Part Geometry Research Articles

Exploring the impact of build direction on overhang design constraints for multiaxis material extrusion

Purpose Material extrusion (MEX) additive manufacturing often requires support structures to enable manufacture of steep overhanging features. Multi-axis deposition (often enabled by a robotic arm) offers novel toolpath planning methods that can significantly reduce or eliminate supports. However, there is currently a lack of established design guidelines for the process. Design/methodology/approach This study investigates the relationship between achievable, support-free overhangs and the multi-axis build direction. Although altering build directions mid-print can increase the layer-to-layer overlap of an overhanging feature, the deposition paths on the overhanging surface may be less supported with respect to gravity. To interrogate these effects, a 6-degree-of-freedom robotic arm MEX platform printed test pieces with overhang angles (relative to the build direction) increasing from 0° to 75° at build directions varying from 0° (i.e., XY-planar) to 60° with respect to the global Z-axis. Findings Characterization of printed surface quality revealed no statistically significant difference in the fidelity of the overhanging surface as the build direction was changed. These results suggest that the overhang threshold observed in traditional XY-planar printing (typically 45°) remain consistent regardless of build direction (e.g. a build direction of 60° successfully printed a relative overhang of 45°), indicating that deposition quality was not negatively impacted by gravitational forces. Originality/value This study provides insight into how tool orientation can be optimized to maximize part accuracy and minimize support material requirements; after quickly screening for the XY-planar overhang threshold, designers can freely select multi-axis build directions throughout part geometries, provided the overhanging surfaces are below that relative threshold.

Influence of varying volume energy densities on the magnetic properties of additively manufactured Ni50Fe50

AbstractThe state of the art of nickel iron alloys specifies that low porosity and large grain sizes are essential to reach sufficient soft magnetic properties, e.g. like low coercivity. Both porosity and grain size are influenced by the volume energy density (VED) used during additive manufacturing (AM) and are relatively independent of the part geometry. Additional factors like residual stresses, also affecting the magnetic properties, are not only influenced by the VED but also the part geometry and are distributed irregularly. Based on this, the geometry independent adjustment of residual stresses is only possible to a limited extent. Due to this, it is of high interest whether the sole consideration and adaption of grain size and porosity is sufficient to reach and assure soft magnetic properties for Ni50Fe50 in as-built condition. In this study, it is investigated whether soft magnetic properties can be achieved during AM of a Ni50Fe50 alloy using a standard laser powder bed fusion (PBF-LB) process by varying the used VED. The influence of increasing VEDs of up to 667 J/mm3 in the manufacturing process on grain size, porosity, saturation flux density and coercivity is analyzed. It could be shown that in a defined parameter field, the magnetic properties can be improved with increasing energy density, as larger grains are formed, while the relative density is not decisively reduced (minimal coercivity 184 A/m). However, it could also be shown that a standard PBF-LB process and the sole consideration of grain size and porosity is not applicable to reach soft magnetic properties (coercivity of < 100 A/m) in as-built condition and additional characteristics like residual stresses need to be taken into consideration in future works.

Robotized 3D Scanning and Alignment Method for Dimensional Qualification of Big Parts Printed by Material Extrusion

Moulds for aeronautical applications must fulfil highly demanding requirements, including the geometrical tolerances before and after curing cycles at high temperatures and pressures. The growing availability of thermoplastic materials printed by material extrusion systems requires research to verify the geometrical accuracy after three-dimensional printing processes to assess whether the part can meet the required geometry through milling processes. In this sense, the application of automated techniques to assess quick and reliable measurements is an open point under this promising technology. This work investigates the integration of a 3D vision system using a structured-light 3D scanner, placed onto an industrial robot in an eye-in-hand configuration and synchronized by a computer. The complete system validates an in-house algorithm, which inspects the whole reconstructed part, acquiring several views from different poses, and makes the alignment with the theoretical model of the geometry of big parts manufactured by 3D printing. Moreover, the automation of the validation process for the manufactured parts using contactless detection of the offset-printed material can be used to define milling strategies to achieve the geometric qualifications. The algorithm was tested using several parts printed by the material extrusion of a thermoplastic material based on black polyamide 6 reinforced with short carbon fibres. The complete inspection process was performed in 38 s in the three studied cases. The results assure that more than 95.50% of the evaluated points of each reconstructed point cloud differed by more than one millimetre from the theoretical model.

