**4.1 Roughing milling in free form geometry manufacturing**

This operation can happen in two circumstances:


Advanced Free Form Manufacturing by Computer Aided Systems – Cax 561

Theoretical thickness

Not milled

Frequently the differences of the volume of material beyond the theoretical stock is not cautiously evaluated, which has repercussions with possible problems in the milling. It is common that the machinists of the CNC machines reduce the speed during the milling process manually in some regions of the piece. To minimize this problem of semi-finishing operations have the objective to remove this excess of material and maintaining the stock as

Depth of cut

Finishing operation of machining can be considered the most important along the manufacturing free form shapes, once that implicates directly on the final product, in terms of surface integrity and geometric errors. A ball-end cutting tool is the most suitable to finish free form shapes by milling due to this geometry which permits to reach different curvature shapes. However, this tool implicates in specifics characteristics in milling free form shapes, once that the contact tool/surface alternates constantly and affects directly the milling process, in terms of cutting speed, cutting force, surface quality and so on (see also

First, the cutting speed usually cannot be calculated by nominal tool diameter. It has to be taken into account the effective diameter according to the axial cutting depth together to shape curvature. For a planar surface milled by a ball-end tool (Figure 7), the maximum effective diameter can be calculated by equation 2. But it has to be taken into account the radius of curvature of a free form geometry alternates constantly (Figure 7b). Therefore, the effective tool diameter following this oscillation and thus, the cutting speed as well. This is

2 2 ( ) *R R Ra ef p* (2)

one of the drawbacks because the machining process became unstable.

Fig. 6. Thickness to finishing

Feed

SOUZA et al, 2010).

Where:

*Ref* = Effective radius [mm]

*R* = Tool radius [mm]

*ap* =axial depth of cutting [mm]

close as possible to the theory value (offset of geometry).

Step

**4.3 The tool-surface contact in free form milling** 

The roughing employs movements in 2 ½ axis. The tool is positioned at a determined height in Z. After movements are executed in 2 axes for the removal of material at this level. When the removal of material at this level is finalized the tool is then positioned at a new level of Z (defined by the depth of cut), the material is removed at this plan. The process is repeated until the roughing is complete. End-mill with corner radius is the cutting tool frequently used for this operation.
