HK1060994A - Improved injection nozzle for a metallic material injection-molding machine - Google Patents

Description

Improved injection nozzle of metal material injection moulding machine

Technical Field

The present invention relates to an improved injection nozzle for a metallic material injection molding machine, and more particularly to a metallic alloy injection molding machine.

Background

In the metallic material injection technique, the facing surfaces between the nozzle and the sprue bushing on the mold are machined to be consistent with each other and are designed to have substantial surface contact. In this design, it is assumed that the delivery cylinders (carriage cylinders) can apply sufficient pressure to the nozzle to prevent its contact with the runner liner from being separated. It has been found, however, that even when the greatest acceptable force is applied to the interface between the nozzle and the sprue bushing, some separation at the interface is not adequately prevented. This separation at the interface causes the injected material to collect on the surface of the interface with the end result that the interface cannot be sealed and sometimes has the catastrophic result that the injected material is leaked.

In prior art designs, the mating geometry between the nozzle and the surface of the sprue bushing was designed to withstand the positive force applied by the delivery cylinder and remain in positive sealing contact throughout the machining cycle. The mating surfaces of the nozzle and sprue bushing may be flat, spherical, tapered, or any other geometry that may provide an acceptable positive contact area. The positive force applied by the transfer cylinder to the interface between the sprue bushing and the nozzle serves to overcome the reaction forces created by the injection pressures generated during injection and any dynamic forces created by the energy transfer between the injection molding machine components involved in the injection process.

Unfortunately, it has been found that it is virtually impossible to provide sufficient clamping force to prevent separation between the nozzle and the sprue bushing when injecting metallic materials, particularly when injecting materials that are in a thixotropic state, because such very high pressures are required and the reaction and dynamic forces reach such high, relatively uncontrolled levels that separation eventually occurs.

Japanese patent 11048286 issued to Japan Steel Works Ltd is another example of such a nozzle: the nozzle still has leakage problems when subjected to the injection pressures normally associated with the injection of metallic materials. In that design, the nozzle has a protruding cylindrical portion that is inserted into a cylindrical recess of the mold. The two annular surfaces formed in the nozzle and the die are maintained in annular contact so that the interface of the nozzle and the die remains sealed. It is this problem of maintaining such a seal that has been overcome by the present invention, which does not require the nozzle to be in face-to-face contact with the mold.

Disclosure of Invention

It is a primary object of the present invention to provide a nozzle to sprue bushing interface in a metallic material injection molding machine that remains sealed during the injection cycle.

It is another object of the present invention to provide an injection nozzle in a metallic material injection molding machine that is movable relative to a sprue bushing without failure of the seal at the interface between the nozzle and the bushing.

It is another object of the present invention to provide a seal between a nozzle and a mold of an injection molding machine within a metallic material injection molding machine that requires only minimal force to be applied between the mold and the nozzle to maintain a seal therebetween.

It is another object of the present invention to provide an injection molding machine nozzle and sprue bushing design in a metallic material injection molding machine that does not require contact between the nozzle and the bushing to maintain a seal therebetween.

The above object is achieved by the following method: with the nozzle extending into the interior surface of the sprue bushing.

The present invention provides an improved nozzle and sprue bushing for a metallic material injection molding machine. The sprue bushing has a cylindrical surface and the nozzle has an annular portion. The annular portion may be suitably mounted within the cylindrical surface to provide sealing engagement between the surface and the portion when the nozzle engages the bush. The surface and the portion have sufficient length to allow limited axial movement therebetween without failure of the seal therebetween. The actual seal may be provided by: a tight fit is formed between the bushing and the nozzle or the metal material is allowed to bleed slightly between the surfaces, and the bled metal material is allowed to solidify between the surfaces, thus providing the desired seal.

The present invention provides, in a metal material injection molding machine: an injection nozzle coupled to an injection cylinder of an injection molding machine; a stationary platen on which a portion of the mold is mounted; and a sprue bushing mounted in the mold. The nozzle engages the sprue bushing when the metallic material is injected into the mold through the sprue bushing. The nozzle has a spigot portion that extends into the passage of the sprue bushing. The outer edge of the spigot fits into the inner surface of the passage creating a seal between the surface and the edge of the spigot or having the metallic material create such a seal, thereby preventing the loss of metallic material through the interface between the nozzle and the sprue bushing during the injection cycle.

The present invention may also be used in any metal material injection or casting process that requires a sealed interface between the nozzle and the sprue bushing. The invention has been found to be particularly useful when injecting metal alloys such as magnesium based alloys in a thixotropic state.

Drawings

FIG. 1 is a perspective view of an injector assembly of a metal injection molding machine for use with the present invention;

FIG. 2 is a cross-sectional view of the barrel portion of the syringe assembly shown in FIG. 1;

FIG. 3 is a schematic view of a prior art nozzle and sprue bushing interface for a metal injection molding machine;

FIG. 4A is a plan view of the interface of the nozzle and sprue bushing of the present invention;

FIG. 4B is a view of section 4B-4B of the interface of the nozzle and the sprue bushing shown in FIG. 4A;

FIG. 5 is a cross-sectional view of the interface of the sprue bushing and the nozzle when the nozzle is in engagement with the sprue bushing in the mold on the stationary platen.

