The process of laser additive manufacturing consists of depositing successive layers of molten metal powder to create a near-net shape. A high-power laser is used to melt incoming metal powder, which forms a molten pool on the surface. As the latter moves beneath the laser, this newly created molten pool solidifies. By properly controlling the trajectory of deposition tracks, one can create a diverse range of shapes with varying complexities. In nature, the laser additive manufacturing technology is a continuous multilayer laser cladding process under the control of computer. The microstructure morphology of cladding layer is essential for the performance of as-deposited metal parts, so the cladding process was studied through related experiment. Based on the solidification theory, the microstructure morphology and the evolution rule were comprehensively analyzed. The results indicate that the temperature gradient and the solidification rate are the primary factor determining the microstructure morphology of cladding layer.

Laser additive direct deposition of metals is a new rapid manufacturing technology, which combines with computer aided design, laser cladding and rapid prototyping. The advanced technology can build fully-dense metal components directly from CAD files without a mould or tool. With this technology, a promising rapid manufacturing system called “Laser Metal Deposition Shaping (LMDS)” is being constructed and developed. Through the LMDS technology, fully-dense and near-net shaped metallic parts can be directly obtained through melting coaxially fed powder with a laser. In addition, the microstructure and mechanical properties of the as-formed samples were tested and analyzed synthetically. The results showed significant processing flexibility with the LMDS system over conventional processing capabilities was recognized, with potentially lower production cost, higher quality components, and shorter lead time.

High-pressure gas quenching is the heat treatment technology which quenches the works by use of high-pressure and high-speed flow gas. FLUENT software is used to simulate the process of gas-solid coupling flow and heat transfer in the nozzle-type vacuum high-pressure gas quenching furnace. The hot wire anemometer is used to measure the inlet velocities of nozzles, which provides the boundary conditions for computer simulation. By the computer simulation, the gas flow fields, work temperature fields and work cooling curves are attained. The results show that the big eddy current occurs at the corner of the furnace and the cooling rate of the work is slow there. Contrasting the simulating result of work cooling rate at the center of furnace with the actual measured one by the thermocouple, we find when work is cooled to the temperature of 430K, the simulating result is faster than the actual one about 50 seconds. The simulating results basically correspond with the actual trend of the gas quenching.

Coaxial powder delivery nozzle plays an important role in metal part direct and rapid prototyping technology and the reasonable structure can ensure uniform and stable flow of metal powder. Gas-solid two-phase flow theory is considered to simulate outside flow field of carrying gas-type coaxial powder delivery nozzle. The physical and mathematical models are erected. FLUENT software is used to simulate the velocity distribution of gas and solid particle, the volume fraction distribution of particle and the focusing properties. The simulative results indicate that both the structure of coaxial powder delivery nozzle and inlet velocity affect the convergence of powder. When the metal powder is only driven by the carrying gas without the shield gas flow, the powder appears focusing and the focus is 8mm far from the nozzle exit, but the volume fraction at the focus is only 2.6 percent, which shows the convergence of powder is not good and the usage rate is not high. In the optimized structure the simulative results show that the powder flow is affected by the flow of shield gas. When the velocity of shield gas is 6m/s, the powder shows good convergence and the volume fraction of powder at the focus reaches 3.3 percent. The higher the velocity of shield gas is, the more uniformly the powder flows, but the volume fraction at the focus is slightly lower. It is obvious that the numerical simulation will benefit for coaxial nozzle designing and performance improving.

In the process of metal powder laser rapid forming, various defects may be caused in forming parts on account of technical parameters, equipment performance, material characteristics and other factors. While dimensional accuracy error and surface sticky powder caused by powder factor are the two major defects of forming parts. The experimental analysis finds that less or over accumulation resulting from powder feed delay is the main reason for affecting the dimensional accuracy of cladding and the main reason which affects the appearance of surface sticky powder is specific energy.