阅读说明：本技术 一种用于激光选区烧结的预热装置 (Preheating device for selective laser sintering ) 是由 王从军 钟凯 江浩 于 2020-12-29 设计创作，主要内容包括：本发明提出了一种用于激光选区烧结的预热装置,包括第一激光发生器和第二激光发生器,第一光束和第二光束分别通过光路设计最终垂直射向烧结平面,第一光束的激光光斑面积小于第二光束的激光光斑面积,且第一光束的激光光斑始终位于第二光束的激光光斑内,第一光束用于对位于第一光束的激光光斑内的区域进行烧结作业,第二光束用于对位于第二光束的激光光斑内且位于第一光束的激光光斑外的区域进行预热；通过光路设计和二向色镜,将两束波长不同且不相干的激光光束同时照射至烧结平面上,且使两个光束彼此重合,其中第一光束用于烧结,而第二光束则同时对围绕烧结区域一定范围内的材料进行预热,从而实现了局部预热的目的。(The invention provides a preheating device for selective laser sintering, which comprises a first laser generator and a second laser generator, wherein a first light beam and a second light beam are respectively vertically emitted to a sintering plane through light path design, the area of a laser spot of the first light beam is smaller than that of a laser spot of the second light beam, the laser spot of the first light beam is always positioned in the laser spot of the second light beam, the first light beam is used for sintering an area positioned in the laser spot of the first light beam, and the second light beam is used for preheating an area positioned in the laser spot of the second light beam and outside the laser spot of the first light beam; through light path design and dichroic mirror, two laser beams with different and incoherent wavelengths are simultaneously irradiated onto a sintering plane, and the two laser beams are overlapped with each other, wherein the first laser beam is used for sintering, and the second laser beam simultaneously preheats materials in a certain range around a sintering area, so that the purpose of local preheating is realized.)

1. The utility model provides a preheating device for selective laser sintering, sets up the horizontal end face in selective laser sintering region place and be sintering plane (8), its characterized in that: comprises a first laser generator (1) and a second laser generator (2), the first laser generator (1) emits a first light beam (3), the second laser generator (2) emits a second light beam (4), the first light beam (3) and the second light beam (4) are respectively vertically emitted to a sintering plane (8) through the light path design, the laser spot area of the first beam (3) is smaller than that of the second beam (4), and the laser spot of the first light beam (3) is always positioned in the laser spot of the second light beam (4), the first beam (3) is used for sintering the area in the laser spot of the first beam (3), the second light beam (4) is used for preheating a region which is positioned in a laser spot of the second light beam (4) and is positioned outside the laser spot of the first light beam (3).

2. A preheating device for selective laser sintering according to claim 1, wherein: the first light beam (3) and the second light beam (4) have different wavelengths.

3. A preheating device for selective laser sintering according to claim 2, wherein: the LED lamp further comprises a dichroic mirror (7), the dichroic mirror (7) is arranged right above the sintering plane (8), the first light beam (3) is emitted to the lower surface of the dichroic mirror (7) and perpendicularly emitted to the sintering plane (8) through reflection, and the second light beam (4) is emitted to the upper surface of the dichroic mirror (7) and perpendicularly emitted to the sintering plane (8) through transmission.

4. A preheating device for selective laser sintering according to claim 3, wherein: the dichroic mirror (7) is free to translate in a horizontal plane parallel to the sintering plane (8).

5. A preheating device for selective laser sintering according to claim 4, wherein: the first light beam (3) can always irradiate to the lower surface of the dichroic mirror (7) through light path design, laser spots vertically irradiating to the sintering plane (8) after reflection freely translate on the sintering plane (8) along with translation of the dichroic mirror (7), the second light beam (4) can always irradiate to the upper surface of the dichroic mirror (7) through light path design, and the laser spots vertically irradiating to the sintering plane (8) after transmission freely translate on the sintering plane (8) along with translation of the dichroic mirror (7).

6. A preheating device for selective laser sintering according to claim 3, wherein: the included angle between the axis of the dichroic mirror (7) and the sintering plane (8) is 45 degrees, the first light beam (3) is parallel to the sintering plane (8) when being irradiated to the lower surface of the dichroic mirror (7), and the second light beam (4) is perpendicular to the sintering plane (8) when being irradiated to the upper surface of the dichroic mirror (7).

7. A preheating device for selective laser sintering according to claim 6, wherein: the device is characterized by further comprising a focusing lens (5), wherein the focusing lens (5) is arranged right above the sintering plane (8) and close to the lower surface of the dichroic mirror (7), the axis of the focusing lens (5) is overlapped with the axis of the first light beam (3) when the first light beam irradiates the lower surface of the dichroic mirror (7), and the first light beam (3) passes through the focusing lens (5) to realize focusing.

