Reduced density foam and method for molding reduced density foam

• US 20070235892A1
• Filed: 03/29/2006
• Published: 10/11/2007
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: Cadillac Products Automotive Company
• Original Assignee: Cadillac Products Automotive Company
• Inventors: Kucejko, Richard, Williams, Michael, Zander, Robert
• Granted Patent: US 7,935,294 B2
• Time in Patent Office: Days
• US Class Current: 264/85
• CPC Class Codes: B29C 44/422 by injecting by forward movement of the plastizising screw

Abstract

A system and method for operating an injection system to create a reduced density polymeric component uses a resin/blowing agent mixture, an injection molding machine having an injection molding screw positioned in a screw section, accumulators, a hydraulic pump, multiple molds, and a cooling system. Coolant is directed into each mold. The injection molding screw is rotated moving the mixture proximate to a receiving portion of the screw section. The injection molding screw is incrementally displaced to one of a plurality of successive injection positions each injecting a portion of the mixture into one of the molds by operating the hydraulic pump and discharging the accumulators. The accumulators are recharged after each injection molding screw displacement using the hydraulic pump. The injection molding screw is displaced and the accumulators recharged for each of the successive injection positions, each defining a stage for filling the molds in a single operating cycle of the injection system.

Claims

1. A foam part injection system, comprising:

an injection molding machine having an injection molding screw operable to inject a foamed polymeric mixture;

a hydraulic system connected to the injection molding machine, the hydraulic system including;

a plurality of hydraulic accumulators alignable in fluid communication with the injection molding screw;

a hydraulic pump alignable with the hydraulic accumulators and the injection molding screw operable to each of displace a volume of hydraulic fluid to displace the injection molding screw and refill the hydraulic accumulators;

a plurality of part molds in fluid communication with the injection molding screw; and

an injection cycle defining a plurality of successive injection stages each including a predetermined axial displacement of the injection molding screw assisted by flow from the hydraulic pump and the hydraulic accumulators to fill one of the part molds, each of the stages defining an initially charged condition of the accumulators, and each of the stages corresponding to a partial volume of the mixture operable to fill the one of the part molds in less than one second.

2. The system of claim 1, further comprising a screw section having the injection molding screw disposed within the screw section for both rotational and longitudinal displacement.

3. The system of claim 2, further comprising a first heating device in communication with the screw section operable to heat the foamed polymeric mixture within the screw section.

4. The system of claim 3, further comprising a mold support member operable to rigidly support the plurality of part molds.

5. The system of claim 4, further comprising a second heating device in communication with the mold support member operable to control a temperature of the foamed polymeric mixture entering any of the plurality of part molds to maintain the foamed polymeric mixture in a liquefied state.

6. The system of claim 1, further comprising a coolant system in communication with the plurality of part molds, the coolant system operable to maintain a temperature of any one of the plurality of part molds.

7. The system of claim 6, further comprising a plurality of electrically controlled coolant valves, the coolant valves individually controllable to establish each of:

a first coolant flow path in communication with the first part mold;

a second coolant flow path in communication with the second part mold;

a third coolant flow path in communication with the third part mold;

wherein a flow rate of a coolant is controllable to any one of the plurality of part molds by control of at least one of the plurality of coolant valves.

8. The system of claim 1, further comprising a plurality of electrically controlled hydraulic valves, the hydraulic valves individually controllable to establish each of:

a hydraulic injection assist flow path;

a hydraulic accumulator discharge flow path in communication with the hydraulic injection assist flow path; and

a hydraulic accumulator recharge flow path.

9. The system of claim 1, further comprising:

a first injection molding screw injection position corresponding to a first portion of the volume of the mixture required to fill a first one of the plurality of part molds;

a second injection molding screw injection position corresponding to a second portion of the volume of the mixture required to fill a second one of the plurality of part molds; and

a third injection molding screw injection position corresponding to a third portion of the volume of the mixture required to fill a third one of the plurality of part molds.

10. The system of claim 1, further comprising a control system including a computer, the control system operable to direct axial displacement of the injection molding screw during the plurality of successive stages.

