JP2007290052A - Surface machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface machining method which forms a recessed part having desired size and cross-sectional form in a surface of a workpiece of metal material or the like in a short period of time. <P>SOLUTION: The method comprises: a first process to carry out heat treatment to the surface of the workpiece by radiation of a laser beam for making hardness of the surface of the workpiece nonuniform; and a second process of carrying out grinding work to the surface of the workpiece after its hardness is made nonuniform. By controlling laser beam radiation conditions, the hardness of the workpiece is finely varied. By carrying out grinding work to the surface after the heat treatment (for hardening) by radiation of the laser beam, hardness difference in the surface of the workpiece causes a step (level difference). A recessed part having desired size and cross-sectional form is thus formed in a short period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface processing method, and more particularly to a surface processing method that can easily form a recess having a desired cross-sectional shape on the surface of a workpiece made of a metal material or the like.

  Conventionally, honing is applied to the surface after cutting and grinding in order to generate minute recesses (grooves) called oil reservoirs on the surface of steel materials, the inner surface of cylinders of automobiles, and the sliding surface of machine tools. Things have been done.

  Further, Patent Document 1 discloses a surface processing method in which a minute recess is formed by laser processing on the inner peripheral surface or the like of a cylinder block, and then grinding (finishing) is performed on the surface on which the raised portion after laser processing is formed. In addition, as a further improvement of such a processing method, Patent Document 1 discloses a laser for absorbing a hardness difference between a laser-processed portion and a laser-processed portion after laser processing. There has also been proposed a method of performing grinding (finishing) after quenching.

  However, honing is a method that can form minute recesses (steps) with high efficiency. However, the finish of the machined surface includes the grinding wheel (size, density, etc.), grinding wheel pressure, spindle speed (honing speed), and grinding direction. Since various factors such as corners act in a complicated manner, it is not easy to form a recess having a desired size and cross-sectional shape.

  On the other hand, in laser processing, the width (size), depth, etc. of the recess can be controlled relatively easily by adjusting the power of the irradiated laser beam, beam diameter, etc., but the recess is the workpiece (irradiated material) Is formed by evaporating by irradiation with laser light, and there is a problem that the processing time for forming the recesses becomes long.

In addition, since burrs (swelled parts) are formed at the periphery of the recesses formed by evaporation of the irradiated material by laser light irradiation, after laser processing as in Patent Document 1, burrs (swells) are formed. It is necessary to perform a grinding process (finishing process) for removing the part), and the processing time is further increased. Also, if burrs (protruding parts) are removed by grinding (finishing), the non-irradiated part of the laser beam on the workpiece is softer than the irradiated part of the workpiece during the grinding (finishing) process. For this reason, it may be preferentially shaved and the unirradiated portion of the laser beam on the surface of the workpiece may become an undesired concave surface. Therefore, in order to maintain the flatness of the periphery of the recess (laser beam non-irradiated portion) on the workpiece surface, as in Patent Document 1, the laser beam is irradiated on the laser beam non-irradiated portion of the workpiece after laser processing. It is necessary to perform quenching by irradiating light and then perform grinding (finishing), which further increases the processing time.
JP 2004-90067 A

In view of the above circumstances, the problem to be solved by the present invention is to provide a surface processing method capable of forming in a short time a recess having a desired size and cross-sectional shape on the surface of a workpiece such as a metal material. It is to be.
Another object is to provide a surface processing method capable of forming a recess having a desired size and cross-sectional shape without causing unnecessary burrs (swelled portions).
Another object is to provide a surface processing method capable of easily forming an uneven surface with high hardness including a recess having a desired size and cross-sectional shape.

  As a result of earnest research to solve the above problems, the present inventor has made the surface of the workpiece non-uniform in surface hardness by subjecting the surface of the workpiece to heat treatment by laser light irradiation, and then The result of further research based on the knowledge that a step corresponding to the hardness difference (change in hardness) in the surface is formed when the surface is cut (turned) with a blade. The present invention has been completed.

