Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROMAGNETIC (EM) METAL FORMING TECHNIQUES FOR
HYDROFORMING PIERCE PUNCHES DRIVEN VIA EM ENERGY, FOR
FORMING TUBULAR METAL WORICPIECES OVER A MANDREL, AND
FOR MAKING CAMSHAFT' ASSEMBLIES
Field Of The Invention
[0001] The present invention generally relates to the field of manufacturing
vehicle
parts, and more particularly to the field of electromagnetic metal forming
techniques
for hydroforming and finishing vehicle parts, for forming tubular metal
workpieces,
and for making camshaft assemblies.
Background Of The Invention
[0002] Hydroforming methods are commonly known as a means for shaping hollow
metal blanks into a component of a predetermined configuration. In particular,
a
typical hydroforming operation involves the placement of a tubular metal blank
into a
hydroforming die cavity and providing a high pressure fluid to the interior of
the blank
to cause the blank to expand into conformity with the surfaces defining the
die cavity.
More particularly, the opposite longitudinal ends of the tubular metal blank
are sealed,
and high pressure water is provided through a hydroforming port or ram sealing
one of
the tubular ends. The fluid provided within the tube is pressurized by a
conventional
intensifier.
[0003] Hydroformed components may be further processed after hydroforming to
their final configuration. Finishing operations may be performed, for example,
by
laser cutting. However, laser cutting is considered a relatively time
consuming and
expensive procedure.
[0004] U.S. Patent No. 6,751,994 issued to Horton et al. and entitled "Method
and
Apparatus for Forming a Structural Member" discloses an apparatus and method
for
using electromagnetic energy to form structural members of the type that may
be used,
for example, in the construction of motor vehicles. The method disclosed
therein may
utilize one or more electromagnetic discharges to move the metallic material
of a wall
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or walls of a workpiece against a die surfaces of a processing die to trim,
pierce and/or
shape the workpiece. The workpiece is first hydroformed in a hydroforming die
and
then transferred to the processing die. The hydroformed workpiece is placed in
the
processing die and a discharging element is inserted into the workpiece so
that the
walls of the workpiece are positioned between the surfaces of the die cavity
of the
processing die an dthe discharging element. When the discharging element is
actuated, the metallic wall of the workpiece presses against the surfaces of
the die
cavity of the processing die. The surfaces of the processing die may be
constructed to
trim, pierce, and/or shape the wall of the hydroformed workpiece.
[0005] It is often necessary that hydroformed parts have various holes and
openings,
for fasteners, location features, etc. As described heretofore, it is possible
to punch or
drill these holes subsequent to the hydroforming operation, but it would be
desirable
to do it simultaneously, in-die. This obviates the need to form the holes in a
subsequent operation, such as by drilling, plasma cutting, or laser cutting,
after the
part has been removed from the hydroforming dies. It is known that one or more
holes required in a hydroformed part may be pierced in the part while the part
remains
in the dies by using the hydroforming pressure to effect the piercing
immediately
following the forming of the part with this pressure. Such piercing operations
performed with the hydroforming fluid used to form the part are referred to as
hydropiercing.
[0006] A prior known hydroforming apparatus including an in-die hydropiercing
apparatus is disclosed by Shimanovski et al. in U.S. Patent No. 5,398,533.
[0007] Typically, the hydropiercing is accomplished by hydraulic cylinders. If
more
than one hole or opening is to be provided in the hydroformed part, the
sequencing of
the hydraulics for multiple cylinders is an issue which needs to be addressed.
During
the hydropiercing sequence of the hydroform cycle, several hydraulic cylinders
of
various diameters attempt to stroke, i.e. move forward, simultaneously. This
action
requires a tremendous amount of oil volume and pressure which is very costly
to
achieve in traditional hydraulic systems. The loss of flow and pressure during
the
hydropiercing sequence can cause some cylinders to stroke after others which
in turn
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can result in poor quality pierced holes. In order to obviate these problems
it is
commonly attempted to sequence the hydraulic cylinders to force them to pierce
at the
same time. Alternatively, it is attempted to size the hydraulic system to
compensate
therefore and to use accumulators. These attempts require considerable effort
while
being very costly and not very reliable.
[0008] Another issue in traditional hydropiercing systems is the die integrity
due to
large hydraulic cylinders that are machined into the die cavity. The hydraulic
cylinders required for hydropiercing are large in size and require lots of
material to be
removed from the primary hydroform cavity for mounting.
[0009] Furthermore, traditional hydropiercing systems are expensive in order
to
integrate the hydraulics and cylinders since the machining required for
mounting, the
valving, and the piping of oil add tremendously to the costs of the
hydroforming dies.
[0010] Therefore, it is desirable to provide a method and an apparatus to
reduce the
problems with traditional hydropiercing systems.
[0011] It is desirable to provide a hydropiercing process and apparatus
wherein the
hydraulic cylinders would operate more rapidly and simultaneously.
[0012] It is desirable to provide a hydropiercing apparatus that is smaller
than a prior
art hydropiercing apparatus and packages more easily into the hydroforming
die.
[0013] Furthermore, it is desirable to provide a more cost effective
hydropiercing
process and apparatus
[0014] Metal spinning is an efficient and flexible metal forming process to
produce
axial-symmetric hollow bodies in a variety of shapes. Metal spinning allows to
form a
wide range of materials, such as steel, stainless steels, light metals like
aluminum and
titanium and non-ferrous high-density metals like brass, nickel, and tungsten.
