Christian Lauter

Manufacturing Processes for Combined Forming of Multi-Material Structures Consisting of Sheet Metal and Local CFRP Reinforcements

A new and promising approach to the reduction of greenhouse gas emissions is the use of improved lightweight constructions based on multi-material systems comprising sheet metal with local carbon fibre reinforced plastic (CFRP) reinforcements. The CFRP is used to reinforce highly stressed areas and can be aligned to specific load cases. The locally restricted application of CFRP means that the material costs can be effectively reduced by comparison to parts made entirely of CFRP on account of the expensive production process requiring the use of an autoclave. These parts are thus only used in high-priced products. The production of hybrid CFRP steel structures in a mass production process calls for an efficient production technology. Current research work within the scope of a collaborative research project running at the University of Paderborn is concentrating on the development of manufacturing processes for the efficient production of automotive structural components made up of sheet metal blanks with local CFRP patches. The project is focusing especially on basic research into the production of industrial components. The aim of the investigation is to create an efficient and controlled process for producing CFRP reinforced steel structures from semi-finished hybrid steel-CFRP material. This includes tool concepts and an appropriate process design to permit short process times. The basis of an efficient process design is an in-depth knowledge of the material behaviour, and hence a thorough characterisation was performed. Material parameters were determined for both simulation and forming. For this, monotonic tensile, shear and bending tests were conducted using both uncured prepregs and cured CFRP specimens. To achieve an accurate simulation of the forming process, a special material model for carbon fibre prepregs has been developed which also includes the anisotropic material behaviour resulting from fibre orientation, the viscoelastic behaviour caused by the matrix and the hardening effects that prevail during curing. Recent results show good qualitative agreement and will be presented in this paper. In order to control the properties of the hybrid components, four different tool concepts for the prepreg press technology have been developed and tested. The concepts are presented and the results of experimental investigations are discussed in this paper.

Influences of interface and surface pretreatment on the mechanical properties of metal-CFRP hybrid structures manufactured by resin transfer moulding

The combination of sheet metal and carbon-fibre-reinforced plastic (CFRP) is a promising approach in the sector of automotive lightweight construction. The hybrid structures allow a symbiotical usage of the specific advantages of each material. First of all, this article specifies the process chain by manufacturing hybrid materials with an intrinsic resin transfer moulding (RTM) process. Subsequently, research results regarding the interface between metal and CFRP component as well as the surface pretreatment of metallic component with laser structuring are illustrated and discussed. By means of four-point-bending tests, it is found that the mechanical properties of metal-CFRP hybrid structures are improved by using a glass fleece or an epoxy-based adhesive film as intermediate layer or due to surface pretreatment of metallic component with laser structuring. Additionally, a finite-element simulation for a four-point-bending test of a hybrid part is compared to an experiment for the linear elastic region, where strain and stress distributions are focused.

Quasistatic and crash tests of steel-CFRP hybrid pillar structures for automotive applications

One promising approach in the field of automotive lightweight construction is the combination of sheet metal and fibre reinforced plastics (FRP). In these hybrid structures the wall thickness of the metallic structure is reduced and a local FRP reinforcement is applied to heavily loaded sections of the part. The present paper sets out current research results in the field of hybrid materials. First of all, the prepreg press technology for manufacturing automotive structural components in a hybrid design is illustrated. In particular, the advantages of this technology compared to conventional processing methods for FRP are highlighted. Next, the joining of the steel and the FRP component by using an epoxy matrix resin as an adhesive is discussed. Subsequently, the results of quasistatic and crash tests on hybrid hat profiles are presented. It was shown that hybrid materials hold a high weight-saving potential for structural automotive components compared to steel-only structures.

