U.S. patent application number 15/308677 was filed with the patent office on 2017-06-29 for method for operating a vacuum die-casting machine.
The applicant listed for this patent is BUHLER AG. Invention is credited to Roman KERN, Claude STALDER.
Application Number | 20170182552 15/308677 |
Document ID | / |
Family ID | 50678015 |
Filed Date | 2017-06-29 |
United States Patent
Application |
20170182552 |
Kind Code |
A1 |
STALDER; Claude ; et
al. |
June 29, 2017 |
METHOD FOR OPERATING A VACUUM DIE-CASTING MACHINE
Abstract
A method of determining the position of at least one opening (9,
10) in a casting chamber (6) of a die-casting machine (1), wherein
a casting plunger (7) is contained in the casting chamber (8), The
casting plunger (7) is movable into a position in which
communication between the opening (9, 10) and the casting chamber
(6) is no longer possible. It is determined, on the basis of the
vacuum in the connecting line (14, 15), when the casting plunger
(7) has reached the position in which communication, between the
opening (9, 10) and the casting chamber (6), is no longer possible.
A method of operating a vacuum die-casting machine, wherein a
casting curve, for performing a casting cycle, is determined by
specified and/or experimentally determined characteristic values of
the die-casting machine by a computer program for operating the
die-casting machine, and to a corresponding computer program
product.
Inventors: |
STALDER; Claude; (Gossau,
CH) ; KERN; Roman; (St. Gallen, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BUHLER AG |
Uzwil |
|
CH |
|
|
Family ID: |
50678015 |
Appl. No.: |
15/308677 |
Filed: |
May 5, 2015 |
PCT Filed: |
May 5, 2015 |
PCT NO: |
PCT/EP2015/059779 |
371 Date: |
November 3, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22D 17/14 20130101;
B22D 17/203 20130101; B22D 17/10 20130101; B22D 17/32 20130101 |
International
Class: |
B22D 17/32 20060101
B22D017/32; B22D 17/20 20060101 B22D017/20; B22D 17/14 20060101
B22D017/14; B22D 17/10 20060101 B22D017/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2014 |
EP |
14167184.2 |
Claims
1-15. (canceled)
16. A method for ascertaining a position of at least one opening in
a casting chamber of a die-casting machine, wherein a casting
piston is contained in the casting chamber, the method comprising:
a) connecting the casting chamber or a mold cavity of a die-casting
moid, which mold cavity is fluidicaliy connected to the casting
chamber, to a pump generating negative pressure or to a tank, which
is brought to negative pressure with the pump, via a connecting
line in a position of the casting piston in the casting chamber, in
which at least a portion of the opening to be ascertained and the
casting chamber can communicate with each other, b) moving the
casting piston into a position in which communication, between the
opening to be ascertained and the casting chamber, is no longer
possible, and c) ascertaining with reference to the negative
pressure in the connecting line when the casting piston has reached
the position in step b).
17. The method as claimed in claim 18, wherein the at least one
opening is a feed opening of the casting chamber of a cold-chamber
die-casting machine.
18. The method as claimed in claim 17, wherein the method is
carried out when the die-casting mold is dosed, and the connection
to the pump generating negative pressure or to the tank, which is
brought to negative pressure with the pump, is produced via the
connecting line which is connected to an extraction hole of the
die-casting mold.
19. The method as claimed in claim 17, wherein the method is
carried out when the die-casting mold is closed, and the connection
of the casting chamber to the pump generating negative pressure or
to the tank, which is brought to negative pressure with the pump,
is produced via the connecting line which is connected to an intake
opening in the casting chamber.
20. The method as claimed in claim 16, wherein the at least one
opening is an intake opening in the casting chamber of a
cold-chamber die-casting machine,
21. The method as claimed in claim 20, wherein the method is
carried out when the die-casting mold is open, and the connection
of the casting chamber to the pump generating negative pressure or
to the tank, which is brought to negative pressure with the pump,
is produced via the connecting line which is connected to the
intake opening in the casting chamber.
22. The method as claimed in claim 18, wherein, during a first
performance of steps a) to c) when the die-casting mold is closed,
the position of a feed opening in the casting chamber is
ascertained, and, during a second performance of steps a) to c)
when the die-casting mold is open, the position of an intake
opening in the casting chamber is ascertained by the intake opening
which is connected to the pump generating negative pressure orto
the tank, which is brought to negative pressure with the pump, via
the connecting line, the casting piston is subsequently moved into
the position in which communication between the intake opening and
the casting chamber is no longer possible, and it is ascertained
with reference to the negative pressure in the connecting line when
the casting piston has reached this position,
23. The method as claimed in claim 18, wherein a gas cleaning
device is located between the pump generating negative pressure or
the tank and the casting chamber or the die-casting mold.
24. A method of operating a vacuum die-casting machine, wherein a
casting curve for carrying out a casting cycle on a basis of
predetermined and/or experimentally ascertained characteristic
values of the die-casting machine is determined with the aid of a
computer program product for operating the die-casting machine.
25. The method as claimed in claim 24, wherein the experimentally
ascertained characteristic values of the die-casting machine
involve a time taken until a predetermined negative pressure is
reached in a mold cavity,
28. The method as claimed in claim 25, wherein a time taken until a
negative pressure corresponding to 90% of the predetermined
negative pressure is reached in the mold cavity and the time taken
until a negative pressure corresponding to 100% of the
predetermined negative pressure is reached in the mold cavity are
ascertained.
27. The method as claimed in claim 24, wherein the predetermined
characteristic values of the die-casting machine involve the
position of the feed opening and/or of the intake opening in the
casting chamber.