[0015] A metal disc blank or pre-form that is produced by drawing or stamping
is
concentrically clamped against the spinning mandrel by the pressurized
tailstock. The
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main spindle then starts to rotate while a spinning roller makes frictional
contact
progressively reforming the original blank or perform until the metal lies
internally on
the spinning mandrel.
[0016] One method of metal spinning and flow forming is tube spinning. A
tubular
preform is placed on a cylindrical mandrel typically made of a hardenable
steel.
Forming rollers with specific profiles are set at predetermined distances from
each
other and the mandrel. When the tube spinning machine is activated and in
dependence upon the configuration of the machine, the rollers either traverse
the
mandrel or the mandrel passes between the stationary, rotating rollers. The
result is a
tube whose material has been significantly cold worked and dimensionally
controlled
by the spinning process to yield a product with uniform or variable wall
thickness,
diameter, and length features.
[0017] When the preform has one closed or semi-closed end, such as a vessel,
the
bottom typically rests against the face of the mandrel while the material
being
flowformed is moved in the same directions as the rollers. This technique is
called
forward flowforming. When the preform has two open ends, such as a tube,
reverse
flowforming is used, in which the force applied by the rollers pushes the
material
against a serrated ring at the end of the mandrel. The ring is driven by and
rotates
with the mandrel. As the rollers compress and extrude the material against the
ring,
the material flows under, and in the opposite direction, of the rollers.
[0018] Using multiple rollers that may be staggered and set at different gaps,
multiple
reductions can be formed in a single machine pass.
[0019] However, the spinning technology is slow and expensive, particularly
having
regard to automotive applications.
[0020] It is desirable to provide an alternative process to the spinning metal
forming
technology.
[0021] It is desirable to provide a metal forming technique with a shorter
cycle time
and hence lower cost.
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[0022] It is further desirable to provide a novel metal forming technique
using an
external electromagnetic coil over a mandrel.
[0023] In the history of the internal combustion engine, camshafts were cast
from iron
in molds and then underwent several finishing processes until the cam lobes
and the
shaft were in precise orientation with respect to one another so as to
facilitate a
precision valve control on combustion engines. Many improvements and different
methods have since been realized. For example, continuous attempts to improve
automobile fuel consumptions have become a major social concern so as to
preserve
fuel reservoirs and protect the environment. As a result, a lightening of
automobile
parts including camshafts has received keen attention.
[0024] Methods of making camshafts for internal combustion engines from hollow
tubular shafts are known in the prior art. For example, U.S. Pat. No.
4,293,995 to
Jordan discloses a method of making a camshaft for reciprocal piston engines
whereby
cams having irregularly shaped apertures are arranged on a hollow shaft and
secured
in a die. The hollow shaft is then widened by means of a rubber rod which
substantially corresponds to the inner diameter of the hollow shaft. The
rubber rod is
compressed from both ends to cause the body of the rod to expand. The hollow
tubular shaft is widened to such an extent that the outside wall of the shaft
surrounded
by the cam reaches into the irregular inner form of the cam producing a tight,
secure,
fit. In addition, the patent also discloses the use of hydraulic or electro-
hydraulic
expansion of the shaft.
[0025] Japanese Patent Application No. 46-21299 relating to a method for
shaping a
camshaft discloses a structure in which a shaft tube and a cam, a journal or
the like are
jointed by setting the cam, the journal or a shaft head in a split mold, by
inserting the
shaft tube into the axial hole of the journal and by radially expanding the
shaft tube
through a die or mandrel.
[0026] Japanese Patent Application No. 5-288014 relating to a camshaft
discloses a
structure in which the camshaft is assembled from a camshaft made of a
sintered alloy
and a camshaft made of a steel pipe by constructing an inner piece and a
hollow shaft
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of an easily expandable steel and by expanding and jointing them with a high-
pressure
fluid and a mandrel.
100271 Japanese Patent Application No. 53-102861 relating to a method for
jointing a
ring to a hollow shaft discloses a structure in which the cam on the hollow
shaft is
fixed in the tuning direction and in the axial direction by forming paddings
on the two
sides of the ring of the hollow shaft.
100281 Japanese Patent Application No. 8-158817 relating to a method for
manufacturing an assembly-type camshaft discloses a structure in which a
projection
of a shaft is registered with a groove of a cam or cam lobe and is bulged and
press-
fitted in the groove by expanding the shaft.
[0029] Other methods include to drive a ball or mandrel of larger diameter
than the
interior diameter of the tubular shaft to expand the same into engagement with
the
interior apertures in the lobes. Such methods require close tolerances in the
lobes,
tube thickness and mandrel or ball.
100301 U.S. Pat. No. 2,892,254 to Garvin discloses a method of making a
camshaft
wherein the cam lobes are formed from the tubular shaft by the application of
internal
pressure to the tubular shaft while the shaft is contained in a die having
cavities
conforming to the shape of the lobes. The cam lobes are formed one at a time
in
sequence in the die by the application of hydraulic pressure within the
tubular shaft
such that the shaft expands into the cavities of the die thereby forming the
cam lobes.
