Patent Publication Number: US-2010122790-A1

Title: Casting tool and core-making machine

Description:
TECHNICAL FIELD AND PRIOR ART 
     The invention relates to a casting tool for the production of castings, in particular cores for sand castings, pressure die castings, and gravity die castings. A generic casting tool comprises a supporting device comprising first and second supporting units which can move toward and away from each other in a joining direction. Furthermore, a generic casting tool of such kind comprises at least two mold elements, of which a first mold element is mounted on the first supporting unit and of which a second mold element is mounted on the second supporting unit. The first and second mold elements each comprise mold recesses oriented toward each other, the mold recesses of the first and second mold elements jointly defining the shape of at least one workpiece to be produced such as a casting core, when the first and second mold elements bear against each other and the mold is thus closed. Furthermore, the invention relates to a core-making machine comprising a generic casting tool. 
     Generic casting tools are known in the prior art. As molding core tools, they are used, for example, for the production of cores such as sand cores or ceramic cores to be used in subsequent casting processes, in order, as lost forms, to prevent, for example, metallic casting material from entering cavities in the workpiece to be cast. In the case of sand cores, production takes place by filling the joint volume formed by the mold recesses of the first and second mold elements described above with a pressurized sand mixture, which is then gas treated such that a binding agent binds the individual grains of sand to each other to form a solid sand core. This solidified sand core is then removed from the core-making tool and placed in a casting tool, where it prevents the cavity defined thereby from being filled with casting material such as a metal. After creation of the workpiece, the cavity of which has been kept free by the sand core, the sand is removed from the workpiece. Cores of this kind are used as lost forms for once-only casting processes. 
     For the production of sand cores described above, it is known from the prior art to use a casting tool in the form of a core-making tool which comprises two shell-shaped molding boxes as supporting units, which are provided with approximately cuboid pockets, into which the respective mold-elements are inserted. These molding boxes known from the prior art also perform the function of sealing the mold elements from the environment in addition to supporting and guiding the same. This seal is of major importance because in an insufficiently sealed system, not all parts of the sand core are sufficiently contacted by gas during gas treatment so that the sand grains do not adequately bind to each other to form a unitary and solid sand core. The necessity of producing this seal between the two halves of the molding box is substantiated by the fact that the mold elements cannot be positioned accurately enough in relation to each other so that they cannot bear against each other in a completely gastight manner along the parting line of the mold. 
     The restricted capability of the first and second mold elements to be accurately positioned is largely due to the imprecise tolerance compliance of the molding boxes. The molding boxes are usually produced as cast parts that are then machined. This machining takes place, with respect to the pockets, by means of which the first and second mold elements are guided and in which the first and second mold elements are mounted, with the aid of a milling process that cannot ensure sufficient dimensional stability in order to achieve the tightness of fit between the first and second mold elements in the closed state of the mold. Apart from the above-described casting production of the molding boxes, production of the latter in the form of welded structures is also known from the prior art, which likewise gives rise to a problem involving production accuracy, since the individual components of the welded molding box become warped to a large extent by thermal stresses occurring during welding, thus necessitating an expensive post-machining step, which however does not result in a degree of precision that would produce high-quality sealing of the mold cavity across the mold elements. 
     In addition to their inadequate dimensional stability, cast or welded molding boxes also suffer from the drawback of being extremely heavy. The weight of these molding boxes is frequently so great that they cannot be stored in high racks but must be stored in a usually very restricted floor space. 
     Another disadvantage associated with previous designs is that it is very difficult to align the mold elements in relation to each other. Since the mold elements come into contact with each other only when the molding boxes of the bottom and top mold elements also bear against each other, it is scarcely possible to align the mold elements in relation to each other. The quality of the cores produced is thus not always ideal. 
     OBJECT OF THE INVENTION AND ITS ACHIEVEMENT  
     It is an object of the invention to develop a generic casting tool in such a way that the disadvantages known from the prior art are eliminated or at least diminished. 
     According to the invention, this object is achieved in that one of the supporting units has a first peripheral frame surrounding the mold element mounted on this supporting unit, the frame being composed, in the form of a multi-segment frame, of at least two frame segments joined to each other with the aid of positively acting connecting means. 
