JP7329093B1 - METAL SURFACE TREATMENT METHOD AND SURFACE TREATMENT APPARATUS - Google Patents

Abstract

Kind Code: A1 A metal surface treatment method and surface treatment apparatus capable of smoothing a metal surface to a specular level only by irradiation with a high-energy beam at a practical treatment speed are provided. A metal surface treatment method for smoothing the surface of an object 90 made of metal by irradiating the surface of the object 90 with a laser beam 30, wherein the surface of the object 90 is irradiated with a laser beam 30 at a first energy density. A melting step of melting the metal on the surface of the object 90, and a melting and holding step of irradiating the molten portion of the metal formed by the melting step with the laser beam 30 at the second energy density to maintain the molten state of the molten portion of the metal. and the melting and holding step is performed continuously after the melting step. [Selection drawing] Fig. 6

Description

The present invention relates to a metal surface treatment method and a surface treatment apparatus for smoothing a metal surface by irradiating it with a high-energy beam.

As a surface treatment technique for smoothing a metal surface, a technique for irradiating a metal surface with a high-energy beam such as an electron beam or a laser beam has been proposed (for example, Patent Document 1). In this surface treatment technique, the surface of the metal is melted to fill the unevenness of the metal surface with the melted metal, and then the melted metal is solidified to flatten the surface.

JP-A-9-216075

However, even with the above-described prior art, it is difficult to smooth the metal surface to a so-called specular level at which the surrounding image is reflected at a practical processing speed. Therefore, in the prior art, in order to finish the surface of the metal to a mirror level, in addition to the high energy beam irradiation, it is necessary to add a polishing process or a chemical surface treatment process, and there is a problem that the number of work steps is large. be.

The inventors of the present application have found that rapid cooling of molten metal causes wrinkles and cracks as a factor that hinders mirror-finishing of the metal surface by a high-energy beam. In addition, it was found that the irradiation of conventional high-energy beams to metal parts containing air bubbles inside, such as cast products or three-dimensional modeled products, cannot ensure sufficient time for burying the blowholes and air bubbles with molten metal.

An object of the present invention is to solve the above problems.

One aspect of the following disclosure is a metal surface treatment method for smoothing a surface of a metal object by irradiating it with a high energy beam, wherein the high energy beam is applied to the surface of the object at a first energy density. a melting step of melting the metal on the surface of the object by irradiating with the high energy beam at a second energy density to melt the metal melted portion formed by the melting step; and a melting and holding step of holding the molten state of the metal, wherein the melting and holding step is performed continuously after the melting step.

Another aspect is a surface treatment apparatus that irradiates a high-energy beam to smooth the surface of a metal, comprising: an irradiation device that irradiates the surface of an object with the high-energy beam; and a driving device that scans the irradiation device. and, the irradiation device is distributed in the center of the high-energy beam and has a high-density irradiation area having a first energy density, and a high-density irradiation area distributed so as to surround the high-density irradiation area and having a higher energy density than the first energy density. and a low-density irradiation region having a second energy density with a lower energy density, and a surface treatment apparatus for irradiating a metal surface with a high-energy beam having a stepwise energy density distribution.

The metal surface treatment method and surface treatment apparatus according to the above aspect can smoothen the metal surface to a specular level at a practical treatment speed and only by irradiating a high-energy beam.

FIG. 1 is a configuration diagram of a surface treatment apparatus according to an embodiment. 2A is a diagram showing the energy density distribution of the laser beam irradiated from the irradiation apparatus of FIG. 1, and FIG. 2B is an explanatory diagram showing the cross-sectional shape of the melted portion of the object (metal) by the laser beam of FIG. 2A. is. FIG. 3 is an explanatory view showing scanning paths of laser beams performed in the surface treatment apparatus of FIG. FIG. 4A is a diagram showing the energy density distribution of a laser beam according to a comparative example, and FIG. 4B is an explanatory diagram showing a cross-sectional shape of a melted portion of an object (metal) by the laser beam of FIG. 4A. 5A is an explanatory view showing the cross-sectional structure of the scanning portion of the laser beam in FIG. 2A, and FIG. 5B is an explanatory view showing the cross-sectional structure of the scanning portion of the laser beam in FIG. 4A. 6A is an illustration showing the action of the laser beam shown in FIG. 2A on an object having a rough surface, and FIG. 6B is an illustration showing the action of the laser beam shown in FIG. 4A on an object having a rough surface. . FIG. 7A is an illustration showing the action of the laser beam shown in FIG. 2A on an object with a gap, and FIG. 7B is an illustration showing the action of the laser beam shown in FIG. 4A on an object with a gap. 8 shows a micrograph (Comparative Example 1) of the metal surface irradiated with the laser beam of FIG. 4A in the upper part, and shows a micrograph (Experimental example 1) of the metal surface irradiated with the laser beam in FIG. 2A in the lower part. is. 9A is a diagram showing the heat transfer coefficient of each metal surface of Comparative Example 1 and Experimental Example 1 at the scanning speed (low speed), and FIG. 9B is a graph showing Comparative Example 1 and Experimental Example at the scanning speed (medium speed). 9C shows the heat transfer coefficient of each metal surface of Comparative Example 1 and Experimental Example 1 at a high scanning speed (high speed); FIG. FIG. 10 is a photomicrograph of the metal surface of Experimental Example 2, in which the energy density of the low-density irradiation region is double that of Experimental Example 1. FIG. 11A is a graph showing the temperature histories of specific parts in Comparative Example 1, Experimental Examples 1 and 2, and FIG. 11B is a heat transfer coefficient of the metal surface in Comparative Example 1, Experimental Examples 1 and 2. It is a figure which shows. 12A is a photomicrograph of the melted region of Experimental Example 1 taken on a cross-section perpendicular to the scanning direction (scanning width direction), and FIG. 12B is a micrograph of the melted region of Experimental Example 2 taken on a cross-section perpendicular to the scanning direction. It is a photomicrograph. FIG. 13A is an explanatory diagram showing a method of measuring the temperature history of the low-density irradiation area, and FIG. 13B is an explanatory diagram showing a method of obtaining the cooling rate of the low-density irradiation area. FIG. 14 is a graph showing the relationship between the reference melting depth of the low-density irradiation region, the cooling rate of the low-density irradiation region, and the quality determination result of the surface roughness (Experimental Example 4). FIG. 15 shows the result of determining whether the surface roughness of a metal (aluminum alloy) is good or bad when the laser beam of FIG. 2A is irradiated at a scanning pitch of 0.15 mm at a medium scanning speed. 10 is a table showing the relationship between the laser light output value and the laser light output value of the low-density irradiation area (Experimental Example 5). FIG. 16 shows the result of determining whether the surface roughness of a metal (aluminum alloy) is good or bad when the laser beam in FIG. 2A is irradiated at a scanning pitch of 0.15 mm when the scanning speed is high. 10 is a table showing the relationship between light output values and laser light output values in low-density irradiation regions (Experimental Example 6). FIG. 17A is a graph showing changes in surface roughness when the scanning speed is set to medium speed and the scanning pitch and the laser light output value of the low-density irradiation region are changed (Experimental Example 7), and FIG. It is a graph which shows the change of the surface roughness at the time of making speed high and changing a scanning pitch and the laser-light output value of a low-density irradiation area|region (Experimental example 8). FIG. 18A is a diagram showing the measurement results of the heat transfer coefficient of the surface obtained by irradiating the cast part of the aluminum alloy with the laser beam, and FIG. 18B shows the first scan of the laser beam on the casting surface. 10 is a graph showing temperature changes (thermal history) caused by two laser beam scanning operations (Experimental Example 9).

