Machining

1
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

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

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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

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Machining Fundamentals
Basic machine processes
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Machining Fundamentals

• Milling Machines

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Basic Machining Parameters

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

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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

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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)

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Cutting Speed Formula

• SFPM (p D N)/12
• where
• SFPM Surface Feet Per Minute
• p 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)

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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)?

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Spindle Speed (RPM)

• The speed of the milling machine is measured at
  the spindle and is measured in REVOLUTIONS PER
  MINUTE (RPM)

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Finding N (RPM)
Same equation different arrangement SFPM (p
D N)/12
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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?

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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)

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Chip Load

• 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

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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

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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 0.004/tooth 12 teeth F
12 per minute
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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

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MRR Formula

• MRR W D F
• where
• MRR Cubic inches removed per minute
• W Width of Cut
• D Depth of Cut
• F Feed rate

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MRR Graphic
Volume In3 / min
Depth
Feed Rate
Width
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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 0.125 inches and the table
  feed rate is 4 inches per minute

3
Feed Rate 4/min
.125
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MRR Example
3
Feed Rate 4/min
.125
MRR WDF
MRR (3) (0.125) (4 per minute) MRR 1.5
cubic inches per minute (in3/min) of material
removed
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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 gt 1 require more than 1
  HP/minute to remove 1 in3 of material
• Materials with HPs lt 1 require less than 1
  HP/minute to remove 1 in3 of material
• HPs can be found in machining and engineering
  handbooks

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Horse Power Formula

• HP HPs MRR
• where
• HP Horse Power required to make a desired
  cut
• HPs specific Horse Power of material
• MRR Material Removal Rate

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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
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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?
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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?