U.S. patent application number 12/161551 was filed with the patent office on 2008-12-04 for method for delaying of cooling and hardening of desired zones of a sheet during a hot metal stamping process.
Invention is credited to Mehmet Terziakin.
Application Number | 20080295563 12/161551 |
Document ID | / |
Family ID | 38179798 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080295563 |
Kind Code |
A1 |
Terziakin; Mehmet |
December 4, 2008 |
Method for Delaying of Cooling and Hardening of Desired Zones of a
Sheet During a Hot Metal Stamping Process
Abstract
It is a die type which reduces the heat transfer from hot sheet
to dies, cutting/piercing tools, and blank holder in necessary
zones in the way process conditions require and can increase it in
die hardening by heat treatment effect, contrary to the approach
used for stamping of hot workpieces between cold dies. This die
type has the capability of forming the sheet and making forming
process by heat transfer in necessary zones simultaneously
according to the properties of workpiece.
Inventors: |
Terziakin; Mehmet;
(Istanbul, TR) |
Correspondence
Address: |
VENABLE, CAMPILLO, LOGAN & MEANEY, P.C.
1938 E. OSBORN RD
PHOENIX
AZ
85016-7234
US
|
Family ID: |
38179798 |
Appl. No.: |
12/161551 |
Filed: |
January 16, 2007 |
PCT Filed: |
January 16, 2007 |
PCT NO: |
PCT/TR07/00002 |
371 Date: |
July 18, 2008 |
Current U.S.
Class: |
72/364 |
Current CPC
Class: |
C21D 1/673 20130101;
B21D 22/22 20130101; B21D 22/02 20130101; B21D 24/00 20130101; B21D
22/208 20130101 |
Class at
Publication: |
72/364 |
International
Class: |
B21D 31/00 20060101
B21D031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2006 |
TR |
2006/00144 |
Claims
1) A method of blanking sheet before a hot stamping process
characterized in that, direct resistive heating of a metallic blank
by applying electrical current to said blank, blanking said work
piece at an elevated temperature by cutting certain peripheral
zones between direct resistive heating and hot forming steps,
obtaining an appropriate blank form facilitating forming, forming
said work piece at an elevated temperature.
2) A method according to claim 1, further comprising, placing upper
(8) and lower (9) cutting tools outside of upper (11) and lower
(12) dies respectively moving down one press table towards other
one, shearing at least one zone at the periphery of the blank sheet
(13) between said upper (8) and lower (9) cutting tools during
movement of said press table, forming said trimmed sheet at an
elevated temperature.
3) A method of improving die quench quality in sheet forming and
die quenching process of a heat treatable metallic blank performed
at an elevated temperature characterized in that, using die(s)
(16,24) including cooling channels (25), heating said metallic
sheet (27) up to a temperature level required for heat treatment,
forming and/or fixing said sheet (27) between said dies with
cooling channels at an elevated temperature, holding formed sheet
under compression of the dies (16,24), sweeping of sheet surface by
the cooling agent which passes through these channels (25) one side
of which is sheet surface increasing the cooling rate of sheet in
the die, quenching formed part and completing the heat
treatment.
4) A method of providing a predetermined strain rate in a hot
forming process of metallic sheet material characterized in that,
grooving channels (4, 5) on the contact surface of blank holder
members (1) to sheet (3), applying a certain contact pressure rate
to the sheet by said blank holders, keeping said contact pressure
below a certain rate so that most of the sheet surface (39 is
avoided from contacting with inner surfaces of said grooves of
contact member(s), holding said sheet between lower edges (4) of
upper blank holder member(s), and upper edges (5) of lower blank
holder member(s), reducing heat loss at the sheet (3) periphery by
reducing contact interface, reducing strength increase resulting
from temperature decrease at the periphery of forming zone,
providing a predetermined strain during material flow towards the
inner forming zone.
5) A method according to claim 4, further comprising; employing
separate contact inserts (1) contacting with hot blank,
manufacturing said contact inserts (1) which made of a material
with lower thermal conductivity than that of material of blank
holder body (2).
6) A method of piercing a hot formed sheet after forming
characterized in that, employing moveable ledge parts (33) around
the piercing zones which placed inside at least one die (31) and
can go in and out of die (31), reducing contact interface between
hot sheet and cold tools at the piercing zone by means of pushing
hot sheet out of the die surface, forming of the hot sheet by
compressing between dies, preventing piercing zone from early
contacting to die surface and from hardening by cooling during the
hot stamping; piercing by entering of the piercing edges (34) into
piercing holes (36).
