Wheels within wheels - TWI contributions to the automotive industry

TWI Bulletin, May/June 1995

Fred Delany gained a Diplome d'Ingenieur in Mechanical Engineering from Compiègne University, France in 1984. After an MSc at Cranfield Institute of Technology in Materials Science, he joined TWI NDT research department. For the last six years, Fred has been responsible for a number of business development activities at TWI, focusing on the automotive industry. He was recently appointed Manager of Membership Development operations at TWI.

This is the first in a series of occasional articles covering TWI's work for many industry sectors, to update on new technologies, materials and processes. These articles will cover recent developments in each area, based both upon work within industry and feedback from TWI's industry-aligned specific panels and teams.

Business Development Manager responsible for automotive work at TWI, Fred Delany, reviews TWI's most recent contributions to this important industry sector.

The automotive industry forms a very significant part of TWI Membership. All the major American vehicle manufacturers are Industrial Members of EWI and most of the European ones and some of the Japanese car companies are Members of TWI. The automotive industry sector, including specialist vehicle manufacturers and parts suppliers, represents about 14% of TWI membership. If we add the steel, aluminium, plastics, and glass materials suppliers, for whom the automotive sector is of prime importance, we realise that about a quarter of TWI members have a direct interest in the industry. In recognition of the significance of the automotive business, TWI has now organised itself specifically in order to satisfy the demands of this sector, which has been achieved through several initiatives.

The automotive industry team

The automotive industry team is an internal TWI group composed of specialist staff from the technical departments. The team maintains regular contact with the industry to ensure TWI is aware of current trends and joining requirements. It reviews all current automotive projects and proposes new ideas for future work. The nucleus of the automotive team is supplied by the Arc, Laser and Sheet Welding Process Department - a new department created by merging all TWI activities in arc welding, resistance spot welding, seam welding, laser welding and mechanical fastening. Other TWI experts on the team represent activities covering friction processes, surface engineering, adhesives, plastics, non-destructive testing, mechanical testing, manufacturing, training and materials science. The current composition of the automotive industry team is given in Table 1.

Table 1: TW1 Automotive Industry Team

Automotive industry panel

In order to respond to the needs of the automotive industry, regular meetings of the Automotive Industry Panel are held. The panel is an advisory committee where representatives from Industrial Members interested in automotive issues are invited to meet and discuss an area of common interest. Topical issues are debated in an open manner between parts suppliers, material suppliers, automotive manufacturers, TWI staff and invited speakers. The Automotive Industry Panel is proving to be a valuable source of contact and information concerning technical requirements of automotive companies. Three very well-attended panel meetings were held in 1994, topics discussed are listed in Table 2. There is no doubt that successful meetings of the automotive industry panels have now improved TWI's understanding of the car industry, and at the same time has enhanced TWI's credibility within the sector. In addition, they provide an excellent forum for attendees to make valuable additional contacts within the industry.

Table 2: Recent topics discussed at the Automotive Industry Panel

Major automotive projects at TWI

One of the most noticeable trends concerning automotive work at TWI has been the resurgence of interest in aluminium alloys. Automotive designers are now working very hard to reduce the weight of vehicles. Aluminium alloys are being seriously considered as an alternative to coated steels in body panels and components. TWI has accumulated much information concerning the application of traditional welding techniques, such as arc welding and resistance spot welding for aluminium alloys. This information is used to advise Members on the opportunities, and a realistic assessment of the difficulties involved in switching production to the assembly of aluminium alloys.

In addition, considerable effort has been spent in evaluating alternative techniques for the joining of aluminium. These include mechanical fastening (such as press joints and self-piercing rivets) and adhesive bonding. Other new methods are being developed, and one of these, friction stir welding, can offer advantages in terms of high processing speeds, low distortion and an avoidance of problems associated with the effect of surface condition on weldability. These developments are making an impact on the techniques which can be considered for aluminium alloy-based vehicles, covering both spaceframe concepts and the more conventional monocoque design.

The steel industry has reacted to the growing interest in aluminium alloys by promoting welded tailored blanks. This is a method of producing pressed body components which reduces cost and weight by combining dissimilar thicknesses of material and by reducing the number of pressing operations, Fig.1. The use of high strength steels is also being evaluated to reduce material thicknesses whilst maintaining structural performance. There are a number of welding techniques which can be used for production of tailored blanks, TWI is about to start a project on this subject with the Edison Welding Institute. In this work the more established laser and mash seam welding techniques for manufacturing tailored blanks will be compared with less well known electron beam and high frequency butt welding techniques.

The same principles of reduced cost and weight can be considered for tailored blanks using aluminium alloys, where there are additional advantages in maximising the yield of this, a more expensive material. It is difficult to produce resistance mash seam welds in aluminium alloys due to electrode pick up, but some promise has been shown in laser welding of aluminium alloys for tailored blank application, Fig.2. Friction stir and electron beam welding may also be candidate techniques.

Plastic components

TWI has been researching a number of novel energy sources to weld thermoplastics. Spectacular success has been achieved with focused infrared power and microwave sources, thereby opening up new possibilities for designers of automotive components such as fuel tanks, dashboards, or manifolds. Figure 3 shows an existing inlet manifold manufactured by the expensive lost core moulding process. This is an example of a component that may be more economically produced by moulding in two parts then using a process such as microwaves to weld the two parts together. A microwave sensitive consumable is placed at the joint, between components, the parts are held in contact and placed in an industrial microwave oven. Microwave energy melts the consumable to form a high integrity welded joint locally at the interface. Geometrical flexibility of this novel joining process makes it particularly attractive to automotive component designers.

On the application side, TWI has successfully developed laser welding procedures to bond PVC substitutes for car interiors, advised material producers on the weldability of novel grades of nylons and assisted parts manufacturers in developing techniques to manufacture under-the-bonnet plastic components.

