JP3374963B2 - Straightening method for repress resintering and straightening mold device used in this method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a straightening method used in a repress re-sinter including a powder forming step, a preliminary sintering step, a straightening step and a main sintering step in powder metallurgy, and a straightening die used in this method. Regarding the device.

[0002]

In powder metallurgy, a raw material powder is compression-molded to form a green compact, and the green compact is heated at a low temperature for temporary sintering, and then re-compressed into a sintered body. In some cases, the correction is applied to increase the density of the sintered body, and the sintered body is heated at a temperature higher than that during the preliminary sintering to perform the main sintering. This is a so-called repress re-sinter. The above-mentioned correction is also called coining and is intended to improve physical properties. In particular, the repress re-sinter is intended to increase the density of the sintered body, and for that reason, in the preliminary sintering before straightening, the heating temperature is lowered so that the sintered body can be largely crushed during straightening.

FIG. 4 shows an example of a work 1 made of a sintered body which is subjected to such correction. This work 1
Has a substantially cylindrical shape, but has a convex portion 2 on one end side of the outer peripheral surface. 6 and 7 show an example of a straightening die device used for straightening the work 1. A die plate 11 has a stepped die 12 fixed to the die plate 11 by a die retainer 13. Die 12
Has a substantially cylindrical shape with the up-down direction as the axial direction, and forms the outer peripheral surface of the work 1 including the convex portions 2. Then, on the inner peripheral surface of the die 12, an upward horizontal step portion 14 that forms the lower surface of the convex portion 2 is formed. Also,
Reference numeral 15 denotes a core rod. The core rod 15 has a columnar shape with the vertical direction as an axial direction and is positioned coaxially in the die 12 to form the inner peripheral surface of the work 1.
The positions of the die 12 and the core rod 15 are fixed, and the upper surface of the die 12 and the upper end of the core rod 15 are located at the same height. 16 is a lower punch, and this lower punch 16 is
The die has a cylindrical shape with the vertical direction as the axial direction.
A lower end surface of the work 1 is formed by fitting between the core 12 and the core rod 15 so as to be vertically slidable from below. Further, 17 is an upper punch, and this upper punch 17 has a cylindrical shape with the vertical direction as an axial direction, and is fitted between the die 12 and the core rod 15 so as to be vertically slidable and removable from the upper side. To form the upper end surface of the work 1.

When straightening, the upper punch 17 is pulled upward from between the die 12 and the core rod 15, and the lower punch 16 is lifted so that the upper end of the lower punch 16 is located at the same height as the upper surface of the die 12. The work 1 is loaded onto the top 16.
Then, the lower punch 16 descends, and the work 1 descends together with the lower punch 16 and is loaded between the die 12 and the core rod 15. Figure 6 shows the state when loading is completed,
In this state, the work 1 is still placed on the lower punch 16, and the convex portion 2 of the work 1 is located apart from the step 14 of the die 12 upward. Pressurization also starts from this position. And
As shown in FIG. 7, the upper punch 17 descends to fit between the die 12 and the core rod 15,
The work 1 is pressed by both punches 16 and 17 between 15 to recompress and correct the work 1. In the middle of this pressurization, the convex portion 2 of the work 1 is changed to the stepped portion 14 of the die 12.
Then, the convex portion 2 is compressed by the step portion 14 of the die 12 and the upper punch 17. In this way, since the compression of the convex portion 2 starts later than the other portions of the work 1,
The compression margin of the work 1 is larger in the other portion than in the convex portion 2, and the compression ratio is uniform in each of the portions. After the pressurization is completed, the upper punch 17 rises again to come out between the die 12 and the core rod 15, and the lower punch 16 rises to move the die.
The work 1 is extracted from between 12 and the core rod 15.
Thereafter, the recompressed work 1 is carried out, the next work 1 is carried in, and the above steps are repeated.

