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This section will deal with the use of gear inspection for diagnostic purposes rather than quality determination. The proper evaluation of various characteristics in the data can be useful for the solution of quality problems. It is important to sort out whether the problem is coming from the machine, tooling and/or cutters, blanks, etc. An article by Robert Moderow in the May/June 1985 issue of Gear Technology is very useful for this purpose.
How well you conduct your inspections can be the difference-maker for securing high-value contracts from your customers. And as with most other segments of the gear industry, inspection continues striving to attain “exact science” status. With that thought in mind, following is a look at the state of gear inspection and what rigorous inspection practices deliver—quality.
The gear companies enjoying the most success in today’s global market are those that firmly believe quality is much more than expert craftsmanship and foolproof inspection methodologies.
I support Clem Miller (Viewpoint May/June) in his skepticism of ISO 9000. The metrology of gears is important, but in the present state of the art, manufacture is more accurate than design.
The complete Industry News section from the October 2012 issue of Gear Technology.
What does it mean to make "better" gears? Better gears more closely resemble the intended design parameters.
Much about ISO 9000 is the subject of noisy debate. But on one thing almost everyone, true believers and critics alike, agrees: Getting ISO 9000 certification can be expensive. Companies can expect to spend at least $35,000 for basic certification and six-month checkup fees over a three-year period. These figures do not include hidden costs like time and money spent on internal improvements required to meet ISO 9000 certification. But the really big-ticket items in the process are employee time and the cost of bringing in outside consultants. Many ISO 9000 consultants charge upwards of $1,800 a day.
On of the key questions confronting any company considering ISO 9000 certification is, how much is this going to cost? The up-front fees are only the beginning. Dissect the ISO 9000 certification procedure with an eye for hidden costs, and two segments of the process will leap out - the cost of consultants and the cost of making in-house improvements for the sake of passing certification. Most of these costs can be controlled by careful selection f the right consultant in the first place.
AGMA has started to replace its 2000-A88 standard for gear accuracy with a new series of documents based largely on ISO standards. The first of the replacement AGMA standards have been published with the remainder coming in about a year. After serving as a default accuracy specification for U.S. commerce in gear products for several decades, the material in AGMA 2000-A88 is now considered outdated and in need of comprehensive revision.
ISO 9000 is the latest hot topic in marketing and manufacturing circles. Everyone seems to be talking about it, but few seem to understand it completely. depending on whom one talks to, it's either the greatest thing to hit industry since the assembly line, another cash cow for slick consultants, a conspiracy on the part of Europeans to dominate global markets, or the next necessary step to compete in the global economy of the twenty-first century. It may be all of the above.
Most readers are at least familiar with continuous improvement programs such as lean and six sigma. Perhaps your shop or company is well along in the implementation of one or the other—if not both. But what about theory of constraints (TOC), introduced in Dr. Eliyahu Goldratt’s 1984 book, The Goal? Despite its rather negative-sounding name, this continuous improvement process has much to offer manufacturers of all stripes. And when combined with lean and six sigma, the results can be dramatic. Dr. Lisa Lang, a TOC consultant and speaker, explains why and how in the following Q&A session with Gear Technology.
What follows is the first of three articles we will be running on ISO 9000 and what it means for the gear industry. This first article will cover what ISO 9000 is, what some of its benefits - and problems - are, and whether your company should be a candidate for this certification process. In our next issue, we will consider the important question of how, when, and if to hire an ISO 9000 consultant. The final article in this series will discuss ways to save money while streamlining the certification process in your company.
A carburized alloy steel gear has the greatest load-carrying capacity, but only if it is heat treated properly. For high quality carburizing, the case depth, case microstructure, and case hardness must be controlled carefully.
Quality gear inspection means doing the "right" inspections "right." A lot of time and money can be spent doing the wrong types of inspections related to function and doing them incorrectly. As we will discover later, such things as runout can creep into the manufacturing and inspection process and completely ruin any piece of data that is taken. this is one of the most important problems to control for quality inspection.
