3D printing process and system for manufacturing a rotor with imbalance compensation

Abstract

A 3D printing method for manufacturing a rotor, comprising a 3D printing device and a static scale, wherein a working area of ​​the 3D printing device for printing the rotor is arranged on a base plate of the scale, such that the working area can accommodate the manufactured rotor with a vertically oriented axis of rotation, and a print head of the 3D printing device is oriented such that the resulting rotor is substantially in a concentric position with respect to a reference point of the scale, wherein, after the application of a layer of the rotor by the printing device, the layer is weighed, its mass and the position of the center of gravity of the layer with respect to the reference point of the scale are determined and transmitted to an evaluation unit which is connected to the printing device and the scale for data exchange, wherein the evaluation unit determines an imbalance of the layer from the data received from the scale.in which the evaluation unit determines a compensation amount and compensation location from the imbalance and transmits this to the printing device, in which the printing device takes the imbalance into account when printing the subsequent layer by adding or removing mass.

Description

[0001] The invention relates to a 3D printing method in which a 3D printer is arranged on a static scale and an imbalance of a printed layer is measured during the printing of a rotor, as well as a system for carrying out such a method.

[0002] Rapid prototyping processes are well known and apply well-known layered manufacturing techniques in which an object (e.g. a metal casting mold, a prototype part, etc.) is progressively manufactured in a series of layers that are built up one on top of the other.

[0003] In conventional 3D printing devices, for example, a laser beam or electron beam is used to apply a sufficient amount of energy to a powdered starting material at a specific point, initiating a process such as melting or sintering of the starting material at the exposed location. This process leads to the bonding of the grains of the starting material. By scanning the laser beam or electron beam across the work area in a raster fashion, the product to be manufactured is created layer by layer. An example of such a use of an electron beam can be found in WO 2014 / 173662 A1.

[0004] US 6 036 777 A discloses a 3D printing prototyping process in which particles made of ceramic, metal or plastic are used, with successive layers of the particles and liquid binder being applied in the printing process.

[0005] US 5 064 463 A relates to a starting material for injection molding processes comprising a metal powder of magnesium, aluminum or titanium coated with cobalt, copper, iron, nickel, tin or zinc and dispersed in a binder.

[0006] DE 11 2005 002 040 B4 discloses a rapid prototyping process in which aluminum or magnesium objects can be produced layer by layer.

[0007] Furthermore, DE 10 2010 046 468 A1 discloses a generative manufacturing process using a metal powder.

[0008] US 2021 / 0 001 539 A1 discloses a method in which, after the application of a layer, excess resin is evenly distributed on the printed workpiece by rotation, thereby compensating for any imbalance.

[0009] Methods and devices for determining static unbalance are known, among others, from DE 10 2012 110 621 B3, DE 33 30 974 C2, and DE 10 2009 016 123 A1. In this method, a body to be examined is centered with great precision relative to the reference point of the scale, and its unbalance is determined.

[0010] Modern scales are usually equipped with an electronic control unit in the form of a microprocessor. This allows for corrections to be made within the measuring scale itself for errors caused by, for example, temperature, mechanical, or electrical components, and output measured values ​​that allow for easier further processing. Such scales therefore usually provide the total mass, the coordinates of the center of gravity, and other data requested by the user as initial values, which then form the basis for further calculations in the evaluation device.

[0011] The problem with existing manufacturing processes is that the resulting objects must subsequently undergo an imbalance measurement to detect any imbalances. The measured imbalance must then be corrected in a subsequent process step. This eliminates one of the advantages of 3D printing processes: fast and easy production.

[0012] The invention is based on the object of providing a manufacturing method in which any imbalance of the manufactured body can be taken into account during production.

[0013] The object is achieved by the features of claim 1. Preferred embodiments are described in the dependent claims.

[0014] The object is achieved according to the invention in that a 3D printing method for producing a rotor is provided, comprising a 3D printing device and a static scale, wherein a working area of ​​the 3D printing device for printing the rotor is arranged on a base plate of the scale, so that the working area can accommodate the produced rotor with a vertically aligned axis of rotation and a print head of the 3D printing device is aligned such that the resulting rotor is essentially in a central position relative to a reference point, in particular the axis center of the scale, in which, after the application of a layer of the rotor by the printing device, the layer is weighed, its mass and the position of the center of gravity of the layer in relation to the reference point of the scale are recorded and transmitted to an evaluation unit which is connected to the printing device and the scale for data exchange,in which the evaluation unit determines an unbalance of the layer from the data received from the scale, in which the evaluation unit determines a compensation amount and compensation location from the unbalance and transmits these to the printing device, in which the printing device takes the unbalance into account by adding or removing mass when printing the subsequent layer.

