In order to achieve high-speed, high-precision machining, high-speed machining machines must first have high-performance CNC and servo systems with fast response capabilities. Such systems not only have a short interpolation cycle, but also require feedforward control, advanced read, automatic acceleration and deceleration, error compensation and other functions. For high-speed machining machines, machining centers and CNC milling machines with a maximum spindle speed of 10,000 r/min or more are often regarded as high-speed machining milling machines. Such high speed machining milling machines generally have the following basic features:
1. High spindle speed, fast feed rate and large addition (decrease) speed
2, micron accuracy
3, high dynamic and static stiffness and lightweight moving parts
The following is a brief introduction to the specific selection of vertical machining centers and horizontal machining centers. The machining center is a CNC machining machine with comprehensive processing capabilities. It combines the functions of milling, boring, drilling, tapping and cutting threads on one piece of equipment, giving it a variety of processes. The machining center is provided with a tool magazine. The tool magazine stores different numbers of various tools or inspection tools, which are automatically selected or replaced by the program during the machining process. Compared with similar CNC machine tools, the machining center has a complicated structure and many control system functions. Its control function can realize at least two-axis linkage control, realize linear interpolation of tool movement and circular interpolation. The machining center also has different auxiliary functions, such as: various machining fixed cycles, tool radius automatic compensation, tool length automatic compensation, tool breakage alarm, tool life management, overload overtravel automatic protection, screw pitch error compensation, screw clearance Compensation, fault automatic diagnosis, work process graphic display, man-machine dialogue, workpiece online detection, offline programming, etc. The selection of the machine tool first determines the machine model of a machine tool factory according to the required precision, table size, stroke and tool magazine capacity, and then compares the same machine tools of each machine tool factory as follows.
1. Type selection of machining center
(1) It is best to use a vertical machining center for workpieces that are processed in a single station (single-sided).
(2) The horizontal machining center should be selected for the processing of workpieces above two stations (double-sided) or for holes and surfaces arranged radially around.
(3) When the positional accuracy of the workpiece is high, the horizontal machining center is used. When multi-station machining cannot be completed in one setup, the five-sided machining center should be selected.
(4) When the workpiece size is large and the working range of the general column type machining center is insufficient, the gantry type machining center should be selected.
2, the processing center's specification selection
(1) The selection of the workbench specification The size of the workbench should ensure that the workpiece can be smoothly clamped on it, and the machining size must be within each coordinate stroke. In addition, the coordinate interference zone limits of the tool change space are also considered.
(2) The processing range should be selected considering the maximum and minimum values ​​of the coordinate travel of the machining center, the maximum distance from the spindle end surface to the center of the table, and the maximum and minimum distance from the spindle center to the work surface. In addition, the total weight of the workpiece and the fixture cannot be greater than the rated load of the workbench, the movement path of the workpiece cannot interfere with the shield of the machine tool, and the exchange tool must not collide with the workpiece.
(3) Machine tool spindle power and torque selection The spindle motor power reflects the cutting efficiency of the whole machine and also reflects the cutting rigidity of the whole machine.
3, the choice of machining center accuracy
The accuracy level of the machine tool is selected according to the machining accuracy of the key parts of the part. Machining centers are divided into two types: ordinary type and precision type. At the same time, attention should be paid to machining accuracy and machine tool precision are two different concepts. Machining accuracy is the sum of various factors including the machine tool, fixtures, tools, cutting amount, machining allowance, machining materials, cutting force and heat of cutting and cooling. Lubrication conditions, etc.
According to the machining accuracy of the workpiece, the user selects the corresponding precision grade machine tool and mass-produced parts. The actual machining error value may be 1.5-2 times of the positioning accuracy. According to experience, it is generally reasonable to select the error value of the machining center as 0.5-0.65 times of the error of the part.
4, the tool magazine capacity selection
The machining center of the same specification usually has 2-3 different capacity magazines. When the magazine capacity is selected, the required quantity is determined according to the process analysis result of the workpiece, usually to meet one part in one loading. The number of tools required in the clip determines the magazine capacity. From the statistical results, the vertical machining center uses a knife magazine of about 20 knives, and the horizontal machining center selects a knives of about 40 knives. For machining centers used in flexible manufacturing units or flexible manufacturing systems, large-capacity tool magazines or even interchangeable tool magazines should be used.
5, processing center selection function and selection of accessories
When selecting a machining center, in addition to the basic functions and basic body, it also provides the functions and accessories that the user selects according to his own requirements. The choice of attachments should be long-term and versatile.
6, cooling function selection
Cooling methods include: large-flow spray cooling, tool internal cooling, and aerosol cooling. Select according to the actual conditions of the workpiece and the tool.
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