A common goal of gear manufacturers is to produce gearing that is competitively priced, that meets all quality requirements with the minimum amount of cost in a timely manner, and that satisfies customers' expectations. In order to optimize this goal, the gear manufacturer must thoroughly understand each manufacturing process specified, the performance capability of that process, and the effect of that particular process as it relates to the quality of the manufactured gear. If the wrong series of processes has been selected or a specific selected process is not capable of producing a quality part, manufacturing costs are greatly increased.
How do we know when the gear material we buy is metallurgically correct? How can we judge material quality when all gear material looks alike?
The traditional way of controlling the quality of hypoid gears' tooth flank form is to check the tooth flank contact patterns. But it is not easy to exactly judge the tooth flank form quality by the contact pattern. In recent years, it has become possible to accurately measure the tooth flank form of hypoid gears by the point-to-point measuring method and the scanning measuring method. But the uses of measured data of the tooth flank form for hypoid gears have not yet been well developed in comparison with cylindrical involute gears. In this paper, the tooth flank form measurement of generated face-milled gears, face-hobbed gears and formulate/generated gears are reported. The authors discuss the advantages and disadvantages of scanning and point-to-point measuring of 3-D tooth flank forms of hypoid gears and introduce some examples of uses of measured data for high-quality production and performance prediction.
Gear manufacturing schedules that provide both quality and economy are dependent on efficient quality control techniques with reliable measuring equipment. Given the multitude of possible gear deviations, which can be found only by systematic and detailed measuring of the gear teeth, adequate quality control systems are needed. This is especially true for large gears, on which remachining or rejected workpieces create very high costs. First, observation of the gears allows adjustment of the settings on the equipment right at the beginning of the process and helps to avoid unproductive working cycles. Second, the knowledge of deviations produced on the workpiece helps disclose chance inadequacies on the production side: e.g., faults in the machines and tools used, and provides an opportunity to remedy them.
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.
The quality of gearing is a function of many factors ranging from design, manufacturing processes, machine capability, gear steel material, the machine operator, and the quality control methods employed. This article discusses many of the bevel gear manufacturing problems encountered by gear manufacturers and some of the troubleshooting techniques used.
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 market demand for gear manufacturers to transmit higher torques via smaller-sized gear units inevitably leads to the use of case-hardened gears with high manufacturing and surface quality. In order to generate high part quality, there is an increasing trend towards the elimination of the process-induced distortion that occurs during heat treatment by means of subsequent hard finishing.
Precise heat treatment plays an essential role in the production of quality carburized gears. Seemingly minor changes in the heat treating process can have significant effects on the quality, expense and production time of a gear, as we will demonstrate using a case study from one of our customer's gears.
The heat treating of gears presents a difficult challenge to both the heat treater and the gear manufacturer. The number and variety of variables involved in the manufacturing process itself and the subsequent heat treating cycle create a complex matrix of factors which need to be controlled in order to produce a quality product. A heat treater specializing in gears or a gear manufacturer doing his own heat treating must have a clear understanding of these issues in order to deliver a quality product and make a profit at the same time. The situation also presents a number of areas that could benefit greatly from continued research and development.
In the quest for ever more exacting and compact commercial gears, precision abrasives are playing a key production role - a role that can shorten cycle time, reduce machining costs and meet growing market demand for such requirements as light weights, high loads, high speed and quiet operation. Used in conjunction with high-quality grinding machines, abrasives can deliver a level of accuracy unmatched by other manufacturing techniques, cost-effectively meeting AGMA gear quality levels in the 12 to 15 range. Thanks to advances in grinding and abrasive technology, machining has become one of the most viable means to grind fast, strong and quiet gears.
