Note: Descriptions are shown in the official language in which they were submitted.
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M13THOD OF STAMPING FOR ALUMINUM OR ALUMINUM ALLOY SHEET
13ACKGROUND OF THE INVENTION
Field of the Invention
The present invention concerns a method of stampin~
for an aluminum or aluminum alloy sheet suitable to such
application uses that ~xcellent formability is required
regarding complicate shapes difficult to be formed, for
example, in automobile parts, electric parts, aircraft
parts and equipments.
Description of the Prior Art
In the forming of automobile parts, electric parts,
aircraft parts and equipments made of aluminum or
aluminum alloys, there has been processing a limit in
usual stamping, and in a case where the processing
degree is large and severe or in a case of an article
havin~ a complicate shape, stampin~ can not be applied
or~ otherwise, an aimed shape has to be obtained
stepwise by a pressing process divided into a plurality
of st~ps. ;
In the latter case, the production cost is
inevitably incxeased. ~owever, forming of articles
needing severe processing degree and having complicate
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shapes has been demanded more and more and cost down by
the reduction of the number of forming steps has keenly
been desired in recent years.
On the other hand, weight reduction of automobiles
has been studied earnestly in order to suppress the
increase of gaseous carbon dioxide in the atmospheric
air with a view point of environmental problems such as
global warming and destruction of ozone layers. As one
o countermeasures for the weight reductionr use of
aluminum or aluminum alloy sheets has been increased
more instead of steel sheets that have been used mainly
as the material for stamping. However, since the
formability of aluminum or aluminum alloy sheets is
inferior to that of the steel plates, there has been
also a strong need for the improvement in view of the
stampin~ process.
Regarding such requirements, there has been made an
attempt for the improvement of the formability of
materials by making the ingredient composition and ~`
production steps for aluminum materials appropriate, as
proposed in Japanese Patent Laid-Open Sho 63-89649 in
view of the materials. ~owever, since the demand for
the fvxming of complicate shapes with more severe
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processing degree has become increased in recent years,
improvement only for the materials is insufficient.
on the other hand, also regarding the processing
technique~ Laid-Open Technical Report 89-15623 published
from Nippon Hatsumei Kyokai (October 10, 1989) has
proposed a forming process at a cryogenic temperature as
a novel forming process. However, the above-mentioned
method only discloses that aluminum or aluminum alloys
are put to a cryogenic temperature and shows the effect
of the forming temperature on the mechanical property
and the Erichsen value of the materials, which is not
yet satisfactory in view of practical situation for the
improvement of actual formability.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome
the foregoing drawbacks in the prior art and provide a
method capable of actually practicing stamping for
aluminum or aluminum alloy plates, particularly,
requiriny large and severe processing degree and having
complicate shapes.
Another object of the present invention is to
provide a method capable of actually practicing stamping
for aluminum and aluminum alloy sheets requiring large
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and severe processin~ degree and having complicate
shapes, by using a forming die of a type not equipped
with a cooling structure.
A further object of the present invention is to
provide a method of stamping for aluminum or aluminum
alloy sheets capable of improving the formability to an
extent equal with or superior to that of steel plates,
by using a forming die of a type having a cooling
structure.
For overcoming the foregoing problems, the present
inventor has made earnest studies on an actually
practicable method of stamping for aluminum or aluminum
alloy sheets as proposed above and, as a result, have
accomplished the present invention based on the finding
that the foregoing problem can be solved effectively by
coating a specific press lubricant and controlling a
forming temperature in a case of using a forming die not
equipped with a cooling structure, or by ccntrolling a
temperature of a forming die and a temperature of a
stock material in a case of using a die equipped with a
specific cooling structure.
In summary, the present invention provides a method
of stamping for an aluminum or aluminum alloy plate,
which comprises coating a liquid lubricant which becomes
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waxy at a cryogenic temperature on an aluminum or
aluminum alloy plate, then cooling the sheet and
conducting stamping in a cryogenic temperature region by
using a die of a non-cooling structure type.
Further the present invention provides, in another
aspect, a method of stamping for an aluminum or aluminum
alloy plate, which comprises coating a specific
lubricant, that is, either a lubricant comprising a
paraffin as the main ingredient and having a viscosity
at 40C of less than 50 cSt, or a lubricant containing
an ester as the main ingredient, having a pour point in
a range from 50 to -100C and a vlscosity at 40C of
less than 50 cSt to an aluminum or aluminum alloy plate 7
and then applying stamping directly.
