Servo presses deliver 50 per cent productivity gains

Paul Boughton

The latest servo presses, developed and manufactured by Schmidt Technology, are playing a crucial role in helping Airbus improve the output and product quality from its wing stringer manufacturing facility at Broughton in Flintshire, Scotland.

In particular, the six Schimdt 460 servo presses with Schmidt 4000 control systems have enabled productivity to be increased by over 50 per cent, while significantly enhancing the control that Airbus’ engineers have over what is a complex stage in the production of safety-critical airframe components.

Wing stringers run down the length of each wing and, in conjunction with the horizontally positioned wing ribs, provide both structural integrity and give each wing its profile, to optimise flight performance and fuel efficiencies.

Top and bottom stringer sets are either bolted or riveted to the outer wing skins and, depending on the model of Airbus aircraft, number between 34, for the single-aisle short haul A320, and 70, for the company’s latest flagship, 525 seat A380.

In each case, the stringers are firstly machined from extruded billets of aluminium to either an I-shaped profile, with a single upright section and cross sections at top and bottom, or a J-shaped profile, with a half length top section; the cross sections are used to fix the stringer to wing skins.  Once machined, the stringers are then cold formed using the SCHMIDT servo presses to give them their specific profile. This typically involves multiple bends to create a carefully determined curve that runs along the length of each stringer; in addition, the stringer profile may be need to incorporate a twist along its length so that the cross sections align correctly with other components to which they are be fixed.

Ian Kerry, Engineering Group Leader at Airbus, explains: “The accuracy, quality and consistency with which we form the profile of each stringer is critical, as in flight they have to withstand a variety of loads, which will vary depending on where in the wing they are located.  Manufacturing tolerances are therefore exceptionally tight and we use a sophisticated and specially developed Universal Contour Checking Machine (UCCM) that measures the profile of each finished stringer to within a few thousandths of an inch.”

Previously, Airbus has used a number of traditional hydraulic presses.  Although these were capable of forming stringers to the required specification they had no computer control facilities which, as Ian Kerry points out, “meant that all of the knowledge about how best to create each stringer resided with the machine operators, making it difficult for us to determine the most efficient method of producing consistent levels of quality.


One consequence of this was that stringers would often need to be moved backwards and forwards between the presses and the UCCM, with many small adjustments being required before we were within tolerance”.

To address these issues, and as part of an ongoing programme of improvement at the Broughton site, Airbus decided to replace the presses, choosing to work with Schmidt Technology as an acknowledged leader in the field.

Manufacturing Engineer at Airbus, John Jones, says,: “We worked closely with the team at Schmidt Technology, who listened carefully to what we wanted to achieve and then helped us over a lengthy period to ensure that the presses and associated software and controls were developed to meet our exact needs.  We also involved our production team in this process, including the press operators, who were influential in determining factors ranging from the positioning of panel controls to refinements in press operation that help to minimise dead time between strokes”.

 The 460 Servo presses are among the largest that Schmidt Technology manufacture and are capable of producing a ram force of up to 150kN, with a resolution better than 0.1µm.  The six presses used by Airbus have been specially developed to include dedicated control technology, based on the Schmidt 4000 control system; plus three-point tooling with fixed top forming tools and swivelling bottom tooling, to simply press operation; and an innovative light curtain, which was specified with help from members of Airbus’ health and safety team.

John Jones is delighted with the operation of the new presses. “A crucial benefit is that the controllers, with Ethernet links, enable us to gather extensive data at every stage of the forming process.  We therefore have the information to enable us continuously to improve quality and repeatability. In practice, this has meant that we are able to create a data set of values for each stringer profile, so that when it is moved to the UCCM it is correctly formed, without the need to be returned to the press for further work, while variations between stringers with the same profile have been eliminated. These factors alone have enabled us to increase our production output of stringers by over 50 per cent.”

Schmidt Technology

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