A surface treatment apparatus 10 according to the present embodiment shown in FIG. 1 is used for flattening the surface of an object 90 made of metal. The surface treatment apparatus 10 irradiates the surface of the object 90 with the laser beam 30 to mirror the surface so that the surrounding image is reflected on the surface. Object 90 is, for example, a cast part such as an engine cylinder head. Moreover, the target object 90 may be a metal part formed by layered manufacturing.

The surface treatment apparatus 10 has a chamber 12 , a stage 14 , an irradiation device 16 , a measurement device 18 , a transfer device 20 and a controller 22 . Chamber 12 has a closed cavity. A stage 14 , an irradiation device 16 and a measurement device 18 are accommodated in the empty space of the chamber 12 . The empty space of the chamber 12 is filled with an inert gas, such as argon gas, so that the object 90 can be irradiated with the laser beam 30 under the inert gas atmosphere. Note that when an electron beam (particle beam) is used instead of the laser beam 30, the empty space of the chamber 12 may be a vacuum.

The empty space of the chamber 12 is partitioned into a measurement area 121 and a processing area 122 . A measuring device 18 is arranged in the measuring area 121 . An irradiation device 16 is arranged in the processing region 122 .

The stage 14 has a mounting surface for supporting the object 90 on its top. The stage 14 rotates to move the object 90 between the measurement area 121 and the processing area 122 .

The measuring device 18 measures the surface shape of the object 90 . The irradiation device 16 outputs the surface shape data of the object 90 to the controller 22 . The irradiation device 16 irradiates the surface of the object 90 with the laser beam 30 . The irradiation device 16 includes a laser oscillator 161 , a drive device 162 , an irradiation optical system 163 , an optical fiber 164 and an arm controller 167 . The laser oscillator 161 includes a first oscillator 165 that outputs laser light that forms the high-density irradiation region 32 (see FIG. 2) and a second oscillator that outputs laser light that forms the low-density irradiation region 34 (see FIG. 2). 166. The laser oscillator 161 can individually adjust the output value of the first oscillator 165 and the output value of the second oscillator 166 . In addition, when the irradiation optical system 163 includes a DOE (diffractive optical element), the laser oscillator 161 may have only the first oscillator 165 .

The optical fiber 164 guides the laser beam 30 output from the laser oscillator 161 to the irradiation optical system 163 (irradiation device 16). The irradiation optical system 163 is attached to the tip of the driving device 162 . The irradiation optical system 163 focuses and irradiates the object 90 with the laser beam 30 having a stepwise energy density distribution in the cross-sectional direction. The driving device 162 is, for example, a robot arm having multiple joints. The driving device 162 moves the irradiation optical system 163 under the control of the arm control unit 167 to scan the irradiation position of the laser beam 30 on the surface of the object 90 . The driving device 162 adjusts the orientation and direction of the irradiation optical system 163 according to the surface shape of the object 90 . The driving device 162 adjusts the orientation of the irradiation optical system 163 so that the laser beam 30 is always perpendicular to the surface of the object 90 .

When an electron beam is used instead of the laser beam 30, an electron beam irradiation device is used instead of the laser oscillator 161. FIG. The electron beam driver is attached to the tip of the driver 162 .

The transfer device 20 carries the object 90 into the chamber 12 and carries out the object 90 for which the surface treatment has been completed from the chamber 12 . The control unit 22 has a memory and a processor (not shown). The memory stores instructions for the processor. The processor performs the surface treatment of the object 90 by the surface treatment apparatus 10 by executing the instructions. A metal surface treatment method using the surface treatment apparatus 10 will be described below.

