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.

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

[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 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 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.