US20020115382A1

US20020115382A1 - Method and apparatus to produce a precisely textured surface on a workpiece

Info

Publication number: US20020115382A1
Application number: US09/785,873
Authority: US
Inventors: G. Luthy
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2001-02-16
Filing date: 2001-02-16
Publication date: 2002-08-22
Also published as: US20030106358A1; US20030177804A1; AU1009002A

Abstract

This invention relates to a method and apparatus to create a pre-established textured surface on a workpiece. The pre-established textured surface includes an average roughness and a non-directional lay pattern being formed to a controlled width.

Description

TECHNICAL FIELD

This invention relates generally to producing a workpiece and more particularly to a method and apparatus for producing a precisely textured surface on a workpiece.

BACKGROUND

In the manufacture of machines such as earthmoving equipment, it is often necessary to produce a surface texture on a part which has a predetermined average roughness and lay pattern.

Roughness can be defined as the finer irregularities of the surface texture, usually including those irregularities which result from the inherent action of the production process, such as traverse feed marks. Average roughness is the arithmetic average of the absolute values of the profile height deviations taken within the sampling length. Average roughness is specified in micro-inches or micro-meters.

Lay pattern refers to the direction and description of the predominant surface pattern. Lay is normally a function of the production method. For example, a workpiece machined on a lathe will typically show a lay pattern that is circular around the workpiece.

One example of a workpiece requiring a specific roughness and lay pattern is a wheel on an off-highway truck. The wheel is typically a casting that is machined to the specific dimensions and tolerances specified by the manufacturer. In some machining operations, a surface is machined to a given dimension and is later configured to finished dimension or configuration.

One example, of a portion of the wheel that is configured after being premachined is a ramp on the inner profile of the wheel. The ramp is a specific area that engages a duo-cone seal. A critical specification of the ramp has an average roughness between 3.75 and 6.250 micro-meters (140 and 240 micro-inches). Additionally, the ramp specification requires that there is no lay pattern. Presence of a lay pattern provides a leakage path at the interface of the duo-cone seal and the ramp. For example, a typical lay pattern created on a lathe may leave a relatively shallow groove in a circular fashion around a part. The groove may act as a path for lubrication to follow past the elastomeric toric of the seal.

A typical method for achieving the desired average roughness without a lay pattern is to grit-blast the ramp area after all other machining has been performed on the workpiece. A first drawback to using the grit-blast method is the need to provide an additional work station for grit-blasting. A second disadvantage is the extra labor expense for transporting the workpiece to and from the grit-blast station. A third drawback to grit-blasting relates to the affected zone of the blast procedure. Grit-blasting leaves an affected zone similar to that of spray painting, i.e. overspray, it is difficult to limit the blast of grit to a precise area, therefore it is possible to damage a portion of the workpiece that has already been machined.

SUMMARY OF THE INVENTION

In one aspect of the present invention a workpiece is adapted for engagement with the elastomeric toric on a duo-cone seal. The workpiece includes a centerline and a pre-established surface texture defined concentrically about the centerline. The pre-established surface texture is defined by having an average roughness and a lay pattern that is non-directional.

In another aspect of the present invention a texturing tool is defined for precisely deforming the surface of a workpiece. The texturing tool includes a tool steel member with a central axis extending though the steel member. A bore is centered about the central axis and has a predetermined diameter. A peripheral surface extends abut the tool steel member and includes a coating having an average roughness that is greater that the desired roughness of the workpiece.

In another aspect of the present invention a method for producing a surface texture having an average roughness and a lay pattern that is non-directional is defined. The method of producing the surface texture includes securing the workpiece, positioning a tool relative to the surface to be textured, interfacing the texturing tool with the surface of the workpiece, and rotating one of the texturing tool or the fixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a lathe having a texturing tool of the present invention attached to the lathe and a sectional view of a workpiece of the present invention is positioned within a fixture. [0011]
FIG. 2 is a side view of the texturing tool of the present invention. [0012]
FIG. 3 is an end view of the texturing tool of the present invention. [0013]
FIG. 4 is a sectional view of a workpiece of the present invention. [0014]
FIG. 5 is an enlarged view of the workpiece of the present invention taken along line [0015] 5 of FIG. 4.

