JPH051303A - Injection molding machine for metal powder - Google Patents

Abstract

PURPOSE:To injection mold a metal powder without restriction of particle diameter or shape of the raw powder by providing a screw in a hollow cylinder and the outer periphery thereof to revolve freely in an injection cylinder and by providing a plunger which is fitted to slide freely in the hollow cylinder. CONSTITUTION:The screw 30 in the injection cylinder 25 revolves by means of the worm 37 and worm wheel 32, and the molding material 27 in the hopper 26 is sent forward to be kneaded and plasticized by heating with the heater 28 and by feed working of the blade 31. When the material fills sufficiently the tip end part of the injection cylinder 25, the plunger 33 is moved forward by a hydraulic device 38 and the material 27 is injected from the nozzle 29 to metal mold at a prescribed pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is so-called metal powder injection molding, in which a powder material such as metal or ceramic is injection molded with a thermoplastic binder such as a synthetic resin, a plasticizer or wax and then sintered to obtain a molded product. Law (hereinafter called MIM)
The present invention relates to an injection molding machine used in.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a product by sintering a powder material such as metal or ceramics, the powder material is first pressed into the shape of the product by press molding, and this pressed powder molded product is placed in a furnace. The product was obtained by sintering at a predetermined temperature. In this case, since the molding is performed by the press, the shape of the product that can be molded is limited, and only a very simple product can be manufactured.

Therefore, in recent years, as a molding technique for obtaining a product by sintering based on a powder material, MIM which uses injection molding, which can accurately and easily mold a product having a complicated shape, instead of press molding. Was developed.

In MIM, powder materials such as metals and ceramics are mixed with synthetic resins such as ethylene / vinyl acetate copolymer resin and acrylic resin, plasticizers such as DBP and waxes such as paraffin wax. After adding a thermoplastic binder compounded in a prescribed amount, injection molding is first performed with a pelletized molding material, then this injection molded product is put in a furnace to melt and remove the binder to remove the binder, and then the binder removal product. Is sintered to obtain a product.

An injection molding machine which has been generally used for injection molding of synthetic resin has a plunger type as shown in FIG. 5, a plunger prepla type as shown in FIG. 7, and an in-line as shown in FIG. There are screw type, etc., and these injection molding machines are used as they are for MIM.

The injection mechanism of the plunger type injection molding machine is as shown in FIG. 1 as an overall view and as a partial view in FIG. 2, 1 is a plunger, 2 is a torpedo, 3 is a hopper, 4 is a cylinder, 5 Is a nozzle, 6 is a heater, 7
Is a mold, and the molding material supplied to the cylinder 4 from the hopper 3 mounted on the body of the cylinder 4 is pushed into the cylinder 4 by the plunger 1 slidably fitted to the inner circumference of the cylinder, It is heated and melted by the heater 6 wound around the outer periphery of the cylinder, and after being uniformly mixed by the torpedo 2, it is injected into the mold 7 from the nozzle 5 mounted on the tip of the cylinder 4.

[0007] The plunger type injection molding machine is a machine which has a simple structure and is easy to handle because it is designed to plasticize by uniformly heating and mixing the molding material by the action of the torpedo 2. It is difficult to obtain a good plasticized state by uniformly heating or mixing the molding material only by the above action, and it is difficult to obtain a good molded product by combining the conditions of plasticization and injection.

In order to solve the above-mentioned drawbacks of the plunger type injection molding machine, a plunger prepla type injection molding machine as shown in FIG. 7 in which plasticization and injection are performed by separate cylinders has been developed. And.

In this injection molding machine, the molding material is supplied from the hopper 8 to the first plasticizing cylinder 9 in which the heater 10 and the torpedo 11 are provided, and is supplied to the first plunger 12 fitted into this first cylinder. It is pushed into a plasticized state and sent to the injection second cylinder 13 in which the nozzle 17 and the heater 14 are provided, and the passage is switched by the switching of the switching valve 15 and fitted into this second cylinder 13. It is pushed by the second plunger 16 and is ejected from the nozzle 17.

In this type of injection molding machine, the molding material can be plasticized relatively uniformly and the injection conditions can be controlled relatively easily, but it has two cylinders and a switching valve. The structure is complicated, the molding material is likely to remain in the cylinder, and it is difficult to remove it, so that the machine is easily damaged.

As described above, since the plunger type injection molding machine has various drawbacks, recently, an inline screw type injection molding machine as shown in FIG. 8 has been widely used.

