FI111523B - Process and use for casting - Google Patents

Description

111523

Method and use for casting

The present invention relates to a method of casting, in which the pre-fabrication step is first to produce a mold which is substantially coated with a ceramic-based material to form a mold casing, to perform the actual casting step after separating the mold and mold casing by feeding the molding material into one or more molds.

The description of the type described above corresponds e.g. to the conventional precision casting or shell mold technology or, for example, to the newer Replicat CS or RP methods.

15 The traditional precision casting method first starts with the production of a disposable wax model, which is usually done by pressing molten wax into an aluminum wax mold. The wax model is still attached to the template tree, to which they can be attached up to dozens of pieces depending on the castings being manufactured. When the model wood is generally ready for the lateral ductwork connected thereto at a later stage, it is dipped in a ceramic slurry to coat it with, for example, various zircon sand.

The slurry used in this context generally comprises, for example, colloidal silica, sodium silicate or ethyl silicate. The actual sanding is done with a sprinkler or fluidized bed. The coating process is continued until the shell is about 6-8 mm thick.

30 The wax is then removed either by heat or by pressure as well, after which the mold is sintered to achieve its final strength.

r This method firstly has the problem that an expensive wax mold is required to make the 35 wax designs, which are usually made by machining from aluminum or steel or then using, for example, a vulcanized: silicone mold. The more complicated the 111523 £ t piece is, the more expensive the wax model you need, of course. Also, the use of a wax model per se causes a number of additional work steps and costs, particularly because of the equipment and equipment required to handle the wax. The precision achieved by the method is today of the highest quality, although precision casting is currently only possible in the manufacture of very small castings. The average 10 weights of the pieces, for example in Finland, are usually in the order of a few tens of grams.

In the process of the above type, in particular the EPS (Expanded Polystyrene) 15 model is used in place of the wax, this is the aforementioned Replicat CS (Cera mic Shell) method, wherein the mold shell is built on an EPS mold produced by expansion, which afterwards, the mold is further sintered to obtain sufficient strength. The mold is usually supported during casting to withstand sand under intense pressure during casting. In order to enhance the support effect of the sand and the degassing, a negative pressure is added to the casting vessel if necessary. Replicast CS can be used to make larger pieces than the precision casting method, but the accuracy of the method is not * nearly the same.

The new RP (Rapid Prototyping) methods still offer some alternative methods to the more traditional precision casting technology.

One such method is the American Reverse DSPC method. The method produces a precision die mold directly from a CAD image without any intermediate steps, such as the preparation of a wax model. Thus, the method is based on a three-dimensional CAD image of the casting model, which is executed in a processor suitable for -. format. The required casting system is added to the casting model and the size changes required for shrinkage are calculated. The processor then slices the die pattern into horizontal 2D slices. At the beginning of the construction phase, the device scatters and spreads a layer of alumina (particle-

size e.g. about 0.05 mm). Next, a print tip, such as an ink jet printer, injects small droplets of colloidal quartz into the desired, i.e., mold wall sites, which binds the powder particles 10 at desired locations. The printer moves X-Y

direction and in addition, the jet can be controlled by electrodes underneath the nozzle, whereby the electric field guides the jet to the correct positions. Next, the substrate is lowered and the steps described above are repeated until the desired mold is completed at full height.

The manufacturing mold is removed from the base and the loose alumina powder is poured out of the mold. The mold is sintered to achieve ultimate strength. Next, casting can be performed.

20

The method described above allows complete freedom of design. No loose cores need be placed in the mold, but all desired shapes can be made at once. According to the literature, the accuracy of the apparatus is good, up to about 0.05 mm.

However, there is still room for improvement in surface quality; afford it. However, the biggest limitation of the method so far is its limited piece size. At present, there are no installations with a maximum platform size larger than 406 x 406 x 406 mm. Further, the method is quite slow as the construction speed is in the order of 38 mm per hour, whereby the total construction time of the largest possible platform of the size described above is more than 10 hours. For this reason, it is not yet possible to utilize this type of process 35 at least today in serial production. Of course, for single production and prototype manufacturing, the method is well suited as a modelless and low cost 4 111523 process. However, the cost of production may increase in practice to a disproportionately high level, in particular for total production.