The surface treatment apparatus 10 irradiates the surface of an object 90 with a laser beam 30 having a cross-sectional shape shown in FIG. 2A, for example. The laser beam 30 has a high density irradiation region 32 and a low density irradiation region 34 . The high-density irradiation region 32 is positioned at the center of the laser beam 30 and has a circular cross-sectional shape. The high density irradiation region 32 has a relatively high first energy density. The low-density irradiation region 34 has a concentric shape with the high-density irradiation region 32 and is circularly distributed around the high-density irradiation region 32 . The low intensity irradiated region 34 has a second energy density that is lower than the first energy density. The laser beam 30 has a diametrically stepped energy density distribution unlike a general Gaussian distribution laser beam. The high-density irradiation region 32 and the low-density irradiation region 34 may be formed by irradiating pulsed laser light with different duty ratios. Further, the high-density irradiation region 32 and the low-density irradiation region 34 may be formed by moving a laser beam having a minute irradiation region at high speed within the high-density irradiation region 32 and the low-density irradiation region 34 .

The diameter of the low-density irradiation region 34 can be set, for example, two to three times the diameter of the high-density irradiation region 32 . For example, when the diameter of the high-density irradiation region 32 is 0.37 mm in this embodiment, the diameter of the low-density irradiation region 34 can be appropriately set within the range of 0.74 to 1.11 mm. However, the diameter of the low-density irradiation area 34 is not limited to the above values because it is also possible to set the low-density area three times or more by using a DOE (diffractive optical element) or the like. Moreover, such a laser beam 30 can be formed, for example, by overlapping two laser beams with different diameters. Note that the cross-sectional shape of the laser beam 30 is not limited to a circular shape, and may be rectangular or elliptical.

The laser beam 30 forms the melted region shown in FIG. 2B in the irradiated portion of the object 90 (metal). The fusion zone has a first fusion zone 92 and a second fusion zone 94 . The high density irradiation region 32 of the laser beam 30 forms a relatively deep first melt region 92 in the center of the irradiation region. Also, the low-density irradiated region 34 forms a second melted region 94 shallower than the first melted region 92 around the irradiated region. That is, both the first energy density and the second energy density have values capable of melting the surface of the object 90 .

The first energy density and the second energy density are appropriately set according to the physical properties such as the melting point and specific heat of the metal forming the object 90 . For example, the first energy density for an aluminum alloy may be higher than the second energy density, eg 13000 to 20000 W/mm ² . Also, the second energy density for the aluminum alloy can be, for example, 1000 to 10000 W/mm ² or less.

Laser beam 30 scans the surface of object 90, as shown in FIG. The laser beam 30 moves linearly along a predetermined scanning direction. As the laser beam 30 scans, the first melting region 92 moves on the surface of the object 90 . The first melting region 92 moves along both sides thereof in the scanning width direction and a second melting region 94 extending rearward in the scanning direction. Focusing on the passing portion of the first melting region 92 on the surface of the object 90, in one scan, following the step of melting the object 90 in the high-density irradiation region 32 of the first energy density, the second energy The process of maintaining the melted state in the low density irradiation region 34 is continuously performed.

The laser beam 30 moves in the scanning width direction at a scanning pitch of a constant width, and then performs backward scanning. It should be noted that the laser beam 30 may perform scanning only in the outward path without performing the scanning in the inward path. After that, the laser beam 30 scans in the forward path with a scanning pitch. The laser beam 30 scans the surface of the object 90 by reciprocating in the scanning direction while moving at a constant scanning pitch (in the scanning width direction). The scanning pitch of the laser beam 30 is set to a range in which the second melted region 94 in the later scan overlaps the passing portion of the first melted region 92 in the immediately preceding scan. Thus, the surface of the object 90 is overwritten at least once with a heat treatment that forms only the second melted region 94 after the first melted region 92 has passed.

Next, the effect of the metal surface treatment method of the present embodiment will be described in comparison with a comparative example. Note that the laser beam 40 according to the comparative example shown in FIG. 4A is composed only of the high-density irradiation region 42 . The energy density of the high density irradiation region 42 is the first energy density. As shown in FIG. 4B, only the first melted region 92 is formed on the surface of the object 90 when the laser beam 40 of the comparative example is applied.

As shown in FIG. 5B, when the laser beam 40 of the comparative example is applied, a first melted region 92 is formed at the tip of the scanning range. As the laser beam 40 moves, the first melted region 92 solidifies from the rear side in the moving direction. The first melted region 92 of the comparative example rapidly solidifies from the thick portion. The solidification of the first melted region 92 is not uniform and forms a wavy mass (not shown) behind the scanning range. As a result, rippling wrinkles 98 are formed on the surface of the object 90 . In addition, since a large temperature difference occurs between the surface and the inside of the solidified portion, cracks 99 occur frequently due to thermal stress. Due to such wrinkles 98 and cracks 99, it is difficult to mirror-finish the object 90 with the laser beam 40 of the comparative example.

As shown in FIG. 5A, the metal surface treatment method of this embodiment scans a laser beam 30 . The laser beam 30 forms a first melted region 92 by the high density irradiation region 32 at the tip of the scanning range. Behind the first melted region 92 in the moving direction of the laser beam 30 is irradiated by the low-density irradiation region 34, and the second melted region 94 shallower than the first melted region 92 is distributed so as to draw a trajectory. The melting depth of the second melting region 94 gradually becomes shallower away from the first melting region 92 . In the second melting region 94, the temperature gradient near the surface of the object 90 is moderated by the gradual cooling of the metal components forming the object 90. FIG. Therefore, the metal surface treatment method of the embodiment can prevent the occurrence of cracks during solidification of the first melted region 92 and the second melted region 94 . The gradual cooling of the metal component by the second melting region 94 can prevent the surface of the object 90 from being wrinkled.

