A Novel Methodology to Manufacture Complex Metallic Sudden Overhangs in Weld-Deposition Based Additive Manufacturing

Amongst various additive manufacturing (AM) techniques for realizing the complex metallic objects, weld deposition (arc) based directed energy AM technique is attaining the more focus over commercially available powder bed fusion techniques. This is due to the capability of high deposition rates, high power and material utilization, simpler setup and less initial investment of arc based AM. Nevertheless, realization of sudden overhanging features through arc based weld deposition techniques is still a challenging task due to the necessity of support structures. The present work describes a novel methodology for producing complex metallic objects with sudden overhangs without using supports. This is possible by re-orienting the workpiece and/or deposition head at every instance using higher order kinematics (5-axis setup) to make sure the overhanging feature is in-line to the deposition direction. The proposed technique identifies the sudden overhangs form a CAD model (.stl) and generates an orthogonal tool path for deposition of the same. To validate this technique, objects with sudden overhangs (illustrative case studies) have been taken up for deposition. An In-house MATLAB routine has developed and presented for performing the same. Although this technique is suitable for any deposition process, it has been demonstrated using gas metal arc welding (GMAW) based weld-deposition, where the raw material to be deposited is in the form of a welding wire.

Microstructure, Mechanical Properties, and Martensitic Transformation in NiTi Shape Memory Alloy Fabricated Using Electron Beam Additive Manufacturing Technique

The electron beam additive manufacturing (EBAM) method was applied in order to fabricate rectangular-shaped NiTi component. The process was performed using an electron beam welding system using wire feeder inside the vacuum chamber. NiTi wire containing 50.97 at.% Ni and showing martensitic transformation near room temperature was used. It allowed to obtain a good quality material consisting of columnar grains elongated into the built direction growing directly from the NiTi substrate, which is related to the epitaxial grain growth mechanism. As manufactured material showed martensitic and reverse transformations diffused over the temperature range from −10 to 44 °C, the applied aging at 500° C moved the transformation to higher temperatures and transformation peaks became sharper. The highest recoverable strain of about 3.5% was obtained in the as-deposited sample deformed along the deposition direction. In the case of deformation of the alloy aged at 500 °C for 2h, the formation of martensite occurs at significantly lower stress; however, at about 2.5% the stress begins to increase gradually and only a small shape recovery was observed due to a higher martensitic transformation temperature. In situ SEM tensile deformation in the direction perpendicular to deposition direction showed that the martensite began to appear at the surface of the sample and at the grain boundaries due to heterogeneous nucleation. In situ studies allowed to determine the following crystallographic relationships between B2 and B19’ martensite: (100)B2||(100)B19’ and (100) B2 || (011)B19’; (011)B2|| (001)B19’ and $${(011)}_{\mathrm{B}2}||{\left(11\bar{1 }\right)}_{\mathrm{B}1{9}^{\mathrm{^{\prime}}}}$$ ( 011 ) B 2 | | 11 1 ¯ B 1 9 ′ . Samples aged at 500 °C exhibited fully austenitic microstructure; however, with increasing degree of deformation, the formation of martensite was observed. The majority of needles were tilted about 45° with respect to the tensile direction, and the presence of type I (11 $$\bar{1 }$$ 1 ¯ ) invariant twin boundaries was observed at higher degrees of deformation.

Assessment of cold resistance and fracture mechanisms of metals obtained by 3D-printing

The cold resistance and fracture mechanisms of specimens made of 08Г2С and 07Х25Н13 steels obtained by 3D printing by electric arc surfacing at low temperatures are considered. It is determined, that with a decrease in temperature, the impact toughness of steels decreases. The impact toughness of specimens cut along the deposition direction is higher than that of specimens cut in the transverse direction. It is shown, that the brittle component prevails in the fracture of 08Г2С steel at temperatures below –40 °C, and the viscous component is observed in the fracture of 07Х25Н13 steel over the entire temperature range. A relationship is established between the fractal dimension of the fracture surface and the amount of the viscous component. Keywords: 3D printing, cold resistance, fracture mechanisms, ductile-brittle transition, fractal dimension. [email protected]

Fabrication of Alumina-Doped Optical Fiber Preforms by an MCVD-Metal Chelate Doping Method

This paper reports on the fabrication of alumina-doped preforms using a modified chemical vapor deposition (MCVD)-vapor phase chelate delivery system with Al(acac)3 as the precursor. The objectives of this work are to study the deposition process, the efficiency of the fabrication process, and the quality of the fabricated fiber preforms. Two parameters are studied, the Al(acac)3 sublimator temperature (TAl °C) and the deposition direction (i.e., downstream and upstream). Other parameters such as the oxygen flow and deposition temperature are fixed. The results show that high uniformity of the refractive index difference (%RSD < 2%) and core size (%RSD < 2.4%) was obtained along the preform length using downstream deposition, while for the combined upstream and downstream deposition, the uniformity deteriorated. The process efficiency was found to be about 21% for TAl °C of 185 °C and downstream deposition. From the EDX elemental analysis, the refractive index was found to increase by 0.0025 per mole percent of alumina.

