Imperial College London

DrLiliangWang

Faculty of EngineeringDepartment of Mechanical Engineering

Reader in Mechanical Engineering
 
 
 
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Contact

 

+44 (0)20 7594 3648liliang.wang Website

 
 
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Location

 

518City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

136 results found

Yu X, Zhao L, Li Y, Jin Y, Politis DJ, Liu H, Wang H, Liu M, He Y-B, Wang Let al., 2024, Weakening ionic coordination for high ionic conductivity composite solid electrolytes, ACS Energy Letters, Pages: 2109-2115, ISSN: 2380-8195

The special chemistry of N,N-dimethylformamide (DMF)-solvated Li+ [Li(DMF)x]+ migration results in polyvinylidene fluoride (PVDF)-based solid polymer electrolytes exhibiting high ionic conductivities. Incorporating ceramic fillers into PVDF electrolytes can further enhance the ionic conductivities. However, there is limited understanding of the desolvation process of Li+ during its transport through the ceramic fillers. Herein, we reveal that this desolvation process exhibits a large energy barrier that hinders the Li+ transport. The introduction of poly(methylhydrosiloxane) (PMHS) can weaken the ion–solvent coordination, forming loosely complexed [Li(DMF)x]+ and reducing their desolvation energy. This promotes rapid ceramic-involved Li+ pathways, enabling the electrolyte with a high ambient ionic conductivity of 7.5 × 10–4 S cm–1. Moreover, the facile desolvation process can enhance the kinetics and reduce side reactions at the electrode/electrolyte interfaces. Therefore, solid-state Li–Li symmetric cells can operate for a record 11 800 h, and LiNi0.8Co0.1Mn0.1O2|Li solid-state batteries also demonstrated exceptional cycling stability for more than 2200 cycles at 2C.

Journal article

Yang X, Liu H, Zhang L, Hu Y, Politis DJ, Gharbi MM, Wang Let al., 2024, Interactive mechanism and friction modelling of transient tribological phenomena in metal forming processes: A review, Friction, Vol: 12, Pages: 375-395, ISSN: 2223-7690

The accurate representation of tribological boundary conditions at the tool-workpiece interface is crucial for analysis and optimization of formability, material flow, and surface quality of components during metal forming processes. It has been found that these tribological conditions vary spatially and historically with process parameters and contact conditions. These time-dependent tribological behaviours are also known as transient tribological phenomena, which are widely observed during forming processes and many other manufacturing application scenarios. However, constant friction values are usually assigned to represent complex and dynamic interfacial conditions, which would introduce deviations in the relevant predictions. In this paper, transient tribological phenomena and the contemporary understanding of the interaction between friction and wear are reviewed, and it has been found that these phenomena are induced by the transitions of friction mechanisms and highly dependent on complex loading conditions at the interface. Friction modelling techniques for transient behaviours for metal forming applications are also reviewed. To accurately describe the evolutionary friction values and corresponding wear during forming, the advanced interactive friction modelling has been established for different application scenarios, including lubricated condition, dry sliding condition (metal-on-metal contact), and coated system.

Journal article

Li C, Zhang D, Xu Z, Wang L, Yi P, Peng L, Lai Xet al., 2024, Tailored nanocrystalline Niobium coatings on steel substrates for superior resistance to micro-crack initiation, Scripta Materialia, Vol: 241, ISSN: 1359-6462

Fracture of metallic thin films during deformation hampers extensive applications of coated engineering components. In this study, the resistance to micro-crack initiation of Niobium (Nb) coatings deposited on stainless steel substrates is improved remarkably by tuning the substrate bias voltages during unbalanced magnetron sputtering. With the tailored nanocrystalline microstructure, the failure strain for coating fracture is increased to 30 %, which is far greater than that of previous metallic coatings (below 10 %). Microstructure characterizations reveal that intergranular nano-pinholes and amorphous phases can be eliminated effectively with a moderate ions bombardment effect to avoid brittle film fracture. At the same time, compact and homogenous nanocrystalline grains with appropriate intragranular defects are obtained via enhanced atom diffusivity during deposition. Therefore, large plastic deformation can be accommodated through both stress-driven grain coarsening and continuous dislocation plasticity, avoiding fracture of the Nb coatings.

