Patent Application
20220266421
Traditionally, bonded abrasive articles (e.g., abrasive wheels, abrasive segments, and whetstones) are made by compressing a blend of abrasive particles (e.g., diamond, cubic boron nitride, alumina, or SiC), a binder precursor (e.g., vitreous, metal or resin) an optional pore inducer (e.g., glass bubbles, naphthalene, crushed coconut or walnut shells, or acrylic glass or PMMA), and a temporary organic binder in a liquid vehicle (e.g., aqueous solutions of phenolic resin, polyvinyl alcohol, urea-formaldehyde resin, or dextrin). The abrasive particles, bond precursor, and, usually, the pore inducer are typically dry blended together. The temporary organic binder solution is then added to wet out the grain mix. The blended mix is then placed in a hardened steel mold treated with a mold release agent and pressed to reach a predefined volume. The pressed part is then removed from the mold in a green stage and put in a furnace to be heated until the binder is fully formed.
In one aspect, the present disclosure provides a bonded abrasive article. The bonded abrasive article has abrasive particles retained within a binder in an active grinding layer. The bonded abrasive article also has an internal reservoir configured to receive a fluid. The bonded abrasive article also has a feature configured to change a property of the fluid. The bonded abrasive article also has a delivery feature configured to deliver to fluid to a contact zone.
In another aspect, the present disclosure provides a method of making a bonded abrasive article. The method includes manufacturing an abrasive article preform. The abrasive article preform has an internal reservoir configured to receive a fluid from an external source. The abrasive article preform also includes a delivery feature configured to deliver the fluid to a contact area. The method also includes heating the abrasive article preform to provide the bonded abrasive article. The method also includes providing an acceleration feature into the internal reservoir. The acceleration feature accelerates a flow of the fluid from the internal reservoir to the delivery feature.
In another aspect, the present disclosure provides a method of using a bonded abrasive article. The method includes contacting the bonded abrasive article to a workpiece. The contact is along an active grinding area. The method also includes moving the abrasive article with respect to the workpiece. The method also includes applying coolant such that the active grinding area is sufficiently lubricant. Applying coolant includes the bonded abrasive article receiving coolant from an external source. Applying coolant also includes adjusting a property of the received coolant while the coolant is within the abrasive article. Applying coolant also includes distributing the coolant to the active grinding area, from within the abrasive article.
Using abrasive articles with such systems may reduce or even prevent surface burning and/or damage to a workpiece subsurface during an abrading operation. Other features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.
Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.
Powder bed binder jetting is an additive manufacturing, or “3D printing” technology, in which a thin layer of a powder is temporarily bonded at desired locations by a jetted liquid binder mixture. Typically, that binder mixture is dispensed by an inkjet printing head, and consists of a polymer dissolved in a suitable solvent or carrier solution. In one method, the binder is a powder which is mixed with the other powder, or coated onto the powder and dried, and then an activating liquid, such as water or a solvent mixture, is jetted onto the powder, activating the binder in select areas. The printed powder layer is then at least partially dried and lowered so that a next powder layer can be spread. The powder spreading, bonding and drying processes can be repeated until the full object is created. The object and surrounding powder is removed from the printer and often dried or cured to impart additional strength so that the now hardened object can be extracted from the surrounding powder.
During an abrasive grinding process, it is essential that coolant be provided. Coolant reduces mechanical, thermal and chemical impact between an abrasive particle and the workpiece being abraded. Lubricant reduces friction between the materials and cools the grinding process area by absorbing and transporting heat generated during grinding away from the process area. If sufficient coolant is not present, the risk of surface burning and/or damage to the subsurface of the workpiece being abraded is high. One goal of abrasive article design is to manage coolant delivery, both too and from a work area, so that enough coolant is available to an active grinding area as needed. As discussed below, embodiments of the present invention achieve this by modifying the abrasive article design. For example, some embodiments use internal coolant features designed to capture coolant from an external source and deliver it to an active grinding area.
Similar issues are present for face grinding processes, as the surface contact area depends on the width of a grinding ring, as well as in periphery grinding processes when the workpiece path forms a partial envelope around the grinding wheel.
Many attempts have been made to solve the coolant delivery problem through the use of specially designed nozzles, such as nozzle 20, illustrated in
Another attempted solution is illustrated in
Another option is to provide an internal coolant source, through a specially designed grinding wheel spindle. Coolant is delivered through the specially designed grinding wheel center (e.g. through a shaft or adapted connection feature) and then passes through the grinding wheel through holes in the abrasive layer. Unfortunately, most older machines, and many new spindles, do not have this feature.
Embodiments described herein solve the coolant delivery problem by driving coolant to an abrading contact zone without the need for a special spindle. Some embodiments accomplish this by collecting fluid from the standard environment such that the fluid is captured from a supply, accelerated through a design feature within the grinding wheel, and then redistributed to the grinding zone through openings in an active layer of the grinding wheel. The openings may be located to take advantage of acceleration by the design feature(s).
Abrasive article 200 may be have a vitreous, metal-based or resin bond that holds abrasive particles in place within a bond matrix. While some of the discussion below focuses on the example of a vitreous bonded abrasive article, it is expressly contemplated that other binders, such as metal-based bond or a resin-based bond, are also possible in some embodiments of the present invention.
Abrasive article 200 also includes openings 250 in the abrasive layer that drive coolant, accelerated by acceleration feature 240, to a contact zone. Additionally, channels 260 distribute coolant throughout the surface area of grinding wheel 200. Illustrated in
Abrasive article 200 is designed to utilize an external coolant source to collect coolant, using reservoir 230, and distribute it to a work zone, using openings 250 and grooves 260, at a desired speed and pressure, achieved through acceleration feature 240.
