JPH03267302A - Method for forming compacting powder - Google Patents

Abstract

PURPOSE:To prevent deformation and crack of a sintered compact by charging a core for reinforcing green body into a compacting die, integrally taking out the core and the green body after executing injection-compacting and integrally executing debinder treatment and sintering treatment. CONSTITUTION:Organic binder (e.g. acrylic resin) is added to raw material powder (e.g. iron-nickel alloy) to make material for injection-compacting. The core 16 having a part of outer shape of the compacted product, is fitted and the dies are clamped to prepare the die 1 for injection-compacting, forming cavity 22 for compacted product. The above material for compacting is injected into this die 1 to integrally compact the above core 10 and the green body 25. Successively, by separating a movable die 3, the dies are opened, and by projecting the above core 16, the integrally compacted product is taken out. Further, after executing the debinder and the sintering treatments to the compacted product cut at gate position 23, the core 16 is separated.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a powder compacting method, in particular, a method of adding a binder to powder such as ceramic powder or metal powder to impart fluidity, and obtaining a compact by injection molding. The present invention relates to a molding method for obtaining a sintered part using powder as a raw material, which is then subjected to binder removal treatment, firing treatment, etc.

[Conventional technology] Conventionally, as a molding method to produce sintered crystals using powders such as ceramic powders and metal powders as raw materials, an organic binder is added to the powders to give them fluidity and shape retention to make them into injection molding materials. For example, in flow molding using screw extrusion injection molding, a molded product (referred to as a green body or green part) is molded in a mold in the same way as synthetic resin, and after the molded product is taken out from the mold, a binder is A sintered part with a desired shape was obtained through a binder removal process (degreasing process) to remove components and a firing process (sintering process) to harden the material.

Further, in some cases, the sintered parts have been subjected to post-processing, surface treatment, etc.

[Problem to be solved by the invention]

However, in the prior art, when the green body (injection molded product) molded in the injection mold is taken out from the mold, the bonding force of the powder in the green body is weak.
If the green body is a thin-walled part (for example, the thickness is less than l+a+), cracking or deformation (collapse of shape) may occur.

In addition, even if the green body does not crack or deform when taken out of the mold, deformation will occur when the green body is heated to remove the binder. It was necessary to process it. When embedded in ceramic powder or the like, it was necessary to remove the ceramic powder adhering to the surface of the sintered part.

As a result of the above, the yield for obtaining fired crystals of a desired shape was extremely poor.

The present invention has been made in view of the above-mentioned problems, and provides a method for forming sintered parts using powder as a raw material, which has an extremely good yield rate and has no cracks or deformation in the green body, and does not deform during binder removal processing. The purpose is to provide.

(Means and effects for solving the problems) The powder molding method of the present invention adds an organic binder to the powder to make it an injection molding material, and molds a core having a part of the external shape of a desired molded product. The core and the green body are integrally molded by injecting the molding material after being mounted in a mold and clamped to form a desired molded product cavity, and the mold is opened to take out the integral molded product. Next, the integrated molded product is subjected to binder removal treatment and firing treatment.

In the above, the core that is removably installed in the molding die is made of a ceramic material or a metal material that is heat resistant to the temperatures during binder removal processing and firing processing (the former).

In addition, in the above, the core, which is removably installed in the mold, is made of zinc, aluminum, or tin, which is heat resistant to the temperature during the binder removal process, but melts or burns at the temperature during the firing process. , made of low melting point metals such as lead, their alloys, or synthetic resin materials (the latter).

Therefore, in the former structure using a heat-resistant core, the green body integrated with the core is treated as one body during the binder removal process and firing process, so it is not a thin-walled part. The resulting sintered part will not crack or deform during handling, even if the sintered part is removed from the core in the final step to obtain the desired sintered part (finished product). The removed core can be reused.

