1. INT 201 Eastern Kentucky University
Machining
Metal Cutting Process
INT 201
Eastern Kentucky University
Lecture References:
Degarmo E.P., Black J.T., Kosher R. (2003). Materials and Processes in Manufacturing, 9th edition. Wiley
Repp, V. (1994). Metalwork: Technology and Practice, 9th edition. McGraw-Hill
Groover, M. (2004). Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 2nd edition. Wiley
Chen, C.S. (2001) ITEC 502: Advanced Design and Manufacturing [Course]. Iowa State University

2. Lesson Objectives REVIEW: Fundamentals of Machining
Identify the basic parameters associated with machining (milling)
Understand how these basic parameters are used to create and remove chips
Understand that machine parameters are directly related to type of material and the machine

3. Machining Fundamentals
REVIEW
Machining is a process of removing unwanted material from a workpiece in the form of chips.
Making and removing chips
Importance of lubricants
$60 billion spent annually on metal removal operations

4. Machining Fundamentals
Basic machine processes

5. Machining Fundamentals
Milling Machines
SPINDLE
KNEE
BASE
TABLE
COLUMN
VERTICALLY
LONGITUDINALLY
TRANSVERSELY

6. Basic Machining Parameters
Cutting Speed
Spindle Speed (RPM)
Feed Rate
Metal Removal Rate
Chip Load
Machine Horse Power

7. Specific process/equipment
Basic Machining Parameters
Machining variables such as cutting speed, RPM, table feed rates, metal removal rates, and depth of cut all depend on:
Work material
Tool material
Specific process/equipment

8. Cutting Speed (SFPM)
Cutting speed is the distance a point on the circumference of the milling cutter travels in one minute
Measured in Surface Feet per Minute (SFPM)
Calculated at the outside diameter of the cutter

9. Cutting Speed (SFPM)
Different cutting speeds should be used when machining different metals
With cutting speeds too fast, cutter will overheat and dulls rapidly
With cutting speeds too slow, time is wasted and production costs will increase

10. Cutting Speed (SFPM) Factors affecting cutting speeds in milling:
Material properties, cutting tool (HSS, carbide, cast alloy), cutting fluids
Cutting speed recommendations for various materials and tooling combinations can be found in sources including: Tooling Mfg. & Engineering Handbooks (Machinist Handbook, etc)

11. SFPM = Surface Feet Per Minute
Cutting Speed Formula
SFPM = (π * D * N)/12
where
SFPM = Surface Feet Per Minute
π = Circumference constant per inch of Diameter
D = Diameter of the cutter, measured in inches
N = revolutions per minute of the spindle (RPM)
12 = 12 inches per foot (conversion calculation to feet)

12. Cutting Speed Example
If a 2 inch dia., 6 tooth milling cutter is turning at 100 revolutions per minute (RPM), what is the calculated cutting speed of the cutter (SFPM)?

13. Spindle Speed (RPM)
The speed of the milling machine is measured at the spindle and is measured in REVOLUTIONS PER MINUTE (RPM)

14. Same equation; different arrangement
Finding N (RPM)
Same equation; different arrangement
SFPM = (π * D * N)/12

15. Determining RPM
When milling with a 3” diameter, 8 tooth milling cutter with a recommended cutting speed of 250 SFPM tooling material combination, what is the recommended RPM?

16. Feed Rate
The linear distance moved along any machine axis, by the cutting tool in inches per minute.
Feed rate in milling is determined by multiplying:
Number of teeth on the cutter
Chip load per tooth
Speed of the cutter (N)

17. Chip Load or Feed per Tooth
The Chip Load is the amount of material removed by each tooth of the milling cutter during one revolution
Chip load recommendations for various materials and tooling combinations can be found in machining and engineering handbooks

18. Milling Feed Rate Formula
F = N * Ct * T
where
F = Feed rate in inches per minute
N = Spindle RPM
Ct = Chip Load per tooth [feed per tooth]
T = Number of teeth on cutter

19. Calculating Feed Rate
A 6 inch dia., 12 tooth milling cutter is turning at 250 RPM. The recommended chip per tooth is 0.004”. What is the feed rate?
F = N * Ct * T
= 250 RPM * ”/tooth * 12 teeth
F = 12” per minute

20. Metal Removal Rate
Metal Removal Rate (MRR) is the volume of material removed from the work piece in one minute.
Limited to available machine power
How much material is removed in 1 minute

21. MRR Formula MRR = W * D * F MRR = Cubic inches removed per minute
where
MRR = Cubic inches removed per minute
W = Width of Cut
D = Depth of Cut
F = Feed rate

22. MRR Graphic
Volume =
In3 / min
Depth
Feed Rate
Width

23. MRR Example
What is the MRR of a surface 3 inches wide that is to be milled with a 6 tooth milling cutter. Each depth of cut is inches and the table feed rate is 4 inches per minute 3”
Feed Rate = 4”/min
.125”

24. MRR Example MRR = W*D*F MRR = (3”) * (0.125”) * (4” per minute)
Feed Rate = 4”/min
.125”
MRR = W*D*F
MRR = (3”) * (0.125”) * (4” per minute)
MRR = 1.5 cubic inches per minute (in3/min) of material removed

25. Horse Power (specific) HPs
HPs = Horse power required to remove 1 cubic inch (in3/min) of material per minute
All machined materials have a HPs rating
HPs is used to determine the HP required for machining.
The standard HPs = 1
Materials with HPs > 1 require more than 1 HP/minute to remove 1 in3 of material
Materials with HPs < 1 require less than 1 HP/minute to remove 1 in3 of material
HPs can be found in machining and engineering handbooks

26. HP = HPs * MRR Horse Power Formula
where
HP = Horse Power required to make a desired cut
HPs = specific Horse Power of material
MRR = Material Removal Rate

27. HP = HPs * MRR HP = 1.8 * 3.94 HP = 7.1 HP Example
How much Horse Power is required to machine a part with a desired MRR of 3.94 in3/min and a specific Horse Power (HPs) of 1.8?
HP = HPs * MRR
HP = 1.8 * 3.94
HP = 7.1

28. Review
What is the maximum MRR of a material with a 1.6 HPs on a 1.2 HP machine?
How much material can be removed from the same material on a 7.1 HP machine?

29. Specific process/equipment
Review
Machining variables such as cutting speed, RPM, table feed rates, metal removal rates, and depth of cut all depend on:
Work material
Tool material
Specific process/equipment
WHY?