A method for anti-chattering layered processing of a U-shaped groove of a nuclear power valve

Abstract

The application discloses a kind of anti-chatter layered processing method for nuclear power valve U-shaped groove, specifically relates to a kind of high-precision, deep groove class part numerical control milling method, especially a kind of anti-chatter layered processing method for U-shaped groove on nuclear power valve seat and other key components.The method of the application is: tool selection;Rough machining - triangular shape layered milling;Finish machining.Through the "triangular shape" layered strategy, the large cutting volume is decomposed into multiple small processing units, which greatly reduces the contact area and lateral force of single cutting of the tool, fundamentally reduces the cutting resistance and torque, avoids tool deformation and machining chatter.The application can ensure smooth and vibration-free during processing, and the tool does not break. The groove bottom surface is smooth and free of chatter marks, and the roughness Ra value is stable below 3.2 μm. The processing time of a single piece is shortened by about 60% compared to the original process, and the tool life is increased by more than 8 times. The application is applied to the field of mechanical processing technology.

Description

Technical Field

[0001] This invention relates to a method for anti-flutter layering processing of U-shaped grooves for nuclear power plant valves. Background Technology

[0002] When manufacturing nuclear power plant units, nuclear power valves are key equipment for the safe operation of nuclear power units, and the processing quality requirements for their core components (such as air intake valve seats) are extremely stringent. These parts typically have a U-shaped groove structure, characterized by a large depth-to-diameter ratio, limited processing space, and high surface quality requirements (usually requiring Ra < 3.2 μm).

[0003] In existing technologies, U-groove machining is generally performed by directly cutting with large-sized tools, which has many inherent drawbacks:

[0004] 1. Tool breakage is common: Due to the deep grooves, the tool's length-to-diameter ratio is too large, resulting in insufficient rigidity. During integral cutting, the large contact area between the tool and the workpiece generates enormous cutting resistance and torque, which can easily lead to tool flexural deformation or even breakage.

[0005] 2. Machining chatter: Under high cutting resistance, the machining system (machine tool-cutting tool-workpiece) is prone to vibration, leaving chatter marks that are difficult to eliminate on the bottom and sidewalls of the groove. The surface finish cannot meet the standards, which seriously affects the sealing performance of the product.

[0006] 3. Difficulty in chip removal and heat dissipation: In deep groove machining, it is difficult to remove iron chips. The accumulation of chips in the groove will not only scratch the machined surface, but also cause the temperature of the cutting zone of the tool to rise sharply (burning tool), which will aggravate tool wear.

[0007] 4. Low processing efficiency: To avoid the above risks, extremely low feed rates (such as 0.1 mm / min) are usually required, which severely restricts production efficiency and becomes a production bottleneck.

[0008] Therefore, there is an urgent need for a deep U-groove machining method that can effectively solve the above problems and achieve high-quality, high-efficiency, and stable machining. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a method for anti-chatter layered machining of U-grooves in nuclear power plant valves. This method, through unique toolpath planning and cutting parameter optimization, effectively reduces cutting resistance, suppresses machining chatter, and improves chip removal conditions, thereby significantly increasing tool life and production efficiency while ensuring machining quality.

[0010] The present invention discloses a method for anti-flutter layering processing of U-grooves for nuclear power plant valves, which is carried out according to the following steps:

[0011] I. Tool Selection: Use a right-angle cutter for roughing and a rounded-corner cutter for finishing;

[0012] II. Rough Machining - Layered Milling: Layered milling is performed on the U-shaped groove, wherein the layered milling method comprises center groove milling for the first layer, side wall milling for the first layer and repeated layered milling until the final depth is reached; wherein the first layer milling is milling the center groove to a first predetermined depth H1 along the center line of the U-shaped groove, the side wall milling for the first layer is performed at the same depth layer H1, milling along the left side wall and right side wall of the U-shaped groove to remove the allowance on both sides, so that the center groove of the depth layer communicates with the regions on both sides to form a flat plane, and the repeated layered milling is repeating the steps of center milling and side wall milling downward layer by layer until the predetermined final depth of the center groove is reached; wherein for each new depth layer, the center region is first machined to the predetermined depth Hn of the current layer, and then the two side regions are machined to the same depth Hn; the layered milling forms a "pin-shaped" or "stepped" tool path;

[0013] III. Finish Machining: After the rough machining reaches the final depth, the round-nose cutter is replaced, and the circular interpolation programming method is used to perform finish machining along the theoretical profile of the U-shaped groove to smooth and joint the groove bottom and the side walls, thus completing the processing.

