Additive Manufacturing System Research Articles

Sequential Solidification of Metal Powder by a Scanning Microwave Applicator.

This study examines the fundamental feasibility of sequential metal-powder solidification by localized microwave-heating (LMH) provided by a scanning, all-solid-state microwave applicator. This continuous process is considered for the additive manufacturing (AM) and 3D printing (3DP) applications of metal parts. In previous studies, we employed LMH for the incremental solidification of small batches of metal powder in a stepwise vertical manner. Here, we study a continuous lateral LMH process, layer by layer, in a fashion similar to laser scanning in powder beds, as performed in common laser-based AM systems. LMH solidification at scanning rates of ~1 mm3/s is obtained in bronze powder using ~0.25-kW microwave power. The effect is studied here by LMH scanning in one lateral dimension (~20-mm long) in layers, each of ~1-4 mm thickness and ~2-4 mm width (mechanically confined). Imperfect solid bars of ~20×4×5 mm3 are obtained with rough surfaces. Their joining in an L shape is also demonstrated. The experimental solidified products are tested, and their hardness and density properties are found to be comparable to laser-based AM products. The capabilities and limitations of the LMH scanning concept for metal-powder solidification are evaluated. The potential feasibility of a solid-state LMH-AM technology is discussed.

Extrusion strategies in fused deposition additive manufacturing: A review

Fused deposition or fused layer additive manufacturing is a technique in which a part is fabricated layer by layer using filament or pellets-form input material. The extruder is the central part of the fused deposition additive manufacturing (FDAM) system. The extrusion mechanism is unique to the geometry and form of the feedstock material. Extrusion of filament-form material through the nozzle needs to design of a material feeding mechanism based on various filament extrusion parameters. At the same time if the material is in the form of pellets, then the design of the feeding mechanism is very different due to the shape and size of the pellets. These two different design strategies for material extrusion namely the design of the feeding mechanism of filament and pellets form materials have been a major concern to avoid unwanted deformation of extruded materials in FDAM. These two design strategies for filament and pellet-form materials have led to the development of several material extrusion strategies. The present paper reviews various material extrusion strategies developed for FDAM of filament or pellets form input material. This article presents the review of design, development, performance evaluation, and process planning for each extrusion strategy. Based on the literature review authors have suggested a possible extrusion method that can accept both forms of materials to fulfill the need for the filament as well as pellets-based additive manufacturing.

Online monitoring for error detection in vat photopolymerization

ABSTRACT Sensor implementation together with data processing in manufacturing provides continuous measurements enabling process monitoring, optimization, and automation. Additive manufacturing (AM) technologies are shifting from one-off and prototyping production to batch, mass, and continuous production. Current AM technologies are mostly focused on small production devices, without monitoring systems. This study aims to bring AM closer to automation by proposing an online monitor system for bottom-up photopolymerization AM (VPP) systems. The sensor-generated data is used to capture the detachment error of built parts from the build platform that otherwise cannot be observed physically by the machine operator. The detachment itself will not stop the build job, which results in lost material and operating time. The online monitoring procedure consists of two phases, an offline and an online one, respectively. The offline phase is used for training a prediction model to be used in connection with a control chart for online monitoring. The monitoring control chart is advantageous as only the detachment predictions need to be recorded. The research carried out in this article brings novelty in both the vat photopolymerization set-up, as well as in an online monitoring procedure that can be easily extended to similar technologies.

The influence of a large build area on the microstructure and mechanical properties of PBF-LB Ti-6Al-4 V alloy

