EP3863785A1

EP3863785A1 - Heating device with infrared radiating elements

Info

Publication number: EP3863785A1
Application number: EP19786559.5A
Authority: EP
Inventors: Oliver Weiss; Holger Zissing; Johannes Lohn; Peter Koppa
Original assignee: Heraeus Noblelight GmbH
Current assignee: Heraeus Noblelight GmbH
Priority date: 2018-10-12
Filing date: 2019-10-09
Publication date: 2021-08-18
Also published as: CN112805102A; CN112805102B; WO2020074571A1; US20220072786A1; JP2022504738A; DE102018125310A1; JP2024079729A

Abstract

The invention relates to a heating device for heating a powder during the production of a 3D moulded part, comprising an IR radiating element and a housing, in which a construction space is provided, which is limited from below by a construction platform for receiving the moulded part, which rests on a carrier plate. In order to provide a corresponding heating device with an IR radiating element for heating a powder in the production of the 3D moulded part in a construction space, which guarantees an optimised heat transfer to the sintering or melting powder with a particularly homogeneous temperature distribution, according to the invention, a separating wall made of a material that is transparent for IR radiation is arranged between the construction space and the infrared radiating element.

Description

Heating device with infrared emitters

description

Technical field

The present invention relates to a heating device for heating a powder during the production of a 3D molded part, with an IR radiator and with a housing in which a space is provided which is facing downwards from a

Construction platform for receiving the molded part is limited, which rests on a carrier plate.

Furthermore, the invention relates to a method for producing a 3D molded part using the heating device.

Three-dimensional (3D) molded parts are usually produced using the layered structure technique and solidifying a loose powder by means of so-called selective laser beam sintering or laser melting. The term SLS is also used for selective laser sintering, for plastic powders, or SLM for selective laser melting, for metal powders. When heating the powder, be it a plastic powder or a metal powder, a homogeneous temperature distribution is required to avoid thermal stresses (cracks, warping) in the finished molded part.

Infrared emitters (short: IR emitters) in the sense of the invention are irradiation units with usually several emitter tubes, so-called fluorescent tubes, made of quartz glass, in which a heating filament (also known as a filament) is arranged. The heating filament determines the radiation spectrum of the IR radiator.

IR-A radiation has wavelengths in the range from 0.78 pm to 1.4 pm; the wavelengths of IR-B radiation are in the range from 1.4 pm to 3.0 pm, those of IR-C radiation in the range from 3 pm to 1000 pm. State of the art

The production of a 3D molded part from a plastic sinter powder is known from DE 10 2015 006 533 A1. To heat the construction platform, a silicone-based, flat heating foil with electrical resistance heating is used, but with which temperatures hardly higher than 200 ° C are reached. This heating power is sufficient for heating plastic sinter powders in the manufacture of 3D molded parts, but not in the manufacture of metallic 3D molded parts, which require significantly higher process temperatures overall. In addition, are on the side of the construction platform

attached spotlights preferred.

Instead of the silicone-based heating foil, DE 10 2015 006 533 A1 alternatively proposes to temper the building platform or the sinter powder on it by means of heating coil through which heating oil flows and which are arranged below the mounting plate and on the side of the building platform. The temperature that can be achieved with the heating coils is not significantly higher than 200 ° C and the heat transfer to the sinter powder is inefficient (slow) due to this construction. A reservoir and, if necessary, a pump must also be provided for the tempering oil in order to convey the tempering oil through the heating coil. Overall, these additional devices result in a complex heating device without an increase in efficiency in terms of rapid heat transfer or an extended temperature range being achievable.

DE 10 2012 012 344 B3 discloses a method and a device for producing workpieces by beam melting powdery material. In order to reduce the process-related temperature gradients, the powdery building material is preheated instead of with a platform heater by heating elements which are arranged on or in the side walls of the storage chamber and / or the process chamber.

DE 10 2015 211 538 A1 describes a construction cylinder arrangement for a

Machine for the layer-by-layer production of three-dimensional objects

Laser sintering or melting of powdered material is known in the a layer of the powdery material is heated with a heater with infrared heating coils.

Technical task

The invention has for its object to provide a heating device with an IR radiator for heating a powder in the manufacture of a 3D molded part in a construction space, which ensures an optimized heat transfer to the sintered or melt powder with a particularly homogeneous temperature distribution. The heating device should also function as a high-temperature heating device and enable simple retrofitting in an existing installation space, so that the heating device can be used in corresponding processes for producing a 3D molded part.