Acceleration feature designs can be varied, as illustrated in the examples of
Acceleration feature 310 includes a plurality of blades 302, each of which curves counterclockwise outward from an internal bore 304 to an abrasive layer (e.g. at reference numeral 306). In one embodiment, each blade 302 has a variable thickness and is thinnest at the connection point to bore 304 and thickest at the connection point to an abrasive layer (e.g at reference numeral 306). In one embodiment, acceleration feature has eight blades 302. However more blades 302, or fewer, may also be present. Blades 302 are configured to extend along an entire length 308 of an internal reservoir.
Acceleration feature 320 includes a plurality of blades 312 that extend from an internal core 314 to the abrasive layer (e.g. at reference numeral 316). While blades 312 in acceleration feature 320 extend substantially straight from an internal core 314 to an abrasive layer (e.g. at reference numeral 316), they do not extend straight along a length 318 of the abrasive article. Instead, each blade in acceleration feature has a twisted surface as it extends along a length of abrasive article. Additionally, each blade 312 has a length longer than an abrasive article length 318, as it curves around the internal bore.
Acceleration feature 330 includes a plurality of blades 322 that do not completely extend from an internal bore 324 to an abrasive layer (e.g. at reference numeral 326). Each blade has some curvature and experiences some twisting along the length 328 of the abrasive article. Blades 322 of acceleration feature 330 also, as shown in
Acceleration feature 340 includes a plurality of blades 332 extending radially outward from an internal bore 334 to an abrasive layer (e.g. at reference numeral 336). Blades 332 extend perpendicularly from a surface of bore 334 along a length 338 of abrasive article 350.
Embodiments discussed thus far illustrate an abrasive grinding wheel that can collect coolant from an external source and provide it to an active grinding area using a single acceleration feature, either build into a grinding wheel or inserted prior to an abrasive operation. However, many abrasive operations require coolant to be delivered to multiple locations, and may require coolant be delivered at different speeds and/or pressures at different locations.
Abrasive wheel 400 has an active layer 410 that can be customized based on the needs of an abrasive operation. For example, diameter, height, abrasive thickness, grit size, number and size of threads, etc. are all customizable variables of abrasive wheel 400. As illustrated in
One or more reservoirs 404, 414 are also present within abrasive wheel 400 to collect fluid provided from an external source. Abrasive wheel 400 also has multiple acceleration features 440. Acceleration features 440 are located at the required levels to accelerate the fluid to the contact zone. Acceleration occurs based on the rotation of the grinding wheel during operation. Acceleration features are, in one embodiment, designed to provide the fluid at a desired speed and/or pressure based on the abrasive application. As illustrated in
Abrasive wheel 400 also has one or more openings 450 to drive the accelerated fluid to the contact zone. Openings 450 are illustrated as having a rectangular shape in
The different features of abrasive wheel 400 may also be designed differently in other embodiments. For example, reservoir 404 could be bigger or smaller. Reservoir 404 could also incorporate an acceleration feature 440 with more blades 402. Acceleration feature 440 could be shaped differently. For example, blades 402 may extend completely, or only partially, from bore 420 to an internal edge of grinding surface 410. Openings 450 could be round, square or another tortuous shape. Additionally, openings 450 can be placed at several heights within the grinding zone, for example in each distributing groove, or in a subset of distributing grooves.
Grinding wheel 500 is designed to grind a double ball bearing outer ring, and has an active abrasive layer designed accordingly. An internal reservoir 510 is configured to collect coolant provided from an external source. Acceleration feature 520 alters a property of the coolant, e.g. the speed and/or pressure, such that it can be delivered through an opening 522 to a contact zone between abrasive wheel 500 and a workpiece (not shown). While only one layer of internal reservoir 510 and acceleration feature 520 are shown in
Grinding wheel 550 is designed for gear grinding. Grinding wheel 550 has an active layer with a plurality of threads. While three threads are shown for simplicity, it is also contemplated that more threads, such as 4, 5, 6, 7, 8 or even more, may be present in other embodiments. Grinding wheel 550 has an internal reservoir 560 and acceleration feature 520 which are configured to receive coolant from an external source and provide it through an opening 520 at a desired speed and pressure.
However, while
Methods of making bonded abrasive articles according to the present disclosure include an additive subprocess. The subprocess comprises sequentially, preferably consecutively (although not required) carrying out at least three steps.
In the first step, a layer 638 of loose powder particles 610 is deposited in a confined region 640. The layer 638 should be of substantially uniform thickness. For example, the thickness of the layer may be less than 500 microns, less than 300 microns, less than 200 microns, or less than 100 microns. The layers may have any thickness up to about 1 millimeter, as long as the jetted liquid binder precursor material can bind all the loose powder where it is applied. Preferably, the thickness of the layer is from about 10 microns to about 500 microns, 10 microns to about 250 microns, about 50 microns to about 250 microns, or from about 100 microns to about 200 microns.
In the embodiment where the bonded abrasive article is a vitreous bonded abrasive article, the loose powder particles comprise vitreous bond precursor particles and abrasive particles. The vitreous bond precursor particles may comprise particles of any material that can be thermally converted into a vitreous material. Examples include glass frit particles, ceramic particles, ceramic precursor particles, and combinations thereof.
The vitreous bond which binds together the abrasive grain in accordance with this disclosure can be of any suitable composition which is known in the abrasives art, for example. The vitreous bond phase, also variously known in the art as a “ceramic bond”, “vitreous phase”, vitreous matrix”, or “glass bond” (e.g., depending on the composition) may be produced from one or more oxide (e.g., a metal oxide and/or boria) and/or at least one silicate as frit (i.e., small particles), which upon being heated to a high temperature react to form an integral vitreous bond phase. Examples include glass particles (e.g., recycled glass frit, water glass frit), silica frit (e.g., sol-gel silica frit), alumina trihydrate particles, alumina particles, zirconia particles, and combinations thereof. Suitable frits, their sources and compositions are well known in the art.
