1、Copyright ASME International Provided by IHS under license with ASMENot for ResaleNo reproduction or networking permitted without license from IHS-,- STD*ASME 687.7.2-ENGL L779 D 0757670 0635963 L)74 The American Society of Mechanical Engineers AN AMERICAN NATIONAL STANDARD MEASUREMENT PLANNING I Co
2、pyright ASME International Provided by IHS under license with ASMENot for ResaleNo reproduction or networking permitted without license from IHS-,- STD-ASME B89.7.2-ENGL L799 0759b70 Obl157b2 300 m Date of Issuance: March 1, 2000 This Standard will be revised when the Society approves the issuance o
3、f a new edition. There will be no addenda issued to this edition. ASME will issue written replies to inquiries concerning interpretation of technical aspects of this Standard. The interpretations are not part of the Standard. ASME is the registered trademark of The American Society of Mechanical Eng
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9、ividuals. No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. The American Society of Mechanical Engineers Three Park Avenue, New York, NY 10016-5990 Copyright O 2000 by THE AMERICAN SOCIETY OF
10、 MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A. Copyright ASME International Provided by IHS under license with ASMENot for ResaleNo reproduction or networking permitted without license from IHS-,-The intent of this Standard is to facilitate agreement between suppliers and customers by s
11、pecifying a standard method for assessing the dimensional acceptability of workpieces. Components of the method are the preparation of an adequate dimensional measurement plan and use of the plan in making measurements. The major input to the method is dimensional specifications developed, for examp
12、le, in compliance with ASME Y 14.5M, Dimensioning and Tolerancing. The first publication of Y14.5 was a significant step forward in manufacturing because it defined methods for the unambiguous expression of design intent on workpiece drawings. Y14.5 specifies design intent in terms of workpiece feat
13、ures (e.g., cylinders, planes, spheres, etc.). A feature is dimensioned by specifying boundaries within which the infinite number of points in the feature surface must lie. Any adequate assessment of whether a feature complies with a Y14.5 drawing specification must consider this infinite number of
14、points. In the early days of Y 14.5, serious attempts to determine compliance of workpiece features with drawings were based on gaging by attributes, e.g., by means of ring gages, plug gages, and functional gages. These gages dealt with the infinite number of points by means of gaging surfaces which
15、 were the ideal counterparts of the surfaces to be measured. Uncertainty due to gage errors was minimized by specifying gages that were highly accurate compared with tolerances of the parts to be measured. Gage dimensions were biased to ensure that no bad parts were accepted, even though such biasin
16、g resulted in the rejection of a few good parts. Since the accuracy of manufacturing processes has improved more rapidly than the accuracy of gaging by attributes, the old methods have led to expensive increases in the rejection of good parts. Statistical analysis capabilities and cost effectiveness
17、 have led to the proliferation of coordinate measuring machines which cannot directly verify dimensional acceptability of the infinite number of points in a workpiece feature surface. In some instances the algorithms used to develop substitute geometries have not been adequate representations of dra
18、wing specifications. Working Group B89.3.2 (now B89.7.2) was formed to address these and related issues. One of these issues is the criterion for acceptable dimensional measurement practice. The measurement process should be designed to balance measurement quality and cost, including the cost of inc
19、orrect decisions based on measurement results. While the analysis of costs is outside the scope of a dimensional measurement standard, the measurement process should be designed to provide the required metrological data for the analysis. Measurement quality is defined in terms of uncertainty. Previo
20、us practice has been to assume that gaging was sufficiently accurate to ensure that uncertainty was negligible. This assumption was applied both to measurement by attributes as described above and to measurement by variables using simple bench tools, e.g., micrometers and height gages. Gage repeatab
21、ility and reproducibility (GR that is, any two opposite points on the cylindrical surface must be at least 24.99 mm apart (d) all points on the left end surface must lie on or between two planes 0.5 mm apart and perpendicular to the axis of the actual mating envelope of the cylinder. Since the left
22、end is not distinguishable from the right, the perpendicularity requirement is met if either end complies with this specification. (e) the actual mating size of the length must be no greater than 75 mm; that is, all points on the ends of the pin must lie on or between two parallel planes 75 mm apart
23、 and nominally parallel to the pin ends cf, the actual local size of the length must be no less than 74 mm; that is, any two opposite points on the pin ends must be at least 74 mm apart. The DMP requests clarification on the 45 deg chamfer and is told that visual inspection is adequate. This is conf
24、irmed by a memorandum. A2.1.2 Review Manufacturing Plan and Manufacturing Process Failure Mode and Effects Analysis. In this step probable stability of the manufac- turing process, probable modes and consequences of process failure, and part quantities are identified from the manufacturing plan. Thi
25、s background information is useful for determining what measurements should be made and what sampling plan should be used. The DMP determines the following to be significant: (a) lot size is 2,500 pieces. Total production is 50,000 pieces. Production rate is 180 pieces per hour. (6) blanks are produ
26、ced on a screw machine and heat- treated. Experience indicates that distortion is within the ASME Y14.5M-I994 and ASME Y14.5.IM-1994 present different interpretations of the size specification. Since the drawing references Y14.5, the interpretation of thar standard is used. I 5 Copyright ASME Intern
27、ational Provided by IHS under license with ASMENot for ResaleNo reproduction or networking permitted without license from IHS-,-450 x 0.5 1.0 1 NONMANDATORY APPENDIX A -J GENERAL NOTE: All dimensions are in millimeters. FIG. AI stock allowance for final finishing. Each piece will have cutoff project
28、ions which must be within the length tolerance. (c) final finishing is by through-feed centerless grind- ing. Experience indicates this may cause lobing, but the process is stable once it is set up. Allowance must be made for lobing when planning the measurement process, see A2.2.10. Experience indi
29、cates taper will be negligible. (d) the major process failure mode, determined from experience, is regulating wheel infeed error, which causes workpiece diameter error. A2.1.3 Dimensional Measurement Planning Constraints. In the approach recommended by this Standard, the most common constraints are
30、the required uncertainty, expressed as acceptable probabilities of pass and fail errors, and measurement cost. In some cases there will be other constraints. There is usually a tradeoff between uncertainty and cost. In some cases constraints will be determined by contract or provided by management.
31、In other cases the DMP will develop the constraints and submit them with the dimensional measurement plan for approval. In this sample plan the DMP develops the constraints by the following reasoning. The pin is used to control relative location of two parts. It is a sliding fit in each. It is to be
32、 manually assembled; thus, jamming in an assembly machine is not an issue. If the pin is too large, it may be usable if holes in the mating parts are not at minimum acceptable size. If it is not usable, the pin is discarded and another pin is used. Cost of rejecting a good pin is small. The DMP esti
33、mates that probabilities of pass and fail errors 6 at the large end of the tolerance interval of 1% will be acceptable and achievable. If further analysis shows these constraints cannot be met, modification of this estimate may be required. If the pin is too small, it will not locate the parts adequ
34、ately, and this condition may not be detected. At the small end of the tolerance range, probability of a pass error is set at zero and of a fail error at 2%. Length of the pin and dimensions of the chamfers are not critical. The DMP estimates, subject to approval, that 100% inspection will not meet
35、cost constraints, but that funds will be available for a moderate amount of special gaging. A2.1.4 Existing Equipment. The DMP deter- mines that all the standard gages suitable for measuring pins are available. A2.2 Plan Development By performing the following steps, the DMP ensures that content of
36、the plan follows the recommendations of para. 4.3 of the Standard. A2.2.1 Measurements to Be Taken. The DMP verifies that length characteristics of the pin are con- trolled in the process for producing the blank. Thus diameter is the only characteristic to be controlled in the plan of this Appendix.
37、 Since diameter may drift during production of a lot, process control measurements will be required. Periodic accept-reject measurements also will be required for a more thorough assessment of diameter. Copyright ASME International Provided by IHS under license with ASMENot for ResaleNo reproduction
38、 or networking permitted without license from IHS-,-STDOASME B89.7-2-ENGL 1999 = 0759b70 Ob15973 196 = NONMANDATORY APPENDIX A A2.2.2 Applicable Standards. The DMP consid- ers the applicability of each of the following standards. ANSI B89.3.1, Measurement of Out-of-Roundness. This standard is not ap
39、plicable because it deals with form, whereas the drawing only specifies diameter. Form is controlled by the diameter (size) specification, but not by the means discussed in B89.3.1.1 ANSI B89.6.2, Temperature and Humidity Environment for Dimensional Measurement. (The provisions of this Standard are
40、applicable.) ANSINCSL 2540- 1 - 1994, American National Standard for Calibration - Calibration Laboratories and Mea- suring and Test Equipment - General Requirements. (Meeting the requirements of this standard is good practice. The DMP determines that meeting the re- quirements is ensured by complia
41、nce with provisions of the company gage control system.) The foregoing is not intended as an exhaustive list of applicable standards. It is intended only as an example of how the applicability of standards is determined. A2.2.3 Lot Sampling Plan. For process qualifica- tion the DMP determines that c
42、ompany policy is to run a lot of 25 pieces through the entire process and to inspect them by the workpiece acceptance method. For process control the DMP decides that every twenty minutes a sample of five successive pins will be taken. This decision is based on an assessment of the stability of the
43、manufacturing process. For accept-reject measurements the DMP decides that one pin will be fully inspected each hour. Since 13.9 hr are required to run a lot, these measurements also will serve as a process audit to ensure the workpiece meets all dimensional requirements. A2.2.4 How Measurements Wil
44、l Be Taken. For process control the DMP decides to use an average and range (X-bar-R) chart. Diameter of each pin in a sample is determined as the mean of three two-point measurements, one at each end of the pin and one at mid-length. For each sample (subgroup) of five pins, the mean diameter of the
45、 subgroup and the range of the subgroup (largest minus smallest) are calculated. The mean is plotted on the X-bar portion of the chart and the range on the R-portion. Each chart has control limit lines determined by reference to previous (historical) or current (natural) experience with this or a si
46、milar process. The relation- ship of the sequence of X-bar or R points to these limits determines the state of control of the process. Since there are many tests for control, they are nor ASME 889.7.2-1999 enumerated here. The reader is referred to any of several handbooks both for the calculation o
47、f control limits and for the interpretation of the charts. If an out-of-control state is detected, the machine operator or other personnel refer to documented correc- tive action procedures to determine what to do. Usually, an adjustment to the manufacturing process can be made and this procedure is
48、 canied out. For accept-reject measurements, the DMP determines that measurements for upper and lower limits of diame- ter will be taken, and pins will be visually inspected for faults. Visual inspection ensures that the entire diametral surface is ground, and that no handling dam- age has occurred.
49、 A2.2.5 Select Gages. For accept-reject measure- ment for compliance with the actual mating size specifi- cation, the DMP chooses a ring gage the length of the part, having a diameter tolerance of +O mm/-0.002 mm. Reference to catalogs and discussion with a gage manufacturer show this gage can be obtained at an acceptable cost. As a first guess, gage tolerance seems consistent with the chosen probabilities of pass and fail errors. Use of a full-form gage is the most reliable method for assess
