Seal ring and method of forming micro-topography ring surfaces with a laser

A seal ring of a shaft seal has micro-topography depth features, such as wavy faces or radial grooves, formed in the seal face which define a hydrodynamic seal region between opposing seal faces. The micro-topography depth features are formed by an excimer laser shaped such that the beam shape at least has non-linear side edges which define convergent side areas of the beam. The convergent side areas are defined by side edge sections which converge toward each other and preferably are non-linear. For example, the beam shape may be circular or elliptical. The laser beam first cuts repeatedly along the same beam path to define a cut with an increasing depth, whereby the laser beam is shifted incrementally sidewardly to define multiple adjacent beam cuts that form the micro-topography feature such as a valley of a wavy face, a radial groove or the like. As the laser beam cuts adjacent parallel grooves, sidewardly adjacent beam passes overlap one with each other and blend the edges of the sidewardly adjacent grooves together. The method of the invention provides micro-topography depth features that are precisely and accurately defined to improve performance of the seal ring.

FIELD OF THE INVENTION

The invention relates to a seal ring for rotating shafts and more particularly, to a seal ring having a micro-topography seal face formed by a laser.

BACKGROUND OF THE INVENTION

To seal rotating shafts of pumps, compressors and the like, it is known to provide a non-contacting shaft seal on the shaft, which includes an axially adjacent pair of seal rings wherein one seal ring rotates with the shaft and the other seal ring is non-rotatably connected to a seal housing. The seal rings each include an end face which faces axially wherein the seal faces are disposed in close opposing relation to define a sealing region extending radially between the outer and inner diameters of the seal rings. The fluid being sealed can either be a liquid or a gas, and the sealing region prevents or minimizes migration or leakage of the fluid radially across the seal faces.

More particularly, the seal faces typically are disposed in contact with each other when the shaft is not rotating to thereby define a static seal. Further, at least one of the seal faces includes a hydrodynamic face pattern that generates a fluid film between the seal faces during shaft rotation to reduce if not eliminate contact between the seal faces.

Hydrodynamic face patterns are known and include wavy faces, spiral grooves, T-grooves and the like. The face patterns are formed in the seal faces through various processes and typically involve providing a flat face and then removing material from the seal face to a very small depth.

For example, U.S. Pat. No. 5,529,317 (Muller) discloses several seal face patterns wherein one of the seal face patterns includes stepped hollows in the seal face that creates a hydrodynamic load support between the seal faces during shaft rotation. The rectangular stepped hollows are formed by means of laser beams which are applied in an overlapping manner.

While a rectangular shaped laser beam may be used to form the rectangular steps of the '317 patent, it has been found that when two adjacent passes of a laser beam overlap, the area of overlap between each adjacent pair of passes has an excessive depth since the overlap area is cut once on the first pass and then cut again on the second pass. In particular, during each pass, the laser beam removes a fixed amount of the seal ring material therefrom by material ablation wherein the ring material is vaporized. For areas that do not overlap, equal amounts of material are removed. However, in each area where the laser beam passes overlap, material is removed during each pass such that the overlap area has been cut deeper and therefore forms an overlap groove having a depth which is greater than the non-overlapped areas. Further, when a rectangular laser beam is used, the opposite ends of each groove formed by a pass of the laser are rectangular and as a result, adjacent ends are stepped across the seal face.

It therefore is an object of the invention to provide a seal ring having micro-topography features formed by multiple passes of a laser beam wherein the beam is shaped to prevent formation of overlap grooves having an excessive depth greater than the desired depth of the feature being formed. It is a further object of the invention to provide a method of forming micro-topography features in the seal ring which blends the laser cuts such that the peripheral edge or boundary of the micro-topography features is cut to a high degree of precision.

To achieve these objectives, the invention generally relates to a seal ring having precisely defined micro-topography depth features in the seal face and a method for forming these micro-topography features.

The micro-topography features are formed in the seal face by a shaped laser beam which removes material in multiple passes along the seal face. During formation of the micro-topography features, the laser beam first cuts through one or more passes along the same beam path to define a cut or groove. To form cuts having an increasing depth in the center thereof as is typically required for a wavy face seal, each successive pass on a single cut is shorter than the preceding pass so that more ablation passes are applied in the center of the cut than at the end of the cut. As a result, the cut has a variable depth whereby the depth increases or tapers away from at least one and possibly both of the opposite ends. The laser beam not only cuts multiple ablation passes along the same beam path, but also is shifted sidewardly to cut along adjacent beam paths. As a result, one or more additional adjacent or contiguous cuts or grooves ultimately define a micro-topography feature such as a valley of a wavy face, a radial groove or the like.

