Patent Application
20080034830
Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings.
While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.
One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting.
As described herein, various embodiments of the invention comprise systems and methods for forging metal parts, where a first portion of each part is formed with a grain flow pattern that has a substantially reduced number of exit points at the seam of the part. In one embodiment, a piece of metal is forged in a series of flash forging steps. In the preliminary steps, the piece of metal is formed into a desired shape by placing it between two dies and applying pressure to the dies in a first direction. This is repeated one or more times to bring the shape of the piece of metal closer to the desired shape of the final part. In each of these steps, the first portion of the part is formed against the face of a single one of the dies so that there is no seam, and no flash, on the first portion of the part. In a final forging step, the part is re-oriented so that the pressure is applied to the dies (and applied by the dies to the part) in a direction which is different from (e.g., perpendicular to) the first direction. In this step, the first portion of the part is formed by both dies, so that there is a seam on the first portion corresponding to the seam between the dies. Because the first portion is already in a shape which is very near its final shape, little or no flash is formed on the first portion of the part during the final forging step. As a result, the grain flow pattern within the first portion of the part does not extend to any substantial degree into the flash, and is less prone to fatigue and failure.
In one particular embodiment, a steering knuckle for a heavy truck is manufactured using a forging process. The steering knuckle has a relatively flat, circular flange, with a spindle extending outward from the flange in one direction, and a pair of attachment ears extending outward from the flange in the opposite direction. Rather than using conventional flash forging techniques which would produce flash along a seam which extends all the way around the part, new techniques are used in order to reduce or eliminate the flash at the seam along the spindle, while allowing flash to form at the seam of the remainder of the part.
In this embodiment, the initial shape of the piece of metal to be forged is cylindrical. In a first blocker step, the metal is extruded into a first die to form a portion that will become the spindle of the steering knuckle. Because the spindle portion is extruded into the die, there is no seam and no flash on the spindle portion. In a second blocker step, the metal is extruded away from the spindle portion to form a portion that will become the attachment ears of the steering knuckle. As in the first blocker step, the spindle portion is pressed against a single die so that there is still no seam and no flash on the spindle portion. In both the first and second blocker steps, the dies are pressed against the part along a direction which is parallel to the axis of the spindle portion.
In a final forging step, the dies are applied to the part along a direction which is perpendicular to the axis of the spindle portion. In this step, a first die is applied to one side of the spindle portion while a second die is applied to the opposite side of the spindle portion. There is therefore a seam along the spindle portion. Because the spindle portion has already been formed into a shape which is very close to the final shape, however, little or no flash is formed at the seam when the dies are pressed together to form the part into its final shape. Because very little of the metal in the spindle portion flows out of the seam as flash, the grain flow pattern of the metal does not extend to any substantial degree into the flash. Consequently, when the small amount of flash is trimmed from the spindle of the finished part, the grain flow pattern has far fewer termination points at the surface of the spindle than conventionally forged steering knuckles. This results in a substantially stronger steering knuckle which is much less likely to fatigue and fail when subjected to the cyclical stress caused by normally use of the part.
It should be noted that, while the following description focuses on the manufacture of a steering knuckle, the techniques disclosed herein can be applied to the manufacture of many other, different parts. The example of the steering knuckle should therefore be construed as illustrative, rather than limiting of the scope of the invention. It is contemplated that these techniques will be most useful in the manufacture of parts that are subjected to cyclical stresses that cause fatigue and subsequent failure of the parts.
Before describing the various exemplary embodiments of the invention, it may be helpful to first describe conventional flash forging. Referring to
It should be noted that, in each step of the forging process of
As the part is forged, the pressure applied to the part breaks down the polycrystalline structure of the metal, forming “grains” of the metal. As the grains of metal flow from one position to another, a pattern (a grain flow pattern) is formed. As the metal flows in the forging, the grains become aligned in the direction of the flow. This alignment of the grains can actually increase the strength of the metal. If the grain flow pattern is interrupted, however, stresses on the metal can be effectively concentrated at the point of interruption, which may result in fatigue cracking or other failures.
Referring to
Referring to
Referring to
As shown in
A second blocker step then forges the metal into the shape shown in
A final forging step is then performed to form the part into the shape shown in
The amount of flash formed on the spindle is controlled, at least in part, by how closely the last blocker step conforms the spindle to its desired final shape. If the last blocker step leaves the spindle in almost its final shape, there will be almost no flash. If the last blocker step is not almost the same as the final shape, some metal may have to be displaced during the finisher step, thereby forming some flash. In the case that no flash is formed on the spindle, there is no flash to be trimmed from the spindle, so the grain flow pattern does not have exit points at the surface of the spindle. Referring to
As noted above, the foregoing description of the steering knuckle and corresponding methods of manufacture are provided as examples, and should be construed as illustrative, rather than limiting, of the invention. The techniques disclosed herein can be applied to the manufacture of many other, different parts.
The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.
While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed within the following claims.
