Optimized surface quality milling method for hard and brittle materials
By optimizing milling conditions and designing specialized milling cutters, the problems of surface damage and stress concentration in the machining of hard and brittle materials have been solved, achieving efficient ductile cutting, improving surface quality and tool life, and making it suitable for electronics, aerospace and medical devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI JIAOTONG UNIV
- Filing Date
- 2025-06-26
- Publication Date
- 2026-07-21
AI Technical Summary
Existing processing methods struggle to balance processing efficiency and surface quality for hard and brittle materials, often leading to problems such as microcracks, subsurface damage, and high surface roughness.
By optimizing milling conditions and designing milling cutters with specific surface structures, including edge treatment and surface treatment, combined with mechanical performance testing, critical parameters for ductile cutting are calculated to achieve ductile cutting and prevent brittle fracture.
It significantly improves the surface quality and efficiency of machining hard and brittle materials, reduces crack formation, and increases tool life, making it suitable for high-end manufacturing applications.
Smart Images
Figure CN120460775B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a technology in the field of machining, specifically a milling method for optimizing the surface quality of hard and brittle materials. Background Technology
[0002] Hard and brittle materials are widely used in electronics, aerospace, and medical devices, and are highly favored for their excellent mechanical properties and wear resistance. However, existing processing methods such as conventional milling and grinding struggle to balance efficiency and surface quality, often leading to problems such as microcracks, subsurface damage, and high surface roughness. Summary of the Invention
[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes an optimized surface quality milling method for hard and brittle materials. By optimizing milling conditions and designing milling cutters with specific surface structures, ductile cutting of hard and brittle materials is achieved, effectively preventing brittle fracture and significantly improving the surface quality and efficiency of hard and brittle material processing. This method solves problems such as surface damage and stress concentration in traditional processing and is applicable to high-end manufacturing fields such as electronics, aerospace, and medical devices, thus promoting the development of precision machining technology for hard and brittle materials.
[0004] This invention is achieved through the following technical solution:
[0005] This invention relates to a milling method for optimizing the surface quality of hard and brittle materials. By testing the mechanical properties of the material under test, the maximum depth of its ductile domain and the maximum depth of its ductile-brittle transition domain are obtained. The critical cutting thickness for ductile cutting and its corresponding diameter-to-thickness ratio of the material under test are then calculated. Based on the diameter-to-thickness ratio, the height difference of the highest point of the bulge of a special milling cutter with edge treatment and surface treatment, the horizontal and vertical spacing of the bulge, the radius of the bulge tip arc, the critical cutting thickness for ductile cutting during machining corresponding to the special milling cutter, the effective number of abrasive grains on the tool surface, and the process adaptability machining parameters, the tool feed rate is calculated to achieve optimized milling.
[0006] The milling method specifically includes:
[0007] Step 1: Determine the type of hard and brittle material to be processed;
[0008] Step 2: Perform mechanical property testing on the processed material to determine the key indicators of its ductility and brittleness. These key indicators include the maximum depth of the ductile region and the maximum depth of the ductile-brittle transition region.
[0009] Step 3: Determine the critical cutting thickness for ductile cutting of the material under the test conditions based on the key indicators of ductility and brittleness of the material being processed during the test.
[0010] Step 4: Determine the cutting diameter-to-thickness ratio of the material to be processed based on the critical cutting thickness of the material under the testing conditions and the radius of the indenter of the testing instrument;
[0011] Step 5: Design and fabricate specialized end mills to achieve high surface quality. Specialized end mills refer to end mills for hard and brittle materials that have undergone specialized cutting edge treatment and surface treatment. The surface of a specialized end mill exhibits multiple convex hull structures.
[0012] Step 6: Determine the evaluation parameters for the distribution of the convex hull structure on the milling cutter surface. The evaluation parameters include: the height difference of the highest point, the spacing in the horizontal and vertical directions, and the radius of the top arc.