The method of the invention provides micro-topography depth features which are more precisely and accurately defined to improve performance of the seal ring. As the laser beam cuts the grooves one next to the other, each successive ablation pass along the groove overlaps the prior beam passes of the sidewardly adjacent groove to ensure complete coverage of the area of the seal surface on which the micro-topography feature is being formed and blend the edges of the sidewardly adjacent grooves together.

In this regard, the laser beam is shaped by a mask into a predefined geometric shape which illuminates the cutting surface whereby the opposite sides of the beam shape have non-linear side edges. These side edges define areas of the beam which will overlap with successive beam passes. For example, the mask in one embodiment includes a circular aperture through which the laser beam passes and is shaped so that the laser beam when striking the seal ring has a circular cross-section.

As the laser beam and seal ring move relative to each other during a continuous cutting process, the circular laser beam shape travels longitudinally and cuts a continuous ablation groove which is semi-circular when viewed from the side. The non-linear side edges of the beam travel longitudinally to define the opposite sides of the ablation groove. Due to the shape of the beam, the depth of the semi-circular groove is non-uniform along the lateral width thereof since a greater amount of ring material is removed at the center region and less material is removed from the opposite side edge regions of the laser beam. The shallower side regions define overlap areas that overlap an adjacent laser beam pass.

Unlike a rectangular shaped beam, the overlap areas of a beam having non-linear side edges may overlap to a significant degree, for example, up to 25% of a circular beam width yet the depth of the overlap area does not exceed the desired depth of the non-overlap areas. This thereby prevents formation of overlap grooves in the overlap area which exceed the maximum depth of the micro-topography feature being formed.

Besides a circular shaped laser beam, the beam may also be shaped to have other non-circular shapes. For example, the laser beam may have an elliptical shape or alternatively have linear edges in a center section with non-linear generally arcuate sections at the opposite ends of the center section. The arcuate side sections may be defined by continuous curves or by short linear sections which effectively define an arc. In these alternate beam shapes, the opposite side edges of the beam are non-linear to define an ablation cut in the seal face having a non-uniform depth.

The inventive seal ring and method for forming the seal ring provide distinct advantages in the formation of micro-topography depth features. For example, by providing a shaped laser beam and optimizing the overlap of the beam cuts, the inventive method eliminates or controls undesirable excessive-depth grooves in the overlapping areas extending along the sides of adjacent beam passes, and furthermore blends the ends of adjacent beam cuts to provide a boundary of the micro-topography features which are more arcuate or curved than the rectangular generally stepped edges resulting from a rectangular shaped laser beam.

The inventive method in the seal ring thereby not only provides a more repeatable and accurate manufacturing process, but also provide a significantly improved ability to construct a wide variety of micro-topography features.

Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.

DETAILED DESCRIPTION

Referring toFIGS. 1,2A and2B, the invention relates to a seal ring10(FIG. 1) for a shaft seal and to seal ring machining equipment12which has a laser unit14that forms micro-topography depth features in the seal face15of the seal ring10. As described in greater detail herein, the laser unit14generates a shaped laser beam which has non-linear edges at least on opposite sides of the beam to provide successive cuts in the seal face15wherein the cuts have a non-uniform depth across the lateral width thereof to permit beam overlap and more accurately and precisely define the micro-topography depth features.

With respect to the seal ring10ofFIG. 1, the seal ring10is formed for use in a generally conventional manner in that the seal ring10has an annular shape defined by an outer diameter17and an inner diameter18. The seal face15extends radially between the outer and inner diameters17and18and defines a sealing region19which extends radially therebetween. When the seal ring10is installed as part of a shaft seal on a rotating shaft of a pump, compressor or other similar piece of equipment, the seal face15is adapted to face axially in facing relation with an opposing seal face of another seal ring.

The structure and function of opposing pairs of seal rings to define a shaft seal (commonly referred to as a mechanical seal) is well known and a detailed discussion as to the construction of the shaft seal is not provided herein. Such construction is illustrated in U.S. Pat. No. 5,833,518 owned by the assignee hereof. The disclosure herein is directed to the specific shape and features of the seal ring10and its formation by the seal ring machining equipment12.

