| 2011 Fall Technical Meeting Presentations |
Presentations by SessionBelow are the 29 papers that will be presented at the 2011 AGMA Fall Technical Meeting. The papers have been organized around four sessions:
Session I – Manufacturing and Inspection
Below each session heading you will find a printable version of the abstracts for that session.
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Session I – Manufacturing and InspectionDownload a printable copy of the abstracts for Session I.
A New Way of Face Gear Manufacturing
There are two major intentions to apply face gears in power transmissions: the advantage to be able to use a cylindrical gear as a pinion member; and particular design solutions which require a plurality of cylindrical driving members as in a propulsion system. While the automotive and truck industry conducted substantial research in the application of face gear systems in their drive trains, the results did not favor face gears versus bevel and hypoid gears. In many cases, the face gear system was found to be the less economical solution, as the manufacturing of the face gear itself was expensive. Machine tools require a special design, are not readily available, and the cutting tools have to be designed specifically for the particular face gear design. The obstacles which prevented manufacturers in the past to apply face gears were removed entirely, when a new way of forming the profile of face gear teeth, using standard bevel gear cutting and grinding machines as well as standard cutter heads was designed. The idea is based on the tools used in straight bevel gear cutting and grinding according to the CONIFLEX method, however, using a generating gear which is not flat like it is for straight bevel gears but cylindrical, resembling the mating cylindrical pinion for the particular face gear design. The complexity of modified cylindrical hobbing and shaping machines and job dependent custom tooling disappears completely with the new CONIFACE cutting and grinding process.
Generating Gear Grinding – New Possibilities in Process Design and Analysis
To improve load carrying capacity and noise behavior, case hardened gears usually are hard finished. One possible process for the hard finishing of gears is the continuous generating gear grinding, which has replaced other grinding processes in batch production of small to medium sized gears due to its high process efficiency. Despite the wide industrial application of this process only a few published scientific analyses exist. The science-based analysis of generating gear grinding needs a high amount of time and effort. This is due to the complex contact conditions between tool and gear flank, which change continuously during the grinding process. These complicate the application of the existing knowledge of other grinding processes onto the generating gear grinding. The complex contact conditions lead to high process dynamics which pose challenges in the design of machine tools, the control engineering and the process design. Furthermore, unfavorable contact conditions can lead to process related profile form deviation. So the knowledge of the cutting forces and their time dependent behavior is necessary to describe and optimize the process dynamics and results. The aim of this report is to determine the existing cutting forces for a sample gear in trials for the first time and to analyze their connection to the process parameters and the appearance of profile form deviations. Simultaneously for the sample gear the same process design will be analyzed using a manufacturing simulation. The results of the trials and the simulation will be compared. The report will present new possibilities in process analysis and will give the process user ideas for future process improvements.
Towards an Improved AGMA Accuracy Classification System on Double Flank Composite Measurements
This document explains the issues related to the use of ANSI/AGMA 2015-2-A06 as an Accuracy Classification System and recommends a revised system which can be of more service to the gearing industry.
First International Involute Gear Intercomparison
Seven national metrology institutes have carried out the first international intercomparison in the field of gear metrology organized from the EURAMET (European Association of National Metrology Institutes) with non-European involvement. As leader the Physikalisch-Technische Bundesanstalt (PTB) provided three of their involute gear artifacts and sent them to the participants from China, Japan, Thailand, United Kingdom, Ukraine and USA. Each of the institutes measured the profile, helix and the pitch artifact and evaluated the specified measurands. The results collected and evaluated by the PTB were compared and analyzed by evaluating the normalized error En. At the end of this comparison the large distribution of the results which lay in the range of today’s required tolerances in industry pose a lot of questions. The presentation explains details of the measurement setup and evaluation parameter, damages of some artefacts due to unqualified handling, and finally the interesting results.
Session II – Design ConsiderationsDownload a printable copy of the abstracts for Session II.
