JP3037405B2 - Pressure heating sintering method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pressure heating sintering method.

[Prior Art] A metal powder material is filled into a cavity of a molding die, and this is press-molded in the molding die to form a molded body, and the molded body is heated and sintered in the molding die. The pressurized heat sintering method described above is conventionally known (for example, see Japanese Patent Application Laid-Open No.
Reference).

Specifically, for example, as shown in FIG. 14, a powdery metal material 104 is filled between a lower punch 102 and an upper punch 103 in a hole 101 ′ of a die 101, and the metal material 104 is filled.
Is pressed by the lower punch 102 and the upper punch 103 to form a molded body 104 (metal material). The lower punch 102 and the upper punch 103 have electrodes 105,
The molded body 104 (metal material) is energized by using the power source 107, and heat is generated in the molded body 104 to form the molded body 104.
Is heated and sintered. Alternatively, as shown in FIG. 15, a heater 108 connected to a power supply 107 is attached to the outer periphery of the die 101, and the molded product 10
4 is heated and sintered.

However, in the above-mentioned conventional methods, since the fluidity of the powder metal material in the molding die is low, it is not possible to form a molded article having a complicated shape at a uniform density, and therefore, a cylindrical or prismatic shaped article cannot be formed. There is a problem that it can be used only for a compact or sintered body having a simple shape.
If the punch is double-acting, the density of the compact can be made uniform. However, since the temperature of the mold set (die, punch, etc.) becomes high, a spring and a pneumatic mechanism for double-acting the punch are used. In addition, it is difficult to incorporate a hydraulic mechanism or the like into a mold set, and there is a problem that it is practically difficult to employ a double-acting punch.

In order to solve the above-mentioned problems, the applicant of the present application used a highly fluid slurry obtained by mixing a powder metal material and a liquid binder, and formed a compact or sintered body having a complicated shape using a single-acting mold. A pressure heating sintering method capable of forming a body has been proposed (see Japanese Patent Application No. 2-77613).

Hereinafter, the above-mentioned pressure heating sintering method according to the present applicant will be described with reference to the process chart shown in FIG.

Step 1: A powder metal material 111 and a liquid binder 112 (for example, glycerin) are prepared.

Step 2: A slurry 113 is prepared by mixing the powder metal material 111 and the binder 112.

Step 3: The slurry 113 is poured into the cavity defined by the inner peripheral surface of the hole 114 'of the die 114 and the upper end surface of the lower punch 115.

Step 4: press-forming the slurry with the upper punch 117,
While performing rough binder removal, a compact 116 is formed.

Step 5: Both the punches 115 and 117 are connected to the power supply 118 to supply electricity to the molded body 116, and the molded body 116 is heated and sintered while being pressed by the heat generated. At this time, the density is made uniform by the plastic flow of the metal material.

Step 6: Take out the sintered body 116 '.

According to such a pressure heating and sintering method, even when a monodynamic molding die is used, a sintered body having a complicated shape is formed by the improvement of fluidity by the liquid binder and the plastic flow at the time of pressure heating. Can be formed with a relatively uniform density.

[Problems to be Solved by the Invention] However, even in the above-mentioned pressurized heat sintering method using the liquid binder according to the present applicant, when the shape of the molded body is complicated, the metal particles are not cornered during the pressure molding. It is very difficult to get them evenly distributed. In particular, when a metal material having high deformation resistance such as stainless steel is used,
Since the plastic fluidity also decreases, the density of the sintered body cannot be made sufficiently uniform. For example, as shown in FIG.
If the difference in the thickness of the compact in the pressing direction is large, sufficient plastic flow cannot be generated, and there is a problem that the density of the sintered body becomes non-uniform. In the case where the thickness t of the portion is small, the above-mentioned problem becomes remarkable. It should be noted that if the sintering temperature is increased, plastic flow can be promoted, but such a problem occurs that the strength of the mold decreases.

The present invention has been made in order to solve the above-mentioned conventional problems, and is directed to a pressurizing method capable of forming a compact or sintered body having a complicated shape at a uniform density with a single-acting punch. An object is to provide a heat sintering method.

