Method and device for producing parts by sintering and/or melting

The invention according to the preamble of claim 1 relates to a method for manufacturing products by freeform sintering and / or melting, in which the products are constructed by means of a data-driven guided high-energy beam of a layered applied material layer by layer.

Furthermore, the invention relates to a device according to the preamble of claim 10 for performing such a method, said apparatus comprising: a beam source for generating this beam, a platform for receiving a layered coatable material and a controller for controlling the beam, by means of which the beam can be guided under data control, to build up the products from the material layer by layer.

Such methods and devices are known. They are used inter alia in the manufacture of dental products, such as. Dental crowns, dental bridges, implants, etc.. You can however also be used for other applications.

From US 5,908,569 a device according to the preamble of claim 10 and a method according to the preamble of claim 1 is known for producing three-dimensional objects by laser sintering, in which a laser beam is directed by means of a deflecting mirror via a powder layer to the points corresponding to the cross section of the to to depart form the object and to sinter the powder at these points. From US 5,427,733 a similar device is known, in which the laser beam is guided in successive lines across a layer of powder in order to connect the powder in the range of the focused beam.

These known devices, however, are very complex equipped for the required high precision of the products to be manufactured and therefore very costly. However, the unit cost of the products to be manufactured can be reduced if the production time of a product to be produced is reduced. As a result, namely to increase the efficiency of such a device.

The invention is therefore the technical problem of reducing the production time in the manufacture of products by freeform sintering and / or melts.

The invention solves this problem in a method of the aforementioned type in that the high-energy beam predetermined positions of a layer of material each multiple, namely m times, irradiated, wherein m is an integer greater than 1, wherein for each of these positions that it is first heated in the first irradiation to a temperature below the melting temperature of the material and during the m-th irradiation to an m-th temperature is heated above the melting temperature and in such a way completely melted over the entire layer thickness of time that the material at that position with the underlying layer connects, according to claim first

The invention solves this problem also by a device of the aforementioned type, wherein the controller is configured such that by means of the control of the beam can be controlled as stated above, according to the claim 10th

The invention has recognized that the production time can be reduced if the energy of the high energy beam is coupled into the material in several steps. In the first step an energy injection takes place at a certain position of the material layer to the corresponding region of the material layer has been heated at this position to a temperature just below the melting point. In the last step of the energy coupling then heated the jet that area above the melting temperature and thereby merges the material with the underlying layer. In this way, the products to be produced is formed.

When melting or sintering by means of a high-energy beam, it is important that each detected by the beam portion reaches the melting point of the material, but without exceeding the boiling point, otherwise the material would simply evaporate without the product to be produced would formed.

The beam but each reaches only a superficial portion of the irradiated material layer. Therefore, first, only the surface of said irradiated region is heated. The beam Rear facing this region is not reached by the beam. The heating of the side facing away from therefore takes place exclusively via a heat transfer within this range. Thereby, the maximum processing speed is limited.

may, however, the invention overcomes this limitation by repeatedly irradiating a or each position, so that a heat transfer within the corresponding area of ​​the material layer of the hot place at the cold side of this range for a period of time during which does not irradiate the surface of this area becomes. This time period can then be used to heat another area. After this additional area has been heated, the beam returns to the first-mentioned area and can continue or complete the process of heating.

By so alternating irradiation no time-consuming temperature equalization processes must await within the irradiated area during irradiation. Rather, this temperature compensation operations can be performed after an irradiation procedure temporarily terminates and another irradiation process is started or continued.

In this manner, the irradiation times of individual positions or areas of the material are substantially reduced. This alternating exposure also permits a higher output of the radiation source, eg a laser or an electron beam source, and thus a higher energy input at the respective position. The danger of explosive evaporations small material particles is namely thereby considerably reduced, that after a short time the beam is directed at a different position.

In a particularly preferred embodiment, the to be irradiated positions of a material layer are irradiated two times. Each of these positions is first irradiated with a first period of time and then not irradiated for a second time period. The second period of time of non-irradiation is at least precisely as long or twice as long as the first time period of irradiation.

