JP4268024B2 - Tire molding mold manufacturing method and tire molding mold - Google Patents

Description

  The present invention is to improve the dimensional accuracy of a tire molding die manufactured by casting, and more specifically, the diameter of a design surface portion of a ring casting for a tire molding die cast in a ring state, a perfect circle The present invention relates to a method for manufacturing a tire molding die that can easily correct the degree characteristic to a target characteristic with high accuracy, and a tire molding die manufactured by the manufacturing method.

  The tire molding die is formed by assembling a plurality of divided piece dies, and an upper and lower divided die (two piece mold) configured by dividing the tire shape into two in the width direction, and a radial direction. Two types of tire molding dies are used, which are an upper and lower integrated type (sectional mold) configured by dividing the outer circumference into about 7 to 13 in the (circumferential direction).

  In such a tire molding die, since it has a large number of thin convex portions such as concave block shape portions and sipe blades having sharp corners, it is not suitable for manufacturing by machining. Manufactured by casting.

  Of the casting methods, the gypsum casting method is often used. This is because the mold is collapsible, has a high degree of freedom in supporting undercut shapes, can be easily assembled with the mold, can be cast into a nearly integral shape, and has high dimensional accuracy. The reason is that the mold cost is low.

  FIG. 14 shows a procedure for producing a two-piece mold by a gypsum casting method. First, a tire mold (master model) 1 is produced by machining using gypsum, resin, etc. as shown in (a), and a rubber mold 2 in which the prototype 1 is inverted with silicone rubber or the like as shown in (b). Is made. Then, as shown in (c), the mold 3 is inverted from the rubber mold 2 by gypsum, and the mold 3 is baked and dried, then cut at a plurality of angles as shown in (d), and as shown in (e). Are assembled into a ring-shaped mold 4. Then, as shown in (f), the mold 4 is surrounded by a casting frame 5 and cast into a casting by filling the casting frame 5 with a molten alloy 6 such as an aluminum alloy. Then, machining is performed, and then mold matching is performed as shown in (g) to obtain a tire molding die 8. In (g), the code | symbol 7 is the some division | segmentation die which comprises the metal mold | die for tire shaping | molding. As shown in FIG. 16 described later, the split mold 7 is assembled into an upper and lower split mold by using a back mold 9, and a tire molding mold 8 is formed by this assembly.

  FIG. 15 shows a procedure for producing a sectional mold by a gypsum casting method. Similarly to FIG. 14, after producing a rubber mold 2 of (b) in which the tire prototype 1 shown in (a) is inverted, (c) And the casting_mold | template 3 is produced with gypsum as shown by (d), It assembles as shown by (e), and it is set as the casting_mold | template 4. Thereafter, as in FIG. 14, casting with a cast metal such as an aluminum alloy is performed, and the casting is mold-matched to obtain a tire molding die 8 shown in (f). In (f), the code | symbol 7 is the division | segmentation metal mold | die which comprises the metal mold | die 8 for tire shaping | molding similarly to FIG.

  More specifically, the method for producing a sectional mold by the gypsum casting method can be divided into a first sectional mold method and a second sectional mold method. The first sectional mold method is a sector end face surplus setting method, in which the split mold 7 is formed with a finishing allowance that is removed by post-processing such as back processing allowance and side processing allowance, The two-section molding method is a sector end face surplus method, in which the split mold 7 is manufactured without finishing machining on both side faces (end faces) of the sector block.

  As shown in FIG. 16, the plurality of divided molds 7 manufactured by the above method are assembled so as to be adjacent to each other in the circumferential direction, and (a) is a sectional mold, (b) is The case of a two-piece mold is shown. In any case, a plurality of split molds 7 are attached to the outer back mold 9 and assembled in a ring shape to form a tire molding mold 8.

  As described above, since the two-piece molding method, the first sectional molding method, and the second sectional molding method are all cast in a ring state, when the molten aluminum alloy is solidified and cooled, the center axis of the ring is reduced. In many cases, non-uniform distortion is generated, and due to this, the roundness of the inner surface (design surface) of an as-cast casting (ring casting) (running value width from the reference perfect circle) tends to deteriorate. is there.

  Further, shrinkage variation of the casting is likely to occur, and due to this, the inner diameter of the ring casting may be deviated from the target (out of the allowable tolerance).

  The diameter and roundness of each part in tire molding dies are important management items that determine tire performance, and their required characteristics are becoming more and more accurate year by year, and are approaching the production limit of casting methods. .

  For example, the current required accuracy is that the tolerance value is about ± 0.2 mm in diameter and about 0.25 mm in roundness, and in the case of high-precision specifications, it is ± 0.1 to 0.15 mm in diameter. The roundness is 0.1 to 0.15 mm, which is almost close to machining specifications.

  From this point of view, to summarize the three conventional gypsum casting methods for tire molding described above, the first section molding method (end face surplus) is aimed at producing a perfect circle casting in sector block units. The meat setting method) is the most effective method of solving these problems in the current method.

  The reason for the radius (diameter) characteristics is that the casting cast in the ring state is divided into sectors in the circumferential direction, and then adjusted so that the inner surface (design surface) comes to the specified diameter position, then the upper and lower surfaces of the sector Since the machining, the end face machining, and the outer circumference machining can be performed, the radius (diameter) characteristic can be improved as compared with the ring state.

  For the same reason, with regard to the roundness characteristics, the first sectional mold method (end face surplus setting method) is a process of dividing and reassembling the sectors even if the roundness characteristics are poor in a continuous ring state. The roundness characteristics can be improved more than in the ring state because the both end portions of the sector dividing surface are brought to the zero position and the end surface angle machining is possible.

  FIG. 17 illustrates the improvement of these characteristics. FIG. 17A shows the state of a ring casting, in which the radius (diameter) of each part of the casting deviates from the target dimension (normal radius R) and the roundness characteristics are not good. In this case, the two-piece mold is used as it is as a mold unless it is corrected by an external force. On the other hand, in the first sectional mold method (end face surplus setting method), as shown in FIG. 17 (b), after dividing the sector, both ends of the circumferential direction Pf surface are positioned at the normal radius R, and Peripheral machining can be performed by adjusting the position of the sector so that the radius is the same between molds (same as for all sectors). Therefore, in the first sectional mold method (end face surplus setting method), both end portions of the sector can be shifted to the position of the normal radius R (as shown in FIG. 17C, before sector position adjustment processing → sector position adjustment processing). Therefore, both the radius (diameter) and roundness are improved compared to the ring state.

  For this reason, the first sectional mold method (end surface surplus setting method) has an advantage not found in the other two manufacturing methods.

