Note: Descriptions are shown in the official language in which they were submitted.
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':
METHOD AND DEVICE FOR ROUNDING BUSHINGS
. .
3 DESCRIPTION .
The invention relates to a method for rounding bushings wherein a sheet
6 bar is inserted into a clearance between a core and a first shaping die ~aving a :
7 first shaping chamber with an inner profile which at least approximately
8 complements the outer profile of the bushing and which extends over at least
9 half of the circumference of the bushing, such that during a pre-shaping step :;
10 when the core moves relative to and penetrates the first shaping chamber, the
11 sheet bar is bent approximately in the form of a U, that the core which is now
12 positioned in the first shaping chamber subsequently moves relative to and :
13 pene~r~tes a second shaping chamber of a second shaping die whereby the two
14 legs of the U-shaped formed body undergo a final shaping step to assume the
15 shape of a bushing, that the edges of each shaping chamber of each shaping
16 die terminate on face planes on the shaping dies which are parallel to each
17 other, and that these face planes at least approximately contact each other when
18 the two shaping chambers are closed.
19
Such a method is known in the art and used to bend most round
21 housings, bush~l igs and bearing slecvcs from pre-stamped sheet bars; however,
22 the flnal shaping step turns out to be unsatisfactory, mainly because rounding is
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inco,nplete in the vicinity of the face planes of the shaping dies. Irregularities are
2 also observed at the bushing ends. In most cases, it is therefore necess~ry to
3 finish the bushings thereafter by a sizing process. It is also impossible to avoid
4 polishing marks on the bushing surfaces with the known methods and expensive
5 materials, for example materials having multiple layers, plastic-coated sheet bars
6 and the like, cannot be processed by this method without introducing surface
7 damage.
9 It is the object of the invention to provide a method for rounding the sheet
bars more accurately and gentler than with the known methods, making it
11 possible to process more delicate materials, and a device for carrying out the
1 2 method.
13
14 In most applications, rounding refers to the shaping of rotationally
symmetrical parts, such as cylindrical or conical bushings, but is not restricted to
16 such shapes alone. The shaped components may also have oval, elliptical, tear-
17 shaped or similar cross-sections.
18
19 The aforementioned inventive method provides a solution for this problem
by having the core penetrate the first shaping chamber by a depth which is
21 greater than the bushing radius, so that the bushing axis in relation to the face
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plane of the first shaping die is located inside the first shaping cl ,amber after the
2 pre-shaping of the bushing is completed.
4 In a further improvement of the invention, the core penel,ales the second
shaping chamber by a depth which is greater than the bushing radius, so that
6 the bushing axis in relation to the face plane of the second shaping die is7 located inside the second shaping chamber after the final shaping of the
8 bushing.
Since the face planes of preferably both shaping dies are located above
11 the bushing center, the bushing is significantly better rounded in the 90~ region
12 and in the 270~ region than was possible with the known bending methods
13 where the shaping dies consistently only move to the center plane of the
14 bushing. This method can only be implemented if the cross-section of the core,
preferably however and in addition also the cross-section of the first shaping die,
16 is changed between the pre-shaping step and the final shaping step. The device
17 of the present invention which will be described hereinafter, advantageously
18 provides a solution for carrying out this method.
19
Another significant feature of the invention provides for an auxiliary
21 shaping step t~ occur between the pre-shaping step and the final shaping step,
22 in which auxiliary step, when the core moves relative to and penetrates the
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second shaping chamber, only the ends of the U-shaped legs of the sheet bar
2 are bent to co"ror", with the curvature of the second shaping chamber, and the
3 section of the U-shaped legs which is located between these ends and the
4 rounded base of the U-shaped sheet bar blank, is not bent. Consequently, thisintermediate shaping step transforms the sheet bar blank into a stretched round
6 profile, thereby facilitating the precise rounding of the bushing ends.
8 Although the inventive method provides the means for very precise
9 rounding the bushings, another embodiment of the invention provides two
10 working areas for processing the bushings, with the pre-shaping step, the
11 intermediate shaping step and the final shaping step assigned to the first
12 working area and the sizing of the bushing performed in the second working
13 area whereto the bushing is moved after the final shaping step by axial
4 displacement.
16 An additional important feature of the invention provides for an enlarged
17 cross-section of the core by axially inserting an auxiliary core before the pre-
18 shaping step, thereby enabling at least one of the shaping dies to travel beyond
19 the bushing center. This auxiliary core is advantageously employed after the
20 final shaping step to push the bushing onto an expansion sleeve of the sizing21 station in the second working area.
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The invention relates furthermore to a rounding device for carrying out the
2 rounding method, the device characterized in that the core and the first shaping
3 chamber have a larger cross-section during the pre-shaping step than during the
4 final shaping step. This feature can be implemented by interchanging the cores.
