Reliability Assessment Based on Design and Manufacturing Tolerances for Control Burst Mechanism of Small Arms

Abstract

Very often specified tolerance is made greater than process tolerance, depending upon (i) the manufacturing process capability, and (ii) the 'aspiration level' of the designer in effecting a specified tolerance. This applies to multiple components merging into an assembly. In assembly tolerance, errors due to mating are inherent. Common errors arise due to clearance, misalignment in planes and distortion that may cause side stack. Such errors affect the functional performance of the subsystem and consequently become the main cause of failure. Probability distribution of the assembly tolerance and probability distribution of stacked up tolerance of the Components in actual practice leave a common zone of interaction, based on which the in-built reliability changes. From the designer's tolerance, one may have an idea about the 'aspiration level' of assembly tolerance stacking error. Assuming both these parameters, viz., actual stacking error and designer's aspiration level of stacking error to follow the normal probability distribution, it is possible to get the reliability of the product assembly. The paper presents a real life case study for assessing the reliability of sub-assembly at the initial stages of development for control burst mechanism (CBM) of rifle.