ComputerAided_Design_Engineering_amp_Manufactur.pdf

FIGURE 5.24 An example rotational part.
1. Secondary pockets: Grooves, threads, and knurls are considered in this stage. There are no roughing
or finishing operations associated with these secondary features; hence, one-to-one mapping
between these features and the operations can be established. All these features are stored as
pockets in the pocket file (Figure 5.25a) and are simultaneously updated to their parent features.
For example, a groove is converted to a turn feature. Similarly, the thread is unthreaded and the
knurl is unknurled. This step results in an intermediate part (Figure 5.25b) without these secondary
features. The material to be removed from the intermediate part (to reach the final part)
forms a single pocket in NC machining, which can be subdivided into finishing and roughing
profiles. For conventional machining, the pocket identification has to be further carried out as
follows.
2. Complex primary pockets: It is assumed that machining the chamfers and fillets and rounding off
the corners will be carried out as distinct operations on conventional machines using form tools.
At this stage, these pockets are stored in the pocket file (Figure 5.25c) and an intermediate
component is regenerated (Figure 5.25d).
3. Finishing pockets: The finishing operations are not primarily used as material removal operations
but are intended to achieve the technological attributes of the surface. Nevertheless, the small
amount of the material being removed in a finishing operation is also represented as a pocket to
facilitate uniform handling by the system. The stepped component, obtained in the previous step,
is then analyzed to offset the elements (usually turn and taper) that require finish machining.
Sometimes, the adjoining elements need to be offset along with the turn and taper elements because
of the accessibility constraints. These finish pockets (offset volumes) are then appended to the same
pocket file (Figure 5.25e). At this stage, what remains is the intermediate part (Figure 5.25f) which
needs to be inverse rough-machined.
4. Roughing pockets: At this stage, the stepped component contains a series of face, turn and taper
features without any technological attributes present. The pocket identification for rough machining
is carried out as follows:
• Face pockets: In this step, the pockets to be removed by a facing operation on either end of the
part are marked (Figure 5.25g) leading to the part shown in Figure 5.25h.
• Taper pockets: Since taper turning is a distinct operation, these are identified as pockets (Figure 5.25i).
This step results in an intermediate part shown in Figure 5.25j.
• Turn pockets: At this stage, the intermediate part contains only face and turn elements. The pattern
The patterns these elements make are used to identify the pockets to be machined in the
rough-turning operation. Three patterns of interest are shown in Figure 5.26. Identifying such