Ceramic mold finishing

• US 6,109,332 A
• Filed: 09/28/1998
• Issued: 08/29/2000
• Est. Priority Date: 11/30/1992
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Sachs, Emmanuel M., Khanuja, Satbir, Bredt, James F., Cima, Michael J.
• Primary Examiner(s): Pyon, Harold
• Assistant Examiner(s): LIN, ING HOUR
• Application Number:
  US09/161,873
• Time in Patent Office: 701 Days
• Field of Search: 164/33, 164/23, 164/518, 164/517, 164/516, 164/519
• US Class Current: 164/33
• CPC Class Codes: B08B 3/10 with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration
• CPC Class Codes: B08B 3/12 by sonic or ultrasonic vibrations washing or rinsing machines for crockery or tableware using sonic or ultrasonic waves A47L15/13; of natural teeth, of prostheses using ultrasonic techniques similar to those used for natural teeth A61C17/20; application of ultrasonic vibrations to chemical, physical or physico-chemical processes in general B01J19/10
• CPC Class Codes: B08B 5/04 Cleaning by suction, with or without auxiliary action B08B9/035 takes precedence; suction cleaners A47L
• CPC Class Codes: B08B 7/00 Cleaning by methods not provided for in a single other subclass or a single group in this subclass
• CPC Class Codes: B08B 9/00 Cleaning hollow articles by methods or apparatus specially adapted thereto B08B6/00 takes precedence
• CPC Class Codes: B22C 9/065 Cooling or heating equipment for moulds
• CPC Class Codes: B22C 9/18 Finishing
• 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 5/007 of moulds
• CPC Class Codes: B24B 1/04 subjecting the grinding or polishing tools, the abrading or polishing medium or work to vibration, e.g. grinding with ultrasonic frequency polishing or abrading surfaces on work by means of tumbling apparatus B24B31/00, involving oscillating or vibrating containers B24B31/06; superfinishing surfaces on work, e.g. by means of abrading blocks reciprocating with high frequency, B24B35/00
• 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 64/165 using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
• CPC Class Codes: B29C 64/35 Cleaning
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 40/20 Post-treatment, e.g. curing, coating or polishing
• CPC Class Codes: B33Y 80/00 Products made by additive manufacturing
• CPC Class Codes: Y02P 10/25 : Process efficiency

Abstract

A technique for smoothing and otherwise changing the surfaces of porous bodies, such as ceramic molds, made using layer manufacturing processes, such as three dimensional printing processes. The surface finish of the mold can be smoothed by casting a slip of fine particles onto the surface to form a generally level, and preferably non-conformal, coating on the surfaces. In general, the fine particles of the slip are caused to be filtered out from the liquid, so that the fine particles come to rest at or near the surface of the body formed. They are typically, preferentially drawn toward concave regions of the surface, as compared to convex regions, thereby forming a non-conformal coating. Furthermore, other surface properties can be changed by tailoring the slip to produce those properties. The coating can be applied to external surfaces, and internal surfaces, such as would become the surface against which a molded part would be formed.

Claims

1. A process for fabricating a porous body comprising the steps of:

a. building up said body by creating successive layers of a powder material, each layer being on average at least three powder particles thick, whereby due to said layer buildup, a surface of said body having a first surface roughness resulting from concave regions that are adjacent to convex regions, with a porous region between said concave and convex regions, made up of an edge of one of said layers that is, on average at least three particles thick; and

b. casting a slip of fine particles against the concave and convex regions of said surface of the body, whereby said fine particles are smaller, on average, than the powder particles, and are drawn preferentially toward said concave regions to a degree greater than toward said convex regions, so that the surface of said body is coated with a surface coating of said fine particles, such that the surface roughness is decreased from said first degree to a smoother, second degree of roughness.

2. A process in accordance with claim 1 wherein said coating is a non-conformal coatings.

3. A process in accordance with claim 1, wherein said building up step comprises providing said porous body with an interior passage, and wherein said step of casting the slip of fine particles comprises applying said slip to the interior passage of said body.

4. A process in accordance with claim 1 wherein the body is substantially a ceramic body and the step of casting a slip of fine particles comprises casting a slip comprising ceramic particles.

5. A process in accordance with claim 4,

a. wherein said building up step comprises providing said porous body with an interior passage;

and

b. wherein said step of casting the slip of fine particles comprises applying said slip to the interior passage of said body to form a mold for metal casting.

6. A process in accordance with claim 1 wherein the porous body has pores that are larger than the fine particles in the slip and said step of casting a slip of fine particles comprises the step of composing said slip of particles having a shape that will allow them to penetrate only a small distance into the pores of said porous body.

7. The process of claim 6, said step of composing said slip comprising composing said slip of plate shaped particles.

8. A process in accordance with claim 1 wherein the porous body has pores that are larger than the fine particles in the slip, further comprising the step of forming a filter layer near the surface of the porous body, such that during said step of casting a slip of fine particles against said surface of said body, said surface coating of said fine particles is formed adjacent to said filter layer.

9. A process in accordance with claim 8 wherein the body is substantially ceramic and the step of forming a filter layer comprises providing colloidal silica from which silica forms said filter layer.

10. A process in accordance with claim 1 wherein the porous body has pores that are larger than the fine particles in the slip, and further comprising the step of partly saturating the porous body with a material that causes the slip to flocculate.

11. A process in accordance with claim 1 wherein said slip comprises a liquid vehicle component and a solids component, and has a solids content, and the step of casting a slip is conducted for a period of time such that for the properties of the liquid vehicle used, the thickness of the surface coating is controlled to a target value by allowing the slip to cast for a convenient casting time.

12. A process in accordance with claim 11 said slip comprising a solids content of about 1% to 10% by volume.

13. The process of claim 11, wherein the step of casting the slip is conducted for a period of time such that the thickness of the surface coating is less than about 60 microns.

14. A process for fabricating a porous body comprising the steps of:

a. building up said body by creating successive layers of a powder material, each layer being on average at least three powder particles thick, whereby due to said layer buildup, a surface of said body comprises concave regions that are adjacent to convex regions, with a porous region between said concave and convex regions, made up of an edge of one of said layers that is, on average at least three particles thick; and

b. casting a slip of fine particles against the concave and convex regions of said surface of the body, whereby said fine particles are much smaller, on average, than the powder particles, and are drawn preferentially toward said concave regions to a degree greater than toward said convex regions, so that the surface of said body is coated with a surface coating of said fine particles, such that the surface properties are changed.