HIGHER STRENGTH STEEL HELPS LIGHTEN A CHASSIS

The challenge

Iroquois Industries Inc., of Warren, Michigan, had already been producing a front-suspension UCA for the Dodge Ram pickup truck. But in the face of rising gasoline prices and fuel economy demands, Chrysler wanted to reduce the UCA’s mass in the Dodge Ram 2009 pickup. The mass reduction program had to be accomplished without giving up the truck’s load carrying or towing capabilities — two critical reasons why customers buy full-size pickup trucks.

The front suspension upper control arm main stamping was made of Docol® HR 700 LA “with a folded under construction" resulting in a saving of 2.72 kg (6 lbs) per vehicle.

Chrysler Purchasing and Engineering dictated that the DS UCA had to have its mass reduced to match the mass of a proposed formed-wire UCA made from cold-drawn steel wire. This arm was 1.3 kg (2.9 lbs) lighter than the DR UCA that Iroquois was producing at the time for the production Dodge Ram pickup.

The solution

One clear solution emerged: use a new design with a smaller section modulus, made from significantly higher strength steel. The steel Iroquois selected was SSAB’s Docol® HR 700 LA. Docol® HR 700 LA steel is an hot rolled ultra-high strength HSLA steel with a yield strength of 700 MPa, which is twice the 340 MPa yield strength HSLA steel used on the former Dodge Ram DR UCA. Since the loading on the UCA was along the plane of the arm, it was clear that a design that maintained about the same plane view shape as the former DR UCA but with a thinner section would offer a more efficient design.

The result

The DS UCA is 1.36 kg (3 lbs) lighter than the DR UCA, and it achieved the Chrysler mass target for the arm, at the same time as the functional requirements are fulfilled. This saves 2.72 kg (6 lbs) per vehicle.

At this moment, Docol® is being tested in numerous projects for new chassis applications.

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