Adhesive technology

Conventional plastic welding techniques can only be used on thermoplastic materials but not on thermosets. However, non-weldable plastics such as sheet moulded compounds are adhesively bonded on to lightweight chassis in a number of low volume sports cars, Fig.4. TWI has shown its commitment to being the focus for all joining technologies by merging with the CAT, The Centre for Adhesive Technology. The CAT has more than doubled in size with new laboratories. Most recent automotive interest in adhesives has focused on a novel surface preparation techniques to enhance adhesion, the development of ultrasonic surface wave techniques for non-destructive evaluation of adhesive bonds, and a comparative study of industrial quality control procedures for adhesive technology.

Mechanical fastener

Mechanical fastening by press joints (clinching) or self-piercing riveting has also been studied at TWI to compare the static and dynamic joint properties with resistance spot welds in steel, aluminium and aluminium/plastic materials, Fig.5. Further work is planned on hybrid joints using adhesives and fasteners. TWI's Automotive Industry Team believes that the industry will need rapid techniques for joining aluminium to steel and predicts a strong growth in the use of mechanical fasteners in the automotive and other high volume production industries.

Structural integrity of automotive components

A 10m drop weight impact testing facility has been used at TWI to assess the impact resistance of safety critical components, such as side beams and steering columns. Impacts have been simulated at up to 50km per hour. The Structural Integrity Department has also been asked to check the fatigue resistance of suspension sub-assemblies on behalf of component suppliers, as well as develop testing procedures to validate the durability and static strength of various automotive parts, Fig.6. Of more fundamental significance, fatigue specialists have improved the understanding of the behaviour of thin-walled structural joints subjected to complex loading. This work is particularly relevant to design of axle casings, simultaneously submitted to bending and torsion stresses when operating in service.

Understanding the distribution and intensity of stresses within a component is also important to designers of special-purpose vehicles for agricultural, mining or defence applications. Using strain gauging, TWI have been able to confirm predictions and approve the design of a number of such vehicles, Fig.7. One project now being launched by the Structural Integrity Department is looking at fatigue performance of welds in areas of complex stress distribution and the project has generated interest among engine and transmission component designers.

Surfacing

The potential of surface engineering, whereby the properties of bulk materials are significantly enhanced by an engineering surface coating, has been recognised by automotive designers. In particular, the advantages of thermal spraying have been evaluated by TWI for a number of component manufacturers anxious to improve the performance of their products, particularly with regard to wear resistance.

Injection nozzles, valve seats, bearings, crankshafts and piston rings are just a few examples of components sprayed at TWI in 1994. In particular, the high velocity oxyfuel (HVOF) thermal spraying technique offers tremendous opportunities to deposit high quality engineering coatings with optimum wear, corrosion or thermal barrier properties on to lightweight bulk material. This presents engine and transmission component designers with unique opportunities for fuel efficiency improvements and weight savings.

One significant achievement of TWI's Core Research Programme in 1994 has been to deposit thermal barrier coatings, based on yttria stabilised zirconia (YSZ), using the HVOF thermal spraying process, Fig.8. Until now, HVOF spraying of YSZ had not been considered possible because of its very high melting point. It is expected that the high quality HVOF deposit will improve substrate resistance to thermal shock, oxidation and corrosion, which are major problems in high temperature engine components, e.g. piston crowns.

Structural changes in automotive R&D

Within the automotive industry, a transition to shift responsibility for research and development towards supply companies is occurring and it has been observed that the most dynamic and ambitious parts suppliers are doing their own research and becoming more technologically self-sufficient. For TWI, this means developing a network of contacts with tier 1, tier 2 and tier 3 suppliers rather than relying on the original equipment manufacturers (OEMs) for funding. TWI is now improving its links with small companies in a number of ways including a large DTI funded technology transfer programme designed to encourage UK small to medium enterprises (SMEs) to use best practice in materials joining technologies. TWI's manufacturing consultancy subsidiary, TMCG, is already carrying out a pilot programme in collaboration with the Society of Motor Manufacturers and Traders (SMMT) intended to improve communications between automotive parts suppliers and OEMs.

As far as European collaborative research is concerned TWI contributes to several Framework IV submissions ( eg BRITE, CRAFT, ESPRIT, etc) of direct relevance to the automotive industry. Two programmes involve the use of surface engineering to extend the life of automotive tooling, and mechanical fastening of dissimilar automotive body materials. In addition, TWI maintains a multi-million pound Core Research Programme, funded by member subscriptions. This has a significant automotive technology content, particularly in laser processing, resistance welding, surfacing, adhesive bonding, mechanical fastening, and the use of robots. In addition, complementary programmes are being carried out at EWI. A significant component of their work is involved with increasing the understanding of electrode wear mechanisms during resistance welding zinc coated steels and to develop a resistance spot welding database for such materials.

Conclusion

TWI is now better structured to cater for the interests of the automotive industry, which has resulted in a significant increase in interface with Industrial Members in the automotive sector. This involves all aspects of materials joining technology, surfacing, non-destructive testing, fatigue and impact testing, training and manufacturing consultancy. The automotive industry panel is a forum for discussion of critical issues affecting the automotive industry, and enhances TWI's ability to respond effectively to the requirements of automotive designers on a short-term consultancy basis. As far as longer term initiatives are concerned, TWI is maintaining close links with the European Commission and industry representatives in Brussels within the Framework IV initiative; organising joint industry-funded projects with the Edison Welding Institute and heavily investing in a multi-million pound Core Research Programme with a significant automotive content.

Further information on the topics mentioned in this article can be obtained by contacting any member of the TWI Automotive Industry Team.