Milling processing method of high-strength medium-modulus carbon fiber reinforced composite material

Abstract

The invention relates to a milling method for a high-strength medium-modulus carbon fiber reinforced composite material, which comprises the following steps: selecting a special milling cutter suitable for the high-strength medium-modulus carbon fiber reinforced composite material, and optimizing a cutter structure and a coating to reduce cutting resistance; secondly, accurately controlling cutting parameters, including the rotating speed of a main shaft, the feeding speed and the cutting depth, so as to reduce the phenomena of layering, burrs and fiber pull-out generated in the machining process; then, a specific cooling and lubricating mode is adopted, heat accumulation is effectively reduced, and cutting stability is improved; and finally, post-treatment is conducted on the machined surface, the surface flatness and the use performance are further improved, and the machining quality and the machining efficiency of the composite material are improved.

Description

Technical Field

[0001] The invention relates to the technical field of composite material machining, and in particular to a milling method for a high-strength medium-modulus carbon fiber reinforced composite material. Background Art

[0002] High-strength medium-modulus carbon fiber reinforced composite materials have the advantages of high specific strength, high specific stiffness, good corrosion resistance, etc., and are widely used in aerospace, automobile, sports equipment and high-end equipment manufacturing.

[0003] Since the carbon fibers in high-strength medium-modulus carbon fiber reinforced composites are hard, brittle, and highly abrasive, traditional mechanical milling methods are difficult to meet the high-speed and high-precision processing requirements in actual production. Under high-speed milling conditions, such composite materials are prone to serious processing defects, such as surface fiber pullout, uneven fiber breakage, fiber-matrix interface damage, internal material delamination and microcracks, etc. These defects not only reduce the surface quality and dimensional accuracy of the processed parts, but also have an adverse effect on the mechanical properties, service life and reliability of the composite parts.

[0004] Therefore, how to improve processing quality and efficiency in actual processing has become an important technical problem that needs to be solved urgently in the current field of composite material machining. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a milling method for high-strength medium-modulus carbon fiber reinforced composite materials, so as to effectively reduce milling defects, improve surface quality and extend tool life.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The present invention provides a milling method for high-strength medium-modulus carbon fiber reinforced composite material, which specifically comprises the following steps:

[0008] S1. Tool selection: Choose a double straight-edge end mill specially designed for high-strength medium-modulus carbon fiber reinforced composite materials;

[0009] S2, milling parameter setting;

[0010] S3. Cooling and lubrication measures: During the milling process, use micro-lubrication technology for cooling and lubrication;

[0011] S4. Surface post-treatment: After processing, the surface is lightly polished or shot peened.

[0012] Furthermore, in step S1, the tool substrate is made of cemented carbide, and a nanocrystalline diamond coating is deposited on the surface.

[0013] Further, in the step S1, the structure of the cutting edge is a symmetric double straight edge design, the rake angle is controlled at 0° to 5°, the clearance angle is controlled at 8° to 15°, and the radius of the cutting edge corner of the tool is 5 to 10 μm.

[0014] Further, in the step S2, the specific settings of the milling parameters are as follows: the spindle speed of the milling process is set at 9500 - 10500 r / min, the feed rate is set at 950 - 1050 mm / min, the axial cutting depth is 0.2 to 2 mm, and the radial cutting width does not exceed 40% of the tool diameter.

[0015] Further, in the step S3, the lubricant is a plant-based or ester-based lubricating oil.

[0016] Further, the injection air pressure of the lubricant is 0.3 to 0.6 MPa, the lubricant flow rate is controlled at 10 to 50 ml / h, and the injection distance is set at 20 to 40 mm.

[0017] Further, in the step S4, the polishing grit size for the mild polishing treatment is selected from 800 to 2000 mesh.

[0018] Further, in the step S4, the shot peening medium for the shot peening treatment is ceramic microbeads, the shot peening pressure is controlled at 0.2 to 0.4 MPa, and the injection distance is 80 to 120 mm.

[0019] The present invention has the following beneficial effects compared with the prior art:

[0020] 1. In terms of tool selection, the present invention adopts a diamond-coated double straight edge end mill dedicated to high-strength medium-modulus carbon fiber reinforced composite materials. The tool substrate is made of cemented carbide, and the surface is coated with nanocrystalline diamond, which has higher hardness, wear resistance and thermal stability. Through the optimized design of the cutting edge structure (symmetric double straight edge, rake angle 0° to 5°, clearance angle 8° to 15°, radius of the cutting edge corner 5 to 10 μm), the cutting force and frictional resistance during high-speed cutting are significantly reduced, effectively preventing fiber pulling out and matrix damage, prolonging the tool life, and reducing the processing cost.