Abrasive articles are typically prepared by forming a green structure comprised of abrasive grain, the vitreous bond precursor, an optional pore former, and a temporary binder. The green structure is then fired. The vitreous bond phase is usually produced in the firing step of the process for producing the abrasive article of this disclosure. Typical firing temperatures are in the range of from 540° C. to 1700° C. (1000° F. to 3100° F.). It should be understood that the temperature selected for the firing step and the composition of the vitreous bond phase must be chosen so as to not have a detrimental effect on the physical properties and/or composition of abrasive particles contained in the vitreous bond abrasive article.
Useful glass frit particles may include any glass frit material known for use in vitreous bond abrasive articles. Examples include glass frit selected from the group consisting of silica glass frit, silicate glass frit, borosilicate glass frit, and combinations thereof. In one embodiment, a typical vitreous binding material contains about 70-90% SiO2+B2O3, 1-20% alkali oxides, 1-20% alkaline earth oxides, and 1-20% transition metal oxides. In another embodiment, the vitreous binding material has a composition of about 82 wt % SiO2+B2O3, 5% alkali metal oxide, 5% transition series metal oxide, 4% Al2O3, and 4% alkaline earth oxide. In another embodiment, a frit having about 20% B2O3, 60% silica, 2% soda, and 4% magnesia may be utilized as the vitreous binding material. One of skill in the art will understand that the particular components and the amounts of those components can be chosen in part to provide particular properties of the final abrasive article formed from the composition.
The size of the glass frit can vary. For example, it may be the same size as the abrasive particles, or different. Typically, the average particle size of the glass frit ranges from about 0.01 micrometer to about 100 micrometers, preferably about 0.05 micrometer to about 50 micrometers, and most preferably about 0.1 micrometer to about 25 micrometers. The average particle size of the glass frit in relation to the average particle size of the abrasive particles having a Mohs hardness of at least about 5 can vary. Typically, the average particle size of the glass frit is about 1 to about 200 percent of the average particle size of the abrasive, preferably about 10 to about 100 percent, and most preferably about 15 to about 50 percent.
Typically, the weight ratio of vitreous bond precursor particles to abrasive particles in the loose powder particles ranges from about 10:90 to about 90:10. The shape of the vitreous bond precursor particles can also vary. Typically, they are irregular in shape (e.g., crushed and optionally graded), although this is not a requirement. For example, they may be spheroidal, cubic, or some other predetermined shape.
Preferably, the coefficient of thermal expansion of the vitreous bond precursor particles is the same or substantially the same as that of the abrasive particles.
Glassy inorganic binders may be made from a mixture of different metal oxides. Examples of these metal oxide vitreous binders include silica, alumina, calcia, iron oxide, titania, magnesia, sodium oxide, potassium oxide, lithium oxide, manganese oxide, boron oxide, phosphorous oxide, and the like. Specific examples of vitreous binders based upon weight include, for example, 47.61 percent SiO2, 16.65 percent Al2O3, 0.38 percent Fe2O3, 0.35 percent TiO2, 1.58 percent CaO, 0.10 percent MgO, 9.63 percent Na2O, 2.86 percent K2O, 1.77 percent Li2O, 19.03 percent B2O3, 0.02 percent MnO2, and 0.22 percent P2O5; and 63 percent SiO2, 12 percent Al2O3, 1.2 percent CaO, 6.3 percent Na2O, 7.5 percent K2O, and 10 percent B2O3.
One preferred vitreous bond has an oxide-based mole percent (%) composition of SiO2 63.28; TiO2 0.32; Al2O3 10.99; B2O3 5.11; Fe2O3 0.13; K2O 3.81; Na2O 4.20; Li2O 4.98; CaO 3.88; MgO 3.04 and BaO 0.26. Firing of these ingredients is typically accomplished by raising the temperature from room temperature to 1149° C. (2100° F.) over a prolonged period of time (e.g., about 25-26 hours), holding at the maximum temperature (e.g., for several hours), and then cooling the fired article to room temperature over an extended period of time (e.g., 25-30 hours).
The vitreous bond precursor particles may comprise ceramic particles. In such cases sintering and/or fusing of the ceramic particles forms the vitreous matrix. Any sinterable and/or fusible ceramic material may be used. Preferred ceramic materials include alumina, zirconia, and combinations thereof.
The vitreous bond precursor particles may be present in an amount from 10 to 40 volume percent of the combined volume of the vitreous bond precursor particles and abrasive particles, preferably from 15 to 35 volume percent of the abrasive composition. Some examples of suitable metal binders include tin, copper, aluminum, nickel, and combinations thereof.
Suitable resin binders include formaldehyde-containing resins, such as phenol formaldehyde, novolac phenolics and especially those with added crosslinking agent (e.g., hexamethylenetetramine), phenoplasts, and aminoplasts, unsaturated polyester resins; vinyl ester resins; alkyd resins, allyl resins; furan resins; epoxies; polyurethanes; cyanate esters; and polyimides. In general, the amount of resin should be sufficient to fully wet the surfaces of all the individual particles during manufacturing such that a continuous resin structure is formed with the inorganic components discretely bonded throughout.
If desired, alpha-alumina ceramic particles may be modified with oxides of metals such as magnesium, nickel, zinc, yttria, rare earth oxides, zirconia, hafnium, chromium, or the like. Alumina and zirconia abrasive particles may be made by a sol-gel process, for example, as disclosed in U.S. Pat. No. 4,314,827 (Leitheiser et al.); U.S. Pat. No. 4,518,397 (Leitheiser et al.); U.S. Pat. No. 4,574,003 (Gerk); U.S. Pat. No. 4,623,364 (Cottringer et al.); U.S. Pat. No. 4,744,802 (Schwabel); and U.S. Pat. No. 5,551,963 (Larmie).
