Metal fusion bonding – Process – With shaping
Reexamination Certificate
1999-12-15
2001-08-14
Cooke, Colleen (Department: 1725)
Metal fusion bonding
Process
With shaping
C228S190000, C228S254000, C156S152000, C156S235000, C156S239000, C264S171130
Reexamination Certificate
active
06273326
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for producing a metallic or ceramic body in which the body is built in layers from a real body elements, wherein the a real body elements are first cut and subsequently connected with the last applied layer by a physical or chemical process. The invention also relates to a device for performing the method.
The inventive manufacturing process is intended, in general, for manufacturing any desired metallic or ceramic bodies. A special field of application is the manufacture of tools as well as prototype molds. The purpose of this inventive method lies in the fast manufacture of metal bodies.
A known method for producing metallic bodies of the aforementioned kind envisions the layered building of a body geometry. The building or generation of the desired geometry can be realized by many very thin layers wherein the respective layer forms the contour of the component at this location. A necessary requirement for all known methods of fast tool construction is the presence of a 3D-CAD construction of the desired geometry. With suitable systems or interfaces the 3D-CAD construction is transformed into a layered model. During the transformation, simultaneously thereto or subsequently, a CNC program for controlling respective devices which are to be used for the layered construction is generated.
The currently known methods for (rapid) tool or component manufacture are based on a direct or indirect sintering process.
In the direct metal-laser-sinter process, a four-phase bronze alloy is used which forms a heterogeneous mixture with high and low melting components. The geometry is built in layers. The entire surface of the respective contour layer is scanned by a laser beam. Based on the principle of liquid phase sintering, the absorbed laser energy will melt the low melting phase and will wet the high-melting phase. The latter remains solid and expands via an irreversible crystal structure conversion. Accordingly, a constant volume can be achieved during sintering. After completion of the sintering process, the component has a granular structure which can be closed by infiltration of an epoxy resin.
In indirect metal-laser-sintering process, a low carbon-containing steel alloy is used having a grain structure that is embedded in a plastic layer. The building of the geometry is also carried out in layers. The laser energy will melt the metal powder only in the area of the plastic layer which results in a gluing of the metal particles. The thus resulting blank has only a minimal mechanical strength and is very porous. Subsequently, the blank is infiltrated by a watersoluble polymer binder and is dried in a heating cabinet at 50° C. (for approximately two days). As a last step, a furnace process will follow, wherein the blank is positioned in a graphite crucible. First, the polymer binder is driven out. Subsequently, the oven temperature is increased to 1050° C. The steel powder is slightly melted but does not completely melt. At this point in time, a very porous component is present which is comprised to approximately 60% of steel. The increase of the furnace temperature to 1120° C. melts the copper alloy that has been added to the graphite crucible and the copper alloy will infiltrate the component by capillary action.
A further method employs the path via generation of a stereo lithography model. The SL model has the contour of the tool to be produced. By molding the SL model in a silicone rubber a mold is produced. The thus resulting mold is filled with fine grain metal powder. The metal powder is provided with a polymer binder which cures at low temperatures. After curing of the polymer binder, t he blank is removed from the silicone mold and is then further processed by a furnace process, during which the blank is positioned in a graphite crucible. First the polymer binder is driven out in the furnace. When increasing the furnace temperature, the steel particles will become glued together. Upon further increase of the furnace temperature, a copper alloy is infiltrated into the porous structure.
The above mentioned methods have numerous disadvantages, which affect the manufacturing time, precision, and possible applications of the components.
Tools manufactured by the direct-metal-laser sintering process have initially a relatively minimal mechanical strength because of the high contents of epoxy resins. Accordingly, the behavior of a fully metallic body is not exhibited. This means that it is not possible to produce by this method highly loadable metal prototype parts. In relation to tools, this has primarily an effect with regard to the service life of the tools. Despite the infiltration with epoxy resin, a more or less granular structure of the surface remains. High gloss polishing of the surface is not possible. Moreover, because of the high epoxy component a relatively bad heat conductivity for tools (for example, injection molding tools) is provided. Based on this, when used as a prototype mold, other finishing conditions as in the later mass-produced tools may result which may have an effect on the properties of the produced components (for example, distortion, mechanical properties, etc.). This is primarily of interest for technical functional models. A further disadvantage is that the produced molds/components have only a limited thermal load resistance, i.e., can be used only in thermoplastic injection molding processes or at low temperatures (less than 200° C.). A use for aluminum or zinc die casting is not possible. When producing prototype molds, it must be further taken into consideration that very thin stays, dome structures, and ribs cause problems because of the mechanical strength of the material. Such details must be subsequently introduced by conventional methods. This requires additional time expenditure. A further disadvantage is that the prototype molds/components cannot be post-machined by sinking by EDM (for example, for tool modifications). Moreover, already during tool construction the manufacturing process of sintering must be taken into account. The component manufacture is limited to dimensions (W, L, H) of 250 mm×250×150 mm. It is a further disadvantage in this context that no free material selection is possible. The produced component is comprised of a material mixture. A disadvantage for the manufacture of injection tools is that the core and cavity must be produced separately, i.e., sequentially. Accordingly, the nominal manufacturing time for the complete tool is doubled (i.e., is approximately four to six days). Furthermore, the manufacture of hollow bodies is not possible. The minimally achievable layer thickness is 0.05 mm. Each contour layer must be a really treated by the laser (time expenditure). In indirect metal-laser-sinter processes, the decisive disadvantage lies in the last processing step. During infiltration of the porous steel structure by the copper alloy, shrinkage of the component of up to 4% occurs. This shrinkage makes the tool design more complicated and can result in great imprecisions of the component. Furthermore, an a real machining of each contour layer by the laser is required (time expenditure). The minimally achievable layer thickness is 0.05 mm. A further disadvantage is the complicated and time-consuming manufacturing process. The manufacturing process per component is five to eight days. In this method it is also not possible to manufacture the core and cavity for an injection tool in a single step. Accordingly, the total manufacturing time for the tools when optimized is two to three weeks. The method does not allow manufacture of hollow bodies. The maximum dimensions are 250 mm×250 mm×150 mm. Furthermore, this method is also limited to certain material combinations (steel copper alloy). It is not possible to produce general metal prototypes.
In the disclosed molding process (stereo lithography part/silicone mold), the components to be produced are limited to a size of 100 mm×100 mm×100 mm. It should be noted in this co
Cooke Colleen
Huckett Gudrun E.
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