JP2013022718A - Tool surface modifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool surface modifying method capable of sufficiently applying work hardening and compressive residual stress to a surface of a tool, and improving surface roughness for the same.SOLUTION: In the method, a mixed shot Sm obtained by mixing a first shot S1 consisting of cemented carbide particles and a second shot S2 consisting of iron-based material particles is projected onto a surface of a tool W, so that the surface of the tool W can be plastically deformed and applied with work hardening and compressive residual stress through projection of the first shot S1, and unevenness formed on the surface of the tool W through the projection of the first shot S1 can be crushed and flattened through projection of the second shot S2. Thereby, the method is capable of sufficiently applying work hardening and compressive residual stress to the surface of the tool W and improving the surface roughness for the same.

Description

  The present invention relates to a surface modification method for a tool, and more particularly to a surface modification method for a tool capable of sufficiently achieving work hardening, compressive residual stress, and improvement of surface roughness on the surface of the tool. It is.

  As a method for increasing the surface strength of steel products, a method is known in which shot peening is performed on the surface to cause work hardening or compressive residual stress. In this case, in order to increase the depth of the work hardening or compressive residual stress layer, it is necessary to use a shot with a relatively large particle size to increase the energy of collision (that is, work hardening and compressive residual stress are plastic). Proportional to the size of the recess formed by deformation). On the other hand, the use of shots with a large particle size causes the surface roughness to be severe, and thus the surface roughness of the treated surface is deteriorated.

  Therefore, two-stage shot peening (after shot peening with a shot with a relatively large particle diameter, then with shot peening with a shot with a relatively small particle diameter) gives work hardening, compressive residual stress, and surface roughness. Although a technique for improving the accuracy is also employed, in this technique, it is necessary to prepare two blasting apparatuses or to change shots when using one blasting apparatus. It was necessary to perform two types of shot peening in two steps. Therefore, equipment cost and work cost increase.

  On the other hand, Patent Documents 1 and 2 disclose a technique in which two types of shots having different particle diameters are mixed and the mixed shots are ejected from one nozzle. According to this technique, since one shot peening may be performed using one blasting apparatus, it is possible to suppress the equipment cost and the work cost as compared with the case of two-stage shot peening.

Patent No. 373015 Japanese Patent No. 4208298

  However, just by mixing and projecting two types of shots having different particle sizes as in the techniques of Patent Documents 1 and 2 described above, it is possible to provide work hardening and application of compressive residual stress and to improve surface roughness. There was a problem that the coexistence was insufficient. That is, even if the sizes of the two kinds of large and small particles are adjusted, it is difficult to improve the surface roughness if work hardening and application of compressive residual stress are ensured. If the surface roughness is ensured, work hardening is achieved. In addition, it becomes difficult to sufficiently apply compressive residual stress.

  The present invention has been made to solve the above-described problems, and the surface of a tool that can sufficiently achieve work hardening, application of compressive residual stress, and improvement of surface roughness on the surface of the tool. It aims to provide a reforming method.

Means for Solving the Problems and Effects of the Invention

  According to the surface modification method for a tool according to claim 1, a mixed shot obtained by mixing a first shot composed of particles made of cemented carbide and a second shot composed of particles made of iron-based material is performed. Since it is projected onto the surface of the tool, the surface of the tool is plastically deformed by projecting the first shot to impart work hardening and compressive residual stress, and the top of the unevenness formed on the surface of the tool by projecting the first shot Can be crushed and flattened by the projection of the second shot. As a result, there is an effect that work hardening, application of compressive residual stress, and improvement of surface roughness can be sufficiently achieved on the surface of the tool.

  That is, the kinetic energy of the shot shot is proportional to the weight, but the cemented carbide particles used as the first shot have a large specific gravity (about twice that of particles made of iron-based material), so the kinetic energy Can be secured. Therefore, even if the particle diameter of the first shot is relatively small, a sufficiently large work hardening and compressive residual stress can be applied to a deeper position. In other words, the unevenness formed on the surface of the tool can be reduced while sufficiently applying work hardening and compressive residual stress. As a result, the surface roughness of the tool can be reliably improved by the projection of the second shot.