It is known in the art to use various additives in the making of bonded abrasive articles both to assist in the making of the abrasive article and/or improve the performance of such articles. Such conventional additives which may also be used in the practice of this disclosure include but are not limited to lubricants, fillers, pore inducers, and processing aids. Examples of lubricants include, graphite, sulfur, polytetrafluoroethylene and molybdenum disulfide. Examples of pore inducers include glass bubbles and organic particles. Concentrations of the additives as are known in the art may be employed for the intended purpose of the additive, for example. Preferably, the additives have little or no adverse effect on abrasive particles employed in the practice of this disclosure.
The loose powder particles may optionally be modified to improve their flowability and the uniformity of the layer spread. Methods of improving the powders include agglomeration, spray drying, gas or water atomization, flame forming, granulation, milling, and sieving. Additionally, flow agents such as, for example, fumed silica, nanosilica, stearates, and starch may optionally be added.
The bond precursor particles may comprise a ceramic precursor (e.g., a precursor of alumina or zirconia) such as, for example, bauxite, boehmite, calcined alumina, or calcined zirconia that when fired converts to the corresponding ceramic form.
Procedures and conditions known in the art for producing bonded abrasive articles (e.g., grinding wheels), and especially procedures and conditions for producing bond abrasive articles, may be used to make the abrasive articles of this disclosure. These procedures may employ conventional and well-known equipment in the art.
The abrasive particles may comprise any abrasive particle used in the abrasives industry. Preferably, the abrasive particles have a Mohs hardness of at least 4, preferably at least 5, more preferably at least 6, more preferably at least 7, more preferably at least 8, more preferably at least 8.5, and more preferably at least 9. In certain embodiments, the abrasive particles comprise superabrasive particles. As used herein, the term “superabrasive” refers to any abrasive particle having a hardness greater than or equal to that of silicon carbide (e.g., silicon carbide, boron carbide, cubic boron nitride, and diamond).
Specific examples of suitable abrasive materials include aluminum oxide (e.g., alpha alumina) materials (e.g., fused, heat-treated, ceramic, and/or sintered aluminum oxide materials), silicon carbide, titanium diboride, titanium nitride, boron carbide, tungsten carbide, titanium carbide, aluminum nitride, diamond, cubic boron nitride (CBN), garnet, fused alumina-zirconia, sol-gel derived abrasive particles, cerium oxide, zirconium oxide, titanium oxide, and combinations thereof. Examples of sol-gel derived abrasive particles can be found in U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.); U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.); and U.S. Pat. No. 4,881,951 (Monroe et al.). Agglomerate abrasive particles that comprise finer abrasive particles in a vitreous bond matrix (e.g., as described in U.S. Pat. No. 6,551,366 (D'Souza et al.)) may also be used.
In order to achieve fine resolution, the loose powder particles are preferably sized (e.g., by screening) to have a maximum size of less than or equal to 400 microns, preferably less than or equal to 250 microns, more preferably less than or equal to 200 microns, more preferably less than or equal to 150 microns, less than or equal to 100 microns, or even less than or equal to 80 microns, although larger sizes may also be used. The size of the powder particles may relate to the size of the abrasive particle used. The vitreous bond precursor particles, abrasive particles, and any optional additional particulate components may have the same or different maximum particle sizes, D90, D50, and/or D10 particle size distribution parameters.
The loose powder particles may optionally further comprise other components such as, for example, pore inducers, and/or filler particles. Examples of pore inducers include glass bubbles and organic particles.
Next, a liquid binder precursor material 670 is jetted by printer 650 onto predetermined region(s) 680 of layer 638. The liquid binder precursor material thus coats the loose powder particles in region 680, and is subsequently converted to a binder material that binds the loose powder particles in region 680 to each other. The liquid binder precursor material may be any composition that can be converted (e.g., by evaporation, or thermal, chemical, and/or radiation curing (e.g., using UV or visible light)) into a binder material that bonds the loose powder particles together according to the jetted pattern (and ultimate 3-D shape upon multiple repetitions).
In some embodiments, the liquid binder precursor material comprises a liquid vehicle having a polymer dissolved therein. The liquid may include one or more of organic solvent and water. Exemplary organic solvents include alcohols (e.g., butanol, ethylene glycol monomethyl ether), ketones, and ethers, preferably having a flash point above 100° C.
Selection of a suitable solvent or solvents will typically depend upon requirements of the specific application, such as desired surface tension and viscosity, the selected particulate solid, for example.
The liquid vehicle can be entirely water, or can contain water in combination with one or more organic solvents. Preferably, the aqueous vehicle contains, on a total weight basis, at least 20 percent water, at least 30 percent water, at least 40 percent water, at least 50 percent water, or even at least 75 percent water.
In some embodiments, one or more organic solvents may be included in the liquid vehicle, for instance, to control drying speed of the liquid vehicle, to control surface tension of the liquid vehicle, to allow dissolution of an ingredient (e.g., of a surfactant), or, as a minor component of any of the ingredients; e.g., an organic co-solvent may be present in a surfactant added as an ingredient to the liquid vehicle. Exemplary organic solvents include: alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, and isobutyl alcohol; ketones or ketoalcohols such as acetone, methyl ethyl ketone, and diacetone alcohol; esters such as ethyl acetate and ethyl lactate; polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,2,4-butanetriol, 1,5-pentanediol, 1,2,6-hexanetriol, hexylene glycol, glycerol, glycerol ethoxylate, trimethylolpropane ethoxylate; lower alkyl ethers such as ethylene glycol methyl or ethyl ether, diethylene glycol ethyl ether, triethylene glycol methyl or ethyl ether, ethylene glycol n-butyl ether, diethylene glycol n-butyl ether, diethylene glycol methyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, and dipropylene glycol dimethyl ether; nitrogen-containing compounds such as 2-pyrrolidinone and N-methyl-2-pyrrolidinone; sulfur-containing compounds such as dimethyl sulfoxide, tetramethylene sulfone, and thioglycol; and combinations of any of the foregoing.
