DE102017204968A1 - Method for producing a casting - Google Patents

Abstract

The present invention relates to a method for producing a cast part (1) for a motor vehicle. The method comprises the following steps:
Producing a casting core (2) from a core material (3) by means of an additive manufacturing process as a placeholder for a cast material (6) of the casting (1) to be produced,
Embedding the casting core (2) with a molding material (4) to produce a casting mold (5),
- Introducing liquid cast material (6) in the mold (5), wherein the casting core (2) is displaced or destroyed, thereby releasing a space for the casting material (6),
Solidification of the casting material (6) introduced into the casting mold (5), and
- Removal of the produced casting (1) from the mold (5).

Description

The present invention relates to a method for producing a cast part, in particular a metal casting, for a motor vehicle by means of the "lost foam" technology.

Lost-Foam technology provides processes for making castings, particularly metal castings, with a lost model and a lost shape. First, a positive model of the cast part to be produced is made of a core material, such as e.g. Polystyrene or polystyrene, polymethylmethacrylate or the like produced. The positive model is also referred to as foaming or casting core. In complex structures and / or casting cores, which have cavities for saving material, the casting core is often composed of several individual parts, which are glued together. By means of such a casting core castings can be produced with very complex structures, which have, for example undercuts and / or holes or cavities.

The finished casting core is then encased by a molding material or embedded in the molding material to produce a casting mold. Here, the molding material is adapted to the outer contours of the casting core. The casting core is designed to maintain its shape in this process step. A commonly used molding material is quartz sand. The molding material has an internal self-bonding to form a dimensional stability. It can be provided that the molding material according to the Vollformguss technology is or is added to a binder to increase the dimensional stability. The dimensional stability can thus be achieved, for example, by drying and / or compacting the molding material. The filigree the outer contours of the casting core are formed, the finer is a grain of the molding material. Alternatively, a viscous molding material can be used, which is solidifiable by drying or a chemical reaction.

In a further method step, the casting mold is filled with a liquid cast material, in particular a liquid metal material. For this purpose, the casting mold has at least one sprue opening. Due to the high temperature of the liquid casting material, the casting core is destroyed and the core material is vaporized, burned, diffused, displaced or the like. A previously filled from the casting core cavity of the mold is thus filled by the casting material. After solidification of the casting material, the casting is removed from the casting mold. In this case, the mold is usually destroyed and can not be reused as such. The molding material, for example, after a preparation again usable to produce a further mold.

Known methods according to the lost foam technology have the disadvantage that the production of the casting cores due to the assembly and bonding of the items is very complex and thus causes high costs. Furthermore, the casting cores often have a relatively high proportion of core material due to the required adhesive surfaces, which also increases the manufacturing costs of the casting.

It is therefore an object of the present invention to remedy the disadvantages described above in a method for producing a casting for a motor vehicle or at least partially correct. In particular, it is an object of the present invention to provide a method for producing a casting for a motor vehicle, which simplifies and / or improves the production of the casting in a simple and cost-effective manner.

The above object is achieved by a method having the features of claim 1. Further features and details of the invention will become apparent from the dependent claims, the description and the drawings.

• - Erzeugen eines Gusskerns aus einem Kernwerkstoff als Platzhalter für einen Gusswerkstoff des herzustellenden Gussteils,
• - Einbetten des Gusskerns mit einem Formwerkstoff zu Erzeugung einer Gussform,
• - Einbringen des flüssigen Gusswerkstoffs in die Gussform, wobei der Gusskern verdrängt oder zerstört wird und dabei einen Raum für den Gusswerkstoff freigibt,
• - Erstarren des in die Gussform eingebrachten Gusswerkstoffs, und
• - Entformen des erzeugten Gussteils aus der Gussform.

According to the invention the object is achieved by a method for producing a casting for a motor vehicle. The method comprises the following method steps:

• Producing a casting core from a core material as a placeholder for a cast material of the casting to be produced,
• Embedding the casting core with a molding material to produce a casting mold,
• Introducing the liquid casting material into the casting mold, whereby the casting core is displaced or destroyed, thereby releasing a space for the casting material,
• Solidification of the casting material introduced into the casting mold, and
• Demoulding the produced casting from the mold.

