Research Projects Index

Project 1 - Improving worm gear performance

This 3½ year research programme, which has been part funded by the DTI and the BGA Collaborators, consisting of Castrol Limited, David Brown Textron, Holroyd M/C Tools/Rotors and Renold Plc has investigated the potential for significant improvements in load carrying capacity in worm gears. A comprehensive contact analysis for cylindrical worm gears has been developed and made available to the collaborators. A back-to-back test rig for worm gears of 160 to 200mm centres was designed, manufactured and commissioned and this can test single and multi-start worm gears at torques up to 18000 Nm.

A number of experimental worm-gear geometries have been developed; but the available facilities for grinding hardened worms and wheels have limited the gear geometries which can be manufactured. It has thus not been possible to explore the full potential of hard to hard worm gear pairings with the experimental gears to fulfill all the original aims of the project. To clarify the contact geometry and performance of the ‘zero pressure angle’ worm gear mating with a helical wheel, further tests have been carried out using a case-carburised worm and a phosphor bronze helical wheel. The performance of the ‘zero angle gear pair was good and exceeded the performance of standard cylindrical worm and globoidal wheel. A number of experimental worm-gear geometries have been developed and further studies of the effect of phosphor bronze on boundary lubrication in cylindrical worms are in hand to improve understanding of gear performance.

In addition to the research at Newcastle University, the University of Wales -Cardiff have been developing software for the prediction of the Elastohydrodynamic Lubrication (EHL) films that are generated in worm gears. This project has been funded by the EPSRC and the results to date have been most promising. For example the project has already revealed regions of poor film generation associated with the orientation of the contact area relative to the effective lubricant entrainment direction at the edges of the contact; this will have considerable implications for future designs.

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Project 2 - Analysis and measurement of Transmission Error in precision worm gear

A follow-on project at Huddersfield University with the same group of collaborators has commenced, based on the findings completed research and using the test facility and will be directed primarily at investigating the effect of detailed gear geometry and gear loading on the bedding-in process in worm gears, and the resulting change - if any - in transmission error.

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Project 3 - Spline stressing and wear research

This successful project, jointly funded by the DTI and by a GRF consortium, aimed to develop an accurate elastic model of contact and stressing in highly loaded splines. It achieved it’s objectives in developing a validated full 3-dimensional spline coupling stressing and contact model, based on Boundary Element techniques, and in conducting research, at Nottingham University, into spline fretting/wear using a range of test rigs.

The outcome of this work is a user friendly computer software programme which will assist a specialist designer in producing efficient and effective spline joint couplings for a wide variety of aerospace applications. A project investigating industrial and automotive splines is planned for the future.

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Project 4 - Generative gear grinding cost reduction

This programme of research, supported by the DTI and The Institute of Grinding, has been successfully completed and the results reported at a technology transfer seminar.

The research revealed significant differences in performance between various grinding wheels and determined both the wheel wear and grinding burn limit for roughing and finish grinding. Improvements were identified in cutting oil delivery and developed a calculation procedure for optimising grinding feed and speed rates to achieve high metal removal rates without grinding burns, while maintaining excellent accuracy.

A follow-on project will investigate the improvement in Form Grinding, in particular the control of grinding burn and wheel wear in this process. This work has wide implications to the majority of high performance gears being manufactured today.

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Project 5 - Improving gear performance by enhancing the fatigue properties of steel

This substantial research programme involves 19 BGA Members and will investigate ways of improving the fatigue strength of gear steels, heat treated by case-carburising, nitriding and induction hardening. The project is supported by both the DTI and MoD(N) and is a development of the first BGA Gear Research Council research programme investigating the fatigue strength of existing gear steels. Alternative heat treatments and surface treatments are being investigated to improve the surface and bending fatigue strength of the following gear steels:

In this programme, helical and spur gears, running at 75mm and 160mm centres, are being tested for surface and bending strength and pulsator tests are being carried out for bending fatigue strength. In particular new test facilities, funded by the BGA consortium and the MoD(N) Navy, have been designed, built and commissioned which are, for the first time, allowing the fatigue testing of helical gears at powers up to 1800KW.

The project's Heat-Treatment sub-committee has identified a number of modern processes which can enhance gear fatigue strength and reduce distortion. In addition to the original project's aims, a limited programme of work on heat treatment distortion utilising the test gears will be carried out and this is currently being planned.

A Gear Cleaning and Shot-Peening sub-committee has similarly been advising the influence of these processes on gear fatigue strength and planning treatment processes, whilst close liaison has been maintained with Project 6 to respect to lubrication and pitting failure criteria.

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Project 6 - Improving Understanding of Micro Pitting

Phase 1

In addition to the practical research, an EPSRC and BGA joint funded project started in Sept 1998 at the University of Wales -Cardiff with the aim of providing a special Elastohydrodynamic Lubrication (EHL) solver for thin film/rough surface conditions, occurring in typical gear tooth contacts. This method will cope with conditions in which the film is an order of magnitude or less than the surface roughness. The time-dependent effect that occurs in gears due to surface roughness that moves relative to the contact shows the interaction of individual asperity contacts, within the overall nominal Hertzian contact, and leads to a prediction of individual asperity pressures and films. The solver is currently being developed to include thermal effects arising from shearing of the lubricant within the contact. The ultimate goal is to provide program which can be used to study the hydrodynamic effects in real gear tooth contacts and provide the basic micro-asperity pressure distribution data required for other surface fatigue studies.

Phase 2

Phase 1 of Project 6 has completed with the final presentations being given by the Design Unit, QinetiQ and the University of Wales, Cardiff on 30th July 2003 at the University of Newcastle-upon-Tyne.

