JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012 - 54

welding

Optimizing ultrasonic welding of carbon-fibre-reinforced polyetherimide
Cost-effective processing of thermoplastic composites has made them increasingly relevant for use in structural and high-performance applications. Welding contributes to reducing manufacturing costs and overcomes some of the drawbacks of traditional composite joining techniques. In ultrasonic welding, heat is generated through surface and intermolecular friction caused by ultrasonic vibration transferred through the material. Several parameters are involved in the welding process, affecting energy, time, power consumption and the quality of the weld. An optimization was carried out for melting time, welding power and single-lap shear strength of the welds. Design of experiments (DoE) was used in order to reduce the number of tests needed for the optimization. An initial study was carried out, defining the tendencies of these responses as well as plausible parameter limits for the designed experiment.
is that they can be melted and consolidated again, reducing the manufacturing times associated to processes such as press forming and welding. Joining techniques are being developed, increasing the cost-effectiveness in manufacturing, and avoiding traditional assembly methods which cause stress concentration and increase weight, such as mechanical fastening (riveting, clamping, bolting) [1]. Ultrasonic welding is based on heat generated through surface and intermolecular friction caused by high-frequency and low-amplitude mechanical vibrations applied to the parts to be welded [2]. In order to concentrate the energy dissipation at the welding interface, energy directors usually made of neat matrix resin are located between the two parts to be joined. The higher cyclic deformation of the energy directors makes them heat up faster than the composite material. The main input parameters for the ultrasonic welding process are the welding pressure, the amplitude and frequency of the vibration and the time during which it is applied. Likewise, the time during which the weld is allowed to cool down under pressure is also a key parameter to ensure a good weld quality [3]. Ultrasonic welding has long been spotted as one of the most promising techniques for joining advanced thermoplastic composites [4]. However, very little research work on this technique is yet available in the open literature. The study presented in this paper has the main aim of gaining further insight into the effect of processing parameters on the quality of CF/PEI ultrasonic welds as well as on the welding process itself. Due to the considerable number of processing parameters, design of experiments (DoE) was used. It reduces to a minimum the number of experiments needed according to the accuracy required, by choosing the inputs to be tested systematically. With a small-size experiment, DoE makes it possible to find the factors that most influence the responses and the interactions among them, noise performance and optimal conditions [5]. The results obtained from the designed experiment were used to find an optimized set of processing parameters for CF/PEI ultrasonic welds.

By
M. Barroso Romero, I. Fernández-Villegas, H.E.N. Bersee DPCS, TU Delft/Faculty of Aerospace Engineering

he specific physical properties of polymeric composites make their use increasingly interesting due to the wide list of advantages that thermoplastic and thermoset polymers offer compared to metals in the same applications. Thermoplastic polymers, as compared to thermosets, offer many advantages. One of the most appreciated characteristics of thermoplastics

Experimental procedure
The material considered in this study was 5-harness satin fabric CF/PEI, provided by Ten Cate Advanced Composites, The Netherlands. PEI is an amorphous thermoplastic polymer with a glass transition temperature of 216ºC. The laminates were manufactured out of 6 layers of prepreg material and consolidated in a

54 jec composites magazine / No70 January - February 2012

JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012