Papers by Keyword: Forming

Abstract: During dry fibre processing, manufacturing geometrically complex composite parts often produces wrinkles when fabrics deform beyond their shear limits. This work proposes a design-for-manufacture approach based on origami principles, which modifies component geometry so that deformation remains within allowable deformation limits. A baseline aircraft spar geometry is considered; an origami-inspired version, along with several intermediate designs between these two extremes, are generated. Preliminary forming trials with unidirectional non-crimp fabrics show that the origami-based geometry is inherently manufacturable without defects, and that a selected intermediate design also form successfully, confirming a larger manufacturable design space than classical origami permits. Results further show that wrinkle severity increases with increasing angular defect. This provides a foundation for linking geometric measures to draping mechanics to guide the design of wrinkle-free composite components without requiring computationally expensive simulations.

Abstract: Despite the growing use of biopolymers in automotive, packaging and structural applications, predictive modelling of their elastic–viscoplastic deformation remains limited. In this work, a micromechanically based constitutive model is proposed to describe the micro‑ to macroscopic behaviour of a semi‑crystalline PLA matrix reinforced with short hemp fibers. The formulation relies on a multiplicative split of the deformation gradient into elastic and viscoelastic–plastic parts, with elasticity governed by fiber and crystalline phases and time‑dependent deformation localized in the amorphous phase. High fiber content and strong fiber–matrix bonding enable the suppression of lattice crystalline anisotropy, leading to a compact model with a reduced number of internal variables. The model is calibrated and validated using uniaxial tensile tests on pellet‑extrusion 3D‑printed specimens with controlled porosity and plasticiser content, and reproduces nonlinear loading, unloading, creep and stress relaxation. In a second step, synthetic data generated by the constitutive model are used to train surrogate machine‑learning models, which are discussed as a perspective for accelerating long‑term simulations and parametric studies in forming applications.

Abstract: Predicting the deformation behavior of rolled and extruded light metal alloys is a challenging task. Due to the high cost of experimental analysis, finite element simulations are often required. A variety of material models at different scales are available for practical use. In this work, the viscoplastic self-consistent (VPSC) approach is employed to consider microstructural effects. These can be incorporated by using measured crystal sizes and orientations - called texture - of the alloy under consideration. For each integration point in the FE mesh, a corresponding texture is assigned and individually deformed in LS-Dyna^®, where VPSC is implemented as a user-defined material model - referred to as FE-VPSC. This study focuses on preprocessing of texture data as well as their compression for accurate and faster FE simulations. For verifying the simulations, a comparison with digital image correlation (DIC) of experimental puncture tests was conducted.

Abstract: Beading has been used in metal construction for decades to reinforce and stabilize thin sheets of metal. In aircraft, washing machine and car manufacturing, this allows for cost-effective, lightweight and material-saving designs to be realized. These indentations are embossed into thin metal sheets to increase their rigidity and stability, thereby preventing fluttering or deformation. The bending stiffness is significantly increased by reshaping the material. The increased stability allows thinner sheets to be used, which reduces the overall weight of the structures and components. Beading is often used on larger surfaces to prevent fluttering or vibrations and to ensure greater dimensional stability. The combination of two old production processes, beading and steam bending for wood is examined in this paper. The use of beads to reinforce thin wooden panels saves material, resources and weight, thereby making production more sustainable. The investigations carried out examined the possibilities of introducing beads into thin panels made from different types of wood. The temperature, water content, water vapour content, soaking time and pressing pressure were varied. In a first step, a test specimen was produced that serves as a mould for the surround. This shape was pressed into the thin wooden panels when varying the processing parameters shown above. In a next step, the indentation depths achieved were measured. The deflection of the thin wooden panels was then measured under different loads and compared with the calculated results.

Abstract: Stamp forming of fiber-reinforced thermoplastic composite materials is governed by large deformations, anisotropic and rate-dependent material behavior, and frictional multi-body contact, making high-fidelity finite element simulations expensive and often impractical for rapid design studies and process optimization. We leverage recent advancements in Machine Learning-based simulations and tailor Algebraic-hierarchical Message Passing Networks (AMPNs) to stamp forming simulation of composite materials. To efficiently handle multi body contact during forming, we model the laminates by a multi-layer graph with explicit ply–ply and tool–ply contact and extend AMPNs by local component-wise contact edges. Using a multiscale graph hierarchy, the method captures local wrinkling effects, global material draw-in, and contact-driven deformation across the full laminate. Trained on high-fidelity data from state-of-the-art Finite Element Method (FEM) simulations, the surrogate accurately simulates the stamp forming process for unseen process settings, while reducing simulation times from hours to seconds, enabling approximately real time simulation of large, complex geometries.

