Powdered metal 3D printing is an important branch of metal additive manufacturing technology. This technology uses the metal powder preset on the powder platform as the raw material, based on the three-dimensional digital model of the part, and uses high energy beams such as laser or electron beam to melt the powder layer by layer on a series of two-dimensional planes separated by the three-dimensional model , And finally manufacture three-dimensional metal parts. Currently, the most widely used is powder-laid metal 3D printing using laser as an energy source, also known as Selected Laser Melting (SLM).

The basic process of SLM processing mainly includes:

1) Generate 3D CAD models of metal parts to be manufactured, including models of auxiliary support structures;

2) The model is discretized (sliced) according to a certain orientation to obtain the contour data of each section, and a fill scan path within the contour is generated according to a certain rule and saved as an STL file;

3) The computer reads the scanning path information file layer by layer, controls the laser beam direction to scan according to the planned path, melts the powder at the corresponding position on the powder bed, generates parts layer by layer, and guarantees processing by controlling process parameters such as laser power and scanning speed. Forming quality and performance of parts.

Figure 1 shows the structure of a typical powdered metal 3D printer. The parts work together through the following steps:

1) Before printing, the powder is stored in the powder preparation tank, and the printing platform (substrate) is placed in the powder molding tank;

2) When printing starts, the powder preparation cylinder moves up to send out a certain amount of powder, and the powder spreading blade scrapes the powder in the direction of the powder molding cylinder, and spreads it on the printing platform to form a uniform thickness powder layer;

3) The laser light source emits laser light. After focusing by the focusing light path, the direction is controlled by the X-Y scanning galvanometer, and the powder layer on the platform is scanned according to the scanning path in the STL file;

4) The laser energy melts the powder on the scanning path and forms a metallurgical bond with the substrate (or the previous formed layer).

5) After the laser scanning and melting of a layer of powder is completed, the printing platform is lowered by a layer of powder height, and the steps 2) -5) are repeated until scanning on all two-dimensional planes of the digital model is completed, and printing of the entire three-dimensional product is completed.

6) After printing, remove the molded part from the powder molding cylinder, separate the sample from the substrate through subsequent processing, and remove the powder on the inner and outer surfaces of the sample.

7) For some suspended structures, support structures need to be designed in the 3D model and printed with the main structure. After printing, the supporting structure needs to be removed.

As the main force in the field of metal additive manufacturing technology, SLM technology has some obvious advantages:

1) Using high-quality single-mode laser, focusing spot size range is 50-200um, highly concentrated energy, can melt most metal materials, high density of molded parts (more than 99%);

2) The laser scanning speed is fast, and the small-sized molten pool brings extremely fast cooling and solidification speed to obtain a uniform and fine metallographic structure, which greatly improves the mechanical properties of the material compared with the coarse-grained cast structure;

3) The powder with a particle size of 53um or less is used, and the thickness of the single-layer powder is controlled to 20-100µm, which can realize precise molding and good surface quality of the molded part;

4) The entire working chamber is sealed in an inert gas environment to avoid oxidation of metal materials at high temperatures, and is suitable for active metals such as titanium alloys

5) Through the design of the support structure, you can print a variety of products with complex shapes, including complex curved surfaces with suspended parts, structures with internal flow channels, and hollowed out complex shapes.

Figure 2

SLM technology made of various complex shapes of metal parts

However, SLM technology also has certain limitations. First, due to the limitation of laser power and scanning galvanometer deflection angle, the size range of parts that can be formed by SLM equipment is limited. Currently, mature commercial equipment can achieve a maximum molding volume of 800 x 400 x 500 mm3. Second, the technical control of SLM is more difficult High, technical personnel with expertise in metallurgical materials are required to develop specific material process packages. The design of the support structure also requires professional software and experienced technicians to avoid problems such as irrational support structures and difficulty in later removal; In practical industrial applications, SLM equipment is expensive, operating and maintenance costs are high, and the molding efficiency is low. Generally, it is below 100cm3 / h, which cannot meet the mass production requirements of most industries. Therefore, it is more suitable for personalized custom parts, and Small batch production.

Bright's SLM Metal Printing Service

Huirui has provided customers with powdered metal 3D printing services since 2016. With the company's many years of production and R & D experience in the field of laser material processing, and the knowledge and talent reserve in the field of metallurgical materials, the company can provide customers with early modeling , A full set of SLM printing services including material technology package development, printing molding and subsequent heat treatment processing. Currently, more than 10 kinds of SLM processes have been developed, including stainless steel, aluminum alloys, titanium alloys, nickel-based superalloys, tungsten alloys, and magnesium silicides, including corresponding post-treatment processes.

Table 1 lists the mechanical property data of several common material samples made by Shui Rui SLM process.

Fig. 3

In718 SLM formed parts mechanical properties and the influence of different subsequent heat treatment processes

Figure 4 shows the effect of different subsequent heat treatments on the mechanical properties of SLM formed parts of nickel-based superalloy In718.

Figure 4 shows an example of the metallographic structure of the Shui Rui SLM product (In625). It can be seen that the material structure is 100% dense, the grains are small, and they are composed of slender dendrites.

Fig. 4 Microstructure of In626 SLM print section, a), b) cross section, c), d) longitudinal section

Optimized design of support and printing posture

Special material process package printing

3D model disassembly

Material technology package print molding