PROCESSING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to copending U.S. provisional application titled "SYSTEM AND METHOD OF MAGNETIC ABRASIVE

SURFACE FINISHING," having serial number 61/604,097 and filed February 28, 2012. This application is hereby incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under

Grant/Contract Number CMMI-085538 awarded by the National Science Foundation. The government has certain rights in the invention.

BACKGROUND

[0003] A freeform surface, such as the femoral component of a knee prosthetic, may require a specific surface pattern and a particularized level of roughness to meet certain specifications. As such, a freeform surface may be shaped and buffed in order to meet these specifications. Processing by hand may raise production costs, increase deviations in surface quality, and limit the variations in surface roughness and topography. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the disclosure.

[0005] FIG. 1 is a drawing representing a cross-section of a magnetic abrasive processing system according to various embodiments of the present disclosure.

[0006] FIGS. 2A-2C are drawings showing a portion of a workpiece subject to the magnetic abrasive processing system of FIG. 1 according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

[0007] The present disclosure is directed towards the use of Magnetic Abrasive Finishing (MAF) to process freeform surfaces. As a non-limiting example, a mixture comprising, for example, magnetic particles, abrasive particles, and/or lubricant is applied to a workpiece. The mixture is then exposed to a rotating magnetic field, causing the components of the mixture to move along the surface of the workpiece. Additionally, the workpiece may be moved in the x, y, and/or z directions with respect to the magnetic field. The movement of the abrasive particles in the mixture with respect to the workpiece can cause patterns to be created on the surface of the workpiece. Accordingly, physical properties of the workpiece may be modified due to the patterns. For example, the wettability, reflectivity, friction characteristics, wear characteristics, resistance to micro-organisms, and/or other properties of the workpiece may be affected.

[0008] In some cases, another mixture may be applied to the workpiece, and the mixture may be exposed to the rotating magnetic field. The mixture may move along the surface of the workpiece in response to the rotating magnetic field and reduce the surface roughness of the workpiece. The workpiece may also be moved in the x, y, and/or z directions with respect to the magnetic field. Thus, in accordance with the present disclosure, the workpiece may retain the created patterns while having a reduced surface roughness. In the following discussion, a general description of the system and its components is provided, followed by a discussion of the operation of the same.

[0009] Turning to FIG. 1 , shown is a cross-section diagram representing an example of a magnetic abrasive processing system 100 according to various embodiments of the present disclosure. The magnetic abrasive processing system 100 may include a workpiece 103, a workpiece holder 106, a magnetic field generator 1 13, and possibly other components not discussed in detail herein.

[0010] The workpiece 103 may be any object that is subject to the surface processing described herein. According to various embodiments, the workpiece

103 may have one or more freeform surfaces. As non-limiting examples, the workpiece 103 may be a medical prosthesis (e.g. , the femoral component of a knee prosthetic or a hip replacement), an aerospace component, an optical component, a die, a mold, or any other type of object for which the surface is to be processed. The workpiece 103 may or may not include a coating according to various embodiments. When subject to the processing described herein, the workpiece 103 may be shaped and/or the surface of the workpiece 103 may be patterned and/or polished.

[0011] The workpiece holder 106 may hold and stabilize the workpiece 103. Additionally, the workpiece holder 106 may move the workpiece 103 in the x, y, and/or z directions with respect to the magnetic field generator 1 13. Even further, the workpiece holder 106 may be used to vibrate, rotate, or move the workpiece 103 in other ways relative to the magnetic field generator 1 13. To this end, the workpiece holder 106 may be attached to a robotic arm (not shown), for example, or any other type of positioning device capable of movement in one or more dimensions.

[0012] The magnetic field generator 13 creates a magnetic field 1 16 that may be constant or dynamic. To this end, the magnetic field generator 1 13 may be embodied in the form of an electromagnet or a permanent magnet, for example. Accordingly, various embodiments of the magnetic field generator 1 13 may include a core 1 19 and an energized coil 123 to generate the magnetic field 1 16. The magnetic field generator 1 13 may also include a pole tip 126 that directs the magnetic field 1 16. In this respect, the pole tip 126 may direct the flux lines of the magnetic field 1 16 between the magnetic field generator 1 13 and the workpiece 103. Additionally, the pole tip 126 may be configured to rotate in the direction indicated by arrow A and/or in the opposite direction. In this regard, the pole tip 126 may rotate about a longitudinal axis for the pole tip 126. In alternative embodiments, the pole tip 26 may be moved in a rotational fashion to produce rotational movement of a mixture 129 that may be applied to the workpiece 103. [0013] Various attributes may be associated with the magnetic field 1 16. As non-limiting examples, the magnetic field strength, the rate of revolution, the direction of revolution, and possibly other attributes may be associated with the magnetic field 16. The attributes may be controlled by the magnetic field generator 1 13 or by using other techniques. Such attributes may be varied or otherwise controlled to achieve desired processing effects on a workpiece 1 03 as is described herein.

