U.S. patent application number 10/589079 was filed with the patent office on 2007-07-19 for method for producing a component by reshaping a plate, and device for carrying out said method.
This patent application is currently assigned to Audi AG. Invention is credited to Gerhard Schiessl.
Application Number | 20070163683 10/589079 |
Document ID | / |
Family ID | 34832643 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163683 |
Kind Code |
A1 |
Schiessl; Gerhard |
July 19, 2007 |
Method for producing a component by reshaping a plate, and device
for carrying out said method
Abstract
The invention relates to a method for producing a component by
reshaping a coated plate consisting of tempering steel, said plate
being austenitized before the reshaping by means of a first heat
treatment, followed by the growth of the layer thickness. The aim
of the invention is to optimize the process and to prevent the
production of scrap plates caused by interruptions to the process.
To this end, after being rapidly cooled, the heat-treated plate is
temporarily stored, and is briefly heated again to the
austenitization temperature, directly before being reshaped to form
the component. Once the structure has been modified, the plate is
reshaped and hardened. Preferably, the plate is heated a second
time by induction.
Inventors: |
Schiessl; Gerhard;
(Kosching, DE) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Audi AG
Ingolstadt
DE
85045
|
Family ID: |
34832643 |
Appl. No.: |
10/589079 |
Filed: |
January 28, 2005 |
PCT Filed: |
January 28, 2005 |
PCT NO: |
PCT/EP05/00853 |
371 Date: |
August 11, 2006 |
Current U.S.
Class: |
148/526 ;
148/531 |
Current CPC
Class: |
Y02P 10/212 20151101;
C21D 2211/008 20130101; C21D 2251/00 20130101; Y02P 10/20 20151101;
C21D 1/673 20130101; C21D 1/78 20130101; C21D 9/46 20130101 |
Class at
Publication: |
148/526 ;
148/531 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C21D 1/10 20060101 C21D001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2004 |
DE |
10 2004 007 071.7 |
Claims
1. A method for producing a component by reshaping a coated plate
of quenched and tempered steel, before reshaping in a first process
step, the plate being supplied to a first furnace and being
austenitized there and a residence time of the plate in the first
furnace being chosen such that in addition to the structure
transformation an increase in the layer thickness takes place, the
method comprising: rapid cooling and subsequent intermediate
storage of a heat treated sheet bar, repeated, brief heating of the
sheet bar in a second furnace to an austenitization temperature
directly prior to forming into the component, and forming and
hardening the sheet bar after completed structure
transformation.
2. The method as claimed in claim 1, wherein the residence time in
the first furnace is between nine minutes and thirty minutes.
3. The method as claimed in claim 1, wherein when the sheet bar is
heated again to an austenitization temperature in the second
furnace, such that only one structure transformation takes place,
but no longer an increase of layer thickness.
4. The method as claimed in claim 3, wherein a residence time of
the sheet bar in the second furnace is from ten seconds to two and
one half minutes.
5. The method as claimed in claim 1, wherein the sheet bar is
heated in the first furnace by electricity or gas, while heating in
the second furnace takes place by induction.
6. The method as claimed in claim 1, wherein the first heating
takes place at a steel or sheet manufacturer, while the second heat
treatment takes place at a processing company.
7. The method as claimed in claim 1, wherein during the second heat
treatment the sheet bar is heated to different temperatures over
its surface.
8. The method as claimed in claim 1, wherein the sheet bar, before
reheating in the second furnace, is locally reinforced by applying
at least one reinforcing sheet.
9. The process as claimed in claim 1, wherein the sheet bar is a
tailored blank.
10. A device for carrying out the process of claim 1, the device
comprising: a tool for producing sheet bars from a coil, a first
furnace for initial heat treatment including inducing an increase
in the layer thickness of the sheet bars, a cooling zone for the
sheet bars, an intermediate storage area for the sheet bars, a
second furnace for repeated heat treatment of the sheet bars, a
forming/tempering tool with a press means and a cooling device, a
trimming device for producing a trimmed finish contour and
holes.
11. The device as claimed in claim 10, wherein the first furnace is
an electricity-based and/or gas-based furnace (7), and the second
furnace is an induction furnace.
