Use of a lost mold in a process for producing complex shaped castings with a die casting machine

Abstract

Use of a lost mold (3) in a process for producing complex shaped castings (9) using a die-casting machine, wherein the lost mold defines at least one area of ​​the complex castings (9), wherein the lost mold (3) is dimensioned with its outer dimensions such that it completely fills a permanent metallic mold (5) or the casting chamber of the die-casting machine, wherein the outer dimension is chosen independently of any other structure of the lost mold (3) which is adapted to the complex castings (9), and wherein the lost mold is formed from a ceramic body produced with the aid of a lost pattern and the surface of which is adapted to prevent penetration or infiltration of liquid casting material (6) during the casting process, wherein the surface of the ceramic body is impregnated, sealed or coated to prevent penetration or infiltration of the liquid casting material (6) during the casting process, or the ceramic body is made of a material composition that changes towards the surface, wherein the material composition in the surface area is selected to prevent penetration of the liquid casting material (6) during the casting process, wherein metals or metallic alloys are used as the casting material in the process, and wherein the lost mold (3) for the casting process is placed in a casting chamber of the die-casting machine or a cavity of a permanent mold (5) used in the die-casting machine.

Description

Technical application area

[0001] The present invention relates to the use of a lost mold in a method for producing complex shaped castings with a die-casting machine, wherein the casting process is carried out with a lost mold that defines at least one area of ​​the complex shaped castings.

[0002] Die casting is one of the most economical manufacturing processes for castings and has therefore experienced very dynamic development in recent years. Due to the high injection speed of the molten casting material into the permanent metal mold, die casting is particularly suitable for producing thin-walled castings with a high surface finish. However, creating undercuts or cavities or openings that are not in the demolding direction requires expensive and complex mechanically or hydraulically actuated cores (slides). State of the art

[0003] One way to produce complex castings without using elaborate slide technology is by employing expendable cores in die casting. This requires a suitable core material, such as salt (NaCl) based, that can withstand the process conditions in die casting, particularly pressure, temperature, and injection speed, and is not infiltrated by the molten casting material. The salt cores can be shaped by pressing powders, casting molten salt, or by core shooting. The core material should be completely removable after the casting process. When using salt as the core material, this can be achieved, for example, by washing it out with water.While initially primarily water-soluble pure substance systems such as KCl or NaCl were used as core materials, more recent developments focus on improving strength while simultaneously simplifying the production of lost cores through the use of material mixtures. For example, DE 10 2010 043 451 A1 proposes the production of a core from a core material mixture consisting of salt, binders, and auxiliary materials such as additives, fillers, wetting agents, and catalysts.

[0004] In DE 10 2007 015 050 A1, a die casting process with cores made of sand, salt or similar materials is proposed, in which penetration of the core material with the molten metal is avoided by using a suitable shot assembly that always keeps the holding pressure below the penetration pressure of the corresponding core material.

[0005] German patent DE 10 2009 024 182 B3 describes the production of cores or molds for casting from an investment material containing a proportion of hollow bodies, such as hollow glass spheres. The shaping can be achieved by casting or core shooting. After the casting material has been poured and solidified during the production of the casting, some of the hollow bodies are ruptured by applying increased pressure, thereby destroying the core or the entire mold and allowing it to be demolded.

[0006] The lost cores made of salt, sand, or investment material with hollow bodies used in die casting to date are produced by pressing, casting, or core shooting, which, however, limits the complexity of the structures that can be created. With the techniques known so far, more complex shaped castings can therefore only be produced in die casting with elaborate slide technology, additional lost cores, or often not at all due to the geometric complexity.

[0007] The object of the present invention is to provide a method for producing castings using a die-casting machine, which enables the production of geometrically complex shaped castings in a simple manner. Description of the invention

[0008] The problem is solved by using a lost mold according to claim 1. Advantageous embodiments of the use are the subject of the dependent claims or can be found in the following description and the exemplary embodiment.

