Variable-polarity electric spark forming hole making method for double-wall turbine blade

Abstract

The invention relates to the technical field of electric spark forming machining, in particular to a double-wall turbine blade variable-polarity electric spark forming hole making method which comprises the steps that low-melting-point alloy is cast in a gap between double walls of a blade till filling is completed, the blade is cooled to the normal temperature, and the low-melting-point alloy is completely solidified; a forming row electrode is used as a tool electrode, the electrode is set as a negative electrode, the blade is set as a positive electrode, feeding and hole forming are started till an outlet of the wall face is machined, and rough machining is completed; and turning the polarity, setting the electrode as a positive electrode, setting the blade as a negative electrode, and continuously feeding and processing by using a small pulse width parameter, so that the loss degree of the electrode is far greater than that of the filling material, and the unlost part at the upper end of the electrode penetrates into the air film hole to finish finish machining. The method can solve the problems that a conventional electric spark forming hole-making process of the double-wall turbine blade is poor in quality, the wall surface is prone to being damaged and the like, and high-precision and efficient hole-making is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of electrospark forming processing, and in particular to a method for making holes in double-wall turbine blades through variable polarity electrospark forming. Background Art

[0002] Electrospark forming machining technology is one of the special machining technologies. It mainly uses the high-temperature ablation phenomenon generated by non-contact pulsed electric spark discharge between the tool and the workpiece, and removes the workpiece metal by "copying" the electrode shape, so as to achieve the purpose of machining specific structures. It is widely used in the machining of various difficult-to-cut materials and complex feature structures. At present, some aircraft engine turbine blades adopt a double-wall structure design. There is only a gap of no more than 0.5mm between the outer wall and the inner wall of the blade, and the blade air film hole is only designed on the wall surface on one side, and does not extend to the corresponding other side wall surface. In the process of hole making using electrospark forming machining technology, when the cylindrical forming electrode discharges and feeds and just penetrates one side of the wall surface, due to the loss of the electrode working end, the outlet end of the air film hole is not completely transparent, and the entire hole shape is conical. If the hole shape is refined to make the hole completely transparent and qualified in size, according to the conventional process, the electrode needs to be fed at least 1 times the length of the hole depth. However, since the gap between the double walls is very small, far less than the hole depth, it causes damage or even penetrates the other side wall, causing the blade to be scrapped. Therefore, conventional EDM processing methods cannot achieve hole making in double-wall turbine blades. Summary of the invention

[0003] (1) Technical issues to be solved

[0004] The present application provides a method for forming holes by variable polarity electrospark forming in double-wall turbine blades, which solves the problem that conventional electrospark forming hole making processes for double-wall turbine blades have poor quality and are prone to damage to the wall surface.

[0005] (2) Technical solution

[0006] The present application provides a method for forming holes by variable polarity electrospark forming of double-walled turbine blades, comprising:

[0007] Casting a low melting point alloy into the gap between the double walls of the blade until it is filled, and cooling it to room temperature to allow the low melting point alloy to completely solidify;

[0008] Use the formed row electrode as the tool electrode, set the electrode as the negative electrode, and the blade as the positive electrode, and start feeding the hole until the exit of the wall is processed to complete the rough processing;

[0009] Reverse the polarity, set the electrode to the positive pole and the blade to the negative pole, and continue the feeding process with a small pulse width parameter. At this time, the electrode wear is much greater than the filling material, so that the unworn part of the upper end of the electrode penetrates into the air film hole to complete the fine processing.

[0010] Furthermore, the step of casting the low melting point alloy in the gap between the double-layer walls of the blade comprises:

[0011] The blade is suspended inside the cavity of the blade fixture and the blade is positioned using a six-point positioning method;

[0012] A low melting point alloy is cast into the gap between the double-layer walls of the blade and into the cavity of the blade fixture, so that an end of one side of the blade is immersed in the low melting point alloy.

[0013] Furthermore, it also includes:

[0014] A row of electrode guide reference holes is reserved on the electrode fixture to clamp the cylindrical electrode, and a multi-axis linkage method is used to synchronously process rows of air film holes with a certain angle.

[0015] Furthermore, the method of using the formed row electrode as the tool electrode, setting the electrode as the negative electrode and the blade as the positive electrode, before starting to feed and make holes, also includes:

[0016] Clamp the mounting shaft on the electrode fixture onto the spindle of the EDM forming processing equipment;

[0017] Place the side reference surface of the blade fixture on the working surface of the machine tool, mark the bottom reference surface of the blade fixture and complete the fixation, and align the hole position of the electrode through the reference surface of the blade fixture.

[0018] Furthermore, the forming row electrode is used as a tool electrode, the electrode is set as a negative electrode, the blade is set as a positive electrode, and feeding and hole making are started, including:

[0019] The hole depth is measured by digital modeling, and the processing depth is set to 0.95 to 1 times the hole depth according to the discharge gap and electrode loss rate. The electrode is set to the negative pole and the blade is set to the positive pole.