In the case of this molding machine, the molding material supplied from the hopper 18 to the cylinder 19 in which the heater 20 and the nozzle 21 are provided is such that the screw 22 fitted in the cylinder 19 has a driving force via the gear 23. The plastic 22 is first accumulated in the tip portion of the cylinder 19 in a plasticized state by being transmitted while being kneaded by being rotated, and the plasticized molding material accumulated in the tip portion of the cylinder 19 is then transferred to the screw 22 by the hydraulic device 24. It is ejected from the nozzle 21 by being pushed and moving forward.

The in-line screw type injection molding machine has a simple structure and is easy to handle. The molding material can be well plasticized and the injection pressure can be easily adjusted to obtain a good molded product. It was useful

As described above, there are various types of injection molding machines for synthetic resins, and molding is performed using these machines in MIM as well. In particular, in-line screw type molding is performed as in the case of molding synthetic resins. Machines are mainly used.

[0015]

[Problems to be Solved by the Invention] However, MIM
In the case of, since the raw material powder for molding occupies about 90% by weight of the powder material of metal or ceramic, if a conventional synthetic resin injection molding machine is used as it is, no matter what type of machine is used, If the particles of the powder material become a little larger, the machine will bite, causing various troubles such as wear and destruction of the cylinder and screw, or failure of the machine itself to operate. The kneading of the raw material powder is not successful, and the powder material and the binder are separated from each other, and a uniform and good molded product may not be obtained.

Therefore, the powder material used for the MIM is required to have an extremely small particle size of 10 μm or less and have a spherical shape. However, such powders become very expensive, and when handled, safety and health problems such as dust explosion and pneumoconiosis occur.

In order to solve the above-mentioned drawbacks of the prior art, the present invention makes it possible to easily mold an inexpensive powder material having a relatively large particle size without causing any trouble.
The object is to provide an optimum injection molding machine for M.

[0018]

That is, according to the present invention, an injection cylinder equipped with an injection nozzle and a molding material supply hopper and having a heater wound around the outer periphery thereof, and a rotatably fitted inside the injection cylinder. It is characterized in that it comprises an integrated hollow cylindrical screw and a plunger slidably fitted in the cylindrical screw, and preferably has an injection mechanism having a plurality of notched grooves at the tip of the plunger. It is a metal powder injection molding machine.

[0019]

The present invention is constituted as described above, and the functions of plasticizing the molding material and injecting the plasticized molding material are divided into a screw and a plunger. The injection of plasticized molding material is performed by rotating the screw fitted in the cylinder, and driving the plunger fitted in the cylindrical screw in the front-back direction.

For this reason, the screw does not move in the front-back direction due to the injection of the plasticized molding material, but it does not require an injection function at the same time, though the screw rotates while the plasticization of the molding material occurs. Since there is no concern about this, the dimensional accuracy when fitting into the cylinder can be somewhat relaxed, so even if a powder material with a relatively large particle size and an irregular shape is used as the molding material, the cylinder and screw No galling occurs between them.

Further, if the precision of the engagement of the plunger with the cylinder is increased, the plasticized molding material does not flow back during injection and enter the gap between the cylinder and the plunger to cause galling. .

Further, the plasticizing of the molding material is effective because it is performed by the screw, and the plasticized molding material is guided to the cylinder tip end portion by being guided by the notch grooves provided as a plurality of guide grooves at the tip of the plunger. Since it is smoothly fed and the injection is performed by extrusion with a plunger, the pressure can be adjusted accurately, and good molding can be performed regardless of the properties of the powder material and binder contained in the molding material. The cutout groove provided at the tip of the plunger also functions as an escape groove for preventing backflow of the molding material during injection.

[0023]

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

First, referring to FIGS. 1 and 2, 25 is an injection cylinder, a hopper 26 for supplying a molding material 27 is attached to a rear portion thereof, and a hopper 26 is provided on an outer periphery for heating the molding material. A heater 28 is wound, and a nozzle 29 for injecting the plasticized molding material 27 into a mold is attached to the tip of the heater 28.

A screw 30 is rotatably fitted in the injection cylinder 25, and has a hollow cylindrical shape, and a spiral blade 31 for kneading the molding material 27 on the outer periphery and sending it to the front of the injection cylinder 25. Is provided, and a drive transmission gear part 32 into which a drive gear 37 is fitted is provided at the rear end.

A plunger 33 is slidably fitted to the screw 30, and a plunger head 34 is slidably fitted to the screw 30 to push out the molding material.
And a plunger rod 35 for transmitting the driving force of the hydraulic device 38 to the plunger head 34.

