Smoothing method

Abstract

To provide a smoothing processing method which enables the alleviation of the ununiformity of smoothing processing on a surface of a workpiece.SOLUTION: A smoothing processing method M includes: a preparation step S1 of mounting a workpiece on a rotary shaft of a rotation mechanism; and a blast processing step S2 of direct pressure type blast-processing on the workpiece while rotating the workpiece with the rotary shaft as an axial center. In the blast processing, an injection material is injected in a direction orthogonal to the rotary shaft, in which the injection material contains a core material constituted of an elastomer and abrasive grains provided on a surface of the core material with the hardness of the core material lower than that of the abrasive grains.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a smoothing method.

Background Art

[0002] There is a known technique for smoothing the surface of a part by blasting. For example, in Patent Document 1, abrasive particles composed of hard fine particles are projected onto the surface of a rolling element to form oil pools on the entire surface, and abrasive particles composed of an elastic body containing abrasive grains are projected onto the surface of the rolling element at a predetermined angle to smooth the surface while maintaining the oil pools.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the polishing method described in Patent Document 1, in order to smooth the surface while maintaining the oil pools, the abrasive particles (spraying material) are projected at a predetermined angle. In this case, since the spraying material collides with the surface at the above angle, the amount of cut can vary depending on the position of the surface. Therefore, there is a risk that the surface cannot be processed uniformly.

[0005] This disclosure describes a smoothing method capable of reducing the non-uniformity of the smoothing process on the surface of a workpiece.

Means for Solving the Problems

[0006] A smoothing method relating to one aspect of this disclosure includes the steps of: attaching a workpiece to the rotating shaft of a rotating mechanism; and applying a direct-pressure blast treatment to the workpiece while rotating the workpiece around the rotating shaft as its axis. In the blast treatment, a blasting material is sprayed in a direction perpendicular to the rotating shaft. The blasting material includes a core material made of an elastic body and abrasive grains provided on the surface of the core material. The hardness of the core material is lower than the hardness of the abrasive grains. [Effects of the Invention]

[0007] According to each aspect and embodiment of this disclosure, it is possible to reduce the non-uniformity of the smoothing process on the surface of the workpiece. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a process diagram of a smoothing process according to one embodiment. [Figure 2] Figure 2 is a schematic diagram showing a part of the processing apparatus used in the smoothing method shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing an example of the abrasive material used in the blasting process shown in Figure 1. [Figure 4] Figure 4 is a diagram illustrating the blasting process shown in Figure 1. [Figure 5] Figure 5 is a diagram illustrating the smoothing mechanism. [Figure 6] Figure 6(a) shows the relationship between the injection angle and the maximum height. Figure 6(b) shows the relationship between the injection angle and the erosion depth. [Figure 7] Figure 7(a) shows the relationship between injection pressure and maximum height. Figure 7(b) shows the relationship between injection pressure and erosion depth. [Figure 8]Figure 8(a) shows the amount of tooth erosion in the tooth trace direction when the injection pressure is 0.01 MPa. Figure 8(b) shows the amount of tooth erosion in the tooth trace direction when the injection pressure is 0.05 MPa. Figure 8(c) shows the amount of tooth erosion in the tooth trace direction when the injection pressure is 0.10 MPa. Figure 8(d) shows the amount of tooth erosion in the tooth trace direction when the injection pressure is 0.20 MPa. [Figure 9] Figure 9(a) shows the relationship between the injection distance and the maximum height. Figure 9(b) shows the relationship between the injection distance and the erosion depth. [Figure 10] Figure 10(a) shows the relationship between the workpiece rotation speed and the maximum height. Figure 10(b) shows the relationship between the workpiece rotation speed and the cutting depth. [Figure 11] Figure 11(a) shows the relationship between the abrasive content of the abrasive material and the maximum height. Figure 11(b) shows the relationship between the abrasive content of the abrasive material and the erosion depth. [Figure 12] Figure 12(a) shows the relationship between the particle size distribution of the auger and the maximum height. Figure 12(b) shows the relationship between the particle size distribution of the auger and the erosion depth. [Figure 13] Figure 13 shows the residual stress values ​​of a workpiece that has undergone peening treatment and the residual stress values ​​of a workpiece that has undergone smoothing treatment after peening treatment. [Modes for carrying out the invention]

[0009] [Summary of the embodiments of this disclosure] First, an overview of the embodiments of this disclosure will be provided.

[0010] (Clause 1) A smoothing method relating to one aspect of the present disclosure includes the steps of: attaching a workpiece to the rotating shaft of a rotating mechanism; and applying a direct-pressure blast treatment to the workpiece while rotating the workpiece with the rotating shaft as its axis. In the blast treatment, a blasting material is sprayed in a direction perpendicular to the rotating shaft. The blasting material includes a core material made of an elastic body and abrasive grains provided on the surface of the core material. The hardness of the core material is lower than the hardness of the abrasive grains.

[0011] In this smoothing method, a direct-pressure blasting process is applied to the workpiece. Therefore, the blasting material directly goes towards the workpiece without spreading from the nozzle, and within the range where the blasting material is injected on the surface of the workpiece, the density of the blasting material is substantially constant. In the blasting process, the blasting material is injected in a direction perpendicular to the rotation axis of the rotation mechanism to which the workpiece is attached, so that the distance between the tip of the nozzle from which the blasting material is injected and the workpiece surface is substantially constant. Therefore, the non-uniformity of the amount of workpiece material removed can be reduced. As a result, it is possible to reduce the non-uniformity of the smoothing process on the surface of the workpiece.

[0012] (Clause 2) In the smoothing method described in Clause 1 above, in the process of applying the blasting process, the injection pressure of the blasting material may be set to be 0.01 MPa or more and 0.10 MPa or less. As the injection pressure of the blasting material increases, the amount of material removed increases, and the airflow near the surface of the workpiece is more likely to be disturbed. Due to the disturbance of the airflow, the injection amount of the blasting material per unit area may vary depending on the position of the workpiece surface. If the injection pressure of the blasting material is too low, the surface of the workpiece cannot be sufficiently machined. On the other hand, if the injection pressure of the blasting material is within the above range, it is possible to suppress the disturbance of the airflow near the surface of the workpiece without excessively machining the surface of the workpiece. Therefore, it is possible to further reduce the non-uniformity of the smoothing process on the surface of the workpiece.

