JPS6128001B2 - - 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 an annular sintered body of metal powder. Sintered bodies of metal powders, that is, sintered alloys, differ from melted alloys in that they do not have so-called solidification segregation, so they can have a uniform structure, which cannot be obtained by conventional melting methods. On the other hand, sintered bodies obtained by ordinary compression, molding, and sintering methods inevitably have pores remaining in their structure, and their porosity is approximately 10. ~20%, which is one of the advantages of sintered alloys in terms of wear resistance, but is often a disadvantage in terms of mechanical properties. In order to reduce 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 is an industrial limit to increasing the compacting ability. Therefore, it is difficult to compress the porosity to the desired low porosity. It is also possible to reduce the porosity by recompressing the sintered body, but for example, annular sintered bodies such as piston rings and valve seat rings have a high carbon content and contain large amounts of alloying elements. In many cases, the structure has a structure in which hard alloy particles are dispersed, and the plastic deformability required to reduce the porosity is small. It requires a large pressurizing force of about 10 to 20 t/cm ² , lowers the porosity of the sintered body, and is accompanied by technical difficulties such as the punch breaking before the sintered body can be densified. An object of the present invention is to provide a processing method for reducing porosity and improving density by forging an annular sintered body that is difficult to plastically deform and is likely to cause damage to a compression device due to its shape. , in a method for reducing the porosity of a metal powder sintered body, the outer surface is provided inside the die by a die that moves up and down with the upper surface elastically abutting against the pressure surface of the upper punch, and the upper surface is An annular shape in which an inner surface is formed by a core that elastically abuts against the pressing surface of the punch and moves up and down, and a bottom surface is formed by a lower punch provided between the die and the core and adjustable up and down. The annular sintered body is inserted into the die groove, and the upper punch, which has a pressure surface in the shape of a right cone with an obtuse apex angle at the tip of the cylinder, is rotated with its center axis inclined toward the upper surface of the annular die groove, and the conical pressure surface is formed. The lower punch is gradually raised to the desired height while rolling it along the upper surface of the die and core, and the sintered compact in the annular die groove is pressed against the conical pressing surface of the upper punch, and the rolling conical surface of the upper punch presses the sintered compact in the annular die groove. The present invention relates to a method for reducing the porosity of an annular sintered body, which is characterized by sequentially applying compressive force locally. The method of the invention will now be described with reference to the apparatus shown in the accompanying drawings. A cylindrical die 1 is fixed to a die holder 2,
A plurality of elastic bodies 4 (springs, urethane resin, etc.) are installed between the die holder 2 and the die base 3.
is fitted to elastically support the die holder 2 with respect to the die base 3. A plurality of guide rods 5 are fixedly fixed to the die holder 2 facing downward, and guide the guide rods 5 up and down in the sleeve 5a fitted to the die base 3 so that the die holder 2 and the die 1 move up and down horizontally and smoothly. . The setscrew 7, which passes through the die base 3 from below to above and is screwed into the die holder 2, has a spacer collar 8 sandwiched between the screw head and the die holder 2, and by adjusting the height of the spacer collar. The distance between the die holder 2 and the die base 3 is regulated, and the distance between the stopper 6 placed on the die base 3 and the lower surface of the die 1 is adjusted, thereby adjusting the depth of the annular die ring 13, which will be described later. can do. The die base 3 is fixed to a base plate 10 by a presser collar 9, and the base plate 10 is connected to a piston of a first fluid pressure cylinder (not shown) to move up and down. A piston 17 of a second fluid pressure cylinder, which will be described later, is housed in the center hole of the base plate 10, and a head flange 17a of the piston 17 rests on a shoulder 10a of the center hole of the base plate 10. It is designed to be able to move up and down as the base plate 10 moves up and down. A cylindrical lower punch 11 is provided inside the die 1 so as to be movable up and down in contact with the inner surface 1a of the die 1. A core 14 is fitted in the center of the cylindrical lower punch 11, and its side surface 14a An annular die groove 13 is formed by the inner surface 1a of the die 1 and the upper surface 11a of the lower punch. The lower end of the core 14 is an elastic body 16 (spring, urethane resin, etc.)
is supported on the bottom surface 12 of the inner hole of the lower punch 11 via the elastic body 16, and is pushed upward elastically by the elastic body 16, and during pressurization by the upper punch, which will be described later, is pressed against the conical pressing surface of the upper punch. It is pressed so that it is at the same height as the top surface of the die 1. The lower punch 11 is connected to a piston 17 of a second fluid pressure cylinder (not shown) by a plurality of setscrews 18, and the piston 17 and therefore the lower punch 11 not only rise together with the base plate 10 as described above, but also , it is also possible to move up and down within the center hole separately from the base plate 10. A core stopper rod 19 horizontally fixed to the center of the core 14 passes through the lower punch on the outer periphery, and both ends of the rod resiliently abut against the inner flange 3a of the die base 3 to prevent the core 14 from slipping out. It also serves as a stopper for regulating the upward position of the lower punch 11. Regarding the clearance between the annular sintered body R and the annular die groove 13, the clearance between the outer periphery of the sintered body R and the inner surface of the die 1 is preferably approximately 0.05 to 1.0 mm; if this is too small, sintering may occur. It is difficult to insert the body,
Moreover, if it is too large, the outer periphery of the sintered body is likely to crack during forging. The clearance between the inner periphery of the annular sintered body R and the core 14 is set to be large within the limit of the deformation capacity of the sintered body relative to the core dimension, which is determined by taking the finishing allowance into the final product shape. It is effective to reduce porosity and increase density by allowing the aggregate to flow and deform as much as possible. The distance between the die base 3 and the die holder 2 is adjusted using the setscrew 7 and the spacer collar 8 so that when the sintered body R is set in the annular die groove 13, the top surface of the sintered body R is below the top surface of the die. It is important to keep it adjusted. The cylindrical upper punch 20 has a conical pressurizing surface 21 with an apex angle θ at its end, is supported by a spherical bearing (not shown), and the central axis OB is moved into the annular die groove by a driving device (not shown). α for the central axis OA of 13
When tilted by an angle of = (180 - θ) x 1/2 and rotated around the neck so that the top rotates around the axis OA using the center of the core as a fulcrum, the pressure surface 21
Then, it rolls flat along the upper surface of the core 14. 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 pressurizing surface approaches a flat surface and the forging effect becomes smaller, 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 annular die groove 1
3, the annular sintered body prepared in advance is inserted, the base plate 10 is raised, the upper surfaces of the die 1 and the core 14 are resiliently brought into contact with the pressing surface of the upper punch 20, and the upper punch is If the base plate 10 is raised little by little by the hydraulic cylinder while swinging and rotating as shown in FIG. The upper punch 2 raises the sintered body and pushes up the sintered body.
Press it against the conical pressure surface 21 of 0. The sintered body is pushed up from below by the lower punch 11, gradually compressed while being pressed by the pressure surface 21 of the upper punch 20 to reduce its height, and placed on the die base 3 to form the sintered body as required. When the stopper 6 whose height matches the final height comes into contact with the lower surface of the die holder 2 and the die 1, the base plate 10 and the lower punch 11 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.
1, the lower punch 11 will hit the core retaining pin 1.
9 and rises slightly above the top surface of the die to push out the sintered body R in the annular die groove 13 from the groove 13, so the sintered body is taken out of the mold by a lever (not shown). Finish forging. Next, an example will be described.