Robust integer optimization of turning parameters for cutting tool sustainability and machining economics in discrete production.

Machining optimization is crucial for determining cutting parameters that enhance machining economics. However, few studies address the significant variation in cutting tool wear and the complexities of discrete production, often leading to lower cutting parameters to prevent operational failures. Moreover, variations in part geometries lead to differing contact conditions between the cutting tool and workpiece, as well as variations in material removal. This study employs a robust optimization approach tailored for discrete workpieces to experimentally determine optimal cutting parameters that balance machining efficiency with cutting tool sustainability. An objective function was proposed to integrate tool wear probability and the number of workpieces, with case studies demonstrating its critical role in enhancing efficiency while achieving a tool overuse probability below 2.1%. Our experiments reveal that processing either too few or too many parts with a single insert can escalate costs due to extreme tool wear or decreased efficiency; notably, the optimal number of parts to be machined was found to be four, yielding an objective function value of 380.6 NTD, which is lower than 394.5 NTD for three parts and 405.4 NTD for five parts in the case study. This research underscores the necessity of considering tool wear distribution and discrete production in machining optimization for sustainable manufacturing applications, providing valuable insights into the impact of cutting parameters and tool wear distribution on the costs for discrete production.

Reusing 316L Stainless Steel Feedstock Powder for Cold Spray Deposition

Abstract Cold spray (CS) is a solid-state deposition of coatings, or an additive manufacturing (CSAM) process employed to make parts maintaining the feedstock powders properties in the deposited material. One of the cons for industrial use of CS or CSAM is their higher costs compared to the traditional coating or manufacturing processes. Reducing the feedstock powder consumption by maximizing the deposition efficiency has been the focus of many works. However, depending on the part geometry (e.g., a plate with holes), and CSAM strategy with low deposition efficiency, a considerable mass of powder can pass through the substrate, failing to bond, and becoming a process waste. This work evaluates CS 316L stainless steel coatings, recovering the unbonded particles and reusing them in a later deposition, thus making coatings with reused powders. The original and recovered powders were characterized in terms of particle shape and size distribution, phase composition, microhardness, and other properties to evaluate the evolution of the particles' properties due to the recovery process. Besides the powders, the CS coatings obtained with original and recovered powders were evaluated through cross-section image analysis, where porosity, deposition efficiency, and microhardness were observed. The results indicate that the powders' physical properties undergo variations over multiple deposition cycles without significantly affecting the quality of the CS coatings, with porosity below 1.5% and microhardness around 350 HV0.3 in most cases. Recovering and reusing powder for CS promotes environmental sustainability and generates significant economic benefits. This study contributes to making CS more economically viable from a life cycle cost assessment perspective. Graphical abstract

Research Progress in Shape-Control Methods for Wire-Arc-Directed Energy Deposition.

Wire-arc-directed energy deposition (WA-DED) stands out as a highly efficient and adaptable technology for near-net-shaped metal manufacturing, with promising application prospects. However, the shape control capability of this technology is relatively underdeveloped, necessitating further refinement. This review summarizes the latest advancements in the shape control of WA-DED technology, covering four pivotal areas: the regulation of various process parameters, optimization of the deposition paths, control through auxiliary energy and mechanical fields, and synergy between additive and subtractive manufacturing approaches. Firstly, this review delves into the influence of deposition current, travel speed, wire feed speed and other parameters on the forming accuracy of additively manufactured parts. This section introduces control strategies such as heat input and dissipation management, torch orientation adjustment, droplet behavior regulation, and inter-layer temperature optimization. Secondly, various types of overlap models and techniques for designing overall deposition paths, which are essential for achieving desired part geometries, are summarized. Next, auxiliary fields for shape and property control, including magnetic field, ultrasonic field, and mechanical field, are discussed. Finally, the application of milling as a subtractive post-process is discussed, and the state-of-the-art integrated additive-subtractive manufacturing method is introduced. This comprehensive review is designed to provide valuable insights for researchers who are committed to addressing the forming defects associated with this process.

