JP2007021502A - Hot runner die assembly for injection molding, and injection molding method for metal powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making the fluidity of a material satisfactory, and improving the yield of a product and a working ratio in injection molding of metal powder, in a hot runner die assembly. <P>SOLUTION: The hot runner die assembly comprises: a cavity 41a; a material injection chamber 54a provided so as to be connected with the injection port 42a of the cavity; a sprue for feeding a melted material into the material injection chamber; and a valve pin 58a provided freely movably in the longitudinal direction thereof for opening/closing the injection port in the material injection chamber. At the inside of the valve pin 50a, a heater 60a of heating the valve pin for melting the material in the injection chamber is provided along the longitudinal direction thereof, by abutting the tip part of the valve pin against a valve seat in the injection port, the injection port is closed, by the separation of the tip part in the valve pin from the valve seat, the injection port is opened, and also, the material heated and melted by the tip part of the valve pin is injected from the injection port into the cavity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hot runner mold apparatus used in metal powder injection molding (MIM) and a metal powder injection molding method.

  Conventionally, a metal powder injection molding method using a hot runner method has been used as one of powder metallurgy methods (PM methods). According to the metal powder injection molding method, it is possible to mass-produce metal parts having complicated shapes close to the final product.

For example, as a method for producing an electrode part of a cold cathode tube, it is shown that metal powder injection molding is performed on a material obtained by kneading various metal powders and a binder resin (Patent Documents 1 and 2). In these conventional methods, a material obtained by kneading a metal powder and a binder resin is formed into a pellet, which is charged from a hopper, heated by a cylinder of an injection molding machine, and melted. It is molded by pouring (filling) this into the cavity at high pressure and cooling while maintaining the pressure.
JP 2003-313603 A JP-A-2005-71972

  However, according to the conventional metal powder injection molding method described above, the metal powder has an extremely good thermal conductivity compared to the resin, so that the material melted by heating is easily solidified. In the molding of the product, there is a problem that the fluidity of the material becomes poor and the mold cavity cannot be filled with the molten material. In addition, when the material is solidified, there is a case where the material on the upper part of the gate cannot be injected under any conditions, and in such a case, there is a problem that molding cannot be performed.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the yield and operating rate of products in metal powder injection molding by improving the fluidity of materials.

  A hot runner mold apparatus for injection molding according to the present invention includes a cavity, a material injection chamber provided to be connected to an injection port of the cavity, a sprue for feeding molten material into the material injection chamber, A valve pin movably provided in the longitudinal direction for opening and closing the injection port in the material injection chamber, and inside the valve pin, the valve pin for melting the material in the material injection chamber A heater for heating the valve pin is provided along the longitudinal direction thereof, and the tip of the valve pin is closed by contacting the inlet, and the tip of the valve pin is separated from the inlet. And the material melted by being heated by the tip of the valve pin from the inlet to the inside of the cavity. Configured to be implanted.

  Preferably, the valve pin has a cylindrical shape as a whole and has a conical tip, and a valve for closing the conical tip in contact with a valve seat provided in the inlet. Part is formed.

  The method according to the present invention is a method for injection molding of metal powder, for feeding a cavity, a material injection chamber provided to connect to the injection port of the cavity, and a molten material into the material injection chamber The valve pin provided to be movable in the longitudinal direction to open and close the inlet in the material injection chamber, and a hydraulic cylinder for reciprocatingly driving the valve pin in the longitudinal direction. Inside, the heater for heating the valve pin in order to melt the material in the material injection chamber uses a hot runner mold device for injection molding provided along the longitudinal direction of the metal powder and the binder resin. Is fed from the sprue into the material injection chamber to form a molten layer of material at least along the outer periphery of the valve pin. Then, from the state where the hydraulic cylinder is pressed so that the tip of the valve pin comes into contact with the inlet and the inlet is closed, the tip of the valve pin is moved away from the inlet by moving the valve pin, As a result, a molten layer of material existing at the tip of the valve pin is injected into the cavity from the injection port, and the material is cooled inside the cavity.

  According to the present invention, the fluidity of the material is improved, and the yield and operating rate of the product in the injection molding of metal powder can be improved. This makes it possible to efficiently form an extremely thin product or a small product.

  1 is a front sectional view of a mold apparatus 1 according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing a state in which a valve pin is closed, FIG. 3 is an enlarged sectional view showing a state in which the valve pin is opened, and FIG. FIG. 5 is a timing diagram showing an example of an injection molding method using the mold apparatus 1. FIG. 5 is a cross-sectional view further enlarging the vicinity of the distal end portion with the valve pin open.