100311 Associated problems with manufacturing camshafts from hollow tubular
shafts
by using hydraulic pressure to expand the tubular shaft outwardly include
expensive
and elaborate piston cylinder arrangements that are utilized to create
sufficient
hydraulic pressure for the expansion of the tubular shaft. Furthermore, the
manufacturing of hollow camshafts via hydroforming requires the use of high
internal
pressures and as a result all systems associated with hydroforming such as
expensive
dies, end sealing and feeding, large press tonnage, and high cost tooling.
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[0032] It is desirable to provide a light assembled hollow camshaft for
engines having
good mechanical durability and maintainability, and a production method
therefore.
[0033] It is desirable to provide a more cost effective method of
manufacturing a
camshaft having a hollow shaft.
[0034] It is further desirable to provide an electromagnetic (EM) coil capable
of
generating sufficient pressure to deform the tubular blank onto the camshaft
lobes
instead of using hydroforming fluid pressure.
Summary Of The Invention
[0035] An object of the present invention is to overcome the problems
delineated
hereinabove. In accordance with this object, the present invention provides an
apparatus for forming a metal work piece into a structural member comprising a
hydroforming mold assembly for hydroforming a metal blank into a hydroformed
member, said hydroforming mold assembly comprising a trimming/piercing
assembly
comprising an electromagnetic coil and an electromagnetic driver for
trimming/piercing the_hydroformed member into the structural member, said
electromagnetic coil and said electromagnetic driver being arranged opposite
to each
other.
[0036] In accordance with another aspect of the invention, the electromagnetic
driver
further comprises an electromagnetic top plate and a trimming/piercing tool.
The
electromagnetic top plate is arranged opposite to the electromagnetic coil and
the
trimming/piercing tool is arranged opposite to the workpiece.
[0037] In accordance with yet another aspect of the invention, the apparatus
further
comprises an electric discharge circuit for discharging the electric discharge
circuit so
as to trigger the electromagnetic driver. The electric discharge circuit is
connected to
the electromagnetic coil.
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[0038] In accordance with a further aspect of the invention, the apparatus
further
comprises a control circuit for timing the electrical discharge circuit. The
control
circuit is connected to the electric discharge circuit.
[0039] In accordance with a further embodiment of the invention, the
trimming/piercing tool is a punch tool for providing an opening through an
interior
wall portion of the hydroformed member to form the structural member.
[0040] In accordance with the invention there is further provided, a method of
forming a metal blank into a structural member of a predetermined shape
comprising
the following steps of placing the metal blank in a hydroforming mold, said
hydroforming mold comprising an electromagnetic trimming/piercing assembly;
hydroforming the metal blank to form a hydroformed member; and applying
electromagnetic energy for at least one of trimming and piercing the
hydroformed
member while the hydroformed member remains in the hydroforming mold.
[0041] In accordance with another aspect of the invention, the step of
applying
electromagnetic energy includes the steps of delivering an electric current to
an
electromagnetic coil and inducing a current in an electromagnetic driver, said
electromagnetic driver including a trimming/piercing tool, and wherein said
structural
member is trimmed/pierced by the trimming/piercing tool as a result of the
repulsive
forces generated by the induced current in the driver.
[0042] In accordance with a further aspect of the invention, the driver is
formed by
disposing an electromagnetic top plate on the driver opposite to the
electromagnetic
coil.
[0043] In accordance with yet another aspect of the invention, the
hydroforming mold
comprises more than one electromagnetic trimming/piercing assemblies.
Furthermore, the method comprises the additional step of controlling the more
than
one electromagnetic trimming/piercing assemblies by a control circuit for
controlling
the discharge circuit.
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[0044] In accordance with one embodiment of the invention, the control circuit
times
an electrical discharge such that all discharges are occurring in a
predetermined
sequence.
[0045] In accordance with another embodiment of the invention, the control
circuit
times an electrical discharge such that all discharges are substantially
simultaneous.
[0046] In accordance with another aspect of the invention, the
trimming/piercing tool
is a punch tool for providing an opening through an interior wall portion of
the
hydroformed member, and in accordance with yet another aspect of the
invention, as
the trimming/piercing tool is a punch tool for providing notches or cut-out
sections in
the hydroformed member.
[0047] Furthermore, in accordance with the instant invention there is
provided, a
method of forming a structural member of a predetermined shape comprising the
following steps of placing a metal blank into a hydroforming mold, said
hydroforming
mold comprising an electromagnetic trimming/piercing assembly; hydroforming
the
metal blank into a hydroformed member; energizing an electric discharge
circuit for
creating an electromagnetic force sufficient for driving an electromagnetic
driver; and
discharging the electric discharge circuit for driving the electromagnetic
driver toward
the hydroformed member, said electromagnetic driver comprising a
trimming/piercing
tool for trimming/piercing the hydroformed member at a predetermined location
to
yield the predetermined shape.
[0048] In accordance with another aspect of the invention, the structural
member is
for use as a structural member in automotive applications.
[0049] This and other objects of the invention can be more fully appreciated
from the
following detailed description of the preferred embodiments.
