Turning and Chip-breaking Technology Part 3 pdf

and later, by Herbert (1928). Around this time, the cut￾ting speeds were steadily improving with the arrival of

new cutting tool materials, such as cemented carbide.

In 1937, Piispanen introduced his so-called ‘Deck of

Cards’ principle as an explanation of the cutting pro￾cess (see Fig. 24 for Piispanen’s idealised model, with

Fig. 25 depicting sheared chips at a range of cutting

speeds). Here, Piispanen’s model depicts the workpiece

material being cut in a somewhat similar manner to

that of a pack of cards sliding over one another, with

the free surface an angle, which corresponded to the

shear angle (ϕ). So, as the tool’s rake face moves rela￾tive to that of the workpiece, it ‘engages’ one card at

a time, causing it to slide over its adjacent neighbour,

this process then repeats itself ‘ad finitum’ – during

the remainder of the cutting process. Some important

Figure 25. Variations in chip morphological surfaces at different cutting speeds, giving an indication

of the various shearing mechanisms. [Source: Watson & Murphy, 1979]

.

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