WO2001066283A1 - Method for producing a cast wheel-rim and a casting mould for the same - Google Patents

Abstract

The invention relates to a method and a casting mould for producing a cast wheel-rim (1) from a light alloy by a casting process in a casting mould (8). At least one pre-formed foamed metal core piece (2) is introduced into the mould (8), fixed in position therein by means of positioning elements (7), e.g. pins and the light alloy (5) is subsequently cast around said piece. The method is characterized in that whilst the light alloy (5) is being cast around the core piece (2), gas which escapes from the core piece (2) as a result of the expansion associated with the heating of said piece is evacuated from the mould (8) through at least one ventilation passage (11) in said mould and in a positioning element (7).

Description

 Process for manufacturing a wheel cast rim and casting tool therefor

The invention relates to a method for producing a wheel cast rim from light metal by casting in a casting tool, wherein at least one preformed metal foam core part is inserted into the casting tool, therein with the aid of positioning elements, e.g. Pins, fixed in position and finally cast over with the light metal.

Furthermore, the invention relates to a casting tool for carrying out the method according to the invention, with molded parts movable relative to one another, and to a metal foam core part for the method according to the invention.

A light metal cast rim is known from WO 99/39923, in which a metal foam core part is provided to reduce the rim weight. In the manufacture of such light metal rims with a metal foam core part, however, it has been shown that voids are formed in the light metal, which renders the light metal rims produced unusable. Studies have finally shown here that the cause of this void formation in the exit of gas from the metal foam core part when it is heated when cast with the light metal - e.g. Aluminum - lay.

On the other hand, EP 356 736 A2 shows a method and a casting tool for producing a wheel cast iron fig, in which a vent hole is provided, to which devices for air outlet or air supply are connected. The vent hole or the devices for air extraction or air supply connected to it are provided in order to overcome the problems which occur in conventional low-pressure casting processes, which occur in the lower region of the casting mold, in which the melt is supplied via a weir. In particular, a cooling device in the lower part of the casting mold also causes different temperatures of the hot melt, as a result of which defects can arise in the casting. In order to prevent such defects, ie air inclusions, and to achieve a high strength of the cast wheel rim, in particular in the area of the melt inflow in the lower area of the main body, the vent hole is used after the melt has reached this area and until then Air could escape, compressed air was introduced, thus increasing the strength of the cast body. However, it is a conventional cast wheel rim is affected, ie without a lost core, the problem of expanding air in the preformed metal foam core part not occurring during the encapsulation.

It is an object of the invention to provide a method and a casting tool for the production of light metal rims with a metal foam core part, the production of light metal cast rims without gas inclusions and a homogeneous structure of the light metal surrounding the metal foam core part being achieved.

The inventive method of the type mentioned is characterized in that during the encapsulation of the core part with the light metal gas, which emerges from the core part when it is heated as a result of the associated expansion, through at least one ventilation opening in the casting tool, optionally also in one inserted therein Venting element that is discharged to the outside.

Since the gas enclosed in the metal foam core part heats up and expands due to the temperature increase during casting, which is carried out at a temperature of approx. 700 ° C, the expanding gas emerging from the core part is discharged from the mold, i.e. "Vented"; This prevents gas from entering the light metal melt, so that there are no voids in the cast light metal. Tests have shown that simply preheating the core part before the casting process in order to avoid gas expansion during casting is not possible to a sufficient extent, since the metal foam core part already becomes quite soft below its melting point and thus loses dimensional stability so that it does not is more manageable. Preheating is therefore only possible to a limited extent and further heating during casting, with the associated expansion of the gases enclosed in the metal foam core part, is practically indispensable. Nonetheless, the invention provides a very simple and efficient solution to prevent the expanding gas from escaping into the light metal surrounding the metal foam core part by diverting the gas through one or, preferably, multiple vents in the mold, i.e. the gas can flow to the environment through these vents.

In addition, one or more ventilation elements can optionally also be provided on the core part in order to prevent the outflow to simplify the gas through these ventilation elements on the core part and through the associated ventilation openings in the casting tool.

If the gas is discharged through a ventilation opening provided in at least one core part positioning element, in particular in a pin, the attachment of additional ventilation elements can advantageously be omitted, since the positioning elements themselves are additionally used for gas discharge.

In order to prevent light metal from penetrating into the core part in the region of the positioning elements, as a result of which the light metal would possibly clog the ventilation openings, it is advantageous if the positioning element is fastened tightly to the core part.

