DE10032843B4 - Process for the production of thin-walled light metal castings - Google Patents

Abstract

method for the production of large-area light metal castings (20) with predominantly thin Wall areas with a thickness of 2.5 - 5 mm, in particular 2.5 to 4 mm in casting process with increasing filling, such as. in low pressure casting processes, characterized in that before each casting process at least two metallic Support moldings (4, 6) to a temperature between 150 ° C and 300 ° C that between a respective metallic surface (12) of the relevant metallic support molding (4, 6) and a the casting to be made (20) corresponding contour model (10) or a contour model half resin-encased thermosetting Molding sand (14) is shot in that the molding sand (14) on the metallic surface (12) to form a 1 - 5 mm thick sand mask thermoset is that after that the contour model (10) or the contour model half of the respective mold part consisting of molded support (4, 6) and sand mask removed and the support moldings (4, 6) together with that of hardened Molding sand (14) formed sand mask to form a closed mold (2) combined ...

Description

The The invention relates to a method for producing large-area light metal castings with mostly thin wall thickness from 2.5 to 5 mm, in particular from 2.5 to 4 mm, in casting processes with increasing filling, such as. low-pressure casting, tilt-casting, Metal melt dosing via a metal pump.

If large-area light metal castings with predominantly thin wall thickness cast, such as body knots, doors, but also bars so far mostly in the die casting process generated. Because of the big Surface of this However, parts of this are associated with the technical casting effort extremely high because of the requirements for the dimensioning of the die casting tool and the machine are significant; in addition, large circulatory quantities fall on.

The Manufacture of such castings in the low-pressure mold casting process would be feasible in itself in a more economical way, but it brings the Difficulty with it that the melt when filling the mold on the mold surface cooled down very much is, so they with large-area geometries with wall thicknesses in the above area before the mold filling at least in some areas stiffens. Once the mold a height of more than 20 cm, it is practically no longer possible to use the Light metal melt in the liquid Condition in the direction away from the sprue Sections of the mold bring to. Heating the casting mold is also practically not possible feasible; the casting mold in such a case heated to temperatures above the solidus point and then again chilled in order to solidify the melt. This is not economical executable.

Next the die casting process are such light metal castings preferred since then in the sand casting process manufactured. In the production of protruding thin-walled Components have to protruding sand mold boxes or shapes and very large Amounts of molding sand are used. This also proves to be complex and cost-intensive. Sand or box casting process are known and roughly in Flemming, E .; Tilch, W .: Molding materials and Molding process, Leipzig, German publishing house for basic material industry, 1993, S 347-364 or in Brunnhuber, Ernst: Giesserei Lexikon, edition 1986, 13th edition Berlin, Fachverlag Schiele & Schön GmbH, pp. 637/638.

Of these, starting from the present invention, the object is an optimized cost effective feasible casting process to be specified for the manufacture of expansive light metal castings with predominantly thin wall thicknesses.

• – dass vor jedem Gießvorgang wenigstens zwei metallische Stützformteile auf eine Temperatur zwischen 150°C und 300°C erwärmt werden,
• – dass zwischen eine jeweilige metallische Oberfläche des betreffenden metallischen Stützformteils und ein dem herzustellenden Gußteil entsprechenden Konturmodell oder eine Konturmodellhälfte ein kunstharzumhüllter warmaushärtbarer Formsand (Croning-Sand) eingeschossen wird,
• – dass der Formsand an der metallischen Oberfläche zur Bildung einer 1 – 5 mm dicken Sandmaske warmausgehärtet wird,
• – dass danach das Konturmodell oder die Konturmodellhälfte von dem jeweiligen Gießformteil bestehend aus Stützformteil und Sandmaske entfernt und die Stützformteile zusammen mit der von ausgehärtetem Formsand gebildeten Sandmaske zur Bildung einer geschlossenen Gießform miteinander kombiniert werden,
• – dass die geschlossene Gießform in steigender Füllung (Niederdruck, Metallpumpe, Kippguß) mit Leichtmetallschmelze befüllt wird.

This object is achieved by a method with the features of claim 1. The method is therefore characterized in that

• That at least two metallic support moldings are heated to a temperature between 150 ° C. and 300 ° C. before each casting process,
• - that a synthetic resin-coated thermosetting molding sand (croning sand) is shot in between a respective metallic surface of the relevant metallic support molding and a contour model corresponding to the cast part to be produced,
• - that the molding sand is heat-cured on the metallic surface to form a 1-5 mm thick sand mask,
• That the contour model or the contour model half is then removed from the respective casting mold part consisting of the support mold part and sand mask and the support mold parts are combined with one another together with the sand mask formed by hardened molding sand to form a closed mold,
• - That the closed mold is filled with light metal melt in increasing filling (low pressure, metal pump, tilting cast).

The Molding sand is therefore preferably in a layer thickness of at least 1 mm, preferably in a layer thickness of 2 to 5 mm on the contour-giving metallic surface the support form applied. The molding sand has a thermal effect - as in principle also in the sand casting process insulating, which means that problems with filling the closed mold due to the heat dissipation to the metallic areas of the mold and an associated unwanted solidification occurs only to a limited extent. Even very thin areas the mold can easily filled with melt become. The mold can advantageously be filled using increasing pressure in the low-pressure casting process, too if they have a height from more than 20 cm to in particular over 1 m.

in the Comparison to the sand casting process only a fraction of the molding sand required there per casting process consumed. This brings cost advantages and benefits to in-house Logistics of material provision and disposal with it.

