A Charts-Based Approach to Estimate Disassembly Time: Hypothesis, Model and Validation

The purpose of this research is to present a generic method to estimate product disassembly time at detail stage by utilizing Boothroyd and Dewhurst classification form. Disassembly time is critical in decision-making process of end-of-life (EOL) operations, such as reuse, recycling, and remanufacturing. Theoretical assembly time for a design can be estimated using well-established Boothroyd and Dewhurst's method, given an assembly sequence. This method breaks single component assembly time into acquisition time, manual time, and insertion time. However, in disassembly processes, component symmetry features are, in most cases, unnecessary. Based on this fact, a hypothesis is made that a component's disassembly time can be estimated by considering replacing time, part removal time, and elements of surrounding components, including visibility, accessibility, and any additional effort. Fastening component disassembly time can be estimated by replacement time and time consumed by thread number. An assembly model is designed to verify this hypothesis with a predefined disassembly sequence. Totally, 31 undergraduate students took part in the manual assembly and disassembly experiment. Difference between theoretical and manual assembly times was found to be 7.4% while the difference between theoretical and manual disassembly times was 2.4%. Statistical evaluation indicated that the theoretical disassembly time falls within manual disassembly time with 95% confidence interval. To further validate the methods, two case studies are carried out with distinct products under same experimental environment. The approach proposed in this study can estimate disassembly time of a product at detail design stage when disassembly sequence is provided. Future work will focus on automating this method while incorporating selective and destructive disassembly time estimations.