Journal article

Li H, Peng LF, Meng B, Xu ZT, Wang LL, Ngaile G, Fu MWet al., 2023, Energy field assisted metal forming: Current status, challenges and prospects, International Journal of Machine Tools and Manufacture, Vol: 192, ISSN: 0890-6955

To meet the various and critical manufacturing requirements including high precision, low cost, good manufacturability, and more demanding from product service and performance aspects such as high performance, light-weight, less energy consumption and low carbon emissions in today's era of rapid product development with short product life circle, it is crucial to re-innovate and re-invigorate metal forming technologies and enable it to play an even more important role in manufacturing arena. Historically, introducing new kinds of energy fields into the forming process drives the innovative advance and rejuvenating of forming technologies due to the physically interactive mechanisms of energy field and certain material deformation behaviors such as thermal-mechanical coupling effects. In this paper, a classification of energy-aided metal forming processes is orchestrated and presented, and three kinds of energy-assisted metal forming technologies, viz., electrically-assisted forming, ultrasonic vibration assisted forming, and electromagnetic field supported forming, are reviewed and delineated as they are currently receiving a widespread attention with promising application potentials. In this paper, the physical essence and the effects of these introduced energy fields on deformation behavior, process performance, microstructure evolution are elucidated and analyzed. The constitutive modeling of these forming processes is recapitulated, and the newly established energy field assisted metal forming technologies are exemplified and discussed. Based on the advantages and limitations of these unique metal forming processes assisted by additional energy fields, the process capacity and application potentials are unraveled and examined. Finally, from the aspects of exploring physical mechanisms, establishing high-fidelity models, coupling the multiple energy fields, and developing intelligent equipment and realizing these forming processes, the current challenges and futu

Journal article

Chantzis D, Liu H, Politis DJ, Fu MW, Wang Let al., 2023, Design optimization of hot stamping tooling produced by additive manufacturing, Additive Manufacturing, Vol: 74, ISSN: 2214-7810

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.

Journal article

Chang S, Wang K, Wang B, Kopec M, Li Z, Wang L, Liu Get al., 2023, Effects of rapid heating on non-equilibrium microstructure evolution and strengthening mechanisms of titanium alloy, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 880, ISSN: 0921-5093

Journal article

He Z, Liang J, Zhang H, Guo E, Du W, Politis DJ, Wang Let al., 2023, Formability and microstructure of laser powder bed fused AlSi10Mg alloy sheets under various deformation conditions, Materials Characterization, Vol: 199, ISSN: 1044-5803

The large thermal gradient and high cooling rate generated in the fabrication of complex thin-walled components by laser powder bed fusion (LPBF) may cause uncontrolled deformation and reduce dimensional accuracy. The existing preheating-assisted LPBF process is still difficult to fabricate complex thin-walled components to large size (e.g., reach 800 mm) with the required dimensional accuracy and structural properties. To solve this problem, a novel integrated process of LPBF and hot metal gas forming (HMGF) was proposed in this study to fabricate complex thin-walled components. In this process, a preform with a geometrical shape close to the final component is first fabricated by LPBF process, and then this preform is formed into the desired shape by HMGF process. The hot formability of the LPBF AlSi10Mg sheets was investigated to verify the feasibility of this novel forming process. Also, the hot formability was compared with that of gravity cast (GC) AlSi10Mg sheets. The microstructure, phase structure, uniaxial and biaxial hot formability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), hot uniaxial tensile and hot biaxial gas bulging experiments, respectively. The results indicated that the cellular microstructure of the LPBF AlSi10Mg gradually disappears with the increase in temperature. The LPBF AlSi10Mg sheet exhibits superior mechanical properties to the GC AlSi10Mg sheet due to the mixed strengthening mechanism among strengthening phase precipitation, grain structure and dynamic recrystallization (DRX) degree. For instance, the former demonstrates a total elongation (obtained from hot uniaxial tensile tests) of 81.2% and an ultimate bulging height (obtained from the hot biaxial gas bulging tests) of 12.16 mm; in contrast, the latter's elongation and bulging height are 56.2% and 9.26 mm, respectively. Moreover, the LPBF AlSi10Mg sheet shows more uniform deformation than the GC AlSi10Mg sheet during the bulging tests. The f