5

The purpose of the method of the present invention is to provide a decisive improvement on the problems and limitations of the prior art described above, and thus to substantially increase the state of the art in the art. To accomplish this purpose, the method of the invention is essentially characterized in that the pre-fabrication step uses a Water Stabilized Plasma to form the mold casing in layers by spraying one or more substantially different overlapping layers of material onto the model surface.

The main advantages of the method according to the invention 20 are its simplicity, efficiency and reliability. The process of the invention makes it possible very quickly to produce a ceramic casing of the desired thickness, which can still be used in the same way as a precision casting mold, unlike conventional technology, without the need for a sintering step. The accuracy of the method can always be raised to the level of the traditional precision casting method with properly defined building parameters. One of the main advantages of the process according to the invention is that it completely eliminates the manufacturing step of the wax model of the conventional precision casting technique. Of course, the mast model utilized in the method according to the invention must be manufactured for each piece separately, 35 but it is still possible to use it in a very long production series. Using suitable manipulators for plasma gun and mast model processing, it is possible to further implement a highly automated, fast and efficient ceramic precision mold making process that does not result in any environmental disadvantages compared to, for example, emissions from dewaxing or EPS degradation processes. Due to the method of the invention, the production costs are also lower than those of the above methods, since it is also possible to limit the basic investments as such to the existing equipment base, and no separate heat treatment or other similar processes are required.

Advantageous embodiments of the method 15 of the invention are disclosed in the dependent claims.

The invention also relates to the use of water-stabilized plasma spray (WPS) in casting, for which there is a separate independent claim.

20

In the following description, the invention will be illustrated in detail with reference to the accompanying drawing, which shows a general principle of the method according to the invention.

25

The present invention relates to a method of casting, in which the pre-fabrication step comprises firstly manufacturing a pattern X which is substantially coated with a ceramic-based material to form a mold shell Y, after casting the mold X from the mold to one, M. Preparation

stage uses a Water Stabilized Plasma Syringe 35 with a mold shell Y

is produced in layers by coating step I, by spraying one or more substantially different overlapping layers Z onto the surface of model X.

As a preferred embodiment of the method, particularly with reference to the accompanying drawings, Model X must be used

the so-called. a positive mast model, incremented by the amount of casting shrinkage from the original body and divided at the partition planes into sections X1, X2 to form the joint surfaces and to form the casting mold M by attaching to the sections X1, X2 the coated mold parts

In practice, Y1, Y2 are glued to each other by gluing to the principle shown in the attached diagram. In this connection, one or more ceramic materials are sprayed onto the surface of model X using injection layers Z of different compositions and / or grain sizes; Z1, Z2, Z3.

In a preferred embodiment of the method according to the invention, Y is injected into the mold shell to be manufactured; First, Y1, 20 Y2 are first of all specially formulated to improve the surface quality of the casting, a finely divided material layer Z2 consisting of e.g. zirconium silicate, screened coarse natural material and / or the like having a grain size of, for example, 50-100 μτη. Further, as a preferred embodiment of the process, a coarse structure bearing core layer Z1 consisting of zirconium silicate, mullite, molocite and / or the like mineral is further sprayed onto the above coating with a grain size typically between 80 and 250 µιη and a layer thickness respectively.

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Further, as a preferred embodiment of the process, thermal, chemical, mechanical and / or physical arrangements are utilized in the casting process, in particular mold Y; Y1, Y2 from X; X1, X2 for assisting removal, or the like 7 7151523. In this context, the cooling / heating arrangement 3 in the template housing X1, X2 of the model X is preferably used as the thermal arrangement, the process medium being e.g. water, alcohol 5, oil-based liquid and / or the like.

In this way, the temperature change achieved by the cooling / heating arrangement 3 placed below the model surface X 'in the model body X1, X2 is adjustable to the surface of the model itself and thereafter to the pin-10 notch Z on it.

