Metal founding – Process – Shaping a forming surface
Reexamination Certificate
1999-01-12
2001-09-04
Dunn, Tom (Department: 1722)
Metal founding
Process
Shaping a forming surface
C164S411000, C164S015000, C264S279100, C264S274000
Reexamination Certificate
active
06283194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing structural elements, preferably prototypes, in which a “lost” model, i.e., a positive model, of the structural element is produced in a first step, the model is subsequently cast with a molding compound for producing a mold, i.e., a negative model, and the mold then produces the structural element, preferably a prototype, by casting.
2. The Prior Art
Processes of this type, which are preferably employed for producing costly prototypes containing, for example complex cavities, are known from the state of the art. The plaster casting process, in which the molding compound is a gypsum compound, is such a process. In some applications, the so-called “fine casting process” is employed for producing such prototypes instead of using the plaster casting method. The drawback common to these two processes is that they are either not suitable at all for producing prototypes with complex shapes and/or complex cavities, or that they are very expensive.
A process for producing structural elements such as prototypes has become known from German Patent No. DE 195 45 167 A1. This process uses a polystyrene model, which is coated with wax by immersing it in liquid wax. A ceramic sludge is then applied to the surface of the wax. The model is then calcinated and the cavity formed by gassing out the polystyrene is filled by pouring in the molding compound using the fine casting process. In order to permit the manufacture of more complex structural elements by this method, several pieces of the structural elements are first produced in this process, which then have to be assembled into a complete structural element following their immersion in wax. This process is relatively complicated and thus costly, because several components of the structural element have to produced separately.
SUMMARY OF THE INVENTION
It is therefore an object of the invention is to provide a process for producing structural elements, in particular prototypes of the type specified above, that permits the structural element to be manufactured with less technical expenditure and at a consistent rate, as well as less expensively.
These and other objects of the invention are accomplished by process for producing structural elements comprising producing a positive model of the structural element in a first step, casting the positive model with a molding compound to produce a negative mold, and manufacturing the structural element by casting the mold.
The model is cast with the molding compound in a number of successive steps, and the arrangement or position of the model is changed relative to a reference plane in each of the individual steps of casting or filling.
The main problem afflicting the prior methods is that reproduction of complex cavities with molding compound is not possible, because air cannot completely escape from these cavities when they are filled with the molding compound. The present invention overcomes this problem in the following manner: In a first part step of the process, the model is first cast with the molding compound and the cavities are filled to the extent possible with the molding compound while the model is in a first arrangement or position relative to the reference plane. In this first step, lateral openings of the model, if any, are closed so that the molding compound cannot exit through these openings. The molding compound is subsequently poured in through openings from the top. The position of the model relative to the reference plane is then changed, for example, turned by 90° about one of its axes. Molding compound is then again filled in through a top opening of the model, and lateral openings of the model, if any, are closed. Since the position of the model was changed, air now can escape from parts of the cavity from which no escape was possible in the previous arrangement of the model. Thereafter, in another step of the process, the position of the model relative to the reference plane is changed again, if need be, and any lateral openings are closed. Molding compound is then filled in again through an opening now disposed at the top.
If, for example, the model is turned by 90° after each of these steps, and all three spatial axes are taken into account, all cavities of the model can be filled with molding compound. A maximum of six different arrangements of the model and, correspondingly, six steps, depending on the structure of the model and the complexity of the cavities are needed to file the model. The model can therefore be completely reproduced.
Even though the process for casting the model with the molding compounds is divided into individual steps, the process as defined by the invention offers the advantage that the model does not have to be divided, and the process can always be carried out with a single-piece model. The process as defined by the invention, furthermore, can be carried out smoothly at a relatively consistent rate.
When certain molding compounds are employed with the process according to the invention, i.e., materials such as plaster which set and cure relatively quickly, it may be advantageous if connecting elements with a suitable geometry are employed. These elements are jointly cast in the molding compound in the respective step of the process. After the molding compound poured in one step has set and cured at the start of the next-following step, bonding of the fresh molding compound to the molding compound already set is enhanced by the connecting elements. Connecting elements with undercut surfaces are preferably employed, so that a positive joint of the individual surfaces of the molding compound is obtained after curing is completed. For example, simple available metal elements such as screws or the like can be used as connecting elements, and do not add additional significant cost to the process.
If the model contains defined cavities, for example relatively long channels which are filled with the molding compound, a reinforcement is preferably incorporated in the regions of the molding compound filling the channels in order to prevent cured parts of the molding compound, e.g., longer arms of filling channels, from breaking off or becoming damaged after the model has been removed. Suitable elements such as wires or other metal parts consisting of flat steel, round steel or the like can be employed for such reinforcement.
It is most preferable that in each step of casting of the model with the molding compound, the model is set up in as favorable a spatial position as possible, so that the fewest individual steps of the casting process is needed depending on the complexity of the cavities present.
Additional advantages of the invention are shown by the following detailed description.
REFERENCES:
patent: 2474186 (1949-06-01), Marks
patent: 2688781 (1954-09-01), Fahlberg et al.
patent: 4812278 (1989-03-01), Natori et al.
patent: 4990292 (1991-02-01), Hattori et al.
patent: 5469908 (1995-11-01), Chmel et al.
patent: 3127313 (1987-04-01), None
patent: 19545167 (1997-06-01), None
patent: 406277794 (1999-06-01), None
Detering Jörg Stefan
Grunewald Christian
Collard & Roe P.C.
Dunn Tom
Grunewald GmbH & Co. KG
Tran Len
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