Note: Descriptions are shown in the official language in which they were submitted.
~EMMING ~RESS
Field of the Invention
This invention relates to hemming sheet metal and
more particularly to an apparatus for forming a hem on an edge of
a sheet of a structural member such as a vehicle body panel.
Backq~ound
Door, hood, and trunk deck lids of vehicles have been
formed of one unitary outer skin of sheet metal joined around
its periphery to a second inner reinforcing panel of sheet metal
by hemming a generally upturned flange along each edge of the
outer sheet over an adjacent edge of the inner panel.
m is hemming has been accomplished in two separate
stages. Prior to performing the first stage, the reinforcing
panel is nested within the outer panel fixtured on an anvil die
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on a base of a prehemming machine. Upon fixturing the assembly,
a tool of the machine, commonly referred to as a hemming steel,
engages and bends an edge of the outer panel to an acute included
angle with respect to the outer panel. ~fter the prehemming of
all edges to be joined, both panels are released, transferred
to and fixtured in a second hemming machine where a second tool
completely bends the prehemmed edge of the outer panel over the
peripheral edge of the reinforcing panel to secure and attach
the panels together as a unitary structural member for assembly
on a vehicle.
Typically, a plurality of both prehemming and final
hemming machines are respectively grouped around the periphery
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of a panel to perform all prehemming and hemming operations for
one assembly either sequentially or substantially
simultaneously. This type of hemming process and equipment has
proven to be commercially successful and is still in widespread
use.
However, this hemming process has disadvantages. Such
a two stage hemmingprocess is costly and inefficient by requiring
multiple components, namely a prehemming machine, a transfer
mechanism and a final hemming machine to perform the entire
hemming assembly operation. Additionally, a considerable amount
of tooling and transfer equipment is required for this type of
process, it consumes a great deal of valuable manufacturing
floor space and it increases the likelihood of equipment
malfunction which can undesirably delay production.
Furthermore, the process requires numerous steps to completely
hem a single component. For ~xample, the assembly must ~be
fixtured, prehemmed, released, transferred, fixtured and final
hemmed resulting in a low finished part production rate. Finally,
this two stage process requires a relatively larger sheet flange
depth which increases component weight and cost.
This two stage process is also susceptible to quality
control problems. During transfer to the final hemming station,
the panels may loosen from each other, become skewed with respect
to each other, or not be properly located'with respect to the
final hemming station resulting in a finished hemmed assembly
of lesser quality and poor structural integrity. An assembly
wlth these characteristics may have to be repaired or scrapped,
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thereby increasinq production costs and lowering profits. Even
worse, an ill-assembled structural member with these flaws, if
incorporated into an assembled vehicle may fit poorly and affect
perceived ~uality by prospective purchasers, thereby reducing
vehicle sales and profits. An assembled defective structural
member may further lose integrity as the vehicle is subjected
to road vibration during use and possibly require replacement
and negatively impact an owners' future vehicle purchasing
decision.
More recently, hemming machines have been designed
which perform both the prehem and final hem operation in a
single machine tool station which eliminates the need for a
complex transfer mechanism. Hemming machines of this type vary
in the kind of mechanism used and the manner of carrying out
the hemming operations. Representative of these hemming machines
are U.S. Patents: Rollar et al 3,191,414; E. R. St. Denis
3,276,409; Dacey Jr. 4,706,489; and Dacey Jr. S,083,355.
The hemming machines embodied in the Rollar '414 and
E. R. St. Denis '409 patents are of similar construction and
operation. Both patents disclose a pair of fluid powered drives
carried by a frame of the machine for driving a single hemming
steel through both the prehem and final hemming stages. Each
machine utilizes one drive to control the sideward motion of
the hemming tool toward the anvil and sheet during the prehem
operation and a second drive for downwardly moving the tool to
clinch the flangein a hem overlapping the structural reinforcing
panel.
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~ disadvantage of these single station prior art
machines is that the hemming tool or steel continuously contacts
the sheet edge during both stages of bending the flange which
may produce undesirable distortion and highlighting in the
sheet. A further drawback is that failure to maintain precise
actuation sequencing of the first and second drives during
hemming may result in the outer panel being defectively hemmed
to the reinforcing panel causing the costly scrapping of the
assembly. Furthermore, they have an abrupt motion of the hemming
steel due to cam drives and high actuation forces. ~lso, the
equipment to accurately sequence the actuation of each drive
adds to the complexity of the machine, reguiring additional
costly maintenance while reducing reliability. Finally, the
se~uencing complexity of this type of hemmer limits the number
of assemblieswhich may be produced during a given period of time.
