Evaluation of sheet metal covers to improve tool life in forging

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262370983

This research project within the German Brazilian research cooperation BRAGECRIM proposes a new method for wear protection in closed die forging using exchangeable sheet metal die covers. The aim of this project is the development of an inexpensive and easily exchangeable sheet metal die cover which is used to protect the engraving. Generally, the results of the first funding period proved that the proposed concept of die cover can be applied to reduce the tool wear and increase the die lifetime in closed-die forging. For an example geometry, the maximum thermal shock was reduced by 140 K and the main principal stress by 10% due to a reduction of the notch effect in the radius of the die. Based upon a die lifetime calculation, an increase of the die lifetime by more than 200% can be expected. Furthermore, in the first funding period, a FEM model was developed, which can realistically predict the material flow of the billet and the behavior of the die cover. The model was validated for different die geometries by forging experiments. Besides these positive results, the first funding period revealed problems like thinning and wrinkling which lead to a destruction of the die cover after just a small number of forging cycles. Both numerical and experimental investigation allowed to analyze the mechanisms for the observed phenomena. The wrinkling and thinning of the die cover are mainly caused by tensile stresses within the sheet resulting from different friction coefficients at the contact between billet and die cover, respectively, die cover and die. Furthermore, the first funding period focused on the investigation of simple die geometries involving strip-like die covers which do not have a self-stiffening 3D curvature. Related work has shown that these self-stiffening effects provide a realistic opportunity to overcome these problems. Therefore, in close cooperation with the Brazilian partner institute LdTM the main focus of the second funding period is put on the analysis of boundary conditions, die geometries and process chains, where the limitations observed in the first funding period do not prevent a successful application of the die cover concept. To eliminate the tensile stresses within the sheet, the influence of different friction coefficients at both contact surfaces will be investigated. In addition, an enhanced fixation of the sheet within the die will be tested in order to prevent a relative movement between the die cover and the forging die. Besides this variation of the boundary conditions, a second main aim will be the investigation of 3D die covers geometries offering a larger stiffness to reduce the undesired effects considerably. After the second funding period, the concept shall be progressed to a point where a transfer to industrial application is realistic. It is planned to cooperate with ThyssenKrupp Metalúrgica Campo Limpo Ltda.

• DFG Programme: Research Grants