Tool wear prediction modelling for sheet metal stamping die in automotive manufacture

Advanced high strength steels (AHSS) are increasingly used in sheet metal stamping in the automotive industry. In comparison with conventional steels, AHSS stampings produce higher contact pressures at the interface between draw die and sheet metal blank, resulting in more severe wear conditions, particularly at the draw die radius. Developing the ability to accurately predict and reduce the potential tool wear during the tool design stage is vital for shortening lead times and reducing production costs. This thesis investigates the influence of draw die geometry on the wear distribution over the draw die radius for AHSS and develops a methodology for optimising the draw die geometry to reduce wear using numerical and experimental methods. Tool wear predictions on automotive sheet metal forming die and recommended protections of the tool surface under the initial production conditions were obtained from AutoForm simulation software. Effects of lubrication coefficients, binder pressure loads and die coating on tool wear distributions were investigated as well. It is concluded that the areas that are most sensitive to tool wear occurs at the locations corresponding to the large gradient of drawing depth. To study the tool wear distributions for more common stamping parts, a numerical tool wear model was developed and applied using the commercial software package Abaqus. Channel tests are carried out using an Erichsen sheet metal tester with high pressure prescale films to verify the numerical model results. Comparing the results obtained from the prescale film with the results from the simulation, it is concluded that the contact pressure distributions indicated by the prescale film are consistent with those from the simulation. Various geometries of radius arc profiles, including standard circular profiles, high elliptical profiles, and flat elliptical profiles, were numerically investigated using the tool wear model developed, and the contact pressure distribution and tool wear work along the radii were determined. The following conclusions were reached from the investigations: (1) The colour contour of the high contact pressure on the die radius can be divided into three distinct zones of high pressure and tool wear; (2) The dominant zone leading to maximum contact pressure and tool wear severity depends on the geometry of die radius profile under the same material and process conditions; (3) The geometry of draw die radius has a significant influence on the tool wear and standard circular and elliptical curves can lead to the achievement of reduced and uniform contact pressure distribution (wear distribution) along most of zones of the draw die radius arc. The results suggest that to minimise contact pressure and tool wear using this approach it would be necessary to optimise the shape for a particular combination of material type, thickness and forming process. Effects of control parameters, such as blank geometry, punch geometry, deep-drawing process parameters and tool material, on wear behaviour in deep-drawing for various shape of die radius were then investigated to provide guidelines for impacts of these parameters. A specialised software routine was then compiled for optimisation of die radius profiles to minimise and achieve uniform contact pressure (wear distribution) using Python programming language. The routine was fully integrated with Abaqus software and has the following functions: (1) To provide a user-friendly Graphical User Interface for pre-processing data input for users who have less experience and skill; (2) To optimise a die radius profile according to the control parameters that users input. The results obtained are relevant to the issue of reducing the high tool wear in automotive stamping tools by predicting the causes of such tool wear related to tool geometry and process parameters. They provide useful guidelines for enhancing the tool life of sheet metal processing in automotive industry.