## 3 Internal Stress in the Component Parts Manufactured via the DMLS Technology  
According to the American patent, the DMLS technology represents a method of fusion process of powder base in which a thin layer of metal powder is without any other binding substance or fusing agent selectively heated by a laser ray to a melting temperature of the given material, in order to form a solid piece of material of the desired shape [12]. The energy of the laser layer is selected in such a way that the layer of metal powder is completely molten along the entire thickness of the lar at the impact point of the laser ray, which is led through the specified area of powder with each cycle partially overlapping with the previous one in order to form correct metal bonds between the actual and previous layer to achieve a creation of homogeneous solid substance. The entire manufacturing of the described procedure takes place in the environment of inert gas to prevent undesired reactions and oxidations. As the powder material is heated to its melting temperature along the layer thickness, the final solid substance has mechanical properties similar to those of the original powdery material. This type of manufacturing is deficient in a tendency of stress formation among the individual layers of a profile during the manufacturing process. The phenomenon has become known as the issue of residual stress and has recently been a topic of various researches and studies. The main issues are accumulation of overall and regional residual stress in the sections of the manufactured component part without a possibility of natural scattering as it could cause cracks and deformations. Even worse case is the component part not being designed correctly, which then during and after machining leads to the reduction of fatigue strength of the component part in comparison with component parts that are volumetrically formed. The difficulties occur especially when component parts are complicated as to shape with overhanging or projecting elements, as internal strain tends to concentrate on the proximity of such parts. Such a situation can cause considerable deformations and can damage the functional parts or destroy the whole part prior to the completion of the manufacturing. The difficulty can be solved, to a certain extent, by the utilization of a temporary supporting structure, which should prevent failures in the manufacturing process; yet its utilization encounters a set of problems. Thus, it would be more practical and also more financially effective if a general theory of design was available for the component parts produced via the DMLS technology. Residual stress is defined as a strain in plastic or elastically deformed material remaining in the structure  
Figure 1: Machine EOSINT M280 [12]. after removal of the load that caused deformations. The main source of residual stress in the cycles of the DMLS process is repeated heat coming out of the laser that clinkers each layer and results in an already solidified layer getting melted and subsequently cooled on inconsistent heat levels. The stress gradients in the particular layer of the manufactured component part during heating show the following two most significant areas--the upper part, i.e., the layer being exposed to laser heat, and the interface between the layer and the previous one, which Figure 2 shows [9; 10; 11; 12; 13; 14]. The tensile stress on the layer surface occurs due to the thermal expansion, whereas the layer is exposed to the compressive stress during cooling. A single manufactured layer would not be considered a problem, since the strain would naturally scatter after cooling of material. A problem occurs when the base layers limit thermal expansion and contraction of the layers right below the welding point; therefore, it can be observed in several layers deep down and can occur several times in the same layer with material not being inevitably molten. It can be caused by the elastic compressive stress present in the layers leading to the stress gradient between the layers.