The seal ring10is illustrated inFIG. 1as having micro-topography depth features in the form of a wavy face. In particular, the seal face15has an annular seal dam20on the inner diameter18thereof which is adapted to contact an opposing seal face. The seal dam20defines an annular region which prevents fluid leakage radially across the sealing region19during non-rotation and start-up conditions. While the seal dam20is located on the inner diameter18, the seal dam20may be positioned at other radial positions such as the outer diameter17.

The seal face15further includes a plurality of circumferentially adjacent waves22wherein each wave22includes a valley23disposed circumferentially between a pair of wave peaks24. In the illustrated seal ring10ofFIG. 1, the cross-sectional shape of the seal ring10at each wave peak24is rectangular such that the seal ring10has a uniform thickness at this location. The thickness of the seal ring10, however, decreases circumferentially away from the wave peaks24along the outer diameter17in a generally sinusoidal manner and radially away from the seal dam20. As a result, each valley23has a tilt or declined surface25which extends radially outwardly away from the seal dam20whereby the difference in thickness between the wave peaks24and the valley23is defined as the amplitude26of the waves22. As can be seen, each wave22has variable depth in two directions, namely radially and circumferentially.

This wavy face thereby defines a hydrodynamic seal which generates a fluid film between opposing seal faces15during shaft rotation and thereby reduces friction and minimizes or eliminates contact across the sealing region19. The actual topography of the seal face is further illustrated by a rectangular topographical graph which is shown on the seal face15for illustrative purposes.

The general principal of using a wavy face on a seal ring is known. In known wavy face seals, such wavy faces are formed by: first applying a shrink band which compresses the outer diameter of a seal ring and distorts the seal ring; lapping the seal face; and then removing the shrink band to eliminate the distortion whereby the resultant seal face has a wavy shape. This shrink-band process, however, permits formation of a seal ring having only a limited number of waves with limited amplitude, and involves checking of all seal rings in a manufacturing batch to ensure the wavy faces are formed within required parameters. As described in further detail hereinafter, these disadvantages are overcome wherein the seal ring machining equipment12allows for the formation of a wavy face by the laser unit14with increased flexibility, accuracy, precision and efficiency.

While much of the following discussion addresses the formation of wavy faced seal rings, the laser unit14of the invention also may be used to form other micro-topography depth features such as radial or spiral grooves, T-shaped grooves and other features, particularly those features which have a size that requires multiple passes of a laser. Further, similar to the wavy face seal, these other depth features may have a variable depth in or more directions.

While additional processes are known for forming these depth features, these known processes also may have limitations and it may be difficult to form seal faces with distinctly different types of depth features on the same seal face. The seal ring machine equipment12and the method thereof do not have such limitations.

Referring toFIG. 2A, the seal ring machining equipment12includes a worktable29comprising a base30and a horizontally enlarged tabletop31which is supported on the base30. The tabletop31has a seal ring support assembly32which is adapted to support the seal ring10thereon.

The support assembly32provides four-axis adjustment for adjusting the position of the seal ring10during a cutting operation since the laser remains stationary during use. In this regard, a support table34is provided on which the seal ring10is supported wherein the support assembly32includes an x-axis slide unit35having a controller motor36for moving the support table35along the x-axis as generally illustrated inFIG. 2A.

Additionally, a y-axis slide unit39is provided which is supported on the x-axis slide unit35so as to be movable therewith along the x-axis. The y-axis slide unit39supports the support table35on the top surface thereof and is movably connected to a control motor40for selectively moving the support table35along the y-axis.

More particularly as to the support table34, the support table34is rotatably supported on the upper surface of the y-axis slide unit39and is rotatably connected to a motorized rotary table42. The motorized rotary table42is selectively rotated to adjust the angular position of the seal ring10supported thereon. A further Z-axis slide unit43is provided as will be described herein to provide the four-axis adjustability.

