Overhang Surfaces Research Articles

Model decomposition method for minimizing the consumption of support structure for FFF

Fused filament fabrication (FFF) often requires additional support structures for manufacturing parts with overhanging areas, leading to substantial material and time wastage. Although several model decomposition techniques have been developed to tackle this issue, most focus solely on the constraint of overhang surface area. As a result, these techniques often struggle with parts that have intricate overhang characteristics, causing reduced printing surface accuracy and quality. This study introduces a precise method for detecting overhang regions and support-relevant overhang regions to improve the accuracy of overhang region identification and printing precision. Additionally, a model decomposition strategy leveraging genetic algorithm optimization is proposed to minimize the need for support structures, aiming for nearly support-free printing. Moreover, for intricate structures with a high topology where support structures are unavoidable, a novel projection support based on the distribution of periodic points in triangular form is developed to address this printing challenge. Experimental results demonstrate that the implementation of the algorithm outlined in this work on an FFF printer has achieved nearly support-free printing. Moreover, the proposed method for generating support structures has the potential to reduce material usage by 27 %.

Understanding coaxial photodiode-based multispectral pyrometer measurements at the overhang regions in laser powder bed fusion for part qualification

Coaxial photodiode monitoring sensors provide a digital signature at the melt pool level in laser powder bed fusion (L-PBF), facilitating faster part qualification. However, current signatures are plagued by significant noise and signal variation and show counterintuitive trends such as a decrease in measured temperature near overhang surfaces. This paper investigates the behavior of coaxial photodiode-based melt pool monitoring (PD-MPM) thermal measurements at overhang regions by conducting a combination of experiments and multiphysics simulations. High-speed in situ synchrotron X-ray imaging is coupled with a coaxial photodiode system to enable comparison of the observed melt pool phenomena and monitoring signals during double-track AlSi10Mg experiments. A multiphysics model is developed to simulate the melt pool dynamics and concurrent sensor signals throughout the process. We propose a surrogate model that clarifies the correlation between sensor signals and melt pool temperature. Both experimental and simulation results emphasize the significant impacts of laser energy and keyhole formation on solid-liquid interface discontinuities and PD-MPM signals. Results reveal that a boiling region with a relatively smaller projected area, as near an overhang, can lead to a decrease in the measured melt pool temperature, even when the true peak temperature remains constant, meaning that PD-MPM temperature measurements cannot be used to estimate absolute melt pool temperature. Consequently, in overhang regions, interaction between the melt pool and underlying powder results in an abruptly deforming melt pool and a pronounced decrease in both individual photodiode intensities and overall measured melt pool temperature. This work illustrates how to correctly interpret the coaxial photodiode monitoring signals in L-PBF by uncovering the intricate dynamics within the melt pool, particularly in challenging overhang regions, and pave the foundation for data-driven part qualification.

A Multi-Objectives Genetic Algorithm Based Predictive Model and Strategy Optimization during SLM Process.

Selective laser melting (SLM) process was optimized in this work using multi-objectives genetic algorithm. Process parameters involved in the printing process have an obvious impact on the quality of the printed parts. As the relationship between process parameters and the quality of different parts are complex, it is quite essential to study the effect of process parameter combination. In this work, the impact of four main process parameters, including defocusing amount, laser power, scan speed and layer thickness, were studied on overhanging surface quality of the parts with different inner structures. A multiple-factor and multiple-level experiment was conducted to establish a prediction model using regression analysis while multi-objective genetic algorithm was also employed here to improve the overhanging surface quality of parts with different inner shapes accordingly. The optimized process parameter combination was also used to print inner structure parts and compared with the prediction results to verify the model we have obtained before. The prediction results revealed that sinking distance and roughness value of the overhanging surface on a square-shape inner structure can reduce to 0.017 mm and 9.0 μm under the optimal process parameters combination, while the sinking distance and roughness value of the overhanging surface on a circle-shape inner structure can decrease to 0.014 mm and 10.7 μm under the optimal process parameters combination respectively. The testing results showed that the error rates of the prediction results were all within 10% in spite of random powder bonding in the printing process, which further proved the reliability of the previous results.