7) A method of piercing of a hot formed sheet characterized in
that, employing notch (41) and ledge (42) structures around
piercing edges (40) which will be placed in the die (44) and female
piercing holes (45) over the opposite die (46); piercing by
entering of the piercing edges (40) into piercing holes (45),
taking back of some parts of sheet from piercing hole surrounding
by the notches (41) and ledge (42) structures around the piercing
zone through standing on each other with compressed sheet between
them, preventing the cooling and shriveling sheet enclosing
piercing edges (40) from squeezing the piercing tool (40) by
sending cut parts of the sheet away from surrounding of the
piercing edges (40) ensuring the piercing tool (40) to exit
easily
8) A method of trimming of a hot formed sheet part made of a heat
treatable metallic material before completing heat treatment at the
shearing zone characterized in that, employing separate and
replaceable cutting tools (29) placed outside of forming dies (16,
24), employing a movement mechanism for shearing action of said
cutting tools (29) acted by pressured fluid piston(s), forming a
metallic blank sheet (27) at an elevated temperature, keeping
formed sheet between the dies (16, 24) to obtain dimensional
stability acting said cutting tool(s) (29) by said pressured fluid
piston(s), trimming excess portions of the formed part.
9) A method as claimed in claim 8 further comprises of, employing
notches (26) at the cutting tools at the trimming and/or piercing
zones of the sheet, avoiding early cooling at the trimming and/or
piercing zone (19) resulted from conductive heat transfer between
hot sheet and cold tools at said zones, avoiding strength increase
before shearing operation at the trimming and/or piercing zones.
Description
[0001] The invention relates with a moulding system that will make
processes of sheet-metal forming, hardening by a locally controlled
heat treatment, cutting and piercing.
[0002] Hot sheet-metal stamping process is a production method that
is getting gradually important especially in automotive industry.
Along with the increasing demand of vehicle safety, structural
parts are required to be made of materials that have strength as
high as possible. Since these materials are required to have high
elongation and forming characteristics while formed materials are
asked to have high strength values, special processes are needed.
On the other hand, vehicles have to be manufactured as light as
possible, because of the increasing fuel costs. This requires using
minimum amount of material to gain a particular strength, so it is
a gradually rising tendency to use high-strength and
hard-to-be-formed types of steel-aluminum alloyed sheets in vehicle
production. Hot stamping and die quenching process has been
developed to meet these demands. In summary this method is to stamp
sheet in high temperature and then holding it in the die for a
while to ensure cooling of the sheet by heat transfer from hot
sheet to cold die. In this process hardening by heat treatment is
done by rapid cooling in the part after forming using hardenable
materials suitable to heat treatment and strength of the workpiece
can be doubled. Common application of this method in industry
consists of followings: Heating of the boron-alloyed, heat
treatment suitable, 22 MnB 5 type steel sheet to 900.degree. C.,
immediately after stamping and hardening by martensitic process
called quenching through holding in the die for a while and rapid
cooling of hot sheet. In this method, sheet, at starting conditions
having yield stress of 350 MPA and elongation of 25%, is heated;
passes to austenite phase at 900.degree. C., and stamped at about
800.degree. C. It is cooled by being hold stamped in the die about
10-20 sec. and contacting to die. At this step cooling rate of
20-30 C/sec. down to about 200.degree. C. must be ensured. When
this heat treatment conditions come true, yield stress limit of
sheet reaches to 1100 MPA and rupture limit reaches to 1500 MPA.
New elongation rate is changeable between 50-80% according to
applied process in stamping and forming capability dramatically
increases compared to cold stamping. Similar process can be carried
out for alloys of metals such as aluminum and magnesium that are
suitable for heat treatment. For example, sheets made of aluminum
7075 type alloy can be processed like that. Generally, at first,
workpiece is heated to a necessary temperature for heat treatment,
then stamped in a temperature suitable for forming capability, and
then heat treatment conditions are ensured through a cooling in
which a particular cooling rate is exceeded, so formed workpiece
has been hardened.
