Key Engineering Materials Vol. 1047

Abstract: Incremental Sheet Forming (ISF) has been widely studied for metallic materials, demonstrating significant potential in flexible and low-cost sheet metal forming (aluminum, magnesium or titanium). Recently, attention has shifted toward polymeric materials due to their growing relevance in medical and customized applications (PCL, UHMWPE, PEEK). However, the availability of commercial sheets is limited to thicknesses, geometries, and material options. In this context, Fused Deposition Modeling (FDM) has emerged as a complementary technique to produce tailored polymeric sheets, enabling the integration of additive manufacturing with ISF processes to overcome limitations in available commercial sheets and expand design flexibility. Considering the success of this hybridization for forming PCL, this work investigates the feasibility of applying Single Point Incremental Forming (SPIF) to PEEK sheets produced via Fused Deposition Modeling (FDM). The study analyzes the influence of printing parameters, forming conditions, and thermal treatment on part quality, porosity, forces, temperature, defects, and fracture behaviour.

Abstract: Tailored welded and patchwork blanks are commonly used in the automotive field to locally tailor the mechanical response of sheet metal components, but conventional manufacturing approaches often introduce structural discontinuities, corrosion-prone interfaces and limited formability. Additive deposition of local reinforcements offers a more flexible alternative, enabling material to be placed only where it provides the greatest structural benefit and reducing overall material usage and environmental impact. This work investigates the flexural behaviour of additively reinforced blanks through finite element simulations. A numerical model was developed in Abaqus to reproduce three-point bending tests on 22MnB5 sheets locally reinforced by the wire-laser additive deposition of a 316L stainless steel. Metallographic cross-sections were used to define the reinforcement geometry and penetration depth, micro-hardness profiles to define the extent of the heat affected zone, and plastometric characterisation to obtain local mechanical properties. The simulations demonstrate that the proposed numerical model reliably reproduces the experimentally observed flexural behaviour of wire-laser additively reinforced blanks. The numerical force-displacement response is consistent with the experimental one, and within this agreement the increase in bending strength obtained with minimal added material is confirmed.

Abstract: The study explores the integration of additive manufacturing for the development of 4D-printed piezopolymer metamaterials, aiming to create dynamic, multifunctional structures capable of distributed sensing and energy harvesting. The focus is on Polyvinylidene fluoride (PVDF), a partially fluorinated polymer renowned for its strong electromechanical coupling, specifically within its polar β-phase. To harness these properties, three distinct experimental strategies were evaluated for integrating PVDF with conductive electrodes necessary for electrical poling: direct 3D printing with manually applied silver paste, printing directly onto pre-integrated aluminium foil substrates, and a novel chemical solvent-based deposition using a DMF/acetone mixture. While high-precision inkjet printing was initially tested for electrode deposition, it demonstrated significant limitations in scalability, throughput, and durability, particularly suffering from structural degradation during the post-poling silicon oil removal process. Consequently, the study advocates for a robust, hybrid multi-material extrusion platform. This approach will enable the simultaneous, monolithic deposition of structural PVDF thermoplastics and highly conductive thixotropic inks.

Abstract: This study provides a comprehensive investigation into the effects of different scanning parameter combinations—specifically scanning speed and hatch distance—on the material properties of IN939 fabricated using the powder bed fusion-laser beam (PBF-LB) process under a constant volumetric energy density (VED). Despite the fixed VED, the fabricated samples experienced different thermal cycles, resulting in distinct microstructural features and corresponding variations in material performance. In-situ infrared monitoring indicated that the sample with the narrowest hatch distance and highest scanning speed (Sample 1) reached the highest normalized temperatures with intense heat accumulation, whereas wider hatch distances (Sample 3) promoted lower and more stable temperature distributions. The results revealed that the intermediate parameter set (Sample 2) achieved the highest relative density (99.29%) and the lowest surface roughness. In contrast, both the narrowest and widest hatch spacing combinations promoted increased porosity, primarily consisting of lack-of-fusion (LoF) and gas pores. Electron backscatter diffraction (EBSD) analysis showed that the area-weighted average grain size increased from 29.5 µm to 36.7 µm as the hatch distance increased. Texture analysis indicated generally weak crystallographic texture development, with only slight intensification of <001>//BD and <111>//BD components, attributed to the 67^o rotation strategy. Furthermore, the microhardness values demonstrated negligible variation across the samples, ranging from 356.7 ± 14.3 HV1 to 360.1 ± 10.5 HV1. This limited variation indicates that the strengthening behavior was predominantly governed by the combined influence of defect density and matrix–defect interactions, rather than being directly correlated with grain size.

Abstract: Integrating topology optimization (TO) with lattice infilling for additive manufacturing provides an effective route to lightweight, high-performance structures for aerospace applications. Reducing structural mass can deliver environmental and economic benefits by lowering fuel consumption and associated emissions. This study evaluates a computational workflow for weight reduction of an aircraft bearing bracket by combining topology optimization with stress guided lattice infilling. First, compliance minimizing TO is performed under additive manufacturing constraints to obtain an efficient global load-path layout. Next, lattice infill is introduced using both Triply Periodic Minimal Surface (TPMS) unit cells (gyroid) and strut-based unit cells (diamond). To avoid manual trial-and-error in selecting unit cell size, and thickness, an implicit modeling approach with Python-driven iteration is used to systematically explore lattice parameters and identify feasible configurations. The proposed method uses the TO-derived stress field to tailor lattice parameters spatially, enabling graded cellular architectures aligned with local load demands. Compared with the baseline bracket, TO alone achieved a 44.42% mass reduction, while the stress-guided lattice designs achieved 70% (gyroid) and 68.6% (diamond) weight savings. Finite element analysis is used to compare the baseline, TO, and lattice-infilled brackets in terms of mass, maximum deflection, and von Mises stress, demonstrating that stress-guided lattice infill can improve structural efficiency beyond TO alone while maintaining AM oriented manufacturability through self-supporting cellular features. A key contribution is an automated, stress-guided ramp mapping for graded lattice-parameter control, which is broadly applicable to other components, loading scenarios, and lattice families.