  In FIG. 1, a mold apparatus 1 is a valve gate type hot runner mold apparatus, and includes a fixed mold (concave mold) 3 and a movable mold (convex mold) 4. The stationary mold 3 and the moving mold 4 are in contact with or away from each other in the parting line PL. The parting line PL is also a surface for taking out a molded product.

  The fixed-side mold 3 includes a manifold 15, a sprue bush 16, and a drive plate 17 in a fixed-side housing 10 in which a mold member 11, a base member 12, a side member 13, and an upper member 14 are connected and integrated. , And hydraulic cylinders 18a, 18b and the like are attached, and various processes are performed.

  In the moving side mold 4, male molds 34a and 34b, mold clamping wedge members 35a and 35b, a protruding rod 36, and the like are attached to a moving side housing 30 including a base member 31, a side member 32, and a bottom member 33. Moreover, various processes are given and comprised.

  Hereinafter, the structure of the stationary mold 3 and the movable mold 4 will be described in detail.

  Referring also to FIGS. 2 to 4, the mold member 11 is formed with female cavities 41 a and 41 b. Injection ports 42a and 42b are provided above the cavities 41a and 41b. In the mold member 11, the outer members forming the cavities 41a and 41b are movable mold members (slide cores) 43a and 43b, which are clamped by the mold clamping wedge members 35a and 35b at the time of mold clamping. Sometimes the mold clamping wedge members 35a and 35b are lowered, the movable mold members 43a and 43b are pulled by the springs 44a and 44b, and the cavities 41a and 41b are opened.

  In addition, although the mold apparatus 1 of this embodiment is provided with two cavities 41a and 41b and simultaneously molds two molded products, these two molded products have the same shape. The mold clamping wedge members 35a and 35b, the cavities 41a and 41b, the movable mold members 43a and 43b, the springs 44a and 44b, or both of them are designated as “clamping wedge member 35” “cavity 41” “moving mold”. It may be described as “member 43”, “spring 44” or the like.

  The base member 12 disposed on the mold member 11 is provided with a hole 51 at a position corresponding to the inlets 42 a and 42 b, and a conical valve seat 52 is formed coaxially with the hole 51. A bush 53 is attached to the hole 51, and a material injection chamber 54 is formed by the inside of the bush 53 and a hole provided in the manifold 15. The bush 53 or its peripheral portion is designed so that an appropriate gap is formed between the members, and the gap functions as an air heat insulating layer, so that the vicinity of the inlet 42 inside the bush 53 is outside. It is insulated from.

  The material injection chamber 54 communicates with the material inlet 57 through a flow path 55 provided in the manifold 15 and a flow path 56 provided in the sprue bushing 16. The molten material ZR for molding is fed at a high pressure from the material inlet 57 and enters the material injection chamber 54 through the flow paths 56 and 55. In the material injection chamber 54, a valve pin 58 for opening and closing the injection port 42 is provided so as to be movable in the longitudinal direction.

  That is, the valve pin 58 is made of a metal material, has an overall shape of a cylinder, has a conical tip, and closes the inlet 42 by contacting the valve seat 52 at the tip of the conical portion. A valve portion 59 is formed. The valve portion 59 has a shape that fits the valve seat 52, and has, for example, a shape having the same conical surface as the valve seat 52, a spherical shape, or another appropriate curved surface shape.

  A heater 60 for heating the valve pin 58 is provided along the longitudinal direction in the valve pin 58 in order to melt the material ZR in the material injection chamber 54. In the heater 60, for example, a cartridge type heating element using a nichrome wire or the like is mounted inside a cylindrical casing made of stainless steel, and a temperature sensor such as a thermocouple is incorporated, and an electrode wire (lead wire) is provided. It is drawn from the upper end. Since the heater 60 is small, it can also be called a micro heater. In order to incorporate the heater 60, the valve pin 58 is provided with a hole in the axial direction. The heater 60 is mounted in the hole of the valve pin 58, and an electrode wire is drawn out from above the valve pin 58 and connected to a control device (not shown). By supplying an AC or DC current to the heater 60 from a power supply of a control device (not shown), the heating element generates heat and raises the temperature of the valve pin 58. The temperature of the valve pin 58 is detected by a temperature sensor built in the heater 60. A current supplied to the heater 60 is adjusted by a control device (not shown) based on the temperature detected by the temperature sensor, the set temperature, and other conditions, and the temperature of the valve pin 58 is controlled. The temperature of the valve pin 58 is controlled to be about 200 to 250 ° C., for example.

