Imperial College London

DrLiliangWang

Faculty of EngineeringDepartment of Mechanical Engineering

Reader in Mechanical Engineering
 
 
 
//

Contact

 

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

 
 
//

Location

 

518City and Guilds BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

121 results found

Wang L, 2021, Experimental and modelling studies of the transient tribological behaviour of a two-phase lubricant under complex loading conditions, Friction, 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

Yang X, Hu Y, Zhang L, Politis DJ, Liu X, Wang Let al., 2021, Experimental and modelling study of interaction between friction and galling under contact load change conditions, Friction, 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, 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

A freestanding polydopamine-normal dodecanethiol coated MWCNT film (PDCNT) was fabricated by an easy and scalable slurry coating - peeling off method. When applied as the current collector, the PDCNT film demonstrated low mass density, excellent flexibility and high electrochemical stability. Composite with hollow structure silicon (HSSi), HSSi-PDCNT anode was able to deliver a specific capacity of 750 mAh g−1 after 200 cycles, reaching equivalent performance of Cu foiled current collectors. This innovative and simple fabricating method proposed in the present study can be widely used to develop high performance flexible current collectors, especially in application of lithium ion batteries (LIBs).

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

Wang L, 2020, Fundamentals, processes and equipment for hot medium pressure forming of light material components, International Journal of Lightweight Materials and Manufacture, Vol: 3, Pages: 1-19, ISSN: 2588-8404

Lightweight tubular components occupy a significant proportion of automobile and aircraft body structures. To manufacture such complex-shaped and integrated structures, Hot Medium Pressure Forming (HMPF) as a cutting-edge technology can be used to enable the forming of lightweight materials with poor ductility that would have otherwise been unable to be formed through traditional technologies. HMPF has been extensively and rapidly developed for over two decades. This field has stimulated new innovations and has inspired a vast range of novel forming processes for different lightweight materials. However, to date there has been a lack of a comprehensive review of HMPF and the developments in this field. In this article, a critical review of HMPF is presented, with the intent of illustrating process principles, summarizing key innovations, effects of processing at elevated temperatures, process capabilities and accomplishments. Moreover, the equipment and forming medium used in the process and specific applications are comprehensively discussed. The materials of particular emphasis were aluminium and magnesium, high strength steel and titanium alloys which are attractive raw material candidates for automotive and aircraft industries. As a result of this review, the intended objective of the paper is to provide direct guidance for industrial engineers and researchers to design a particular HMPF process considering the raw material characteristics, component geometrical features and in-service properties, and uncover major trends for future scientific and application efforts.

Journal article

Sun Y, Wang K, Politis DJ, Chen G, Wang Let al., 2020, An experimental investigation on the ductility and post-form strength of a martensitic steel in a novel warm stamping process, Journal of Materials Processing Technology, Vol: 275, Pages: 116387-116387, ISSN: 0924-0136

Journal article

Liu X, El Fakir O, Cai Z, Dalkaya B, Wang K, Gharbi MM, Wang Let al., 2019, Development of an interfacial heat transfer coefficient model for the hot and warm aluminium stamping processes under different initial blank temperature conditions, Journal of Materials Processing Technology, Vol: 273, ISSN: 0924-0136

Different initial blank temperatures, or forming temperatures, are applied in hot and warm aluminium stamping processes depending on the component being formed and the desired post-form properties. An initial blank temperature dependent interfacial heat transfer coefficient is therefore an essential boundary condition in such non-isothermal forming processes for obtaining precise temperature fields from the formed components in finite element simulations. This precision is crucial for the optimisation of the processing window and tool design, to subsequently achieve the desired cooling rates and post-form strength of the aluminium components being formed. The IHTC between a 7075 aluminium alloy and tungsten carbide cobalt coated cast-iron was found to approximately increase linearly with increasing initial blank temperature in the present research. The effect of the initial blank temperature was identified as a combination of two mechanisms; the effects of material strength and thermal conductivity. The IHTC was found to decrease with increasing strength of the blank when the contact pressure was lower than a threshold value, while a larger thermal conductivity of the aluminium blank increased the IHTC values. Furthermore, an initial blank temperature-dependent model was developed to predict the IHTC at different initial blank temperatures, which was subsequently verified by the results of non-isothermal forming tests.

