JP6528940B2 - Preheating member and hot forging method using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a preheating member used for hot forging for keeping warm a die-cutting surface formed on a hot forging die and a hot forging method using the same.

For example, hot forging (including constant temperature forging, hot die and the like) of difficult-to-process materials such as Alloy 718 and Ti alloy is performed at a high temperature of 700 ° C. or higher. In hot forging of the above-mentioned difficult-to-process material, since hot workability will change with changes of temperature, it is preferable to forge under the same conditions as possible.
However, even if the temperature of the forging material is the same, the temperature of the hot forging die is lower than the hot forging temperature, so the contact of the hot forging die and the forging material causes The temperature of the forging material decreases. Since the temperature drop of the forging material reduces the hot workability or increases the wear amount of the hot forging die, the life of the hot forging die becomes short.
In order to address this problem, for example, in JP-A-2002-96134 (Patent Document 1), as a heating jig for heating a first mold and a second mold for forging disposed opposite to each other, A forging metal is provided with a heater at the center and one surface has a shape along the forged surface shape of the first mold, and the other surface has a shape along the forged surface shape of the second mold. An invention using a mold heating jig has been proposed.
Further, for example, in Japanese Patent Application Laid-Open No. 2004-230397 (Patent Document 2), a forged work is inserted into a mold, clamped by a press ram slide, and a forged work for forming the work inserted into the mold. A method of the forging method is proposed which includes the step of stopping the press ram slide at a position where the heat of the work can be transferred to the mold between the completion of the clamping and the opening of the mold.
Further, for example, in JP 2001-340935 A (patent document 3), in the mold heating method for warm or hot forging mold, the outer peripheral portion of the mold is flexible as a heating heater wire. The invention of a method of heating a mold using a heater having a structure in which a plurality of ceramic insulators in which a conductive nichrome wire is embedded is combined has been proposed.

Japanese Patent Application Laid-Open No. 2002-096134 JP 2004-230397 A JP 2001-340935 A

The method of using the heating jig shown in Patent Document 1 described above is to raise the temperature of the surface of the heating jig by heat conduction from a heater provided in the jig. Further, the hot forging method disclosed in Patent Document 2 transmits the heat possessed by the forging material to the lower and upper molds, heats and heats the mold to a necessary temperature, and separates the product from the mold. In the lubricant application step carried out after molding, the required mold temperature can be maintained, and the moisture of the lubricant can be evaporated smoothly to form a good lubricant film on the mold. .
Moreover, also in patent document 3, the surface temperature of a metal mold | die is raised using the heater for heaters.
The method of raising the temperature of the mold surface using a heater as in Patent Document 1 and Patent Document 3 is a simple method, and has an advantage that local heating can be performed.
Further, as in Patent Document 2, the method of utilizing the heat stored in the forged material after clamping is suitable for retaining heat in a relatively small mold.
By the way, recently, a large forging device having a press load of tens of thousands of tons has been introduced. The mold used for such a large forging apparatus becomes large, and the mold itself is large even if local heating is performed, so the problem of the mold surface temperature falling immediately after removing the heater proceeds Was found to occur. In particular, if the surface temperature of the mold is lowered during the waiting time occurring between each shot of hot forging, the hot forging conditions will change.
An object of the present invention is to provide a preheating member capable of suppressing a decrease in surface temperature of a hot forging die and a hot forging method using the same.

The present invention has been made in view of the problems described above.
That is, the present invention is a preheating member for keeping the engraved surface formed on a pair of hot forging dies consisting of an upper mold and a lower mold, wherein the preheating member is made of a Ni-based super heat resistant alloy or stainless steel. The preheating member has a shape along the embossing surface, the preheating member preheats the embossing surface formed on the upper mold, and the preheating component preheats the embossing surface formed on the lower mold. A preheating member which is an assembly of

The present invention is a hot forging method using the preheating member, wherein the preheating member is heated to a hot forging temperature + 100 ° C. to a hot forging temperature -300 ° C., and a pair of hot forging dies The preheating member is sandwiched between a die engraving surface formed on the upper mold and a die engraving surface formed on the lower mold, and the pair of hot forging dies is formed by the preheating member while pressing the preheating member. Preheating member removing step for removing the preheating member from the pair of hot forging dies preheated by the die preheating step, and the pair of heat after the preheating member removing step A hot forging method including a hot forging step of hot forging a material to be forged using an inter-forging die to form a forging material.
In the hot forging method of the present invention, a glass lubricating film is preferably formed on the surface of the preheating member.

