U.S. patent application number 14/835156 was filed with the patent office on 2016-03-03 for method and press for producing sheet metal parts that are hardened at least in regions.
This patent application is currently assigned to Benteler Automobiltechnik GmbH. The applicant listed for this patent is Benteler Automobiltechnik GmbH. Invention is credited to Georg Frost.
Application Number | 20160059295 14/835156 |
Document ID | / |
Family ID | 54007520 |
Filed Date | 2016-03-03 |
United States Patent
Application |
20160059295 |
Kind Code |
A1 |
Frost; Georg |
March 3, 2016 |
METHOD AND PRESS FOR PRODUCING SHEET METAL PARTS THAT ARE HARDENED
AT LEAST IN REGIONS
Abstract
A method for producing a sheet metal part with a press includes
the steps of heating a sheet metal blank at least in regions to a
above the austenitizing temperature Ac3, inserting the heated sheet
metal blank into a forming tool station of the press, hot forming
the sheet metal blank to the sheet metal part in the forming tool
station, during which the press performs a closing movement,
holding the forming tool station closed for a first holding time
and cooling the formed sheet metal part during the first holding
time, transferring the formed sheet metal part into a second tool
station, hardening at least regions of the sheet metal part by
cooling in the second tool station within the at least one second
holding time, wherein the forming tool station during the closing
movement of the press from an upper reversal point to a lower
reversal point is moved relative to the press by at least one
elastic actuating element so that the hot forming is terminated and
the step of holding the forming tool station closed starts before
the press reaches the lower reversal point.
Inventors: |
Frost; Georg; (Steinheim,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Benteler Automobiltechnik GmbH |
Paderborn |
|
DE |
|
|
Assignee: |
Benteler Automobiltechnik
GmbH
Paderborn
DE
|
Family ID: |
54007520 |
Appl. No.: |
14/835156 |
Filed: |
August 25, 2015 |
Current U.S.
Class: |
72/354.6 |
Current CPC
Class: |
B21D 22/022 20130101;
B21D 22/02 20130101; C21D 1/673 20130101; B21D 22/208 20130101;
B21D 24/005 20130101; B21D 37/16 20130101; B21D 53/88 20130101;
B21D 35/003 20130101 |
International
Class: |
B21D 22/02 20060101
B21D022/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2014 |
DE |
10 2014 112 244.5 |
Claims
1. A method for producing a sheet metal part which is hardened at
least in regions in a press, which has a press table, a press ram
and multiple tool stations, comprising the steps of: heating at
least regions of a sheet metal blank to a temperature above
austenitizing temperature Ac3; inserting the heated sheet metal
blank into a first one of the tool stations of the press, said
first tool station being configured as forming tool station; hot
forming the sheet metal blank to the sheet metal part in the
forming tool station, wherein the press during the hot forming step
performs a closing movement from an upper reversal point to a lower
reversal point; holding the forming tool station closed for a first
holding time; cooling the formed sheet metal part during the first
holding time; transferring the formed sheet metal part into a
second one of the tool stations tool; and hardening the sheet metal
part at least in regions by cooling the sheet metal part in the
second tool station within a second holding time, wherein the
forming tool station during the closing movement of the press is
moved relative to the press by at least one elastic actuating
element so that the hot forming is terminated and the step of
holding the forming tool station closed starts before the press
reaches the lower reversal point, wherein the upper die and the
lower die have cooling channels through which a coolant is
conducted.
2. The method of claim 1, wherein the step of holding the forming
tool station closed is terminated by the at least one elastic
actuating element during an upward movement of the press after the
press has completely passed the lower reversal point.
3. The method of claim 1, further comprising performing a trimming
and/or a hole punching in the forming tool station,
4. The method of claim 3, wherein the trimming and/or hole punching
is performed before the press is completely closed.
5. The method of claim 1, wherein a second one of the multiple tool
stations is moved at least in regions relative to the press during
the closing movement of the press by at least one other actuating
element, so that a closed state of the second tool station is
initiated before the press has reached the lower reversal
point.
6. The method of claim 5, wherein the closed state of the second
tool station is terminated at least in regions by the at least one
other elastic actuating element during an upward movement of the
press after the press has completely passed the lower reversal
point.
7. The method of claim 1, wherein the forming tool station and
preferably also the second tool station are mechanically,
hydraulically or pneumatically spring supported by the at least one
elastic actuating element.
8. The method of claim 1, further comprising transporting the sheet
metal part between two respective ones of the multiple tool
stations with a transfer system, in particular with a linearly
guided transfer bar with grippers, within a transfer time between 1
to 4 seconds, preferably between 2 to 3 seconds.
9. The method of claim 1, further comprising, in the forming tool
station cooling a first section of the sheet metal part to a first
cooling temperature that is greater than a martensite start
temperature required for transformation of a martensite
microstructure, and cooling a second section of the sheet metal
part to a second cooling temperature that is smaller than the
martensite start temperature, wherein the first cooling temperature
is in particular between 540 to 660.degree. C., thereby producing a
sheet metal component that is hardened in regions.