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Brief Description of the Drawings
[0050] Exemplary embodiments of the invention will now be described in
conjunction
with the following drawings wherein like numerals represent like elements, and
wherein:
[0051] Fig. la is a schematic presentation of a tubular blank for use in
hydroforming;
[0052] Fig. lb is a schematic presentation of a hydroformed member;
[0053] Fig. lc is a schematic presentation of a trimmed and pierced
hydroformed
member in accordance with an embodiment of the instant invention;
[0054] Fig. 2 shows a schematic presentation of a portion of a hydroforming
die
assembly including an EM trimming/piercing assembly in accordance with the
instant
invention;
[0055] Fig. 3 shows a schematic top view of an electromagnetic coil connected
to an
electric discharge circuit in accordance with an embodiment of the invention;
[0056] Fig. 4 shows a schematic side view of an electromagnetic coil connected
to an
electric discharge circuit in accordance with an embodiment of the invention;
and
[0057] Fig. 5 shows a schematic presentation of a portion of a hydroforming
die
assembly including an EM trimming/piercing assembly in accordance with the
instant
invention after discharging the electric discharge circuit.
[0058] Fig.6 shows a schematic cross-sectional view of a portion of an
apparatus in
accordance with the invention;
[0059] Figs. 7a-c show schematic cross-sectional end views of a variety of
differently
shaped hollow tube members;
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[0060] Fig. 8 shows a schematic top view of an electromagnetic coil connected
to an
electric discharge circuit in accordance with an embodiment of the invention;
[0061] Fig. 9 shows a schematic side view of an electromagnetic coil connected
to an
electric discharge circuit in accordance with an embodiment of the invention;
[0062] Fig. 10 shows a schematic cross-sectional view of an apparatus in
accordance
with the instant invention;
[0063] Fig. 11 shows a schematic cross-sectional view of the apparatus
depicted in
Fig. 5 in operation, after the electric discharge switch is closed;
[0064] Fig. 12 shows an oblique view of a formed hollow tubular member after
it has
been removed from the apparatus depicted in Fig. 11; and
[0065] Figs. 13a-j show a schematic presentation depicting various examples of
shapes available with metal forming, such as a flanged and dished head (Fig.
13a), a
cylindrical shell (Fig. 13b), a stepped cover (Fig. 13c), a re-entrant flared
shape (Fig.
13d), a venturi shape (Fig. 13e), a hemispherical shape (Fig. 13f), a flanged
cover
(Fig. 13g), a cone shape (Fig. 13h), and a parabolic nose shape (Fig. 13j).
[0066] Fig. 14 shows a schematic cross-sectional view in accordance with an
embodiment of the invention wherein the tool mandrel is designed to be a two-
part
mandrel;
[0067] Fig. 15 shows an oblique view of a camshaft assembly in accordance with
the
invention having a hollow shaft and a plurality of cam lobe and journal
elements
affixed thereon;
[0068] Fig. 16 shows an exploded view illustrating various elements of a
camshaft
assembly in accordance with one embodiment of the invention;
[0069] Fig. 17 shows an oblique view of a tool used for pre-positioning
various
elements before locking them on a camshaft assembly;
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[0070] Fig. 18a shows a schematic cross-sectional view of a portion of a
hollow shaft
inserted through the openings of cam lobe and/or journal elements and a spacer
element disposed between and separating the cam lobe and/or journal elements;
[0071] Fig. 18b shows a schematic cross-sectional view of the assembly
depicted in
Fig. 4a having an electromagnetic coil placed inside the hollow shaft; and
[0072] Fig. 18c shows a schematic cross-sectional view of the assemblies
depicted in
Figs. 18a and 18b and further illustrating an electric discharge circuit
connected
thereto.
Detailed Description Of The Preferred Embodiments
[0073] In accordance with the present invention, a method and an apparatus are
provided which combine the use of hydroforming and the use of electromagnetic
energy to form structural members that may be used, for example, in the
construction
of motor vehicles.
[0074] In general, hydroformed members are formed by placing a tubular blank
102,
such as shown in Fig. la, into a cavity of a hydroforming die assembly and
providing
a high pressure fluid into an interior of the tubular blank 102. The blank 102
is
positioned in the cavity and a hydroforming fluid is injected into the blank.
The high
pressure fluid expands the wall of the blank102 outwardly into conformity with
the
surfaces of the cavity of the hydroforming die and thereby forming a
hydroformed
member 104, such as shown in Fig. lb. Such hydroformed members can be used in
many applications, including their use as structural members, such as pillars
and side
rails for vehicle frame construction, in automotive applications. After the
hydroforming operation is finished, the hydroformed member 104 may be further
processed, such as by trimming and/or piercing. In accordance with the instant
invention, this is advantageously performed while the hydroformed member
remains
in the cavity of the hydroforming die assembly using an electromagnetic
trimming/piercing assembly. Fig. lc shows a processed hydroformed member 106
wherein notches or cut out sections 108, 110 are formed in an end portion of
the
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hydroformed member 106, and one or more openings 112, 114, 116 are formed
through interior wall portions of the hydroformed member 106.
[0075] The method and the apparatus of the instant invention make use of
electromagnetic technology to provide a relatively large amount of energy in
an
extremely rapid event, for example in the order of approximately tens of
microseconds. When harnessed properly, this energy can be used to perform
useful
work, such as applying an energy to stroke hydroform pierce punches for the
piercing
sequence of the hydroform cycle. If desired, more than one pierce punch may be
employed. The electromagnetic energy is delivered simultaneously to all the
pierce
punches employed and thus obviates typical hydraulic problems of pressure loss
as
soon as the oil begins to flow in prior art hydraulic cylinders. Furthermore,
electromagnetic pressure coils can be designed to be much smaller in size than
an
equivalent hydraulic piercing cylinder and thus will not require as much
machining as
is required for the mounting of hydraulic pierce cylinders. The method and the
apparatus in accordance with the instant invention may be used to pierce
and/or trim a
hydroformed member in the hydroforming mold subsequently to the hydroforming
process as described heretofore.
