Table 3.

Comparison of various beamless metal AM processes.

	Advantages		Disadvantages	Metals	Ultimate Tensile Strength (UTS)	Ref
Extrusion	Pure Metal	No post-processing required, low-cost hardware, low to no shrinkage during or after additive process	Limited use of metals (low temperature)	Low-melting alloys, bulk metallic glasses (BMG)	Bi58Sn42: 51.7 MPa Zr44Ti11Cu10Ni10Be25: 1200 MPa	[89,94]
	Composite materials	High adoption rate, low cost process, high versatility in materials, isotropic microstructure and mechanical properties, high mechanical properties	Mostly a multi-step process, needs sintering equipment, needs further machining to achieve required tolerances	Stainless steel, Cu, a wide range of metals available as MIM feedstock	316L: 465 MPa (filament) 316L: 524 MPa (MIM feedstock) 17-4 PH: 1.1 GPa (MIM feedstock, hardened) Copper: 6.7 MPa (crushed particles) 17-4 PH: 1.0 GPa (rods)	[90,91] Desktop Metal‘s website
Material jetting	Liquid metal jetting	Single step process without the need for further post-processing, and thus relatively high production speed	A high temperature melting process, limited to low melting point metals, low surface quality and accuracy, protective build chamber is required, simple geometries without overhang are printable	Low melting point metals such as tin, Cu and Al alloys	7075 Aluminum (373 MPa)	[154]
	Nano-particle ink jetting printing	High accuracy (dimensional tolerance of 50 to 100 µm depending on part size), smooth surface finish due to ultra-thin layer thickness (8–10 µm), low sintering-induced shrinkage and residual stress, complex 3D shapes can be printed using water-soluble support material, isotropic properties and higher green strength than binder jetting due to higher level of layer packing	Relatively low print speed (0.5 to 1 kg/hr) due to fine layer thickness, needs sintering equipment, sintering-induced distortion for large parts, sintering process increases overall production time and cost, difficulties to develop new materials system (as the suitable nanoparticle inks should be engineered), nanoparticle sedimentation and possible nozzle clogging, high technology cost	Ag, stainless steel	No report	XJet’s website
Binder jetting	Scalable process (micro to large parts are possible), high accuracy and smooth surface finish (Ra of ~6 µm), high printing speed (0.8–1.5 kg/hr depending on material and layer thickness), lower residual stress than beam-based systems, highly complex 3D shapes and assemblies can be printed without support, relatively low printing cost, suitable for serial production of small parts		High level of porosity (green and sintered density of approx. 50% and 95%, respectively), further heat treatment routes such as infiltration and/or HIP is required, needs sintering equipment, sintering process increases overall production time and cost, sintering-induced distortion for large parts, anisotropic mechanical properties, high technology cost	Cu and Al alloys, stainless steel, titanium, super alloys, iron–manganese alloys, WC-CO hard metals, cobalt-chrome, and magnetic materials	316L (520 MPa, sintering + HIP) SS420(730 MPa, sintering + infiltration with bronze) 17-4PH (900 MPa, sintering + HIP) Ti6-Al-4V (890 MPa, sintering + HIP) Cu (145 MPa, sintered) Cu (176 MPa, sintering + HIP)	[58,71,155]
CSAM	A solid-state process without melting, low residual stress, open atmosphere process with very large build area, extremely high deposition rate (up to 38 Kg/hr for titanium), multiple materials and MMcs are possible, very complex geometries can be printed by incorporation of a robotic arm, can be used for both AM and repair applications, microstructure with refined grains		A net-shape process with low accuracy and surface finish, needs further machining to achieve required tolerances, very low spatial resolution (normally 4 mm), needs expensive helium driving gas, low ductility of printed parts, needs further heat treatment to improve ductility	Cu alloys, Al alloys, stainless steel, titanium, and super alloys	Cu (N2 driving gas): 220 MPa Cu-Ag-Zr (He driving gas): 500 MPa Ti (He driving gas): 600 MPa Ti-6Al-4V (He driving gas): 765MPa Al7075 (He driving gas): 560 MPa Al6061 (He driving gas): 200 MPa 304L (He driving gas): 420 MPa In718 (He driving gas): 800 MPa	[9,96,104,108,112,113,116,156,157,158]