     In the case of a casting tool of the invention, at least one part of the usually welded or cast prior supporting unit is composed of segments that are connected to each other neither by co-casting nor by weld seams. Instead, the frame segments are connected to each other with the aid of positively-acting connecting means, particularly by screws, such that, depending on the precision with which the segments are manufactured, very precise dimensional stability of the overall frame can be achieved during production thereof without any warping of the original components due to thermal stress. The expression “frame segments” is to be understood, for the purposes of the invention, to mean those parts of the frame that constitute at least subregions of that inner surface of the frame that faces the respective mold element. In addition to the fact that the production of the frame using positive connecting means ensures a high degree of precision of the shape of the frame, another major advantage of the structure described is that standardized parts can be used as segments of the frame in the manner of a modular system, such parts being selected and assembled according to the required dimensions of the casting tool. The segments are connected preferably peripherally and the interconnected segments thus form a closed segment ring having the shape of the first frame. Said modular design principle makes it possible to considerably reduce the currently still very long production time required for a molding box of individually specified size, since the individual segments of the multi-segment frame can be reserved in a storehouse in a fully machined or almost fully machined form and can be assembled according to the specific size required. Another advantage of building the frame using segments that are assembled with the aid of positively acting connecting means is that this makes it possible to use materials that are not weldable or castable or only poorly so. Thus it is possible, in particular, to use those materials that combine particularly high tensile strength with low specific gravity. 
     A casting tool of the invention comprises at least two mold elements, which together define the shape of a workpiece, particularly a core such as a sand core. However, several mold elements may be provided on each of the two supporting units. For the purpose of the present invention, in such a case, the mold elements mounted on the first supporting unit are referred to as first mold elements and the mold elements mounted on the second supporting unit are referred to as second mold elements. The first and second mold elements together form a single mold, which, in the closed state, comprises a cavity formed by the mold recesses in each mold element to form the negative of the workpiece to be produced, which is in particular a core. 
     The frame can be adapted in such a way to the size of the mold elements so as to form a guide therefor. This is achieved by providing a close clearance between the mold elements and the frame. It is preferred, however, that the frame has a free internal area in the manner explained below, which free internal area is significantly larger than the base area of the mold elements so that the frame does not perform a guiding function. 
     It is also preferred to provide a multi-segment frame described above on only one of the supporting units, which multi-segment frame surrounds both mold elements in the state in which the latter bear against each other. However, it is also conceivable to provide two such frames, each of the frames surrounding those mold elements that are fixed to that supporting unit to which the respective frame is assigned. 
     Preferably, the casting tool is a core-making tool for the production of casting cores, which core-making tool has the features typical thereof, such as the presence of a leveler for leveling the excess sand in the region of sand-shooting bores after the sand has been shot in. 
     In a design comprising only one frame that surrounds the first and second mold elements, it is preferable to mount the frame on the first supporting unit. For the purposes of the following description, the first supporting unit is that supporting unit which is raised in relation to the stationary second supporting unit during the course of demolding the workpiece produced, in particular the cores produced. However, the movements carried out are relevant only in terms of relative displacements of the components so that provision may be made for lowering the second supporting unit while the first supporting unit remains stationary. 
     The preferred embodiment, in which the first frame forms part of the first supporting unit, has the advantage that in the event of the first supporting unit being provided above the second supporting unit, the first frame will be automatically raised together with the first supporting unit relatively to the second supporting unit during the demolding operation such that the part of the mold staying down with the second supporting unit and the second mold element attached thereto facilitates demolding of the workpiece produced, in particular the core produced, for example with the aid of a so-called rake or a handling system, without the first frame being obstructive during said operation. 
     In a further development of the invention, the first supporting unit has a first supporting plate, to which the mold element mounted on the first supporting unit is attached and to which the first frame is also attached. 
     In connection with the first supporting plate, the term “plate” is regarded as a component offering at least one completely plane surface for the attachment of the first frame and the first mold element. By definition, no part of this supporting plate protrudes beyond any area that is used for attachment of the first mold elements. The use of such a supporting plate that is completely plane on at least one side is advantageous, since such a plate can be produced at comparatively low cost within a small tolerance range, for example by surface grinding. The result is that the first mold element attached to the plate can be oriented very accurately. That plane side of the supporting plate oriented in the direction of the first mold element attached thereto preferably has a planarity tolerance of less than 0.2 mm, more preferably less than 0.1 mm and most preferably less than 0.05 mm. 
     Likewise, the first frame is preferably attached to this first supporting plate by means of positively acting releasable connecting means such as screws. Such a connection produced with the aid of positive connecting means makes it possible to produce the first supporting unit without recourse to any damaging thermal effects. The detachability of these connecting means further allows for rapid coupling of the first frame to the first supporting plate and its detachment therefrom. This detachability is advantageous, since the casting tool of the invention is, in principle, suitable, by virtue of its design, to be operated entirely without the frame so that this frame can occasionally be omitted. In particular, it is advantageous to remove the frame only during installation of the casting tool so that it is possible to bring the mold elements of the two supporting units into perfect register when the frame is removed, and subsequently to reconnect the frame to the first supporting plate as a supplementary protective measure. 
