The present work focuses on a new approach to hot form hard-to-work materials by Single Point Incremental Forming (SPIF) technology using a global heating of the sheet. A set of trials was carried out in order to identify the optimum temperature cycles to minimize geometric distortions associated to each process stage on the fabrication of parts made of Ti–6Al–4V. On the one hand, heating trials allowed defining the optimal procedure to improve the temperature distribution homogeneity along the sheet and consequently to minimize its thermal distortion previous to the forming stage. On the other hand, the influence of both working temperature and the applied cooling on the geometric accuracy was evaluated by means of SPIF trials. For this purpose, a generic asymmetric design with typical aeronautical features was used. These trials pointed out that high forming temperatures allow reducing significantly the material springback whereas a controlled cooling (with an intermediate stress relief treatment) minimizes both the distortion of the part during the cooling and the mechanical stresses accumulated on the clamping system. Furthermore, the work includes a post-forming material evaluation to determinate the influence of the employed processing conditions on microcracks, alpha-case layer, microstructure and hardness.

中文翻译：

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Ti-6Al-4V合金热SPIF中热相关效应的研究

本工作着重于通过单点增量成型（SPIF）技术使用板材的整体加热来热成型难加工材料的新方法。为了确定最佳的温度循环，以最大程度地减少与T​​i-6Al-4V制成的零件制造过程中每个工艺阶段相关的几何变形，进行了一系列试验。一方面，加热试验允许定义最佳程序，以改善沿薄板的温度分布均匀性，从而最大程度地减小成形阶段之前的热变形。另一方面，通过SPIF试验评估了工作温度和所施加的冷却对几何精度的影响。为此，使用了具有典型航空特性的通用不对称设计。这些试验指出，较高的成型温度可显着降低材料的回弹，而受控的冷却（采用中间应力消除处理）可将零件在冷却过程中的变形和在夹紧系统上累积的机械应力均降至最低。此外，该工作还包括对成型后材料的评估，以确定所采用的加工条件对微裂纹，α-表面层，微观结构和硬度的影响。