Optimization of process parameters in fused deposition modelling of thermoplastics: A review

Among the several techniques for additive manufacturing (AM), fused deposition modelling (FDM) is widely used. Fused deposition modelling process uses a thermoplastic material, which is melted and then extruded layer by layer through a nozzle, in order to create a three-dimensional object. As a result of the default setting of process parameters provided by the manufacturers, produced parts normally have a poor surface finish, low mechanical properties, low dimensional accuracy, and increased residual stresses compared to the parts produced using conventional manufacturing processes like molding (casting). Qualities of fused deposition modelled (FDMed) parts are generally affected by process parameters including the layer thickness, extrusion temperature, build orientation, printing speed, raster angle, infill density, raster width, nozzle diameter, and air gap. Increasing infill density, printing temperature, and decreasing print speed and layer thickness lead to increase mechanical strength and improve the surface finish of the printed parts. The optimal process parameters are preferred to achieve superior properties of the parts. This paper reviews the optimal fused deposition modelling process parameters on part qualities for making the stability of used deposition modelled parts for use. Various process parameters are identified in order to obtain desirable qualities in the manufactured parts. Areas for future research are proposed.     

Performance evaluation of ProJet multi-material jetting 3D printer

The purpose of this paper is to quantitatively evaluate the performance of a multi-material jetting 3D printer, ProJet 5500X, especially the capability for micro manufacturing. Unlike other single material 3D printer, ProJet 5500X uses photopolymers as the build material and wax as the support material. The building performance was evaluated by building a modified version of the standard benchmark model with a high-resolution printing mode. The dimensional error, forming quality and surface roughness of the printed parts have been measured and analysed using a microscope, a 3D coordinate measuring machine and a surface profilometer. Using wax as the support material, fine features as small as 0.25?mm, lateral features and sharper edges could all be properly built, despite the rough side surfaces observed in the printed part. Identical features (3?mm pins) were precisely built with an accuracy of 15?µm. The research provides first-hand detailed performance knowledge in the ProJet system for understanding the working principle and comparison with other 3D printing systems.     

Investigation on the effect of surface modification of 3D printed parts by nanoclay and dimethyl ketone

Fused deposition modeling (FDM) has emerged as one of the most utilized 3D printing technique. However, the surface properties of the FDM built parts lacks integrity due to layer by layer manufacturing technique. Therefore, post treatment is done on FDM printed parts. In the present research work, an effort has been made to improve the surface properties of the 3D printed parts by surface modification via chemical/nanoparticles. Nanoclay and dimethyl ketone were utilized for the surface modification of acrylonitrile butadiene styrene specimens. Parameters namely nanoclay content, immersion time, heat treatment and layer thickness were investigated to study their effect on surface roughness, surface hardness and dimensions. Also, the effect of nanoclay on UV absorbance of 3D printed parts was observed. Structural and morphological analysis was performed to characterize the surface of the 3D printed specimens after surface modification process. The results show that the surface roughness was reduced by 94.9%, surface hardness was increased by 9.7% while maintaining minimum dimensional deviation of ?0.03 and +0.07?mm. Also, UV absorbance was increased in 350–380?nm range. The results of the present study highlight the capability of the surface modification process for improving the surface properties of FDM parts.     

An experimental and theoretical investigation of surface roughness of poly-jet printed parts

The present study has attempted to investigate and model surface roughness on parts printed using a poly-jet additive manufacturing system. Initially the study investigated the effect of layer thickness, local surface orientation and finish type on surface roughness in poly-jet printed parts. The study shows that the surface orientation and finish type are the major factors affecting surface roughness of poly-jet parts. Then a detailed experimental study was conducted by varying surface orientation in very close intervals to obtain the surface roughness distribution. The study reveals that surface roughness distribution for poly-jet parts is different from that obtained for parts made by other additive manufacturing processes. A detailed experimental and theoretical analysis of droplet geometry, as formed by the jetting process, and its effect on the edge profile of the polymerised layer is presented. A surface roughness prediction model is proposed based on these studies and validated using profilometric measurements.     

