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Ch24-I044963.fm Page 118 Monday, August 7, 2006 11:27 AM
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that satisfy the same constraints are to be continually machined. So the strings described by the correctly sorted
numbers, whose order represents machining sequence are delivered to the next step. Then the decoding process is
applied, translating each code into the string of the features. At last, a number of process plans which comprised of
a set of feature interpretation and its machining sequence are provided for optimum plan determination. A simple
example about two MF sets desired to be machined continually are shown in Fig.6.

5. OPTIMUM PROCESS PLAN

Because the determination of feature interpretation and sequencing are based on the requirements in qualities and
functions, in this system machining time is used as the major criterion in effectiveness evaluation to decide optimal
or near-optimal plan. The factors that affect the machining time involve (a) cutting condition generated by
case-base reasoning in this system, (b) path length estimated by considering the sizes and machining sequences of
the MFs, (c) the effect of surface quality. The machining time consists of cutting time, tools exchanging time and
the time cost when tools travel between manufacturing features. The total machining time in a level of a MF set is
calculated with the following equation.

-*- level -*• i'L'*jtiiFe -*- too! cxch-jtige -*• Vi&tejf
Where T(level) is the time cost in the process of machining all the MFs of this level. T(Feature) is the time spent
on removing MFs, T (toolexchange) is time for exchanging tools, and T(travel) stands for the time used in
traveling the tools between MFs. Until this step one MF set still possesses more than one appropriate machining
sequence each of which cause different machining time. The calculated machining times of every level in one MF
set are aligned as Fig. 7. The nodes in the figure show the machining time of every sequenced level in every MF
set, the two numbers in the node indicate the level number and the machining sequence number respectively, the
time which are spent on traveling tools between levels are taken into account as well. The path with the minimum
time in the tree means the most efficient machining flow of this MF set. Compared with other MF sets, the
corresponding process plan with the shortest machining time is decided as optimum plan for manufacturing this
part.

6. CONCLUSION

By taking into account the designer's intentions and making use of the functional and technical constraints, the
system proposed in this paper can provide the most optimum process plan for manufacturing the designed part.

REFERENCES

[1] Nagafune N., Kato Y, and Matsumoto T.(1998). Flexible Process Planning based on Flexible Machining
Features. JSME journal 75,127-128.
[2] Shirase K., Nagano T, Wakamatsu FL, and Arai E.(2000). Automatic Selection of Cutting Conditions Based on
Case-Based Reasoning. Proceedings of 2000 International Conference on Advanced Manufacturing Systems
and Manufacturing Automation, 524-528