Pressure difference control method for filling a cavity with melt

• US 6,247,521 B1
• Filed: 08/15/1996
• Issued: 06/19/2001
• Est. Priority Date: 08/15/1996
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Isuzu Seisakusho, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Isuzu Seisakusho, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Furukawa, Yasutaka, Hirata, Seiji, Kawai, Hiroshi
• Primary Examiner(s): Pyon, Harold
• Assistant Examiner(s): LIN, ING HOUR
• Application Number:
  US08/698,110
• Time in Patent Office: 1,769 Days
• Field of Search: 164/457, 164/155.3, 164/63, 164/255, 164/119
• US Class Current: 164/457
• CPC Class Codes: B22D 18/04 Low pressure casting, i.e. making use of pressures up to a few bars to fill the mould
• CPC Class Codes: B22D 18/08 Controlling, supervising, e.g. for safety reasons controlling or regulating in general G05

Abstract

A melt filling pressure difference control method controls a pressure difference used to supply melt from a holding furnace to a cavity of a casting machine by generating a pressure difference between an interior space of holding furnace and the cavity formed inside the mold. The method includes the steps of setting up a program pattern comprising time-varying characteristics of pressure difference target values, controlling the pressure difference so as to follow the program pattern that was set up, detecting whether the melt surface has risen to a predetermined level inside the cavity, compensating the program pattern based on the melt surface level when the melt surface has risen to a predetermined level inside cavity, and controlling the pressure difference between space inside the holding furnace and the cavity so as to follow the compensated program pattern.

Claims

1. A method of manufacturing a cast product using a casting machine,

said casting machine including:

a holding furnace that stores melt;

a mold with a cavity formed in its interior;

a melt duct that interconnects the holding furnace and the cavity; and

a device that generates a pressure difference between the pressure inside the holding furnace and the pressure inside the cavity; and

wherein said cavity is filled by the melt stored in said holding furnace via said melt duct due to the pressure difference,

the method comprising the steps of;

providing a pressure difference control program defining a pattern of pressure difference increase rate target values, each pressure difference increase rate target value being associated with a target time period;

applying a first selected pressure difference increase rate target value to the melt stored in the holding furnace for a first target time period;

detecting an actual time period in which the melt moves from a first predetermined level inside the casting machine to a second predetermined level inside the casting machine as a result of applying the first selected pressure difference increase rate target value to the melt; and

replacing the first target time period stored in the control program with the actual time period detected in the detecting step.

2. The method of claim 1, wherein the casting machine includes an electrode that is insulated from said mold and exposed to said cavity;

and a device for detecting the electrical resistance between the electrode and the cavity;

wherein the detecting step comprises detecting the timing at which the electrical resistance changes to a set value.

3. The method of claim 2, wherein a strength of said electrode is at least of the same level as a strength of said mold.

4. The method of claim 2 wherein said electrode is surrounded by a ceramic insulating member.

5. The method as in claim 1, further comprising correcting the target time periods of the pattern based on the difference between the first target time period and the actual time period detected in the detecting step so as to correct the pattern prior to the cavity being filled by the melt.

6. A method of manufacturing a cast product using a casting machine,

said casting machine including:

a holding furnace that stores melt;

a mold with a cavity formed in its interior extending vertically from a top end to a bottom end;

a melt duct that interconnects the holding furnace and said bottom end of the cavity; and

a device that generates a pressure difference between the pressure inside the holding furnace and the pressure inside the cavity; and

wherein said cavity is filled by the melt stored in said holding furnace via said melt duct due to the pressure difference,

the method including the steps of;

forcing the melt from the holding furnace and through said melt duct by applying a first rate of pressure difference increase to the melt stored in the holding furnace;

detecting when the melt has reached the bottom end of said cavity;

applying a second rate of pressure difference increase to the melt stored in the holding furnace when the melt has reached the bottom end of said cavity, wherein the second rate of pressure difference increase is less than the first rate of pressure difference increase;

detecting when the melt has reached the top end of said cavity; and

applying a third rate of said pressure difference increase when the melt has reached the top end of said cavity, wherein the third rate of said pressure difference increase is greater than the second rate of pressure difference increase.

