Lecture-13 The Size Effect
L 13.1 The Size Effect
The
resultant tool force in metal cutting is distributed over the
area of the tool that contacts the chip and workpiece. No cutting
tool is perfectly sharp and in the idealized picture
shown in figure 13.1. The cutting edge is
represented by a cylindrical surface joining the tool flank and
the tool face. As the tool edge "plows” it's a way
through the work material, the force that
acts on the tool cutting edge forms only a small
proportion of the cutting force at a large value of the
undeformed chip thickness t1. A small value of t1, however, the force that acts only tool edge
is proportionality large and cannot be
neglected.
Because of the high stresses acting near the tool cutting edge, deformation of the tool material may occur in the reason. The deformation would cause contact between the tool and the new workpiece surface over a small area of the tool flank.
The force acting only tool edge and the force that may act on the tool flank does not contribute to the removal of the chip. These forces will be referred to collectively as the plowing force (Fp).
The existence of the plowing force result in certain important effects and can explain the so-called “size effect”. This term refers to the increase in specific cutting energy (Ps) at a low value of undeformed chip thickness (t1).
At the relatively small values of chip thickness occurring in process, the specific cutting energy (Ps) increases rapidly with decreasing undeformed chip thickness (t1). It is thought that the plowing force (Fp) is constant and therefore become a greater proportion of the total cutting force as the chip thickness decreases. (Fig.13.2 & 13.3)
