Induction heat treatment method and article treated thereby

Abstract

A method of induction heat-treating certain surfaces of an article comprising a hub and a plurality of trunnions or shafts extending therefrom, wherein the surfaces to be heat-treated comprise the surfaces of the trunnions. The method employs an induction coil that provides a planar magnetic field that is adapted to the irregular shape of the article, such that the induction coil produces magnetic fields that are adapted to induce currents in, and thereby heat, the trunnion surfaces of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment for trunnion surfaces of trunnions used in steel spiders of spider or tripod-type constant velocity joints.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of induction heat treatment. More specifically, the invention comprises a method for induction hardening certain metal components, particularly those having a shape that prevents uniform induction coupling over the entire surface to be hardened in a single step. Most particularly, the invention comprises a method for induction hardening the outer surfaces of the trunnions of a spider of a steel tripod-type constant velocity joint. BACKGROUND OF THE INVENTION [0002] The tripod-type constant velocity joint is widely used in automotive vehicles. It is most frequently used to provide a plunging and angulating constant velocity joint for use with halfshafts, the name given to the two driveshafts or axle shafts that run from the transaxle to the wheels in front wheel drive vehicles. A plunging joint is one that permits axial movement between the shafts. Because it is widely used in automotive vehicles, the tripod join...

AI Technical Summary

Benefits of technology

[0011] The present invention undertakes to improve the production of such components as compared to previous methods, such as carburizing, by enabling the use induction hardening, and thereby providing better control over the hardening process by hardening one component at a time, improving the metallurgical and mechanical and properties of the components, and allowing for a reduction in heat treatment cost.

[0012] The hardening operation will be simplified, and allow improved control, by the application of this invention because the components will be processed one at a time. The integration of the part location, heating, and quenching functions into a single, robust machine simplifies the heat treatment operation compared to previous methods, such as carburizing, by reducing the part handling requirements and reducing complex cycle parameters (e.g. adjusting the entire process for part-to-part variations in a batch of parts due to different temperature and environmental conditions that exist in a large heat treating furnace) to a small set of control parameters for each individual part (e.g. power, induction time, quench flow rates, etc.). Enabling the automatic control of process variables, such as the power level, total power delivered, quench temperature, quench flow rate, and cycle timing parameters, along with other process variables, will enable improved process control.

[0013] The mechanical properties of the components may also be improved by the selective application of heat in only the areas where high hardness is desired to give more precise control over the hardness and properties of the critical areas of the component while minimizing distortion from the hardening process.

[0014] Benefits from this invention include increased component strength (as compared to components processed by conventional methods such as carburizing), use of lower cost materials, shortened process times, reduced forging costs, reduced distortion, improved microstructures, improved tool life, deeper case depth capabilities, and the use of cellular process lines.

Problems solved by technology

The use of carburizing for case hardening has a number of well-known limitations.

These include the fact that the process treats the entire surface of the component, the material and processing costs associated with the process, the processing time necessary to heat the parts to temperature and produce the required carburized case depth, as well as limitations related to process control, batch processing, capital expense and facility requirements for large furnaces, environmental issues, and control of the finished part quality.

Also, the carburizing process has the potential to form undesirable microstructures, which include carbides, grain boundary oxidation, decarburization and retained austenite that can each affect the functionality of the finished part.

However, induction hardening has significant limitations in cases where the surface requiring heat treatment is irregular, such as gears having relatively larger teeth where the distance from the tip to the root of a tooth is such that the electromagnetic coupling, and hence induction heating, varies significantly from the tip to the root.

While some solutions have been proposed to facilitate the use of induction hardening with articles having irregular surfaces, such as the use of a plurality of different coils and different induction frequencies to treat different portions of the surface, or the use of coil designs that are adapted to the contour of the irregularities in order to provide more uniform coupling, induction hardening has not been used for various types of irregularly shaped components, including spiders, perhaps because the use of the techniques described above are not applicable to provide a single pass induction heat treatment of the critical surfaces of a spider due to its irregular shape.

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