     It is particularly advantageous when the second supporting unit also has a second supporting plate, to which the second mold element mounted on the second supporting unit is attached. The same advantages hold for the second supporting plate as described for the first supporting plate: By virtue of its design, the plate allows for the production of a high degree of planarity, which is achievable, for example, by surface grinding, so that in an embodiment comprising two supporting plates of high planarity, the mold elements abut each other almost perfectly in the mold parting line when the mold is closed and thus themselves seal the jointly formed mold, effectively without the frame being absolutely necessary for this purpose. 
     With regard to the two supporting plates, it is required that they can be attached to their respective connecting components within a small tolerance range so that the supporting plates are preferably such that their parallelism tolerance in relation to the two opposing sides of the plate is likewise less than 0.2 mm, preferably less than 0.1 mm and more preferably less than 0.05 mm. 
     In a further development of the invention, the second supporting unit also has a second peripheral frame which is attached to that side of the second supporting plate that is remote from the second mold element or second mold elements. While the first frame serves the purpose of protecting and possibly guiding the mold elements and the purpose of providing a supplementary seal in relation to the environment, the second frame is provided as a heavy-duty force-transmitting component for absorbing the forces by means of which the mold elements are pressed together during the injection of the casting material, i.e. sand for example. This second frame is preferably likewise in the form of a multi-segment frame. In addition to its function as a force-transmitting component between a machine table and the second mold element, the second frame at the same time forms a protective cover for a lifting device of the casting tool serving the purpose of ejecting the finished workpiece or the finished core from the second mold element. The second frame can be directly mounted on a machine table or attached to the machine table via an adapter plate on that side thereof which is remote from the second supporting plate. 
     For both frames, it is required that they have preferably four side plates oriented at right angles to each other, as main segments, the side plates being connected to each other directly or indirectly via intermediate segments, particularly via corner segments. The design of the frame comprising at least four side plates is a particularly simple embodiment. The side plates can be directly connected to each other, for example, by providing all or some of the side plates with bores in their end faces for the accommodation of connecting screws and/or by providing through-bores for those connecting screws at those ends of the adjacent side plates which are near the corners. Alternatively, the side plates comprise only bores in their end faces and are connected to each other by, in all, four corner segments. The use of simple side plates reduces production costs and shortens production times considerably, since standardized plates can be used that merely need to be adapted for each specific application in terms of their height in the joining direction and their length transversely to the joining direction. The use of corner segments is particularly advantageous, since they require that bores need be provided only in the end faces of the side plates. One result of this configuration is that all four side plates are identically designed with bores in their end faces and without through-bores. Furthermore, the corner segments are well-suited to provide supplementary functions such as points of engagement for lifting means facilitating handling of the first frame, in particular. 
     All four side plates can be designed identically in terms of their cross-section but may differ from each other merely in terms of their length. However, it is preferred to provide at least two opposing side plates with recesses allowing for engagement of a grasping device for handling the top supporting unit. These recesses are preferably provided on the outer top edge of the respective two side plates in the form of a milled groove, the recess being closed in the upward direction preferably only when the respective frame is attached to the first or second supporting plate, by which means it is able to fulfill its purpose. 
     The corner segments are preferably formed as profile sections, particularly extrusion profile sections extending in the joining direction. Preferably, these extrusion profiles are directly produced so as to have the required cross-section of the corner segments so that only a small amount of subsequent machining is necessary. Alternatively, it is possible to use standardized profiles such as square profiles that obtain the shape of the corner segment by means of subsequent machining. In both cases, the corner segments must be prepared for the means providing positive connection to the side plates, for example, bores for connecting screws, which bores are oriented transversely to the longitudinal direction of the profile. 
     Preferably, lifting rings are disposed on at least two opposing corner segments, preferably on all four corner segments, the lifting rings being formed and attached in such a way that they do not protrude beyond the alignment of the side plates adjacent to the respective corner segment. The lifting rings are thus provided in such a way that, in an idle state, they are located in an open space delimited on one side by the corner segment and on the other side by two imaginary planes, each of which corresponds to the plane of the outside surface of the respective adjacent side plate. This design makes it possible to store the entire casting tool or at least the first or the second frame thereof, in spite of the presence of the lifting rings, on a floor space that need not be larger than the area defined by the distances between the outside surfaces of the opposing side plates. The purpose of the lifting rings is to facilitate handling of the supporting units or the frames, which can thus be transported easily with the aid of the lifting rings. 