If the positioning element is partially foamed in during the foaming of the core part, a very tight connection between the core part and the positioning element is advantageously achieved. This also eliminates the need for an additional step to connect the positioning element to the core part.

Since the positioning of the positioning elements into the core part can sometimes lead to difficulties in the production of the core part, since the core part is subject to large thermal expansions during production and the positioning elements attached to it are difficult to remove from the casting mold after the metal foam core part has cooled down on the other hand, it is advantageous if the positioning element is screwed into the prefabricated core part with the aid of a threaded section.

In order to prevent the light metal from penetrating into the metal foam core part in a particularly secure manner, it is advantageous if a separate sealant, such as e.g. a refractory putty on which positioning element fastening parts are attached.

Preferably, the core part is coated with the light metal before the casting in order to avoid infiltration of light metal when casting with a sealant, for example graphite. This coating reduces the outer porosity of the metal foam core part. This has the advantage that the undesirable penetration of the liquid light metal surrounding the core part into the metal foam core part is avoided becomes .

In order to keep the expansion of the metal foam core part and the gas enclosed in it as low as possible, it is advantageous if the core part is heated with the light metal before being cast around it. Rapid heating of the core part from room temperature to approx. 700 ° C, which occurs during casting, would lead to a very strong, rapid expansion of the core part, which would result in a poor quality alloy wheel. If the core part is heated to a temperature between 350 ° and 450 °, it is still sufficiently dimensionally stable that it can also be mechanically captured and inserted into the casting mold.

If after the casting with the light metal and its solidification, the ventilation opening in the ventilation element cast in is sealed, for example with synthetic resin or by tightly inserting a pin, the penetration of liquid, e.g. splash water, when using the light alloy cast rim.

If, during the encapsulation of the core part with the light metal, the removal of the gas is at least initially supported by applying a negative pressure to the ventilation opening, the expanding gas can be discharged from the interior of the casting tool in a particularly reliable manner.

After the gas trapped in the metal foam core part has escaped through the ventilation openings, it can be advantageous if a pressure - e.g. Ambient pressure - is built up in the core part via the ventilation opening in order to counteract infiltration of the light metal into the core part.

So that the metal foam core part is easily positioned exactly between the mold parts of the casting tool arranged one above the other, it is advantageous if the positioning element, in particular the pin, is used to clamp the core part to a molded part of the casting tool, the positioning element in the Vent hole is fixed in the mold. The core part is thus brought into position and held in place by fixing the positioning elements in the area of the ventilation openings. For this fixation, the positioning element preferably has a conical outer surface, through which a self-locking effect in the ventilation opening can be achieved.

For a precise adjustment of the distance between the upper and the lower mold part of the casting tool and in particular for a precise connection between the ventilation openings and the positioning elements, it is advantageous if the core part is attached to the upper, movable molding part of the casting tool with the aid of several positioning elements when it moves down on the is fixed on a temporary base core part until the stops limiting the downward stroke of the casting mold part are reached. The height of the stroke-limiting stops for the upper molded part should rather be designed in the direction of a slight pushing in of the positioning elements into the metal foam core part, since this has no disadvantages and, on the other hand, brings about a reliable connection between the positioning elements and the ventilation openings. Tests have shown that with usual manufacturing tolerances for the positioning elements and ventilation openings, a pressing of the positioning elements into the core part of at most 0.5-1 mm can be expected.

In order to ensure that the finished cast rim does not have an adverse impression due to visible ventilation openings, it is advantageous if the gas is discharged through a number of ventilation openings in the area of the rear of the cast rim.

The casting tool of the type mentioned at the outset is characterized in that at least one ventilation opening is provided in at least one molded part. This ventilation opening advantageously enables the gases enclosed in the metal foam core part to escape from the casting mold when the core part is heated during casting and thus to avoid the inclusion of these gases in the cast wheel rim to be produced.

If the ventilation opening is provided in the upper, movable molded part of the casting tool, the gas flowing upwards can be discharged particularly easily; Furthermore, the vent opening can advantageously be automatically connected to a positioning element which may be provided in the metal foam core when the upper molded part of the casting tool is shut down.

For a self-locking connection between the position nierelement and the ventilation opening, whereby the metal foam core part is automatically held precisely in the position to be cast, it is advantageous if the ventilation opening has an inner shoulder.

