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The higher load carrying capacities, compact dimensions and longer life of hardened gears is an accepted fact in industry today. However, the costs involved in case hardening and subsequent finishing operations to achieve these advantages are considerable. For example, in order to achieve desired running properties on larger gears, it has been necessary to grind the tooth flanks. This costly operation can now be replaced, in many cases, by a new Hard Cutting (HC) process which permits the cutting of hardened gears while maintaining extremely low tooling costs.
Some years back, most spiral bevel gear sets were produced as cut, case hardened, and lapped. The case hardening process most frequently used was and is case carburizing. Many large gears were flame hardened, nitrided, or through hardened (hardness around 300 BHN) using medium carbon alloy steels, such as 4140, to avoid higher distortions related to the carburizing and hardening process.
Today's high technology hobs are visible different from their predecessors. Gear hobs have taken on a different appearance and function with present day technology and tool and material development. This article shows the newer products being offered today and the reasons for investigating their potential for use in today's modern gear hobbers, where cost reduction and higher productivity are wanted.
CNC technology offers new opportunities for the manufacture of bevel gears. While traditionally the purchase of a specific machine at the same time determined a particular production system, CNC technology permits the processing of bevel gears using a wide variety of methods. The ideological dispute between "tapered tooth or parallel depth tooth" and "single indexing or continuous indexing" no longer leads to an irreversible fundamental decision. The systems have instead become penetrable, and with existing CNC machines, it is possible to select this or that system according to factual considerations at a later date.
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.
Not long ago, many manufacturing managers thought sensitivity to environmental protection standards meant additional expenses, decreased productivity, and a plethora of headaches and hassles.
Question: Do machines exist that are capable of cutting bevel gear teeth on a gear of the following specifications: 14 teeth, 1" circular pitch, 14.5 degrees pressure angle, 4 degrees pitch cone angle, 27.5" cone distance, and an 2.5" face width?
Okay, so you want to make some high quality gears for your customers, and you want to make a profit for your company, but you don't want to make a mess of the environment. What can you do?
In today's economy, when purchasing a new state-of-the-art gear shaper means a significant capital investment, common sense alone dictates that you develop strategies to get the most for your money. One of the best ways to do this is to take advantage of the sophistication of the machine to make it more than just a single-purpose tool.
What Is Whisker-Reinforced Ceramic? Whisker-reinforced ceramic as applied to cutting tool inserts comprises a matrix of aluminum oxide into which approximately 50% by volume of high-purity silicon carbide "whiskers" are randomly dispersed. The "whiskers" are, in fact, single crystals having dimensions of approximately 0.6 microns in diameter x 10-80 microns in length. These "whiskers" have a tensile strength on the order of 1,000,000 psi (690 MPa). The composite material that is the best known and most widely applied using this technology is designated WG-300 and manufactured by the Greenleaf Corporation of Saegertown, PA.
The dimensions of the worm and worm gear tooth surfaces and some of the worm gear drive parameters must be limited in order to avoid gear undercutting and the appearance of the envelope of lines of contact on the worm surface. The author proposes a method for the solution of this problem. The relations between the developed concept and Wildhaber's concept of the limit contact normal are investigated. The results of computations are illustrated with computer graphics.
New freedom of motion available with CNC generators make possible improving tooth contact on bevel and hypoid gears. Mechanical machines by their nature are inflexible and require a special mechanism for every desired motion. These mechanisms are generally exotic and expensive. As a result, it was not until the introduction of CNC generators that engineers started exploring motion possibilities and their effect on tooth contact.
The paper describes a procedure for the design of internal gear pairs, which is a generalized form of the long and short addendum system. The procedure includes checks for interference, tip interference, undercutting, tip interference during cutting, and rubbing during cutting.
The objective, according to Dr.- Ing. Hansjörg Geiser, head of development and design for gear machines at Liebherr, was to develop and design a combined turning and hobbing machine in which turning, drilling and hobbing work could be carried out in the same clamping arrangement as the hobbing of the gearings and the subsequent chamfering and deburring processes.
