1. Milling Processes

2. Objectives
The students are able to identify:
 Various Types of Milling Machine & Layout
 Industrial Applications
 Milling Tools
 Operation Factors - Speed, Feed, ...
 Milling Methods
 Planning & Setup Procedures
 Practices

3. Classification of Machining Processes

4. Milling Process
 Milling is a machining
operation in which a
workpiece is fed past a
rotating cylindrical tool with
multiple cutting edge.
 Multi-points cutting process Cutting
Direction
 Chips are cut off by the Tooth
rotating cutter
 Workpiece is fed in linear
motion Milling
 Tool with one cutting edge is Cutter
called fly-cutter (rarely used) Workpiece
Feed Direction

5. Basic Milling Processes
 Two types of milling processes
 Up milling or conventional milling process
 Down milling or Climb milling process

6. Up Milling (Conventional Milling)
 The metal is removed in form of small chips
 The chip thickness is minimum at the start of the cut and maximum at the end.
 Cutting force varies from zero to the maximum value
 Advantages of Up Milling
 It does not require backlash eliminator
 It is safer in operation ( the cutter does not climb on the workpiece)
 Loads on the teeth are acting gradually
 Built-up-edge (BUE) fragments are absent from the machined surface
 The cutter is not affected by the sandy surfaces of the workpiece
 Disadvantage of Up Milling
 The tendency of cutting force to lift the work piece from the fixtures and
 poor surface finish obtained

7. Up Cut
FEED

8. Up Cut
FEED

9. Up Cut
FEED

10. Up Cut
FEED

11. Up Cut
FEED

12. Up Cut
FEED

13. Up Cut
FEED

14. Up Cut
FEED

15. Up Cut
FEED

16. Up Cut
FEED

17. Up Cut
FEED

18. Up Cut
 Cutter rotates in a
direction opposite
to the table feed
CUTTER
FEED

19. Down Milling (Climb Milling)
 A cutter rotating in the same directions of the feed of the workpiece.
 Chip thickness is maximum at the start of the cut and minimum in the end.
 There is less friction involved and consequently less heat is generated on the contact surface of the
cutter and workpiece
 Advantages
 Fixtures are simpler and less costly, as cutting forces are acting downward
 Flat workpiece (that cannot be firmly held) can be machined by down-milling
 Cutter with higher rake angles can be used, which decreases the power requirements
 Tool blunting is less likely
 Better surface finish
 It is characterized by less tendencies of chattering and vibration

20. Down Cut
FEED

21. Down Cut
FEED

22. Down Cut
FEED

23. Down Cut
FEED

24. Down Cut
FEED

25. Down Cut
FEED

26. Down Cut
FEED

27. Down Cut
FEED

28. Down Cut
FEED

29. Down Cut
FEED

30. Down Cut
FEED

31. Down Cut
 Cutter rotates in
the same direction
as the table feed
FEED
CUTTER

32. Up Cut Vs Down Cut
 Up Cutting  Down Cutting
 Will not cause the  Better surface finishing
table to a step  Not suitable for
motion conventional machine
 Recommended for  Suitable for CNC machine
conventional or the machine equipped
machine with BACKLASH
ELIMINATOR

33. Types of Milling Cutters

34. Type of Milling Cutter

35. Type of Milling Operations
 Two basic type of milling
operations
 Peripheral milling (Plain Milling)
 Axis of the tool is parallel to the
surface being machined.
 Face milling

36. Example of Peripheral Milling
 (a) Slab milling; (b) Slot Milling; (c) Side Milling (d) Straddle
Milling (e) Form Milling

37. Peripheral Milling
 Direction of Cutter Rotation
 Two form of milling
 Up milling and down milling
 Up milling (Conventional milling): the direction of motion of the cutter
teeth is opposite the feed direction when teeth cut into the workpiece.
 It is milling “ against the feed”
 Down Milling (Climb Milling): the direction of cutter motion is the same
as the feed direction when teeth cut into the workpiece.
 It is milling “ with the feed”

38. Face Milling
 The axis of the cutter is perpendicular the surface being milled.
 Various forms of face milling
 (a) Conventional face milling; (b) Partial face milling; (c) End Milling; (d) Profile Milling;
(e) Pocket Milling; (f) surface contouring Milling

39. Milling Method
• Plain Milling  End Milling
 Cutter axis perpendicular to the
– Cutter axis parallel to the
machined surface
machined surface
 Peripheral & end cutting edges
– Peripheral cutting edges
 Vertical milling normally
– Horizontal milling normally
PLAIN MILLING END MILLING

40. Milling Machines
 It has a horizontal spindle and well suited for performing
the peripheral milling (e.g. slab milling, slotting milling, side
milling and straddle milling)
 It has a vertical spindle and well suited for performing the
face milling (e.g. end milling, surface contouring milling)

41. Horizontal Milling Machine
 Spindle arbor rotates parallel
to the table
 Machine table moves along the
3 axes - X,Y, & Z
 Cutter being used: x
 Slab milling cutter y
 Side & face cutter
 Slitting saw z

42. Cutters for Horizontal Milling
Machine
SLITTING SAW
SLAB MILLING CUTTER
SIDE & FACE CUTTER

43. Vertical Milling Machine
 Spindle rotates
perpendicular to the table
normally
 Milling Head can be adjusted
in different angle
 Cutter being used :
 End mill
 Face milling cutter

