EP1261445B1 - Method for producing a cast wheel-rim and a casting mould for the same - Google Patents

Description

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

The invention further relates to a casting tool for implementation of the inventive method, with each other movable molded parts, at least in an upper, movable Molding of the casting tool provided a vent is, as well as a metal foam core part for that inventive method.

A light alloy cast rim is known from WO 99/39923, a metal foam core part to reduce the rim weight is provided. In the manufacture of such alloy wheels with metal foam core part, however, has been shown to a void formation in the light metal comes that the generated Makes alloy wheels unusable. Investigations have here finally reveal that the cause of this void formation in the Gas escapes from the metal foam core when it is heated when casting with the light metal - e.g. Aluminum - lay.

A hollow spoke wheel is known from DE 297 23 749 U1, in which shell-like hollow elements as cast cores or Core elements made of metal foam with a closed outer skin are provided. Here, too, however, can be from the core Warming gas leaking out, forming voids in the light metal occurs.

DE 195 01 508 C1 is a steering knuckle of a chassis shown, which consists of die-cast aluminum and a cavity profile has a core in the cavity Aluminum foam located. Again, it happens due to expanding Gases when the core is heated to form voids in the aluminum body.

On the other hand, EP 356 736 A2 describes a method and a Casting tool for the production of a cast wheel rim shown in the a vent hole is provided on which facilities connected to the air outlet or air supply. The vent hole or the facilities connected to it Air extraction or air supply are provided to conventional Low pressure casting process to overcome the problems in lower part of the mold occur where the melt over a weir is fed. In particular, a Cooling device in the lower part of the mold different Temperatures of the hot melt caused, causing defects in the Castings can arise. For such defects, i.e. Air pockets, to prevent and high strength of the cast wheel rim especially in the area of the melt inflow in the lower To achieve area of the main body is through the vent hole, after the melt has reached this area and until then air could escape, compressed air was introduced and thus increasing the strength of the cast body. But there is a conventional cast wheel rim is affected, i.e. without lost Core, the problem of expanding air in the preformed Metal foam core part does not occur when casting.

Also from US 4,760,874 A and JP 61-219458 A are only Devices for the production of conventional wheel cast rims known with gas exhaust ducts, but these are devices not for light alloy rims with inserted, preformed metal foam core parts intended. The problem of air pockets due to from the preformed metal foam core part escaping gases during the casting process can occur not at all.

It is an object of the invention, a method and a Casting tool for the production of alloy wheels with a To provide metal foam core part, the manufacture of Light alloy cast rims without gas inclusions and one homogeneous structure of the surrounding metal core part Light metal is achieved.

The inventive method of the type mentioned is characterized in that during the casting around the core part with the light metal gas that comes from the core part at its Warming due to the associated expansion, via at least one ventilation element used in the casting tool and through at least one vent in the mold is derived to the outside.

Because the gas trapped in the metal foam core part due to the temperature increase during casting, which at a temperature of about 700 ° C is carried out, heated and expanded, becomes the expanding, emerging from the core part Gas derived from the mold, i.e. "Vented"; thereby the entry of gas into the light metal melt is avoided, so that there are no cavities in the cast as a result Alloy comes. Tests have shown that a mere Preheating the core part before the casting process by a gas expansion to avoid when pouring, not possible to a sufficient extent is because the metal foam core part is already below its melting point becomes quite soft and thus loses shape stability, so that it is no longer manageable. So preheating is only limited possible and further heating during casting, with the associated expansion of the metal foam core part trapped gases, practically indispensable. Nonetheless The invention creates a very simple and efficient way Solution to the outflow of the expanding gas into the Avoid metal foam core part surrounding light metal by the gas through one or preferably more vents in the Casting tool is derived, i.e. the gas can pass through these vents flow to the surroundings.

If the gas is inserted through at least one Core part positioning element, in particular provided in a pin Vent opening can be advantageously derived the attachment of additional ventilation elements omitted, since the positioning elements themselves in addition to the gas discharge be used.

To prevent light metal from penetrating into the core part in the area to avoid the positioning elements, which makes the light metal could block the vents, it is advantageous if the positioning element is tight on the core part is attached.

