The present invention is based on an operational method for a production machine,
The present invention is furthermore based on a production machine, wherein the production machine has a pressure vessel, a conveyor line with a feed point and a discharge point, an extrusion head with a nozzle, a manipulator and a gas compressor,
Such an operational method and the associated production machine are used, for example, in the context of additive manufacturing—colloquially often referred to as FDM=Fused Deposition Modeling or as FFF=Fused Filament Fabrication. In this method, a smeltable material—as a rule, a plastic—is supplied to an extrusion head as granules or powder, melted there and applied to a structure in a punctiform manner via a nozzle of the extrusion head. This creates a product layer by layer.
In the context of additive manufacturing, the material to be processed is supplied to the extrusion head during the manufacturing process. This results in the necessity to supply the conveyed goods continuously to the continuously changing position of the extrusion head—sometimes even against gravity. The conveyed goods are, generally speaking, a dry, disperse solid. Such substances can, in particular, be conveyed by means of mechanical conveying (for example, via feed screws). This type of conveyor has the advantages of good dosing and the possibility of continuous operation. A disadvantage, however, is that the grains of the conveyed goods are often very small, resulting in purely mechanical solutions being subject to the risk of jamming. As an alternative to mechanical conveying, the conveyed goods can also be conveyed pneumatically. In the case of pneumatic conveying, the grains of the conveyed goods are conveyed by means of an air or other gas flow through pipes over greater distances (sometimes several 100 m). In the case of pneumatic conveying, a distinction is in principle made between suction conveying and pressure conveying. In the case of suction conveying, the conveyor line is located on the negative pressure side of the gas compressor, in the case of pressure delivery on the positive pressure side of the gas compressor. In the case of pressure conveying, the reservoir, via which the conveyed goods are fed into the conveyor line, is also under pressure. It is therefore designed as a pressure vessel. In the pneumatic transport of conveyed goods (in the context of the present invention, these are powder and granules), suction conveying usually takes place. Suction conveying is usual, in particular in the supply of conveyed goods to plastic injection molding machines. In suction conveying, relatively large, bulky components are necessary, which must be arranged in the region of the discharge point. In the case of conventional plastic injection molding machines operated in a stationary manner, these components can be easily arranged. In additive manufacturing, on the other hand, the extrusion head is moved dynamically. If, in such a situation, the associated components for the suction conveying were to be arranged on the extrusion head, this would lead to reduced precision, to a reduced dynamic and to a restriction of the freedom of movement of the extrusion head.
A 3D-printing system and a 3D-printing method are known from EP 3117982 A1, in which a print head with a nozzle is moved relative to a building platform. Pellets are extruded in the print head which are fed to the print head by means of a flexible line using compressed air from a reservoir.
A method and a device for the pneumatic conveying of bulk material are known from the publication DE 19943504 A1, in which the bulk material is fed through a conveying line by means of a sluicing element in at least one place of consignment into an adjustable conveyor gas flow and is transported in the shape of discrete bulk material plugs spaced apart from one another by padding of conveyor gas from the place of consignment to at least one destination.
An automation system for an additive manufacturing process is known from WO 2016/088042 A1, which includes, inter alfa, a conveyor belt and a movable material print head. A filament to be printed is fed to the print head by means of a flexible line from a reservoir.
The object of the present invention is to provide possibilities by means of which a reliable supply of the extrusion head with conveyed goods can be ensured in a simple and efficient manner.
This object is achieved by an operational method for a production machine with the features of claim 1. Advantageous embodiments of the operational method are the subject of the dependent claims 2 to 9.
According to the invention, an operational method of the type mentioned at the outset is embodied such that,
The basic idea of the present invention therefore consists of exerting a compressive force from the feed point on the conveyed goods conveyed in the conveyor line. In particular, there is therefore no suction of the conveyed goods originating from the discharge point, whereby a tensile force would be applied to the conveyed goods in the conveyor line. Implementation as a pressure supply makes it possible in particular to set a conveying state in the conveyor line in a targeted manner and thereby to adapt the conveying process to the conveyed material to be conveyed in a targeted manner.
