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News Release from: Renishaw | Subject: HS10 laser scale system
Edited by the Engineeringtalk Editorial
Team on 01 June 2000
Jigless aerostructure assembly with
laser scales
Airbus has equipped one of its long-bed skin panel routers with the first Renishaw HS10 laser scale system in the UK, giving an accuracy of +/-1um/metre.
With the long-term view of achieving jigless assembly of aerostructures, the Filton factory of BAe Systems, Airbus has equipped one of its long-bed skin panel routers with the first Renishaw HS10 laser scale system in the UK; the system has an accuracy of +/-1um/metre The company embarked on its Jigless Assembly research Project three years ago, the target was to produce accurately drilled components
This article was originally published on Engineeringtalk on 3 Sep 2008 at 8.00am (UK)
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With the introduction of Jigless philosophies the company expects to save up to 75% of its multi-million pound investments in manufacturing assembly jigs for new aircraft.
Substantial savings could also be realised in existing sub-assembly procedures for Airbus wing and fuselage sections.
"The project highlighted the need to examine the whole question of machine tool accuracy in more detail.
We needed a real time temperature-compensated measurement system," said Development Manager, Manufacturing Systems Engineering, Colin Mitchell.
He continued, "We are working on a production pilot project for jigless assembly which will offer up to 20% in recurring costs savings and up to 75% in jig investments.
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By accurately drilling components prior to assembly, we will eliminate the expensive jigging and manual alignment work which is presently carried out in jig." Guaranteeing accuracy and repeatability of the location of datum holes in components is a demanding process.
To achieve the required repeatability, machine tools need to continually compensate for the thermal expansion of the machine structure and the component, something conventional scales cannot do.
Interconnecting Renishaw's HS10 laser scale system, with the machine tool's controller, the company has successfully produced large area components with accurately-drilled datum holes.
Eliminating expensive jigs Normally, individual components are set up in large, complex jigs to form a complete assembly.
Once the components have been positioned, holes are drilled, countersunk and rivetted.
The more detailed drilling and rivetting work to assemble the components, are performed manually or with semi-automatic machines.
Accurately pre-machining the components will eliminate much of the jigging originally designed to position them.
Instead, parts will be self-locating, and be ready for drilling and rivetting using simple holding fixtures that reduce assembly costs.
"The next step will be to enhance the CNC (Computer Numerically Controlled) machinery for drilling and rivetting during assembly.
Our target is to realise jigless assembly for the smaller and medium-sized sub-assemblies.
The key assemblies are panels, wing leading and trailing edges, and any machined component assemblies.
We are also looking at how to apply improved assembly techniques to components for the new wide-body Airbus, the A3XX," says Mitchell.
"All this work demands a much better definition of assembly accuracy.
It involves a whole new philosophy of moving away from jigs and fixtures." Mitchell says that the results of an earlier Panel Demonstrator Project identified the need for far more repeatable components.
To do this, BAe Systems Airbus has to control machine tool accuracy, machine tool calibration, tolerance budgeting and temperature compensation.
BAe Systems Airbus Research and Technology Group, selected an Asquith Butler 8-metre long-bed, travelling gantry, single-head high speed router to evaluate retrofitting with the Renishaw HS10 laser scale system.
The machine is normally producing a variety of panels for Airbus and Avro RJ.
The two main factors affecting repeatable positioning accuracy when machining components are: * Thermal expansion of aluminium alloy is 23um/1C/metre and the skin will move in response to changes in ambient air temperature.
Thermal expansion of steel, and therefore accumulative ballscrew error, can be 12um/1C/metre Gareth Tomkinson, Renishaw's UK Account Manager (Laser Products) explains: "All these variables can occur during the machining cycle, even when the machine pauses to change tools, from drilling to tapping.
Essentially, the laser scale system eliminates the effects of any structural expansion in the machine tool.
The system, using temperature sensors, detects temperature changes in the component and applies an expansion coefficient in the software, to precisely track movement in real time." Thermal distortion of +/-150um (+/- 0.15mm) in a 16-metre long aluminium sheet, arises from only a +/-0.5C temperature variation! On a 'move and stop' basis, the HS10 laser scale system has an accuracy of +/-1um/metre up to 60 metres.
For example, again on a 'move and stop' basis, cumulative error over 8 metres would be limited to +/-8um.
The system can also eliminate any 'crabbing' effect on machine tool gantry's which have dual drives, as they traverse the machine bed (X axis).
Normally, when clamped on a vacuum table, skin panels do not move.
However, the table itself can move due to variations in temperature.
Thermocouple sensors are therefore fixed to the vacuum table to enable compensation for these errors.
Retrofitting the lasers Two HS10 laser scale units are fitted, one on the X-axis which targets a reflector mounted on the travelling gantry.
The second laser scale is located on Y-axis, the 5-metre wide gantry bridge, which tracks the traversing machining head.
These are connected to a PSU card data unit, linked to the machine tool's Allen Bradley 8600 controller.
The HS10 laser scale system comprises three components.
An 'eye safe' <1mW helium-neon laser a stationary interferometer, and a moving reflector.
The system's basic accuracy is +/-1ppm, or +/-1m/m, and resolution is configurable down to 79nm (0.079um).
The HS10 system will cope with machine tool axis feed rates up to 1m/sec.
Renishaw has designed the system components to be resilient to machine tool operating conditions (oil, swarf, lubricants, coolants and vibration).
On the BAe Filton installation, the beam is fired through conduits to avoid any physical interruptions.
It is a fully work-hardened system.
Retrofitting the HS10 laser scale system was carried out by Sedin UK, under the direction of Peter Willoughby.
"The system needs hardly any maintenance," says Willoughby.
"The optics should be cleaned every six to twelve months, depending on machine shop conditions." An electronic signal indicates 'beam low' to the machine operator when the optics require cleaning.
In addition, no special surface preparation is required to mount the equipment, as is the case with conventional linear scales.
The beam can be fired under a machine's telescopic slideway covers or, like the Filton installation, outside the moving parts and protected by a simple conduit.
"We bought the laser system with the long-term view of eventually fitting such systems to long-bed machines at our other Airbus site at Broughton," says Mitchell.
"Most of the work we undertake is for Airbus, which is the prime target.
We aim to produce our first production components using this philosophy early this year.
The Demonstrator panel - a fuselage section - has been very successful, the culmination of some three years' work on a relatively low budget.
Renishaw has given us a real time temperature compensation system.
As for realising the ambitions of our project, we are nearly there.
We now understand all the elements and we are confident we can take it into production," says Mitchell summing up.
Renishaw has supplied HS10 laser scale systems to plants worldwide.
In the UK, systems are in operation on the Giddings and Lewis Variax 'hexapod' machine tool at the University of Nottingham.
Laser scale systems are also being commissioned on long-bed milling machines at the BAe Systems site at Chester.
Tomkinson concludes.
"Renishaw is offering machine tool users a proven, in-process, highly accurate real-time measurement system. Request a free brochure from Renishaw ...
In our opinion, the HS10 laser scale system offers the biggest single improvement in process capability for large machine tools.".
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