JP2019005786A - Correction method of punch - Google Patents

Abstract

To provide a correction method of a punch capable of bringing a position of a top face with respect to a die of the punch subjected to face correction close to a position of the initial state with a convenient and simple method.SOLUTION: A correction method of a punch as the correction method of the punch which is fitted to a press machine to be used for compression forming of raw material powder and forms a forming space together with a die, the punch having a head part to be inserted to a forming hole of the die and a base part to be fitted to a punch holder of the press machine includes a punch correction process of performing face correction by working a top face for the abraded punch and, at the same time, forming a build-up part on a bottom surface of the base part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a punch correction method.

  Conventionally, when a green compact is manufactured by compression molding raw material powder, a powder metallurgy mold (hereinafter simply referred to as “mold”) including a die having a molding hole and a punch inserted into the molding hole. ) Is used (see, for example, Patent Document 1). Usually, the mold is provided with an upper punch and a lower punch that are arranged opposite to each other above and below the die, and the upper and lower punches are attached to respective punch holders provided in the press machine. The punch also has a head that is inserted into the die forming hole and a base that is attached to the punch holder. As a method for attaching the punch, for example, the punch is fixed to the punch holder by holding the flange formed on the base against the punch holder by a pressing jig.

  When forming a green compact using a press, raw material powder is filled in a forming space formed by a die and a punch, and the raw material powder is compressed from above and below with a punch to form. Specifically, the lower punch is inserted into the die forming hole, the lower punch is set at a predetermined position of the die, the raw material powder is filled in the molding space formed by the die and the lower punch, and then the press machine Then, the upper punch is lowered, and the raw powder is compressed by the upper and lower punches to form a green compact. Thereafter, the upper punch is raised and the lower punch is raised relative to the die to take out the green compact from the die, and then the lower punch is lowered and returned to a predetermined position. By repeating this, the green compact can be continuously formed.

JP 2000-117497 A

  While the compression molding of the raw material powder is repeated, the top surface of the punch head may be worn due to friction with the raw material powder, resulting in sagging. When the punch head is worn, burrs are generated in the green compact, and the dimensional accuracy of the green compact is deteriorated and the surface properties are deteriorated. Therefore, when a sag occurs in the punch head, the punch is removed from the press and the top surface of the punch is corrected. The corrected punch is reattached to the press and used.

  When the top surface of the punch is modified, the length of the punch is reduced accordingly, and the position of the top surface of the punch relative to the die is different from the initial position before wear, which affects the dimensional accuracy of the green compact. There is concern. Therefore, when using a corrected punch whose surface has been corrected, it is desirable that the positional relationship between the die and the punch be brought close to the initial state by adjusting the height of the punch.

  Conventionally, as a method for adjusting the height of the punch, for example, a plate is sandwiched between the bottom surface of the base of the punch and the punch holder. As a result, it is possible to make the length of the punch combined with the plate the same as the length of the punch in the initial state before wear, and return the position of the top surface of the punch with respect to the die to the initial state position. Can do. However, in this case, it is necessary to prepare a plate having a thickness corresponding to the height adjustment amount. In addition, when pressing the flange formed on the base of the punch against the punch holder with a holding jig, the position of the flange becomes higher from the surface of the punch holder by the thickness of the plate, so it can be held by the holding jig Thus, it is necessary to cut and thin the flange portion. When the flange portion is thinned, the strength of the flange portion decreases, so when the punch head is moved relatively in the direction of pulling out from the die forming hole, a force in the pulling direction acts on the punch due to friction with the die. In such a case, there is a risk of damage such as cracking in the flange.

  Patent Document 1 describes a molding apparatus including a height adjusting mechanism (adjusting screw) that adjusts the height of the lower punch. However, when the height adjusting mechanism is adopted in the molding apparatus, there is a problem that the apparatus cost becomes high due to the complicated or large structure of the apparatus.

