SE520709C2 - Three-dimensional product manufacturing device includes camera for sensing surface characteristics of surface layer at the powder bed - Google Patents

Abstract

A three-dimensional product manufacturing device includes a camera for sensing surface characteristics of a surface layer at the powder bed. A three-dimensional product (3) manufacturing device comprises a work table (2) on which the product is to be built, a powder dispenser (4) which is arranged to lay down a thin layer of powder on the work table for the formation of a powder bed (5), and a ray gun (6) for giving off energy to the powder so that fusion of the powder takes place. Deflection coils (7) control the beam released by the ray gun across the powder bed for the formation of a cross-section of the product through fusion of parts of the powder bed. A controlling computer (8) stores information about successive cross-sections of the product. It is intended to control a mechanism for guiding the ray gun across the powder bed according to a running schedule forming a cross-section of the three-dimensional body. The product is formed by successive fusion of successively formed cross-sections from powder layers laid down by the powder dispenser. A camera senses surface characteristics of a surface layer at the powder bed. An Independent claim is also included for a method for manufacturing the three-dimensional bodies comprising laying down a powder layer on a work table, supplying energy from a ray gun according to a predetermined running schedule for the powder layer, and forming the bodies through successive fusion of successively formed cross-sections from powder layers laid down, and sensing the surface characteristics of a surface layer situated at the powder bed.

Description

520 709 power is only controlled with respect to the melting temperature as information about the cooling process requires knowledge of the temperature distribution across the surface.

When a device according to the prior art is used for the production of three-dimensional products, it has been found that deviations from the desired shape, size and strength arise.

BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide an apparatus for producing three-dimensional bodies by successively fusing selected parts of powder layers successively applied to a work table, where reduction of deviations from the desired shape, size and strength of a formed three-dimensional body is possible.

This object is achieved by a device according to the characterizing part of claim 1. By providing a means for sensing surface properties of a surface layer located in the powder bed in the form of a camera, it is possible to measure and correct the surface properties, whereby a product with reduced deviation from desired dimensions and surface roughness can be achieved. In a preferred embodiment, the surface roughness is measured, with the aid of a camera, whereby shadow formation on the surface is registered, which means that the structure of the surface can be read. When detecting the presence of surface irregularities, for example arising from a welding flea or otherwise, the beam gun can be ordered to the identified coordinate to melt down the identified irregularity. In a preferred embodiment of the invention, the temperature at the fusion of the powder grains is measured, whereby it is possible to ensure that the melting takes place within a defined temperature range, whereby the risk of defects by, for example, evaporation or boiling of the material can be reduced.

Evaporation and boiling of the material can give rise to welding fleas or other surface unevenness. This means also enables the cooling temperature of fused selected parts of a powder layer to be measured, whereby the risk of occurrence of, and the order of magnitude of any surface stresses of the fused part can be reduced and thereby undesired deformations can be reduced. Furthermore, a measurement of the dimensions of the cross-section is made possible, whereby a comparison of the dimensions of the formed cross-section with the intended dimensions of the object can be used for calibration of control means for the beam cannon. The means also enables the measurement of the temperature of the undigested powder bed, whereby the maintenance of a temperature favorable from a process point of view can be monitored.

According to a preferred embodiment of the invention, information about the temperature distribution of the surface layer of the powder bed is fed back to the control computer for changing the travel schedule over the surface layer of the powder bed. By changing the driving schedule and the power and / or appearance of the jet, it is possible to maintain the correct temperature of the different parts of the powder bed.

In a further preferred embodiment of the invention, the information on the temperature distribution of the powder bed surface layers is used to increase the energy supply in areas of the powder bed surface layers with too low temperature and to reduce the energy supply in areas with too high temperature whereby a more even working temperature of the cross sections can be obtained. By adapting the energy supply to selected parts, a more correct temperature distribution is obtained, whereby the quality of the product can be increased.

In a further preferred embodiment of the invention, the device is arranged to control the energy supply of the jet gun to the powder bed at areas which are fused within the currently uppermost powder layer, so that the maximum temperature after fusion at these areas is within a limited range. By controlling the energy supply so that excessive temperatures are avoided, the risk of boiling and evaporation of the material, with the following defects, can be reduced.

