JP3957868B2 - Molding method of green compact - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In particular, the present invention has a thickness in the compression direction, such as having a step or a groove on the compression surface, or having a hole or a notch extending in the direction intersecting the compression direction in the middle of the thickness in the compression direction. The present invention relates to a method of forming a green compact having a non-constant shape, and to a technique for making the density of the green compact uniform.
[0002]
[Prior art]
For example, as shown in FIGS. 5 (a) and 5 (b), both end portions are horizontally long rectangular parallelepiped sections, and in the width direction (arrow Z direction) in the middle of the height direction (arrow X direction). In obtaining the member 2 having the penetrating rectangular cross-sectional lateral hole 1 from the green compact as a sintered product, the following method has been tried to form the green compact. First, as shown in FIG. 6A, a part of the raw material powder P to be used is filled in the cavity 12 formed by the die 10 and the lower punch 14, and the horizontal hole 1 is formed on the raw material powder P. The core 13 is set. Next, as shown in FIG. 6B, after filling the remaining raw material powder P, the raw material powder P is compressed by the upper and lower punches 11 and 14 as shown in FIG. 2B is molded. Thereafter, the green compact 2B is extracted from the die 10, and the core 13 is extracted to obtain the green compact 2B.
[0003]
[Problems to be solved by the invention]
In the case of the above method, the compression direction by the upper and lower punches 11 and 14 is the height direction of the member 2, and rather than taking a longer longitudinal direction (the arrow Y direction in FIG. 5A) as the compression direction. The filling depth of the raw material powder P is shallow. By shortening the compression direction in this way, the filling property of the raw material powder P is improved, the green compact 2B can be easily extracted from the die 10, and the compressive density of the raw material powder P is the lowest. , 14, the so-called neutral zone is small, and the overall density tends to be uniform.
[0004]
However, in the green compact 2B, as shown in FIG. 5 (b), the upper and lower portions 3 of the horizontal hole 1 and the portion 4 that occupies the entire height of both sides of the horizontal hole 1 (hereinafter, the former is thin-walled). The portion 3 and the latter are referred to as the thick portion 4 for convenience), of course, because the compression height differs, the thick portion 4 tends to have a lower density than the thin portion 3. Therefore, as described above, although the overall density tends to be uniform by shortening the compression direction, the uniformity is insufficient and the quality after sintering may not be satisfied. As a measure for overcoming this problem, a method is proposed in which the thin portion 3 and the thick portion 4 are compressed with different punches, and the pressure is controlled according to the compression height to make the entire density uniform. In this case, the apparatus is complicated, and it is assumed that molding is difficult or impossible depending on the shape of the member.
[0005]
Accordingly, the present invention provides a method for forming a green compact in which the whole density is sufficiently uniformed and high quality can be stably obtained when forming a green compact whose thickness in the compression direction is not constant. The purpose is to provide.
[0006]
[Means for Solving the Problems]
The present invention is a method of molding a green compact having a thick part and a thin part having different thicknesses in the compression direction, and includes a primary compression molding step using a primary molding die, and a secondary molding die following this. has two steps of the secondary compression molding step, the primary compression molded stroke, the thick portion, imparting excess thickness portion that is green compact make uniform the density of the green compact and projects anti compression direction the state, the whole of the raw material powder was compression-molded in the secondary compression molding process, pressure of a desired shape and dimension with the primary compression molded body obtained in the primary compression molding step, compressing while crushing the excess thickness portion It is characterized by obtaining powder .
[0007]
According to this method, first, in the primary compression molding step, the raw material powder filled in the primary molding die is compressed to obtain a primary compression molded body. This primary compression-molded body has a near net shape corresponding to the green compact to be molded, and is provided with a surplus portion protruding in the compression direction on the thick portion . Atmosphere of the excess thickness portion is controlled appropriately so as to equalize the overall density of the green compact to be molded. For example, when the green compact is as shown in FIG. 5B, it protrudes in the anti-compression direction on at least one compression surface of the thick portion 4, that is, at least one of the upper surface and the lower surface. A surplus part of a certain thickness is integrally formed.
