Thermische Analyse des Zerspanens metallischer Werkstoffe bei hohen Schnittgeschwindigkeiten
Thermische Analyse des Zerspanens metallischer Werkstoffe bei hohen Schnittgeschwindigkeiten
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金属材料加工过程中的热力学分析
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
U. Renz
中科院分区：
文献类型：
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作者：
B. Müller;U. Renz
由于刀具磨损、材料性能和摩擦等参数受到影响，加工操作中的温度会影响整个过程。在本工作中，研究了工件材料AISI 1045钢，AA 7075铝和Ti6Al4V钛的车削工艺，切削速度高达100 m/s。结果表明：随着切削速度的增加，切屑底表面温度有明显的升高，逐渐接近一个极限值，这与AA 7075铝合金的熔化温度相对应；工件表面温度也随切削速度的增加而显著升高，且受刀具磨损的影响较大。为测量切屑和工件表面的温度，研制了一种快速光纤双色高温计。双色原理允许在不知道表面发射率的情况下进行高绝对精度的温度测量。直径小的石英纤维可以在光学通道有限的位置进行测量。此外，还应用高速红外摄像机测量正交车削过程中切屑形成过程中的温度分布。对原始剪切区的温度分布进行了评估，表明材料的行为取决于切削速度。在另一种实验装置中测量了工具随时间变化的温度分布。由于尺寸小，温度梯度高，很难在每个感兴趣的位置进行温度测量，例如在刀具和切屑之间的摩擦区或成品工件的次表层。为了确定刀具、工件和切屑的完整温度分布，对二维能量方程进行了数值求解。采用结构网格的有限体积法求解，可以计算稳态温度场和随时间变化的温度场。通过计算温度与实测值的比较，对热源项在不同位置的理论分布进行了修正。结果表明：AISI 1045钢在摩擦区可以达到工件材料的熔化温度；工件亚表层出现了极高的温度梯度，温度超过了铁素体/珠光体向奥氏体转变的组织转变温度。研究了相变焓对温度的影响。根据温度场计算了热通量。进入刀具的热通量随着时间的增加而急剧减小，在稳定状态下可以忽略不计。即使在常规速度下，进入工件的热流也比过去假设的要高得多。
The temperatures occuring in a machining operation affect the whole process, since parameters as tool wear, material behaviour and friction are influenced. A turning process with cutting speeds up to 100 m/s is investigated in this work for the workpiece materials AISI 1045 steel, AA 7075 aluminium, and Ti6Al4V titanium. The results show a strong temperature increase with rising cutting speed for the chip bottom surface approaching asymptotically a limiting value, which corresponds to the melting temperature in case of AA 7075 aluminium alloy. The workpiece surface temperatures also show a strong increase with cutting speed and are strongly affected by tool wear. For temperature measurements of chip and workpiece surfaces a fast fibre-optic two-colour pyrometer has been developed. The two-colour principle allows temperature measurements with high absolute accuracy without knowledge of the surface emissivity. Quartz fibres with small diameters enable measurements at locations with limited optical access. Additionally a high-speed infrared camera has been applied to measure temperature distributions during the chip formation in an orthogonal turning process. The temperature distributions in the primary shear zone have been evaluated, which show that material behaviour is depending on the cutting speed. The time dependent temperature distribution of the tool has been measured in an alternative experimental set-up. Temperature measurements are hardly possible at each location of interest, e. g. in the friction zone between tool and chip or in the finished workpiece subsurface layer, due to the small scales and high temperature gradients. To determine the complete temperature distribution of tool, workpiece, and chip the two-dimensional energy equation is solved numerically. A finite-volumemethod with structured grids is applied for the solution, which allows the calculation of steady-state and time dependent temperature fields. The theoretically determined distribution of the heat source terms at different locations has been corrected by a comparison of the calculated temperatures with measured values. The results show that the melting temperature of the workpiece material can be reached in the friction zones for AISI 1045 steel. Extremely high temperature gradients occur in the workpiece subsurface layer and the temperatures exceed the structural transformation temperature at which Ferrite/Pearlite changes into Austenite. The influence of the transformation enthalpy on the temperatures has also been investigated. Heat fluxes have been evaluated from the temperature fields. The heat flux into the tool decreases strongly with increasing time and is negligible for the steady state. Even for conventional speeds the heat flux into the workpiece is significantly higher than assumed in the past.