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For a long time, TROX, the manufacturer of air-conditioning and ventilation components located in Isselburg-Anholt has looked for a flexible production line for short tubes which is able automatically to process different piece numbers of tubes with different dimensions without manual refitting. Now, they have found a suitable solution with the manufacturing cell Flexistar made by weil technology.

TROX GmbH manufactures components and systems for mechanical ventilation, air-conditioning, and fire protection systems at their factory in Isselburg-Anholt.  Within the course of a new investment, they had looked for a flexible production line for short tubes. It should be able to automatically produce short tubes with diameters of 76 to 400 mm and lengths of 250 to 1,250 mm.  95 % of the tubes are being made of galvanized steel sheets with a thickness of 0.6 to 1.25 mm, as well as of high-alloyed metal sheets, e.g. made of the material 1.4301, with the same dimensions as mentioned above.  They act as the housings for components made by TROX for fire and smoke protection as well as control units for air diffusers.

In contrast to the earlier joining method of “overlapping – resistance-welded”, the new joining method posed to be a particular challenge for the new plant.  The joint needed to be made with a nearly smooth inside and outside surface and should not require additional corrosion protection especially for the galvanized tubes.  Further more, the different diameters of an ordered batch should be guided through the line without manual intervention.

After the performance specification had been created, about four months lapsed for market research and preliminary conversations. Finally, TROX decided in favour of the flexible manufacturing cell made by weil technology from Müllheim (Baden-Württemberg), a supplier of semi- and fully-automatic system solutions for roll-forming, welding, and handling technologies.  

In April 2009, the plant was ordered. weil engineering should design, deliver, and install the short-tube production plant with all its required safety devices and extraction systems. The feed material consisted of cut sheets which were roll-formed to form a tube whose longitudinal seam was welded.  Laser welding was specified as welding method. The plant had to be designed for a total annual capacity of 350,000 tubes manufactured in two shifts. At the end of February 2010, the plant was delivered by weil technology as planned and shortly after that, it was placed into service. 

All requirements met

“We have found a partner in weil technology who offered a production line which exactly met our technical specifications and moreover, exceeded our requirements through innovative ideas. During the bidding phase, the company turned out to be a competent and reliable partner who endeavoured to meet the customer’s specifications”, they say at the TROX-location in Isselburg-Anholt.

And: “The special advantages of the Flexistar-production line were the implementation of our requirements in regard to the minimum refitting process of the preceding roll-forming machine as well as the connected welding machine.  They allowed us to process different diameters and housing lengths one after another within an ordered batch without refitting the plant.

We had the choice between two types of roll-forming machine, the 2-roller rounding machine and a multiple-roller rounding machine. The two-roller rounding machine rolls the cut metal sheets over the whole circumference, but if there are any variations of the material quality and changes of the diameter, it will require considerable set-up time.  In the multiple roller rounding machine, a CNC control adjusts the tool rollers without additional refitting when the material dimensions vary or the diameter has to be changed. The disadvantage of roll forming with multiple-rollers is the starting straight at the beginning and at the end of the cut sheets due to the process method.  This causes a roof-shaped cross section along the joint of the produced tube when the longitudinal seam is formed.

“Fortunately, weil-engineering was able to compensate this disadvantage with a fully integrated “Pre-rounding” machine which pre-rounded the edges of the metal sheet at the beginning and at the end using a tool turret to achieve the required diameter.  This met our demands on minimum tool change and maximum quality in equal shares,” explained a TROX employee.

A finished tube every 20 seconds

The production in Isselburg-Anholt mainly consists of a destacking unit with two pallet places, equipped with double sheet recognition and double sheet separation, which can be fed with the processed material during the machining process. A suction tool with automatically controlled suction system transports the cut sheets to the testing and centering station with servo-axis from where the cut sheets are brought to the pre-rounding station.

After the edges have been rounded, the sheets are transferred to a feed table from where they are fed into the multiple-roller rounding machine of the Flexistar. After the roll-forming process, the tubes are pushed into the continuous welding machine with flexible clamping design and vertical welding axis. The main component of the welding machine is a CO2-Laser TruFlow with 2000 W laser power made by Trumpf.  The whole production line is equipped with a safety fence to meet the accident prevention requirements.

The welded tubes are placed on a storage table with which the tubes can be moved out of the safety area. On average – depending on size and length – every 20 s, a finished tube leaves the line.