On the characterization of roughness and geometrical irregularities of additively manufactured single titanium-alloy struts

The purpose of this study is to expose data analysis techniques based on X-ray computed microtomography (XCT) for measuring the complex geometric characteristics of millimeter-sized specimens fabricated by additive manufacturing, and their modification induced by surface treatment. A set of Ti-6Al-4V struts was produced by Electron Beam Melting (EBM) at two angles, at 45° and vertically. They were scanned by XCT before and after electropolishing (EP). Extensive analysis allowed for measuring the amount and size of partially melted particles attached to the surface, the cross-section geometry along the axis of the strut, and the roughness over the whole surface at the micrometer scale. The variation of these characteristics was correlated to the EP conditions. The accuracy of the roughness values measured by XCT was validated by Laser Scanning Confocal Microscopy. The as-built 45° specimens showed the usual characteristics of EBM fabricated struts, such as elongated cross-sections, and a smooth overhanging surface. Less expected was the increased roughness on the lateral sides of these specimens, rather than on the underhanging sides. Similarly, the vertically fabricated struts showed a moderate, yet measurable, roughness variation over their circumference. Despite this lack of uniformity, all the specimens fabricated at a given angle were remarkably similar. The average quantities and sizes of attached particles were quantified for all conditions. The amount of removed material after EP correlated well with the total exchanged electric charge related to the formation of tetravalent Ti 4+ ions. Local SEM observations before and after EP put into evidence the removal of partially melted particles. • Novel custom methods for extensive analysis of 3D geometries applied to mm-sized EBM struts: cross-section analysis, surface unfolding, surface granulometry. • Quantitative assessment of attached particles, surface roughness and cross-sectional shape before and after electropolishing and related effects of process parameters. • Relating process parameters to the heterogeneity of attached particles, roughness, and equivalent diameters along the circumferences of full EBM struts. • Precise measurements of surface feature modification during electropolishing on mm-sized EBM specimens and its consequence on surface roughness evolutions. • Documentation of the mechanism of surface particles teared off during electropolishing leaving nanometer sized craters with crystallographic features.

Contact-Free Support Structures for the Direct Metal Laser Melting Process.

Although Direct Metal Laser Melting (DMLM), a powder bed fusion (PBF) Additive Manufacturing (AM) for metallic materials, provides many advantages over conventional manufacturing such as almost unlimited design freedom, one of its main limitations is the need for support structures beneath overhang surfaces. Support structures are generally in contact with overhang surfaces to physically prop them up; therefore, they need to be removed after manufacturing due to not constituting a part of the main component design. The removal of supports is a process sequence adding extra time and cost to the overall manufacturing process and could result in damaging the main component. In this study, to examine the feasibility of contact-free supports for overhang surfaces in the DMLM process, coupons with these novel types of supports were prepared from CoCrMo alloy powder. This study aims to understand the effect of two parameters: the gap distance between supports and overhang surfaces and the inclination angle of overhang surfaces, on the surface topography and microstructural properties of these surfaces. Visual inspection, roughness measurements, and optical microscopy were utilized as characterization methods The roughness parameters (Ra, Rq, and Rz) were obtained using the focus variation method, and optical microscope analysis was performed on the cross-sections of the overhang surfaces to investigate the sub-surface microstructure and surface topology. Results showed that contact-free supports have a positive effect on decreasing surface roughness at all build angles when the gap distance is correctly set to avoid sintering of the powder in between the overhang and supports or to avoid too large gaps eliminating the desired effect of the higher thermal conductivity.

Rocky reef biodiversity survey: Punta Pardelas, Argentina.