  The valve pin 58 is supported by the slide bush 61 so as to be slidable in the axial direction, and is sealed by the slide bush 61 so that the material injection chamber 54 does not leak to the outside.

  The upper end portion of the valve pin 58 is connected to the drive plate 17 and moves integrally as the drive plate 17 moves up and down. Both ends of the drive plate 17 are connected to the rods 62 of the double-acting hydraulic cylinders 18a and 18b. Accordingly, as the hydraulic cylinder 18 is reciprocated, the drive plate 17 is reciprocated in the vertical direction of FIG. In the hydraulic cylinders 18a and 18b, two pressure oil supply ports are drawn out to the outside by piping, and pressure oil is supplied from the outside via an appropriate electromagnetic valve or the like.

  In FIG. 1, the left hydraulic cylinder 18a shows a state in which the rod 62a is contracted, and thus shows a state in which the valve pin 58a is in contact with the valve seat 52a and closes the inlet 42a. The right hydraulic cylinder 18b shows a state in which the rod 62b is extended, and thus shows a state in which the valve pin 58b is separated from the valve seat 52b and the inlet 42b is opened. 2 and 4 show the same state as the left side of FIG. 1, and FIG. 3 shows the same state as the right side of FIG.

  Further, the manifold 15 is provided with holes at appropriate positions, and cartridge heaters 63, 63... Are mounted in the holes. In FIG. 1, four cartridge heaters 63 are shown. A current is supplied to the cartridge heater 63 from a control device (not shown), and the manifold 15 is controlled to have an appropriate temperature.

  However, the inside of the material injection chamber 54, particularly the portion close to the injection port 42, cannot be heated to a sufficiently high temperature only by the cartridge heater 63. That is, for example, the material ZR inside the bush 53 in the portion near the injection port 42 tends to change from a molten state to a cooled and solidified state, and when there is no heater 60, the material ZR of the portion ZR The whole becomes a solidified layer that does not flow. However, by heating the valve pin 58 with the heater 60, at least the periphery of the valve pin 58 forms a molten layer without the material ZR solidifying, and the molten layer material ZR flows and is injected into the cavity 41 from the injection port 42. The Rukoto.

  That is, as shown in FIG. 2, the inlet 42 is closed when the valve portion 59 at the tip of the valve pin 58 is in contact with the valve seat 52 (inlet 42). In this state, the material ZR around the valve pin 58 is heated by the valve pin 58, and at least a thin molten layer is formed. Therefore, as shown in FIG. 3, when the valve portion 59 is separated from the valve seat 52 (injection port 42), the injection port 42 is opened, and the material ZR heated and melted by the valve pin 58 is discharged from the injection port 42 into the cavity 41. Injected into the inside.

  The base members 12 and 31 are provided with a plurality of holes 64, 64... For cooling by flowing cooling water (hot water). In FIG. 1, three holes 64 are shown in each of the base members 12 and 31.

  Incidentally, in the related art, since the heater 60 is not provided, the heat dissipation amount is larger than the heating amount from the valve pin 58 with respect to the material ZR above the gate (injection port), and the temperature decreases due to the heat dissipation. The material above the gate will solidify. Once the material has solidified, it cannot be remelted and cannot be injected into the cavity 41. On the other hand, by providing the heater 60 as in the present embodiment, heat is supplied from the valve pin 58 to the material ZR above the gate, the material ZR is kept in a molten state, and flows into the cavity 41. It can be done.

  Next, a metal powder injection molding method using the mold apparatus 1 will be described.

  As shown in FIG. 5, first, the material ZR is supplied from the material inlet 57. The material ZR is, for example, a pellet in which a powder such as tungsten, molybdenum, or nickel and a resin such as polyethylene or polystyrene are mixed by about 50 percent by volume. The material ZR is heated to a high temperature and is in a molten state, and is filled into the material injection chamber 54 through the flow paths 56 and 55. The material injection chamber 54 is heated by the cartridge heater 63 and the heater 60, and is about 200 to 300 ° C. Further, the temperature of the base member 12 is as low as about 20 to 30 ° C. because it is cooled by the cooling water flowing through the hole 64, but since the valve pin 58 is heated by the heater 60, at least the periphery of the valve pin 58 is made of material. A thin molten layer of ZR is formed.

  In this state, the hydraulic cylinder 18 extends from the contracted state, thereby driving the valve pin 58 in the upward direction. By the upward movement of the valve pin 58, the valve portion 59 is separated from the valve seat 52, and the material ZR in the material injection chamber 54 flows into the cavity 41 from the injection port 42. The time required for filling the cavity 41 with the material ZR is one tenth of a second to a few seconds, for example, about 0.1 to 0.2 second.