Further, the present invention, in a further
aspect, provides a method of stamping for an aluminum or
aluminum alloy plate, which comprises conducting
stamping by using a die for forming made of a material
not causing transient temperature and of a coolin~
structure type in which a liquid nitrogen is circulated
through the inside of a punch for cooling and jetted out
from the upper portion, controlling the die temperature
to a range from -50C to -196C and controlling the
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temperature of the aluminum or aluminum alloy sheet to a
range from -50C to -196C.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an explanatory view illustrating a
spherical top extended die (non-cooling structure type)
used in a forming test. . :
Fig. 2 is an e~planatory view illustrating a die
cooling device used in a forming test.
Fig. 3 is a view illustrating the effect of forming
temperature and cooling condition on the extending
height in Example 5.
Fig. 4 is a view illustrating the change of the
temperature sheet when it is immersed into and taken out
of the liquid nitrogen in Example 3.
BRIEF DESCRIPTION OF THE INVENTION
(1) Forming by Using a Die of Non-cooling Structure Type
Usually, stamping is carried out by coating a pres~
lubricant to a forming mater.ial or a forming die at a
room temperature and it has been considered so fax that
the lubricant is degraded when it is cooled to a
cryogenic temperature lower than -40~C to deteriorate
the lubricity. However, it has been found that the
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liquid lubricant actually becomes waxy to rather improve
the lubricity when it is cooled to a cryo~enic
temperature.
That is, it has been found that when the forming
material coated with a liquid lubrisant is immersed in a
liquid nitrogen and then taken out therefrom, the
lubricant changes as: non-waxy state ~ waxy state ~
liquid with elapse of time, in which the lubricity is
improved in the waxy state. Furthermore, it has al50
been found that stamping at a cryogenic temperature is
extremely effective in view of the formability since the
mechanical property of the stock material at the
cryogenic temperature i5 improved more both for the
strength and the elongation than those at 2 room
temperature even not in the waxy state. Accordingly, in
the present invention, stamping is conducted at a
cryogenic temperature, preferably, in a state where the
liquid lubricant becomes waxy.
The liquid lubricant is previou~ly coated to a
forming material prior to stamping, that isl prior to
immersion in the li~uid nitrogen. The coating method
and the amount of coating may be determines in a
customary manner. The liquid lubricant is coated as it
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As the liquid lubricant, there can be mentioned
mineral oils (paraffinic or naphthenic series) or
synthetic oils (ester) but the mineral oils are
preferred. As the example of the former, mineral oil
(liquid paraffin) can be mentioned.
Further, as other example of the liquid lubricallt,
a lubricant comprising paraffin 2S the main ingredient
and having a viscosity at 4~C of less than 50 cSt can
be mentioned. Generally, the lubricant has higher
viscosity as the temperature is lower and, when a
paraffin-containing lubricant is cooled, paraffin
solidifies into a waxy state to form a lubricant ;~
membrane thereby improving the lubricating effect.
Further, the higher the viscosity the better the
lubricity of the lubricant. However, if the viscosity
at 40C exceeds 50 cSt, though formability is
preferable, the lubricant becomes solid wax at a normal
temperature tending to cause degreasing failure in the
degreasing step, which results in joining failure in the
subsequent joining step such as adhes;on or welding.
The paraffin-rich lubricant may be composed only of
the paraffin (100~ by weight) and, in addition,
preferably contains more than 50% by weight of paraffin,
bec~use it is advantageous in that a homogeneous
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membrane is formed when the paraffin as the ingredient
becomes waxy at a low temperature. Further, ingredients
other than the paraffin, for exampler an extreme
pressure agent may also be added as required, except for
those ingredients which coagulate at a low temperature
(frozen) and result in the destruction of the lubricant
membrane (water or the like).
Further, as another examplP of the liquid
lubricant, there can be mentioned a lubricant comprising
an ester as the main ingredient, haviny a pour point
within a range from -50~C to -100C and a viscosity at
40C of less than 50 cSt. As the temperature of the
lubricant is lower, the viscosity is higher and the
lubricancy is improved more. However, since the pour
point is as high as 10C in mineral oils and the
lubricating effect is lowered remarkably, an ester type
synthesis oil capable of lowering the pour point is used
as the lubricant. The ester type synthesis oil can
include, for example, diester and polyol ester.
Further, it is better that the pour point is lower.
However, if it is higher than -50C, lubricity is
degraded remarkably at a low temperature, whereas
preparation of a lubricant with a pour point of lower
than -100C i5 industrially difficult and it is not
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preferred in view of production cost as well.Accordingly, the pour point of the ester type synthetic
oil is limited to a range from -50C to ~100C.
Further, in the course of cooling the oil, the highest
temperature at which the oil loses fluidity is referred
to as a coagulation point and a temperature higher by
2.5 than that is referred to as a pour point which is a
temperature at the instance the oil loses the fluidity
The reason why the viscosity of the lubricant is limited
as described above is the same as that in the case of
the paraffin-rich lubricant.