[Means for Solving the Problems] In order to achieve the above object, a first invention is to prepare a slurry by mixing a solid powder and a liquid binder, fill the slurry into a cavity of a molding die, Pressing the slurry inside to squeeze the binder and pressing the slurry into a predetermined shape corresponding to the mold to form a molded body,
A pressure and heat sintering method for heating and sintering the compact to form a sintered body having a predetermined shape, wherein the solid powder is formed into a large particle having a relatively large particle size and a relatively large particle size. After having a bipolar particle distribution configuration in which small particles of
In advance, a large particle slurry is prepared by mixing the large particles and the binder, while a small particle slurry is prepared by mixing the small particles and the binder using another container, and should be filled in the cavity of the mold. A pressure heating sintering method characterized in that a slurry is prepared by mixing a large particle slurry and a small particle slurry at a predetermined mixing ratio before filling.

A second invention is characterized in that, in the pressure and heat sintering method according to the first invention, the particle diameter of the small particles is set to a size such that the small particles can pass through the gap between the large particles that are in contact with each other. Pressure sintering method.

According to a third aspect of the present invention, in the pressure and heat sintering method according to the first aspect of the present invention, the molded body is constituted by a thick part and a thin part, and corresponds to a thick part of a molding die. Pressure heating sintering, wherein a binder outflow portion for discharging the binder is formed in the portion, and the binder is caused to flow out of the cavity from the binder outflow portion in the pressure forming step of the slurry in the cavity. Provide a way.

According to the first aspect, if the particle size of the small particles is set sufficiently smaller than the particle size of the large particles,
The small particles are carried by the flow of the binder to a portion where the large particles are not filled with sufficient density, and the gap between the large particles is filled with the small particles. For this reason, a compact or sintered body with uniform filling and high density can be formed.

In general, when large particles and small particles are mixed using a liquid binder in one relatively large container, the distribution of both particles in the container becomes non-uniform due to the weight difference between the two particles. In this case, the mixing ratio of both particles varies from lot to lot. However, in the first invention, the large particles and the small particles are mixed with the binder in separate containers to prepare the large particle slurry and the small particle slurry, and the large particle slurry and the small particle slurry are prepared immediately before filling the mold. Since the slurry is prepared in a required amount by mixing the small particle slurry with a predetermined mixing ratio, it is possible to reduce the variation in the mixing ratio between the large particles and the small particles.

According to the second aspect, the same operation and effect as those of the first aspect can be obtained. Further, since the particle size of the small particles is set to be smaller than the gap between the large particles that are in contact with each other, the small particles can freely pass between the large particles during pressure molding. For this reason, even when the packing density of the large particles is not uniform, the small particles can enter into the gaps between the large particles all over, and a compact or sintered body with uniform filling and high density can be formed.

According to the third aspect, the same operation and effect as those of the first aspect can be obtained. Further, small particles are gathered along the flow of the binder in a portion where the binder flows out, so that the small particles can be effectively collected in a portion where a large amount of small particles are to be distributed. That is, the concentration of the small particles can be increased in a desired portion of the molded body. By utilizing this, for example, the composition of the small particles can be made different from the composition of the large particles, and the composition can be preferably adjusted at an arbitrary portion.

[Examples] Examples of the present invention will be specifically described below.

<First Embodiment> As shown in FIG. 1, a die 1 of a pressure and heat sintering apparatus D for manufacturing a gear sleeve (not shown, but having substantially the same shape as the gear sleeve in FIG. 17). Has a cylindrical shaped hole
1a is formed, and a mandrel 2 is formed at the center of the forming hole 1a.
(Shaft) is disposed. The lower punch 3 and the knockout punch 4 are fitted in the space between the peripheral surface of the forming hole 1a and the outer peripheral surface of the mandrel 2. As described later, the mixing slurry 5 is formed in a cavity formed by the peripheral surface of the forming hole 1a, the peripheral surface of the mandrel 2, the upper end surface of the lower punch 3, and the upper end surface of the knockout punch 4. It is designed to be filled.

Here, the lower punch 3 is fixed to a die set plate 9 arranged on an upper surface of the bolster 8 by using a mounting bolt 6 and a fastener 7. The mandrel 2 is also fixed to the die set plate 9 by fastening bolts 11.

The knockout punch 4 is slidable in the vertical direction, and a knockout pin 13 is provided to move the knockout punch 4 up and down. The knockout pin 13 is connected to a knockout piston 15 via a knockout plate 14, and is moved up and down by the knockout piston 15.

