Machining

Turning Milling Drilling

Broaching PlaningSawing

Traditional Machining

• Turning

• Drilling

• Milling

• Other machining operationsShaping/PlanningBroachingSawing

CUTTING

Cutting

Turning Milling Drilling

Machining

• Grinding

• OthersHoningLappingSurface FinishingPolishing & Buffing

ABRASIVE MACHINING

Grain Action during GrindingCuttingPloughingRubbing

Wheel wear modeGrain fractureAttritious wearBond fracture

Traditional Machining

Non-Traditional Machining

• Mechanical Energy Processes

• Chemical Energy Processes

• Thermal Energy Processes

• Chemical Energy Processes

d

Depth of cut (d) = (D0‐Df)/2V = π*Df*N, N= rev./sec

3 Dimensions of Machining Speed (V)• Relates velocity of the cutting tool to the work piece (Primary motion).

Feed (f)• Amount of material removed per revolution or per pass of the tool over the work piece. linear translation of tool with respect to the  work piece (Secondary motion)

• Depth of Cut (d)Distance the tool has plunged into the surfaceMRR = vfd

d

Depth of cut (d) = (D0‐Df)/2V = π*Df*N, N= rev./sec

Single‐Point Tool Multiple‐ Point Tool

Single‐Point Tool Multiple‐ Point Tool

Cutting Tool

Tool AnglesRake Angles (α)

• Influence cutting forces, power and surface finish

• Large α– lowers forces and improves surface finish

– In general, power consumption ↓by ~ 1% for 1o

change in α

– Has adverse effect on tool strength because less metal is available to support the tool.

– Greatly reduced capacity to conduct heat away from the cutting edge

• 0 or negative rake angles employed on carbide, ceramic and similar “hard” tools– Increases tool forces, but keeps the tool in compression and provides added support to the cutting edge

• Particularly important in making intermittent cuts and in absorbing impact during initial tool‐workpiece contact

• Rake angles: 5 – 15 degrees for HSS; Lower for harder materials

Tool  Angles

Rake Angle

Positive Negative

Flank Angle

• Minimizes rubbing of flank faces with the machined surface

• Higher values of flank angle will reduce rubbing but also weaken the tool

• Flank angles have no influence on cuttingforces and power. So angles large enough toavoid rubbing is generally chosen

• Angle: 5 – 12 degrees for HSS; higher forsofter and lower for brittle material

Tool Angles

Nose radius 

• Improves tool life, surface finish, and conductivity

• Large nose radius– Increase cutting forces and power

– Causes chatter

Inserts

• Addresses the problem of frequent tool “regrinding”

• Inserts are individual cutting tools with several cutting points– A square insert has eight cutting points– A triangular insert has six

Inserts

Chip  Breaker

Orthogonal MachiningOblique Machining

Cutting edge is perpendicularto the direction of cutting speed

Cutting edge is obliqueto the direction of cutting speed

Orthogonal Machining

• Principles of orthogonalmachining can be used tounderstand mechanism ofchip formation and powerrequirement.

• Use a single‐edge wedgetool.

• Cutting edge of the wedgeis perpendicular to thecutting velocity vector Rake face

Cutting action involves shear deformation of work material to form a chip  

• As chip is removed, a new surface is exposed

Orthogonal Machining

Schematic representation of chip‐forming shear process 

Onset of shear takes place along the lower boundary of shear zone defined by the shear angle.Φ

Shear Zone

Orthogonal Cutting Model

ααφ

sin1costanr

r−

=Cttr =

φSinOAt .=

)(. αφ −= CosOAtC

Shear Angle

Shear Strain

BDDC

BDAD

BDDCAD

BDAC

+=+

==γ

φαφγ cot)tan( +−=

Forces in Machining

F = Frictional force between the tool and chipN = Normal forceβ = Friction angle; FS = Shear forceFn = Normal force to shear 

FC = Cutting forceFt = Thrust force

φτ

sin; twA

AF

SS

SS ==

F = FC sin α + Ft cos αN = FC cos α - Ft sin αFS = FC cosφ - Ft sinφFn = FC sin φ + Ft cos φ

Forces in Machining

twFF

twA

AF

tcs

s

s

ss

φφφτ

φ

τ

2sincossinsin

−=

=

=

The Merchant Equation

224

sincossin 2

βαπφ

φφφτ

−+=

−=

twFF tc

s

Eugene Merchant; J. App. Phys (1945)