RU2725465C2 - 3d printer - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to three-dimensional printing of composite volumetric parts from metal by layer-by-layer synthesis and can be used in various fields of machine building. Device is characterized by that feed mechanism of initial material, made in form of wire with sectioned profile of repeating sections, including bulges and thin connecting sections, wherein cross-section area of connecting sections is less than cross-section area of bulges of not less than 10 times, and their length is not more than longitudinal size of bulges, is made with possibility of step-by-step supply of initial material and accurate positioning in given point of space of next section of wire, and the energy beam focus is oriented to the next section of the wire positioned in a given point of space.EFFECT: technical result is possibility of obtaining objects of any shape with preservation of high speed of printing and high surface cleanliness without additional machining.1 cl, 2 dwg

Description

The invention relates to means for manufacturing volumetric labor-intensive parts and structures made of metal by layer-by-layer synthesis and can be applied in various branches of mechanical engineering.

Three-dimensional (3D) printing (layer-by-layer synthesis) is the process of manufacturing a three-dimensional solid object from a digital model. 3D printing is typically achieved using an addition process in which successive layers of material are stacked in different shapes.

Three-dimensional (3D) printing or additive manufacturing is defined as “a method of joining materials in which there is a layer-by-layer creation of an object according to a given digital three-dimensional model”.

However, there are problems with 3D printing, in particular regarding the use of metallic materials for printing. Direct feed technologies are divided into two groups: powder feed and wire feed.

Despite the high accuracy and low surface roughness of the parts obtained for the production of large products, powder feeding technologies are not applicable due to the low construction speeds (powder - 10 g / min, wire - 330 g / min for stainless steel).

The price of the powder is significantly higher than the price of the wire (titanium powder -200 USD / kg, titanium wire -60 USD / kg), and powder loss during printing can be up to 50%.

Products printed with a powder supply, as a rule, have a higher porosity (0.1-2% depending on the material).

Also, a significant drawback of this feeding method is the high requirements for labor protection when working with fine powders and the environmental aspect.

3D printing devices (3D printers) that use wire as a consumable material, depending on the source of concentrated energy, can be divided into laser, electron beam and electric arc.

3D printers using laser beams as an energy source are characterized by increased accuracy compared to other methods using wire, but have a low energy efficiency of about 2 ... 5%.

3D printers using electron-beam additive surfacing have more significant energy efficiency - 15 ... 20%, but initially such printers operate in a vacuum environment. Accordingly, the size of the parts produced by electron beam welding with wire is limited by the size of the vacuum chamber (taking into account the equipment placed in it). In addition, the need to work with vacuum equipment imposes certain difficulties.

Compared to laser and electron-beam surfacing, arc welding of arbitrary shapes, involving an electric arc welding with a consumable or non-consumable electrode in a protective gas, has significant energy efficiency. However, the high energy efficiency of the arc does not make electric arc welding devices popular, because the arc has high instability, the mode of operation of which depends on many parameters, including the properties of the material. Working with an arc requires a protective atmosphere of inert gas.

Technologies using electron beams in terms of energy efficiency and accuracy of construction are between laser and arc, and are optimal for the construction of large-sized products with sufficiently high accuracy.

All metal wire additive surfacing devices have common disadvantages:

- residual stresses and deformations of manufactured objects caused by intense heating,

characteristic "stepped" surface, i.e. manufactured objects have a low surface finish and, as a consequence, a relatively low manufacturing accuracy,

- all devices of additive printing with wire feed are characterized by a simplified geometry of products, which is caused by the fact that it is impossible to abruptly interrupt the flow of molten metal, the molten drop will stretch behind the head, creating unnecessary connections not provided by the program, i.e. printing with wire is used in the manufacture of parts with a closed path. Complex objects usually do not print with wire.

The prior art technical solutions aimed at reducing the above disadvantages of 3D printers using wire for printing.

