JPS6148565B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a processing method for reducing the porosity and increasing the density of a sintered body.

Unlike ingot alloys, sintered metals produced by powder metallurgy have a uniform structure because they do not have so-called solidification segregation. However, the sintered bodies obtained by conventional compression, molding, and sintering methods inevitably have pores remaining in the structure.
The porosity is approximately 10-20%. Although the presence of these pores has the advantage of contributing to oil retention and improving wear resistance, it also causes the following disadvantageous factors. That is, the presence of pores impairs mechanical strength.
Makes pitching wear more likely. Surface treatments such as carburization and nitriding extend deep into the material, making it brittle, making it difficult to plate, and making it susceptible to oxidation and corrosion.
This makes casting with other metals difficult, making brazing difficult, etc.

If the porosity is lowered, that is, the density is increased, the above problems can be solved. In order to lower the porosity, it is possible to increase the compacting pressure when compacting the powder, but for example, many high-alloy powders have poor compactability, or there are industrial limits to increasing the compacting ability. Therefore, it is difficult to compress it to the desired low porosity. In addition, for example, in the case of iron-based sintered metals, so-called liquid phase sintering, in which B, Sn, P, etc. are added to produce a liquid phase during sintering, causes large shrinkage during sintering and is problematic in terms of dimensional accuracy and distortion. There are some difficulties, and also B, Sn, and P.
Both have the effect of making the material brittle. Also,
One possible method is to re-compress the sintered body to reduce the porosity, but iron-based sintered metals that require wear resistance have a high carbon content and contain large amounts of alloying elements. It often has a structure in which hard alloy particles are dispersed, and the plastic deformability required to reduce the porosity is small. For example, 10
It requires a large pressing force of ~20t/cm ³ , lowers the porosity of the sintered body, and is accompanied by technical difficulties such as the punch breaking before the density can be increased. The so-called sintering process, in which this recompression is performed hot at 900 to 1100°C, can increase the density of materials with low plastic deformability, which is impossible with cold processing, but it requires heating equipment, atmosphere conditioning equipment, presses, etc. The equipment costs are high, the molds are expensive, their lifespan is short, and dimensional accuracy is poor.

The purpose of the present invention is to provide a processing method for reducing porosity and increasing density by pressing a sintered body that is difficult to plastically deform. The sintered body is inserted into a die groove formed by a plurality of cavities arranged in the die at equal intervals and a lower punch that slides into contact with the cavities, and an apex angle is formed at the tip of the cylinder. The upper punch, which has a pressure surface in the shape of a right cone with an obtuse angle, is rotated with its central axis inclined to the upper surface of the die groove, and the lower punch is rotated relative to the upper punch while the conical pressure surface is rolled along the upper surface of the die. porosity of the sintered body, which is characterized in that the sintered body in the die groove is pressed against the conical pressing surface of the upper punch, and compressive force is applied locally and sequentially by the rolling conical surface of the upper punch. This relates to a reduction processing method.

The method of the invention will now be explained with reference to the accompanying drawings. FIG. 1 is a perspective view showing an example 1 of a high-density sintered body to be manufactured, and has an arcuate surface 2.

FIG. 2 is a plan view of the die 3 used to manufacture the high-density sintered body shown in FIG. Multiple pieces (4 pieces in this example) at equal intervals so that the arc surfaces are located on the same circumference
It is provided to penetrate through the die 3.

FIG. 3 shows an outline of a pressurizing device suitable for use in the present invention.

A disk-shaped die 3 is fixed to a die holder 4, and a plurality of elastic bodies 6 (springs, urethane resin, etc.) are fitted between the die holder 4 and the die base 5, and the die holder 4 is fixed to the die base 5. We are enthusiastically supporting this. A plurality of guide rods 7 are fixedly fixed to the die holder 4 facing downward, and guide the guide rods 7 up and down in a sleeve 7a fitted to the die base 5 so that the die holder 4 and the die 3 can move up and down horizontally and smoothly. The setscrew 9 that passes through the die base 5 from below to above and is screwed into the die holder 4 has a spacer collar 10 sandwiched between the screw head and the die holder 4, and by adjusting the height of the spacer collar, the set screw 9 can be attached to the die holder 4. To regulate the distance between the die base 5 and the distance between the first stopper 8 placed on the die base 5 and the lower surface of the die 3, thereby adjusting the depth of the die groove 15 described later. I can do it. The die base 5 is fixed to a base plate 12 by a presser collar 11, and the base plate 12 is connected to a piston of a first fluid pressure cylinder (not shown) to move up and down. Base plate 1
A piston 16 of a second fluid pressure cylinder, which will be described later, is housed in the central hole of the piston 16.
The head flange 16a rests on the shoulder 12a of the center hole of the base plate 12, so that it can move up and down as the base plate 12 moves up and down.

