Forming die assembly for microcomponents

A forming die assembly for microcomponents includes a forming die, a plunger, and a punch. The forming die is formed with an outer die, an inner die, a storage portion formed at the inner die, and a punch hole formed at the inner die. The inner die slidably inserted into the outer die forms a part of a cavity between the inner die and the outer die. The storage portion stores a raw material with a metal powder and a binder having plasticity. The punch hole connects the cavity and the storage portion and forms a gate therebetween. The plunger slidably inserted into the storage portion fills the raw material stored in the storage portion into the cavity through the punch hole. The punch is slidably inserted into the plunger, and it closes the gate and compresses the raw material in the cavity.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a forming die assembly including dies that may be used for producing microcomponents such as microgears. In the dies, a raw material with a metal powder and a binder having plasticity is compacted into a green compact with a shape similar to that of the microcomponent.

2. Background Art

Recently, in the production of digital home appliances, advanced medical equipment, and IT devices, there are trends toward decreasing dimensions and increasing performances of the devices. Therefore, requirements for decreasing dimensions and wall thicknesses have been increasing for components of such devices. In view of this, although microcomponents basically have small dimensions and thin walls, the microcomponents are also required to be even smaller and have thinner walls. A production method for such microcomponents is disclosed in Japanese Patent Application of Laid-Open No. 2006-344581. In this method, a raw material with a metal powder and a binder having plasticity is filled in a die and is compressed by a punch, whereby a green compact with a shape similar to that of the target shape is formed. Then, the green compact is sintered.

According to the production method of the green compact disclosed in Japanese Patent Application of Laid-Open No. 2006-344581, the raw material is sufficiently filled at a portion of the die, which corresponds to a thin-walled portion of the target shape. Therefore, a green compact with high accuracy is obtained. In this case, since the raw material is different from a raw powder, which is used in an ordinary powder metallurgy process, and has plasticity, the raw material is difficult to use. That is, a predetermined amount of the raw material must be directly filled in the die, and this increases the steps in the process. The raw material is filled in the die at each compacting as is the case in an ordinary die forming for compacting a powder. However, in a case of forming a microcomponent, since the amount of raw material required for one compacting is extremely small, this production method is not efficient.

SUMMARY OF THE INVENTION

The present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a forming die assembly for microcomponents. According to the forming die assembly, a raw material with a metal powder and a binder having plasticity (hereinafter called a “raw material”) is easily supplied to dies and is thereby efficiently compacted, whereby a green compact is obtained.

The present invention provides a forming die assembly for microcomponents, and the forming die assembly includes a forming die, a plunger, and a punch. The forming die is formed with an outer die, an inner die, a storage portion formed at the inner die, and a punch hole formed at the inner die. The inner die is formed so as to be slidably inserted into the outer die and to form at least a part of a cavity between the inner die and the outer die. The storage portion is used to store a raw material with a metal powder and a binder having plasticity. The punch hole connects the cavity and the storage portion so as to form a gate therebetween. The plunger is formed so as to be slidably inserted into the storage portion and to fill the raw material stored in the storage portion into the cavity through the punch hole. The punch is slidably inserted into the plunger in the sliding direction of the plunger, and it opens and closes the gate by reciprocatory sliding. The punch closes the gate and compresses the raw material in the cavity into a green compact by sliding in the direction of the cavity.

According to the present invention, the raw material stored in the storage portion of the forming die is filled in the cavity by the plunger, and the raw material in the cavity is compacted into a green compact by the punch. Then, the forming die assembly is opened, whereby the green compact is obtained. By repeating the above operation, green compacts are continuously obtained. The raw material in a small amount is easily supplied to the cavity by the plunger, and the punch is not required to be pulled out, whereby the green compact is efficiently produced.

The raw material is supplied to the storage portion when the plunger is pulled out from the storage portion. The plunger and the inner die, into which the punch is inserted, may be used as a set, and plural sets may be prepared. In this case, while one set is inserted to the outer die and is operated, maintenance can be performed on the other sets of the inner die, the plunger, and the punch. Moreover, the raw material can be supplied to the storage portion of each set beforehand. Therefore, it is not required to intermit the operation for the supply of the raw material, whereby the production efficiency is more improved.