According to the invention, the casting core is produced by means of an additive manufacturing process.

An additive manufacturing process in the context of the invention is a production process in which an object to be produced is produced by material application. A manufacturing apparatus used in the context of carrying out the method according to the invention for the additive production of the casting core is preferably designed to have the casting core Automatically generate base of 3D data. Thus, any number of casting cores can be generated with a 3D data set. Interaction of an operator of the manufacturing device can be limited in this way to a minimum, eg for general process monitoring.

The core material is preferably a plastic, in particular a styropolymer, such as e.g. expanded polystyrene (EPS), which is also known under the name "Styrofoam", polymethyl methacrylate or acrylic glass or the like. The molding material used is preferably a foundry sand, in particular a quartz sand. It can be inventively provided that the binder material, in particular the molding sand or quartz sand, a binder is mixed or is to increase the dimensional stability.

The casting core is preferably arranged on a casting surface, in a casting box or the like, on a layer of molding material or a bottom layer and preferably embedded in the molding material such that the casting core is completely surrounded by the molding material. In this case, the molding material is preferably nestled against the mold material exposed surfaces of the casting core, so as to image the shape of the casting core as a negative mold in the molding material. The molding material can be compacted according to the invention for the exact negative imaging of the casting core and / or for achieving a dimensional stability and / or subjected to a thermal and / or chemical treatment. In this way, a mold is created. The casting mold has at least one sprue opening for introducing the liquid cast material. At the gate, the casting core is preferably directly accessible from the outside. It can also be provided as a feeder openings formed in the mold, via which the casting core is accessible from the outside.

The liquid cast material used is preferably a metal, in particular aluminum or an aluminum alloy. The casting material is introduced into the casting mold via the sprue opening. Due to the relatively high temperature of the casting material, the casting core is destroyed in this case. The core material can be melted and / or burned and / or vaporized, for example. In this case, the core material is preferably displaced from the casting mold or escapes at least substantially from the casting mold. Alternatively, according to the invention, it may be provided that the casting core is heated before introduction of the casting material, e.g. by exposure to a high temperature and / or a solvent, destroyed or removed or at least substantially removed. A cavity inside the mold, which was occupied by the casting core prior to introduction of the casting material, is filled by the introduction of the casting material into the casting mold from the casting material.

After solidification of the casting material, the casting is removed from the mold. In this case, it is preferred that the casting mold is destroyed and the casting is exposed in this way. The molding material is preferably supplied for recycling. It may be provided that the casting is subsequently subjected to a post-treatment, e.g. for deburring, separating gate or feeder or the like.

The inventive method for producing a casting for a motor vehicle has the advantage over conventional methods that particularly high accuracies and very complex structures can be achieved by means of additive manufacturing processes, so that a quality of the casting can be improved. Furthermore, by means of the additive manufacturing method, a material cost for the production of the casting core can be reduced. This has the further advantage that less core material has to be displaced from the casting mold so that an effect of the casting core on the introduction of the casting material into the casting mold can be reduced. Furthermore, eliminates the need for tools for the production of the components of the casting core. Thus, by the additive production of the casting core costs and manufacturing time of the casting core are reduced.

According to a preferred development of the invention, it can be provided in a method that the casting core is produced by means of melt stratification or selective laser sintering. Melt stratification is also referred to as "fused deposition modeling" or "FDM" for short. In melt layers, the core material is arranged in a flowable, in particular highly viscous, state for producing the casting core, for example on a building platform. The core material can be brought into the flowable state, for example, by heating or already have a flowable state and solidify by drying or a chemical reaction or cooling. The production of the casting core by means of melt layers is preferably carried out in layers, but can also be carried out in segments. Selective laser sintering is also referred to as "selective laser sintering" or "SLS" for short. In selective laser sintering, a layer of granular sintered material is applied to a base, for example a construction platform. The casting core is produced in layers by a defined melting or melting of areas of the layer. The melted or fused areas are then solidified and thus form parts of the casting core. After completion of a shift, another layer of granules is placed on the finished layer and the process repeated for the new layer. It can be provided that the construction platform is lowered after generation of a layer by one layer thickness. This process is repeated until the casting core is completed. The excess granules can then be removed and reused for the production of further casting cores. By means of this method, casting cores can be produced with high accuracy as well as relatively inexpensively.