The lower punch 13 is provided so as to be in contact with the cavity 3a of the die 3 and move up and down inside the die 3, and the upper surface 13a of the lower punch 13 is connected to the cavity 3a.
A die groove 15 is formed by this. lower punch 1
3 is connected to a piston 16 of a second fluid pressure cylinder (not shown) by a plurality of setscrews 17, and in addition to rising together with the base plate 12,
It is also possible to move up and down inside the center hole separately. Flange 13 of lower punch 13
A second stopper 14 is placed on top of b, and when only the lower punch is raised, the upper surface of the second stopper 14 comes into contact with the shoulder 5a of the die base 5, regulating the raised position of the lower punch. It's like this.

Regarding the clearance between the sintered body R and the die groove 15, it is recommended that the clearance between the sintered body R and the outer surface of the die cavity 3a be approximately 0.05 to 1.0 mm; if this is too small, the sintered body may not be inserted. difficult to do,
Moreover, if it is too large, the outer periphery of the sintered body is likely to be cracked during plating. The clearance between the sintered body R and the inner surface of the die cavity 3a is set to be large within the limit of the deformation force of the sintered body with respect to the inner surface of the die cavity 3a, which is determined by taking into account the finishing allowance for the final product shape. It is effective to reduce porosity and increase density by allowing the sintered body to undergo fluid deformation as much as possible.

When the sintered body R is set in the die groove 15, the distance between the die base 5 and the die holder 4 is adjusted using the setscrew 9 and the spacer collar 10 so that the top surface of the sintered body R is below the top surface of the die. It is important to keep

The cylindrical upper punch 18 has a conical pressurizing surface 19 with an apex angle θ at its end, and is supported by a spherical bearing (not shown), and the center axis OB of the die 3 is moved by a drive device (not shown). α=(180−
When the top is tilted by an angle of θ)×1/2 and rotated so that the top rotates around the axis OA with the center of the die as a branch, the pressure surface 19 rolls flat along the top surface of the die 3. It becomes like this. The apex angle θ should be an obtuse angle, and according to experimental results, it is preferable to set it to 170 to 176°.If the angle is larger than this, the upper punch pressing surface will approach a flat surface and the pressure effect will be reduced, and if the angle is smaller than this. This is not preferable because the pressure effect is exerted only on the surface of the sintered body and the surface layer is likely to peel off.

With this structure, the sintered body prepared in advance is inserted into the die groove 15, the base plate 12 is raised, and the upper surface of the die 3 is elastically brought into contact with the pressing surface of the upper punch 18. When the upper punch is oscillated as described above and the base plate 12 is raised little by little by the fluid pressure cylinder, the base of the lower punch 13 is connected to the base plate 12 through the head flange 16a of the piston 16. Since the upper punch 18 is engaged with the upper punch 18, they rise together, pushing up the sintered body and pressing it against the conical pressure surface 19 of the upper punch 18.

The sintered body is pushed up from below by the lower punch 13 and gradually compressed while being pressurized by the pressure surface 19 of the upper punch 18 to reduce its height, and is placed on the die base 5 to form the sintered body as required. When the first stopper 8 whose height matches the final height comes into contact with the lower surface of the die 3 and/or the die holder 4, the base plate 12 and the lower punch 13 stop rising. The state at this time is shown in FIG.

After stopping in this state for a while, the first fluid pressure cylinder for the base plate is operated in reverse to lower it, and the second fluid pressure cylinder is operated to lower the lower punch 1.
3, the lower punch 13 is regulated by the second stopper 14 and rises slightly above the top surface of the die, pushing out the sintered body R in the die groove 15 from the groove 15. The sintered body is then taken out of the mold and the plating process is completed.

As a method of lubrication between the die groove and the sintered body, it is preferable to apply a lubricant such as zinc stearate.

In addition, if the plastic deformability of the material is particularly low,
Prior to the porosity reduction treatment, it is desirable to subject the sintered body to a heat treatment to improve its plastic deformability, such as spheroidizing annealing.