[0003] This process whose main features is summarized above, has
important problems in industrial application. These problems are
listed as follows: [0004] In hardening in moulding process,
sufficient cooling rate can be achieved in the zones in which
sufficient contact pressure between sheet and die exists. Because
of the die structure sufficient contact pressure can not be
obtained in many zones, so critical cooling rate can not be
achieved in every zone. This causes non-homogenous hardening and
many places of workpiece stay semi-hardened. [0005] Blank holder
can not be used in application. Blank holder causes a sudden
cooling and hardening in the surfaces of hot sheet and cold blank
holder which contact surface to surface, when it press from
surrounding. Material shifting from surrounding to forming zone is
getting hard. Therefore, only workpieces that are simple shaped and
can be formed by single-axis strain, can be hot stamped; many
workpieces that will be formed by double-axis strain are cold
formed and then heated and quenched in the die. This increases the
costs and causes that forming advantages of hot stamping can not be
used. [0006] Zones of formed workpiece on which trimming and
piercing will be applied are hardened too. Then, some expensive
solutions such as laser cutting or cutting by special equipments
will be required.
[0007] In summary, the structure which is used in cold sheet
moulding and only for forming causes defects in many aspects and
process problems in hot stamping.
[0008] Invented system is a die type which will make the contact
between hot sheet and cold die, cooling and hardening in required
order, prevent the early cooling complicating the process difficult
and ensure the post-forming critical cooling conditions.
[0009] This hot stamping die type has the capability of forming the
workpiece, including blank holder, in necessary shape; ensure the
critical cooling rate in the required parts of workpiece; making
the blank holder slide in the required strain holding the sheet in
control; preventing early hardening due to cooling from
surrounding; cutting the parts to be cut during stamping or leaving
unhardened to be cut easily later.
[0010] In this die structure, there are channels allowing flow of
cooling fluid which contacts the hot sheet and ensures the critical
cooling rate during die quenching process. While hot stamped sheet
will be hold stamped ensuring size sensitivity and preventing the
reverse bouncing, air or another fluid, which will pass through the
channels which grooved on the workpiece viewing surface of die,
will ensure the critical cooling rate and homogenous hardening by
sweeping the workpiece surface.
[0011] 5 figures have been drawn to explain the invention on
figures in details.
[0012] FIG. 1 shows the structure of blank holder involved in this
process.
[0013] FIG. 2 show the trimming process, process in which needless
extensions on the outer edge of workpiece are being cut during
stamping.
[0014] FIG. 3 shows the structure which will be able to leave some
parts of the workpiece unhardened so that processes such as
cutting, piercing and bending will be applied later. This figure
shows also cooling air flow channels and additional cooling system
on places where the die contact can not secure the sufficient
cooling rate during die quenching process.
[0015] FIG. 4 shows the structure which will secure piercing before
contact and hardening during hot stamping.
[0016] FIG. 5 shows another structure which will be able to be used
for piercing that can be done with stamping.
[0017] In FIG. 1 a blank holder which will be used for hot stamping
is shown. In this blank holder, parts (1) which will contact the
sheet are placed on the channels/chamfers (6) caved on the body of
blank holder (2) or die. Contact interfaces (4) of these parts (1)
to sheet (3) are not planar but in sawtooth shape (4). End points
(4) of these contact lines should be rounded so that sheet can
slide. It is aimed that contact lines of these upper and lower
parts don't contact the same points of the upper and lower planes
of the sheet and pressure will be homogenously distributed along
the contact lines through bouncing between lower (5) and upper (4)
contact lines on the sheet. For this reason, locations of lower (5)
and upper (4) contact lines are different. For example, such
positioning that upper contact lines (4) will be facing the
cavities between the lower contact lines (5) can be made. These
lower (5) and upper (4) contact lines preferably should be parallel
and should not intersect each other.
[0018] Existences of the string functioning hard strips (7) under
the channels (6) on which these parts (1) are located have
following benefits: supplying homogenous pressure over the sheet by
pushing out the part (1); preventing the crack of parts by
smoothing the stroke impact in the contact moment to the sheet (3)
if the parts are made of rigid and breakable materials.
[0019] These contacting parts (1) can be made of heat-resistant and
having low thermal conductivity glass or ceramic-based materials or
hard metal type materials by powder metallurgy. Such materials are
generally hard and have low thermal permeability. If channels (6)
and contacting parts (1) are in standard structure replacement of
new parts will be an easy solution in case of crack in these
components. If they are to be made of metal, hard stainless steels
will be good options because of their low thermal permeability.
[0020] FIG. 2 shows the application of trimming process--cutting
the needless extensions of workpiece in edges--in hot stamping.
This structure is applicable especially in process in which sheet
is heated by current passing through (Terziakin, U.S. Pat. No.
