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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (29 February 2024) | Viewed by 23428

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Dr. Wenzheng Wu

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Guest Editor

School of Mechanical and Aerospace Engineering, Jilin University, Changchun 130025, China
Interests: 3D printing; polymer additive manufacturing; biomimetic manufacturing; 4D printing; hybrid additive manufacturing
Special Issues, Collections and Topics in MDPI journals

Dr. Guiwei Li

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Guest Editor

School of Mechanical and Aerospace Engineering, Jilin University, Changchun 130025, China
Interests: 3D printing; additive manufacturing; biomimetic manufacturing; 4D printing; hybrid additive manufacturing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Additive manufacturing (AM), including 3D/4D printing, can be applied in many areas of engineering. Generally, 4D printing is described as the 3D printing of smart materials that can change shape or other properties over time under external stimuli, such as humidity, light, heat, electric fields, or magnetic fields. Polymer is the main material of additive manufacturing, and 3D/4D printing of complex polymer-based parts can be processed via FDM/FFF, SLS, SLA/DLP, IDW, and hybrid additive manufacturing technologies.

This Special Issue of Polymers aims to cover the state of the art of polymer-based materials in additive manufacturing, especially in 3D and 4D printing, with special emphasis on novel processing methods. Further, perspectives and critical reviews about the current limitations as well as future directions and emerging applications in the field are welcome.

Prof. Dr. Wenzheng Wu
Dr. Guiwei Li
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

3D printing
polymer additive manufacturing
4D printing
hybrid additive manufacturing
biomimetic manufacturing
FDM
FFF

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Research

20 pages, 38233 KiB

Open AccessArticle

Characterization of Exterior Parts for 3D-Printed Humanoid Robot Arm with Various Patterns and Thicknesses

by Dikshita Chowdhury, Ye-Eun Park, Imjoo Jung and Sunhee Lee

Polymers 2024, 16(7), 988; https://doi.org/10.3390/polym16070988 - 4 Apr 2024

Cited by 4 | Viewed by 1153

Abstract

Currently, metal is the most common exterior material used in robot development due to the need to protect the motor. However, as soft, wearable, and humanoid robots are gradually being developed, many robot parts need to be converted into artificial skin using flexible materials. In this study, in order to develop soft exterior parts for robots, we intended to manufacture exterior robot arm parts via fused filament fabrication (FFF) 3D printing according to various structural and thickness conditions and analyze their mechanical properties. The exterior parts of the robot arms were manufactured utilizing Shore 95 A TPU (eTPU, Esun, Shenzhen, China), which is renowned for its softness and exceptional shock absorption characteristics. The exterior robot arm parts were modeled in two parts, the forearm and upper arm, by applying solid (SL) and re-entrant (RE) structures and thicknesses of 1, 2, and 4 mm. The mechanical properties were analyzed through the use of three-point bending, tensile, and compression testing. All of the characterizations were analyzed using a universal testing machine (AGS-X, SHIMADZU, Kyoto, Japan). After testing the samples, it was confirmed that the RE structure was easily bendable towards the bending curve and required less stress. In terms of the tensile tests, the results were similar to the bending tests; to achieve the maximum point, less stress was required, and for the compression tests, the RE structure was able to withstand the load compared to the SL structure. Therefore, after analyzing all three thicknesses, it was confirmed that the RE structure with a 2 mm thickness had excellent characteristics in terms of bending, tensile, and compressive properties. Therefore, the re-entrant pattern with a 2 mm thickness is more suitable for manufacturing a 3D-printed humanoid robot arm. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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18 pages, 2599 KiB

Open AccessArticle

Additive and Lithographic Manufacturing of Biomedical Scaffold Structures Using a Versatile Thiol-Ene Photocurable Resin

by Michael Kainz, Stjepan Perak, Gerald Stubauer, Sonja Kopp, Sebastian Kauscheder, Julia Hemetzberger, Adrián Martínez Cendrero, Andrés Díaz Lantada, Disha Tupe, Zoltan Major, Dominik Hanetseder, Veronika Hruschka, Susanne Wolbank, Darja Marolt Presen, Michael Mühlberger and Elena Guillén

