Method for fabricating a plastic optic element injection mold

• US 20020116808A1
• Filed: 01/14/2002
• Published: 08/29/2002
• Est. Priority Date: 01/19/2001
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Puchammer, Julius, Kilroy, Clinton P., Saccomanno, Robert J.
• Granted Patent: US 6,735,844 B2
• Time in Patent Office: Days
• US Class Current: 29/423
• CPC Class Codes: B23P 15/007 injection moulding tools
• CPC Class Codes: C25D 1/10 Moulds; Masks; Masterforms
• CPC Class Codes: Y10T 29/49796 Coacting pieces
• CPC Class Codes: Y10T 29/4981 Utilizing transitory attached element or associated separate material
• CPC Class Codes: Y10T 29/49893 Peripheral joining of opposed mirror image parts to form a hollow body
• CPC Class Codes: Y10T 29/49982 Coating
• CPC Class Codes: Y10T 29/49986 Subsequent to metal working
• CPC Class Codes: Y10T 29/49989 Followed by cutting or removing material
• CPC Class Codes: Y10T 29/49995 Shaping one-piece blank by removing material

Abstract

In order to produce precision optic elements using injection molded plastic, a metal mold is fabricated from two positive masters comprising exact metallic reproductions of the desired plastic part and on which a metal shell has been electroformed or otherwise plated. Two positive masters are required for each mold, one being formed to define the upper part of the mold and the other the lower part of the mold. Each positive master is scribed with an axial line and with a cutting line slightly offset from the axial line, the cutting line for the upper part of the mold being below the axial line and the cutting line for the lower part of the mold being above the axial cutting line. The positive masters are then cut along their cutting lines, the metal shells removed, and the portion of the remaining metal shells between their axial lines and their cutting lines is then trimmed. The upper and lower parts of the mold are then combined to define the complete injection mold.

Claims

1. A method for fabricating an injection mold for a plastic optical component comprising the steps of:

(a) forming at least two metal models of the plastic optic component to be produced;

(b) forming a metal shell on each of said metal models;

(c) scribing an axial line on each of said metal shells;

(d) cutting a first of said shells along a line below its axial line and the other of said shells along a line above its axial line;

(e) discarding the portion of the metal shell and the portion of the metal model from the cutting line away from the axial line for each of said shells;

(f) removing the metal model from the remaining of the metal shell and trimming the portion of the metal shell between its cutting line and the axial line for each of said shells; and

(g) combining the resulting two metal shell portions to form the injection mold.

2. The method in accordance with claim 1 wherein the step of forming said metal models includes the steps of:

(a) determining the shrinkage rate of the plastic to be molded; and

(b) adjusting the dimensions of said models accordingly.

9. The method of claim 1, wherein said mold is suitable for injection molding of plastic materials selected from the group consisting of cyclo-olefin polymer, clear acrylic resin, and polystyrene.

3. A method for fabricating an injection mold suitable for forming a plastic optical component comprising the steps of:

fabricating a plurality of duplicate positive masters of the optical component from a first metal;

polishing each of said plurality of duplicate positive masters to an optical surface finish;

placing each of said duplicate positive masters in an electroforming bath;

electroforming a shell of a second metal on each of said duplicate positive masters to a predetermined thickness;

scribing an axial mold line on each of said electroformed shells;

cutting each of a set of positive masters along predetermined cutting lines to form a set of negative master segments, wherein each of negative master segments comprises a portion of the electroformed shell about a positive master;

trimming each of said negative master segments by removing an overlap region comprising a portion of the electroformed shell interposed between one of said predetermined cutting lines and said mold parting line;

separating each of said positive master segments from each of said negative master segments to form a set of negative master mold segments; and

building up a mold from a set of negative master mold segments, wherein said set of negative master mold segments completely defines the plastic optical component.

4. The method of claim 3, further comprising the preliminary steps of:

determining the shrinkage rate of the material to be molded; and

modifying the dimensions of said duplicate positive masters to compensate for said shrinkage rate.

5. The method of claim 4, wherein the step of modifying the dimensions of said duplicate positive masters is performed using computer-aided design techniques.

6. The method of claim 3, wherein said first metal is selected from the group consisting of copper, steel, copper-coated steel, and nickel-coated steel.

7. The method of claim 3, wherein said second metal is a hard metal.

8. The method of claim 7, wherein said hard metal is nickel.

10. A method for fabricating an injection mold for a plastic optical component comprising the steps of:

forming two exact metal models of the plastic optic component to be produced by the mold;

forming a metal shell on each of said metal models;

defining a line through each of said shells, which lines delineate upper and lower portions of said shells, said upper portions being equal and said lower portions being equal;

cutting one of said shells along a cut line above its delineating line and the other of said shells along a cut line below its delineating line;

removing the portion of said one shell below its cut line and the portion of said other shell above its cut line;

removing the part of the metal mold above its cut line from said one shell and the part of the metal mold below its cut line from said other shell;

trimming away the segments of each shell between its delineating line and its cut line; and

combining the remaining portions of said one and said other shell to form the injection mold.

11. The method in accordance with claim 10 wherein said step of forming two exact metal models includes the steps of:

determining the shrinkage rate of the plastic to be molded; and

adjusting the dimensions of said models accordingly.

12. The method in accordance with claim 11 wherein the metal of said models is selected from the group consisting of copper, steel, copper-coated steel, and nickel-coated steel and the metal of said shells is nickel.

13. The method in accordance with claim 12 wherein said step of forming said metal shell on each of said molds comprises electroforming.