6,463,779), flow cross section of current doesn't change
(rectangular) so homogenous current density and heating is
obtained. Sheet having rectangular cross section are reduced to
required size by peripheral cutting. An important point in this
subject is that, sheet is hold by a blank holder having reduced
(linear) contact interfaces (4, 5) or a ceramic passing type
contact parts indicated in previous figure, without being wrinkled,
but doesn't get hardened through cooling by contacts. This type of
blank holder can be placed between die and cutting edges as well,
so sheet which has been peripheral cut can be ensured to be sliding
to die blank with a controlled strain. This option is defined in
description but not shown in figure to avoid having figure to be
complicated. The upper, moveable die is indicated as female, lower
stationary die is indicated as male in the figure. This is not
related with subject, opposite of this is applicable.
[0021] No. 8 and 9 cutting tools are mounted so that one will move
with moveable die, other one will stay stationary. Cutting edges
are shaped to scissor the sheet between them. Lower and upper
surfaces of cutting tools which will contact the sheet are
intentionally roughed in order to reduce the heat transfer from
sheet and cooling and hardening of sheet.
[0022] Cutting process in the figure is done as following: Upper
cutting edges (8) which are mounted to outer side of upper die
moves as connected with upper die (11). In FIG. 2A, sheet (13) is
placed on hinged nails (10) in order to minimize cooling due to
contact. These hinged nails (10) hold the sheet (13) by a spring or
a mechanism not shown in the figure; they don't turn by the weight
of sheet but if sheet is pushed from above they allow the sheet to
move down by turning downward. They turn into previous positions
when sheet is released from nails. Upper die (11) going down and
cutting tools (8) release the sheet (13) from nails and drop it
onto lower stationary cutting tool (9). Moveable cutting tool (8)
keeping going down along the inner side of lower stationary cutting
tool (9) scissors and cuts the sheet (13) staying between them. In
FIG. 2B dropping of this cut out sheet onto lower die. In order to
avoid shift of sheet, contact to preferably lower die or another
stationary part should be ensured simultaneously with cutting. In
FIG. 2B contact to lower die simultaneously with cutting is
ensured. Upper die (11) and moveable cutting tool (8) keep going
down and stamp the sheet between lower (12) and upper (11) dies. If
die quenching will be done in order to harden with heat treatment
effect, it will stay in this position for a while. If heat
treatment with rapid cooling by spraying a cooling agent is to be
done, upper die is lifted up after stamping and heat treatment with
rapid cooling will be done through spraying air, pulverized water
or a fluid in gas form over the sheet by nozzles which are not
shown in the figure. Another important point in this subject is
that slots or blanks which will allow the moveable cutting tool to
go down should exist around the lower die.
[0023] FIG. 3 shows how to leave desired parts unhardened during
the die quenching process. Structure of the blank holder in the
figure is the same as in previous figures. Open state and closed
state of die are shown in FIGS. 3A and 3B respectively. In this
figure, heat loss of sheet surface which contacts the blank holder
is reduced as in other two figures. Hot sheet is placed on the
nails having little contact surfaces to avoid of contacting with
blank holder and die and cooling. First of the basic subjects
explained here is that some parts of die surface which will face
the parts of the sheet which are to be cut or bended later (19, 20)
have notches (21, 26) to ensure slow cooling without contact with
die in order to ease cutting process to be done later. In the
figure, this type noncontacting zones are made in trimming (19) and
piercing (20) zones. This type noncontacting notches are grooved on
the lower (24) and upper (16) die surfaces corresponding trimming
zone (19). In the lower part of male die, this type noncontacting
notches are made on the die surface which corresponds the sheet
parts which are to be pierced later. Notches and sheet don't
contact each other in these zones. Cooling in these zones of sheet
(19, 20) occurs by heat transfer to air, which is relatively cold,
and to other neighboring parts of sheet. Since required cooling
rate for hardening can only be ensured by contact between hot sheet
and cold die, these zones will be left unhardened. For example,
critical cooling rate of 25-30 C/sec. is required for hardening of
22 MnB 5 sheet gaining martensitic structure. Martensitic hardening
can be ensured in case of cooling of sheet to about 200-250 C with
this critical cooling rate. For 7075 aluminum alloy cooling rate of
75 C/sec. is required. There will be passing strips between the
hard and soft zones in the sheet after treatment. These should be
analyzed experimentally for each material. For example, if a hole
with diameter of 20 mm. is to be made later by piercing diameter of
notch circles (17) may be required to be 30 mm. Hot stamped sheet
released from this die will be cut from relatively soft trimming
zone (19) and pierced from soft piercing zone (20) in a cutting die
later. Since outer part is hold by blank holder structure (28, 29)
having reduced contact surface, hardening from outer parts will not
occur and material shift to inward with controlled strain will be
ensured. That will be beneficial especially for process in which
double-axis strain occurs and stamping and hardening operations of
complex shaped workpieces perform in the same die and the same
step.
