U.S. patent application number 13/967047 was filed with the patent office on 2015-02-19 for method of hemming sheet metal panels with friction element applying a counteraction force to prevent hem creep.
This patent application is currently assigned to Ford Global Technologies, LLC. The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Alan John Gillard, Sergey Fedorovich Golovashchenko, Chatchai Wanintradul.
Application Number | 20150047178 13/967047 |
Document ID | / |
Family ID | 52465740 |
Filed Date | 2015-02-19 |
United States Patent
Application |
20150047178 |
Kind Code |
A1 |
Wanintradul; Chatchai ; et
al. |
February 19, 2015 |
Method of Hemming Sheet Metal Panels with Friction Element Applying
a Counteraction Force to Prevent Hem Creep
Abstract
A hemming tool for forming a hem securing an outer panel to an
inner panel. The hemming tool includes a hemming die that has a
first portion of a forming surface with a first coefficient of
friction and a second portion that has a second coefficient of
friction that is greater than the first portion. A flange on the
outer panel is initially engaged by the first surface to begin
forming the hem flange toward the inner panel. The flange is
engaged by the second hemming surface to continue forming the
flange toward the inner panel. A method of hemming a sheet metal
assembly including an inner and an outer panel is also disclosed
that utilizes the hemming die that has a forming surface with a
second coefficient of friction that is greater than the first
portion to reduce flange creep and roll-in during a hemming
operation.
Inventors: |
Wanintradul; Chatchai;
(Madison Heights, MI) ; Golovashchenko; Sergey
Fedorovich; (Beverly Hills, MI) ; Gillard; Alan
John; (Dearborn, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Assignee: |
Ford Global Technologies,
LLC
Dearborn
MI
|
Family ID: |
52465740 |
Appl. No.: |
13/967047 |
Filed: |
August 14, 2013 |
Current U.S.
Class: |
29/509 ; 72/419;
72/470 |
Current CPC
Class: |
B21D 19/08 20130101;
B21D 39/021 20130101; Y10T 29/49915 20150115 |
Class at
Publication: |
29/509 ; 72/470;
72/419 |
International
Class: |
B21D 39/02 20060101
B21D039/02; B21D 19/08 20060101 B21D019/08 |
Claims
1. A hemming tool for forming a hem to secure an outer panel to an
inner panel comprising: an anvil die that supports the inner panel
on the outer panel inside a flange formed on the outer panel that
extends away from the anvil die in an initial position; and a
hemming die spaced from the flange in an initial position, the
hemming die having a first portion of a forming surface that has a
first coefficient of friction and a second portion that has a
second coefficient of friction that is greater than the first
portion, wherein the first portion engages the flange to begin
forming the flange over the inner panel, and wherein the second
portion subsequently engages the flange to continue forming the
flange towards the inner panel.
2. The hemming tool of claim 1 further comprising a clamping pad
that engages the inner panel and holds the inner panel against the
outer panel on the anvil die.
3. The hemming tool of claim 1 wherein the flange is oriented at an
oblique angle relative to the outer panel and further comprising a
beveled surface outboard of the first portion of the forming
surface, and wherein the beveled surface contacts the flange before
the first portion of the forming surface to reduce the angle of the
flange from an oblique angle to an acute angle.
4. The hemming tool of claim 1 further comprising a flange
finishing tool that is inserted between the forming surface and the
flange after the second portion engages the flange to complete
forming the flange.
5. The hemming tool of claim 1 wherein the flange has a distal end
that slides across the first portion of the forming surface with
less friction than when the distal end slides across the second
portion.
6. The hemming tool of claim 5 wherein the coefficient of friction
of the second portion prevents creep on the flange.
7. The hemming tool of claim 1 wherein the hemming die defines a
recess in the second portion of the forming surface, and further
comprising an insert received in the recess and attached to the
hemming die, and wherein the insert provides the surface that has
second coefficient of friction.
8. The hemming tool of claim 7 wherein the insert is formed of
polyurethane.
9. The hemming tool of claim 1 wherein the anvil die includes an
end wall that is engaged by the hem flange as the hem flange is
formed over the inner panel, and wherein the hem flange is driven
into the end wall by the hemming tool when the second portion of
the forming surface is in engagement with the hem flange.
10. A method of hemming a sheet metal assembly comprising: loading
an inner panel and an outer panel that includes a flange into a
hemming tool that includes a hemming die that has a first hemming
surface and a second hemming surface that has a higher coefficient
of friction than the first hemming surface; engaging the flange
with the first hemming surface to begin forming the flange towards
the inner panel; engaging the flange with the second hemming
surface to continue forming the flange towards the inner panel; and
forming the flange against the inner panel.
