Metal deforming – By three or more coacting relatively movable tools – Yieldable face portion or auxiliary tool on tool-couple element
Reexamination Certificate
1999-12-17
2001-09-18
Larson, Lowell A. (Department: 3725)
Metal deforming
By three or more coacting relatively movable tools
Yieldable face portion or auxiliary tool on tool-couple element
C029S898057
Reexamination Certificate
active
06289711
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for rounding bushings wherein a sheet bar is inserted into a clearance between a core and a first shaping die having a first shaping chamber with an inner profile which at least approximately complements the outer profile of the bushing and which extends over at least half of the circumference of the bushing, that the sheet bar is bent approximately in the form of a U through relative movement of the core into the first shaping chamber during a pre-shaping step, that the core penetrated into the first shaping chamber shapes both legs of the U-shaped formed body in a final shaping step to a bushing through relative movement into a second shaping chamber of a second shaping die, and that the edges of both shaping chambers of both shaping dies terminate in parallel end face planes of the shaping dies, with these end face planes at least approximately contacting each other when the two shaping chambers are closed.
A method of this type is known. Most round housings, bushings and bearing sleeves are bent in this fashion from pre-stamped sheet bars; however, the result after the final shaping step is unsatisfactory, mainly because rounding is incomplete in the vicinity of the end face planes of the shaping dies. Irregularities are also observed at the bushing ends. In most cases, it is therefore necessary to finish the bushings thereafter by a sizing process. It is also impossible to avoid polishing marks on the bushing surfaces with the known methods, and high-quality materials, e.g. materials having multiple layers, plastic-coated sheet bars and the like, cannot be processed by this method without all
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introducing surface damage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and device for carrying out the method, by which the sheet bars can be rounded more accurately than previously known and this bending can be executed in more gentler fashion, so that even more delicate materials can be processed.
In most applications, rounding refers to the bending of rotationally symmetrical objects, such as cylindrical or conical bushings, but is not restricted thereto. The bent components may also have oval, elliptical, drop-shaped or similar cross-sections.
This object, and others which will become apparent hereinafter, is attained by a method of the aforementioned type in accordance with the invention by having the core penetrate the first shaping chamber by a depth which is greater than the bushing radius, so that the bushing axis lies after the pre-shaping step at a distance from the end face plane of the shaping die within the first shaping chamber.
In a further development of the invention, the core penetrates the second shaping chamber by a depth which is greater than the bushing radius so that the bushing axis, after the final shaping of the bushing, lies at a distance from the end face plane of the second shaping die within the second shaping chamber.
As the bushing center of preferably both shaping dies is respectively passed by their end faces, the rounding of the bushing is significantly improved in the 90° region and in the 270° region compared to known bending methods in which the shaping dies respectively travel precisely to the center plane of the bushing. In order to implement this method, the cross-section of at least the core, preferably however also of the first shaping die must be changed between the pre-shaping step and the final shaping step. The device according to the invention advantageously provides a solution which will be described hereinafter.
Another significant feature of the invention provides for an auxiliary shaping step between the pre-shaping step and the final shaping step for bending only the ends of the U-shaped legs of the sheet bar to conform with the curvature of the second shaping chamber through relative displacement of the core into the second shaping chamber, without also bending the U-shaped legs disposed between these ends and the arched base of the U-shaped sheet bar blank. Consequently, this intermediate shaping step transforms the sheet bar blank into a stretched round profile, thereby promoting especially the precise rounding of the bushing ends.
Although the method according to the invention allows a highly accurate rounding of bushings, another embodiment of the invention provides a processing of the bushing in two working planes, with the pre-shaping, the intermediate shaping and the final shaping being assigned to the first working plane, and with the bushing being pushed axially into the second working plane after the final shaping for sizing there.
An important feature of the method according to the invention provides for an enlarged cross-section of the core by axially inserting an auxiliary core before the pre-shaping, thereby enabling at least one of the shaping dies to travel past the bushing center. This auxiliary core is advantageously employed after the final shaping step to push the bushing onto an expansion sleeve of the sizing station in the second working plane.
The invention relates furthermore to a bending device for carrying out the bending method, and this device is characterized in that the core and the first shaping chamber have a larger cross-section during the pre-shaping step than during the final shaping step. This feature can be implemented by interchanging the cores. Another alternate advantageous approach would be to employ an auxiliary core which is temporarily removed during the final shaping step. This auxiliary core preferably bears on the core with a concave surface and has a convex working surface which is complementary to the inner surface of the shaping chamber. Consequently, the auxiliary core has a sickle-shaped cross-section, with the working surface and the inner surface being positioned on circular cylinders of identical size.
The first shaping die preferably supports a slider displaceable in axial direction of the bushing and forming a part of the first shaping chamber, with the end face of the shaping chamber being formed on this slider and defining the partition plane of the shaping dies during the pre-forming and the intermediate or auxiliary forming steps. This partition plane is then positioned at a distance from the bushing center on the side of the first shaping die. The auxiliary core can now be advantageously combined with the slider into a conjointly movable unit so that the core and the first shaping chamber are provided with new cross-sectional configurations for the final shaping step of the bushing after this structural unit is retracted from the first working plane to thereby enable the unchanged second shaping die to travel past the bushing center for the final shaping step of the bushing.
Whereas conventionally, smaller sheet bars are suspended from a support tape centered above a rib, the sheet bars in the method according to the invention are secured to the support tape via two ribs located near the end sections of the sheet bar. Consequently, the sheet bar can be positioned more accurately inside the bending device. Since these ribs leave shear marks on the bushing face after separation from the support tape, the bushings produced in accordance with the invention differ from the state of the art in that the shear marks are located near the quarter girth adjacent to the bushing gap.
The three-step bending method with changing cross-sections of the core and shaping chambers results in a careful and very precise rounding of sheet bars, making the method according to the invention also suitable for extremely delicate laminated sheet bar materials.
The width of both shaping dies of the device according to the invention exhibit a width which is at least double the width of the bushing being bent and include in the axial direction next to their shaping chambers at least one respective sizing chamber, wherein both sizing chambers are mirror images of one another, have a same curvature as the curvature of the associated shaping chambers; but extend respectively only over a circum
Day Ursula B.
Feiereisen Henry M.
Krauss-Maffei AG
Larson Lowell A.
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