  According to the surface modification method for a tool according to claim 2, in addition to the effect of the surface modification method for a tool according to claim 1, the surface of the tool is suppressed from being scraped, and work hardening and compressive residual stress are achieved. Can be efficiently provided.

  That is, the first shot composed of cemented carbide particles collided again with another particle that collided with work hardening or compressive residual stress due to the next projection because the hardness was high. The surface of the part is scraped off. For this reason, the surface roughness is deteriorated, but it is difficult to lead to work hardening and an increase in compressive residual stress. Therefore, mixing a second shot made of an iron-based material that has a lighter specific gravity and lower hardness than the first shot alleviates the scraping of the surface of the tool, and efficiently reduces work hardening and compressive residual stress. In particular, the upper limit of the ratio of the first shot is 30 wt% of the total weight, and the remainder is the second shot, so that the above-mentioned scraping is surely relieved and uniform over the entire surface to be treated. Work hardening and compressive residual stress can be imparted to. On the other hand, when the ratio of the first shot is 2 wt% or more of the total weight, work hardening and application of compressive residual stress can be sufficiently performed.

  According to the surface modification method for a tool according to claim 3, in addition to the effect exhibited by the surface modification method for a tool according to claim 1 or 2, the specific gravity of the cemented carbide particles constituting the first shot is determined. The specific gravity difference between the first shot and the second shot is set to 13.9 to 15.0, and the specific gravity of the particles made of the iron-based material constituting the second shot is set to 7.2 to 8.3. As a result, there is an effect that work hardening, application of compressive residual stress, and improvement of surface roughness can be reliably achieved on the surface of the tool.

  In addition, by setting the specific gravity of the first shot and the second shot as in claim 3, generally commercially available particles can be applied to the first shot and the second shot. Can be easy.

  According to the surface modification method for a tool according to claim 4, in addition to the effect of the surface modification method for a tool according to any one of claims 1 to 3, Since the particle diameter of the particles constituting the two shots is set to 10 μm to 150 μm and is relatively small, the unevenness formed on the surface of the tool is reduced while imparting work hardening and compressive residual stress. The surface roughness can be improved.

  That is, the use of a shot having such a relatively small particle size cannot be used with a conventional technique that only mixes two kinds of particles having different particle sizes, as in the present invention. It became possible to use for the first time by mixing two kinds of particles with different specific gravity and making the two kinds of particles a cemented carbide particle and a ferrous material particle. Application of residual stress and improvement of the surface roughness of the tool can be achieved simultaneously.

  According to the surface modification method for a tool according to claim 5, in addition to the effect of the surface modification method for a tool according to claim 4, the particle diameter of the first shot and the particle diameter of the second shot are substantially the same. Therefore, since the second shot has an appropriate particle diameter with respect to the irregularities formed by the projection of the first shot, the top of the irregularities can be efficiently crushed and flattened. . As a result, there is an effect that the surface roughness of the tool can be further improved.

  Further, since the particle diameter of the mixed shot obtained by mixing the first shot and the second shot is constant, for example, the mixing ratio of the first shot and the second shot is maintained in the shot transport path from the hopper to the nozzle. There is an effect that it can be made easy.

  According to the surface modification method for a tool according to claim 6, in addition to the effect exhibited by the surface modification method for a tool according to any one of claims 1 to 5, the tool performs a rolling process on the workpiece. Therefore, it is possible to perform high-precision rolling on the workpiece by improving the surface roughness of the tool while improving the durability of the tool by applying work hardening and compressive residual stress. There is an effect that a rolled tool can be obtained.