[0009] In the proposed use of a lost mold in a process for producing complex-shaped castings with a die-casting machine, a lost mold is used in the casting process to define at least one area of ​​the complex-shaped castings. The lost mold is formed from a ceramic body produced using a lost pattern, and its surface, which comes into contact with the casting material, is adapted to prevent penetration or infiltration of the molten casting material during the casting process.

[0010] The use of expendable molds offers the advantage that both external contours and internal cavities can be represented. Additionally, the draft angles indispensable in permanent mold processes can be completely eliminated. Furthermore, the high mold wear that occurs with permanent mold processes when working with high-melting-point metals and alloys (e.g., copper and copper alloys) is avoided when using expendable molds or mold inserts. With this approach, mold wear is reduced exclusively to the casting chamber area, so that with a suitable coating, a replaceable wear insert, or the use of a ceramic casting chamber, the processing of higher-melting-point metals (copper or iron) would also be possible.By choosing a lost-wax mold made of a ceramic material, its production can be carried out using techniques familiar from investment casting, such as the well-known lost-wax casting process. These techniques enable the production of molds with highly complex geometric structures and high precision. For example, the lost-wax models can be produced with the desired complex or intricate structure using a rapid prototyping process, for instance, from wax or plastic. Other manufacturing methods for the lost-wax models are, of course, also possible. However, ceramic investment materials always exhibit a certain degree of open porosity, which inherently precludes their use in pressure-assisted casting due to the potential for penetration or infiltration by the molten casting material.In the proposed application, the ceramic body for the formation of the lost mold is therefore adapted on the surface coming into contact with the casting material in such a way as to prevent penetration or infiltration of the liquid casting material during the casting process.

[0011] In the proposed application, the surface of the ceramic body is therefore impregnated, sealed, or coated to prevent penetration or infiltration of the liquid casting material during the pressure-assisted casting process. In contrast to the method described in DE 10 2007 015 050 A1, the aim is to achieve the lowest possible porosity throughout the entire molding material, and especially in the surface area. Core removal cannot therefore be achieved by sudden pressure application and the resulting collapse of the molding material due to the targeted porosity (DE 10 2007 015 050 A1), but is instead accomplished through mechanical processing or dissolution in aqueous media, or a combination thereof. In one embodiment, overflow beads, venting channels, or forced venting can be provided to improve component quality. Furthermore, filling the cavity during vacuum casting is also conceivable.Alternatively, the ceramic body is manufactured from a material composition that changes towards the surface. The material in the surface area is selected so that it either has no porosity or its porosity is insufficient to prevent penetration or infiltration by the liquid casting material under the pressures encountered during casting. A combination of the above alternatives is, of course, also possible.

[0012] Preferably, the pressures and / or injection or injection piston speeds of the die-casting machine are selected during the casting process such that the pressures are below 10 MPa and / or the injection piston speeds are below 1.0 m / s. This reduces the requirements for the surface of the expendable mold with regard to infiltration or penetration of the liquid casting material without sacrificing the advantages of die casting. However, higher injection pressures and filling speeds are also possible in principle.

[0013] In a further embodiment, the lost models can be equipped with additional functional components such as threads, sensors, actuators, fibers, or wire structures. These functional elements are embedded so that a connection area to the mold cavity remains when the model is burned out. The portion of the functional element protruding into the mold cavity is cast in during the casting process, creating a form-fit and / or material-fit connection.