[0013] (Clause 3) In the smoothing method described in Clause 1 or Clause 2 above, in the process of applying the blasting process, the injection distance of the blasting material may be set to be 50 mm or more and 100 mm or less. As the injection distance of the blasting material decreases, the amount of material removed tends to increase. If the injection distance of the blasting material is too long, the surface of the workpiece cannot be sufficiently machined. On the other hand, if the injection distance of the blasting material is within the above range, it is possible to reduce the surface roughness of the workpiece without excessively machining the surface of the workpiece.

[0014] (Clause 4) In the smoothing method described in any one of Clauses 1 to 3 above, the rotation speed of the workpiece may be set to 30 revolutions per minute or less in the step of applying blast treatment. When the rotation speed of the workpiece is high, the relative speed between the blasting material and the workpiece also increases. As a result, a stronger frictional force is generated on the workpiece surface, and the amount of erosion tends to increase. In contrast, if the rotation speed of the workpiece is within the above range, the surface roughness of the workpiece can be reduced without excessively eroding the workpiece surface.

[0015] (Clause 5) In the smoothing method described in any one of Clauses 1 to 4 above, the abrasive content of the spray material may be 15% by mass or more and 26% by mass or less. As the abrasive content of the spray material increases, the number of times the abrasive particles come into contact with the workpiece surface increases, so the amount of abrasion tends to increase. If the abrasive content of the spray material is too low, the surface of the workpiece cannot be sufficiently abraded. On the other hand, if the abrasive content of the spray material is within the above range, the surface roughness of the workpiece can be reduced without excessive abrasion of the workpiece surface.

[0016] (Clause 6) In the smoothing method described in any one of Clauses 1 to 5 above, the aerated material may have a particle size distribution of 125 μm or more and 600 μm or less. If the particle size of the aerated material is large, there is a higher possibility that the aerated material will not reach a part of the workpiece surface if the workpiece has a complex shape. On the other hand, if the particle size of the aerated material is small, the aerated material can come into contact with the entire surface of the workpiece even if the workpiece has a complex shape. For this reason, the smaller the particle size of the aerated material, the greater the amount of material removed tends to be. In contrast, if the particle size of the aerated material is within the above range, it is possible to increase the possibility that the entire surface of the workpiece will be processed without excessive material removal from the workpiece surface.

[0017] (Clause 7) In the smoothing method described in any one of Clauses 1 to 6 above, in the step of applying blast treatment, a first period in which the workpiece is rotated in a first rotational direction with the rotation axis as the axis, and a second period in which the workpiece is rotated in a second rotational direction opposite to the first rotational direction, may be alternately repeated. If the blasting material slides on the workpiece surface in only one direction, the workpiece surface may not be processed uniformly. In contrast, since the blasting material slides not only on the workpiece surface in one direction but also in the opposite direction, it is possible to further reduce the non-uniformity of the smoothing treatment on the workpiece surface.

[0018] (Clause 8) The smoothing method described in any one of Clauses 1 to 7 above may further include a step of applying a peening treatment to the workpiece before the blasting treatment. When a workpiece is subjected to a peening treatment, compressive residual stress is imparted to the workpiece. This compressive residual stress is maximum at a predetermined depth from the surface of the workpiece. Therefore, by performing a blasting treatment after the peening treatment, the surface of the workpiece is removed, and the portion with high compressive residual stress is exposed on the workpiece surface. Thus, the strength of the workpiece after processing can be increased.

[0019] [Examples of embodiments of this disclosure] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Each figure may show an XYZ coordinate system. The Y-axis direction intersects (in this case, orthogonal to) the X-axis and Z-axis directions. The Z-axis direction intersects (in this case, orthogonal to) the X-axis and Y-axis directions. For example, the X-axis and Y-axis directions are horizontal, and the Z-axis direction is vertical. In this specification, numerical ranges indicated using "~" indicate a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively. The individually stated upper and lower limits can be combined in any way.

[0020] A smoothing method according to one embodiment will be described with reference to Figures 1 to 5. Figure 1 is a process diagram of the smoothing method according to one embodiment. Figure 2 is a schematic diagram showing a part of the processing apparatus used in the smoothing method shown in Figure 1. Figure 3 is a schematic diagram showing an example of the aerosol used in the blasting process shown in Figure 1. Figure 4 is a diagram for explaining the blasting process shown in Figure 1. Figure 5 is a diagram for explaining the smoothing mechanism. The smoothing method M shown in Figure 1 is a method for smoothing the surface of a workpiece W. The workpiece W is, for example, a part having a complex shape. Examples of workpiece W include sliding parts or drive parts. In this embodiment, a gear is used as an example of workpiece W.

[0021] As shown in Figure 2, a processing device 10 is used in the smoothing method M. The processing device 10 is a direct-pressure type blasting device. The processing device 10 includes a rotating mechanism 11 and a nozzle 12. The rotating mechanism 11 is a mechanism (device) that rotates a workpiece W attached to a rotating shaft 11a around the rotating shaft 11a (the central axis AX). The rotating shaft 11a extends in the X-axis direction. The rotating mechanism 11 is configured so that the rotating shaft 11a can move forward and backward in the X-axis direction. The nozzle 12 sprays a propellant 30 toward the surface of the workpiece W attached to the rotating shaft 11a. A nozzle opening 12a is provided at the tip of the nozzle 12. The nozzle opening 12a is located above the rotating shaft 11a and faces the rotating shaft 11a (workpiece W). The diameter of the nozzle opening 12a is, for example, 10 mm.

