A cycloid rough machining method for outer wrapping groove of inverted T-shaped blade root of steam turbine blade

Abstract

A cycloidal roughing method for the outer groove of an inverted T-shaped turbine blade root is disclosed. This invention relates to the field of turbine blade machining. Existing methods for roughing and finishing the outer groove of an inverted T-shaped blade root use radially fed form milling cutters. These cutters are custom-made according to the contour of the outer groove, resulting in high manufacturing costs and the need for complete replacement after wear. This invention includes the following steps: the inverted T-shaped outer groove structure of the blade root is divided into two regions for milling. The inverted T-shaped groove is the first region, and the outer groove is treated as an independent roughing region, which is designated as the second region. An end mill is used in the second region. First, the first region is machined radially using an end mill A to remove excess material from the groove before machining the second region. The cycloidal toolpath is set to an elliptical structure, and the Ellipse Move command is selected, based on the dimensions of the blade outer groove and the diameter of the end mill B. This invention is applied to the field of machining inverted T-shaped turbine blade roots.

Description

Technical Field

[0001] This invention relates to the field of turbine blade processing, and specifically to a cycloidal roughing method for an inverted T-shaped blade root with an outer groove. Background Technology

[0002] The inverted T-shaped outer casing of the turbine blade is a key part connecting the blade to the turbine disk, and its machining accuracy directly affects the assembly performance and operational safety of the blade.

[0003] In existing technologies, both roughing and finishing of the outer groove of the inverted T-shaped blade root are done using radially fed form milling cutters. These cutters are custom-made according to the contour of the outer groove, resulting in high manufacturing costs and requiring replacement after wear. The roughing stage involves significant material removal, and frequent cutter replacements not only reduce machining efficiency but also increase the machining allowance and difficulty of finishing. Furthermore, due to the excessively large tool length-to-diameter ratio, radial cutting and chip removal are difficult, making it highly susceptible to tool breakage, blade damage, or chatter marks at the groove bottom during finishing due to excessive allowance.

[0004] Therefore, there is an urgent need for a roughing method for the outer groove of the inverted T-shaped blade root that can reduce tooling costs and improve roughing efficiency and stability. Summary of the Invention

[0005] To address the problem that existing methods for roughing and finishing inverted T-shaped blade root outer grooves use radially fed forming milling cutters, which are customized according to the contour of the outer groove, resulting in high manufacturing costs and the need for complete replacement after wear, this invention provides a cycloidal roughing method for inverted T-shaped blade root outer grooves of steam turbine blades.

[0006] The technical solution of this invention is:

[0007] A cycloidal rough machining method for an inverted T-shaped blade root groove of a steam turbine blade, the method comprising the following steps:

[0008] Step 1: Define the processing area:

[0009] The inverted T-shaped outer structure blade root is divided into two areas for milling. The inverted T-shaped groove is the first area, and the outer groove is an independent rough milling area, which is the second area.

[0010] Step 2: Tool Selection

[0011] Based on the machining area in step one, the second area uses an end mill;

[0012] Step 3: Cycloidal path planning:

[0013] First, process the first area radially using end mill A in the traditional manner to remove excess material from the groove, and then process the second area.

[0014] Step 4: Cycloidal parameter settings:

[0015] The cycloidal toolpath is set to an elliptical structure. Select the Ellipse Move command and adjust the size of the blade's outer groove and the diameter of the end mill B according to the dimensions of the end mill B.

[0016] Step 5: Subsequent Processing

[0017] After rough milling, the second area is finished milled using existing forming milling cutters to ensure the final dimensional accuracy and surface quality of the outer structure.

[0018] Furthermore, the machining tool selection is based on the method described in step two:

[0019] Step 21: Selecting the diameter of the cutting tool:

[0020] The diameter of the cutting tool is determined based on the width of the outer groove, and the cutting tool is smaller than the minimum width of the outer groove;

[0021] Step 22: Selecting the cutter length:

[0022] The cutting edge length of the tool should be sufficient to completely cover the radial depth of the groove when machining in both the inner and outer radial directions.

