RELATED APPLICATION

[0001] This application claims the full Paris Convention benefit of and priority to U.S. Patent Application Serial No. 12/459,987, filed July 10, 2009, the contents of which are incorporated by reference herein in its entirety, as if fully set forth herein.

BACKGROUND

[0002] 1. Field

[0003] This disclosure relates to fluid flushing devices, systems, and methods for enhancing the erosion of a workpiece by an electrode through dielectric breakdown of the fluid.

SUMMARY

[0004] In order to aid in the understanding of the present disclosure, it can be stated in summary form that one or more exemplary implementations are directed to a method and apparatus for the targeted high velocity flushing of an electrical discharge machine work zone. Flushing is accomplished by a sufficient and properly directed flow of dielectric fluid through the sparking work zone to carry away the separated particles and ensure a clean work zone for continuous stable high-quality spark erosion. The dielectric fluid flow has a sufficient volume and proper direction to maintain the surface temperature of the workpiece sufficiently low so that its metallurgical characteristics are substantially unaffected. It has been found that a critical flow rate through the work zone of a single point electrode accomplishes both of these results and workpiece degradation is avoided so that there is no detectable recast layer and Heat Affected Zone (HAZ). It has been found that when this critical flushing level and direction has been reached, subsequent micro-cracking in the recast layer or the base metal layer is eliminated.

[0005] According to one or more exemplary implementations, targeted flushing is provided at the sparking work zone of an electrical discharge machine to minimize the workpiece temperature near the electrode gap so that the workpiece metallurgical qualities are not degraded.

[0006] According to one or more exemplary implementations, sufficient flushing of sufficient critical value is provided at the work zone of a single point electrode to ensure rapid and thorough removal of the workpiece and electrode particles eroded by sparking. This allows the EDM system to run very high power resulting in faster material removal rates, that would otherwise result in unacceptable levels of recast and HAZ.

[0007] According to one or more exemplary implementations, sufficient flushing of the workpiece is provided at the work zone of an electrical discharge machine to limit damage to the workpiece at the newly cut surface to avoid subsequent micro-cracking of the surface.

[0008] According to one or more exemplary implementations, a system is provided by which the flushing direction can be dynamically changed during cutting to suit different topological conditions throughout the cut, ranging, for example, from machining a groove in a concave area transitioning to a convex area, or buried cutting transitioning to through cutting.

[0009] Other purposes and advantages of the present disclosure will become apparent from a study of the following portion of the specification, the claims and the attached drawings.

[0010] According to one or more exemplary implementations, disclosed is a device for flushing a work zone, comprising: an electrical discharge machine having an electrode; a flushing nozzle configured to flush the work zone between the electrode and a workpiece with a flushing fluid; a coolant tank having an inlet fluidly connected to the work zone and an outlet fluidly connected to the flushing nozzle; wherein the device is configured to recirculate the flushing fluid from the coolant tank, through the work zone, and back to the coolant tank.

[0011] The device may further comprise a temperature control unit fluidly connected between the coolant tank and the work zone, wherein the temperature control unit is configured to modify the temperature of the flushing fluid. The temperature control unit may be a cooler. The device may further comprise a physical conditioner fluidly connected between the coolant tank and the work zone and configured to apply physical pulses to the flushing fluid. The physical conditioner may be a mechanical agitator. The device may further comprise a pump fluidly connected between the coolant tank and the work zone. The flushing fluid may be selected from the group consisting of: water having a resistance of no less than about 500 kiloohms, gas, oil liquid and viscous liquid. The device may further comprise a power supply configured to provide a voltage to the electrode relative to the workpiece. The device may further comprise a positioner configured to control the position of the electrode relative to the workpiece. The device may further comprise an enclosure enclosing the work zone and configured to prevent fluid splash to outside the enclosure.