The purpose of the arrangement 3 described above is twofold: on the one hand, it prevents the model from heating up during coating and cracking of the coating due to elevated stresses. On the other hand, various thermal expansion coefficients can be used to assist in particular to remove the newly prepared coating from the surface of the model.

20 In this context, a change in temperature can be practically treated using a variety of media. Water cooling can always be used to cool the unit to near 0 ° C and to heat up to 100 ° C. Similarly, with alcohol-based liquid 25, cooling can be brought up to about -30 ° C, with a heating capability correspondingly in the same order as water. Various oily products can raise the model temperature to over 100 ° C. Similarly, air-assisted cooling / heating can still be used, but with lower temperature differences and lower thermal conductivity.

In this context, the so-called. as a physical arrangement-35, of course, the quality of the surface of the model (sandblasting / machining) is also utilized in the removal of the sprayed coating, i.e. the manufactured mold casing.

. f In addition, the coating can of course be removed from the surface of the i 8 111523 by various mechanical arrangements, such as presses or ejectors.

Further utilizing the process according to the invention, it is possible to spray onto the surface of the model X as a first step, in particular to release the freshly prepared coating Z from the model X or for similar purposes, a finely divided material Z3 consisting of zirconium silicate, yttrium 10 and / or - 65 μιη and a layer thickness of 0,1-0,5 mm respectively.

The so-called so-called. In addition to the chemical and physical release arrangement, it is also possible to utilize a purely chemical arrangement using, for example, waxy, ceramic and / or graphite-based medium ZO, which is applied, e.g., by dripping, spraying or brushing on the Model X surface prior to 20 actual coating steps. The purpose of this type of medium is thus to alleviate the thermal stresses between the model X and the coating Z and, on the other hand, to reduce the mechanical and chemical bonding between them. Of course, it should be noted that the medium used must not interfere with the use of the mold shell as such in the casting, i.e., it must not contain reactive or gaseous materials or similar undesirable materials for the casting process.

30

The invention thus also relates to the use of a water-stabilized plasma syringe (WSP) 1 for the layered production of mold shell Y by injection of one or more substantially overlapping ceramic-based material layers Z in a coating step (I) onto a molding surface of a preform After separating X and mold shell Y from 9111523 by feeding casting material into mold M formed from one or more mold shell Ys.

WSP plasma temperatures are typically up to 28000 K.

Correspondingly, the feed rate of the powder can be up to 50 kg / h. Due to its high power, it is thus possible to spray even grain sizes of 50-200 μ raα. The injection distance is typically up to about 350 mm, with a current of e.g. 380-400 A and a voltage of -103 to 300 V.

Obviously, the invention is not limited to the embodiments described or described above, but can be very substantially modified within the basic idea of the invention. Of course, it is obvious that it is possible to start the production of a mast model of the type described in the drawing, for example, from three-dimensional modeling, whereby a suitable geometry for the mold is sought and the most favorable dividing planes are determined. When using, for example, a metal model, the model must, with a few exceptions, usually be made of two or more parts. As an exception-25, a very simple cylindrical or square piece with no negative angles can be mentioned. In other words, the piece allows, for example, the use of 1-2 degree release angles in the model, whereby the injected shell 30 can be removed from the model. In all other cases, the model shall be subdivided into two or more divisions, as determined by the emissions and distribution levels, • depending on these distribution levels. In addition, suitable guide and gluing surfaces must of course be designed for the dividing planes so that the mold halves can be precisely and easily connected. Naturally, as in the case of full-mold molding techniques 10 111523, the disposable model can also be used instead of the permanent mast model. In this type of application, the model must, of course, be completely removed from the inside of the injection molded shell before casting. This type of 5 'arrangement may allow for the production of a casting slightly looser in shape than the mast model.

The structure of the mold shell, i.e., what kind of 10 layers it is composed of, naturally contributes significantly to the casting result. In principle, a mold shell can be constructed of only one material by spraying it in layers with sufficient layer thickness on the mold shell. However, for best casting / cost-effectiveness, it is preferable to spray a plurality of different overlapping layers, whereby the first thin spray layer is composed of fine material producing good surface quality, and the subsequent outer layers are coarser, but more resistant to heat and gas. ceramic materials.