For over 50 years, grinding has been an accepted method of choice for improving the quality of gears and other parts by correcting heat treat distortions. Gears with quality levels better than AGMA 10-11 or DIN 6-7 are hard finished, usually by grinding. Other applications for grinding include, but are not limited to, internal/external and spur/helical gear and spline forms, radius forms, threads and serrations, compressor rotors, gerotors, ball screw tracks, worms, linear ball tracks, rotary pistons, vane pump rotators, vane slots, and pump spindles.
The quality of a gear and its performance is determined by the following five parameters, which should be specified for each gear: Pitch diameter, involute form, lead accuracy, spacing accuracy, and true axis of rotation. The first four parameters can be measured or charted and have to be within tolerance with respect to the fifth. Pitch diameter, involute, lead, and spacing of a gear can have master gear quality when measured or charted on a testing machine, but the gear might perform badly if the true axis of rotation after installation is no longer the same one used when testing the gear.
The working surfaces of gear teeth are often the result of several machining operations. The surface texture imparted by the manufacturing process affects many of the gear's functional characteristics. To ensure proper operation of the final assembly, a gear's surface texture characteristics, such as waviness and roughness, can be evaluated with modern metrology instruments.
A considerable improvement in the performance of the machining of hard to grind materials can be achieved by means of CBN wheels.
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.
The merits of CBN physical characteristics over conventional aluminum oxide abrasives in grinding performance are reviewed. Improved surface integrity and consistency in drive train products can be achieved by the high removal rate of the CBN grinding process. The influence of CBN wheel surface conditioning procedure on grinding performance is also discussed.
It takes confidence to be the first to invest in new manufacturing technology. But the payback can be significant. That has been the experience at the Ford Motor Company's Transmission & Chassis Division plant at Indianapolis, IN, which boasts the world's first production application of dry hobbing.
The modern day requirement for precision finished hobbed gears, coupled with the high accuracy characteristics of modern CNC hobbing machines, demands high tool accuracy.
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.
What is a quality product? This is not an idle question. In the Darwinian business world in which we operate, knowing the answer to this question is key to our survival. A whole library of standards and benchmarks is available to help us gage how we're doing, but they don't really tell the whole story.
Notes from Detroit...Overall, Gear Expo 97, the AGMA biennial trade show, was a success. While attendance may not have been what some people had hoped for, the quality of the attendees was high. Serious buyers came and brought their checkbooks.
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.
Heat treating is a critical operation in gear manufacturing. It can make or break the quality of your final product. Yet it is one that frequently gear manufacturers outsource to someone else. Then the crucial question becomes, how do you know you're getting the right heat treater? How can you guarantee your end product when you have turned over this important process to someone else?
New innovations in the management of hear treating parts washers and yielding powerful, unexpected benefits. Simply, cost effective shop floor practices are being combined in new ways to deliver big quality improvements and significant help to the bottom line. Employing these steps early in the process can dramatically cut waste hauling expenses and greatly reduce environmental liabilities while continuously producing cleaner parts.
In recent years, gear inspection requirements have changed considerably, but inspection methods have barely kept pace. The gap is especially noticeable in bevel gears, whose geometry has always made testing them a complicated, expensive and time-consuming process. Present roll test methods for determining flank form and quality of gear sets are hardly applicable to bevel gears at all, and the time, expense and sophistication required for coordinate measurement has limited its use to gear development, with only sampling occurring during production.
Ausforming, the plastic deformation of heat treatment steels in their metastable, austentic condition, was shown several decades ago to lead to quenched and tempered steels that were harder, tougher and more durable under fatigue-type loading than conventionally heat-treated steels. To circumvent the large forces required to ausform entire components such as gears, cams and bearings, the ausforming process imparts added mechanical strength and durability only to those contact surfaces that are critically loaded. The ausrolling process, as utilized for finishing the loaded surfaces of machine elements, imparts high quality surface texture and geometry control. The near-net-shape geometry and surface topography of the machine elements must be controlled to be compatible with the network dimensional finish and the rolling die design requirements (Ref. 1).
