Large-format additive manufacturing of polymers: a review of fabrication processes, materials, and design

Figures & data

Figure 1. Various setup to increase the build volume in SLA. (a) Projector system attached to the translational stage (Adapted from [26,28]) (b) a dead layer–free approach to rapid SLA printing, HARP (high-area rapid printing) (Adapted from [27]).

Figure 2. Diagram illustrating: (a) the individual scanning area of a single laser, and the overlapping areas for dual- and quad-laser in ML-PBF; additionally, alternating x/y raster scan strategy, (c) single-, dual- and quadruple-L-PBF locations on the platform. (d) Density comparison among various scan strategies [39] (reproduced with permission).

Table 1. List of commercially available extruders for large-format polymer AM.

	Model	Weight (kg)	Max temperature (°C)	Available nozzle sizes (mm)	Max flow (kg/h)
Dyze	Pulsar	7	500	1.0, 3.0, 5.0	3
Rev3rd	RD-M10	18	500	2.5–10.0	12
	RD-M25	40	500	3.0–12.0	25
	RD-M40	90	500	2.0–20.0	50
Massive Dimension	MDPE 2	8.4	450	0.4–4.0	0.9
	MDPE 10	14	450	1.5	5.7
	MDPE 50	59	400	–	22.7
Extrudinaire		1.2	500	0.2–4.2	0.3
Weber	AE 16	–	450	–	2
	AE 20	–	450	–	4.5
	AE 30D	–	450	–	20
CEAD	E25	<29	450	2–18	12
	E40	<70	450	4–24	40
	E50	165	450	8–20	84

Figure 3. (a) The dual-hopper setup on the big area additive manufacturing (BAAM) system. (b) An illustration showing a bead consisting of four layers, where transitions are restricted to a single direction per layer; grey represents Material A and white symbolises Material B. This also demonstrates the variation in material composition based on the distance covered in the initial two layers. (c) Representation of the sample positions for assessing the consistency of the process, with the central number in each rod indicating the distance from the hopper switch [51] (reproduced with permission).

Table 2. List of materials for FGF LFAM.

Materials	Suppliers	Refs.
CF/ ABS	Techmer Engineered Solutions	[50,51]
PLA, PP, ABS, and PET	Nature Works LLC, McDonnough Plastics, Northwest Polymers and CiorC	[48]
PEEK 90G and PEEK 450G	Victrex®	[52]
TPU (Shore hardness 25A-65A)	Kraiburg TPE (Waldkraiburg, Germany)	[53]

Figure 4. (a) Sequence of images (a to h) showing how robotic extruder can overcome the need of support structure to print overhanging features, which normally requires support structures 3-axes gantry-based system [57], (b) Flexibility of robotic extruder to lay fibre along the stress lines [58], (c) Robotic printer on a mobile base [59] (reproduced with permissions).

Figure 5. (a) Angle layer print and (b) vertical layer print to overcome limitation on the vertical height, allowing long objects to be fabricated [69] (reproduced with permission).

Figure 6. (a) Innovative multi material feeding mechanism to improve throughput [70] (Adapted from [70]) (b) hangprinter that consists of printhead hoisted with cables [71] (reproduced with permission).

Figure 7. (a) 3D printed tool, machined and vacuumed sealed, for fabrication of helicopter’s rotor blade [82] (b) 3D printed concept car's monocoque [83] (reproduced with permission).

Figure 8. (a) 3D printed boat printed in University of Maine, Advanced Structures and Composites Center [93]. (b) Interior cabin parts being printed for the prototype. (c,d) External view of the completed PLA 3D 850 prototype [96] (reproduced with permission).

Figure 9. Z-tamping mechanism and IR heating studies conducted by ORNL researchers. (a) Print head with IR lamp and z-tamping mechanism [136], (b) detailed description of the z-tamping mechanism [47] (c) chart showing improvement in tensile strength due to IR heating (reproduced with permissions).

Figure 10. (a) Design of the posiverter and (b) the flow profiles before and after the posiverter and the difference between (c) the extruded filament with and (d) without feedforward control [138] (reproduced with permission).

Figure 11. Variable size nozzle to improve surface quality without significantly sacrificing print time. (a) Mechanism of variable size nozzle (Adapted from [138]) and (b) the difference in surface finish using different nozzle size [138] (reproduced with permission).

Table 3. Summary of the challenges and potential in LFAM.

Study focuses	Challenges	Existing approaches	Potential research directions
Material development	Polymer shrinkage leading to warping Sedimentation of fibres in vat-photopolymerisation [112,114] Nozzle clogging at high fibre loading in material extrusion technique [113]	Addressing shrinkage problem through print process optimisation [108,109] Addressing shrinkage problem through modification of CTE of polymers [110]	Improving the printability of composite materials with high fibre loading Functionalising LFAM parts through the use of composite materials Functionally graded multimaterial Interfacial study in LFAM
Interlayer bonding	Weak z-direction strength [119] Poorer z-direction strength in composites [120,121]	print process optimisation [129] microwave heating [131] laser-based heating [134] Infrared heating [136,137] Tampering device [47]	Tampering device with heating to overcome excessive cooling
Process Control and Quality Assurance	Inconsistency of extrudate shape during transient operation shrinkage of 3D printed parts in vat-photopolymerisation	‘Posiverter’ that diverts the material flow and eliminates the delayed response	Defects detection using machine learning techniques
Optimising production speed and surface finishing	Poor surface finish for LFAM	Adaptable nozzle design [138] Non-planar printing with 6 DOF robotic manipulators [145] multi-nozzle system [146] collaborative robots [148]	more advanced nozzle design toolpath planning for collaborative robots
Toolpath generation	motions of individual axes of robotic arms are coupled	Curved Layered FDM toolpath in a single scripting environment [152]	interoperability of the data and integration of the necessary functions for robotic 3D printing
Recyclability of materials	Composites materials are hard to be separated into their constituent materials Degradation of thermoplastics during recycling [155]	chemical recycling [153,154] development of bio-based composites that are simpler to decompose and recycle [160]	establishment of industry standards optimising the transition between the two methods to ensure a seamless interface software tools need to be developed to manage the complex path planning
Design Considerations	change in the thermo-mechanical behaviours of materials at larger scale multiple print strategies available	develop design guideline for each print strategy	machine learning or optimisation algorithms for efficient and reliable design recommendation and path planning for LFAM.
Post-processing	Managing microstructural heterogeneity that affects mechanical properties Navigating complex surface finishing and metrology for large and intricate parts	isothermal annealing[168] localised heating methods [137] tactile coordinate measurement machines (CMM), optical methods, and X-ray computed tomography (XCT) [169]	development of new techniques for effective heat distribution Development of suitable measurement method of large 3D printed parts

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Data availability statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.