JP2006346857A - Polishing tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing tool suitable to precisely polish a hard and brittle material such as ceramics and a composite comprising ceramics at grinding wheel peripheral velocity up to 160 m/s. <P>SOLUTION: This polishing tool includes a grinding wheel core 2 mounted on a dense metal bonded superabrasive segment 8 by a thermally stable bond 6. The tool favorable for back grinding of a ceramic wafer includes a graphite filler and abrasive 4 of a comparatively low degree of concentration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  This application is filed in US application Ser. No. This is a continuation-in-part application of 09 / 049,623. The present invention is suitable for precision grinding of hard and brittle materials such as ceramics and composites containing ceramics at peripheral speeds up to 160 m / s, and surface grinding of ceramic wafers ( The present invention relates to abrasive tools suitable for surface grinding.

The abrasive tool includes a grindstone core or hub attached to the metal that is bonded to the superabrasive rim with a thermally safe binder during the grinding operation. These polishing tools grind ceramics at a high removal rate (for example, 19 to 380 cm ³ / min / cm), have less grinding wheel wear than conventional polishing tools, and damage to a workpiece is small.
A polishing tool suitable for grinding sapphire and other ceramic materials is disclosed in US Pat. No. 5,607,489 to Li. The tool is described as containing metal clad diamond bonded in a vitrified matrix having a solid lubricant of 2-20 vol% and a porosity of at least 10 vol%.

An abrasive tool comprising diamond bonded in a metal matrix having a selected filler of 15-50 vol% such as graphite is disclosed in Keat US Pat. No. 3,925,035. The tool is used to grind cemented carbides.
A cutting-off wheel made of metal bonded diamond abrasive is disclosed in US Pat. No. 2,238,351 to Van der Pyl. The binder includes copper, iron, tin, and optionally nickel, and the fixed abrasive is sintered to the steel core, but optionally with a soldering process to ensure proper adhesion. Also good. The best binder is reported to have a Rockwell hardness of 70.

  An abrasive tool comprising fine diamond grains bonded in a relatively low melting temperature metal binder such as a bronze binder is disclosed in US Reissue Patent No. 21,165. ing. The low melting point binder helps to avoid the oxidation of fine diamond grains. The abrasive rim is assembled as a single, annular abrasive segment and then attached to a central disk of aluminum or other material.

  None of these polishing tools have been shown to be fully satisfactory in precision grinding of ceramic components. These tools do not meet strict specifications for part shape, size and surface quality when operated at commercially viable grinding speeds. The most mass-produced polishing tools recommended for use in these operations are resin or vitrified bonded designed to operate with relatively low grinding efficiency to avoid surface and half-surface damage to the ceramic components It is a superabrasive grindstone. Grinding efficiency is further reduced due to the tendency of ceramic workpieces to clog the grinding wheel surface, often requiring the grinding wheel to be dressed and reshaped to maintain a precise shape.

Improved polishing for precision grinding of ceramics as products have increased market demand for precision ceramic components in products such as engines, refractory equipment and electronic devices (eg, wafers, magnetic heads and display windows) There is an increasing demand for tools.
For example, in finishing high performance ceramic materials for electronic components such as alumina-titanium carbide (AlTiC), surface grinding or “back grinding” operation is a relatively slow grinding operation with low force, Requires a high quality, flat surface finish.In the back grinding of these materials, the grinding efficiency is controlled by controlling the quality of the workpiece surface and the resistance used, as well as the high removal speed and wear resistance of the wheel. It is determined.

The present invention relates to an abrasive defined by a core having a minimum specific strength parameter of 2.4 MPa-cm ³ / g, a core density of 0.5 to 8.0 g / cm ³ , a circular perimeter, and a number of abrasive segments. A surface grinding and polishing tool including a grain rim; wherein the abrasive segments are selected in a total amount of 100 vol%, superabrasive grains 0.05 to 10 vol%, brittle filler 10 to 35 and a metal binder matrix having a fracture toughness of 1.0 to 3.0 MPa M1 ^{/ 2} , 55 to 89.95 vol%. The specific strength parameter is defined as the smaller ratio of the material's yield strength or fracture strength divided by the material density. The brittle filler is selected from the group consisting of graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline sianite, pumice, calcined clay and glass spheres and combinations thereof. In a preferred embodiment, the metal binder matrix has a porosity of up to 5 vol%.

  The polishing tool of the present invention is a grinding wheel including a core having a center hole for attachment to a grindstone, and the core is designed to support a superabrasive rim that is metal-bonded along the outer periphery of the grindstone. . These two parts of the wheel are supported by a thermally stable binder under grinding conditions, and the wheel and its components are stresses generated at a peripheral speed of the wheel of at least up to 80 m / sec, preferably up to 160 m / sec. Designed to withstand. Preferred tools are a 1A type grindstone and a cup-shaped grindstone, for example, a 2 or 6 type grindstone, or an 11V9 type bell-shaped cup grindstone.

The core is substantially circular in shape. The core may comprise any material having a minimum specific strength of 2.4 MPa-cm ³ / g, preferably 40-185 MPa-cm ³ / g. The core material has a density of 0.5 to 8.0 g / cm ³ , preferably 2.0 to 8.0 g / cm ³ . Examples of suitable materials are steel, aluminum, titanium and bronze, as well as their composites and alloys and combinations thereof. Reinforced plastics having a specified minimum specific strength can also be used to assemble the core. Composite and reinforced core materials usually have a continuous phase of a metal or plastic matrix, often in powder form, to which fibers, particles of harder, more rebound and / or lower density materials are impregnated. It is added as a continuous phase. Examples of reinforcing materials suitable for use in the tool core of the present invention are glass fibers, carbon fibers, aramid fibers, ceramic fibers, ceramic particles and hollow filler materials such as glass, mullite, alumina and zeolite spheres. is there.

