【作者】 苏宇；

【导师】 何宁；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 难加工材料在航空航天工业、兵器工业、化学工业及电子工业中有着广泛的应用。但刀具的快速磨损是制约难加工材料加工效率提高的瓶颈,而低温MQL切削技术是在目前已有的工艺基础上能进一步提高难加工材料加工效率的有效途径之一。本文针对低温MQL切削的关键技术,以及其在难加工材料加工中的应用等问题进行探索性研究。主要研究工作包括:1.采用复合制冷方法研制了一种新型低温MQL装置,并对其进行了较为全面的性能测试。结果表明,该装置具有制冷速度快、负荷可调性强、调节响应能力好、可靠性高、易于实现冷风温度的连续调节和精确控制等优点,为低温MQL切削技术的研究与应用提供了一种新的有效手段。2.通过不同冷却润滑条件下钛合金高速切削时的切削温度、切削力、及刀具前刀面摩擦状况的对比试验分析,研究了低温MQL的冷却润滑作用,发现了低温MQL在高速切削中的冷却润滑作用机理:低温MQL对切削区良好降温效果减少了润滑油因切削高温而蒸发,且益于润滑膜强度的保持,进而提高了润滑油的润滑效果。3.通过镍基高温合金的高速车削试验,研究了冷却润滑条件对刀具磨损、表面粗糙度和切屑形态的影响;分析了低温MQL条件下高速车削镍基高温合金的刀具磨损机理,探讨了低温MQL对镍基高温合金高速车削切屑形态的影响作用机理。4.分析了低温MQL条件下硬质合金刀具高速铣削钛合金的刀具磨损、破损机理,指出刀具磨损机理主要为粘结磨损和扩散磨损,破损机理主要为热裂破损;低温MQL改善了摩擦接触状态,抑制了粘结磨损和扩散磨损,其润滑作用是延长高速铣削钛合金刀具寿命的主要原因;研究了高速铣削钛合金时刀具的热裂破损,发现湿式切削由于热疲劳引起热裂纹以很快的速度形成与扩展,刀具在铣削初期便发生严重的热裂破损而失效,而低温MQL条件下刀具虽然也会出现热裂纹,但一般不会因热裂纹导致刀具的早期破损。更多还原

【Abstract】 Difficult-to-machine materials have been widely used in the aerospace, weapon, chemical, and electronic industry. However, rapid tool wear is the bottleneck that restricts the enhancement of machining efficiency of difficult-to-machine materials. As one of the effective approaches, cryogenic MQL may improve the machining efficiency of difficult-to-machine materials better than the current techniques. Aiming at some problems such as the key technologies of cryogenic MQL and its application in the machining of difficult-to-machine materials, the groping research was conducted in this dissertation. The main research works are included as follows:1. Composite refrigeration method was adopted to develop new cryogenic MQL equipment, and meanwhile experiments were carried out to test its performance. The results indicate that this equipment has many merits such as high refrigeration speed, adjustment capacity, credibility and control abilities of the temperature of refrigerated gas, which provides a new effective means for the research and application of cryogenic MQL cutting technology.2. By comparing the cutting temperature, cutting force and friction state at the rake face of cutting tool in the high-speed cutting of titanium alloys under different cooling/lubrication conditions, the cooling/lubrication effect of cryogenic MQL was investigated. The cooling/lubrication mechanism of cryogenic MQL in the high-speed cutting was disclosed as follows: the good cooling effect of cryogenic MQL reduces the evaporation of cutting oil, and benefits the maintenance of strength of lubrication film, thus improving the lubrication effect of cutting oil.3. High-speed turning experiments of nickel-based alloys were conducted to investigate the influence of cooling/lubrication conditions on tool wear, surface roughness and chip shape. The tool wear mechanism in the high-speed turning of nickel-based alloys was analyzed under cryogenic MQL condition. The effect mechanism of cryogenic MQL on chip shape was discussed in the high-speed turning of nickel-based alloys. 4. The tool wear mechanism and fracture mechanism of cemented carbide tools in the high-speed milling of titanium alloys were analyzed under cryogenic MQL condition. It was pointed out that the main wear mechanisms were adhesion and diffusion, and the main fracture mechanism was thermal cracking. The cryogenic MQL may improve friction and contact state, restrain the adhesion wear and diffusion wear. And its lubrication effect is the main reason of improvement of tool life in the high-speed milling of titanium alloys. Through the investigation of thermal cracking of cutting tool in the high-speed milling of titanium alloys, it was found that due to thermal fatigue, flood coolant resulted in the formation and propagation of thermal cracks at very fast rate, thus causing severe thermal cracking of cutting tool at the initial stage of milling. Although thermal cracks were also observed under cryogenic MQL condition, they did not generally induce the early fracture of cutting tool.更多还原