JP2004508202A - Body molding method from metal foam - Google Patents

Abstract

The present invention relates to a method of forming a body from a metal foam, the method comprising: a) supplying a first powder consisting of a metal and a second powder consisting of a foaming agent; b) a first and a second powder. Supplying the powder to an extruder, wherein the first and second powders are in an unformed state, and c) mixing a powder mixture of the first and second powders from the extruder into a mold. The step of conveying, wherein during this step the mixed powder is partially dissolved and the gas pressure generated by the blowing agent is higher for the at least partially dissolved mixed powder. Applying pressure and d) injecting the at least partially dissolved powder mixture into the mold; and e) reducing the pressure to a level below the gas pressure to form the metal foam. Comprising the step of completely filling the mold (9).
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a body from a metal foam.
[0002]
[Prior art]
In the method for molding a body from a metal foam disclosed in EP 0 804 982 A2, a mixture obtained by molding a gas release blowing agent and metal powder is used as an initiator. Usually, this type of molding mixture is formed by extrusion. The shaped admixture is rod-shaped, tube-shaped, or granular. To mold the metal foam, the molding mixture is heated in a heat treatment chamber until the metal dissolves and the blowing agent decomposes. The gas released at that time foams the metal. The metal foam thus formed is extruded from the chamber into a mold using a plunger.
[0003]
In the method for molding bodies from metal foams as disclosed in DE 197 34 394 A1, a molding semi-finish is also used first of all. Alternatively, the material initially used may be a non-foamed metal and the addition of gas or blowing agent is performed separately to form the metal foam.
[0004]
According to DE 42 06 303 C1, it is known for the molding of bodies from metal foam that after extrusion processing is repeated, powdered ones are used as molding initiators.
[0005]
DE 197 44 300 A1 discloses a further method for molding bodies from metal foam. In this method, a forming semi-finish consisting of a gas releasing foaming agent and metal powder is heated in a receptacle. The metal foam thus formed is conveyed to a mold connected downstream.
[0006]
However, in all of the above methods, it is costly and time-consuming to produce a molding initiator or a molding semi-finishing agent. Often it requires special equipment, such as an extrusion press.
[0007]
DE 1 164 102 discloses a further method for molding bodies from metal foam. In this method, a melt of metal is poured into a mixer and mixed with a gas generating substance in the mixer. In order to melt the metal, it is necessary to separately provide a melting device.
[0008]
US 5,865,237 discloses a method of molding a body from a metal foam. This method uses a heat treatment chamber connected to a mold. The heat treatment chamber is filled with a molding mixture generated by powder metallurgy and containing a metal and a foaming agent, and heated until a metal foam is molded. The metal foam thus formed is then extruded into a mold.
[0009]
[Problems to be solved by the invention]
The structure of the molded body depends on the filling state of the chamber, the degree of mixing of the powder and the foaming agent, and the heating of the powder in the chamber. These parameters cannot always be set optimally and reproducibly. In order to minimize the consumption of the foaming agent and to realize an economical treatment, it is preferable on the one hand to carry out heating rapidly. However, on the other hand, rapid heating causes a non-uniform temperature distribution, resulting in an uneven cell structure of the molded body. Components molded in the conventional manner have non-uniform structures.
[0010]
An object of the present invention is to eliminate the disadvantages of the conventional example. In particular, it is an object of the present invention to provide a method in which a body is formed of a metal foam having a constant quality and can be formed as simply and at low cost as possible.
[0011]
Means for Solving the Problems and Effects of the Invention
This object is achieved by the features of claim 1. The advantageous results of the present invention are apparent from the features of claims 2 to 19.
[0012]
According to the present invention, there is provided a method of forming a body from a metal foam,
a) supplying a first powder composed of a metal and a second powder composed of a foaming agent;
b) supplying the first and second powders to an extruder, wherein the first and second powders are in an unformed state;
c) transporting the mixed powder consisting of the first and second powders from the extruder to the mold, during which the mixed powder is partially dissolved and at least partially Apply a pressure higher than the gas pressure generated by the foaming agent to the dissolved mixed powder,
d) injecting the at least partially dissolved mixed powder into the mold, and e) completely filling the mold (9) with the metal foam formed by reducing the pressure to a level below the gas pressure. A method comprising steps.
[0013]
According to the method of the present invention, the powder is fed directly to the extruder in an unformed state and then mixed and at least partially dissolved. This eliminates the costly and time-consuming steps for producing the molding start powder. No special equipment is required to produce the molding mixture.
