06-12-2009 | BARDEN CORPORATION | PLYMOUTH UK
By working closely with its bearings supplier, Ultra Electronics Precision Air Systems has reduced bearing costs and assembly times by 40-50 per cent on its high pressure pure air generator.
Ultra Electronics Precision Air Systems (Ultra) is part of Ultra Electronics, a group of specialist businesses that design and manufacture electronic and electromechanical systems, sub-systems and products for defence, security and aerospace applications.
Worldwide, Ultra Electronics employs around 4,000 staff, focused on high integrity sensing, control, communication and display systems. Ultra's products and services are used on aircraft, ships, submarines, armoured vehicles, surveillance and communication systems, airports and transport systems.
Ultra is a leading manufacturer of compact on-board gas solutions, including compact gas compressors for the defence industry. Applications include cryogenic cooling systems, stores ejection and release systems, and pneumatic systems. The company produces a range of mini-compressors known as HiPPAGTM (High Pressure Pure Air Generators). These are compact, lightweight, electrically powered air compressors that are carried on-board various military platforms.
The HiPPAG airborne compressor provides a continuous source of high-pressure pure air to cool the infrared seekers of an aircraft's defensive missiles, keeping them ready for action. HiPPAG also provides a controllable energy source for the pneumatic ejection of aircraft munitions, whilst meeting the emerging requirement for launching increased quantities of smaller, smart munitions.
More than 5,600 HiPPAGs have been delivered for defence applications around the world. HiPPAG has been developed for the F-35 JSF aircraft and is being supplied for Boeing's Small Diameter Bomb programme, the Eurofighter Typhoon, the US Marine Corps AV-8B Harrier, AH-1W Super Cobra, F/A-18 C/D Hornet, and the US Navy F/A-18 E/F Super Hornet aircraft.
At the heart of the HiPPAG system is a bearing assembly that is based on a swash plate configuration. Supplied by The Barden Corporation (UK) Limited, this super precision bearing is a custom-designed assembly that comprises a pair of bearings mounted on a cranked shaft with a 15-degree offset between axes.
Essentially, the function of the bearing is to transfer rotary motion into linear motion, enabling the axial motion of the HiPPAG compressor pistons. Typically, the bearing assembly will comprise a pair of solid, pre-loaded angular contact bearings on the swash axis and a second pair of angular contact bearings for the shaft axis, which are spring preloaded and share a double row inner ring. The bearings are made from carbon chrome and use standard steel balls, as the HiPPAG application speeds are relatively low (less than 700rpm).
These two bearing sub-assemblies are then mounted onto the offset shaft. Ultra subsequently receives this completed sub-assembly from Barden, which it simply drops into its HiPPAG housing to mate with the brushless DC motor, which sits on one side of the bearings, with the compressor on the other side.
"Since working with Barden, I would estimate that Ultra PAS has saved between 40 and 50 per cent on bearing costs and around 50 per cent on bearing assembly costs," states Martin Carpenter, Engineering Director at Ultra PAS.
The relationship between Barden and Ultra PAS goes back some 10 years or so. As Carpenter confirms: "Over the years, Barden has evolved and simplified the design of our HiPPAG bearing assembly, leading to a significant reduction in both component count, bearing costs and assembly times. We now have two or three different designs of bearing assembly that we use regularly on our HiPPAG units."
"Originally, we approached a number of bearing suppliers, including Barden, because we needed to take some cost out of our original HiPPAG. One of our customers at the time was Boeing, who suggested we carry out a DFM [Design-For-Manufacture] project on the HiPPAG. One of the areas we looked at first was the bearing assembly. Essentially, our engineers started again with a clean sheet of paper and went back to basics. We wanted to see which suppliers could come up with the best bearing design."
Carpenter says that Barden's original design was selected because it utilised lower cost manufacturing methods using existing tooling and (at the time) a cellular manufacturing approach that also contributed to a lower cost bearing solution.
The new bearing assembly integrates directly with the HiPPAG unit and is smaller and lighter than the original. The original flange mounted assembly has been replaced with a threaded outside diameter that enables through-grinding. Gary Hughes, Application Engineering Manager Aerospace at Barden comments: "The latest design incorporates precision-milled 'pots' in the outer ring for the piston road ends, which reduces the component count. Over the years, we've made lots of design iterations, including a low duty unit in SAE52100 and a special high duty unit that uses our 'Cronidur 30' corrosion resistant steel with its increased fatigue strength."
According to Hughes, there were several engineering challenges to be overcome. For Barden, HiPPAG is a low speed - high load application with a short life of less than 500 hours and so the design had to reflect this. Through a 360-degree revolution of the HiPPAG, there's a constantly varying load cycle on the bearings and so we had to develop new methods of modelling this," explains Hughes. "This led to a bearing devolved from the original Ultra design to two bearing pairs and a cranked shaft. Investment in new machinery at Barden also enabled us to reintegrate the bearings into the HiPPAG shaft. We were able to eliminate the use of external clamping by incorporating threaded outside diameters on the bearings."
But it's not all been about design challenges. As Martin Carpenter puts it: "Over the years, we've developed a great working relationship with Barden. Their engineers are very proactive and are prepared to invest time and effort in engineering new concepts and prototypes for us. It's a truly collaborative approach between the two companies' engineering teams.
"We also like having local support that's only a couple of hours' drive away from our own factory. There's nothing quite like having a face-to-face meeting between engineers to discuss and share new design concepts. We've done a lot of this with Barden and it has culminated in some very good, cost-effective designs."
A market leader in the design and manufacture of super precision ball bearings for more than 60 years, Barden supplies products to a range of extreme environment applications, including vacuum pumps and the aerospace industry. With a customer base that includes NASA, BAE Systems and a number of other leading aerospace and defence companies, Barden boasts state-of-the-art production technology and a wealth of engineering expertise.
A high percentage of Barden bearings are tailor-made for specific applications. The product range encompasses predominantly radial, single row, super precision, angular contact and deep groove ball bearings which meet and exceed ABEC 7/9 (P4/P2) standards. Bearings are manufactured and controlled under strict aerospace procedures, providing full traceability, controlled lubrication and complete retention of records. Manufactured bearing sizes range from 5mm to 180mm outside diameter. The company is capable of manufacturing bearings to a geometric tolerance of P2 or better, and envelope dimensions to P4 or better. Raceway roundness is better than 0.5μm, with raceway surface finish better than 0.025μm Ra.
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