28. The method as claimed in claim 24, wherein the time taken until
a predetermined negative pressure is reached in the mold cavity is
checked at regular intervals in order to identify any leak which
may occur.
29. The method as claimed in claim 24, wherein the casting curve is
additionally determined as a function of a degree of filling of the
casting chamber.
30. A computer program product for operating a vacuum die-casting
machine, wherein the software product executes the step of
determining a casting curve for carrying out a casting cycle on the
basis of predetermined and/or experimentally ascertained
characteristic values of the die-casting machine.
Description
[0001] The present invention relates to a method for operating a
vacuum die-casting machine, with which a casting cycie can be
carried out more efficiently and more rapidly.
[0002] In order to produce castings, appropriate casting material
can be introduced into a casting mold having contours corresponding
to the shape of the casting and can be allowed to solidify there.
Die-casting machines are suitable for the production of metallic
castings, such as, tor example, engine blocks. A die-casting
machine comprises a casting moid which consists at least of two
mold halves (a fixed and a movable mold half) which together form a
hollow space (also referred to as cavity or moid contour)
corresponding to the component to be produced. A molten material of
the material to be molded, for example aluminum, is pressed, into
said hollow space under high speed and high pressure with the aid
of a casting piston. After the molten metal has solidified in the
hollow space, the mold is opened by movement of the movable mold
half and the finished casting is ejected with the aid of
ejectors.
[0003] 3y way of example, WO 2008/131571 A1 describes a horizontal
two-plate die-casting machine. Said two-plate die-casting machine
comprises a movable platen (BAP) and a fixed platen (FAP), on which
one casting mold half is arranged in each case. By movement of the
movable platen, the die-casting mold can be opened and closed. In
the closed position, the two platens are pressed fixedly against
each other such that the two casting mold halves form a closed
mold. A molten metal is introduced under pressure into the closed
moid and cooled by solidifying. The solidified casting can be
[0004] removed after the mold is opened (by movement of the movable
platen).
[0005] For the manufacturing of automobiles, particular
requirements are placed on thin- to medium-walled structural
components. The latter have to have, inter alia, good weldability,
nigh mechanical load-bearing capability and a low manufacturing
scatter. In the case of a conventional die-casting method, even
when the mold is well vented, there is the risk of air or gas
inclusions in the molten material, which may result in undesirable
porosity in the casting. Under some circumstances, the casting may
therefore no longer reliably meet precisely the high requirements
demanded for manufacturing automobiles.
[0006] As an alternative, certain castings, for example for
manufacturing automobiles, are therefore produced in a vacuum
die-casting method. The vacuum die-casting method is known to a
person skilled in the art. In this case, the gas atmosphere present
in the casting mold is removed at least partially, preferably as
completely as possible, i.e. a negative pressure is applied. In
particular for castings which have to be subjected to a subsequent
heat treatment, tne vacuum die-casting method has proven a
preferred production method.
[0007] For carrying out the vacuum die-casting method, the
die-casting machine has to be provided with powerful vacuum
eguipment (in particular a powerful vacuum pump and good vacuum
regulation), and the mold fittings and casting fittings have to be
able to be readily seated off from the environment.
[0008] In order to carry out a vacuum die-casting method, a flow
duct is provided in the casting mold, said flow duct leading from
the hollow space (also referred to as cavity or moid contour),
which corresponds to the component to be produced, into a gas line
which is connected to a vacuum pump. The fluidic connection between
hollow space and vacuum pump can be opened and closed with the aid
of a closing device, preferably a valve.
[0009] In addition, the casting chamber can be connected via an
intake hole, which is arranged in the casting chamber, to a vacuum
pump in order to be able to carry out the operation of evacuating
the machine even more rapidly and efficiently. The fluidic
connection between casting chamber and vacuum pump can be opened
and closed with the aid of a closing device, preferably a valve. A
corresponding vacuum die-casting machine is shown, for example, in
DE 10 2004 057 324 A1.
[0010] A desired negative pressure can only be applied to the
casting chamber and the mold cavity when casting chamber and mold
cavity no longer have a connection to the environment. In the case
of a cold-chamber die-casting machine, this is the case only when
the mold is closed and the feed opening for filling the casting
chamber with a molten material is sealed by the casting piston,
i.e. when the casting piston in the casting chamber has reached a
position in which the rest of the casting chamber and the mold
cavity no longer have any connection to the feed opening.
[0011] Care shouid be taken in the first phase of a casting cycle
to ensure that the casting piston does not exceed a certain
critical speed. This is illustrated in FIG. 1. The casting piston
pushes a wave of molten material therebefore when it moves within
the casting chamber. At a low speed (FIG. 1a), a gas space remains
in the casting chamber above the molten material, as a result of
which the risk, of air inclusions rises. At excessive speeds of the
casting piston (FIG. 1c), the molten material wave breaks, as a
result of which air
[0012] inclusions likewise occur. At an optimum speed, what is
referred to as critical speed, the wave of molten material has an
optimum height (FIG. 1b), and the risk of air inclusions is
minimized.
[0013] The carrying out of a casting cycle in a die-casting machine
takes place on the basis of the "casting curve". The casting curve
is understood as meaning the profile of the casting piston speed as
a function of the casting piston travel or, after the mold filling
has ended, the profile of the casting pressure as a function of the
time. The casting curve is customarily divided into three phases.
During the preliminary phase or first phase, the molten material is
first of all built up in the casting chamber, at a comparatively
low piston speed, and transported in the direction of the moid
cavity. At the beginning of the moid filling phase or second phase,
the casting piston is accelerated to a high speed in order to
completely fill the component cavity within a very short time. At
the end of the moid filling phase, the pressure rises sharply
within a very short time, as a result of which the piston speed
drops and the casting piston comes virtually to a standstill. This
marks the beginning of the holding pressure phase or third phase,
in which a high holding pressure is applied to the molten material
via the casting piston.