Epicyclic Load Sharing Map – Application as a Design Tool
One of the main advantages of planetary transmissions is that the input torque is split into a number of parallel paths. However, equal load sharing between the planets is possible only in the ideal case due to the presence of positional type manufacturing errors, equal load sharing is not realized, and the degree of inequality in load sharing has major implications for gear system sizing, tolerancing schemes, and torque ratings. The sensitivity of load sharing to torque, tolerance level, directionality of error, system flexibility, number of planets, and amount of float in the system have all been studied. However, a physical understanding of the true mechanism that leads to the load sharing phenomenon was lacking. In a recent paper, the author has proposed a physical mechanism that explains all known load sharing behavior. The physical explanation leads to simple expressions that seem to completely describe the complex load sharing behavior. Comparisons to computational models and experimental results have shown excellent correlation. The proposed physical explanation leads to the concept of an epicyclic load sharing map (ELSM). The ELSM is a plot of the load ratio (or % of input torque) versus a non dimensional parameter Xe. The non-dimensional parameter is a function of combined system stiffness, tolerance level, and operating torque. The ELSM contains curves for 3, 4, 5, 6 and 7 (and more) planet systems. Once a gear set is located on the ELSM, its behavior under any load and error condition can be quickly predicted. Also, the advantages of adding extra planets can be accurately estimated. The use of the ELSM as a design tool for the general case when there are errors on the position of every carrier pin-hole are illustrated. Statistical simulations are performed for a given manufacturing error distribution for 3 to 7 planet systems.
Gear Tooth Single vs. Reversal Bending Life Evaluation
There is a wealth of literature and test results regarding the subject on single directional gear tooth bending stress and life relationships (S-N curves), they have been published on various journals and handbooks over the past decades, and several of them had been widely accepted and adapted as industry standards by different gear societies around the world. However, very limited information regarding the bi-directional tooth bending life has been revealed. To fill in the above mentioned gap for practical usages, the authors first intended to apply the traditional fatigue theories such as modified Goodman, Gerber, Morrow or similar theories with minor modifications to derive a series of S-N equations for different loading conditions, but the correlation with the actual test results was not satisfied. Nevertheless, from the observation on these test results, the slopes and endurance limits on the fitted S-N curves from all the test points were reasonable closer to each other, as long as the test gears were produced by the same material and similar manufacturing process. Based on the above observation, the author proposes a new approach that uses the common (or averaged) slope and endurance limit, and a series of S-N curve equations on any loading conditions can be derived, once the single directional S-N curve has been obtained.
The Effects of Helix Angle on Root Stresses of Helical Gears
The ISO and AGMA Gear Rating Committees have for several years been comparing the results of different rating methods for several sets of gear pairs that have similar normal sections but different helix angles. The analysis presented here uses a finite element code that was developed specifically for gear and bearing contacts to analyze the example gear sets. Analyses are also performed using a more conventional load distribution analysis program. The results for the original gear sets show that the narrow face width gear teeth twist significantly, thus moving the load to one edge of the face width and essentially showing that the example gear sets are highly unrealistic. Yet when analyzed by the ISO and AGMA rating methods, the results do not reflect this twisting action. In an effort to come up with a valid comparison of stresses for different helix angles, three adjustments using wider face widths were attempted. The first uses a narrow load patch in the middle of the tooth pair and results in the stresses increasing with helix angle. The second scheme again uses a wider face width, but with perfect involutes. Edge effects result in the peak stresses being near the ends of the face width. The third method, which uses the wide face width with teeth that have some lead crown and tip relief, gives the most reasonable results, with the root stresses being at a maximum in the center region of the tooth face widths. The paper compares each of the results to earlier analyses performed by others using both the AGMA and ISO calculations.
