Milling method of SA508-3 steel based on supercritical CO2 cooling

Abstract

The present invention discloses a SA508-3 steel milling processing method based on supercritical CO2 cooling, which adopts supercritical CO2 cooling milling to realize SA508-3 steel milling processing, which can give full play to the advantages of supercritical CO2 cooling, effectively utilize the dual effects of supercritical CO2 sublimation endothermic cooling and improving the lubrication conditions of the cutting zone, especially improve the lubrication cooling state of the cutting zone, reduce the cutting temperature, and improve the surface processing quality of the workpiece and the life of the tool. The strong cooling effect of the supercritical CO2 of the present invention can reduce the surface temperature of the workpiece and the tool, which is conducive to chip breaking and reduces the adhesion of chips on the tool surface, inhibits the generation of chip nodules on the tool surface, thereby ensuring the quality of the processed surface and improving the quality of the tool. The supercritical CO2 of the present invention is quickly sublimated after being sprayed into the cutting zone, and the gas expansion can effectively remove the chips in the cutting zone, reduce the adhesion of chips on the workpiece surface and the tool tip, and avoid the influence of chips on the surface processing quality.

Description

Technical Field

[0001] The present invention relates to the field of mechanical processing, and in particular to a SA508-3 steel milling method based on supercritical CO2 cooling. Background Art

[0002] SA508-3 steel has the characteristics of high strength, good toughness and low sensitivity to radiation embrittlement. It is widely used in core components such as nuclear power pressure vessels, evaporators and stabilizers. However, it has problems such as large cutting force, high temperature in the cutting area and severe tool wear during machining, resulting in poor surface roughness and flatness, which in turn leads to poor healing effect of the constructed interface, which is a technical bottleneck restricting the application of construction forming technology.

[0003] At present, there is little research and exploration on the milling of SA508-3 steel at home and abroad, and there is no suitable processing method, which leads to poor surface processing quality of SA508-3 steel and short tool life.

[0004] In the existing technology, in order to effectively reduce the cutting temperature and cutting force during the cutting process, cutting fluid is often used for lubrication and cooling. However, since the construction forming technology has high requirements for the cleanliness of the plate processing surface (≤10RFU), dry cutting is required for processing; the use of liquid nitrogen (-196℃) and dry ice (-78.5℃) low-temperature cooling milling processing technology can effectively improve the temperature of the cutting zone, but the lubrication effect is not good. However, the liquid nitrogen cooling temperature is too low (the cooling temperature can be as low as -196℃), which can easily cause low-temperature brittleness and cold work hardening of the processed material and thermal fatigue failure of the tool material, resulting in increased cutting force and thermal fatigue failure of the tool. Summary of the Invention

[0005] In order to solve the problems of large cutting force, high cutting zone temperature and severe tool wear in the milling of SA508-3 steel, the present invention provides a SA508-3 steel milling method based on supercritical CO2 cooling, which can effectively reduce the cutting temperature and tool wear while reducing the surface roughness of the workpiece and improving the cleanliness of the processed surface.

[0006] The technical means adopted by the present invention are as follows: a SA508-3 steel milling method based on supercritical CO2 cooling, comprising the following steps:

[0007] Step 1: Check and ensure that the working characteristics of each axis system of the CNC machining center are normal, and preheat the machine tool until it reaches thermal stability. The CNC machining center is placed in an ultra-precision machining laboratory with preset constant temperature, constant humidity and air cleanliness;

[0008] Step 2: Fix the SA508-3 steel workpiece on the vise of the machining center work platform;

[0009] Step 3: Clamp the tool and use the machining center's own measurement system to determine the machining origin;

[0010] Step 4: Rough cutting the SA508-3 steel workpiece using a carbide tool under preset cutting parameters, and generating a machining path based on the cutting parameters and tool parameters, wherein the preset cutting parameters include axial cutting depth, radial cutting depth, feed rate, and spindle speed;

[0011] Step 5. Connect the nozzle of the supercritical CO2 cooling device to the machine tool spindle, align the two nozzles with the tool tip, with a distance of 5 to 10 mm between the nozzle and the tool tip, and an angle of 30° to 40° between the nozzle and the axial direction of the machine tool spindle;

[0012] Step 6: Turn on the supercritical CO2 cooling device and adjust the output parameters of the supercritical CO2 cooling device, including the CO2 input pressure and the compressed air pressure, to focus the supercritical CO2 spray at the tip of the knife.