  However, the first sectional mold method (end surface surplus setting method) also has a demerit that the design division shape often causes displacement / distortion in the sector division surface (both end surfaces) by the adjustment described above. .

  In addition, the first sectional molding method (end face surplus setting method) has a problem that the die cost increases because the man-hours for outer periphery processing of the casting are larger than those of the other two manufacturing methods. .

  On the other hand, the two-piece molding method and the second sectional molding method are intended to manufacture a ring casting aiming at a perfect circle, but the as-cast diameter and roundness characteristics of the manufactured ring casting are set to predetermined values. If it does not enter, it cannot be corrected by position adjustment by machining. Therefore, it is necessary to correct the diameter or correct the roundness of the ring-shaped casting.

    Conventionally, two methods of diameter (radius) expansion type and diameter (radius) reduction type have been adopted as diameter correction and roundness correction.

  FIG. 18 is a ring casting used for the diameter (radius) expansion type, FIG. 18A is an as-cast state A1, and FIG. 18B is an as-cast state A1 with the feeder part B removed. Ring casting A is shown.

  FIG. 19 illustrates a first correction method of the diameter (radius) expansion type. This first correction method uses a cam-type expander E that uses a fan-shaped slide piece e in which a disk is divided into 12 to 20 as an expansion means. In this case, the as-cast surface a of the ring casting A in FIG. 18B is used as a reference diameter portion.

  FIG. 19 (a) is a method in which the upper and lower as-cast surfaces a are used to project the same amount of fan-shaped slide piece e at the same time up and down, and φd1 and φd2 are expanded at the same time, and FIG. FIG. 19 (c) shows an upper as-cast surface in which the lower as-cast surface a is used to project the fan-shaped slide piece e by a certain amount only on the lower side, and only the φd1 side is expanded. This is a method of extending a fan-shaped slide piece e by a certain amount only on the upper side using a, and expanding only the φd2 side.

  Further, A, B, and C in FIG. 19 indicate the correction status, crown R shape change, and roundness of each part in each of the methods (a), (b), and (c).

  As can be seen from FIG. 19B, in the case of (a), only the diameter (radius) is expanded only in the vicinity of the part that protrudes vertically, and the central part is in a state close to the original diameter. In the case of (b), the diameter (radius) in the vicinity of the lower protruding portion is expanded, and at the same time, the diameter is slightly reduced by the reaction on the upper side, In the case of (c), the diameter (radius) in the vicinity of the upper protruding portion is expanded, and at the same time, the diameter is slightly reduced on the lower side due to the reaction.

  In FIG. 19C, the inner broken line shows the as-cast state, and the outer solid line shows the corrected state of the same part. As is clear from these, the correlation between the design surface portion and the roundness tendency is shown. Since the upper and lower reference diameter parts (as cast surface part) are projected into a perfect circle with a fan-shaped slide piece, the place where the curvature is small (that is, the place where the radius is large) is larger in the ring casting. Will receive. Furthermore, in addition to this straightening strain, by receiving the overall tensile strain due to diameter (radius) overhang, the roundness of the vicinity of the portion that has undergone overhang straightening is improved from the as-cast state at the same time as the diameter (radius) is expanded. (Improved roundness by the Bausinger effect) This is a feature of diameter expansion correction using the as-cast reference diameter part (even if diameter expansion correction is performed on the lathe processing surface, the roundness improvement phenomenon does not occur).

  However, this first correction method of the diameter (radius) expansion type uses any of the correction patterns shown in FIGS. 19A to 19C to cause a buckling phenomenon of a crown R shape (cross-sectional shape in the tire width direction) (FIG. 19B). Has a problem that it is easy to occur.

  FIG. 20 shows a ring casting used for a reduced diameter (radius) type, FIG. 20 (a) shows an as-cast state A1, and FIG. 20 (b) shows an as-cast state A1 with the feeder part B removed. Ring casting A is shown.

  FIG. 21 illustrates a second diameter (radius) reduction type second straightening method. This second straightening method is performed in a state in which a restraining ring F is fitted into a processing surface b formed on the back surface of the ring casting A. Intersizing is performed.

  FIG. 21A shows a case where the entire back surface (machined surface b) of the ring casting A is covered with a constraining ring F having an inner surface of the same shape (tapered shape) and heat-treated in this state. ) Covers only the lower part of the back surface (working surface b) of the ring casting A with the constraining ring F and heat-treats in this state. FIG. 21 (c) shows the back surface (working) of the ring casting A. Only the upper part of the surface b) is covered with the restraining ring F and heat-treated in this state. At this time, the constraining ring F is formed using a material having a smaller thermal expansion amount than the ring casting A (aluminum alloy), for example, a steel material.

  Further, A, B, and C in FIG. 21 indicate the correction status, crown R shape change, and roundness of each part in each of the methods (a), (b), and (c).

  As is clear from FIG. 21B, in the case of (a), since it is tightened as a whole by the constraining ring F, the inner diameter of the ring casting A is reduced overall, and the mackerel breakage phenomenon is unlikely to occur. In the case of (b), the inner diameter is small only in the vicinity of the lower restraining ring, and the upper diameter is slightly increased in the reaction on the upper side. In the case of (c), the inner diameter is only in the vicinity of the upper restraining ring. The inner diameter is slightly increased by the reaction on the lower side.

  In FIG. 21C, the broken line on the outer side indicates the as-cast state, and the solid line on the inner side indicates the state after correction of the same part. As is clear from these, this correction is a lathe surface that is a perfect circle. Since the diameter reduction correction is performed based on b, the phenomenon that the roundness is improved by the correction does not occur. Although it is not impossible to perform diameter reduction correction in the as-cast state of the back surface of the ring casting A, since there is no correlation in the roundness tendency between the design surface portion and the back surface portion, The circularity improvement effect cannot be obtained.

  In this second diameter (radius) reduction type correction method, when the upper and lower portions are simultaneously reduced in diameter by the same amount (FIG. 21 (a)), the mackerel breakage phenomenon of the crown R shape (see B in FIG. 21) occurs. Although it is difficult to occur, the other cases (FIGS. 21B and 21C) have a problem that a mackerel breakage phenomenon basically occurs.

  FIG. 22 shows still another radius reduction type (FIG. 22 (a)) and radius expansion type (FIG. 22 (b)).

  The third correction method as a radius reduction type at this time is a striking method using a pendulum type hammer, and is a method used when it is desired to improve the roundness of the as-cast ring casting A1 by locally reducing the radius. Since the striking energy can be controlled by the pendulum mass W and the swing-down angle θ, it is possible to correct the radius reduction in units of 0.1 mm.