Preferably, the casting core is produced as a foam component. A foam component is in the context of the invention, a component which is made of a porous material or has a porous material. The foam component has a multiplicity of pores. The pores preferably have a pore diameter between 0.2 mm and 2 mm. The casting core can be produced, for example, with a homogeneous or at least substantially homogeneous structure, so that the pores are at least substantially evenly distributed over the casting core. Alternatively it can be provided that the casting core is produced in such a way that different regions of the casting core have a different pore density and / or different pore sizes. A foam component has the advantage that a material requirement for producing the casting core is reduced. Thus, the manufacturing cost can be further reduced. Furthermore, a lower material requirement has the advantage that in the implementation of the method less core material must be removed from the mold, in particular by combustion, evaporation or the like.

It is preferred in a method that when the casting core is produced, a blowing agent for producing pores is introduced into the core material. The introduction of the propellant can be done for example during or after the generation of a basic shape of the casting core. The blowing agent displaces the core material, so that the pores are produced. As propellant, a propellant gas is preferably used. Additionally or alternatively, as the blowing agent, a chemical can be used which reacts with the core material or develops the propellant gas under the influence of temperature. The propellant can thus act physically and / or chemically. By means of a blowing agent, the pores of the casting core formed as a foam component can be produced inexpensively and in defined regions.

According to a preferred development of the method, it can be provided according to the invention that a defined foam structure of the casting core is produced by means of the additive manufacturing method. A defined foam structure according to the invention is a foam structure in which the position and size of the pores are predefined. The individual walls that surround the pores are thus produced selectively by means of the additive manufacturing process. The generation of a defined foam structure by means of the additive manufacturing method has the advantage that no foaming of the core material is required. Thus, a casting core with more precise contours and dimensions can be generated.

Preferably, the casting core is produced as a hollow component with an edge layer and at least one cavity surrounded by the edge layer. The edge layer is designed to protect the cavity from penetration of the molding material. The edge layer thus defines the outer surfaces of the casting core, which are covered when embedding in the molding material of this. A cavity in the sense of the invention is comparable to a pore, but may have a substantially larger volume and extend, for example, from an edge layer of a first side of the casting core to an edge layer of an opposite second side of the casting core. Preferably, the surface layer has such intrinsic stability that resists pressure when embedded in the molding material. Such a cast core has the advantage that core material can be saved due to the hollow space. Thus, the manufacturing cost of the casting are further reduced.

More preferably, at least one supporting device for supporting the edge layer is produced in the cavity. The support device has, for example, a strut which extends in the interior of the cavity between at least two different edge layer sections and supports them against each other. The supporting device is preferably produced such that it supports two opposite edge layer sections against each other. The strut can be produced according to the invention as a solid structure, profile structure and / or foam structure. A support device has the advantage that the edge layer can be made thinner. Thus, core material and production costs can be further reduced. Basically, a support device has the advantage that a dimensional stability of the casting core is improved. The risk of yielding the casting core when embedding with the molding material is thus reduced and increases process reliability of the process.

In a preferred development of the invention, the supporting device has a lattice structure with a plurality of struts. Such a grid structure is preferably produced in such a way that the struts are supported against one another and thus distribute pressure forces acting on the outer layer over the cast core. Thus, the dimensional stability of the casting core is further improved.

Preferably, a strut volume of the struts is less than 10% of a void volume of the cavity surrounded by the boundary layer. This means that preferably at most 10% of the cavity is filled by struts. With such a ratio, a good stabilization of the casting core can be achieved with a low molding material requirement.