[0013] Step 7: Using an infrared thermometer to measure the nozzle outlet temperature of the supercritical CO2 cooling device, when the outlet temperature reaches a preset temperature range, using an Al2O3 coated carbide tool to finish-machine the SA508-3 steel workpiece under preset cutting parameters, and generating a machining path based on the cutting parameters and tool parameters;

[0014] Step 8: turn off the supercritical CO2 cooling device and the CNC machining center in sequence, remove the SA508-3 steel workpiece, dry it and store it, and obtain the SA508-3 steel machined surface processed by supercritical CO2 cooling milling.

[0015] Furthermore, the cutting parameters of the rough machining are set as follows: a p =0.5 mm, a e =20 mm, f z =0.2 mm, n =1200 r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n The spindle speed.

[0016] Furthermore, the CNC machining center is a three-axis CNC machining center having an X-axis, a Y-axis and a Z-axis.

[0017] Furthermore, the SA508-3 steel is in the shape of a cuboid with a length of 200 mm, a width of 100 mm, and a height of 50 mm.

[0018] Furthermore, the cemented carbide tool is an 85° parallelogram milling insert with an 11° clearance angle, and the cutting edge radius of the tool is 0.8 mm.

[0019] Furthermore, the Al2O3 coated cemented carbide tool is an 85° parallelogram milling insert with an 11° back angle, and the cutting edge radius of the tool is 0.8 mm.

[0020] Furthermore, the CO2 inlet pressure of the supercritical CO2 cooling device is set to 7.5 MPa.

[0021] Furthermore, the cutting parameters for the finishing process are set as follows: a p =0.2 mm, a e =20 mm, f z =0.1 mm, n =1800 r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n The spindle speed.

[0022] The present invention uses supercritical CO2 cooling milling to achieve SA508-3 steel milling. After rough machining of the workpiece, milling is performed using Al2O3-coated carbide tools under supercritical CO2 cooling conditions. Compared with other milling methods for SA508-3 steel, the present invention has the following advantages:

[0023] 1. The present invention can give full play to the advantages of supercritical CO2 cooling when milling SA508-3 steel by supercritical CO2 cooling, effectively utilize the dual effects of supercritical CO2 sublimation heat absorption cooling and improving the lubrication conditions of the cutting area, especially improving the lubrication and cooling state of the cutting area, reducing the cutting temperature, and improving the surface processing quality of the workpiece and the tool life.

[0024] 2. The powerful cooling effect of the supercritical CO2 of the present invention can reduce the surface temperature of the workpiece and the tool surface, increase the brittleness of the workpiece material to a certain extent, facilitate chip breaking and reduce chip adhesion on the tool surface, inhibit the generation of chip edge on the tool surface, thereby ensuring and improving the quality of the processed surface.

[0025] 3. The supercritical CO2 of the present invention sublimates rapidly after being sprayed into the cutting zone, and the gas expansion can effectively remove the chips in the cutting zone, reducing the adhesion of chips on the workpiece surface and the tool tip, and avoiding the influence of chips on the surface processing quality.

[0026] 4. The supercritical CO2 of the present invention has a strong solubility for non-polar organic compounds, which can effectively reduce pollutants on the processed surface and improve the cleanliness of the processed surface.

[0027] 5. The supercritical CO2 of the present invention evaporates naturally after being ejected, and no post-processing is required, which reduces the subsequent processing cost and is safe and environmentally friendly.

[0028] 6. The cutting life of the Al2O3 coated carbide tool of the present invention is 200 min, the surface roughness of SA508-3 steel is reduced from 1.5 μm to 0.8 μm, the cutting force is reduced from 248 N to 132 N, the cutting temperature is reduced from 450°C to 274°C, and the workpiece surface uniformity is good without processing defects such as pits and microcracks.

[0029] 7. Based on the above reasons, the present invention can be widely promoted in the field of cryogenic milling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0031] Figure 1 It is a structural schematic diagram of the device used in the present invention.

