Milling speed, feed and cut
depth.
Tom Underhill
Week 12
2023.
A three factor, three level Box Behnken design
•
•
•
•
Three factors.
Three levels.
3D cube in ‘factor space’
Take midpoint of each side
plus cube centre.
• (4+1)+ (4+1) + (4+1) tests.
Cut depth
• 15 tests in all.
-1
• Spindle speed is controlled by
HAAS milling machine.
• Feed rate is controlled by
HAAS milling machine.
• Cut depth is controlled by
HAAS milling machine.
0
Spindle speed
1
IF the milling
machine has
enough power.
A three factor, three level Box Behnken design
>> bbdesign(3)
Populated with experimental values
Spindle
speed
Spindle
speed
rpm
Feed rate
Cut Depth
-1
0
1
-1
-1
1
1
-1
-1
1
1
0
0
0
0
0
0
0
-1
1
-1
1
0
0
0
0
-1
-1
1
1
0
0
0
0
0
0
0
-1
1
-1
1
-1
1
-1
1
0
0
0
Feed rate Cut Depth
mm/min mm
400
75
0.5
1200
150
5
2400
300
10
400
75
5
400
300
5
2400
75
5
2400
300
5
400
150
0.5
400
150
10
2400
150
0.5
2400
150
10
1200
75
0.5
1200
75
10
1200
300
0.5
1200
300
10
1200
150
5
1200
150
5
1200
150
5
Milling experiment.
Workshop
manager’s
office
Milling
machine
• Two groups of up to 10 students will go to watch milling in progress.
• About 20 minutes per group.
• Safety boots essential.
• Stay in safe viewing area while machine is running.
Safe
viewing
area
TV
screen
End Milling – controlled and uncontrolled
factors.
•
•
•
•
•
•
•
•
Spindle speed
Note %age milling machine power on digital control unit.
Feed rate
Cut depth
%age of milling machine power capacity
Direction of milling.
Fixtures.
Coolant.
Environment
• Etc. etc.
Actual milling plan.
Machine
Order
Side 1 Speed
1
2400
2
400
3
1200
4
2400
5
1200
6
2400
7
1200
8
1200
Machine
Order
Side 2 Speed
1
400
2
1200
3
400
4
400
5
1200
6
1200
7
2400
Depth
0.5
5
10
5
10
5
0.5
5
Depth
10
5
0.5
5
0.5
5
10
Feed
150
75
300
75
75
300
75
150
Cut No.
ref TU
7
1
12
3
10
4
9
15
Feed
150
150
150
300
300
150
150
Cut No.
ref TU
6
13
5
2
11
14
8
Cut 3:1200 rpm, 10mm depth, 300 mm/min
feed.
Cutter failure (contact with vice)
2
3
1
4
New 4 flute cutter
New 4 flute cutter after cut 3!
Diagnosing the failure.
• Cut depth control failure due to cutter being pulled out of chuck.
Collet chuck – screw tightened
Planned path
Actual path
Diagnosing the failure – flute overload due to
chip load.
CHIP LOAD = Feed rate / (RPM x Number of teeth)
Fx = feed rate per min (mm)
RPM = revolutions per min.
RPM x number of teeth = cuts per minute
mm per minute = mm per cut = chip load
cuts per minute
Actual chip loads
Machine
Order Side
1
1
2
3
4
5
6
7
8
Machine
Order Side
2
1
2
3
4
5
6
7
Speed Depth Feed
2400 0.5
150
400
5
75
1200
10
300
2400
5
75
1200
10
75
2400
5
300
1200 0.5
75
1200
5
150
Speed Depth Feed
400
10
150
1200
5
150
400
0.5
150
400
5
300
1200 0.5
300
1200
5
150
2400
10
150
Cut
No. ref
TU
7
1
12
3
10
4
9
15
Cut
No. ref
TU
6
13
5
2
11
14
8
Chip
load
(mm)
0.016
0.047
0.063
0.008
0.016
0.031
0.016
0.031
0.094
0.031
0.094
0.188
0.063
0.031
0.016
Recommended chip load.
• ITC product catalogue – on learning hub.
Cutter chip load recommendation = 0.09 mm
Our calculated chip load = 0.063mm
I.T.C. 4081 end mill
HAAS calculated chip load.
• Double our calculated chip load.
• Recalculate chip load at double
load.
New settings – increased spindle speed.
Machine
Cut
Order
No. ref
Side 1 Speed Depth Feed TU
1
4800 0.25
75
7
2
800
2.5 37.5
1
3
2400
5
150
12
4
4800 2.5 37.5
3
5
2400
5
37.5
10
6
4800 2.5
150
4
7
2400 0.25 37.5
9
8
2400 2.5
75
15
Machine
Order
Side 2
1
2
3
4
5
6
7
Chip
load
(mm)
0.008
0.023
0.031
0.004
0.008
0.016
0.008
0.016
Cut
No. ref
TU
800
2400
800
800
2400
2400
4800
5
2.5
0.25
2.5
0.25
2.5
5
75
75
75
150
150
75
75
6
13
5
2
11
14
8
0.047
0.016
0.047
0.094
0.031
0.016
0.008