If the positioning element when foaming the core part is partially foamed, is advantageously a very tight connection between the core part and the positioning element reached. This can also be an additional step for connecting the positioning element to the core part omitted.

As it is foaming the positioning elements into the core part sometimes causing difficulties in manufacturing the core part can come because the core part during large thermal expansions is subject to manufacture and the positioning elements attached to it heavy after cooling the metal foam core part are to be removed from the mold, on the other hand it is advantageous if the positioning element in the prefabricated core part Is screwed in using a threaded section.

To make the light metal particularly safe from penetrating into the To prevent metal foam core part, it is advantageous if for tight attachment of the positioning element on the core part a separate Sealants such as a refractory putty, at the positioning element attachment point is attached.

Preferably, the core part is cast with the Light metal to avoid infiltration of light metal when pouring a sealant, e.g. Graphite, coated. This coating reduces the outer porosity of the metal foam core reduced. This has the advantage that the unwanted intrusion of the surrounding the core part liquid light metal avoided in the metal foam core part becomes.

About the expansion of the metal foam core part and in it To keep trapped gas as low as possible, Advantage if the core part before casting with the light metal is heated. If the core part of Room temperature to about 700 ° C, which occurs during casting it to a very strong, rapid expansion of the core part come, resulting in a low-quality alloy wheel would. If doing the core part to a temperature between Heated to 350 ° and 450 °, it is still sufficiently dimensionally stable, so that it is also captured mechanically and inserted into the mold can be.

If after the casting with the light metal and its solidification the ventilation opening in the molded-in ventilation element is closed, 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 be prevented.

If during the casting of the core part with the light metal at least initially the discharge of the gas by applying a negative pressure to the vent opening is supported, the expanding gas can be particularly reliable from the inside of the casting tool.

After the gas trapped in the metal foam core part leaked through the vents, it can be an advantage if there is pressure again towards the end of the casting - e.g. Ambient pressure - built up in the core part via the ventilation opening is to infiltrate the light metal into the core part counteract.

So that the metal foam core part is simple and precise between the mold parts of the casting tool arranged one above the other is positioned, it is advantageous if the positioning element, especially the pin, for clamping fixation of the Core part is used on a molded part of the casting tool, the positioning element in the ventilation opening in the casting tool is attached. Thus the core part is about fixation of the positioning elements in the area of the ventilation openings positioned and held. For this fixation that points Positioning element preferably has a conical outer surface, through which a self-locking effect in the vent opening can be achieved.

For an exact distance adjustment between the upper and the lower mold part of the casting tool and especially for one precise connection between the ventilation openings and the positioning elements it is an advantage if the core part with Using several positioning elements on the upper, movable molded part of the casting tool when it is lowered to the one temporary core lying part until reaching the stops limiting the downward stroke of the casting mold is fixed. The stroke-limiting stops for the upper one The height of the molded part should be closer to one the positioning elements are easily pressed into the metal foam core be designed as this has no disadvantages and on the other hand a reliable connection between the positioning elements and causes the vents. Have tests show that with usual manufacturing tolerances for the Positioning elements and vents an indentation of the Positioning elements in the core part of at most 0.5-1 mm expect.

This means that the finished cast rim is not visually disadvantageous Impression is created due to visible ventilation openings, it is convenient if the gas is derived by a number of ventilation openings in the area of the rear of the cast rim is carried out.

The casting tool according to the invention of the above Art is characterized in that the vent opening a inner paragraph for the installation of a ventilation opening Has core part positioning element. This vent advantageously enables it in the metal foam core part trapped gases during heating of the core part during of casting to escape from the mold and thus the Inclusion of these gases in the cast wheel rim to be manufactured avoid; moreover, the vent can advantageously when lowering the upper mold part of the mold with the positioning element provided in the metal foam core automatically be associated. With the help of the inner The vent opening becomes a self-locking connection between the positioning element and the ventilation opening obtained, whereby the metal foam core part automatically is held precisely in the position to be cast.

If at least one the downward stroke of the movable mold part limiting stop is provided, a reliable joining between the positioning element and the ventilation opening in the exact position you want.

