Patent Application
20150165520
The present invention relates to a cooling device for cooling a component produced in a lost foam casting method by way of an EPS pattern, in particular a component of a motor vehicle which is subject to high loads, such as a cylinder head, wherein the cooling device includes at least one cooling element, which can be disposed in a planer manner on at least one region of the EPS pattern. The invention further relates to a method for cooling a component produced in a lost foam casting method by way of an EPS pattern, in particular a component of a motor vehicle which is subject to high loads, such as a cylinder head.
Sand casting is a traditional casting method for producing complex components, in particular for a motor vehicle. However, creating and preparing the sand cores is associated with high costs. Secondary machining of the finished castings is also associated with high complexity and costs.
The lost foam method has emerged as an alternative to the sand casting method. In the lost foam casting method, a positive model made of EPS (expanded polystyrene) serves as the casting model. It is therefore what is known as a full mold casting method. After a mineral refractory coating has been applied, which is known as the wash, the EPS pattern is embedded in unbonded sand. Thereafter, casting metal, this being the melt, is poured onto the EPS pattern, as a result of which the same burns out and thereby the metal takes on the shape of the model. This means that the model made of EPS, such as polystyrene, evaporates due to the melt. The coating made of the refractory material is not only used as a separating layer between the metal and the sand, it also assures discharge of the waste gases into the sand.
Cooling, and the attendant solidification, of the metal take place by heat transfer from the metal into the sand. However, compared to other materials, the thermal conductivity of sand is very low. This leads to very slow cooling, and consequently also to very slow solidification. Slow solidification of metallic casting materials, such as aluminum, gray cast iron and the like, results in the formation of a “coarse structure” and in worsening of the mechanical properties of the component being generated. These drawbacks make the lost foam casting method only conditionally suitable for components that are subject to high loads, such as cylinder heads for turbocharged engine of motor vehicles. This means that the actual advantages of the lost foam casting method, such as weight savings due to an optimized design, a high degree of automation, and efficiency associated therewith for such components, cannot be utilized.
A lost foam casting method is known from EP 2 357 049, in which an EPS pattern is introduced into a rigid enclosure, which is intended to be used for cooling the component being generated. Due to the improved heat dissipation, such a lost foam casting method can also be used for components in which the requirements in regard to the mechanical properties of the component being generated are high. However, this lost foam casting method, and more particularly the cooling enclosure, also has weaknesses. The pressing pressure of the cooling plates of the enclosure is lost as the volume shrinkage increases during the solidification of the metal that is poured in. It is not possible for the cooling plates to follow the movement due to the rigid enclosure construction. The cooling power is thus relatively low. The cooling power of the cooling plates of the enclosure construction in particular decreases during solidification of the casting metal, in particular if there is insufficient contact with the solidifying component.
It is an object of the present invention to at least partially eliminate the above-described disadvantages of a lost foam casting method. In particular, it is an object of the present invention to provide a cooling device and a method for cooling a component produced in a lost foam casting method by way of an EPS pattern, in particular a component of a motor vehicle which is subject to high loads. The cooling device and the method allow for good cooling of the generated component in a cost-effective and simple manner, and more particularly assures permanent cooling action during the solidification process of the component.
This and other objects are achieved by a cooling device, and corresponding method of cooling, for cooling a component produced in a lost foam casting method by way of an EPS pattern, wherein the cooling device comprises at least one cooling element, which can be disposed in a planar manner on at least one region of the EPS pattern. The cooling device is characterized in that the at least one cooling element can be fixed in a materially bonded and/or non-positive manner on the at least one region of the EPS pattern
Such a cooling device allows good cooling of the component being generated, in particular of a component for the automotive field which is subject to high loads, in a cost-effective and simple manner in a lost foam casting method by way of an EPS pattern. In particular, such a cooling device can assure permanent cooling action during the solidification process of the component.
By bonding and/or non-positively attaching at least one cooling element on the EPS pattern, the solidification rate of the melt that is poured-in can be drastically increased locally. As a result of a local increase in the solidification rate, directional solidification of the metal melt can be induced, and additionally the structure of the component being generated can become considerably finer. The at least one cooling element advantageously has high thermal conductivity and adequate thermal capacity. The at least one cooling element is designed so that it can be attached in a planar manner, which is to say in a form-locked manner, on at least one region of the EPS pattern.