As shown in FIG. 6A, the metal surface treatment method of the present embodiment forms a first melted region 92 with a deep melt depth. Therefore, even if the surface of the object 90 has relatively large unevenness 990 , the unevenness 990 can be flattened by the first melting region 92 . When the object 90 is a cast product, it may have relatively large unevenness 990 as a casting surface. The metal surface treatment method of the present embodiment can flatten a cast product having unevenness 990 .

Further, as shown in FIG. 7A, when the target object 90 is a cast product or a three-dimensional modeled product, voids 992 (cast cavities) may be formed on the surface. According to the metal surface treatment method of the present embodiment, the first melted region 92 formed by the high-density irradiation region 32 has a sufficient melting amount, and the solidification rate is increased by the continuously irradiated low-density irradiation region 34 . , the voids 992 can be reliably filled with the molten metal 994 flowing into the voids 992, and the voids 992 can be flattened by a single surface treatment.

Furthermore, in the metal surface treatment method of the present embodiment, the roughening process by the first melting region 92 is followed by the finish processing by the low-density irradiation region 34 substantially. Therefore, in the metal surface treatment method of the present embodiment, even if the object 90 has rough unevenness 990 or has gaps 992, the surface can be mirror-finished by one-time surface treatment by a series of scans with the laser beam 30. It can be flattened to level.

In the laser beam 40 of the comparative example shown in FIG. 6B, in order to prevent wrinkles 98 and cracks 99 on the surface, it is conceivable to set the intensity to form a shallow melting depth. In this case, as shown in FIG. 6B, the object 90 having rough unevenness 990 cannot be completely removed by one scan, and multiple irradiations are required, which increases the processing time. do. Further, when the above-described laser beam 40 is irradiated to an object 90 having a relatively large gap 992 as shown in FIG. 7B, the amount of molten metal 994 is small and solidifies relatively early, so that the gap 992 is completely filled. I can't. Therefore, the surface treatment method of the comparative example requires multiple surface treatments.

Experimental results in which the laser beam 30 and the laser beam 40 were irradiated and scanned on the surface of the object 90 made of an aluminum alloy will be described below.

(Comparative example 1)
In Comparative Example 1, the laser beam 40 scanned the surface of the aluminum alloy. The diameter of the laser beam 40 of Comparative Example 1 was 0.37 mm, and the surface was observed by changing the scanning speed of the laser beam 40 into three stages of low speed, medium speed, and high speed. The power of the laser beam 40 is 1.6 kW when the feed speed is low and medium speed, and 2.6 kW when the feed speed is set to high. The scanning pitch is 0.15 mm in both cases.

The results are shown in the upper part of FIG. As shown in the upper part of FIG. 8, in the surface treatment of Comparative Example 1, a large number of irregularly wavy wrinkles were generated on the surface after scanning with the laser beam 40, and black spots were generated here and there. I can see it. A large number of wrinkles 98 and cracks 99 were generated on the surface, and blowholes remained in places, resulting in a rough surface.

(Experimental example 1)
In Experimental Example 1, the laser beam 30 scanned the surface of the aluminum alloy. The laser beam 30 of Experimental Example 1 has a high-density irradiation region 32 with a diameter of 0.37 mm and a low-density irradiation region 34 with a diameter of 0.97 mm. As in Comparative Example 1, in Experimental Example 1, observations were made when the scanning speed was set to three stages of low speed, medium speed, and high speed. In both cases, the scanning pitch was 0.15 mm. The laser light output value of the high-density irradiation region 32 was 1.6 kW when the scanning speed was low and medium speed, and was 2.0 kW when the scanning speed was high. In addition, the laser light output value of the low-density irradiation region 34 is 2.0 kW when the scanning speed is low, 2.5 kW when the scanning speed is medium, and 3.5 kW when the scanning speed is high. 0.5 kW.

As shown in the lower part of FIG. 8, the surface treatment of Experimental Example 1 resulted in less wrinkles 98 and cracks 99 on the surface compared to Comparative Example 1, and also reduced the number of blowholes.

Next, in Experimental Example 1 and Comparative Example 1, the specular level of the metal surface was evaluated. In this evaluation, the degree of specular surface level of the metal surface was evaluated as the heat transfer coefficient. A heat transfer coefficient is a value obtained from the temperature rise of a metal surface when a flame of a predetermined temperature is brought into contact with the metal surface for a predetermined time. If the metal surface is rough and non-mirror, the heat transfer coefficient will increase due to the increased absorption of radiant light from the flame. Also, when the metal surface becomes a mirror surface, the reflectance of the radiant light of the flame increases and the heat transfer coefficient decreases. The heat transfer coefficient reflects the surface roughness of the metal as a relative value.

As shown in FIGS. 9A to 9C, in Comparative Example 1 and Experimental Example 1, the heat transfer coefficient tends to increase as the scanning speed of the laser beams 30 and 40 increases. The heat transfer coefficient of Experimental Example 1 is lower than that of Comparative Example 1 at any scanning speed. Thus, the laser beam 30 of this embodiment is effective in making the metal surface mirror-like.

