Mass production forming of high strength steel with durable tooling (Duratool)

The use of (advanced) high strength sheet (A)HSS in forming, shearing and punching applications places increasing demands upon tool materials, particularly in terms of wear performance. A range of tool and sheet steel materials has been studied within the Duratool project. Tribological tests were used to assess wear and friction in forming. High volume forming, shearing and punching trials were also conducted. The tribological findings indicate that conventional tool materials do not perform well in terms of adhesive wear or abrasive wear for steels of tensile strengths above 800 MPa and that more advanced tool materials and coatings must be considered. Tool roughness and lubrication should be controlled to minimise adhesive wear. A finite element model has been developed to predict abrasive tool wear in forming. The model can be used to simulate tool wear and changes in subsequent part geometry. Studies show that changes in part geometry due to tool wear are significant for (A)HSS. For best performance in shearing, the process should be optimised. A cutting clearance equal to 5 % of sheet thickness and a shear angle of 1 ° is suitable for all sheet strengths. High volume shearing trials show that edge quality is more dependent on sheet ductility than tool wear. High strength steels produce a good edge with small burrs simply due to their reduced ductility, despite incurring increased tool wear. In punching trials, conventional tool steels were found to work well to 200 000 strokes for low carbon and mid-range high strength steels. For more demanding AHSS grades, only PM tool steels offered acceptable performance. The results of the project have been summarised in the form of tool selection guidelines.