HU222463B1 - Abrasive tools - Google Patents

Abstract

The present invention provides an abrasive tool for grinding hard, brittle materials such as ceramics and ceramic composites at a circumferential speed of up to 160 m / s. The tumbler consists of a wear ring comprising the disk core (2) and the solid abrasion parts (8) attached thereto, which are metal bonded superconducting segments, thermally stable bonded. A preferred tool for grinding ceramic tiles consists of a graphite filler and a relatively small amount of abrasive bead. ŕ

Description

FIELD OF THE INVENTION The present invention relates to an abrasive tool for the precision grinding of hard, brittle materials such as ceramics and ceramic composites. The tool has a circumferential speed of up to 160 m / s. The tool is also suitable for surface grinding of ceramic plates. The abrasive tool comprises a disc core or hub to which a metal bonded superabrasive material is attached to the ring by a bond that is thermally stable during the grinding process. These abrasive tools grind ceramic materials with high material removal rates (19-380 cm ³ / min / cm), less disk wear and workpiece damage than conventional abrasive tools.

Li is disclosed in US-A-5,607,489 for abrasive tools for grinding sapphires and other ceramic materials. According to the description, the tool comprises a metal-coated diamond bonded to a glass-like matrix. The matrix contains from 2 to 20% by volume of solid lubricant and has a porosity of at least 10% by volume.

Keat, U.S. Pat. No. 3,925,035, discloses an abrasive tool containing 15 to 50% by volume of selected filler such as graphite and a metal matrix bonded diamond. The tool is used for grinding cemented carbides.

Van Der Pyl discloses a metal-bonded diamond abrasive particle in US-A-2,238,351. The bond contains copper, iron, tin and optionally nickel. The bonded abrasive particles are color-coded on the steel core, optionally by soft soldering, to ensure proper adhesion. The best bond described is Rockwell B hardness 70.

An abrasive tool containing relatively low melting point metal bonded (e.g., bronze) fine diamond particles (industrial diamond) is disclosed in US-Re-21,165. The low melting point bond is used to prevent oxidation of fine diamond particles. The abrasive tire is designed as a single annular abrasive segment and is connected to a central aluminum or other material disc.

None of these abrasive tools are perfectly suited for precision grinding of ceramic components. These tools do not meet the stringent requirements for shape, size and surface quality when operating at a commercially appropriate grinding speed. Most commercial abrasive pads recommended for operation under these conditions are designed with resin or glass-like super-wear discs designed to operate with relatively low grinding efficiency to prevent surface or sub-surface damage to the ceramic component. The grinding efficiency is further reduced by the fact that the ceramic workpiece seals the disc surface, which requires frequent disc removal and sharpening to maintain the precision shape.

As the market demand for precision ceramic components, such as motors, heat-resistant equipment and electronic devices (such as plates, magnetic heads and displays), the demand for advanced precision ceramic grinding tools has increased.

In finishing high performance ceramic materials such as aluminum titanium carbide (AlTiC) used in the electronics industry, surface grinding or "Jig grinding" operations require a high quality, smooth surface finish in a low-power, low-speed grinding process. In the back grinding of these materials, the efficiency of grinding is determined at least as much by the surface quality of the workpiece and the control of the applied force as by the high material removal rate and the abrasion resistance of the grinding wheel.

The present invention relates to an abrasive tool for surface grinding comprising a core and a circular abrasive wear pattern characterized by a plurality of abrasive segments. The core has a minimum specific strength of 2.4 MPa cm ³ / g and a density of 0.5-8.0 g / cm ³ . The abrasive segments contain a total of up to 100% by volume, of which 0.05 to 10% by volume are superabrasive particles, 10 to 35% by volume of crumbling filler, and 55 to 89.95% by volume of a metal bonding matrix with a tensile strength of 1.0 to 3.0 MPa m ^1Z2 . The specific strength parameter is defined as the ratio of the material's lower flow stress or tensile strength divided by the density of the material. The crumbling filler, graphite, hexagonal boron nitride, hollow ceramic ball, feldspar, nepheline syenite, pumice stone, calcareous clay and glass ball, and combinations thereof were selected. In a preferred embodiment, the metal bonded matrix has a porosity of up to 5% by volume.

Description of the drawings

The diagram illustrates a continuous ring of abrasive segments attached to the circumference of a metal core forming a 1A1 type grinding wheel;

Figure 2 shows a discontinuous ring of abrasive segments secured to the circumference of a metal core forming a cup-shaped grinding wheel;

Figure 3 shows the relationship between the amount of material removed from the workpiece and the normal force applied during grinding for the AlTiC workpiece and the grinding wheel produced in Example 5.

The abrasive tools of the present invention are grinding wheels comprising a core having a central bore for mounting in a grinding machine. The core is designed to support a metal bonded super-wear ring around the circumference of the disk. These two parts of the disc are held together by a bond that is thermally stable under grinding conditions. The disk and its components are designed to withstand the stress induced by a circumferential velocity of up to 80 m / s, preferably up to 160 m / s. Preferred tools are Type 1A grinding wheels, cup-shaped grinding wheels, or 11V9 bell-shaped grinding wheels.

The core is essentially circular. The disc may be made of any material having a specific strength of at least 2.4 MPa cm ³ / g, preferably 40-185 MPa cm ³ / g. The density of the core material is 0.5-8.0 cm ³ / g, preferably 2.0-8.0 cm ³ / g. An example of suitable materials is steel,

EN 222 463 Bl aluminum, titanium and bronze, and composites, alloys and combinations thereof. Reinforced plastics of the required minimum strength are also suitable for core production. Composites and reinforced core materials typically have a continuous metal or plastic matrix phase, often in powder form, to which are added harder, more resilient and / or lower density fibers, particles, or particles than the discontinuous phase. Suitable reinforcing materials for the core material of the tool according to the invention are glass fiber, carbon fiber, aramid fiber, ceramic fiber, ceramic particles and particles and hollow fillers such as glass, mullite, alumina and Zeolite® spheres.

