A grinding head for electrolytic grinding of micro-holes

Abstract

The application discloses a grinding head for electrolytic grinding of micro holes, which mainly comprises an elastic tool shank and a combined grinding head. The elastic tool shank is composed of an internal elastic material and an external insulating layer; the combined grinding head is composed of a cylindrical surface grinding part and a hemispherical surface grinding part and has an electrically insulating abrasive layer adhered to the surface. A spiral groove is arranged on the combined grinding head, which not only ensures the inflow of electrolyte but also carries away electrolysis products and heat generated in the reaction by the electrolyte through the spiral groove. The electrolytic grinding head has a simple structure, is suitable for further finishing of pre-punched holes and can obtain a micro hole structure with higher precision.

Description

Technical Field

[0001] This invention relates to a grinding head for electrolytic grinding of micro-holes, belonging to the field of electrolytic grinding-composite machining. Background Technology

[0002] Turbine blades on aero engines need to withstand the engine's thermal and mechanical loads, operating in high-temperature environments ranging from 1600℃ to 1800℃. To improve the turbine blades' ability to withstand such harsh operating conditions, micro-film cooling holes are typically machined onto the turbine blades. These film cooling holes have small diameters, generally 0.3mm to 0.8mm, are densely arranged in a spatial distribution, and the axis of some film cooling holes makes a very small angle with the blade surface.

[0003] The machining requirements for film cooling holes are very high: the hole wall surface must be free of microcracks and defects, with no or very thin recast layer, low surface roughness, and high dimensional accuracy. Therefore, machining film cooling holes is quite difficult. Currently, film cooling holes for aero-engine blades are mainly machined using electrical discharge machining (EDM), electro-hydraulic beam machining (EDM), and laser machining. Film cooling holes machined by EDM and laser machining generally have a thicker recast layer, microcracks, and are relatively rough, making them difficult to directly meet application requirements. Therefore, they often require post-processing such as grinding, lapping, and polishing.

[0004] Electrolytic grinding is a method of material removal that combines electrolytic action with mechanical grinding. It offers advantages such as good surface integrity, absence of recast layer microcracks, high forming accuracy, and low tool wear, making it particularly beneficial for machining difficult-to-machine metals. In electrolytic grinding, a conductive rod-shaped grinding head serves as the tool cathode, and the workpiece as the anode. Electrolyte is sprayed into the machining area through an external nozzle, while the tool cathode rotates and feeds, removing material. During machining, most of the metal material is removed through electrolysis, and the passivation film formed by oxidation is ground away. Therefore, the machined surfaces of the tool and workpiece experience low thermal stress, resulting in high machining quality. Electrolytic grinding based on a rod-shaped tool cathode is often considered a preferred process for finishing micro-holes. However, existing electrolytic grinding tool cathodes are not well-suited for post-processing with blade-type film-cooled holes.

[0005] Chinese patents with patent numbers 201510663857.6 and 201610391212.6 propose a tool cathode with a flat bottom and an arrangement of liquid passage holes in each layer of the sidewall designed according to requirements. This flat-top tool cathode can electrolytically mill a relatively good workpiece surface. However, it is not suitable for the finishing of fine holes. Chinese patents with patent numbers 200820032604.4 and 201010555654.2 propose an internal spray composite cathode with an embedded diamond abrasive layer and liquid passage holes or grooves. Both of these cathodes adopt an embedded abrasive belt structure and a hemispherical arc surface at the bottom. Although they can process holes, they are difficult to use for the finishing of small holes, and they are almost unusable for processing holes arranged on curved surfaces.

[0006] In summary, it is necessary to research and develop an electrolytic grinding tool cathode suitable for finishing the film cooling holes of aero-engine blades. Summary of the Invention

[0007] In view of the shortcomings of electrolytic grinding heads, the purpose of this invention is to provide a grinding head for electrolytic grinding of micro-holes that is suitable for the precision machining of micro-through holes, thereby obtaining metal components with micro-holes of higher precision.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0009] A grinding head for electrolytic grinding of micro-holes includes a flexible tool holder and a combined grinding head, characterized in that: the combined grinding head includes a cylindrical grinding section and a hemispherical grinding section; the flexible tool holder includes a flexible central rod and an electrically insulating layer; the hemispherical grinding section is located at the front end of the cylindrical grinding section, and the axes of the two are collinear; the flexible tool holder and the cylindrical grinding section are fixedly connected coaxially; the substrate of the hemispherical grinding section is made of an electrically insulating elastic material; and the surface of the combined grinding head is coated with an electrically insulating abrasive layer.

[0010] The grinding head for electrolytic grinding of micro-holes is characterized in that: the surface of the combined grinding head is provided with a spiral groove.

[0011] The grinding head for electrolytic grinding of micro-holes is characterized in that: the elastic tool holder is made of titanium alloy or amorphous alloy material.