The sintered body whose porosity has been reduced as described above is re-sintered. The sintered compact that has been pressed in this way is plastically deformed and hardened, or small cracks are generated within the sintered compact starting from the remaining pores, so in order to improve this, recrystallization and re-sintering are performed. The sintering temperature for this purpose is preferably 1000 to 1150°C for iron-based sintered bodies.

If necessary, heat treatment such as quenching and tempering, surface hardening treatment such as carburizing and nitriding, plating, etc. can be finally performed.

In addition, as a means for stopping the rise of the die base, the above-mentioned first stopper is brought into contact with the lower surface of the die and/or the die holder to stop the rise of the die base. A higher density sintered body can also be obtained by employing a control method using pressurizing force so that the rise of the die base is sometimes stopped.

Furthermore, instead of raising the lower punch to pressurize the sintered body, the upper punch can be lowered to pressurize the sintered body.

The above is a method of reducing the porosity of a sintered body having an arcuate surface by the method of the present invention. However, for a sintered body that does not have an arcuate surface, for example, for a sintered body that has a flat surface, the corresponding plane is from the center. It is sufficient to use a die having cavities located at approximately equal distances. That is, a die having a cavity in which a substantially regular polygon is formed by corresponding planes and their extensions may be used, and the other methods may be the same as those described above. The above method may be applied to a sintered body having neither an arcuate surface nor a flat surface.

Examples will be described below.

Example 1 Manufactured by the usual powder metallurgy method, having the dimensions shown in Fig. 1 plus compression allowance, 0.01%
C, 2% Ni, 0.5% Mo, and the balance is substantially Fe, and the density is 6.5 g/cc.
was inserted into the die groove 15 using the die shown in FIG. 2 and the pressurizing device shown in FIG. 5, and pressurized by the method described above. The clearance between the sintered material R and the outer surface of the die cavity 3a is approximately 0.1 mm, and the clearance between the inner surface and the upper punch 1 is approximately 0.1 mm.
The rotation speed of 8 is 160 rpm, θ is 176°, α is 2°, and the rising speed of the base plate 12 is 0.2 mm/min. 12 was lowered. Note that lubrication was performed by applying zinc stearate to the mold.

The density of the sintered body thus obtained was 7.6 g/cc.

Next, this sintered body was resintered by heating at 1120°C for 50 minutes in a vacuum to form a thrust block.

Conventionally, this part was manufactured using a sintering process in which a sintered body was heated to 900°C for 10 seconds using high-frequency heating in a protective atmosphere such as Ar, and then hermetically molded using uniaxial pressure in a hot forging mold. It was manufactured using a keizukuri method, which required a large amount of money for equipment and molds.

Example 2 0.016%C, 0.18%Mn, 3.20%Cr, 0.35%Mo,
84.4% of -100 mesh alloy powder, the balance of which is essentially Fe, 15% of -100 mesh of low carbon ferromolybdenum powder containing 70% Mo, and 0.6% of graphite powder.
It is manufactured by the usual powder metallurgy method using a mixed powder containing _% of
Using the die shown in Fig. 6, a sintered body S having the shape shown in Fig. 5 and having a structure in which Fe-Mo hard alloy particles having a hardness of ~1300 are uniformly dispersed and a density of 6.7 g/cc is used. Then, pressure was applied in the same manner as in Example 1 above. FIG. 6a is a plan view of the die, and FIG. 6b is a cross-sectional view taken along line _b -- _b shown in FIG.

The die 21 has five arc-shaped cavities 21a provided at equal intervals on the same circumference, penetrating the die 21, and a uniform cavity extending inward at the upper end of the cavity 21a. A groove portion 21b having a width of about 100 mm is provided.

Prior to pressurization, the sintered body was previously heat-treated at 750°C for 60 minutes and then cooled to room temperature at a cooling rate of 8°C/min.

FIG. 7 shows the process in which the sintered body is inserted into the die groove formed by the cavity of the die and the upper surface of the lower punch, and the sintered body is deformed as it is pressurized.

FIG. 7a is a cross-sectional view of the vicinity of the sintered compact just before the start of pressurization, and the top surface of the sintered compact S inserted into the die groove 28 is located slightly below the top surface of the die 21, and The groove portion 21b is a blank space.