UAM	A low temperature solid-state process, low residual stress, open atmosphere process with large build area, high accuracy and smooth surface finish similar to machining, low energy consumption, very small to large parts are possible, multiple dissimilar material and non-weldable alloys can be printed, different components from optical and SMA fibres to sensitive sensors and electronic devices can be embedded into the parts, mechanical properties of metal foils (feedstock) are retained after printing		A hybrid process with fairly low print speed that needs machining process, high material wastage, anisotropic mechanical properties with considerably lower strength in build direction, high porosity of as-printed parts, design constrains (build height to width ratio), difficult to print complex geometries	A wide range of metals and multi-materials such as Al/Cu, Ni/Stainless steel, Al/Ti, Al/In, Al/Metpreg, Ag/Au, Al/Mo, and Al/Invar	Al-6061 (225 MPa normal to build direction) Al-6061 (46 MPa in build direction) Al-6061 (70 MPa in build direction after HIP)	[128,129,159,160]
AFSD	A solid-state process without melting, low residual stress, open atmosphere process with large build area, dissimilar materials, non-weldable alloys, and MMCs can be printed, high deposition rate (up to 9 Kg/h for Al), low operation cost, feedstock flexibility (both metal powder and rod), a single step process (no need for further heat treatment), near wrought microstructure with isotropic and higher mechanical strength than metal bulks due to dynamic recrystallization		A net-shape process with low accuracy and surface finish, needs further machining to achieve required tolerances, low spatial resolution, complex geometries with overhangs can’t be printed	Al alloys, Mg alloys, Cu, steel, Ti alloys, and Ni super alloys, MMCs (Al-SiC, Al-Fe, Al-Mo, Al-CNT, etc.)	Ti-6Al-4V alloy (1.15 GPa) AA5083 (362 MPa) AA6061 (149 MPa) Mg-based WE43 alloy (400 MPa)	[119,141]
WAAM	High processing speed (2500 cm3/h/ 2–6 kg/h), high material utilization rate, relatively low production and equipment cost, high equipment flexibility and scalability		Low accuracy and resolution (1.5 ± 0.2 mm) microstructural anisotropy and porosity residual stresses and distortions	a wide range of metals	Ti-6Al-4V: 480 MPa (GTAW) 903 MPa (GMAW) Inconel 718: 328 MPa (GMAW) Al:6.3, Cu: 262 MPa	[145,161]
EFAB	Very high accuracy and spatial resolution (20 µm), Highly robust microparts and complex mechanisms without the need for assembly can be printed		A multi-step micromanufacturing process with low print speed, limited choice of materials, limited build height (1.25 mm), complete removal of sacrificial material is difficult in some cases	noble palladium, nickel–cobalt alloy, rhodium, Cu	nickel–cobalt alloy: 1.1 GPa	[150]
FluidFM 3DP	A single step micro-manufacturing process, very high accuracy and resolution (below 1 µm), complex 3D parts can be printed with pinpoint accuracy directly onto existing structures such as contact pads that are pre-defined on the surface of an integrated circuit (IC) boards, on MEMS, etc.		Limited build height (1 mm), limited choice of materials	Cu, Au, Ag	Not reported	[151]
3DSP	Low cost process, relatively high print speed can be achieved, fine to medium size parts can be printed at high resolution (60 µm) and surface finish		A multi-step process, needs sintering equipment, needs screen preparation, simple 2.5D shapes can be printed, further post-heat treatment is required	stainless steel, steel, Cu, a number of different iron-based alloys (17-4-PH)	Not reported	[152,162]