In yet another embodiment of the invention, said information on the temperature distribution is used to control energy supply from a jet cannon included in the device to the powder bed at areas which are partly fused within the present uppermost powder layer and are to be combined with areas within a next layer so that the minimum temperature in these areas not less than a certain limit value. By ensuring that the temperature does not fall below a certain limit value, the risk of surface stresses and thereby deformation of the product can be reduced.

In yet another embodiment of the invention, said information is used if the temperature distribution is arranged to control the energy supply of the jet gun to the powder bed at areas within the surface layer of the powder bed which are not fused so that the temperature within these areas does not fall below a second determined limit value.

By maintaining a certain temperature of the powder bed which is not to be fused, the cooling process of the areas which are or are to be fused can be controlled more closely, and disturbances of the powder bed which occur when the jet moves over areas which are not to be fused to reach different areas to be fused is reduced.

In a preferred embodiment of the invention, the powder bed and the jet gun are enclosed in a chamber which is provided with a transparent window which is protected by a film which is feedable arranged along the window, whereby new film is fed. By loading film as the film is coated, transparency through film and windows can be maintained.

Further preferred embodiments are set out in the appended subclaims.

DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below in connection with the accompanying drawings, in which: Fig. 1 shows a cross-section of the invention, Fig. 2 shows a side view of a chamber provided with a transparent window, 520 709 ih 5 Fig. 3 shows a device for feeding and fixing a protective film to maintain the transparency of the window, 4 shows a fate diagram for generating primary driving diagrams, fi g. 5 shows a circuit diagram of a circuit diagram of the device, circuit g. Fig. 6 shows a fate diagram for correcting said driving diagram, Fig. 7 shows a schematic construction of a three-dimensional object and fi g. 8 shows a number of cross-sections from figure 7.

EMBODIMENT SEWING Figure 1 shows an apparatus for producing a three-dimensional product generally designated 1. The apparatus comprises a work table 2 on which a three-dimensional product 3 is to be built, one or two powder dispensers 4 and means 28 which are arranged to lay out a thin layer of powder on the work table 2 for forming a powder bed 5, a jet gun 6 for delivering energy to the powder bed whereby fusion of parts of the powder bed takes place, means for guiding the jet emitted by the jet gun 6 over said work table to form a cross section of said three-dimensional product by fusing said powder and a control computer 8 in which information about successive cross-sections of the three-dimensional product is stored, which cross-sections make up the three-dimensional product. During a work cycle, the workbench will be gradually lowered in relation to the beam cannon or each applied powder bearing. In order to enable this, in a preferred embodiment of the invention, the work table is arranged in a vertical direction, ie in the direction indicated by the arrow P. This means that the work table starts in a starting position 2 'in a position where a first powder layer of necessary thickness is applied. In order not to damage the underlying work table and to provide sufficient quality of this layer, this layer makes thicker than other applied layers, thus melting of this first layer is avoided. The work table is then lowered in connection with the laying of a new powder layer for the formation of a new cross-section of the three-dimensional product. For this purpose, in an embodiment of the invention, the work table is supported by a stand 9 which comprises at least one rack 10, provided with toothing 11. A step or servomotor 12 provided with a gear 13 adjusts the work table 2 to the desired height position. Other devices known to those skilled in the art for adjusting the working height of a work table can also be used. For example, adjusting screws can be used instead of racks.

The means 28 is arranged to cooperate with said powder dispensers for filling material. Furthermore, the sweep of the member 28 over the working surface is driven in a known manner by a servomotor (not shown), which moves the member 28 along a guide rail 29 which runs along the powder bed.

When applying a new powder layer, the thickness of the powder layer will be determined by how much the work table is lowered relative to the previous layer. This means that the bearing thickness can be varied as desired. It is therefore possible that when a cross-section shows a large deformation between adjacent layers to make thinner layers, whereby a higher surface unit is achieved and when there is little or no change in shape, make layers with a maximum penetration thickness for the beam.