[0076] Reference is now being made to Fig. 2 showing a schematic presentation
of a
portion of apparatus 200 in accordance with the instant invention. Apparatus
200
includes a hydroforming die assembly 202 to hydroform workpiece 204. The
hydroforming die assembly 202 further includes an electromagnetic
trimming/piercing
assembly 206 including an insulator 208, an electromagnetic (EM) coil 210, and
an
electromagnetic driver 212 including an EM top plate 214 and a
trimming/piercing
tool 216. The EM coil 210 is embedded in the EM trimming/piercing assembly 206
and should be electrically insulated from surrounding metal objects. For this
reason,
insulator 208 is provided in the EM trimming/piercing assembly 206 in form of
a
insulating plate. If desired, EM coil 210 can also be covered by an
electrically
insulating material.
[0077] As can be seen from Figs. 3-4, EM coil 210 of the EM trimming/piercing
assembly 206 is electrically connected via conductors 308, 310 to an electric
discharge
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circuit 300 including an electric power source 302 and a high current rapid
discharge
switch 304. Discharge switch 304 is connected to a control circuit 306 to
control the
discharge and hence the operation of the EM trimming/piercing assembly 206.
[0078] In case a plurality of trimming/piercing operations are to be performed
on a
workpiece, they can be performed simultaneous or in a predetermined sequence.
If
the trimming/piercing operations are to be performed in a simultaneous manner
it is
sufficient to provide a single discharge circuit for the plurality of EM
trimming/piercing assemblies. If the trimming/piercing operations are to be
performed in a predetermined sequence, each EM trimming/piercing assembly is
provided with an electric discharge circuit. An electric current is discharged
between
each pair of electrodes. A control circuit can time the electrical discharge
between the
electrodes such that all discharges are simultaneous or in a predetermined
sequence.
[0079] The distance between the EM trimming/piercing assembly 206 and the
electric
discharge circuit 300 can be chosen in dependence upon the particular
circumstances
of an application. For example, should it be necessary to place the discharge
circuit
further away from the hydrofonning die assembly of the instant invention
including an
EM trimming/piercing assembly, it can be achieved by selecting conductors 308,
310
of a respective length.
[0080] In operation, a huge pulse of current is forced through the EM coil by
rapidly
discharging a high voltage capacitor bank using an ignitron or a spark gap as
a switch.
This creates a rapidly oscillating, ultrastrong electromagnetic field around
the EM
coil. The rapidly changing magnetic field induces a circulating electrical
current
within the drive plate through electromagnetic induction, and the induced
current
creates a corresponding magnetic field around the metal drive plate. Because
of
Lenz's Law, the magnetic fields created within the metal drive plate and EM
coil
strongly repel each another driving the drive plate and the attached
trimming/piercing
tool toward the workpiece. This occurs very quickly, typically tens of
microseconds.
[0081] Reference is now being made to Fig. 5 showing a schematic presentation
of an
activated EM trimming/piercing assembly 206 upon discharging the electric
discharge
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circuit. The EM pressure coil 210 is used to generate a magnetic field which
repels
drive plate 212 having an EM top plate 214. The trimming/piercing tool 216 is
attached to the drive plate 212. Thus, if the discharge circuit is discharged,
the drive
plate 212 is driven through the EM coil 210 and the EM top plate 214. The
driver 212
in turn advances the trimming/piercing tool 216. In the embodiment depicted in
Fig.
5, the trimming/piercing tool 216 is a punch tool to provide an opening 502
through
an interior wall portion of workpiece 204 after it has been hydroformed while
remaining in the hydroforming die assembly 202. Alternatively, other
trimming/piercing tools may be employed to provide predetermined notches or
cut-out
sections or openings in the hydroformed workpiece.
[0082] Advantageously, in accordance with the present invention, the
combination of
a hydroforming die with an EM trimming/piercing assembly to trim/pierce a
workpiece in a hydroforming die subsequently to the hydroforming process
obviates
the difficulties encountered with conventional hydraulic cylinders of various
diameters in their attempt to move simultaneously. In order to achieve this,
hydraulic
cylinders require a tremendous amount of oil volume and pressure which makes
such
systems very costly: Furthermore, once one of the hydraulic cylinders performs
a
trimming/piercing operation, a pressure loss is observed in the workpiece.
However,
this pressure is needed in the workpiece so that the other trimming/piercing
assemblies can be successful. An EM trimming/piercing assembly in accordance
with
the instant invention can advance trimming/piercing tools fast and
substantially
simultaneous.
[0083] Moreover, in accordance with another advantage of the instant
invention, an
EM trimming/piercing assembly is smaller than a conventional hydraulic
cylinder
assembly and thus packages easily in the hydroforming die. Furthermore, EM
pressure coils are easier to mount into the die and thus eliminating costs.
