Development of the new fabrication system of dental prostheses using the computer assisted combined machining

为了减少实验室劳动，制造出更高质量的假体，我们已经提出了数控组合加工。焊接是将分立零件装配式铸造、机械加工和电火花加工相结合的一项关键技术。为此，我们研制了数控激光焊机。我们对振荡电池进行了改造，采用脉宽调制技术控制焊接能量，在初始脉冲之后施加脉冲高度较低的附加脉冲，以提高焊接性能。我们对纯钛进行单次脉冲照射，观察其熔化特性。由于冷却速度太快，熔池在波聚焦之前就凝固了，我们发现样品的内部气孔和表面粗糙。我们还发现，获得良好焊接的可用能量的空间受到了限制。相反，由于…后开始凝固，采用脉宽调制可以减少内部气孔率和表面粗糙度更多的是熔化池塘的浪潮聚焦。此外，可用能级的自由度随着PWM的增加而增加，我们希望将PWM应用于数字控制焊接，尽管我们发现熔池的蒸发量更大，凹陷更深。此外，我们还利用PWM进行了焊接收缩的实验，将直径为2 mm的钛棒焊接在厚度为3 mm的钛板上，并测量了焊接时的收缩。未加脉宽调制的收缩为24微米，未加脉宽调制的为6微米。金相观察表明，未加脉宽调制时，由于熔池底部和表面在熔池中心之前凝固，产生了较大的收缩应力。相反，由于熔池底部先于表面凝固，脉宽调制可获得较小的收缩应力和收缩间隙，但凹陷较深。这些结果表明，采用脉宽调制能量控制，降低了焊点的残余应力，防止了变形和焊接裂纹的发生。成功地将数字控制焊接技术应用于金属模具上的桥梁金属骨架制造。较少

In order to reduce labor in the laboratory works and to fabricate prostheses with higher quality we already proposed the numerically controlled combined machining. Welding is a key technology to combine the separated parts fabricated casting, mechanical machining, and electric discharging machining. Therefore, we developed the numerically controlled Nd : YAG laser welder. We remodeled the oscillating battery to control the welding energy using PWM where additional pulse with lower pulse height was applied after the initial pulse to increase welding properties. We shot the single pulse to pure titanium to observe the melting properties. We found internal porosity and rough surface on the specimens since the cooling rate was too fast and molten pond solidified before the wave focused. We also found the room for the available energy to obtain good welding was restricted. On the contrary, we could reduce internal porosity and surface roughness with PWM since the solidification started afte … More r the wave of molten pond focused. In addition, freedom of available energy level increased with PWM and we expected to apply the PWM to numerically controlled welding although we found the higher amount of evaporation and deeper concavity of molten pond. Additionally, we performed the experiments to evaluate the welding shrinkage with PWM.We welded a titanium rod with the diameter of 2 mm on the titanium plate with the thickness of 3 mm and measured the shrinkage at the welding. Shrinkage was 24 mum without PWM and 6 mum with PWM.Metallurgical observation indicated larger contraction stress was produced without PWM since the both bottom and surface of molten pond solidified before the center part of the molten pond. On the contrary, smaller contraction stress and gap but deeper concavity were obtained with PWM since the bottom of the molten pond solidified prior to the surface. These findings indicated energy control with PWM reduced the residual stress at the welding spot and prevented the deformation and the occurrence of welding crack. We successfully applied the numerically controlled welding to fabricate the metal frameworks for bridge on the metal molds. Less