Element Hitchin/MERL aims to be active in new and emerging technologies by developing new knowledge, know-how and data for industrial exploitation. Element Hitchin/MERL provides a multi-disciplinary approach combining expertise in chemistry, physics and engineering. Approximately two thirds of staff have degrees or higher degrees. Research is funded in several ways.

Click on the titles below to see recent and ongoing materials research work at Element Hitchin/MERL.

European Commission part funded projects
MERL has extensive experience of projects funded by the European Commission and participated in project consortia under the fourth (FP4), fifth (FP5) and sixth (FP6) framework programmes. In addition MERL is participating in various Technology Platforms for the formation of the seventh programme. Under FP5, MERL was co-ordinator and technical lead in three RTD projects and Work Package leaders in two Thematic Networks. Under FP6 MERL is active in several projects as partners in the transport sector, materials sector and aerospace sector - click here to see current project involvement. MERL is open to approaches from other organisations for partnering opportunities. For more information contact Dr Rod Martin.

UK Government funded projects
MERL conducts a range of UK government funded projects either as the project lead or as a partner or subcontractor. Typically projects are funded via the Technology Strategy Board (TSB), The Department for Innovation, Universities and Skills' Grant for Research and Development, and the Waste and Resources Action Programme (WRAP). For further information on funding opportunites contact Dr Rod Martin.

Consortium projects or joint industry project (JIP)
Consortium projects are fully funded by a group of organisations on a cost sharing basis. Projects usually have a strong industrial focus and international participation. Typically projects are 2 - 3 years duration and in some cases are continued into a second phase. Participants in consortium projects monitor and guide the work programmes via a project steering committee. Benefits of participation include cost effectiveness and direct influence on the work programme. MERL is proactive in developing new projects; if you have a particular research need that you would like to discuss contact Dr Rod Martin

Internal research projects
MERL funds internal research to develop new know-how and technology for exploitation. Examples include low temperature cure (LTC) rubber which has US and EU patents, impact protective coatings for composites and ED resistant materials. MERL also works with Universities on student projects at undergraduate and post graduate level. For further information please contact Dr Rod Martin.

Project Introduction
Continuous carbon and glass fibre reinforced composite materials (CFRP, GFRP) are recognized as having significant weight saving potential and are therefore important materials for many applications. There are clear examples in the field of mobility including aerospace, automotive, marine and rail sectors. However the need for components based on fibre reinforced composites is particularly increasing within the field of energy, e.g. wind and tidal turbines, heavy-duty pipelines for off-shore applications and electronics, as well as within the field of sports and leisure.

In particular CFRP is characterized by high stiffness and strength, excellent corrosion resistance as well as good resistance to static and dynamic loads. An outstanding property of CFRP is the potential of significant weight reduction compared to metallic materials, e.g. up to 30% for aluminium. Thus CFRP is an important material to contribute significantly to energy and CO2 savings by use in advanced light weight structures.

Although thermoset polymers mainly based on epoxy resins are the predominant matrix material, reinforced composites based on thermoplastic polymer matrices (TPC) are of increasing interest due to their superior formability and recyclability as well as the added benefit of material consolidation in just one process step. Thermoplastics offer several other benefits such as uncritical and unlimited storage times, a better impact tolerance compared to thermoset matrices, a good ultimate strain performance, reduced crack propagation, excellent chemical resistance and rapid forming processes. Another significant advantage over thermoset based composites is their weldability.

A current barrier for the comprehensive use of TPC structures is the lack of economic, quick and reliable component manufacturing processes. To overcome this deficit, fully-automated process chains for the manufacturing and assembly of thermoplastic composites have to be developed in order to achieve production rates and cycle times required by automotive and aircraft industry as well as the civil engineering sector. Integrated process cells can be adapted to specific material requirements and to new process elements including laser based techniques for cutting and in particular joining applications. Different techniques like resistance welding, ultrasonic welding, vibration welding or induction welding are used, revealing respective advantages and disadvantages.

It is the aim of the LaWocs project to develop a novel joining technique for TPC parts based on the laser transmission welding technology (LTW). Currently LTW is an industrially established welding technique for unreinforced and partially reinforced thermoplastics offering the possibility of flexible, controllable and contact-free processing with a high automation potential.Within the framework of the project this technology will be transferred to the specific requirements of TPC materials. Besides the manufacturing of pure TPC components, combinations of reinforced and unreinforced or partially reinforced materials will be evaluated.

In order to achieve these goals, a project working plan has been arranged consisting of the following main activities:
- Development of adapted TPC base materials and manufacturing of real components
- Development of laser welding process for TPC materials and welding of real parts
- Testing of novel TPC structures and real parts according to industrial specifications
- Exploitation of project results.

Besides the aerospace sector, the products and services of the SMEs are established on other markets including wind and tidal turbines, Oil and Gas pipelines and electronics. The availability of this new welding technique will represent a unique feature, which will strengthen the position of the SMEs and open new markets for these materials and manufacturing technologies.

