Original Equipment Manufacturers (OEMs) in the automotive industry have set out an objective to significantly reduce the weight of vehicle structures, and composite materials are central to this process of weight reduction. Despite recent material processing advances, uptake of composites in the medium to high volume automotive manufacturing sector has been restricted by the challenge of joining composites to metals in a body-shop environment.

A consortium of partners including Far-UK, Gestamp, Ansys Granta, Jaguar Land Rover, Nissan Motor Manufacturing (UK) Ltd., Scott Bader, Stadco, TWI and WMG at the University of Warwick launched the Innovate UK-funded LightJoin project in April 2017. Focusing on overcoming this challenge of joining composites to metals, the consortium explored joining techniques to enable multiple materials to be used in a ‘Body-in White’ structure; the main structure that sits under the surfaces of a vehicle.

As OEMs on the project, Jaguar Land Rover and Nissan were interested in exploring lap shear, fatigue and environmental data to ensure material joining processes are as informed and efficient as possible. Providing testing standards and their automotive expertise, JLR and Nissan were interested in the concept of producing a database to make joining selection more efficient. Bob Bateman, Senior Engineer at Nissan Technical Centre, Europe said:

“We wanted to better understand the process of joining composites to metals, particularly in relation to design, and LightJoin produced a set of results that we fed directly back to our Headquarters in Japan.

“This will leave Nissan with a better understanding of the requirements around building a multi-material car. LightJoin has justified Nissan’s efforts in terms of conducting research in the UK, and has triggered a number of other composites-based projects that we’ve been involved in since.”

Uncovering suitable material and joining combinations

To help increase the uptake of lightweight composites in medium to high volume automotive manufacturing and help the consortium determine suitable material and joining combinations, WMG introduced information technology experts Ansys Granta to the project with the idea of creating an innovative collaborative database to help inform the joining of materials – What is claimed as a “world first decision support tool” guiding engineers when making choices about joining materials. Darren Hughes, Associate Professor in Materials and Manufacturing at WMG comments:

“WMG has a keen interest in high volume joining technologies, and the LightJoin project was a good platform to expand this, providing the freedom to trial and experiment with OEMs. Having the WMG centre of excellence for high volume joining involved in this project allowed the upskilling of our staff and encouraged knowledge transfer directly into our undergraduate and postgraduate programmes as well as professional training programmes at WMG.”

Donna Dykeman, Programme Manager at Ansys Granta added: “An important aspect of the LightJoin project was that the supply chain for polymer composites in the automotive sector was represented (material producers, design/testing/simulation experts, Tier 1 suppliers, OEMs). This variety highlighted what is critical for decision-making in joint selection, design and manufacturing to achieve high volume targets.

“Ansys Granta, supported by our partners, made significant in-roads to producing a software decision-support tool for selection of joints which are multi-material, multi-configuration, according to automotive requirements.”

The LightJoin database includes a selection tool, which responds to a user’s specification around a set of joint properties and fastening mechanisms by presenting material and joint data to show suitable options when looking to join a composite with a metal. Donna added:

“Capturing the knowledge (data and information) required to connect supply chain members for decision-making in a single tool can be incredibly complex. The ability to demonstrate across a supply chain innovation project such as LightJoin is at the forefront of meeting industry expectations for up-scaling design concepts.”

In order to produce a database offering these joining solutions, the expertise of individual consortium members was leveraged. This included Scott Bader’s experience in joining multi materials with adhesives, Stadco’s consideration of risks and steps for applying large scale joining and composites manufacture to industry, and Gestamp’s development of a demonstrator jig in partnership with FAR-UK as they looked to expand expertise from metals to composites and understand the joining implications. David Goodwin, Engineering Manager at FAR-UK said:

“We saw an increasing customer need to light-weight multi-material structures. There was a short coming in the solutions offered in the market place. Also the project built upon our expertise with analysis led design of light-weight structures, so was a perfect fit.”

As part of providing technical advice and evaluating joining technologies under rigorously controlled conditions, WMG conducted a detailed analysis of joining techniques using in excess of 1,000 individual test samples and explored joint performance, durability, life-cycle and ease of manufacture. This generated test results that would populate the majority of the LightJoin database, helping identify the most viable lightweight composite joining options for large industrial scale production. Sullivan Smith, Automotive Programme Manager at TWI commented:

“Our main goal through LightJoin was to develop more knowledge, which would in turn enable us to offer more services at TWI. We have half a century of experience in composites but the project has enabled us to transfer knowledge from joining processes, reflected through lab-based data and performance results, to expand our technology offering. We are interested in doing more work with WMG on this.

“As a result of the project we have successfully won business in the area of joining composites and metals, and have learnt how to apply these techniques in an economic and reliable way for production. Based on the significant return on investment from this, we are now applying for more government funding in this area.”

Replacing aluminium structures with carbon fibre composites

Culminating in June 2019, the project compared and tested joining technologies including adhesives, self-piercing rivets and blind rivets. The LightJoin database and joining selection tool provides a robust source of data for use in the medium/high volume automotive manufacturing supply chain.

As part of the project, FAR-UK developed the joining cell, which with Gestamp’s contribution helped to manufacture a chassis frame. Based on FAR-UK’s Final Report when producing the lightweight chassis frame, the original steel structure (3248g) was replaced with a Carbon Fibre Reinforced Polymer (composite) structure using guidance from the LightJoin database, and saw weight reductions of 50%. David Goodwin, Engineering Manager at FAR-UK added:

“The outputs of LightJoin have certainly helped to develop near term solutions which perhaps have a useable life in automotive of 5-7 years. We have more work to do in this area, as the landscape is changing rapidly with new materials, new vehicle architectures and increased priority given to the efficient use of sustainable materials for a circular economy.

“LightJoin allowed us to develop and demonstrate capability for designing and manufacturing of prototype multi-material structures. This has improved our offering to customers for light-weight, cost-effective structures making use of fibre reinforced composites, aluminium and steel with a right material in the right place philosophy.

“As a result of the project, we now have a robotic joining cell installed at our facility available for use, which is capable of trimming, pick and place, drilling, riveting and bonding assemblies, and in April 2020, Far-UK will be opening a pilot line for low volume vehicle bodies using some of the learnings and technologies proven out in LightJoin. This will be in a new facility dedicated to advanced manufacturing.”

In response to Nissan’s investigations into replacing steel with composites, LightJoin took a Nissan Leaf floor and demonstrated joining technologies on it.

The LightJoin analysis is now supporting Tucana - a major Innovate UK project.