【摘要】：飛秒激光具有高功率、高精確度、熱影響區(qū)小等優(yōu)點,可直接去除表面材料,實現(xiàn)微納加工,在航空、航天、半導體、生物等材料表面加工領(lǐng)域具有不可替代的優(yōu)勢。然而,在多脈沖飛秒激光的作用下,材料內(nèi)部可能產(chǎn)生熱積累和溫升,導致發(fā)生相變、氧化、甚至熔化。因此如何優(yōu)化飛秒加工參數(shù),控制熱積累和溫升是一個迫切需要解決的問題。本文對飛秒激光加工材料表面的熱積累效應進行了論述,并且應用有限差分法,利用MATLAB軟件對飛秒激光加工AZ31鎂合金表面的熱積累效應進行了數(shù)值模擬,模擬了不同的掃描速度、激光重復頻率、光斑直徑、激光能量對加工過程熱積累效應的影響,優(yōu)化激光工藝參數(shù)。并且通過對不銹鋼加工過程的模擬,與其他的模型進行了對比�？紤]與材料相關(guān)的熱傳導系數(shù)和熱容,利用中心差分法分別模擬了AZ31鎂合金在掃描速度為1 m/s、2 m/s、3 m/s、4 m/s下的表面熱積累和溫度變化。結(jié)果表明,掃描速度的提高會使熱積累溫度會有所降低,在掃描速度為1~3 m/s時,AZ31鎂合金表面的熱積累溫度并沒有穩(wěn)定,當掃描速度為4 m/s時,AZ31鎂合金表面的熱積累溫度在經(jīng)過10個脈沖的作用后會趨于平衡。掃描速度主要是通過改變光斑重疊率影響加工過程的熱積累;此外,分別模擬了AZ31鎂合金在激光重復頻率為100 kHz、500 kHz、1 MHz、2 MHz下的表面熱積累和溫度變化。結(jié)果表明,激光重復頻率的提高使表面熱積累溫度升高,并且對熱積累效應的影響非常大。激光重復頻率可以影響光斑重疊率和熱傳遞的時間這兩個因素,從而影響加工過程的熱積累;對減小光斑直徑和提高激光能量這兩種提高激光能量密度的方法進行了對比,結(jié)果表明,減小光斑直徑所產(chǎn)生的熱積累效應較弱;最后對不銹鋼鋼的飛秒加工過程進行模擬,并與其他模型的模擬結(jié)果進行了對比,結(jié)果表明本文所用模型可以有效的預計飛秒激光加工中的熱積累和溫度。
[Abstract]:Femtosecond laser has the advantages of high power, high accuracy and small heat affected zone, which can remove surface materials directly and realize micro-nano machining. It has irreplaceable advantages in the field of aerospace, semiconductor, biological and other materials surface processing. However, under the action of multi-pulse femtosecond laser, thermal accumulation and temperature rise may occur in the material, resulting in phase transition, oxidation, and even melting. Therefore, how to optimize femtosecond processing parameters and control heat accumulation and temperature rise is an urgent problem to be solved. In this paper, the thermal accumulation effect of femtosecond laser processing on the surface of AZ31 magnesium alloy is discussed, and the thermal accumulation effect of femtosecond laser processing on AZ31 magnesium alloy surface is numerically simulated by using finite difference method and MATLAB software. The effects of different scanning speed, laser repetition rate, spot diameter and laser energy on the thermal accumulation effect during processing were simulated, and the laser process parameters were optimized. And through the simulation of stainless steel processing process, compared with other models. Considering the heat conduction coefficient and heat capacity related to the material, the surface thermal accumulation and temperature change of AZ31 magnesium alloy at a scanning speed of 1 m / s ~ 2 m / s ~ (2) m / s ~ (3) m / s ~ (4) m / s were simulated by the central difference method, respectively. The results show that the thermal accumulation temperature of AZ31 magnesium alloy surface is not stable when the scanning speed is 1 ~ 3 m / s. When the scanning speed is 4 m / s, the thermal accumulation temperature of AZ31 magnesium alloy surface will be balanced after 10 pulses. The scanning speed mainly affects the thermal accumulation in the process of processing by changing the overlap rate of the spot, and the surface thermal accumulation and temperature change of AZ31 magnesium alloy at the laser repetition rate of 100 kHz,500 kHz,1 MHz,2 MHz are simulated respectively. The results show that the laser repetition rate increases the surface thermal accumulation temperature and has a great influence on the thermal accumulation effect. The laser repetition rate can affect the overlap rate and the time of heat transfer, thus the thermal accumulation in the process is affected, and the two methods of increasing laser energy density and reducing the spot diameter are compared. The results show that the heat accumulation effect caused by reducing the spot diameter is weak. Finally, the femtosecond machining process of stainless steel is simulated and compared with the simulation results of other models. The results show that the model can effectively predict the thermal accumulation and temperature in femtosecond laser processing.
【學位授予單位】：遼寧科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG665

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