That is, the present invention
(1) A first step in which the surface of the workpiece is subjected to heat treatment by laser light irradiation to make the hardness of the workpiece surface non-uniform, and the surface of the workpiece having the non-uniform hardness is cut. A surface processing method comprising: a second step;
(2) In the first step, the surface processing method according to (1) above, wherein the surface of the workpiece is irradiated with laser light so that a part of the new heat treatment region overlaps the heat treatment region once formed,
(3) In the first step, the surface of the workpiece is irradiated with laser light such that heat treatment regions by laser light irradiation and unheated regions not irradiated with laser light are alternately formed, (1) The surface processing method as described,
(4) The workpiece is a columnar member, and the first step is a step of irradiating the surface of the columnar member rotating about its axis as the rotation axis while moving the laser beam in the axial direction of the columnar member. The surface processing method according to any one of the above (1) to (3), and (5) the above (1) to (4), wherein the workpiece is a member made of an iron-based metal material. The surface processing method as described in any one of these.

  According to the surface processing method of the present invention, the surface hardness of the workpiece can be finely changed by controlling the irradiation conditions (beam diameter, power, scanning speed, feeding speed, etc.) of the laser beam, and Since the hardness difference on the workpiece surface appears as a step (level difference) by cutting the workpiece surface thus formed, the recess having the desired size and cross-sectional shape is shortened. Can be formed in time.

  In addition, the surface of the work piece is irradiated by irradiating the surface of the work piece with laser light so that a part of the heat treatment area formed by laser light irradiation once overlaps a part of the heat treatment area formed by new laser light irradiation. While increasing the hardness of the entire predetermined area to be formed with the plurality of recesses, a hardness difference can be generated in the area. Therefore, by performing cutting on the surface of the workpiece including the region to be processed, it is possible to easily form an uneven surface whose surface is a hardened surface including a recess having a desired size and cross-sectional shape.

  Further, in the first step, the laser beam is moved so that the heat treatment regions by laser light irradiation and the non-heat treatment regions not irradiated with laser light are alternately formed on the surface of the workpiece, thereby processing the workpiece. Cured regions are intermittently formed on the object surface. Therefore, by cutting (turning) the surface of the workpiece, the hardened area remains, the non-hardened area is cut as it is, and the flatness is maintained, and the concave portion is formed without generating unnecessary burrs (raised parts). Can be formed.

  According to the surface processing method of the present invention, the hardness difference on the surface of the workpiece is directly expressed as a step (height difference) by the cutting process. This is the back of the cutting force acting on the cutting tool when cutting with the cutting tool (tool). The force changes according to the hardness of the workpiece surface (that is, the softer the surface, the smaller the back force, and the harder the surface, the greater the back force), resulting in varying cutting depth. This is probably because of this. On the other hand, in grinding processing (finishing processing, polishing processing) in which processing is performed by contacting a surface of a workpiece while rotating a grindstone (hard discs formed by bonding hard abrasive grains into a disk shape) The hardness difference on the surface of the workpiece is not faithfully reflected as the height difference, and the size and cross-sectional shape of the recess cannot be controlled. This is because back contact force acts on the grindstone rotating during grinding, but the contact area between the grindstone and the work piece is large, so the hardness change of the work piece surface does not accurately reflect the cutting depth, and the work piece is processed. It is considered that the hardness difference on the surface of the object is less likely to appear as a step (level difference).

  In general, when materials with different materials mixed (that is, materials with different mechanical properties) are cut (turned), the occurrence of steps due to the difference in elastic deformation during cutting of the material to be cut and the optimal finish Cutting conditions (optimal tool, cutting speed, etc.) to obtain the state differ for each material, so cutting (turning) of materials with different materials has been called “co-cutting” and has traditionally been avoided. It was. Therefore, conventionally, there has been no idea of performing cutting on a surface whose hardness has been made non-uniform by laser light irradiation as in the present invention.

