Raised island abrasive, lapping apparatus and method of use Number:7,520,800 from the United States Patent and Trademark Office (PTO) owispatent

Title: Raised island abrasive, lapping apparatus and method of use

Abstract: Flexible abrasive sheet materials having annular bands of precise height flat-topped raised island structures that are coated with a mono layer of abrasive particles or abrasive agglomerates, processes for manufacture of the abrasive sheet materials, processes for using the abrasive sheeting in high speed lapping/abrading processes, and apparatus for using the abrasive sheeting are described. The process for manufacturing the abrasive sheeting provides an economical method for providing an improved configuration of abrasive sheeting that can provide precisely flat workpiece surfaces that are also highly polished.

Patent Number: 7,520,800 Issued on 04/21/2009 to Duescher

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Inventors:	Duescher; Wayne O. (Roseville, MN)
Appl. No.:	10/816,275
Filed:	August 16, 2004

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	10824107	Apr., 2004
	10418257	Apr., 2003

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Current U.S. Class:	451/527 ; 451/530
Current International Class:	B24D 3/28 (20060101)
Field of Search:	451/526,527,529,530,550,56,41

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References Cited [Referenced By]

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Primary Examiner: Rose; Robert
Attorney, Agent or Firm: Mark A. Litman & Associates, P.A.

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATION

This invention is a continuation-in-part of U.S. patent application Ser. No. 10/824,107, filed Apr. 14, 2004, which in-turn is a a continuation-in-part of U.S. patent application Ser. No. 10/418,257, filed Apr. 16, 2003, now abandoned, and which applications are incorporated herein by reference.

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Claims

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What is claimed:

1. A flexible, continuous abrasive sheet web comprising a flexible polymeric sheet or flexible metal backing web sheet having an full web width array of raised abrasive structures, the abrasive structures comprising islands of a first structural material having a raised flat top surface, the top surface having at least a monolayer of abrasive particles or abrasive agglomerates supported in a polymeric resin, wherein the heights of all islands measured from the raised flat top surface of the abrasive coated islands to an island-side flat surface of the web backing sheet have a standard deviation in abrasive particle coated islands height of less than 0.01 mm.

2. The abrasive web of claim 1 where the full web width array of islands is made up of circular island shapes.

3. The flexible abrasive web of claim 1 wherein the island structures are top coated with a monolayer of diamonds or other hard abrasive particles or abrasive agglomerates at least 7 up to 400 micrometers in average particle diameter.

4. The flexible abrasive web of claim 1 wherein the island structures are top coated with a slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin.

5. The flexible abrasive web of claim 1 wherein the raised island structure material comprises a particle filled polymer resin or a non-particle filled polymer resin.

6. The island structures of claim 5 wherein the island material flat top surface is formed by mold plates or the surface is formed by mold rolls or the surface is machined or the surface is abrasively ground to a precise raised island structure total web thickness wherein the web thickness is measured from the flat top surface of the non-abrasive coated island material structure to the bottom support surface of the web backing sheet.

7. A process of applying a resin coating to form the at least monolayer of the abrasive web of claim 1 wherein top exposed surfaces of the island foundation structures are precision thickness polymeric resin coated by a web sheet transfer coating process where a liquid-state resin coated transfer web sheet is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the resin wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the resin within the island areas of contact attached as a uniform layer on the island top surfaces, after which abrasive particles or abrasive agglomerates are deposited onto the wet resin coated islands wherein the particles or agglomerates are supported in the polymeric resin.

8. A process of applying a resin coating to form the at least monolayer of the abrasive web of claim 1 wherein top exposed surfaces of the island foundation structures are precision thickness abrasive slurry resin mixture coated by a web sheet transfer coating process where a liquid-state abrasive resin slurry mixture coated transfer web sheet, the slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin, is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the slurry mixture wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the abrasive slurry mixture within the island areas of contact attached as a uniform layer on the island top surfaces.

9. A flexible, continuous abrasive sheet web comprising a flexible polymeric sheet or flexible metal backing web sheet having an full web width array of raised abrasive structures, the abrasive structures comprising islands of a first structural material having a raised flat top surface, the top surface having at least a monolayer of abrasive particles or abrasive agglomerates supported in a polymeric resin, wherein the total web thickness of all islands measured from the flat top surface of the abrasive coated islands to an upper surface of the bottom support surface of the backing sheet has a standard deviation in abrasive particle coated islands thickness of less than 0.03 mm.

