CN110814521A - Laser texturing test method for die steel surface - Google Patents
Laser texturing test method for die steel surface Download PDFInfo
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- CN110814521A CN110814521A CN201910486351.0A CN201910486351A CN110814521A CN 110814521 A CN110814521 A CN 110814521A CN 201910486351 A CN201910486351 A CN 201910486351A CN 110814521 A CN110814521 A CN 110814521A
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- die steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
- B23K26/3568—Modifying rugosity
- B23K26/3584—Increasing rugosity, e.g. roughening
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/20—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring contours or curvatures, e.g. determining profile
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/40—Investigating hardness or rebound hardness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/20—Metals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/20—Metals
- G01N33/204—Structure thereof, e.g. crystal structure
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/026—Specifications of the specimen
- G01N2203/0286—Miniature specimen; Testing on microregions of a specimen
Abstract
The invention discloses a laser texturing test method for a die steel surface, which comprises the following steps: A. fixing a die steel sample, and adjusting a laser head to enable the surface of the sample to be positioned on a focal plane of a laser spot; B. processing the die steel by adopting an optical fiber laser processing system, wherein a processing test is carried out by using a single-factor alternation method aiming at three factors of laser power, pulse width and auxiliary gas respectively, the defocusing amount is adjusted to be 0, the pulse width is adjusted to be 100-1300 mu s, the laser power is 40-100W, and the nitrogen pressure is O.1-0.4 MPa; C. and after the processing is finished, measuring the shape and size of the processed textured point by using a surface three-dimensional shape analyzer. The method improves the multi-axis numerical control milling technology through reasonable determination of design variables, optimization of a cutter path and deep cavity machining error analysis so as to improve the machining depth and the machining accuracy of the deep cavity curved surface multi-axis numerical control machining technology.
Description
Technical Field
The invention relates to a die steel surface machining test method, in particular to a die steel surface laser texturing test method.
Background
The laser texturing technology is characterized in that a high-power-density laser beam is irradiated on the surface of a material by utilizing a rapid fusing principle, so that the fusing process of the material in an action area is instantly finished, and textured protrusions with compact internal tissues and enhanced surface hardness are formed on the surface of the material, so that the purpose of modifying the surface of the material is achieved. The application of the laser texturing technology in die steel brings great value to the improvement of the service life and the quality of the die. However, the influence rule of different process parameters on the geometric dimension of the textured spot is less known at present, and therefore, it is necessary to carry out intensive research on the problem.
Disclosure of Invention
The influence rules of different process parameters of the existing laser texturing technology on the geometric dimension of textured points are less known at present, and in order to overcome the defect, the invention provides the die steel surface laser texturing test method which is beneficial to researching the influence rules of different process parameters on the geometric dimension of textured points and knowing the mechanical property of the textured fused topography area material.
The technical scheme of the invention is as follows: a laser texturing test method for the surface of die steel comprises the following steps:
A. fixing a die steel sample, and adjusting a laser head to enable the surface of the sample to be positioned on a focal plane of a laser spot;
B. processing the die steel by adopting an optical fiber laser processing system, wherein a processing test is carried out by using a single-factor alternation method aiming at three factors of laser power, pulse width and auxiliary gas respectively, the defocusing amount is adjusted to be 0, the pulse width is adjusted to be 100-1300 mu s, the laser power is 40-100W, and the nitrogen pressure is O.1-0.4 MPa;
C. and after the processing is finished, measuring the shape and size of the processed textured point by using a surface three-dimensional shape analyzer.
The method can explore the influence rule of three factors of laser power, pulse width and auxiliary gas on the geometric dimension of the texturing points and acquire the mechanical property of the textured fused topography area material.
Preferably, the die steel coupon in step a is not subjected to any other surface heat treatment. The die steel sample is not subjected to any other surface heat treatment, so that the influence of the laser power, the pulse width and the auxiliary gas on the formation of the textured point is truly and accurately reflected in the subsequent laser texturing test.
Preferably, the surface of the die steel sample in the step A is polished by sand paper, and the surface roughness is 0.04-0.06 μm. Because the laser melting points are very small, the roughness of the surface of the die steel sample must be controlled at a lower level in advance, otherwise the texturing effect cannot be reflected.
Preferably, the surface of the sample is wiped clean with a cotton ball soaked with absolute ethanol before the processing test is performed. Because the laser melting has small roughened points, any impurities such as dust, grease and the like on the surface of the sample can greatly influence the test result, and therefore the sample needs to be cleaned.
Preferably, the fiber laser processing system includes a fiber laser and a stage. The workbench is used for fixing the die steel sample, and the fiber laser is used for melting the surface of the die steel to form textured points.