Next, the primary compression molded body obtained in the primary compression molding step is set in a secondary mold having a cavity corresponding to the green compact to be molded and compressed to form a desired green compact. In this secondary compression molding step, the compressed surplus portion is a portion where the density is lower than other portions when the surplus portion is not molded (in the case of FIG. Therefore, the density of the portion increases as much as the other portions. Therefore, the green compact obtained after the secondary compression molding has a sufficiently uniform overall density. Moreover, by carrying out the compression molding process separately for the primary and secondary, the absolute density of the green compact finally obtained becomes higher than that of one compression molding, and the strength is improved. From these things, a high-quality green compact can be obtained stably.
[0008]
Further, the present invention is characterized in that the raw material powder is heated in the primary compression molding step or the primary compression molded body is heated in the secondary compression molding step, thereby further increasing the density of the compression molding body. it can. It is assumed that the increase in density due to this heat compression molding is caused by the promotion of the formation of interparticle bonds in the raw material powder. As the form of heating, either the secondary compression molding process is heated only (the primary compression molding process is performed cold) or both the primary and secondary compression molding processes are heated. The form is more preferable from the viewpoint of increasing density. In addition, it is important in terms of quality that the heating temperature is selected at a temperature lower than the temperature at which blue brittleness occurs in the material based on the raw material powder and higher than normal temperature. For example, carbon containing 0.25% carbon In the case of steel, a preferable heating temperature is in the range of 100 to 220 ° C.
[0009]
Further, the present invention is characterized in that, in the primary compression molding step, as a lubricating means for the raw material powder, the mold wall of the primary molding die filled with the raw material powder is coated with a lubricant. In general, as a lubrication means for reducing friction between the raw material powder and the mold wall, either mixing the lubricant in the raw material powder or coating the mold wall with the lubricant is adopted. In the present invention, the latter means is a preferred lubricating means. As means for coating the mold wall with a lubricant, a liquid lubricant such as wax is applied to the mold wall, or a powdery lubricant is adhered to the mold wall by an electrostatic coating method. Means are used. By adopting such a lubricating means, the density of the primary compression molded body is increased and the strength is improved as compared with the mixing of the lubricant into the raw material powder. Further, in this case, the primary compression molded body is in a state where the lubricant adheres only to the surface (friction surface with the mold wall). For this reason, in the secondary compression molding process as described above, the primary compression molded body is used. When the method of heating is applied, the working environment is difficult to deteriorate because the amount of volatilization of the lubricant due to heating is small, and further, the primary compression molded body bursts due to the increase in internal pressure due to volatilization of the mixed lubricant. Prevented in advance.
[0010]
Furthermore, in the secondary compression molding process, the surplus portion is compressed and plastically flowed, so that it is required that the surface of the surplus portion and the mold wall be sufficiently lubricated. Therefore, the present invention is characterized in that, in the secondary compression molding step, as a means for lubricating the primary compression molded body, at least one of the primary compression molded body or the mold wall of the secondary molding die is covered with a lubricant. .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, with reference to the drawings, an embodiment of the present invention for forming a green compact as a material of the member 2 shown in FIGS. 5A and 5B will be described.
1A to 1E show the primary compression molding process, FIGS. 2A to 2D show the secondary compression molding process, and FIG. 3 shows the concept of the method. . The material based on the raw material powder in this case is used for hard alloys such as low-carbon steel, high-carbon steel, low-alloy steel containing carbide-generating elements such as Cr, Mo, V, and W, for example. Moreover, the raw material powder to be used is not mixed with a lubricant. Hereinafter, a procedure for forming a green compact through a primary compression molding process and a secondary compression molding process will be described.
