摘要
随着计算机技术和自动控制技术的发展,在金属切削加工中的辅助时间大为缩短,刀具因磨损而导致的频繁换刀时间已成为制约提高切削加工效率的主要因素。长期以来,人们习惯于用切削液冷却、润滑刀具来减小刀具磨损。然而,随着环境保护及可持续发展要求的不断提高,传统浇注式切削液的使用越来越受到限制,迫切需要研究开发新的绿色冷却润滑方式,以满足切削加工效率不断提高的要求。
小量冷却润滑MQL是目前一种新兴的绿色冷却润滑技术,其冷却润滑效果直接受切削液被雾化的程度支配。传统雾化喷嘴由于受切削液粘度的影响,很难达到理想的雾化效果。基于气泡雾化原理的雾化喷嘴(含混合器),克服了这些不足,且具有工作压力低、耗液耗气量小和雾化质量高等特点,已引起人们的重视,但目前关于气泡雾化喷嘴的理论和应用研究还很不完善。本文结合气泡雾化MQL切削系统的研制开发,以气泡雾化喷嘴为研究对象,用流体动力学软件FLUENT研究分析了对雾化喷嘴内部(混合器部分)和外部(喷嘴下游)流场特性及雾化特性,设计并制作了一套基于气泡雾化原理的MQL切削系统,并进行了切削试验研究。其结果对气泡雾化喷嘴的研究和应用具有一定的借鉴意义。
论文在对液体雾化基本理论和气泡雾化喷嘴工作原理分析的基础上,用FLUENT的前处理软件Gambit实现了对雾化喷嘴内部和外部流场的几何建模及网格划分;用FLUENT中的通用多相流模型——混合模型对喷嘴内部流场特性进行了模拟分析,给出了喷嘴内部流场的压力场、速度场和气液组分分布,以及气、液相的运动迹线图,分析了喷嘴内部的流场特性及气液两相的混合效果,证明了气泡喷嘴内部有均匀泡状流存在;用FLUENT中的离散相模型(DPM)对喷嘴下游的流场特性和雾化特性进行了模拟分析,研究了气泡雾化喷嘴外部流场的速度场分布、颗粒粒径分布及雾化角,分析了工况参数对流场特性和雾化特性的影响,获得了喷嘴外部流场的速度场分布、颗粒粒径分布和雾化角随工况参数的变化规律。
通过以上研究分析,充实了气泡雾化喷嘴的结构设计及参数选择,制作了一套气泡雾化MQL切削系统,并与先进涂层高速钢刀具结合,分别对Z107铝硅合金和45号钢进行了钻削及铣削试验,研究分析了刀具的切削性能和磨损特性。结果表明:在钻削铝硅合金时,切屑粘结现象明显减少,排屑顺畅,涂层的性能优势得以充分发挥;在铣削45钢时,立铣刀的磨损得到改善,尤其是主切削刃边界磨损明显减小,有利于延长立铣刀的使用寿命。
With the development of computer technology and automatic control technology, non-cutting time in metal-cutting fields has been reduced greatly. But because of cutting tool wear, the time for changing the tools frequently has became the primary factor in the restriction of enhancing the metal-cutting efficiency. For a long time, the people are accustomed to reduce the cutting tool wear by using cutting fluid for cooling or lubricating. However, with the continuous improvement of environmental protection and sustainable development requests, the traditional manner of cutting fluid used is restricted more and more so that new green cooling lubrication ways is in the urgent needs for satisfying the request of the machining efficiency.
At present, minimum quantity lubrication (MQL) is one kind of green cooling lubrication technology which is mature and applied widespread and its cooling lubrication effect directly controlled by the atomizing degree of the cutting fluid. The traditional atomizer nozzle is difficult to achieve the desired spraying effects because of the coolant fluid viscosity. The effervescent atomize based on the principle of bubble atomizing spray nozzle (with mixer) overcomes such deficiencies and works with characteristics of low-pressure, low-liquid consumption and high spry quality. But the theory and applied research about the effervescent atomize is imperfect. In this paper, referring to the development of the MQL cutting system, taking the effervescent atomize as the object of study, the flow field characteristics and atomization characteristics of atomization nozzle (mixer) and external (downstream of the nozzle) were analyzed with fluid dynamics software—FLUENT and a kind of atomization MQL machining system was designed, at last, giving some cutting experiments. The result has certain significance for the effervescent atomize research and application.
Based on the basic theory of liquid atomization and the principle of effervescent atomize, using the pre-treatment software named Gambit of FLUENT, the paper was achieved geometric model and mesh for the internal and external flow field of the effervescent nozzle and used FLUENT general multiphase flow model - the hybrid model to analysis nozzle flow characteristics, presenting the internal flow nozzle pressure field, velocity field and gas-liquid component distribution, proving that exists even bubbles within the nozzle by analyzing flow field characteristics and mixing effect of effervescent atomize; Besides, the flow field and atomization characteristics in the nozzle downstream was simulated by using discrete phase model (DPM) of FLUENT. The speed field distribution, particle size distribution and spray angle and the impacts of operating parameters on them were studied. Obtaining the rule about the speed field distribution, the particle size distribution and the atomization angle go along with the operating parameters in the exterior flow field of spray nozzle.
Based on the study above, the effervescent atomize structure design and parameter selection was improved and one set of cutting system of bubble atomization MQL was designed, and the drilling and milling tests to Z107 Al-Si alloys and steel 45 respectively was done using high-speed steel cutting tools with advanced coatings and cutting performance and wear characteristics of the tool was analyzed. The result show that the ship sticking phenomenon reduces obviously and the escape of chips is smooth when drilling Al-Si alloys, the coating performance superiority can display fully; for steel 45, the tool wear, especially the boundary wear of main cutting edges is improved, which is good for prolong the tools life.
引文
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