Detailed Description

Referring to fig. 1 and 2, the injector assembly 10 includes an injection cylinder 11, the injection cylinder 11 having an extrusion screw 12, the extrusion screw 12 feeding a thixotropic metallic material into a nozzle 13. The transfer cylinder 14 moves the assembly 10 toward and away from the stationary platen 15 and clamps the assembly 10 in place, while the nozzle 13 is operatively connected to a sprue bushing that is connected to a mold that is mounted between the stationary platen 15 and a movable platen (not shown) in a manner well known in the art. The connecting tie-rods are connected to the fixed platen 15 at the four corners of the platen 15 (these corners are indicated at 17) and to the frame of the injection machine when the nozzle is in the injection position in a manner known in the art. The tie rods ensure that pressure is applied uniformly to the platen 15 and the mold mounted thereon in a manner well known in the art.

To inject the metallic material into the mold, the delivery cylinder 14 moves the barrel 11 toward the stationary platen 15 until the nozzle 13 is operatively engaged with the sprue bushing in the mold. When the nozzle 13 engages the bushing, the delivery cylinder 14 clamps the assembly 10 in place, thereby injecting the metal material into the mold.

The rotation source 18 rotates the screw 12, thereby moving the metallic material from the feed throat 19 into the nozzle 13. Heating tape 20 along the length of the barrel 11 heats the metal material to the desired injection temperature. The check valve 21 allows the metallic material to drive the screw 12 back into the injector housing 22 as the metallic material passes the head of the screw 12. This produces a shot (injection charge) of metal material at the head of the screw 12.

In operation, sheets of metal material (chips) are fed at a feed throat 19 on the barrel 11 of the injection machine. The chips are transported through the cylinder 11 by means of an extrusion screw 12, while they are heated to a thixotropic state by means of heating bands 20 arranged at the circumference of the cylinder. When sufficient metallic material for injection moves past the check valve 21, the screw 12 is then advanced by means of an injection member within the injection housing 22 to inject the metallic material into the mold. Since the metallic material cools very quickly as it enters the mold, the metallic material must be injected into the mold as quickly as possible to ensure that all parts of the mold are filled. To achieve this requires the injection plunger to move forward quickly with a large force during the injection cycle. Even if the nozzle 13 is indeed clamped onto the runner liner by means of the delivery cylinders 14, the high speed and the high forces make it very difficult to keep the nozzle 13 in contact with the runner liner throughout the injection cycle, the delivery cylinders 14 being set sufficiently to prevent any separation between the runner liner and the nozzle 13 by means of the connecting tie-rods and tie-rods. In fact, it has been found that the nozzle 13 and sprue bushing do separate during the injection cycle.

Dynamic and inertial loads develop at various parts of the injection cycle. Between each injection cycle, the metal material solidifies in the nozzle, forming a cylindrical "plug". At the beginning of each injection cycle, the shot sleeve is pressurized by hydraulic fluid which moves the screw forward and increases the pressure on the thixotropic metallic material located in front of the screw but behind the plug. Finally, the force from the injection plunger is sufficient to separate the stopper from the nozzle and blow into the mold with the thixotropic metal material. The injection plunger continues to move forward and the screw forces the metal material into the mold until the mold is filled. When the plug leaves the nozzle, it creates a recoil force that acts in the nozzle to reduce the sealing load at the interface with the sprue bushing. The reduction in the sealing load causes separation at the sealing interface, thereby creating a leak of metallic material.

Another payload is generated when the mold is filled and the screw is brought to a sudden stop. The screw, plunger and metal material are decelerated in front of the screw, which creates a secondary force at the nozzle and sprue bushing junction. At the same time that the melt pressure is at its highest, the nozzle is rebounded and the sealing force is reduced. This causes leakage of metallic material from between the sealing surfaces of the nozzle and the sprue bushing.

As shown in FIG. 3, the prior art nozzle 13' has a machined spherical surface 23 that substantially mates with a spherical surface 24 of a sprue bushing insert 25 over a predetermined angular range. The sprue bushing insert 25 provides thermal insulation between the nozzle 13 'and the sprue bushing 16' so that the bushing 16 'cannot excessively cool the nozzle 13'. When the nozzle 13 'is brought into pressure contact with the sprue bushing insert 25, the bushing insert 25 and nozzle 13' provide a perfect seal so that metallic material injected through the injection passage does not leak out of the injection passage. Unfortunately, however, as noted above, the nozzle 13 'and sprue bushing insert 25 do separate during the injection cycle and metallic material begins to collect on the surfaces of the sprue bushing insert 25 and nozzle 13' that have been machined to enable an accurate fit. This means that over time the connection between the nozzle 13' and the sprue bushing insert 25 will fail and have to be replaced with a new nozzle and sprue bushing insert. This leads to increased costs and wasted time, and it is therefore desirable to be able to find such connections: the connection will not fail or at least be able to function properly over more injection cycles. While the nozzle and sprue bushing interface shown in fig. 4A and 4B provides this connection.