10. The abrasive web of claim 9 where the full web width array of islands is made up of circular island shapes.

11. The flexible abrasive web of claim 9 wherein the island structures are top coated with a monolayer of diamonds or other hard abrasive particles or abrasive agglomerates at least 7 up to 400 micrometers in average particle diameter.

12. The flexible abrasive web of claim 9 wherein the island structures are top coated with a slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin.

13. The flexible abrasive web of claim 9 wherein the raised island structure material comprises a particle filled polymer resin or a non-particle filled polymer resin.

14. The island structures of claim 13 wherein the island material flat top surface is formed by mold plates or the surface is formed by mold rolls or the surface is machined or the surface is abrasively ground to a precise raised island structure total web thickness wherein the web thickness is measured from the flat top surface of the non-abrasive coated island material structure to the bottom support surface of the web backing sheet.

15. A process of applying resin coating to form the at least monolayer of the abrasive web of claim 9 wherein top exposed surfaces of the island foundation structures are precision thickness polymeric resin coated by a web sheet transfer coating process where a liquid-state resin coated transfer web sheet is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the resin wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the resin within the island areas of contact attached as a uniform layer on the island top surfaces, after which abrasive particles or abrasive agglomerates are deposited onto the wet resin coated islands wherein the particles or agglomerates are supported in the polymeric resin.

16. A process of applying abrasive slurry to form the at least monolayer coating the abrasive web of claim 9 wherein top exposed surfaces of the island foundation structures are precision thickness abrasive slurry resin mixture coated by a web sheet transfer coating process where a liquid-state abrasive resin slurry mixture coated transfer web sheet, the slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin, is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the slurry mixture wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the abrasive slurry mixture within the island areas of contact attached as a uniform layer on the island top surfaces.

17. A flexible, continuous abrasive sheet web comprising a flexible polymeric sheet or flexible metal backing web sheet having an full web width array of raised abrasive structures, the abrasive structures comprising islands of a first structural material having a raised flat top surface, the flat top surface having at least a monolayer of abrasive particles or abrasive agglomerates supported in a polymeric resin, where the total thickness of all islands measured from the flat top surface of the abrasive coated islands to the bottom support surface of the backing sheet has a standard deviation in abrasive particle coated islands thickness of less than 80% of the average diameter of the abrasive particles or abrasive agglomerates.

18. The abrasive web of claim 17 where the full web width array of islands is made up of circular island shapes.

19. The flexible abrasive web of claim 17 wherein the island structures are top coated with a monolayer of diamonds or other hard abrasive particles or abrasive agglomerates at least 7 up to 400 micrometers in average particle diameter.

20. The flexible abrasive web of claim 17 wherein the island structures are top coated with a slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin.

21. The flexible abrasive web of claim 17 wherein the raised island structure material comprises a particle filled polymer resin or a non-particle filled polymer resin.

22. The island structures of claim 21 wherein the island material flat top surface is formed by mold plates or the surface is formed by mold rolls or the surface is machined or the surface is abrasively ground to a precise raised island structure total web thickness wherein the web thickness is measured from the flat top surface of the non-abrasive coated island material structure to the bottom support surface of the web backing sheet.

23. A process of applying resin to form the at least monolayer coating of the abrasive web of claim 17 wherein top exposed surfaces of the island foundation structures are precision thickness polymeric resin coated by a web sheet transfer coating process where a liquid-state resin coated transfer web sheet is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the resin wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the resin within the island areas of contact attached as a uniform layer on the island top surfaces, after which abrasive particles or abrasive agglomerates are deposited onto the wet resin coated islands wherein the particles or agglomerates are supported in the polymeric resin.

24. A process of applying abrasive slurry to form the at least monolayer coating of the abrasive web of claim 17 wherein top exposed surfaces of the island foundation structures are precision thickness abrasive slurry resin mixture coated by a web sheet transfer coating process where a liquid-state abrasive resin slurry mixture coated transfer web sheet, the slurry mixture comprising abrasive particles or abrasive agglomerates and a polymer resin, is pressed into conformation in uniform contact with the nominally flat top surfaces of the full web width array of raised islands until the slurry mixture wets the full top surface area of each island, after which wetting the coated transfer web sheet is removed, leaving at least 5% of the abrasive slurry mixture within the island areas of contact attached as a uniform layer on the island top surfaces.