If at least one stop is provided which limits the downward stroke of the movable casting tool part, reliable joining takes place between the positioning element and the vent opening in the desired exact position.

According to the invention, a metal foam core part is also provided, which is characterized by at least one positioning element provided for gas discharge with a ventilation opening.

The invention is explained in more detail below on the basis of preferred exemplary embodiments illustrated in the drawing, to which, however, it is not intended to be limited. The drawing shows in detail:

Figure 1 is a perspective view of a partially broken light alloy cast rim with a metal foam core part.

FIG. 2 shows a section through this light metal cast rim according to line II-II in FIG. 1;

3 shows a section of the light metal cast fig along the line III-III in Fig. 1.

4 shows a perspective view of the back of a metal foam core part together with positioning elements in the form of pins;

5 shows a cross section of a part of a casting tool with a metal foam core part inserted therein, including the foamed-in positioning element, prior to casting;

6 shows a corresponding cross section of a metal foam core part which has been introduced into the casting tool and has a screwed-in positioning element before casting;

7 shows a schematic view of a casting tool for producing a light metal rim while inserting a metal foam core part, which lies on a temporarily pivoted-in base; and

Fig. 8 is a plan view of the lower part of the base temporarily pivoted into the casting tool without a core part.

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To hold the desired position, the positioning element 7 has a conical lateral surface 12, which, by abutment against a shoulder 13 forming a cross-sectional constriction, causes a self-locking effect in the vent opening 11.

In the embodiment shown in FIG. 5, the positioning element 7 is partially foamed in the core part 2 with the aid of an end flange 14 and therefore does not have to be subsequently connected to the core part 2.

To shape the light metal fig 1, the casting tool is composed of the upper mold part 9, a lower mold part 15 and lateral core slides 16 (only one is shown in FIG. 5); For example, there can be four quarter-circle-shaped individual parts as the core slide 16, which, when the mold 8 is closed, are moved radially inwards from the outside to rest on the mold lower part 15.

Since at the beginning of the pouring of the liquid light metal, for example an aluminum-silicon alloy, the metal foam core part 2 heats up very strongly (this being preheated to about 350 to 450 ° C. in order to obtain a certain dimensional stability which leads to It is necessary to insert the core part 2 into the mold 8), since the liquid light metal has a temperature of approx. 700 ° C., the gases enclosed in the core part 2 expand strongly. These gases are discharged through the ventilation openings 11 and the positioning elements or centering pins 7. A pipe or hose system can be connected to the ventilation openings 11 in order to support the discharge of the gases with the aid of a pump (not shown): To also ensure that these gases initially penetrate into the light metal shell 5 (see FIG. 2) to prevent, a negative pressure can be applied to the ventilation opening 11 in order to facilitate the escape of the expanding gas from the core part 2 via the ventilation opening 11.

Towards the end of the casting process, when the temperatures of the metal foam core part 2 and the liquid light metal have adjusted, the risk that gases from the core part 2 leak into the light metal 5 and cause voids is no longer so great, but there is Risk of light metal 5 entering core part 2 due to the porous structure of core part 2. In order to counteract this, a counter pressure (at least like the ambient pressure) can be applied via the ventilation openings 11

Fig. 7 not shown) to record, compensate. Column-shaped stops 22 'are provided on the plate support 22, which serve to set the desired distance from the upper mold part 9, which is pushed down by means of a carrier plate 23, when the core part is received. When designing the height of the stops 22 ′, a dimension is set at which the positioning elements or pins 7 are rather pressed in or slightly yielding in the direction of the core part 2 in order to reliably fix the positioning elements 7 in the ventilation openings 11 of the upper mold part 9 to achieve (see. Fig. 5 and 6).

In an end region 24 flanged to the upper mold part 9, ejection pins 25 are provided in a conventional manner, which serve to separate the light metal cast rim from the upper part 9 of the mold.

8 shows a top view of the plate support 22 with the stops 22 '. It can be seen here that the plate 22 has depressions 26 which serve to position the ribs 4 of the metal foam core part 2 (cf. FIG. 1).

The use of ventilation elements - which are preferably implemented directly by the positioning elements 7 - can be omitted if the metal foam core part 2 at least partially borders directly on the casting tool 8, i.e. in the finished rim 1 is accessible from the outside; it is then sufficient for the vent opening 11 in the casting tool 8 at this point so that the expanding gas can escape directly from the core part 2.