[0021] 2. In terms of milling parameter control, the present invention strictly limits the spindle speed to 9500 - 10500 r / min, the feed rate to 950 - 1050 mm / min, the axial cutting depth to 0.2 to 2 mm, and the radial cutting width not to exceed 40% of the tool diameter. This precise and reasonable parameter setting enables the tool to effectively avoid vibration and uneven workpiece stress during high-speed cutting, significantly reducing defects such as material delamination, burrs, fiber pulling out and microcracks during the processing, and effectively ensuring the accuracy and quality of the workpiece processing surface.

[0022] 3. In terms of the cooling and lubrication method, the present invention adopts the minimum quantity lubrication (MQL) technology, uses plant-based or ester-based lubricants, and precisely sprays them into the cutting area at an air pressure of 0.3 - 0.6 MPa and a flow rate of 10 - 50 ml / h. Compared with the traditional large amount of cutting fluid cooling, this lubrication measure significantly reduces the coolant consumption, reduces environmental pollution, ensures the temperature stability in the cutting area, inhibits material thermal damage and tool wear, and improves the thermal and mechanical stability and machining quality of the machining process.

[0023] 4. In terms of the surface post-treatment technology, the present invention adopts mild polishing with 800 - 2000 meshes or ceramic microbead shot peening treatment (shot peening pressure 0.2 - 0.4 MPa, spraying distance 80 - 120 mm) to further improve the flatness and micro-integrity of the machined surface. After the post-treatment, the surface micro-defects are significantly reduced, and the surface roughness Ra value is controlled within a lower range, improving the mechanical properties and anti-fatigue performance of the workpiece under long-term service conditions.

[0024] Through the optimization and improvement of each of the above links, the present invention achieves the goals of high-speed and high-precision milling of high-strength medium-modulus carbon fiber reinforced composite materials. Compared with the traditional method, the present invention can effectively avoid serious defects such as fiber pull-out, delamination, and micro-cracks that are prone to occur during the machining process, significantly improve the micro-structure and internal stability of the machined surface, ensure the overall mechanical properties and long-term reliability of the material, and is applicable to the production and application of high-performance composite material parts with strict requirements for machining accuracy and quality in the fields of aerospace, automotive, sports equipment, and high-end equipment manufacturing. Brief Description of the Drawings

[0025] Figure 1 It is a schematic flow chart of a milling method for high-strength medium-modulus carbon fiber reinforced composite materials proposed in an embodiment of the present invention;

[0026] Figure 2 It is a schematic diagram of the rough detection of the machined surface of the material in an embodiment of the present invention;

[0027] Figure 3 It is a schematic diagram of the rough detection of the cross-section of the machined material in an embodiment of the present invention;

[0028] Figure 4 It is a schematic diagram of the scanning electron microscope of the machined surface of the material in an embodiment of the present invention;

[0029] Figure 5 It is a schematic diagram of the scanning electron microscope of the cross-section of the machined material in an embodiment of the present invention. Detailed Embodiments

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] A milling method for a high-strength medium-modulus carbon fiber reinforced composite material proposed by the present invention is as Figure 1 shown, and the specific preparation process is as follows:

[0032] S1. Tool selection: Select a diamond-coated double straight-edge end mill dedicated to high-strength medium-modulus carbon fiber reinforced composite materials. The tool substrate is made of cemented carbide, and a nanocrystalline diamond coating is deposited on the surface. The cutting edge structure is a symmetric double straight-edge design. The rake angle is controlled within 0° - 5°, and the clearance angle is controlled within 8° - 15°. The radius of the tool edge fillet is 5 - 10 μm to ensure the cutting stability and accuracy of the tool under high-speed conditions. The above optimized tool structure combined with the coating can effectively reduce the cutting resistance.