25. The flexible abrasive web of claim 17 wherein the continuous web is shape-cut to form circular abrasive disks.

26. The flexible abrasive web of claim 17 wherein the continuous web is shape-cut to form rectangular abrasive sheets.

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Description

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BACKGROUND OF THE ART

1. Field of the Invention

The present invention relates to a new class of precision flat and precision thickness abrasive media, processes for using the abrasive media, and apparatus for practicing processes with the abrasive media. The media are thin flexible abrasive sheeting used for grinding, flat lapping, polishing, finishing or smoothing of workpiece surfaces. In particular, the present invention relates to such processes and apparatus that use removable or replaceable sheeting having abrasive particle or abrasive agglomerate coated raised islands formed in annular bands that are able to operate at high surface speeds, and apparatus that secures the abrasive sheeting to a supporting platen. The support may optionally move the sheeting at those high speeds (preferably without the use of adhesive layers between the sheeting and the support). The apparatus, processes and abrasive media provide a high degree of control over the contact area or contact plane of the abrasive sheeting and the article that is to be lapped, polished, finished or smoothed. Uniform wear of the abrasive is experienced across the full annular band of abrasive material that allows a continuously flat abrasive surface to be presented to a workpiece. Also, the disks having narrow annular band of abrasive reduces areas of uneven wear material removal rates compared to conventional disks. Abrasive articles including sheets, long strips, and circular disks without annular bands all can have abrasive particle coated raised island structures that are attached to flexible backing materials can all be manufactured with abrasive island surfaces that are located in a common plane that is precisely parallel to the back mounting surface of the backing sheet. All of these abrasive articles having thin coatings of abrasive particles or abrasive agglomerates can be used at high and slow abrading surface speeds where all or most of the abrasive particles are utilized in grinding or lapping flat workpiece surfaces. Hydroplaning of the workpiece does not occur as a large proportion of the abrasive coolant water can pass between the raised island structures. The precision thickness control of the backing sheet abrasive articles assures that all of the abrasive material contacts a flat workpiece.

2. Background of the Invention

High speed lapping and grinding using fixed abrasive on sheet disks for both rough grinding and smooth polishing is now a practical reality. Most performance issues relate to two primary concerns, 1) hydroplaning caused by water lubricant and 2) vibrations created by grinding machine component dimensional inaccuracies and thickness variations of abrasive disks along their tangential surfaces. Unique answers for the first problem of hydroplaning have been defined, numerous solutions have been created and most of these solutions have been implemented or evaluated.

High quality abrasive article sheets that have certain important characteristics that are necessary for high speed flat lapping are not presently available in the marketplace. The sheets should be of a sufficient dimension (e.g., at least a 6 inch (15.2 cm) diameter, at least a 12 inch (30.5 cm) diameter, or at least an 18 inch (45.7 cm) or larger diameter, and have islands comprising abrasive structures (preferably secured to a substrate and preferably arranged in an annular band). The structures have an uppermost abrasive surface that is extremely flat and of uniform thickness. Conventional flat surface grinding or lapping platens are set up to use the full surface area of a circular shaped flat flexible sheet of abrasive. However, the abrasive contact surface speed of the rotating disk varies from a maximum speed at the outer radius to zero at the innermost center at the disk (where the radius is zero). The grinding material removal rate is roughly proportional to the surface speed of the moving abrasive, so that most of the grinding or lapping action, and the most efficient grinding or lapping action occurs at the outer portion of a rotating disk. Not only is the inside portion of the abrasive disk not used to remove workpiece surface material, but also this portion of the abrasive is not worn down by the workpiece, resulting in a shallow, cone shape of the abrasive disk surface. This uneven wear continues with usage of the disk, with the cone angle progressively increasing to a sharper angle. This cone angle is translated to the surface of the workpiece that is intended for rigid axis lapping of a workpiece and prevents precision flatness grinding of the workpiece, transferring uneven surface contour to the workpiece surface. An effective answer to this uneven wear is to create an abrasive disk with a narrow annular band of abrasive material (at the outer edges of the annulus), allowing the abrasive to wear down more evenly across the full surface of the abrasive disk (which is essentially the annulus, not a continuous circular surface) as the disk is used. This type of media is not available commercially and probably would not be with present production methods. This is because the continuous method of manufacturing abrasive disks cannot technically or economically produce the necessary annular configuration. Presently, an important method of manufacturing a circular abrasive sheets is to coat a continuous web backing with diamond particles or abrasive agglomerates to form a coated sheet material and then to punch out round disks from the coated sheet material. Effectively, most of the expensive inner surface area of these disks is wasted. If a conventional coated disk is used with a platen having an outer raised annular ring, then all of the abrasive coated area located at a radius inside the ring is not used as it does not contact the workpiece surface.