The at least one cooling element advantageously has the shape of the region of the EPS pattern on which it is to be disposed. As a result of the at least one cooling element being bondable and/or non-positively fixable on the at least one region of the EPS pattern, in addition to the planar or form-locked contact, it is assured that the at least one cooling element consistently assures high cooling action during the solidification of the melt.
In particular, such a cooling device can assure that dimensional deviations of the EPS pattern are compensated for, in particular if the model halves are not parallel. The bonded and/or non-positive fixation of the at least one cooling element on the EPS pattern assures secure adherence of the cooling element on the EPS pattern. High cooling action on the component generated from the casting metal is assured in particular by the non-positive fixation of the at least one cooling element on the at least one region of the EPS pattern. As a result of a non-positive fixation, the pressing pressure of the at least one cooling element can be maintained throughout the entire solidification process of the component. The pressing pressure of the at least one cooling element in particular is not lost even in the event of volume shrinkage during the solidification of the casting metal, in particular due to the non-positive fixation of the at least one cooling element on the EPS pattern, and subsequently also on the component being generated.
Since the at least one cooling element is applied to the EPS pattern in a form-locked manner, and is also bonded and/or non-positively applied thereto, prior to the casting process and separation of the at least one cooling element after the casting has been removed from the mold, reuse of the at least one cooling element is assured. Using a cylinder head as an example, cooling elements, such as cooling plates, can be attached in the region of the combustion chambers and of the combustion chamber sealing area.
The local increase in the solidification rate of the metal melt poured onto the EPS pattern results in a considerable improvement of the structure, and thus of the mechanical properties of the casting, in these regions. The directional solidification, proceeding from the cooled region, can be utilized for improved feeding, which is to say for an improved compensation of the volume deficit that is created during solidification. Since many components are not subjected to high loads across the entire geometries thereof, the cooling device according to the invention allows the lost foam casting method to also be employed for components that previously could not be implemented by the method due to their requirements. One possible application is cylinder heads for supercharged gasoline engines made of a light alloy, for example. The action of the at least one cooling element can be controlled via the selection of the materials and of the volumes that are used.
According to a preferred development of the invention, the at least one cooling element includes an adhesive element for the bonded fixation on the at least one region of the EPS pattern. An adhesive tape, and more particularly a double-sided adhesive tape, can be provided as the adhesive element. This is applied to the cooling element. As an alternative to adhesive tape, the adhesive element can be a hot-melt adhesive or a cold-bonding agent, which is applied to the cooling element. The adhesive element ensures that the cooling element is seated particularly rigidly, and more particularly in a form-locked manner, on the EPS pattern.
According to a particularly preferred development of the invention, the cooling device includes two or more cooling elements, and that at least one tensioning element and/or at least one clamping element are provided for non-positively fixing the two or more cooling elements. Such a cooling device ensures that a consistent pressing pressure of the two or more cooling elements can be exerted on the component, and thus a consistent cooling action of the cooling elements can be applied to the solidifying component, despite volume shrinkage of the component during the solidification of the melt. The cooling elements can be pressed against the component being generated during the solidification of the melt by the at least one tensioning element and/or the at least one clamping element. This means that the at least one tensioning element, or the at least one clamping element, ensures that the cooling elements are consistently seated against the component in a form-locked manner during the solidification process. By bracing or clamping the cooling elements on the EPS pattern, the solidification rate of the melt can be drastically increased locally. As a result of a local increase in the solidification rate, directional solidification of the melt can be induced and additionally the structure of the component being generated can become considerably finer.
In particular, a cooling device is preferred in which the at least one tensioning element and/or the at least one clamping element are designed for mutually bracing, or for mutually clamping, the two or more cooling elements with respect to the EPS pattern. In particular, two or more tensioning elements or clamping elements can be provided. It can thus be assured that the cooling elements are pressed evenly and consistently against particular regions of the solidifying component in a form-locked manner during the solidification of the component. The associated local increase in the solidification rate of the solidifying component results in a considerable improvement of the structure of the component being generated, and thus of the mechanical properties of the component being generated, in these regions. The directional solidification and the pressing of the cooling elements by way of the at least one tensioning element or clamping element result in better compensation for the volume deficit of the casting that is created during solidification. The option of mutually bracing or clamping the cooling elements is particularly advantageous. This means that the cooling device is preferably designed so that the at least one tensioning element, or the at least one clamping element, presses or pulls the cooling elements together. Such a cooling device also allows components that are subject to high loads, and more particularly motor vehicle parts, such as cylinder heads made of light alloy, to be generated by a lost foam casting method.
