Robots and rivets keep trucks rolling

WHEN Freightliner LLC launched the new Cascadia Class 8 heavy duty prime mover in the US, the highly aerodynamic vehicle was set to lead the industry in performance.

WHEN Freightliner LLC launched the new Cascadia Class 8 heavy duty prime mover in the US, the highly aerodynamic vehicle was set to lead the industry in performance.

In tandem with the new design features, Freightliner’s manufacturing engineering team set out to build the aluminum cab-in white (CIW) in a fully automated production line at their North Carolina truck assembly plant.

The main advantage for Freightliner in using aluminum is reduced weight leading to reduced fuel consumption. The Cascadia model release coincides with recent introduction of strict new laws in the US that specify a reduction in pollutant and particulate matter emissions by up to 80%.

Significant advances in assembly methods introduced in 1995 included the use of self-pierce riveting (SPR) and robotic automation for cab assembly on the Columbia product line and progressing to the M2 medium duty truck model. These changes were major advancements in an industry dominated by manual assembly methods. Faster and less costly than spot welding or conventional fasteners, the Henrob SPR (HSPR)process has been used on CIW assembly lines since 1995.

With a design throughput of roughly 15 cabs per hour, the duty cycle per tool is heavy by automotive standards (a rate of up to 45 joints per tool per cab). The challenge facing the engineers was to get maximum utilistion out of the automation and robots.

For this reason, tool changing wrists are fitted to the robots, some of which perform as many as three distinct riveting operations as well as material handling duties. Also, some HSPR tools are shared between several robots.

Automated processes

In order to achieve a completely automated process, there was a requirement for the largest robot-mounted HSPR tools ever made, reaching to the center of the floor deck assembly to secure the skin to the cross members.

This drove the design of a special light weight C-frame with throat reach of 1250 mm and weighing in around 300kg.

The large tools led to a mix of robot payload ratings of 200kg and 340kg. Over 50 of the 80 ABB robots at the Cleveland facility perform riveting.

The fully automated process also set high standards for system uptime and availability. To meet this challenge, Henrob developed a second generation of its servo-electric riveting equipment and a fourth generation of its rivet delivery system using sprocket tape feed.

As the assembly line solidified and transformed from cell concepts to tool designs, Henrob’s engineering team worked closely with Comau-Pico (system integrator) to develop tooling based on the process capabilities of HSPR, and combined with Freightliner’s engineering team to achieve a seamless process. All Henrob tooling was developed using 3D CAD models and simulated on the virtual parts and fixtures prior to manufacture.

The result of this integrated approach to process development, enabled the Cascadia CIW production system to ramp up to full throughput quickly and produce cabs with the best dimensional integrity ever from a Freightliner assembly plant. The new trucks have also shown themselves to be the quietest on the road in their class.

For more information contact:

Henrob Australia

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