Method for making products by freeform laser sintering

[0001] This application is claiming priority from German application, Ser. No. 102 19 983.3-24 filed on May 3, 2002.9

[0002] The invention relates to a method for making metallic or non-metallic (i.e. ceramic or plastic) products by freeform laser sintering, in which the products are fabricated from powdery material on a substrate plate in vertically additive, layer-by-layer fashion by means of a computer-controlled laser beam.

[0003] Such a method is known from U.S. Pat. No. 4,863,538, for example. When applying said method to the fabrication of products with small dimensions, such as those needed in dental technology in the form of tooth replacements and auxiliary dental parts, difficulties arise from the fact that these small products—of which several are usually built up on a substrate plate of the usual size—must resist the substantial horizontal forces relative to their inherent moment of resistance when the excess powder is stripped off during application of the next powder layer, on the one hand, and, on the other hand, must be and remain joined to the substrate plate in such a way that they can be removed from same without damage after the fabrication procedure has been completed.

[0004] The invention solves this problem by constructing at least one support between the substrate plate and the outer surface of the product, said support being joined via a predetermined breaking area with the outer surface of the product, wherein the predetermined breaking area is formed by reducing the strength of the support along the outer contour of the product. The support constitutes a sufficiently secure and stable connection between the substrate plate and the product, yet the predetermined breaking area ensures that a finished product requiring little or no follow-up work can be removed. The preferred way of reducing the strength of the support is to decrease its cross-sectional thickness and/or to provide holes through the support.

[0005] It is also advantageous to configure the support or supports with a small cross-sectional thickness and oblong shape, and to orient it/them lengthwise on the substrate plate in the direction that the powder layers are added. In this way, they provide sufficient opposition to the forces occurring on the addition of layers, but on completion of the fabrication process vertical thereto can be easily broken off from the product if they have adhered to the latter on removal from the substrate plate.

[0006] Insofar as the products to be fabricated are bowl-shaped dental products, such as caps, crowns and the like, a development of the invention provides for the latter to be built up with their full cross-section resting on the support(s). In other words, the entire base surface of the product is made first, onto which the closed, ring-shaped wall is added.

[0007] Additional advantageous developments of the invention derive from the following description of an embodiment and from the further subclaims.

[0014] With the help of the notorious laser sintering method, the bowl-shaped dental products 1 and 2 shown in FIG. 1 are built up layer by layer from pulverised material, in particular metal powder of varying particle size, on a substrate plate 3 of the apparatus executing said method. Whereas the schematic view shows identically shaped bodies, in practice the latter are individually shaped, namely with the help of data, scanned intra-orally or extra-orally, about the patient's teeth or tooth stumps for which the products are intended.

[0015] FIG. 1 also shows that the separate products 1, 2 are joined to the substrate plate 3 by a support 4 (or two thereof). The supports 4 are oblong in shape and disposed lengthwise in the direction in which the powder layers are added (arrow 5), and transversely thereto are of relatively small thickness. Both aspects can be seen more precisely in FIGS. 2 and 3, which show a dental product 1 in even greater enlargement than in FIG. 1. The particle size of the respectively deposited layer may be modified—while retaining the same thickness of layer—based on the height that the product has reached.

[0016] FIGS. 2 and 3 clearly show the bowl shape of the dental product 1. In the schematic view, the thickness d of the conically annular side wall 5 is uniform over its entire height, and is equal to the thickness of the base 6; in practice, this is not the case. In particular, the edge region 7 runs to a wall thickness of 50-200 μm, but on the inner side—as suggested by FIG. 3—a thickening is performed on the inner edge region 7 by modifying the product data relative to the scanned data. In that region, the surface is smoothed by melting the surface, resulting in the inner edge surface being polished.

[0017] As also shown by FIGS. 2 and 3, the supports 4 are drawn upwards a little at their two ends, congruent with the outer surface of the product 1. Over the entire length that the support 4 is joined to the product 1, the cross-sectional thickness of the support 4 is decreased in a small part of its height—immediately adjacent to where it is joined to the outer surface of the product 1—, such that a predetermined breaking line 8 results between the outer surface of the product 1 and the support 4. By exerting lateral pressure on the product 1 against support 4, or vice versa, the support 4 can be easily and cleanly broken off from product 1. In the embodiment pursuant to FIG. 4, the predetermined breaking area or line 8 is formed by providing holes 11 in the support in addition to reducing the cross-sectional thickness of the support 4, said holes being contiguous with the outer surface of the product 1 and not only facilitating the separation of the support from the product, but also achieving a cleaner outer surface of the product. ‘Holes’ or ‘perforations’ are also understood to mean a porosity—invisible or barely visible from the outside—of the powder layer portions adjoining the outer surface of the product.

[0018] FIG. 5 shows in schematic form the path that the laser beam 10 traces when treating sufficiently large surfaces of the respective powder layer, such as the cross-sectional surface of the base 6 of a product 1 (FIG. 3). There, too, however, the edge (here annular in shape) is heated by a laser beam that is correspondingly guided in circles, and the same applies for the cross-section of thin walls. Depending on the energy input required, the track pitch 12 or the stripe width 13 is changed in the case of plane heating, and preferably according to the respective ratio of the surface—such as the surface of the base 6 of a product 1—to the length of the edge of the powder layer to be treated—such as the length of the edge of the base 6. The energy input can also be modified by changing the lumination or spot velocity of the laser beam 10, in particular by automatic means following analysis of the relevant data for the respective powder layer to be sintered. Other variables influencing the energy input are the diameter and the power of the laser beam 10. When these are modified in accordance with the surface to be sintered, the beam power is changed first and then, if necessary and permissible, the diameter of the laser beam is changed.

[0019] FIG. 1 shows two alternatives for marking the single products in a way that avoids confusion. In one case, the marking 14a is applied directly to the product, in the other case, the marking 14b is applied to the substrate plate 3 beside the product 1, in either case with laser sintered powder.