Previous Research Projects
Project 3 - Spline stressing and wear research...
This jointly funded project by the DTI and a GRF consortium aimed to develop an accurate elastic model of contact and stressing in highly loaded splines. The following objectives were achieved:
1.To develop a validated full 3-dimensional spline coupling stressing and contact model based on Boundary Element techniques.
2.To conduct research into spline fretting/wear using a range of test rigs at Nottingham University
The result of this work was the development of a user friendly computer software programme which can assist the specialist designer in producing efficient and effective spline joint couplings for a wide variety of aerospace applications.
Project 7 - Improved gear stress analysis...
Two programmes of work, both jointly funded by the DTI and the BGA, were conducted at the Design Unit, Newcastle University with the aim of producing better stress analysis tools for the gear designer.
1.A computer program was written to implement the BS-ISO 6336: 1996 - Calculation of Load Capacity of Spur & Helical Gears standard. The program was demonstrated in March 1998 and, having incorporated several suggested improvements, was then evaluated and trialled by eight BGA consortium companies. This software was widely used until the 1996 edition was superseded by the 2006 version of this BS ISO Standard.
2.A 2-D mesh model was developed based on a thin-slice FE model of pinion and wheel and an analytical elastic mesh analysis. The aim was to provide the gear designer with 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 was usable by itself or as a precursor to a 3D FE analysis. It enabled 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 were written together with the input routine and an elastic mesh analysis tool was also developed. This software was used commercially for a number of years until superseded by more comprehensive programs becoming available in the market.
Project 8 - Net forgings ...
This three year project was centred at the University of Birmingham and commenced in April 1998. It was funded by EPSRC and a consortium of 6 BGA members. It aimed to develop forging techniques/die designs etc to enable the production of gears of single helical and spur form, up to 200mm dia and of at least ISO Grade 5 accuracy. In addition, it was desired that the post forged surface finish would be of good enough quality such that no other final machining operations would be necessary. This latter objective was not unfortunately achieved in this work programme. The effects of surface hardening were considered and the production of forged gears with profile modification and crowning was also investigated.
Project 5 - Improving gear performance by enhancing the fati...
This substantial research programme involved 19 BGA Members and investigated ways of improving the fatigue strength of gear steels, heat treated by case-carburising, nitriding and induction hardening. The project was supported by both the DTI and MoD (N) and was 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 were investigated to improve the surface and bending fatigue strength of the following gear steels:
Carburising Steels: 16 MnCr5; 17CrNiMo6; Sl56; 590x17
Nitriding Steel: 897M39(En40C); 709 M 40(En19); 3S132
Induction Hardened Steel: 709M40 - En19 (42CrMo4)
In this programme, helical and spur gears, run at 75mm and 160mm centres, were tested for surface and bending strength. Pulsator tests were carried out for bending fatigue strength. New test facilities, funded by the BGA consortium and the MoD(N)Navy, were designed, built and commissioned which for the first time allowed the fatigue testing of helical gears at powers of up to 1800KW.
The project's Heat-Treatment sub-committee identified a number of modern processes which could 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 was carried out.
A Gear Cleaning and Shot-Peening sub-committee similarly advised on the influence of these processes on gear fatigue strength and planning treatment processes. Close liaison was maintained with Project 6 (Improving Understanding of Micro Pitting) with respect to lubrication and pitting failure criteria.
Project 6 Phase 1 - Improving Understanding of Micro Pitting...
This comprehensive programme of research was instigated to investigate many aspects of micro-pitting failure in gears, an aspect of growing importance in the industry. Phase 1 of this research was funded by the DTI, MoD(N) and a consortium of 17 BGA members. The research was conducted at the Design Unit, Newcastle University and at DERA Pyestock (later QinetiQ).
Phase 1 of the work started in September 1998 and compared potential micropitting testing methods, including FZG and Disc testing which was a pre-requisite for identifying the detail of work required in subsequent phases.
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 which occurs in gears due to surface roughness moving 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 was 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.
Project 4 - Generative gear grinding cost reduction...
This programme of research, supported by the DTI and The Institute of Grinding was successfully completed with the results being reported at a BGA 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 a calculation procedure was developed for optimising grinding feed and speed rates to achieve high metal removal rates without grinding burns whilst maintaining excellent accuracy.
Project 1 - Improving worm gear performance...