8. A preheating device for selective laser sintering according to claim 6, wherein: the light-emitting device is characterized by further comprising a beam expanding lens (6), wherein the beam expanding lens (6) is arranged right above the sintering plane (8) and close to the upper surface of the dichroic mirror (7), the axis of the beam expanding lens (6) is overlapped with the axis of a second light beam (4) when the second light beam (4) irradiates the upper surface of the dichroic mirror (7), and the second light beam (4) penetrates through the beam expanding lens (6) to expand the beam.

9. A preheating device for selective laser sintering according to claim 1, wherein: the laser spot radius of the second light beam (4) is two to ten times that of the first light beam (3).

Technical Field

The invention relates to the technical field of laser selection, in particular to a preheating device for selective laser sintering.

Background

Due to the development of processes and materials of additive manufacturing technology and the deep understanding of the basic design concept, additive manufacturing technology has matured rapidly in recent years. Powder bed additive manufacturing technology, one of the seven major additive manufacturing technologies defined by the american society for materials and testing, mainly includes selective laser melting, direct metal laser sintering, selective laser sintering, and electron beam melting. The technology is widely applied to the fields of aerospace, mold manufacturing and the like.

Currently, this technique is not ideal for the quality of the finished product formed from many materials. In order to improve the finished product performance of the material, one solution is to preheat the forming material in the early stage before sintering the forming material, so as to improve the prefabrication temperature of the material, which is proved to be effective and feasible through experiments.

In the prior art, the purpose of preheating the material is generally achieved by directly increasing the temperature in the forming cavity. However, in the case that the preheating temperature required for some materials is relatively high, directly raising the temperature in the chamber may have adverse effects on the parts in the chamber, resulting in a decrease in the working performance of the apparatus. Meanwhile, the existing preheating mode cannot meet the requirement of shape-following preheating along the sintering path, so that the preheating efficiency is low, and the cost is high.

In view of the above situation, it is a problem to be urgently solved by the technical staff to design a method or a mechanism capable of realizing local preheating and conformal preheating.

Disclosure of Invention

In view of the above, the present invention provides a preheating device for selective laser sintering.

The technical scheme of the invention is realized as follows: the invention provides a preheating device for selective laser sintering, wherein a horizontal end face where a selective laser sintering area is located is set as a sintering plane and comprises a first laser generator and a second laser generator, the first laser generator emits a first light beam, the second laser generator emits a second light beam, the first light beam and the second light beam respectively vertically irradiate the sintering plane through light path design finally, the area of a laser spot of the first light beam is smaller than that of a laser spot of the second light beam, the laser spot of the first light beam is always located in the laser spot of the second light beam, the first light beam is used for sintering an area located in the laser spot of the first light beam, and the second light beam is used for preheating an area located in the laser spot of the second light beam and located outside the laser spot of the first light beam.

Based on the above technical solution, preferably, the wavelengths of the first light beam and the second light beam are different.

Still further preferably, the laser sintering device further comprises a dichroic mirror, the dichroic mirror is arranged right above the sintering plane, the first light beam is emitted to the lower surface of the dichroic mirror and vertically emitted to the sintering plane through reflection, and the second light beam is emitted to the upper surface of the dichroic mirror and vertically emitted to the sintering plane through transmission.

It is further preferred that the dichroic mirror is free to translate in a horizontal plane parallel to the sintering plane.

Preferably, the first light beam can always irradiate the lower surface of the dichroic mirror through the light path design, the laser spot vertically irradiated to the sintering plane after being reflected can freely translate on the sintering plane along with the translation of the dichroic mirror, and the second light beam can always irradiate the upper surface of the dichroic mirror through the light path design, and the laser spot vertically irradiated to the sintering plane after being transmitted can freely translate on the sintering plane along with the translation of the dichroic mirror.

Still further preferably, the included angle between the axis of the dichroic mirror and the sintering plane is 45 degrees, the first light beam is parallel to the sintering plane when being irradiated to the lower surface of the dichroic mirror, and the second light beam is perpendicular to the sintering plane when being irradiated to the upper surface of the dichroic mirror.

Still further preferably, the optical device further comprises a focusing lens, the focusing lens is arranged right above the sintering plane and close to the lower surface of the dichroic mirror, the axis of the focusing lens coincides with the axis of the first light beam when the first light beam irradiates the lower surface of the dichroic mirror, and the first light beam passes through the focusing lens to realize focusing.

