Patent Application
20120156969
This application describes abrasive jet systems, such as abrasive jet systems utilizing fluid repelling materials, and methods associated with abrasive jet systems.
Abrasive jet systems that produce high-velocity, abrasive-laden fluid jets for accurately and precisely cutting various materials are well known. Abrasive jet systems typically function by pressurizing water (or another suitable fluid) to a very high pressure (e.g., up to 90,000 pounds per square inch (psi) or more) by, for example, a high-pressure pump connected to an abrasive jet cutting head. The pressurized water is forced through an orifice at a very high speed (e.g., up to 2500 feet per second or more). The orifice forms the water jet. The orifice is typically a hard jewel (e.g., a synthetic sapphire, ruby, or diamond) held in an orifice mount. The resulting water jet is discharged from the orifice at a velocity that approaches or exceeds the speed of sound. The liquid most frequently used to form the jet is water, and the high-velocity jet may be referred to as a “water jet,” or a “waterjet.”
Abrasives can be added to the water jet to improve the cutting power of the water jet. Adding abrasives to the water jet produces an abrasive-laden water jet referred to as an “abrasive water jet” or an “abrasive jet.” To produce an abrasive jet, the water jet passes through a mixing region in a nozzle. The abrasive, which can be under atmospheric (ambient) pressure or pressurized in an external hopper, is conveyed through a meeting orifice via a gravity feed or a pressurized feed from the hopper through an attached abrasive supply conduit to the nozzle. A quantity of abrasive regulated by the meeting orifice is entrained into the water jet in the mixing region. Typical abrasives include garnet and aluminum oxide. Generally, the maximum diameter of individual abrasives should be no greater than approximately one third of the internal diameter of the abrasive supply conduit to prevent bridging of two particles, which can lead to clogging of the abrasive supply conduit. The abrasives can have grit mesh sizes ranging between approximately #36 and approximately #320, as well as other smaller and larger sizes.
The resulting abrasive-laden water jet is then discharged against a workpiece through a nozzle tip that is adjacent to the workpiece. The abrasive jet can be used to cut a wide variety of materials. For example, the abrasive jet can be used to cut hard materials (such as tool steel, aluminum, cast-iron armor plate, certain ceramics and bullet-proof glass) as well as soft materials (such as lead). A typical technique for cutting by an abrasive jet is to mount a workpiece to be cut in a suitable jig, or other means for securing the workpiece into position. The abrasive jet can be directed onto the workpiece to accomplish the desired cutting, generally under computer or robotic control. It is generally not necessary to keep the workpiece stationary and to manipulate the abrasive jet cutting tool. The workpiece can be manipulated under a stationary cutting jet, or both the abrasive jet and the workpiece can be manipulated to facilitate cutting.
This application describes various embodiments of abrasive jet systems for cutting materials, including abrasive jet systems utilizing hydrophobic materials or other fluid or liquid phobic materials. For example, abrasive jet systems as disclosed herein can be used with a variety of suitable working fluids or liquids to form the fluid jet. More specifically, abrasive jet systems configured in accordance with embodiments of the present disclosure can include working fluids such as water, aqueous solutions, paraffins, oils (e.g., mineral oils, vegetable oil, palm oil, etc.), glycol, liquid nitrogen, and other suitable abrasive jet cutting fluids. As such, the term “water jet” or “waterjet” as used herein may refer to a cutting jet formed by any working fluid associated with the corresponding abrasive jet system, and is not limited exclusively to water or aqueous solutions. In addition, although several embodiments of the present disclosure are described below with reference to water, other suitable working fluids can be used with any of the embodiments described herein. Moreover, the term “hydrophobic” as used herein to describe components and/or characteristics of the present disclosure is intended to mean the tendency to repel the working fluid, not to be wetted by the working fluid, not to absorb the working fluid, not to be attracted to the working fluid, and/or to otherwise lack an affinity for the working fluid. As such, the term hydrophobic as used herein is intended to refer to the working fluid of the abrasive jet system, and is not limited to refer exclusively to water or aqueous solutions as the working fluid of the abrasive jet system. Certain details are set forth in the following description and in
Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments. Accordingly, other embodiments can have other details, dimensions, angles and features. In addition, further embodiments can be practiced without several of the details described below.