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

Fig. 1 eine perspektivische Ansicht einer teilweise aufgebrochenen Leichtmetall-Gussfelge mit einem Metallschaum-Kernteil;

Fig. 2 einen Schnitt durch diese Leichtmetall-Gussfelge gemäß der Linie II-II in Fig. 1;

Fig. 3 einen Schnitt der Leichtmetall-Gussfelge gemäß der Linie III-III in Fig. 1;

Fig. 4 eine perspektivische Ansicht auf die Rückseite eines Metallschaum-Kernteils samt Positionierelementen in Form von Stiften;

Fig. 5 einen Querschnitt eines Teils eines Gießwerkzeugs mit einem darin eingebrachten Metallschaum-Kernteil samt eingeschäumten Positionierelement vor dem Gießen;

Fig. 6 in einem entsprechenden Querschnitt einen in das Gießwerkzeug eingebrachten Metallschaum-Kernteil mit einem eingeschraubten Positionierelement vor dem Gießen;

Fig. 7 eine schematische Ansicht eines Gießwerkzeugs für die Herstellung einer Leichmetallfelge unter Einlegen eines Metallschaum-Kernteils, der auf einer vorübergehend eingeschwenkten Unterlage liegt; und

Fig. 8 eine Draufsicht auf den unteren Teil der vorübergehend in das Gießwerkzeug eingeschwenkten Unterlage ohne Kernteil.

The invention is explained in more detail below on the basis of preferred exemplary embodiments illustrated in the drawing, to which, however, it should not 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 along the line II-II in FIG. 1;

3 shows a section of the light metal cast rim 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 introduced into the casting tool with a screwed-in positioning element before casting;

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

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

In Fig. 1 is a partially broken perspective View of a light metal cast rim 1 in a composite structure shown with a metal foam core part 2, which is in a light metal, e.g. Aluminum is cast. The metal foam core part 2 shows in the example shown an annular rim outer part 3 radially inward spokes or Ribs 4 on.

2 shows a section through a spoke or rib 6 the light alloy cast rim 1 shown. In contrast, in Fig. 3 is a Cut at one point on the light alloy cast rim 1 between adjacent spokes or ribs 6 shown. So in this Area only the circular outer part 3 of the metal foam core part 2 can be seen.

4 is a perspective view of the back of the metal foam core part 2 shown. Here are on the back the rib 4 positioning elements 7 can be seen, which one have conical outer surface. The positioning elements 7 serve for the exact alignment of the core part 2 in the casting tool 8 (s. 5 and 6).

With the help of the very light metal foam core part 2 can the total weight of the cast rim 1 can be significantly reduced. However, in the manufacture of such alloy wheels with metal foam core parts 2 problems regarding a homogeneous Structure of the light metal shell enveloping the core part 2 5 occur: Because those enclosed in the metal foam core part 2 If gases expand when the core part 2 is heated, they escape Gases at least partially from core part 2 and they would be without further measures a strong formation of voids in the light metal shell 5 cause, causing sufficient strength of the Alloy rim 1 is no longer given.

Since the positioning elements 7 with the upper movable anyway Molded part 9 of the casting tool 8 (hereinafter upper mold part 9) for centering the core part 2 in the mold 8 connect, they can also be used for deriving that from the core part 2 when it is heated during casting escaping gases are used. 5, there is a vent hole for this inside the positioning element 7 10 is provided, via which the core part 2 escaping gases into a vent 11 aligned therewith occur in the upper mold part 9 and thus discharged into the atmosphere can be. A simple, self-locking connection between the upper mold part 9 and the metal foam core part 2 to reach the core part 2 in its for casting hold the desired position, the positioning element 7 on a conical lateral surface 12, which by abutment on a a cross section narrowing paragraph 13 in the vent 11 produces a self-locking effect.

The positioning element 7 is the one shown in FIG. 5 Embodiment in the core part 2 with the help of an end flange 14 partially foamed and therefore does not have to be added the core part 2 can be associated.

The casting tool is used to shape the light metal rim 1 from the upper mold part 9, a lower mold part 15 and lateral core slides 16 (only one is shown in Fig. 5) together; for example, four quarter-circle shaped as core slide 16 Items are present, which when closing the Chill 8 radially inward from the outside to rest against the lower mold part 15 are moved.