[0014] A mixture 129 may be applied to the workpiece 1 03. The mixture 1 29 may include various components, such as magnetic particles 133, abrasive particles (not shown), lubricant (not shown), and/or other components. In the presence of a magnetic field 1 6, the magnetic particles 133 may align with the magnetic field 1 16 and form flexible "chains" between the workpiece 103 and the pole tip 126. In this sense, the magnetic particles 33 may form a flexible connection between the workpiece 103 and the pole tip 126 in approximate alignment with the magnetic field 1 16.

[0015] Additionally, as the magnetic field 1 16 is adjusted, the magnetic particles 1 33 respond accordingly. For instance, if the magnetic field 1 16 rotates, the chains of the magnetic particles 1 33 may rotate in conjunction with the magnetic field 1 16. As another example, if the strength of the magnetic field 1 16 is increased, the flexible chains of the magnetic particles 133 may become more rigid in response to the increased strength of the magnetic field 1 16.

Furthermore, if the strength of the magnetic field 1 16 is decreased, the flexible chains of magnetic particles 133 may become less rigid in response to the decreased strength of the magnetic field 6. [0016] Various characteristics may be associated with the mixture 129 and/or its components. Such characteristics may be, for example, the types of particles in the mixture 129, the amount of the mixture 129 (e.g. , its mass), the particle size(s), the particle composition, the ratio of magnetic particles 33 to abrasive particles, or other characteristics. By configuring the mixture 129 to have particular characteristics, the mixture 129 may be used to create particular patterns on and/or a particular surface roughness for the workpiece 03. For instance, patterns comprising continuous and/or non-continuous grooves may be created on the surface of the workpiece 103. Additionally, grooves that are substantially parallel with respect to each other may be created in the surface of the workpiece 103. Furthermore, cross-hatched grooves may be created on the surface of the workpiece 103.

[0017] Next, a general description of the operation of the various

components of the magnetic abrasive processing system 100 is provided. To begin, it is assumed that a mixture 129 has been applied to the workpiece 103 and that the magnetic field generator 1 13 is energized and providing a magnetic field 1 16.

[0018] The pole tip 126 may begin rotating in the direction indicated by arrow A. Because the pole tip 126 directs the magnetic field 1 16, the magnetic field 16 may rotate in accordance with the pole tip 126. In turn, the chains of magnetic particles 133 that respond to the magnetic flux lines of the magnetic field 1 16 may rotate as well. The magnetic particles 33 may also cause the abrasive particles to move along the surface of the workpiece 103.

[0019] The moving magnetic particles 33 and/or abrasive particles may cause patterns to be created in the surface of the workpiece 103. The patterns may include multiple grooves that are formed in the surface of the workpiece 03. In accordance with the present disclosure, various attributes of the magnetic field 1 16 and/or characteristics of the mixture 129 may be chosen so as to determine features of the grooves and thus the patterns on the workpiece 103.

[0020] For example, applying a relatively strong magnetic field 1 16 may result in the flexible chains of the magnetic particles 133 being relatively rigid, thereby creating continuous grooves in the surface of the workpiece 103.

Furthermore, applying a relatively weak magnetic field 1 16 may result in the flexible chains of the magnetic particles 133 being less rigid, thereby causing non-continuous grooves to be created in the surface of the workpiece 103.

Additionally, the magnetic field 1 16 may be pulsed or alternated in direction and/or magnitude to affect the characteristics of the grooves that may be created on the surface of the workpiece 103.