For example, if the work 1 has a length of about 20 mm, the compression allowance is about 0.4 mm in the case of normal straightening performed after sintering in powder metallurgy in which sintering is performed only once. However, in the case of correction in repress re-sinter,
The compression margin is about 2.5 to 3 mm, and most of the pores in the work 1 made of a sintered body are crushed. Particularly when the compression margin is large as described above, in the conventional straightening method and the straightening die apparatus, the pressing is started in a state where the convex portion 2 of the work 1 floats from the stepped portion 14 of the die 12 as follows. Was causing problems. That is, during pressurization, the portion of the outer peripheral surface of the work 1 below the convex portion 2 and above the stepped portion 14 of the die 12 is the die.
Since it is not regulated by 12, it bulges outward to form a bulge 3 as shown in FIG. The bulging portion 3 is crushed separately from the convex portion 2 and therefore the convex portion 2 of the work 1 after recompression is formed.
8 has a shape having a narrow groove portion 4 at the bottom as shown in FIG. 8, and the work 1 becomes a defective product.

The present invention is intended to solve such a problem, and a straightening method for a repress re-sinter which can prevent occurrence of a straightening defect when straightening a work having a convex portion in the re-press re-sinter and a method. It is an object of the present invention to provide a straightening die device used in this method.

[0007]

In order to achieve the above object, a straightening method for a repress re-sinter according to a first aspect of the present invention compresses a raw material powder to form a green compact and reduces the green compact. Repress re-sinter that heats at a temperature to perform temporary sintering, re-compresses the sintered body obtained by this temporary sintering and corrects it, and heats the corrected sintered body at a high temperature to perform main sintering In the stepped die, the one side punch located on the convex side and the other side punch located on the opposite side to the convex side are used for the work having a convex portion on the outer peripheral surface one end side. In the straightening method of pressing and straightening, the pressing by the one side punch is started in a state where the convex part of the work is in contact with the step in the die, and the die is pressed by the one side by the pressing by the one side punch. After moving a predetermined amount by the side punch, press the die by stopping the die. Is performed.

Since the convex portion of the work is in contact with the stepped portion of the die from the beginning of pressurization in this way, the entire outer peripheral surface of the work is reliably regulated by the die, and the outer peripheral surface of the work is deformed illegally. Can be prevented. Also, after the die moves by a predetermined amount in the pressing direction of the one-side punch due to the pressing by the one-side punch, the die is stopped and the pressing by the punch is continued, so that the work is compressed more than the convex portion. The other parts are larger. Thus, even though the convex portion of the work comes into contact with the stepped portion of the die from the beginning of the pressurization, the compression allowance becomes a predetermined value for each of the convex portion of the work and the other portions.

According to a second aspect of the present invention, in the straightening method for a repress re-sinter according to the first aspect of the invention, the work is located away from the other side punch at the time when the pressing by the one side punch is started, and the die is The work comes into contact with the punch on the other side during the movement of.

Thus, if the work is positioned away from the punch on the other side at the start of pressurization, the convex portion of the work can surely contact the step portion of the die from the start of pressurization. Then, when the die slightly moves due to the pressurization of the one side punch, the work comes into contact with the other side punch, and the pressurization by the other side punch is performed.

According to a third aspect of the present invention, there is provided a straightening die apparatus used in the straightening method for a repress re-sinter according to the first or second aspect, wherein one side of the inside is a thick hole portion and the other side is thinner due to the step portion. A die that has a small hole portion, a one-side punch that is slidably and insertably inserted into the die from the thick hole portion side, and slides in the die from the small hole portion side. The other side punch that is freely fitted and a die plate that holds the die are provided, and the die is movable in a predetermined range in the moving direction of the punch with respect to the die plate, and is biased. It is biased to the one side punch side by means.

When pressing is started by the one-side punch in a state where the convex portion of the work is in contact with the stepped portion in the die, the die is pressed against the pressing direction of the one-side punch against the pressing force of the one-side punch. Move to. Then, the die moves within a predetermined range and then stops, and thereafter, the convex portion of the work is also compressed by the step portion of the die and the one-side punch.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a straightening method for a repress re-sinter and a straightening die apparatus used in this method will be described below with reference to FIGS. 1 to 3.
The work 1 to be recompressed and corrected is the one shown in FIG. 4 described above.