The amounts of organic solvent and/or water within the liquid vehicle can depend on a number of factors, such as the particularly desired properties of the liquid binder precursor material such as the viscosity, surface tension, and/or drying rate, which can in turn depend on factors such as the type of ink jet printing technology intended to be used with the liquid vehicle ink, such as piezo-type or thermal-type printheads, for example.
The liquid binder precursor material may include a polymer that is soluble or dispersible in the liquid vehicle. Examples of suitable polymers may include polyvinyl pyrrolidones, polyvinyl caprolactams, polyvinyl alcohols, polyacrylamides, poly(2-ethyl-2-oxazoline) (PEOX), polyvinyl butyrate, copolymers of methyl vinyl ether and maleic anhydride, certain copolymers of acrylic acid and/or hydroxyethyl acrylate, methyl cellulose, natural polymers (e.g., dextrin, guar gum, xanthan gum). Of these, polyvinyl pyrrolidones are preferred for use with liquid vehicles that are predominantly water. Other organic polymers than those listed above may be used instead or in addition if desired.
The liquid binder precursor material may include one or more free-radically polymerizable or otherwise radiation-curable materials; for example, acrylic monomers and/or oligomers and/or epoxy resins. An effective amount of photoinitiator and/or photocatalysts for curing the free-radically polymerizable or otherwise radiation-curable materials may also be included. Examples of suitable (meth)acrylate monomers and oligomers and otherwise radiation-curable materials (e.g., epoxy resins) can be found in, for example, U.S. Pat. No. 5,766,277 (DeVoe et al.).
In some preferred embodiments, the liquid binder precursor material is essentially free of (e.g., contains less than 1 percent, less than 0.1 percent, less than 0.01 percent, or is even free of) metal nanoparticles and/or metal oxide nanoparticles. As used herein, the term “nanoparticles” refers to particles having an average particle diameter of less than or equal to one micron; for example less than or equal to 500 nanometers (nm), or even less than or equal to 150 nm.
Alternatively, or in addition, the liquid binder precursor may be an aqueous sol including a ceramic precursor for alumina and/or zirconia. Examples include aqueous boehmite sols and zirconia sols. In such cases, after firing, the liquid binder precursor may have the same or different composition as the abrasive particles. Details concerning zirconia sols can be found, for example, in U.S. Pat. No. 6,376,590 (Kolb et al.). Details concerning boehmite sols can be found, for example, in U.S. Pat. No. 4,314, 827 (Leitheiser et al.), U.S. Pat. No. 5,178,849 (Bauer) U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 4,960,441 (Pellow et al.) U.S. Pat. No. 5,011,508 (Wald et al.), U.S. Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963 (Larmie), U.S. Pat. No. 5,725,162 (Garg et al.), and U.S. Pat. No. 5,776,214 (Wood)).
The jetted liquid binder precursor material is converted into a binder material that bonds together the loose powder particles in predetermined regions of the loose powder particles to form a layer of bonded powder particles; for example, by evaporation of a liquid vehicle in the liquid binder precursor material. In these embodiments, heating the binder material to sufficiently high temperature causes it to volatilize and/or decompose (e.g., “burn out”) during a subsequent firing step. Cooling may be accomplished by any means known to the art (e.g., cold quenching or air cooling to room temperature).
Referring again to
The above steps are then repeated (step 685) with changes to the region where jetting is carried out according to a predetermined design resulting through repetition, layer on layer, in a three-dimensional (3-D) abrasive article preform. In each repetition, the loose powder particles and the liquid binder precursor material may be independently selected; that is, either or both or the loose powder particles and the liquid binder precursor material may be the same as, or different from those in adjacent deposited layers.
The abrasive article preform comprises the bonded powder particles and remaining loose powder particles. Once sufficient repetitions have been carried out to form the abrasive article preform, it is preferably separated from substantially all (e.g., at least 85 percent, at least 90 percent, preferably at least 95 percent, and more preferably at least 99 percent) of the remaining loose powder particles, although this is not a requirement.
If desired, multiple particle reservoirs each containing a different powder may be used. Likewise, multiple different liquid binder precursor materials may be used, either through a common printhead or, preferably, through separate printheads. This results in different powders/binders distributed in different and discrete regions of the bonded abrasive article. For example, relatively inexpensive, but lower performing abrasive particles and or vitreous bond precursor particles may be relegated to regions of the bonded abrasive article where it is not particularly important to have high performance properties (e.g., in the interior away from the abrading surface).
Generally, bonded abrasive articles made in such ways have considerable porosity throughout their volumes. Accordingly, the abrasive article preform may then be infused with a solution or dispersion of additional bond precursor material, or grain growth modifiers.
Powder bed jetting equipment suitable for practicing the present disclosure is commercially available, for example, from ExOne, North Huntington, Pa. Further details concerning powder bed jetting techniques suitable for practicing the present disclosure can be found, for example, in U.S. Pat. No. 5,340,656 (Sachs et al.) and U.S. Pat. No. 6,403,002 B1 (van der Geest).
Advantageously, abrasive articles made according to embodiments described herein are configured to receive a coolant fluid from an external source and provide the coolant to an active grinding area. Abrasive articles described herein have an internal reservoir that receives coolant from an external source. Within the internal reservoir is a feature that changes a property of the coolant. For example, the coolant pressure and/or flow speed may increase. The coolant is then delivered to an active grinding area, for example through one or more openings extending through a grinding layer of the abrasive article. Additionally, one or more fluid channels may be present along the surface of the grinding area. Using abrasive articles with such systems may reduce or even prevent surface burning and/or damage to a workpiece subsurface during an abrading operation.
While
Embodiment 1 is a bonded abrasive article. The bonded abrasive article includes abrasive particles retained within a binder in an active grinding layer. The bonded abrasive article also includes an internal reservoir configured to receive a fluid. The bonded abrasive article also includes a feature configured to change a property of the fluid. The bonded abrasive article also includes a delivery feature configured to deliver to fluid to a contact zone.
