8. Tips for CNC machining Polycarbonate
CNC milling and CNC turning are the two common forms to create precise CNC parts. Below are 7 useful tips to get an accurate component.
8.1 Use the right coolant to keep the frictional heat down
Due to the contentious tool-to-substrate rubbing during CNC machining, there will be heat generated. When drilling deep holes and cuts, there will more more heat. To improve the machined parts’ surface finish and keep the tolerance within limit, the frictional heat shall be reduced by coolants.
There are three types of coolants for plastic machining, air, misting system and flood coolants. For polycarbonate CNC machining, non-aromatic, water-soluble flood coolant is recommended, because they are most suitable for ideal surface finishes and close tolerances.
For plastics CNC machining, Trim 9106CS and Polycut are always suitable.
8.2 Use the right cutter and keep it sharp
To achieve high-quality polycarbonate CNC machining, the right cutter and keeping it sharp is the priority. Use a single-edged carbide(HSS) cutter and choose the right diameter.
Below the table is the cutter diameter suggestion for different PC sheet thickness milling.
PC sheet thickness
8.3 Use the air gun to clear the chips
During polycarbonate milling, there will be chips generated which may leave scratches on the surface, affecting the finish of the machined parts. Always use the air gun or vacuum cleaner to blow the chips away. An effective chip removal mechanism is also important to get high-quality CNC machining of polycarbonate parts.
8.4 Use the correct feed rate and cutting speed
Suitable feed rate and cutting speed are the keys to getting precise polycarbonate CNC parts.
Cutting speed is the feet per minute that the tool bit passes over the workpiece. Feed rate is the rate a milling tool moves through the material being cut. Blunt tools, deep cuts, and a lack of coolants will reduce the feed rate.
Polycarbonate are best routed with lower spindle speeds ranging from 12,000 rpm to 18,000 rpm along with a high feed speed.
Read more about PC milling speed talk here.
Machining Polycarbonate in Practicalmachinist
Machining Polycarbonate in CNCZone
8.5 Minimize chatter
During CNC machining, chatter may occur unexpectedly. Chatter is a vibration where the machine or the workpiece vibrates. Sometimes, it will generate a distinctive loud noise.
The vibration can lead to unsteady contact between the tool and the workpiece, generating irregular cutting forces, and affecting the machining quality and the machined parts’ surface smoothness.
Chatter usually occurs at high cutting speeds, in unstable cutting conditions, or when the tool is worn out. The following are some of the reasons why chatter may occur:
Unstable cutting parameters: Chatter can occur if the cutting speed, feed rate or depth of cut are not set correctly.
Inadequate machine stiffness: Inadequate machine stiffness can cause the machine to vibrate under cutting loads, which in turn can cause chatter.
Tool wear: Tool wear changes the distribution of cutting forces and can cause chatter.
Poor workpiece holding: If the workpiece is not held securely, this can also cause vibration problems.
Effective management and control of chatter is an important task in CNC machining. The following measures are usually taken:
Optimize cutting parameters to ensure they are within reasonable limits.
Use more rigid tools and tool-holding systems.
Regularly inspect and replace worn tools.
Improve the machine tool’s rigidity and stability.
Ensure that the workpiece is clamped securely and firmly.
8.6 Mill in several steps
For a thicker PC sheet, you may have to mill it in several steps to get a clean edge finish. In one go, you can mill 5mm at maximum. To give a cleaner milling edge, always mill against the direction of rotation of the cutter. Mill 10mm in two steps and larger panel thickness in four steps. Reduce the cutter speed at the fourth time to get a better edge finish.
8.7 Annealing Polycarbonate
Polymers like polycarbonate (PC) are susceptible to stress cracking and premature part failure under high temperatures and tensile loads. Therefore, the annealing process is critical if you want quality, precision-machined parts from the original shape.
At ECOREPRAP, the annealing process greatly reduces the possibility of these stresses being caused by the heat generated when processing PC and other polymers. Our machinists use computer-controlled annealing furnaces for the highest quality precision machining.
By following the above 7 tips, you can get polycarbonate CNC milling easily. Some companies machine metals and plastics on the same CNC machines, which has bad outcomes for machined plastics, because the coolant and cutter are different. Plastic parts may develop surface cracks and warp over time due to exposure to metal machine shop fluids.
To get polycarbonate CNC service, be sure to use a facility that produces polymers and metals with different CNC machines.