Steel and other metals having a density in the range of 0.5 to 8.0 g / cm ³ may also be used to produce the core of the tool according to the invention. In the manufacture of tool cores for high-speed grinding (at least 80 m / s), light alloys in powder form (having a density of about 1.8 to 4.5 g / cm ³ ), such as aluminum, magnesium and titanium, alloys or mixtures thereof are preferred. Aluminum and aluminum alloys are particularly preferred. Metals having a sintering temperature of 400 to 900 ° C, preferably 570 to 650 ° C, are used when a cosine sintering process is used to produce the tool. Adding a low density filler can reduce the weight of the core. Porous and / or hollow ceramic or glass fillers such as glass spheres or mullite spheres are suitable materials for this purpose. Inorganic and non-metallic fibers are also useful. When processing conditions make it necessary, effective amounts of lubricants or other processing aids used in metal bonding or super abrasive materials may be added to the metal powder prior to pressing and sintering.

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

The specific strength parameter is defined as the ratio of the flow stress (or tensile strength) of the material divided by the density of the material. For brittle materials with lower tensile strengths, the specific strength parameter is determined using the lower value of tensile strength. The tensile stress of the material is the minimum force applied during stretching at which the tension of the material continues to increase without further increasing the force. For example, ANSI 4140 steel has a tensile strength of more than 700 MPa when cured above 240 (Brinell scale). The density of this steel is approx. 7.8 g / cm ³ . Thus, its specific strength parameter is 90 MPa cm ³ / g. Similarly, certain aluminum alloys, such as Al 2024, Al 7075, and Al 7178, which have a Brinell hardness that can be increased above 100 by heat treatment, have tensile strengths above 300 MPa. These aluminum alloys have a low density of approx. 2.7 g / cm ³ , so that their specific strength parameter is more than 110 MPa cm ³ / g. Titanium alloys, bronze composites and alloys with a density of up to 8 g / cm ^{3 are} also suitable.

The core material must be tough, stable at temperatures occurring in the grinding zone (e.g., about 50-200 ° C), chemically resistant to grinding refrigerants and lubricants, and resistant to erosion caused by the movement of cutting waste in the grinding zone. Although some alumina or other ceramics have acceptable failure rates (e.g., greater than 60 MPa cm ³ / g), they are generally too brittle and are structurally destroyed by high-speed grinding. Thus, the ceramics are not suitable for use in the core of the tool. Metals, particularly hardened tool grade steels, are preferred.

The abrasive part of the grinding wheel used in the present invention is a split or continuous ring. Figure 1 shows an abrasive ring divided into parts. The core 2 has a central bore 3 so that the disk can be mounted on the drive motor shaft (not marked). The abrasive ring of the disk includes the super-wear particles 4 contained in the metal matrix 6 (preferably in constant concentration). A number of abrasive parts 8 in Fig. 1 form the abrasive ring. Although the solution illustrated consists of ten parts, the number of segments is not significant. The individual segment shown in Figure 1 has the shape of a truncated rectangular ring (curved shape) characterized by its length 1, its width w and its thickness d.

The embodiment of the grinding wheel shown in Figure 1 is to be considered without limitation as representative of the inventive wheels. Many of the geometrical versions of the split grinding disc are suitable, including the cup shape shown in Figure 2. Discs having an opening in the core and / or a gap between successive segments, as well as discs having a width other than the core, are suitable. The openings and gaps are sometimes designed to introduce refrigerant into the grinding zone and to remove grinding waste from the zone. The abrasive parts wider than the core are designed to protect the core structure, which prevents erosion from contact with the grinding stone powder when the grinding wheel penetrates the workpiece radially.

In making the disc, the individual segments are first formed into predetermined dimensions and then the preformed segments are secured to the periphery 9 of the core with a suitable adhesive. Another preferred method of production involves making "semi-finished" segment units from a powder mixture of abrasive particles and binder, melting the mixture around the core circumference, and applying heat and pressure to form and join the segments (i.e., cosine sintering of the core and ring). The cosine sintering process is favored by hard disks and chips made of hard ceramics, such as AlTiC.

EN 222 463 Bl to produce grinding wheel discs.

The abrasive ring of the abrasive tool of the present invention may be a continuous or intermittent ring, as shown in Figures 1 and 2, respectively. The continuous abrasive ring may include one abrasive segment or at least two abrasive segments which are individually colored in the tool and then individually mounted on the core by thermally stable bonding (i.e., at a temperature away from the segment abrasive surface during grinding). . The discontinuous rings shown in Figure 2 are made of at least two such segments, which segments are separated by slots or openings in the ring and have no contact along their length at their ends, as in continuous grinding wheels. The drawings illustrate preferred embodiments of the invention, not limiting the type of tools of the invention, i.e., a discontinuous ring may be applied to a 1A disc and a continuous ring may be applied to the cup discs.

For high speed grinding, especially for cylindrical workpieces, a type 1A continuous ring disc is preferred. A split continuous abrasion ring is more appropriate than a one-piece continuous abrasion ring that is molded in a one-piece, ring-shaped tool, since it is easier to produce a truly round, flat shape from multiple abrasive parts.

For lower speed grinding operations (for example 25-60 m / s), especially for surface grinding and smoothing of flat workpieces, a discontinuous abrasive ring (i.e., the cup disc shown in Figure 2) is preferred. Because surface quality is important for low-speed surface finishes, gaps can be created between sections, or certain segments of the ring can be omitted, thereby helping to remove scrap material that could scratch the workpiece surface.

The abrasive ring contains super-abrasive particles in a metal-bonded matrix, typically produced by sintering a mixture of metal powder and abrasive particles in a tool. The tool is configured to produce the desired size and shape of the abrasion ring or abrasion ring segment.

The super-wear particles used in the abrasive ring are selected from natural or synthetic diamond, CBN, and combinations thereof. The choice of particle size and type depends on the nature of the workpiece and the type of grinding process. For example, for grinding or polishing sapphire or AlTiC, a range of 2-300 µm of super-wear particles is preferred. For other alumina grinding, super-abrasive materials having a particle size of 125-300 pm (60-120 particle size, Norton Company particle size) are generally preferred. For grinding silicon nitride, a particle size of 45-80 µm (200-400) is generally preferred. A finer particle size is preferred for surface finishing and a larger particle size for rollers, profiles, or internal diameter grinding operations where larger amounts of material have to be removed.

