stiffness. In methods like SLS, support structures need to be carefully removed, as any residual material can adversely affect the final properties of the part. Incomplete removal of support material can lead to defects that compromise mechanical strength.

The mechanical properties of high-performance polymer parts produced by additive manufacturing are highly dependent on the processing conditions. High-performance polymers such as PEEK and Ultem exhibit high tensile strength, making them ideal for structural applications. However, the tensile properties of AM parts can be lower than those of injection-molded parts due to poor interlayer bonding and the presence of voids. The modulus of elasticity is a key indicator of a material's stiffness. For high-performance polymers, achieving a high modulus is critical for applications where dimensional stability and resistance to deformation under load are important. Processing conditions such as temperature and print speed can significantly influence the modulus of the final part. High-performance polymers are generally chosen for their excellent impact resistance. In AM parts, impact resistance can be influenced by factors such as layer bonding, porosity, and the choice of material.

For parts subjected to cyclic loading, fatigue resistance is crucial. The mechanical properties of AM high-performance polymers can be influenced by layer bonding, which plays a significant role in fatigue strength. Parts printed with optimal parameters exhibit better resistance to crack initiation and propagation.

High-performance polymers like PEEK and Ultem are expensive, and the variety of AM-compatible grades is limited. Developing cost-effective alternatives or new grades of high-performance polymers is crucial to expanding the applications of AM in industries like aerospace and automotive. Ensuring consistent quality and performance across different printing machines and batches of material remains a challenge. Process optimization techniques and advanced monitoring systems are needed to ensure that parts meet the required specifications. Post-processing methods such as annealing or surface treatments often require specialized equipment and add to the overall production time and cost. Developing new, more efficient postprocessing techniques is essential for improving the mechanical properties of AM parts. As demand for customized components increases, the development of materials that can be tailored for specific applications, such as highperformance composites or hybrid materials, is essential.

Conclusion

The additive manufacturing of high-performance polymers offers immense potential for producing parts with excellent mechanical properties, suitable for demanding applications in aerospace, automotive, and medical industries. However, achieving the desired performance in AM parts requires a careful balance of processing parameters, including temperature, print speed, layer height, and post-processing techniques. By optimizing these factors, it is possible to enhance the mechanical properties of printed parts, enabling the successful use of high-performance polymers in a wide range of industrial applications. Future developments in material science, processing technologies, and post-processing techniques will continue to drive the growth of additive manufacturing in high-performance sectors.

Acknowledgement

None.

Conflict of Interest

None.

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