Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PRESS FORMING METAL TUBES
FIELD OF THE INVENTION
[0001] The present invention relates to a process for manufacturing
tubular members; particularly, to such a process including a press forming
operation.
BACKGROUND OF THE INVENTION
[0002] Tubular members have historically been made by continuous roll
forming of a flat material into a tubular member having a circular cross-
section.
These tubular members can then be cut into sections or pipes of desired
length.
In order to provide tubular members with circular cross-sections that vary in
diameter along the axial length, various pipe sections have been welded
together
after formation of these tubular members.
[0003] More recently, tubular members have been formed using
various press forming processes. The use of press forming processes have
enabled more flexibility in manufacturing tubular members having cross-
sections
which vary along their axial length. Additional cross-sectional variation
along the
axial length has been achieved by subjecting the tubular members to a
subsequent hydroforming operation. There remains a desire, however, for
tubular manufacturing processes which can enable the manufacture of improved
tubular members, which can enable increased variability in the manufacture of
tubular members, which can enable costs reductions and/or which can enable
other benefits.
SUMMARY OF INVENTIVE ASPECTS
[0004] In one inventive aspect of the present disclosure a process of
making a tubular member is provided. The process includes forming a first sub-
blank having a thickness and a second sub-blank having different thickness.
The
first and second sub-blanks are joined together along a joint line to create a
flat
blank having a step at the joint between first and second sub-blanks and
opposing side edges. The blank is located between two press forming die halves
so that the step faces outwardly toward the die halves. The two die halves are
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pressed together to form the blank into a tubular member, thereby reducing the
step at the joint.
[0005] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes forming a first
sub-blank and a second sub-blank and joining the first and second sub-blanks
together along a joint line having an axial directional component to create a
flat
blank having opposing side edges. The opposing side edges of the flat blank
are
joined together to form a tubular member.
[0006] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes creating a flat
blank comprising a first portion adjoining a second portion along a boundary
line,
wherein at least one of a material and a thickness of the first portion is
different
from that of the second portion, and wherein the boundary line has both an
axial
directional component and a radial directional component. The blank is formed
into a tubular member by joining the opposing side edges of the blank
together.
[0007] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes creating a flat
blank having a tendency to spring back that varies along the axial length of
the
flat blank. A central axial force is applied to the blank to create a U-shaped
structure with two substantially parallel arms, each of the arms having a
distal
edge. Another force is applied to move the distal edges of the arms together
by a
distance, wherein the distance varies along the axial length of the U-shaped
structure.
[0008] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes forming a
substantially tubular member having an initial cross-sectional shape. The
substantially tubular member is located in a press forming die between two
female die halves which together define a mold cavity with a cross-sectional
shape that is different from the initial cross-sectional shape and that is not
substantially circular. The two female die halves are moved together to cause
the tubular member to take on the cross-sectional shape of the mold cavity.
[0009] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes forming a
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substantially U-shaped member and locating the substantially U-shaped member
in a press forming die between two female die halves which together define a
mold cavity with a cross-sectional shape that is not substantially circular.
The
two female die halves are moved together to cause the tubular member to take
on the cross-sectional shape of the mold cavity.
[0010] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes forming a first
sub-blank and a second sub-blank and joining the first and second sub-blanks
together along an arcuate joint line to create a flat blank having opposing
side
edges. The opposing side edges of the flat blank are joined together to form a
tubular member.
[0011] In another inventive aspect of the present disclosure a process
of making a tubular member is provided. The process includes forming a first
sub-blank from a flat sheet of a material and forming a second sub-blank from
a
flat sheet of a different material. The first and second sub-blanks are joined
together along a joint line to create a flat blank having opposing side edges.
The
flat blank is press formed into a substantially U-shaped member and the
substantially U-shaped member is transformed into a substantially tubular
member. The opposing side edges of the substantially tubular member are
joined together to form a tubular member.
[0012] In another inventive aspect of the present disclosure, a process
of making a tubular member is provided. The process includes forming a first
sub-blank from a flat sheet of material and forming a second sub-blank from a
flat
sheet of material. The first and second sub-blanks are friction stir welded
together along a joint line to create a flat blank having opposing side edges.
