An experimental and numerical investigation of the effect of macro-textured tool surfaces in hot stamping

Abstract

This paper presents a method of increasing drawability of materials in hot stamping processes using forming tools with macro-scale textures on the tool surfaces. Firstly, a series of tool texture designs and orientations were presented and a test programme was designed for the experimental investigation. Top-hat shape drawing experiments in cold and hot stamping conditions were conducted to evaluate the effect of macro-scale tool surface textures on the material drawing. Texture directional and texture feature effects of the blankholders on the draw-ability of the material have been investigated. A finite element model of the top-hat drawing process with textured tool surfaces has been established and validated from experimental data. Further FE process modelling has been carried out and the effects of texture features and forming speed have been studied. The relationships between texture designs and material drawing results have been analysed. The developed FE model can provide a guide to design the geometry of tool textures and optimise the hot stamping process parameters.

A study on the buckling behaviour of aluminium alloy sheet in deep drawing with macro-textured blankholder

“…The clearance between the die and punch was 0.1 times of test-piece thickness. Macro-textures were machined on blankholder surfaces in the radial direction to avoid the constraint effect if the macro-textures are not parallel with material flow direction [14], using CNC milling and related to function, and can be divided into two features: groove and surface.…”

“…Costa and Hutchings [12][13] found that friction was significantly reduced through the use of patterned tool surfaces in strip drawing processes, where these grooves were believed to act as lubricant reservoirs to enhance the lubrication effect. Zheng et al [14] investigated hot stamping processes of aluminium alloys using macro-textured tools, which enabled the blank temperature at the flange area to be relatively preserved, with a significant increase in draw-ability being observed due to a more uniform temperature distribution throughout the blank. However, for components with complex geometry, macrotextures may cause wrinkling in the flange area due to the absence of blank-holding contact in the region of a texture hollow.…”

A Physical-Based Plane Stress Constitutive Model for High Strength AA7075 under Hot Forming Conditions

“…Unlike the elastic-plastic dominated cold stamping process, typical characteristics for elevated temperature forming are: (1) microstructure evolution is complex with the coupled effects of dislocation, recovery and dynamic recrystallization in some particular conditions on the hot flow and post proper-ties [8]; (2) strain rate sensitive viscoplastic deformation becomes dominant [9]. The uniformity of deformation is highly dependent on the forming speed and temperature [10]. Therefore, the design of process and selection of process parameters for forming a complex-shaped component are challenging, requiring the aid of robust finite element (FE) simulations.…”

A buckling model for flange wrinkling in hot deep drawing aluminium alloys with macro-textured tool surfaces

“…The nonisothermal feature of hot stamping processes due to the heat transfer between the hot work-piece and the cold dies results in non-uniform deformations, which affect hot formability significantly. This issue can be alleviated with the use of macro-textured tool surfaces, such as the one introducted by Zheng et al [9]. The use of textured tools significantly reduces the contact area and heat transfer compared to traditional flat tool designs.…”