Robotised solution raises safety

The challenge came from a prominent French steel producer looking to boost safety in the workplace. At a repair station, operators had to manually unwind and cut 5 to 15 metres from each steel coil that had to be supplied without any damage to the customer. The operators achieved this by using a manually operated plasma cutter. For proper access from all sides, they regularly stepped on and over the sheet to be cut. This undesirable situation needed to be remedied. Tebulo Industrial Robotics therefore developed a robotised repair station with a plasma cutter for all material qualities and thicknesses. It even includes an option for separate disposal of special materials and processing for inspection plates, making it a world debut. 

In most steel mills in the world, people often still repair the mentioned types of defects by hand, simply by manually operating a plasma cutter or scissors. What makes this work so dangerous is that each steel coil has different properties, so the behaviour may be different for each unit. For example, thin sheet material crumples, whereas high-strength steel rapidly coils up as a result of the material’s internal tension. 

Additionally, the operator must be aware of cutting hazards, since steel plates are very sharp. Hence, it is a combination of factors that not only make the work unpleasant, but also hazardous, boring, noisy and dirty. This was the reason why the French company was looking for a robust, automated solution for a wide variety of steel plates (ranging from soft material with a thickness of 0.35 mm to highstrength steel with a thickness of 4 mm). In addition to the cutting line and the disposal of recyclable materials, the retractor with pressure rollers and plate separation mechanism had to be fully integrated in the new solution. So this integration had to ensure that no hazardous work was needed in the vicinity of this repair station, other than remote automation.

New repair station

The new station has been designed in such a way that steel coils with a width varying from 700 to 1,850 mm and a diameter of approximately 2 metres are supplied one by one. An incoming coil is picked up by the walking beam and placed on the station’s cradle rolls, wrapped in rubber. Prior to starting to unwind the steel coil, two pressure rollers and a scraper blade are raised by means of two hydraulic cylinders, each with an 800 mm stroke. As soon as the pressure rollers press against the steel coil, the coil starts to unwind and the robot seeks the start of the plate to be machined, picks it up and peels it away while the pressure rollers help push the material towards the table. 

Once the sheet has been positioned correctly on the table, the plasma cutter can be put into operation. The plasma torch is integrated in the robot head and is mounted in a floating assembly allowing it to follow potential undulations in the sheet material. The robot cuts the sheet with the plasma unit over a special opening in the table. The robot, fitted on a single carrier together with the plasma unit, then picks up the cutoff material transporting it to the containers specially prepared for recycling.

Safety

Once the robot holds a steel sheet, it will function with a lower degree of freedom of movement and, depending on the weight of the transported sheet, with a somewhat reduced speed for safety reasons. If the robot returns from the waste container without a steel sheet, it will operate at such a high speed that the cycle time can be secured. In order to guarantee safety at all times, the robot is equipped with a so-called ‘safe move’ or safety programme, covering the standard programme as a kind of ‘shell’. This safety programme continuously monitors all robot movements and checks whether they match pre-set limits.