Routing Polycarbonate Material
Polycarbonate is widely used by thermoformers and sheet fabricators because of its high impact strength and favorable machining characteristics.
Tooling
In routing applications, polycarbonate is generally treated as a soft plastic. O-flute tooling is therefore a strong starting point.
O-flute cutters use a distinctive half-moon flute shape and are available in both single- and double-edge configurations.
High-speed steel versions are commonly used for hand-fed applications, while solid carbide tools are preferred for CNC routing.
High-speed steel O-flutes are generally available in straight-flute configurations. Solid carbide versions are available in both straight and spiral geometries.
Straight, Upcut, and Downcut Geometry
The choice between straight and spiral tooling depends heavily on how the chip needs to be controlled.
Sheet fabrication: Upcut spiral O-flutes can improve chip evacuation from the cutting area.
Figure 1 Single Edge O-Flute Straight61-000P Series
Figure 2 Double Edge O-Flute Straight56-600 Series
Figure 3 Single Edge O-Flute Spiral63-750 Series
Figure 4 Double Edge O-Flute Spiral52-600 Series
Proper tool selection is only one part of a successful routing process. Machine rigidity, fixturing, and CNC programming can have an equally large effect on the finished part.
Rigidity
Rigidity is critical in both hand-fed and CNC routing. This applies to the machine itself as well as the way the workpiece is held.
Machine Rigidity
In hand-fed applications using electric or air routers, machine rigidity depends heavily on the condition of the collet system.
Air routers also require regular bearing and spindle-vane maintenance. Adequate air pressure is necessary to maintain horsepower, and tooling must be properly toleranced for the air-router system.
In CNC routing, properly lubricated slides and drive systems are essential to maintaining feed rate, productivity, and consistent finish.
Preventive maintenance becomes especially important when surface finish is a critical requirement.
Fixture Rigidity
Workholding is equally important. Fixtures should be rigidly constructed and securely mounted to the work surface.
Vacuum supply should be oversized where practical, and mechanical fixtures should be mounted without allowing movement.
On 5-axis fixtures, unsupported edges should be minimized and vacuum distribution should be concentrated near the cutting area.
Rubberized coatings and gasket materials can also be used to increase friction and improve hold-down.
Programming
Once the correct cutter has been selected and the machining setup is rigid, feed rate, spindle speed, and toolpath become the primary considerations.
Chipload
Chipload is the thickness of the chip removed by each cutting edge. It is controlled by feed rate, spindle speed, and the number of cutting edges.
For many polycarbonate applications, an effective starting range for finish is approximately 0.004 to 0.012 inch.
In polycarbonate, maintaining an appropriate chipload helps curl the chip correctly and contributes to a cleaner finished edge.
Cut Direction
Both climb cutting and conventional cutting can be used, but conventional cutting often produces the better finished edge.
The scrap edge should also be inspected. If the scrap side consistently produces the better finish, reversing the toolpath direction may improve the finished part.
Cutter Entry
Direct plunging can be problematic because it gives chips little room to escape.
This can lead to chip wrap, deformation, or melted material at the entry point.
Control Scrap
Scrap should also be controlled during the machining process.
Loose scrap can contribute to part ejection, vibration, poor finish, and cutter breakage.
Conclusion
Polycarbonate is relatively easy to machine when the correct tooling and routing practices are used.
O-flute geometry, rigid fixturing, proper machine maintenance, appropriate chipload, correct cut direction, and controlled cutter entry all contribute to a cleaner and more repeatable finished part.