[0022] As shown in Figure 3, the propellant 30 includes a core material 31 and abrasive grains 32. The core material 31 is made of an elastic material. The elastic material is made of, for example, a thermoplastic resin. From the viewpoint of ease of manufacturing the propellant 30, an example of a thermoplastic resin is a hot melt resin. A hot melt resin is a solid (solid phase) at room temperature and melts into a liquid (liquid phase) at a temperature above its melting point. By changing the hot melt resin from its liquid phase to a solid phase while it is in contact with another material, the hot melt resin is bonded to the other material. Hot melt resins have a low melting point and are elastic, making it easy to manufacture the propellant 30.

[0023] As an example, a hot melt resin with a melting point of 60°C or higher and 100°C or lower may be used. If the melting point is lower than 60°C, there is a risk of it becoming a liquid phase during blasting. If the melting point exceeds 100°C, the process of fixing the abrasive grains 32 may be costly, and the softening point also tends to be high, which may make it difficult to control the rubber elasticity. The softening point is the temperature at which the hot melt resin begins to soften. A hot melt resin in which the rubber elasticity changes with temperature in a temperature range of 80°C or lower may be used. For example, a hot melt resin in which the change in rubber hardness is 1.3(A) or more for a temperature change of 1°C in the temperature range of 20°C to 50°C may be used.

[0024] Hot melt resins that meet the above conditions include, for example, those primarily composed of ethylene vinyl acetate, polyurethane, low-density polyethylene, polyester, polyamide, polyolefin, ionomer, or polyvinyl alcohol. Hot melt resins primarily composed of ethylene vinyl acetate have a melting point in the range of 60°C to 97°C and a softening point of 69°C or less (if the melting point is 60°C, the softening point is 40°C or less). Hot melt resins primarily composed of polyurethane have a melting point of 90°C.

[0025] The shape of the core material 31 may be spherical, plate-shaped, columnar, conical, or polyhedron-shaped. The particle size (particle size) of the core material 31 may be in the range of 125 μm to 600 μm, or in the range of 150 μm to 500 μm. The core material 31 may contain resins other than thermoplastic resins and other components.

[0026] The abrasive grains 32 are particles made by pulverizing a material harder than the workpiece W to a predetermined particle size range. The hardness of the abrasive grains 32 is higher than the hardness of the core material 31. The abrasive grains 32 may be composed of alumina, silicon carbide, cerium oxide, tungsten carbide, zirconia, boron carbide, or diamond. The average particle size (grain size) of the abrasive grains 32 may be in the range of 1 μm to 25 μm.

[0027] The abrasive grains 32 are provided on the surface of the core material 31. When the resin that forms the core material 31 is melted by heat and the abrasive grains 32 are in close contact with it, the resin solidifies upon cooling, resulting in a spray material 30 with the abrasive grains 32 adhered to the surface of the core material 31. The abrasive grains 32 may be fixed to the core material 31 such that a portion of the abrasive grains 32 is embedded in the core material 31 and the rest of the abrasive grains 32 are exposed from the surface of the core material 31. The entire abrasive grain 32 may be embedded in the core material 31.

[0028] The abrasive content of the abrasive grains 32 in the propellant material 30 is, for example, 15% to 26% by mass. The particle size distribution of the propellant material 30 is, for example, 125 μm to 600 μm.

[0029] As shown in Figure 1, the smoothing method M includes a preparation step S1 and a blasting step S2. Each step will be described in detail below.

[0030] <Preparation process S1> First, preparation step S1 is performed. Preparation step S1 is the process of preparing the workpiece W. In preparation step S1, the workpiece W is attached to the rotating shaft 11a of the rotating mechanism 11. The workpiece W (gear) is attached to the rotating shaft 11a such that the center of the workpiece W coincides with the central axis AX of the rotating shaft 11a.

[0031] <Blasting process S2> Next, the blasting process S2 is performed. The blasting process S2 is a process in which the workpiece W is subjected to direct pressure blasting while the workpiece W is rotated around the rotation axis 11a (central axis AX). In the blasting process S2, the aerosol 30 is sprayed in a direction perpendicular to the central axis AX of the rotation axis 11a (Z-axis direction). That is, the center of the nozzle 12a is located substantially directly above the central axis AX of the rotation axis 11a, and the spray angle is substantially 90°. The spray angle is the angle formed by the central axis AX of the rotation axis 11a and the central axis of the nozzle 12. "Substantially directly above" means a position that can be considered directly above, and for example, a deviation of about ±5 mm from the central axis AX of the rotation axis 11a is acceptable. "Substantially 90°" means an angle that can be considered 90°, and for example, a deviation of about 90° ± 2° is acceptable.

[0032] The blasting process is carried out under predetermined processing conditions. Various processing parameters are set so that the desired amount of material removed (blasting depth) is obtained and the surface roughness of the workpiece W is reduced. Here, the amount of material removed (blasting depth) D from the surface of the workpiece W follows Preston's law. That is, the amount of material removed D is expressed by equation (1) using the blasting pressure P, the velocity Va of the blasting material 30, the moving velocity Vw (rotational speed) of the workpiece W, the blasting time T, and the Preston coefficient k. As shown in equation (1), the amount of material removed D is proportional to the blasting pressure P, the relative velocity, and the blasting time T. The relative velocity is obtained by adding the velocity Va and the moving velocity Vw. The relative velocity represents the frictional force between the workpiece W and the blasting material 30. As the rotational speed of the workpiece W increases, the relative velocity also increases. The velocity Va is the velocity of the blasting material 30 when it collides with the workpiece W. Therefore, as the injection distance increases, the propellant 30 is affected by air resistance, and its velocity Va decreases.

[0033]

number

[0034] For example, the injection pressure of the propellant 30 is set within the range of 0.01 MPa to 0.10 MPa. The injection distance of the propellant 30 is set within the range of 50 mm to 100 mm. The injection distance of the propellant 30 is the distance between the injection port 12a of the nozzle 12 and the workpiece W (in this embodiment, the distance between the injection port 12a of the nozzle 12 and the tip of the gear tooth, which is the workpiece W). The rotational speed of the workpiece W (the rotational speed of the rotating shaft 11a) is set to 30 revolutions per minute (30 rpm) or less. The injection time of the propellant 30 is adjusted as appropriate according to the degree of processing.