Polymers 2024, 16(5), 655; https://doi.org/10.3390/polym16050655 - 28 Feb 2024

Cited by 1 | Viewed by 1470

Abstract

Additive and lithographic manufacturing technologies using photopolymerisation provide a powerful tool for fabricating multiscale structures, which is especially interesting for biomimetic scaffolds and biointerfaces. However, most resins are tailored to one particular fabrication technology, showing drawbacks for versatile use. Hence, we used a resin based on thiol-ene chemistry, leveraging its numerous advantages such as low oxygen inhibition, minimal shrinkage and high monomer conversion. The resin is tailored to applications in additive and lithographic technologies for future biofabrication where fast curing kinetics in the presence of oxygen are required, namely 3D inkjet printing, digital light processing and nanoimprint lithography. These technologies enable us to fabricate scaffolds over a span of six orders of magnitude with a maximum of 10 mm and a minimum of 150 nm in height, including bioinspired porous structures with controlled architecture, hole-patterned plates and micro/submicro patterned surfaces. Such versatile properties, combined with noncytotoxicity, degradability and the commercial availability of all the components render the resin as a prototyping material for tissue engineers. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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23 pages, 4366 KiB

Open AccessArticle

Process Parameter Optimization for Hybrid Manufacturing of PLA Components with Improved Surface Quality

by Sergiu Pascu and Nicolae Balc

Polymers 2023, 15(17), 3610; https://doi.org/10.3390/polym15173610 - 31 Aug 2023

Cited by 7 | Viewed by 1361

Abstract

This paper presents a new method of process parameter optimization, adequate for 3D printing of PLA (Polylactic Acid) components. The authors developed a new piece of Hybrid Manufacturing Equipment (HME), suitable for producing complex parts made from a biodegradable thermoplastic polymer, to promote environmental sustainability. Our new HME equipment produces PLA parts by both additive and subtractive techniques, with the aim of obtaining accurate PLA components with good surface quality. A design of experiments has been applied for optimization purposes. The following manufacturing parameters were analyzed: rotation of the spindle, cutting depth, feed rate, layer thickness, nozzle speed, and surface roughness. Linear regression models and neural network models were developed to improve and predict the surface roughness of the manufactured parts. A new test part was designed and manufactured from PLA to validate the new mathematical models, which can now be applied for producing complex parts made from polymer materials. The neural network modeling (NNM) allowed us to obtain much better precision in predicting the final surface roughness (

R_{a}

), as compared to the conventional linear regression models (LNM). Based on these modelling methods, the authors developed a practical methodology to optimize the process parameters in order to improve the surface quality of the 3D-printed components and to predict the actual roughness values. The main advantages of the results proposed for hybrid manufacturing using polymer materials like PLA are the optimized process parameters for both 3D printing and milling. A case study has been undertaken by the authors, who designed a specific test part for their new hybrid manufacturing equipment (HME), in order to test the new methodology of optimizing the process parameters, to validate the capability of the new HME. At the same time, this new methodology could be replicated by other researchers and is useful as a guideline on how to optimize the process parameters for newly developed equipment. The innovative approach holds potential for widespread equipment functionality enhancement among other users. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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17 pages, 7731 KiB

Open AccessArticle

Thermomechanical Modeling of Material Flow and Weld Quality in the Friction Stir Welding of High-Density Polyethylene

by Bilal Ahmad, Fahad Almaskari, Jamal Sheikh-Ahmad, Suleyman Deveci and Kamran Khan

Polymers 2023, 15(15), 3230; https://doi.org/10.3390/polym15153230 - 29 Jul 2023

Cited by 3 | Viewed by 1866

Abstract

A thermomechanical model of the friction stir welding (FSW) of high-density polyethylene (HDPE) was developed by incorporating a Coupled Eulerian–Lagrangian (CEL) approach. A Johnson Cook (JC) material model of HDPE was developed through experimentally generated strain-rate- and temperature-dependent stress strain data. Two sets of FSW process parameters with minimum and maximum weld defects were numerically modeled. The numerically calculated temperature distribution, material flow and flash and potential defects were validated and discussed with the experimental results. Tracer particles allowed to visualize the material movement during and after the tool had traversed from the specified region of the workpiece. Both numerical models presented similar maximum temperatures on the upper surface of the workpiece, while the model with high traverse speed and slow rotational speed had narrower shoulder- and heat-affected zones than the slow traverse, high rotational speed model. This contributed to the lack of material flow, hence the development of voids and worm holes in the high traverse speed model. Flash and weld defects were observed in models for both sets of process parameters. However, slow traverse, high rotational speeds exhibited smaller and lesser weld defects than high traverse, slow rotational speeds. The numerical results based on the CEL approach and JC material model were found to be in good agreement with the experimental results. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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15 pages, 5651 KiB