Klingelnberg's new tool and machine concept allow for precise production.
Indexable carbide insert cutting tools for gears are nothing new. But big gears have recently become a very big business. The result is that there's been a renewed interest in carbide insert cutting tools.
A brief introduction to the subject of Thin Film Coatings and their application to gear hobs and shaper cutters is followed by a detailed description of the Chemical Vapor Deposition Process and the Physical Vapor Deposition Process. Advantages and disadvantages of each of these processes is discussed. Emphasis is placed upon: application engineering of coated gear tools based on laboratory and field test results. Recommendations are suggested for tool design improvements and optimization of gear cutting operations using coated tools. Productivity improvements potentially available by properly utilizing coated tools are considered in terms of both tool cost and machining cost.
Universal machines capable of cutting both spur and helical gears were developed in 1910, followed later by machines capable of cutting double helical gears with continuous teeth. Following the initial success, the machines were further developed both in England and France under the name Sunderland, and later in Switzerland under the name Maag.
The cutting tool is basic to gear manufacturing. Whether it's a hob, broach, shaper cutter or EDM wire, not much gets done without it. And the mission of the tool remains the same as always; removing material as quickly, accurately and cost-effectively as possible. Progress in the field tends to be evolutionary, coming gradually over time, but recently, a confluence of emerging technologies and new customer demands has caused significant changes in the machines, the materials and the coatings that make cutting tools.
Gear shaping is one of the most popular production choices in gear manufacturing. While the gear shaping process is really the most versatile of all the gear manufacturing methods and can cut a wide variety of gears, certain types of gears can only be cut by this process. These are gears closely adjacent to shoulders; gears adjacent to other gears, such as on countershafts; internal gears, either open or blind ended; crown or face gears; herringbone gears of the solid configuration of with a small center groove; rack; parts with filled-in spaces or teeth, such as are used in some clutches.
The last decade has been a period of far-reaching change for the metal working industry. The effect of higher lubricant costs, technical advances in machine design and increasing competition are making it essential that manufacturers of gears pay more attention to testing, selecting and controlling cutting fluid systems. Lubricant costs are not a large percentage of the process cost relative to items such as raw materials, equipment and labor, and this small relative cost has tended to reduce the economic incentive to evaluate and to change cutting fluids.
Cutter Sharpening Cutter sharpening is very important both during manufacturing and subsequently in resharpening after dulling. Not only does this process affect cutter "over cutting edge" quality and the quality of the part cut, but it can also affect the manner in which chip flow takes place on the cutter face if the surface finished is too rough or rippled.
Physical Vapor Deposited (PVD) coatings such as TiN (Titanium nitride) have been a boon for cutting tool manufacturers. They reduce wear and, therefore, extend tool life, which in turn reduces production costs. But PVD coatings are expensive, and when they fail, they cost both time and money, and they causes of the failure are not always readily apparent.
The hob is a perfect example of how a little manufacturing ingenuity can make a reliable, highly productive cutting tool. It's an engineering specimen that creates higher cutting speeds, better wear resistance and increases rigidity. The cutting tool alone, however, can't take all the credit for its resourcefulness. Advanced coating technology from companies like Sulzer, Oerlikon Balzers, Ionbond, Seco Tools and Cemecon helps improve cutting tools by reducing overall costs, increasing tool life and maintaining the highest levels of productivity. The following is a quick recap of new technologies and the latest information in the coating market.
Sandvik presents the latest in gear milling technologies.
Previews of manufacturing technology related to gears that will be on display at IMTS 2012.
Booth previews from exhibitors showing products and services for the gear industry.
Investment in advanced new manufacturing technologies is helping to reinvent production processes for bevel gear cutters and coarse-pitch hobs at Gleason - delivering significant benefits downstream to customers seeking shorter deliveries, longer tool life and better results.