  In addition, since the rolling tool is a tool that plastically deforms the surface of the workpiece, if the surface has irregularities, the workpiece is caught and resistance to plastic deformation occurs. Therefore, the application of surface modification by shot peening to rolling tools was not possible because the conventional shot peening technique was insufficient in improving the surface roughness (provided resistance to plastic deformation). . On the other hand, as in the present invention, two kinds of particles having different specific gravities are mixed, and the two kinds of particles are made of cemented carbide particles and iron-based material particles, so that it can be applied to a rolling tool. Has become possible for the first time, and this makes it possible to improve the durability of the tool and improve the rolling accuracy at the same time.

It is an outline schematic diagram of a shot peening apparatus in one embodiment used for carrying out the present invention. It is a table | surface which illustrates the relationship between the mixing ratio of the 1st shot and 2nd shot to a mixing shot, the particle diameter of a mixing shot, and the hardness of the process surface of a tool. It is a graph which illustrates the number of processes of a processed product of this application, and the number of processes of an untreated product.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. First, the shot peening apparatus 1 will be described with reference to FIG. FIG. 1 is a schematic diagram of a shot peening apparatus 1 according to an embodiment used for carrying out the present invention.

  As shown in FIG. 1, the shot peening apparatus 1 mixes two types of shots (hereinafter referred to as “first shot S1” and “second shot S2”), and processes from a single nozzle 17. (Hereinafter referred to as “tool W”), which is a direct pressure type device for modifying the surface of the tool W, and includes a first hopper 11 that houses the first shot S1, and a second shot S2. And a second hopper 12 that accommodates the first and second hoppers 12 with the accommodation opening facing upward.

  In the present embodiment, as will be described later, the first shot S1 is made of cemented carbide particles, and the second shot S2 is made of iron-based material particles. The tool W is a rolling tool (screw rolling flat die) for rolling a male screw, and is made of die steel.

  The mixing device 13 is connected to the take-out ports of the first hopper 11 and the second hopper 12 through piping. Each pipe is provided with an open / close valve (not shown), and the shots S1 and S2 accommodated in the hoppers 11 and 12 are mixed at a desired ratio by adjusting and controlling the opening degree. It is supplied to the device 13 and mixed by the mixing device 13.

  A pressure tank 14 is connected to the downstream side of the mixing device 13, and a mixer 16 is connected to the downstream side of the pressure tank 14. Further, an air supply source 15 configured as a supply source of compressed air is connected to the pressurized tank 14 and the mixer 16.

  Therefore, the shot mixed by the mixing device 13 and supplied into the pressurized tank (hereinafter referred to as “mixed shot Sm”) is pumped from the pressurized tank 14 together with the compressed air to the mixer 16 and from the mixer 16. The compressed air is pumped to the nozzle 17. Thereby, the mixed shot Sm is projected from the nozzle 17 to the tool W.

  Next, a detailed configuration of the mixed shot Sm (first shot S1 and second shot S2) will be described. In this description, FIG. 1 is referred to as appropriate.

  The first shot S1 is made of cemented carbide particles, and the second shot S2 is made of iron-based material particles. Examples of the iron-based material include cast iron, cast steel, high-speed tool steel, alloy tool steel, or metal glass (iron amorphous particles).

  Therefore, a mixed shot Sm obtained by mixing the first shot S1 made of cemented carbide particles and the second shot S2 made of iron-based material particles is projected onto the surface of the tool W. Therefore, the surface of the tool W is plastically deformed by the projection of the first shot S1 to impart work hardening and compressive residual stress, and the top of the unevenness formed on the surface of the tool W by the projection of the first shot S1 is The projection can be flattened by the projection of the second shot S2. As a result, work hardening, application of compressive residual stress and improvement of surface roughness can be sufficiently achieved on the surface of the tool W.

  Here, where the kinetic energy of the particles projected from the nozzle 17 is proportional to its weight, one shot (the first shot S1) constituting the mixed shot Sm is made of cemented carbide particles, and the specific gravity is Because it is large (about twice that of particles made of iron-based material), its kinetic energy is secured. Therefore, even if the particle diameter of the first shot S1 is relatively small, a sufficiently large work hardening and compressive residual stress can be applied to the surface of the tool W up to a deeper position. In other words, the unevenness formed on the surface of the tool W can be reduced while sufficiently imparting work hardening and compressive residual stress to the surface of the tool W. As a result, the surface roughness of the tool W can be reliably improved by the projection of the second shot S2.