BackgroundTemperate rocky reefs in the SW Atlantic are productive areas that support highly diverse communities of invertebrates, algae and fishes. Rocky outcrops form complex structures which offer a diversity of microhabitats that lead to a great variety of co-existing species. Subtidal biodiversity within the Natural Protected Area Península Valdés is largely unexplored and studies are mainly limited to fish. A total of 560 high definition photoquadrats from seven rocky reefs (1-25 m depth) at Punta Pardelas were obtained during March 2019. In total, 4491 occurrences were recorded and identified to phyla (n = 2), superclasses (n = 1), classes (n = 5), subclasses (n = 2), orders (n = 2), families (n = 1), subfamilies (n = 1), genera (n = 10) and species (n = 43) levels. This dataset was developed to provide a baseline inventory of Punta Pardelas inside the Natural Protected Area, that was only partially reported more than 50 years ago. Such data represent the first step towards monitoring these less-accessible ecosystems.New informationMost of the available information about Atlantic Patagonian marine biodiversity is related to rocky intertidal communities or rocky reef fish communities. Despite having more than 4000 km of coastline, in the last 20 years only four studies have focused on subtidal benthic communities from shallow rocky reefs in Argentina (Genzano et al. 2011, Rechimont et al. 2013, Bravo et al. 2015, Bravo et al. 2020a). However, none of them described the epi-benthic community of different surface orientations on the rocky reefs. This dataset includes several surface orientations (i.e. horizontal, vertical, overhang and cave floor) and their microhabitats. We found almost double the number of taxa previously reported for the area. Through stratified sampling of different surface orientations, we recorded species that are often overlooked and thus registered as part of the existing biodiversity. For example, overhang surfaces in our study showed a unique assemblage and a great diversity of sponges. This work will be valuable as baseline information that is currently out of date in Nuevo Gulf rocky reefs.

The relationship between the macro- and microstructure and the mechanical properties of selective-laser-melted Ti6Al4V samples under low energy inputs: Simulation and experiment

The occurrence of structural defects in selective laser melting (SLM) damages the mechanical properties and fabrication accuracy of components and is closely related to the processing parameters. Therefore, having a good grasp of the interaction mechanism between the material and laser is useful for designing an improved process window. In this study, we experimentally investigated the relationship between the samples' macro- and microstructure and their mechanical properties under low energy inputs, and the response behaviour of as-built parts under these parameters was calculated using a thermal fluid flow (TFF) model with a modified and surface-tracking heat source. The results showed that Ti6Al4V parts obtained via SLM under low energy inputs exhibited a strong relationship between the macro- and microstructure and the mechanical properties. Single-track TFF models were built to better understand the underlying phenomena that are influenced by process parameters and then affects the depositing process. The models provided insight into the thermal history, deposition behaviour, densification, size accuracy, and surface morphology and by considering the velocity field, the phenomenon of powder adhesion caused by the Bernoulli effect could be investigated. Interestingly, the TFF model with a volume energy density (Ev) of 90 J/mm3 captured the formation of pores, however, high smoothness of the surface and size accuracy was obtained in the sample. It can be proved that densification is hardly related to the surface morphology or the fabrication precision. In addition, our experiments showed that the fabrication process was less sensitive to process parameters at Ev = 38 J/mm3. Densification was also more sensitive to the laser power than to the scanning speed.The results suggest that good-quality samples can be synthesised via SLM under low energy inputs, and the TFF model is a powerful tool for the systematic optimisation of the process parameters. Our findings could be applied to improve the controllability of the overhang surface with severe powder adhesion in further studies.

Investigation the effect of electron beam melting parameters on overhang structure deformation

ABSTRACT Electron beam melting (EBM) is a new and rapidly developing metal additive manufacturing (AM) technology. The unique capabilities of EBM have opened the door for this technology in high-performance applications such as medical implants, aerospace, automotive, etc. However, the building of overhang surfaces without support structure leads to dross formation, distortions and warping. Using the support structures is the solution to avoid the mentioned problems, but increased support structure leads to increased use of materials, and post-processing time, which eventually increases the costs of the final process. This study aims to investigate the effect build parameters EBM process on the warping deformation. The main process parameters are considered and evaluated. The results indicate that the process parameter play a role in overhang structure warping deformations. The minimum deformation (0.28 mm) is resulted with 15 mA current, 4530 mm/s scan speed, 3 mm focus offset and 0.3 mm line offset.

