JP6657558B2 - Processed parts excellent in corrosion resistance and method of manufacturing the same - Google Patents

Description

  The present invention relates to a machined part having a rounded hole end face shape, which improves the corrosion resistance of the end face of a machined hole of a thin steel plate.

  At present, steel sheets are widely used in automobiles, home appliances, and the like, and most steel sheets are subjected to machining such as cutting, drilling, and bending. Parts formed from these steel plates are generally subjected to a surface treatment (rust prevention treatment). In this case, for example, a steel sheet, such as a galvanized steel sheet, which has been subjected to surface treatment on one or both sides in advance, is machined into a material having a predetermined shape. In some cases, untreated steel sheet is used as a material, machined into a part having a predetermined shape, and then subjected to surface treatment such as painting.

  When a steel sheet which has been subjected to a surface treatment is used as a material and machined, the base steel sheet is exposed on the processed end face, so that there is a problem that the processed end face has insufficient corrosion resistance. Patent Literature 1 discloses a technology for limiting the content of steel plate components including impurity components, reducing the starting point of rust on a processed end surface as much as possible, and improving the corrosion resistance of the processed end surface in an indoor environment. ing.

  On the other hand, when a surface treatment is performed after forming a part having a predetermined shape, the machined end face is also coated, so that a part having excellent corrosion resistance on the processed end face can be obtained as compared with the case described above. However, even if surface treatment is applied to a part that has been subjected to punching or drilling, there is a problem that red rust is generated early around the hole.

  This is because burrs are formed in the processed part of the part, and the coating film is not easily formed on the sharp burr part, and the coating thickness of this part is easily thinner than other parts, so the corrosion resistance by the coating film is low. This is because they are not sufficiently exhibited and the periphery of the hole is easily corroded.

  Conventionally, in order to reduce burrs formed in drilled parts, appropriate clearance, counter punching, improvement of finished surface roughness of cutting edge, selection of blade material, strength (yield stress) or elongation of steel plate member Selection of characteristics, punching speed, selection of lubricant, and the like are being studied. However, these have problems such as limitations in applying any of them and deterioration of economic efficiency.

  Therefore, it is conceivable to apply the technology described in Patent Literature 1 as a rust preventive measure for a burr portion formed in a drilled portion. However, this technology is effective for steel sheets with a specified composition, because it limits the content of steel sheet components including impurity components, but is applicable to steel sheets without that composition. Cannot be used, and lacks versatility.

  In addition, as measures to prevent rust in the drilled part, designs that do not expose the edge, paint development, and deburring are being performed. However, design and development of paint that do not expose the edge are desirable. Effect has not yet been obtained.

  Grinding and polishing are generally employed as deburring processing. However, when performing the grinding and polishing on the drilled portion, it is difficult to insert a grinding and polishing tool into the processed hole, so that the deburring workability is poor and considerable work time must be spent. Further, there is a problem that polishing marks remain on the portion after the deburring process, and the surface is not smooth.

  On the other hand, as one of the deburring processes that solves such a problem, there is a method of irradiating burrs with a laser (see, for example, Patent Document 2). In this method, burrs can be removed, and the surface layer is melted and solidified by irradiating a laser, so that a smooth surface with small surface roughness is obtained. However, there may be a stepped portion around the deburred portion, and the coating film thickness at the stepped portion is smaller than other portions. Therefore, the corrosion resistance is not sufficiently exhibited by the coating film, and the periphery of the deburred portion is likely to corrode.

JP 2004-217960 A JP 2000-317660 A

  The present invention has been made in view of such circumstances, and in a machined part to be subjected to surface treatment such as painting after forming a part having a predetermined shape, the coating film thickness on the boring face is made uniform, and the boring face of the machined part is formed. An object of the present invention is to provide a processed part having excellent corrosion resistance.

  The present inventors have diligently studied a method for solving the above problem. As a result, by forming the drilling end face into a rounded end face shape without burrs, the coating environment (temperature, raw material supply amount, etc.) on the end face becomes uniform when forming the coating film, and It was found that the coating amount of the coating film was constant, that is, a uniform coating film thickness was obtained, and the processed part had improved paintability.