Journal article

Zhang Q, Luan X, Dhawan S, Politis DJ, Du Q, Fu MW, Wang K, Gharbi MM, Wang Let al., 2019, Development of the post-form strength prediction model for a high-strength 6xxx aluminium alloy with pre-existing precipitates and residual dislocations, International Journal of Plasticity, Vol: 119, Pages: 230-248, ISSN: 0749-6419

The applications of lightweight and high strength sheet aluminium alloys are increasing rapidly in the automotive industry due to the expanding global demand in this industrial cluster. Accurate prediction of the post-form strength and the microstructural evolutions of structural components made of Al-alloys has been a challenge, especially when the material undergoes complex processes involving ultra-fast heating and high temperature deformation, followed by multi-stage artificial ageing treatment. In this research, the effects of pre-existing precipitates induced during ultra-fast heating and residual dislocations generated through high temperature deformation on precipitation hardening behaviour have been investigated. A mechanism-based post-form strength (PFS) prediction model, incorporating the flow stress model and age-hardening model, was developed ab-initio to predict strength evolution during the whole process. To model the stress-strain viscoplastic behaviour and represent the evolution of dislocation density of the material in forming process, constitutive models were proposed and the related equations were formulated. The effect of pre-existing precipitates was considered in the age-hardening model via introducing the complex correlations of microstructural variables into the model. In addition, an alternative time-equivalent method was developed to link the different stages of ageing and hence the prediction of precipitation behaviours in multi-stage ageing was performed. Furthermore, forming tests of a U-shaped component were performed to verify the model. It was found that the model is able to accurately predict the post-form strength with excellent agreement with deviation of less than 5% when extensively validated by experimental data. Therefore, the model is considered to be competent for predicting the pre-empting material response as well as a powerful tool for optimising forming parameters to exploit age hardening to its maximum potential in rea

Journal article

Wang L, Liu X, Elfakir O, Zheng Y, Gharbi MMet al., 2019, Effect of tool coatings on the interfacial heat transfer coefficient in hot stamping of aluminium alloys under variable contact pressure conditions, International Journal of Heat and Mass Transfer, Vol: 137, Pages: 74-83, ISSN: 0017-9310

The interfacial heat transfer coefficient (IHTC) is an essential parameter in hot stamping for determining the optimal process parameters necessary to achieve the critical cooling rate and thus the desired post-form strength in a formed component. Aluminium chromium nitride, chromium nitride and titanium nitride are currently being widely studied in the hot stamping industry as tool coatings due to their excellent wear performance, although their effects on the IHTC have yet to be determined. In practical hot stamping processes, the contact pressure may also change over extremely short periods of time, leading to abrupt changes in the IHTC and consequently the temperature evolutions of the workpiece. These abrupt changes in contact pressure and their effects on the IHTC have yet to be studied either. In this paper, to address those challenges, the IHTCs between an AA7075 aluminium alloy and different coated tools with a 3-stage evolutionary variable contact pressure were quantitatively determined, and a mechanism-based model developed to accurately predict their values.

Journal article

Wang L, Hu Y, Zheng Y, Politis D, Masen M, Cui Jet al., 2019, Development of an interactive friction model to predict aluminum transfer in a pin-on-disc sliding system, Tribology International, Vol: 130, Pages: 216-228, ISSN: 0301-679X

In aluminum forming processes, it is observed that the coefficient of friction increases and a transfer layer is formed on the tool surfaces. In the current paper, this phenomenon is studied via pin-on-disc dry sliding tests with aluminum alloy 6082 sliding against cast iron G3500. The results showed that the aluminum transfer layers generated at the sliding interface were identified as the origin of this behaviour that affects both friction and wear. To model this phenomenon, an interactive friction model was developed enabling the prediction of friction and the evolution of the transfer layer from the running in to the steady state. This mechanism based model can be used for representing friction variations and material transfer in sliding systems.

Journal article

Sun Y, Cai Z, Politis DJ, Luan X, Chen G, Wang Let al., 2019, Springback characteristics of a martensitic steel for warm U-shape bending: Experiments and FE simulation, 38th Annual Conference of the International-Deep-Drawing-Research-Group (IDDRG), Publisher: IOP PUBLISHING LTD, ISSN: 1757-8981

Conference paper

Yang X, Hu Y, Zheng Y, Politis DJ, Wang Let al., 2019, Coating effects on the galling behaviour of aluminium metal forming processes, 38th Annual Conference of the International-Deep-Drawing-Research-Group (IDDRG), Publisher: IOP PUBLISHING LTD, ISSN: 1757-8981

Conference paper

Wang L, 2018, Multi-objective finite element simulations of a sheet metal forming process via a cloud based platform, International Journal of Advanced Manufacturing Technology, ISSN: 0268-3768