[0032] Figure 2 This is a white light interferometer image of the surface of the SA508-3 steel workpiece processed by the present invention.

[0033] Figure 3 This is a wear morphology diagram of the Al2O3 coated cemented carbide tool used in the present invention.

[0034] In the figure: 1. CNC machining center, 2. Vise, 3. Workpiece, 4. Machining tool, 5. Milling cutter head, 6. Spindle, 7. X-axis, 8. Y-axis, 9. Z-axis, 10. CO2 compressed gas cylinder, 11. CO2 delivery pipe, 12. Supercritical CO2 cooling device, 13. Supercritical CO2 delivery pipe, 14. Nozzle fixture, 15. Nozzle. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0036] The embodiment of the present invention provides a method for milling SA508-3 steel based on supercritical CO2 cooling, wherein the device used in the milling process is as follows: Figure 1 As shown, it includes a milling system and a cooling system. The machining system includes a CNC machining center 1, a milling cutter head 5 mounted on a spindle 6, and a machining tool 4 mounted on the milling cutter head 5. The cooling system includes a CO2 compressed gas cylinder 10, which is connected to a supercritical CO2 cooling device 12 via a CO2 delivery pipe 11. After the connection is completed, it is placed on the side of the CNC machining center 1. A nozzle 15 is installed at the head of the supercritical CO2 delivery pipe 13 to ensure that the supercritical CO2 can be sprayed smoothly. The supercritical CO2 nozzle 15 is fixed to the spindle using a nozzle fixture 14 and the position is adjusted to ensure that the supercritical CO2 spray can be focused on the tool tip.

[0037] The method comprises the following steps:

[0038] A. Ensure that the working characteristics of each axis system of CNC machining center 1 are normal, and preheat the machine tool until it reaches thermal stability;

[0039] B. Ensure that the working characteristics of each axis system of the CNC machining center (JDGR300, Beijing Jingdiao, is used in this embodiment) with X-axis 7, Y-axis 8 and Z-axis 9 are normal, and preheat the machine tool until it reaches thermal stability;

[0040] C. Install a SA508-3 steel workpiece 3 (rectangular in shape, 200 mm in length, 100 mm in width, and 50 mm in height in this embodiment) on a work platform vise 2 and perform alignment adjustment of the SA508-3 steel workpiece 3 (in this embodiment, the machining center's built-in probe (OMP 40-2, Renishaw) is used to perform alignment of the workpiece 3);

[0041] D. Clamp the machining tool 4 and use the machining center's own measurement system to complete the tool setting (in this embodiment, the machining center's own contact tool setting instrument is used to complete the tool setting work);

[0042] E. Use a carbide tool (in this embodiment, the tool is an 85° parallelogram milling insert with an 11° clearance angle and a cutting edge radius of 0.8 mm, produced by Mitsubishi CNC tool, Japan) to perform rough cutting on the SA508-3 steel workpiece 3 under preset cutting parameters. The machining path is generated based on the cutting parameters and tool parameters. The cutting parameters are set as follows: a p =0.5 mm,a e =20 mm, f z =0.2 mm, n =1200 r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n is the spindle speed;

[0043] F. Turn on the supercritical CO2 cooling device 12 and adjust the output parameters of the supercritical CO2 cooling device 12 (in this embodiment, the CO2 inlet pressure of the supercritical CO2 cooling device 12 is set to 7.5 MPa, and the supercritical CO2 spray is focused at the tip of the knife);

[0044] G. Use an infrared thermal imager (FLIR, X6520sc) to measure the outlet temperature of the nozzle 15 of the supercritical CO2 cooling device 12. When the outlet temperature reaches the preset temperature range, supercritical CO2 cooling milling is performed under preset cutting parameters and machining paths (in this embodiment, an Al2O3-coated carbide tool with an 85° parallelogram, 11° clearance angle milling insert, and a cutting edge radius of 0.8 mm, obtained from Mitsubishi CNC tools, is used to mill the SA508-3 steel workpiece 3). The machining path is generated based on the cutting parameters and tool parameters. The cutting parameters are set as follows: a p =0.2 mm, a e =20 mm, f z =0.1 mm, n =1800r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n is the spindle speed;

[0045] The supercritical CO2 cooling device 12 and the CNC machining center 1 were sequentially closed, and the SA508-3 steel workpiece 3 was removed, dried, and then stored to obtain a SA508-3 steel machined surface machined by supercritical CO2 cooling milling.