Abstract: Continuous monitoring of additively manufactured structures is essential for understanding their mechanical behavior and durability. This study investigates the electromechanical behavior of additively manufactured PETG specimens reinforced with continuous carbon fiber, with a particular focus on the influence of reinforcement geometry on strain-sensing performance. Specimens were fabricated using Fused Filament Fabrication and designed with four different reinforcement configurations: a reference single-layer layout, an extended-length reinforced region, a wider reinforced region, and a double-layer reinforcement. A total of twelve specimens were experimentally characterized. Electrical resistivity measurements were conducted under unloaded conditions and during bending induced by a low applied load of approximately 1.6 N. The initial electrical resistivity was found to depend on reinforcement geometry, with average values of approximately 523 Ω for the reference configuration, 888 Ω for the extended-length reinforcement, 1066 Ω for the wider reinforcement, and 285 Ω for the double-layer configuration. Under mechanical loading, the relative resistance variation remained below 0.6% for all specimens, indicating that the induced strain was very small. To further quantify strain sensitivity, the gauge factor was calculated for each configuration. Low average gauge factor values were obtained for the reference (K ≈ 0.1), extended-length (K ≈ 0.38), and wider (K ≈ 0.5) configurations. In contrast, the double-layer reinforcement exhibited a higher average gauge factor of approximately 2.24. These results indicate that reinforcement architecture affects the electromechanical sensitivity under low applied loads and offer insights for the design of multifunctional additively manufactured composite structures.

Abstract: The use of 3D-printing simplifies and accelerates the development of moulds for a thermoforming process. This article examines several aspects of the effective design of 3D-printed polymer moulds. The focus is on prototyping and applications in engineering education. Experiments are conducted on PLA mould to determine the actual temperature loads and permanent deformations. Measures to improve the durability of the moulds are discussed and approaches to material and cost optimization are investigated. Examples of the use of PLA-moulds in thermoforming are presented.

Abstract: Additively manufactured Nitinol components often exhibit rough surfaces and defects that affect functional performance. This study investigates the feasibility of electropolishing Nitinol in a deep eutectic solvent (ethaline). Linear sweep voltammetry was used to identify anodic potentials suitable for controlled dissolution, and electropolishing was performed at selected potentials. Surface evolution was analysed by SEM, EDX, optical microscopy, and confocal microscopy. Electropolishing in ethaline effectively reduced surface scratches and produced more homogeneous surfaces without altering alloy composition. Higher applied potentials (12.5 V) resulted in complete removal of surface scratches and visually homogeneous surfaces, whereas lower potentials (6 V) mainly reduced the visibility of surface scratches. Compared to conventional inorganic electrolytes, the process exhibits a lower dissolution rate, offering a safer and more controllable approach.

Abstract: Wire Arc Additive Manufacturing (WAAM) is a promising technology for producing large, high-performance metallic components, though process stability and geometric control remain critical challenges. The present work investigates the influence of deposition trajectory on the geometry, surface quality, and microhardness of wire arc additive manufactured Inconel 625 walls, produced by a Cold Metal Transfer (CMT) process. A conventional linear double-pass strategy is directly compared with a single-pass triangular weave trajectory under equivalent heat input per unit length, in order to isolate the effect of the torch path from other process variables. Single-layer and multi-layer walls were fabricated and characterized in terms of geometry, dimensional stability, surface waviness, and Vickers microhardness. The results show that the weave trajectory leads to improved geometric consistency, reduced variability, and significantly lower surface waviness compared to the linear strategy, while maintaining comparable mean wall width and microhardness. These findings demonstrate that appropriate trajectory design can enhance geometric stability and near-net-shape capability in WAAM-CMT without altering thermal input or material properties.

Abstract: In Laser Powder Bed Fusion (LPBF), ensuring reproducible part quality remains a ma-jor challenge despite the availability of high-resolution in-situ monitoring systems, such as ExposureOptical Tomography (EOT). While EOT provides detailed layer-wise optical information, most exist-ing approaches focus on single-layer analysis or real-time process control and do not exploit the fullvolumetric information contained in the acquired data.This work presents a modular framework for the volumetric reconstruction and post-process anal-ysis of EOT image data. Sequential EOT images are processed using volumetric component segmen-tation (VCS) and fused into a three-dimensional OT Image Cube, forming a central volumetric datastructure called LPBF Cube. Each voxel encodes spatial and radiometric information and can option-ally be augmented with additional process metadata.Based on this representation, high-resolution two-dimensional slices are rendered along arbitraryorientations using profile-based slicing strategies for planar, cylindrical, and complex geometries.These slices enable intuitive, part-level inspection of laser exposure history and spatial process vari-ations. The framework is validated using geometric and radiometric analyzes, demonstrating goodagreement with nominal CAD geometry and a clear correlation between EOT-derived emission val-ues, laser energy input, and local cross-sectional area.The proposed approach extends the use of EOT data beyond layer-wise monitoring toward com-prehensive, volumetric part inspection and provides a practical basis for geometry-aware quality as-sessment in LPBF, particularly for prototyping and post-build evaluation.