As a percentage of the volume of the abrasive ring, the tool contains from 0.5 to 10% by volume, preferably from 0.5 to 5% by volume, of a super-wear particle. A crumbling filler with a hardness lower than the metal binder matrix can be added to the binder to increase its wear rate. As a percentage of the volume of the abrasive ring, the tool contains 10-35% by volume, preferably 15-35% by volume, of filler particles. The crumb material to be used must be characterized by appropriate thermal and mechanical properties to withstand the sintering temperature and pressure used to produce abrasive segments and disc assembly. Graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline syenite, pumice stone, calcareous clay and glass balls, and combinations thereof, are examples of useful crumbling fillers.

Scavengers for each super abrasive material, from 1.0 to 6.0 MPa, preferably 2.0 to 4.0 MPa m ^{1Z2 2.1} m tensile strength of metallic binder useful herein. Tensile strength is the stress intensity factor at which cracks in the material propagate and lead to the rupture of the material. The tensile strength can be expressed as follows:

K _lc = (a _f ) (jr ^1/2 ) (c ^1/2 ) where K _{lc is} the tensile strength, _{f is} the applied stress at fracture, ca is half the crack length. Tensile strength is decisive in a number of methods, each of which initially involves the formation of a known size crack on the specimen and the application of tension until the material is fractured. Awakening the fracture stress and the crack length by fitting the equation to calculate the tensile strength (such as steel tensile strength of 30-60 MPa m ^1/2, that of alumina of 2-3 MPa m ^1/2, the silicon nitride of 4-5 MPa m ^1/2 , zirconium 7-9 MPa m ^1/2 ).

In order to optimize the life and grinding performance of the disc, the wear rate of the binder during the grinding process must be equal to or slightly higher than the wear rate of the abrasive particles. Fillers such as those mentioned above may be added to the binder to reduce its wear rate. Metal powders which tend to form a relatively dense bonding structure (i.e., less than 5% porosity) are preferred to achieve higher material removal rates during grinding.

Metals that may be used as ring material include, but are not limited to, bronze, copper and zinc alloys (brass), cobalt and iron, and alloys and mixtures thereof. These metals may optionally be used in combination with titanium or titanium hydride, or other super-reactive reactive (e.g., active metal bond) materials which, under the used sintering conditions, are capable of forming a carbide or nitride chemical bond between the particle and the reinforce the particle / binder interaction. The stronger particle / binder interaction limits premature particle loss and workpiece damage and shortening tool life caused by premature particle loss.

HU 222 463 Β1

In a preferred embodiment of the abrasive ring, the metal matrix is 55 to 89.95 vol%, more preferably 55 to 84.5 vol. The friable filler comprises 10-35% by volume, more preferably 15-35% by volume of the wear ring. The porosity of the metal matrix should be maintained at a maximum of 5% by volume during the manufacture of the abrasive segment. The Knoop hardness of the metal bond is preferably 2-3 GPa.

In a preferred embodiment of the Type 1A grinding wheel, the core is made of aluminum, the ring is made of copper and tin powder (80/20% by weight) and optionally 0.1-3.0% by weight, preferably 0.1-1.0% by weight of phosphorus. / consists of added phosphorus in the form of copper powder. In the manufacture of the abrasive segment, this metal powder composition is mixed with diamond abrasive grains having a grain size of 100-400 (160-45 pmes), and then formed into abrasive ring segments and sintered or compacted at 400-550 ° C, 20-33 MPa to form a compact abrasive ring. preferably at least 95% of the theoretical density (i.e., porosity of not more than 5% by volume).

In a typical cosine sintering disc production process, the metal powder of the core is filled into a steel tool and cold pressed at 80-200 kN (about 10-50 MPa) to obtain a green piece having a size of approx. 1.2-1.6 times greater than the desired final thickness of the core. The green core is placed in a graphite tool and a mixture of abrasive grains (2-300 µm) and metal binder powder is inserted into the gap between the core and the outer edge of the graphite tool. An adjusting ring can be used to compact the abrasive grains and the metal binder powder so that its thickness is the same as the core. The contents of the graphite tool are then pressed hot at 370-410 ° C and 20-48 MPa for 6-10 minutes. As is known, the temperature may be raised (e.g., from 25 to 410 ° C for 6 minutes and then held at 410 ° C for 15 minutes) or gradually raised before applying pressure to the contents of the tool.

After hot pressing, the graphite tool is separated from the piece, cooled and then finished by conventional methods to obtain a wear ring of the desired size and tolerance. For example, the workpiece may be finished to a size similar to that used on glass-type grinding wheels or carbide cutting lathes.

When the core and ring of the invention are cosinated, little material is required to bring the piece to its final shape. In another method of forming a thermally stable bond between the core and the ring, both core and ring machining may be required prior to the gluing, bonding, or diffusion step to provide the appropriate surface for joining and bonding the pieces.

Any thermally stable adhesive that is strong enough to withstand a disc peripheral speed of 160 m / s can be used to thermally form the ring and core using a split wear ring. The thermally stable adhesives are stable at the grinding temperature, which is expected to occur at a distance from the grinding surface of the abrasive segment. This temperature is typically in the range of 50-350 ° C.

The bonded bond must be mechanically very strong to withstand the destructive forces that occur during the grinding process as the grinding wheel rotates. The use of a two part epoxy resin binder is preferred. A preferred binder is Technodyne® HT-18 Epoxy Resin (Taoka Chemicals, Japan) and its modified amine starch, which can be mixed with 100 parts of resin in a ratio of 19 parts to starch. Fillers such as fine silica powder can be added to increase the viscosity of the binder in a ratio of 3.5 parts to 100 parts resin. The segments can be secured with the adhesive to the whole circumference of the grinding wheel core or to a portion thereof. The core of the metal cores can be sandblasted before joining the segments to provide the required surface roughness. The thickened epoxy adhesive is applied at the ends and bottom of the segments, which are applied around the core, and as indicated in Figure 1, is held in the desired position by mechanical force during curing. The epoxy adhesive is allowed to cure (e.g., for 24 hours at room temperature and then for 48 hours at 60 ° C). Leakage of adhesive and movement of segments during curing are minimized since the viscosity of the epoxy adhesive can be optimized by adding the appropriate filler.

