40 results found
Ganapathy M, Li N, Lin J, et al., 2018, A Novel Grip Design for High-Accuracy Thermo-Mechanical Tensile Testing of Boron Steel under Hot Stamping Conditions, EXPERIMENTAL MECHANICS, Vol: 58, Pages: 243-258, ISSN: 0014-4851
Shao Z, Bai Q, Li N, et al., 2018, Experimental investigation of forming limit curves and deformation features in warm forming of an aluminium alloy, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, Vol: 232, Pages: 465-474, ISSN: 0954-4054
© 2016, © IMechE 2016. The determination of forming limit curves and deformation features of AA5754 aluminium alloy are studied in this article. The robust and repeatable experiments were conducted at a warm forming temperature range of 200 °C–300 °C and at a forming speed range of 20–300 mm/s. The forming limit curves of AA5754 at elevated temperatures with different high forming speeds have been obtained. The effects of forming speed and temperature on limiting dome height, thickness variation and fracture location are discussed. The results show that higher temperatures and lower forming speeds are beneficial to increasing forming limits of AA5754; however, lower temperatures and higher forming speeds contribute to enhancing the thickness uniformity of formed specimens. The decreasing forming speed and increasing temperature result in the locations of fracture to move away from the apexes of formed specimens. It is found that the analysis of deformation features can provide a guidance to understand warm forming process of aluminium alloys.
Ganapathy M, Li N, Lin J, et al., 2017, Investigation of a new hot stamping process with improved formability and productivity, ICTP 2017, Publisher: Elsevier, Pages: 771-776, ISSN: 1877-7058
In order to improve the drawability of boron steel and also to increase the productivity of hot stamping process, a new hot stamping process with pre-cooling has been proposed. Stress-strain behavior at various temperatures was investigated and compared with that in traditional hot stamping processes. Detailed studies were carried out on the strain hardening parameter, n, at different temperatures and deformation rates. To evaluate this concept, hot stamping experiments were performed with both conventional (without pre-cooling) and new process (with pre-cooling) for a scaled down B-Pillar automotive component. The new hot stamping process with pre-cooling was able to produce the B-Pillar at low temperature (500°C) with less thinning than the hot stamping carried out without precooling at high temperature (765°C). Also the in-die quenching time was reduced by about 60%, by adopting the new hot stamping process with pre-cooling, which would increase the productivity significantly for automotive mass production without compromising the part quality.
Ganapathy M, Li N, Lin JG, et al., 2017, Test-Piece and Test-Rig Designs to Obtain High Accuracy Experimental Data for Boron Steel at Hot Stamping Conditions, 3rd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU), Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 109-113
Jiang J, Hooper P, Li N, et al., 2017, An integrated method for net-shape manufacturing components combining 3D additive manufacturing and compressive forming processes, ICTP 2017, Publisher: Elsevier, Pages: 1182-1187, ISSN: 1877-7058
Published by Elsevier Ltd. Additive manufactured (AM) or 3D printed metallic components suffer poor and inconsistent mechanical properties due to the presence of a large number of micro-voids, residual stress and microstructure inhomogeneity. To overcome these problems, a new forming process has been proposed, which effectively combines AM and compressive forming. The aim of this study is to prove the feasibility of this newly proposed method by providing preliminary results. Thus, we compared the tensile performance of hot-forged additive manufactured stainless steel 316L samples to none-hot-forged additive manufactured ones. Significant improvement in mechanical properties has been found in the tensile tests as well hardness test. In addition, our EBSD characterized grain orientation maps at each stage of the process revealed the corresponding microstructure revolution which provides insights into underlying mechanistic.
Kong XX, Li N, O'Keeffe R, et al., 2017, Experimental Investigation on the Accuracy of Uniaxial Tensile Data of AA6082 Under HFQ (R) Conditions, 3rd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU), Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 390-394
Li N, Zheng J, Zheng K, et al., 2017, A fast ageing method for stamped heat-treatable alloys, WO2017021742 A1
Shao Z, Li N, 2017, A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions, Journal of Visualized Experiments
Shao Z, Li N, Lin J, 2017, The comparison of two continuum damage mechanics-based material models for formability prediction of AA6082 under hot stamping conditions, 36th IDDRG Conference – Materials Modelling and Testing for Sheet Metal Forming, Publisher: IOP Publishing, ISSN: 1742-6588
The hot stamping and cold die quenching process has experienced tremendous development in order to obtain shapes of structural components with great complexity in automotive applications. Prediction of the formability of a metal sheet is significant for practical applications of forming components in the automotive industry. Since microstructural evolution in an alloy at elevated temperature has a large effect on formability, continuum damage mechanics (CDM)-based material models can be used to characterise the behaviour of metals when a forming process is conducted at elevated temperatures. In this paper, two sets of unified multi-axial constitutive equations based on material's stress states and strain states, respectively, were calibrated and used to effectively predict the thermo-mechanical response and forming limits of alloys under complex hot stamping conditions. In order to determine and calibrate the two material models, formability tests of AA6082 using a developed novel biaxial testing system were conducted at various temperatures and strain rates under hot stamping conditions. The determined unified constitutive equations from experimental data are presented in this paper. It is found that both of the stress-state based and strain-state based material models can predict the formability of AA6082 under hot stamping conditions.