Stereolithographic 3D Printing of Ceramics: Challenges and Opportunities for Structural Integrity

This article reviews the current activities at the Montanuniversität Leoben on the design, processing, and characterization of 3D printed advanced ceramics using the lithography-based manufacturing technology. An overview of the challenges and the opportunities offered to improve the mechanical properties of printing ceramics is given. Their brittle failure is analyzed within the framework of linear elastic fracture mechanics, considering specific aspects of additive manufacturing. Several issues associated with the printing process are addressed, such as surface quality, geometry control, influence of printing directions, as well as the need to establish testing protocols for 3D printed parts. Based on the layer-by-layer capabilities of the stereolithographic process, bio-inspired material design concepts are discussed aiming to enhance the mechanical resistance of 3D-printed ceramics. By tailoring the layer architecture and microstructure of the parts, high strength and fracture resistance may be achieved.     

脱脂工艺对光固化3D打印堇青石陶瓷性能的影响

光固化3D打印是制造高度复杂结构陶瓷的一种有效方法。打印的样件需要经历脱脂和烧结等热处理才能成为可用的陶瓷件, 脱脂工艺对打印件性能影响巨大。本工作通过研究脱脂工艺对DLP光固化3D打印制备的堇青石陶瓷性能的影响规律, 建立缺陷抑制策略。比较并分析了脱脂气氛和升温速率对陶瓷样件的表面裂纹和元素分布状态的影响, 还对比进一步烧结后样件显微组织、尺寸收缩率、相对密度和弯曲强度等性能。研究发现脱脂气氛对样件各性能影响最大, 使用氩气脱脂可显著降低表面裂纹, 提高相对密度与弯曲强度; 并确定最佳升温速率为1 ℃/min。最终获得表面完整无裂纹且相对密度为(94.6±0.3)%, 弯曲强度为(94.3±3.2) MPa的堇青石陶瓷样件。本研究为光固化3D打印堇青石陶瓷的无缺陷制造与应用提供了科学依据与技术参考。     

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

Abstract

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.     

Numerical study of the interfaces of 3D‐printed concrete using discrete element method

3D concrete printing is an additive manufacturing method which reduces the time and improves the efficiency of the construction process. Structural behavior of printed elements is strongly influenced by the properties of the material and the interface surfaces. The printing process creates interface surfaces between layers in the horizontal and vertical directions. The bond strength between layers is the most critical property of printed elements. In this paper, the structural behavior of printed elements is studied using the discrete element method. The material is modelled using discrete particles with bonding between them. A new discrete model of a multilayer geometry is presented to study the behavior of the interfaces of printed concrete. The layers are made up of randomly placed particles to simulate the heterogeneous nature of concrete. The numerical model is developed to simulate the flexural behavior of multilayer specimens. A four‐point flexural test is simulated considering the interface surfaces between layers. This numerical model provides relevant results to improve the behavior of this kind of structural elements. The aim of this work is to provide a discrete element model to predict the mechanical behavior of 3D concrete printed components.     

Thermal and mechanical properties of 3D printed boron nitride – ABS composites

The current work investigates the thermal conductivity and mechanical properties of Boron Nitride (BN)-Acrylonitrile Butadiene Styrene (ABS) composites prepared using both 3D printing and injection molding. The thermally conductive, yet electrically insulating composite material provides a unique combination of properties that make it desirable for heat dissipation and packaging applications in electronics. Materials were fabricated via melt mixing on a twin-screw compounder, then injection molded or extruded into filament for fused deposition modeling (FDM) 3D printing. Compositions of up to 35 wt.% BN in ABS were prepared, and the infill orientation of the 3D printed composites was varied to investigate the effect on properties. Injection molding produced a maximum in-plane conductivity of 1.45 W/m-K at 35 wt.% BN, whereas 3D printed samples of 35 wt.% BN showed a value of 0.93 W/m-K, over 5 times the conductivity of pure ABS. The resulting thermal conductivity is anisotropic; with the through-plane thermal conductivity lower by a factor of ~3 for injection molding and ~4 for 3D printing. Adding BN flakes caused a modest increase in the flexural modulus, but resulted in a large decrease in the flexural strength and impact toughness. It is shown that although injection molding produces parts with superior thermal and mechanical properties, BN shows much potential as a filler material for rapid prototyping of thermally conductive composites.     

3D Printed Graphene-Based Metamaterials: Guesting Multi-Functionality in One Gain

Advanced functional materials with fascinating properties and extended structural design have greatly broadened their applications. Metamaterials, exhibiting unprecedented physical properties (mechanical, electromagnetic, acoustic, etc.), are considered frontiers of physics, material science, and engineering. With the emerging 3D printing technology, the manufacturing of metamaterials becomes much more convenient. Graphene, due to its superior properties such as large surface area, superior electrical/thermal conductivity, and outstanding mechanical properties, shows promising applications to add multi-functionality into existing metamaterials for various applications. In this review, the aim is to outline the latest developments and applications of 3D printed graphene-based metamaterials. The structure design of different types of metamaterials and the fabrication strategies for 3D printed graphene-based materials are first reviewed. Then the representative explorations of 3D printed graphene-based metamaterials and multi-functionality that can be introduced with such a combination are further discussed. Subsequently, challenges and opportunities are provided, seeking to point out future directions of 3D printed graphene-based metamaterials.     