  In the mixed shot Sm, 2 wt% to 30 wt% of the total weight is preferably the first shot S <b> 1 and the remaining portion is preferably the second shot S <b> 2. That is, the shot peening apparatus 1 controls the supply amount of each shot S1, S2 from each hopper 11, 12 to the mixing apparatus 13 so as to be a desired ratio within the above range, and the mixing apparatus 13 performs mixing. To do.

  The first shot S1 composed of cemented carbide particles has a high hardness. That is, the cemented carbide particles have a Vickers hardness of 1400 HV. For example, when the tool W is made of die steel, the hardness difference is 250 HV or more. For this reason, when another particle collides again with the next projection at a position to which work hardening or compressive residual stress is applied by the collision of the particles, the surface of the re-collised position is scraped off. As a result, the surface roughness is deteriorated, but it is difficult to lead to work hardening and an increase in compressive residual stress.

  In this case, in the present invention, the surface of the tool W is scraped off by mixing the second shot S2 made of an iron-based material having a lighter specific gravity and lower hardness (for example, 700 HV to 900 HV) than the first shot S1. Can be relaxed and work hardening and compressive residual stress can be efficiently applied. In particular, the upper limit of the proportion of the first shot S1 is 30 wt% of the total weight, and the remaining portion is the second shot S2, so that the surface of the tool W is scraped off by the first shot S1, and the tool is reliably relieved. Work hardening and compressive residual stress can be uniformly applied to the entire surface to be treated with W. On the other hand, by setting the ratio of the first shot S1 to 2 wt% or more of the total weight, work hardening and application of compressive residual stress can be sufficiently performed.

  The first shot S1 is composed of particles made of super steel alloy having a specific gravity of 13.9 to 15.0, and the second shot S2 is composed of particles made of iron-based material having a specific gravity of 7.2 to 8.3. It is preferred that As a result, the difference in specific gravity between the first shot S1 and the second shot S2 can be made appropriate. As a result, work hardening, application of compressive residual stress and surface roughness of the surface of the tool W can be achieved. Improvement can be achieved reliably. This specific gravity range is a condition after satisfying the above-described weight ratio between the first shot S1 and the second shot S2.

  Here, if the specific gravity of the first shot S1 is less than 13.9, the hardness is insufficient due to a decrease in the proportion of tungsten carbide, and sufficient work hardening or compressive residual stress is imparted to the surface of the tool W. It becomes difficult. On the other hand, if the specific gravity of the first shot S1 exceeds 15.0, the surface of the tool W will be scraped off excessively as the kinetic energy increases. Further, as the proportion of cobalt is reduced, the particles are easily broken and it is difficult to continuously use them.

  Further, if the specific gravity of the second shot S2 is less than 7.2, the hardness is insufficient, and it becomes difficult to flatten the surface by crushing the top of the unevenness, and it is difficult to sufficiently improve the surface roughness. Become. On the other hand, if the specific gravity of the second shot S2 exceeds 8.3, the difference from the specific gravity of the first shot S1 is reduced, and the effect of making the specific gravity different cannot be achieved.

  In addition, by setting the specific gravity of the first shot S1 and the second shot S2 in this manner, generally commercially available particles can be applied to the first shot S1 and the second shot S2. Can be made easy.

  The particle diameter of the particles constituting the first shot S1 and the particle diameter of the particles constituting the second shot S2 are preferably set to 10 μm to 150 μm. Thus, by making the particle diameter of each shot S1, S2 relatively small, the unevenness formed on the surface of the tool W is reduced while imparting work hardening and compressive residual stress. The surface roughness can be improved.