Dacey Jr. '489 discloses a hemming machine utilizing
a single drive and hemming steel connected by a complicated -
system of linkages and a cam and follower arrangement to perform
both the prehem and final hem operations. Dacey Jr. '355
discloses a hemming machine having dual drives and a single
hemming steel connected by a linkage and eccentric shaft
arrangement to perform both the prehem and final hem operations.
j A shor~coming of these prior art machines is that the
hemming tool follows an arcuate sideways path, literallyRwiping~
the flange while preheDming the sheet edge which can introduce
unwanted distortion or highlights in the outer panel adjacent
the hem which are visual even after finishing and painting it.
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Moreover, the outer panel bends immediately adjacent the edge
of the inner panel rather than at a predetermined desired break
point which results in undesirable variations and
inconsistencies from one panel assembly to another. The drive
and sequencing machanism is also complicated and requires
frequent and costly production-delaying adjustment and is prone
to unacceptable wear limiting the machines commercial
usefulness.
Su~marv of the Invention
A press for prehemming and final hemming a sheet
received on an anvil with separate prehemming and final he~ming
tools or steels each driven through linkage powered by the same
prime mover, such as a cylinder or a screw and servo motor.
Each steel is mounted on a separate carrier or subframe pivotally
mounted by links in a main frame and each driven through separate
toggle joints to produce the force for bending the sheet by the
steels. Preferably, to provide a more compact structure the
pre-hem carrier is also eccentrically as well as pivotally
mounted on the main frame. Preferably, the toggle joints are
connected through rocker arms to the prime mover and the linkage
provides a dwell in the movement of the prehemming steel so that
it does not interfere with movement of the final hemming steel.
Objects, features and advantages of this invention
are to provide a combined prehemming and hemming press which
eliminates highlights, provides a consistent bréak point in the
outer panel, produces a hem with improved tolerances, requires
only one prime mover to drive both the prehemming and hemming
.
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steels, utilizes mechanical linkage to sequence and synchronize
the movement of both steels, is of relatively simple design,
compact constrl~ction and arrangement and is rugged, reliable,
durable, of economical manufacture and assembly, has a long
useful life in service and requires relatively little maintenance
and repair in use.
Brief DescriPtion of the Drawinqs
These and other objects, features and advantages of
this invention will be apparent from the following detailed
description, appended claims and accompanying drawings in which:
FIG. 1 is a fragmentary side view of a hemming press
embodying this invention.
FIG. 2 is a fragmentary front view of the hemming
press of FIG. 1.
FIG. 3 is a top view of the hemming press.
FIG.4 is a kinematicdiagram illustra~ing-aprehemming
tool and drive linkage of the press in a retracted position.
FIG. 5 is a fragementary sectional side view of an
anv l supporting a panel assembly and the prehemming tool in
the retracted position of FIG. 4.
FIG. 6 is a kinematic diagram illustrating the
prehemming tool and its drive linkage in an extended position.
FIG. 7 is a fragmentary sectional side view of the
anvil supporting the panel and the prehemming tool in the
extended position of FIG. 6.
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FIG. 8 is a kinematic diagram illustrating a final
hemming tool and its drive linkage in a retracted position in
solid lines and in an extended position in phantom lines.
FIG. 9 is a fragmentary sectional side view of the
final hemming tool adjacent the prehemmed edge of the shéet on
the anvil.
FIG. 10 is a fragmentary sectional side view of the
final hemming tool in a final hem position having formed a
return bend in the outer sheet and forced the flange into
overlapping engagement with the edge of the inner sheet of the
panel assembly received on the anvil.
FIG. 11 is a fragmentary side view of a screw drive
and servo motor operably connected with a crank arm of the
hemming press of FIG. 1.
Detailed DescriPtion
Referring in moré detail to the drawings, Figs. 1-3
illustrate a hemming press 20 embodying this invention with a
prehemming tool 22 and a hemming tool 24 for prehemming and
final hemming an upright flange 26 along an edge 28 of a sheet
' ~etal panel 30. me edge 28 to be hemmed is supported by an
--j anvil 32 fixed to a main frame 34. Each tool or steel 22 & 24
i8 received on a separate carrier or subframe 36 & 38 assembly
mounted on the main frame 34. Each steel 22 & 24 is driven by
a seprate toggle linkage assembly 40 & 42 both of which are
powered by a single prime mover 44, such as a fluid actuated
cylinder assembly.