[0046] The surface of SA508-3 steel workpiece 3 obtained by supercritical CO2 cooling milling was observed using white light interferometer. Figure 2As shown in Figure 3, the surface roughness of workpiece 3 reaches 0.5 μm, the surface uniformity of workpiece 3 is good, and there are no processing defects such as pits and microcracks. The surface of the milling tool was observed using a scanning electron microscope, as shown in Figure 3. Figure 3 As shown in the figure, when the cutting time is 200 min, the tool does not reach the blunt standard ( VB <300μm). The surface cleanliness value measured by a contamination detector (SITA ConSpector) was 0.5 RFU. The SA508-3 steel milling method based on supercritical CO2 cooling proposed in this invention can achieve efficient surface cleaning.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. SA508-3 steel milling method based on supercritical CO2 cooling, characterized by: The steps include: Step 1: Check and ensure that the working characteristics of each axis system of the CNC machining center are normal, and preheat the machine tool until it reaches thermal stability. The CNC machining center is placed in an ultra-precision machining laboratory with preset constant temperature, constant humidity and air cleanliness; Step 2: Fix the SA508-3 steel workpiece on the vise of the machining center work platform; Step 3: Clamp the tool and use the machining center's own measurement system to determine the machining origin; Step 4: Rough machining the SA508-3 steel workpiece using a carbide tool under preset cutting parameters, and generating a machining path based on the cutting parameters and tool parameters, wherein the preset cutting parameters include axial cutting depth, radial cutting depth, feed rate, and spindle speed; Step 5. Connect the nozzle of the supercritical CO2 cooling device to the machine tool spindle, align the nozzle with the tool tip, with a distance of 5 to 10 mm between the nozzle and the tool tip, and an angle of 30° to 40° between the nozzle and the axial direction of the machine tool spindle; Step 6: Turn on the supercritical CO2 cooling device and adjust the output parameters of the supercritical CO2 cooling device, including the CO2 input pressure and the compressed air pressure, to focus the supercritical CO2 spray at the tip of the knife. Step 7: Using an infrared thermometer to measure the nozzle outlet temperature of the supercritical CO2 cooling device, when the outlet temperature reaches a preset temperature range, using an Al2O3 coated carbide tool to finish-machine the SA508-3 steel workpiece under preset cutting parameters, and generating a machining path based on the cutting parameters and tool parameters; Step 8: turn off the supercritical CO2 cooling device and the CNC machining center in sequence, remove the SA508-3 steel workpiece, dry it and store it, and obtain the SA508-3 steel machined surface processed by supercritical CO2 cooling milling.

2. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1 is characterized in that: The cutting parameters for the rough machining are set as follows: a p =0.5 mm, a e =20 mm, f z =0.2 mm, n =1200 r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n The spindle speed.

3. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1 is characterized in that: The CNC machining center is a three-axis CNC machining center with an X-axis, a Y-axis and a Z-axis.

4. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1, characterized in that: The SA508-3 steel is in the shape of a cuboid with a length of 200 mm, a width of 100 mm and a height of 50 mm.

5. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1 is characterized in that: The carbide tool is an 85° parallelogram milling insert with an 11° back angle, and the cutting edge radius of the tool is 0.8 mm.

6. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1, characterized in that: The Al2O3 coated carbide tool is an 85° parallelogram milling insert with an 11° back angle, and the cutting edge radius of the tool is 0.8 mm.

7. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1, characterized in that: The CO2 inlet pressure of the supercritical CO2 cooling device is set to 7.5 MPa.

8. The SA508-3 steel milling method based on supercritical CO2 cooling according to claim 1, characterized in that: The cutting parameters for the finishing process are set as follows: a p =0.2 mm, a e =20 mm, f z =0.1 mm, n =1800 r / min, where a p is the axial cutting depth, a e is the radial cutting depth, f z is the feed per tooth, n The spindle speed.

Images