Generalized SmartScan: An Intelligent LPBF Scan Sequence Optimization Approach for Reduced Residual Stress and Distortion in Three-Dimensional Part Geometries

Abstract Laser powder bed fusion (LPBF) is an additive manufacturing technique that is gaining popularity for producing metallic parts in various industries. However, parts produced by LPBF are prone to residual stress, deformation, cracks, and other quality defects due to uneven temperature distribution during the LPBF process. To address this issue, in prior work, the authors have proposed SmartScan, a method for determining laser scan sequence in LPBF using an intelligent (i.e., model-based and optimization-driven) approach, rather than using heuristics, and applied it to simple 2D geometries. This paper presents a generalized SmartScan methodology that is applicable to arbitrary 3D geometries. This is achieved by (1) expanding the thermal model and optimization approach used in SmartScan to multiple layers, (2) enabling SmartScan to process shapes with arbitrary contours and infill patterns within each layer, (3) providing the optimization in SmartScan with a balance of exploration and exploitation to make it less myopic, and (4) improving SmartScan’s computational efficiency via model order reduction using singular value decomposition. Sample 3D test artifacts are simulated and printed using SmartScan in comparison with common heuristic scan sequences. Reductions of up to 92% in temperature inhomogeneity, 86% in residual stress, 24% in maximum deformation, and 50% in geometric inaccuracy were observed using SmartScan, without significantly sacrificing print speed. An approach for using SmartScan for printing complex 3D parts in practice, by integrating it as a plug-in to a commercial slicing software, was also demonstrated experimentally, along with its benefits in significantly improving printed part quality.

Enhancing the superplastic deformation capabilities of the Ti-6Al-4V alloy using superimposed oscillations

This study investigates the effect of imposing low frequency, low amplitude oscillations during uniaxial tensile tests on the mechanical behaviour of the Ti-6Al-4V alloy under a typical superplastic temperature of 900 °C. Different material models were used to simulate these tests with the finite element software ABAQUS. A creep strain power model fit through an iterative FEA process yielded a high correlation to the force/displacement and thinning results from uniaxial tensile tests. The developed material models with and without oscillation materials were also used to simulate a free-bulge forming process within the strain rate range of 0.0003 to 0.01 s−1 under constant strain rate testing. Within the domain of the parts formed in this study, the improvement in the forming time ranged from a 120 % reduction at elevated strain rates and reduced part complexity to 520 % in the most complex part geometry.

Computational Design of a Kit of Parts for Bending Active Structures

Bending-active structures are composed of elastic elements that deform to achieve a desired target shape. To support effective design, inverse algorithms have been proposed that optimize the geometry of each element specifically for each design. This makes it difficult to reuse elements across designs or gain efficiency in fabrication through mass production. We address this issue and propose a computational framework to rationalize bending-active structures into a sparse kit of parts. Our method solves for the optimal part geometry such that multiple input designs can be faithfully realized with the same kit of parts. Assigning parts to different assemblies leads to a combinatorial explosion that makes exhaustive search intractable. Instead, we propose a relaxed continuous optimization incorporating a physics-based simulation in its inner loop to model the elastic deformation of the bending-active structure accurately. Our algorithm allows analyzing different design trade-offs of a kit of parts to tune the balance between fabrication complexity and fidelity to the original designs. We demonstrate our method on three different classes of bending-active structures, showcasing the effectiveness of our approach for part reuse and sustainable practices in fabrication-driven design.

Atmosphere Effects in Laser Powder Bed Fusion: A Review.

The use of components fabricated by laser powder bed fusion (LPBF) requires the development of processing parameters that can produce high-quality material. Manipulating the most commonly identified critical build parameters (e.g., laser power, laser scan speed, and layer thickness) on LPBF equipment can generate acceptable parts for established materials and moderately intricate part geometries. The need to fabricate increasingly complex parts from unique materials drives the limited research into LPBF process control using underutilized parameters, such as atmosphere composition and pressure. As presented in this review, manipulating atmosphere composition and pressure in laser beam welding has been shown to expand processing windows and produce higher-quality welds. The similarities between laser beam welding and laser-based AM processes suggest that this atmosphere control research could be effectively adapted for LPBF, an area that has not been widely explored. Tailoring this research for LPBF has significant potential to reveal novel processing regimes. This review presents the current state of the art in atmosphere research for laser beam welding and LPBF, with a focus on studies exploring cover gas composition and pressure, and concludes with an outlook on future LPBF atmosphere control systems.