The strength of the bonded bond can be measured by a rotational test at an acceleration of 45 revolutions per minute, as is the case for measuring the crack speed of a disk. The disc must be proven to have a crack speed equivalent to a tangential contact velocity of at least 271 m / s in order to be licensed to operate at a tangential contact velocity of 160 m / s under current US safety regulations.

The abrasive tool of the present invention is primarily designed for the precision grinding and smoothing of brittle materials such as state-of-the-art ceramics, glass and systems and ceramic composites containing ceramic materials. The tool according to the invention is particularly useful but not limited to grinding ceramic materials, for example, non-ceramic matrix composites of silicon, mono- and polycrystalline oxides, carbides, borides and silicides, polycrystalline diamonds, glass, and ceramics, and combinations thereof. Non-limiting examples of typical workpieces include AlTiC, silicon nitride, silicon oxide, stabilized zirconia, alumina (e.g. sapphire), boron carbide, boron nitride, titanium diboride, aluminum nitride, composites of these ceramics, as well as certain metal matrix composites, such as cemented carbides, and hard, brittle, amorphous materials like mineral glass. Either ceramic single crystals or polycrystalline ceramics can be ground with these advanced abrasive tools. With each type of ceramic, the quality of the ceramic part and the efficiency of the grinding operation can be increased as the peripheral speed of the disc according to the invention is increased to 80-160 m / s.

Among the ceramic pieces improved by the tool according to the invention are ceramic motor valves and rods, pump seals, ball bearings and fittings, cutting tool inserts, wear parts, metal forming pulling tools, heat-resistant parts, visible display panel5

EN 222 463 Blocks, flat glass for windshields, doors and windows, insulators and electrical components, ceramic electronic components including, but not limited to, silicon wafer, AlTiC chips, read / write heads, magnetic heads and carriers.

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

Example 1

The abrasive wheel of the present invention was manufactured as a Form 1A metal bonded diamond wheel using the materials described below.

43.74% copper powder (dendritic FS grade, + 200 / -325 mesh particle size, purchased from Sintertech International Marketing Corp., Ghent, NY), 6.24% phosphorus / copper powder (1501 grade, + 100 / -325 mesh particle size, purchased from New Jersey Zinc Company, Palmerton, PA) and 50.02 weight percent tin powder (MD115 grade, +325 mesh, 0.5% maximum particle size, purchased from Álcán Metallic Powders Inc., Elizabeth, New Jersey). Diamond abrasive grains (320 grain size synthetic diamond, purchased from General Electric, Worthington, Ohio) were added to the metal powder mixture and blended until a uniform mixture was obtained. The mixture was placed in a graphite tool and pressed hot at 2073 N / cm ² (3000 psi) for 15 minutes at 407 ° C until a matrix with a density greater than 95% of theoretical density was formed (e.g., the # 6 disk mentioned in Example 2). > 98.5% of theoretical density). The # 6 disk segments have a Rockwell B hardness of 108. The segments contained 18.75 vol.% Abrasive grains. The segments were polished to the desired exact size to fit the circumference of the machined aluminum core (7075 T6 aluminum, purchased from Yardé Metals, Tewksbury, MA). thus approx. A disc with an outside diameter of 393 mm and segments with a thickness of 0.62 cm were produced.

The abrasive segments and the aluminum core were secured with a silica-filled epoxy adhesive system (Technodyne HT-18 adhesive, purchased from Taoka Chemicals, Japan) to form a multi-segment continuous ring grinding wheel. The contact surfaces of the core and segments were degreased and blasted with sand to ensure proper adhesion.

To determine the maximum operating speed of a new type of disc, a full-size disc was deliberately rotated to failure to determine crack strength and rated at maximum operating speed by the Norton Company's maximum operating speed measurement method. The following table summarizes the experimental results of the crack test for a typical example of a 393 mm diameter metal bonded disk.

Experimental data on the crack strength test of a metal bonded disc

Puck Disc diameter (cm) (inch) Crack (Rev / min) Cracking speed (m / s) Crack speed (whistle) Max operating speed (m / s) ⁴ 39.24 (15.45) 9,950 204.4 40,242 115.8 5 39.29 (15.47) 8,990 185.0 36,415 104.8 7 39.27 (15.46) 7,820 160.8 31657 91.1 9 39.27 (15.46) 10,790 221.8 43,669 125.7

Based on the above data, the 40 grinding wheels manufactured according to the above plan are certified up to an operating speed of 90 m / s (17,717 surface feet / min - sfpm). Higher optional grinding speeds (up to 160 m / s) can be achieved by modifying blade design and manufacturing technology.

Example 2

Grinding performance evaluation

Three, manufactured according to the method of Example 1 above,

393 mm diameter, 15 mm thick, 127 mm center 50 hole bore (15.5 inch χ 0.59 inch χ 5 inch) experimental metal bonded segment grinding wheel was tested for performance. The density of the # 4 segments is 95.6% of the theoretical density, # 5 is 97.9% of the theoretical density, and # 6 is 98.5% of the theoretical density. Initial investigations have found that at 32 and 80 m / s, # 6 of the three discs has the best grinding performance, although the performance of all three discs was acceptable. The # 6 wheel was tested at three speeds, 32 m / s (6,252 sfpm), 56 m / s (11,000 sfpm), 60 and 80 m / s (15,750 sfpm). Two earlier commercial disks recommended for grinding advanced ceramic materials served as control samples which were tested with the discs of the present invention. One was a glass compacted bond diamond disc (SD320-N6V10 disc, purchased from Norton Company, Worcester, MA) and the other was a resin bound diamond disc (SD320-R4BX619C disc, purchased from Norton Company, Worcester, MA). The resin disk was tested at all three speeds. The glass disc was tested at 32 m / s (6,252 sfpm) only due to velocity mismatch conditions.

More than one thousand 6.35 mm (0.25 inch) wide and 6.35 mm (0.25 inch) deep grooves were performed on silicon nitride workpieces.