Preferably, when the morphology of the textured points is measured, cutting is carried out along the shape-entering line of the symmetrical plane of the textured points, and after inlaying, coarse grinding, fine grinding, polishing and 4% nitric acid alcohol etching, a section microscopic picture of the morphology of the textured points is obtained. .
Preferably, the die steel coupon is made of Crl2MoV die steel. The Cr12MoV die steel has high hardenability, hardness, strength and toughness after quenching and tempering, and small quenching deformation. The Cr12MoV is suitable for manufacturing seed mixing dies and tools with large sections, complex shapes and heavy working loads.
The invention has the beneficial effects that:
by a single-factor analysis method, a laser texturing processing test is carried out on the surface of a die steel sample to obtain different types of texturing point appearances, so that the forming mechanisms of different types of texturing points can be analyzed and discussed conveniently, and the metallographic structure and microhardness of a texturing area material can be detected and analyzed, thereby exploring the influence rule of different process parameters on the geometric dimension of the texturing points and obtaining the mechanical property of the texturing and fusing appearance area material.
Drawings
FIG. 1 is a spherical crown two-dimensional topography of textured points;
FIG. 2 is a concave-topped spherical crown-shaped two-dimensional topography of textured spots;
FIG. 3 is a crater-like two-dimensional topography of textured points;
FIG. 4 is a geometric representation of a crater-like topography of textured points;
FIG. 5 is a graph showing the influence of laser power on the texture point profile;
FIG. 6 is a graph showing the influence of pulse width on the texture point profile;
FIG. 7 is a graph showing the influence of assist gas pressure on the texture point profile;
FIG. 8 is a schematic illustration of the microhardness measurement position after laser texturing;
FIG. 9 is a graph showing the hardness change law of the roughened surface of the die steel.
Detailed Description
The invention is further illustrated by the following specific embodiments in conjunction with the accompanying drawings.
Example 1:
a laser texturing test method for the surface of die steel comprises the following steps:
A. fixing a die steel sample, adjusting a laser head to enable the surface of the sample to be positioned on a focal plane of a laser spot, wherein the die steel sample is not subjected to any other surface heat treatment, and the surface of the die steel sample is polished by abrasive paper, and the surface roughness is about 0.05 mu m;
B. processing the die steel by adopting an optical fiber laser processing system, wherein the optical fiber laser processing system comprises an optical fiber laser and a workbench, a processing test is carried out by aiming at the laser power factor by using a single-factor rotation method, the defocusing amount is adjusted to be 0, the fixed pulse width in the test is 1100 mus, no auxiliary gas is used, and the laser power is adjusted to be 40, 50, 60, 70, 80, 90 and 100W;
C. and after the processing is finished, measuring the shape and size of the processed textured point by using a surface three-dimensional shape analyzer.
Before the processing test, the surface of the sample was wiped clean with a cotton ball soaked with absolute ethanol. When the morphology of the textured points is measured, cutting is carried out along the shape entering line of the symmetrical surface of the textured points, and after inlaying, coarse grinding, fine grinding, polishing and 4% nitric acid alcohol corrosion, a section micrograph of the morphology of the textured points is obtained. The die steel sample is made of Crl2MoV die steel.
Laser irradiates the surface of a die steel sample material, a partial region of the material absorbs enough heat to form a metal molten pool, molten pool solution flows under the drive of surface force and volume force, and micro-morphology is formed after solidification. The flow of the solution in the molten pool has an important influence on the final formation of the micro-morphology, while the flow of the molten liquid mainly comprises Marangoni convection and natural convection, the effect of the natural convection is very little, the Marangoni convection plays an important role in the flow of the liquid in the molten pool, the surface tension of the molten liquid is the main reason for the formation of the Marangoni convection, and the surface tension of the solution is related to the physical temperature gradient and the surface chemical concentration gradient. Therefore, in the absence of surface chemical active agents, temperature plays a major role in the formation of Marangoni convection. In the test, the incident laser beam belongs to a Gaussian beam, so the surface temperature of the material is also in Gaussian distribution, namely the temperature center is high, the periphery is low, and the surface tension in the middle is large and the surface tension in the periphery is small. The surface tension gradient drives the molten metal to flow from the periphery to the center, and finally the molten metal is solidified into the spherical crown textured point morphology, as shown in FIG. 1. The higher the laser peak power density, the higher the temperature of the central area of the molten pool, and the higher the temperature difference between the central area and the surrounding solution, and correspondingly, the higher the surface tension gradient, the stronger the Marangoni convection. When the peak power density of the laser is increased to a certain critical value, the central area of the molten pool breaks through the vaporization threshold value of the material, vaporization occurs, recoil pressure is generated, and convection from the periphery to the center is added, so that the center of the molten pool forms a depression, and a concave-top spherical crown shape appears, as shown in fig. 2. As the laser peak power density continues to increase, the surrounding molten metal increases, the central region vaporizes more obviously, the recoil pressure is higher, the vaporization loss speed of the central material is higher than the flow filling speed of the molten pool to the center, so that the central depression increases, and the crater shape is finally formed, as shown in fig. 3.