[0023] Furthermore, in step two, the second area of ​​the machining tool selection uses an end mill, which is a non-forming tool.

[0024] Furthermore, based on the cycloidal path planning described in step three:

[0025] Step 31: Processing trajectory in the second area:

[0026] The second area is changed to end mill B to process along the blade height direction. The tool path adopts cycloidal machining, that is, while end mill B makes a circular motion with a preset radius, it continuously feeds along the blade height direction, superimposed with the cycloidal motion of the preset radius, forming a composite trajectory of spiral propulsion cutting trajectory.

[0027] Step 32: Machining the T-shaped outer groove area:

[0028] The inverted T-shaped outer groove is machined separately in the inner and back radial directions. That is, the end mill B is used to machine half the depth of the inverted T-shaped outer groove in the blade root and in the back radial direction to ensure that there are no unmachined areas after machining.

[0029] Furthermore, according to the cycloidal parameter settings described in step four:

[0030] Step 41: Setting the width of milling cutter B:

[0031] Width = (Width of outer groove - Diameter of end mill B) ÷ 2 - Semi-finish allowance, where the semi-finish allowance is 0.1;

[0032] Step 42: Setting the milling cutter B step length value:

[0033] The step size is set to 0.1;

[0034] Step 43: Setting the feed rate and cutting speed of milling cutter B:

[0035] Feed rate and cutting speed are set according to the blade material and tool diameter.

[0036] Furthermore, according to the definition of the independent rough milling area in the machining area in step one, the rough milling area is defined as a groove with a width of 6.5mm, a radial depth of 20.8mm, and a blade height direction depth of 5mm.

[0037] Furthermore, according to the tool selection described in step two, a carbide end mill with a diameter of 6mm is selected based on the blade groove width of 6.5mm.

[0038] Furthermore, according to the cycloidal path setting in the cycloidal path planning described in step three, when the tool enters the groove, the 6mm diameter end mill must enter the groove from the outside and must not touch the unmachined part. The milling depth in the inner radial direction and the back radial direction is 12mm respectively.

[0039] Furthermore, according to the cycloidal parameter settings described in step four, when the feed speed is 150 mm / min, the spindle speed is 5000 rpm, and the feed per tooth is 0.0075 mm;

[0040] Width = (6.5 - 6) ÷ 2 - 0.1 = 0.15;

[0041] Set the step size to 0.1.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] This invention improves the machining accuracy and quality of the blade root by reconstructing the machining direction and adjusting the combination strategy of roughing and finishing tools, thus overcoming the problems of high cost and low efficiency caused by the reliance on forming milling cutters in the roughing of the inverted T-shaped outer structure in the prior art.

[0044] This invention reduces tooling costs (data calculated based on implementation case products). The outer groove uses a general-purpose end mill (cost 600 RMB / piece) instead of a dedicated form milling cutter (2000 RMB / piece). The form milling cutter is only used after finishing, increasing its lifespan by more than three times.

[0045] The invention reduces overall costs by 75%. For example, the cost of 150 blades in a certain unit is reduced from 18,000 yuan to 4,000 yuan.

[0046] This invention improves processing efficiency, with roughing time reduced by 88%, such as reducing the roughing time of a single blade from 23.17 min to 2.32 min.

[0047] This invention improves machining quality and solves the contour error caused by large vibration of the forming milling cutter in traditional machining. The cutting force fluctuation of cycloidal milling is significantly reduced, and there are no tool breakage or groove bottom chattering phenomena. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the inverted T-shaped outer casing blade structure of the present invention;

[0049] Figure 2 for Figure 1 Schematic diagram of the first and second regions of the intermediate milling process;

[0050] Figure 3 This is a schematic diagram of the structure of the first area when machining in the radial direction using end mill A in the traditional way, where the toolpath is represented by pink dashed lines;

[0051] Figure 4 This is a schematic diagram of the structure when the second region is machined radially using a conventional forming milling cutter.

