ASME B89.7.1 pdf download

ASME B89.7.1 pdf download.Dimensional Measurement Planning.
1.1 Objective
The objective of this Standard is to ensure correctness and acceptability of dimensional measurements.
1.2 Requirements
This Standard specifies requirements for preparation and approval of dimensional measurement plans and for the use of approved plans in making dimensional measurements.
1.3 Appilcability
This Standard considers that a dimensional measurement method is acceptable if its associated measurement uncertainty per the Guide to the Espression of Uncertainty in Measurement (GUM) 121 meets business needs, e.g., cost of measurements, consequences of pass and fail errors, liability, specific policies, and customer requirements. in assessing the acceptability of a stated measuring procedure, management should take into account the importance and difficulty of evaluating measurement uncertainty in such a way as to quantitatively capture the effects of all significant sources of measurement error.
1.4 Purpose
This Standard is intended for use by process and quality engineers or personnel performing a similar function in planning dimensional measurements.
2 DEFINITIONS
accept-reject neasurernent: measurement made for the purpose of accepting or rejecting a workpiece or work- piece feature or property.
attribute gage: gage that verifies conformance of a work- piece property with a specified requirement without yielding a measured value.
C-3.4 Aliasing in Point Data Sets
When a surface has a cyclic error, the distribution of sampled points can interact with the form error to give highly misleading results. Two particular examples are
(a) lithe surface is sampled at intervals slightly different from the wavelength of the form error, the resulting data set can suggest a cyclic error very different from the actual form error.
(b) if the measured points are uniformly distributed with a period equal to the period of the form error (or a submultiple of this period), the resulting fitted feature can look perfect (neglecting measurement noise). A cylindrical bore with a pure eight-lobed form error, for example, will appear to have zero form error if sampled at eight points (or four points) uniformly distributed around the circumference. The diameter of the resulting fitted circle will depend on the phase of the sampled point di’trihution with respect to the actual form error.
The DM1’ must devise a point sampling plan that avoids these interaction problems, or assign a component of measurement uncertainty associated with such interactions.
For cylindrical surfaces, useful information regarding the interaction of measured point distributions with cyclic form errors, with a focus on measurement uncertainty, can be found in reference 1141.
C-3.5 Workpiece Distortion
Clamping and/or gravitational forces can distort a workpiece. If such problems are judged to be significant and cannot be avoided, estimates of their effects and associated uncertainty components must be assigned.
C-3.6 Operator (Metrologist) Effects
The person performing the measurements should check gages and test setups for stability and proper functioning, read gage outputs accurately and objectively, and generally avoid problems that could significaiitl affect the quality of the rncasurenwnts.
l’articular attention should be given to avoiding parallax errors, applying gaging forces, the effects of body temperature on workpieces and measuring instruments, etc. An uncertainty component associated with operator- related measurement variation must be assigned if such variation is judged to be significant.
C-4 GAGE-RELATED INFLUENCE QUANTITIES
C-4.1 Attributes Gages
The uncertainty coniponent msociated with the gage is typically assigned based on the supplier’s specifications or from calibration data. The condition of the gage relative to its condition at its last calibration will contribute to the associated uncertainty.
C-5.2 Temperature: General Considerations
The general effects of temperature in dimensional measurement are discussed in detail in ASME 1589.6.2 1161. Howevet since the objectives of ASME 889.6.2 and ASME 138q7.2 are different, some interpretation is necessary For example, ASMF 889.6.2 advocates use of a thermal error index as a means for judging acceptability of a thermal uncertantv, while ASME 1589.72 recommends combination of temperature-related uncertainty components with other contributors in order to determine the probabilities of pass and fail ermr (consumer’s and producer’s risks).
By international agreement, dimensions and forms of workpieces are defined at the standard reference temperature of 20°C 1171, Thus if both a gage and a workpiccc to be measured could be maintained at exactly 20°C, there would be no thermally related component of measurement uncertainty. Usually it is impractical to adequately approximate this condition. For temperatures other than 20°C, one must consider the effects of thermal expansion on both the gage and the workpiece.