In a further preferred embodiment, the to be irradiated positions of a material layer are irradiated triplicate. Each of these positions in turn, is first irradiated with a first period of time and then not irradiated for a second time period. This process is then repeated at this position. Finally, a third irradiation with the first time period is done. The second period of time of non-irradiation respectively is at least precisely as long, twice as long or four times as long as the first time period of irradiation.

In a particularly preferred embodiment, the beam is guided with a first substantially linear movement forwards and backwards.

In this case, the forward movement creates a longer distance than the movement back backward. In this way one achieves a simple alternation of the irradiation / non-irradiation of lying in an adjacent environment positions.

Preference is given to this first movement, a second meander-shaped motion is superimposed. In this manner, dimensionally shaped areas of the product to be produced can be produced in a particularly uniform.

In a further preferred embodiment, a resultant or resultant contour of the product is optically measured during and / or after irradiation of a layer. The measurement data obtained in this manner are then compared with reference data. If a deviation is detected in this comparison, the beam corresponding to the detected deviation is regulated. In this way, the precision and dimensional stability of the products to be produced can be further improved.

Further preferred embodiments are evident from the reference to the accompanying drawings embodiments explained. It shows:<dl id="dl0001"><dt>Fig. 1</dt><dd>is a schematic sectional view of a device for manufacturing products by freeform laser sintering and / or melts according to one embodiment of the invention;</dd><dt>FIG. 2</dt><dd>is a schematic representation for illustrating the coupling of heat and the temperature compensation operation within a powder grain of a powder material during laser sintering or melts;</dd><dt>Fig. 3</dt><dd>on the facing is a diagram illustrating the time course of the temperatures at or in the powder grain to a laser beam and the laser beam irradiation side facing away at two different strategies; </dd><dt>Fig. 4</dt><dd>a possible guiding a laser beam to irradiate predetermined positions;</dd><dt>Fig. 5</dt><dd>another possible guiding a laser beam to irradiate predetermined positions; and</dd><dt>Fig. 6</dt><dd>on the facing another diagram for illustrating the time course of the temperatures at or in the powder grain to a laser beam and the laser beam irradiation side facing away at two different strategies.</dd></dl>

FIG. 1 shows a device 1 for producing metallic and / or non-metallic products 2, in particular of dental products such as dental crowns, - bridges, implants, etc. by freeform laser sintering and / or melts. The device 1 comprises a table 3 with a height-adjustable platform 4 on which a substrate plate 4A is. The platform 4 is progressively over a drive, not shown in their height, in particular adapted to the size of grains of a powder present in powder form material 5 steps adjustable.

The device 1 also has an above the table 3 arranged Laser 6, for example. A CO₂Laser, on whose beam 7 is guided by a suitable device, in particular a computer-controlled mirror galvanometer 8.

The device 1 further comprises a coating mechanism 9, by means of which the pulverulent material 5 is distributed uniformly over the surface of the table 3, so that in particular the space between the surface of the platform 4 and the surface of the table 3 to the surface of the table 3 is filled with powdery material 5

The production of a product 2 is as follows: First, the platform is 4 in an upper starting position. Then, the laser 6 is activated and its laser beam 7 directed to the powdered material. 5 The laser beam 7 solidifies and melts due to produce from it heat the powdery material 5, which - is sintered or fused with the surrounding powder particles - depending on the level of the applied on the powdery material 5 energy. The laser beam 7 is irradiated in accordance with a pre-programmed shape of the product 2, that is data-driven, predetermined positions of the pulverulent material 5 is produced at the irradiated areas by the laser beam 7 a layer of fused or sintered material.

Once a layer is finished, the laser 6 is deactivated and the platform 4 to a thickness that is adapted for example to the average diameter of the powder grains of the material 5, reduced. By means of the coating mechanism 9 is then applied a new layer of powder material 5 and smoothed. Is then activated again, the laser 6 and 7, the laser beam travels again computer controlled from predetermined positions within which the pulverulent material 5 merged with the previously produced layer or intended to be sintered, or at thereto adjacent or non-adjacent areas. This process of applying layers of powdered starting material 5, and sintering or melting of these layers with the previously applied layers by means of the laser beam 7 is repeatedly carried out until the product has 2 is formed in the desired shape.