Effect of Ceramic Matrix Composites on the Thermal Efficiency of a Power Generation Turbine

Abstract Ceramic matrix composites (CMCs) offer higher allowable temperatures and reduced weight, making them an attractive prospect for parts in the hot section of a gas turbine engine. As CMCs are increasingly adapted into aero and land-based engines, there is a need to quantify the performance increase based on the potential for reduced cooling and increased firing temperatures. In this work, two static hot section components—the first-stage turbine vane and the first-stage turbine tip shroud (outer casing above the blade)—of a mid-sized power generation engine were modeled. Informed approximations about part geometry and cooling architectures were made to determine the cooling requirements of each part. Thermal boundary conditions for the turbine tip shroud and turbine vane were generated as a function of coolant mass flowrate using data from literature and applied to a 2D finite element analysis of the parts to determine maximum temperatures for both metallic and ceramic materials. A gas turbine cycle model was developed to simulate the performance of a mid-sized power generation turbine and used to determine the increase in efficiency due to a reduction in the cooling requirement for the CMC part compared to a conventional metal superalloy-based part. The potential reduction in chargeable cooling seen for the tip shroud ring was between 0.09% and 0.4% of the compressor mass flowrate, which corresponds to an increase in thermal efficiency between 0.11% and 0.45%. A similar analysis of the turbine vane resulted in a cooling reduction of 10.71% at the maximum turbine entry temperature considered which corresponds to a 3.4% increase in thermal efficiency.

Design and validation of fixation points of polymeric components for the automotive industry

ABSTRACT The incorporation of polymeric materials in car structure components plays a key role in the automotive sector, enabling the production of more efficient and ecological vehicles. Among the many options to fix these components, there are clips and snap-fits, which not only facilitate assembly and disassembly, but also contribute to reduce the total mass of the car. This work aims to design and validate these fixation points of polymeric components using the Design Science Research (DSR) methodology. The work resulted from the need for a more rigorous control involving some internal standardized fixation points, namely interior trim parts. Experimental tests were carried out according to the specifications of the automotive brand, including the strength of the fixation points, to enable incorporation as standard components. Using the Finite Element Method (FEM), static simulations were performed in the Abaqus® software, where the conditions of the physical tests were replicated to correlate both tests and validate the numerical approach. Improvement of the fixation points was next undertaken, by making changes in the areas that were identified as critical. The improved fixation points were able to meet the specifications of the company and were proposed as new geometry for standard interior trim parts.

Evaluation of Image Segmentation Methods for In Situ Quality Assessment in Additive Manufacturing

Additive manufacturing (AM), or 3D printing, has revolutionized the fabrication of complex parts, but assessing their quality remains a challenge. Quality assessment, especially for the interior part geometry, relies on post-print inspection techniques unsuitable for real-time in situ analysis. Vision-based approaches could be employed to capture images of any layer during fabrication, and then segmentation methods could be used to identify in-layer features in order to establish dimensional conformity and detect defects for in situ evaluation of the overall part quality. This research evaluated five image segmentation methods (simple thresholding, adaptive thresholding, Sobel edge detector, Canny edge detector, and watershed transform) on the same platform for their effectiveness in isolating and identifying features in 3D-printed layers under different contrast conditions for in situ quality assessment. The performance metrics used are accuracy, precision, recall, and the Jaccard index. The experimental set-up is based on an open-frame fused filament fabrication printer augmented with a vision system. The control system software for printing and imaging (acquisition and processing) was custom developed in Python running on a Raspberry Pi. Most of the segmentation methods reliably segmented the external geometry and high-contrast internal features. The simple thresholding, Canny edge detector, and watershed transform methods did not perform well with low-contrast parts and could not reliably segment internal features when the previous layer was visible. The adaptive thresholding and Sobel edge detector methods segmented high- and low-contrast features. However, the segmentation outputs were heavily affected by textural and image noise. The research identified factors affecting the performance and limitations of these segmentation methods and contributing to the broader effort of improving in situ quality assessment in AM, such as automatic dimensional analysis of internal and external features and the overall geometry.