(Experimental example 2)
In Experimental Example 2, the optimum irradiation energy density of the low-density irradiation region 34 was examined. In Experimental Example 2, the laser light output of the low-density irradiation region 34 was set to 6 kW, which is larger than in Experimental Example 1. FIG. The laser light output of the high-density irradiation region 32 in Experimental Example 2 is the same as in Experimental Example 1. FIG. In Experimental Example 2, the laser beam 30 scanned the surface of the metal (aluminum alloy) at a scanning speed of medium speed and a scanning pitch of 0.15 mm. The results are shown in FIG. As shown, many cracks 99 were generated on the metal surface according to Experimental Example 2. As shown in FIG. 11B, it was found that the metal surface of Experimental Example 2 has a higher heat transfer coefficient than Experimental Example 1 and Comparative Example 1, and that the flattening effect of the metal surface is reduced for the cast aluminum alloy.

When the laser beams 30 and 40 of Comparative Example 1, Experimental Example 1, and Experimental Example 2 are scanned at high speed, the surface of a specific irradiated portion of the metal exhibits temperature changes shown in FIG. 11A. As shown in FIG. 11A , the slope of the temperature change over time, which indicates the cooling rate, decreases in the order of Comparative Example 1, Experimental Example 1, and Experimental Example 2. FIG. Therefore, the slope of the cooling rate of the laser beam 30 having the low-density irradiation region 34 is gentler than that of the laser beam 40 having only the high-density irradiation region 32 . Furthermore, as the laser light output of the low-density irradiation region 34 increases, the slope of the cooling rate becomes gentler.

However, as shown in FIG. 11B, the heat transfer coefficient of Experimental Example 2 is greater than the heat transfer coefficients of Experimental Example 1 and Comparative Example 1. Experimental Example 2 revealed that the surface roughness is not determined only by the cooling rate.

12A and 12B respectively show the results of cutting the metals of Experimental Examples 1 and 2 and observing the cross section near the metal surface. The dashed line in the figure indicates the boundary of the melted portion. As shown in the figure, the melted portion of the metal surface changes so as to become deeper as it approaches the portion through which the high-density irradiation region 32 of the laser beam 30 passes from the end in the width direction of the scanning range.

In FIGS. 12A and 12B, the range of arrows marked with 0.15 mm is the scan pitch, which indicates the range of movement of the current scan from the previous scan. In the laser beams 30 of Experimental Examples 1 and 2, the difference between the radius of the high-density irradiation region 32 and the radius of the low-density irradiation region 34 is 0.3 mm, which is larger than the scanning pitch of 0.15 mm. Therefore, the 0.15 mm arrow range reflects the melted portion formed only by the low intensity irradiation region 34 . In Experimental Example 2, in which the low-density irradiation region 34 has a high laser light output, a deeper part is melted than in Experimental Example 1, in which the low-density irradiation region 34 has a low laser light output. From this result, it can be seen that it is necessary to consider not only the cooling rate but also the melting depth of the low-density irradiation region 34 in the metal surface treatment method using the laser beam 30 .

(Experimental example 4)
In Experimental Example 4 described below, the inventors determined the relationship between the melting depth and cooling rate of the low-density irradiation region 34 and the surface roughness of the metal. The melting depth and cooling rate of the low-density irradiated region 34 are obtained by the following methods.

The melting depth of the low-density irradiated region 34 is determined by observation of a section cut through the metal surface. A cross-sectional image of the portion last scanned with the laser beam 30 is obtained from the microscope image. From the cross-sectional image, the boundary between the melted portion and the unmelted portion is obtained by image processing. Next, the melt depth of the portion located inside the scan width direction from the end of the melted portion by the width of the scan pitch (for example, 0.15 mm) is the melt depth of the low-density irradiation region 34 (hereinafter referred to as the reference melt depth). measured as

The cooling rate is then measured using a radiation thermometer. As the radiation thermometer, an ultra-high-speed radiation thermometer capable of measuring the surface temperature of a circular measurement spot 52 having a predetermined measurement diameter (for example, 1.5 mm) at sampling intervals of several microseconds can be used. In Experimental Example 4, measurements were performed using a radiation thermometer manufactured by Yamazato Sangyo Co., Ltd. (model number IGA740-LO).

As for the cooling rate, as shown in FIG. 13A, the measuring spot 52 of the radiation thermometer and the passing position of the laser beam 30 are matched. A portion of the measurement spot 52 overlaps the position through which the outer periphery of the high-density irradiation area 32 passes. Also, the position through which the low-density irradiation region 34 passes overlaps with the measurement spot 52 closer to the center. Next, the laser beam 30 is scanned at a predetermined scanning speed, and the change in temperature over time is obtained as a cooling speed curve using a radiation thermometer. FIG. 13B shows measurement examples of the cooling rate curves of the laser beams 30 in Experimental Examples 1 and 2. As shown in FIG.

Next, a cooling rate curve is extracted in the range from the time when the temperature shows a peak value to the time when the metal surface solidifies. The solidification of the metal surface can be determined, for example, from the change in slope of the curve in FIG. 13B showing temperature change. The cooling rate is obtained as a value obtained by differentiating the extracted cooling rate curve with respect to time.

In Experimental Example 4, the laser light output of each of the high-density irradiation region 32 and the low-density irradiation region 34 was changed, and the scanning speed was changed to determine the surface roughness, the cooling speed, and the melting depth of the low-density irradiation region 34. asked for In Experimental Example 4, metal surface treatment was performed in an argon gas atmosphere. The results of Experimental Example 4 are shown in FIG.