In the present invention, the forming die may be provided with an upper die and a lower die which are arranged so that they can relatively vertically make contact with each other and separate from each other. In this case, one of the upper die and the lower die may be provided with the outer die and the inner die. The cavity may be formed when the upper die and the lower die are brought into contact with each other.

In the present invention, the green compact may have a flange portion and a shaft portion, and the shaft portion may project from the flange portion.

Moreover, in the present invention, in order to improve the flowability of the raw material and to easily fill the raw material into the cavity, the forming die is preferably provided with a heating means for heating the raw material in the storage portion.

According to the present invention, a forming die assembly for microcomponents is provided, and the raw material is easily supplied to the forming die, and thereby a green compact is efficiently obtained.

PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will be described with reference to the figures hereinafter.

1 First Embodiment

FIG. 1shows a microgear (hereinafter called a “gear”) of a microcomponent. The gear1is obtained by sintering a green compact that is formed by a forming die assembly of a First Embodiment. The gear1has a spur wheel portion3and columnar shaft portions4and5which have the same length. The spur wheel portion3is formed with plural teeth2at the outer circumferential surface thereof. Each of the shaft portions4and5perpendicularly extends on either side from the center of the spur wheel portion3. The gear1may have the following dimensions. For example, the spur wheel portion3has an outer diameter D1of several hundred micrometers to several millimeters, and the shaft portions4and5have a diameter D2of several dozen to several hundred micrometers.

1-2 Forming Die Assembly

FIGS. 2A to 2DandFIGS. 3A to 3Dshow steps for forming a green compact of the gear1by a forming die assembly of a First Embodiment. First, the structure of the forming die assembly will be described with reference toFIGS. 2A to 2D. As shown inFIGS. 2A to 2D, a reference numeral10denotes a forming die, and the forming die10is formed of an upper die20and a lower die30. The upper die20and the lower die30are vertically movably provided and are arranged so that they can relatively vertically make contact with each other and separate from each other.

The upper die20is provided with an outer die21and an inner die25. The outer die21and the inner die25have horizontal lower surfaces21aand25a, respectively. The outer die21is formed with a cylindrical hole22that vertically penetrates through the outer die21, and the inner die25in a cylindrical shape is slidably inserted into the cylindrical hole22. The cylindrical hole22has an inner circumferential surface with a shape corresponding to the shape of the teeth2of the spur wheel portion3of the gear1. Alternately, as shown inFIG. 4, the cylindrical hole22may have an inner circumferential surface at the lower end portion, and this inner circumferential surface is formed with internal teeth22afor forming the teeth2of the spur wheel portion3of the gear1.

The inner die25has an inside that is formed with a storage portion26for storing a raw material, and the storage portion26extends in the vertical direction and has an opening at the upper side. The storage portion26has a cylindrical inner circumferential surface and has a tapered portion26aat the lower end portion, and the tapered portion26ahas a conical shape that is downwardly tapered. The inner die25is also formed with an upper punch hole27at the inside and has a lower surface25a. The upper punch hole27downwardly extends from the lower end of the tapered portion26aand has an opening at the side of the lower surface25a. The upper punch hole27is concentric with the storage portion26, and the upper punch hole27and the storage portion26have a gate28therebetween. The upper punch hole27has an inner diameter that is set so as to be the same as the diameters of the shaft portions4and5of the gear1.

The storage portion26of the inner die25is formed so as to be filled with a raw material P, which has plasticity, from the opening at the upper side, whereby the raw material P is stored. The raw material P may be a powder that is formed by mixing 40 to 60 volume % of a binder with a metal powder and by kneading them. The metal powder may be an iron powder, and the binder may be made of thermoplastic resin and wax.

The storage portion26is formed so that a plunger40is slidably inserted thereinto from the opening at the upper side. The plunger40has a shaft center through which an upper punch50slidably penetrates in a vertical direction that is a sliding direction of the plunger40. The upper punch50has a lower end portion, and the lower end portion is slidably inserted into the upper punch hole27when the upper punch50is lowered. In this case, the gate28is closed by the upper punch50. By raising the upper punch50in a condition in which the gate28is closed, the upper punch50is pulled out from the upper punch hole27, and the gate28is opened as shown inFIG. 2B.

