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The purpose of this paper is provide a broad view for the standardization efforts of color quality evaluation of color 3D printing techniques. Further, this review paper demonstrates the processes and color properties of most color 3D printing techniques with specific devices and applications to extend the range of possible memberships of standardization group.

Six color 3D printing techniques including plastic-based, paper-based, powder-based, organism-based, food-based and metal-based color 3D printing have been introduced and illustrated with colorization principles and forming features in detail. Moreover, for printed 3D color objects, literature about color measurement, color specification and color reproduction are described and analyzed, respectively.

Four color 3D printing techniques including plastic-based, paper-based, powder-based and food-based color 3D printing show great affinity toward standardization of color quality evaluation, while their colorization principles indicate that it is difficult with a single standard frame. It is possible to develop a completed color quality evaluation standard for color 3D printing based on approaches in color 2D printing when color measurement method and devices are standardized together.

The paper provides an important guide focusing on the efforts to standardize the colorization processes and color quality evaluation of the color 3D printing techniques.

This paper aims to summarize the up-to-date research performed on combinations of various biofibers and resin systems used in different three-dimensional (3D) printing technologies, including powder-based, material extrusion, solid-sheet and liquid-based systems. Detailed information about each process, including materials used and process design, are described, with the resultant products’ mechanical properties compared with those of 3D-printed parts produced from pure resin or different material combinations. In most processes introduced in this paper, biofibers are beneficial in improving the mechanical properties of 3D-printed parts and the biodegradability of the parts made using these green materials is also greatly improved. However, research on 3D printing of biofiber-reinforced composites is still far from complete, and there are still many further studies and research areas that could be explored in the future.

The paper starts with an overview of the current scenario of the composite manufacturing industry and then the problems of advanced composite materials are pointed out, followed by an introduction of biocomposites. The main body of the paper covers literature reviews of recently emerged 3D printing technologies that were applied to biofiber-reinforced composite materials. This part is classified into subsections based on the form of the starting materials used in the 3D printing process. A comprehensive conclusion is drawn at the end of the paper summarizing the findings by the authors.

Most of the biofiber-reinforced 3D-printed products exhibited improved mechanical properties than products printed using pure resin, indicating that biofibers are good replacements for synthetic ones. However, synthetic fibers are far from being completely replaced by biofibers due to several of their disadvantages including higher moisture absorbance, lower thermal stability and mechanical properties. Many studies are being performed to solve these problems, yet there are still some 3D printing technologies in which research concerning biofiber-reinforced composite parts is quite limited. This paper unveils potential research directions that would further develop 3D printing in a sustainable manner.

This paper is a summary of attempts to use biofibers as reinforcements together with different resin systems as the starting material for 3D printing processes, and most of the currently available 3D printing techniques are included herein. All of these attempts are solutions to some principal problems with current 3D printing processes such as the limit in the variety of materials and the poor mechanical performance of 3D printed parts. Various types of biofibers are involved in these studies. This paper unveils potential research directions that would further widen the use of biofibers in 3D printing in a sustainable manner.

The purpose of this work is to introduce a novel approach of using additive manufacturing (AM) to produce dense complex ceramic and metallic parts. Powder 3D printing has been gaining popularity due to its ease of use and versatility. However, powder-based methods such as Selective Laser Melting (SLM) and Sintering (SLS), utilizes high power lasers which generate thermal shock conditions in metals and are not ideal for ceramics due to their high melting temperature. Indirect additive manufacturing methods have been explored to address the above issues but have proven to be wasteful and time-consuming.

In this work, a novel approach of producing high density net-shaped prototypes using subtractive sintering (SS) and solvent jetting is developed. AM combined with SS (AM-SS) is a process that includes five simple steps. AM-SS can produce repeatable and reliable results as has been shown in this work.

As a proof-of-concept, a zirconia dental crown with a high density of 97% is fabricated using this approach. Microstructure and properties of the fabricated components are analyzed.