Development and characterisation of 3D printing finishing process applying recycled plastic waste

In recent years, additive manufacturing technologies have been playing an important role in the global economy. Consequently, low-cost 3D printers rose in the domestic environment, accelerating the development of startup companies and new market segments. Nevertheless, with regard to 3D printing based on fused filament fabrication, several challenges still need to be overcome, such as those related to surface finishing and mechanical strength. Moreover, 3D printing in the domestic environment also generates untreated plastic waste, which can cause environmental problems. For these reasons, the main goal of this work is to introduce and characterise 3D printing surface finishing post-processing using recycled plastic waste. As the main results of this work, the proposed recycling process was confirmed to improve object properties. Whereas surface roughness was reduced from 27 to 3?µm, while mechanical strength was increased in 20 times. The application of recycled material for chemical welding was also seen to be feasible.     

Flexural properties of three-dimensional printed continuous wire polymer composites

Recently, continuous fibre reinforcement has been combined with three-dimensional (3D) printing to create stiffer printed components. This study investigates the effect of wire volume fraction, type of polymer matrix, and wire treatment on the flexural properties of 3D printed continuous wire polymer composites (CWPCs) through a design of experiment study. CWPC samples were printed using a modified, open-source 3D printer. The flexural properties were measured and compared to non-reinforced samples. An analytical model was developed to describe the stress distribution across unidirectional CWPCs as a function of the geometrical printing parameters, reinforcement dimensions, and material properties. Sample failure analysis was performed to investigate failure modes and offer insight into further enhancement of the composite’s properties.     

Nanofinishing of FDM-fabricated components using ball end magnetorheological finishing process

Fused deposition modeling (FDM) is among the extensively used and the most economical additive manufacturing processes. Currently, the surface finish obtained for FDM additive manufactured parts are not at par with the current industrial application. To overcome the limitation of high surface roughness of 3D printed parts, a novel finishing technique has been proposed which includes primary and secondary finishing processes. While facing and lapping has been used as primary finishing technique, the secondary finishing involves the use of ball end magnetorheological finishing (BEMRF) process. BEMRF process is an unconventional finishing process which utilizes an advanced approach to impart finish on magnetic as well as non-magnetic materials that may be flat or freeform in shape. This article presents the experimental and analytical study to finish a polylactic acid (PLA) workpiece material manufactured by FDM process and finished using the BEMRF technique. The surface roughness of the FDM component has been reduced from initial surface roughness Ra = 20 µm to final value of Ra = 81 nm by combined primary and secondary finishing processes. The effect of magnetorheological polishing (MRP) fluid’s composition and finishing time is discussed and is followed by optimization of MRP fluid for maximum percentage reduction in surface roughness.     

3D printing of tuneable agglomerates: Strain distribution and effect of internal flaws

The current study presents a novel and reliable method for producing 3D printed agglomerates with different colour distributions and material properties with 2-fold aims: providing feasible and accurate control on compression of agglomerates under different compression angles, and better tracking of individual particle position after agglomerate breakage. Multi-coloured agglomerates in cubic tetrahedral and random sphere shapes were printed with both rigid and soft bonds. The printed agglomerates were analysed thoroughly of their surface and structural properties including surface roughness and printing accuracy. The agglomerate breakage behaviours under static compression were analysed as a function of bond strength, loading rate and loading directions, with strain distribution plotted over the random sphere agglomerate structure. In addition, agglomerate structures with designed internal macro-voids in different positions and sizes were also created for breakage study, in an effort to better understand parameters governing the mechanical properties of agglomerates with cavities and voids which is inevitable in particle industry but poorly understood at present.     

Modeling thermal and mechanical cancellation of residual stress from hybrid additive manufacturing by laser peening

Additive manufacturing(AM) of metals often results in parts with unfavorable mechanical properties. Laser peening(LP) is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties. Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material. This work investigates the role of LP on layer-by-layer processing of 3 D printed metals using finite element analysis. The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening. Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process. Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties. With this study, hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.     