44. Cutters for Vertical Milling Machine
END MILL FACE MILLING CUTTER

45. Type of Milling Machines
 Special purposes milling machine

46. Knee and Column Milling Machine

47. Planer Type Milling Machine

48. Rotary Table Milling Machine

49. Surface Finishing
 Cylindrical marks are left on
surface by end milling
 Parallel marks are left on surface
by plain milling
 Roughness of milling is directly END MILLING
proportional to the feed rate &
depth of cut
 Finishing measurement (Roughness
Value) in milling
Ra = 6.3 ~ 0.8 m
PLAIN MILLING

50. Tool Life
 Tool life is defined as the length of cutting time that the tool can be used.
Operating the tool until final catastrophic failure is also defined as tool life.
 Taylor Tool Life Equation is expressed as
VT n C
Where, V cutting speed (m/min);T tool life (min);
n and C are parameters whose values depend on feed,
depth of cut, work materials, tooling and tool life criterion used.
 Milling cutter is a Multi-point cutting tool
 Ground by special grinding machine
 Precision cutting angles
 Cutter re-shape is very time consumable
 Tool life can be increased by
 Correct spindle speed & feed rate
 Apply cutting fluid
 Correct cutting method

51. Tool Material
 High Speed Steel
 An alloy of iron, chromium, nickel, cobalt & some molybdenum etc..
 High resistance to wear, loss hardness at 600°C
 Two basic types:
 Tungsten –type (T-grades by AISI)
 Molybdenum –type (M-grades by AISI)
 Carbide
 Widely apply in modern industry
 Suitable for very higher cutting speed, hard material, & high accuracy
 Smooth surface
 Ceramic & Diamond cutting tool

52. Cutting Speed
 Cutting Speed of milling is defined by the
movement of each cutting edge per minute
(m/min)
TOOL HIGH SPEED
CARBIDE
MATERIAL STEEL
Cutting Cutting
Feed Feed
MATERIAL Speed Speed
mm/Tooth mm/Tooth
m / min. m / min.
MILD STEEL 25 0.08 100 0.15
ALUMINUM 100 0.15 500 0.3
HARDEN STEEL 50 0.1

53. Machining Variables and Relationships
Formula
DN
Cutting Speed V
1000
Feed rate F f r nt N
Cutting Time T L/ F
Material Removal Rate MRR Wc dF
Power, hp (cutter) HP Cutter HPu MRR
HP (actual)=HP (tare) + HP (actual)/Em
Cutting Speed,V m/min; Workpiece Diameter or tooldiameter, D mm,
N rpm, F mm/min, f r mm/rev;nt number of cutter tee MRR
th, mm3 /min
L Piece Length Lead Length Pretraveland Overtravel Depth of cut d ;
;
Length of Lead, for Face/end milling, l D (mm)
2
for slab/slot milling, l R2 R d d D d
HP(tare) horsepower(kW) to run machine (cutting air)
Em Motor efficiency

54. Example
 An end mill is used to put a 25-mm slot with a depth of 5 mm in a cast iron block with a high-
speed cutter. The block is 50 mm wide, 20 mm tall, and 100 mm long. The cutter, a high-speed
cutter with a diameter of 25 mm, has four teeth. The pretravel and overtravel combine to a
total length of 5 mm. The cut will be made at a feed rate of 0.130 mm/tooth and a cutting speed
of 40 m/min. The unit kilowatt power is 0.005 kW/mm3/min, the tare horsepower is 75 kW and
the motor efficiency is 80 %. Figure indicates the final shape to be produced.
(1) What is the RPM used?
(2) What is the length of the lead?
(3) What is the cutting time?
(4) What is the metal removal rate?
(5) What is the power (kW) required at the cutter?
(6) What is the motor horsepower requirements?

55. Sample Calculation
 Data Given
 Width of cut, Wc = 25 mm
 Depth of cut, d = 5 mm
 Diameter of cutter, D = 25 mm
 Number of teeth , nt = 4
 Pretravel and Overtravel = 5 mm
 Feed , fr = 0.130 mm/tooth
 Unit horsepower, HPu = 0.005 kW/mm3/min
 Tare horsepower, Hptare = 75 kW
 Motor efficiency, Em= 80% = 0.8

56. (1) Cutting speed:
DN 1000 V 1000 (40)
V N 510 rpm
1000 D (25)
(2) Length of Lead for end milling, l = D = 25 mm
(3) Cutting time, T= L/F
Length of Lead, L = Piece length+ Lead length + pretravel
and Overtravel
L = 100+25+5 = 130 mm
Feed rate, F f r nt N 0.130 4 510 265 mm/min
L 130
The cutting time, T 0.49 min
F 265
(4) Material removal rate:
MRR Wc dF 25 5 265 33125 mm 3 /min
(5) Power HP cutter HPu MRR 0.005 33125 mm 3 /min 155 kW
(6) Motor power requirement
HP ( Actual ) HP ( Tare ) HP cutter / Em
0.005 33125 mm 3 /min 75 kW 155 kW/0.8 268 .75 kW

57. Cutting Fluid
 Cooling the workpiece & the cutting tool
 Maintain hardness of cutting tool
 Provide lubrication
 Reduce fraction between workpiece & cutting tool
 Wash away the chips
 Prolong tool life
 Soluble oil is widely use in our workshop
 5 ~ 20 % soluble oil mixed with water

58. SAFETY
 Consult Staff Where are the Dangerous Points
 Familiar with the Controls
 Stop the Machine in Emergency
 Only One Man Operates One Machine
 Suitable & Safety Protection of Yourself
 Don't Leave the Machine when it is Running
 Don't Touch the Work while it is Running
 Don't Operate the Machine Without Staff Supervised

60. End