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Carbon steels have primarily been used to manufacture aerospace gears due to the steels' mechanical characteristics. An alloyed low carbon steel is easily case-hardened to obtain a hard wear surface while maintaining the ductile core characteristics. The microstructure achieved will accept the heavy loading, shocks, and elevated temperatures that gears typically experience in applications. The carbon steel machinability allows for general machining practices to be employed when producing aerospace gears versus the more advanced metal removal processes required by stainless and nickel-based alloys.
This work establishes a baseline for aerospace spur gear behavior under oil-off conditions. The collected test results document a different oil-off time, dictated by material used.
A look at several American organizations doing cutting edge gear-related research for aerospace applications.
Aerospace manufacturing has seen quite a turnaround in the past few years. The world's manufacturers of airplanes, helicopters, missiles, space vehicles and satellites are all extremely busy right now--and that's keeping quite a few gear manufacturers busy as well.
The design of any gearing system is a difficult, multifaceted process. When the system includes bevel gearing, the process is further complicated by the complex nature of the bevel gears themselves. In most cases, the design is based on an evaluation of the ratio required for the gear set, the overall envelope geometry, and the calculation of bending and contact stresses for the gear set to determine its load capacity. There are, however, a great many other parameters which must be addressed if the resultant gear system is to be truly optimum. A considerable body of data related to the optimal design of bevel gears has been developed by the aerospace gear design community in general and by the helicopter community in particular. This article provides a summary of just a few design guidelines based on these data in an effort to provide some guidance in the design of bevel gearing so that maximum capacity may be obtained. The following factors, which may not normally be considered in the usual design practice, are presented and discussed in outline form: Integrated gear/shaft/bearing systems Effects of rim thickness on gear tooth stresses Resonant response
The seemingly simple process of placing a uniform chamfer on the face ends of spur and helical gears, at least for the aerospace industry, has never been a satisfactory or cost effective process.
An experimental effort has been conducted on an aerospace-quality helical gear train to investigate the thermal behavior of the gear system as many important operational conditions were varied.
One of the most effective methods in solving the edge loading problem due to excess misalignment and deflection in aerospace actuation gearing is to localize tooth-bearing contact by crowning the teeth. Irrespective of the applied load, if the misalignment and/or deflection are large enough to cause the contact area to reduce to zero, the stress becomes large enough to cause failure. The edge loading could cause the teeth to break or pit, but too much crowning may also cause the teeth to pit due to concentrated loading. In this paper, a proposed method to localize the contact bearing area and calculate the contact stress with crowning is presented and demonstrated on some real-life examples in aerospace actuation systems.
A major source of helicopter cabin noise (which has been measured at over 100 decibels sound pressure level) is the gearbox. Reduction of this noise is a NASA and U.S. Army goal. A requirement for the Army/NASA Advanced Rotorcraft Transmission project was a 10 dB noise reduction compared to current designs.
Over the past few months we've talked with a lot of gear manufacturers. Many of them tell us business is strong, while others are struggling with reduced demand. The difference between them isn't so much in the quality of their manufacturing operations, but rather trends in the end markets they serve.
A major source of helicopter cabin noise (which has been measured at over 100 decibels sound pressure level) is the gear box. Reduction of this noise is a NASA and U.S. Army goal.
News from around the Gear Industry
Oil-out conditions, or conditions in which an aircraft is operating without any oil in its gearbox or transmission, are devastating for an aircraft's hardware. Even the sturdiest gears usually can't last 30 minutes under such conditions before they catastrophically fail, and the whole system usually follows shortly after. That doesn't leave pilots with a whole lot of time to find a suitable location to land in the case of an oil-out emergency.
Aerospace/Defense contracts offer unique challenges for gear manufacturers.
