US20110081839A1

US20110081839A1 - Method and apparatus for polishing a curved edge

Info

Publication number: US20110081839A1
Application number: US12/580,934
Authority: US
Inventors: Simon Lancaster; Thomas Johannessen
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2009-10-06
Filing date: 2009-10-16
Publication date: 2011-04-07
Also published as: US8690640B2; US20110081837A1

Abstract

A method and an apparatus for polishing a curved edge of a molded part. A surface of the curved edge is abraded by contacting a polishing surface of a first polishing wheel to the curved edge repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel. The abraded surface of the curved edge is polished by contacting a polishing surface of a second polishing wheel to the curved edge in the first direction and in a second direction opposite to the first direction. The polishing surfaces of the first and second polishing wheels are shaped to conform to a portion of the surface of the curved edge of the molded part. The polishing wheel is maintained at a constant rotational speed by a controller when contacting the curved edge. The polished surface of the curved edge is visually smoothly uniform in reflective appearance.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. patent application Ser. No. ______ (APL1P607) entitled “METHOD AND APPARATUS FOR POLISHING A CURVED EDGE” by Lancaster et al. takes priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 61/249,200 entitled “COMPLEX GEOGRAPHICAL EDGE POLISHING” by Johannessen filed Oct. 6, 2009 and incorporated by reference in its entirety.
This U.S. patent application is also related to and incorporates by reference in their entireties for all purposes the following co-pending patent applications filed concurrently herewith:

- (i) U.S. patent application Ser. No. ______ (APL1P602) entitled “PORTABLE COMPUTER DISPLAY HOUSING” by Bergeron et al.;
- (ii) U.S. patent application Ser. No. ______ (APL1P603) entitled “PORTABLE COMPUTER ELECTRICAL GROUNDING AND AUDIO SYSTEM ARCHITECTURES” by Thomason et al.;
- (iii) U.S. patent application Ser. No. ______ (APL1P604) entitled “PORTABLE COMPUTER HOUSING” by Casebolt et al.;
- (iv) U.S. patent application Ser. No. ______ (APL1P601) entitled “COMPUTER HOUSING” by Raff et al.;
- (v) U.S. patent application Ser. No. ______ (APL1P608) entitled “SELF FIXTURING ASSEMBLY TECHNIQUES” by Thompson et al.;
- (vi) U.S. patent application Ser. No. ______ (APL1P593X1) entitled “BATTERY” by Coish et al. that is a continuation in part of U.S. patent application Ser. No. 12/549,570 filed Aug. 28, 2009;
- (vii) U.S. patent application Ser. No. ______ (APL1P612) entitled “PORTABLE COMPUTER DISPLAY HOUSING” by Bergeron et al.; and
- (viii) U.S. patent application Ser. No. ______ (APL1P613) entitled “COMPUTER HOUSING” by Raff et al.

TECHNICAL FIELD

The present invention relates generally to the polishing of a three dimensional curved edge of an object. More particularly, a method and an apparatus are described for polishing the edge of an injection molded part, formed using a thermoplastic compound, to a visually smooth and consistent reflective appearance.

BACKGROUND OF THE INVENTION

The proliferation of high volume manufactured, portable electronic devices has encouraged innovation in both functional and aesthetic design practices for enclosures that encase such devices. Manufactured devices can include a casing that provides an ergonomic shape and aesthetically pleasing visual appearance desirable to the user of the device. Surfaces of casings molded from thermoplastic compounds can be shaped and polished to a highly reflective finish; however, the polished reflective surface can reveal minor variations in the final surface geometry. Molded casings can include complex geometric shapes that are difficult to finish to a uniform surface appearance. Prior art techniques can result in a tactilely smooth finish with an undesirable variation in visual reflective appearance. Thus there exists a need for a method and an apparatus for polishing a three dimensional curved edge of an object resulting in a visually smooth and consistent reflective appearance.

