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1 Engineered Gear Steels: A Review (November/December 2002)

The selection of the proper steel for a given gear application is dependent on many factors. This paper discusses the many aspects related to material, design, manufacture, and application variables. The results of several studies on the optimization of alloy design for gas- and plasma- carburization processing and reviewed.

2 Superfinishing Gears -- The State of the Art (November/December 2003)

Superfinishing the working surfaces of gears and their root fillet regions results in performance benefits.

3 Experimental Characterization of Bending Fatigue Strength in Gear Teeth (January/February 2003)

The effort described in this paper addresses a desire in the gear industry to increase power densities and reduce costs of geared transmissions. To achieve these objectives, new materials and manufacturing processes, utilized in the fabrication of gears, and being evaluated. In this effort, the first priority is to compare the performance of gears fabricated using current materials and processes. However, once that priority is satisfied, it rapidly transforms to requiring accurate design data to utilize these novel materials and processes. This paper describes the effort to address one aspect of this design data requirement.

4 Carburizing of Big Module and Large Diameter Gears (September/October 2002)

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.

5 Case Depth and Load Capacity of Case-Carburized Gears (March/April 2002)

Compared to non-heat-treated components, case-carburized gears are characterized by a modified strength profile in the case-hardened layer. The design of case-carburized gears is based on defined allowable stress numbers. These allowable stress numbers are valid only for a defined "optimum" case depth. Adequate heat treatment and optimum case depth guarantee maximum strength of tooth flank and tooth root.

6 Properties of Tooth Surfaces due to Gear Honing with Electroplated Tools (November/December 2001)

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.

7 Net-Shape Forged Gears - The State of the Art (January/February 2002)

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.

8 Atmospheric vs. Vacuum Carburizing (March/April 2002)

In recent years, improvements in the reliability of the vacuum carburizing process have allowed its benefits to be realized in high-volume, critical component manufacturing operations. The result: parts with enhanced hardness and mechanical properties.

9 The Alignment of High Speed Gears (January/February 2003)

This paper reviews the necessity for detailed specification, design and manufacture to achieve required performance in service. The precise definition of duty rating and a thorough understanding of the environmental conditions, whether it is in a marine or industrial application, is required to predict reliable performance of a gearbox through its service life. A case study relating to complex marine gears and other general practice is presented to review the techniques used by Allen Gears to design and develop a gearbox that integrates with the requirements of the whole machinery installation. Allen Gears has considerable experience in the design of a variety of industrial and marine gears(Ref. 1,2).

10 Spiral Bevel Gear Development: Elminiating Trial and Error with Computer Technology (January/February 2003)

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.

11 The Two-Sided-Ground Bevel Cutting Tool (May/June 2003)

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.

12 Direct Gear Design: Bending Stress Minimization (September/October 2003)

Bending stress evaluation in modern gear design is generally based on the more-than-one-hundred-year-old Lewis equation.

13 Local 3-D Flank Form Optimizations for Bevel Gears (September/October 2003)

Optimizing the running behavior of bevel and hypoid gears means improving both noise behavior and load carrying capacity. Since load deflections change the relative position of pinion and ring gear, the position of the contact pattern will depend on the torque. Different contact positions require local 3-D flank form optimizations for improving a gear set.

14 Large Scores and Radial Cracks on Case-Hardened Worms (May/June 2003)

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.

15 Performance of Skiving Hobs in Finishing Induction Hardened and Carburized Gears (May/June 2003)

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.

16 Gear Damage Detection Using Oil Debris Analysis (January/February 2003)

The purpose of this paper was to verify, when using an oil debris sensor, that accumulated mass predicts gear pitting damage and to identify a method to set threshold limits for damaged gears.

17 Heat Treat Process and Material Selection for High Performance Gears (March/April 2003)

The selection of the heat treat process and the congruent material required for high performance gears can become very involved.

18 Dry Machining for Gear Shaping (November/December 2001)

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).

19 Cutting Hardened Gears (November/December 2002)

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.