As shown in FIG. 2, the plunger head 35 has a V-shaped groove as a guide groove for feeding the molding material to the tip thereof.
A plurality of V-shaped cutout grooves 36 are provided at equal intervals.

Next, the operation of the molding machine configured as described above will be described with reference to FIGS.

FIG. 3 shows a state in which the molding material is supplied to the cylinder and is plasticized, and in this state, the plunger 33 has the notch groove 36 of the plunger head 34.
The rear end of the rear end corresponds to the front end of the screw 30.

In this state, when the screw 30 is rotated by driving the drive gear 37, the molding material 27 put in the hopper 26 enters the injection cylinder 25, is heated by the heater 28, and is kneaded by the blades 31 of the screw 30. While being plasticized, it is sent forward and guided from the tip of the screw 30 to the notch groove 36 of the plunger head 34 to accumulate at the tip of the injection cylinder 25.

When a predetermined amount of plasticized molding material 27 has accumulated at the tip of the injection cylinder 25, the screw 30 stops rotating and is locked firmly so as not to move.

After that, as shown in FIG. 4, the plunger 33 is moved forward by driving the hydraulic device 38 to push out the plasticized molding material 27 from the nozzle 29 and inject it into a mold (not shown) at a predetermined pressure. .

At the time of injection, a negative pressure is applied to the molding material 27.
If the dimensional accuracy of the fitting between the plunger head 34 and the injection cylinder 25 is high, the notch groove 36
It will stop there, so there will be no backflow to the Skrieux 30. Therefore, even if the dimensional accuracy of fitting the screw 30 and the injection cylinder 25 is slightly loose, the molding material 2
There is no risk of galling when 7 flows backward, and the dimensional accuracy of this fitting may be appropriately determined in consideration of the particle size of the powder material mixed in the molding material 27.

[0034]

Next, the result of injection molding of the molding material for MIM under the following conditions using the injection molding machine of the present invention will be described. (1) Molding material (a) Powder material Pure iron (a) Particle size distribution (μm, weight%) +177 ≦ 2 +149 ≦ 7 +105 to +74 55 to 75 +63 to +44 10 to 30 −40 5 to 25 (c) Binder (Wt%) Polyamide resin 5 APP 2.5 Paraffin wax 5 (2) Molding conditions (a) Nozzle tip temperature 155 ° C (b) Screw rotation speed 150 rpm. (C) Plunger injection pressure 450 kg / cm. s
qr

After molding under these conditions, the molded product was cut and the internal condition was examined, but product defects such as cavities and voids were not observed at all and it was in a good condition. This is because the conventional injection molding contained a paraffin wax with a low melting point and a high fluidity, so that a strong backflow of the molding material occurred, but in this case no backflow of the molding material occurred. It is shown that. Another reason why the product defects did not occur is considered to be that the gas was sufficiently degassed during plasticization because the molding material was transferred by the screw, and in a mere plunger type molding machine. The advantage that was not obtained was recognized.

Furthermore, the state of the molding machine was examined after molding for about 700 shots, but it was completely abnormal despite the fact that a powder material having a very large particle diameter of about 90 μm was used. Was not recognized.

As described above, the present invention utilizes the powder material of metal or ceramic which is stably supplied at a low cost, has a relatively large particle size, and is not a specific shape such as a sphere, and is MI.
M enables the production of sintered products.

[Brief description of drawings]

FIG. 1 is a side sectional view of an embodiment,

FIG. 2 is a perspective view of the plunger of the embodiment,

FIG. 3 is a side sectional view showing a plasticized state of the molding material of the example,

FIG. 4 is a side sectional view showing an injection state of the molding material of the embodiment,

FIG. 5 is a side sectional view of a conventional plunger type molding machine,

FIG. 6 is a partial side sectional view of a conventional plunger type molding machine,

FIG. 7 is a side sectional view of a conventional plunger prepreg molding machine,

FIG. 8 is a side sectional view of a conventional in-line screw type molding machine.

[Explanation of symbols]

25, injection cylinder 26, Hopper 27, molding material 28, heater 29, nozzle 30, screen 33, Plunger 34, Plunger Head 36, notched groove

Claims (2)

[Claims] 1. An injection cylinder equipped with an injection nozzle and a molding material supply hopper and having a heater wound around the outer periphery thereof, and a hollow cylindrical screw rotatably fitted in the injection cylinder. A metal powder injection molding machine having an injection mechanism composed of a plunger slidably fitted in the cylindrical screw. 2. The metal powder injection molding machine according to claim 1, wherein the plunger has a plurality of notched grooves at its tip.