The appearance of the textured points extracted in the test is mostly like craters. FIG. 4 is a schematic diagram of the geometrical characteristics of the crater appearance, wherein d is the diameter of the textured points and h is the height of the protrusions of the textured points.
Test results show that the laser power influences the diameter and the height of the texture spot appearance as shown in fig. 5, and the diameter and the height of the texture spot appearance increase with the increase of the laser power, because when the pulse width is constant, the single pulse energy increases with the increase of the laser power, the diameter of a light spot is constant, the laser peak power density increases, the melted material becomes more, the geometric size of a molten pool becomes larger, and the diameter and the height of a texture projection both increase. When the laser power reaches 80W, the diameter of the texturing point is increased and then is reduced, the height of the protrusion is increased after being reduced, the top of the molten pool is sunken and deepened due to the influence of recoil pressure, so that the height of the protrusion is reduced, and then along with the increase of the laser power, the reverse pressure in the center of the molten pool is continuously increased to form an extrusion effect on two sides of the molten pool, so that the height of the protrusion is continuously increased.
Example 2:
the machining test was conducted using a single-factor alternation method for the pulse width factor, in which the fixed laser power was 70W, the assist gas was not used, and the pulse widths were adjusted to 100, 300, 500, 700, 900, 1100, and 1300 μ s. The rest is the same as example 1.
The influence relationship of the pulse width and the convex diameter and the height of the textured point topography obtained through experiments is shown in FIG. 5. When the pulse width is less than 100 mu s, the diameter and the height of the textured point are very small, and the texture of the textured point is hardly formed. This is because when the pulse width is small, the energy of a single pulse is small, and the diameter of the laser spot is not changed, so that the peak power density is small and almost does not reach the ablation threshold of the material itself, and the texturing phenomenon is not obvious at this time, and the formation of textured protrusions on the surface of the material is difficult to detect. With the increase of the pulse width, the single pulse energy is slowly increased, the texturing phenomenon becomes obvious, and the diameter and the height of the texturing bulge are gradually increased. After the pulse width reached 1000 mus. The melting and the solidification slowly reach a relative equilibrium state, so that the diameter and the height of the textured point change gradually
Example 3:
the machining test was conducted using a single-factor alternating method for the factor of the assist gas, in which the pulse width was fixed at 700. mu.s, the laser power was fixed at 90W, the assist gas nitrogen was blown vertically, and the gas pressures were adjusted to 0.1, O.2, O.3, and 0.4 MPa. The rest is the same as example 1.
The influence relationship of the gas pressure on the diameter and the height of the protrusions of the textured point morphology is obtained through experiments, as shown in FIG. 6, when the gas pressure is below 0.3MPa, the diameter and the height of the textured point morphology are reduced along with the increase of the gas pressure, and when the gas pressure is more than 0.3MPa, the diameter and the height of the textured point rapidly increase. The nitrogen can act on the surface of the molten pool stably when the gas pressure is low, the nitrogen element fused into the molten pool is increased along with the increase of the gas pressure, the nitrogen element changes the flow of the molten pool and plays a role in inhibiting the melting process, so that the diameter and the height of a textured point are reduced, and when the gas pressure is increased to 0.3MPa, the gas leaks due to high gas pressure, the nitrogen amount directly acting on the molten pool is reduced, the content of the nitrogen element in the molten pool is reduced, the inhibiting effect on the melting process is obviously reduced, and the appearance size is rapidly increased.
As shown in fig. 7, a microscopic picture of the spherical crown-shaped textured point morphology cross section is obtained by cutting along the shape-entering line of the symmetry plane of the textured point, and it can be seen that the texture of the textured fusing region is highly refined, mainly being cryptocrystal martensite, which is formed by mixing substructure dislocation-type lath martensite and needle-shaped martensite, the martensite is formed by high-temperature primary austenite phase in the rapid cooling process, and because the temperature gradient and the solidification speed are extremely fast in the fusing process of the laser, the crystal grains of the fusing layer are highly refined; the heat affected zone is equivalent to high-temperature tempering and is formed by mixing acicular martensite, troostite and unmelted ferrite, and a formed crystal grain obviously small-particle fusion zone; the matrix is composed of ferrite and pearlite, and both grains are relatively large. The microhardness after the laser texturing treatment was measured by an HV-100099314 microhardness meter at a position shown in fig. 8, and measured in the depth direction at points l, 2, 3. As shown in FIG. 9, the fused layer has a high microhardness after laser texturing with respect to the substrate, which is 647.6HV as high as about 2.2 times that of the substrate, but the microhardness of the surface layer of the fused layer is not the highest and that of the subsurface layer is the highest, because the surface layer material is in direct contact with air when the laser is applied to the surface of the die steel material, and decarburization and ablation occur, resulting in a carbon content of the surface layer lower than that of the subsurface layer and a hardness lower than that of the subsurface layer.
