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Materials Research Projects at Element Hitchin/MERL
Main Contact - Dr. Rod Martin

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 Focus  
 

Laser Transmission Welding of Composite Structure (LaWocs) Project
by

Peter Hansen
Abstract
 

© Laser Zentrum Hanover
Lightweight carbon and glass fibre reinforced thermoplastics will play an important role in being able to meet the ambitious energy saving and reduced CO2 emissions targets for future aircraft and vehicles. Since adhesive bonding of most thermoplastics cannot be performed without extensive surface preparation, mechanical fastening is usually the obvious choice when using traditional joining techniques. However, a number of new joining techniques like ultrasonic, resistance or induction welding have been investigated formanufacturing reliable high performance components. Laser transmission welding is a technique with great potential for joining reinforced or un-reinforced thermoplastic components, offering the possibility of a flexible, controllable and contact free process with high automation potential. MERL is coordinating the LaWocs EUROSTARS funded project. A project consortium has been assembled comprising five R&D-performing SMEs,all operating within the field of thermoplastic composites and working on the manufacturing of TPC base materials for specific applications, injection moulding, forming of TPC components, induction welding and testing of composites.The SMEs are supported by one large company, representing the global market leader in manufacturing of TPC materials as well as two non-university research institutes, specialized within the fields of fibre technology and laser technology. The other project partners are:

 

 
 


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

 
 
technique are the high flexibility of the process, the low mechanical load, the weldability of complex geometries as well as the precise energy deposition within the process zone and the attainability of high welding velocities.

The main advantage of laser transmission welding in comparison to other welding processes is the precise and controllable energy deposition, which allows for localizing the melting zone to a small region around the contact zone of the plastic parts in combination with a high optical quality of the weld seam. Tensile strengths of the value of the base material can be achieved.

Usually, both joining partners are of the same base material, but different polymers which have similar melting points and sufficient chemical compatibility may be welded as well (e.g. the combination PMMA to ABS) and the La Wocs project is seeking to develop the methods for joining such materials. The NIR absorption by the lower partner is generated by means of adequate colorant technologies, in the simplest case the addition of carbon black. Currently, additives are available which yield plastic parts that are colored or black for the human eye, but transparent for the laser radiation. On the other hand, there are additives white or colored for the human eye, but absorbing for the laser radiation. Thus, even black-to-black or white-to-white combinations can be realized using polymers with absorption characteristics specifically adapted to the laser process.
Figure 1: Principles of laser transmission 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.


 
Partners 
Materials Engineering Research Laboratory Ltd (MERL) provides R&D, mechanical and chemical testing, finite element services & general consultancy services on polymer materials for engineering systems & structures and are recognized internationally as one of the foremost experts in evaluation of durability of composites in the oil & gas industry and aerospace industry. MERL has a client base of several thousand industrial companies worldwide covering all industry sectors and provides testing solutions from concept/feasibility and materials selection to disposal and re-use.

 

Kok & Van Engelen Composite Structures BV (KVE) has evolved to a full service engineering partner in composites, system design and research and technology development. KVE has contributed significantly in making composites available not only in the domain of aerospace, but also for more down to earth applications. Optimal product design and engineering, R&D for efficient manufacturing technologies and systems engineering with integrated composite parts are keywords in the services delivered. The major markets are aerospace, medical, civil, automotive, and machine construction.
 
EPL Composite Solutions Ltd (EPL) specializes in the design, development and commercialization of advanced polymer composite solutions. Spanning the complete development cycle from applied research through product design, process development, material testing and certification, to setting up manufacturing plant, EPL work with OEMs and end-users to develop and demonstrate composite solutions that provide clear technical, economic and environmental benefits over existing structures. EPL will help develop the manufacturing and process conditions to fully evaluate and commercialise the laser welding technology.
 
Tods Aerospace Ltd (TODS) is an AS9100 accredited company that specialises in the design, development and manufacture of Aerospace composite components, structures and assemblies. The company’s main customers include – Augusta Westland, Airbus, GKN Aerospace, BE Aerospace and Contour Premium Aircraft Seating. Tods have extensive engineering capability, the main CAD Design tools are CATIA V4 and V5, Solid Works is also used; FE Analysis is performed using NASTRAN/PATRAN. The company has an excellent record for developing production methods, designing components and manufacturing using – glass, carbon, and Kevlar fibres – thermoplastic and thermoset matrix and novel honeycomb materials.
 
DEVA Kunststoff-Technik GmbH (DEVA) works in the field of plastics processing and tool manufacture with high competence, productivity and reliability, providing continuous innovation and most up-to-date technologies. Products made from conventional (PA6.6, PC, PP, etc) as well as high-temperature plastics (PEEK, Teflon, etc) are manufactured, using mainly injection molding technology. Consequently, DEVA has customers in medical technology, electrical, sanitary engineering and office furniture industries, as well as navigation, white goods and especially aerospace industry.
 
TEN CATE ADVANCED COMPOSITES BV (TENCATE) as a Dutch global operating company is a leader in growing market niches for specialist, functional materials, which primarily relate to the areas of safety and protection and improvement of the performance of the material in the broad sense. TenCate Advanced Composites is a leading supplier of thermoplastic and thermoset solutions for the Aerospace and Industrial industry. The thermoplastic prepregs are known in the industry under the Cetex brand and are found in commercial and military aircraft ranging from structural to interior applications. TenCate provides both thermoplastic prepregs in unitape or fabric form in a variety of high end thermoplastics including PEEK, PEKK, PPS, PEI and Nylon 11.

 

Laser Zentrum Hannover e. V. (LZH) supports applied research in laser technology on a non-profit basis. LZH is involved in national and international R&D projects in the field of laser development and laser applications, technical and scientific consulting to link research and practice, and industry-oriented training of experts for applying and operating laser systems. The close cooperation between production engineers, material scientists, and physicist allows for finding interdisciplinary solutions in all fields of laser applications.
 
Faserinstitut Bremen e.V. (FIBRE) has numerous competences in modeling, manufacturing, processing and testing of single fibers, fiber bundles and textile products as well as in reinforced plastics with carbon, glass or natural fibers in thermoplastic and thermoset matrices. Research work is based on modern laboratories, e.g. equipped with mechanical testing machines for static and dynamic load under variable conditions (temperature, humidity etc). FIBRE is member of the “CFK-Valley” Stade.
 
 
   

 

 

 

 
 

© 2013 Element Hitchin. The registered company address of:
Element Materials Technology Hitchin Limited is 5 Fleet Place, London EC4M 7RD,
Registered in England. Company registration number: 08149114.

Tel: +44(0)1462 427 850
Polymer Engineering, Testing, Inspection, Research and Development, UK