22 is a die holder, 23 is a die base, 24 is an elastic body, 25 is a first stopper, and 26 is a lower punch. When pressurization is started, the upper surface of the sintered compact S is located on the same plane as the upper surface of the die 21, and soon, as shown in FIG. The sintered body protrudes into the groove portion 21b of the cavity, and finally, as shown in FIG. Finally, as shown in Figure d, the rotation of the upper punch 29 is stopped, the die base 23 is lowered, and the lower punch 26 is raised to extrude the processed sintered body S' onto the die 21 and sinter it. Take out the body, at this time lower punch 26
The position of the upper surface of the die base 23 is regulated by the shoulder 23a of the die base 23 and the second stopper 27.

In this way, an arc-shaped sintered body S' having an inverted L-shaped cross section and having a protrusion S'a extending inward as shown in FIG. 8 was obtained. The density of this sintered body was 7.6 g/cc.

Finally, this was resintered by heating at 1150°C for 30 minutes.

As an application of the present invention, it is also possible to provide steps or unevenness on the pressurizing surface of the upper punch, the upper surface of the lower punch, or the die cavity so that the upper surface, lower surface, or side surface of the sintered body is deformed in accordance with the shape of these molds. . Further, by doing so, it is also possible to partially impart a desired density to the sintered body.

As explained above, when the method of the present invention is used, sintered bodies that conventionally had to be densified by hot recompression can be easily compressed in a single cold process. Therefore, it becomes possible to increase the density of a plurality of sintered bodies, and it also becomes possible to perform local molding. In particular, even sintered bodies of materials with low plastic deformability, such as high-carbon, high-alloy sintered alloys, can be easily densified, which is expected to expand the range of application of sintered alloys, and improve industrial It has great utility value.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a thrust block, which is an example of a high-density sintered body manufactured by the method of the present invention;
This figure is a plan view of a die used in the porosity reduction process of the thrust block shown in FIG. 1. FIG. 3 is a sectional view of a main part of an example of a rotary forging machine suitable for carrying out the present invention, and FIG. 4 is a sectional view of the same at the final stage of forging. FIG. 8 is a perspective view showing another example of a high-density sintered body manufactured by the method of the present invention, and FIG. 5 is a sintered body of the high-density sintered body shown in FIG. 8 before porosity reduction treatment. A perspective view of the material, FIG. 6 is a die used in the porosity reduction treatment to obtain the high-density sintered body shown in FIG. 8, a is a plan view, and b is a die shown in a. It is a bb sectional view. FIG. 7 is a sectional view of the main part showing the process of rotary forging to obtain the high-density sintered body shown in FIG. 8 from the sintered body material shown in FIG. c shows the state during pressurization, c shows the state at the end of pressurization, and d shows the state when the sintered body after pressurization is removed from the die. 1 and S′ are sintered bodies with reduced porosity, R and S
3 and 21 are sintered material, 3 and 21 are dies, 5 and 23 are die bases, 6 and 24 are elastic bodies, 7 is a guide rod,
8, 14, 25 and 27 are stoppers, 9 is a set screw, 10 is a spacer collar, 12 is a base plate, 13 and 26 are lower punches, 15 and 28 are die grooves, 16
is a piston, 18 and 29 are upper punches, 19 is a conical surface (pressure surface), OA is the center axis of the die groove, and OB is the upper punch center axis.

Claims (1)

[Claims] 1. A plurality of cavities passing through the die and arranged at equal intervals in the die so that corresponding surfaces are located at approximately equal distances from the center, and a lower punch that slides into contact with the cavities. The sintered body is inserted into the die groove thus formed, and an upper punch having a pressure surface in the shape of a right cone with an obtuse apex at the cylindrical tip is rotated with its central axis inclined toward the upper surface of the die groove to form a conical shape. While rolling the pressure surface along the top surface of the die, the lower punch is raised relative to the upper punch, and the sintered body in the die groove is pressed against the conical pressure surface of the upper punch, and the rolling conical surface of the upper punch presses the sintered compact in the die groove. A method for reducing the porosity of a sintered body, characterized by sequentially applying compressive force locally. 2. The cavity according to claim 1, wherein the cavity is a plurality of cavities that penetrate the die and are arranged at equal intervals on the die so that corresponding arcuate surfaces are located on substantially the same circumference. A method for reducing porosity of a sintered body having at least one arcuate surface.