SUMMARY OF THE DESCRIBED EMBODIMENTS

A method for polishing a three dimensional curved edge of a molded part is disclosed. The method can be carried out by at least abrading a surface of the curved edge of the molded part by contacting a polishing surface on a first polishing wheel to the unpolished surface of the curved edge of the molded part. The abrading can occur repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel. The polishing surface on the first polishing wheel can be shaped to substantially conform to a portion of the surface of the curved edge of the molded part. The abraded surface of the curved edge of the molded part can subsequently be polished by contacting a polishing surface on a second polishing wheel to the abraded surface. The polishing can be accomplished by alternating contact in the first direction and in a second direction opposite to the first direction. The polishing surface on the second polishing wheel can also be shaped to substantially conform to the portion of the surface of the curved edge of the molded part.
In a second embodiment, a method for polishing at least two surfaces of a three dimensional curved edge of a molded part is disclosed. The method can include abrading a first surface and a second surface of the curved edge using at least two different polishing surfaces on a first polishing wheel. Each polishing surface on the first polishing wheel can be shaped to substantially conform to a corresponding portion of the surface of the curved edge of the molded part. The abrading can be carried out by contacting the polishing surfaces of the first polishing wheel with the surfaces of the curved edge of the molded part repeatedly in a direction concurrent with a rotational spinning direction of the first polishing wheel. The method can also include polishing the first and second surfaces using different polishing surfaces on a second polishing wheel. Each polishing surface on the second polishing wheel can be shaped to substantially conform to a corresponding portion of the surface of the curved edge of the molded part. The polishing can be carried out by contacting the polishing surfaces of the second polishing wheel to the abraded surface, alternately in the first direction and in a second direction opposite to the first direction. In an embodiment, molded parts can be formed from an injection molded thermoplastic compound. The surface of the three dimensional curved edge of the molded part to be polished can include a parting line surface defect. The parting line surface defect can have a vertical displacement greater than 10 microns approximately perpendicular to the surface of the curved edge of the molded part.
In an embodiment, the polishing wheel can be maintained at a constant rotational speed by a controller when contacting the surface of the curved edge of the molded part. The polished surface of the curved edge of the molded part can be visually smoothly uniform in reflective appearance.
In another embodiment an apparatus for polishing a three dimensional curved edge of a molded part is described. The apparatus can include two polishing wheels, and two positioning assemblies to contact surfaces of the two polishing wheels to a surface of the curved edge of the molded part. Each polishing wheel can include a polishing surface shaped to substantially conform to a portion of the surface of the curved edge of the molded part. The first positioning assembly can be configured to contact the polishing surface of the first polishing wheel to the surface of the curved edge of the molded part repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel, thereby abrading the surface of the curved edge of the molded part to a first smoothness. The second positioning assembly can be configured to contact the polishing surface of the second polishing wheel to the abraded surface of the curved edge of the molded part alternating in the first direction and a second direction opposite to the first direction, thereby polishing the abraded surface of the curved edge of the molded part to a second smoothness.
In another embodiment, each polishing wheel of an apparatus for polishing a curved edge of a molded part can include a second polishing surface shaped to substantially conform to a second portion of the surface of the curved edge of the molded part. The first positioning assembly can be configured to contact the second polishing surface of the first polishing wheel to abrade the second portion of the surface of the curved edge of the molded part repeatedly in the first direction concurrent with the rotational spinning direction of the first polishing wheel, thereby abrading the second portion of the surface of the curved edge of the molded part to a first smoothness. The second positioning assembly can be configured to contact the second polishing surface of the second polishing wheel to the abraded second surface of the curved edge of the molded part alternating in the first direction and a second direction opposite to the first direction, thereby polishing the abraded second surface of the curved edge of the molded part to a second smoothness.
In yet another embodiment, a computer readable medium for storing program code executed by a processor for controlling a computer aided manufacturing operation for polishing a three dimensional curved edge of a molded part is disclosed. The computer program code can control abrading and polishing a surface of the curved edge of the molded part. Abrading can be accomplished by contacting a polishing surface of a first polishing wheel to the curved edge of the molded part repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel. The polishing surface of the first polishing wheel can be shaped to substantially conform to a portion of the surface of the curved edge of the molded part. Polishing can be accomplished by contacting a polishing surface of a second polishing wheel to the abraded surface of the curved edge of the molded part, alternately in the first direction and in a second direction opposite to the first direction. The polishing surface of the second polishing wheel can also be shaped to substantially conform to the portion of the surface of the curved edge of the molded part.
In a further embodiment, the computer program code for controlling the computer aided manufacturing operation for polishing at least two surfaces of the three dimensional curved edge of the molded part is disclosed. The computer program code can control abrading and polishing the at least two surfaces using different surfaces on different polishing wheels. The computer program code can direct a first polishing wheel to abrade at least two different surfaces shaped to conform to two different portions of the surface of the curved edge of the molded part. The computer program code can also control a second polishing wheel to polish the at least two different surfaces shaped to conform to the two different portions of the surface of the curved edge of the molded part.
In an embodiment, the computer program code can maintain the polishing wheels at a constant rotational speed when in contact with the surfaces of the curved edge of the molded part. The computer program code can also vary the position of the polishing wheels with respect to the surfaces of the curved edge of the molded part while abrading or polishing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

