JP6303920B2 - Manufacturing method of powder molded product - Google Patents

Description

  The present invention relates to a method for producing a molded product by packing powder into a mold and pressing it. More specifically, the present invention relates to a method for manufacturing a powder molded product in which the quality of the molded product is stabilized by uniformly filling the mold with the powder.

  Conventionally, as one method for producing a molded product, a mold molding compression method using powder as a raw material has been used. In this method, a mold is filled with powder and pressed to obtain a molded body having a desired shape. In many cases, the raw material powder is metallic, and the pressed body is made into a product through a sintering process by heating. As a conventional technique related to this mold molding compression method, a technique described in Patent Document 1 can be cited. In the technology of this document, when powder is supplied from an upper powder box to a mold, a powder box having a shutter mechanism at its supply port is used. The shutter mechanism is opened only when the powder box supply port is aligned with the upper opening of the mold. In this way, the filling of the powder into the mold is made uniform.

JP 2006-37219 A

  However, the conventional mold molding compression method has a problem that it has become difficult to uniformly fill the mold with powder, particularly with recent downsizing. If the size of the molded product to be manufactured is small, the internal space of the mold is naturally small. This means that the wall effect is highly governed by the movement of powder moving from the powder box to the mold. For this reason, when the powder is charged with static electricity, the electrostatic force between the powder and between the powder and the wall surface of the mold affects the filling degree. In particular, when using a large powder box that contains a large number of powders instead of a single molded product, the electrostatic charge of the powder varies with each supply, so the degree of filling varies and quality varies. It was connected. Even with the technique of the above-mentioned Patent Document 1, it has not been a sufficient improvement for this problem.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide a method for producing a powder molded product in which the degree of filling of the powder into the mold is made uniform and a molded product of stable quality can be obtained.

The method for producing a powder molded product according to one aspect of the present invention includes a filling step of supplying raw material powder from above into a mold having an opening on the upper surface and filling the inside of the mold with raw material powder; A method of manufacturing a powder molded product by performing at least a pressurizing step of pressurizing the raw material powder filled therein, and in the filling step, the lower surface is an opening surface on the mold opening. performs the supply of the raw material powder by powder box housing the raw material powder therein to pass, as a powder box, along with a zoned shape in a direction intersecting the direction of the passing over, within each zone The volume distribution of the space is proportional to the volume distribution of the internal space of each zone when the internal space of the mold is zoned similarly to the zoning of the powder box.

  In the method for manufacturing a powder molded product in the above aspect, the raw material powder supplied from the powder box does not often move beyond the zone in the mold in the filling step. For this reason, the raw material powder is less likely to be electrostatically charged due to friction during supply. As a result, the inside of the mold is uniformly filled with the raw material. For this reason, there is little variation in the quality of the finished powder molded product.

  According to this configuration, there is provided a method for manufacturing a powder molded product in which the degree of powder filling into the mold is made uniform, and a molded product of stable quality can be obtained.

It is a partial cutaway perspective view which shows an example of the metal mold | die made into object by embodiment. It is a top view of the metal mold | die of FIG. It is sectional drawing of the metal mold | die of FIG. It is a perspective view of the powder box used by an embodiment to a metallic mold of Drawing 1. It is a top view explaining the relationship between the metal mold | die of FIG. 1 and the powder box of FIG. It is a graph which shows the cavity volume for every zone in the metal mold | die of FIG. (Comparative example) It is a graph which shows the transition of the weight of each molded object at the time of using a large sized powder box. It is a perspective view which shows the metal mold | die and powder box in another embodiment. It is a flowchart explaining the procedure of the shape design of a powder box. It is a top view of the metal mold | die of FIG. It is a perspective view explaining allocation of the volume to a metallic mold and a powder box. It is a perspective view which shows the shape of the powder box used with respect to the metal mold | die of FIG.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. First, an example of the metal mold | die used for manufacture of a molded article by this form is shown in FIGS. 1-3. 1 to 3 has a substantially cylindrical shape as a whole, and a circular dish-shaped recess 91 is formed on the upper surface. The diameter of the dish-shaped recess 91 is slightly smaller than the overall diameter of the mold 90. In addition, a pit-shaped recess 92 deeper than the dish-shaped recess 91 is formed at three locations on the edge of the dish-shaped recess 91. Each pit-shaped recess 92 is formed straight in parallel with the axial direction of the mold 90, and its cross-sectional shape is a shape obtained by slightly deforming a trapezoid into an arc shape. The dish-shaped recess 91 as well as the pit-shaped recess 92 are bottomed and do not penetrate the mold 90.