Recently, a new type of hob with carbide inserts has been introduced, providing higher cutting speeds, longer tool life and higher feed rates when compared to re-grindable, high-speed steel hobs. But with this kind of hob, new challenges occur due to positional errors of the cutting edges when mounted on the tool. These errors lead to manufacturing errors on the gear teeth which must be controlled. In this paper, the tooth quality of a gear manufactured by hobs with different quality classes is analyzed using a simulation model in combination with Monte Carlo methods.
Manufacturing involute gears using form grinding or form milling wheels are beneficial to hobs in some special cases, such as small scale production and, the obvious, manufacture of internal gears. To manufacture involute gears correctly the form wheel must be purpose-designed, and in this paper the geometry of the form wheel is determined through inverse calculation. A mathematical model is presented where it is possible to determine the machined gear tooth surface in three dimensions, manufactured by this tool, taking the finite number of cutting edges into account. The model is validated by comparing calculated results with the observed results of a gear manufactured by an indexable insert milling cutter.
Sentences that start off with some variance of “I don’t want to brag, but…” are generally a good indicator that it’s precisely what the speaker intends to do and typically end with bold proclamations that are immediately and eminently quotable — the kind of quotes perfect for beginning a feature story with an eye-catching artistic flourish.
The complete Industry News section from the November/December 2014 issue.
In the past, the blades of universal face hobbing cutters had to be resharpened on three faces. Those three faces formed the active part of the blade. In face hobbing, the effective cutting direction changes dramatically with respect to the shank of the blade. Depending on the individual ratio, it was found that optimal conditions for the chip removal action (side rake, side relief and hook angle) could just be established by adjusting all major parameters independently. This, in turn, results automatically in the need for the grinding or resharpening of the front face and the two relief surfaces in order to control side rake, hook angle and the relief and the relief angles of the cutting and clearance side.
In order to increase the load carrying capacity of hardened gears, the distortion of gear teeth caused by quenching must be removed by precision cutting (skiving) and/or grinding. In the case of large gears with large modules, skiving by a carbide hob is more economical than grinding when the highest accuracy is not required.
High-speed machining using carbide has been used for some decades for milling and turning operations. The intermittent character of the gear cutting process has delayed the use of carbide tools in gear manufacturing. Carbide was found at first to be too brittle for interrupted cutting actions. In the meantime, however, a number of different carbide grades were developed. The first successful studies in carbide hobbing of cylindrical gears were completed during the mid-80s, but still did not lead to a breakthrough in the use of carbide cutting tools for gear production. Since the carbide was quite expensive and the tool life was too short, a TiN-coated, high-speed steel hob was more economical than an uncoated carbide hob.
Fig. 1 shows the effects of positive and negative rake on finished gear teeth. Incorrect positive rake (A) increase the depth and decreases the pressure angle on the hob tooth. The resulting gear tooth is thick at the top and thin at the bottom. Incorrect negative rake (B) decreases the depth and increases the pressure angle. This results in a cutting drag and makes the gear tooth thin at the top and thick at the bottom.
This article summarizes the development of an improved titanium nitride (TiN) recoating process, which has, when compared to conventional recoat methods, demonstrated tool life increases of up to three times in performance testing of hobs and shaper cutters. This new coating process, called Super TiN, surpasses the performance of standard TiN recoating for machining gear components. Super TiN incorporates stripping, surface preparation, smooth coating techniques and polishing before and after recoating. The combination of these improvements to the recoating process is the key to its performance.
A new method for cutting straight bevel gears.
the gear industry is awash in manufacturing technologies that promise to eliminate waste by producing gears in near-net shape, cut production and labor costs and permit gear designers greater freedom in materials. These methods can be broken down into the following categories: alternative ways to cut, alternative ways to form and new, exotic alternatives. Some are new, some are old and some are simply amazing.
The cutting tool industry has undergone some serious changes in the last couple of years in both technology and the way the industry does business. The emerging technology today, as well as for the foreseeable future, is dry cutting, especially in high volume production settings. Wet cutting continues to be as popular as ever with lubrication advances making it more economical and environmentally friendly. There has also developed a process called "near dry cutting." this process offers many of the benefits of fluids while eliminating many of hte associated problems.
