TABLE OF CONTENTS Vijay Srinivasan, Ph.D
IBM Research and Columbia University
New York
Dr. Vijay Srinivasan is a research staff member at the IBM Thomas J.Watson Research Center, Yorktown Heights, NY. He is also an adjunct professor in the Mechanical Engineering Department at Columbia University, New York, NY. He is a member of ASME Y14.5.1 and several of ISO/TC 213 Working Groups. He is the Convener of ISO/TC 213/WG 13 on Statistical Tolerancing of Mechanical Parts. He holds membership in ASME and SIAM.
Statistical tolerancing is an alternative to worst-case tolerancing. In worst-case tolerancing, the designer aims for 100% interchangeability of parts in an assembly. In statistical tolerancing, the designer abandons this lofty goal and accepts at the outset some small percentage of failures of the assembly.
Statistical tolerancing is used to specify a population of parts as opposed to specifying a single part. Statistical tolerances are usually, but not always, specified on parts that are components of an assembly. By specifying part tolerances statistically the designer can take advantage of cancellation of geometrical errors in the component parts of an assembly a luxury he does not enjoy in worst-case tolerancing. This results in economic production of parts, which then explains why statistical tolerancing is popular in industry that relies on mass production.
In addition to gain in economy, statistical tolerancing is important for an integrated approach to statistical quality control. It is the first of three major steps specification, production, and inspection in any quality control process. While national and international standards exist...