  The fourth straightening method as the radius expansion type is a drop impact method using a fixed hammer, and is a method used when it is desired to locally increase the radius to improve the roundness of the ring casting A. Since the impact energy can be controlled by the weight of the ring casting A1 and the drop of the drop, the radius can be reduced in units of 0.1 mm.

  A and B in FIG. 22 are the correction statuses in the third and fourth correction methods (a) and (b), and the roundness of each part (in FIG. 22B, the broken lines indicate the as-cast state. The solid line shows the post-correction).

  As is apparent from FIG. 22B, in the case of the third correction method (a), the striking portion preferentially reduces the radius, but the radius of the portion shifted by 90 ° on both sides slightly expands, In general, there is almost no difference in the average diameter (radius) before and after the correction. In the case of the fourth correction method (b), the striking site preferentially enlarges the radius, but shifted by 90 ° on both sides. In general, the radius of the portion is slightly reduced, and as a whole, there is almost no difference in the average diameter (radius) before and after correction.

  Although the crown R shape change of the third and fourth straightening methods is not shown in the figure, the crown R shape can be used before and after the correction if the impact load acts uniformly on the entire surface in the tire width direction of the ring casting. It can be said that there is almost no change, but if a biased load is applied, mackerel breakage deformation may occur. Since it can be said that it is extremely difficult to apply a uniform impact load in the tire width direction, the third and fourth straightening methods also have a problem that the crown R-shaped mackerel breaks.

  Furthermore, since the first straightening method as a diameter expansion straightening by an expander can improve (correct) the diameter (inner diameter) and roundness characteristics at the same time, “the cast casting inner diameter of the ring mold for tire mold is intended. The most common method is to make it smaller than the target size (drawing size) and correct the diameter and roundness simultaneously by diameter expansion correction.

  However, this first correction method has the following problems.

  (1) Since the diameter expansion is corrected by external force such as a cam type expander, advanced prediction technology is required to expand to the target diameter by springback of the ring casting when the external force is removed (multiple expander processing) May need to be done or may be overextended).

  (2) The crown R shape accuracy is necessarily deteriorated (deteriorated) (however, there is an advantage that the roundness characteristic is improved).

  (3) If the amount of diameter expansion exceeds the elongation at break of the ring casting, it leads directly to breakage.

  (4) When the sipe is cast, the cast strength may decrease.

  (5) Residual strain after diameter expansion (due to local plastic deformation) may adversely affect the subsequent use of the tire mold (change in dimension over time, occurrence of deformation during mold processing, etc.).

  Further, the second straightening method for reducing the diameter by using the restraining ring is “correcting the diameter by intentionally creating an as-cast inner diameter of the ring casting for a tire mold larger than a target dimension (drawing dimension). The following problems exist with this method.

  (6) It is difficult to set hot correction conditions such as setting of heating temperature and heating holding time, and advanced prediction technology is required to reduce to the target diameter (if multiple hot corrections are required or , It may shrink too much.)

  (7) The R shape accuracy of the crown may be deteriorated (deteriorated) (roundness characteristics are not basically improved).

  It can be said that the second correction method for reducing the diameter is advantageous in that the problems (3) to (5) of the first correction method for expanding the diameter do not become a problem. That is, the second straightening method does not break because of compression straightening, there is no gap in the sipe cast-in surface, and since the straightening is performed hot, residual strain is unlikely to remain. That is why.

  Further, the third and fourth correction methods for correcting (correcting) roundness have the following problems.

  (8) Basically, the diameter cannot be corrected.

  (9) Residual strain after correction (due to local plastic deformation) has a risk of adversely affecting subsequent use of a tire mold (change in dimensions over time, occurrence of deformation during mold processing, etc.).

  As described above, all of the conventional first to fourth straightening methods have serious problems, and there are no diameter and roundness straightening methods that have few problems in all aspects. That is the situation.

  The present invention has been made on the basis of the above situation, and the diameter reduction and roundness characteristics of a ring casting for a tire mold are simultaneously achieved by diameter reduction correction that hardly causes springback and residual distortion after correction. It is an object of the present invention to provide a method for manufacturing a tire molding die that corrects and hardly damages the crown R shape, and a tire molding die.

In order to achieve the above object, the invention of claim 1 is a method of manufacturing a tire molding die manufactured by a casting method,
A first step of producing a shape by casting a reference diameter portion that can be removed by post-processing to the inner diameter portion in the ring casting state and immediately close to the upper and lower ends, and becomes a perfect circle of a predetermined diameter;
A second step of casting and manufacturing a ring casting for a tire molding die so that the inner diameter of the reference diameter portion and the design surface portion is about 0.05 to 0.2% larger than the target diameter;
After machining the outer periphery of the ring molding for tire molding mold so as to have the same diameter as the inner diameter of the restraining ring used for diameter reduction correction, the ring casting for tire molding mold is fitted into the restraining ring. A third step;
The thermal expansion coefficient of the ring casting material for the tire molding die is processed in a state as close to a perfect circle as possible so that the reference diameter portion has an outer diameter substantially the same as the target diameter of the reference diameter portion. A fourth step of fitting an inner diameter shrinkage-preventing ring made of a material equivalent to or less than the rate and having a high yield strength characteristic;
In this state, the ring casting for tire molding die is compressed and yielded by heating and holding in the heating furnace and then cooling, and the reference diameter portion and the design surface portion of the ring casting for tire molding die are set to a predetermined inner diameter. And at the same time, the fifth step of correcting the roundness characteristic to a shape that conforms to the roundness characteristic of the inner diameter shrinkage prevention ring,
The constraining ring and the inner diameter shrinkage-preventing ring are removed from the ring casting for a tire molding die, and a sixth step of peripherally processing the ring casting after the removal is sequentially performed.

  In the first aspect of the present invention, the ring casting for a tire molding die that has been manufactured (first step and second step) with a large inner diameter (larger than the target diameter of 0.05 to 0.2%) in advance. Hot correction (diameter reduction correction), which is a conventional method, is performed in a state in which an inner diameter shrinkage prevention ring having a target diameter of the corresponding reference diameter portion as an outer diameter is fitted in the extraction reference diameter portion (third step and fourth step). Step), the inner diameter and the roundness characteristic of the ring casting can be corrected simultaneously (fifth step).

  For this reason, regardless of the two-piece molding method, the first sectional molding method, or the second sectional molding method, the condition setting for hot correction is misread, and the ring casting is excessively reduced in inner diameter. Even in this case, the inner diameter shrinkage-preventing ring is not reduced to an inner diameter smaller than that.

