Probabilistic approach and inertial tolerancing for H/C ramp-up in production

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Krebs, M.
Gatti, J.L.
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The functional Geometrical Tolerance Management is a top-down approach leading to systems specification at each level of the Aircraft assembly, and following the 3 main phases of the Helicopter lifecycle: Design phase, Development phase and Serial life. During Serial life, we shall provide optimized methods and tools matching with quality and production objectives (OTD, OQM, ramp-up) and viewing results format. Since the tolerances are represented by a network, we have defined a format for injecting the results at a given level as input data to the next level. Due to the nature and interconnections of this network, the volume of data to be processed can be significant. So we have implemented an appropriate numerical technique to deal with a continuous influx of measurement data. The objective is to purpose a comprehensible representation of the re-evaluated risks at each stage of the process, i.e.: Initial risks related to the current helicopter definition, Re-evaluated risks related to an aircraft serial number completed with each new measurement of characteristics for this aircraft, Re-evaluated risks related to the observed variability of the product / process at assembly level. Our new industrial model leads to change our approach from a curative model to another model applied to QN process with root cause identification and manufacturing process monitoring allowing deploying preventive and corrective action plan. Behind that our objective is to avoid recurring QN and to switch to a Risk management model by several lever deployments. When a functional geometrical target is too much tight, its cascade of tolerances is at the feasibility limit of production. In this case, Geometrical Tolerancing method loses its benefits. The aim of this paper focus on our process deployment based on the last A/C development in Airbus Heli-copters, presenting the first results, the advantages and drawback for Industrialization & serial phase based on the antitorque brackets integration. The antitorque bracket is the master element of the junction between Main Gear Box and fuselage. The antitorque bracket has tight tolerances due to the stress way and its functional geometrical tolerance cascade. Its manufacture is at the limit of production means. The production of antitorque bracket generates many QN. Each part is going to generate recurring cost and added time of production. To solve this problem, we have chosen to understand what phenomena are in cause and manage non-quality risk with the ap-plication of inertial Tolerancing approach. In function of the level of nonconformity calculated, an action plan is defined.