Journal article

Yang X, Zhang L, Liu H, Politis DJ, Gharbi MM, Shi H, Wang Let al., 2023, Effect of Tooling Temperature on the Transient Lubricant Behavior in Hot Metal Forming Processes, STEEL RESEARCH INTERNATIONAL, Vol: 94, ISSN: 1611-3683

Journal article

Yang X, Liu H, Dhawan S, Politis D, Zhang J, Dini D, Hu L, Gharbi M, Wang Let al., 2022, Digitally-enhanced lubricant evaluation scheme for hot stamping applications, Nature Communications, Vol: 13, ISSN: 2041-1723

Digitally-enhanced technologies are set to transform every aspect of manufacturing. Networks of sensors that compute at the edge (streamlining information flow from devices and providing real-time local data analysis), and emerging Cloud Finite Element Analysis technologies yield data at unprecedented scales, both in terms of volume and precision, providing information on complex processes and systems that had previously been impractical. Cloud Finite Element Analysis technologies enable proactive data collection in a supply chain of, for example the metal forming industry, throughout the life cycle of a product or process, which presents revolutionary opportunities for the development and evaluation of digitally-enhanced lubricants, which requires a coherent research agenda involving the merging of tribological knowledge, manufacturing and data science. In the present study, data obtained from a vast number of experimentally verified finite element simulation results is used for a metal forming process to develop a digitally-enhanced lubricant evaluation approach, by precisely representing the tribological boundary conditions at the workpiece/tooling interface, i.e., complex loading conditions of contact pressures, sliding speeds and temperatures. The presented approach combines the implementation of digital characteristics of the target forming process, data-guided lubricant testing and mechanism-based accurate theoretical modelling, enabling the development of data-centric lubricant limit diagrams and intuitive and quantitative evaluation of the lubricant performance.

Journal article

Chantzis D, Liu X, Politis DJ, Wang Let al., 2022, Additive Manufacturing of Lattice Structured Hot Stamping Dies with Improved Thermal Performance, The 19th International Conference on Experimental Mechanics, Publisher: MDPI

Conference paper

Zhang L, Yang X, Zhang Q, Zheng Y, Liu X, Politis DJ, Fakir OE, Wang Let al., 2022, Investigation of Friction Coefficient Evolution and Lubricant Breakdown Behaviour at Elevated Temperatures in a Pin-on-Disc Sliding System, ICEM 2022, Publisher: MDPI

Conference paper

Liu H, Yang X, Zheng Y, Wang Let al., 2022, Experimental Study on Galling Behavior in Aluminum Stamping Processes, ICEM 2022, Publisher: MDPI

Conference paper

Liu X, Di B, Yu X, Liu H, Dhawan S, Politis DJ, Kopec M, Wang Let al., 2022, Development of a Formability Prediction Model for Aluminium Sandwich Panels with Polymer Core, MATERIALS, Vol: 15

Journal article

Yang X, Hu Y, Zhang L, Politis DJ, Liu X, Wang Let al., 2022, Experimental and modelling study of interaction between friction and galling under contact load change conditions, Friction, Vol: 10, Pages: 454-472, ISSN: 2223-7690

The galling process remains one of the least understood phenomena in metal forming. The transfer of material from a work-piece onto the tool surface can cause an evolutionary increase in COF and thus the use of a constant COF in FE simulations leads to progressively inaccurate results. For an aluminium work-piece, material transfer, which has history and pressure dependency, is determined by a dynamic balance between the generation and ejection of wear particles acting as a 'third body' abrasive element at the contact interface. To address this dynamic interactive phenomenon, pin-on-disc tests between AA6082 and G3500 were performed under step load change conditions. The COF evolutions, morphologies of the transfer layer and its cross-section were studied. It has been found that contact load change will disequilibrate and rebuild the dynamic balance and high load will increase the generation and ejection rate of third body and vice versa. Moreover, based on the experimental results, an interactive model was developed and presented to simulate the dynamic formation process of the aluminium third body layer under load change conditions, enabling multi-cycle simulations to model the galling distribution and friction variation.

