U.S. patent number RE33,990 [Application Number 07/565,806] was granted by the patent office on 1992-07-14 for method of forming box-like frame members.
This patent grant is currently assigned to TI Corporate Services Limited. Invention is credited to Ivano G. Cudini.
United States Patent |
RE33,990 |
Cudini |
July 14, 1992 |
Method of forming box-like frame members
Abstract
A box-like frame member is formed by compressing an
internally-pressurized tubular blank within a die having a cavity
conforming to the final box-like cross section desired for the
product, and increasing the pressure to exceed the yield limit of
the wall of the blank to expand the blank into conformity with the
die cavity. The blank is selected so that the final product and the
die cavity have a circumference preferably no more than about 5%
larger than the circumference of the blank, to avoid weakening or
cracking of the blank through excessive circumferential expansion.
The internal pressure forces the blank evenly into the corners of
the die on closing and allows the blank to be confined within the
die without sections of the die pinching the blank on closing of
the die.
Inventors: |
Cudini; Ivano G. (Woodstock,
CA) |
Assignee: |
TI Corporate Services Limited
(London, GB2)
|
Family
ID: |
26724076 |
Appl.
No.: |
07/565,806 |
Filed: |
May 15, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
046567 |
May 6, 1987 |
04744237 |
May 17, 1988 |
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Current U.S.
Class: |
72/370.22;
72/360; 72/370.26; 72/61 |
Current CPC
Class: |
B21D
11/18 (20130101); B21D 26/033 (20130101) |
Current International
Class: |
B21D
11/18 (20060101); B21D 11/00 (20060101); B21D
022/10 () |
Field of
Search: |
;72/58,60,61,62,57,63,367,369,370 ;29/421.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0001344 |
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Jan 1970 |
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JP |
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57-19114 |
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Feb 1982 |
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JP |
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57-165134 |
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Oct 1982 |
|
JP |
|
59-130633 |
|
Jul 1984 |
|
JP |
|
61-227126 |
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Oct 1986 |
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JP |
|
519593 |
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Apr 1940 |
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GB |
|
523948 |
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Jul 1940 |
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GB |
|
544466 |
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Apr 1942 |
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GB |
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Other References
Patent Abstracts of Japan, vol. 11, No. 69 (C-407) [2516] Mar. 3,
1987. .
Isachenkov, E. I., Molding by Rubber and Liquid, Mashinostroenie,
Moscow, 1967..
|
Primary Examiner: Spruill; R. L.
Assistant Examiner: Gurley; Donald
Attorney, Agent or Firm: Kinzer, Plyer, Dorn, McEachran
& Jambor
Claims
I claim:
1. Method of forming a box section frame member of which at least
an elongate portion is of uniform smoothly continuous cross
sectional profile having at least two generally opposed and planar
side faces .Iadd.and corners.Iaddend., comprising, .Iadd.providing
a die defined by die sections having open and closed positions,
.Iaddend.each having a channel section die cavity portion, a planar
mating surface portion and the cavity portion having each channel
side extending perpendicular to the mating surface portion, which
die sections in the closed position have the mating surface of each
section in mating engagement with the mating surface of each
adjacent section and the cavity portions defining a die cavity up
to about 5% larger in circumference than the circumference of
.[.the.]. .Iadd.a .Iaddend.tubular blank and with a smoothly
continuous box section cross section profile corresponding to the
box section cross sectional profile of the desired final frame
member, providing a tubular blank having a continuously smooth
arcuate cross section; .Iadd.the circumference of which is such
that forming of said blank to the shape of said die cavity will
cause expansion of the circumference of said blank by no more than
about 5%; .Iaddend.positioning the blank between open die
sections.[.j.].applying internal hydraulic pressure to the blank at
least sufficient to overcome frictional forces exerted on the blank
by the die sections on closing of the die sections and tending to
expel the wall of the blank laterally outwardly between adjacent
mating surfaces of the die sections and less than the yield limit
of the wall of the blank; closing the die sections after
pressurizing the blank to deform the blank inwardly in the areas
corresponding to the generally opposed planar side faces and to
force the blank evenly into the corners of the box section
.Iadd.profile.Iaddend.; expanding the blank circumferentially by
increasing the internal hydraulic pressure within the blank above
the yield limit of the wall until all exterior surfaces of the
blank conform to the die cavity .Iadd.and thereby increasing the
circumference of the tubular blank by no more than 5%.Iaddend.;
separating the die sections; and removing the expanded blank from
the die.
