Difficulties in five-axis machining

Five-axis machining methods and machine tools have been used by the foreign aviation industry as early as the 1960s in order to process some large parts with continuous smooth and complex free-form surfaces, but they have not been adopted in more industries. It is widely used and has developed rapidly only in the past 10 years. The reason is mainly that there are many difficulties in five-axis machining, such as:

1. Programming is complex and difficult.

Because five-axis machining is different from three-axis machining, in addition to three linear motions, there are also two rotational motions involved. The spatial trajectory of the resulting synthetic motion is very complex and abstract, and is generally difficult to imagine and understand. For example, in order to process the required spatial free-form surface, it is often necessary to go through multiple coordinate transformations and complex spatial geometric operations. At the same time, the coordination of the motion of each axis must be considered to avoid interference and collision, and the interpolation motion must be timely and appropriate, etc. In order to ensure the required machining accuracy and surface quality, programming is even more difficult.

2. High requirements for CNC and servo control systems.

Since five-axis machining requires five-axis simultaneous coordinated motion, this requires that the CNC system must first have at least five-axis linkage control functions; in addition, since rotational motion is added to the synthetic motion, this not only increases the workload of interpolation operations, but also increases the workload of interpolation operations. And because small errors in rotation may be amplified and greatly affect the accuracy of machining, the CNC system is required to have higher operating speed (i.e. shorter processing time for a single program segment) and accuracy. All of this means that the CNC system must increase the processor of the RISC chip for processing (ie, use multiple high-bit CPU structures). In addition, as mentioned before, the mechanical configuration of the five-axis machining machine tool includes tool rotation mode, workpiece rotation mode and a mixture of the two. The CNC system must also be able to meet the requirements of different configurations. Finally, in order to achieve high-speed, high-precision five-axis machining, the CNC system must also have a look-ahead function and a large buffer storage capacity, so that motion data can be calculated and processed in advance and multi-stage buffering can be performed before program execution. Storage to ensure that the error remains small when the tool is running at high speed. All these requirements will undoubtedly increase the complexity of the CNC system structure and the difficulty of development.

The mechanical structure design and manufacturing of three- and five-axis machine tools are also more complex and difficult than those of three-axis machine tools.

Because the machine tool needs to add two rotation axis coordinates, it must use a worktable that can tilt and rotate or a spindle head component that can rotate and swing. The two added components require not only a compact structure, but also sufficient torque, motion sensitivity and precision, which is obviously much more difficult than designing and manufacturing ordinary three-axis processing machine tools.

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