Ultrasonic measurement of electrode depth during electrical discharge machining.

Abstract

The electrical discharge machine includes an electrode configured to machine a conductive workpiece by application of a repetitive electric charge, and a controller operably coupled to the electrode and configured to control the application of the repetitive electric charge. The EDM also includes an ultrasonic sensor operably coupled to the electrode and to the controller. The controller also determines a depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor.

Description

[Technical Field]

[0001] TECHNICAL FIELD This disclosure relates generally to machining, and more particularly to ultrasonic measurement of electrode depth during electrical discharge machining. [Background technology]

[0002] Electrical discharge machining (EDM) is a machining process that removes material from a conductive workpiece by a series of repetitive discharges between an electrode and the conductive workpiece being machined. One challenge with EDM is detecting when the electrode is about to penetrate the surface of the conductive workpiece opposite the surface being machined. Current methods attempt to infer the depth of the electrode within the part from other process parameters, such as duration, but none of these methods directly measure the depth of the electrode within the conductive workpiece being machined. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0072488 Summary of the Invention

[0004] All aspects, examples, and features described below can be combined in any technically possible manner.

[0005] One aspect of the present disclosure provides an electrical discharge machining (EDM) machine comprising: an electrode configured to machine a conductive workpiece by application of a repetitive electric charge; an electrode positioner operably coupled to the electrode and controlling positioning of the electrode in three-dimensional space; a controller operably coupled to the electrode and the electrode positioner and configured to control the application of the repetitive electric charge; and an ultrasonic sensor operably coupled to the electrode and to the controller, wherein the controller determines a depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor and the electrode positioner.

[0006] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the ultrasonic sensor includes an electromagnetic acoustic transducer (EMAT) disposed around the electrode.

[0007] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the ultrasonic sensor includes a piezoelectric ultrasonic transducer disposed about the electrode.

[0008] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the controller further determines a distance to punch-through of the conductive workpiece at a given position during operation based on a depth of the electrode within the conductive workpiece and a known thickness of the conductive workpiece at the given position.

[0009] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the controller intermittently operates the ultrasonic sensor with the application of repetitive charges from the electrode and determines a depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor during the EDM operation.

[0010] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the controller operates the ultrasonic sensor after the application of the series of repetitive charges from the electrodes is completed.

[0011] One aspect of the present disclosure includes a method including the steps of: electrical discharge machining a conductive workpiece using an electrode, wherein a three-dimensional position of the electrode is known from an electrode positioner; determining a length of the electrode using an ultrasonic sensor operably coupled to the electrode; and determining a depth of the electrode within the conductive workpiece based on the length of the electrode and the three-dimensional position of the electrode.

[0012] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the ultrasonic sensor includes an electromagnetic acoustic transducer operably coupled to the electrode.

[0013] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the ultrasonic sensor includes a piezoelectric ultrasonic transducer disposed about the electrode.

[0014] Another aspect of the present disclosure includes any of the aspects described above, further including determining a distance to punch-through of the conductive workpiece at a given location during operation based on a depth of the electrode within the conductive workpiece and a known thickness of the conductive workpiece at the given location.

[0015] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the controller applies a repetitive charge from the electrode to intermittently operate the ultrasonic sensor and determines a depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor during the electrical discharge machining.

[0016] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the controller operates the ultrasonic sensor after the application of the series of repetitive charges from the electrode is completed, and a step of determining a depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor occurs after the electrical discharge machining.

[0017] Two or more aspects described in this disclosure, including those described in this Summary section, may be combined to form an embodiment not specifically described herein.

[0018] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, workpieces, and advantages will be apparent from the description and drawings, and from the claims.

[0019] These and other features of the present disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure, taken in conjunction with the accompanying drawings which illustrate various embodiments of the present disclosure. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic partial cross-sectional view of an electrical discharge machine having an ultrasonic sensor according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic partial cross-sectional view of an electrical discharge machine having an ultrasonic sensor according to an embodiment of the present disclosure. [Figure 3] 1 is a flow chart illustrating a method of operating an electrical discharge machine in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0021] It should be noted that the drawings of the present disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the present disclosure and therefore should not be considered limiting of the scope of the present disclosure. In the drawings, like numbers represent like elements between the drawings.

