Project ForgeManufacturing Engineering
Machining Processes
GATE 2012
Hard
In a single pass drilling operation, a through hole of 15 mm diameter is to be drilled in a steel plate of 50 mm thickness. Drill spindle speed is 500 rpm, feed is 0.2 mm/rev and drill point angle is 118°. Assuming 2 mm clearance at approach and exit, the total drill time (in seconds) is
- 35.1
- B32.4
- C31.2
- D30.1
Explanation
Approach distance due to the drill's conical point: A=0.5D·cot(θ/2)=0.5×15/tan(59°)=7.5/1.6643≈4.51 mm. Total travel = plate thickness + point-approach + entry clearance + exit clearance = 50+4.51+2+2=58.51 mm. Feed rate=0.2×500=100 mm/min. Time=58.51/100 min=0.5851 min≈35.1 s.
Source: GATE ME 2012 (Booklet Code A) (2012)
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