An innovative robot with process arm sold Czech hoist manufacturer STROS on a ABB welding system. Not only does the robot system provide multiple-axis movements, it can also rotate the weld torch 360 degrees to reach welds that other robots found impossible.
Located near the sleepy town of Sedlčany about an hour’s drive south of Prague, STROS-sedlčanské strojírny’s premises look nondescript from the outside, but inside the production hall an impressive manufacturing operation is at work. With 50 years in the business, STROS is one of the world’s leading suppliers of hoist machinery for building sites. It supplies high-quality work platforms as well as customized personnel and material hoists – hoists that can be expected to carry loads of 3,200 kilograms at speeds of 90 metres per minute to heights of 350 metres. And its tetrahedral vertical masts are a crucial component in the hoist assembly. Each mast section needs a total of 222 reliable welds and manufacturing them was an extremely labor intensive process.

Difficulty in recruiting skilled welders
Until recently, STROS had to use highly skilled welders to make these mast sections. Although it has been using robots for 25 years, those machines could not manage the complex arc welds in narrow spaces needed for these particular components. Consequently, in order to produce a satisfactory number of mast sections it had to employ three welders per shift at three separate workstations.

Apart from the obvious outlay this required in terms of manpower and space, STROS found it increasingly difficult to recruit the highly skilled welders needed for this work. That’s why in 2007 the company decided to go out to tender for the complete robotization of its manufacturing process for mast sections. Of the four firms who responded only ABB Robotics could fulfil all the requirements.

Robot, workpiece positioners and programs are all part of the solution.
“ABB was the only company that could supply the entire workstation,” says STROS project manager Milan Škorpa. “We didn’t want to buy just a robot. We wanted a completely robotized workplace, which would include a workpiece positioner and would also handle the transfer of components. ABB also did all the programming for us; which means they effectively delivered a complete solution.”

The IRB 1600ID industrial robot with "process arm" was a key feature of the robot automation system now in place at STROS. The robot's arm is extremely slim and can combine multiple-axis movements and rotate 360 degrees; which makes it ideal for entering narrow spaces to carry out the complex arc welds required to complete the mast sections. An integrated welding cable follows the arm’s movements, which ensures that it doesn’t get caught in any surrounding fixtures or workpieces. In addition to the process arm’s manoeuvrability the ABB positioners for holding the workpieces to be welded were also a major selling point. Škorpa says “The fact that the positioner can turn on more than one axis was crucial. It’s critical to be able to coordinate the robot’s movements on the track with the positioner.”

Good collaboration between STROS and ABB
The process arm’s interaction with the positioner is an impressive feat of synchronization, which according to Škorpa, could not have been achieved without ABB’s readiness to work closely with STROS in designing the system. “The workers who make the mast sections had to collaborate with ABB to ensure the system could be put into operation the way we wanted it,” he says. “First and foremost, the people at ABB were perfect experts. And they also responded immediately to any problems we encountered.”

The robot is three times quicker
STROS uses a rotating IRBP 500D workpiece positioner with two fixtures to hold the individual parts of the mast section that are to be welded. This means that the robot is in constant use, because an operator can prepare pieces for welding on one side of the positioner while the other part is being welded. The positioner then rotates and welding continues while the operator removes the completed part on the other side and prepares the next component. The standard combined cycle time for making one mast section is 54 minutes, which is three times quicker than the time required by a human welder to make the same piece. “The robot effectively does the work of three welders using just one workstation,” says Škorpa.

Consistent high quality and no recruitment headaches
Such obvious savings means that Škorpa believes STROS’s investment of CZK 7.5 million (EUR 300,000) in the robot system will be recovered in two to three years; especially as the company was able to get 50 percent of the cost subsidised by a special EU grant for modernizing production technologies.

In addition to the productivity gains Škorpa claims the system’s intangible advantages are also significant. “There are important returns on the investment that can’t be quantified,” he says. “For instance, we now don’t have to worry about trying to hire properly trained welders, who are in short supply these days. It also pays off in terms of the quality of the welding. Even if you have a good welder, you are never going to get the same consistency that a robot gives you. Robots don’t forget any welds.”


About STROS

* STROS is one of the world’s leading suppliers of equipment for building sites.
* The company has been in business for more than 40 years and has a long-standing focus on manufacturing hoists for material and personnel, working platforms and other steel structures.
* It employs 220 people and exports its products to 35 countries in Europe, Asia, the Middle East and the Americas.


Benefits

* One tailor-made robotized workstation produces the same number of pieces per eight-hour shift as three human welders.
* Robot welding ensures consistent high-quality welds without any of the deviations produced by human welders.
* Need to recruit qualified welders eliminated.
* Welding mast sections with robots guarantees constant high levels of geometric precision, which means that the sections fit perfectly with each other when being assembled.
* The systems can be easily reprogrammed to manufacture other parts.