OVERCOMP: Interface Formation and Bond Strength Prediction in Composite Injection Overmoulding

全球复合材料市场的快速增长主要是由对轻量化的日益迫切的需求推动的，特别是在占英国复合材料需求70%以上的汽车和航空航天行业。仅仅依靠耗时的传统复合材料加工技术不能满足日益增长的对复合材料部件大批量制造的需求。这是英国依赖非国内生产的主要因素之一，特别是在汽车行业，目前所需复合材料部件的50%以上是进口的。通过高度自动化的注塑覆盖成型工艺(或混合注塑成型)高速制造近净形状的混合热塑性复合材料组件可以说是满足这种巨大需求的唯一可用的解决方案之一。复合注塑成型的特点是能够在几分钟内制造选择性增强的、高度复杂的多材料部件，从而省去了几个小时的制造步骤，否则就需要生产类似复杂程度的部件。反过来，这将在很大程度上减少废物的形成、碳足迹和飞行比。然而，尽管有这些优点，这项技术的采用一直受到超模组件在加载下不一致和不可预测的性能的阻碍，这主要是由于界面过早故障造成的。对注射聚合物和热塑性复合材料插入物之间的界面形成缺乏基本的了解是目前无法控制粘结强度从而影响过度模塑复合材料性能的根本原因。问题的复杂性主要源于影响高分子链和界面相互渗透的多种因素。即使是注塑聚合物或热塑性塑料嵌件的加工条件或组成的最微小变化，也会显著影响粘接质量，从而影响部件的使用寿命。由于缺乏可靠的方法来支持对超模部件结构性能的高置信度预测，制造商别无选择，只能考虑进行昂贵的试验或求助于其他通常非常耗时的劳动密集型多步替代工艺。为了解决知识库中的这一差距，OVERCOMP项目旨在提供一个可靠的多尺度模型，以预测覆盖成型部件中涉及的两个热塑性相之间的界面强度。为此，该项目将重点关注在复模过程中促成界面形成的三个主要方面。这包括(I)热传递和流变学；(Ii)材料的兼容性；以及(Iii)聚合物链在界面上随时间和温度的相互扩散(愈合)。这样，模型将确保覆盖成型过程中界面形成的完整画面，并降低过渡到此处理方法的风险。该模型将使制造商和零件设计者能够在材料选择步骤中做出明智的决定，并在开始生产之前对零件的性能有一个清晰的了解。

The rapid growth of the global composite market is primarily driven by the ever-more critical need for lightweighting, especially in the automotive and aerospace sectors constituting over 70% of the UK's demand for composites. The increasing need for high-volume manufacture of composite components cannot be addressed by solely relying on time-consuming traditional composite processing technologies. This is one of the main factors contributing to the UK's reliance on non-domestic production, especially in the automotive industry, where over 50% of the required composite parts are currently imported. High-speed manufacture of near-net-shape hybrid thermoplastic composite components via the highly automated injection over-moulding process (or hybrid injection moulding) is arguably one of the only available solutions to address such a significant demand. Composite injection overmoulding is characterised by its capability to manufacture selectively reinforced, highly complex multi-material components within a few minutes, thereby eliminating several hours-long manufacturing steps that would otherwise be required to produce a part at a similar level of complexity. This will, in turn, largely reduce the waste formation, carbon footprint, and by-to-fly ratio. However, despite these advantages, the adoption of this technology has been hampered by the inconsistent and unpredictable performance of the overmoulded components under loading, predominantly caused by a premature failure at the interface. The lack of a fundamental understanding of the interface formation between the injected polymer and the thermoplastic composite insert is the underlying reason for the current inability to control the bond strength and hence the performance of the overmoulded composite. The complexity of the problem mainly arises from the multitude of factors that affect the interpenetration of the polymer chains and at the interface. Even the slightest changes in processing conditions or the composition of the injected polymer or the thermoplastic insert can significantly affect the bonding quality and hence the service life of the components. The absence of a reliable method to support a high-confidence prediction of the structural performance of overmoulded components has left the manufacturers with no other option but to consider costly trials or resort to other, often highly time-consuming labour-intensive multistep alternative processes. To address this gap in the knowledge base, the OVERCOMP project aims to deliver a reliable multi-scale model to predict the interfacial strength between the two thermoplastic phases involved in an overmoulded component. To this end, the project will focus on the three main aspects that contribute to interface formation during overmoulding. These include (i) heat transfer and rheology, (ii) material compatibility; and (iii) time and temperature-dependent interdiffusion of the polymer chain at the interface (healing). This way, the model will ensure a complete picture of the interface formation during overmoulding and reduce the risk of transitioning to this processing method. This model will enable the manufacturers and part designers to make informed decisions during the material selection step and have a clear picture of the part performance before undertaking to manufacture.