Calibration tool for fabricating disk springs

1. A calibration tool for fabricating disk springs, said calibration tool comprising: a circular cylindrical tool body that includes a circular opening having an insertion bevel at an upper face end portion for receiving and centering a workpiece within an inner circumferential enveloping surface of the tool body opening, and a tool surface at the inner circumferential enveloping surface for aligning the workpiece relative to a movable die disposed within the inner circumferential enveloping surface, wherein the tool surface includes a first surface portion having an inner diameter that increases in size along the axial longitudinal direction of movement of the movable die into the tool body, and a second surface portion having an inner diameter that decreases in size along the axial longitudinal direction of movement of the movable die into the tool body, whereby no radially inwardly oriented force loading of the workpiece occurs during movement of the movable die into the tool body to form the disk spring and cause internal stress within the workpiece that results in warping of the workpiece.

2. A calibration tool according to claim 1 , wherein the first portion is disposed adjacent to the insertion bevel.

3. A calibration tool according to claim 1 , wherein the first portion and the second portion are disposed adjacent to one another.

4. A calibration tool according to claim 1 , wherein the tool surface includes a circular segment shaped indentation interconnecting the first portion and the second portion in a cross-sectional view taken along a longitudinal axis of the tool body.

5. A calibration tool according to claim 1 , wherein the tool surface includes a shape in the portion of the first portion and of the second portion in a cross-sectional view taken along a longitudinal axis of the tool body, which shape substantially corresponds to a movement path of a point at an outer diameter of the workpiece during formation of the workpiece into a disk spring.

6. A calibration tool according to claim 1 , wherein the tool surface includes a third portion adjacent to the second portion, which third portion has a substantially constant inner diameter.

7. A calibration tool according to claim 6 , wherein the third portion extends to a lower face surface of the tool body, which lower face surface is disposed at a lower face end of the tool body that is opposite to the upper face end adjacent to the insertion bevel.

8. A calibration tool according to claim 1 , wherein in an axial longitudinal direction of the tool body a ratio of a length of the first and second surface portions of the tool surface having varying inner diameters to a length of the tool surface portion having a substantially constant inner diameter is approximately 2:1.

9. A forming tool for fabricating disk springs, said forming tool comprising: an upper die and a lower die forming a die cavity for receiving a workpiece to be formed into a disk spring, wherein the die cavity is enclosed by a calibration tool having a circular cylindrical tool body that includes a circular opening having an insertion bevel at an upper face end portion for receiving and centering a workpiece within an inner circumferential enveloping surface of the tool body opening, and a tool surface at the inner circumferential enveloping surface for aligning the workpiece relative to a movable die disposed within the inner circumferential enveloping surface, wherein the tool surface includes a first surface portion having an inner diameter that increases in size along the axial longitudinal direction of movement of the movable die into the tool body, and a second surface portion having an inner diameter that decreases in size along the axial longitudinal direction of movement of the movable die into the tool body, whereby no radially inwardly oriented force loading of the workpiece occurs during movement of the movable die into the tool body to form the disk spring and cause internal stress within the workpiece that results in warping of the workpiece.

10. A forming tool according to claim 9 , wherein the lower die includes an inner support surface facing the upper die for supporting the workpiece, which support surface is disposed in an axial longitudinal direction of the calibration tool below a front end portion of the cylindrical tool body of the calibration tool, which front end portion includes an insertion bevel.