12. The device as claimed in claim 11, wherein an inductor is
integrated into the transport device which is located between the
intermediate storage and the forming/tempering tool.
13. The device as claimed in claim 10, further comprising a station
for applying at least one reinforcing sheet to the sheet bar
between the cooling zone and the second furnace.
14. The method of claim 1 wherein the plate is an aluminum-coated
plate.
15. A method of producing a component comprising: providing a
coated sheet of quenched and tempered steel; shaping the sheet;
heat treating the shaped sheet to perform a first austenitization
of the sheet, during which a structure transformation occurs
increasing the layer thickness thereof; cooling and quenching the
heat treated sheet; storing the cooled and quenched sheet;
performing a second heat treatment to perform a second
austenitization of the sheet; and forming the sheet into the
component.
16. The method of claim 15 wherein the first heat treatment is
performed in a gas or electric furnace and/or the second heat
treatment is performed in an induction furnace.
17. The method of claim 15, further comprising reinforcing the
sheet between the heat treatment steps.
18. The method of claim 15 wherein the first heat treatment
comprises a residence time of between approximately 9 and 30
minutes.
19. The method of claim 15 wherein second heat treatment comprises
a residence time of between approximately 10 seconds to two
minutes.
20. The method of claim 15 wherein during the second heat treatment
step, no change in thickness of the sheet occurs.
21. The method of claim 15 wherein the sheet has a martensitic
structure following the forming step.
22. The method of claim 15, further comprising transporting the
sheet from a first location, where the first heat treatment is
performed.
23. The method of claim 22 wherein the second heat treatment is
performed during the transporting.
24. The method of claim 15 wherein the second heat treatment
comprises heating the sheet to different intensities at different
locations thereof.
25. A product produced by the method of claim 15.
Description
[0001] The invention relates to a method for producing a component
by reshaping a coated, preferably aluminum-coated plate of quenched
and tempered steel as claimed in the preamble of claim 1. The
invention furthermore relates to a device for carrying out said
method.
[0002] The prior art generally discloses various forming processes
for sheet bars from quenched and tempered steel in conjunction with
hardening processes. In a so-called "direct" forming process a flat
sheet bar of quenched and tempered steel is austenitized in a
furnace, preferably a continuous furnace, in a protective gas
atmosphere. For example, a quenched and tempered steel of 22MnB5
grade which is annealed for several minutes at approximately
950.degree. C. for austenitizing can be used. Then the hot,
austenitized flat sheet bar is inserted with a preferably automated
transfer means into a forming/tempering tool which is cooled for
serial processes. This tool is a component of a press and when the
latter is closed, the hot sheet bar is formed into a component of
the final shape and in the closed tool, when the closing force is
applied, it is cooled relatively quickly and thus hardened. The
hardened component is removed from the tool, and if it is uncoated
sheet, it is descaled in a cleaning step, for example by sand
blasting or shot peening (this is not essential for coated
components, since for example aluminized sheets offer sufficient
corrosion protection and scaling is prevented). This is followed by
finish contour and hole trimming of the finish-formed and hardened
component, preferably by means of laser cutting. Mechanical cutting
in a so-called press combination is also conceivable.
[0003] During heat treatment in the furnace, for example an
aluminum coating approximately 25 .mu.m thick in the initial state
undergoes growth in layer thickness to approximately 45 .mu.m, and
directly bordering the base material of the sheet bar an AlSi layer
with iron diffused therein is formed therefrom, which layer bears a
relatively hard and brittle AlSi layer also forming which performs
the actual anticorrosion function.
[0004] A typical process sequence (hot forming curve 20) with
respect to heat treatment of the sheet bar in the course of its
forming is shown for example in FIG. 1 in a time-temperature
diagram. Depending on the grade of the quenched and tempered steel
used, sheet metal thickness, initial layer thickness, etc., the
values given in FIG. 1 are of course subject to certain
fluctuations (lower/upper heat treatment boundary 18, 19). Thus it
is easily conceivable for the sheet bar to be in the furnace over a
residence time of up to 30 minutes.