[0052] Figure 5 This is a schematic diagram of the structure of end mill B when machining along the blade height direction, where the compound trajectory is a pink spiral line;

[0053] Figure 6 A structural diagram illustrating the machining dimensions of the inverted T-shaped outer leaf root;

[0054] Figure 7 yes Figure 6 The left view in the middle; Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Specific implementation method one:

[0057] Combination Figure 1 — Figure 5 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade;

[0058] Step 1: Define the processing area:

[0059] The inverted T-shaped outer structure blade root is divided into two parts for milling: the inverted T-shaped groove is the first area, and the outer groove is an independent rough milling area, i.e., the second area.

[0060] Step 2: Tool Selection

[0061] Figure 2 The second area uses a general-purpose end mill (non-form cutter). The diameter of the cutter is determined according to the width of the outer groove (it should not be too small, nor should it be greater than the minimum width of the outer groove). The cutting edge length should be sufficient to completely cover the radial depth of the groove when machining in both the inner and outer radial directions.

[0062] Step 3: Cycloidal path planning:

[0063] First, machine the first area radially using end mill A, as is traditionally done. The toolpath is represented by the pink dotted line. Figure 3 As shown, the purpose is to remove excess material from the groove. Then, the second area is processed.

[0064] Figure 2 The second region is machined radially by a conventional form milling cutter, such as... Figure 4 As shown, instead, use end mill B to machine along the blade height direction, as follows. Figure 5 As shown. The toolpath uses cycloidal machining, meaning that the end mill B makes a circular motion with a preset radius while continuously feeding along the blade height direction. This, combined with the preset radius cycloidal motion, forms a composite trajectory of spiral propulsion cutting, as shown. Figure 5 The pink spiral in the middle.

[0065] Because the inverted T-shaped outer groove of the blade is small and the end mill B is typically small in diameter, machining through the radial depth would cause tool wear and significant vibration. Therefore, the inverted T-shaped outer groove is machined separately in the inner and outer radial directions. Specifically, the end mill B is used to machine half the depth of the inverted T-shaped outer groove both inside the blade root and in the outer radial direction, ensuring no unmachined areas remain after machining. Figure 5 As shown.

[0066] Step 4: Cycloidal parameter settings:

[0067] Set the cycloidal toolpath to an elliptical structure, select the Ellipse Move command, and then set the corresponding values ​​as follows based on the dimensions of the blade's outer groove and the diameter of the end mill B:

[0068] Width = (Width of outer groove - Diameter of end mill B) ÷ 2 - Semi-finish allowance (usually 0.1);

[0069] The step size is set to 0.1;

[0070] Feed rate and cutting speed are set according to the blade material and tool diameter.

[0071] Step 5: Subsequent Processing

[0072] After rough milling, use an existing form milling cutter to mill the second area, such as... Figure 2 As shown, precision milling is performed to ensure the final dimensional accuracy and surface quality of the outer structure. Specific Implementation Method Two:

[0074] Combination Figure 6 and Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade;

[0075] Taking the inverted T-shaped outer blade root structure of a certain type of steam turbine blade as an example (dimensions as follows) Figure 6 Processing using this method:

[0076] Define the rough milling area as a groove with a width of 6.5 mm, a radial depth of 20.8 mm, and a depth of 5 mm in the blade height direction.

[0077] Based on the blade groove width of 6.5mm, select a carbide end mill with a diameter of 6mm.

[0078] Cycloidal path settings. When feeding, the 6mm diameter end mill must feed from outside the outer groove, avoiding contact with unmachined areas. The milling depth in the inner and back radial directions is 12mm respectively.