  According to the present invention, it is possible to prevent or suppress the decrease in the surface temperature of the hot forging die in the waiting time occurring between each shot of the hot forging. In addition, it is economically advantageous because no special heating means such as a heater is used.

It is a schematic diagram which shows an example of the preheating member of this invention. It is a schematic diagram which shows an example of another pre-heating member of this invention. It is a schematic diagram which shows an example which clamped the preheating member of this invention with the upper mold | type and the lower mold | type.

The present invention will be described in detail below.
As described above, an important feature of the present invention is to sufficiently increase the temperature of the surface of the hot forging die used for hot forging on which the engraved surface is formed.
The term "hot forging" in the present invention includes constant temperature forging, hot die forging and hot pressing in addition to hot forging.
(Preheating member)
As shown in FIG. 1 and FIG. 2, the preheating member 1 of the present invention is a preheating member for keeping warm the engraved surface formed on a pair of hot forging dies consisting of an upper die and a lower die. Therefore, the surface of the preheating member in contact with the upper and lower molds has a surface shape along the mold engraving surface of the mold that has substantially the same shape as the shape of the engraved surface formed on the upper and lower molds. . This allows the entire upper and lower mold engraving surfaces to be kept warm. This is because if the surface shape of the die-cutting surface and the surface shape of the preheating member are substantially the same, the temperature in the surface of the die-cutting can be made substantially the same. In addition, since it is possible to reduce the gap between the preheating member 1 and the upper and lower molds if the surface shape of the preheating member is substantially the same along the engraved surface, hot forging by contact with the outside air The temperature drop on the mold surface can be prevented more reliably. Of course, it is also possible to use a preheating member having a surface having substantially the same shape as the entire surface where the upper and lower molds face each other, including the mold engraving surface of the mold.
In order to make the surface of the preheating member substantially the same as the shape of the die-cut surface, for example, the material to be used as the preheat member is hot-forged by test pressure, and the surface substantially the same as the shape of the die-cut surface It is preferable to set it as the preheating member which it has. The material of the preheating member is preferably one having a small heat transfer coefficient. If the heat transfer coefficient is small, the preheating effect of the preheating member can be enhanced. As a material therefor, for example, a Ni-based super heat-resistant alloy or stainless steel may be used. Among them, Ni-based super heat-resistant alloys containing 50% by mass or more of Ni, such as 718 alloy, are hard to produce oxide scale and have a small heat transfer coefficient. Are particularly preferred.
In order to enhance the preheating and heat retaining effects, it is preferable to form a glass lubricating film on the surface of the preheating member. Since the glass lubricating film has a heat retaining effect, it is possible to enhance the preheating and heat retaining effect of the hot forging die by the preheating member.

The preheating member of the present invention is an assembly of a preheating part 2a for preheating a mold engraving surface formed in the upper mold and a preheating part 2b for preheating a molding surface formed in the lower mold. By forming an assembly, the heat storage amount of the heat retaining member can be increased, and the upper mold and the lower mold can be sufficiently kept warm before hot die forging or constant temperature forging. In addition, when performing hot forging with a forging load on the order of tens of thousands, the total weight of the mold itself may exceed 30 tons. Therefore, although it is necessary to enlarge the preheating member if the preheating member is used to keep the die-cutting surface more effectively, the preheating parts are assembled to increase the heat capacity of the preheating parts according to the total weight of the mold. In particular, the heat retention of a mold for a large-scale hot forging device of 10,000 tons or more is greatly effective. For example, in the case of using a preheating member in a hot forging die for a large forging device for 50,000 ton scale, when preheating the mold engraving surface is to be preheated, for example, when making the preheating member in one piece, its weight is 1 ton May be exceeded. The method of making the assembly of the present invention is a suitable method for making a large-sized preheating member, since it becomes difficult to manufacture if it is used as a preheating member of a predetermined shape.
In addition, although shown as an assembly body of two preheating parts in FIG.1 and FIG.2, it is good also as three or more.
The preheating member 1 of the present invention is, for example, assembled so as to laminate a plurality of preheating parts and then bonding the preheating parts by a fastening part such as welding or bolt to form an assembly (laminated body). It is simple. In that case, if it is a shape that is difficult to stack and assemble, as shown in FIG. 2, the contact surface on which the preheated parts are stacked may be easily stacked by machining or the like to form an assembly.