[0005] The furnace used is often a so-called continuous furnace
with mold nests or sheet bar receivers, or a grate pusher-type
furnace with grates which carry the sheet bars and heat them within
approximately 2 minutes by means of gas burners to the
austenitization temperature and then keep them at this temperature
for several minutes by means of electrical heating. The advantage
of the gas burner is higher output, conversely conventional
electrical heating can be better controlled.
[0006] As shown in FIG. 1 the sheet bar is heated in the furnace to
a target temperature of approximately 950.degree. C. and kept at
this temperature. Austenitization is done at temperatures above
approximately 720.degree. C. Conventionally the residence time in
the furnace is approximately 9 minutes, the sheet bars within the
first two minutes heating to the target temperature, while in the
following approximately 7 minutes regranulation of the base
material from a cubic-space centered ferrite-perlite structure into
cubic surface-centered austenite which is necessary for hardening
takes place. In addition, the indicated time interval is also
important mainly to achieve sufficient growth of the ALSi
protective layer.
[0007] In particular, with respect to the minimum annealing
temperature and maximum residence time of the sheet bar in the
furnace there are certain, more or less narrow limits, within which
the process delivers quality components, i.e., that the sheet bars
removed from the furnace can still be used for the forming process
and further applications. If a problem arises in the continuing
process, whether when a sheet bar is removed from the furnace and
further transported to the forming/tempering tool or within the
finish contour and hole trimming station, for the duration of the
problem no more sheet bars can be removed from the furnace, the
maximum allowable residence time is generally exceeded, and all the
sheet bars in the furnace are scrap and must be disposed of.
[0008] The object of the invention is to develop the generic
process for producing a component by forming a coated sheet bar of
quenched and tempered steel such that the process sequence can be
optimized and that especially the costly formation of scrap sheet
bars can be prevented if process disruptions arise.
[0009] This object is achieved with respect to the process with the
other features according to the characterizing part of claim 1 and
with respect to the device for carrying out the process as claimed
in the invention with the features of claim 10.
[0010] The advantages of the procedure as claimed in the invention
are manifold. Thus, now there is no longer any relationship with
respect to the residence time of the sheet bars within the furnace
and problems in the process outside the furnace. By decoupling the
sequences for the actual process of sheet bar forming, the amount
of area required and infrastructure are less.
Buffering/intermediate storage of the quenched and tempered sheet
bars is possible so that heat treatment, to influence the AlSi
layer, additionally can easily take place at the steel manufacturer
or sheet metal supplier.
[0011] This upstream heat treatment removed from storage is already
known, as follows from EP 0 946 311 B1 and DE 102 12 400 C1.
Annealing treatment by means of induction heating viewed in itself
is also already prior art, as is also mentioned for example in the
latter document.
[0012] Advantageous embodiments and developments of the invention
are claimed in the dependent claims.
[0013] The invention will be detailed below using the exemplary
embodiment.
[0014] FIG. 1 shows the process sequence as claimed in the
invention for producing a component by forming a sheet bar,
[0015] FIG. 2 shows the temperature-time diagram of the first sheet
bar heat treatment, and
[0016] FIG. 3 shows the temperature-time diagram of the second
sheet bar heat treatment.
[0017] FIG. 1 schematically shows the process sequence as claimed
in the invention for producing a component 5 by forming a coated
sheet bar 1 of quenched and tempered steel by means of a device 2
suited for this purpose. From the steel delivered in the rolled
state, a so-called coil 3, by means of a tool 4 the steel is
unrolled, flattened, and the size of the sheet bar 1 necessary for
the finished component 5 is punched out or cut to size. From there
the sheet bars 1 are supplied to a buffer zone 6. This intermediate
storage is not absolutely necessary, rather the sheet bars 1 can
also be supplied directly after leaving the tool 4 to a first
furnace 7 in which they undergo heat treatment according to the
temperature-time diagram shown in FIG. 2. Directly downstream from
the first furnace 7 is a cooling zone 8 in which the sheet bars 1
are quenched and pass through the concluding phases of heat
treatment. Leaving the cooling zone 8, the quenched and tempered
sheet bars 1 are supplied to an intermediate storage 9.