10. The method of claim 9, further comprising adjusting a cooling
temperature in the second tool station so that at the end of the
second holding time a temperature of the first section of the sheet
metal part is between 350 to 500.degree. C. and a temperature of
the second section of the sheet metal part is smaller than a
martensite finishing temperature required for a complete
transformation of the martensite microstructure, wherein the second
section of the sheet metal part is preferably cooled in the second
tool station to below 200.degree. C., in particular to room
temperature.
11. The method of claim 1, wherein the first holding time is
between 2 and 8 seconds and the second holding time is between 2
and 10 seconds.
12. The method of claim 1, wherein a cycle time of the press to
move between the upper reversal point and the lower reversal point
is between 3 and 11 seconds.
13. The method of claim 1, wherein the hardening step is terminated
in a third tool station, and wherein after the hardening step an
entirety of the sheet metal part has a cooling temperature of below
200.degree. C.
14. The method of claim 13, wherein the press comprises a third
tool station and wherein a cycle time of the press to move between
the upper reversal point and the lower reversal point is between 3
and 9 seconds.
15. A press for producing a sheet metal part that is hardened at
last in regions, in particular for implementing the method of claim
1, said press comprising: multiple tool stations, at least one of
the multiple tool stations being constructed as a forming tool
station that is coolable at least in regions and being configured
for hot forming of sheet metal blanks, said forming tool station
having an upper die and a lower die which in a closed state of the
forming tool station form a hollow mold space; a press ram; and a
press table; at least one elastic actuating element arranged
between the press table and the lower die so that either the lower
die is liftable relative to the press table and/or the upper die is
impingable with pressure at a distance relative to the press ram to
cause the forming tool station to assume the closed state before
the press is completely closed, wherein the upper die and the lower
die have cooling channels through which a coolant is
conductible.
16. The press of claim 15, wherein the at least one elastic
actuating element is configured so that a vertical travel of the
press is adjustable by the at least one elastic actuating element,
said vertical travel being at least 100 mm and smaller than a
maximal stroke traveled by the press between the upper and the
lower reversal point of the press.
17. The press of claim 15, wherein the at least one elastic
actuating element exerts an actuating force, which increases at
least over a portion of a travel of the press from the upper
reversal point to the lower reversal point of the press, in
particular the actuating force is at least 20 percent greater in
the closed state of the forming tool station.
18. The press of claim 12, wherein at least the forming tool
station is heatable in regions by a heating source so as to effect
a reduced cooling rate in a first section of the sheet metal part,
wherein unheated regions of the forming tool station have cooling
channels for conducting a coolant.
19. The press of claim 12, wherein the press comprises a second
tool station following the forming tool station, and wherein the
forming tool station and at least the second tool station are
heatable at least in regions in particular by a heating source to
prevent a complete hardening at least in a first section of the
sheet metal part.
20. The press of claim 19, wherein an unheated region of the second
tool station has an active cooling source that corresponds at least
to a transition section between the first section and the second
section of the sheet metal part.
21. The press of claim 20, wherein the first section and the
transition section of the sheet metal part are form fittingly
fixable at least in the second tool station by fixing elements.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority of German Patent
Application, Serial No. 10 2014 112 244.5, filed Aug. 26, 2014,
pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method and a press for
producing sheet metal parts that are hardened at least in
regions.
[0003] The following discussion of related art is provided to
assist the reader in understanding the advantages of the invention,
and is not to be construed as an admission that this related art is
prior art to this invention.
[0004] In the forming technology it is known to form sheet metal
parts from metal strip material, in particular made of steel, in a
pressing tool, by a forming operation which involves at least one
step. For this the sheet metal is uncoiled from the strip and sheet
metal blanks of defined geometry are cut from the strip.
Subsequently the sheet metal blank is formed in a press having at
least one forming tool station.
[0005] Especially in the automobile industry it is common to
produce complex geometries and along with the forming to also
adjust defined mechanical properties. For this purpose hot forming,
also known as press-hardening or forming-hardening, has been widely
used for producing chassis- and structural parts of motor
vehicles.
[0006] It would be desirable and advantageous to provide an
improved reliable method that can be used in large-scale industrial
applications, and a press for producing hardened sheet metal parts,
which has an increased production throughput and a higher resulting
product quality.
SUMMARY OF THE INVENTION
[0007] According to one aspect of the present invention, a method
for producing a sheet metal part which is hardened at least in
regions in a press which has a press table, a press ram and
multiple tool stations, includes the steps of heating at least
regions of a sheet metal blank to a temperature above austenitizing
temperature Ac3; inserting the heated sheet metal blank into a
first one of the tool stations of the press, wherein the first tool
station is configured as forming tool station; hot forming the
sheet metal blank to the sheet metal part in the forming tool
station, wherein the press during the hot forming step performs a
closing movement from an upper reversal point to a lower reversal
point; holding the forming tool station closed for a first holding
time; cooling the formed sheet metal part during the first holding
time; transferring the formed sheet metal part into a second tool
station; and hardening the sheet metal part at least in regions by
cooling the sheet metal part in the second tool station within a
second holding time, wherein the forming tool station during the
closing movement of the press is moved relative to the press by at
least one elastic actuating element so that the hot forming is
terminated and the step of holding the forming tool station closed
starts before the press reaches the lower reversal point, wherein
the upper die and the lower die have cooling channels through which
a coolant is conducted.
