Development of Roll Formable Ultra High Strength Steels for Energy Efficient Manufacture of Lightweight Crash Resistant Automotive Structures

Lead Research Organisation: University of Warwick
Department Name: WMG

Abstract

This project is concerned with the development of Ultra High Strength Steels (UHSS - steels with a ultimate tensile strength greater than 1000 MPa) specifically designed to be formed by a novel low energy and flexible manufacturing process, known as 3D roll forming, to produce lightweight crash resistant structures for the automotive industry. The roll forming process is an incremental bending process that turns a flat sheet into a structural profile as compared to traditional stamping processes that involves severe stretching of the sheet to create the required part geometry. The 3D roll forming process is extremely flexible - leading developers of the technology claim a single set of tooling can be used to manufacture up to a quarter of the automotive structure, whereas the stamping process requires an expensive set of tools to be manufactured for each individual part. Furthermore a roll forming line only take 10 to 16 weeks to setup as compared to 18 months for a stamping line. Today ultra high strength automotive steels are usually formed using the energy intensive hot stamping as it is very difficult, and costly, to design steels that achieve the required high room temperature uniform ductility in combination with an ultimate tensile strength in excess of 1000 MPa. As roll forming only requires the material to be bendable, it is proposed that steels with low work hardening rates and a high yield ratio (yield strength /ultimate tensile strength) could be suitable for shaping using this process. The development of UHSS for roll forming allows simpler compositions that are leaner and have a lower alloy cost which reduces exposure to raw materials supply issues (scarcity), have better compatibility with existing capabilities and are more consistent (higher yield/lower scrap). This is potentially a disruptive technology that could revolutionise the manufacture of automotive structural members. It will: eliminate the need for energy intensive hot stamping currently used for shaping UHSS; dramatically reduce tooling requirements and the energy associated in their manufacture; increase material utilisation; avoid the need to use energy intensive materials for lightweighting such as Al, Mg and CFRP; all whilst producing a product that will yield significant CO2 savings during use. It is estimated that if roll formed steel replaced 50 kg of hot stamped components in a vehicle, then 40,000 tonnes of CO2 could be saved in the UK automotive manufacturing industry per annum.

Planned Impact

Project partners: The primary beneficiaries of the project will be the industry partners who will benefit through exploitation of the research outcomes. Tata Steel will gain a competitive advantage in a key market by offering a considerable advantage over other steels and competitor materials such as aluminium and carbon fibre composites. Hadley Group will find a sustainable market for their process and upstream users, such as Jaguar LandRover, who will benefit from the availability of an ultra high strength steel that can be formed at low temperature in a simple process.
Wider Industrial Impact: Apart from the benefits to the industrial partners given above, Tata Steel works directly with numerous engine and car manufacturers (who cannot be named for commercial reasons), and these sectors will see their products improve as a result of this research through the use of UHSS, offering a competitive advantage over more expensive materials such as aluminium alloys and CFRP. More importantly, energy consumption will be reduced both in terms of the alloy production and the forming process. The research will also be directly disseminated via collaborations with the HVM Catapult centres, in particular the AFRC (a partner in the project). In addition, the project outcomes will provide scientific support for further development of 3D roll forming.
Societal: The wider public will benefit from the longer term benefits of lightweighting of passenger cars with improved safety. This research has direct impact on reducing the environmental impact of passenger vehicles by lowering the CO2 emissions generated from primary metal production, component manufacture and fuel consumption over the lifetime of the vehicle. The results will also be fed into the relevant topics of the school science curriculum (materials,CO2 usage) to ensure that teaching and students have access to cutting edge research.

Publications

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Alharbi K (2015) Damage in dual phase steel DP1000 investigated using digital image correlation and microstructure simulation in Modelling and Simulation in Materials Science and Engineering

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Celotto S (2018) Deformation-Induced Microstructural Banding in TRIP Steels in Metallurgical and Materials Transactions A

 
Description This project was concerned with the development of Ultra High Strength Steels (UHSS - steels with an ultimate tensile strength greater than 1000 MPa) that are specifically designed to be formed by roll forming to produce lightweight crash resistant structures for the automotive industry. These materials typically behave in a brittle manner in cold stamping processes, the most common process used to manufacture crash structures. As a result, high strength materials are stamped at elevated temperatures to improve their formability. This project proposed that an alternative route forward is to change the type of manufacturing from stamping to roll forming, which involves the more favourable bending deformation mode. The main advantage of roll forming is that these materials can be processed at room temperature, thus making them more sustainable.
The objective of the project was to establish the roll formability of UHSS and to determine if low yield ratios improve roll formability. The project assessed 3 UHSS' and the following were found:

1. The stretch formability of UHSS was low. The result confirmed that these materials will perform poorly in stamping processes, which involve stretch and drawing
2. We measured strain distributions through the thickness of sheet, along the length of the material 'flow' and in the microstructure of the material as it underwent bending. The measurements were carried out using digital image correlation. The results showed that the major strain increased non-linearly from the inside radius of the sheet to its outside radius. This variation of strain suppressed the 'necking' failure response allowing the material in the outer radius to sustain higher strains than it would in stretch. The material experiences significant shearing along its length as it is deformed by each stage and the microstrucural strain distribution was affected by its phase composition.
3. We carried out an industrial trial on one of the materials, a dual-phase steel, on a process to produce a physically realistic geometry. The process consisted of 15 stages and included bending the material around a variety of radii, including up to 80º around a 2.6 mm radius. Using circle-grid analysis, the peak deformation of the material was found to be 0.42 strain and the material did not exhibit failure. We concluded that the roll formability of the material was sufficient to form reasonably complex geometries.
Exploitation Route The findings of the project identified material and process parameters that are not currently considered in roll forming such as the shearing of the material along its length and the influence of phase composition and morphology on microstructural strain distribution. We expect that the findings of the project will be useful to future investigators as it may be used as a basis for studies that seek to optimise the material composition and parameters of the process. Our measured strain distributions will be particularly useful to validate multi-scale simulation models that may be used in such optiisation studies. The industrial trial showed that reasonably complex components can be manufactured in a process that was not fully optimised. The findings therefore, highlighted the potential of using UHSS in roll formed components. Because roll forming results in little scrap and consumes little energy, we expect that the findings of this project will encourage OEMs and suppliers to exploit this material and process more widely in their products.
Sectors Aerospace, Defence and Marine,Agriculture, Food and Drink,Construction,Manufacturing, including Industrial Biotechology,Transport

 
Description The project brought together and automotive OEM (Jaguar Land Rover), a 1st Tier supplier of roll formed components (Hadley Group) and a material supplier of ultra-high strength steels (Tata Steel). The project has had two impacts beyond academia: 1. The regular partner meetings that were held at WMG raised awareness amongst partners of the presence of world-class suppliers of roll formed components and materials and of an alternative manufacturing process that is cheap and environmentally friendly. As a result, the partners supported a follow-on EPSRC proposal on roll forming that was submitted by WMG in October 2017. 2. During the course of the project, the Hadley Group contributed to the project by granting access to their development roll forming line to run a series of industrial trials. By actively participating in the trials, they gained confidence in using ultra-high strength steels and appreciated the limits of manufacturing with it. As a result of acquiring this unique knowledge, they were invited to bid for a contract to supply parts for an automotive structural component for a vehicle developed by a major European manufacturer.
First Year Of Impact 2017
Sector Manufacturing, including Industrial Biotechology,Transport
Impact Types Economic

 
Description EPSRC iCase with Tata Steel
Amount £24,000 (GBP)
Organisation Tata Steel Europe 
Sector Private
Country United Kingdom
Start 10/2015 
End 09/2018
 
Description Data M 
Organisation Datam Limited
PI Contribution access to experimental data
Collaborator Contribution access to software
Impact software knowledge
Start Year 2015
 
Description Hadley Group 
Organisation Hadley Group
PI Contribution Scoped out further research activities with these partners.
Collaborator Contribution Hadley Group - Expert guidance (time) and access to kit.
Impact Multidisciplinary scoping workshops to identify future research priorities and their alignment with the Industrial Strategy.
Start Year 2015
 
Description Jaguar Land Rover 
Organisation Jaguar Land Rover
Country United Kingdom 
Sector Private 
PI Contribution Co-created research program
Collaborator Contribution Research objective definition and discussion; component design
Impact , further collaboration on metal forming
 
Description Tata Steel 
Organisation TATA Steel
Country India 
Sector Private 
PI Contribution Work extensively to develop new alloys and applications
Collaborator Contribution provision of industrial expertise and materials
Impact publications, iCase award
Start Year 2014
 
Description Presentation to the Catapult Body-in-White Guild 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Industry/Business
Results and Impact The Body-in-White Guild is a forum for the directors of companies that supply sheet metal forming components to automotive OEMs. The Guild includes the major Tier 1 suppliers based in the West Midlands such as Stadco Ltd, Sertec , Liberty Pressings, Premier Group and Whiston Industry Ltd. An hour presentation was delivered to create awareness of the roll-forming process that is capable of processing the high-strength, low ductility material that is difficult to stamp. The presentation included WMG's research activity in roll-forming and the emergence of flexible roll-forming that will allow a greater variety of geometries to be roll-formed. The outcome of the presentation was to raise awareness of alternative processing routes for high-strength materials.
Year(s) Of Engagement Activity 2016