General description of the invention

This object is achieved in that between the

Installation space and the infrared radiator is a partition made of a transparent material for IR radiation.

The installation space is separated from the infrared radiator by a partition made of a material transparent to IR radiation.

At least one IR radiator is attached to the outside of the partition and emits the IR radiation in the direction of the powder or the 3D molded part on the build platform in the build space. The construction platform lies directly on the height-adjustable support plate or is indirectly connected to the support plate via a so-called mounting plate.

The heating device optionally includes a partition wall, which surrounds the installation space on the side as a jacket that is transparent to IR radiation (side wall).

When producing a 3D molded part using the SLM process, a laser scans over the powder applied to the build platform and melts it

in layers locally. Especially with metallic materials with high melting points, high temperature gradients between the

Melt areas and the surrounding powder. During one Uneven heating and cooling of the workpiece can often result in stress cracks during the molding process.

With the heating device according to the invention, when the powder is heated before and during the laser treatment for local melting or before the application of a new powder layer, temperature differences between the molded part that has already solidified in part and a new layer of powder are leveled or avoided entirely. Rather, the powder and the 3D molded part are heated particularly uniformly and without temperature gradients, so that any thermal aftertreatment of the molded part to relieve thermal stresses after its completion can be omitted. This makes the manufacturing process faster and more economical.

Another advantage of the heating device is that the partition can be easily replaced in the event of a repair, and retrofitting of an existing installation space with the heating device according to the invention is also possible.

As a rule, several IR radiators are arranged on the partition of the installation space, the IR radiator preferably being part of a radiator arrangement comprising a plurality of IR radiators and the IR radiators of the radiator arrangement being individually electrically controllable. The fact that several IR radiators can be provided means that individual radiators can be switched off or on in order to obtain the desired radiation spectrum and at the same time the predetermined total irradiation power.

It has proven itself if the at least one infrared emitter is on the

Absorption characteristics of the powder matched emission spectrum in the IR-A range, that is, an IR-A emitter. The preferred shortwave

Emission spectrum in the IR-A range shows peak wavelengths from 09 pm to 13 pm. IR radiation in the IR-A range has a higher radiation energy than IR-B radiation. Basically, the larger the radiation energy, the shorter the radiation process can be selected. The IR-A radiation component therefore contributes to an efficient process using the heating device.

It has proven to be advantageous if the one that is transparent to IR radiation

Partition made of quartz glass or a glass ceramic. Has quartz glass a high transparency for IR radiation and is also at relatively high

Electrically insulating temperatures, has good resistance to corrosion, temperature and temperature changes and is available in high purity.

It is therefore particularly useful for high-temperature heating processes. In addition to quartz glass, glass ceramic can also be used as a material that is permeable to IR radiation to form the side wall.

It has proven particularly useful if the installation space is surrounded in the radial direction by a side wall, preferably in the form of a cylindrical sleeve, which is formed at least in sections, in particular completely, as a partition. The partition can be designed as a side wall surrounding the installation space. It can have the shape of a hollow cylinder based on a circular or rectangular surface and can be adapted to the geometry of the construction platform surface. In this way, the heat transfer to the powder bed or the molded part is optimized.

An advantageous embodiment of the heating device is to provide the IR radiators with at least one reflector on their side facing away from the molded part. The reflector causes the infrared radiation to be directed onto the powder and / or the 3D molded part on the construction platform and thus increases the efficiency of the heating device.

The reflector can be designed as a primary reflector, the IR radiator having a cladding tube which is covered on its side facing away from the molded part with a primary reflector in the form of a reflector layer applied to the cladding tube. Preferably, a reflective inner side of a housing wall of the housing facing the molded part additionally forms a secondary or, if appropriate, also a tertiary reflector.

In order to limit the heat development in the area of the housing, the housing wall can be equipped with coolants and / or insulation agents. The cooling and / or insulating means isolate the IR radiator from the outside

Environment and can be present as a thermal insulation layer and / or a cooling plate.