Each plot in FIG. 14 shows the cooling rate and the melting depth (relative value) of the low-density irradiation region 34 under each measurement condition. In the laser beam 30 of Experimental Example 4, the diameter of the high-density irradiation region 32 is 0.37 mm, and the diameter of the low-density irradiation region 34 is 0.95 mm. The scanning pitch was 0.15 mm under all measurement conditions. The laser light output value of the high density irradiation area 32 was changed according to the scanning speed. When the scanning speed was low, the laser light output value of the high-density irradiation area 32 was set to 1.6 kW. When the scanning speed was medium speed, the laser light output value of the high-density irradiation area 32 was set to 1.6 kW. When the scanning speed was high, the laser light output value of the high-density irradiation area 32 was set to 2.0 kW. In Experimental Example 4, the cooling rate [°C/msec] changes according to the scanning speed.

The laser light output value of the low-density irradiation region 34 was changed in the range of 0 kW to 6 kW. The reference melt depth changes according to the laser light output value of the low-density irradiation region 34 . In FIG. 14, the condition satisfying the arithmetic mean height Sa (mirror finish) of 0.25 μm or less (0.25 μm or less in this embodiment, but a value that can be appropriately set according to desired requirements) is defined as “ ◯” is plotted, and the condition where the arithmetic mean height Sa exceeds 0.25 μm is plotted with “×”. In Experimental Example 4, the scan pitch was fixed at 0.15 mm in all measurements.

According to Experimental Example 4, for the aluminum alloy, the arithmetic mean height Sa was 0.25 μm in the range of the reference melting depth of 8 μm or more and 40 μm or less. More preferably, as shown below the hatched line in FIG. 14, the upper limit of the standard melting depth is such that the value obtained by dividing the standard melting depth [μm] by the cooling rate [° C./msec] is 0.25. By setting the range below, the arithmetic mean height Sa of the metal surface can be made 0.25 μm or less.

(Experimental example 5)
In Experimental Example 5, under the condition that the scanning speed is medium speed and the scanning pitch is fixed at 0.15 mm, the laser light output of the high-density irradiation region 32, the laser light output of the low-density irradiation region 34, and the arithmetic operation of the metal surface A relationship with the average height Sa was investigated. The respective diameters of the high-density irradiation region 32 and the low-density irradiation region 34 in Experimental Example 5 are the same as in Example 4. In Experimental Example 5, similarly to Experimental Example 4, metal surface treatment was performed in an argon gas atmosphere. The results are shown in the table of FIG. The numerical values in the table indicate the arithmetic mean height Sa.

As shown in FIG. 15, in Experimental Example 5, it was confirmed that the arithmetic mean height Sa of the metal surface treatment could be 0.25 μm or less under predetermined conditions. It has been confirmed that under the processing conditions in which the arithmetic mean height Sa is 0.25 μm or less, there is a range in which the laser light output of the high-density irradiation region 32 is less susceptible to fluctuations of about 0.6 kW. In addition, it can be confirmed that the processing conditions in which the arithmetic mean height Sa is 0.25 μm or less have a range in which the laser light output of the low-density irradiation region 34 is not easily affected by fluctuations of about 1.0 kW. Ta.

(Experimental example 6)
In Experimental Example 6, under the condition that the scanning speed is high and the scanning pitch is fixed at 0.15 mm, the laser light output of the high-density irradiation region 32, the laser light output of the low-density irradiation region 34, and the arithmetic mean of the metal surface A relationship with the height Sa was investigated. The respective diameters of the high-density irradiation region 32 and the low-density irradiation region 34 in Experimental Example 6 are the same as in Example 4. In Experimental Example 6, similarly to Experimental Example 4, metal surface treatment was performed in an argon gas atmosphere. The results are shown in the table of FIG. The numerical values in the table indicate the arithmetic mean height Sa.

As shown in FIG. 16, also in Experimental Example 6, it was confirmed that the arithmetic mean height Sa of the metal surface treatment could be 0.25 μm or less under predetermined conditions. It has been confirmed that under the processing conditions in which the arithmetic mean height Sa is 0.25 μm or less, there is a range in which the laser light output of the high-density irradiation region 32 is less susceptible to fluctuations of about 0.6 kW. In addition, it can be confirmed that the processing conditions in which the arithmetic mean height Sa is 0.25 μm or less have a range in which the laser light output of the low-density irradiation region 34 is not easily affected by fluctuations of about 1.0 kW. Ta.

(Experimental example 7)
Experimental Example 7 shows the result of examining the effect of the scanning pitch on the roughness of the metal surface. In Experimental Example 7, the laser light output of the high-density irradiation region 32 was fixed at 1.6 kW, the scanning speed was fixed at a medium speed, and the scanning pitch and the laser light output of the low-density irradiation region 34 were variously changed. The surface treatment of the aluminum alloy was performed under the conditions. Arithmetic mean height Sa was measured. In the laser beam 30 of Experimental Example 7, the diameter of the high-density irradiation region 32 is 0.37 mm, and the diameter of the low-density irradiation region 34 is 0.97 mm.

As shown in FIG. 17A, increasing the scan pitch from 0.15 mm to 0.2 mm, 0.25 mm, and 0.3 mm resulted in a rapid increase in the arithmetic mean height Sa of the surface of the aluminum alloy. An increase in scanning pitch leads to an improvement in processing speed. However, from the result of FIG. 17A, it was found that the scan pitch is limited to 0.15 mm in the case of the laser beam 30 with the diameter of the low-density irradiation region 34 of 0.97 mm.