The geometry of fault reactivation and uplift along the central part of the Maacama Fault Zone, Northern California Coast Ranges (USA)

Abstract Fault reactivation of bedrock structures in active fault zones influences stress state and earthquake rupture phenomena through the introduction of weak slip surfaces that impact fault zone geometry and width. Yet, geometric relationships between modern faults and older reactivated faults are difficult to quantify in rocks that have experienced multiple deformation episodes. We used new geologic mapping, geomorphic tools, and structural modeling to quantify rock uplift and subsurface fault geometry of the central part of the Maacama Fault Zone near Ukiah, California, USA, and the surrounding area. Results suggest that the northern Mayacamas Mountains are in a tectonically driven disequilibrium, with differential rock uplift focused on the western side of the range. Steeply east-dipping fault surfaces and splays characterize the geometry of the Maacama Fault Zone. We mapped two newly identified faults to the east of the main Maacama Fault, the Cow Mountain–Mill Creek Fault, and Willow Creek Fault, which align with a moderately east-dipping cluster of microseismicity between 4–10 km depth beneath the Mayacamas Mountains. Static stress modeling on the Maacama Fault Zone and newly identified faults to the east quantify slip tendency values of 0.5–0.4, which suggests that the faults are moderately to poorly suited for slip in the modern stress field and may be weak. We infer that modern uplift is driven by oblique reverse, up-to-the-east, dip-slip motion on the reactivated Cenozoic Cow Mountain–Mill Creek and Willow Creek Faults as material is advected through a restraining bend on the Maacama Fault. This study shows that reactivated bedrock faults increase the fault zone width and introduce fault surfaces that contribute a component of vertical deformation and uplift in major strike-slip fault zones. Deformation is accommodated on an interconnected network of new and reactivated faults that delineate a complex seismic hazard.

Interlayer-free laser coating of AISI H11 tool steel for H11/Cu composite material

Copper-based materials in combination with steels are of great interest for various applications in industry, such as tool manufacture, due to their high thermal conductivity. Additive manufacturing (AM) is beneficial for both tailored part geometry and customized material design. With laser-based AM, the copper-steel interface is highly prone to cracking. This study investigates a strategy of laser coating AISI H11 tool steel for a composite material consisting of AISI H11 tool steel and copper (H11/Cu) without using Ni-based interlayers. As an austenite stabilizing element, Ni dilution in H11 could lead to soft retained austenite, impeding wear resistance. The approach in this work employed presintering of tool steel powder to generate a porous H11 preform. Laser-based directed energy deposition (DED-LB/M) was used for coating H11 tool steel on the porous H11 preform followed by copper infiltration of the preform. The investigation of the effects of the main processing parameters: laser power, feed rate, and powder mass flow on the weld track geometry, clearly revealed different mechanisms when coating the porous preform compared to the conventional substrate. Defects at the coating/substrate interface such as cold crack formation were successfully avoided by adjusting the process parameters and process sequence. The developed processing strategy may in the future combine material extrusion of metals (MEX/M) and DED-LB/M to allow for intricate preform geometries and to generate H11 coatings on H11/Cu, respectively.

Benefits derived from WASP (a Grasshopper plugin) to Design for Disassembly Principles in the Built Environment

Abstract Design for Disassembly (DfD, henceforth) is a way to improve the effectiveness of the disassembly process in built environments, and it mainly contains ten principles. Examples of the principles include deconstruction techniques; selected materials; reachable connections; utilizing connections with fewer bolts, screws, and nails; the straightforwardness of the structure and design; and versatility. On the other hand, the WASP plugin for Grasshopper (on Rhinocheros©) is a toolkit for discrete computational design to simulate the aggregation and assembly possibilities in the building system. This paper explores the integration of the WASP plugin within the context of DfD through three criteria: the aggregation processes of part geometries, connection locations, and their orientation toward the building elements. Design with discrete elements, which can be defined as shape grammars for building structure, is the primary approach for the joining behavior and detaching behavior of elements discussed in this paper. Also, this type of component-based design can optimize the geometry and data-driven generation of the structure. The design process in this way can be disassembly sequence planning and knowledge-based design by applying the design constraints. To illustrate the integration, research is conducted through WASP simulation in designing a traditional Iranian timber pavilion-inspired structure with a 3×3m footprint in a roof structure. The fusion of WASP and DfD represents a promising avenue for advancing circular design principles and achieving more sustainable, resource-efficient buildings. It is concluded from this study that WASP makes the aggregation simulation and assembly possibilities of the vertical and horizontal components in a building more accessible.

