JP2005305530A - Powder molding method of two-layer green compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder molding method of two-layer green compact capable of maintaining simplicity of a powder molding device and powder molding step for two-layer green compact, preventing occurrence of any trouble even when the powder molding pressure during the compression is increased, and consistently performing the powder molding with high accuracy. <P>SOLUTION: The powder molding method of two-layer green compact comprises a first powder filling step of filling first powder 5 in a cavity formed by an inner hole of a die, a core rod and a lower punch by using a powder molding device having a die 11, a lower punch 13, a core rod 12, an upper punch 14, and a temporary pushing punch 15, a temporary compression step of temporarily compressing first powder 5 by the temporary pushing punch, a space forming step of forming a space below a temporarily compressed body which is temporarily compressed in, for example, the temporary compression step by lowering the lower punch or elevating the die, and a second powder filling step of filling second powder 6 in a cavity formed by an upper face of the temporary compressed body, the inner hole of the die, and the core rod, and a permanent compression step of lowering the upper punch which carries out compacting, integrally and densely compressing second powder and the temporarily compressed body while downwardly moving them on the space side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is, in particular, a two-layer green compact in which a second powder compact is laminated in an inclined state on a first powder compact, that is, a boundary layer between the two compacts is obliquely laminated. The present invention relates to a powder molding method for a green compact.

  Valve seats for internal combustion engines use iron-based sintered alloys in which intermetallic compounds and carbides are dispersed, and high-temperature wear resistance in order to meet the higher wear resistance associated with higher performance of engines, etc. Elements that contribute to characteristics (Ni, Cr, etc.) are added to the iron powder. For this reason, manufacturing costs are also naturally high. As a countermeasure, for example, as in Patent Documents 1 and 2, a two-layer valve seat made of a high-grade sintered alloy is used for the inclined seat portion in contact with the valve and a low-grade iron-based sintered alloy is used for the other body. It has been put into practical use.

  The forming apparatus of Patent Document 1 includes a die forming an inner hole, a lower punch, an upper punch, a temporary pressing punch, and the like. In the molding method using the apparatus, after the cavity is defined by the inner hole of the die and the lower punch and the core rod, the first powder is filled into the cavity. Thereafter, the die is raised slightly, and then the temporary pressing punch is lowered to temporarily compress the first powder. After the temporary pressing punch is retracted, the second powder is filled on the temporary compression body. The temporarily compressed body and the second powder are compressed and integrated and densified by the upper punch that is lowered. The formed green compact is pushed up from the inner hole of the die by the rise of the lower punch and released.

  As schematically shown in FIG. 4, the forming apparatus of Patent Document 2 includes a die 1, a core rod 2, a lower punch 3, an upper punch 4, and the like that form an inner hole. The core rod 2 has a groove 2a formed on the upper outer periphery. In the lower punch 3, the upper side 3 a is formed in a wide sliding portion, and the lower side 3 b is thin to form a gap with the core rod 2. As shown in FIG. 4C, the lower punch 3 and the core rod 2 are provided so as to be movable between a position where the groove 2a communicates with the cavity and a position where the groove 2a is located below the cavity. In the molding method using the apparatus, after the first powder 5 is filled into the cavity through the first feeder 7A as shown in FIG. 4A, the core rod 2 is raised or lowered as shown in FIG. 4B. The punch 3 is lowered to communicate the groove 2a with the cavity. Then, a part of the first powder 5 flows into the groove portion 2a, and forms a cavity for the second powder whose upper surface is substantially mortar, that is, the outer peripheral side is high and the inner peripheral side is low. After that, as shown in FIGS. 4C and 4D, the second powder 6 is filled into the cavity for the second powder through the second feeder 7B, and then the upper punch 4 is lowered and the lower punch 3 The first powder 5 and the second powder 6 are integrated and densified. The molded green compact 10 is a molding material for the valve seat, and the molded body 6a of the second powder 6 is integrated in a layered manner with the inclined portion of the molded body 5a of the first powder 5.

