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Spot welding or resistance welding was often used to join steel sheets, but today this is no longer economical due to the modern material mix. In addition, the automotive industry is under pressure from legal requirements to reduce CO2

emissions, reduce weight and to find

alternative joining methods. Where access to both sides of the

connection point is available rivets can be used, but if only one side is accessible then the direct screwdriving flow form principle can be used. Here, a flow form screw is positioned on an aluminium or steel sheet without pre-drilled holes and the screw is applied with a high pressure down-force and rotates at high speed, generating a frictional heat which forms a crater through which the screw’s thread passes under reduced pressure. A machined thread is then created. After the flow passage has been formed the speed is reduced and the screw is tightened to the head connecting surface. The final tightening of the fastener to the pre-determined parameters of torque and angle then takes place. The entire procedure usually takes less than two seconds. FFS (flow form screwdriving) units

usually shoot the flow drill screws tip first through the mouthpiece, which can damage the screw tip geometry. But, with the DEPRAG flow form screwdriving unit, the screw is shot in head first and an integrated revolver separator positions the screw so that its position is secured even for overhead assemblies. The next screw is reloaded already as the first screw is being seated.

Jürgen Hierold, sales manager at DEPRAG said: “We were approached by one of the largest internationally active companies in the automobile industry with the demand for a system which presented screws without a feedhose. We have developed a magazine system for our customer which is based on three basic elements: the screw magazine, the magazine exchange station and the screw feeder.” So, while one magazine is in operation, docked on the FFS unit systematically and presenting 32 fasteners, the second magazine is being filled at the exchange station by the screw feeder. The screw feeder is outside the activity range of the robot, refilling screws without interference in the danger zone. If the first magazine is empty then a robot on the exchange station removes it to be refilled and replaces it with an already filled magazine so that assembly may continue. In use, the operator must only enter the

screw geometry (shaft diameter and length), information relevant to the part (quantity, material and strength of the sheet, with/without drill hole) and the tightening parameters onto the HMI panel. Another benefit is the mouthpiece exchange device for the application. The adjustment to a different screw type or fault clearance is taken care of at the touch of a button. The lock is loosened and the mouthpiece can simply be exchanged.

Furthermore, with the FFS unit the cylinder controlled nosepieces

control the release of the screws as soon as the screw begins to form the passage. Therefore, friction between the screw head and nosepiece is greatly reduced.

Deprag Schulz Enter 208

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