[0008] This enables a highly economical production process,
especially for large-scale industrial production, and at the same
time improves the quality of the part. Concretely, the cycle time
of the hot forming and hardening of the sheet metal part can be
reduced, in that the forming is initiated and terminated very early
and the holding time period for quenching the formed sheet metal
part is maximally used in the individual tool stations. In addition
inaccuracies regarding the positioning of the upper and lower dies
of the forming tool station and unevenness in the surface
properties and thickness of the sheet metal blank can be
compensated by the elastic actuating elements.
[0009] The sheet metal blank is further processed by hot forming
into the sheet metal part, wherein in the following description
both terms are also used synonymously, when the properties caused
by the forming are not the focus, but the method steps, in
particular the heat treatment and the press are explained.
[0010] Within the framework of the invention, the sheet metal blank
is heated at least in regions by known heating methods to a
temperature above austenitizing temperature of the used steel
alloy. It is useful within the framework of the invention to use
heating devices with a high heating rate, for example heating
devices that are based on contact heating with inductively or
conductively heated contact masses, direct burner heating or
furnace heating with over-temperature in the furnace chamber. Also
a combination of these heating devices with each other or with
other known furnace types is possible, for example when using sheet
metal blanks with a metallic coating.
[0011] The austenitizing temperature Ac3 is also referred to as
recrystallization temperature, wherein the degree of the
austenitizing temperature depends on the exact alloy composition.
For the method according to the invention the use of
Manganese-Boron steels has proven advantageous, which after the
heating are hardened throughout as a result of transformation of
the austenitic microstructure into martensitic microstructure.
Along with the hardness the mechanical properties yield strength
Rp0.2 and tensile strength Rm increase, while the maximal bending
angle and elongation at fracture A50 decrease.
[0012] The term holding time within the context of the present
invention means the time period in which the upper die and the
lower die of at least the forming tool station and the second tool
station are closed, i.e., at least regions of the upper die and the
lower die are in close contact with the formed sheet metal blank or
with the sheet metal part.
[0013] The term transfer includes any handling operation that
effects the transport of the sheet metal part from one tool station
into the temporally following tool station, including the removal
from the respective tool station and insertion into the respective
tool station.
[0014] The definition of the term reversal point of the press
according to the invention is that within the operating cycle the
press reaches exactly one open position, the upper reversal point,
and exactly one maximally closed position, the lower reversal
point. From the foregoing a respective maximally open position of
the press for maintenance and tool change purposes is to be
distinguished, which depends on the type of press involved and
which may be greater than the upper reversal point.
[0015] According to another advantageous feature of the invention,
edge trimming and/or hole punching are performed during or after
the hot forming in the forming tool station, in particular before
the press is fully closed. This has the advantage that a subsequent
hole-punching or edge trimming does not have to be performed when
the sheet metal part is in the cold and hardened state, which
reduces tool wear and avoids additional handling steps. Because the
hole-punching or edge trimming occurs before the press is
completely closed, the closing movement can be used for driving the
tools that are required for the hole-punching or edge trimming.
Subsequent thereto the trimmed steel sheet part is transferred into
the second tool station for fast cooling of at least regions of the
sheet metal part.
[0016] According to another advantageous feature of the invention,
the second tool station is also moved relative to the press, at
least in regions, during the closing movement of the press by at
least one elastic actuating element, so that the step of holding
the second tool station closed begins before the press has reached
the lower reversal point. However, it is also possible that the
step of holding the second tool station closed is terminated at
least in regions by an elastic actuating element only during the
upward movement of the press, after the press has completely
traversed the lower reversal point. Most preferably, the second
tool station is supported relative to the press by at least one
elastic actuating element so that during a significant portion of
time of the closing movement and during a significant portion of
time during the upward movement, the upper die and the lower die
remain closed. A significant portion of time in this context means
more than 30 percent of the duration of the closing movement and/or
the upward movement of the press.
[0017] The forming tool station, and also preferably the second
tool station can be mechanically, hydraulically or pneumatically
spring-supported by the elastic actuating element. The elastic
actuating elements themselves can act either passively purely
mechanically by permanently exerting a force on the upper or lower
die, which acts in opposition to the pressing force. A simple
example for this are helical springs or spring packages made of
other mechanical springs. However, it is also possible that at
least one elastic actuating element is actively controlled in order
to adjust a course of an actuating force of the actuating element
during the movement of the press in a differentiated manner. The
latter makes it possible to differentiate between an actuating
force level that is sufficient for the hot forming and an actuating
force level that is required for holding the tool station closed,
while at the same time reducing stress on the elastic actuating
element and the actuating system associated therewith. This also
allows reducing the overall holding time for performing the fast
cooling and for the hardening of the sheet metal part.