JP 2002-239793 A (FIG. 8 etc.) Japanese Unexamined Patent Publication No. 2003-200244 (FIGS. 1-5, etc.)

  Each of the above-mentioned Patent Documents 1 and 2 makes a two-ply green compact in which a second powder compact is laminated on a first powder compact in an inclined state, that is, the boundary surface between the two compacts is formed obliquely. Is. In this case, in the former, the upper surface of the first powder is formed in a substantially mortar shape by a temporary pressing punch, and in the latter, when a part of the filled first powder is released into the groove portion, the upper surface of the first powder is changed depending on the position and shape of the groove portion. Is formed into a substantially mortar shape. However, in the configuration of Patent Document 1, in order to increase the angle of the mortar-shaped inclined surface, if the taper angle of the temporary press punch is increased, it is difficult to move upward because the powder moves while being compressed, and Since the pressing force on the powder acts in the vertical direction with the taper surface, only the vertical force component of the taper surface of the punch pressure force acts, and when the taper surface is increased, the taper surface vertical force component is reduced. There is a problem that it is difficult to increase the density of the taper edge, and the taper edge tends to collapse due to a load or the like when filling the second powder. On the other hand, in the configuration of Patent Document 2, even if an attempt is made to increase the inclination angle of the mortar-shaped inclined surface due to the position and shape of the groove portion, it cannot be formed at an angle greater than the repose angle of the first powder, and the second powder It tends to collapse due to the load when filling Further, the core rod is complicated and expensive because the groove portion must be formed with high accuracy. In addition, the first powder that has escaped to the groove is useless because it is removed from the gap between the lower punch and the core rod, and it is not economical because it must be refined for reuse.

  The object of the present invention is to eliminate the above-mentioned problems and to make the inclination of the inclined surface of the boundary between the first powder and the second powder without complicating the powder forming apparatus and forming process for the double-layer green compact. There is no problem even if the size is increased, and it is possible to form with high accuracy and stability.

In order to achieve the above object, the present invention of claim 1 is a powder molding method for obtaining a two-layer green compact in which a second powder compact is laminated in an inclined state on a first powder compact. A die having an inner hole that forms an outer peripheral surface of the body, a cylindrical lower punch that slidably fits with the inner hole of the die to form a lower end surface of the green compact, and an inner portion of the lower punch A cylindrical core rod that is slidably fitted to the hole, and a cylindrical body portion that is slidably fitted to the inner hole of the die, the lower end surface being equal to the diameter of the core rod, An upper punch having a tapered portion whose diameter increases as it goes upward from the lower end surface, and a step portion provided between the tapered portion and the body portion to form the upper end surface of the green compact; An inner hole that is slidably fitted to the hole and slidably fitted to the core rod, and the inner hole of the die and the Aroddo and using at least provided with which the powder molding apparatus and the temporary press punch the first powder to be supplied to the cavity formed by the lower punch to temporary compression,
A first powder filling step of supplying and filling the first powder into a cavity formed by the inner hole of the die, the core rod and the lower punch with a feeder or the like; A gap forming step of forming a predetermined gap under the temporary compression body temporarily compressed in the temporary compression step by lowering the lower punch or raising the die after performing the temporary compression step of temporarily compressing. The order of the second powder filling step of supplying and filling the second powder with a feeder or the like into the cavity formed by the upper surface of the temporary compression body, the inner hole of the die and the core rod, or the second powder filling step, The order of the gap forming step, or the gap forming step and the second powder filling step are simultaneously performed, and then the upper punch is lowered to move the second powder and the temporary compression body downward toward the gap. Together to be integrated with reluctant compression is characterized by undergoing the compression step of densification.

  In the above powder molding method, after the second powder filling step is completed, the main compression step is performed after the powder scattering prevention cylindrical member communicating with the inner hole of the die is installed on the upper surface of the die. (Claim 2). Moreover, in the temporary compression step, it is preferable to temporarily compress the molding pressure at 30 to 300 MPa (Claim 3). The two-layer green compact of the present invention was developed as a valve seat material made of a sintered alloy. In this valve seat material, in particular, as a taper portion that expands above the inclination angle of the seat portion, that is, the upper punch, it can be molded well even at a taper angle of 7 to 50 degrees.