[00841 In accordance with another embodiment of the present invention, a
tubular
member is formed employing an electromagnetic (EM) forming method and
apparatus. More particularly, an external electromagnetic pressure coil is
employed to
generate a magnetic field and hence pressure which in turn repels a tubular
member at
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a rapid speed and forces the tubular member to conform to the shape of an
inner
mandrel provided in a bore of the tubular member.
[0085] EM Technology can be used to provide a relatively large amounts of
energy in
an extremely rapid event, for example in the order of approximately tens of
microseconds. When harnessed properly, this energy can be used to perform
useful
work such as metal forming. The energy is applied very rapidly which causes
extremely high strain rates in the material and thus allows a level of
formability which
would otherwise be unattainable.
[0086] Fig. 6 shows a schematic cross-sectional view of a portion of an
apparatus
1100 in accordance with the invention. An inner mandrel 1102 is placed inside
a bore
1106 about an axis 1104 of a hollow tubular member 1108. A multi-turn coil
1110 is
placed about an outer surface of the hollow tubular member 1108. The inner
mandrel
1102 has a forming surface 1112. In operation, an electric current rapidly
discharges
through the multi-turn coil 1110 resulting in a pulsed magnetic force which
causes a
rapid movement of the hollow tubular member 1108 towards the forming surface
1112 of the inner mandrel 1102, and thus the hollow. tubular member 1108
assumes
the shape of the forming surface of the inner mandrel.
[0087] It will be appreciated that the shape of the inner mandrel which
defines the
shape of the hollow tubular member as shown in Fig. 6 is exemplary and inner
mandrels with a variety of predetermined forming surfaces may be used in
accordance
with the instant invention. Figs. 7a-c show schematic cross-sectional end
views of a
variety of differently shaped hollow tube members, viz. Fig. 7a shows a
circular cross-
sectional configuration, Fig. 7b shows a rectangular cross-sectional
configuration, and
Fig. 7c shows a cross-shaped cross-sectional configuration.
[0088] Figs. 8-9 present a schematic top and side view of an electromagnetic
coil
1301 connected to an electric discharge circuit 1300 in accordance with an
embodiment of the instant invention. EM coil 1301 is electrically connected
via
conductors 1308, 1310 to an electric discharge circuit 1300 including an
electric
power source 1302 and a high current rapid discharge switch 1304. Discharge
switch
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1304 is connected to a control circuit 1306 to control the discharge and hence
the
operation of an EM forming apparatus in accordance with the invention as will
be
explained in more detail hereinafter.
100891 In case a plurality of forming operations are to be performed on a
workpiece,
such as a hollow tubular member, they can be performed simultaneous or in a
predetermined sequence. If the forming operations are to be performed in a
simultaneous manner it is sufficient to provide a single discharge circuit for
the
plurality of EM forming assemblies. If the forming operations are to be
performed in
a predetermined sequence, each EM forming assembly is provided with an
electric
discharge circuit. An electric current is discharged between each pair of
electrodes. A
control circuit can time the electrical discharge between the electrodes such
that all
discharges are simultaneous or in a predetermined sequence.
[0090] The distance between an EM forming assembly and the electric discharge
circuit 1300 can be chosen in dependence upon the particular circumstances of
an
application. For example, should it be necessary to place the discharge
circuit further
away from an EM forming assembly in accordance with the instant invention, it
can
be achieved by selecting conductors 1308, 1310 of a respective length.
[0091] In operation, a large pulse of current is forced through EM coil 1301
by rapidly
discharging a high voltage capacitor bank using, for example, an ignitron or a
spark
gap as a switch. This creates a rapidly oscillating, ultrastrong
electromagnetic field
around the EM coil. The rapidly changing magnetic field induces a circulating
electrical current within the metallic tubular member through electromagnetic
induction, and the induced current creates a corresponding magnetic field
around the
metallic tubular member. Because of Lenz's Law, the magnetic fields created
within
the metallic tubular member and the EM coil strongly repel each another
driving the
metallic tubular member toward the tool mandrel. This occurs very quickly,
typically
in the range of tens of microseconds.
[0092] Reference is now being made to Fig. 10 showing a schematic cross-
sectional
view of an apparatus 1500 in accordance with the instant invention comprising
an
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inner mandrel 1502 having a forming surface 1504. The inner mandrel 1502 is
provided inside a passage of a hollow tubular member 1506. Tubular member 1506
is
surrounded by an electromagnetic (EM) coil assembly 1508. The EM coil assembly
1508 comprises an EM coil 1510 embedded within a space 1512 of a supporting
member 1514. Preferably, supporting member 1514 is made from a non-metallic
material. Furthermore, the EM coil 1510 should be electrically insulated from
any
surrounding metal objects, including the hollow tubular member 1506. For this
reason, the EM coil 1510 is covered with an electrically insulating material.
Alternatively, space 1512 may be filled with an electrically insulating
material.
[0093] As can be seen from Fig. 10, EM coil 1510 is electrically connected to
an
electric discharge circuit 1516 including a capacitor 1518 and a high current
rapid
discharge switch 1520 which is controlled by control circuit 1522. The
operation of
the discharge circuit was explained in more detail heretofore.