To support the seal ring10, the support table34includes an upper surface44defined by a circular plate45. The seal ring10is positioned on the plate45and then clamped in place by three stops47which project upwardly from the plate45. Each stop47is defined by an upstanding rod-like projection48and a resilient o-ring49on the projection48. The stops47are movable simultaneously together radially outwardly to provide enough clearance for positioning of the seal ring15therebetween, and radially inwardly for gripping the outside diameter17of the seal ring10. Accordingly, the seal ring10is clamped onto the support table34and then the position of the seal ring10can be adjusted along the x-axis, y-axis and the angular position theta can also be adjusted. The support table34further provides for rotation of the seal ring10through multiple revolutions wherein the laser unit14cuts grooves circumferentially along the seal face15at a cutting radius, and then the x-axis and y-axis position of the seal ring10is adjusted to provide successive cuts at different cutting radiuses.

To provide adjustment in the vertical z-axis, the seal ring support assembly32further includes the z-axis slide unit43which comprises a pair of sidewardly spaced apart upright support posts50which are adapted to support components of the laser unit14thereon. The seal ring support assembly32also includes a drive motor51and a drive belt52extending horizontally between drive motor51and precision linear slides71mounted to the posts50for adjusting the vertical height of the laser unit components.

All of the motors of the seal ring support assembly32are connected to a computer control unit by appropriate control cables53. The control unit is programmable so that the various motors36,40and51as well as the rotary table motor which rotates the support table34are selectively operated to control the position of the seal ring10for laser machining of the seal face15. The control unit is run using the computer program Labview which is commercially available.

A displacement laser54(FIGS. 2A and 3) also is provided which is directed toward the seal ring10and is connected to the control unit to identify the initial position of the seal ring10relative to the final objective lens84of the laser and permit precise control of the position of the seal ring10. During the start of the laser cutting process, the seal ring10is moved below the displacement laser54and the z-axis position is adjusted so that the proper focal length for the laser is provided.

Depending upon the programming of the control unit, the laser unit14not only is used to define a wavy face on the seal ring10but also may be used to define other micro-topography features such as spiral grooves and the like.

Turning to the laser unit14as illustrated inFIG. 2A, an excimer laser59is provided within the base30and includes a laser beam exit port60which opens sidewardly therefrom. The excimer laser59is a krypton fluoride (KrF) laser which operates in the ultraviolet wavelength region of about 248 nanometers. This laser is selected since little if any heat is produced in the seal ring10when forming the micro-topography features.

Generally, the laser59generates a laser beam62(FIG. 2B) which contacts the seal face15and removes material therefrom by ablation. To direct the laser beam62from the exit port60on the side of the base30to the seal ring10provided on the top of the tabletop31, a series of lenses and mirrors are provided.

More specifically, the laser beam62exits sidewardly and strikes a turning mirror64which is supported on a side of the base30to redirect the beam upwardly to an attenuator65that is mounted to a side of the base30. The beam62then exits upwardly from an attenuator port66to a vertically spaced apart pair of homogenizer lenses67that are supported on a support rail arrangement68.

As to the support rail arrangement68, this arrangement includes a pair of upright rails70wherein the lower ends of the rails70are slidably connected to the posts50by the linear slides or vertical actuators71. The actuators71connect the rails70and posts50together whereby the above-described drive motor51is selectively operated to displace the entire support rail arrangement68vertically along the z-axis.

The upper ends of the rails70support a horizontal optics rail72wherein the optics rails72includes a plurality of horizontal slots73for slidably supporting optical components thereon. The rearward end of the optics rail72has a downwardly depending support rail76on which the homogenizer lenses67are slidably supported. The lenses67may be adjusted vertically for adjusting the characteristics of the laser beam62. Additionally, the opposite end of the optics rail72further includes another downwardly depending support rail77.

With respect to the optics rail72, a first turning mirror79is provided directly above the homogenizer lenses67to receive the beam therefrom and redirect the beam sidewardly along the length of the optics rail72. Proximate the other end of the optics rail72, a field lens80is slidably supported on the rail slots73which lens80further includes a generally rectangular mask81adjacent thereto on the downstream side of the field lens80. As will be described in further detail herein, the mask81serves to shape the laser beam prior to application of the laser beam62to the seal ring10.

The shaped laser beam62thereby travels horizontally downstream from the field lens80and is redirected downwardly by another turning mirror83. Lastly, the shaped laser beam62passes through a final objective lens84and then projects downwardly onto the seal face15as generally illustrated inFIG. 2B.

