Numerical product design: Springback prediction, compensation and optimization

Numerical simulations are being deployed widely for product design. However, the accuracy of the numerical tools is not yet always sufficiently accurate and reliable. This article focuses on the current state and recent developments in different stages of product design: springback prediction, springback compensation and optimization by finite element (FE) analysis. To improve the springback prediction by FE analysis, guidelines regarding the mesh discretization are provided and a new through-thickness integration scheme for shell elements is launched. In the next stage of virtual product design the product is compensated for springback. Currently, deformations due to springback are manually compensated in the industry. Here, a procedure to automatically compensate the tool geometry, including the CAD description, is presented and it is successfully applied to an industrial automotive part. The last stage in virtual product design comprises optimization. This article presents an optimization scheme which is capable of designing optimal and robust metal forming processes efficiently

Development of a shear test to determine the cyclic behaviour of sheet materials

In many industrial stamping operations, the sheet material is subject to a series of loading and reverse loading cycles. In order to accurately predict the outcome of such forming processes, numerical simulation models rely on advanced constitutive models to rigorously reproduce the cyclic work hardening behaviour of the sheet material. The objective of this research was to develop a testing facility that is capable of generating the experimental stress-strain data of sheet materials when they are subjected to cyclic shearing loads. A suitable specimen geometry and a corresponding loading fixture were designed and fabricated. Cyclic shear tests were successfully carried out on four different grades of automotive sheet steel using this new testing fixture mounted in a universal testing machine. The experimental data thus generated can be used to determine the material parameters in advanced constitutive models, in order to virtually simulate metal forming operations and the subsequent spring back

AI-based design methodologies for hot form quench (HFQ®)

This thesis aims to develop advanced design methodologies that fully exploit the capabilities of the Hot Form Quench (HFQ®) stamping process in stamping complex geometric features in high-strength aluminium alloy structural components. While previous research has focused on material models for FE simulations, these simulations are not suitable for early-phase design due to their high computational cost and expertise requirements. This project has two main objectives: first, to develop design guidelines for the early-stage design phase; and second, to create a machine learning-based platform that can optimise 3D geometries under hot stamping constraints, for both early and late-stage design. With these methodologies, the aim is to facilitate the incorporation of HFQ capabilities into component geometry design, enabling the full realisation of its benefits. To achieve the objectives of this project, two main efforts were undertaken. Firstly, the analysis of aluminium alloys for stamping deep corners was simplified by identifying the effects of corner geometry and material characteristics on post-form thinning distribution. New equation sets were proposed to model trends and design maps were created to guide component design at early stages. Secondly, a platform was developed to optimise 3D geometries for stamping, using deep learning technologies to incorporate manufacturing capabilities. This platform combined two neural networks: a geometry generator based on Signed Distance Functions (SDFs), and an image-based manufacturability surrogate model. The platform used gradient-based techniques to update the inputs to the geometry generator based on the surrogate model's manufacturability information. The effectiveness of the platform was demonstrated on two geometry classes, Corners and Bulkheads, with five case studies conducted to optimise under post-stamped thinning constraints. Results showed that the platform allowed for free morphing of complex geometries, leading to significant improvements in component quality. The research outcomes represent a significant contribution to the field of technologically advanced manufacturing methods and offer promising avenues for future research. The developed methodologies provide practical solutions for designers to identify optimal component geometries, ensuring manufacturing feasibility and reducing design development time and costs. The potential applications of these methodologies extend to real-world industrial settings and can significantly contribute to the continued advancement of the manufacturing sector.Open Acces

Sac metallerin şekillendirilmesinde kullanılan süzdürme çubuğunun modellenmesi ve kontrolü