11. A method for creating foamed polymeric parts using a resin/blowing agent mixture, an injection molding machine having an injection molding screw including a screw thread positioned in a screw section, a plurality of accumulators, a hydraulic pump, and a plurality of molds, the method comprising:

co-rotating the injection molding screw together with the screw thread to transfer the resin/blowing agent mixture into a receiving portion of the screw section;

heating the resin/blowing agent mixture;

performing a first stage operation including operating the hydraulic pump in combination with discharging the accumulators to axially displace the injection molding screw from an initial position to a first injection position operable to inject a first portion of the resin/blowing agent mixture into a first one of the molds;

recharging the accumulators; and

executing a second stage operation including further operating the hydraulic pump in combination with discharging the accumulators to axially displace the injection molding screw from the first injection position to a second injection position operable to inject a second portion of the resin/blowing agent mixture into a second one of the molds.

12. The method of claim 11, further comprising:

repeating the recharging step; and

conducting a third stage operation including further operating the hydraulic pump in combination with discharging the accumulators to displace the injection molding screw from the second injection position to a third injection position operable to inject a third portion of the resin/blowing agent mixture into a third one of the molds.

13. The method of claim 12, further comprising controlling a plurality of electrically controllable valves to align the hydraulic pump with the accumulators prior to the recharging step.

14. The method of claim 13, further comprising repositioning the plurality of electrically controllable valves following the recharging step to align the accumulators in fluid communication with the injection molding screw.

15. The method of claim 11, further comprising automatically opening a plurality of first valve gates in the first one of the molds prior to the performing step.

16. The method of claim 15, further comprising:

automatically closing the plurality of first valve gates after the performing step and prior to the executing step; and

automatically opening a plurality of second valve gates in the second one of the molds after the closing step and prior to the executing step.

17. The method of claim 11, further comprising flowing a coolant into each of the plurality of molds.

18. The method of claim 17, further comprising individually controlling a temperature of the coolant entering each of the plurality of molds.

19. A method for operating an injection system to create a reduced density polymeric component using a resin/blowing agent mixture, an injection molding machine having an injection molding screw including a screw thread and a one-way valve positioned in a screw section, a plurality of accumulators, a hydraulic pump, a plurality of molds, and a cooling system, the method comprising:

directing a flow of coolant from the cooling system into each of the plurality of molds;

rotating the injection molding screw to translate the resin/blowing agent mixture to a receiving portion of the screw section;

incrementally axially displacing the injection molding screw by operating the hydraulic pump in combination with discharging the accumulators to axially displace the injection molding screw to one of a plurality of successive injection positions each operable to inject a portion of the resin/blowing agent mixture into one of the molds;

recharging the accumulators using the hydraulic pump;

repeating each of the displacing and recharging steps for the plurality of successive injection positions, the injection positions each defining one of a plurality of stages for filling the plurality of molds in a single operating cycle of the injection system.

20. The method of claim 19, further comprising positioning a plurality of electrically controlled valves using a control system to align the hydraulic pump in fluid communication with the accumulators.

21. The method of claim 20, further comprising repositioning the plurality of valves after the recharging step to direct the hydraulic fluid in a next one of the plurality of stages to further displace the injection molding screw.

22. The method of claim 21, further comprising pre-programming a control system to control each of the plurality of valves and the hydraulic pump.

23. The method of claim 19, further comprising refilling the receiving portion of the screw section to axially displace the injection molding screw to an initial position after injection of the mixture into the plurality of molds.

24. The method of claim 19, further comprising removing a cooled part from each of the plurality of molds following a predetermined cooling period variable for each of the molds to complete the single operating cycle.

25. The method of claim 19, further comprising heating the resin/blowing agent mixture in the screw section prior to the displacing step.

26. The method of claim 19, further comprising sizing the hydraulic pump and the accumulators to permit the recharging step to be accomplished in a time period of 1 to 5 seconds.

27. The method of claim 19, further comprising controlling the hydraulic pump and the accumulators to accomplish the displacing step in a time ranging between 0.3 to 0.7 seconds.

28. The method of claim 19, further comprising orienting the one-way valve to permit flow of the resin/blowing agent mixture in the receiving portion of the screw section only toward the plurality of molds.