The Costs associated with the casting process according to the invention, are opposite the extremely complex die casting process very low, since the technical expenditure in terms of molding and casting technology is very high is lower.

With the invention therefore provided a casting process for the first time, with the inexpensive castings with predominantly thin wall thicknesses in a thickness of 2.5 to 5 mm can be cast.

It it should also be noted that the required tempering the shaped support parts, the ones to harden of the injected molding sand is required, at the same time supporting the filling of the mold acts.

By the shooting the molding sand becomes an even and preferably uninterrupted coating of the inner surface of the support moldings reached. It becomes explicit pointed out that according to the inventive method, the molding sand coating is not serves to control the solidification and that there is also no need the layer thickness of the molding sand coating the casting geometry to adapt because of the subject of castings with predominantly thin wall areas or at least with protruding areas with a thin wall thickness of up to 5 mm should be cast. The solidification is steered therefore exclusively through the increasing filling the mold and the resulting solidification process directed at the gate. The support form acts as a support structure for the molding sand layer, which as such could not be handled separately. Handling a very thin sand mold in low pressure casting processes is namely not possible. The choice of materials for the support form becomes much freer than that for a mold.

Further Features, details and advantages result from the claims, the graphic representations and subsequent description of the casting method according to the invention.

The 1 and 2 show a schematic sectional view through a casting mold.

The mold 2 consists of the two support mold parts or halves shown in the figures 4 . 6 with heating devices 8th and a bowl-shaped sand mold mask to be described in more detail. Before carrying out a respective casting process, the support mold parts 4 . 6 heated to a temperature between 150 ° C and 300 ° C. There is then a contour model corresponding to the casting to be produced in each mold half 10 inserted. The contour model 10 and the respective molded support part 4 . 6 are complementary to each other in such a way that between the contour model 10 and the surface 12 of the shaped support parts 4 . 6 a gap remains in the range of a few millimeters, preferably 2 to 5 mm. This gap is covered with a resin-encapsulated thermosetting molding sand 14 (Croning sand) backfilled between the surface 12 and the surface of the contour model 10 is blown or shot. Because the respective molded support parts 4 . 6 have been heated to a temperature between 150 and 300 ° C, the molding sand 14 artificially aged. Then the contour model part 10 of the respective molded support part 4 . 6 removed, and a 1 to 5 mm thick layer of the mask made of molding sand remains 14 , which reproduces the contour of the casting to be produced on the respective surface 12 of the shaped support parts 4 . 6 ,

The mold 2 can now be brought together by bringing the masked shaped support parts or halves together 4 . 6 getting closed. The remaining cavity corresponds to the predominantly thin-walled light metal casting to be produced 20 ( 2 ). The distance between the molding sand surfaces 16 the mask in the case shown is essentially over the entire extent of the thin-walled casting between 2.5 to 5 mm, in particular 2.5 to 4 mm. The surface 12 of the shaped support parts 4 . 6 is provided with protrusions or undercuts, which have a negative draft 17 have during demolding. This prevents uncontrolled detachment of the molding sand mask.

The closed mold 2 can then be taken to a low-pressure furnace and filled with light metal melt in increasing filling using the low-pressure casting process or an adequate filling method. The light metal melt therefore fills the casting mold 2 from the bottom up. The molding sand coating provides thermal insulation to the metal molded support parts or halves 4 . 6 causes so that the temperature of the melt during the filling of the casting mold, which is preferably pressure-controlled, that is to say given a predetermined or predeterminable rate of rise of the melt in the mold, is not significantly reduced. An unwanted solidification of the melt in the mold before the mold is completely filled is therefore not to be feared.

Claims (3)

Process for the production of large-area light metal castings ( 20 ) with predominantly thin wall areas with a thickness of 2.5 - 5 mm, in particular 2.5 to 4 mm in casting processes with increasing filling, such as in low-pressure casting processes, characterized in that at least two metallic support molded parts ( 4 . 6 ) are heated to a temperature between 150 ° C and 300 ° C that between a respective metallic surface ( 12 ) of the relevant metallic support molding ( 4 . 6 ) and one to manufacture lumbar casting ( 20 ) corresponding contour model ( 10 ) or a contour model half a resin-encapsulated thermosetting molding sand ( 14 ) that the molding sand ( 14 ) on the metallic surface ( 12 ) to form a 1 - 5 mm thick sand mask, that the contour model ( 10 ) or the contour model half of the respective mold part consisting of a support mold part ( 4 . 6 ) and sand mask removed and the support moldings ( 4 . 6 ) together with that of hardened molding sand ( 14 ) formed sand mask to form a closed mold ( 2 ) can be combined, and that the closed mold ( 2 ) is filled with light metal melt in increasing filling. A method according to claim 1, characterized in that the molding sand ( 14 ) is applied in a fluidized bed process. A method according to claim 1 or 2, characterized in that the hardened molded sand shell by undercuts or projections with a negative draft ( 17 ) on the contour ( 12 ) of the shaped support parts ( 4 . 6 ) is hooked.