By the way, the larger the volume of the preheating member, the larger the amount of heat stored in the preheating member. Therefore, the volume of the preheating member is preferably a preheating member having a volume twice or more that of the forged material after hot forging. When the volume is twice or more, the temperature drop of the pair of hot forging dies themselves can be suppressed while preventing the temperature decrease of the mold engraving surface (working surface) of the hot forging die, and the heat It is possible to suppress the variation in the conditions for each shot of the forging between the two. More preferably, it is better to prepare a preheating member 2.5 times or more the volume of the forged material after hot forging. Although the upper limit of the volume of the preheating member is not particularly limited, it may be appropriately determined in consideration of the dimensions of the forged material after hot forging, the product shape, the preheating time, etc. If so, it takes time to raise the temperature of the preheating member itself to a desired temperature, and there is a risk that the hardness of the mold for hot forging may decrease due to the heat stored in the preheating member. Therefore, the upper limit of the volume of the preheating member may be five times.
For example, the same material as the material to be forged and having the same shape and subjected to hot forging with a test pressure is used as a preheated component, and a plurality of such preheated components are prepared and assembled into an assembly to be used as a preheated member be able to. Further, if the preheating member is made of the same material as the material to be forged, not only preheating management becomes easy, but also thermal expansion in the engraving surface is matched, so that the inside of the engraving surface can be efficiently preheated. Especially preferred.

Next, the hot forging method of the present invention using the above-described preheating member will be described.
(Mold preheating process)
First, in the present invention, as shown in FIG. 2, a preheating member heated to a hot forging temperature + 100 ° C. to a hot forging temperature -300 ° C. in a pair of hot forging dies (upper mold 11 and lower mold 12). A mold preheating step of holding for 1 hour while pressing the preheating member 1 using the weight of the upper mold 11 is performed. In the present invention, the pair of hot forging dies refers to the upper die 11 and the lower die 12. Further, the preheating member 1 does not have a heater as in the prior art.
In the present invention, the preheating member 1 heated to the hot forging temperature + 100 ° C. to the hot forging temperature -300 ° C. is inserted into the above-described pair of hot forging dies. The reason for setting the temperature of the preheating member to hot forging temperature + 100 ° C. to hot forging temperature -300 ° C. is to prevent a rapid temperature drop of the forging material when the forging material is placed on the lower die. . If the upper limit of the temperature of the preheating member 1 is higher than the hot forging temperature + 100 ° C., there is a possibility that the preheating member thermally expands and can not fit in the mold. In addition, when the lower limit of the temperature of the preheating member 1 is lower than the hot forging temperature -300 ° C, particularly when using a large-sized hot forging die, the holding heat possessed by the preheating member is low in a short time When the material to be forged is placed on the lower die 2, the material to be forged tends to be cooled.
Therefore, in the present invention, the temperature of the preheating member 1 is set to a hot forging temperature + 100 ° C to a hot forging temperature-300 ° C. The upper limit of the heating temperature of the preheating member is preferably the hot forging temperature + 50 ° C. Moreover, the minimum of the heating temperature of a preferable preheating member is hot forging temperature -100 degreeC.

Further, in the present invention, the above-described preheating member 1 is sandwiched and held for a predetermined time. Since the preheating member is sandwiched between the upper and lower hot forging dies, it is pressurized by the weight of the upper die, and it is possible to prevent the temperature decrease of the hot forging die surface. Of course, for example, a specific load may be applied by the press load of a hot forging machine. The press load in this case may be appropriately selected between 100 and 25,000 tons. According to the study of the inventor, the press load can be sufficiently preheated at a level of several hundred tons.
Then, while holding this preheating member, it is held for a fixed time. The holding time is not particularly limited, but it is preferable to consider the materials of the upper and lower molds and the temperature of the preheating member.
For example, if the material of the upper mold and the lower mold is described as “for hot mold” in JIS-G 4404 (alloy tool steel), it is defined in the present invention if it is a steel for hot mold (hereinafter, steel for hot mold). When the preheating member heated to the above temperature range is sandwiched between the upper mold and the lower mold, the hardness of the upper mold and the lower mold may be reduced by long-time preheating. Therefore, when the upper mold and the lower mold are steel for hot die, it is preferable to set the time for sandwiching the preheating member within 20 minutes.
Moreover, even if it is an upper mold or a lower mold using the above-mentioned "for hot metal mold" steel, for example, when a buildup layer of Ni-based super heat resistant alloy is formed, preheating for up to about 30 minutes In the case where both the upper and lower molds are, for example, a Ni-based super heat-resistant alloy, it may be preheated for, for example, more than 30 minutes to about 2 hours.
In addition, as a material of the metal mold | die for hot forgings, if it is described as said steel for hot metal molds, since it is comparatively cheap, it is preferable. More preferably, a buildup layer of a Ni-based super heat-resistant alloy is formed on the above-described steel for hot die. Alternatively, using a portion having a large amount of deformation of the material to be forged during hot forging as a core made of a Ni-based super heat resistant alloy, a composite metal of a steel for hot die and a core made of Ni-based super heat resistant alloy It is good to use as a type. By using this Ni-based super heat-resistant alloy, the life of the mold can be increased by increasing its strength, and the heat retention effect can be further improved.

