EP2480357B1 - Vacuum die casting device and method for oprating a vacuum die casting device - Google Patents

Description

The invention relates to a vacuum die casting system according to the preamble of claim 1.

Such vacuum die casting systems are for example from the JP 2004 268051 A , of the JP 1 313171 A and the JP 1 313174 A known.

Vacuum die casting is known for the production of castings from metals and metal alloys, in particular from alloys of the metals AI, Mg, Zn and Cu. Other systems for vacuum pressure casting are, for example, in the DE 4312647 A1 , of the DE 102004057324 A1 or the DE 102006101560 A1 described.

Vacuum die casting is used in particular where there are high demands on tightness, elongation at break, strength and weldability of the cast parts. Vacuum die-casting achieves a higher quality castings because less air and gases are trapped in the material. This applies in particular to cast parts made of aluminum or an aluminum alloy that are still heat-treated or welded in a later process.

In addition to the use of liquid metals or metal alloys, there are various special processes for vacuum pressure casting, such as those used for " Rolf Roller (ed.): Specialist for foundry professions, Haan-Gruiten, 2007; Pages 186 - 187 "The present invention also encompasses such special processes insofar as the corresponding vacuum pressure casting systems have a casting chamber with a filling opening, a casting piston movable in the casting chamber and a piston rod, the latter connecting the casting piston to a casting drive, and between the outer jacket of the casting piston and the inner wall the casting chamber an annular gap is formed, which usually forms a leak - as described below.

In vacuum die casting, as is known, a negative pressure or vacuum is generated in the mold cavity of the casting mold of the vacuum die casting system after the casting chamber has been filled with molten casting fluid and the casting piston has passed the filling opening of the casting chamber.

In order to minimize the negative pressure generated in the mold cavity of the casting mold or in the casting chamber connected to the mold cavity during vacuum pressure casting, it is necessary to largely seal off all possible leaks or imperfections within the complete vacuum system.

An extremely important leak is the annular gap between the inner wall of the casting chamber and the outer jacket of the casting piston. At this leak, gases penetrating from the rear of the casting piston, the casting melt foams up in the casting chamber, which is under vacuum, and generates gas porosity in the casting, which minimizes or excludes heat treatment and weldability.

The DE 43 12 647 A1 offers a solution to close this leakage point, after which a technically very complex evacuable sliding sleeve is pushed over the casting chamber or casting piston system in order to create a vacuum behind the piston. A particular disadvantage here is the very high maintenance requirements of such vacuum die casting systems.

The object of the invention is to avoid the disadvantages of the prior art and, in particular, to improve the serviceability of vacuum die-casting systems.

According to the invention, this object is achieved in a vacuum pressure casting system which has a casting chamber with a filling opening, a casting piston movable in the casting chamber and a piston rod which connects the casting piston to a casting drive, an annular gap being formed between the outer jacket of the casting piston and the inside wall of the casting chamber, where the casting piston has at least one evacuable depression or cavity in flow connection with the annular gap and means are provided via which the depression or cavity can be evacuated, in that the means comprise at least one, preferably two or more suction lines, in particular suction tubes, which are each fluidically connected at one end to the evacuable depression or cavity and at the other end fluidically to a vacuum system, the suction line, in particular the suction pipe, along the piston rod in e The groove introduced on the outside of the piston rod runs and with its one end passes through a piston or workpiece area facing the piston rod into the recess or cavity and is connected to it in terms of flow technology.

According to the invention, the exchange of the means and the manufacture of vacuum die casting systems designed in this way are facilitated.

The term piston rod is broadly defined according to the invention. In addition to a piston rod in the narrower sense, which is preferably advantageous for the majority of applications, it also includes other actuating means which move the casting piston linearly within the casting chamber. For certain applications it can be advantageous if the piston rod is a connecting rod. For certain applications, it can in turn be useful if the rod driving the casting piston is part of an eccentric.