Still further preferably, the laser sintering device further comprises a beam expanding lens, the beam expanding lens is arranged right above the sintering plane and close to the upper surface of the dichroic mirror, the axis of the beam expanding lens coincides with the axis of the second light beam when the second light beam irradiates the upper surface of the dichroic mirror, and the second light beam penetrates through the beam expanding lens to expand the beam.

On the basis of the above technical solution, preferably, the laser spot radius of the second beam is two to ten times as large as the laser spot radius of the first beam.

Compared with the prior art, the preheating device for selective laser sintering has the following beneficial effects:

(1) the invention uses light path design and dichroic mirror to irradiate two laser beams with different and incoherent wavelengths onto the sintering plane simultaneously, and make the two beams coincide with each other, wherein the first beam is used for sintering, and the second beam preheats the material in a certain range around the sintering area simultaneously, thereby realizing the purpose of local preheating.

(2) The dichroic mirror is arranged to be capable of translating, and laser spots of the first light beam and the second light beam on the sintering plane can be translated through light path design, so that the purpose of shape following and local preheating is achieved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic diagram of a laser path of the preheating device of the present invention.

In the figure: 1. a first laser generator; 2. a second laser generator; 3. a first light beam; 4. a second light beam; 5. a focusing lens; 6. a beam expanding lens; 7. a dichroic mirror; 8. and sintering the plane.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

As shown in fig. 1, the preheating device for selective laser sintering according to the present invention is configured such that a horizontal end surface where a selective laser sintering area is located is a sintering plane 8, and includes a first laser generator 1, a second laser generator 2, a focusing lens 5, a beam expanding lens 6, and a dichroic mirror 7.

Wherein the first laser generator 1 emits a first light beam 3 and the second laser generator 2 emits a second light beam 4. Preferably, the first light beam 3 and the second light beam 4 are not of the same wavelength, so that the incoherent first light beam 3 and the second light beam 4 are directed to coincide via the dichroic mirror 7. It should be noted that, for different materials, the laser spot radius of the first beam 3 may vary according to the set of additive manufacturing process parameter requirements.

The first light beam 3 and the second light beam 4 are respectively vertically emitted to the sintering plane 8 through the light path design, and the laser spot area of the first light beam 3 is smaller than that of the second light beam 4. Preferably, the laser spot radius of the second beam 4 is two to ten times that of the first beam 3.

Meanwhile, the laser spot of the first light beam 3 is always located in the laser spot of the second light beam 4, the first light beam 3 is used for sintering the area located in the laser spot of the first light beam 3, and the second light beam 4 is used for preheating the area located in the laser spot of the second light beam 4 and located outside the laser spot of the first light beam 3.

The dichroic mirror 7 is arranged right above the sintering plane 8, the first light beam 3 is emitted to the lower surface of the dichroic mirror 7 and vertically emitted to the sintering plane 8 through reflection, and the second light beam 4 is emitted to the upper surface of the dichroic mirror 7 and vertically emitted to the sintering plane 8 through transmission.

The focusing lens 5 is arranged right above the sintering plane 8 and close to the lower surface of the dichroic mirror 7, the axis of the focusing lens 5 is overlapped with the axis of the first light beam 3 when the first light beam 3 irradiates the lower surface of the dichroic mirror 7, and the first light beam 3 passes through the focusing lens 5 to realize focusing.

The beam expanding lens 6 is arranged right above the sintering plane 8 and close to the upper surface of the dichroic mirror 7, the axis of the beam expanding lens 6 is coincided with the axis of the second light beam 4 when the second light beam 4 irradiates to the upper surface of the dichroic mirror 7, and the second light beam 4 passes through the beam expanding lens 6 to realize beam expansion.

Specifically, the invention is realized by the following technical scheme.

Preferably, the dichroic mirror 7 is free to translate in a horizontal plane parallel to the sintering plane 8.

The first light beam 3 can be always emitted to the lower surface of the dichroic mirror 7 through light path design, the laser light spot vertically emitted to the sintering plane 8 after reflection can freely translate on the sintering plane 8 along with the translation of the dichroic mirror 7, the second light beam 4 can be always emitted to the upper surface of the dichroic mirror 7 through light path design, the laser light spot vertically emitted to the sintering plane 8 after transmission can freely translate on the sintering plane 8 along with the translation of the dichroic mirror 7, and therefore the light spot and the dichroic mirror 7 can move along with the shape at the same time.

As a specific example, it is preferable that the angle between the axis of the dichroic mirror 7 and the sintering plane 8 is 45 degrees, the first light beam 3 is parallel to the sintering plane 8 when being irradiated to the lower surface of the dichroic mirror 7, and the second light beam 4 is perpendicular to the sintering plane 8 when being irradiated to the upper surface of the dichroic mirror 7.