This 3 year research programme was part funded by the DTI and the BGA Collaborators (Castrol Limited, David Brown Textron, Holroyd M/C Tools/Rotors and Renold Plc) investigated the potential for significant improvements in load carrying capacity in worm gears. A comprehensive contact analysis for cylindrical worm gears was developed and made available to the collaborators. A back-to-back test rig for worm gears with 160 to 200mm centres was designed, manufactured and commissioned. It was possible to test single and multi-start worm gears on this rig at torques up to 18000 Nm.
A number of experimental worm-gear geometries were developed. However, the available facilities for grinding hardened worms and wheels limited the gear geometries which could be manufactured. Thus it was not possible to explore the full potential of hard to hard worm gear pairings with the experimental gears to fulfil all the original aims of the project. In order to clarify the contact geometry and performance of the Âzero pressure angle worm gear mating with a helical wheel, further tests were carried out using a case-carburised worm and a phosphor bronze helical wheel. The performance of the Âzero angle gear pair was good and exceeded the performance of standard cylindrical worm and globoidal wheel. A number of experimental worm-gear geometries were developed and further studies of the effect of phosphor bronze on boundary lubrication in cylindrical worms were made to improve understanding of gear performance.
In addition to the research at Newcastle University, the University of Wales(Cardiff) developed software for the prediction of the Elastohydrodynamic Lubrication (EHL) films that are generated in worm gears. This project was funded by the EPSRC and a key result was that the project revealed that regions of poor film generation were associated with the orientation of the contact area relative to the effective lubricant entrainment direction at the edges of the contact. This finding will have considerable implications for future designs.
Project 2 - Analysis and measurement of Transmission Error i...
This project was funded by the DTI, EPSRC and the GRF Collaborators. It was successfully completed with the full commissioning of a test facility for worm-gear transmission error measurement and the experimental validation of the contact and TE analysis software.
The same group of collaborators took part in a follow-on project (Project 9) at Huddersfield University using the same test facility where the aim was to investigate 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.
Project 10 - The Development of the Magnetic Barkhausen Nois...
This 3-year project completed in November 2006 in which the overall aim was to investigate the feasibility of using the Magnetic Barkhausen Noise (MBN) technique (also known as Magnetic Barkhausen Emission (MBE) for the non-destructive evaluation of various material properties in gear steels.
The focus of the project was to develop the MBN technique for the assessment of progressive damage caused by bending and contact fatigue and the evaluation of residual stresses.
The final report covered the development of the MBN technique detailing the work performed to optimise the MBN system and measurement parameters, The report presented the results of the effect of applied and residual stresses, bending fatigue at different maximum stress levels and contact fatigue damage at different stress levels on the MBE signal in different gear steels. Discussions pertaining to the potential use of the MBE technique for evaluating the alteration in material conditions such as hardness and case-depth variations, grinding damage, shot-penning effect etc were also included. Suggestions were also made for future studies towards enhancing the sensitivity of MBE further for reliable quantification of changes in different material properties
Project 6 Phase 2 - Better Understanding of Micropitting ...
Phase 1 of Project 6 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. Phase 2 was a direct continuation of Phase 1 and completed in December 2009. One of the most interesting results arising from Phase 2 was the fact that under the same test conditions, form ground gears did not micropit whereas those produced by generation grinding did. This highlighted the importance of surface texture in micropitting performance which is being further explored in Phase 3.
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:
655H13 (En 36)carburising steel
20MnCr5 carburising steel
SAE 8620H carburising steel
722M24 (En 40B nitriding steel
This ambitious investigation, of approx. GBP 0.8million, was funded by the DTI, MOD(N) and the BGA, with contributions in kind from industry and the Newcastle University Gear Design Unit.
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.
In parallel with the BGA funded work, the EPSRC supported metallurgical research. Thisinvestigated the initiation of cracks and the propagation of fatigue failures in these case hardened steels, and researched grinding burn and residual stress.
All test gears were manufactured from clean steel produced by British Steel Engineering Steels and heat treated to best industrial practice, before finish grinding to DIN quality 4/5. The fatigue characteristics (SN curves) were determined by testing gears to failure in four purpose built back-to-back rigs, using gears of 2mm, 4.2mm and 8mm module, running at 75mm and 160mm centres. To validate bending fatigue strength correlations with less expensive pulsator testing, a full programme of single tooth pulsator testing for bending fatigue strength was also undertaken.
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 significantly 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 Materials"