Requirements of CNC Machine Tools for Mechanical Structure

The main structure of CNC machine tools has the following characteristics:

1) Due to the use of high-performance continuously variable speed spindles and servo transmission systems, the limit transmission structure of CNC machine tools is greatly simplified and the transmission chain is greatly shortened;

2) In order to adapt to continuous automated processing and improve processing productivity, the mechanical structure of CNC machine tools has higher static and dynamic stiffness and damping accuracy, as well as higher wear resistance, and less thermal deformation;

3) In order to reduce friction, eliminate transmission clearance and obtain higher processing accuracy, more efficient transmission components are used, such as ball screw pairs and rolling guides, anti-backlash gear transmission pairs, etc.

4) In order to improve working conditions, reduce auxiliary time, improve operability, and improve labor productivity, auxiliary devices such as automatic tool clamping devices, tool magazines and automatic tool changing devices, and automatic chip removal devices are used.

According to the applicable occasions and structural characteristics of CNC machine tools, the following requirements are put forward for the structure of CNC machine tools:

1. Higher static and dynamic stiffness of the machine tool

CNC machine tools are automatically processed according to instructions provided by CNC programming or manual data input. Since the positioning error caused by the geometric accuracy and deformation of the mechanical structure (such as the machine tool bed, guide rails, worktable, tool holder and spindle box, etc.) cannot be adjusted and compensated during the processing, the elastic deformation of the mechanical structure components must be controlled within a small limit to ensure the required processing accuracy and surface quality. Under the influence of internal and external heat sources, the various parts of the machine tool will undergo different degrees of thermal deformation, which will destroy the relative motion relationship between the workpiece and the tool, and also cause the quarterly decline of the machine tool. For CNC machine tools, because the entire processing process is controlled by calculated instructions, the influence of thermal deformation is more serious. Heavy. In order to reduce thermal deformation, the following measures are usually adopted in the structure of CNC machine tools: (1) reduce heat generation; (2) control temperature rise; (3) improve the machine tool mechanism.

3. Reduce friction between movements and eliminate transmission clearance

The displacement of the CNC machine tool worktable (or slide) is equivalent to a small unit in eleven pulses, and it is usually required to move at the base speed. In order for the worktable to respond accurately to the instructions of the CNC device, corresponding measures must be taken. Currently, there are obvious differences in the friction damping characteristics of the commonly used sliding guides, rolling guides and hydrostatic guides. Use ball screws instead of sliding guides in the feed system The same effect can be achieved with the lead screw. At present, CNC machine tools almost all use ball screw transmission. The machining accuracy of CNC machine tools (especially open-loop system CNC machine tools) depends largely on the accuracy of the feed transmission chain. In addition to reducing the machining errors of transmission gears and ball screws, another important measure is to use a gapless transmission pair. For the cumulative error of the ball screw pitch, a pulse compensation device is usually used for pitch compensation.

Life and precision retention of machine tools

4. In order to improve the life and precision retention of machine tools, the wear resistance of CNC machine parts should be fully considered during design, especially It is the wear resistance of the main parts that affect the progress, such as the machine tool guide rails, feed servo spindle components, etc. During use, the lubrication of all parts of the CNC machine tool should be ensured to be good.

5. Reduce auxiliary time and improve operating performance

In the single-piece processing of CNC machine tools, auxiliary time (non-chip time) accounts for a large proportion. To further improve the productivity of machine tools, it is necessary to take measures to minimize the auxiliary time.

At present, many CNC machine tools have adopted multiple spindles, multiple tool holders, and automatic tool changers with tool magazines to reduce tool change time. For CNC machine tools with increased chip consumption, the bed structure must be conducive to chip removal.