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A single press 20 may be used to produce a finished
hem along an edge of a single sheet or an edge of an outer panel of
a nested assembly 46 of inner 48 and outer panels 50. However,
frequently either two or four of these presses are arranged
around the periphery of a sheet 30 or panel assembly 46 to
either sequentially or simultaneously hem either two or four
peripheral edges of the sheet 30 or assembly 46.
Yrame
As shown in Figs. 1 and 2, the main frame has two
pairs of upright inner 52 and outer 54 or long and short
upstanding support plates fixed at their lower ends to a base or
a base plate (not shown). ~he prehemming carrier 36 is mounted
on the inner plates 52 and the final hemming carrier 34 is
mounted on all of the plates. Preferably, the anvil 32 is also
supported by all of the plates.
For some applications, usually to facilitate insertion
in, removal from and transfer of the panels through the press
20, it is pivotally mounted so it can be tilted by stub shafts
fixed to the outer plates 54 and received in a cradle like base
~not shown).
Prehemmina Tool
The prehemming steel 22 extends longitudinally the
length of the flange to be hemmed 26 and, as shown in Fig. 1, has
a horizontally projecting lip 58 with a downwardly and inwardly
inclined face 60 which in use bears on the flange 26 to bend it
over an adjacent portion of the sheet 30, usually to an acute
included angle of about 35 to 55 and preferably about 45.
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Preferably, the face 60 is inclined downwardly and inwardly at
an angle of about 45 to the horizontal. Preferably, to limit
the extent to which the steel 22 can be advanced toward the
anvil 32, it is constructed so that its botto~ edge bears on a
shoulder 62 in the anvil 32 when the steel 22 is fully advanced
by the press 20.
Prehemminq Carrier
In use, the steel 22 is secured by cap screws 64 to
a mounting plate 66 of the carrier or subframe assembly 36.
The mounting plate 66 is fixed such by welding to a pair of
spaced apart and parallel side plates 68. The carrier 36 is
pivotally mounted on the main frame 34 for movementin agenerally
arcuate path by a pair of torque tubes 70 "2 journalled for
rotation by bearings 73 received in the side plates 68 and
eccentrically mounted for pivotal movement on the main frame
34. Each tube 70,72 is eccentrically mounted by stub shafts
74 journalled in bearings carried by the inner support plates
52 of the main frame. So that the torque tubes 70,72 can be
rotated in unison to advance and retract the carrier 36 and
~teel 22, a pair of spaced apart anms 76,78 are fixed to each
tube and connected by a link 80 and pivot pins 82 received in
- the arms.
To provide the desired arcuate motion for the steel
22, as viewed in Figs. 1 and 4, the eccentric pivot point for
~ each stub shaft 74 of the tubes 70,72 is in the lower right
hand quadrant of the tube when the prehemming steel 22 and
carrier 36 is in the fully retracted or raised position.
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This arrangment of torque tubes, location of the
eccentric pivot points, connecting arms and links provides a
compact arrangement for mounting the prehemming carrier and
steel. However, where a less compact arrangement is acceptable,
a single torque tube could be utilized by locating the eccentric
pivot points of its shaft in the upper right hand quadrant as
viewed in Figs. 1 and 4. This would eliminate the second torque
tube 72 and the interconnecting link 80 and arms 76,78.
Preh _ in~ Toqqle Joint
The carrier 36 and steel 22 are driven through a
toggle joint assembly 40 which provides a mechanical advantage
multiplying the force applied to the flange 26 of the sheet 30
as the steel 22 approaches its fully advanced position. The
toggle assembly 40 has a pair of spaced apart arms 84 fixed to
a shaft 86 journalled for rotation on the upright inner plates
52 of the frame 34and pivotally connected by a pin 88 to one end
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of a link 90, the other end of which is received between and
pivotally connected by a pin 92 to one end of a pair of arms
94 fixed to the lower torque tube 70.
Dri~e Asse~bl~
The toggle joint 40 is powered by a drive assembly
44 having a single fluid, preferably air, actuated cylinder 96
connected through linkage to the toggle joint 40. A piston rod
98 of the cylinder is connected by a clevis 100 and pin 102 to
one end of an arm 104 fixed to a drive torque tube 106 journalled
for rotation by a pair of stub shaft and bearing assemblies 108
mounted on the outer plates 54 of the main frame 34. The toggle
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joint 40 is operably connected with the torque tube 106 through
an arm 110 which is fixed at one end to the torque tube 106 and
at the other end pivotally connected by a pin 112 to one end of
a link 114, the other end of which is pivotally connected by a
pin 116 to one end of the pair of arms 84 fixed to the shaft 86
of the toggle joint assembly 40. m e housing of the cylinder 96
is pivotally mounted on the inner plates 46 of the main frame 34
by stub shaft and bearing assemblies 118 and a yoke 120 secured
to the housing.
