Understand the Vocabulary
The first task in analysis is to understand the vocabulary used by the users and the experts in the problem domain. The most important terms used are those that describe the dimensions and geometry in the sheet metal.
As shown in Figure 3-1, a piece of sheet metal is cut to a particular size and has shapes cut out inside it. Experts call these cutouts by the general name “feature.” A piece of sheet metal can be fully specified by its external dimensions and the features contained in it.
The types of shapes—features—that may be found in a piece of sheet metal are described in Table 3-1. These are the shapes the system will have to address.
| Shape | Description |
|---|---|
| Slot | Straight cuts in the metal of constant width that terminate with either squared or rounded edges. Slots may be oriented to any angle. They are usually cut with a router bit. Figure 3-1 has three slots on the left side; one is oriented vertically while the others are oriented horizontally. |
| Hole | Circles cut into the sheet metal. Typically they are cut with drill bits of varying width. Figure 3-1 has a hole toward the left surrounded by the three slots and has a larger hole toward the right of the sheet metal. |
| Cutout | Squares with either squared or rounded edges. These are cut by a high-powered punch hitting the metal with great impact. Figure 3-1 has three cutouts; the lower right one is oriented at 45 degrees. |
| Special | Preformed shapes that are not slots, holes, or cutouts. In these cases, a special punch has been made to create these quickly. Electrical outlets are a common “special” case. The star shape in Figure 3-1 is a special shape. |
| Irregular | Anything else. They are formed by using a combination of tools. The irregularly shaped object toward the bottom right of Figure 3-1 is an irregular shape. |
CAD/CAM experts also use additional terminology that is important to understand, as described in Table 3-2.
| Term | Description |
|---|---|
| Geometry | The description of how a piece of sheet metal looks: the location of each of the features and their dimensions and the external shape of the sheet metal. |
| Part | The piece of sheet metal itself. I need to be able to store the geometry of each of the parts. |
| Dataset or model | The set of records in the CAD/CAM database that stores the geometry of a part. |
| NC machine and NC set | Numerically controlled (NC) machine. A special manufacturing tool that cuts metal using a variety of cutting heads that are controlled by a computer program. Usually, the computer program is fed the geometry of the part. This computer program is composed of commands called the NC set. |