[0014]
According to this method, the mixed powder that is at least partially dissolved is intensively mixed. Furthermore, it is possible to apply pressure in the extruder which acts in a direction that counteracts the undesirably early decomposition of the blowing agent, without any extra expense. The heating of the mixed powder can be precisely controlled along the transport path. Since the at least partially dissolved mixed powder does not foam until it is extruded from the extruder into the mold, the composition of the metal foam transfers to the mold. Therefore, the cell structure does not have an uneven composition. As a result, a molded body having a constant quality can be manufactured.
[0015]
The average particle diameter of the first powder is in the range of 5-250 μm, preferably 100 μm. The average particle diameter of the second powder is in the range of 5 to 20 μm, preferably 10 μm. According to a further design feature, the first and second powders are mixed and prepared before entering the extruder. The first and / or second powder may be supplied to the extruder under an inert gas atmosphere. In this case, undesired oxidation of the powder can be prevented. Component quality is improved, and reproducibility is also improved.
[0016]
The first and second powders are mixed in an extruder, preferably by the action of shear forces. The mixing and / or conveying of the mixed powder is performed by the rotational movement of the screw of the extruder. In this case, the shearing forces also act on the mixed powder which is at least partially dissolved. Undesirable dendrite formation can be avoided. The rotation speed of the screw is preferably about 100 rotations per minute.
[0017]
Preferably, the dust or mixed dust is continuously heated along a transport path extending from the feed opening toward the ante chamber. The powder mixture is at least partially converted into an effervescent melt, which takes place along the transport path in one process step. In this step, the mixed powder and the at least partially dissolved mixed powder are continuously mixed. In addition, the mixed dust is conveyed toward the Antechamber containing the at least partially dissolved mixed dust. Since this step can be performed by one extruder, it can be performed at low cost. If the forming starting materials are individually produced by extrusion, it is necessary to grind the semi-finished material after extrusion, but the step of transporting the forming starting materials to the extruder is omitted.
[0018]
In the extruder, the mixed powder is heated to a temperature higher than the liquidus temperature. Suitably, in the extruder, the melt is heated to about 50 ° C, preferably 20 ° C above the liquidus temperature. It has proven to be very suitable if the heating temperature of the mixed powder is between the solidus temperature and the liquidus temperature. In this case, the mixed powder is only partially dissolved. The solids content of the at least partially dissolved mixed powder is from 20 to 50%, preferably from 30 to 40%. The at least partially dissolved mixed powder is accumulated in the ante chamber in a semi-solid thixotropic state. In a partially dissolved state, its viscosity is significantly increased compared to a completely dissolved state. This continuously forms the melt front during injection molding into the mold. That is, it is possible to prevent undesired atomization of the material injected into the mold and prevent the gas generated by the foaming agent from leaking at an early stage. Still, the injection material completely dissolves because the pressure is released inside the mold. However, injection molding of at least partially dissolved mixed powders delays the release of gas generated by the blowing agent. In this case, a molded body having a uniform foam structure can be molded, and in particular, the bubbles can be prevented from being enlarged.
[0019]
In order to minimize the generated gas pressure, the blowing agent used is preferably a pre-oxidizing blowing agent.
[0020]
The mixed powder is heated in the extruder by an external heating device, for example, an external strip heater, an electromagnetic heating device, or the like. With this type of heating device, the heating rate when the mixed powder is heated by the extruder can be set accurately. As a result, the foaming agent can be decomposed at an early stage, and foaming of the melt can be prevented. Further, the temperature can be set so as to prevent dendritic formation of the melt. Appropriate pressure setting can be controlled using known mechanical and process engineering techniques. The pressure applied to the extruder at a temperature above 300 ° C. is above 10 bar, preferably above 30 bar.
[0021]
Injection molding of the mixed powder, at least partially dissolved, is effected by axial movement of the screw towards the mold. The extruder includes, for convenience, a mechanical valve for opening and closing the ante chamber located downstream of the screw as needed. Suitable devices are known from US 5,040,589 or EP 0 409 966 B1, the disclosure of which is incorporated herein by reference.
[0022]
According to a further design feature, the mold is pre-heated. This can prevent excessive solidification of the portion where the melt is in contact with the mold. To carry out this method, the metal used is preferably magnesium or a magnesium alloy.
[0023]
According to a further design feature, the size of the cavity defined by the mold is increased after injection molding. In this case, the mold to be used is preferably a positive mold. The use of this type of mold allows at least one surface of the mold to move with the movement of the plunger, which can increase the size of the cavity.
[0024]
The metal used is magnesium, aluminum, magnesium alloy, or aluminum alloy. The blowing agent used is a metal hydride, preferably TiH ₂ Or MgH ₂ It is. Usually, the blowing agent makes up 0.5% of the total weight of the dust.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Exemplary embodiments of the present invention will be described below in more detail with reference to the drawings.
