Induction Melt Incremental Thermoforming of Advanced Thermoplastic Composites

交通运输占英国温室气体排放总量的四分之一左右。轻质可回收材料，如热塑性复合材料，被认为是通过“轻量化”减少交通排放的可持续解决方案。与热固性聚合物复合材料相比，热塑性复合材料有几个优点，包括加工速度更快，可回收性更好，韧性更高，尽管它们的加工更具挑战性，这在一定程度上解释了它们的市场份额较小（约为热固性聚合物的1/3）。因此，迫切需要解决制造问题，以实现其全部重量和节省燃料的潜力。然而，将先进的热塑性复合材料成形成复杂的几何形状并不总是直截了当的，而且诸如起皱、桥接和成形板撕裂等生产缺陷是常见的。该项目的主要思想是为先进的热塑性复合材料开发一种新颖的板材成型工艺，旨在减轻热成型多轴层压板成复杂几何形状时的制造缺陷。这将通过使用感应加热和新型增量成形工艺的组合来创造抗皱的“润滑毛坯”来实现。通常，为了在复合材料结构中获得最佳的机械性能，需要在多个方向上放置纤维以适应复杂的加载条件。然而，尽管先进复合材料板材成型工艺的发展可以追溯到30多年前，但有关生产缺陷的问题尚未得到令人满意的回答，即：“如何从预固结的多轴热塑性层压板中形成复杂的部件而不会产生褶皱？”以及“如何在不桥接或不撕裂成型层压板的情况下，形成包含多个凹槽的高度复杂几何形状？”这项拟议的研究结合了两种截然不同的新观点。第一种方法是制造“润滑空白”，使用感应加热和熔化放置在成型复合材料板内的金属中间层，以促进超低层间滑动摩擦，从而实现多轴预固结高级热塑性复合材料的无皱成型。某些金属的电磁特性，加上它们在熔融时的高表面张力和低粘度，意味着它们可以作为一种介质，用于感应加热和润滑成形复合材料毛坯，从而防止起皱。第二个想法是使用一个多步骤成形工具，旨在创建一个自动顺序和增量成形过程在一个单一的冲压成形冲程，从中心开始，随后向外移动到板材的周长。多步骤成形工具既可以减轻桥接和撕裂，关键的是，在热成型过程中，将熔融金属从复合材料层中挤出（就像从管子中挤出牙膏一样！）并进入周围的橡胶隔膜，使最终固结的复合材料部件几乎完全没有嵌入的金属夹杂物。

Transport is responsible for around a quarter of the UK's total greenhouse gas emissions. Light-weight recyclable materials, such as thermoplastic composites, are recognised as a sustainable solution to reducing transport emissions via "light-weighting". Thermoplastic composites have several advantages over their thermosetting polymer composite cousins, including faster processing, improved recyclability and increased toughness, though they are more challenging to process which partly explains their smaller market share (~1/3rd that of thermosets). Consequently, there is an urgent need to address the manufacturing issues to realise their full weight and fuel saving potential. However, forming advanced thermoplastic composites into complex geometries is not always straightforward and production defects such as wrinkling, bridging and tearing of the forming sheet are commonplace.The main idea of the project is to develop a novel sheet forming process for advanced thermoplastic composites designed to mitigate manufacturing defects when thermoforming multi-axial laminates into complex geometries. This will be achieved through the creation of wrinkle-resistant 'lubricated-blanks' using a combination of induction heating and a novel incremental forming process. Typically, to achieve optimum mechanical properties in composites structures, placement of fibres in multiple directions is required to accommodate complex loading conditions. However, despite the development of sheet forming processes for advanced composites dating back over 30 years, questions regarding production defects have yet to be satisfactorily answered, namely: 'How to form complex components from pre-consolidated multi-axial thermoplastic laminates without inducing wrinkles?' and 'How to form highly complex geometries involving multiple recesses, without bridging or tearing of the forming laminate?' The proposed research combines two distinct new ideas. The first is to create a 'lubricated blank', using induction heating and melting of metallic inter-layers placed within the forming composite sheet to facilitate ultra-low inter-ply sliding friction and consequently, wrinkle-free forming of multi-axial pre-consolidated advanced thermoplastic composites. The electromagnetic properties of certain metals coupled with their high surface tension and low viscosity when molten mean they can be used as a medium with which to both inductively heat and lubricate the forming composite blank, thereby preventing wrinkles. The second idea is to use a multi-step forming tool designed to create an automatic sequential and incremental forming process in a single press-forming down stroke, beginning at the centre and subsequently moving outwards towards the perimeter of the sheet. The multi-step forming tool serves to both mitigate bridging and tearing and crucially, squeezes the molten metal out of the composite layup (like squeezing toothpaste from a tube!) and into the surrounding rubber diaphragm during the thermoforming process, leaving the final consolidated composite part almost completely free of embedded metallic inclusions.