The lower die30has a horizontal upper surface30athat can be brought into contact with the lower surface21aof the outer die21of the upper die20. The lower die30is formed with a lower punch hole33that vertically extends and penetrates the lower die30, and the lower punch hole33is coaxial with the upper punch hole27. The lower punch hole33has the same diameter as that of the upper punch hole27, that is, has an inner diameter corresponding to the diameters of the shaft portions4and5of the gear1. The lower punch hole33is formed so that a lower punch60is slidably inserted thereinto.

(1-2-2) Forming Step

A forming step for a green compact of the gear1using the forming die assembly of the First Embodiment will be described with reference toFIGS. 2A to 2DandFIGS. 3A to 3D. First, the inner die25of the upper die20is inserted into the outer die21so that the internal teeth22aat the lower end portion of the cylindrical hole22are exposed. The lower surface21aof the outer die21and the upper surface30aof the lower die30are brought into contact and are clamped. Then, the upper punch50at the side of the upper die20is inserted into the upper punch hole27so as to close the gate28, and the lower punch60at the side of the lower die30is lowered. Thus, a cavity11with a cruciform section is formed in the forming die10. The cavity11has a portion corresponding to the spur wheel portion3and the shaft portion4at the upper side of the gear1at the side of the upper die20. The cavity11also has a portion corresponding to the shaft portion5at the lower side of the gear1at the side of the lower die30. On the other hand, the raw material P is supplied to the storage portion26of the inner die25until the storage portion26is almost filled, and the leading end of the plunger40is inserted into the storage portion26(FIG. 2A).

Next, the upper punch50is raised and is pulled out from the upper punch hole27, whereby the gate28is opened. Thus, the cavity11and the storage portion26are connected via the upper punch hole27. In this condition, the plunger40is pressed down, whereby a necessary amount of the raw material P is filled from the gate28to the cavity11(FIG. 2B).

Then, the upper punch50is pressed down so as to close the gate28, and the upper punch50is further pressed down so as to compact the raw material P in the cavity11(FIGS. 2C and 2D). Thus, the spur wheel portion3is formed between the inner die25of the upper die20and the lower die30, and the shaft portions4and5are formed at the upper punch hole27and the lower punch hole33, respectively. Accordingly, a green compact1A of a gear1is formed.

After the green compact1A is formed in the forming die10as described above, the forming die10is opened so as to pull out the green compact1A. In this case, the outer die21of the upper die20is raised so that the lower surface21ais at the same level as the lower surface25aof the inner die25, whereby the spur wheel portion3is exposed (FIG. 3A). Then, the outer die21and the inner die25are raised while the upper punch50holds down the green compact1A, whereby the shaft portion4at the upper side of the gear1is exposed (FIG. 3B). Next, the entire of the structural components at the side of the upper die20is raised (FIG. 3C), and the lower punch60is raised, whereby the shaft portion5at the lower side of the gear1is upwardly pulled out from the lower punch hole33(FIG. 3D).

As described above, one green compact1A is formed by such an operation. After the green compact1A is removed from the forming die assembly, the condition of the forming die assembly is returned to the condition shown inFIG. 2A. Then, by repeating the above operation, a green compact1A is formed. Such forming operation of the green compact1A is repeated until the raw material P in the storage portion26is used up.

According to the forming die assembly of the First Embodiment, the upper punch50is raised so as to open the gate28, and the raw material P stored in the storage portion26in the forming die10is filled in the cavity11by the plunger40. Next, the upper punch50is pressed down so as to close the gate28, and the raw material P in the cavity11is subsequently compacted by the upper punch50. Then, the forming die assembly is opened, whereby a green compact1A is obtained. By repeating this operation, green compacts1A are successively obtained. A small amount of the raw material P is easily filled in the cavity11by pressing down the plunger40without pulling out the upper punch50. Accordingly, even when the amount of the raw material P is small in one forming, the green compact1A is efficiently produced.

