Product category:
Gears, brakes, couplings and engines
News Release from: Brammer UK | Subject: Gearboxes
Edited by the Engineeringtalk Editorial
Team on 31 October 2000
Bespoke gearbox on precision welding
cell
BSL have designed and built a bespoke gearbox to drive the central clamping mechanism for an innovative eight axis precision welding cell, built by Bauromat (UK)
BSL have designed and built a bespoke gearbox to drive the central clamping mechanism for an innovative eight axis precision welding cell, built by Bauromat (UK) Ltd designers and integrators of special purpose machines The project was a real design challenge, involving six output shafts that had to turn in unison to an accuracy of 0.5 minutes of a degree, a 600mm diameter design envelope and a clean room operating environment
This article was originally published on Engineeringtalk on 7 Jun 2000 at 8.00am (UK)
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The welding cell consists of a central mandrel mounted on a swinging cradle arm manipulator inside a frame and a laser guided welding torch attached to a robot arm.
The gearbox forms the central drive unit for the expanding mandrel that holds a three tonne toroidal super conducting electromagnet in place while its stainless steel pressure jacket is welded.
The magnet is manoeuvred into place by a crane and clamped from inside by six horizontal composite cushions mounted on bars.
The bars are attached to linear guides and driven outwards by six ballscrew shafts extending from the central gearbox.
The magnet and the mounting assembly are then rotated as a complete unit during the welding process.
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Gary Price, BSL's product manager for geardrives describes the accuracy involved, "The fine tolerance of the gearbox output shafts, at 0.5 minutes of a degree between all six shafts in one revolution, is required to ensure that the weight of the magnet can be supported firmly by the six separate composite cushions without distorting the shape of the steel jacket while it is being welded".
The welding operation secures stainless steel lugs to the outside of the body and completes a continuous welded seam around two diameters at both ends.
Minimising distortion is crucial to ensure the uniformity of the weld, which in turn is vital for a pressure vessel that will hold liquid Helium at -2700C within a vacuum.
The lack of distortion prevents dimensional stresses being welded into the shape that could cause metal fatigue during repeated temperature induced expansion and contraction.
Keeping the vessel centred during the weld is also important to ensure the welding guidance system remains within its field of vision to keep the weld consistent.
The welding torch is guided by a laser and a solid state camera.
It will compensate for slight deviations from perfect roundness in the pressure vessel, but the accuracy of the gearbox ensures the vessel is centred to achieve the best result.
Fitting the gearbox unit into a 600mm diameter space was also a challenge.
In order to ensure the strength and precision of the unit, the six outputs shafts are mounted in a six inch thick annealed steel body by two opposed tapered roller bearings.
To prevent backlash, the output shafts have internal pinion gears precision mounted onto the ends and are driven by two bevelled gears mounted at the top and bottom of a single drive shaft.
To optimise the accuracy of the whole drive system, all the gears are matched sets.
The complete welding cell is designed to operate in a clean room environment, hence the mechanical option was favoured to power the mandrel over hydraulics - which can leak, or pneumatics which require a separate compressor and air supply.
All the shafts in the gearbox are fitted with high temperature seals, the gearbox is sealed for life and will require no maintenance.
Gordon Biggs of Bauromat (UK) Ltd.
commented: "The quality of the general advice and expertise available from BSL has ensured that the majority of the power transmission components for this project have been sourced from them.
The gearbox itself fits our design specifications with a strong, simple and practical solution ensuring that reliability and precision are maintained throughout the life of the machine.
The magnets are produced by Oxford Magnet Technology and destined for use in medical body scanning machines so these attributes are paramount".
The BSL service is available from over a hundred local Customer Service Centres, offering sales and technical support nation wide.
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