FIG. 1A illustrates a top view of a portable computing device including a molded thermoplastic casing.

FIG. 1B illustrates a front view of the portable computing device of FIG. 1A.

FIG. 2 illustrates a cross section of the molded thermoplastic casing of FIG. 1B including a shaped geometric edge.

FIG. 3A illustrates a cross section of a polishing wheel with surfaces that conform to the cross section of the molded thermoplastic casing of FIG. 2.

FIG. 3B illustrates a magnified view of a surface defect on the shaped geometric edge of the thermoplastic casing of FIG. 2.

FIG. 3C illustrates a top view of the polishing wheel and two directions of movement of the polishing wheel relative to the surface defect on the shaped geometric edge of the thermoplastic casing of FIG. 2.

FIG. 3D illustrates a representative embodiment of a polishing wheel including two surfaces and a representative embodiment of a molded thermoplastic casing including a shaped geometric edge.

FIG. 3E illustrates the polishing wheel and the thermoplastic casing of FIG. 3D with one of the surfaces of the polishing wheel in contact with the thermoplastic casing.

FIG. 4A illustrates three front and side views of the surface of the shaped geometric edge of the thermoplastic casing of FIG. 2 with different polishing results.

FIG. 4B illustrates a surface defect on an edge of an unpolished thermoplastic casing and a second thermoplastic casing including a polished edge with a surface defect removed.