Furthermore, it is not practical to punch out radial rings from a coated web sheet for a number of reasons. First, there is not necessarily a ready market for the smaller disk that remains left over from the center punch-out for the annular ring. Also, there is a large waste of coated web material left over between the circular disks that are cut out, even with proficient "nesting" of the circular rings. Furthermore, the annular ring of coated abrasives made of thin 0.005 inch (0.127 mm) thick polyester web has limited structural body strength for handling and mounting so that it cannot be practically used on a platen without creating many problems, including the problem that water and grinding swarf tend to collect under the inside edge of the loose annular ring sheet. Furthermore, round or bar raised-abrasive islands having a thin top coating of expensive diamond particles are needed to compensate for hydroplaning affects at high surface speed lapping. The only island type of abrasive media now available which can reduce hydroplaning is a diamond particle metal plated Flexible Diamond Products abrasive sheet supplied by the 3M Company (Minnesota Mining and Manufacturing Co.). Disk shapes of this abrasive media is created by cutting circular shapes from a rectangular sheet of this material. However, due to the manufacturing process of this product, the product is commercially limited by at least two counts. First, each disk has large variations in flatness, or thickness, and, due to its unique construction, cannot be made flat enough to use effectively at high speeds where the unevenness is accentuated by the speed. Second, the Flexible Diamond Product abrasive sheet is constructed from plated diamonds which have been unable to produce a smooth polished finish.

Another widely used product from 3M Company is the pyramid shaped Trizact.RTM. abrasive which helps with hydroplaning effects. However, it is only practical for this product to be created with inexpensive abrasive media such as aluminum oxide which tends to wear fast and unevenly across its surface. Again, this is a continuous web type of product which does to have the capability of having precise thickness control.

Two common types of abrasive articles that have been utilized in polishing operations include bonded abrasives and coated abrasives. Bonded abrasives are formed by bonding abrasive particles together, typically by a molding process, to form a rigid abrasive article. Coated abrasives have a plurality of abrasive particles or abrasive agglomerates bonded to a backing by means of one or more binders. Coated abrasives utilized in polishing processes are typically in the form of endless belts, tapes, or rolls which are provided in the form of a cassette. Examples of commercially available polishing products include "IMPERIAL" Microfinishing Film (hereinafter IMFF) and "IMPERIAL" Diamond Lapping Film (hereinafter IDLF), both of which are commercially available from Minnesota Mining and Manufacturing Company (3M Company), St. Paul, Minn.

Structured abrasive articles have been developed for common abrasive applications. Pieper et al., U.S. Pat. No. 5,152,917 discloses a structured abrasive article containing precisely shaped abrasive composites. These abrasive composites comprise a plurality of abrasive grains and a binder. Mucci, U.S. Pat. No. 5,107,626, discloses a method of introducing a pattern into a surface of a workpiece using a structured abrasive article.

A new class of large diameter precise thickness disks which have an annular ring of raised islands coated with a thin coat of diamond abrasive particles or abrasive agglomerates is required for high speed lapping which requires a completely different manufacturing technique than has been employed in the past by the abrasives industry. The new batch type of processing required to produce these disks must be practical and cost effective. Eventually, this batch process of manufacturing a abrasive disk as a separate item can be converted partially or wholly into a continuous web-line process when the product sales volume demand warrants the investment in the required process equipment and converting technology. The abrasive agglomerates used include spherical shaped beads that have small diamond or other abrasive particles enclosed in a friable ceramic or metal oxide matrix where the ceramic erodes as the bead is abrasively worn down thereby progressively exposing new sharp abrasive particles. Abrasive agglomerates may also have many shapes other than spherical.