Since at the start of pouring the liquid light metal, for example an aluminum-silicon alloy, the Metal foam core part 2 warmed up very much (this up to about 350 to 450 ° C is preheated to a certain dimensional stability to get which for inserting the core part 2 into the mold 8 is necessary) because the liquid light metal has a temperature of approx. 700 ° C, the gases enclosed in core part 2. These gases are generated by the Vent openings 11 and the positioning elements or centering pins 7 derived. At the vents 11 can a pipe or hose system must be connected to the To help discharge the gases using a pump (not shown): In order to also allow these gases to initially penetrate into the light metal shell 5 (see FIG. 2) can safely prevent a negative pressure is applied to the ventilation opening 11 in order to the exit of the expanding gas from the core part 2 via to facilitate the vent 11.

Towards the end of the casting process when the temperatures of the Adjusted metal foam core part 2 and the liquid light metal have, is the danger that gases from the core part 2 in the Escape light metal 5 and cause voids, no longer so large, however, there is a risk that due to the porous Structure of core part 2 light metal 5 enters core part 2. To counteract this, you can use the ventilation openings 11 a counter pressure (at least like the ambient pressure) is applied and thus the infiltration of light metal into the core part 2 are made more difficult.

Furthermore, it is possible to provide a sealing coating on the core part 2, for example made of graphite, Al ₂ O ₃ or water glass, in order to reduce the porosity of the outer surface of the core part 2 and also to counteract infiltration of light metal into the core part 2.

In the production of core parts 2 with foamed positioning elements 7, as shown in Fig. 5, can cause problems with regard to the large thermal expansions of the core part 2 at the Manufacturing occur, the positioning elements 7 can after cooling difficult to remove from the mold. So far a separate, subsequent attachment of the positioning elements 7 after the core part 2 has been foamed.

In Fig. 6 an embodiment is now shown in which the Positioning element 7 by means of a threaded portion 17 in the otherwise finished core part 2 is screwed in. This brings the Advantage with it that the production of the metal foam core part 2 is easier for itself, but the core part 2 must be attached the positioning elements 7 are "post-treated".

To ensure a good sealing surface between the positioning elements 7 and to reach the core part 2, this points at each position of the positioning element a plateau 18, which after casting the core part 2 is post-treated to a flat surface in Preserve area of plateau 18.

To prevent expanding gas in the area of the Threaded section 17 emerges in the light metal 5 or that Light metal 5 in the area of the thread 17 in the metal foam core part 2 occurs, there is a sealant 19 between the plateau 18 of the core part 2 and the positioning element 7 are provided. This - known per se - sealant 19 is based on a ceramic Base and has refractory properties, being essential is that it does not outgass when hardening, as this in turn Blow holes in the light metal 5 would arise.

7 is a schematic view of the casting tool 20 shown. Above the lower mold part 15 is on a pivotable lower plate 21 of the device 20 a plate-shaped Core part pad 22 resiliently mounted to any Inequalities when lowering the upper mold part 9 this pad 22 to the core part 2 (in Fig. 7 not shown) to record, compensate. On the plate underlay 22 column-shaped stops 22 'are provided, which serve the desired distance when picking up the core part to the upper mold part 9, which by means of a carrier plate 23 is pushed down. When interpreting the height the stops 22 'is set to a degree at which an impression is made or slightly giving in the positioning elements or Pins 7 towards the core part 2 is reached to be reliable Fixing the positioning elements 7 in the ventilation openings 11 of the upper mold part 9 to be reached (cf. 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 for separating the light alloy cast rim from the upper mold part 9 serve.

8 is a top view of the plate support 22 shown with the stops 22 '. It can be seen here that the Plate 22 has recesses 26, which for positioning the Ribs 4 of the metal foam core part 2 (see FIG. 1) serve.

The use of ventilation elements - which are preferred are directly realized by the positioning elements 7 - can then fail if the metal foam core part 2 at least partially directly adjacent to the casting tool 8, i.e. at the finished Rim 1 is accessible from the outside; the vent opening is then sufficient 11 in the casting tool 8 at this point, so that 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 also used several separate metal foam core parts be, each with at least one vent stay in contact.