The invention of claim 2 is a method for manufacturing a mold for molding a tire according to claim 1,
The restraint ring is manufactured by intentionally reducing the Young's modulus of the ring as a whole and approaching the Young's modulus of the ring casting for a tire mold.
Examples of the Young's modulus adjusting method include a method of making a hole in each portion of the constraining ring or using a foam metal or a sintered metal having a high porosity as the constraining ring material.

  In the invention of claim 2, the Young's modulus of the ring casting and the restraining ring is well balanced, and the diameter of the ring casting can be reduced until the entire ring casting is compression-plastically deformed and the reference diameter portion of the ring casting comes into contact with the inner diameter shrinkage-preventing ring. it can.

Invention of Claim 3 is a manufacturing method of the metal mold | die for tire shaping | molding of Claim 1 or 2, Comprising:
The inner diameter shrinkage prevention ring is manufactured as an assembly structure separable into two or more parts.

  In the invention of claim 3, when the inner diameter shrinkage-preventing ring is cooled to room temperature, the inner diameter shrinkage-preventing ring is in a state as if it was “tightly fitted” by the ring casting due to a difference in cooling shrinkage between the ring casting and the inner diameter shrinkage-preventing ring. Even so, it can be easily removed.

  The invention of claim 4 is manufactured by the method for manufacturing a mold for forming a tire according to any one of claims 1 to 3.

  According to the invention of claim 2, since the Young's modulus of the constraining ring is made close to that of the ring casting, strain energy can efficiently reach the “design surface (inner surface)” where the diameter is most desired to be reduced in the ring casting, Thereby, in addition to the effect of the invention of claim 1, the diameter and roundness characteristic of the ring casting can be improved more reliably.

  According to the invention of claim 3, since the inner diameter shrinkage prevention ring can be easily removed, in addition to the effect of the invention of claim 1 or 2, the manufacturing method can be further simplified.

  Hereinafter, the present invention will be specifically described with reference to embodiments illustrated in the drawings. In each embodiment, the same members are assigned the same reference numerals.

  The present invention is a method of manufacturing a tire molding die manufactured by a casting method, which can be removed by post-processing to an inner diameter portion closest to the upper and lower ends in a ring casting state and aims to become a perfect circle with a predetermined diameter. The first step of manufacturing the reference diameter portion by casting, and the tire forming mold so that the inner diameter of the reference diameter portion and the design surface portion is about 0.05 to 0.2% larger than the target diameter After the second step of casting and manufacturing the ring casting, and the outer peripheral portion of the ring casting for tire molding die are machined so as to have a diameter substantially the same as the inner diameter of the restraining ring used for diameter reduction correction, the tire A third step of fitting a ring casting for a molding die into the constraining ring, and processing in a state as close to a perfect circle as possible so that the reference diameter portion has an outer diameter that is substantially the same as the target diameter of the reference diameter portion. The coefficient of thermal expansion is the ring casting for the tire molding die. A fourth step of fitting an inner diameter shrinkage-preventing ring made of a material having the same or lower thermal expansion coefficient than that of the material and having a high yield strength characteristic, and in this state, is heated and held in a heating furnace and then cooled. The ring casting for tire molding die is compressed and yielded, and the reference diameter portion and the design surface portion of the ring casting for tire molding die are set to a predetermined inner diameter. A fifth step of correcting the shape according to the degree characteristic and a sixth step of removing the constraining ring and the inner diameter shrinkage-preventing ring from the ring casting for tire molding mold and processing the outer periphery of the ring casting after the removal are sequentially performed. It is characterized by going through.

  Specifically, it demonstrates based on FIGS. 1-3. 1 to 3, (a), (b), and (c) are respectively a two-piece molding method, a second sectional molding method (no sector end surface surplus method), and a first sectional mold method (sector end surface surplus). Setting method), and a simple process description is attached to the left side.

  First, an as-cast (ring casting) is manufactured. This step corresponds to the first step described above, and can be removed by post-processing on the inner diameter portion in the vicinity of the upper and lower end portions of the design surface portion d of the ring casting A1 for a tire molding die. A reference diameter c intended to be a circle is given by “casting”. This is created at the stage of the master model or mold shape. In the figure, reference numeral f denotes a product part.

The ring casting A1 is made so that the inner diameters of the reference diameter part c and the design surface part d are larger by 0.05 to 0.2% (0.5 / 1000 to 2.0 / 1000) than the target diameter. The casting is manufactured (the shrinkage rate is set in advance or the mold assembly diameter is adjusted), which corresponds to the second step described above.

  In the ring casting A1, the two-piece molding method (FIG. 1A) and the second sectional molding method (FIG. 1B) both have a shape close to a perfect circle in both the reference diameter portion c and the design surface portion d. The reference diameter portion c can be manufactured integrally with the design surface portion d at the time of casting, but only for the first sectional mold method (FIG. 1C), the design surface portion d is “ Since it becomes a “petal shape”, it is necessary to provide another part (dummy) to be a reference diameter portion c aimed at a perfect circle at the top and bottom of the mold when assembling the mold.

  Next is an intermediate processing step, which corresponds to the first half of the third step described above. In this step, the hot metal portion of the ring casting A1 for tire molding dies is cut and removed to form the ring casting A, and the back surface shape is machined to approximately the same shape as the inner surface shape of the restraining ring 10 to be fitted later. .

  Next is a restraint ring installation process, which corresponds to the latter half of the third process described above. In this step, the tire mold ring casting A is fitted into the restraining ring 10 so that the processed back surface portion is in close contact with the inner surface of the restraining ring 10. It is essential that the restraining ring 10 is made of a material having a higher yield strength and a smaller coefficient of thermal expansion than the material of the ring casting A for the tire mold.

  Next is an inner diameter shrinkage prevention ring installation step shown in FIG. 2, which corresponds to the fourth step described above. In this step, the reference diameter part c of the ring mold A for the tire mold has the target diameter at the reference diameter part c as the outer diameter, and is processed into a substantially circular shape. An inner diameter shrinkage stop ring 11 made of a material equivalent to or lower than that of the casting A and having high yield strength characteristics is fitted. Since the design surface portion and the reference diameter portion of the ring casting for a tire mold are formed to be 0.05 to 0.2% larger than the target diameter in the second step, in order to fit the inner diameter shrinkage prevention ring 11 There is almost no trouble.

