Methodology for a near net shape, wrinkle-free production of textile preforms by using a segment based die draping

在过去的几年里，能源和资源的短缺显著增加了轻量化建筑在工业应用中的重要性。一种可能的减轻重量的方法是使用纤维增强塑料，因为它们在密度方面表现出特别突出的特征，如比刚度和比强度。在这种情况下，树脂传递模塑(RTM)是一种很有前途的方法，因为一方面它允许生产连续的纤维增强塑料-获得最高的轻量化水平-另一方面显示了工业化的潜力，以一分钟为间隔进行大批量生产。然而，RTM工艺链中的预成型必须被认为是一个关键的工艺步骤，因为非常柔软的纺织纤维的成形和悬垂显著影响部件的机械性能。为了确保预成形过程的效率和竞争力，在许多项目中对不同预成形技术的自动化进行了研究。粘结剂成形技术显示出巨大的规模化生产潜力。自动悬垂的一个有趣的方法是使用分段冲压模具。因此，纺织品层叠序列的形状类似于通过矩阵、冲头和滑块的拉深工艺。层与层之间的固定以及预制件的形状保持是通过使用粘结剂来实现的。为了开发针对大量不同几何形状的分段冲头的悬垂工艺的最大潜力，需要一种系统的工艺设计方法。基于几何分析和有限元覆盖模拟，必须确定模具的分段和冲头的顺序。在这里，必须制定足够的案例区分、阈值或数量限制以及递归或迭代规则，并将其整合到有针对性的方法方案中。计划中的调查应有助于理解分段冲头自动预成形过程中的机理。通过采用这种方法，设计工程师将获得几乎任何壳形几何形状的模具划分和冲压顺序。

The shortage of energy and resources has significantly increased the importance of lightweight construction in industrial applications in the past years. One possible way of reducing weight is the use of fibre-reinforced plastics because they show particularly prominent characteristics in terms of density such as specific stiffness and specific strength. In this context, the resin transfer moulding (RTM) constitutes a promising method considering that on the one hand it allows the production of continuous fibre-reinforced plastics - awarded the highest lightweight levels - and on the other hand shows the potential of industrialisation with high volume production at one-minute intervals. Preforming within the RTM process chain has to be considered a critical process step though, since the shaping and draping of the very flexible textile fibres significantly influences the mechanical properties of the component. To ensure efficiency and competitiveness of the preforming process, the automation of different preforming technologies was investigated in many projects.The binder-forming-technology shows a great potential to reach a large-scale production. An interesting approach for automated draping is the use of segmented stamping dies. Accordingly, the textile ply stacking sequence is shaped similar to a deep drawing process by means of matrices, punches and sliders. The fixation of the layers to one another as well as the shape retention of the preforms is achieved by using a binder.To exploit the maximum potential of the draping process with segmented punches for a large number of different geometries, a systematic method for the process design is necessary. Based on a geometric analysis and a finite element draping simulation, a segmentation of the die and the sequence of the punches have to be determined. Here, adequate case distinctions, threshold values or quantitative restrictions as well as recursion or iteration regulations must be formulated and integrated into a targeted methodical scheme.The planned investigatons shall contribute to understand the mechanism during the automated preforming process using segmented punches. By following this method, design engineers shall obtain a division of dies and a sequence of the punches for nearly any shell-shaped geometry.