[0013] Step 7: Measure the convex hull structure on the surface of the specific milling cutter to determine the height difference of the highest point of the convex hull structure, the horizontal and vertical spacing, and the radius of the top arc.
[0014] Step 8: Determine the critical ductility cutting thickness of the specific milling cutter based on the radius of the top arc of the convex hull structure on the surface of the specific milling cutter and the cutting diameter-to-thickness ratio of the workpiece.
[0015] Step 9: Determine the tool speed and tool feed rate based on the relationship between the evaluation parameters of the ductile critical cutting thickness corresponding to the specific end mill for the material being machined, the tool surface convex hull distribution, and the machining parameters.
[0016] The aforementioned mechanical performance testing includes: scratch detection method, indentation detection method, and chip morphology observation method.
[0017] The scratch detection method refers to: performing a scratch test on hard and brittle materials, recording the scratch length corresponding to the scratch depth, observing whether there are cracks or micro fractures on the scratch surface, the depth corresponding to the crack is the maximum depth of the ductile region, and the depth corresponding to the crack-filled scratch surface is the maximum depth of the ductile-brittle transition region.
[0018] The indentation detection method refers to: conducting indentation experiments at different depths on hard and brittle materials, recording the loading-unloading curves, changes in hardness and elastic modulus, and residual indentation morphology. The depth at which hardness and elastic modulus fluctuate and cracks appear in the indentation morphology is the maximum depth of the ductile domain. The depth at which hardness and elastic modulus fluctuate significantly and numerous cracks appear in the indentation morphology is the maximum depth of the ductile-brittle transition domain.
[0019] The chip morphology observation method refers to: conducting cutting experiments on hard and brittle materials at different cutting depths, recording the chip characteristics at different cutting depths, and determining the maximum depth of the ductile region when cracks begin to appear in the chips, and the maximum depth of the ductile-brittle transition region when the chips become irregular fragments or granules with rough surfaces and accompanied by cracks or fractures.
[0020] The maximum depth of the ductile domain refers to the maximum depth to which a hard and brittle material can be removed without producing brittle cracks, while the maximum depth of the ductile-brittle transition domain refers to the minimum depth to which a hard and brittle material can be removed completely in a brittle state.
[0021] The critical cutting thickness δ0 of the workpiece under the aforementioned detection conditions is determined based on the maximum depth of the ductile-brittle transition zone of the workpiece under the detection conditions, and the two are numerically equal.
[0022] The aforementioned cutting diameter-to-cutting thickness ratio Where: r0 is the radius of the indenter of the testing instrument, and δ0 is the critical cutting thickness of the material to be processed under the testing conditions.
[0023] The specific milling cutter surface has multiple convex hull structures, and the convex hulls remove material by abrasive grinding during the cutting process.
[0024] The specific cutting edge treatments include: cutting edge passivation, cutting edge chamfering, and cutting edge micro-geometry optimization. Cutting edge passivation is achieved through sandblasting, electrolysis, or manual grinding to reduce the risk of brittle fracture and prevent tool damage due to excessive cutting forces when machining hard and brittle materials. Cutting edge chamfering is achieved through manual chamfering, mechanical chamfering, or laser chamfering to reduce the sharpness of the cutting edge and decrease the likelihood of brittle fracture when cutting hard and brittle materials. Cutting edge micro-geometry optimization is achieved through inclined cutting edge design and micro-bent cutting edge design. The inclined cutting edge design helps achieve a better friction reduction effect during cutting, mimicking the effect of grinding, while the micro-bent cutting edge design can produce a thin-layer removal effect similar to grinding.
