1、 FECDS D-1 Engineering CAD & Drafting Standards Ford Proprietary and/or Confidential Information - Do not distribute to others w/o prior written authorization. Version 28 TOC Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D11 Printed copies are uncontrolled.DIMENSIO
2、NING AND TOLERANCING 1 INTRODUCTION 1.1 An amended version of ASME Y14.5-2009 (Dimensioning and Tolerancing) has been adopted for use in Ford Motor Company and their Suppliers for all engineering drawings. The amendments are detailed under para. 3. REQUIREMENTS below. The latest issue of ASME Y14.5-
3、2009 is appended to this Standard. 1.2 ASME Y14.5.1M-1994 (Mathematical Definition of Dimensioning and Tolerancing Principles) has been re-confirmed by Ford Motor Company as the current mathematical definition of ASME Y14.5-2009. The latest issue of ASME Y14.5.1M-1994 is appended to this standard. W
4、hen the ASME Y14.5.1M-1994 has been updated to agree with ASME Y14.5-2009, it will be considered for adoption. 1.3 Many Standards referenced in ASME Y14.5-2009 and ASME Y14.5.1M-1994 have not been adopted by Ford Motor Company. The Ford Motor Company Engineering CAD & Drafting Standard takes precede
5、nce, unless otherwise specified. 1.4 Application of Standards 1.4.1 For annotating drawings using orthographic projection (see Standard C-5), ASME Y14.5-2009 shall be used. 1.4.2 If a conflict occurs between ASME Y14.5.1M-1994 and ASME Y14.5-2009, ASME Y14.5-2009 is to be used. 1.4.3 For annotating
6、all other drawings produced in non-orthographic projection ASME Y14.41-2003 (see Standard D-7) shall be used. Note: ASME Y14.41 is also undergoing revisions by the ASME Organization and Ford will review these changes upon its publication. 1.5 The Dimensioning and Tolerancing concepts described in AS
7、ME Y14.412003 take precedence over any other reference standard when working with annotated CAD models. If a conflict occurs with unique concepts introduced by the ASME Y14.412003 and concepts existing in ASME Y14.5-2009 or any other adopted standard, ASME Y14.412003 is to be used. 1.6 All issues pe
8、rtaining to Geometric Dimensioning and Tolerancing (GDT) are referred to, and approved by, the Ford Motor Company Ford GDT TC prior to submission to the Ford Motor Company Engineering CAD and Drafting Standards Committee for inclusion in this standard. (For the Ford GDT TC Charter see Appendix G). E
9、NGINEERING CAD & DRAFTING STANDARDS Return to TOC 2 DEFINITIONS (Reserved) 3 REQUIREMENTS 3.1 These amendments were developed by the Ford GDT Technical Committee and address the following areas: 3.1.1 Selecting an option from ASME Y14.5-2009. 3.1.2 Clarifying a concept from ASME Y14.5-2009. 3.1.3 Di
10、scouraging the use of a concept from ASME Y14.5-2009. 3.2 These amendments follow the structure of ASME Y14.5-2009. All paragraph numbers and figures refer to paragraph numbers and figures in ASME Y14.5-2009. Only changes are identified and the remaining content of ASME Y14.5-2009 applies as written
11、: NOTE: Ford revisions to ASME Y14.5-2009 are indicated as follows: Italics EXPLANATORY INFORMATION only and not intended as part of the amended standard 1. Scope, Definitions, and General Dimensioning 1.3 DEFINITIONS 1.3.23 Dimension, Basic. Dimension, basic: a theoretically exact dimension. Values
12、 taken from CAD data are basic. NEW 1.3.68 Element. A point, line, arc or circle derived from a feature. NEW 1.3.69 Aligned. The term aligned means oriented and located. 1.4 FUNDAMENTAL RULES (Add the following text to paragraph 1.4 of ASME Y14.5.) NEW (q) Unless otherwise specified all dimensions a
13、pply after heat treat and surface treatment/coating. NEW (r) Direct tolerancing methods as described in paragraph 2.2 shall not be used to locate or orient features. However, this method may be used when dimensioning elements such as the angles of countersinks and chamfers. Original Issue: 19960419
14、Copyright, Ford Motor Company. Latest Re-issue: 20111231D12 Printed copies are uncontrolled.ENGINEERING CAD & DRAFTING STANDARDS Return to TOC 1.7 APPLICATION OF DIMENSIONS 1.7.1 Dimension Lines. (Replace the text before the note with the following) A dimension line, with its arrowheads, shows the d
15、irection and extent of a dimension. Numerals indicate the number of units of a measurement. Dimension lines shall be broken for the insertion of numerals as shown in Fig. 1-6. 1.7.9 Dimensions Not to Scale. (Replace the text in paragraph 1.7.9(b) with the following) (b) Where the sole authority for
16、the product definition is a dataset prepared on a computer graphics system, agreement shall be maintained between the defining dimension and the graphics presentation of the feature, in all views. The defining dimension and the true size, location, and direction of the feature shall be in agreement
17、within the accuracy of the CAD system. See ASME Y14.41-2003 and FECDS D-7. 1.9 LOCATION OF FEATURES 1.9.5 Repetitive Features or Dimensions. Repetitive features or dimensions may be specified by the use of an X in conjunction with a numeral to indicate the “number of places” required. See Figs. 1-53
18、 through 1-57. Where used with a basic dimension, the X shall be placed outside the basic dimension frame. See Fig. 4-39. 2.1.1.2 Basic Dimensions (d) specifying on the drawing for charted values, use the Charted Dimensions note: UNTOLERANCED CHARTED DIMENSIONS ARE BASIC 2.17 The statistical toleran
19、cing methods shown in 2.17 and associated paragraphs are not adopted for use at Ford Motor Company. While many tolerances are derived statistically within Ford, the selective labeling of each tolerance with the hexagon-ST symbol is not necessary & would only add confusion to our current processes fo
20、r controls on dimensional requirements 2.2 Direct Tolerancing Methods Direct tolerancing, as noted in paragraphs (a) and (b), should not be used for location or orientation. 4. Datum Referencing 4.8 DATUM FEATURES 4.8.1 Temporary and Permanent Datum Features. Features of in-process parts such as cas
21、tings, forgings, machinings, or fabrications, may be used as temporary datum features to create permanent datum features. Such temporary datum features may or may not be subsequently removed by machining. It is recommended that temporary datum features not be subsequently removed by manufacturing pr
22、ocesses. Permanent datum features should be surfaces or diameters not appreciably changed by subsequent processing operations. Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D13 Printed copies are uncontrolled.ENGINEERING CAD & DRAFTING STANDARDS Return to TOC 4.20
23、RESTRAINED CONDITION (Add the following text to paragraph 4.20 of ASME Y14.5.) Restraint is necessary to overcome excessive variation inherent in many components. Restraint notes on the drawing shall be clear to the extent that only one interpretation is possible. Specifying the restraint parameters
24、 ensures proper correlation of the datum features of the part or assembly with the datum feature simulators on the gauge. The combination of choosing the proper datum reference frame and restraint parameters will ensure proper fit and function of the part or assembly. The amount of force designated
25、shall either be stated by a specific value with tolerance designated where applicable, see ASME para. 5.5, or with widely used and understood industry terminology. Restraint notes may also reference other formal documents such as ES specifications to outline the force applied, see ASME Fig. 5-14. Wh
26、en part features are used to restrain the part and these features, such as the mounting holes, cannot feasibly be checked in the restrained condition, use the Free-State modifier to ensure the fit and function is established. 4.24 DATUM TARGETS 4.24.7 Datum Target Dimensions. The location and size,
27、where applicable, of datum targets are defined with basic dimensions except when the datum target is moveable, expandable or collapsible. In these cases, the motion is limited by the part tolerance(s). For examples, see Figs. 4-47 thru 4-54. For the basic dimensions, established tooling or gaging to
28、lerances apply. NOTE: For information on datum feature simulator tolerances and toleranced relationships between the simulators, see ASME Y14.43. 5. Tolerances of Form 5.4 FORM TOLERANCES NEW 5.4.1.1.1 MEASUREMENT OF CIRCULARITY & CYLINDRICITY. The default Assessment Type for the measurement of Circ
29、ularity & Cylindricity shall be Minimum Radial Separations (MRS). Any Assessment Type other than MRS shall be specified next to the individual callouts or in a general note. Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D14 Printed copies are uncontrolled.ENGINEERI
30、NG CAD & DRAFTING STANDARDS Return to TOC 5.5 APPLICATION OF FREE-STATE SYMBOL (Add the following text to paragraph 5.5 of ASME Y14.5.) The Free-State modifier along with Restraint notes may be used on both non-rigid parts as well as rigid parts when specific assembly conditions must be met (e.g. th
31、e flatness of sealing surfaces) See ASME para. 4.20. The Free-State modifier may be used with datum references, features and features of size when a restraint condition is invoked on a drawing. See ASME para. 3.3.20. The following elements must be part of a restraint note on a drawing: UNLESS SPECIF
32、IED BY THE FREE-STATE MODIFIER: Identify: o What the restraint applies to (e.g. all tolerances, all geometric tolerances) o Features to be restrained o Assign Restraint Forces o Where the forces are applied, when applicable 6.6 ALTERNATIVE PRACTICE Do not use the alternative practice. This forces al
33、l angles in CAD models to be queried to determine their true angular value. For features that are to be controlled parallel or perpendicular, the Parallelism and Perpendicularity orientation controls shall be specified instead of Angularity to avoid any potential confusion. 7. Tolerances of Location
34、 7.6.4 CONCENTRICITY Note: The use of concentricity is not recommended for most applications. Concentricity can be very expensive to verify and is only necessary when a size tolerance is not the primary consideration for an axis to axis control. 7.7.2 SYMMETRY TOLERANCING TO CONTROL THE MEDIAN POINT
35、S OF OPPOSED OR CORRESPONDINGLY-LOCATED ELEMENTS OF FEATURES Note: The use of symmetry is not recommended. Symmetry can be very expensive to verify. Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D15 Printed copies are uncontrolled.ENGINEERING CAD & DRAFTING STANDAR
36、DS Return to TOC NONMANDATORY APPENDIX B FORMULAS FOR POSITIONAL TOLERANCING B1 GENERAL The purpose of this Appendix is to present formulas for determining the required positional tolerances or the required sizes of mating features to ensure that parts will assemble. The formulas are valid for all t
37、ypes of features or patterns of features and will give a “no interference, no clearance” fit when features are at maximum material condition with their locations in the extreme of positional tolerance. Consideration must be given for additional geometric conditions that could affect functions not ac
38、counted for in the following formulas. When calculating positional tolerancing, conditions such as fastener straightness, thread to shank runout, and projected fastener length, need to be considered to ensure assembly. 3.3 OTHER DIMENSIONING PRACTICES 3.3.1 Product Manufacturing Information (All CAD
39、 models must be fully toleranced. This is also required on 3D models without 2D formats) 3.4 UNITS OF MEASUREMENT 3.4.1 Linear Units. Use of the ENGLISH (INCH) UNIT is not recommended. 3.5 NUMBERING OF HOLES 3.5.1 On complicated drawings it may be advantageous to number the holes for clarity and ide
40、ntification. The same number should appear on the hole in every view that it is individually shown. In order not to confuse the number with a drawing dimension the arrowhead on the leader line should be omitted. 3.5.2 The last hole number should be listed in the general note area. Similar hole data
41、may be contained in a block on the drawing or listed in one of the views. 3.5.3 On drawings that consist mostly of hole dimensioning such as electrical circuit boards where there are many holes that vary only slightly in size, it may be advantageous to code the holes for clarity. 3.6 ROUNDING OFF FO
42、R DIMENSIONS 3.6.1 Where a decimal value is to be rounded off to fewer decimal places proceed as follows: 3.6.1.1 Where the first digit being discarded is less than 5, the last digit retained is not changed. 3.6.1.2 Where the first digit being discarded is exactly 5, the last digit retained is uncha
43、nged if even but increased by one if odd. Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D16 Printed copies are uncontrolled.ENGINEERING CAD & DRAFTING STANDARDS Return to TOC Original Issue: 19960419 Copyright, Ford Motor Company. Latest Re-issue: 20111231D17 Print
44、ed copies are uncontrolled.3.6.1.3 Where the first digit being discarded is more than 5, or is 5 followed by further significant digits, the last digit retained is increased by one. EXAMPLES: 4.6348 rounded to 2 decimal places becomes 4.63 1.65 rounded to 1 decimal place becomes 1.6 1.55 rounded to
45、1 decimal place becomes 1.6 3.4500 rounded to 1 decimal place becomes 3.4 3.3500 rounded to 1 decimal place becomes 3.4 5.2575 rounded to 1 decimal place becomes 5.3 5.29 rounded to 1 decimal place becomes 5.3 3.7 APPLICATION OF TOLERANCES 3.7.1 All tolerances shall be specified as absolute limits (
46、also known as accept/reject limits) consistent with ensuring fit and function of the components or machine parts. An arbitrary factor shall not be applied to existing tolerances to make it appear that they are statistically compliant. This does not preclude the use of other factors for establishing
47、absolute limits prior to specifying them on the drawing, provided the fit and function is maintained via a review of tolerance accumulation. See also clause 2.16 of the USCAR agreement pertaining to Statistical Tolerancing and E-2, Application of Tolerances. 4 SPECIFICATIONS (Reserved) 5 ADDENDUM WHERE FORD MOTOR COMPANY REQUESTS CERTIFICATION OF GDT PROFESSIONALS, THAT CERTIFICATION IS CARRIED OUT ON BEHALF OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) BY PROMETRIC. CONTACT PROMETRIC AT HTTP:/WWW.PROMETRIC.COM