[0014] Currently, the casting curve is still worked out empirically
by the person operating the die-casting machine, in order to
overcome the shortcomings associated therewith, automization of the
operation for working out the casting curve would be highly
desirable.
[0015] It was the object of the present invention to provide a
method for operating a vacuum die-casting machine, with which a
casting cycle can be carried out snore efficientiy ana more
rapidly.
[0016] According to the present invention, measures are proposed
with which a casting cycle of a vacuum die-casting machine can be
carried out more efficiently and therefore more rapidly. In
particular in the first phase of the casting cycle, a time saving
of some seconds can be achieved with the method according to the
invention, which, in the mass production of castings, leads to a
considerable gain in overall time and therefore to a considerable
economic advantage.
[0017] According to a first aspect of the present invention, the
above object is achieved by the position of the feed opening in the
casting chamber or of further openings in the casting chamber being
determined in a previous learning cycle.
[0018] The present invention therefore relates to a method for
ascertaining the position of at least one opening in a casting
chamber of a die-casting machine, wherein a casting piston is
contained in the casting chamber, comprising the following
steps:
[0019] a) connecting the casting chamber or a mold cavity of a
die-casting moid, which moid cavity is fluidicaily connected to the
casting chamber, to a pump generating negative pressure or to a
tank, which is brought to negative pressure with the pump, via a
connecting line in a position of the casting piston in the casting
chamber, in which at least a portion of the opening to be
ascertained and the casting chamber can communicate with each
other,
[0020] b) moving the casting piston into a position in which
communication between the opening to be ascertained and the casting
chamber is no longer possible, and
[0021] c) ascertaining with reference to the negative pressure in
the connecting line when the casting piston, has reached the
position in step b).
[0022] The positions of the openings in the casting chamber involve
geometrical parameters of the die-casting machine that do not
remain constant, but rather are subject to changes, for example
because of a change of moid or wear. The positions of the openings
in the casting chamber therefore have to be ascertained
regularly.
[0023] With knowledge of the precise position of the openings in
the casting chamber, the casting piston can be brought as rapidly
as possible into a position in which the die-casting machine is
sealed off from the environment and an effective negative pressure
can be generated in the die-casting machine. Up to now, the
positioning of the casting piston and the time of the generation of
negative pressure in the die-casting machine took place solely by
means of the operator. However, even an experienced operator
requires a certain time for carrying out these steps. According to
the invention, the position of the feed opening in the casting
chamber and optionally also the position of further openings, such
as the intake hole, are determined in a learning process. The data
thus determined can be stored and taken into account when working
out a casting curve for the actual casting cycle. By means of the
automization which is thus possible, a first saving on time during
the casting cycle can be achieved.
[0024] The at least one opening is preferably the feed opening in a
casting chamber of a coid-chamber die-casting machine.
[0025] Casting chambers of cold-chamber die-casting machines are
well known. A casting piston which can be moved, preferably
hydraulicaliy, with the aid of a casting cylinder is located in
trie casting chamber. In the case of a vacuum die-casting machine,
the casting piston is dimensioned in such a manner that it divides
the casting chamber into an annular space and a piston space which
are sealed off fluidically from each other.
[0026] The casting chamber is filled via a feed opening with the
material to be cast. This is preferably molten metal from metals or
metal alloys customarily used for die casting. However, it is also
possible to use other molten materials. For example, salt cores can
be produced from corresponding molten salts. The feed opening is
preferably arranged in the top of the casting chamber, in the case
of a horizontally arranged casting chamber.
[0027] The casting chamber of a vacuum die-casting machine is
connected to the actual moid cavity. The molten material fed into
the casting chamber is transferred by movement of the casting
piston into the raold cavity where it solidifies and forms the
actual casting. A flow duct is provided in a vacuum die-casting
machine, said flow duct leading from the moid cavity into a gas
line (connecting line) which is connected to a vacuum pump. The
fluidio connection between hollow space and vacuum pump can
therefore be undertaken by an extraction hole, wherein the
connection can be opened and closed with the aid of a closing
device, preferably a valve, via said extraction hole, not only can
the mold cavity be evacuated, but so too can the casting chamber
which is tluidically connected, to the moid cavity.
[0028] As long as the feed opening is open, the interior of the
casting chamber is connected to the environment, in order to be
able to generate negative pressure in the casting chamber and
therefore also in the moid cavity, the feed opening has to be
sealed. This can be achieved by the casting piston being moved
within the casting chamber into a position in which it
fiaiOically
[0029] decouples that part of the casting chamber which is
connected to the moid cavity from the feed opening. For this
purpose, the casting piston has to be moved at least into a
position in which its front end facing the mold is located in the
same position as that end of the feed opening which faces the mold.
As soon as the casting piston has been moved into this position, an
effective negative pressure can be generated in the moid cavity and
the casting chamber with the aid of the vacuum pump.
[0030] According to the invention, use can be made of any vacuum
pump as are conventionally used in the case of vacuum, die-casting
machines, vacuum pumps of this type are known to a person skilled
in the art.
[0031] According to the invention, a negative pressure, i.e. a
pressure lying below the atmospheric pressure of 101, 325 kFa
(1.013 bar), is generated in the moid cavity and/or the casting
chamber of the vacuum die-casting machine. According to the
invention, preferably a negative pressure of 300 mbar to up to 50
mbar, particularly preferably of 200 mbar to up to 50 mbar ana in
particular preferably of 100 mbar to up to 50mbar is generated.