Journal article

Fakir OE, Wang A, Zhang Q, Liu X, Liu J, Wang Let al., 2018, Multi-objective sheet metal forming simulations using a software agnostic platform, IOP Conference Series: Materials Science and Engineering, ISSN: 1757-8981

© Published under licence by IOP Publishing Ltd. The development of new technologies for forming lightweight sheet metals into vehicle components has resulted in a rapid growth of advanced predictive models to analyze such processes. Simulations of the warm and hot forming of aluminium alloys in particular have been conducted on numerous finite element (FE) software packages with various specific phenomena being captured through the implementation of subroutines, to ensure that parts formed are free of defects and meet the required post-form strength. However, access to such models is lacking, with each having to be adapted to the software being used, and are computationally expensive to run, limiting the capabilities of simulations and increasing the challenges of utilizing new forming technologies effectively. Smart Forming is a knowledge-based cloud platform that was developed to overcome these challenges. It is composed of functional modules based on predictive models made accessible on the cloud that can be run individually or simultaneously. A conventional forming simulation is first run locally in any FE software of choice, and the required results uploaded to the modules on the platform for remote computation to investigate the phenomena of interest. In this work, simulation data from two different software packages, PAM-STAMP and Autoform, were processed for the same U-shaped component in the Smart Forming modules 'Formability' and 'Tailor', to demonstrate the multi-objective simulation and software agnostic capabilities of the platform.

Conference paper

Zhang Q, Luan X, Dhawan S, Politis DJ, Cai Z, Wang Let al., 2018, Investigating the quench sensitivity of high strength AA6082 aluminium alloy during the new FAST forming process, IOP Conference Series: Materials Science and Engineering, ISSN: 1757-8981

© Published under licence by IOP Publishing Ltd. Optimised manufacturing rates offer enormous cost saving benefits to industry. FAST (Fast light Alloys Stamping Technology) has been recently developed to rapidly and economically manufacture high-strength panel components from sheet metal alloys. For heat treatable aluminium alloys, artificial ageing is subsequently employed to strengthen the formed components. The diffusion-controlled precipitation response is dependent on the cooling rate. The temperature evolution during FAST quenching significantly affects the final strength. In the present research, the AA6082 specimens were heated to the target temperature at an ultra-fast rate and cooled by either air (providing different quenching rates) or water, followed by artificial ageing at 180°C. Hardness measurements were conducted to track the strength evolution of the specimens during thermal cycles. Transmission electron microscopy was also performed to characterise the microstructures under different cooling conditions. Based on the experimental results, quench sensitivity during FAST has been analysed in depth and modelled. This detailed quenching sub-model was incorporated in the post-form strength prediction model, for simulating strength of the components. A great agreement between experimental data and modelled results has been achieved with the deviation less than 7%. By identifying undesirable quenching methods, optimisation of the forming process is thus possible, improving the final strength of the formed parts.

Conference paper

Kopec M, Wang K, Wang Y, Wang L, Lin Jet al., 2018, Feasibility study of a novel hot stamping process for Ti6Al4V alloy, MATEC Web of Conferences

© The Authors, published by EDP Sciences, 2018. To investigate the feasibility of a novel hot stamping process for the Ti6Al4V titanium alloy using low temperature forming tools, mechanical properties of the material were studied using hot tensile tests at a temperature range of 600 - 900°C with a constant strain rate of 1s-1. Hot stamping tests were carried out to verify the feasibility of this technology and identify the forming window for the material. Results show that when the deformation temperature was lower than 700°C, the amount of elongation was less than 20%, and it also had little change with the temperature. However, when the temperature was higher than 700°C, a good ductility of the material can be achieved. During the forming tests, parts failed at lower temperatures (600°C) due to the limited formability and also failed at higher temperatures (950°C) due to the phase transformation. The post-form hardness firstly decreased with the temperature increasing due to recovery and then increased due to the phase transformation. Qualified parts were formed successfully between temperatures of 750 - 850°C, which indicates that this new technology has a great potential in forming titanium alloys sheet components.

Conference paper

Liu X, Fakir OE, Gharbi MM, Wang Let al., 2018, Effect of tool coating on interfacial heat transfer coefficient in hot stamping of AA7075 aluminium alloys, 17th International Conference on Metal Forming, Publisher: Elsevier BV, Pages: 1127-1133, ISSN: 2351-9789

Conference paper

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00584290&limit=30&person=true