The
flat blank is press formed into a substantially U-shaped member. The
substantially U-shaped member is press formed into a substantially tubular
member. The opposing side edges of the substantially tubular member are
friction stir welded together to form a tubular member.
[0013] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter. It should
be
understood that the detailed description and specific examples, while
indicating
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the preferred embodiment of the invention, are intended for purposes of
illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention will become more fully understood from
the detailed description and the accompanying drawings, wherein:
[0015] Figure 1 is a top plan view of an exemplary blank formed in
accordance with an exemplary process of the present invention;
[0016] Figure 2 is a top plan view of an alternative exemplary blank
formed in accordance with an exemplary process of the present invention;
[0017] Figure 3 is a top plan view of another exemplary blank formed in
accordance with an exemplary process of the present invention;
[0018] Figure 4 is a top plan view of an additional exemplary blank
formed in accordance with an exemplary process of the present invention;
[0019] Figure 5 is a greatly enlarged fragmentary perspective view of a
weld joint line at an opposing edge of the blank of Figure 3;
[0020] Figure 6 is a side elevation illustration of a U-forming operation,
including a female die half and a male die half;
[0021] Figure 7 is a side elevation illustration of an overbending
operation;
(0022] Figure 8 is an enlarged perspective illustration showing an
embodiment of a female die half for use in the overbending operation;
[0023] Figure 9 is an end elevation illustration with the substantially U-
shaped structure located within the mold cavity between two female die halves;
[0024] Figure 10 is an end elevation view similar to Figure 9, but with
the mold halves pressed together;
[0025] Figure 11 is a perspective view of a substantially tubular
member;
[0026] Figure 12 is a perspective view of the substantially tubular
member of Figure 11 undergoing a welding operation; and
[0027] Figure 13 is an end view illustration similar to Figure 10, wherein
the mold cavity has a non-circular cross-section.
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DESCRIPTION OF VARIOUS PREFERRED EMBODIMENTS
[0028] The following description of the preferred embodiments) is
merely exemplary in nature and is in no way intended to limit the invention,
its
application, or uses. For example, although each of the substantially U-shaped
member forming operations and other substantially tubular shaped member
forming operations are disclosed herein as press forming operations, in
certain
instances one or more of these operations may be replaced by a roll forming
operation.
[0029] One exemplary process generally includes creating a flat blank,
forming the flat blank into a generally U-shaped structure, forming the
generally
U-shaped structure into a generally tubular structure with a small
longitudinal gap
between the distal ends of the blank, and joining the distal edges together to
complete the tubular structure. As used herein, "tubular" describes a member
that has a cross-section defined by a wall that extends completely around a
360°
circumference, regardless of the circumferential or peripheral shape of the
member. A tubular member may simultaneously have additional cross-sections
which, for example, intersect apertures in the tubular member and, therefore,
do
not provide a complete 360° wall. Similarly, as used herein "U-shaped"
structures include structures with a smooth curved radius at the base and
structures with other shaped bases.
[0030] Figures 1 through 4 illustrate various flat blanks that may
alternatively be created as part of the process. Referring to Figure 1, this
exemplary flat blank 20 is comprised of a centrally located sub-blank 22 that
has
a somewhat rectangular shape. Along each side of the centrally located sub-
blank 22 are additional laterally located sub-blanks 24, 26. Each of these
lateral
sub-blanks 24, 26 are identical and have a generally rectangular portion and a
somewhat trapezoidal portion. Each of the sub-blanks 22, 24, 26 is stamped or
otherwise formed from a flat sheet of metal.
[0031 ] Each of the lateral sub-blanks 24, 26 is then joined to the central
sub-blank 22 along a joint line 28, 30, respectively. Each joint line 28, 30
provides a boundary line between various portions of the flat blank 20. These
joint lines 28, 30 or boundary lines have an axial directional component. In
other
words, the joint lines 28, 30 or boundary lines extend in a direction that is
not
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simply perpendicular'to the axis of blank 20 and/or to the central axis of the
subsequently formed tubular member 220. In fact, in this example, the joint
lines
28, 30 or boundary lines extend in a direction that is generally parallel to
the axis
of blank 20 and/or to the axis of the formed tubular member 220.
