On behalf of the AGMA Board of Directors, Show Committee and our 123 exhibiting companies — thank you for supporting Motion + Power Technology Expo 2021 (MPT Expo).
Lately, the use of asymmetric gears in automotive and other applications is an upcoming trend, though few applications
are known to have asymmetric teeth. However, an increased interest in asymmetric gears can be seen. Many companies have started to design and test such applications.
A reader asks: We are currently revising our gear standards and tolerances and a few questions with the new standard AGMA 2002-C16 have risen. Firstly,
the way to calculate the tooth thickness tolerance seems to need a "manufacturing profile shift coefficient" that isn't specified in the standard; neither is another standard referred to for this coefficient. This tolerance on tooth thickness is needed later to calculate the span width as well as the pin diameter. Furthermore, there seems to be no tolerancing on the major and minor diameters of a gear.
In many gear transmissions, tooth load on one flank is significantly higher and is applied for longer periods of time than on the opposite one; an asymmetric tooth shape should reflect this functional difference. The advantages of these gears allow us to improve the performance of the primary drive tooth flanks at the expense of the opposite coast flanks, which are unloaded or lightly loaded during a relatively short work period by drive flank contact and bending stress reduction. This article is about the microgeometry optimization of the spur asymmetric gears’ tooth flank profile based on the tooth bending and contact deflections.
A reader asks: We are currently revising our gear standards and tolerances, and a few problems with the new standard AGMA 2002-C16 have arisen. Firstly, the way to calculate the tooth thickness tolerance seems to need a "manufacturing profile shift coefficient" that isn't specified in the standard; neither is another standard referred to for this coefficient. This tolerance on tooth thickness is needed later to calculate the span width as well as the pin diameter. Furthermore, there seems to be no tolerancing on the major and minor diameters of a gear.
The deformation of the gear teeth due to load conditions may cause premature tooth meshing. This irregular tooth contact causes increased stress on the tooth flank. These adverse effects can be avoided by using defined flank modifications, designed by means of FE-based tooth contact analysis.
In order to improve load-carrying capacity and noise behavior, gears usually have profile and lead modifications. Furthermore, in gears where a specified tooth-flank load application direction (for drive and coast flanks) is a design enhancement, or even compulsory, the asymmetric tooth profile is a further solution. Nowadays, many gears need to be hard finished. Continuous generating grinding offers a very high process efficiency, but is this process able to grind all modifications, especially asymmetric gears? Yes, it is!
The results of our Annual State of the Gear Industry Survey (See page 26) provided insight on 2016 as well as forecasts for 2017. Here is additional insight from some of the industry's leaders.
This paper presents a new approach to repair industrial gears by showing a case study where pressure angle modification is also considered, differently from the past repairing procedures that dealt only with the modification of the profile shift
coefficient. A computer program has been developed to automatically determine the repair alternatives under two goals: minimize the stock removal or maximize gear tooth strength.
Plastic gears are everywhere
today - throughout your car, at
the oceans' lowest depths, in deep
space. The question, when is a
metal gear a candidate for plastic
conversion, can be addressed in
three words, i.e. what's the application?
Chapter 2, Continued
In the previous sections, development of conjugate, face milled as well as face hobbed bevel gearsets - including the application of profile and length crowning - was demonstrated. It was mentioned during that demonstration that in order to optimize the common surface area, where pinion and gear flanks have meshing contact (common flank working area), a profile shift must be introduced. This concluding section of chapter 2 explains the principle of profile shift; i.e. - how it is applied to bevel and hypoid
gears and then expands on profile side shift, and the frequently used root angle correction which - from its gear theoretical
understanding - is a variable profile shift that changes the shift factor along the face width. The end of this section elaborates on
five different possibilities to tilt the face cutter head relative to the generating gear, in order to achieve interesting effects on the
bevel gear flank form. This installment concludes chapter 2 of the Bevel Gear Technology book that lays the foundation of the following
chapters, some of which also will be covered in this series.
Since we began publishing in 1984, Gear Technology's mission has been to educate our readers. For 31 years, we've shown you the basics of gear manufacturing as well as the cutting edge. We take our educational mission quite seriously, and we go through steps that most publishers don't have time for or wouldn't consider.
Helical gear teeth are affected by cratering wear — particularly in the regions of low oil film thicknesses,
high flank pressures and high sliding speeds. The greatest wear occurs on the pinion — in the area of
negative specific sliding. Here the tooth tip radius of the driven gear makes contact with the flank of the
driving gear with maximum sliding speed and pressure.
