Product category:
Metals and materials, stockholding
News Release from: SSAB Tunnplat | Subject: High tensile steel
Edited by the Manufacturingtalk Editorial
Team on 22 November 2004
Strongest steel tamed for Ford hybrid
Trim Trends in the USA was nominated for the Swedish Steel Prize 2004 for an automotive battery holder which combines strength with light weight
There's increasing consumer demand for more environmentally friendly hybrid drivetrain cars But this demand has produced new challenges for the car designers
This article was originally published on Manufacturingtalk on 26 Feb 2002 at 8.00am (UK)
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Trim Trends in the USA has succeeded in meeting one such challenge with a successful product that at the same time has achieved a breakthrough in tool design.
The company has now been nominated for the Swedish Steel Prize 2004, which is an annual international design award.
Its product is a new crashworthy battery holder for the substantial batteries powering the Ford Escape Hybrid SUV.
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The battery, which weighs more than 50 kilograms, is positioned under the luggage compartment, at the back of the car.
But how do you make the battery holder strong enough to meet collision safety requirements, while also being light enough to meet other requirements in the vehicle? The battery holder is manufactured with press tools which represent a significant technical step forward for high strength steel working - an advance which opens the way for more widespread production of large components made from very high strength steels.
Lighter, safer and more environmentally-friendly cars at a reasonable cost is just one of the possible outcomes.
The battery holder is of crucial importance to the safety of the car - obviously the heavy battery should not injure the vehicle's passengers in the event of a crash.
Kevin Bilkey, an Engineer at Trim Trends says: "Very high strength steel is needed to hold such heavy batteries in place, while also serving as collision protection.
"In a rear-end crash, the energy is transferred from the bumper to the battery holder which will move forward and upwards but without the batteries intruding into the interior." In the early stages, designers tried to use a conventional steel grade, but the design was not strong enough and turned out to be too heavy.
They then decided to try one of the strongest steels available, a martensitic steel with a tensile strength of 1200 N/mm2.
However, no-one had previously pressed this material into such a large and advanced component, and they did not know whether it could actually be produced.
The problem was to find an appropriate method of production which minimised or eliminated the risk of cracking.
Kevin Bilkey continued: "It turned out that the solution lay in allowing the 7kg sheet steel blank freedom to move in the die, so that it would be pressed without restraint." Once the engineers had determined how to press the hard steel, they had to find a practical method of welding the securing wedges under the holder, so that it would be able to slide up the slide rails behind the seat backrests in a rear-end crash.
A battery holder has six production stages - from punching holes and trimming away any excess material, through to welding the wedges for the slide rails.
The pressing operation which shapes the battery holder takes place in a single operation.
Cut away material is used for the wedges, making material utilisation very efficient.
David A Crowe, who is the toolmaking specialist at Trim Trends, added: "Although we have been supplying complicated parts to the large carmakers in Detroit for many years, this turned out to be our most difficult assignment.
"We had to forget old theories and preconceived notions, and start from scratch." The team was able to devise a method of leading the heat away when welding the sheet.
After solving this, they were then asked to make regular deliveries within a month! Production is now in full swing, with sheets for the finished battery holders being pressed at 150 a day.
These are shipped to Sanyo, so the batteries can mounted in the holders, and Ford receives a complete unit ready to mount in the vehicle.
Ford has ordered 30,000 of these battery holders at the time of writing, but demand for the new car is very high, and it is likely that many more battery holders will be needed in the future; Bilkey says: "We expect to be delivering battery holders to Sanyo for a long time ahead, and we believe that the Ford Escape Hybrid SUV will be a success.
"To meet the increasingly tough demands of the automotive industry, suppliers must be innovative in finding sound solutions to difficult problems." (Updated by CR, May 2007).
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