The gist of the present invention is as follows.
(1) A machined part having a coating film on a surface including an inner surface of a through-hole of a steel member having a plate thickness of 1 to 10 mm and having a through-hole, wherein the steel member has a cross-section parallel to a penetration direction of the through-hole. between the bore transition end portion of one surface hole transition end portion and the other surface of the are connected by a curve, Ri convex der the curve toward the central axis of the through hole, the end surface of the hole is rounded end face shape der workpiece, characterized in Rukoto.
(2) A method for producing a machined part having a coating film on a surface including an inner surface of a through-hole of a steel member having a thickness of 1 to 10 mm and having a through-hole, wherein a laser beam is perpendicular to an end face of the as-machined hole. To melt and solidify the end face, and in a cross section parallel to the penetration direction of the through hole, a curved line is formed between the hole transition end on one surface and the hole transition end on the other surface of the steel member. Connected, the curve is convex toward the central axis of the through-hole, and after forming the through-hole having a rounded end surface, the surface of the steel member is painted. Method of manufacturing processed parts.
(3) A reflecting mirror is arranged inside the hole as machined, a laser is irradiated to the reflecting mirror, and a laser is irradiated perpendicularly to an end face of the hole as machined. The method for manufacturing a processed part according to the above (2).
(4) The method according to (3), wherein the reflecting mirror has a conical shape.
(5) The method for manufacturing a machined part according to any one of (3) and (4), wherein the laser is scanned circumferentially on the surface of the reflecting mirror.
(6) The manufacturing of the machined part according to any one of (3) and (4), wherein the reflecting mirror is rotated around an axis parallel to a central axis of the machined hole as a rotation axis. Method.

  ADVANTAGE OF THE INVENTION According to this invention, the processed part which is excellent in the corrosion resistance after the coating of the end surface of a through-hole can be provided.

It is a figure showing the outline of the processed part of the steel member which has a hole. (A) is a perspective view of a machined component, (b) is an XX cross section of a machined component having a machined hole as it is, and (c) has a through hole with a rounded hole end surface. It is XX cross section of a processed part. (B) shows a photographic image of the test piece after the corrosion resistance test with a magnifying glass, and (A) and (C) show scanning electron microscope photographic images of the test piece before the corrosion resistance test. (A) is an image and a figure which show the external appearance of test piece a, (b) and test piece b. It is a figure which shows the outline of the apparatus which irradiates a laser perpendicularly with respect to a hole end surface. 4 shows a means for irradiating a laser perpendicular to a hole end face. (A) is an example in which the focal point of the laser is fixed by a conical reflecting mirror, and (b) is an example in which the focal point of the laser is fixed by a reflecting mirror inclined with respect to the axis of the laser. The figure which imitated the scanning electron microscope photograph image of the hole end surface after the coating of test pieces AE is shown. (A) is a view of the entire hole end face, and (b) is an enlarged view of a burr portion. The photograph image by the magnifying glass around the through-hole after the corrosion resistance test of the test pieces AE is shown.

  Hereinafter, the processed part of the present invention will be described.

  First, a machined part having a hole as machined will be described. 1: is a figure which shows the outline of the processed part of the steel member which has a hole. (A) is a perspective view of a machined component, and (b) is an XX cross section of the machined component as it is. The machined part 1 has been machined by bending, cutting, or the like, and has a machined hole 2 obtained by punching or drilling as shown in FIG. A hole formed by punching, drilling, or the like and being machined before forming a coating film is hereinafter referred to as a “machined hole” for convenience.

  In the present invention, the shape of the processing hole 2 is an annular shape having a continuous curved surface such as a circular shape and an elliptical shape, and the diameter is 5 to 30 mm. The processed part 1 is formed of a steel member having a plate thickness of 1 to 10 mm, and the steel type and composition of the steel member are not particularly limited.

