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Structure classification of gantry CNC machining center

The gantry of the gantry CNC machining center is composed of two columns, beams, sliding saddles and other components. The gantry machining center can be fixed beam, moving beam and moving column gantry machining centers according to the gantry. The cross beam of the top beam gantry machining center is fixed and the worktable moves; The beam of the moving beam gantry machining center moves up and down, and the worktable moves back and forth; The worktable of the movable column gantry machining center is fixed and the gantry moves. Gantry machining centers are vertical between the spindle and the workbench, which is more suitable for machining large-scale parts.

Application of gantry CNC machining center

Gantry CNC machining center is a large machine tool, which is specially designed to process large parts. It is mainly used in heavy industries, such as aircraft, automobile, ship and other heavy industries. It mainly processes large and complex shaped workpieces, such as beams and frames of aircraft and some parts of large machinery. In a word, gantry CNC machining center is a large machine tool designed to process large and complex parts. It is suitable for various industries, especially large parts industries.

Classification of gantry CNC machining centers

Gantry CNC machining center is mainly suitable for machining planes, holes and other complex surfaces of cavities.  Equipped with various forms of accessory milling heads, the workpiece can be clamped once to complete the machining of the workpiece pentahedron.  In view of the large width, long length and heavy weight of the workpiece, it is necessary to select different models to correspond to the processing of the product.

The gantry CNC machining center is divided into fixed gantry and moving gantry in the overall layout, as well as fixed beam and moving beam. Bridge layout also belongs to a form of moving gantry. Here, we mainly compare the fixed gantry worktable and the fixed gantry worktable in form and accuracy. With the continuous development of information technology and computer digital technology, the performance and efficiency of NC machine tools are also improving. At present, the high-grade CNC system has high efficiency and high precision, which is suitable for the processing of complex curved surfaces and spatial hole systems. However, for the whole machine tool, it requires good rigidity, high precision, thermal deformation compensation, strong cutting force, good stability, fast response speed of CNC system, automatic monitoring and other functions.

For the fixed gantry CNC machining center, that is, the worktable moving CNC machine tool, its worktable moves with DC or AC servo motor to drive the x-axis through the forms of worm gear, ball screw and gear rack.  The selection of transmission form is important according to different length and different requirements.  When the moving length of the worktable exceeds 8m, the general manufacturers will adopt the transmission mode of double tooth tooth strips.  The motion track of the worktable runs in two directions: the straightness of the horizontal plane and the straightness perpendicular to the horizontal plane.Ensuring the accuracy of processed products is also an important index. The x-axis guide rail length of this fixed gantry CNC machine tool is twice the length of the workbench, excluding the length of protective covers on both sides, so it occupies a large area for the plant. The table moving CNC gantry milling machine tool can be divided into dynamic friction and static friction. There are many structural forms in the form of dynamic friction, such as linear guide rail in the form of ball and roller plus preload, rolling body guide rail, combined composite guide rail combined with rolling and sliding, and complete dynamic friction.Linear guide rail and rolling element guide rail are more suitable for light load high-speed cutting. They move evenly and are not easy to crawl at low speed.  It has good positioning accuracy, small traction, good accuracy retention, long service life and strong maintainability, but it has poor seismic and impact resistance.

Structural characteristics of gantry CNC machining center 

In the rolling and sliding composite guide rail, the rolling part plays the role of controlling the accuracy of linear motion, and the sliding part plays the role of bearing, which improves the bearing capacity of the workbench, and has a certain impact resistance. With the development and innovation of cutting tools and the transformation and renewal of machining process concept, the current method of high-speed light load machining process is booming, which is in line with the development law of low-speed heavy load large torque and high-speed light load small torque.

Another kind of hydrostatic guide rail belongs to the form of static friction. It has the characteristics of heavy load and no wear on the guide rail surface, and has strong impact resistance for workpiece loading and unloading. However, it is greatly affected by oil temperature, complex manufacturing process and high cost.