[0035] As shown in Figure 4, in the blasting process S2, periods T1 (first period) and T2 (second period) are repeated alternately. Period T1 is the period during which the workpiece W is rotated in rotation direction C1 (first rotation direction) and moved in direction D1 while the abrasive material 30 is sprayed onto the workpiece W. Period T2 is the period during which the workpiece W is rotated in rotation direction C2 (second rotation direction) and moved in direction D2 while the abrasive material 30 is sprayed onto the workpiece W. The rotation direction C1 is clockwise with the rotation axis 11a (central axis AX) as the axis. The rotation direction C2 is counterclockwise, opposite to the rotation direction C1, with the rotation axis 11a (central axis AX) as the axis. Direction D1 is the direction away from the drive device that drives the rotation axis 11a in the direction in which the rotation axis 11a extends (X-axis direction). Direction D2 is the opposite direction to direction D1.

[0036] In the blasting process S2, with the workpiece W rotating around the rotation axis 11a (central axis AX), the abrasive material 30 is sprayed from the nozzle 12 toward the workpiece W at a substantially 90° angle. As shown in Figure 5, the abrasive material 30 is sprayed toward the workpiece W on the airflow F and collides with the surface of the workpiece W. At this time, the core material 31 elastically deforms along the surface of the workpiece W, and the periphery of the abrasive grains 32 catches on the protrusions on the surface of the workpiece W. Near the surface of the workpiece W, the airflow F is blocked and dispersed by the surface of the workpiece W, so the airflow F flows along the surface of the workpiece W. Therefore, the abrasive material 30 slides along the surface of the workpiece W on the airflow F that follows the surface of the workpiece W, and the abrasive grains 32 scrape away the protrusions on the surface of the workpiece W. After that, the core material 31 returns to its original shape due to elastic force, and the abrasive material 30 separates from the surface of the workpiece W. As a result, the surface of the workpiece W is smoothed.

[0037] In the smoothing method M described above, a direct-pressure blast treatment is applied to the workpiece W. Therefore, the aerosol 30 is directed towards the workpiece W without spreading out from the nozzle 12, and the density of the aerosol 30 is approximately constant in the area of ​​the workpiece W's surface where the aerosol 30 is sprayed. In the blast treatment, the aerosol 30 is sprayed in a direction perpendicular to the rotating shaft 11a to which the workpiece W is attached, so the distance between the tip of the nozzle 12 (spray opening 12a) from which the aerosol 30 is sprayed and the surface of the workpiece W is approximately constant. Therefore, the non-uniformity of the amount of material removed from the workpiece W can be reduced. As a result, it is possible to reduce the non-uniformity of the smoothing treatment on the surface of the workpiece W.

[0038] As shown in equation (1), the amount of material removed increases as the injection pressure of the abrasive material 30 increases. Furthermore, as the injection pressure of the abrasive material 30 increases, the airflow near the surface of the workpiece W becomes more turbulent. Due to the turbulence of the airflow, the amount of abrasive material 30 injected per unit area may vary depending on the position on the surface of the workpiece W. On the other hand, if the injection pressure of the abrasive material 30 is too low, the surface of the workpiece W cannot be sufficiently removed. In contrast, in the blasting process S2, the injection pressure of the abrasive material 30 is set to 0.01 MPa to 0.10 MPa. Therefore, it is possible to suppress the turbulence of the airflow near the surface of the workpiece W without excessively removing material from the surface of the workpiece W. Thus, it is possible to further reduce the non-uniformity of the smoothing process on the surface of the workpiece W.

[0039] As the spraying distance of the abrasive material 30 decreases, the velocity Va in equation (1) increases, and the amount of material removed tends to increase. On the other hand, if the spraying distance of the abrasive material 30 is too long, it becomes impossible to sufficiently remove material from the surface of the workpiece W. In contrast, in the blasting process S2, the spraying distance of the abrasive material 30 is set to 50 mm to 100 mm. Therefore, the surface roughness of the workpiece W can be reduced without excessively removing material from the surface of the workpiece W.

[0040] As the rotational speed of the workpiece W increases, the relative speed between the blasting material 30 and the workpiece W also increases. As a result, a stronger frictional force is generated on the surface of the workpiece W, and the amount of material removed tends to increase. In contrast, in the blasting process S2, the rotational speed of the workpiece W is set to 30 revolutions per minute or less. Therefore, the surface roughness of the workpiece W can be reduced without excessively removing material from the surface of the workpiece W.

[0041] As the abrasive content of the blasting material 30 increases, the number of times the abrasive grains 32 come into contact with the surface of the workpiece W increases, and the amount of erosion tends to increase. On the other hand, if the abrasive content of the blasting material 30 is too low, it becomes impossible to sufficiently abrade the surface of the workpiece W. In contrast, in the blasting process S2, the abrasive content of the blasting material 30 is set to 15% by mass to 26% by mass. Therefore, the surface roughness of the workpiece W can be reduced without excessively abrading the surface of the workpiece W.

[0042] If the particle size of the abrasive material 30 is large, there is a higher possibility that the abrasive material 30 will not reach a part of the surface of the workpiece W if the workpiece W has a complex shape. On the other hand, if the particle size of the abrasive material 30 is small, the abrasive material can contact the entire surface of the workpiece W even if the workpiece W has a complex shape. For this reason, the smaller the particle size of the abrasive material 30, the greater the amount of material removed tends to be. In contrast, in the blasting process S2, abrasive material 30 having a particle size distribution of 125 μm to 600 μm is used. Therefore, it is possible to increase the possibility that the entire surface of the workpiece W will be processed without excessive material removal.