Gear engineers have long recognized the importance of considering system factors when analyzing a single pair of gears in mesh. These factors include important considerations such as load sharing in multi-mesh geartrains and bearing clearances, in addition to the effects of flexible components such as housings, gear blanks, shafts and carriers for planetary geartrains. However, in recent years, transmission systems have become increasingly complex—with higher numbers of gears and components—while the quality requirements and expectations in terms of durability, gear whine, rattle and efficiency have increased accordingly.
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?
Gear grinding is one of the most expensive and least understood aspects of gear manufacturing. But with pressures for reduced noise, higher quality and greater efficiency, gear grinding appears to be on the rise.
Today motion control systems are migrating from analog to digital technology at an ever increasing rate because digital technology at an ever-increasing rate because digital drives provide performance equal to or exceeding that of analog drives, plus information to run your machine more effectively and manage your quality program and your business. Most of this data is simply not available from analog drives.
Ready or not, QS-9000 is here. If you are a first-tier supplier to one of the Big Three automotive companies, you've already heard that compliance with this new quality standard is now an entry-level requirement for doing business with Ford, General Motors and Chrysler. If you're a second-or third-tier supplier, you can expect the ripple effect of this new standard to hit your company one way or another.
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.
Many people seem to be counting this year's Gear Expo in Nashville as a resounding success. There were 180 American and international exhibitors occupying over 50,000 square feet of exhibit space in the Nashville Convention Center, with total attendance of 2,700. This figure is dramatically down from past shows but that doesn't seem to be an issue with the show organizers. According to Kurt Medert, vice president of AGMA;s Administrative Division, even though attendance was off from the 1997 show, the exhibitors were pleased with the quality of the people who did come to the show. "This was an excellent show for us," said Marty Woodhouse, vice president of sales for Star Cutter Company and chairman of AGMA's Gear Expo committee. "Our customer base was there and they came to buy. It was very active."
Computer technology has touched all areas of our lives, impacting how we obtain airline tickets, purchase merchandise and receive medical advice. This transformation has had a vast influence on manufacturing as well, providing process improvements that lead to higher quality and lower costs. However, in the case of the gear industry, the critical process of tooth contact pattern development for spiral bevel gears remains relatively unchanged.
Technology creates excitement. Just consider the natural buzz around IMTS, where manufacturers will go to explore ways they can increase productivity, improve quality, decrease costs or provide better service.
Bodine Electric Co. of Chicago, IL., has a 97-year history of fine-and medium-pitch gear manufacturing. Like anywhere else, traditions, old systems, and structures can be beneficial, but they can also become paradigms and obstacles to further improvements. We were producing a high quality product, but our goal was to become more cost effective. Carbide hobbing is seen as a technological innovation capable of enabling a dramatic, rather than an incremental, enhancement to productivity and cost savings.
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.
A large number of technologies aimed primarily at higher productivity were presented by exhibitors at the AMB, International Exhibition for Metal Working at the Stuttgart Trade Fair Centre in September. Following the successful 2010 show, AMB 2012 boasted further developments in energy and resource efficiency, higher productivity, life cycle performance, quality assurance and user-friendliness.
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.
Audits of the heat treating department are a vital part of any good quality program - either as part of a self-assessment or ISO program for a captive shop or - of equal importance - as part of an evaluation of the capabilities of a commercial heat treat supplier. In either case, the audit process needs to be formal in nature and follow specific guidelines.
Romax Technology, the gearbox, bearing and driveline engineering specialist, has launched a new design software package that will increase speed, quality, creativity and innovation when designing gearboxes and drivelines. Called Concept, the new product delivers on the Romax vision of streamlining the end-to-end, planning-to-manufacture process with open, easy to use software solutions. It has been developed in close collaboration with engineers in the largest ground vehicle, wind energy and industrial equipment companies around the globe.
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.
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.