Steel and other metals having a density of 0.5-8.0 g / cm ³ can be used to make the core for the tool of the present invention. Light metal powder forms such as aluminum, magnesium and titanium, and their alloys and mixtures thereof are suitable for the manufacture of cores used for high speed grinding (eg at least 80 m / sec). Aluminum and aluminum alloys are particularly suitable. If a co-sinter assembly process is used to produce the tool, a metal with a sintering temperature of 400-900 ° C, preferably 570-650 ° C is selected. Low density filler material can be added to reduce the mass of the core. Porous and / or hollow ceramic or glass fillers, such as glass spheres and mullite spheres, are suitable materials for this purpose. In addition, useful are inorganic and non-metallic fiber materials. When indicated by processing conditions, lubricants or other processing aids known in the field of metal binders and superabrasives can be added to the metal powder prior to molding and sintering. .

The tool should be strong, durable and dimensionally stable to withstand potentially destructive forces that occur during high speed operation. The core must have a minimum specific strength in order to operate the wheel at the very high angular velocities necessary to achieve a tangential contact speed of 80-160 m / s. The minimum specific strength parameter required for the core material used in the present invention is 2.4 MPa-cm ³ / g.

The specific strength parameter is defined as the ratio of the yield (or fracture) strength of the core material divided by the core material density. In the case of brittle materials having a fracture strength lower than the yield strength, the specific strength parameter is determined using the fracture strength, which is the smaller number. The yield strength of a material is the minimum resistance to which the strain of the material is subject to increasing tension without further increase in resistance. For example, ANSI 4140 steel hardened above about 240 (Brinell hardness) has a tensile strength greater than 700 MPa. The density of this steel is about 7.8 g / cm ³ . Thus, the specific strength parameter is about 90 MPa-cm ³ / g. Similarly, certain aluminum alloys, such as Al2024, Al7075, and Al7178, which can be heat treated to a Brinell hardness of greater than about 100, have a tensile strength greater than about 300 MPa. Such an aluminum alloy has a low density of about 2.7 g / cm ³ and thus exhibits a specific strength parameter greater than 110 MPa-cm ³ / g. Titanium alloys and bronze composites and alloys made to have a density of 8.0 g / cm ³ or less are also suitable for use.

The core material is tough, thermally stable at temperatures reached in the grinding zone (eg, about 50-200 ° C.), resistant to chemical reactions with coolants and lubricants used in grinding, and the grinding zone It should be resistant to wear due to corrosion due to the movement of cutting waste. Although some alumina and other ceramics have acceptable failure values (ie, greater than 60 MPa-cm ³ / g), they are usually too brittle and structurally with high speed grinding due to failure fall into disrepair. Ceramics are therefore not suitable for use in tool cores. Metals, especially hardened tool grade steel, are preferred.

  The abrasive grain segment of the grinding wheel used in the present invention is a segmented or continuous rim attached to the core. A segmented abrasive rim is shown in FIG. The core 2 has a center hole 3 for attaching a grindstone to an arbor of a power drive (not shown). The abrasive rim of the grindstone includes superabrasive grains 4 embedded in metal matrix binder 6 (preferably to a uniform concentration). A large number of abrasive grain segments 8 constitute the abrasive rim shown in FIG. Although the exemplary embodiment shows 10 segments, the number of segments is not important. As shown in FIG. 1, each abrasive grain segment has a rectangular ring shape (arch shape) with a truncated end characterized by a length l, a width w, and a depth d.

  The embodiment of the grinding wheel shown in FIG. 1 is a representative example of a grinding wheel that can be successfully operated in accordance with the present invention and should not be considered limiting. Numerous shapings of segmented grinding wheels that appear to be suitable include: cup-shaped wheels as shown in FIG. 2, wheels with openings between cores and / or gaps between successive segments, and cores Includes whetstones having abrasive segments of different widths. The opening or gap may be used to provide a passage for introducing coolant into the grinding zone and for delivering cutting waste from the zone. Segments wider than the core width may be used to protect the core structure from corrosion through contact with the chips as the grindstone penetrates the workpiece radially.

  The wheel can be manufactured by first shaping individual segments of preselected dimensions and then attaching the pre-formed segments to the core periphery 9 with a suitable adhesive. Another suitable manufacturing method is to form a segment precursor unit of the abrasive and binder powder mixture, shape the composition around the periphery of the core, and create and attach the segments in situ ( That is, applying heat and pressure to the core and rim for co-sintering). The co-sintering method is suitable for producing a surface grinding cup grindstone used for back grinding hard ceramic wafers and chips such as AlTiC.

  The abrasive rim component of the polishing tool of the present invention can be a continuous rim or a discontinuous rim, as shown in FIGS. A continuous abrasive rim includes one abrasive segment, or at least two abrasive segments, which are separately sintered in a mold and then thermally stable binder (ie, a segment directed from the grinding surface). At a temperature encountered during grinding, usually about 50-350 ° C., and a stable binder). As shown in FIG. 2, discontinuous abrasive rims are manufactured from at least two such segments, and the segments are separated by rim grooves or gaps, such as in a segmented continuous abrasive rim wheel. The edges cannot be matched along the length 1 of the. The figures illustrate preferred embodiments of the invention and are not intended to limit the type of tool design of the invention. For example, discontinuous rims can be used for 1A wheels and continuous rims can be used for cup wheels.