So in the 3D printing device according to patent US 20170144242, the required accuracy of the manufactured object is ensured by the refinement of the manufactured objects in the process of printing the object. For this, the 3D printing device directly contains a 3D printer, which includes an energy source, a movable platform on the surface of which a three-dimensional object is manufactured; a source material supply system, a drive device for moving the platform and / or a source material supply system in accordance with a 3D model of an object, a computer system that is part of a device that stores 3D models of objects (database) and a tool that is capable of removing metal deposited with an energy source during the manufacture of metal parts without removing the part from the platform.

Thus, high surface cleanliness and accuracy of the manufactured object in the described device is obtained by introducing into the device an additional tool (for example, surface machining heads), which are controlled by a computer, which leads to a significant complication and cost of the device and an increase in manufacturing time.

A 3D printing device according to GB 2539485 is known, in which, to improve the quality of manufacturing of objects, a pre-formed, for applying to the object, source material in the form of wire or balls is used. The device described in the patent contains an assembly platform and a print module including an ultrasonic head for surfacing the source material on the fabricated object, a source material supply device, which is preformed balls or wire, and a controller for processing the print file. Surfacing is carried out by an ultrasonic head in direct contact with the source material, which is supplied by the device directly to the assembly platform, which allows you to hold the balls of the source material at predetermined points.

The 3D printing device of GB 2539485 has the following disadvantages:

- surfacing is carried out by ultrasonic method. In this case, friction and a slight plastic deformation of the metal layer in the weld zone occur. The melting of the entire volume of the wire or ball portion does not occur and it is difficult to obtain high uniformity in the volume of the final product. Therefore, using such a device, only small parts can be surfaced.

Despite the fact that the alleged invention claims the form of the starting material, by the number of common features closest to the claimed device is the technical solution described in patent US 7168935, which is selected as a prototype.

A device is known according to patent US 7168935, using a wire for printing, and as an energy source an electron beam and containing:

a vacuum chamber in which the assembly platform, a print module with a feed mechanism for the source material (wire), an electron beam forming device, a drive device for moving the print module and / or assembly platform in accordance with the 3D model, a computer system in which 3D models of the manufactured an object that controls the movement of the print module and / or assembly platform.

The device described above implements a method for layer-by-layer creation (growing) of a metal object based on the use of an electron beam that focuses on a metal source (wire) continuously supplied to the beam (electron beam) in a vacuum. The electron beam melts the metal on the rotating surface of the platform, laying it in layers in accordance with the 3D model of the object stored in the computer's memory. The process continues until the complete formation of the object. The 3D printing process in the device according to patent US 7168935 is carried out in a vacuum chamber.

The described device is ineffective in the manufacture of objects of complex shape since it is impossible to abruptly interrupt the flow of molten metal, the molten drop will stretch behind the print module, creating unintended extra connections between the elements of the object. Using the described printer, it is possible to obtain objects with simplified geometries. In addition, using the device described above, it is impossible to realize a high surface purity of the fabricated object due to the unstable droplet sizes of the molten source material.

Thus, using the device described above, it is impossible to produce objects of complex shape with good surface cleanliness. After manufacturing, objects require machining.

The aim of the invention is the creation of a 3D printing device with metal, which allows to obtain objects of any shape, while maintaining high printing speed and higher surface finish without additional machining.

To do this, in a 3D printing device, including a camera in which a platform is placed on the surface of which a three-dimensional object is made, a print module with a source material supply mechanism, an energy beam forming device, a drive device for moving the platform or print module in accordance with the 3D model of the object, a computer system in which 3D models of objects are stored (database), the source material used is a wire with a sectioned profile made in the form of repeating sections, including thickenings and thin connecting sections, the cross-sectional area of the connecting sections is less than the cross-sectional area of the thickenings less than 10 times, its length is not more than the longitudinal size of the thickenings, and the feed mechanism of the source material is made with the possibility of step-by-step supply of the source material and precise positioning at a given point in the space of the next section of the wire, and the focus of the energy beam oriented to the above, positioned at the right point in space, the next section of wire.