[0043] If the aerosol 30 slides only in one direction on the surface of the workpiece W, the surface of the workpiece W may not be processed uniformly. In contrast, in the blasting process S2, a period T1 in which the workpiece W is rotated in the rotation direction C1 and a period T2 in which the workpiece W is rotated in the rotation direction C2 are alternately repeated. Therefore, since the aerosol 30 slides not only in one direction on the surface of the workpiece W but also in the opposite direction, it is possible to further reduce the non-uniformity of the smoothing process on the surface of the workpiece W.

[0044] The smoothing method relating to this disclosure is not limited to the embodiments described above.

[0045] For example, in the blasting process S2, only one of period T1 or period T2 may be performed. During period T1, the workpiece W does not need to be moved in direction D1. During period T2, the workpiece W does not need to be moved in direction D2. As described above, each machining parameter can be appropriately changed so that the desired amount of shave (shave depth) is obtained and the surface roughness of the workpiece W is reduced.

[0046] The smoothing method M may further include a step of peening the workpiece W before the blasting step S2. When the workpiece W is peened, compressive residual stress is imparted to the workpiece W. This compressive residual stress is maximum at a predetermined depth from the surface of the workpiece W. Therefore, by performing blasting after peening, the surface of the workpiece W is removed, and the portion with high compressive residual stress is exposed on the surface of the workpiece W. Thus, the strength of the workpiece W after processing can be increased. [Examples]

[0047] The present disclosure will be further explained below with reference to examples in order to illustrate the effects described above. The present disclosure is not limited to these examples. In the following examples, the smoothing method M shown in Figure 1 was performed under predetermined processing conditions, and the effect of each processing parameter included in the processing conditions on the smoothing process was evaluated. In the following evaluations, all processing conditions except for the parameter being evaluated were set to be the same. The processing conditions were adjusted as appropriate so that the effect of the parameter being evaluated would be clear.

[0048] <Evaluation of spray angle> The effect of the spray angle on the smoothing process was evaluated under the following processing conditions. A 25mm diameter round bar made of vacuum carburized SCM material (chromium-molybdenum steel) was used as the workpiece. A spray material with a particle size distribution of 125μm to 600μm and an abrasive content of 20% by mass was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain for the spray material. A nozzle with a 10mm diameter nozzle was used. The spray pressure was set to 0.20MPa, the spray distance to 25mm, and the workpiece rotation speed to 2 revolutions per minute.

[0049] The maximum height Rz and erosion depth were measured when the spray angles were set to 30°, 45°, 60°, and 90°. Measurements were taken at 1 minute, 2 minutes, 4 minutes, and 10 minutes after the start of spraying (spray time). The measurement results are shown in Figures 6(a) and 6(b). Figure 6(a) shows the relationship between the spray angle and the maximum height. Figure 6(b) shows the relationship between the spray angle and the erosion depth. The horizontal axis in Figures 6(a) and 6(b) represents the amount of spray per unit area of ​​the workpiece (unit: g / cm²). 2 Figure 6(a) shows the maximum height Rz (in μm). Figure 6(b) shows the erosion depth (in μm). Note that the injection volume per unit area is proportional to the injection time, so it can also be said to represent the injection time.

[0050] As shown in Figure 6(a), when the spray angle was 45° and 60°, the maximum height Rz decreased significantly relatively early after the start of spraying and then stabilized at a constant value. When the spray angle was 30°, the maximum height Rz decreased significantly relatively early after the start of spraying, but then increased as the spraying time progressed. This is thought to be because, due to the small spray angle, the frictional force between the spray material and the workpiece surface became too large, resulting in an over-blasted state (wavy surface). When the spray angle was 90°, the reduction rate of the maximum height Rz was smaller compared to other spray angles, but the value at which the maximum height Rz stabilized was the same. Note that the reduction rate refers to the amount of reduction per unit time.

[0051] As shown in Figure 6(b), the erosion depth increased as the injection angle decreased. This is thought to be because a smaller injection angle results in a greater force from the injected material along the workpiece surface, and thus a greater frictional force between the injected material and the workpiece surface. For each injection angle, the erosion depth at the injection rate per unit area (injection density) when the maximum height Rz reached a certain value was compared.

[0052] It was confirmed that when the spray angle is 90°, the maximum height Rz (surface roughness) can be reduced without excessively abrading the workpiece surface.

[0053] <Evaluation of injection pressure> The effect of spray pressure on smoothing was evaluated under the following processing conditions. A spur gear with a diameter of 150 mm and a length of 30 mm in the tooth trace direction, made of vacuum carburized SCM415, was used as the workpiece. A spray material with a particle size distribution of 125 μm to 600 μm and an abrasive content of 20 mass% was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain of the spray material. A nozzle with a 10 mm diameter nozzle was used. The spray angle was set to 90°, the spray distance to 50 mm, and the workpiece rotation speed to 30 revolutions per minute.

[0054] The maximum height Rz and erosion depth were measured when the injection pressure was set to 0.01 MPa, 0.05 MPa, 0.10 MPa, and 0.20 MPa. Measurements were taken at 1 minute, 2 minutes, 4 minutes, and 10 minutes after the start of injection (injection time). The measurement results are shown in Figures 7(a) and 7(b), and Figures 8(a) to 8(d). Figure 7(a) shows the relationship between injection pressure and maximum height. Figure 7(b) shows the relationship between injection pressure and erosion depth. Figure 8(a) shows the amount of erosion in the tooth trace direction when the injection pressure is 0.01 MPa. Figure 8(b) shows the amount of erosion in the tooth trace direction when the injection pressure is 0.05 MPa. Figure 8(c) shows the amount of erosion in the tooth trace direction when the injection pressure is 0.10 MPa. Figure 8(d) shows the amount of erosion in the tooth trace direction when the injection pressure is 0.20 MPa.