The ester type synthetic oil includes a case that
it is composed only of the ester (100% by weight~ and
in addition, preferably include a case of containing
more than 70~ by weight of ester, because it is
advantageous in that a homogeneous membrane is formed
when the ester as the main ingredient becomes a film-
like state at a lo~ temperature. Further, other
ingredients than the ester, for example, an extreme
pressure agent may also be added as required, except for
those ingredients which coagulate at a low temperature
~fro2en) and result in the destruction of the lubricant
membrane (water or the like)~ As a method of cooling
the mateFial coated with the liquid lubxicant to a
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cryogenic temperature, the material is immersed in a
liquid nitrogen in view of the general applicability and
the cost. A measure that the liquid lubr.icant stays
waxy when it is taken out after immersion is within 15
to 45 sec in a case of using the liquid n:itrogen as a
coolant. Since this is more than 15 sec, the operation
time is torelable from take-out to stamping, which is
practically advantageous.
After cooling, the material is formed in a
cryogenic temperature region, preferably, from -50C to
-196C. In a case of using a lubricant having paraffin
as the main ingredient and a viscosity at 40C of less
than 50 cSt, or a lubricant comprising an ester as the
main ingredient, having a pour point from -50C to -
100C and a viscosity at 40C of less than 50 cSt, it is
preferred to conduct forming within a temperature range
from -50C to -150C, because the effect of improv.ing
the formability is insufficient in a case of a
temperature higher than -50C, whereas reduction of the
formability is caused due to the degradation of the
lubricant and the cost i5 increased in a case of a
temperature lower than -150C.
In a case of using a lubricant having the paraffin
as the main ingredient and the viscosity at 4UC of less
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than 50 cSt or a lubricant having the ester as the main
ingredient, the pour point from -50C to -150~C and the
ViSCQSity at 40C of lower than 50 cStl .it is possible
to coat the lubricant to the material sheet and can be
formed directly (at normal temperature) without cooling.
Although the effect for improving the forming product i5
lower, the de~reasing property is better as compared
with the case of conducting forming within the above-
mentioned temperature range (-50C to ~15~C).
As a die not equipped with a cooling structure, a
structure, for example, as shown in Fig. 1 can be
mentioned. In the drawing, are shown die 1, a blank
holder 2 ~nd a punch 3.
(2) Forming by Using a Die of a Cooling Structure Type
The method previously proposed by the present
inventor, et al is a method of conducting forming at a
normal temperature although the aluminum alloy is
applied with a cryogenic treatment. Accordingly, it is
considered that the temperature of the sheet is elevated
by the die and the atmosphere and performance at a
cryogenic temperature can not be obtained~ However,
lowering of the die leads to embrittling crack of the
die which is not practical. In view of the above, the
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present inventors have made study and experiment on the
material of the die, and made a close investigation for
the effect of the die temperature and the atmospheric
temperature on the formability.
That is, the present inventors, et a:L
experimentally confirmed that a conventional die
material (alloy tool steel SKD 11) results in
embrittling fracture at a temperature lower than -100C/
whereas austenite series stainless steel and Cu Ni alloy
having face-centered cubic lattice does not result in
embrittling fracture even at -196C and causes no
problem as the die material even in repeating pressing.
On the other hand, an aluminum alloy sheet coated with a
lubricant was inserted into a die, the temperature both
for the sheet and the die was lowered and the effect of
temperature lowering on the formability was
investiyated. As a result, it was confirmed that the
formability was improved as the temperature was lowered
and, in particular, a formability comparable with that
of the steel sheet could be obtained at -196C.
A diel though different depending on the shape of
products, basically comprises a punch and a die~
Various methods may be considered for lowering the die
temperature to a ~ryogenic temperature (-196C). What
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is essential i~ ho~ to make the entire die to the
cryogenic temperature.
According to the study of the present inventors, et
al, it has been found that a method of circulating a
liquid nitrogen in the punch and then jetting out the
liquid nitrogen over the entire die needs a shorter time
for reaching the cryogenic temperature and is effective.
Specifically, as shown in Fig. 2, (1) liquid nitrogen is
spirally circulated through the inside of the punch, and
(2) the liquid nitrogen is jetted out from the upper
portion of the die to cool the entire die. In the
drawing, are shown a die cooling valve 1, a temperature
control valve 2, a punch cooling valve 3, a liquid
nitrogen cylinder 4, a die 5, a blank holder 6 and a
punch 7. ~n the case of using the liquid nitrogen, the
temperature of the liquid nitrogen for cooling the punch
7 and the entire die is controlled by the temperature
control valve 2 respectively but it is of course
possible to use other coolant in combination with the
liquid nitrogen.