DETAILED DESCRIPTION

Referring to FIG. 1, a [0016] horizontal lathe 10 is illustrated. The horizontal lathe 10 includes a base 12, a fixture 14, and a tool carrier 16. The fixture 14 is adapted to hold a workpiece 18 in a position that allows a texturing tool 22 to interface with a surface 24 of the workpiece 18 that is to be textured. In this application the workpiece is a casting 25 which may or may not have a plurality of premachined surfaces. The tool carrier 16 may be moveable along multiple axis's (x, y and z) 26. The tool carrier 16 may additionally be used to move the texturing tool 22 rotationally about the workpiece 18. The texturing tool 22 for precisely creating a textured surface 24 having a pre-established average roughness and non-directional lay pattern is attached to a tool holder 28. The tool holder 28 may included a first portion 30 for attaching to the tool carrier 16 and a second portion for attaching to the texturing tool 22. The first portion 30 and the second portion 32 of the tool holder 28 may be adapted to slidingly engage each other, and may further include a spring 34 positioned between the first and second portions 30, 32.
Referring to FIGS. 2 and 3, the [0017] texturing tool 22 of the present invention is illustrated. The texturing tool 22 includes a tool steel member 40 having a central axis 42 extending through the tool steel member 40. A bore 44 is centered about the central axis 42 of the texturing tool 22 and has a predetermined diameter 48. The bore 44 is adapted to interface with a bearing member 50 or an axle to allow the texturing tool 22 to rotate about its central axis 42. A peripheral surface 52 extends about the tool steel member 40. The peripheral surface 52 preferably matches at least a portion of a profile of the surface 24 profile 60 to be textured. A coating 54 having a texture mirroring a desired pre-established surface texture 56 is applied to the peripheral surface 52 of the tool steel member 40. The coating 54 may be applied through conventional coating techniques, such as, plasma sprayed carbide or cemented diamond processes. An alternative to using a textured coating is to created the texture mirroring the pre-established surface texture 56 on the tool steel member 40 and then harden the tool steel member using conventional hardening methods. A critical factor of the coating 54 is the capability to withstand the force required to deform the workpiece 18. Excessive force on the coating may damage the coating 54. In order to achieve the desired roughness on the workpiece 18 it may be necessary to use a coating 54 having a roughness that is proportionally greater than the desired roughness of the workpiece 18. For example, experimentation has shown that a textured surface on a workpiece that has a hardness of approximately 3.9 Brinell with an average desired roughness between 3.75 and 6.25 micro-meter (150 and 240 micro-inch), the texturing tool 22 should be coated with the coating 54 having an average roughness of approximately 300 micro-inch.
Referring to FIG. 4, a sectional view of the [0018] workpiece 18 of the present invention is shown. The workpiece 18 includes a centerline 58 and a profile 56 defined about the centerline 58. At least a portion of the profile 60 has the pre-established surface texture 56. The pre-established surface texture 56 includes a precise average roughness having no lay pattern. Additionally the pre-established surface texture 62 includes a controlled width 64. The controlled width 64 is defined by a first border 66 and a second border 68 spaced at a predetermined distance from the first border 66.
Referring to FIG. 5, an enlarged view of the section as taken along line [0019] 5 of FIG. 4. Shown is a portion of the profile 60 that includes the pre-established surface texture 56. A ramp 72 or angled portion has a substantially smooth surface prior to being acted on by the texturing tool 22 which creates the pre-established surface texture 56 having a specified average roughness and no lay pattern. One example of a specified average roughness is between 3.75 and 6.25 micro-meters (148 and 246 micro-inches). It should be noted that the present invention could be applied to a wide degree of specified average roughness. Additionally the ramp 72 portion of the profile 60 includes the controlled width 64.
Industrial Applicability [0020]
With reference to the drawings, and the previous detailed description, the [0021] workpiece 18 of the present invention is machined from a rough casting 25 that is substantially similar in shape to the finished workpiece 18. The casting 25 is positioned in the fixture 14 in the lathe 10. Using conventional machining tools and practices material is removed from the casting 25. Material removal continues until the workpiece 18 dimensions are within the range of tolerances specified by the manufacturing drawings. After the portion of the surface 24 to be textured of the workpiece 18 to be textured has been machined to the substantially smooth finish, the texturing tool 22 and tool holder 28 is attached to the tool carrier 16 of the lathe 10. The tool carrier 16 moves the texturing tool 22 into a position near the portion of the surface 24 profile 60 to be textured. At least one of the texturing tool 22 or the fixture 14 holding the workpiece 18 is then rotated and the texturing tool 22 is moved into contact with the portion of the surface 24 profile 60 to be textured. The amount of deformation of the workpiece 18 is controlled by the force that the texturing tool 22 exerts on the workpiece 18 and the number of passes that the texturing tool 22 makes over the portion of the surface 24 profile 60 to be textured. Adjusting the force exerted on the workpiece 18 is the simplest way to affect the amount of texturing. In the case of the spring 34 being loaded within the tool holder 28, the force exerted on the workpiece 18 is a function of how far the spring 34 is compressed. The distance that the spring 34 is compressed is equal to the distance that the tool carrier 16 moves toward the workpiece 18 after the texturing tool 22 contacts the workpiece 18. The greater the force exerted on the workpiece 18, the greater the average roughness of the texturing. However, it must be realized that increasing the force that the texturing tool 22 exerts on the workpiece 18 will not create a rougher surface than that of the texturing tool 22. Additionally excessive forces exerted on the texturing tool 22 may increase wear or damage the texturing tool 22. Repeated application of the texturing tool 22 to the workpiece 18 surface has been found to be most effective in creating a uniform surface appearance.
The above identified invention provides an effective method for applying a pre-established textured surface to a workpiece without the previously mentioned disadvantages caused by grit blasting. [0022]
Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims. [0023]