Embodiment 2 includes the features of Embodiment 1, however the feature is an acceleration feature configured to change the property of the fluid based on a rotation of the abrasive article about a mechanical shaft.
Embodiment 3 includes the features of Embodiments 1 or 2, however the property is speed.
Embodiment 4 includes the features of Embodiments 1 or 2, however the property is pressure.
Embodiment 5 includes the features of any of Embodiments 1-4, however the delivery feature is an opening extending substantially through the bonded abrasive article from the internal reservoir to the active grinding layer.
Embodiment 6 includes the features of any of Embodiments 1-5, as well as a fluid channel within the active grinding layer.
Embodiment 7 includes the features of Embodiment 6, however the fluid channel extends substantially along a length of the bonded abrasive article, such that fluid can travel along the length of the bonded abrasive article.
Embodiment 8 includes the features of Embodiment 6, however the delivery feature comprises an opening extending from the internal reservoir to the fluid channel.
Embodiment 9 includes the features of any of Embodiments 1-8, however the feature comprises a plurality of blades.
Embodiment 10 includes the features of Embodiment 9, however each of the plurality of blades extend outward from a bore to the active grinding layer.
Embodiment 11 includes the features of Embodiment 10, however each of the plurality of blades has a curved surface.
Embodiment 12 includes the features of Embodiments 10 or 11, however each of the plurality of blades has a twisted surface.
Embodiment 13 includes the features of any of Embodiments 9-12, however each of the plurality of blades extends completely from the bore to the active grinding layer, and wherein the internal reservoir is a plurality of internal reservoir portions.
Embodiment 14 includes the features of any of Embodiments 1-13, however the feature is manufactured as a single structure with the active grinding layer.
Embodiment 15 includes the features of any of Embodiments 1-14, however the feature is manufactured separately from the active grinding layer.
Embodiment 16 includes the features of any of claims 1-15, however the internal reservoir is a first internal reservoir, the feature is a first feature, the delivery feature is a first delivery feature, and the contact zone is a first contact zone. The abrasive article further includes a second internal reservoir, configured to receive the fluid, a second feature configured to change the property of the fluid, and a second delivery feature configured to deliver the fluid to a second contact zone.
Embodiment 17 includes the features of Embodiment 16, however the second contact zone comprises a different area of the active grinding layer than the first contact area.
Embodiment 18 includes the features of Embodiment 16, however the active grinding layer is formed into a plurality of threads.
Embodiment 19 includes the features of Embodiment 18, however it also includes a number of internal reservoirs less than a number of the plurality of threads. Embodiment 20 includes the features of any of claims 1-19, however the bonded abrasive article is a grinding wheel.
Embodiment 21 includes the features of Embodiment 20, however the bonded abrasive article is a gear grinding wheel.
Embodiment 22 includes the features of Embodiment 20, however the bonded abrasive article is a bearing outer ring grinding wheel.
Embodiment 23 includes the features of Embodiment 20, however the bonded abrasive article is an internal grinding wheel, a plunge grinding wheel or a surface grinding wheel.
Embodiment 24 includes the features of Embodiment 15, however the feature is formed from a polymer, a ceramic or a metal.
Embodiment 25 includes the features of any of Embodiments 1-24, however the bonded abrasive article comprises a vitreous bond, a metal bond, or a resin bond.
Embodiment 26 is a method of making a bonded abrasive article. The method includes manufacturing an abrasive article preform. The abrasive article preform includes an internal reservoir configured to receive a fluid from an external source and a delivery feature configured to deliver the fluid to a contact area. The method also includes heating the abrasive article preform to provide the bonded abrasive article. The method also includes providing an acceleration feature into the internal reservoir. The acceleration feature accelerates a flow of the fluid from the internal reservoir to the delivery feature.
Embodiment 27 includes the features of Embodiment 26, however providing the acceleration feature comprises simultaneously manufacturing the acceleration feature with the abrasive article preform, prior to heating.
Embodiment 28 includes the features of any of Embodiments 26-27, however providing the acceleration feature comprises inserting the acceleration feature into the internal reservoir after the abrasive article preform is heated to provide the bonded abrasive article.
Embodiment 29 includes the features of any of Embodiments 26-28, however the acceleration feature comprises ceramic, polymer or metal.
Embodiment 30 includes the features of any of Embodiments 26-29, however manufacturing the abrasive article preform comprises additive manufacturing.
Embodiment 31 includes the features of any of Embodiments 26-30, however the acceleration feature comprises a plurality of blades.
Embodiment 32 includes the features of Embodiment 31, however the plurality of blades extend radially outward through the internal reservoir.
Embodiment 33 includes the features of Embodiment 32, however the plurality of blades extend to an active grinding area, such that the internal reservoir is separated into a plurality of internal reservoir portions.
Embodiment 34 includes the features of any of Embodiments 31-33, however the plurality of blades have a curved surface.
Embodiment 35 includes the features of any of Embodiments 31-34, however the plurality of blades have a twisted surface.
Embodiment 36 includes the features of any of Embodiments 26-35, however the abrasive article preform comprises a second internal reservoir, with a second acceleration feature, and a second delivery feature configured to deliver accelerated fluid to a second contact area.
Embodiment 37 includes the features of Embodiment 36, however the second internal reservoir is separated from the internal reservoir, and wherein the second contact area is a different surface portion of the active grinding surface than the first contact area.
Embodiment 38 includes the features of any of Embodiments 26-37, however the bonded abrasive article is a grinding wheel.
Embodiment 39 includes the features of any of Embodiments 26-38, however the bonded abrasive article comprises a vitreous, metal or resin bond.