After the raw material P in the storage portion26is used up, the plunger40is pulled out from the inner die25, and new raw material P is supplied to the storage portion26. Then, the plunger40is inserted into the inner die25again in order to proceed the forming operation. In this embodiment, the plunger40and the inner die25, into which the upper punch50is inserted, may be used as a set. In this case, plural sets may be prepared, and one set is inserted into the outer die21and is operated. According to this manner, maintenance can be performed on the other sets of the inner die25, the plunger40, and the upper punch50, while the forming die assembly is operated. Moreover, the raw material P can be supplied to each set beforehand. Therefore, it is not required to intermit the operation for the supply of the raw material P, whereby the production efficiency is more improved.

Next, a Second Embodiment and a Third Embodiment of the present invention will be described with reference toFIGS. 5,6A to6D,7A to7D, and8, andFIGS. 9A to 9D,10A to10D, and11, respectively. In these figures, structural components similar to the structural components in the First Embodiment have the same reference numerals as those of the structural components in the First Embodiment, and descriptions for these structural components are omitted or simplified.

2 Second Embodiment

FIG. 5shows a microgear of a microcomponent. The gear7is obtained by sintering a green compact that is formed by a forming die assembly of a Second Embodiment. The gear7is a two-step gear in which a spur wheel portion6is formed on a side (upper side inFIG. 5) of a spur wheel portion3. The spur wheel portion6has a smaller diameter, and the spur wheel portion3has a larger diameter. The spur wheel portion6is formed with plural teeth2at the outer circumferential surface thereof. The gear7also has shaft portions4and5. The shaft portion4projects from the spur wheel portion6, and the shaft portion5projects from the spur wheel portion3. The gear7may have the following dimensions. For example, the spur wheel portion3has an outer diameter D1of several hundred micrometers to several millimeters, and the shaft portions4and5have a diameter D2of several dozen to several hundred micrometers.

2-2 Forming Die Assembly

FIGS. 6A to 6DandFIGS. 7A to 7Dshow a forming step of a green compact of the gear7by the forming die assembly of the Second Embodiment. In the forming die assembly of the Second Embodiment, the cylindrical hole22of the outer die21of the upper die20has an inner circumferential surface with a shape corresponding to the shape of the teeth2of the spur wheel portion3of the gear7. Alternately, as shown inFIG. 8, the cylindrical hole22may have an inner circumferential surface at the lower end portion that is formed with internal teeth22aas is the case in the First Embodiment. The internal teeth22aare used for forming the teeth2of the spur wheel portion3of the gear7.

On the other hand, the lower die30is formed with a cylindrical hole31. The cylindrical hole31has openings at both ends and has an inner circumferential surface with a shape corresponding to the shape of the teeth2of the spur wheel portion6of the gear7. The cylindrical hole31is formed so that an inner die32is vertically slidably inserted thereinto. Alternately, as shown inFIG. 8, the cylindrical hole31may have an inner circumferential surface at the upper end portion, and this inner circumferential surface is formed with internal teeth31afor forming the teeth2of the spur wheel portion6of the gear1. The inner die32has a center formed with a lower punch hole33, and the lower punch hole33is formed so that the lower punch60is slidably inserted thereinto. The inner die32and the lower punch60are coaxially arranged with the plunger40and the upper punch50at the side of the upper die20.

(2-2-2) Forming Step

The above structural components are different from the structural components of the First Embodiment. A forming step for a green compact of the gear7using the forming die assembly of the Second Embodiment will be described with reference toFIGS. 6A to 6DandFIGS. 7A to 7D. First, the inner die25of the upper die20is inserted into the outer die21so that the internal teeth22aat the lower end portion of the cylindrical hole22are exposed. The lower surface21aof the outer die21and the upper surface30aof the lower die30are brought into contact and are clamped. Then, the upper punch50at the side of the upper die20is inserted so that the lower end surface is at the same level as the lower surface25aof the inner die25, whereby the gate28is closed. The inner die32is positioned lower than the lower die30so as to expose the internal teeth31aat the upper end portion of the cylindrical hole31. Moreover, the lower punch60is lowered more than the inner die32so as to form a cavity11in the forming die10. The cavity11has a portion corresponding to the spur wheel portion3of the gear7at the side of the upper die20. The cavity11also has a portion corresponding to the spur wheel portion6and the shaft portion4of the gear7at the side of the lower die30. On the other hand, the raw material P is supplied to the storage portion26of the inner die25until the storage portion26is almost filled, and the leading end of the plunger40is inserted into the storage portion26(FIG. 6A).

