DE19606210A1 - Stereolithographic technique departs from thin planar construction, into three dimensional deposition within gel matrix - Google Patents

Abstract

Free form models are automatically generated in this process, in which the material of the model (5) is positioned in or on a supporting matrix (2) of gel. The material is introduced along a spatial curve. Preferably, the support matrix and vessel (1) are transparent, and the matrix temperature is controlled. It is multilayer and may have layers of differing colour, the layer thickness being at most the depth of insertion of the introduction tool. The matrix is a gel based on gelatine, pectin, silicic acid or a setting resin. The introduction tool is implemented with a hollow needle (4). The length over which material is introduced.

Description

The invention relates to a method for generating spatial free-form surface-based Model representations according to the preamble of claim 1.

It is known that spatial structures, the geometric model z. B. with CAD systems was created to scale using NC-controlled processes in different materials can be generated. Lately wins alongside milling Generation processes for free-form surfaces - models using so-called rapid prototyping - or also solid freeform techniques, such as selective laser sintering, fused deposition Modeling, laminated object manufacturing, 3D printing or laser stereolithography increasingly important. The aim of using these techniques is to generate them quickly of prototypes in the design, function and manufacturing phase of a product scale products of sufficient dimensional accuracy (usual tolerances between 0.1 and 0.5 mm). The most important rapid prototyping techniques are in their mode of operation vivid and current in A. Gebhardt, "Rapid Prototyping", Carl Hanser Verlag, Munich, Vienna, 1996, pp. 91-156, the basic layer-by-layer model generation by V.O.J. Munz was already described in 1951 (US Patent 2775758). With the laser Stereolithography is exposed by a laser beam controlled by a scanning mechanism Surface of a photopolymer bath along the geometry contour of the current model height. The exposure leads to a targeted polymerization or bath curing along the Laser track. By gradually lowering the solidified polymer layer, covering with fresh unexposed photopolymer, which in the following cycle corresponds to the new one Geometry height is exposed again, a scale is created in layers Polymer model. A disadvantage is the need to generate thin-walled ones Support structures that deform the liquid To prevent polymer sub-model. The generation of columns extends the one Construction process, but also the post-processing process after the model has been removed the photopolymer bath, because the supports are carefully hardened and dry must be removed manually from the generated model. Furthermore, it leads in layers Build up a layered appearance of the model surface, which is usually also in a rework must be reground manually. The principle of contour lines oriented layered model construction, in which the untreated starting material as There is also a matrix with a supporting effect arranged around the partially manufactured model selective laser sintering, laminated object manufacturing and 3D printing. The Fused deposition modeling can do without a support matrix, but it does here, too, the model is layered by the solidification of a spiral-shaped contour Plastic or wax melt thread built. Therefore, it is a real three-dimensional In turn, model area generation was not realized. There is also a procedure for the latter due to the lack of a support matrix, restrictions regarding the model extension into the Horizontal. In all of the above-mentioned methods, the necessary leveling requires everyone new material layer to be machined considerable extensions of construction time.  

The object of the invention is to provide a method
with which the generation of three-dimensional free-form surface models is possible, the construction of which no longer necessarily has to be carried out in thin horizontal contoured layers, but also along curve or surface segments which can be defined in any spatial manner
and which also makes it possible to generate three-dimensional visual models that can remain in a transparent support matrix.

This object is achieved by a method having the features of claim 1.

What is essential about the new process is that the material or fluid used to generate the model is different can differ from the surrounding support material and that this is initially fluid present support material at the time of generation in a gel-like Transition stage to a partial or complete solidification passes.

It has surprisingly been found that liquids are in the gel state are suitable, for example, via hollow needles or flat nozzles, (hereinafter Entry Tool called), injected materials or fluids with sufficient accuracy on the Can hold position at the time of injection, even if the entry tool is relative is moved rapidly in the gelling liquid. The gel state must be advantageous at the time of injection be chosen to be high enough so that the material (or Maintain fluid) positioning in the gel that acts as a support matrix with sufficient accuracy secondly, the brief local disturbance of the support matrix (caused by the Displacement tool caused by displacement) after its change of position Backflow of the gel-shaped support matrix is reversed.

Thixotropic gels based on silica (eg Aerosile) or aqueous gels can be used advantageously Use on gelatin or pectin basis to create optimal support matrices.

Interestingly, the process leaves several possible uses for the generation spatial models.

In principle, two main applications of the process can be distinguished:

• - The generation of fixed models, which solidify by entering in the support matrix Plastic or wax melts are generated and after solidification from the compliant gel mass can be easily removed.

Compared to the known methods, a layer-by-layer model creation is indeed here also possible (with the advantage of integration two-dimensional already introduced on the market Die application mechanisms and tool controls), but are also three-dimensional controlled entry strategies with the geometry display adapted Entry toolpaths feasible.

The monitoring and regulation of the temperature of the support matrix is advantageous Heat exchange devices to achieve an even gel state.

• - The generation of those remaining in the support matrix after the material entry Illustrative models. The support matrix must of course be as transparent as possible be how z. B. obtained by using aqueous gels based on gelatin or pectin becomes. This can also be used to achieve final strengths of the gels  unproblematic transport of the visual models e.g. B. in a glass or Allow acrylic glass containers. For this application, it is also advantageous that only the Surfaces of the model geometries must be generated, but not the respective one Wall thickness. This leads to a quick and low material (fluid) entry.