Economic production is one of the main concerns of any manufacturing facility. In recent years, cost increases and tougher statutory requirements have increasingly made cutting fluids a problematic manufacturing and cost factor in metalworking. Depending on the cutting fluid, production process and supply unit, cutting-fluid costs may account for up to 16% of workpiece cost. In some cases, they exceed tool cost by many times (Ref. 1). The response by manufacturers is to demand techniques for dry machining (Ref. 2).
Users of gear-cutting tools probably do not often consciously consider the raw material from which those hobs, broaches or shavers are made. However, a rudimentary awareness of the various grades and their properties may allow tool users to improve the performance or life of their tools, or to address tool failures. The high-speed steel from which the tool is made certainly is not the only factor affecting tool performance, but as the raw material, the steel may be the first place to start.
Quality gear manufacturing depends on controlled tolerances and geometry. As a result, ferritic nitrocarburizing has become the heat treat process of choice for many gear manufacturers. The primary reasons for this are: 1. The process is performed at low temperatures, i.e. less than critical. 2. the quench methods increase fatigue strength by up to 125% without distorting. Ferritic nitrocarburizing is used in place of carburizing with conventional and induction hardening. 3. It establishes gradient base hardnesses, i.e. eliminates eggshell on TiN, TiAIN, CrC, etc. In addition, the process can also be applied to hobs, broaches, drills, and other cutting tools.
A gear shaper cutter is actually a gear with relieved cutting edges and increased addendum for providing clearance in the root of the gear being cut. The maximum outside diameter of such a cutter is limited to the diameter at which the teeth become pointed. The minimum diameter occurs when the outside diameter of the cutter and the base circle are the same. Those theoretical extremes, coupled with the side clearance, which is normally 2 degrees for coarse pitch cutters an d1.5 degrees for cutters approximately 24-pitch and finer, will determine the theoretical face width of a cutter.
This article presents some of the findings of cutting investigations at WZL in which the correlation of cutting parameters, cutting materials, tool geometry and tool life have been determined.
In his Handbook of Gear Design (Ref.1), Dudley states (or understates): "The best gear people around the world are now coming to realize that metallurgical quality is just as important as geometric quality." Geometric accuracy without metallurgical integrity in any highly stressed gear or shaft would only result in wasted effort for all concerned - the gear designer, the manufacturer, and the customer - as the component's life cycle would be prematurely cut short. A carburized automotive gear or shaft with the wrong surface hardness, case depth or core hardness may not even complete its basic warranty period before failing totally at considerable expense and loss of prestige for the producer and the customer. The unexpected early failure of a large industrial gear or shaft in a coal mine or mill could result in lost production and income while the machine is down since replacement components may not be readily available. Fortunately, this scenario is not common. Most reputable gear and shaft manufacturers around the world would never neglect the metallurgical quality of their products.
So, you've been assigned the task to buy an induction heating system for heat treating: It's an intimidating, but by no means impossible, assignment. With the help of the information in this article, you could be able to develop common ground with your supplier and have the tools to work with him or her to get the right machine for your jobs.
Many potential problems are not apparent when using new induction heat treating systems. The operator has been trained properly, and setup parameters are already developed. Everything is fresh in one's mind. But as the equipment ages, personnel changes or new parts are required to be processed on the old equipment ages, personnel changes or new parts are required to b processed on the old equipment, important information can get lost in the shuffle.
Graded hardening technology has proven over the years to yield very good results when used in the heat treating of carburized gears. It is especially advantageous for smaller companies, subject to higher competitive pressures. Unfortunately, despite the fact that graded hardening is a very well-known method, its use has been limited. We strongly recommend this technology to all of those who need to produce gears with high metallurgical quality.
The tooth-by-tooth, submerged induction hardening process for gear tooth surface hardening has been successfully performed at David Brown for more than 30 years. That experience - backed up by in-depth research and development - has given David Brown engineers a much greater understanding of, and confidence in, the results obtainable from the process. Also, field experience and refinement of gear design and manufacturing procedures to accommodate the induction hardening process now ensure that gears so treated are of guaranteed quality.
