Abstract:Various process variables influence on the quality of the end product when SLM (Selective Laser Melting) synthesizing items of powder materials. The authors of the paper suggest using the model of distributing the temperature fields when forming single tracks and layers of copper powder PMS-1. Relying on the results of modeling it is proposed to reduce melting of powder particles out of the scanning area.
IntroductionA lot of process variables are taken into account when SLM synthesizing products. More than a hundred of variables are outlined in the literature, influencing somehow the SLM process [12], however, the researchers point at some key variables, inter alia: scanning speed; laser emission power; diameter of the laser; thickness of the powder layer; gaseous medium; the strategy of scanning. For instance, the authors [2-4, 8] have considered in details the relevance of speed of scanning, laser emission power, and powder thickness for synthesizing products of copper powder PMS-1. In papers [5][6][7] the impact of a gaseous medium on forming the single layers of copper powder is studied, as well as the effect of laser beam diameter on the thickness of the layer to be sintered is examined. The papers [9,10] are focused on the importance of laser beam scanning strategy for development of thermal stresses and strains of the sintered samples. The most appropriate process conditions for sintering products of copper powder PMS-1 are determined on the base of research results outlined in paper [2]. Cubic samples with the sides 10×10×10 мм (Figure 1) are produced in these conditions. The mechanical compressive strength of the samples exceeds 105 MPа, and the porosity approximates to 15%. Further investigations require the production of samples in the form of a 6×6×30 mm bar in process conditions № 1 and № 2 ( Figure 1).All the samples produced in process conditions № 1 appear not to have any significant defects and meet the pre-set configuration (Figure 1, а). No visible defects are detected on the cubic sample produced in process conditions № 2, however, some defects occur on the lateral faces when synthesizing a bar (Figure 1, b). The defects are melted particles of powders, located on the lateral faces out of the scanning area. The defects originate mainly during the second phase of sintering the layer.A 3D thermal model concentrated on sintering a single track and a single layer according to a pre-set strategy is developed to detect the causes of defects. The model problems are solved by a mathematical package COMSOL Multiphysics, which is an efficient interactive environment for FEM simulating and calculating a great number of scientific and technical issues based on differential
At present the development of methods of layer-by-layer and line-by-line synthesis of finished prototypes and functional products made of powder materials furthers introduction of these technologies into different areas of human activities from light to heavy industry and medicine. The research has been carried out to describe how gamma radiation of the Co60radioactive isotope and the mechanical activation makes an impact on the copper powder, as well as the nature of sintering by the layer-by-layer laser synthesis. The changes of the structure and properties of the powder, which generally affects the layer-by-layer laser process of products sintering, have been detected.
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