  After filling the material 41 with the material ZR, the moving die 4 is lowered by waiting for the material ZR to cool, thereby opening the cavity 41 and extracting the male die 34 from the cavity 41. Then, the protruding rod 36 is raised to raise the base member 31, thereby extracting the molded product from the male die 34. Thus, one molding is completed, and a cup-shaped molded product is obtained. In addition, as for the dimension of this molded article, a diameter is about 1-2 mm and length is about 5 mm, for example.

  As described above, in the mold apparatus 1 of the present embodiment, the valve pin 58 is heated by the heater 60 built in the valve pin 58, whereby the material can be maintained in a molten state, and the material ZR flows. Thus, the cavity 41 is filled at a high speed. Even when the material ZR contains metal powder and is easy to cool, the sufficient fluidity of the material ZR is maintained and the occurrence of defective products is suppressed. As a result, the yield of the product is improved, and the operating rate is improved without the material being solidified and being unable to be injected as in the prior art.

  Thus, the mold apparatus 1 of the present embodiment is particularly effective when the thermal conductivity of the kneaded material ZR is about 3 to 20 times that of the plastic material.

  In the above embodiment, the shape of the cavity 41 can be variously changed according to the molded product. For example, in the case where the above-described cup-shaped one has a shape in which a rod-shaped one is connected to the bottom thereof, the mold member 11B and the male mold 34B shown in FIG. 6 may be used.

  That is, in FIG. 6, the mold member 11B is provided with a cylindrical hole 41Bb, and a cavity 41B is formed between the male mold 34B and a bar-like shape connected to a cup-shaped bottom. .

  In the embodiment described above, the structure, shape, dimensions, number, material, temperature, pressure, etc. of the whole or each part of the material injection chamber 54, the valve pin 58, the heater 60, the injection port 42, and the mold apparatus 1 are as follows. It can change suitably according to the meaning of invention.

  The present invention can be used as a mold apparatus used in a metal powder injection molding method.

It is a front sectional view of a metallic mold device concerning an embodiment of the present invention. It is an expanded sectional view showing the state where a valve pin was closed. It is an expanded sectional view showing the state where a valve pin was opened. It is sectional drawing which expands further and shows the front-end | tip part of the state which the valve pin opened. It is a timing diagram which shows the example of the injection molding method using a metal mold apparatus. It is sectional drawing which shows the other example of the shape of a cavity.

Explanation of symbols

1 Mold device (hot runner mold device)
16 Sprue bushing (Sprue)
41 Cavity 42 Inlet 52 Valve seat (inlet)
54 Material injection chamber 58 Valve pin 59 Valve part 60 Heater

Claims (3)

A hot runner mold apparatus for injection molding,
A cavity,
A material injection chamber provided to connect to the inlet of the cavity;
A sprue for feeding molten material into the material injection chamber;
A valve pin movably provided in the longitudinal direction to open and close the injection port in the material injection chamber,
Inside the valve pin, a heater for heating the valve pin to melt the material in the material injection chamber is provided along its longitudinal direction,
The inlet is closed when the tip of the valve pin comes into contact with the inlet, the inlet is opened when the tip of the valve pin is separated from the inlet, and is heated by the tip of the valve pin. The molten material is injected into the cavity from the inlet,
A hot runner mold apparatus for injection molding. The valve pin has a cylindrical shape as a whole and has a conical tip, and a valve portion is formed at the conical tip to abut against a valve seat provided at the inlet. Become,
The hot runner mold apparatus for injection molding according to claim 1. A method for injection molding of metal powder,
A cavity,
A material injection chamber provided to connect to the inlet of the cavity;
A sprue for feeding molten material into the material injection chamber;
A valve pin provided to be movable in the longitudinal direction in order to open and close the injection port in the material injection chamber;
A hydraulic cylinder that reciprocates the valve pin in the longitudinal direction;
Inside the valve pin, a heater for heating the valve pin in order to melt the material in the material injection chamber uses a hot runner mold device for injection molding provided along the longitudinal direction,
A material obtained by kneading metal powder and binder resin is sent from the sprue to the material injection chamber, and a molten layer of the material is formed at least along the outer periphery of the valve pin,
The tip of the valve pin is moved away from the inlet by moving the valve pin from the state where the inlet is closed by pressing the tip of the valve pin against the inlet by the hydraulic cylinder. Injecting a molten layer of material present at the tip of the valve pin into the cavity from the inlet;
Cooling the material inside the cavity;
A metal powder injection molding method.