It is inventively preferred that a mold is produced, which is designed for producing a cylinder head for an engine, in particular for a motor vehicle, wherein a metal or a metal alloy is used as the casting material. It is inventively preferred to use aluminum or an aluminum alloy as the casting material. Cylinder heads work well with a Lost-Foam technology process. Due to high cost pressure and high quality requirements in the automotive industry, the inventive method, especially because of the high achievable dimensional accuracy and the economical use of resources, particularly suitable.

• 1 in einer Seitenansicht die additive Erzeugung eines Gusskerns,
• 2 in einer Seitenansicht den erzeugten Gusskern aus 1,
• 3 in einer Schnittdarstellung eine erste Ausgestaltung des Gusskerns aus 2,
• 4 in einer Schnittdarstellung eine zweite Ausgestaltung des Gusskerns aus 2,
• 5 in einer Schnittdarstellung eine mittels des Verfahrens erzeugte Gussform vor dem Einbringen des Gusswerkstoffs,
• 6 in einer Schnittdarstellung die Gussform aus 5 nach dem Einbringen des Gusswerkstoffs,
• 7 in einer Seitenansicht das fertige Gussteil, und
• 8 in einer Schnittdarstellung einen Gusskern nach dem Stand der Technik.

An inventive method for producing a casting for a motor vehicle is explained in more detail with reference to drawings. Each show schematically:

• 1 in a side view the additive production of a casting core,
• 2 in a side view of the cast core produced 1 .
• 3 in a sectional view of a first embodiment of the casting core 2 .
• 4 in a sectional view of a second embodiment of the casting core 2 .
• 5 in a sectional view, a mold produced by the method before the introduction of the casting material,
• 6 in a sectional view of the mold 5 after introducing the casting material,
• 7 in a side view of the finished casting, and
• 8th in a sectional view of a casting core according to the prior art.

Elements with the same function and mode of action are in the 1 to 8th each provided with the same reference numerals.

In 1 is the additive production of a casting core 2 shown schematically in a side view. In this example, the casting core becomes 2 generated by means of a fused deposition modeling (FDM) process. By means of a manufacturing device 16 becomes flowable core material 3 on a building platform 17 arranged in layers and thus the casting core 2 generated. After placing the core material 3 through the manufacturing device 16 it solidifies and is therefore dimensionally stable. It can be provided that the core material 3 is foamed before solidification, for example using a propellant. The core material preferably has a polystyrene (PS) or an expanded polystyrene (EPS).

2 shows the finished casting core 2 out 1 schematically in a side view. The casting core 2 In this example, it is completely made of the core material 3 formed and has a continuous edge layer 9 on which a heart of the casting core 2 covering to the outside. An illustrated form of the casting core 2 is for illustrative purposes only. According to the invention, the casting core 2 have a much more complex shape, such as in 8th represented, wherein the casting core according to the invention 2 preferably formed in one piece and not from several cast core segments 2a (see. 8th ) is composed.

In 3 is a first embodiment of the casting core 2 out 2 schematically shown in a sectional view. The casting core 2 has a boundary layer 9 which may be solid or porous. In this example, the boundary layer is 9 solid from the core material 3 educated. The boundary layer 9 defines a plurality of cavities 10 of the casting core 2 to the outside and thus prevents penetration of molding material 4 (see. 5 ) in the cavities 10 , To increase the dimensional stability of the casting core 2 this has two support devices 11 on, of which a first support device 11 as a strut 13 and a second support device 11 as a lattice structure 12 with a plurality of struts 13 is trained. Of course, the casting core can 2 other shape elements, such as paragraphs, curves, channels or the like, have.

In 4 is a second embodiment of the casting core 2 out 2 schematically shown in a sectional view. The casting core 2 has a boundary layer 9 which may be solid or porous. In this example, the edge layer 9 is solid from the core material 3 educated. Within the boundary layer 9 has the casting core 2 a foam structure 8th on. The foam structure 8th has core material 3, in which the pores 7 are formed. The pores 7 For example, air and / or gas inclusions in the core material 3 , Of course, the casting core 2 further mold elements, such as paragraphs, curves, channels or the like, have.

