Abrading – Abrading process – Utilizing nonrigid tool
Reexamination Certificate
2000-11-17
2004-08-03
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Utilizing nonrigid tool
C451S036000, C451S041000, C451S287000
Reexamination Certificate
active
06769969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to 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 lapping, polishing, finishing or smoothing of workpiece surfaces. In particular, the present invention relates to such processes and apparatus that use removable or replaceable abrasive sheeting that are able to operate at high surface speeds, and apparatus that secures the abrasive sheeting to a support (particularly in an annular distribution of abrasive material on a face of the abrading 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 point or contact plane of the abrasive sheeting and the article that is to be lapped, polished, finished or smoothed.
2. Background of the Art
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.
The most serious problem remaining is the availability of high quality abrasive article sheets that have certain important characteristics. The sheets should be of a sufficient dimension (e.g., at least a 6 inch (15.3 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 particles (preferably secured to a substrate and preferably arranged in an annular band). The particles 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 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.). 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 is the pyramid shaped Trizact 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 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, 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 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
Hail III Joseph J.
Keltech Engineering, Inc.
Mark A. Litman & Assoc. P.A.
Thomas David B.
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