Ortwin Hahn

Innovative joining technologies for multi-material structures

The affordable implementation of lightweight constructions in automotive engineering depends not only on the availability of suitable processing technologies for new lightweight materials but also on suitable, cost-efficient joining methods for multi-material combinations with high process reliability. Therefore, joining technology plays a key role in realizing energy-efficient vehicles. The systematic development of joining methods is necessary to overcome the metallurgical and thermal incompatibility of steel/aluminium or steel/fibre-reinforced plastic combinations. This paper presents two innovative and highly productive joining technologies and characterizes these processes based on their technological properties for one specific steel/aluminium material combination.

Evaluation of Simulation Models for the Estimation of Deformation of Adhesively Bonded Steel Sheets during Curing

One-component adhesives are proved to be very advantageous in the automotive industry. The occurrence of deformations during adhesive bonding of thin@ steel sheets is caused by the local and temporal temperature distribution during curing. The influence of thermal expansion and curing shrinkage, as well as relative movements of the adherends on the resulting deformations have been investigated experimentally and numerically. To investigate various boundary conditions a sample geometry, consisting of a stiff substructure and a thin top element, as well as a real part, namely a sunroof, were used. Dynamic mechanical thermal analysis (DMTA) was used for evaluating the mechanical properties of the adhesive, which was treated as a viscoelastic continuum with temperature dependent properties. Possibilities of how to simulate the so-called bondline read-through effect are discussed.

Mechanical Joining of Magnesium Components by Means of Inductive Heating - Realization and Capability

The aspect of lightweight constructions becomes more and more important. This particularly applies to the automotive industry which wants to lower the fuel consumption by a smaller vehicle weight. Under this point of view in recent years steel has often been replaced by aluminum alloys. In comparison with this the application of lightweight magnesium alloys, whose specific density is appropriate within the range of plastics, opens further prospects for weight reduction. The pre-condition for this purpose is the supply of suitable joining processes for magnesium alloys, which are universally applicable and offer the maximum utilization of the materials of the joined parts under operating loads. Mechanical joining techniques provide the opportunity of connecting magnesium components homogeneously as well as in material mix. However, the anisotropic deformation characteristics of the hexagonal crystal structure of magnesium at room temperature contain the application for mechanical joining techniques. Only starting from temperatures of approx. 225°C a sufficient plastic deformation and thus a crack-free shaping of the magnesium material is given. Therefore preheating of magnesium substrates leads to a broad extension of deformability and offers the chance to realize a high quality mechanical joint. This article describes a process-safe realization of the mechanical joining operations clinching, self piercing riveting and clinch riveting of magnesium sheets by means of an inductive heating of the substrates in laboratory scale. In this context, feasibilities and limits of the considered joining techniques are shown.

Fuegesystemoptimierung fuer Mischbauweisen im Karosseriebau

Als Beitrag zur Schonung der Ressourcen und Minimierung der Kohlendioxid-Emissionen hat sich die europaische Automobilindustrie verpflichtet, den Flottenverbrauch aller verkauften Fahrzeuge vom Bezugsjahr 1995 bis zum Jahr 2008 um zirka 25 % zu reduzieren. Hierbei werden neben Masnahmen zu Motoroptimierung und Kraftstoffeinsparung vor allem Aspekte zum Leichtbau verfolgt. Dieser Beitrag von Universitat Paderborn, Daimler-Chrysler, Porsche und Volkswagen berichtet uber Ziele und Ergebnisse eines Projekts, finanziert durch das Bundesministerium fur Bildung und Forschung (BMBF), zur Optimierung von Fugesystemen bei Mischbauweisen mit Stahl, Aluminium und Kunststoffen.

Thermally Supported Mechanical Joining of Magnesium Components

In modern car concepts the aspect of lightweight constructions becomes more and more important. Lightweight materials, as aluminum and magnesium, get in the spotlight, thereby. Particularly because of the enormous potential for lightweight constructions industrial interests in magnesium wrought- and casting materials have increased in recent years. Against this background new alternative methods in the range of joining techniques are necessary which consider the specific mechanical-technological properties, such as limited deformability at room temperature and high corrosion-affinity of magnesium. The present article discusses the integration of heating principles in a mechanical joining process of magnesium components without an additional pre-punch operation. In this connection, feasibilities and limits of the considered joining techniques are shown and a concept for thermal support is presented.

