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Ch24-I044963.fm Page 117 Monday, August 7, 2006 11:27 AM
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grouped into distinguished levels according to their geometrical position. MCPs whose top Z axis-perpendicular
faces share the same Z coordinate value are defined as same level MCPs. An example of remained MCPs, which
are classified into 3 levels are illustrated in Fig.5. Because tool properties such as length and strength restrict the
sizes of machinable MFs, recomposition is to be executed level by level to avoiding creating MFs which are
machinably unavailable in TAD (Tool Approach Direction).

Z level 1
CD 0.1
Z level 2

Z level 3

(b) ( c ) Figure 7: Determination of the shortest machining time of aMF set

(a) SRV with one lace demanded by the same constraint of flatness which is valued 0.1
(b) Three MFs ought to be machined continually
(c) Two MFs ought to be machined continually
Figure 6: Determination of machining sequence

4 MACHINING SEQUENCE

One of the important and difficult activities in process planning is the determination of sequence which causes
high-quality parts to be produced efficiently. For producing the part here are more than one set of features
available to be chosen Even tor one of such sets of MFs, there are many ways to sequence these features for
machining. But the utilization of all the possible MF set as removal area descriptions to determine the optimum
process plans is rather time-consuming because the huge number of alternatives will overload the system. The
constraints h workplace environment and design intentions are considered to eliminate the improper MF sets
before they are further used for process planning, Because the majority of current systems focus too much on
creating sequences based on part geometry, and fail to utilize other information which describes the designers'
intentions, The final sequence plans often dissatisfy the requirement of qualities and functions, or are relatively
time-consuming. Based on the constraint rules, which are developed and applied, the constraints obtained from the
designer's intentions or the factory environment will be used to resolve this problem. F)ue to tools' restrictions in
length and hardness, machining the MFs that are too large in TAD should be avoided. Therefore in this system
sequencing is executed in each level. The solution of one MF set begins with recreating ID numbers to identify
remained MFs in one level and sorting all these MFs in this level to generate all possible machining sequences as
candidates. The vast number of feasible sequences will become evident through this mean. Without consideration
of the constraints in manufacturing, it would be possible 6r a level composed of N manufacturing features to be
processed from one of N factorial sequences. An obvious choice would be to represent a sequence as a string,
whose elements are ID of features in a level of this MF set But in reality this number of the alternatives is reduced
by the feasible constraints. Appropriate sequences of each level are extracted from these choices. All the feasible
sequences are checked based on geometry constraints, tolerance constraints, and quality constraints. Finally only
the satisfactory sequences are picked out for machining time evaluation. Main constraints taken into
considerations in this system are: Cylindricity, flatness, dimension tolerance, concentricity, surface finish. The MFs