It has been shown that the decisive parameters for the flow velocity of the gases within the leak between the inner wall of the casting chamber and the outer jacket of the casting piston are the gap thickness between the casting piston and the casting chamber and the pressure difference across the gap.

Since it is not possible to work without gaps due to large differences in heat in the casting chamber area, the provided recess or cavity ensures that - if this is evacuated - less or preferably no gases or air flow through the gap into the casting chamber containing the casting melt, if a negative pressure is generated in the casting mold cavity or in the casting chamber connected to it in terms of flow technology.

A region that is preferably essentially free of pressure differences is created, so that fewer, preferably only minimally or no, or no gases or air flow through the gap into the casting chamber filled with casting melt.

Advantageously, the negative pressure in the depression or cavity can even be greater than in the casting chamber filled with molten melt, so that the direction of flow is virtually reversed and gases and air flow from the pouring chamber filled with molten melt into the depression or cavity. In the latter case there is of course a desired pressure difference across the annular gap.

As a result, an effective sealing of the annular gap between the outer jacket of the casting piston and the inner wall of the casting chamber during vacuum pressure casting is achieved in such a way that no gases or air flow through the annular gap into the casting chamber filled with casting melt. In addition, an undesirable, so-called pulling out of the melt from the casting chamber into the mold cavity is prevented.

The functionality of the vacuum pressure casting system is advantageously easy to check and the vacuum pressure casting system does not require any additional components for the sealing of the annular gap between the casting piston and the casting chamber, which would be disadvantageously very susceptible to wear and maintenance.

Advantageously, all components of the vacuum die casting system according to the invention are very easily accessible and easily replaceable for maintenance work on the vacuum die casting system.

Overall, the further development according to the invention can also be produced cost-effectively for vacuum pressure casting systems which are already in use.

The control effort for evacuating the recess or cavity is minimal and is preferably carried out via path and / or time control.

The further development of known vacuum die casting systems according to the invention advantageously does not lead to an increase in the cycle time. Rather, a shortening or acceleration of the cycle time, that is, the period between the completion of two cast parts, can be achieved. In addition to minimizing or eliminating the undesired leakage through the annular gap, this can also be attributed to a less complex process management of the vacuum die-casting system according to the invention, which tends to result in fewer system failures and maintenance work.

In addition, the further development according to the invention can itself be implemented without conversion work on the casting mold and can be applied to differently dimensioned vacuum pressure casting systems.

For certain applications, it can be advantageous if the depression or hollow is formed in the casting piston itself. This can advantageously be done by master shaping of such a casting piston or preferably later by machining the casting piston, in particular by milling or grinding.

For other applications, it can be advantageous if the recess or cavity is at least directly or indirectly behind the casting piston by arranging it a workpiece is formed behind the casting piston, the arrangement of the depression or cavity behind the casting piston being such that the depression or cavity can be brought into the casting chamber before it is evacuated into the region of the casting chamber which is not filled with molten melt by moving the casting piston into it.

For certain purposes, the depression or hollow can be formed in the workpiece itself. For other purposes, it can be advantageous if the workpiece is spaced from the casting piston in such a way that the depression or cavity is formed between the casting piston or at least one further workpiece arranged behind the casting piston and the first-mentioned workpiece. For still other purposes, it can also be advantageous if the depression or hollow in the workpiece itself is designed in combination with the aforementioned spaced arrangement.

In particular for retrofitting existing die casting systems, it can be advantageous if the workpiece is ring-shaped and can preferably be pushed and fixed onto the piston rod. Such a workpiece can be fixed in a simple manner by clamping on the piston rod, in particular through a conical configuration of the ring opening and / or the piston rod. Of course, the workpiece can also be arranged behind the casting piston by other, less preferred, but nevertheless advantageous types of fastening, in particular by screwing, pressing in or welding.

For certain applications, it may be expedient if the casting piston is constructed in several parts. However, the casting piston is preferably formed in one piece or in one piece.