Journal article

Wang L, 2021, Experimental and modelling studies of the transient tribological behaviour of a two-phase lubricant under complex loading conditions, Friction, Vol: 10, ISSN: 2223-7690

The transient tribological phenomenon and premature lubricant breakdown have beenwidely observed in metal forming, leading to excessive friction at the contact interfaces. Inthis research, the transient tribological behaviour of a two-phase lubricant were studiedunder complex loading conditions, featuring abrupt interfacial temperature, contact load andsliding speed changes, thus representing the severe interfacial conditions observed inwarm/hot metal forming applications. The strong experimental evidence indicates that theevolution in friction was attributed to the physical diminution and chemical decompositioneffects. As such, a visco-mechanochemical interactive friction model was developed toaccurately predict the transient tribological behaviour of the two-phase lubricant undercomplex loading conditions. The new friction model exhibited close agreements between themodelling and experimental results.

Journal article

Wang L, 2021, Adding value by advancing metal forming technology, 13th International Conference on the Technology of Plasticity, Publisher: Springer, Pages: 319-331

The metal forming industry is responding to changing technical and commercial demands of customers and increasingly stringent legislative restrictions. In addition, on demand delivery requires lead times having to contract. Also Original Equipment Manufacturers are demanding deliveries just-in-time on changeable schedules and for many products batch quantities have become smaller than they were a few years ago. Thus, lead times must be shortened. To meet these challenges, in the metal forming industry, the rate at which new and existing process technologies and production practices are being developed is increasing. Computer-aided design and manufacturing systems have been allied to computer process simulation, to form powerful Cloud based, knowledge-based tools for producing parts right-first-time through identifying the customers’ needs. The purpose of this paper is to illustrate the contribution made by the authors to enhance the added value of metal formed parts, through advancing scientific process knowledge and developing software to support computer-aided manufacture.

Conference paper

Wang L, Yang X, Liu X, Liu H, Politis DJ, Leyvraz Det al., 2021, Experimental and modelling study of friction evolution and lubricant breakdown behaviour under varying contact conditions in warm aluminium forming processes, Tribology International, Vol: 158, Pages: 1-11, ISSN: 0301-679X

The lubricant behaviours under varying contact conditions were investigated by conducting pin-on-strip tests between P20 tool steel and AA7075 aluminium alloy using an automated testing system, Tribo-Mate. The effects of temperature changes, and rapid load and speed changes on the coefficient of friction (COF) and lubricant breakdown phenomenon were experimentally studied. The evolutions of COF showed three distinct stages, indicating the transformation from boundary lubrication condition to dry sliding condition. The value of COF at the initial stage was found to increase with increasing temperature. The increase of temperature, contact load and sliding speed caused an earlier breakdown of the lubricant. An interactive friction model was developed to predict friction evolutions at varying contact conditions. A close agreement with errors less than 6.8% were achieved between the model predictions and experimental results.

Journal article

Yu X, Jiang Y, Yang X, Cai Z, Hua Y, Yang S, Wang H, Liu X, Wang Let al., 2021, Dodecanethiol coated multi-walled carbon nanotube films as flexible current collector for lithium-ion batteries, MATERIALS LETTERS, Vol: 291, ISSN: 0167-577X

Journal article

Yang X, Zhang Q, Zheng Y, Liu X, Politis DJ, Elfakir O, Wang Let al., 2021, Investigation of the friction coefficient evolution and lubricant breakdown behaviour of AA7075 aluminium alloy forming processes at elevated temperatures, International Journal of Extreme Manufacturing, Vol: 3, Pages: 1-8, ISSN: 2631-8644

