JP4454004B2 - Forming method of thin plate compact - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for forming a sheet-shaped green compact having a small thickness and a large width with respect to the thickness.
[0002]
[Prior art]
In powder molding using a mold for producing a sintered product, a hydraulic press or a mechanical press is usually used. The upper punch of the molding die used for such press molding is generally fixed to the upper ram side, but when molding a stepped green compact, it is a non-fixed mold. That is, a floating upper punch is employed.
[0003]
Such an upper punch moves the filled powder so as to have a shape similar to that of the green compact in the compression process. For example, one of the two upper punches divided into the inside and the outside is interposed via a spring. For example, a device attached to the upper ram side in a floating state has been proposed (for example, see Patent Document 1). In addition, one in which two upper punches are attached in a floating state by pneumatic pressure or hydraulic pressure has been proposed (see, for example, Non-Patent Document 1). Furthermore, when using a hydraulic press, the thing which relieves | impacts the impact force transmitted to powder and prevents defects, such as a crack of a molded object by a vibration of a ram, and a chip | tip, is proposed (for example, refer patent document 2). ).
[0004]
[Patent Document 1]
JP-A-5-214405 [Patent Document 2]
Japanese Examined Patent Publication No. 52-45594 [Non-Patent Document 1]
Press terminology for powder metallurgy Powder Metallurgy Industry Association JPMA G 01-1995
Revised June 16, 1995, pages 38-39 [0005]
[Problems to be solved by the invention]
Usually, the powder filled in the mold contains about 70% of air by volume ratio. Therefore, the powder molding described in Patent Document 1, Patent Document 2, and Non-Patent Document 1 described above. In the method, when the upper punch enters the filled powder cavity, the powder may be scattered with the air, and the green compact may not have a predetermined weight. In addition, the air left in the green compact may cause the green compact not to have a predetermined density, or may form large pores and cause defects in the sintered material.
[0006]
In particular, when the powder filling depth is small, as in the case of forming a thin plate-shaped green compact, the compaction is performed after the upper ram (or upper punch) starts to descend and then starts to compress the powder. It takes a short time to complete. For this reason, when the powder is compressed by the lowering of the upper ram, the powder in the vicinity of the punch is scattered and the powder is liable to leak out. Moreover, since the required time is not sufficiently secured, air cannot be sufficiently removed from the powder during powder compression, and air is easily trapped in the green compact. Therefore, when the thin plate-shaped green compact is molded by the conventional molding technique, the above-mentioned problems regarding the weight of the green compact, the density, and the defect of the sintered material have been remarkably exhibited. Note that even if the green compact has a flat end face, or has grooves or protrusions, the pores near the center and outer periphery of the upper punch are dense, especially when the compression area is large for the thickness. Therefore, there was a tendency that the pores in the middle part became rough.
[0007]
In order to solve such a problem, the present invention suppresses both the leakage of the filled powder and the entrapment of air into the green compact, and a predetermined weight and density can be obtained. An object of the present invention is to provide a technique for forming a green compact without defects.
[0008]
[Means for Solving the Problems]
The thin plate-shaped green compact molding method of the present invention includes a die, a lower punch that fits into the die and forms a powder filling cavity together with the die, and is attached to the upper ram and attached downward by elastic means. Forming a thin plate-shaped green compact having a thickness of 10 mm or less and a width of 8 times or more of the thickness using a powder molding apparatus having an upper punch that is urged and fitted to the die In the method, the press molding step of the powder accompanying the lowering of the upper ram includes an initial lowering step (1) of the upper ram in which the upper punch enters the cavity and contacts the upper surface of the powder, The pressure in the elastic means increases, and the time required for the upper punch in the floating state to initially compress the powder and abut against the stopper means is 0.8 seconds or more, and the air in the powder is gently discharged to the outside. Upper ram mid-term descent stage (2) and The upper punch is characterized by including the above on the late drop step (3) of the ram and that the compression of the powder in contact with the said stop means.
