DE4122326C1 - Three=dimensional shaped bodies prodn. - by putting powder on photosemiconductor by electrostatic force and transferring to workpiece support - Google Patents

Abstract

Three-dimensional shaped bodies, e.g., casting patterns, dies etc., are mfd. from powder, which is put on a photosemiconductor by electrostatic force and then transferred to a workpiece support. Additional layers are formed and each layer or the assembly of layers is sintered. The initial application technique uses the essential components of a laser printer. ADVANTAGE - No tools are required, rapid and accurate process.

Description

The invention relates to a method for manufacturing without tools of three-dimensional shaped bodies using stereolithography.

Stereolithography means processes with which to create spatial models of workpieces or simply bodies can, which were previously mostly constructed using CAD on computers. The requirement here is now, this body in unrestricted Manufacture variety of shapes and with the highest possible accuracy. At the same time, the production time plays an important role.

The current state of the art only partially offers solutions for these Conditions. At the moment only accuracies of approx. +/- 0.3 mm can be achieved. In addition, these procedures are subject to restrictions the shape of the body. Furthermore, these procedures are very slow (up to 10 hours each Model). Existing processes also have the disadvantage that only a specific one Material e.g. B. wax or photopolymer can be used (depending on the procedure).

In an existing process (US 49 29 402) a liquid Partially exposed photopolymer with a UV laser, which by the UV radiation cures. A computer with a suitable CAD program breaks down a virtual body into different layers and send them back one after the other Exposure unit. The body is created by several layers on top of each other made of hardened photopolymer. This method has the following disadvantages:

• 1. To expose parts of the body that are in the layer to be exposed are not yet connected to the main part of the body Support bars are also exposed, otherwise the parts "float away".
• 2. The accuracy is not good because there is no arbitrarily thin layer liquid photopolymer applied to existing layers and also can be exposed.  
• 3. The photopolymer needs a relatively large amount of light to cure. This creates long exposure times.
• 4. Dyes cannot be added to the photopolymer.

Another method (laser sintering) uses a plastic powder to build up the individual layers. A thin layer of powder is placed on a workpiece carrier applied until heated to just before the melting point and then exposed to a high power laser, so that the individual powder grains fuse with the neighboring grains. A large number of such layers one above the other form a shaped body.

This method has the following disadvantages:

• 1. Because the individual grains are relatively uncontrolled with each other merge, the surface of the individual layers does not become smooth. It becomes necessary after the next layer of powder has been applied smooth individual layers using a roller, taking the risk there is that fine not yet connected to the main body Layer parts are shifted during smoothing.
• 2. Only certain materials can be used because they definitely have to have a low melting point, to keep the laser power low. The same applies to the temperature range in which a material from solid changes to the liquid state. If this temperature range increases, the necessary one also increases Laser power. Furthermore, the material must have a favorable absorption behavior for the radiation from the laser. A "transparent" material is not melted by the laser.
• 3. An often uncontrolled loss of shape occurs one that adversely affects the dimensional accuracy of the parts.

Both methods also have the disadvantage of not being used for exposure the relatively simple raster scanning process can be used because otherwise the individual layers warp or shrink. This saves valuable computing time when preparing the CAD data wasted.

The task now was to design a system that would enable Manufacture moldings without tools, quickly and with high accuracy. It should also have a large number of different materials be processable.  

The problem is solved by a method according to the characteristic Features of claim 1 and by shaped bodies according to claim 4. The invention is also based on the system of layered construction of bodies, but does not show the disadvantages of the other systems. The new system can be used to estimate the accuracy of reach at least +/- 0.03 mm. This system can also be used to make very delicate parts produce, e.g. B. a lifelike model of an entire movement. There is actually only one limitation to the shape of the molded body, and indeed no closed cavities can be produced.

An embodiment of the invention is based on the following text and the drawings.

The system essentially consists of the parts of a laser printer ( Figure 3). In the further course of the description, the explanation of the exposure part is only partially described, since this is the “prior art” of a laser printer or photocopier. The centerpiece is a master from a photo semiconductor, e.g. For example: cadmium sulfide, selenium, selenium arsenide, zinc oxide or an organic photo semiconductor (E).

