On the High Fluid Pressure in Hydrostatic Forming for Sheet Metal
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International Journal of Precision Engineering and Manufacturing https://doi.org/10.1007/s12541-020-00426-5
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On the High Fluid Pressure in Hydrostatic Forming for Sheet Metal Thu Thi Nguyen1 · Trung Dac Nguyen1 Received: 30 January 2020 / Revised: 10 September 2020 / Accepted: 6 October 2020 © Korean Society for Precision Engineering 2020
Abstract In hydrostatic forming, technological parameters have a significant influence on the thin shell product formation. One of the most important factors is the forming liquid pressure. This pressure exerts directly on the workpiece, pulling the workpiece closely to the die’s profile. Therefore, this parameter should be kept large enough for shaping the product with the required shape and size. In practice, however, it is very difficult to achieve and maintain the high value of this parameter. In addition, it is also necessary to set up a mathematical model of this parameter to support the calculation and control. This paper has suggested a simple solution for maintaining fluid pressure during forming. The solution has been applied into the experimental system. Using this system to investigate forming liquid pressure parameter, the paper has given a suitable mathematical model when shaping cylindrical details from sheet metal. The results of the study contribute to data in die design, parameter calculation and control as well as forming process stabilization in hydrostatic forming for sheet metal. Keywords Forming pressure · Sheet metal · Hydrostatic forming · Regression method Abbreviations d Diameter of die (mm) D0 Diameter of workpiece (mm) F1 The force caused by the blank holder force F2 The force caused by the workpiece sliding on the seal. Ft Tabulated value according to Fisher criterion Fα Adequacy according to Fisher criterion H* Depth of each die (mm) H* Relative depth of die (%) P Forming fluid pressure (bar) Ppeak The maximum forming fluid pressure (bar) Q* Blank holder pressure (bar) Rc Radius of bottom die (mm) S* Relative thickness of workpiece (%) s0 Thickness of workpiece (mm) x1 Coded variation of blank holder pressure x2 Coded variation of relative depth of die x3 Coded variation of relative thickness of workpiece ρ Unit weight (kg/cm3)
* Thu Thi Nguyen [email protected] 1
School of Mechanical Engineering, Hanoi University of Science and Technology, No. 1, Dai Co Viet, Hai Ba Trung, Hanoi, Vietnam
σf Yeild stress (Mpa) σm Ultimate strength (Mpa)
1 Introduction Hydrostatic forming or punch-less hydroforming as shown in Fig. 1 is an innovative technology which uses high pressure fluid to form a product according to the shape of the die cavity. This technology flourished in the 1990s when car industry developed to produce sheet components with a high strength/weight ratio and therefore suitable for light weight [1]. Now, with great potentials, it has large applications in manufacture of thin-shell parts with complex profiles in many fields such as automobile and aerospace industries [2–9]. Due to its high app
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