  Next, the heating and holding step and the cooling step correspond to the fifth step described above. In FIG. 2, reference numeral 12 in the heating and holding step is a heater, and reference numeral 13 is a heating furnace. In this step, the tire mold ring casting A is thermally expanded larger than the constraining ring 10 during heating, so that it is crushed by the constraining ring 10 and plastically deformed in the direction of decreasing the diameter when cooled. It will be. When the inner diameter of the ring casting for a tire mold becomes smaller due to the plastic deformation during heating and the cooling shrinkage of the ring casting during cooling, the inner diameter shrinkage prevention ring 11 is present. When the reference diameter portion c comes into contact with the outer peripheral portion of the inner diameter shrinkage prevention ring 11, the ring casting A does not exhibit any further inner diameter shrinkage behavior, and at the same time, the inner surface roundness characteristic of the ring casting A This follows the roundness characteristic of the outer peripheral portion of the shrinkage-preventing ring 11, whereby the effect of improving the diameter correction and the roundness characteristic can be obtained at the same time.

  Next is a removal step and an outer periphery processing step of the restraining ring and the inner diameter shrinkage prevention ring shown in FIG. 3, which correspond to the sixth step described above. In this process, the upper and lower molds (product part f) are manufactured in the case of the two-piece molding method, the tire molding die is completed by mold matching, and the product part f is manufactured in the case of the second sectional molding method. After that, a tire molding die is completed by assembling sector blocks (not shown) divided by sector division of the product part f, and in the case of the first sectional molding method, the outer peripheral portion of the ring casting A is processed. Then, a tire molding die is completed by assembling sector blocks obtained through subsequent sector division and peripheral processing of the divided sectors.

  According to this method for manufacturing a tire molding die, the casting standard of the ring casting A for a tire molding die that has been manufactured in advance with a large inner diameter (larger than the target diameter of 0.05 to 0.2%). By performing hot correction (diameter reduction correction) in a state in which the inner diameter shrinkage prevention ring 11 having the target diameter of the reference diameter part c as the outer diameter is fitted in the diameter part c, the inner diameter of the ring casting A can be increased. Even if the circularity characteristics can be corrected at the same time and the condition setting for hot correction is misread, and the ring casting A is excessively reduced in inner diameter, The advantage is that it is not reduced to the following inner diameter.

  Further, consider each process in detail.

  First, in the first step, the reference diameter portion c is formed by casting. The diameter shrinkage prevention ring 11 is applied to this portion at the time of diameter reduction correction, and the inner diameter and roundness characteristics of the ring casting A are determined. When straightening, since some compression plastic deformation is involved, it is necessary to give a finishing allowance that can be finished, so it is not a design surface but a surface that fits with the sidewall (side plate) of the tire mold ( This is because it is most convenient in terms of work to be arranged in the vicinity of the upper and lower end portions, which are cylindrical surfaces or conical surfaces without design.

  In the second step, the inner diameters of the reference diameter part c and the design surface part d of the ring casting A for tire molds are made larger by about 0.05 to 0.2% than the target diameter. This is because the roundness characteristic is corrected at the same time by the diameter reduction correction.

  This range is set to 0.05% or less, because the ring casting A cannot be given sufficient compressive strain at the time of correction, and the roundness correction effect using the Bausinger effect is difficult to be exhibited. If it is 2% or more, the amount of the ring casting A subjected to compressive plastic deformation in the circumferential direction during correction becomes too large, and the roundness deterioration due to buckling deformation tends to appear.

  Further, in the third step, the material of the restraining ring 10 needs to have a higher yield strength and a lower coefficient of thermal expansion than the material of the ring casting for the tire mold, and the difference in the amount of thermal expansion due to heating is used. Therefore, even if the ring casting is further thermally expanded and tightened by the restraining ring 10, the restraining ring 10 side is not plastically deformed, and only the ring casting A side is plastically deformed. The reason why the back surface of the ring casting A is machined in advance so as to be in close contact with the inner surface shape of the constraining ring 10 is to maximize the strain energy generated in the ring casting A due to the difference in thermal expansion amount and to efficiently correct the diameter reduction. It is.

Further, in the fourth step, the inner diameter shrinkage-preventing ring 11 is installed on the reference (diameter) reference diameter portion c of the ring casting A for the tire molding die when the diameter reduction correction using the thermal expansion amount difference is performed. The following problems of the conventional method of
i. It is difficult to set hot correction conditions such as setting of heating temperature and heating holding time, and advanced prediction technology is required to reduce to the target diameter (if multiple hot corrections are required, It may be too small), and
ii. The roundness characteristic is basically not improved,
This is to eliminate the problem.

   Also, the material of the inner diameter shrinkage stop ring 11 needs to have a thermal expansion coefficient equal to or lower than that of the material of the ring casting A for tire molds. This is to ensure that it does not come into contact with the reference diameter part c of the ring casting A even if it is thermally expanded (because the inner diameter shrinkage prevention ring 11 spreads the ring casting A and does not expand the inner diameter). The strength needs to be high after the ring casting A comes into contact with the inner diameter shrinkage prevention ring 11 during hot straightening (and during cooling), and the ring casting A is preferentially plastically deformed to become a perfect circle. This is to correct the degree.

  In addition, in the fifth step, the heating and holding conditions (hot correction conditions) are subtly changed due to changes in the material, representative diameter, thickness of each part, etc., and therefore cannot be uniquely defined. It is as follows.

    i. The heating temperature is generally 100 to 400 ° C. Since the material which is the object of the ring casting A for tire molds is predominantly “aluminum alloy”, assuming this, if the temperature is less than 100 ° C., a sufficient difference in thermal expansion coefficient between the ring casting A and the restraining ring 10 is obtained. I can't have it. That is, since sufficient compressive strain energy cannot be administered to the ring casting A during hot straightening, the inner diameter cannot be reduced. There is also a reason that it is difficult to compressively deform plastically because the yield strength of the ring casting A due to heating is small. On the other hand, when the temperature exceeds 400 ° C., the strength characteristics of the ring casting A after hot straightening are remarkably deteriorated, and the oxidative damage of the restraining ring 10 and the inner diameter shrinkage prevention ring 11 is increased.

    ii. The heating temperature theoretically required can be calculated by the following equation.