  Then, as shown in FIG. 1 (b), the machined hole 2 is formed so as to penetrate one surface 3 of the steel member and the other surface 4 of the steel member. It has hole transition ends 5 and 6 which are ends that transition from the surface to the machining hole 2. The hole transition ends 5, 6 shown in FIG. 1 (a) are circular. In addition, as shown in FIG. 1B, in a cross section parallel to the through direction of the hole, the hole transition end 5 on one surface and the hole transition end 6 on the other surface are connected in a substantially straight line. Have been. A burr portion (not shown) is provided around one of the hole transition ends 5 and 6.

  The present invention restricts the shape of the hole end surface up to the hole transition ends 5 and 6 on both surfaces of the steel member in such a processed part, so that the coating film thickness on the surface of the processed part becomes uniform, This is to provide a machined part with improved paintability.

  In general, a method of processing a drilled end surface including a burr portion (hereinafter, referred to as “hole end surface”) by grinding and polishing is adopted. In these treatment methods, burrs are eliminated, but polishing marks remain on the portion after the deburring process. In addition, since the end face inside the hole is not subjected to the treatment, as shown in FIG. 1B, the gap between the hole transition end 5 on one surface and the hole transition end 6 on the other surface is almost equal. It remains connected in a straight line. Therefore, there is a portion where the angle changes at the boundary between the portion after the deburring and the end surface inside the hole.

  The present inventors have found that, unlike the surface of an open steel member, when the hole end surface has irregularities such as burrs, polishing marks, and portions where the angle changes, the coating environment on the end surface during the formation of the coating film. Was considered to be non-uniform, a uniform coating film thickness could not be obtained, and the periphery of the hole was likely to corrode.

  Therefore, a laser was irradiated from obliquely above the hole toward the hole end face, and the hole end face including the burr portion was subjected to a melting treatment to form a hole end face without irregularities. By this processing, burrs were eliminated on the hole end face, and a smooth hole end face was obtained. However, the molten metal melted off, and a stepped end face was formed toward the back side of the workpiece. For this reason, the coated part was coated, but the thickness of the coating was reduced at the step, and the coating thickness could not be made uniform.

  From these, the present inventors consider that by making the hole end face round and round without the above-mentioned unevenness and steps, the coating film thickness can be made uniform, and the shape of the hole end face is adjusted and studied. did.

  First, a machined part as shown in FIGS. 1A and 1B was prepared by forming a punched hole (punch diameter φ20 mm) in a hot-rolled steel sheet of 2.3 mm in thickness and 440 MPa class. One of the processed parts is a test piece a that is to remain a processed hole, and the other processed part is a test piece b that has a through-hole 9 having a rounded end face shape by melt-solidification. . A hole having a round end shape before forming a coating film is hereinafter referred to as a “through hole” for convenience and is distinguished from a “machined hole”.

  Then, the test piece a and the test piece b were coated, a corrosion resistance test was performed, and the influence of the shape of the hole end face 7 on the corrosion resistance was examined. The corrosion resistance test was carried out by repeating a treatment of 8 hours per cycle for 30 cycles based on a method for testing corrosion of automotive materials (JASOM609-91). One cycle consists of a salt spray test (2 hours, 5% NaCl, 35 ° C.), drying (4 hours, 30% RH, 60 ° C.), and wet test (2 hours, 95% RH, 50 ° C.).

  FIG. 2B is a photograph of a test piece after the corrosion resistance test, and FIGS. 2A and 2C are views showing the test piece before the corrosion resistance test. (A) shows the appearance of test piece a, and (b) shows the appearance of test piece b. FIG. 2 shows the appearance of the test piece a and the test piece b in the row direction. The figure in the stage (a) shows the left half of the center line 8 of the hole in the cross section in the through direction of the hole (FIG. 1 (b)). Or (c) corresponds to the left side of the center line 8 of the hole), wherein the figure of (b) is a plan view of the test piece, and the figure of (c) is a figure of (a). It is an enlarged view of the part of the frame shown in the figure of the column. (A) is a scaled down view of a photograph taken at 100 × magnification with a scanning electron optical microscope after cutting a steel plate along a line passing through the center of the hole and polishing the cut surface. . (C) is a reduced view of a scanning electron microscope photograph taken at a magnification of 2000 times.