[0012] According to one or more exemplary implementations, disclosed is a closed-loop flushing system for flushing a work zone, comprising: a coolant tank having an inlet fluidly connected to the work zone and an outlet fluidly connected to the flushing nozzle; wherein the work zone defines a space between an electrode and a workpiece; and wherein the flushing system defines a closed-loop recirculation path from the coolant tank, through the work zone, and back to the coolant tank.

[0013] The closed-loop flushing system may further comprise an enclosure enclosing the work zone and configured to prevent fluid splash to outside the enclosure. The closed-loop flushing system may further comprise a temperature control unit fluidly connected between the coolant tank and the work zone, wherein the temperature control unit is configured to modify the temperature of the flushing fluid. The closed-loop flushing system may further comprise a physical conditioner fluidly connected between the coolant tank and the work zone and configured to apply physical pulses to the flushing fluid. The closed-loop flushing system may further comprise a pump fluidly connected between the coolant tank and the work zone. The closed-loop flushing system may further comprise a filter configured to remove debris particles from the flushing fluid and recondition the flushing fluid to regain its electrical properties. The flushing nozzle may be configured to present the flushing fluid at a flow rate of at least about 75 inches per second.

[0014] According to one or more exemplary implementations, disclosed is a method of flushing a work zone, comprising: proving a flushing fluid from a coolant tank; delivering the flushing fluid to a work zone between an electrode and a workpiece; providing a voltage to the electrode relative to the workpiece, whereby a spark event occurs and a portion of the workpiece is eroded; and returning the flushing fluid from the work zone to the coolant tank.

[0015] Delivering the flushing fluid may comprise applying pressure pulses to the flushing fluid. The method may further comprise controlling the temperature of the flushing fluid. Controlling the temperature of the flushing fluid may maintain the flushing fluid below boiling point. The method may further comprise removing debris particles and reconditioning the flushing fluid to regain its electrical properties. Delivering the flushing fluid may be sufficient to prevent metallurgical damage to a portion of the workpiece that remains after the spark event. The flushing fluid may be delivered to the work zone at a flow rate of at least about 75 inches per second. The flushing fluid may be selected from the group consisting of: water having a resistance of no less than about 500 kiloohms, gas, oil liquid and viscous liquid.

DRAWINGS

[0016] The above-mentioned features of the present disclosure will become more apparent with reference to the following description taken in conjunction with the accompanying drawings wherein like reference numerals denote like elements and in which:

[0017] Figure 1 shows a sectional view of a workpiece in which an EDM electrode is cutting a cavity, showing a nozzle by which dielectric fluid is delivered through the work zone;

[0018] Figure 2 shows an enlarged view of a portion of the view of Figure 1 ;

[0019] Figure 3 shows a sectional view of a workpiece in which an EDM electrode is cutting a cavity, showing a nozzle by which dielectric fluid is delivered through the work zone and the dielectric fluid flow associated with a through hole;

[0020] Figure 4 shows an enlarged view of a portion of the view of Figure 3; and

[0021] Figure 5 shows a side elevational view of an EDM cutting machine, with parts broken away.

DETAILED DESCRIPTION

[0022] Methods of machining metal or other conductive material workpieces include utilization of electrical discharge machining (EDM) to remove particles from the workpiece. In some electrical discharge machines, a preformed tool (e.g., an electrode) with the shape of the hole to be created is plunged into the workpiece (i.e., sinker EDM). High voltage, when applied at high frequency, creates sparking generally at the closest position between the workpiece and the electrode, and particles are removed from the workpiece where sparking occurs. In another type of electrical discharge machining, a moving length of wire is used to cut through the material (i.e., wire EDM). In both these methods, cutting occurs submerged in a vat, or bath of dielectric fluid— typically deionized water or oil.

[0023] In an application of an EDM process, the end of a single point electrode is moved in the appropriate controlled direction to remove workpiece material to obtain a selected shape. The electrode may be a rod or a wire and may be of various sizes and materials. The electrode is advanced to overcome and accurately replace electrode erosion and wear, and moved on appropriate axes to remove material to create the desired contour or cavity shape. The shape is determined by a software program which controls the equipment which moves the electrode. A preferred example of this type of electrode discharge machine tool is shown in U.S. Patent Number 6,225,589 to Stephen Bartok, the entire disclosure of which being incorporated herein by reference.

