METHOD AND DEVICE FOR 3D PRINTING WITH A NARROW WAVELENGTH SPECTRUM

Abstract

The invention relates to a 3D printing method and a device with a narrow wavelength range.

Claims

1. A method of producing 3D molded parts, wherein particulate construction material is applied onto a construction field in a defined layer by means of a coater, one or more liquids or particulate material of one or more absorbers is/are selectively applied, energy is input by suitable means, resulting in selective solidification of the areas printed with absorber, at a solidification temperature or sintering temperature above the melting temperature of the powder, the construction field is lowered by one layer thickness, or the coater is raised by one layer thickness, these steps being repeated until the desired 3D molded part is produced, characterized in that at least the energy input of printed areas is effected by means of substantially monochromatic radiation or/and within a narrow wavelength spectrum having a width of 0.1 μm to 0.2 μm.

2. The method according to claim 1, wherein an overhead radiator is used for basic heating and a sintering radiator is used to heat the printed areas to a temperature above the melting temperature.

3. The method according to claim 2, wherein the sintering radiator has a wavelength for heating the printed areas to a temperature above the melting temperature and a wavelength for heating the unprinted areas to a temperature above the recrystallization temperature.

4. The method of claim 1, wherein no static radiator is used or wherein a static radiator having a wavelength for heating the printed surface to a temperature above the melting temperature and having a wavelength for heating the unprinted surface to a temperature above the rectrystallization temperature is used.

5. The method of claim 3, wherein no movable sintering radiator is used.

6. The method of claim 2, wherein the power of the respective elements can be adjusted and the respective heating can be regulated.

7. The method of claim 1, wherein for selective heating of printed and unprinted areas, selective activation and deactivation of sources of radiation is performed during a pass over the construction surface.

8. The method of claim 1, wherein selective activation and deactivation of stationary sources of radiation is performed.

9. The method of claim 1, wherein the absorber is a liquid.

10. The method of claim 9, wherein the liquid is an oil-based ink containing carbon particles.

11. The method of claim 1, wherein the melting temperature is 180-190° C. or the recrystallization temperature is 140-150° C.

12. The method of claim 1, wherein the melting temperature is 180-190° C. and the recrystallization temperature is 140-150° C.

13. The method of claim 1, wherein heating takes place such that only the areas printed with absorber connect by partial melting and sintering; or the construction material is in the form of a powder or dispersion; or the temperature of the construction field is controlled; or the temperature of the material applied is controlled; or the absorber comprises radiation-absorbing components, plasticizers for the particulate construction material or one or more substances for interfering with recrystallization.

14. The method of claim 1, wherein heating takes place such that only the areas printed with absorber connect by partial melting and sintering; and the construction material is in the form of a powder or dispersion; and the temperature of the construction field is controlled; and the temperature of the material applied is controlled; and the absorber comprises radiation-absorbing components, plasticizers for the particulate construction material or one or more substances for interfering with recrystallization.

15. The method of claim 1, wherein the liquid is selectively applied by means of one or more print heads.

16. The method of claim 15, wherein the amount of the absorber or absorbers is regulated via grayscale values of the print head or via dithering methods.

17. The method of claim 15, wherein the one or more print heads are adjustable in terms of droplet mass.

18. The method of claim 15, wherein the particulate construction material is selectively solidified and sintered.

19. The method of claim 18, wherein the one or more print heads selectively apply the liquid in one direction of travel.

20. The method of claim 18, wherein the one or more print heads selectively apply the liquid in both directions of travel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] FIG. 1. Method according to the state of the art, using thermal radiators.

[0118] FIG. 2A. Schematic energy input and output curves of a powder such as polyamide 12.

[0119] FIG. 2B. Temperature curves showing liquidus and solidus temperatures of the unprinted area type.

[0120] FIG. 2C. Temperature curves showing liquidus and solidus temperatures of the printed area type.

[0121] FIG. 3A. High-resolution, schematic representation of the temperature of the unprinted area type using a thermal source of radiation in the sintering radiator unit.

[0122] FIG. 3B. High-resolution, schematic representation of the temperature of the unprinted area type using a monochromatic source of radiation in the sintering radiator unit.

[0123] FIG. 4A. Arrangement of an LED source of radiation with different wavelengths.

[0124] FIG. 4B. Further possible arrangement.

[0125] FIG. 5. Sequence of a process according to the invention using a device without an overhead radiator;

[0126] FIG. 6. Device for carrying out the method according to the invention using a monochromatic LED sintering radiator.

[0127] FIG. 7: Device for carrying out the method according to the invention using a monochromatic sintering radiator and a monochromatic overhead radiator.

[0128] FIG. 8: Transformation of radiation from the sintering lamp by a fluorescent medium.

[0129] FIG. 9: Spectral distributions of various thermal sources of radiation and of genuinely monochromatic sources of radiation.