To prevent contamination of the final objective lens84particularly in view of the proximity of the final objective lens84to the rotary support table34, the final objective lens84also includes a funnel-like shroud86(FIGS. 2B and 3) having a downward opening exit port87. An air feed88is connected to the shroud86and provides an air flow into the shroud86which air flow blows downwardly through the exit port87so that any debris from the laser process is blown away from the objective lens84.

During operation, the laser is selectively turned on, i.e. fired or pulsed, to cut and vaporize seal ring material as the laser beam62is applied to an exposed area of the seal ring10. By selectively turning the laser on and off, circumferentially spaced apart cuts may be made to the seal ring.

In the illustrated embodiment, the seal ring support assembly32not only positions the seal ring10relative to the laser beam62, the seal ring support assembly32also effects rotation of the seal ring10by the rotary table34relative to the laser beam62. This thereby creates circumferential cutting of the seal face15during pulsing of the laser beam62, although it also should be understood that it is possible to shift the seal ring10in the x-axis and y-axis directions to effect linear displacement of the seal ring10if desired rather than just rotatable displacement thereof. Further, it will be understood that relative movement between the laser beam62and seal ring10may be provided with a movable laser beam62wherein the seal ring10instead is kept stationary, or even simultaneous movement of both the laser beam62and seal ring10.

With respect to the mask81, this mask serves to shape the laser beam62to a desired cross-sectional shape which optimizes cutting of the seal ring10. For example, as diagrammatically illustrated inFIG. 4, the mask81is a rectangular thin plate preferably formed of a stainless-steel material although a thin sheet of other suitable material may be used. While a mask81is provided along the length of the beam, the mask81can be positioned at other locations, and further, any other shaping device which shapes the laser beam62alternatively may be used.

The mask81includes therein a shaping aperture or hole90which opens horizontally therethrough and has a predefined geometric shape. The hole90is shown substantially enlarged although it will be understood that the aperture90has a significantly smaller diameter relative to the dimension of the plate81. Preferably, the shaping aperture90has a diameter of 0.4 to 0.5 inches, and the beam is demagnified by the objective lens84to form a beam shape diameter of 0.04 to 0.05 inches. The objective lens84, however, is adjustable to vary the demagnification of the beam62.

As seen inFIG. 5, the shaped laser beam62exits the aperture90of the mask81, and is redirected downwardly to the final objective lens84through the turning mirror83. Thereafter, the shaped laser beam62illuminates the seal face15of the seal ring10with a substantially circular beam shape defined at the terminal end92of the laser beam62. The circular beam end92defines the exposed area of the beam62on the seal face15and defines the area in which ablation or vaporization of the seal ring material occurs.

More particularly with respect toFIG. 4, first and second radiuses R1and R2of the shaping aperture90are identified therein. Since the illustrated aperture90is a circle, the first and second radiuses are equal. These radiuses, however, are identified separately since the first radius R1extends horizontally of the mask81and due to redirection of the beam62, thereby defines the lateral width of the laser beam end92on the seal face15.

In particular, the lateral width of the beam62is twice the first radius or in other words is defined by the diameter of the circular shaping aperture90. Due to the orientation of the seal ring10relative to the beam62, the lateral width of the beam62extends radially on the seal face15. The second radius is oriented perpendicular to the first radius and defines the length of the beam end92, which due to the orientation of the seal ring10extends circumferentially along the seal face15in the direction along which the laser beam62travels.

Referring toFIG. 6, the beam end92moves progressively along the seal face15due to the relative rotation of the seal ring10and the laser beam62. Since continuous relative movement is provided therebetween, a circumferentially elongate ablation cut or groove94is defined in the seal face15. Due to the circular shape of the beam62, more laser energy passes through the central section95of the mask opening90and less energy passes through the side regions96of the circular beam shape. As a result, the circular beam shape defines a groove94that has a semi circular interior surface97which is deeper in the middle thereof and shallower along the longitudinal side edge sections98of the ablation cut94.

The shape of the ablation cut94thereby distinctly differs from the shape of an ablation cut100that is otherwise defined by a laser beam101having a square shape. The circular beam shape provides distinct advantages as described in further detail herein.

Turning first to the rectangular shaped beam101, the laser unit14of the invention was tested with a square or rectangular opening in the mask81to shape the laser beam62with the square shape diagrammatically illustrated inFIG. 6. The resulting rectangular cut100has a uniform depth across the entire radial width, whereby the seal ring10(as illustrated inFIG. 7) was rotated so that the seal surface15moved circumferentially relative to the laser beam end102(FIG. 6).