To avoid interference and provide clearance between
the prehemming 22 and hemming 24 steels, preferably the
prehemming steel 22 dwells in its retracted postiion while the
hemming steel 24 is in its extended position, as shown in Fig.
1. This dwell is provided by the arcuate or circumferential
location of the arm 110 on the torque tube 106 relative to the
toggle assembly 40^when the pist~n-rod 98 of the cylinder 96
i~ fully extended. With these components disposed in the
position shown in Fig. 1, so that the axis of the arm 110 extends
at an angle of about 15 below a line through the centers of
the main tube lQ6 and the pivot pin 112, the prehemming steel
22 substantially dwells through about 30 of rotation of the
torque tube 106 and arm 110 by the cylinder 96.
lnal He _ ina Tool
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m e final hemming steel 24 extends longitudinally the full
; length of the flange 26 to be hemmed and has a preferably
slightly arcuate bottom face 122 which bears on the prehemmed
flange 26 and bends it to the final fully hemmed position (Fig.
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10), as the steel 24 is fully advanced by the press 20.
Preferably, the steel 24 is removably received on a spacer plate
126 which is secured to a mounting plate 128 of the carrier
assembly 38.
Final ~e ina Carrier
As shown in Figs. 1 and 2, the mounting plate 128 of
the carrier assembly 38 is fixed to the upper end of the carrier
or subframe assembly. The carrier 38 has a pair of ~paced apart
and parallel side plates 130 fixed by welds to spacer plates
132 disposed on their front edges.
The carrier is pivotally mounted on the main frame
for generally arcuate movement by four link assemblies 134.
Each link assembly has a pair of spaced apart arms 136 pivotally
connected adjacent one end by-a pin 138 to one of the carrier
~ide plates 130 and fixed adjacent the other end to a bushing
140 journalled on a pin and bearing_ assembly 142 mounted on
each pair of inner 52 and outer 54 plates of the main frame 34.
Pinal H d n~ Toqqles
The final hemming carrier 34 and steel 24 are driven
through a pair of toggle assemblies 42. Each toggle assembly
~2 has an arm 146 fixed at one end to the main drive tube 106
and adjacent the other end pivotally connected by a pin and
bearing assembly 148 to one end of a pair of toggle links 150,
the other ends of which are pivotally connected by a pin and
bearing assembly 152 to one of the side plates 130 of the carrier
assembly.
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Press OPeration
In a hemming cycle of the press 20, initially the
piston rod 98 of the cylinder 96 is fully retracted which places
both the prehemming steel 22 and the final hemming steel 24 in
their fully raised and retracted positions. The assembly 46 of
an outer panel 50 with an upturned flange 26 along an edge to
be hemmed 28 over an adjacent edge of a reinforcing panel 48
nested therein is deposited on the anvil 32. Usually, a fixture
is utilized to accurately locate the panel assembly on the anvil
32.
The prehemming operation is initiated by energizing
the cylinder 96 to advance its piston rod 98. The hemming tool
22 and carrier 36 are moved downwardly in a generally arcuate
path to bear on and bend the flange 26 from the position shown
in Fig. 5 to that shown in Fig. 7 by movement of the drive
linkage and toggle 40 from the posi$ion shown schematically in
solid line Fig. 4 to that shown in Fig. 6. ~s the toggle joint
40 moves to its mid point position (Fig. 6), it provides the
maximum multiplication of the force produced by the cylinder
96 and applied to the steel 22 as the steel approaches its fully
extended position to complete the prehemming bend of the flange
26.
To prevent distortion and highlighting of the panel
adjacent the hem during bending, the curve of the generally
arcuate movement of the steel 22 is designed to substantially
eliminate relative sliding motion between the flange 26 and the
inclined face 60 of the tool 22 as it forces the flange 26 into
its prehemmed position. This is accomplished by constructing
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and arranging the eccentric mounting of the carrier 36 to produce
a path of movement of the steel 22 complementary to that of the
flange 26 during bending about its desired break point.
After the prehemming bend is completed, the steel 22
is retracted by continuing advancement of the cylinder piston
rod 98 which continues to rotate the arm 84 of the toggle joint
40 clockwise (from the position shown in Fig. 6) to the position
shown in phantom in Fig. 4. This movement of the toggle joint
40 rotates the carrier torque tubes 70,72 clockwise which raises
and thereby retracts the carrier 36 and hence the steel 22 alon~
the generally arcuate path to its fully raised or retracted
position.
