Method for abrasive cutting in a liquid

Abstract

Materials are immersed in a liquid and then cut by propelling a stream of abrasive particles, which are carried in a fluid, towards the material. The liquid covering the material restricts the stream of abrasive particles to the area to be cut so as to avoid the disadvantage of abrading away the material surface adjacent the cut.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The instant invention relates to a method for cutting materials. In particular, the invention is directed to abrasive cutting of materials while the materials are covered by a liquid.

2. Description of the Prior Art

There are many well-known methods in the prior art directed to severing or cutting materials. These known methods tend to result in the cutting away of too much material, provide rough or uneven cuts, or cause undesirable stresses in the material. Although such results may be acceptable in certain circumstances, they cannot be tolerated in applications where a relatively expensive and sensitive material such as quartz crystal is to be severed or cut.

Several well-known methods are presently used for cutting quartz. One such method makes use of a diamond string saw to perform the cutting operation. However, diamond string saws are very expensive, cut slowly, require frequent replacement, cause undesirable stresses, and tend to chip the quartz. Such chipping results in deeply penetrating damage and alteration of the crystalline lattice structure of the quartz. Quartz may also be cut by the use of an air abrasive tool wherein a high velocity stream of abrasive particles is directed towards the quartz to erode or abrade the material. Although this method has been found to be effective in substantially eliminating chipping and is faster than cutting by diamond saws, it disadvantageously abrades the surface adjacent the cut and results in more material being removed than desired due to the outward expansion of the stream of abrasive particles once they pass through the nozzle of the air abrasive tool. Such surface abrading and the excessive removal of quartz has a deleterious affect on the electromechanical response of quartz crystal in addition to the expense incurred due to the loss of significant amounts of quartz.

SUMMARY OF THE INVENTION

The instant invention solves the foregoing problems with a method for cutting material by covering the surface of the material at the cutting site with a liquid, and propelling a stream of abrasive particles, carried in a fluid under pressure, towards the material to cut the material to a predetermined configuration.

This method results in minimal abrasive damage to the surface of the material adjacent to the cut and provides substantially parallel edges at the cut or severed areas which advantageously decreases the loss of quartz.

These results accrue due to the fact that the abrasive particles are restricted to a limited path from the nozzle to the material to be cut. The liquid about this path acts as a funnel or a mask which confines and directs the movement of the particles towards the material to be cut. The velocity of any abrasive particles leaving the restricted path will be quickly dampened by the surrounding liquid.

Advantageously, by immersing the material to be cut in a liquid any dust or debris generated from the cutting operation remains in the liquid.

An additional advantage is obtained by having the liquid continuously flowing to remove the debris caused by the cutting operation.

Another advantage is that in cutting piezoelectric material such as quartz the instant method has been found to cause a minimal amount of stress at the severed or cut sections resulting in a more accurate and reproducible electromechanical response characteristic.

A further advantage is in cutting under a liquid that electrostatic adhesion of abrasive particles to the surface of the material to be cut is precluded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art abrasive cutting method.

FIG. 2 illustrates the instant inventive abrasive cutting method.

FIG. 3 is an isometric view of an illustrative embodiment of the instant invention showing a monolithic crystal filter being abrasively severed using the instant inventive method.

DETAILED DESCRIPTION

FIG. 1 shows a prior art abrasive cutting operation wherein a tool nozzle 10 is located proximate an object 11 to be cut or severed. The nozzle 10 has a restrictive discharge orifice 12 through which an abrasive material 13 carried in a fluid 14 is propelled towards the object 11. The propelled fluid 14 expands or flares outwardly from the discharge orifice 12 to form a substantially triangular cross-section between the nozzle discharge orifice 12 and the surface 15 of the object 11 to be cut or severed. The stream of abrasive material 13, carried in fluid 14, is moved across the surface 15 of the object 11. A cut defined by walls 21-21, when viewed in cross-section, forms an opening wherein the width of exit 22 is narrower than the width of entrance 23 with the walls having a steepening angle from entrance to exit. This steepening angle from entrance 23 to exit 22 results in a rounded shoulder appearance which is caused by both the flaring out of the fluid 14 and by a secondary cutting action resulting from the abrasive material 13 in the fluid 14 striking the surface 15 of the object 11 and rebounding to strike the object again. These rebounding particles of abrasive material 13 not only cause an undesirable enlargement of the entrance 23 but also disadvantageously abrades the surface 15 at points remote from the actual cut.

FIG. 2 depicts the same tool nozzle 10 and object 11; however, the surface of the object to be cut is covered by a liquid 26 which surprisingly has been found to substantially limit the aforementioned flaring out and secondary cutting action of the abrasive material 13. The liquid 26 acts as a mask or shield which dampens the secondary action of the rebounding particles of abrasive material 13 while restricting the abrasive particles to a narrow stream to provide a smaller cut entrance 23 resulting in a cut, when viewed in cross-section, having nearly parallel sides. This restriction of the path of the abrasive material 13 and the dampening action of the liquid 26 essentially eliminates the undesirable abrading of the surface 15 adjacent to opening 23 and lessens the amount of material removed in the locale of the cut. The type of liquid 26 which can be used is substantially unlimited, for a wide variety of liquids such as freon, oil, alcohol, and water have been found to be effective.

