Machinist Group of Northeast Indiana

Cutting Tool Theory IntroSpeeds and Feeds

July 8, 2014

What RPMs & IPM would you run?• Specifications (dry machining)• Material: 1018 CRS• Endmill:

– 5/8” diameter (.625)– 8 flute– High Speed Steel– TiN Coating

• Amount to remove– “Z” total depth = 1.22”– “Y” total material = 3.5”– “X” total material = 6.25”

Machine limits7.5 horsepower

550-10,000 RPMs200 IPM max (X&Y axis)

Important Formulas(applies to any rotating tool)

OR better known as

n =Vc x 12p x Dm

RPM = SFPM x 3.82Diameter

Lathe (Sandvik Coromant)Dm Machined diameter mm (inch) mm (inch) fn Feed per revolution mm/r (inch/r) ap Cutting depth mm (inch) n Spindle speed rpm Pc Net power kW (HP)

Q Metal removal rate cm3/min (inch3/min)

hm Average chip thickness mm (inch)

hex Maximum chip thickness mm (inch)

Tc Period of engagement min lm Machined length mm (inch) kc Specific cutting force N/mm2 (N/inch2) KAPR Entering angle degree PSIR Lead angle degree

  

Milling Machines(multi-flute cutters)

Vf = n x Fz x ZnOR

IPM = RPM x IPT x # of Flutes

Milling(Sandvik Coromant)

Milling: Up or Down?• Conventional Milling (fights the rotation)

– Aka: UP milling– Starts at ZERO chip thickness and progresses to MAX– In most materials, should only be used with machines

with backlash• Climb Milling (acts like a wheel)

– Aka: Down Milling– Starts at MAX chip thickness and progresses to ZERO– In most materials and set-ups, this is the best choice

Face Milling

Climb MillingFeed per Tooth

Maximum chipthickness

average chip thickness

Workingengagement

Traditional Milling Engagement

Radial Chip Thickness

How does new concepts in metal cutting help us on smaller machines?

• Specifications (dry machining)– Material: 1018 CRS– Endmill:

• 5/8” diameter (.625)• 8 flute• High Speed Steel• TiN Coating

– Amount to remove• “Z” total depth = 1.22”• “Y” total material = 3.5”• “X” total material = 6.25”

Machine limits7.5 horsepower

550-10,000 RPMs200 IPM max (X&Y axis)

What we ran at SA with our old tools

• RPM = 2200• IPM = 190 • 1.22 = “Z” depth of cut per pass

– Total depth needed to finish part• .030 = “X” step over (radial width of cut)

Results:• It took 208 passes to finish the part• 3 minutes 50 seconds: Total time to remove 27

in3 of steel• We actually changed our cutting to G00 (rapid)

moves• Cutter looked like it was new when we were

done• Part and tool was cool enough to touch at the

completion of the material removal

Good Reading:

• Cutting Tool Engineering Magazine• “Limited Engagement” by Bill Kennedy• July 2011 / Volume 63 / Issue 7• http://www.ctemag.com/aa_pages/2011/110

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