Evaluation of sheet metal covers to improve tool life in forging

这项研究项目在德国巴西研究合作BRAGECRIM提出了一种新的方法，在封闭模锻磨损保护使用可交换的钣金模具盖。该项目的目的是开发一种廉价且易于交换的金属板模具盖，用于保护雕刻。总的来说，第一个资助期的结果证明，所提出的模具盖概念可以应用于减少闭式模锻中的刀具磨损和提高模具寿命。例如几何形状，由于减少了模具半径中的缺口效应，最大热冲击减少了140 K，主应力减少了10%。根据模具寿命计算，模具寿命预计将增加200%以上。此外，在第一期资助阶段，建立了一个有限元模型，可以真实地预测坯料的材料流动和模盖的行为。通过锻压实验，验证了该模型在不同模具几何形状下的正确性。除了这些积极的结果之外，第一个资助期揭示了诸如变薄和起皱等问题，这些问题导致模具盖在少量锻造循环后被破坏。数值和实验研究都可以分析所观察到的现象的机理。模盖起皱和变薄主要是由于坯料与模盖、模盖和模具接触处的摩擦系数不同而引起板料内部的拉应力所致。此外，第一个资助期侧重于简单模具几何形状的研究，涉及没有自加强三维曲率的条形模具盖。相关工作表明，这些自加强效应为克服这些问题提供了现实的机会。因此，在与巴西合作伙伴研究所LdTM的密切合作下，第二个资助期的主要重点放在对边界条件、模具几何形状和工艺链的分析上，在第一个资助期观察到的限制并不妨碍模具盖概念的成功应用。为了消除板材内部的拉应力，将研究两个接触面上不同摩擦系数的影响。此外，为了防止模盖和锻模之间的相对运动，将测试在模具内增强的板的固定。除了边界条件的这种变化之外，第二个主要目标将是研究3D模具盖几何形状，提供更大的刚度，以大大减少不希望的影响。在第二个筹资期之后，这一概念将发展到可以实际应用于工业的程度。计划与蒂森克虏伯Metalúrgica Campo Limpo Ltda合作。

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.