According to this cooling method, the die
temperature can be controlled easily within a range from
-50 to -196C. That is, it can rapidly cool the entire
die, as well as make the temperature o the entire punch
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lower in view of the formability. In particular,
improvement of the formability depends on the balance
between the strength of the punch shoulder and the
deformation strength in the dice~ in which the
improvement for the strength of the former is
particularly important. The punch main body can be
cooled more efficiently by spirally arranging a pipe in
the punch for circulating the coolant ~liquid nitrogen).
In a case of forming under such a condition, there
are a mode of forming while making the temperature of
the die and the temperature of the aluminum or aluminum
alloy sheet identical and a mode of forming while giving
a temperature slope. In each of the cases, no
improvement is obtainable for the formability at a
temperature exceeding -50C (elevated temperature)~
which has no significant difference with that at a
normal temperature. Further, a cryogenic temperature
lower than -196C (for example, -200C) can not be
obtained easily by using the liquid nitrogen and it
requires liquid helium, which results in a problem in
view of handling and cost. Accordingly, the
temperatures for the die and the aluminum or aluminum
alloy sheet are controlled, respectively, to a range
from -50~C to -196C.
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As in the former mode, when forming is applied~
w.ith the temperature for the aluminum or aluminum alloy
sheet being identical with that for the die, the
formability is improved as the temperature approaches -
196C.
On the other hand, as in the latter case, when
forming is conducted under a temperature slope, a
further improvement is obtainable for the formability.
In order to attain this, it is ne~essary to fully open
the supply of the liquid nitrogen to the inside of the
punch and control the amount of the liquid nitrogen from
the blank holder. The formability more excellent than
that obtained in a case where the temperature of the
aluminum or the aluminum alloy sheet is made identical
with that of the die at -196C can be attained by
controlling the temperature for the punch constant at -
1~6C and the temperature for the die corresponding to
the flange and the material at -5G to -100C. If the
temperature corresponding to the flange is within a
range from normal temperature to -50C, instantaneous
cooling of the punch material (cooling from the punch)
is insufficient in which no improvement can be expected
for the strength of the shoulder and the formability is
not improved. On the other hand, in a case of a
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temperature lower than -100C, the deformation
resistance of the Flange is increased, by which no
remarkable improvement can be obtained for the
formability.
It is important for the material of the die that it
is free from embrittllng fracture at the cryogenic
temperature and it is necessary that the die can be
manufactured easily and at a low cost. With the above-
mentioned view point, austenite series stainless steel
and Cu~Ni alloy are suitable as the material of the die
showing no abrupt change of characteristics depending on
the temperature (transition temperature). As the
austenite series stainless steel, SUS 304 is a typical
steel species, while Colson alloy Ni-3%, can be
mentioned as the Cu-Ni alloy. It will be apparent that
any of materials may be used so long as it causes no
embrittling fracture or cracking in the stamping at a
cryogenic temp~rature.
The aluminum or the aluminum alloy sheet can be
controlled to a desired temperature within the above-
mentioned temperature range by an appropriate method.
Usually, a method of passing (immersing) the sheet in
the liquid nitrogen or a method of jetting out a coolant
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on the sheet just before the forming process is adopted.
A particularly preferred method is as follows.
That is, after coating the aluminum or aluminum
alloy sheet coil or sheet with a lubricant, it is
immersed in a liquid nitrogen for more than 15 sec, the
temperature of the sheet is lowered to a cryogenic
temperature lower than -100C and, subsequently, the die
is inserted into the cooling structure within lS sec.
After coating the lubricant, the sheet is immersed in
the liquid nitrogen. It is desirable that the sheet
temperature is at least lower than -100C and uniform.
If the immersion time is shorter than lS sec, such a
temperature can not be ensured and, as a result, (1
improvement for the formability at a cryogenic
temperature can not be obtained and (2) defect
prevention due to increased strength under the cryogenic
temperature can not be obtained. Accordingly, more than
15 sec of time is required as the immersion time in the
liquid nitrogenO Immersion for a longer period of time
gives a problem in productivity but this is effective
for a further improvement of the formability Then, the
material taken out of the liquid nitrogen is inserted
into the die of the cooling structure shown in Figi 20
If it is inserted after a period beyond 15 sec, the
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sheet temperature is elevated leading to the result in
(1) above. According~y, the material taken out of the
liquid nitrogen is inserted within 15 sec.