This study investigated the print homogeneity of Ti-6Al-4 V alloy parts, when printed over a large build area of 250 times 250 times 170 mm3, using a production scale laser powder bed additive manufacturing system. The effect of part location across this large build area was investigated based on printed part porosity, microstructure, hardness, and tensile properties. In addition, a Hot Isostatic Pressing (HIP) treatment was carried out on the as-built parts, to evaluate its impact on the material properties. A small increase in part porosity from 0.01 to 0.09%, was observed with increasing distance from the argon gas flow inlet, which was located on one side of the build plate, during printing. This effect, which was found to be independent of height from the build plate, is likely to be associated with enhanced levels of condensate or spatter residue, being deposited at distances, further from the gas flow. Despite small differences in porosity, no significant differences were obtained for microstructural features such as prior β grain, alpha lath thickness, and phase fraction, over the entire build area. Due to this, mechanical performances such as hardness and tensile strengths were also found to be homogenous across the build area. Additionally, it was also observed based on the lattice constants that partial in-situ decomposition of {alpha }^{^{prime}}to alpha +beta phases occurred during printing. Post HIP treatment result showed a decrease of 7 and 6%, in the yield strength (YS) and ultimate tensile strength (UTS), respectively, which was associated with a coarsening of alpha lath widths. The potential of the laser powder bed system for large area printing was successfully demonstrated based on the homogenous microstructure and mechanical properties of the Ti-6Al-4 V alloy parts.

Development of Cementitious Mortars for Aerial Additive Manufacturing

Additive Manufacturing (AM) methods in the construction industry typically employ ground-based deposition methods. An alternative to transform the role of AM in construction is to introduce an aerial capability. A recent project titled Aerial Additive Manufacturing (AAM), the first AM system to use untethered, unmanned aerial vehicles (or ‘drones’), has demonstrated the 3D-printing of cementitious materials during flight. An autonomous aerial system would minimise requirements for working at height, thus reducing safety risks and release AM from ground-based constraints. This study investigates viscous cementitious mortars for AAM. To assess workability and buildability, a robotic arm representing UAV movement in three-dimensional space moved a lightweight deposition device to extrude multiple layers. Constituents such as Pulverised Fuel-Ash, Silica fume, polyol resin, limeX70 and Polypropylene fibres were added to cement-based material mixes. Sand:binder ratios were a maximum of 1.00 and Water:binder ratios ranged from 0.33–0.47. Workability and buildability of mixes were evaluated using performance parameters such as power required for extrusion, number of layers successfully extruded, the extent of deformation of extruded layers and evaluation of mechanical and rheological properties. Rheology tests revealed mortars with a suitable workability-buildability balance possessed a Complex modulus of 3–6 MPa. Mechanical tests showed that resistance to deformation and buildability positively correlate and indicate compressive strengths in excess of 25 MPa. This study has demonstrated that structural cementitious material can be processed by a device light enough to be carried by a UAV to produce an unsupported, coherent multiple-layered object and further demonstrated the feasibility of untethered AAM as an alternative to ground-based AM applications in construction.

The Effect of B4C Powder on Properties of the WAAM 2319 Al Alloy

With ER2319 and B4C powder as feedstocks and additives, respectively, a wire arc additive manufacturing (WAAM) system based on double-pulse melting electrode inert gas shielded welding (DP-MIG) was used to fabricate single-pass multilayer 2319 aluminum alloy. The results showed that, compared with additive manufacturing component without B4C, the addition of which can effectively reduce the grain size (from 43 μm to 25 μm) of the tissue in the deposited layer area and improve its mechanical properties (from 231 MPa to 286 MPa). Meanwhile, the mechanical properties are better in the transverse than in the longitudinal direction. Moreover, the strengthening mechanism of B4C on the mechanical properties of aluminum alloy additive manufacturing mainly includes dispersion strengthening from fine and uniform B4C granular reinforcing phases and fine grain strengthening from the grain refinement of B4C. These findings shed light on the B4C induced grain refinement mechanism and improvement of WAAM 2319 Al alloy.

