In high-voltage applications welded aluminium pipes are used for gas insulated switchgear. In pressure resistant piping systems high currents are being switched under SF6 (sulphur hexafluoride) inert gas.
To prevent electric breakdown, the junctions of the gas-filled piping have to be smooth. Such a pipe consists of a cylindrical centre section with cast aluminium flanges welded on on both sides. To meet the requirements, the weldseams between centre section and flanges have to be flattened.
The workpieces range from 200 to 500mm in diameter and measure up to 7000mm in length.
The flattening takes place in two steps. First the better part of the welding bead is removed with a milling tool. Afterwards the finish is done using a flap wheel.
While being processed, the workpiece is held on a clamping device which consists of two independent workpiece holders so that while one piece is being processed, a finished one can be removed and be replaced by a raw part. The clamping device consists of a rigid longitudinal girder with workpiece holders on both sides. Each holder features two prismatic supports of which one is fixed and the other is moveable along the beam to accommodate to different workpiece dimensions. Together these two supports can move in vertical direction. First to lift the pipes off the transport carts used to feed them and secondly to perform the actual clamping.
Because the workpieces are firmly clamped during machining, the above mentioned tools have to be guided on the circular path by a roboFlex. The latter one is arranged centred above the clamping device with its linear axis beam parallel to the clamped pipes. Thus different positions along the length of the pipes can be approached and the same work can be performed on both sides of the clamping device.
The milling tool and the flap wheel are being grabbed by the robot consecutively. The latter one bears an electric spindle with an adequate tool changer.
The machining process is completely automated. The cell operator is only responsible for feeding and removing of the pipes as well as the reading in of the workpiece data. The adjusting of the clamping device to the pipe dimensions is being performed automatically as is the detection of the weldseams to be machined by the robot. The latter one is done using optical and acoustic sensors.
Scope of supply
Besides the standard product roboFlex RF-4, GÜDEL also delivers the complete clamping device which makes use of several components of the size 62.
The machining spindle with the milling tool and the flap wheel are also part of GÜDEL's scope of supply as is the rack which accommodates the tool not in use respectively.
Finally the complete system control as well as the security-relevant electrical components are provided through GÜDEL.
So far the machining of welded aluminium pipes has been a monotonous and sudatory, manually performed work. The fluctuation of employees has been above-average high with the personnel deployed therefore.
With the automated pipe machining cell, these tasks could be reduced to a minimum because only very special flange shapes and pipes with overlength can not be machined by the robot. The cycle time for a pipe could be vastly reduced. While manual machining of the weldseams takes up to about 45 minutes, the robot can handle the same task in less than ten minutes. For both sides of a pipe, nota bene.
Finally an increase in quality can be observed because the robot delivers a constant output. A verification of the applied tools is taking place prior to every machining cycle and the operator is being informed if for example the flap wheel has reached a certain amount of wear.