A Comprehensive System for Predicting Assembly Variation with Potential Application to Transmission Design
Recent advances in tolerance analysis of assemblies allow designers to: predict tolerance stackup due to process variations; examine variation in clearances and fits critical to performance; use actual production variation data or estimates from prior experience; and use engineering design limits to predict the percent rejects in production runs. A comprehensive system has been developed for modeling 1D, 2D, and 3D assemblies, which includes three sources of variation: dimensional (lengths and angles), geometric (GD&T), and kinematic (small internal adjustments due to dimensional variations). Once the assembly has been described, an algebraic model is created, in which each dimension is represented by a vector, with a nominal +/- tolerance. The vectors are linked into chains or loops, describing each critical clearance or assembly feature in terms of the contributing dimensions. The chains form vector loops describing the interaction and accumulation of the three sources of variation in the assembly. Small variations are applied to each source and analyzed statistically to predict the resulting variation in the critical assembly features. Solutions for the mean and standard deviations are obtained by matrix algebra. Only two assemblies are analyzed: one for the mean and another for the variance of the assembly features. The same modeling elements may be used to model complex assemblies. Benefits of tolerance analysis include reduced reject rates, fewer problems on the assembly floor, reduced costs, and shorter time to market. Critical requirements of shaft alignment, gear meshing and controls in transmissions and gear trains are ideally suited for this efficient, comprehensive system.
Standardization of Load Distribution Evaluation: Uniform Definition of KHß for Helical Gears
The load distribution measurement of gear teeth and the determination of the face load factor for contact stress KHß are of fundamental importance to the gear manufacturing industry. The factor is a measure for the uniformity of the load along the face width. The closer this factor is to one the more uniform is the load distributed along the face width. In the design phase this factor is determined with the help of approximation equations and finite element analysis and is used to dimension the flank modifications. In addition KHß is used in the lifetime calculations according to DIN 3990 and ISO 6336 required by the certification societies. In the testing phase this factor is experimentally determined by strain measurements of the tooth fillets in order to verify the load distribution calculations and the suitability of the used modifications. For spur gears with no helix angle the interpretation of the measurements to a face load factor is intuitively easy. For helical gears, used more frequently in large gearboxes, the determination of the factor gets more difficult. The line of contact of these gears runs inclined over the face width of the teeth flank. In this context the question arises whether the face load factor is evaluated along the face width or along the path of contact. Evaluation of the measured values and the interpretation to a face load factor is a complex challenge and is not standardized. The standardization of load distribution evaluation and a uniform definition of KHß especially for helical gears enable a safer design for the manufacturers and an easier comparability of the results for the customers. The paper will compare the different suggestions to the KHß definition and will derive a new definition suitable for the calculation methods in DIN 3990 and ISO 6336.
New Methods for the Calculation of the Load Capacity of Bevel and Hypoid Gears
Pitting and tooth root breakage are still the two most frequent failure types occurring in practical applications of bevel gears. There are several national and international standards for the calculation of the load carrying capacity of these gears such as DIN 3991, AGMA 2003 and ISO 10300. But up to now these standards do not cover bevel gears with offset (hypoid gears). For that reason a research project was carried out at FZG (Gear Research Centre, Munich, Germany) to analyze the influence of the hypoid offset on the load capacity of bevel gears by systematic theoretical and experimental investigations. The results of the tooth root tests showed, as expected, an increasing load capacity with higher offsets. In contrast, the pitting tests showed an increasing, but after reaching a maximum, a decreasing load capacity with higher offsets. This can be explained by two interfering phenomena: On the one side higher offsets lead to decreasing pinion loads and thus decreasing contact stresses; on the other side the permissible stresses are decreasing due to the higher sliding velocities. Regarding these test results a new standard capable calculation method was developed on the basis of ISO 10300. First the bevel gear geometry is transformed into a virtual cylindrical gear. Systematic theoretical investigations and comparisons with tooth contact analysis methods have shown that the new virtual cylindrical gears have representative mesh conditions compared to the bevel gears. This includes the size and shape of the contact area as well as the load distribution between the mating teeth. Particularly with regard to hypoids it is necessary to consider the unbalanced mesh conditions between drive and coast side flank, what can be described by the limit pressure angle. Several influence factors were adjusted considering geometry, material properties and operating conditions of the gear set. For the tooth root safety factor the influence factors were adapted to the specific conditions of hypoid gears. For the calculation of the pitting safety factor two new influence factors were introduced to consider the hypoid specific sliding conditions on the gear flanks. The recalculation of the pitting and tooth root tests showed a very good correlation of calculated with real load capacity of the test gears. Meanwhile the newly developed calculation method is widely-used in the gear manufacturing industry. For that reason it is currently introduced into the revision of ISO 10300 as method B1 beside method B2 based on the AGMA calculation method for bevel and hypoid gears.