FIG. 1 is a cross-sectional view of an apparatus suitable for performing the method according to the present invention;
FIG. 2 is a cross-sectional view of the first molded body,
FIG. 3 is a cross-sectional view of the second molded body.
[0026]
The die casting machine, designated generally by the reference numeral 1 in FIG. 1, includes a feed hopper 2 suitable for charging granules or powder. The granules or powder are conveyed to a feed opening 3 of an extrusion cylinder 4 via a conveying device (not described in detail).
[0027]
In order to prevent oxidation of the feed material, the transport device and feed hopper 2 are purged with an inert gas. The inert gas used is, for example, argon or nitrogen.
[0028]
The screw 5 provided inside the extrusion cylinder 4 is rotatable and can move in the axial direction. The screw 5 is spirally wound around the blade 6. The open end of the screw 5 is designated by reference numeral 7. The extrusion cylinder 4 has a die 8 at its outflow end. The die 8 opens to the gate of the two-part mold 9 and can be closed by a valve (not shown). The mold 9 is formed of two parts to form the cavity 10.
[0029]
The opposite end of the screw 5 is connected to a high-speed injection molding machine 11 known per se. This device comprises a storage battery 12 and a cylinder 13 fixed by bearings 14 and 16. A shot or injection plunger 15 extending to and reaching the back pressure bearing of the coupling 17 is arranged downstream of the cylinder 13. This allows a connection to the drive shaft 18 in a manner known per se and, if necessary, the injection plunger 15 only performs a reciprocating movement without rotation. Drive shaft 18 extends from rotary drive 19 in a conventional manner. Accordingly, when the drive shaft 18 reciprocates in the horizontal direction, the injection plunger 15 moves. The drive shaft 18 is connected to the screw 5 via a drive coupling 20 in a known manner. This is to transmit the rotational movement to the screw 5. Similarly, axial movement can be transmitted to the screw 5.
[0030]
(Example 1)
The powder is fed through the feed hopper 2. This powder consists of a magnesium alloy, for example of the AZ91 type. MGH ₂ having an average particle size of 100 μm and an average particle size of 10 μm used as a foaming agent. Mix with dust. The foaming agent makes up 0.5% of the weight of the dust.
[0031]
This premixed powder is conveyed to the feed opening 3 of the extrusion cylinder 4 via a conveying device under an inert gas, for example, argon atmosphere. Due to the movement of the screw 5, the mixed powder is carried toward the die 8. At the same time, the mixed powder is heated and pressurized at an accelerated rate. This mixed powder is heated by an external heating device such as a strip heater.
[0032]
The screw 5 rotates almost 100 times per minute. As it approaches the die 8, the mixed powder is heated to above the solid state temperature of 465 ° C. The internal pressure of the ante chamber provided in the extrusion cylinder 4 and indicated by the reference numeral 21 can exceed 30 bar and can reach 500 or 1000 bar. The temperature immediately before injection molding is about 20 ° C. higher than 596 ° C., which is the liquidus temperature of the alloy. Therefore, the mixed powder is in a completely dissolved state. The lysate is mixed until uniform. The pressure acting on the melt in the ante chamber 21 is higher than the gas pressure generated by the foaming agent at the above temperature. Therefore, the melt does not foam.
[0033]
As soon as a sufficient amount of melt has entered the ante chamber 21, the die 8 is ready for opening. At the same time, the open end 7 of the screw 5 is driven toward the die 8 by the high-speed injection molding machine 11. The melt is carried into the cavity 10 and the pressure is released. The gas pressure is higher than the ambient pressure. The melt suddenly starts foaming, completely closing the cavity 10. The two parts constituting the mold 10 are preferably heated in advance.
[0034]
(Example 2)
An alloy containing 99% of aluminum, 1% of magnesium and a small amount of silicon is used as the first powder. The average particle size of the first powder is and 100 μm. The second powder includes TiH ₂ having an average particle size of 10 μm. Is used. The first and second powders are conveyed to the feed opening 3 of the injection cylinder 4 under an inert gas, for example, argon gas atmosphere. The mixed powder is intensively kneaded along a transport path extending from the feed opening 3 to the ante chamber 21, and is heated by an external heating device to a liquidus temperature, here 630 ° C., to a temperature as low as about 20 ° C. An argon pressure of 100 bar is applied. As a result, the mixed powder is partially dissolved. The solid phase content of this dissolved part is approximately 35%.
[0035]
As soon as the partially dissolved mixed powder is filled in the ante chamber 21, the die 8 opens. The partially dissolved mixed powder is injected into a mold while being in a thixotropic state. The pressure in the mold is released to 26 bar.