The at least one tensioning element can have a variety of designs. A cooling device in which the at least one tensioning element includes a band, a wire, a spring, a spring compressor and/or a screw tensioner is preferred. In this way, a high pressing pressure of the cooling elements on the casting can be ensured throughout the entire solidification process of the casting. Ribbons can thus surround the cooling elements, and consequently the EPS pattern, under tension. Moreover, twisted wires can be disposed around the cooling elements and the EPS pattern under a particular preload. In particular, it is also possible to provide springs, which are attached to the cooling elements and press the cooling elements against the EPS pattern. It is particularly preferred if two or more cooling elements are preloaded with respect to each other by two or more springs. This means that the springs are designed and attached on the cooling elements in such a way that these press the cooling elements against the surface of at least regions of the EPS pattern. The springs can be braced by way of spring compressors.
According to a further preferred development of the invention, the at least one clamping element is designed for hydraulically, pneumatically or mechanically clamping the two or more cooling elements with respect to the EPS pattern. In this way, permanent pressing of the cooling elements onto the solidifying component is assured. For example, screw clamps can be used for mechanical clamping. Hydraulic or pneumatic clamping of the cooling elements with respect to the EPS pattern allows the cooling elements to be consistently pressed against the solidifying component after the casting metal has been poured in, so as to enable improved cooling of the component. In this way, a local increase in the solidification rate can be achieved, and thus directional solidification of the casting can be induced and the structure of the solidifying component can become considerably finer.
A cooling device in which two or more cooling elements are connected to each other by spring elements, and more particularly by spiral springs, for clamping with respect to the EPS pattern is particularly preferred. This represents a simple and cost-effective manner of mutually clamping the cooling elements with respect to the EPS pattern and the component being generated. This type of clamping in particular also allows the regions of the component being generated to be cooled which are not oriented parallel to each other. By applying the at least one cooling element in a form-locked manner to the EPS pattern, prior to casting, by way of gluing, clamping, tensioning and the like, and separating the same after the solidified component has been removed from the mold, reuse of the at least one cooling element is assured.
According to a further preferred development of the invention, the at least one cooling element is designed for active cooling. Active cooling means that the cooling element is cooled for heat dissipation. This can take place by attaching a further cooling element to the cooling element, for example. As an alternative, the at least one cooling element can be designed as a heat exchanger. It can be particularly preferably provided in a cooling device that the at least one cooling element includes at least one line, at least one borehole and/or at least one cavity for conducting through a cooling medium from and to a cooling unit of the cooling device. The cooling medium can be gaseous or liquid. This means that active cooling of the cooling element by way of a cooling medium, such as by water, can be provided so as to further increase the effectiveness of the at least one cooling element. For this purpose, a closed cooling system, including a cavity, boreholes and/or lines, for example, can be integrated in the cooling element and connected to a cooling unit during casting and solidification.
Advantageous are cooling elements that have high thermal conductivity and adequate thermal capacity. Such cooling elements are made of steel, gray cast iron, tungsten, aluminum, graphite or copper, for example.
A local increase in the solidification rate of the component can be achieved by the above-described cooling devices for cooling a component produced in a lost foam casting method by way of an EPS pattern, resulting in a considerable improvement of the structure, and thus of the mechanical properties of the casting, in these regions. Since many components are not subjected to high loads across the entire geometries thereof, the above-described cooling device allows the lost foam casting method to also be employed for components that previously could not be implemented by a lost foam casting method due to their requirements. The action of a cooling element can be controlled via the selection of the materials and of the volumes that are used.