[0020] Furthermore, the forming row electrode is used as the tool electrode, the electrode is set as the negative electrode, the blade is set as the positive electrode, and the process parameters for starting feeding and hole making are:

[0021] Pulse width 10~120μs, pulse interval 10~120μs, peak current 15~150A, voltage 60~150V.

[0022] Furthermore, the polarity is reversed, the electrode is set as the positive electrode, the blade is set as the negative electrode, and the process parameters for continuing the feeding process with a small pulse width parameter are:

[0023] The pulse width is 3 to 45 μs, the pulse interval is 5 to 50 μs, the peak current is 3 to 60 A, the voltage is 80 to 200 V, and the processing depth is set to 1.05 to 1.15 times the hole depth.

[0024] Furthermore, it also includes:

[0025] After completing the processing of a row of holes, there is no need to change the electrode or move the coordinates, and the same method can be used to process the next row of holes.

[0026] (3) Beneficial effects

[0027] The above technical solution of the present application has the following advantages:

[0028] The variable polarity electrospark forming hole-making method for double-walled turbine blades provided in the present application fully utilizes the advantages of low-melting-point alloys such as easy melting, good fluidity, small expansion and contraction rate, high strength, and easy use, and can quickly and completely fill gaps; through the variable polarity method, the low-melting-point alloy is used as a tool electrode for trimming the hole-making electrode, and the original hole-making electrode is used as a workpiece, effectively etching away the worn working end of the hole-making electrode, creating space for its continued feeding processing, so that the unworn part of the upper end of the hole-making electrode can enter the interior of the hole, thereby completing the fine processing, solving the problems of poor quality and easy damage to the wall surface of conventional electrospark forming hole-making processes for double-walled turbine blades, and achieving high-precision and efficient hole-making. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 Schematic diagram of a double-walled turbine blade provided for this application;

[0031] Figure 2 A schematic diagram of the clamping of double-walled turbine blades provided for this application;

[0032] Figure 3 A schematic diagram of the forming row electrode feeding process provided in this application;

[0033] Figure 4 Schematic diagram of the positive polarity rough machining process provided for this application;

[0034] Figure 5 Schematic diagram of the negative polarity finishing process provided for this application.

[0035] Figure numerals: 1. blade; 2. blade fixture; 3. low melting point alloy; 4. mounting shaft; 5. electrode fixture; 6. cylindrical electrode; 7. low melting point alloy. DETAILED DESCRIPTION

[0036] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0037] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0038] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0039] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways. "Multiple" means "two or more".

[0040] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0041] The embodiment of the present application provides a method for forming holes by variable polarity electrospark forming in double-wall turbine blades, comprising: casting a low-melting-point alloy in the gap between the double-walls of the blades until the filling is complete, cooling to room temperature, and allowing the low-melting-point alloy to completely solidify; using a forming row electrode as a tool electrode, setting the electrode to the negative electrode and the blade to the positive electrode, and starting to feed the holes until the exit of the wall is processed to complete the rough processing; reversing the polarity, setting the electrode to the positive electrode and the blade to the negative electrode, and continuing the feeding processing with a small pulse width parameter, at which time the electrode wear is much greater than the filling material, so that the unworn part of the upper end of the electrode penetrates into the air film hole to complete the fine processing.

[0042] In some embodiments, the casting of the low-melting-point alloy in the double-wall gap of the blade includes: suspending the blade inside the cavity of the blade fixture and using a six-point positioning method to complete the positioning of the blade; casting the low-melting-point alloy into the double-wall gap of the blade and the cavity of the blade fixture so that one end of the blade is immersed in the low-melting-point alloy.

[0043] In some embodiments, it also includes: reserving a row of electrode guide reference holes on the electrode fixture to clamp the cylindrical electrode, and using a multi-axis linkage method to synchronously process rows of air film holes with a certain angle.

[0044] In some embodiments, the forming row electrode is used as the tool electrode, the electrode is set as the negative electrode, and the blade is set as the positive electrode. Before starting to feed and make holes, it also includes: clamping the mounting shaft on the electrode fixture on the spindle of the electrospark forming processing equipment; placing the side reference surface of the blade fixture on the working surface of the machine tool, marking the bottom reference surface of the blade fixture and completing the fixation, and the electrode aligns the hole position through the reference surface of the blade fixture.

[0045] In some embodiments, the forming row electrode is used as the tool electrode, the electrode is set to the negative electrode, the blade is set to the positive electrode, and feeding and hole making begin, including: measuring the hole depth through digital modeling, and setting the processing depth to 0.95 to 1 times the hole depth according to the discharge gap and the electrode loss rate, setting the electrode to the negative electrode, and the blade to the positive electrode.

