Industrie 4.0 conformant welding cell for batch sizes down to 1
Doka, with headquarters in Amstetten, Lower Austria, currently employs a workforce of over 6,000 worldwide and has more than 160 sales and logistics locations in over 70 countries. The company, founded in 1958, supplies economically optimized, state-of-the-art formwork solutions worldwide. Impressive building projects such as the Burj Khalifa, the world’s highest building at 828 metres, the Three World Trade Center in New York or the Lotte World Tower in Seoul were constructed with the aid of innovative Doka formwork technology.
No doubt about it, the company’s products are setting technological standards, and precisely these maxims apply to its production methods. The objective was to eliminate the time-consuming manual welding of certain components for a wide range of formwork systems. The solution lay in investment in a fully automatic robot welding cell according to the latest state of technology.
Erwin Schwarzl, production technician at Doka, explains the overriding goal for this investment: “We wanted to produce a wide range of manually welded parts more cost-efficiently. The aim was to convert our cost-intensive warehousing system to just-in-time production of various components. This task was to be assumed by a jigless robot cell that could handle different production orders down to a batch size of 1 in unattended shifts.”
Jigless welding with multiple advantages
Jigless robot welding offers significant advantages, alone due to the elimination of onerous clamping and tack welding, and the possibility of autonomous welding in unattended shifts. It does, however, places great demands on robotics and the know-how of suppliers and users. “Jigless is one of the particularly challenging disciplines in automation technology. Jigless cells are true guarantors of flexibility, but only when they are optimally conceived, suitable premium robots are used and the user has the appropriate expertise.” Sepp Hautzinger, Sales Manager Office Austria of Yaskawa Europe GmbH, knows that from experience.
These prerequisites were sufficiently fulfilled at Doka. The Austrians have been employing robots since 1980. Today far in excess of 100 robots are engaged in production at the Amstetten works. There is certainly no lack of robotics experience here, as the approach to this project demonstrates: the decision was taken only after completion of an extensive pilot phase, in which the Doka team examined a number of reference facilities with robots of the leading premium manufacturers.
“Yaskawa was able to present several applications that been successful in practical tests. There was no doubt that we had found the right partner for the realization of a technologically advanced welding system. In addition, our company had already had experience with Yaskawa robots,” Schwarzl stresses.
Even before investing in the new cell, the Doka production team and Yaskawa welding experts together reviewed the complete spectrum of welding tasks to be addressed for jigless suitability – not every component can be welded freely in space after positioning with a handling robot. Put simply, small tolerances of the components to be welded and a less anticipated warping speak in favour of jigless welding whilst in contrast large production-related deviations from target contours and particularly difficult fusing configurations can make the process significantly more complex or even impossible.
Jigless robot cell with all technical refinements
Once the question of technical feasibility had been settled, the team set about designing the high-tech cell. The outcome of their efforts is currently setting new standards in automated welding. “The Industrie 4.0 jigless cell at Doka is one of the most advanced robot welding systems worldwide,” explains Hautzinger. The system comprises Yaskawa’s latest DX 200 robot controllers, the cutting edge Fronius welding power source, which is currently celebrating its premiere, together with a new, fully automatic torch neck exchange system, the MotoSense laser-based seam tracking system recently introduced by Yaskawa, an application-specifically modified Kardex Shuttle feeding system, an innovative, fully-automated gripper exchange system for the handling robot and an overriding PLC of the latest generation – that is the maximum high-tech currently possible.
A closer look at the system layout reveals the signature of the knowledgeable welding and automation expert. That starts with the feeding process, which can take place either via a rotary transfer system with 16 workpiece carriers or via a Kardex tower shuttle system with 60 workpiece carriers. While the rotary transfer system is designed mainly for the production of small to medium-sized series, the shuttle system is expedient for unattended shifts. With its 60 positions it guarantees autonomous system operation far exceeding one shift and permits the welding of components in a batch size of 1.
Two Motoman robots work hand-in-hand
Masters of procedures in the cell are the Motoman MH280 II handling robot and MH24 welding robot, both equipped with state-of-the-art technology. The two six-axis robots demonstrate unparalleled jigless welding in the cell. While the handling robot precisely positions the component to be welded, the welding robot performs the fusion task.
Optimum path behaviour and a high degree of precision are required on the part of the robot, while the superior DX200 controller ensures perfect synchronization and coordination of the two six-axis robots. The large working radius of almost 2.5 metres for the handling robot and 1.73 metres for the welding robot ensure that all points are reached effortlessly and each welding procedure is carried out in the optimum flat position.
MotoSense camera system permits seam tracking in real time
For perfect welding seams the MH24 is equipped with the recently introduced MotoSense camera system. This laser-based vision system enables the robot to recognize and track seams in real time. Integration is remarkably simple, and takes place via a direct interface to the Yaskawa DX200 controller. With this system absolute component positioning is no longer necessary. It is thus ideally suited to jigless applications and guarantees optimum welding results, even in the case of complex tasks.
A further major contribution to the high quality of the welding seams was made by the modern Fronius TPS500i welding power source, as Schwarzl stresses: “The new welding power source provides for much improved fusion penetration and significantly higher welding speeds. That has a positive effect on the process times.”
Besides the process times, in order to reduce non-productive times as far as possible, both the handling and welding robot are equipped with automatic exchange systems. The handling robot independently retrieves the required gripper from the gripper station integrated into the cell. The same applies to the welding robot: it is programmed to cyclically change the torch neck being used for a new one at the changing station. This also guarantees smooth operation with maximum welding quality in the unattended shifts.
Complex system fulfils all expectations
For production technician Schwarzl the jigless welding cell has fulfilled the expectations placed in it with flying colours: “Depending on the component, with jigless robot welding we are up to three times faster compared to manual welding. In addition, we achieve astounding flexibility, as we can produce to order down to a batch size of 1 in unattended operation. In economic terms that is a bullseye, as expensive warehousing will no longer be necessary in future and manufacturing costs are likewise cut.” It is no surprise that Doka is already contemplating further investments in jigless robot cells.
Text & Pictures: Ralf Högel
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