The lubricant is coated prior to the cooling of the
aluminum or aluminum alloy sheet foil or sheet. There
is no particular restrlction on the lubricant but it
should be noted that this gives an effect on the
formability at the cryogenic temperature. In
particular, a lubricant that crystallizes in the
cryogenic temperature region due to the water content
(exhibiting icy surface) is not preferred since it
results in unevenness in the stamping and gives less
effect for the improvement of the formability. Further,
a lubricant having no fluidity at a normal temperatu-re
is not preferred since this causes defects in the
subsequent step. Accordingly, a lubricant that hecomes
waxy or film-like state also at a cryogenic temperature
and has a viscosity at 20C of less than S0 cSt is
preferredO As one of themr liquid paraffin can be
mentioned.
The forming material is an aluminum sheet or an
aluminum alloy plate. Among them, there is no
particular restriction, for example, on the material of
the aluminum alloy sheet and a material of an
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appropriate ingredient system and composition may be
selected depending on the required performance of the
final product. For instance, Al-Mg sexies alloys
containing more than 2.5 weight ~ Mg, more preferably,
Al-high Mg (3 - 6~ Mg) systems are preferred in view of
the formability and the strength. The reason is that My
is an element giving strength and formability and they
are most suitable as the material for forming having
both of the characteristics together. However, if the
Mg content is less than 2.5% by weight, the strength of
the product after forming is insufficient. So long as
Mg is incorporated by a predetermined amount, an
ingredient composition that can be used for the
application use of this type is obtainable and,
accordingly, other alloy ingredlents can be contained
properly as required.
BEST MODE CARRYING OUT THE INVENTION
Examples of the present invention are to be shown.
It will be apparent that the present invention is not
limited only to these examples but various modes of
practice are possible within a scope of the present
invention.
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Example 1
Using JIS 5182 alloy O material of 1 mm sheet
thickness as the material for forming, stamping was
carried out by a spherical head extended dle shown in
Fig. 1 using a mechanical press. In this case, after
Goating mineral oil (liquid paraffin) as a liquid
lubricant to the material, it was immersed in a liquid
nitrogen for 2 min, then taken out and soon applied with
stamping. The formability was evaluatedi by changing the
stroke length of the punch and the result of measuring
the formable height is shown in Table 1. From the
table, it can be seen that the formable height was
increased in the example of the present invention in
which the material was immiersed in the liquid nitrogen,
cooled to a cryogenic temperature then taken out and
applied with stamping as compared with a conventional
stamping not immersed in liquid nitrogen (comparative
example).
Example 2
Using Al-Mg series alloy O material of 1 mm sheet
thickness having the chemical ingredient as shown in
Table 2 as the material for forming, the same stamping
test as in Example 1 was conducted. Result for the
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measurement of the fGrmability and the hardness of
forming products are shown in Table 2. In a case where
the Mg content is low, strength as the forming product
is insufficient.
Example 3
Using JIS 5182 alloy 0 material of l mm sheet
thickness as the material for forming, a processing test
was conducted while immersing the material in a liquid
nitrogen and varying the time before processingO Other
conditions are the same as those in Example 1. The
results are shown in Table 3. In Table 3, it is
recognized for the improvement of the formability when
processing was applied after elapse of about 30 sec
immediately after the immersion. This well corresponds
to the waxy state. That is, since the waxy state ls not
formed just after take-out whereas it is already changed
into liquid 60 sec after take-out, by which the
lubricity is reduced. The formability in each of the
cases i.e., just after take out and 60 sec after take
out was improved as compared with a case of no~
immerslng in the liquid nitrogen (comparative example in
Example l).
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Example 4
JIS 5182 alloy O material of 1 mm sheet thickness
was used as the material for forming. A forming test
(BHF: 4.0 Tonf. Mean velocity: 15 m/min) was conducted
using the spherical head die shown in Fig. 1 and using a
crank press. In this case, the material was coated with
various oils shown in Table 4 were coated as the
lubricant, immersed and cooled in a liquid nitrogen for
two min and then served for the test. A portion of the
samples was served to the test directly after coating
the lubricant.
For the evaluation of the formability, the height
of the forming product was gradually increased by
changing the lower dead point of position of the press
and it was judged depending on the forming limit height
at which cracks were caused to the forming product.
Further, for the evaluation of the degreasing property,
the material coated with the lubricant was degreased by
using a commercially available degreasing agent
(degreasing condition are shown in Table 4) r and the
situation of the remaining lubricant was judged based on
the water leak area ratioO The results are as shown in
Table 4, and an improvement for the forming limit height
was recognized in the example of the present invention
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as compared with the comparative exa~ple and the
degreasing property was also satisfactory. In
particular, formability at low temperature (-148C) was
remarkable.
