Turning Operation :-
Let,
l = length of surface to be machined, mm,
l1= Distance required for feeding the tool cross-wide, to increase the depth of cut, mm(tool approach),
l2= Overtravel of the tool at the end of each cut, mm,
d= Depth of cut, mm,
f = Feed, mm/revolution,
N= Speed of work, r.p.m.,
Np= Number of passes or cuts taken for obtaining the required diameter,
Di= Initial diameter of the workpiece, and
Df = Final diameter of the workpiece.
Now, the distance travelled by the tool in the direction of the feed in a single cut,
L=l + l1 + l2
(Approach of most of the single point cutting tools is negligible)
Then, machining time is given by :
Tmp = L/fN , per pass (cut)
Also, V = πDN/1000 m/min
Or, N = 1000V/πD
Therefore,
Tmp (per pass or cut) = L/f×(1000v/πD)
= πDL/1000Vf min.
Total machining time, Tmt = Tmp × n
Therefore, Number of passes or cuts, Np
= Total machining allowance/Material removed per cut
Now, total machining allowance = Di - Df/2
Material removed per cut = Depth of cut.
"Depth of cut" is half the difference between the work diameter at the start of the cut and the diameter of machined surface obtained after the cut.
In practice, the depth of cut per pass is not constant. For roughing operations, it is much greater than for the finishing operations.
Total manufacturing time =
Machining time + Set-up time + Moving and waiting time + Inspection time.
Drilling Operation :-
Let,
Lj= Hole length or depth mm,
l1 = Tool approach = 0.29D (with point angle of 118°),
l2 = Tool overtravel, 1 to 2 mm.
Machining time,
Tm. = Lj + l1 + l2 /fN, min
Milling Machine :-
Machining time (Tm) iz defined as the time required for one pass of width of cut B for milling or machining a surface and is expressed in minutes.
Mathematically,
Tm = Length of cut/Feed rate = L/f
= L/ft . Z . N min
Above time is for making one pass across the length of surface. If the width of cutter is more than the width of surface to be milled, only one pass will machine the whole surface.
However, if more than one pass is required the above time is multiplied by the number of passes.
Shaping operation :-
The time required to complete on double stroke, from cutting speed (Vc), is given by :
t = L ( 1+k )/1000Vc min
With a feed of f mm/double stroke, number of double strokes required to machine a surface of width B will be
Ns = B/f
Hence, total time for machining the surface will be
Tm = LB (1+k )/1000Vcf
Or,
In terms of ram strokes N, the time for machining the surface is given by
Tm = B/fN min.
Machining time(Tm) can also be calculated as follows :
Tm = B/f (L/Vc × 1000+L/Vr × 1000) min
Where,
B = Width of the job, mm,
f = Feed, mm/stroke,
L = Length of stroke, mm
Vc = Cutting speed, m/min, and
Vr = Return stroke speed, m/min.
If Vav is the average or mean speed, then
Tm = B/f × 2L/Vav × 1000 min
Where,
Vav = 2Vc × Vr/Vc + Vr m/min
Credit:-Author-R.K.RAJPUT
Let,
l = length of surface to be machined, mm,
l1= Distance required for feeding the tool cross-wide, to increase the depth of cut, mm(tool approach),
l2= Overtravel of the tool at the end of each cut, mm,
d= Depth of cut, mm,
f = Feed, mm/revolution,
N= Speed of work, r.p.m.,
Np= Number of passes or cuts taken for obtaining the required diameter,
Di= Initial diameter of the workpiece, and
Df = Final diameter of the workpiece.
Now, the distance travelled by the tool in the direction of the feed in a single cut,
L=l + l1 + l2
(Approach of most of the single point cutting tools is negligible)
Then, machining time is given by :
Tmp = L/fN , per pass (cut)
Also, V = πDN/1000 m/min
Or, N = 1000V/πD
Therefore,
Tmp (per pass or cut) = L/f×(1000v/πD)
= πDL/1000Vf min.
Total machining time, Tmt = Tmp × n
Therefore, Number of passes or cuts, Np
= Total machining allowance/Material removed per cut
Now, total machining allowance = Di - Df/2
Material removed per cut = Depth of cut.
"Depth of cut" is half the difference between the work diameter at the start of the cut and the diameter of machined surface obtained after the cut.
In practice, the depth of cut per pass is not constant. For roughing operations, it is much greater than for the finishing operations.
Total manufacturing time =
Machining time + Set-up time + Moving and waiting time + Inspection time.
Drilling Operation :-
Let,
Lj= Hole length or depth mm,
l1 = Tool approach = 0.29D (with point angle of 118°),
l2 = Tool overtravel, 1 to 2 mm.
Machining time,
Tm. = Lj + l1 + l2 /fN, min
Milling Machine :-
Machining time (Tm) iz defined as the time required for one pass of width of cut B for milling or machining a surface and is expressed in minutes.
Mathematically,
Tm = Length of cut/Feed rate = L/f
= L/ft . Z . N min
Above time is for making one pass across the length of surface. If the width of cutter is more than the width of surface to be milled, only one pass will machine the whole surface.
However, if more than one pass is required the above time is multiplied by the number of passes.
Shaping operation :-
The time required to complete on double stroke, from cutting speed (Vc), is given by :
t = L ( 1+k )/1000Vc min
With a feed of f mm/double stroke, number of double strokes required to machine a surface of width B will be
Ns = B/f
Hence, total time for machining the surface will be
Tm = LB (1+k )/1000Vcf
Or,
In terms of ram strokes N, the time for machining the surface is given by
Tm = B/fN min.
Machining time(Tm) can also be calculated as follows :
Tm = B/f (L/Vc × 1000+L/Vr × 1000) min
Where,
B = Width of the job, mm,
f = Feed, mm/stroke,
L = Length of stroke, mm
Vc = Cutting speed, m/min, and
Vr = Return stroke speed, m/min.
If Vav is the average or mean speed, then
Tm = B/f × 2L/Vav × 1000 min
Where,
Vav = 2Vc × Vr/Vc + Vr m/min
Credit:-Author-R.K.RAJPUT
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