In the Figures, identical reference numbers identify identical, or at least generally similar, elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refer to the Figure in which that element is first introduced. For example, element 100 is first introduced and discussed with reference to
In one embodiment, an abrasive jet system includes an abrasive container and a nozzle assembly. The nozzle assembly has a mixing region or cavity downstream of a fluid inlet aperture and an abrasive inlet aperture. The abrasive jet system can also include an abrasive supply conduit that is operably coupleable between the abrasive container and the abrasive inlet aperture. The abrasive supply conduit includes a first interior surface portion configured to be positioned proximate to the abrasive inlet aperture and a second interior surface portion, different from the first interior surface portion, configured to be spaced apart from the abrasive inlet aperture. In one aspect of this embodiment, the first interior surface portion has a greater ability to repel fluid (e.g., water) than the second interior surface portion, thereby reducing a tendency of the abrasives to clog the abrasive supply conduit.
In another embodiment, an abrasive jet system includes a nozzle assembly having a mixing region or cavity downstream of a fluid inlet aperture, and an abrasive inlet aperture proximate to the mixing cavity. The abrasive jet system of this embodiment also includes an abrasive container containing abrasives that are not wettable, or at least generally not wettable, by a working fluid such as water, and an abrasive supply conduit operably coupleable between the abrasive container and the abrasive inlet aperture.
In a further embodiment, a method of manufacturing an abrasive jet system includes forming an abrasive supply conduit. The abrasive supply conduit can be formed by operably coupling a first tube portion to a second tube portion. The first tube portion includes a hydrophobic interior surface portion, and the second tube portion includes a non-hydrophobic interior surface portion. In some applications however, the second tube portion can also include a hydrophobic interior surface portion. Moreover, the first and second tube portions can be integral portions of the abrasive supply conduit or separate connected portions of the abrasive supply conduit. The method can further include operably coupling the second tube portion of the abrasive supply conduit to an abrasive source and operably coupling the first tube portion of the abrasive supply conduit to an abrasive inlet port on a abrasive jet nozzle assembly, such that the first tube portion is proximate to the abrasive inlet port.
Abrasive jet systems, such as abrasive waterjet systems or abrasive slurry jet systems, may be used for micromachining workpieces. In general, micromachining refers to machining features of less than 500 microns (0.02 inch) in size. Abrasive jet systems that may be used for micromachining typically include a nozzle assembly having a mixing tube (alternatively referred to as a discharge tube) with a small inside diameter, as the inside diameter is proportional to a micromachining kerf width.
In some cases, an accumulation of abrasives (as indicated by reference number 130) may form in one or more portions of the abrasive supply conduit 120 proximate to the abrasive inlet port 135. The abrasives accumulation 130 may thereby clog or otherwise prevent a sufficient quantity of abrasives from entering the mixing region 115 and mixing with the water jet 110, potentially leading to poor cutting performance.
Without wishing to be bound by any particular theory, it is believed that the abrasives accumulation 130 may be caused at least partly by the small inside diameter of the axial passage 150 of the mixing tube 145. For example, when the abrasive jet system is turned off after an operating cycle, water may fill the axial passage 150 due to capillary action, leaving a column of water trapped in the axial passage 150 and causing a mixture of water and abrasives to fill an inlet region of the mixing tube (as indicated by reference number 140). When the abrasive jet system is turned back on, the water jet 110 impacts an upper surface of the water and abrasives mixture 140. The impact can cause a splash that includes water and abrasives. A portion of the splash may pass the abrasive inlet port 135 and land on and adhere to the interior surface 125 of the abrasive supply conduit 120, thereby forming the abrasives accumulation 130. After a certain number of on and off operating cycles of the abrasive jet system, the abrasives accumulation 130 may accumulate to the point that the vacuum induced by water jet 110 is insufficient to remove the abrasives accumulation 130 from the interior surface 125 of the abrasive supply conduit 120. This abrasive accumulation 130 may also prevent pressurized, vacuum, or forced feeding of the abrasives. The abrasives accumulation 130 may thus prevent a sufficient quantity of abrasives from being mixed with the water jet 110 or otherwise adversely affect the function of the nozzle assembly 100. An insufficient quantity of abrasives may adversely affect the ability of the abrasive jet system to cut a workpiece according to a desired quality. Accordingly, it would be useful to wholly or partially reduce the abrasives accumulation 130 on the interior surface 125 of the abrasive supply conduit 120, both to facilitate nozzle operations and to maintain a desired cut quality.