[0079] Cutting parameters. Based on the cycloidal parameter settings described in step four, when the feed rate is 150 mm / min, the spindle speed is 5000 rpm, and the feed per tooth is 0.0075 mm;

[0080] Width = (6.5 - 6) ÷ 2 - 0.1 = 0.15; Step size is set to 0.1. Specific implementation method three:

[0082] Combination Figure 1 — Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade, based on the machining area defined in step one:

[0083] The locking T-shaped outer casing blade is cleverly divided into two parts for milling. The locking T-groove is defined as Region 1, while the outer casing groove is a separate milling area, Region 2. This division helps to select the most suitable machining strategy and tools based on the characteristics and machining requirements of different regions, thereby improving machining efficiency and quality. Specific implementation method four:

[0085] Combination Figure 1 — Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade, based on the tool selection in step two:

[0086] for Figure 2 Area 2 is machined using a general-purpose end mill (non-form cutter). The diameter of the cutter needs to be precisely determined based on the width of the outer groove. It cannot be too small, otherwise it will increase the number of machining passes and time, reducing efficiency; nor can it be larger than the minimum width of the outer groove, so as not to prevent effective machining. At the same time, the cutting edge length must be sufficient to completely cover the radial depth of the groove when performing bidirectional machining on the inner back and radial sides, to ensure the integrity and accuracy of the machining. Specific implementation method five:

[0088] Combination Figure 1 — Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade, based on the cycloidal path planning in step three:

[0089] First, region 1 is machined radially using milling cutter A according to traditional machining methods (the toolpath is a radial straight line, such as...). Figure 3 As shown. The main purpose of this step is to remove excess material from the groove, preparing it for subsequent finishing. After completing the machining of the first area, the machining of the second area will proceed.

[0090] Will Figure 2 The second region is machined radially by a conventional form milling cutter, such as... Figure 4 As shown, instead, use end mill B to machine along the blade height direction, as follows. Figure 5 As shown. The specific machining method is cycloidal machining, that is, the end mill B makes a circular motion with a preset radius, while continuously feeding along the blade height direction. The superimposed cycloidal motion of the preset radius forms a composite trajectory of spiral propulsion cutting path, as shown. Figure 5 The pink spiral trajectory in the image.

[0091] Because the outer groove of the locking T is relatively small, the end mill B experiences a sharp increase in tool wear during normal radial depth machining, affecting machining quality and tool life. Therefore, for the outer groove of the locking T, we adopt a separate inner and outer radial machining method. That is, the end mill B is used to machine half the depth of the outer groove of the locking T in both the inner and outer radial directions within the blade root. This effectively reduces tool wear during machining, ensures no unmachined areas after machining, and guarantees machining accuracy and integrity. Specific implementation method six:

[0093] Combination Figure 1 — Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade, based on the cycloidal parameter settings in step four:

[0094] Set the cycloidal toolpath to an elliptical structure and select the EllipseMove command. Then, set the corresponding values ​​according to the dimensions of the blade's outer groove and the diameter of the end mill B.

[0095] The formula for calculating the width is: (outer groove width - end mill B diameter) ÷ 2 + half the finishing allowance (usually 0.1). This width setting needs to consider both the actual size of the outer groove and the diameter of the end mill to ensure that the trochoidal machining can cover the entire groove area, while reserving an appropriate finishing allowance to guarantee subsequent finishing.

[0096] The step size is set to 0.1. The choice of step size directly affects the machining accuracy and efficiency. A smaller step size can improve machining accuracy but increase machining time; a larger step size will reduce machining accuracy but improve machining efficiency. After comprehensive consideration, the step size is set to 0.1 to maximize machining efficiency while ensuring machining accuracy.

[0097] The feed rate and cutting speed need to be set according to the blade material and tool diameter. Different blade materials and tool diameters have different requirements for feed rate and cutting speed. For example, for blade materials with high hardness, the feed rate and cutting speed need to be appropriately reduced to reduce tool wear; while for larger tool diameters, the feed rate and cutting speed also need to be adjusted accordingly to ensure machining stability and safety. Specific implementation method seven:

[0099] Combination Figure 1 — Figure 7 This embodiment describes a cycloidal rough machining method for an inverted T-shaped blade root outer groove of a steam turbine blade, based on the subsequent machining in step five:

[0100] After rough milling, use the existing form milling cutter to mill the second region 2, such as... Figure 2 As shown, finish milling is performed. The purpose of finish milling is to ensure the final dimensional accuracy and surface quality of the outer structure. During finish milling, machining parameters, such as feed rate and cutting speed, need to be strictly controlled to ensure that the dimensional accuracy after machining meets the requirements, while also achieving the expected surface quality. Through finish milling, machining marks left during rough milling can be removed, making the surface of the outer structure smoother and flatter, improving its assembly performance and operational safety.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A cycloidal roughing method for an outer wrap groove of an inverted T-shaped blade root of a steam turbine blade, characterized by, The method includes the following steps: Step 1: Define the processing area: The inverted T-shaped outer structure blade root is divided into two areas for milling. The inverted T-shaped groove is the first area, and the outer groove is an independent rough milling area, which is the second area. Step 2: Tool Selection Based on the machining area in step one, the second area uses end mill B; Step 3: Cycloidal path planning: First, process the first area radially using end mill A in the traditional manner to remove excess material from the groove, and then process the second area. Step 4: Cycloidal parameter settings: The cycloidal toolpath is set to an elliptical structure. Select the Ellipse Move command and adjust the size of the blade's outer groove and the diameter of the end mill B according to the dimensions of the end mill B. Step 5: Subsequent Processing After rough milling, the second area is finished milled using existing form milling cutters to ensure the final dimensional accuracy and surface quality of the outer structure; Based on the cycloidal path planning described in step three: Step 31: Processing trajectory in the second area: The second area is changed to end mill B to process along the blade height direction. The tool path adopts cycloidal machining, that is, while end mill B makes a circular motion with a preset radius, it continuously feeds along the blade height direction, superimposed with the cycloidal motion of the preset radius, forming a composite trajectory of spiral propulsion cutting trajectory. Step 32: Processing the outer groove area: The outer groove is machined separately in the inner and back radial directions, that is, half the depth of the outer groove is machined in the blade root and in the back radial direction using end mill B, to ensure that there are no unmachined areas after machining. Set the cycloidal parameters as described in step four: Step 41: Setting the width of milling cutter B: Width = (outer groove width - end mill B diameter) ÷ 2 - semi-finishing allowance, where the semi-finishing allowance is 0.1; Step 42: Setting the milling cutter B step length value: The step size is set to 0.1; Step 43: Setting the feed rate and cutting speed of milling cutter B: The feed rate and cutting speed are set according to the blade material and the tool diameter.

2. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 1, characterized in that, Select the machining tool as described in step two: Step 21: Selecting the diameter of the cutting tool: The diameter of the cutting tool is determined based on the width of the outer groove, and the cutting tool is smaller than the minimum width of the outer groove; Step 22: Selecting the cutter length: The cutting edge length of the tool should be sufficient to completely cover the radial depth of the groove when machining in both the inner and outer radial directions.

3. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 2, characterized in that, In step two, the second area of ​​the machining tool selection uses an end mill, which is a non-forming tool.

4. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 1, characterized in that, According to the definition of the independent rough milling area in the machining area in step one, the rough milling area is defined as a groove with a width of 6.5mm, a radial depth of 20.8mm, and a blade height direction depth of 5mm.

5. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 1, characterized in that, As described in step two, the machining tool used is end mill B. Based on the blade groove width of 6.5mm, a carbide end mill with a diameter of 6mm is selected.

6. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 1, characterized in that, According to the cycloidal path setting in the cycloidal path planning described in step three, when the tool is fed in, the 6mm diameter end mill B must be fed in from the outside of the outer groove and must not touch the unmachined part. The milling depth in the inner radial direction and the back radial direction is 12mm respectively.

7. The cycloidal rough machining method for the inverted T-shaped blade root outer groove of a steam turbine blade according to claim 5, characterized in that, According to the cycloidal parameter settings described in step four, when the feed speed is 150 mm / min and the spindle speed is 5000 rpm, the feed per tooth is 0.0075 mm. Width = (6.5 - 6) ÷ 2 - 0.1 = 0.15; Set the step size to 0.1.

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