Grinding conditions of experiments

Machine: S40 CNC Stud Grinder

Disc details: SD320-R4BX619C,

SD320-N6V10

Size: 393 mm diameter, 15 mm thickness, 127 mm bore

HU 222 463 Bl

Disc speeds: 32, 56, and 80 m / s (6,252, 11,000, and 15,750 sfpm)

Refrigerant: Inversol 22® 60% oil and 40% water

Refrigerant pressure: 19 kg / cm ² (270 psi) Material removal rate: Variable, 3.2 mm ³ / s / mm (0.3 inch ^{3 /} min./inch)

Workpiece Material: Si ₃ Ni 4 (NT551 Silicon Nitride Rods, purchased from Norton Advanced Ceramics, Northboro, Massachusetts), 25.4 mm (1 inch) diameter x 88.9 mm (3.5 inch) length

Working speed: 0.21 m / s (42 sfpm), constant

Diameter at start of work: 25.4 mm (1 inch)

Diameter at end of work: 6.35 mm (0.25 inch)

The peeling and sharpening conditions required for operation according to the metal bonded discs of the present invention were as follows:

Pull operation

Disc: 5SG46IVS (purchased from Norton

Company)

Wheel Size: 152mm Diameter (6 Inches)

Disc speed: 3000 rpm; +0.8 Ratio to Grinding Wheel Elevation: 0.38mm (0.015 inch)

Alignment: 0.0002 inch

The sharpening operation

Rod: 37C220H-KV (SiC)

Method: Hand sharpening

The experiments were carried out in the insert grinding mode on the cylindrical outer diameter of the silicon nitride rods. To preserve the best rigidity of the work material during grinding, the 88.9 mm (3.5 inch) samples subjected to grinding should be approx. It is held in a 31mm (1-1 / 4 inch) chuck. Each set of insertions began at the far end of the rods. First, the disc made a 6.35 mm (1/4 inch) wide and 3.18 mm (1/8 inch) radial deep insertion for an examination. The workpiece speed is then adjusted again to compensate for the speed loss caused by the workpiece diameter reduction. Two more similar insertions were made in the same place to reduce the workpiece diameter from 25.4 mm (1 inch) to 6.35 mm (1/4 inch). The disc was then moved sideways 6.35 mm (1/4 inch) in the direction of the chuck to make the next 3 insertions. Four lateral displacements were made on the same side of the sample to make twelve insertions at one end of the sample.

The sample was then inverted to make another twelve grindings at the other end. A total of 24 insertion grindings were performed on each sample.

Initial comparative studies of the metal-bonded discs of the present invention with resin and glass discs at a circumferential velocity of 32 m / s, three material removal rates (MRR '), ca. 3.2 mm ³ / s / mm (0.3 inch ^{3 /} min./inch) approx. 10.8mm to ³ / s / mm (1.0 inch ^{3 /} min./inch). Table 1 shows the power differences of the three different types of discs in G ratios after three grouting. Steam is the ratio of the volume of material removed to the volume of disc wear. The data show that the G-ratio of a Class N glass disk is higher at higher material removal rates than that of a Class R resin bond, indicating that the performance of a softer disk in ceramic workpieces is better. The harder experimental metal bonded disk (# 6) was much better at any material removal rate than either the resin disk or the glass disk.

Table 1 contains estimated G ratios for the resin disk and the new metal bonded disk (# 6) for each material removal rate. Since no metal wear was detected at any material removal rate after twelve grinds, a symbolic value of 0.25 pm (0.01 mi) for each grind was taken into account. This resulted in a calculated G ratio of 6051.

Although the metal-bonded disc of the present invention contains 75 diamond concentrations (approximately 18.75% by volume of abrasive grain in the abrasion portion), while the resin and glass-like discs contain 100 and 150 concentrations (25% by volume and 37.5% by volume), however, it showed higher grinding performance. At these relative particle concentrations, control discs containing a higher volume of abrasive grains would be expected to have better grinding performance. so that was not the expected result.

Table 1 describes the differences in grinding power consumption at different material removal rates for the three types of discs. The power consumption of the resin disk is lower than that of the other two, while the experimental metal bonded disk and the glass-like disk have a comparable performance. The test disk provides acceptable performance for the ceramic grinding operation, especially when considering the preferred G ratio and surface smoothness data obtained with the inventive disk. In general, the power consumption of the disc according to the invention is proportional to the material removal rate.

Table 1

Sample MRR '(mm ³ / s / mm) Puck- speed (M / s) Axial force (N / mm) Specific performance (W / rnrn) Specific consumption (W s / mm ³ ) G-ratio Surface smoothness (Ra pm) Waviness (Wt pm) Resin 1 973 3.2 32 0.48 40 12.8 585.9 0.52 0.86 1040 6.3 32 0.98 84 13.3 36.6 0.88 4.01

HU 222 463 Bl

Table 1 (continued)

Sample MRR '(nun ³ / s / mm) Puck- speed (M / s) Axial force (N / mm) Specific performance (W / mm) Specific consumption (W s / mm ³ ) G-ratio Surface smoothness (Ra pm) Waviness (Wt pm) 980 8.9 32 1.67 139 9.5 7.0 0.99 4.50 1016 3.2 56 0.49 41 13.1 586.3 0.39 1.22 1052 6.3 56 0.98 81 12.9 293.2 0.55 1.52 992 3.2 80 0.53 45 14.2 586.3 0.42 1.24 1064 6.3 80 0.89 74 11.8 293.2 0.62 1.80 1004 9.0 80 1.32 110 12.2 586.3 0.43 1.75 Crumbling material 654 3.2 32 1.88 60 19.2 67.3 0.7 2.50 666 9.0 32 4.77 153 17.1 86.5 1.6 5.8 678 11.2 32 4.77 153 13.6 38.7 1.7 11.8 Experimental metal 407 3.2 32 2.09 67 2.1 6051 0.6 0.9 419 6.3 32 4.03 130 20.6 6051 0.6 0.9 431 9.0 32 5.52 177 19.7 6051 0.6 0.8 443 3.2 56 1.41 80 25.4 6051 0.6 0.7 455 6.3 56 2.65 150 23.9 6051 0.5 0.7 467 9.0 56 3.70 209 23.3 6051 0.5 0.6 479 3.2 80 1.04 85 26.9 6051 0.5 1.2 491 6.3 80 1.89 153 24.3 6051 0.6 0.8 1 503 9.0 80 2.59 210 23.4 6051 0.6 0.8