The working principle is as follows:

the first laser generator 1 emits a first light beam 3 and the second laser generator 2 emits a second light beam 4.

The first light beam 3 is focused by the focusing lens 5, horizontally emitted to the lower surface of the dichroic mirror 7 through the light path design, and finally vertically irradiated to the sintering plane 8 through the reflection of the dichroic mirror 7 to form a light spot. The first beam 3 is used for sintering the material because of its beam concentration and the extremely small spot radius.

After being expanded by the beam expanding lens 6, the second light beam 4 is emitted to the upper surface of the dichroic mirror 7 along the plumb line direction through the light path design, and finally vertically irradiates a sintering plane 8 through the transmission of the dichroic mirror 7 to form a light spot. Because the light beams of the first light beam 3 are expanded, the radius of the light spot is larger, and the light spot formed by the second light beam 4 surrounds the light spot formed by the first light beam 3; the radiation heating efficiency of the second light beam 4 to the material in unit area is reduced due to the fact that the second light beam 4 expands, and therefore in unit time, the temperature rise temperature of the material in the light spot irradiation range of the second light beam 4 is lower than that of the material in the light spot irradiation range of the first light beam 3, and when the temperature is still higher than the ambient temperature, the purpose of preheating the material in a certain range around the light spot of the first light beam 3 is achieved.

When the first light beam 3 and the second light beam 4 are translated on the sintering plane 8 under the effect of the light path design, the second light beam 4 preheats the material in the area around the sintering point position along with the sintering of the first light beam 3, so that the purpose of shape-following local preheating is realized.

It should be noted that, in actual operation, the powder for selective laser sintering is first preheated in the charging basket to raise the temperature to some intermediate temperature, and then the second light beam 4 is used to locally preheat the neighborhood of the sintering point during sintering to make the temperature in the neighborhood of the sintering point reach the proper preheating temperature.

With regard to how the powers of the first laser generator 1 and the second laser generator 2 are selected according to the forming material so as to realize the emission of the first light beam 3 and the second light beam 4 with different wavelengths, the skilled person finds through research that the heat transfer modes include three transfer modes of heat conduction, heat convection and heat radiation. Thermal convection and thermal radiation are relatively fast in terms of heat transfer rate, but thermal convection requires strong convection conditions, otherwise the heat transfer effect is less than ideal.

When the ventilation fan is not opened in the closed state of the forming chamber, the sintering powder has no air convection at all, so that no convection heat transfer exists, and the radiation heat exchange mode is mainly adopted in the forming chamber.

In the system, the thermal radiation between two objects, which is obtained by the Stefan Boltzmann law,

E_(i,j)＝ε_(i,j)σ(T_i^4-T_j^4)X_(i,j)

where E _ (i, j) is the blackness between object i and object j, σ is the Stefan Boltzmann constant, Ti and Tj are the temperatures of object i and object j, respectively, and X _ (i, j) is the angular coefficient from object i to object j.

The thermophysical parameter of the transient temperature field of the laser selection area changes along with the change of the temperature, so the transient sintering temperature T (T, x, y, z) of the laser selection area relates to the problem of three-dimensional nonlinear heat conduction, the heat conduction equation can be expressed as,

in the formula, rho is the average density of the powder bed, c is the constant-pressure specific heat capacity of the material, and K is the local effective heat conductivity coefficient of the powder bed.

In the selective laser sintering process, under the irradiation of laser, the upper surface of the powder bed absorbs the laser energy and is converted into heat energy, and then diffusion from the outside to the inside and from high temperature to low temperature is carried out; meanwhile, convection and radiation heat exchange also exist between the upper surface of the powder bed and the surrounding environment. Therefore, laser heating, radiation and convection heat flow exist on the upper surface of the powder bed at the same time, and the heat exchange boundary condition can be comprehensively expressed as,

in the formula, alpha 'r' is a surface radiation heat exchange coefficient, h _ c is a surface convection heat exchange coefficient, T _ alpha is an ambient temperature, and q is a heat flow density.

Wherein the radiant energy of the laser beam is the primary source of heating. Assuming that the laser is Gaussian distributed, the heat flux density q and the laser power are related,

q＝αP/(πr^2)

where α is the absorption rate, P is the laser power, and r is the beam radius.

The temperature field can be analyzed using the program finite element analysis software ANSYS, which is commonly used in the art, to select the appropriate power of the first laser generator 1 and the second laser generator 2.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.