Research in Impulse Joining of Self Pierce Riveting

Results are shown in impulse joining of aluminium sheets with self-pierce-riveting. Two institutes are testing impulse-riveting with different setting velocities of the punch – up to 10 m/s by using pneumatic cylinders and about 100 m/s by using a propellant charge. One aim focus consists in riveting without a C-frame against a flat anvil instead of using a C-frame with a contoured die. So accessibility is increased and disadvantages of occurring misalignments are avoidable. The strength properties of the realised joints are tested.

Simulation of no-flow underfill process for flip-chip assembly

The no-flow underfill process and materials were investigated for flip-chip interconnects in active components for the automotive market. The desired mechanical reliability of these components requires an underfill process in order to reinforce the flip-chip interconnects. The conventional underfill process uses epoxy resins that are dispensed after solder bump reflow. Capillary effects force the resin to flow underneath the chip and to fill the gap between chip and chip carrier. The resin is then cured in a heating operation. No-flow underfill materials do not require subsequent reflow, dispense and cure processes. They are applied prior to chip attachment, act as fluxing agent for the solder reflow and form a solid during reflow cycle that reinforces the interconnects. This process provides significant cost savings as it reduces the number of process steps and increases the throughput. However, it requires a well-optimised set of process parameters. The curing procedure of the resin is very different from that of the conventional capillary flow applications. A good understanding of the reaction kinetics of the resin is required in order to get a high assembly yield and reliable interconnects. Motorola recently completed an extensive study of the no-flow underfill process and materials. Results of this study are presented, such as differential scanning calorimeter (DSC) tests, thermal simulations of the cure process under different conditions, assembly experiments and accelerated fatigue tests of flip-chip interconnects.

Ultrasonic Riveting and Hot-Air-Sticking of Fiber-Reinforced Thermoplastics

Mechanical fastening, e.g. screwing or riveting, or thermal joining techniques like ultrasonic riveting or hot-air-sticking, are used to join thermoplastic composites and metallic structures. This paper compares the experimental results of ultrasonic riveting and hot-air sticking of fiber-reinforced polypropylene (PP-GM30, PP-LGF40) and polyamide6 (PA6-GF30) with steel. The influence of glass fiber volume fraction on process stability and the tensile strength of the joint are evaluated from micrographs and X-ray photographs. The influence of the thermoplastic matrix material and the glass fiber length on the wear of the sonotrode during ultrasonic riveting is investigated based on SEM-micrographs and surface roughness measurements.

Influence of the dosing and mixing technology on the property profile of two-component adhesives

Adhesive bonding has become a more and more important joining technique in most branches of industries because of the increasing interest in protecting natural resources and the related trend towards lightweight design. The adhesive bonding technology enables the joining of various, sometimes temperature-sensitive materials, so that multi-material design and thereby, lightweight constructions can be realized. At the same time, the adhesive bonding helps to increase the rigidity of the component (Russo 2011). In industrial practice, not only single-component adhesives are used, but also two-component adhesives whose curing process starts once the components are mixed. In general, the automated conveying, dosing and mixing of the two adhesive components are performed by batchers. The quality of the adhesive bonding can be influenced by the dosing process (Fricke et al. 2009). Within the research project, the boundaries of automated processing of cold curing two-component adhesives were investigated. Therefore, industrially relevant adhesive processing technologies and process parameters were selected. These technologies and parameters were varied and evaluated with regard to their significance for the joining process and adhesive joint as reported by Gräter and Storz (2005) and Stipp (2007).

Predicting production influences on adhesively bonded joints subjected to cyclic load

IntroductionTolerances in the design of adhesive joints were determined and their influence on the mechanical behaviour of adhesively bonded steel joints under quasi-static and under cyclic loads was evaluated in this work.Test preparation and test performanceThe paper focuses on adhesive layer thickness, filling ratios, and surface treatments as the main production tolerances. They were varied at different levels. Four different bondline thicknesses, three different filling ratios, and two different surface treatments were investigated. The influence of tolerances was analysed on single-lap shear joints and peel joints. Toughened epoxy-based adhesives were used. Mechanical properties of bonded steel joints were investigated under static load and under cyclic load.ResultsIn both load cases, adhesive layer thickness has the highest influence on the resulting shear strength. Peel strength decreased with reduced filling ratios.ConclusionsThe influence of adhesive layer thickness on fatigue could be predicted by shift factors. Furthermore, it was possible to describe the influence of production tolerances in an analytical way. This allows an evaluation of fatigue based on quasi-static tests.