Marine Reversing Main Gear Rating Factor vs. Number of Loading Cycles and Shrink Fit Stress
The marine vessel reversing main gear tooth is subjected to three different loading cycles: ahead travel with load pulsing from zero to 100% of full power; astern travel with load pulsing from zero to about minus 66% of full power; and reversal of direction with load changing from 100% of full power to about minus 66% of full power. The number of repetitions of these three different loading cycles varies with the vessel duty cycle and life. The published values of allowable design stress for teeth are based on pulsing loads, which must be modified for this third loading cycle. The tooth may also be subjected to mean stress due to shrink fitting of the gear onto a hub. Publications which address these conditions include:
Session III – MicropittingDownload a printable copy of the abstacts for Session III.
The Application of the First International Calculation Method for Micropitting
The international calculation method for micropitting, ISO/TR 15144, was recently published. It is the first official international calculation method to check for the risk of micropitting ever published. Years ago AGMA published a method for the calculation of the specific oil film thickness containing some comments about micropitting, and the German FVA published a calculation method based on intensive research results. The FVA and the AGMA are close to the ISO/TR. New is the calculation of the micropitting safety factors. The technical report presents two calculation rules, method A and B. Method A needs as input the Hertzian pressure on every point of the tooth flank, based on an accurate calculation of the meshing of the gear pair, considering tooth and shaft deflections to get the load distribution over the flank line in every meshing position. Method B is much simpler; the load distribution is defined for different cases as spur or helical gears, with and without profile modifications. The risk of micropitting is highly influenced by profile and flank line modifications. A new software tool can evaluate the risk of micropitting for gears by automatically varying different combinations of tip reliefs, other profile modifications and flank line modifications, in combination with different torque levels, using method A. The user can define the number of steps for variation of the amount of modification. Then all possible combinations are checked combined with different (user defined) torque levels. Any modifications including flank twist, arc-like profile modifications, etc. can be combined. The result is presented in a table, showing the safety factor against micropitting for different subsets of profile/flank modifications, depending on the torque level. Some applications from wind turbine and industrial gearboxes, known to the author, will be discussed.
Investigations on the Flank Load Carrying Capacity in the New Developed FZG Back-to-Back Test Rig for Internal Gears
Micropitting, pitting and wear are typical gear failure modes, which can occur on the flanks of slowly operated and highly stressed internal gears. However the calculation methods for the flank load carrying capacity have mainly been established on the basis of experimental investigations on external gears. The target of a research project was to verify the application of these calculation models to internal gears. Therefore two identical back-to-back test rigs for internal gears have been designed, constructed and successfully used for gear running tests. These gear test rigs are especially designed for low and medium circumferential speeds and allow the testing of the flank load carrying capacity of spur and helical internal gears for different pairings of materials at realistic stresses. The three planet gears of the test rig are arranged uniformly around the circumference. Experimental and theoretical investigations regarding the load distribution across the face width, the contact pattern and the load sharing between the three planet gears have been carried out. Furthermore substantial theoretical investigations on the characteristics of internal gears were performed. Internal and external spur gears were compared regarding their geometrical and kinematical differences as well as their impact on the flank load. Based on the results of these theoretical investigations an extensive test program of load stage tests and speed stage tests on internal gears of different material, different finishing of the flanks and different operating conditions has been carried out. The main focus of this test program was on the fatigue failures of micropitting and wear at low circumferential speeds. The paper describes the design and functionality of the new developed test rigs for internal gears and shows basic results of the theoretical studies. Furthermore it presents basic examples of experimental test results.