[0014] In the proposed application, the lost mold is dimensioned with its outer dimensions to completely fill an existing permanent metal mold or the casting chamber of the die-casting machine. The outer dimensions are chosen independently of the other structure of the lost mold, which is adapted to the specific casting to be produced. This eliminates the previously costly and casting-specific production of die-casting molds using a master mold (permanent mold) into which ceramic molds with a standardized outer geometry but freely selectable inner geometry are inserted. The lost mold then assumes an adapter function, enabling the production of various components or castings in the same permanent mold. This makes the manufacturing and design of the master mold independent of the component geometry and dependent only on its size and volume. Thus, master molds or...Permanent molds for various product families can be produced cost-effectively. This allows for high production flexibility, as the process is equally suitable for series production and for small and pilot runs. The geometry of the models can be continuously modified without requiring time-consuming changes to the permanent metal mold. This ensures the process's suitability for use in rapid prototyping.

[0015] The use of expendable ceramic molds according to the proposed method enables the cost-effective production of complex-shaped castings using a die-casting machine. These castings were previously only achievable with die casting through the use of complicated and expensive slide technologies, or not at all. The targeted use of elements from die casting and investment casting in conjunction with expendable ceramic molds allows the advantages of both technologies to be combined. In particular, the precisely controllable parameters in the die-casting process allow for optimal adaptation of the displacement profile (mold filling) and the pressure profile (feeding) to the specific geometry of the casting. Compared to investment casting, the parameters mold filling time, mold filling speed, and pressure can be varied more flexibly and precisely, resulting in improved casting quality. The production of, for example,On the other hand, wax models, as known from investment casting, offer the possibility of producing lost molds with the highest geometric design freedom. Brief description of the drawings

[0016] The proposed method is explained in more detail below using an exemplary embodiment in conjunction with the drawing. This shows: Fig. 1 An example of the process flow for the manufacture of a complex component with the proposed use of a lost mold. Ways to implement the invention

[0017] The present invention employs expendable molds for the production of complex, cost-effective castings using a die-casting machine. The expendable molds are made from an inorganic ceramic investment material that undergoes alloy-specific adaptation. First, a wax model 1 is produced using suitable methods known from investment casting processes. The wax model 1 is then cast, either individually or in a cluster, with a suitable ceramic investment material. The embedded wax model 2 is subsequently burned out, resulting in the expendable mold 3 used for the die-casting process. This is shown schematically in the upper part of the Fig. 1 indicated.

[0018] The forming surface of the lost mold must be designed such that, during the subsequent casting process, no penetration or infiltration of the liquid or molten casting material occurs due to the pressures involved. This can be prevented by ensuring that the ceramic mold material has a surface porosity that is not wettable by the molten casting material, is dense and non-porous, or has closed porosity. For example, material compositions of two or more mold materials can be used to guarantee the requirements of a dense mold surface. Furthermore, the surface is sealed, coated, or modified using suitable methods to prevent penetration and infiltration of the liquid casting material. Additionally, the process-related pressures are preferably selected to be less than 10 MPa, and the piston speeds of the die-casting machine are selected to be less than 1.0 m / s.However, higher pouring pressures and filling speeds are also possible in principle.

[0019] In the Fig. Two examples of casting are shown below. In one of the examples, the casting of the lost mold 3 is carried out by placing it in the casting chamber of the die-casting machine (upper variant of the Fig. 1) In the other example, a permanent metallic mold 5 is used, into whose cavity the expendable mold 3 is placed. The expendable mold 3 completely fills the corresponding cavity (casting chamber or cavity in the permanent metallic mold) and ensures that no molten metal enters the interface between the expendable mold 3 and the casting chamber or permanent mold 5.

[0020] Depending on the mold material, the metals or metallic alloys used for casting, and the selected process parameters, the expendable molds 3 are used in the process either cold or preheated. For casting, a metered quantity of the molten casting material 6 is poured into the filling opening of the filling box 4. The casting piston 7 then moves and injects the molten metal into the mold 3 at a predetermined piston speed. After the holding time has elapsed, the molten metal has solidified, and the mold 3, containing the solidified casting, can be removed. The expendable mold 8, filled with the casting material, is in the Fig. 1 is shown schematically. The casting 9 is then demolded in the known manner.

[0021] The following section describes individual steps of the process in more detail using the example of the production of a perforated grid as a cast part 9.

