Daimler Chrysler Ag

Mercedes-benz Aktiengesellschaft

Gustav Hanisch

Christoph Duell

Volker Keck

Gerhard Haubold

Reiner Schmid

A method for the production of hollow shafts from welded or seamlessly produced steel tubes having a maximum carbon content of 0.35% includes (1) carburizing a tube to a carbon content greater than 0.5%; (2) slowly cooling the carburized steel tube down from the process temperature, so that it undergoes no increase in hardness; (3) machining and/or non-cutting processing the carburized and soft steel tube to produce a workpiece blank; and (4) hardening the workpiece blank by local heating and quenching at desired points.

Method for the manufacture of hollow shafts

In a device for inductive hardening of profiled camshafts (especially those having valve cams and zero cams) during a hardening operation, the camshaft is surrounded by an inductor and is heated by means of a magnetic field emanating from the inductor. The inductor has several axial members and radial members through which the induction current flows during the hardening operation. Dynamo sheets provided on the axial branches focus the magnetic field in the radial direction. The position and the width of the dynamo sheets is adapted to the surface profile of the camshaft, so that the focusing is aimed at areas with a small diameter.

Arrangement and process for the inductive hardening of profiled camshafts

A built-up camshaft has cam discs which are secured to a tube under mechanical prestress, are of annular design, and are inductively hardened all the way around at a boundary layer on their outer periphery before they are secured to the tube. The hardening of the boundary layer is formed in such a manner that, due to the hardening, high residual compressive stresses (at least -450 N/mm.sup.2) are produced in an at least approximately 0.5 mm deep boundary zone near the surface in such a manner that, even after the cam discs are mounted on the tube, the superimposing residual tensile stresses in the boundary zone, induced by the joining, only partly compensate the original residual compressive stresses, i.e. there are still only residual compressive stresses (at least -150 N/mm.sup.2) in the boundary zone near the surface even after the pressing-on. Sufficiently high residual compressive stress in the boundary zone can be produced by effecting the inductive heating of the cam disc in two stages. Specifically, first of all the cam disc is loaded with a medium-frequency alternating magnetic field and thus the entire annular body of the cam disc is preheated to at least 250.degree. C. but below the transformation temperature. The cam disc is then loaded with a second alternating magnetic field changed in its intensity and/or its frequency relative to the alternating magnetic field of the first stage, as a result of which only the boundary zone is heated up to the transformation temperature or below it. After the quenching of the cam disc heated in such a manner, the high residual compressive stresses appearing a boundary zone of sufficient depth.

Method of inductively hardening the cams of a camshaft

A built-up camshaft has cam discs which are secured to a tube under mechanical prestress, are of annular design, and are inductively hardened all the way around at a boundary layer on their outer periphery before they are secured to the tube. The hardening of the boundary layer is formed such that, due to the hardening, high residual compressive stresses (at least -450 N/mm.sup.2) are produced in an at least approximately 0.5 mm deep boundary zone near the surface such that, even after the cam discs are mounted on the tube, the superimposing residual tensile stresses in the boundary zone, induced by the joining, only partly compensate the original residual compressive stresses, i.e. there are still only residual compressive stresses (at least -150 N/mm.sup.2) in the boundary zone near the surface. Sufficiently high residual compressive stress in the boundary zone are produced by effecting the inductive heating of the cam disc in two stages. First of all, the cam disc is loaded with a medium-frequency alternating magnetic field and thus the entire annular body of the cam disc is preheated to at least 250.degree. C. but below the transformation temperature. The cam disc is then loaded with a second alternating magnetic field changed in its intensity and/or its frequency relative to the alternating magnetic field of the first stage, as a result of which only the boundary zone is heated up to the transformation temperature or below it. After the quenching of the cam disc heated in such a manner, the high residual compressive stresses appear in a boundary zone of sufficient depth.

Growing community of inventors

Hochdorf, Germany

Gustav Hanisch