EP2983848A1

EP2983848A1 - Pore die casting

Info

Publication number: EP2983848A1
Application number: EP14716780.3A
Authority: EP
Inventors: Torsten SÖDERBERG; Christian Hannemann
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; SMA Solar Technology AG
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; SMA Solar Technology AG
Priority date: 2013-04-11
Filing date: 2014-04-04
Publication date: 2016-02-17
Anticipated expiration: 2034-04-04
Also published as: EP2983848B1; DE102013103672A1; WO2014166841A1

Abstract

In a process for die casting moulded bodies having pores filled with gas (6) from a die-cast alloy (3), in which the liquid die-cast alloy (3) is pressed together with the gas (6) into a mould cavity having a negative mould of the moulded body, the gas (6) and the die-cast alloy (3) are together enclosed in a casting cylinder (1) without prior mixing, and a casting piston (5) is advanced in the casting cylinder (1) at such a high speed that the gas (6) and the liquid die-cast alloy (3) mix by no later than upon entry into the mould cavity.

Description

Pore-CAST

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for pressure casting of gas filled pores having moldings of a die-cast alloy, wherein the liquid die casting alloy is pressed together with the gas in a Formkavitat having a negative mold of the moldings.

The term "liquid diecasting alloy" is used here as a synonym for the term "melt of the diecasting alloy".

The production of gas-filled moldings from a die-cast alloy, compared to solid moldings without pores leads to a saving of material, d. H. of die-cast alloy, and to a weight reduction.

STATE OF THE ART

US 2002/0121157 A1 and US 2003/0049150 A1 disclose processes for die-casting gas-filled shaped bodies from a diecasting alloy in which a blowing agent is added to the liquid diecasting alloy. This blowing agent releases the gas after injection of the liquid die casting alloy into a mold cavity, which forms the desired pores. Since the gas release is thermally triggered, the blowing agent of the liquid die casting alloy can be added only just before being pressed into the mold cavity, which makes a uniform distribution of the blowing agent in the liquid die casting alloy difficult. Even if the blowing agent of the liquid melt is added just before pressing into the mold cavity, the pressing in the Negative mold with comparatively high pressure to delay the rapid onset of the gas due to the high temperature of the melt by the blowing agent until the liquid die casting alloy has arrived with the blowing agent in the mold cavity. Furthermore, the blowing agent may contaminate the diecasting alloy in such a way that problems may arise in recycling the molded articles produced by this known process.

From FR 2921281 and US 3,177,574 methods for producing a porous aluminum alloy body are known, a liquid Aluminiumlegieru ng during casting in a mold cavity in the salt particles are added, which then dissolved out of the resulting by solidification of the aluminum alloy moldings become. The thus-formed open pores of the shaped body can be closed only in another procedural document, for example by coating with a shell made of solid aluminum.

From EP 1 288 320 B1 a method for the production of metal foam is known, which has the features of the ei ngangs besch riebenen type, ie the preamble of u nabhängigen patent claim 1 corresponds. Air is introduced through fine nozzles into the liquid die casting alloy while it is in a melt vessel. This is done by a gas inlet tube projecting into the liquid die-cast alloy with a small gas outlet cross-section. This should be more uniform bubble and thus pore distributions are achieved than with a nozzle opening on the wall of the melt vessel.

A disadvantage of this known method is that it can be carried out only with special equipment, d. H. if there is a melt container with a gas inlet tube and further equipment connected thereto.

From EP 0 877 658 B1 and its German translation published as DE 697 00 431 T2, it is known for the formation of an alloy material for semisolid shaping to introduce into liquid metal a certain amount of a gas which is soluble in the metal bath and chemically unreacted with it and therefore ensure that the gas bubbles are distributed finely and evenly. The most suitable gas should be hydrogen, possibly mixed with a neutral gas such as nitrogen or argon. As a source of hydrogen, fluxes of hydrous salts may also be used. To initiate Hydrogen can be used a treatment pan, which is usually arranged between holding furnace and casting, z. B. a provided with a gas injector with a rotating nozzle pan. It can also be used a static Gaseinblasanlage.

From DE 41 12 753 A1 and belonging to the same patent family EP 0 581 786 B1 methods for controlling casting parameters of a die casting machine are known. Both documents do not deal with pores in the moldings produced. The same applies to WO 01/81027 A1, which describes a method for the controlled drive of the casting axis of die casting machines with a drive piston.

