JP2002035884A - Gear die for warm or hot forging and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a forging die for manufacturing a gear by warm or hot forging, which has an extended life. SOLUTION: In manufacturing a gear die for hot forging, a rough material is produced by electric discharge machining or cutting of a mold blank and a subsequent electric discharge machining, and a fine working and a polishing finish are successively performed. 1) After providing a layer (2a) of a heat-resistant metal by build-up welding on the surface of the mold that is to be the tip of the mold, the process proceeds to electric discharge machining or cutting, and the cutting edge of the mold is removed. A gear die for hot forging having a heat-resistant metal layer (2b) on the surface is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a mold for manufacturing various gears by forging in a warm or hot state, and includes a manufacturing method thereof. According to the present invention, a mold having a long life is provided.

[0002]

2. Description of the Related Art Forging is widely used, for example, as a method of manufacturing a gear constituting a transmission device of an automobile. The mold used for this forging starts with electric discharge machining or cutting of the blank and subsequent electric discharge machining, and the product is obtained through fine finishing and polishing, but it is counted as one of the difficult molds to manufacture . This is because, for both straight gears and helical gears, forging dies require high accuracy and vary depending on the size of the gears, but often have to satisfy a tolerance standard of about several microns.

[0003] This type of mold is used in a wide temperature range from cold to hot.
The drawback of cold forging is that the life of the mold is extremely short. The reason is that toothed forging has many local and unsteady deformations,
Cracks and seizures are likely to occur on the gear part of the mold,
Another problem is that the deformation load is large and it is difficult to control the elastic deformation of the mold. Thus, in recent years, efforts have been made to manufacture gears by precision hot forging.

[0004] However, hot forging can significantly reduce the load at the time of forging as compared with cold, and can almost avoid breakage due to stress concentration on the tip of the gear of the mold. Heat check is seen. Therefore, the problem that the mold life is short cannot be solved at all. Forging dies for gears that require high dimensional accuracy of products usually have a life of 1000 shots or better and 2000 shots at best.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is a mold for manufacturing a gear by warm or hot forging, which has a longer life than that of the prior art, and a method of manufacturing the same. Is to provide.

[0006]

SUMMARY OF THE INVENTION A gear mold for hot forging according to the present invention is a mold for manufacturing a gear by warm or hot forging. A rough material is manufactured by the subsequent electric discharge machining, and the mold manufactured by the fine machining and the polishing finish is used as shown in FIG.
As shown in FIG. 6 and FIG. 6, the cutting edge portion has a layer (2b) of a heat-resistant metal formed on the surface thereof by overlay welding.

[0007] The method of the present invention for manufacturing such a forging die is a method for manufacturing a die for manufacturing a gear by warm or hot forging. A rough material is manufactured by the subsequent electric discharge machining,
In a manufacturing method comprising a step of forming a product by fine processing and polishing finish, as shown in FIG. 1, a surface (outside in FIG. 1) of the surface of the blank (1) which becomes a cutting edge portion of a mold. Next, as shown in FIG. 2, after providing a heat-resistant metal layer (2a) by build-up welding of a heat-resistant metal, the process proceeds to electric discharge machining or cutting to form a rough material as shown in FIG. Features.

The example shown in FIGS. 1 to 3 is a mold for forging an internal gear having an outer edge with a cutting edge of the mold. In the case of manufacturing a mold having a cutting edge inside, a heat-resistant metal layer (2a) may be provided inside the cylindrical blank and subjected to electric discharge machining in the steps shown in FIGS.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The short life of a mold used for manufacturing gears by hot forging is due to the fact that a heat check occurs at the cutting edge portion. This is because the cutting edge portion receives the strongest load during forging, And the longest time it comes in contact with the forged material, it becomes the highest temperature, and the high temperature time is long, and after knocking out the forged product, it is cooled strongly and repeatedly subjected to heating and cooling. .
Therefore, in the present invention, a heat-resistant metal layer is provided at the cutting edge to prepare for heat check, based on the expectation that dealing with such thermal damage is important for extending the life of the mold. It is.

The steps of manufacturing the mold after the steps shown in FIGS. 3 and 6 are the same as the steps of manufacturing the gear mold for warm forging up to now. Gear forging using the forging die of the present invention may also be performed according to a known technique. That is, in the case of the mold of FIG. 3, a cylindrical blank surrounding the mold is placed around the mold in a state where the blank is heated to an appropriate temperature, and further, a ring-shaped die is placed around the mold to surround the mold. The blank is plastically deformed by pressing from above and below with a punch, and the blank is penetrated between the cutting edges of the forging die, thereby forming the teeth of the internal gear. In the case of the mold shown in FIG. 6, a cylindrical blank is put in the mold and pressed by a punch to form an external gear.

As the blank material for the forging die of the present invention, tool steel, preferably matrix high-speed steel, is used, although it depends on factors such as the material of the product gear and the processing temperature.

The heat-resistant metal to be welded to the tooth tip is preferably a stellite alloy (Co-based alloy) or a colmonoy alloy (Ni-based alloy). It is well known that these alloys have high heat resistance, but their hardness is not high when compared to matrix high-speed steel or the like. Therefore, it was feared that even if a layer of a refractory metal that was not too hard was provided on the cutting edge of a mold under heavy load, it could be possible to extend the life of the mold. Was done. This fact indicates that what mainly determines the mold life is heat damage, as expected by the inventors.

[0013] The thickness of the layer of heat-resistant metal provided by overlay welding needs to be at least about 0.5 mm, but it is not necessary to make it too thick, and the maximum is about 5 mm. Usually 1mm
It is enough.

The overlay welding may be performed by TIG welding or MIG welding using a heat-resistant metal rod as a filler material,
Weld the heat-resistant metal powder on the plasma arc,
So-called PPW (plasma powder welding) can also be used. Regardless of which welding method is employed, it is recommended to perform preheating and post-heating, as in the examples described below, for heating the welding base metal before and after the buildup. Usually, preheating is performed at 200 to 400 ° C and postheating is performed at 300 to 550 ° C.

[0015]

[Example] SKD61 is selected as a material for a forging die.
The powder of the heat-resistant alloy shown in Table 1 was prepared as a build-up material.

[0016] Table 1 Composition of heat-resistant alloy C Si Ni Cr W Co B Fe stellite No.6 1.2 1.0 - 30 4 balance - ≦ 2.0 Colmonoy No.5 0.5 4.0 balance 12 - −2.5 3.0

These heat-resistant metal powders were build-up welded to the inside of the cylindrical blank by PPW to provide a heat-resistant metal layer having a thickness of 3 mm. 300 before and after build-up welding
Preheating at ℃ for 1 hour and post-heating at 525 ° C for 1 hour were performed. The hardness in the depth direction from the surface of the build-up layer was measured, and the results shown in FIG. 7 were obtained. The change in hardness at the transition from the heat-resistant metal layer to the base metal is smooth, indicating that both are well melted.

Next, a forging die for a straight gear having a shape shown in FIG. 6 was manufactured for two kinds of heat-resistant alloys by a series of rough machining and finishing machining starting from ordinary electric discharge machining. For comparison, a forging die was also manufactured without the heat-resistant alloy layer.

Each of these three types of forging dies was used in two pieces (No.
1 and No. 2), and a gear forging test was performed to evaluate the life of each mold. Table 2 shows the specifications of the forged gear.

Table 2 Specifications of gear to be forged Gear tip diameter (mm) Root diameter (mm) Crossover (mm) 2.5 75.0 ^{± 0.1} 63.25 26.81 ^{-0.1, -0.15}

The test conditions for the evaluation of the mold life are as shown in Table 3.