[0014] Beneficial effects of the present invention:

[0015] 1. Significant load reduction and vibration prevention: Through the "pin-shaped" layering strategy, the large cutting volume is decomposed into a plurality of small processing units, which greatly reduces the contact area and lateral force of the tool in a single cutting, fundamentally reduces the cutting resistance and torque, and avoids tool deformation and processing chatter.

[0016] 2. Optimized chip removal and heat dissipation: The alternate layered path provides sufficient discharge space for chips, and in combination with high-pressure cooling, effectively avoids chip blockage, winding and the resulting tool wear and overheating of the processing area.

[0017] 3. Improved processing quality and efficiency: Chatter marks are fundamentally eliminated, and the surface quality stably meets the standard (Ra<3.2μm). The tool life is increased by multiple times, and meanwhile, due to the improved cutting conditions, a higher feed speed can be adopted, so the processing efficiency is significantly improved.

[0018] 4. Strong versatility: The method is not only applicable to nuclear power valves, but also has important reference and promotion value for processing difficult-to-process materials, deep cavity and chatter-prone parts in other fields such as aerospace and energy equipment. Description of Drawings

[0019] Figure 1 is a schematic diagram of the pin-shaped layered milling of the present invention;

[0020] Figure 2 is a schematic diagram after integral milling and finish machining in the prior art;

[0021] Figure 3 is the circular interpolation program of the processing method of the present invention. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is not limited to the specific embodiments listed below, and also includes any combination between the respective specific embodiments.

[0023] Specific Embodiment 1: The anti-chatter layered processing method for a U-shaped groove of a nuclear power valve in this embodiment is carried out according to the following steps:

[0024] Step 1: Tool selection: a square shoulder cutter is selected for rough machining, and a radius cutter is selected for finish machining;

[0025] Step 2: Rough machining - layered milling: layered milling is performed on the U-shaped groove, the layered milling method comprises first center slot milling of the first layer, then side wall milling of the first layer, and repeated milling layer by layer until the final depth is reached; wherein the first layer milling is milling the center slot to a first predetermined depth H1 along the center line of the U-shaped groove, the first layer side wall milling is milling to remove allowances on both sides along the left side wall and the right side wall of the U-shaped groove at the same depth layer H1, so that the center slot of the depth layer is communicated with the areas on both sides to form a flat plane, the layered repeated milling is repeating the steps of center milling and side wall milling layer by layer downward until the predetermined final depth of the center slot is reached; wherein, for each new depth layer, the center area is first processed to the predetermined depth Hn of the current layer, and then the areas on both sides are processed to the same depth Hn; the layered milling forms a "pin-shaped" or "stepped" tool path;

[0026] Step 3: Finish machining: after the rough machining reaches the final depth, the radius cutter (ball end milling cutter) is replaced, and the circular interpolation programming mode is adopted to perform finish machining along the theoretical profile of the U-shaped groove to smoothly connect the groove bottom and the side walls, thus completing the processing.

[0027] wherein the specific method of the circular interpolation is as follows:

[0028] (1) Machining plane selection

[0029] The G18 command is used to select the X-Z machining plane, so that the tool performs circular interpolation movement in the plane formed by the X-axis and the Z-axis, and finish machining of the arc contour of the groove bottom of the U-shaped groove is completed.

[0030] (2) Circular direction command

[0031] The G03 counterclockwise circular interpolation command is adopted to machine the arc of the groove bottom, so that the tool moves continuously from the theoretical tangent point of the right side wall and the groove bottom arc to the theoretical tangent point of the left side wall and the groove bottom arc; when the machining direction is opposite, the G02 clockwise circular interpolation can be adopted.

[0032] (3) Definition of circular geometric parameters

[0033] The tool radius parameter is set to R4, and the geometric relationship of the tool center trajectory is established according to the design dimensions of the U-shaped groove. The starting point of the arc, R1, is determined by the theoretical tangency point between the right side wall and the bottom arc of the groove. The tool first rapidly positions itself to the X=R1 position, then feeds linearly along the Z-axis to the starting height of the bottom arc. Incremental compensation of the tool radius R4 is used along the Z-axis to bring the tool center to the starting position of the circular interpolation. The X coordinate is R1, and the Z coordinate is determined by the groove depth and the tool radius. The ending point of the arc is located at the theoretical tangency point between the left side wall and the bottom arc of the groove. It is defined using incremental coordinates, moving R2 relative to the starting point along the negative X-axis and R2 along the negative Z-axis. This is achieved by executing G03 X=-R2 Z=-R2 CR=R2 to complete the circular interpolation, where R2 = the groove width design value minus the tool radius R4. The arc radius is defined using the CR radius programming method, with a radius value of CR=R2. When machining an arc with an included angle less than 180°, a positive radius value is used; when machining an arc with an included angle greater than 180°, a negative radius value is used.