(Experimental example 8)
Experimental Example 8 shows the result of examining the effect of the scanning pitch on the roughness of the metal surface. In Experimental Example 8, the laser light output of the high-density irradiation region 32 of the laser beam 30 was fixed at 2.0 kW, and the scanning speed was increased. Other processing conditions in Experimental Example 8 are the same as in Experimental Example 7.

As shown in FIG. 17B, when the scanning pitch is set to a value greater than 0.15 mm, the arithmetic mean height Sa of the surface of the aluminum alloy exceeds 0.25 μm. From the result of FIG. 17B, it was found that the limit of the scanning pitch is 0.15 mm in the case of the laser beam 30 with the diameter of the low-density irradiation region 34 of 0.97 mm even when the scanning speed is high.

(Experimental example 9)
Experimental Example 9 shows the results of examination of surface treatment conditions for aluminum alloy cast parts. In Experimental Example 9, the machined surface and the casting surface of the aluminum alloy cast part were subjected to surface treatment with a laser beam 30 . Sample 70 has a surface irradiated with laser beam 30 against the machined surface of a cast part in an argon gas atmosphere. The sample 72 has a surface obtained by irradiating the casting surface (unprocessed surface) of an aluminum alloy cast part with the laser beam 30 in an argon gas atmosphere. A sample 74 has a surface obtained by irradiating the casting surface (unprocessed surface) of an aluminum alloy cast part with the laser beam 30 twice in an argon gas atmosphere. The sample 76 has a surface irradiated with the laser beam 30 with respect to the machined surface in the atmosphere.

The heat transfer coefficients of samples 70, 72, 74, 76 are shown in FIG. 18A. As shown in the figure, it is found that the surface of the sample 72, in which the unprocessed casting surface is irradiated once, has the largest heat transfer coefficient.

Next, in Experimental Example 9, the temperature change when the casting surface was irradiated with the laser beam 30 was measured with a radiation thermometer. The temperature change (thermal history) due to the first scanning of the laser beam 30 and the temperature change due to the second scanning showed changes shown in FIG. 18B. As shown, the temperature in the first scan of the laser beam 30 showed a higher value than the temperature in the second scan of the laser beam 30 . The temperature change in the first scan on the casting surface causes a temperature rise due to an oxidation reaction. In the first scan, the temperature rise is large, so the cooling rate of the melted portion is increased and the surface roughness is increased.

Therefore, from the results of Experimental Example 9, it can be seen that it is preferable to perform a step of removing the casting surface in advance for metal cast parts. That is, it is effective to add a step of removing the casting surface by irradiating the cast metal part with a laser beam.

The above embodiments are summarized below.

The metal surface treatment method of the present embodiment is a metal surface treatment method in which the surface of an object 90 made of metal is irradiated with a high-energy beam to smooth the surface of the object, and the surface of the object is irradiated with a first energy density. a melting step of irradiating the high-energy beam to melt the metal on the surface of the object; a melting and holding step of holding the molten state of the molten portion of the metal, wherein the melting and holding step is continuously performed after the melting step.

According to the metal surface treatment method, the molten state of the metal is maintained for a longer time by the melting and holding step. As a result, the molten metal can flow into recesses such as cavities, smoothing the surface of the metal.

In the metal surface treatment method described above, the second energy density is lower than the first energy density, and the high-energy beam is irradiated so that the melting depth is shallower in the melting and holding step than in the melting step. good too. This metal surface treatment method prevents the rapid solidification of the molten metal, thereby preventing the occurrence of wrinkles and cracks on the surface and making it possible to finish the metal surface to a state close to a mirror surface.

In the metal surface treatment method described above, the high-energy beam is distributed so as to surround the high-density irradiation region 32 with the first energy density located in the center and the periphery of the high-density irradiation region with the second energy density. , and may have a stepped energy density distribution. In this metal surface treatment method, since the area of the low-density irradiation region is large, the duration of the melting and holding process can be lengthened.

In the metal surface treatment method described above, the melting step may be performed in the high-density irradiation region, and the melting and holding step may be performed in the low-density irradiation region. This metal surface treatment method can make the melting depth of the portion where the melting and holding process is performed shallower than the melting depth of the melting process, so that the metal surface can be finished to a state closer to a mirror surface.

In the metal surface treatment method described above, the high-density irradiation region and the low-density irradiation region are distributed concentrically, and the ratio of the diameter of the high-density irradiation region to the diameter of the low-density irradiation region is 1:1. It may be 2 to 1:3. The high-density irradiation region and the low-density irradiation region may be distributed non-circularly, and the ratio of the dimension of the high-density irradiation region to the dimension of the low-density irradiation region may be 1:3 or more. This metal surface treatment method makes it possible to secure a sufficient time for the melting and holding step by widening the area of the low-density irradiation region.

In the metal surface treatment method described above, the high-energy beam irradiation is performed by scanning the surface of the object to be irradiated with the high-energy beam so as to move forward and backward in a predetermined direction. The high-energy beam may be scanned so that the low-density irradiation region in the return pass overlaps the high-density irradiation region in the forward pass. In this metal surface treatment method, by overwriting the irradiated area of the high-density irradiation area with the low-density irradiation area, finishing can be performed at the same time, and the metal surface can be made to a near-mirror surface at a practical processing speed. can be smoothed.

In the metal surface treatment method, the metal is aluminum or an aluminum alloy, and the depth of the melted portion at a position closer to the center of the high-energy beam by the scanning pitch from the end of the melted region of the low-density irradiation region. The second energy density may be set in a range in which the reference melting depth is in the range of 18 μm to 40 μm. This metal surface treatment method can efficiently smoothen the surface of aluminum or an aluminum alloy to a state close to a mirror surface.