[0012]
(1) Primary compression molding process As shown in FIGS. 1A to 1E, a molding apparatus used in the primary compression molding process includes an upper punch 21 and an internal punch 22a inside a die (primary molding die) 20. And the lower punch 22 comprised by the combination of a pair of external punch 22b is a single axis | shaft type inserted so that each can move to a vertical direction. The internal punch 22a constituting the lower punch 22 is a punch for compressing and molding one thin portion 3 of the green compact, and the external punch 22b is arranged on both sides of the internal punch 22a and has each thickness of the green compact. It is a punch for compression-molding the meat part 4. A cavity 23 corresponding to the shape of the primary compression molded body is formed inside the die 20 by the die 20 and the upper and lower punches 21 and 22. The horizontal hole 1 of the green compact is formed by the core 13, and the planes of the core 13 and the internal punch 22a have the same shape and size.
[0013]
Next, the primary compression molding process by the said shaping | molding apparatus is demonstrated.
First, as shown in FIG. 1A, the upper surface of the inner punch 22a of the lower punch 22 is located slightly below the upper surface of the die 20, and the upper surface of the outer punch 22b of the lower punch 22 is higher than the upper surface of the inner punch 22a. The initial state is located slightly below. Next, as a means for lubricating the raw material powder P, at least the mold wall which is the inner surface of the die 20 is coated with a lubricant (not shown). As the means, a liquid lubricant such as wax is applied to the mold wall, or a powdery lubricant is adhered to the mold wall by an electrostatic coating method. Thereby, compared with mixing of the lubricant in the raw material powder P, the density of the primary compression molded body is increased and the strength is improved. Subsequently, a part of the raw material powder P to be used is filled in the cavity 23 formed by the die 20 and the lower punch 22.
[0014]
Next, as shown in FIG. 1 (b), the die 20 is raised to a predetermined powder filling position, above the filled raw material powder P where the lateral hole 1 is to be formed, that is, above the internal punch 22a. The core 13 is set with the internal punch 22a and the planar projection shape matched. Subsequently, as shown in FIG. 1C, the remaining raw material powder P to be used is filled in the cavity 23. In this state, the core 13 is disposed between the upper and lower thin portions 3 to be molded.
[0015]
Next, as shown in FIG.1 (d), the upper punch 21 is lowered | hung, the raw material powder P is compressed by the predetermined pressure in the vertical direction, and the primary compression molding 2a is shape | molded. When the molding is completed, as shown in FIG. 1 (e), the die 20 is lowered and the primary compression molded body 2a is extracted from the die 20 to obtain the primary compression molded body 2a containing the core 13. The primary compression molded body 2a is formed by integrally forming a surplus portion 4a protruding in the anti-compression direction (downward in this case) on one side of a thick portion 4 in a near net shape corresponding to a green compact to be molded. It becomes. This surplus portion 4a is formed on the basis of the displacement of the relative position of the lower punch 22, that is, the descending amount of the external punch 22b with respect to the internal punch 22a, and its thickness makes the entire density of the green compact to be formed uniform. It is appropriately controlled to make it happen.
[0016]
(2) Secondary compression molding process The primary compression molding 2a obtained in the primary compression molding process is heated by the heating means 25 in a state where it is turned upside down as shown in FIG. 2 (a). As the heating means 25, for example, an electromagnetic induction heating furnace or the like is used. The heating temperature is selected in a range lower than the temperature at which blue brittleness occurs in the material based on the raw material powder P and higher than normal temperature. For example, in the case of carbon steel containing 0.25% carbon, the heating temperature is 100 to 220 ° C. Scope. If the primary compression molding 2a is heated, it will progress to secondary compression molding.
