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The purpose of this paper is to supplement and upgrade existing research on LPBF of NiTi alloys. Laser powder bed fusion (LPBF) is a promising method for fabricating nickel–titanium (Ni–Ti) alloys. It is well known that the energy density is mainly adjusted through the scanning speed and laser power. Nevertheless, there is lack in research on the effects of separately adjusting the scanning speed and laser power on the properties of the final Ni–Ti components. On the other hand, although Ni-rich Ni–Ti alloys [such as Ni54(at.%)Ti] have great potential in structural applications because of their high hardness and good shape stability, at present, there are few studies focusing on this grade of Ni–Ti alloy.

In this work, the energy density was adjusted by changing the laser power and scanning speed separately, and the corresponding process parameters were used to fabricate Ni54(at.%)Ti alloys. The formability (including the relative density, impurity content, etc.) and tensile properties of the LPBF Ni54(at.%)Ti alloys fabricated with different combinations of process parameters were analyzed.

The effects of increasing the laser power and reducing the scanning speed on the properties of the LPBF Ni54(at.%)Ti alloys and the property differences between components manufactured with different combinations of laser power and scanning speed under the same energy density were analyzed. The optimal process parameters were selected to fabricate the components that achieved the highest ultimate tensile strength of 537 MPa, a high relative density of 98.23%, a relatively low impurity content (0.073 Wt.% of carbon and 0.06 Wt.% of oxygen) and an ideal pseudoelasticity (95% recovery rate loaded at 300 MPa).

The effects of increasing the laser power and reducing the scanning speed on the properties of LPBF Ni54(at.%)Ti alloys were studied in this paper. This work is an upgrade and supplement to the existing research on fabricating Ni-rich Ni–Ti alloys by the LPBF method.

During the 3D printing process, the model needs to add a support structure to ensure structural stability. Excessive support structure reduces printing efficiency and results in material cost. A flexible support platform for 3 D printing has been designed. It can form an external support structure to replace the original support structure. This paper aims to study the influence of a model’s build orientation on properties when the model is printed on the platform, aiming to provide users with suitable solutions.

A fitness function for estimating the support structure with a support length is constructed. The particle swarm optimization (PSO) algorithm is modified and applied to find the build orientation that minimizes the support structure. However, when the model is printed on the platform, the build orientation of the minimum support structure enhances the complexity of the working path, resulting in an increase of printing time, which needs to be avoided. This paper applies a multi-objective particle swarm optimization (MOPSO) algorithm to minimize the support structure while minimizing printing time. The Pareto solution is obtained by the algorithm.

It is found that the model that has the cantilever structure can reduce more support structure after optimization on the platform, when there is surface quality requirement. When there is no limit, the modified algorithm can minimize the support structure of each model. Considering support structure and printing time, the MOPSO algorithm can easily get optimization results to guide the practical work.

This paper optimizes the model’s build orientation on the flexible support platform by PSO, thereby reducing material cost and improving work efficiency.

Fused filament fabrication (FFF) is a common additive manufacturing method that is widely used owing to its low cost, environmental friendliness and safety. Colour models are needed because of their ability to express more information, but high printing quality and efficiency are difficult to achieve with the existing FFF colour printing methods because of the “inertia” of printing. Inertia refers to the feature of the former colour material remaining in the molten cavity when switching colours in colour FFF printing. The purpose of this paper is to propose a new FFF colour printing method to reduce printing material usage and printing time.

A new FFF colour printing method that uses transitioning waste to construct the part is proposed. Based on the freedom of the colour surface model’s interior space, the internal fill and support of the print model are generated using the transitioning waste to reduce printing material usage and printing time and to achieve environmentally friendly colour printing. The modified elite ant system (EAS) algorithm is used to construct and optimize this method based on the colour surface model.

A colour printing experiment is performed using a colour-mixing FFF printer platform with a special waste extrusion module. The experimental results show that this method can significantly reduce material and time consumption compared to the commonly used method. The printed part produced by this method also has high surface quality.

A new FFF colour printing method that uses transitioning waste to construct the part is proposed. Based on the freedom of the colour surface model’s interior space, the internal fill and support of the print model are generated using the transitioning waste to reduce printing material usage and printing time and to achieve environmentally friendly colour printing. The modified EAS algorithm is used to construct and optimize this method based on the colour surface model. A special waste extrusion module is developed.

3D printing for objects whose size exceeds the scope of the printer is still a tough challenge in application. The purpose of this paper is to propose a visual stitching large-scale (VSLS) 3D-printing method to solve this problem.

The single segmentation point method and multiple segmentation point method are proposed to adaptively divide each slice of the model into several segments. For each layer, the mobile robot will move to different positions to print each segment, and every time it arrives at the planned location, the contours of the printed segments are captured with a high-definition camera by the feature point recognition algorithm. Then, the coordinate transformation is implemented to adjust the printing codes of the next segment so that each part can be perfectly aligned. The authors print up layer by layer in this manner until the model is complete.