The abrasive inlet port 335 has an approximately 90-degree orientation (as indicated by reference number 320) to the external surface 315 of the nozzle assembly 225. In some embodiments, the abrasive feed port 335 can have a less than 90 degree orientation (e.g., a 45-degree orientation) to the external surface 315 of the nozzle assembly 225. In such embodiments, the abrasive supply conduit 220 may be sufficiently tensioned between the abrasive container 235 and the nozzle assembly 225 to partially or wholly eliminate any sagging of the abrasive supply conduit 220. In such embodiments, gravitational forces may assist in reducing the accumulation of abrasives in the abrasive supply conduit 220. In other embodiments, however, pressure, vacuum, or mechanical components can be used to assist the flow of abrasives through the supply conduit 220.
In one aspect of this embodiment, the first abrasive supply portion 302 includes a first interior surface portion 305 that repels or at least partially repels water. For example, the first interior surface portion 305 can include hydrophobic material such as polytetrafluoroethylene (sold by DuPont under the trade name Teflon®) that repels or at least partially repels water. In addition to or as an alternative to including polytetrafluoroethylene, the first interior surface portion 305 may include other hydrophobic materials, such as fluoropolymers, fluorocarbons, and/or other at least generally hydrophobic materials that prevent or at least inhibit water from adhering to the first interior surface portion 305, or otherwise repel or at least partially repel water from the first interior surface portion 305.
Referring to
As abrasives 235 flow through the abrasive supply conduit 220, the abrasives 235 may roughen the first interior surface portion 305. The first interior surface portion 305 may then become superhydrophobic. Referring to
Returning to
One reason for the second interior surface portion 310 to be non-hydrophobic is that using a hydrophobic material for the entire length of the abrasive supply conduit 220 may allow for the buildup of static electricity. The buildup of static electricity may prevent abrasives 235 from flowing uniformly and consistently through the abrasive supply conduit 220. Using hydrophobic material in the first interior surface portion 305 and non-hydrophobic material in the second interior surface portion 310 can wholly or partially alleviate the buildup of static electricity, thus facilitating uniform and consistent flow of abrasives 235 through the abrasive supply conduit 220. In other embodiments, however, each of the first interior surface portion 302 and the second interior portion 304 can be hydrophobic. In such embodiments, for example, the entire length or a substantial portion of the entire length of the interior surface of the abrasive supply conduit 220 can be hydrophobic. Moreover, the abrasive supply conduit 220 can be grounded to eliminate or at least partially prevent static electricity buildup in the abrasive supply conduit 220. In still further embodiments, the first conduit portion 302 and the second conduit portion 304 can be integral portions of the abrasive supply conduit 220.
In one embodiment, the abrasive container 230 may carry hydrophobic abrasives 235 (for example, garnet or other suitable media) that are not wettable by water or other fluids. For example, the hydrophobic abrasives 235 may include hydrophobic (or superhydrophobic) material on an exterior surface of the hydrophobic abrasives. As another example, the hydrophobic abrasives 235 may be formed entirely of hydrophobic (or superhydrophobic) material. The hydrophobic abrasives 235 can be created by treating the abrasives to include hydrophobic material as a result of a nanotechnology process. As another example, the hydrophobic abrasives 235 can be created by reacting trimethylchlorosilane [(CH3)3SiCl] at surfaces of silicate-based materials to render the silicate-based materials hydrophobic. As a further example, the hydrophobic abrasives 235 can be created by coating abrasives with hydrophobic or superhydrophobic materials (e.g., hydrophobic materials sold by 3M under the trade name Scotchguard). In other embodiments, other types of hydrophobic and/or partially hydrophobic materials, and/or other hydrophobic treatments can be used without departing from the present disclosure. The hydrophobic abrasives 235 repel or at least partially repel water and stay dry when exposed to or submerged in water or other working fluids.