[0046] In some embodiments, the formed row electrode is used as the tool electrode, the electrode is set as the negative electrode, the blade is set as the positive electrode, and the process parameters for starting feeding and hole making are: pulse width 10~120μs, pulse interval 10~120μs, peak current 15~150A, voltage 60~150V.

[0047] In some embodiments, the polarity is reversed, the electrode is set to the positive pole, the blade is set to the negative pole, and the process parameters for continuing the feeding process with small pulse width parameters are: pulse width 3 to 45 μs, pulse interval 5 to 50 μs, peak current 3 to 60A, voltage 80 to 200V, and the processing depth is set to 1.05 to 1.15 times the hole depth.

[0048] In some embodiments, it also includes: after completing the processing of a row of holes, there is no need to replace the electrodes, move the coordinates, and use the same method to process the next row of holes.

[0049] In view of the technical difficulties in electrospark forming holes for double-walled turbine blades, this application proposes the following improvement solutions:

[0050] The low melting point alloy is slowly and steadily cast in the gap between the double-layer walls of the blade until it is filled and cooled to room temperature to completely solidify the low melting point alloy. The forming row electrode is used as the tool electrode, the electrode is set as the negative electrode, and the blade is set as the positive electrode, and the hole is fed until the exit of the wall is processed to complete the rough processing.

[0051] Reverse the polarity, that is, set the electrode to the positive electrode and the blade to the negative electrode, and continue to feed the processing with a small pulse width parameter. At this time, under the action of the electric field, the electrons in the discharge channel rush to the electrode (positive electrode), and the positive ions rush to the blade (negative electrode). Due to the small mass of electrons, they can easily obtain a higher movement speed than positive ions in a short time, and the energy transferred to the electrode is also higher, resulting in the electrode loss being greater than the loss of the low-melting-point alloy in the blade gap. Moreover, under the action of a small pulse width, the difference in the degree of loss is more obvious (the positive ions do not have time to obtain enough speed to impact the negative electrode). At this time, it is equivalent to the low-melting-point alloy in the double-wall gap as a tool electrode, and the original hole-making electrode as a workpiece. Therefore, after changing the polarity, the originally lost part of the electrode working end will be gradually eroded during the rough machining process, while the loss of the low-melting-point alloy is relatively small, which creates enough space for the electrode to continue feeding, so that the unworn part of the upper end of the electrode can penetrate into the air film hole to complete the fine machining, achieve a qualified aperture and complete transparency, and will not damage the other side wall.

[0052] Through the above method, the same piece or the same group of electrodes can be used to complete the rough and fine processing of a single hole or a group of holes at one time, and the next hole or the next group of holes can be processed without changing the electrode, which saves the time of changing and adjusting the electrode, facilitates the realization of automated processing, and greatly improves the efficiency.

[0053] The following is an explanation through specific embodiments.

[0054] Example

[0055] A method for forming holes by variable polarity electrospark forming of double-wall turbine blades, such as Figure 1 to Figure 5 shown.

[0056] (1) The blade 1 is positioned using a six-point positioning method, and then a low-melting-point alloy 3 is slowly and steadily cast into the cavity of the blade fixture 2 so that one end of the blade is immersed in the low-melting-point alloy 3, and a low-melting-point alloy 7 is cast into the gap between the double walls of the blade until the filling is completed and cooled to room temperature.

[0057] (2) A row of electrode guide reference holes is reserved on the electrode fixture 5 for clamping the cylindrical electrode 6. A multi-axis linkage method can be used to synchronously process rows of air film holes with a certain angle. The mounting shaft 4 on the electrode fixture 5 is clamped on the main shaft of the electrospark forming processing equipment.

[0058] (3) Place the side reference surface of the blade fixture 2 on the working surface of the machine tool, mark the bottom reference surface of the blade fixture 2 and complete the fixation, and align the hole position of the electrode 6 through the reference surface of the blade fixture 2.

[0059] (4) The hole depth is measured by digital modeling, and the processing depth is set to 0.95 to 1 times the hole depth according to the data such as the discharge gap and the electrode loss rate. The electrode 6 is set as the negative electrode and the blade 1 is set as the positive electrode. The process parameters are set as follows: pulse width 10 to 120 μs, pulse interval 10 to 120 μs, peak current 15 to 150 A, voltage 60 to 150 V, and the hole making is started until the wall exit is processed to complete the rough processing.

[0060] (5) Reverse the polarity of electrode 6 and blade 1, set electrode 6 as positive electrode and blade 1 as negative electrode, set process parameters: pulse width 3-45μs, pulse interval 5-50μs, peak current 3-60A, voltage 80-200V, continue discharge feed processing, and set the processing depth to 1.05-1.15 times the hole depth. At this time, the low-melting-point alloy 7 in the double-wall gap is used as the tool electrode, and the original electrode 6 is used as the workpiece. During the rough processing, the originally lost part of the working end of the electrode will be gradually eroded away, and the loss degree of the low-melting-point alloy 7 is relatively small, so that the unworn part of the upper end of the electrode can penetrate into the air film hole to complete the fine processing.