T (° C.) = 25 (room temperature: ° C.) + (ΦDA−φDF) / {(αP−αR) × φDA}
here,
αP: Thermal expansion rate (%) of ring casting A from room temperature to heating temperature
αR: Thermal expansion rate (%) of the restraining ring 10 from room temperature to heating temperature
φDA: Inner diameter (diameter) of the reference diameter c of the ring casting A before straightening
φDF: Target inner diameter (diameter) after correction at the reference diameter c of the ring casting A
Actually, the strain energy generated by the difference in thermal expansion between the ring casting A and the constraining ring 10 only exceeds the yield strain of the ring casting A, which leads to plastic deformation of the ring casting A. In many cases, sufficient correction cannot be achieved only with the theoretical heating temperature required in (1). For this reason, the actual heating temperature is set to the value T plus about 50 to 100 ° C.

    iii. The heating time varies depending on the size (inner diameter, wall thickness, height, weight) of the ring casting A to be corrected. The main reason is that the entire ring casting A rises to the above heating temperature. This is the main reason, but it can be said that one hot correction can be completed by heating for approximately 2 to 12 hours.

  Further, preferably, the restraint ring 10 has a Young's modulus as a whole of the ring such that holes are formed in each part of the restraint ring 10 or the restraint ring 10 is manufactured using a foam metal or a sintered metal having a high porosity. It is made intentionally small by a technique and is made close to the Young's modulus of the ring casting A for a tire mold.

  The material of ring castings for tire molds is predominantly an aluminum alloy. For this reason, if steel is used as the material of the restraint ring 10, the condition that the thermal expansion coefficient is lower than that of the ring casting A for tire molds and the yield strength is high can be cleared at low cost.

  In the diameter reduction correction process of the ring casting A in the diameter reduction correction by the hot correction, the (cast) strain generated in the ring casting A due to the difference in thermal expansion between the ring casting A and the constraining ring 10 is effectively improved. It can be said that the inner diameter dimension of the ring casting A after correction is determined depending on whether or not the material is compressed and yielded.

  The (compression) strain generated in the ring casting A during hot straightening includes the difference in thermal expansion between the ring casting A and the constraining ring 10, the diameter of the ring casting A, and the Young's modulus (longitudinal length) of the ring casting A and the constraining ring 10. It can be said that it is determined by the elastic modulus. As the Young's modulus of the restraint ring 10 is larger than the Young's modulus of the ring casting A, the strain generated in the ring casting A increases, but this compressive strain is more at the outer peripheral surface of the ring casting A (contact surface with the restraint ring 10). It has a characteristic that it is conspicuously concentrated and compression strain does not easily reach the inner surface of the ring casting A.

  Therefore, when a situation occurs in which the maximum compressive strain generated in the outer peripheral portion of the ring casting A is excessively large during hot correction, only this portion is preferentially plastically deformed, and it is desired to reduce the diameter most in the ring casting A. A phenomenon occurs in which strain energy does not efficiently reach the “design surface (inner surface)”.

  FIG. 4 illustrates the above phenomenon, and the case where the balance of the Young's modulus of the ring casting A and the constraining ring 10 is good is indicated by “G00d” in the figure. The case where the Young's modulus of the ring 10 is too high is indicated by “NG”. In the case of “G00d”, the entire ring casting A is compressed and plastically deformed well, and the diameter is reduced until the reference diameter portion c of the ring casting A comes into contact with the inner diameter shrinkage prevention ring 11. However, in the case of “NG”, the ring casting Only the contact surface portion of the A-restraining ring 10 preferentially undergoes plastic deformation g, and the reference diameter portion c and the design surface portion d of the ring casting A cannot be sufficiently reduced in diameter.

Thus, in the combination of simply the material of ring casting A = aluminum alloy and the material of restraint ring 10 = general steel,
Young's modulus of aluminum alloy ≒ 7000kgf / mm2 (68650MPa)
Young's modulus of steel ≒ 21000kgf / mm2 (205900MPa)
Since this is the case in most cases, there is a problem that the situation of “NG” in FIG.

  Therefore, even if the restraining ring 10 is made of a steel material (iron material), it can be manufactured by using a material that is microscopically foamed and that has a low Young's modulus only. For example, a material in which fine “graphite (carbon: C)” is distributed in a spherical shape inside the metal crystal structure of steel, such as spheroidal graphite cast iron (FCD450 to FCD700) (Young's modulus ≈ 17000 kgf / mm2) Alternatively, a sintered metal having a high porosity (Young's modulus varies greatly with the porosity) can be used.

  By doing so, even if the restraining ring 10 is made of a steel material (iron material) that is inexpensive and easily available, the Young's modulus can be brought close to that of an aluminum alloy, and thus the diameter of the ring casting A is most desired to be reduced. Strain energy can efficiently reach the “design surface (inner surface)”, and the diameter and roundness characteristics of the ring casting A can be improved more reliably.

  More preferably, the inner diameter shrinkage prevention ring 11 is manufactured as an assembly structure separable into two or more parts.

  FIG. 5 illustrates the hot straightening process, and shows each state before hot straightening, after hot straightening, and removal of the straightening jig.

  In the hot straightening process, a diameter reduction distortion may be excessively applied to the ring casting A during straightening. Even in this case, the inner diameter of the ring casting A is maintained at the target size due to the presence of the inner diameter shrinkage prevention ring 11. In some cases, the amount of cooling shrinkage significantly exceeds the amount of cooling shrinkage of the inner diameter shrinkage prevention ring 11.

  At this time, the inner diameter shrinkage prevention ring 11 is in a state of being “tightly fitted” by the ring casting A, and it may be difficult to remove the inner diameter shrinkage prevention ring 11 from the ring casting A. (Refer to “Removing the correction jig” in FIG. 5).

  In order to facilitate the removal of the inner diameter shrinkage prevention ring 11 in this case, the inner diameter shrinkage prevention ring 11 is manufactured as an assembly structure that can be separated into two or more parts.

  FIG. 6 shows an inner diameter shrinkage stop ring 11A as the first embodiment. The inner diameter shrinkage stop ring 11A is movable in a radial direction to a disk-shaped cam surface plate 14 provided with a thin strip-shaped claw accommodating portion 15 along the outer periphery, and the claw accommodating portion 15 of the cam surface plate 14. A plurality of movable claws 16 accommodated therein are roughly configured. The movable claw 16 has a substantially fan-shaped flat surface on the outer end side and is formed with a movable inclined surface 16a on the inner end side. In the present embodiment, eight movable claws 16 are provided for one cam surface plate 14. It is used. The claw accommodating part 15 is configured by forming a fixed slope 15a along which the movable slope 16a of the movable claw 16 abuts slidably along the inner periphery. In FIG. 6, reference numeral 17 is a fastening hole formed in the cam surface plate 14.