7. The method of claim 6, further comprising the step of applying the second rate of pressure difference increase when a set first time period after applying the first rate of pressure difference increase has elapsed, if the melt has not yet reached the bottom end of the cavity.

8. The method of claim 6, further comprising the step of applying the third rate of said pressure difference increase when a set second time period has elapsed after detecting that the melt has reached the bottom end of said cavity, if the melt has not yet reached the top end of the cavity.

9. The method of claim 6, wherein said cavity is opened to the atmosphere, and said pressure difference is generated by applying pressure to the holding furnace, which is sealed.

10. The method of claim 6, wherein said pressure difference is generated by reducing the pressure in said cavity.

11. The method of claim 6, wherein said casting machine includes a first electrode, which is insulated from said mold and exposed to said cavity at said bottom end of said cavity;

a first device, which detects a first electrical resistance between the mold and said first electrode;

a second electrode, which is insulated from the mold and exposed to said cavity at said top end of said cavity; and

a second device, which detects a second electrical resistance between the mold and said electrode;

wherein the second timing is detected from the timing at which the second electrical resistance changes to a set value.

12. The method of claim 6, further comprising reducing the pressure difference increase to zero when a set third time period has elapsed after detecting that the melt has reached the top end of said cavity.

13. The method of claim 12, further comprising reducing the pressure difference to zero when a set fourth time period has elapsed after expiration of the predetermined third time period.

14. A method for manufacturing a cast product by controlling a differential pressure between a holding furnace and a mold cavity within a casting machine, wherein melt flows from the holding furnace through a melt duct to the mold cavity at a rate proportional to an increasing rate of said differential pressure, comprising the steps of:

setting up a differential pressure control program defining at least a first and second target increasing rates of said differential pressure, the first and second target increasing rates being assigned to a first and second pre-determined time intervals, respectively;

applying said differential pressure at the first target increasing rate during the first pre-determined time interval;

detecting a time when the melt reaches a bottom level inside the mold cavity; and

adjusting the increasing rate of said differential pressure to the second target increasing rate (a) when the first pre-determined time interval has expired or (b) when the melt reaches the first pre-determined level inside the mold cavity if the bottom time interval has not yet expired.

15. The method as in claim 14, wherein the increasing rate of said differential pressure is adjusted from the first target increasing rate to the second target increasing rate prior to the expiration of the first pre-determined time interval when the melt reaches the bottom level inside the mold cavity prior to the expiration of the first pre-determined time interval.

16. A method of claim 14 further comprising a step of:

adjusting the increasing rate of said differential pressure to a third target increasing rate assigned to a third pre-determined time interval (c) when the second predetermined time interval has expired or (d) when the melt reaches a top level inside the mold cavity if the second pre-determined time interval has not yet expired.

17. The method as in claim 16, wherein the increasing rate of said differential pressure is adjusted from the second target increasing rate to the third target increasing rate prior to the expiration of the second pre-determined time interval when the melt reaches the top level inside the mold cavity prior to the expiration of the first pre-determined time interval.

18. A method for manufacturing a cast product by controlling a pressure difference between a holding furnace and a mold cavity within a casting machine, wherein melt flows from the holding furnace through a melt duct to the mold cavity at a rate proportional to an increase rate of said pressure difference, comprising the steps of:

setting up a pressure difference control program defining at least a first and second target increase rates of said pressure difference, the first and second target increase rates being assigned to a first and second pre-determined time interval, respectively;

applying the pressure difference at the first target increase rate during the first pre-determined time interval;

detecting a time when the melt reaches a bottom level inside the mold cavity; and

shifting the first and second pre-determined time intervals in the pressure difference control program based on a difference between the time detected in said time detecting step and a changing time from the first pre-determined time interval to the second pre-determined time interval in the pressure difference control program.

19. The method of claim 18, further comprising a step of:

shifting the predetermined time intervals in the pressure difference control program based on a difference between a time when the melt reaches a top level inside the mold cavity and a changing time from the second pre-determined time interval to a third pre-determined time interval in the pressure difference control program.

20. The method of claim 18, wherein said detecting step comprises detecting a time when electrical resistance between the mold cavity and an electrode disposed within the mold cavity changes to a pre-determined value.

21. The method of claim 20, wherein a mechanical strength of said electrode is at least of the same level as a mechanical strength of said mold.