Until recently, there was a void in the quality control of gear manufacturing in this country (Ref. 1). Gear measurements were not traceable to the international standard of length through the National Institute of Standards and Technology (NIST). The U.S. military requirement for traceability was clearly specified in the military standard MIL-STD-45662A (Ref. 2). This standard has now been replaced by commercial sector standards including ISO 9001:1994 (Ref. 3), ISO/IEC Guide 25 (Ref, 4), and the U.S. equivalent of ISO/IEC Guide 25 - ANSI/NCSL Z540-2-1997 (Ref. 5). The draft replacement to ISO/IEC Guide 25 - ISO 17025 states that measurements must either be traceable to SI units or reference to a natural constant. The implications of traceability to the U.S. gear industry are significant. In order to meet the standards, gear manufacturers must either have calibrated artifacts or establish their own traceability to SI units.
The induction hardening and tempering of gears and critical components is traditionally a hot subject in heat treating. In recent years, gear manufacturers have increased their knowledge in this technology for quality gears.
The quality of the material used for highly loaded critical gears is of primary importance in the achievement of their full potential. Unfortunately, the role which material defects play is not clearly understood by many gear designers. The mechanism by which failures occur due to material defects is often circuitous and not readily apparent. In general, however, failures associated with material defects show characteristics that point to the source of the underlying problem, the mechanism by which the failure initiated, and the manner in which it progressed to failure of the component.
Nowadays, finish hobbing (which means that there is no post-hobbing gear finishing operation) is capable of producing higher quality gears and is growing in popularity.
For high-quality carburized, case hardened gears, close case carbon control is essential. While tight carbon control is possible, vies on what optimum carbon level to target can be wider than the tolerance.
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.
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.
You're already a veteran of the computer revolution. Only you and your controller know how much money you've spent and only your spouse knows how many sleepless nights you've had in the last ten years trying to carve out a place in the brave new world of computerized gear manufacturing. PC's, CNCs, CAD, CAM, DNC, SPC, CMM: You've got a whole bowl of alphabet soup out there on the shop floor. Overall these machines have lived up to their promises. Production time is down, quality is up. You have fewer scrapped parts and better, more efficient machine usage.
For heat treatment of tool and alloy steels, the end-user has a wide range of basic types of heat treating equipment to choose from. This article reviews them and details the criteria that must be considered in selecting equipment for a specific application. In making this choice, the most important criterion must be the quality of the tool or part after processing.
Relic of an era when quality was an afterthought.
There are several methods available for improving the quality of spur and helical gears following the standard roughing operations of hobbing or shaping. Rotary gear shaving and roll-finishing are done in the green or soft state prior to heat treating.
In this article, gear buyers have been given an opportunity to discuss quality, value, customer service and how gear manufacturers can improve business practices.
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 most conclusive test of bevel and hypoid gears is their operation under normal running conditions in their final mountings. Testing not only maintains quality and uniformity during manufacture, but also determines if the gears will be satisfactory for their intended applications.
Modern manufacturing processes have become an ally of the product designer in producing higher quality, higher performing components in the transportation industry. This is particularly true in grinding systems where the physical properties of CBN abrasives have been applied to improving cycle times, dimensional consistency, surface integrity and overall costs. Of these four factors, surface integrity offers the greatest potential for influencing the actual design of highly stressed, hardened steel components.
The quality of the finished gear is influenced by the very first machining operations of the blank. Since the gear tooth geometry is generated on a continuously rotating blank in hobbing or shaping, it is important that the timed relationship between the cutter and workpiece is correct. If this relationship is disturbed by eccentricities of the blank to its operating centerline, the generated gear teeth will not be of the correct geometry. During the blanking operations, the gear's centerline and locating surfaces are established and must be maintained as the same through the following operations that generate the gear teeth.
Recent breakthroughs in profile grinding software are helping Anderson Precision Gears and others meet wind power’s insatiable appetite for faster production of large, high-quality gears.
The proper control of distortion after thermal treatment of powertrain components in the automotive industry is an important measure in ensuring high-quality parts and minimizing subsequent hard machining processes in order to reduce overall production costs.