AGMA 925-A03 Predicted Scuffing Risk to Spur and Helical Gears in Commercial Vehicle Transmissions
The risk of gear tooth scuffing in commercial vehicle transmissions has gained more attention because of increasing demand for fuel-efficient powertrain systems in which diesel engines run at lower speeds, power density is higher, and lubricants are modified to improve efficiency and compatibility with components of new technologies, such as dual clutch transmissions. Thus, predicting scuffing risk during the design phase is vital for the development of commercial vehicle transmissions. AGMA 925-A03 is a comprehensive method to predict the probability of gear scuffing. Therefore, this paper presents the AGMA 925-A03 scuffing risk predictions for a series of spur and helical gear sets in transmissions that are used in commercial vehicles ranging from SAE class 3 through class 8. Limiting scuffing temperatures of mineral and synthetic lubricants were determined from FZG scuffing tests, dynamometer tests and field data. The agreement between prediction, test results and actual usage can provide confidence in the predictor of scuffing risk of gears in commercial vehicle transmissions.
Micropitting – a Real Damage? Testing, Standards and Practical Experience
Micropitting is a surface fatigue phenomenon on highly loaded case hardened gear flanks. Main contributors are local stress, surface roughness, sliding speed and lube oil properties. To determine the lube oil performance with respect to micropitting, different test methods have been established in the past. Actual proposals are evaluated for adopting suitable calculation methods for micropitting resistance to the ISO 6336 gear rating standards. But is micropitting necessarily a damage in any case? Practical experience shows, that a certain level of micropitting is actually acceptable, leading to even more favorable load distribution and can end up in a stable flank condition performing without problems for the designed service live. The paper describes testing, calculation approaches and application to practical cases with respect to micropitting on wind turbine and high speed gears and perennial observations and experience.
Gear Lubrication – Stopping Micropitting By Using The Right Lubricant
Micropitting is a type of fatigue failure occurring on hardened tooth flanks of highly loaded gears. This failure consists of very small cracks and pores on the surface of tooth flanks. Micropitting looks greyish and causes material loss and a change in the profile form of the tooth flanks, which can lead to pitting and breakdown of the gears. The formation of micropitting depends on different influences. Besides material, surface roughness, and geometry of the tooth flanks, the lubricant and the operating conditions show a main influence on micropitting formation. The micropitting load-carrying capacity of gears can be calculated according to ISO/TR 15144-1, where the influence of lubricant, operating conditions, and surface roughness is considered with the specific lubricant film thickness. For this purpose, the specific lubricant film thickness of a practical gear is compared with a minimum required specific lubricant film thickness. The latter is the specific film thickness where no micropitting risk is given for a lubricant and can be determined by performing a micropitting test according to FVA 54/7. This test procedure consists of a load stage test and an endurance test. Lubricants with a high micropitting load-carrying capacity reach the failure criterion of a profile form deviation of 7.5 µm due to micropitting in load stage greater than or equal to LS 10 of the load stage test. In the endurance test, a stagnation of micropitting formation compared with the micropitting area at the end of the load stage test is preferred but not required. In field applications, micropitting formation is often reported even though industrial gear oils with a high micropitting load-carrying capacity are used. Such oils offer a good micropitting protection determined in the load stage test, but with a low micropitting performance in the endurance test. The aim of research is therefore the investigation whether a change from an oil with low micropitting performance in the endurance test to an oil with high micropitting performance in the endurance test can stop the micropitting formation.
Morphology of Micropitting
Micropitting occurs in gears and rolling-element bearings that operate in the mixed or micro EHL lubrication regime. It manifests in many different ways depending on the loads, speeds, rolling and sliding velocities, macrogeometry, surface topography, edge effects, metallurgy, and lubricant properties. The failure analyst must discern whether the micropitting is a primary failure mode or a secondary failure that occurs because of prior damage. Understanding the morphology of micropitting is the key to determining the primary failure mode and root cause of failure. Several examples of micropitting in gears and rolling-element bearings are presented to illustrate the morphological variation that can occur in practice.
Session IV – Drive Design and ApplicationDownload a printable copy of Session IV abstracts.
Longitudinal Tooth Contact Pattern Shift
After a period of operation turbo gears may exhibit a change in the tooth contact pattern, reducing full face width contact, and thereby increasing the risk of tooth distress due to the decreased loaded area of the teeth. The phenomena may or may not occur. In some units the shift is more severe than others and has been observed in cases where there is as little as 50,000 hours of operation. In other cases there is no evidence of any change for units in operation for more than 100,000 hours. This condition has been observed primarily in single helical gears with low helix angles (10-13°). All recorded observations have been with case carburized hardened and ground gear sets. This paper describes the phenomena observed among some of many installed high speed gear units in field operation that have been inspected. The authors have not found any written material describing this behavior and upon further investigation suggest a possible cause. Left unchecked and without corrective action, this occurrence may result in tooth breakage.