First, the structure of the mold device will be described. 21 is a die plate, and this die plate 21 is a lower die plate member.
An upper die plate member 23 is fixed on top of 22, and has a hole 24 that penetrates vertically. And this hole 24
An annular recess 25 is formed on the inner peripheral surface of the. This recess
The lower end 25 has an upward lower step surface 26 formed by the lower die plate member 22 at the lower end and an upper downward step surface 27 formed by the upper die plate member 23 at the upper end. A substantially cylindrical die holder is provided in the hole 24.
31 is slidably fitted in the vertical direction and held.
The die holder 31 has a convex portion 32 located in the concave portion 25 of the hole portion 24 on the outer peripheral surface, and urges between the lower surface of the convex portion 32 and the lower step surface 26 of the concave portion 25. A plurality of springs 33 as means are attached. The die holder 31
A spring retainer 34 for retaining the spring 33 from below is fixed to the lower surface of the. In this way, the die holder 31 is movable within a predetermined range between the upper limit position where the protrusion 32 contacts the upper step surface 27 of the recess 25 and the lower limit position where the spring 33 is compressed to the maximum extent. Along with
The spring 33 urges the spring upward.

On the inner peripheral side of the die holder 31, a substantially cylindrical stepped die 36 whose axial direction is the vertical direction is fixed. The die 36 has a horizontal upwardly facing stepped portion 37 on its inner peripheral surface, and the inside of the die 36 has a large hole portion above the stepped portion 37.
38, and a finer pore portion 39 is formed below the step portion 37. The die 36 forms the outer peripheral surface of the work 1, and the step 37 forms the lower surface (step) 5 of the convex portion 2 of the work 1. The upper surface of the die 36 and the upper surface of the die holder 31 are located on the same horizontal plane, and the upper surfaces of the die holder 31 and the die 36 are located at the same height as the upper surface of the die plate 21. .

Reference numeral 41 is a core rod whose axial direction is the vertical direction. The core rod 41 is located at the center of the die 36 and forms the inner peripheral surface of the work 1. The core rod 41 is fixed in position together with the die plate 21, and the upper surface thereof is located at the same height as the upper surface of the die plate 21.

Reference numeral 42 denotes a lower punch serving as the other side punch. The lower punch 42 has a substantially cylindrical shape with the vertical direction being the axial direction, and is located on the outer peripheral side of the core rod 41 and has pores of the die 36. It is slidably fitted into the portion 39 from below.
That is, the lower punch 42 forms the lower end surface of the work 1 opposite to the convex portion 2. The lower punch 42 is fixed on the lower punch plate 44 via the holder 43,
It moves up and down together with the lower punch plate 44.

Reference numeral 46 denotes an upper punch as one side punch. The upper punch 46 has a substantially cylindrical shape with the vertical direction being the axial direction, and is located on the outer peripheral side of the core rod 41 and has a large hole in the die 36. It is fitted into the portion 38 so as to be slidable and insertable and removable from the upper side. That is, the upper punch 46 is the work 1
The upper end surface on the side of the convex portion 2 is formed. The upper punch 46 is fixed to the lower side of an upper punch plate (not shown), and moves in the vertical direction together with the upper punch plate.

Next, a straightening method using the mold device will be described. In the repress re-sinter, the raw material powder is compression-molded by a powder molding press to make a green compact, and the green compact is heated at a low temperature in a sintering furnace to be temporarily sintered,
The density of the sintered body is increased by applying the correction that is recompression to the sintered body by the straightening press assembled with the straightening die device, and the sintered body is heated in the sintering furnace at a temperature higher than that during the temporary sintering. Main sintering is performed by heating at.