[0024] EDM machining is very useful in cutting workpieces which are hard to machine by conventional chip-cutting methods, in which the tool is directly applied to the workpiece to cut off portions thereof. During EDM machining the presence of heat at the sparking point can have the effect of degrading the quality of the metallurgical aspects of the workpiece. The workpiece material is often alloyed, heat treated, and physically worked to bring it to a certain alloy and grain structure.

[0025] Excessive heat from the EDM process degrades the metallurgical quality. In addition, while the machining occurs by the erosion of particles from the workpiece, excessive heat causes the material surface to become molten briefly, which when quenched with dielectric fluid, causes the creation of an undesirable surface layer. These two degradations of the workpiece at or near the surface are known as Heat Affected Zone (HAZ) and recast, respectively. They may result in a hard, brittle layer which weakens the final part and provides micro-crack propagation sites. Furthermore, the hardness of the HAZ and recast zones makes removal of the layer very challenging and time consuming.

[0026] As used herein, "closed-loop recirculation path" is a flow path within which a fluid from a given source is recirculated, recycled, or returned to the source for reuse.

[0027] As used herein, a "closed-loop system" is a system that includes a closed-loop recirculation path. [0028] As used herein, a "work zone" is a space between an electrode and a workpiece.

[0029] According to one or more exemplary implementations, Figure 1 shows workpiece 10 with cavity 12 already at least partially machined therein. The machining may be accomplished by electric discharge machining, which employs a rod or wire electrode 14. Some examples of electrodes, mountings, controls, and powering are described in the above mentioned Stephen Bartok patent. Electrode 14 is supplied with a voltage of such magnitude that sparks occur between tip 16 and generally the closest part of workpiece 10. The frequency is high so that sparks occur in rapid succession. The sparks erode pieces of workpiece 10 to thereby reshape it. Conductive debris in the gap affects spark location and as does the ionized dielectric fluid which was converted to plasma by the previous arc or arcs. Flushing is provided to mitigate these conditions. The shape of workpiece 10 is controlled by motion of electrode 14. Electrode 14 is mounted on suitable positioning mechanism so that the desired shape of the cavity is accomplished by eroding small particles of workpiece 10 by sparking.

[0030] According to one or more exemplary implementations, workpiece 10 need not be entirely submerged. Rather, a fast flowing stream of fluid is directed at the well-defined sparking region or work zone. The fluid is a dielectric fluid. For example, de-ionized water may be used. A considerable amount of heat is generated at the work zone. The dielectric fluid flow is applied to remove heat from workpiece 10 and remove the sparked-off particles, which become separate from workpiece 10. In addition to flushing the debris and cooling workpiece 10, flushing the spark gap with dielectric fluid plays a critical role in dispersing ionized portions of the dielectric fluid after each spark.

[0031] The dielectric properties of the fluid may be selected for a given application. According to one or more exemplary implementations, fluid with an electric resistance of at least 500 kiloohms is necessary to maintain the process. Likewise, dielectric properties of a dielectric fluid may shift during conversion to a plasma state, as will be readily recognized by those having ordinary skill in the art. According to one or more exemplary implementations, "absolute" dielectric is not required. Water, viscous liquids, gases, particularly inert gases, and oils are useful in particular applications. When water is used, it may contain an antirust compound. Water dielectric fluid may also contain a wetting agent to aid in the flow and enable entry into small spaces. The process of sparking and eroding pieces is sufficient to achieve material removal. According to one or more exemplary implementations, a large amount of power is delivered to electrode tip 16. This electric power turns into heat, much of which goes into workpiece 10. Dielectric fluid is delivered to the work zone by nozzle 18 or

19 for cooling purposes. In addition, it is necessary to remove from the sparking area those particles which have been eroded by previous spark events. In traditional applications, the workpiece and electrode were immersed in a vat or bath of dielectric fluid where the dielectric fluid flow rate in the vat was so low as to not flush the work zone adequately, resulting in: (1) unstable cutting, (2) frequent pauses to "pump-out" or clean the work zone, (3) limitations to the power which can be applied, and/or (4) excessive recast and HAZ.

