Hello,
I am designing a CNC machine and plan to cast it using concrete (kind of UHPC or at least a mix with a low water/cement ratio). I would like to ask for your advice.
The travel distances of the machine in the X / Y / Z axes are:
- Metric: 400 mm / 300 mm / 380 mm
- Imperial: 15.75" / 11.81" / 14.96"
Initially, I assumed the heaviest machining scenario I am aiming for is:
- Material: D2 steel (HRB:95|HB:209)
- Tool diameter: 10 mm (0.39")
- Number of cutters: 4
- Cutting speed: 70 m/min (230 sfm)
- DOC: 12 mm (0.47")
- WOC: 0.3 mm (0.012")
- Feed per tooth: 0.1 mm (0.004")
which gives:
- 225 N (50.6 lb) of tangential cutting force
- 1.12 Nm (9.96 in-lb) torque at cutter
- 0.47 kW (0.4 hp) spindle motor
- 94 cm^3/min material removal rate
- 2228 RPM
- 891 mm/min (36 ipm) feed rate
To be sure, in my FEM simulation I used 300 N (67.4 lb) of force applied to the spindle nose instead of 225 N (50.6 lb).
The FEM results show a maximum deflection of:
- 0.032 mm (0.00126") in both the -X and +X direction
- 0.037 mm (0.00146") in both the -Y and +Y direction
My first question is whether those cutting parameters are to ambitious/aggressive for such a small machine.
I have very little experience in machining; all I have done previously was to machine aluminum with a DOC of 1 mm and a WOC of 3 mm in slotting.
Thus, I lack a reference point.
One thing that tells me that it is to ambitious is the material removal rate of 94 cubic centimeters per minute - I would probably be happy having it 10 times slower. However if such a performance could be achieved that would be nice.
The second question is about the consequences of the deflections mentioned above. Could they lead to tool breakage? I'm not worried about the dimensions of the parts since finishing passes will have much lower deflection. Or should I be worried about it?
I was planning to equip the machine with 1.5 kW (2 hp) spindle motor and 8.5 Nm (75 in-lb) steppers with encoders.
I did the calculations but for even heavier machining.
But now I wonder if that might be overkill, given the low rigidity of the machine's body.
I would be grateful for any advice.