Claims

What is claimed is:

1. A workpiece being adapted for engagement with an elastomeric toric on a duo-cone seal, said workpiece comprising:

a centerline;

a surface having a pre-established surface texture and defined concentrically about said centerline;

said surface defining an average roughness and a lay pattern which is non-directional; and

a controlled width being defined by a first border and second border spaced at a distance away from said first border.

2. The workpiece of claim 1 having said average roughness between 3.25 and 6.75 micro-meter (126 and 263 micro-inch).

3. A texturing tool for precisely deforming the surface of a workpiece, said tool comprising:

a tool steel member;

a central axis extending through said tool steel member;

a bore centered about said central axis and having a predetermined diameter;

a peripheral surface extending about said tool steel member; and

a coating being applied to said peripheral surface wherein said coating is equal or greater in roughness to a pre-established surface texture desired on said workpiece.

4. The texturing tool of claim 3, further having said coating that is 20-40 percent greater in roughness than said pre-established surface texture desired on said workpiece.

5. The texturing tool of claim 3, including said coating being manufactured using a plasma sprayed carbide process.

6. The texturing tool of claim 3, including said tool steel member having said peripheral surface including a texture mirroring said pre-established surface texture.

7. A method for producing a precise textured surface, said surface having an average roughness and a lay pattern which is non-directional, said method for producing said precise textured surface comprising the steps of:

securing said workpiece in a fixture;

positioning a texturing tool relative to said surface to be textured;

interfacing said tool with said surface;

rotating one of said tool and said fixture about an entire profile of said surface; and

forming a controlled width of said textured surface.

8. The method of claim 7, further including the step of repeatably interfacing said tool with said surface, whereby said textured surface increases in uniformity.