[0032] According to one or more exemplary implementations, dielectric fluid is delivered at high pressure to target a well-defined work zone which is present in the EDM process. The flow passes around tip 16 and flushes the work-zone at high pressure and flow rate. Results have shown near elimination of recast and HAZ with dielectric water delivered at about 150 psi through a single about 0.04" nozzle, at the rate of about 15 Gallons per hour (GPH). Though the overall fluid flow rate is not high at about 1 cubic inch per second, targeted delivery through a small nozzle orifice results in a stream velocity greater than about 75 inches/second. When the power supply is driving the electrode at about 100,000 spark pulses/second, the dielectric moves about 0.0075 inches/pulse. With about 0.020" diameter fluid nozzle, the gap fluid is replaced in only 3 spark pulses, based on laminar flow. This is adequate flushing for three purposes: to keep the workpiece below HAZ and recast temperatures, to flush out debris, and to replace the dielectric fluid in the spark zone.

[0033] In Figure 1, an embodiment of flushing structure which has one dielectric fluid nozzle 18 is shown. Nozzle 18 is supplied with clean dielectric fluid under pressure. The dielectric fluid nozzle 18 is directed to supply dielectric fluid flow as shown by flow arrows

20 to the area where electrode tip 16 is closest to workpiece 10, because this is where the sparking occurs. Nozzle 18 is directed so that the dielectric fluid flow, shown by flow arrows 20, is from behind electrode 14 in the direction of electrode motion shown by motion arrow 22. The dielectric fluid flow is adequate between tip 16 and workpiece 10 to substantially flush away the eroded particles from the work zone and to minimize the temperature rise of workpiece 10 so that its temperature does not rise sufficiently to affect its properties. These properties, including grain size and shape as well as mutual solubility of the alloy compounds would be adversely affected if the temperature rose above a critical point. This critical point is different for each alloy. The dielectric fluid mass flow rate may be controllably configured to be sufficient to prevent any local area from exceeding this value.

[0034] Another result is achieved by limiting the temperature of the workpiece surface. Some present electrical discharge machining practices raise the surface temperature so that there is enough thermal stress caused near the surface so that micro-cracking occurs. This cracking is not present when the part is made, but after temperature cycling, micro-cracking occurs. This micro-cracking is absent from the parts made by this system, because surface temperatures are held sufficiently low to eliminate this thermal stress failure mechanism.

[0035] The proper delivery of dielectric fluid to achieve these purposes may require two or more nozzles directing the dielectric fluid flow to maximize flow at the critical point between the sparking point on the electrode and the sparking point on the workpiece. According to one or more exemplary implementations, flow in this region is generally in the direction of electrode motion. Flow past electrode 14, as shown in Figure 2, accomplishes sweeping the particles away and keeps the temperature of the adjacent workpiece down.

[0036] The dielectric fluid in the single point electrode machine in one specific example is deionized water, but it may also be viscous liquid or oil. The deionized water contains an anti-rust agent and may be recirculated, as shown in Figure 5. According to one or more exemplary implementations, it is filtered to remove debris particles and reconditioned to regain its electrical properties before reuse.

[0037] As disclosed in the above referenced Stephen Bartok patent, electrode 14 may be moved to progressively cause spark erosion of the workpiece surface to achieve the desired shape. Dielectric fluid nozzle 18 can be mounted directly on the same structure which positions electrode 14. On the other hand, if it is found to be desirable for better positioning of the dielectric fluid nozzles, one or more can be mounted separately and directed separately. This may be necessary, particularly in a cutting configuration as disclosed in Figure 1 where it is difficult to get flow past tip 16. According to experimental data, best results have been achieved with dielectric fluid flow in the same direction as electrode motion, however other combinations and modes are contemplated.

