WO2004091837A2

WO2004091837A2 - Method and apparatus for manufacturing partial spherical shapes

Info

Publication number: WO2004091837A2
Application number: PCT/US2004/011556
Authority: WO
Inventors: Rodney M. Kramer
Original assignee: Rockford Products Corporation
Priority date: 2003-04-15
Filing date: 2004-04-15
Publication date: 2004-10-28
Also published as: WO2004091837A3

Abstract

The present assembly provides a method and apparatus for forming partial geometric spheres. The method and apparatus involves rotating a workpiece (26) around a first axis (32) and bringing a machining tool (28) towards the workpiece along a second axis (34) to form a geometric spherical shape on the workpiece, wherein the first and second axes (32,34) form an angle (A) between approximatel zero and ninety degrees. The machining tool (28) may be rotated around the second axis (34). The machining tool may be a hollow mil including cutting tools (36) for milling or a grit surface (38) for grinding. The method and apparatus forms geometric spherical shapes throughout a production run despite cutting tool wear.

Description

METHOD AND APPARATUS FOR MANUFACTURING PARTIALLY SPHERICAL SHAPES

Technical Field The present subject matter relates generally to a method and apparatus for manufacturing partially spherical shapes. More specifically, the subject matter relates to a method and apparatus for machining partially spherical shapes.

Background

There were known techniques for machining partially spherical shapes in the field of material removal. For example, a spherical shape could be machined onto a workpiece using a lathe. Typically, the unfinished workpiece was cylindrically shaped or a molded or forged rough-shaped ball having a stem. One technique for turning a spherical shape on a lathe included holding the workpiece in a lathe and holding a single point cutting tool in an automated tool saddle. As the workpiece was rotated on the lathe around the y-axis, the cutting tool was moved in both the y-axis direction and the z-axis direction forming an arc to machine a spherical form on the workpiece. The y-axis and z-axis directional movements of the cutting tool interpolated between zero and one hundred and eighty degrees of the arc to form as much of a spherical shape as desired. Alternatively, the cutting tool could have been held in a manual swing arm attached to a lathe post. As the workpiece was rotated, an operator manually swung ^•the cutting tool along an arc to machine a spherical shape onto the workpiece. Varying the amount of the arc swung enabled the operator to vary the amount of the sphere formed.

Known techniques for machining spherical shapes did not form geometrically perfect spherical shapes throughout a production run, in which the cutting tool experienced wear. For example, as the cutting tool machined successive workpieces, the cutting surface of the tool was worn away from the surface of the workpiece. Consequently, the predetermined automated movements of the cutting tool in the automated tool saddle, or the predetermined manual movements of the cutting tool on the swing arm, no longer formed perfect geometric spherical shapes along the workpiece. The size of the flat spot increased as the cutting tool continued to wear. Known methods of machining spherical shapes were also limited in speed by the use of single point cutting tools. Moreover, backlash in the axes of the lathe and cutting tool holders caused flat spots to be formed in the machined spherical shape in much the same manner as those caused by cutting tool wear. For example, backlash in the cutting tool movement along the z-axis caused a flat spot to be formed along the equator of the spherical shape. Accordingly, known methods of machining spheres produced spheres that varied in diameter as the cutting tool wore, as well as geometrically flawed spheres typically having flat spots along the sphere's equator. Typically, workpieces were machined into spherical shapes to orbit within a cup portion of a cup assembly. The spherical portion was designed to orbit freely within the cup portion at a predetermined amount of torque. However, if the sphere machined onto the spherical portion had a flat spot at the equator, or was otherwise not geometrically spherical, the imperfect spherical portion formed angles of inclination with the cup portion. The increased friction between the imperfect spherical portion and the cup portion prevented the spherical portion from orbiting freely when the proper amount of torque was applied. The increased friction between the spherical portion and the cup assembly caused the spherical portion to wear more quickly. Moreover, the increased torque required to rotate the spherical portion within the cup assembly further increased wear on the spherical portion. Summary The present assembly provides a method and apparatus for forming geometric spheres. The system involves rotating a workpiece around a first axis, providing a machining tool having one or more cutting tools rotated about a second axis to form a circular cutting motion about the second axis, and moving the rotating machining tool towards the workpiece along a second axis to form a spherical shape on the workpiece. The first and second axes may form any angle between approximately zero and ninety degrees to form any amount of a spherical shape on the workpiece. The machining tool may alternatively include non-cutting material removal methods, such as, electric discharge machining ("EDM") and electro-chemical machining ("ECM"). In the case of EDM or ECM, the machining tool does not need to be rotated, only rotation of the workpiece is required, as will be evident to one of ordinary skill in the art in light of the present disclosure. The machining tool may be a hollow mill including cutting tools for milling or, alternatively, a grit surface for grinding. The method and apparatus forms spherical shapes that do not exhibit the typical flat spots created by known methods of machining spheres.

