Device and method for applying layers of a powder material onto a surface

A device (51) for applying layers or a powder material (71) by means of an application device (52) is described, wherein the application device (52) can be moved back and forth between two end positions in order to apply a layer of material (71) and the application device (52) comprises a blade (56) for removing excess material during the application of a layer of material (71). The device (51) is characterized by a material transport device (53), by which the material can be transferred from one side of the blade (56) to the other side of the blade. The device has the particular advantage that layers of material (71) can be applied without any loss of material and is particularly applicable in a laser sintering device.

The present invention is related to a device and a method for applying layers of a powder material onto a surface according to the preamble of the claims as well as to a device for manufacturing a three-dimensional object according to the preamble of the claims.

Such a device and such a method for applying layers of a powder material are known e.g. from DE 195 14 740 C1. The application device described in DE 195 14 740 C1 with respect to a laser sintering device comprises a single blade, which shifts a supply of material in front of it when applying a layer. Here, the problem is that the supply of material for a layer either is too small, so that no complete layer can be applied within the work space (production area), or else that the supply is larger than the amount that is necessary for one layer, so that excess material is shifted out of the work space to the outside. This excess material is no longer used for the application of a further layer. Therefore, it has to be collected in special collecting receptacles and contributes to an increased material consumption.

From EP 945 202 A2 a application device having two blades is known. Like the application device described in DE 195 14 740 C1 also this application device has the problem that while a layer is applied, excess material in front of the leading blade in the direction of movement of the application device is shifted out of the work space to the outside. Also here, this material, which is shifted to the outside by the blade, is not used for the application of a further layer and therefore contributes to an increased material consumption as above.

The material to be applied may consist of various materials such as polymers, metals, ceramics or composite materials. Depending on the material and the process control in a device for manufacturing a three-dimensional object a heating of the layers can be applied. In this case the material that has been accumulated in the peripheral region can be thermally damaged during the manufacturing of a three-dimensional object depending on the material, in particular when using polymers, and thus may become useless for a re-use.

Therefore, the object of providing a device and a method for applying layers of a powder material, by which the layers may be applied reliably and without any loss of material, forms the basis of the present invention.

The object is achieved by a device and a method, respectively, for applying layers of a powder material according to the claims.

The invention has the advantage that the material, which is shifted by a blade of the application device from the work space to the outside while a layer is applied, is reused for the application of the next layer. Therefore, no loss of material occurs.

When using a supply system, where the supply of material to a supply area is halted when a predetermined amount of material is present in the supply area, a self-regulating dosage of the material supply occurs, even when the excess material incurred while a layer is applied is transported by the blade into the supply area.

A further advantage of the invention is that the thermal stress of the material that accumulates in excess when a layer is applied, is small.

When an elevated process temperature is needed, the use of a material transport system having a heated tray has the advantage that the material is preheated before the application as a layer. Thereby, the building time is reduced.

When using a material transport device formed as fluidization device, wherein the fluidization occurs through a pre-heated gas, there is the advantage that the fluidized powder is pre-heated and thus the building time can be shortened, in case an elevated process temperature is needed.

FIG. 1shows a laser sintering device as embodiment of a device for manufacturing a three-dimensional object, in which the device according to the invention and the method according to the invention are used. The laser sintering device has a container1open to the top. A support2for supporting the object3to be formed is provided in the container1. The support2can be moved in the container1in the vertical direction A up and down by means of a drive4. The upper edge of the container1defines a work plane5(construction field). An irradiation device6in the form of a laser, which emits a directed laser beam that is deflected onto the work plane5by a deflection device7, is arranged above the work plane5. Moreover, an application device8for applying a layer of the powder material to be solidified onto the surface of the support2or a previously solidified layer is provided. The application device8can be moved back and forth across the work plane5between two end positions by a drive that is schematically indicated by the arrows B. The application device is fed from two powder supply containers10via two material supply devices9at the left side and the right side of the construction field as well as two material transport devices11.

Moreover, the device comprises a heating device12arranged above the work plane5for pre-heating an applied but not yet sintered powder layer to a working temperature TAsuitable for the solidification and the sintering, respectively.

A temperature measuring device13in the form of e.g. a pyrometer or IR camera, which serves for measuring the temperature of the previously applied powder layer or top powder layer in a measurement area14, is provided at a distance above the work plane5.