Although it is not fully understood why the liquid 26 restricts the flaring of the particles 13, the following theory has been advanced. The center of the stream of particles 13 passing through the nozzle 12 meet with less resistance and therefore have a higher velocity than those particles at the perimeter of the stream which are adjacent to the inner surface of the nozzle. By introducing the stream of particles 13 into a liquid 26 the outer or lower velocity particles are readily dampened and the inner or high velocity particles remain and form a near cylindrical stream of particles.

FIG. 3 shows an illustrative embodiment of the instant invention wherein a Monolithic Crystal Filter (MCF) 27 is abrasively cut under a liquid 26, into two sections. Such a MCF 27 is used as a band pass filter. By cutting the MCF 27 into two sections certain undesirable response modes of the filter are eliminated. The structure and function of the MCF 27 is fully described in U.S. Pat. No. 3,564,463 to W. D. Beaver and R. A. Sykes and U.S. Pat. No. 3,576,506 to R. L. Reynolds and R. A. Sykes.

It should be emphasized that the instant invention is not limited to the cutting of quartz crystal, for a variety of hard or brittle materials such as ceramics, aluminum, sheet steel, glass, etc. have been cut using the instant method. Any material that can be abrasively cut whilee not in a liquid can be cut under a liquid with attendant advantages herein described.

In the exemplary embodiment of FIG. 3 the MCF 27 is shown seated in recessed sections 28--28 of supports 29--29 under the surface of the liquid 26 in container 30. The supports 29--29 can be moved in unison, towards and away from the top edge 36 of the container 30 along guide rails 31 under the control of an actuating apparatus 37 which communicates with the supports via a Y-shaped member 38. Nozzle 10 is located directly above the MCF 27 within container 30 and is mounted for movement transverse to the MCF.

The MCF 27 is comprised of a quartz crystal plate 39 upon which upper metallic electrodes 41--41, such as gold, are deposited on a first surface 42 of the quartz crystal plate and corresponding aligned lower metallic electrodes 43--43 (indicated by hidden lines) are deposited on a second surface 44 thereof. The upper metallic electrodes 41--41 are connected by upper conductors 46--46 to upper terminals 47--47 which in turn are terminated on a rectangular shaped ceramic ring 48. The lower metallic electrodes 43--43 are connected in a similar manner to the rectangular shaped ceramic ring 48 via lower conductors 49--49 and lower terminals 56--56. Upper terminals 47--47 and lower terminals 56--56 provide output terminations for electrically connecting the MCF 27 when in an operational circuit while also providing mounting support for the crystal plate 39 to the ceramic ring 48.

At the start of the cutting operation the nozzle 10 is located to one side of the MCF 27 and supports 29--29 are in a full upward position, above the surface of the liquid 26. The operator then places the MCF 27 in the recessed sections 28--28 of supports 29--29 which are then lowered into the liquid 26 under the control of the actuating apparatus 37 and the Y-shaped member 38. The nozzle 10 is then positioned proximate an edge 57 of the crystal plate 39. The fluid 14 containing the abrasive 13 is activated to project the stream of abrasive material through the orifice 12 of nozzle 10 as the nozzle is moved across the first surface 42 of the quartz plate 39 causing a cut 58 which severs the quartz plate into two sections. Once the quartz plate 39 has been severed, the abrasive 13 carrying fluid 14 from the nozzle 10 is stopped and the nozzle moved back again to one side of the MCF 27. Supports 29--29 are then raised to the full upward position, the MCF 27 is removed and a new MCF is placed on the supports and the foregoing steps repeated.

In a particular working model of the exemplary embodiment of the instant invention the quartz crystal plate 39, having dimensions of 1 11/32 .times. 7/16 inches and a thickness of 0.008 inch, was cut using 27 micron aluminum oxide powder as the abrasive 13 with shop air under a pressure of 90 psi as the carrying fluid 14. The MCF 27 was submerged to a depth of one-fourth inch in water with the nozzle 10, having a round orifice 12 of 0.011 inches, placed at a distance of 0.015 inch from the quartz crystal plate 39. The cut was accomplished at a cutting rate of 0.40 inch per minute resulting in a clean cut 58 with an average entrance or shoulder opening of 0.013 inch and an exit opening of 0.0085 inch in the quartz. Acceptable cuts have been made up to speeds of 0.56 inch per minute.

The aluminum oxide powder used as the abrasive material 13 in the above example may be replaced with any of a variety of abrasive materials depending upon the type of cut that would be acceptable. Abrasive materials 13 such as sand, silicon carbide, boron carbide, carborundum powder or the like carried in a fluid 14 such as air, nitrogen, alcohol, water, or other gas or liquids under pressures between 20 and 120 psi could be used.

As the distance between the orifice 12 and the quartz plate 39 is increased, the parameters in the working model above remaining the same, the entrance shoulders become more rounded. Where this distance is increased to 0.025 inch an entrance opening of between 0.019 to 0.20 inch and from 0.009 to 0.085 inch at the exit was measured.

