Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-12-17
2004-07-13
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S107000, C399S388000
Reexamination Certificate
active
06763217
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to precision forming of sheet metal and more particularly to a simplified and lower cost method for stamping raised relief features in sheet metal without inducing significant metal stresses that warp the sheet. A particular application is formation of ridges that help guide paper along high speed paper paths formed of sheet metal.
BACKGROUND AND SUMMARY
Pressing or stamping of raised relief features in sheet metal is a common operation used in fabricating many industrial components. In such processes, the sheet metal is stressed as the feature is drawn, or stretched, away from the initial planeness of the base sheet of metal. Such stresses under prior art processes warp the base of sheet metal from which the feature is drawn.
In applications where a high degree of planeness in the base sheet of a sheet metal component is required after the drawing process, prior art methods and procedures have countered the warping of the base sheet through a number of techniques. In one prior art technique, planeness can be improved by stretching the work piece, especially when the stretched sheet is rolled while stretched. U.S. Pat. No. 6,216,521 describes one such process in relation to production processes for hot rolled and quenched metal sheets. Among the shortcomings of this techniques are the requirement for expensive high pressure hydraulic equipment and gripping fixtures as well as indentations or distortions introduced into the part by the gripping fixtures themselves. In another prior art technique to increase planeness, a component is heated to soften the metal before the raised relief feature is drawn. A shortcoming of this second method is that the subsequent cooling process itself may introduce warping in the base sheet. In addition, temperatures that are hot enough to soften the metal may adversely alter the crystalline characteristics of the metal. Yet another prior art technique involves striking, or pushing small “dimples” into the workpiece to introduce surface stresses that offset the stresses previously introduced by the drawing process. Such striking process often requires manual manipulation since variations in the workpiece base substrates make the stresses introduced by drawing irregular. Such manual manipulation takes time, is imprecise, depends greatly upon the intuition and skill of the manipulator, and other ways significantly increases costs while diminishing quality.
One example of a component with raised relief features that requires a high degree of planeness in the base sheet is a substrate guide in a high speed electrostatographic printer. This guide is designed to help position any number of printing cut sheet or web substrates, including paper, transparencies, cut sheets, other plastics and, generally, any planar material suitable for printing. An example of such a paper guide component is shown in FIG.
1
. Such a guide component
10
is typically used in the portion of a printer or copier that guides the substrate to the photoreceptor. Raised relief ribs
14
-
20
and similar ribs are designed to reduce friction as paper slides over guide component
10
as well as to help paper continue in a straight path from paper feed system to the photoreceptor/substrate image transfer area, while inhibiting skew of the paper. Additionally, ribs such as
14
-
20
reduce the area of contact between guide member
10
and the copy substrate, thereby minimizing the risk that contaminant toner that falls onto guide component
10
will smudge the reverse side of the copy substrate. Ribs
14
-
16
are skewed in relation to the paper path direction in order to prevent paper edge jamming on rib edges and also to guide paper sizes from A5 to A4, in various registration modes.
FIGS. 2-4
provide close-up and cross-sectional views of guide component
10
. In
FIG. 2
, a series of ribs are shown in detail with cross-sectional perspectives indicated by lines A—A and B—B.
FIG. 3
shows the elevated cross-sectional view along line A—A of FIG.
2
. In this view, two ribs,
15
and
16
are in raised relief from base sheet
12
.
FIG. 4
shows the elevated cross-sectional view along line B—B of FIG.
2
. This cross-sectional view shows the cross-sectional raised relief profile of rib
15
in relation to base sheet
12
. In the embodiment shown in
FIGS. 1-4
, ribs
14
-
17
in guide component
10
are in the range of 15 mm long and are drawn in a relief of approximately 1.2 mm above base plate
12
. Ribs
14
-
17
are drawn with a high aspect ratio as shown particularly in FIG.
3
. Of course, the shape and dimensions of paper guide components such as guide component
10
with ribs
14
-
20
vary greatly depending upon the particular apparatus and function that they are to serve.
Under prior art processes, guide component
10
is manufactured in a progressive die cut process as indicated in FIG.
5
. This process is conventionally finished with a manual striking process to straighten the part after the progressive cutting and stamping procedures. Moving from right-to-left in
FIG. 5
, the die cut process begins at step
1
with a blank sheet
50
of stainless steel comprised of
304
alloy or similar material. Piercing slots are first begun in step
2
in a die-cut along the edges leading to a bending and cutting step in step
3
that forms slotted mounting features such as lugs
51
along each side. Another set of piercing cuts are made at step
3
to begin separation of the various guide components
10
from each other. A last separation cut is made at step
4
to separate each guide component
10
except for its end region proximate to mounting lugs
51
.
At step
6
, ribs such as ribs
14
-
20
are drawn in a stamping process. In
FIG. 5
, this drawing process takes several intermediate iterations in order to minimize the stamping force required any one step of the drawing process. At step
7
, a striking process is applied by stamping strategically placed dimples into guide component
10
in an attempt to offset the internal stresses causes by drawing step
6
. At step
8
, the long edges are folded over to increase the end-to end rigidity of guide component
10
and to form crested flat region
21
, shown in FIG.
2
. At the far left of
FIG. 5
, mounting lugs
51
are finally free cut to fully separate each guide component
10
from the base sheet
50
, thereby to form the completed guide component.
One additional step is generally after the free cut is made. Although the striking step of step
7
attempts to remove stress and to thereby provide straightness along the long dimension of guide component
10
, such automated striking process rarely succeeds in obtaining the desired straightness. Accordingly, an additional manual re-striking step is required to obtain the required flatness. This re-striking process adds cost, complexity, and, because it is manually performed, imprecision to the finished guide component
10
. The particular purpose of this re-striking process is to remove the stresses introduced along the long dimension of guide component
10
by the drawing process at step
6
that forms the ribs.
Prior art achievement of flatness across the long dimension of various portions of guide component
10
has been difficult. Without hand straightening, typical flatness of a formed guide component
10
under the prior art was as follows:
(A) end-to-end flatness over ribs such as ribs
14
-
20
: ≦3.0 mm;
(B) end-to end flatness of ribbed base sheet
12
: ≦3.0 mm; and
(C) end-to-end flatness over crested flat region
21
: ≦3.0 mm.
The reason for such lack of flatness is that the drawing process stretches metal in the vicinity of the drawn features, thereby creating differential stresses in various regions of the base metal. The result is that drawing the raised relief ribs such as
14
-
20
not only causes ripples in the ribbed base sheet
12
but, in addition, causes the metal to ripple in the crested flat region
21
as well. With manual straightening using an expensive and tedious striking process, flatnes
Bloemen Peter J. M.
Meijer Wilhelmus
Chen Sophia S.
Spooner Richard F.
Xerox Corporation
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