The work plane is secluded from the environment by a process chamber16. Thereby, the oxidation of the powder may be prevented, if necessary.

A control and/or regulation device17serves for controlling and/or regulating the movement B of the application device8, the movement A of the support2, the power of the heating device12, the power of the irradiation device6and the deflection by a deflection device7. For this purpose the control and/or regulation device17is connected to the drive of the application device8, the drive4, the heating device12, the temperature measuring device13, the deflection device7as well as the irradiation device6.

FIG. 2shows a first embodiment of the device for applying layers of a material in powder form.

The device51for applying a layer of a material in powder form according to a first embodiment comprises an application device52, a material transport device designed as conveyor roller53as well as a material supply device designed as a feeding chute54.

The application device52is movable back and forth between two end positions above a work plane55(construction field) by a drive indicated by the arrow B. It comprises a blade56, a first actuation element57and a second actuation element58.

The conveyor roller53has two paddles60,60′ that are rotating around a common axis59. Perpendicular to the axis59a cam plate61having two cams61aand61bis fixed to the conveyor roller53.

Each of two oblong con-rods62,62′ has a first end that is connected to the cam plate61in such a way that an eccentrical rotation is possible. Each con-rod62,62′ has at its other, second, end a hook-shaped portion62aand62a′, respectively, which serves as point of application for the second actuation element58of the application device. The axes or rotation63,63′, around which the two con-rods62,62′ are rotatable with respect to the cam plate61, together with the axis59are located in a common plane and are parallel to the axis59. The con-rods62,62′ in each case have an elongated hole62band62b′, respectively, between the first and the second end. The movement of the con-rods62,62′ is guided by a pin64inserted into both elongated holes62b,62b′, wherein the pin can not be moved with respect to the position of the conveyor roller. The elongated holes62b,62b′ are designed such that both hook-shaped portions62a,62a′, when the conveyor roller is rotated, do not only move parallel to the work plane55due to the guidance by the pin64, but also do move up and down perpendicularly to the work plane.

When looking in the direction of movement B of the application device, the conveyor roller is located in a trough65provided with a heating66at the side of the work plane55. This trough65is adapted to the conveyor roller53such that the ends of the paddles60,60′ move along the wall of the trough when the conveyor roller53is rotated in the trough65.

The feeding chute54is located at the side of the trough65facing away from the work plane55. The feeding chute54serves for feeding the powder for the manufacturing of a powder layer to the application device52.

In the following the operation of the previously described laser sintering device corresponding to a method according to a first embodiment is described.

As illustrated inFIG. 2, initially a first powder layer71is applied onto the support2or a previously solidified layer by moving the application device52in parallel to the work plane55. In the process excess powder72is moved out of the construction field to the outside by the blade56.

In an operating stage of the device according to the first embodiment, which is shown inFIG. 2, the first paddle6bis positioned below the work plane55and the application device approaches the conveyor roller53in order to produce a first layer71of the material in powder form. Finally, the above-mentioned excess material72is pushed by the blade56onto the first paddle60(for clarity reasons inFIG. 2no powder is shown in the material transport device).

In a stage of operation of the device shown inFIG. 3the application device pushes against the cam61bwith the first actuation element57and rotates the conveyor roller by an angle of approximately 20°-40° until it has arrived in a first end position. Thereby, powder on the first paddle60is lifted at the side of the blade56facing the construction field (construction field side). When the application device is in the first end position, a good portion of the powder on the paddle60(seen in a direction perpendicular to the work plane) is above the level that is defined by the lower end of the blade. Simultaneously to the rotation of the conveyor roller the hook-shaped portion62a′ at the one end of the con-rod62′ is lifted with respect to the work plane55. Thus, the device is prepared for the application of a next powder layer by moving the application device in a direction away from the conveyor roller to the second end position at the other side of the construction field.

After the application of the layer71of the material in powder form the solidification at positions in this layer corresponding to the cross-section of the object is effected by exposition to the laser in a manner known as such.