[0022] As an initial matter, in order to clearly explain this disclosure, it is necessary to select specific terminology when referring to and describing relevant machine components within an exemplary application of an electrical discharge machine. In doing so, common industry terminology will be used where possible and consistent with its accepted meaning. Unless otherwise noted, such terminology should be given a broad interpretation consistent with the context of this application and the scope of the appended claims. Those skilled in the art will understand that in many cases, a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single component may, in another context, be referred to as including and consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single component.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It will be further understood that the terms "comprise" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. "Optional" or "optionally" means that the subsequently stated event may or may not occur, or that the subsequently stated feature may or may not be present, and that the statement includes instances where the event occurs or the feature is present, as well as instances where the event does not occur or the feature is absent.

[0024] When an element or layer is referred to as "on," "engaged," "disengaged," "connected," or "coupled," or "mounted" to another element or layer, the element or layer may be directly engaged, connected, or coupled to the other element or layer, or there may be intervening elements or layers. Conversely, when an element is referred to as being "directly," "directly engaged," "directly connected," or "directly coupled" to another element or layer, there are no intervening elements or layers. Other terms used to describe relationships between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent to" versus "directly adjacent to," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The verb forms of "couple" and "mount" are sometimes used interchangeably herein.

[0025] As described above, the present disclosure provides an electrical discharge machining (EDM). The EDM includes an electrode for machining a conductive workpiece by applying a repetitive charge, and a controller operably coupled to the electrode and controlling the application of the repetitive charge. The EDM also includes an ultrasonic sensor operably coupled to the electrode and to the controller. The controller can determine the depth of the electrode within the conductive workpiece based on data from the ultrasonic sensor. By knowing the thickness of the conductive workpiece at a given location, the controller can also determine the distance to punch-through in the conductive workpiece based on data from the ultrasonic sensor, making the EDM process more accurate and preventing punch-through when undesired and / or damage to other features of the workpiece due to not knowing the depth of the electrode.

[0026] 1 shows a schematic partial cross-sectional view of an EDM 100 according to an embodiment of the present disclosure. Electrical discharge machining is a manufacturing process in which an electrical charge, e.g., a spark, is used to remove and / or shape a conductive workpiece to obtain a desired shape. Electrical discharge machining is also known as spark erosion, spark machining, die sinking, wire erosion, or wire burning.

[0027] The EDM 100 includes an electrode 110 configured to machine a conductive workpiece 112 by applying a repetitive electrical charge. The conductive workpiece 112 (hereinafter, "workpiece 112") can include any conductive metallic structure, and possibly some conductive ceramic structures. In one non-limiting example, the workpiece 112 can include a turbine nozzle or blade. The electrode 110 can include any suitable material typically used in EDM. Although shown as rectangular in cross section, the electrode 110 can have any shape and / or size to perform the desired machining on the workpiece 112. As is understood in the art, as the EDM 100 operates, the electrode 110 wears and changes length over time.

[0028] The EDM 100 may also include a tank 114 for holding a dielectric 116 on which the conductive workpiece 112 is supported. The dielectric 116 may include any now known or later developed liquid dielectric suitable for electrical discharge machining. The dielectric 116 may be circulated through the tank 114 and a machining region 118 adjacent the electrode 110, i.e., the workpiece 112, using any now known or later developed pumping system 120 and associated piping. For example, the dielectric 116 may be delivered to the machining region 118 at an outlet 122, such as a nozzle. Optionally, the dielectric 116 may be passed through an opening in the electrode 110 (not shown for clarity). The workpiece 112 may be supported on any form of support 124 within the tank 114.