  For high-speed grinding, particularly grinding of a workpiece having a cylindrical shape, a continuous rim and a grindstone of type 1A are suitable. A segmented continuous abrasive rim is preferred and spans a single continuous abrasive rim as it is very easy to achieve a truly round and planar shape while manufacturing a tool from multiple abrasive segments. It is shaped like a single piece in a ring shape. For relatively low speed (e.g. 25-60 m / sec) operations, especially flat workpiece surfaces and finish grinding, discontinuous abrasive rims (e.g. the cup wheel shown in Fig. 2) are preferred. Since surface quality is important in low speed surface finishing operations, grooves are formed in the segments, or some segments are omitted from the rim to help remove scrap material that can scratch the workpiece surface. sell.

The abrasive rim component comprises superabrasive grains held in a metal matrix binder and the metal binder powder in a mold designed to produce the desired size and shape of the abrasive rim or abrasive rim segment. And is usually obtained by sintering a mixture of abrasive grains.
The superabrasive used in the abrasive rim may be selected from natural or synthetic diamond, CBN, and combinations of these abrasives. The choice of particle size and type will vary depending on the nature of the workpiece and the type of grinding process. For example, in grinding and polishing sapphire or AlTiC, a superabrasive grain size in the range of 2 to 300 μm is preferred. For grinding other aluminas, a superabrasive grain size of about 125-300 μm (60-120 grit; Norton Company grit diameter) is usually preferred. For grinding silicon nitride, a particle size of about 45-80 μm (200-400 grit) is usually preferred. A relatively fine grit diameter is suitable for surface finishing and a relatively large grit diameter is suitable for cylindrical, profile or innermeter grinding where a relatively large amount of material is ground. is there.

  As volume% of the abrasive rim, the tool contains 0.5-10 vol% superabrasive, preferably 0.5-5 vol%. A small amount of filler, which has a lower hardness than the metal binder matrix, can be added as a binder filler to increase the wear rate of the binder. As volume% of the rim component, the filler can be used at 10 to 35 vol%, preferably 15 to 35 vol%. A suitable brittle filler material is characterized by suitable thermal and mechanical properties to withstand the sintering temperature and pressure conditions used to produce the abrasive segments and to assemble the wheel. Graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline sianite, pumice, calcined clay and glass spheres, and combinations thereof are examples of useful brittle filler materials.

Any metal binder suitable for bonding superabrasives and having a fracture toughness of 1.0-6.0 MPa · m ^1/2 , preferably 2.0-4.0 MPa · m ^1/2 , It can be used here. Fracture toughness is a stress strength factor that causes cracks in a material to spread into the material and lead to material failure. Fracture toughness is expressed as K _1c = (σ _f ) (π ^1/2 ) (c ^1/2 ), where K _1c is the fracture toughness, σ _f is the stress subjected to fracture, and c is It is 1/2 of the crack length. There are several methods that can be used to measure fracture toughness, each having an initial stage in which a known size crack occurs in the test material and then stressed until material failure. Stress at fracture and crack length are substituted into the equation to calculate fracture toughness (for example, fracture toughness of steel is about 30-60 MPa · m ^1/2 , alumina is about 2-3 MPa. M ^1/2 , silicon nitride is about 4-5 MPa · m ^1/2 , and zirconia is about 7-9 MPa · m ^1/2 ).

  In order to optimize wheel life and grinding performance, the binder wear rate must be equal to or slightly greater than the abrasive wear rate during the grinding operation. Fillers as described above may be added to the metal binder to reduce the wear rate of the grindstone. Metal powders that tend to form a relatively dense binder structure (i.e., less than 5 vol% porosity) are preferred because they allow a relatively high grinding rate during grinding.

  Materials useful in the rim metal binder include, but are not limited to, bronze, copper and zinc alloys (brass), cobalt, and iron, and alloys thereof and mixtures thereof. These metals can be carbide or nitrided between the abrasive grains and the binder at the surface of the superabrasive grains under selected sintering conditions such as titanium or titanium hydride, or strengthening the abrasive / binder status. It can be used with other superabrasive materials that have the ability to form chemical bonds of objects (ie, active binding components).

The relatively strong abrasive / binder interaction limits the rapid loss of abrasive and workpiece damage, as well as the shortened tool life caused by rapid abrasive loss.
In a preferred embodiment of the abrasive rim, the metal matrix comprises 55-89.95 vol%, preferably 60-84.5 vol% of the rim. The brittle filler contains 10-35 vol%, preferably 15-35 vol% of the abrasive rim. The porosity of the metal matrix binder should be maintained at a maximum of 5 vol% during the manufacture of the abrasive segment. Preferably, the metal binder has a Knoop hardness of 2-3 GPa.

  In a preferred embodiment of the type 1A grinding wheel, the core is made of aluminum and the rim includes a bronze binder made of copper and tin powder (80/20 wt%), which optionally contains phosphorus to phosphorus / copper powder. In the form of 0.1 to 3.0 wt%, preferably 0.1 to 1.0 wt% may be added. During the manufacture of the abrasive segment, the metal powder of this composition is mixed with 100-400 grit (160-45 μm) diamond abrasive, molded into an abrasive rim segment and 400-550 ° C. at 20-33 MPa. To produce a dense abrasive rim that is sintered or densified, preferably having a density of at least 95% of the theoretical density (ie, having a porosity of less than 5 vol%).