DE 10 201 0 054 272 A1 discloses a method for simulating casting defects and microstructures of castings which simulates casting defects and the microstructure of the respective molding using an integrated model of pore growth and interdendritic flow. From this, the size, the percentage by volume and / or the distribution of casting defects and microstructures of a molding are predicted.

EP 0 904 875 B1 (German translation published as DE 698 09 166 T2), EP 0 802 840 B1 (German translation published as DE 696 28 139 T2), DE 1 558 261 C, DE 42 09 868 A1, DE 20 2010 009 838 U1 and DE 42 16 293 A1 are concerned with the avoidance of air or gas inclusions during die casting of moldings.

OBJECT OF THE INVENTION

The invention has for its object to provide a method for die casting of moldings from a gas-filled pores having diecasting alloy, without special supplements to the die-casting alloy and without the need for special equipment, d. H. with a normal die-casting machine, is executable.

SOLUTION

The object of the invention is achieved by a method having the features of independent claim 1. Preferred embodiments of the method according to the invention are defined in the dependent claims. DESCRIPTION OF THE INVENTION

In a method according to the invention to die casting of gas-filled pores having moldings of a die-cast alloy, wherein the die-cast alloy is pressed in the liquid state together with the gas in a Formkavitat having a negative mold of the moldings, the gas and die casting alloy without prior mixing enclosed together in a casting cylinder. A casting piston is in this case advanced in the casting cylinder at a speed selected in such a way that the gas and the die casting alloy mix at the latest when they enter the mold cavity.

In the method according to the invention, therefore, first the required amount of gas is simply introduced into the casting cylinder next to the die-cast alloy or left therein, and the casting cylinder is closed - typically by advancing the associated casting piston beyond the filling opening of the casting cylinder. Then, the casting piston is further advanced, over at least a portion of its feed path with comparatively high height, but with a conventional die casting machine speed still achievable. Surprisingly, it turns out to be easy to tune this relatively high speed so that the gas and the liquid die casting alloy mix at the latest when entering the mold cavity so that high-quality moldings arise with homogeneously distributed pores in a significant proportion. At the same time, the finished molded body has a closed surface.

The method according to the invention leads to an advantageous result if a comparatively large volume of gas is included in the casting cylinder together with the liquid melt. Thus, when closing, the casting cylinder can be filled to a maximum of one-half, preferably a maximum of one-fourth, such as about one-seventh, with the liquid pressure alloy and otherwise with the gas. This mixing ratio significantly determines the achievable porosity of the cast body.

The gas may be air from the environment, so there is no need to introduce any special gas besides the liquid die casting alloy into the casting cylinder. It may nevertheless be useful to fill the casting cylinder with another gas, for example an inert gas such as nitrogen or a noble gas to avoid a chemical reaction in the melt. It is believed that it is advantageous for the mixing of the gas and the liquid die casting alloy already in the casting cylinder if the speed of the casting piston in the casting cylinder is selected so as to have a roll of liquid die casting alloy in the casting cylinder formed. The prerequisite for the formation of the overturning shaft is, in addition to the speed of the casting piston, the lower degree of filling of the casting cylinder compared to the previously known methods. The dynamically approaching, resting on the stationary die-casting liquid casting casting deflects this upwards in the area of the above the liquid die-casting alloy gas. The occurrence of a deflecting wave of the liquid diecasting alloy was concretely observed in the method according to the invention. The formation of the shaft and thus the mixing of melt and gas can be significantly influenced by suitable shaping of the casting cylinder and / or the piston.

Another cause for the mixing of the gas and the liquid die casting alloy in the method according to the invention will be a turbulent flow, which forms from the gas and the liquid die cast alloy in the casting cylinder in front of the rapidly advanced casting piston. When discussing a turbulent flow, this does not necessarily mean that the flow meets the physical criteria of turbulence. On the contrary, a flow is regarded as turbulent even here if it comprises sufficient heat for continued mixing and distribution of the gas into the liquid diecasting alloy.