A major advantage of this method is the ability to efficiently fabricate high density parts using either metal powder and more importantly, ceramic powder which is traditionally difficult to densify using AM. Additionally, any powder particle size (including nano) and shape can be used which is not the case for traditional powder-based 3D printing.

This paper aims to present the results that can be achieved using continuous three-dimensional (3D) printing technology.

In the first section, conventional additive manufacturing and continuous 3D-printing are described and compared against each other. Essential is the new approach to coat the particulate material and to print it on a tilted surface. For this special setup, theoretical considerations for sources of distortions are given. These considerations define the design of the test parts. For the evaluation of a tilted setup a prototype using large dimensions is shown. Of special interest is the exact transportation using a large mass of particulate material.

The 3D-printing principle is suitable for tilted surfaces, making production without any downtime possible. The parts produced using the prototype continuous 3D-printer have sufficient accuracy for foundry use, although various considerations and the setup show that angular deflections can be caused by inaccuracies in the feeding system.

The parts’ accuracy is additionally affected by the thickness of unbound particle material under the building area. The amount of unbound particle material is of a constructive nature. Thus, the setup is limiting the investigations. Using the current material system, the printing should take place as near to the conveyor belt as possible.

This paper outlines which kind of parts can be manufactured using continuous 3D-printing.

This article shows a first evaluation of parts printed using continuous 3D-printing. It gives a perspective on future designs from rapid prototyping machines based on these principles and shows the possible benefits. The change over from rapid prototyping to rapid manufacturing will be strongly accelerated by said machine design.

In recent years, 3D printing technologies have been widely used in the construction industry. 3D printing in construction is very attractive because of its capability of process automation and the possibility of saving labor, waste materials, construction time and hazardous procedures for humans. Significant researches were conducted to identify the performance of the materials, while some researches focused on the development of novel techniques and methods, such as building information modeling. This paper aims to provide a detailed overview of the state-of-the-art of currently used 3D printing technologies in the construction areas and global acceptance in its applications.

The working principle of additive manufacturing in construction engineering (CE) is presented in terms of structural design, materials used and theoretical background of the leading technologies that are used to construct buildings and structures as well as their distinctive features.

The trends of 3D printing processes in CE are very promising, as well as the development of novel materials, will gain further momentum. The findings also indicate that the digital twin (DT) in construction technology would bring the industry a step forward toward achieving the goal of Industry 5.0.

This review highlights the prospects of digital manufacturing and the DT in construction engineering. It also indicates the future research direction of 3D printing in various constriction sectors.

This paper aims to focus on redesigning a 3D printing machine, using piezoelectric demand‐mode technology head in order to improve the factors of accuracy, surface finishing and color quality of fabricated models.

The work first identifies two kinds of ink‐jet printing heads, and then develops a new design of 3D printing machine, based on piezoelectric head technology. Fabricated models by this new 3D printing machine were compared with the same models fabricated by current 3D printing machines (z406).

The comparison between the constructed models by two types of 3D printing machines shows improvement factors of accuracy, surface finishing and color quality using piezoelectric head in the current 3D printing machine.

In order to provide a colorful binder, a type of binder such as ZB56 was combined with six different colors of ink namely black, cyan, magenta, yellow, light cyan, and light magenta.

The new designed and manufactured 3D printing machine provides the ability to construct more accurate models with improved quality.

Apart from the above practical implications, this work provides an accurate tool for injection of the live cells into vital textures in order to create bones, members and dentures without any chemical or physical changes in cells.

This paper aims to investigate the mechanical behavior of three-dimensional (3D) calcium sulfate porous structures created by a powder-based 3D printer. The effects of the binder-jetting and powder-spreading orientations on the microstructure of the specimens are studied. A micromechanical finite element model is also examined to predict the properties of the porous structures under the load.