[0009]
In the thin plate-shaped green compact molding method of the present invention, the powder press molding process accompanying the lowering of the upper ram is divided into the three stages described above. In step (1), the upper punch is moved into the cavity by the initial lowering of the upper ram as a preparation for powder molding, and moved to the upper surface of the powder. Next, in stage (2), the powder is initially compressed by the medium-term depression of the upper ram. That is, the upper punch lightly presses the powder at a low speed in a floating state without following the lowering speed of the upper ram, and the air in the powder is gently discharged to the outside. For this reason, the blowout leakage of the filling powder can be suppressed. Further, at this stage, the density of the powder in a semi-molded product state rises to such an extent that it is difficult to be scattered by further compression. Further, on the basis of the increase in the density of the powder, in step (3), the powder is finally compressed to a desired shape by the latter descent of the upper ram and finally has a predetermined weight. Can be obtained. Further, at this stage, for example, when a crank press is used, the lowering of the upper ram is close to the minimum value in the operating curve, so the compression speed is relatively slow, and the trapping of air in the powder is reduced. And the green compact can have a predetermined density. As described above, since the weight and density of the green compact have predetermined values, large pores are not generated in the green compact, and defects in the sintered material can be suppressed. From the above, according to the molding method of the present invention, in particular, by suppressing the blowout leakage of the filled powder in the step (2) and by suppressing the air intrusion into the green compact in the step (3), The green compact can have a predetermined weight and density, and the generation of defects can be suppressed as a sintered material of the green compact. Moreover, even when a green compact having a large compression area for its thickness is manufactured, the pores in the vicinity of the center, the middle part, and the outer periphery of the upper punch can be made uniform by the above effect.
[0010]
The powder compression process is as described above, but after the compression is finished, even if the upper ram starts to rise, the upper punch is in a floating state under the bias of the elastic means. For this reason, the upper punch remains in contact with the green compact until the distance between the upper end surface of the upper punch and the lower end surface of the stopper on the upper ram side is maximized. The thin plate-shaped green compact is extracted by lowering the die until it comes below the upper end surface. Therefore, according to the molding method of the present invention, the thin plate green compact can be extracted without applying a bending force. By the way, conventionally, when the upper ram starts to rise after completion of compression, the upper punch moves away from the green compact, so that a bending force is applied when the die is lowered and the thin plate-shaped green compact is extracted thereafter. There was a bug.
[0011]
In the method for forming a thin plate-shaped green compact of the present invention , as described above, the time required for the middle ramming stage (2) of the upper ram is set to 0.8 seconds or more . This condition ensures sufficient time for the upper punch to lightly press the powder at a low speed in a floating state without following the lowering speed of the upper ram, so that the air in the powder is gently discharged to the outside. Can be further enhanced. For this reason, it is possible to further suppress blowout leakage of the filled powder.
[0012]
In order to further suppress the blowout leakage of the filled powder by setting the required time to 0.8 seconds or more, it is desirable to set the elastic means to a compressed air pressure of 0.4 to 0.5 MPa. As described above, by using the compressed air pressure as the elastic means, the manufacturing cost can be reduced as compared with the case where hydraulic pressure is used. Further, by suitably setting the compressed air pressure as described above, it is possible to effectively suppress the leakage of the filled powder in the step (2). Moreover, by optimizing the compression air pressure, when the upper ram starts to rise after the compression is completed, it is possible to prevent the upper punch from leaving the green compact. There is an effect that no bending force is applied when the green compact is extracted. As for the upper limit value and lower limit value of the compressed air pressure, when the compressed air pressure is less than 0.4 MPa, the upper punch comes into contact with the upper ram side soon when the upper ram is lowered, and the above stage (2 ) Required time is not sufficiently secured, and powder blowing out easily occurs. Also, when the compressed air pressure exceeds 0.5 MPa, the powder compression speed in the above step (2) is close to the upper ram descending speed, so the air in the powder cannot be gently discharged, and the powder The body blowing suppression effect is not sufficiently obtained.
[0013]
Further, as described above, in order to more effectively suppress the leakage of the filled powder, the upper end surface of the floating upper punch biased downward by the compressed air pressure and the stopper means positioned on the upper ram side are provided. Is preferably 10 mm or more. For example, taking the case of using a crank press as an example, the relationship between the stroke of the upper ram and time is represented by a cosine curve, and one operation cycle is about 10 seconds. Under these conditions, when the powder filling depth is about 7 mm, the compression distance is about 4 mm, and the upper punch stroke is 10 mm or more, the initial compression time of the powder in the above step (2) is a suitable value. Therefore, no leakage of the filled powder was observed.
[0014]
In the method for forming a thin plate-shaped green compact as described above, it is preferable that the upper punch enters the cavity after filling the powder and applying underfill. Here, underfill is a powder that lowers the lower punch or raises the die after completion of powder filling to prevent the powder from overflowing or splashing around the die when the upper punch is pushed into the die. This is a powder filling method in which the upper punch is lowered from the upper surface of the die and then the upper punch is lowered to enter the cavity. By adopting the underfill, the air pressure in the cavity acts on the upper punch, and the lowering speed of the upper punch is further reduced. In particular, in the step (2), the air in the cavity is slowly discharged. For this reason, it can further suppress that a filling powder is extruded to the outer periphery of a cavity, and leaks or scatters.