In addition, in the latter configuration using a core that melts or burns, the green body integrated with the core is treated as one body during the binder removal process, so even thin-walled parts can be handled easily. In the subsequent firing process, the core is melted or burned at the firing temperature without causing any cracks or deformation in the core, so that only the sintered part with a part of the external shape of the core transferred remains, and the desired sintered part ( finished product)
is obtained.

The raw material powders to be sintered include metals such as iron-nickel alloy powder and stainless steel powder, and ceramics such as silicon carbide and silicon nitride.

〔Example〕

Hereinafter, the present invention will be explained in detail based on examples.

(First Example) Figure 1 is a sectional view of the main parts of an injection mold for explaining the first example to which the present invention is applied, and Figure 2 is a cross-sectional view of a molded product taken out from the injection mold. FIG. 3 is a diagram illustrating the main parts, FIG. 3 is a state diagram in which the molded product is subjected to binder removal treatment and firing treatment, and FIG. 4 is a sectional view of the sintered part separated from the core after firing.

The injection molding die 1 shown in FIG. 1 is constructed by disposing a movable mold 3 on a PL (parting line) surface 4 with respect to a fixed mold 2 so as to be openable and closable.

The fixed mold 2 has a fixed plate 6 fixed to the fixed side mounting plate 5, and a sprue bush 8 having a sprue 7 is mounted thereon through the mounting plate 5 and the fixed plate 6, and is connected to the sprue bush 8 and fixed. It is constructed by attaching a locate ring 9 to a side mounting plate 5. Also, P of the fixed plate 6
LL12 is the molding surface 1 corresponding to the external shape of the desired molded product.
0 is drilled to a size that takes into account the shrinkage allowance.

On the other hand, the movable mold 3 has a movable plate 14 fixed to the movable mounting plate 11 via a spacer block 12 and a receiving plate 13, and a protruding plate 15 that can move vertically between the spacer blocks 12. It is configured. Further, the PLL 12 of the movable plate 14 is connected to the molded surface l of the fixed plate 6.
The base 16a of the core 16 is removable in accordance with the position of O.
A fitting hole 17 for fitting (drop-fitting) is formed, and the head of this core 16 constitutes a molding surface 18 for molding a part of the external shape of the desired molded product. There is. A protrusion rod 19 for protruding the core 16 and a protrusion rod 21 of the runner 20 are attached to the protrusion plate 15 .

Further, a gate 23 and a runner 20 are formed on the fixed plate 6 and the movable plate 14 so as to communicate with a cavity 22 formed by the molding surface 10 of the fixed plate 6 and the molding surface 18 of the core 16. is connected to.

A method of molding a bottomed thin-walled part as shown in FIG. 4 from powder using the injection molding die 1 having the above configuration will be described.

First, in order to give fluidity and shape retention to the raw material powder (iron-nickel alloy), 50% by volume organic binder (acrylic resin) and a small amount of wax are mixed, kneaded and granulated, and then injection molded. The material of the core 16 in the injection mold 1 is silicon carbide ceramic. Note that synthetic resins such as polyethylene, polystyrene, polyamide, etc. may be used instead of the acrylic resin, and the volume ratio thereof can be varied from 30 to 70%.

Then, from a nozzle of an injection molding machine (not shown), the compound is filled as a molten powder into the cavity 22 via the sprue 7, runner 20, and gate 23, and a holding pressure is applied to cool the mold 1. . At this time, the cavity 22
The molded product (green body) 23 (see FIG. 2) molded inside the core 16 becomes integral with the core 16. Next, the PLL 12 separates the movable mold 3 and opens the mold. The green body 25 moves along with the movable mold 3 together with the movable plate 14 together with the core 16. After completing the mold opening,
Enter the ejection process. That is, the protruding plate 15 is activated (forward).
The ejection rod 21 then ejects the runner 20, and the ejection bottle 19 ejects the core 16 with the green body 25.

Figure 2 shows only the left side of the cross section of the molded product obtained by molding as described above, but it is possible to mold the green bodies as a pair or to mold three or more pieces equally spaced.
It is also possible to provide multiple cavities within the mold.