[0018] According to another advantageous feature of the invention,
the sheet metal part is transferred by a transfer system, in
particular by a linearly guided transfer bar with grippers, within
a cycle time of 1 to 4 seconds, preferably 2 to 3 seconds, between
at least two tool stations. This makes it possible to minimize heat
losses during the movement of the sheet metal part between the tool
stations and ideally to dispense with complex multi-axes handling
devices. Hereby it can be provided that the grippers of the
transfer system are already moved close to the sheet metal part
before the press has reached the upper reversal point. In
particular for this purpose recesses can be provided in the tool
stations for guiding the transfer system therethrough while
avoiding collision or to move the grippers close to the sheet metal
part so that the sheet metal part is immediately removed and
further transported by the transfer system or the grippers of the
forming tool station when the upper die and the lower die move
apart, i.e., after expiration of the holding time.
[0019] The method according to the invention also enables in a
particularly simple and reliable manner producing a sheet metal
part that is only hardened in regions. Hardened in regions within
the context of the present invention means that the sheet metal
part has at least a first section with a relatively low strength
and yield strength with a microstructure that is preferably
non-hardened or only hardened to a low degree and at least one
second section with high strength Rm and yield strength Rp0.2 but
reduced elongation at fracture A50 and has essentially a
martensitic microstructure. This means that the first section of
the sheet metal part has a tensile strength between 400 and 800
Mega Pascal (MPa), in particular between 450 and 650 MPa, and
predominantly ferrite-perlite microstructure components.
[0020] According to another advantageous feature of the invention,
a cooling temperature of the sheet metal part is adjusted in the
forming tool station, that is greater in a first section of the
sheet metal part than the martensite start temperature Ms required
for martensite transformation, and is smaller in a second section
than Ms, wherein the sheet metal part in the first section is in
particular cooled to a cooling temperature of between 540 and
660.degree. C. Beside the cooling temperature it is important in
the second section to also adhere to a high cooling rate above 25
Kelvin per second (K/s), in particular above 70K/s, in order to
ensure a sufficient through-hardening of the microstructure in this
section. Cooling the first section of the sheet metal part to a
lesser degree and to a higher temperature compared with the cooling
in the second section achieves that a microstructure transformation
in the sheet metal part from the austenitic state to the
martensitic state is prevented, however at the same time a
microstructure transformation from austenite to ferrite and/or
perlite is initiated.
[0021] In order to obtain a particularly stretchable sheet metal
part that can also be reliably formed, in particular deformed,
without crack-formation, a cooling temperature of the sheet metal
part can be adjusted in the second tool station which at the end of
the second holding period is between 350 and 500.degree. C. in the
first section and is smaller in the second section than the
martensite finishing temperature Mf required for complete
martensite microstructure transformation, wherein the sheet metal
part in the second section is preferably cooled to below
200.degree. C., in particular to room temperature. This ensures
that the microstructure in the first section has sufficient time at
a temperature that is significantly higher than the first section
to transform the microstructure to ferrite and/or perlite, without
significant formation of bainite or even martensite. On the other
hand the temperature treatment of the second section is intended to
achieve that a completely martensitic microstructure is generated,
which results in a tensile strength between 1400 and 2100 MPa,
preferably 1450 and 1800 MPa, depending on the steel alloy, in
particular depending on the carbon and manganese content.
[0022] The sheet metal part may also be held for a first holding
period of 2 to 8 seconds and for a second holding period between of
2 to 10 seconds. Thus the time period available for the cooling of
the formed sheet metal part and for the associated microstructure
transformation is almost doubled, while the cycle time of the press
remains unchanged. The difference between the two holding times
results in particular from the time period required for the hot
forming in the forming tool station.
[0023] According to another advantageous feature of the invention,
the press has a forming tool station and a second tool station that
follows the forming tool station in temporal succession, and the
cycle time of the press to move between its upper reversal point
and its lower reversal point is between 3 and 11 seconds. This
makes it possible to achieve a very high production rate or a high
throughput and with this very low manufacturing costs. In
combination with the production of sheet metal parts in which
regions are hardened, the additional advantage is achieved that the
properties and the quality of the sheet metal part are not
adversely affected by the fast production cycle. The produced sheet
metal parts have a high dimensional accuracy, in contrast to a
one-step hot forming and press hardening process for producing
sheet metal parts of which regions are press hardened with heated
tool sections.
[0024] According to another advantageous feature of the invention,
the hardening is only terminated in a third tool station, wherein
after this the entire sheet metal part has a cooling temperature
below 200.degree. C. This has the advantage that the cycle time of
the press can still further be reduced and at the end of the press
a cold sheet metal part can be removed that is not critical with
regard to touching. A residual heat deformation is in particular
entirely prevented by adjusting the cooling temperatures of the two
sections of the sheet metal part.
[0025] According to another advantageous feature of the invention,
the cycle time of the press with forming tool station and a second
tool station and a third tool station, i.e., in a process with
three temporally successive stations, between its upper reversal
point and its lower reversal point is between 3 and 9 seconds. In
order to achieve this short cycle time of the press, preferably a
mechanical crank press or eccentric press or a servo-electric press
is used, wherein the mechanical press is capable of traveling
through the reversal points without significant interruption of the
movement of the press. A holding time as a result of standstill of
the press is thus advantageously not required.