  The range of the particle diameter is a condition after satisfying the above-described weight ratio of each shot S1, S2 and / or the specific gravity range of each shot S1, S2.

  Here, the use of such a shot having a relatively small particle diameter cannot be used with the conventional technique of simply mixing two kinds of particles having different particle sizes, as in the present invention. In addition, two types of particles having different specific gravities (each shot S1, S2) are mixed, and the two types of particles are cemented carbide particles (first shot S1) and iron-based material particles (second shot S2). As a result, it can be used for the first time, and thereby it is possible to simultaneously achieve work hardening, application of compressive residual stress, and improvement of the surface roughness of the tool.

  It is preferable that the particle size of the first shot S1 and the particle size of the second shot S2 are substantially the same. Thereby, since the second shot S2 has an appropriate particle diameter with respect to the irregularities formed on the surface of the tool W by the projection of the first shot S1, the second shot S2 crushes the top of the irregularities. Thus, the planarization can be performed efficiently. As a result, the surface roughness of the tool W can be further improved.

  In addition, since the particle diameter of the mixed shot Sm obtained by mixing the first shot S1 and the second shot S2 is constant, each shot S1 is transported in the transport path of each shot S1, S2 from each hopper 11, 12 to the nozzle 17. , S2 can be easily maintained. That is, the mixed shot Sm in which the mixing ratio of the shots S1 and S2 is maintained at a desired value can be projected from the nozzle 17.

  In addition, making the particle diameters substantially the same means that the weight ratio of each of the shots S1 and S2 and / or the range of the specific gravity of each of the shots S1 and S2 and / or the respective shots S1 and S2. The condition is that the range of the particle diameter is satisfied.

  Further, that the particle size of the first shot S1 and the particle size of the second shot S2 are substantially the same, the average value of the particle size of the first shot S1 and the average value of the particle size of the second shot S2 It means that they are almost the same. Therefore, it is naturally possible that the particles constituting each of the shots S1 and S2 have variations in the particle diameter. The average value is substantially the same, which means that the average value of the particle size of the second shot S2 is allowed to differ by ± 15% with respect to the average value of the particle size of the first shot S1. It is not the purpose.

  Next, the detailed configuration of the tool W will be described. In this description, FIG. 1 is referred to as appropriate.

  The tool W is a rolling tool for rolling a workpiece, and the shaft-shaped material is rolled on the rolling tooth mold surface, and the outer peripheral surface of the material is plastically deformed. Configured as a rolling tool for rolling male threads. In the present embodiment, the mixed shot Sm is projected from the nozzle 17 onto the entire rolling tooth profile surface of the tool W (the chamfered portion, the finished portion, and the relief portion), and the surface modification is performed.

  In the present invention, it is particularly effective to employ the tool W as such a rolling tool as an application target of the surface modification.

  That is, since the rolling tool is a tool that plastically deforms the surface of the workpiece, if the surface (the surface of the rolled tooth surface) has irregularities, the workpiece is caught and resistance to plastic deformation occurs. . Therefore, the application of surface modification by shot peening to rolling tools was not possible because the conventional shot peening technique was insufficient in improving the surface roughness (provided resistance to plastic deformation). . On the other hand, as in the present invention, two types of particles having different specific gravity (each shot S1, S2) are mixed and the two types of particles are made of cemented carbide alloy particles (first shot S1) and an iron-based material. This makes it possible for the first time to be applied to a rolling tool, thereby simultaneously improving the durability of the tool W and improving the rolling processing accuracy. can do.

  Next, with reference to FIG. 2, the test result of the surface modification of the tool W performed by projecting the mixed shot Sm onto the tool W using the shot peening apparatus 1 will be described. FIG. 2 is a table illustrating the mixing ratio of the first shot S1 and the second shot S2 to the mixed shot Sm, and the relationship between the particle diameter of the mixed shot Sm and the hardness of the processing surface of the tool W.