[0025] The surface treatments include: physical vapor deposition (PVD) coating, chemical vapor deposition (CVD) coating, laser surface treatment, microblasting, and electrical discharge machining (EDM). Specifically: PVD coating refers to depositing a hard coating on the tool surface using physical vapor deposition methods, forming tiny protrusions or particles to simulate an abrasive effect; CVD coating refers to depositing a coating on the tool surface through a chemical reaction, forming a hard, wear-resistant surface and creating different shaped bump structures; laser surface treatment refers to using the concentrated high-energy action of a laser beam to treat the tool surface... The surface is treated to form micron or nanometer-scale convex structures, creating specific microstructures on the tool surface to simulate the effect of abrasive grinding; micro-blasting refers to sandblasting the tool surface by spraying fine abrasives (such as alumina, silica sand, etc.) to form micro-protrusions or granular structures, mimicking the grinding effect of abrasive grains on hard and brittle workpieces, and improving the surface roughness and hardness of the tool; electrical discharge treatment refers to removing tiny materials from the tool surface through electrical discharge between the electrode and the tool surface, forming certain convex or microporous structures, producing a cutting effect similar to abrasive grains during the machining process.
[0026] According to the grinding principle, the effective number of abrasive grains per unit area k is the effective abrasive particle ratio parameter, calculated as the percentage of abrasive particles whose highest point height difference Δh is greater than the critical cutting thickness δ within a unit area. l1 is the transverse spacing between abrasive particles, l2 is the longitudinal spacing between abrasive particles; the abrasive particle shape factor C = 4tanθ, where θ is the abrasive particle apex angle.
[0027] Based on the effective number of abrasive particles N d The calculation formula for the critical cutting thickness δ of ductility is used to determine the evaluation parameters of the convex hull distribution as the height difference Δh of the highest point of the convex hull structure on the tool surface, the transverse spacing l1, the longitudinal spacing l2, the convex hull apex angle θ, and the radius r of the convex hull apex arc. The detection methods include: confocal microscope, white light interferometer, and other detection methods.
[0028] The specific end mill corresponding to the critical ductility cutting thickness Where: r is the radius of the arc at the top of the convex hull, and λ is the cutting diameter-to-thickness ratio.
[0029] The optimal processing parameters are determined by the following relationship. , where: N d The effective number of abrasive particles per unit area, C is the abrasive particle shape factor C=4tanθ, d s v is the diameter of the cutting tool. s v is the cutting speed of the tool. w a is the tool feed rate. p This represents the cutting depth of the tool.
[0030] Technical effect
[0031] This invention is designed for milling hard and brittle materials. It features a special milling cutter with multiple convex structures on its surface. Compared with the prior art, this invention effectively prevents brittle fracture, reduces crack formation, and achieves high surface quality in the milling of hard and brittle materials. Attached Figure Description
[0032] Figure 1 This is a flowchart of the present invention;
[0033] Figure 2 Image of graphite scratch morphology;
[0034] Figure 3 Load-unload curve for graphite scratch test;
[0035] Figure 4 Comparison of specific milling cutter edge treatments;
[0036] Figure 5 This image shows the morphology of a chemical vapor deposition diamond coating on the surface of a specific milling cutter.
[0037] Figure 6 A three-dimensional topographic image of the convex hull structure on the surface of a specific milling cutter;
[0038] Figure 7 This is a cross-sectional profile of the convex hull structure on the surface of a specific milling cutter;
[0039] Figure 8 Diagram of the experimental environment for graphite milling;
[0040] Figure 9 The three-dimensional morphology of the graphite surface was designed using a coated milling cutter for this invention.
[0041] Figure 10 This invention designs a defect diagram for the processing of graphite using a coated milling cutter;
[0042] Figure 11 Three-dimensional topography of graphite surface machined with existing coated milling cutters;
[0043] Figure 12 This image shows a defect in the machining of graphite using an existing coated milling cutter. Detailed Implementation
[0044] like Figure 1 As shown in this embodiment, a milling method for optimizing the surface quality of a hard and brittle material includes:
[0045] Step 1: Determine the type of hard and brittle material to be processed, including: graphite, cemented carbide, glass, ceramics, etc.