When an additional grinding test measured grinding power at 35 80 m / s (15,750 sfpm), the resin disk and the experimental metal bonded disk had an energy consumption of 9.0 mm ³ / s / mm (0.8 inch ³ ) under the same conditions. / min./mch) was comparable. As shown in Table 2, the experimental crown was operated at an increasing material removal rate without loss of power or unacceptable motor load. The power consumption of the metal bonded disk is roughly proportional to the rate of material removal. The highest material removal rate achieved in the study was 47.3 mm ³ / s / mm (28.4 cm ³ / min / cm).

Table 2 shows the average of twelve grinding results. For each pass, the individual power scanners remained substantially constant over the test disk, within 50 material removal rates. Under normal circumstances, an increase in the energy absorbed can be observed as successive grinding operations have taken place and the abrasive grains have started to dull or the disc face has been filled with workpiece material. This is often observed when increasing the material removal rate. Although constant energy use was observed within each material removal rate at the twelve grinding demonstrations, surprisingly, the experimental disc maintained its sharp cutting points throughout the experiment at all material removal rates. 60

During this full experiment, 9.0 mm ³ / s / mm (0.8 inch ^{3 /} min./inch) to 47.3 mm ³ / s / mm (4.4 inch ^{3 /} min./inch) it was not necessary to sharpen or detach the test disk in the range of material removal rates.

The total cumulative amount of silicon nitride material ground without any sign of disc abrasion corresponded to a disc width of 271 cm ³ / cm (42 inch ³ / inch). In contrast, the concentration resin wheel 100 G-583 ratio was approximately 8.6 mm ³ / s / mm (0.8 inch /min./inch ³⁾ material removal rate after twelve insertion. The test disc showed no measurable wear after 168 insertions at 14 different material removal rates.

Table 2 shows the surface smoothness of the test metal bonded discs for all 14 material removal rates between 0.4 µm (16 pinch) and 0.5 µm (20 pinch) and a waveguide value of 1.0 µm (38 pinch) to 1.7 pm (67 pinch) was constant. Resin discs have not been tested at such high material removal rates. Although approx. At a material removal rate of 8.6 mm ³ / s / mm (0.8 inch ^{3 /} min./inch), the surface smoothness of the resin-ground ceramic bar was slightly better, but comparable (0.43 versus 0.5 pm), while its waviness it was weak (1.73 versus 1.18 pm).

HU 222 463 Β1

Surprisingly, as the material removal rate increased, there was no visible deterioration in surface smoothness when the ceramic rod was ground with a new metal bonded disk. This is in contrast to the standard surface disintegration observed with increasing cutting speeds for standard discs such as the control discs used herein.

The results of all-over tests show that the experimental metal disc is actually capable of a material removal rate of more than five times the standard commercially available resin-bonded material. The G-ratio of the experimental disk at lower material removal rates is more than ten times that of the resin disk.

Table 2 Material removal rate (MRR ') measured at 80 m / s disk speed

Sample MRR '(mm ³ / s / mm) Axial force (N / mm) Specific performance (W / mm) Specific consumption (W s / mm ³ ) G-ratio Surface smoothness (Ra pm) Waviness (Wt pm) Resin 1004 9.0 1.32 110 12.2 586.3 0.43 1.75 Metal according to the invention | 805 9.0 1.21 98 11.0 6051 0.51 1.19 1817 18.0 2.00 162 9.0 6051 0.41 0.97 1 829 22.5 2.62 213 9.5 6051 0.44 1.14 841 24.7 2.81 228 9.2 6051 0.47 1.04 853 27.0 3.06 248 9.2 6051 0.48 1.09 865 29.2 3.24 262 9.0 6051 0.47 1.37 I 877 31.4 3.64 295 9.4 6051 0.47 1.42 889 33.7 4.01 325 9.6 6051 0.44 1.45 901 35.9 4.17 338 9.4 6051 0.47 1.70 913 38.2 4.59 372 9.7 6051 0.47 1.55 925 40.4 4.98 404 10.0 6051 0.46 1.55 _ 42.7 5.05 409 9.6 6051 0.44 1.57 949 44.9 5.27 427 9.5 6051 0.47 1.65 961 47.2 5.70 461 9.8 6051 0.46 1.42

Operating at disc speeds of m / s (6,252 sfpm) and 56 m / s (11,000 sfpm), the power consumption of the metal bonded disc is higher than that of the resin disc at any of the material removal rates tested. The energy consumption of the metal-bonded disc at high disc speeds (80 m / s, 15,750 sfpm) becomes comparable or slightly lower than that of the resin disc (Tables 1 and 2). Overall, the trend shows that the energy consumption of both the resin disk and the experimental disk decreases with increasing disk speed when grinding at the same material removal rate. Much of the energy used during grinding is spent on heating the workpiece, which is less important in ceramic grinding due to their better thermal stability than metals. As evidenced by the surface quality of the ceramic samples ground by the disc of the invention, the energy consumption is acceptable and does not deteriorate the finished piece.

The G-ratio of the experimental metal-bonded disk is substantially constant at 6051 at all material removal and disk speeds. For the resin disk, the G ratio decreases with increasing material removal rate at each constant disk speed.

Table 2 shows the improvement in surface smoothness and waviness of the ground samples at higher disc speeds. In addition, the measured waviness of the samples ground with the experimental disc was the lowest at all the disc and material removal rates tested.

In these experiments, the lifetime of the metal-bonded disk was much higher than that of the control disk. Unlike commercial control discs, there was no need to sharpen and pull off experimental disks9

EN 222 463 Blind during extensive grinding experiments. The test disc was successfully operated up to 90 m / s disc speed.