[0094] Having regard now to Fig. 11, in operation, the discharge switch 1520
is
closed in response to a signal from control circuit 1522, thereby rapidly
discharging an
electric current through EM coil 1510. As a result of the discharge of the
electric
current through the coil, a pulsed magnetic force is produced which causes a
rapid
movement of the hollow tubular member 1506 away from the EM coil 1510 and
toward mandrel 1502. The hollow tubular member 1506 is pressed against the
forming surface 1504 of the mandrel 1502 and thus complements the shape of the
mandrel, as can be seen from Fig. 11, to yield a formed tubular member 1524.
[0095] Fig. 12 presents an oblique view of a formed hollow tubular metal
member
after it has been removed from the forming apparatus and the mandrel has been
removed from the inside of the formed tubular member.
[0096] The specific shape of the formed tubular member as shown in Fig. 12 is
only
one example in accordance with the invention. A person of skill in the art
appreciates
that a plurality of other shapes can be achieved in accordance with the method
and
apparatus of the instant invention. Turning now to Figs. 13a-j, a schematic
presentation is shown depicting various examples of shapes available with
metal
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forming, such as a flanged and dished head (Fig. 13a), a cylindrical shell
(Fig. 13b), a
stepped cover (Fig. 13c), a re-entrant flared shape (Fig. 13d), a venturi
shape (Fig.
13e), a hemispherical shape (Fig. 13f), a flanged cover (Fig. 13g), a cone
shape (Fig.
13h), and a parabolic nose shape (Fig. 13j).
100971 In accordance with the embodiment presented in Figs. 11 and 12, the EM
coil
surrounds the entire circumference of the hollow tubular member to be formed.
However, in accordance with another embodiment of the invention, the EM coil
only
covers a portion of the hollow tubular member in an axial direction.
100981 Furthermore, in accordance with yet another embodiment of the instant
invention, the forming of the tubular member can be accomplished in a
plurality of
stages. If the workpiece or tubular member remains in the same apparatus, a
control
circuit can be used to time the electrical discharge of a plurality of
discharge circuits
used in the plurality of forming stages.
100991 In accordance with yet another embodiment of the instant invention, the
tool
mandrel is designed to be a two-part mandrel having a first mandrel member 902
and
a second mandrel member 904, as depicted in Fig. 14. Such a mandrel design is
advantageously used where a formed tubular member 1906 includes a relatively
narrow passage 1908 along an axial extent of the tubular member between a
first
relatively wider passage 1910 and a second relatively wider passage 1912. The
relatively narrow passage 1908 would prevent the mandrel from being removed
from
the formed tubular member 1906. However, if a releasable two-part mandrel is
employed, the first and second mandrel members 1902, 1904 are released from
one
another and then they can be removed from either side of the formed tubular
member,
as indicated by arrows A and B of Fig. 14, respectively.
1001001 If desired, a multi-part tool mandrel can be employed to facilitate
the
removal of the tool mandrel from within a formed tubular member of a more
complicated structure. In a similar manner as described above, a plurality of
mandrel
members are released from one another and are then individually removed from
within the formed tubular member.
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100101] In accordance with another embodiment of the present
invention, a
camshaft is provided having a hollow shaft as well as a method of
manufacturing said
camshaft.
[00102] Turning now to Fig. 15, a camshaft assembly 2100 is shown having a
hollow shaft 2102 with a plurality of cam lobe elements 2104, 2106, 2108,
2110, 2112,
2114, 2116 and journal element 2118 affixed thereon. Additional elements, such
as
gears, eccentrics or sprockets, could also be included if desired. The cam
lobe and
journal elements are longitudinally spaced and the cam elements are angularly
oriented
in predetermined positions, for example for actuating valve gears in an
internal
combustion engine. A cam timing gear or sprocket (not shown) can be attached
to one
end of the camshaft 2102 for operably connecting the camshaft assembly 2100 to
the
timing apparatus of an engine (not shown).
[00103] The shaft 2102 is essentially a cylindrical elongate tubular member
which can be formed by drilling out the center of a regular forged or cast
camshaft or
via a welded assembly. Alternatively, it can be formed from an ordinary steel,
cold
extruded to a predetermined inside and outside diameter and cut to a
predetermined
length.
[00104] Fig. 16 shows an exploded view illustrating various elements
of the
camshaft assembly 2202. Each cam lobe element 2204. 2206, 2208, 2209 is a non-
cylindrical disc having an opening 2210, 2212, 2214, 2216, respectively, for
receiving
the hollow shaft 2218 therethrough. Each journal element 2220, 2224 is an
essentially
cylindrical disc having an axial opening 2226, 2228, respectively, for
receiving the
hollow shaft 2218 therethrough.
[00105] The openings 2210, 2212, 2214, 2216, 2226, 2228 have a
diameter that
is slightly larger than the outer diameter of the hollow shaft 2218. The shape
of the
openings may be circular or slightly non-circular. Fig. 16 depicts the
openings as
having a slightly non-circular hexagonal shape. Alternatively, other slightly
non-
circular polygonal shapes may be chosen. Advantageously, the slightly non-
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shape of the openings provides a better torsional retention of the cam lobes
and
journal elements and/or other elements on the shaft.