By the advancement of the cylinder rod 98, the carrier
38 and hence the final hemming steel 24 is also lowered or
advanced in a generally arcuate path from the solld line to the
- phantom line positions shown in Fig. 8 to bear on the prehemmed
flange 26 and bend it into the fully hemmed position, shown in
Fig. 10, to form a return bend with the flange 26 overlying and
finmly engaging an edge 154 of the inner panel 48. As shown in
Fig. 8, the clockwise rotation of the drive tu~e 106 moves the
toggle jo~nts 144 from the solid line position to the phantom
line position in which the toggle joints 144 approach their
respective mid points m to thereby lower or advance the steel 24
to its fully extended position. As the toggle joints 144
approach their mid point position m, they produce the greatest
multiplication of the force produced by the cylinder 96 and
applied to the steel 24 as the steel approaches its fully
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advanced position to complete the bend and force the flange 26
into firm engagement with the underlying edge 154 of the
reinforcing panel 48 to complete the hem 156.
To prevent distortion and highlighting of the panel
during final hemming, even though the carrier 38 and steel 24
move in an arcuate path, as the flange 26 approaches its fully
hemmed position (Fig. 10), the associated segment of the path
is substantially at a right angle to the plane of the final
fully hemmed position of the flange 26 and there is substantially
no relative lateral movement between the flange 26 and the face
122 of the tool 24 bearing on the flange 26. This is achieved
by the construction and arrangement of the pivotal link
assemblies 134 so that (as shown in Fig. 8) when the steel 24
approaches the fully hemmed position there is substantially no
lateral movement of the carrier 38 and steel 24 due to the
portion of the arc in which the pivot link as,,s,,e,m,bl,,ies 134,are
moving in which (as shown in phantom in Fig. 8) the longitudinal
axis through their pivot points extends substantially parallel
to the plane of the flange 26 when in its fully hemmed position.
After the finished hem is completed, the steel 24 is
retracted by actuating the cylinder 96 to move its piston rod 98
to the fully retracted position. ~his rotates the main tube
106 counter-clockwise (as viewed in Figs. 1, 4, 6 and 8), which
through the associated linkage and toggle ~oints, retracts and
raises both carriers 36,38 and their associated steels 22,24
to their fully retracted positions. As will be apparent, while
the main steel 24 is being raised and retracted, the prehemming
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steel 22 will be initially again moved to its advanced position
and then retracted. However, since the hem 156 has already
been completed, the prehemming steel 24 will not strike it when
it is advanced.
~ulti~le Presses
In some applications, it may be desirable to arrange
two or more presses to operate simultaneoulsy or sequentially
for hemming different edges on the same panel assembly while it
is received in a fixture. For example, a generally rectangular
hood assembly may have an outer panel with upturned flanges
along all four sides to be hemmed. This panel assembly could
be received on a fixture disposed between four hemming presses
each positioned to hem one of the flanges of the hood panel
assembly. To minimize the tendency of the panel being forced
during hemming to shift or move relative to the fixture, all
four edges of the panel could be prehemmed and final hemmed
simultaneoulsy. Alternatively, one pair of generally opposed
flanges can be prehemmed and hemmed simultaneously by two of
the presses and thereafter the other opposed pair of flanges
can be prehemmed and hemmed simultaneoulsy by the other two
pres~es.
Where at least two presses are operated simultaneoulsy
or in a rapid sequence, it is preferred to utilize as the prime
mover for each press a screw and servo motor 158 in lieu of a
fluid acutated cylinder. This servo motor and screw drive 158
provides a more accurate and precise control of the cycle of
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each press which facilitates synchronizing the cycle and
operation of two or more presses.
Fig. 11 illustrates a suitable screw and servo motor
prime mover 158 with a screw 160 journalled for rotation in a
housing 162 and driven by a reversible servo motor 164 which
is preferably a stepper motor. The housing is pivotally mounted
on the main frame 34 by a pair of stub shaft bearing assemblies
108 secured to the upright inner plates 52 of the frame 34. A
traveling nut 166, preferably with recirculating ball bearings,
is received on the screw 160 and pivotally connected to a pair
of arms 104 fixed to the main drive tube 106. The use of a
servo motor 164 also facilitates manual "jogging~, by controlled
stepping or manual cycling of a press for setup, maintenance
and repair purposes, such as when installing, adjusting or
changing the prehemming 22 and hemming steels 24.
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