22. The method of claim 20, wherein the electrode is surrounded by a ceramic insulating member.

23. A method of manufacturing a cast product, comprising the steps of:

forcing melt from a holding furnace through a melt duct into a mold cavity by adjusting a pressure difference between the holding furnace and the mold cavity, the melt flowing into the mold cavity at a rate proportional to an increase rate of said pressure difference;

detecting when the melt has risen to a bottom end of the mold cavity;

reducing the increase rate of said pressure difference when the melt has reached the bottom end of the mold cavity;

detecting when the melt has risen to a top end of the mold cavity; and

increasing the increase rate of said pressure difference when the melt has reached the top end of the mold cavity.

24. The method of claim 23, wherein the increase rate of said pressure difference is reduced after a first predetermined time interval has expired if the melt has not risen to the bottom end of the mold cavity before the first pre-determined time interval has expired.

25. The method of claim 23, wherein the increase rate of said pressure difference is increased after a second pre-determined time interval has expired if the melt has not risen to the top end of the mold cavity before the second pre-determined time interval has expired.

26. The method of claim 23, further comprising a step of:

setting the pressure difference to a constant value when a third pre-determined time interval has expired.

27. The method of claim 23, further comprising a step of:

setting the pressure difference to zero when a fourth pre-determined time interval has expired.

28. The method of claim 23, wherein the melt is forced from the holding furnace to the mold cavity by opening the mold cavity to the atmosphere, sealing the holding furnace and applying pressure to the holding furnace.

29. The method of claim 23, wherein the melt is forced from the holding furnace to the mold cavity by opening the holding furnace to the atmosphere, sealing the mold cavity and reducing pressure inside the mold cavity.

30. The method of claim 23, wherein the first detecting step comprises detecting when electrical resistance between,the mold cavity and a first electrode disposed at the bottom end of the mold cavity changes to a pre-determined value and the second detecting step comprises detecting when electrical resistance between the mold cavity and a second electrode disposed at the top end of the mold cavity changes to a predetermined value.

31. The method as in claim 23, wherein the second pre-determined time interval begins (i) after the increase rate of said pressure difference has been reduced, and (ii) when the melt has risen to the bottom end of the mold cavity.

32. A method of manufacturing a cast product, comprising the steps of:

generating a differential pressure between a holding furnace and a mold cavity, wherein melt flows from the holding furnace to the mold cavity via a melt duct at a rate proportional to an increasing rate of said differential pressure, wherein during a first pre-determined determined time interval (i) a first constant increasing rate of said pressure differential is applied and (ii) after the first constant increasing rate of said pressure differential is applied, a second constant increasing rate of said differential pressure different from said first constant increasing rate of said pressure differential is applied to force the melt to rise from the holding furnace to a bottom end of the mold cavity;

detecting when the melt reaches the bottom end of the mold cavity;

applying a third constant increasing rate of said differential pressure for a second pre-determined time interval that begins either (a) when the first pre-determined time interval has expired or (b) when the melt reaches the bottom end of the mold cavity if the first pre-determined time has not yet expired, the third constant increasing rate of said differential pressure being less than the first and second constant increasing rates of said differential pressure;

detecting when the melt fills the cavity; and

applying a fourth constant increasing rate of said differential pressure for a third pre-determined time interval that begins either (c) when the second predetermined time interval has expired or (d) when the melt fills the cavity if the second pre-determined time has not yet expired, the fourth constant increasing rate of said differential pressure being greater than the third constant increasing rate of the said differential pressure.

33. A method according to claim 32, further comprising the step of applying a constant differential pressure for a fourth pre-determined time interval after the third pre-determined time interval has expired.

34. A method according to claim 32, further comprising the step of reducing said differential pressure to zero upon expiration of the fourth pre-determined time interval.

35. The method as in claim 32, wherein:

the third constant increasing rate of said differential pressure is applied for the second pre-determined time interval that begins (i) when the melt reaches the bottom end of the mold cavity, and (ii) before the first pre-determined time has expired; and

the fourth constant increasing rate of said differential pressure is applied for the third pre-determined time interval that begins (i) when the melt fills the cavity, and (ii) before the second pre-determined time has expired.