Design and validation of a suction device to reduce cross-contamination in multi-material laser-based powder bed fusion

Powder suction modules for additive manufacturing systems in the field of multi-material laser powder bed fusion (PBF-LB/M) have a critical influence on the quality of the manufactured components. In particular, metal powder cross-contamination originating from insufficient removal of foreign particles during multi-material processing can lead to undesired changes in material properties. In this paper, a suction device was simulated, designed, and validated to reduce cross-contamination. Requirements and necessary characteristic values of the multi-material PBF-LB/M system, the powder suction module, and the materials used were determined. Furthermore, an iterative simulative method and procedure for the design of suction devices was applied. For this purpose, a flattened bell-shaped geometry with flow-optimized fins was presented. This design led to both a high flow velocity and a homogenous velocity distribution at the nozzle inlet for full-surface multi-material PBF-LB/M suction modules. The developed method was validated by applying it to the material combination of tool steel 1.2709 and copper alloy CW106C. The aim was to reduce the cross-contamination generated during the in-process on an SLM 280HL multi-material PBF-LB/M system. Multi-material samples were built using the original nozzle design as well as the newly developed improved powder suction module and investigated in terms of resulting cross-contamination using energy-dispersive X-ray spectroscopy. The improved suction module had a significantly higher flow velocity and a more homogenous velocity distribution at the nozzle inlet compared to the original suction module. Cross-contamination of the manufactured multi-material samples was reduced by up to 93 % due to the improved suction model.

Analysis of the social impact of 3D Printing and its future development

This paper introduces basic process and social impact of 3D printing, which is also named as additive manufacturing (AM), and prospects for future development of AM technology. This paper starts with the historical background of AM technology, as it creates a new era of mechanical manufacturing. The AM can be summed up in five major steps: create 3d CAD model, convert file format to STL, divide model into layers using software, print the model from bottom in AM system, and finally, some end-part finishing process will be applied. The advantages of AM technology are outstanding, but its limitation also restraint the further development of the technology. I have discussed in details about types and impacts of current application and what are the key problems. Overall, even though there are still many unpredictable factors of development in AM technology, it is still progressing in a positive way and hopefully will move to its next step in next decade.

A framework for production planning in additive manufacturing

Additive manufacturing (AM) introduces a set of technology-specific problems, such as the proper orientation of parts or the placement of several heterogeneous parts in the same build cycle, which are not addressed by traditional approaches to production planning and scheduling. Although these new production subproblems have been implicitly addressed by several works according to generic nesting and scheduling concepts, a literature review revealed that there is no uniformity in identifying and, thus, solving all these subproblems. For this reason, and as a result of an in-depth analysis of the existent literature on AM production planning and an analogy with classic cutting and packing typologies, the present paper offers a framework to formalise the production planning problem in AM at the operational level. This framework can be used as a reference to focus on and address these AM-related problems for efficient production planning. It is designed at the subproblem level and centres on production order processing in AM. A coding strategy is specifically developed for the framework, which is applied to a review of relevant works that propose models for the production planning of AM systems. Finally, the review results are discussed and possible extensions of the framework are proposed.

In Vitro Evaluation of Pore Size Graded Bone Scaffolds with Different Material Composition.

The demand for biomimetic and biocompatible scaffolds in equivalence of structure and material composition for the regeneration of bone tissue is relevantly high. This article is investigating a novel three-dimensional (3D) printed porous structure called bone bricks with a gradient pore size mimicking the structure of the bone tissue. Poly-ɛ-caprolactone (PCL) combined with ceramics such as hydroxyapatite (HA), β-tricalcium phosphate (TCP), and bioglass 45S5 were successfully mixed using a melt blending method and fabricated with the use of screw-assisted extrusion-based additive manufacturing system. Bone bricks containing the same material concentration (20 wt%) were biologically characterized through proliferation and differentiation tests. Scanning electron microscopy (SEM) was used to investigate the morphology of cells on the surface of bone bricks, whereas energy dispersive X-ray (EDX) spectroscopy was used to investigate the element composition on the surface of the bone bricks. Confocal imaging was used to investigate the number of differentiated cells on the surface of bone bricks. Proliferation results showed that bone bricks containing PCL/HA content are presenting higher proliferation properties, whereas differentiation results showed that bone bricks containing PCL/Bioglass 45S5 are presenting higher differentiation properties. Confocal imaging results showed that bone bricks containing PCL/Bioglass 45S5 are presenting a higher number of differentiated cells on their surface compared with the other material contents.