11. The method of claim 10 further comprising: inserting a finish
hem tool between the hemming die and the flange after the second
hemming surface forms the flange towards the inner panel.
12. The method of claim 11 further comprising: retracting the
hemming die away from the inner panel and the flange after the
second hemming surface forms the flange towards the inner panel and
before the step of inserting the finish hem tool between the
hemming die and the flange.
Description
[0001] TECHNICAL FIELD
[0002] This disclosure relates to sheet metal hemming tools and
methods of hemming a flange of one panel over another panel to form
a sharp hem flange.
BACKGROUND
[0003] This disclosure is directed to hemming processes for forming
a flange into a hem that joins together two sheet metal panels.
Sheet metal panels formed from aluminum alloys and AHSS have a
reduced ability to be bent over another panel to form a hem having
a sharp radius.
[0004] Several techniques have been developed to address this
issue. In one known press hemming process, the hemming area is
compressed in a die while forming the hem. A roller hemming process
has been proposed in which local pressure is applied to the blank
to better control the hemming process than in a press hemming
process. However, the roller hemming process is substantially
slower and is feasible only for low volume or mid-volume
applications. The roller hemming process requires several roll
hemmers and possibly several sets of tools to meet the production
demands that are comparable to the production rates of conventional
hemming processes. Three passes of roller hemming tool may be
required in some instances to form a hem with some materials.
[0005] An alternative technique is to form a sharp flanging radius
during the flanging step with the inner radius being controlled by
the inner radius of the flanging die.
[0006] One problem that is not resolved is the problem of the outer
panel creeping during the hemming process. "Creep" occurs due to
the tendency of the flange to continue to bend during the
subsequent hemming process. The flanging radius may roll-in during
the hemming process. Creep causes material in the flange to move
from the outer side of the flange towards inner area of the hem.
Creep can change the overall radius of the hem and strain the
previously formed corner at the base of the flange.
[0007] This disclosure is directed to solving the above problems
and other problems as summarized below.
SUMMARY
[0008] This disclosure is of a method and tool for sharp hemming in
a press hemming operation that uses tools having selected areas
with different coefficients of friction to create a frictional
counteraction force to minimize creep and roll-in during the
hemming process. Avoiding creep and roll-in preserves the sharp
flange radius formed in the sharp flanging operation. The
frictional counteraction force is applied at certain stages of the
hemming operation using friction to limit creep. The counteraction
force is applied through the use of a high friction material or a
high friction coating on a localized part of the surface of the
tool that engages the flange.
[0009] One example of a tool that can supply a frictional
counteraction force includes a strip of polyurethane set in a
groove on the final hemming tool. The surface of the polyurethane
strip is flush with the surface of the hemming tool. Increased
frictional force is provided by the polyurethane strip.
Alternatively, the frictional counteraction force can be provided
by applying a coating of a material, or a surface treatment to a
selected limited portion of the hemming die that has a higher
coefficient of friction than the steel surface of the die.
[0010] A limited amount of friction is present at the interface
between the tip of the sheet metal flange and the steel hemming
tool. The frictional force applied by the tool changes when the tip
of the sheet metal flange reaches a predetermined point on the
hemming tool where the polyurethane strip or high friction coating
is located. The coefficient of friction of the material used to
make the insert is selected to balance the other forces applied to
the flange during hemming. The strip or coating with a higher
coefficient of friction must be disposed at a predetermined
location to contact the tip of the flange at a selected time during
the hemming process.
[0011] The hemming tool may be used to hem either closed flanges or
open flanges. A closed flange is a flange with an inner angle of
less than 90 degrees. The hemming tool may be used to form a hem on
an open flange having an inner angle greater than 90 degrees. A
hemming tool for forming an open flange may include angled outboard
sections that pre-hem the open flange to bend the flange to an
orientation that is inside of 90 degrees and in a position for
final hemming. The tip of the flange comes into contact with an
area having an increased coefficient of friction (eg. a
polyurethane insert) in the hem tool once the flange reaches a
critical point in the bending and hemming process. The polyurethane
strip applies a frictional force to the tip of the flange to apply
pressure through the flange toward the corner of the outer panel.
The frictional force counteracts the bending moment that causes
creep and roll-in during the hemming processes.
[0012] According to one aspect of this disclosure, a hemming tool
is provided for forming a hem to secure an outer panel to an inner
panel. The hemming tool comprises an anvil die that supports the
inner panel on the outer panel inside a flange formed on the outer
panel that extends away from the anvil die in an initial position.
A hemming die is spaced from the flange in the first position. The
hemming die includes a first portion of a forming surface that has
a first coefficient of friction and a second portion that has a
second coefficient of friction that is greater than the first
portion. The first portion engages the flange to begin forming the
flange over the inner panel, and the second portion subsequently
engages the flange to continue forming the flange towards the inner
panel.