[0026] A further aspect of the invention relates to a press for
producing a sheet metal part, which is hardened at least in
regions. The press has multiple tool stations, a press ram and a
press table and can in particular be used to implement the method
described above. According to the invention it is provided that at
least one tool station is a forming tool station for hot forming
sheet metal blanks which can be cooled at least in regions and
which has an upper die and a lower die which form a hollow mold
space in the closed state.
[0027] The press is characterized in that between the press table
and the lower die at least one elastic actuating element is
arranged so that either the lower die can be lifted relative to the
press table and/or the upper die can be impinged with pressure at a
distance to the press ram in order to achieve the closed state of
the forming tool station before the press is completely closed,
wherein the upper die and the lower die have cooling channels
through which a coolant can be conducted.
[0028] In other words it is possible that the lower die and/or the
upper die are spaced apart from the press table or press ram at
least until the press reaches the lower reversal point. The
distance can be adjusted by the elastic actuating element and
deceases during the hot forming and preferably also during a time
period of the holding time when the upper die and the lower die are
in the closed state. For compensating the position of the upper die
and lower die relative to each other and possible uneven thickness
of the sheet metal part, it is sufficient to arrange an elastic
actuating element only on one side. However, it is also conceivable
to provide corresponding actuating elements on both sides, i.e.,
between the upper die and the press ram and between the lower die
and the press table. When a trimming or a hole punching is to be
performed in the forming tool station simultaneously with or after
the hot forming, it is also conceivable to additionally provide a
trimming tool which can be supported on an elastic actuating
element.
[0029] According to another advantageous feature of the invention,
a vertical travel of the press is adjustable by the elastic
actuating element, wherein the vertical travel is smaller than the
maximal press stroke between the upper and the lower reversal
points of the press, however, at least 100 mm. In combination with
the speed that is predetermined by the press drive during the
closing movement and during the upward movement of the press it is
thus advantageously possible to extend the holding time by contact
between the sheet metal blank, upper die and lower die.
[0030] According to another advantageous feature of the invention,
the elastic actuating element has an actuating force which
increases at least over a part of the travel from the upper
reversal point to the lower reversal point of the press, in
particular the actuating force in the closed state of the forming
tool station is at least 20% greater, which increases the contact
pressure between the tool station and the sheet metal part and with
this enables a high heat transfer or respectively makes it possible
to quickly reach at least one quenching temperature of the sheet
metal part.
[0031] In order to produce the part that is hardened only in
regions, it is further preferably provided that at least the
forming tool station is partially heatable by a heating source, in
order reduce the cooling rate in a first section of the sheet metal
part, wherein unheated regions have cooling channels for conducting
a cooling medium therethrough. Concretely this allows setting a
temperature close to room temperature in the unheated region of the
tool station, in any case however, below 200.degree. C. The heat
source allows setting a temperature of between 650 and 450.degree.
C. in the heated region. Thus the upper die and the lower die are
configured to cool the formed sheet metal part during the holding
time with different cooling rates and thereby different quenching
temperatures or to hold the sheet metal part at these temperatures.
As described above this causes a first section of the sheet metal
part to have a smaller tensile strength and a second section of the
sheet metal part to have a high strength.
[0032] As an alternative or preferably in addition it is also
possible that the forming tool station and also the second
subsequent tool station is heatable in regions in particular by a
heating source, in order to prevent the first section of the sheet
metal part to be completely hardened. This results in the same
features and advantages as described with regard to the second tool
station in the method for producing sheet metal parts only sections
of which are hardened.
[0033] According to another advantageous feature of the invention,
the unheated region of the second tool station can have an active
cooling source, which at least corresponds to a transition region
between the first section and the second section of the sheet metal
part. The cooling source serves for reducing a heat transfer
between the differently tempered sections of the sheet metal part
and thereby ensures a most narrow transition section. This has the
advantage that constructors have to take only a small surface into
consideration when designing sheet metal parts for the vehicle
industry, to which no mechanical characteristic values can directly
be assigned or for which no mechanical characteristic values can be
guarantied. This also ensures that the second region has a
continuously uniform distribution of the microstructure and the
mechanical properties. The cooling source can hereby be formed by
the coolant itself and/or can include a heat exchanger which is
arranged outside the press, and which is operatively connected with
the coolant and the cooling channels of at least the forming tool
station.
[0034] According to another advantageous feature of the invention,
the first section and the transition section of the sheet metal
part are form fittingly fixable at least in the second tool station
by fixing elements. In the case of a three-station press with
forming tool station, second tool station and third tool station,
the sheet metal part is preferably also form fittingly fixable in
the third tool station also by fixing elements. In the press
according to the invention this results in an even distribution of
the pressing force in all tool stations and in particular prevents
that the press table and the press ram are oriented unevenly
relative to each other.