The objective of this paper is to demonstrate that transmission gears of rotary-wing aircraft, which are typically scrapped due to minor foreign object damage (FOD) and grey staining, can be repaired and re-used with signifi cant cost avoidance. The isotropic superfinishing (ISF) process is used to repair the gear by removing surface damage. It has been demonstrated in this project that this surface damage can be removed while maintaining OEM specifications on gear size, geometry and metallurgy. Further, scrap CH-46 mix box spur pinions, repaired by the ISF process, were subjected to gear tooth strength and durability testing, and their performance compared with or exceeded that of new spur pinions procured from an approved Navy vendor. This clearly demonstrates the feasibility of the repair and re-use of precision transmission gears.
When gears are case-hardened, it is known that some growth and redistribution of stresses that result in geometric distortion will occur. Aerospace gears require post case-hardening grinding of the gear teeth to achieve necessary accuracy. Tempering of the case-hardened surface, commonly known as grinding burn, occurs in the manufacturing process when control of the heat generation at the surface is lost.
Today’s ever-evolving global economic engine is, in many ways, a wonderful phenomenon; you know—a rising-tide-lifting-all-boats, trickle-down-theory-of-economics dynamic at work.
In the August 2008 issue of Gear Technology, we ran a story (“Gearbox Speed Reducer Helps Fan Technology for ‘Greener” Jet Fuel Efficiency’) on the then ongoing, extremely challenging and protracted development of Pratt & Whitney’s geared turbofan (GTF) jet engine.
Gears with an asymmetric involute gear tooth form were analyzed to determine their bending and contact stresses relative to symmetric involute gear tooth designs, which are representative of helicopter main-drive gears.
Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of noninvolute gears with low numbers of teeth and low contact ratios for the use in advanced application. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 8.89 cm (3.50 in.) with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K (116 degrees F), a maximum Hertz stress of 1.49 GPa (216 ksi), and a speed of 10,000 rpm. The following results were obtained: The noninvolute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design. The surface pitting fatigue life of the 3.43-pitch AISI 8620 noninvolute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load, but at a considerably higher maximum Hertz stress.
Cubic boron nitride (CBN) finishing of carburized gearing has been shown to have certain economic and geometric advantages and, as a result, it has been applied to a wide variety of precision gears in many different applications. In critical applications such as aerospace drive systems, however, any new process must be carefully evaluated before it is used in a production application. Because of the advantages associated with this process, a test program was instituted to evaluate the load capacity of aerospace-quality gears finished by the CBN process as compared to geometrically identical gears finished by conventional grinding processes. This article presents a brief description of the CBN process, its advantages in an aerospace application, and the results of an extensive test program conducted by Boeing Helicopters (BH) aimed at an evaluation of the effects of this process on the scoring, surface durability, and bending fatigue properties of spur gears. In addition, the results of an x-ray diffraction study to determine the surface and subsurface residual stress distributions of both shot-peened and nonshot-peened CBN-ground gears as compared to similar conventionally ground gears are also presented.
This report presents some interim results from an ongoing project being performed by INFAC, the Instrumented Factory for Gears. The purposes of this initial phase of the project were to demonstrate the feasibility of robotic automated deburring of aerospace gears, and to develop a research agenda for future work in that area.
Prior to receiving airworthiness certification, extensive testing is required during the development of rotary wing aircraft drive systems. Many of these tests are conducted to demonstrate the drive system’s ability to operate at extreme conditions, i.e. — beyond that called for in the normal to maximum power operating range.
Except for higher-end gear applications found in automotive and aerospace transmissions, for example, high-performance, sintered-steel gears match wrought-steel gears in strength and geometrical quality. The enhanced P/M performance is due largely to advances in powder metallurgy over last two decades, such as selective surface densification, new materials and lubricants for high density and warm-die pressing. This paper is a review of the results of a decade of research and development of high- performance, sintered-steel gear prototypes.