In the metal surface treatment method, the scanning speed of the high-energy beam is such that the value obtained by dividing the reference melting depth value (μm) by the cooling speed of the molten portion (° C./msec) is 0.25 or less. It may be set as a range. According to this metal surface treatment method, the difference in solidification speed between the surface layer and the deep layer of the molten metal is kept within a range that does not cause cracks, so the surface of the metal can be smoothed.

In the metal surface treatment method described above, the melting step and the melting and holding step may be performed in an inert gas atmosphere. This metal surface treatment method can prevent roughening of the metal surface due to oxidation and smooth the metal surface.

In the metal surface treatment method described above, the high-energy beam may be a laser beam. This metal surface treatment method can perform surface treatment at atmospheric pressure, and can reduce equipment costs.

The metal surface treatment method may include, prior to the melting step, removing an oxide film or plating film from the metal surface by irradiation with a high-energy beam. This metal surface treatment method suppresses the temperature rise of the surface by suppressing the surface reaction during the irradiation of the high-energy beam, and can prevent the surface of the metal from being roughened.

This embodiment is a surface treatment apparatus 10 that irradiates a high energy beam to smooth the surface of a metal, and includes an irradiation device 16 that irradiates the surface of an object with a high energy beam, and a drive that scans the irradiation device. a device 162, wherein the irradiation device is distributed in the center of the high-energy beam and has a high-density irradiation area of a first energy density; and a low-density irradiation region having a second energy density lower than the density, and irradiating the metal surface with a high-energy beam having a stepped energy density distribution.

The surface treatment apparatus described above prevents the rapid solidification of the molten metal, thereby preventing the occurrence of wrinkles and cracks on the surface and making it possible to finish the metal surface to a state close to a mirror surface.

It should be noted that the present invention is not limited to the above-described embodiments, and can take various configurations without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10... Surface treatment apparatus 16... Irradiation apparatus 30, 40... Laser beam 32, 42... High density irradiation area 34... Low density irradiation area 90... Object 162... Driving device

Claims (12)

A metal surface treatment method for smoothing the surface of an object made of metal by irradiating it with a high-energy beam,
a melting step of irradiating the surface of the object with the high energy beam at a first energy density to melt the metal on the surface of the object;
a melting and holding step of irradiating the high-energy beam at a second energy density to the molten portion of the metal formed by the melting step to maintain the molten state of the molten portion of the metal;
The melting and holding step is performed continuously after the melting step,
Metal surface treatment method. 2. The method of surface treating a metal according to claim 1, wherein said second energy density is lower than said first energy density, and said melting and holding step is performed at said high energy such that the melting depth is shallower than said melting step. emit a beam
Metal surface treatment method. 3. The metal surface treatment method according to claim 1, wherein the high-energy beam is distributed so as to surround the high-density irradiation area of the first energy density located in the center and the periphery of the high-density irradiation area. and a low-density irradiation region of the second energy density, having a stepwise energy density distribution,
Metal surface treatment method. 4. A method of surface treating a metal according to claim 3, wherein said melting step is performed in said high density irradiation region and said melting and holding step is performed in said low density irradiation region. The metal surface treatment method according to claim 3 or 4,
The high-density irradiation region and the low-density irradiation region are distributed concentrically,
The ratio of the diameter of the high density irradiation area and the diameter of the low density irradiation area is 1:2 to 1:3.
Metal surface treatment method. 6. The metal surface treatment method according to any one of claims 3 to 5, wherein the irradiation of the high-energy beam is such that the surface of the object is irradiated with the high-energy beam in forward and backward passes in a predetermined direction. while scanning so as to move and
scanning the high-energy beam so that the low-density irradiation region in the return pass overlaps with the high-density irradiation region in the forward pass;
Metal surface treatment method. 7. The metal surface treatment method according to claim 6, wherein the metal is aluminum or an aluminum alloy, and the metal is aluminum or an aluminum alloy, and at a position closer to the center of the high-energy beam by a scan pitch from the end of the melted region of the low-density irradiation region, When the depth of the melted portion is set as a reference melt depth, the second energy density is set in a range where the reference melt depth is in the range of 18 μm to 40 μm.
Metal surface treatment method. 8. The metal surface treatment method according to claim 7, wherein the scanning speed of the high energy beam is such that the value obtained by dividing the reference melting depth (μm) by the cooling speed (° C./msec) of the molten portion is 0.00. 25 or less,
Metal surface treatment method. 9. The metal surface treatment method according to claim 7 or 8, wherein the melting step and the melting and holding step are performed in an inert gas atmosphere.
Metal surface treatment method. The metal surface treatment method according to any one of claims 1 to 9, wherein the high-energy beam is a laser beam.
Metal surface treatment method. The metal surface treatment method according to any one of claims 1 to 10, comprising a step of removing an oxide film or a plating film on the metal surface by irradiating the high-energy beam prior to the melting step. ,
Metal surface treatment method. A surface treatment apparatus that irradiates a high-energy beam to smooth the surface of a metal,
an irradiation device for irradiating the surface of an object with the high-energy beam;
and a driving device for scanning the irradiation device,
The irradiation device is distributed in the center of the high-energy beam and includes a high-density irradiation region having a first energy density and a second energy distribution surrounding the high-density irradiation region and having a lower energy density than the first energy density. and a low-density irradiation region, and irradiating the metal surface with the high-energy beam having a stepwise energy density distribution;
Surface treatment equipment.

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