BRIEF DESCRIPTION OF THE DRAWING
[0035] Other features and advantages of the present invention will
be more readily apparent upon reading the following description of
currently preferred exemplified embodiments of the invention with
reference to the accompanying drawing, in which:
[0036] FIG. 1 a first embodiment of the press according to the
invention in cross section;
[0037] FIG. 2a a cross sectional view of a second embodiment of a
forming tool station of the press according to the invention;
[0038] FIG. 2b a longitudinal sectional view of the second
embodiment of FIG. 2a;
[0039] FIG. 3 a third embodiment of a press according to the
invention in longitudinal section;
[0040] FIGS. 4a and 4b a longitudinal section through the forming
tool station illustrating the method according to the invention at
different time points of the press cycle;
[0041] FIG. 5 an embodiment of a forming tool station of press
according to the invention for producing sheet metal parts that are
hardened in regions,
[0042] FIG. 6 an alternative embodiment of a forming tool station
of a press according to the invention for producing sheet metal
parts that are hardened in regions,
[0043] FIG. 7a a longitudinal sectional view of an alternative
embodiment of a press according to the invention for producing
sheet metal parts that are hardened in regions;
[0044] FIG. 7b a horizontal sectional view of the alternative
embodiment of FIG. 7a;
[0045] FIG. 8a a longitudinal sectional view of an alternative
embodiment of a press according to the invention for producing
sheet metal parts that are hardened in regions;
[0046] FIG. 8b a horizontal sectional view of the alternative
embodiment of FIG. 8a;
[0047] FIG. 9a a time temperature course of the sheet metal blank
for the method according to the invention in a two-station press
and separate cooling station; and
[0048] FIG. 9b a time-temperature course of the sheet metal blank
for the method according to the invention in a three-station
press.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0049] Throughout all the Figures, same or corresponding elements
are generally indicated by same reference numerals. These depicted
embodiments are to be understood as illustrative of the invention
and not as limiting in any way. It should also be understood that
the drawings are not necessarily to scale and that the embodiments
are sometimes illustrated by graphic symbols, phantom lines,
diagrammatic representations and fragmentary views. In certain
instances, details which are not necessary for an understanding of
the present invention or which render other details difficult to
perceive may have been omitted.
[0050] Turning now to the drawing, and in particular to FIG. 1,
there is shown a longitudinal section of a press 1 according to the
invention with two tool stations, the forming tool station 2 and a
second tool station 3. An initially unformed sheet metal blank 26
first passes through the forming tool station 2 to be formed into a
sheet metal part 27 and then passes through the second tool station
3. The press 1 has a press ram 6 and a press table 5, wherein on
the press table 5 two clamping plates 10 are arranged. Each
clamping plate 10 further has multiple elastic actuating elements
7, which extend from the clamping plate 10 in the direction of the
press ram 6, wherein on the ends of the press ram 6 that face away
from the press table 5 a tool camping plate 9 is fixed. The
clamping plates 10 are respectively fixed on the press table 5 via
clamping elements 31. The tool clamping plates 9 are also fixed to
the ends of the actuating elements 7 that face away from the press
table 5.
[0051] On the tool clamping plates 9 two respective lower dies 12,
i.e., the lower die of the forming tool station 2 and the lower die
of the second tool station 3, are fixed via clamping elements 31'.
Corresponding to the lower die 12, an upper die 11 is fixed on the
press ram 6, wherein between the upper die 11 and the lower die 12
a sheet metal blank 26 can be arranged. The upper die 11 and the
lower die 12 each have cooling channels 17, through which a coolant
18 can be conducted. The lower die 12 further has guide elements
32', which are configured to be inserted into corresponding guide
recesses 32 and enable the guiding of the upper die 12 and the
lower die 11 relative to each other. As a result of the floating
support of the lower dies 12 provided by the elastic actuating
elements 7, possible positional deviations relative to the upper
dies 11 transversely to the movement of the press can be
compensated through the guide elements 21 and the guide recesses
32. The elastic actuating elements 7 in FIG. 1 are configured as
pneumatic spring packages, i.e., they are actuating elements 7 that
can be impinged with gas pressure, and which can be actively
controlled. Shown is the state of the press in the upper reversal
point OP, with the elastic actuating members 7 lifting the lower
die 12 relative to the press table 5, whereby the travel of the
closing movement Y of the forming tool station 2 and the second
tool station 3 is shorter than the press lift travel between the
upper reversal point OP and the lower reversal point UP of the
press.
[0052] FIG. 2a shows a further embodiment of the press according to
the invention, wherein the press 1 has two tool stations, of which,
however, only the dual forming tool station 2 is shown in the
longitudinal section. Arranged behind the forming tool stage 2 is
the not shown second tool station 3 which is also configured as
dual tool station, which receive the sheet metal blanks 26 that
were already hot formed in the forming tool stage 2 and further
cool the sheet metal blanks. The term dual tool station means that
in the tool two parts can be hot formed and cooled simultaneously
within the press cycle. In contrast to the embodiment of FIG. 1,
mechanical spring packages 8 are formed as elastic actuating
elements 7, here as a plurality of helical springs.
[0053] In the second embodiment, the press 1 also has additional
cutting means 33 on the upper die 11 and cutting means 33 on the
lower die 12, which serve for trimming the formed sheet metal blank
or the sheet metal part 27 in the still hot and unhardened state.
In particular a border trimming is performed, wherein as exemplary
shown the upper cutting means 33' are fixed on the upper die 11 via
elastic actuating elements 34. Similar to the actuating elements 7,
the elastic actuating elements 34 can act actively or passively.