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Günümüzde otomotiv sektörü başta olmak üzere sac metal malzemeleri şekillendirme işlemi hemen hemen her alanda kullanılmaktadır. Buruşma, yırtılma ve geri esneme gibi kusurlar sac şekillendirme sırasında oluşan en bilindik kusurlardır. Bu gibi kusurlara genellikle sac malzemenin kalıp boşluğuna kontrolsüz ve istenmeyen bir oranda akışı neden olur. Sac malzemenin akışını kontrol etmek için bazı yöntemler kullanılır. Bunlar baskı plakası kuvvetinin ayarlanması ve kalıp ile sac yüzeyleri arasındaki sürtünmenin azaltılması gibi. Ancak bu yöntemler sadece sac malzemenin tamamının genel akışını düzenlemek için kullanılabilir. Malzeme akışını belirli bölgelerde düzenleyen süzdürme çubuğunun batma miktarının ayarlanmasıyla oluşturulan kontrol edilebilir frenleme kuvveti şekillendirilebilirliği iyileştirebilir.Bu çalışmada, ilk olarak süzdürme çubuğu frenleme kuvvetini kestirmek için bir matematiksel model geliştirildi. Modelde sac malzeme özellikleri, sac kalınlığı ve süzdürme çubuğunun batma miktarına bağlı süzdürme çubuğu frenleme kuvveti hesaplanabilmektedir. Matematiksel modelin sonuçları ile literatürdeki deneysel veriler karşılaştırılmış ve süzdürme çubuğu frenleme kuvvetine ait kestirimler deney sonuçları ile oldukça iyi uyum göstermiştir.Geliştirilen matematiksel model süzdürme çubuğunu temsil etmek üzere kullanılmış ve sac üzerinde istenen frenleme kuvvetini sağlamak için batma miktarını ayarlayan bir model öngörülü kontrolör geliştirilmiştir. Model öngörülü kontrolör farklı referanslar altında çalıştırılmış ve elde edilen proses cevabı referansları oldukça yakından kararlı bir şekilde yakalamıştır.Nowadays, sheet metal forming process is used in almost every area especially in the automotive industry. The defects such as wrinkles, fractures and springback are common failures that usually occur on the sheets during sheet metal forming process. Such failures are caused by the use of an unwanted and uncontrolled flow rate of the sheet material. A number of techniques generally are used to control of the flow rate of the metal sheet: regulating the blank holder force and reducing the friction between the die and metal sheet surfaces. However, these techniques can only be used to regulate the overall flow rate of the whole metal sheet. A controllable restraining force caused by adjusting the penetration of drawbeads, which are regulated the flow rate at certain parts of the sheet, can improve the formability.In this study, mathematical model was developed to predict drawbead restraining force. Drawbead restraining force depends on material properties, sheet thickness and penetration of the drawbead can be calculated with model. Comparison of the results of mathematical model with the corresponding experimental results shows that the predictions of drawbead restraining force in excellent agreement with experimental data in the literature.Furthermore, model predictive controller regulated penetration of drawbead to obtain reference of drawbead restraining force was developed. Model predictive controller was run with given different references and obtained process response closed to reference in a stable manner

Solving optimisation problems in metal forming using FEM: A metamodel based optimisation algorithm

During the last decades, Finite Element (FEM) simulations of metal forming processes have\ud become important tools for designing feasible production processes. In more recent years,\ud several authors recognised the potential of coupling FEM simulations to mathematical opti-\ud misation algorithms to design optimal metal forming processes instead of only feasible ones.\ud This report describes the selection, development and implementation of an optimisa-\ud tion algorithm for solving optimisation problems for metal forming processes using time\ud consuming FEM simulations. A Sequential Approximate Optimisation algorithm is pro-\ud posed, which incorporates metamodelling techniques and sequential improvement strate-\ud gies for enhancing the e±ciency of the algorithm. The algorithm has been implemented in\ud MATLABr and can be used in combination with any Finite Element code for simulating\ud metal forming processes.\ud The good applicability of the proposed optimisation algorithm within the ¯eld of metal\ud forming has been demonstrated by applying it to optimise the internal pressure and ax-\ud ial feeding load paths for manufacturing a simple hydroformed product. Resulting was\ud a constantly distributed wall thickness throughout the ¯nal product. Subsequently, the\ud algorithm was compared to other optimisation algorithms for optimising metal forming\ud by applying it to two more complicated forging examples. In both cases, the geometry of\ud the preform was optimised. For one forging application, the algorithm managed to solve\ud a folding defect. For the other application both the folding susceptibility and the energy\ud consumption required for forging the part were reduced by 10% w.r.t. the forging process\ud proposed by the forging company. The algorithm proposed in this report yielded better\ud results than the optimisation algorithms it was compared to