  In the above-described method of the present invention, the inclined surface is formed by the upper punch that is lowered in the main compression step from the second powder and the temporary compression body that are filled on the upper side from a state where a gap is maintained under the formed temporary compression body. However, the temporary compression body moves downward while being deformed toward the gap, and is compressed and densified. Since the deformation of the temporary compression body in the downward gap direction is not the taper surface vertical component force but the pressurizing direction, the pressure utilization efficiency is higher than the method of Patent Document 1, and the upward powder Since the movement is not utilized, an inclined surface having a large inclination angle can be easily obtained. Compared with the method of Patent Document 2, the inclination angle of the boundary surface between the first powder compact and the second powder compact can be increased, the molding die can be simplified, and the first powder can be used efficiently.

  Hereinafter, the powder molding method of the present invention will be described in detail with reference to FIGS. Here, the invented double-layer compact 10 is a valve seat material made of a sintered alloy as shown in FIG. 2 (d), for example. To finish a valve seat of a predetermined size and shape.

(Device Structure) The powder molding apparatus used in the method of the present invention is used for molding a two-layer green compact 10 in which a molded body 6a of a second powder 6 is laminated in an inclined state on a molded body 5a of a first powder 5. . The constituent members are a die 11 having an inner hole 11 a that forms the outer peripheral surface of the green compact 10, and a cylinder that slidably fits with the inner hole 11 a of the die 11 to form the lower end surface of the green compact 10. Lower punch 13, cylindrical core rod 12 slidably fitted into the inner hole of lower punch 13, upper punch 14 corresponding to inner hole 11 a of die 11, inner hole 11 a of die 11, A temporary pressing punch 15 slidably fitted to the core rod 12 and a powder supply feeder (not shown) are provided. The upper punch 14 is extended to a cylindrical body portion 14a, and a lower end surface 14b is equal to the diameter of the core rod 12, and a taper portion 14c having a diameter increasing upward from the lower end surface 14b, and the taper portion 14c. Between the lower punch 13 in a state of being fitted in the inner hole of the die 1. Compress. The tapered portion 14c is formed at a taper angle of 7 to 50 degrees and has a steep slope. The temporary pressing punch 15 has an inner hole slidably fitted to the inner hole 11a of the die 11 and slidably fitted to the core rod 12, and the inner hole 11a of the die 11, the core rod 12 and The first powder 5 supplied to the cavity formed by the lower punch 13 is temporarily compressed.

  For example, the die 11, the lower punch 13, the upper punch 14, and the temporary pressing punch 15 are actuated by driving means similar to a known press mechanism unit, and the core rod 12 is biased upward. Therefore, it is lowered against the biasing force. Specifically, for example, the die 11 is fixed, or the lower punch 13 is fixed and the core rod 12 and the die 11 move up and down as in the withdrawal method. Further, although not shown, the powder supply feeder is on standby at a position away from the die cavity, and the first powder first feeder and the second powder are not shown. It consists of a second feeder.

(Molding method) A powder molding method for producing the two-layer green compact 10 by the above powder molding apparatus will be described. The molding method of FIG.1 and FIG.2 is a 1st powder cavity formation process with respect to the method of patent document 1, the 1st powder filling process shown to Fig.1 (a), and the temporary compression process shown to FIG.1 (b). 1d, a second powder filling step, a main compression step shown in FIGS. 2a to 2c, and a mold release step for extracting the molded body 10 shown in FIG. 2d. It is similar in that it is different in that a gap forming step shown in FIG. 1C is added after the temporary compression step. Details are as follows.