Next, the molded product shown in FIG. 2 is cut at the gate portion, and the core 16 and the green body 25 are subjected to a binder removal process in an integrated state as shown in FIG. 3.

That is, the binder is removed by heating in a furnace (not shown).

This superheat temperature is 380°C. The upper limit of this temperature is 4
The range is up to about 00°C, and the heating rate of the furnace is 20°
C/hour or less, so that the binder is slowly decomposed and vaporized. After that, while leaving a small amount of binder on the green body 25 to maintain the shape of the molded body,
It is subjected to a firing process together with the core 16. Note that the molded body containing a small amount of binder is not sintered at all, so it has approximately the same dimensions as when it was injection molded. The molded body including the cough core is placed in a sintering furnace.

The temperature of this sintering furnace is 1300°C. As a result, the molded body shrinks as it sinters, and becomes denser.

During this shrinkage, the dimensions of a portion of the molded body are determined by the molding surface of the core 16.

After sintering is completed, by separating the core 16 from the sintered body, a sintered part 26 having the desired external shape shown in FIG. 4 is obtained.

According to the above embodiment, since the green body molded in the injection mold is made to protrude from the mold together with the core, there is no cracking or deformation of the green body, and the green body and the core are easily separated. Since the molded body is handled as one unit, no deformation occurs in the molded body during the binder removal process and firing process.

Therefore, highly accurate powder sintered parts can be formed even in complex-shaped parts or thin-walled parts.

In the above examples, heat-resistant ceramics were used as the core during sintering of the raw material powder, but the core is not limited to ceramics, and may also be a heat-resistant metal such as titanium material. A material that does not deform at the firing temperature can be appropriately selected.

(Second Embodiment) A second embodiment of the present invention will be described with reference to a sectional view showing the main parts of an injection mold shown in FIG.

The rest of the structure is the same as that of the injection mold in the first embodiment, so the same reference numerals are given to the same components and the explanation thereof will be omitted.

In FIG. 5, the fitting hole 17 drilled in the PL surface 4 of the movable plate 14 has a base 31a of a core 31 having a molding surface 30 for molding a part of the external shape of the molded product on the head. are removably fitted.

The material of the core 31 is made of a zinc alloy that does not deform at the temperature in the furnace that is high enough to remove pine dust, but melts at the sintering temperature in the firing process.

An injection molded product is molded using the same injection molding compound as in the first embodiment using the mold configured as described above, the mold is opened, and the core 31 integral with the green body 25 is projected. Next, the sprue and runner are separated from each other at the gate portion of the molded product, and the core 31 and green body 25 are integrally subjected to a mite removal process as in FIG. 3. That is, as in the first embodiment, the molded body including the core is placed in a heating furnace (approximately 400°C) to remove the binder.Then, with a small amount of binder remaining, the molded body including the core is placed in a sintering furnace (approximately 1300°C). Put it in C). In the sintering furnace, the core 31 melts and flows out of the molded body, and sintering begins, and shrinkage occurs to increase the density, resulting in a sintered part having a desired external shape.

According to this embodiment, in addition to the advantages of the first embodiment, there is an advantage that the work step of separating the cores is not required.

In addition, in the above, the core was made of zinc alloy, but
It may be a low melting point metal such as zinc, aluminum, tin, or lead that melts at the sintering temperature, or an alloy thereof.

(Third Embodiment) FIG. 6 is an explanatory diagram of a nodal ring of a bending portion for an endoscope to which a third embodiment of the present invention is applied, and FIG. 7 is a sectional view of a core for the nodal ring.

