ComputerAided_Design_Engineering_amp_Manufactur.pdf

A metal stamping can have the following features:
Stamped features: holes, notches, cutouts, slots, etc.
Formed/bend features: bends, flanges, hems, seams, drawings, embossing, etc.
Formed/stamped features: countersinks, etc.
Each of these features can be associated with a metal stamping operation. They have attributes in the
form of their geometrical and topological descriptions and technical specifications (e.g., tolerancing and
finishing properties). A product can be described by connecting these features using feature relationships
such as ‘‘connect_to’’ and ‘‘part_of.’’ The feature representation of a workpiece is shown in Figure 7.2.
There are several advantages associated with the use of metal-forming features to describe a workpiece
in an intelligent system:
• The feature representation provides an “intelligent” description of the product.
• The feature representation provides a convenient means for representation as objects in a knowledgebased
system.
• As each feature is associated with a stamping operation, it facilitates the generation of the process
plan and the generation of the die. For example, when we are staging the die operations, we can
build the rules to ensure that the sides of the wall of a bend feature must be notched before it is
bent. Thereafter, the punches can be configured from the notch features and the tools associated
with bending (i.e., bending punch, bending block, pressure pads, etc.) can be configured from the
bend feature.
• The ‘‘intelligent’’ association between a feature and the stamping operation required to manufacture
it makes it possible to develop product design tools that provide product designers with tooling
advice. For example, Mantripragada et al. (1996) developed an interactive design tool for box-type
sheet metal parts that can be used to alert the designers to potential production problems, defects,
and failures; it can also provide them with information that can be used to explore alternative design,
evaluate trade-offs, and arrive at optimal design for the given process conditions.
• The features and the associated ‘‘feature-relationship tree’’ can be used as a criterion to index the
product in a design data base. The design data base is a data base of products and their associated
progressive dies manufactured by a company. A die designer usually builds a progressive die by
adopting an old design to meet the manufacturing requirements of the new product. Hence the
features and the feature-relationship tree of a new product can be used to search through the
design data base and retrieve the past design of the nearest product manufactured by the company
for use as a reference to manufacture the new product. The use of features to index a product can
be considered as the basis for the development of a case-based planning system for progressive
dies. We will discuss the application of a case-based planning approach for progressive die design
in another section.
7.5 Pattern Processing and Recognition Tasks Associated
with Operations Planning
In essence, the operations planning task to develop the strip layout is a spatial planning exercise involving
pattern processing and shape recognition skills best performed by human beings. Very little research
work has been done to solve this problem and the operations planning task remains a major stumbling
block in the development of an integrated system for the manufacture of progressive dies. Computerassisted
pattern processing and shape recognition tasks are computationally intensive in nature. If the
computer takes too long to perform these tasks, it would render the interactive, iterative feedback planning
system ineffective. Therefore, there is a need to reduce the spatial planning tasks into smaller and simpler
pattern processing and shape recognition subtasks done by the computer, while leaving the more complex
decision making tasks to the user.