  First, in the first powder cavity forming step, the lower punch 13 and the core rod 12 are arranged in the state shown in FIG. 1A with respect to the inner hole 11a of the die 11 to partition and form a cavity for the first powder. In the first powder filling step, the first powder 5 is filled into the first powder cavity by the first feeder that is driven back and forth along the die 11 to be rubbed.

  In the temporary compression step, the temporary pressing punch 15 is lowered to temporarily compress the filled first powder 5. Here, as shown in FIG. 1C, the temporarily compressed body 5b after molding is brought into contact with the inner surface of the inner hole of the die 11 with a predetermined pressure so that it can be independently held in the inner hole of the die 11 by the corresponding contact force. . For this reason, it is preferable that a shaping | molding pressure is set in the range of 30-300 MPa. The reason is that if the molding pressure is less than 30 MPa, the temporary compression body cannot be held alone in the inner hole of the die 11, and if the molding pressure is greater than 300 MPa, the temporary compression body is hardly deformed in the main compression step, This is because the temporary compressed body simply moves downward in the same shape, and a good inclined surface of the second powder cannot be obtained.

  In the gap forming step, the lower punch 13 is lowered by a predetermined dimension (instead, the die 11 and the core rod 12 may be raised by a predetermined dimension), thereby lowering the temporary compression body 5b formed in the temporary compression step. A predetermined large gap 17 is formed. The gap 17 is set in consideration of the size and the degree of compression of the temporary compression body 5b. In the second powder filling process, the second powder 6 is supplied by a feeder or the like to the cavity formed by the upper surface of the temporary compression body 5b, the inner hole of the die 11 and the core rod 12, and is made to be rubbed.

  FIG. 2A shows an initial stage of the main compression process, FIG. 2B shows an intermediate stage of the main compression process, and FIG. 2C shows a final stage of the main compression process. In this step, first, the upper punch 14 is lowered while the lower end surface 14b of the upper punch 14 is brought into contact with the upper end surface of the core rod 12, and then the core rod 12 is pushed down against a biasing force or the like. In this main compression step, the taper portion 14c of the lowered upper punch 14 hits the second powder 6, and the second powder 6 is compressed. Next, with the second powder 6 in the semi-compressed state placed on the upper portion of the temporary compression body, the gap on the core rod side is caused by the frictional force accompanying the downward movement of the core rod 12 and the pressure force of the tapered portion 14c of the upper punch 14. Deforms to the lower side. And after the whole lower end surface of the temporary compression body 5b contact | abuts to the lower punch 13, the temporary compression body 5b and the 2nd powder 6 are compressed and integrated and densified by the upper punch 14 and the lower punch 13. FIG. In the mold release step, the upper punch 14 is raised, and the lower punch 13 is raised to push up the green compact 10 and extract it from the inner hole of the die 11. Thereby, the green compact 10 is sent to the next sintering process as a valve seat raw material, for example.

  In the above compacting method, the gap 17 is formed between the temporary compression body 5b and the lower punch 13 particularly in the gap formation step, and the second powder 6 filled on the temporary compression body 5b and the temporary compression are formed. The body 5b is compressed and densified while being moved downward toward the gap 17 by the upper punch 14 lowered in the main compression step. For this reason, in this configuration, the temporary compression body 5b is temporarily deformed to adjust the mixing of the first powder and the second powder, and is likely to occur after sintering in the molded body 5a or the boundary between the molded bodies 5a and 6a. Breaking can be eliminated. Moreover, since the temporary compression body 5b deform | transforms with the 2nd powder 6 of a semi-compression state mounted in the upper part, the angle of the interface of both powder can be made higher than before.

(Modification) FIG. 3 shows a modification of the powder molding method. This modification is an example in which an arrangement step of the cylindrical member 16 is added between the second powder filling step and the main compression step. This cylinder member 16 is a cylinder having an inner diameter that is substantially the same diameter as the inner hole 11 a of the die 11, and is installed on the upper surface of the die 11 after the second powder filling step. The upper punch 14 is lowered and enters the inner hole 11a of the die 11 from the inside of the cylindrical member 16, and compression-molds the second powder 6 and the temporary compression body 5b as described above. In this configuration, the scattering of the second powder 6 can be reliably prevented by attaching the cylindrical member 16.

