The new trend of compound CNC machine tools from single function to multifunctional direction. Composite machining tools such as turning milling composite, turning grinding composite, and milling grinding composite have emerged one after another with the changing requirements of part processing. The emergence of this type of machine tool has changed the layout and structure of traditional CNC machine tools, enabling one machine to be used for multiple purposes. The workpiece can be clamped in one go to complete all or most of the machining processes, thereby reducing the number of workpiece clamping times, improving machine tool processing efficiency, reducing the number of machine tools used, and saving energy.
Turning and milling composite machining machine tools are rapidly developing and widely used CNC equipment in the field of composite machining machines. For high-speed precision turning and milling composite CNC machine tools, the spindle system is an electric spindle structure, and the machining accuracy of the machine tool largely depends on the accuracy of the electric spindle system, and is affected by the position accuracy of the tool holder and the dynamic performance of the machine tool. Therefore, in the manufacturing and assembly process of turning and milling composite machine tools, how to improve the accuracy of the electric spindle system, improve the position accuracy of the tool holder, and improve the overall dynamic performance of the machine tool is the key to machine tool design. This article analyzes the factors that affect the machining accuracy of turning and milling composite machine tools from the following aspects, and proposes corresponding solutions.
1、 The accuracy of the electric spindle system
1. The indexing accuracy and accurate stopping accuracy of the electric spindle system
The indexing accuracy and accurate stopping accuracy of the electric spindle system of the turning and milling composite machining machine tool are important indicators for evaluating the spindle accuracy of the machine tool, and are important factors affecting the machining accuracy of the machine tool. In order to achieve high indexing accuracy and accurate stopping accuracy of the electric spindle system, CNC turning and milling composite machining centers internationally all use a built-in spindle type motor, which is assembled with the motor rotor to reduce the impact of intermediate transmission links on the spindle accuracy. During operation, the rotation of the motor rotor drives the spindle to rotate. The speed and position loops of the spindle rotation adopt high-precision feedback components to achieve full closed-loop control. The position signals collected by the feedback components are divided and processed by the CNC system, resulting in a spindle indexing resolution of 0.001 ° or less, thereby making the machine tool spindle system have high indexing accuracy and accurate stopping accuracy.
2、 Rotation accuracy of electric spindle system
The CNC turning and milling composite machining center is a high-precision machining machine tool, and the spindle group is a key component. The rotational accuracy of the spindle group directly affects the accuracy of the processed workpiece.
To ensure high rotational accuracy of the spindle group, a series of process measures have been taken in the electric spindle system, including the connection between the spindle and the motor rotor, the fit between the stator sleeve and the spindle box, and the fit between the two ends of the spindle and the bearing group
1. Before assembling the electric spindle, ensure the accuracy of the spindle box hole, and ensure that the roundness, dimensional tolerance, and coaxiality of the front and rear bearing holes of the hole are within the required range; The radial runout of the spindle journal, the coaxiality of the front and rear journals, and the radial runout and end face runout tolerances of the spindle end are all controlled within 0.002mm.
2. During assembly, grind the spindle housing hole according to the size of the outer ring of the bearing, and strictly control the fit tolerance with the outer ring of the bearing within the specified range; The motor rotor of the electric spindle adopts special assembly techniques with the spindle.