The primary competitor for the sheet fixed abrasive polishing technology is slurry lapping, which is necessarily very slow, even though it has been progressively up-dated. Slurry lapping produces a flatter surface on a workpiece at the present time than can be accomplished by high speed lapping, which has limited the sale of the high speed lapper machines. Other traditional grinding wheel machines can produce about the same flatness accuracy as the present configuration lapper but these machines can not produce the associated smooth polish that typical precision workpiece parts require. Accurate flat and smooth workpiece part surfaces are used to prevent leakage when these parts are mated stationary with other moving parts or when the workpiece parts are joined to dynamically rotate against each other.

High speed lapping uses expensive thin flexible abrasive coated disks that must be very precise in thickness and must also be attached to a platen that is very flat and stable. As the platen rotates very fast, this speed tends to "level" the abrasive as it is presented to the workpiece surface. As only the high spots of the abrasive contact the workpiece, the remainder of the disk abrasive is not used until the high spots wear down. Thus, it is necessary for the total system to be precisely aligned and constructed of precision components to initialize the grinding. Furthermore, the wear of the abrasive must proceed uniformly across both the surface of the sheet and the surface of each island to maintain the required flatness of both the effective abrasive surface and correspondingly, the workpiece surface. These issues have all been addressed here in defining various configurations of high speed lapper machines along with different abrading process techniques employed in operating the machines. To generate even workpiece surface wear with rotating abrasive disks, an annular raised abrasive flat surface is used as taught by Duescher in U.S. Pat. Nos. 6,149,506, 6,120,352; 6,102,777; 6,048,254; 5,993,298; 5,967,882; and 5,910,041 which are incorporated herein by reference. However, the desired large diameter flexible backing disks which are required for abrading large workpiece parts are not available as the size of commercially available abrasive disks is presently limited to about 12 inches (30.5 cm) diameter. This relatively small disk size severely limits the width of the annular abrasive band (or ring). A wide abrasive band on a small diameter disk results in a much slower surface grinding speed at the inside diameter of the band than the surface speed at the outside diameter of the band. This slower surface speed also results in reduced material removal from the portion of the workpiece that is located at this inside radial location. Furthermore, as the inside radial section of the abrasive disk wears slowly, the outside diameter portion of the abrasive progressively wears down much faster which results in an uneven abrasive surface across the surface of the annular band. Having larger nominal diameter abrasive disks with narrow annular bands, relative to the disk diameter, will inherently take care of most of these problems. A large diameter disk can have a wide annular band, where the annular width is measured in a radial direction, and the variation of the abrading surface speed across the radial width of the abrasive band will be minimized. The surface speed of an annular band will vary in direct proportion to the radial location of the abrasive. If a large nominal annular band diameter is used and the abrasive band width is narrow, the radius of the extreme inner radius of the band and the radius of the extreme outer radius of the annular band will be close in value. Because the radii of the inner and outer edges of the annular band are close in value, the abrading surface speed of the whole abrasive area will be fairly uniform. The larger the inner and outer annular band radii change in proportion to each other, the larger the variation the surface speed will occur across the radial width of the annular band width.

The typical workpieces that are lapped initially are not flat and have rough surfaces. Most potential customers seem to want both very flat (within 2 Helium light bands or 22.3 microinches or 0.6 micrometers) and smooth polished surfaces.

A preferred abrasive flat lapping process is now done in two separate steps. First, the parts are ground flat using a rigid spindle running at full 3,000 RPM speed, a very small contact force of 1 to 2 lbs. (0.454 to 0.908 kg) and typically, 3M Company's metal plated diamond abrasive. Water flows between the round islands of abrasive, reducing hydroplaning. Hydroplaning typically produces a cone shaped ground surface. Second, parts are polished using a spherical action workpiece holder, with low to moderate contact forces of 2 to 15 lbs. (0.908 to 6.81 kg), and uses a smooth coated abrasive disk operating at lower speeds of about 1,000 RPM or less to prevent hydro