It is possible to produce objects of any shape using the inventive device due to the fact that the starting material is supplied in normalized doses in the form of a molten metal drop, printing can be interrupted at any point, just as printing can be started at any point on the object. Moreover, the specified ratio between the cross-sectional area of the thickening and the cross-sectional area of the thin part provides on the one hand sufficient flexibility and strength of the sectional wire, on the other hand, the thermal conductivity of the thin part should be insufficient for melt thickening of the next section.

The length of the thin section is selected from the following conditions:

- on the one hand, the distance between the thickenings of the sections should be sufficient so that only one bulge is in the focus of the beam (one section of wire),

- but increasing the distance between the bulges leads to a decrease in the feed rate of the source material, which reduces the printing speed.

The amount of molten starting material is determined by the size of the thickening of the wire section and does not depend on the time of the beam (since the starting material is supplied step by step). When the beam acts on the source material, only that section melts on the thickening of which the beam is focused, so from drop to drop the amount of molten material remains constant. The thin connecting part of the section practically does not change the mass of the drop. The melt zone of the source material on the platform is smaller compared to the prototype, the size of this zone being controlled and repeated from drop to drop, which significantly reduces the likelihood of molten material going beyond the size of the object, thereby increasing the accuracy of the fabricated object and reducing its surface roughness (increasing the purity surface).

High printing speed, (not less than in the prototype) is due to the fact that the thickening melt occurs faster than the usual wire melt (at the same power of the energy beam). This is because the power transmitted along the wire due to thermal conductivity is determined by the formula:

где

Where

- λ is the thermal conductivity of the material;

- S _wire - wire cross-sectional area;

- длина проволоки;-

- wire length;

- (T ₂ -T ₁ ) is the temperature difference at the ends.

Thus, with a decrease in the cross-sectional area and an increase in the length of the wire, the power transmitted along the wire decreases. So for a copper wire with a diameter of 2 mm, the power lost due to is about 900 watts. In the assessment, it was assumed that the wire is substantially cooled at a distance of 1 mm from the melt zone. Thus, the thin connecting part has low thermal conductivity and the beam power is not transmitted to the next section, i.e. not scattered along the length of the wire, as in the prototype, but the whole is used to melt the thickening section. Therefore, the melt is faster.

In addition, due to the fact that at any time only one thickening of one section is heated, the intensity of the preliminary heating of the starting material is reduced, thereby reducing residual stresses and deformation of the manufactured objects.

In the inventive device, an electron beam or a laser beam can be used as an energy beam.

When using an electron beam as an energy beam, the object is manufactured in a vacuum medium, and when using a laser beam, as a rule, in an inert gas medium, but can also be in a vacuum, or even the atmosphere for some metals.

The drawings show the claimed technical solution:

FIG. 1 3D printer

FIG. 2 Source material feed mechanism.

The 3D printer contains a camera 1, in which a platform 2 is placed, on the surface of which a three-dimensional object 3 is made, a printing module, which includes an energy beam forming device 4 and a source material supply mechanism 5 with a sectioned wire 6, moved by means of a gear wheel 7, mechanically connected with a stepper motor 8, and a pressure roller 9, spring-loaded with a spring 10, a drive device for moving the print module 11 in accordance with the 3D model of the object, a computer system 12 that controls the printing process.

When used as an energy beam of an electron beam, the device 4 forms an electron beam, and can be performed as described in patent CN 105655215 A.

When using a laser beam in a 3D printer as an energy beam, the chamber is usually filled with inert gas (but may have a vacuum, and even an atmosphere for some metals), and the energy beam forming device can be performed as described in US 6143378 A.

The device operates as follows

The operation of the device begins with the creation of a digital model of the manufactured object by loading into the computer system 12. A platform 2 is installed in the vacuum chamber 1. The sectioned wire 6 is inserted into the feed material 5 and the initial positioning of the section thickening relative to the focus of the electron beam is performed.

The feed material feed mechanism provides step-by-step feed of the source material with precise positioning at a given point in the space of the next wire section. The wire feed is as follows:

- initial positioning is carried out programmatically. The initial positioning of the wire involves installing a thickening section in the focus of the beam.