Through the above experiments, it was concluded that:
(1) in a laser texturing processing experiment on the die steel, three texturing point appearances can be obtained: spherical crown, concave crown, volcano-mouth shape.
(2) The physical temperature gradient and the chemical concentration gradient on the surface of the molten pool comprehensively influence the final texture point appearance. When no chemical concentration gradient exists on the surface of the molten pool, the temperature gradient plays a main role, the temperature gradient is small, the spherical crown shape can be formed, the temperature gradient is large, and the concave top spherical crown shape or the volcano-crater shape is formed.
(3) Different process parameters have different influences on the appearance of the textured points, and the diameter and the height of the textured points increase and then slow down with the increase of the laser pulse width; along with the increase of the laser power, the diameter of the texturing point is increased firstly and then becomes gentle, and the height of the bulge is increased firstly, then is reduced and then is increased. When the auxiliary gas is chlorine gas, the diameter and height of the texturing point are reduced and then rapidly increased along with the increase of the gas pressure.
(4) The texture of the melting zone of the textured point is highly refined, mainly cryptocrystalline martensite and has higher microhardness, but the microhardness of the surface layer of the melting layer is not the highest, and the apparent hardness of the subsurface layer is the highest, because when laser acts on a metal material, the surface layer material is directly contacted with air, so that decarburization and ablation phenomena are generated, the carbon content of the surface layer is lower than that of the subsurface layer, and the hardness is lower than that of the subsurface layer.
Claims (7)
1. A laser texturing test method for the surface of die steel is characterized by comprising the following steps:
A. fixing a die steel sample, and adjusting a laser head to enable the surface of the sample to be positioned on a focal plane of a laser spot;
B. processing the die steel by adopting an optical fiber laser processing system, wherein a processing test is carried out by using a single-factor alternation method aiming at three factors of laser power, pulse width and auxiliary gas respectively, the defocusing amount is adjusted to be 0, the pulse width is adjusted to be 100-1300 mu s, the laser power is 40-100W, and the nitrogen pressure is O.1-0.4 MPa;
C. and after the processing is finished, measuring the shape and size of the processed textured point by using a surface three-dimensional shape analyzer.
2. The method of claim 1, wherein the die steel sample in step A is not subjected to any other surface heat treatment.
3. The method for testing the laser texturing of the surface of the die steel according to claim 1, wherein the surface of the die steel sample in the step A is polished by sand paper, and the surface roughness is 0.04 to 0.06 μm.
4. The method of claim 1, wherein the surface of the sample is wiped clean with a cotton ball soaked with absolute ethanol before the machining test.
5. The die steel surface laser texturing test method of claim 1, wherein the fiber laser processing system comprises a fiber laser and a workbench.
6. The laser texturing test method for die steel surface according to claim 1 or 2 or 3 or 4 or 5, characterized in that when measuring the texture of the textured points, cutting along the symmetrical surface contour line of the textured points, and obtaining the cross-sectional microscopic image of the texture of the textured points after inlaying, rough grinding, fine grinding, polishing and 4% nitric acid alcohol etching.
7. The method for die steel surface laser texturing test according to claim 1 or 2 or 3 or 4 or 5, characterized in that the die steel test piece is made of Crl2MoV die steel.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4462660A (en) * | 1981-08-06 | 1984-07-31 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Modulating a laser beam |
| CN107363394A (en) * | 2017-07-04 | 2017-11-21 | 安徽腾龙泵阀制造有限公司 | A kind of surface of cold-rolled steel plate laser roughening processing method |
-
2019
- 2019-06-05 CN CN201910486351.0A patent/CN110814521A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4462660A (en) * | 1981-08-06 | 1984-07-31 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Modulating a laser beam |
| CN107363394A (en) * | 2017-07-04 | 2017-11-21 | 安徽腾龙泵阀制造有限公司 | A kind of surface of cold-rolled steel plate laser roughening processing method |
Non-Patent Citations (3)
| Title |
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| 刘莹等: "轧辊表面微凸体形貌激光毛化技术的试验研究", 《机械工程学报》 * |
| 李成冬等: "模具钢表面激光毛化工艺的试验研究 ", 《光学与光电技术》 * |
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