Vacuum Selective Laser Melting Research Articles

Suppression of denudation zone using laser profile control in vacuum selective laser melting

A vacuum selective laser melting method with a beam profile control was developed to fabricate the high quality 3D object. To investigate the quality of 3D fabrication, the denudation zone (DZ) as a quality indicator was evaluated to make a single bead. The main challenge is to clarify the correlation between the DZ and beam profiles. The beam profiles, such as a Gaussian mode, a doughnut mode, and a flat-top mode, were formed in several modes, by a dioptric system with a beam shaper. A stainless steel 316L (SS316L) powder was irradiated in arbitrary pressure to form a single bead, and then the DZ was measured. As a result, it was found that the flat-top mode recorded the minimum value of the DZ under atmospheric pressure. Thus, the dynamics of the metal vapor while the laser irradiation were observed by the Schlieren imaging technique under atmospheric pressure. The average velocity of metal vapor with flat-top mode was the slowest, i.e., 0.199 m/s. It was found that the DZ becomes small depending on the dynamics of metal vapor. The ambient pressure was reduced to 300 Pa in order to reduce the gas movement, and the DZ with flat-top mode was improved to record a minimum value of 0.048 mm, 1/3 of the DZ at atmospheric pressure.

Effect of modulated pulses on the fabrication of Ti-6al-4v by spatter-less selective laser melting in vacuum

Effect of modulated pulses on the fabrication of Ti-6al-4v by spatter-less selective laser melting in vacuum

Pure titanium fabrication with spatter-less selective laser melting in vacuum

Selective laser melting (SLM), which is an additive manufacturing technology, is attractive due to its ability to freely form shapes. SLM forms a 3D material by building it layer-by-layer from a metal powder. However, some issues have yet to be resolved, including dimensional accuracy, surface finish, processing time, and mechanical properties such as surface roughness, hardness, and crystal orientation. We demonstrate that pure titanium (Ti), which is clinically used for artificial bone and hard tissue implants because it is lightweight and biocompatible, can be fabricated by the SLM process in vacuum to develop a spatter-less process. The amount of spatter was dependent on the laser scanning rate; at 10 mm/s and an output power of 200 W, the spatter was minimized so that the surface roughness was reduced to 4.2 µm from 50 µm with a laser scanning rate of 50 mm/s. Defects such as pores, voids and delamination were found to be caused with an increase in the amount of spatter.

Effect of energy on Ti plate fabrication by vacuum selective laser melting for uniformity of grain size

Grain size homogenization by controlling heat input using modulated pulses in additive manufacturing was verified. A Ti plate was fabricated with a modulated pulsed laser by vacuum selective laser melting. 20-layer fabrication was performed with modulated pulsed laser and continuous wave laser. As a result of cross-sectional observation, it was found that the variation of the grain size was smaller when the modulated pulsed laser was used. These experimental results suggest that it is possible to control the grain size by using a modulated pulsed laser.

真空雰囲気中SLMで積層造形したニッケル基超合金の組織

真空雰囲気中SLMで積層造形したニッケル基超合金の組織

Preheat effect on titanium plate fabricated by sputter-free selective laser melting in vacuum

The dynamics of titanium (Ti) melted by laser irradiation was investigated in a synchrotron radiation experiment. As an indicator of wettability, the contact angle between a selective laser melting (SLM) baseplate and the molten Ti was measured by synchrotron X-rays at 30 keV during laser irradiation. As the baseplate temperature increased, the contact angle decreased, down to 28° at a baseplate temperature of 500 °C. Based on this result, the influence of wettability of a Ti plate fabricated by SLM in a vacuum was investigated. It was revealed that the improvement of wettability by preheating suppressed sputtering generation, and a surface having a small surface roughness was fabricated by SLM in a vacuum.

Investigation of the microstructure and surface morphology of a Ti6Al4V plate fabricated by vacuum selective laser melting

As an additive manufacturing technology, the selective laser melting (SLM) process is useful to directly form complicated shapes. The SLM process in a vacuum has been used to fabricate three-dimensional Ti6Al4V (Ti64) plates because this method can control the phase transformation. To investigate the laser melting and solidification dynamics, the formation of a Ti64 plate by SLM in a vacuum was captured by a high-speed video camera. Due to the effects of temperature and scanning speed on the phase transformation, the crystal orientation was evaluated with X-ray diffraction. A phase transformation of the crystal orientation occurred as the baseplate temperature was heated up from 50 to 150 °C.

Surface morphology of Ti–6Al–4V plate fabricated by vacuum selective laser melting

A plate made of Ti–6Al–4V (Ti64) was built by vacuum selective laser melting (SLM) at a pressure of 10−2 Pa. The vacuum SLM system employed a single-mode fiber laser and three-axis galvanic mirror in order to form 3D metallic structure. In order to investigate the surface morphology on the fabricated plates, Vickers microhardness and surface roughness R a were measured. From the results, the Vickers microhardness of the fabricated plates was recorded at 391 HV, higher than the typical 340 HV for a Ti64 plate. It was also determined that crystal orientation was evaluated with X-ray diffraction. From the results, the crystal orientation of powder is composed mainly of martensitic alpha. Diffraction peaks corresponding to β (110) were detected in vacuum SLM processed samples.

Microstructure evolution and density behavior of CP Ti parts elaborated by Self-developed vacuum selective laser melting system

This work mainly focuses on the evolution of density behavior and microstructure of commercial pure (CP) Ti parts elaborated by SLM under vacuum system (1×10−4bar) developed at the IRTES-LERMPS laboratory. The mechanism of melt and evaporation process during selective laser melting (SLM) under vacuum environment is also presented in this paper. The surface quality, density and microhardness of Ti samples were measured as a mechanical property. Fine hexagonal crystal structure of α can be found with low scanning velocity, martensitic formation α′ can be observed with high scanning velocity, the method of scanning twice can enlarge the of grain size. A systemic SLM process under vacuum is proposed to calculate the maximum temperature of the molten pool and reveals the evolution of the solidification of melting pool under the laser beam irradiation.

Selective laser melting commercially pure Ti under vacuum

A commercially pure Ti part was produced using self-developed vacuum selective laser melting system. A smooth surface with roughness Ra 5 μm can be obtained due to avoiding balling process. The density value of the samples with low laser scanning velocity was the same as the theoretical density value. The evolution of microstructural feature is also observed with increasing scanning velocity. The phase transformation was shown as follows: fine and homogenous α → irregular acicular martensite α′ → refined zigzag martensite a″.