ADDITIVE MANUFACTURING: A NEW CONCEPT FOR END USERS. THE CASE OF MAGNETIC MATERIALS

Metal additive manufacturing (AM) technology is growing up as a technology. Although up today slower and less reliable than traditional production methods, AM systems are showing to be very successful when producing parts with unconventional topologies or in small quantities. In addition, it is showing its capability to produce components with chemical compositions which should not be realized with standard production processes. In this paper some examples are reported of magnetic materials specifically designed for AM. In this work, powder of FeSi electric steel, with 6.5 wt.% Si content is considered to produce samples by AM. Aim of this paper is to investigate the microstructural and texture evolution of FeSi steels, with 6.5% Si, following annealing heat treatment, with the aim of identifying the conditions under which it could be possible to obtain the best magnetization behavior of the alloys.

When physics-informed data analytics outperforms black-box machine learning: A case study in thickness control for additive manufacturing

Aerosol jet printing (AJP) has emerged as a promising noncontact additive manufacturing method for high-resolution printing for a wide range of material systems. A key challenge limiting the broader adoption of AJP in the material science community is the lack of methods to precisely control thickness. Herein, we develop a model-based design of experiment (MBDoE) framework that integrates physics-informed models, nonlinear regression, and information criteria to postulate, select and calibrate the best model to describe and optimize the AJP manufacturing process. Starting with already available data from system commissioning (e.g., prior single variable sensitivity analysis), four candidate physics-informed models are postulated and trained. MBDoE identifies a single additional optimal experiment to validate these predictive models with quantified uncertainties, which are then used to determine the best experimental conditions to control printed film thickness. As a comparative benchmark, the analysis is repeated using the same dataset with nonparametric Gaussian process regression (GPR) model that does not incorporate physical information. Using MBDoE principles, we find that only five experiments are necessary to calibrate the nonlinear physics-informed parametric model, and with said limited data, this model outperforms the black-box machine learning GPR model. This key result underscores an emerging trend in the data science community: incorporating physical information into predictive models often drastically reduces the data requirements. Leveraging MBDoE further increased the data efficiency. By design, the proposed data science framework is general in nature and can be easily extended to other experimental and additive manufacturing systems beyond AJP.

Process modeling of laser scanning vat-photopolymerization operating under intermittent exposure conditions

Process modeling is an important tool in additive manufacturing (AM) because it elucidates the relationship between processing parameters and material properties. Ultraviolet laser scanning vat-photopolymerization (VPP-UVL) is a common additive manufacturing technique, with a strong physical modeling based on the Jacobs work curve framework. The work curve model was developed for continuous UV exposure (CE) systems, however most VPP-UVL systems to date operate under intermittent exposure (IE) conditions due to the wide adoption of solid-state pulsed-laser sources. Despite their fundamental differences, the Jacobs work curve model is still successfully employed in IE systems under high overlap conditions between pulses, however there are few investigations regarding the limiting conditions for the applicability of the Jacobs work curve model to describe the total exposure profile in intermittent exposure (IE) setups. To address this issue, a model describing a VPP-UVL-IE process was developed. The VPP-UVL-IE model presented here has the same logarithmic dependence as the Jacobs work curve model, but with the addition of a multiplying factor carrying information on the spatial distribution of energy, that is, the overlap of individual pulses. The model is adaptable for non-gaussian beam profiles and can be solved for bidimensional analysis representing layer fabrication. To test the model, a custom-built VPP-UVL-IE additive manufacturing system was used, and structures were printed and characterized using SEM and stylus profilometry. The model`s reliability was investigated under constant overlap and exposure conditions. The model is very robust under constant overlap conditions, with good agreement between experimental data and simulation. For constant exposure, there is good qualitative agreement, but discrepancies occur due to insufficient modeling of the spatial distribution of energy. The 3D printing of complex structures is demonstrated, and the model indicates that VPP-UVL-IE can offer, theoretically, faster printing compared to VPP-UVL-CE for large beam radius (>275 μm), under the assumption of Gaussian beam profile, constant irradiance during the pulses, and dwell time longer than beam travel time. Conversely, same levels of exposure can be achieved at higher scan speed using CW laser sources instead of pulsed sources for small beam radius (<275 μm). • The work curve equation can model VPP-UVL with pulsed light sources. • Pulsed light VPP-UVL can print faster than continuous scanning. • Single pulse energy dose and spatial distribution of energy dose are independent.

