Method of making a ceramic die

• US 5,638,724 A
• Filed: 06/06/1995
• Issued: 06/17/1997
• Est. Priority Date: 10/01/1993
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Sanders, Daniel G.
• Primary Examiner(s): JONES, DAVID B
• Application Number:
  US08/469,960
• Time in Patent Office: 742 Days
• Field of Search: 76/107.1, 76/107.4, 72/60, 72/54, 72/63, 29/DIG. 5
• US Class Current: 76/107.1
• CPC Class Codes: B21D 26/055 Blanks having super-plastic properties
• CPC Class Codes: B21D 37/20 Making tools by operations not covered by a single other subclass
• CPC Class Codes: Y10S 72/709 Superplastic material

Abstract

A method of producing a ceramic die for use in superplastic forming includes designing a free standing generally block-shaped ceramic monolithic die base with a bottom surface on which the die rests, and a top surface, opposite to the bottom surface, in which a forming cavity is located and which is surrounded by a contact surface. The forming cavity is shaped like the desired shape of sheet metal parts to be formed by superplastic forming in the die. A die lid is designed having a horizontal cross sectional shape and size approximately equal to the die base, and having a contact surface corresponding in size and contour to the die base contact surface, so that the lid may be placed on the base with the contact surfaces aligning and in contact. A forming cavity model is produced having a shape substantially the same as the part to be formed, and a mold is built having substantially the same internal shape as the intended peripheral shape of the die and having sufficient continuity and strength to contain liquid castable ceramic material. A surface smoothing material and parting agent is applied to the mold and the model, and the model is placed within the mold at a location consistent with the desired shape of the part to be formed. A castable ceramic material for the die base is selected that provides sufficient compressive strength to resist a compressive load exerted by a press to hold the lid on the die against oppositely directed force generated by gas at superplastic forming pressures within the die, and provides sufficient tensile strength, when under pressure of compressive loads exerted by the press to resist internal bursting forces exerted by gas at superplastic forming pressures within the die. The castable ceramic material is mixed with water and is poured into the mold and allowed to set until in substantial thermal equilibrium with ambient temperature. The set die is removed from the mold and is cured at a temperature between approximately 100°-211° F. for a period between approximately three days and ten days. The die is then dried for a period of between two days and four days at temperatures progressing from approximately the curing temperature to approximately 200° F. and back to ambient temperature.

Claims

1. A method of producing a ceramic superplastic forming die, comprising the steps of:

designing a free standing generally block-shaped ceramic monolithic die base having a bottom surface on which said die rests, and a top surface, opposite to said bottom surface, in which a forming cavity is specified and which is surrounded by a contact surface, said forming cavity having a shape like the desired shape of sheet metal parts to be formed by superplastic forming in said die;

designing a die lid having a horizontal cross sectional shape and size approximately equal to said die base, and having a contact surface corresponding in size and contour to said die base contact surface, whereby said lid may be placed on said base with said contact surfaces aligning and in contact;

producing a forming cavity model having a shape substantially the same as the part to be formed;

producing a mold, said mold having substantially the same internal shape as said die'"'"'s intended peripheral shape, said mold having sufficient continuity and strength to contain liquid castable ceramic material;

placing said model within said mold at the location consistent with the desired shape of the part to be formed;

applying a surface smoothing material and parting agent to said mold and said model;

selecting a castable ceramic material for said die base that provides sufficient compressive strength to resist a compressive load exerted by a press to hold said lid on said die against oppositely directed force generated by gas at superplastic forming pressures within said die, and provides sufficient tensile strength, when in pressure of compressive loads exerted by said press to resist internal bursting forces exerted by gas at superplastic forming pressures within said die;

mixing said castable ceramic material with water in a ratio consistent with that specified by said ceramic material'"'"'s manufacturer;

pouring said castable ceramic material into said mold;

allowing said poured die to set until in substantial thermal equilibrium with ambient temperature;

removing said die from said mold;

curing said die at a temperature between approximately 100 degrees Fahrenheit and 211 degrees Fahrenheit for a period between approximately three days and ten days;

drying said die for a period of between two days and four days at temperatures progressing from approximately said curing temperature to approximately 2000 degrees Fahrenheit and back to ambient temperature.

2. A method of producing a ceramic die for superplastic forming as defined in claim 1 wherein:

said die base design includes at least one cavity in said die'"'"'s lower external surface, said cavity being a blow-out cavity;

said blow-out cavity being located approximately under said forming cavity, said blowout cavity having a depth into said die of at least approximately two inches, and a surface area on said die'"'"'s lower external surface of between fifteen and one hundred square inches;

said die having a material thickness between said blow-out cavity and said forming cavity of between approximately four inches and two inches;

said blow-out cavity having a plurality generally cylindrical holes extending from said blow-out cavity to said die'"'"'s exterior side, said holes being vent ports.