| With the development of science and technology, CNC machine tool industry, as their basement, is also developing very fast. As the representative of the CNC, the milling-turning machining center, with its high precision, high efficiency and relatively low prices, quickly led the market and become the vanguard of CNC machine tools. High-precision and high-efficiency machine needs configuring some high-precision and fast response functional units. As functional units of milling-turning machining center, direct-drive turntable and power turret not only have the strong output torque, high load capacity, high reliability, but also have the fast dynamic response and high accuracy. Two functional units adapt direct drive technology to eliminate the middle of the transmission link and achieve zero transmission, which not only occupies a smaller space, but possesses faster response speed and dynamic response. Whether Static and dynamic characteristics of two functional parts meet the machining accuracy requirements and both of them affect the precision greater is worthy of our study and discussion.Using the direct-drive turntable and power turret as the study, the topic carries out the static and dynamic analysis, compares the effect sizes for precision, possesses milling dynamics chatter analysis for turret and attains stability lobe diagram. After that, the topic analyzes the effects of cutter teeth, cutting force coefficients, the natural frequency for machining stability. The main contents are as follows:(1) The topic describes the basic structure of direct-drive turntable and working principle of turning and milling; it studies hydrostatic guideways which is a key component of the direct-drive turntable, calculates its film stiffness to pave the way for finite element analysis and computes double row cylindrical roller bearings stiffness. The topic establishes three-dimensional model of the direct-drive turntable, carries out static and dynamic analysis and gets static deformation of the turret milling the six natural frequencies and mode shapes. Besides, amplitude-frequency curves in the excitation force are got in the topic. From the amplitude-frequency characteristic curve it can be seen that the amplitude of the maximum reaches0.0324mm when the frequency is416Hz. The corresponding speed of the frequency needs avoiding.(2) The topic describes the working mechanism of power turret and calculates support spindle of angular contact ball bearing stiffness and preload. It establishes a three-dimensional model of the power tool holder, carries out static and dynamic analysis with finite element software and gets static deformation, the six natural frequencies, mode shapes and frequency characteristic curve under excitation force. From the amplitude-frequency characteristic curve it can be seen that the amplitudes in the X and Y directions reach2.66mm and1.55mm respectively in the frequency of480Hz and440Hz. The corresponding speeds of the frequency need avoiding.(3) By comparing the power turret and direct-drive turntable static deformation and the size of the resonance amplitude, we obtains that the power turret has a bigger impact on the workpiece precision. Considering the distance from the turret axis to tool tip, milling vibration will further affect machining accuracy, so the topic carries out processing dynamics analysis and gets the stability lobe diagram. The stability lobe diagram tells us how spindle speed and axial depth of cut affect processing stability, which provides a reference on the choice how to decide the cutting parameters. In addition, the paper also analyzes the influence of cutter teeth, the natural frequencies and cutting force coefficients to processing stability, which show that the more teeth, the bigger cutting force coefficient and the higher natural frequency will cause the more serious chatter. |
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