The step up to full automation
When Freightliner LLC launched the new Cascadia Class 8 heavy duty prime mover, the highly aerodynamic vehicle was expected to have high performance and driver comfort.
In tandem with the new design features, Freightliner’s manufacturing engineering team set out to build the aluminium cab-in white (CIW) in a fully automated production line at its flagship Cleveland, North Carolina truck assembly plant.
Aluminium has been the material of choice for Freightliner cabs for over 20 years. The main advantage for Freightliner in using aluminium is reduced weight leading to reduced fuel consumption.
The Cascadia model release coincides with recent introduction of strict new laws in the USA 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, Henrob’s SPR process has been the cornerstone of Freightliner’s CIW assembly lines since 1995 when buck rivets were replaced in favour of Henrob’s self-pierce rivet process (HSPR).
Building on experience
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 utilisation 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.
In order to achieve a completely automated process, there was a requirement for the largest robot-mounted HSPR tools ever made, reaching to the centre 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 200 kg and 340 kg. Fifty-five of the eighty 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.
This ensured Freightliner would have to be fast and a reliable fastening system.
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.