Here is some history that bears repeating - or at least re-reading. So take a few minutes to give it up for a long-gone Brit named Henry Maudslay
(August 22, 1771 - February 14, 1831) - also known as "A Founding Father of Machine Tool Technology." You might
also consider him an early leader in inspection, as he also invented the first bench micrometer capable of measuring to one ten-thousandth of an inch.
The name Gleason is practically synonymous with gear manufacturing. Since the company was founded in 1865, the technology of gear manufacturing has
been its focus, its core and its competitive advantage.
At the dawn of the Industrial
Revolution, so-called mechanics
were tasked with devising the precise methods that would make mass production possible. The result was the first generation of machine tools, which in turn required improved tooling and production methods.
Introduction
The standard profile form in cylindrical
gears is an involute. Involutes are
generated with a trapezoidal rack — the
basis for easy and production-stable
manufacturing (Fig. 1).
Gears with a diametral pitch 20 and
greater, or a module 1.25 millimeters
and lower, are called fine-pitch or low-module gears. The design of these gears has its own specifics.
Measurement institutions of seven different countries — China, Germany, Japan, Thailand, Ukraine, United Kingdom and the U.S. — participated in the implementation of the first international comparison of involute gear measurement standards. The German metrology institute Physikalisch-Technische Bundesanstalt (PTB) was chosen as the pilot laboratory as well as the organizer. Three typical involute gear measurement standards provided by the PTB were deployed for this comparison: a profile, a helix and a pitch measurement standard. In the final analysis, of the results obtained from all participants, the weighted mean was evaluated as reference value for all 28 measured parameters. However, besides the measurement standards, the measured parameters, and, most importantly, some of the comparison results from all participants are anonymously presented. Furthermore, mishandling of the measurement standards as occurred during the comparison will be illustrated.
Vibration and noise from wind turbines can be significantly influenced - and therefore reduced - by selecting suitable gearing modifications. New options provided by manufacturers of machine tools and grinding machines, and especially state-of-the-art machines and controls, provide combined gearing modifications - or topological gearing corrections - that can now be reliably machined. Theoretical investigations of topological modifications are discussed here with the actual machining and their possible use.
With technologies such as the Zenith 400 Rotor Grinding Center and the Holroyd TG Series of rotor grinding machines, Precision Technologies Group company, Holroyd Precision Limited...
In November, Gear Technology conducted
an anonymous survey of gear manufacturers. Invitations were sent by e-mail to thousands of individuals around the world. More than 300
individuals responded to the online survey, answering questions about their manufacturing operations and current challenges facing their businesses.
India is rapidly turning into a global manufacturing hub, thanks to the country’s manufacturing and engineering
capabilities, vast pool of skilled expertise and its size. These qualities offer it a strategic advantage for the manufacturing segment. A large number of international companies in varied
segments have already set up a manufacturing base in India and others are following suit. It only makes sense to bring this industry segment together under one roof to discuss the current
trends and technology prevalent to the marketplace. IPTEX 2012 is scheduled from February 9–11, 2012 at the Bombay Exhibition Center in Mumbai, India.
Profile corrections on gears are a commonly used method to reduce transmission error, contact shock, and scoring risk. There are different types of profile corrections. It is a known fact that the type of profile correction used will have a strong influence on the resulting transmission error. The degree of this influence may be determined by calculating tooth loading during mesh. The current method for this calculation is very complicated and time consuming; however,
a new approach has been developed that could reduce the calculation time.
Modern gearboxes are characterized by high torque load demands, low running noise and compact design. In order
to fulfill these demands, profile and lead modifications are being applied more often than in the past. This paper will focus on how to produce profile and lead modifications by using the two most common grinding processes—threaded
wheel and profile grinding. In addition, more difficult modifications—such as defined flank twist or topological flank corrections—will also be described in this paper.
The gear tooth fillet is an area of maximum bending stress concentration. However, its profile is typically less specified in the gear drawing and hardly controlled during gear inspection in comparison with the gear tooth flanks. This paper presents a fillet profile optimization technique for gears with symmetric and asymmetric teeth based on FEA and a random search method. It allows achieving substantial bending stress
reduction in comparison with traditionally designed gears. This bending stress reduction can be traded for higher load capacity, longer lifetime, lower noise and vibration and cost reduction.
