Wheeling to the millennium - TWI and the automotive industry

Richard Freeman joined TWI from industry in 1996. He works for the Materials Department in a Business Development role, with particular emphasis on the development of the aerospace and automotive sectors. He is chairman of the TWI Automotive Industry Team.

The automotive industry sector, including the vehicle manufacturers and component suppliers, accounts for approximately 10% of TWI industrial membership. Richard Freeman reviews TWI's ever increasing role in supporting the automotive industry.

The automotive industry sector forms a significant part of TWI's industrial membership base. Most of the European and Japanese car companies are Members of TWI, while all of the American car manufacturers are Members of EWI. Approximately 10% of TWI membership is associated with companies operating in this industry sector as OEMs (original equipment manufacturers) or Tier suppliers ( Table 1 ). The Automotive Industry Team and Panel help TWI to focus sharply on the needs of the industry, in order that a continuously developing range of services can be offered.

The automotive industry team and panel

• Joining and cutting processes: arc, laser and electron beam welding; resistance spot, projection and seam welding; MIAB and friction welding; brazing; soldering; adhesive bonding; weldbonding and mechanical fastening (self-piercing riveting and clinching).
• Materials and weldability: Steels (coated and uncoated); engineering steels; low cost stainless steels; aluminium and non-ferrous alloys; intermetallics; engineering plastics; ceramics and composites.
• Surface engineering: plasma and HVOF spraying; sol-gel coatings; friction and laser surfacing and surface preparation.
• Structural performance: stress and fatigue measurement and analysis; finite element and failure analysis; mechanical and corrosion testing; wear testing; dropweight testing and structural design.
• Quality and process control: in-process monitoring; instrumentation; NDT statistical process control; process improvement techniques and quality standards.
• Design and manufacturing engineering and support: providing solutions and guidance for supply chain needs; simultaneous engineering and design-for-manufacture; factory-layout; project management; robots and automation.
• Training: through scheduled and specialist courses at TWI's training centres and on-site.
• Certification: qualifications for welding specialists, technologists and engineers to EWF; welding inspectors to CSWIP and NDT operators to PCN and ASNT.

The Panel meets twice each year to respond to the needs of the automotive industry. It consists of representatives of Industrial Member companies, who are invited to meet and discuss issues relating to their industry. It is proving to be an extremely valuable forum for discussion, covering many technical requirements in the short, medium and long term planning strategies of many companies operating in this industry sector. A similar event takes place at the Edison Welding Institute for the North American Industrial Members. Some recent topics discussed at TWI Panel Meetings are shown in Table 2. The mechanical fastening and lightweight vehicle seminars attracted in excess of 200 people in total. The next Panel meeting, scheduled for September 1999, will focus on 'Improved reliability and efficiency through surface engineering'.

Table 2: Recent presentations at the Automotive Industry Panel

Applicable technologies

Reducing vehicle weight

During this decade the automotive industry has seen unprecedented attempts to cut weight by the use of different materials. The ULSAB (ultra lightweight steel auto body) project completed a four year $22 million international collaborative project in 1998. With the innovative use of design, 'high-strength' steel and advanced joining and manufacturing technologies, the consortium produced a 203kg BIW (body-in-white) structure, a 25% saving compared to benchmark vehicles in the same class. Two further projects, concentrating on weight saving body closures and suspension systems (ULSAC and ULSAS), will be reporting results in the very near future. The aluminium industry has been fighting back, however, and work within the US consortia PNGV (Partnership for New Generation Vehicles), USCAR (US Co-operative Automotive Research) and sustained research in Europe, has led to the increased use of aluminium for monocoques, space frames, and individual closure panels for a variety of volume and niche vehicles ( Figs 1 and 2).

With the use of steel hydroformed tubes and aluminium extrusions, one of the major concerns in vehicle assembly is the need to demonstrate robust industrially accepted joining processes that can operate from one side.

