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Welding of Thermoplastic Composites

Project Code: 22429


The objectives of the project are to develop one or more innovative welding/joining processes for thermoplastic composites that offer Industrial Members solutions to the problems encountered as thermoplastic composites continue to grow and find new applications. Innovation includes the progress beyond state-of-the-art and will ideally incorporate advances in areas such as process control (quality), speed, cost, and industrialisation etc. in a range of applications.

The project will concentrate on induction and ultrasonic welding as these are two of the promising techniques for industrial applications. Induction will attempt to improve the control of the process by adding non-metallic subsector materials at the interface. These could include increased electrical conductivity materials such as carbon nanotubes or graphene. Ultrasonic welding will concentrate of focusing the energy at the weld interface and preventing it dissipating along the fibres and away from the weld. Both these techniques must be capable of forming, and demonstrating, good quality welds, and therefore inspection of the joints will play a key part in the project. Current NDT techniques will be evaluated to determine the best (cost, reliability, speed and automation-ready) technique for any welding process developed. The performance of the welds must also be determined before the techniques can be used in industrial applications and therefore mechanical testing of the joints will be carried out. Simple single lap shear tests (ASTM D1002-10) will be determined as this test is most commonly used to compare joint performance both in welded and adhesively bonded joints. In addition, tests such as DCB, the T-pull off or inverted four point bend will be used to evaluate the through thickness performance of the joints. Simulation of the joining process is also important step in the design process and this project will attempt to demonstrate the feasibility of modelling the welding processes as a tool to predict the effect of key processing parameters.

The objectives of the project can therefore be summarised as:

  • Develop improvements in the control of induction and ultrasonic welding techniques.
  • Validate the performance of the techniques through measurement of lap shear strength.
  • Further qualify of the joint performance with through-thickness testing.
  • Demonstration of a reliable NDT technique to confirm weld quality.
  • Demonstrate feasibility of modelling welding process.

Project Outline

The project will build on the innovative welding process developed previously, developing innovative methods for joining thermoplastic composites (to themselves or to other materials). The project will also include other innovations in fusion bonding technology such as ultrasonic and linear friction. Concepts will also explore joining thermoplastic composites to other materials such as metals using techniques that may include variations of Comeld and filament winding.

Current state-of-the-art welding technology for thermoplastic  composites is limited to a few examples of resistive implant and induction welding processes. No single technique has shown to be viable on an industrial scale. Limitations are due to variability of results, cost of equipment, tooling, and the difficulties on evaluating and ensuring the quality of the joints.

This project will continue the development of the induction welding technique that has been invented at TWI. This technique promises to be the first viable process that offers improved control and therefore better quality joints. New concepts will concentrate on innovations in focused ultrasonic welding; a solution to the problem of energy dissipation along the fibres in the composite parts away from the weld interface. Further innovations will include techniques to mix fibres across the interface in a linear friction welding process; a technique that may provide a rapid method of joining flat composite parts with improved joint strength. Comeld has been of interest as a composite-to-metal joining technique for a number of years now, but little has been done with thermoplastic composites, where a precision filament winding process may allow metal fittings to be applied to thermoplastic composite pipes in the oil and gas industry.

Relevant Industry Sectors

Technical and Economic Benefits

There will always be a need to join parts together, and with the growth expected in thermoplastic composites industry will continue to demand innovation in joining technology. Aerospace industry is currently on the verge of ramping up their use of thermoplastic composites in order to meet the expected increase in production volume of single aisle aircraft. Automotive industry is also looking to thermoplastic composites to meet light-weighting requirements as they strive to meet ever increasing fuel efficiency targets. All these applications involve significant operations that require high performance joining at high speed and low cost. Welding techniques are available, but what is lacking is improved quality welding techniques.

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