Grinding Pad

Abstract

The method of providing a replaceable grinding pad for a lens-grinding tool, having a surface thereon for grinding optical and ophthalmic lenses. The pad is formed about the curve-determining surface of the grinding tool, thus providing the grinding surface of the pad with substantially the same curvature as that of the tool. The pad is formed by interposing a sheet metal blank between the tool and a die member of an elastic material and thereafter deforming the blank with the tool by depressing it into the elastic material, whereby to form a grinding pad having the same configuration as that of the tool.

Parent Case Text

This is a divisional application based upon parent application Ser. No. 662,379 filed Aug. 22, 1967, and entitled "GRINDING PAD."

Description

BACKGROUND OF THE INVENTION

Optical and ophthalmic lenses are commercially produced by grinding a lens blank precisely to a predetermined curvature thus imparting the desired optical qualities to the lens. The grinding is generally performed by use of a tool made of cast iron or the like which is provided with a lapping surface having a curvature precisely corresponding to the curvature desired to be impressed upon the lens blank surfaces. During the grinding process, an abrasive slurry is deposited over the lapping surface and a relative rotary, oscillatory or combination rotary and oscillatory motion is imparted between the lens blank and lapping surface. As will readily be appreciated, since the lapping surface of the grinding tool as well as the lens blank is subjected to the abrasive action of the slurry, it will wear fairly rapidly, thus requiring truing or refinishing at frequent intervals to restore the lapping surface to the desired curvature. It is therefore desirable to provide a replaceable grinding surface for use with such a grinding tool and heretofore several attempts have been made at providing an adequate replaceable pad having such a grinding surface thereon. However, all of these attempts have met with one objection or another. The principal difficulties were those of forming the pad accurately to curve, maintaining adequate adhesion of the pad to the tool, and the too short working life of such pads.

SUMMARY OF THE INVENTION

It is therefore a principal object of this invention to provide an economical and efficient replaceable grinding pad for a lens-grinding tool which is easily replaceable, accurate in curvature and can be positively secured to the grinding tool and the method of fabricating and replacing such pads.

This and other objects and advantages are most effectively attained by producing a grinding pad directly over the curve-determining surface of the grinding tool. A flat blank of metal or other suitable material is interposed between this surface of the grinding tool and a die block filled with an elastic material. The tool is then forced against the blank into the elastic material under relatively high pressure, thus deforming the blank to conform to the curvature of the surface.

In the preferred embodiment of the present invention, the pad is somewhat smaller than the curve-defining surface of the tool and a pressure sensitive adhesive coating or contact cement can be used between the tool and pad to provide securement during use.

In the manufacture of pads for grinding toric lenses it has been found that the formation of an intermediate, spherical, shell may be required before the final toric shape can be formed if the sheet metal blank from which the pad is to be formed is relatively thick or inflexible. Thus, in the manner described above, a flat metal blank is interposed between the spherical end of a mandrel and a die block filled with an elastic material. The mandrel is then pressed against the blank into the elastic material thus deforming the blank into a spherical shell. The shell is then interposed between a grinding tool having the desired toric curvature and a die block filled with an elastic material. The grinding tool is forced against the shell into the elastic material thereby causing the shell to deform to the desired toric shape. The intermediate spherical shell may be manufactured somewhat larger than the toric lap of the grinding tool. In this case, when the final grinding pad is produced, the excess material may be conveniently bent to form a peripheral retaining rim adapted to secure the grinding pad to the grinding lap during use.

As was previously stated, an abrasive slurry is spread over the grinding surface of the tool during use. The tool may thus be used for grinding or polishing lenses, dependent on the particle size and abrasiveness of the slurry used. In order to evenly distribute this slurry over the lapping surface, the metal blank may be provided with a series of cutouts or slots which serve as feed channels when the pad is affixed to the grinding tool. The slots, when properly positioned and shaped, are also utilized to assure a grinding pad which possesses a wear pattern that results in its curvature remaining substantially unchanged throughout its life and which will enable the grinding of wave-free lenses.

DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an exploded fragmentary side elevational sectional view of a die block and press for manufacturing grinding pads in accordance with the present invention;

FIG. 2 is a view similar to FIG. 1 after the pad is formed;

FIG. 3 is a side elevational sectional view of the pad produced in FIG. 2;

FIG. 4 is a view similar to FIG. 1 wherein an intermediate spherical shell is used as a workpiece for manufacturing toric grinding pads in accordance with the alternate embodiment of the present invention;

FIG. 5 is a view similar to FIG. 2 showing the actual production of the toric pad;

FIG. 6 is a fragmentary side elevational sectional view of a grinding tool having a grinding pad secured thereto by an adhesive bonding agent;

FIG. 7 is a fragmentary side elevational sectional view of a grinding tool having a grinding pad manufactured in accordance with the alternate embodiment of the present invention disposed about its lapping surface wherein the pad is provided with a peripheral rim for retaining it to the grinding tool;

FIG. 7a is a bottom plan view of the grinding view of FIG. 7;

FIG. 8 is a fragmentary side elevational sectional view of a die block and press for manufacturing concave grinding pads;

FIG. 9 is a plan view of a tool provided with a multiplicity of depressed grooves covered by a grinding pad formed in accordance with the present invention wherein the grooves in the tool have become formed on the pad;

FIG. 10 is a plan view of a metal blank which is particularly well suited for use in forming a replaceable pad for the grinding of spherical surfaces;

FIG. 11 is a plan view of an embodiment of a metal blank particularly suited for forming a replaceable pad for the grinding of toric surfaces;

FIG. 12 is a plan view of another embodiment of a metal blank for use in grinding toric surfaces;

FIG. 13 is a plan view of still another embodiment of a metal blank for use in grinding toric surfaces;

FIG. 14 is a fragmentary elevational sectional view of a die block and press for forming a continuous grinding pad about a grinding wheel in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to the drawings to FIG. 1 in particular, wherein an apparatus 10 for practicing the method of the present invention is shown. The apparatus 10 includes a tough elastic material 12 confined within a die block 14. The elastic material 12, which may consist of a natural resilient elastomer such as rubber or various rubber compounds, or a synthetic elastomer such as polyurethane, serves to provide an opposite die for the pressing member or mandrel 16 during the operative condition of the apparatus. The pressing member 16 may be hydraulically operated (the hydraulic equipment is not depicted) and, in accordance with the present invention, the die portion 18 of the pressing member 16 may have a spherical, toric or any desired configuration and curvature. The spacing between the die block 14 and pressing member 16 is such that the pressing member will be forced into the elastic material 12 of the die block when the hydraulic press is made operative.

In use, a flat grinding pad blank 20 which consists essentially of a thin sheet of steel or other metal, is interposed between the elastic material 12 and pressing member 16 and aligned relative to the pressing member. In the preferred embodiment of the present invention, the upper surface of the blank and the lower or die portion 18 of the pressing member 16, which comprises the curve-determining surface of a grinding tool, will have previously been coated with a suitable contact cement of adequate bonding strength to hold the pad in its formed configuration to the tool and to withstand the stresses of abrasive grinding. The press is then activated, causing the pressing member to advance toward the die block thereby deforming the blank 20 to conform to the shape of the lower portion 18 of the pressing member 16, and thereby forming the assembly depicted in FIG. 6 consisting of the tool 38, adhesive 44 and pad 30.

The grinding pad of the present invention, may be formed over and used with the individual grinding tools as depicted in FIGS. 6 and 7 or, it may be used in conjunction with a grinding wheel 52 as depicted in FIG. 14. In the latter case, a succession of pads may be formed about the periphery of the grinding wheel 52 in end-to-end relationship in the same manner as that described above using the wheel as the pressing member for each pad, or, a continuous pad 30c may be formed by using a sufficiently long blank 56 and rolling the wheel 52 against the blank into an elastic wheel 54 under sufficient pressure to deform the blank in the manner described above. The apparatus for practicing the latter method is depicted in FIG. 14.