[0032] The sub-blanks can be joined together by a welding operation
that is suitable for the material, including laser welding, gas metal arc
welding,
high frequency welding, mash seam welding, friction stir welding, or the like.
In
some cases, friction stir welding can be particularly preferred. Friction stir
welding involves holding the materials to be welded together against each
other.
A non-consumable pin (not seen) is rotated and forced into the material along
the
joint line under pressure. A shoulder associated with the pin is also
typically
brought into contact with the materials at the joint line.
[0033] The rotation of the pin heats up and plasticizes the contacting
material. As the pin moves along the joint line, material from the front of
the pin
is swept around to the rear and consolidates to form a bond between the
materials. The depth of the pin can be adjusted during welding to accommodate
for various thickness changes in the material. In addition, the pin can move
in
any direction necessary to follow complicated joint paths. Typically, the pin
can
rotate between about 180 and 300 revolutions per minute. The dowel can
typically be forced into the material under pressure between about 5,000 to
about
10,000 pounds per inch.
[0034] As indicated above, the joint lines 28, 30 or boundary lines
separate the flat blank 20 into various portions. The portion of the flat
blank 20
corresponding to the central sub-blank 22 is formed from a relatively thick
material. In addition, the portions of the flat blank 20 corresponding to the
lateral
sub-blanks 24, 26 are made from the same material as that of the central sub-
blank 22 portion, but are relatively thin in comparison thereto. Thus, a step
portion is provided at each of the joint lines 28, 30 or boundary lines as
seen in
Figure 6. Alternatively, the various portions 22, 24, 26 may be formed by
rolling a
single sheet material into various thickness portions.
[0035] Referring to Figure 2, an alternative exemplary flat blank 32 is
created that is similarly formed from two sub-blanks 34, 36 that are stamped
or
otherwise cut from a flat sheet of material. In this case, a substantially
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rectangular sub-blank 34 is cut from a sheet material that is relatively
thick. A
substantially trapezoidal sub-blank 36 is cut from a sheet of material that is
relatively thin. As discussed above, these sub-blanks are subsequently joined
together by welding or another appropriate process along a joint line 38 or
boundary line to form the flat blank 32.
[0036] The joint line 38 or boundary line has only a radial directional
component and no axial directional component. In other words, the joint line
38
or boundary line extends in a direction that is perpendicular to the axis of
blank
32 and/or to the axis of the subsequently formed tubular member. This joint
line
38 or boundary line separates the flat blank 32 into two portions. Since the
portion of the flat blank 32 corresponding to the rectangular sub-blank 34 is
formed from a relatively thin material and the trapezoidal sub-blank 36
portion is
relatively thick in comparison thereto, a step is formed at the joint line 38
or
boundary line similar to that discussed above with respect to the embodiment
of
Figure 1.
[0037] Referring to Figure 3, another alternative exemplary flat blank 40
is created. In this case, the flat blank 40 includes a portion 42 with
material that
has been treated and/or surface coated and a portion 44 with material which
has
not. Thus, as used herein, each portion 42, 44 is made of a material that is
different from the other portion. In this case, the flat blank 40 is stamped
or
otherwise cut from a flat sheet of material. The surface coating and/or
treating
can be provided to the treated portion 42 either before or after the cutting
operation.
[0038] As an alternative, the flat blank 40 can be formed from two
different sub-blanks corresponding to the two portions 42, 44 of the flat
blank 40.
The two sub-blanks 42, 44 are joined together by welding, for example, as
discussed above. Examples of different materials that can be used to form the
sub-blanks 42, 44 include mild strength steel, high strength steel, stainless
steel,
galvanized steel and annealed steel.
[0039] A boundary line 46 is illustrated that demarks the boundary
between the treated portion 42 and the untreated portion 44. In this case, the
boundary line 46 between the portions of the flat blank 40 has an arcuate
shape,
and therefore, includes an axial directional component. In fact, the boundary
line
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46 includes a segment that is substantially parallel to the axial direction.
In
addition, the boundary line 46 includes segments that are substantially
perpendicular to the axial direction. Furthermore, the boundary line 46
intersects
both opposing side edges 48, 50 of the flat blank 40.
