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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.
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...
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.
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 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.
A new method for cutting straight bevel gears.
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.
Spiral bevel and hypoid gear cutting has changed significantly over the years. The machines, tools, processes and coatings have steadily advanced.
Machine tool manufacturers supplying machines to the gearing world have been in existence for many years. The machines have changed, and so has the acceptance criteria for the machines.
NC and CNC metal cutting machines are among the most popular machine tools in the business today, There is also a strong trend toward using flexible machining centers and flexible manufacturing systems. The same trend is apparent in gear cutting. Currently the trend toward CNC tools has increased, and sophisticated controls and peripheral equipment for gear cutting machines are now available; however, the investment in a CNC gear machine has to be justified on the basis of economic facts as well as technical advantages.
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.
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.
A fundamental characteristic of the gear industry is that it is capital intensive. In the last decade, the gear manufacturing industry has been undergoing an intense drive toward improving and modernizing its capital equipment base. The Department of Commerce reports that annual sales of gear cutting equipment have increased nearly 60% since 1990. While this effort has paid off in increased competitiveness for the American gear industry, it is important to remember that there is another capital crucial to manufacturing success - "human capital."
Imagine the flexibility of having one machine capable of milling, turning, tapping and gear cutting with deburring included for hard and soft material. No, you’re not in gear fantasy land. The technology to manufacture gears on non gear-dedicated, mult-axis machines has existed for a few years in Europe, but has not yet ventured into mainstream manufacturing. Deckel Maho Pfronten, a member of the Gildemeister Group, took the sales plunge this year, making the technology available on most of its 2009 machines.
Beveloid gears are used to accommodate a small shaft angle. The manufacturing technology used for beveloid gearing is a special setup of cylindrical gear cutting and grinding machines. A new development, the so-called Hypoloid gearing, addresses the desire of gear manufacturers for more freedoms. Hypoloid gear sets can realize shaft angles between zero and 20° and at the same time, allow a second shaft angle (or an offset) in space that provides the freedom to connect two points in space.
Increased productivity in roughing operations for gear cutting depends mainly on lower production costs in the hobbing process. In addition, certain gears can be manufactured by shaping, which also needs to be taken into account in the search for a more cost-effective form of production.
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.
Recent trends in gear cutting technology have left process engineers searching for direction about which combination of cutting tool material, coating, and process technology will afford the best quality at the lowest total cost. Applying the new technologies can have associated risks that may override the potential cost savings. The many interrelated variables to be considered and evaluated tend to cloud the issue and make hobbing process development more difficult.
Never have so few served so many. That, in essence, describes gear makers and the role they play in our world. Think of it—although the gear cutting industry represents much less than one percent of the global workforce—the gears it produces are what make things run in practically every industry and profession imaginable. From bulldozers to Rolexes, gears are an integral part of the mix.
We are all looking for ways to increase production without sacrificing quality. One of the most cost-effective ways is by improving the substrate material of your hob. Solid carbide hobs are widely used in many applications throughout the world. LMT-Fette was the first to demonstrate the use of solid carbide hobs in 1993 on modern high-speed carbide (HSC) hobbing machines. Since then the process of dry hobbing has been continuously improving through research and product testing. Dry hobbing is proving to be successful in the gear cutting industry as sales for dry hobbing machines have steadily been rising along with the dramatic increase in sales of solid carbide hobs.
The Pentac Plus is the latest generation of Gleason’s Pentac bevel gear cutting system. It is designed to allow much higher tool life and improved productivity, especially for cutters using multiple face blade geometry.
Prior to the introduction of titanium nitride to the cutting tool industry in the early 1980s, there was very little progress in the general application of hobbing in the gear cutting industry. The productivity gains realized with this new type of coating initiated a very active time of advancement in the gear manufacturing process.
We make a lot of single-start worm and worm gear sets, and it always seems as though we're buying another special hob. We also do a lot of spur gear cutting, and the spur gear hobs and the worm gear hobs look alike, so we wonder why we cannot use the standard hobs for cutting worm gears too. Can we do this?
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.
