Self supporting core-in-a-core for casting

• US 8,196,640 B1
• Filed: 07/01/2011
• Issued: 06/12/2012
• Est. Priority Date: 07/02/2010
• Status: Expired due to Fees

• Current Assignee: Mikro Systems, Inc.
• Original Assignee: Mikro Systems, Inc.
• Inventors: Paulus, John R., Appleby, Michael P.
• Primary Examiner(s): LIN, KUANG Y
• Application Number:
  US13/382,325
• Publication Number:
  US 20120138252A1
• Time in Patent Office: 347 Days
• Field of Search: 164/34, 164/45, 164/246, 164/369, 164/516
• US Class Current: 164/34
• CPC Class Codes: B22C 9/10 Cores; Manufacture or installation of cores breaker cores B22C9/084

Abstract

A core-in-a-core casting method and hybrid core (40) for use in the method. An inner core (42) formed of process-inert particles disposed in a binder material is used as a mold for casting an outer core ((44) formed of particles that will sinter during a subsequent firing step. The inner core provides mechanical support for the outer core during the firing step, and during which the inner core devolves into compacted but unbonded particles that can be removed conveniently from the outer core following the firing step to reveal the fired hollow outer core (44).

Claims

1. An apparatus comprising:

an inner ceramic body comprising first ceramic particles disposed in a first binder material, the inner ceramic body in a green state defining a mold surface for an outer ceramic body cast over the green body inner ceramic body;

the outer ceramic body comprising second ceramic particles disposed in a second binder material;

wherein the first and second ceramic particles and the first and second binder materials are selected to exhibit respective properties such that during a firing regiment the first and second binder materials become fugitive and the second ceramic particles sinter but the first ceramic particles do not sinter.

7. The apparatus of claim 1, wherein the first and second binder materials are the same type of material.

2. The apparatus of 1, wherein the first ceramic particles comprise zircon or alumina.

3. The apparatus of 1, wherein the first binder material comprises a polymer exhibiting a first volatilization temperature and the second binder material comprises a polymer exhibiting a second volatilization temperature different than the first volatilization temperature.

4. The apparatus of 1, further comprising an engineered surface feature formed on the inner ceramic body mold surface and reflected in reverse in an opposed inner surface of the outer ceramic body.

5. The apparatus of 4, further comprising an engineered surface feature formed on an outer surface of the outer ceramic body.

6. The apparatus of 1, further comprising an engineered surface feature formed on an outer surface of the outer ceramic body.

8. A method of forming a core for a casting process, the method comprising:

forming an inner body comprising first particles disposed in a first binder material;

casting an outer body comprising second particles disposed in a second binder material onto a surface of the inner body;

firing the outer body using a firing regiment effective to volatize the first and second binder material and to sinter the second particles without sintering the first particles, such that the first particles provide mechanical support for the outer body during the firing regiment even after devolving into unbonded particles when the first binder material volatizes; and

removing the unbonded ceramic particles from the fired outer body.

9. The method of 8, wherein the step of forming the inner body further comprises:

forming an inner body die comprising an inner body die surface, the inner body die surface comprising an engineered surface feature;

casting the inner body onto the inner body die surface to replicate a reverse of the engineered surface feature onto the inner body surface; and

removing the inner body from the inner body die to reveal the reverse of the engineered surface feature.

10. The method of 9, further comprising:

forming the inner body die of a flexible material; and

deforming the flexible material around an undercut surface of the engineered surface feature during the step of removing the inner body from the inner body die.

11. The method of 9, further comprising selecting the first particles in response to a design geometry of the engineered surface feature.

12. The method of 8, further comprising selecting the first particles in response to a design geometry of the inner body.

13. A method of forming a core for a casting process, the method comprising:

forming an inner body comprising first particles disposed in a first binder material using a tomo lithographic molding process to define an engineered surface on an outer surface of the inner body;

casting an outer body comprising second particles disposed in a second binder material onto the outer surface of the inner ceramic body, thereby replicating the engineered surface feature on an inside surface of the outer body;

firing the outer body using a firing regiment effective to volatize the first and second binder material and to sinter the second particles without sintering the first particles, such that the first particles provide mechanical support for the outer body during the firing regiment even after devolving into unbonded particles when the first binder material volatizes; and

removing the unbonded ceramic particles from the fired outer body to reveal an inner cavity having the engineered surface feature on its surface.