[0013] According to other aspects of this disclosure, the flange
may be oriented at an oblique angle relative to the outer panel,
and a beveled surface may be provided that is outboard of the first
portion of the forming surface. The beveled surface may contact the
flange before the first portion of the forming surface to reduce
the angle of the flange from an oblique angle to an acute angle. A
flange finishing tool may be inserted between the forming surface
and the flange after the second portion engages the flange to
complete forming the flange.
[0014] According to additional aspects of this disclosure, the
flange has a distal end that slides across the first portion of the
forming surface with less friction than when the distal end slides
across the second portion. The increased friction force of the
second portion prevents the flange from bending at a larger radius
outside the initial flange radius. The hemming die may define a
recess in the second portion of the forming surface and an insert
may be received in the recess and attached to the hemming die. The
insert may provide the surface that has second coefficient of
friction or the area may be provided by coating, machining or
otherwise treating the surface to create a surface with a higher
coefficient of friction that the first portion of the surface.
[0015] The anvil die may include an end wall that is engaged by the
hem flange as the hem flange is formed over the inner panel. The
hem flange may be driven into the end wall by the hemming tool when
the second portion of the forming surface is in engagement with the
hem flange.
[0016] According to another aspect of this disclosure, a method of
hemming a sheet metal assembly is disclosed that provides a sharper
radius and reduced creep and roll-in. The method includes loading
an inner panel and an outer panel that includes a flange into a
hemming tool. The hemming tool includes a hemming die that has a
first hemming surface and a second hemming surface that has a
higher coefficient of friction than the first hemming surface. The
flange engages the first hemming surface to begin forming the
flange towards the inner panel. The flange then engages the second
hemming surface to continue forming the flange towards the inner
panel until the hem flange is formed against the inner panel.
[0017] According to other aspects of the method, a finish hem tool
may be inserted between the hemming die and the flange after the
second hemming surface forms the flange towards the inner panel.
The method may also include the step of retracting the hemming die
away from the inner panel and the flange after the second hemming
surface forms the flange towards the inner panel and before the
step of inserting the finish hem tool between the hemming die and
the flange.
[0018] The above aspects of this disclosure and other aspects will
be described in greater detail below with reference to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a fragmentary perspective view of a hemming die
for a hemming tool that includes an area having an increased
coefficient of friction, for example, a polyurethane insert;
[0020] FIG. 2 is a cross-sectional view taken along line 2-2 in
FIG. 1;
[0021] FIG. 3 is a cross-sectional view of a hemming tool including
a hemming die and anvil die shown engaging a flange prior to
hemming over an inner panel flange;
[0022] FIG. 4 is a cross-sectional view similar to FIG. 3 showing
the flange engaging a polyurethane insert;
[0023] FIG. 5 is a cross-sectional view similar to FIG. 3 showing a
rigid tool disposed between the hemming die with a polyurethane
insert and the hem flange;
[0024] FIG. 6 is a cross-sectional view similar to FIG. 3 showing
the hem being completed with the rigid tool;
[0025] FIG. 7 is a cross-sectional view of a hemming tool and anvil
engaging an open flange at the beginning of a hemming operation;
and
[0026] FIG. 8 is a cross-sectional view similar to FIG. 7 showing
the flange being formed toward the flange of the inner panel.
DETAILED DESCRIPTION
[0027] A detailed description of the illustrated embodiments of the
present invention is provided below. The disclosed embodiments are
examples of the invention that may be embodied in various and
alternative forms. The figures are not necessarily to scale. Some
features may be exaggerated or minimized to show details of
particular components. The specific structural and functional
details disclosed in this application are not to be interpreted as
limiting, but merely as a representative basis for teaching one
skilled in the art how to practice the invention.
[0028] Referring to FIGS. 1 and 2, a hem die 10 is illustrated that
may be used to form a relatively small hem flange. It should be
understood that additional hem dies may be used in conjunction with
the illustrated hem die to form a larger hem. Alternatively, a
longer hem die 10 may be provided and the hem die may be curved or
non-linear. The hem die 10 includes a flange engaging surface
generally indicated by reference numeral 12. A beveled edge 14 is
shown that may be used to deflect a hem flange inwardly, but it
should be understood that the beveled edge 14 is optional and may
not be required in all applications. A recess 16 is formed in the
flange engaging surface 12, and a polyurethane insert 18 may be
received in the recess 16.
[0029] The flange engaging surface 12 is divided into a first
portion 22 and a second portion 24. The second portion 24 comprises
the surface of the polyurethane insert 18 in the illustrated
embodiment. The first portion 22 has a coefficient of friction that
is less than the coefficient of friction of the second portion 24.