[0034] (4) Profile adaptation relationship

[0035] After rough machining, the bottom of the groove retains a stepped allowance formed by the triangular layered cutting. During finishing, the endpoint of the straight finishing trajectory of the sidewall serves as the starting point of the circular interpolation trajectory. The endpoint of the circular interpolation trajectory is theoretically tangent to the starting point of the straight finishing trajectory of the other sidewall, ensuring a smooth and continuous transition between the groove bottom arc and the left and right sidewalls. Because the groove bottom arc is formed in one step using single-segment circular interpolation, the stepped residue formed by rough machining can be effectively removed, achieving a seamless connection between the groove bottom arc and the sidewalls, thus improving the contour accuracy and surface quality of the U-shaped groove. In this embodiment, the groove bottom machining is completed using a single-segment circular arc, therefore there is no multi-segment circular arc splicing; when multi-segment circular arc machining is used, the endpoint of each segment coincides with the starting point of the next segment, maintaining tangential continuity.

[0036] (5) Range of process parameters

[0037] Preferably, during finishing, the tool is first rapidly positioned to a safe approach height Z = 5 mm, then fed along a straight path to the starting position of circular interpolation, and then the circular interpolation is performed to complete the finishing of the groove bottom. After machining, the tool is retracted to a safe height Z = 20 mm. The spindle speed S is preferably 7–15 r / min, the feed rate F is preferably 0.5–2 mm / min, and the depth of cut ap is preferably 0.05–0.30 mm. The above process parameters can be adjusted according to the workpiece material, tool specifications, and machine tool performance.

[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the diameter of the right-angle cutter mentioned in step one is smaller than the width of the U-shaped groove, preferably φ8mm. Everything else is the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the radius (R) of the rounded corner cutter described in step one is smaller than the radius of the groove bottom, and the preferred diameter is φ9mm. Everything else is the same as in Specific Implementation Method One or Two.

[0040] Specific Implementation Method Four: This implementation method differs from one of Specific Implementation Methods One to Three in that the first predetermined depth H1 in step two is 4-8 mm. Everything else is the same as in one of Specific Implementation Methods One to Three.

[0041] Specific Implementation Method Five: This implementation method differs from one of Specific Implementation Methods One to Four in that the first predetermined depth H1 in step two is 6 mm. Everything else is the same as in one of Specific Implementation Methods One to Four.

[0042] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the depth increment for each layer ranges from 2 to 6 mm. Everything else is the same as in Specific Implementation Methods One to Five.

[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: during the rough machining process in Step Two, high-pressure coolant is used for forced cooling and chip removal. Everything else is the same as in Specific Implementation Methods One through Six.

[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the processing method is applicable to nuclear power valve seats made of austenitic stainless steel, duplex stainless steel, or high-temperature alloys. Everything else is the same as in Specific Implementation Methods One to Seven.

[0045] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0046] Example 1

[0047] An example of machining a U-shaped groove for the inlet valve seat of a nuclear power plant valve. The U-shaped groove is approximately 18.5 mm wide and 25 mm deep, with an R9 spherical bottom.

[0048] The processing method is as follows:

[0049] 1. Clamp the workpiece on a five-axis CNC milling machine and align it.

[0050] 2. Select a φ7.8mm right-angle cutter, with a rotation speed S=10rpm and a feed rate F=1mm / min.

[0051] 3. Perform rough machining in a "triangular" layered pattern:

[0052] Step 1: Mill the center of the groove to a depth of 6mm. See Figure 1 Middle ①

[0053] Step 2: Mill the left and right sides separately, to a depth of 6mm each. See Figure 1 Middle ②

[0054] Step 3: Return to the center and mill to a depth of 12mm. See Figure 1 Middle ③

[0055] Step 4: Mill the left and right sides separately, to a depth of 12mm each. See Figure 1 Middle ④

[0056] Step 5: Return to the center and mill to a depth of 16mm. See Figure 1 Middle ⑤

[0057] Step 6: Mill the left and right sides separately, to a depth of 16mm each. See Figure 1 Middle ⑥

[0058] Step 7: Finally, mill the center to a depth of 24.18 mm. See Figure 1 Middle ⑦

[0059] 4. Replace with a φ9mm R-angle cutter, with a rotation speed S=10rpm and a feed rate F=2mm / min.