[0033] In the present invention, a double straight-edge end mill with a cemented carbide substrate and a nanocrystalline diamond coating is selected to take into account high hardness, high wear resistance and thermal stability, and resist the strong abrasion of carbon fibers. In terms of the geometric parameters of the tool, setting the rake angle within 0° - 5° can achieve sharp cutting without easy chipping, and setting the clearance angle at 8° - 15° helps to reduce friction and improve the surface quality. The radius of the tool edge fillet is 5 - 10 μm, which can enhance the edge strength and inhibit fiber pulling out, so as to realize the stable, efficient and low-defect milling of high-strength medium-modulus carbon fiber composites. This is the key tool design basis for the present invention to achieve high-speed and high-precision goals.

[0034] S2. Milling parameter setting: The spindle speed of the milling process is set to 9500 - 10500 r / min, the feed speed is set to 950 - 1050 mm / min, the axial cutting depth is 0.2 - 2 mm (about 33% of the tool diameter), and the radial cutting width does not exceed 40% of the tool diameter. The above parameter settings can effectively reduce the phenomena of delamination, burrs and fiber pulling out generated during the processing.

[0035] The matching of the spindle speed of 9,500 - 10,500 r / min and the feed rate of 950 - 1,050 mm / min is the key combination to achieve high-speed and high-precision machining effects in this embodiment, belonging to the safe micro-feed range for carbon fiber composite material machining. A reasonable combination of high speed and feed rate can effectively reduce the cutting load per tooth of the tool, reduce the instantaneous impact force, and suppress the chatter of the workpiece and the tool. At the same time, it avoids the instantaneous impact and fiber migration caused by excessive feed rate and the "friction-dominated" cutting behavior (i.e., the tool slides against the material instead of shearing, resulting in ablation of the machining surface or polished peeling of the matrix) caused by too small feed rate. It ensures a stable and efficient cutting process and helps to form regular fiber fractures and low-roughness surfaces. The shallow cutting depth setting of 0.2 - 2 mm in the axial direction effectively avoids the delamination defect caused by large-area compression of fibers. The cutting width of 2 mm in the radial direction is controlled within 40% of the tool diameter, which ensures the rigid support of the tool during the cutting process, avoids tool deformation during machining, and ensures high-quality cutting effects on the surface and inside of the material.

[0036] S3. Cooling and lubrication measures: During the milling process, minimum quantity lubrication (MQL) technology is used for cooling and lubrication; among them, the lubricant is plant-based or ester-based lubricating oil, the injection air pressure is 0.3 - 0.6 MPa, the lubricant flow rate is precisely controlled at 10 - 50 ml / h, and the injection distance is 20 - 40 mm. The above cooling and lubrication measures can effectively reduce heat accumulation and improve cutting stability.

[0037] In the cooling and lubricating measures of the present invention, plant-based or ester lubricating oils are selected because such lubricants have excellent thermal oxidation stability and lubricating film adhesion ability and good extreme pressure and anti-wear properties, and can stably form an oil film under high temperature and high speed milling conditions, effectively reducing friction and heat accumulation at the tool-workpiece interface, while avoiding softening or decomposition of the resin matrix due to overheating. In addition, such lubricants have good biodegradability and environmental compatibility, meeting green manufacturing requirements. The injection air pressure is controlled at 0.3-0.6MPa to ensure that the lubricant can be fully atomized and efficiently transported to the tool cutting area. If the air pressure is lower than 0.3MPa, the atomized particle size is large, the distribution is uneven, and the lubrication effect is poor. If it is higher than 0.6MPa, the mist beam is too high, which may cause the lubricant to rebound, scatter or disrupt the chip discharge path, which in turn causes cutting instability and safety risks. Therefore, this pressure range is an optimization result of the coupling of empirical verification and physical laws to ensure lubrication effect, cooling performance and system stability. The lubricant flow rate is precisely controlled at 10-50ml / h, which can take into account both the cooling and lubrication effects and green environmental protection requirements. If it is lower than 10ml / h, it may be difficult to form a stable oil film. If it is higher than 50ml / h, it will exceed the original intention of minimal lubrication and easily cause lubricant accumulation, splashing, or affect the visibility of the processing area and chip discharge, thus destroying the processing stability. The spray distance is set to 20-40mm, which is the effective action area calculated based on the atomization cone angle and the mist beam diffusion distance. If it is too close, it will cause concentrated impact of the oil mist, which is difficult to diffuse and cover the entire cutting interface; if it is too far, the mist particle speed will decay and the energy will disperse, making it difficult to penetrate the chip and hot air flow barrier to enter the tool-workpiece contact area. The distance range of 20-40mm just achieves a dynamic balance between the jet concentration and the atomization coverage range, and is a key process control window for improving the MQL lubrication efficiency.

