Design optimization of hot stamping tooling produced by additive manufacturing

The design flexibility of Additive Manufacturing (AM) can be utilized to develop innovative and sustainable hot stamping tools with enhanced quenching capability compared to tools manufactured by conventional manufacturing processes. This study proposes a concept for hot stamping tools with integrated lattice structures that selectively substitute a die's solid areas. A lattice structure demonstrates reduced thermal mass and can affect the ability of the tool to absorb heat from the blank and the rate at which the tool is cooled between two consecutive stamping cycles. This study explores the design space of a hot stamping tool with integrated lattice structures. It presents the optimized design for an effective compromise between cooling performance, structural integrity, and several other design parameters shown in the study. The proposed method utilizes a 2D thermo-mechanical finite element analysis model of a single cooling channel combined with Design of Experiments (DoE) to reduce the computational cost. The results show that the integration of lattice structure cannot only deliver improved cooling performance with minimum change in the dimensions of the cooling system but also achieves a faster AM build time since less material is required to be printed

Reduced order modelling for spatial-temporal temperature and property estimation in a multi-stage hot sheet metal forming process

A concise approach is proposed to determine a reduced order control design oriented dynamical model of a multi-stage hot sheet metal forming process starting from a high-dimensional coupled thermo-mechanical model. The obtained reduced order nonlinear parametric model serves as basis for the design of an Extended Kalman filter to estimate the spatial-temporal temperature distribution in the sheet metal blank during the forming process based on sparse local temperature measurements. To address modeling and approximation errors and to capture physical effects neglected during the approximation such as phase transformation from austenite to martensite a disturbance model is integrated into the Kalman filter to achieve joint state and disturbance estimation. The extension to spatial-temporal property estimation is introduced. The approach is evaluated for a hole-flanging process using a thermo-mechanical simulation model evaluated using LS-DYNA. Here, the number of states is reduced from approximately 17 000 to 30 while preserving the relevant dynamics and the computational time is 1000 times shorter. The performance of the combined temperature and disturbance estimation is validated in different simulation scenarios with three spatially fixed temperature measurements

A Novel Grip Design for High-Accuracy Thermo-Mechanical Tensile Testing of Boron Steel under Hot Stamping Conditions

Achieving uniform temperature within the effective gauge length in thermo-mechanical testing is crucial for obtaining accurate material data under hot stamping conditions. A new grip design for the Gleeble Materials-Simulator has been developed to reduce the long-standing problem of temperature gradient along a test-piece during thermo-mechanical tensile testing. The grip design process comprised two parts. For the first part, the new design concept was analysed with the help of Abaqus coupled Thermal-Electric Finite element simulation through the user defined feedback control subroutine. The second part was Gleeble thermo-mechanical experiments using a dog-bone test-piece with both new and conventional grips. The temperature and strain distributions of the new design were compared with those obtained using the conventional system within the effective gauge length of 40 mm. Temperature difference from centre to edge of effective gauge length (temperature gradient) was reduced by 56% during soaking and reduced by 100% at 700 °C. Consequently, the strain gradient also reduced by 95%, and thus facilitated homogeneous deformation. Finally to correlate the design parameters of the electrical conductor used in the new grip design with the geometry and material of test-piece, an analytical relationship has been derived between the test-piece and electrical conductor

Aluminium extrusion analysis by the finite volume method

Present work proposes a novel numerical scheme to calculate stress and velocity fields of metal flow in axisymmetric extrusion process in steady state. Extrusion of aluminium is one main metal forming process largely applied in manufacturing bars and products with complex cross section shape. The upper-bound, slab, slip-line methods and more recently the numerical methods such as the Finite Element Method have been commonly applied in aluminium extrusion analysis. However, recently in the academy, the Finite Volume Method has been developed for metal flow analysis: literature suggests that extrusion of metals can be modelled by the flow formulation. Hence, metal flow can be mathematically modelled such us an incompressible non linear viscous fluid, owing to volume constancy and varying viscosity in metal forming. The governing equations were discretized by the Finite Volume Method, using the Explicit MacCormack Method in structured and collocated mesh. The MacCormack Method is commonly used to simulate compressible fluid flow by the finite volume method. However, metal plastic flow and incompressible fluid flow do not present state equations for the evolution of pressure, and therefore, a velocity-pressure coupling method is necessary to obtain a consistent velocity and pressure fields. The SIMPLE Method was applied to attain pressure-velocity coupling. This new numerical scheme was applied to forward hot extrusion process of an aluminium alloy. The metal extrusion velocity fields achieved fast convergence and a good agreement with experimental results. The MacCormack Method applied to metal extrusion produced consistent results without the need of artificial viscosity as employed by the compressible flow simulation approaches. Therefore, present numerical results also suggest that MacCormack method together with SIMPLE method can be applied in the solution of metal forming processes in addition to the traditional application for compressible fluid flow