An additional possibility for the mixing of air and melt or for the formation of a turbulent flow would be a rotary movement of the piston during the advance in connection with a shaped and formed piston, for example with the piston formed on the plunger, into the melt dipping mixing blades. Optionally, by one or more convoluted mixing blades even without rotational movement, the forward movement of the piston snowplough-like in a sideways / upward movement of the melt can be implemented. The shaft opposite the casting piston end of the casting cylinder can in this case likewise form an overturning shaft upon impact with the casting cylinder end and thus contribute to the mixing of melt and gas. For this purpose, structures at the end of the casting cylinder and / or in the runner can also be helpful for the best possible mixing or for the formation of a turbulent flow of melt and gas. The speed of the casting piston in the casting cylinder determines the porosity of the cast body. Speed values of at least 2 m / s, preferably at least 6 m / s lead to satisfactory results. For example, it is about 6.5 m / s. This speed is advantageously adjusted after closing the casting cylinder by means of a speed control as a constant value. For example, this constant value over a feed distance of at least 50%, so for example over 60% of the total piston movement can be maintained. In particular, at the end of the speed-controlled feed-forward, for example for the maximum 5% of the total feed, the setpoint of the speed control can be considerably reduced, for example by 50%, so that at the end of the feed motion a controlled reduction of the feed rate is achieved Piston speed results. Thus, additional wear of the system can be avoided by a casting piston striking the end of the casting cylinder at high speed. However, it is also conceivable to travel the entire feed path, which is controlled by means of a speed control, at a constant speed.

In an advantageous embodiment of the invention, the forward movement of the casting piston is changed over from the speed control during the feed to a pressure control when the casting piston is pressed in the casting cylinder. When repressing a constant pressure can be exercised until solidification of the die-cast alloy. The pressure may, for example, be applied for one second or less, in particular not more than 0.5 seconds. Here it is advantageous not to exceed pressure values of 50 MPa, that is, for example, to use less than 25 MPa. In one embodiment, a pressure of 16 MPa was used.

To displace an equal volume, a casting piston of lesser diameter must be advanced further forward than a casting piston of larger diameter. A displacement of this volume in the same time thus results in very different speeds of the casting piston. The ratio between the diameter of the casting piston and its feed in the closed casting cylinder thus also affects the achievable feed rates. In the method according to the invention, a ratio between the diameter and the feed of the casting piston in the closed casting cylinder of at most 1: 4 is preferred. Even more preferred is a ratio of 1: 5 or even smaller. That is, the displacement of the internal volume of the Casting cylinder is achieved less by a large end face of the casting piston than by a higher path and a higher speed of the casting piston.

A proportion of the pores in the volume of the molding with the method according to the invention of 40% is quite achievable. By a suitable choice of the process parameters with the method according to the invention, for example, stable proportions of the pores were set in a range of 20-25%, without impairing the integrity of the molded bodies produced or accepting substantial losses in the throughput of the casting plant. This means a savings in die-cast alloy and a weight reduction in just this size. The diecasting alloy may in particular be an aluminum alloy. The process according to the invention was successfully carried out with a remelting alloy 331 (G Al Si 12 Cu 1 (Fe)).

Since the die-casting alloy is free from any gas-releasing additives in the process of the present invention, moldings produced by the method of the present invention are easy to recycle.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the description are merely exemplary and can take effect alternatively or cumulatively, without the advantages having to be achieved by embodiments according to the invention. Without altering the subject matter of the appended claims, as regards the disclosure of the original application documents and the patent, the following applies: Further features can be found in the drawings. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to features that are shown in separate drawings or are used in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted. The features mentioned in the patent claims and the description are to be understood in terms of their number that exactly this number or a greater number than the said number is present, without requiring an explicit use of the adverb "at least". For example, when talking about an element, it should be understood that there is exactly one element, two elements or more elements. These features may be supplemented by other features or be the only characteristics that make up the product in question.

The reference signs contained in the patent claims do not limit the scope of the objects protected by the claims. They are for the sole purpose of making the claims easier to understand.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be explained and described in more detail below with reference to the accompanying drawings.

FIG. 1 is a longitudinal section through a casting cylinder having thereon. FIG

Casting a otherwise not shown die-casting machine.

Fig. 2 is a velocity profile over the feed of the casting piston

Casting cylinder according to FIG. 1 in the method according to the invention.

FIG. 3 is a detail of an enlarged longitudinal section through the casting cylinder according to FIG

Fig. 1 during rapid advancement of the casting piston at the highest speed of FIG. 2; and

Fig. 4 is a pressure profile over time during pressing with the casting piston according to

Fig. 1 in the inventive method.

