Note: Descriptions are shown in the official language in which they were submitted.
CA 02361521 2001-07-31
Method and Device for Forming Metals
This invention relates to a metal working method, in particular a
compressive deformation method, for metal workpieces such as pipes, wires or
sections, and a compressive deformation device.
s According to the state of the art, swellings are accomplished, as a rule,
in such a way that a pipe or a metal section having the largest wall thickness
is
provided, and the thickness is reduced at the desired places through targeted
cutting out or hammering out. This cutting out or hammering out starting from
the thickest sections is a tedious process, in particular when the proportion
of
to swelling is only small compared to the remaining portion of the pipe or
section.
Various attempts to thicken sections through direct compressive deformation
have failed so far. Attempts to thicken pipes or rods have often caused the
sections to widen laterally or yield to buckling already in the initial phase
of the
compressive deformation, whereby pile-ups and overlaps result. Furthermore,
is a non-homogeneous, crystalline structure of the reshaped material thereby
results, which is undesirable with respect to stability. Wr7nkles also thereby
occur in the section, like in an elephant's trunk.
Resolving the phenomenon through formation of folds has been
attempted in that various die stages of different shape are put in, which is a
2o rather time-consuming method.
It is therefore the object of the present invention to make available a
metal working method by means of which swellings in pipes, rods or other
sections can be produced quickly and economically.
It has been found that desired, targeted places in pipes, rods and other
as sections can be thickened through compressive deformation if the workpiece
to
be thickened is prestressed in the Hooke range, and the workpiece is
processed with a compressive deformation hammer in a pulsating way.
Through the impulses of the compressive deformation hammer, the material of
the workpiece undergoes a transition for a short time from the Hooke range
into
3o the plastic range. The impulse causes the material in the compressive
deformation zone to be brought to flow, the deformation space is thereby
filled
a little, the compressive deformation hammer follows the movement, the
pressure drops, the workpiece once again returning to the crystalline state,
but
still being under prestressing, however. Further periodic compressive
CA 02361521 2001-07-31
deformation impulses are subsequently delivered to the workpiece, a transition
into the plastic range and a recrystallization occurring again each time. By
means of this procedure, a homogeneous, thickened section with
homogeneous structure can be obtained.
The subject matter of the present invention is thus the compressive
deformation method according to the definition in claim 1 and the compressive
deformation device according to the definition in claim 10.
The method according to the invention is referred to as "stutter
compressive deformation." It is thereby important that the active thrust
forces
io are directed in such a way that they come to bear only in the deformation
space
and serve only the transport of material.
To this end it is necessary that the profile to be compressively deformed
be free in the deformation space and the remaining section held in such a way
that the compressive deformation forces are equalized outside the deformation
is space or are neutralized, ineffective against the walls. Owing to the
prevailing
pressure relations, the material is exposed to increased temperatures. The
energy thereby brought in must be correspondingly carried off in the region of
the Damping so that the transition zone does not flow at the same time and the
material is not able to expand in an uncontrolled way.
2o Prior to the actual compressive deformation action, the material to be
reshaped has to be prestressed with corresponding hydraulic pressure so that
the stutter pulses come to bear correctly. The prestressing takes place
preferably in a region located just before the transition into the plastic
range.
The material is therefore still in the prestressed state in the elastic phase.
2s Through suitable measures, the prestressing is maintained during the entire
compressive deformation action, i.e. the metal part to be worked remains under
prestressing between the individual impulses. The stressed material is
preferably preheated up to just before the yielding state, in particular in
the
case of larger sections. The energy to be supplied and the frequency are
3o determined according to Brillouin (first Brillouin zone). The preheating
preferably takes place locally in the deformation space by means of
microwaves. With thin sections, the preheating can be omitted. The pressure
pulse can now be applied to the prestressed and preheated material, the
prestressed material being brought to flow. Because the material becomes
CA 02361521 2001-07-31
soft, the pressure piston is able to move forward, and the pressure subsides;
the material can recrystallize. The prestressing of the material is maintained
between the individual pressure pulses. This can take place in that a
hydraulic
system is used for the application of force, which system comprises two
s hydraulic pumps, namely a prestressing pump for the prestressing pressure
for
example at 40 bar (4 ~ 106 Pa) and a smaller impulse pump for a pressure up to
700 bar (7 . 10' Pa). The pipelines of these pumps to the piston ("stutter
piston") must be provided with a return valve.
A hydraulic system is preferably used for exerting a pressure pulse upon
io the compressive deformation hammer. The impulse is thereby transmitted from
the hydraulic or stutter piston to the compressive deformation hammer. The
stutter piston is moved with oil up to the material to be compressively
deformed,
then the pressure increases such that the stressed oil causes the desired
prestressing in the workpiece. The lines between pumps and stutter pistons
is are to be designed non-elastic, and for the pulse frequency anechoic. The
pressure pulses are modulated upon the prestressed oil, for example with a
frequency-controlled piston control, so that an unattenuated transmission of
the
pulse from the hydraulic piston to the compressive deformation hammer can
take place (compressibility of the hydraulic oil approximately 10'6).
2o The time of the compressive deformation is determined according to the
Hooke Law; the first half cycle of the stutter frequency is established
thereby.
For the second half cycle, it is only to be checked whether the available time
suffices for the recrystallization. With this method, the stutter frequency is
always matched to the material. After the last tension release of the material
in
is the compressive deformation region, the material is still in the Hooke
range,
that is prestressed. It is to be seen to it that the material can relax in the
compressive deformation region through removal of the compressive
deformation hammer since otherwise undesired swellings can arise adjacent to
the compressive deformation region.
3o The invention will be explained more closely in the following, with
reference to the attached drawings. Shown are:
Figure 1 a sectional drawing of a compressive deformation device for canying
out the method according to the invention: state prior to the
compressive deformation action,
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4
Figure 2 the same compressive deformation device as in Figure 1, however
after the compressive deformation action,
Figure 3 an alternative embodiment of a compressive deformation device,
namely a head compressive deformation device for carrying out the
s method according to the invention, applied to a different material or
product,
Figure 4 a configuration of hydraulic pumps on the stutter piston,
Figure 5 a pressure/course diagram of the compressive deformation action,
Figure 6 a pressure/time diagram of the method according to the invention,
io Figure 7 an enlarged cutout of a compressive deformation device similar to
Figure 1,
Figure 8 another embodiment of a compressive deformation device designed
for compressively deforming a hollow section in a region between its
ends,
~s Figure 9 the detail D of Figure 7 and 8 on an enlarged scale,
Figure 10 in a depiction similar to Figure 7, a device for producing a non
rotational-symmetrical swelling at the end of a pipe,
Figure 11 in a depiction similar to Figure 8, a device for producing a non-
rotational-symmetrical swelling between the ends of a pipe,
zo Figure 12 a diagrammatic section through a pulse generator.
Figure 1 shows a stutter compressive deformation device 1, which is
intended for compressively deforming a pipe 2 at its end, while forming a
greater wall thickness. Inserted in the pipe 2 is a pin 3 which serves to hold
the
section of the pipe in that the material is prevented from being able to
escape
2s into the section interior. The pipe is held through a Damping device 4,
which
exerts a counter-pressure upon the pin 3. The Damping device exerts a
pressure around the pipe on all sides. Prevented thereby is that material can
escape in an uncontrolled way. The pipe 2 to be compressively deformed
projects further into the die 5 which is provided with a cooling coil 6 which
is fed
so with a cooling medium 14. The temperatures arising through the high
pressures are thereby dissipated, as far as necessary. The pin 3 projects
through the pipe 2 to be compressively deformed partially into the die 5. A
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bore 9 is provided at the end of the pin 3 penetrating into the die, which
bore
serves as a guide for the extension 8 of the compressive deformation hammer
7. This extension, together with the die, defines the deformation space 13
into
which the material of the pipe can spread during the compressive deformation
s action. The pressure or respectively the required impulses on the
compressive
deformation hammer 7 are exerted by the stutter piston 10. This is
hydraulically operated, 11 designating the hydraulic line and 12 the chamber
for the expanding hydraulic oil. Before the compressive deformation action can
begin, the pipe to be compressively deformed, with the pin 3 inserted, is
io brought into the desired position in the clamping device 4, and the
clamping
device is tightened as much as necessary. The compression deformation
hammer 7 is applied on the face of the pipe located in the die 5. Then the
pipe
to be compressively deformed is prestressed to the extent that the material is
still in the elastic range (Hooke range).
is Since the hydraulic oil likewise has an elastic lower pressure range, the
prestressing has the advantage here that not only is the metal piece to be
worked prestressed, but also the hydraulic oil. During the compressive
deformation action, the oil is thus in a range in which it has practically no
elasticity.
zo Figure 2 shows the same stutter compressive deformation device as in
Figure 1, however after completed compressive deformation action. The
reference numerals have the same meaning as in Figure 1. In this figure it can
be seen that the stutter piston 10 has moved to the right, compared to Figure
1.
The stutter piston 10 has thereby been driven into the die 5, the part of the
pipe
zs to be compressively deformed turned toward the compressive deformation
hammer being compressively deformed and the deformation space according
to Figure 1 now being filled up by the entire compressively deformed part 15
of
the pipe 2 to be compressively deformed.
Figure 3 shows an alternative embodiment of a stutter compressive
3o deformation device for carrying out the method according to the present
invention. The device 20 is a head compressive deformation device. The
device serves to compressively deform a metal rod or metal wire at one end
with formation of a head. A metal wire (not shown) is inserted into the bore
21
of the clamping device 22 until the one end projects into the hemispherical
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6
depression 23 of the compression deformation hammer 24 until the limit stop.
The compressive deformation hammer 24 can exert a pressure on the
workpiece through the piston 25, whereby during the compressive deformation
action, which takes place the same way as described above, the material is
s able to escape into the die 26 and the hemispherical depression 23 in the
compression deformation hammer 24. The piston 25 is actuated hydraulically.
Details of the clamping device and also of the hydraulic system are not
depicted in this figure, since they are obvious for one skilled in the art.
Figure 4 shows a typical configuration of hydraulic pumps 31, 32 at the
~o piston (Figures 1 and 2) or respectively 25 (Figure 3), which exerts
pressure on
a compressive deformation hammer (not shown). The larger hydraulic pump 32
serves to maintain a permanent prestressing pressure during the compressive
deformation action, e.g. 40 bar. The smaller pump 31 serves to exert periodic
impulse pressures, with a higher pressure, e.g. of 700 bar, which is
sufficient
is for the transition of the material from the Hooke into the plastic range.
The
lines 34, 35 of the pumps 31, 32 to the piston are provided with return valves
36, 37. Shown, for better clarity, above the pump symbols are little diagrams
38, 39 with a schematic indication of the course of pressure.
Figure 5 shows a pressurelcourse diagram a for a compressive
2o deformation action according to the present invention. h shows the Hooke
range and A the prestressing point.
Figure 6 shows a pressure/time diagram b for a compressive
deformation process for steel according to the present invention. Clearly
visible is the pulsating pressure course during the impulses. In the area h,
the
2s material is prestressed in the Hooke range until the prestressing point A.
As
soon as this point is reached, a first impulse is exerted upon the material to
be
compressively deformed, whereby the first peak of the curve arises. During
this impulse, the material to be reformed undergoes transition from the
elastic
range into the yielding range f, in which a reforming takes place since the
so material is brought to flow. The piston is thereby able to move further
forward,
and the pressure subsides until (it reaches) the prestressing pressure, the
material being able to recrystallize. The recrystallization phase is shown by
the
area r. Then an impulse is again delivered to the material to be reformed,
until
the summit of the second peak. The same thing thereby happens as with the
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7
first peak: The pressure piston is able to move further forward, the material
undergoing transition into the plastic range, which allows a reforming. Then
the pressure diminishes again, a renewed recrystallization of the material
being
made possible. This action is repeated until the desired reforming is
achieved.
s Further indicated on the diagram is the pressure difference pressure; this
is a
material-dependent constant which has to be calculated or found out otherwise.
Figure 7 shows important details of a compressive deformation device
which is constructed in a similar way to the compressive deformation device of
Figure 1, on a larger scale compared to Figure 1. Same parts are given the
io same reference numerals in Figure 7 as in Figure 1. The clamping device
generally designated by 4 comprises a plurality of hydraulic cylinders which
act
upon clamping jaws 16. Shown in Figures 1 and 7 are only two sets of
hydraulic cylinders situated next to each other in the longitudinal direction
of
the pipe and distributed on the periphery of the clamping jaws. In practice,
is however, three or more sets of hydraulic cylinders are preferably provided.