Fabrication of Alumina Doped Optical Fiber Preforms by MCVD-Metal Chelate Doping Method

This paper reports on the fabrication of alumina doped preforms using MCVD-vapor phase chelate delivery system with Al(acac)3 as the precursor. The objectives of the work are to study the deposition process, the efficiency of the fabrication process, and the quality of the fabricated fiber preforms. Two parameters are studied, Al(acac)3 sublimator temperature (TAl&deg;C) and deposition direction (i.e. downstream and upstream). Other parameters such as oxygen flow and deposition temperature are fixed. The results showed that a high uniformity of refractive index difference (%RSD &amp;lt; 2%) and core size (%RSD &amp;lt; 2.4%) was obtained along the preform length using downstream deposition while for the combined upstream and downstream deposition the uniformity was deteriorated. The process efficiency was found to be about 21% for TAl&deg;C of 185&deg;C and downstream deposition. From the EDX elemental analysis, the refractive index was found to increase by 0.0025 per mole percent of alumina.

Cracks Repairing by Using Laser Additive and Subtractive Hybrid Manufacturing Technology

A laser additive and subtractive hybrid manufacturing technology was proposed to repair Inconel 718 cracks in this paper. Microstructures and the mechanical properties such as the micro-hardness, the tensile strength, and the friction-wear of the repair zone were investigated in detail. The microstructure analysis showed that a metallurgical bonding could be achieved between the repair zone and the matrix. The typically columnar and dendrite crystal appeared in the repaired zone, and the crystal epitaxial grew along the deposition direction, and the heat-affected zone in the groove boundary was coarse equiaxial crystal. The mechanical test result showed that the micro-hardness and tensile strength of the repaired tissue was about 87% and 89% of the original Inconel 718 wrought substrate. And, the wear resistance of the repaired zone was similar to that of the substrate. It was found that the surface quality of the repair zone for laser polishing is better than that for mechanical milling.

Effect of Process Parameters on Cellulose Fiber Alignment in Bio-Printing

Three dimensional (3D) bio-printing or direct writing technique has become a popular tool in tissue engineering applications that uses a computer-controlled process to deposit bio-ink for reproducing 3D tissue. Among multiple bio-printing modal, extrusion-based printing is capable of depositing diverse range of hydrogel materials and their compositions as bio-ink. Both acellular bio-ink and cell-laden bio-ink can be extruded by controlling the writing parameters to achieve high (&gt;80%) cell survivability and density along with spatial precision and accuracy in 3D space. To increase cell viability and improve mechanical properties, nano-materials are often added in the bio-ink. However, the interplay between 3D bio-printing process parameters, solid fiber content and deposited fiber orientation has not been investigated yet. A novel cellulose based nano-fiber filled bio-ink (i.e. TEMPO nano fibrillated cellulose fiber) is developed and used in this research. The distribution of fiber is explored with respect to the 3D bio-printing process parameters such as nozzle diameter, applied pressure, fiber content and, alginate content. We found, fiber alignments has a very strong correlation with the deposition direction and about 70% fiber falls within 20 degree of the deposition direction.

Development of a Multi-Directional Metal 3D Printing System Based on Direct Metal Deposition

Process parameters, including deposition direction, are crucial in direct metal deposition (DMD) for microstructure formation and mechanical properties of the final part. Multi-directional deposition along with in-situ deposition control can minimize deposition anisotropy and improve dimensional accuracy. In this paper, a DMD system is developed to achieve multi-directional metal deposition by using 6 degree-of-freedom (DOF) motion of the workpiece platform rather the laser head for a highly compact design. An in-situ control strategy with two independent loops of laser focus and power is developed to control the printing process based on the feedback from real-time melt pool geometry and intensity. Experimental results have shown that the laser focus and power control can significantly improve geometrical accuracy and reduce heat accumulation. In addition, system kinematics are derived and verified for the 6-DOF hexapod to achieve multi-directional deposition. Oblique structures have been successfully printed to demonstrate the effect of optimized build direction.