The master spans two rollers that take over its drive. The master rotates constantly around the two rollers (T) and is meanwhile with a high voltage corona (F) through a high DC voltage electrostatically charged. After loading the master is done with a He-Ne or IR laser or another light source line by line, exposed according to the shape of the 1st layer (G). This layer was previously done by a computer based on CAD data calculated. A virtual body is broken down into layers, which then be broken down again into lines and halftone dots. The modulator (H) takes over the brightness control of the Laser beam corresponding to the individual halftone dots. The deflection unit (I) directs the laser beam line by line onto the master. The charge now flows through the exposed areas Photo semiconductor effect. The charge remains in the unexposed areas. There is now a latent "electrostatic image" on the master. Then a molding material is applied to the master using a magnetic brush applied in powder form (toner).

The molding material was previously charged by friction with the developer with opposite charges. This is done in developer box 1 (J).

The molding material is in turn transferred from the transfer corana (M) Transfer the master to the workpiece carrier (Q). To do this, the workpiece carrier is synchronized with the master movement by means of the motor (R) under the corona (M). The layer thickness can be limited by the voltage can be controlled on the loading corona (F).

After the transfer of the first layer, the master is discharged by the discharge corona (O), post-exposed by the post-exposure lamp (K) and cleaned by the cleaning station (U). Now a second "similar process" is started with the only difference that in this process a filler with different chemical, thermal or mechanical properties is transferred to the workpiece carrier and with a complementary shape ( Fig. 2 A + B). The filler comes from the developer box 2 (L), which is moved towards the roller (T), at the same time the developer box 1 (J) is moved away from the roller. Molding material and filler together form the first layer on the carrier (Q).

Then this layer is fixed by means of a high-precision heating roller (N), that is, the molding material and filler are sintered. A thin, sintered layer of molding material and Filling material on the workpiece carrier (5-100 µm thick).

To now apply the next layer, the workpiece holder with the height adjustment motor (S) by the layer thickness of the last one Layer lowered. Now the next layer can be applied. This process is applied layer by layer, until a complete body is processed. The powder grains bake together and form a solid block two different materials, which is now removed from the workpiece holder becomes for further processing.

The filler parts are now removed, this can be done, for example, by washing, etching or the like. The resistant molding material remains as a finished model. Both materials must have approximately the same melting point, so that they can be sintered at the same temperature. Basically, almost all thermoplastic materials come as material, they just have to be suitable have electrostatic properties.  

Because of the temperature, the possibility of heating roll sintering only at consists of thermoplastics, can also without fixation next layer can be applied. In this case, the powder block that has been stacked up will be added subsequently sintered, which has the disadvantage, however, that the workpiece is sintered shrinks. But it is also possible, instead of a melting filler, e.g. B. to use glass powder with the necessary surface sintering a thermoplastic material must be used as a molding material, e.g. B. waxes, plastics, sugar. Then, however, the powder block must pass through a side boundary be protected from falling apart. This side boundary is simply made from molding material by a frame is exposed and stacked. In this case, the finished model can simply be made from the glass powder removed and shaken off.

Processing of oxide ceramics is also possible, even processing of metals is possible. The metal toner grains must then be very thin with one Flux / insulators may be coated to make them electrostatic to be able to process. The insulating layer can then serve as a flux during sintering e.g. B. glass, borax or the like

When processing metals or ceramics however only a complete powder block with loose layers are produced, which then is then sintered in the furnace. In this case a shrinkage allowance has to be made, because the workpieces "shrink" during sintering.

When processing ceramics and metals, molding material and Filler have approximately the same melting point, so that the molding material and filler "shrink" at the same time during sintering.

Claims (4)

1. A process for the production of three-dimensional shaped bodies, in particular functional models, cast models and dies in mold construction, characterized by stereolithography ,
that powdery materials are applied to a photo semiconductor (E) by means of electrostatic forces,
that the molding material is transferred from the photo semiconductor (E) to a workpiece carrier (Q),
that additional layers are applied, and
that after the application of each individual layer is sintered or all layers are sintered together. 2. The method according to claim 1, characterized in that
that a filler is transferred to the material carrier (Q), the molding material and filler together forming the first layer, and
that the filling material is removed from the three-dimensional block of molding material and filling material, so that the actual molding remains. 3. The method according to claim 1 or 2, characterized in that after the application and sintering of all Lay the two materials through thermal, chemical or mechanical processing can be separated.   4. Three-dimensional shaped bodies, which are produced by a process according to Claims 1, 2 or 3 were made, in particular Function models, cast models or dies in mold making, characterized in that they are made of sintered layers powder material exist.