  FIG. 7 shows a mold breaking process from a state in which the inner diameter reduction correction (hot correction) is performed using the inner diameter shrinkage-preventing ring 11A and cooled to room temperature. FIG. 7A shows a state cooled to room temperature, and the upper and lower inner diameter shrinkage prevention rings 11 </ b> A and 11 </ b> A are fastened by fastening bolts that pass through the fastening holes 17. Even when an inner tightening force is generated in the inner diameter shrinkage prevention ring 11A due to a difference in cooling shrinkage between the ring casting A and the inner diameter shrinkage prevention ring 11A at the time of cooling to this room temperature, FIG. When the fastening bolt 18 is loosened, the ring casting A is tightened by the cam-type slide (cam action in the direction of the arrow) of the movable claw 16 by mutual sliding between the fixed slope 15a and the movable slope 16a. The strain is released, and the inner diameter shrinkage prevention ring 11A can be removed easily as shown in FIGS. 7 (c) and 7 (d). In FIG. 7B, reference numeral A0 indicates the position of the ring casting A before the fastening bolt 18 is loosened.

  FIG. 8 shows an inner diameter shrinkage stop ring 11B as the second embodiment. This inner diameter shrinkage-preventing ring 11B is of a two-divided type, and comprises a substantially C-shaped ring body 20 and a detachable part 21 that detachably connects both ends of the ring body 20. The detachable part 21 is coupled to both ends of the ring body 20 via bolts (not shown) that are screwed into the coupling holes 22.

  As shown in FIG. 9, the inner diameter shrinkage prevention ring 11 </ b> B facilitates the diameter reduction deformation (change from the broken line to the solid line) of the ring body 20 by detaching the detachable part 21 from the ring body 20. Demolding from the ring casting is easily performed.

  Hereinafter, the present invention will be described more specifically with reference to examples. FIG. 10 shows a tire molding die 100 used in common for all the following examples.

  The tire molding die 100 is a 2P mold type tire molding die for tire size 205 / 65R15, and has the following conditions.

3 types of basic pitch types S, M, and L Number of pitches S pitch 11 pieces, M pitch 13 pieces, L pitch 12 pieces No sipe blade casting Figure 11 shows mold 101, as-cast ring casting A1, and tire molding gold The mutual relationship of the mold 100 is shown, and each is formed according to the following conditions.

Basic mold manufacturing method: Plaster casting method Set shrinkage ratio 11-15 / 1000 (varies depending on the part)
Gypsum mold material USG Hydro Palm Foam Gypsum
Mixed with 70% by weight water content and 60% foaming increase Casting alloy AC4C alloy (7% Si, 1% Cu, 0.5% Fe, 0.4% Mg, remaining Al)
Casting method Gravity casting (casting method)
The numerical values in FIG. 10 and FIG. 11 indicate each part in mm (the same applies to the following drawings). In particular, the numerical values in the upper and lower reference diameter parts in FIG. It is a numerical value when it is made with the aim of regular dimensions of 10 design surface portions.

Example 1
An as-cast ring casting A1 (see FIG. 11) was manufactured with the aim of increasing the diameter of the design surface part by about 0.5 mm (0.7 / 1000).

The radius of each part of the design surface portion of this as-cast ring casting A1 was measured at a total of 288 locations, 4 equal in the tire width direction and approximately 72 equal in the circumferential direction. The results are shown in Table 1.

  Next, the ring casting A is manufactured by cutting and removing the feeder portion of the as-cast ring casting A1. Then, for this ring casting A, as shown in FIG. 12, a “curved surface R” is defined, and after turning the back surface of the ring casting A in this shape, the FCD600 material (with the corresponding machining surface shape on the inner surface) ( It is fitted into a restraining ring made of (spheroid graphite cast iron material) having a thickness of 50 mm. At this time, in the upper and lower reference diameter portions c of the ring casting A, an inner diameter shrinkage prevention ring made of S50C (steel) having an outer diameter of 560 mm and 720 mm and a wall thickness of 20 mm is set in the heating furnace. (Refer to “Heat-holding step” in FIG. 2), and held at 250 ° C. for 5 hours to reduce the inner diameter. Thereafter, the ring was taken out of the furnace and cooled with air, and then the restraining ring and the inner diameter shrinkage prevention ring were removed, and the ring casting A was recovered. A boron nitride release agent was applied to the outer peripheral portion of the inner diameter shrinkage stop ring so that it was slippery.

Table 2 summarizes the characteristics of the radii of the design surface portions of the ring casting A thus obtained. The measurement point at this time was set to be approximately the same as the measurement of the as-cast ring cast A1 before correction.

  As is apparent from Tables 1 and 2, the ring casting A can be improved from the as-cast state A1 with respect to all of its diameter, roundness and crown R shape. It can be understood that a molding die can be manufactured.

(Example 2)
An as-cast ring casting A1 (see FIG. 11) was manufactured with the aim of increasing the diameter of the design surface part by about 0.5 mm (0.7 / 1000).

The radius of each part of the design surface portion of this as-cast ring casting A1 was measured at a total of 288 locations, 4 equal in the tire width direction and approximately 72 equal in the circumferential direction. The results are shown in Table 3.

   Next, the hot metal portion of the as-cast ring casting A1 is cut and removed to form a ring casting A (see FIG. 12), and this ring casting A is subjected to outer periphery processing in the same manner as in Example 1 and fitted into the restraining ring. Thereafter, the upper and lower reference diameter portions c (see FIG. 12) on the ring casting A are divided into two types, each having an outer diameter φ560 mm, 720 mm, and a S50C ring body 20 and a detachable part 21. The inner diameter shrinkage-preventing ring 11B (see FIG. 13) was set in a heating furnace and held at 350 ° C. for 5 hours. Then, it removed from the furnace and air-cooled, and then the restraining ring and the inner diameter shrinkage stop ring 11B were removed. At this time, since the inner diameter shrinkage-retaining ring 11B is held in the ring casting A and is difficult to be removed in the assembled state, after removing the detachable part 21, the ring body 20 is reduced in diameter and removed. Typed.

The properties of the radii of the design surface portions of the ring casting A thus obtained are summarized in Table 4. The measurement point at this time was set to be approximately the same as the measurement of the as-cast ring cast A1 before correction.

  As is apparent from Tables 3 and 4, in Example 2, the diameter reduction amount is larger than that in Example 1, so that the effect of correcting the diameter and roundness of each part at the time of correction is more greatly exhibited. It became. That is, the roundness and the crown R shape accuracy were improved as compared with the first embodiment.

  In addition, the difficulty in removing the inner diameter shrinkage prevention ring 11B from the ring casting after air cooling, which is a problem in such a case, can be avoided by using the inner diameter shrinkage prevention ring 11B having a two-part structure.