According to a second aspect of the invention, the object is achieved by a method for cooling a component produced in a lost foam casting method by way of an EPS pattern, wherein the method includes the following method steps:
a) a cooling device according to the first aspect of the invention is bonded and/or non-positively fixed on at least one region of the EPS pattern in a planar manner, wherein the EPS pattern comprises a runner for a metal melt;
b) the EPS pattern comprising the cooling device has been or is introduced into a flask;
c) the EPS pattern comprising the cooling device is completely embedded into the flask by filling in unbonded sand;
d) metal melt is filled into the runner of the EPS pattern for evaporating the EPS pattern; and
e) at least one region of the filled-in metal melt is cooled by the at least one cooling element.
In a first step, the at least one cooling element of the cooling device is fixed in a form-locked manner on at least one region of the EPS pattern. The fixation of the cooling element takes place by bonding and/or non-positively. In particular, the cooling element can be fixed on the EPS pattern, in particular in areas of the EPS pattern that later require rapid cooling, by way of an adhesive element such as an adhesive tape, a hot-melt adhesive or a cold-bonding agent. It is particularly advantageous if the at least one cooling element is non-positively fixed, such as by way of one or more tensioning elements and/or clamping elements, on the EPS pattern at a particular pressing pressure. The EPS pattern includes a runner for the metal melt. In the simplest case, the runner is formed by the EPS pattern itself. However, it is also possible to provide additional channels to the EPS pattern, through which the metal melt is conducted to the EPS pattern. The fixation of the at least one cooling element of the cooling device on the EPS pattern can take place within a flask. This means that it is possible for the EPS pattern to initially be introduced into a flask, and subsequently for the at least one cooling element of the cooling device to be fixed in a form-locked manner on at least one region of the EPS pattern. As an alternative, the at least one cooling element of the cooling device can be fixed in a form-locked manner on at least one region of the EPS pattern, and subsequently the EPS pattern comprising the cooling device can be introduced into a flask. The fixation of the at least one cooling element on the EPS pattern can take place hydraulically or pneumatically, for example. Thereafter, the EPS pattern including the cooling device is embedded in sand, in particular unbonded sand. The EPS pattern, which represents what is known as a positive model of the component to be generated, is completely surrounded by sand. After the embedding in sand, metal melt is filled into the runner of the EPS pattern so that the EPS pattern evaporates. This means that the EPS pattern burns out by the metal melt that is poured in, so that the metal melt takes on the shape of the EPS pattern. After the metal melt has been filled in, the region of the filled-in metal melt on which the cooling element is disposed is cooled by the at least one cooling element of the cooling device.
Cooling, and the attendant solidification, of the metal melt takes place by heat transfer from the metal melt into the sand and, where a cooling element is present, into the cooling element. Compared to the thermal conductivity of the sand, the thermal conductivity of the cooling element is high, so that increased cooling of the metal melt takes place where the cooling element makes contact with the metal melt. Due to the more rapid cooling of the metal melt in the region of the cooling element, more rapid solidification of the metal melt is achieved in this region. In metallic casting materials, such as aluminum, gray cast iron and the like, this results in the formation of a “fine structure” and in the improvement of the mechanical properties of the component being generated. The regionally improved cooling makes the lost foam casting method also suitable for components that are subject to high loads, such as cylinder heads for turbocharged engines of motor vehicles. In addition, advantages of the lost foam casting method, such as weight savings due to an optimized design, a high degree of automation, and efficiency associated therewith for such components, can be utilized.
According to a particularly preferred development of the invention, it may be provided in a method that a mineral refractory coating is applied to the EPS pattern prior to fixing the cooling device on the EPS pattern. This means that a mineral refractory coating, which is known as the wash, is applied to the EPS pattern. Only then are one or more cooling elements of the cooling device fixed on the EPS pattern. As a result, the mineral refractory coating is present between a cooling element and the EPS pattern. After the metal melt has been poured in, the EPS pattern made of polystyrene evaporates. The coating made of the refractory material is not only used as a separating layer between the metal melt and the sand, it also ensures discharge of the waste gases into the sand. The refractory coating, which is applied to the EPS pattern and is also located between the EPS pattern and a cooling element, also fulfills the function thereof there as an absorber for decomposition products. Moreover, the refractory coating prevents the direct contact between casting metal and the cooling element, and thus prevents the casting flaws associated therewith, such as cold shuts, voids and the like. Since the thickness of the refractory coating advantageously only ranges in the tenth of a millimeter range, the insulating effect of the refractory coating is negligible or can be compensated for by the volume and/or the thermal conductivity of the cooling element.