Convoloid Gearing Technology — The Shape of the Future
Since the invention of the involute curve and the application thereof to gearing, the world has embraced and developed this type of gear tooth form to a very high degree of engineering and manufacturing excellence. Improvements in recent years have been relatively modest, since this form has been so rigorously studied and applied. The long term adoption of the involute is rooted in large part to the simplicity of its tools and field operation. Straight sided tools and conjugacy, even with limited changes in center distance, were consistent with the industrial revolution of the 18th, 19th, and 20th centuries, and the mechanically based machine tools of these ages. The recent ubiquitous nature of computers and CNC machinery exacerbates the cost effective freedom to optimize many parameters affecting gear tooth forms. Convoloid is a new gear tooth form capable of increasing torques 20% to 35% over those of conventionally designed involute pairs. The form is computer optimized, is compatible with the world’s existing capital asset infrastructure, and mirrors the manufacturing sequences, processes and basic production costs of involute gears. The result is a major enhancement in gear drive system power density and cost reduction for a given power requirement. Convoloid gearing is totally scalable and is used in parallel axis helical, planetary, and other configurations. The design, rating (surface durability and bending), flash temperature analysis and other important performance criteria for this technology along with the manufacturing and inspection protocols in keeping with AGMA and ISO specifications will be discussed. Test results confirming many of the superior load carrying characteristics of this tooth form will be presented. Side by side comparisons of involute versus Convoloid designs and test performance results will be presented confirming the validity of the theory.
Case Study Involving Surface Durability and Improved Surface Finish
Gear tooth wear and micro-pitting is a very difficult phenomenon to predict analytically. The failure mode of micro-pitting is closely correlated to the lambda ratio. Micropitting can be the limiting design parameter for long-term durability. Also, the failure mode of micropitting can progress to wear or macropitting, and then manifest into more severe failure modes such as bending. The results of a gearbox test and manufacturing process development program will be presented to evaluate super finishing and its impact on micropitting Testing was designed using an existing aerospace two stage gearbox with a low lambda ratio. All gears were carburized, ground and shot peened. Two populations were then created and tested. One population was finish honed and the second was shot peened and isotropic super finished. A standard qualification test was conducted for 150hrs at maximum continuous load. The honed gears experienced micro and macro pitting during the test. The Isotropic Super Finishing (ISF) gears were also tested for 150hr under the same loading. The ISF gears were absent of any surface distress. The ISF gears were further subjected to a 2000hr endurance test. The ISF gears had less surface distress after 2000hr than the baseline honed gears after 150 hrs.
Gearbox Service Life – A Matter of Mastering Many Design Parameters
The service life of a gearbox is determined by many factors. The bearings in the gearbox play a major role since they themselves deliver an important function, and in addition interact with the shafts, the casing and the oil. Without a doubt, the sizing of the bearings is of great importance for the gearbox reliability. Since more than 50 years the bearing dynamic carrying capacity has been used to determine a suitable size needed to deliver a sufficient fatigue life – but despite the advanced calculation methods developed, the methods do not fully predict service life. Producers of high quality bearings have introduced high performance class bearings and, lacking better ways to express the improved performance, this is only represented by increased dynamic carrying capacity. The availability of high-strength shaft materials in combination with bearings with high carrying capacity allows slimmer shafts to be used. The modulus of elasticity remains the same, so seat design for bearings and gears must be given close attention. This paper covers the following: sizing of bearings based on dynamic carrying capacity and how this relates to service life; how the design of the interface between bearing and shafts should be adapted to modern shaft materials; how the design of the interface between bearing and gearbox casing influences service life of the gearbox; and influence of modern electric motor speed controls in bearing type selection.
