Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2001-06-22
2002-06-04
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S572000, C148S906000, C464S145000, C464S906000, C073S001790, C073S001810
Reexamination Certificate
active
06398886
ABSTRACT:
The invention relates to a process of finishing outer joint parts formed in a non-cutting way and intended for constant velocity joints in the form of tripode joints or ball joints; the outer joint parts have a longitudinal axis and an inner recess which extends in the direction of the longitudinal axis and which is substantially undercut-free. The inner recess is provided with tracks for form-fittingly receiving rolling members which, in turn, are held in a form-fitting connection by the inner joint part. The tracks comprise hardened contact zones for the rolling contact of rolling members. Furthermore, the invention relates to a device for finishing outerjoint parts formed in a non-cutting way and intended for constant velocity joints of the above-mentioned type.
The invention relates to tripode joints and ball joints in the form of UF joints (undercut-free) and DO joints (double offset). For reasons of cost, the process of forming such joints in a non-cutting way is nowadays perfected to such an extent that the tracks with their respective roller contact zones (in the case of tripode joints) and ball contact zones (in the case of ball joints) comprise their finish dimension and do not require subsequent machining. It is, however, necessary to harden at least the contact zones on which the rolling members run, with such hardening usually being carried out in the form of induction hardening. In view of the axially asymmetric , conditions of mass and thermal capacity at the respective ends of the tracks, i.e. due to a relative heat accumulation at the axial ends of the contact zones to be hardened, the contact zones are subject to hardness distortions which cannot be perfectly compensated for, not even by an axially adapted introduction of heat and/or cooling during the hardening operation. In consequence, the contact zones, along their axial length, are radially distorted at their ends, and the internal dimension of the inner recess between symmetrically opposed contact zones at the axial ends of the outer joint part is normally reduced. Subsequent machining in the form of grinding is impossible for reasons of costs. As a result the joint suffers from tolerance defects with too close a fit at the open end of the outer joint part and/or too wide a fit in the rear inner region of the outer joint part.
It is therefore the object of the present invention to provide a process of and device for finishing outer joint parts of said type, which improve the dimensional accuracy of the hardened contact zones of the tracks and thus reduce the tolerance defects at the joint.
The objective is achieved by providing a process which is characterised by the following sequence of process stages:
non-cutting forming of the outer joint part, surface-layer-hardening of the inner recess at least along the length of the contact zones, for the purpose of producing a hardened surface layer, at least in the region of the contact zones, above an unhardened matrix and
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
By leaving a non-calibrated surface strip between each two surface-layer-hardened, calibrated contact zones, it is possible to sufficiently deform the hardened contact zones with the matrix or within the matrix without there occurring any fractures of the hardened contact zones. It is particularly advantageous if, while calibrating the contact zones, the unhardened matrix behind the hardened surface layer is made to flow over large portions, starting from the outer surface of the component; circumferential movements in the matrix should also be permitted. Flowing in the matrix, which occurs by generating an inwardly directed pressure on the outer surface of the component should take place in those cases where the internal dimension of the inner recess between opposed contact zones has to be reduced and also in those cases where said internal dimension has to be increased. The hardened surface layer can be produced with a thickness of up 1.2 mm. The stresses necessarily occurring within the hardened calibrated strips of the surface layer can be reduced by a subsequent heat treatment without incurring a substantial loss of hardness. If the radial dimension of the inner recess between opposed hardened contact zones is too small after hardening, especially at the axial end of the outer joint part, it can be increased by pressing in strips of (hardened) surface layers into the matrix. If, on the other hand, the radial dimension of the inner recess between opposed hardened contact zones is too large after hardening, it can be reduced by pressing in the matrix material behind the strip of the (hardened) surface layers. Both measures are effected by axially pressing a calibrating mandrel into the outer joint part in a first process stage and by radially pressing outer calibrating jaws on to the outer joint part in a second process stage while the calibrating mandrel is in an introduced condition. Both measures can be carried out jointly in one calibrating operation in different regions of the contact zones.
According to a first variant in accordance with the invention, there is proposed a process having the following process stages:
non-cutting forming of the outer joint part,
surface-layer-hardening of the inner recess along the length of the contact zones while
producing a hardened surface layer in the region of the contact zones above an unhardened matrix, and retaining an unhardened surface strip between the adjoining contact zones,
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
Between each two surface-layer-hardened contact zones there is retained a surface strip in which the unhardened matrix forms the inner face of the inner recess. This permits high deformation rates, and the internal dimension of the inner recess between two symmetrically opposed contact zones can be changed by up to 0.3 mm.
If the inventive method is applied to the outer parts of tripode joints which comprise three inner longitudinally extending roller tracks which each comprise pairs of symmetrically arranged roller contact zones, it is proposed that between the roller contact zones of one roller track, there is retained an unhardened strip of the matrix and, according to a preferred embodiment, that between adjoining roller contact zones of two adjoining roller tracks, there is retained an unhardened strip of the matrix. If the inventive method is applied to the outer parts of ball joints which comprise at least three longitudinally extending ball grooves which form pairs of symmetrically arranged ball contact zones, it is proposed that between adjoining ball contact zones of two adjoining ball grooves, there is retained an unhardened strip of the matrix. In such a case, either the surface layer of an entire ball groove is completely hardened or it can be proposed that between the two ball contact zones of a ball groove, there is also retained an unhardened strip of the matrix. In both cases, the two ball contact zones of a ball groove can be deformed relative to one another.
According to a second variant in accordance with the invention, there is proposed a process having the following process stages:
non-cutting forming of the outer joint part,
surface-layer-hardening of the inner recess along the length of the contact zones, thereby producing a hardened surface layer which is continuously hardened in the inner recess, above an unhardened matrix,
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
In this case, the inner surface of the inner recess is surface-layer-hardened all around in a simplified way. As a result, when calibrating the contact zones, the intermediate surface-layer-hardened re
Fuhrmann Peter
Kinzel Hans-Willi
GKN Automotive AG
Yee Deborah
LandOfFree
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