With the design shown in fig. 4A and 4B, the nozzle 13 "includes a spigot portion (spilotpro) 26 which is machined to fit snugly within the sprue bushing channel 27. The shoulder 28 on the nozzle 13 "may or may not bear on the surface 29 of the sprue bushing 16" and is held there by the pressure exerted by the transfer cylinder 14. With this design, it has been found that the nozzle 13 "and sprue bushing 16" are in fact axially movable relative to each other without any drag on the process. While the metallic material may reach between the wall of the sprue bushing 16 "and the surface of the plug portion 26 of the nozzle 13", it may not reach further. The alloy solidifies in this region and prevents further entry into the exterior of the nozzle 13 ". As the molded part is ejected from the mold, metallic material on the surfaces between the sprue bushing 16 "and the nozzle 13" is removed through the gate.

Thus, by simply changing the shape of the nozzle, the problem of nozzle seal failure can be solved.

In addition, such design improvements have many additional advantages. For example, the nozzle shoulder 28 need not be in contact with the surfaces 29 of the sprue bushing 16 ", so wear can be avoided on these surfaces. Of course, if the thermal insulation provided by the separation between the surface 29 and the shoulder 28 is insufficient, a screw bushing insert, identical to 24 in FIG. 3, may be provided on the end of the sprue bushing 16 "to further thermally insulate the nozzle 13" from the bushing 16 ".

A wide variety of metallic materials can be injected using the new nozzle, however, the nozzle works particularly well with metal alloys such as magnesium-based alloys. The nozzle may also operate with other metal alloys such as aluminum or zinc based alloys.

Figure 5 is a cross-sectional view of the actual nozzle 13 "engaging the sprue bushing 16" on the stationary platen 15. (the figures show the mold at least in outline)

It is to be understood that the invention is not limited to the examples described and illustrated herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention, of course, includes all such modifications within the spirit and scope as defined by the appended claims.

Claims (12)

1. In a metallic material injection molding machine, an injection nozzle is joined to an injection cylinder of the injection molding machine; a fixed platen is provided with a part of the mold; a sprue bushing is mounted in the mold, the nozzle engages the sprue bushing when the metallic material is injected into the mold through the sprue bushing, the nozzle having a plug portion extending into a channel of the sprue bushing, an outer edge of the plug fitting snugly within a face of the channel creating a seal between the face and the edge of the plug, thereby preventing loss of metallic material through an interface between the nozzle and the sprue bushing during an injection cycle.

2. The metal injection molding machine as claimed in claim 1, wherein said metal material is a metal alloy.

3. A metallic material injection molding machine as claimed in claim 2 wherein said alloy is selected from alloys of magnesium, zinc or aluminum.

4. An injection machine according to claim 1, 2 or 3, wherein said plug portion and said channel are dimensioned such that during an injection cycle, said plug portion and channel are free to move axially relative to each other a distance less than the length of said plug portion.

5. An injection molding machine according to any one of claims 1 to 4, wherein the plug portion has a length long enough to maintain a seal between the channel and the plug portion during an injection cycle and short enough to allow any metallic material held between the channel and the plug portion to be released when the gate is released from the channel.

6. An improved nozzle for a metallic material injection molding machine, said nozzle having a first main portion and a second minor portion, an injection passage extending for an equal length of said nozzle, the tubular thickness of said first portion being substantially greater than the tubular thickness of said minor portion, whereby said main portion can withstand injection pressures and said minor portion can withstand injection pressures when installed within the confines of a mating sprue bushing.

7. An improved nozzle and sprue bushing connection for a metallic material injection molding machine, said sprue bushing having a first cylindrical surface and said nozzle having a second cylindrical surface wherein the diameter of the second cylindrical surface is smaller than the diameter of said first surface, said second surface being fittingly mountable within said first cylindrical surface to provide a sealing engagement between said first surface and said second surface when said nozzle is engaged within said bushing, said first and second surfaces being of sufficient length to permit limited axial movement therebetween without loss of sealing between said surfaces.

8. The improved connection according to claim 7, wherein said nozzle has a third cylindrical surface having a diameter similar to that of said first cylindrical surface, wherein said first and third cylindrical surfaces are in intimate non-contacting relationship when said nozzle is engaged within said runner liner.

9. An improved nozzle and sprue bushing connection according to claim 7 or claim 8 wherein a small gap between said surfaces allows a limited amount of metallic material to enter into the gap and solidify in the gap to form said seal, said limited amount of material adhering to the gate and being removed.

10. An improved nozzle and sprue bushing connection for a metal injection molding machine wherein said nozzle has a first portion which is fittingly received within a surface portion of said sprue bushing so that said nozzle is axially movable within said sprue bushing without loss of sealing between said nozzle and said bushing.

11. An improved nozzle and sprue bushing connection according to claim 10 wherein said first portion and said surface portion are separated by a small gap which allows a limited amount of metallic material to flow into said gap and solidify within said gap to form said seal.

12. An improved connection as claimed in claim 10 or 11 wherein said portions are cylindrical.