In certain applications, such as micromachining applications, the nozzle assembly is typically downsized to form an abrasive jet with a relatively fine beam diameter. As noted above, however, the maximum particle diameter of individual abrasives should generally be no greater than approximately one third of the internal diameter of the abrasive supply conduit to avoid the bridging of two abrasive particles thereby leading to clogging of the abrasive supply conduit. As a result, in micromachining applications the size (e.g., diameter) of individual abrasives is typically reduced proportionally to the internal diameter of the abrasive supply conduit. It is known, however, that the ability of fine abrasives (e.g., 220 mesh and finer) to flow through the abrasive supply conduit solely under the force of gravity is poor. Moreover, such fine abrasives also tend to coagulate or clump together and further reduce the ability to flow through the abrasive supply conduit. Coating fine abrasives with hydrophobic materials according to embodiments of the present disclosure helps to at least partially improve the flowability of these fine abrasives. However, coagulation of these hydrophobic abrasives may still occur, thereby leading to clogging of the abrasive supply conduit or in the mixing region. As such, in certain embodiments, anti-coagulation agents can be added into the abrasives before coating the abrasives with hydrophobic materials. Therefore, the coated abrasives would not only be hydrophobic, but also exhibit anti-coagulation properties thereby ensuring that the fine abrasives would be fed smoothly and steadily via gravity through abrasive supply conduits without relying on vacuum assist and water flushing. In certain embodiments, suitable anti-coagulation agents can include, for example, fumed silica.
As such, hydrophobic abrasives 235 neither coagulate nor adhere to the interior surface of the abrasive supply conduit 220 or to a surface of the inlet region of the mixing tube 145 of the nozzle assembly 225. As a result, any splash from the nozzle directed toward the abrasive supply conduit 220 contains both droplets of water or other fluids and the dry hydrophobic abrasives 235. The dry hydrophobic abrasives 235 do not adhere to the first interior surface portion 305 of the abrasive supply conduit 220, and thus can be entrained into the water jet 110 and exit through the mixing tube 145 (see
The hydrophobic abrasives 235 are not wettable, or at least generally not wettable, by water, and therefore do not adhere to the abrasive supply conduit 220. The hydrophobic abrasives 235 thus can be forced back into the mixing region 115 of the nozzle assembly 225 when the water jet 110 passes through the orifice and creates a vacuum effect. During a transition period before the water jet 110 reaches its maximum speed, the hydrophobic abrasives 235 stay dry and do not adhere to the first interior surface portion 305 of the abrasive supply conduit 220. Accordingly, use of hydrophobic abrasives 235 in the abrasive jet system 200 as described herein reduces the clogging in the abrasive supply conduit 220. Such reduction in clogging ensures a sufficient quantity of hydrophobic abrasives 235 are able to be mixed with the water jet 110, thereby ensuring that a workpiece being cut (or otherwise processed) by the abrasive jet system 200 is cut with a desired quality.
The combination of an at least partially hydrophobic supply conduit and hydrophobic abrasives will provide increased reliability of cutting. Moreover, utilizing an abrasive supply conduit 220 to which abrasives do not adhere and/or hydrophobic abrasives in an abrasive jet system may partially or completely remove the need to use vacuum assist devices and/or flushing devices to prevent clogging. A typical vacuum assist device attaches to a nozzle assembly via a port connected to the mixing chamber. The vacuum assist device creates a vacuum that removes residue water and wet abrasives in the mixing region and inlet region of the mixing tube. Flushing devices may also be used to remove wet abrasives that remain in the abrasive supply conduits and the mixing chamber. Using a vacuum assist device and/or a flushing device may have several disadvantages. For example, 1) the vacuum assist and the flushing device may result in a complex and/or bulky nozzle assembly; 2) additional software and/or hardware controls for operating the vacuum assist and the flushing device may be required; 3) additions of the vacuum assist and flushing operation may increase the odds of system malfunction; 4) the increase in the bulkiness of the nozzle assembly may make articulation of the nozzle assembly more difficult; and 5) more abrasives must be used as some abrasives are removed by the vacuum assist and/or flushing device and thus do not contribute to cutting, which may increase overall system cost.