(Comparative Example 1)
An as-cast ring casting A1 (see FIG. 11) was manufactured with the aim of increasing the diameter of the design surface part by about 0.5 mm (0.7 / 1000).

The radius of each part of the design surface portion of this as-cast ring casting A1 was measured at a total of 288 locations, 4 equal in the tire width direction and approximately 72 equal in the circumferential direction. The results are shown in Table 5.

  This as-cast ring casting A1 was subjected to diameter reduction correction under basically the same conditions as in Example 2.

  However, the material of the restraint ring used in this Comparative Example 1 was S50C (steel material).

Table 6 summarizes the characteristics of the radii of the design surface portions of the ring casting A (see FIG. 12) after the diameter reduction correction. The measurement point at this time was set to be approximately the same as the measurement of the as-cast ring cast A1 before correction.

As is clear from Tables 5 and 6, the results of the roundness and crown R shape accuracy of Comparative Example 1 were worse than the results of Example 2. The rate is high (Young's modulus of the constraining ring of Example 2≈16000 kgf / mm ² versus Young's modulus of the constraining ring of Comparative Example 1≈21000 kgf / mm ² ), and the strain energy acting on the ring casting A during hot straightening is It seems that it becomes easy to concentrate locally on the back surface of the ring casting A, and a part thereof is consumed in the form of local deformation on the back surface side of the ring casting A.

In the pre-process of the manufacturing method of the tire molding die as one embodiment of the present invention, (a) is a two-piece molding method, (b) is a second sectional molding method, and (c) is a first sectional molding method. Each is shown. In an intermediate step of a method for manufacturing a tire mold according to an embodiment of the present invention, (a) is a two-piece molding method, (b) is a second sectional molding method, and (c) is a first sectional molding method. Each is shown. In a subsequent step of the method for manufacturing a tire mold according to an embodiment of the present invention, (a) is a two-piece molding method, (b) is a second sectional molding method, and (c) is a first sectional molding method. Each is shown. FIG. 3 is an operation explanatory diagram of the intermediate process of FIG. 2. FIG. 4 is an operation explanatory diagram of a post-process in FIG. 3. FIG. 1A is a plan view in which a part of the operation is written, and FIG. 2B is a cross-sectional view taken along line VIb-VIb in FIG. FIG. 7 is an operation explanatory view of the inner diameter shrinkage prevention ring of FIG. 6, (a) is a cooled state after hot correction, (b) is a state in which the inner diameter shrinkage prevention ring is loosened, (c), (d) is a mold breaking process. Each is shown. FIG. 7A is a plan view of an assembled state, and FIG. 5B is a side view in which a removal action of a detachable part is entered. FIG. 9 is an operation explanatory diagram of the inner diameter shrinkage prevention ring of FIG. 8. It is a fragmentary sectional view of the metal mold | die for tire molding used in common with the Example. It is principal part sectional drawing which shows the relationship between the as-cast ring casting as an Example, and a casting_mold | template. It is principal part sectional drawing of the ring casting as an Example. It is detail explanatory drawing of the internal diameter shrinkage prevention ring used for the Example. (A)-(g) is process drawing which shows the procedure which produces a 2 piece mold by the gypsum casting method. (A)-(f) is process drawing which shows the procedure which produces a sectional mold by the gypsum casting method. (A) And (b) is a perspective view of the metal mold | die for tire molding assembled using the back mold. (A)-(c) is explanatory drawing of the adjustment method of the roundness characteristic in a 1st sectional mold method. (A), (b) is process drawing which shows the procedure which produces the ring casting used for the diameter (radius) expansion type of FIG. (A)-(c) is explanatory drawing of the conventional 1st correction method of another diameter (radius) expansion type, respectively. (A), (b) is process drawing which shows the procedure which produces the ring casting used for the diameter (radius) reduction type of FIG. (A)-(c) is explanatory drawing of the conventional 2nd correction method of another diameter (radius) reduction type, respectively. (A) is each explanatory drawing of the conventional 3rd correction method as a radius reduction type, (b) is each explanatory drawing of the conventional 4th correction method as a radius expansion type.

Explanation of symbols

10 Restraint ring 11 Inner diameter shrinkage prevention ring 11A Inner diameter shrinkage prevention ring 11B Inner diameter shrinkage prevention ring 13 Heating furnace 14 Cam surface plate (parts)
16 movable claws (parts)
20 Ring body (parts)
21 Detachable parts (parts)
100 Tire Mold A A Ring Casting c Reference Diameter Part d Design Surface Part

Claims (3)

A method of manufacturing a tire molding die manufactured by a casting method,
A first step of producing a shape by casting a reference diameter portion that can be removed by post-processing to the inner diameter portion in the ring casting state and immediately close to the upper and lower ends, and becomes a perfect circle of a predetermined diameter;
A second step of casting and manufacturing a ring casting for a tire molding die so that the inner diameter of the reference diameter portion and the design surface portion is about 0.05 to 0.2% larger than the target diameter;
After machining the outer periphery of the ring molding for tire molding mold so as to have the same diameter as the inner diameter of the restraining ring used for diameter reduction correction, the ring casting for tire molding mold is fitted into the restraining ring. A third step;
The thermal expansion coefficient of the ring casting material for the tire molding die is processed in a state as close to a perfect circle as possible so that the reference diameter portion has an outer diameter substantially the same as the target diameter of the reference diameter portion. A fourth step of fitting an inner diameter shrinkage-preventing ring made of a material equivalent to or less than the rate and having a high yield strength characteristic;
In this state, the ring casting for tire molding die is compressed and yielded by heating and holding in the heating furnace and then cooling, and the reference diameter portion and the design surface portion of the ring casting for tire molding die are set to a predetermined inner diameter. And at the same time, the fifth step of correcting the roundness characteristic to a shape that conforms to the roundness characteristic of the inner diameter shrinkage prevention ring,
A tire molding die characterized by sequentially passing through a sixth step of removing the constraining ring and the inner diameter shrinkage-preventing ring from the ring casting for tire molding die and processing the outer periphery of the ring casting after removal. Production method. A method for manufacturing a tire molding die according to claim 1,
The method for producing a mold for molding a tire is characterized in that the restraint ring is manufactured by intentionally reducing the Young's modulus of the ring as a whole and approaching the Young's modulus of the ring molding for a tire mold. . A method for producing a tire molding die according to claim 1 or 2,
The method for manufacturing a tire molding die, wherein the inner diameter shrinkage prevention ring is manufactured as an assembly structure separable into two or more parts.

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