US20080188161A1

US20080188161A1 - Method and system for forming a workpiece

Info

Publication number: US20080188161A1
Application number: US11/671,008
Authority: US
Inventors: Shane E. Bremer; Ihab M. Hanna; Jason J. Wiedyk; Aleksandar J. Filipovic
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2007-02-05
Filing date: 2007-02-05
Publication date: 2008-08-07

Abstract

A method for shaping a workpiece having a base portion using a tool is provided. The method includes rotating the tool at a fixed rotational speed in a first direction and rotating the workpiece in the first direction. The tool is positioned in contact with the workpiece at a first portion of the base portion of the workpiece. The workpiece is rotated at a first rotational speed when the tool contacts the first portion of the base portion of the workpiece. The workpiece is rotated at a second rotational speed when the tool contacts a second portion of the base portion of the workpiece. The first rotational speed and the second rotational speed are different.

Description

FIELD

The present disclosure relates to a grinding system, and more particularly to a grinding system configured to reduce grinding chatter.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A common and useful method of shaping metal components is to use a grinding machine. A grinding machine typically includes a mounting for receiving the workpiece and a grinding wheel for shaping the workpiece. Both the workpiece and the grinding wheel are rotated at predefined workspeeds to maximize efficiency.
For workpieces that have simple shapes, a constant rotational speed is employed. For workpieces that require lobes or ramps, such as, for example, camshafts used in motor vehicle engines, the rotational speed of the workpiece must be reduced in non-regular shaped areas. However, using a constant speed requires that the workpiece be formed at the lowest allowable rotational speed. This reduces efficiency and the number of parts that can be manufactured. One solution is to vary the speed of the workpiece such that the workpiece rotates slower at non-regular shaped areas and faster in regular shaped areas.
However, grinding systems using these variable speeds can still produce vibrations that are difficult to control. These vibrations are caused by imbalances in the grinding system, such as, for example, by the grinding wheel imbalance, by the grinding wheel being out of roundness, or by grinding wheel or spindle axial misalignment. These imbalances result in a surface that has grinding chatter. The frequency of the chatter is a relationship between the workpiece speed and the grinding wheel speed. For example, a 10,000 RPM grinding wheel speed and a 50 RPM workpiece rotation speed would make a chatter frequency of 200 undulations per revolution. This chatter can cause machine damage and result in uneven workpiece grinding, which in turn can increase engine noise in a motor vehicle if the workpiece is a camshaft. Accordingly, there is room in the art for an improvement in reducing grinding chatter without significantly slowing grinding speeds.

SUMMARY

The present invention provides a method for shaping a workpiece having a base portion using a tool.
In a first aspect of the present invention, the method includes rotating the tool at a fixed rotational speed in a first direction and rotating the workpiece in the first direction. The tool is positioned in contact with the workpiece at a first portion of the base portion of the workpiece. The workpiece is rotated at a first rotational speed when the tool contacts the first portion of the base of the workpiece. The workpiece is rotated at a second rotational speed when the tool contacts a second portion of the base of the workpiece. The first rotational speed and the second rotational speed are different.
In another aspect of the present invention, the first portion is located at the beginning of a semi-circle on the base portion.
In still another aspect of the present invention, the second portion is located at a middle of the semi-circle on the base portion.
In still another aspect of the present invention, the second rotational speed is greater or less than the first rotational speed.
In still another aspect of the present invention, the workpiece increases rotational speed at a constant rate between the first rotational speed and the second rotational speed.
In still another aspect of the present invention, the method further includes the step of rotating the workpiece at a third rotational speed when the tool contacts a third portion of the base portion of the workpiece.
In still another aspect of the present invention, the third portion is located at an end of the semi-circle of the base portion.
In still another aspect of the present invention, the third rotational speed is equal to the first rotational speed.
In still another aspect of the present invention, the controller decreases rotational speed of the mounting portion at a constant rate between the second rotational speed and the third rotational speed.
The present invention further provides a system for shaping a workpiece having a semi-circular base portion.
In one aspect of the present invention, the system includes a rotatable mounting portion for receiving the workpiece therein, the rotatable mounting portion operable to rotate the workpiece, a rotatable grinder positioned proximate to the mounting portion for contacting the workpiece, and a controller in communication with the mounting portion and the grinder. The controller includes a memory with control logic. The control logic includes a first control logic for rotating the grinder at a fixed rotational speed in a first direction, a second control logic for rotating the mounting portion in a second direction opposite the first direction, a third control logic for positioning the tool in contact with the workpiece at a first portion of the base portion of the workpiece, a fourth control logic for rotating the mounting portion at a first rotational speed when the tool contacts the first portion of the base portion of the workpiece, and a fifth control logic for rotating the mounting portion at a second rotational speed when the tool contacts a second portion of the base portion of the workpiece. The first rotational speed and the second rotational speed are different.
In another aspect of the present invention, the first portion is located at the beginning of a semi-circle on the base portion.
In still another aspect of the present invention, the second portion is located at a middle of the semi-circle on the base portion.
In still another aspect of the present invention, the second rotational speed is greater than the first rotational speed.
In still another aspect of the present invention, the controller increases rotational speed of the mounting portion at a constant or variable rate between the first rotational speed and the second rotational speed.
In still another aspect of the present invention, the system includes a sixth control logic for rotating the mounting portion at a third rotational speed when the tool contacts a third portion of the base portion of the workpiece.
In still another aspect of the present invention, the third portion is located at an end of the semi-circle of the base portion.
In still another aspect of the present invention, the third rotational speed can be equal to the first rotational speed.
In still another aspect of the present invention, the controller decreases rotational speed of the mounting portion at a constant or variable rate between the second rotational speed and the third rotational speed.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic view of a grinding machine according to the principles of the present invention illustrated with an exemplary workpiece;