(Example) Next, as an example of the above-described powder molding method, an example will be given when the influence of the molding pressure at the time of temporary compression is examined in the temporary compression step. In this example, a Fe-6.5Co-1.5Ni-1.5Mo alloy powder and 1.2% by mass of graphite powder added and mixed, Fe-6.5Co-1.5Ni-1.5Mo, 18 mass% Co-28Mo-8Cr-25Si alloy powder and the 2nd powder which added and mixed 1.2 mass% graphite powder to the alloy powder were prepared. In the temporary compression step, the molding pressure of the temporary compression is changed as shown in Table 1, the first powder is temporarily compressed, the second powder is filled, and the main compression step is performed at a molding pressure of 600 MPa. Sintered with. In Table 1 below, “interface state” indicates the result of observing the interface between the two powders for each sintered body produced as described above.

(Table 1)

  From the above examples, it was found that a two-layer composite member having a good joint interface was obtained when the molding pressure during temporary compression was 30 to 300 MPa.

It is a schematic block diagram which shows the apparatus and shaping | molding method of this invention. It is a schematic block diagram which shows the apparatus and shaping | molding method of this invention similarly to FIG. It is a schematic block diagram which shows the modification of this compression process among the methods of this invention. It is a schematic block diagram for demonstrating the conventional problem.

Explanation of symbols

11 ... Die (11a is an inner hole)
12 ... Core rod 13 ... Lower punch 14 ... Upper punch (14a is the trunk, 14b is the lower end surface, 14c is the taper)
15 ... Temporary press punch 5 ... First powder (5a is a compact, 5b is a temporary compact)
6 ... second powder (6a is a molded product)
10 ... Double-layer compact

Claims (3)

A powder molding method for obtaining a two-layer green compact in which a molded body of a second powder is laminated in an inclined state on a molded body of a first powder,
A die having an inner hole forming the outer peripheral surface of the green compact;
A cylindrical lower punch that slidably fits with the inner hole of the die to form the lower end surface of the green compact,
A cylindrical core rod slidably fitted to the inner hole of the lower punch;
A tapered portion that extends to a cylindrical body portion that is slidably fitted to the inner hole of the die, has a lower end surface that is equal to the diameter of the core rod, and that increases in diameter toward the upper side of the lower end surface; An upper punch having a step portion provided between the tapered portion and the body portion and forming an upper end surface of the green compact;
The inner hole of the die is slidably fitted and the inner hole is slidably fitted to the core rod, and is supplied to the cavity formed by the inner hole of the die, the core rod and the lower punch. Using a powder molding apparatus comprising at least a temporary pressing punch for temporarily compressing the first powder
A first powder filling step of supplying and filling the first powder into a cavity formed by the inner hole of the die, the core rod and the lower punch with a feeder or the like; After performing the temporary compression step for temporary compression in order,
A gap forming step in which a predetermined large gap is formed under the temporary compression body that is temporarily compressed in the temporary compression step by lowering the lower punch or raising the die, and an upper surface of the temporary compression body and an inner hole of the die And the order of the second powder filling step of supplying and filling the second powder into the cavity formed by the core rod with a feeder or the like, or the order of the second powder filling step, the gap forming step, or the gap forming step, Performing the second powder filling step simultaneously,
Next, the upper punch is lowered, and the second powder and the temporary compression body are compressed and integrated while being moved downward to the gap side, and then undergoes a main compression step in which the pressure is integrated and densified. Powder molding method for powder.   After the second powder filling step is completed, the main compression step is performed after a powder scattering prevention cylindrical member communicating with the inner hole of the die is installed on the upper surface of the die. Item 2. A method for forming a powder of the two-layer green compact according to Item 1. 3. The powder molding method for a double-layer green compact according to claim 1, wherein in the temporary compression step, the molding pressure is temporarily compressed at 30 to 300 MPa.

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