Example 5
JIS 5182 alloy 0 material and steel sheet were used
as the stock material, and paraffinic mineral oil having
a viscosity at 40C of lO cSt was coated as a lubricant
(polyethylene sheet was used for a portion of the stock
material), and the stock materials were stamped at
various forming temperatures. The results are shown in
Fig. 3. From the figure, it can be seen that the
forming limit height of the aluminum alloy is improved,
in parti~ular, at a low temperature of lower than -503C
by using the lubricant according to the present
invention. Further, the forming height is most improved
at a stock material temperature of -196C, and 20
minutes of period was required per one stock material
for cooling down to the above-mentioned temperature.
Example 6
JI5 51~2 alloy 0 material of l mm sheet thickness
was used as the material for fQrming. A forming test
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(BHF. 4.0 Tonf, mean velocity: 15 m/min) was conductedby using a spherical head die shown in Fig. 1 and using
a crank press. In this case, various oi]s shown in
~able 5 were coated as the lubricant to the materials,
which were immersed and cooled in a liquid nitrogen for
2 min and then served to the test. A portion of the
samples was directly served to the test just after
coating the lubricant. Evaluation for the formability
and the degreasing property was made in the same manner
as in Example 4 and the results are as shown in Table 5.
Improvement in the forming limit height was recognized
and the degreasing property was also desirable in the
example of the present invention as compared with the
comparative example. Particularly, the formability at
low temperature (-148C) was remarkable.
Example 7
A die made of SUS 304 and a die mechanism shown in
Fig~ 2 were used. Test material of 5182-0 material (1.0
mm thickness) was coated w.ith a liquid paraffin,
inserted in a die for cryogenic temperature and the
formability was evaluated while varying the die
temperature and the temperature for the test material.
The method of lowering the temperature was conducted by
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spirally circulating a liquid nitrogen through the
inside of the punch, jetting out it to the entire and to
the test material. The temperature was controlled from
the normal temperature to -196C and the temperature of
the material in contact with the punch was measured by
using a contact type thermometer. The formability was
evaluated by the extruding height of a 50 mm~ spherical
head punch (disposed in a 45 ton crank press). From the
test results as shown in Table 6, it can be seen that
the formability (extending property) was improved
together with temperature lowering and it was comparable
with that of the steel sheet at ~196C.
Example 8
In the test temperatures in Example 7, the die
material was changed in ea~h of the tests at -100C and
~196C, and low temperature brittleness of the die was
evaluated. As a result, minute cracks were recognized
after forming for three times at -100C for the steel
material (dice steel SKD 11) and the test was
interrupted. On the other hand, no minute cracks were
recognized even after 100 cycles of press tests at -
196C in the case of austenite type stainless steel ~SUS
- 26 -
,: :
.:
,j . , : , . :
- ~ .
~ 3 ~
304~ and Cu-Nl alloy (Colson alloy) and it was confirmed
that such materials were effective.
Example 9
5182-0 material (1 mm thickness) was coated with a
liquid paraffin, which was immersed into and taken out
of a liquid nitrogen and left to examine the temperature
change. From the results as shown in Fig. 4, it can be
seen that the immersion time was preferably 15 sec and
it was preferably inserted in a short period of time
into the press under the condition of ensuring the
temperature upon insertion in the die to lower than -
50C while considering the productivity. Further, for
ensuring a lower temperature, it is necessary to take a
longer immersion time. However, if it exceeds 40 sec,
it may cause time loss according to the result of this
test.
Example 10
5182-0 material ~1 mm thickness) wais coated with a `
li~uid paraffin, which was immersed into and taken out
of a liquid nitro~en and evaluated while varying the
sheet temperature. The die temperature was constant for
the punch and the dice~ and the material was inserted
- 27 -
, . : . :- . ~:
, , : ~ : . ... . : . :: .:: .:
:., .: : : -; .:
2 ~ 3 ~
into the die just after the sheet temperature was
reached (within 2 sec). For the formability, the limit
was determined by 50 mm~ spherical head e~tendiny
processing. The results are shown in Table 7. If the
sheet temperature is within the present invention, the
formability is satisfactory. The performance is poor as
compared with the material sufficiently cooled in the
die to -196C but it is remarkably excellent over the
room temperature processing by the conventional method.
Example 11
5182-0 material (1 mm thickness) was coated with a
liquid paraffin, which was immersed in a liquid nitrogen
and then left to change the sheet temperature~ The
punch temperature was set to -196C while the
temperature for the flange was set to -70C and -150C,
and the material was inserted into the die just after
the sheet temperature was reached (within 2 sec). After
about 2 sec (punch portion cooled), pressing was applied
and the results are shown in Table 9. Satisfactory
formability is shown in each of the cases in the method
according to the present invention and it can be seen
that the condition capable of obtaining formability more
excellent than the case of -196C both for the sheet and
28
; . . ..