- further on command from the computer system 12, a command is issued to drive the feed mechanism of the source material 8 (in the described device it is a stepper motor), the drive rotates the gear wheel 7 by a predetermined angle, the teeth of the wheel capture the next section of wire and advance it. The pressure roller 8 eliminates the possibility of deflection of the wire, thereby ensuring accurate positioning of the wire section in space. And this, in turn, ensures that the thickening of the section always falls into the focus of the beam, and at the time of the melt only one thickening will be in focus (one section)

Further, depending on the size of the wire sections and the material of the wire, the size of the focal spot of the electron beam, its energy and current are programmatically set. The necessary vacuum is created in the chamber, on the order of 10 ^-2 Pa. The drive unit for moving the print module 7 sets the print module to its initial position (print start point) in accordance with the digital model of the object. The beam forming device 4 forms a beam, the section is molten, and a molten drop of metal falls on the platform 2, where the object is formed. After melting, the beam-forming device 4, upon a signal from the computer system 12, turns off the beam, the drive unit of the print module 11 moves it in accordance with the 3D model, and the feed mechanism 5, controlled by the computer system 12, feeds the next section of wire into the beam focus.

The electron beam enters the center of the thickening section and heats it. The section melts away from the wire and falls onto the platform. Heat from the molten section of the wire is transferred to the neighboring section through a thin section of the wire (until it breaks), it is not enough to melt the next section of the wire. Thus, the printing of the object is carried out in separate metered drops that do not stretch behind the print module.

Tests of the prototype showed that with the claimed dimensions of the sectional wire, namely, the cross-sectional area of the connecting sections is less than 10 times the cross-sectional area of the bulges, and its length is not more than the longitudinal size of the bulges-provides

- at the time of the melt, the location in focus of only one section,

- precise positioning at a given point in space relative to the created part or beam focus of the next wire section.

Using an electron beam as an energy source allows the metal to be melted with high productivity (speed) and energy efficiency with high accuracy and repeatability.

Using a laser beam as an energy source allows you to create large-sized metal objects in a shielding gas or atmosphere with high accuracy and repeatability.

The 3D printer device proposed in the application with the source material in the form of a partitioned wire and using an energy beam retains the advantages and eliminates the disadvantages characteristic of known devices for the additive manufacturing of objects. The device allows to significantly increase the accuracy of the construction of the object and reduce the roughness of the manufactured object. At the same time, the claimed device using sectioned wire allows printing complex metal products with thin partitions, channels, cellular structure, etc. from metal wire. This will significantly reduce the cost and increase the demand for additive manufacturing of metal products in most metal-intensive industries.

Sources of information taken into account during the examination

1. Patent No. US 20170144242 op. 05/25/2017 IPC B23K 9/042 "3D printer and method of metal printing"

2. Patent No. GB 2539485 op. 12/21/2016 IPC V23K 20/10, B33Y 30/00 “3D printer and corresponding printing method”

3. Patent No. US 7168935 op. 01/30/2007 IPC V23K 15/00 “Device and method for forming a three-dimensional object

4. Patent US 6143378 op. 11/07/2000 IPC В29С 67/00

Energy deposition process with feed wire

5. Patent CN 105655215 op. 06/08/2016 IPC H01J 29/48

An electron gun for producing an electron beam in additive manufacturing equipment.

Claims (1)

A 3D printer for printing an object from a metal sectioned wire, including a camera in which a platform is placed, on the surface of which a three-dimensional object is made, a print module with a feed mechanism, an energy beam forming device, a drive device for moving the platform or print module in accordance with a 3D model of the object, a computer system in which 3D models of objects are stored in the form of a database, characterized in that the source material used is a wire with a sectioned profile made in the form of repeating sections, including thickenings and thin connecting sections, transverse area the cross-section of the connecting sections is less than 10 times less than the cross-sectional area of the bulges, and their length is not more than the longitudinal size of the bulges, and the feed material supply mechanism is configured to step-by-step feed the raw material and accurately position at a given t point of space of the next section of wire, and the focus of the energy beam is oriented to the next section of wire, positioned at the right point in space, mentioned above.

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