CNC routing is an ideal way to cut our panels.
Polystyrene is an elastic, viscous material. When polystyrene is heated, its viscosity increases. In the process of routing polystyrene, large energies are transferred to the material through the bit and the material inevitably heats up, and part of the material melts and sticks to it.
Melting and sticking of swarf occurs at the moment when the bit enters the sheet along the Z axis. When the bit moves along the XY axis, the temperature begins to decrease and sticking decreases or disappears completely. This effect is used in "slant infeed" mode when the bit enters the material tangentially.
The results will be better if you employ forced cooling of the material using compressed air during the routing process and use single-tooth bits as they better eject swarf and minimise the sticking effect.
Another way to get rid of sticking is to monitor the depth of milling.
The depth of cut should not exceed 2.5-3.5 cutter diameters. This means that a 6mm bit can comfortably mill a polystyrene sheet with a thickness of 15-20 mm.
When choosing processing modes, it is important to take into account how rigidly the workpiece is fastened to the machine, the hardness of the workpiece, the conditions for swarf removal, and cooling. When routing metals, increasing the cutting speed and reducing the feed reduces the resistance of the material being machined and increases tool life. However, this strategy will not work for plastics, as it will lead to increased heat generation. Routing of polymer materials is carried out mainly at high feed rates.
Some general recommendations for routing polymer materials:
Excess heat can be reduced well by removing swarf. When routing plastics, cooling is carried out with compressed air or plain water.
Routing of soft plastics is performed using single-thread cutters with a polished flute for swarf removal.
The spindle speed should be chosen so that the swarf is crumbly.
With up routing, there is less roughness than with down routing.
The surface quality is improved if finishing is performed with an allowance of 0.2-0.5 mm after the workpiece has completely cooled down.
One of the most serious problems with routing is the winding of swarf on the bit. To solve this problem on CNC machines, we recommend that you plunge at a low feed rate and then increase it to the optimum feed rate. When routing grooves, a spiral tool movement is used.
Cutting mode recommendations
| Cutter type | Feed rate, mm | RPM | Cutting depth, mm | Hard/ viscous | Softening point, *C | Comments | | --- | --- | --- | --- | --- | --- | --- | | D6-8 one-way milling bit | 8,000-10,000 | 15,000 | 2-4 | Viscous | 90 | Air cooling recommended |