  In the test piece a, as shown in the figures of (a) and (c), a high burr is formed at the hole transition end of the processed part 1, and the thickness of the coating film 10 (the upper left corner) is formed at the burr portion. From the lower right to the lower right) is thinner. Then, as shown in the figure in the row (b), red rust 11 indicated by a black line is generated around the processing hole indicated by light gray.

  On the other hand, in the test piece b, the hole end face 7 has a rounded shape as shown in the figure of the step (a), and the upper end of the hole as shown in the figure of the step (c). There are no burrs near the part, and the coating film thickness (shaded area from upper left to lower right) is uniform. In the middle diagram (b), almost no red rust 11 is generated around the through hole. FIG. 1C is an XX cross section of a machined part having a through hole with a rounded hole end surface, and shows a hole end surface 7 of a test piece b.

The results of the study are summarized below.
In the cross section parallel to the direction of penetration of the hole, the work piece 1 is connected in a curved manner over the entire length between the hole transition end 5 on one surface and the hole transition end 6 on the other surface 4 of the steel member. A through-hole (9) is provided so that the curve is convex toward the hole center axis (8). By forming the machined component 1 having such a hole end surface 7, as shown in FIG. 2, when the coating is applied, the thickness of the coating becomes uniform, and the coating becomes excellent in corrosion resistance.

  The present invention has been made to the invention described in the above (1) through the above-described examination process, and the necessary and preferable requirements of the present invention will be further described sequentially.

  In a cross section parallel to the direction of penetration of the hole, the convex shape of the curve connecting between the hole transition end 5 on one surface and the hole transition end 6 on the other surface 4 of the steel member is defined as the hole center. This means that a portion that is convex in the direction opposite to the axis 8, that is, a portion that is concave is not included. When a portion that is convex in the direction opposite to the hole center axis 8 is included, the coating film thickness is reduced at that portion. However, this recess does not include a fine recess of 3 μm or less. When the direction from the hole transition end to the hole center is defined as the height, the height from the hole transition end to the maximum protrusion is not limited as long as it can be used as a hole, but is preferably 1 mm or less.

  Further, the coating film included in the processed component is formed on the surface including the inner surface of the through hole 9 of the steel member. Any coating may be applied as long as it is applied to the surface. The thickness is preferably 5 to 50 μm. If it is less than 5 μm, a uniform film may not be obtained. On the other hand, if it exceeds 50 μm, the effect of corrosion resistance is saturated.

Next, a method for manufacturing a machined part according to the present invention will be described.
The machined component of the present invention is manufactured by irradiating a laser to the hole end surface of the machined component having a machined hole, and then painting the surface of the steel member. Then, at the time of laser irradiation, the laser output is adjusted so that the molten metal (steel) does not drip. Thus, when the laser is applied to the hole end surface, the surface layer is melted, and the melted metal is held in a convex shape in cross section by the action of surface tension. At this time, the material is rearranged, not removed.

  When the through hole 9 is formed by irradiating a laser, the hole end surface is melted and the hole end surface becomes rounded due to surface tension, so that the coating conditions on the end surface become uniform and the coating film thickness becomes uniform. It is preferred. Also, depending on the material and the initial roughness, the height of the unevenness on the hole end face is 3 μm or less.

  On the other hand, if the through holes 9 are formed by grinding or polishing, polishing marks remain on the end faces of the holes, and the film may become thinner at the polishing marks. Since the hole end surface formed by melting has no polishing marks, it can be distinguished from the hole formed by grinding or polishing by measuring the surface roughness. Alternatively, since the hole end surface is melted by a laser at a depth of about 20 to 300 μm, a steel sheet is cut along a line passing through the center of the hole, and the cut surface is polished and etched to reveal a structure. By observing the change in the structure with an optical microscope, it can be distinguished from holes formed by grinding or polishing.