In the mold 90, the dish-shaped recess 91 and the pit-shaped recess 92 are cavities, and the entire upper surface is an opening 93. Further, as can be seen from FIG. 3, a back recess 94 is formed from the lower surface side of the mold 90. Back recess 94, because you are installing the die 90 to the press apparatus, and a shape for weight reduction. Of course, neither the dish-shaped recess 91 nor the pit-shaped recess 92 is connected to the back recess 94.

  In FIG. 1, a part of the mold 90 is cut out. This is to show the state of the pit-like recess 92 formed inside. Of course, the actual mold 90 is not incised. 2 is a plan view of the mold 90, and FIG. 3 is a sectional view of the mold 90 (position AA in FIG. 2). With this mold 90, a molded product having a shape having a disc portion derived from the dish-shaped recess 91 and a leg portion derived from the pit-shaped recess 92 is manufactured.

In this embodiment, a molded product is manufactured by the following procedure (1) → (2) → (3).
(1) Filling process (2) Pressurizing process (3) Sintering process

  The feature of this embodiment is the filling step (1) among the above three steps. The filling process of this embodiment is basically based on a scraping method. That is, a powder box is used separately from the mold 90, and the powder that is the raw material of the molded product to be manufactured is stored in the powder box. The powder box has an open bottom surface. As the powder box passes over the opening 93 of the mold 90, the powder is supplied from the powder box to the mold 90. The supplied powder fills the dish-shaped recess 91 and the pit-shaped recess 92 of the mold 90. The basics of filling the mold 90 by this scraping method are as described in Patent Document 1 (reference: FIG. 2 of Patent Document 1).

  However, in this embodiment, as described in the same document, it is not necessary to start supplying the powder for the first time in a state where the supply port of the powder box matches the opening of the upper part of the mold. The powder supply may be started as soon as the opening 93 of the mold 90 and the lower surface (supply port) of the powder box start to partially overlap due to the movement of the powder box. Therefore, in this embodiment, it is not necessary to provide a “shutter mechanism” as described in Patent Document 1 on the lower surface of the powder box. The feature of the filling process in this embodiment is the shape of a powder box as will be described later.

  In the pressurizing step (2) subsequent to the filling step, the powder filled in the mold 90 is pressurized. That is, using an appropriate press device, the upper punch is pressed against the powder from above, and the mold 90 is pressed upward and the upper punch is pressed downward (reference: FIG. 1 of Patent Document 1). As a result, the powder in the mold 90 is compressed into a molded body in the shape of the cavity of the mold 90. In applications where this molded body can be used as it is, it may be a product as it is, but in many cases, this molded body is made into a product through the subsequent sintering step (3). That is, in the sintering process, the powders are fixed to each other by local melting by heating, and the entire compact becomes a solid body having one stable shape.

  Next, the powder box used in this embodiment will be described. The powder box 10 used with respect to the metal mold | die 90 with this form is shown in FIG. The powder box 10 has a shape partitioned into four zones 1 to 4. That is, the size in the length direction (upper right-lower left in FIG. 4) differs depending on the zone. The size in the height direction (vertical direction in FIG. 4) is the same in any zone. The size in the width direction (upper left-lower right in FIG. 4) will be described later.

  The powder box 10 is used by being moved in a fixed direction with respect to the mold 90. This will be described with reference to FIG. In the plan view of FIG. 5, the arrow B is the moving direction of the powder box 10 relative to the mold 90. This moving direction B corresponds to the length direction of the powder box 10 described above. The arrangement of the mold 90 with respect to the moving direction B is also determined. That is, in the case of the example of FIG. 5, two of the three pit-shaped recesses 92 are positioned parallel to the moving direction B, and the remaining one is in a direction perpendicular to the moving direction B (the width direction of the powder box 10 described above). It arrange | positions so that it may be located in the end. With respect to the cavity of the mold 90 arranged in this way, the zones 1 to 4 are defined as follows.