In a preferred embodiment of the invention, the beam gun 6 is constituted by an electron gun, the means for guiding the beam 7 of the beam gun being constituted by deflection coils. The deflection coil generates a magnetic field which controls the beam generated by the electron gun, whereby melting of the surface layer of the powder bed at the desired location can be effected. Furthermore, beam guns comprise a high voltage circuit 20 which is intended in a known manner to supply the beam gun with an acceleration voltage for from an emitter electrode 21 arranged at the beam gun. The emitter electrode is connected in a known manner to a current source 22 which is used to heat the emitter electrode. 21 whereby electrons are released. The action and composition of the cannon is well known to a person skilled in the art.

The deflection coil is controlled by the control computer 8 according to a laid-out travel schedule for each bearing to be fused, whereby control of the beam according to the desired travel schedule can be achieved.

A detailed description regarding the generation and correction of driving diagrams follows below in connection with the description of the drawings 4 ~ 6.

Furthermore, there is at least one focusing coil 7 'which is arranged to focus the beam on the surface of the powder bed on the work table.

Deflection coils and focus coils can be arranged according to a number of alternatives well known to those skilled in the art.

The device is enclosed in a housing 15 which encloses the jet gun 6 and the powder bed 2. The housing 15 comprises a first chamber 23 which encloses the powder bed and a second chamber 24 which encloses the jet gun 6. The first chamber 23 and the second chamber 24 communicate with each other via a channel 25, which allows emitted electrons, which are accelerated in the high voltage field in the second chamber, to continue into the first chamber to later hit the powder bed on the work table 2.

In a preferred embodiment, the first chamber is connected to a vacuum pump 26 which lowers the pressure in the first chamber 23 to a pressure of preferably approx. 103 - 10'5 mBar. The second chamber 24 is preferably connected to a vacuum pump 27 which lowers the pressure in the second chamber 24 to a pressure of approx. 104 - 1O'6 mBar. In an alternative embodiment, both the first and the second vessels can be connected to the same vacuum pump.

The control computer 8 is further preferably connected to the jet gun 6 for regulating the delivered power of the jet gun and connected to the stepper motor 12 for setting the working position 2 of the work table between each consecutive application of powder layers, whereby the individual thickness of the powder layers can be varied.

Furthermore, the control computer is connected to said means 28 for powder application on the work surface. This means is arranged to sweep over the working surface, whereby a layer of powder is applied. The means 28 is driven by a servomotor (not shown) which is controlled by said control computer 8. The control computer controls the sweep along and ensures that powder is replenished if necessary.

For this purpose, load sensors can be arranged in the means 28, whereby the control computer can obtain information that the means is empty.

As shown in Fig. 2, the device further comprises means 14 for sensing surface properties of a surface layer located near the powder bed. This means 14 for sensing the temperature distribution of a surface layer located near the powder bed 5 is preferably constituted by a camera. In a preferred embodiment of the invention, the camera is used partly to measure the temperature distribution on the surface layer, partly to measure the presence of surface irregularities through the shading that surface irregularities give rise to. Information about the temperature distribution is used partly to achieve as even temperature distribution as possible over the parts of the surface layer to be melted, and information can be used to check any dimensional deviations between the generated three-dimensional product and the model because the temperature distribution reflects the shape of the product. In a preferred embodiment of the invention, the video camera is mounted on the outside of the housing 15 enclosing the powder bed 5 and the jet gun 6. To enable temperature measurement, the housing is provided with a transparent window 16. The powder bed 5 is visible to the camera through this window.

In a preferred embodiment of the invention, which is shown in figure 3, the window 16 is covered by a protective film 17. The protective film is fed from a discharge unit 18 to a collecting unit 19, the film being successively replaced, which means that the transparency can be maintained. The protective film is necessary because coatings occur as a result of the melting process. Figure 15 schematically shows the procedure for generating primary driving diagrams.

In a first step 40 a 3D model, for example in a CAD program, of the product to be manufactured is generated, alternatively a ready-generated 3D model of the product to be manufactured is input to the control computer 8. Then in a second step 41 a matrix containing information on the cross-sectional appearance of the product. Figure 7 shows a model of a hammer with examples of associated cross-sections 31-33. These cross-sections are also shown in Figures 8a-8c. The cross-sections are laid with a density corresponding to the thickness of the different layers to be fused to form the finished product. The thickness can advantageously be varied between the different layers. Among other things, it is advantageous to make the bearings thinner in areas where there is great variation in the appearance of the cross-sections between adjacent bearings. When generating the cross-sections, a matrix containing information about the appearance of all cross-sections is thus created, which together build up the three-dimensional product.