In the figure, the node ring 35 is in the shape of a pipe with an inner diameter of 10mm and a wall thickness of 0.4mm, and has a pair of ears 36° and 37° at both ends, respectively.
They are formed at different degrees. Also, on the inside of the pipe corresponding to one ear 36, there is a protrusion 39 (only one of the pair is shown) having an insertion hole 38 for a wire (not shown) for bending the tip of the endoscope. It is formed. The core 40 of the injection mold for molding the thin-walled joint ring is shown in FIG.
In order to mold the sintered part shown in FIG. (The molding surface to be formed is not shown). The base 40a of the core 40 was fitted to the movable plate in the same manner as in the first embodiment, and an injection molding compound made of stainless steel powder with 45% polyethylene resin added by volume was used. An injection molded product is formed, the mold is opened, and a core 40 (not shown) integral with the green body is taken out. Next, the molded product and the runner are separated at the gate part, and the core and green body are put into a heating furnace (approximately 400°C) for the binder removal process, with a small amount of binder remaining. The molded body including the core is placed in a sintering furnace (approximately 1300°C).

In the sintering furnace, the core 40 burns and disappears from the compact, and sintering begins, and shrinkage occurs to increase the density, resulting in a sintered part with the knots shown in FIG. 7(a).

The holes for the ears 36, 37 and the insertion holes 38 are then drilled into the sintered part.
By drilling, the node ring shown in Fig. 6 is obtained.

In this embodiment as well, the same effects as in the second embodiment can be obtained.

In this embodiment, the core that burns in the sintering step is made of acrylic resin, but it may be made of synthetic resin such as polycarbonate, polystyrene, ABS, or AS, or synthetic resin such as epoxy or phenol. It goes without saying that the sintered parts of this embodiment can be molded by the molding methods of the first and second embodiments.

In each of the above embodiments, the bases of the cores to be fitted into the fitting holes drilled in the movable plate were formed with the same outer diameter.
As shown in the figure, the fitting hole may be sloped (angled) together with the base of the core 41 to facilitate insertion.

〔Effect of the invention〕

According to the present invention, a core for reinforcing the green body is installed in a molding die, and after powder injection molding, the core and the green body are integrated and the core protrudes from the mold, and each Since a sintered part is obtained after the treatment, deformation and cracking of the green body can be prevented by the core during removal of the green body from the mold and during binder removal treatment.

Therefore, the yield of desired sintered parts can be improved and productivity can be increased.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main parts of the injection mold of the first embodiment to explain the present invention, Fig. 2 is an explanatory view of the main parts of the molded product, and Fig. 3 is a diagram of the state of the molded product during processing. , FIG. 4 is a cross-sectional view showing an example of a sintered part, FIG. 5 is a cross-sectional view of the main parts of the injection mold of the second embodiment, and FIG. 6 is an explanatory diagram of members that can be used in the third embodiment. , FIGS. 7(a) and 7(b) are diagrams showing examples of the sintered parts and core according to FIG. 6, and FIG. 8 is an explanatory diagram of the base of the core. 1-... Injection mold 6-----------Fixing plate 10-----One molding surface 14--------
One movable plate 16, 31--One core 18.30-
Molding surface 22------Cavity 25------
Green type figure 1

Claims (4)

[Claims] (1) An organic binder is added to the raw material powder to make an injection molding material, a core having a part of the external shape of the desired molded product is mounted in an injection mold and the mold is clamped, and the cavity of the desired molded product is formed. After forming the tee, the molding material is injected to integrally mold the core and green body, the mold is opened and the core is protruded to take out the integral molded product, and then the integral molded product is subjected to a binder removal process. A powder compacting method characterized by performing a firing treatment. (2) The powder compacting method according to claim 1, wherein the core is formed of a heat-resistant metal or ceramic that does not deform at the temperature of the firing process, and is separated from the sintered part after the firing process. . (3) The core is made of a low melting point metal that has heat resistance that does not deform at the temperature of the binder removal process and melts at the temperature of the firing process, and the core is made to flow out of the integral molded product during the firing process. 2. The method for molding powder according to claim 1, further comprising molding a sintered part. (4) The core is made of a synthetic resin that has heat resistance that does not deform at the temperature of the binder removal treatment and burns at the temperature of the firing treatment, and during the firing treatment, the core is flowed out from the integral molded product and fired. 2. The method for molding powder according to claim 1, further comprising molding a bonded part.