This article shows the newest developments to reduce overall cycle time in grinding wind power gears, including the use of both profile grinding and threaded wheel grinding.
This paper will demonstrate that, unlike commonly used low-contact-ratio spur gears, high-contact-ratio spur gears can provide higher power-to-weight ratio, and can also achieve smoother running with lower transmission error (TE) variations.
While universally known as a Japanese “invention” that was popularized by Toyota, lean in fact traces its roots to the work of
post-World War II American occupation forces in Japan.
In this article, equations for finding profile and base pitch errors with a micrometer are derived. Limitations of micrometers with disc anvils are described. The design of a micrometer with suitable anvils is outlined.
Traditionally, high-quality gears are cut to shape from forged blanks. Great accuracy can be obtained through shaving and grinding of tooth forms, enhancing the power capacity, life and quietness of geared power transmissions. In the 1950s, a process was developed for forging gears with teeth that requires little or no metal to be removed to achieve final geometry. The initial process development was undertaken in Germany for the manufacture of bevel gears for automobile differentials and was stimulated by the lack of available gear cutting equipment at that time. Later attention has turned to the forging of spur and helical gears, which are more difficult to form due to the radial disposition of their teeth compared with bevel gears. The main driver of these developments, in common with most component manufacturing, is cost. Forming gears rather than cutting them results in increased yield from raw material and also can increase productivity. Forging gears is therefore of greater advantage for large batch quantities, such as required by the automotive industry.
Early in the practice of involute gearing, virtually all gears were made with the teeth in a standard relationship to the reference pitch circle. This has the advantages that any two gears of the same pitch, helix angle and pressure angle can operate together, and that geometry calculations are relatively simple. It was soon realized, though, that there are greater advantages to be gained by modifying the relationship of the teeth to the reference pitch circle. The modifications are called profile shift.
Base helix error - the resultant of lead and profile errors is the measured deviation from the theoretical line of contact (Fig. 1). It can be measured in the same way that lead error on a spur gear is measured, namely, by setting a height gage to height H based on the radial distance r to a specified line of contact (Fig. 2), rotating the gear so as to bring a tooth into contact with the indicator on the height gage, and then moving the height gage along two or more normals to the plane of action. The theoretical line of contact on helical gear must be parallel to the surface plate, which is attained by mounting the gear on a sine bar (Fig. 3).
This is the fourth and final article in a series exploring the new ISO 6336 gear rating standard and its methods of calculation. The opinions expressed herein are those of the author as an individual. They do not represent the opinions of any organization of which he is a member.
A programmable algorithm is developed to separate out the effect of eccentricity (radial runout) from elemental gear inspection date, namely, profile and lead data. This algorithm can be coded in gear inspection software to detect the existence, the magnitude and the orientation of the eccentricity without making a separate runout check. A real example shows this algorithm produces good results.
It isn't for everyone, but...
Within the installed base of modern CNC gear profile grinding machines (approximately 542 machines worldwide), grinding from the solid isn't frequent, but a growing number of gear profile grinder users are applying it successfully using CBN-plated wheels.
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.
There are problems in dimensional measurement that should be simple to solve with standard measuring procedures, but aren't. In such cases, using accepted practices may result in errors of hundreds of microns without any warning that something is wrong.
When designing hardened and ground spur gears to operate with minimum noise, what are the parameters to be considered? should tip and/or root relief be applied to both wheel and pinion or only to one member? When pinions are enlarged and he wheel reduced, should tip relief be applied? What are the effects on strength, wear and noise? For given ratios with enlarged pinions and reduced wheels, how can the gear set sized be checked or adjusted to ensure that the best combination has been achieved?
Could the tip chamfer that manufacturing people usually use on the tips of gear teeth be the cause of vibration in the gear set? The set in question is spur, of 2.25 DP, with 20 degrees pressure angle. The pinion has 14 teeth and the mating gear, 63 teeth. The pinion turns at 535 rpm maximum. Could a chamfer a little over 1/64" cause a vibration problem?
Question: I have just become involved with the inspection of gears in a production operation and wonder why the procedure specifies that four involute checks must be made on each side of the tooth of the gear being produced, where one tooth is checked and charted in each quadrant of the gear. Why is this done? These particular gears are checked in the pre-shaved, finish-shaved, and the after-heat-treat condition, so a lot of profile checking must be done.
