Laser Applied Rapid Prototyping of Metallic and Ceramic Dies

在提出的工艺中，激光在金属粉末的表面上扫描以制作导线，然后通过在间隙中平行制作许多导线来制作表面。通过添加层，可以形成三维模型。首先用CO_2激光扫描各种金属粉末，观察其凝固特征。研究发现，用铜粉可以制成凝固块体，但块体内部留下了许多空隙。为了减少空隙，粉末被压实并增加初始密度。虽然通过这种方法减少了空隙，但由于传热更大，需要更多的能量。从凝固过程的简单分析可知，成形特性受热导率和激光吸收率的影响。为了进行有限元分析，测量了不同密度金属的换热系数。利用这些系数，用开发的有限元程序模拟了粉末的凝固行为。通过有限元分析，发现需要峰值输出高的脉冲激光器，下一步采用脉冲型YAG激光器，并寻找适合该工艺的材料。由于该工艺被认为是连续熔覆，因此对Ni基和Cu基熔覆材料进行了测试。通过使用包层材料，可以获得几乎没有空洞的凝固线材。从力学性能测试结果来看，凝固后的Ni基合金硬度值约为800Hv， Co基合金硬度值约为600hv。凝固后的镍基合金虽然脆，但经热处理后性能得到改善。最后提出了一种三维模具成形的新方法。由于用这种方法制造大型车身需要很长时间，因此只有表面外壳和支撑部件采用激光成型，其余部分采用低熔点金属铸造填充。通过一些简单的三维模型验证了该方法的有效性。少

In the proposed process, laser is scanned over the surface of metallic powders to make a wire, and then by making many wires in parallel with a gap a surface could be made. By adding the layrs, three dimensional model could be formed. At first CO_2 laser is scanned over various metal powders and the solidified features are observed. It is found that solidified blocks can be made with copper powders but many voids are left inside of the block. To reduce the voids, the powders are compacted and the initial density is increased. Although the voids are reduced by this method, much more energy is needed due to a greater heat transfer. From the simple analysis of solidification process, the forming characteristics are affected by the heat conductivity and the rate of laser absorption. To carry out finite element analysis, heat transfer coefficients of various metals with some densities are measured. By using the coefficients, the solidification behavior of the powders is simulated by the dev … More eloped finite element code. By using the finite element analysis, it is found that pulse laser with a high peak output is desirable, and pulse type YAG laser is employed for the next step and the materials suitable for this process is looked for. Since the process is considered to be a continuous cladding, Ni base and Cu base cladding materials are tested. By using the cladding materials, solidified wires with almost no voids are obtained. From the result of mechanical testing, the hardness numbers of the solidified Ni base alloys are about 800Hv and that of Co base alloy is about 600 Hv. Although the solidified Ni base alloy is brittle, it is improved by heat treatments. Finally a new method of forming a three dimensional die is proposed. Since a long time is needed to make a large body by this process, only the surface shell and the sustaining parts are to be made by laser prototyping and the remaining parts are filled by casting of lower melting point metals. The proposed method is ascertained by some simple shaped 3D models. Less