The strengths of additive manufacturing (AM), especially the tool-less manufacturing paradigm and rapid production of low-volume products, are well-aligned with the needs of manufacturing of expensive, high-temperature resistant, engineering thermoplastic polymers. High temperature polymer parts made with AM for either tooling or end-use applications have been implemented in the aerospace, automotive, and biomedical fields. However, parts made from these polymers using traditional manufacturing processes are generally high-value parts in low-quantity production runs. Moreover, AM processing of these polymers present significant challenges due to limitations associated with large thermal gradients, residual stress buildup, and interlayer adhesion as well as the inability of the printers to consistently maintain required high processing temperatures. This review highlights the current state of the art for processing high-temperature (i.e., traditional processing temperatures exceeding 250°C) thermoplastic polymers by the melt-based, AM processes of material extrusion (MatEx) and laser powder bed fusion (PBF). The authors address common challenges to AM of high-temperature polymers and gaps in fundamental understanding of the process-structure-property relationships needed to identify the machine design, process parameter selection, and synthetic modifications to enable processing.

Current understanding and challenges in high temperature additive manufacturing of engineering thermoplastic polymers

ABSTRACT Fused filament fabrication (FFF) is an additive manufacturing process, which constructs physical items by fused melt material, selectively deposited layer-by-layer through a heated extrusion mechanism. Parameters’ selection and control in FFF are of utmost importance since they significantly affect the surface quality (SQ) and dimensional accuracy (DA) of the FFF printed parts. In the present paper, initially, the FFF process is briefly presented. Next, a cause-and-effect diagram exhibits the process parameters’ categorization with the SQ and DA of the manufactured parts. Then, according to the robust design theory, the process parameters are divided into three classes, i.e., the signal, the control, and the noise. This classification supports the selection of appropriate FFF printers, according to the control parameters, whereas it facilitates the optimization of the SQ and DA of printed parts, concerning the signal parameters. Finally, the impact of each parameter on SQ and DA is presented, supported by an extensive literature review. Overall, the process parameters’ optimization is critical for the SQ and DA. Therefore, they should be adjusted to achieve higher quality and less post-processing work.

Key parameters controlling surface quality and dimensional accuracy: a critical review of FFF process

Role of infill parameters on the mechanical performance and weight reduction of PEI Ultem processed by FFF

Recent advances in additive manufacturing (AM), also known as 3D printing, have enabled exponential growth in its application to the field of electronics and radio frequency (RF) technology. One of the most common 3D printing technologies, fused filament fabrication (FFF), can be used to fabricate a wide range of parts and is compatible with robust, production-ready materials. While FFF 3D printed parts have several attractive attributes, they tend to suffer from poor surface morphology – a critical parameter for printing high-quality conductive traces for electronics devices. In this paper, we present a novel methodology for modifying the surface of polyetherimide (PEI) FFF printed substrates using inkjet printed layers to form a smooth surface for accurate conductive trace formation. PEI substrates are commonly used in applications that must withstand harsh environments and require good dielectric performance. Therefore, the surface modification approach must also meet these high-performance requirements. As part of this work, an inkjet-compatible, thermally robust dielectric polyimide (PI) ink was utilized for the surface modification of the PEI substrates. However. the aggressive solvent present in the PI ink was not compatible with the PEI substrate. To solve this material compatibility issue, an intermediate layer of poly(ethylene glycol) diacrylate (PEGDA) was introduced between the PI and PEI substrate. It was demonstrated that the inkjet surface modification process dramatically reduces the surface roughness, making it suitable for printing conductive ink traces with improved RF performance. This surface modification methodology therefore presents an entirely AM-based fabrication solution for high quality AM components for next generation electronics and RF devices.