  Accordingly, it is an object of the present invention to provide a punch correction method capable of bringing the position of the top surface of the punch whose surface has been corrected to the die in the initial state close to the initial position by a simple and simple method.

The punch correction method according to the present disclosure is:
A punch correction method that is attached to a press used for compression molding of raw material powder and forms a molding space together with a die,
The punch has a head that is inserted into a molding hole of the die, and a base that is attached to a punch holder of the press.
For the worn punch, the top surface of the head is machined to correct the surface, and a punch correcting step for forming a built-up portion on the bottom surface of the base portion is provided.

  The punch correction method is a simple and simple method, and the position of the top surface of the punch whose die has been corrected can be brought close to the initial position.

It is the schematic which shows an example of a punch. It is the schematic which shows an example of the punch after correction which formed the build-up part.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

(1) A punch correction method according to an aspect of the present invention includes:
A punch correction method that is attached to a press used for compression molding of raw material powder and forms a molding space together with a die,
The punch has a head that is inserted into a molding hole of the die, and a base that is attached to a punch holder of the press.
For the worn punch, the top surface of the head is machined to correct the surface, and a punch correcting step for forming a built-up portion on the bottom surface of the base portion is provided.

  According to the punch correcting method, the length of the punch whose surface has been corrected can be brought close to the initial length before the wear by forming the build-up portion on the bottom surface of the worn punch base. Accordingly, it is not necessary to use a plate or provide a height adjusting mechanism in the press machine as in the prior art, and the position of the top surface with respect to the die of the punch whose surface has been corrected is set to the initial state by a simple and simple method. Can be close to the position. Furthermore, by adjusting the thickness of the built-up portion to be formed, it is possible to make the length of the punch whose surface has been corrected the same as the length of the initial state before wear, and the position of the top surface of the punch with respect to the die It can be returned to the initial position. In addition, since the build-up part is integrally formed on the bottom of the punch, when the flange part formed on the base part of the punch is pressed against the punch holder with a pressing jig, the flange part is held so that it can be held by the pressing jig. Even if it cuts, the thickness of a flange part will be maintained by the buildup part. Therefore, the strength reduction of the flange portion can be suppressed by the build-up portion, and damage to the flange portion when a force in the pulling direction acts on the punch due to friction with the die can be greatly reduced.

  (2) As an aspect of the punch correction method, in the punch correction step, the shape of the punch is adjusted so that the rigidity of the corrected punch that has formed the build-up portion is the same as the rigidity in the initial state. And processing.

  The demand for dimensional accuracy of green compacts has become stricter year by year. As a result of extensive studies by the present inventors, it has been found that the rigidity of the punch has a subtle effect on the dimensional accuracy of the green compact. Depending on the shape of the punch, the rigidity of the corrected punch that has formed the build-up portion may change from the initial state, and the dimensional accuracy of the green compact may change due to the change in the rigidity of the punch. Therefore, when the corrected punch is used, there may be a deviation in the dimensional accuracy of the green compact.

  By processing the shape of the punch so that the rigidity of the corrected punch that has formed the overlay is the same as the rigidity in the initial state, the same dimensional accuracy as in the initial state can be obtained even if the corrected punch is used. Therefore, high dimensional accuracy can be maintained.

  (3) As one aspect of the punch correcting method, the build-up portion may be formed by layered modeling by irradiating a laser while laminating steel powder on the bottom surface of the base portion.

  By forming a build-up portion by irradiating a laser while laminating steel powder on the bottom surface of the base portion of the punch to form a build-up portion, a build-up portion having a uniform thickness can be formed with high accuracy.