[0040] Referring to Figure 4, an additional exemplary flat blank 52 is
illustrated which has a sub-blank 54 insert that is formed from a material
that is
different and which has a different thickness than the surrounding sub-blank
56
material. As with the flat blank 20 of Figure 1 and the flat blank 32 of
Figure 2,
this flat blank 52 is comprised of two sub-blanks 54, 56 that are joined
together
along a joint line 58 or boundary line as discussed above. As an alternative,
the
material of sub-blank 56 may not be removed in the area of the sub-blank 54.
Instead, sub-blank 54 can be welded or otherwise joined to the surface of the
sub-blank 56 to create the thicker portion.
[0041 ] The joint line 58 or boundary line has both an axial directional
component and a radial directional component. In fact, the joint line 58 or
boundary line includes two segments that are substantially parallel to the
axial
direction. In addition, the joint line 58 or boundary line includes two
segments
that are substantially perpendicular to the axial direction.
[0042] Referring to the blank of Figure 1 as representative, the
opposing edges 60, 62 of the flat blank 20 are optionally provided with an
angle
so that the opposing side edges 60, 62 are substantially parallel to each
other
during the press forming operation as discussed below. The angle can be
provided on the opposing edges 60, 62 of the blank 20 by a shearing operation
or
by a skiving operation. The skiving operation generally results in the removal
of
significantly less material than the shearing operation, which can save
meaningful
material costs.
[0043] Referring to Figure 5, an enlarged fragmentary perspective view
of the joint line 38 at the intersection with one of the opposing side edges
66 of
the flat blank 32 of Figure 2 is illustrated. It can be seen that a material
gap 70
often results when at this termination of a weld line. It is desirable to
remove
sufficient material along the opposing edge 64 that any material gap 70 at the
joint line 38 is removed as a result of the operation to provide an angled
edge
along the opposing side edges 64, 66 of the flat blank 32.
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[0044] Referring to Figure 6 and Figure 7, this exemplary process
involves locating the flat blank 20 over a pair of spaced apart rollers 72, 74
forming part of a female die half 76 and subjecting the flat blank 20 to a
central
axial force provided by the downward motion of a male die half 78. The flat
blank
20 is located so that the step created at the joint lines 28, 30 by
differences in
thickness between various portions 22, 24, 26 of the flat blank 20 face away
from
the male die half 78 and toward the female die half 76 or the outward side of
the
U-shaped member 120 into which the flat blank 20 is being formed.
[0045] As seen in Figure 7, male die half 78 moves downwardly, forcing
the flat blank 20 against the rollers 72, 74 of the female die half 76. As the
blank
contacts the bottom 80 of the female die half 76, the rollers 72, 74 are
pivoted
inwardly to overbend the blank 20 more than 180 degrees. This overbending
operation helps insure that the blank 20 remains bent at least about 180
degrees
upon being removed from the female die half 76, despite the springiness of the
15 material (i.e., the tendency of the material to spring back towards a
flatter shape).
Thus, when the blank 20 is removed from the female die half it will remain in
a
generally U-shape having substantially parallel arms 121, 123. In this manner,
the flat blank 20 is formed into a generally U-shaped member 120.
[0046] Referring to Figure 8, when, for example, the substantially U-
20 shaped member varies in thickness and/or stiffness along its axial length,
the
tendency of the substantially U-shaped member to spring back after a forming
operation can also vary along its axial length. In instances where the
tendency of
the substantially U-shaped member to spring back varies along its axial
length, it
may be desirable to apply different amounts of overbending along its length.
[0047] Referring to the blank 32 of Figure 2 as representative in this
regard, the female die half 76 includes a first section 82 that moves the arms
of
the inwardly toward each other a relative small distance along the length of
the
substantially U-shaped member 132 which corresponds to the thicker portion 34
of the blank. The female die half 76 also includes a second section 84 that
moves the arms 133, 135 inwardly toward each other a relative large distance
which corresponds to the thinner portion 36 of the blank 32. Thus, although
the
thinner portion 36 has a tendency to spring back further than that of the
thicker or
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stiffer portion 34, the two portions will be substantially aligned after being
subjected to this overbending operation and removed from the female die half
76.