[0055] The horizontal axis in Figures 7(a) and 7(b) represents the injection rate per unit area of ​​the workpiece (unit: g / cm²). 2 Figure 7(a) shows the maximum height Rz (unit: μm). Figure 7(b) shows the erosion depth (unit: μm). Figures 8(a) to (d) show the measured length in the tooth trace direction (unit: mm) on the horizontal axis and the erosion depth (unit: mm) on the vertical axis. Since the origin (0,0) was arbitrarily set for each measurement, there is variation in the values ​​of the horizontal and vertical axes in Figures 8(a) to (d). For this reason, the relative values ​​of the erosion depth were compared.

[0056] As shown in Figure 7(a), the maximum height Rz stabilized at 1.1 to 1.4 μm for each of the above injection pressures. Therefore, it was found that injection pressures within this range do not affect the maximum height Rz. The maximum height Rz is thought to depend on the grain size of the abrasive grains, but since abrasive grains of equivalent grain size were used in this evaluation, it can be said that the maximum height Rz after processing was approximately the same.

[0057] As shown in Figure 7(b), the amount of material removed tended to increase with increasing injection pressure. This is thought to be because higher injection pressure leads to higher injection energy, thus increasing the amount of material removed. For each injection pressure, the amount of material removed per unit area (injection density) at which the maximum height Rz reached a certain value was compared. Furthermore, as shown in Figures 8(a) to (c), when the injection pressure was 0.01 MPa, 0.05 MPa, and 0.10 MPa, the amount of material removed was approximately uniform in the direction of the tooth trace of the workpiece. However, as shown in Figure 8(d), when the injection pressure was 0.20 MPa, a bias in the amount of material removed occurred in the direction of the tooth trace of the workpiece.

[0058] The standard deviation σ of the difference between the maximum and minimum erosion depths at each injection pressure was 0.12 for an injection pressure of 0.01 MPa, 0.06 for an injection pressure of 0.05 MPa, 0.81 for an injection pressure of 0.10 MPa, and 1.57 for an injection pressure of 0.20 MPa. A standard deviation σ greater than 1.00 indicates a bias in the erosion depth.

[0059] As the injection pressure increases, the airflow near the workpiece surface becomes more turbulent, and it is thought that this turbulence causes an unevenness in the erosion depth. On the other hand, although not included in the measurement results, it is thought that if the injection pressure is too low, the workpiece surface cannot be sufficiently eroded, and the maximum height Rz cannot be sufficiently reduced.

[0060] It was confirmed that within the range of 0.01 MPa to 0.10 MPa, the maximum height Rz (surface roughness) can be reduced almost uniformly without excessively abrading the workpiece surface.

[0061] <Evaluation of spray distance> The effect of spray distance on smoothing was evaluated under the following processing conditions. A spur gear with a diameter of 150 mm and a length of 30 mm in the tooth trace direction, made of vacuum carburized SCM415, was used as the workpiece. A spray material with a particle size distribution of 125 μm to 600 μm and an abrasive content of 20 mass% was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain of the spray material. A nozzle with a 10 mm diameter nozzle was used. The spray angle was set to 90°, the spray pressure to 0.10 MPa, and the workpiece rotation speed to 30 revolutions per minute.

[0062] The maximum height Rz and erosion depth were measured when the spray distance was set to 25 mm, 50 mm, 75 mm, and 100 mm. Measurements were taken at 1 minute, 2 minutes, 4 minutes, and 10 minutes after the start of spraying (spray time). The measurement results are shown in Figures 9(a) and 9(b). Figure 9(a) shows the relationship between spray distance and maximum height. Figure 9(b) shows the relationship between spray distance and erosion depth. The horizontal axis in Figures 9(a) and 9(b) represents the amount of spray per unit area of ​​the workpiece (unit: g / cm²). 2 The vertical axis in Figure 9(a) shows the maximum height Rz (unit: μm). The vertical axis in Figure 9(b) shows the erosion depth (unit: μm).

[0063] As shown in Figure 9(a), the reduction rate of the maximum height Rz was the same for all the spray distances mentioned above. The value at which the maximum height Rz stabilized was also the same for all the spray distances mentioned above. Therefore, it was found that spray distances within the above range do not affect the reduction rate of the maximum height Rz or the maximum height Rz itself. Although not included in the measurement results, it is thought that if the spray distance is too long, the workpiece surface cannot be sufficiently removed, and the maximum height Rz cannot be reduced.

[0064] As shown in Figure 9(b), the erosion depth tended to decrease as the injection distance increased, and at an injection distance of 25 mm, the erosion depth was excessively large. At injection distances of 50 mm or more, the erosion depth was similar. For each injection distance, the erosion depth was compared based on the injection volume per unit area (injection density) when the maximum height Rz reached a certain value. Since the specific gravity of the propellant is low, it is easily affected by air resistance. Therefore, at injection distances of 50 mm or more, it is thought that the kinetic energy of the propellant was attenuated by air resistance, resulting in similar erosion depths.

[0065] It was confirmed that the maximum height Rz (surface roughness) can be reduced without excessively abrading the workpiece surface when the spray distance is between 50 mm and 100 mm.

[0066] <Evaluation of workpiece rotation speed> The effect of workpiece rotation speed on smoothing was evaluated under the following processing conditions. A spur gear with a diameter of 150 mm and a length of 30 mm in the tooth trace direction, made of vacuum carburized SCM415, was used as the workpiece. A spray material with a particle size distribution of 125 μm to 600 μm and an abrasive content of 20 mass% was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain for the spray material. A nozzle with a 10 mm diameter nozzle was used. The spray angle was set to 90°, the spray pressure to 0.10 MPa, and the spray distance to 25 mm.

[0067] The maximum height Rz was measured when the workpiece rotation speed was set to 2 rpm, 16 rpm, and 30 rpm. Measurements were taken at 1 minute, 2 minutes, 4 minutes, and 10 minutes after the start of spraying (spray time). The measurement results are shown in Figures 10(a) and 10(b). Figure 10(a) shows the relationship between the workpiece rotation speed and the maximum height. Figure 10(b) shows the relationship between the workpiece rotation speed and the erosion depth. The horizontal axis in Figures 10(a) and 10(b) represents the amount of sprayed material per unit area of ​​the workpiece (unit: g / cm²). 2The vertical axis in Figure 10(a) shows the maximum height Rz (unit: μm). The vertical axis in Figure 10(b) shows the erosion depth (unit: μm).

