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Vacuum, mechanical clamps team to mill Airbus skin: to mill large but thin sheets of aluminium, without damaging the pre-formed aluminium sheets forming the fuselage, Airbus is using a combination of mechanical and vacuum clamping and work handling equipment.

Manufacturing of fuselage parts for different Airbus projects is carried out in Nordenham, in Northern Germany. Typically in the aircraft industry weight is an important factor and in almost all areas weightsaving has been exploited to the extreme.

In order to enable manufacture of lightest possible fuselage parts without any loss of quality Witte Bleckede and Airbus Nordenham have developed a special fixture for clamping pre-formed aluminum sheets during machining

A cylindrical Airbus fuselage segment consists of several single metal sheets. The parts, measuring up to 34.47' (10,500mm) X 8.86' (2,700mm), run through several work processes, such as rolling, before they reach their final cylindrical form.

[ILLUSTRATION OMITTED]

After the rolling process weight reducing pockets are machined into those parts of sheets, which are statically under less stress. If pockets were machined beforehand they would not come up to quality standards.

Chemical milling was considered as the first option for removing this material. However, for economical and environmental reasons Airbus Nordenham wanted to eliminate chemical processes and presented this challenge to Witte Bleckede with the aim of finding a solution for positioning, clamping, and machining of preformed parts.

Machining Preforms

"We want to start with machining of pre-formed parts", says Guenther Kuck, of Airbus. "Our fundamental idea--external forces should temporarily flatten the pre-formed parts into their original shape and they should be machined in that position. That seemed the most economical solution, anything else would have cost too much time and money."

A custom fixture was developed to press down these parts and hold them using vacuum and clamping elements during machining. After machining, the sheets are released and go back to their former contour.

The fixture design incorporated mechanical, hydraulic, and vacuum clamping elements.

Press - Roll - Clamp

First, all sheet metal parts are lifted with a crane and vacuum cross bar onto clamping fixture and positioned using stops on one long side. Hydraulic clamps are activated along length, clamping the part along its positioned edge. On the same long side, a bar approximately 46' (14m) long, equipped with special rubber rollers, starts to move and presses parts down flat. It is guided by linear guiding elements and servomotors positioned on both side edges of clamping surface. Hydraulic and mechanical clamps along the sides are activated step-by-step, according to flattening process. All clamping elements are monitored by sensors and shown on a display.

[ILLUSTRATION OMITTED]

While the roller bar is moving, the sheet metal is pressed onto the clamping surface. At the same time, corresponding vacuum areas are activated from underneath, clamping section-by-section until the whole area is secure. Pressure difference switches control each vacuum area.

After the part has been pressed flat and is completely clamped, a visual check of position and operating vacuum takes place. The bar goes back to its start position and milling can begin.

"The complete vacuum clamping area measures about 13.5' (4100mm) X 42.7' (13000mm). The total surface is divided into 36 individually operated areas. This means parts of different sizes can be clamped effectively, giving a high degree of flexibility," Bodo Winowsky, sales manager at Witte Bleckede explains.

A total of 50 hydraulic and 11 mechanical clamping units ensure part positioning along the sides. "To stop a part moving sideways we used hydraulic clamping on three sides and mechanical clamps on the fourth because hoses necessary for hydraulic clamping would have limited access and disturbed operators on that side," says Airbus's Kuck.

"We welcome complicated clamping challenges," adds Winowsky. "In this case we made a small sample fixture to check clamping process and assess small problems as early as possible in order to avoid them on the real thing." Witte Bleckede

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Title Annotation:WORKHOLDING / TOOLHOLDING
Publication:Modern Applications News
Geographic Code:4EUFR
Date:Jul 1, 2005
Words:624
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