The turbines are still spinning. They’re spinning on large wind farms in the Great Plains, offshore in the Atlantic and even underwater where strong tidal currents offer new energy solutions. These turbines spin regularly while politicians and policy makers— tied up in discussions on tax incentives, economic recovery and a lot of finger pointing—sit idle. Much like the auto and aerospace industries of years past, renewable energy is coping with its own set of growing pains. Analysts still feel confident that clean energy will play a significant role in the future of manufacturing—it’s just not going to play the role envisioned four to five years ago.
Composite spur gears were designed, fabricated and tested at NASA Glenn Research Center. The composite web was bonded only to the inner and outer hexagonal features that were machined from an initially all-metallic aerospace quality spur gear. The hybrid gear was tested against an all-steel gear and against a mating hybrid gear. Initial results indicate that this type of hybrid design may have a dramatic effect on drive system weight without sacrificing strength.
Reshoring offers an opportunity for increased domestic gear production. Reshoring is growing at a steady pace in most industries, and is particularly strong in the gear intensive industries such as automotive, aerospace and construction equipment (Table 1). This article provides background on the overall trend and tools for the gear buyer and the gear producer to make the offshore vs. domestic decision.
If you've got a gear performance problem, the Gear Research Institute (GRI) is here to help you. Since inception in 1982, GRI has been a primarily industry sponsored, experimentation driven research facility. Whether establishing the fatigue life of gears or evaluating the impact of manufacturing processes on the performance of gears, GRI has pioneered methods and procedures for characterizing such properties that are accepted by the aerospace, vehicle and other industry sectors.
Although gear geometry and the design of asymmetric tooth gears are well known and published, they are not covered by modern national or international gear design and rating standards. This limits their broad implementation for various gear applications, despite substantial performance advantages in comparison to symmetric tooth gears for mostly unidirectional drives. In some industries — like aerospace, that are accustomed to using gears with non-standard tooth shapes — the rating of these gears is established by comprehensive testing. However, such testing programs are not affordable for many other gear drive applications that could also benefit from asymmetric tooth gears.
Gear metrology is a revolving door of software packages and system upgrades. It has to be in order to keep up with the productivity and development processes of the machines on the manufacturing floor. Temperature compensation, faster inspection times and improved software packages are just a few of the advancements currently in play as companies prepare for new opportunities in areas like alternative energy, automotive and aerospace/defense.
A single tooth bending (STB) test procedure has been developed to optimally map gear design parameters. Also, a test program on case-carburized, aerospace standard gears has been conceived and performed in order to appreciate the influence of various technological parameters on fatigue resistance and to draw the curve shape up to the gigacycle region.
The benefits of ground gears are well known. They create less noise, transmit more power and have longer lives than non-ground gears. But grinding has always been thought of as an expensive process, one that was necessary only for aerospace or other high-tech gear manufacturing.
An experimental effort has been conducted on an aerospace-quality helical gear train to investigate the thermal behavior of the gear system. Test results from the parametric studies and the superfinishing process are presented.
With growing markets in aerospace and energy technologies, measuring hob cutters used in gear cutting is becoming an essential requirement for workpieces and machine tools. Zoller, a provider of solutions for tool pre-setters, measuring and inspection machines and tool management software, has developed a new partnership with Ingersoll/Germany for shop floor checking of hob cutters by a combined hardware and software approach.
Induction hardening is widely used in both the automotive and aerospace gear industries to minimize heat treat distortion and obtain favorable compressive residual stresses for improved fatigue performance. The heating process during induction hardening has a significant effect on the quality of the heat-treated parts. However, the quenching process often receives less attention even though it is equally important.
History comes around full circle. It is interesting to talk to gear manufacturers who service the defense, aerospace, automotive and computer industries and find that their sales, production and backlogs reflect excellent and, in some cases, record breaking business.