36. A method of making a cast product using a casting apparatus comprising a furnace that stores melt;

a mold cavity disposed above the furnace having a bottom surface, a top surface and a bottom portion;

a melt duct connecting the furnace to the bottom portion of the mold cavity;

means for applying a pressure difference between the melt stored inside the furnace and the pressure inside the mold cavity;

target value storing means for storing a set of target values for controlling pressure differences between the furnace and the mold cavity;

a first melt sensor disposed on the bottom surface of the mold cavity;

a second melt sensor disposed on the top surface of the mold cavity; and

a timer for determining;

(a) a first amount of time from initiating an increase in the pressure difference to force melt from the furnace until detection of the melt by the first melt sensor, and

(b) a second amount of time from detection of the melt by the first melt sensor until detection of the melt by the second melt sensor,

the method comprising the steps of;

storing an initial set of target values in the target value storing means, the initial set of target values representing;

(1) a first rate of pressure increase, (2) a second rate of pressure increase, (3) a third rate of pressure increase, (4) a first time period for applying the first rate of pressure increase, and (5) a second time period for applying the second rate of pressure increase, wherein the first rate of pressure increase is greater than the second rate of pressure increase, and the second rate of pressure increase is less than the third rate of pressure increase;

applying the first rate of pressure increase to the melt to force the melt up the melt duct and into the mold cavity and simultaneously beginning the first time period for applying the first rate of pressure increase;

using the first melt sensor to detect when the melt has reached the first melt sensor;

using the timer to determine the first amount of time from initiating the first rate of pressure increase to force melt from the furnace until detection of the melt by the first melt sensor;

applying the second rate of pressure increase to the melt at the earlier of (1) expiration of the first time period for applying the first rate of pressure increase, or (2) detection of the melt by the first melt sensor, and simultaneously beginning the second time period for applying the second rate of pressure increase when the second rate of pressure increase is applied to the melt;

wherein, if the first melt sensor detects the melt before the first time period for applying the first rate of pressure increase has expired, replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor, and

wherein, if the first melt sensor detects the melt after the first time period for applying the first rate of pressure increase has expired, restarting the second time period for applying the second rate of pressure increase when the melt is detected and replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor;

using the second melt sensor to detect when the melt reaches the second melt sensor;

using the timer to determine the second amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor; and

applying the third rate of pressure increase to the melt at the earlier of (1) expiration of the second time period for applying the second rate of pressure increase or (2) detection of the melt by the second melt sensor;

wherein, if the second melt sensor detects the melt before or after the second time period for applying the second rate of pressure increase has expired, replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the second amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.

37. The method as in claim 36, comprising:

detecting the melt with the first melt sensor before the first time period for applying the first rate of pressure increase has expired; and

replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor,

wherein the first time period is replaced before the mold cavity is filled with the melt.

38. The method as in claim 36, comprising:

detecting the melt with the first melt sensor after the first time period for applying the first rate of pressure increase has expired;

restarting the second time period for applying the second rate of pressure increase when the melt is detected; and

replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor,

wherein the first time period is replaced before the mold cavity is filled with the melt.

39. The method as in claim 36, wherein the third rate of pressure increase is applied for a third time period, and the method further comprises applying a constant rate of pressure after the third time period expires.

40. The method as in claim 39, wherein a constant pressure is applied for a fourth time period and the pressure is reduced to zero when the fourth time period expires.

41. The method as in claim 40, wherein the first and second melt sensors detect the melt reaching the respective first and second melt sensors as a change in electrical resistance of the respective first and second melt sensors.

42. The method as in claim 41, wherein the first and second melt sensors are each surrounded by a ceramic insulating member.

43. The method as in claim 40, wherein the first and second melt sensors detect the melt reaching the respective first and second melt sensors as a change in current flow through the respective first and second melt sensors.

44. The method as in claim 43, wherein the first and second melt sensors are each surrounded by a ceramic insulating member.