     It is considered to be particularly advantageous if a casting tool of the invention comprising a first and a second frame uses side plates on each of the first and the second frames, which side plates match in terms of their height in the joining direction, their length transversely to the joining direction, their thickness, the arrangement of their connection bores for attachment to the corner segments and/or a supporting plate, and/or the material of which they are made. It is still advantageous if only individual characteristics of the side plates match. It is not strictly necessary for all of the side plates of the respective frame to be designed identically. An advantage is achieved when only one or two side plates of the two frames are identical in terms of the individual features cited above. Matching features as cited above serve to comply with the aforementioned modular principle. A plurality of machining operations on the side plates can be carried out on account of the similarity of design of the side plates of the two frames within the scope of a standard machining process, such standard machining being irrespective of whether the side plates are those of the first or of the second frame. This makes it possible to have at one&#39;s disposal all necessary components in a comparatively small storage space in order to produce, within a short period of time, a casting tool, which is adapted to suit individual specifications. In the case of the side plates described above, it is possible that some machining operations, for example, the production of a groove for a sealant on the first frame or the production of connection bores for attachment to a machine table or to an adapter on the second frame will have to be carried out by customization; but these machining operations can be carried out at short notice. 
     In a similar manner, it is advantageous if the corner segments of the first and second frame match in terms of the height of the corner segments in the joining direction, the cross-section of the corner segments, the connection bores for attachment to the side plates and/or the lifting rings and/or the material of which the corner segments are made. Here again, it is advantageous when individual features match. The purpose and the advantages are identical to those discussed with reference to the side plates of similar design. Again, in the case of the corner segments of the first and second frames, only slight adjustments are required over and above standard machining thereof, such as the insertion of a groove for a sealant on the corner segments for the first frame. 
     The first and second supporting plates preferably also match in terms of one or more characteristics, for example, in terms of the dimensions of the supporting plates transversely to the joining direction, the thickness of the supporting plates, the connection bores for attachment to the side plates and/or the mold elements and/or the material of which the supporting plates are made. Again, with respect to the supporting plates, this makes it possible to use a comprehensive standard machining process without the latter being dependent on the purpose of the supporting plate as a first or second supporting plate. Possible adjustments that may be necessary in addition to the standard machining operations include, for example, the insertion of shooting bores in the first supporting plate or bores for ejector rods in the second supporting plate. 
     As already mentioned, the first frame can be provided for guiding the at least one first mold element. In such a case, the frame is dimensioned in such a way that there exists a narrow clearance between it and the first mold element or the first mold elements. However, it is advantageous if the first mold elements are peripherally spaced from the first frame by at least 2 mm in relation to a plane of which the normal vector coincides with the joining direction. With such a design, the frame cannot perform any guiding function as specified. The orientation of the at least one first mold element is therefore achieved solely by attachment thereof to the supporting plate. 
     However, this is adequate in the case of a sufficiently accurately machined first supporting plate so that it is possible to dispense with the guiding function of the frame. The frame can therefore be designed to be larger in terms of its free cross-section so that a collision between the frame and the mold elements during assembly of the casting tool is avoided. Preferably, the peripheral spacing is more than 2 mm, more preferably more than 5 mm and most preferably more than 20 mm. 
     The first frame preferably extends in the joining direction toward the second supporting unit over a distance that is smaller than the total thickness of the first and second mold elements. In a closed state of the mold, in which the mold elements bear against each other, the first frame thus abuts only against the supporting plate to which it is attached while it is at least slightly spaced from the second supporting plate. Therefore, it does not itself transfer any forces. The forces applied to the casting tool are therefore invariably or predominantly transferred via the mold elements themselves so that the same are pressed very tightly against each other. The height of the first frame is preferably dimensioned such that it is less than the total thickness of the two mold elements by at least 0.2 mm and preferably by at least 0.3 mm. As mentioned above, sufficiently precise positioning and design of the mold elements does not require an additional seal. 
     Preferably, a peripheral seal is provided on that side of the first frame that is oriented in the direction of the opposing supporting unit, which seal rests peripherally against the opposing supporting unit when the mold is closed. This provides additional protection that firstly prevents dirt from penetrating into the mold core tool and is secondly an additional gas seal for the process step involving gas treatment during the production of the sand cores. 