[0061] (6) After completing the processing of a row of holes, the coordinates can be moved without changing the electrodes, and the next row of holes can be processed using the same method.

[0062] This application proposes a method for forming holes by variable polarity electrospark forming of double-walled turbine blades, which has the following advantages:

[0063] First, the advantages of low melting point alloys such as easy melting, good flow performance, small expansion and contraction rate, high strength, and convenient use are fully utilized to quickly and completely fill the gap; second, the low melting point alloy is used as a tool electrode for trimming the hole-making electrode through the polarity change method, and the original hole-making electrode is used as a workpiece, effectively etching the worn working end of the hole-making electrode, creating space for its continued feeding and processing, so that the unworn part of the upper end of the hole-making electrode can enter the hole, thereby completing the fine processing, solving the problems of poor quality and easy damage to the wall surface of the conventional electrospark forming hole-making process of double-wall turbine blades, and achieving high-precision and efficient hole-making; third, the same piece or the same group of electrodes can be used to complete the rough and fine processing of a single hole or a group of holes at one time, and the next or the next group of holes can be processed without changing the electrode, saving the time of replacing and adjusting the electrode, facilitating the realization of automated processing, and greatly improving efficiency. The invention has the advantages of low cost, high quality, high reliability and high efficiency, and meets the hole-making requirements of military and civilian products.

[0064] It should be clear that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. The present application is not limited to the specific structures described above and shown in the figures. In addition, for the sake of simplicity, detailed descriptions of known methods and technologies are omitted here.

[0065] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for forming holes by variable polarity electrospark forming of double-walled turbine blades, characterized in that: include: Casting a low melting point alloy into the gap between the double walls of the blade until it is filled, and cooling it to room temperature to allow the low melting point alloy to completely solidify; Use the formed row electrode as the tool electrode, set the electrode as the negative electrode, and the blade as the positive electrode, and start feeding the hole until the exit of the wall is processed to complete the rough processing; Reverse the polarity, set the electrode to the positive pole and the blade to the negative pole, and continue the feeding process with a small pulse width parameter. At this time, the electrode wear is much greater than the filling material, so that the unworn part of the upper end of the electrode penetrates into the air film hole to complete the fine processing.

2. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: The method of casting a low melting point alloy in the gap between the double-layer walls of the blade comprises: The blade is suspended inside the cavity of the blade fixture and the blade is positioned using a six-point positioning method; A low melting point alloy is cast into the gap between the double-layer walls of the blade and into the cavity of the blade fixture, so that an end of one side of the blade is immersed in the low melting point alloy.

3. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: Also includes: A row of electrode guide reference holes is reserved on the electrode fixture to clamp the cylindrical electrode, and a multi-axis linkage method is used to synchronously process rows of air film holes with a certain angle.

4. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: The method of using the formed row electrode as the tool electrode, setting the electrode as the negative electrode and the blade as the positive electrode, before starting to feed and make holes, also includes: Clamp the mounting shaft on the electrode fixture onto the spindle of the EDM forming processing equipment; Place the side reference surface of the blade fixture on the working surface of the machine tool, mark the bottom reference surface of the blade fixture and complete the fixation, and align the hole position of the electrode through the reference surface of the blade fixture.

5. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: The method of using the formed row electrode as a tool electrode, setting the electrode as a negative electrode, setting the blade as a positive electrode, and starting to feed and make holes includes: The hole depth is measured by digital modeling, and the processing depth is set to 0.95 to 1 times the hole depth according to the discharge gap and electrode loss rate. The electrode is set to the negative pole and the blade is set to the positive pole.

6. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: The forming row electrode is used as the tool electrode, the electrode is set as the negative electrode, the blade is set as the positive electrode, and the process parameters for starting feeding and hole making are: Pulse width 10~120μs, pulse interval 10~120μs, peak current 15~150A, voltage 60~150V.

7. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades according to claim 1, characterized in that: The process parameters for reversing the polarity, setting the electrode as the positive electrode and the blade as the negative electrode, and continuing the feeding process with a small pulse width parameter are: The pulse width is 3 to 45 μs, the pulse interval is 5 to 50 μs, the peak current is 3 to 60 A, the voltage is 80 to 200 V, and the processing depth is set to 1.05 to 1.15 times the hole depth.

8. The method for forming holes by variable polarity electrospark forming of double-walled turbine blades as claimed in claim 1, characterized in that: Also includes: After completing the processing of a row of holes, there is no need to change the electrode or move the coordinates, and the same method can be used to process the next row of holes.

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