This rectangular laser beam101was used to define a wavy shaped seal ring wherein one circumferential section of the seal ring is diagrammatically illustrated inFIG. 7. In the construction of the illustrated seal ring10-1with the laser unit14of the invention, a valley23is formed which is defined between a circumferentially spaced apart pair of peaks24and radially outwardly of a sealing dam20. The wavy face was formed by starting in the shallower end of the valley23near the sealing dam20and then cutting additional ablation cuts radially outwardly therefrom. The peaks24and sealing dam20are defined by the original seal surface outside of the boundary of the valley23and thus, no laser cutting was performed in these areas.

More particularly, the process of the invention was tested with a rectangular aperture mask. The valley23is formed by moving the laser beam101through a first plurality of passes along a first cutting radius CR1to cut a first ablation cut103having a desired shape. The first pass at this first cutting radius CR1is initiated at a first circumferential location104wherein the laser beam101is pulsed on or fired and continued through a circumferentially spaced apart second location105wherein the laser beam101is pulsed off to cause ablation of the seal ring material along the circumferential length defined between these locations104and105. The depth of this first cut is uniform across the radial width thereof as generally indicated byFIG. 6and is uniform along the circumferential length thereof. During the next successive revolution of the seal ring10by rotation of the support table34, the laser beam101is fired at location106and turned off at location107. Additional cutting passes are provided at the first cutting radius during successive revolutions of the seal ring10. The first cut103has a longitudinal depth which progressively increases away from the opposite ends defined at locations104and105to the deepest location defined by the sixth cutting pass at location108.

Once the first ablation cut103is completed, the seal ring10is moved radially relative to the beam end102so that the laser beam101now cuts along a second cutting radius CR2which is located radially outwardly of the first cut radius CR2and defines a second cut110. This second cut110has a longer circumferential length than the first cut103and is formed by a greater number of passes then the first cut103so as to have a greater depth but otherwise is cut with the same process as the process discussed above.

As each cut is completed by one or mare passes of the laser beam62, the seal ring10is shifted radially relative to the beam101such that the ablation cuts are shifted progressively outwardly to greater cutting radiuses until the final cut111is completed along the outer radius17. As a result of this cutting process, each cut such as cut103is contiguous to the next radially outward cut such as cut110wherein these adjacent ablation cuts103and110are disposed sidewardly adjacent to each other in contiguous relation.

If the sealing dam20is at the outer diameter17, the process remains the same except that the laser beam62starts near the outer diameter17and is progressively shifted radially inwardly so that the cutting radiuses progressively decrease.

It was found, however, that the rectangular laser beam101, even with this circumferential cutting process, results in excessive depth grooves being formed between contiguous ablation cuts which is a problem similar to that which occurred in prior processes used to define seal faces with lasers.

More particularly, as illustrated inFIG. 8, the circumferentially elongate sides of contiguous cuts such as cuts103and110overlap at least to a limited extent which thereby causes a greater amount of ablation in the overlap regions and the formation of an excessive depth groove115(FIGS. 6 and 7) therebetween. Similar excessive depth grooves116and117are defined between a third ablation cut118and a fourth ablation cut119with the groove117being longer than the groove115. These excessive depth grooves115,116and117as well as additional such grooves defined by overlapped contiguous ablation cuts thereby extend along the circumferential length of the ablation cuts. These excessive depth grooves can adversely impact seal performance.

Further, as illustrated inFIG. 7, the rectangular ends of each cut such as the ends104and105of the first cut103define abrupt steps along the peripheral edge or boundary120of the valley23being formed.

With the circular beam shape ofFIG. 6and the semi circular cut94resulting therefrom, the cutting process of the laser unit14is optimized and the disadvantages associated with the rectangular beam shape are substantially eliminated. Referring toFIG. 9, it is possible to form a first cut generally identified by reference numeral94-1and then define a second cut94-2which is radially contiguous or adjacent to the first cut94-1. For illustrative purposes, the first and second cuts94-1and94-2are vertically offset to more clearly illustrate the area of overlap125which is defined therebetween. This area of overlap is defined by the radial distance between one side section98of the first cut94-1and the side section98of the second cut94-2wherein overlap area95is defined as extending radially between the side sections98.