DESCRIPTION OF THE FIGURES

In Fig. 1, a casting cylinder 1 of a die-casting machine not shown is shown schematically. From the casting cylinder 1 is a sprue distributor 2, which is divided into several Sprue channels 9 can branch, which then open into a Formkavitat 8. This Formkavitat 8 has a negative mold of molded articles to be produced. These moldings are made of a Druckgusslegieru ng 3, which is filled in the liquid state, ie as a melt in the casting cylinder 1 via a filling opening 4. By advancing a casting plunger 5 in the casting cylinder 1, the liquid die casting alloy 3 is pressed through the casting manifold 2 into the mold cavity. As soon as the casting piston 5 arrives behind the filling opening 4 in the feed direction, it closes the casting cylinder 1. At this point, the degree of filling of the casting cylinder 1 with the die-cast alloy 3 in the method according to the invention is so low that the closed casting cylinder 1 only contains the die-cast alloy 3 and otherwise air for example about 1/7.

FIG. 2 is a velocity profile of the casting piston 5 through its feed in the casting cylinder 1 according to FIG. 1. In a region I, the casting piston 5 moves at a low speed. After a path Si, he has closed the casting cylinder 1 according to FIG. 1 by being advanced to the end of the filling opening 4. Then the speed of the casting piston 5 is increased to a maximum value V _max , for example to 5 m / s. This speed V _max is maintained in the range II until shortly before the end of the feed distance S ₂ , where the casting piston 5 is braked towards the end of its feed into the casting cylinder 1 optionally by setting a second speed value. In this case, it is not decisive whether the second speed value set as the setpoint value is actually reached until the feed S ₂ is reached. In this case, the mixing of melt and air is accomplished and the mold cavity is filled with the mixture of the die casting alloy 3 and the air trapped in the casting cylinder 1.

During the rapid feed of the casting piston 5 in the casting cylinder 1 between Si and S _{2 shown in} FIG. 2 wi thus the basis for the mixing of the gas 6 in the die-cast alloy 3 is placed at the latest when entering the mold cavity. Fig. 3 outlines that is located in the casting cylinder 1, the therein liquid die-casting alloy 3 is deflected upward forward by the rapid advancement of the casting piston 5 and thus forms an overturning shaft 7 in the gas 6 into it. The gas taken in this way enters with the diecasting alloy 3 into the distributor 2 according to FIG. 1 and the adjoining sprue channels 9. The continuing from the casting cylinder 1 turbulent flow of the liquid die-casting alloy 3 results in a fine distribution of bubbles from the gas 6 in the mold cavity forming in the mold cavity. These bubbles form the Most closed pores in the molding and thus define the porosity of the molded body.

4 shows an exemplary pressure profile over the time t, which represents the pressure conditions in the casting cylinder 1 during the feed in the region I and II, as well as during a subsequent Nachdrückens in the area III. Here, the time t-ι corresponds to the feed Si, and the time t _{2 to} the feed S ₂ , at which the piston movement substantially ends and the Nachdrückschritt begins. During the re-pressing process in the region III, a constant pressure P _{Nach is} applied to the casting piston 5 which serves the purpose of displacing remaining larger contiguous gas volumes, leaving the desired fine-pored gas inclusions defining the porosity. As a result, a complete filling of the mold cavity 5 is achieved with a porous filling of the die-cast alloy 3 until time t ₃ . A slight further advance of the casting piston 5 during the push-back phase as a result of the displacement is neglected in the representation of the velocity profile according to FIG. The forcing process may have a duration of, for example, between 0.5 and 1 second, and is preferably tuned for the duration until the die cast alloy solidifies. After solidification of the diecasting alloy, maintaining the reprinting is no longer necessary.

