Lecture 6 Machining Part-2 PDF

Mechanical Engineering Dept. Production Technology Cutting conditions and machining time Assistant Prof. Mohamed A. Bhlol  Topics Cutting conditions Machining time definition Machining time calculations - turning operation - milling operation...

Mechanical Engineering Dept. Production Technology Cutting conditions and machining time Assistant Prof. Mohamed A. Bhlol  Topics Cutting conditions Machining time definition Machining time calculations - turning operation - milling operation - drilling operation  Cutting conditions Cutting conditions are the numerical values to be selected before starting the machining operation 1. Main motion (Speed) 2. Feed motion (Feed) 3. Auxiliary motion (Depth of cut)  Cutting conditions 1. Cutting Speed (V) The cutting speed of a tool is defined as “the number of feet or meters of workpiece surface, measured at the circumference that passes the tool in one minute”. Cutting speed is measured in m/min Cutting speed Rotational Linear (milling, turning, drilling) (shaping)  Cutting conditions Cutting Speed (V) (Rotational) n rpm V=ω.r  Cutting conditions 1. Cutting Speed (V) (Rotational) Where; D : diameter in mm n : RPM (rev/min)  Cutting conditions 1. Cutting Speed (V) (Linear) QRM: quick return mechanism is used to save time in returning (non-effective stroke)  Cutting conditions 1. Cutting Speed (V) (Linear) Return n Cut The main motion in shaping and planning is reciprocating linear motion α α :The cutting stroke angle β β :The return stroke angle n : rev/min "RPM"  Cutting conditions 1. Cutting Speed (V) (Linear) Return n Cut α L :The cutting stroke length (mm) β n: The rotational speed (r.p.m) K: cut to return ratio (α/β =2)  Cutting conditions 2. Feed & Feed rate: (S, S\) Feed is the movement of the tool cutting edge in millimeters per revolution of the workpiece (mm/rev) parallel to machined surface”. Feed rate is the rate of feed per unit time”. S : is Feed in mm/rev S\ : is Feed Rate in mm/min Sz : is Feed per Tooth in mm/tooth (Milling, drilling)  Cutting conditions 2. Feed & Feed rate: (S, S\) Sz : mm/tooth S = Z. Sz mm/rev Where Z: No. of teeth S\ = n. S mm/min Where n: is rpm  Cutting conditions 3. Depth of cut: "a": The distance between the machined and work surface. It is measured in a direction perpendicular to the feed direction. a is measured in mm  Machining time definition Is the time for which the machine works on the component that is from the time when the tool touches the work to when the tool leaves the component after completion of the operations. Major Factors That Govern Machining Time: Length of cut Feed Depth of cut Cutting speed  Machining time calculations Turning operation  Machining time calculations Turning operation (Tm): machining time (machining time to produce one product) L: tool travel distance in feed direction S\: feed rate (mm/min) i: number of cutting passes (It should be integer no.)  Machining time calculations a) Longitudinal Turning  Machining time calculations a) Longitudinal Turning  Machining time calculations a) Longitudinal Turning Assume la = lb = 5 mm h: Machining allowance (total depth of cut) a: depth of cut per one pass  Machining time calculations a) Longitudinal Turning The average or mean cutting speed m/min.Dm: the average or mean diameter (mm) D: workpiece diameter (mm) d: machined diameter (mm)  Machining time calculations a) Longitudinal Turning Example 1: How much machining time will be required to reduce the diameter of a cast iron rod from 120 mm to 110 mm over a length of 100 mm by turning using a carbide insert at cutting speed of 60 m/min, and 0.25 mm/rev feed at step depth of 2 mm. Data D = 120 mm d = 110 mm lw = 100 mm V = 60 m/min S = 0.25 mm/rev a = 2 mm  Machining time calculations Solution: L = 5 + 100 + 5 = 110 mm h = 120 – 110 / 2 = 5 mm  Machining time calculations Solution: S\ = n. S = 166 x 0.25 = 41.5 mm/min  Machining time calculations Solution: Tm = 8 min  Machining time calculations b) Face Turning Assume la = 2 mm (for facing)  Machining time calculations b) Face Turning Assume i = 1 (for facing)  Machining time calculations b) Face Turning Example 2: Estimate the machining time required to face turn a workpiece of 60 mm diameter using a HSS tool at cutting speed of 50 m/min, and 0.15 mm/rev feed at step depth of 2 mm. Data: D = 60 mm V = 50 m/min S = 0.15 mm/rev a = 2 mm  Machining time calculations b) Face Turning Example 2: Solution:  Machining time calculations b) Face Turning Example 2: Solution:  Machining time calculations Milling operation Plain Milling A cylindrical milling cutter with t eeth on the periphery only; use d for milling plain or flat surface s. Also known as slab cutter. is the most commonly used tool in a horizontal milling machine.  Machining time calculations Milling operation Plain Milling machining time for plain milling a flat surface is:  Machining time calculations Milling operation Plain Milling  Machining time calculations Milling operation Plain Milling  Machining time calculations Plain Milling Example 3: Estimate the machining time that is required to mill a block of steel of length 300 mm and 100 mm width at depth 10 mm by an 8 teeth HSS milling cutter of 60 mm diameter and 110 mm length using suitable milling machine. Assume, V = 30 m/min, Sz = 0.12 mm/tooth.  Machining time calculations Plain Milling Data: D = 60 mm V = 30 m/min Sz = 0.12mm/tooth Z = 8 teeth a = h =10 mm w.p)width< tool)width Solution:  Machining time calculations Plain Milling Solution:  Machining time calculations Drilling operation  Machining time calculations Drilling operation S\ = n. S mm/min.Sz = the feed per edge (mm/edge) Z = no. of cutting edges (two cutting edges for twist drill).  Machining time calculations Drilling operation L= lw+ la + lb + l1 2ø = twist drill angle D = diameter of the twist drill (mm)  Machining time calculations Drilling operation  Machining time calculations Drilling operation Example 4: Calculate the machining time required to drill two holes with dimensions shown in Figure. The cutting speed = 25 m/min and the feed = 0.20 mm/rev, drill point angle = 118o. Assume (la = lb = 3 mm)  Machining time calculations Drilling operation Data: D = 30 mm V = 25 m/min S = 0.2mm/rev 2ø = 118o lw = 50 mm (through hole) lw = 40 mm (blind hole) Solution: For through hole: L= lw+ la + lb + l1 L = 50 + 3 + 3 + 9 = 65 mm  Machining time calculations Drilling operation Solution: For through hole: n = 265 r.p.m S\ = n. S = 265 x 0.2 = 53 mm/min  Machining time calculations Drilling operation For blind hole: L= lw+ la + l1 L = 40 + 3 + 9 = 52 mm n = 265 r.p.m S\ = n. S = 265 x 0.2 = 53 mm/min 52 / 53 = 0.98 Thank you