     As regards the second frame, it is advantageous if the same at least partially surrounds a lifting device which comprises at least one ejector rod which extends in the joining direction and can be pushed into the mold recess of the second mold element through an ejector bore in the second supporting plate and/or in the second mold element. This lifting device makes it possible to press the resultant workpiece or core out of the recess in the second mold element, it being possible to adapt the arrangement of the preferably more than one ejector rods individually to the shape of the workpiece or core. The lifting device is preferably operatively coupled to the first supporting unit in such a way that when the supporting units are moved away from each other during the course of demolding, the lifting device is actuated and the ejector rods are raised to cause ejection of the workpiece or core produced. 
     In principle, the design of a casting tool of the invention can be used for casting tools, particularly core-making tools, of any size. It is more preferably used for casting tools in which the area covered by the first and/or the second frame with the normal vector of which coinciding with the joining direction is at least 600 mm×600 mm, preferably at least 1,000 mm×1,000 mm. The design of the invention is particularly advantageous in large molds of this type since with such molds, the production methods known from the prior art, particularly production by casting and welding of the molding boxes, is particularly detrimental, since the subsequent machining required in each case and the negative effects of the thermal influences result in particularly severe positional inaccuracy of the mold elements during operation. 
     In a further development of the invention, the casting tool is characterized in that the first and/or the second frame consists, at least in certain parts, of a material having a tensile strength of at least 400 N/mm 2 , preferably at least 450 N/mm 2 , the side plates and/or corner segments being preferably made of this material which is more preferably an aluminum alloy. The high tensile strength has been found to be advantageous in order to ensure particularly accurate positioning of the mold elements during the production process. Preferably, all segments of the frame and preferably the supporting plates are also made of a material of this type. High-strength aluminum alloys, for example ENAW 7075, have proved to be particularly suitable. The proposed design of the casting tool comprising a multi-segment frame is useful with respect to aluminum alloys that can be cast or welded either not at all or only with difficulty. 
     Furthermore, the invention relates, in particular as a development of the design described above, to a generic casting tool in which the first supporting unit and/or the second supporting unit comprises a supporting plate, to which the mold element mounted thereon can be attached and which is completely plane at least on its side facing said mold element. This side is preferably surface ground. As explained above, the first frame can be dispensed with even though this is not recommendable. By using very plane supporting plates, that is to say, supporting plates of which the planarity tolerance is less than 0.2 mm, preferably less than 0.1 mm, it is possible that the seal between the mold elements is itself sufficient to prevent a gas leak during the gas treatment phase. High production accuracy can be achieved, in particular, by surface-grinding the respective supporting plate and the contact surfaces of the mold elements, there being no requirement for any sort of thermal joining process so that the high degree of precision of the surface ground surface is not adversely affected. 
     Although the first frame can be dispensed with, it is advantageous to provide a first frame of such type which preferably corresponds to the first frame described above. Alternatively, it is possible to provide a one-piece frame. A one-piece frame of such type can be produced by casting or welding. It preferably comprises four bonded side sections that surround an open area in which mold elements to be fixed to the supporting plate, for example, can be disposed. 
     The frame is preferably attached to the supporting plate with the aid of detachable, positively acting connecting means so that the frame can be removed for purposes of orientation in order to allow better accessibility to the mold elements. The positively acting connecting means further avoid warping of the surface ground supporting plate as would result from a thermal joining process. 
     The invention further relates to a core-making machine comprising a casting tool in the form of a core-making tool as described above. A core-making machine of such type is equipped with supply means with the aid of which sand can be shot into the mold elements under high pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional aspects and advantages of the invention will become apparent from the claims and the following description of a preferred exemplary embodiment of the invention described below with reference to the Figs. 
         FIG. 1  is an exploded view of a complete casting tool of the invention in the form of a core-making tool. 
         FIGS. 2   a  to  2   f  are sectional views of the core-making tool shown in  FIG. 1 . 
         FIG. 3  is a partial sectional view of a frame of the core-making tool as shown in the preceding Figs. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1  is an exploded view of a casting tool of the invention. This casting tool is a core-making tool comprising the following main components that are explained below with reference to  FIG. 1  from top to bottom thereof. 