The positive pressure is temporarily applied to the conveyed goods by means of the gas compressor in order to feed the conveyed goods into the conveyor line while bypassing the conveyor line via a first valve.
The feeding of the conveyed goods into the conveyor line is thereby rendered particularly efficient in that during the pressurization of the pressure vessel with the positive pressure, a second valve which is arranged in the conveyor line between the feed point and the gas compressor is closed.
The conveyor gas should be removed from the conveyed mass flow as completely as possible at the discharge point to enable the conveyed goods to be supplied to the extrusion head in a state which is as free from gas as possible. A particularly efficient embodiment of the discharge point is provided in that the discharge point forms the last part of the conveyor line and is designed as a hose which is permeable to the conveyor gas.
In the conveying of conveyed goods, that is to say, granules, powders and similar substances, by a conveyor gas, various types of conveying are known. These are explained in turn below. In the context of the following embodiments, it is initially assumed that the conveyor line runs horizontally.
The conveyor types explained above for the case of horizontal conveying also occur in a similar manner in the case of vertical conveying. This is well known to those skilled in the art.
Pure airborne delivery is also often referred to as dilute flow conveying, for the other types of conveying the term dense phase conveying is also often used as a collective term. With an airborne delivery, as a rule only relatively low loads can be achieved, which is usually 15:1 maximum. Loading is defined as the ratio of transported mass of conveyed goods and conveyed mass to conveyor gas. Airborne delivery is most often realized in practice. The reasons for this are the low pressure differentials required and the simplicity of ensuring a reliable, stable operating state. In the context of the present invention, however, dense phase conveying, in particular, plug conveying, is preferably carried out in the conveyor line. Considerably larger loads can be realized in dense flow conveying, for example of 100:1 or above, sometimes even up to 400:1.
In the case of pneumatic conveying, different pressure ranges are also differentiated. The pressure range between 0.2 bar and 1 bar is usually referred to as medium-pressure conveying. The use of pressures below 0.2 bar is referred to as low-pressure conveying, the use of pressures above 1 bar (as a rule, up to 10 bar maximum) is referred to as high-pressure conveying. In low-pressure conveying, fans are used as gas compressors. The flow velocity of the conveyed gas can be up to 30 m/s. As a rule, loading is up to 5:1, In medium-pressure conveying, rotary blowers are usually used. The flow velocity of the conveyed gas is usually between 15 m/s and 40 m/s. As a rule, the load is between 5:1 and 20:1, In high-pressure conveying, screw compressors or piston compressors are required as gas compressors. The flow velocity of the conveyed gas may be relatively low, for example approx. 2 m/s to approx. 10 m/s. Loading can reach values above 100:1, in particular, up to 150:1 and in some cases even up to 4100:1. In the context of the present invention, high-pressure conveying is preferably realized. Positive pressure is therefore preferably above 1 bar.
The average grain size is preferably at least 0.5 mm. An average grain size of 2.0 mm—better 1.5 mm and even better 1.0 mm—should not be exceeded, however. The grains are preferably spherical in shape. In the case of deviations from the exact spherical shape, the statistical variance of the distance of individual surface points from the center of gravity of the respective grain should be at most 10%. Furthermore, the average grain size should preferably be as uniform as possible. In particular, the statistical variance (lσ-variance) of the average grain size should be 20% maximum,
In order to ensure stable operation, a conveying state in the conveyor line is preferably detected by means of at least one sensor. In this case, the conveying state in a control device is compared with a target conveying state. The feeding of the conveyed goods into the conveyor line and/or the conveying of the conveyed goods in the conveyor line can be regulated by the control device as a function of the comparison.
For example, pressure sensors at certain points on the conveyor line can be used to record the respective local pressure in order to record the conveying state. From the evaluation of the pressure or its chronological sequence or (in the case of several detection points) of the local sequence or the chronological-local sequence, the conveying state can then be concluded. Controlling the feeding of the conveyed goods into the conveyor line can be done, for example, by varying the rhythm with which feeding takes place. In the simplest case, the period during which feeding takes place can be varied. In order to influence the distribution of the conveyed goods in the conveyor line, it is possible, for example, to inject gas into the conveyor line at predetermined points in addition. For this purpose, corresponding valves can be provided by way of which the supply of conveyor gas to the predetermined locations can be adjusted. A gas line (in other words, a line in which only the conveyor gas but not the conveyed goods is conveyed) is preferably laid in parallel with the conveyor line for this purpose.