[0130] Further preferred exemplary embodiments:

Example 1

Device Comprising a Sintering Lamp which includes LED Radiators of One Wavelength and a Thermal Overhead Lamp

[0131] According to FIG. 1A, the construction process or process cycle begins with the coating of one powder layer onto the construction platform. The powder is heated by the overhead radiator (108) already during the coating process performed by the coater (101), unless optically masked by the coater (101). The sintering radiator (109), which only provides radiation resulting in good heating of the printed area, is not activated in this step.

[0132] The overhead radiator (108) includes a measuring device designed to control the surface temperature of the construction field. Ideally, the measuring device is embodied as a pyrometer (508) which can determine the temperature in a contactless manner. The control has to make allowance for the fact that the measuring device is masked time and again by the print head (100) and the coater (101). This may be done by deactivating the measurement function or by using insensitive control loop parameters.

[0133] In a second step, the activator is applied by the print head (100) which is adjusted precisely to the wavelength of the source of radiation. The image applied by the print head (100) onto the particulate material corresponds to the cross-section of the current molded article. At the beginning of a process, it is often required to print a base layer. In this case, the print head prints on the entire area provided as the construction surface.

[0134] The third step is the sintering pass. For this purpose, the sintering radiator unit (109) is activated and passed over the construction field. The power of the source of radiation and its speed determine the radiation power on the construction field. In contrast to the prior art, the single-wavelength sintering radiator (500) does not heat unprinted areas during this pass. Thus, the temperature of the printed areas increases while unprinted areas slowly cool down due to the energy loss by radiation (FIG. 3B, area II).

[0135] The fourth step is the lowering of the construction platform (102) by the thickness of one powder layer (107). During this process, the construction field is open to the overhead radiator (108), allowing temperature readjustment. After this, the process cycle starts over with the coating process.

[0136] FIG. 6 describes a device for implementing the process mentioned in the example. The overhead radiator (108) is embodied as a thermal source of radiation. The sintering radiator is composed of small-sized individual LED radiators (400 or 500). The temperature of the construction container bottom and the construction platform is controlled by resistance heaters (504). In the device serving as an example the coater (101) and the sintering radiator unit (109) are connected. This unit and the print head (100) can be moved separately over the construction field.

[0137] FIG. 7 shows a specific embodiment of this example. Here, the overhead radiator is also equipped with an LED source of radiation. This generates much less waste heat in the machine than in the prior art devices.

Example 2

Device of a Sintering Radiator Unit which includes LED Radiators having Two Wavelengths and No Overhead Lamp

[0138] According to FIG. 5, the construction process or process cycle begins with the coating of one powder layer onto the construction platform (102). The sintering radiator (501) of the unit (109), which also provides radiation resulting in good heating of the unprinted area, is activated in this step and heats the powder to a basic temperature below the melting temperature but above recrystallization temperature of the powder. The energy supply for this is controlled by the power and the traversing speed.

[0139] Favourably, the temperature generated is measured and adjusted.

[0140] In a second step, the activator is applied which is adjusted precisely to the wavelength of the source of radiation (500) for the printed areas. The image applied by the print head (100) onto the powder corresponds to the current molded article. At the beginning of a process, it is often required to print a base layer. In this case, the print head prints on the entire area provided as the construction surface.

[0141] The third step is the sintering pass. For this purpose, the sintering unit (109) is activated and passed over the construction field. The power of the source of radiation and its speed determine the radiation power on the powder bed. In contrast to the prior art, the unit having two wavelengths (500,501) can specifically influence unprinted and printed areas during this pass. Thus, the temperature of the printed areas increases while the energy loss by radiation in the unprinted areas can be compensated for.

[0142] The fourth step is the lowering of the construction platform (102) by one layer thickness and is kept extremely short in this exemplary process. There is no adjustment here and any delay leads to energy loss by thermal radiation. Therefore, this step is not shown in the drawing.

LIST OF REFERENCE NUMERALS

[0143] 100 print head

[0144] 101 coater

[0145] 102 construction platform

[0146] 103 parts

[0147] 107 layers

[0148] 108 overhead radiator

[0149] 109 sintering radiator unit

[0150] 110 construction container

[0151] 400 monochromatic radiator in sintering unit

[0152] 401 monochromatic radiator of a different wavelength in sintering unit

[0153] 402 sintering radiator unit with radiators in nested design

[0154] 500 monochromatic sintering radiator

[0155] 501 sintering radiator of a different wavelength

[0156] 503 insulation for construction container

[0157] 504 resistance heater or heating coil

[0158] 506 downward insulation of construction platform

[0159] 507 resistance heater for coater

[0160] 508 pyrometer

[0161] 601 material with fluorescent layer

[0162] 602 secondary radiation emitted by fluorescent layer

[0163] 603 overhead radiator, embodied by monochromatic radiators

[0164] 604 radiation on fluorescent layer

[0165] 701 typical radiation spectrum of conventional radiators with secondary peak

[0166] 702 radiation spectrum of conventional radiators at lower power

[0167] 703 monochromatic radiation