Embodiment 40 is a method of using a bonded abrasive article. The method includes contacting the bonded abrasive article to a workpiece. The contact is along an active grinding area. The method also includes moving the abrasive article with respect to the workpiece. The method also includes applying coolant such that the active grinding area is sufficiently lubricant. Applying coolant includes the bonded abrasive article receiving coolant from an external source, adjusting a property of the received coolant while the coolant is within the abrasive article, and distributing the coolant to the active grinding area, from within the abrasive article.
Embodiment 41 includes the features of Embodiment 40, however the property is speed.
Embodiment 42 includes the features of Embodiment 40, however the property is pressure.
Embodiment 43 includes the features of any of Embodiments 40-42, however distributing the coolant comprises the coolant flowing through openings extending through an active grinding layer of the bonded abrasive article.
Embodiment 44 includes the features of Embodiment 43, however distributing further comprises the coolant flowing through fluid channels within an active grinding layer of the bonded abrasive article.
Embodiment 45 includes the features of any of Embodiment 40-44, however adjusting a property of the received coolant comprises the coolant flowing through a feature within an internal reservoir of the bonded abrasive article.
Embodiment 46 includes the features of Embodiment 45, however the feature is a built-in feature of the bonded abrasive article.
Embodiment 47 includes the features of Embodiment 46, however the feature comprises a separate material from the bonded abrasive article.
Embodiment 48 includes the features of Embodiment 47, however the feature is made of a material comprising a polymer, a ceramic, a metal or a combination thereof.
Embodiment 49 includes the features of any of Embodiments 40-48, however moving the abrasive article comprises rotating the abrasive article about a shaft.
Embodiment 50 includes the features of any of Embodiments 40-49, however the bonded abrasive article comprises abrasive particles within a binder.
Embodiment 51 includes the features of Embodiment 50, however the binder is a vitreous binder, a metal binder or a resin binder.
Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. In the Examples: ° C.=degrees Celsius, g=grams, min=minute, mm=millimeter, sec=second, and rpm=revolutions per minute.
Table 1, below, lists abbreviations for materials used in the Examples.
A mixture of abrasive type PDR1 or PDR5 and frit PDR3 or PDR4 is filled in an adequate container which can be introduce in a turbula mixer. Additionally to the mentioned abrasives, a secondary abrasive PDR2 can be added. The container is introduced into the turbula mixer, dry mixed during 30 minutes. After this time, the mixture is sieved on a 200 μm sieve. No other additive is used.
The printer used is the Exone Innovent from North Huntingdon, Pa. 15642 USA. The prepared mixture is placed in the hopper of the printer.
A 3D model was created into Solidworks 2017 CAD software. The saved file represents a rotating grinding wheel having features as grooves, openings, coolant collector and accelerating system. The file was saved as STL file format which is readable by the printer.
The file was loaded into a print job of the printer. Printing was made of successive steps to spread powder layers, to jet binder in 2D patterns made from cross sections of the 3D objects, and to at least partially dry that binder between jetting and spreading steps.
The main used parameters were: Recoat speed (mm/s): 25—Oscillator speed (rpm): 2800—Roller Speed (rpm): 200—Roller Traverse speed (mm/s): 15. This print job was run and completed on the printer, and the result was a powder bed holding loose powder and 3D shapes of binder and powder. That powder bed was removed from the printer and baked in an oven at 195° C. during 6 hours.
After cooling, those 3D shapes or “green” parts were extracted and depowdered (removing the loose powder from the platform). Those depowdered parts were placed into a furnace for burning out the binder and, in a second step, melting and sintering the vitreous based frit which bonded the abrasives grits into a solid matrix.
A print material was prepared by mixing, based on the mixture weight, 90 wt. % of PDR1 and 10 wt. % of PDR3. The print material was filled into the build box of an Innovent printer, obtained from The ExOne Company, North Huntingdon, Pa. The binder supply bottle of the printer was filled with BIN. 3D printing according to design parameters shown in
A print material was prepared by mixing, based on the mixture weight, 70 wt. % of PDR1, 20% wt. % of PDR2 and 10 wt. % of PDR3. The procedure generally described in Example 1 was repeated, except that: spreader speed=10 mm/sec, printing saturation=60% level, drying time=45 sec at 90% heater power, and furnace sintering temperature=900° C. for 4 hours.
A print material was prepared by mixing, based on the mixture weight, 80 wt. % of PDR5 and 20 wt. % of PDR4. The procedure generally described in Example 1 was repeated, except printing saturation=100% level, drying time=25 sec at 90% heater power, and furnace sintering temperature=at 850° C. for 4 hours.
A print material was prepared by mixing, based on the mixture weight, 80 wt. % of PDR5 and 20 wt. % of PDR4. The procedure described in Example 1 was repeated, except that the design parameter is shown in
A print material was prepared by mixing, based on the mixture weight, 80 wt. % of AG2 and 20 wt. % of PDR3. The procedure described in Example 4 was repeated, except that the furnace sintering temperature was set at 630° C. for 4 hours.
A print material was prepared by mixing, based on the mixture weight, 80 wt. % of AG2 and 20 wt. % of PDR3. The procedure described in Example 1 was repeated, except that the design parameter is shown in
When printed the two parts are glued together with a 3M epoxy based glue sold under the name DP460. During the gluing stage a specific attention is done in order to have the hole of the abrasive layer just in front of a space area of the PA12 piece and not blocked by the printed blade.
An abrasive product prepared following the example 6 was simulated with the ANSYS Fluent CFD simulation software from ANSYS, based in Canonsburg, Pa., US, to evaluate the quantity of fluid distributed through the holes on the workpiece, as illustrated in
An abrasive product prepared following the example 6 except that the holes design parameter was modified from 1.5 mm diameter up to 2.5 mm diameter. The same simulating procedure was followed with the same ANSYS Fluent CFD simulation software and the same single-phase model constrained by the same parameters. For this improved design, the flow rate coming out of the 8 holes was evaluated at 2 1/min which is 20% better than in example 7.