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The effects of temperature, initial lubricant volume, contact pressure and sliding speed on the lubricant behaviour (i.e. evolutions of the coefficient of friction (COF) and the breakdown phenomenon) were experimentally studied. The evolutions of COF at elevated temperatures consisted of three distinct stages with different friction mechanisms. The first stage (stage I) occurred with low friction when the boundary lubrication was present. The second stage (stage II) was the transition process in which the COF rapidly increased as the lubricant film thickness decreased to a critical value. In the final plateau stage (stage III), lubricant breakdown occurred and intimate contact at the interface led to high friction values. At the low friction stage (stage I), the value of COF increased with increasing temperature. The increase in temperature, contact pressure and sliding speed as well as the decrease in initial lubricant volume accelerated the lubricant breakdown.

Journal article

Chantzis D, Liu X, Politis DJ, Shi Z, Wang Let al., 2021, Design for additive manufacturing (DfAM) of hot stamping dies with improved cooling performance under cyclic loading conditions, Additive Manufacturing, Vol: 37, ISSN: 2214-8604

Additive Manufacturing (AM) provides almost infinite design flexibility enabling the fabrication of intricate components. This study proposes a Design for AM (DfAM) method for hot stamping dies which exploits the benefit of lattice structures’ reduced thermal conductivity. The term effective cooling area of a cooling channel is introduced and is used for lattice structure integration into a hot stamping die. Four hot stamping dies with 4 different effective cooling areas were AMed using selective laser melting and subsequently tested in the hot stamping of AA7075 aluminum alloy blanks under cyclic loading conditions. Temperature evolutions, for both the blank and die, are presented with associated computed cooling rates. The analysis of the results shows that the proposed lattice structure AMed stamping dies significantly improve the cooling performance of a hot stamping die with printing times reduced by at least 12% compared to traditionally manufactured AM dies.

Journal article

Zhou X, Shao Z, Zhang C, Sun F, Zhou W, Hua L, Jiang J, Wang Let al., 2020, The study of central cracking mechanism and criterion in cross wedge rolling, International Journal of Machine Tools and Manufacture, Vol: 159, ISSN: 0890-6955

Cross wedge rolling (CWR) is an innovative metal forming process to manufacture axisymmetric stepped shafts used in the transport industry. Central cracking, also called the Mannesmann Effect, consistently occurs in the central region of the CWR workpiece. This results in reduced product quality and increased costs due to rejected and failed parts. However, the understanding of central cracking mechanism and criterion is limited due to the complex stress states in CWR and the experimental limitations. A large number of CWR tests and different die geometries are required in the identification of the potential mechanistic factors such as the axial tensile stress, secondary tensile stress, shear stress and cyclic loading. Also, there is as yet no efficient method of determining the material constants associated with the central cracking fracture criteria. These problems are addressed in the present study. A physical model was built to reproduce the industrial CWR process. A newly designed model material (plasticine/flour composite) was used to mimic the material flows and internal fracture behaviours found in commercial CWR workpieces. This allowed a variety of die shapes to be rapidly and cost-effectively 3D printed, thereby enabling specific stress states to be achieved within the workpiece. Via experimental observations and the corresponding finite element modelling under different die geometries, the maximum shear stress was identified as the dominant factor for central cracking. The fracture criterion involving the maximum shear stress was quantitatively verified to be accurate and robust in predicting central cracking moments and locations. A novel approach using simplified die geometries to determine the associated material constants was proposed and validated. The high accuracy and cost/time efficiency of this new approach will be a significant benefit to fundamental research and also in industrial applications.

