Five axis simultaneous forming control of digital sand mold

Compared with the traditional casting, the precision forming technology of digital dieless casting, which uses the sand mold as the cavity or sand core, does not need wood mold and metal mold. It has the advantages of less pollution, short cycle and low cost, and has become an important development trend in the field of rapid green casting. With the development of Dieless casting technology, more and more complex thin-walled castings, such as impeller, special-shaped cabin and complex shell, are used in sand mold casting, and complex sand mold and sand core need five axis simultaneous forming [3-4]. Five axis linkage machining is based on X axis, Y axis, Z axis three linear axis, add two rotation axis, used for tool or workpiece rotation.

Due to the existence of rotation, in order to ensure that the tool tip is always on the programming track, the control system needs to adjust the position of the rotation axis center in real time, that is, it has RTCP function, also known as “tool tip programming”. As the core function of high-end five axis CNC system, RTCP has become the core technology of many enterprises. At present, the research of five axis linkage control technology is mainly concentrated in the field of metal cutting, and the research of RTCP is mainly based on simulation. Open control systems, such as PMAC (programmable multi axes controller), are built on the PC platform and can be customized to write forward and inverse solutions and servo algorithm programs, which have great advantages in the development of five axis linkage system.

It often takes several days to process the sand mold of complex thin-walled components. In order to shorten the mold production cycle, it is urgent to improve the forming efficiency. The cutting force of sand mold is small, which makes it possible to form sand mold at high speed.

In the process of high-speed feed machining, in case of over speed or sharp corner processing, the look ahead control adjusts the acceleration and deceleration in advance within the allowable range of accuracy through the advanced processing of the processing program, so that the motion speed is not higher than the limit value and is always within the allowable capacity of the motor and equipment. Therefore, prospective technology has become one of the key technologies of high-speed feed machining. In the aspect of look ahead control of 5-axis linkage high-speed machining, some scholars have studied the look ahead interpolation algorithm of 5-axis machining path from the perspective of maximum constraints of speed, acceleration and acceleration; analyzed the limiting relationship between the speed and acceleration of each axis in the process of five axis machining, proposed the look ahead buffer processing method; studied the five axis linkage non-uniform rational B Speed look ahead control technology in spline interpolation. In order to realize the five axis linkage rapid prototyping manufacturing of sand mold, the kinematics model of five axis linkage RTCP with B-C double swing head structure is deduced, the mechanism of speed fluctuation in the process of five axis linkage machining is analyzed, and the single axis look ahead control method of five axis linkage high-speed forming of sand mold is proposed, and the experiment is carried out based on PMAC control system.

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