[0032] It is preferred according to the invention not to connect
the vacuum pump to the moid cavity and/or the casting chamber
directly, but ratter via a tank. This is a buffer container which
can be rapidly evacuated with, a comparatively small vacuum pump
and, for its part, can rapidly generate the desired negative
pressure in a vacuum die-casting machine. The tank is arranged in a
connecting line between vacuum pump and die-casting machine and can
be opened ana closed both in relation to the vacuum pump and in
relation to the die-casting machine with the aid of a closing
device, preferably a valve. It is also known and possible to
provide a plurality of tanks of this type between vacuum pump and
mold cavity or casting chamber.
[0033] According to a preferred embodiment of the present
invention, the above method for ascertaining the position of the
feed opening is carried out when the die-casting moid is closed,
and the connection of the casting chamber to a pump generating
negative pressure is produced via an extraction hole in the
die-casting mold,
[0034] According to a further preferred embodiment of the present
invention, the above method for ascertaining the position of the
feed opening is carried out when the die-casting mold is closed,
and the connection, of the casting chamber to a pump generating
negative pressure is produced via an intake opening in the casting
chamber. In this embodiment, the casting chamber has a dedicated
intake opening via which said casting chamber is connected to the
vacuum pump. The fluidic connection between casting chamber and
vacuum pump can be opened and closed with the aid of a closing
device, preferably a valve. If present, said intake opening is
located in a region, of the casting chamber between the feed
opening and the connection of the casting chamber to the mold
cavity. The intake opening is preferably arranged in the top, in
the case of a horizontally arranged casting chamber.
[0035] The above method for ascertaining the position is otherwise
carried out identically in both embodiments (generation of negative
pressure via an extraction hole in the moid cavity or via an intake
opening in the casting chamber).
[0036] In an embodiment according to the invention with an intake
opening in trie casting chamber, the position of the intake opening
can also be ascertained with the aid of the method according to the
invention. In this case, the method is carried out when the
die-casting mold is open, and the connection of the casting chamber
to a pump generating negative pressure or to a tank brought to
negative pressure with the pump is produced via the connecting line
which is connected to an intake opening in the casting chamber.
[0037] In a particularly preferred embodiment of the above method,
in a first performance of steps a) to c) when the die-casting moid
is closed, the position of the feed opening in a casting chamber is
ascertained, as described above, and, in a second, performance of
steps a) to c) when the die-casting mold, is open, the position of
the intake opening in the casting chamber is ascertained by the
intake opening being connected to the pump generating negative
pressure or to the tank, which is brought to negative pressure with
the pump, via a connecting line, the casting piston is subsequently
moved into a position in which communication between the intake
opening and the casting chamber is no longer possible, and it is
ascertained with reference to the negative pressure in the
connecting line when the casting piston has reached this
position.
[0038] As described above, the intake opening is located in a
region of the casting chamber between the feed opening and the
connection of the casting chamber to the moid cavity. When the feed
opening in the casting chamber is sealed by the casting piston and
the mold cavity is closed, a negative pressure can be generated
within the moid cavity and/or the casting chamber, as described
above.
[0039] If the mold is then opened, the piston space of the casting
chamber also obtains contact again to trie environment via its
connection to the mold cavity, which is now open, and the negative
pressure in the casting chamber is eliminated. It is no longer
possible to generate a negative pressure in the casting chamber
with the aid of a vacuum pump via the intake opening in the casting
chamber.
[0040] If the casting piston is subsequently moved in the casting
chamber in the direction of the intake opening, the casting piston
ultimately passes into a position in which it seals the intake
opening. A negative pressure now arises again in the connecting
line between intake opening and vacuum pump or tank. Said negative
pressure can be used for ascertaining the position of the intake
opening.
[0041] The above-described method according to the invention for
ascertaining the position of openings in a casting chamber is
therefore carried out by ascertaining a negative pressure at a
certain position of the casting piston. The position of the casting
piston, at which position the negative pressure assumes a
predetermined value at the measurement position, is used as being
representative of the position of the corresponding opening.
[0042] According to the invention, the pressure measurement
preferably takes place within the connecting lines of vacuum pump
or tank to the moid cavity or casting chamber, Devices for pressure
measurement are known to a person skilled in the art.
[0043] Preferably according to the invention, a gas cleaning device
is located between the pump generating negative pressure or the
tank ana the casting chamber. The intention therewith is to prevent
soiling of the vacuum pump by constituent parts of the molten
material that could also be sucked up by the vacuum pump. Such gas
cleaning devices, for example filters, are known to a
[0044] person skilled in the art. A gas cleaning device which is
preferred according to the invention is described in European
patent application No. EP 13178708,7 from the same applicant. This
involves a gas cleaning device in which a tangential separator
(cyclone cleaner) and a conventional filter element are arranged
sequentially following one another in a device.
[0045] Preferably according to the invention, a pressure
measurement takes place upstream and dawnstream of a gas cleaning
device of this type in order to be able to identify a possible
clogging of the gas cleaning device.
[0046] According to a particularly preferred embodiment of the
present method of the present invention, at the beginning of the
method the casting moid is closed and therefore the mold cavity is
closed off from the environment. The casting piston is then moved
forward in the casting chamber until the front end of said casting
piston has reached approximately the center of the feed opening.
The piston is now moved further forward at an adequate speed, for
example in the range of 0.13 to 0.16 m/s, and the vacuum pump is
activated. The vacuum pump or the tank evacuated by the fatter is
connected to the extraction hole in the mold cavity and/or to the
intake opening of the casting chamber, depending on the variant
according to the invention. The pressure in the casting chamber
only drops marginally since the feed opening is stiff partially
open. However, as soon as the front cast frig-piston end facing the
mold has reached the front feed-opening end facing the moid, the
casting chamber is sealed in relation to the environment, and the
pressure in the casting chamber drops significantly. From a certain
negative pressure, it can be assumed that the casting chamber is
sealed in relation to the environment. The position or the front
casting-piston end facing the mold is ascertained ana is assumed to
be representative of the position for the front feed-opening edge
facing the mold.