[0015]
In addition, in the case of a taper shape in which the die inlet on the upper side of the upper surface of the filled powder after underfilling is expanded upward, on the upper side of the upper surface of the filled powder subjected to underfill. Since a slight gap is formed between the cavity and the outer periphery of the upper punch, when the upper punch enters the cavity, the air in the cavity can be easily discharged. In this case, the molded body can be easily released by the gap.
[0016]
In the present invention, in order to form a thin plate-shaped green compact having a thickness of 10 mm or less and a width of 8 times or more of the thickness , the above three press forming processes of powder accompanying the lowering of the upper ram are described. The molding method is divided into stages . According to the present invention, as compared with the case of adopting the by powder molding techniques described in Patent Documents 1 and 2, and Non-Patent Document 1, into the balloon leakage suppression and compact filling powder The effects of both air entrainment suppression are noticeable.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an operation diagram of the upper ram (one rotation of the crank) in a mechanical press in which the upper ram is a crank mechanism among the mechanical presses used in carrying out the method for forming a thin plate-shaped green compact of the present invention. . As shown in the figure, the change in the upper ram position by one rotation of the crank is represented by a cosine curve. The time required for one rotation of the crank is 10 seconds when the compacting speed of the green compact is 6 (pieces / minute). The upper ram stroke shown on the vertical axis in the figure varies depending on the size of the press machine. For example, in the case of a 200-ton press, it is about 200 mm. In this case, the maximum compression distance by the upper punch Is about 70 mm.
[0018]
A powder molding apparatus having an upper ram according to the operation diagram shown in FIG. 1 is shown in FIG.
In the powder molding apparatus shown in FIG. 2, the lower punch 11 is attached to the center of the upper surface of the base plate 10, and the lower punch 11 and the die 13 attached to the die plate 12 are fitted together. A cavity C for filling powder is formed. The die plate 12 is connected to a yoke plate 15 via a pair of guide rods 14 penetrating the base plate 10, and a lower ram 16 is connected to the center of the lower surface of the yoke plate 15. The die 13 can slide in the vertical direction with respect to the lower punch 11.
[0019]
In the same figure, a floating upper punch 17 is arranged above the cavity C so as to face the lower punch 11. The upper punch 17 has an upper portion 17a slidably fitted to the cylinder member 18 and a cylinder through a compressed air supply port 18a formed on the side of the cylinder member 18 from an air compressor (not shown). The compressed air A supplied into the member 18 is biased downward. An upper punch plate 19 is connected to the upper portion of the cylinder member 18. A stopper means 19 a is attached to the center of the lower surface of the upper punch plate 19, and an upper ram 20 is attached to the center of the upper surface of the upper punch plate 19. However, when the upper ram 20 moves up and down, it moves in the up and down direction under the action of compressed air pressure.
[0020]
Below, the operation | movement and effect of the said powder shaping | molding apparatus at the time of enforcing the shaping | molding method of the thin plate-shaped green compact of this invention are demonstrated.
When the thin plate-shaped green compact molding method of the present invention is carried out, first, as shown in FIG. 3A, after the powder P is filled into the cavity C, the upper ram 20 is lowered (initially lowered). Then, the upper punch 17 enters the cavity C until the upper punch 17 comes into contact with the upper surface of the powder. At this stage, the upper punch 17 is biased downward by the compressed air A supplied into the cylinder member 18, but is in a floating state.
[0021]
Next, as shown in FIG. 3B, the upper ram 20 is further lowered (mid-term drop) from the state in which the upper punch 17 is in contact with the upper surface of the powder. At this stage, every time the upper ram 20 descends, the upper punch 17 slides upward with respect to the cylinder member 18. For this reason, the compressed air pressure in the cylinder member 18 is slightly increased, and accordingly, the downward biasing force of the upper punch 17 is also somewhat increased, and the powder P is further compressed. Thus, since the upper punch 17 lightly presses the powder P at a low speed in a floating state without following the lowering speed of the upper ram 20, the air in the powder P is gently discharged to the outside. In addition, the density of the powder that has been in a semi-molded product state at this stage rises to such an extent that it is difficult to be scattered by further compression. Such an operation of the upper punch 17 sliding on the cylinder member 18 is continuously performed until it comes into contact with the stopper means 19a.
[0022]
Further, after the upper punch 17 comes into contact with the stopper means 19a, the upper ram 20 is further lowered (later lowering) as shown in FIG. At this stage, the upper punch 17 is integrated with the stopper means 19a to compress the powder P, and a green compact with a predetermined weight is obtained. Further, at this stage, the lowering of the upper ram 20 is close to the minimum value in the operating curve shown in FIG. 1, so that the compression speed is relatively slow, and the trapping of air in the powder P can be reduced. The green compact can have a predetermined density.