[0038] S4. Surface post-treatment: After processing, the surface is lightly polished or shot peened to further improve surface flatness and performance;

[0039] The polishing particle size for light polishing is 800-2000 mesh;

[0040] The shot peening medium of the shot peening treatment is ceramic micro beads, the shot peening pressure is controlled at 0.2-0.4MPa, and the spraying distance is 80-120mm.

[0041] Improve the service performance of the composite material surface, such as fatigue life, stress concentration sensitivity, etc. Among them, the polishing particle size for mild polishing is selected from 800 to 2000 mesh, the shot peening medium for shot peening is ceramic microbeads, the shot peening pressure is controlled at 0.2 - 0.4 MPa, and the spraying distance is 80 - 120 mm. The sandpaper used in the present invention is 800 - 2000 mesh, which is in the medium - high mesh range, having both moderate material removal ability and high polishing accuracy. It can effectively process the slight defects below the micro - scale (tens of microns) on the surface of carbon fiber composite materials without damaging the integrity of the matrix resin or weakening the fibers. Selecting ceramic microbeads as the shot peening medium is because it has high hardness, good chemical stability, and excellent impact flexibility. It can introduce a favorable residual compressive stress layer on the material surface without damaging the carbon fiber and resin matrix, thereby improving the fatigue resistance and inhibiting the propagation of micro - cracks. And under the same impact kinetic energy, the unit action area of ceramic microbeads is smaller and the indentation is shallower, which is more conducive to realizing the "gentle stress control" of impact. The shot peening pressure is controlled within the range of 0.2 - 0.4 MPa to ensure that the impact energy is sufficient to produce a strengthening effect to form an effective stress layer but does not exceed the damage threshold of the material, avoiding problems such as fiber fracture, matrix erosion, or even destructive pits. The spraying distance is set to 80 - 120 mm to balance the energy density and distribution uniformity of the spraying beam, preventing micro - damage caused by local over - impact and ensuring the continuity and uniformity of the surface strengthening area. It is the best window parameter combination for realizing the fine surface strengthening of lightweight composite materials.

[0042] The following further illustrates the effect of the present invention through specific embodiments:

[0043] Embodiment

[0044] The object processed in this embodiment is a high - strength medium - modulus carbon fiber - reinforced composite material plate with a thickness of 5 mm, the fiber volume fraction is about 60%, the fiber laying method is a cross - woven structure, and the matrix material is epoxy resin.

[0045] The milling method is as Figure 1 shown, and the milling process is completed on a three - axis CNC machining center.

[0046] First, select the tool: Use a diamond - coated double - straight - edge end mill with a diameter of 6 mm. The tool material is a cemented carbide matrix, with a nanocrystalline diamond coating deposited on the surface. The cutting edge adopts a symmetric double - straight - edge structure design, the rake angle is set to 3°, the clearance angle is set to 12°, and the cutting - edge fillet radius of the tool is 8 μm.

[0047] Strict control of milling parameters: The spindle speed is 10,000 r / min, the feed rate is set at 1,000 mm / min, the axial cutting depth is 0.5 mm, and the radial cutting width is set at 2 mm. The milling process is carried out in the up-milling mode, with a stable movement between the tool and the workpiece and no obvious vibration.

[0048] During the milling process, minimum quantity lubrication (MQL) technology is simultaneously used for cooling and lubrication. The lubricant used is an ester-based lubricant, with compressed air as the carrier gas. The injection pressure is 0.4 MPa, the supply rate of the lubricant is stably controlled at 30 ml / h, and the injection distance between the nozzle and the tool is approximately 30 mm to ensure that the lubricant accurately enters the tool-workpiece contact area, effectively reducing the machining temperature rise and reducing the friction in the cutting area.

[0049] After milling, the machined surface is lightly polished with 1200-mesh sandpaper to further eliminate the fine fiber burrs on the surface.

[0050] As Figure 2 shown, the surface of the milled material is detected by a high-precision three-dimensional surface profiler, and the obtained surface roughness Ra value is approximately 1.138 μm, indicating that the surface accuracy of the machining method meets the requirements of high-precision milling. It is observed that the surface profile heights are evenly distributed, without obvious ripples, grooves, fiber protrusions or local depressions, and the surface flatness is good, indicating that the tool movement is stable under high-speed machining conditions, and no obvious chatter and workpiece vibration occur.

