Form Error
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Form Error Albert A. Weckenmann Quality Management and Manufacturing Metrology, University Erlangen-Nuremberg, Erlangen, Germany
Synonyms Deviation of form; Form deviation; Shape deviation; Shape error
Definition The form error deviation of the real (manufactured) feature (i.e., line, axis, surface, center plane) from the geometrically ideal nominal feature is to be measured and evaluated by analogy to the definition of the form tolerance in ISO 1101. It is the minimum distance of the quasiparallel boundaries of a zone, in which the entire surface of a real feature, its line element, its axis, or its center plane remains. The boundaries of the zone are formed: • For standard features – In 2D case by two geometrically ideal 2D features (lines), which are in a common plane – In 3D case by two – geometrically ideal – nominal features
The nominal 3D features or the nominal 2D lines must show everywhere the same distance to each other (Euclidian distance evaluated for the entire feature mathematically by Chebyshev criterion). • For profiles (free-form lines or sculptured surfaces): – For “profile any line” or “profile any surface,” the zone is formed in another special way (see “profile any line” and “profile any surface”).
Theory and Application General: What Is a Form Error? Irregularities of surfaces or profiles can be decomposed into form, waviness, and roughness according to the ratio of the distance between irregularities (deviations, waves, peaks, cracks, etc.) to their depth. A form error is the overall parameter describing the maximum of the local deviations of the real form of a line or surface from the nominal – geometrically ideal – feature. The parameter has to be evaluated according to the specification (see below). One can discriminate between “local form error” (here would be more precise: “local form deviation”) and “form error” which is valid holistically for the entire feature (Humienny et al. 2001).
# CIRP 2016 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_6683-4
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Form Error
Form Error, Fig. 1 Example of a workpiece without and with form deviations
In the figure below, the nominal workpiece and an example of the workpiece with form deviation/ form error are demonstrated (Fig. 1). Form Errors in the Technical Product Documentation The maximum admissible form deviation of a feature is called form tolerance. A design engineer wishing to specify tolerances of form for geometrical features on workpieces can make use of six different types of form tolerances: straightness, flatness, roundness, cylindricity, profile of any line, and profile of any surface (Table 1). The tolerances of form defined in ISO 1101 (2012) are not mutually exclusive, so that several different form tolerance specifications are possible for a single toleranced feature (e.g., the cylinder form tolerance includes straightness tolerance of the axis or generatrix and the roundness tolerance of a cross section). The form tolerance defined in any p
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