Zone 1: A zone which is located at the end in the width direction and includes only the dish-shaped recess 91 and does not include the pit-shaped recess 92.
Zone 2: A zone including a dish-shaped recess 91 and two pit-shaped recesses 92.
Zone 3: A zone that is not at the end in the width direction, includes only the dish-shaped recess 91, and does not include the pit-shaped recess 92.
Zone 4: A zone that is located at the extreme end in the width direction (however, opposite to zone 1) and includes one pit-like recess 92 and a few dish-like recesses 91

  However, the arrangement of the mold 90 and the zoning are examples, and the present invention is not limited to this.

Corresponding to this zoning, the size of each zone of the powder box 10 is determined as follows.
Width direction size: It matches the width of each zone.
Length direction size: The length is determined so that the volume of each zone of the powder box 10 is proportional to the volume of the cavity of the mold 90 in each zone.

  According to the above-mentioned definition in the width direction, the full width of the powder box 10 coincides with the full width occupied by the cavity of the mold 90 in the width direction. In the example of FIG. 5, this is equal to the diameter of the dish-shaped recess 91. Moreover, it can be seen from the definition in the length direction that the volume of each zone of the powder box 10 is proportional to the volume of the cavity of the mold 90 in each zone.

The determination of the size in the length direction of each zone of the powder box 10 will be further described with reference to FIG. The graph of FIG. 6 shows the cavity volume for each zone in the mold 90. The following can be said about each volume V1-V4.
The volume V1 of the zone 1 includes only the dish-shaped concave portion 91 having a shallow depth, and the area is not so large, so V1 is small.
Zone 2 volume V2: V2 is considerably larger than V1 because it includes two deep recesses 92.
The volume V3 of zone 3 includes only the dish-shaped recess 91, but V3 is larger than V2 because the area is very large.
Volume V4 of zone 4: Although the area itself is smaller than zone 1, it includes one pit-like recess 92, so V4 is larger than V1. However, it is not as high as V2.

  Of course, this size relationship is also an example, and depending on the relationship between the depth of the dish-shaped recess 91 and the pit-shaped recess 92 and the cross-sectional area, the size may be different from the above.

The volumes U1 to U4 of the zones of the powder box 10 are proportional to the volumes V1 to V4. That is, using the coefficient k that takes into account compression in the pressurization process,
U1 = k × V1
It can be expressed as. The same applies to the volumes U2 to U4.

Further, the widths W1 to W4 of each zone are determined from FIG. Furthermore, when the height direction size of the powder box 10 in FIG. 4 is H, the length direction sizes L1 to L4 of each zone are determined. That is, for the length L1 of zone 1,
L1 = U1 / (W1 × H)
It can be expressed as. The same applies to the lengths L2 to L4. The shape of the powder box 10 is determined in this way. Moreover, although the partition plate which partitions off each zone may be inside the powder box 10, it does not need to be. Basically, there is no such partition plate.

  In addition, as described above, the powder box 10 is basically a small-sized container that accommodates the raw material powder for one supply to the mold 90. Since the powder box 10 having the shape determined as described above is used, in this embodiment, the state of movement from the powder box 10 at the time of supply to the mold 90 is not significantly different in any zone. In particular, the powder hardly moves between the zones after entering the cavity of the mold 90. Thereby, a substantially uniform filling state can be obtained anywhere in the cavity of the mold 90. Since it is used in the pressurization process in this state, there is almost no variation in the quality of the finished product depending on the part.

  Furthermore, since the powder box 10 is small, the pressing device in the pressing process itself can be small, and there is little variation in quality among products when many products are manufactured. This will be described with reference to FIG. FIG. 7 is a graph showing the change in the weight of each molded body when a molded body having the same shape is continuously molded using a large powder box. In the graph of FIG. 7, the weight of the subsequent molded body gradually decreases with respect to the weight G1 of the first molded body. And after about 30th, it is almost stable near the weight G2. The weight G2 is about 4 to 5% lighter than the weight G1, and this is not a small difference.