- - -' - ~ ' : ' ': ' '
:: .,~ :: : ~ ,
::
-
the die is the condition at a temperature on the side of
the punch of -196C and at a temperature within a range
of -50 to -100C for the sheet as the flanye and the
die.
INDUSTRIAL APPLICABILITY
As has been described above accordin~ to the
present inventionl since press processing is applied in
a cryogenic temperature region, formability can ~e
improved. In addition, since processing can be appliecl
also in a preferred lubricating state, the formability
can further be improved. Therefore, it can provide an
excellent effect for forming at severe processing degree
and for complicate shapes, can reduce number of forming
steps, which is economical and can be put to practical
use.
In particular, the formability of the aluminum
alloy sheet can be improved to an extent equal with or
superior to that of a steel sheet by using a die
equipped with a cooling structure and controlling the
temperature for the die and the sheet andl in
particular, a formability superior to that of the steel
sheet can be obtained by a cooling method providing a
temperature slope. Therefore, it can provide an
- 29 - . .
- . . ~, - . ~ . . . . ,..... -
, "
:, .. . .: :
. ,:, . ~; ,. . .
~ i3 ~
e~cellent effect for the weight reduction of automobile
parts, that is, promotion for the use of aluminum
material and can contribute as a countermeasure to
environmental problems such global warming.
- 30 -
. ~ . , ~ .
2 ~ 3 ~
Table 1
.. l
~toriol Lubricnnt ¦ stamping , FormabIe Note
eig
. Atter coating
lubricont, i~mor
Min~3ral sed in liquid Ex~mplo of
nitrogen for tho inventiD
oil 2 min ond then 2 ~;~m
stamped soon
JISS182-O . .
material .,
.: _ _ _
Af t~3 r coat i ng .
lubricont, Conperative
. stamped cs it is 2 2 ~
. E xample .
~;-- ... _ _ .. ._
Table 2
._
Ni~ ChemiCi9l ~(Vt%) Formable height t~rdness of
. _i~l i~ . . forming product
Mg S i ~?~ (~m) (~v)
1 ~ 4~2 0.11 0.21 2 ~ 9 3
2 ¦2.8 0.13 0.22 2 3 B 1 ¦ . :
_ .
3 2~3 ~11 0.22 2 O 7 3
_ 1~ ~.13 ~.2~ 2 1 _ _
Table 3
_ , i .
Tima z~ter--liquid. nitrogen ¦ Formable height
t rea tmen t I . ~lo ~ e
~sec) ¦ (0~)
, ._ .
Immediately after ¦ 2 ~
.. _ _ . . .
1 ~ ¦ 2 6 3efore woxy state
_ . _ . _
3 O 2 8 ~axy state
6 O 2 ~ L iqu id
'~
'. ' ' ', ' . , ' ,..... : :` : :; ' ~ .:', . : . . :, ,, . : ,
s~ ~
~ ~ c; c: o ~
- ~1' ' ~ ~ ,
C' ~ Cl,1~ ~ 111 Cl L~ ;! C
z tJ XX rl 3 X E ~ E al E ;~ X
a~C~ ~rx~ ~ ~ Y~O
_ _ _ _ _ _ .
_ ~ ~ ~ 1~ ;e E{ ~ ~ ~ Z! ~ c ~ ~ Dl ~
E ~ JEI ~IIIi ii~ le 131 1~ D R ~i Tf} ~ ;i e ~3 ~
t~` O ID C O ID O O C:1 LD O O O O O C::) IC ' _
~J E ~ .* d~ tl:3 t:l ) ~ ~ s:~a C~', 1:~ ~ tD ~ ~ ~;1 0.:
I ~ C~ ~ c;l ~ ~J ~a ~ C~ 3 ~ C~ t:~l C~ ~
_ _ _ _ _ _ _ _ 0 C: _ ~: X C
~ . L~ .~ V'
O ~ "~:~ ~ : . . ~ '~S .. . ~ .- _ CO
~I h _I _1 _ $ _ . _ . _ --/ ~ ~a C ~ C
U~ _ ~ 1 t/~ U~ ~'7 U~ _ _ __ _ _ ~ o r~^
_ nl _ I ~ ~ X~:: I ~ V ~
l a ~ 1 1 _ E Vl h l c~
~oI u O _ I I',~, _ o I ~ V
E I _L~_I h~ E~ h~ O
~E I ~'~ ~ E ~ I L' h O 4 L, L U I V
R~ I ~ o EE O 0 ¦ ¢~ ~ ~ ~ E I I O --_ ~ O
¦ . . ¦ . . I C -- E Ll D~ O
IUIL~IOI lololLolololL~lol ~ololL~lolo L,'Z~
~-~ ~~ ~~ ~~o~
I I I I J I _ I _ I I I ~ I I E ~ 8 E ~J
I I I ¦ ¦ ~ I II I ¦ ¦ C ¦ L~ O -- C~
. ¦ ~ ¦ C I L' I ¦ ¦ ~ ¦ ¦ C: a ~ a E
¦ $ ¦ ¦ ~ 1 1 ¦ ¦ ¦ ~ 1 ~ æ~
¦ ¦ E ¦ r ¦ ~ ¦ a ¦ ~ ¦ E ¦ _ ¦ ~ ¦ Ll_ I _
l I I ~ I O I _ I ,~, I I C I O ~_ ¦ ~4 Z
,~
~ ro o
~LI I
_ I
~ .. ' '
:
: " ' ~ ' '': ~ .
