中密度纤维板平面立式铣削排屑特征的数值模拟与试验验证

Numerical simulation and experiment validation for characteristics of gas-solid flow in chip discharging field with vertical milling on MDF

立式铣削切屑颗粒细小质轻且排屑不规则,常因吸尘罩的结构与安装不合理,这类机床周边的作业环境粉尘污染严重。优化吸尘罩的设计是改善作业环境的重要途径,掌握排屑特征是吸尘罩优化设计的基础和依据。笔者根据立式铣削常见的基材对象和高转速等加工特点,运用计算流体力学FLUENT仿真软件,模拟研究了铣刀环形气流场,采用非结构化和局部加密的网格处理方法,使用欧拉-拉格朗日计算模型,模拟排屑气固流场,研究了排屑方向与速度、颗粒分布与速度等特征参数。研究表明,铣刀转速在10000~24000 r/min时,铣刀环形流场切向最大的速度为6.93~15.72 m/s,并与其半径的增大呈指数关系降低。排屑显现了主排屑区和次排屑区两个区域,主排屑区是以切削区为顶点的椭圆状锥体,切屑在水平锥角为83°~86°、垂直锥角为20°~22°范围呈辐射状抛射。主排屑区排屑由密集流和稀疏流两部分构成,密集流和稀疏流中颗粒的初始速度分别在7.57~17.85和3.34~8.22 m/s范围,与铣刀转速呈正相关函数关系,密集流和稀疏流中颗粒速度随喷射距离的增加呈线性降低,在距切削区10倍铣刀直径处密集流和稀疏流的颗粒分别在1.14~6.63和0.75~1.40 m/s范围。次排屑区内为细小的颗粒,随铣刀旋转以1~5 m/s的速度向四周散发。试验表明,排屑方向、颗粒分布等特征与模拟相吻合,密集流和稀疏流的颗粒初始速度及10倍铣刀直径处速度的实测与模拟误差为3.1%~7.1%。

Vertical milling produceslarge amount fine dust particles which are thrown around due to the rotation of the milling cutter.The dust pollution around the milling workplaces is a serious problem in the wood processing industry because of the unreasonable structure and installation position of the dust hood.It is obvious that optimizing the design of dust hood is an efficient way to reduce the dust pollution on working environments.However,the characteristics of dust removal are the basis for the optimal design of dust hood.Therefore,this study analyzed the wood material commonly used in CNC milling for the panel furniture production,tool configurations and cutting parameters.Based on the principle of gas-solid two-phase flow dynamics and gas turbulence theory,the Eulerian-Lagrange method was used to simulate air flow field around the milling tool,and the gas-solid flow in the chip flow field.The results showed that the tangential velocity of the annular air flow field decreased exponentially with the increase of the radius of the annular flow field,and the maximum velocity varied from 6.93 to 15.72 m/s accordingly with the milling speed in the range of 10000-24000 r/min.The chip flow appeared two obvious areas(the main chip removal area and the secondary chip removal area).The main chip discharge area was an elliptical cone with the cutting area as the apex.,and the chips were thrown within the range of cone angle of 83°-86°in horizontal and 20°-22°in vertical.The main chip discharge area composited dense and dilute sections.The initial velocities of chips in dense and dilute sections were 7.57-17.85 and 3.34-8.22 m/s,respectively,and increased with the milling speed linearly.The velocities of chips were 3.34-8.22 m/s,respectively,at the point of 10 times distance from cutting area.In the secondary chip discharge area,there were fine particles which were distributed in all directions with the velocity of 1-5 m/s as the milling tool rotated.The simulated chip removal direction and particle distribution were in good agreement with the experiment.The errors between the actual measurements and simulation results were 3.1%-7.1%for the initial particle velocity of the dense and dilute flow,and the velocity at 10 times the diameter of the milling cutter.