[0051] As Figure 3 shown, for the three-dimensional roughness detection results of the cross-section of the material milling, through fine contour measurement, the obtained cross-section roughness Ra value is approximately 1.297 μm, indicating that no obvious machining damage or fiber delamination occurs inside the material during high-speed milling. The cutting interface between the internal fiber structure and the resin matrix is clear and neat. The overall cross-section profile is uniform, and no obvious fiber pulling out, matrix cracking or abnormal defects are seen, reflecting the rationality of the tool sharpness and the selection of cutting parameters.

[0052] As Figure 4 shown, to further verify the machining quality inside the material, a cross-section sample of the machined material is intercepted for scanning electron microscope observation. By magnifying the SEM image of the milled surface of the material, it is found that the cutting positions of the carbon fibers are regular and neat, without obvious fiber tearing or matrix peeling. The interface between the fiber and the resin matrix is clear and tightly bonded, and no fiber melting, matrix overheating cracking or obvious thermal deformation caused by thermal damage is observed. This phenomenon indicates that under high-speed milling and minimum quantity lubrication conditions, the accumulation of machining heat is effectively inhibited, ensuring the surface integrity and good microscopic quality of the material.

[0053] As Figure 5As shown, the SEM image of the cross-section after material milling further shows that the bonding interface between carbon fibers and the epoxy resin matrix in the cross-section is dense, the fiber arrangement state has not been significantly disturbed, there is no delamination or microcracks between the fibers and the matrix, the cross-section of the fibers is neat and there is no obvious interface damage induced by processing. The fiber surface is smooth and flat, and no holes, cracks or other microscopic defects are observed inside the resin matrix, indicating that the high-speed and high-precision milling process method proposed in this embodiment successfully avoids the common material internal damage problems in traditional milling processing and significantly improves the internal structural stability of the composite material.

[0054] Matters not elaborated in this invention are all well-known technologies.

[0055] The embodiments described above are only used to describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A milling method for high-strength and medium-modulus carbon fiber reinforced composite materials, characterized in that, The process includes the following steps: S1. Tool selection: Select a double straight-edge end mill dedicated to high-strength medium-modulus carbon fiber reinforced composite materials; S2. Milling parameter setting; S3. Cooling and lubrication measures: During the milling process, minimum quantity lubrication technology is used for cooling and lubrication; S4. Surface post-treatment: After processing, the surface is subjected to light polishing or shot peening.

2. The milling method for a high-strength and medium-modulus carbon fiber reinforced composite material according to claim 1, wherein: In the step S1, the tool substrate is made of cemented carbide, and a nanocrystalline diamond coating is deposited on the surface.

3. A milling method for a high-strength medium-modulus carbon fiber reinforced composite material according to claim 1 or 2, characterized in that: In the step S1, the structure of the cutting edge is a symmetric double straight-edge design, the rake angle is controlled at 0°-5°, the clearance angle is controlled at 8°-15°, and the radius of the tool edge fillet is 5-10μm.

4. A milling method for a high-strength medium-modulus carbon fiber reinforced composite material according to claim 1, characterized in that: In the step S2, the specific settings of the milling parameters are as follows: the spindle speed of the milling process is set at 9500-10500r / min, the feed rate is set at 950-1050mm / min, the axial cutting depth is 0.2-2mm, and the radial cutting width does not exceed 40% of the tool diameter.

5. A milling method for a high-strength medium-modulus carbon fiber reinforced composite material according to claim 1, characterized in that: In the step S3, the lubricant is a plant-based or ester-based lubricating oil.

6. The milling method for a high-strength and medium-modulus carbon fiber reinforced composite material according to claim 5, characterized in that: The injection air pressure of the lubricant is 0.3-0.6MPa, the lubricant flow rate is controlled at 10-50ml / h, and the injection distance is set at 20-40mm.

7. A milling method for a high-strength medium-modulus carbon fiber reinforced composite material according to claim 1, characterized in that: In the step S4, the polishing grit of the light polishing treatment is selected from 800-2000 mesh.

8. A milling method for a high-strength medium-modulus carbon fiber reinforced composite material according to claim 1, characterized in that: In the step S4, the shot peening medium for the shot peening treatment is ceramic microbeads, the shot peening pressure is controlled at 0.2-0.4MPa, and the injection distance is 80-120mm.

Images