It can also be advantageous if the casting piston is solid.

In order to prevent undesirable substances, e.g. flakes or lubricants, from reaching the at least one evacuable depression or cavity through the annular gap during vacuum pressure casting, it can be expedient if at least one collecting depression is provided which is in flow connection with the annular gap and before the at least one an evacuable depression or cavity is arranged. The at least one collecting recess then serves as a kind of dirt trap and in particular also prevents the undesired substances from getting into the vacuum system or clogging the vacuum suction lines emanating from the at least one evacuable recess or cavity.

It can be advantageous if the collecting recess and / or evacuable recess is designed as a recess encircling the outer jacket of the casting piston, the piston rod and / or the workpiece, preferably in the form of an annular groove.

A circumferential evacuable depression is advantageously arranged completely within the flow path of the gases or the air, so that little or preferably no gases or air get into the casting chamber through the gap between the casting chamber and the casting piston. An undesired pressure difference known according to the prior art, which arises when the casting mold cavity or the casting chamber is evacuated and leads to the inflow of gases or air through the annular gap into the casting chamber, is significantly reduced or preferably eliminated. The undesired pressure difference is even more preferably reversed by selecting the negative pressure inside the depression or cavity to be greater than in the casting chamber filled with molten casting material or in the mold cavity of the casting mold which is connected to the casting chamber in terms of flow. A desired pressure difference thus arises which causes the flow direction to be reversed.

A circumferential collection recess can be particularly expedient in order to create the broadest possible border for undesirable substances and to largely prevent the penetration of such substances into the recess or cavity.

For certain applications, however, it can also be advantageous if the collecting recess and / or the evacuable recess or hollow is provided only in the upper outer jacket region of the casting piston, the piston rod and / or the workpiece. It has been shown that, depending on the vacuum pressure casting system used or the dimension and weight of the casting piston movable in the casting chamber, the annular gap between the outer jacket of the casting piston and the inner wall of the casting chamber is not uniform, but is larger at the top than at the bottom.

Furthermore, it can be expedient if a plurality of depressions or hollows spaced apart from one another in the circumferential direction of the casting piston, the piston rod and / or the workpiece are provided.

It can be advantageous if these depressions are arranged distributed over the circumference of a workpiece designed as a ring. These depressions can be through-holes to the inside of the ring. The workpiece can be arranged directly behind the casting plunger, only a vacuum having to be applied to the inside of the ring to evacuate these depressions. A circumferential recess can advantageously be created here if the ring mentioned has a smaller outer diameter than the casting piston, with a further workpiece, preferably also a ring, having the same outer diameter as that being then arranged to produce the circumferential recess behind the ring Pouring plunger. In this case, the individual depressions or bores then form a type of nozzle field through which the only circumferential depression can be evacuated uniformly.

In addition, it can be expedient if a plurality of collecting recesses are provided which are spaced apart from one another in the circumferential direction of the casting piston, the piston rod and / or the workpiece.

It may be expedient if the evacuable depression or cavity is dimensioned and evacuable in such a way that when the mold cavity or the casting chamber is evacuated, less or preferably no gases or air flow into the casting chamber through the annular gap, and the flow direction in the annular gap is particularly preferably reversed and the gases or air flow towards the evacuable depression or hollow. A pressure difference prevailing in the prior art when evacuating the mold cavity or the casting chamber, which leads to the inflow of gases or air through the gap into the casting chamber, i.e. quasi a pressure difference between the chamber filled with casting melt in front of the casting piston and the depression or cavity is minimized, preferably eliminated, particularly preferably reversed, by evacuating the depression or cavity.

It can be advantageous if a vacuum is applied to the evacuable depression or cavity such that when the mold cavity or the casting chamber is evacuated, less or preferably no gases or air flow into the casting chamber through the gap mentioned, and the flow direction in the flow is particularly preferred The gap reverses and the gases or air flow in the direction of the evacuable depression or hollow.