[0046] In this embodiment, graphite is selected as the hard and brittle material to be processed.
[0047] Step 2: Select scratch detection method, indentation detection method or chip morphology observation method to test the mechanical properties of the material to be processed, and obtain the maximum depth of the ductile region and the maximum depth of the ductile-brittle transition region;
[0048] In this embodiment, scratch detection is used as a key indicator for detecting the ductility and brittleness of the material to be processed. The scratch morphology is as follows: Figure 2 As shown, the load-unload curve in the scratch test is as follows: Figure 3 As shown, the maximum depth of the ductile domain is determined to be 338 nm, and the maximum depth of the ductile-brittle transition domain is determined to be 920 nm.
[0049] Step 3: Based on the experimental results of Step 2, the critical cutting thickness for ductile cutting of the material to be processed under the test conditions is determined to be 920 nm according to the key indicators of ductility and brittleness of the material to be processed.
[0050] Step 4: Calculate the cutting diameter-to-thickness ratio of the material to be processed based on the critical cutting thickness of the material under the testing conditions and the radius of the indenter of the testing instrument. The radius of the indenter of the testing instrument, r0, is 6 μm. Based on the critical cutting thickness δ0 of the material under the testing conditions obtained in Step 3, which is 0.92 μm, calculate the cutting diameter-to-thickness ratio of the material to be processed. It is 6.5.
[0051] Step 5: Select and design and manufacture specialized end mills that achieve high surface quality by using edge passivation treatment, edge chamfering treatment, or edge micro-geometry optimization treatment. Specialized end mills refer to end mills for hard and brittle materials that have undergone edge treatment and surface treatment. The surface of specialized end mills exhibits multiple convex hull structures.
[0052] In this embodiment, edge passivation is used as a cutting edge treatment method to reduce stress concentration during cutting, laying the foundation for tool surface treatment. Images of the tool before and after edge treatment are shown below. Figure 4 As shown;
[0053] The surface treatments include, but are not limited to, physical vapor deposition coating treatment, chemical vapor deposition coating treatment, laser surface treatment, microblasting treatment, and electrical discharge machining.
[0054] In this embodiment, chemical vapor deposition (CVD) diamond coating is used for tool surface treatment. Through the design and fabrication of a micron-nano composite diamond coating, a diamond protrusion structure is formed on the tool surface to achieve an abrasive grinding effect. Images of the tool surface before and after CVD diamond coating treatment are shown below. Figure 5 As shown.
[0055] Step Six: Based on the effective number of abrasive grains N d The evaluation parameters for determining the distribution of the convex hull structure on the milling cutter surface, as determined by the formula for calculating the critical cutting thickness δ for ductility, are: the height difference Δh between the highest points of the convex hull structure on the tool surface, the transverse spacing l1, the longitudinal spacing l2, the convex hull apex angle θ, and the radius r of the convex hull apex arc.
[0056] Step 7: Measure the convex hull structure on the surface of the specific milling cutter. In this embodiment, a confocal microscope is used to determine the evaluation parameters of the convex hull structure. The three-dimensional morphology of the convex hull structure on the surface of the specific milling cutter is as follows: Figure 6 As shown, the cross-sectional profile of the convex hull structure is as follows: Figure 7 As shown; the distribution of the highest point height difference Δh data, the horizontal spacing l1=9.16um, the vertical spacing l2=9.10um, the convex hull vertex angle θ=45° and the radius of the convex hull top arc r=5.55μm;
[0057] Step 8: Based on the cutting diameter-to-thickness ratio of the material to be machined obtained in Step 4 and the radius of the top arc of the convex hull structure on the surface of the specific end mill obtained in Step 7, calculate the ductile critical cutting thickness corresponding to the specific end mill. .
[0058] In this embodiment, the critical cutting thickness for ductility is calculated to be δ=0.85μm.