Claims (22)

1. A method for producing a cast wheel rim (1) of light metal by casting in a casting tool (8), wherein at least one preformed metal-foam core part (2) is inserted into the casting tool (8), fixed therein in its position by the aid of positioning elements (7) and finally cast round with said light metal (5), characterized in that, during the casting round of the core part (2) with the light metal (5), gas emerging from the core part (2) during heating of the same due to the accompanying expansion is drained outwards via at least one vent element (7) inserted in the casting tool (8) and through at least one vent (11) provided in the casting tool (8).
2. A method according to claim 1, characterized in that pins are provided as said positioning elements (7).
3. A method according to claim 1 or 2, characterized in that the gas is drained through a vent (10) provided in at least one inserted core-part positioning element (7).
4. A method according to any one of claims 1 to 3, characterized in that the positioning element (7) is tightly fastened to the core part (2).
5. A method according to claim 4, characterized in that the positioning element (7) is partially foamed in concurrently with the foaming of the core part (2).
6. A method according to any one of claims 1 to 4, characterized in that the positioning element (7) is screwed into the prefabricated core part (2) by the aid of a threaded section (17).
7. A method according to any one of claims 4 to 6, characterized in that a separate sealing means (19) is attached to the positioning-element fastening site (18) to sealingly attach the positioning element (7) to the core part (2).
8. A method according to claim 7, characterized in that a refractory cement is used as said sealing means (19).
9. A method according to any one of claims 1 to 8, characterized in that the core part (2), prior to being cast round with said light metal (5), is coated with a sealing means to avoid the infiltration of light metal (5) during casting round.
10. A method according to claim 9, characterized in that the core part (2) is coated with graphite prior to being cast round.
11. A method according to any one of claims 1 to 10, characterized in that the core part (2) is heated prior to being cast round with said light metal (5).
12. A method according to claim 11, characterized in that the core part (2) is heated to a temperature of between 350° and 450°.
13. A method according to any one of claims 1 to 12, characterized in that the vent (10) provided in the concurrently cast-in vent element (7) is closed after casting round of said light metal (5) and its solidification.
14. A method according to claims 13, characterized in that the concurrently cast-in vent (10) provided in the vent element (7) is closed by synthetic resin or by tightly inserting a pin.
15. A method according to any one of claims 1 to 14, characterized in that, during the casting of light metal (5) round the core part (2), gas drainage is at least initially assisted by applying an underpressure to the vent (11).
16. A method according to claims 10, characterized in that a pressure is again built up within the core part (2) via the vent (11) towards the end of casting in order to counteract any infiltration of light metal (5) into the core part (2).
17. A method according to any one of claims 3 to 16, characterized in that the positioning element (7) is used to clampingly fix the core part (2) to a mold part (9) of the casting tool (8), whereby the positioning element (7) is fixed in the vent (11) within the casting tool (8).
18. A method according to claims 17, characterized in that the core part (2) is fixed by the aid of several positioning elements (7) to the upper, movable mold part (9) of the casting tool (8) during lowering of the same onto the core part (2) resting on a temporary support (15, 21) until stops (22) delimiting the downward stroke of the casting-tool mold part (9) is reached.
19. A method according to any one of claims 1 to 18, characterized in that gas drainage is effected through a number of vents (11) provided in the region of the rear side of the cast wheel rim (1).
20. A casting tool for carrying out the method according to any one of claims 3 to 19, including relatively movable mold parts and at least one vent (11) provided in an upper, movable mold part (9) of the casting tool (8), characterized in that the vent (11) comprises an internal step (13) for abutment of a core-part positioning element (7) including a vent (10).
21. A casting tool according to claim 20, characterized in that a movable core-part support (15, 21) comprising at least one stop (22) delimiting the downward stroke of the movable casting-tool mold part (9) is provided.
22. A metal-foam core part (2) for use in a method according to any one of claims 3 to 19, characterized by at least one positioning element (7) including a vent (10) and provided for gas drainage.

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