What Are The Difficulties And Resistances In Developing Five-axis CNC Technology

Mosi Li
Mosi Li

Director Project Engineer at 3Q Machining - China top CNC Machining Custom Part Manufacturer

5 axis cnc machined precision brass alloy parts

Advantages of five-axis machining

Five-axis CNC machining is the most difficult and most widely used technology in CNC technology. It integrates computer control, high-performance servo drive, and precision machining technology, and is used for efficient, precise, and automated machining of complex curved surfaces. Compared with three-axis CNC machining, from the perspective of technology and programming, five-axis CNC machining for complex curved surfaces has the following advantages:

  1. Improve processing quality and efficiency
  2. Expand the process range
  3. Meet the new direction of composite development

However, due to interference and position control of the tool in the machining space, five-axis CNC machining has a much more complicated CNC programming, CNC system, and machine tool structure than a three-axis machine tool. Therefore, it is difficult to truly realize five-axis machining, and it is even more difficult to operate and use it well.

True and false five-axis machining

When talking about five-axis machining, we have to talk about true and false five-axis machining. The main difference between true and false five-axis machining is whether it has the RTCP function. RTCP is the abbreviation of “Rotational Tool Center Point”. Only five-axis machining with RTCP function is true five-axis machining. Five-axis machine tools and CNC systems that do not have the RTCP function must rely on CAM programming and post-processing, and plan the tool path in advance. For the same part, if the machine tool is changed, or the tool is changed, CAM programming and post-processing must be performed again, so it can only be called false five-axis machining. In short, true five-axis machining means five-axis five-linkage, while false five-axis machining may be five-axis three-linkage, and the other two axes only play a positioning function.

5-axis machining of aluminum alloy parts

Difficulties and resistances in developing five-axis CNC technology

Although we all know the superiority and importance of five-axis CNC technology. But the application of five-axis CNC technology is still limited to some relatively large-scale enterprises, and there are still unsolved problems. Some of the difficulties and resistances are detailed below.

Five-axis CNC programming is abstract and difficult to operate

This is a problem that every traditional CNC programmer feels deeply difficult. Three-axis machine tools only have linear coordinate axes, while five-axis CNC machine tools have various structures. The same NC code can achieve the same processing effect on different three-axis CNC machine tools, but the NC code of a five-axis machine tool cannot be applied to All types of five-axis machine tools. In addition to linear motion, CNC programming must also coordinate related calculations of rotational motion, such as rotation angle stroke inspection, non-linear error check, tool rotation calculation, etc. The amount of information processed is very large, and CNC programming is extremely abstract.

The operation of five-axis CNC machining is closely related to programming skills. The programming and operation will be more complicated if the user adds special functions to the machine tool. Only by repeated practice, programming and operating personnel can master the necessary knowledge and skills. The operation of five-axis CNC machining is closely related to programming skills. The programming and operation will be more complicated if the user adds special functions to the machine tool. Only by repeated practice, programming and operating personnel can master the necessary knowledge and skills. The lack of experienced programming and operators is a major obstacle to the popularization of five-axis CNC technology. If technical training and services are not in place, the inherent functions of a five-axis CNC machine tool will be difficult to achieve, and the utilization rate of the machine tool will be very low. In many cases, it is better to use a three-axis machine tool.

Very strict requirements for NC interpolation controller and servo drive system

The movement of a five-axis machine tool is a combination of five-coordinate axis movements. The addition of rotating coordinates will increase the burden of interpolation calculations, and the small errors of the rotating coordinates will greatly reduce the processing accuracy. Therefore, the controller is required to have higher arithmetic accuracy. The motion characteristics of the five-axis machine tool require the servo drive system to have good dynamic characteristics and a large speed range.

NC program verification of five-axis CNC is particularly important

To improve the efficiency of mechanical processing, it is urgent to eliminate the traditional “trial cutting method” verification method. In five-axis CNC machining, the verification of NC programs has also become very important, because workpieces processed by five-axis CNC machine tools are usually very expensive, and collisions are a common problem in five-axis CNC machining:

  1. The tool cuts into the workpiece
  2. The tool collides with the workpiece at a very high speed
  3. The tool collides with the machine tool, fixture, and other equipment within the processing range
  4. The moving parts and fixed parts on the machine collide with the workpiece

In five-axis CNC, collisions are difficult to predict, and the calibration program must comprehensively analyze the machine tool kinematics and control system.

If the CAM system detects an error, the tool path can be processed immediately, but if an NC program error is found during the machining process, the tool path cannot be modified directly as in the three-axis CNC. On a three-axis machine tool, the machine operator can directly modify the tool radius and other parameters. In five-axis machining, the situation is much more complicated, because the change of tool size and position has a direct impact on the subsequent rotary motion trajectory.

Tool radius compensation

In the 5-axis NC program, the tool length compensation function is still valid, but the tool radius compensation is invalid. When using cylindrical milling cutters for contact forming milling, different programs need to be programmed for cutters of different diameters. The current popular CNC systems are unable to 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 when performing CNC machining. The tool path should be sent back to the CAM system for recalculation according to the normal processing procedure. As a result, the efficiency of the entire processing process is very low.

Postprocessor

The difference between a five-axis machine tool and a three-axis machine tool is that it also has two rotating coordinates. The tool position is transformed from the workpiece coordinate system to the machine tool coordinate system, and several coordinate transformations are required in the middle. Using the widely used postprocessor generator in the market, you only need to input the basic parameters of the machine tool to generate the postprocessor of the three-axis CNC machine tool. For five-axis CNC machine tools, there are currently only some improved postprocessors. The postprocessor of the five-axis CNC machine tool needs further development.

Non-linear errors and singularity problems

Due to the introduction of rotating coordinates, the kinematics of a five-axis CNC machine tool is much more complicated than that of a three-axis machine tool. The first problem related to rotation is the nonlinear error. The non-linear error should be attributed to the programming error, which can be controlled by reducing the step distance. In the pre-calculation stage, the programmer cannot know the magnitude of the non-linear error. Only after the machine tool program is generated by the post-processor can the non-linear error be calculated. Tool path linearization can solve this problem. Some control systems can linearize the tool trajectory while processing, but it is usually linearized in the postprocessor.

Another problem caused by rotating shafts is the singularity. If the singular point is at the extreme position of the rotation axis, a small oscillation near the singular point will cause the rotation axis to flip by 180°, which is quite dangerous.

Requirements for CAD/ CAM system

For the operation of pentahedron processing, the user must rely on a mature CAD/CAM system and must have experienced programmers to operate the CAD/CAM system.

3Q Machining provides a variety of precision CNC machining services including milling, turning, EDM (electrical discharge machining) and wire EDM, and surface grinding. With our precision 3-, 4- and 5-axis CNC machining centers, combined with other advanced capabilities and our experienced team, we can handle all technical aspects of creating your prototypes and parts.

5 Axis CNC Machined Precision Medical Parts

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