[0029] The EDM 100 also includes a controller 130 operably coupled to the electrode 110. The controller 130 may include any computerized industrial control system capable of controlling, among other things, the application of repetitive charges to the electrode 110 and workpiece 112, the operation of the pumping system 120, and the ultrasonic sensor 140. The controller 130 also controls and interacts with an EDM positioner 132 to position the electrode 110. The EDM positioner 132 may include any now-known or later-developed robotic positioning system operably coupled to the electrode 110 to control the positioning (e.g., location and movement) of the electrode 110 in three-dimensional (X, Y, Z) space relative to the workpiece 112, for example. For example, the EDM positioner 132 may position and move the electrode 110 to any X, Y, Z position relative to the workpiece 112. The controller 130 also knows the relative position of the electrode 110 with respect to the workpiece 112 via the EDM positioner 132 and controls the vector along which the electrode 110 moves into the workpiece 112, i.e., the tooling vector. For purposes of illustration, the tooling vector is shown as being in the Z direction (vertical on the page), but it will be appreciated that the tooling vector may be in any direction depending on the direction the electrode 110 advances into the workpiece 112. In either case, the controller 130 knows the position of the electrode 110 at any X, Y, Z location relative to the workpiece 112.

[0030] The EDM 100 also includes an ultrasonic sensor 140 operably coupled to the electrode 110 and to the controller 130. The ultrasonic sensor 140 can take several forms. In one embodiment, the ultrasonic sensor 140 includes an electromagnetic acoustic transducer (EMAT) 142 disposed at least partially around the electrode 110. The position of the EMAT 142, particularly its coil, relative to the electrode 110 is known. The EMAT 142 can transmit / induce an ultrasonic signal 144 into the workpiece 112 using two interacting magnetic fields. A radio frequency (RF) field is generated by the coil of the ultrasonic sensor 140 and interacts with a lower or static frequency field generated by a magnet to generate a Lorentz force. The Lorentz force propagates to the workpiece 112, generating elastic waves. In the reversal process, the elastic waves interact in the presence of a magnetic field to generate a return signal 146 that generates a current in the coil of the EMAT 142. The EMAT 142 may operate in a standard manner, but the propagation mode and / or frequency of its transmit signal 144 may be customized to the material of the workpiece 112 and the material of the dielectric 116 to minimize leakage into the dielectric 116 and provide the desired reflection from the electrode 110 to enable time-of-flight measurements.

[0031] The controller 130 determines the length L1 of the electrode 110 using an ultrasonic sensor 140 operably coupled to the electrode 110, for example, based on data from the EMAT 142. In this manner, the position of the tip of the electrode 110 can be determined. The controller 130 can also determine the depth D1 of the electrode 110 within the workpiece 112 using data from the EDM positioner 132 and the ultrasonic sensor 140. The controller 130 determines the depth D1 of the electrode 110 within the workpiece 112 based on the length L1 of the electrode 110 (from the ultrasonic sensor 140) and the three-dimensional position of the electrode 110 relative to the workpiece 112, i.e., its 3D position relative to the workpiece 112, as known from the EDM positioner 132. More specifically, the transmit signal 144 and the return signal 146 can be evaluated by the controller 130 using any suitable time-of-flight calculation in conjunction with the EDM positioner to determine the length L1 of the electrode 110. Furthermore, by knowing the length L1 and the relative position of the electrode 110 and the workpiece 112, the controller 130 can determine the depth D1 of the electrode 110 within the workpiece 112, i.e., by simply subtracting the length of the electrode 110 from how far the electrode 110 has moved relative to the known surface of the workpiece 112.

[0032] 2, ultrasonic sensor 140 can include a piezoelectric ultrasonic transducer (PUT) 242 disposed on electrode 110. The length L2 of electrode 110 below PUT 242 is referenced by controller 130. PUT 242 functions similarly to EMAT 142 described above.