2. Method as claimed in claim 1 wherein the bottom of each channel
.Iadd.section cavity .Iaddend.is planar.
3. Method as claimed in claim 1 wherein the die cavity is of
uniform cross section throughout its length.
4. Method as claimed in claim 1 comprising bending the tube before
placing it between .Iadd.the .Iaddend.die sections each having a
cavity conforming to the bent shape of the tube. .Iadd..[.
5. Method as claimed in claim 1 wherein the circumference of the
die cavity is no more than about 5% larger than the circumference
of the tubular blank..]..Iaddend.
6. Method as claimed in claim .[.6.]. .Iadd.1 .Iaddend.wherein the
circumference of the die cavity is about 2 to about 4% larger than
the circumference of the tubular blank. .Iadd.
7. Method of forming a box section frame member of which at least
an elongate portion is of uniform smoothly continuous
cross-sectional profile having at least two generally opposed and
planar side faces and corners, comprising, providing a die defined
by die sections having open and closed positions, each having a die
cavity portion having in cross section a corner, a planar mating
surface portion, which die sections in the closed position have the
mating surface of each section in mating engagement with the mating
surface of each adjacent section and the cavity portions defining a
die cavity up to about 5% larger in circumference than the
circumference of a tubular blank and with a smoothly continuous box
section cross section profile corresponding to the box section
cross-sectional profile of the desired final frame member,
providing a tubular blank having a continuously smooth arcuate
cross section the circumference of which is such that forming of
said blank to the shape of said die cavity will cause expansion of
the circumference of said blank by no more than about 5%;
positioning the blank between open die sections; applying internal
hydraulic pressure to the blank at least sufficient to overcome
frictional forces exerted on the blank by the die sections on
closing of the die sections and tending to expel the wall of the
blank laterally outwardly between adjacent mating surfaces of the
die sections and less than the yield limit of the wall of the
blank; closing the die sections after pressurizing the blank to
deform the blank inwardly in the areas corresponding to the
generally opposed planar side faces and to force the blank evenly
into the corners of the box section profile; expanding the blank
circumferentially by increasing the internal hydraulic pressure
within the blank above the yield limit of the wall until all
exterior surfaces of the blank conform to the die cavity and
thereby increasing the circumference of the tubular blank by no
more than 5%; separating the die sections; and removing the
expanded blank from the die. .Iaddend. .Iadd.
8. Method as claimed in claim 7 wherein the die cavity is of
uniform cross section throughout its length. .Iaddend. .Iadd.9.
Method as claimed in claim 7 comprising bending the tube before
placing it between the die sections each having a cavity conforming
to the bent shape of the tube. .Iaddend. .Iadd.10. Method as
claimed in claim 7 wherein the circumference of the die cavity is
about 2 to about 4% larger than the circumference of the tubular
blank. .Iaddend. .Iadd.11. Method as claimed in claim 7 wherein the
die consists of two die sections. .Iaddend. .Iadd.12. Method as
claimed in claim 11 wherein each die section has a channel section
cavity. .Iaddend. .Iadd.13. Method as claimed in claim 12 wherein
the bottom of each channel section cavity is planar. .Iaddend.