FLAW3D: A Trojan-Based Cyber Attack on the Physical Outcomes of Additive Manufacturing

Additive manufacturing (AM) systems such as 3-D printers use inexpensive microcontrollers that rarely feature cybersecurity defenses. This is a risk, especially given the rising threat landscape within the larger digital manufacturing domain. In this work, we demonstrate this risk by presenting the design and study of a malicious Trojan (the FLAW3D bootloader) for AVR-based Marlin-compatible 3-D printers ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 100 commercial models). We show that the Trojan can hide from programming tools, and even within tight design constraints (less than 1.7 KB in size), it can compromise the quality of additively manufactured prints and reduce tensile strengths by up to 50%.

Tailoring coil geometry for secondary heating of substrate towards the development of induction heating-based wire additive manufacturing

Induction heating (IH), a clean energy source, is potentially used to develop wire additive manufacturing (AM) system. The optimised parameters that simultaneously melt the mild steel wire and raise the substrate temperature is established. A fully coupled thermal-electromagnetic model of AM system is developed to perform numerical experiments on temperature development. The proposed hybrid helical-pancake coil with circular cross-section melt the metallic wire and raise the substrate temperature to 1490 K. The hybrid coil provides rapid heating to the wire (2819 K) and substrate together by enhancing magnetic field strength. The experiments using high-frequency IH system (550 A and 353 kHz) with a 3-turn helical coil is validated with model results for 2 mm mild steel wire.

Virtual-point-based geometric error compensation model for additive manufacturing machines

PurposeThe lack of geometric and dimensional accuracy of parts produced by additive manufacturing (AM) is directly related to the machine, material and process used. This paper aims to propose a method for the analysis and compensation of machine-related geometric errors applicable to any AM machine, regardless of the manufacturing process and technology used.Design/methodology/approachFor this purpose, an error calculation model inspired by those used in computerized numerical control machines and coordinate measuring machines was developed. The error functions of the model were determined from the position deviations of a set of virtual points that are not sensitive to material and process errors. These points were obtained from the measurement of an ad hoc designed and manufactured master artefact. To validate the model, off-line compensation was applied to both the original designed artefact and an example part.FindingsThe geometric deviations in both cases were significantly smaller than those found before applying the geometric compensation. Dimensional enhancements were also achieved on the example part by using a correction parameter available in the three-dimensional printing software, whose value was adjusted from the measurement of the geometrically compensated master artefact.Research limitations/implicationsThe errors that persist in the part derive from both material and process. Compensation for these type of errors requires a detailed analysis of the influencing parameters, which will be the subject of future research.Originality/valueThe use of the virtual-point-based error model increases the quality of additively manufactured parts and can be used in any AM system.

Experimental investigation on deposits of ER70S-6 wire on SiO2 substrate using non-transferred arc-based wire arc additive manufacturing

Recent trends in additive manufacturing (AM) are to produce geometrically complex structures at minimal wastage of material, time and cost without sacrificing part quality and mechanical performance and to introduce ease in processing and part removal. Here, a non-transferred arc (NTA)-based wire arc additive manufacturing (WAAM) system has been developed to achieve the above objectives, where the arc is only generated between tungsten electrode and consumable filler wire. No electrical contact with the substrate facilitate deposits even on the non-conductive substrate surface, which helps to remove the final deposits easily. The influence of deposition parameters (welding current, voltage, wire feed speed (WFS) and travel speed) on response characteristics (bead uniformity, height deviation, droplet diameter, and droplet transfer frequency) is studied on a multi-performance level using grey relational analysis (GRA). Then, single- and multi-bead layer is fabricated over SiO2 substrate for ease in part removal after complete fabrication. WFS is referred to as a key deposition parameter that influences all deposition characteristics. It has been observed that NTA-based WAAM results in high bead uniformity with minimal spatter and low bead height difference between start and exit arc point. Complete ferrite microstructure with few pearlites is observed on the deposits with similar elemental composition on the top, bottom and interface surfaces. X-ray diffraction (XRD) study reveals ferrite diffraction planes ({110}, {200}, {211} and {220}) with no intermetallic formations on deposits. Also, compressive residual stress with less variation in crystallite size, stress, strain and microhardness among the top, bottom and lateral deposit surfaces indicates the fabricated part’s isotropic nature.