5 Another alternate advantageous approach would be to employ an auxiliary core
6 which is temporarily removed during the final shaping step. This auxiliary core is
7 preferably seated on the core with a concave surface and has a convex working
8 surface shaped to complement the shape of the inner surface of the shaping
9 chamber. Consequently, the auxiliary core has a sickle-shaped cross-section,
10 with the working surface and the inner surface positioned on circular cylinders of
11 identical size.
12
13 The first shaping die preferably supports a slider forming a part of and
14 also the face of the first shaping chamber, the face defining the plane of
15 oscul~tion between the shaping dies during the pre-forming and the intermediate
16 or auxiliary forming steps. This plane of oscul~tion is displaced from the bushing
17 center towards the first shaping die. The auxiliar,v core can now be
18 advantageously combined with the slider into a conjointly movable unit, so that
19 the core and the first shaping chamber are provided with new cross-sectional
20 shapes for final shaping of the bushing after the unit is retracted from the first
21 working area fQr enabling the unchanged second shaping die to travel beyond
22 the bushing center for the final shaping step of the bushing.
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Whereas in devices representative for the present state of the art smaller
2 sheet bars are suspended from a support tape centered above a rib, the sheet
3 bars in the method according to the invention are secured to the support tape via
4 two ribs located near the end sections of the sheet bar. Consequently, the sheet
5 bar can be positioned more accurately inside the rounding device. Since these
6 ribs leave shear marks on the bushing face after separation from the support
7 tape, the bushings fabricated with the inventive method or inventive device, as
8 the case may be, are dirrerenliated from the state of the art in that the shear
9 marks are located near the quarter girth proximate to the slot in the bushing.
11 The three-step rounding method wherein the cross-sections of the core
12 and shaping chambers are changed, provides for a careful and very precise
13 rounding of sheet bars, enabling extremely delicate laminated sheet bar
14 structures to be shaped by the inventive method.
16 The width of both shaping dies of the inventive device is at least double
17 the width of the bushing to be rounded and include in the axial direction aside
18 from the shaping chambers at least one sizing chamber, wherein both sizing
19 chal"bers are the mirror image of each other, but are otherwise identical and
20 have the same curvature as the respective shaping chambers; the sizing
21 chambers, however, span only an angle at circumference of 180~. Both sizing
22 chambers form a sizing cavity which is closed at the circumference and
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co" espGnds to the outer bushing envelope. This sizing cavity includes a
2 spreader device, preferably in the form of a spreader sleeve, adapted for
3 expansion or contraction by means of an interior cone axially movable by an
4 ~ctu~tor rod.
s
6 This advanced feature advantageously allows not only shaping of a
7 bushing with the same tool, but also sizing of the bushing by using the same tool
8 in a second working area, thus obviating the need for repeatedly withdrawing
9 and inserting the sheet bars and bushing blanks and the inaccuracies
associated therewith.
11
12 An embodiment of the invention will be described hereinafter in greater
13 detail with reference to the drawing.
14
The drawing shows in:
16
17 FIG. 1 - FIG. 6 The shaping device with the sheet bar to be shaped,
18 showing sl~ccessive operating sequences;
19
FIG. 7 - FIG. 12 Cross-sectional views of the shaping device during
21 the operali~1g sequences corresponding to the respective views.
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The figures schematically depict fixturing parts of a shaping device 10
2 comprising a first shaping die 12, a second shaping die 14, a circular-cylindrical
3 hollow core 16, an auxiliary core 18 and a slider 20 slidably supported on the
4 first shaping die 12 for axial movement parallel to the core 16. The auxiliary
5 core 18 and the slider 20 form a unit which is moved back and forth parallel to
6 the direction of the arrow A (FIG. 10) by an actuator (not shown). The first
7 shaping die 12 includes a shaping chamber 22 formed as a section of a cylinder
8 and having a partly cylindrical bottom. In the region of the slider 20, the partly
9 cylindrical inner surface of the shaping chamber 22 becomes semicylindrical,
10 and terminates with parallel inner surface sections at the face plane 23 of the
11 first shaping die 12.
12
13 The second shaping die 14 comprises two die halves 14a and 14b
14 conjointly forming a second shaping chamber 24. The second shaping
15 chamber 24 is formed approximately as a mirror image of the shaping
16 chamber 22 and has, aside from a step between the two die halves 14a and 14b,
17 a semicylindrical profile with downwardly pointing parallel inner surface sections
18 depending therer,o",. The die part 14a is supported on the die part 14b for
19 vertical displacement and is resiliently biased by a spring 15 (shown only
20 schematically) against a stop on the die part 14a in such a way that a step 17 is
21 created in the center plane of the shaping chamber 24.