     A first supporting plate  10  forms the top closure of the core-making tool. A first frame  20  can be screwed to this first supporting plate with the aid of screws (not shown) so that the first supporting plate  10  and the first frame  20  can be joined together to form a first, top supporting unit  10 ,  20  for first mold elements  30 . In all, four first mold elements  30  are mounted in the bottom-open molding box formed by the first supporting plate  10  and the first frame  20 . These first mold elements  30  each comprise bottom-open mold recesses  33  (not shown in  FIG. 1 ), and the four mold recesses  33  of the first mold elements  30  form, together with corresponding top-open mold recesses  43  of four corresponding second mold elements  40 , closed cavities representing a negative shape of the core to be produced using the core-making tool. The four second mold elements  40  are adapted for attachment to a second, bottom supporting plate  50 , to the underside of which a second frame  60  is attached. An adapter plate  70 , which is adapted for positioning the core-making tool on a machine table, is connected to the underside of the second frame  60 . A lifting plate  80 , which has a plurality of vertically extending ejector rods  82 , is disposed within the second frame  60 . Corresponding to the positions of the ejector rods  82 , bores  52 ,  42  are provided in the bottom supporting plate  50  and in the second mold elements  40 , through which bores the ejector rods  82  can be moved into the cavity  33 ,  43  formed by the first mold elements  30  and the second mold elements  40 . 
     Detailed Description of the Aforementioned Components 
     The top supporting plate  10  has a thickness of 30 mm and a width and length of 1,400 mm each. The supporting plate is surface ground on both its top surface  10   a  and its underside  10   b,  the maximum planar deviation being 0.05 mm and the parallelism of the top surface  10   a  and the underside  10   b  likewise having a maximum value of 0.05 mm. The top supporting plate  10  is made of steel 1.2312/2080 which, though not castable, is used in this particular case as a prefabricated plate that has a predetermined thickness and is machined solely by milling with respect to its external dimensions. A plurality of connection bores  11  is provided along the outer edge around the top supporting plate  10 , which connection bores  11  serve to detachably connect the supporting plate  10  to the frame  20 . Furthermore, connection bores  14  are provided on the supporting plate  10  for attachment of the first mold elements  30 . Furthermore, a plurality of bores  12  extending in the joining direction  2  are provided which penetrate the top supporting plate  10  and which are used for shooting in the casting material, in this case sand. Furthermore, guide bores  15  that serve to guide a shooting plate (not illustrated) and a leveling plate (not illustrated) are provided. 
     The bottom supporting plate  50  is designed very similarly to the top supporting plate  10 . Its thickness of 30 mm and its width and length of 1,400 mm each are consistent with the dimensions of the top supporting plate  10 . Likewise consistent with the top supporting plate, connection bores  51 ,  54  are provided around the second supporting plate  50  and in its central area. In the case of the second supporting plate, the connection bores  51 ,  54  serve for attachment to the second frame  60  and the second mold elements  40  respectively. The material of the supporting plates  10 ,  50  is likewise steel 1.2312/2080. Differing from the first supporting plate  10 , the aforementioned bores  52  are provided in the bottom supporting plate  50  for ejector rods  82 . The supporting plates  10 ,  50  therefore match each other in terms of all features except for the shooting bores  12  and the bores  52  for the ejector rods  82 . 
     This makes it possible to reserve the supporting plates  10 ,  50  in storage in a fully machined form, but without the shooting bores  12  and the bores  52 , this basic machining being irrespective of the final purpose of the supporting plate. 
     The top frame  20  consists, in all, of eight segments, which are shown separately in  FIG. 1  for the sake of clarity. In the frame  20 , opposing side plates  22  and opposing side plates  24  are used as the main segments, these being connected to each other by way of corner segments  26 . In terms of their thickness, the side plates  22  are unmachined plates, and otherwise they are merely machined, for example, by a milling process to give the desired height of 210 mm and the desired length of 1,100 mm. The only difference between the other side plates  24  and the side plates  22  is that a groove  24   a  has been provided in the top region on the outside surface of the side plates  24 , by milling. Following attachment of the frame  20  to the top supporting plate  10 , this groove  24   a  forms a gripping channel which simplifies the storage or handling of the supporting unit comprising the supporting plate  10  and the frame  20 . Furthermore, the side plates  22 ,  24  each comprise connection bores  21  on their top sides, the arrangement of these connection bores corresponding to the connection bores  11  in the top supporting plate  10  for connecting the supporting plate  10  to the frame  20 . The side plates  22 ,  24  are connected by means of all of the four corner segments  26 , which are each produced as a cut-off from an extruded profile and have an outside depression  26   a.  For connection to the corner segments  26 , the side plates  22 ,  24  comprise connection boreholes on their end faces, corresponding to which there are provided, in the depression  26   a  of the corner segments  26 , connection bores oriented in the direction of the side plates  22 ,  24 . These bores in the side plates  22 ,  24  and in the corner segments  26  allow the segments  22 ,  24 ,  26  to be connected to each other easily and quickly to form the frame  20 . The design implementing side plates  22 ,  24  that significantly influence the external dimensions of the frame  20  allows the size of the frame  20  to be easily adapted to meet specific requirements, particularly with regard to size. Preferably, the product range of a manufacturer of core-making tools of the invention will include frames that can be supplied in various sizes to accommodate fixed grid dimensions, the increments in both main directions of extension preferably being 100 mm, so that the manufacturer needs to store only a few sizes of side plates in order to be able to rapidly supply any size within the confines of the grid dimensions. Also, the segments  22 ,  24 ,  26  are invariably produced from the poorly castable aluminum alloy ENAW 7075 and are therefore relatively light. 
