Metal 3d printing is one of the high-tech manufacturing methods. Unlike machining methods which are subtractive techniques, in this method, parts are manufactured layer by layer. Materials used for this method are polymers, metal alloys, ceramics, and composite in powder or wire form. Depending on the desired material and geometry, different techniques are implemented to generate layers and adhere them together. One of the most famous techniques uses powder material and laser for adhering them.
Selective laser melting (SLM) refers to techniques which their operation principles are illustrated below schematically.

Additive manufacturing (AM) is one the most important techniques developing. It has been anticipated that AM will affect manufacturing to a great extent in the future. Not requiring molds or fixtures, AM is an excellent method for manufacturing parts that are difficult to be manufactured with other methods. The ability to make complex-shaped parts and the possibility of customization are some advantages of AM. According to the aforementioned reasons, the design to production procedures will be decreased using AM. The AM makes the opportunity for industries to manufacture parts, even one part, cost-effectively. Also, it provides the chance to make a product with different designs without any excess cost. Due to the layer-by-layer manufacturing, many costs of manufacturing and assembling are eliminated. Also, there will be no limitation for the internal structure of the final product. Since AM is categorized as a near-net-shape manufacturing method, the money and time needed for post-processing will be reduced. In addition, less wasted material makes manufacturing various parts with minimum pollution (green-manufacturing) possible.
Generally, additive manufacturing with laser is needed for all industries. Especially, their unique features have made them necessary for the aerospace, military, and jewelry industries as well as medical applications.
This technique can manufacture complex parts with high accuracy. Since the metallic powders are used as the material, final porosity can be very small (even smaller than the porosity of the final product manufactured by casting) via controlling various parameters. Thus, the mechanical properties of the final product will be similar to a product made by casting or even better than that. Also, by some heat treatments, the mechanical properties can be improved. The possibility of manufacturing final products of the digital file makes the opportunity for designers to design complex parts regardless of manufacturing considerations.