[0017]
As shown in FIGS. 2B to 2D, the molding apparatus used for the secondary compression molding process is a combination of an internal punch 31a and a pair of external punches 31b inside a die (secondary molding die) 30. The upper punch 31 and the lower punch 32 that are configured are each a single-axis type that is inserted so as to be movable in the vertical direction. The internal punch 31a constituting the upper punch 31 is a punch for compression-molding the thin portion 3 between the surplus portions 4a of the primary compression molded body 2a, and the external punch 31b is arranged on both sides of the internal punch 31a. This is a punch for compressing and molding each thick part 4 of the green compact. A cavity 33 corresponding to the shape of the green compact is formed in the die 30 by the die 30 and the upper and lower punches 31 and 32. The die 30 incorporates a heater 34 that holds the heated primary compression molded body at the above temperature.
[0018]
Next, the secondary compression molding process by the molding apparatus will be described.
The die 30 is heated to the above temperature by the heater 34, and the mold wall of the die 30 is covered with a lubricant (not shown) as in the primary compression molding process. Next, as shown in FIG. 2B, the primary compression molded body 2a in a heated state is formed into a cavity 33 formed by the die 30 and the lower punch 32 with the surface on which the surplus portion 4a is formed facing up. Then, the upper punch 31 is lowered. As shown in FIG. 2 (c), the inner punch 31a and the outer punch 31b of the upper punch 31 are lowered at the same pressure to compress the primary compression molded body 2a, thereby forming the secondary compression molded body, that is, the green compact 2A. . During this secondary compression, the surplus portion 4a is plastically flowed and crushed by entering the thick portion 4, and the upper compression surface by the upper punch 31 becomes flat like the lower surface. Thereafter, as shown in FIG. 2 (d), the upper punch 31 is raised, the die 30 is lowered, the green compact 2A containing the core 13 is extracted from the die 30, and the core 13 is further compressed. By extracting from the body 2A, a green compact 2A having a lateral hole 1 is obtained.
[0019]
The green compact 2A obtained through the primary compression molding process and the secondary compression molding process described above is sintered at a predetermined sintering temperature, and is further heat-treated as necessary to obtain a sintered product.
[0020]
In the above-described molding method, in the primary compression molding process, when compressed with the same compression ratio (filling thickness / compact thickness), the density of the thick-walled portion 4 is usually lower than that of the thin-walled portion 3 in advance. The surplus portion 4a is molded in advance, and the whole is compressed at the same pressure in the next secondary compression molding process, and the surplus portion 4a is plastically flowed into the thick portion 4 during the secondary compression. The thick part 4 has the same density as the thin part 3. As a result, the density of the entire green compact 2A obtained is sufficiently uniform. In addition, by performing the compression molding process separately for the primary and secondary, the absolute density of the molded green compact 2A becomes higher than that of one compression molding, and the strength is improved. In addition, in the secondary compression molding step, the primary compression molded body 2a is compressed while being heated, so that the density of the green compact 2A can be further increased. Moreover, since the heating temperature is lower than the temperature at which blue brittleness occurs in the material based on the raw material powder P, the green compact 2A cannot be a brittle material. From these things, a high-quality green compact can be obtained stably.
[0021]
By the way, if the raw material powder P is compressed at a high pressure in the primary compression molding, it is possible to obtain a dense green compact 2A. However, when the compression ratio of the filled raw material powder P is about 2.5, for example. The die 20, the upper and lower punches 21, 22 and the core 13 are required to be longer in the compression direction, and application of high pressure tends to cause damage to these molding die parts. In addition, large distortion occurs in the upper and lower punches 21 and 22 and the core 13, leading to cracks in the primary compression molded body 2 a. In that respect, according to the above molding method, the primary compression molding process is compressed with a reasonable compression ratio and molding pressure to perform primary molding, and in the next secondary compression molding process, general sizing and forging techniques and Since it can handle similarly, there exists an advantage that the burden concerning the metal mold | die part for shaping | molding falls.