.Iadd.14. Method as claimed in claim 13 wherein said channel
section cavities define sides, and the bottom of each channel
section cavity is substantially
perpendicular to its sides. .Iaddend. .Iadd.15. Method of forming a
box section frame member of which at least an elongate portion is
of uniform smoothly continuous cross-sectional profile having at
least two generally opposed and planar side faces and corners,
comprising, providing a die defined by die sections having open and
closed positions, each having a die cavity portion having in cross
section a corner, a planar mating surface portion, which die
sections in the closed position have the mating surface of each
section in mating engagement with the mating surface of each
adjacent section and the cavity portions defining a die cavity up
to about 5% larger in circumference than the circumference of a
tubular blank and with a smoothly continuous box section cross
section profile corresponding to the box section cross-sectional
profile of the desired final frame member, providing a tubular
blank having a continuously smooth arcuate cross section the
circumference of which is such that forming of said blank to the
shape of said die cavity will cause expansion of the circumference
of said blank by no more than about 5%, positioning the blank
between open die sections; applying internal hydraulic pressure to
the blank less than the yield limit of the wall of the blank, such
that as the blank is compressed, the internal pressure acting on
the wall of the blank is sufficient to force the wall of the blank
evenly into each of the corners defined by said die sections,
thereby, maintaining the blank within the envelope defined by the
die cavity; closing the die sections after pressurizing the blank
to deform the blank inwardly in the areas corresponding to the
generally opposed planar side faces and to force the blank evenly
into the corners of the box section profile; expanding the blank
circumferentially by increasing the internal hydraulic pressure
within the blank above the yield limit of the wall until all
exterior surfaces of the blank conform to the die cavity and
thereby increasing the circumference of the tubular blank by no
more than 5%; separating the dies sections; and removing the
expanded blank from the die. .Iaddend.
.Iadd. The method as claimed in claim 15 comprising bending the
tube before placing it between the die sections and further
providing a die which defines a cavity conforming to the bent shape
of the tube. .Iaddend. .Iadd.17. Method as claimed in claim 15
wherein the die consists of two die sections. .Iaddend. .Iadd.18.
Method as claimed in claim 15 wherein each die section has a
channel section cavity. .Iaddend. .Iadd.19. Method as claimed in
claim 18 wherein bottom of each channel section cavity is planar.
.Iaddend. .Iadd.20. Method as claimed in claim 19 wherein the
channel section cavities define sides, and, the bottom of each
channel section cavity is substantially perpendicular to its sides.
.Iaddend.
.Iadd.21. The method as claimed in claim 18 wherein said channel
section die cavity portion of each die section has each channel
side extending perpendicular to the mating surface portion.
.Iaddend. .Iadd.22. Method as claimed in claim 15 wherein the
circumference of the blank is such that forming of said blank to
the shape of said elongate portion will result in expansion of the
circumference of said blanks by no more than from about 2% to 4%.
.Iaddend.
Description
The present invention relates to a modification of the method of
forming box-like frame members which is the subject of U.S. Pat.
No. 4,567,743 issued Feb. 4, 1986 in the name Ivano G. Cudini.
In the method described in detail in the above-mentioned patent, a
box section frame member having generally opposed and planar side
frames is formed from a tubular blank by performing it in a
preforming die to deform the side walls of the blank inwardly and
thereby form the side walls with inwardly recessed concavely curved
side wall portions in areas corresponding to the areas that will
form the opposed planar side walls in the final frame member. The
deformed .[.block.]. .Iadd.blank .Iaddend.is then placed in a final
sectional die having a cavity corresponding to the desired shape of
the final frame member and after the die is closed the blank is
expanded under internal fluid pressure exceeding the yield limit of
the walls of the blank, the walls thus expanding outwardly to
conform to the interior of the final die cavity.
The preforming step is required in order to reduce the blank to a
compact profile allowing it to be placed in a final sectional die
having a die cavity not substantially larger than and preferably no
more than about 5% larger in circumference than the initial blank,
without the sections of the final die pinching the blank on closing
the die sections together. If the blank is expanded by more than
about 5% in circumference the blank tends to weaken or crack unless
special precautions are taken.
The requirement for a separate preforming step, however, increases
the complexity of the method, and requires manufacture and
operation of two distinct sets of dies, and transport of the
preformed items between the preforming and the final dies.
The inventor has now found that the incidence of pinching results
from frictional drag exerted on the blank by the surface of the die
cavity. This frictional drag locks the die surface onto the
adjacent portions of the blank as the die closes and prevents the
blank from slipping laterally into the corner portions of the die
cavity. As a result, lateral portions of the blank as seen in cross
section tend to be expelled laterally outwardly so that they form a
sharply angular portion and become pinched between the mating
surfaces of the die sections as these are closed together. Further,
the inventor has found that the frictional drag can be overcome by
pressurizing the blank with internal fluid pressure less than the
yield limit of the wall of the blank before closing the die
sections. As the die sections close, the internal pressure as the
blank is compressed inwardly in the portions corresponding to the
planar opposed side faces serves to cause the wall of the blank to
bend evenly into the corners of the die section which can thus be
of a shape of cavity corresponding to the desired final section,
the wall of the blank thus slipping over the die surface and
avoiding the pinching problem above referred to.