The device 1 comprises a controller 10, by means of which in particular the activation and deactivation of the laser 6 as well as the positioning of the laser beam 7 via the mirror galvanometer 8 and the height adjustment of the platform 4 is controlled. The coordination of these components of the device 1 ensures the desired formation of the products. 2

The controller 10 generates its orders on the one hand as a function of pre-stored model data on the product. On the other hand, the controller 10 commands its function of during and / or measurement data obtained after irradiation of a layer by means of optical surveying of an emerging or contour of the product resulting 2nd These measurement data obtained are compared by the controller 10 with data target. If this comparison a deviation of the target data determined from the measured data, the laser beam 7 by means of the controller 10 by the action of the laser 6 and the mirror galvanometer 8 controlled according to the detected deviation.

The laser beam 7 is very strongly focused to achieve a high energy density. The laser beam 7 thus meets almost spotted on to the material. 5 Such a "point" but has an areal extent.

Fig. 2 shows the laser beam 7 in a greatly enlarged representation, as it is incident on a powder particle 11 of the pulverulent material fifth In laser sintering or laser melting a plurality of layers applied powder grains 11 has completely melted and fused to the underlying layer. For this, each body must be reached within the powder grain 11 the melting point of the material, but without exceeding the boiling point.

The incident laser beam 7 heats the surface of the powder particle 11. However, the laser beam 7 Rear facing the grain 11 is not obtained directly from the laser radiation. The warming of the opposite side thus takes place exclusively via a heat transfer Q within the powder particle 11. A powder grain 11 thus has two locations with extreme temperature values, namely a first high temperature T₁ at the laser beam 7 facing side and a comparatively low temperature T₂ at the laser beam 7 remote from the powder grain 11th

As already stated above, also the low temperature T must₂ reach the melting point of the material. However Meanwhile may the high temperature T₁ not exceed the vaporization point. As a result of heat transfer Q within the powder particle 11 is a maximum temperature difference is T₁-T₂Which defines a maximum processing speed.

Fig. 3 shows the course of temperatures at the laser beam 7 facing and the laser beam abgewanden side on a powder particle and the rate of two irradiation strategies (A and B).

The first irradiation Strategy (A) is shown with dashed lines. It corresponds to the conventional procedure. The time temperature profile T_1A describes the temperature at the laser beam to the facing side of the powder grain 11. In a corresponding manner, describes the temperature profile T_2A the temperature on the side facing away from the laser beam. The powder particle 11 is melted completely, when both the temperature T_1A and the temperature T_2A the melting temperature T_enamel exceeded. After this melting temperature is exceeded, even on the opposite side of the laser beam powder grain can be started with the melting of the next position.

A second irradiation strategy (B) is shown in FIG. 3 by solid lines. This irradiation strategy corresponds to an embodiment of the present invention. The temperature profile T_1B refers to the temperature at the laser beam 7 facing side of the powder particle 11, while the temperature curve T_{2 B} the temperature at the laser beam 7 side facing away from the powder grain 11 describes.

The laser beam 7 is first for a period of time .DELTA.t_at switched on. The laser beam 7 facing side of powder grain 11 starts to heat up to a temperature below the melting temperature T_enamel, Then, the laser beam is no longer directed to this position so that no more energy injection takes place at this position. The duration of the lack of energy coupling or non-irradiating this position in Fig. 3 with .DELTA.t_out in. Then, the laser beam directed to the same position again, so that once again an energy input takes place, which in turn to a sharp rise in the temperature T_1B for a period of time .DELTA.t_at leads. D ie temperature at the laser beam opposite side of powder grain 11 pulls a short time later also considerably until the melting temperature T_enamel is achieved.