[00106] The individual cam lobe, journal, and/or other elements are
inserted
into a tool so as to pre-position them in their predetermined final
orientations with
their openings aligned for insertion of the tube or hollow shaft. The elements
are
securely held in a tool in a predetermined longitudinally spaced apart
relationship to
one another. Furthermore, the cam lobe elements are securely held in a
predetermined
rotationally or angularly oriented relationship to one another as they are
secured in the
tool. This is shown in more detail in Fig. 17, illustrating a tool 2300 having
a base
2302 and a longitudinal recess 2304. The journal elements 2316, 2318 and cam
lobe
elements 2320, 2322, 2324, 2326, 2328 are provided in recess 2304. The
elements are
pre-positioned by a plurality of supporting and positioning elements 2306 a-g
and
separated by a plurality of spacer elements 2308a-g, all of which are retained
in the
tool between walls 2310 and 2311. A cover 2312 having fixing elements 2314a-c
(only a few of which are denoted by reference numeral for clarity reasons) is
provided
to maintain the elements in their positions with their openings in axial
alignment for
insertion of hollow shaft or tube 2330.
[00107] Once the hollow shaft as well as the cam lobe, journal and/or
other
elements are pre-positioned in the tool, an electromagnetic coil is inserted
in the
hollow shaft. In accordance with the instant invention, electromagnetic (EM)
technology can be used to provide large amounts of pressure in an extremely
rapid
event, for example in the order of approximately tens of microseconds. When
harnessed properly, this pressure can be used to perform useful work such as
is
required in this application to mechanically join the tubular blank to the cam
lobe
elements, journal elements, and/or other elements. Advantageously, EM
technology
overcomes the disadvantages of other camshaft forming methods by having a very
short cycle time and by obviating the complex technical features related to
hydro/fluid
forming as mentioned above.
[00108] Turning now to Figs. 18a and 18b, more detailed schematic
cross-
sectional views are presented, illustrating the method in accordance with the
instant
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invention. Fig. 18a shows a cross-sectional view of a portion of a hollow
shaft 2402
inserted through the openings of cam lobe and/or journal elements 2404, 2406
and a
spacer element 2408 disposed between and separating the cam lobe and/or
journal
elements 2404, 2406. All elements are provided with their openings in axial
alignment with axis As of hollow shaft 2402. The cam lobe and/or journal
elements
have openings of a diameter that is slightly larger than the outer diameter of
the
hollow shaft so as to fit closely on the hollow shaft. Spacer element 2408 is
designed
so as to have a clearance 8 to the outer diameter of the hollow shaft to allow
for an
expansion of the tube in the areas between the cam lobe elements, journal
elements
and/or other elements of the camshaft assembly in accordance with the
invention. As
can be seen from Fig. 18b, an electromagnetic coil 2410 is placed inside the
hollow
shaft. EM pressure coil 2410 is used to generate a magnetic field (pressure)
which
repels the hollow shaft or tube at a rapid speed so as to join the hollow
shaft or tube to
the plurality of cam lobe elements, journal elements and/or other elements via
mechanical lock.
1001091 In operation, a large pulse of current is forced through EM
coil 2410 by
rapidly discharging a high voltage capacitor bank using, for example, an
ignitron or a
spark gap as a switch. This creates a rapidly oscillating, ultrastrong
electromagnetic
field around the EM coil. The rapidly changing magnetic field induces a
circulating
electrical current within the metallic hollow shaft or tube through
electromagnetic
induction, and the induced current creates a corresponding magnetic field
around the
metallic hollow shaft or tube. Because of Lenz's Law, the magnetic fields
created
within the metallic hollow shaft or tube and the EM coil strongly repel each
another
driving the metallic hollow shaft or tube toward the plurality of cam lobe
elements,
journal elements, spacer elements and/or other elements provided in the tool.
This
occurs very quickly, typically in the range of tens of microseconds.
[00110] The electromagnetic pressure causes the hollow shaft or tube
to expand
diametrically and thus forming a mechanical bond between the hollow shaft or
tube
and the various elements provided thereon. The diametrical expansion of the
hollow
shaft or tube forces the outer surface of the hollow shaft or tube into a
mechanical
locking relationship. As shown in Fig. 18b, the portions of the hollow shaft
or tube
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CA 02612998 2014-07-29
adjacent to the spacer element are diametrically expanded beyond the opening
diameter
by a predetermined difference 6e, so as to positively lock the various
elements in their
predetermined longitudinal relationship.
[00111] Once all of the elements are affixed to the hollow shaft or tube,
the
electromagnetic coil is removed from the hollow shaft or tube and the final
camshaft
assembly is removed from the fixing tool. Finally, the wearing surfaces of the
various
elements of the camshaft assembly are ground to the desired surface finish and
dimensions.
[00112] Having regard now to Fig.18c, a schematic cross-sectional view
of a
portion of expanded hollow shaft 2402 is shown, and further illustrating an
electric
discharge circuit 2412 connected thereto. The electric discharge circuit 2412
includes a
capacitor 2414 and a high current rapid discharge switch 2416 which is
controlled by
control circuit 2418. As shown, in Fig. 18c, in operation, the discharge
switch 2416 is
closed in response to a signal from control circuit 2418, thereby rapidly
discharging an
electric current through EM coil 2410 and thus diametrically expanding the
hollow
shaft or tube 2402.
[00113] The above described embodiments of the invention are intended to be
examples of the present invention and numerous modifications, variations, and
adaptations may be made to the particular embodiments of the invention without
departing from the scope of the invention, which is defined in the claims.