In recent years, the demands for load capacity and fatigue life of gears constantly increased while weight and volume had to be reduced. To achieve those aims, most of today's gear wheels are heat treated so tooth surfaces will have high wear resistance. As a consequence of heat treatment, distortion unavoidably occurs. With the high geometrical accuracy and quality required for gears, a hard machining process is needed that generates favorable properties on the tooth surfaces and the near-surface material with high reliability.
In the last couple of years, many research projects dealt with the determination of load limits of cylindrical worm gears. These projects primarily focused on the load capacity of the worm wheel, whereas the worm was neglected. This contribution presents investigations regarding damages such as large scores and cracks on the flanks of case-hardened worms.
The need for improved power transmissions that use gears and gearboxes with smaller overall dimensions and with lower noise generation has left manufacturing engineers searching for different methods of gear processing. This search has led to the requirement of hardened gears.
Carburized gears have higher strengths and longer lives compared with induction-hardened or quench-tempered gears. But in big module gears, carburizing heat-treatment becomes time-consuming and expensive and sometimes cannot achieve good hardness due to the big mass-effect. Also, it is not easy to reduce distortion of gears during heat treatment.
In the typical gear production facility, machining of gear teeth is followed by hear treatment to harden them. The hardening process often distorts the gear teeth, resulting in reduced and generally variable quality. Heat treating gears can involve many different types of operations, which all have the common purpose of producing a microstructure with certain optimum properties. Dual frequency induction hardening grew from the need to reduce cost while improving the accuracy (minimizing the distortion) of two selective hardening processes: single tooth induction and selective carburizing.
In a very general sense, increasing the hardness of a steel gear increases the strength of the gear. However, for each process there is a limit to its effectiveness. This article contains background information on each of the processes covered. In each section what is desired and what is achievable is discussed. Typical processes are presented along with comments on variables which affect the result. By reviewing the capabilities and processes, it is possible to determine the limits to each process.
Induction hardening is a heat treating technique that can be used to selectively harden portions of a gear, such as the flanks, roots and tips of teeth, providing improved hardness, wear resistance, and contact fatigue strength without affecting the metallurgy of the core and other parts of the component that don’t require change. This article provides an overview of the process and special considerations for heat treating gears. Part I covers gear materials, desired microsctructure, coil design and tooth-by-tooth induction hardening.
Corus Engineering Steels' formula for its new gear steels: Maintain achievable hardness while using fewer alloys, thereby cutting steel costs for gear manufacturers.
This article covers preventive maintenance and modification to machinery to induction harden different types of gear.
Part I, which was published in the September/October 2008 issue, covered gear materials, desired microstructure, coil design and tooth-by-tooth induction hardening. Part II covers spin hardening and various heating concepts used with it.
Fuji's VTP-1000 is designed for highly accurate fine finishing of cylindrical components up to one meter in diameter.
In recent years, there has been significant interest in expanding the use of induction hardening in gear manufacturing operations. Over the past several years, many of the limits to induction hardening have shrunk, thanks to recent advances in technology, materials and processing techniques.
Carburized and hardened gears have optimum load-carrying capability. There are many alternative ways to produce a hard case on the gear surface. Also, selective direct hardening has some advantages in its ability to be used in the production line, and it is claimed that performance results equivalent to a carburized gear can be obtained. This article examines the alternative ways of carburizing, nitriding, and selective direct hardening, considering equipment, comparative costs, and other factors. The objective must be to obtain the desired quality at the lowest cost.
Gear gashing is a gear machining process, very much like gear milling, utilizing the principle of cutting one or more tooth (or tooth space) at a time. The term "GASHING" today applies to the roughing, or roughing and finishing, of coarse diametral pitch gears and sprockets. Manufacturing these large coarse gears by conventional methods of rough and finish hobbing can lead to very long machining cycles and uneconomical machine utilization.
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.
The complete Product News section from the October 2012 issue of Gear Technology.
The complete Product News section from the March/April 2013 issue of Gear Technology.