FIG. 2 is a side cross-sectional view of a portion of the grinding machine and the exemplary workpiece taken in the direction of arrows 2-2 in FIG. 1;

FIG. 3 is chart of the rotational speed of the exemplary workpiece corresponding to an angular position of the workpiece; and

FIG. 4 is a chart of the acceleration of the exemplary workpiece corresponding to an angular position of the workpiece.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
FIG. 1 illustrates a grinding system 10 according to the principles of the present invention. The grinding system 10 is shown with an exemplary workpiece 12. The grinding system 10 includes a mounting assembly 14, a grinding wheel 16, and a controller 18 in electronic communication with the mounting assembly 14 and the grinding wheel 16.
In the particular example provided the workpiece 12 is a camshaft for use in a motor vehicle, but it should be appreciated that the workpiece 12 may take various forms without departing from the scope of the present invention such as, for example, fuel pump eccentrics. The workpiece 12 as illustrated includes a generally cylindrical body 18 having a first end 20 and a second end 22. The workpiece 12 further includes a plurality of cams 24 formed along the cylindrical body 18. The shape of the cylindrical body 18 and the cams 24 are formed by operation of the grinding system 10, as will be described in further detail below.
The mounting assembly 14 includes a first mounting portion 26 and a second mounting portion 28. The first mounting portion 26 is adapted to receive the first end 20 of the workpiece 12 therein. The second mounting portion 28 is adapted to receive the second end 22 of the workpiece 12 therein. In this way, the workpiece 12 extends between the first mounting portion 26 and the second mounting portion 28. The first mounting portion 26 and the second mounting portion 28 are both rotatable and are both operable in turn to rotate the workpiece 12.
A motor 30 is drivingly coupled to the second mounting portion 28. The motor 30 is operable to rotate the second mounting portion 28 in a first direction “A”, which in turn rotates the workpiece 12 and the first mounting portion 26 in the first direction “A”. It should be appreciated that the rotational direction “A” may be opposite to that indicated in FIG. 1 without departing from the scope of the present invention.
The mounting assembly 14 is coupled to a worktable (not shown) and is moveable along an axis “X”. Movement of the mounting assembly 14 along the “X” axis allows the grinding system 10 to position the length of the workpiece 12 relative to the grinding wheel 16.
The grinding wheel 16 includes a grinding disc 32. The grinding disc 32 has a grinding surface 34 for engaging the workpiece 12 and removing material therefrom. The grinding surface 34 is preferably roughened and formed from a tough material, such as, for example, carbon-boron nitrite, ceramic, or a conventional stone. In the particular example provided, the grinding disc 32 is annular in shape, but it should be appreciated that the grinding disc 32 may have other shapes without departing from the scope of the present invention. The grinding wheel 16 is drivingly connected to a motor (not shown) and is rotatable in the first direction “A”. Furthermore, the grinding wheel 16 is moveable along an axis “Y”. Movement of the grinding wheel 16 along the “Y” axis allows the grinding system 10 to position the grinding wheel 16 such that it is in contact with the workpiece 12 and to allow the grinding wheel 16 to follow the shape of the workpiece 12.
The controller 18, as noted above, is in electronic communication with the mounting assembly 14 and the grinding wheel 16. The controller 18 is an electronic device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O section. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. The controller 18 is operable to send electronic control signals to the mounting assembly 14 and the grinding wheel 16 in order to control the rotational speed of the workpiece 12 through the rotation of the second mounting portion 28, to control the position of the mounting assembly 14 along the “X” axis, to control the rotational speed of the grinding wheel 16, and to control the position of the grinding wheel 16 along the “Y” axis. To this end, the controller 18 includes a workspeed data file that contains instructions for rotational speeds and grinder wheel 16 and mounting assembly 14 positions.
During operation of the grinding system 10, the grinding wheel 16 is rotated in the first direction “A” and the mounting assembly 14 in FIG. 1 rotates the workpiece 12 in the first direction “A”. The grinding wheel 16 is rotated at a fixed rotational speed. The workpiece 12 is rotated according to the workspeed data table found in the memory of the controller 18. The controller 18 controls the position and rotational speed of the mounting assembly 14 and grinding wheel 16. When the workpiece 12 and the grinding wheel 16 are in contact and in rotation, the grinding surface 34 removes material from the workpiece 12. By positioning the grinding wheel 16 along the “Y” axis, different amounts of material may be removed, thereby forming the base portion 36 and the ramp portion 38. By positioning the workpiece 12 along the “X” axis, different sections of the workpiece 12 may be shaped.
