In-Plant Transport System Design: An Integrated Approach for an Aircraft Component MRO Facility

Abstract

In-plant transport systems are indispensable in facilities like manufacturing plants and warehouses as they enable the internal flow of goods. Facilities in the Maintenance Repair & Overhaul industry are no exception to this, but face some distinct challenges. This research presents an integrated approach to the conceptual design of an in-plant transport system for an MRO facility in the aerospace industry. The integrated approach distinguishes conceptual design as a separate phase and structures design efforts within this phase using the Define, Measure, Analyze, Design, Evaluate (DMADE) cycle. One major iteration through this cycle is done for a real-life case system at an MRO facility for aircraft components. After an exploratory literature survey, demand for the case is analyzed using enhanced Value Stream Mapping (denoted as VSM-Information) and data analysis. Design requirements and decision criteria are established that determine the effectiveness of an in-plant transport system.Here, a fundamental trade-off is shown to exist in Transport Lead Time and capacity. Three Service Level targets are set for the case to make this trade-off in design. A generic Design Interactions Framework for (vehicle-based) in-plant transport systems is proposed that addresses a lack of guidance in literature on forming integral designs during synthesis. The framework is applied to the case to compose three integral alternatives in which both call systems with Automated) Guided Vehicles and in-plant milk-runs are used. The logistic performance of the design alternatives is reviewed using Discrete Event Simulation. Minimum Viable Configurations (MVCs) are derived that state the minimum amount of transport resources per design alternative per Service Level target. Cost estimation and implementation risk assessment are performed for the MVCs found. Multi-Criteria Decision Analysis is applied using the Weighted Sum Method to establish a preference ranking for the MVCs. The robustness of this ranking is assessed using a scenario-based sensitivity analysis. Results show that four MVCs exist for the design alternatives and Service Level targets defined. Two of these MVCs compete for the first place in the preference ranking and hence no clear preferred alternative is identified for the case. The ranking between the top-two MVCs is highly sensitive to setting the weight factors in the WSM. It turns out that their effectiveness highly depends on the monetary implications of a certain TLT performance and implementation risk; which couldnot be quantified in this research due to time restrictions and data unavailability. Although the results of the case study are highly case-specific, the approach taken, design principles derived and tools used are widely applicable in the design of effective in-plant transport systems and show the specific characteristics of these systems in an MRO context.