Once the cross-sections are generated, in a third step 42, a primary flow chart is generated for each cross-section. The generation of primary flow charts is based partly on shape recognition of the parts that make up a cross section, and partly on knowledge of how the flow chart affects the cooling temperature of local parts of a cross section.

The goal is to create a flow chart that means that the cooling temperature is as even as possible for the parts that are fused together before the next layer is applied, while the cooling temperature must be kept within the desired interval to reduce the risk of shrinkage stresses in the product and reduce the size of shrinkage stresses in the product. , with deformation of the product as a result.

Primarily, a primary flow chart is generated based on the shape of different constituent parts of the cross section.

Thus, in a preferred embodiment of the invention, primary flow charts are laid out based on experience of which flow charts give a good temperature distribution on the cooling temperature of the cross section, whereby the risk of shrinkage stresses in the product with deformation of the product as a result can be reduced. For this purpose, there is a set of driving schedules for areas of different shapes stored in a memory. In a preferred embodiment, this memory is updated as results of driving schedule corrections are evaluated, thereby obtaining a self-learning system.

In an alternative embodiment of the invention, already completed cross-sections, which are generated by a stand-alone computer, are fed into a memory in the control computer, where said primary driving diagrams are generated. In this case, information is obtained directly to the third stage 42 via an external source 40a.

Figure 5 schematically shows a method in which the beam from the jet gun is guided over the powder bed to generate a cross section of a product. In a first step 50, control of the steels over the powder bed is started according to the primary driving scheme defined in step 42. In the next step 51, the temperature distribution on the surface layer of the powder bed is measured by the camera. From the measured temperature distribution, a temperature distribution matrix is then generated, Tij - measure where the temperature in small sub-areas of the powder bed surface layer is stored. When the matrix is generated, each temperature value Tij-.uppmän in the matrix is compared with the desired value of a setpoint matrix Tjjböwärde.

The powder bed surface layer can be roughly divided into three categories. First, areas where fusion is taking place by machining the beam gun. In these areas, maximum melting temperature Tij-.max is of interest. Secondly, areas that have already merged and thereby cool down. In these areas, a minimum allowable cooling temperature Tij - cooling coefficient is of interest because too cold cooling temperature gives rise to stresses and thereby deformations of the surface layer. Third, areas not processed by the beam cannon. In these areas, bed temperature Tij is both of interest. It is also possible that the temperature is compared only in machined areas, whereby the Tij bed is not stored and / or controlled.

In a third step 52, it is examined whether the Tij measurement deviates from the desired value Tij setpoint and whether the deviation is greater than the permitted limit values. Limit values ATijqnax, ATijüvsvalning and ATíjtbäd belonging to the three different categories are stored in the control computer 8. It is also possible that the bed temperature is not controlled. In this case, the associated limit value is not stored. If the deviation between Tijuppnjän and Tij - böwäfde does not exceed this limit value, it is examined in a fourth step 53 whether the surface layer is finished. If this is not the case, continue driving according to the current driving schedule, whereby the above-mentioned method steps 50 - 53 are completed once more.

If the deviation between Tij-.uppmäu and Tij-böwänic exceeds any of the said limit values, a correction of the timetable 42 takes place in a fifth step. Said correction is performed in a preferred embodiment according to the diagram shown in Figure 6.

In a preferred embodiment of the invention, a new powder layer is laid only after the completion of each layer, the product being built up by successive fusions of powder layers until the product is finished. In this case, after a sixth step 55, a new layer is started, if the product as a whole is not finished, when in the fourth step 53 it is determined that the running schedule for a bearing has been completed. In a preferred embodiment, the correction of the running schedule comprises the following method steps: In a first step 56, Tijmx is compared with Tij-m ,, x.bö, vå, de, If Til-max deviates from Tijqmx. should be woven exceeding ATiJ - max is calibrated in a step 56a the energy supply to the powder layer by either changing the power of the jet or changing the sweeping speed of the jet.