Embodiments of the present invention will be described below with reference to the drawings.
In the present invention, the “workpiece” may be any material that is quenched (that is, can be cured) by heat treatment by laser light irradiation, and is not particularly limited. From the viewpoint of easy control of the degree of progress, for example, iron-based metal materials such as steel materials (carbon steel, alloy steel) and cast iron can be mentioned.

  In the surface processing method of the present invention, first, the surface of the workpiece is subjected to a heat treatment by laser light irradiation to make the surface hardness of the workpiece uneven.

  The method of laser light irradiation may be appropriately determined according to the shape of the workpiece. That is, the laser beam may be fixed and the workpiece may be moved, the workpiece may be fixed and the laser beam may be moved, or the laser beam and the workpiece may be moved together. From the viewpoint of work efficiency, it is preferable to move both the laser beam and the workpiece and move the laser beam irradiation (heat treatment region).

  FIG. 1 shows that a cylindrical member 1 made of carbon steel S45C is rotated about its axis as a rotation axis, and a laser beam (beam) 2 by a carbon dioxide laser is applied to the surface (outer peripheral surface) of the cylindrical member 1 in a circle. An example of a state in which the surface hardness of the columnar member 1 is made non-uniform by irradiating while feeding at a constant speed in the axial direction of the columnar member 1 (direction of arrow a in the figure) is shown. It is a figure. Reference numeral 3 in the figure denotes a shielding plate.

  As shown in FIG. 1, in the present invention, when the workpiece is a columnar member (including a cylindrical member), the columnar member 1 is rotated about its axis as a rotation axis, and the laser beam 2 is It is efficient to irradiate while moving in the axial direction of the cylindrical member 1 (direction of arrow a in the figure).

  FIG. 2 shows a laser power of 900 W, a spot diameter of a laser beam (laser beam): a diameter of 2 mm, a beam scanning speed (rotational speed of a cylindrical member) of 12.5 mm / sec, a beam feed speed (by the method of FIG. Laser beam is irradiated spirally on the surface of the cylindrical member (diameter φ: about 60 mm) made of carbon steel S45C under the irradiation condition of 1.6 mm / rev. Optical micrograph (FIG. 2 (a)) of the cross-section of the surface layer portion of the cylindrical member 1 after heat treatment (FIG. 2 (b)), and the surface of the cylindrical member 1 on the surface layer FIG. 2 (c) shows the relationship between the depth position and hardness (Vickers hardness). In FIG. 2C, the vertical axis indicates the hardness (Vickers hardness), and the horizontal axis indicates the same length as the distance in the horizontal direction (direction parallel to the axis of the cylindrical member) on the photograph. ) Is the measurement position, and the plot in FIG. 2 (c) is the Vickers hardness at that position.

  In FIG. 2 (a), 11a, 11b, and 11c indicate heat treatment regions formed by laser light (laser beam) irradiation for each rotation of the cylindrical portion 1, and a portion 12 surrounded by a dotted line indicates the cylindrical member 1 This is a portion where a part of the heat treatment region 11c formed during the subsequent rotation of the cylindrical member 1 overlaps the heat treatment region 11b formed during the rotation before the rotation. The dots (dots) in FIG. 2 (b) indicate the measurement points of hardness, and FIG. 2 (c) is a graph showing the relationship between the measurement points and the hardness (Vickers hardness).

  From FIG. 2A to FIG. 2C, a part of the heat treatment region 11 c formed during the subsequent rotation of the columnar member 1 overlapped with the heat treatment region 11 b formed during the previous rotation of the columnar member 1. In the portion 12, the heat treatment (quenching) time by laser light irradiation is the longest and the curing is most advanced, and it can be seen that the surface layer of the columnar member 1 has a hardness difference due to the difference in the degree of curing.