Formability investigations for the hot stamping process

International audienceArcelor Research is developing a numerical tool to support the feasibility analysis and to optimize the design of hot stamped parts made of USIBOR 1500P®. To provide formability data and to feed the development of a fracture criterion, experimental hot stamping tests are carried out at Cemef (Centre for Material Forming). These hot stamping experiments are based on a modified Nakazima-type test. Results reveal that the achievable strain levels depend on process parameters (stroke, velocity, temperature, friction and heat exchange) and blank parameters (initial temperature, thickness and shape). In parallel, a numerical model of these hot stamping tests has been developed with finite element softwares (Forge2®, Forge3® and Abaqus). The numerical simulations confirm the location and the magnitude of the blank thinning. Furthermore, the numerical results are similar to the experimental measurements in terms of punch load, cooling rate and strain distribution. A formability analysis is then performed to study the influence of the blank geometry and the blank temperature on formability

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

Numerical Investigations on Stresses and Temperature Development of Tool Dies During Hot Forging

Hot-forming tools are subjected to high thermal and mechanical stresses during their application. Therefore, a suitable design of the tool die is important to ensure a long tool life. For this purpose, numerical simulations can be used to calculate the occurring stresses and the temperature development in the tools during the course of a stroke or over several forging cycles. The aim of this research is to investigate the effect of different radii on the resulting stresses in the lower die of the forming tools. Furthermore, the temperature evolution over several cycles is analysed to determine their effect on the temperature. When investigating the stress, it was found that a larger radius leads to a reduction in stresses. In addition, it could be numerically proven that the base temperature of the die levels off after a certain number of cycles. These findings will be used in further research dealing with the service life calculation of dies subjected to thermo-mechanical alternating stresses

Development of a novel Fast-Warm stamping (FWS) technology for manufacturing high-strength steel components

Hot and warm stamping are preferable sheet metal forming technologies used in manufacturing high-strength parts with the twofold objectives of reducing fuel consumption and improving automotive crashworthiness. Great efforts have been made to improve the production rate in these processes and it is difficult to further improve productivity. Therefore, the development of new forming technologies may be an alternative solution to form high-strength steels into complex shapes whilst reducing the cycle time. The present work aims to develop a novel lightweight forming technology, namely fast-warm stamping (FWS) technique, to manufacture high-strength steel components with the desired properties. The concept of this process is to utilise ultra-fast heating of a steel blank to an appropriate temperature, whilst minimising the major negative changes to microstructure which are detrimental to the post-form strength. Mechanical properties such as ductility and post-form strength (PFS) of the MS-W900Y1180T (MS1180) steel were examined via uniaxial tensile tests at various temperatures (25–500°C) and strain rates (0.01–5/s). Special attention has been afforded to the effect of heating rate on thermo-mechanical properties and microstructure of the MS1180 steel with different heating rates. The results suggest that the ductility and post-form hardness of the MS1180 steel were simultaneously improved by 25.7% and 5%, with an increase in heating rate from 1 to 150°C/s. The increased hardness is attributed to the finer precipitated carbides and lower recovery at fast heating rate conditions, which was validated by microstructural observations. The validation of the FWS technology was conducted by forming U-shaped components through a dedicated pilot production line caller Uni-form. The fast-warm stamped components exhibited over 92% mechanical strength of the original as-received material consisting of 1140MPa post-form strength and 370HV hardness. The overall manufacturing cycle time in the FWS process was within 10 seconds. Springback of the formed parts under FWS conditions IV was successfully characterized at various temperatures and forming speeds. Close agreements were achieved between the experimental and simulated results for temperature, thickness distribution and springback prediction of the formed parts which validated the accuracy of the developed finite element (FE) model. FWS technology is a promising solution to manufacture components with desirable mechanical properties and dimensional accuracy. In this work, a feasibility study of the FWS technology was extended from martensitic steels to 60Si2Mn spring steel by producing commercialized disc springs. A separate forming tool set with a replaceable forming surface was developed to reduce manufacturing cost. Experimental results showed that a disc spring was successfully formed using the proposed forming process with the required dimensional precision, post-form strength and surface roughness. This forming technique has shown to enable a tremendous reduction of overall cycle time from 30 minutes to less than 20 seconds and subsequent productivity improvement for a mass-production setting.Open Acces