Turning now to FIG. 2, a cross-section is illustrated of the workpiece 12 at a cam 24 and of the grinding wheel 16. The cam 24 includes a base portion 36 and a ramp portion 38. The base portion 36 is semi-circular in shape and includes a first portion 40, a second portion 42, and a third portion 44. The first portion 40 corresponds to the beginning of the semi-circle of the base portion 36. The second portion 42 corresponds to the middle of the semi-circle of the base portion 36. The third portion 44 corresponds to the end of the semi-circle of the base portion 36.
The ramp portion 38 includes a first flank 46, a second flank 48, and a point 50. The first flank 46 extends from the first portion 40 of the base portion 36 to the point 50. The second flank 48 in turn extends from the third portion 44 of the base portion 36 to the point 50. In this way, the ramp portion 38 has a generally triangular shape.
FIG. 3 illustrates a chart 100 showing the preferred method of varying the rotational speed of the workpiece 12 with respect to the angular position of the cam 24. This method of varying the rotational speed of the workpiece 12 is represented by line 102. The “x” axis of the chart 100 is the angular position of the workpiece 12 with respect to contact with the grinding wheel 16. Specifically, angular position “0” and “360” corresponds to the grinding wheel 16 contacting the point 50 in FIG. 2. Angular position “120” corresponds to the grinding wheel 16 contacting the first portion 40 in FIG. 2. Angular position “180” corresponds to the grinding wheel 16 contacting the second portion 42 in FIG. 2. Angular position “240” corresponds to the grinding wheel 16 contacting the third portion 44 in FIG. 2. The “y” axis of the chart 100 is the rotational speed of the workpiece 12 represented as a percentage of a nominal workspeed. The nominal workspeed is a predefined constant speed.
In the preferred method of shaping the workpiece 12 of the present invention, the rotational speed of the workpiece 12 is varied between the first portion 40 in FIG. 2 and the third portion 44 in FIG. 2. Specifically, when the grinding wheel 16 is positioned to contact the workpiece 12 at the first portion 40, the workpiece 12 has a first rotational speed, as indicated by reference numeral 104 on the line 102. As the workpiece 12 rotates, the grinding wheel 16 moves to contact the second portion 42 and the rotational speed of the workpiece 12 increases to a second rotational speed, indicated by reference numeral 106 on line 102. In the example provided, the second rotational speed is 30% greater than the first rotational speed, however, various other percentages may be employed without departing from the scope of the present invention. Also in the example provided, the rotational speed of the workpiece 12 increases at a constant rate, as indicated by the straight section on the line 102 and indicated by reference numeral 108. Alternatively, the rotational speed of the workpiece 12 may increase at a changing rate.
As the workpiece 12 continues to rotate, the grinding wheel 16 moves to contact the third portion 44 and the rotational speed of the workpiece 12 decreases from the second rotational speed at point 106 to a third rotational speed, indicated by reference numeral 110 on line 102. In the example provided, the third rotational speed is equal to the first rotational speed, though various other speeds may be employed so long as the rotational speed of the workpiece 12 is not kept constant between first portion 40 and the third portion 44. In the preferred embodiment, the rotational speed of the workpiece 12 decreases at a constant rate, as indicated by the straight section on the line 102 and indicated by reference numeral 112. Alternatively, the rotational speed of the workpiece 12 may decrease at a changing rate.
FIG. 4 illustrates a chart 200 showing the preferred acceleration of the workpiece 12 with respect to the angular position of the cam 24. This acceleration of the workpiece 12 is represented by line 202. The “x” axis of the chart 200 is the angular position of the workpiece 12 with respect to contact with the grinding wheel 16. Specifically, angular position “0” and “360” corresponds to the grinding wheel 16 contacting the point 50 in FIG. 2. Angular position “120” corresponds to the grinding wheel 16 contacting the first portion 40 in FIG. 2. Angular position “180” corresponds to the grinding wheel 16 contacting the second portion 42 in FIG. 2. Angular position “240” corresponds to the grinding wheel 16 contacting the third portion 44 in FIG. 2. The “y” axis of the chart 200 is the acceleration of the workpiece 12. Acceleration changes are kept to a minimum by keeping the transitions of workpiece 12 rotation speed at points 104, 106, and 110 rounded.
By varying the rotational speed of the workpiece 12 during shaping of the base portion 36, the chatter is forced to have an inconsistent spacing. This in turn reduces the amplitude at any one particular frequency of chatter, thereby reducing the chatter. At the same time, rotational speed is not reduced and therefore inefficiency is kept to a minimum.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

