Do you really know about five axis machining?

Five Axis Machining, as the name implies, is a mode of NC machine tool processing. Linear interpolation movement of any five coordinates in X, Y, Z, A, B, C is adopted. The machine tool used for five axis machining is usually called five axis machine tool or five axis machining center. But do you really know five axis machining?

Development of Five Axis Technology
For decades, it is generally believed that five axis NC machining technology is the only way to process continuous, smooth and complex surfaces. Once people encounter unsolvable problems in designing and manufacturing complex surfaces, they will turn to five axis machining technology. But...
Five axis linkage CNC is the most difficult and widely used CNC technology. It integrates computer control, high-performance servo drive and precision machining technology, and is applied to efficient, precise and automatic machining of complex surfaces. In the world, the five axis linkage numerical control technology is regarded as the symbol of a country's production equipment automation technology level. Due to its special status, especially its important influence on aviation, aerospace and military industries, as well as the complexity of technology, the western industrial developed countries have always implemented the export license system as a strategic material.

Compared with three-axis CNC machining, from the perspective of process and programming, 5-axis CNC machining for complex surfaces has the following advantages:
(1) Improve processing quality and efficiency
(2) Expand process scope
(3) Meet the new direction of compound development
But, haha, but again... Because of interference and tool position control in the machining space, the NC programming, NC system and machine tool structure of five axis NC machining are much more complex than those of three axis machine tools. So, five axes is easy to say, but it is really hard to realize! In addition, it is more difficult to operate well!

Speaking of five axes, I have to say the true and false five axes? The difference between the true and false 5 axes mainly lies in whether the RTCP function is available. For this reason, Xiao Bian specifically searched for this word!
RTCP, please explain that Fidia's RTCP is the abbreviation of "Rotating Tool Center Point", which literally means "rotating tool center". The industry often translates it into "turning around the tool center", and some people also translate it directly as "programming of rotating tool center". In fact, this is just the result of RTCP. RTCP of PA is the abbreviation of the first few words of "Real time Tool Center Point rotation". Heidegger calls similar so-called upgrade technology TCPM, which is the abbreviation of "Tool Centre Point Management", namely tool centre point management. Others refer to similar technology as TCPC, which is the abbreviation of "Tool Center Point Control".
From the literal meaning of Fidia's RTCP, if the RTCP function is executed manually at a fixed point, the tool center point and the actual contact point between the tool and the workpiece surface will remain unchanged. At this time, the tool center point falls on the normal at the actual contact point between the tool and the workpiece surface, and the tool handle will rotate around the tool center point. For ball head cutters, the tool center point is the target track point of the NC code. In order to enable the tool handle to simply rotate around the target track point (i.e. the tool center point) when executing the RTCP function, the offset of the linear coordinates of the tool center point caused by the tool handle rotation must be compensated in real time, so that the included angle between the tool handle and the normal at the actual contact point of the tool and the workpiece surface can be changed while keeping the tool center point and the actual contact point of the tool and the workpiece surface unchanged, It can play the best cutting efficiency of the ball end cutter and effectively avoid interference. Therefore, RTCP seems to stand on the tool center point (i.e. the target track point of NC code) more to handle the change of rotation coordinates.
Five axis machine tools and CNC systems without RTCP must rely on CAM programming and post-processing, and the tool path must be planned in advance. For the same part, if the machine tool is changed or the tool is changed, CAM programming and post-processing must be carried out again, so they can only be called false five axes. Many domestic five axis CNC machine tools and systems belong to this kind of false five axes. Of course, there is nothing wrong with people who insist on calling themselves five axis linkage, but this (false) five axis is not that (true) five axis!

Xiao Bian also consulted experts in the industry. In short, the real five axis is five axis five linkage, the false five axis may be five axis three linkage, and the other two axes only play a positioning function!
This is a popular statement, not a standard statement. Generally speaking, five axis machine tools can be divided into two types: one is five axis linkage, that is, all five axes can be linked at the same time; the other is five axis positioning processing, which is actually five axis three linkage: that is, two rotating axes can rotate and position, and only three axes can be linked at the same time. This is commonly known as the 3+2 mode of five axis machine tool, which can also be understood as a false five axis machine tool.
Current forms of five axis CNC machine tools