Referring to the graphs ofFIGS. 10–12, contiguous ablation cuts127and128formed in the seal ring face15are illustrated as well as the final profile of the depth feature formed by the ablation cuts127and128. As shown herein, the area of overlap can be varied while still avoiding the formation of excessive depth grooves which exceed the depth of the ablation cuts127and128. As for these graphs, the ablation depth of the ablation cuts is illustrated along the vertical axis in −10 micro inch increments which are measured negatively from the seal face15. The horizontal graph axis identifies the radial position along the seal face15in 0.1 inch increments measured positively and negatively from a 0 position located approximately at the center of the first ablation cut127.

With the laser set as illustrated inFIG. 10, the beam end92as it is moved through two contiguous cuts127and128are overlapped by 10 percent of the diameter of the beam end92. As a result, only a relatively shallow intermediate groove126is defined between the adjacent pair of cuts127and128. In particular, the ablation cut127is defined by a single pass, and the cut128is defined by two passes, i.e. a double pass of the laser beam62through two revolutions of the seal ring10. It will be understood that the profile of the second ablation cut128will be substantially the same only deeper if additional beam passes are performed.

More particularly, the single ablation cut127has a depth of 20 micro inches, while the radially adjacent double pass or double ablation cut128cuts the seal ring10to a depth of 40 micro inches into the seal face15. In the area of overlap, the continuity of the arc of the interior surface97is broken in the region of overlap to define the shallow intermediate groove126. However, the depth of the shallow groove126is controlled so as to be less than 30 micro inches and still does not exceed the maximum acceptable depth of 40 micro inches which is the depth of the second ablation cut128.

FIG. 11illustrates the resulting profile of the same cutting process except that a 25 percent overlap is provided. Notably the first cut127and the second cut128have the same maximum depths as the corresponding cuts defined inFIG. 10. However, the middle groove126has a greater depth of approximately 40 micro inches. This is close to the maximum 40 micro inch depth of the second cut128and thereby reflects a maximum amount of overlap for the circular beam shape92which avoids excessive depth grooves.

Referring toFIG. 12, this graph depicts the profile of the cuts127and128with a 50 percent diameter overlap. Notably, the depth of the intermediate groove126is approximately 52 micro inches which exceeds the maximum acceptable depth of the deeper groove128. This graph therefore establishes that exceeding the 25 percent overlap limit results in excessive depth grooves being formed and indicates that it is undesirable to have an overlap of greater than 25 percent.

With respect to the lower overlap limit, this limit is believed to be zero percent since the depth of the groove126decreases with a corresponding decrease in the percentage of overlap and accordingly, with a zero percent overlap, no intermediate groove126would be formed.

In view of the foregoing, the circular beam shape is shown to eliminate excessive depth grooves when the percentage overlap is between zero and about 25 percent of the circular beam shape. Notably, the maximum overlap may exceed 25 percent if the seal ring is deemed to operate acceptably with such a groove. Even at 50 percent overlap, the circular beam shape is shown to result in an intermediate groove126having a depth which is less than the depth which would result from a rectangular shape beam since the excessive depth groove resulting from a rectangular beam shape would be 60 micro inches.

In addition to the reduction and ability to eliminate excessive depth intermediate grooves, the use of the circular shaped beam and the other alternate beam shapes discussed in further detail hereinafter is believed to provide desirable blending of the adjacent edges of each laser cut. In this regard,FIG. 13diagrammatically illustrates that the stepped peripheral edge120resulting from rectangular beam shapes (seeFIG. 7) is substantially eliminated with the beam shapes of the invention disclosed herein. In particular, the leading and terminal edges of the circular laser beam identified by reference numerals132and133(FIG. 4) are arcuate due to the curvature defined by the second radius R2identified inFIG. 4. Therefore, the leading and trailing ends of each successive cut, such as ends134and135of cut136, are curved rather than having a stepped rectangular shape. As such, the resulting periphery or boundary137, for example, of the valley23being defined in the seal ring10is believed to have a more blended arcuate shape. This is also true in areas located between the trailing and leading ends134and135of each cut and specifically, at the opposite ends138and139of each pass of the laser beam. These ends138and139define intermediate transition lines which are identified by reference lines140inFIG. 13and extend generally parallel to the boundary line137.