Everyone makes mistakes. Nobody's perfect. We've all heard those or similar words, and if you happen to be in charge of your company's quality efforts, you've probably heard them more than most people.
Bevel gear systems are particularly sensitive to improper assembly. Slight errors in gear positioning can turn a well-designed, quality manufactured gear set into a noisy, prone-to-failure weak link in your application.
There are great advantages in dry hobbing, not only for friendliness toward the environment, but also for increasing productivity and for decreasing manufacturing cost. Dry hobbing, however, often causes failures in hob cutting edges or problems with the surface quality of gear tooth flanks. These difficulties are not present when hobbing with cutting oil. Pinching and crushing of generated chips between the hob cutting edge and the work gear tooth flank is considered a major cause of those problems.
High demands for cost-effectiveness and improved product quality can be achieved via a new low pressure carburizing process with high pressure gas quenching. Up to 50% of the heat treatment time can be saved. Furthermore, the distortion of the gear parts could be reduced because of gas quenching, and grinding costs could be saved. This article gives an overview of the principles of the process technology and the required furnace technology. Also, some examples of practical applications are presented.
Romax Technology is automating the design iteration process to allow companies to be faster to market with the highest quality, most robust gear products.
Applying "Dynamic Block Contours" allows the designer to predict gear quality at the earliest stage of the design process.
The quality of molded plastic gears is typically judged by dimensional feature measurements only. This practice overlooks potential deficiencies in the molding process.
A net-shaped metal forming process has been developed for manufacturing quality, durable, high-yield and cost-efficient gears for high-volume production.
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.
Optimization is applied to the design of a spiral bevel gear reduction for maximum life at a given size. A modified feasible directions search algorithm permits a wide variety of inequality constraints and exact design requirements to be met with low sensitivity to initial values. Gear tooth bending strength and minimum contact ration under load are included in the active constraints. The optimal design of the spiral bevel gear reduction includes the selection of bearing and shaft proportions in addition to gear mesh parameters. System life is maximized subject to a fixed back-cone distance of the spiral bevel gear set for a specified speed ratio, shaft angle, input torque and power. Significant parameters in the design are the spiral angle, the pressure angle, the numbers of teeth on the pinion and gear and the location and size of the four support bearings. Interpolated polynomials expand the discrete bearing properties and proportions into continuous variables for gradient optimization. After finding the continuous optimum, a designer can analyze near-optimal designs for comparison and selection. Design examples show the influence of the bearing lives on the gear parameters in the optimal configurations. For a fixed back-cone distance, optimal designs with larger shaft angles have larger service lives.
Primitive gears were known and used well over 2,000 years ago, and gears have taken their place as one of the basic machine mechanisms; yet, our knowledge and understanding of gearing principles is by no means complete. We see the development of faster and more reliable gear quality assessment and new, more productive manufacture of gears in higher materials hardness states. We have also seen improvement in gear applications and design, lubricants, coolants, finishes and noise and vibration control. All these advances push development in the direction of smaller, more compact applications, better material utilization and improved quietness, smoothness of operation and gear life. At the same time, we try to improve manufacturing cost-effectiveness, making use of highly repetitive and efficient gear manufacturing methods.
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.
Shot peening is widely recognized as a prove, cost-effective process to enhance the fatigue characteristics of metal parts and eliminate the problems of stress corrosion cracking. Additional benefits accrue in the areas of forming and texturizing. Though shot peening is widely used today, the means of specifying process parameters and controlling documents for process control are not widely understood. Questions regarding shot size, intensity, and blueprint specification to assure a high quality and repeatable shot peening process are continually asked by many design and materials engineers. This article should answer many of the questions frequently asked by engineering professionals and to further assist companies interested in establishing a general shot peening specification.
In 1985 a new tooling concept for high volume gear production was introduced to the gear manufacturing industry. Since then this tool, the wafer shaper cutter, has proven itself in scores of applications as a cost-effective, consistent producer of superior quality parts. This report examines the first high-production installation at the plant of a major automotive supplies, where a line of twenty shapers is producing timing chain sprockets.