FIG. 4C illustrates two thermoplastic casings including polished edges using two different polishing methods.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention relates generally to the polishing of a three dimensional curved edge of a molded object. More particularly, a method and an apparatus are described for polishing the edge of an object, formed using an injection molded thermoplastic compound, to a visually smooth and consistent reflective appearance.
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention.
High volume manufactured portable electronics devices can include injection molded thermoplastic parts with various geometrically shaped surfaces. Thermoplastic compounds can provide a lightweight moldable material that exhibits desirable properties, such as strength, heat resistance and structural flexibility well suited for casings of portable electronic devices. A representative thermoplastic compound can include PC/ABS (polycarbonate acrylonitrile butadience styrene) polymer, although other thermoplastic compounds can be used. Both the tactile and visual appearance of a portable electronics device can enhance the desirability of the device to the consumer. A cosmetic outer layer formed from a thermoplastic blend can be polished to a desired reflective appearance while retaining an aesthetically pleasing shape. In some embodiments, a continuously smooth shape having a uniformly visually smooth appearance can be desired.
Prior to post-process finishing, injection molded thermoplastic parts can include surface defects, e.g. parting lines, at seams where individual sections of a mold, in which the thermoplastic molded part is formed, come apart. Parting lines can occur for numerous reasons, e.g. because the edges of two individual sections of the mold cannot perfectly align or because the surface of the mold can become slightly damaged or wear over time during repeated use in high volume manufacturing. The molding process can also require high pressure injection of a thermoplastic compound which can cause slight deviations in the positions of the mold sections. It is desirable to post-process finish the surface of molded thermoplastic parts so that the parting lines cannot be detected tactilely or visually.
FIG. 1A illustrates a top view of a portable electronics device 101 including markings of several possible parting lines 102 on a molded thermoplastic top casing of the portable electronics device 101. FIG. 1B illustrates a front view of the portable electronics device 101 of FIG. 1A including a molded thermoplastic top casing 105, a molded thermoplastic center casing 103 and a base 106. The top casing 105 and the center casing 103 can be formed separately in two different injection molds, each with differently located parting lines in general, even though a parting line 107 of the center casing 103 aligns with the parting line 102 of the top casing 105 as illustrated in FIG. 1B. Each of the parting lines of the center casing 103 can be removed by appropriate polishing. The three-dimensional edge 104 of the center casing can have a specific complex geometric shape that provides an aesthetically pleasing appearance for the portable electronics device 101. FIG. 2 illustrates a cross section 203 of the center casing 103 (along the dashed line and viewed in the direction A in FIG. 1A) including a complex shaped edge 206 (cross section of edge 104 of FIG. 1B). The complex shaped edge 206 can include three distinct regions, a corner region 205 where the side meets the top, an upper region 202 of the side and a lower region 204 of the side. The three different regions 202, 204 and 205 can be finished using one or more different polishing methods. In particular, the corner region 205 can be finished to produce an unsharpened rounded edge using a conventional technique. Such techniques are well known to those skilled in the art. The upper region 202 and the lower region 204 of the complex shaped edge can be finished to achieve a tactilely and visually uniformly smooth reflective surface using a new polishing method as described herein.
Conventional polishing techniques applied to a thermoplastic molded part that includes a complex three-dimensional geometric shape, such as edge 104 of the center casing 103 of FIG. 1B, can result in a visually non-uniform surface, even when the polished surface provides a smooth tactile finish. Highly reflective, glossy polished surfaces can reveal even minute irregularities in surface finish. A visually uniformly smooth, reflective polished surface can be achieved using two stages of polishing, each using different directional movements of one or more polishing wheels. It has been found that shaping the surface of the polishing wheel to mirror the shape of the edge can improve the final resulting surface appearance.
FIG. 3A illustrates a cross section of a polishing wheel 306 having an edge with two abrasive surfaces 302 and 303 that are shaped to match to portions of the complex three dimensional edge 104 of the center casing 103 of FIG. 1B. An end cross section 301 of the three dimensional edge 104 (i.e. an end portion of the cross section edge 206 of FIG. 2) can include a convex upper region 202 and a convex lower region 204. The concave surface 302 of the polishing wheel 306 can match to the convex upper region 202 of the edge 301, while the concave surface 303 of the polishing wheel 306 can match to the convex lower region 204 of the edge 301. Depending on the geometry of a complex three-dimensional edge, a surface can be polished using one or more surfaces of a polishing wheel, where each surface can polish a different region of an edge. Lower curvature edges can use one polishing surface of the polishing wheel 306, while higher curvature edges can use two or more polishing surfaces of the polishing wheel 306.
In a representative embodiment, the polishing wheel 306 can be turned in a rotational direction 305 along a longitudinal axis of the edge 301 that it polishes. To align each of the surfaces of the edge 301 of the center casing 103 to a surface of the polishing wheel 306, either the polishing wheel 306 or the center casing 103 can be positioned appropriately in an assembly fixture. In an embodiment, the center casing 103 can be fixed on a stand, while the polishing wheel 306 can be moved along one or more axes in three dimensions and tilted at an angle to align a surface of the polishing wheel 306 to a portion of an edge of the center casing 103. The position and rotational velocity of the polishing wheel 306 can be controlled by a computer to maintain a desired position and consistent speed when contacting a surface of the center casing 103.
Both the upper region 202 and the lower region 204 of the center casing 103, formed of an injection molded thermoplastic compound, can contain surface defects along boundaries where separate portions of a mold in which the center casing 103 can be formed come apart. As shown in FIG. 3B, a surface defect 308 can include a change in vertical displacement approximately perpendicular to the surface edge. A surface defect can be at least 10 microns high and typically can be approximately 20 microns high. This relatively small displacement can be visible as a discrete line surface defect 308 across the edge of the molded center casing 103 as shown by a side view 401 in FIG. 4A. To remove the discrete line surface defect 308 from the edge of the molded center casing 103, a two stage polishing method can be used, a first abrading stage to eliminate the vertical displacement and a second polishing stage to remove any residual visible variation in surface reflectance along the edge of the center casing 103. Surface defects up to approximately 30 microns high can be removed using the two stage polishing method described herein.