Simulation of Wear for High Contact Ratio Gear – A Mixed FE and Analytical Approach
High contact ratio gears offer high load carrying capacity and increased life with less volume and weight. Gear tooth wear of high contact ratio gears is of great importance as excessive wear is characterized by loss of tooth profile and thickness, which might result in higher dynamic gear mesh and tooth forces. Surface wear changes not only the contact pattern and load distribution, but also the vibration and noise characteristics of the gear system. This paper deals with the simulation of wear for high contact ratio (HCR) and normal contact ratio (NCR) gears using a Mixed Finite Element (FE) and analytical approach. A numerical model for wear prediction of gear pair is developed. The methodology employs single point, observation-based gear contact mechanics in conjunction with the Archard’s wear formulation to predict the tooth wear in spur gears. The contact pressure and loads are determined using a FE approach in which a two dimensional deformable body contact model of HCR and NCR gears is analyzed in ANSYS software, and ANSYS Parametric Design language (APDL) is used for capturing the load sharing ratio and contact stress variation on the complete mesh cycle of the gear pair. A MATLAB code program is developed to determine the sliding velocities, equivalent contact radius and contact width along the path of contact for both HCR and NCR gears. The contact loads and pressures obtained using FEM are used for predicting the wear depth for NCR and HCR gear pair.
Bearing Contribution to Gearbox Efficiency and Thermal Rating: How Bearing Design Can Improve the Performance of a Gearbox
Gearbox efficiency is a topic of rising interest amongst both OEM and end-users due to an increased sensitivity to gearbox performance, reliability, total cost of ownership (energy cost), overall impact on the environment, and also anticipating future regulations. In a gearbox there are difference sources of losses: gear, lubrication, seal and bearing loss. The use of modern simulation tools makes easier the evaluation of losses in various load case conditions. It has been demonstrated that the contribution of bearing loss on the system efficiency is dependent on the load cases. Even if the bearing is by far not the primary source of losses, the optimization of the bearing set can significantly improve gearbox performance. Simulation of a single stage gearbox using tapered roller bearings shows that the running temperature of the gearbox can be reduced up to 10C, by using latest bearing generation. Such a saving could improve the thermal rating of the gearbox by up to 30%. Experiments also demonstrated that different design of tapered roller bearing shows significant variation in friction performance. Having proper bearing design can significantly improve the performance of a gear unit: by a lower running temperature, by improving lubricant life, potentially simplified lubrication system, and consequently reduced running cost.
Session V – Heat TreatmentDownload a printable copy of Session V abstracts.
Integration of Case Hardening into the Manufacturing-Line: “One Piece Flow”
For decades the gear industry has addressed the challenge to produce high performance components in a cost-efficient manner. To meet quality-specifications the components need to be heat treated, which traditionally takes place in a central hardening shop. However this separation between machining and heat treatment results in high costs for transportation and logistics within the production-plant. Therefore for many years it has been being discussed how to integrate heat treatment into the manufacturing line. For about 10 years it has been possible to integrate heat treatment into the machining facility by applying the technology of Low Pressure Carburizing (LPC) and High Pressure Gas Quenching (HPGQ). The components are collected after soft-machining into big batches and treated with LPC- and HPGQ-technology. This means however that the heat treatment is not synchronized with soft- and hard-machining since the components must be collected in buffers before heat treatment and must be singularized again after heat treatment. In order to totally integrate heat treatment into the manufacturing line and in order to synchronize heat-treatment with machining, a new heat treatment cell has been developed. Following the philosophy of “One Piece Flow” the parts are: taken one by one from the soft machining unit; then heat treated in time with the cycle-time of soft machining (“synchronized heat treatment”) and then passed down one-by-one to the hard machining unit. To allow for rapid case hardening, the components are low pressure carburized at high temperatures (1050°C) followed by gas quenching. In addition to the cost-savings for logistics, the new concept in equipment offers the following advantages: individual processes customized for each gear-component; homogenous and quick heating of the components and therefore low spread of distortion; homogenous and controllable gas quenching and therefore low spread of distortion; environmentally friendly carburizing and quenching; and compact and space-saving heat treat unit. The paper shows first results achieved with the new process technology applied in the new heat treatment cell.