It is one of the principal objectives of the present disclosure to provide a method and apparatus of forming spherical shapes.

Another objective is to provide a method of forming spherical shapes wherein tool wear does not alter the geometric shape of the sphere formed. A further objective is to provide a method of forming spherical shapes that does not require multi-axis cutting tool movement.

Yet another objective is to provide a method of forming spherical shapes that are much closer to true geometric spherical form than spherical shapes formed by conventional machining. Still another objective is to provide a method of forming spherical shapes that may be applied to any type of machining method, such as, for example, vertical milling, horizontal milling, grinding, EDM and ECM.

Additional objects, advantages and novel features of the examples will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following description and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the concepts may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims. Brief Description of Drawings

The drawing figures depict one or more implementations in accord with the present concepts, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.

Fig. 1 is a side view of a machining assembly according to the present teachings, wherein a machining tool is provided for material removal.

Fig. 2 is the side view of the machining assembly of Fig. 1, wherein a machining tool has formed a partially spherical shape onto a portion of a workpiece.

Fig. 3 is the side view of the machining assembly of Fig. 1, wherein the machining tool has formed a partially spherical shape onto a greater portion of the workpiece than shown in Fig. 3.

Fig. 4 is an alternative configuration of a side view of the machining assembly of Fig. 1, wherein the machining tool intersects the workpiece at a greater angle than shown in Fig. 2 to form a spherical shape onto a larger portion of the workpiece than shown in Fig. 2. Fig. 5 is a flow chart depicting a method according to the present teachings. Detailed Description of the Preferred Embodiments

Fig. 1 illustrates an embodiment of a machining assembly 20 for machining a partially spherical shape. As shown in Fig. 1, the machining assembly 20 includes a spindle 22 having a workpiece holder 24 for holding a workpiece 26 to be machined, as well as a machining tool 28 held in a tool holder 30. The spindle 22 may be associated with a vertical mill. Alternatively, the spindle may be associated with a horizontal mill, a lathe, or any other turning and/or machining apparatus. The spindle 22 facilitates rotation of the workpiece 26 around a workpiece axis 32. The spindle 22 may additionally facilitate translation along the workpiece axis 32. The machining tool 28 facilitates translation along a tool axis 34 that intersects the workpiece axis 32 at an angle A. The angle A may be any angle between approximately zero and ninety degrees, depending on the portion of the sphere desired to be machined, as further described below. Although it may be beneficial for both the spindle 22 and the machining tool 28 to translate along the workpiece axis 32 and the tool axis 34, respectively, translational movement by either the spindle 22 or the machining tool 28 may be sufficient to perform the method 10 according to the present teachings, as will be recognized by one of ordinary skill in the art.