The term "blanking" refers to the initial metal cutting operations in the process planning sequence which produce the contour of a part starting from rough material. The scope of blanking is: To remove the excess material To machine the part to print specifications, except for those surfaces with subsequent finishing operations. To leave adequate machining stock for finishing operations. To prepare good quality surfaces for location and clamping of the part throughout the process.
Popular wisdom has it that manufacturing in the United States is no longer a viable entity. We are told that quality is poor, skilled labor is difficult to obtain, if not impossible, demand is low, and the government is helping to discourage business. So what should we do, give up?
The advent of CNC technology as applied to gear shaping machines has, in the last 10 years, led to an astonishing improvement in both productivity and quality. As is usual when developments such as this take place, the technology of the machine tool suddenly jumps ahead of that of the cutting tool, and the machine is then capable of producing faster than the cutting tool can withstand.
The purpose of gear inspection is to: Assure required accuracy and quality, Lower overall cost of manufacture by controlling rejects and scrap, Control machines and machining practices and maintain produced accuracy as machines and tools wear, Determine hear treat distortions to make necessary corrections.
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.
Many CAD (Computer Aided Design) systems have been developed and implemented to produce a superior quality design and to increase the design productivity in the gear industry. In general, it is true that a major portion of design tasks can be performed by CAD systems currently available. However, they can only address the computational aspects of gear design that typically require decision-making as well. In most industrial gear design practices, the initial design is the critical task that significantly effects the final results. However, the decisions about estimating or changing gear size parameters must be made by a gear design expert.
The manufacturing quality of spiral bevel gears has achieved a very high standard. Nevertheless, the understanding of the real stress conditions and the influences. of certain parameters is not satisfactory.
This article discusses briefly some common manufacturing problems relating to coarse pitch gears and their suggested solutions. Most of the discussion will be limited to a low-quality production environment using universal machine tools.
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.
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.
Runout is a troublemaker! Good shop practice for the manufacture or inspection of gears requires the control of runout. Runout is a characteristic of gear quality that results in an effective center distance variation. As long as the runout doesn't cause loss of backlash, it won't hurt the function of the gear, which is to transmit smooth motion under load from one shaft to another. However, runout does result in accumulated pitch variation, and this causes non-uniform motion, which does affect the function of the gears. Runout is a radial phenomenon, while accumulated pitch variation is a tangential characteristic that causes transmission error. Gears function tangentially. It is also possible to have a gear with accumulated pitch variation, but little or no runout.
Tom Lang liked what he saw in the Gear Generation Pavilion at IMTS 2004. Standing in his booth, Kapp Technologies’ vice president/general manager talked with many attendees during the show and afterward said: “We had an increase of both quality and quantity of visitors.”
The bevel gear grinding process, with conventional wheels, has been limited to applications where the highest level of quality is required.
Durability is the most important criterion used to define the quality of a gear. The freezing of metals has been acknowledged for almost thirty years as an effective method for increasing durability, or "wear life," and decreasing residual stress in tool steels. The recent field of deep cryogenics (below -300 degrees F) has brought us high temperature superconductors, the superconducting super collider, cryo-biology, and magnotehydrodynamic drive systems. It has also brought many additional durability benefits to metals.
Quality, materials and technology continue to challenge the big gear manufacturing market.
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.
Grinding in one form or another has been used for more than 50 years to correct distortions in gears caused by the high temperatures and quenching techniques associated with hardening. Grinding improves the lead, involute and spacing characteristics. This makes the gear capable of carrying the high loads and running at the high pitch line velocities required by today's most demanding applications. Gears that must meet or exceed the accuracy requirements specified by AGMA Quality 10-11 or DIN Class 6-7 must be ground or hard finished after hear treatment.
I would like to comment on David Arnesen's article, "Dry Hobbing Saves Automaker Money, Improves Gear Quality," in the Nov/Dec, 1996 issue.
News Items About quality
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