In addition, as described later, the pressure and heat sintering apparatus D
Heating and sintering is performed by directly energizing the molded body 5 (see FIG. 3), so that the die 1, the mandrel 2, the punches 3, 4, etc., which come into contact with the molded body 5 (see FIG. 3), The die set plate 9 is electrically insulated using a plurality of insulators 16 to 19.

As will be described later, in order to equalize the density of the sintered body 5 '(see FIG. 4), the gap between the knockout punch 4 and the mandrel 2, the knockout punch 4 and the lower punch 3, Between them, there are provided binder outflow portions 21 for allowing the liquid binder to flow out, respectively.

Hereinafter, a method for manufacturing a sintered body (gear sleeve) using the pressure heating and sintering apparatus D will be described.

As shown in FIG. 5, a large particle slurry 31 is prepared by mixing a powder metal material having a large particle diameter with glycerin, while a powder metal material having a small particle diameter is mixed with glycerin using a separate container. A particle slurry 32 is prepared.

As metal material, Fe-1% C-1.45% Cr-0.25% Si
An alloy powder corresponding to high carbon chromium bearing steel having a composition of -0.3% Mo is used. The average particle diameter of metal material particles having a large particle diameter (hereinafter, referred to as large particles) is approximately
The average particle diameter of metal material particles having a small particle diameter of 150 μm (hereinafter, referred to as small particles) is about 10 μm.
The particle size distributions of the large particles and the small particles are shown by curves G ₁ and G in FIG. 7, respectively.
Indicated by ₂ . FIG. 9 shows an example of the particle size distribution of the powder metal material in the conventional pressure heating sintering method using a liquid binder.

The large particle slurry 31 and the small particle slurry 32 are mixed at a predetermined mixing ratio to prepare a small amount (for example, for a few lots) of mixed slurry 33 having a bipolar particle size distribution. In general, when two types of solid powders having greatly different particle diameters are mixed with a liquid in one large container, the mixing ratio of large particles and small particles partially varies due to a weight difference. However, in the present invention, the mixed slurry is composed of the large particle slurry 31 and the small particle slurry 32.
Since 33 is prepared little by little, the variation in the mixing ratio of large particles and small particles is reduced.

Note that, without preparing such a large particle slurry 31 and a small particle slurry 32, a direct mixing slurry was obtained by using a powder metal material having a particle size distribution obtained by combining the curves G ₁ and G ₂ in FIG. It may be prepared. In this case, for example, as shown in FIG.
Of course, a metal material having a continuous particle size distribution having peaks at about 150 μm and about 10 μm may be used.

Slurry discharge cylinder 34 for one lot of mixed slurry 33
And the mixed slurry in the slurry discharge cylinder 34 is supplied to the pressurized heating sintering apparatus D using the drive cylinder 35.

At this time, as shown in FIG. 1, a cavity formed by the peripheral surface of the forming hole 1a of the die 1, the peripheral surface of the mandrel 2, the upper end surface of the lower punch 3, and the upper end surface of the knockout punch 4. Then, the mixed slurry 5 of the current lot is held.

As shown in FIG. 2, the upper punch 23 is inserted into the forming hole 1a from the upper opening, and the mixed slurry 5 is pressed and compressed. At this time, the upper punch 23 has a small thickness in the pressing direction.
5a and the thick portion 5b having a large thickness in the pressing direction are compressed by the same length, so that the packing density of large particles is high in the thin portion 5a, but the packing density of large particles is large in the thick portion 5b. Becomes lower.

On the other hand, as described above, the binder outflow portion 21 is provided between the knockout punch 4 and the mandrel 2 and between the knockout punch 4 and the lower punch 3, respectively. Accordingly, the binder in the mixed slurry 5 passes through the lower end of the thick portion 5b and flows out of the binder outlet 21.
Squeezed (B ₁ ). Here, since the average size of the small particles is about 1/15 of that of the large particles, the small particles having a small inertia force pass through the gap between the large particles and move together with the binder. Therefore, the small particles are gradually accumulated upward from the lower end of the thick portion 5b from which the binder is squeezed.

As shown in FIG. 3, at the end of pressurization / compression by the upper punch 23, in the thick portion 5b, small particles are densely filled in the gaps between the large particles, and the density of the thick portion 5b is increased. But thin part
5a higher than the density. Note that the pressurized圧終period, outflow B ₂ also slight binder resulting from the clearance portion between the die 1 and the upper punch 23. In this way, the mixed slurry 5 becomes a molded body 5 having a predetermined shape.