Journal article

Liu X, Cai Z, Zheng Y, Elfakir O, Wang Let al., 2020, Development of a general interfacial heat transfer coefficient model to characterise the critical processing parameters in hot and warm aluminium stamping processes, Applied Thermal Engineering, Vol: 181, ISSN: 1359-4311

Different hot and warm stamping technologies with particular processing parameters were applied to deform aluminium alloy sheets to satisfy desired requirements, of which the post-form strength of formed components is one of the most important criteria. In order to save experimental efforts, the present research described an efficient method to determine the critical processing parameters, i.e. the integration of the finite element (FE) simulated temperature evolutions with the continuous cooling precipitation (CCP) diagrams of the aluminium alloys. Through the optimisation of the processing parameters, the temperature evolutions and CCP diagrams do not intersect, indicating that the post-form strength of the aluminium alloys could be fully retained after proper artificial ageing processes. Therefore, a precise FE simulation of the temperature evolution is of great importance to this method, which requires the implementation of an accurate interfacial heat transfer coefficient (IHTC) as a decisive boundary condition. A general aluminium alloy-independent model with one set of fixed model constants was therefore developed to predict the IHTC evolutions as a function of contact pressure, surface roughness, initial blank temperature, initial blank thickness, tool material, coating material and lubricant material. Subsequently, the predicted IHTCs for 6082 and 7075 aluminium alloys were used to simulate their temperature evolutions, which were then integrated with their CCP diagrams to identify the critical processing parameters in hot/warm stamping processes and thus meet the desired post-form strength of the 6082 and 7075 aluminium alloys. The developed IHTC model and determined critical processing parameters were then experimentally verified by the fast alloy stamping (FAST) of the dissimilar aluminium alloys.

Journal article

Kumar Anand V, Aherwar A, Mia M, Elfakir O, Wang Let al., 2020, Influence of silicon carbide and porcelain on tribological performance of Al6061 based hybrid composites, Tribology International, Vol: 151, ISSN: 0301-679X

The impact of silicon carbide (5 wt%) and porcelain (1.5–6.0 wt%) reinforcements on mechanical and tribological features of Al-based hybrid composite (manufactured by metal stir casting) is investigated. A pin-on-disc tribometer was used for experiment and SEM for the characterization of wear for different operating conditions. The hardness of the hybrid composites enhanced approximately by 57% with an increment in porcelain particulates from 1.5 to 6 wt%. However, the wear loss and average coefficient of friction decrease when the porcelain content was added and was found to be minimum at 4.5 wt% porcelain. Hence, the presence of 4.5 wt% porcelain in the Al6061/5SiC hybrid composites produces the best wear properties.

Journal article

Wang L, 2020, Enhanced formability and forming efficiency for two-phase titanium alloys by Fast light Alloys Stamping Technology (FAST), Materials and Design, Vol: 194, Pages: 1-12, ISSN: 0264-1275

During hot stamping of titanium alloys, insufficient forming temperatures result in limited material formability, whereas temperatures approaching the β phase transus also result in reduced formability due to phase transformation, grain coarsening and oxidation during the long-time heating. To solve this problem, Fast light Alloys Stamping Technology (FAST) is proposed in this paper, where fast heating is employed. Effects of heating parameters on the formability and post-form strength were studied by tensile tests. Forming of a wing stiffener was performed to validate this new process. Results show that microstructure of TC4 alloy after fast heating was in nonequilibrium state, which could enhance ductility significantly compared with the equilibrium state. When TC4 alloy was first heated to 950 °C with heating rate of 100 °C/s and then cooled to 700 °C, the elongation at 700 °C was more than 3 times that of a slow heating rate with soaking. Nano-scaled martensite with high dislocation density transformed from β phase was observed under fast heating condition. A complex shaped wing stiffener was successfully formed from TC4 titanium alloy in less than 70 s including heating, transfer and forming, and the post-form strength was almost the same with the initial blank.

Journal article

Wang L, 2020, Review on additive manufacturing of tooling for hot stamping, International Journal of Advanced Manufacturing Technology, Vol: 109, Pages: 87-107, ISSN: 0178-0026

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 manufactur

Journal article

Wang L, 2020, Characterization of thermomechanical boundary conditions of a martensitic steel for a FAST forming process, Journal of Manufacturing and Materials Processing, Vol: 4, Pages: 1-16, ISSN: 2504-4494

The present work characterized and modelled the interfacial heat transfer coefficient and friction coefficient of a non-alloy martensitic steel, for a novel Fast light Alloy Stamping Technology (FAST) process. These models were validated through temperature evolution, thickness distribution and springback measurements on experimentally formed demonstrator components, which were conducted on a pilot production line and showed close agreement, with less than 10% variation from experimental results. The developed models and finite element simulations presented in this work demonstrate that non-isothermal processes can be precisely simulated with implementation of the accurate thermomechanical boundary conditions.