Thereby, it is in particular decisive for the quality of the finished object that the temperature of the top-most powder layer to be solidified has a temperature within a certain range, the process window. Above this process window the powder is already sintered without additional irradiation energy, whereas at temperatures below the process window warping occurs in the solidified layer. In many cases also the so-called curl effect, where the edges of the solidified layer bend up or roll up, is ascribed to a temperature of the top-most powder layer that is too low. Therefore, in order to achieve good results, in particular in order to avoid a warping in the manufactured object, the powder layer applied with the application device before the solidification has to be heated with the heating device12to a working temperature TAwithin the process window.

To this effect after the application of the powder layer the temperature of this layer is measured by the temperature measuring device13. Depending on the temperature measured in this process the heating power of the heating device12is determined. After the top-most powder layer has been heated up to the working temperature TA, the positions in the layer of the building material corresponding to the cross-section of the object are solidified by irradiation with the laser.

After the solidification of a layer the support2is lowered by a distance corresponding to the layer thickness and a new powder layer73is applied with the application device onto the layer71that has been previously exposed to the laser.

In an operating stage that is shown inFIG. 4the application device52moves away from the conveyor roller53in a direction, which is parallel to the work plane55, in order to create the next powder layer73. In the process the second actuation element58finally pushes the lifted hook-shaped portion62a′ of the con-rod62′. Thereby, the con-rod62′ is taken along in the direction of movement of the application device52and the conveyor roller53is further rotated. In this process the conveyor roller is rotated by an angle of approximately 140°-160°. The excess powder that is still on the paddle60is conveyed to the feeding area below the feeding chute54. At the same time powder from the feeding area is transported by the second paddle60′ from the feeding area in a direction towards the construction field. The powder in the feeding area consumed in this process thereby re-trickles from the feeding chute. When the feeding area is filled up with powder, the re-trickling, i.e. the feeding of powder from the feeding chute, stops by itself. At this stage, with the movement of the con-rod62′ the hook-shaped portion62a′ again drops towards the work plane55until the second actuation element no longer bears against it and the con-rod62′ is no longer taken along by the application device52.

InFIG. 5the device is illustrated at the operating stage, in which the application device52is positioned on the other side of the construction field, which is not illustrated inFIGS. 2 to 5. The application device is moved in a direction away from the conveyor roller53until within the whole construction field a layer73of the powder material has been applied by the application device. At this stage the conveyor roller53is rotated by 180° with respect to the position that is illustrated inFIG. 2.

With the help ofFIGS. 2 to 5the operation of the material transport device and the material supply device on a first side of the construction field has been described. At the other, second, side, which is opposed to the first side of the construction field, a similar device is provided, which consists of a conveyor roller, a trough, a feeding device and con-rods and works in the same way as it was described byFIGS. 2 to 5above. In order to create the next layer, the application device52is again moved in a direction towards the conveyor roller53, as shown inFIG. 2.

Then, the previously described steps are repeated until the manufacturing of the three-dimensional object is finished.

InFIG. 6a device100for applying layers of a powder material according to a second embodiment is shown.

The device for a repeated creation of a powder layer according to a second embodiment comprises an application device101, a material transport device formed as fluidization device102and a feeding device104provided with a cover103.

The application device101is movable back and forth above a work plane107between two end positions by means of a drive indicated by an arrow B in the same way as in the first embodiment. It comprises a blade105and an actuation element106.

The fluidization device includes a chamber108for pre-heating the nitrogen that is used for the fluidization, a fluidization sheet109, by which the chamber108is closed at the top, and a pipe111for supplying nitrogen into the chamber108, which is provided with a valve112. The chamber108is provided with a heating device117(e.g. a resistive heating with temperature control) for pre-heating the nitrogen. The fluidization sheet109is provided with a plurality of small openings110that have a smaller diameter D than the powder grains that are used. A gas supply111leads into the chamber108, wherein the supply of gas into the chamber can be controlled via a valve112.

A material feeding device104having a cover103is formed above the fluidization sheet. The cover103is formed and positioned in such a way that when moving the application device to its end position by the actuation element106, it is pushed aside and thereby the material feeding device having an opening116is opened towards a feeding region located below the material feeding device. To this effect, the actuation element106is formed in such a way that during the opening of the cover the actuation element106itself does not get into the opening region of the material feeding device. In particular, during the opening the actuation element pushes the cover103behind or in front of the opening116of the container104when seen from a direction, which is perpendicular to the drawing plane ofFIG. 6. The cover is laterally attached to a side wall by a spring113, which presses the cover into the closed position when the actuation element106does not push against the cover103.