[0033] The machining operation of the EDM 100 may interfere with the operation of the ultrasonic sensor 140. To address this situation, in certain embodiments, the controller 130 may apply repetitive charges from the electrode 110 to operate the ultrasonic sensor 140 intermittently. That is, the signals 144, 146 of the ultrasonic sensor 140 are transmitted and received between charges emitted from the electrode 110. More specifically, the signals 144, 146 of the ultrasonic sensor 140 are transmitted and received during the normal duration between charges when the EDM 100 operates. In this case, the controller 130 can determine the depth D1 of the electrode 110 within the workpiece 112 based on data from the ultrasonic sensor 140 while the EDM 100 is operating, i.e., without stopping machining. In another embodiment, the controller 130 may operate the ultrasonic sensor 140 after the application of a series of repetitive charges from the electrode 110 is complete. That is, the signals 144, 146 of the ultrasonic sensor 140 are transmitted and received during periods when no charge is being discharged from the electrode 110, ie, not during the normal duration between charges when the EDM 100 is operating.

[0034] In certain embodiments, the controller 130 can further determine a punch-through distance D2 of the workpiece 112 at a given position during operation based on the depth D1 of the electrode 110 within the workpiece 112 and the known thickness T1 of the workpiece 112 at the given position. More specifically, the punch-through distance D2 is equal to the known thickness T1 minus the depth D1 of the electrode 110, i.e., D2=T1−D1.

[0035] FIG. 3 shows a flow diagram illustrating a method of operation of EDM 100. This method embodiment may include, in process P10, electrical discharge machining a workpiece 112 using an electrode 110. In process P12, controller 130 may determine the length of electrode 110, for example, based on data from ultrasonic sensor 140. In process P14, controller 130 may determine the depth of electrode 110 within workpiece 112 based on the length of electrode 110 (from ultrasonic sensor 140) and the three-dimensional position of electrode 110. The three-dimensional position of electrode 110 is known from electrode positioner 132. The depth of electrode 110 within workpiece 112 may be determined by knowing the lengths and relative positions of electrode 110 and workpiece 112, i.e., by simply subtracting the length of workpiece 112 from a known surface position.

[0036] As described above, the ultrasonic sensor 140 may include an EMAT 142 ( FIG. 1 ) or a PUT 242 ( FIG. 2 ) operably coupled to the electrode 110. In optional process P16, the controller 130 may determine a distance D2 to punch-through of the workpiece 112 at a given position during operation based on a depth D1 of the electrode 110 within the workpiece 112 and a known thickness T1 of the workpiece 112 at the given position. The controller 130 may intermittently operate the ultrasonic sensor 140 by applying repetitive charges from the electrode 110 and may determine the depth D1 of the electrode 110 within the workpiece 112 based on data from the ultrasonic sensor 140 during electrical discharge machining (i.e., process P14 occurs during process P10). In another embodiment, the controller 130 operates the ultrasonic sensor 140 after the application of a series of repetitive charges from the electrode 110 is completed, and the step of determining the depth D1 of the electrode 110 within the workpiece 112 based on data from the ultrasonic sensor 140 is performed after the electrical discharge machining (i.e., process P14 is not performed during process P10).

[0037] Embodiments of the present disclosure provide various technical and commercial advantages, examples of which are described herein. The use of ultrasonic sensors with EDM potentially provides direct measurement of electrode depth as machining is occurring, thereby allowing for desired control of penetration of the conductive workpiece. This technique also allows for direct measurement of the thickness of the remaining material before the electrode breaks through.

[0038] Approximate language used throughout this specification and claims can be applied to modify any quantitative expression that can be permissibly varied without resulting in a change in the relevant basic function. Thus, values ​​modified by terms such as "approximately," "about," and "substantially" are not limited to the exact value specified. In at least some instances, approximate language can correspond to the precision of the instrument used to measure the value. Herein and throughout this specification and claims, range limitations can be combined and / or substituted, and unless the context or language dictates otherwise, such ranges are identified and include all subranges encompassed therein. "About," as applied to a particular value in a range, applies to both endpoints and can indicate + / - 10% of the stated value, unless otherwise dependent on the precision of the instrument used to measure the value.

