In the production of roller according to the requirement of the situation and structure characteristics of nc machine tool

In the initial stage of nc machine tool development, and its mechanical structure compared with general machine tools has little change, only in the automatic transmission, automatic tool carrier and the workbench transposition and lever operation and so on to make some change.With the development of numerical control technology, considering it the idler roller production control mode and use characteristics, to the productivity of machine tools, machining accuracy and life put forward higher request.Body of nc machine tool has the following characteristics: 1) the adoption of high performance of infinitely variable speed spindle and servo drive system, the limit of the CNC machine transmission structure is greatly simplified, transmission chain also shorten;2) in order to adapt to the continuous automatic machining and improve productivity, numerical control machine mechanical structure has high static precision and dynamic stiffness and damping, and high wear resistance, small thermal deformation and;3) to reduce friction, eliminate transmission clearance and gain higher machining precision, more efficient transmission parts, such as ball screw vice and rolling guide, anti-backlash gear transmission, etc.;4) in order to improve working conditions, reduce the auxiliary time, improve operational, improve labor productivity, the tool automatic clamping device, tool storage and automatic tool change device, automatic chip removal device assist device, etc.According to the roller production with applicable occasions and institutional characteristics of nc machine tool, structure of nc machine tool for the following requirements: one, the higher static\/dynamic stiffness CNC machine tools is according to the numerical control programming or manual input data provide instructions, automatically 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 process of processing can’t for the 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 stiffness of nc machine tool spindle, not only often use three support structure, and choose good rigidity double row short cylindrical roller bearing and angular contact centripetal thrust bearing articulated believe te force bearing, as to reduce the radial and axial deformation of the spindle.In order to improve the stiffness of machine tool big, adopting closed lathe bed of the interface, and USES the hydraulic balance to reduce deformation of machine tool moving parts due to position change.In order to improve the contact stiffness of machine tool parts, increase the bearing capacity of the machine tool, using the method of scraping the inquiry increase per unit area of contact, and applying large enough preloading in combination with surface between, to increase the contact area.These measures can effectively improve the contact stiffness.Efficient processing capacity in order to give full play to the numerical control machine tool, and can be stable cutting, under the premise of guarantee the static stiffness, must also improve the dynamic stiffness.Commonly used measures are mainly improve the stiffness of system, increasing damping and adjust the natural frequency of vibration of structures, etc.Tests show that improve the damping coefficient is one of the effective methods to improve the vibration resistance.Steel plate welded structure can increase the static stiffness, reducing the structure weight, also can increase the damping of the component itself.Therefore, in recent years on the nc machine tool is made of the steel plate welded structure of lathe bed, column, beam, and the workbench.Sand casting and conducive to vibration attenuation, also have better effect to improve the vibration resistance.Second, reduce the thermal deformation of machine tool under the influence of internal and external heat source, machine tool parts will be different levels of heat deformation, make the relative motion relationship between the workpiece and tool was broken, and machine tool quarterly decline.For nc machine tool, because all the processing process is calculated command control, the influence of thermal deformation is more serious.In order to reduce the thermal deformation, usually adopt the following measures in the structure of nc machine tools.1) reduce the heating machine internal heat generated when the main heat source of hot deformation, should as far as possible to the heat source is separated from the host.2) control after took a series of measures to reduce the heat source temperature, the thermal deformation of the situation will improve.But to completely eliminate machine internal and external heat source is often very difficult, even impossible.So must be good to control the temperature of cooling and cooling, in order to reduce the influence of heat source.Which department is in the machine tool is a effective method of forced cooling heating parts, also can be in low temperature machine parts, by using the method of heating machine each point temperature uniformity, so that we can reduce the buckling deformation caused by temperature difference.3) improve the machine tool mechanism under the condition of same fever, machine body has a great influence on the thermal deformation is also.Such as nc machine tools in the past using single mast mechanism may be replaced by double column body.Due to the left and right sides is symmetrical, dual axis line of the mast mechanism after heated in addition to produce the vertical translation, other direction deformation is small, and vertical axis movement can easily use a coordinate correction to compensate.Thermal deformation occurred in cutter cuts the vertical axis direction.This can make the spindle thermal deformation reduced to minimal impact on machining diameter.In structure should also minimize the spindle center and the main shaft to the distance of the ground, in order to reduce the amount of the thermal deformation, at the same time should be made before and after the temperature rise of headstock is consistent, to avoid the main shaft deformation after the tilt.Ball screw in numerical control machine tool in large load, high speed and poor heat dissipation is expected under the conditions of work, so the screw easy to fever.Ball screw heat production and the consequences are serious, especially in the open loop system, it can make the loss of positioning accuracy of feed system.Some current machine with pretension method to reduce the thermal deformation of a ball screw.For the above measures still cannot eliminate thermal deformation, can be made by CNC system according to the results of the measurement compensation pulse were revised.Three, reduce the friction between the movement and the elimination of transmission clearance of nc machine table (or dragging plate) displacement of the eleven equivalent as the smallest unit of arteries and veins, usually requires to * * speed movement.In order to make the table can instructions for the numerical control device make accurate response, corresponding measures must be taken.At present commonly used sliding guide rail, rolling guideway and hydrostatic guideway there is obvious difference in the aspect of friction damping characteristics.In the feed system with ball screw instead of sliding screw can also get the same result.Now, almost without exception, numerical control machine using ball screw transmission.Numerical control machine (especially the open-loop system of nc machine tool) machining accuracy to a great extent, depends on the precision of feed drive chain.In addition to reducing gear and ball screw machining error, another important measure is to use no clearance transmission vice.For the accumulation of ball screw pitch error, usually using pulse compensation device to pitch compensation.Four, increase the service life of machine tool and accuracy stable in order to improve the service life of machine tool and accuracy stable, should be given due consideration in the design of nc airport parts abrasion resistance, especially the spindle component of machine tool guideway, feed bar harbor, affect the progress of the wear resistance of main parts.In use process, should guarantee good lubrication performance of the numerical control machine tool parts.Five, reduce the auxiliary time and improve operation performance piece machining of CNC machine tools, auxiliary time (the chip) occupies a large proportion.To further improve the productivity of machine tools, it is necessary to take prompt maximum compression auxiliary time.There are a lot of nc machine tools the spindle, tool post, as well as the knife library automatic tool change device, etc., to reduce the time of the knife.For nc machine tool cutting dosage increase, lathe bed institutions must be beneficial to chip removal.