Journal article

Wang K, Wang L, Zheng K, He Z, Politis DJ, Liu G, Yuan Set al., 2020, High-efficiency forming processes for complex thin-walled titanium alloys components: State-of-the-art and Perspectives, International Journal of Extreme Manufacturing, Vol: 2, Pages: 1-24, ISSN: 2631-8644

Complex thin-walled titanium alloy components play a key role in the aircraft, aerospace and marine industries, offering the advantages of reduced weight and increased thermal resistance. The geometrical complexity, dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems, which brings new challenges to titanium alloy forming technologies. Traditional forming processes, such as superplastic forming or hot pressing, cannot meet all demands of modern applications due to their limited properties, low productivity and high cost. This has encouraged industry and research groups to develop novel high-efficiency forming processes. Hot Gas Pressure Forming (HGPF) and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components, and are believed to be the cut-edge processes guaranteeing dimensional accuracy, microstructure and mechanical properties. This article intends to provide a critical review of high-efficiency titanium alloy forming processes, concentrating on latest investigations of controlling dimensional accuracy, microstructure and properties. The advantages and limitations of individual forming process are comprehensively analyzed, through which, future research trends of high-efficiency forming are identified including trends in process integration, processing window design, full cycle and multi-objective optimization. This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.

Journal article

Liu X, Kopec M, Elfakir O, Qu H, Wang Y, Wang L, Li Zet al., 2020, Characterisation of the interfacial heat transfer coefficient in hot stamping of titanium alloys, International Communications in Heat and Mass Transfer, Vol: 113, ISSN: 0735-1933

The interfacial heat transfer coefficient (IHTC) for titanium alloys is an important parameter in non-isothermal hot stamping processes to determine the temperature field as well as temperature-dependent material behaviours that consequently affect the post-form properties of the formed components. However, the IHTC for titanium alloys in hot stamping processes has seldom been studied before. In the present research, the effects of contact pressure, lubricant, surface roughness, tooling material and initial blank temperature on the IHTC for the titanium alloy Ti-6Al-4V were studied and modelled to characterise the IHTC values under various hot stamping conditions as well as identify the functional mechanisms affecting the IHTC. Furthermore, the results of hot stamping of Ti-6Al4V wing stiffener components were used to verify the simulation results of the temperature field of the formed component with an error of less than 5%.

Journal article

He Z, Zhu H, Lin Y, Politis DJ, Wang L, Yuan Set al., 2020, A novel test method for continuous nonlinear biaxial tensile deformation of sheet metals by bulging with stepped-dies, International Journal of Mechanical Sciences, Vol: 169, ISSN: 0020-7403

In this paper, a novel test method named bulging with stepped-dies is proposed to overcome the difficulty of traditionaltest methods in realizing continuous nonlinear loading paths from initial yield up to fracture on a sheet metal. Toachieve this aim, the section shape of a stepped-die cavity is varied with increasing depth. During bulging with astepped-die, the stress state at the pole of bulging area of the sheet changes continuously with the increase in bulgingheight, which results in a specific nonlinear loading path. A theoretical model is established to calculate the stresscomponents at the pole based on the assumption that the bulged surface near the pole was approximated by arotational ellipsoid. Bulging experiments with three different stepped-dies are performed by using ST16 steel sheet.Stress and strain paths up to fracture and equivalent stress-strain curves at the pole are analyzed and compared withthe results of bulging with elliptical dies. It is shown that continuous nonlinear loading paths can be effectively realizedthrough bulging with stepped-dies and the stress ratio at the pole changes from 0.5 up to 2.0 at most in one bulgingexperiment. The feasibility of the novel test method is validated successfully. And the experimental data obtained areuseful to determine constitutive and forming limit models suitable for complex loading conditions.

Journal article

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