a b s t r a c tAn FE model of the solution heat treatment, forming and in-die quenching (HFQ) process was developed. Good correlation with a deviation of less than 5% was achieved between the thickness distribution of the simulated and experimentally formed parts, verifying the model. Subsequently, the model was able to provide a more detailed understanding of the HFQ process, and was used to study the effects of forming temperature and speed on the thickness distribution of the HFQ formed part. It was found that a higher forming speed is beneficial for HFQ forming, as it led to less thinning and improved thickness homogeneity.

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In this paper, the springback of the aluminium alloy AA5754 under hot stamping conditions was characterised under stretch and pure bending conditions. It was found that elevated temperature stamping was beneficial for springback reduction, particularly when using hot dies. Using cold dies, the flange springback angle decreased by 9.7 % when the blank temperature was increased from 20 to 450°C, compared to the 44.1 % springback reduction when hot dies were used. Various other forming conditions were also tested, the results of which were used to verify finite element (FE) simulations of the processes in order to consolidate the knowledge of springback. By analysing the tangential stress distributions along the formed part in the FE models, it was found that the springback angle is a linear function of the average through-thickness stress gradient, regardless of the forming conditions used.

Sustainability is a key factor in an automotive OEMs' business strategy. Vehicle electrification in particular has received increased attention, and major manufacturers have already undertaken significant investments in this area. However, in order to fully confront the sustainability challenge in the automotive industry, lightweight design in additional to alternative propulsion technologies is also required. Vehicle weight is closely correlated with fuel consumption and range for internal combustion and electrified vehicles, respectively, and therefore, weight reduction is a primary objective. Over the past decades, advanced steel and aluminium-forming technologies have seen considerable development, resulting in significant weight reduction of vehicle components. Hot stamping is one of the most established processes for advanced steel and aluminium alloys. The process offers low-forming loads and high formability as well as parts with high strength and minimal springback. However, the high temperatures of the formed materials over numerous cycles and the significant cooling required to ensure desirable component properties necessitate advanced tooling designs. Traditionally, casting and machining are used to manufacture tools; although in recent years, additive manufacturing has gained significant interest due to the design freedom offered. In this paper, a comprehensive review is performed for the state-of-the-art hot-forming tooling designs in addition to identifying the future direction of Additive Manufactured (AM) tools. Specifically, material properties of widely used tooling materials are first reviewed and selection criteria are proposed which can be used for the transition to AM tools. Moreover, key variables affecting the success of hot stamping, for example cooling rate of the component, are reviewed with the various approaches analysed by analytical and numerical techniques. Finally, a number of future directions for adopting additive manufacturing in the production of hot stamping tools are proposed, based on a thorough analysis of the literature.

An intrinsic feature of the hot stamping process, in which a hot blank is quenched and formed between water cooled dies, is the severe thermo-mechanical deformation that the blank experiences under the combined influences of non-isothermal and non-proportional loadings. This results in challenges for conventional forming limit prediction models to accurately predict material behavior. In this paper, a novel viscoplastic-Hosford-MK model was developed to predict the forming limits of an Al-Li alloy under hot stamping conditions. The effectiveness of the developed model was verified by the demonstration of accurate responses to cold die quenching, strain rate and loading path changes, enabling the developed model to reveal a realistic critical material response under complex deformation conditions. Finally, by applying the developed model to the hot stamping of an AA2060 component, its accuracy was successfully validated. It was indicated that the onset of necking during hot stamping of the component did not necessarily occur at the maximum thinning region, and this was due to the comprehensive effects of varying loading path, strain rate and temperature. A detailed mathematical analysis of the developed M-K model was also conducted, and it was found that the incremental work per unit volume ratio (View the MathML source) between Zone b (where a thickness inhomogeneity exists) and Zone a (the remainder of the material) was a significant parameter that determined the formability of AA2060 under hot stamping conditions

The interfacial heat transfer coefficient (IHTC) is an important thermophysical parameter in hot stamping processes and must be identified not only to retain the full mechanical strength of formed components, but also to optimise the production rate. In this work, a novel experimental facility was developed and applied to measure the temperature evolutions of the specimens and tools in stamping processes. Simulated temperature evolutions obtained using the FE software PAM-STAMP were then fit to this data. The IHTC values between AA7075 and three different tool materials were characterized at different contact pressures under both dry and lubricated conditions. In addition, a mechanism based IHTC model was developed and validated as a function of contact pressure, tool material and lubricant thickness to predict the IHTC values under different conditions

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In the present investigation, magnesium strips were produced by twin roll casting (TRC) and melt conditioned twin roll casting (MC-TRC) processes. Detailed optical microscopy studies were carried out on as-cast and homogenized TRC and MC-TRC strips. The results showed uniform, fine and equiaxed grain structure was observed for MC-TRC samples in as-cast condition. Whereas, coarse columnar grains with centreline segregation were observed in the case of as-cast TRC samples. The solidification mechanisms for TRC and MC-TRC have been found completely divergent. The homogenized TRC and MC-TRC samples were subjected to tensile test at elevated temperature (250 to 400C). At 250C, MC-TRC sample showed significant improvement in strength and ductility. However, at higher temperatures the tensile properties were almost comparable, despite of TRC samples having larger grains compared to MC-TRC samples. The mechanism of deformation has been explained by detailed fractures surface and sub-surface analysis carried out by scanning electron and optical microscopy. Homogenized MC-TRC samples were formed (hot stamping) into engineering component without any trace of crack on its surface. Whereas, TRC samples cracked in several places during hot stamping process.