It can be advantageous if the means for evacuating the recess or cavity have at least one recess, in particular a longitudinal recess, within the piston rod, which are fluidically connected at one end to the evacuable recess or cavity and at the other end by fluid technology from a vacuum system .

It can be particularly advantageous if the at least one evacuable depression, when it is not being evacuated, can be used for introducing a lubricant or another functional substance into the casting chamber, the lubricant or the other functional substance then via the at least one vacuum suction line connected to the recess or another for this purpose provided line can be introduced into the recess or cavity and thus into the casting chamber.

It can be particularly advantageous if the means for evacuating the depression or cavity comprise at least one line or bore contained in the piston rod, in particular a coolant line or bore.

It may be advantageous if the cross section of the recess or the suction recess, in particular of the suction tube, is selected to be large enough that the vacuum that can be set in the recess or cavity, despite the presence of leakage between the recess or cavity and the area behind the recess or The cavity is arranged and connected to the cavity or cavity via the annular gap extending from the cavity or cavity and leading to the piston rod, is maintained for a predetermined time, in particular over the time in which the casting chamber and the mold cavity are evacuated and a Negative pressure is maintained in the mold cavity.

It can be expedient if at least one suction pipe is provided within the piston rod, which has one end merging into the depression or cavity and being connected to it in terms of flow technology.

It can be advantageous if the vacuum pressure casting system is a cold chamber vacuum pressure casting system.

It can be advantageous if a control is provided for the vacuum die casting system, which is connected to a control for the vacuum system and via this connection a start signal is transmitted to the vacuum system for evacuating the depression or cavity.

It can be advantageous if the depression or hollow is arranged as close as possible to the area of the casting piston facing the casting chamber filled with melt is. The result of this is that the recess or cavity can be evacuated at an early stage, so that the switching time or usage time of the vacuum increases and the quality of the cast products is further improved by a correspondingly improved vacuum.

1. a) Einbringen einer Gießschmelze durch die Einfüllöffnung in die Gießkammer
2. b) Bewegen des Gießkolbens, bis die Vertiefung oder Aushöhlung die Einfüllöffnung passiert hat, oder dichtes Verschließen der Einfüllöffnung und gegebenenfalls Bewegen des Gießkolbens, bis die Vertiefung oder Aushöhlung in der Gießkammer positioniert ist, und
3. c) Evakuieren der Vertiefung oder Aushöhlung, derart, dass weniger bis vorzugsweise keine Gase oder Luft durch den Spalt zwischen Gießkolben und Gießkammer in die Gießkammer einströmen, besonders bevorzugt derart, dass sich die Strömungsrichtung im Spalt umkehrt und die Gase oder Luft in Richtung evakuierbare Vertiefung oder Aushöhlung strömen.

It can be advantageous if the operation of a vacuum pressure casting system is carried out with the following process steps:

1. a) Introducing a casting melt through the filling opening into the casting chamber
2. b) moving the casting piston until the depression or cavity has passed the filling opening, or sealing the filling opening and, if appropriate, moving the casting piston until the depression or hollow is positioned in the casting chamber, and
3. c) Evacuating the depression or cavity in such a way that less or preferably no gases or air flow into the casting chamber through the gap between the casting piston and the casting chamber, particularly preferably in such a way that the flow direction reverses in the gap and the gases or air in the direction of the evacuable depression or gouge.

Such a process leads to a significant qualitative improvement in the castings.

It can be advantageous if the evacuation of the recess or hollow is started for some applications via a path control and for other applications via a time control. A combination of path and time control can also be advantageous for certain applications.

