Routing & Trimming PET
PET, or polyethylene terephthalate, is widely used in thermoforming and is available in several formulations. Tooling, speeds, feeds, and fixturing may need to change depending on the specific grade being machined.
Understanding PET Materials
PET can be supplied as unreinforced material, glass-fiber reinforced material, other reinforced formulations, and PETG.
Each formulation has different machining characteristics and may require different cutting tools, spindle speeds, feed rates, and fixturing methods to optimize edge finish and production rate.
Unreinforced PET and PETG are flexible materials and can flutter during machining if they are not fixtured securely.
V-flute and Z-flute cutters should generally be avoided with PET. PET grades can be susceptible to crack propagation, and these geometries can increase the likelihood of cracking during machining.
CNC Router Tool Selection
PET is commonly used for point-of-purchase displays, drafting templates, window-well covers, beverage centers, automotive accessories, and various transparent covers.
For CNC routing, solid carbide single-edge O-flute router bits are a strong starting choice.
When a rounded edge is required, a solid carbide O-flute edge-rounding tool can be used.
Both tool styles are also available in two-flute configurations. A two-flute version can be tested if the single-flute tool does not provide the desired finish.
Air Router Tooling
When air routers are used to trim or rout unreinforced PET or PETG, high-speed steel O-flute tooling may provide a cost-effective option.
Solid carbide O-flute tools are also suitable for air-router applications across the various PET formulations.
Programming PET on a CNC Router
Programming technique can have a significant effect on production rate, scrap, and finished edge quality.
Use Ramped Entry
Entry into the cut should generally use a ramping motion rather than a direct plunge.
Ramping reduces the abrupt cutting forces and heat associated with straight plunging and can help limit cracking and other entry-related defects.
Keep the Tool Moving Through Corners
Sharp outside or perimeter corners should be programmed with a loop or exit-ramp movement.
This prevents the tool from stopping or dwelling in the corner, where heat buildup can contribute to burning or crack propagation.
Starting Speeds and Feeds
PET should generally be cut as quickly as practical in a single pass once the proper tool and programming method have been established.
After the correct cutting tool has been selected and proper entry and corner programming are in place, optimization largely involves identifying the highest feed rate that still produces the required finish.
Conclusion
Successful PET routing depends on matching tooling and programming to the specific PET formulation.
Secure fixturing is particularly important with flexible PET and PETG, while O-flute geometry helps manage the gummy, tough cutting characteristics found throughout the PET family.
Ramped entry, continuous tool motion through corners, appropriate spindle speed, and aggressive feed rates can help improve finish while reducing heat and crack propagation.