The workpiece 26 shown in Fig. 1 is a cylindrically shaped workpiece 26. Alternatively, the workpiece 26 may be a rough shaped ball having a stem or any other unfinished item requiring a spherical portion to be machined therein. The workpiece holder 24 may be specially adapted for holding the workpiece 26. Alternatively, the workpiece holder 24 may be a standard workpiece holder 24. The workpiece 26 shown in Fig. 1 may be formed of steel or any other metal or other material as will be recognized by one with ordinary skill in the art. The machining tool 28 shown in Fig. 1 is a hollow mill having a plurality of cutting tools 36 extending into the interior of the hollow mill. Alternativly, the machining tool 28 may be a hollow mill having a grit coating 38 applied to the interior surface of the machining tool 28. In another alternative embodiment, the machining tool 28 may be an electrode for use in an electric discharge machining ("EDM") system or an electro-chemical machining ("ECM") system. It is contemplated that the technique of the present invention may be applied to any type of machining method, such as, for example, vertical milling, horizontal milling, grinding, EDM and ECM.

Fig. 2 illustrates the machining tool 28 forming a spherical shape on the workpiece 26. As shown in Fig. 2, the workpiece 26 is held in the spindle 22 and is rotated around the workpiece axis 32. As further shown in Fig. 2, the machining tool 28 is rotated around the tool axis 34 and is moved along the tool axis 34 to contact the rotating workpiece 26. The rotation of the workpiece 26 and the machining tool 28 may be clockwise or counter-clockwise and the workpiece 26 and the machining tool 28 may rotate in the same direction or in opposite directions. It is recognized that in the case of EDM or ECM the machining tool 28 does not need to be rotated, only rotation of the workpiece 26 is required. It is further recognized that the rate of material removal may be controlled by the rotational speeds of the workpiece 26 and the cutting tool 28, as well as the speed at which the workpiece 26 and the machining tool 28 are brought into contact with each other. It is anticipated that when rotated at relatively high speeds, the workpiece 26 and the machining tool 28 should be brought into contact relatively slowly to prevent seizing or breakage of the workpiece 26 or machining tool 28.

The angle A between the workpiece axis 32 and the tool axis 34 shown in Fig. 2 is approximately forty-five degrees; however, the angle A may be any angle between approximately zero and ninety degrees, to form the desired amount of a sphere, as described further below.

The machining tool 28 includes a machining circumference for removing material from the workpiece 26. In the embodiment of the machining tool 28 shown in Fig. 2, the machining circumference is formed by the circular path along which the cutting tools 36 rotate. In embodiments of the machining tool 28 utilizing EDM or ECM technology, the machining tool 28 accomplishes material removal along the machining circumference without the use of cutting tools 36. Further, the machining circumference may alternatively be formed by a grit coated surface.

In the embodiment shown in Fig. 2, the plurality of cutting surfaces formed by the plurality of cutting tools 36 enables the machining tool 28 to remove material more quickly than a single point tool. For example, a machining tool 28 having three cutting tools 36 may remove material from the workpiece 26 approximately three times faster than a single point tool.

As the machining tool 28 shown in Fig. 2 is brought into contact with the workpiece 26, the cutting tools 36 generate a circular cutting path along the surface of the workpiece 26. As the workpiece 26 rotates, the machining circumference generates an infinite number of circular cutting paths along the workpiece 26 to remove material from the workpiece 26 to form a spherical shape. Consequently, a sphere is formed on the workpiece 26 without requiring multi-axis movement by either the workpiece 26 or the machining tool 28. Moreover, the sphere formed on the workpiece 26 is geometrically perfect.

As the cutting tools 36 wear during the production of successive workpieces 26, the spheres formed on successive workpieces 26 becomes progressively larger in diameter. However, the sphere on any given workpiece 26 has a consistent diameter. Accordingly, the spherical shapes formed by the machining method and apparatus according to the present teachings are better adapted for use when a true geometric spherical shape is required than the known methods of forming spherical shapes.