[0047] Preferably according to the invention, use is made of the
position of the front casting-piston end facing the moid, at which
end the second derivative of the pressure curve (cf. FIG. 3)
assumes the value of zero, i.e. a reversal point is present.
[0048] The piston can now be stopped, and the method for
ascertaining the position of the feed opening can be ended.
[0049] If, in addition, an intake opening is present in the casting
chamber and if the position of said intake opening is intended to
be ascertained, in a second, part of the method according to the
invention the moid can now be opened, and the vacuum pump switched
off. The negative pressure present in the casting chamber
disappears. The casting piston is moved in the casting chamber into
a position in which its front end is located approximately in the
center of the intake opening. The vacuum pump is activated and the
pump or a tank evacuated by the latter is connected via a
connecting line to the intake opening in the casting chamber:. The
pressure in the connecting line only drops marginally since the
intake opening is still partially open. However, as soon as the
front casting-piston end facing the mold has reached the front
intake-opening end facing the mold, the casting chamber is sealed
in relation to the vacuum pump, and the pressure in the connecting
line between vacuum pump and casting chamber drops significantly.
From a certain negative pressure, it can be: assumed that the
casting chamber is sealed in relation uo the vacuum pump. The
position of the front end of the casting piston is ascertained and
it is assumed to be representative of the positron of the
[0050] edge of the intake opening. Preferably according to the
invention, use is also made here of the positron of the front
casting-piston end facing the mold, at which end the second
derivative of the pressure curve (cf. FIG. 3) assumes the value of
zero, i.e. a reversal point is present.
[0051] The position determined in this manner of the feed opening
and optionally of the intake opening in the casting chamber can be
used for determining a casting curve.
[0052] A casting curve for a vacuum die-casting machine according
to the invention is substantially based on the speed of the casting
piston in the casting chamber, As described above with reference to
FIG. 1a)-c), the speed of the casting piston in the casting chamber
has to be carefully selected in order to avoid undesirable air
inclusions in the molten material. It is advantageous to select the
speed of the casting piston in the casting chamber in such a manner
that the speed corresponds as fair as possible to the critical
speed illustrated in FIG. 1a)-c).
[0053] The present invention therefore furthermore relates to a
method for operating a vacuum die-casting machine, characterized in
that a casting curve for carrying out a casting cycle on the basis
of predetermined and/or experimentally ascertained characteristic
values of the die-casting machine is determined with the aid of a
computer program product for operating the die-casting machine.
[0054] According to the invention, a casting curve for carrying out
a casting cycle is proposed to the operator of the die-casting
machine , with the aid of which casting curve the casting cycle can
be carried out more rapidiy, especially in toe first phase of the
casting cycle. Said casting curve is determined by a computer
program product with which the are-casting machine is operated.
[0055] Computer program products for operating die-casting machines
are known. The applicant's program Dat@net is mentioned by way of
example. Die-casting machines have corresponding components, such
as processors and memory modules with the aid of which a computer
program product can be operated. Via an interface, for example a
monitor, and an associated input medium, such as a keyboard, mouse
or touchscreen, the die-casting machine can be operated by an
operator with the aid of the computer program product.
[0056] The computer program product determines a casting curve on
the basis of predetermined and/or experimentally ascertained
characteristic values of the die-casting machine. Said
characteristic values change, for example, depending on the
die-casting moid used or due to wear ana therefore have to be
regularly adapted or newly ascertained.
[0057] The characteristic values for determining the casting curve
can be input manually into the computer program, product. However,
preferably according to the invention, said characteristic values
are at least partially determined previously experimentally and the
experimental data obtained are transmitted directly to the computer
program product.
[0058] It has been shown that, in the case of a vacuum die-casting
machine, the evacuation time, i.e. the time required until a
predetermined negative pressure is reached, is a substantial
factor. With a decrease in qas volume in the casting chamber, the
risk of gas inclusions in the molten material drops and the casting
piston can correspondingly be moved more rapidly.
[0059] As explained above, a desired negative pressure in a casting
chamber and the closed moid cavity associated therewith can only be
generated when the casting chamber is sealed in relation to the
environment, i.e. the teed opening in the casting chamber is closed
by the casting piston.
[0060] According to an embodiment according to the invention, in
order to determine a casting curve, a learning cycle is carried out
in advance, in which the evacuation time, i.e. the time until a
predetermined negative pressure is reached in the mold cavity, is
determined experimentally.
[0061] According to a preferred embodiment of the present
invention, said, learning cycle is carried out taking into
consideration the position of the feed opening and optionally of
the intake opening in the casting chamber, which positions have
been ascertained, by the method described above. This permits a
more rapid and more efficient procedure.
[0062] In order to carry out the learning cycle, the die-casting
mold is closed, and the casting piston is moved, within the casting
chamber into a position in which the front casting-piston end
facing the mold is located approximately level with the center of
the feed opening. The casting chamber is now connected, either
directly via an intake opening of the casting chamber or indirectly
via an intake hole in the moid cavity connected, to the casting
chamber, to the vacuum pump or to a tank evacuated by the vacuum
pump. The casting piston is moved, as previously described, into a
position in which it seals the casting chamber in relation to the
environment by closing the feed opening. The time until the
negative pressure in the
[0063] casting chamber reaches a predetermined value is now
ascertained,
[0064] Preferably according to the invention, the time taken until
a negative pressure corresponding to 90% of the predetermined
negative pressure is reached in the moid cavity and the time taken
until a negative pressure corresponding to 100% of the
predetermined negative pressure is reached in the moid cavity are
ascertained. This permits a more precise ascertaining of the
operability of the vacuum, system of the die-casting machine.
[0065] Preferably, in a first step of the learning cycle, the
negative pressure in the connecting line connected to the vacuum
pump or to an evacuated tank is ascertained before said connecting
line is fiuidicaily connected to the casting chamber and/or to the
moid cavity. In order to reach a desired negative pressure in the
casting chamber and/or in the mold cavity, the appropriate negative
pressure has to be present in the connecting line. Should the
negative pressure, which is determined, in the first step of the
learning cycle, in the connecting line lie above the negative
pressure which is intended to be reached subsequently in the
casting chamber and/or the mold cavity, the learning cycle is
broken off and an error analysis should be carried out (for example
a search for a leakage in the apparatus or for a plugged gas
cleaning device.
[0066] In the event of adequate negative pressure in the connecting
line, the learning cycle, as described above, is carried, out. With
the learning cycle, not only can the evacuation time be ascertained
here, as described above, but so too can the overall state of the
vacuum system. For the efficient carrying out of a vacuum
die-casting process, a predetermined negative pressure has to be
able to be reached within a predetermined time, for example a
negative pressure of 100 mbar within 3 s from sealing of the
casting chamber from the environment. Should said predetermined
values not be reached within the learning cycle, an error analysis
should be carried out before the actual die-casting process is
initiated.
[0067] If, according to a preferred embodiment of the present
invention, the time until a negative pressure corresponding no 90%
of the predetermined negative pressure in the mold cavity is
reached is additionally ascertained, the value thus determined can
be used for evaluating the suction capability of the vacuum device
of the die-casting machine.
[0068] Preferably according to the invention, the time until a
predetermined negative pressure is reached in the mold cavity is
checked at regular intervals in order to identify leaks which may
occur or a clogging of a gas cleaning device.
[0069] According to the invention, the casting curve is
additionally determined as a function of the degree of filling of
the easting chamber. The degree of filling in the casting chamber,
i.e. the quantity of molten material in the casting chamber in
relation to the maximum quantity of molten material to be fed into
the casting chamber, is a substantial factor for the behavior of
the molten material in the casting chamber, as shown in FIG. 1.
[0070] Preferably according to the invention, the computer program
product determines the casting curve of a cold-chamber die-casting
machine as a function of she evacuation time determined in the
learning cycle and as a function of a predetermined degree of
filling. Preferably according to the invention, a degree of filling
of the casting chamber of 20 to 50%, preferably 30 to 4 0%, is used
with respect to a casting chamber with a casting piston in the
starting position (i.e. in the position as far away as possible
from the mold;.
[0071] Preferably according to the invention, further geometrical
characteristic data of the die-casting machine are used by the
computer program product for determining the casting curve. In
particular, the positions of feed opening and intake opening in the
casting chamber, which positions are determined in the position
ascertaining method previously, are taken into consideration in
order to set the speed of the casting piston and the process of the
evacuation of the casting chamber and of the moid cavity as
optimally as possible.
[0072] According to a preferred embodiment of the present
invention, the speed of the casting piston is determined at a
position in which its front end has reached that edge of the intake
opening in the casting chamber which faces the moid. According to
the invention, this speed is determined as a function of the
reciprocal value of the degree of filling of the casting chamber
and is taken into consideration in the calculation of the other
points of the casting curve.
[0073] As further geometrical characteristic data, for example the
diameter of the casting piston, the active length of the casting
chamber (i.e. the casting-chamber length available for the casting
process), the weight of the casting to be produced (with and
without a gate), the density of the casting and the density factor
of liquid/solid of the molten material used can be taken into
consideration in the computer program product.
[0074] The casting curve is therefore determined case-specifically
with trie aid of a computer program product on the basis of
predetermined and/or previously ascertained characteristic data. A
person skilled in the art can undertake the required modification
of a computer program product conventionally used in vacuum
die-casting machines on the basts of hts expert knowledge and cam
optionally adapt same if the casting curve determined by the
computer program product does not supply any optimum and/or desired
results during the die-casting process.
[0075] With the aid of the present invention, it is possible to
carry out the casting cycle, in particular the first phase of the
casting cycle, more rapidly and more efficiently. Customarily, a
time saving of 1 to 10 s, preferably 2 to 5 s, can be achieved per
casting cycle. This results in a considerable economic: advantage
in the productfon of castings in large piece numbers.
[0076] The present invention furthermore relates to a computer
program product for operating a vacuum die-casting machine, wherein
the software product executes the step of determining a casting
curve for carrying out a casting cycle on the basis of
predetermined and/or experimentally ascertained characteristic
values of the die-casting machine.
[0077] Computer program products for operating die-casting machines
are known. The applicant's program. Dat@nef is mentioned by way of
example. The computer program product, according to the invention
preferably corresponds to such a known computer program product and
has been modified to the effect that it can execute the
above-described step according to the invention of determining a
casting curve, A person skilled in the art can undertake the
required modification of a computer program product conventionally
used in vacuum die-casting machines on the basis of his expert
knowledge and can optionally adapt same if the casting curve
determined by the computer program product does not supply any
optimum and/or desired results daring the die-casting process.