  In a typical co-sintered whetstone manufacturing method, the core metal powder is poured into a steel mold and cold compressed at 80-200 kN (pressure about 10-50 MPa) to give about 1 of the desired final thickness of the core. Form raw parts having a size of 2 to 1.6 times. The raw core part is placed in a graphite mold and a mixture of abrasive grains (grit diameter 2-300 μm) and metal binder powder blend is added to the cavity between the core and the outer edge of the graphite mold. A setting ring can be used to compress the abrasive and metal binder powder to the same thickness as the co-appli foam. The graphite-type contents are then hot compressed at 370-410 ° C. under a pressure of 20-48 MPa for 6-10 minutes. As is known in the art, the temperature is ramped (eg, from 25 ° C. to 410 ° C. for 6 minutes; held at 410 ° C. for 15 minutes) or increased in removal before pressure is applied to the mold contents You may let them.

Following hot compression, the graphite mold is removed from the part, the part is cooled, and then the part is finished by conventional methods to obtain an abrasive rim having the desired dimensions and tolerances. For example, the part may be sized using a vitrified grinding wheel on a grinder or a carbide on a lathe.
When co-sintering the core and rim of the present invention, little grinding is required to bring the part to its final shape. In other methods of forming a thermally stable bond between the abrasive rim and the core, both the core and rim cuts to match the parts and ensure a suitable surface for bonding It may be necessary before the joining, connecting or diffusion stage.

  When using a segmented abrasive rim to create a thermally stable bond between the rim and core, use any thermally stable adhesive with strength to withstand wheel peripheral speeds of up to 160 m / sec Can be done. A thermally stable adhesive is stable to the grinding process temperature likely to be encountered at the portion of the abrasive grain segment directed from the grinding surface. Such temperatures usually range from about 50 to 350 ° C.

  The adhesive bond must be mechanically very strong to withstand the destructive resistance that exists during the rotation of the grinding wheel and during the grinding operation. A two-part epoxy resin bonding agent is preferred. A suitable epoxy adhesive, Technodyne ™ HT-18 epoxy resin (obtained from Taoka Chemical, Japan), and its modified amine curing agent, can be mixed with 19 parts curing agent in a ratio of 100 parts resin. . Fillers such as fine silica powder can be added in a ratio of 3.5 parts per 100 parts of resin to increase the viscosity of the binder. The segments can be attached with a bonding agent around the entire circumference of the grinding wheel core or partially around the core. The perimeter of the metal core may be sandblasted to achieve a degree of roughness prior to segment attachment. A densified epoxy bond is used at the end and bottom of the segment that is positioned around the core substantially as shown in FIG. 1 and is held appropriately mechanically during curing. The epoxy bonding agent is cured (eg, 24 hours at room temperature and then 48 hours at 68 ° C.). During curing and segment transfer, bond drainage is minimized during cure by adding sufficient filler to optimize the viscosity of the epoxy bond.

  The strength of the adhesive bond can be tested by a spin test at an acceleration of 45 rev / min so that it can be used to determine the grinding wheel burst rate. The wheel must exhibit a burst rating equal to a tangential contact speed of at least 271 m / s in order to qualify for operation at a safety standard currently applicable in the United States, 160 m / s tangential contact speed It is.

  The abrasive tool of the present invention is specifically designed for precision grinding and finishing of brittle materials, such as advanced ceramic materials, glass, and components including ceramic materials and ceramic composites. The tools of the present invention include silicon, single and polycrystalline oxides, carbides, borides and silicides; polycrystalline diamond; glass; and ceramic composites in a non-ceramic matrix; and combinations thereof. Suitable for (but not limited to) ground ceramic materials.

  Examples of representative workpiece materials are AlTiC, silicon nitride, silicon oxynitride, stabilized zirconia, aluminum oxide (eg, sapphire), boron carbide, boron nitride, titanium diboride, and aluminum nitride, and ceramics thereof. Composites, as well as certain metal matrix composites such as cemented carbide, and hard brittle amorphous materials such as mineral glasses. Both single crystal ceramics and polycrystalline ceramics can be ground with these improved polishing tools. For any type of ceramic, the quality of the ceramic parts and the efficiency of the grinding operation increase as the peripheral speed of the grinding wheel of the present invention increases from 80 to 160 m / s.

  Among the ceramics, parts improved with the polishing tool of the present invention are ceramic engine valves and rods, pump seals, ball bearings and fittings, cutting tool inserts, wear parts, metal forming draw dies, refractory elements Ceramic electronic elements including, but not limited to, visual display windows, windshields, flat glass for doors and windows, insulators and electronic components, and silicon wafers, AlTiC chips, read-write magnetic heads, and substrates .

  Unless otherwise indicated, all parts and percentages in the following examples are by weight. The examples are merely illustrative of the invention and are not intended to limit the invention.

Example 1
The grindstone of the present invention was manufactured in the form of a 1A1 metal bonded diamond grindstone using the following materials and methods.

Copper powder (dendritic FS grade, particle size + 200 / -325 mesh, obtained from Sintertech International Marketing Corp., Ghent, NY) 43.74 wt%; phosphorus / copper powder (1501 grade, + 100 / -325 mesh particle size, (Obtained from New Jersey Zinc Company, Palmerton, PA) 6.24 wt%; and tin powder (MD115 grade, +325 mesh, up to 0.5%, particle size, obtained from Alcan Metal Powders, Inc., Elizabeth, New Jersey) 50 A blend of 0.02 wt% was prepared. Diamond abrasive (320 grit diameter synthetic diamond obtained from General Electric, Worthington, Ohio) was added to the metal powder blend and mixed until uniformly blended. The mixture is placed in a graphite mold until a matrix with a target density greater than 95% of theory is formed (eg, for the # 6 wheel used in Example 2: greater than 98.5% of theoretical density). And compressed hot at 3000 psi (2073 N / cm ² ) for 15 minutes at 407 ° C. The Rockwell B hardness of the segment produced for the # 6 grindstone was 10 ⁸ . The segment contained 18.75 vol% abrasive. The segment is ground to an arcuate shape required to fit around a ground alumina core (7075 T6 aluminum, obtained from Yarde Metals, Tewksbury, Mass.) And has an outer diameter of about 393 mm and a thickness of 0.62 cm Got.