In addition, the generation speed can be increased if the Surface marking materials or fluids are not punctiform from small circular ones Nozzle openings are entered, but via porous protruding from a sleeve or perforated wicks, the entry length of which is currently controlled by a control mechanism generating area is adjusted. This way you can expand two-dimensionally Larger areas are displayed much faster than by line arrangement.

There are also different ways of creating a model representation Replace entry tools, including material type and color. With circular curved slot nozzles with cylindrical outlet openings can be, for example Easily generate tubular structures by guiding the nozzle in the direction of the tube axis.

An advantage of the gel-shaped support matrix, which should not be underestimated, is the possibility in it selectively position objects generated by other methods and over the controlled material (fluid) entry afterwards to complete an overall model. A interesting application would be z. B. in plant model construction the subsequently generated Piping through color line connection between previously positioned in the support matrix Plastic container.

Furthermore, gels allow targeted, spatially limited staining.

A stable mixture with fluorescent pigments or photochemical substances is just as possible as mixing with thermochromatic substances, so that, for. B. Using a controlled laser beam, a targeted local change in the appearance of the Support matrix can be brought about.

Embodiments of the invention are shown in the drawings and are in following described in more detail.

Show it

Fig. 1 is a perspective view of a model generation apparatus with gel support matrix,

Fig. 2 is a sectional view of a material entry tool with a porous mandrel.

In the glass container 1 there is a transparent gelatin-water mixture 2 filled in in the liquid state. To temper the mixture which changes to the gel state, the container 1 is placed in a water container 3 , the water filling of which is continuously circulated via a commercial thermostat or cryostat, not shown. The initial temperature of the approximately 2% gelatin solution is advantageously approximately 50 ° C.

With the help of the thermostatted circulating water, a gradual cooling of the gelatin mixture to 10 ° C is possible by heat transfer over the wall of container 1 . Gel formation begins at a bath temperature of 18 ° C-22 ° C and is complete at approx. 15 ° C. The cooling rate should be chosen to be sufficiently low so that the material (fluid) entry via the entry tool 4 for the entire model geometry to be displayed can proceed from liquid to solid during the transition phase of the gel-shaped support matrix 2 .

For the positioning of the entry tool 4 , the CNC control mechanism of a 3-axis or 5-axis milling machine, not shown, is used, the milling tool of which is replaced by the entry tool 4 . The material 5 to be entered can be a preferably water-insoluble paint or a wax melt solidifying in the gel, which is fed hydraulically or pneumatically via a feed line 6 from a storage container (not shown) to a small intermediate container 4 a. At the exit of the intermediate container 4 a there is a hollow needle 4 b made of stainless steel or plastic, via which the material 5 is introduced into the solidifying gel matrix. The tool feed speed should be selected so that a clean line entry of the material is achieved. Usual feed speeds for wax insertion are between 50 and 100 mm / sec.

The filling level of the gel matrix should be adapted to the maximum immersion depth of the hollow needle. With the depicted method, a thick-layer structure of the gel matrix is possible, so that model geometries can be generated, whose vertical position is greater than b, the maximum depth of immersion of the hollow needle. 4

Fig. 2 shows the execution of an insertion tool, in which the insertion material (or fluid) is introduced into the gel via a wick 7 made of porous sintered metal, plastic or ceramic.

The wick is enclosed by a thin-walled hollow cylinder 8 . The entry width of the model-generating material (fluid) can be regulated via a control piston 9 , which leads to a vertical displacement of the wick. It is thus possible to realize material (fluid) entries of different widths.

Claims (9)

1. A method for automatically generating free-form surface models, characterized in that the model-building materials or fluids ( 5 ) are positioned in one or more multi-axis controlled insertion tools ( 4 ) in or on a support matrix ( 2 ) made of gel, the material or fluid entry can take place along a space curve. 2. The method according to claim 1, characterized in that the support matrix ( 2 ) consists of transparent gel-forming substances and that the support matrix receiving container ( 1 ) is provided with a transparent wall. 3. The method according to claim 1 or 2, characterized in that the temperature of the support matrix ( 2 ) is controlled by a temperature control device. 4. The method according to any one of the preceding claims, characterized in that the support matrix is constructed in multiple layers is colored and layered differently, if necessary, whereby the layer thickness is maximum corresponds to the immersion depth of the entry tool. 5. The method according to any one of claims 1-4, characterized in that the support matrix ( 2 ) is created from a gel based on gelatin or pectin. 6. The method according to any one of the preceding claims, characterized in that the support matrix ( 2 ) is created from a gel based on silica or from hardenable casting resin. 7. The method according to any one of the preceding claims, characterized in that the entry tool ( 4 ) is designed with a hollow needle. 8. The method according to any one of the preceding claims, characterized in that the length of the material entry or fluid entry into the support matrix is accomplished via a porous or perforated wick ( 7 ) which can be changed in the immersion length and is located at the end of the entry tool. 9. The method according to any one of claims 3 to 6, characterized in that the transparent support matrix with fluorescent or photochemical or thermochromatic or reflective substances is provided by controlled and directed energy or light rays to be activated.