The object is further achieved by a production machine with the features of the claim 10. Advantageous embodiments of the production machine are the subject of the dependent claims 11 to 15.
According to the invention, a production machine of the type mentioned at the outset is characterized in that,
The advantageous embodiments of the production machine essentially correspond to those of the operational method.
The properties, features and advantages of this invention described above and the manner in which these are achieved will become dearer and more readily comprehensible in connection with the following description of the exemplary embodiments which are explained in more detail in connection with the drawings. In a schematic representation, the drawings show in:
According to
In the framework of the operation of the production machine, initially a pressure vessel 4, for example an autoclave, is filled from a reservoir 5, for example a silo, with a conveyed material 6. As a rule, the pressure vessel 4 is arranged in a fixed position. As a rule, the conveyed goods 6 are a plastic material. Alternatively, in individual cases it can be a metal. The conveyed goods 6 consist of a plurality of grains 7. After filling the pressure vessel 4, the pressure vessel 4 and the reservoir 5 are shut off. Furthermore, a positive pressure p is applied to the pressure vessel 4. The pressurization of the pressure vessel 4 with the positive pressure p takes place via a gas compressor 8 of the production machine which applies positive pressure p to a conveyor gas 9. As a rule, positive pressure p is above 1 bar, for example, between 1.5 bar and 10 bar. As a rule, the conveyor gas 9 is air. However, it may alternatively be another gas, for example a protective gas. The gas compressor 8 should have as steep a characteristic curve as possible (high increase in the pressure loss as a function of the velocity of the conveyed gas 9 emerging from the gas compressor 8). For example, the gas compressor 8 can be designed as a rotary blower or as a de Laval nozzle fed from a conventional compressed air network,
The conveyed goods 6 are fed from the pressure vessel 4 into a conveyor line 11 of the production machine at a feed point 10. The feed point 10 is located in the vicinity of the pressure vessel 4. The feeding of the conveyed goods 6 into the conveyor line 11 takes place in that the positive pressure p is temporarily applied to the conveyed goods 6—see
From the feed point 9, the conveyed goods 6 are fed via the conveyor line 10 to a discharge point 13. For this purpose, the conveyor gas 9 can be compressed into the conveyor line 11 by means of the gas compressor 8 in the region of the feed point 10. At the discharge point 13, the conveyed goods 6 are discharged out of the conveyor line 11 and supplied to the extrusion head 1. Before feeding and supplying, however, the conveyor gas 9 leaks out of the conveyor line 11 at a separation point 14. As a result, the conveyed goods 6 are fed to the extrusion head 1 virtually free of conveyor gas 9. The leaking takes place automatically because of the positive pressure p. Active suction of the conveyed gas 9 is not necessary,
The separation point 14 can, for example, in accordance with the representation in
Depending on the embodiment of the production machine and arrangement of its individual components, the conveyor line 11 can be relatively short in individual cases (length of only a few meters). It is also possible, however, for the conveyor line 11 to be of a considerable length, for example several 100 m or even more than 1000 m.
In accordance with the representation in
The conveyed goods 6 are plasticized in the extrusion head 1. For example, they can be melted by means of a heating device (not shown). The extrusion head 1 also has a nozzle 16. After plasticization, the conveyed goods 6 (which now no longer comprise grains 7 but are a plasticized mass) are extruded via the nozzle 16 in a punctiform manner. The plasticized mass is applied to a substrate 17 (which may in principle be of any nature). During the extrusion of the plasticized conveyed goods 6 (or the plasticized mass), the extrusion head 1 is moved dynamically by means of the manipulator 2. As a result, the desired structure is built up gradually. Due to the dynamic method of the extrusion head 1, even during the conveying of the conveyed goods 6, the conveyor line 11 is designed as a flexible hose at least in certain sections. Alternatively, or in addition, an embodiment may be possible with pipe sections which are connected to one another by means of joints.