[Details of the embodiment of the present invention]
A specific example of the punch correcting method according to the embodiment of the present invention will be described below. The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

<Punch correction method>
The punch correction method according to the embodiment is a method of correcting a punch that is attached to a press used for compression molding of raw material powder and forms a molding space together with a die. As shown in FIG. 1, the punch 1 has a head portion 11 inserted into a forming hole 20 of a die 2 and a base portion 12 attached to a punch holder 100 of a press machine. One of the features of the punch correction method according to the embodiment is that, as shown in FIG. 2, the top surface 11 h of the head 11 is machined to correct the surface of the worn punch 1 and the bottom surface of the base 12 is corrected. 12b is provided with a punch correcting step for forming the build-up portion 3. Hereinafter, the punch correction method of this embodiment will be described in detail with reference to the drawings. The same reference numerals in the figure indicate the same names. Below, the case where the punch 1 is the lower punch will be described as an example with the head 11 side of the punch 1 being the upper side and the base 12 side being the lower side. In FIG. 2, the overlaid portion 3 is hatched for easy understanding.

(punch)
The punch 1 shown in FIG. 1 shows an initial state before wear. The head 11 inserted into the forming hole 20 of the die 2, the base 12 attached to the punch holder 100, and the head 11 to the base 12. And a shaft portion 13 extending in the vertical direction (axial direction). The head 11 of the punch 1 is a portion that is inserted into the molding hole 20 of the die 2 and compresses the raw material powder, and the top surface 11h forms a molding space and serves as a surface that presses the raw material powder. The base 12 of the punch 1 is disposed on the punch holder 100 and is attached so that the bottom surface 12 b is in contact with the upper surface of the punch holder 100. In this example, the base portion 12 is thicker than the head portion 11, and has an inclined portion 13 b that widens toward the base portion 12 side at the lower end portion of the shaft portion 13. Is formed. The punch 1 is attached to the punch holder 100 by fastening the holding jig 110 to the punch holder 100 with the bolt 111 so that the flange portion 12f is pressed and held by the holding jig 110 from above. Thus, the punch 1 is fixed.

  The punch 1 is formed of a steel material having high strength and excellent wear resistance. Typically, the punch 1 is a high-speed tool steel (hereinafter referred to as “high-speed steel”), an alloy tool steel (hereinafter referred to as “die steel”), or the like. Made of tool steel.

(Raw material powder)
Examples of the raw material powder used as the raw material for the green compact include metal powder such as iron, aluminum, or an alloy thereof, ceramic powder such as alumina, and the like. A lubricant may be added to the raw material powder for the purpose of improving the lubricity during compression molding. From the viewpoint of increasing the density of the green compact, the molding pressure at the time of compression molding is, for example, 500 MPa or more, and further 600 MPa or more. The density of the green compact is, for example, 6.5 g / cm ³ or more and 7.2 g / cm ³ or less when an iron-based powder such as pure iron powder or iron alloy powder is used as the raw material powder.

(Punch correction process)
In the punch correction process, as shown in FIG. 2, the top surface 11 h of the head 11 is corrected on the worn punch 1 and the bottom surface 12 b of the base 12 is overlaid. In FIG. 2, the shape of the punch 1 in the initial state is indicated by a two-dot chain line.

  The surface correction is an operation for processing the top surface 11h of the head 11 of the worn punch 1 and returning it to the initial state. For example, cutting processing such as milling, electric discharge processing such as wire cutting, and grinding processing such as surface polishing. It is mentioned that it is performed by machining. The amount of surface correction is appropriately determined according to the wear state of the head 11. When the surface is corrected, a part of the upper end of the head 11 is removed, so that the length of the head 11 is shortened.

