Enhancement of thermal properties of tooling made by solid free form fabrication techniques

• US 5,775,402 A
• Filed: 10/31/1995
• Issued: 07/07/1998
• Est. Priority Date: 10/31/1995
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Michaels, Steven P., Allen, Samuel M., Sachs, Emanuel
• Primary Examiner(s): Lin, Kuang Y.
• Application Number:
  US08/551,012
• Time in Patent Office: 980 Days
• Field of Search: 164/4.1, 164/97, 164/98, 164/150.1, 164/154.1, 164/456
• US Class Current: 164/4.1
• CPC Class Codes: B22C 9/065 Cooling or heating equipment for moulds
• CPC Class Codes: B22D 17/22 Dies manufacture, see the appropriate class, e.g. B23P15/24; Die plates; Die supports; Cooling equipment for dies; Accessories for loosening and ejecting castings from dies
• CPC Class Codes: B22D 17/2218 Cooling or heating equipment for dies for permanent moulds B22C9/065; for plastics B29C45/73
• CPC Class Codes: B22D 25/06 by its physical properties B22D27/00 takes precedence
• CPC Class Codes: B22F 10/14 by jetting of binder onto a bed of metal powder
• CPC Class Codes: B22F 10/38 to achieve specific product aspects, e.g. surface smoothness, density, porosity or hollow structures
• CPC Class Codes: B22F 10/62 by chemical means
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/115 by spraying molten metal, i.e. spray sintering, spray casting
• CPC Class Codes: B22F 5/007 of moulds
• CPC Class Codes: B22F 5/10 of articles with cavities or holes, not otherwise provided for in the preceding subgroups
• CPC Class Codes: B22F 7/004 comprising at least one non-porous part
• CPC Class Codes: B29C 2045/7362 turbulent flow of heating or cooling fluid
• CPC Class Codes: B29C 33/04 using liquids, gas or steam tyre moulds with incorporated heating or cooling means using liquids, gas or steam B29D30/0601
• CPC Class Codes: B29C 33/3828 Moulds made of at least two different materials having different thermal conductivities
• CPC Class Codes: B29C 33/56 Coatings , e.g. enameled or galvanised; Releasing, lubricating or separating agents in-mould coating B29C37/0028; using or applying separating agents B29C37/0067
• CPC Class Codes: B29C 45/7312 Construction of heating or cooling fluid flow channels
• CPC Class Codes: B29C 64/135 the energy source being concentrated, e.g. scanning lasers or focused light sources
• CPC Class Codes: B29C 64/153 using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• CPC Class Codes: B33Y 10/00 : Processes of additive manufacturing
• CPC Class Codes: B33Y 70/00 : Materials specially adapted for additive manufacturing
• CPC Class Codes: B33Y 70/10 : Composites of different types of material, e.g. mixtures of ceramics and polymers or mixtures of metals and biomaterials
• CPC Class Codes: B33Y 80/00 : Products made by additive manufacturing
• CPC Class Codes: F28D 2021/0078 : in the form of cooling walls
• CPC Class Codes: F28F 13/00 : Arrangements for modifying heat-transfer, e.g. increasing, decreasing F28F1/00 - F28F11/00 take precedence
• CPC Class Codes: F28F 7/02 : Blocks traversed by passages for heat-exchange media F28D7/0008 takes precedence
• CPC Class Codes: Y02P 10/25 : Process efficiency

Abstract

Processes for providing enhanced thermal properties of tooling, particularly metal and metal/ceramic molds, made by solid free form fabrication techniques, such as the three dimensional printing process, and the tooling made by these processes are disclosed. The methods of enhancing thermal properties include incorporating integral contour coolant channels into the mold, adding surface textures to the coolant channels, creating high thermal conductivity paths between the surfaces and the coolant channels, and creating low thermal inertia regions in the mold.

Claims

1. A process for fabricating a part having an internal void, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal void;

substantially simultaneously with said selectively binding step, selectively depositing an infiltration stop material adjacent the region defining a wall of the internal void;

providing an outlet from said unbound regions that will form said void;

removing any unbound powder to form said void; and

processing the intermediate part to attain full density by infiltrating the intermediate part with an infiltrant, whereby said infiltration stop material prevents infiltration of the infiltrant into the internal void, to provide a finished part having an internal void.

2. The process of claim 1, wherein the void includes a textured wall.

3. The process of claim 1, further comprising a heat transfer element on a surface of the void.

4. The process of claim 3, wherein the heat transfer element comprises a protrusion into the void.

5. The process of claim 1, said part comprising tooling, and said step of selectively binding comprising selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal channel.

6. The process of claim 1, wherein the selective depositing of an infiltration stop step further comprises depositing an infiltration stop material in the region defining the wall of the internal void.