(About laser irradiation)
In order to make the hole end face 7 of the workpiece 1 round, the laser is irradiated perpendicularly to the hole end face 7. Irradiating the laser perpendicular to the hole end face 7 means irradiating the laser at an angle of 85 to 95 ° with respect to the hole end face 7. However, the irradiation angle is preferably 90 °. FIG. 3 is a schematic view of an apparatus for irradiating a laser beam perpendicularly to a hole end face. As described above, the laser 13 is irradiated from the laser irradiation device 12 to the hole end face 7 via the reflecting mirror 14. In this way, when the laser is applied to the end face of the hole, the end face of the hole is uniformly heated, so that the end face of the hole is partially heated and the molten metal does not melt off.

  The laser irradiation device 12 is not particularly limited as long as it has an oscillator that can obtain a high-output laser 13. Examples of such an oscillator include a fiber laser, a YAG laser, a disk laser, a semiconductor laser, and a carbon dioxide laser. The output and beam diameter of the laser 13 may be selected according to the material of the processed part, and the output is preferably 0.1 to 10 kW and the beam diameter is preferably 0.5 to 3.0 mm. However, if the beam diameter of the laser 13 is larger than the thickness of the hole, the hole end face 7 is not irradiated with the laser, but is irradiated on the surface of the machined component or the jig of the reflecting mirror 14, so that the surface quality is deteriorated and the jig is damaged. Therefore, the thickness should be smaller than the thickness of the hole.

  The laser 13 is reflected by the reflecting mirror 14 arranged inside the processing hole so as to be radiated perpendicularly to the hole end face 7 and is radiated in the entire circumferential direction of the hole end face 7, so that the hole end face 7 has a round shape. It can have a tinged shape. In FIG. 3, the reflecting mirror 14 is formed in a conical shape, and the laser 13 is irradiated on the entire surface of the hole end face 7 by scanning the surface of the reflecting mirror 14 with the laser 13 in the circumferential direction. The material of the reflector is not limited as long as it has heat resistance, but a metal such as copper or a copper alloy is preferable. Further, the reflecting mirror may be one in which a reflecting film is formed on a support.

  The irradiation position of the laser 13 onto the reflecting mirror 14 is a position where the horizontal plane at the center in the thickness direction of the hole of the processed part intersects the reflecting mirror 14. Thereby, the center of the hole end face is irradiated with the laser, and the entire hole end face is easily melted and solidified. Then, the beam diameter of the laser 13 on the end face of the hole is not excessively reduced so as not to cause local heating. Further, the distance between the irradiation position of the laser 13 on the reflecting mirror and the irradiation position of the laser 13 on the end face of the hole is preferably 1 to 5 mm.

  The laser 13 is preferably moved using a remote laser method in which the laser 13 is scanned along the circumferential direction on the surface of the reflecting mirror 14 by mirror scanning. According to this, the irradiation of the laser 13 to the hole end face 7 can be performed instantaneously, the time can be reduced, and the circumferential scanning can be easily and efficiently performed. Scanning on the surface of the reflecting mirror 14 is preferably performed at 20 to 70 cm / min in the circumferential direction. Scanning may be performed once or two or more times.

  In FIG. 3, the laser 13 is irradiated in the entire circumferential direction of the hole end face 7 by making the reflecting mirror 14 conical and scanning the laser in the circumferential direction on the surface of the reflecting mirror 14, but is not limited thereto. Instead, if the laser 13 can be irradiated in the entire circumferential direction of the hole end face 7, the focal point of the laser and the shape of the reflecting mirror 13 can be changed according to the hole shape. Next, another example of a means for irradiating a laser beam with respect to a hole end face in a vertical direction will be described.

  FIG. 4 shows a means for irradiating the laser perpendicular to the hole end face. (A) is an example in which the focal point of the laser is fixed by a conical reflecting mirror, and (b) is an example in which the focal point of the laser is fixed by a reflecting mirror inclined with respect to the axis of the laser.

  Although the shape of the reflecting mirror 14 shown in FIG. 4A and the shape of the reflecting mirror 14 shown in FIG. 3 are the same, the means shown in FIG. The reflecting mirror 14, the workpiece 1, and the laser irradiation device 12 are adjusted so that the center axis of the diameter and the center line 8 of the hole coincide with each other. Then, the laser 13 is irradiated to the reflecting mirror 14 and is reflected simultaneously in all directions in the circumferential direction so as to be perpendicular to the hole end face 7.

