Metal deforming – By application of fluent medium – or energy field – With actuated tool engaging work
Reexamination Certificate
2000-04-14
2002-09-03
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
With actuated tool engaging work
C072S059000, C072S061000
Reexamination Certificate
active
06442987
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of producing a shaft from a piece of tubing, the shaft having at least one bulging portion such as a lifting bearing, a cam or a bearing step. The invention also relates to an apparatus for the production of such a shaft. Lastly, the invention also relates to a camshaft produced from a piece of tubing. Shafts, more particularly camshafts of the kind specified, are as a rule made from metal, more particularly steel. They are used, for example, for the reduction of engine weight, being substituted for forged or cast components intended for motor vehicles.
A multistage method of producing a camshaft, an apparatus for the performance of said method and a camshaft of the kind specified are known from U.S. Pat. No. 2,892,254. According to that specification, for the production of the known camshaft, use is made of a molding tool formed from two block-like tool halves. The surfaces of the tool halves, lying one upon the other in the closed state, are formed with cavities which jointly form a hollow mold for the bulging cam portion to be produced on the shaft. To produce the shaft by the known apparatus, first the portion of piping on which the first cam of the shaft is to be produced is laid in the tool and the piece of tubing is filled with fluid. Then the piece of tubing is sealed and by means of a suitable pressure generating device, an internal pressure is generated which is high enough to press the material of the portion of tubing in question into the hollow mold of the tool. At the same time an axial pressure is operative which encourages the material of the tubing to flow into the cavity. On completion of the first stage of molding, the tool is opened and the piece of tubing is moved axially forwards until the previously produced bulging cam portion lies in a further cavity in the tool. Then the internal pressure is built up again, a further bulging cam portion is produced, and the operation is repeated in steps, until all the cams of the shaft are finished.
It is true that the known apparatus enables a lightweight camshaft to be produced. However, practical trials carried out on camshafts produced in this way show that they failed to meet the demands on operational properties. Moreover, the production of such camshafts via the prior art methods is laborious and time-consuming. Furthermore, cams of different shapes cannot be produced on a shaft by the prior art method.
To obviate the disadvantages of the method disclosed in U.S. Pat. No. 2,892,254, the German Specification DE 44 27 201 C2 suggests the production of a preliminary mold for the cams to be made by a similar multistage cold extrusion method for the production of a camshaft. The construction of such a preliminary mold enables more material to be accumulated in the zone of the cam tip than is possible by the known method explained hereinbefore. The application of an axial compressive force to the piece of tubing ensures that supplementary material is always provided on both sides during preliminary molding, the result being a more advantageous distribution of masses of material in the zone of the particular cam. In the method known from DE 44 27 201 C2, following preliminary molding the final shape of the cams is produced in at least one further processing stage.
It is true that the method known from DE 44 27 201 C2 enables a camshaft of improved properties to be produced, but in practice it was found that even the camshafts produced by this method failed to meet the demands made on a component fully developed for serial production. Moreover, it has proved difficult to produce camshafts of suitable quality in large numbers by the method disclosed in DE 44 27 201 C2, since a large number of tools and changes of the apparatus are necessary for the performance of the method.
It is an object of the invention to provide a method and an apparatus of the kind specified which enable shafts, more particularly camshafts provided with bulging portions to be produced in a cheap and practicable manner. Another object is to provide a camshaft produced from a piece of tubing which has improved operational properties in comparison with prior art camshafts produced from pieces of tubing.
SUMMARY OF THE INVENTION
The problem stated is solved by a method of producing from a piece of piping, a shaft having at least one bulging portion such as a lifting bearing, a cam or a bearing step, wherein: the piece of tubing bears radially against a portion adjoining the zone of the bulging portion to be produced; the piece of tubing is subjected to internal pressure, by which through the co-operation of an axially operative compressive force applied to the piece of tubing, a portion of tubing adjoining the radially borne portion is so upset that the external diameter of said upset piece of tubing is larger than the external diameter on the unupset piece of tubing; then applied to the upset piece of tubing is a molding tool having a hollow portion forming a cavity corresponding to the final shape of the bulging portion to be produced; and the bulging portion is formed from the upset piece of tubing by the application of radially operative compressive forces by means of the molding tool, the piece of tubing continuing to experience internal pressure throughout the entire molding operation.
In the method according to the invention first of all, unimpeded by a molding tool, the co-operation of internal pressure and axial pressure produces an upsetting of the piece of tubing in the zone at which the particular bulging portion is to be produced. The internal pressure ensures that the collection of material caused by the upsetting leads to a widening in the diameter of the pieces of tubing in the portion in question. In the portion of tubing in question, this results in an accumulation of material which is required for the subsequent complete molding of the cam. Then the molding tool is closed. As soon as the tool contacts the upset portion, a pressure is exerted on the piece of tubing from the radial direction. This pressure imposes on the material of the piece of tubing, preferably a metal, more particularly steel, which is still under internal pressure, a particular direction of flow resulting from the shape of the tool cavity.
The special feature of the cold extrusion method according to the invention consists, as already mentioned, in the feature that the material of the tubing is not forced into any particular shape prior to the start of production of a bulging proportion, but first of all an upsetting of the material of the tubing is produced, accompanied with an accumulation of material, whose shape is not determined. Since during upsetting the material can flow freely, this ensures in a simple manner that during the production of the final shape of the bulging portion, enough material is available to prevent thinnings in the walls of the bulging portion. In this way, the method according to the invention enables a large quantity of material to be collected in a controlled manner at such places of the bulging portion as are subjected to increased loading in use, this possibility being created by a corresponding shaping of the cavity of the molding tool and by a suitable selection at the time at which the tool is applied.
Another advantage of the succession of processing steps according to the invention is that the production of shafts furnished with bulging portions can be performed on a single machine. Costly and time-consuming changes of tools or apparatuses must not be performed. The method according to the invention is therefore particularly suitable for the serial production of shafts, more particularly camshafts equipped with bulging portions for motor vehicle construction.
A particularly advantageous distribution of material in the zone of the walls of the bulging portion can be achieved by the feature that the piece of tubing is kept loaded by the axial compressive force during the molding performed by means of the molding tool. The maintenance of the axial pressure during s
Jones David
Proskauer Rose LLP
LandOfFree
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