  It is thought that the cause of this phenomenon is that the powder is charged with static electricity. There is a certain waiting time after the powder is stored in the powder box until the supply to the mold is actually started. Even if a certain amount of static electricity is generated when the powder is stored in the powder box, the static electricity is considered to have been discharged during the waiting time. For this reason, the powder first supplied from the powder box is hardly charged with static electricity and has high fluidity. Therefore, the filling degree in the mold is high. As a result, the molded product obtained at this time has a high density.

  However, when the supply of powder from the powder box is started, the powder moves, and static electricity is generated by friction. For this reason, static electricity gradually accumulates in the powder in the powder box. Then, the fluidity of the powder decreases due to the electrostatic attractive force between the powders, and the filling degree of the mold decreases. Therefore, the result shown in FIG. 7 is obtained. It can be seen from FIG. 7 that the powder charge is saturated when the supply of the powder proceeds to some extent, and is stable in that state. Further, the reason why the weight is temporarily increased at the 200th position in FIG. 7 is that the supply of the powder is temporarily stopped at that time. It is considered that the static electricity was discharged to some extent during the pause and the charge amount decreased. Even in the example as shown in FIG. 7, if the initial molded product is excluded, the variation between the remaining products is small. But that will always be a waste.

  On the other hand, if the small powder box 10 is used as in this embodiment, only the first molded product in FIG. 7 is obtained each time. For this reason, it is possible to manufacture with little variation in quality and without waste. This effect is not obtained simply by downsizing the powder box, but can be obtained only by using the powder box 10 having the special shape described above. This is because, in a powder box that is simply miniaturized, the powder moves between zones in the mold.

  Then, the example which designs the specific shape of a powder box with respect to the shape of a metal mold | die is demonstrated. In this example, it is assumed that the powder box 20 is supplied to the mold 80 shown in FIG. However, the powder box 20 in FIG. 8 is a conceptual stage in the course of design, and does not indicate a fixed shape of the powder box 20.

  The mold 80 in FIG. 8 differs from the mold 90 in FIG. 1 in the following two points. First, the die 80 has four pit-like recesses 82 (three pit-like recesses 92 of the die 90). Secondly, the dish-shaped recess 81 of the mold 80 is annular (the dish-shaped recess 91 of the mold 90 is circular). There is an island portion 85 inside the annular dish-shaped recess 81. The part of the island part 85 is not a cavity. From such a mold 80, a molded product having a shape having a disk portion with a hole derived from the annular dish-shaped concave portion 81 and four leg portions derived from the pit-shaped concave portion 82 is manufactured.

The shape design of the powder box 20 is performed according to the procedure shown in FIG. First, the moving direction of the powder box relative to the mold 80 is determined (step 1). Although there is no absolute method for this determination, the direction of movement is selected so that the following two points can be divided when zoning later.
1.1 Zones that do not have significantly different cavities.
2. The total number of zones is not very large.

  Here, the moving direction is determined as indicated by an arrow P with respect to the plan view of the mold 80 shown in FIG. The mold 80 shown in FIG. 10 has four pit-like recesses 82 positioned at the upper right, lower right, upper left, and lower left. On the other hand, the moving direction P is determined in the horizontal direction in the figure. This is a moving direction intended to be divided into three zones, zone 11 to zone 13. That is, the zones 11 and 13 include two pit-like recesses 82 and one dish-like recess 81 therebetween, and the zone 12 includes two dish-like recesses 81 separated by an island 85. In FIG. 10, the letters “foot” are applied to the pit-shaped recess 82 and the letters “rib” are applied to the dish-shaped recess 81. They are identified by the front and rear and the left and right with respect to the moving direction P.

  Subsequently, the volume distribution of each part of the cavity in the mold 80 is calculated (step 2 in FIG. 9). That is, as shown in FIG. 11, the four pit-shaped concave portions 82 of the mold 80 are defined as a C part (right rear), a D part (left rear), an E part (right front), and an F part (left front). In addition, in the dish-shaped recess 81, a rear portion with respect to the moving direction P is a J portion, and a front portion is an M portion. The volume of each part can be calculated from the shape data of the mold 80.

  Next, the volume distribution to each partial element of the powder box 20 is assigned corresponding to the calculated volume of each part of the mold (step 3 in FIG. 9). Here, the filling order when the powder box 20 is moved is also considered. That is, the volume of the partial elements C1, D1, E1, F1, J1, M1 in the powder box 20 corresponding to the above C part, D part, E part, F part, J part, M part. To decide. This determination is based on multiplying the volume of the C part, D part, E part, F part, J part, and M part calculated in the previous step by the compression coefficient k described above.