The proposals for Phase 2 were also presented and interested parties are invited to examine the documents.

For further information, please contact Andy Harry at BGA.

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Project 7 - Improved gear stress analysis

• A computer program has been written to implement the new BS-ISO 6336 (1996) gear standard. This was demonstrated in March 1998 and, having incorporated several suggested improvements, was then evaluated and trialed by eight BGA consortium companies. This software has now completed its evaluation period and is available for purchase; and further details can be obtained from the BGA Office.
• A 2½ D mesh model is being developed based on a ‘thin-slice’ FE model of pinion and wheel and an analytical elastic mesh analysis and this work is nearing completion. The aim is to provide the gear designer a more detailed and comprehensive analysis tool than a 2D FE model but being an order of magnitude quicker than a full 3D FE model. This package can be used by itself or as a precursor to a 3D FE analysis and will enable gear geometry (crowning, end relief, tip and root relief) to be optimised for minimum stress and for minimum transmission error. The FE modeller and solver have been written, together with input routines, and work has nearly completed on the elastic mesh analysis. This work was reported at a recent BGA Research Committee meeting and a more detailed presentation of the finished product will take place at the next meeting.

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Project 8 - Net forgings

This three year project centred at the University of Birmingham, commencing in April 1998, is funded by EPSRC and by 6 BGA members. It aims to develop forging techniques/die designs etc to be able to produce gears of single helical and spur form, up to 200mm dia and of at least ISO 5 accuracy. In addition, the post forged surface finish will be such that no other final machining operations are necessary. The work will take account of surface hardening and will look at producing forged gears with profile modification and crowning. The first gears, of a spur design, are currently being forged and this stage will be followed by the production of two types of helical gears.

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The Fatigue Strength of Gear Materials

A BGA research programme entitled "The Fatigue Strength of Gear Materials" was concluded in 1997 and determined the surface and root bending fatigue strength characteristics for gears manufactured from the following gear steels:

• 655 H13 (En 36) carburising steel
• 20 MnCr 5 carburising steel
• SAE 8620 H - carburising steel
• 722 M24 (En 40B) - nitriding steel.

Details of the Project work were presented at two seminars, in June 1996 and July 1997 in Sheffield for GRF Members. The final report was available to Members in the form of a full report and a summary of design data. Individual seminars and workshops will be held according to demand. The programme determined the surface and root bending fatigue strength characteristics for gears manufactured from the following gear steels:

• 655 H13 (En 36) carburising steel
• 20 MnCr 5 carburising steel
• SAE 8620 H - carburising steel
• 722 M24 (En 40B) - nitriding steel.

In 1996 the following work was carried out:

• The test gears in 722 M 24 (En 40 B) nitriding steel were machined, hobbed, ground and nitrided, the heat treatment being carried out by Flame Hardeners and Allen Gears.
• The programme of back-to-back testing of 20 Mn Cr 5 gears was completed, with very satisfactory
• performance recorded for this low alloy steel.
• The pulsator testing of the carburised 20 Mn Cr 5 test gears, and of the 722 M 24 (En 40 B) nitrided gears was completed which showed that fatigue strength varied signifcantly with tooth size.
• The surface fatigue (Hertzian) strength of the nitrided gears in 722 M 24 (En 40 B) has been established by back-to-back testing on both the 75mm and the 160mm test rigs. Excellent surface fatigue strengths were achieved, but these are again significantly size dependant, with different modes of surface fatigue initiation and propagation.
• Further metallurgical investigations were carried out to seek to understand the cause of the different fracture initiation observed in nitrided gears, and the relative importance of case thickness and residual stress distribution.

The subsidiary programme of research into gear cleaning and the effect of different cleaning media and shot peening on root bending fatigue strength was extended and the following cleaning techniques rigorously evaluated:

• Vapour blasting with wet and dry aluminium oxide
• Blasting with chilled iron grit
• Blasting with steel shot
• Blasting with glass beads

It was found that there were significant differences in the performance of these different techniques, and that this also depended on the size of the gears.

A second subsiduary programme of research into the measurement of and the effect of grinding burn was also extended, with the evaluation of the Barkhausen Noise technique for surface residual stress and hence grinding burn measurement.

The work was completed in early 1997 and has generated reliable design data for the four steels being considered, providing considerable insight into the effect of process variables on the performance of gears. In supplying base data for current gear steels and processing and improving our manufacture and test procedures, this work has laid a firm foundation for BGA Research Project 5 to "Improve Gear Performance by Enhancing the Fatigue Strength of Gear Material".

The final report is available to Members in the form of a full report and a summary of design data. Individual seminars and workshops will be held according to demand.

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Project 11 - Materials for Enhanced Gear Bending Fatigue Performance

This latest BGA research project (Project 11) is a continuation of a series of research projects aimed at improving the fatigue properties of gears which dates back to the mid 1990s. This latest phase will be strongly materials-focused and will concentrate on evaluating gear tooth bending fatigue strength using single tooth pulsator testing as has been used in previous phases of the project. The variables to be investigated include the base steel type, heat treatment method and post heat treatment processing To see the latest project proposal document please click here.

The BGA is actively seeking additional consortium members and if you would like to learn more without obligation, there will an open meeting at the Design Unit, Newcastle University on Wednesday 9 December. Actual contributions will of course depend on the final size of the consortium but it is estimated that the cost per member will be £4 - 6k pa for 3 - 4 years.

If you wish to attend the meeting on 9 December, please email or call Andy Harry at BGA (andy@bga.org.uk; +44.1283 515521) as soon as possible.