On a die casting machine Frech DAK 100-1 12 from a remelted alloy 331 using a casting cylinder with a closed internal volume of about 4,400 cm ³ , in which about 620 cm ³ die-cast alloy and otherwise air were included, and a casting piston 5 with a diameter of about 10 cm and a feed in the closed casting cylinder 1 of about 55 cm were prepared by the novel process molding with a stable pore content of 20-25%. The following parameters were used. Phase piston feed speed / pressure (setpoint)

I close 0 - 120 mm 0.2 m / s

II die casting 120 - 640 mm 5.0 m / s

II caster 640 - 665 mm 2.0 m / s

III reprint 0 - 1 sec 16 MPa

The maximum feed rate of the casting piston, which was set directly after closing the filling opening at a feed rate of 120 mm by means of a speed control, was 5 m / s. At a pressure of about 4 MPa due to the movement, the alloy-air mixture was pressed into the mold cavity. Subsequently, the speed control of the casting piston changed over to a pressure control of the casting piston. At subsequent pressing in the casting plunger, a maximum pressure P of 16 MPa _After achieved. The pores were closed, finely distributed in the moldings and did not affect their surface quality.

LIST OF REFERENCE NUMBERS

1 casting cylinder

2 sprue distributors

3 die-cast alloy

4 filling opening

5 plunger

6 gas

7 overturning wave

8 mold cavity

9 sprue

S way

t time

V speed

p pressure

Claims

1 . Method for pressure casting of gas-filled (6) filled pores having moldings of a die-cast alloy (3), wherein the liquid die casting alloy (3) is pressed together with the gas (6) in a Formkavitat having a negative mold of the moldings, characterized that the gas (6) and the die casting alloy (3) are included together in a casting cylinder (1) without prior mixing and that a casting piston (5) is advanced in the casting cylinder (1) at a speed (V) selected in such a way mix the gas (6) and the liquid diecasting alloy (3) at the latest when entering the mold cavity.

2. The method according to claim 1, characterized in that the casting cylinder (1) when closing a maximum of half, preferably to a maximum of one quarter, with the liquid die-casting alloy (3) and otherwise filled with the gas (6).

3. The method according to claim 1 or 2, characterized in that the gas (6) is air.

4. The method according to any one of the preceding claims, characterized in that the speed (V) of the casting piston (5) in the casting cylinder (1) is selected such that an overturning shaft (7) of the liquid die casting alloy (3) in the casting cylinder (1) trains.

5. The method according to any one of the preceding claims, characterized in that the Gießkoben (5) at such a selected speed (V) in the casting cylinder (1) is advanced, that is a turbulent flow of the gas (6) and the liquid die casting alloy (3) in the casting cylinder (1) and / or a subsequent sprue distributor (2) is formed.

6. The method according to any one of the preceding claims, characterized in that the speed (V) of the casting piston (5) in the casting cylinder (1) is at least 2 m / s, preferably at least 6 m / s.

7. The method according to any one of the preceding claims, characterized in that a ratio between the diameter of the casting piston (5) and the feed of the casting piston (5) in the closed casting cylinder (1) is at most 1: 4, preferably at most 1: 5 ,

8. The method according to any one of the preceding claims, characterized in that the casting piston (5) after the closing of the casting cylinder (1) speed-controlled at a constant first speed (V) in the casting cylinder (1) is advanced.

9. The method according to claim 8, characterized in that the constant first speed (V) of the casting piston (5) after closing the casting cylinder (1) over at least 50%, preferably at least 60%, of the path (S) of the casting piston (5 ) is maintained in the casting cylinder (1).

10. The method according to claim 8 or 9, characterized in that the casting piston (5) is advanced after advancing at the constant first speed (V) at a second speed, which is reduced by at least 50% compared to the first speed.

1 1. Method according to one of claims 8 to 10, characterized in that at the end of the forward movement of the casting piston (5) in the casting cylinder (1) from a speed control during the feed to a pressure control when pressing the casting piston (5) in the casting cylinder (1) becomes.

12. The method according to claim 1 1, characterized in that upon pressing of the casting piston (5) in the casting cylinder (1) the pressure (PNach) until the solidification of the die-cast alloy (3) is kept constant.

13. The method of claim 1 1 or 12, characterized in that s s at m subsequent pressures of the casting piston (5) in the casting cylinder (1) the pressure (PNach) a maximum of 50 MPa, preferably below 25 MPa, in particular not more than 16 MPa, is.

14. The method according to any one of claims 1 1 to 13, characterized in that the casting piston (5) for not more than 1 second, preferably not more than 0.5 seconds, is pushed.

15. The method according to any one of the preceding claims, characterized in that the casting piston (5) during the forward movement in the casting cylinder (1) is rotated.