TWI recently launched a Group Sponsored Project (GSP) to optimise three single sided joining techniques (MIG/MAG welding including twin wire processes, single sided resistance welding/weldbonding and laser welding) for vehicle body assembly.

With the increased use of low density materials such as magnesium alloys, plastics and composites, the need for proven joining technologies has never been more apparent. It is amply demonstrated in the manufacture of this seat pan, in more traditional steel and aluminium material ( Fig.3), which incorporates self piercing rivets, spin rivets, MAG welding and resistance welding in its assembly.

Some major automotive projects will be referenced throughout this article, but care will be exercised to ensure that confidentiality is maintained.

Laser welding

Laser welding is attractive for mass production in the automotive industry. It is fast and creates little distortion. TWI has generated a considerable amount of data in recent years in developing the parameters for CO ₂ laser welding of steel tailored blanks ( Fig.4), via its Core Research Programme (CRP) and a joint GSP with EWI. The advent of commercial high power Nd:YAG laser sources, with improved fibre optic delivery has led to more flexibility, and increased productivity, in the tailored welded blanks industry.

TWI has also been very active in the laser welding of aluminium alloy tailored blanks, skins and structural panels for cars and trucks, for a number of Industrial Member companies. A CRP project on the laser welding of magnesium alloys was also recently completed, with successful CO ₂ and Nd:YAG welds made in the die cast AM50 and AM60 alloys, which are finding applications in many automotive components.

Resistance spot welding

Despite the challenge of alternative joining methodologies, and the use of tailored welded blanks and hydroformed tubes, resistance spot welding is still an essential part of steel vehicle assembly. TWI has been very active in the development of best practice for spot welding and has published a number of CRP reports on process and quality control. A recent CRP report also includes a troubleshooting guide. Member companies have also requested work concerned with the spot welding of sound deadened sandwich steel structures recently.

Another example of spot welding's continued use is in the recent LIVEMAN (lightweight vehicle manufacture) collaborative programme, which relates to the manufacture of a plenum chamber ( Fig.5). The component consists of four panels of both uncoated and zinc coated steel between 0.75-0.80mm in gauge, which is spot welded along the four flanges at an approximate weld pitch of 40mm. The objective of the work was to examine the use of adhesive bonding in combination with resistance spot welding (weldbonding), self-piercing rivets and clinching. Further details of the LIVEMAN project will be given later in this article.

TWI's expertise is often sought by automotive companies to train spotwelding equipment operators. Courses are customised to the client's needs and conducted either at TWI or on a client's premises.

Mechanical fastening

One of the most frequently used joining technologies in this industrial sector is mechanical fastening. The self-piercing riveting and press joining (clinching) techniques provide fast, economical joining methods for sheet materials. TWI has considerable experience in the joining of zinc coated carbon steel, 5000 and 6000 series aluminium alloys and sandwich materials (such as aluminium/polypropylene). Recent CRP projects have been run to investigate dissimilar material joints, including aluminium alloy to varying thicknesses of coated and uncoated low carbon steel, using the riveting and clinching methods. A GSP is currently underway, with seven Industrial Member companies, to investigate the mechanical fastening behaviour and mechanical properties of sheet aluminium to die cast magnesium alloy joints.

TWI is also programme managing a CRAFT project, with six other partners, concerned with self-piercing riveting and hybrid joining technologies (SPRYTE). The objectives are to design and develop high volume production hardware, evaluate process monitoring and control techniques, generate process capability data for high volume mass production and prepare design and application guidelines. It is an important project that will aim to address the issues that are preventing widespread use of this technology in high volume manufacturing industries.

Within the LIVEMAN project, considerable effort has been directed towards the assessment of static mechanical performance of mechanical fastened joints (with and without adhesives). The use of thinner gauge, high strength steels for BIW structures, has led to the need for greater joint stiffness to improve or maintain the torsional stiffness of the vehicle. Figure 5 refers to a component using mechanical fastening technology, and the work in this project has concentrated on resistance welding, weldbonding, clinching, clinchbonding, self-piercing riveting, riv-bonding and adhesive bonding.

Arc welding

Adhesive bonding

Adhesives have been used in the industry for many years ( Fig.6), but with the drive to reduce weight they are playing a major part in increasing the stiffness of selected joints. TWI has carried out a considerable amount of work in evaluating the mechanical performance of hybrid joints. A CRP project, in the area of fatigue performance for adhesively bonded joints in steel and aluminium, is also being conducted. This follows on from the fracture mechanics based approach used in a previous CRP. Another very important project is concerned with the use of environmentally acceptable surface pre-treatments for aluminium alloys, particularly prior to adhesive bonding.

The Adhesives Group has also been involved in the development of a user friendly programme for the finite element analysis of adhesive joints. The package, known as Gluemaker is available to Industrial Member companies to allow them to validate the use of a wide range of adhesives for their particular applications. The variables contained in Gluemaker include: adhesive modulus, cure schedule, bondline thickness, modulus of materials, temperature of operation, joint dimensions, fillet shape and loading profile. This FE programme, in addition to the information gained in the recent TWI led EUREKA project AIMS (adhesives in marine structures), will be used in their recently launched GSP 'Basic adhesive classification in engineering'. One of the target sectors for this project is the transport industry, in addition to the offshore, marine and building and construction sectors.

Friction welding

Joining technologies for non-metallic materials

TWI has been involved in the use of ceramics for automotive applications for approximately 25 years, but is now in a far stronger position following the opening of the Ceramics Centre in 1998. The brazing of silicon nitride to mild steel using a number of interlayers to accommodate residual stress for a turbocharger wheel, and the brazing of ceramic faced tappets are examples of single client projects that have been carried out for Tier 1 automotive suppliers. The development of sol gel technology is also attracting considerable interest, and the anti-scratch coatings were recently applied to train carriage windows as an anti-vandalism initiative ( Fig.7). TWI successfully applied a glass coating system on a horizontal surface, which filled scratches of 0.5mm wide and 50 microns deep. This was the first time this had been attempted. The work for Angel Train Contracts in the UK will continue to refine the coating so that it can be applied vertically and ultimately be used on windows in-situ to save time and money. There has been considerable interest by vehicle manufacturers in the use of these transparent coatings for windscreens, visors and light clusters.

Plastics have been used in under bonnet applications for years, and many low volume niche cars are following the example of the Formula 1 industry in using such materials as the major part of the monocoque ( Fig.8). TWI has been developing joining methods for the materials commonly used in the industry. A GSP is underway, with Cambridge University, to predict the strength of thermoplastic welds and weldlines, and CRP funds have been committed to a project to develop further the transmission laser welding of plastics.

Microjoining technologies

All of the electrical and electronic parts in a car use microjoining techniques. The myriad of small joints, that enable emission control, performance monitoring ( Fig.9) and the deployment of safety equipment to be carried out effectively, use techniques that can be found on a larger scale in the assembly of BIW structures. These processes include: soldering, resistance, ultrasonic and laser welding and adhesive bonding and are housed within TWI's Microtechnology Centre from which a large number of consultative projects, and a wide range of training courses are administered.

Surfacing

Non-destructive evaluation

Despite the high volume nature of the industry, the considerable number of joints made in a multitude of components have to be checked at points during the manufacturing cycle ( Fig.10). TWI is developing NDE methods for surface coatings, with particular emphasis being placed on the emerging thermographic techniques. Ultrasonic inspection of resistance spot welds is an area where TWI has been active in the past, although previous work suggested that probe design and flaw detection needed to be improved in order to rely upon the technique in production. TWI is therefore aiming to move into the area of neural networks in the near future, in order to address these concerns.

Despite the high volume nature of the industry, the considerable number of joints made in a multitude of components have to be checked at points during the manufacturing cycle ( Fig.10). TWI is developing NDE methods for surface coatings, with particular emphasis being placed on the emerging thermographic techniques. Ultrasonic inspection of resistance spot welds is an area where TWI has been active in the past, although previous work suggested that probe design and flaw detection needed to be improved in order to rely upon the technique in production. TWI is therefore aiming to move into the area of neural networks in the near future, in order to address these concerns.

