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CNC numerically controlled machine tools are crucial equipment for the development of civil industries, defense industries, and aerospace industries. They are also important equipment for electromechanical integration. Generally, the design of CNC machine tools requires structural design and key component integration on the hardware side. On the software side, applications involve controllers and sensors. Modern CNC machine tools incorporate sensors for IoT and intelligent design. Their important development goals and directions are to reduce human intervention, achieve high precision and high efficiency. Therefore, design on the hardware side of CNC machine structure is extremely important. The initial phase involves rational design, followed by the second phase involving the analysis and modification of the structure using software tools.
This unit will discuss rational design in conjunction with the Ministry of Economic Affairs' CNC machine tool talent certification. Generally, CNC machine tools are divided into two major categories: CNC lathes and CNC milling machines. Similar mechanisms include the feed system and spindle, while different mechanisms include mechanical structures, controllers, tool change mechanisms, ATC, chuck systems, and power turrets. The technologies related to machinery and electrical control correspond to courses related to applied mechanics, materials mechanics, dynamics, electrical principles, and control principles offered in schools.
General CNC machine tools have different types and applications, primarily determined by the workpieces being processed. When workpieces are produced in fixed forms in large quantities, special machines are used. For different forms produced in large quantities, standard CNC machine tools are applied. When the geometric shapes of the workpieces differ, they are classified into lathes and milling machines. Notable differences exist in the mechanical structures and controllers of CNC lathes and milling machines. The structural design and key components must be integrated. The bed structure of CNC lathes and vertical machining centers varies the most; therefore, design of CNC machine structure must follow mechanical design principles.
In the principles of CNC machine tool design, the structure of functional components like the feed system and spindle system is greatly simplified, but requirements for rigidity have become increasingly stringent. High rigidity and lightweight need to be considered simultaneously during high-speed and high-precision cutting processes. Therefore, the design of CNC machine structure must consider the relationship of force flow lines. Although the concept of force flow lines is relatively simplified, it can be applied to the concept design phase in the design of CNC machine structure. What is meant by force flow lines? Force flow lines are the routes for the transmission of forces between the acting force and the reaction force in the structure. The shorter the force flow line in structural design, the smaller the deformation and the higher the rigidity. Particularly, force flow lines perpendicular to the direction of the applied force are most prone to reducing structural rigidity.
In the design of CNC machine structure, how can mechanical principles be applied to achieve rational design? Rationally designed structures should undergo finite element analysis, allowing the structure to obtain optimized design and rigidity values. Static forces cause static deformation in the structural system, leading to positioning errors and affecting the dimensional accuracy of workpieces. Dynamic forces acting on the structural system can easily excite the natural frequencies of the structure, amplifying vibration phenomena and causing surface irregularities that affect surface roughness. The natural frequency of the structural system is related to the distribution of structural mass, the inertia of moving parts, and the static rigidity of the structure. Generally, smaller mass and higher rigidity result in higher natural frequencies of the system. This is also why high-speed machines require high rigidity and low inertia design. Therefore, in rational design, relevant mechanical principles need to be referenced.
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