It
has been shown namely that good reforming results are achieved if the
clamping force is high in the vicinity of the end of the pipe 2 to be
reformed,
and decreases, then increases again, in the direction of the opposite end of
the
pipe 2. With such a clamping course, undesired flowing of the material of the
2o pipe 2 in the clamping region is avoided. Therefore the hydraulic cylinders
of
the embodiment according to Figure 7, situated behind one another in the
longitudinal direction of the pipe to be reformed, have separate supply lines
for
the pressure medium, in contrast to the embodiment according to Figure 1.
These supply lines are not shown in Figure 7. By means of these separate
Zs supply lines, it is possible to supply adjacent hydraulic cylinders with
different
pressure in order to achieve the clamping course described above. To further
improve the holding force exerted on the pipe 2 by the clamping device 4, the
surfaces of the clamping jaws 16 that come into contact with the pipe 2 are
provided with a friction-increasing coating, in particular of tungsten
carbide,
3o and at least the surface areas of the pipe 2 that come into contact with
the
clamping jaws 16 are roughened.
A further measure to increase the holding force, directed in a way
opposing the reforming force in the longitudinal direction of the workpiece,
consists of a small, encircling shoulder19 provided between the die 5 and the
3s clamping jaws 16. The shoulder 19 is shown in Figure 9, which shows on an
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8
enlarged scale the cutout designated D in Figures 7 and 8. During the
reforming action, a small accumulation of the working material of the pipe
forms
on this shoulder, whereby the pipe 2 is also held in a form-fitting way in
longitudinal direction.
s Shown in Figure 7 is the compressive deformation device immediately
prior to the compressive deformation action. The deformation space 13 is
delimited in this embodiment by the contact surface 17 of the compression
deformation hammer, the extension 8 of the compression deformation hammer
7, the face 29 of the pin 3 and of course the die 5. The compression
io deformation hammer 7 is situated with its contact surface 17 on the face of
the
pipe 2 to be reformed. In simplified terms, the crosshatched end region of the
pipe 2 is shifted in the direction of arrows 18 into the deformation space 13
through the reforming action. So that the force transmitted by the compressive
deformation hammer 7 onto the pipe is really directed toward the deformation
~ s space 13, the contact surface 17 of the compression deformation hammer
does
not run at a right angle to the longitudinal axis of the pipe 2, but is
instead
slightly inclined plate-like in direction toward the pipe. If it is important
for the
finished, reformed pipe 2 to have a face deviating from the shape of the
contact
surface 17, which is, for example, precisely orthogonal, this face is brought
into
Zo its final form by means of the compression deformation hammer in a further
working step.
Shown in Figure 8 is an embodiment of the compressive deformation
device designed for compressively deforming a pipe 2 in a region between its
ends. The left half of the device according to Figure 8 corresponds
zs substantially to the right half of Figure 7. Visible at the far left in
Figure 8 is in
addition a bottom 27 on which the pipe 2 abuts. On the right side of the die 5
is
a further clamping device 4, which holds firmly the end of the pipe 2. The
compressive deformation hammer 7 here is stepped twice. The first step is
formed by a contact surface 17, which transmits the compressive deformation
so force to the pipe 2 to be reformed at the beginning of the reforming
action.
Since the compressive deformation force has to be transmitted within the right
clamping device 4 through the pipe 2 to the deformation space 13 and the pipe
must shift itself in this clamping device to the left toward the deformation
space
13, corresponding to the degree of reforming, it is important that the
clamping
3s force of the right clamping device 4 be adjustable. Together with the
extension
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9
8, the face 29 of the pin 3 and the die 5, the second step, formed by the
slightly
inclined surface 28, delimits the deformation space 13. As soon as the working
material begins to deform on the surface 28, this surface also transmits part
of
the compressive deformation force to the pipe 2. Of course it is advantageous
s if the surfaces 28 and 29 are inclined in such a way that their normal lines
are
directed toward the deformation space 13, as has been described further above
for the contact surface 17.