[0038] Effective dielectric fluid flow has been found to be delivered through an about 0.040 inch diameter nozzle at about 15 GPH and about 150 psi (not accounting for frictional losses). According to one or more exemplary implementations, linear velocity of the stream must be at least about 75 inches/second.

[0039] Figure 3 shows a view in which workpiece 10 has been cut through. When the cutting produces a through hole, the opportunity for the dielectric fluid to flow away is much better, as seen by flow arrows 30 in Figures 3 and 4. In this type of machining process, it is easier to get the necessary dielectric fluid past the active sparking point of electrode tip 16 because of the direct open passage for dielectric fluid outflow. When the cut has broken through, better dielectric fluid flow is achieved when nozzle 19 directs the flow through the spark zone from the front of travel direction. Even though achieving the flow rate is easier, the flow rate past the tip in the critical sparking area may be achieved as described above.

[0040] It has been seen in the cutting configuration of Figures 1 and 2 that the dielectric fluid is best supplied from the back of electrode 14, in the direction of electrode motion. When the cutting configuration changes to a pass through cut, as shown in Figures 3 and 4, the dielectric fluid flow is most effective when delivered to the sparking area from the front, as defined by the direction of electrode motion. According to one or more exemplary implementations, the dielectric fluid nozzle is a movable nozzle so that it can be directed to the sparking zone from the most effective direction. According to one or more exemplary implementations, a plurality of nozzles are employed and one (or more) that is properly directed for that type of spark cutting will be employed. For example, as illustrated in Figure 5, both nozzles 18 and 19 are present adjacent to the sparking electrode. According to one or more exemplary implementations, only one of these nozzles is used at a time. Utilizing two nozzles at the same time from the two sides may not be as effective where it interferes with dielectric fluid flow past the sparking point. According to one or more exemplary implementations, more than one nozzle is utilized. When plural nozzles are used, they may all be directed so that cumulative flow is in the directions illustrated in Figures 2 or 4.

[0041] An example of an apparatus in which the target is high velocity flushing of an EDM work zone is generally indicted at 40 in Figure 5. According to one or more exemplary implementations, an apparatus comprises table 42 which has enclosure 44 to protect the work environment and prevent coolant splash to the outside. Table 42 includes platen 46 which is insulated from table 42. Workpiece 10 is mounted on platen 46. Positioner 48 may be a computer driven device that positions and moves electrode 14 with respect to workpiece 10. Positioner 48 may be managed by position control computer 50 which carries the information for properly moving electrode 14 with respect to workpiece 10. Electrode 14 and workpiece 10 are connected to cutting control system and power supply 52. This control system senses the arc conditions and controls the power supply appropriately. It also controls the advance of the electrode, to compensate for wear. Its goal is to maximize cutting efficiency.

[0042] According to some exemplary implementations, dielectric flushing fluid is supplied from coolant tank 54. According to some exemplary implementations, pump 56 delivers the dielectric fluid to temperature control unit 58. According to some exemplary implementations, where the recycled fluid is heated in the spark zone, temperature control unit 58 is a cooler. Temperature control unit 58 may be necessary to maintain the fluid in the spark zone below boiling, for example, for it to be fully effective. Thus, the fluid may be cooled in temperature control unit 58. According to some exemplary implementations, temperature control unit 58 is a heater.