Shao Z, Li N, Lin J, 2017, The optimisation of cruciform specimen for the formability evaluation of AA6082 under hot stamping conditions, ICTP 2017, Publisher: Elsevier, Pages: 735-740, ISSN: 1877-7058
The hot stamping and cold die quenching process is increasingly adopted to form complex-shaped structures of sheet metals in the automotive industry. However, it is difficult to obtain formability data of sheet metals under hot stamping conditions by using conventional experimental testing methods. In this study, a novel in-plane biaxial testing system, which is attached to a Gleeble materials thermo-mechanical simulator, had been developed for determining forming limit diagrams (FLDs) under hot stamping conditions. However, there is no standard of cruciform specimen geometries available for this type of biaxial tests. In this paper, the features of thickness reduction in the central region and slots in the arms of a type of cruciform specimen of aluminium alloy 6082 were verified first to increase strain uniformity of the biaxial loading zone on a cruciform specimen, based on the selective heating and cooling method. Finite Element (FE) thermo-electrical and thermo-mechanical models with UAMP and VUMAT subroutines were then implemented in ABAQUS 6.12 to optimise specimen dimensions so that fracture occurs in the concerned central region of the specimen during testing. By the use of the optimised specimen for AA6082 in the biaxial testing system, formability tests under the designated strain paths were conducted at specified hot stamping conditions. Strain fields in the gauge region of the cruciform specimens were measured using the digital image correlation (DIC) system and the experimental results were presented and analysed in order to verify the cruciform specimen design.
Shao Z, Li N, Lin J, et al., 2017, Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 120, Pages: 149-158, ISSN: 0020-7403
Shao Z, Li N, Lin J, et al., 2017, Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, Pages: 095440621771401-095440621771401, ISSN: 0954-4062
Zheng K, Lee J, Politis DJ, et al., 2017, An analytical investigation on the wrinkling of aluminium alloys during stamping using macro-scale structural tooling surfaces, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 92, Pages: 481-495, ISSN: 0268-3768
Zuo B, Wang B, Li Z, et al., 2017, An investigation of involute and lead deflection in hot precision forging of gears, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 88, Pages: 3017-3030, ISSN: 0268-3768
Li N, Lin J, Balint DS, et al., 2016, Experimental characterisation of the effects of thermal conditions on austenite formation for hot stamping of boron steel, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 231, Pages: 254-264, ISSN: 0924-0136
Li N, Lin J, Balint DS, et al., 2016, Modelling of austenite formation during heating in boron steel hot stamping processes, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 237, Pages: 394-401, ISSN: 0924-0136
Li N, Politis D, Foster AD, et al., 2016, Prediction of thinning behavior for complex-shaped, lightweight alloy panelsformed through a hot stamping process*, 2nd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU2015):, Publisher: World Scientific
This paper provides an overview of hot stamping of light alloys using a method known as HFQ®forming. We present a new method of forming complex shaped automotive components through theuse of a hot stamping process for high strength AA6082 alloy. In particular, the component selectedfor study is a complex automotive door inner component that could not be conventionally formedfrom such a strong alloy. The forming process is described and the post-formed thicknessdistribution is presented. An FE simulation is given to demonstrate the potential to predict theforming process and to provide guidance as to the final component thicknesses.
Li N, Shao Z, Lin J, et al., 2016, Investigation of uniaxial tensile properties of AA6082 under HFQ® Conditions, Key Engineering Materials, Vol: 716, Pages: 337-344, ISSN: 1013-9826
© 2016 Trans Tech Publications, Switzerland. For a metal forming process, the uniaxial tensile properties of a material are the most fundamental and important properties to investigate. Solution heat treatment, forming and in-die quenching (HFQ®) is a patented process to form complex shape panel components using aluminium alloys at high efficiency and low cost. A Gleeble materials thermo-mechanical simulator was used to conduct uniaxial tensile testing of AA6082 under HFQ® conditions. A set of grips were specially designed to reduce the heat loss of specimen during testing in a Gleeble and allow the strain measurement by using digital image correlation (DIC) system. A large dog-bone specimen with parallel length of 80mm was designed to minimise the temperature gradient along the gauge section. Temperature gradient was measured and uniaxial tensile tests were conducted at the range of deformation temperature of350-535 °C and the range of strain rate of 0.1-4/s. The uniaxial tensile properties of AA6082 at different temperatures and strain rates under HFQ® conditions were summarised and the viscoplastic response of the material was discussed.