AME cBN size B91 grit from World Wide Superabrasives was dry mixed with glass frit SP2436 from Specialty Glass, respectively 74% and 26% by weight until homogeneously distributed. This mixture was placed in the hopper of the Innovent machine by ExOne. The CAD files for the first and second 3D objects shown in
Key process parameters were set as follows: Layer thickness of 150 microns, Oscillator speed 2800 rpm, Recoater Speed 50 mm/s, Recoater Speed 240 rpm, Roller Traverse Speed 10 mm/s, Binder Saturation of 40% and Drying Time of 30 seconds with set point temperature of 40 degrees C. The print job was run, repeatedly spreading a layer of powder, jetting the ExOne solvent binder in areas that represented successive 2D cross-sections of the 3D object shapes, and drying that binder layer before starting the powder spreading process again. The build box containing powder with and without binder was removed from the Innovent machine and placed into an oven at 195 degrees C. for 4 hours.
After cooling to room temperature, those “green” parts of powder and binder illustrated in
Abrasive wheels made using the process described above.
ANSYS CFX part of ANSYS CFD Premium from ANSYS, Inc. software was use. The features and assumptions of the model include: single phase numerical model assuming the grinding wheel is immersed in fluids, i.e., the grinding wheel is flooded; Fluid selected: water (in laminar and turbulent behavior); The model is transient, i.e., the motion of rotation is explicit captured; No cavitation considered; Ambient temperature (25° C.) and pressure (1 atm) were selected; and Adiabatic walls without roughness effect.
The model was used to investigate fundamental parameters on the fluid flow (flow rate, velocity, pressure), specifically: (1) Gap between the wheel and the work piece; (2) Effect of boundary condition at the end of work piece; (3) RPM of the wheel; and (4)
Rotational direction of the wheel.
The gap between the wheel and the work piece is labeled as L1. The value L1 has significate effects on the results. When the value L1 is set 0 means contact with the workpiece; when L1 is set 2 mm means the grinding wheel side which is opposite to the workpiece. BC2 is set as the inlet for fresh coolant. BC1 has two different settings, one is wall, one is opening, depends on the settings, the results are different. Both cases are existing in real grinding process at customers.
L1=0 mm gap
L1=2 mm gap
As shown in
The fluid dispensed from the holes only exit from the top portion of the gap. The fluid Y velocity near the bottom half the wheel is very low, which again which indicated a lack of coolant replacement motion near the bottom half of the wheel. The total suction flow rate at 20 k rpm was 3.15 LPM.
L1=2 mm gap
A mixture of white fused alumina grade F120 from Imerys ESK and vitreous bond precursor mix V601 was prepared in a cyclomix mixer from Hosokawa Micron, dry mixed for 10 minutes. After this time, the mixture was sieved on a 300 μm sieve.
The prepared mixture was placed in the hopper of the Exone Innovent lab printer.
A 3D model was prepared into file to make a rotating grinding wheel having features as in the FEM flow simulation study.
The CAD file was created into Soliworks CAD system and saved as STL file format which is readable by the Exone Innovent lab printer.
The file was prepared into print job for the ExOne Innovent lab printer with the help of Netfabb software from Autodesk. Printing was made of successive steps to spread powder layers, to jet binder in 2D patterns made from cross sections of the 3D objects and to at least partially dry that binder between jetting and spreading steps. The main used parameters were: Recoat speed (mm/s): 25—Oscillator speed (rpm): 2800—Roller Speed (rpm): 200—Roller Traverse speed (mm/s): 15.
This print job was run and completed on the printer, and the result was a powder bed holding loose powder and 3D shapes of binder and powder. That powder bed was removed from the printer and baked in an oven at 195° C. for 6 hours. After cooling, those 3D shapes or “green” parts were extracted and depowdered. Those depowdered parts were placed into a furnace for burning out the binder and then melting and sintering the vitreous based frit which bonded the abrasive grits into a solid matrix.
The result is shown in
The produced grinding wheels were glued on a 6 mm steel shaft and mounted on a rotating spindle of a milling machine.
A specifically designed transparent container is fixed on the milling machine table. The wheel was mounted in the spindle, run-out was checked and wheel was centered into the transparent container, as illustrated in
A video of fluid behavior made with the high-speed camera confirms the predicted flow behavior means that with a hole in the middle height of the grinding wheel, the upper part of the groove is mainly used by the fluid.
From the high-speed video, it can be seen that air and water co-exist inside the grooves and on the surface of the wheel. Therefore, the model is revised to include both air and water.
The new model considers the filling of coolant inside the grinding wheel and the interactions between the air and coolant.
Additionally, the model studies the effects of coolant injection location and flow rate.
In parallel, using the same material and the same printing process as described in Example 11, just modifying the CAD file, another grinding wheel was produced having a hole at the bottom of the grinding wheel to verify the prediction of the FEM simulation and validates the developed model, as illustrated in
Simulations were performed taking into account a situation closer to a real internal grinding process at customer with one side of the grinding wheel in contact with the workpiece and the other one “far” from the workpiece surface. The wheel axis is positioned eccentric to the axis of the workpiece, as illustrated in
The FEM flow simulation surprisingly demonstrates that nearly no fluid is captured by the grooves when designed with grooves only.
When fluid is coming from the center through a hole done in the grinding wheel then fluid is distributed much better and can reach much more easily the grinding contact area.
Compared with the designs of previous examples, the number of blades of the internal impeller was reduced keeping the same number of holes. It was discovered that the flow movement inside of the grinding wheel has also a vertical component which is not negligible. Therefore, a special design to keep the coolant longer in the wheel and have less coolant coming out of the wheel is presented in
Using the same material and the same printing process as described in Example 10, just modifying the CAD file, another grinding wheel was produced having the new design. This resulted in the printed parts of
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/056599 | 7/14/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62874140 | Jul 2019 | US |