[0048] Referring to Figures 9 and 10, the U-shaped member 120 is
placed in the mold cavity between two female die halves 86, 88 and subjected
to
a press forming operation. In an alternative embodiment, the lower female die
half 86 may be the same female die half 76 as used in the previous U-forming
operation. The two female die halves 86, 88 form a mold cavity therein 90.
During the press forming operation the two die halves 86, 88 are pressed
together. As the die halves 86, 88 are moved toward each other the distal ends
of the arms 121, 123 of the substantially U-shaped member 120, which
correspond to the opposing side edges 60, 62 of the flat blank 20, come into
contact with each other.
[0049] Thus, the substantially U-shaped member 120 becomes a
substantially tubular member 220 and the arms 121, 123 press against each
other to cause the substantially tubular member 220 to resist compression and
take on the shape of the mold cavity 90. In addition, this causes the material
around the step at the joint lines 28, 30 to move outwardly, creating a
relatively
smooth transition between the thicker portions 22 and the thinner portions 24,
26
of the substantially tubular member 120. This can be particularly beneficial,
for
example, when internal mandrels are used in subsequent forming operations.
[0050] Referring to Figure 11, the substantially tubular member 220 is
removed from the female die halves 86, 88 and has a small gap 227 along its
entire axial length where the distal ends of the arms 121, 123 have been
brought
together. As seen in Figure 12, the gap 227 is closed by a clamping operation
illustrated by the opposing arrows. The gap 227 can be oriented by using a
locating knife (not shown) that is removed from the gap 227 as the
substantially
tubular shaped member 220 is clamped in place. Once clamped, the distal ends
of the arms 121, 123, which correspond to the opposing side edges 60, 62 of
the
flat blank 20, are welded or otherwise appropriately joined together along
joint
line 229 as illustrated in Figure 12.
[0051] When friction stir welding is used to join the opposing side
edges together, the opposing side edges are held in place such that they can
withstand the pressures involved without separating from each other. In
addition,
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the shearing or skiving operation discussed above can be optional, depending,
e.g., upon the method of joining the opposing side edges together. For
example,
the shearing or skiving operation can in many cases be eliminated when the
opposing side edges are joined using friction stir welding. After the opposing
side
edges are joined together, the tubular member 220 may be subjected to a
subsequent press forming operation. For example, the tubular member 220 may
be subjected to a hydroforming operation.
[0052] Referring to Figure 13, the welded tubular shaped member 220
may alternatively be subjected to a subsequent press forming operation. In
this
case, the welded tubular member 220 is again placed within a die having two
female die halves 92, 94. As the die halves 92, 94 are pressed together, the
tubular member 220 takes on the shape of the mold cavity 96 female die 92, 94.
Thus, in this case, a substantially U-shaped member 120 is press formed into a
substantially tubular member 220 having an initial cross-sectional shape. The
axial gap 227 can then be welded. The substantially tubular member 220 is
subjected to a further press forming operation using a mold cavity 96 that has
a
different, non-circular cross-sectional shape.
[0053] As another alternative, the substantially U-shaped member 120
can be directly formed into a substantially tubular member 220 having a non-
circular cross-sectional shape. In this case, the female die halves 86, 88 of
Figures 9 and 10 in which the substantially U-shaped member 120 is transformed
into the substantially tubular member 220 can have a mold cavity 96 with a non
circular cross-section. For example, these female die halves 86, 88 can be
replaced with the female die halves 92, 94 of Figure 13 having a mold cavity
96
with a non-circular cross-section shape.
[0054] In either case, the non-circular cross-sectional shape can be
defined by more than two radii, each having a different dimension.
Alternatively,
the different cross-sectional shape is defined by at least three radii
separated
from each other. At least two of the three radii can have a substantially
identical
dimension. A portion of the cross-section defined by each of the three radii
can
be separated from the other portions by another radiused portion of the cross-
section, or by a substantially straight portion of the cross-section, or by
both
another radiused portion and a substantially straight portion.
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[0055] The description of the invention is merely exemplary in nature
and, thus, variations that do not depart from the gist of the invention are
intended
to be within the scope of the invention. Such variations are not to be
regarded as
a departure from the spirit and scope of the invention.
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