The use of an abrasive supply conduit 220 and/or the use of hydrophobic abrasives 235 in an abrasive jet system as described herein may partially or wholly eliminate the clogging in the abrasive supply conduit 220. Such use may wholly or partially obviate the need for vacuum assist devices and/or flushing devices. Accordingly, such use 1) may provide for a simpler and more compact nozzle assembly; 2) may obviate the need to add additional software and/or hardware; 3) may reduce the odds of system malfunction and/or part rejection; 4) may provide for a more articulable nozzle assembly; and 5) may reduce abrasive waste. In embodiments where vacuum assist devices and/or flushing devices are not used, the nozzle assembly 225 does not have an external aperture, opening, or port to which vacuum assist devices and/or flushing devices may be operably coupled.
Moreover, the use of an abrasive supply conduit 220 and/or the use of hydrophobic abrasives 235 as described herein facilitates micromachining by allowing for use of mixing tubes and orifices with smaller diameters. For example, a nozzle assembly having an orifice with an inside diameter of about 0.0035 inch (0.09 mm) and a mixing tube with an inside diameter of about 0.008 inch (0.25 mm) can be used. In some embodiments, the nozzle assembly can have an orifice with an inside diameter smaller than 0.0035 inch and/or a mixing tube with an inside diameter smaller than 0.008 inch. Accordingly, an abrasive jet system utilizing the abrasive supply conduit 220 and/or hydrophobic abrasives 235 as described herein can provide significant advantages.
In some embodiments, the abrasive jet system may heat the fluid to a temperature sufficient to cause the fluid to change phase after the fluid exits the mixing tube. Such an abrasive jet system may be referred to as a flash vaporizing abrasive jet system, and may use heating techniques described in U.S. Patent Application Publication No. 2008/006049, which is hereby incorporated by reference in its entirety. Such heating can reduce piercing damage to materials such as laminates, composites and/or other brittle materials. Upon exiting the nozzle assembly, the superheated water evaporates, thereby reducing piercing pressure buildup and mitigating piercing damage to the workpiece. In such embodiments, use of abrasives that are not wettable and/or an abrasive supply conduit that repels or at least partially repels water may reduce or eliminate the need for vacuum assist devices and/or water flushing devices to remove wet abrasives. In such embodiments, an abrasive that may not lose its hydrophobicity when exposed to very high temperatures (e.g., water at or above approximately 100 degrees Celsius, such as 250 degrees Celsius) can be utilized.
Those skilled in the art will appreciate that the steps shown in any of
One of the challenges of abrasive jets or waterjets is their tendency to induce damage during piercing delicate materials. Certain materials, such as composite materials and brittle materials, may be difficult to pierce with an abrasive jet. For example, an abrasive jet directed at a workpiece composed of such material strikes a surface of the workpiece and begins forming a cavity or blind hole in the surface. As the cavity forms, a hydrostatic pressure may build within the cavity resulting from conversion of the kinetic energy of high-speed water droplets into the potential energy. This hydrostatic pressure may act upon sidewalls of the cavity and may thereby negatively impact the workpiece material. For example, in the case of composite materials such as laminates, this hydrostatic pressure may cause composite layers to separate or delaminate from one another as the hydrostatic pressure exceeds the tensile strength of the weakest component of the materials, which is typically the composite binder. In the case of brittle materials such as glass, polymers, and ceramics, the hydrostatic pressure may cause the material to crack or fracture if the hydrostatic pressure acts upon intergranular cracks or micro fissures in the material. Other aspects or effects of the abrasive jet other than the hydrostatic pressure may, in addition or as an alternative to the hydrostatic pressure, cause damage to the material during abrasive jet piercing operations.