[0036]
FIG. 2 is a cross-sectional view of a body formed in the above-described manner by a microscope under direct illumination. No air bubbles are observed at the edge of the molded body. This is because, since the semisolid and thixotropic material is injection-molded, the melt does not foam uncontrollably in the mold. The cell structure is uniform.
[0037]
(Example 3)
A series of steps is the same as in Example 2. The only difference is that the pressure in the mold is released up to 11 bar.
[0038]
FIG. 3 is an image showing a cross section of a body formed in this way by a microscope under direct illumination. The length of the sample is also 20 mm. Similarly, there are substantially no bubbles at the edge. The cells inside the molded body are evenly distributed, but the average size of the cells is larger than that of the molded body shown in FIG. This is due to the lower foaming pressure in the melt.
[Brief description of the drawings]
FIG.
1 is a sectional view of an apparatus suitable for carrying out the method according to the invention.
FIG. 2
It is sectional drawing of a 1st shaping | molding body.
FIG. 3
It is sectional drawing of a 2nd molded body.
[Explanation of symbols]
1 Hot Chamber Die Casting Machine 2 Feed Hopper 3 Feed Opening 4 Extrusion Cylinder 5 Screw 6 Blade 7 Open End 8 Die 9 Mold 10 Cavity 11 High Speed Injection Molding Machine 12 Storage Battery 13 Cylinder 14 Bearing 15 Injection Plunger 16 Bearing 17 Coupling 18 Drive Shaft 19 Rotary drive 20 Drive coupling 21 Ante chamber

Claims (19)

A method of molding a body from metal foam,
a) supplying a first powder composed of a metal and a second powder composed of a foaming agent;
b) supplying the first and second powders to an extruder (4, 5, 6, 7), wherein the first and second powders are in an unformed state;
c) a step of transporting the mixed powder comprising the first and second powders from the extruder (4, 5, 6, 7) to the mold (9), while the step is being performed. The mixed powder is partially dissolved, and applying a pressure higher than the gas pressure generated by the blowing agent to the at least partially dissolved mixed powder,
d) injecting the mixed powder, at least partially dissolved, into the mold (9); and e) reducing the pressure to a level below the gas pressure to reduce the formed metal foam to the mold. A method comprising the step of completely filling (9). Method according to claim 1, characterized in that the average particle diameter of the first powder is in the range of 5-250 [mu] m, preferably 100 [mu] m. Method according to claim 1 or 2, characterized in that the average particle diameter of the second powder is in the range from 5 to 50 [mu] m, preferably 10 [mu] m. Method according to any of the preceding claims, characterized in that the first and second powders are mixed before being introduced into the extruder (4, 5, 6, 7). The method according to any of the preceding claims, characterized in that the first and / or second powder is supplied to the extruder (4, 5, 6, 7) under an inert gas atmosphere. Method. Method according to any of the preceding claims, characterized in that the first and second powders are mixed in the extruder (4, 5, 6, 7) by the action of shear forces. The method according to any of the preceding claims, characterized in that the mixing and / or conveying of the mixed powder is carried out by a rotary movement of a screw (5) of the extruder (4, 5, 6, 7). the method of. Method according to any of the preceding claims, characterized in that the mixed powder is continuously heated along a transport path extending from the feed opening (3) towards the ante chamber (21). The method according to any of the preceding claims, characterized in that the mixed powder is heated in the extruder (4, 5, 6, 7) to a temperature of about 50 ° C, preferably 20 ° C above the liquidus temperature. Crab method. Method according to any of the preceding claims, characterized in that the solid content of the at least partially dissolved powder mixture is between 20 and 50%, preferably between 30 and 40%. A method according to any of the preceding claims, characterized in that the mixed powder, at least partially dissolved, accumulates in an antechamber (21) in a semi-solid thixotropic state. A method according to any of the preceding claims, characterized in that the blowing agent used is a pre-oxidizing blowing agent. Method according to any of the preceding claims, characterized in that the mixed powder is heated in the extruder (4, 5, 6, 7) by an external heating device. A method according to any of the preceding claims, characterized in that a pressure of more than 10 bar, preferably more than 30 bar, is applied to the extruder (4, 5, 6, 7) at a temperature of more than 300 ° C. Method. Method according to any of the preceding claims, characterized in that the injection molding of the mixed powder, at least partially dissolved, is performed by an axial movement of the screw (5) towards the mold (9). Method according to any of the preceding claims, characterized in that the mold (9) is pre-heated. Method according to any of the preceding claims, characterized in that the size of the cavity enclosed by the mold (9) is increased after injection molding. Method according to any of the preceding claims, characterized in that the metal used is magnesium, aluminum, magnesium alloy or aluminum alloy. The blowing agent used is a metal hydride, preferably TiH ₂ Or MgH ₂ A method according to any of the preceding claims, characterized in that: