Advance Manufacturing
System
Instructor: Abuzar Jamil
What is Manufacturing?
What is an engineer’s job, when it
comes to Manufacturing?
Modern manufacturing involves
• Design
• Processing
• Quality Control
• Planning
• Marketing
• Cost accounting
• Primary Industry
Manufacturing • Secondary Industry
Industry • Tertiary Industry
What is Conventional Machining?
Advantages of Machining
• Variety of Material
• Variety of part shapes and geometric features
• Dimensional accuracy (±0.025 𝑚𝑚 ±0.001𝑖𝑛
• Good Surface finish up to 0.4 microns (16 μ-in).
Disadvantages
• Material Wastage
• Time Consuming
Cutting Conditions
Rate of Material removal
• RMR= Vfd
• Units: ?
Categories of Machining Operation
• Roughing (High feed & high depths)
feeds of 0.4 to 1.25 mm/rev (0.015–0.050 in/rev)
depths of 2.5 to 20 mm (0.100–0.750 in)
• Finishing (Low feed & low depths)
feeds of 0.125 to 0.4 mm (0.005–0.015 in/rev)
depths of 0.75 to 2.0 mm (0.030–0.075 in)
Orthogonal Cutting Model
to
r
tc
Determining Shear Plane Angle
• Based on the geometric parameters of the orthogonal model,
the shear plane angle can be determined as
r cos
tan
1 r sin
where r = chip ratio, and = rake angle
Shear Strain
Four Basic Types of Chip in Machining
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with Built-up Edge (BUE)
4. Serrated chip
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Segmented Chip
• Brittle work materials
(e.g., cast irons)
• Low cutting speeds
• Large feed and depth of
cut
• High tool-chip friction
Figure 21.9 - Four types of chip
formation in metal cutting:
(a) segmented
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Continuous Chip
• Ductile work materials
(e.g., low carbon steel)
• High cutting speeds
• Small feeds and depths
• Sharp cutting edge on the
tool
• Low tool-chip friction
Figure 21.9 - Four types of chip
formation in metal cutting:
(b) continuous
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Continuous with BUE
• Ductile materials
• Low-to-medium cutting
speeds
• Tool-chip friction causes
portions of chip to adhere to
rake face
• BUE formation is cyclical; it
forms, then breaks off
Figure 21.9 - Four types of chip
formation in metal cutting: (c)
continuous with built-up edge
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Serrated Chip
• Semi continuous - saw-
tooth appearance
• Cyclical chip formation of
alternating high shear
strain then low shear
strain
• Most closely associated
with difficult-to-machine
metals at high cutting
speeds
Figure 21.9 - Four types of chip
formation in metal cutting: (d)
serrated
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Engineering
Forces in Metal Cutting
Forces in Metal Cutting
• Equations can be derived to relate the forces that cannot be
measured to the forces that can be measured:
F = Fc sin + Ft cos
N = Fc cos - Ft sin
Fs = Fc cos - Ft sin
Fn = Fc sin + Ft cos
• Based on these calculated force, shear stress and coefficient of
friction can be determined
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Engineering
The Merchant Equation
• Of all the possible angles at which shear deformation
could occur, the work material will select a shear plane
angle which minimizes energy, given by
45
2 2
• Derived by Eugene Merchant
• Based on orthogonal cutting, but validity extends to 3-
D machining
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• Higher shear plane angle means smaller shear plane
which means lower shear force
• Result: lower cutting forces, power, temperature, all of
which mean easier machining
Figure 21.12 - Effect of shear plane angle : (a) higher with a
resulting lower shear plane area; (b) smaller with a corresponding
larger shear plane area. Note that the rake angle is larger in (a), which
tends to increase shear angle according to the Merchant equation
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Power
• A machining operation requires power
The power to perform machining can be computed from:
Pc = Fc v
where Pc = cutting power; Fc = cutting force; and v = cutting speed
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Unit Power in Machining
• Useful to convert power into power per unit
volume rate of metal cut
• Called the unit power, Pu or unit horsepower, HPu
Pc HPc
Pu or HPu
MRR MRR
where MRR = material removal rate
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Power
Gross power to operate the machine tool Pg or HPg
is given by
Pc HPc
Pg or HPg
E E
where E = mechanical efficiency of machine tool
• Typical E for machine tools = 90%
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Cutting Temperature
• Approximately 98% of the energy in machining is converted into heat
• This can cause temperatures to be very high at the tool-chip
• The remaining energy (about 2%) is retained as elastic energy in the
chip
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