Furthermore, it is of course conceivable that, depending on the shape of the rim 1, instead of a one-piece metal foam core part 2, several separate metal foam core parts are used, each of which is connected to at least one ventilation opening.

Claims

Claims: 1. Method for producing a wheel cast fig (1) from light metal by casting in a casting tool (8), at least one preformed metal foam core part (2) being inserted into the casting tool (8), with the aid of positioning elements (7), fixed in position and finally cast around with the light metal (5), characterized in that during the casting of the core part (2) with the light metal (5) gas, which comes out of the core part (2) when it is heated as a result of the associated Expansion emerges, is discharged to the outside through at least one vent opening (11) in the casting tool (8). 2. The method according to claim 1, characterized in that pins are provided as positioning elements (7). 3. The method according to claim 1 or 2, characterized in that the gas is discharged via at least one ventilation element used in the casting tool. 4. The method according to any one of claims 1 to 3, characterized in that the gas is discharged through a vent opening (10) provided in at least one core part positioning element (7). 5. The method according to any one of claims 1 to 4, characterized in that the positioning element (7) on the core part (2) is tightly attached. 6. The method according to claim 5, characterized in that the positioning element (7) is partially foamed when foaming the core part (2). 7. The method according to any one of claims 1 to 5, characterized in that the positioning element (7) is screwed into the prefabricated core part (2) with the aid of a threaded section (17). 8. The method according to any one of claims 5 to 7, characterized in that for the tight attachment of the positioning element (7) a separate sealant (19) is attached to the positioning element fastening point (18) on the core part (2). 9. The method according to claim 8, characterized in that a refractory cement is used as the sealant (19). 10. The method according to any one of claims 1 to 9, characterized in that the core part (2) before the casting with the light metal (5) to avoid infiltration of light metal (5) is coated with a sealant during casting. 11. The method according to claim 10, characterized in that the core part (2) is coated with graphite before casting. 12. The method according to any one of claims 1 to 11, characterized in that the core part (2) is heated before casting with the light metal (5). 13. The method according to claim 12, characterized in that the core part (2) is heated to a temperature between 350 ° and 450 °. 14. The method according to any one of claims 1 to 13, characterized in that after the casting with the light metal (5) and its solidification, the vent opening (10) is closed in with the vent member (7) cast in. 15. The method according to claim 14, characterized in that the vent opening (10) in the cast-in vent member (7) with synthetic resin or by sealingly inserting a pin is closed. 16. The method according to any one of claims 1 to 15, characterized in that during the casting of the core part (2) with the light metal (5) at least initially the discharge of the gas is supported by applying a negative pressure to the ventilation opening (11). 17. The method according to claim 11, characterized in that towards the end of the casting again a pressure in the core part (2) over the Vent opening (11) is built up to counteract infiltration of the light metal (5) into the core part (2). 18. The method according to any one of claims 4 to 17, characterized in that the positioning element (7) for clamping fixation of the core part (2) on a molded part (9) of the casting tool (8) is used, the positioning element (7) being fastened in the ventilation opening (11) in the casting tool (8). 19. The method according to claim 18, characterized in that the core part (2) with the aid of a plurality of positioning elements (7) on the upper, movable molded part (9) of the casting tool (8) when the casting tool (8) moves down on the temporary base (15, 21). lying core part (2) until the stops (22) limiting the downward stroke of the casting mold part (9) are fixed. 20. The method according to any one of claims 1 to 19, characterized in that the gas is discharged through a number of ventilation openings (11) in the region of the rear of the cast rim (1). 21. Casting tool for carrying out the method according to one of claims 1 to 20, with molded parts movable relative to one another, characterized in that at least one vent opening (11) is provided in at least one molded part (9). 22. Casting tool according to claim 21, characterized in that the ventilation opening (11) is provided in the upper, movable molded part (9) of the casting tool (8). 23. Casting tool according to claim 21 or 22, characterized in that the vent opening (11) has an inner shoulder (13). 24. Casting tool according to claim 22 or 23, characterized in that a movable core part support (15, 21) with at least one downward stroke of the movable casting tool shaped part (9) limiting stop (22) is provided. 25. Metal foam core part (2) for a method according to one of claims 1 to 20, characterized by at least one positioning element (7) provided for gas discharge with a vent opening (10).