20 Hard Finishing and Fine Finishing Part 2 (November/December 1989)

After shaping or hobbing, the tooth flanks must be either chamfered or duburred. Here it is paramount that the secondary burr produced will not be formed into the flank, but to the face of the gear, because during hardening, the secondary burr will straighten up and, due to its extreme hardness, will lead to excessive tool wear.

21 Selection of the Optimal Parameters of the Rack-Tool to Ensure the Maximum Gear Tooth Profile Accuracy (January/February 1999)

An analysis of possibilities for the selection of tool geometry parameters was made in order to reduce tooth profile errors during the grinding of gears by different methods. The selection of parameters was based on the analysis of he grid diagram of a gear and a rack. Some formulas and graphs are presented for the selection of the pressure angle, module and addendum of the rack-tool. The results from the grinding experimental gears confirm the theoretical analysis.

22 Metallurgical Aspects to be Considered in Gear and Shaft Design (March/April 1999)

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.

23 Hard Finishing and Fine Finishing Part 1 (September/October 1989)

Profitable hard machining of tooth flanks in mass production has now become possible thanks to a number of newly developed production methods. As used so far, the advantages of hard machining over green shaving or rolling are the elaborately modified tooth flanks are produced with a scatter of close manufacturing tolerances. Apart from an increase of load capacity, the chief aim is to solve the complex problem of reducing the noise generation by load-conditioned kinematic modifications of the tooth mesh. In Part II, we shall deal with operating sequences and machining results and with gear noise problems.

24 Estimating Hobbing Times (July/August 1989)

Hobbing is a continuous gear generation process widely used in the industry for high or low volume production of external cylindrical gears. Depending on the tooth size, gears and splines are hobbed in a single pass or in a two-pass cycle consisting of a roughing cut followed by a finishing cut. State-of-the-art hobbing machines have the capability to vary cutting parameters between first and second cut so that a different formula is used to calculate cycle times for single-cut and double-cut hobbing.

25 Material Properties and Performance Considerations for High-Speed Steel Gear-Cutting Tools (July/August 2001)

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.

26 Gear Design Options (May/June 1987)

When specifying a complete gear design, the novice designer is confronted with an overwhelming and frequently confusing group of options which must be specified. This array of specifications range from the rather vague to the very specific.

27 A New Approach to Heat Treating Parts Washing (March/April 1999)

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.

28 Superfinishing Gears - The State of the Art, Part II (July/August 2005)

In a previous article, the authors identified two misconceptions surrounding gear superfinishing. Here, they tackle three more.

29 Precision Finish Hobbing (July/August 2000)

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.

30 Dry Hobbing Process Technology Road Map (March/April 2001)

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.

31 Cast Iron: A Solid choice for Reducing Gear Noise (September/October 1999)

Material selection can play an important role in the constant battle to reduce gear noise. Specifying tighter dimensional tolerances or redesigning the gear are the most common approaches design engineers take to minimize noise, but either approach can add cost to the finished part and strain the relationship between the machine shop and the end user. A third, but often overlooked, alternative is to use a material that has high noise damping capabilities. One such material is cast iron.

32 A Practical Guide for Molding Better Plastic Geared Transmissions (May/June 2000)

Plastic gears and transmissions require a different design approach than metal transmissions. Different tools are available to the plastic transmission designer for optimizing his geared product, and different requirements exist for inspection and testing. This paper will present some of the new technology available to the plastic gear user, including design, mold construction, inspection, and testing of plastic gears and transmissions.

33 Gear Measurement Traceability and Uncertainty (July/August 2000)

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.

34 Hard Gear Finishing with a Geometrically Defined Cutting Edge (November/December 1999)

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.

35 Reducing Production Costs in Cylindrical Gear Hobbing and Shaping (March/April 2000)

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.

36 The Effect of Material Defects on Gear Perfomance - A Case Study (March/April 2000)

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.

37 The Effects of Pre-Rough Machine Processing on Dimensional Distortion During Carburizing (September/October 2006)

A study was conducted to isolate the influence of pre-rough machine processing on final dimensional distortion.