The present invention provides a method of forming a box section
frame member of which at least an elongate portion is of uniform
smoothly continuous cross sectional profile having at least two
generally opposed and planar side faces, comprising, providing a
tubular blank having a continuously smooth arcuate cross section;
positioning the blank between open die sections each having a die
cavity portion and a mating surface portion, which die sections in
the closed position have the mating surface of each section in
mating engagement with the mating surface of each adjacent section
and the cavity portions defining a die cavity at least as large in
circumference as the circumference of the tubular blank and with a
smoothly continuous box section cross sectional profile
corresponding to the box section cross sectional profile of the
desired final frame member; applying internal fluid pressure to the
blank at least sufficient to overcome frictional forces exerted on
the blank by the die sections on closing of the die sections and
tending to expel the wall of the blank laterally outwardly between
adjacent mating surfaces of the die sections and less than the
yield limit of the wall of the blank; closing the die sections
after pressurizing the blank to deform the blank inwardly in the
areas corresponding to the generally opposed planar side faces to
and force the blank evenly into the corners of the box section;
expanding the blank circumferentially by increasing the internal
fluid pressure within the blank above the yield limit of the wall
until all exterior surfaces of the blank conform to the die cavity;
separating the die sections; and removing the expanded blank from
the die.
The invention will now be more fully described with reference to
the accompanying drawings which show, by way of example only, one
form of method in accordance with the invention.
FIG. 1 is a perspective view showing, somewhat schematically, a
sectional die and a bent tubular blank for use in the present
method;
FIGS. 2, 3 and 4 are end views of the dies and blank of FIG. 1 in
successive stages of the frame member forming process; and
FIG. 5 which appears on the same sheet as FIG. 1, shows a
perspective view of the final frame member product.
Referring to the drawings FIG. 1 shows an upper and a lower
sectional die 11 and 13, respectively, and a bent tubular metal
blank 15 which it is desired to form into an approximately
rectangular cross section product 16, having throughout the uniform
cross section shown in FIG. 4 and comprising relatively long upper
and lower planar sides 17 and 19 and planar opposite lateral sides
21 and 23, the sides being interconnected smoothly by rounded
corners, as seen in FIG. 4.
It is desired in this example to form a box section frame member 16
of approximately S shape. The upper and lower dies are therefore
provided with channel section die cavities of corresponding form,
each cavity being uniform along its length and as seen in plan
comprising parallel offset opposite end portions 25 and 27, an
intermediate portion 29 inclining between the portion 25 and 27 and
arcuate elbow portions 31 and 33 connecting between end portion 25
and intermediate portion 29 and between the latter portion 29 and
the opposite end portion 27.
The cavity formed on closing together of the sections 11 and 13 is
of uniform cross section throughout its length, and corresponds to
the outer surface profile desired for the product shown in FIG. 4.
Hence, as best seen in FIG. 2 the channel section cavity in each
die section has an approximately planar bottom and in cross section
has a cavity consisting of a relatively long linear side segment
35, short linear lateral side segments 37, and rounded corners 39
smoothly continuously connecting the segments 37 and 37.
The staring material cylindrical tubular blank (not shown) is first
bent into a shape conforming approximately to the desired S shape
of the product frame member, without changing the circumference of
the cross section of the tubular blank. In the present case,
therefore, the cylindrical blank is first bent into an approximate
S shape as seen in FIG. 1, which is of circular section
throughout.
The starting material blank is selected so that its circumference
is the same as or somewhat less than the circumference of the die
cavity formed on closing together the sections 11 and 13, and hence
also of the final frame member 16.