The lower cutting means 33 on the other hand are connected with the
lower die 12 in a fixed and immovable manner. However, the opposite
arrangement of connecting the cutting means 33, 33' on the forming
tool station 2 is also possible. The left hand side in the image
plane exemplary illustrates that the cutting tools 33 are fixedly
but exchangeably connected to the upper die 11 and the lower die
12. Of course in praxis the same type of connection can be provided
for both, for the right halves and also for the left halves of the
forming tool station 2.
[0054] FIG. 2b shows a cross sectional view of the second
embodiment of the press 1 through the forming tool station 2, which
also in this case is arranged on the mechanical spring package 8 so
as to be movable relative the press table 5. It can be seen that
the cooling channels 17 extend over the entire longitudinal extent
of the upper die 11 and the lower die 12, including (here not
shown) an inlet and outlet of the cooling channels 17 to a cooling
source 19, which is situated for example in the form of a heat
exchanger outside of the forming stage tool 2, preferably also
outside of the press 1.
[0055] FIG. 3 shows a longitudinal sectional view of an alternative
embodiment of the press 1 according to the invention with a forming
tool station 2 and a second tool station 3, which follows the
forming tool station 2 in temporal sequence. It can be seen that
elastic actuating elements 7 in the form of mechanical spring
packages 8 are arranged on a common press table 5 via a clamping
plate 10. The ends of the elastic actuating elements 7, which face
away from the press table 5, can be coupled with a tool clamping
plate 9, which in turn is connected with the lower die 12 or is an
integral component of the lower die 12. As in the preceding
embodiments, the upper die 11 and also the lower die 12 have
cooling channels 17 for conducting a coolant 18.
[0056] FIG. 4a shows the respective operating position of the press
1 and the associated forming tool stage 2 at different time points
of the press cycle. In the center of the image on the left hand
side the press is shown in the upper reversal point OP, on the
right hand side at the time point at which the forming tool station
2 completely encloses the sheet metal blank 26 in the hollow mold
space 13 between the upper die 11 and the lower die 12 and the hot
forming takes place. The lower die 12 is still completely raised at
this time point by the elastic actuating elements 7. The closing
movement Y of the press 1 continues uninterruptedly. The actuating
travel W7 is the proportion of the press stroke by which the upper
die 11 and the lower die 12 are moved toward each other starting
from the upper reversal point UP, until the forming tool station 2
is completely closed, forming the hollow mold space 13.
[0057] FIG. 4b again shows on the left hand side the time point at
which the press is in the upper reversal point OP, however, the
right hand side illustrates the press 1 at the time point at which
the press passes through the lower reversal point UP or
respectively the time point at which the distance A that can be
adjusted by the actuating elements 7 between the lower die 12 and
the press table 5 is minimal. The press stroke travel W1 is the
distance that the press 1 travels from its upper reversal point OP
to its lower reversal point UP.
[0058] FIG. 5 shows an embodiment of a forming tool station 2 of
the press 1 according to the invention for producing sheet metal
parts 27, which are hardened in regions. The forming tool station 2
includes an upper die 11 and a lower die 12, which each have an
unheated region 22 and a heated region 21. Extending through the
unheated region 22 are cooling channels 17 for conducting a coolant
18, wherein the cooling channels 17 are connected so that the
coolant 18 can be supplied from the forming tool station 2 from
outside in a not shown cooling source, for example a heat
exchanger. In this embodiment the heated regions 21 are configured
as mold inserts 15 and are fixedly but exchangeably connected with
the unheated regions 22. In this case heating cartridges that are
heated by the gas burner or electrical resistor serve as heating
source 14. The forming tool station 2 can be coupled to the press
ram 6 via the clamping plate 10, and additionally to the press
table 5 via the mold clamping plate 9 and elastic actuating
elements 7 or to the clamping plate 10 fixed on the press table
5.
[0059] In contrast to the embodiment of FIG. 5 described above,
FIG. 6 shows a segmented upper die 11 and lower die 12 configured
for producing sheet metal parts that are hardened in regions. A
heated region 21 is arranged as separate tool segment 16 and
separated by an insulation 20 from the unheated region 22 in the
upper die 11 and in the lower die 12. This enables an
energy-efficient use of the heating source 14 and cooling sources.
After the mold closing time t.sub.2 and the first holding time
t.sub.2' in the forming tool station 2 a temperature profile is
established in the sheet metal part with a first section of the
sheet metal part having a relatively high temperature and a second
section having a relatively low temperature. This prepares the
transformation of the microstructure into martensite in the second
section and into ferrite and/or perlite in the first section.
Between the first and second sections a small transition region 30
exists which later has relatively undefined mechanical
properties.
[0060] Of course it is also possible to provide more than one
heated region 21 in the forming tool station 2, as well as in the
second tool station 3.
[0061] FIGS. 7a and 7b show a further embodiment of the entire
press 1 for producing sheet metal parts 27 that are hardened in
regions. FIG. 7a shows a longitudinal section through the press 1.