Constrained stacking in DLP 3D printing

Using stacked models for 3D printing could significantly improve printing efficiency and save printing time. For standard 3D printing techniques like Fused Deposition Modeling (FDM) or Digital Light Processing (DLP), support structures are required for overhanging areas, even between the stacked models. However, there are requirements from medical applications like 3D printed dental implant guides, that support structures are not allowed to be placed on some restricted regions to maintain models’ appearance quality and accuracy. This paper introduces a constrained multi-level stacking scheme for DLP 3D printers, aiming to stack as many models as possible in the printing space; meanwhile, no support is placed on the restricted regions. We rotate each stacked model along the axis and calculate the feasible pose set that restricted regions have no overhanging surface. We further propose a level-based scaffold structure to arrange the stacked models level by level. Therefore, support structures could be generated on the scaffold, and the stacked model does not need to support each other. We employ a heuristic strategy for each level to iteratively select a candidate model and its posture to achieve a locally optimal arrangement. We then introduce perturbations in the arrangement order, using a hill-climbing method to approximate the most volume-efficient arrangement.

The Importance of Surface Orientation in Biodiversity Monitoring Protocols: The Case of Patagonian Rocky Reefs

Temperate rocky reefs in Atlantic Patagonia are productive areas that support a high diversity of invertebrates, algae, and fishes. Complex surface structures on rocky reefs offer a range of microhabitats, which in turn, lead to a broad variety of co-existing species. Despite their ecological importance and the ecosystem services they provide, Patagonian rocky reef habitats have received limited attention. Until now studies have not discerned nor consequently described the assemblages found on each of the different surface orientations, namely horizontal, vertical, overhang and cavefloor. During this study we developed a protocol for sampling different surface orientations on subtidal rocky reefs using georeferenced high-resolution photoquadrats. We described and compared the epibenthic assemblage of surface orientations on 7 rocky reefs within 1–25 m depth in a northern Patagonia gulf. A total of 70 taxa were identified (12 macroalgae, 44 invertebrates, 10 tunicates, and 4 fishes), which doubles the number of species previously reported for the area. Each surface orientation presented a different assemblage structure while species richness was higher on vertical surfaces. The overhang surfaces had the most distinct assemblage conformed by cnidarians, tunicates, sponges and the absence of algae. The average overall species richness increased with depth due to the increase of sponge and tunicate species. Our results highlight the need of including several surface orientations in rocky reef biodiversity monitoring. This study offers a protocol for large-scale programs aimed at monitoring changes in biodiversity, which is broadly accessible and will provide accurate information. With robust yet simple, non-destructive and relatively low-cost practices this protocol can adequately assess changes in marine habitats, which provide important ecosystem services.

Effect of processing parameters on overhanging surface roughness during laser powder bed fusion of AlSi10Mg

Abstract It is often required to add a support structure for overhanging surface in additive manufacturing (AM), especially during laser powder bed fusion (LPBF), which has a considerable impact on the promotion and wide application of this technique. The aim of this study is to evaluate the influence of process parameters on the overhanging surface roughness of AlSi10Mg specimens without a support structure under different build angles, 30°, 45° and 60°, respectively. A design of experiment (DoE) approach was adopted to clarify the correlations between the overhanging surface roughness and the causative the process parameters such as contour laser power, contour scanning speed, infill laser power, infill scanning speed and infill scanning angle. The results showed that the influence of each process parameter on the overhanging surface roughness varies with the change in build angle. Above all, the dominant factor was the contour scanning speed. The results of the comparison show that the contour process parameters are much more influential than the infill process parameters. In addition, the process parameters affected the overhanging surface roughness were on the decrease as the build angle increases. When the build angle was 30°, it was necessary to comprehensively consider the influence of infill scanning angle, contour scanning speed and infill scanning speed to obtain a smooth overhanging surface with a low roughness. However, as the build angle increased to 60°, only the contour scanning speed had a highly significant impact. The results also revealed that apart from the contour scanning speed, the interaction between contour scanning speed and contour laser power should be given priority when the build angle is 30° or less. The lowest roughnesses of overhanging surface with build angles of 30°, 45° and 60° were 10.9 μm, 7.9 μm and 4.22 μm, respectively.