1. A method for shaping a workpiece using a tool, the workpiece having a semi-circular base portion, the method comprising:

rotating the tool at a fixed rotational speed in a first direction;

rotating the workpiece in the first direction

positioning the tool in contact with the workpiece at a first portion of the semi-circular base portion of the workpiece;

rotating the workpiece at a first rotational speed when the tool contacts the first portion of the semi-circular base portion of the workpiece; and

rotating the workpiece at a second rotational speed when the tool contacts a second portion of the semi-circular base portion of the workpiece; and

wherein the first rotational speed and the second rotational speed are different.

2. The method of claim 1 wherein the first portion is located in a first half of the semi-circular base portion.

3. The method of claim 2 wherein the second portion is located in a second half of the semi-circular base portion.

4. The method of claim 3 wherein the second rotational speed is greater than the first rotational speed.

5. The method of claim 4 wherein the workpiece increases rotational speed at a constant rate between the first rotational speed and the second rotational speed.

6. The method of claim 5 further comprising the step of rotating the workpiece at a third rotational speed when the tool contacts a third portion of the semi-circular base portion of the workpiece.

7. The method of claim 6 wherein the third portion is located at an end of the semi-circular base portion.

8. The method of claim 7 wherein the third rotational speed is equal to the first rotational speed.

9. (canceled)

10. A system for shaping a workpiece, the workpiece having a semi-circular base portion, the system comprising:

a rotatable mounting portion for receiving the workpiece therein, the rotatable mounting portion operable to rotate the workpiece;

a rotatable grinder positioned proximate to the mounting portion for contacting the workpiece;

a controller in communication with the mounting portion and the grinder, the controller having a memory with control logic, the control logic including a first control logic for rotating the grinder at a fixed rotational speed in a first direction, a second control logic for rotating the mounting portion in the first direction, a third control logic for positioning the tool in contact with the workpiece at a first portion of the semi-circular base portion of the workpiece, a fourth control logic for rotating the mounting portion at a first rotational speed when the tool contacts the first portion of the semi-circular base portion of the workpiece, and a fifth control logic for rotating the mounting portion at a second rotational speed when the tool contacts a second portion of the semi-circular base portion of the workpiece; and

11. The system of claim 10 wherein the first portion is located in a first half of the semi-circular base portion.

12. The system of claim 11 wherein the second portion is located in a second half of the semi-circular base portion.

13. The system of claim 12 wherein the second rotational speed is greater than the first rotational speed.

14. The system of claim 13 wherein the controller increases rotational speed of the mounting portion at a constant rate between the first rotational speed and the second rotational speed.

15. The system of claim 14 further comprising a sixth control logic for rotating the mounting portion at a third rotational speed when the tool contacts a third portion of the semi-circular base portion of the workpiece.

16. The system of claim 15 wherein the third portion is located at an end of the semi-circular base portion.

17. The system of claim 16 wherein the third rotational speed is equal to the first rotational speed.

18. The system of claim 17 wherein the controller decreases rotational speed of the mounting portion at a constant rate between the second rotational speed and the third rotational speed.