Fig. 1

in a) einen Schnitt durch eine erfindungsgemäß ausgebildete Kolbenstange und in b) eine Ansicht (mit Teilschnitten) von oben auf den Gießkolben samt Kolbenstange und umlaufender Vertiefung,

Fig. 2

einen Ausschnitt der Gießkammer mit erfindungsgemäß ausgebildetem Gießkolben mit einer Teilansicht der Kolbenstange,

Fig. 3

in a) einen Schnitt durch eine erfindungsgemäß ausgebildete Kolbenstange, wie in Fig. 1 a), und in b) eine Ansicht (mit Teilschnitten) von oben auf den Gießkolben samt Kolbenstange und umlaufender Vertiefung mit Düsenfeld und

Fig. 4

in a) einen Schnitt durch eine erfindungsgemäß ausgebildete Kolbenstange, wie in Fig. 1 a), und in b) eine Ansicht (mit Teilschnitten) von oben auf den Gießkolben samt Kolbenstange und umlaufender Vertiefung sowie vorgeschalteter Sammelvertiefung.

Further details and advantageous embodiments of the invention result from the following description in conjunction with the drawing. In this show:

Fig. 1

in a) a section through a piston rod designed according to the invention and in b) a view (with partial sections) from above of the casting piston together with the piston rod and circumferential recess,

Fig. 2

1 shows a section of the casting chamber with a casting piston designed according to the invention with a partial view of the piston rod,

Fig. 3

in a) a section through a piston rod designed according to the invention, as in 1 a) , and in b) a view (with partial sections) from above of the casting piston together with the piston rod and circumferential depression with nozzle field and

Fig. 4

in a) a section through a piston rod designed according to the invention, as in 1 a) , and in b) a view (with partial sections) from above of the casting piston including the piston rod and circumferential recess as well as an upstream collection recess.

Are in the 1 to 4 If the same reference numbers are used, they also denote the same parts or areas.

The vacuum die casting system according to the invention has a casting mold, not shown here, which is constructed from two mold halves, for example. The interior of the casting mold, that is to say the cavity or the mold cavity, is connected to the casting chamber 10, which is filled with melt for the casting process. This is filled through the filling opening 12 and pressed into the mold cavity by means of the casting piston 14. The gas present in the mold cavity is extracted via a vent valve, not shown here, for example a so-called washboard. During the casting process, the solidifying metal rises up to this vent valve. The casting piston 14 is driven by a casting drive, not shown here Casting piston rod 16 moves, that is, moved in the casting chamber 10. It is controlled by the casting plant control.

The vacuum pressure casting system also has a vacuum system, not shown here, which is connected to the casting chamber 10 and / or the mold cavity via corresponding vacuum lines and the mold cavity together with the space 32 of the casting chamber 10 located in front of the casting piston, for example at a predetermined time during the casting process, evacuated after a predetermined distance of the casting piston 14 or according to other criteria.

Since there is an annular gap 18 between the inner wall of the casting chamber 10 and the outer jacket of the casting piston 14, through which air or gases are drawn from the rear of the casting piston 14 into the casting chamber 10 or into the melt filled therein, the penetrating gases Foam the melt in the casting chamber under vacuum and generate a gas porosity in the cast part that, among other things to minimize or exclude heat treatment and the suitability for welding, it is now provided that the casting piston 14 has at least one evacuable depression 20 which is fluidically connected to the annular gap 18 and means are provided via which the depression or cavity is evacuated.

As a result, a pressure difference which is known from the prior art and which arises when the casting chamber and / or the mold cavity of the casting mold is evacuated, which leads to the inflow of gases or air into the casting chamber, is minimized to preferably eliminated, particularly preferably even the other way round, that the direction of flow changes and gases or air flow from the space 32 of the casting chamber 10, which is located in front of the casting piston 14, through the annular gap 18 into the depression 20.

The evacuable recess 20 is - as in the 1 to 4 shown - formed as an annular groove 24 encircling the casting piston 14 and is therefore advantageously located completely in the flow path of the gases or air actually flowing according to the prior art through the annular gap 18 into the space 32 of the casting chamber 10.