Open AccessArticle

Optimizing the Rheological and Thermal Behavior of Polypropylene-Based Composites for Material Extrusion Additive Manufacturing Processes

by Giulia Bernagozzi, Daniele Battegazzore, Rossella Arrigo and Alberto Frache

Polymers 2023, 15(10), 2263; https://doi.org/10.3390/polym15102263 - 11 May 2023

Cited by 6 | Viewed by 2422

Abstract

In this study, composites based on a heterophasic polypropylene (PP) copolymer containing different loadings of micro-sized (i.e., talc, calcium carbonate, and silica) and nano-sized (i.e., a nanoclay) fillers were formulated via melt compounding to obtain PP-based materials suitable for Material Extrusion (MEX) additive manufacturing processing. The assessment of the thermal properties and the rheological behavior of the produced materials allowed us to disclose the relationships between the influence of the embedded fillers and the fundamental characteristics of the materials affecting their MEX processability. In particular, composites containing 30 wt% of talc or calcium carbonate and 3 wt% of nanoclay showed the best combination of thermal and rheological properties and were selected for 3D printing processing. The evaluation of the morphology of the filaments and the 3D-printed samples demonstrated that the introduction of different fillers affects their surface quality as well as the adhesion between subsequently deposited layers. Finally, the tensile properties of 3D-printed specimens were assessed; the obtained results showed that modulable mechanical properties can be achieved depending on the type of the embedded filler, opening new perspectives towards the full exploitation of MEX processing in the production of printed parts endowed with desirable characteristics and functionalities. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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18 pages, 7737 KiB

Open AccessArticle

The Energy Absorption Behavior of 3D-Printed Polymeric Octet-Truss Lattice Structures of Varying Strut Length and Radius

by Matthew Bolan, Mackenzie Dean and Alexander Bardelcik

Polymers 2023, 15(3), 713; https://doi.org/10.3390/polym15030713 - 31 Jan 2023

Cited by 10 | Viewed by 2951

Abstract

We investigate the compressive energy absorption performance of polymeric octet-truss lattice structures that are 3D printed using high-resolution stereolithography. These structures are potential candidates for personal protective equipment, structural, and automotive applications. Two polymeric resins (high-strength/low-ductility and moderate-strength/high-ductility) were used in this work, and a comprehensive uniaxial tensile characterization was conducted to establish an optimal UV curing time. The external octet-truss structure geometry (3″ × 3″ × 3″) was maintained, and four different lattice cell densities (strut length, L) and three different strut radii (R) were printed, UV cured, and compression tested. The compressive stress–strain and energy absorption (EA) behavior were quantified, and the EA at 0.5 strain for the least dense and smallest R structure was 0.02 MJ/m³, while the highest density structure with the largest R was 1.80 MJ/m³ for Resin 2. The structural failure modes varied drastically based on resin type, and it was shown that EA and deformation behavior were related to L, R, and the structures’ relative density (

\bar{ρ}

). For the ductile resin, an empirical model was developed to predict the EA vs. compressive strain curves based on L and R. This model can be used to design an octet-truss lattice structure based on the EA requirements of an application. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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26 pages, 5872 KiB

Open AccessArticle

Parametric Modeling and Optimization of Dimensional Error and Surface Roughness of Fused Deposition Modeling Printed Polyethylene Terephthalate Glycol Parts

by Prithu Mishra, Shruti Sood, Vipra Bharadwaj, Aryan Aggarwal and Pradeep Khanna

Polymers 2023, 15(3), 546; https://doi.org/10.3390/polym15030546 - 20 Jan 2023

Cited by 8 | Viewed by 2387

Abstract

Polyethylene Terephthalate Glycol (PETG) is a fused deposition modeling (FDM)-compatible material gaining popularity due to its high strength and durability, lower shrinkage with less warping, better recyclability and safer and easier printing. FDM, however, suffers from the drawbacks of limited dimensional accuracy and a poor surface finish. This study describes a first effort to identify printing settings that will overcome these limitations for PETG printing. It aims to understand the influence of print speed, layer thickness, extrusion temperature and raster width on the dimensional errors and surface finish of FDM-printed PETG parts and perform multi-objective parametric optimization to identify optimal settings for high-quality printing. The experiments were performed as per the central composite rotatable design and statistical models were developed using response surface methodology (RSM), whose adequacy was verified using the analysis of variance (ANOVA) technique. Adaptive neuro fuzzy inference system (ANFIS) models were also developed for response prediction, having a root mean square error of not more than 0.83. For the minimization of surface roughness and dimensional errors, multi-objective optimization using a hybrid RSM and NSGA-II algorithm suggested the following optimal input parameters: print speed = 50 mm/s, layer thickness = 0.1 mm, extrusion temperature = 230 °C and raster width = 0.6 mm. After experimental validation, the predictive performance of the ANFIS (mean percentage error of 9.33%) was found to be superior to that of RSM (mean percentage error of 12.31%). Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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15 pages, 4382 KiB

