ComputerAided_Design_Engineering_amp_Manufactur.pdf

a larger value, the die operations will be spaced further apart. Second, interactive commands can be
provided to allow the user to insert idle stations and to move a die operation from one station to another.
7.8 Iterative Feedback Approach for Operations Planning
We have described the intelligent techniques that can be used to assist in the various tasks involved in the
operations planning in progressive die design. These tasks are interdependent and decisions made in one
task will affect the outcome in the others. For example, the actual punch shapes selected will depend on
the piloting schemes used. On the other hand, the actual pilot holes (for an indirect piloting scheme) cannot
be selected until the shapes of the notching punches are known. In other words, an effective computer aid
must provide the following facilities for the user to manage the iterative feedback design process:
1. Generate a ‘‘first-guess’’ solution for each of the subtasks quickly.
2. Provide interactive aids to modify the solution.
3. Use the modified solution as a starting point to generate the solutions for the other subtasks.
4. At any time, move from one subtask to another to study how the solutions affect each other, and,
if necessary, modify them to ensure that the constraints in all the subtasks are satisfied.
The iterative feedback design procedure can be achieved by integrating an interactive graphics user
interface (preferably in the form of a CAD system) with a knowledge-based system. The CAD system
will provide interactive graphics aids for the user to visualize and manipulate the plan as it is developed
and stored in the knowledge base. Commands can also be provided via the CAD interface to let the user
define break points in a task and to step from one task to another.
Using the techniques described so far, a prototype design system can be developed to generate the strip
layout from the feature-based description of a product. As an illustration, the staging and strip layout
required to manufacture the product shown in Figure 7.2 is shown in Figure 7.8. In addition, Cheok et al.
(1995) described how these techniques are used to generate the plans to manufacture a different workpiece
using a prototype progressive die design system developed at the National University of Singapore.
7.9 A Model-Based Reasoning (MBR) Approach for Die Synthesis
The operations planning process converts the features of a product into a plan model describing the stamping
operations at each station required to manufacture the product. The next stage in progressive die design is to
generate the engineering description of the die from the plan model. Once the engineering model is described
in the knowledge base, a 3-D solid modeling description of the die can be produced in the CAD system for
visual inspection and verification and down-stream manufacturing. The symbolic relationships between entities
in the CAD data base, the feature tree, the plan model and the engineering model are shown in Figure 7.9.
Dym and Levitt (1991) have described an architecture and some methodological ideas for building
knowledge-based engineering systems using the model-based reasoning (MBR) approach. The MBR
approach can be used as the framework to automate the synthesis of a progressive die from strip layout.
The features of the MBR approach for die synthesis are as follow:
1. The die structure is represented by a hierarchy of its components classified into branches of
subassemblies and by topological links which are automatically deduced using spatial reasoning
techniques. The generic hierarchy of die components represented in the knowledge base is shown
in Figure 7.10.
2. The die components can be classified into two synthesis models:
a. Components or subassemblies whose descriptions are directly dependent on the product features and
the strip layout—The
rules and formulation to describe these components are specially coded
and stored in a library of standard components in a component hierarchy based upon standard
naming conventions given in Figure 7.10. Rules or procedures that reference additional attributes
of named components then generate multiple abstraction links for components. Examples of