[0022]
Specifically, for example, when low-alloy iron powder is compressed with a pressure of 1000 MPa warm, the compression ratio becomes 2.5 and a green compact with a density of 7.5 g / cm ³ is obtained. The shape of the green compact is restricted due to its properties. When the same low alloy iron powder is compressed with a pressure of 500 MPa at ordinary temperature, which is a general condition, the compression ratio becomes 2.2 and a green compact with a density of 6.5 g / cm ³ is obtained. When this is again inserted into the mold as a primary compression molded body and compressed at a pressure of 1000 MPa, that is, when secondary compression molding is performed, the compression ratio becomes 1.2 and the green compact has a density of 7.5 g / cm ³ . You can get a body. Thus, in the secondary compression molding process, the compression ratio can be suppressed, so that a high pressure can be applied, and thus a high-density green compact can be molded.
[0023]
Further, in the primary compression molding process, the mold wall of the die 20 is coated with a lubricant as a means for lubricating the raw material powder P, so that the lubricant is attached only to the surface (friction surface with the die 20). . For this reason, when the primary compression molded body 2a is heated in the secondary compression molding process, the amount of volatilization of the lubricant due to heating is reduced and the working environment is hardly deteriorated. Further, the primary pressure is increased by the increase in internal pressure due to volatilization of the mixed lubricant. Problems such as the bursting of the compression molded body 2a are prevented in advance. Furthermore, since the mold wall of the die 30 is covered with the lubricant also in the secondary compression molding process, lubrication between the surface of the surplus part 4a and the mold wall is sufficient, and the plastic fluidity of the surplus part 4a is improved. . In the secondary compression molding step, the effect is the same even if the surface of the primary compression molded body 2a is covered with a lubricant instead of the die wall of the die 30, and therefore at least one of the two is covered with the lubricant. You just have to do it.
[0024]
In the lubricating means for the raw material powder P in the primary compression molding process described above, a method such as applying a lubricant to the entire surface of the mold wall in contact with all the raw material powders P to be filled is desirable. The method is used. As one of them, the process up to the step of FIG. 1 (a) is the same as described above. As shown in the next FIG. 1 (b), the die 20 is raised and then lubricated again before filling the remaining raw material powder P. The agent is applied to the mold wall of the die 20. In addition, a deep cavity is first formed as shown in FIG. 1 (c), and a lubricant is applied to the mold wall of the die 20 at this stage, and thereafter, FIGS. 1 (a) to (e). Perform compression molding in this order. Such a method is suitable when a lubricant having a relatively low adhesion to the mold wall is used.
[0025]
The above is one embodiment of the present invention, but the present invention is not limited to this embodiment, and for example, the following modifications are possible.
In the above embodiment, the primary compression molding process is a cold (room temperature) treatment and the secondary compression molding process is a warm treatment. However, both processes may be performed cold, and both processes are warm. You may go. When both steps are performed warmly, in the primary compression molding step, the raw material powder P and the die 20 to be filled are heated at the same temperature as the secondary compression molding step, that is, the material based on the raw material powder P becomes blue-hot brittle. The condition is that the temperature is lower than the temperature and higher than the normal temperature. Further, the surplus portion 4a may be formed not only on one side of the thick portion 4 but also on both sides as necessary. In addition, as a means for lubricating the raw material powder P, mold wall lubrication in which the inner surface of the die 20 is coated with a lubricant is employed, but a raw material powder mixed with a lubricant may be used as necessary.
[0026]
In addition, although the said one embodiment is a method of shape | molding the green compact used as the raw material of the member 2 shown to Fig.5 (a), (b), of course, this invention is not limited to this, A compression surface is used. Pressures of various shapes with non-constant thickness in the compression direction, such as having steps or grooves, or having holes or notches extending in the direction intersecting the compression direction in the middle of the thickness in the compression direction Applicable to powder. FIG. 4 shows an example of such a green compact.
[0027]
FIG. 4A shows a green compact as a material for the cam. This green compact is provided with a thin portion 3 and another thick portion 4 by forming a notch 40 at the center in the thickness direction of the cam bottom, and a shaft hole 41 is formed in the thin portion 3.