Desirably, the circumference of the blank 15 is selected so that
the circumference of the product frame member 16 as seen in FIG. 4
is at no point more than about 5% larger than the circumference of
the starting material blank 15. At least with the readily available
grades of tubular steel, if the blank is expanded in circumference
by more than about 5%, there is a tendency for the material of the
wall of the blank to excessively weaken or to crack. While
expansions of the tube circumference of up to about 20% can be
performed if the metal of the tube is fully annealed, it is
preferred to conduct the method without employing special
pretreatments of the material of the blank, such as annealing. In
the preferred form, in order to impart to the blank desired cross
sectional profiles without introducing points of weakness, or
cracking the wall of the tube, the product frame member 16 has, at
all cross sections, a profile with a circumference which is
uniform, and is in the range about 2 to about 4% larger than the
circumference of the blank 15.
In order to avoid structural weaknesses in the product, it is
desirable to select the design of the product so that at all
transverse cross sections, the profile is smoothly continuous, and
does not include sharp angularities or discontinuities which can
give rise to concentrations of stress and can lead to structural
weaknesses. Thus, for example, in the product 16 shown in FIG. 4,
the sides are joined through gently rounded corner portions, and
each of the sides 17, 19, 21 and 23 may themselves be gently
convexly curved.
In the method of forming the product 16, the cylindrical blank is
first bent into approximately the S configuration of the desired
product frame member 16, as noted above, without the blank 15
substantially changing its circumference at any cross section
thereof. The bending operation may be performed using conventional
bending procedures, for example using internal mandrels and
external bending tools, i.e. mandrel bending, or by stretch
bending, which employs no internal mandrel. These bending
procedures are generally well known among those skilled in the art,
and need not be described in detail herein. In mandrel bending, the
minimum radius of bend that may be imparted to the tube is
approximately twice the diameter of the cylindrical tube blank, and
the minimum distance between adjacent bent portions is
approximately one tube diameter. With mandrel bending, a cross
sectional area reduction of about 5% is usually achieved. Where
stretch bending, employing no mandrel, is employed, the minimum
bend radius will be approximately 3 times the diameter of the
blank, and the minimum distance between adjacent bends will be
approximately one-half of the diameter of the blank. Usually, a
cross sectional area reduction of about 15 % is achieved.
In the case of the member illustrated in the accompanying drawings,
it is preferable to use mandrel bending, employing an internal
mandrel and external bending tools.
Internal fluid pressure is then applied to the bent blank 15 by
sealing its ends and injecting liquid hydraulic fluid through one
of these seals to achieve a low internal fluid pressure within the
blank. The pressure is selected so that it is below the yield limit
of the wall of the blank 15, i.e. is below the pressure which
causes the blank to commence to .Iadd.permanently .Iaddend.swell or
expand radially outwardly, but on closing of the die is sufficient
to overcome frictional drag exerted by the die sections.
On closing of the die sections, e.g. the sections 11 and 13, the
blank 15 is compressively deformed as its upper and lower sides
engage the planar sides of the die cavity portions which in cross
section provide the linear segments 35. The compression urges the
lateral sides of the blank laterally outwardly to a point where a
lateral portion of the deformed blank engages a lateral side
segment 37 of the die cavity. One quadrant of the deformed blank as
it would be in the absence of sufficient internal pressure, is
shown in broken lines in FIG. 2, it being understood that the other
quadrants of the deformed blank are configured symmetrically with
respect to the illustrated portions. As will be seen, the deformed
lower side of the blank and the lateral side of the blank engage
the ends of the segments 35 and 37 at the zones indicated at 41 and
43, respectively in FIG. 2. Because of the reaction between the die
sections 11 and 13 and the blank 15 there is a strong frictional
force exerted on the side wall of the blank so that the side wall
is effectively locked into contact with the inner surface of the
die cavity. As a result, the side wall cannot slide transversely
over the inner surfaces of the die cavity to enter the rounded
corner 39. On compression of the blank as the die sections close
further, the lateral side portion 45 of the blank, between the
portions held by frictional zone at the zones 43, is bent outwardly
and expelled beyond the envelope which is defined by the die
cavities in the closed position.
Each die section 11 and 12 has adjacent each side of its die cavity
portion a planar mating surface portion 47, these portions being
brought into mating engagement along a single plane in the closed
position as seen in FIGS. 3 and 4. Hence, as the die closes, the
portions 45 expelled laterally from the die cavity become pinched
between the portions 47.