In the mechanical design of 5-axis machining centers, machine tool manufacturers have always been committed to developing new motion modes to meet various requirements. Considering all kinds of five axis machine tools on the market, although their mechanical structures are various, they mainly have the following forms:
Two rotation coordinates directly control the direction of the tool axis (double swing head form)
The two axes are at the top of the tool,
However, the rotation axis is not perpendicular to the linear axis (vertical pendulum type)
Two rotation coordinates directly control the rotation of space (double turntable form)
The two axes are on the workbench,
However, the rotation axis is not perpendicular to the linear axis (vertical worktable)
One of the two rotation coordinates acts on the tool,
One acts on the workpiece (one swing and one turn)

Having seen these five axis machine tools, I believe we should understand what and how the five axis machine tools are moving.
Difficulties and Resistance in Developing Five Axis NC Technology
We have already realized the superiority and importance of five axis numerical control technology. But so far, the application of five axis CNC technology is still limited to a few departments with abundant funds, and there are still unsolved problems.
The following section collects some difficulties and resistance to see if they correspond to your situation?

Abstract 5-axis NC programming, difficult to operate
This is a headache for every traditional NC programmer. Three axis machine tools only have linear coordinate axes, while five axis CNC machine tools have various structural forms; The same NC code can achieve the same machining effect on different three axis NC machines, but the NC code of a certain five axis machine tool cannot be applied to all types of five axis machine tools. 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 five 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 major resistance to the popularization of five axis CNC technology.

Many domestic manufacturers have purchased five axis CNC machine tools from abroad. Due to inadequate technical training and service, the inherent functions of five axis CNC machine tools are difficult to achieve, and the utilization rate of machine tools is low. In many cases, it is better to use three axis CNC machine tools.
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 rotation coordinates not only increases the burden of interpolation, but also greatly reduces the machining accuracy due to the small error of rotation coordinates. Therefore, the controller is required to have higher calculation 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.

The verification of NC program of 5-axis NC is particularly important
In order to improve the machining efficiency, it is urgent to eliminate the traditional "trial cut" calibration method. In 5-axis NC machining, the verification of NC program is also very important, because workpieces usually processed by 5-axis NC machine tools are very expensive, and collision is a common problem in 5-axis NC machining: cutting tools into workpieces; The tool collides with the workpiece at a very high speed; The tool collides with the machine tool, fixture and other equipment within the processing range; Moving parts on the machine tool collide with fixed parts or workpieces. In five axis NC, collision is very difficult to predict. The calibration program must comprehensively analyze the kinematics and control system of the machine tool.

If the CAM system detects an error, it can immediately process the tool path; However, if NC program errors are found during machining, the tool path cannot be directly modified as in three-axis NC. On the three-axis machine tool, the machine tool operator can directly modify the parameters such as tool radius. In five axis machining, the situation is not so simple, because changes in tool size and position have a direct impact on the subsequent rotation trajectory.

Tool radius compensation
In the five 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 systems 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. As a result, the efficiency of the whole processing process is very low.

To solve this problem, Norwegian researchers are developing a temporary solution called LCOPS (Low Cost Optimized Production Strategy). The data required for tool path correction is transferred to the CAM system by the CNC application program, and the calculated tool path is directly sent to the controller. LCOPS requires a third party to provide CAM software, which can be directly connected to CNC machine tools. In the meantime, CAM system files are transmitted instead of ISO codes. The final solution to this problem depends on the introduction of a new generation of CNC control system, which can recognize workpiece model files (such as STEP) or CAD system files in a common format.
Post Processors

The difference between a five axis machine tool and a three-axis machine tool is that it also has two rotation coordinates, and the tool position is converted from the workpiece coordinate system to the machine coordinate system, which requires several coordinate transformations. Using the popular post processor generator in the market, the post processor of three-axis CNC machine tools can be generated by inputting the basic parameters of the machine tool. For five axis CNC machine tools, there are only some improved post processors. The post processor of five axis CNC machine tool needs further development.

In three-axis linkage, the position of the workpiece origin on the machine tool workbench is not necessary to be considered in the tool path, and the post processor can automatically handle the relationship between the workpiece coordinate system and the machine coordinate system. For five axis linkage, for example, when machining on a horizontal milling machine with five axis linkage of X, Y, Z, B, C, the position size of the workpiece on the C turntable and the position size between the B and C turntables must be considered when generating the tool path. Workers usually spend a lot of time to deal with these positional relationships when clamping workpieces. If the post processor can process these data, the workpiece installation and tool path processing will be greatly simplified; Just clamp the workpiece on the workbench, measure the position and direction of the workpiece coordinate system, input these data to the post processor, and post process the tool path to obtain the appropriate CNC program.