EVALUATION OF OVERHANG ANGLE IN TIG WELDING-BASED WIRE ARC ADDITIVE MANUFACTURING PROCESS

Wire Arc Additive Manufacturing (WAAM) is a relatively new manufacturing method. It is a novel technique to build net-shaped or near-net-shaped metal components in a layer-by-layer manner via applying metal wire and selection of a heat source such as laser beam, electron beam, or electric arc. WAAM process is preferable as an alternative to traditional manufacturing methods especially for complex featured and large scale solid parts manufacturing and it is particularly used for aerospace structural components, manufacturing and repairing of dies/molds. TIG welding-based WAAM method is implemented by depositing continuous wire melted via heat. In this study, the overhang (self-supporting) angle in TIG welding-based wire arc additive manufacturing process is investigated. The overhang angles are the angles at which a 3D printer can build tapered (overhang) surfaces without the need to supporting material below the printing layer. The material, bead height, TIG weld parameters and the environment temperature (cooling rate of printed layer) are the parameters which affect the overhang angle. The results show that the maximum overhang angle is also dependent on the temperature of the previous layer. For the selected set of process parameters, the maximum overhang angle is found as 28o, if the temperature of the previous layer is cooled to 150oC before the subsequent layer is deposited.

Modeling the Effect of Different Support Structures in Electron Beam Melting of Titanium Alloy Using Finite Element Models

Electron beam melting (EBM) technology is a novel additive manufacturing (AM) technique, which uses computer controlled electron beams to create fully dense three-dimensional objects from metal powder. It gives the ability to produce any complex parts directly from a computer aided design (CAD) model without tools and dies, and with variety of materials. However, it is reported that EBM has limitations in building overhang structures, due to the poor thermal conductivity for the sintered powder particles under overhang surfaces. In the current study, 2D thermo-mechanical finite element models (FEM) are developed to predict the stresses and deformation associated with fabrication of overhang structures by EBM for Ti-6Al-4V alloy. Different support structure geometries are modeled and evaluated. Finally, the numerical results are validated by experimental work.

Support optimization for overhanging parts in direct metal laser sintering

The present work focuses mainly on the utilization of different support profiles for overhang structures in EOS M290 Direct Metal Laser Sintering (DMLS) machine. Maraging steel (MS1) parts with large overhangs were produced using various support parameters to reveal the effects of support profile on dimensional stability of overhang structures and surface quality of the downward facing surfaces. Overhangs supported by weak support profiles require less post processing due to easy support removal and low surface roughness values at the cost of dimensional stability. On the other hand, parts with stronger support profiles are less prone to thermal warping and provided better dimensional stability at the cost of surface quality. The hardness shows no remarkable variation along the overhang surface in the same structure as well as between different parts. The study reveals that the designer should choose different support assemblies depending upon the overhang surface size and location.

Parameters optimization for horizontally built circular profiles: Numerical and experimental investigation

Selective laser melting (SLM), a type of additive manufacturing (AM) process, is chosen for direct fabrication of powder-based functional metallic objects. The designing of small circular geometries or overhang surfaces built parallel to platform bed has been a subject of concern in the industrial application of SLM. This paper presents an attempt to design and fabricate horizontally built circular holes in a simple cubic model in SLM machine. The processing parameters for down-skin such as laser power, scan speed, and the number of scanned layers were found to play a significant role in the sustainability of small hole built without support structures. The lower incident energy in down-skin region prevents excess melting of powder particles. The Numerical study on ANSYS was first carried out to identify the melt pool depth with different processing parameters and later SLM machine was used to produce the specimens for visual inspection. The results were found satisfactory with the application of down-skin parameters (65 W, 1000 mm/s) subjected to scanning of 3–5 layers above the exposed surface.

Optimizing Fabrication Outcome in Low-cost FDM Machines. Part 1 - Metrics

Several models of FDM machines, characterized by different architecture and hardware components, have flooded the market in the last 5 years. As a result, given the high sensitivity of FDM to the specific machine characteristics, the search for optimal printing parameters is a renown problem. This two-parts paper proposes an easy-to-follow and low-cost procedure for the characterization of any given FDM machine. The method allows the evaluation of the effects of a wide selection of FDM process parameters on the quality of 3D printed parts. The first part focuses on the definition of a series of metrics to be measured on a series of test prints to evaluate the quality of the produced parts. Specifically, several effects are considered: dimensional accuracy, small details, overhang surfaces, ability of printing small holes/thin extrusions and overall quality of the prints. The evaluation of seven quality parameters on a single print is made possible thanks to: i) a specifically designed specimen that is made available to the user and ii) a rigorous and repeatable measurement procedure, which are both discussed in the first part of the paper. The second part presents the characterization procedure, the statistical tools used in the experimentation and provides guidelines to be used for the characterization of any FDM machine. The whole procedure is tested on a desktop FDM machine to demonstrate obtainable results.