On the other side of the construction field a further second material feeding device and a further second fluidization device are provided mirror-symmetrically to the above-mentioned material feeding device and fluidization device.

During operation at first a first powder layer115is applied onto the work plane107by moving the application device across the construction field parallel to the work plane107in a direction towards the material feeding device. Thereby, excess powder is shoved out of the construction field to the outside onto the fluidization sheet109. The application device is further moved to its end position and by a pushing of the actuation element106against the cover103thereby opens the material feeding device104, from which powder re-trickles into the feeding region below the material feeding device until this is filled up and the re-trickling stops by itself. Subsequently the application device is moved just as far from the end position as is sufficient for closing again the material feeding device via the spring113and the cover103.

By opening the valve112for a short time and letting nitrogen into the chamber108via the supply pipe111, a pressure impulse is created in this chamber, which leads to a discharge of pre-heated nitrogen out of the openings110into the powder above the fluidization sheet109. Thereby this powder is fluidized and flows through the gap between the blade and the fluidization sheet from the feeding region at the one side of the blade105to the other side of the blade that faces the construction field. Thereby, the application device is prepared for the application of a next powder layer.

As in the first embodiment, the powder layer is pre-heated by the heating device12in a manner known as such and is solidified at the positions corresponding to the cross-section of an object.

In the next step after the lowering of the support2as in the first embodiment the application of a next powder layer onto the work plane within the construction field takes place by moving the application device from the first end position to the second end position at the other side of the construction field.

The operation of the second feeding device and the second material transport device is like the above-described operation of the devices shown inFIG. 6.

Then, the previously described steps are repeated until the manufacturing of the three-dimensional object is finished.

Alternatives and variations of the above-described devices and the above-described methods are possible.

The device according to the second embodiment has been described having a fluidization device, wherein the fluidization is achieved by introducing pre-heated nitrogen. However, the fluidization can also be effected by introducing another gas. A further possibility of achieving the fluidization is to set the powder into vibrations.

The device according to the first and the second embodiment has been described such that on both sides of the construction field the same material transport devices and material feeding devices are provided. However, it is possible to combine the devices according to the first and the second embodiments such that on the one side of the construction field a material transport device and a material feeding device according to the first embodiment are provided, whereas on the other side a material transport device and a material feeding device according to the second embodiment are provided.

It is also possible, like in the first and second embodiments, to provide on both sides of the construction field a material transport device according to the invention, however, to provide a material feeding device only on one side of the construction field. Accordingly, during operation the material transport device on that side, at which the material feeding device is located, has to provide an amount of material that is sufficient for two layers. This modification allows a simpler and more compact design of the device.

The invention has been described by means of a laser sintering device, in which a laser is used as radiation source. Any other radiation source by which electromagnetic or particle radiation may be introduced into the building material, is possible. Thus, e.g. a radiation source for incoherent light radiation, for IR radiation, for X-ray radiation or for electron radiation may be used as radiation source. Accordingly, a building material has to be used, which can be solidified by the corresponding radiation.

Alternatively, the device for applying powder layers according to the invention may also be used in 3D printers, in which the powder layers are solidified by selectively applying a binder or adhesive at the cross-section of the object to be manufactured.

In the above-described device an infrared radiator above the work plane is described as heating device. Other possibilities of heating a previously applied layer of the building material are conceivable. For example, the circulation of warm air or nitrogen that is led across the recently applied layer can be used for a pre-heating of the layer.

The embodiment of a device for manufacturing a three-dimensional object has been provided with a heating device for pre-heating an applied, but not yet sintered, powder layer to a work temperature TAthat is suitable for the solidification and sintering, respectively, as well as with a temperature measuring device that serves for measuring the temperature of the previously applied and top-most powder layer, respectively. Depending on the material that is used and the process control a pre-heating of the applied material layer can be abandoned in the device for manufacturing of a three-dimensional object according to the invention. Accordingly, the device for manufacturing a three-dimensional object may also be constructed without a heating device and without a temperature measuring device.

The second embodiment has been described such that the fluidization is accomplished by means of a pre-heated gas. However, it is also possible to implement the fluidization by a gas that was not pre-heated. Accordingly, the fluidization device need not necessarily include a heating device for pre-heating the gas used for fluidization.