In a preferred variant of the heating device, the IR radiator and the side wall are arranged in a frame of a heating unit, which in the Housing can be used. The frame has a frame outer wall with a reflective inner side facing the molded part, which forms a secondary reflector. The frame advantageously surrounds a closed interior in which the IR radiator is arranged. These designs of the heating device are particularly advantageous in connection with a retrofit solution for existing systems for the production of 3D molded parts.

The installation space preferably has at least one measuring cell for detecting the temperature of the powder and / or the molded part. The temperature in the installation space can be measured continuously. For this purpose, pyrometers, thermal imaging cameras or heat sensors such as thermocouples or resistance sensors can be used as measuring means.

In a further advantageous embodiment of the heating device, the

Partition is double-walled with the formation of at least one intermediate space, the at least one IR radiator in the intermediate space

is arranged.

The IR radiator in the space between the double-walled side or partition wall comprises at least one heating filament with an emission spectrum in the IR-B range. Individual heating filaments can be mechanically and electrically separated from one another by webs in the double-walled side wall of the installation space.

IR radiation in the IR-B range has a lower radiation energy compared to IR-A radiation. With a corresponding duration of the irradiation process and in many cases high absorption of the IR-B radiation from the powder or from the molding, good irradiation results can also be achieved with IR-B radiation. In addition, the separation of individual heating filaments by means of webs in the double-walled side or partition wall enables targeted control, so that individual heating filaments can be switched off or on in order to achieve the desired radiation spectrum at the same time

Get total irradiation power.

The heating device is preferably used in a method for

Production of 3D molded parts. A 3D molded part is produced by sintering a preferably at least partially metallic powder in a construction space using a laser, the powder and / or the 3D molded part being sintered are heated with at least one IR radiator, and between which

Execution example

The invention is based on a patent drawing and a

Embodiment explained in more detail. In detail, a schematic representation shows:

Figure 1 shows an embodiment of the heating device according to the invention in a side view, and

Figure 2 shows another embodiment of the heating device with a

Partial view of the installation space.

Figure 1 shows schematically an embodiment of the heating device. The installation space 1 has a circumferential, cylindrical side wall or partition 2 made of quartz glass. A plurality of IR radiators 3, 3 'are attached to the outside of the partition 2 and emit the IR radiation in the direction of the powder P or the 3D molded part 5 on the building platform 4 in the building space 1. Above the building space 1 is the process chamber 6 , in which units (not shown here) for controlling the assembly process of the molded parts 5 are accommodated. At the upper end of the process chamber 6 there is schematically arranged a laser unit 7 which is suitable for using the powder P with a high-energy laser beam emanating from it

Production of the 3D molded part 5 to sinter and / or melt selectively.

Powder P is typically a metal powder, but can also be

Plastic powder can be used. The powder P is on the

Construction platform 4, which is arranged on a height-displaceable support plate 9 indicated by the double directional arrow 8 with a stamp 9.1.

The construction platform 4 is mounted on a mounting plate 10, which simplifies the exchange of the construction platform 4.

The infrared emitters 3, 3 'emit radiation in the IR-A range and are provided with a reflector 11 on their side facing away from the molded part 5. The reflector 11 has the effect that the infrared radiation is directed onto the powder P and / or the 3D molded part 5 on the building platform 4. The reflector 11 is designed as a so-called primary reflector in the form of a reflector layer applied to the cladding tube of the IR radiator 3, 3 '(not shown here). The reflector layer is, for example, a gold layer or a layer of white-opaque quartz glass. The primary reflector can alternatively also be present as a separate sheet metal part which bears on the cladding tube of the IR radiator.

Furthermore, a reflective inner side 12.2 of the housing wall 12.1 of the housing 12 facing the molded part 5 additionally forms a secondary reflector.

The reflective inside 12.2 is formed by a gold or aluminum layer.

In the case of a circular-cylindrical construction space 1 with a correspondingly circular construction platform 4 and a circular-cylindrical side wall 2 around the construction space, the IR radiator 3, 3 ′ from FIG. 1 shows two sections of a

Ring radiator (also called omega radiator), which is arranged on the outside around the cylindrical side wall 2.

If the construction space 1 is provided with a construction platform 4 with a rectangular base area, the IR emitters 3, 3 'are to be understood as individual, linear emitters which are attached to the partition 2 in several planes, the

Partition 2 has the shape of a rectangular cylinder.

In order to limit the development of strands in the area of the housing 12, the housing wall 12.1 is further equipped with a cooling plate and / or insulation layer, not shown here.