In order to maximize the effects of the preheating member, it is preferable to preheat a pair of hot forging dies used for hot forging. By preheating the hot forging die itself, when the preheating member is sandwiched between the pair of hot forging dies, the diffusion of the holding heat of the preheating member to the hot forging die can be delayed. It is also possible to keep the hot forging die warm.
The preheating temperature of the above-described hot forging die is, for example, the material for the upper die and the lower die described as “for hot die” indicated in JIS-G 4404 (alloy tool steel). The tempering temperature is the upper limit of the preheating temperature.
Further, with regard to preheating of the preheating member itself, it is preferable to heat the preheating member together when heating the forging material to the forging temperature. This eliminates the need for separately preparing a heating furnace for heating the preheating member, which is economical.

(Preheating member removal process)
Next, in the present invention, the preheating members are removed from the pair of molds preheated by the above-described mold preheating step. It is convenient to use a manipulator to remove the preheating member.
As the timing for removing the preheating member, it is sufficient to take out the forging material from the preheating furnace.
As described above, according to the hot forging method of the present invention to be described, it is possible to sufficiently suppress the temperature decrease of the surface of the mold for hot forging, and not only to suppress the variation of the hot forging conditions It is also possible to improve the life of the casting mold.
In particular, the hot forging according to the present invention is suitable for hot forging of a difficult-to-work material of a Ti alloy such as 6Al-4V-Ti alloy or a Ni-based super heat resistant alloy such as Alloy 718, for example.

Example 1
First, the effect of the preheating member of the present invention was confirmed before actual hot forging.
The hot forging simulates the hot forging of a 718 alloy disk material (hot forging material). There are two preheating members prepared, and the material is 718 alloy.
The preheating member is previously hot pressed (testing pressure) with a hot forging die used for hot forging, and thereby a surface having substantially the same shape as the shape of the engraved surface formed on the upper mold and the lower mold. Is formed. The preheating member has the structure shown in FIG. Further, one to which a glass lubricant was applied was used as one of the preheating members, and no glass lubricant was applied to the other. The temperature of the test pressure may be in the range of the actual hot forging temperature plus or minus 100 ° C. or so.
The above-described preheating member was heated to 1000 ° C., which is the same as the hot forging temperature, and the pair of upper and lower hot forging dies was heated to approximately 500 ° C. When the surface temperature of the hot forging die is 500 ° C. or more, the friction condition of the glass lubricant used at the time of hot forging becomes good, and the hot forging condition can be made appropriate.
The above-described preheating members were inserted into a pair of upper and lower hot forging dies, one with a light load of 200 tons and the other with a load of 20,000 tons, and changes in the hot forging temperature were confirmed. When the preheating member was not used, it was confirmed that the surface temperature of the mold for hot forging having a temperature of 500 ° C. decreased to about 460 ° C. after 3 minutes.
The hot forging die used is a hot forging die for large forgings for a maximum load of 50,000 tons, and the material is JIS-SKD61 (hereinafter referred to as SKD61). The tempering temperature of SKD 61 is 650.degree.
The results are shown in Table 1. Table 1 shows that, before sandwiching the preheating member (before heating the preheating member), the preheating by the preheating member is finished, and immediately after releasing the upper mold (immediately after the heating is completed), one minute after removing the preheating member from the mold 2 The results of measuring the surface temperatures of the upper mold and the lower mold after 3 minutes, 3 minutes and 4 minutes are shown. The temperature of the lower mold “immediately after the end of heating” was not measured for the surface temperature of the lower mold because the preheating member was placed on the lower mold.