[0059] Step 9: Calculate the optimal machining parameters based on the results obtained in Steps 7 and 8, i.e., the tool feed rate v that is suitable for the process. w Specifically: , where: N d The effective number of abrasive grains per unit area is calculated based on the abrasive grain height distribution and abrasive grain spacing. The abrasive grain shape factor C = 4tanθ, d s Where v is the tool diameter and the cutting speed under machining conditions. s , tool cutting depth a p Effective number of abrasive particles per unit area k is the effective abrasive particle ratio parameter, which is calculated as the percentage of abrasive particles whose highest point height difference Δh is greater than the critical cutting thickness δ within a unit area, based on the statistics obtained after measurement in step seven.
[0060] In this embodiment, the tool diameter d s The thickness is 0.8mm, and the cutting speed v in the machining environment is... s =95m / min, tool cutting depth a p =0.03mm, effective abrasive ratio k is 0.2, number of effective abrasive particles per unit area N d =2400mm -2 The tool feed rate in this embodiment can then be calculated. .
[0061] Through specific practical experiments, graphite milling experiments were conducted using the V33i graphite milling machine to verify the results. Figure 8 As shown, experiments were conducted with a cutting speed of 95 m / min, a cutting depth of 0.03 mm, and a feed rate of 70 mm / min. The experimental data obtained are as follows: The three-dimensional morphology of the graphite surface machined using the coated milling cutter designed in this method is as follows. Figure 9 As shown, the machining defects are as follows Figure 10 As shown, the surface roughness is 1.062 μm; the three-dimensional morphology of the graphite surface machined by the existing coated milling cutter is as follows. Figure 11 As shown, the machining defects are as follows Figure 12 As shown, the surface roughness is 1.653 μm. The coated milling cutter designed in this method significantly improves the surface roughness of the machined surface, while reducing defects such as pits and cracks on the machined surface.
[0062] Compared with existing technologies, this method significantly improves the surface quality and efficiency of machining hard and brittle materials, solving problems such as surface damage and stress concentration in traditional machining. By optimizing milling conditions and designing milling cutters with specific surface structures, ductile cutting of hard and brittle materials is achieved, effectively preventing brittle fracture. This method increases tool life, reduces crack formation, and is suitable for high-end manufacturing fields such as electronics, aerospace, and medical devices, thus promoting the development of precision machining technology for hard and brittle materials.
[0063] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.
Claims
1. A milling method for optimizing the surface quality of hard and brittle materials, characterized in that, By testing the mechanical properties of the material under test, the maximum depth of its ductile domain and the maximum depth of its ductile-brittle transition domain are obtained. The critical cutting thickness of the material under test and its corresponding diameter-to-thickness ratio are then calculated. Based on the diameter-to-thickness ratio, the height difference of the highest point of the convex hull of the special milling cutter after edge treatment and surface treatment, the horizontal and vertical spacing of the convex hull, the radius of the convex hull top arc, the critical cutting thickness of ductile cutting during machining of the special milling cutter, the number of effective abrasive grains on the tool surface, and the process adaptability machining parameters, the tool feed rate is calculated to achieve optimized milling. The aforementioned mechanical property testing includes: scratch testing methods, indentation testing methods, and / or chip morphology observation methods; The maximum depth of the ductile domain refers to the maximum depth to which a hard and brittle material can be removed without generating brittle cracks, and the maximum depth of the ductile-brittle transition domain refers to the minimum depth to which a hard and brittle material can be removed completely in a brittle state. The ductile critical cutting thickness , where: N d v is the effective number of abrasive grains per unit area calculated based on the abrasive grain height distribution and abrasive grain spacing. s v is the cutting speed of the tool. w For tool feed rate, The cutting depth of the tool is given by the abrasive grain shape factor C = 4tanθ, d s The diameter of the cutting tool; the number of effective abrasive grains per unit area. l1 is the transverse spacing of abrasive grains, l2 is the longitudinal spacing of abrasive grains, and k is the effective abrasive grain ratio parameter, which is calculated as the percentage of abrasive grains whose highest point height difference Δh is greater than the critical cutting thickness δ within a unit area. The aforementioned cutting diameter-to-cutting thickness ratio Where: r0 is the radius of the indenter of the testing instrument, and δ0 is the critical cutting thickness of the material to be processed under the testing conditions.