  The reflecting mirror 13 shown in FIG. 4B is a reflecting mirror 14 having a surface inclined with respect to the axis of the laser. This reflecting surface is a rectangular surface obtained by cutting a rectangular parallelepiped so as to be inclined with respect to the long axis, or an elliptical shape obtained by cutting a cylinder so as to be inclined with respect to the height direction. It may be a cross section. The means shown in FIG. 4B fixes the focal point of the laser 13, irradiates the laser 13 to the reflecting mirror 14, rotates the reflecting mirror 13 around the hole center line 8 as a rotation axis, and The light is reflected vertically in all directions in the circumferential direction.

(About painting)
Although any coating method may be adopted for the coating of the processed part, electrodeposition coating is preferably applied to the base coating of the automobile part, which is performed for improving corrosion resistance.

  In the electrodeposition coating, an object to be coated is immersed as an electrode in the electrodeposition paint, and a voltage is applied to form an electrodeposition coating film on the object. When the workpiece to be electrodeposited is required to have high corrosion resistance, such as an automobile body, various surface treatments are performed before the electrodeposition coating. As such a surface treatment, for example, after alkali degreasing, a chemical conversion treatment of forming an inorganic film using a chemical conversion agent such as a zinc phosphate chemical conversion agent is performed.

  As the paint, either a cationic electrodeposition paint or an anion electrodeposition paint can be used, but a cationic electrodeposition paint is employed from the viewpoint of corrosion resistance and the like. The film thickness is 5 to 50 μm. When it is 5 μm or more, a uniform cationic electrodeposition coating film can be obtained. When it is 50 μm or less, it is economically advantageous. The coating conditions are not particularly limited, and general conditions can be adopted. For example, baking conditions can be 100 to 220 ° C. for 10 to 30 minutes.

  Next, an example of the present invention will be described. The conditions in the example are one condition example adopted to confirm the operability and effects of the present invention, and the present invention is based on this one condition example. It is not limited. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  A test piece was prepared by forming a punched hole (punch diameter φ20 mm) in a hot-rolled steel sheet having a thickness of 2.3 mm and a class of 440 MPa. At that time, test pieces having different burrs at the punched portions were formed by adjusting the mold clearance. The clearances were 4%, 22% and 48%. The clearance is represented by (h / t) × 100%, where h is the gap formed between the side surface of the punch and the side surface of the die, and t is the plate thickness of the test piece.

  Then, the test piece A was subjected to a process of grinding and removing burrs, the test pieces B to D were left punched, and the test piece E was subjected to a laser melting process. Test pieces A to D are comparative examples, and test piece E is an invention example.

The laser melting treatment for the test piece E was performed using the apparatus shown in FIG. 3 under the following conditions.
Laser oscillator: Semiconductor-pumped YAG laser Laser output: 1 kW
Laser scanning speed: 50 cm / min, one rotation scan on the circumference Laser spot diameter: φ1.0 mm
Reflecting mirror: Conical copper made with a 45 degree angle of inclination from the hole center axis

  Table 1 shows the clearances and burr heights of the test pieces A to E.

  Next, the test pieces A to E were coated. First, the test piece was subjected to alkali degreasing and zinc phosphate conversion treatment, and thereafter, painting was performed using a Pb-free cationic electrodeposition paint so as to have a target film thickness of 20 μm. FIG. 5 is a diagram simulating a photograph taken by a scanning electron microscope of the end faces of the test pieces A to E after coating. (A) is an image of the entire hole end face, and (b) is an enlarged image of a burr portion.

  The clearance between the test piece A and the test piece B is 4%, but since the test piece A has been subjected to a burr grinding process, the burr height is 0 μm, and no burr can be confirmed. And the test pieces BD changed the clearance, and when the clearance was set to 48%, the burr height became large, and high burr was confirmed. On the other hand, the test piece E was subjected to laser melting treatment to form a rounded through hole on the inner end face, so that the clearance was the same as the test piece C, but no burrs were observed. The test piece E has an inner end surface that is convex toward the center axis of the hole.

