Evaluation of sheet metal covers to improve tool life in forging

该研究项目是德国-巴西研究合作组织BRAGECRIM的一项研究项目，它提出了一种在闭式模锻件中使用可交换板材模盖进行磨损保护的新方法。本项目的目的是开发一种价格低廉、易于更换的金属板材模盖，用于保护雕刻。总体而言，第一个资金周期的结果证明，提出的模盖概念可以应用于闭式模锻件，减少刀具磨损，提高模具寿命。以几何形状为例，由于凹口半径的缺口效应减小，最大热震降低了140K，主应力降低了10%。根据芯片寿命计算，可以预期芯片寿命增加200%以上。此外，在第一个注资期，建立了有限元模型，该模型能够真实地预测坯料的材料流动和模盖的行为。通过锻造实验验证了该模型对不同模具几何形状的适用性。除了这些积极的结果外，第一个资助期发现了诸如变薄和起皱等问题，这些问题导致仅在少量锻造周期后模具盖就被破坏了。数值和实验研究都允许分析观察到的现象的机制。模盖起皱和变薄主要是由于坯料与模盖接触处的摩擦系数不同导致板材内的拉应力所致。此外，第一个资助期的重点是调查简单的模具几何形状，包括没有自加强3D曲率的条状模具盖。相关工作表明，这些自我强化效应为克服这些问题提供了现实的机会。因此，与巴西伙伴机构LdTM密切合作，第二个资助期的主要重点是分析边界条件、模具几何形状和工艺链，在第一个资助期观察到的限制并不妨碍成功应用模盖概念。为了消除薄板内部的拉应力，将研究在两个接触面上不同摩擦系数的影响。此外，将测试板材在模具内的强化固定，以防止模具盖和锻模之间的相对移动。除了这种边界条件的变化，第二个主要目标将是研究3D模盖几何结构，提供更大的刚度，以显著减少不希望看到的影响。在第二个资助期之后，这一概念应取得进展，以使向工业应用的转移成为现实。计划与蒂森克虏伯金属公司Campo Limpo Ltd.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.