  In the table shown in FIG. 2, the “first shot ratio (wt%)” in the left column is a value representing the mixing ratio of the first shot S1 with respect to the mixed shot Sm as a mass percentage. Therefore, when the “first shot ratio (wt%)” is, for example, 1 wt%, 1 wt% is the first shot S1 and the remaining (99 wt%) is the second shot S2 with respect to the total weight of the mixed shot Sm. Means that.

  In the table shown in FIG. 2, the “particle diameter (μm)” in the upper column is the value of the particle diameter of the first shot S1 and the second shot S2. That is, in this test, the particle size of the first shot S1 and the particle size of the second shot S2 were set to be substantially the same.

  In this test, particles of cemented carbide having a specific gravity of 14.5 were used as the first shot S1, and particles of high-speed steel having a specific gravity of 7.8 were used as the second shot S2. The tool W was made of die steel. The hardness of the first shot S1 and the second shot S2 is 1400 HV and 800 HV, respectively, and the hardness of the tool W is 700 HV. Further, the test was performed with the projection pressure from the nozzle 17 of the shot peening apparatus 1 fixed at a constant value (0.5 MPa).

  As shown in FIG. 2, when the “first shot ratio” is 1 wt%, the hardness of the processing surface of the tool W is 880 HV, 920 HV, 900 HV, and 950 HV for “particle diameter” of 10 μm, 100 μm, 150 μm, and 200 μm. Increased compared to before surface modification. As the “particle diameter” increases, the hardness of the processing surface of the tool W increases because the kinetic energy of the projected particles increases.

  In this case, the hardness of the treated surface of the tool W increases as compared with that before the surface modification, but the amount of increase in the hardness is insufficient. In order to sufficiently increase the hardness of the processing surface of the tool W, a ratio of the first shot S1 that plays a role of imparting work hardening and compressive residual stress is secured with respect to the second shot S2 that plays the role of flattening the unevenness. It was found that the ratio of the first shot S1 was insufficient when the “first shot ratio” was 1 wt%.

  When the “first shot ratio” is 15 wt%, the hardness of the processing surface of the tool W is 1320 HV, 1350 HV, 1320 HV, and 1150 HV with respect to the “particle diameter” of 10 μm, 100 μm, 150 μm, and 200 μm. When the particle size is 25 wt%, the hardness of the treated surface of the tool W is 1310 HV, 1380 HV, 1400 HV, and 1280 HV with respect to “particle diameter” of 10 μm, 100 μm, 150 μm, and 200 μm, both of which are increased compared to those before the surface modification. .

  Thus, it was confirmed that when the “first shot ratio” is 15 wt% and 25 wt%, the hardness of the processing surface of the tool W can be sufficiently increased. Further, in this case, when the “particle diameter” is 10 μm, 100 μm, and 150 μm, the surface roughness of the processing surface of the tool W is 1.0 μm to 1.3 μm, and it has been confirmed that sufficient smoothing can be obtained. It is considered that the mixing ratio of the first shot S1 that plays the role of imparting work hardening and compressive residual stress and the second shot S2 that plays the role of flattening the unevenness is appropriate.

  In this case (“first shot ratio” = 15 wt% or 25 wt%), if the “particle diameter” is 200 μm, the hardness is compared with other “particle diameters” (10 μm, 100 μm, 150 μm). As the amount of increase is inferior, the surface roughness becomes rough. This is because the “particle diameter” is large, and the unevenness formed on the processing surface of the tool W by the first shot S1 becomes large. On the other hand, the “first shot ratio” is relatively smaller than the case of 1 wt% described above. Since it is high (that is, the mixing ratio of the second shot S2 is low), the top of the unevenness formed by the projection of the first shot S1 is sufficiently crushed and flattened by the projection of the second shot S2. This is due to the difficulty.

  When the “first shot ratio” is 40 wt%, the hardness of the treated surface of the tool W is 980 HV, 1000 HV, 1100 HV, and 910 HV for “particle diameter” of 10 μm, 100 μm, 150 μm, and 200 μm, which is compared with that before the surface modification. Increased.