Instead of providing a polyurethane insert 18, an insert made of
another material having a different coefficient of friction than
the first portion 22 may be used.
[0030] In another alternative, the second portion 24 may be
provided with a higher coefficient of friction by machining,
grinding, etching or otherwise treating the second portion 24 of
the flange engaging surface 12.
[0031] Referring to FIG. 3, a hemming die assembly 30 is shown with
an outer panel 32 and an inner panel 34. The outer panel 32 and
inner panel 34 are supported by an anvil die 36. The anvil die 36
includes a wall 38 that constrains the outer panel 32 while a hem
is being formed by the hem die 10. The hem die 10 is reciprocated
relative to the anvil die 36.
[0032] A clamp 40 may be provided to hold the inner panel 34
against the outer panel 32 during a hemming operation. The clamp 40
engages a flange 42 on the inner panel 34 and holds the flange 42
against the outer panel 32.
[0033] In the embodiment shown in FIGS. 3-6, the flange 44 extends
at an acute angle of slightly less than 90.degree. relative to the
other portions of the outer panel 32. The flange 44 has a distal
end 46 that is initially engaged by the flange engaging surface 12
of the hem die 10. The first portion 22 of the flange engaging
surface 12 initially contacts the distal end 46 of the flange 44.
The first portion 22 bends the flange 44 inwardly. The distal end
46 slides across the first portion 22 with the sliding action of
the distal end 46 across the first portion 22 being resisted by the
friction provided by the first portion 22 against the flange
engaging surface 12.
[0034] Referring to FIG. 4, the hemming process is shown at a later
stage. The distal end 46 of the flange 44 is in contact with the
second portion 24 that, in this embodiment, comprises the surface
of the polyurethane insert 18. The coefficient of friction of the
polyurethane insert 18 is higher than the coefficient of friction
of the first portion 22 and, as a result, greater resistance is
encountered to the sliding movement of the distal end 46 over the
second portion 24 of the polyurethane insert 18. The hem die 10 may
continue to form the flange 44 until it fully engages the flange 42
of the inner panel 34.
[0035] Referring to FIGS. 5 and 6, the flange 44 may require an
additional tool element to complete the hemming operation due to
the reduced rigidity of the polyurethane insert 18 and the material
used to form the outer panel 32.
[0036] Referring to FIG. 5, a finish hem tool 50 that may be formed
of tool steel may be used to complete the hemming operation. The
hem die 10 is retracted from the position shown in FIG. 4 and the
finish hem tool 50 is inserted in the direction indicated by the
arrow on the left side of FIG. 5 between flange engaging surface 12
including the polyurethane insert 18 and the flange 44. A slide cam
assembly 51 may be used to insert and retract the finish hem tool
50. Alternatively, a gas cylinder, hydraulic cylinder, or linear
motor drive may be used to move the finish hemming tool 50.
[0037] Referring to FIG. 6, the hem die 10 is shown after driving
the finish hem tool 50 into engagement with the flange 44 (shown in
FIG. 5) to hem the outer panel 32 to the inner panel 34. The outer
edge 54 of the hem flange 52 is shown engaging the wall 38. The
outer edge 54 of the hem flange 52 is formed into a tight radius to
insure superior fit and finish of the hem flange 52.
[0038] Referring to FIGS. 7 and 8, a hem die 10 is shown with a
flange closing member 56 that closes a flange 58 that extends from
outer panel 32 at an obtuse angle that is slightly greater than
90.degree.. The flange closing member 56 functions to begin closing
the flange 58 causing the hem flange 58 to slide toward the first
portion 22 of the flange engaging surface 12. As shown in FIG. 8,
the flange 58 has a distal end 60 that is shown in engagement with
the first portion 22 of the hem die 10. The hem die 10 continues
moving toward the flange 42 of the inner panel 34, as shown in FIG.
4. The flange continues to slide across the second portion 24 of
the flange engaging surface 12. The higher coefficient of friction
of the second portion 24 forces the flange 58 toward the wall 38
and reducing flange creep or roll-in as the flange 58 is formed
into a finished hem flange 52 (as shown in FIG. 6).
[0039] As shown in FIG. 6, the hem die 10 may continue moving
towards the flange 42 of the inner panel 34 to complete the
formation of the hem flange 52. The finish hem tool 50 may be used
with the embodiment shown in FIGS. 7 and 8 depending upon the
malleability of the material comprising the hem flange 52.
[0040] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
disclosed apparatus and method. Rather, the words used in the
specification are words of description rather than limitation, and
it is understood that various changes may be made without departing
from the spirit and scope of the disclosure as claimed. The
features of various implementing embodiments may be combined to
form further embodiments of the disclosed concepts.
* * * * *