Development of hybrid lifecycle cost estimating tool (HLCET) for manufacturing influenced design tradeoff.

摘要

In complex aerospace system design, making an effective design decision requires multidisciplinary knowledge from both product and process perspectives.;Integrating manufacturing considerations into the design process is most valuable during the early design stages since designers have more freedom to integrate new ideas when changes are relatively inexpensive in terms of time and effort. Several metrics related to manufacturability are cost, time, and manufacturing readiness level (MRL). Yet, there is a lack of structured methodology that quantifies how changes in the design decisions impact these metrics. As a result, a new set of integrated cost analysis tools are proposed in this study to quantify the impacts. Equally important is the capability to integrate this new cost tool into the existing design methodologies without sacrificing agility and flexibility required during the early design phases.;To demonstrate the applicability of this concept, a ModelCenter environment is used to develop software architecture that represents Integrated Product and Process Development (IPPD) methodology used in several aerospace systems designs. The environment seamlessly integrates product and process analysis tools and makes effective transition from one design phase to the other while retaining knowledge gained a priori. Then, an advanced cost estimating tool called Hybrid Lifecycle Cost Estimating Tool (HLCET), a hybrid combination of weight-, process-, and activity-based estimating techniques, is integrated with the design framework.;A new weight-based lifecycle cost model is created based on Tailored Cost Model (TCM) equations [3]. This lifecycle cost tool estimates the program cost based on vehicle component weights and programmatic assumptions. Additional high fidelity cost tools like process-based and activity-based cost analysis methods can be used to modify the baseline TCM result as more knowledge is accumulated over design iterations. Therefore, with this concept, the additional manufacturing knowledge can be used to identify a more accurate lifecycle cost and facilitate higher fidelity tradeoffs during conceptual and preliminary design.;Advanced Composite Cost Estimating Model (ACCEM) is employed as a process-based cost component to replace the original TCM result of the composite part production cost. The reason for the replacement is that TCM estimates production costs from part weights as a result of subtractive manufacturing of metallic origin such as casting, forging, and machining processes. A complexity factor can sometimes be adjusted to reflect different types of metal and machine settings. The TCM assumption, however, gives erroneous results when applied to additive processes like those of composite manufacturing.;Another innovative aspect of this research is the introduction of a work measurement technique called Maynard Operation Sequence Technique (MOST) to be used, similarly to Activity-Based Costing (ABC) approach, to estimate manufacturing time of a part by virtue of breaking down the operations occurred during its production. ABC allows a realistic determination of cost incurred in each activity, as opposed to using a traditional method of time estimation by analogy or using response surface equations from historical process data. The MOST concept provides a tailored study of an individual process typically required for a new, innovative design.;Nevertheless, the MOST idea has some challenges, one of which is its requirement to build a new process from ground up. The process development requires a Subject Matter Expertise (SME) in manufacturing method of the particular design. The SME must have also a comprehensive understanding of the MOST system so that the correct parameters are chosen. In practice, these knowledge requirements may demand people from outside of the design discipline and a priori training of MOST. To relieve the constraint, this study includes an entirely new sub-system architecture that comprises 1) a knowledge-based system to provide the required knowledge during the process selection; and 2) a new user-interface to guide the parameter selection when building the process using MOST.;Also included in this study is the demonstration of how the HLCET and its constituents can be integrated with a Georgia Tech' Integrated Product and Process Development (IPPD) methodology. The applicability of this work will be shown through a complex aerospace design example to gain insights into how manufacturing knowledge helps make better design decisions during the early stages. The setup process is explained with an example of its utility demonstrated in a hypothetical fighter aircraft wing redesign. The evaluation of the system effectiveness against existing methodologies is illustrated to conclude the thesis.