Effect of specimen thickness on mode I stress intensity factor for additive manufactured compact tension specimen

In this paper Mode I stress intensity of compact tension specimen was studied for different specimen thicknesses built by additive manufacturing system. Three sets of compact tension specimen of five different thicknesses of 4, 8, 12, 16 and 20 mm were prepared and tested for mode I stress intensity factor according to ASTM D 5045–14. Finite element analysis (FEA) was also performed by modelling compact tension specimen in ABAQUS software to obtain J - integral from which stress intensity factor was calculated. The values of mode I stress intensity factors obtained were 18.61, 51.45, 60.82, 66.93 and 63.31 MPa.mm1/2 for specimen with thickness of 4, 8, 12, 16 and 20 mm, respectively, with maximum value for 16 mm specimen. Also, mode I stress intensity factors obtained by finite element analysis using ABAQUS software are close to the experimental results with average bias error equal to 4.08 %.

New Approach for Extrusion Additive Manufacturing of Soft and Elastic Articles from Liquid-PVC-Based Consumable Materials.

The article deals with the experimental development of a novel additive manufacturing (AM) process using a liquid consumable based on polyvinyl chloride plastisol. A conventional additive manufacturing system designed for deposition of melt filaments was converted to deposition of liquid material. Additive manufacturing with liquid plastisol enables the production of parts with low Shore A hardness and high ductility, surpassing the performance of the conventional filament process. The novel AM process enables the production of articles with a Shore A hardness of 5 to 60, and the mechanical properties of the additively manufactured articles are similar to those produced in the mold. This was achieved by varying the parameters of the AM process as well as the composition of the plastisol composition, including those filled with an inorganic filler. The application of different material distribution patterns also has a significant effect on the mechanical properties of the samples. A potential application of the investigated AM method was proposed and practically evaluated.

Scheduling of build and post processes for decomposed parts in additive manufacturing

Recently, production planning has been highlighted in the Additive Manufacturing (AM) literature. However, most AM studies have focused on a build process performed by an AM machine (also known as a 3D printer). Compared to the build process, AM studies for post-processing have lagged behind in production planning at the macro level. Post-processing needs highly sophisticated and complicated tasks requiring a lot of process time and cost. Therefore, some AM systems need to primarily cover post-processing as well as the build process, which leads to a more comprehensive approach to production planning. This paper addresses the AM systems based on flow-shop, comprehensively including the build and post processes. For post-processing, we consider trimming, coloring, and assembly processes. This paper introduces three scheduling policies: (1) all-for-one-job; (2) one-for-one-job; and (3) hybrid. The first policy is packing every part into the same job, which means that all parts are simultaneously fabricated during the same build process. The second policy is assigning each part to a particular job, which results in parts being fabricated one by one during the build process. The last policy is a compromise between the former two policies. We propose a mixed-integer programming (MIP) model to minimize the makespan for each policy. In computational experiments with test models, the scheduling optimization for AM is applied to various cases: multiple parts, scheduling policies, and multiple AM machines. One of the main comparisons provides that the MIP model of the hybrid policy is more preferred than the all-for-one-job policy, reducing the makespan by 27.68%. In conclusion, our paper quantitatively shows that packing is not a significant factor in minimizing the makespan when comprehensively considering build and post processes. It is a different perspective from that the traditional scheduling for AM has focused on a packing issue to improve the productivity in the build process. • A two-phased framework is proposed for minimizing the makespan in AM systems. • Mixed-integer programs are developed to optimize the scheduling of AM tasks. • Decomposing an original model into pieces is preferred in reducing the makespan. • Experimental results show that packing all the parts into a job is less productive.