FIG. 1 shows a state in which the work 1 after straightening is taken out and when the work 1 is carried in. In this state, the upper punch 46 is pulled out upward from the die 36 and the core rod 41, the die 36 is at the upper limit position due to the bias of the spring 33, and the lower punch 42 is also raised so that the upper end surface thereof is
It is located at the same height as the upper surface of 36. Lower punch 42 in this state
The work 1 is loaded on top. Thereafter, as shown in FIG. 2, the lower punch 42 descends, and the work 1 placed on the lower punch 42 is loaded between the die 36 and the core rod 41. When this loading is completed, the convex portion 2 of the work 1 abuts on the stepped portion 37 of the die 36, but the lower end surface of the work 1 has a lower punch 42.
It is located slightly above the upper end surface of the. Pressurization starts in this state.

That is, pressing is started when the descending upper punch 46 is fitted between the die 36 and the core rod 41 and abuts against the upper end surface of the work 1 as shown by the chain line in FIG.
In the initial stage of this pressurization, the upper punch 46 pressurizes the die 36 together with the die holder 31 against the bias of the spring 33.
Is lowered by a predetermined amount. Work 1 during the lowering of the die 36
The lower end surface of the lower punch contacts the upper end surface of the lower punch. From this time point, the pressing by the lower punch 42 starts, and the work 1 is compressed by the lower punch 42 and the upper punch 46. In addition, the die
After 36 reaches the lower limit position and stops, upper punch 46 and die 36
The projecting portion 2 of the work 1 is also compressed by the step portion 37 of. Figure 3
Indicates the time when the pressurization was completed.

After that, the upper punch 46 moves the die 36 and the core rod.
41, and the die 36 also rises to the upper limit position due to the urging of the spring 33. Also, lower punch 42
Moves up to the position shown in FIG. 1 and the work 1 is extracted from between the die 36 and the core rod 41. Thereafter, the recompressed work 1 is carried out, the next work 1 is carried in, and the above steps are repeated.

According to the above-described straightening method, since the convex portion 2 of the work 1 is in contact with the stepped portion 37 of the die 36 from the beginning of the pressing, the outer peripheral surface of the work 1 from the start to the completion of the pressing. Although the entire die is surely regulated and the compression margin is large because it is a repress re-sinter, it is possible to prevent the outer peripheral surface of the work 1 from being deformed improperly, and to prevent correction defects. That is, it is possible to prevent the bulging portion 3 and the groove portion 4 from being formed below the convex portion 2 of the work 1 as in the conventional case.

Further, since the die 36 is movable up and down within a predetermined range with respect to the die plate 21 and is biased upward by the spring 33, the convex portion 2 of the work 1 is moved to the step of the die 36 from the beginning of pressurization. Despite contact with the portion 37, the compression allowance can be set separately for the convex portion 2 of the work 1 and other portions. That is, as the upper punch 46 pressurizes, the die
After the die 36 descends by a predetermined amount, the die 36 stops and punches 42, 46
By continuing the pressurization by, the compression margin of the work 1 becomes larger in the other portion than in the convex portion 2. Thereby, the compression allowance can be set to a predetermined value in each of the convex portion 2 and the other portion of the work 1.

Moreover, since the work 1 is positioned slightly above the lower punch 42 at the start of pressurization, even if there is a dimensional error, for example, the convex portion 2 of the work 1 becomes It surely abuts the stepped portion 37 of 36. Therefore, it is possible to more reliably prevent the correction failure from occurring on the lower surface 5 side of the convex portion 2 of the work 1.

Further, the structure of the die apparatus in which the die 36 is supported by the die plate 21 so as to be movable up and down and the die 36 is biased upward by the spring 33 is simple, and its manufacturing cost is low. The cost is low and the operation is highly reliable.

The present invention is not limited to the above embodiment, but various modifications can be made. For example,
In the above-described embodiment, the urging means for urging the die 36 upward with respect to the die plate 21 is a spring, but the urging means is not limited to this, and may be an air cylinder or the like. However, if a spring is used as in the above-described embodiment, the structure of the mold device is simplified and the cost required for manufacturing the mold can be reduced. Further, as shown in FIG. 4, the work 1 to be corrected has a convex portion 2 on the entire circumference on one end side of the outer peripheral surface.
Is not limited to a brim shape, but may have one or a plurality of convex portions 2 partially on one end side of the outer peripheral surface as shown in FIG.

