Machine tool errors typically include the following: machine tool geometric errors, control errors, thermal (deformation) errors, force (deformation) errors, motion errors, positioning/positioning errors, and machining errors.
Machine tool geometric errors
Machine tool geometric error refers to the deviation of the actual geometric parameters and positions of various components or parts of a CNC machine tool from their ideal geometric parameters and positions under standard testing conditions (standard atmospheric pressure and a constant temperature of 20°C), in a stable operating environment and under no-load conditions. This deviation is caused by defects in the machine tool's design, manufacturing, and assembly. This error is generally related to the geometric elements of the machine tool's components or parts and is an inherent error of the machine tool itself.
CNC machine tool control error
The deviation between the actual and ideal motion trajectories of moving parts in a CNC machine tool is caused by the inaccuracies of the CNC machine tool control system. Control errors include deviations arising from servo drive components, measurement and sensing components, and CNC interpolation and other control-related components.
Motion error
The degree to which the actual motion trajectory of the main moving parts such as the worktable and spindle deviates from the ideal motion trajectory during the operation of a CNC machine tool. Generally, the motion error of a CNC machine tool includes the aforementioned geometric errors as well as the control errors of the CNC machine tool, and falls under the category of static errors.
Thermal (deformation) error
Due to the influence of internal heat sources such as cutting heat and frictional heat, as well as external heat sources around the work area, the temperature distribution of CNC machine tools changes, resulting in additional thermal deformation compared to the standard steady-state state. This alters the relative positions of the components within the CNC machine tool, leading to additional errors (excluding the existing geometric errors of the CNC machine tool), referred to as thermal errors. Thermal errors exhibit nonlinear characteristics and are a quasi-static error, which can technically be treated as static errors.
Force (deformation) error
The additional geometric deformation of a CNC machine tool under the action of cutting force, clamping force, gravity and inertial force, which disrupts the original positional relationship between the components of the machine tool, is called force error. It is related to the rigidity of the machine tool.
Positioning/location error
Machine tool positioning/positional error specifically refers to the degree of difference between the ideal position and the actual position of a machine tool's worktable or cutting tool as it moves from one point to another within the machine tool's workspace. It generally falls under the category of machine tool geometric errors.
Machining error
Machining error refers to the undesirable changes in the relative motion between the tool and the workpiece caused by factors such as uneven heat distribution of the machine tool and machining load during machining. Specifically, this manifests as additional dimensional errors, shape errors, and positional errors on the workpiece. The machining accuracy of a workpiece primarily depends on the correctness of the relative positions of the workpiece and the cutting edge during machining. There are two different understandings of machine tool error: a narrow one and a broad one. In a narrow sense, machine tool error refers to errors related to the CNC machine tool itself, such as machine tool position errors, spindle rotation errors, and CNC system control errors. In a broad sense, machine tool error also includes all error items related to the machine tool's design, manufacturing, assembly, inspection control, and machining operation, including thermal (deformation) errors and force (deformation) errors caused during machine tool operation.
Among them, geometric error and control error are the original errors of the machine tool, while thermal error and force error are errors generated during the machining process.
Geometric errors, thermal errors, and force errors account for 65% of the total error, making them the main error factors affecting the machining accuracy of CNC machine tools. The proportion of each error source varies under different working conditions; the more precise the machine tool or the more precise the machining, the greater the proportion of thermal errors.