Abstract: Bipolar plates are key components of fuel cell systems, as they significantly determine efficiency, power density, and service life. In aerospace applications, their importance is further emphasized due to the dual requirement of corrosion resistance and strict weight reduction. Titanium Grade 1 combines low density and excellent corrosion resistance. However, its industrial application is limited by restricted formability. The aim of this paper is a systematic investigation of the forming behavior of Titanium Grade 1 foil material in order to define forming limits and derive manufacturing-oriented design recommendations for bipolar plates in aviation. Procedure. Sixteen distinct geometry features were developed to represent characteristic forming conditions. In addition to cross-section variations, the flow field angle was systematically altered to assess its influence on local stress and strain distribution. Furthermore, the key process parameters forming speed, forming force, and lubricant amount were varied to evaluate their impact on the forming quality. The assessment focused on form filling and material thinning. For this purpose, metallographic cross-sections were prepared, and optical 3D measurements were conducted using a Keyence system to precisely capture local wall thickness variations. Key findings Process parameters: The forming behavior of Titanium Grade 1 is strongly influenced by the applied forming force and lubrication. Form filling becomes sufficient only above 350 MPa (3.000 kN), while the lubricant amount is decisive for achievable forming depths due to the hydrostatic oil cushion effect. In contrast, forming speed shows no significant influence. Anisotropy remains a critical factor, particularly in 0° rolling direction, where premature thinning leads to fracture. Geometry parameters: Small radii are highly critical, while feature depth leads to expectedly higher thinning. Steeper flank angles improve form filling but at the cost of increased thinning. Pitch shows limited influence, although it may become relevant at very small values. Channel design is challenging, as sharp flow field angles consistently result in severe thinning and pose difficulties in tool manufacturing.

Abstract: Accurate yet computationally efficient simulation models are essential for the virtual design and optimization of thermoforming processes for fiber-reinforced composites. Selecting an appropriate material model remains challenging, particularly when balancing model fidelity against computational cost. In this work, a framework is developed to validate material models used in thermoforming simulations for fiber-reinforced composites. The framework evaluates model performance based on time-series data using covariance-based input-output statistics, without prior calibration. Two numerical studies of increasing complexity demonstrate the versatility of the approach. First, the framework is applied to one-dimensional rheological models, verifying its applicability to mechanical problems relevant to thermoforming simulation. These insights are then applied to complex finite element thermoforming simulations to assess the ability of isothermal material models to predict wrinkling behavior in comparison to a fully coupled thermomechanical reference model. A curvature-based method is introduced to quantitatively evaluate wrinkling severity relative to natural curvatures induced by the tool geometry. The results show that isothermal models are sufficient for short total process times with minor temperature-driven effects, whereas longer total process times with pronounced thermal effects require thermomechanical models to ensure accurate predictions. The findings offer practical guidance for selecting appropriate material models based on specific process conditions, as well as objective criteria for assessing model validity in virtual process design.

Abstract: In the aerospace industry, hot forming processes, using materials like Ti-6Al-4V titanium, are known for their complexity and cost. Senior Aerospace Thermal Engineering (SATE) has traditionally relied on a trial-and-error approach for new product introductions (NPIs), which, while effective, has led to significant time and resource expenditures. This paper examines the transition of SATE's NPI processes to a more efficient digital approach using AutoForm Forming simulation software. By doing so, SATE has been able to accurately predict forming outcomes, optimize tooling designs, and significantly reduce both the number of physical tryouts and the overall project costs. Two case studies are presented to demonstrate the practical applications of this digitalization, highlighting how important engineering decisions were taken. The paper concludes with an assessment of the impact on SATE's operations, noting improvements in development time, feasibility assessments, and overall production efficiency.

Abstract: The composite materials are high on demand in various applications, because of the wide range of properties that they offer, for that, they need to adapt into complex shapes to serve as a functional part. So, the forming process must be mastered and studied to benefit from what composites offer. The most used manufacturing process for composite materials are the resin transfer molding (RTM), which require a preforming of the dry fabric into the desired shape. During the pre-forming process yarns networks orientation change and different defects can be generated due to a variety of factors that have a role in their appearance, such as the process settings, type of the reinforcement, the characteristics of the shapes’ geometry. In this study, we concentrate on the effect of the geometries’ characteristics on the appearance of the different defects and the induced shear on the fabric. Different geometries have been selected based on a benchmark of the shapes studied in the literature [1–3]. The pre-forming was conducted on 3 types of dry fabrics. Woven and non-woven, balanced, and unbalanced fabrics have been intentionally selected as fabrics with completely different structures (type of material, weaves, balance...) to observe the change in the fabric’s behavior and he induceddefects, in terms of profil, location and amplitude.

Abstract: The increased production rate targets of the aerospace industry have driven the development of dry fibre infusion processes. Biaxial Non-Crimp Fabrics (NCFs) are considered in this work due to their potential high deposition rates and higher mechanical performance to woven fabrics. Forming is an integral step prior to infusion and curing. Understanding the forming behaviour of NCFs at scale is therefore key to achieving high quality parts at high rates. To investigate the draping and shearing behaviour of NCFs, geometries with complexities associated with the composite structure are used. This study presents an experimental campaign on two large scale (2 metres in span) geometries with complexities seen in primary aerostructures. The combination of features such as ramps and curvature with corner radii leads to distinctive out-of-plane wrinkling. The relationship between geometry, material and resulting preform quality is observed through the use of 3D scans. Results show differing preform quality in terms of wrinkling phenomena, showing the importance of geometry of choice for material drapability tests at an industrial scale.