| Abstract | This thesis presents development and implementation of an expert system for computer aided
process planning (EXCAPP-ROT) of axi-symmetric parts. The system is basically divided
into two sections: database modules and process planning modules. The database modules
represent domain knowledge about process, material, tool, machining parameters, machine,
setup time, production cost, and coolant. The CAPP modules comprise of part data input,
blank size computation, process selection, tool selection, machining parameters selection,
machine selection, setup planning, operation time and cost computations, operations
sequencing, coolant selection, and process plan output.
The part input module accepts geometrical data about the part drawing by entering the point
coordinates alongwith the information about surface finish, tolerance and special features
corresponding to each segment of the part. Based on the part geometry, the minimum size of
blank piece is computed. All these data are anlayzed to identify the suitable process and
surface type requirements and the amount of machining for each segment of the part. The tools
are selected based on those process and the surface type requirements, and the tooling material
is selected as per the part material entered in the part input module. According to the
combination of workpiece material, tool material and the process type, the machining and
drilling parameters are selected from the relevant databases. The parameter selection modules
also compute the minimum power required for each operation. The system validates
dimensional and power consumption constraints while selecting the machines for each
process. This module is also able to suggest alternative machines. In setup planning module,
the different setup groups are formed as per the requirement of tool, machine and process.
Total times and operation costs are calculated by considering the setup and operation times. A
set of thumb rules is also applied to assign the setup priorities. Operation sequences are
created based on geometric constraints, precedence relationships, and the setup priorities.
Finally, the output of the process plan is generated by integrating the information from the
earlier modules.
The system also consists of a variant module to provide the facility to retrieve and edit the
standard process plans. To facilitate this, KK3 classification and coding system has been
employed for the part family formation. This module is integrated with the part input and
blank size selection module. However, part family formation module can be executed together
with or independently from the other modules.
Oracle 8.0.5 is used to create and maintain the database tables. Graphical user interfaces for
CAPP modules are constructed on Developer/2000 forms and the expert system inference
logic is written in PL/SQL programming language. The test results on generic axis symmetric
parts show that the prototype model of EXCAPP-ROT is able to achieve the objectives of
creating a process plan in few minutes and can be used by any user even with the very little
programming background. Likewise, the domain knowledge can be updated from the front end
without writing any programming codes. |