Interpass temperature impact on bead geometry of mild steel in wire-arc additive manufacturing

In wire-arc additive manufacturing (WAAM), melt pool dynamics produce variations in bead geometry that create undesired part geometries and can also lead to material defects. In the current state of the art, reducing melt pool and bead variation is still an aspect of WAAM that is underdeveloped. Several factors influence the bead geometry including the type of material that is being deposited and process inputs. In this study, ER70S-3 mild steel was deposited onto steel build plates using a cold metal transfer (CMT) deposition process. Varying plate preheat surface temperatures were used from ambient temperature to 300 °C using different welding travel speeds. To control build plate surface temperature, a preheat stage was designed and implemented to simulate different interpass temperatures. Beads were deposited and subsequently measured to determine their geometric properties such as bead height and bead width. Initial results indicate that as the preheat temperature increases, resulting bead height decreases, bead height variation decreases, and bead width increases. Initial microstructural data also indicates that as preheat temperature increases, the microstructure becomes more equiaxed with decreasing grain sizes.

Smart design and additive manufacturing of bending tools to improve production flexibility

For the automotive industry, especially on the part of Tier 1 and Tier 2 suppliers, the future will be about maintaining sovereignty in the form of technology openness and accelerating digitization. The product portfolio, which is generally passed on by OEMs to suppliers for production, often includes body parts that cannot always be manufactured economically with the prevailing production technology. The reason for this is a high diversity of model-variants, which requires smaller batches. To this end, highly flexible large-series production cells for body sheet components that can be scaled in all dimensions are being developed and tested. For the first time, they will make it possible to redesign the process planning in series production on a component-specific basis. The aim is to reduce production costs for new, geometrically different component variants. The basic components of the flexible manufacturing system are, firstly, new flexible forming technologies which have the potential to produce typical vehicle part geometries. Secondly, a process generator develops the corresponding production plan. A digital mapping of the manufacturing processes enables the selection of cost-, efficiency-, flexibility- and resilience-optimized production chains depending on the number of parts. Established manufacturing processes to produce car body components are supplemented in the cell by flexible processes such as 3D swivel bending. As a use case for flexible manufacturing, a concept for Rapid Tooling of 3D swivel bending tools is developed. In the flexible manufacturing system to be developed, a method of a standardized process sequence to produce forming tools within 24 h has been lacking to date. For this purpose, the concept of an automated design is being developed in which a reconfigurable tool body can be sliced into sheet metal stripes The active tool surface is additively manufactured after the tool has been packaged using LMD and adapted to individual requirements. The goal in the application of Rapid Tooling is to reduce lead times and development costs through a largely automated tool design and lead time-optimized manufacturing concept.

Iterative correction of robotic grinding using spatial feedback for precision applications

Since the advent of robots, many tasks that were originally performed by humans have now been tasked to industrial robots. From a manufacturing standpoint, robots have primarily been used in pick-and-place or other non-machining operations that require high repeatability. However, with the increasing availability of CAD/CAM software and the development of high-precision metrology, comes the opportunity to integrate robots into a wider variety of manufacturing processes through the use of feedback control. One such machining operation that is being explored is precision grinding of metal parts. Most other work in this area has focused on force regulation to improve grind quality; however, this paper takes a different approach. In this work, an Iterative Learning Control (ILC) algorithm is implemented to correct the geometric error directly by altering the toolpath trajectory. Specifically, in this framework, a conservative initial cutting trajectory is implemented using a 6-DoF robotic grinding system, and the resulting part geometry is measured via a high-precision laser scanner. Based on the resultant geometric error, the toolpath is corrected and then rerun on the part. This process is then repeated iteratively until sufficient accuracy is achieved. Due to the inability to replace material in overground regions, the controller is designed with an emphasis on reducing overshoot which cannot be corrected. The controller is experimentally validated by grinding an elliptical pocket which meets FAA specifications for corrosion removal in aircraft. The results showed that within seven iterations the entire error surface could be brought to a tolerance of ±0.150 mm for the given geometry.

Effect of varying part geometry and mold constraints on dimensional deviations of sand cast parts

Effect of varying part geometry and mold constraints on dimensional deviations of sand cast parts