Degree Name

Doctor of Philosophy


School of Mechanical, Materials, and Mechatronic Engineering


The manufacturing industry recognises that recycling worn-out products is a major contribution to conserving natural resources and solving landfill problems, but for recycling to be as effective as possible, as well as economical, the disassembly of reused products is critical (Garcia 2000). An appropriate disassembly sequence generation can maximise the gain from recycling and minimize the waste dumped to land fill.

In this thesis, two new methods are developed for optimal disassembly sequence generation. The first method is called Combined AND/OR and Petri Net. The second method is called Category Sequence which consists of Direct Disassembly, Level Disassembly and Group Disassembly.

The Combined AND/OR and Petri Net method is based on the fundamental theories of AND/OR and Petri Net, and then uses part accessibility and end-of-life strategy to obtain the optimal disassembly sequence. Firstly, all the feasible disassembly sequences are obtained using AND/OR graphs. Secondly, AND/OR graphs are converted into Petri Net models. Finally, by adding all the accessibility values and life span values to the Petri Net model as the conditions to execute the transitions, the optimal disassembly sequence, possessing the maximum combination of part accessibility and life span value, is obtained. The accessibility values and end-of-life values are obtained by analysing the structure of the liaison among each of the subassemblies and parts. The different life spans of reusable parts affect the disassembly order in the sequence generation.

When the AND/OR theory is applied to disassemble the reused products consisting of a large number of parts, the processes to obtain all the possible disassembly sequences become very complicated. A new method, Category Sequence, is applied to classify the reused products into three categories in terms of the number of parts, which makes the process less complicated in generating all the possible disassembly sequences. For products consisting of a small number (n

Several disassembling examples are given. In chapter 4, a case study of disassembling a Cclamp consisting of 4 parts is illustrated by using Combined AND/OR and Petri Net together with Directly Disassembly. In chapter 5, a case study of dismounting a Kodak MX single-use outdoor camera consisting of 19 parts is illustrated by using Combined AND/OR and Petri Net together with Level Disassembly. In chapter 6, a case study of a two-shaft helical gearbox consisting of 103 parts is taken apart to demonstrate how to apply Group Disassembly to a product consisting of a large number of parts.

These two new methods - Combined AND/OR and Petri Net, and Category Sequence – are suitable for all used products and make it possible to maximise the gain from the disassembly process and, at the same time, simplify the disassembly process.



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.