FIG. 2 shows a variant of the pickling device, here the construction space 1 with a partition 2 in the form of a double-walled side wall 22 made of quartz glass with an intermediate space 23 is shown only schematically. In the space 23 of the double-walled side wall 22, fleece filaments 30 made of Kanthal wires are arranged, which emit IR radiation in the IR-B range. The double-walled side wall 22 has the function of a cladding tube for the fleece filaments 30. The fleece filaments can either be designed as a single, long filament, which is wound from bottom to top in the space 23 of the double-walled side wall 22, or in shape from individually electric controllable rings are present. To separate the rings or the turns, webs 40 made of temperature-resistant, electrically insulating material are provided. The webs 40 consist of quartz glass, glass ceramic or ceramic such as a calcium silicate ceramic with the trade name Calcast®. A reflector layer 24 made of gold is applied to the outside of the double-walled side wall 22 and reflects the IR-B radiation of the heating filaments 30 in the direction of the powder P and the molded part 5, so that the heating device operates efficiently.

Claims

1. Heating device for heating a powder (P) during the production of a 3D molded part (5), with an infrared radiator (3; 3 '; 30) and with a housing (12) in which a space (1) is provided which is bounded at the bottom by a building platform (4) for receiving the molded part (5), which rests on a carrier plate (9), characterized in that between the

Installation space (1) and the infrared radiator (3; 3 '; 30) a partition (2) made of a material transparent to IR radiation is arranged.

2. Heating device according to claim 1, characterized in that the transparent material for IR radiation of the partition (2) consists of quartz glass or a glass ceramic.

3. Heating device according to claim 1 or 2, characterized in that the installation space (1) is surrounded in the radial direction by a preferably cylindrical sleeve-shaped side wall which is formed at least in sections, in particular completely, as a partition (2).

4. Heating device according to one of claims 1 to 3, characterized in that the infrared radiator (3; 3 '; 30) on its side facing away from the molded part (5) has at least one reflector (11).

5. Heating device according to claim 4, characterized in that the IR radiator (3; 3 '; 30) has a cladding tube, which on its the molded part (5)

opposite side is covered with a primary reflector in the form of a reflector layer applied to the cladding tube, and preferably a reflecting inner side (12.2) of a housing wall (12.1) of the housing (12) facing the molded part (5) forms a secondary reflector.

6. Heating device according to claim 5, characterized in that the

Housing wall (12.1) is equipped with coolants and / or insulation.

7. Heating device according to one of the preceding claims, characterized

characterized in that the installation space (1) has at least one measuring cell for detecting the temperature of the powder and / or the molded part.

8. Heating device according to one of claims 1 to 7, characterized in that the partition (2) with at least one intermediate space (23) is double-walled, the at least one IR radiator (3; 3 '; 30) in the intermediate space ( 23) is arranged.

9. Heating device according to claim 3 and 8, characterized in that the double-walled partition (2) comprises a double-walled side wall (22) of the installation space (1) and that individual heating filaments mechanically and by webs (40) in the double-walled side wall (22) are electrically separated.

10. Heating device according to one of the preceding claims, characterized

characterized in that the at least one IR radiator (3; 3 '; 30) comprises an IR-B radiator with at least one heating filament with an emission spectrum in the IR-B range.

11. Heating device according to one of the preceding claims, characterized

characterized in that the heating device comprises a plurality of IR emitters (3; 3 '; 30) and that the IR emitters

Radiator arrangement are individually electrically controllable.

12. Heating device according to one of claims 1 to 8, characterized in that the at least one infrared radiator (3; 3 '; 30) is an IR-A radiator with an emission spectrum in the IR which is matched in particular to the absorption characteristic of the powder (P) -A area.

13. Heating device according to one of claims 3 to 12, characterized in that the at least one IR radiator (3; 3 '; 30) and the side wall are arranged in a frame of a heating unit which can be inserted into the housing (12).

14. Heating device according to claim 13, characterized in that the

Has a frame outer wall with a reflecting inner side (12.2) facing the molded part (5), which forms a secondary or a tertiary reflector.

15. Heating device according to claim 13 or 14, characterized in that the frame surrounds a closed interior in which the IR radiator is arranged.

16. Process for producing a 3D molded part using the

Heating device according to one of claims 1 to 15.