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Almost all machines or mechanical systems contain precision contact elements such as bearings, cams, rears, shafts, splines and rollers. These components have two important common requirements: first, they must possess sufficient mechanical properties, such as, high hardness, fatigue strength and wear resistance to maximize their performance and life; second, they must be finished to close dimensional tolerances to minimize noise, vibration and fatigue loading.
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).
A net-shaped metal forming process has been developed for manufacturing quality, durable, high-yield and cost-efficient gears for high-volume production.
Letters to the editor on a variety of subjects, including couplings, gear planers and ausforming.
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.
The forming of gear teeth has traditionally been a time-consuming heavy stock removal operation in which close tooth size, shape, runout and spacing accuracy are required. This is true whether the teeth are finished by a second forming operation or a shaving operation.
Part I of this series focused on gear shaving, while Part II focuses on gear finishing by rolling and honing.
Material losses and long production times are two areas of conventional spur and helical gear manufacturing in which improvements can be made. Metalforming processes have been considered for manufacturing spur and helical gears, but these are costly due to the development times necessary for each new part design. Through a project funded by the U.S. Army Tank - Automotive Command, Battelle's Columbus Division has developed a technique for designing spur and helical gear forging and extrusion dies using computer aided techniques.
The authors have developed a rack-type rolling process in which a rack tool is used to roll gear teeth. The results and analysis show that the proposed method reduces errors.
New Technique for Forging Crowned Helical Gears Createch Co. Ltd., a forging die manufacturer from Shizuoka, Japan, has developed a net-shape cold-forging process for forming helical gears and splines with crowned teeth.
First, the facts: powder metallurgy is a cost-effective method of forming precision net-shape metal components that allows for more efficiently designed products. It saves valuable raw materials through recycling and the elimination of costly secondary-machining. PM competes with wrought steel gears as the technology continues to advance. You'll find PM components in everything from automobile transmissions to aircraft turbine engines, surgical equipment and power tools.
This paper addresses the lubrication of helical gears - especially those factors influencing lubricant film thickness and pressure. Contact between gear teeth is protected by the elastohydrodynamic lubrication (EHL) mechanism that occurs between nonconforming contact when pressure is high enough to cause large increases in lubricant viscosity due to the pressure-viscosity effect, and changes of component shape due to elastic deflection. Acting together, these effects lead to oil films that are stiff enough to separate the contacting surfaces and thus prevent significant metal-to-metal contact occurring in a well-designed gear pair.
The cutting process consists of either a roll only (only generating motion), a plunge only or a combination of plunging and rolling. The material removal and flank forming due to a pure generating motion is demonstrated in the simplified sketch in Figure 1 in four steps. In the start roll position (step 1), the cutter profile has not yet contacted the work. A rotation of the work around its axis (indicated by the rotation arrow) is coupled with a rotation of the cutter around the axis of the generating gear (indicated by the vertical arrow) and initiates a generating motion between the not-yet-existing tooth slot of the work and the cutter head (which symbolizes one tooth of the generating gear).
Involute spur gears are very sensitive to gear misalignment. Misalignment will cause the shift of the bearing contact toward the edge of the gear tooth surfaces and transmission errors that increase gear noise. Many efforts have been made to improve the bearing contact of misaligned spur gears by crowning the pinion tooth surface. Wildhaber(1) had proposed various methods of crowning that can be achieved in the process of gear generation. Maag engineers have used crowning for making longitudinal corrections (Fig. 1a); modifying involute tooth profile uniformly across the face width (Fig. 1b); combining these two functions in Fig. 1c and performing topological modification (Fig. 1d) that can provide any deviation of the crowned tooth surface from a regular involute surface. (2)
Powder metallurgy (P/M) is a precision metal forming technology for the manufacture of parts to net or near-net shape, and it is particularly well-suited to the production of gears. Spur, bevel and helical gears all may be made by made by powder metallurgy processing.
8 Gear Technology advertisers will have booths at IMTS 92, the largest trade show in the Western Hemisphere. The show opens in Chicago on Sept. 9 and runs through the 17th. More than 800 companies from around the world will cover some 931,000 sq. ft. of exhibit space to show the latest manufacturing technology - everything from forming and fabrication products to environmental and plant safety equipment.
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.
Traditional methods of manufacturing precision gears usually employ either hobbing or shaper cutting. Both of these processes rely upon generating the conjugate tooth form by moving the work-piece in a precise relation to the tool. Recently, attention has been given to forming gear teeth in a single step. Advantages to such a process include reduced production time, material savings, and improved performance characteristics. Drawbacks include complicated tool designs, non-uniformity of gears produced throughout the life of the tooling, and lengthy development times.
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.
Powder metal (PM) gears normally sell due to the lower cost and their relatively high mechanical performance. The reason behind the lower cost is that most of the machining is omitted due to the net-shape forming process. So how net-shape are powder metal gears? In this article some hard-to-find information about the tolerances through the manufacturing steps will be presented.
News Items About forming
1 PMA Announces 2017 Awards of Excellence in Metalforming (November 16, 2017)
The Precision Metalforming Association (PMA) has announced the winners of its 2017 Awards of Excellence in Metalforming. Presented annual... Read News
2 PMA Accepts Entries for 2014 Awards of Excellence in Metalforming (March 20, 2014)
The Precision Metalforming Association (PMA) invites industry-leading companies to submit an entry for its 2014 Awards of Excellence in Metalforming... Read News
3 PMA Announces Awards of Excellence in Metalforming (November 25, 2013)
The Precision Metalforming Association (PMA) has announced the winners of its 2013 Awards of Excellence in Metalforming. Presented ... Read News
4 Metalforming Companies Expect Business Conditions to Decline (November 23, 2011)
According to the November 2011 Precision Metalforming Association (PMA) Business Conditions Report, metalforming companies predict a cont... Read News
5 Dillon Jaw Forming Ring Maximizes Jaw Life Through Uniform Grip (September 22, 2017)
The Dillon jaw forming ring is an easy-to-use tool that provides a more uniform grip on the workpiece, thereby maximizing jaw life for cu... Read News
6 Emuge Introduces General Purpose Forming Tap (February 12, 2013)
Emuge Corp. has announced the introduction of MultiTAP-Form, the industry’s first high performance forming tap designed to deliver ... Read News
7 October Report Looks Positive for Metalforming Industry (November 9, 2007)
According to the October 2007 Precision Metalforming Association (PMA) Business Conditions Report, business conditions will dip slightly ... Read News
8 Ransohoff LeanDrum CF Washer Offers Energy Efficient High-Volume Cold Forming Solution (June 28, 2017)
Ransohoff, a division of Cleaning Technologies Group LLC, has introduced its LeanDrum CF Washer. This new platform provides an energy eff... Read News
9 PMAEF Issues Awards to Metalforming Industry (February 22, 2011)
The PMA Educational Foundation (PMAEF) has received a grant from The Hitachi Foundation to launch a new project searching for and profili... Read News