[Table] 1% zinc stearate (wt%, same hereinafter) was mixed with atomized powder of high-speed steel having the composition shown in Table 1 (annealed at 900℃ for 2 hours in hydrogen gas), and the mixture was placed in a mold. The annular compact compacted by compression molding was pre-sintered by holding it at 650℃ in hydrogen gas for 60 minutes, then sintering by holding it at 1200℃ in a vacuum atmosphere for 60 minutes, and then lowered it to 850℃. After holding for 60 minutes, it was slowly cooled and the porosity was 25.9%, outer diameter 36.0mm, circle diameter 29.0mm, height
It was made into a 4.0 mm annular sintered body. This sintered body was inserted into an annular die groove with a die inner diameter of 36.1 mm, a core outer diameter of 27.9 mm, and a depth of 6 mm, which had been coated with zinc stearate and dried, and the base plate and lower punch were pushed up as described above. Forging was performed by rolling the conical surface of the upper punch. The conditions were as follows. Apex angle θ = 176°, α = 2°, upper punch outer diameter =
100mm, upper punch rotation speed = 160r.pm, base plate rising speed = 0.3mm/min. The maximum load during forging was detected and recorded by a pressure detector installed in the hydraulic circuit, and the relationship with the porosity of the forged sintered body was determined. The results are shown in FIG. When the compressive load is approximately 13 tons or more, the porosity becomes almost constant. Incidentally, since the area of the annular body having an outer diameter of 36.1 mm and an inner diameter of 27.9 mm is 4.12 cm ² , the above-mentioned load of 13 tons corresponds to a load per unit area of 13 tons/4.12 cm ² =3.16 tons/cm ² . Conventionally, the so-called hot coining method has been used to make materials with low plastic deformability to a porosity of about 1 to 5%. According to this method, a sintered body is heated for 900°C in a protective atmosphere such as argon. ~
The method of the present invention is heated to 1100°C by high frequency heating, etc., set in an expensive mold such as hot work tool steel, and pressurized and compressed with a pressure of about 10 ton/cm ² or more. According to the method, compared to the hot coining method, it requires press equipment with a much smaller pressure, and furthermore, there is no need for heating equipment, and the mold can be made of a material suitable for cold working, among other advantages.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of an example of a rotary forging machine suitable for carrying out the method of the present invention, and FIG. 2 is a sectional view of the rotary forging machine at the final stage of forging. FIG. 3 is a graph showing an example of the relationship between compressive load and porosity according to the present method. 1... Die, 3... Die base, 4... Elastic body, 5... Guide rod, 6... Stopper, 7... Set screw, 8... Spacer collar, 10... Base plate, 1
1... Lower punch, 13... Annular die groove, 14...
Core, 16... Elastic body, 17... Piston, 19
... Core retaining pin, 20 ... Upper punch, 21 ...
Conical surface (pressure surface), OA...center axis of annular die groove (or core), OB...center axis of upper punch, R...
...Sintered body.

Claims (1)

[Claims] 1. In a method for reducing the porosity of a metal powder sintered body, a die whose upper surface elastically contacts the pressurizing surface of an upper punch and moves up and down causes the outer surface to touch the inner side of the die. The core is provided between the die and the core and the upper surface elastically contacts the pressure surface of the upper punch and moves up and down. The annular sintered body is inserted into the annular die groove where the bottom surface is formed, and the upper punch, which has a pressure surface in the shape of a right cone with an obtuse apex angle at the cylindrical tip, is rotated with its central axis inclined toward the upper surface of the annular die groove. The lower punch is gradually raised to the desired height while rolling the conical pressure surface along the upper surface of the die and core, and the sintered compact in the annular die groove is pressed against the conical pressure surface of the upper punch. A method for reducing the porosity of an annular sintered body, characterized by sequentially applying compressive force locally using a rolling conical surface.