2. The milling method for optimizing the surface quality of hard and brittle materials according to claim 1, characterized in that, The scratch detection method refers to: performing a scratch test on hard and brittle materials, recording the scratch length and corresponding scratch depth, observing whether there are cracks or micro fractures on the scratch surface, the depth corresponding to the crack is the maximum depth of the ductile region, and the depth corresponding to the crack-filled scratch surface is the maximum depth of the ductile-brittle transition region. The indentation detection method refers to: conducting indentation experiments at different depths on hard and brittle materials, recording the loading-unloading curves, changes in hardness and elastic modulus, and residual indentation morphology; the depth at which hardness and elastic modulus fluctuate and cracks appear in the indentation morphology is the maximum depth of the ductile domain; and the depth at which hardness and elastic modulus fluctuate significantly and numerous cracks appear in the indentation morphology is the maximum depth of the ductile-brittle transition domain. The chip morphology observation method refers to: conducting cutting experiments on hard and brittle materials at different cutting depths, recording the chip characteristics at different cutting depths, and determining the maximum depth of the ductile region when cracks begin to appear in the chips, and the maximum depth of the ductile-brittle transition region when the chips become irregular fragments or granules with rough surfaces and accompanied by cracks or fractures.
3. The milling method for optimizing the surface quality of hard and brittle materials according to claim 1, characterized in that, The cutting edge treatment includes: cutting edge blunting treatment, cutting edge chamfering treatment, and cutting edge micro-geometry optimization treatment.
4. The milling method for optimizing the surface quality of hard and brittle materials according to claim 1, characterized in that, The surface treatments include: physical vapor deposition coating treatment, chemical vapor deposition coating treatment, laser surface treatment, micro-blasting treatment, and electrical discharge machining treatment.
5. The milling method for optimizing the surface quality of hard and brittle materials according to any one of claims 1-4, characterized in that, specifically include: Step 1: Determine the type of hard and brittle material to be processed; Step 2: Perform mechanical property testing on the processed material to determine the key indicators of its ductility and brittleness. These key indicators include the maximum depth of the ductile region and the maximum depth of the ductile-brittle transition region. Step 3: Determine the critical cutting thickness for ductile cutting of the material under the test conditions based on the key indicators of ductility and brittleness of the material being processed during the test. Step 4: Determine the cutting diameter-to-thickness ratio of the material to be processed based on the critical cutting thickness of the material under the testing conditions and the radius of the indenter of the testing instrument; Step 5: Design and fabricate a special end mill to achieve high surface quality. The special end mill refers to a hard and brittle material end mill that has undergone special cutting edge treatment and surface treatment. The surface of the special end mill exhibits multiple convex hull structures. Step 6: Determine the evaluation parameters of the convex hull structure distribution on the milling cutter surface based on the calculation formula of effective abrasive grain number and ductile critical cutting thickness. The evaluation parameters include: the height difference of the highest point, the horizontal and vertical spacing, and the radius of the top arc. Step 7: Measure the convex hull structure on the surface of the specific milling cutter to determine the height difference of the highest point of the convex hull structure, the horizontal and vertical spacing, and the radius of the top arc. Step 8: Determine the critical ductility cutting thickness of the specific milling cutter based on the radius of the top arc of the convex hull structure on the surface of the specific milling cutter and the cutting diameter-to-thickness ratio of the workpiece. Step 9: Determine the tool speed and tool feed rate based on the relationship between the evaluation parameters of the ductile critical cutting thickness corresponding to the specific end mill for the material being machined, the tool surface convex hull distribution, and the machining parameters.