  In this case, compared with the case where the “first shot ratio” is 15 wt% or 25 wt%, the mixing ratio of the first shot S1 which plays a role of imparting work hardening and compressive residual stress is increased. The increase in hardness itself decreased. This is because the mixing ratio of the first shot S1 is too high, so that another particle (first shot S1) is applied to the place where work hardening or compressive residual stress is applied by collision of the particles (first shot S1) by the next projection. Is caused by the collision again, and the surface of the re-collision portion is scraped off. That is, with this “first shot ratio”, even if projection is continued, the effect of increasing the hardness is not accumulated on the processing surface, and the effect cannot be maximized.

  Thus, in order to alleviate that the surface of the tool W is scraped off and efficiently apply work hardening and compressive residual stress, the second shot S2 is lighter in specific gravity and lower in hardness than the first shot S1. Must be mixed at a predetermined ratio or more. When the “first shot ratio” is 40 wt%, the mixing ratio of the first shot S1 is too large (that is, the mixing ratio of the second shot S2 is too small). There was found.

  In this case (“first shot ratio” = 40 wt%), when the “particle diameter” is 200 μm, the amount of increase in hardness is compared to the other “particle diameters” (10 μm, 100 μm, 150 μm). And the surface roughness becomes rough. This is because the “particle diameter” is large as in the case of the “first shot ratio” = 15 wt% or 25 wt% described above, and the unevenness formed on the processing surface of the tool W due to the first shot S1 becomes significant. Since the “first shot ratio” is high (that is, the mixing ratio of the second shot S2 is low), the top of the unevenness formed by the projection of the first shot S1 is flattened by the projection of the second shot S2. This is due to the fact that it has become difficult to perform sufficient conversion.

  Here, the surface roughness in the case of “particle diameter” of 10 μm, 100 μm, and 150 μm at “first shot ratio” of 40 wt% is better than that in the case of “particle diameter” of 200 μm. However, compared with the case where the “first shot ratio” is 15 wt% or 25 wt%, it becomes rough. This is because the “first shot ratio” is high, and, as described above, the surface to be roughed is roughened by the projection of the first shot S1 on the processing surface, rather than the form in which the unevenness is formed on the processing surface. This is because it is easy.

  Next, with reference to FIG. 3, the result of a rolling test performed using the tool W after the surface modification will be described. This rolling test is performed by rolling a screw on the outer peripheral surface of a rod-shaped material with the tool W (hereinafter referred to as “processed product of the present application”) subjected to surface modification of the present invention. It is a test to measure.

  In the surface modification, cemented carbide particles having a specific gravity of 14.5 were used as the first shot S1, and particles made of high-speed steel having a specific gravity of 7.8 were used as the second shot S2. The particle diameter of these shots S1, S2 is an average of 50 μm. In the mixed shot Sm, 15 wt% of the total weight is the first shot S <b> 1, and the remaining part (85 wt%) is the second shot S <b> 2.

  The processed product of the present application is made of die steel as a thread rolling flat die, and surface modification by projecting the mixed shot Sm is performed on the entire surface of the rolled tooth profile (that is, the chamfered portion, the finished portion, and the relief portion). Is done. The material to be rolled is a round bar of SCM440 (equivalent to 38HRC), and an M10 × 1.5 male screw is rolled on the outer peripheral surface thereof.

  The hardnesses of the first shot S1 and the second shot S2 are 1400 HV and 800 HV, respectively. The treated product has a hardness before surface modification of 700 HV and an altitude after surface modification of 1340 HV. Moreover, the projection pressure from the nozzle 17 of the shot peening apparatus 1 is 0.5 MPa.

  FIG. 3 is a graph illustrating the number of processed products of the present application and the number of processed unprocessed products. Note that the difference between the untreated product and the present application product is only the presence / absence of surface modification, and the other configurations are the same, and the description thereof will be omitted.

