Study on the Optimized Manufacturing of Hybrid Laminates for a Leaf Spring

Abstract

Economically feasible lightweight design represents an important objective for large-scale automobile production. According to the background of a high degree of lightweight design with sufficient cost-effectiveness, hybrid multi-material composites are increasingly getting into the focus of interest. In this case, composites and metals are combined to produce integrated components with optimized properties. These materials allow the creation of customized components. In addition, the component costs can be reduced by component-integrated functions. This reduction also allows a downstream of various process steps. [1] Due to their high lightweight potential, leaf springs offer a good opportunity for weight reduction in the vehicle. In heavy and light commercial vehicles, weight savings of up to 75% can be achieved for the leaf spring through the use of composites in comparison to conventional spring steel [2]. The variation of the spring rate in a limited design space is restricted for unidirectional (UD) composite laminates since each additional variant requires a new mold for manufacturing. The development of different variants has therefore only been achievable by the expense of increased tooling costs. However, composite leaf springs are not economically feasible for the use in a high variety and large-scale automobile production. So far, there are no suitable spring designs and production concepts for hybrid leaf springs. A high potential for specific variation of the spring rate is provided by adapted laminate architectures. With a hybrid laminate made from unidirectional fabrics and spring steel, a wide variation of spring rates with the same spring geometry can be implemented. Thus, many variants can be produced with one single mold. The challenge in manufacturing of a hybrid laminate lies in the process control. This process has to enable a complete wetting of the sheet steel insert and void-less infiltration of the reinforcing fibers. This study involves the systematic development and optimization of process arrangement for the manufacturing of hybrid laminates by means of vacuum infusion. The parameters influencing the process are fully determined and described. Their effects on the component quality are evaluated. The result of this study is a scalable strategy for vacuum infusion process of hybrid laminates at the high variant manufacturing of hybrid leaf springs. The solution method is divided into three steps. First, the basic physical and chemical effects and processes are characterized. Following, the materials are analyzed. This analysis focuses on the interaction of the materials with the infiltration-resin. This is supplemented by a discussion of the method for manufacturing a hybrid leaf springs using standardized specimens. For the methodological procedure, the setting parameters and results of vacuum infusion are determined and discussed. Based on the infiltration experiments, the effects of the variation of the setting parameters on the void-less infiltration are examined. Eventually, the results are discussed and processing recommendations are derived.