Claims (10)

A method of casting, wherein during a preliminary manufacturing shift, a model (X) is first coated, which is covered with a substantially ceramic-based material for making a mold frame (Y), to perform the actual casting during a casting shift, when the model (X) and mold frame (Y) have been separated from each other by feeding the molding material into a mold (M) composed of one or more mold frames (Y), characterized in that during the preliminary production shift, a water stabilized plasma gun ( Water Stabilized Plasma), with which the mold frame (Y) is formed in layers during a spraying shift (I), by spraying one or more substantially different and layered material layers (Z) on the surface of the model (X). 20 The method of claim 1, wherein the model (X) to be used is a so-called positive master model which has been enlarged relative to the original piece in accordance with the amount of mold shrinkage and which has been distributed in parts (X1, X2). locations of dividing planes for forming connecting surfaces and for forming the mold (M) by interconnecting the parts of the mold frame (Y1, Y2) which have been coated on the parts (X1, X2) with each other by gluing or in a corresponding manner, characterized thereof, on the surface of the model (X) being sprayed using different spray layers (Z; Z1, Z2, X3) using one or more ceramic material, whose composition and / or particle size differ from each other. Method according to claim 1 or 2, characterized in that, in the mold frame (Y; Y1, Y2) to be manufactured, a fine-grained blank layer 11 is sprayed (Z2) in particular to improve the surface quality of the casting, which layer consists of zirconium silicate, screened. coarser natural material and / or the corresponding, the particle size being between 50-100 μτη and the layer thickness preferably between 0.5-1 mm. 4. A method according to claim 3, characterized in that on the mold frame (Y; Y1, Y2) to be manufactured, as on the fine-grained blank layer 10 (Z2), a more coarse-textured supporting layer (Z1) is sprayed, which consists of zirconium silicate, mullite. , molokite and / or the corresponding material, the particle size being between 80-250 µm and the layer thickness preferably between 1 - 3.5 mm. Process according to any of the above claims 1-4, characterized in that thermal, chemical, mechanical and / or physical devices are used in particular in the casting process, in particular to assist the release of the mold frame (Y; Y1, Y2) from the model (X ; X1, X2) or for a corresponding purpose. Method according to claim 5, characterized in that, as a thermal device *, a cooling / heating device (3) is used in the model body (X1, X2), which belongs to the model (X). Process according to claim 6, characterized in that, as a process medium in the cooling / heating device (3), water, alcohol, oil-based liquid and / or the like are used, a temperature change which has been achieved through it, below the model surface (X ') located in the model body 35 (X1, X2) of the cooling / heating device (3), is directed to the surface of the model (X) itself and further from there to the existing coating (Z) on it. 111523 Method according to any of the above claims 5-7, characterized in that, in particular to assist the release of the manufactured coating (Z) from the model (X) or for a corresponding purpose, the surface of the model (X) is sprayed below. a first layer a special fine grained stock (Z3) consisting of zirconium silicate, yttrium oxide and / or the corresponding, the particle size being between 20 - 65 µm and the layer thickness preferably between 0.1 - 0.5 mm. Method according to any of the above claims 5-8, characterized in that as a chemical device a wax-like, ceramic and / or graphite-based medium (ZO) is used, which is caused on the surface of the model (X) by dipping, spraying, pressing. or in a corresponding manner prior to the start of the actual coating shift (I). 2 0 Use of a Water Stabilized Plasma Gun (1) to fabricate a molding frame (Y) in layers by spraying one or more substantially separate and layered ceramic based layer layers (I) under one coating layer (I) Z) on a surface of a model 1 * (X) made during a preliminary production shift, to perform the actual casting during a casting shift, when the model (X) and the molding frame (Y) have been separated from each other by 3. feeding the molding material into a mold (M) which is composed of one or more mold frames (Y). • a k i