38 Hard Gear Processing with Skiving Hobs (March/April 1985)

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.

39 Technical Calendar (November/December 1988)

November 1-3. SME Gear Processing and Manufacturing Clinic, Sheraton Meridian, Indianapolis, IN. November 5-10. international Conference on Gearing, Zhengzhou, China

40 The Winds of Change (January/February 1991)

Nashville - One of the highlights of this year's SME Advanced Gear Processing and Manufacturing Clinic was a tour of the new GM Saturn automobile manufacturing plant outside the city. There in the Tennessee hills is a hopeful vision of the future of the American automobile industry. It may well be the future of American large-scale manufacturing in general.

41 Technical Calendar (July/August 1986)

October 5-8, 1986 AGMA Fall technical Conference & Gearing Exhibit September 17-19, 1986 Ohio State University Gear Noise Seminar November 11-13, 1986 SME Gear Processing and Manufacturing Clinic November 19-21, 1986 Seminar: Gear System Design for Minimum Noise

42 Technical Calendar (September/October 1988)

September 27-29. American Society for Metals 11th Annual Heat Treating Conference October 10-12. AGMA Fall Technical Meeting. Fairmont Hotel, New Orleans, LA November 1-3. SME Gear Processing and Manufacturing Clinic, Sheraton Meridian, Indianapolis, IN

43 Powder Metal Gear Design and Inspection (September/October 1996)

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.

44 New Approaches to Nitriding (March/April 1997)

The process of nitriding has been used to case harden gears for years, but the science and technology of the process have not remained stagnant. New approaches have been developed which are definitely of interest to the gear designer. These include both new materials and new processing techniques.

45 New ECM Furnace Improves Manufacture Efficiency of PM Components (March/April 2014)

The heat treatment processing of powder metal (PM) materials like Astaloy requires four steps -- de-waxing, HT sintering, carburizing and surface hardening -- which are usually achieved in dedicated, atmospheric furnaces for sintering and heat treat, respectively, leading to intermediate handling operations and repeated heating and cooling cycles. This paper presents the concept of the multi-purpose batch vacuum furnace, one that is able to realize all of these steps in one unique cycle. The multiple benefits brought by this technology are summarized here, the main goal being to use this technology to manufacture high-load transmission gears in PM materials.

46 Gear Teeth as Bearing Surfaces (May 2017)

A reader wonders about gears where the tops of the teeth are the bearing surface, as used in spur gear differentials. Do they require any special construction or processing?

47 Gear Heat Treating in the 90s: Beyond Black Magic (March/April 1995)

Heat Treating - The evil twin of the gear processing family. Heat treating and post-heat treating corrective processes can run up to 50% or more of the total gear manufacturing cost, so it's easy to see why, in these days when "lean and mean" production is the rage, and every part of the manufacturing process is under intense scrutiny, some of the harshest light falls on heat treating.

48 Heat Treating Equipment Selection (March/April 1995)

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.

49 Achievable Carburizing Specifications (January/February 1990)

A widespread weakness of gear drawings is the requirements called out for carburize heat treating operations. The use of heat treating specifications is a recommended solution to this problem. First of all, these specifications guide the designer to a proper callout. Secondly, they insure that certain metallurgical characteristics, and even to some extent processing, will be obtained to provide the required qualities in the hardened gear. A suggested structure of carburizing specifications is give.

50 Induction Heat Treating Gains Ground through Advances in Technology (March/April 2011)

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.

51 CNC Technology and the System-Independent Manufacture of Spiral Bevel Gears (September/October 1992)

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.

52 The Fundamentals of Gear Press Quenching (March/April 1994)

Most steel gear applications require appreciable loads to be applied that will result in high bending and compressive stresses. For the material (steel) to meet these performance criteria, the gear must be heat treated. Associated with this thermal processing is distortion. To control the distortion and achieve repeatable dimensional tolerances, the gear will be constrained during the quenching cycle of the heat treatment process. This type of fixture quenching is the function of gear quench pressing equipment.

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