Example 3

In successive grinding experiments of the experimental disc (# 6), at a speed of 80 m / s and operating conditions similar to those described in the previous examples, 380 cm ³ / min / cm were achieved. The surface smoothness (Ra) was only 0.5 pm (12 pinch), and energy consumption remained at an acceptable level. The high material removal rate achieved by using the disc of the present invention without damaging the surface of the ceramic workpiece has not yet been disclosed in connection with any ceramic grinding process or any bonded commercial abrasive tool.

Example 4

A cup-shaped abrasive tool was made and a sapphire grinding test was carried out on a vertical-axis "blanchard type" machine. The cup-shaped disc (250mm diameter) was made from abrasive segments identical to the disc # 6 of Example 1, except that (1) the diamond was 45 µm (US mesh 270/325) and 12.5% by volume. (50 concentrations) in the abrasion segment; (2) the segments were 46.7 mm string length (133.1 mm radius), 4.76 mm wide, and 5.84 mm deep. These segments are fixed along the circumference of the side surface of the cup-shaped steel core. The steel core has a central bore hole. There are grooves on the core surface, circumferentially, which form discrete, shallow nests that have the same width and length as the segments. An epoxy adhesive (Technodyne HT-18 adhesive, purchased from Taoka, Japan) was placed in the nests, then the segments inserted, then the adhesive was cured. The finished disk is similar to the disk shown in Figure 2.

The cup-shaped disk has been successfully used to grind the surface of a 100 mm diameter solid sapphire cylindrical workpiece. Grinding resulted in an acceptable smooth surface with favorable grinding conditions, G ratio, material removal rate and energy uptake.

Example 5

A Type 2A2 abrasive tool (280 mm in diameter) was manufactured for back grinding AlTiC or silicon wafers. The tool contained the abrasion segments described in Table 3 below, except that the segments had a radius of 139.3 mm, a width of 3.13 mm, and a depth of 5.84 mm, to produce a mixture of diamond abrasive grains sufficient to produce 16 segments per disk. The proportions of the ingredients are shown in Table 3. The weighed ingredients were sieved through a US 140/170 mesh screen, and the components were evenly mixed. The powder required for each segment was weighed and then leveled and compressed into a graphite tool. The graphite segment tool was pressed hot at 405 ° C for 15 minutes at 2073 N / cm ² (3000 psi). After cooling, the segments were removed from the tool.

The disc assembly was performed by gluing the segments to the machined 7075 T6 aluminum core as described in Example 1. The segments were degreased, blasted with sand, glued and then inserted into recesses in the periphery of the disc. After curing the adhesive, the disk was resized, balanced and speed tested.

Table 3

Composition of binder

Crowd% Volume% Cu sn P Graphite Cu sn P Graphite Sample control (Ex. 1.) 49.47 50.01 0.52 0.00 43.71 54.03 2.26 0.00 (1) 7.5 / 2040 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18,30 (2) 7.5 / 2040 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18,30 (3) 7.5 / 2051 45.76 46.26 0.48 7.50 34.02 42.07 1.75 22.16 (4) 5/2040 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18,30 (5) I 25/2052 43.53 44.01 0.46 12.00 29.55 36.54 1.53 32.37

HU 222 463 BI

Table 4

The composition of the abrasive segment is by volume

Sample Binding Graphite Diamond Porosity ^b Sample control (Ex. 1) > 80 0.00 18.75 (75 conc) <5 (1) 7.5 / 2040 > 80 17.93 1.88 (7.5 conc) <5 (2) 7.5 / 2040 > 80 17.93 1.88 (7.5 conc) <5 (3) 7.5 / 2051 > 75 21.72 1.88 (7.5 conc) <5 (4) 5/2040 > 80 18.07 1.25 (5 conc) <5 (5) 25/2052 > 63 30.35 6.25 (25 conc) <5

^of each diamond particle used in the segments was 325 mesh (49 μιη) particle size, except sample 1 which was 270 mesh (57 (pm) particle size. The diamond concentration levels are given below the value% diamond by volume.

^b Porosity was estimated based on the microstructure of the segments. Because of the formation of intermetallic alloys, the density of the samples often exceeds the theoretical density derived from the data of materials used in the segments.

Example 6

Grinding performance evaluation

The grinding performance of the discs produced in accordance with Example 5, consisting of small graphite-filled experimental segments of 280 mm diameter, 29.3 mm thick, 228.6 mm center bore (11 inchx 1.155 inchx9 inch), was tested. The performance of these samples was compared to that of the control back grinding discs of Example 5. The control discs contained the high-diamond (# 75) abrasion segment of Example 1 (# 6) without graphite filler.

More than 70 grindings were performed on AlTiC workpieces (210 grade AlTiC, purchased from 3M Cor- poration Portion, Minneapolis, MN). Each grind was 114.3 mm (4.5 inches) wide and 1.42 mm (0.056 inches) deep. The workpieces were either 114.3 mm (4.5 inches) or 152.4 mm (6.0 inches) square pieces. The pms removed from the workpiece and the normal grinding force were measured. Grinding! the condition of the experiment was as follows:

Circumstances of grinding experiments

Machine: Strasbaugh Grinder 7AF model

Grinding mode: Vertical axis insertion grinding

Disc details: 280 mm diameter, 29.3 mm thickness, 229 mm hole

Disc speed: 1200 rpm

Working speed: 19 rpm

Refrigerant: deionized water

Material removal rate: variable, from 1.0pm / s to 5.0pm / s

The discs were peeled off and sharpened on a wide 62.4 mm (6 inch) trowel (38A240-HVS type, purchased from Norton Company, Worchester, MA). After initial operation, stripping and sharpening were carried out at intervals as needed and as the downward feed rate changed.

The grinding experimental results (normal force against the amount of material removed) of samples 2, 4 and 1 of Example 5 are shown in Table 5 and Figure 3.

