CN101607311B - Fast forming method of fusion of metal powder of three beams of laser compound scanning - Google Patents

Abstract

The invention discloses a rapid prototyping method for composite scanning of three beams of lasers. In the method, a long-wavelength laser ( _CO2 laser) is used to preheat the metal powder, and then a short-wavelength laser (YAG or fiber laser) is used to preheat the metal powder. Melting and finally heat treatment of the solidified metal with a long wavelength laser ( _CO2 laser). The present invention uses three beams of laser compound scanning, that is, long-wavelength laser preheating, short-wavelength laser melting, and long-wavelength laser heat treatment, so as to realize the composite process of metal powder preheating, melting, and heat treatment. This three-beam laser composite scanning method can reduce the internal stress of metal parts, avoid warping and cracking, improve structure and performance.

Description

A rapid prototyping method for three-beam laser composite scanning metal powder melting

technical field

The invention belongs to the field of rapid manufacturing, and specifically relates to a compound scanning rapid prototyping method of two long-wavelength lasers (carbon dioxide) and one short-wavelength laser (optical fiber or Nd:YAG), which can realize micro-area preheating/melting/heat treatment of metal powder process.

Background technique

A rapid prototyping device for directly manufacturing metal parts using Selective Laser Melting (SLM) technology has been reported, see "A Rapid Prototyping System for Directly Manufacturing Metal Parts" (public number: CN1631582A, public date: June 29, 2005). While they enable direct fabrication of arbitrarily complex metal parts, such scanning devices do not have a preheating system. In this case, the metal powder is scanned by the rapidly moving laser beam and undergoes rapid melting and rapid solidification, and the temperature field distribution of the powder bed is uneven, forming a large temperature gradient and thermal stress, which easily leads to cracks in the metal parts , warping, etc.

The overall preheating of the powder bed can reduce the temperature gradient and ease the thermal stress, thus greatly reducing the defects such as cracking and warping during the forming process of metal parts. Moreover, the overall preheating of the powder bed can reduce the laser energy input, and a faster scanning speed can be selected, which is conducive to improving the efficiency of forming metal parts. However, the overall preheating of the powder bed requires heating of the working cylinder. However, the entire forming device is composed of metal parts, and the heat conduction of the machine parts cannot be ignored during the overall preheating: the overall preheating of the powder bed will easily lead to the operating temperature of various electrical systems such as motors, laser scanning systems, and lasers. If it is too high, it will hinder the normal operation of the machine or even damage the machine parts.

Contents of the invention

Aiming at the shortcomings of the existing rapid prototyping preheating system for directly manufacturing metal parts, the present invention provides a three-beam laser composite scanning metal powder melting rapid prototyping method, which can continuously complete preheating, solidification and heat treatment during the part forming process process, eliminate residual stress, and greatly reduce cracks and warpage of formed parts.

The laser composite scanning metal powder melting rapid prototyping method provided by the present invention, its steps include:

(1) Using the first laser beam with a wavelength greater than 10000nm to scan the metal powder along the scanning path in advance, increasing the temperature of the metal powder, and controlling the laser power so that the preheating temperature is lower than the melting point of the metal powder;

(2) Using the second laser beam with a wavelength of less than 1100nm to follow the path scanned by the first laser beam at the same speed to repeatedly scan to melt the metal powder, and then cool and solidify;

(3) Using the third laser beam with a wavelength greater than 10000nm to repeatedly scan the path scanned by the second laser beam at the same speed to heat the metal solidification area to realize heat treatment.

The method of the present invention is preheated by long-wavelength laser (wavelength greater than 10000nm, such as _CO2 laser), melted by short-wavelength laser (wavelength less than 1100nm, such as YAG laser or fiber laser), and then annealed by long-wavelength laser heat treatment, so that metal parts During the forming process, the preheating, melting and heat treatment processes are continuously completed. This three-beam laser composite scanning method not only achieves the functions of preheating, melting and heat treatment, eliminates residual stress, and greatly reduces the crack and warpage of formed parts. This scanning method is suitable for forming a variety of metal powder materials, such as forming complex parts of iron-based, nickel-based, titanium-based, and tungsten-based metal alloys, and can greatly reduce warpage and cracks during the forming process.

Specifically, this three-beam laser composite scanning method has the following advantages:

(1) The long-wavelength laser beam has a large spot diameter, and the absorption rate of the metal powder to the long-wavelength laser is low, which can preheat or heat treat the micro-area of the powder bed without melting the metal powder; the short-wavelength laser beam With smaller spot diameter, higher metal absorption rate, and extremely high energy density, the metal powder can be melted instantly.

(2) The first long-wavelength laser preheats the metal powder in the area to be melted to make the temperature field uniform, slowing down the drastic change of the temperature field when the powder is directly melted, thereby reducing the temperature gradient and easing the stress field. Finally, defects such as warping and cracking can be reduced;

(3) When the second short-wavelength laser melts metal powder, there is no need to provide high energy density of single-beam laser scanning, which not only reduces the short-wavelength laser scanning power, but also uses high scanning speed, thereby improving scanning efficiency;

(4) The scanning of the solidified metal by the third long-wavelength laser can realize heat treatment, eliminate the residual stress inside the metal, improve the structure, and help improve the performance of the formed metal parts;

(5) This three-beam laser scanning method greatly saves the forming time compared with the single-scanning method, replaces the traditional preheating and heat treatment process, and can improve the forming efficiency of parts.

