Question

02: A bar of 60 mm diameter and length of 3 meter is used to produce 500 pieces on a center lathe having the following characteristics: . Maximum rotational speed .Minimum rotational speed .Number of speeds Lathe overall efficiency The turning process is performed at 40 m/min cutting velocity. 0.5 mm/rev longitudinal feed, 0.25 mm/rev transverse feed and 2 mm depth of cut REQUIRED 1. Calculate the TWELVE rotational speeds in rpm. 2. What rotational speed would you choose? 3. Calculate the rate of metal removal in mm/s 4. Calculate the required motor power if the specific cutting energy of the cut material is 4.0 J/mm3 5. Determine the suitable change gears required for cutting a thread of 2.25 mm on a center lathe if pitch lead screw is (1/4) inch. 6. The number of bars required if parting allowance is 5 mm, and minimum gripping length is 50 mm 7. Calculate the total production time for 250 mm machined length, if tool return time is 15 S and bar change time is 40 S. (10 Marks) - 2500 rpnm - 16 rpm, = 12 ,-80 %.

Answer 1

1. The speed ration is given by

(25 )カー1.582844 2500、六

Thus the speed 1=16 rpm

speed 2= 16*1.582844=25.3255 rpm

speed 3=25.3255*1.582844=40 rpm

speed 4=40*1.582844=63.45 rpm

speed 5=63.45*1.582844=100.43 rpm

speed 6=100.43*1.582844=159 rpm

speed 7=159*1.582844=251 rpm

speed 8=251*1.582844=398 rpm

speed 9=398*1.582844=630 rpm

speed 10=630*1.582844=997 rpm

speed 11=997*1.582844=1579 rpm

speed 12=1579*1.582844=2500 rpm

2. Given, the cutting speed =40 m/min

We know

I D cutting speed = 2πΝ m / min

Where N is speed

By substituting the known values of speed we can find out that the desired cutting speed is produced for speed 7 which produces 251 rpm thus providing a cutting speed of 47 m/min.

3. Since both longitudinal and transverse motion of tool is occuring, we can neglect the depth of cut as it occurs initially.

material removal rate=0.25*0.5*40000 mm/min

=5000 mm³/min

=83.33 mm³/sec

4. Motor energy required= energy to cut * material removal rate

=4*83.3

=333 Watts