For a high-tech company group like AIRBUS production they should be of top standard right the way down the line.
Because of this in the Varel plant, where for instance fuselage parts for the AIRBUS are machined, a Fladder machine is being used for deburring of these large aluminium workpieces. In order to hold these parts optimally on the machine, the manufacturing specialists use a Witte Flip-Pod System, which works with vacuum.
For aircraft builders quality is top priority. Quality thinking is firmly anchored in the heads of the staff at the Airbus plant in Varel, where mostly milled parts are manufactured for the Airbus series A318-A321, A330/A340 and A380. Parts of the Eurofighter also belong to the range as well as fixtures and assembly docks which are supplied to assembly plants.
Wilfried Frerichs is master craftsman in large parts manufacturing, where the part sizes start at 1.20m and go up to 7.0m, for instance fuselage parts for the Airbus-Giant A380 coming on to the market in 2006, manufacture of which is just starting. These parts with large surface areas are mostly made of aluminium and milled out of the solid. Before they are sprayed, sharp edges have to be removed, to ensure sufficient spray adhesion.
In addition to skid-grinding methods the Airbus staff have an automatic Fladder 400/GYRO deburring machine at their disposal, with which parts up to 150mm high and 2,000mm wide can be machined and the necessary roundness/radius of 0.15 to 0.2mm is achieved. The workpiece length can be varied. It becomes especially profitable all for workpieces with many or large edges, which have sufficient flat surface area underneath to be able to be held with vacuum and the are plenty of those at AIRBUS VAREL.
The “heart” of a Fladder 400/GYRO is a grinding tip with 6 spindles, on which grinding cylinders are clamped. They comprise of flexible grinding tools like for instance double sided grinding rings which turn in pairs in opposite directions. While workpieces run through the machine, the grinding head rotates and oscillates, so that the tool machines from different angles during deburring process. Parameters can be adjusted, but are coordinated by the machine manufacturer. A change in spindle-turning speed also changes the rotation and a change in feed causes a change in oscillation.
However before the workpiece can go into the machine on a rail-guided transport trolley it has to be cleanly clamped. Because of different workpiece geometries as well as possible interfering edges due to conventional clamps, mechanical clamping solutions for the VAREL technicians were rejected right from the start “We are a high-tech company and want the optimal clamping solution.” They found this at Horst Witte Gerätebau, Bleckede.
The vacuum clamping system Flip Pod offered by Witte was exactly what the machining specialists had in mind from the beginning. Their immediate trust perhaps had tro do with the positive experience they had already had with Witte products i.e. Alufix in other areas, or was perhaps dependant on their long-term experience with vacuum clamping in general.
This technology involves a vacuum pump sucking out air between workpiece and chuck, so that the force created by atmospheric pressure effectively presses down on the surface. This hold-down force increases in proportion to the workpiece surface area.
Especially when milling large aluminium workpieces with thin material thicknesses, vacuum clamping offers unbeatable advantages, workpieces are clamped on an even surface over a large area corresponding to their geometry; magnetic clamping technology is not even an option.
For deburring with the Fladder machine a clean fast clamping solution is involved, for which relatively low clamping forces are required. The Flip-Pod vacuum system comprises of a vacuum chuck with a universal grid in which so-called pods lie. These pods are the contact points to the workpiece, onto which it is sucked and thereby clamped. Pods not required are flipped over and stored in hollows in the pod plate and are available at any time for using with other parts with different geometry.
The workpieces do not always have a flat base surface over their whole area. Aircraft parts especially must have high rigidity and minimum weight, which is why they are specifically ribbed and have irregular surfaces and steps. Standard pods are therefore not sufficient. For this reason Witte developed further pod models: There are half and three-quarter pods, exentric and even height-adjustable pods. The latter can be set using a slide caliper rule, pre-adjustment equipment or even by hand. A special locking device avoids unintended movement. And if in spite of the large range on offer no suitable pod is available, the AIRBUS specialists help themselves and change an exisiting solution to fit.
The processes in end machining are fairly simple. When a workpiece is on the deburring machine for the first time, first of all tests must be run to establish the optimal position of the pods. The experience of the staff plays a large role in this. Once the positions are set the clamping plan is entered into a computer. Special software has been developed in which the various clamping layouts can be entered. The software comes into its own when a workpiece has already been registered.
Uwe Hentschel, skilled worker for end machining, explains: “There is a bar code on each workpiece which we enter into the PC. On screen the relevant clamping plan appears, according to which we set the pods.”
Until now the PC stood next to the machine but for the future Wilfried Frerichs has had a smart idea: the clamping plan should be projected onto a large screen, so that his staff can still read it well from a distance of ten metres and save themselves having to walk backwards and forwards to the PC.
Generally clamping with the Flip-Pod vacuum system is a time saving matter. Since the clamping procedure takes place at the press of a button, clamping and releasing of the workpiece is possible in a second – or rather in five seconds, due to the fact that at AIRBUS in Varel the clamping table comprises of 5 elements with one pressure station each, which are activated by a hand lever. With this system deformation or damage of workpieces, which for example always occurs when using vises or clamps, is as good as eliminated. Therefore after one year’s experience with this clamping system Wilfried Frerichs is also extremely satisfied: “With the pods modified according to our requirements we can clamp all relevant workpieces securely and quickly. Just like we expected.”
Horst Witte Gerätebau, Bleckede
This company founded in 1969 today employs around 150 staff, including 20 apprentices, and is specialised in precision machining of large workpieces made of high-tensile aluminium alloys. Development and manufacture of different workpiece clamping systems is part of the production range as well as subcontracting for aerospace and medicinal technology. Witte is considered market leader as far as flexible fixturing systems and vacuum clamping technology is concerned. In their own design and development department new products are added to the current range and work on new solutions take place, so that meanwhile more than 80 registrations for Witte’s new developments have been granted.