     The bottom frame  60  substantially corresponds to the top frame  20 . It is likewise composed of corner segments  66  and side plates  62 ,  64 , all features mentioned with regard to the frame  20  being equally applicable. One difference is that the side plates  62 ,  64  of the bottom frame  60  additionally comprise connection bores  63  that are formed as bottom-open threaded blind bores and are used for fixing the bottom frame  60  to the adapter  70 , which can in turn be fixed to the machine table. These connection bores  63 , of which only one is shown in  FIG. 1  by way of example, are not required in the case of the top frame  20 . Instead, the top frame  20  has a peripheral groove  23  that extends along the side plates  22 ,  24  and along the corner segments  26  and serves to accommodate a sealant such as a sealing cord, the purpose of which will be explained below. Another difference between the frames  20  and  60  is that lifting rings  68  are screwed into the depressions  66   a  of the corner segments  66 . These lifting rings  68  and a mounting ring  69  provided on the same are arranged in such a way, by virtue of their countersunk attachment to the corner segments  66  in the state illustrated, that they do not collide with the alignment of the outside surfaces of the side plates  64 ,  62  and thus do not protrude beyond the base area defined by the outside dimensions of the frame. 
     Thus, as regards the frames  20  and  60 , the vast majority of the features of both frames are realized in the same way so that it is again possible to store the side plates and the corner segments in a basic machined form, this basic machining being irrespective of any specific application. Instead, the intended use of the side plates and the corner segments can be stipulated from case to case for provision of appropriate connection bores  63  and the bores for the lifting rings  68  and the peripheral groove  23 . 
     The aforementioned first mold elements  30  are adapted for attachment to the top supporting plate  10 , which first mold elements  30  have connection bores  34  by means of which they can be screwed to the top supporting plate  10  through the connection bores  14  in the latter. Furthermore, the first mold elements  30  have shooting bores  32  which are arranged so as to correspond to the shooting bores  12  in the top supporting plate  10 . The top connecting surfaces  30   a  of the first mold elements  30  are machined, for example surface ground, in the same way as the underside  10   b  of the supporting plate  10  and with similar accuracy so that the first mold elements  30  are extremely accurately positioned with regard to the joining direction  2  relative to the supporting plate when screwed thereto. 
     The second mold elements  40  are designed similarly to the first mold elements  30 . That side  40   b  of the second mold elements  40  that faces the supporting plate  50  has connection bores  44  for attachment to the bottom supporting plate  50  by way of the connection bores  54  provided therein in similar configuration. However, in the case of the second elements  40 , the aforementioned bores  42  for the ejector rods  82  are provided instead of shooting bores  32 . As in the case of the top supporting plate  10  and the first mold elements  30 , the undersides  40   b  of the second mold elements  40  are machined or surface ground to the same high degree of precision as in the case of the top surface  50   a  of the bottom supporting plate  50  for the purpose of achieving exact positioning in the joining direction  2 . 
     The last major component is the lifting plate  80  with the ejector rods  82 . This lifting plate  80  is not fixed to any of the other components described. It can be raised separately relatively to the bottom supporting unit  50 ,  60  with the aid of a mechanism (not illustrated) so that the core located in the mold recess  43  can be raised out after the top supporting unit  10 ,  20  has been separated from the bottom supporting unit  50 ,  60  for the purpose of demolding by a joint upward movement of the lifting plate  80  and the ejector rods  82 . 
       FIGS. 2   a  to  2   f  show the assembled core-making tool of  FIG. 1  illustrating a simplified procedure for the production of sand cores. 