5 shows a mold produced by the method 5 before introducing the casting material 6 (cf. 6 ) schematically in a sectional view. The mold 5 has the casting core 2 made of core material 3 out 2 on, of molding material 4 , in particular quartz sand, is surrounded. The casting core 2 thus fills a cavity 18 from which of the molding material 4 surrounded and thus by the molding material 4 is limited to the outside. Over a gate 14 is a liquid casting material 6 from the outside the casting core 2 fed. Due to the high temperature of the casting material 6 is the casting core 2 destructible, so that the casting material 6 in the cavity 18 is distributable. The mold 5 has a feeder 15 from the outside to the casting core 2 extends. Melted or burned core material 3 as well as extruded casting material 6 are over the feeder 15 from the cavity 18 dischargeable. Furthermore, by means of the feeder 15 a uniform distribution of the casting material 6 in the cavity 18 be improved.

In 6 is the mold 5 out 5 after the introduction of the casting material 6 schematically shown in a sectional view. By introducing the casting material 6 is the casting core 2 destroyed and the nuclear material 3 for example, burned and out of the cavity 18 escaped. The cavity 18 is completely filled with the casting material 6. As a result, the casting to be produced 1 educated.

Part of the cast material 6 is in the gate 14 , another part of the casting material 6 in the feeder 15 arranged.

The finished casting 1 made of cast material 6 is in 7 schematically shown in a side view after demolding. The mold 5 as well as the casting material 6 from the gate 14 and the feeder 15 are removed in this state. The casting shown here 1 is designed for example as a cylinder head of an engine of a motor vehicle. A preferred casting material 6 has aluminum.

In 8th is a casting nucleus 2 schematically represented in a sectional view according to the prior art. The casting core 2 has several casting core segments 2a made of a foam material, which has adhesive surfaces 2 B glued together. The gluing of the cast core segments 2a requires a precise alignment of the casting core segments 2a to each other and therefore is very expensive.

LIST OF REFERENCE NUMBERS

1

casting

2

casting core

2a

Cast core segment

2 B

adhesive surface

3

Core material

4

Mold material

5

mold

6

Cast material

7

pore

8th

foam structure

9

boundary layer

10

cavity

11

support device

12

lattice structure

13

strut

14

gate

15

Speiser

16

manufacturing device

17

building platform

18

cavity

Claims (10)

Method for producing a cast part (1) for a motor vehicle, comprising the following steps: - producing a cast core (2) from a core material (3) as a placeholder for a cast material (6) of the cast part (1) to be produced, - embedding the cast core ( 2) with a molding material (4) for producing a casting mold (5), introducing the liquid casting material (6) into the casting mold (5), wherein the casting core (2) is displaced or destroyed, leaving a space for the casting material (6 solidification of the casting material (6) introduced into the casting mold (5), and removal of the produced casting (1) from the casting mold (5), characterized in that the casting core (2) is produced by means of an additive manufacturing process. Method according to Claim 1 , characterized in that the casting core (2) is produced by means of melt stratification or selective laser sintering. Method according to Claim 1 or 2 , characterized in that the casting core (2) is produced as a foam component. Method according to Claim 3 , characterized in that in the production of the casting core (2) a blowing agent for generating pores (7) in the core material (3) is introduced. Method according to Claim 3 or 4 , characterized in that a defined foam structure (8) of the casting core (2) is produced by means of the additive manufacturing process. Method according to at least one of the preceding claims, characterized in that the casting core (2) is produced as a hollow component with an edge layer (9) and at least one cavity (10) surrounded by the edge layer (9). Method according to Claim 6 , characterized in that in the cavity (10) at least one supporting device (11) for supporting the edge layer (9) is generated. Method according to Claim 7 , characterized in that the supporting device (11) has a grid structure (12) with a plurality of struts (13). Method according to Claim 8 , characterized in that a strut volume of the struts (13) is less than 10% of a void volume of the of the edge layer (9) surrounded cavity (10). Method according to at least one of the preceding claims, characterized in that a casting mold (5) is produced which is designed to produce a cylinder head, wherein a metal or a metal alloy is used as the casting material (6).

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