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FIG. 1 shows the two shaping dies 12, 14 sp~ced apart. The core 16 is
2 fixedly supported. A sheet bar 26 is inserted into the clearance between the
3 core 16 and the face of the first shaping die 12. The shaping die 12 then moves
4 upwardly in the direction of the arrow as shown in FIG. 1 and bends the sheet
5 bar 26 in the shape of a U, as shown in FIG. 2. The center of the core which
6 coincides with the bushing center, is located below the face 23 of the first
7 shaping die 12. Consequently, the core 16 has penel, aled the shaping
8 chamber 22 by a depth which is greater than the bushing radius. As a result,
9 the 90~ and 270~ points of the bushing to be formed are located inside the
10 shaping chamber 22, thereby preventing the formed U-legs of the sheet bar 26
11 from springing outwardly, but forcing them instead to sit close to the auxiliary
12 core 18. This completes the shaping process of the sheet bar 26.
13
14 At this point, the second shaping die 14 moves downwardly, as shown in
15 FIG. 3. The ends 26' of the U-legs of the sheet bar blank are bent inwardly upon
16 touching the wall of the shaping chamber 24 and sit close to the auxiliary
17 core 18 when the auxiliary core 18 seats on the shaping die 14. The rectilinearity
18 of the U-legs of the sheet bar blank 26 is preserved in the region of the parallel
19 sections of the chamber surfaces of both shaping dies 12, 14. The step 17 in the
20 shaping chamber 24 c~uses the two leg ends 26' to be bent with a slight time
21 delay. The bending step of the two leg ends 26' between the second shaping
22 die 14 and the auxiliary core 18 represe,)ls an intervening auxiliary shaping step
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for shaping the leg ends 26' exactiy as a circular cylinder and providing them
2 already with their final shape.
4At this point, the auxiliary core 18 together with the slider 20 is retracted
5between the shaping dies 12, 14 by axial movement along the direction of the
6arrow A (FIG. 10), possibly necessitating a slight lifting of the second shaping
7die 14. Subsequently, the second shaping die 14 moves downwardly once more
8for providing the final shaping step of the bushing. After the slider 20 is pulled
9out of the first shaping die 12, the shaping die 14 can travel to a greater depth,
10beyond the face 23 of the first shaping die 12, to the bottom surface 28 of the
11shaping die 12, with the face 19 of the second shaping die 14 traveling
12downwardly beyond the center of the core, until the inner surface of the shaping
13chamber 24 bends the straight U-leg sections of the bushing blank likewise into
14a circular-cylindrical shape, thereby completing the final shaping of the
15bushing 27.
16
17The bushing ends are normally interlocked by mutually engaging
18protrusions and cut-outs provided on the bushing ends. Since the die half 14b
19initially presses one of the bushing ends against the core 16, the bushing 27 can
20be seamed and interlocked during the last phase of the downward movement of
21die half 14a. Both dies 12 and 14 subsequently separate (FIG. 5), allowing
22removal of the completed bushing 27 from the core 16.
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Figs. 7 to 12 illustrate an additional sizing process of bushing 27
2 pe,rorl"ed in the same device 10 in a second working area. For this purpose,
3 tools are secured to the right side of both shaping dies 12, 14, each tool
4 provided with a sizing chamber 34, 36 having the same curvature as the shaping
5 chambers 22, 24, but spanning only an angle at circu",ference of 180~. When
6 the dies 12, 14 are closed, the plane of osculation of the sizing chambers 34, 36
7 coincides with the center of the core. The hollow core 16 is penetrated by an
8 actuator rod 38 supporting in the second working area a cone 40 surrounded by
9 a spreader sleeve 42.
11 Starting with Figs. 5 and 11, the unit comprising the auxiliary core 18 and
12 the slider 20 moves once more to the first working area after the final shaping of
13 bushing 27 is completed, whereby the auxiliary core 18 pushes the bushing 27
14 which is located on the core 16, over the spreader sleeve 42 in the second
15 working area. The bushing 27 which was sized during the previous processing
16 cycle, is at the same time expelled from the device 10 (FIG. 12). The device 10
17 is now ready to accept a new sheet bar 26 in the first working area. The
18 processing steps of pre-shaping, intermediate shaping and final shaping of the
19 bushing 27 are repeated and the two tools 30, 32 are closed in the position
20 shown in Figs. 4 and 10, forming a cylindrical sizing cavity enclosing the
21 bushing 27. In t-his position, the ~otu~tor rod 38 is pulled in the direction of the
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arrow A (FIG. 10), ll ,ereby expanding the spreader sleeve 42 through the action
2 of the cone 40 and sizing the bushing 27.
4 Consequently, the device 10 enables - without additional handling tools -
very accurate rounding and seaming of a sheet bar 26 in a first working area and6 sizing in a second working area.