Numerical investigation of heat current study across different platforms in SLM processed multi-layer AlSi10Mg

Selective Laser Melting (SLM) of three dimensional multi-layer model is being numerically investigated using finite element method with academic ANSYS software. The temperature distribution and melt pool formation with underlying solid base, support structure and loose powder is investigated in a single scan track. The results illustrate that the melt pool depth is deepest with the loose powder base but the regions adjacent to solid surface reduces the pool depth due to improved heat dissipation. Moreover, the liquid penetration increases with the layer addition and its intensity is dependent on input specific energy. The study suggests the selection of lower specific energy in the initial layers while designing overhang surfaces, clearance etc. to prevent excess powder melting beyond the layer thickness to achieve smooth surface.

Developing Topology Optimization with Additive Manufacturing Constraints in ANSYS®

Topology Optimization is an effective technique to optimize structural design and to minimize waste. Additive manufacturing (AM) is potentially a great approach to fabricate the complex organic geometric features of these optimized designs. However, topology optimization without considering manufacturing constrains may result in topologies that are expensive and difficult to manufacture. In order to satisfy the constraints imposed by AM processes, this paper proposes a topology optimization methodology using the compliance minimization approach with a constraint on overhanging surfaces. Compliance of a body is approximated through a finite element analysis procedure. To constrain the gradient and converge towards a structure without overhang surfaces, a function has been developed to estimate the overhang sensitivities. The gradient of the compliance with respect to densities are penalized using the determined overhang sensitivities. To introduce a reliable platform for research, as well as solving the resulting constrained topology optimization problems, a topology optimizer has been developed in ANSYS® using ANSYS Parametric Design Language (APDL). Using a conventional topology optimization method, the results of two different case studies solved by the developed APDL program are shown. Finally, an implementation of the proposed topology optimization methodology with AM constraints is used to solve a problem. The result is a structure that does not need support material to be manufactured.

Collembola cuticles and the three-phase line tension.

The cuticles of most springtails (Collembola) are superhydrophobic, but the mechanism has not been described in detail. Previous studies have suggested that overhanging surface structures play an important role, but such structures are not a universal trait among springtails with superhydrophobic cuticles. A novel wetting experiment with a fluorescent dye revealed the extent of wetting on exposed surface structures. Using simple wetting models to describe the composite wetting of the cuticular surface structures results in underestimating the contact angles of water. Including the three-phase line tension allows for a prediction of contact angles in the observed range. The discrepancy between the contact angle predicted by simple models and those observed is especially large in the springtail Cryptopygus clavatus which changes, seasonally, from superhydrophobic to wetting without a large change in surface structure; C. clavatus does not have overhanging surface structures. This large change in observed contact angles can be explained with a modest change of the three-phase line tension.

Improving additive manufacturing processability of hard-to-process overhanging structure by selective laser melting

In this paper, a selective laser melting (SLM) physical model describing the melt pool dynamics and the response of downward-facing surface morphology evolution of overhanging structure under different laser processing conditions was proposed, in which an enormous difference in thermal conductivity and laser absorption capacity between the as-fabricated part and powder material was taken into consideration. The underlying thermal physical mechanism of the dross formation phenomenon during SLM preparing overhanging surface was revealed by numerical simulation analysis and experimental studies. It was found that both high and low laser volume energy density (ω) resulted in an inferior downward-facing surface quality. As an optimal processing parameter (60–80J/mm3) was settled, the overhanging structure obtained a relatively smooth downward-facing surface due to the sound melt pool dimension and steady melt flow behavior. The experimental studies were compared with the simulated results, showing a good agreement with the predictions obtained in the simulations. It was interesting to find that the variation rules of surface quality and densification level of overhanging structure with different ω were exactly converse. As the ω decreased from 80J/mm3 to 60J/mm3, the surface roughness could be reduced from 59μm to 33μm while, contrarily, the porosity was elevated from 3.2% to 8.4%. In order to fabricate complicated metal parts with lower risk, four solutions for improving the processability of hard-to-process overhanging structure were provided.