  In the present invention, various laser oscillators can be used as the laser oscillator used for irradiating the workpiece surface with laser light. In addition to the carbon dioxide laser described above, an argon laser, an excimer laser, a YAG laser, a helium neon laser, a ruby laser, and the like can be given. Among these, a carbon dioxide laser and a YAG laser are preferable from the viewpoint that large heat energy necessary for processing can be easily obtained (high output is easily obtained). Note that irradiation conditions (beam diameter, power, beam scanning speed, etc.) of the laser light may be appropriately selected according to the type of workpiece, the form of the groove to be formed, and the like.

For example, when the above carbon steel S45C is subjected to heat treatment (quenching) by irradiating a laser beam with a carbon dioxide laser, it is necessary to consider the laser absorptivity due to the difference in the surface condition. From this point, it is preferable to irradiate the laser beam by setting the laser power density and the processing time to appropriate values within the range of the square section labeled “surface quenching” in FIG.
In the present invention, as described above, cutting (turning) is performed on the surface of the workpiece that has been subjected to heat treatment by laser light irradiation to make the hardness nonuniform (that is, the surface of the workpiece that has caused a hardness difference). Apply processing. Such a cutting (turning) process is a process of cutting the surface of a workpiece with a constant cutting amount. That is, a cutting condition for obtaining a constant cutting amount on the surface of an uncured workpiece before laser beam irradiation (quenching) is determined, and cutting is performed under the cutting condition. When such cutting is performed, the back component of the cutting force acting on the cutting tool (tool) is smaller as the workpiece surface is softer according to the hardness of the workpiece surface (as the workpiece surface is harder). As a result, the cutting depth fluctuates, and a level difference (level difference) corresponding to the hardness difference on the workpiece surface appears.

  FIG. 3 shows the following cutting conditions A using an NC lathe on the surface of a cylindrical member made of carbon steel S45C whose hardness is made non-uniform by heat treatment (quenching) by laser light irradiation shown in FIG. Fig. 3 (b) is a schematic cross-sectional view corresponding to the optical micrograph of Fig. 2 (a), showing a sketch of the cross-section of the cylindrical member 1 after cutting (Fig. 3 (a)). It is shown together.

(Cutting condition A)
Tool: P30, rotational speed (v) of cylindrical member: 60 m / min, cutting amount (d): 0.5 mm, feeding amount (f): 0.1 mm / rev, cutting agent: not used

  FIG. 3 (a) shows the actual shape of the surface (uneven surface) of the cylindrical member 1 after machining, and the Vickers hardness (Hv) of each of the top A and the bottom B of the recess 10 on the uneven surface is also shown. ing.

  In FIG. 3B, 11a ′, 11b ′, and 11c ′ indicate heat treatment regions formed on the surface layer of the cylindrical member 1 by laser light irradiation, and 12a and 12b indicate overlapping portions of adjacent heat treatment regions. The dotted line indicates a planned cutting line with a cutting amount (0.5 mm).

  From the comparison between Fig. 3 (a) and Fig. 3 (b), using an NC lathe on the surface of a cylindrical member made of carbon steel S45C whose surface hardness is non-uniform by heat treatment (quenching) by laser light irradiation, When cutting is performed with a predetermined cut amount in the center direction, portions 12a and 12b where the heat treatment regions overlap on the surface of the cylindrical member (the portions are the portions where the heat treatment time by laser light irradiation is the longest and hardened to the maximum hardness) )), The portion becomes the top portion A, the hardness decreases with increasing distance from the portion, the amount of scraping increases, and the amount of scraping becomes maximum at the minimum hardness portion. It can be seen that this portion becomes the bottom B of the recess 10, and as a result, an uneven surface in which the recess 10 is continuous is formed.

