Machine tools and measuring machines with 3 to 5 axes can be found in vast numbers and all areas of modern production: from automotive to aerospace, from the production of consumer goods to medical goods. Accurate parts can only be achieved by a controlled and deterministic manufacturing process. While the repeatability of the machine is a necessary requirement for a well-controlled process, the geometric accuracy of the part can be achieved either by a feedback loop through part metrology or by accurately calibrated machine tools. Due to shorter product life cycles and small series production, the absolute accuracy of machine tools is of increasing importance.
The accuracy of machine tools and CMMs is affected by many error sources. The following reported error sources may affect the accuracy of the machined part:
The kinematic structure is defined by the layout of machine components and their axes. Most machine tools and measuring machines have a serial structure: One axis of motion is building up on another. A notation based on Schwerd can be used to describe the serial kinematic structure from the tool to the workpiece [FIGURE 1].
Relevant errors of a machine tool are relative error motions between the tool and the workpiece. Each movement of a machine axis can be described by six degrees of freedom: three translations and three rotations. The notation of an axis movement is standardized in ISO 841: X, Y, and Z denote the linear movements, A, B, and C the rotations around X, Y, and Z respectively.
For a nominal linear movement, the six component errors are the position error, two straightness error motions, roll error motion and two tilt error motions, which are called pitch and yaw error motion for horizontal axes. Under the assumption of rigid body behaviour, these errors are functions of the nominal movement only and do not depend on the location of the other axes (see animations).
For a nominal rotational movement, the six component errors are two radial error motions, one axial error motion, the angular position error, and two tilt error motions. Figure 6 shows these component errors for a C movement [FIGURE 3].
Etalon offers an effective and accurate way to measure and compensate these errors.
The following animations show the single error components. The error components are listed with the res-pective abbreviations from the standards (VDI 2617/ISO 230-1).Position deviation in X-direction (XTX, EXX) Straightness deviation in Y-direction (XTY, EYX) Straightness deviation in Z-direction (XTZ, EZX) Roll around X-axis (XRX, EAX) Pitch around Y-axis (XRY, EBX) Yaw around Z-axis (XRZ, ECX)