Q 3 5
._ .
_ C' o~ -c ~C _
~ ~ ~ -1 ~ c cc -
Z tJ X X ~ o x ~
E ~ e _ ~ a ~ ~ ~. e ~ .
_ O L~ O ID O C ~: O O O O O
~ . . . . . . . . .. . .
~ C C~ --~ ~ ~ ~ ~ ~ ~ ..~ ~ ~
_ C~ ~ C~ C~ ~ C~ ~ ~ ~ ~ ~ ~
=, _ _ _ _ ~ _ _ _ _ _ _ ,,,
~ ~ C' ~ ~
C . Ul O X O
u ~ ~ ~ ~ ~: .~ O~ ~ ~ .
¢ _ ~' _1 E' :7' O' O E ~ ~ )~ ~: C
V~l ~ U~ ~ ~ ~1 ~4 U~ U~ _ ~ - C
~ C ' O` V C
_ ~ __, O_, la G
C O~ ~ E Q: ~ h ~ O
C _~ O _ ~ E J ~.- C C~ V t~
C U ~ h C h h ~ h :1 C C
cn h ~h C Ul ~ J h ~
If ~ E C; E E E (J E t~J E ~ ~ O E ~ ~ ~ .0 V C
.. ~" ¢ q.~ ¢ .~1 c 1~ h ~ E I o ~ C ~ , C
.û ~ ~ ~ ~ O ~ ,~ X O
~ I I r I O c c ~
I ~ ol I lololl~DII I 111 ~ ~.
¦ ~ ~ ¦ 1 1 1 cocncn
~ _ __
~ l ~I h h C
_ I I I I e I I I I c: I ~ a a a ~
~ ~ r I h
_~ I ~ I I C: 1 01 1 1 1 C: I Ul O
I l ~ l o ~ o ~ _
¦ ~ ¦ O ¦ _ ¦ ~ ¦ C ¦ O I ~ 1 ¦ U .
l ~ ~ I C I E 1' C I -~
I 1 1~ 1 C~ I O I ~ I ~ . I O I
I I ~ LU) I Cl~ G I Ul I ~ I V~
U~ o
h ~ 1
' ',
'-, ~ '
3 3
Table 6
Formability - ~ -
Test temper2ture for Note
j extending formability
I (C) Limit extendiDg height (mm~
! - _ Conventional
¦ Normal temperature ¦ 2 1 ~ a ¦ exa ple
.Comparz'.iYe
-- 3 ~) ~ 2 3 . ~ l exam?le
- 1 0 0 2 ~ . 5 Exam?le of
the inven--
¦ - 1 3 0 ¦ 2 7 . 0 tion
- 1 9 6 3 0 ~ 0 .
.
Steel sheet 3 0 0 ComparatiYe
(Dormal sheet) example
Table 7
I Extending
Sheet Die ! property Note
temperature temper2turq ~xtending
( C) ~ (C) _ I heiqht (mm) _
-- 3 ~ O ¦ 2 ~ examDl e
- ~30 ~ 0 1 27~0
Example of
- 1 2 0 - 1 ~ 0 2 7 ~ O the inven-
_ tion
- 1 7 0 - 1 ;: 0_ 2 7~ ;:
-170 -196 3 0.
_ _ Cl~nventional
Normal temperature 1 2 ~ examDle
At normal temperature 1 3 0 0 1 co~paratiYe
for steel sheet I . IexamPle .
Table 8
, _ ,
temperature ~ temperature Frange temperature heigh ~ Note
-- 4 0 ¦ --1 9 ~i -- 7 0 2 7 0 Icomparative
¦ _ ~ O ¦ ~ ¦ n ¦ 3 1. ~ Example of
_ , the inven-
- 1 2 0 _ I ¦ 2 6. 0 tion
i-l7~ 1 I -l~o 7 2~3.0 .
i: ~ . . -, .. ..