As illustrated by FIG. 3C, the polishing wheel 306 can be turned in a rotational direction 305 about a central rotational axis 304 and moved longitudinally in two directions 309 and 310 along regions 202 or 204 of the edge 206 of the molded part when polishing their surfaces. For clarity, FIG. 3C is shown as a two-dimensional cross section of a three-dimensional surface with the polishing wheel moving along one axis. It should be understood that the polishing wheel 306 also can be positioned along the two other axes perpendicular to the directions 309/310 shown, as well as tilted as needed to match a surface of the polishing wheel 306 to the edge 104. The three-dimensional edge 104 may be curved, and the polishing wheel 306 may be positioned to follow along the three-dimensional edge 104 when polishing.
We will describe polishing the upper region 202 of the edge cross section 301; however the same method described can apply to polishing the lower region 204. In the first abrading stage of polishing the upper region 202, the surface defect 308 can be reduced in height by contacting the rotationally spinning polishing wheel 306 along the direction 309 that points into the face of the surface defect 308. The rotating polishing wheel 306 can contact the upper region 202 at a portion of the surface 311 below the surface defect 308 and traverse longitudinally along the edge into the face of the surface defect 308 and then along a portion of the surface 312 above the surface defect 308. Contacting the surface repeatedly can abrade the surface defect 308 to remove the change in vertical displacement thereby producing an even surface.
The rotating polishing wheel can be moved laterally to sever contact with the portion of the surface 312 and reoriented to start the wheel at the portion of the surface 311 below the surface defect 308 for each successive pass during the first abrading stage of polishing. By removing the surface defect 308 uni-directionally during the first abrading stage of polishing rather than bi-directionally, as can be used conventionally, the surface of the edge can be polished in the second stage to achieve a desired visually uniformly smooth appearance. In the second polishing stage of polishing, the rotating polishing wheel 306 can contact the surface of the edge bi-directionally in both the first direction 309 and a second direction 310 longitudinally along the edge. In some embodiments a second rotating polishing wheel can be used have a finer abrasive surface than the coarser abrasive surface of the first rotating polishing wheel 306 used to abrade the surface defect. The second polishing wheel can be similarly shaped to match geometrically to the portion of the edge to which it would contact. The first polishing wheel 306 can be used to produce a first smoothness on the surface, while the second polishing wheel can be used to produce a second finer smoothness on the surface. The surface having a first smoothness can be tactilely smooth but visually non-uniform, while the second surface having a finer smoothness can be additionally visually uniformly smooth in appearance.
FIG. 3D illustrates a representative embodiment of a polishing wheel 314 including a concave surface 315 that conforms to the convex shape of a portion of the surface of the complex geometric edge 316 on a representative embodiment of a thermoplastic casing 313 for a portable computing device. FIG. 3E illustrates the concave surface 315 of the polishing wheel 314 contacting the portion of the surface of the complex geometric edge 316 of the thermoplastic casing 313. The polishing wheel 314 can move laterally along the edge 316 when abrading or polishing the surface of the edge 316 of the thermoplastic casing 313. The polishing wheel 314 of FIG. 3D can correspond to an embodiment of the polishing wheel 306 of FIG. 3A including the concave surface 315 corresponding to an embodiment of the convex surface 302. Similarly the complex geometric edge 316 of the thermoplastic casing 313 can correspond to an embodiment of the portion of the surface 202 that conforms to the surface of the polishing wheel.
FIG. 4A illustrates two different surface appearances that can result when polishing a complex geometrically shaped edge to remove a surface defect 308. A uniform surface appearance 405 with no visible variations can result when using the method described above. A non-uniform surface appearance 403 can result when using a polishing method that abrades the surface bi-directionally during the first stage rather than uni-directionally as described herein, even when followed by a bi-directional polishing during the second stage. By abrading the surface defect 308 in one direction only during the first stage of polishing, the resulting polished surface edge can change height approximately linearly with a uniform surface appearance 405, while abrading the surface bi-directionally can result in a polished surface edge having a “dip” resulting in a visually non-uniform appearance 403.
FIG. 4B illustrates the surface defect 308 on a surface edge of a first thermoplastic casing 406 which can be visible before polishing and can be visually uniformly smooth after polishing as shown by the surface 405 on the second thermoplastic casing 407. FIG. 4C illustrates a third thermoplastic casing 408 with a surface of a geometric edge abraded and polished bi-directionally resulting in a visually non-uniform surface 403. While the visually non-uniform surface 403 on the thermoplastic casing 408 may be tactilely smooth, the non-uniform surface 403 reflects light irregularly. Using the method described herein instead to abrade the surface uni-directionally followed by polishing the surface bi-directionally, the surface defect 308 of a fourth thermoplastic casing 409 is completely removed providing a visually uniformly smooth surface 405 as illustrated in FIG. 4C.
One embodiment of the polishing method described herein can use two different polishing wheels to remove a surface defect on a complex geometric shaped edge, one polishing wheel to abrade the surface and a second polishing wheel to polish the surface. The polishing wheels can include multiple surfaces, each shaped to conform to a different portion of the surface of the complex geometric shaped edge to be polished. The use of two polishing wheels in the embodiment is not intended to limit the invention. The number of polishing wheels and the number of surfaces on each polishing wheel can vary based on the size of the defect and the complex geometric shape of the edge to be polished. More complex geometric shaped edges can use one or more surfaces on one or more wheels. In some embodiments a single polishing wheel can be used, such as when the surface defect is less than 15 microns in height.
In high volume manufacturing it is also desired to provide consistency between multiple parts even as the polishing surfaces 302 and 303 of the polishing wheel 306 can change with repeated use (and the unpolished edges of different molded parts can vary as well). The polishing wheel can be connected to a controller that measures the rotational velocity (in terms of revolutions per minute, or RPM) of the polishing wheel and maintains the rotational velocity within a specified range when contacting the surface of the molded part by controlling the exact position of the rotational axis 304 of the polishing wheel in three dimensions with respect to the molded part. The angular tilt of the polishing wheel can also be controlled. By controlling the polishing to use a constant rotational velocity even as the abrasive surfaces of the polishing wheel change shape can provide consistency in the resulting surface appearance of the polished molded part.
It should be noted that RPM can be set according to material type. For example, for example, blends of poly-carbonate (PC) and acrylonitrile butadiene styrene (ABS), or PC/ABS, has a lower melting point than PC alone and thus RPM should be reduced to lower the chance of overheating and damaging the unit. Otherwise a cooling system can be used such as a cooled holding fixture or air conditioning.
The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line used to fabricate thermoplastic molded parts. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, optical data storage devices, and carrier waves. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

