Product category:
Workholding - miscellaneous clamping systems, components
News Release from: Horst Witte Geratebau | Subject: Clamping system
Edited by the Manufacturingtalk Editorial
Team on 12 July 2007
Clamping system holds skin structures
for milling
As conventional chemical milling had to be replaced with milling, an aerospace company needed a customised clamping system to hold aircraft skins while machining.
An aerospace company wished to mill large, pre-rolled, cylindrical-shaped Airbus skins These were formerly chemically milled - a process considered now to be time-consuming and ebvironmentaly unfriendly
This article was originally published on Manufacturingtalk on 3 Jul 2007 at 8.00am (UK)
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But, to mill contours and pockets into the cylindrically formed aluminium workpieces exceeding 3000mm long, they have to be pressed into a flat position.
Witte developed a clamping system for the job.
It consists of several sections, designed to fit onto an existing machine within a confined space.
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The equipment consists of the following.
* Mobile vacuum table comprising of a substructure - it houses hydraulic, pneumatic, electric and control accessories as well as vacuum grid plates, on which adapter plates together with workpieces are clamped.
* Adapter plate - it corresponds to the outline and drill hole-pattern of the workpieces.
The plates are positioned and secured on to the vacuum grid chucks.
* Moveable roller bar - it is used for rolling the cylindrical parts down flat.
* Frame structure mounted over and around the machine - this item is firmly fixed to the floor and houses and guides the roller bar.
* Control unit and SPS controls.
* Hydraulic and vacuum units with switch cabinet.
The vacuum grid chuck consists of two segments, each has eight separately adjustable vacuum areas.
The arrangement gives a high degree of flexibility to accommodate different workpiece sizes.
The parallelism of the grid plates is < = 0.05mm and guarantees adherence to tolerances.
Hydraulically operated clamps are permanently fixed on the three open sides of the roller bar equipment.
On the side facing the gantry there are also hydraulically operated clamps, but these can be moved pneumatically to adjust to different workpiece lengths.
The clamping process is as follows.
* The machine table is moved to loading position (on the extreme right of the machine).
Depending on which part is to be machined the correct adapter plate is mounted on to the vacuum grid chuck.
* The operator then selects the correct program to control the clamping process.
* A crane lifts the workpiece, with up to 5mm thickness, above the clamping equipment and sets it down against stops on one edge.
The part is clamped on the operator's side.
* The automatic clamping process is set in motion.
The bar has six rollers and is activated as it descends from 'park' position down on to the part.
The bar rolls at a speed of 2m/min over the curved workpiece, gradually flattening it.
Simultaneously, the hydraulic clamps are operated on the outside edges, while the corresponding vacuum clamping areas are switched on.
The bar stops just before the end of the workpiece.
The hydraulic clamps on the remaining open side are activated.
* The entire workpiece is securely fixed in a flat position, the roller bar moves back into the 'park' position and the machine table is moved to the opposite end of the machine into machining position.
* Milling pockets, drilling hole-patterns and contours can begin.
"Witte's 3D designers, in dialogue with the user, came up with a custom-built solution for this new technology," explained Lesley Osborne, Witte regional manager, who coordinated the project.
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