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The machinability of metals such as steel can be influenced by the constituents

ID: 1853240 • Letter: T

Question

The machinability of metals such as steel can be influenced by the constituents within the microstructure. Using examples explain which microstructural features effect machining and the ease of chip formation. [10] a twist drill with a major cutting angle of 60 degree (kr) is used to make a hole in aluminium. If the feed (f) is 0. 25 mm per revolution and the maximum power is 1kW what is the maximum hole diameter that can be made if the drill speed (N) is 600 rpm? In order to solve this problem use the information provided in Table 1 and the graph. [10] [Note: Material Removal Rate (MRR) = P eta /p] Where. P is the motor power, eta is the efficiency of cutting and p is the specific cutting energy.

Explanation / Answer

Conversion of feedrate f (mm/rev) to feedrate f (mm/min)
f = N fr (mm/min)
f=600*0.25
=150 mm/min
Motor power =1KW=P
from table =0.75

Uncut chip thickness=(f/2)*sin(60)=0.06

assume that material is cast iron the =3GJ/m^3

MRR=P*/=250mm^3/sec

MRR = (D2 / 4) (f) =250mm^3/sec

D=11mm