Multi axis machine tool

With the development of modern NC machining towards high speed, high precision, high intelligence, high flexibility, high automation and high reliability, higher requirements are put forward for the machining ability and efficiency of the machining center, so the multi axis NC machining technology has been developed unprecedentedly

What is a multi axis machine tool?

Multi axis machine tool refers to simultaneous processing on multiple coordinate axes of a machine tool, and simultaneous coordinated movement can be carried out under the control of a computer numerical control system.

Multi axis NC machining can simultaneously control the linkage of more than 4 coordinate axes, and combine the functions of NC milling, NC boring, NC drilling, etc.

After the workpiece is clamped once, the machining surface can be milled, bored, drilled and other multiple processes, effectively avoiding the positioning error caused by multiple installations, effectively shortening the production cycle and improving the machining accuracy.

At present, the CNC system can control more than 32 axes, or even 64 axes

Types of multi axis NC machining

Machining centers are generally divided into vertical machining centers and horizontal machining centers. The most effective machining surface of the three-axis vertical machining center is only the top surface of the workpiece, while the horizontal machining center can only complete the machining of four sides of the workpiece with the help of a rotary table.

If a 5-axis linkage high-end CNC system is configured, it can also process complex spatial surfaces with high precision, which is very suitable for processing the forming dies of auto parts, aircraft structural parts and other workpieces

According to the form of rotary axis, the multi axis CNC machining center can be set in two ways:

• Rotary shaft of workbench

The advantages of this multi axis CNC machine tool are: the spindle structure is relatively simple, the spindle rigidity is very good, and the manufacturing cost is relatively low.

But generally, the worktable cannot be designed to be too large, and the bearing capacity is also small. Especially when the rotation angle of Axis A is ≥ 90 °, the worktable will have a large bearing moment when the workpiece is cut

• Vertical spindle head rotation

The advantages of this multi axis CNC machine tool are that the spindle is very flexible and the workbench can be designed very large.

When the spherical milling cutter is used to machine the surface, when the cutter centerline is perpendicular to the machining surface, the workpiece surface quality cut by the vertex will be poor because the vertex linear speed of the spherical milling cutter is zero.

The design of spindle rotation is adopted to make the spindle rotate an angle relative to the workpiece, so that the spherical milling cutter can avoid vertex cutting, and ensure a certain linear speed, which can improve the surface processing quality. This is difficult for the rotary machining center of the workbench.

Advantages of machine tool multi axis linkage

Multi axis machine tool is the general trend of machine tool development. With the development of technology, there are more and more “axes” of machine tools. Why do factories emphasize more and more on their own machine tool shafts? What are the advantages?

It can improve the machining accuracy of the workpiece

Multi axis machining can effectively reduce the change of datum plane. This kind of machining can effectively integrate processes, not only improve the effectiveness of the process, but also realize the one-time clamping of the workpiece, making the machining accuracy easier to ensure.

Reduce the number of fixtures and floor space

In the current market, multi axis processing equipment is relatively expensive, but it has summarized a variety of processes, reducing the number of equipment, the number of fixtures, workshop floor space and equipment maintenance costs. To a certain extent, the cost has been reduced.

Simplify the production process

Multi axis CNC machine tools can effectively shorten the production process chain, making the production process management get useful simplification. Multi axis CNC equipment has more significant advantages in processing messy workpieces. Shortening the production process chain is also conducive to reducing production operation and handling costs

Shorten the development cycle of new products

For enterprises in the aerospace, car processing and other fields, the parts of new products will be relatively messy, and the precision requirements are also high. This requires the equipment to have the processing ability of high precision, high flexibility and high integration. Multi axis machining equipment can be well qualified for this work and effectively shorten the development cycle.

Technical difficulties of multi-axis CNC machining

People have already realized the superiority and importance of multi axis NC machining technology. But so far, the application of multi axis NC machining technology is still limited to a few departments with abundant funds, and there are still unsolved problems.

Due to interference and tool position control in machining space, the NC programming, NC system and machine tool structure of multi axis NC machining are much more complex than those of 3-axis machine tools. The problems of multi axis NC machining technology are as follows:

Abstract multi axis NC programming, difficult to operate

This is a headache for every traditional NC programmer: 3-axis machine tools have only linear coordinate axes, while 5-axis NC machine tools have various structural forms. For example, the same NC code can achieve the same machining effect on different 3-axis NC machines, but the NC code of a 5-axis machine cannot be applied to all types of 5-axis machines.

In addition to linear motion, NC programming also coordinates the calculation of rotation motion, such as rotation angle travel inspection, nonlinear error check, tool rotation motion calculation, etc. The amount of information processed is large, and NC programming is extremely abstract.

The operation of multi axis NC machining is closely related to programming skills. If users add special functions to the machine tool, the programming and operation will be more complex.

Only through repeated practice can the programming and operating personnel master the necessary knowledge and skills. The lack of experienced programmers and operators is a big resistance to the popularization of multi axis NC machining technology.

Difficulty in tool radius compensation

In the 5-axis linkage NC program, the tool length compensation function is still valid, but the tool radius compensation is invalid. When cylindrical milling cutter is used for contact forming milling, different programs need to be compiled for cutters with different diameters.

At present, the popular CNC system cannot complete the tool radius compensation because the ISO file does not provide enough data to recalculate the tool position.

The user needs to change the tool frequently or adjust the exact size of the tool during NC processing. According to the normal processing program, the tool path should be sent back to the CAM system for recalculation, which leads to low efficiency in the entire processing process.

The final solution to this problem depends on a new generation of CNC control system, which can recognize the workpiece model files (such as STEP) or CAD system files in a common format.

The purchase of machine tools requires a large investment

The price gap between multi-axis CNC machining machine tool and 3-axis CNC machining machine tool is very large. In addition to the investment of the machine tool itself, the CAD/CAM system software and the post-processor must be upgraded to meet the requirements of the multi-axis CNC machining, and the calibration program must be upgraded to make the whole machine tool can be simulated.

In a word, the more “axis” of the machine tool, the better the processing power and processing accuracy, and the lower the cost, which is the reason why the multi-axis linkage of the machine tool is sought after.

Our country has also made a lot of advantageous exploration in the multi-axis machine tool, believe that in the near future, domestic multi-axis machine tool will be able to meet us.