1. A method for polishing a curved edge of a molded part, the method comprising:

abrading a first surface of the curved edge of the molded part by contacting a first polishing surface on a first polishing wheel to the first surface of the curved edge of the molded part repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel, the first polishing surface shaped to substantially conform to a portion of the first surface of the curved edge of the molded part; and

polishing the abraded first surface of the curved edge of the molded part by contacting a second polishing surface on a second polishing wheel to the abraded first surface of the curved edge of the molded part, alternating contact in the first direction and in a second direction opposite to the first direction, the second polishing surface shaped to substantially conform to the portion of the first surface of the curved edge of the molded part.

2. The method of claim 1 further comprising:

abrading a second surface of the curved edge of the molded part by contacting a third polishing surface on the first polishing wheel to the second surface of the curved edge of the molded part repeatedly in the first direction concurrent with the rotational spinning direction of the first polishing wheel, the third polishing surface shaped to substantially conform to a portion of the second surface of the curved edge of the molded part; and

polishing the abraded second surface of the curved edge of the molded part by contacting a fourth polishing surface on the second polishing wheel to the abraded second surface of the curved edge of the molded part, alternating contact in the first direction and in the second direction opposite to the first direction, the fourth polishing surface shaped to substantially conform to the portion of the second surface of the curved edge of the molded part.

3. The method of claim 1 wherein the molded part is formed from an injection molded thermoplastic.

4. The method of claim 1 wherein the first surface of the curved edge of the molded part comprises a parting line surface defect.

5. The method of claim 4 wherein the parting line surface defect comprises a step having a displacement greater than 10 microns perpendicular to the first surface of the curved edge of the molded part.

6. The method of claim 5 wherein the first direction of abrading is into a face of the parting line surface defect.

7. The method of claim 1 further comprising:

maintaining the first polishing wheel at a constant rotational speed when in contact with the first surface of the curved edge of the molded part.

8. The method of claim 7 wherein the maintaining comprises varying a position of the first polishing wheel with respect to the first surface of the curved edge of the molded part while abrading or polishing.