In this strategy, the present invention therefore a position on the layer of powder is several times successively irradiated, so that during the time durations of the non-irradiation take place a transient phenomenon within the previously irradiated material particle and another position of the powder layer may be irradiated during this time. Due to this irradiation strategy, the temperature difference T is reduced_1B-T_{2 B} compared to the temperature difference T_1A-T_2A in particular the date of full melting of Pulverkoms. Thanks to this reduced temperature difference, a higher laser power may be used so that the production time can be shortened. Furthermore, during the periods of time .DELTA.t_out begin the heating of other points. Overall, one thus achieves a considerable shortening of the production times. Finally, this strategy irradiation also has the advantage that explosive evaporations smaller powder grains can be avoided, as the dwell times of the laser beam at individual positions is substantially shorter than in the conventional irradiation strategy (A).

Fig. Figure 4 illustrates the lead of the laser beam along predetermined positions P1, P2, P3, P4, P5 and P6. The laser beam is first directed to the position P1, and for the duration .DELTA.t_at, Then, the laser beam on the next but one position P3 directed to also for a period of time .DELTA.t_at to heat this position. Subsequently, the laser beam is again returned to irradiate the lying between the positions P1 and P3 position P2. There the laser beam dwells also for a period of time .DELTA.t_at, Subsequently, the laser beam skips back the position P3 and is directed to the following position P4 and that in turn for a period of time .DELTA.t_at, Subsequently, the laser beam is directed at the position P3 again to turn on this position P3 for a period of time .DELTA.t_at to linger.

It can be seen that the laser beam irradiates the position P3 twice, in each case for the duration .DELTA.t_at and during a period of time .DELTA.t_outWhich is substantially twice the period of time .DELTA.t_at corresponding to this position is not irradiated.

However, the invention is not limited to such irradiation strategy. Rather, it also includes other irradiation strategies.

Fig. 5 shows another irradiation strategy, wherein each individual item is irradiated triplicate. The irradiation takes place here in the order P1, P2, P3, P2, P3, P4, P3, P4, P5, P4, P5, P6, ...

In this irradiation strategy, the time duration of the non-irradiation between two irradiation procedures the same position is substantially just as long as the duration of the irradiation of the individual items.

Fig. Figure 6 shows the corresponding temperature curves T_1C and T_2C as shown in Fig. 3. turn to confrontation and the temperature curve after single irradiation of each item T_1A and T_2A in dashed lines (irradiation strategy A).

The solid lines in Fig. 6 show that during a first irradiation period .DELTA.t_at a first temperature value below the melting temperature T_enamel is achieved. Also, during a second irradiation process for the duration .DELTA.t_at Although there is an increase of the temperature of the corresponding position, but also up to a temperature just below the melting temperature T_enamel, Only during a third irradiation procedure then exceeds the temperature T_1B and, temperature T_{2 B} the melting temperature T_enamelSo that then the respective position of the powdery material is completely melted.

In Figs. 4 and 5 has a substantially linear movement of the laser beam is shown in each forward and backward, the forward movements each perform a longer distance than the rearward movement. Since the products being manufactured are however usually formed not only of very thin linear outlines, this linear movement of the laser beam is respectively superimposed on a second, meandering movement. This meander-shaped motion is used in particular, that is, structures that have a wider dimension than the diameter of the laser beam to generate spread structures.

Other movements of said first linear and said second meandering motion are superimposed to form complex contours of the product to be produced.

Overall, the invention enables, due to multiple exposure of each position along a predetermined path of a laser beam a significant reduction of production times, since it is quasi fed at multiple locations energy "simultaneously". By temperature transients between two irradiation procedures, a higher laser power is also used without problems, without causing explosive evaporations, in particular of smaller powder particles. Overall, the invention thus allows a more efficient utilization of devices for freeform laser sintering or melts

Above, the invention has been explained in connection with laser sintering or laser melting. However, the invention is not limited to the use of a laser beam for sintering or melting. Instead of a laser beam such as an electron beam also may be used. Therefore, the laser described above can be readily replaced by an electron beam source. Generally therefore, the invention relates to any type of a sintering or melting process, which is generated by a high energy beam from an appropriate source for such a high-energy beam.