[0015] The calculation of the unbalance or the amount of correction and the correction location can be carried out using methods known to those skilled in the art, preferably by a corresponding program of the evaluation unit. The geometric data of the rotor to be manufactured are available to the evaluation unit. The method according to the invention makes it possible to consider one unbalance per layer and to compensate for it essentially immediately, so that the manufactured rotor essentially no longer has any unbalance after completion. This is especially true since this method achieves a precise unbalance determination. However, it can be advantageous to perform a random unbalance measurement after the completion of a series of rotors.

[0016] The evaluation unit can be a tablet or a computer with appropriately connected hardware and software and can be connected to the printing device or the scale via wireless or wired means for data exchange.

[0017] It is preferred that after each layer of the rotor is applied by the printing device, the imbalance is taken into account by adding or removing mass during the printing of the subsequent layer. According to this embodiment, after each layer is applied, an imbalance of the respective applied layer is determined and compensated for in the subsequent layer.However, it can also be advantageous that after a layer, in particular a previously defined control layer of the rotor, has been applied by the printing device, the layers applied so far are weighed, their mass and the position of the center of gravity of the layers in relation to the reference point of the scales are recorded and transmitted to an evaluation unit, wherein the evaluation unit determines an imbalance of the previous layers from the data received from the scales, determines a compensation amount and compensation location and transmits this to the printing device, whereupon the printing device takes the unbalance into account by adding or removing mass when printing the subsequent layer. In this embodiment, a control layer is defined depending on the rotor to be produced, the imbalance of which is determined and compensated for in the subsequent layer or layers.This has the advantage that rotor production takes less time, since the imbalance is only determined and corrected in isolated cases. Furthermore, it can be advantageous to provide compensation surfaces as cavities in the subsequent layer to be compensated, especially for later compensation. Such cavities can also be used as bores.

[0018] In a preferred embodiment, at least one surface structure, such as in particular a blade, a groove or another structure, is formed on the rotor.

[0019] It may be preferred for the rotor to be manufactured to have centering surfaces whose position relative to the reference point of the scale is measured by at least two electrical displacement sensors arranged at a defined angular distance from one another, and the resulting measurement data is fed to the evaluation unit, which calculates the eccentricity of the centering surface relative to the reference point of the scale. This eliminates the need for precise, centric positioning of the rotor to be manufactured relative to the reference point of the scale, and accepts inaccurate positioning of the print head. Displacement sensors can be used to measure the precise position of at least one centering surface, and the existing eccentricity of the center of the centering surface relative to the reference point of the scale can be taken into account and compensated for when determining the unbalance. This allows for precise unbalance determination with high repeatability.

[0020] The displacement sensors can be calibrated using a calibration block. The position of a rotationally symmetrical calibration block placed on the base plate is measured by the displacement sensors and the center of the calibration block is determined as the origin of a sensor coordinate system assigned to the displacement sensors. Subsequently, by weighing the calibration block using the scale, a vector is determined that describes the eccentricity of the sensor coordinate system with respect to a scale coordinate system whose origin lies at the scale's reference point. This calibration procedure is quick and easy to perform and ensures precise calibration of the scale. For example, non-contact sensors or sensors with movable sensing elements can be used as displacement sensors.

[0021] To determine the unbalance, in one embodiment, the total unbalance of the rotor can be calculated from the unbalance measurement of each individual disk and its axial position in the rotor by applying the lever law. Alternatively, in another embodiment, the complementary unbalance data in two planes can also be expressed as static unbalance and moment unbalance.

[0022] In order to align the individual position of the rotational axis of the rotor to be printed on the scale with the origin of the scale coordination system and thus enable improved unbalance measurement, a calibration model of the rotor to be produced with a known mass distribution and center of gravity can be printed to align the rotational axis of the rotor to be produced with the reference point of the scale before printing the rotor onto the base plate. The unbalance of the rotor is determined by the scale. A vector offset is calculated and from this the deviation of the symmetry axis of the calibration model from an origin of the scale coordinate system is determined. This can be achieved, for example, by printing points with a known distance and unbalance. Further designs are possible. This makes it easy to automatically adjust the 3D printer using the scale's coordinate system.The rotor's axis center then no longer needs to be precisely aligned with the axis center of the balance coordination system. The calibration model can also be referred to as a calibration body within the meaning of the invention.