An investigation of hot forming quench process for AA6082 aluminium alloys

This thesis is concerned with the mechanical properties and microstructure evolution during the novel solution Heat treatment Forming cold die Quenching (HFQ) process. HFQ is a hot sheet forming technology which incorporates the forming and quenching stages to produce high strength and high precision Al-alloy sheet parts. The work in the thesis divided into three main sections: Firstly, viscoplastic behaviour of AA6082 at different deformation temperatures and strain rates was identified through analysis of a programme of hot tensile tests. Based on the results from the hot tensile tests, a set of unified viscoplastic-damage constitutive equations was developed and determined for AA6082, providing a good agreement with the experimental results. SEM tests were carried out to investigate the damage nucleation and failure features of the AA6082 during hot forming process and the results are discussed. Secondly, the viscoplastic-damage constitutive equations were implemented into the commercial software ABAQUS via the user defined subroutine VUMAT for the forming process simulation. An experimental programme was designed and testing facilities were established for the validation of the FE process modelling results. A fairly good agreement between the process simulation and the experimental results was achieved. This confirms that the established FE process simulation model can be used for hot stamping of AA6082 panel parts. Further process modelling work was carried out to identify the optimal forming parameters for a simplified representation of a panel part. Finally, a precipitation hardening model was developed to predict the post-ageing strength of AA6082 panel parts, having varying amounts of forming-induced plastic strain. The model was tested against results of experiments which were carried out to investigate the effect of pre-deformation on the ageing kinetics of AA6082. The model is shown to fit and can be used to explain changes in the strength of the material. This set of equations was implemented in the VUMAT, in combination with the viscoplastic damage constitutive equation set, to model the whole HFQ process. The FE model was tested with experimental ageing and hardness results providing good agreements, which are discussed in light of the future development of the HFQ process

JOINING SEQUENCE OPTIMIZATION IN COMPLIANT VARIATION SIMULATION

Disturbances in the manufacturing and assembly processes cause deviation and geometrical variation from the ideal geometry. This variation eventually results in functional and aesthetic problems in the final product. Being able to control the disturbances is the desire of the manufacturing industry. This, in other words, means turning the noise factors to control factors, in a robust design perspective.With the recent breakthroughs in the technology, the new digitalization reform, and availability of big data from the manufacturing processes, the concepts of digital twins have grasped the attention of the researchers and the practitioners.In line with this trend, S\uf6derberg et al. have introduced the geometry assurance digital twin and the concept of the self-compensating individualized assembly line. Steering the assembly process with online real-time optimization, through the digital twin medium is the vision of such a concept.Joining sequences impact the final geometrical outcome in an assembly considerably. To optimize the sequence for the optimal geometrical outcome is both experimentally and computationally expensive. In the simulation-based approaches, several sequences need to be evaluated together with the finite element method and Monte Carlo simulations.In this thesis, the simulation-based joining sequence optimization, using compliant variation simulation is studied. Initially, the limitations of the formulations and the applied algorithms in the literature have been addressed. Two evolutionary algorithms have been introduced to compare the computational performances to the genetic algorithm. Secondly, a reduced formulation of the sequence optimization is introduced through the identification of the critical points to lock the geometry, geometry joints. A rule-based method has been proposed to initiate the evolutionary algorithm and thereby to increase the algorithm’s computational efficiency. This approach has been further improved by a contact displacement minimization approach to generate model-dependent rules. Finally, a surrogate-assisted approach has been introduced to parallelize the computation process, saving computation time drastically. The approach also unveiled the potential of the simulation-based geometry joint identification, simultaneous to complete sequence determination.The results achieved from the presented studies indicate that the simulation-based real-time optimization of the joining sequences is achievable through a parallelized search algorithm, to be implemented in the geometry assurance digital twin concept. The results can help to control the joining sequence in the assembly process, improving the geometrical quality in a cost-effective manner, and saving significant computational time

Modelling the Deformation, Recrystallization and Microstructure-Related Properties in Metals

In the special issue related to Modelling the Deformation, Recrystallization and Microstructure-Related Properties in Metals, we presented a wide spectrum of articles dealing with modelling of microstructural aspects involved in deformation and recrystallization as well as simulation of microstructure-based and texture-based properties in various metals. The latest advances in the theoretical interpretation of mesoscopic transformations based on experimental observations were partially discussed in the current special issue. The studies dealing with the modelling of structure-property relationships are likewise analyzed in the present collection of manuscripts. The contributions in the current collection evidently demonstrate that the properties of metallic materials are microstructure dependent and therefore the thermomechanical processing (TMP) of the polycrystalline aggregates should be strictly controlled to guarantee the desired bunch of qualities. Given this, the assessment of microstructure evolution in metallic systems is of extraordinary importance. Since the trial-error approach is a time-consuming and quite expensive methodology, the materials research community tends to employ a wide spectrum of computational approaches to simulate each chain of TMP and tune the processing variables to ensure the necessary microstructural state which will provide desired performance in the final product. Although many hidden facets of various technological processes and related microstructural changes were revealed in the submitted works by employing advanced computational approaches, nevertheless, the contributions collected in this issue clearly show that further efforts are required in the field of modelling to understand the complexity of material’s world. The final goal of modelling efforts might be a development of a comprehensive model, which will be capable of describing many aspects of microstructure evolution during thermomechanical processing