Additive ram material extrusion and diddling of fully compounded thermoset nitrile rubber

Abstract

A ram extruder is described for high-pressure extrusion of fully compounded thermoset rubber to achieve additive manufacturing. The extruder uses a piston driven by a geared stepper motor to provide volumetric displacement of the rubber charge residing in a temperature-controlled barrel. Along with activators, accelerators, and a vulcanizing agent, the rubber compound is a formulation of 30 parts carbon black per hundred parts nitrile rubber. Sets of serpentine patterns are printed in parallel and transverse orientations relative to the load direction. From printing to post-cure, the printed specimens exhibited linear shrinkage of 65% in the print direction. Although printed samples had relatively low void content compared with typical additively manufactured parts by material extrusion, significant decreases in the tensile properties were observed relative to compression-molded specimens of the same rubber compound. The mean strain to failure was observed as 462% for compression-molded samples, compared with 347% and 183% for printed specimens with parallel and transverse orientations. To reduce the shrinkage and increase the interfacial area between extruded roads, backstitch and sinewave diddling patterns were implemented to superimpose oscillatory motions along the print path with a periodicity of 1 mm. The specimens printed with the diddling patterns were observed to provide less shrinkage and improved properties compared to the regular serpentine patterns. The mean strain to failure in the transverse orientation, respectively, increased to 218% and 265% for the backstitch and sinewave patterns. Suggested future research is discussed, and the diddling program is provided in the appendix. K E Y W O R D S material extrusion, nitrile rubber, diddling patterns, 3D printing, thermoset rubber 1 | INTRODUCTION Additive manufacturing provides a means by which complex products may be made without tooling. ASTM F2792: Standard Terminology for Additive Manufacturing Technologies defines seven families of additive manufacturing. Of

Polymer composites–Special issue review for additive manufacturing of composites

“…There remains a strong industrial need for thermoset composites to be fabricated using AM techniques. This is shown by Kazmer et al 27 who compound a nitrile rubber thermoset. Rahman et al 29 introduce a UV curable resin for continuous carbon fiber thermoset composites.…”

“…This issue is highlighted by several review articles detailing recent advances in the additive manufacturing technology space including advances in the area of smart materials, 1 coatings of bio-polymer systems, 2 applications with natural materials for the matrix and the fiber, 3 recent advances in the performance of fiber filled polymer systems for the FFF process. 4 Papers in this special issue range from the use of bio and bio-inspired materials, 2,3,5-12 materials and material systems that benefit from nanoscale enhancements, [13][14][15][16][17][18][19][20][21][22][23] advances in the medical field, [24][25][26] additive material systems utilizing thermosets, [27][28][29] large scale additive manufacturing, [30][31][32] and some rather novel applications in AM. 1,[33][34][35] Several articles focus on improvements for characterization, [36][37][38][39] and quite a few seek to identify parameters to enhance the final part performance through processing improvements.…”

Polybutadiene Click Chemistry: A Rapid and Direct Method for Vat Photopolymerization

“…Fused filament fabrication and direct ink write have been used to print flexible materials such as thermoplastic polyurethane 1,2 and compounded rubber, 3 but due to the inherent mechanical properties of elastomers, these techniques remain limited for a wide range of soft materials compared to the possibilities offered via vat photopolymerization (VP). 4 In addition to the growing number of commercial VP resins with undisclosed formulations, academic research has been prolific in recent years, 3 using VP techniques to print elastomers such as high molecular weight latexes 5 and polysiloxanes with high stretchability. 6 Although the soft materials listed above are indeed significant advancements in 3D printing, there is a need to expand the library of available materials that can be printed, especially to include commodity polymers such as diene rubbers.…”

Polymer composites: Additive manufacturing of composites

“…Researchers are studying a wide variety of polymer systems, with some authors identifying ways to form hybrid materials using both thermosets and thermoplastics, such as the work of Setter [ 9 ] who hybridizes thermoplastic powders with a liquid thermoset or the work of Subbarayan [ 15 ] and solution casting. Kazmar [ 28 ] demonstrates a material system with improved toughness by the addition of nitrile rubbers to the thermoset in an extrusion‐based AM process. Bio‐ and sustainability inspired research was a major theme, including the use of nature‐derived materials, green or environmentally friendly materials, sustainable applications, and medical applications.…”

“…The papers published in this special issue of Polymer Composites give the polymer composites engineer insight into challenges that exist in the field of additive manufacturing (AM) of composites, the presentation of new materials and material systems, improvements on the resulting properties of 3D printed parts using existing manufacturing methods, new and novel applications of 3D printed polymer composite parts, and how problems that arise from these innovations are being addressed by the research community. [ 1–29 ]…”