[0023]
The above is the basic operation of the powder forming apparatus used in the method for forming a thin plate-shaped green compact according to the present invention. A more preferred embodiment will be described below.
The inner edge of the upper entrance of the die 13 shown in FIG. 2 is usually slightly chamfered with an arc cross section so that the floating upper punch 17 can easily enter. Under such a configuration, for example, when the upper end surface of the powder P and the upper end surface of the die 13 coincide with each other when the powder P is filled in the cavity C, the powder P is filled. When the upper punch 17 enters the cavity C, the powder is ejected through the chamfered portion. This jet has little effect on the whole green compact when the powder filling depth is large, but when the powder filling depth is small as in the case of producing a thin plate compact, The effect on the whole powder is large. For this reason, in order to further improve the effect of compression molding by the upper punch 17 in the floating state described above, it is effective to underfill the filling powder P. By applying underfill to the filled powder at least below the chamfered portion, the ejection can be suppressed, and a green compact with a predetermined weight can be obtained.
[0024]
However, by applying underfill in this way, if the amount of air trapped when the cavity C is closed with the upper punch 17 becomes too large, the powder is blown out. Therefore, it is desirable to reduce the underfill enforcement height. In order to reduce the amount of air trapped when the upper punch 17 enters the cavity C and approaches the powder P, the upper entrance side of the die 13 shown in FIG. It is preferable to make it a taper shape which expands toward. The inclination of the tapered portion of the cavity C with respect to the horizontal plane can be about 500 to 2000.
[0025]
The thin plate-like green compact formed by the above method is then sintered and used after additional processing such as sizing according to the purpose. The above-described molding method is preferably applied to a sintered product having a small thickness, a large area, and no holes, but substantially the same effect can be obtained when applied to other various shapes. .
[0026]
【Example】
As described above, in the method for forming a thin plate-shaped green compact according to the present invention, the powder pressing process associated with the lowering of the upper ram is performed by floating the upper punch without attaching the upper punch to the upper ram side. As described above, there are three stages. Hereinafter, it will be described by way of example that the use of the upper punch of the present invention is more advantageous than the case of using the upper punch attached to the upper ram side.
[0027]
[Comparative example]
The solid line in FIG. 4 is an enlarged view of the vicinity of the bottom dead center in the operation curve of the fixed upper punch when the upper punch is attached to the stopper means in the molding apparatus shown in FIG. In this way, when a fixed upper punch is used, the upper punch operates integrally with the upper ram, so the solid line in FIG. 4 is an enlarged view of the vicinity of the bottom dead center of the cosine curve shown in FIG. Become. The horizontal axis in FIG. 4 indicates the crank rotation angle as in FIG. 1, and the vertical axis indicates the vertical height position of the lower end surface of the upper punch. When the fixed upper punch descends according to such a curve, it contacts the surface of the filled powder at point A. Then, the fixed upper punch rises after compressing the powder up to point B and leaves the green compact. In the figure, point B is the bottom dead center of the fixed upper punch, the height position of point H is the lower punch surface position, the height position of point A is the filled powder surface, and the distance between point H and point A is The powder filling depth, the distance between points A and B indicates the compression distance of the powder, and the distance between points H and B indicates the green compact thickness.
[0028]
Here, the required time from the point A which is the compression start position of the powder to the point B which is the compression completion position is that the powder filling depth is 7.5 mm, the compression distance is 4.5 mm (the green compact thickness is 3 mm). ), And the time required for one stroke is 10 seconds, it was 0.43 seconds, and the leakage of the filled powder was observed. In particular, when a thin plate-shaped green compact is formed using a powder containing a large amount of fine powder or a powder having a low specific gravity, the above-mentioned powder blowout leakage appears remarkably, and the air in the green compact The confinement was not sufficiently suppressed, and the density of the green compact was lower than a predetermined value. In addition, when the shape of the green compact is variously changed, the thickness of the green compact is 10 mm or less, particularly about 2 to 6 mm, and the width (including diameter) is 8 times or more the thickness. When the green compact was molded, the above-mentioned powder blowout leakage and air confinement in the green compact appeared remarkably.