Open AccessArticle

Hybrid Manufacturing of Acrylonitrile Butadiene Styrene (ABS) via the Combination of Material Extrusion Additive Manufacturing and Injection Molding

by Ke Gong, Handai Liu, Cheng Huang, Zhi Cao, Evert Fuenmayor and Ian Major

Polymers 2022, 14(23), 5093; https://doi.org/10.3390/polym14235093 - 23 Nov 2022

Cited by 15 | Viewed by 3426

Abstract

Acrylonitrile Butadiene Styrene (ABS) is a common thermoplastic polymer that has been widely employed in the manufacturing industry due to its impact resistance, tensile strength, and rigidity. Additive manufacturing (AM) is a promising manufacturing technique being used to manufacture products with complex geometries, but it is a slow process producing mechanically inferior products when compared to traditional production processes like injection molding (IM). Thus, our hybrid manufacturing (HM) process combining materials extrusion AM and IM to create a single article was investigated in this study, in which eleven batches of specimens were made and extensively tested. These include the AM, IM, and hybrid manufactured (HYM) samples, in which the HYM samples were made by inserting AM substrates into the IM tool and were varied in infill density of AM preforms and geometries. The HYM samples outperformed AM parts in terms of mechanical performance while retaining customizability dependent on the HYM processing parameters, and the best mechanical performance for HYM samples was found to be comparable to that of IM samples, implying that the overmolding process in HM had primarily improved the mechanical performance of AM products. This work leads to a deeper knowledge of applications to confirm the optimal component fabrication in high design flexibility and mass production. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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10 pages, 1904 KiB

Open AccessArticle

Influence of Parameters and Performance Evaluation of 3D-Printed Tungsten Mixed Filament Shields

by Myeong Seong Yoon, Hui Min Jang and Kyung Tae Kwon

Polymers 2022, 14(20), 4301; https://doi.org/10.3390/polym14204301 - 13 Oct 2022

Cited by 2 | Viewed by 1894

Abstract

Currently, protective clothing used in clinical field is the most representative example of efforts to reduce radiation exposure to radiation workers. However, lead is classified as a substance harmful to the human body that can cause lead poisoning. Therefore, research on the development of lead-free radiation shielding bodies is being conducted. In this study, the shielding body was manufactured by changing the size, layer, and height of the nozzle, using a 90.7% pure tungsten filament, a 3D printer material, and we compared its performance with existing protection tools. Our findings revealed that the shielding rate of the mixed tungsten filament was higher than that of the existing protective tools, confirming its potency to replace lead as the most protective material in clinical field. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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22 pages, 16294 KiB

Open AccessArticle

Hybrid Additive Manufacturing of Fused Filament Fabrication and Ultrasonic Consolidation

by Wenzheng Wu, Haiming Wang, Jiaqi Wang, Qingping Liu, Zheng Zhang, Ke Li, Yuhan Gong, Ji Zhao, Luquan Ren and Guiwei Li

Polymers 2022, 14(12), 2385; https://doi.org/10.3390/polym14122385 - 12 Jun 2022

Cited by 8 | Viewed by 2716

Abstract

Fused filament fabrication (FFF) additive manufacturing technology has the advantages of being low cost, having a simple operation, using wide types of molding materials, and producing less pollution during the printing process. However, the mechanical properties of the molded sample are unsatisfactory due to the limited bonding force between the filaments during the forming process, which limits its further development and application in the engineering field. Herein, the hybrid additive manufacturing technology for heterogeneous materials based on the ultrasonic-assisted enhanced fused filament fabrication technology was proposed. The mechanism of ultrasonic vibration on the strengthening of FFF samples was explored. The influence mechanisms of bonding time and ultrasonic strengthening times, ultrasonic strengthening and static load compression on the strengthening of mechanical properties of the sample were investigated. The effects of the thickness and printing angle of the FFF samples on the ultrasonic-enhanced mechanical properties were explored. The tensile strength of the one-time ultrasonic-strengthened sample is up to 43.43 MPa, which is 16.12% higher than that of the original. The maximum bending strength of the four-time ultrasonic-strengthened sample is 73.38 MPa, which is 78.98% higher than that of the original. Ultrasonic strengthening not only re-fused the pores inside the sample, but also improved the bond strength between the rasters. With the increase in the thickness of the sample, the increase rate of ultrasonic to the strength of the sample decreased significantly. The effects of ultrasound on the interlayer adhesion of samples with various printing angles were different. Based on the systematic research on the influence mechanism of ultrasonic process parameters and molding process parameters on the strengthening of FFF, a molding method for additively manufacturing heterogeneous material parts while strengthening the mechanical properties of FFF samples was proposed, and the influence mechanisms of the molding process on the mechanical properties and shape memory properties of the sample were explored, which can broaden the application of FFF technology in the engineering field. Full article

(This article belongs to the Special Issue Additive Manufacturing of Polymers)

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