Beamless Metal Additive Manufacturing

Abstract

The propensity to manufacture functional and geometrically sophisticated parts from a wide range of metals provides the metal additive manufacturing (AM) processes superior advantages over traditional methods. The field of metal AM is currently dominated by beam-based technologies such as selective laser sintering (SLM) or electron beam melting (EBM) which have some limitations such as high production cost, residual stress and anisotropic mechanical properties induced by melting of metal powders followed by rapid solidification. So, there exist a significant gap between industrial production requirements and the qualities offered by well-established beam-based AM technologies. Therefore, beamless metal AM techniques (known as non-beam metal AM) have gained increasing attention in recent years as they have been found to be able to fill the gap and bring new possibilities. There exist a number of beamless processes with distinctively various characteristics that are either under development or already available on the market. Since this is a very promising field and there is currently no high-quality review on this topic yet, this paper aims to review the key beamless processes and their latest developments.

Keywords: metal additive manufacturing (AM), beamless metal AM; non-beam metal AM.

Figure 1

Classification of the main current metal AM processes, including beam-based and beamless techniques.

Figure 2

Growth in beamless metal-AM systems comparing with beam-based systems (column numbers indicate the number of most common commercially launched systems), data acquired from the Scopus database, and the Wohlers Report [1].

Figure 3

Optical microscopy images of 316L samples in etched condition (Glyceregia etchant): (a) BJ 50× (b) EBM 50×; (c) DMLS 50×. Scale bars are 150 µm [70].

Figure 4

Process scheme of an extrusion-based system: (a) 3D printing of the green part (b) debinding of the green part in a debinding furnace; (c) sintering of the resulting brown part in a high-temperature furnace; (d) final metal part [85].

Figure 5

(a) CEM printed and sintered 316L part and using conventional MIM feedstock Catamold (BASF, Ludwigshafen, Germany) (b) optical microscopy of CEM printed 316L part showing microstructure and inclusions of carbon and foreign particles comparable to conventional manufactured MIM parts.

Figure 6

Schematic view of (a) high and (b) low pressure CS.

Figure 7

Schematic view of AFSD process (left), AFSD head in operation (right image, courtesy of Aeroprobe Corporation, USA).

Figure 8

Schematic view of UAM process.

Figure 9

(a) The Inverse Pole Figure (IPF) map of as-received original AA 3003 alloy foil in which the grains are elongated along the rolling plane, and fine equiaxed grains are observed between the elongated grains, (b) The IPF of the VHP-UAM sample in which the interface region is represented by the white colored arrows. Many grains in the both top and bottom bulk regions are elongated along the rolling plane of the original tape, and fine grains are seen between these elongated grains, while all grains in the interface region are fine and equiaxial [132].

Figure 10

Schematic view of the (a) GMAW, (b) GTAW, and (c) PAW process [149].

Figure 11

Schematic view of (a) EFAB [150] and (b) FluidFM printing cell. the iontip dispenses the electrolyte into a buffer bath. At the working electrode, Cu²⁺ ions are deposited as solid copper [151].

Figure 12

The main possibilities and advantages of the beamless metal-AM over beam-based systems they are low energy, can achieve higher dimensional accuracy, can be used for printing parts from micro to mega scale parts with improved mechanical properties as they do not comprise material melting and rapid solidification.

Figure 13

Comparison of the key beamless metal AM systems in terms of part complexity and size. EFAB, 3DSP, FluidFM 3DP are suitable for micro-scale applications. Binder jetting is a scalable process that can be used for micro to medium size parts while material jetting and extrusion methods are normally used for medium size parts. In contrast, CSAM, AFSD, UAM, and WAAW are more suitable for medium to mega-scale parts.

Figure 14

Comparison of the key beamless metal AM systems in terms of part size and productivity. As can be seen, UAM, WAAM, material jetting, extrusion, and FluidFM 3DP are suitable for low-volume production while binder jetting, 3DSP, CSAM, and EFAB have higher deposition rate for high-volume production of metal parts.

Figure 15

Comparison of the key beamless metal AM systems in terms of part complexity and minimum feature size. Material jetting, binder jetting, and EFAB processes have the capability to print sophisticated 3D parts and assemblies. FluidFM 3DP, extrusion, and CSAM can be used for manufacturing of true 3D parts, while the other processes are normally served for parts with less complexity.

Figure 16

The identification map of the beamless metal AM technologies in comparison with DED and PBF beam-based methods. As can be seen, AFSD offers the highest mechanical strength and the lowest process and operation cost. Extrusion process is also a low-cost process suitable for low-volume production, while CSAM offers the highest deposition rate (up to 38 kg/h). EFAB and FluidFM 3DP processes possess the highest dimensional accuracy and surface quality.

Figure 17

Uniform pillars and complex copper parts printed in single step using FluidFM 3DP without support structure (Courtesy of Cytosurge AG).

Figure 18

A metal tissue staple 3D printed using (a,b) EFAB (Courtesy of Microfabrica, USA) and (c,d) BJ technology (material 316L).

Figure 19

The double enlarged staple (to allow fabrication using beam-based system) printed using (a,b) SLM process (source: MICA Freeform vs Selective Laser Melting published by Microfabrica, USA) and (c,d) BJ technology (material 316L).

Figure 20

(a) Thin walls 316L printed using BJ technology, (b) serial production of micro-parts aspect ratio of 1:50 printed using 3DSP [152], (c) a benchmarking sample part printed using BJ technology, (d) the benchmark sample printed using 3DSP [162].

Figure 21

(a) A single step 3D printed titanium bicycle frame in 25 min using Titomic’s CSAM system (Courtesy of Titomic, Melbourne, Australia), (b) Al6061 hollow dome as fabricated by MELD technology and after finish machining, 115 mm tall, 100 mm diameter part with 25 mm wall thickness, fabrication time: 2 h (Courtesy of Aeroprobe, Christiansburg, VG, USA), (c) MMC laminates (MetPreg) composed of continuous alumina fibers and a matrix of pure aluminum are selectively layered for selective reinforcement of the rib structure (Courtesy of Fabrisonic, Columbus, OH, USA), (d) 50 mm radius semicircle printed using WAAM [163].