  From FIG. 5 (b), it can be confirmed that in the test piece A, the coating film thickness is different between the burr portion subjected to the grinding process and another straight portion. In addition, in the test pieces B to D, it can be confirmed that the coating thickness of the burr portion is thin. On the other hand, the test piece E has a uniform coating film thickness.

  Next, a corrosion resistance test was performed on the coated test pieces A to E. The corrosion resistance test was carried out by repeating the process of 8 hours per cycle for 30 cycles, as described above, based on the automotive material corrosion test method (JASOM609-91).

  FIG. 6 shows a photograph of the test pieces A to E taken with a magnifying glass around the hole after the corrosion resistance test. The clearance is also shown. Further, in this figure, red rust is indicated by a black line around the hole displayed in light gray, and the ratio of red rust to the circumference of the hole is defined as the red rust occurrence rate. Table 2 shows the red rust occurrence rate of 30% or less as A, the red rust occurrence rate of 31 to 70% as B, and the red rust occurrence rate of 71 to 100% as C.

Test pieces A to D have red rust. On the other hand, the test piece E has almost no red rust around the through hole. The clearance between the test piece A and the test piece B is 4%, but since the test piece A has been subjected to the burr grinding treatment, the generation of red rust is small, and the red rust generation category is B. However, red rust is generated because the coating film thickness is not uniform. In specimens B to D, remains punching, since burr is high, occurrence of red rust is remarkable, red rust classification is C.

On the other hand, since the test piece E was subjected to laser melting treatment to form a rounded through hole at the inner end face, the occurrence of red rust was reduced as compared with the test pieces A to D, and the red rust occurrence category was A. . From the comparison between the test piece E and the test piece C having the same clearance, the corrosion resistance is remarkably improved by forming the end face of the hole as a rounded through hole.

  ADVANTAGE OF THE INVENTION According to this invention, the processed part which is excellent in the corrosion resistance after the coating of the end surface of a through-hole can be provided. Therefore, the present invention has high industrial applicability.

REFERENCE SIGNS LIST 1 processed part 2 processed hole 3 one surface of steel member 4 other surface of steel member 5 hole transfer end of one surface 6 hole transfer end of other surface 7 hole end face 8 hole center line 9 through hole 10 painting Film 11 Red rust 12 Laser irradiation device 13 Laser 14 Reflector

Claims (6)

A processed part having a coating film on a surface including an inner surface of a through hole of a steel member having a thickness of 1 to 10 mm having a through hole,
In a cross section parallel to the penetration direction of the through hole, a hole transition end on one surface of the steel member and a hole transition end on the other surface are connected by a curve, and the curve is a central axis of the through hole. convex der towards is, workpiece end face of the hole and wherein the end face shape der Rukoto rounded. A method for producing a processed part having a coating film on a surface including an inner surface of a through hole of a steel member having a thickness of 1 to 10 mm having a through hole,
A laser is irradiated perpendicularly to the end face of the hole as machined to melt and solidify the end face, and in a cross section parallel to the penetration direction of the through hole, the hole transition end of one surface of the steel member and the other. The surface is connected with a hole transition end portion by a curve, the curve is convex toward the central axis of the through hole, and the end surface of the hole forms the through hole having a rounded end surface shape . After that, a method for manufacturing a machined part, wherein a surface of a steel member is coated.   3. The method according to claim 2, further comprising: arranging a reflecting mirror inside the as-machined hole, irradiating a laser to the reflecting mirror, and irradiating the laser perpendicularly to an end face of the as-machined hole. A method for producing a machined part according to item 1.   4. The method according to claim 3, wherein the reflecting mirror has a conical shape.   The method according to claim 3, wherein the laser is scanned circumferentially on the surface of the reflecting mirror.   The method according to claim 3, wherein the reflecting mirror is rotated around an axis parallel to a central axis of the machined hole as a rotation axis.