3D Printing Technology of Manufacturing Metallic Material

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Generally, rapid laser prototyping requires to expose the surface of the specimen to high power laser in order to melt metal powder into liquid state, then move the laser beam to melt the powder in the front and let the liquid metal in the rear go through cooling and solidification. But all these need surrounding measures like powder feeding devices and the protection of inert gas and nozzle control to support.

3D printing technology of manufacturing metallic materials is rather problematic due to the relatively high-melting point metal and the involving of solid-liquid phase change, surface diffusion, heat conduction and other physical processes. Besides that, issues need to be considered might also include whether the crystal structure generated is good, and whether the whole specimen is uniform, and the size of internal impurities and pores, etc. In addition, the rapid heating and cooling can cause large residual internal stress within the specimen. To solve these problems, cooperations of more complex manufacturing parameters were required, such as power and energy distribution of the laser, the moving speed and path of laser focal point, the feeding speed, protection pressure, and external temperature, etc.
Making-metal-parts

In all kinds of metal alloys, titanium alloy received particular attention. It is an ideal kind of aerospace material owing to its low density, high strength, corrosion resistance, and high melting point. However, it can never be cast through cutting or shaping as it is hard and brittle. Instead, the heat generated during heating procedures can never cause local deformation due to its low thermal conductivity. Thus, rapid prototyping technique is a better fit. Finally, titanium alloy is very expensive, the application of 3D printing technology can reduce the weight of the aircraft and save the cost of raw materials at the same time.

There is a variety of different types of 3D printing technologies evolved by different institutes, but the elementary principles are almost the same. Most of these technologies began in the mid of 1990s, later than the FDM, SLA and SLS technologies which use resins and plastics as raw materials. Laser molded parts perform no poorer than those cast by forging and pressing in static mechanical properties, but because the processing time is very long, external disturbance will cause the unevenness macrostructure, besides that there might be a gap on the fatigue performance.

In addition to the equipment, metal powder as a consumable material is also very important, especially titanium powder. It is estimated that the world’s total annual consumption is 140,000 tons, amounting to 40 billion dollars. Most of these titanium are titanium sponge produced by magnesium or sodium reduction methods, while titanium powder is mainly produced by dehydrogenation method. Currently titanium in powder form is only consumed at a rather insignificant proportion. 3D printing techniques demands a lot on titanium powder, such as its shape, size distribution and purity, etc. Titanium powder produced through hydrogenation-dehydrogenation method usually is irregular in shape and uneven in size, affecting the accumulation of powder molding and making it difficult to be applied into 3D printing, thus titanium powder usually needs to be prepared through aerosol polarization method or rotating electrode method. These techniques are not very abstruse. However, different 3D printing techniques have different requirements on devices and raw material powder as well. In other words, the printing of unique materials requires different devices and processes to support. Therefore, the vast majority of equipment manufacturers are supplying equipments, technologies, materials and softwares at the same time, supplies also take up an important part of their income while selling equipments.