CNC MILLING MACHINE FOR SALE

Precautions for CNC machining center in high temperature environment:

1 In order to reduce thermal deformation, the following measures are usually used in the structure of CNC machining center:

Reduce heat: machine internal heat is the main heat source of thermal deformation, heat source should be separated from the host machine as far as possible;

Control temperature rise: after adopting a series of measures to reduce heat sources, the situation of thermal deformation will be improved.  However, it is often difficult or even impossible to completely eliminate the internal and external heat sources of machine tools.  Therefore, it is necessary to control the rise of temperature through good heat dissipation and cooling to reduce the influence of heat sources on the CNC machining center.  The more effective method is forced cooling in the heating part of the machine tool, but also in the low-temperature part of the machine tool through the heating method, so that the temperature of the machine tool is consistent so that the warpage deformation caused by the temperature difference can be reduced;

The ball screw in CNC machining center often works under the conditions of large load, high speed and poor heat dissipation, so the lead screw is easy to heat up.  Ball screw heating is serious for production, especially in the open loop system, it will cause the feed system to lose positioning accuracy.  At present, some machine tools use pre-drawing method to reduce the thermal deformation of lead screw.  For the thermal deformation which cannot be eliminated by the above measures, the NUMERICAL control system can send compensation pulse to correct it according to the measurement results.

2 CNC machining center is in accordance with CNC programming or manual input data provided by the instruction of automatic processing.  Due to mechanical structure (such as machine tool lathe bed and guide rail, workbench, head and spindle box, etc.) of the positioning errors caused by geometric accuracy and deformation in the machining process can not be artificially adjustment and compensation, therefore, must take all the elastic deformation of mechanical structure parts control within the minimal, to ensure that the required machining accuracy and surface quality.

In order to improve the rigidity of the CNC machine tool spindle, not only the three-support structure is often used, but also the double row short cylindrical roller bearing with good rigidity and angular contact thrust bearing is selected to reduce the radial and axial deformation of the spindle.  In order to improve the rigidity of large parts in NC machining center, a bed with a closed interface was adopted, and hydraulic balance was adopted to reduce the deformation of the machine tools caused by the position change of moving parts.  In order to improve the contact stiffness of each part of the machine tool and increase the bearing capacity of the machine tool, the scraping method is adopted to increase the contact points per unit area, and sufficient preloading load is applied between the joint surfaces to increase the contact area.  All these measures can effectively improve the contact stiffness.

In order to give full play to the efficient machining capability of the NC machining center and to carry out stable cutting, dynamic stiffness must be improved on the premise of ensuring static stiffness.  The commonly used measures are to improve the stiffness of the system, increase damping and adjust the natural vibration frequency of components.  Experiments show that increasing the damping coefficient is an effective method to improve vibration resistance.  The welded steel plate structure can not only increase the static stiffness, reduce the weight of the structure, but also increase the damping of the member itself.  Therefore, in recent years, NC machine tools have adopted the steel plate welding structure of the bed, column, beam, and workbench.  Sand sealing castings also benefit vibration attenuation and improve vibration resistance.

3 Improve the service life and accuracy of machine tools.  In order to improve the service life and accuracy retention of machine tools, the wear resistance of CNC machine tools should be fully considered in the design, especially the wear resistance of CNC machining center guide rails, feed servo spindle parts, and other main parts that affect the accuracy.  In the process of use, it is necessary to ensure that the parts of the CNC machining center are well lubricated.

4 Reduce auxiliary time and improve operating performance.  In the single machining of NC machining center, the auxiliary time occupies a large proportion.  To further improve the productivity of machine tools, it is necessary to maximize the compression of auxiliary time.  At present, there are a lot of CNC machining centers using multi-spindle, multi-tool rest, and automatic tool changing device with tool library, etc., to reduce tool changing time.  For CNC machining center with increased chip consumption, the bed mechanism must be conducive to chip removal.

5 Reduce friction between motion and eliminate transmission clearance

The displacement of CNC machining center table is the minimum unit of pulse equivalent, and usually requires to move at the speed of feed.  In order to make the worktable can make accurate response to the instructions of numerical control device, corresponding measures must be taken.  There are obvious differences between sliding guide, rolling guide and hydrostatic guide in friction damping characteristics.  The same effect can be achieved by using ball screws instead of sliding screws in the feed system.  At present, CNC machine tools almost without exception use ball screw drive.

The machining accuracy of the CNC machining center depends largely on the accuracy of the feed drive chain.  In addition to reducing the machining error of transmission gear and ball screws, another important measure is to adopt a non-clearance transmission pair.  For the accumulated error of ball screw pitch, the pulse compensation device is usually used to compensate the pitch.

The service life of CNC machining center is not only related to the quality of the machine itself but also closely related to the actual use of customers.  The cost of a machine is relatively high, only prolong the service life of CNC machining center can create more benefit value for customers.  Therefore, in the actual use of the process should always keep in mind all kinds of precautions.