[0024] In FIG. 3 another important feature is that cooling channels
which will be used together with the contact between hot sheet and
cold die which will not usually be sufficient for hardening in a
workpiece that is to be hot stamped and die quenched. Uncompleted
hardening resulted from this insufficient contact is encountered on
the side edges of the sheet. Space between lower and upper dies
which allows sheet to slide, prevent the solid contact pressure
between sheet and die surfaces even when dies are completely
closed. Air channels (25) which will be grooved on the parts of die
surface, which correspond these zones, will form an air flow
channel which will be bounded by sheet surface from one side and
channel notch on the die surface from other side. There are air
pipes (22, 23) placed in the die which deliver air flow from an air
pressure system. Entrance (22) and exit (23) should be designed by
considering the channel structures (25) and feeding pressure should
be determined by considering the air flow speed required for
cooling. These channels (25) are formed when sheet is compressed
between lower (24) and upper (16) dies during hot stamping, and
pumped air or another cooling agent will increase the cooling rate
by quickly sweeping the sheet surface. By this way critical,
cooling conditions will able to be ensured easily. Sheet can be
secured to stay horizontally flowing in balance by making spaces on
the other die surface which faces the channels of one die. Those
can be appropriately designed for each workpiece according to die
shape and material properties.
[0025] Same function can be done by other ways. For example; holes
are opened on the female die surface so that sheet can be seen from
outside through these holes; nozzles which can be placed to see the
stamped sheet blows the cooling agent from this holes and this flow
sweeps the hot sheet. Since this is another application of same
principle, it is not shown on the figure. Important point in this
subject is that sheet will be hold between two dies so that it
won't make spring back or another form deviation and this form will
be fixed and permanent by cooling.
[0026] It can also be seen from the figure that at the end of
forming stage sheet is controlled and hold by blank holder and
edges which will be cut are in flat form. These edges will be
relatively soft since there is no any metallic surface contact to
these zones and they will be able to be cut easily in a cutting die
after forming.
[0027] FIG. 3 shows also a feature which performs trimming
operation between hot stamping and die quenching stages. In FIG. 3A
and FIG. 3B a blank holder type with reduced contact interface is
situated outside of the die. Inner edges of these blank holders and
outer edges of the die surface are designed as cutting tools to be
used for trimming extensions of the stamped sheet. Spacing between
these inner and outer cutting edges and their sharpness rate are
determined properly for cutting at the end of the stamping stage.
These cutting edges are preferably made as separate and replaceable
parts fixed to die and blank holder. In this way they can be
sharpened or replaced in the case of wear or damage without
changing other tools. There are spacings between edges of the dies
and hot sheet at the trimming (26) and piercing zones (21) for
avoiding early contact and hardening before cutting of the sheet
(19, 20). In the figure there are noncontacting zones at the
trimming zone (19) and piercing zone (20) for facilitating
following cutting operations by means of preventing early
hardening. Cutting edges (26) of the dies are avoided to be in
contact with the hot sheet during stamping stage. As soon as die
pair completely compress the hot sheet, outer cutting tool is moved
up or down by an external force and extensions of the sheet (19) is
cut between outer and imler cutting edges. Then hot stamped and
trimmed part is hardened by die quenching operation. During
stamping stage blank holder provides controlled strain in material
flow. At the end of the forming stage inner cutting edges of the
same tool is used for trimming operation by being acted by an
external force. In double action hydraulic presses, (secondary)
hydraulic system used for blank holder action can be used for
acting of cutting tools. Or separate hydraulic pistons (not shown
in figure) can be used for acting part (29) upward for cutting
sheet between cutting edges of part 26 and 29.
[0028] In FIG. 4 cutting tool which will be placed into hot
stamping die. FIG. 4A show the system structure when piercing tool
is in its slot (unpushed state) and ledge strip which encloses the
piercing zone is out. This state is the beginning of stamping. FIG.
4B shows the state in which sheet has been formed and piercing has
been done at the end of stamping. Application of the structure
which is used in cold cutting dies, to the hot cutting dies results
in some problems such as trying to cut of hardened workpiece and
form defects. For this reason, the structure shown in FIG. 4 should
be used. Basic principle of this subject is to prevent the contact
of zones to be cut-pierced to die surfaces and cooling-hardening
resulted from this contact before cutting operation. When suitable
conditions are achieved, that is workpiece has been formed,
piercing zones which have been prevented from contacting to cold
die surfaces and from cooling and hardening will be pierced by
piercing tool.