It includes the forming tool, station 2 according to FIG. 6 and a
second tool station 3 of which regions are heated. The second tool
station 3 has fixing elements 24 configured to in particular form
fittingly receive the sheet metal part (not shown). The second tool
station 3 also has regions 21 in form of a further tool segment 16
that are heated by heating sources 14. The tool segment 16 can be
configured identical in the forming tool station 2, or can be
configured stronger or more robust than in the second tool station
3 with regard to the material, the quality of the material, the
heat capacity or the temperature resistance.
[0062] In addition transfer bars 25 are indicated with dashed lines
and gripper recesses 25' in the forming tool station 2, which
recesses make it possible that grippers (not shown), which are
connected with the transfer bars 25, can be moved close to the
sheet metal part as soon as possible when the sheet metal part 27
is removed, without colliding with the lower die 12 during the
upward movement Z.
[0063] Arranged subsequent in temporal order to the second tool
station 3 is a further tool station 4, which here serves primarily
for further cooling of the sheet metal part. Like the unheated
region 23 of the second tool station 3 it has fixing elements 24 by
which the sheet metal part can be accurately fixed in position for
further cooling. The cooling itself can occur by not shown cooling
sources for example by air ventilation, air or coolant shower or by
immersion according to the German patent DE 10 2005 028 010 B3, in
that a part of the third tool station 4 can be immersed with the
sheet metal part 27 in the coolant.
[0064] As shown in FIG. 7b, in this embodiment each tool station is
configured dual action and has two molds in each of the forming
tool station 2, the second tool station 3 and the third tool
station 4. Not shown is the transfer bar for transporting the sheet
metal blank or the sheet metal part into the tool stations 2, 3, 4
or remove them form these tool stations. A heating device 35 is
indicated in which the sheet metal blanks 26 are at least partially
heated to Ac3 temperature.
[0065] In FIGS. 8a and 8b an alternative embodiment of the entire
press 1 for producing sheet metal parts 27 that are hardened in
regions is shown, in FIG. 8a as longitudinal section and in FIG. 8b
as horizontal section through the lower dies 12. In contrast to
FIG. 7, the third tool station 4' is here arranged separately in
another press 36, which has the advantage that the final cooling
can be decoupled from the fast press cycle and more space remains
in the press 1 for the forming tool station 2 and the second tool
station 3. In the present case a triple forming tool station 2 and
a triple second tool station 3 and the heating device 35 are
exemplary shown in front of the press 1.
[0066] In the third tool station 4' one of the produced sheet metal
parts 27 is shown, wherein the first section 28 and the second
section 29 and the transition section 30 can be seen with the above
described different mechanical properties and different
microstructure adjusted to the application of the sheet metal part.
Of course the sheet metal part 27 as shown here can also be
produced as shown in the embodiment according to FIG. 7.
[0067] FIGS. 9a and 9b show time-temperature courses of the sheet
metal blank 26 or sheet metal part 27 during the performance of the
method according to the invention, which time-temperature courses
are assigned to the last two embodiments.
[0068] Starting from a sheet metal blank 26 that has been heated at
least in regions to austenitizing temperature Ac3, the sheet metal
blank is transferred within 2 seconds from the heating device 35
into the forming tool station 2 of the press 1. Then the closing
movement of the press and the mold begins until the forming tool
station 2 is completely closed and the sheet metal blank 26 is hot
formed to the sheet metal part 27. Then the first holding time
t.sub.2' starts for cooling the sheet metal part 27 while the press
1 passes through the lower reversal point UP and the upward
movement begins. During the upward movement the forming tool
station 2 is opened with a delay, wherein the sheet metal part 27
due to the different temperatures and/or material properties of the
tool has cooled to different cooling temperatures T.sub.1.1 and
T.sub.1.2. The sheet metal part 27 is then further transferred
within the transfer time t.sub.3 from the forming tool station 2
into the second tool station 3. Thereafter the sheet metal part 27
is further cooled, while the second tool station 3 is closed and
the sheet metal part 27 is held fixed in position. The temperature
difference between the cooling temperature T.sub.2.1 and T.sub.2.2
in the sections 28, 29 of the sheet metal part 27 is again set by
different cooling rates by the heated and unheated regions 21, 23
of the second tool station 3 (FIG. 8b).
[0069] Subsequently the sheet metal part 27 is transferred into the
third tool station 4, 4' within the transfer time t.sub.5, wherein
FIGS. 9a and 9b differ from each other regarding this aspect. FIG.
9a corresponds to the embodiment of the press according to FIG. 8,
and FIG. 9b corresponds to the embodiment according to FIGS. 7a and
7b. It can be seen that the cooling at the cooling time t.sub.6 in
FIG. 9a lasts longer than in FIG. 9b, because the latter process
occurs linked to the cycle time of the press 1. The cooling
temperatures T.sub.3.1 and T.sub.3.2 have approached each other
very closely and are in both sections below 200.degree. C.
[0070] While the invention has been illustrated and described in
connection with currently preferred embodiments shown and described
in detail, it is not intended to be limited to the details shown
since various modifications and structural changes may be made
without departing in any way from the spirit of the present
invention. The embodiments were chosen and described in order to
best explain the principles of the invention and practical
application to thereby enable a person skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated.
[0071] What is claimed as new and desired to be protected by
Letters Patent is set forth in the appended claims and includes
equivalents of the elements recited therein:
* * * * *