7. The process of claim 6, wherein the infiltration stop material comprises colloidal silica.

8. The process of claim 7, wherein the step of processing the intermediate part includes removing the colloidal silica after infiltration by etching.

9. The process of claim 1, wherein the selective depositing of an infiltration stop step further comprises depositing an infiltration stop material in the region defining the internal void.

10. The process of claim 9, wherein the infiltration stop material comprises colloidal silica.

11. The process of claim 10, wherein the step of processing the intermediate part includes removing the colloidal silica after infiltration by etching.

12. A process for fabricating tooling having a channel therethrough, said process, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part, having an internal channel having a wall;

removing said unbound powder to form said channel; and

processing the intermediate part to attain full density by infiltrating the intermediate part with an infiltrant, while preventing infiltration of the infiltrant into the internal channel, to provide the finished tool element having an internal channel.

13. The process of claim 12, wherein the unbound powder is removed by vibration of the tool element.

14. The process of claim 12, wherein the unbound powder is removed by blowing air through the cooling channel.

15. The process of claim 12, wherein the cooling channel has a circular cross section.

16. The process of claim 12, wherein the cooling channel has a rectangular cross section.

17. The process of claim 12, wherein the cooling channel includes a textured wall.

18. The process of claim 12, further comprising a heat transfer element on a surface of the cooling channel.

19. The process of claim 18, wherein the heat transfer element comprises a protrusion into the cooling channel.

20. A process for fabricating a part having an internal void, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal void;

removing said unbound powder to form said channel; and

processing the intermediate part by infiltrating the intermediate part with an infiltrant while providing a pressure differential between an atmosphere in the internal void and the infiltrant of a value preselected to prevent infiltration of the infiltrant into the void to provide a finished part having an internal void.

21. The process of claim 20, said part comprising tooling, and said step of selectively binding comprising selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal channel.

22. A process for fabricating tooling having enhanced thermal properties, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving the powder unbound in other regions to provide an intermediate part with a heat transfer channel having an inlet and an outlet and a configuration that conforms to a surface portion of a finished tool element;

removing said unbound powder to form said heat transfer channel; and

processing the intermediate part to provide the finished tool element having regions of different thermal properties, by infiltrating the intermediate part with an infiltrant while providing a pressure differential of a value preselected to prevent infiltration of the infiltrant into the heat transfer channel, the pressure differential being provided by disposing the intermediate part on a stilt assembly formed of a material through which the infiltrant rises by capillarity, a lower portion of the stilt assembly being placed in a pool of the infiltrant, the stilt assembly having a height preselected to cause the infiltrant to infiltrate the intermediate part and to maintain the heat transfer channel free of infiltrant.

23. The process of claim 22, wherein the stilt assembly is formed integrally with the intermediate part.

24. The process of claim 22, wherein the stilt assembly is formed of the powder material of which the intermediate part is formed.

25. The process of claim 24, wherein the stilt assembly is of a height sufficient to prealloy the infiltrant prior to infiltrating the intermediate part.

26. The process of claim 22, wherein the stilt assembly comprises stilts located to direct entry of the infiltrant in a preselected manner into the intermediate part.

27. A process for fabricating a part having an internal void, said process, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal void;

providing at least one opening to said unbound regions that will form said void; and

removing unbound powder to form the void by immersing the intermediate part in a vessel of water and CO₂ dissolved in the water and reducing the pressure inside the vessel to cause the CO₂ to come out of solution as bubbles, thereby pushing the powder out of at least one opening to provide the intermediate part having an internal void; and

infiltrating said intermediate part with an infiltrant to form a finished part having said internal void.

28. A process for fabricating tooling having enhanced thermal properties, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, wherein the selective binding step further comprises depositing a high thermal conductivity material in one of the regions to form a high thermal conductivity region; and

processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties by infiltrating the intermediate part with an infiltrant.

29. The process of claim 28, wherein the high conductivity material includes copper or silver.

30. The process of claim 28, wherein the selective binding step further comprises leaving the powder unbound in one of the regions to form a cooling channel, the cooling channel having open ends and a configuration which conforms to a surface portion of the tool element, the high thermal conductivity region being in proximity to the cooling channel.

31. A process for fabricating a part, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder leaving the powder unbound in one of the regions to form a pocket, to provide an intermediate part; and

processing the intermediate part by removing the powder from the pocket and filling the pocket with an infiltrant having a high thermal conductivity to provide a finished part having regions of differing thermal properties.

32. The process of claim 31, said part comprising tooling.

33. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, wherein the selective binding step further comprises leaving the powder unbound in a first one of the regions to form a channel having two open ends and in a second one of the regions to form a channel having one open end; and

processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties, the step of processing the intermediate part further comprising removing the unbound powder, sealing the open end of the second one of the channels, and infiltrating the intermediate part with an infiltrant having a high thermal conductivity, and draining the infiltrant from the first one of the channels to form a heat transfer channel.

34. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, wherein the selective binding step further comprises selectively depositing a compositional gradient of a high conductivity material in one of the regions to form a region having a thermal conductivity gradient; and

processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties by infiltrating the intermediate part with an infiltrant.

35. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, leaving the powder unbound in selected ones of the regions to form a cellular network, the cellular network having a lower thermal inertia than other regions of the tool element; and

processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties by infiltrating the intermediate part with an infiltrant.

36. The process of claim 35, wherein the cellular network comprises a truss structure.

37. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a material onto a surface in layers;

selectively binding the material in selected regions and leaving the material unbound in further selected regions to form a cellular network, the cellular network comprising a region of lower thermal inertia; and

processing said cellular network to attain full density by infiltrating the cellular network with an infiltrant to provide a finished tool element having a region of lower thermal inertia than an adjacent region.

38. The process of claim 37, wherein the cellular network comprises a truss structure.

39. The process of claim 37 further comprising leaving the material unbound in a still further selected region to form a heat transfer channel conformal to a surface of the finished tool element, the heat transfer channel located between the surface and the region of lower thermal inertia.

40. The process of claim 37, further comprising selectively binding the material in selected regions and leaving the powder unbound in further selected regions to form cooling channels, the cooling channels having an inlet and an outlet, the cooling channels located between a surface of the tool element and the region of lower thermal inertia.

41. A process for fabricating a part having an internal void, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving the powder unbound in other regions to provide an intermediate part with an internal void; and

providing an outlet to said unbound regions that will form said void;

removing any unbound powder to form said void;

processing the intermediate part to provide a finished part having an internal void, by infiltrating the intermediate part with an infiltrant while providing a pressure differential of a value preselected to prevent infiltration of the infiltrant into the void, the pressure differential being provided by disposing the intermediate part on a stilt assembly formed of a material through which the infiltrant rises by capillarity, a lower portion of the stilt assembly being placed in a pool of the infiltrant, the stilt assembly having a height preselected to cause the infiltrant to infiltrate the intermediate part and to keep the infiltrant out of the void.

42. A process for fabricating a part having an internal void, comprising the steps of:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving the powder unbound in other regions to provide an intermediate part with an internal void having a characteristic radius r; and

providing an outlet to said unbound regions that will form said void;

removing any unbound powder to form said void; and

processing the intermediate part to provide a finished part having an internal void, by infiltrating the intermediate part with an infiltrant while providing a pressure differential of a value preselected to prevent infiltration of the infiltrant into the void, the pressure differential being provided by disposing a lower portion of the intermediate part in fluid communication with a pool, having a free melt surface, of infiltrant that will rise through said intermediate part by capillarity, and orienting said part such that said void is spaced above said free melt surface a distance ##EQU2## to cause the infiltrant to infiltrate the intermediate part and to maintain the void free of infiltrant, where ρ

is the density of the molten infiltrant, γ

is the surface tension of said molten infiltrant, θ

is the contact angle of the infiltrant against said walls of said void, and g is the acceleration of gravity.

43. The process of claim 42, said selectively binding step comprising the step of selectively binding regions of each layer of the powder and leaving the powder unbound in other regions to provide an intermediate part with an internal channel.

44. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, by leaving the powder unbound in a first region to form a first channel and in a second region to form a second channel;

providing at least one opening in each of said first and second regions that will form said channels;

removing the unbound powder to form said first and second channels;

sealing all openings of the second channel;

infiltrating the intermediate part with an infiltrant having a high thermal conductivity; and

draining the infiltrant from the first channel to form an open internal channel;

thereby processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties.

45. A process for fabricating tooling having enhanced thermal properties, comprising:

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder to provide an intermediate part, by leaving the powder unbound in a first region to form a channel;

providing at least one opening in said regions that will form said channel;

removing the unbound powder to form said channel;

sealing all openings of the channel; and

infiltrating the intermediate part with an infiltrant having a high thermal conductivity;

thereby processing the intermediate part to attain full density to provide a finished tool element having regions of differing thermal properties.

46. A process for fabricating tooling of a material having a thermal diffusivity of α

to be used in a molding cycle having a duration of τ

per part to be molded, having an internal heat transfer channel therethrough, said process comprising;

depositing a powder onto a surface in layers;

selectively binding regions of each layer of the powder and leaving other regions of each layer of the powder unbound to provide an intermediate part having an internal heat transfer channel that is spaced away from said surface portion less than twice (α

τ

)^-1/2 ;

removing any unbound powder to form said heat transfer channel; and

densifying the intermediate part to attain full density of a finished tool.

47. The process of claim 46, said step of selectively binding comprising providing an intermediate part having an internal heat transfer channel that is spaced away from said surface portion less than (α

τ

)^-1/2.