     The state existing when preparing the core-making tool is apparent from  FIG. 2   a . For this purpose, the top frame  20  is removed beforehand so that the supporting unit comprises only the supporting plate  10 , which is connected in a manner (not illustrated in the figures) to a lowerable lifting device (not shown) which is provided with connections for feeding in sand as core casting material. The top supporting plate  10  is lowered together with the first mold elements  30  until the surface ground undersides  30   b  of the first mold elements  30  lie in the correct position on the likewise surface ground top surfaces  40   a  of the second mold elements  40 . If there is an offset normal to the joining direction  2 , this offset can be compensated in the illustrated state, for example by shifting the top supporting plate  10  relatively to the lowerable hood (not shown) or by a displacement of the first mold elements  30  and second mold elements  40  relative to the supporting plates  10  and  50  respectively. Once the proper alignment is ensured, the top supporting plate  10  is raised together with the first mold elements  30  to an extent such that the frame  20  can be subsequently attached to the top supporting plate  10 . 
     The state achieved after attaching the frame is shown in  FIG. 2   b . This state represents the initial state for the subsequent procedure for the production of sand cores. The orientation described can be carried out as part of the production process by the manufacturer or it can alternatively be carried out directly on a core-making machine of which the height-adjustable hood can serve as a lifting device in this case. 
     The actual procedure for the production of sand cores begins from the state shown in  FIG. 2   b . To this end, the top supporting unit consisting of the top supporting plate  10  and the top frame  20  is lowered until the undersides  30   b  of the first mold elements  30  again come into contact with the top surfaces  40   a  of the second mold elements  40 . In this state shown in  FIG. 2   c , the bottom surfaces of the frame  20  do not contact the bottom supporting plate  50 , but instead, they are at a distance therefrom of about 0.5 mm. The peripheral sealing cord  27  inserted in the groove  23  produces a gastight seal of the open space formed by the top supporting plate  10 , the bottom supporting plate  50  and the frame  20 . In this state, a holding force of 600 kN is applied to the bottom frame  60 , which holding force is transmitted from the top supporting unit  10 ,  20  to the bottom supporting unit  50 ,  60  almost entirely by way of the first mold elements  30  and the second mold elements  40  so that the first and second mold elements  30 ,  40  are firmly pressed against each other. The force component by passing the first and second mold elements  30 ,  40  through the frame  20  directly to the bottom supporting plate  50  is very small. 
     In this state loaded with 600 kN, pressurized sand is shot in through the corresponding bores  12 ,  32  resulting in the state shown in  FIG. 2   d , in which the mold recesses  33 ,  43  in the first and second mold elements  30 ,  40  are completely filled with sand. Additional vent bores can be provided in order to ensure the escape of the air previously present in the mold recesses  33 ,  43 . The sand remaining in the bores  32  is then leveled with the aid of a leveler (not illustrated). For the purpose of solidifying the sand, the sand volume in the mold recesses  33 ,  43  that has not yet been bonded to form a solid body is subjected to gas treatment. This gas treatment can be carried out through the shooting bores  12 ,  32  or through separate gas treatment openings provided for this purpose. In the case of sufficiently precise orientation of the first and second mold elements  30 ,  40 , the gas can leave the mold recesses  33 ,  43  through annular gaps between the walls of the bores  42 ,  52  and the ejector rods  82  located therein or through gas treatment vents specially provided for this purpose. This assures that gas is supplied to the total volume of sand so that the sand is homogeneously solidified to form solid sand cores  90 . Even if the mold elements  30 ,  40  are not superposed with great precision sufficient to totally prevent gas from escaping through the gap separating the mold elements  30 ,  40 , a total gas treatment is ensured, since the leakage merely causes the space surrounding the mold elements  30 ,  40  to be filled with gas. The escape of gas from this space is not possible due to the frame  20  and the sealing cord  27 . 
     On completion of the gas treatment, the gas is purged out. The top supporting unit  10 ,  20  is raised together with the first mold elements  30 , while the sand cores  90  remain in position in the mold recesses  43  of the second mold elements  40 . Only on completion of the upward movement of the top supporting unit  10 ,  20  and first mold elements  30 , shown in  FIG. 2   e , is the lifting plate  80  also raised so that the ejector rods  82  protrude into the mold recess  43  of the second mold elements  40  to lift the sand cores  90 . 
     This results in the state shown in  FIG. 2   f , which allows for automated or manual removal of the sand cores. 
       FIG. 3  shows another section through the core-making tool of the invention. It is a partial sectional view of the frame  20 , while the frame  60  is constructed in almost identical manner to that described above. It can be seen that the corner segments  26  are connected with the aid of front-sided screw connections to the side plates  22 ,  24 . The contact surfaces on the side plates and/or on the corner segments, precisely machined, for example, by milling, ensure that the frame is of exactly the right size without necessitating, for the purpose, the creation of a customized casting tool or the use of an expensive welding procedure followed by a complex machining phase.