Method for making a die for stamping metal reflectors

• US 4,424,727 A
• Filed: 09/15/1980
• Issued: 01/10/1984
• Est. Priority Date: 09/15/1980
• Status: Expired due to Term

• Current Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Original Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Inventors: Mader, John J.
• Primary Examiner(s): Parker, Roscoe V.
• Application Number:
  US06/187,311
• Time in Patent Office: 1,212 Days
• Field of Search: 76/107 R, 76/101 R, 76/4, 72/702
• US Class Current: 76/107.1
• CPC Class Codes: B21D 37/20 Making tools by operations not covered by a single other subclass
• CPC Class Codes: B21D 53/883 reflectors
• CPC Class Codes: Y10S 72/702 Overbending to compensate for springback

Abstract

A method for making a metal stamping die suitable for use in forming sheet metal reflectors for photographic use. The structure of the metal stamping die is made in the manner of the method to compensate for spring-back characteristics of a material used to form a reflector by first constructing a test die which has a predetermined shape related to the desired reflector shape. A comparison is then made between a test workpiece made with the test die and the desired reflector shape to determine the die shape that produces a corresponding portion of the reflector shape. Finally, another die is constructed by shaping it in accordance with the comparison to obtain a final die shape that will acceptably produce the desired reflector shape.

Claims

1. A method for making a metal stamping tool suitable for use in forming a concave, open ended reflector having a cross-sectional shape in the form of a nonconic, asphere that is bilaterally symmetric about a central axis therethrough and has a radius of curvature that continuously increases with distance along said axis comprising the steps of:

constructing a trial metal stamping tool having a cross-sectional shape in the form of nonconic, asphere that is more concave than the reflector, said trial tool curve being of the same general shape as said reflector but having a continuously changing radius of curvature that is generally smaller than that of the reflector at corresponding points along the reflector axis of symmetry;

forming a trial reflector by stamping with said trial tool a metal blank workpiece of predetermined thickness and material composition; and

constructing a final metal stamping tool having a cross-sectional shape whose radius of curvature varies continuously along the reflector axis of symmetry in accordance with the ratio between said radius of curvature of said trial tool and said trial reflector at corresponding points along the reflector axis of symmetry.

2. The method of claim 1 wherein said radius of curvature of said final metal stamping tool has centers of curvature which are identical with those of the reflector.

3. A method for making a metal stamping tool suitable for use in forming a concave, open-ended reflector having a cross-sectional shape in the form of a nonconic, asphere that is bilaterally symmetric about a central axis therethrough and has a radius of curvature that continuously increases with distance along said axis comprising the steps of:

constructing a trial metal stamping tool having a cross-sectional shape in the form of plurality of linked together circular arcs, one each for a corresponding curve segment of the reflector curve and each having a radius which approximately matches the shape of a corresponding curve segment of the reflector, said circular arcs being arranged and connected so that at adjoining end points thereof the slopes of said circular arcs are equal, said trial tool shape being of the same general shape as, but being more concave than, the shape of the reflector at corresponding points along the reflector axis of symmetry;

forming a trial reflector by stamping with said trial tool a metal blank workpiece of predetermined thickness and material composition; and

constructing a final metal stamping tool having a cross-sectional shape in the form of a plurality of linked together circular arcs, one each for a corresponding segment of the reflector curve, and each having a radius which depends on the ratio of radii between corresponding segments of said trial tool and said trial reflector at corresponding points along the reflector axis of symmetry.

4. The method of claim 12 wherein the number of circular arcs is given by:

##EQU4## wherein S is the number of curve segments, K is a constant no greater than 0.5, and R-max and R-min are respectively the maximum and minimum radii of curvature of the curve.

5. The method of claim 4 wherein adjoining end points of said circular arcs have centers lying on the same line.

6. The method of claim 4 wherein K is no more than 0.2.