The following article is a collection of data intended to give the reader a general overview of information related to a relatively new subject within the gear cutting industry. Although carbide hobbing itself is not necessarily new, some of the methods and types of application are. While the subject content of this article may be quite broad, it should not be considered all-inclusive. The actual results obtained and the speeds, feeds, and tool life used in carbide hobbing applications can vary significantly.
Most gear cutting shops have shelves full of expensive tooling used in the past for cutting gears which are no longer in production. It is anticipated that these cutters will be used again in the future. While this may take place if the cutters are "standard," and the gears to be cut are "standard," most of the design work done today involves high pressure angle gears for strength, or designs for high contact ratio to reduce noise. The re-use of a cutter under these conditions requires a tedious mathematical analysis, which is no problem if a computer with the right software is available. This article describes a computerized graphical display which provides a quick analysis of the potential for the re-use of shaving cutters stored in a computer file.
The concept of "transmission error" is relatively new and stems from research work in the late 1950s by Gregory, Harris and Munro,(1) together with the need to check the accuracy of gear cutting machines. The corresponding commercial "single flank" testing equipment became available in the 1960s, but it was not until about ten years ago that it became generally used, and only recently has it been possible to test reliably at full load and full speed.
A recent U.S. Army Tank-Automotive Command project, conducted by Battelle's Columbus Laboratories. successfully developed the methodology of CAD/CAM procedures for manufacturing dies (via EDM) for forging spiral bevel gears. Further, it demonstrated that precision forging of spiral bevel gears is a practical production technique. Although no detailed economic evaluation was made in this study, it is expected that precision forging offers an attractive alternative to the costly gear cutting operations for producing spiral bevel gears.
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.
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 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 complete Industry News section from the November/December 2014 issue.
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.
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.
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.
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.
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.
Environmentally friendly cutting fluids aren't just good for the environment. They can also be good for performance.
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.
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.
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.
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 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.
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.
Some results of evaluation by this method in the automotive industry.
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.
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.
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.
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.
Not long ago, many manufacturing managers thought sensitivity to environmental protection standards meant additional expenses, decreased productivity, and a plethora of headaches and hassles.
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.
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?
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 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.
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.
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.
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?
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.
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.
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.
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.
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.
Good References In the 7th Edition of McGraw Hill Encyclopedia of Science and Technology, 10 pages are devoted to the subjects of Gears, Gear Cutting and Gear Trains.
I received a letter from Mr. G. W. Richmond, Sullivan Machinery Company, N.H., in which in addition to correcting mistyping, he made several suggestions concerning my article "General Equations for Gear Cutting Tool Calculations."
News Items About gear cutting
1 Engineered Tools Opens Gear Cutting Systems Division (April 15, 2006)
Engineered Tools Corp. of Caro, MI, has introduced its new gear cutting system division. Cutter body repair will take place at ETC... Read News
2 Mitsubishi Heavy Industries Completes Gear Cutting Tool Production Plant in India (August 30, 2007)
Mitsubishi Heavy Industries Ltd. completed construction of a new plant at Mitsubishi Heavy Industries India Precision Tools, Ltd., an Ind... Read News
3 Luren Offers Gear Cutting Technology (November 18, 2010)
Luren Precision Co., Ltd., founded in Hsinchu, Taiwan in 1994, has been dedicated in gear technology including the design and manufacture... Read News
4 MAG Introduces VTC with Gear Cutting Capability (June 15, 2011)
The first technology advancement for large vertical turning centers (VTCs) resulting from MAG's recent acquisition of Modul, a gear m... Read News
5 Riten Offers Gear Cutting Live Center (July 3, 2013)
American gear manufacturers have traditionally used an imported center for hobbing, cutting and grinding. Many of these companies have ex... Read News
6 Advanced Coatings Provide Gear Cutting Edge (April 20, 2012)
Balinite Alcrona Pro, the second generation of ALCr-based coatings, is now available on new and re-sharpened tools from Star SU. Develope... Read News
7 MHI Develops ‘Super Skiving System’ for High-speed Gear Cutting (November 24, 2014)
Mitsubishi Heavy Industries, Ltd. (MHI) has completed development of the “Mitsubishi Super Skiving System” for machining inte... Read News