Next, considering the ease of storing the powder in the powder box 20, the respective subelements C1, D1, E1, F1, J1, and M1 are reorganized for each zone (FIG. 9). Step 4). Individually, the above-mentioned zoning (zone 11 to zone 12) is followed. That is, each subelement belongs to each element as follows.
Zone 11: All of D1 and F1 parts, part of J1 and M1 part Zone 12: Part of J1 and M1 part Zone 13: All of C1 part and E1 part, J1 part and M1 part Each part of

  That is, the J1 portion and the M1 portion are further divided in the width direction at this stage. Thereby, the volume for each zone in the powder box 20 is determined. In this example, the volumes of the zone 11 and the zone 13 are relatively large. This is because it includes two pit-like concave portions 82 each having a deep depth. On the other hand, the volume of the zone 12 is small. This is because only the dish-shaped recess 81 having a shallow depth is included.

  Finally, the specific shape of the powder box 20 is determined based on the volume for each zone obtained in the previous step (step 5 in FIG. 9). Here, as in the case of the powder box 10 described above, the height direction size of the powder box 20 is made uniform, and the volume distribution of each zone is realized by the length direction size. The result is shown in FIG.

  That is, the powder box design method in this embodiment is such that the lower surface is an opening surface for supplying raw material powder from above to a mold having an opening on the upper surface and filling the inside of the mold with raw material powder. And a volume distribution calculation process for calculating a volume distribution of each divided element obtained by dividing the internal space of the mold into a plurality of parts, and a volume distribution calculated in the volume distribution calculation step. Based on the zone volume allocation determination process for determining the volume allocation for each zone in the direction intersecting the direction in which the powder box moves the mold to supply the raw material, and the zone volume allocation determination process. A shape determining process for determining a dimensional element for each zone in the powder box so as to realize volume distribution for each zone.

  As described in detail above, according to the present embodiment, the powder boxes 10 and 20 have a shape having a volume corresponding to a required supply amount for each zone of the molds 80 and 90 to be supplied for each zone. ing. As a result, the degree of powder filling in the mold was made uniform. Therefore, a method for producing a powder molded product has been realized in which the variation in quality of each part of the molded product is small and the variation in quality among a large number of molded products is also small.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the present embodiment, volume distribution for each zone in the powder boxes 10 and 20 is realized by adjusting the lengthwise size of each zone. However, the present invention is not limited to this, and may be realized by adjusting the height direction size of each zone, or may be realized by adjusting both the length direction size and the height direction size. That is, it is sufficient that at least one of the length direction size and the height direction size is different depending on the zone. However, in order to reduce the overall height of the powder box and cope with the downsizing of the press machine, the method of this embodiment that realizes volume distribution only by the length direction size, with the height direction size of the powder box uniform. It is advantageous. Providing a zone with a small size in the height direction is because that portion becomes a dead space.

  In the powder boxes 10 and 20 of this embodiment, the size in the length direction of each zone is realized by making the rear end side in the moving direction a flat surface and making the front end side uneven. However, the present invention is not limited to this, and the length in the length direction of each zone may be realized in the same manner by providing unevenness on the rear end surface side with the front end side being a flat surface. Of course, both the front end face side and the rear end face side may be uneven.

1-4, 11-13 Zone 10, 20 Powder box 80, 90 Mold 93 Opening

Claims (1)

A filling step of supplying raw material powder from above into a mold having an opening on the upper surface and filling the inside of the mold with raw material powder; and a pressurizing step of pressurizing the raw material powder filled in the mold; In a method for producing a powder molded product by performing at least
In the filling step,
On the opening of the mold, the lower surface is an open surface and the raw material powder is supplied by passing through the powder box containing the raw material powder inside.
As the powder box ,
With a zoned shape in a direction intersecting the direction of the passing over,
The volume distribution of the internal space of each zone is proportional to the volume distribution of the internal space of each zone when the internal space of the mold is zoned in the same manner as the zoning of the powder box. A method for producing a powder molded product.

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