It is clear that both the compressive deformation hammer 7 and the pin 3
and/or its bore 9 can be designed in almost any desirable way, for example
io with multiple steps, in order to give the deformation space 13 a desired
shape.
One must only see to it that compressive deformation hammer 7 and pin 3 are
designed such that they are also able to be driven apart again after the
forming, without the formed workpiece being damaged. Furthermore, in all the
embodiment examples described above of the stutter compressive deformation
is device, the parts to be reformed are rotationally symmetrical. It is easily
possible, however, within the framework of the present invention, to reshape
non-rotationally-symmetrical sections or pipes or to form non-rotationally-
symmetrical regions on rotationally symmetrical sections or pipes. Two
examples of this are shown in Figures 10 and 11.
2o Figure 10 shows, in a diagram similar to Figure 7, a device for producing
a non-rotationally-symmetrical swelling at the end of a pipe 2. The surtace
29'
delimiting the deformation space 13 on the side of the pin 3 is not oriented
at a
right angle to the longitudinal axis of the pipe 2 in this embodiment.
Accordingly, the clamping jaws 16 and the die 5 are also of asymmetrical
Zs construction, as can be Dearly discerned in the drawing.
Figure 11 shows, in a diagram similar to Figure 8, a device for producing
a non-rotationally-symmetrical swelling between the ends of a pipe. In this
embodiment, it is the surface 28' delimiting the deformation space 13 on the
side of the compressive deformation hammer 7 which is not oriented at a right
3o angle to the longitudinal axis of the pipe 2. Accordingly, the clamping
jaws 16
of the further clamping device 4 and the die 5 are of asymmetrical design.
The frequency with which the compressive deformation hammer pulses
is to be established empirically for each workpiece. It is suspected that the
best results are achieved if a stationary wave arises in the area to be
reformed
CA 02361521 2001-07-31
of the pipe 2 between the contact surface 17 of the compressive deformation
hammer 7 and a virtual reflecting wall in the region of the shoulder 19. It is
therefore advantageous if the pulse frequency is adjustable and preferably
changeable even during the reforming action.
s The mentioned impulse pump 31 can be a conventional reciprocating
pump. A rotating pulse generator is more effective, however. Figure 12 shows
a diagrammatical section through a possible embodiment of such a pulse
generator 40. A central rotor 41 has at its center a longitudinal bore 42
which,
via a rotary seal, can be pressurized with a high pressure of 700 bar, for
to example. For the purpose of minimizing friction, the rotor is coated on its
cylinder generated surface with a layer 43 of ceramic, for example, and is
surrounded by a stator 44. Radial channels 45 in the rotor conduct the high
pressure from the longitudinal bore 42 to the outside. Provided in the stator
44
are also radial channels 46, which communicate with the channels 45 of the
is rotor in each case for short periods during the rotation of the rotor. Each
channel 46 of the stator 44 has a return valve at its outer, radial end.
According to this embodiment example, the return valve 47 consists of a ball
with a cylindrical extension which is led in the bore of a radial connecting
line
48. The ball and the extension are bored through to ensure the flow of the
2o pressure agent through the connecting line 48 into an outer annular chamber
49 in which the prestressing pressure, of 40 bar, for example, prevails. It is
this
prestressing pressure which also presses the ball of the return valve 47
against
its seat as long as the channels 45 and 46 are not in connection with one
another. All return valves 47 are held in a valve ring 50. Of course other,
as known return valves can also be used, however, the valve body of which is a
ball, for example, and is pressed against its seat by means of a spring, for
instance. Each time when a flow connection between a rotor channel 45 and a
stator channel 46 occurs, a pressure impulse arises in the latter. These
pressure impulses achieve especially steep edges when the channels have a
so cross-section delimited by straight lines, i.e. are rectangular, for
example, in the
transitional region between rotor and stator. In the example shown, all four
rotor channels enter into connection with the four stator channels at the same
time. A symmetrical load is thereby ensured, and the quantities of pressure
agent flowing through the channels add up. Embodiments are also
3s conceivable, however, in which the number and the arrangement of the
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channels is selected in such a way that the connections take place in
succession. With such a configuration, high pulse frequencies can be
achieved already at low rpm of the rotor.
