Question

A hollow workpiece with an outside diameter of 40 mm and a length of 100 mm is held on a mandrel between centres and turned all the way around in four passes. Estimate the machining time if the approach length is 10 mm, over travel is 5 mm, average feed is 0.8 mm/rev, and cutting speed is 30 m/min.

Answer 1

To estimate the machining time, calculate the remaining length of material after each pass. Use the approach length, over travel, average feed, and cutting speed to determine the number of revolutions and time for each pass. The total machining time is the sum of the times for each pass.

Step-by-step explanation:

To estimate the machining time, we need to calculate the total length of material that needs to be machined. Each pass removes a certain amount of material, so we need to calculate the remaining length after each pass. Starting with the initial length of 100 mm, each pass will remove the approach length, over travel, and the length of material that is machined, which is the product of the average feed and the number of revolutions in each pass. The final remaining length after the fourth pass will be the time needed for machining. Let's calculate:

1. Approach length = 10 mm
2. Over travel = 5 mm
3. Average feed = 0.8 mm/rev
4. Cutting speed = 30 m/min

In the first pass, the length of material that needs to be machined is 100 - 10 - 5 = 85 mm. The number of revolutions needed to machine this length is 85 / 0.8 = 106.25 rev. Since we can't have fractional revolutions, we round up to 107 rev. The time needed for the first pass is (85 / 1000) / (30 / 60) = 0.17 minutes.

In the second pass, the remaining length of material is 85 - 10 - 5 = 70 mm. The number of revolutions needed is 70 / 0.8 = 87.5 rev. Rounding up to 88 rev, the time needed for the second pass is (70 / 1000) / (30 / 60) = 0.14 minutes.

In the third pass, the remaining length is 70 - 10 - 5 = 55 mm. The number of revolutions needed is 55 / 0.8 = 68.75 rev. Rounding up to 69 rev, the time needed for the third pass is (55 / 1000) / (30 / 60) = 0.11 minutes.

In the fourth pass, the remaining length is 55 - 10 - 5 = 40 mm. The number of revolutions needed is 40 / 0.8 = 50 rev. The time needed for the fourth pass is (40 / 1000) / (30 / 60) = 0.08 minutes.

The total machining time is the sum of the times for each pass: 0.17 + 0.14 + 0.11 + 0.08 = 0.5 minutes.