  The build-up is an operation of forming the build-up portion 3 on the bottom surface 12b of the base 12 of the punch 1, and includes, for example, building up a steel material. By forming the built-up portion 3 integrally on the bottom surface 12b of the punch 1, the length of the punch 1 whose surface is corrected is brought close to the initial length, and the position of the top surface 11h of the punch 1 relative to the die 2 is set to the initial state. Can be close to the position. The thickness of the built-up portion 3 to be formed is, for example, set to be equal to or more than the same thickness as the surface corrected amount from the viewpoint of bringing the length of the punch whose surface is corrected as close as possible to the length of the initial state. In the present embodiment, the thickness of the build-up portion 3 is adjusted so that the length of the punch 1 whose surface has been corrected is the same as the length in the initial state, and the position of the top surface 11 h of the punch 1 with respect to the die 2 is initially set. It can be returned to the state position. The corrected punch 1 in which the build-up portion 3 is formed is attached so that the lower surface of the build-up portion 3 is in contact with the upper surface of the punch holder 100.

  The build-up can be performed by a known method such as thermal spraying, plasma powder build-up, or laser powder build-up. Laser powder build-up is a so-called powder bed fusion method in which laser powder is radiated and laminated while sequentially laminating steel powder, and laser is simultaneously radiated and shaped while jetting steel powder. There is a so-called laser metal deposition method. The powder bed fusion method can be performed using a commercially available metal 3D printer (for example, OPM250L manufactured by Sodick Co., Ltd.). When the build-up portion 3 is layered and formed by irradiating a laser while laminating steel powder, the build-up portion 3 having a uniform thickness can be formed with high accuracy.

  The steel material to be built up may be the same type of steel material as punch 1 or a different type of steel material. For example, in addition to tool steel such as high-speed steel or die steel, stainless steel or maraging steel may be used. There may be. When the steel material of the same steel type as that of the punch 1 is built up, the familiarity between the punch 1 and the built-up portion 3 is good, and the entire punch 1 including the built-up portion 3 can be homogenized.

  It is preferable that the surface hardness of the built-up portion 3 is 90% or more of the surface hardness of the punch 1 in terms of Vickers hardness (HV). In this case, the steel material having a hardness of 90% or more of the steel material forming the punch 1 may be selected as the steel material to be built up. Thereby, since the build-up portion 3 has a hardness equal to or higher than that of the punch 1, it is possible to secure deformation resistance comparable to that of the punch 1 in the initial state. The surface hardness of the built-up portion 3 is more preferably 95% or more of the surface hardness of the punch 1. The upper limit of the surface hardness of the built-up portion is not particularly limited, but steel materials tend to have lower toughness as the hardness is higher. For example, the surface hardness of the punch 1 is 140% or less, and further 120% or less. Can be mentioned.

  After the build-up portion 3 is formed, the build-up portion 3 may be finished as necessary to correct the dimensional error of the build-up portion 3. Examples of the finishing process include performing a machining process such as a milling process, an electric discharge process such as a wire cut, and a grinding process such as planar polishing.

  Furthermore, you may provide the tempering process of tempering the punch 1 in which the build-up part 3 was formed. Depending on the build-up method, the entire structure of the build-up portion 3 may not be a martensite structure, and an austenite structure (residual austenite) may remain in part. After the build-up portion 3 is formed, the hardness of the build-up portion 3 can be improved by precipitating carbides or converting the retained austenite into martensite by tempering. The conditions for the tempering treatment are appropriately set according to the type of steel material forming the build-up portion 3. For example, in the case of high-speed steel, the heating temperature is 530 ° C. or more and 630 ° C. or less, and the holding time is 1 hour or more and 4 hours or less, preferably 2 hours or more. In the case of stainless steel (SUS420J2), the heating temperature is For example, 150 ° C. or more and 250 ° C. or less and a holding time of 0.5 hour or more and 2 hours or less can be mentioned. When performing the tempering process, it is preferable to finish the built-up portion 3 as necessary after the tempering process.

  In the present embodiment, the built-up portion 3 is integrally formed on the bottom surface 12b of the punch 1, and the flange portion 12f including the built-up portion 3 is thickened. Therefore, the upper surface of the flange portion 12f is cut so that it can be held by the holding jig 110 so that the thickness of the flange portion 12f including the build-up portion 3 is the same as the thickness of the flange portion 12f in the initial state. Processing. That is, the thickness of the flange portion 12f is maintained before and after the correction. In this case, since the built-up portion 3 is integrated with the bottom surface 12b of the punch 1, and the thickness of the flange portion 12f is maintained by the integrated built-up portion 3, the strength of the flange portion 12f is reduced. Can be suppressed.