In a second step 58, Tijtavsvajning is compared with Tij_avsvai ,, i ,, g-böfvä, de_ If Tijavsvalnmg deviates from Tij-.avsvainingiiöfväfdc exceeding ATij - svsvanning, the beam's travel schedule is changed in a step 58a. There are fl your ways to change the driving schedule of a beam. One way to change the driving schedule is to allow the jet to reheat areas before they have cooled down too much. The beam cannon can then sweep over already fused areas with lower energy intensity and / or higher sweeping speed. 10 15 20 25 30 520 709 12 In a third step 60 it is examined whether Tijbädd deviates from Tiybädijp setpoint. If the deviation is greater than ATij bed, in an embodiment of the invention the temperature of the bed can be corrected in a step 60a, for example by forcing the jet to sweep over the bed for supply of energy. It is also possible to connect separate bed heating equipment to the device.

It is also possible that a size control of the object to be manufactured is done through the thermal imager installed in the device. According to what has been described above, the bed and the parts that are fused are measured. The measured heat distribution completely reflects the shape of the object in a section of the three-dimensional body to be created. A check of the dimensions of the object can thereby be made in a fourth step 62 and feedback of X-Y deflection of the beam of the beam cannon can thereby be performed. This check is performed in a preferred embodiment of the invention in a step 62a where the deviation between dimensions of the cross section is made and if the deviation is greater than allowed, the X-Y deflection of the beam cannon is corrected.

In addition, input signals from the camera can be used to identify the presence of surface irregularities, for example in the form of a welding flea. Once the coordinates of a surface roughness have been identified, the driving schedule can be updated so that the beam gun is ordered to the identified coordinate to melt down the surface roughness.

The invention is not limited to the exemplary embodiment described above, for example the beam cannon may be constituted by a laser, the deflection means being constituted by controllable mirrors and or lenses.

The invention can further be used in a device for producing a three-dimensional product by energy transfer from an energy source to a product raw material, which device comprises a work table on which said three-dimensional product is to be built, a dispenser which is arranged to lay a thin layer of product raw material on the work table. for forming a product bed, a means for delivering energy to selected areas of the surface of the product bed, a phase transition of the product raw material being allowed to form a fixed cross section within said area and a control computer which handles a memory in which information on successive cross-sections of the three-dimensional product are stored, which cross-sections make up the three-dimensional product, where the control computer is intended to control said means for emitting energy so that energy is supplied to said selected areas, said three-dimensional product being formed by successive interconnection of successive vt formed cross-sections from powder layers successively applied by the powder dispenser.

In this case, the embodiment is not limited to fusing powder by a jet gun irradiating the surface of a powder bed. The product raw material can consist of any material which after a phase transition forms a solid body, for example solidification after melting or curing. The energy-emitting means can be an electron gun, a laser which is controlled by the working surface or alternatively by an energy-emitting means which can project a cross-section directly on the product bed.

This embodiment can otherwise be equipped with all the features that are described in relation to the previously described embodiment.

Claims (2)

1. 520 709 th. A device for producing a three-dimensional product, which device comprises a work table on which said three-dimensional product is to be built, a powder dispenser which is arranged to lay a thin layer of powder on the work table to form a powder bed, a jet gun for dispensing energy to the powder, thereby fusing the powder, means for controlling the beam emitted by the beam gun over said powder bed to form a cross section of said three-dimensional product by fusing parts of said powder bed and a control computer in which information on successive cross-sections of the three-dimensional product are stored, which cross-sections make up the three-dimensional product, where the control computer is intended to control said means for guiding the beam cannon over the powder bed according to a flow chart forming a cross-section of said three-dimensional body, said three-dimensional product being formed by successive assembly. kneading of successively formed cross-sections of powder layers successively applied by the powder dispenser, the device further comprising means for sensing surface properties of a surface layer located at the powder bed, characterized in that said means for sensing surface properties of a surface layer located at a powder bed and the product bed is located in a closed chamber, that the closed chamber has a transparent window and that the camera is arranged to register said surface property of the powder bed through this window. Device according to claim 1, characterized in that the transparent window is protected by a film, that said film is inputtably arranged along the window, a new film being fed, the transparency through film and windows being maintained.