[[alternative]]The Numerical and Experimental of the Joining of Dot Matrix Printing Pin by Micro-Laser Brazing Method

碩士機電工程學系[[abstract]]點陣式印表機印字針係由撞針及針座所組成，印字針之製造技術除材質的調配與外形製作外，最重要的關鍵技術在於撞針與針座之微細接合。本研究主要使用脈衝式Nd：YAG雷射作為加熱源，將印字針以硬銲方式接合於針座，研究過程中先以有限元素分析軟體ANSYS，模擬印字針雷射硬銲接合過程之暫態熱傳現象及熱應力分佈情形，以求得較佳硬銲參數進行硬銲實驗，實驗過程中雷射硬銲參數有脈衝頻率、脈波寬度、脈衝功率、聚焦位置及銲點走速等，並探討印字針雷射硬銲接合後之機械性質，包括銲道界面金相分析、微硬度分析、微拉伸分析及微疲勞分析。研究結果顯示使用CF50-2銀基硬銲膏，於雷射脈衝功率600W、雷射光斑直徑0.6mm、脈波寬度10ms、工件表面離焦量6.5mm可成功接合印字針，並經銲道界面金相分析及微硬度試驗結果顯示，印字針於雷射硬銲後熱影響區不明顯。銲後分析部份AISI-M42雷射硬銲件與Fujitsu雷射硬銲件之最大拉力值相似，而遠大於火焰硬銲件；AISI-M42撞針硬度值較Fujitsu撞針硬度值約小7.84 %，且兩者經同樣雷射硬銲接合後，熱影響區與母材之硬度值相似；AISI-M42銲件疲勞限較Fujitsu銲件之疲勞限小13.48 %。 潤濕性分析CF50-2銀基銲膏比CF42銀基銲膏具有較佳潤溼能力。數值模擬結果顯示撞針底部與針座間有較高熱應力存在，且接近銲接熱源的區域亦產生較高的熱應力，而遠離硬銲熱源處，如撞針前端及針座下方幾乎沒有熱應力的存在。[[abstract]]The purpose on this study is to braze the pin to the armature of dot matrix printer with the pulsed Nd：YAG laser. A three-dimensional printer needle finite element model has been setup to analyze the temperature field and thermal stress distribution in the process of laser brazing to find a better brazing condition. The experimental parameters designed include: laser power, spot size, pulse duration, focus position respectively. After brazing, the following tests were done including metallurgical analysis, micro-hardness, micro-tensile, micro-fatigue tests respectively. During the brazing process, the thermal cycle of armature was recorded to verify the result of finite element analysis. The study result shows that the laser peak power 600W, spot size 0.6mm, pulse duration 10ms, defocus-6.5mm, using type CF50-2 brazing paste can successfully join the pin to the armature. According to the metallurgic analysis, the type AISI-M42 pin and Fujitsu pin do not change its microstructure significantly during brazing process. In the micro-tensile test, the tension strength of type AISI-M42 pin is similar to of type Fujitsu pin. In micro-hardness test, the average hardness of type AISI-M42 pin is 7. 84% less than of type Fujitsu pin. In the micro-fatigue test, fatigue limit of the AISI-M42 pin is 13.4% less than of the Fujitsu pin. In addition, the wetting ability of type CF50-2 brazing paste has better on the surface of the low steel sample with the same surface roughness. The numerical analysis result shows that the interface between the pin and the armature, and the region near the laser source both have larger thermal stress during brazing process