The DTC came into being in 1992 under the auspices of the U.S. Navy MANTECH program. It is currently sponsored by various Federal agencies and the gear and transmission manufacturing industry (aerospace, automotive and marine) in the United States and abroad. R&D services to the gear/drivetrain industry include gear manufacturing/process support, performance testing and characterization of all things gear related, including metrology, metallurgy, failure analysis, prognostics, etc. The DTC also operates the AGMA, ASME Gear Research Institute, under a multi-year contract.
The primary objectives of the R&D efforts at the DTC are to increase performance and reduce costs of mechanical power transmission systems and components. The metrics of performance can be several. They include higher power density, increased component durability and reduced operational vibration and noise. To fulfill these objectives a variety of sponsored projects focused on manufacturing, materials and metrology have been undertaken or are ongoing at the DTC.
In the area of manufacturing we spend a considerable amount of effort characterizing the impact of current manufacturing processes on the durability of transmission components such as gears, while focusing efforts in developing novel manufacturing processes for the same. Characterizing the durability of various advanced steels for gear applications and optimizing their performance is a major component of the DTC’s efforts in the area of materials.
Based on algorithms developed over the last few decades that correlate vibrations in a gear mesh to the geometry, load and the accuracy to which the gear is fabricated, our contributions to gear design and metrology has ranged from evaluating and correcting for gear noise, developing gear design methodology for low vibration, advancing the state of gear measurement and most recently, developing methods for gear prognostics.
The DTC is very well equipped with the necessary hardware to conduct R&D efforts in these areas. In collaboration with the Gear Research Institute, the DTC houses the most comprehensive gear and gear materials test facility in the nation. A battery of rolling/sliding contact fatigue testers, tooth bending test facilities and low speed and high speed re-circulating gear testers are available. A gear metrology facility equipped with an M&M CNC gear inspection machine, a MAAG gear checker and a ZEISS coordinate measuring machine (CMM) are also available at the DTC. Also resident at the DTC is the world’s first production capable, double-die gear ausform finishing machine (discussed below).
High Strength Powder Metal Gears for Vehicle Transmissions
It is well established that complex metal parts can be manufactured more economically with powder metal (P/M), especially in large quantities. However, P/M components generally do not have the strength and durability to replace wrought metal parts in critical power transmission applications.
In a project sponsored by the United States Army/TARDEC/NAC, the DTC is working very closely with a manufacturer of P/M components to enhance the strength and durability of P/M (spur and helical) gears for vehicle transmissions at a lower cost than current gears made from wrought steel.
The key to enhancing the strength and durability of P/M gears is the Penn State developed finishing process called Ausform Finishing.
This is a thermomechanical process that sequentially combines the three operations of induction heating, marquenching and roll finishing to produce a hardened and high quality gear. In this process the carburized gear is contour induction heated to convert the carburized layer to the austenitic phase, immediately followed by marquenching and roll finishing at an elevated temperature, while the steel is still in the austenitic phase. The roll finishing operation produces a gear with very high surface finish and accuracy and the final quenching produces the high hardness/high strength martensitic phase, resulting in a finished gear, ready for assembly after deburring.
Tests to date on P/M gears finished by ausform finishing, on the DTC’s world’s first gear asuform finishing machine, have validated this approach and it is anticipated that the introduction of P/M gears into vehicle transmissions will occur in the very near future.
Development of Design Allowables for Advanced Gear Steels
In response to DoD requirements for extended rotorcraft gear box operation under “loss of lube” conditions, the United States steel industry has introduced a variety of “High Hot Hardness” gear steels. The DTC, under the sponsorship of the Gear Research Institute’s Aerospace Bloc (consortium of aerospace gear manufacturers), is conducting several projects to characterize the contact fatigue, bending fatigue and scoring resistance properties of gear made from these steels.
Test specimen design details, specimen manufacturing processes and test conditions for the various tests for this project were arrived at in a collaborative and cooperative manner within the Bloc. Gear tests were conducted under carefully controlled conditions and the data obtained shared between the participants. The actual gear design stress allowables is determined from this data by each individual company, based on their own internal procedures. Several “High Hot Hardness Steels” are being evaluated in this project.
Gear-Vibration Diagnostics Software Project with USCAR
USCAR is a consortium of General Motors, Ford, and Chrysler. In an earlier project, a Drivetrain Center faculty member (W. D. Mark) had developed a method of measuring manufacturing deviations on a single spur or helical gear and predicting from these measurements the vibratory excitation (transmission-error contribution) caused by these manufacturing deviations that would take place if the measured gear were run in meshing action with another gear. The mating gear is not required. After computing the rotational-harmonic transmission-error spectrum caused by the measured errors, the user of this software can compute the manufacturing-error contribution on the working surface of each tooth of the measured gear that is the cause of any user-specified rotational harmonic (ghost tone) of the computed transmission-error spectrum, thereby providing diagnostic information useful for eliminating the manufacturing cause of the chosen single or multiple harmonics. USCAR has contracted with the Drivetrain Technology Center to provide a user-friendly package that will enable the user to measure any external or internal spur or helical gear, and to compute the transmission-error spectrum and diagnostic information as described above.