In order to confirm the above-mentioned effects, using a low-alloy powder of low carbon (0.005 wt%), a 400 times photomicrograph of the metal structure of the thin part and the thick part of the molded body formed by the above method, These are shown in FIGS. 10 and 11, respectively. As is clear from FIGS. 10 and 11, large particles are crushed by the high pressure in the thin part (FIG. 10), whereas the pressure is not so increased in the thick part, so that the large particles are crushed so much. Although not performed, small particles have entered the gaps between the large particles, and the gaps have disappeared.

The power is supplied to the compact 5 using a power supply device (not shown), and the binder remaining in the compact 5 is gasified and removed by the heat generated by the compact 5 itself.
After sintering for 5 minutes, a sintered body 5 'is obtained as shown in FIG.
During this sintering, the density of the sintered body 5 ′ is increased by the plastic flow of the metal material,
It becomes relatively large at 5a 'and relatively small at the thick part 5b'. Therefore, at the time of sintering, the density increase of the thin portion 5a 'is larger than the density increase of the thick portion 5b'. On the other hand, since the density of the thick portion 5b is higher than the density of the thin portion 5a when the compact 5 (see FIG. 3) is formed as described above, they are canceled at the end of sintering, and the sintered compact 5 'is formed. Density is made uniform.

As shown in FIG. 6, in the case where the molded body 41 projects both up and down, it is preferable to provide a binder outflow portion on both upper and lower sides of the molded body 41. That is, a lower binder outflow portion 45 is provided between a lower punch 43 and a lower knockout punch 44 arranged in the forming hole 42 of the die 42, and an upper binder is provided between the upper punch 46 and the upper knockout punch 47. An outflow portion 48 may be provided.

As described above, according to the first embodiment, even when a sintered body having a complicated shape is manufactured using a metal material having a large deformation resistance, the sintered body having a uniform density is produced by a single-acting pressurized heating sintering apparatus. Can be manufactured.

Second Embodiment Hereinafter, a second embodiment will be described.

As shown in FIG. 12, rocker chip 56 (see FIG. 13)
A lower punch 52 is arranged in a forming hole 51a formed in a die 51 of a pressure and heat sintering apparatus D 'for manufacturing a hollow body formed in an axis of the lower punch 52. A knockout punch 53 is fitted into 52a.

In the second embodiment, the upper punch 54 includes first to fourth parts.
It is divided into 54a-54d. Although the upper punch 54 is divided into first to fourth parts 54a to 54d, the operation is a single-acting type, and the mixing slurry 50 is integrally pressurized during pressure molding. And the die 51 and the first part
A first binder outflow portion 55a is provided between the first binder outflow portion 55a.
Second to fourth binder outlets 55b to 57d are provided between the fourth parts 54a to 54d, respectively.
A fifth binder outflow portion 55e is provided between the first and second portions.

Hereinafter, the rocker chip 56 by the pressure and heat sintering device D 'will be described.
(See FIG. 13) will be described.

A predetermined amount of the mixed slurry 50 is supplied to a cavity formed by the peripheral surface of the forming hole 51a of the die 51, the upper end surface of the lower punch 52, and the upper end surface of the knockout punch 53.

Here, the mixing slurry 50 is prepared by previously mixing iron powder (large particles) having a particle size of 88 to 175 μm and graphite (small particles) having a particle size of 20 to 1 μm with an appropriate amount of a liquid binder (for example, glycerin). Has been prepared. The content of graphite in the solid material is set to about 0.2 wt%.

Press and compress the mixed slurry 50 with the upper punch 54 to form a compact
Form 50. At this time, the first to fifth binders
It is squeezed by the binder outlets 55a to 55e. Therefore, graphite, which is small particles, is carried by the binder and is accumulated downward from the upper surface of the molded body 50. For this reason, the compact 50
In the vicinity of the upper surface, there is formed a concentration distribution in which the graphite concentration is highest at the upper end surface, and the graphite concentration decreases as going downward.

The molded body 50 is energized and heated and sintered to obtain a rocker chip 56 as shown in FIG.