  As described above, in the present invention, the surface of the workpiece (working region) is made non-uniform by irradiation with laser light (quenching), and then the cutting (turning) is performed. It can be seen that a step corresponding to the hardness difference on the surface of the object is formed, and a recess having a desired cross-sectional shape can be formed on the workpiece. Moreover, since the hardness difference of the surface of a workpiece reflects in the depth of a recessed part, the recessed part of comparatively deep depth can be formed easily. Incidentally, in the embodiment described with reference to FIGS. 1 to 3, a recess having an opening width of about 3 mm and a depth of about 20 μm could be formed.

  As in the embodiment described in FIGS. 1 to 3, the surface of the workpiece is irradiated with laser light so that a part of the new heat treatment region overlaps the heat treatment region once formed. When the hardened surface thus obtained is cut, an uneven surface whose surface is a hardened surface (that is, a post-processed surface in which concave portions whose inner surface is a hardened surface is continuous) can be easily formed. Such an uneven surface having a hardened surface (processed surface including a concave portion having an inner surface made of a hardened surface) is hardened (quenched) over the entire surface, and therefore has, for example, an oil pool due to the concave portion. However, when the entire surface is cured (quenched), it can be a sliding surface exhibiting excellent wear resistance. Therefore, if the surface processing method of the present invention is used, a highly durable sliding member can be easily produced.

  FIG. 4 (a) shows the laser power of 900 W, the spot diameter of laser light (laser beam): 2 mm in diameter, the beam scanning speed (rotational speed of the cylindrical member): 12.5 mm / sec, the beam in the method of FIG. Laser beam is spirally irradiated on the surface of a cylindrical member (diameter: 60 mm) made of carbon steel S45C under an irradiation condition of feed rate (moving speed in the axial direction of the cylindrical member): 1.6 mm / rev. FIG. 4B is a schematic diagram of a partial cross section of the cylindrical member 1 after the heat treatment, and FIG. 4B is a diagram of the cylindrical member under the grinding condition A using an NC lathe after the heat treatment. It is a schematic diagram of the partial cross section of the cylindrical member 1 after giving a cutting process to the surface of this.

  That is, in this embodiment, the axial direction of the cylindrical member 1 is such that the heat treatment regions 11a, 11b, 11c by the laser beam formed after one rotation of the cylindrical member 1 made of carbon steel S45C do not overlap each other. By irradiating the laser beam with a beam feeding speed of the laser beam to that higher than that of the above-described embodiment, the heat treatment regions 11a, 11b, 11c by laser beam irradiation are intermittently formed, and the cylindrical member 1 The surface of the cylindrical member 1 is cut with a cutting depth (0.5 mm) to form the recess 20.

  4 (a) and 4 (b), the amount of scraping is minimized at the maximum hardness portion where the quenching (hardening) of the center of the heat treatment regions 11a, 11b, and 11c by laser light irradiation has progressed most by cutting, and the center Since the hardness decreases and the amount of chipping increases as the distance from the center increases, the unheated region between the two adjacent heat-treated regions (11a and 11b, 11b and 11c) is not quenched (hardened), so the maximum amount of scraping As a result, it can be seen that the concave portion 20 whose cross-sectional shape reflects the shape of the heat treatment regions 11a, 11b, and 11c is formed. The recess 20 had an opening width of about 3 mm and a depth of about 20 μm.

  As described above, in the present invention, the workpiece is irradiated with the laser beam so that the heat treatment region by the laser beam irradiation and the unheated region not irradiated with the laser beam are alternately formed, and the hardness is made non-uniform. If surface processing is performed in such a manner that the surface is subjected to cutting, a concave portion having a shape reflecting the cross-sectional shape of the heat treatment region (cured region) is formed, and unheated between two adjacent heat treatment regions (cured region) Since the region (uncured region) is cut as it is to maintain its flatness, a concave portion can be formed without causing unnecessary burrs (raised portions) or the like. Further, according to this aspect, the hardness of the heat treatment region by laser light irradiation is directly reflected in the depth of the recess, so that it is possible to form a recess having a larger depth.