Table 5

Normal grinding force against the amount of material removed

Puck- sample Control (Ex. 1) Control (Ex. 1.) Control (Ex. 1.) 2a 2a 2b 4 MMR (p / s) Complete ground block (pm) 1 3 5 1 2 2 2 Normal grinding force (kg) (pounds) 25 2.7 (6) 3.6 (8) 5.0 (11) 5.0 (11) I 50 7.3 (16) 9.1 (20) 10.4 (23) 2.7 (6) 3.2 (7) 8.6 (19) 9.1 (20)

HU 222 463 Bl

Table 5 (continued)

puck- sample Control (Ex. 1) Control (Ex. 1.) Control (Ex. 1.) 2a 2a 2b 4 MMR (μ / s) Whole ground block (μιυ) 1 3 5 1 2 2 2 Normal grinding force (kg) (pounds) 75 5.4 (12) 3.2 (7) 10.4 (23) 10.0 (22) 100 10.9 (24) 15.4 (34) 18.2 (40) 7.7 (17) 3.2 (7) 12.3 (27) 12.7 (28) 150 12.3 (27) 20.4 (45) 22.7 (50) 10.0 (22) 3.2 (7) 14.1 (31) 14.5 (32) 200 15.0 (33) 22.7 (50) 26.8 (59) 12.7 (28) 9.5 (21) 15.4 (34) 16.3 (36) 250 16.8 (37) 24.1 (53) 27.2 (60) 14.1 (31) 13.6 (30) 17.3 (38) 17.3 (38) 300 18.7 (40) 25.9 (57) 28.6 (63) 15.0 (33) 15.9 (35) 18.2 (40) 16.3 (36) 350 16.3 (36) 17.7 (39) 19.1 (42) 17.3 (38) 400 17.7 (39) 18.6 (41) 18.2 (40) 15.0 (33) 450 19.1 (42) 19.1 (42) 18.2 (40) 15.4 (34) 500 19.1 (42) 20.4 (45) 18.6 (41) 15.9 (34) 550 19.5 (43) 20.9 (46) 19.5 (43) 15.9 (35) 600 20.9 (46) 20.9 (46) 17.7 (39) 14.1 (31)

2a corresponds to the pattern ^of the two samples of Table 3, abrasive segments having a 3.13 mm wide. ^b pattern 2b is the same as pattern 2 in Table 3 with a 2.03 mm wide abrasion segment.

These results demonstrate that a significant increase in normal force was required to remove a greater amount of material from the array at a higher material removal rate (from 1 to 3 and then 5 μιη / s material removal) when surface grinding of the control disk at 75 concentrations of diamond abrasive particles but no graphite filler. In contrast, grinding with graphite-filled discs of low diamond concentration according to the invention in Example 5 (samples 2a, 2b and 4) required significantly less neutral force.

The force required to remove a quantity of material equivalent to the material of the present invention at a rate of removal of 2 µm / s was the same as that required for the reference disk at a material removal rate of 1 µm / s. 45

In addition, grinding with disk 2a required approximately the same normal force at both 1 pm / min and 2 pm / min material removal rates. The discs of the invention 2a, 2b and 4 of Example 5 also show a relatively stable normal force requirement 50 as the amount milled from the array moves from 200 to 600 µm. This type of grinding performance is highly desirable when back grinding AlTiC blades as these low forces and steady state conditions minimize the thermal and mechanical damage to the workpiece 55.

The control disk (Ex. 1) could not be tested at higher material removal levels (for example, above 300 pm) because the power required for grinding with these discs exceeds the normal power of the machine. As a result, the machine stopped automatically, preventing data collection at higher material removal rates.

While not wishing to be bound by any special theory, we believe that the extremely good grinding performance of low-diamond, graphite-filled discs is associated with a smaller number of abrasive particles per unit surface of abrasive segments that may come into contact with any point on the workpiece surface. Although experts in the art expect a lower material removal rate at lower diamond concentrations, the grinding force improvement achieved by the present invention is surprisingly achieved without a decrease in material removal rate. Grinding with disc 2b having a wear segment of 2.03 mm wide required less force to achieve the same speed and amount of material removed as did the 3.13 mm wide abrasive segment 2a. Sample disk 2b has a smaller surface area and less grinding points that come into contact with the sample surface during the grinding operation than sample 2a.

Claims (11)

PATENT CLAIMS 1. Abrasive tool for surface grinding, consisting of a core having a specific strength parameter of at least 2.4 MPa cm ³ / g, a density of 0.5 to 8.0 g / cm ³ , and having a circumferential and multiple abrasive segments12 It consists of an abrasive segment comprising a total of 100% by volume, comprising 0.05-10% by volume of superabrasive granules, 10-35% by volume of glassy filler, and 55-89.95% by volume of metal. contains a binder with a tensile strength of 1.0-3.0 MPa m ^1/2 . Abrasive tool according to claim 1, characterized in that the core metal material is selected from the group consisting of aluminum, steel, titanium and bronze, their composites and alloys, and combinations thereof. The abrasive tool of claim 1, wherein the abrasive segments comprise 60-84.5% by volume of metal binder, 0.5-5.0% by volume of abrasive grain, 15-35% by volume of glassy filler, and the porosity of the metal binder up to 5 volumes ⁰ / ^ Abrasive tool according to claim 1, characterized in that the crumble-filler is selected from the group consisting of graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline selenium, pumice stone, calcareous clay and glass balls, and combinations thereof. The abrasive tool of claim 1, wherein the abrasive grain is selected from the group consisting of diamond, cubic boron nitride, and combinations thereof. The abrasive tool according to claim 1, characterized in that the abrasive particles have a size of 2 to 300 microns. Abrasive tool according to claim 1, characterized in that the metal bond contains 35-84% by weight copper and 16-65% by weight tin. Abrasive tool according to claim 7, characterized in that the metal bond further contains 0.2 to 1.0% by weight of phosphorus. The abrasive tool according to claim 1, characterized in that the abrasive tool comprises at least two abrasive segments, the abrasive segments are elongated, arcuate, their inner curve fits to the circumference of the core, and the two ends of each segment are formed to fit the adjacent segment. so that the abrasion ring is continuous and substantially free of gaps between segments when the segments are attached to the core. Abrasive tool according to claim 1, characterized in that the tool comprises a group comprising discs 1A1 and cups. 11. The abrasive tool of claim 1, wherein the thermally stable bond is substantially selected from the group consisting of epoxy adhesive, metallic binder, mechanical and diffusion binder, and combinations thereof.