  As a result of this test, the number of unprocessed products that can be processed was 5000, whereas the number of processed products of this application was 10400, and as a result of applying the surface modification of the present invention, It was confirmed that the life was improved and the number of machinables increased 2.1 times.

  In addition, the test product (not shown) which gave the surface modification different from the above with respect to this-application processed product was created, and the rolling test by this test product was done. Specifically, the test product is subjected to surface modification by mixing shots Sm having different mixing ratios (35 wt% of the total weight is the first shot S1 and the remaining (65 wt%) is the second shot S2). Is called. Except for the point that the mixing ratio is different, there is no difference between the test product and the processed product of the present invention (the material, the surface modification method, the material to be rolled, etc.).

  In the test product, since the mixing ratio of the first shot S1 is high, the treated surface is scraped off by the first shot S1, and the surface roughness is rough. Could not be rolled.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  The numerical values given in the above embodiment are merely examples, and other numerical values can naturally be adopted. In particular, any value can be adopted as the value specified by the numerical range in which the lower limit and the upper limit are specified as long as the value is within the numerical range.

  In the above embodiment, the case where the tool W is made of die steel has been described. However, the present invention is not necessarily limited to this, and other materials can naturally be employed. Examples of other materials include high-speed tool steel.

  In the above-described embodiment, the case where the tool W is configured as a flat die type (screw rolling flat die) has been described. However, the present invention is not necessarily limited to this, and it is naturally possible to adopt other types. . Examples of other types include a planetary type (rotary screw rolling die) and a round die type (screw rolling round die).

  Moreover, although the case where a screw was rolled on the outer peripheral surface of a material to be rolled was described, the present invention is not necessarily limited to this, and other shapes can naturally be rolled. Examples of other shapes include serrations, splines, worms, and tapping screws. Also in these cases, the tool W is not limited to the flat die type, and other types may be adopted.

  Moreover, the tool W may be comprised as a rolling tap for rolling a female screw. Alternatively, it may be configured as a burnishing tool for performing burnishing.

  In the above-described embodiment, the case where the shot peening apparatus 1 is configured by the direct pressure type has been described. However, the present invention is not necessarily limited thereto, and may be, for example, a siphon type or a gravity type, or other It may be a type.

  Although the description thereof is omitted in the above embodiment, the shape of the shot (particle) may be a spherical shape or an acute angle shape.

  In the above embodiment, the case where the first shot S1 and the second shot S2 having the same particle diameter are mixed as the mixed shot Sm has been described. However, the first shot S1 and the second shot S2 having different particle diameters are mixed. Also good. In this case, it is preferable that both the first shot S1 and the second shot S2 have a particle diameter in the range of 10 μm to 150 μm.

DESCRIPTION OF SYMBOLS 1 Shot peening apparatus S1 1st shot S2 2nd shot Sm Mixed shot W Tool

Claims (6)

In a surface modification method for a tool that modifies the surface of the tool by shot peening that projects a shot onto the surface of the tool,
A tool surface characterized by projecting a mixed shot obtained by mixing a first shot composed of cemented carbide particles and a second shot composed of iron-based material particles onto the surface of the tool. Modification method.   2. The surface modification method for a tool according to claim 1, wherein 2 to 30 wt% of a total weight of the mixed shot is the first shot, and the remainder is the second shot.   The first shot is composed of particles made of super steel alloy having a specific gravity of 13.9 to 15.0, and the second shot is composed of particles made of iron-based material having a specific gravity of 7.2 to 8.3. It is described in Claim 1 or 2 characterized by the above-mentioned.   4. The tool according to claim 1, wherein a particle diameter of the particles constituting the first shot and a particle diameter of the particles constituting the second shot are set to 10 μm to 150 μm. 5. Surface modification method.   The method for modifying the surface of a tool according to claim 4, wherein the particle diameter of the first shot and the particle diameter of the second shot are substantially the same. The rolling tool according to any one of claims 1 to 5, wherein the tool is a rolling tool for rolling a workpiece.

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