[0012] The grinding head for electrolytic grinding of micro-holes is characterized in that: the thickness of the electrical insulation layer is 0.05-0.1 mm, and it is made of acid and alkali resistant polymer material or ceramic material.

[0013] The grinding head for electrolytic grinding of micro-holes is characterized in that the base material of the cylindrical grinding part is stainless steel.

[0014] The grinding head for electrolytic grinding of micro-holes is characterized in that: the thickness of the electrically insulating abrasive layer is 0.02-0.03 mm, and the abrasive grain size in the electrically insulating abrasive layer is 0.01-0.02 mm.

[0015] The grinding head for electrolytic grinding of micro-holes is characterized in that: the width of the spiral groove is 0.5-1mm, the depth is 0.05-0.1mm, and the pitch is 3-5mm.

[0016] The grinding head for electrolytic grinding of micro-holes is characterized in that: the diameter of the elastic tool holder is at least 0.1 mm smaller than the outer diameter of the cylindrical grinding part.

[0017] The main advantages of this invention compared to the prior art are as follows.

[0018] (1) Higher machining accuracy can be obtained. When using this electrolytic grinding head to finish micro-holes, the machining accuracy can be greatly improved due to the suppression of stray corrosion by the hemispherical electrically insulating grinding head, the self-guiding effect of the spiral guide groove, and the self-adaptive effect of the flexible tool holder.

[0019] (2) It can significantly reduce stray corrosion at the inlet and outlet of the hole and improve the forming quality of the micro-hole. The substrate of the hemispherical grinding part of the cathode of this tool is made of electrically insulating elastic material, and the tool holder is also electrically insulating, so that stray current can be effectively suppressed during the machining process, thereby significantly reducing stray corrosion and improving machining accuracy.

[0020] (3) It is easy to automatically position and can realize conformal machining. The end of the electrolytic grinding head of the cathode of this tool is an elastic hemispherical structure, and the tool holder is a high-elasticity and high-strength metal material. During machining, the two work together to achieve good results in finding holes on curved surfaces, self-positioning, and conformal machining of inclined holes.

[0021] (4) Higher hole surface quality can be obtained. This grinding head is an electrolytic tool cathode for further finishing of pre-processed micro-holes. It uses the principle of anodic electrochemical oxidation to transform difficult-to-machine metal materials into soft passivation film materials, and then removes them with the scraping action of micro abrasive grains. In this way, the damage to the machined surface is minimal, and there are almost no recast layers and microcrack defects caused by mechanical, thermal and other effects.

[0022] (5) It can avoid wall damage. Since the end of the grinding head of the present invention is made of an electrically insulating material, when the grinding head is fed to the outlet position of the air film cooling hole, although current and electrolyte are still applied, it will not cause electrolytic effect on the adjacent area, including the wall at the outlet of the hole being processed, thereby avoiding wall damage. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0024] Figure 1 This is a schematic diagram illustrating the working principle of a grinding head used for electrolytic grinding of micro-holes, as per this patent.

[0025] Figure 2 This is a schematic diagram of the structure of a grinding head for electrolytic grinding of micro-holes according to this patent;

[0026] Figure 3 This is a schematic diagram of a self-configuration grinding head for electrolytic grinding of micro-holes, as per this patent.

[0027] Labels and names in the diagram: 1. Flexible tool holder; 2. Combined grinding head; 2-1. Cylindrical grinding section; 2-2. Hemispherical grinding section; 1-1. Flexible center rod; 1-2. Electrically insulating layer; 2-3. Insulating abrasive layer; 2-4. Spiral groove; 3. Pre-drilled hole; 4. Workpiece; 5. Electrolyte circulation filtration system; 6. Nozzle; 7. Electrolyte; 8. Power supply Detailed Implementation