Indexable carbide insert (ICI) cutting tools continue to play a pivotal role in gear manufacturing. By offering higher cutting speeds, reduced cycle times, enhanced coatings, custom configurations and a diverse range of sizes and capabilities, ICI tools have proven invaluable for finishing and pre-grind applications. They continue to expand their unique capabilities and worth in the cutting tool market.
Hobbing is probably the most popular gear manufacturing process. Its inherent accuracy and productivity makes it a logical choice for a wide range of sizes.
The proper design or selection of gear cutting tools requires thorough and detailed attention from the tool designer. In addition to experience, intuition and practical knowledge, a good understanding of profile calculations is very important.
Some results of evaluation by this method in the automotive industry.
Hobs, broaches, shaper cutters, shaver cutters, milling cutters, and bevel cutters used in the manufacture of gears are commonly made of high speed steel. These specialized gear cutting tools often require properties, such as toughness or manufacturability, that are difficult to achieve with carbide, despite the developments in carbide cutting tools for end mills, milling cutters, and tool inserts.
The gear hobbing process is a generating type of production operation. For this reason, the form of the hob tooth is always different from the form of the tooth that it produces.
Rolled out at EMO 2007, the Scudding process is a continuous cutting operation that uses a tool design similar to a helical shaper cutter. It can be used for a wide range of gear applications...
Today, because of reduced cost of coatings and quicker turnaround times, the idea of all-around coating on three-face-sharpened blades is again economically viable, allowing manufacturers greater freedoms in cutting blade parameters, including three-face-sharpened and even four-face-sharpened blades.
As we approach the problem of hard gear processing, it is well to take a look at the reason for discussing it at this time. In our present economic atmosphere throughout the world, more and more emphasis is being placed upon efficiency which is dictated by higher energy costs.
The method of cutting teeth on a cylindrical gear by the hobbing process has been in existence since the late 1800s. Advances have been made over the years in both the machines and the cutting tools used in the process. This paper will examine hob tool life and the many variables that affect it. The paper will cover the state-of-the-art cutting tool materials and coatings, hob tool design characteristics, process speeds and feeds, hob shifting strategies, wear characteristics, etc. The paper will also discuss the use of a common denominator method for evaluating hob tool life in terms of meters (or inches) per hob tooth as an alternative to tool life expressed in parts per sharpening.
To meet the future goals of higher productivity and lower production costs, the cutting speeds and feeds in modern gear hobbing applications have to increase further. In several cases, coated carbide tools have replaced the commonly used high speed steel (HSS) tools.
This back-to-basics article describes the main methods used for hardness testing of gears: Rockwell, Brinell, Vickers and Knoop.
The complete Industry News section from the May 2013 issue of Gear Technology
This paper examines the expanding capabilities of induction hardening of gears through methods like spin hardening or tooth-by-tooth techniques.
The complete Product News section from the October 2013 issue of Gear Technology.
What gear material is suitable for high-temperature (350 – 550 degree C), high-vacuum, clean-environment use?
The complete Industry News section from the August 2014 issue of Gear Technology.
Contact fatigue and bending fatigue are two main failure modes of steel gears, while surface pitting and spalling are two common contact fatigue failures -- caused by alternating subsurface shear stresses from the contact load between two gear mates. And when a gear is in service under cyclic load, concentrated bending stresses exist at the root fillet -- the main driver of bending fatigue failures. Induction hardening is becoming an increasingly popular response to these problems, due to its process consistency, reduced energy consumption, clean environment and improved product quality -- but not without issues of its own (irregular residual stresses and bending fatigue). Thus a new approach is proposed here that flexibly controls the magnitude of residual stress in the regions of root fillet and tooth flank by pre-heating prior to induction hardening. Using an external spur gear made of AISI 4340 as an example, this new concept/process is demonstrated using finite element modeling and DANTE commercial software.
New technology from Eldec/EMAG helps control the induction hardening process.
Environmentally friendly cutting fluids aren't just good for the environment. They can also be good for performance.