Modulated toolpaths for chip breaking

Figure 1. When using an experimental modulated toolpath, chip length is selectable.

When turning, the formation of long, stringy chips is undesirable because they can become tangled around the tool and dragged back through the cutting zone, potentially damaging the tool and workpiece. In contrast, short, comma-shaped chips easily fall out of the cutting zone, away from the tool and workpiece. Ensuring chips reliably break is a challenge, especially for ductile workpiece materials. Among the common techniques to combat long, stringy chips are chip breaking geometries and high-pressure coolant.

“Chip breaking geometry” means the rake face of the cutting tool is modified by the addition of a sudden step change in the profile. The step, which may be a separate component clamped in place or an integral part of an insert, causes the chip to bend and break. The chip may break when its free end contacts the tool, the workpiece or the chip itself, or when the bending stress becomes high enough. There are various chip breaking geometries, and substantial effort is spent on selecting a suitable one for a particular application.

“High-pressure coolant” means that a stream of coolant with a pressure of hundreds of atmospheres or more is directed down the tool’s rake face toward the chip. The coolant helps break chips by providing a force that causes the chip to curl, and by providing rapid cooling of the hot chip.

Figure 2. Modulated toolpath in profile turning.

Figure 3. Conditions under which chips break.