Definition of cutting parameters
Definition ofcutting
parameters
The first notion to assimilate before attacking your work: machining is a profession in its own right and therefore there is no room for improvisation!
If you are a beginner, you should start by learning the trade through training or by consulting a professional and perfect your experience with hours of machining before claiming to "tickle the hundredth"!
Often users criticize the equipment before questioning themselves and in many cases it is the operator who has to reconsider his way of working according to the work tool he has at his disposal: for example, one will not take the same depths of pass when using a stationary milling machine of 1T and 15Kw or a drill-milling machine of 300Kg and 1500W. This seems obvious but in fact it is not because for the manufacture of certain types of parts against all expectations the second will be more efficient and productive than the first!
In order to get the most out of your machine and cutting tools, here are some basic formulas to determine the cutting parameters directly related to:
- The material you are machining;
- The cutting tool you are using (HSS or carbide);
- The rigidity of the machine and the type (traditional or CNC);
- The machining operation: roughing or finishing;
- The lubrication (ancillary or directly from the tool center).
1/ Spindle rotation frequency
Whether it is a lathe or a milling machine, you have a range (variator) or a choice of speed(s) of rotation of the spindle (gearbox or stepped pulleys). Here is the mathematical formula to determine the rotation frequency:
N = (1000 x Vc) / (¶ x D)
N : rotation frequency in rpm
D : diameter of the workpiece (lathe) or diameter of the milling cutter or cutting tool (milling machine)
¶ : constant : 3.14159
Vc : cutting speed in m/min
La notion de vitesse de coupe (Vc, exprimée en m/min) est extrêmement importante car déterminante dans le calcul de la fréquence de rotation. De plus, cette variable doit être déterminée directement par l’opérateur en fonction des travaux qu’il effectue.
En règle générale, sur machine conventionnelle :
Ebauche ARS :
5<Vc<20 m/min pour les aciers jusqu’à 100 kg/mm², inox, aluminium 7075
20<Vc<45 m/min pour les laitons, bronze UE12, aluminium 2017
Finition en HSS :
20<Vc<45 m/min pour les aciers jusqu’à 100 kg/mm², inox, aluminium 7075
40<Vc<60 m/min pour les laitons, bronze UE12, aluminium 2017
Ebauche au carbure :
60<Vc<150 m/min pour les aciers jusqu’à 100 kg/mm², inox, aluminium 7075
100<Vc<180 m/min pour les laitons, bronze UE12, aluminium 2017
Finition au carbure :
120<Vc<220 m/min pour les aciers jusqu’à 100 kg/mm², inox, aluminium 7075
140<Vc<260 m/min pour les laitons, bronze UE12, aluminium 2017
2/ Feed speed
The feed rate is expressed by the speed of movement of the workpiece (milling) or the slide (turning):
Vf = fz x Z x n
Vf: Feed rate (mm/min in milling and mm/rev in turning)
fz: Chip thickness in mm (depends mainly on the material to be machined, type of tool HSS or carbide)
Z : Number of teeth of the milling cutter (for turning, take value 1)
n : Rotational frequency in rpm
Average fz values:
HSS machining :
0.010 to 0.020 for steels up to 100 kg/mm²
0.010 to 0.015 for brass, bronze UE12, aluminium
Carbide machining :
0.015 to 0.025 for steels up to 100 kg/mm²
0.02 to 0.03 for brass, bronze UE12, aluminium
Remarques :
En général, en opération d’ébauche on utilise :
> des vitesses de coupe (Vc) inférieures à celles utilisées en finition ;
> des vitesses d’avance importantes.
Inversement, pour obtenir des états de surface aux indices de rugosité faible (Ra<0.8), on utilise des vitesses de coupe (Vc) plus élevées en finition et des vitesses d’avance (Vf) plus faibles.
Particular care must always be taken when clamping the workpiece in the vice of the milling machine or in the chuck of the lathe, in order to limit as much as possible the vibration-generating overhangs which are the enemy N°1 for quality machining.
Therefore, when turning, always limit the overhang value of the jaws to 3x the Ø as much as possible.