The authors printed cylindrical porous and solid samples based on a predefined designed model to study the mechanical behavior of the prototypes. They investigated the effect of three main build bed orientations (x, y and z) on the mechanical behavior of solid and porous specimens fabricated in each direction then evaluated the micromechanical finite-element model for each direction. The strut fractures were analyzed by scanning electron microscopy, micro-computed tomography and the von Mises stress distribution.

Results showed that the orientation of powder spreading and binder jetting substantially influenced the mechanical behavior of the 3D-printed prototypes. The samples that were fabricated parallel to the applied load had higher compressive strength compared with those printed perpendicular to the load. The results of the finite element analysis agreed with the results of the experimental mechanical testing.

The mechanical behavior was studied for the material and the 3D-printing machine used in this research. If one were to use another material formulation or machine, the printing parameters would have to be set accordingly.

This work aimed to re-tune the control factors of an existing rapid prototyping process for the given machine. The authors achieved these goals without major changes in the already developed hardware and software architecture.

The results can be used as guidelines to set the printing parameters and a model to predict the mechanical properties of 3D-printed objects for the development of patient- and site-specific scaffolds.

A solid freeform fabrication (SFF) technique is described where powder is deposited layer‐by‐layer using electrophotographic printing. In the electrophotography process, powder is picked up and deposited using an electrostatically charged surface. A test bed was designed and constructed to study the application of electrophotography to SFF. It can precisely deposit powder in the desired shape on each layer. A polymer toner powder was used to build small components by thermally fusing each layer of printed powder using a hot compaction plate. The feasibility of 3D printing using this approach was also studied by printing a binder powder using electrophotography on to a part powder bed.

The purpose of this paper is to describe, review, classify and analyze the current challenges in three-dimensional printing processes for combined electrochemical and microfluidic fabrication areas, which include printing devices and sensors in specified areas.

A systematic review of the literature focusing on existing challenges is carried out. Focused toward sensors and devices in electrochemical and microfluidic areas, the challenges are oriented for a discussion exploring the suitability of printing varied geometries in an accurate manner. Classifications on challenges are based on four key categories such as process, material, size and application as the printer designs are mostly based on these parameters.

A key three-dimensional printing process methodologies have their unique advantages compared to conventional printing methods, still having the challenges to be addressed, in terms of parameters such as cost, performance, speed, quality, accuracy and resolution. Three-dimensional printing is yet to be applied for consumer usable products, which will boost the manufacturing sector. To be specific, the resolution of printing in desktop printers needs improvement. Printing scientific products are halted with prototyping stages. Challenges in three-dimensional printing sensors and devices have to be addressed by forming integrated processes.

The research is underway to define an integrated process-based on three-dimensional Printing. The detailed technical details are not shared for scientific output. The literature is focused to define the challenges.

The research can provide ideas to business on innovative designs. Research studies have scope for improvement ideas.

Review is focused on to have an integrated three-dimensional printer combining processes. This is a cost-oriented approach saving much of space reducing complexity.

To date, no other publication reviews the varied three-dimensional printing challenges by classifying according to process, material, size and application aspects. Study on resolution based data is performed and analyzed for improvements. Addressing the challenges will be the solution to identify an integrated process methodology with a cost-effective approach for printing macro/micro/nano objects and devices.

Three-dimensional (3D) printing technology allows geometric complexity and customization with a significant reduction in the structural environmental impact. Nevertheless, it poses a serious threat to the environment when organic binders are used. Binder jet printing of alkali-activated geopolymer precursor can represent a successful and environmental-friendly alternative.

The present work reports about the successful 3D printing of metakaolin-based alkali-activated concrete, with dimensional integrity and valuable mechanical behavior.

The geometric behavior was studied as a function of alkali activator flow rate, and the minimum geometric deviation with complete saturation was recorded at 103 mg/s. The printed specimen is characterized by a modulus of rupture as high as 4.4 MPa at 135 mg/s.

The 3D printed geopolymer-based concrete can be potentially used in a wide range of structural applications from construction to thermal insulation elements.

The analysis of the 3D geopolymer-based concrete printing system and material conducted in this paper is original.