Conventional techniques used to mitigate piercing damage to materials include pressure ramping and vacuum assist devices. Pressure ramping can involve using a reduced water pressure to form the waterjet in an attempt to ensure that abrasives are fully entrained in the waterjet before a hydrostatic pressure induced by fluid water alone reaches a magnitude capable of causing damage to the material being pierced. A vacuum assist device can also be used to draw abrasive into a mixing chamber of a waterjet cutting head prior to the arrival of water into the mixing chamber. Such a technique attempts to ensure that a water-only jet does not strike the surface of the material. Other piercing damage mitigation techniques include superheating high pressure water downstream of the pump and upstream of the nozzle such that the pressurized high-temperature water remains in the liquid state upstream of the inlet orifice in the nozzle and then evaporates upon exiting the nozzle, as disclosed in U.S. Pat. No. 7,815,490, which is incorporated herein by reference in its entirety. As a result, only high-speed abrasives and very little liquid water enters the cavity or blind hole in the delicate material. Therefore, the hydrostatic pressure buildup inside the cavity is minimized leading to the mitigation of piercing damage to delicate materials. Yet another piercing damage mitigation technique involves pressurized abrasive feeding to degrade the abrasive jet in a controlled manner, as disclosed in U.S. Provisional Patent Application No. 61/390,946, entitled “SYSTEMS AND METHODS FOR ALTERING AN ABRASIVE JET FOR PIERCING OF DELICATE MATERIALS,” filed Oct. 7, 2010, and incorporated by reference herein in its entirety. The degradation of the abrasive jet would reduce the magnitude of the hydrostatic pressure inside the cavity while the pressurized abrasive feeding would ensure abrasives reach the workpiece simultaneously with the waterjet.
The above remedies, however, require additional hardware to implement. In contrast, systems and methods configured in accordance with additional embodiments of the disclosure can take advantage of the non-wetting and non-clogging properties of hydrophobic abrasives to reduce or otherwise mitigate piercing or other damage to delicate materials, such as composites, laminates, and brittle materials. For example, by intentionally leaving at least some abrasives inside the nozzle before the jet is turned on and/or after the jet is turned off, these abrasives in the nozzle will be delivered to the workpiece as soon as the jet is turned on. Delivering these abrasives in the initial impact or contact of the jet can at least partially avoid or reduce piecing damage to the workpiece. For example, piercing damage is usually induced when the jet is void of abrasives such that a large hydrostatic pressure is developed inside a blind hole in the workpiece. A workpiece with a tensile strength lower than the induced hydrostatic pressure would likely be damaged by cracking, chipping, and delamination. Accordingly, systems and methods configured in accordance with the present disclosure can profit from the non-wetting and non-clogging properties of hydrophobic abrasives by setting a delay time to deliver the fluid or the abrasives (e.g., before the jet is turned on and after the jet is turned off) to reduce the piercing damage on delicate materials, such as G10 for example. More specifically, in one embodiment, the delivery of the fluid to the nozzle can be delayed until after conveying a sufficient quantity of abrasives in the nozzle. In other embodiments, the abrasives can continue to be conveyed to the nozzle after terminating the delivery of the fluid to the nozzle. Accordingly, the delay time would enable some abrasives to remain in the mixing region or chamber and/or the feed tube (e.g., near the nozzle end) so that the abrasives will be present in the jet as soon as the jet is turned on. As a result, abrasives reach the workpiece simultaneously with the waterjet. An additional advantage of such a process is that there is no added hardware to the jet system. Rather, the delay time can be set or programmed in the system as appropriate. Moreover, for delicate materials with extremely low tensile strength and for very brittle materials, embodiments of the present disclosure can further include gradually increasing or ramping up the jet pressure gradually via software control to further minimize piercing damage.
From the foregoing, it will be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the present disclosure. Those skilled in the art will recognize that numerous liquids other than water can be used with embodiments disclosed herein, and the recitation of a jet as comprising water should not necessarily be interpreted as a limitation. For example, fluids other than water can also be employed to cut materials that cannot be in contact with water. The customary term for the process of cutting with a fluid is “water-jet cutting” and the like, but the term “water-jet cutting” is not intended to exclude cutting by abrasive jets of fluid other than water. If a fluid other than water is utilized in an abrasive jet system, the first interior surface portion 305 (
This application claims the benefit of U.S. Provisional Patent Application No. 61/310,658, entitled “ABRASIVE JET SYSTEMS, INCLUDING ABRASIVE JET SYSTEMS UTILIZING HYDROPHOBIC MATERIALS, AND ASSOCIATED METHODS” filed Mar. 4, 2010, and U.S. Provisional Patent Application No. 61/432,580, entitled “ABRASIVE JET SYSTEMS, INCLUDING ABRASIVE JET SYSTEMS UTILIZING HYDROPHOBIC MATERIALS, AND ASSOCIATED METHODS” filed Jan. 13, 2011, both of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61310658 | Mar 2010 | US | |
| 61432580 | Jan 2011 | US |