Surface modification of fused filament fabrication (FFF) 3D printed substrates by inkjet printing polyimide for printed electronics

Fused filament fabrication (FFF) is increasingly adopted for direct manufacturing of end use parts in an aviation industry. However, the application of FFF technique is still restricted to manufacturing low criticality lightly loaded parts, due to poor mechanical performance. To alleviate the mechanical performance issue, thermal annealing process is frequently utilized. However, problems such as distortion issues and the need for jigs and fixtures limit the effectiveness of the thermal annealing process, especially for low volume complex FFF parts. In this research, a novel low temperature thermal annealing is proposed to address the limitations in conventional annealing. A modified orthogonal array design is applied to investigate the performance of ULTEM™ 9085 FFF coupons. Further, the coupons are annealed with specialized support structures, which are co-printed with the coupons during the manufacturing process. Once the annealing process is completed, multiscale characterizations are performed to identify the mechanical properties of the specimens. Geometrical measurement of post annealed specimens indicates an expansion in the layering direction, which indicates relief of thermal stresses. Moreover, annealed coupons show an improvement in tensile strength and reduction in strain concentration. Mesostructure and fracture surface analysis indicate an increase in ductility and enhanced coalescence. This research shows that the proposed annealing methodology can be applied to enhance the mechanical performance of FFF parts without significant distortion.

The Effect of Annealing on Additive Manufactured ULTEM™ 9085 Mechanical Properties.

Mechanical study on the impact of an effective solvent support-removal methodology for FDM Ultem 9085 parts

Additive manufactured parts often require post-processing to obtain the desired surface finish. In this sense, this work investigates the ball burnishing process’s applicability as a finishing method for fused filament fabricated (FFF) parts. Ball burnishing is a mechanical finishing procedure based on the plastic deformation of the treated surface that could provide significant advantages, as it is non-abrasive and does not chemically interact with the model material. Following Taguchi’s design methodology, optimal values of four burnishing parameters have been identified, and significant improvements in surface quality have been quantitatively and qualitatively proven. Mechanical performance under tensile and flexural loading, impact testing, and bending fatigue of ball-burnished samples has been compared to pristine values. Besides the enhanced surface quality of the samples, a notable finding of the study is a minimum twofold increase in the fatigue life of ball-burnished samples, as well as a higher impact energy absorption. Accordingly, this research provides experimental evidence to set ball burnishing as a novel post-processing technique for FFF parts.

On the effect upon the surface finish and mechanical performance of ball burnishing process on fused filament fabricated parts

Additive manufacturing technologies are increasingly being used in production systems because they shorten product development time and production cost, but surface integrity remains a limitation to meet the standards set by conventional manufacturing. In this research article, two chemical, one thermal, and three mechanical finishing operations are proposed to post-process fused filament fabricated Ultem 9085 parts. Their effects on the parts’ surface quality and dimensional accuracy (changes in their width, height, length, and mass) are examined through optical and electron scanning microscopy, and the advantages and disadvantages of each method are discussed. Microscope evaluation has proven to be a powerful tool to observe apparent differences and understand the nature of different morphological changes. Results indicate that chemical and thermal treatments and ball burnishing are good candidates to significantly enhance the finish of the parts, despite requiring the use of solvents or provoking dimensional changes to the parts. The effects of abrasive mechanical treatments are more moderate at a macroscopic scale, but the surface of the filaments suffers the most remarkable changes.

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A Comparative Analysis of Chemical, Thermal, and Mechanical Post-Process of Fused Filament Fabricated Polyetherimide Parts for Surface Quality Enhancement

Ariadna Chueca de Bruijn

Papers

Mechanical study on the impact of an effective solvent support-removal methodology for FDM Ultem 9085 parts

On the effect upon the surface finish and mechanical performance of ball burnishing process on fused filament fabricated parts

A Comparative Analysis of Chemical, Thermal, and Mechanical Post-Process of Fused Filament Fabricated Polyetherimide Parts for Surface Quality Enhancement

Thermal annealing as a post-process for additively manufactured Ultem 9085 parts