Apparatus and method for thermoplastic extrusion

• US 6,578,596 B1
• Filed: 04/18/2001
• Issued: 06/17/2003
• Est. Priority Date: 04/18/2000
• Status: Active Grant

• Current Assignee: Stratasys Incorporated
• Original Assignee: Stratasys Incorporated
• Inventors: Zinniel, Robert L., Batchelder, John Samuel
• Primary Examiner(s): CHAMBERS, A MICHAEL
• Application Number:
  US09/837,813
• Time in Patent Office: 790 Days
• Field of Search: 137/13, 137/341, 137/828, 137/334, 137/338, 137/15.09
• US Class Current: 137/15.09
• CPC Class Codes: B29C 31/045 moving along predetermined circuits or distributing the material according to predetermined patterns
• CPC Class Codes: B29C 41/36 Feeding the material on to the mould, core or other substrate
• CPC Class Codes: B29C 41/52 Measuring, controlling or regulating
• CPC Class Codes: B29C 48/05 Filamentary, e.g. strands
• CPC Class Codes: B29C 48/09 Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• CPC Class Codes: B29C 48/345 Extrusion nozzles comprising two or more adjacently arranged ports, for simultaneously extruding multiple strands, e.g. for pelletising
• CPC Class Codes: B29C 48/86 at the nozzle zone
• CPC Class Codes: B29C 48/87 Cooling
• CPC Class Codes: B29C 64/106 using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
• CPC Class Codes: B29C 64/118 using filamentary material being melted, e.g. fused deposition modelling [FDM]
• CPC Class Codes: Y10T 137/0391 Affecting flow by the addition of material or energy
• CPC Class Codes: Y10T 137/0447 Including joint or coupling
• CPC Class Codes: Y10T 137/2196 Acoustical or thermal energy
• CPC Class Codes: Y10T 137/6416 With heating or cooling of the system
• CPC Class Codes: Y10T 137/6525 Air heated or cooled [fan, fins, or channels]

Abstract

An apparatus and method for controlling the extrusion of thermoplastic through one or more discharge orifices is described. An apparatus comprises one or more thermally conductive flow tubes defining flow channels in a heated thermally conductive body and terminating in discharge orifices. Each flow channel may be independently valved on and off, by selectively supplying a flow of coolant. An array of flow channels can be independently opened and closed in a predetermined pattern, so as to vary the extrudate configuration of thermoplastic emerging from the discharge orifices. By extruding thermoplastic layer-by-layer onto a base in this manner, a three-dimensional object may be formed.

Claims

1. A freeze valve apparatus for thermoplastic, comprising:

a thermally conductive body heated to a temperature at which a thermoplastic is flowable and having a cavity which contains a thermal insulator;

a thermally conductive hollow flow tube defining a flow channel for a flow of the thermoplastic and having an inlet region, an outlet region terminating in an exit orifice and a mid-section between the inlet and outlet regions, the flow tube extending through the thermally conductive body such that its inlet and outlet regions are captured within the thermally conductive body and its mid-section passes through the cavity; and

means for directing a flow of coolant having a temperature lower than a lowest flowable temperature of the thermoplastic through the insulator in the cavity and around a portion of the flow tube mid-section, such that heat transfer to the coolant causes solidification of thermoplastic in the flow channel in a region of the flow tube mid-section.

2. The apparatus of claim 1, wherein the thermal insulator is stagnant air, and wherein the means for directing comprises a coolant inlet tube secured in the cavity such that an outlet of the coolant inlet tube is proximate the flow tube.

3. The apparatus of claim 1, wherein the thermal insulator is a block of material separated from the flow tube by a flow gap, and wherein the means for directing comprises the flow gap together with an inlet passage and an exhaust passage each extending through the thermal insulator to the flow gap.

4. The apparatus of claim 1, wherein the flow channel in the region of the flow tube mid-section in which the thermoplastic solidifies has a reduced cross-section.

5. The apparatus of claim 4, wherein the reduced cross-section is created by a tubular insert.

6. The apparatus of claim 1 and further comprising:

means for selectively providing the flow of coolant to the means for directing.

7. The apparatus of claim 6, wherein the means for selectively providing can be controlled to vary the flow rate of the flow of coolant.

8. The apparatus of claim 6, wherein a flow of ABS thermoplastic solidified in the flow channel will reach 90 percent of a steady state flow rate through the flow channel in 2-200 milliseconds time after the flow of coolant is ceased.

9. The apparatus of claim 1 and further comprising:

a thermoplastic supply manifold within the thermally conductive body and flowably connected to the inlet region of the flow tube.

10. The apparatus of claim 1, embodied in an extrusion head for three-dimensional deposition modeling.

11. The apparatus of claim 1, wherein the thermally conductive flow tube is press-fit into a hole in the thermally conductive body.

12. The apparatus of claim 11, wherein the thermally conductive flow tube is made of stainless steel and the thermally conductive body is made of aluminum.

13. The apparatus of claim 1, wherein the flow tube has a length of less than 1 inch and the flow channel diameter is less than 0.1 inches.

14. A method of manufacturing the apparatus of claim 1, comprising:

drilling a hole in the thermally conductive body by electric discharge machining; and

press-fitting the thermally conductive flow tube into the hole in the thermally conductive body.

15. The method of claim 14, and further comprising:

cutting the flow tube to a final length by electric discharge machining after it is press-fit into the thermally conductive body.

16. A freeze valve apparatus for thermoplastic, comprising:

a thermally conductive body heated to a temperature at which a thermoplastic is flowable and having a cavity which contains a thermal insulator;

a thermally conductive hollow flow tube extending through the thermally conductive body such that a mid-section thereof passes through the cavity, the flow tube having an inlet above its mid-section for receiving a flow of the thermoplastic and an exit orifice below its mid-section for discharging the thermoplastic; and

means for causing solidification of the thermoplastic in a region of the flow tube mid-section to valve-off the flow channel.

