Question

A 3.00 inch diameter workpiece that is 25 in long is to be turned down to n2.384 inches. Process Specifications:

a) Cutting Speed (V) = 300 ft/min, b) Feed (f) = 0.015 in/rev c) Depth of cut (d) = 0.044 in

The bar will be held in a chuck and supported on the opposite end in a live center. With this work-holding setup, one end (15 inches) must be turned to diameter; then the bar must be reversed to turn the other end (10 inches). Allow a 0.5” lead-in distance to each pass. Using an overhead crane available at the lathe, the time required to load and unload the bar is 4.2 minutes.

Determine the following:

1. Spindle RPM

2. Machining time for each pass.

3. Total cycle time per part to complete this turning operation.

4. Material removal rate (RMR)

Answer 1

Answer 2

To determine the required values, we'll go through the calculations step by step:

Given data: Diameter of the workpiece (D1) = 3.00 inches Final diameter to be turned down (D2) = 2.384 inches Length of the workpiece (L) = 25 inches Cutting Speed (V) = 300 ft/min Feed (f) = 0.015 in/rev Depth of cut (d) = 0.044 in Lead-in distance = 0.5 inches Loading and unloading time (T_load/unload) = 4.2 minutes

1. Spindle RPM: The cutting speed (V) is given in feet per minute (ft/min), and we need to find the spindle RPM (N). The formula for spindle RPM is: N = (V * 12) / (π * D1)

Substitute the values: N = (300 * 12) / (π * 3.00) N ≈ 1200 RPM

1. Machining time for each pass: The machining time for each pass is the time required to turn down one end of the workpiece (15 inches) to the desired diameter (D2). The formula for machining time (T_machining) is: T_machining = (L1 + L2) / V

Where: L1 = Length of material to be turned down in the first pass (15 inches) L2 = Lead-in distance for each pass (0.5 inches)

Substitute the values: T_machining = (15 + 0.5) / 300 T_machining ≈ 0.052 minutes

1. Total cycle time per part to complete this turning operation: The total cycle time per part includes the machining time for each pass and the loading/unloading time. The formula for total cycle time (T_cycle) is: T_cycle = 2 * T_machining + T_load/unload

Substitute the values: T_cycle = 2 * 0.052 + 4.2 T_cycle ≈ 4.304 minutes

1. Material removal rate (RMR): The material removal rate (RMR) is the volume of material removed per unit time. The formula for RMR is: RMR = (f * N * d) / 12

Substitute the values: RMR = (0.015 * 1200 * 0.044) / 12 RMR ≈ 0.066 cubic inches per minute

Summary of results:

1. Spindle RPM ≈ 1200 RPM

2. Machining time for each pass ≈ 0.052 minutes

3. Total cycle time per part ≈ 4.304 minutes

4. Material removal rate (RMR) ≈ 0.066 cubic inches per minute