45. A method of making a cast product using a casting apparatus comprising a furnace that stores melt;

a mold cavity disposed above the furnace having a bottom surface, a top surface and a bottom portion;

a melt duct connecting the furnace to the bottom portion of the mold cavity;

means for applying a pressure difference between the melt stored inside the furnace and the pressure inside the mold cavity;

means for storing a set of target values for controlling the pressure difference between the furnace and the mold cavity;

a first melt sensor disposed on the bottom surface of the mold cavity;

a second melt sensor disposed on the top surface of the mold cavity; and

a timer for determining;

(a) a first amount of time from initiating an increase in the pressure difference to force melt from the furnace until a first time period expires,

(b) a second amount of time from expiration of the first time period until detection of the melt by the first melt sensor, and

(c) a third amount of time from detection of the melt by the first melt sensor until detection of the melt by the second melt sensor,

the method comprising the steps of;

storing an initial set of target values in the target value storing means, the initial set of target values representing (1) a first rate of pressure increase, (2) a second rate of pressure increase, (3) a third rate of pressure increase, (4) a fourth rate of pressure increase, (5) a first time period for applying the first rate of pressure increase, (6) a second time period for applying the second rate of pressure increase, (7) a third time period for applying the third rate of pressure increase, and (8) a fourth time period for applying the fourth rate of pressure increase, wherein the first rate of pressure increase is greater than the second rate of pressure increase, the second rate of pressure increase is greater than the third rate of pressure increase and the third rate of pressure increase is less than the fourth rate of pressure increase;

applying the first rate of pressure increase to the melt to force the melt up the melt duct and into the mold cavity and simultaneously beginning the first time period for applying the first rate of pressure increase;

applying the second rate of pressure increase after the first time period for applying the first rate of pressure increase has expired and simultaneously beginning the second time period for applying the second rate of pressure increase;

using the first melt sensor to detect when the melt reaches the first melt sensor;

using the timer to determine a first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor;

applying the third rate of pressure increase to the melt at the earlier of (1) expiration of the second time period for applying the second rate of pressure increase, or (2) detection of the melt at the first melt sensor, and simultaneously beginning the third time period for applying the third rate of pressure increase;

wherein, if the first melt sensor detects the melt before the second time period for applying the second rate of pressure increase has expired, replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor, and

wherein, if the first melt sensor detects the melt after the second time period for applying the second rate of pressure increase has expired, restarting the third time period for applying the third rate of pressure increase when the melt is detected and replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor,

using the second melt sensor to detect when the melt reaches the second melt sensor;

using the timer to determine a second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor, and

applying the fourth rate of pressure increase to the melt at the earlier of (1) expiration of the third time period for applying the third rate of pressure increase, or (2) detection of the melt by the second melt sensor;

wherein, if the second melt sensor detects the melt before or after the third time period for applying the third rate of pressure increase has expired, replacing the third time period for applying the third rate of pressure increase stored in the target value storing means with the second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.

46. The method as in claim 45, comprising:

detecting the melt with the first melt sensor before the second time period for applying the second rate of pressure increase has expired;

replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor,

wherein the second time period is replaced before the mold cavity is filled with the melt.

47. The method as in claim 45, comprising:

detecting the melt with the first melt sensor after the second time period for applying the second rate of pressure increase has expired;

restarting the third time period for applying the third rate of pressure increase when the melt is detected;

replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor,

wherein the second time period is replaced before the mold cavity is filled with the melt.

48. The method as in claim 45, comprising:

detecting the melt with the second melt sensor before or after the third time period for applying the third rate of pressure increase has expired; and

replacing the third time period for applying the third rate of pressure increase stored in the target value storing means with the second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.

49. The method as in claim 45, wherein the fourth rate of pressure increase is applied for a fourth time period, and the method further comprises applying a constant pressure after the fourth time period expires.

50. The method as in claim 49, wherein the constant pressure is applied for a fifth time period and the pressure is reduced to zero when the fifth time period expires.

51. The method as in claim 50, wherein the first and second melt sensors detect the melt reaching the respective first and second melt sensors as a change in electrical resistance of the respective first and second melt sensors.

52. The method as in claim 51, wherein the first and second melt sensors are each surrounded by a ceramic insulating member.

53. The method as in claim 50, wherein the first and second melt sensors detect the melt reaching the respective first and second melt sensors as a change in current flow through the respective first and second melt sensors.

54. The method as in claim 53, wherein the first and second melt sensors are each surrounded by a ceramic insulating member.