Manufacturing and Investigation of Steel-CFRP Hybrid Pillar Structures for Automotive Applications by Intrinsic Resin Transfer Moulding Technology

Automotive lightweight design can be achieved by the combination of sheet metal and carbon fibre-reinforced plastic (CFRP). The hybrid structure enables a simultaneous usage of the specific advantages of both materials. This paper is focused on basic technological investigations in the field of manufacturing of hybrid structures by utilising the intrinsic RTM technology. Initially, the production process of automotive pillar structures in a steel-CFRP hybrid design is exemplified by an omega profile. Further, the viscosity measurement is carried out to identify the curing properties of the deployed epoxy matrix system used. Finally, the results of four-point bending tests and crash tests on hybrid omega profiles are presented, analysed and evaluated. It could be shown that the mechanical properties in the bottom area and the flank area are consistent. Additionally, hybrid materials exhibit a satisfying weight-saving potential for automotive structural components comparing pure steel structures.

Textile composites in the automotive industry

This chapter takes a look at the automotive application of textile composites regarding different aspects of fatigue. After giving an introduction to modern lightweight design principles and the use of textile composites in automobiles in general, multi-material and hybrid design approaches for lightweight design in the automotive sector are presented. Because an automotive application implies large series production, cost and, in particular, quality play an important role for those critical parts for which high performance even after a long exposition to fatigue loads is vital for the systems total performance and safety of passengers. One aspect this chapter covers is, therefore, the need for cost-effective quality control in the production process of textile semi-finished products and complex preforms.

Endkonturennahe Fertigung von höchstfesten Hybridbauteilen

Leichtbau im Automobil lässt sich durch die verschiedensten Maßnahmen realisieren. Aktuell ist ein Megatrend in Richtung Multimaterial-Systeme und seit neuestem in Richtung Hybridbauweisen offensichtlich, Bild 1. Bei diesen Bauweisen werden verschiedene Werkstoffe symbiotisch miteinander verbunden, um die jeweiligen sich bietenden Vorteile der Einzelwerkstoffe bestmöglich nutzen zu können. Seit einiger Zeit rücken insbesondere Faserverbundkunststoffe für diese Anwendungen in den Mittelpunkt des Interesses. Durch eine Kombination zum Beispiel von Aluminium und Faserverbundkunststoffen lassen sich mittels der Hybridbauweise bis zu 35 % an Gewicht einsparen [1]. Um diese Technologie auch für große Serien attraktiv zu machen, bedarf es geeigneter Fertigungstechnologien. Eine Möglichkeit bietet an dieser Stelle die Prepreg-Press-Technologie. S T A n D D E R T E c H n I K Um dem Trend der steigenden Fahrzeuggewichte entgegenzuwirken, sind in der Automobilindustrie in der jüngeren Vergangenheit unterschiedliche Leichtbauansätze verfolgt worden. Hierzu zählen häufig werkstoffliche Konzepte, das heißt der Einsatz von Leichtbauwerkstoffen, wie Aluminium, Magnesium und Faserverbundkunststoffe, oder höchstfesten und somit massereduzierten Stahlbauteilen. Das stahlbasierte Konzept Tailored Blanks wurde von der ThyssenKrupp AG entwickelt und zielt darauf ab, eine belastungsangepasste Stahlstruktur zu realisieren und somit das Bauteilgewicht zu senken. Da die mechanischen Belastungen in Bauteilen in der Regel nicht homogen verteilt sind, führt eine konstante Materialstärke dazu, dass das Bauteil in den meisten Bereichen überdimensioniert ist. Aus diesem Grund wurden Tailored Blanks entwickelt.

Methodik für die Produktentstehung hybrider Leichtbaustrukturen

Die Anwendung von Leichtbau ermöglicht die Realisierung von Strukturen mit einer geringeren Masse bei gleichen oder sogar besseren Eigenschaften. Bei vielen Produkten ist jedoch real über die letzten Jahre ein Gewichtsanstieg zu verzeichnen. Dieser ist im Automobilbau unter anderem auf steigende Sicherheitsund Komfortanforderungen zurückzuführen und betrug im Schnitt 100 kg Zuwachs pro Dekade. Um diesem Trend entgegenzuwirken, bedarf es innovativer und vor allem ganzheitlicher Leichtbauansätze.