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GUIDELINE TOLERANCES FOR IMPRESSION DIE FORGINGS A word about national standard ASME Y14.5. This tolerance guide provides dimensioning and tolerancing that is considered linear and not geometric. Geometric dimensioning and tolerancing to ASME's ANSI Y14.5M standard are being increasingly applied to forged products. Giving consideration to the fact that forgings undergo dimensional changes due to cooling and because forgings are formed in most cases between two impression dies that are not precisely on the same centerline, the ANSI Y14.5M guidelines for tolerancing are not totally appropriate to forgings. These are reasons for FIA to refer also to the 1989 version of ASME Y14.8M an American National Standard for "Engineering Drawing and Related Document Practices for Castings and Forgings". This document more closely interprets the needed dimensional and tolerance modifications for forgings discussed in this booklet. PRINTS AND SPECIFICATIONS It is important that forging drawing be accurate and complete. The purchaser should indicate his first operation locating points, normally a part of the drawing, and give prior notice should these points be changed. It is equally important that the purchaser provide drawings of the finish machined part, or equivalent information. This will assist in the design of forging dies and tools, and in establishing effective inspection procedures. Unless the purchaser's drawings and specifications direct otherwise, all dimensions are normally assumed to refer to lines intersecting at right angles to each other (commonly referred to as X, Y, and Z axes). Furthermore, unless the purchaser's drawings or specifications direct otherwise, circular shapes are normally assumed to be figures of revolution with a center on an axis, and all circular dimensions are normally shown as diameters. GENERAL All individual tolerances apply to each and every forged part unless specifically noted otherwise. Tolerances as stated in all tables are considered for use by final inspection departments at the forge plant and/or by receiving or by customer source inspection. UNITS OF MEASURE Tolerances in this publication are expressed in decimal inch with metric equivalents (sometimes referred to as "soft" metric conversion) in the belief that this represents a practice most common in the industry at the time of publication. NOTE: THESE ARE GUIDELINES BASED ON AVERAGES IN THE FORGING INDUSTRY. REFINEMENTS TO THE ENCLOSED TOLERANCES CAN BE MADE IN RELATIONSHIP TO SMALLER DRAFT ANGLES, TIGHTER SQUARENESS, ROUNDNESS, PARALLELISM, HOLD STEP DESIGNS AND STRAIGHTNESS. OPERATIONS CAN BE PERFORMED BY FORGE PLANTS TO PROVIDE ADDITIONAL SERVICES WHICH IN MANY CASES REPLACE THE NEED FOR MACHINING. |