As shown in Table 1, it can be seen that the temperature immediately after the end of heating does not exceed the tempering temperature of the hot forging die (SKD 61). Moreover, it turns out that the surface temperature of the metal mold | die for hot forgings of the upper and lower sides is maintaining the temperature over 500 degreeC even after 3 minutes progress. In addition, due to the fact that the shape of the preheating member is approximately the same shape as the shape of the engraved surface formed on the upper mold and the lower mold and the effect of applying the glass lubricant, the load is light (200 tons) There was no significant difference between the temperature change when added and the temperature change when heavy load (20,000 tons) was added.
From this result, the preheating member used in the present invention does not deteriorate the mechanical properties of the hot forging die, and the surface temperature of the die decreases in the waiting time generated between each shot of the hot forging. It confirmed that it could prevent and maintain the surface temperature of the die for hot forgings at the temperature of 500 ° C or more.

(Example 2)
Next, hot forging was actually performed. The shape of the engraved surface of the hot forging die used and the shape of the preheating member were the same as those used in Example 1 above. Further, the prepared preheating member 1 is an assembly integrated by welding after assembling so as to laminate two preheating parts (2a, 2b) as shown in FIG.
In addition, among portions of the mold engraving surface of the hot forging die, a portion to which a load is applied is, in particular, one having a buildup layer of a Ni-based super heat-resistant alloy formed. The hot forging machine used a large forging machine with a maximum load of 50,000 tons.
Hot forging is for hot forging a disk material (hot forging material) made of 718 alloy coated with a glass lubricant. The volume of the prepared preheating member 1 was twice that of the disk material (hot forging material) made of the 718 alloy, and a glass lubricant was applied to the surface of the preheating member 1. The preheating member 1 and the forging material were heated to a forging temperature of 1000 ° C. in the same heating furnace. The pair of hot forging dies were preheated to 500 ° C.
Next, the hot forging die is set in a large forging machine, and the preheating member heated to 1000 ° C. is sandwiched between the pair of hot forging dies consisting of the upper die 11 and the lower die 12, and the pair of heat The forging die was preheated for 5 minutes to keep the die-cutting surface of the hot forging die at a temperature of 500 ° C. or more.
Next, the forged material was taken out from the heating furnace, and the preheated member 1 was removed from the pair of molds being preheated, and after 8 minutes, hot forging was started. The temperature at which the die surface of the die before hot forging was 530 ° C., and the effect of preventing the decrease in the die surface temperature by the preheating member was confirmed.
Since the temperature decrease of the pair of hot forging dies was prevented, the friction condition of glass lubrication was good at the time of hot forging, and the hot forging conditions could be made appropriate, so problems such as seizure did not occur. .
This hot forging was repeated several times. In the waiting time which occurs between each shot of hot forging, the surface temperature of the pair of hot forging dies is within the range of 500 to 600 ° C. using the preheating member reheated to the same 1000 ° C. as the forging temperature. The hot forged products after each shot did not suffer from seizure and the like.

  From the above results, it was confirmed that the reduction of the surface temperature of the mold is prevented and the hot forging conditions can be performed under almost constant conditions in the waiting time occurring between each shot of hot forging. In particular, there is no need to use a heating means such as a heater when producing a forged product that will become larger in size in the future, which is also advantageous in reducing energy costs.

1 Preheating member 2a, 2b Preheating part 11 Upper mold 12 Lower mold

Claims (3)

It is a preheating member for keeping warm the mold engraving surface formed in a pair of hot forging molds consisting of an upper mold and a lower mold, wherein the preheating member is made of a Ni-based super heat resistant alloy or stainless steel, Has a shape along the surface,
The preheating member is an assembly of a preheating part for preheating a mold engraving surface formed on the upper mold and a preheating part for preheating a mold engraving surface formed on the lower mold. A hot forging method using the preheating member according to claim 1, wherein
The preheating member is heated to a hot forging temperature + 100 ° C. to a hot forging temperature -300 ° C., and a pair of mold engraving surfaces formed on the upper mold of the hot forging die and a mold engraving surface formed on the lower mold And a mold preheating step of preheating the pair of hot forging dies with the preheating member while sandwiching the preheating member between them and pressurizing the preheating member;
A preheating member removing step of removing the preheating member from the pair of hot forging dies preheated by the die preheating step;
A hot forging step of hot forging the forging material using the pair of hot forging dies after the preheating member removing step to make the forging material;
A hot forging method characterized by including.   The hot forging method according to claim 2, wherein a glass lubricating film is formed on the surface of the preheating member.

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