Quantitative Characterization of Warpage for Composite Components

Abstract

Introduction: Many governments have adopted stringent emissions standards for automobiles in order to reduce the detrimental effects they have on the environment [9]. The reduction of vehicle weight is one avenue to reduce vehicle emissions [7],[13] and composite components can play a key role in many potential solutions [1]. However, there are still many challenges to be overcome when it comes to the widespread use of the composite materials, particularly with respect to the mass production of composite parts and assemblies. One option for composite part fabrication is the long fiber thermoplastic direct (LFT-D) manufacturing process. According to this technology, parts can be produced from individual matrix and fiber components. This approach eliminates the need for a semi-finished product like glass mat thermoplastic (GMT) to be acquired from a material supplier and thus translates into cost savings for the composite part manufacturer [5]. Like many other thermal forming processes, the parts fabricated through LFT-D can experience a significant amount of deformation. Warpage can make parts difficult to incorporate in downstream assemblies. However, despite the importance of this problem, the quantitative characterization of the warpage presented in the surveyed literature is relatively simplistic. While no clear metric for part warpage exists at this time, prior studies have highlighted that part warpage can be reduced by changing molding processing parameters [3],[4],[6],[10],[11]. For many of these studies, part warpage is typically evaluated by the maximum deviation between the nominal and fabricated parts. Nonetheless, while the maximum value of the deviation between the two shapes is indeed important, warpage could be defined in many other ways. One alternative is to evaluate specific regions of the part, particularly those that are involved in subsequent assembly operations. Along these lines, the current study aims to propose alternative metrics capable of evaluating part warpage.