In terms of structure, the gantry form of this table mobile CNC gantry machine tool adopts the method of integral connection of the frame, which has certain requirements for the installation foundation. The weight of the whole machine is basically in the middle position, especially in the position of the two columns. Under the influence of temperature, the accuracy of the two columns will tilt back or forward at different heights due to the change of temperature, In the state of overall connection, it will also affect the change of the connecting part of the machine bed, resulting in the change of the accuracy of the machine bed.

The empirical data is that in the length of 1m, the change of temperature of 1 ℃ will affect the accuracy of 0.01mm, that is, the often mentioned “three ones”. Therefore, for products with high precision requirements in the processing vertical plane, the machine tool should be adjusted and tested frequently when the temperature difference between seasons is large, because the movement of the deformed machine tool bed workbench on it is a deformed curve rather than a straight line, and the straightness of the processed product is also consistent with the deformed curve, which affects the processing accuracy of the product.

The factors affecting the machining accuracy of the worktable moving gantry machining center involve a wide range, and there is a certain interference with each other during adjustment. However, due to the overall structure, it is relatively stable, and the accuracy of the processed products is guaranteed. At present, in order to solve the problem of mutual interference in machine tools, some manufacturers use the method of transitional connection and non connection between two columns and the bed.

Compared with the gantry mobile machining center, its worktable has large bearing capacity and does not interfere with the deformation of the machine tool due to the impact of upper and lower workpieces and other factors. It has the advantages of small floor area and convenient workpiece clamping, and can give full play to the actual effective length of the worktable to process workpieces.

Comparison of several gantry CNC machining centers

Many machine tool companies in the world have adopted the structure of gantry movement to manufacture pentahedral machining centers suitable for processing large and heavy products. The manufacturing technology and cost of gantry frame mobile machine tool are difficult and higher than that of worktable mobile machine tool, and the manufacturing cost is about 25% higher. In particular, it is difficult to fix and stabilize the whole machine when manufacturing the gantry column and running synchronously. The x-axis shall bear the weight of the whole machine when running, with large driving torque, slow action and inertia. If the weight is too light, the rigid mass of the whole machine will be reduced and unstable, with drift and vibration.

This moving beam moving gantry frame moving pentahedral machining center adopts Hayden Hein’s “gantry” synchronization technology in the gantry frame movement, and enables the whole frame structure to have the ability of high rigidity and high precision to bear heavy cutting. In the gantry moving mechanism, the x-axis is composed of X1 and X2, which is driven by double AC servo motors and gapless tooth strips, In the full closed-loop detection system loop composed of Hayden Hein high-precision double gratings, under the action of optimizing the coupling beam structure, X1 is always used as the main driving position axis and X2 as the follow-up position axis, which is controlled by the numerical control system to track and compensate uniformly and continuously, so as to keep x2 and X1 synchronized all the time. In order to ensure that the processed products and parts do not produce scrap and defective products during processing, A large tracking error value is set in the system. If it exceeds this value, an alarm will be given and the machine tool will stop working.

The key of this gantry frame moving machining center lies in the stability of two parallel X-axis installed bases, which determines the accuracy of the guide rail and the accuracy of the whole machine tool. Unlike the worktable moving gantry machining center, the overall frame structure interferes with each other, and the frame moving machining center is not affected by the deformation of the worktable, However, the two X-axis guide rails should always keep the two directions parallel, and should also be continuously tested and adjusted. Secondly, although the synchronous technology is adopted when the two columns of the x-axis are running, the driver characteristics of the AC servo motor of the two axes require fast response speed, otherwise it will cause instantaneous vibration and affect the accurate positioning of the x-axis.

In these two forms of gantry machining centers, the accuracy of the straightness of the horizontal plane and the straightness in the vertical plane of the x-axis determines the positioning accuracy of the x-axis. The long-term maintenance of the static accuracy of x-axis guide rail and gantry column is the premise to determine the quality of products, and a good environment and relatively stable foundation are also necessary conditions.If you need CNC machining center, please contact us. We have rich production experience and high-quality after-sales service, which will be your ideal choice. High quality CNC gantry machining center will bring you high income and good use experience.