The angular amount of a sphere formed on the workpiece 26 can be controlled by the depth the machining tool 28 is applied to the workpiece 26. For example, in the embodiment shown in Fig. 3, the machining tool 28 is applied to cut deeper onto the workpiece 26 than the embodiment shown in Fig. 2. Consequently, a larger angular amount of a sphere is formed on the workpiece 26 shown in Fig. 3.

Further, the angular amount of a sphere formed on the workpiece 26 can be controlled by the angle A. For example, in the embodiment shown in Fig. 4, the angle A is greater than the angle A shown in Fig. 3. Consequently, a larger angular amount of a sphere is formed on the workpiece 26 shown in Fig. 4. The angular amount of a sphere formed on the workpiece 26 can be increased from no sphere when the angle A is zero degrees, to an almost complete sphere when the angle A approaches ninety degrees. Referring back to Fig. 1, the machining tool 28 includes a plurality of drain holes 38 to allow material removed from the workpiece 26 to escape the interior of the machining tool 28. Rotation of the machining tool 28 causes the material to escape through the drain holes 38. Alternatively, air, water, coolant or other fluid may be flushed through the interior of the machining tool 28 to push the material removed from the workpiece 26 through the drain holes 38.

Fig. 5 depicts a method 40 of machining a spherical shape. As shown in Fig. 5, the method 40 may include a first step 42 of holding the workpiece 26 in the spindle 22. The method 40 may further include a second step 44 of rotating the workpiece 26 around the workpiece axis 32. The method 40 may additionally include a third step 46 of positioning the machining tool 28 such that the machine tool axis 34 forms an angle between approximately zero and ninety degrees with the workpiece axis 32. When the method 40 is applied to a cutting technique, such as a milling operation, the method 40 may include a fourth step 48 of rotating the machining tool 28 around the tool axis 34. The method 40 may also include a fifth step 50 of bringing the workpiece 26 and the machining tool 28 into contact at the intersection of the workpiece axis 32 and the tool axis 34, to machine a sphere onto the workpiece 26.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages.

Claims

ClaimsI claim:

1. A machining apparatus comprising: a workpiece holder, wherein said workpiece holder rotates a workpiece around a first axis; and a machining tool including a machining circumference, wherein said machining circumference is centered around a second axis, wherein said first axis and said second axis intersect to form an angle between approximately zero and ninety degrees and said workpiece and said machining circumference of said machining tool may be brought into contact at the intersection of said first axis and said second axis.

2. The system of claim 1 wherein said machining tool rotates around said second axis.

3. The system of claim 1 wherein said machining tool includes one or more cutting tools.

4. The system of claim 1 wherein said machining circumference is formed by a grit coated machining surface.

5. The system of claim 1 wherein said machining tool is an electrode discharge machining tool.

6. The system of claim 1 wherein said machining tool is an electro-chemical machining tool.

7. The system of claim 1 wherein said machining tool includes one or more drain holes.

8. The system of claim 1 wherein said workpiece holder translates along said first axis and said machining tool translates along said second axis.

9. A method of utilizing a machining tool to form a partially spherical shape on a workpiece comprising the steps of: holding the workpiece in a first position; rotating the workpiece about a first axis; positioning the machining tool along a second axis, wherein said first axis and said second axis intersect to form an angle between approximately zero and ninety degrees; and bringing the workpiece and the machining tool into contact at the intersection of said first axis and said second axis to machine a partial sphere onto the workpiece.

10. The method of claim 9 further comprising the step of rotating the machining tool about said second axis.

11. The method of claim 9 wherein the machining tool includes one or more cutting tools.

12. The method of claim 9 wherein said machining tool includes a grit coated, machining surface.

13. The method of claim 9 wherein the machining tool is an electrode discharge machining tool.

14. The method of claim 9 wherein the machining tool is an electro-chemical machining tool.

15. The method of claim 9 wherein said workpiece is held in a lathe.

16. The method of claim 9 wherein said machining tool comprises a hollow cylindrical body having a machining circumference disposed towards a first end of said hollow cylindrical body.