(6) The method of the present invention can realize the preheating, melting and heat treatment of the local area of the metal powder bed without increasing the overall working temperature of the equipment, and avoiding the damage of the overall preheating to the machine.

Description of drawings

Figure 1 is a schematic diagram of long-wavelength laser preheating, short-wavelength laser melting, and long-wavelength laser heat treatment.

Detailed ways

The method adopts three-beam laser scanning, and combines long-wavelength laser beam preheating, short-wavelength laser melting, and long-wavelength laser heat treatment to perform three-beam composite scanning to form metal parts.

The present invention will be described in further detail below in conjunction with the accompanying drawings and the actual process.

(1) Vacuum the SLM forming cavity first and then enter a protective atmosphere, spread the metal powder to be formed on the forming substrate, and the thickness of the powder coating is about 0.02-0.1mm. Use 3D modeling software to design the CAD model of the required forming parts, then process it with the slicing software and save it in STL format, and generate the path of each slicing layer, and import the STL data into the SLM equipment;

(2) Use the first laser beam ( _CO2 laser) to scan and preheat the powder bed along the set scanning path with optimized laser power and scanning speed;

(3) Subsequently, use the second laser beam (YAG or fiber laser) to scan and melt along the scanning path with optimized laser power and the same scanning speed as the first laser beam. The spot position of the second laser beam is located at the position of the first laser beam The spot scanning direction is behind and separated by a certain distance;

(4) Finally, use the third laser beam ( _CO2 laser) to perform scanning heat treatment along the scanning path with optimized laser power and scanning speed. The position of the third laser spot is located behind the scanning direction of the second laser spot and at a certain distance ;

(5) After one layer of scanning is completed, continue to form the next layer until the entire part is processed.

The above-mentioned metal materials include: metal powder materials such as iron-based, nickel-based, copper-based, etc. The scanning method can control the time difference and laser parameters of the three laser beams to adjust the effect of preheating and heat treatment. The purpose of preheating the metal powder is to increase the temperature of the metal powder before it melts, avoiding a large temperature gradient caused by a sudden increase in temperature when the short-wavelength laser is irradiated, thereby greatly reducing cracks and warping. The purpose of heat treatment is to improve the organization, reduce stress, and improve the overall performance of the formed part.

The above process is shown in Figure 1. First, the first long-wavelength laser beam 1 is irradiated on the metal powder bed 7 to form a long-wavelength laser spot 4, and the second short-wavelength laser beam 2 is irradiated on the preheated metal powder bed 7. A laser spot 5 is formed on the metal powder bed 7, and a third long-wavelength laser beam 3 is irradiated on the metal powder bed 7 to form a laser spot 6. Spots 4, 5, 6 scan at the same interval, at the same speed, and in the same direction. Among them, the heat generated by the interaction between the spot 4 and the metal powder preheats the powder bed; the interaction between the spot 5 and the metal powder produces a higher energy density, which makes the metal powder melt rapidly, and then solidifies rapidly; finally, the spot 6 heats the solidified metal heat treatment.

Example 1:

The spherical 316L stainless steel powder with a particle size of 20 microns is selected for SLM forming, and three-beam laser composite scanning is used to prepare metal parts with low stress, no warping, and uniform structure. The part graphics are designed by CAD software, processed by slicing software and path software, saved as STL, and input into SLM equipment for SLM forming. The specific scanning method of each layer is as follows:

Use the CO ₂ laser as the first laser beam, set the laser power to 50W, and the scanning speed to 200mm/s, and scan and preheat the 316L stainless steel powder bed along the set scanning path;

Use the fiber laser as the second laser beam, set the laser power to 200W, and the scanning speed to 200mm/s, scan and melt along the scanning path, and make the position of the second laser spot be behind the scanning direction of the first laser spot with a distance of 0.1 mm;

Use the _CO2 laser as the third laser beam, set the laser power to 50W, and the scanning speed to 200mm/s, and perform scanning heat treatment along the scanning path, so that the position of the third laser spot is located behind the scanning direction of the second laser spot and is 0.1 mm;

Through layer-by-layer processing and repeated cycles, high-quality 316L stainless steel parts are finally formed.

The present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can implement the present invention by adopting other various specific embodiments according to the disclosed content of the implementation examples and accompanying drawings. Some simple changes or modified designs all fall within the protection scope of the present invention.

Claims (1)

1. fusion of metal powder of three beams of laser compound scanning quick forming method, its step comprises:

(1) utilize wavelength to scan metal dust along scanning pattern in advance, improve the metal dust temperature, and the control laser power makes preheat temperature be lower than the fusing point of metal dust greater than first laser beam of 10000nm;

(2) utilize wavelength less than second laser beam of 1100nm with the speed identical with first laser beam immediately following first laser beam and along the path multiple scanning of first laser beam flying, make fusion of metal powder and solidify;

(3) utilize wavelength greater than the 3rd laser beam of 10000nm with the speed identical with first laser beam immediately following second laser beam and along the path multiple scanning of first laser beam flying, to the heating of metal freezing zone, realize heat treatment.

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