  Abrasive segments and aluminum cores use silica-filled epoxy bonding system (Technodyne HT-18 adhesive, available from Taoka Chemical, Japan) to create a grinding wheel with a continuous rim consisting of multiple abrasive segments. Assembled using. The core and segment contact surfaces were degreased and sandblasted to ensure proper adhesion.

In order to characterize the maximum working speed of this new type of grinding wheel, the full-scale grinding wheel is intentionally rotated to failure to measure burst strength and the maximum working speed evaluated by the Norton Company's maximum working test method. It was done. The table below summarizes the burst test for a representative example of an experimental metal bonded wheel with a diameter of 393 mm.
Explosive strength data of experimental metal binder wheels ───────────────────────────────────
Grinding wheel # Grinding wheel diameter Burst Burst speed Burst speed Maximum working speed
cm (inch) RPM (m / s) (sfpm) (m / s)
──────────────────────────────────
4 39.24 9950 204.4 40242 115.8
(15.45)
──────────────────────────────────
5 39.29 8990 185.0 36415 104.8
(15.47)
──────────────────────────────────
7 39.27 7820 160.8 31657 91.1
(15.46)
──────────────────────────────────
9 39.27 10790 221.8 43669 125.7
(15.46)
──────────────────────────────────
According to these data, the experimental grinding wheel of this design is qualified for working speeds up to 90 m / s (17,717 surface feet / min). Higher working speeds up to 160 m / s can easily be achieved by making some further changes to the manufacturing process and the wheel design.

Example 2
Grinding performance evaluation:
An experimental metal bonded segment grindstone (15.5 × 0.59 × 5 inches) with a diameter of 393 mm, a thickness of 15 mm, and a center hole of 127 mm made by the method of Example 1 above (# 4 is the theoretical density of 95 .6% density segments, # 5 97.9% of theoretical density, and # 6 98.5% of theoretical density) were tested for grinding performance. Initial tests at 32 and 80 m / s confirmed the # 6 wheel as the wheel with the best grinding performance of the three, but all experimental wheels were acceptable. The # 6 wheel was tested at three speeds: 32 m / s (6252 sfpm), 56 m / s (11,000 sfpm), and 80 m / s (15,750 sfpm). Two commercial prior art wheels recommended for grinding advanced ceramic materials were used as control wheels and they were tested with the wheel of the present invention. One was a Vitrified bonded diamond wheel (SD320-N6V10 wheel from Norton Company, Worcester, MA) and the other was a resin bonded diamond wheel (SD320-R4BX619C wheel from Norton Company, Worcester, MA). The wheel was tested at all three speeds, and the vitrified wheel was tested only at 32 m / s (6252 spf) considering speed tolerance.

Over 1000 plunge grindings of 6.35 mm (0.25 inches) wide and 6.35 mm (0.25 inches) deep were performed on silicon nitride workpieces. Grinding test conditions are:
Grinding test conditions:
Machine: Studer Grinder Model S40 CNC
Wheel specifications: SD320-R4BX619C, SD320-N6V10,
Size: Diameter 393mm, thickness 15mm and hole 127mm
Wheel speed: 32, 56, and 80 m / s (6252, 11000, and 15750 sfpm)
Coolant: Inversol 22 (60% oil and 40% water)
Coolant pressure: 270 psi (19 kg / cm ² )
Grinding speed: variation. 3.2 mm ³ / s / mm (0.3 inch ³ / min / inch) at the start
Material: Si ₃ N ₄ (Rod made from NT551 silicon nitride, obtained from Norton Advanced Ceramics, Northboro, MA), diameter 25.4 mm (1 inch) x length 88.9 mm (3.5 inch)
Workpiece speed: 0.21 m / s (42 sfpm), constant Workpiece starting diameter: 25.4 mm (1 inch)
Workpiece finish diameter: 6.35 mm (0.25 inch)
For work that requires reshaping and reworking, suitable conditions for the metal bonded wheel of the present invention are:
Reshaping work:
Whetstone: 5SG46IVS (obtained from Norton Company)
Grinding wheel size: Diameter 152mm (6 inches)
Wheel speed: 3000 rpm; +0.8 ratio compared to grinding wheel.

Lead: 0.015 inch (0.38 mm)
Correction: 0.0002 inch adjustment work:
Stick: 37C220H-KV (SiC)
Mote: Hand Stick Rework Test was performed in cylindrical outer diameter plunge mode for grinding silicon nitride rods. In order to maintain the best stiffness of the workpiece during grinding, its 88.9 mm (3.5 inch) sample was subjected to grinding and a chuck of about 31 mm (1/4 inch) chuck. ). A series of plunge grinding tests started from the far end of each rod. First, the grindstone was plunge with a width of 6.35 mm (1/4 inch) and a radial depth of 3.18 mm (1/8 inch) to complete one test. The workpiece rpm was then readjusted, reducing the workpiece diameter, to compensate for workpiece speed fluctuations. In addition, two similar plunges have been reduced from 25.4 mm (1/4 inch) to 6.35 mm (1/4 inch) at the same location. The wheel was then moved 6.35 mm (1/4 inch) laterally close to the chuck to perform the next three plunges. Four lateral movements were made on the same side of the sample to complete 12 plunges at one end of the sample. The sample was then inverted and exposed on the other side for another 12 grindings. A total of 24 plunge grindings were performed on each sample.

