Homework • Chapter 22 – Re Revi view ew que quest stio ions ns:: • 1, 1,2, 2,5, 5,7, 7,11 11,1 ,15, 5,16 16,2 ,20 0
– Mu Mult ltip iple le ch choi oice ce:: • 2,9
– Problems: • 1,2,5,12,13
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Cutting Parameters • We re requ quir ire e rel relat ative ive mo moti tion on be betwe tween en th the e cutt cutter er and material to perform the machining operation • 2 Motions: Sp Speed and Feed – Speed: Speed: How How fast fast the mate materia riall moves moves past the cutting edge – Fe Feed: ed: Ho How w fast fast the the cutt cutting ing edg edge e moves moves across(into) the material
• For example: – How much you squee squeeze ze the the trig trigger ger on a hand dril drilll will change the SPEED – How fast you push push the the drill drill bit bit into into your your mater material ial will change the FEED 2
Cutting Parameters for Turning
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f : FEED, in turning is distance per revolution (in/rev) revolution (in/rev) or (m/rev)
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v : Linear cutting SPEED, given in distance per minute (in/min) minute (in/min) or (m/min)
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N :: Rotational speed (rev/min) or RPM N
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Cutting Parameters for Turning
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L : The total length (along the axis ax is of rotation) that we are cutting
• D o : The original Diameter • D f : The final Diameter depth of the cut cut (measured (measured radia radially) lly) = (Do-Df)/ (Do-Df)/2 2 • d : The depth
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Turning Calculations • Speeds and Speeds and Feeds Feeds are are material and operation specific and can be found in a Machinist’s Handbook • We ne need ed to ca calc lcul ulat ate e the the sett settin ings gs fo forr our our machine, how long it will take to machine the piece, and how fast we will remove material
• So, Rotatio ion nal Speed:
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Turning Calculations •
Rate is the linear travel rate (along the axis) r : Feed Rate is f
f r = N * f Feed Rate is in (in/min) or (mm/min)
o to D f f is • Th The e ti time me to tu turn rn a pa part rt fr from om D o simply the time to travel across the length L…so, r Tm: Time to machine = L / f
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Turning Calculations • Mate Materi rial al Re Remo mova vall Rat Rate e (MR (MRR) R):: volumetric amount of material being cut away per unit time – In Turning MRR ~ v * f * d (approximation) NOTE: units of feed of feed in in this calculation is simply distance not (in/rev)
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Turning Calculations (example) •
We wish to turn a piece of of 1” 1” steel ro round st stock do down to 0. 0.8” in in one pass. pass. The total length of the cut is to to be 4”. We want want to to calculate the feedrate and rotational speed for our lathe, material removal rate, rate, and the time it will take to machine.
1. 2. 3. 4.
Look up feed feed and and speed speed in in handbook. We need: depth of cut, cut, material material,, tool Depth of cut (D o - D f 0.1”” o-D f) / 2 = (1.0-0.8) / 2 = 0.1 From handbook, f = 0.03125 (inch/rev) v v = = 240 (feet/min)
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Turning Calculations (example) •
We wish to turn a piece of of 1” 1” steel ro round st stock do down to 0. 0.8” in in one pass. pass. The total length of the cut is to to be 4”. We want want to to calculate the feedrate and rotational speed for our lathe, material removal rate, rate, and the time it will take to machine.
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N = v v // (pi*Do) = (240 * 12) / (pi * 1.0) = 916 rpm
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Feedrate: f f = 916 * 0.03125 = 28 r = N * f = inches/min MRR ~ v * f * d = d = (240 * 12) * 0.03125 * 0.1 = 9in3/min
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r = 4 / 28 = 0.143min (8.5seconds Tm = L /f (8.5seconds))
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Milling Calculations N N
w
v
f = feed (chip load): inch/tooth (mm/tooth) (SET ON THE MACHINE) • f r = feed rate = inch/min = N * nt * f ( • n t = number of cutter teeth • v = cutting speed (feet/min) (m/min) •
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Milling Calculations N N
w
v
• N N = = rotational speed (RPM) = v / (pi * D D )) (SET ON THE MACHINE) • MRR = w * d * fr
• d = depth of cut • w = width of cut 14
Milling Calculations:
Appro App roac ach h and and Ov Over ertr trav avel el Peripheral or “slab” milling
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Time fo for ma machining: in includes approach distance
• D D = = diameter of cutter
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r For slab milling: Tm = (L + A) / f
• d d = = depth of cut
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Where: A =
• A = approach length
d ( D − d )
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Milling Calculations:
Appro App roac ach h and and Ov Over ertr trav avel el FACE MILLING (CENTERED)
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Time for machining: includes approach and overtravel distance
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For centered face milling: – Tm = (L + 2A) / fr
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Where: A = O = D / 2 D = D = diameter of cutter A = approach length, O = overtravel length
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Milling Calculations:
Appro App roac ach h and and Ov Over ertr trav avel el FACE MILLING (OFFSET)
Time for machining: includes appr ap proa oach ch and ov over ertr trav avel el di dist stan ance ce
D = D = diameter of cutter
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For face milling: Tm = (L + 2A) / fr
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Where: A = O =
A = approach length, O = over ov ertr trav avel el le leng ngth th
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w( D − w)
w = width of cut
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Machining Calculations (example) • We wish to face mill the top of a block of aluminum of aluminum as shown, at a cutting depth of 0.1” We will use a 2” wide face mill with 1.5” 5 cutting inserts. inserts. 9.” • From a handbook: – Feed f = 0.010 (inch/tooth) – Speed v = 350 feet/min
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Machining Calculations (example) • N = v / (p (pii * D) = 350 350*1 *12/ 2/ (p (pi* i*2) 2) = 668 668 RP RPM M • Feed rate = f * n t * N = 0.010 * 5 * 668 = 33inches/min • Ti Time me to ma mach chin ine e = (L + 2A) 2A) / Fee Feed d rat rate e= (9 + 2(D/2)) / 33 = .33minutes
1.5” 9.”
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Machining Calculations (example) • Material removal rate MRR = feedrate * width of cut * depth of cut = 33 * 1.5 * 0.1 = 4.95in3/min 1.5” 9.”
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