In the present method, the blank 15 is internally pressurized so
that as the blank is compressed the internal pressure acting on the
wall of the blank adjacent the corners 39, where the blank is
initially unsupported on its outer side is sufficient to force the
wall of the blank evenly into each of the corners 39. As a result
the wall of the blank slips transversely over the inner surface of
the die cavity, overcoming the frictional force tending to resist
such transverse slippage, the wall of the blank being thereby
maintained or withdrawn within the envelope defined by the die
cavity, and therefore the above noted pinching problem is
avoided.
The internal pressure required in order to overcome the frictional
force and to form the blank so that it is evenly forced into the
corners of the cavity can readily be determined by trial and
experiment for given dimensions and configurations of blank and of
the die cavity. Typically the pressure will be about 300 psi.
In order to avoid or reduce risk of the compression of the blank
causing a rise in the internal pressure sufficient to cause
yielding of the wall of the blank, it is desirable to maintain the
pressure within the blank below a predetermined limit less than the
yield limit of the wall of the tubular blank. This can be readily
accomplished by providing a pressure relief valve in one of the
above mentioned end seals, the valve being set to release liquid
when the pressure rises above a predetermined limit.
Where, as in the preferred form, the circumference of the die
cavity is somewhat larger, preferably up to 5% larger, than the
circumference of the tubular blank 15, a clearance will remain
between the blank 15 and the die cavity, particularly in the
corners 39, as seen in FIG. 3. Further, it is found that the
reaction between the blank 15 and the die sections 11 and 13 is
such that the sides of the blank adjacent the planar sides of the
die cavity, i.e. adjacent the linear segments 35 and/or 37, as seen
in cross section tend to be bowed or dished inwardly so that they
take on a slightly concavely curved configuration as shown
exaggeratedly in broken lines at 49 in FIG. 3.
Once the die is closed, the deformed blank can be expanded to final
form by applying internal pressure sufficient to exceed the yield
limit of the wall of the blank.
The upper and lower die sections 11 and 13 are held together with
sufficient force to prevent any movement during the procedure of
expansion of the blank to the final form. The expansion procedure
produces the cross section illustrated to a very high degree of
accuracy, uniformity and repeatability.
After the completion of the expansion step, the pressure is
released, the hydraulic fluid is pumped out of the interior of the
deformed tube, and the upper and lower die sections 11 and 13 are
separated and the final product is removed from the die.
Any material having sufficient ductility to be processed by the
method described above can be employed. In the preferred form,
wherein the final product has a substantially uniform
circumference, which is no more than about 5% larger than the
original circumference of the blank, materials such as mild steel
can be employed without any special pretreatment such as annealing.
In a typical example, a 31/2 inch diameter by 0.080 inch wall
thickness by 60 inch long tube of SAE 1010 steel was employed, and
was formed and expanded to a product having the configuration shown
in FIG. 4, the degree of circumferential expansion being about
3%.
Various modifications may be made to the procedure described above.
For example, a starting material blank 10 of a smoothly-rounded
non-circular cross section, for example of eliptical cross section,
may be employed.
In the step of deforming the pressurized blank on closing the die
sections there is limited rubbing contact between the surfaces of
the blank and the die, but this produces very little wear of the
surfaces of the die, so that excellent repeatability of the process
is obtained. Further, the die may be formed from relatively soft
and inexpensive materials, without requiring any special surface
hardening treatments In the preferred form, each die cavity in the
die sections 11 and 13 has its side surfaces 37 disposed at slight
draft angles. This avoids any tendency for the final product to
engage within the die cavity, and permits the final product to be
readily removed from the die.
Generally, lubricants do not need to be applied to the surfaces of
the blank or to the surfaces of the die sections 11 and 13.
Generally, as in the procedure described above, it is more
convenient to bend the blank 15 into conformity with the
configuration desired for the final product before deforming and
expanding the tubular blank, since this permits bending mandrels
and other bending tools which have simply curved surfaces to be
employed for engaging and bending the tube blank. It will be
appreciated, however, that, where special bending tools having
surfaces adapted to conform to the surfaces of the deformed and
expanded blank are employed, the bending operation may be carried
out after the blank has been deformed and expanded.
* * * * *