  In the surface processing method of the present invention, the cutting conditions (cutting speed, cutting depth, feed amount, etc.) are the material and shape of the workpiece, and the hardness of the heat treatment zone (hardening zone) by laser irradiation of the workpiece. It is determined appropriately according to the above. In the above embodiment, the cutting fluid is used in the dry process without using the cutting fluid, but the cutting fluid may be used. As the cutting fluid, a known cutting fluid conventionally used in the field of cutting can be used, and either oily or water-soluble can be used. When a cutting fluid is used, the cutting temperature is increased by high-speed machining in high-efficiency cutting, so that water solubility with a high cooling capacity is preferable from the viewpoint of suppressing the cutting temperature.

  In addition, when forming a recess (groove) equivalent to the recess (groove) formed by the method of the present invention by forming the recess (groove) only by cutting, the tool interferes with a portion that is not scraped during the movement of the tool. In order to avoid this, the tool moving distance becomes long, and the machining time is greatly increased. In addition, in order to control the cross-sectional shape of the recess in units of microns, the processing machine is required to have extremely high processing accuracy and cannot be easily implemented. On the other hand, the surface processing method of the present invention can shorten the processing time, and the cutting processing itself is not required to have extremely high processing accuracy, and can be handled by a general-purpose processing machine, and therefore is easy to implement.

  The surface processing method of the present invention can be used for forming functional surfaces of various members, but is particularly suitable for processing of sliding surfaces of various sliding members and processing of wear-resistant surfaces of various members.

It is the figure which showed typically an example of a mode that the surface of the workpiece (cylindrical member) of this invention was irradiated with a laser beam, and the hardness of the workpiece surface was made non-uniform | heterogenous. FIG. 2 (a) is an explanatory view of the present invention, FIG. 2 (a) is an optical micrograph of a cross section of a surface layer portion of a cylindrical member whose surface has been heat-treated by laser light irradiation, and FIG. 2 (b) is a diagram of FIG. FIG. 2 (c) is a diagram showing the relationship between the depth position from the surface of the surface layer portion and the hardness (Vickers hardness). FIG. 3 (a) is an explanatory view of the present invention, FIG. 3 (a) is a sketch drawing of a cross section of a main part of a cylindrical member after the surface is subjected to heat treatment by laser light irradiation and further subjected to cutting, and FIG. 3 (b) is a diagram. It is a schematic diagram of the cross section corresponding to the optical micrograph of 2 (a). 4A and 4B are explanatory views of the present invention, in which FIG. 4A is a schematic diagram of a cross-section of a surface layer portion of a cylindrical member whose surface is heat-treated by laser light irradiation, and FIG. 4B is a cut after heat treatment by laser light irradiation. It is a schematic diagram of the cross section of the surface layer part of the cylindrical member after giving a process. It is explanatory drawing of this invention, and is a figure which shows each suitable range of a laser power density and processing time when irradiating the laser beam by a carbon dioxide laser, and performing heat processing (quenching).

Explanation of symbols

1 Workpiece (cylindrical member)
2 Laser light 3 Shield plate

Claims (5)

  A first step in which the surface of the workpiece is subjected to heat treatment by laser light irradiation to make the hardness of the workpiece surface non-uniform, and a second step in which the workpiece surface having the non-uniform hardness is cut. And a surface processing method.   The surface processing method of Claim 1 which irradiates a laser beam so that a part of new heat processing area | region may overlap with the heat processing area | region once formed in the surface of the workpiece in the 1st process.   The surface processing according to claim 1, wherein in the first step, the surface of the workpiece is irradiated with laser light so that heat treatment regions by laser light irradiation and unheated regions not irradiated with laser light are alternately formed. Method.   The workpiece is a columnar member, and the first step is a step of irradiating the surface of the columnar member rotating about its axis as a rotation axis while moving the laser beam in the direction of the axis of the columnar member. The surface processing method as described in any one of Claims 1-3. The surface processing method according to claim 1, wherein the workpiece is a member made of an iron-based metal material.