Metal binding wheels of this invention, as well as resins and the initial comparison tests for vitrified grindstone, about ^{3.2mm 3 /s/mm(0.3in 3 / min / in} ) to about 10.8mm ³ / s / mm (1 The test was carried out at a peripheral speed of 32 m / s with three workpiece removal rates (MRR ') of 0.0 in ³ / min / in. Table 1 shows that there are performance differences between the three different types of wheels after 12 plunge grindings, as indicated by the G-ratio. The G-ratio is a unitless ratio of the grinding amount to the grinding wheel wear amount. The data showed that with a relatively high workpiece removal rate, the N grade vitrified wheel had a better G-ratio than the R grade resin wheel, which is a relatively soft wheel for grinding ceramic workpieces. Shows better. However, the relatively hard, experimental metal bonded wheel (# 6) is far superior to the resin and vitrified wheels at all workpiece removal rates.

  Table 1 shows the estimated G-ratio for the resin wheel and the new metal bonded wheel (# 6) at all workpiece removal rate conditions. Since there was no measurable wheel wear after 12 grinding at each workpiece removal rate for metal bonded wheels, a symbolic value of 0.01 mil (0.25 μm) of radial wheel wear is given for each grinding. It was. This resulted in a calculated G-ratio 6051. The metal bonded whetstone of the present invention had a diamond concentration of 75 (about 18.75 vol% abrasive in the abrasive grain segment), and the resin and vitrified whetstone had a concentration of 100 and 150, respectively. The grindstone still showed excellent grinding performance. At these relative abrasive concentrations, superior grinding performance would have been predicted from a control wheel containing relatively high abrasive vol%. Thus, these results were unpredictable.

  Table 1 shows the surface finish (Ra) and waviness (Wt) data measured for samples ground with three wheels at low test speeds. The waviness value Wt is the maximum peak with respect to the height of the valley of the waviness profile. All finish surface roughness data were measured on surfaces created by cylindrical plunge grinding without spark-out. Typically, these surfaces will be relatively rougher than those created by traverse grinding.

  Table 1 shows the difference in power consumption for the three types of wheels at various workpiece removal rates. The resin whetstone had lower power consumption than the other two whetstones; however, the experimental metal bonded whetstone and vitrified whetstone had comparable power consumption. The experimental whetstone consumed a satisfactory amount of power for the ceramic grinding operation, especially in view of the preferred G-ratio and finished surface roughness data observed for the whetstone of the present invention. In general, the wheel of the present invention exhibited a power draw proportional to the workpiece removal rate.

When grinding performance is measured at 80 m / s (15,750 sfpm) in additional grinding tests under the same conditions, the resin and experimental metal wheels are 9.0 mm ³ / s / mm (0.8 in ³ It had the same power consumption with a workpiece removal rate (MRR) of / min / in. As shown in Table 2, the experimental wheel is operated with increased MRR without performance degradation or unacceptable power loads. The power consumption of the metal bonded grindstone was roughly proportional to the MRR. Maximum MRR achieved in this study was ^{47.3mm 3 /s/mm(28.4cm 3 / min / cm} ).

  The data in Table 2 is an average of 12 grinding results. Individual power readings for 12 grindings remained highly compatible with the experimental wheel within each workpiece removal rate. As continuous grinding is performed, the power will typically increase as the grindstone begins to crush or the grindstone surface becomes loaded with workpiece material. This is often seen as MRR increases. However, during 12 grindings, the level of stable power consumption seen within each MRR was surprisingly that the experimental wheel maintained sharp cutting points during the entire test period at all MRRs. Indicates.

Furthermore, the workpiece removal rate ranging from ^{9.0mm 3 /s/mm(0.8in 3 / min / in} ) to ^{47.3mm 3 /s/mm(4.4in 3 / min / in} ), all of this test During this time, it was not necessary to reshape or reshape the experimental wheel.
The total cumulative amount of silicon nitride material ground without signs of wheel wear was equal to 271 cm ³ (42 in ³ / in) per cm of wheel width. In contrast, at a workpiece removal rate of 8.6 mm ³ / s / mm (08 in ³ / min / in), the G-ratio of the 100 grindstone grindstone was about 583 after 12 plunges. The experimental wheel showed no measurable wheel wear after 168 plunges with 14 different workpiece removal rates.

Table 2 shows that for all 14 workpiece removal rates, samples ground with an experimental metal bonded grindstone have a constant finished surface roughness of 0.4 μm (16 μin.) To 0.5 μm (20 μin.). It was maintained and had a swell value of 1.0 μm (38 μin.) To 1.7 μm (67 μin.). Resin wheels were not tested with these high workpiece removal rates. However, with a workpiece removal rate of about 8.6 mm ³ / s / mm (0.8 in ³ / min / in), the ceramic rod ground with the resin grindstone is slightly improved and has an equivalent finished surface roughness ( 0.43 to 0.5 μm), and relatively poor undulations (1.73 to 1.18 μm).

Surprisingly, as the workpiece removal rate increased, there was no obvious degradation in the finished surface roughness when the ceramic rod was ground with a new metal bonded wheel. This is different from the typical deterioration of the finished surface roughness with increasing cutting speed for a standard wheel, such as the control wheel used here.
The overall results show that the experimental metal wheel could be effectively ground with an MRR of more than 5 times that achievable with a standard, commercially used resin bonded wheel. The experimental wheel has a low MRR and has a G-ratio that is more than 10 times that of the resin wheel.

