DESIGN FOR RELIABILITY – RELIABILITY PREDICTION & CORRELATION STUDY USING TEST RESULTS AND FIELD FEEDBACK

In the competitive market, Quality and Reliability are playing a vital role. Reliability is a measure of quality, which is a key characteristic at each stage of the product starting from Design through Manufacturing, Assembly, Delivery & Usage in the field. Reliability is differentiated from quality by being particularly concerned with time [1]. Reliability gives the data about how long the product will work with specified quality. Reliability is defined as the probability that an item will perform a required function for a given period of time when used under stated operating conditions [1]. The reliability stresses on four elements namely [1]; Probability, Intended function, Time, and operating conditions. Reliability / Design life of the product could not be predicted accurately using Lab test failures unless it is correlated with Field conditions. This gap can potentially result in increased Cost of Poor Quality (COPQ) [2], increase in warranty returns & most importantly Customer dissatisfaction. On the other hand, over designing due to inaccurate reliability / Design life predicted results in the unnecessary increase in product cost, reducing the profit. The conventional way of product development is, designing & developing the product as per requirements & then validation of design by physical testing. The testing process involves, subjecting the samples to various test conditions like vibration test, corrosion test, etc., for pre-defined test duration as per national & international standards. If the sample passes all the required tests, then the product will be launched. A major drawback in this system is tested standards do not always reveal the field failures. Unless we know the correlation between test conditions & field conditions, field failures cannot be predicted or eliminated. This paper estimates the reliability of carburetor from its lab test and field failures. A warranty period of one year is accounted for the calculation of reliability. This means product reliability at the end of one year is predicted and the same is compared with the reliability calculated from warranty / field failures, to check if any Over design exists or opportunity exists to improve the reliability of the product. A two-wheeler carburetor is selected for this study & the methodology can be horizontally deployed to any product