[0022] First, a wax model of the perforated grid is produced in the usual way. Then, a sizing agent, in this example boron nitride sizing, is applied to the wax model. For this, the wax model can be slowly dipped into a container filled with the sizing agent and then withdrawn. The coated model is then hung up to dry.

[0023] In this example, the commercially available Wiroplus® ceramic investment material is used. After mixing, this investment material is poured into a mold in which the coated model is fixed. After a setting time of at least 60 minutes, the hardened material is placed on a ceramic base in a convection oven and fired. The heating process liquefies the wax, which then flows out through a gate provided in the wax model. The coating on the wax model seals the surface of the ceramic mold, preventing the subsequent penetration of the casting material used in die casting.

[0024] The fired ceramic mold is then placed in the casting chamber of the die-casting machine. The casting process can be carried out with the following parameters: alloy : 226D T (Gießkam.) : 150 °C Switching criteria : Holding time : 45 s T (fixed / moving) : 150 °C - Distance: 300 mm Casting weight : 2700 g T (melt) : 700 °C - Pressure: 25 bar Reprint : 25 bar V (piston) : 0,1 m / s - V K% : 100 %

[0025] After the ceramic mold is placed in the casting chamber, both halves of the metal permanent mold close. A metered amount of molten metal is poured into the filling opening of the casting chamber. The pouring piston then moves and injects the molten metal into the ceramic mold at a predetermined piston speed. After the set holding time, the molten metal solidifies, and both halves of the permanent mold open. The ceramic mold, containing the solidified casting, can then be removed from the permanent mold.

[0026] The ceramic mold is mechanically split in the middle parallel to the casting, and the casting is freed from the coarsest investment material. The remaining material is removed by sandblasting in the blasting cabinet.

[0027] The proposed application enables the casting of geometrically complex shaped castings using a die-casting machine, employing a expendable ceramic mold or partial mold, which can, for example, be inserted into a main tool. In its preferred embodiment, the process, with regard to mold filling speeds and pressure parameters, falls between gravity casting and die casting. Components made of light and heavy metals and their alloys can be produced. The use of expensive and complex movable cores is eliminated. Reference symbol list 1 wax model 2 embedded wax model 3 lost form 4 filling cans 5 Permanent form 6 molten cast material 7 casting pistons 8 filled lost molds 9 demolded casting

Claims

Use of a lost mold (3) in a process for producing complex-shaped castings (9) using a die-casting machine, wherein the lost mold defines at least one region of the complex castings (9), wherein the lost mold (3) is dimensioned with its outer dimensions such that it completely fills a permanent metallic mold (5) or the casting chamber of the die-casting machine, wherein the outer dimension is chosen independently of any other structure of the lost mold (3) adapted to the complex castings (9), and wherein the lost mold is formed from a ceramic body produced using a lost pattern and the surface of which is adapted to prevent penetration or infiltration of liquid casting material (6) during the casting process, wherein the surface of the ceramic body is impregnated, sealed, or coated.to prevent penetration or infiltration of the liquid casting material (6) during the casting process, or the ceramic body is made of a material composition that changes towards the surface, wherein the material composition in the surface region is selected to prevent penetration of the liquid casting material (6) during the casting process, wherein metals or metallic alloys are used as the casting material in the process, and wherein the lost mold (3) for the casting process is placed in a casting chamber of the die-casting machine or a cavity of a permanent mold (5) used in the die-casting machine. Use according to claim 1, characterized in that the casting process is carried out with the die-casting machine at pressures of less than 10 MPa. Use according to claim 1 or 2, characterized in that the casting process is carried out with the die-casting machine with casting piston speeds of less than 1.0 m / s. Use according to one of claims 1 to 3, characterized in that the lost model is produced using a rapid prototyping method. Use according to any one of claims 1 to 4, characterized in that the lost model is made of wax or plastic.

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