In accordance with the representation in
In accordance with the representation in
In accordance with the representation in
The conveying state F is supplied to a control device 19. The control device 19 can, for example, be realized as a software block within the automation device 3. In the control device 19, the conveying state F is compared to a target conveying state P. Depending on the comparison, the feeding of the conveyed goods 6 into the conveyor line 11 and/or the conveying of the conveyed goods 6 in the conveyor line 11 is regulated by the control device 19.
For example, the control device 19 can vary the periods at which feeding takes place—that is to say, the total of the periods T1 and T2. Variation can take place alternatively with or without variation of the ratio of the periods T1 and T2 in relation to one another. To the extent necessary and appropriate, the control device 19 can alternatively or in addition also vary the periods T3 and T4. Alternatively, or in addition, it is possible in addition to inject conveyor gas 9 into the conveyor line 11 at predetermined points. A gas line 20 is preferably laid parallel to the conveyor line 11 for this purpose. Only conveyor gas 9 is conveyed in the gas line 20, but not conveyed goods 6. The gas line 20 and the conveyor line 11 are connected to one another at predetermined points via valves 21. The additional conveyed gas 9 is injected by means of corresponding actuation of the valves 21 by the control device 19. Alternatively, or in addition, it is possible to vary the positive pressure p by means of appropriate actuation of the gas compressor 8.
If, in the context of the embodiments explained above the conveyed goods 6 are completely fed out of the pressure vessel 4 into the conveyor line 11 and conveyed to the extrusion head 1, the conveying of the conveyed goods 6 is briefly interrupted. After the positive pressure p has been reduced, the pressure vessel 4 is opened, refilled from the reservoir 5 and dosed again. Conveying of the conveyed goods 6 is then recommenced. Alternatively, it is possible to provide several pressure vessels 4 which can be connected in parallel or in series. By means of these embodiments it is possible to carry out conveying of the conveyed goods 6 almost continuously.
In summary, the present invention thus relates to the following facts:
Conveyed goods 6 consisting of grains 7 are fed from a pressure vessel 4 into a conveyor line 11 at a feed point 10, conveyed from there to a discharge point 13 via the conveyor line 11, discharged out of the conveyor line 11 and supplied to an extrusion head 1. The conveyed goods 6 are plasticized in the extrusion head 1 and then extruded in a punctiform manner via a nozzle 16 of the extrusion head 1. The extrusion head 1 is moved dynamically by means of a manipulator 2 during the extrusion of the plasticized conveyed goods 6. A conveyor gas 9 is compressed into the conveyor line 11 in the region of the feed point 10 by means of a gas compressor 8. It leaks out of the conveyor line 11 at a separation point 14 in the region of the discharge point 13.
The present invention has many advantages. By conveying the conveyed goods 6 through the conveyor line 11 by means of compression (as opposed to suction), simple conveying of the conveyed material 6 is made possible without adversely affecting the operation of the extrusion head 1 (in particular its dynamic positioning including the static and/or dynamic positioning accuracy). As a result of dense phase conveying, energy-efficient, low-wear operation of the conveyor line is obtained. This applies, in particular, in the case of plug conveying. Very high loads (as a rule, of at least 100:1, in extreme cases up to 400:1) can be conveyed over long conveyor lines (in some cases up to several km). In particular, in an application in a printer park with a plurality of production machines, longer conveyor lines 11 can be used as a result which are fed with conveyed goods 6, for example, from a common pressure vessel 4. Under certain circumstances, additional treatments of the conveyed goods 6 can take place within the conveying section, for example drying or preheating. It may even be possible to feed different conveyed goods 6 from a plurality of pressure vessels 4 sequentially into the conveyor line 11 in a controlled manner and thereby supply the extrusion head 1 with a premixed mixture of conveyed goods 6 which need only be melted in the extrusion head 1 but need no longer be further mixed.
Number | Date | Country | Kind |
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17157668.9 | Feb 2017 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/052690 | 2/2/2018 | WO | 00 |