[0028]

According to the straightening method for a repress re-sinter of the first aspect of the present invention, the one-side punch located on the side of the convex portion in the state where the convex portion on one end side of the work is in contact with the step portion in the die. After the pressurization by the one side punch is started and the die is moved by a predetermined amount in the pressurizing direction by the one side punch,
Since the die is stopped and pressure is applied, even if the compression margin is large because it is a repress re-sinter, the convex portion of the workpiece and the other portions can secure the predetermined compression margin while maintaining the step of the convex portion. It is possible to prevent a correction defect from occurring on the part side.

According to the straightening method for a repress re-sinter of the second aspect of the invention, in addition to the effect of the first aspect of the invention, the work is positioned away from the punch on the other side at the start of pressing by the one side punch. Since the work comes into contact with the punch on the other side during the movement of the die, the convex portion of the work can be surely brought into contact with the step portion of the die from the start of pressurization, and the step portion of the convex portion is corrected. It is possible to more reliably prevent the occurrence of defects.

According to the straightening mold apparatus of the third aspect of the present invention, the die having the step portion is movable in a predetermined range in the punch moving direction with respect to the die plate, and
Since the one side punch side is biased by the biasing means, the straightening method according to claim 1 or 2 can be implemented with a die device having a simple structure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a straightening die apparatus showing an embodiment of the present invention, showing a state before loading a work.

FIG. 2 is a sectional view of the same straightening mold apparatus showing a state in which a work is loaded.

FIG. 3 is a cross-sectional view of the same straightening mold apparatus, showing a time when a work is pressurized.

FIG. 4 is a perspective view showing an example of a work to be corrected.

FIG. 5 is a perspective view showing another example of a work to be corrected.

FIG. 6 is a sectional view showing an example of a conventional orthodontic mold device,
The state where the work is loaded is shown.

FIG. 7 is a sectional view of the same as above, showing the time point when the pressurization of the work is completed.

FIG. 8 is a sectional view of the work corrected as above.

[Explanation of symbols]

1 work 2 convex 21 die plate 33 Spring (biasing means) 36 step dies 37 steps 38 Thick hole 39 Pores 42 Lower punch (Punch on the other side) 46 Upper punch (one side punch)

Claims (3)

(57) [Claims] 1. A raw material powder is compressed to form a green compact, the green compact is heated at a low temperature to be temporarily sintered, and the sintered body obtained by this temporary sintering is recompressed. It is a straightening method used for a repress re-sinter for straightening and then sintering the sintered body after straightening at a high temperature. In a straightening method in which one side punch located on the convex side and the other side punch located on the opposite side to the convex side pressurize in the axial direction to correct, the convex part of the work abuts the step inside the die. In this state, pressurization by the one-side punch is started, the die is moved by a predetermined amount in the pressurizing direction by the one-side punch, and then the die is stopped to perform the pressurization. A straightening method for a repress re-sinter, which is characterized by being performed. 2. The work is located away from the other-side punch at the time when the pressing by the one-side punch is started, and the work comes into contact with the other-side punch during the movement of the die. Item 2. A straightening method for a repress re-sinter according to Item 1. 3. A straightening mold apparatus for use in the straightening method for repress re-sinter according to claim 1, wherein one side of the inside is a large hole portion and the other side is a narrower hole portion by the step portion. A die, a one-side punch that is slidably fitted in the die from the side of the large hole portion, and a one-side punch that is slidably fitted in the die, and is slidably fitted in the die from the side of the small hole portion. The other side punch and a die plate for holding the die, the die is movable in a predetermined range in the moving direction of the punch with respect to the die plate, and the one side is urged by an urging means. A straightening mold device characterized by being urged toward the punch side.