[0039] The corresponding structure, material, acts, and equivalents of all means-plus-function or step-plus-function elements in the following claims are intended to encompass any structure, material, or acts for performing that function in combination with other specifically claimed claim elements. The description of the present disclosure has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The present embodiments were chosen and described in order to best explain the principles and practical application of the disclosure and to enable others skilled in the art to understand the disclosure in various embodiments with various modifications as suited to the particular uses envisioned. [Explanation of symbols]

[0040] 100 Electric discharge machine, EDM 110 electrodes 112 workpieces 114 Tank 116 Dielectric 118 Machining area 120 Pumping System 122 Exit 124 Support 130 Controller 132 Electrode Positioner 140 Ultrasonic Sensor 142 Electromagnetic Acoustic Transducer 144 Transmitted Signal 146 Return Signal 242 Piezoelectric Ultrasonic Transducer

Claims

1. an electrode (110) configured to machine a conductive workpiece (112) by application of a repetitive electric charge; an electrode positioner (132) operatively coupled to the electrode (110) and configured to control the positioning of the electrode (110) in three-dimensional space; a controller (130) operably coupled to the electrode (110) and the electrode positioner (132) and configured to control the application of the repetitive charges; an ultrasonic sensor (140) operably coupled to the electrode (110) and to the controller (130); the controller (130) determines a depth (D1) of the electrode (110) within the conductive workpiece (112) based on data from the ultrasonic sensor (140) and the electrode positioner (132); Electrical discharge machining machine (EDM) (100).

2. The EDM (100) of any preceding claim, wherein the ultrasonic sensor (140) comprises an electromagnetic acoustic transducer (EMAT) (142) disposed about the electrode (110).

3. The EDM (100) of any preceding claim, wherein the ultrasonic sensor (140) comprises a piezoelectric ultrasonic transducer (242) disposed about the electrode (110).

4. 2. The EDM of claim 1, wherein the controller further determines a distance to punch through the conductive workpiece at the given location during operation based on the depth of the electrode within the conductive workpiece and a known thickness of the conductive workpiece at the given location.

5. 2. The EDM (100) of claim 1, wherein the controller (130) applies the repetitive charge from the electrode (110) to intermittently operate the ultrasonic sensor (140) and determines the depth (D1) of the electrode (110) within the conductive workpiece (112) based on the data from the ultrasonic sensor (140) during operation of the EDM (100).

6. The EDM (100) of claim 1, wherein the controller (130) activates the ultrasonic sensor (140) after a series of the repetitive charge applications from the electrode (110) is completed.

7. Electric discharge machining a conductive workpiece (112) using an electrode (110), the three-dimensional position of the electrode (110) being known from an electrode positioner (132); determining a length (L1) of the electrode (110) using an ultrasonic sensor (140) operably coupled to the electrode (110); determining a depth (D1) of the electrode (110) within the conductive workpiece (112) based on the length (L1) of the electrode (110) and the three-dimensional position of the electrode (110); A method comprising:

8. The method of claim 7, wherein the ultrasonic sensor (140) comprises an electromagnetic acoustic transducer (142) operably coupled to the electrode (110).

9. The method of claim 7, wherein the ultrasonic sensor (140) comprises a piezoelectric ultrasonic transducer (242) disposed about the electrode (110).

10. 8. The method of claim 7, further comprising determining a distance (D2) to punch-through of the conductive workpiece (112) at a given position during operation based on the depth (D1) of the electrode (110) within the conductive workpiece (112) and a known thickness (T1) of the conductive workpiece (112) at the given position.

11. 8. The method of claim 7, wherein the steps of the controller (130) applying the repetitive charge from the electrode (110) to intermittently operate the ultrasonic sensor (140) and determining the depth (D1) of the electrode (110) within the conductive workpiece (112) based on the data from the ultrasonic sensor (140) are performed during the electrical discharge machining.

12. 8. The method of claim 7, wherein the controller (130) operates the ultrasonic sensor (140) after the application of the series of repetitive charges from the electrode (110) is completed, and the step of determining the depth (D1) of the electrode (110) within the conductive workpiece (112) based on the data from the ultrasonic sensor (140) occurs after the electrical discharge machining.

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