In Section 3, two specimens, whose sizes are 166 per cent and 252 per cent of the scope of the 3D-printing robot, are successfully printed. Meanwhile, the completed models of the specimens are printed using a suitable traditional printer for comparison. The result shows that the specimens in the test group have basically identical sizes to those in the control group, which verifies the feasibility of the VSLS method.

Unlike most of the current solutions that demand harsh requirement for positioning accuracy of the mobile robots, the authors use a camera to compensate for the lost positioning accuracy of the device during movement, thereby avoiding precise control to the device’s location. And the coordinate transformation is implemented to adjust the printing codes of the next sub-models so that each part can be aligned perfectly.

The staircase effect and support structure under overhanging geometry are two inherent weaknesses that reduces the surface quality and induces material waste. This paper aims to design a five-axis fused deposition modeling system with interference-free nozzle to solve the problems.

To facilitate the application of five-axis printing machine, three new printing methods are proposed according to different geometries and application requirements, which include tangential direction printing, normal sculpture printing and compatible printing.

The static flow beading characteristic is researched to establish the criterion for switching the mode between three-axis printing and five-axis printing. Experiment proves the critical point existing and 51° is the critical point at the given parameters. The concept of dynamic flow beading is proposed. The relationship between equivalent volume and roughness is established based on elaborate experiments, which helps to figure out the boundary between safe area and beading area under different parameters of layer thickness and nozzle diameter.

Three new printing methods are proposed according to different geometries and application requirements, which include tangential direction printing, normal sculpture printing and compatible printing. Considering the special movement situation during five-axis printing process, the dynamic flow beading issue is proposed. The relationship between equivalent volume and roughness is established based on elaborate experiments, which helps to figure out the boundary between safe area and beading area under different parameters of layer thickness and nozzle diameter.

Fused deposit modeling (FDM) additive manufacturing technology is widely applied in recent years. However, there are many defects that may affect the surface quality, accuracy, or even cause the collapse of the parts. This paper presents a solution to the problem of detecting defects on the outer surface in the additive process of FDM.

A multi-view and all-round vision detection method is introduced where the detection field of view is changing with the vector of the outer surface during the printing process on the six degrees of freedom robot FDM printer.

After the image is preprocessed, this paper can identify the defects effectively according to its laminate structure, and introduces a mathematical matrix to represent the defects which will be classified into three typical types according to the geometry shape and area distribution.

This research only focuses on the feasibility of the defects detection method. To create the object of high quality, more research is needed to account for the process parameters which significantly cause the defects.

This work will help to detect the defects online, monitor the printing quality of the outer surface, reduce the waste of printed filaments, etc.

This study is among the first to present a multi-view and all-round vision detection method to detect defects on the outer surface in the additive process of FDM; proposes a means of identifying defects according to its laminate structure; and introduces a mathematical matrix to represent the defects which may be used in quality assessment.

Mg-Al powder mixture was used to manufacture Mg-Al alloy by laser powder bed fusion (LPBF) process. This study aims to investigate the influence of initial Al content and processing parameters on the formability, microstructure and consequent mechanical properties of the laser powder bed fused (LPBFed) component.

In this study, Al powder with different weight ratio ranged from 3 to 9 per cent was mixed with pure Mg powder, and the powder mixture was processed using different LPBF parameters. Microstructure and compressive properties of the LPBFed components were examined.

It was found that the presence of Al significantly modified the microstructure and improved the mechanical properties of the LPBFed components. Higher volume of ß-Al12Mg17 precipitates was produced at higher initial Al content and higher laser energy density. For this reason, the a-Mg was significantly refined and the compressive strength was improved. The highest yield compressive strength achieved was 279 MPa when using Mg-9 Wt. % Al mixture.

This work demonstrates that LPBF of Mg-Al powder mixture was a viable way to additively manufacture Mg-Al alloy. Both Al content and processing parameters can be modified to control the microstructure and mechanical properties of the LPBFed components.

Additive manufacturing based on arc welding is a fast and effective way to fabricate complex and irregular metal workpieces. Thin-wall metal structures are widely used in the industry. However, it is difficult to realize support-free freeform thin-wall structures. This paper aims to propose a new method of non-supporting thin-wall structure (NSTWS) manufacturing by gas metal arc welding (GMAW) with the help of a multi-degree of freedom robot arm.

This study uses the geodesic distance on the triangular mesh to build a scalar field, and then the equidistant iso-polylines are obtained, which are used as welding paths for thin-wall structures. Focusing on the possible problems of interference and the violent variation of the printing directions, this paper proposes two types of methods to partition the model mesh and generate new printable iso-polylines on the split meshes.

It is found that irregular thin-wall models such as an elbow, a vase or a transition structure can be deposited without any support and with a good surface quality after applying the methods.

The experiments producing irregular models illustrate the feasibility and effectiveness of the methods to fabricate NSTWSs, which could provide guidance to some industrial applications.