The means for evacuating the depression 20 comprise two suction tubes 22, each of which is connected at the one end 24 to the evacuable annular groove 20 in terms of flow technology and at the other end with the other or a further vacuum system in terms of flow technology. The suction pipes 22 are arranged opposite one another along the piston rod 16 in a groove 26 each made on the outside of the piston rod 16, the ends 24 passing through the piston region 28 facing the piston rod 16 into the annular groove 20 and being connected to the latter in terms of flow technology. The piston rod 16 itself is hollow and has a piston cooling 30.

The casting piston 14 can be formed in one piece, the piston region 28 then being part of the one-piece casting piston 14 and the depression 20 in the form of an annular groove being introduced into the casting piston 14, for example by machining.

Another of the numerous possibilities for producing the depression 20 is that the piston region 28 is a separate workpiece, for example in the form of a connecting ring, which is arranged at a distance from the casting piston 14, in particular is clamped onto the piston rod 16. As a result, as in Fig. 1 it can be seen that a depression 20 is designed in the form of an annular groove.

In Fig. 3 Another of the numerous possibilities for producing the depression 20 is shown. There, a first workpiece in the form of a ring 34 is arranged behind the casting piston 14, the ring 34 having a smaller outside diameter than the casting piston 14. The ring 34 has numerous depressions distributed over the circumference in the form of bores 36 which are fluidically connected on the inside of the ring. It is advantageous here that an evacuation on the inside of the ring leads to a uniform evacuation of the circumferential depression 20. This Numerous depressions in the form of bores 26 form a kind of nozzle field. Another workpiece in the form of a connecting ring connects to the ring 24. This connecting ring then forms the aforementioned piston region 28 and corresponds in its outer diameter to that of the casting piston 14.

Fig. 4 finally shows the device according to Fig. 1 , However, has an additional collecting recess 38 in the form of an annular groove, which serves to trap undesirable substances, such as flakes or lubricants, and is connected upstream of the evacuable recess.

The control for the vacuum die casting system is advantageously connected to a control of the vacuum system for evacuating the annular groove 20, wherein a simple path-controlled or time-controlled start signal transmitted to the vacuum system is sufficient for evacuating the annular groove 20.

In the method for operating a vacuum pressure casting system, it is advantageous that after the casting melt has been introduced into the casting chamber 10 through the filling opening 12, the casting piston 14 is first moved to such an extent that the annular groove 20 has passed the filling opening 12. Subsequently, preferably essentially simultaneously with the evacuation of the mold cavity and the casting chamber 10, the annular groove 20 is evacuated in such a way that no gases or air flow into the casting chamber 10 through the gap 18 mentioned.

Reference list (is not part of the description)

10th

Casting chamber

12th

Filling opening

14

Pouring plunger

16

Piston rod

18th

gap

20th

Ring groove

22

Exhaust pipe

24th

The End

26

Groove

28

Piston area

30th

Piston cooling

32

Room of the casting chamber in front of the casting piston

34

ring

36

Deepening / drilling

38

Collective deepening

Claims (1)

1. Vacuum pressure die-casting installation comprising a casting chamber (10) with a filling opening (12), a casting piston (14) which is movable in the casting chamber (10), and a piston rod (16) which connects the casting piston (14) to a casting drive, wherein an annular gap (18) is formed between the outer casing of the casting piston (14) and the inner wall of the casting chamber (10), wherein the casting piston (14) has at least one evacuable depression or cavity (20, 36), which is connected in terms of flow to the annular gap (18), and provision is made of means via which the depression or cavity (20, 36) is able to be evacuated, characterized in that the means comprise at least one, preferably two or more, suction lines (22), in particular suction tubes, each of which is connected in terms of flow to the evacuable depression or cavity (20, 36) by one of its ends and is connected in terms of flow to a vacuum installation by its other end, wherein the suction line (22), in particular the suction tube, extends along the piston rod (14) in a groove (26) formed on the outer side of the piston rod (14) and, with one of its ends, passes into the depression or cavity (20, 36) through a piston or workpiece region (28) facing the piston rod (14) and is connected in terms of flow to said depression or cavity.

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