Moreover, a method is preferred in which the at least one cooling element of the cooling device is actively cooled. In this way, cooling in particular regions of the component being generated can be increased yet again. A particularly advantageous method is one in which a cooling medium is conducted from a cooling unit through at least one line, at least one borehole and/or at least one cavity of the at least one cooling element for locally cooling the metal melt that is filled in, and more particularly in a closed cooling circuit from and to the cooling unit. The cooling power of the at least one cooling element can thus be increased yet again, and the structure and the mechanical properties of the component being generated can be influenced in a targeted manner.
Using a cylinder head for a motor vehicle as an example, cooling elements can be attached in the region of the combustion chambers and the combustion chamber sealing area. The effectiveness of the cooling elements is considerably increased by the active cooling, which is to say by way of the cooling medium that is conducted through the cooling elements. For example, water may be used as cooling medium. During casting and solidification of the metal melt, such cooling elements are connected to a cooling unit of the cooling device.
Viewed in general terms, the EPS pattern can include foamed plastic materials, and more particularly expanded polystyrene, which are entirely matched to the metals to be cast. For example, in the case of ferrous materials, a copolymer, and more particularly polymethyl methacrylate and EPS can be selected, and in the case of non-ferrous metals, EPS having special coatings and grain sizes can be selected.
If a mineral refractory coating is used, the same must ensure good gas permeability. This means that advantageously a mineral refractory coating is used which is composed in such a way that it is able to absorb the respective decomposition products and pass these on into the surrounding sand and to the cooling elements. In the case of cast steel, advantageously a refractory coating is used which is easily able to absorb hydrogens that develop. In the case of cast aluminum, advantageously a ceramic coating having high gas permeability is used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
Elements having identical functions and modes of operation are in each case denoted by identical reference numerals in
Such a cooling device 1 allows good local cooling of the component being generated in a cost-effective and simple manner in a lost foam casting method by way of an EPS pattern. By bonding and/or non-positively attaching the cooling elements 2, 3 to the EPS pattern 4, it is ensured that the solidification rate of the metal melt that is poured-in can be drastically increased locally. As a result of the local increase in the solidification rate of the metal melt, directional solidification of the metal melt can be induced, and the structure of the solidifying metal melt can thus be refined, in the regions of the cooling elements 2, 3.
The cooling elements have the shape of the region of the EPS pattern on which they are arranged. Due to the bonding and/or non-positive fixation of the cooling elements 2, 3 on two regions of the EPS pattern 4, in addition to contact in a planar manner or in a form-locked manner, that the cooling elements 2, 3 ensure high cooling action during the solidification of the metal melt that is poured onto the EPS pattern 4. In particular, such a cooling device 1 can ensure that dimensional deviations of the EPS pattern 4 are compensated for, in particular if the model halves are not parallel. The bonded and/or non-positive fixation of the cooling elements 2, 3 on the EPS pattern assures secure adherence of the cooling elements 2, 3 on the EPS pattern 4.
In
In particular, high cooling action on the component being generated by the casting metal can be assured by a non-positive fixation of the cooling elements 2,3 on the EPS pattern 4. As a result of a non-positive fixation, the pressing pressure of the cooling elements 2,3 can be maintained throughout the entire solidification process of the metal melt. This means that the pressing pressure of the cooling elements 2, 3 is not lost during the solidification of the metal melt that is poured in, even in the event of volume shrinkage during the solidification of the metal melt, due to the non-positive fixation of the cooling elements 2, 3 on the EPS pattern 4.
By applying the cooling elements 2, 3 shown in
Using a cylinder head for a motor vehicle as an example, the cooling elements 2, 3 can be attached in the region of the combustion chambers and the combustion chamber sealing area, for example.
The EPS pattern 4 shown in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 209 805.4 | Jun 2012 | DE | national |
This application is a continuation of PCT International Application No. PCT/EP2013/061753, filed Jun. 7, 2013, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2012 209 805.4, filed Jun. 12, 2012, the entire disclosures of which are herein expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2013/061753 | Jun 2013 | US |
| Child | 14564178 | US |
