problems for practice

PROBLEMS FOR PRACTICE

1. A shaper is operated at 130 cutting strokes per minute and is used to machine a workpiece of 300 mm in length and 122 mm in width. Use a feed of 0.7 mm per stroke and a depth of cut of 5 mm. Calculate the total machining time for machining the component. The forward stroke is completed in 220°. Calculate the percentage of the time when the tool is not contacting the workpiece.

2. Calculate the power required for shaping steel with a depth of cut of 2.6 mm, cutting speed 73 m/min and the work length 54 mm. The feed rate is 0,6mm/rev. Take machining constant k as 79×10-6.

3. Estimate the shortest machining time required in a shaper to machine a plate of 220 mm × 80 mm under the following conditions.

Cutting speed = 13.3 m/min

Feed = 0.67 mm/double stroke

Number of passes = one

Approach + over run (longitudinal) = 25 mm

(Lateral) = 45 mm

Ratio of cutting speed to rapid return = 0.86.

4. The cross-feed on a shaper consists of a lead screw having 0.25 threads per mm. A ratchet and pawl on the end of the lead screw is driven from the shaper crank such that the pawl indexes the ratchet by one tooth during each return stroke of the ram. Ratchet has 23 teeth.

(a) Find the cross feed in mm.

(b) If a plate 120 mm wide has to be machined in 15 minutes. Find the cutting speed in m/s. The ratio of return to cutting speed is 2.5:1 and the length of the stroke is 130 mm.

5. Calculate the spindle speed to drill a hole of 40 mm using cutting speed as 23 m/min.

6. Calculate the feed in mm/rev to drill a hole of 35 mm in one minute to a plate thickness of 42 mm and using a spindle speed of 650 rpm.

7. Calculate the machining time required for making 18 holes on a M.S. plate of 20 mm thickness with the following data.

Drill diameter = 30 mm

Cutting speed = 25 m/min

Feed = 0.15 mm/rev.