Additive manufacturing of mechanical testing samples based on virgin poly (lactic acid) (PLA) and PLA/wood fibre composites

3D printing in additive manufacturing is considered as one of key technologies to the future high-precision manufacturing in order to benefit diverse industries in building construction, product development, biomedical innovation, etc. The increasing applications of 3D printed components depend primarily on their significant merits of reduced weight, minimum used materials, high precision and shorter production time. Furthermore, it is very crucial that such 3D printed components can maintain the same or even better material performance and product quality as those achieved by conventional manufacturing methods. This study successfully fabricated 3D printed mechanical testing samples of PLA and PLA/wood fibre composites. 3D printing parameters including infill density, layer height and the number of shells were investigated via design of experiments (DoE), among which the number of shells was determined as the most significant factor for maximising tensile strengths of PLA samples. Further, DoE work evaluated the effect of material type (i.e., neat PLA and PLA/wood fibres) and the number of shells on tensile, flexural and impact strengths of material samples. It is suggested that material type is the only predominant factor for maximising all mechanical strengths, which however are consistently lower for PLA/wood fibre composites when compared with those of neat PLA. Increasing the number of shells, on the other hand, has been found to improve almost all strength levels and decrease infill cavities. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0211-3     

印刷法制备功能芯片的研究进展

目的概述印刷芯片的制备方法和研究现状,开拓印刷技术的研究思路和应用场景,为印刷芯片的发展提供参考。方法从印刷材料、印刷方法和芯片应用3个方面介绍近年来印刷芯片的研究进展,重点对比各种印刷方法的关键科学问题及特点,并且指出芯片印刷的发展方向。结果基于印刷方法在大面积制备、材料兼容性、绿色环保等方面的优势,印刷芯片在显示、能源、生物、智能包装等诸多方面快速发展,不过仍然面临高精度、规模化、功能集成方面的挑战。结论通过更好地调控印刷过程中液滴成型,构筑功能材料精细微纳结构,实现高精度器件与芯片全印刷制造。未来在实现智能、自动、互联化功能芯片制造的同时,发展绿色可持续印刷新策略。     

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.     

Fracture Surface Analysis of 3D-Printed Tensile Specimens of Novel ABS-Based Materials

One of the most common materials utilized by material extrusion 3D printing is acrylonitrile butadiene styrene (ABS). The work presented in this research explored the effect of the addition of reinforcing materials on the mechanical properties of ABS in an effort to create materials with enhanced physical properties. A comparison was made between pure ABS, two ABS matrix composites, and one ABS/elastomer blend with the purpose of characterizing the effect of additives on the mechanical properties. Tensile test results of specimens built in different orientations showed that ABS reinforced with 5% by weight TiO₂ exhibited the highest ultimate tensile strength for specimens built in both horizontal and vertical directions with 32.2 and 18.4 MPa, respectively. The compounding of an elastomeric material with ABS improved the surface finish of parts as they were visibly smoother compared to those printed from the ABS baseline material, though there was an observable decrease in the ductility of tensile specimens. Analysis was performed on the fracture surface of the tensile specimens through the use of scanning electron microscopy. Fractography revealed different modes of failure related to the different additives. The effects of additives on the anisotropy associated with the mechanical properties of 3D-printed parts were also analyzed.     

Two-Way 4D Printing: A Review on the Reversibility of 3D-Printed Shape Memory Materials

The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional (4D) printing. With the right external stimulus, the need for human interaction, sensors, and batteries will be eliminated, and by using additive manufacturing, more complex devices and parts can be produced. With the current understanding of shape memory mechanisms and with improved design for additive manufacturing, reversibility in 4D printing has recently been proven to be feasible. Conventional one-way 4D printing requires human interaction in the programming (or shape-setting) phase, but reversible 4D printing, or two-way 4D printing, will fully eliminate the need for human interference, as the programming stage is replaced with another stimulus. This allows reversible 4D printed parts to be fully dependent on external stimuli; parts can also be potentially reused after every recovery, or even used in continuous cycles—an aspect that carries industrial appeal. This paper presents a review on the mechanisms of shape memory materials that have led to 4D printing, current findings regarding 4D printing in alloys and polymers, and their respective limitations. The reversibility of shape memory materials and their feasibility to be fabricated using three-dimensional (3D) printing are summarized and critically analyzed. For reversible 4D printing, the methods of 3D printing, mechanisms used for actuation, and strategies to achieve reversibility are also highlighted. Finally, prospective future research directions in reversible 4D printing are suggested.