[0021] Furthermore, in various embodiments, the movement of the magnetic field 1 16 with respect to the workpiece 103 may be specified so that various types of grooves are formed on the workpiece 103. For instance, the motion of the workpiece 103 relative to the pole tip 126, or the motion of the pole tip 126 relative to the workpiece 103 may be specified so as to form grooves that are substantially parallel to each other. In alternative embodiments, the

characteristics for the magnetic field 1 16 and/or the movement of the magnetic field 1 16 with respect to the workpiece may be chosen such that cross-hatched grooves or other types of grooves are created in the surface of the workpiece 103. These grooves may affect surface properties of the workpiece 103, such as its wettability, reflectivity, friction characteristics, wear characteristics, resistance to micro-organisms, and/or other properties.

[0022] The surface roughness of the workpiece 103 may also be reduced. To this end, the workpiece 103 may be cleaned, and another mixture 129 may be applied to the workpiece 103. This other mixture 129 may be the same type or may be different from the mixture 129 that was previously used to create the cutting marks in the surface of the workpiece 103. The characteristics of the mixture 129 may be selected in order to facilitate reducing the surface roughness of the workpiece 103 while maintaining or altering the previously created patterns in the workpiece 103.

[0023] The process of rotating the magnetic field 1 16 and the magnetic particles 133 may be repeated to reduce the surface roughness and/or change the surface topography of the workpiece 103. Additionally, attributes of the magnetic field 1 16 may be selected and/or adjusted to facilitate this operation. For example, the strength of the magnetic field 1 16, the rate of rotation of the magnetic field 1 16 and/or the pole tip 126, and/or the rate of moving the workpiece 103 with respect to the magnetic field 116 may be selected and/or adjusted to reduce the surface roughness and/or change the surface topography of the workpiece 103.

[0024] With reference to FIG. 2A, shown is a drawing showing a portion of a workpiece 103 subject to the magnetic abrasive processing system 100 (FIG. 1 ) according to various embodiments of the present disclosure. In particular, shown is a portion of a workpiece 103 prior to the workpiece 03 being processed by the magnetic abrasive processing system 100. As shown, the workpiece 103 may have a relatively rough surface. Additionally, the surface of the workpiece 103 may have scratches (not shown) or other types of features that may not be desirable for the workpiece 103.

[0025] Turning to FIG. 2B, shown is another drawing showing a portion of the workpiece 03 subject to the magnetic abrasive processing system 100 (FIG. 1) according to various embodiments of the present disclosure. In particular, shown in FIG. 2A is a portion of the workpiece 03 of FIG. 2A after the magnetic abrasive processing system 100 has generated a pattern comprising grooves 203 in the surface of the workpiece 103. To this end, the magnetic particles 133 in the mixture 129 (FIG. 1 ) may have been displaced along the surface of the workpiece 103 by the rotating magnetic field 16. As a result, the magnetic particles 133 (FIG. 1) and/or the abrasive particles in the mixture 129 may have cut into the surface of the workpiece 103, thereby generating the grooves 203.

[0026] In the example of FIG. 2B, the grooves 203 are continuous and are substantially parallel with respect to each other. In order to generate different types of patterns in the surface of the workpiece 103, the characteristics for the mixture 129 and/or the magnetic field 1 16 may be chosen to result in the desired pattern. According to the characteristics selected for a particular application, the grooves 203 for the pattern ma e, for example, continuous, non-continuous, substantially parallel, cross-hatched, and/or any other type of arrangement.

[0027] Turning to FIG. 2C, shown is another drawing showing a portion of the workpiece 103 subject to the magnetic abrasive processing system 100 (FIG.

1 ) according to various embodiments of the present disclosure. In particular, shown is a portion of the workpiece 103 of FIGS. 2A-2B after the magnetic abrasive processing system 100 has reduced the surface roughness of the workpiece 103. To this end, characteristics for the mixture 129 (FIG. 1) and the magnetic field 1 16 may be chosen to result in the surface roughness of the workpiece being reduced. By selecting the characteristics for the mixture 129 (FIG. 1 ) or the magnetic field 1 16 (FIG. 1 ), the surface roughness of the workpiece 103 may be reduced to a desired level. In addition, the workpiece may retain the created grooves 203 while having a reduced surface roughness. As a result, the wettability, reflectivity, friction characteristics, wear

characteristics, resistance to micro-organisms, and other characteristics of the workpiece may be affected. Additionally, in alternative embodiments, the characteristics of the mixture 129 and/or the magnetic field 1 16 may be chosen and applied to increase the surface roughness of the workpiece 103.

[0028] It is emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.