[0068] As shown in Figure 10(a), the reduction rate of the maximum height Rz increased slightly with increasing workpiece rotation speed. This is thought to be due to the fact that as workpiece rotation speed increases, the relative speed between the spray material and the workpiece increases, resulting in a stronger frictional force on the workpiece surface. The value at which the maximum height Rz stabilized was approximately the same for all the rotation speeds mentioned above. As shown in Figure 10(b), the erosion depth tended to increase with increasing workpiece rotation speed. This is also thought to be due to the magnitude of the frictional force due to the relative speed. For each rotation speed, the erosion depth at the spray volume per unit area (injection density) when the maximum height Rz reached a certain value was compared.

[0069] It was confirmed that the maximum height Rz (surface roughness) can be reduced without excessively abrading the workpiece surface when the rotational speed of the workpiece W is 30 rpm or less.

[0070] <Evaluation of abrasive content in propellant> The effect of the abrasive content of the abrasive material on the smoothing process was evaluated under the following processing conditions. A vacuum carburized SCM material with a diameter of 40 mm and a length of 10 mm was used as the workpiece. An abrasive material with a particle size distribution of 125 μm to 600 μm was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain of the abrasive material. A nozzle with a 6 mm diameter nozzle was used. The spray angle was set to 45°, the spray pressure to 0.20 MPa, and the spray distance to 1 mm.

[0071] The maximum height Rz and erosion depth were measured when abrasive materials with abrasive content of 15 mass%, 17 mass%, 24 mass%, 25 mass%, 26 mass%, 29 mass%, 37 mass%, and 39 mass% were used. Measurements were taken at 3 minutes, 6 minutes, 12 minutes, and 30 minutes after the start of abrasive spraying (spraying time). The measurement results are shown in Figures 11(a) and 11(b). Figure 11(a) shows the relationship between the abrasive content of the abrasive material and the maximum height. Figure 11(b) shows the relationship between the abrasive content of the abrasive material and the erosion depth. The horizontal axis of Figures 11(a) and 11(b) is the amount of abrasive sprayed per unit area of ​​the workpiece (unit: g / cm²). 2 The vertical axis in Figure 11(a) shows the maximum height Rz (in μm). The vertical axis in Figure 11(b) shows the erosion depth (in μm).

[0072] As shown in Figure 11(a), the reduction rate of the maximum height Rz was the same for all the abrasive content ratios mentioned above. The value at which the maximum height Rz stabilized was also the same for all the abrasive content ratios mentioned above. Therefore, it was found that abrasive content ratios within the above range do not affect the reduction rate of the maximum height Rz or the maximum height Rz itself. The maximum height Rz is thought to depend on the grain size of the abrasive grains, but since abrasive grains of the same grain size were used in this evaluation, it can be said that the maximum height Rz after processing was approximately the same. On the other hand, although not included in the measurement results, it is thought that if the abrasive content ratio is too low, the workpiece surface cannot be sufficiently machined, and the maximum height Rz cannot be sufficiently reduced.

[0073] As shown in Figure 11(b), the erosion depth tended to increase as the abrasive content increased. This is thought to be because a higher abrasive content increases the number of contacts between the workpiece surface and the abrasive grains, thus increasing the erosion depth. For each abrasive content, the erosion depth at the injection rate per unit area (injection density) when the maximum height Rz reached a certain value was compared. In all abrasive content settings, the maximum height Rz stabilized at approximately 1.5. The injection density at that time was 400-500 g / cm³. 2Therefore, when comparing the erosion depth at these injection densities, the erosion depth was similar when using abrasive materials with abrasive content of 15 mass%, 17 mass%, 24 mass%, 25 mass%, and 26 mass%. When using abrasive materials with abrasive content of 29 mass%, 37 mass%, and 39 mass%, the erosion depth was excessively large.

[0074] It was confirmed that within the range of 15% by mass to 26% by mass of abrasive grain content, the maximum height Rz (surface roughness) can be reduced without excessively abrading the workpiece surface.

[0075] <Evaluation of particle size distribution of propellant> The effect of the particle size distribution of the abrasive material on the smoothing process was evaluated under the following processing conditions. A vacuum carburized SCM material with a diameter of 40 mm and a length of 10 mm was used as the workpiece. WA#2000 abrasive grains manufactured by Shinto Kogyo Co., Ltd. were used as the abrasive material. A nozzle with a 6 mm diameter nozzle was used. The spray angle was set to 45°, the spray pressure to 0.20 MPa, and the spray distance to 1 mm.

[0076] The maximum height Rz and erosion depth were measured when abrasive materials with particle size distributions of 125 μm to 600 μm, 212 μm to 500 μm, and 75 μm to 300 μm were used. Measurements were taken at 3 minutes, 6 minutes, 12 minutes, and 30 minutes after the start of abrasive spraying (spraying time). The abrasive content of the abrasive material with a particle size distribution of 125 μm to 600 μm was 25 mass%, the abrasive content of the abrasive material with a particle size distribution of 212 μm to 500 μm was 20 mass%, and the abrasive content of the abrasive material with a particle size distribution of 75 μm to 300 μm was 36 mass%.

[0077] The measurement results are shown in Figures 12(a) and 12(b). Figure 12(a) shows the relationship between the particle size distribution of the auger and the maximum height. Figure 12(b) shows the relationship between the particle size distribution of the auger and the erosion depth. The horizontal axis of Figures 12(a) and 12(b) represents the amount of auger sprayed per unit area of ​​the workpiece (unit: g / cm²). 2The vertical axis in Figure 12(a) shows the maximum height Rz (in μm). The vertical axis in Figure 12(b) shows the erosion depth (in μm).

