Up milling:-
In up milling, cutter rotates against the direction of table feed.
Chip load on teeth (or uncut chip thickness) increases gradually from zero at the point of engagement to maximum at the point of disengagement.
Here, tooth experience gradual loading as contact starts with a line.
Cutting force is directed upward so it tends to lift off the workpiece from the worktable. This necessitates rigid and expensive fixture for mounting the workpiece.
Thin parts may get distorted due to upward cutting force.
Due to gradual buildup of chip load, heat generation is also high. So there exists a tendency of chip welding with the teeth.
Burr is formed only on unfinished surface, which is subsequently removed in the same pass.
At the starting of engagement, teeth rub with lay or feed marks on the machined surface. Thus surface finish improves.
However, rubbing during engagement results in heat generation and thus work hardening.
No chipping action occurs on teeth. So tool wear rate is quite low.
No backlash eliminator is required.
If the workpiece or cutter material is brittle (such as ceramic), up milling is always preferred.
Surface finish produced in up milling is not so good.
Down Milling :
In down milling, cutter rotates along the direction of table feed.
Chip load on teeth (or uncut chip thickness) decreases gradually from maximum at the point of engagement to zero at disengagement.
Here, tooth experience impact loading because of sudden contact with full depth.
Cutting force is directed downward and tends to press the workpiece, which is advantageous. So cheap fixture can be employed.
It is suitable for milling thin parts.
Here tendency of chip welding is less but chip re-deposition on finished surface occurs frequently, which may degrade quality of finished surface.
Burr is formed at finished surface, which may degrade cut quality.
No such rubbing action takes place.
Chance of work hardening is minimal.
Due to impact loading at engagement, chipping occurs and this may cause notch wear. Thus tool wear rate is high. Even there exists a chance of catastrophic failure of the teeth.
Backlash eliminator is required, especially if the milling machine is an older one.
Down milling is not a good choice if the workpiece or cutter material is brittle.
Usually down milling produces better surface finish as compared to up milling.
Credit:- www.difference.minaprem.com/machining/difference-between-up-milling-and-down-milling/
In up milling, cutter rotates against the direction of table feed.
Chip load on teeth (or uncut chip thickness) increases gradually from zero at the point of engagement to maximum at the point of disengagement.
Here, tooth experience gradual loading as contact starts with a line.
Cutting force is directed upward so it tends to lift off the workpiece from the worktable. This necessitates rigid and expensive fixture for mounting the workpiece.
Thin parts may get distorted due to upward cutting force.
Due to gradual buildup of chip load, heat generation is also high. So there exists a tendency of chip welding with the teeth.
Burr is formed only on unfinished surface, which is subsequently removed in the same pass.
At the starting of engagement, teeth rub with lay or feed marks on the machined surface. Thus surface finish improves.
However, rubbing during engagement results in heat generation and thus work hardening.
No chipping action occurs on teeth. So tool wear rate is quite low.
No backlash eliminator is required.
If the workpiece or cutter material is brittle (such as ceramic), up milling is always preferred.
Surface finish produced in up milling is not so good.
Down Milling :
In down milling, cutter rotates along the direction of table feed.
Chip load on teeth (or uncut chip thickness) decreases gradually from maximum at the point of engagement to zero at disengagement.
Here, tooth experience impact loading because of sudden contact with full depth.
Cutting force is directed downward and tends to press the workpiece, which is advantageous. So cheap fixture can be employed.
It is suitable for milling thin parts.
Here tendency of chip welding is less but chip re-deposition on finished surface occurs frequently, which may degrade quality of finished surface.
Burr is formed at finished surface, which may degrade cut quality.
No such rubbing action takes place.
Chance of work hardening is minimal.
Due to impact loading at engagement, chipping occurs and this may cause notch wear. Thus tool wear rate is high. Even there exists a chance of catastrophic failure of the teeth.
Backlash eliminator is required, especially if the milling machine is an older one.
Down milling is not a good choice if the workpiece or cutter material is brittle.
Usually down milling produces better surface finish as compared to up milling.
Credit:- www.difference.minaprem.com/machining/difference-between-up-milling-and-down-milling/
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