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Metal Machining - Theory and Applications Episode 1 Part 2

Tham khảo tài liệu 'metal machining - theory and applications episode 1 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Machine tool technology 13 Fig. 1.13 A traditional - column and knee - design and right and below partly-built and complete views of a modern bed design of milling machine In Figures 1.16 a and b the capacity of a milling machine is measured by its crosstraverse capacity. This defines maximum workpiece size in a similar manner to defining the capacity of a turning centre by maximum work diameter Figure 1.8 . Figures 1.16 a and b show that torque and power increase as cross-traverse cubed and squared respectively. An assumption that machines are designed to accommodate larger diameter cutters in proportion to workpiece size yields the D3 and D2 relations derived in the previous paragraph. 14 Introduction Fig. 1.14 A 5-axis milling machine with interchangeable work tables If Figure 1.16 b is compared with Figure 1.8 b it is seen that for given workpiece size cross-traverse or work diameter a milling machine is likely to have from one fifth to one half the power capacity of a turning machine depending on size. This means that milling machines are designed for lower material removal rates than are turning machines for a given size of work. Figure 1.16 c when compared with Figure 1.10 a shows that milling machines are up to twice as massive per unit power as turning machines reflecting the greater need for rigidity of the more prone to vibration milling process. Figure 1.16 d admittedly based on a rather small amount of data shows little difference in price between milling and turning machines when compared on a mass basis. Combining all these relationships the price of a milling machine is about 2 3 that of a turning machine for a 200 mm size workpiece but rises to 1.5 times the price for 1000 mm size workpieces. The consequences for economic machining of these different capital costs as well as the different removal rate capacities that stem from the different machine powers are returned to in Section 1.4. The D3 and D2 torque and power relationships found for milling