[0078] As shown in Figure 12(a), the reduction rate of the maximum height Rz was the same for all particle size distributions described above. The value at which the maximum height Rz stabilized was also the same for all particle size distributions described above. Therefore, it was found that the particle size distribution of the propellant material described above does not affect the reduction rate of the maximum height Rz or the maximum height Rz itself.

[0079] As shown in Figure 12(b), the erosion depth varied depending on the particle size distribution of the abrasive material. For each particle size distribution, the erosion depth at the injection rate per unit area (injection density) when the maximum height Rz reached a certain value was compared. When abrasive material with a particle size distribution of 75 μm to 300 μm was used, the erosion depth was excessively large. When abrasive material with a particle size distribution of 212 μm to 500 μm was used, the erosion depth was suppressed, but a portion of the workpiece surface was not sufficiently processed. When the workpiece has a complex shape, abrasive material with a large particle size is more likely to not reach a portion of the workpiece surface. On the other hand, even if the workpiece has a complex shape, if the abrasive material has a small particle size, the area of ​​the workpiece surface that the abrasive material collides with (contacts) (coverage) increases. Therefore, abrasive material with a smaller particle size has a higher probability of contacting the workpiece surface than abrasive material with a larger particle size. Furthermore, the smaller the particle size, the greater the surface area of ​​the abrasive material, and thus the higher the abrasive content. Based on these findings, it can be concluded that the smaller the particle size of the propellant, the greater the erosion depth.

[0080] It was confirmed that when a spray material having a particle size distribution of 125 μm to 600 μm is used, the possibility of processing the entire workpiece surface without excessive erosion of the workpiece surface can be increased.

[0081] <Workpiece residual stress value> First, a workpiece was prepared under the following processing conditions for peening. A 40mm diameter x 10mm length SCM material that had undergone vacuum carburization was used as the workpiece. SBM210C (cast steel abrasive with a particle size of 125μm to 250μm) manufactured by Shinto Kogyo Co., Ltd. was used as the abrasive material. The projection angle was set to 90°, the projection pressure to 0.30MPa, and the projection distance to 200mm. The projection angle is the angle between the central axis of the rotating shaft on which the workpiece is mounted and the direction in which the abrasive material is projected. The projection distance is the distance between the nozzle opening from which the abrasive material is projected and the workpiece. The projection rate was set to 9kg / min, and the projection time to 12 seconds. The peening coverage was 300%. Then, residual stress values ​​were measured at several depths from the workpiece surface.

[0082] The peened workpiece was further smoothed under the following processing conditions: A spray material with a particle size distribution of 125 μm to 600 μm and an abrasive content of 20% to 24% by mass was used. WA#2000, manufactured by Shinto Kogyo Co., Ltd., was used as the abrasive grain. A nozzle with a 6 mm diameter nozzle was used. The spray angle was set to 45°, the spray pressure to 0.20 MPa, and the spray distance to 1 mm. The spray time was set to 6 minutes.

[0083] The measurement results are shown in Figure 13. Figure 13 shows the residual stress values ​​of a workpiece that has undergone peening treatment and the residual stress values ​​of a workpiece that has undergone smoothing treatment after peening treatment. The horizontal axis of Figure 13 shows the depth from the workpiece surface (unit: μm). The vertical axis of Figure 13 shows the residual stress value (unit: MPa). Positive residual stress values ​​indicate tensile residual stress, and negative residual stress values ​​indicate compressive residual stress. Note that the measurement results shown in Figure 13 were not measured using the same workpiece. Therefore, due to differences in workpieces and measurement errors, the shapes of the curves showing the residual stress values ​​of the workpiece that has undergone peening treatment and the curve showing the residual stress values ​​of the workpiece that has undergone smoothing treatment after peening treatment are slightly different.

[0084] As shown in Figure 13, in a workpiece that had undergone peening but not smoothing, compressive residual stress was imparted to the workpiece, and it was confirmed that the compressive residual stress value was maximum at a depth of approximately 20 μm from the workpiece surface. When the workpiece was further smoothed, the workpiece surface was removed to a depth of approximately 7 to 10 μm. At this time, the workpiece surface was removed with almost no effect on the compressive residual stress value. As a result, it was confirmed that the portion with high compressive residual stress was exposed on the surface of the workpiece. [Explanation of Symbols]

[0085] 10... Processing device, 11... Rotating mechanism, 11a... Rotating shaft, 12... Nozzle, 12a... Injection port, 30... Injection material, 31... Core material, 32... Abrasive grains, W... Workpiece.

Claims

1. The process of attaching the workpiece to the rotating shaft of the rotating mechanism, A step of applying a direct-pressure blast treatment to the workpiece while rotating the workpiece with the aforementioned rotation axis as its axis, Includes, In the blasting process described above, the material is ejected in a direction perpendicular to the rotation axis. The aforementioned propellant includes a core material made of an elastic body and abrasive grains provided on the surface of the core material. The hardness of the core material is lower than the hardness of the abrasive grains. A smoothing method comprising the process of performing the blast treatment, wherein a first period in which the workpiece is rotated in a first rotational direction with the rotation axis as the axis, and a second period in which the workpiece is rotated in a second rotational direction opposite to the first rotational direction, are alternately repeated.

2. The smoothing method according to claim 1, wherein in the step of performing the blasting treatment, the injection pressure of the injection material is set to 0.01 MPa or more and 0.10 MPa or less.

3. The smoothing method according to claim 1 or claim 2, wherein in the step of performing the blasting treatment, the spraying distance of the spraying material is set to 50 mm or more and 100 mm or less.

4. The smoothing method according to claim 1 or claim 2, wherein in the step of performing the blasting treatment, the rotation speed of the workpiece is set to 30 revolutions per minute or less.

5. The smoothing method according to claim 1 or claim 2, wherein the abrasive content of the propellant is 15% by mass or more and 26% by mass or less.

6. The smoothing method according to claim 1 or claim 2, wherein the spray material has a particle size distribution of 125 μm or more and 600 μm or less.

7. The smoothing method according to claim 1 or claim 2, further comprising the step of applying a peening treatment to the workpiece before the step of applying the blast treatment.

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