Precision drive developed for aircraft wing spar former

Hot drape formers are popular with the aerospace industry because they can be used to make strong but lightweight parts for aircraft. In this case the former is to be used to produce wing spars.

AIC has been working in the field since its founding in 1990 and has always been at the forefront of the technology. It has incorporated many advanced features into its former designs, including zoned heating beds, precise bed location, tool pre-heating, sophisticated vacuum control and double diaphragm technology. These, combined with sophisticated software and controls, provide the ability to deliver solutions for the production of the most complex spars and ribs.

The Russian former is, at 11x2m, relatively large and like every AIC machine, is a bespoke design that allows laminates of over 20mm thickness to be formed to precise dimensions.

Essentially it consists of a vacuum bed containing the forming tool. Located over this is a ‘hot box’ which heats up the tool. There is also a ‘lamp bank’ which is used to heat the composite materials so that they mould themselves onto the tool. The hot box and the lamp bank are mounted in a lifting frame which can be raised by a drive mechanism, specified by Drive Lines, to allow clear access to the vacuum bed.

The lamp bank weighs 12 tonnes and, at 8.5 tonnes, the hot box is only a little lighter. They need to be raised by 1250mm, with the full extent of travel being achieved in 75s (i.e.1m per minute).

Matt Jones, who worked on the project for Drive Lines said: “The load was both large and heavy, and we had to be confident that it would always be lifted straight upwards, because any misalignment could potentially cause significant structural damage to the former.”

Working with AIC design team, it was decided to use a single central motor driving four screw jacks through a bevel reduction gearbox. In order to ensure an absolutely even lift Matt Jones knew he had to specify drive shafts that would not have unpredictable amounts of backlash or wind-up, but which would all transmit precisely the same torque over exactly the same distance.

The screw jacks selected were Drive Lines’ Grob MJ4 units and each was fitted with a bespoke safety nut and trunnion adapter designed specifically for the machine. The gearbox chosen was a Drive Lines PowerGear precision bevel unit and was connected to the jacks by R+W high speed elastomer line shafts.

The Grob MJ4 screw jacks are available from Drive Lines in a variety of designs, sizes and options to suit the application in hand. They are typically used to move a load linearly between positions and can be used vertically or horizontally. Maximum lifting force is up to 50kN each and stroke lengths are available up to 4m as standard – though these can be made longer by special request.

PowerGear bevel gearboxes are robust, reliable and capable of transferring considerable torques, so are suitable for this hot drape former project. They are also very compact, so often used in mobile applications and are designed to be maintenance free.

Drive Lines specifies R+W line shafts when there is a need to ensure precise motion and/or torque transmission. They are torsionally stiff so highly accurate even in the most dynamic servo applications. Used with Servomax elastomer couplings they eliminate vibration to provide smooth motion as well as accurate positioning.

Because of the combined reduction effect of the gearbox and screw jacks, a 7.5kW brake motor was specified by Drive Lines and this provides all the motive power needed.

Edd Hoyland, AIC’s Project Engineer, said: “Hot Drape Formers are essential in the aerospace industry. With our continued research and development, our Hot Drape Formers take carbon forming to new levels, enabling our customers to more efficiently produce aerospace wings and other composite parts.”