9. The method of claim 1 wherein the polished first surface of the curved edge of the molded part is visually smoothly uniform in reflective appearance.

10. An apparatus for polishing a curved edge of a molded part, the apparatus comprising:

a first polishing wheel comprising a first polishing surface shaped to substantially conform to a portion of a first surface of the curved edge of the molded part;

a second polishing wheel comprising a second polishing surface shaped to substantially conform to the portion of the first surface of the curved edge of the molded part;

a first positioning assembly configured to contact the first polishing surface of the first polishing wheel to the first surface of the curved edge of the molded part repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel to abrade the first surface of the curved edge of the molded part to a first smoothness; and

a second positioning assembly configured to contact the second polishing surface of the second polishing wheel to the first surface of the curved edge of the molded part alternately in the first direction and in a second direction opposite to the first direction to polish the abraded first surface of the curved edge of the molded part to a second smoothness.

11. The apparatus of claim 10 further comprising:

the first polishing wheel further comprises a third polishing surface shaped to substantially conform to a portion of a second surface of the curved edge of the molded part;

the second polishing wheel further comprises a fourth polishing surface shaped to substantially conform to the portion of the second surface of the curved edge of the molded part;

the first positioning assembly further configured to contact the third polishing surface to the second surface of the curved edge of the molded part repeatedly in the first direction concurrent with the rotational spinning direction of the first polishing wheel to abrade the second surface of the curved edge of the molded part to the first smoothness; and

the second positioning assembly further configured to contact the fourth polishing surface to the second surface of the curved edge of the molded part alternately in the first direction and in the second direction opposite to the first direction to polish the second surface of the curved edge of the molded part to the second smoothness.

12. The apparatus of claim 10 wherein the molded part is formed from an injection molded thermoplastic.

13. The apparatus of claim 10 wherein the unpolished first surface of the curved edge of the molded part comprises a parting line surface defect.

14. The apparatus of claim 13 wherein the parting line surface defect comprises a step having a displacement greater than 10 microns perpendicular to the first surface of the curved edge of the molded part.

15. The apparatus of claim 14 wherein the first direction of abrading is into a face of the parting line surface defect.

16. The apparatus of claim 10 further comprising

a controller to maintain a constant rotational speed of the first polishing wheel when in contact with the first surface of the curved edge of the molded part.

17. The apparatus of claim 10 wherein the second smoothness is visually smoothly uniform in reflective appearance.

18. A computer readable medium for storing computer program code executed by a processor for controlling a computer aided manufacturing operation for polishing a curved edge of a molded part, the computer readable medium comprising:

computer program code for abrading a first surface of the curved edge of the molded part by contacting a first polishing surface on a first polishing wheel to the first surface of the curved edge of the molded part repeatedly in a first direction concurrent with a rotational spinning direction of the first polishing wheel, the first polishing surface shaped to substantially conform to a portion of the first surface of the curved edge of the molded part; and

computer program code for polishing the abraded first surface of the curved edge of the molded part by contacting a second polishing surface on a second polishing wheel to the abraded first surface of the curved edge of the molded part, alternating contact in the first direction and in a second direction opposite to the first direction, the second polishing surface shaped to substantially conform to the portion of the first surface of the curved edge of the molded part.

19. The computer readable medium of claim 18 further comprising:

computer program code for abrading a second surface of the curved edge of the molded part by contacting a third polishing surface on the first polishing wheel to the second surface of the curved edge of the molded part repeatedly in the first direction concurrent with the rotational spinning direction of the first polishing wheel, the third polishing surface shaped to substantially conform to a portion of the second surface of the curved edge of the molded part; and

computer program code for polishing the abraded second surface of the curved edge of the molded part by contacting a fourth polishing surface on the second polishing wheel to the abraded second surface of the curved edge of the molded part, alternating contact in the first direction and in the second direction opposite to the first direction, the fourth polishing surface shaped to substantially conform to the portion of the second surface of the curved edge of the molded part.

20. The computer readable medium of claim 18 further comprising:

computer program code for maintaining the first polishing wheel at a constant rotational speed when in contact with the first surface of the curved edge of the molded part.

21. The computer readable medium of claim 20 wherein the maintaining comprises varying a position of the first polishing wheel with respect to the first surface of the curved edge of the molded part while abrading or polishing.