Metal Cutting: Controlled Separation and Chip Formation

(Metal) Cutting - Controlled separation of a material – to make something! Creates two new surfaces. – Not splitting like wood or slate – can't put the surfaces back together. What about floppy slices? Cucumber? Lots of plastic deformation. Relatively low forces, but very high stresses (force applied over tiny areas)

Positive = Could be independent of the wedge and clearance angle
Negative = Not independent of the wedge and clearance angle

Cutting edge: to separate a chip from the parent work material
Rake face: direct the flow of newly formed chips.
Rake angle: it is measured relative to a plane perpendicular to the work surface.
Relief angle: the flank of the tool provides a clearance between the tool and the newly generated work surface.

Cutting Zones
Primary shear zone: The zone in which the deformation is formed by shear deformation
Secondary shear zone: A zone of shear deformation in the chip as a result of the friction between the chip and the tool as the chip slides along the rake face of the tool. Its effect increases with increased friction between the tool and chip. Cutting action involves shear deformation of work material to form a chip, and as the chip is removed, a new surface is exposed. (a) positive (b) negative
Orthogonal cutting: The cutting edge is straight and is set in a position that is perpendicular to the direction of primary motion. Two-dimensional mechanics.
Oblique cutting: The cutting edge is set at an angle (the tool cutting edge inclination λs). Three-dimensional mechanics. Orthogonal Cutting: Cutting edges of more complex tools can be modeled as oblique or orthogonal elements.

Chip Formation includes Shear plane: A plane along which a chip is formed by shear deformation
Shear angle: An angle between the shear plane and the surface of work, Shear strain – Increase with decreasing shear angle or rake angle
Velocity in cutting zones includes Cutting speed ( ): traveling speed of the tool relative to the workpiece
Velocity of chip ( ): flowing speed of the chip over the tool rake face
Shearing speed ( ): the velocity at which shear occurs in the shear plane