[0023] The method according to the invention advantageously enables the use of various materials such as plastic, metal, or a combination thereof. In particular, it is advantageous if a material mixture comprising a material of a first strength and at least one material with a strength higher than the first strength is used as the material for 3D printing. The materials and their strength can advantageously be varied depending on the application. In this case, it is advantageous if a material transition from the material of the first strength to at least the material with the strength higher than the first strength is created in the axial and / or radial direction of the rotor.

[0024] The invention further relates to a system for carrying out the method, comprising a 3D printing device, a static scale having a base plate, measuring sensors arranged beneath the base plate, and an evaluation unit connected to both the static scale and the 3D printing device for data exchange. A working area of ​​the 3D printing device for printing the rotor is arranged on the base plate of the scale, and a print head of the 3D printing device is aligned such that the resulting rotor is substantially centrally positioned relative to a reference point of the scale. The previously explained advantages and embodiments of the method are analogously applicable to the system. The scale has, in particular, a base plate in the shape of a flat circular disk and possessing at least two degrees of freedom.The base plate is supported vertically by several, in particular three, measuring sensors, preferably designed as force sensors, located beneath the base plate. These sensors emit analog or digital electrical measurement signals. The measurement signals can be transmitted to the evaluation unit via a cable or wirelessly. Displacement sensors can also be provided, arranged, for example, radially around the base plate.

[0025] In addition to the actual 3D printer, the 3D printing device includes a rod assembly that can be arranged, for example, on the foundation of the static scale or reversibly connected to it.

Claims

[1] 3D printing method for producing a rotor, comprising a 3D printing device and a static scale, wherein a working area of the 3D printing device for printing the rotor is arranged on a base plate of the scale, so that the working area can accommodate the produced rotor with a vertically aligned axis of rotation and a print head of the 3D printing device is aligned such that the resulting rotor is essentially in a central position relative to a reference point of the scale, in which, after the application of a layer of the rotor by the printing device, the layer is weighed, its mass and the position of the center of gravity of the layer in relation to the reference point of the scale are recorded and transmitted to an evaluation unit which is connected to the printing device and the scale for data exchange, in which the evaluation unit determines an imbalance of the layer from the data received from the scale,in which the evaluation unit determines a compensation amount and compensation location from the unbalance and transmits this to the printing device, in which the printing device takes the unbalance into account when printing the subsequent layer by adding or removing mass. [2] 3D printing method according to claim 1, characterized by that after each layer of the rotor has been applied by the printing device, the imbalance is taken into account by adding or removing mass when printing the subsequent layer. [3] 3D printing method according to claim 1, characterized bythat after application of a layer, in particular a previously defined control layer of the rotor by the printing device, the layers applied so far are weighed, their mass and the position of the center of gravity of the layers in relation to the reference point of the scale are recorded and transmitted to an evaluation unit, wherein the evaluation unit determines an unbalance of the previous layers from the data received from the scale, determines a compensation amount and compensation location and transmits these to the printing device, in which the printing device takes the unbalance into account by adding or removing mass when printing the subsequent layer. [4] 3D printing method according to one of the preceding claims, characterized by that at least one surface structure is formed on the rotor. [5] 3D printing method according to one of the preceding claims, characterized bythat the rotor to be manufactured has centering surfaces whose position in relation to the reference point of the scale is measured by means of at least two electrical displacement sensors arranged at a defined angular distance from one another and the measurement data obtained are fed to the evaluation unit which calculates an eccentricity of the centering surface with respect to the reference point of the scale. [6] 3D printing method according to one of the preceding claims, characterized by that in order to adjust the axis of rotation of the rotor to be manufactured to the reference point of the balance, before the rotor is printed on the base plate, a calibration model of the rotor to be manufactured with a known mass distribution and known center of gravity is printed, the imbalance of which is determined by the balance, whereby a vectorial offset is calculated and from this the deviation of the axis of symmetry of the calibration model to an origin of the coordinate system of the balance is determined. [7] 3D printing method according to one of the preceding claims, characterized by that a material mixture of a material of a first strength and at least one material with a strength higher than the first strength is used as material for 3D printing. [8] 3D printing method according to one of the preceding claims, characterized by that a material transition from the material of the first strength to at least the material with the higher strength than the first strength is produced in the axial and / or radial direction of the rotor. [9] System for carrying out the method according to claims 1-8, with a 3D printing device, a static scale having a base plate, measuring sensors arranged under the base plate and an evaluation unit connected to both the static scale and the 3D printing device for data exchange, wherein a working area of the 3D printing device for printing the rotor is arranged on the base plate of the scale and a print head of the 3D printing device is aligned such that the resulting rotor is substantially in a centric position to a reference point of the scale.