[0029]
[Example]
Next, an alternate long and short dash line in FIG. 4 is an enlarged view of the vicinity of the bottom dead center in the punch surface operation diagram of the upper punch 17 when the molding apparatus shown in FIG. 2 is used as it is. In this molding apparatus, the distance between the upper end surface of the upper portion 17a and the lower end surface of the stopper means 19a in FIG. 2 is 25 mm. The lower punch 17 is lowered by the lowering of the upper ram 20 and comes into contact with the surface of the filling powder at a point D in FIG. In the state of the point D, the floating upper punch 17 is urged downward by the compressed air A introduced into the cylinder member 18a. When the upper ram 20 is further lowered, the filled powder is compressed by the inertial force depending on the compressed air pressure, the weight of the upper punch 17 and the speed of its entry. When the upper ram 20 is further lowered with respect to the upper punch 17 on the powder, the upper end surface of the upper portion 17a and the lower surface of the stopper means 19a come into contact with each other. This point is point E in FIG. The time required from the point D to the point E is 0.85 seconds, and the filled powder is lightly compressed with a slight pressure to be formed into a low density lump. The upper punch 17 integrated with the upper ram 20 compresses the powder with a curve indicated by a solid line, and reaches the bottom dead center of the point B. The time required from the point D where the upper punch 17 in the floating state contacts the filled powder to the point B where the compression is completed is 1.17 seconds, and the compression takes about 2.7 times as long as the case of the fixed upper punch. Is completed. When such a means was adopted, no leakage of the filled powder was observed, the air in the green compact was sufficiently suppressed, and the density of the green compact was also a predetermined value.
[0030]
When the upper ram 20 rises after the compression is completed at the point B, compressed air is introduced into the upper portion 17a shown in FIG. 3C, and the upper punch 17 in a floating state is urged downward. For this reason, the lower end surface of the upper punch 17 remains in contact with the green compact, and the floating upper punch 17 contacts the lower end of the cylinder member 18 through a point F where extraction starts when the die plate 30 descends. The green compact is held by the upper and lower punches 11 and 17 up to the point G where it comes into contact. The green compact extraction initial stage hold-down time between points F and G was 0.77 seconds.
[0031]
Thus, when the upper punch 17 in the floating state is used, the thickness of the stopper means 19a is changed to shorten the initial pressurization holding time, and the limit value at which the filled powder does not leak out is investigated. When the time between point D and point E in FIG. 4 was 0.8 seconds or more, no blowout leakage was observed.
[0032]
【The invention's effect】
As described above, according to the present invention, in the compact molding of a thin plate shape, the predetermined weight and density can be reduced by suppressing both the leakage of the filled powder and the leakage of air into the green compact. As a result, it is possible to provide a technology for forming a thin plate-shaped green compact without defects as a sintered material. Therefore, the present invention is promising in that a sintered product suitable for various fields can be produced.
[Brief description of the drawings]
FIG. 1 is an operation diagram of an upper ram in a crank press.
FIG. 2 is a longitudinal sectional view showing a powder molding apparatus used in carrying out the method for molding a thin plate-shaped green compact of the present invention.
FIG. 3 is a view showing, over time, a powder press-molding process that accompanies the lowering of the upper ram in the thin plate-shaped green compact molding method of the present invention.
FIG. 4 is an enlarged view showing the vicinity of the bottom dead center in the operation curve of the upper punch used in the comparative example and the example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Base plate, 11 ... Lower punch, 12 ... Die plate, 13 ... Die, 14 ... Guide rod, 15 ... Yoke plate, 16 ... Lower ram, 17 ... Upper punch, 17a ... Upper part, 18 ... Cylinder member, 18a ... Compression Air supply port, 19 ... upper punch plate, 19a ... stopper means, 20 ... upper ram, C ... cavity.

Claims (3)

A die, a lower punch to form a cavity for powder filling with die fitted into the die, attached to the upper ram, and a punch on which is urged downward by an elastic means fitted to said die A molding method for forming a sheet-shaped green compact having a thickness of 10 mm or less and a width of 8 times or more of the thickness using a powder molding apparatus comprising:
The press molding process of the powder accompanying the lowering of the upper ram,
An initial lowering step of the upper ram in which the upper punch enters the cavity and abuts the upper surface of the powder;
The pressure in the elastic means increases and the time required for the floating upper punch to initially compress the powder and abut against the stopper means is 0.8 seconds or longer, and the air in the powder is gently discharged to the outside. A mid-term descent phase of the upper ram;
A method for forming a thin plate-shaped green compact, comprising: a late descent step of the upper ram in which the powder is compressed in a state where the upper punch is in contact with the stopper means.   2. The method for forming a thin plate-shaped green compact according to claim 1, wherein the upper punch is inserted into the cavity after filling with powder and underfilling.   3. The molding of a sheet-shaped green compact according to claim 2, wherein the inlet of the die on the upper side of the upper surface of the filled powder after the underfill is tapered so as to expand upward. Method.

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