[0018] The first furnace 7 can be the aforementioned continuous
furnace, a revolving furnace, or the like in terms of its
structural design.
[0019] The individual phases of heat treatment were explained in
the introductory section with reference to FIG. 2. The relatively
slow heating to the target temperature and the remaining residence
time in the first furnace 7 for inducing austenitization and for
changing the topography (coating structure, layer thickness) add up
to the total residence time of approximately 9 minutes, and
empirically a maximum residence time of 30 minutes should not be
exceeded, so that the sheet bar does not become unusable. The
transport into the cooling zone 8 and the quenching of the sheet
bar 1 there take place within relatively short time intervals,
while the remaining cooling to room temperature RT can take place
in the intermediate storage 9. At the end of heat treatment the
sheet bar 1 has a martensitic structure.
[0020] By means of a suitable transport device 10, for example an
articulated arm robot, the sheet bars 1 are supplied to an
induction furnace 11, from where they are inserted into a cooled
forming/tempering tool 13 suitable for serial processes by way of
another transport device 12, for example in turn an articulated arm
robot. A press means 14 and a cooling device 15 are assigned to the
tool 13, and when the press means 14 is closed the hot sheet bar 1
is formed into a component 5 with the final shape and is rapidly
cooled and hardened in the closed forming/tempering tool 13 with
the closing force applied. In the last process step each component
5 is supplied via a transport means 16 to a trimming device 17,
where finish contour and hole trimming of the completely formed and
hardened component 5 is done preferably by means of laser cutting.
Of course this can also take place mechanically by way of suitable
trimming blades.
[0021] The heat treatment of the sheet bar 1 which takes place in
the induction furnace 11 and in the downstream forming/tempering
tool 13 is illustrated in the temperature-time diagram as shown in
FIG. 3 using the hot forming curve 20 and lower/upper heat
treatment boundary 18, 19. It is characterized by an extremely
short residence time of the sheet bar in the induction furnace 11.
While heating to the target temperature (austenitization
temperature) takes place within a few seconds (approximately ten
seconds), a downstream short residence time of approximately ten
seconds up to a maximum two minutes is used to allow a structure
transformation to take place. A change of thickness and structure
of the coating is no longer necessary since this has already taken
place in the first furnace 7. After an accordingly extremely short
residence time in the induction furnace 11, the sheet bar can be
supplied to the forming/tempering tool 13 in which in addition to
forming, quenching takes place in the same manner (same behavior of
the hot forming curve 20) as in the cooling zone 8. When leaving
the forming/tempering tool 13 the component 5 already has a
martensitic structure, cooling to room temperature RT can take
place upon further transport to or within the trimming device
17.
[0022] In this way a sheet bar 1 having an original tensile
strength of approximately 500 to 600 N/mm.sup.2 is formed into a
component 5 having a tensile strength of approximately 1300 to 1500
N/mm.sup.2.
[0023] In an advantageous development of the invention it would be
conceivable to heat the sheet bar 1 in the induction furnace 11 in
part to different intensities, with the result that if desired the
formed and quenched component 5 has partially different
strengths.
[0024] Furthermore, it would be possible preferably to locally
reinforce the sheet bar 1 before the second heat treatment
(induction furnace 11) for example by welding on reinforcing sheets
(patches). A composite sheet patched in this way could then be sent
to the second furnace and afterwards to the forming/tempering tool
13. This would have altogether positive effects on the material
properties and accuracy of shape.
[0025] The process as claimed in the invention can also be
advantageously used when using tailored blanks as sheet bars.
[0026] One important advantage of the invention is the possibility
of decoupling the individual process steps. Thus the first heat
treatment in the furnace 7 can take place at the steel or sheet
manufacturer and the sheet bars 1 pretreated in this way can then
be made available to the processing company (for example, motor
vehicle manufacturer) (intermediate storage 9).
[0027] In another advantageous development of the invention it is
conceivable to assign an inductor to the transport device 10 and to
structurally integrate it into the transport device 10, so that the
heat treatment of the sheet bar 1 can proceed during its transport
to the forming/tempering tool 13. A separate induction furnace 11
and another transport device 12 downstream from it can thus be
eliminated.
* * * * *