As a special application of CNC milling machines, the machining accuracy of CNC crescent groove milling machines directly determines the size, shape, and surface quality of crescent groove parts, thereby affecting the performance of the final product. The factors affecting its accuracy are multifaceted and can be mainly divided into three categories: machine body factors, process factors, and external environmental factors.
I. Main structure and rigidity of the machine tool
1、Rigidity of bed and column
The material of the basic casting (such as resin sand cast iron), rib design, and vibration resistance directly determine the degree of deformation of the machine tool under cutting forces. Minor deformations can lead to deviations in slot width, depth, and position.
2、Spindle system
Radial/axial runout of the spindle: It affects the stability of the tool center trajectory, leading to uneven groove widths and vibration marks on the side walls.
Spindle thermal deformation: Axial/radial expansion caused by spindle heating during prolonged operation can alter the actual position of the tool, affecting depth and contour accuracy.
Spindle drive power and torque stability: Insufficient power or torque fluctuations may lead to speed variations during the cutting process, affecting surface quality and dimensional consistency.
3、Feed system
Accuracy of lead screw and guide rail: The pitch error and backlash of the ball screw, as well as the straightness and parallelism of the guide rail, will be directly translated into positioning errors of the X/Y/Z axes.
Servo drive responsiveness: The dynamic characteristics of servo motors and drives (such as tracking error and stiffness) can affect the interpolation motion accuracy, especially the formation of crescent curve contours.
II. Tool system factors
1、Tool geometric accuracy and dynamic balance
Errors in the diameter of the milling cutter and runout of the cutting edge can lead to groove width exceeding the tolerance limit.
During high-speed cutting, dynamic imbalance of the tool can induce vibration, which can enlarge the actual cutting size and affect the sidewall roughness and straightness.
2、Tool clamping rigidity
Inadequate concentricity and rigidity between the tool shank type (such as HSK, BT) and the clamping method (hydraulic, thermal expansion) can amplify spindle runout and reduce cutting stability.
III. Control system and feedback
1、Interpolation algorithm and resolution of CNC system
The interpolation accuracy of complex curves (such as gradually changing crescent-shaped slots) is influenced by the system's computing power. Insufficient resolution can result in the contour appearing as a tiny polygon.
2、Position detection and closed-loop control
Fully closed-loop feedback systems such as grating scales can compensate for mechanical transmission errors. However, if only relying on semi-closed-loop systems (motor encoders), errors such as thermal elongation of the lead screw cannot be corrected.
IV. Thermal deformation and environmental factors
1、Thermal stability of machine tool
The non-uniform thermal deformation of the structure caused by heat sources such as the spindle, screw, and motor can alter the relative position of the tool and the workpiece, necessitating mitigation through thermal symmetry design, cooling systems, or preheating.
2、Environmental temperature and vibration
Temperature fluctuations in the workshop affect the geometric accuracy of machine tools, and external vibrations (such as from nearby equipment) may be transmitted through the foundation, causing micro-vibrations during cutting.