Induction Hardening of Gears with Superior Quality and Flexibility Using Simultaneous Dual Frequency (SDF)
Induction hardening of gear teeth is well known for its challenges, but also for its potential for improved quality and process control. For complex geometric parts like gears, the power density and induction frequency need to be adjusted very precisely to achieve the required hardening pattern. Since 1940s it is known that working with two simultaneous frequencies (1-15 kHz and 200-20000 kHz) is the optimal way to heat a geared part to hardening temperature. The key point in this process is that the medium frequency (about 10 kHz) affects primarily the tooth root and the high frequency affects first of all the tip of the tooth and the flanks. The right combination of the power densities of medium- and high frequency energy values and the heating time are the crucial factors to reach a contour true heating pattern and, thereby, a contour true hardening pattern. The authors will describe the state of the art of induction hardening of gears with simultaneous dual frequency using some examples of use and present the possibilities to manipulate the hardening pattern in a positive way for different gear geometries.
Controlling Gear Distortion and Residual Stresses During Induction Hardening
Induction hardening is widely used in both automotive and aerospace gear industries to reduce distortion and obtain favorable residual stresses. The heating process during induction hardening has a significant effect on the quality of the heat-treated parts, but the importance of the quench portion of the process often receives less attention. However, experiences have shown that the cooling rate, cooling fixture design and cooling duration can significantly affect the quality of the hardened parts in terms of distortion, residual stresses, as well as the possibility of cracking. DANTE is a commercial heat treatment software based on finite element method. In this paper, DANTE is used to study an induction hardening process for a helical ring gear made of AISI 5130 steel. Prior to induction hardening, the helical gear is gas carburized and cooled at a controlled cooling rate. In this study, two induction frequencies in sequential order are used to heat the gear tooth. After induction heating, the gear is spray quenched using a polymer/water solution. By designing the spray nozzle configuration to quench the gear surfaces with different cooling rates, the distortion and residual stresses of the gear can be controlled. The crown and unwind distortions of the gear tooth are predicted and compared for different quenching process designs. The study also demonstrates the importance of the spray duration on the distortion and residual stresses of the quenched gear.
Atmosphere Furnace Heating Systems
A detailed evaluation of furnace heating systems is presented. Topics of discussion include application guidelines for both gas fired and electrically heated furnaces. Heating system selection considers operating temperature, processing atmosphere and heating method (radiant or convective heating) along with heating system orientation within the furnace chamber. The evaluation consists of a comparison of operating costs, environmental considerations and lifetime maintenance costs of the various systems. Systems to be evaluated consist of alloy radiant tubes (single ended, U-tube, etc.), ceramic radiant tubes (single ended and U-tubes) and a variety of electrical element designs. Actual case studies of the various heating systems are presented with respect to maintenance and operating costs.
Manufacturing and Processing of a New Class of Vacuum-Carburized Gear Steels with Very High Hardenability
Ferrium C61 and C64 are new secondary-hardening steels that provide superior mechanical properties versus 9310, 8620, Pyrowear Alloy 53 and other steels typically used for power transmission, such as significantly higher core tensile strength, fracture toughness, fatigue strength and thermal stability (i.e. tempering temperature). One recent example of their application is the application of C61 to the forward rotor shaft of CH-47 Chinook helicopter, in order to reduce the weight of the shaft by 15-25% and provide other benefits. This paper reviews the significant manufacturing and processing benefits that arise from this new class of secondary-hardening steels, and analyze the potential implications and opportunities. C61 and C64 were computationally designed to take advantage of high-temperature, low-pressure (i.e. vacuum) carburization technology, in part by combining carburizing and austenizing steps as well as being designed to have very high hardenability. The very high hardenability of these steels permits a mild gas quench subsequent to low-pressure vacuum carburizing and reduces part distortion, thus reducing grind stock removal, simplifying final machining and heat treat operations. A framework analysis is used to compare total manufacturing/production costs and impacts (including environmental) of these new steels versus traditional gear steels. Conclusions and recommendations are drawn regarding best manufacturing practices and appropriate use of these new steels for product applications.
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