It should be realized that the parameters of speed of cut, pressure of the propelling fluid 14, orifice 12 size and shape, distance between the nozzle orifice 12 and the material 11 to be cut, and the abrasive 13 to be used will vary depending on the type and thickness of material 11 to be cut and steepness required at the walls 21--21 of the cut. However, the important concept, to which the instant invention is directed, is that the material 11 to be cut or severed be placed under the surface of the liquid 26 while directing a stream of abrasive particles 13 thereat.

It is not necessary that any part of the nozzle 10 be immersed in the liquid 26. Cutting may be accomplished with the nozzle orifice 12 above the surface of the liquid 26 while the material 11 to be cut is fully immersed in the liquid. This may result in uneven cuts but could be acceptable where there are less stringent requirements as to the slope of the sides 21--21 and the loss of material 11.

It should be realized that in the instant exemplary embodiment the MCF 27 can easily be immersed or submerged in the liquid 26. However, where it is required to cut or sever larger objects such as large sheets of aluminum or other materials, the liquid 26 could be confined to cover the surface of the material at the cutting site only.

Although the illustrative embodiment describes the severing of a quartz crystal plate 39 into two equal size sections, the instant inventive concept is not so limited. Clearly, the instant method for abrasively cutting under a liquid could be used to advantageously cut an unlimited number of shapes, slots, holes, or other configurations by the simple expedient of causing the nozzle 10 and/or the supporting structure to move along a predetermined path. Circular and arcuate shaped designs have been cut in quartz crystal using the instant method.

By placing the surface of the object 11 to be cut under a liquid 26, the dust and debris associated with such a cutting operation is confined to the liquid. In addition, the instant embodiment can be arranged in a well-known manner to have the liquid 26 continuously flowing. The liquid 26 could then be filtered to remove the debris and reintroduced or discharged as waste and makeup liquid added. In addition, the liquid 26 has been found to substantially preclude any electrostatic adhesion of abrasive particles 13 to the surface 15 of the material 11 to be cut.

The instant abrasive cutting method, by providing a cut with substantially parallel sides, has been found to produce a minimal amount of stress in the cut material 11. This is clearly advantageous when cutting piezoelectric materials where such stresses would affect the electromechanical response characteristics of the material.

Finally, it should also be clear that a plurality of nozzles 10 used to simultaneously or sequentially cut materials is clearly feasible based upon the concepts of this invention.

Claims

I claim:

1. A method of forming an aperture in material, comprising the steps of:

covering the surface of the material at a site at which the aperture is to be formed, with a liquid; and

propelling a stream of abrasive particles, carried in a fluid under pressure, against the covered surface of the material to form the aperture in the material.

2. A method of forming an aperture in material, comprising the steps of:

immersing the material in a liquid; and

propelling a stream of abrasive particles, carried in a fluid under pressure, against the immersed surface of the material to form the aperture in the material.

3. An improved method of forming an aperture in material with abrasive particles comprising the step of:

propelling a stream of abrasive particles, carried in a fluid under pressure, against the surface of the material to form the aperture in the material;

wherein the improvement comprises the additional step of:

covering the material in the vicinity of the area wherein the aperture is to be formed, with a liquid, prior to propelling the stream of abrasive particles, the liquid restricting the stream of abrasive particles to the area wherein the aperture is to be formed.

4. A method for cutting a quartz crystal plate having metallic electrodes deposited thereon, comprising the steps of:

immersing the crystal plate in a liquid;

positioning a nozzle of an abrasive projecting tool proximate the crystal plate; and

activating the abrasive projecting tool to project a stream of abrasive material towards the immersed crystal plate, cutting the plate.

5. The method for cutting a quartz crystal plate as set forth in claim 4, including the additional step of:

immersing the nozzle in the liquid a predetermined distance from the crystal plate.

6. A method for cutting a monolithic crystal filter plate having metallic electrodes thereon, comprising the steps of:

placing the filter plate on supports;

immersing the supports and filter plate in a liquid;

positioning a nozzle of an air abrasive tool proximate the filter plate;

activating the air abrasive tool to project abrasive material towards the immersed filter plate;

moving the nozzle across the filter plate to sever the plate into two sections;

deactivating the air abrasive tool;

raising the filter plate above the surface of the liquid; and

removing the severed filter plate.

7. A method of cutting out a desired configuration from material, comprising the steps of:

covering the surface of the material with a liquid;

propelling a stream of abrasive particles, carried in a fluid under pressure, against the covered surface of the material to sever the material; and

imparting relative motion between the stream of abrasive particles and the material to cut out the desired configuration from the material.

8. A method of severing material into sections, comprising the steps of:

covering the surface of the material, at a severing site, with a liquid; and

propelling a stream of abrasive particles, carried in a fluid under pressure, against the covered surface of the material to sever the material into sections.

9. A method of forming an aperture in quartz, comprising the steps of:

immersing the quartz in a liquid; and

propelling a stream of abrasive particles, carried in a fluid under pressure, against the immersed surface of the quartz to form the aperture therein.