17. The apparatus of claim 16, wherein the means for causing solidification comprises:

a flow regulator which selectively provides a flow of coolant having a temperature lower than a lowest flowable temperature of the thermoplastic; and

means for contacting the flow of coolant with a portion of the flow tube mid-section.

18. The apparatus of claim 17, wherein the flow regulator is a solenoid.

19. The apparatus of claim 17, wherein a flow of ABS thermoplastic valving-off the flow channel will reach 90 percent of a steady state flow rate through the flow channel in 2-200 milliseconds time after the flow of coolant is ceased.

20. The apparatus of claim 16, wherein the thermally conductive flow tube is press-fit into a hole in the thermally conductive body.

21. The apparatus of claim 16, wherein the flow channel in the region of the flow tube mid-section in which the thermoplastic solidifies has a reduced cross-section.

22. The apparatus of claim 16 and further comprising:

a thermoplastic supply manifold within the thermally conductive body and flowably connected to the inlet of the flow tube.

23. The apparatus of claim 22 and further comprising:

a pressure sensor in the thermoplastic supply manifold.

24. The apparatus of claim 16, wherein the thermally conductive body includes a resistive element ohmically controlled in response to external electrical temperature control signals, and further comprising:

a temperature sensor mounted to the thermally conductive body for providing electrical feedback signals indicative of the temperature of the thermally conductive body, which feedback signals can be monitored by a controller and used by the controller to generate the temperature control signals.

25. The apparatus of claim 16, embodied in an extrusion head for three-dimensional deposition modeling.

26. The apparatus of claim 16, wherein a flow of ABS thermoplastic valving-off the flow channel will reach 90 percent of a steady state flow rate through the flow channel in 2-200 milliseconds time after the flow of coolant is ceased.

27. A multi-orifice freeze valve apparatus for thermoplastic, comprising:

a thermally conductive body heated to a temperature at which a thermoplastic is flowable and having a cavity which contains a thermal insulator;

a plurality of thermally conductive hollow flow tubes defining a plurality of flow channels for a flow of the thermoplastic, each flow tube having an inlet region, an outlet region terminating in an exit orifice through which thermoplastic is extruded and a mid-section between the inlet and outlet regions, and each flow tube extending through the thermally conductive body such that its inlet and outlet regions are captured within the thermally conductive body and its mid-section passes through the cavity; and

means for independently causing solidification of the thermoplastic in a region of each flow tube mid-section to selectively valve-off the flow channels.

28. The apparatus of claim 27, wherein the means for independently causing solidification comprises:

a plurality of flow regulators, each associated with one of the plurality of flow tubes, which selectively provide a flow of coolant having a temperature lower than a lowest flowable temperature of the thermoplastic; and

means for contacting the flow of coolant with a portion of each flow tube mid-section.

29. The apparatus of claim 28, wherein the flow regulators each comprise a solenoid.

30. The apparatus of claim 28, wherein the thermal insulator is stagnant air, and wherein the means for contacting comprises a plurality of coolant inlet tubes each associated with one of the plurality of flow regulators and secured in the cavity such that an outlet of each coolant inlet tube is proximate one of the plurality of flow tubes.

31. The apparatus of claim 28, wherein the thermal insulator is a solid material and wherein the means for contacting comprises a flow gap interposed between each flow tube and the thermal insulator together with a plurality of inlet passage and an exhaust passage pairs each extending through the thermal insulator to the flow gap of an associated one of the flow tubes, each such inlet passage being associated with one of the plurality of flow regulators.

32. The apparatus of claim 28, wherein a flow of ABS thermoplastic valving-off any one of the flow channels will reach 90 percent of a steady state flow rate through the flow channel in 2-200 milliseconds time after the flow of coolant is ceased.

33. The apparatus of claim 27 and further comprising:

a thermoplastic supply manifold flowably connected to the inlet region of each flow tube.

34. The apparatus of claim 33, wherein the thermoplastic supply manifold is within the thermally conductive body.

35. The apparatus of claim 33 and further comprising:

pumping means for providing flowable thermoplastic to the supply manifold in response to pump control signals from a controller.

36. The apparatus of claim 35 and further comprising:

a pressure sensor in the thermoplastic supply manifold for providing electrical feedback signals to the controller indicative of the pressure in the manifold, which feedback signals are used by the controller to generate the pump control signals.

37. The apparatus of claim 27, wherein the thermally conductive body includes a resistive element ohmically controlled in response to external electrical temperature control signals, and further comprising:

a temperature sensor mounted to the thermally conductive body for providing electrical feedback signals indicative of the temperature of the thermally conductive body, which feedback signals can be monitored by a controller and used by the controller to generate the temperature control signals.

38. The apparatus of claim 27, wherein the plurality of thermally conductive flow tubes are press-fit into a plurality of holes in the thermally conductive body.

39. The apparatus of claim 27, wherein the low channels have a reduced cross-section in the region of each flow tube mid-section wherein thermoplastic solidifies.

40. The apparatus of claim 27, wherein each flow tube has a length of less than 1 inch and each flow channel diameter is less than 0.1 inches.

41. The apparatus of claim 27, wherein the exit orifices are aligned in a one-dimensional array.

42. The apparatus of claim 27, wherein the exit orifices are aligned in a two-dimensional array.

43. The apparatus of claim 27, embodied in a machine that builds up three-dimensional objects in multiple layers onto a base by extruding thermoplastic from selected orifices of the apparatus in synchrony with relative movement of the apparatus and the base in a predetermined spatial pattern.