Next, the upper punch50is raised and is pulled out from the upper punch hole27, whereby the gate28is opened. Thus, the cavity11and the storage portion26are connected via the upper punch hole27. The upper punch hole27functions as a part of the cavity11. In this condition, the plunger40is pressed down, whereby a necessary amount of the raw material P is filled from the gate28to the cavity11with a cruciform section including the upper punch hole27(FIG. 6B).

The upper punch50is pressed down so as to close the gate28, and the upper punch50is further pressed down so as to compact the raw material P in the cavity11(FIGS. 6C and 6D). Thus, the spur wheel portion3and the shaft portion5are formed at the side of the upper die20, and the spur wheel portion6and the shaft portion4are formed at the side of the lower die30. Accordingly, a green compact7A of the gear7is formed.

The forming die10is opened so as to pull out the green compact7A. First, the outer die21of the upper die20is raised so as to expose the spur wheel portion3(FIG. 7A). Then, while the upper punch50holds down the green compact7A, the outer die21and the inner die25are raised so as to expose the shaft portion5(FIG. 7B). The lower die30is lowered as to the expose the spur wheel portion6(FIG. 7C). Moreover, the lower die30and the inner die32are further lowered, whereby the shaft portion4is pulled out from the lower punch hole33(FIG. 7D). After the entire of the structural components at the side of the upper die20is raised, the green compact7A is removed from the forming die assembly. As described above, one green compact7A is formed by such an operation. After the green compact7A is removed from the forming die assembly, the condition of the forming die assembly is returned to the condition shown inFIG. 6A. Then, by repeating the above operation, plural green compacts7A are obtained.

The forming die assembly of the Third Embodiment can be also used for forming the green compact of the gear7shown inFIG. 5.

3-2 Forming Die Assembly

FIGS. 9A to 9DandFIGS. 10A to 10Dshow a forming step of a green compact of the gear7by the forming die assembly of the Third Embodiment. In the forming die assembly of the Third Embodiment, the cylindrical hole22of the outer die21of the upper die20has a lower end portion. This lower end portion is reduced in the diameter via a tapered portion22band is formed with a smaller diameter portion22c. The inner die25, which is formed so as to be slidably inserted into the cylindrical hole22, has a lower end portion. This lower end portion is reduced in the outer diameter via a tapered portion25band is formed with a smaller diameter portion25cso as to correspond to the shape of the lower end portion of the cylindrical hole22. The smaller diameter portion25cis formed so as to be slidably inserted into the smaller diameter portion22cof the cylindrical hole22. As shown inFIG. 11, the smaller diameter portion22cat the side of the upper die20has an inner circumferential surface, which is formed with internal teeth22dfor forming the teeth2of the spur wheel portion6of the gear7.

The lower die30of the Third Embodiment is formed with a cylindrical hole35, which has openings at both ends and has an inner circumferential surface with a shape corresponding to the shape of the teeth2of the spur wheel portion3of the gear7. The cylindrical hole35is formed so that an inner die36is vertically slidably inserted thereinto. Alternately, as shown inFIG. 11, the cylindrical hole35may have an inner circumferential surface at the upper end portion, and this inner circumferential surface is formed with internal teeth35afor forming teeth2of the spur wheel portion3. The inner die36is formed with a lower punch hole33, and the lower punch hole33vertically extends and is formed so that the lower punch60is slidably inserted thereinto. The inner die36and the lower punch60are coaxially arranged with the plunger40and the upper punch50at the side of the upper die20.