As described above, since the concentration distribution of graphite occurs near the upper surface of the molded body 50 (see FIG. 12), a carburized structure is formed on the sliding portion 56a of the rocker chip 56 after sintering. As the distance from the sliding portion 56a to the main body portion 56b increases, the structure gradually becomes richer in ferrite structure (iron-only structure).

In this way, a rocker chip 56 having a carburized structure having high wear resistance formed on the sliding portion 56a and a ferrite structure easily formed on the main body portion 56b is obtained. The main body 56b of the rocker chip 56 is cast with an aluminum alloy or the like, and serves to hold the sliding portion 56a.

[Brief description of the drawings]

FIG. 1 is an elevational cross-sectional view of a pressure and heat sintering apparatus, showing a first embodiment of the present invention. FIG. 2 is an elevational sectional view of a main part of the pressure-heating and sintering apparatus shown in FIG. 1 in an early stage of a pressure-forming step. FIG. 3 is a view similar to FIG. 2 at the end of the pressure forming step. FIG. 4 is a view similar to FIG. 2 in a sintering step. FIG. 5 is a process chart showing a process of preparing a mixed slurry in the first embodiment. FIG. 6 is an elevational cross-sectional view of a pressurized and heated sintering apparatus in which binder outflow portions are provided on both upper and lower punch sides. FIG. 7 is a view showing the particle size distribution of the powder metal material in the first embodiment. FIG. 8 is a diagram showing another example of a preferable particle size distribution of the powder metal material. FIG. 9 is a diagram showing an example of a particle size distribution of a metal material used in a conventional pressure heating sintering method using a liquid binder. FIG. 10 is a photomicrograph showing the metal structure of the thin portion of the compact in the first example. FIG. 11 is a photomicrograph showing the metal structure of the thick part of the compact in the first example. FIG. 12 is an elevational cross-sectional view of a pressure and heat sintering apparatus showing a second embodiment of the present invention. FIG. 13 is an elevational cross-sectional explanatory view of a rocker chip manufactured by the pressure and heat sintering apparatus shown in FIG. FIG. 14 is an elevational cross-sectional view of a conventional pressure heating and sintering apparatus that does not use a liquid binder. FIG. 15 is an elevational sectional view of another conventional pressure heating sintering apparatus that does not use a liquid binder. FIG. 16 is a process chart showing a conventional pressure heating sintering method using a liquid binder. FIG. 17 is an elevational sectional view of a formed body (gear sleeve) in which a thin portion and a thick portion are formed. D, D '... Pressurized heat sintering device, 1 ... Die, 1a ... Forming hole, 2 ... Mandrel, 3 ... Lower punch, 4 ... Knockout punch, 5 ... Mixed slurry (compact) ), 5 '...
... Sintered body, 21 ... Binder outlet, 23 ... Top punch,
31 large particle slurry, 32 small particle slurry, 51 die, 52 lower punch, 53 knockout punch, 54
... Upper punch, 55a to 55e, first to fifth binder outlets, 56, rocker chips.

Claims (3)

(57) [Claims] A slurry is prepared by mixing a solid powder and a liquid binder, the slurry is filled into a cavity of a mold, and the slurry in the cavity is pressurized to squeeze the binder, and the slurry is formed into a mold. A pressure-and-heat sintering method for forming a compact by press-molding into a corresponding predetermined shape to form a compact and heating and sintering the compact to form a sintered body having a predetermined shape, The powder has a bipolar particle size distribution configuration in which large particles having a relatively large particle diameter and small particles having a relatively small particle diameter are blended, and the large particles are mixed in advance with the large particles and the binder. While preparing the slurry, the small particles and the binder are mixed using another container to prepare a small particle slurry, and the slurry to be filled in the cavity of the mold is prepared before the filling by the large particle slurry and the small particle slurry. And in a predetermined mixing ratio Pressurizing heater sintering method characterized by the. 2. The pressure-heating and sintering method according to claim 1, wherein the small particles have a particle size set so as to pass through a gap between the large particles that are in contact with each other. Pressure heating sintering method. 3. The pressure-heating and sintering method according to claim 1, wherein the molded body is composed of a thick part and a thin part, and the molded body corresponds to a thick part of a molding die. Forming a binder outflow part that allows the binder to flow out in the part, In the pressure forming process of the slurry in the cavity, the binder is
A pressure and heat sintering method characterized by flowing out of a cavity from a binder outflow portion.