News Items About aerospace
1 Seco Tools Launches Aerospace Website (February 4, 2011)
Seco Tools has launched a new website dedicated to supporting aerospace manufacturers. The website hosts a wealth of information pertinen... Read News
2 Oven Industries, Inc. Receives Aerospace Certification (March 24, 2010)
Oven Industries, Inc. recently announced it has been awarded official accreditation to the AS9100 international aerospace quality standar... Read News
3 Northstar Aerospace Focuses on Record Backlog, Divests Non-Core Business (December 2, 2008)
In order to handle a significant core-business backlog in manufacturing aerospace gears and transmissions, Northstar Aerospace is divesti... Read News
4 Mazak Targets Aerospace and Medical Manufacturing Technology (March 7, 2013)
In support of the growing aerospace and medical industries, Mazak Corporation is hosting a Discover More With Mazak event at its Northeas... Read News
5 QuEST Expands Into Aerospace Manufacturing (April 3, 2006)
QuEST, a Bangladore-based provider of engineering services, today announced the expansion into aerospace manufacturing through a fully ow... Read News
6 GF Machining Unveils Aerospace EDM (September 23, 2014)
GF Machining Solutions debuted its new Cut 200 Dedicated wire electrical discharge machine (EDM) for aerospace work at IMTS in Chicago. T... Read News
7 Northstar Aerospace Reports Increased Revenue (April 14, 2006)
Northstar Aerospace reported revenue totaling $36.8 million for the three months ending June 30, 2006, an increase of $3.6 million when c... Read News
8 Northstar Aerospace Expands, Creates 70 U.S. Jobs (October 21, 2008)
Increasing its production of gears, components and spare parts for the CH-47 Chinook helicopter and Rolls-Royce programs, Northstar Aer... Read News
9 Northstar Aerospace Receives Contract for New Drive System Development (August 30, 2007)
Northstar Aerospace was awarded a $4.5 million development contract from The Boeing Co. for its Enhanced Rotor Rotorcraft Drive System (E... Read News
10 Northstar Aerospace and Rolls Royce Sign Long Term Agreement (April 27, 2006)
Northstar Aeropsace was awarded a seven-year contract by Rolls-Royce Corp. to provide machining for gearboxes and related parts used in c... Read News
11 Northstar Aerospace Announces Executive Appointments to Accelerate Manufacturing Ramp-Up (May 24, 2007)
Northstar Aerospace announced several executive management changes in accordance with the company's plans to drastically accelerate i... Read News
12 Endmills Suitable for Aerospace Materials (December 23, 2010)
ATI Stellram has released the new XE solid carbide endmill engineered specifically for machining exotic and difficult to machine material... Read News
13 5ME Delivers Machining Fluids for Aerospace and Heavy Equipment (February 14, 2014)
5ME's Cyclo Cool 900 series synthetic metal machining fluids utilize a unique, near-neutral pH formula developed to meet heavy-duty, ... Read News
14 LMI Aerospace Appoints Jay Inman President of Engineering Services, Keith Schrader Vice President of Operations (January 20, 2017)
LMI Aerospace Inc. has appointed Jay Inman as president of engineering services, a role he had been serving on an interim basis since Sep... Read News
15 QuesTek Gets Second Alloy Approved for Aerospace Applications (January 8, 2014)
QuesTek Innovations LLC is pleased to announce that its ultra high-strength, high-toughness Ferrium M54TM steel has been approved for inc... Read News
16 Micro Precision Joins Aerospace Supply Chain Program (December 21, 2012)
In line with its policy of continually improving all aspects of its operations, Hemel Hempstead based Micro Precision has signed up to th... Read News
17 Mecof Powermill Machining Center Offers Ideal Solution for Aerospace and Large Workpiece Handling (March 1, 2017)
The large Powermill machining center from Mecof, part of EMCO Group, provides users precision, high dynamics, operational flexibility and... Read News
18 Sandvik Coromant Appoints Aerospace Manager (June 21, 2010)
Sandvik Coromant recently announced the promotion of Kevin Mayer to the position of Manager of Aerospace. Prior to this appointment, Maye... Read News