[0060] 5. Write a circular interpolation program to finish mill the R9 spherical surfaces on both sides and bottom of the U-shaped groove, ensuring a smooth finish to meet the dimensions and surface finish requirements specified in the drawing. The circular interpolation finishing process should be performed using the following parametric programming method: Figure 3 :

[0061] First, select the XZ machining plane using the G18 command; set the tool radius parameter to R4, and define the following geometric relationships based on the actual groove width and depth before finishing the U-groove:

[0062] The starting point of the arc is determined by the theoretical tangent point between the right side wall and the bottom arc of the groove. The X coordinate is R1, and the Z coordinate is given by the groove depth and the tool radius.

[0063] Arc endpoint: X = -R2, Z = -R2, where R2 = groove width design value 8mm - R4;

[0064] Arc radius: CR = R2;

[0065] Arc direction: Using the G03 counterclockwise arc interpolation command, combined with the CR=radius programming method, the bottom arc milling of the groove is completed in one go.

[0066] As a specific example, when using a tool with a diameter of φ7.8mm, R4 = 3.9mm; when the groove width design value is set to 8mm, R2 = 8 - 3.9 = 4.1mm; the sidewall offset R1 = 9.25 - 3.9 - 1 = 4.35mm. During finishing, the tool is first rapidly positioned to X = R1, then fed linearly to the starting point of the arc, and then G03 X=-R2 Z=-R2 CR=R2 is executed to complete the arc trajectory of this layer. After machining, the tool retracts to a safe height Z=20 and resets the geometric axis configuration.

[0067] Those skilled in the art can directly replace the assigned values ​​of R4, R2, and R1 according to the actual groove width and tool diameter, and adapt to different specifications of U-shaped grooves without modifying the programming framework.

[0068] This invention provides a smooth, vibration-free machining process with no tool breakage, a smooth groove bottom surface free of chatter marks, and a surface roughness Ra value consistently below 3.2 μm. The machining time per piece is reduced by approximately 60% compared to the original process, and tool life is increased by more than 8 times.

Claims

1. A method for anti-chatter layering processing of U-shaped grooves for nuclear power plant valves, characterized in that, The processing method is carried out according to the following steps: I. Tool Selection: Use a right-angle cutter for roughing and a rounded-corner cutter for finishing; II. Rough Machining - Layered Milling: The U-shaped groove is milled in layers. The layered milling method is as follows: first layer center groove milling, first layer side wall milling, and repeated layered milling until the final depth is reached. The first layer milling is to mill the center groove along the center line of the U-shaped groove to a first predetermined depth H1. The first layer side wall milling is to remove the excess material on both sides along the left and right side walls of the U-shaped groove at the same depth layer H1, so that the center groove of this depth layer is connected with the side areas to form a flat plane. The repeated layered milling is to repeat the above center milling and side wall milling steps layer by layer downwards until the predetermined final depth of the center groove is reached. In each new depth layer, the center area is first machined to the current layer's predetermined depth Hn, and then the side areas are machined to the same depth Hn.

3. Finishing: After the roughing reaches the final depth, switch to the rounded corner cutter and use the circular interpolation programming method to perform finishing along the theoretical profile of the U-shaped groove to smoothly connect the bottom and sidewalls of the groove, thus completing the process.

2. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, The diameter of the right-angle cutter mentioned in step one is smaller than the width of the U-shaped groove, preferably φ8mm.

3. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, The radius (R) of the rounded corner cutter mentioned in step one is smaller than the radius of the groove bottom, and the preferred diameter is φ9mm.

4. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, In step two, the first predetermined depth H1 is 4-8 mm.

5. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, In step two, the first predetermined depth H1 is 6 mm.

6. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, The depth increment for each layer ranges from 2 to 6 mm.

7. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, In step two, during the rough machining process, high-pressure coolant is used for forced cooling and chip removal.

8. The anti-chatter layering processing method for U-shaped grooves in nuclear power plant valves according to claim 1, characterized in that, The processing method is applicable to nuclear power valve seats made of austenitic stainless steel, duplex stainless steel or high-temperature alloys.

Images