3D printing has become commonplace for the manufacturing of objects with unusual geometries, and recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping . This is a work of making three-dimensional solid objects from digital files . Compared to conventional manufacturing methods, 3D products can be created by acquired data or structures built in computer - aided design (CAD) software and reduce waste while reaching satisfactory geometric accuracy, thus, 3D printing has the advantage of higher quality, greater efficiency and reduce maintenance cost. 3D printing has found industrial applications in the automotive and aerospace industries for printing prototypes of car and airplane parts, and in the architectural world for printing structural models . According to the state of materials, 3D printing can be divided into many types, such as stereolithography (SL) , Polyjet  fused deposition modeling (FDM) , laminated object manufacturing (LOM) , selective laser sintering (SLS) , laminated engineered net shaping (LENS) , Prometal , and so on.
FDM, as a kind of rapid prototyping technology, is one of the most widely used methods for rapid prototyping in the world and developed by Scott Cump of Stratasys. Low price, high speed and convenience of the process are the main benefits of FDM. The physical process of FDM method was a thermoplastic polymer is used to print layers of materials. The filament is heated at the nozzle to reach a molten or semi-liquid state and then extruded on the platform or on top of previously printed layers. The direction in which the head and platform are free to move depends on 3D printer type. In this study, the head moves on X-Y plane and deposits materials according to the geometry of the currently printed layer. After finishing a layer, the platform holding the part moves vertically in the Z direction to begin depositing a new layer on top of the previous one . The thermoplasticity of the polymer filament is an essential property for this method, which allows the filaments to fuse together during printing and then to solidify at room temperature after printing . An excellent advantage of FDM is that it can be used to create objects fabricated from multiple material types by printing and subsequently changing the print material, which enables more producer control over device fabrication for experimental use. Besides conventional materials such as PC , polystyrene (PS) , ABS , FDM can also be used to print 3D models by using metal , ceramics  and biomaterials . FDM 3D printing technology can be applied in many fields, including energetic materials.
Melt cast explosives are used in mortars, grenades, artillery shells, warheads, and antipersonnel mines. 2,4,6-trinitrotoluene (TNT) based melt cast high explosive (HE) compositions occupy a premier position as fillings for warheads and projectiles due to extensive production facilities all over the globe, despite their limitations and the emergence of cast cured HE compositions . An ideal melt-cast explosive or its formulations should have the following properties: (1) melting point 70–120℃, (2) low vapor pressure, (3) no shrinking and cracking on cooling, (4) no separation from the shell or casing, (5) high density and good energetic performance . FDM 3D printing technology has been employed to fabricate melt-cast explosive. Previous researcher used an independently developed melt-cast explosive 3D printing principal prototype to prepare TNT/HMX based melt-cast explosives. The results show that 3D printing melt-cast explosives have more compacting internal structures with the density of 1.65 g/cm3, the compressive strength of 5.56 MPa, and the detonation velocity of 7143 m/s . Using this method can effectively avoid the generation of the shrinkage cavity and avert the internal porosity in the process of extrusion charge. In addition, He et al. prepared a gradient structured HMX/Al composite by using 3D printing technology, which can control the burning rate by change the component ratio . In a word, FDM provides an innovative and reliable manufacturing method for explosive and can be regarded as one of the satisfactory ways to fabricate next-generation explosives with higher safety and better performance.