Table 3 Test conditions for mold life evaluation Forging speed Work heating temperature Lubricant Mold material / hardness 4 pieces / min 1200 ± 20 ° C Water-soluble graphite SKD61 HV560

The life of the three molds was as shown in Table 4. The life criterion was the time when it was recognized that a clear heat crack had occurred on the cutting edge of the mold and was transferred to the forged gear product.

[0024] Table 4 die life test results padding refractory metal No. 1 No. 2 None 1322 951 Stellite No. 2 6 2669 3005 Colmonoy No. 5 2876 2922

In the above forging example, the work heating temperature is 12
Although it is hot forging of 00 ° C., even if it is used for forging in lower temperature warm forging (about 600 to 800 ° C.) or sub-hot forging (about 800 to 1000 ° C.), The mold shows a long life.

[0026]

The gear die for hot forging according to the present invention is hardly damaged by heat because the blade is provided with a build-up layer of a heat-resistant metal, and the life of the die due to heat cracks can be shortened. Significantly slower than conventional ones. As is known from the above-described embodiment, the life of the mold, which was conventionally within or outside 1000 shots, is increased by a factor of 2 to 3.

The method of the present invention for producing a gear mold for hot forging is the same as the conventional method for producing a forging mold except that a step of overlay welding of a heat-resistant metal is added. Since its presence does not affect the processing steps, it can be carried out without any changes to the conventional method. Clearly extending the life of the mold also has the advantage of reducing the number of man-hours for replacing the mold, and it goes without saying that it can more than compensate for the increase in cost due to the addition of the overlay welding process.

[Brief description of the drawings]

FIG. 1 is a perspective view of a raw material for explaining a method of manufacturing a die for forging an internal gear in a gear die for hot forging according to the present invention. Indicates a stage.

FIG. 2 shows a stage following FIG. 1 in which the outer surface of the blank is overlaid with a heat-resistant metal.

FIG. 3 shows a stage following FIG. 2 in which a blade is formed by performing electrical discharge machining on the blank.

FIG. 4 is a perspective view of a raw material for explaining a method of manufacturing a metal mold for forging an external gear in a gear mold for hot forging according to the present invention, the blank being formed into a cylindrical shape; Indicates a stage.

FIG. 5 shows a stage following FIG. 4 in which a build-up welding of a heat-resistant metal is performed on the inner surface of the blank.

FIG. 6 shows a stage of forming a blade by performing electric discharge machining on the blank, following FIG. 5;

FIG. 7 is a graph showing a change in hardness from a build-up weld layer of a heat-resistant metal toward the inside in the stage of FIG. 2;

[Explanation of symbols]

 1 Blank 2a Overlaid welded layer of heat-resistant metal (during welding) 2b Overlaid welded layer of heat-resistant metal (after electric discharge machining)

Claims (4)

[Claims] 1. A mold for manufacturing a gear by warm or hot forging, wherein a rough material is manufactured by electric discharge machining or cutting of a blank followed by electric discharge machining, and fine machining and polishing are performed. In the mold manufactured by
A gear mold for hot forging, wherein a tooth tip portion is formed of a heat-resistant metal welded by overlay welding. 2. A matrix high-speed steel is used as a blank, and a heat-resistant metal welded to the tooth tip by overlay welding is made of a stellite alloy (Co-based alloy) or a colmonoy alloy (Ni
2. The gear mold for hot forging according to claim 1, which is a base alloy). 3. The gear mold for warm forging according to claim 1, wherein the thickness of the layer of the heat-resistant metal welded by overlay welding is 0.5 to 5 mm. 4. A method for manufacturing a gear for manufacturing a gear by warm or hot forging, wherein a rough material is manufactured by electric discharge machining or cutting of a blank and subsequent electric discharge machining, and In a manufacturing method consisting of a process of forming a product by precision processing and polishing finish, after performing build-up welding of heat-resistant metal on the surface of the blank surface that will be the tip of the mold, A method for manufacturing a gear mold for hot forging, characterized by proceeding.