[0028] like Figure 1-3As shown, a grinding head for electrolytic grinding of micro-holes includes a flexible tool holder 1 and a combined grinding head 2. The combined grinding head 2 includes a cylindrical grinding section 2-1 made of conductive material and a hemispherical grinding section 2-2 made of electrically insulating elastic material. The hemispherical grinding section 2-2 is located at the front end of the cylindrical grinding section 2-1, and their axes are collinear. The flexible tool holder 1 includes a flexible central rod 1-1 and an electrically insulating layer 1-2. The flexible central rod 1-1 is made of titanium alloy, and the electrically insulating layer 1-2 is made of ceramic with a thickness of 0.08 mm. The flexible central rod 1-1 and the flexible hemispherical grinding section 2-2 cooperate to facilitate the positioning of the electrolytic grinding head on the central through-hole. The flexible tool holder 1 and the cylindrical grinding section 2 are fixedly connected coaxially. The diameter of the flexible tool holder 1 is 0.3 mm, and the outer diameter of the cylindrical grinding section 2-1 is 0.6 mm. The combined grinding head 2 has an electrically insulating abrasive layer 2-3 adhered to its surface and is provided with spiral grooves 2-4. The electrically insulating abrasive layer 2-3 has a thickness of 0.03 mm and an abrasive particle size of 0.015 mm. The spiral grooves have a width of 0.6 mm, a depth of 0.07 mm, and a pitch of 4 mm. The electrically insulating abrasive layer 2-3 scrapes a passivation film from the workpiece surface, which affects the electrolytic machining speed and surface quality. This effectively improves the surface quality of the micro-pre-drilled holes. Furthermore, the rotation of the abrasive particles with the spindle enhances the replacement of the electrolyte in the machining gap, allowing for timely removal of machining products and reducing polarization. The spiral grooves 2-4 provide a stable machining gap for electrolysis, ensuring the stability of the machining process. Additionally, the electrolyte travels a certain distance within the spiral grooves 2-4, ensuring sufficient contact between the electrolyte and the pre-drilled holes 3, which is beneficial for the complete electrolytic reaction and improves the accuracy of the electrolytic grinding.

[0029] A grinding head for electrolytic grinding of micro-holes, wherein the machining of through holes includes the following steps, characterized in that:

[0030] S1: The tool cathode is vertically clamped along the axial direction on the milling machine tool holder, and the metal workpiece to be processed is clamped on the fixture, wherein the tool electrode is connected to the negative terminal of the electrolytic power supply 8, and the workpiece electrode 4 is connected to the positive terminal of the electrolytic power supply 8.

[0031] S2: Adjust the spatial position of nozzle 6, adjust the distance between nozzle 6 and pre-drilled hole 3 to 4-5cm, and align nozzle 6 with guide rod 1;

[0032] S3: Start the electrolysis power supply 8 with a voltage of 6V, turn on the electrolyte circulation system 5, and spray the electrolyte 7 from the nozzle 6 in the form of a jet at a flow rate of 2L / min to the guide rod 1, and flow along the guide rod 1 to the pre-drilled hole 3.

[0033] S4: Adjust the grinding head speed to 1000 r / min, operate the motion control system to feed the grinding head downwards, and start the grinding process;

[0034] S5: The tool cathode rotates downward along the pre-drilled hole 3 to perform grinding electrolytic machining. The electrolyte flows in along the spiral groove 2-4 and fully contacts the cylindrical grinding part 2-1 of the electrolytic grinding head and the pre-drilled hole 3. Then it flows out from the spiral groove 2-4 and the electrolytic products are discharged in time. The surface material of the pre-drilled hole 3 is removed under the combined action of electric field, flow field and friction force, and its surface quality and roughness are greatly improved.

[0035] S6: After the through hole is processed, turn off the electrolytic power supply 8, move the grinding head out of the processing area, turn off the electrolyte, and the processing is complete.

Claims

1. A grinding head for electrolytic grinding of micro-holes, comprising a resilient tool holder (1) and a combined grinding head (2), characterized in that: The combined grinding head (2) includes a cylindrical grinding section (2-1) and a hemispherical grinding section (2-2); the elastic tool holder (1) includes an elastic central rod (1-1) and an electrically insulating layer (1-2); the hemispherical grinding section (2-2) is located at the front end of the cylindrical grinding section (2-1), and the axes of the two are collinear; the elastic tool holder (1) and the cylindrical grinding section (2-1) are fixedly connected coaxially; the substrate of the cylindrical grinding section (2-1) is made of conductive material; the substrate of the hemispherical grinding section (2-2) is made of electrically insulating elastic material; the surface of the combined grinding head (2) is provided with a spiral groove (2-4) and an electrically insulating abrasive layer (2-3) is adhered thereto.

2. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The surface of the combined grinding head (2) is provided with spiral grooves (2-4).

3. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The elastic center rod (1-1) is made of titanium alloy or amorphous alloy material.

4. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The electrical insulation layer (1-2) has a thickness of 0.05-0.1 mm and is made of acid and alkali resistant polymer or ceramic materials.

5. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The base material of the cylindrical grinding part (2-1) is stainless steel.

6. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The thickness of the electrically insulating abrasive layer (2-3) is 0.02-0.03 mm, and the particle size of the abrasive particles in the electrically insulating abrasive layer (2-3) is 0.01-0.02 mm.

7. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The diameter of the elastic tool holder (1) is at least 0.1 mm smaller than the outer diameter of the cylindrical grinding part (2-1).

8. A grinding head for electrolytic grinding of micro-holes according to claim 1, characterized in that: The spiral groove (2-4) has a groove width of 0.5-1mm, a depth of 0.05-0.1mm, and a pitch of 3-5mm.

Images