On many occasions a reasonably approximate, but not exact, representation of an involute tooth profile is required. Applications include making drawings, especially at enlarged scale, and laser or EDM cutting of gears, molds, and dies used to produce gears. When numerical control (NC) techniques are to be used, a simple way to model an involute can make the NC programming task much easier.
An investigation of transmission errors and bearing contact of spur, helical, and spiral bevel gears was performed. Modified tooth surfaces for these gears have been proposed in order to absorb linear transmission errors caused by gear misalignment and to localize the bearing contact. Numerical examples for spur, helical, and spiral bevel gears are presented to illustrate the behavior of the modified gear surfaces with respect to misalignment and errors of assembly. The numerical results indicate that the modified surfaces will perform with a low level of transmission error in non-ideal operating environments.
Our research group has been engaged in the study of gear noise for some nine years and has succeeded in cutting the noise from an average level to some 81-83 dB to 76-78 dB by both experimental and theoretical research. Experimental research centered on the investigation into the relation between the gear error and noise. Theoretical research centered on the geometry and kinematics of the meshing process of gears with geometric error. A phenomenon called "out-of-bound meshing of gears" was discovered and mathematically proven, and an in-depth analysis of the change-over process from the meshing of one pair of teeth to the next is followed, which leads to the conclusion we are using to solve the gear noise problem. The authors also suggest some optimized profiles to ensure silent transmission, and a new definition of profile error is suggested.
This article describes a method of obtaining gear tooth profiles from the geometry of the rack (or hob) that is used to generate the gear. This method works for arbitrary rack geometries, including the case when only a numerical description of the rack is available. Examples of a simple rack, rack with protuberances and a hob with root chamfer are described. The application of this technique to the generation of boundary element meshes for gear tooth strength calculation and the generation of finite element models for the frictional contact analysis of gear pairs is also described.
The newer profile-shifted (long and short addendum) gears are often used as small size reduction gears for automobiles or motorcycles. The authors have investigated the damage to each cutting edge when small size mass-produced gears with shifted profiles are used at high speeds.
The NASA Lewis Research Center investigated the effect of tooth profile on the acoustic behavior of spur gears through experimental techniques. The tests were conducted by Cleveland State University (CSU) in NASA Lewis' spur gear testing apparatus. Acoustic intensity (AI) measurements of the apparatus were obtained using a Robotic Acoustic Intensity Measurement System (RAIMS). This system was developed by CSU for NASA to evaluate the usefulness of a highly automated acoustic intensity measurement tool in the reverberant environment of gear transmission test cells.
The use of dimensionless factors to describe gear tooth geometry seems to have a strong appeal to gear engineers. The stress factors I and J, for instance, are well established in AGMA literature. The use of the rack shift coefficient "x" to describe nonstandard gear proportions is common in Europe, but is not as commonly used in the United States. When it is encountered in the European literature or in the operating manuals for imported machine tools, it can be a source of confusion to the American engineer.
The art of gear hobbing has advanced dramatically since the development and introduction of unique machine and tool features such as no backlash, super rigidity, automatic loading of cutting tools, CNC controls, additional machine power and improved cutter materials and coatings. It is essential to utilize all these features to run the machine economically.
A change has taken place within the industry that is going to have an enormous effect on the marketing, sales, and purchasing of gear manufacturing and related equipment. This change was the American Gear Manufacturers' Association, first biennial combination technical conference and machine tool minishow.
Curvic Couplings were first introduced in 1942 to meet the need for permanent couplings and releasing couplings (clutches), requiring extreme accuracy and maximum load carrying capacity, together with a fast rate of production. The development of the Curvic Coupling stems directly from the manufacture of Zerol and spiral bevel gears since it is made on basically similar machines and also uses similar production methods. The Curvic Coupling can therefore lay claim to the same production advantages and high precision associated with bevel gears.
Sub: 'Finding Tooth Ratios' article published in Nov/Dec 1985 issue
Let us congratulate you and Orthwein, W.C. for publishing this superb article in Gear Technology Journal. We liked the article very much and wish to impliment it in our regular practice.
Your May/June issue contains a
letter from Edward Ubert of Rockwell
International with some serious questions
about specifying and measuring tooth thickness.
Much information has been written on gear inspection, analytical. functional. semiautomatic and automatic. In most
cases, the charts, (if you are lucky enough to have recording
equipment) have been explained.