[0078] The present invention is explained in more detail below with
reference to non-limiting examples and figures, in which:
[0079] FIGS. 1a-c: snow the above-explained relationship between
the speed of the casting piston in the casting chamber and the
shape of the wave of molten material moved by the casting
piston,
[0080] FIG. 2: shows a schematic illustration of an embodiment of a
die-casting machine according to the invention,
[0081] FIG. 3: shows a schematic illustration of an embodiment of
the vacuum, arrangement of a die-casting machine according to the
invention,
[0082] FIG. 4: shows a schematic illustration of an embodiment of
the method according to the invention for ascertaining the position
of the feed opening and of the intake opening,
[0083] FIG. 5: shows an explanation of the evacuation times t1 and
t2 which are determined in a learning process,
[0084] FIG. 6: shows an example of a casting curve determined
according to the invention.
[0085] The conditions, which are shown in FIG. 1, within a casting
chamber, which is filled with molten material, as a function of the
speed of the casting piston have already been explained above. The
casting piston pushes a wave of molten material therebefore when it
moves within the casting chamber. At a low speed (FIG. 1a), a gas
space remains above the molten material in the casting chamber, as
a result of which the risk of air inclusions rises. At excessive
speeds of the casting piston (FIG. 1c), the molten material wave
breaks, as a result of which air inclusions likewise occur. At an
optimum speed, what is referred to as critical speed, she wave of
molten material has an optimum height (FIG. 1b), and the risk of
air inclusions is minimized.
[0086] FIG. 2 shows a schematic illustration of an embodiment of a
die-casting machine 1 according to the invention. This is a
cold-chamber vacuum die-casting machine. The die-casting machine 1
comprises a movable platen 2 with a mold half 4 arranged thereon,
and a fired platen 3 with a mold half 5 arranged thereon. In the
closed state, the moid halves 4 and. 5 form the mold cavity 11
which corresponds to the shape of the casting to be produced.
[0087] The die-casting machine 1 according to FIG. 2 furthermore
has a casting chamber 6 which extends through, the fixed platen 3
and the mold half 5 as far as the mold cavity 11 and is
fluidicali.y connected to the mold cavity 11. The casting piston 7
is arranged movably in bhe casting chamber 6. The casting piston 7
has a front end 7a and is connected to a casting cylinder (not
shown) via the casting rod 8.
[0088] A feed opening 9 for filling the casting chamber 6 with
molten material, and an intake opening 10 for connecting the
casting chamber 6 to a vacuum pump 17 are arranged in the top of
the casting chamber 6,
[0089] The moid cavity 1.1 is fluidically connected to the vacuum
pump 17 via a flow line 12 and a valve 13 (referred to as
chill-vent). The intake opening 10 and the flow line 12 are
connected to a tank 16 via lines 14 and 15, The tank 16 can be
evacuated via the vacuum pump and, for its part, can generate a
desired negative pressure in the casting chamber 6 or the moid
cavity 11. This arrangement has the advantage that a comparatively
large volume can be brought to the desired negative pressure in the
tank 16 with a comparatively small, vacuum pump. Said tank volume
cam be used to generate a desired negative pressure in the casting
chamber 6 or in the moid cavity 11 within a short time interval. As
a result, the time during the casting cycle can be used in order to
reproduce the desired negative pressure in the tank 16 with the
vacuum pump 17 in order, if the need arises, to be able to reset, a
desired negative pressure in the casting chamber 6 or the mold
cavity 11.
[0090] Pressure measurement devices 18 and 19 are arranged in the
connecting lines 14 and 15.
[0091] FIG. 3 shows a schematic illustration of an embodiment of
the vacuum arrangement of a die-casting machine according to the
invention, wherein, the same reference signs denote identical
elements in FIGS. 1 and 2.
[0092] The casting chamber 6 comprises an intake opening 10 which
is connected via a connecting line 15 to a tank 16 which can be
evacuated by a vacuum pump 17. A gas cleaning device 20 is arranged
in the connecting line 15. The gas cleaning device is preferably a
device as described in European patent application No. EP
13173706.7 of the same applicant. A gas cleaning device is involved
here in which a tangential separator (cyclone cleaner) and a
conventional filter element are arranged following one another
sequentially in a device.
[0093] Pressure measurement devices 19 which can be decoupled from
the connecting line 15 via valves 21 are arranged upstream and
downstream of the gas cleaning device 20. The pressure in the
connecting line 15 and therefore in the casting chamber 6 can be
determined with the pressure measurement devices 19. In addition,
it can be checked with the pressure measurement devices 19 whether
the gas cleaning device 19 is operable or, for example, is
plugged.
[0094] The casting chamber 6 can be decoupled from the tank 16 and
the vacuum pump 17 with the aid of a valve 22.
[0095] The mold cavity 11 is connected via a flow duct 12 and a
connecting line 14 to the tank 16 which can be evacuated by a
vacuum pump 17. A gas cleaning device 20a is also arranged in the
connecting line 14, The gas cleaning device is preferably a device
as described in European patent application No. EP 13178708.7 of
the same applicant, A gas cleaning device is involved here, in
which a tangential separator (cyclone cleaner) and a conventional
filter element are arranged following one another sequentially in a
device.
[0096] A pressure measurement device 19 which can be decoupled from
the connecting line 14 via a valve 21 is arranged upstream of the
gas cleaning device 20a. The pressure in the connecting line 14 and
therefore in the mold cavity 11 can be determined with the pressure
measurement device 19.
[0097] The vacuum cavity 11 can be decoupled from the tank 16 and
the vacuum pump 17 with the aid of a valve 23.
[0098] A hydraulic closing unit 24, which can be decoupled via a
valve 25, can optionally he connected to the system, as shown in
FIG. 3.
[0099] FIG. 4 shows a schematic illustration of an embodiment of
the method according to the invention for ascertaining the position
of the feed opening and of the intake opening. FIG. 4 shows the
pressure profile as a function of the position of the casting
piston during the carrying out of the method according to the
invention.
