Basics of cutting

Question 1

Cutting force

Answer 1

Depends on: - specific cutting force of the workpiece material
- cross section area of chip

cutting speed * cutting force = required power

Question 2

Cutting energy and tool

Answer 2

• energy input converts to heat
• Heat and abrasion cause tool wear
• Tool economic lifetime is typically 15 - 30 minutes for basic cutting methods

Question 3

Differences Turning and Milling

Answer 3

• Chip breaking

- Tool load (continuous and discontinous)

Question 4

Tool geometry in turning (angles)

Answer 4

α Clearance angle
β Wedge angle
ε Included angle 
γ Rake angle
κ Major cutting edge angle 
κn Minor cutting edge angle 
λ Inclination angle
r Tool nose radius

(Freiwinkel, 
Keilwinkel, 
Eingeschlossener Winkel, 
Spanwinkel, 
Hauptschneidkantenwinkel, 
Kleiner Schnittkantenwinkel, 
Neigungswinkel, 
Radius der Werkzeugschneide)

Question 5

Tool geometry in turning (points and surfaces)

Answer 5

a tool holder
b cutting edge
c clearance face
d minor clearance face
e minor cutting edge
f rake face

(a Werkzeughalter
b Schneide
c Freifläche
d Nebenfreifläche
e Nebenschneidkante
f Spanfläche)

Question 6

Relation Rake angle and Angle of inclination

Answer 6

when inclination angle rises, the rage angle rises

Question 7

Factors influencing the cutting force

Answer 7

• Workpiece material
• Tool geometry
• cutting parameters

Question 8

Components of the resulting cutting force (turning)

Answer 8

• Axial/feed component
• Radial/passive component
• Tangential/main component

Question 9

Relation cutting force and cutting speed

Answer 9

Very little influence

Question 10

Formula for main cutting force

Answer 10

Fy ≈ f apkc

feed f, specific cutting force kc, depth of cut ap

Question 11

Relation specific cutting force and chip thickness

Answer 11

kc increases when h decreases (exponential)

–> Small cutting depth requires sharp cutting edge

Question 12

Formulas surface roughness

Answer 12

Ry=f^2/(8*r) (maximum peak to valley

Ra=f^2/(20*r) (arithmetic average)

Question 13

Temperature and heat

Answer 13

• Most heat generated in shear zone and due to friction on the rake surface
• Workpiece material and cutting speed are the most important affecting factors
• thermal energy goes to: 80% chips, 10% workpiece, 10% tool

Question 14

FEM modeling of cutting

Answer 14

• modelling of bodies as meshes
• balance equations mainly for force and heat –> minimization
• regeneration of mesh after every movement

Question 15

Purposes of FEM

Answer 15

• Chip form
• Cutting forces
• Tool and workpiece temperature
• Tool wear
• Workpiece deflection

Question 16

Where does tool wear affects?

Answer 16

• Workpiece surface and dimensions
• Chip form
• Cutting forces

Question 17

Tool wear types and main cause

Answer 17

• abrasive wear (Abtrag) (low tool hardness)
• crater wear (high temperature)
• Notch wear (Kerben) (adhesion)
• Build-up edge (adhesion of workpiece material, low cutting speed and temperature)
• cracking (mechanical overload)
• plastic deformation (high temperature)

Question 18

Characteristics rough cutting

Answer 18

• Objective is efficient material removal
• high cutting depth and feed considering rigidity limitations due to tool-
fixture-workpiece-machine tool system
• Cutting speed is optimized with the objective of minimizing total cost or sometimes
output (pieces/hour)

Question 19

Characteristics finishing

Answer 19

• Objective is on surface quality and precision
• The allowance left from rough cutting determines cutting depth, which must be
small in order to keep cutting forces, deformation, and vibration low
• Feed is selected according to the defined surface roughness
• Cutting speed is optimized with the objective of minimizing total cost

Question 20

Cost factors while machining

Answer 20

• Labor
• Depreciation
• Interest (Zins)
• Rent
• Energy
• Maintenance
• Tools