  When operating at a grinding wheel speed of 32 m / s (6252 spfpm) and 56 m / s (11,000 spfpm) (Table 1), the power consumption for the metal bonded wheel is the resin at all tested workpiece removal rates. It was higher than the grindstone. However, the power consumption for the metal bonded wheels was equal to or slightly lower than the resin wheels at a high wheel speed of 80 m / s (15,750 sfpm) (Tables 1 and 2). Overall, the trend showed that for both the resin wheel and the experimental metal bonded wheel, grinding with the same workpiece removal rate, the power consumption decreased with increasing wheel speed. The power consumption during grinding is mostly directed to the workpiece as heat, but due to the relatively large thermal stability of the ceramic material, grinding ceramic materials rather than grinding metal materials Relatively unimportant. As indicated by the surface quality of the ceramic samples ground with the grinding wheel of the present invention, power consumption was acceptable without compromising the finished workpiece.

For experimental metal bonded wheels, the G-ratio was essentially constant at 6051 for all workpiece removal rates and wheel speeds. For the resin grindstone, the G-ratio decreased with increasing workpiece removal rate at a constant grindstone speed.
Table 2 shows that the finished surface roughness and waviness of the sample ground at a relatively high grinding wheel speed was improved. In addition, the samples ground with the new metal bonded wheel had the measured swell, which was the lowest at all wheel speeds and compound removal rates tested.

  In these tests, the metal bonded wheel showed superior wheel life compared to the control wheel. Unlike commercially available control wheels, there was no need to reshape or rework the experimental wheel during the extended grinding test. The experimental wheel worked well with a wheel speed of up to 90 m / s.

Example 3
When the next grinding test of the experimental wheel (# 6) was performed at 80 m / sec under the same working conditions as used in the previous example, a finished surface roughness measurement of only 0.5 μm (12 μin) ( Ra) was generated and an MRR of 380 cm ³ / min / cm was achieved even though an acceptable level of power was utilized. The observed high workpiece removal rate without surface degradation of the ceramic workpiece is achieved by utilizing the tool of the present invention, but grinding any ceramic material using any commercial grindstone of the bonded type. There was no report on work.

Example 4
A cup-shaped abrasive tool was prepared and tested in grinding sapphire with a vertical spindle “Blanchard type” machine.

  A cup-shaped grindstone (diameter 250 mm) was made from an abrasive segment of the same composition as used in grindstone # 6 of Example 1 except for the following. (1) Diamond had a grit diameter of 45 μm (US mesh 270/325) and was present in the abrasive grains at 12.5 vol% (concentration 50). (2) The segment size was 46.7 mm (radius 133.1 mm) in chord length, 4.76 mm in width and 5.84 mm in depth. These segments were joined along the periphery of the side of a cup-shaped steel core with a center spindle hole. The surface of the core had grooves arranged along the perimeter forming a separate, shallow pocket with the same width and length dimensions as the segment. An epoxy bonding agent (Technodyne HT-8 bonding agent obtained from Taoka, Japan) was added to the pocket and the segments and bonding agent placed in the pocket were cured. The finished wheel was similar to the wheel shown in FIG.

  The cup wheel has been successfully used to grind the surface of a workpiece material consisting of a 100 mm diameter solid sapphire cylinder and to be an acceptable surface flat under suitable grinding conditions of G-ratio, MRR and power consumption Caused a degree.

Example 5
A 2A2 type cup diameter polishing tool (diameter 280 mm) suitable for back grinding AlTiC or silicon wafers was prepared using the abrasive segments described in Table 3 below. Except as indicated below, the segment size was a radial length of 139.3 mm, a width of 3.13 mm, and a depth of 5.84 mm. Diamond abrasive grains containing a binder batch mixture sufficient to produce 16 segments per wheel at the proportions shown in Table 3 S. Prepared by sieving the weighed ingredients through a mesh 140/170 sieve and mixing and blending the ingredients uniformly. The powder required for each segment was weighed, introduced into a graphite mold, leveled and compressed. The graphite segment mold was hot pressed at 3000 psi (2073 N / cm ² ) for 15 minutes at 405 ° C. As it cooled, the segments were removed from the mold.

  The assembly of the grindstone by attaching segments to a cut 7075 T6 aluminum core was performed as in Example 1. The segments were degreased, sandblasted, coated with adhesive, and placed in a machined cavity and fitted around the wheel. After curing of the adhesive, the grindstone was machined, sized, balanced, and speed tested.

a. All diamond grains used in the segment were 325 mesh (49 μm) grit diameter except that sample (1) was 270 mesh (57 μm) grains. Diamond concentration level is shown below diamond vol%.
b. The porosity was evaluated from observation of the segment microstructure. Due to the formation of intermetallic alloys, the density of the test samples often exceeded the theoretical density used for the segments.

Example 6
Grinding performance evaluation:
An experimental segment grindstone (11 in × 1.155 in × 9 in) made of Example 5 with a diameter of 280 mm, a thickness of 29.3 mm, a center hole of 228.6 mm, a low diamond concentration, and filled with graphite. The grinding performance was tested. The performance of these samples was compared to that of the control back grinding wheel of Example 5 made with the high (concentration 75) diamond abrasive grain segment composition of Example 1 (Wheel # 6) without the graphite filler.

More than 70 grindings, each 114.3 mm (4.5 inches) wide and 1.42 mm (0.056 inches) deep, are 114.3 mm (4.5 in) or 152.4 mm (6.0 in) squares A shaped AlTiC workpiece (210 grade AlTiC obtained from 3M Corporation, Minneapolis, Minn.) Was performed and the recorded removed (μm) and normal grinding force was recorded. Grinding test conditions are:
Grinding test conditions:
Machine: Strasbaugh Grinder Model 7AF
Grinding mode: Vertical spindle plunge grinding Grinding wheel specifications: Diameter 280mm, thickness 29.3mm and hole 229mm
Wheel speed: 1,200 rpm
Workpiece speed: 19rpm
Coolant: Deionized water Workpiece removal rate: Varies. 1.0 μm / sec to 5.0 μm / sec
The wheel was reshaped and reshaped with a 6 inch (152.4 mm) sized pad of 38 A240-HVS specification obtained from Norton Company, Worcester, MA. After the first operation, reshaping and reworking was done periodically as needed and when the down feed rate was changed.