[0100] At the beginning of the method according to the invention,
the casting piston 7 is located in the. casting chamber 6 in a
position S.sub.i,0 its which the feed opening 9 in the casting
chamber 6 is not sealed and is located in the piston space of the
casting piston 7, The two mold halves 4 and 5 are closed by
movement of the movable platen 2 into the closed position,, and
therefore the mold cavity is sealed in relation to the environment.
At this time, normal pressure (approximately 1000 mbar) prevails in
the casting chamber 6 since the casting chamber 6 is in contact
with the environment via the feed opening 3.
[0101] The casting piston 7 is now moved in the casting chamber 6
into a position in which its front end 7a is located approximately
level with the middle of the feed opening 9 (position "vacuum
start"). The valve 13 to the mold cavity 11 is closed and the valve
22 to the intake opening 10 is opened. Alternatively, it is also
possible for the valve 22 to the intake opening 10 to be closed and
the valve 13 to the moid cavity 11 to be opened. A slight drop in
pressure .DELTA.p.sub.n occurs in the casting chamber 6. The
casting piston 7 is now moved in the casting chamber 6 until the
front end 7 a of said casting piston reaches that edge of the feed
opening 9 which faces the mold. This position is referred to as
s.sub.hol, fin. From said position s.sub.hol, fin of trie casting
piston 7, the casting chamber 6 is sealed in relation to the
environment, and a significant drop in pressure occurs. The casting
piston is moved somewhat further as far as a position at which the
pressure profile has a reversal point, i.e. the second derivative
of the p-S curve assumes the value 0. This position is referred to
as s.sub.ph, eff1 and is considered to be representative of the
position of the feed opening 9 (more precisely of the edge thereof
facing the mold).
[0102] In the embodiment according to FIG. 4, the casting piston 7
is now stopped and the evacuation of the casting chamber 6 ended.
The tank 16 is evacuated to the desired value with the vacuum pump
17, and the moid halves 4 and 5 are opened from each other by
movement of the movable platen 2 into an open position (position
"vacuum stop 1"), The mold cavity 11 thereby obtains contact with
the environment, and the pressure in the casting chamber 6
connected to the mold cavity 11 rises again to normal pressure. The
casting piston 7 is now moved in the casting chamber 6 into a
position in which the front end 7a of said casting piston is
located approximately level with the middle of the intake opening
10 (position "vacuum start"). The valve 13 to the moid cavity 11 is
closed and the valve 22 to the intake opening 10 is opened. A
slight drop in pressure .DELTA.p.sub.n occurs in the casting
chamber 6, The casting piston 7 is now moved in the casting chamber
6 until the front end 7a of said casting piston reaches that edge
of the intake opening 10 which faces the moid. This position is
referred to as S.sub.Saugloch, fin. From said position
s.sub.Saugloch, fin of the casting piston 7, the casting chamber 6
is sealed in relation to the intake opening 10, and a significant
drop in pressure occurs in the connecting line 15. The casting
piston is moved somewhat further as far as a position at which the
pressure profile has a reversal point, i.e. the second derivative
of the p-S curve assumes the value 0. This position is referred to
as S.sub.eh, eff2 and is considered to be representative of the
position of the intake opening 10 (more precisely of the edge
thereof racing the mold).
[0103] In the embodiment according to FIG. 4, the evacuation of the
connecting line 15 is now ended. If the casting piston 7 is now
moved forward further in the casting chamber 6, it releases the
intake opening 10 from the position "vacuum stop 2". As a result,
the connecting line 15 comes into contact with the casting chamber
6 and the mold cavity 11, which are in contact with the
environment. The pressure in the connecting line 15 thereby rises
again to approximately normal pressure. FIG. 5 explains the
evacuation times t1 and t2 which are determined during a learning
cycle of an embodiment according to the invention of the present
invention. The period of time t1 corresponds to the period of time
in which the pressure profile (indicated by the curve A shown in
bold) in the connecting line 14 or 15 between casting chamber 6 or
moid cavity 11 and tank 16, which is evacuated by the vacuum pump
17, corresponds to a drop in pressure from, normal pressure to a
value which corresponds by 90% to the predetermined negative pres-
sure to be reached. The period of time t2 corresponds to the period
of time in which the pressure profile findicated by the curve A
shown in bold) in the connecting line 15, 15 between casting
chamber 6 or mold cavity 11 and tank 16, which is evacuated by the
vacuum, pump 17, corresponds to a drop in pressure from the value
reached after the period of time t1 to the predetermined negative
pressure to be achieved. The curve B, which is shown by a thin
line, corresponds to the parallel pressure profile in the tank 10.
The pressure rises there by absorption of gas from the casting
chamber 6 or the moid cavity 11. Prior to the next evacuation, the
tank 16 has to be brought again to the corresponding negative
pressure.
[0104] FIG. 6 shows an example of a casting curve according to the
invention. The profile of the speed of the casting piston 7 is
illustrated as a function of the piston travel, and the change in
the degree of filling of the casting chamber 6 is shown as a
function of the movement of the casting piston 7. The speed profile
of the casting piston 7 is determined by the computer program
product, as described above, and indicated to the user. In the case
of the casting curve shown here, the casting piston 7 is
overproportionaliy accelerated, Shoi where s=100 mm as far as the
mold-side end of the feed opening 3. The speed of the castfng
piston 6 is subsequently increased substantially proportionally to
the distance covered (constant acceleration) until, when a degree
of filling of 100% is reached in the casting chamber 6, the casting
piston 7 is no longer accelerated, but rather the casting piston 7
is moved further in the casting chamber 6 at a constant speed.
* * * * *