Metallurgical and analytical support

With a well equipped laboratory, TWI has carried out a multitude of single client projects for Tier 1 supply companies. They range from a wide variety of failure investigations, the provision of welding metallurgy knowledge, to the development of long life spark plugs for mass production high performance engines. The department is also leading a GSP concerned with the joining of die cast magnesium alloys to aluminium sheet material. The one year project, sponsored by seven companies, is concentrating on self-piercing riveting and clinching techniques to make the joints, which will be mechanically tested to determine tensile and shear performance.

TWI is also active in the measurement of welding fume, and recently produced a Welding Fume Tutor in CD ROM format. It is a multimedia training course aimed at educating people in the risks to health that could arise from inhalation of welding fume, and the actions required to control exposure. The tutor aid recently won 2 ^nd prize in the multimedia competition at the 15th World Congress on Occupational Health & Safety held in Brazil. It also won 1 ^st prize in a similar European event.

Large single client projects have been carried out for a number of Industrial Members, concerned with the measurement of fume using a variety of analytical techniques and exposure limits for welding fume. Following a number of enquiries from member companies regarding risk assessment when resistance spot welding through adhesives, sealants, coated materials and oily plates ( Fig.11), a GSP has been launched to tackle the problem. It is likely that the project will be backed by the Health & Safety Executive.

JoinIT ^TM - computer-based technology transfer

Projects

Reference has already been made to a number of projects carried out by TWI on behalf of the automotive industry sector. A more detailed list of the GSPs, Collaborative Projects, and mention of the CRP now follows. For further details on any of the Group Sponsored or Collaborative projects listed, contact Keith Johnson (Associate Director - Contract R&D) or the author.

Group Sponsored Projects

The current GSPs relevant to the industry include:

• Application of friction stir welding to automotive lightweight structures
• The joining of magnesium alloys to dissimilar materials for automotive applications
• Mechanical and corrosion properties of friction stir welds in aluminium alloys
• Thermoplastics welding: analysis of strength developments in welds and weldlines
• Friction stir welding for transport structures

Other GSPs currently being formed include:

• Optimisation of single sided welding techniques for vehicle body assembly
• Fume emissions from spot welding through sealants, adhesives, oils and coated materials
• Basic adhesive classification in engineering
• Improvement to contact tip life and arc stability in continuous wire mechanised and robotic arc welding
• Fatigue of welds in areas of complex stress distribution

Collaborative Projects

TWI is currently involved in the following automotive related collaborative projects:

• LIVEMAN - TWI is programme managing, and contributing to a number of the joining work packages in, the EPSRC funded three year project which has the following partners: Air Products, British Steel, Cambridge University, Cranfield University, ESAB, Ford Motor Company, GKN Sankey, Hawtal Whiting, Henrob, Jaguar Cars, Krupp Camford, Liverpool University, Oerlikon, Oxford Brookes University and Permabond.
• SPRYTE - TWI is programme manager of this CRAFT project, under the Framework IV banner, with six other industrial and academic partners.
• High Power Nd:YAG laser welding - this project, jointly funded by industrial partners and the UK Department of Trade and Industry, currently has over 20 sponsors.
• Best practice for level 1 automotive suppliers Phase II - this DTI sponsored project has recently been completed.

TWI is also involved in the formation of a number of collaborative projects, some of which are related to the automotive industry, and will be closely monitoring the call for proposals for the Framework V programme (1998-2002).

Core Research Programme

TWI maintains a multi-million pound CRP and, in the current suite of projects (1998-2000), almost half of the 55 projects are relevant to the industry sector. A list of the current projects and completed research reports from previous CRP programmes is available from the Membership Department.

Conclusion

Table 1: Current Industrial Member companies in the automotive industry sector