The Roll forming line converts coils of steel strip to ready-made reinforcements for metal mesh baskets. The reinforcements are neatly delivered to a transfer station, where they are automatically collected for the next step in the production process.
The highly automated Roll forming line can be operated with minimum manpower. The Siemens PLC system controls a number of servo-drives on 7 different stations. Software engineer Erik Klaassen knows the ins and outs of the Roll forming line. “The line delivers a finished product every 7 seconds. That means high demands for the speed and accuracy of movements. We had several nice challenges in this project!”
At the entry of the line, a large decoiler holds up to 5 steel strip coils. The required type of steel strip is fed into the first unit in the line: the roll forming unit. Here the strip is cold formed to the right shape for the reinforcement profile. A measuring wheel is used to determine the exact length of a profile, which is then cut to length, by a flying shear, while moving at 50 mtr/min. “At this speed, we have enough capacity to fill the buffer while we are producing product.” says Erik.
The cut profiles are handled by a placement unit that either stores the profile in the buffer or feeds it to the cue of the first bending station. In that station the ends of the profile are bent inward once. In the second bending station the profile is bent to a closed rectangular shape. The third station is a welding station, where the rectangle is closed with a contact weld. The next station makes a vertical bend in some of the product variants. The final step is the transfer station. In this station the product is rotated 90 degrees and handed over to the basket production line.
Speed and accuracy
Each process step must be verified, before a profile can be moved to the next station. In each station, or unit, there are a number of sensors and actuators that must be checked and controlled. “We keep response times low by using Siemens ET200S remote I/O stations and local valve blocks.” Erik explains.
Motion in the production line is provided by a range of actuators. Servo-motors are used, but also hydraulic and pneumatic cylinders. These all have different behavior’s and our software must deal with that.” Erik points out.
The product is transferred between stations by an overhead Pick and Place unit. This unit accelerates at up to 10 m/s2 and reaches speeds of up to 180 mtr/min. The demand for accuracy in the line leads to high stiffness requirements for the Pick & Place unit. This means that a considerable mass must be moved. According to Erik: “A serious amount of power is needed to move everything at the speeds we need.”
The control system continuously monitors where the product and the moving parts of the machine are. Both absolute and incremental encoders are used on the line. Some components need to “home” on their “zero” position first. Of others, like the flying shear and the Pick and Place unit, the exact position is always known. The angle of the product in the final transfer station is also closely watched, to prevent the profile from hitting the machine.
Through the control screens on the large touch panel, the operators can enter parameters that will adjust the units of the line for the manufacturing of different product variants. On the main screen, the entire process can be monitored. All servo-motor data (temperatures, powers, speeds etc.) and the current positions of the actuators are presented on the main screen in clear colour coding. The operators can see at a glance if anything out of the ordinary is taking place on the line. Or, if any component is working outside its normal parameters.
A wireless remote control unit allows the operators to safely enter new material into the line. The operator can stand next to the unit that he wants to control and observe what is happening on the spot. This is particularly useful when running the line in step-by-step mode. This operating mode lets the production cycle take place one step at a time. “A powerful tool for troubleshooting a process that normally takes place too fast to see what actually happens.” says Erik.
The Roll forming line beautifully illustrates the breadth of Eltra’s know-how. It is a tightly controlled and tightly running production line that delivers the promised Return on Investment.