[0043] According to some exemplary implementations, the fluid is delivered to the physical conditioner 60. Applying physical pulses to the fluid flow stream aids in sweeping out the debris and fluid in and near the spark zone. This is accomplished by utilizing a mechanical agitator in conditioner 60 to apply pressure waves to the flowing fluid. Subsonic and ultrasonic pressure wave frequency can be utilized to enhance sweeping on the spark zone. According to one or more exemplary implementations, from physical conditioner 60, the fluid is delivered through tube 62 to parallel valves 64 and 66. These valves respectively supply fluid to nozzles 18 and 19. Control system 52 selects which valve to be open, as described above and shown in Figures 1, 2, 3, and 4. Fluid is thus directed to a selected one of nozzles 18 or 19, depending on the direction in which it is desired that the coolant flow past electrode tip 16. According to one or more exemplary implementations, only one of these is used at a time. The nozzle in use may be selected by the cutting control system.

[0044] According to some exemplary implementations, as shown in Figure 5, the flow of dielectric fluid defines a closed-loop recirculation path, wherein the dielectric fluid is taken from a given source (e.g., coolant tank 54), delivered to a work zone, and subsequently recirculated, recycled, or returned to the source (e.g., coolant tank 54) for reuse. One of more components, such as pump 56, temperature control 58, and physical conditioner 60, may be disposed along the closed-loop recirculation path. Accordingly, each component along the closed-loop recirculation path has at least one inlet and at least one outlet for, respectively, receiving and delivering a fluid along the closed-loop recirculation path. The closed-loop recirculation path may be part of a closed-loop system. It shall be appreciated based on the foregoing disclosure that one or more components of the above devices, systems, or methods may be used in isolation or in combination. For example, various components may be selectably provided in series, parallel, alone, or together to provided customizable capabilities and controlled outcomes.

[0045] While the method and agent have been described in terms of what are presently considered to be the most practical and preferred implementations, it is to be understood that the disclosure need not be limited to the disclosed implementations. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. The present disclosure includes any and all implementations of the following claims.

[0046] It should also be understood that a variety of changes may be made without departing from the essence of the disclosure. Such changes are also implicitly included in the description. They still fall within the scope of this disclosure. It should be understood that this disclosure is intended to yield a patent covering numerous aspects of the disclosure both independently and as an overall system and in both method and apparatus modes.

[0047] Further, each of the various elements of the disclosure and claims may also be achieved in a variety of manners. This disclosure should be understood to encompass each such variation, be it a variation of an implementation of any apparatus implementation, a method or process implementation, or even merely a variation of any element of these.

[0048] Particularly, it should be understood that as the disclosure relates to elements of the disclosure, the words for each element may be expressed by equivalent apparatus terms or method terms— even if only the function or result is the same.

[0049] Such equivalent, broader, or even more generic terms should be considered to be encompassed in the description of each element or action. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this disclosure is entitled. [0050] It should be understood that all actions may be expressed as a means for taking that action or as an element which causes that action.

[0051] Similarly, each physical element disclosed should be understood to encompass a disclosure of the action which that physical element facilitates.

[0052] Any patents, publications, or other references mentioned in this application for patent are hereby incorporated by reference. In addition, as to each term used it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood as incorporated for each term and all definitions, alternative terms, and synonyms such as contained in at least one of a standard technical dictionary recognized by artisans and the Random House Webster's Unabridged Dictionary, latest edition are hereby incorporated by reference.

[0053] In this regard it should be understood that for practical reasons and so as to avoid adding potentially hundreds of claims, the applicant has presented claims with initial dependencies only.

[0054] To the extent that insubstantial substitutes are made, to the extent that the applicant did not in fact draft any claim so as to literally encompass any particular implementation, and to the extent otherwise applicable, the applicant should not be understood to have in any way intended to or actually relinquished such coverage as the applicant simply may not have been able to anticipate all eventualities; one skilled in the art, should not be reasonably expected to have drafted a claim that would have literally encompassed such alternative implementations.

[0055] Further, the use of the transitional phrase "comprising" is used to maintain the "open-end" claims herein, according to traditional claim interpretation. Thus, unless the context requires otherwise, it should be understood that the term "compromise" or variations such as "comprises" or "comprising", are intended to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps.

[0056] Such terms should be interpreted in their most expansive forms so as to afford the applicant the broadest coverage legally permissible.