[0029] There is a group of piercing edges (34) connected to a
hydraulic piston (30) here. On the other die there are spacings
(35) in place where corresponds these edges. The ledge (33) around
the zone where these piercing edges are placed encloses this zone
on the die and prevents the sheet in this zone (36) from contacting
die surface and from early cooling-hardening. This enclosing
operation which suppresses contact and cooling can be done in two
ways:
[0030] In first option, there is a zone with ledges (33) which
encloses the piercing zone in the die. The sheet which will be
pushed by these ledges (33) will be prevented from contacting to
piercing zone and hardening by this way. There are two basic
options about this ledge structure. First, these ledges (33) are of
springy structure which can enter into die, prevent parts of sheet
in piercing zone from contacting during forming stage and then
enter into slot (32) on the die by being pushed by other die during
complete closing of two dies. The spring which pushes the ledges is
so strong that it can push the sheet during forming stage but can
be closed during closing of dies. These ledges are in such a form
that it can be on the same level of surrounding after entering into
die. By the use of this system, there will no bulging strip etc.
around the holes in produced workpiece. System is pushed from back
by a springy mechanism or hydraulic piston. It is situated a little
(several mm.) out of its surrounding and prevents the die
contacting sheet in piercing zone during stamping. In stamping
moment it is pushed back by contact to other die and getting on the
same level of surface of die which it is mounted. In FIG. 4B, it is
shown that this ledge (33) enters its slot (32) on the die. At this
moment piercing edges enter into spaces of other die and pierces
the compressed sheet. In FIG. 4B, for being clear, the space
between two dies is shown wide and sheet is shown away from upper
die. This has been done to show details, actually in piercing stage
two dies close, sheet is compressed between them and ledge (33)
enters its slot (32). Various options based on this principle can
be improvable.
[0031] Another option of piercing subject based on the same
principle is shown in FIG. 5. In FIG. 5, there are one male die and
connected piercing tool and a female die on which piercing holes
are placed. Although they normally stand facing each other, they
are drawn next to each other in order to show the structure of
both. In FIG. 5, hydraulic piercing tool (38, 39, 40) is placed
inner side (43) of one of dies (44). On the other die, there are
piercing holes (45) in the corresponding place which is opposite of
the location of this tool. According to the basic principle of
invention, during sheet forming, piercing zones are prevented from
contacting to die surface (46) and hole zone (45) by ledge strip
(42). On the die (44) on which piercing tool is placed, since
piercing set is located inner side (40) piercing zone of sheet is
prevented from early cooling and hardening.
[0032] During stamping, when two facing dies (44, 46) are
completely closed hydraulic piercing piston (39) is pushed out and
piercing edges (40) pierce the compressed sheet by entering into
piercing holes (45). Parts which have been cut are released from
other side of piercing holes (45). For this reason, placement of
piercing tool on upper die, downward piercing and dropping down of
parts will be beneficial. Base (38) below the piercing edges (40)
is pushed away until it seats on the opposite surface (46).
Meanwhile, notches (41) and ledges (42) around male (40) and female
(45) piercing zones seat on each other so that sheet is compressed
between them. At this moment, circles enclosing piercing zones
appear in the sheet. For this reason, a little material shift from
piercing zone to out is ensured. This situation will prevent the
sheet drilled by piercing edges (40) from standing back and cooling
and shriveling sheet from squeezing the piercing edges from
surrounding. If cooling and quenching with heat treatment effect
will be done in the die workpiece is hold in the die for a while
and then released. Piercing edges, independent from die, may be
immediately pushed and pulled or pushed for a while and then
pulled, according to the process conditions.
[0033] Notch (41) and ledge (42) pairs, which are placed around
piercing edges and corresponding piercing holes respectively and
shown as connected to moveable hydraulic piston in FIG. 5, may be
directly placed around male and female piercing sets. In this
situation, when two dies are completely closed piercing and being
pulled away of sheet from piercing tools by this notch and ledge
pairs will be done. This option will be cheaper and easier to
apply.
[0034] Since this type hot stamped workpieces are generally used in
inner structural parts in automotive industry, formation of circles
and similar figures around pierced places should be considered in
design stage. Such little changes in the shape of such workpieces
will not generally cause a problem.
* * * * *