  The results (grid resistance vs. grinding amount) of Example 5, Samples 2, 4 and 1 are shown in Table 5 below and FIG.

a. 2a is Sample 2 of Table 3 having an abrasive segment rim width of 3.13 mm.
b. 2b is Sample 2 of Table 3 having an abrasive segment rim width of 2.03 mm.
These results show that the significant increase in normal resistance is relatively high MRR (1-3-5 μm / sec) when surface grinding with a control wheel sample without graphite filler and having a diamond abrasive concentration of 75. It shows that it was required to obtain a large grinding amount. In contrast, at the low diamond concentration of Example 5 of the present invention, the graphite-filled wheels (Samples 2a, 2b and 4) only require significantly less normal resistance during grinding. The resistance required to obtain an equivalent grinding amount for the grinding wheel of the present invention at 2 μm / second MRR was equivalent to that required for the comparative grinding wheel sample at 1 μm / second MRR.

  In addition, the 2a sample required approximately equal normal resistance to grind at 1 μm / sec or 2 μm / sec MRR. Furthermore, the grindstones 2a, 2b and 4 of the present invention of Example 5 showed a relatively stable normal resistance requirement even though the grinding amount was advanced from 200 to 600 μm. This type of grinding performance is highly desirable in back grinding of AlTiC wafers. This is because this low resistance, steady state condition minimizes thermal and mechanical damage to the workpiece.

The control wheel (Example 1) was not tested at high grinding levels (eg, greater than about 300 μm). Because the resistance required to grind with these wheels exceeds the normal resistance capability of the grinding machine, thereby automatically stopping the machine and accumulating data at relatively high grinding levels. Because it interferes.
While not wishing to be bound by any particular theory, the excellent grinding performance of the inventive wheel, filled with graphite, with low diamond concentration, is that the grinding surface is in contact with the surface of the workpiece at any point during grinding. This is considered to be related to relatively few individual particles per unit area of the grain segment. Although those skilled in the art will predict a relatively low MRR at low diamond concentrations, the improvement in grinding resistance of the present invention is surprisingly achieved without reducing the MRR. The grindstone 2b having an abrasive segment width of 2.03 mm required less resistance to grind at the same grinding rate and speed as the grindstone 2a having an abrasive segment width of 3.13 mm. The grindstone 2b sample has a relatively small surface area and relatively few grinding points that contact the surface of the workpiece at any point during the grinding operation than the grindstone 2a sample.

Figure 2 shows a continuous rim of abrasive segments bonded around a metal core to form a 1A1 grinding wheel. Figure 3 shows a discontinuous rim of abrasive segments bonded around a metal core to form a cup-shaped wheel. The relationship between the grinding amount and the normal resistance during grinding of an AlTiC workpiece with the grinding wheel of Example 5 is shown.

Claims (11)

A core having a minimum specific strength parameter of 2.4 MPa-cm ³ / g, a core density of 0.5 to 8.0 g / cm ³ , a circular perimeter, and an abrasive rim defined by multiple abrasive segments; A surface grinding and polishing tool including the abrasive segments in a quantity selected for a total of 100 vol%, superabrasive grains 0.05 to 10 vol%, brittle filler 10 to 35 vol%, and fracture dust A surface grinding and polishing tool comprising 55 to 89.95 vol% of a metal binder matrix having a property of 1.0 to 3.0 MPa M ^1/2 .   The polishing tool according to claim 1, wherein the core includes a metal material selected from the group consisting of aluminum, steel, titanium and bronze, composites and alloys thereof, and combinations thereof.   The abrasive segment comprises 60-84.5 vol% metal binder matrix, 0.5-5 vol% abrasive grain, and 15-35 vol% brittle filler, and the metal binder matrix has a porosity of The polishing tool according to claim 1, which has a maximum of 5 vol%.   The abrasive tool according to claim 1, wherein the brittle filler is selected from the group consisting of graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline sianite, pumice, calcined clay and glass spheres, and combinations thereof.   The polishing tool according to claim 1, wherein the abrasive grains are selected from the group consisting of diamond and cubic boron nitride and combinations thereof.   The polishing tool according to claim 5, wherein the abrasive is a diamond having a grit diameter of 2 to 300 μm.   The polishing tool according to claim 1, wherein the metal binder comprises 35 to 84 wt% copper and 16 to 65 wt% tin.   The polishing tool according to claim 7, wherein the metal binder further contains 0.2 to 1.0 wt% of phosphorus.   The polishing tool includes at least two abrasive segments, the abrasive segments having an elongated, arcuate shape, and an internal curve selected to match the circumference of the core, and each abrasive grain The segment has two ends designed to coincide with adjacent abrasive segments so that the abrasive rim is continuous and between the abrasive segments when the abrasive segments are bonded to the core The polishing tool according to claim 1, wherein there is substantially no gap between.   The polishing tool according to claim 1, wherein the tool is selected from the group consisting of a 1A1 type grindstone and a cup grindstone.   The abrasive tool of claim 1, wherein the thermally safe binder is selected from the group consisting essentially of epoxy adhesive binders, metallurgical binders, mechanical binders and diffusion binders and combinations thereof.

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