(3-2-2) Forming Step

A forming step for a green compact of the gear7using the forming die assembly of the Third Embodiment will be described with reference toFIGS. 9A to 9DandFIGS. 10A to 10D. First, the inner die25of the upper die20is inserted into the outer die21so that the internal teeth22dat the lower end portion of the cylindrical hole22are exposed. The lower surface21aof the outer die21and the upper surface30aof the lower die30are brought into contact and are clamped. Then, the upper punch50at the side of the upper die20is inserted into the upper punch hole27so as to close the gate28. The inner die36is positioned lower than the lower die30so as to expose the internal teeth35aat the upper end portion of the cylindrical hole35. Moreover, the lower punch60is lowered more than the inner die36so as to form a cavity11in the forming die10. The cavity11has a portion corresponding to the spur wheel portion6and the shaft portion4of the gear7at the side of the upper die20. The cavity11also has a portion corresponding to the spur wheel portion3and the shaft portion5of the gear7at the side of the lower die30. On the other hand, the raw material P is supplied to the storage portion26of the inner die25until the storage portion26is almost filled, and the leading end of the plunger40is inserted into the storage portion26(FIG. 9A).

Next, the upper punch50is raised and is pulled out from the upper punch hole27, whereby the gate28is opened. Thus, the cavity11and the storage portion26are connected via the upper punch hole27. In this condition, the plunger40is pressed down, whereby a necessary amount of the raw material P is filled from the gate28to the cavity11(FIG. 9B).

The upper punch50is pressed down so as to close the gate28, and the upper punch50is further pressed down so as to compact the raw material P in the cavity11(FIGS. 9C and 9D). Thus, the spur wheel portion6and the shaft portion4are formed at the side of the upper die20, and the spur wheel portion3and the shaft portion5are formed at the side of the lower die30. Accordingly, a green compact7A of the gear7is formed.

The forming die10is opened so as to pull out the green compact7A. First, the outer die21of the upper die20is raised so as to expose the spur wheel portion6(FIG. 10A). Then, while the upper punch50holds down the green compact7A, the outer die21and the inner die25are raised so as to expose the shaft portion4(FIG. 10B). After the entire of the structural components at the side of the upper die20is raised (FIG. 10C), the lower punch60is raised, whereby the shaft portion5is upwardly pulled out from the lower punch hole33(FIG. 10D). As described above, one green compact7A is formed by the operation. After the green compact7A is removed from the forming die assembly, the condition of the forming die assembly is returned to the condition shown inFIG. 9A. Then, by repeating the above operation, plural green compacts7A are obtained.

4 Effects of the Second Embodiment and the Third Embodiment

According to the Second Embodiment and the Third Embodiment, a green compact7A of a gear7having two wheel portions and shafts is obtained. In this case, the gear7has a spur wheel portion3and a spur wheel portion6which are coaxially arranged, and the spur wheel portion3has a larger diameter and the spur wheel portion6has a smaller diameter. In the Second Embodiment and the Third Embodiment, as in the case in the First Embodiment, the raw material P is easily supplied to the forming die10, whereby a green compact is efficiently obtained. In addition, the plunger40and the inner die25, into which the upper punch50is inserted, may be used as a set, and plural sets may be prepared so as to efficiently perform maintenance of the set and to efficiently supply the raw material P.

5 Variations of the Present Invention

In the above embodiments, a gear is formed as a microcomponent, which has shaft portions at both sides of a spur wheel portion. In addition to the microcomponent having the shaft portions at both sides of the spur wheel portion, a microcomponent having the shaft portion at one side of the spur wheel portion may be formed. Alternately, a microcomponent having only the spur wheel portion may be formed. On the other hand, a microcomponent may be formed so as to have shaft portions at both sides of a simple disc-shaped flange portion instead of the spur wheel portion. In this case, a microcomponent may be formed so as to have a shaft portion at one side of the flange portion. Moreover, a microcomponent in a simple disc shape may be formed.

Furthermore, the upper die20having the storage portion26is preferably provided with a heating means for heating the raw material P in the storage portion26. By heating the raw material P with this heating means, the flowability of the raw material P is increased, and filling of the raw material P into the cavity is smoothly and sufficiently performed. In this case, the heating temperature is set to be approximately the softening point of the thermoplastic resin added to the binder of the raw material P. It should be noted that the heating means may be provided at both the upper die20and at the lower die30to heat the cavity.