In addition to the circular beam shape discussed above, alternate beam shapes are illustrated inFIGS. 14–16which beam shapes are shaped or created by providing the mask opening90with a corresponding shape. With respect toFIG. 14, the opening provided in the mask81is elliptical wherein opposite side edges142and143have a curvature defined by a first radius R1, and leading and trailing end edges144and145have a curvature defined by a second radius R2greater than the first radius.

This elliptic beam shape has a greater lateral width to provide a greater width to the ablation cut being formed thereby. Further, if the laser beam exiting the attenuator port66is rectangular, the elliptic beam shape maximizes the area of the initial laser beam which is finally used for cutting the seal face.

The overlap limits discussed above relative toFIGS. 10–12are applicable hereto although the upper limit is converted to about 50% of the radius R1of the side edges142and143. This limit will also be affected if the transition T1between the radiuses of curvature of the side edges142,143and the end edges144,145is located at a distance away from the apex A1of the side edges142,143which is less than half the radius of curvature (R1/2).

Further, the leading and trailing end edges144and145have a more gradual curvature compared to the circular beam shape which is believed to provide improved blending along the boundary line137of the valley23being formed.

As to the alternate beam shape ofFIG. 15, linear end edges are provided which define the leading and trailing ends147and148of the beam shape. The opposite side edges149and150of this geometric beam shape are semi-circular sections having the same radius R1. Preferably the side edges149and150are half circles so that the overlap limits discussed above relative toFIGS. 10–12are equally applicable hereto although the overlap limits are 0 to 50% of the radius of each side edge149and150rather than 0 to 25% of the diameter of the circular beam shape.

A further alternate beam shape is illustrated inFIG. 16, wherein the curved edges151and152define the leading and trailing ends of the beam while linear edges153and154define the opposite side edges of the beam shape. This shape is believed to provide similar results as the circular beam shape discussed above.

In all of these alternate beam shapes the opposite side edges generally converge toward the apex thereof so that the longitudinal length of the beam shape progressively decreases from the center thereof. While these side edges could be defined by a pair of linear side edge sections which converge to the apex, the side edge sections are non-linear and preferably are continuously curving such as by arcs, curves or short linear line sections. For example with respect to the circular beam shape ofFIG. 4, the side edge sections156and157are quarter circles which extend laterally from the points158and converge to the apex point159. As a result, the longitudinal length of the side edge regions generally identified by length line160decreases non-linearly due to the curvature of the side sections156and157.

These non-linear side edges are found to remove less material along adjacent edges of contiguous ablation cuts so as to be less sensitive to variations in the overlap percentage than would occur if the side edge sections were linear. Accordingly, the non-linear nature of the shaping aperture90blends contiguous ablation cuts more effectively and with less sensitivity to overlap accuracy and will result in a cut depth closer to the depth desired.

With the above-described arrangement, the formation of excessive depth grooves between contiguous ablation cuts is eliminated. Further, the ablation cuts are blended in two dimensions, radially between adjacent cuts and circumferentially at the ends of the cuts.

In actual comparative testing of wavy face seals formed by the inventive method and formed by shrink bands, the inventive seal ring10is found to have a reduction of gas leakage of up to 25% statically and up to 50% dynamically. This improvement is believed to result from the laser process of the invention including the increased accuracy and precision by which the seal ring is constructed.

While the side sections curve or bow outwardly, at least one of these side sections165may be inverted so as to bow inwardly toward the center of the beam shape166as seen inFIG. 17. This inverted side section165thereby has a generally forked shape, and is able to be overlapped with the outward bowing side section167on the opposite side of the beam shape166. The side sections165and167preferably have the same radius R1.

In operation, the seal ring10is constructed as follows: a seal ring is provided preferably having a flat seal face; a laser is provided having a laser beam that is directed to said seal face; the laser beam is shaped so as to have a geometric shape with convergent non-linear side edges so that the cut of the laser beam has a non-uniform depth across the width thereof; a plurality of ablation cuts are provided with said laser beam over at least a portion of the seal face to create one or more micro-topography depth features such as a wavy face, each cut being formed by one or more passes of the laser beam relative to the seal face. The ablation cuts are contiguous to each other wherein the adjacent side edge regions of each pass of the laser beam are overlapped. The adjacent cuts are overlapped to prevent formation of excessive depth grooves.