FIG. 4B shows a green compact as a material of a substantially S-shaped rocker arm for swinging the valve. The green compact is formed with a rocking shaft hole 42 in the center and a notch 40 in which bearings are housed in the center in the thickness direction of both ends, thereby forming the thin portion 3 and the other thick portions 4. A shaft hole 41 of a bearing is formed in the thin portion 3.
FIG. 4 (c) is a green compact which is a modification of the rocker arm of FIG. 4 (b) and is formed in a straight line. Similarly, a rocking shaft hole 42 is formed at the center, and the thickness of both ends is shown. By forming a space 43 penetrating in the width direction in which the bearing is accommodated in the center in the vertical direction, the thin portion 3 and the other thick portion 4 are provided. In the thin portion 3, a shaft hole 41 of the bearing is formed. ing.
[0028]
In any of the green compacts of FIGS. 4A to 4C, after the primary compression molding for molding the surplus portion similar to that of the one embodiment on at least one surface of the thick portion 4, the surplus thickness By performing the secondary compression molding for compressing the part, the entire density can be made sufficiently uniform.
[0029]
【The invention's effect】
As described above, according to the present invention, when forming a green compact having a thick part and a thin part having different thicknesses in the compression direction, the green part protrudes in the anti-compression direction from the thick part . The primary compression molding process in which the raw material powder is compression-molded by the primary molding die in a state in which the surplus part for equalizing the density is provided, and the primary compression molding body obtained in the primary compression molding step are obtained by the secondary molding die. since comprises a desired shape and a secondary compression molding step of compression molding the dimensions as well as compressing the excess meat portion can be the density of the whole can be stably a quality higher it is well homogenized There are effects such as.
[Brief description of the drawings]
FIGS. 1A to 1E are cross-sectional views sequentially showing a primary compression molding process according to an embodiment of the present invention.
FIGS. 2A to 2D are cross-sectional views sequentially illustrating a secondary compression molding process according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing the concept of one embodiment of the present invention.
FIG. 4 is a perspective view showing an example of a green compact that can be molded according to the present invention.
FIG. 5A is a perspective view showing an example of a green compact, and FIG. 5B is a cross-sectional view.
FIG. 6 is a cross-sectional view showing an example of a conventional green compact forming method in the order of steps.
[Explanation of symbols]
2A ... green compact, 4a ... surplus part, 20 ... die (primary molding die),
30 ... Die (secondary mold), P ... Raw material powder.

Claims (5)

A method of forming a green compact having a thick part and a thin part having different thicknesses in the compression direction,
It has two processes, a primary compression molding process with a primary mold and a secondary compression molding process with a secondary mold,
In the primary compression molding step, the whole raw material powder is compression-molded in a state in which the thick-walled portion is provided with a compacted surplus portion that protrudes in the anti-compression direction and uniforms the density of the green compact,
In the secondary compression molding step, the primary compression molded body obtained in the primary compression molding step is compressed while crushing the surplus portion, and a green compact having a desired shape and size is obtained. Powder molding method.   2. The green compact according to claim 1, wherein, in the primary compression molding step, the raw material powder is heated to a temperature lower than a temperature at which blue brittleness occurs in a material based on the raw material powder and higher than a normal temperature. Body molding method.   2. The secondary compression molding step, wherein the primary compression molded body is heated at a temperature lower than a temperature at which blue brittleness occurs in a material based on the raw material powder and higher than a room temperature. The green compact molding method.   3. The green compact molding method according to claim 1 or 2, wherein in the primary compression molding step, a mold wall of the primary molding die is covered with a lubricant as a lubricating means for the raw material powder.   The said secondary compression molding process WHEREIN: At least one of the said primary compression molding body or the mold wall of the said secondary molding die is coat | covered with a lubricant as a lubrication means of the said primary compression molding body. 4. A method for forming a green compact according to 1 or 3.

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