Simple entry of production order

The production order for a prepared pallet consisting of several items including the parameters for piece number and the 16-digit alphanumeric program name is entered into the control mask for each item.  The entry mask is designed for at least 15 items.  Alternatively, the operator can call the order from the TROX server in the network drive as character-separated file and automatically transfer it into the mask. It is possible to enter data while a pallet stack is automatically processed.  The operator manually assigns the order to one of the two possible preparation places.

According to the transferred order, the different sheet cuts are sorted according to the size and a coil punching machine provides them on a pallet.  The pallet is then placed in a transfer station using a pallet truck. At least two staging places for pallets are provided and so, the pallet change can be carried out during the machining process. The pallet stacking height is maximum 300 mm. A destacking unit takes the stack while checking for double sheets, separates the sheets and optionally transfers them using a feed table to the pre-rounding machines which do not require any change-over and then to the CNC-multiple-roller rounding machines.

By using an integrated part-identification system via sensors, the plate sizes are checked for their specified diameters and target/actual comparison is carried out.  In case of any deviations, the machine will be stopped in a controlled way. The destacking unit automatically adapts itself to the cut sizes. The circuits of the suction groups are automatically selected or deselected.

No manual refitting

It is not necessary to refit the machine for changing cut sizes. The sheet separation system is designed to handle ferritic and austenitic sheets. After the tube has been rounded, it is transferred to the laser welding station where it is held by a flexible clamping unit and is guided under the welding head. This process runs automatically. Changing nominal tube sizes or lengths within one job can be processed without manual refitting or the operator’s intervention.

The finished part is then placed on a storage table and moved out of the safety area.  Then, the tubes are transported to an automatic tube end forming machine in which the tubes are calibrated by expanding and several bracing beads are placed by roller beading tool.

Break through with Flexistar

„The particular benefits of Flexistar are based on the possibility to automatically process tubes with different dimensions and number pieces within one job order without manual refitting in a way that they can be destacked by our coil punching machine – forming one stack of sheets with large and small diameters.  For about ten years, we have had our eyes on such a machine. Only now, we have made the breakthrough.  On the one hand, this happened because the company weil-engineering had launched their machine Flexistar and on the other hand, because, in coordination with the product development, we had newly defined our requirements on our future “round” products. This was the basis for a new production method and with this, for a new production line”, emphasized the production manager.

He adds: In addition to the already named advantages, the new production method, in connection with the new opens a high potential for the future product development tube-end processing machine, also made by weil technology, and the resulting high precision of the manufactured short tubes, opens up a high potential for the future product development.”


TROX is leading in development, manufacture and sales of components and systems for the ventilation and air-conditioning of rooms. With 25 subsidiaries in 22 countries and 14 production locations, TROX is the market leader in Europe and of worldwide importance in the field of air-conditioning and ventilation components.  Founded in 1951, TROX achieves a turnover of 340 million euros with 3000 employees around the world.  More than 25 further sales offices and more than 50 agencies and importers have introduced the TROX-products and the TROX-concepts overall in the world.

Flexistar – Flexibility in tube clamping

The flexibility of the production cell Flexistar made by weil engineering is based on the fast change of diameters when the product changes and for alternating production for a lot size higher than 1. These two processes run without tool change, refitting, mechanical adaptation and loss of cycle time. The core of the machine line is the automatic diameter adaptation unit for the rounding and the welding processes.  Outside arranged movable clamping bars provide for the continuous passage of the tube to be formed below a welding source and the proper welding process.  This allows the fully-automatic production from the metal sheet to the welded tube.

From the flexible production cell, the tubes of different diameters roll on the storage table. This is done completely program-controlled by a clamping design which changes continuously between different diameters.  With this, approved concepts of weil-engineering, e.g. the multiple-roller rounding machine, are interconnected with a newly developed tube guiding system in an automatic production line.  The rounded tube is automatically welded during the run through the machine and ejected to the storage table.

The clamping concept of Flexistar consists of a tool basket with several clamping elements. The diameters are adapted by a servo-control. To adapt the diameter centrally, the radial clamping elements are moved. After that, the rounded tube is automatically pushed through the welding station and transferred to the storage table. Thanks to the CNC-controlled change of diameters, no tool change is required.  This allows the alternating production of different tube diameters without refitting. 

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