Li N, Sun C, Guo N, et al., 2016, Experimental investigation of boron steel at hot stamping conditions, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 228, Pages: 2-10, ISSN: 0924-0136
Lin J, Zheng K, Wang L, et al., 2016, Material and Process for Preparing and Forming an Aluminium Alloy Material, WO/2016/067045
Matsumoto T, Li N, Shi X, et al., 2016, An Investigation of Deformation Effects on Phase Transformation in Hot Stamping Processes, SAE INTERNATIONAL JOURNAL OF MATERIALS AND MANUFACTURING, Vol: 9, Pages: 501-505, ISSN: 1946-3979
Shao Z, Li N, Lin J, et al., 2016, Development of a New Biaxial Testing System for Generating Forming Limit Diagrams for Sheet Metals Under Hot Stamping Conditions, EXPERIMENTAL MECHANICS, Vol: 56, Pages: 1489-1500, ISSN: 0014-4851
Shao Z, Li N, Politis D, et al., 2016, A Review on of Forming Limit Prediction and Determination at Elevated Temperatures, 2nd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU2015), Publisher: World Scientific
The evaluation of the formability of sheet material is of great importance for forming complex-shapecomponents in automotive applications. However, for hot and warming forming conditions, thisusually requires formability tests with specialist devices and testing procedures and is difficult toobtain accurate and comparable results due to the lack of testing standards. In this paper, the conceptand development of strain-based forming limit diagram (FLD) are introduced. The testing methodsto experimentally determine the FLD, classified into formability tests and planar tensile tests, arewidely reviewed. The applications of both types to obtain FLD at elevated temperatures for differentforming processes are introduced, and the advantages and disadvantages of the methods areanalysed.
Yang L, Li N, Wang B, et al., 2016, Unified constitutive modelling for two-phase lamellar titanium alloys at hot forming conditions, MANUFACTURING REVIEW, Vol: 3, ISSN: 2265-4224
Ganapathy M, Li N, Lin J, et al., 2015, Analysis of new Gleeble tensile specimen design for hot stamping application, 4th International Conference on New Forming Technology (ICNFT), Publisher: E D P SCIENCES, ISSN: 2261-236X
Gao H, Li N, Ho H, et al., 2015, Determination of a set of constitutive equations for an Al-Li alloy at SPF conditions, MATERIALS TODAY-PROCEEDINGS, Vol: 2, Pages: 408-413, ISSN: 2214-7853
Li N, Lin JG, Dean TA, 2015, Development of Unified Viscoplastic-Damage Model for Crashworthiness Analysis of Boron Steel Safety Components with Tailored Microstructures, Applied Mechanics and Materials, Vol: 784, Pages: 427-434, ISSN: 1662-7482
Hot stamped boron steel panels with tailored properties are popular as car safety components for maximised energy absorption. In this study, dynamic and quasi-static tensile tests (strain rate: 0.001/s – 500/s) combined with microstructural observation were carried out to study the mechanical properties of press hardened boron steel with various microstructures (martensite volume fraction: 0 – 100%) at room temperature. Based on the test results, a physically-based unified viscoplastic-damage constitutive model has been developed and determined, which takes the volume fraction of martensite into account. Thus the crashworthiness and failure mode of boron steel parts having graded microstructure distributions can be described through a single set of equations.
Li N, Zheng J, Zhang C, et al., 2015, Investigation on fast and energy-efficient heat treatments of AA6082 in HFQ processes for automotive applications, 4th International Conference on New Forming Technology (ICNFT), Publisher: E D P SCIENCES, ISSN: 2261-236X
Li X, Li N, Zhu Q, et al., 2015, A Testing System and Method to Generate Forming Limit Diagrams at Elevated Temperatures, CN102749253 B
Mohamed M, Li N, Wang L, et al., 2015, An investigation of a new 2D CDM model in predicting failure in HFQing of an automotive panel, 4th International Conference on New Forming Technology (ICNFT), Publisher: E D P SCIENCES, ISSN: 2261-236X
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