300 weld seams in 90 minutes

It was primarily the high quality requirements and developing technology that motivated Hüffermann Transportsysteme GmbH to break new ground in chassis production. The lorry trailer manufacturer based in Neustadt (Dosse) in the Brandenburg region of Germany now manufactures 16 skeletal and container trailers using the EWM-Euen system every week, almost doubling its production while reducing manpower.

The same assemblies are always used to construct skeletal and container trailers: two longitudinal beams, a pivot support panel on the front, the tail area on the back, spring hangers to hold the axles and two locks which will later be used to secure the container on the trailer. In order to make welders’ jobs easier, a new clamping device was planned for the 7-metre-long, 2.4-metre-wide trailers. It is intended to align the components with one another and hold them in position. The integrated longitudinal axis of rotation also improves accessibility, allowing almost all seams to be welded in the flat position. However, a question was raised during the planning of the clamping device: “Why not automate the welding process too?”

9-axis gantry system

But special challenges also came to light in the detailed planning. The ceiling height was restricted by the crane runway on one side and the axis of rotation for the components on the other. The components are easily accessible from the ground in the starting position. However, after a 90-degree rotation, the component looms almost three metres in the air. The robot on the gantry system needs to adjust to this major height difference as well, so the solution must ensure that the crane runway and the welding robot don’t collide. The control of the positioner takes place independently and couldn’t be implemented into the robot control. Therefore, the entire welding unit has to be completely removed from the working area of the axis of rotation when positioning. This requires an additional z-axis, which is unusual in gantry machines. The system has a total of nine independently controlled axes: three axes for the gantry system (x, y and z) and six robot axes (x, y and z plus a, b and c). The high stroke on the z-axis also necessitated a special solution for extraction. It is split down the middle, thus leaving space for the axis.

Phoenix puls and drive 4X

The welding machine, a Phoenix puls from EWM, is located at the partition separating the two sections. The drive 4X wire feeder is situated directly above the drums with the welding consumable and conveys the wire via the cable drag chain (which also carries electricity and gas) to the robot. forceArc puls is the only welding process used. The arc is powerful and deeply penetrates the material. At the same time, the heat input is reduced by the pulsing. The welding speed and the adjustment of the parameters take place directly during teaching and depend on the material thickness and geometries.

Higher requirements for the assemblies

Preparation of the individual parts and assemblies massively helps to speed up the loading process. They have become much more precise. This high standard of precision is fundamental in automated welding processes. Due to the lack of space in the chassis, no seam finding or seam tracking systems are used, so the entire welding process is based on taught curves. Therefore, the robot always welds at the pre-programmed position, regardless of the actual circumstances. The weld seam needs to be where the robot’s welding torch is, not the other way around. If the deviations or tolerances (which can of course be compensated for manually) are too big, the robot will simply weld next to the seam. This results in time-consuming post weld work, where the

weld seam has to be ground out and reworked. Therefore, more precise preparatory work and smaller tolerances in the components will produce a better welding result. “It is essential to speak plainly beforehand about the robot’s capabilities and limits”, stresses Andreas Euen, Managing Director of EWM-Euen. These requirements apply to the company's own assemblies but must of course also be passed on to suppliers. “This initially sparked a lot of disagreements with suppliers, and it was often tricky”, admits André Schneider, Divisional Manager of Steel Construction at Hüffermann.