In one successful operation of the above-described process, cold rolled, deep drawn sheet steel blanks having a maximum hardness of Rockwell B55 and thickness of between 0.005 and 0.010 inch were formed into pads under a pressure of between 20 and 25 tons. The elastic material 12 contained within the die block 14 consisted of Elasta Cast Polyurethane Elastomer, supplied by Acushnet Process Company of New Bedford, Mass. Satisfactory results have also been obtained with the use of a hydrostatic bag consisting of a liquid-tight nonelastic cover filled with an incompressible fluid as the elastic material. A suitable adhesive is that supplied by the Minnesota Mining and Manufacturing Company as No. 1357 cement. This is a contact cement which is supplied in liquid form and is applied to the surfaces of the tool and pad to be contacted in accordance with the manufacturer's instructions.

FIG. 8 depicts an apparatus for producing concave pads in accordance with the present invention. The elastic material 12b confined within the die block 14b includes a hemispheric dome 40 protruding toward the pressing member. The radius of the dome 40 is smaller than the shortest radius intended to be formed on the pad 30b. In all other respects, the apparatus and method are the same as that described above for the formation of convex pads.

An alternative method of practicing the present invention has been found to be most useful in the manufacture of relatively thick pads or pads from less flexible materials. In this alternate procedure, a spherical, intermediate shell is first formed and thereafter, the intermediate shell is further worked to the desired shape. Thus, in the manner described above, a spherical shell 30a may be produced by utilizing a die portion 18 having a spherical tool. Referring to FIG. 4, the spherical shell 30a is thereafter interposed between a second pressing member 16a and a die block 14a filled with an elastic material. The die block used in this second step, may, of course, be the same as that utilized in the initial step and serves the same function.

The die portion 18a used in this second pressing step consists of a tool having the desired toric or spherical curvature and thus, when the apparatus 10a is activated to the position shown in FIG. 5, the shell 32 so produced will conform to the toric or spherical curvature of the tool 18a.

In the alternative embodiment as depicted in FIGS. 4 and 5, the intermediate spherical shell 30a produced during the initial pressing process is somewhat larger than the grinding tool serving as the die portion 18a in the second pressing step. Thus, as shown in FIGS. 5, 7 and 7a, when the second pressing step is completed, the retaining rim 34 will be formed out of the excess material. This rim 34 serves to secure the shell 32 about the grinding tool 38 by frictionally engaging the sidewall of the grinding tool.

It can thus be appreciated that the deformed blank forms a pad about the grinding surface of the grinding tool 38 and the outer surface 42 of the pad thereby serves as a replaceable grinding surface for the grinding tool 38. When the grinding surface of the grinding pad wears out through the abrasive action of the slurry used in the lens-grinding operation, the entire pad can easily be removed from the grinding tool and a new pad substituted therefor in one of the manners described above.

The surface blank 20 from which the grinding pad is formed may be made from sheet steel or from any material having the appropriate softness for forming and having suitable properties for glass grinding. Stamped sheet steel blanks of thicknesses varying between 0.005 and 0.010 inch have produced particularly successful results. By providing the blank 20 with a multiplicity of slots and cutouts in various geometrical arrays, desirable wear and slurry distribution characteristics may be imparted to the grinding pad produced from such a blank. Particularly, it is desirable to produce an grinding pad that possesses a wear pattern that results in the curvature remaining substantially uncharged during its life and one which will permit the grinding of wave-free lenses. FIGS. 10 through 13 depict various forms that the blank 20 may take prior to its formation into a grinding pad and with which successful results have been obtained.

FIG. 9 depicts a tool provided with a multiplicity of depressed grooves 46 covered with a grinding pad 20a formed thereon in accordance with the present invention in which the grooves have become formed in the pad by the elastic action of the elastic material 12. The depressed grooves serve as channels for distributing the grinding slurry.