  Further, the shape of the punch 1 after correction is shorter than the initial state, the head 11 is shortened by the surface correction, and the base 12 is lengthened by the integrated built-up portion 3. In this embodiment, since the base 1 of the punch 1 is thicker than the head 11, the head 11 becomes shorter when the corrected punch 1 forming the build-up portion 3 is viewed in the axial direction. On the other hand, while the thin section decreases, the base 12 becomes longer by the thickness of the build-up portion 3, and the thick section increases. Therefore, the shape of the punch 1 after correction changes from the initial state, and the rigidity of the punch 1 after correction may change from the initial state. Therefore, in the present embodiment, as shown in FIG. 2, the outer peripheral surface of the inclined portion 13b that connects the shaft portion 13 and the base portion 12 is cut, and the rigidity of the punch 1 after correction becomes the same as the rigidity in the initial state. As such, the shape of the punch is processed. Specifically, processing is performed so that the length of the base 12 combined with the overlay 3 is the same as the length of the base 12 in the initial state. The rigidity of the punch 1 can be obtained by CAE (Computer Aided Engineering) analysis.

{Effect of punch correction method}
The punch correction method according to the embodiment described above has the following effects.

  By forming the build-up portion 3 on the bottom surface 12b of the worn punch 1, the length of the punch 1 whose surface has been corrected can be brought close to the initial length before wear. Accordingly, it is not necessary to use a plate or to provide a height adjusting mechanism in the press machine as in the prior art, and the position of the top surface 11h with respect to the die 2 of the punch 1 whose surface has been corrected is simple and simple. It can be brought closer to the initial position. In particular, when the build-up portion 3 is formed so that the length of the punch 1 whose surface is corrected is the same as the length in the initial state, the position of the top surface 11h of the punch 1 with respect to the die 2 is returned to the initial state. Can do. Moreover, since the build-up portion 3 is integrally formed on the bottom surface 12b of the punch 1 and the thickness of the flange portion 12f is maintained by the build-up portion 3, a decrease in strength of the flange portion 12f can be suppressed. Therefore, damage to the flange portion 12f when a force in the pulling direction is applied to the punch 1 due to friction with the die 2 can be greatly reduced.

  Further, by processing the shape of the punch 1 so that the rigidity of the punch 1 after correction is the same as that in the initial state, the same dimensional accuracy as in the initial state can be obtained even if the punch 1 after correction is used. Therefore, high dimensional accuracy can be maintained.

{Use of punch correction method}
The punch correcting method according to the embodiment can be used for correcting a punch attached to a press used for compression molding of raw material powder.

DESCRIPTION OF SYMBOLS 1 Punch 11 Head 11h Top surface 12 Base 12b Bottom 12f Flange part 13 Shaft part 13b Inclined part 2 Die 20 Molding hole 3 Overlay part 100 Punch holder 110 Holding jig 111 Bolt

Claims (3)

A punch correction method that is attached to a press used for compression molding of raw material powder and forms a molding space together with a die,
The punch has a head that is inserted into a molding hole of the die, and a base that is attached to a punch holder of the press.
A punch correcting method comprising a punch correcting step of processing the top surface of the head to correct the surface of the worn punch and forming a build-up portion on the bottom surface of the base.   The punch correction method according to claim 1, wherein in the punch correction step, the shape of the punch is processed so that the rigidity of the punch after the correction in which the build-up portion is formed is the same as the rigidity in the initial state.   3. The punch correction method according to claim 1, wherein the build-up portion is formed by irradiating a laser while laminating a steel powder on the bottom surface of the base portion and performing layered modeling.

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