Laser Welding Technology
Laser transmission welding of thermoplastics is increasingly gaining importance as an alternative welding process compared to conventional techniques, such as heated tool welding, friction welding or ultrasonic welding. The advantages of a laser based welding

Four variants of laser transmission welding are used:
• Contour
• Simultaneous
• quasi-simultaneous
• mask welding.

In contour welding, the laser beam is guided along the joining contour. With this technique, either the laser beam or the materials to be joined have to be moved. With the use of robots it is possible to generate two-dimensional and three-dimensional contours. With contour welding, very stringent tolerance requirements for the surface and planarity of the parts to be welded have to be set. One important factor determining the success of the process is the bridging of gaps.

In simultaneous welding, diode lasers in a welding head are arranged individually in such a way that they fit to the joining contour. Both materials to be joined are exposed simultaneously so that they melt and are welded to each other. No relative movement between laser beam and the parts to be welded is necessary. A relatively new variant of the simultaneous welding process, presented by Leister Process Technologies, Sarnen/Switzerland, is the so-called radial welding used to join cylindrical components. Here, a mirror deflects a circular laser beam in such way that the outer symmetrical surface of the cylindrical component is irradiated radially to generate a circumferential weld seam.

In quasi-simultaneous welding the laser beam is repeatedly guided along the joining contour by scanning mirrors with very high feed rates (up to 10 m/s). Due to the high speed, the whole joining area is heated and plasticized almost simultaneously. This method is very flexible, but slower than the simultaneous method.

When mask welding is used, a mask is placed between the laser source and the parts to be welded. The laser beam with linear profile is guided across the mask so that only those areas are welded where the mask is left open. With this method, very fine welding seams with a width of less than 100 µm can be realized.

Investigations have shown that one polymer type behaves differently regarding laser weldability depending on the producer, even if the colouring is comparable and a constant thickness is used. Possible reasons for varying optical material properties are different parameters used during the production process of the material, the varying content of other filling materials and differences in size and distribution of the particles of added colouring agents, as well as different modifications of the original granulated material used for the injection moulding of the samples. The granulated material can be coloured on delivery by adding colour pigments, or the colour pigments are added to the natural material when injection-moulded. Due to this wide spectrum of materials, selection of polymer types, suitable for a specific welding process, and collection of relevant data for successful process implementation is challenging.

Therefore, the determination of main factors influencing the weldability of different thermoplastic materials (absorbing and transparent), taking into account properties like colour and filling content, has become a focus of interest. An initial step in the process to determine the weldability of materials is to characterize the optical properties of partially transparent materials and to perform transmittance measurements at different wavelengths in the near infrared spectral range.

Practical welding experiments showed that not all laser-transparent samples are suited for laser beam welding. Thus, conventionally measured transmittance values do not provide enough information about the weldability, since they do not contain any details about thermal characteristics or about losses due to reflection at the polymer surface. Furthermore, the determination of transmittance values is difficult in the case of semi-crystalline or filled polymers due to their light scattering ability which is dependent on the degree of crystallization or the filler content as well as the size and shape of the crystallites or the filler particles. Due to limitations of the instrumentation, conventionally measured transmittance values are often too small.

Therefore, a thermographic system for an easy to handle, fast and non-destructive evaluation of thermal and optical properties of materials regarding laser beam weldability was developed.

Expected Project Results
The results expected at the end of the project can be divided into two main categories. Firstly, new materials will be available, which are specifically designed to the requirements for LTW as well as for the required mechanical properties. Secondly, a joining process will be available, providing all necessary process knowledge regarding the laser transmission welding of different TPC material combinations.

The project includes the development of adapted, hybrid/graded structures including the complete process knowledge with respect to fibre and matrix handling and the integration of dissimilar reinforcements. Besides the applicability of LTW, this knowledge will be useful also for the fabrication of additional structures with the objective of manufacturing light-weight products.

At the end of the project, the novel joining technology will be demonstrated by preparation of a laser transmission welding process suitable for the fabrication of at least 3 pilot parts, arising from the fields of supports and retainers, structural elements based on high-performance polymers as well as endless-fibre reinforced composites based on lower graded polymers.

It is expected that for at least one of the investigated pilot parts, a minimum weight reduction of 30% compared to mechanical joining techniques will be realized. The corresponding processing time shall be reduced by 25%.

The project results will be useful for the end-users, such as the aerospace manufacturers, automotive OEMs, marine and rail companies. The “real” drivers of innovation in these areas, however, are usually their suppliers. Therefore, the companies within the project – many of which are already suppliers to these end users – will use the methods and materials developed within the project to produce innovative and light-weight components as a demonstration of the advantages of these technologies.

New markets and the respective end users will be approached by the SME partners, such as electronics/computers (housings, screenings), car/railway/yacht interiors, furniture industry (design elements, covers, functional elements), white goods/household appliances (design elements, stiffeners). This will be facilitated by the high throughput of these fast, flexible and automated production processes which enables this technology to be applied to lower cost markets.