The pad 20b depicted in FIG. 10 is particularly well suited for forming spherical grinding pads. It is substantially circular and symmetric about the diameter defined by slots 48b and 49b. A multiplicity of slots extending radially inwardly is provided including the T-shaped slot which include portions 51b parallel to the axis of symmetry and portion 50b perpendicular to the axis.

The irregularly shaped pad depicted in FIG. 11 and intended for the grinding of toric lens surfaces, is also symmetrical about the major axis which runs through the middle of slot 48c and also includes a multiplicity of inwardly directed slots and cutouts including slots 49c parallel to the major axis and slots 50c and cutout 51c which are directed toward the center of the pad. The pad is substantially octagonally shaped with opposite sides 53 and 55 through which the major and minor axis pass provided with V-shaped cutouts directed toward the center. The cutouts located in sides 55c and 55c' extend from one end of the respective side to the other while the cutouts located in sides 53c and 53c' terminate intermediate the ends.

The pad 20d depicted in FIG. 12, also intended for use in grinding toric surfaces is a substantially rectangular member having major and minor axis and a series of slurry distributing slots 48d disposed symmetrically about a diagonal. The slots extend inwardly intermittently beginning one one side of the axis of symmetry and then the other.

The pad 20e depicted in FIG. 13 is similar to that of FIG. 12 with the exception that slots 48e are substantially parallel to the minor axis.

In addition to (with the distribution of slurry, the cutouts described above serve to facilitate the precise conforming of the pad to the tool during the pressing step. It has been found that with the use of such cutouts, the force necessary to properly form the pad has been reduced from between 20 and 25 tones (without cutouts) to between 5 and 10 ton with cutouts).

Thus it can be appreciated by one skilled in the art that the teachings as set forth above provide an economic and efficient method of making replaceable grinding pads for a lens-grinding tool which are accurate and inexpensive. It should be understood that modifications may be made in the illustrated and described embodiments of my invention without departing from my invention as set forth in the accompanying claims.

Claims

I claim:

1. The method of assembling a replaceable lens-grinding pad to a lens-grinding tool having a selected curved surface thereon cooperable in grinding a surface on a lens to a related prescribed curvature, comprising the steps of: interposing a lens-grinding pad blank between a body of compressible elastic material and a lens-grinding tool and in alignment with the curved surface of said lens-grinding tool, causing relative movement between the curved surface of the tool and the elastic material to press the pad blank into the elastic material and to deform the pad blank into conformity with the curved surface of the tool whereupon the pad blank has impressed thereon a curvature substantially corresponding with that of the curved surface of the tool, and simultaneously removably securing the deformed pad blank to the tool for grinding the prescribed curvature on the lens by the use of the deformed pad blank on the tool.

2. The invention in accordance with claim 1 wherein the deformed pad blank is secured to the tool by interposing a cement between the pad blank and the curved surface of the tool.

3. The invention in accordance with claim 1 wherein the deformed pad blank is secured to the tool by bending peripheral surfaces of the pad blank into frictional engagement with surfaces of the tool.

4. The invention in accordance with claim 1 wherein the lens-grinding pad blank is initially provided from a substantially flat sheet of deformable metal.

5. The invention in accordance with claim 4 wherein slots are provided in the flat pad blank for enhancing the grinding operation of the deformed pad blank secured to the tool.

6. The invention in accordance with claim 1 wherein the curved surface of the tool is concave and a substantially hemispherical dome is provided on part of the elastic material extending in the direction of the tool, the radius of the dome being smaller than the shortest radius of the curved surface of the tool.

7. The invention in accordance with claim 1 wherein the elastic material is a polyurethane elastomer placed in a die block.

8. The invention in accordance with claim 1 wherein the grinding tool is coupled with a hydraulic press, and the tool is hydraulically moved against the pad blank and hydraulically presses the pad blank into the elastic material.

9. The invention in accordance with claim 1 wherein initially the pad blank is deformed by pressing it into an elastic material by a mandrel having a spherical pad blank engaging surface, and thereafter the spherically shaped pad blank is deformed by and secured to said grinding tool with the curved surface thereof being toric.