SpecialFocus

Jim Bullis, Thermwood Corporation in an interview with IAPD

NC routers are extremely popular among performance plastics fabricators with nearly endless combinations of machines, tooling and configurations that can be tailored to suit most any plastic. Additionally, CNC routers offer high-level precision paired with faster cycle times with proper configurations.

To have success with CNC routers in performance plastics, fabricators must consider machine and router bit selection, part hold-down, maintenance and safety.

Jim Bullis, Vice President of Sales at Thermwood Corporation offers insights from his nearly 30 year-long career in 3/5 axis CNC routers in plastics applications and Large Scale / Large Format 3D Polymer Printers.

CNC Router Selection

“CNC routers are available in many different types, from hobbyist/entry/light-duty to multipurpose to fully automated with a high-level of robot integration to support ‘lights out’ operations,” said Bullis.

When you begin your CNC router selection journey, the internet can be a valuable tool for research. Though with the wide range of machines and configurations available, plus the range of potential end applications, consulting with colleagues in the industry and reputable machine manufacturers will ensure you are setting yourself up for success.

“An industrial CNC router is intended for just that — industry use. As such, it should be more refined in hardware, control OS/HMI interface and manufacturing standards. These will all lend to a higher quality part along with better throughput than what may be expected off an entry-level CNC router,” Bullis explained. “You should also expect a higher level of comprehensive support direct from the factory, the ability to upgrade and to retrofit the machine when desired— features and capabilities not available from entry-level machines.”

When you have researched and selected a router, it is essential that you ensure the machine is properly configured for the best results.

“It’s ideal the CNC router be properly equipped with a programmable/variable speed spindle (≤ 30,000 RPM) along with an automatic tool changer,” Bullis said. “True gantry drive machines, along with high-performance, high-reliability Intelligent Servo Drives Systems enable the broad spectrum of plastics to be machined and router bits to be utilized. Highly coordinated and smooth motion controls provide accuracy without sacrificing speed.”

Tooling selection is largely dependent upon the material being machined and the fabrication end-goal. Each material has a different thickness, hardness and texture that will respond differently to tooling. Just as there are countless options for materials, there are countless options for router bits and coatings.

“That’s a good thing. Competition drives innovation and, as they say, the cream rises to the top,” Bullis commented.

Tooling options range from single, twin and triple flutes to straight, compression and spiral flutes. Selecting the right flute for your job can be the difference between a clean, smooth cut or a rough, uneven finish.

A single flute upward spiral is recommended for trimming/sheet operations and achieves optimal chip extraction; while a two or three flute upward spiral is recommended for finishing.

Carbide tool coatings also further tailor your tooling to your application.

“Coatings to extend the life of a tool are in continuous development,” Bullis said. “The benefit coatings have provided can be substantial. This is especially true when it comes to 3D printing carbon or glass-fiber-filled polymers, such as PESU/PEI/PSU, commonly ran on industrial large-format/large-scale additive manufacturing systems.”

The 3 most common coatings used on carbide tools are:

• Diamond Like Carbon (DLC): coating thickness 1 – 5 microns,
• Polycrystalline Diamond (PCD): coating thickness 2 – 5 microns
• Chemical Vapor Deposition (CVD): coating thickness 5 – 10 microns

The most common coating thickness for DLC coatings is 2 – 4 microns, but the coating can range from 1 – 5 microns. A high-quality surface finish can be achieved when using DLC coatings with the proper machining strategies for part shape and material being machined, however very large parts will require many tool path passes.

“At some point the sharpness of the tool wears and surface quality will continuously degrade to where, if not addressed, it could damage the part,” Bullis said. “An industrial CNC router with an intelligent control system will have the ability to assign a ‘time-in-use’ life to a given tool, monitor the use of the tool and when the ‘life’ expires and automatically exchange the (now) dull tool with a new, sharp tool.”

The DLC coating will not last as long as the CVD coating. The trade-off is that the CVD coating will not produce the same super high surface finish as the PVD or DLC coatings will. CVD will still give a surface finish that, to the naked eye, will look and feel the same as the others, but with specialized measuring devices, surface quality differences can be detected.

“CVD has a coating thickness of 5 – 10 microns and has a slightly rougher surface than PCD. Since CVD is 99% pure diamond, it has the highest hardness and the highest price tag,” Bullis explained. “PCD is cheaper due to its cobalt composition, but the edge may wear faster than desired when used on certain materials. Due to CVD’s pure diamond coating, the edge radius maintains sharpness for a longer period of time.”

“Most any plastic can be machined, although some sheet material will exert stresses throughout the sheet as machining operations are occurring,” Bullis said.

Stress throughout the sheet can lead to a defeated hold-down, making it likely that the router bit and part being machined will be lost. There are ways to overcome these challenges, though with the help of CNC router experts.

To ensure continued success when fabricating performance plastics with CNC routers, proper maintenance of routers and tooling are essential.

“Chose a CNC router that has on board preventative maintenance schedules, can run self-diagnostics and display maintenance video’s when called up,” Bullis recommends.

These integrated maintenance tools will help to prevent late or incorrect maintenance mistakes that could be very costly. Additionally, it is recommended that fabricators partner with CNC router manufacturers that are able to provide upgrades to extend the life of the machine and retrofit packages that allow for new peripheral equipment to be implemented to aid throughput, such as material handlings systems and conveying systems.

“Machine manufacturers that offer upgrades and retrofits may expect indefinite life out of a machine,” Bullis said.

Maintenance for machine tooling is generally straight forward. Typical maintenance in the form of lubrication, air conditioner and vacuum pump filter cleanings, along with general housekeeping should keep your operation running smoothly.

“An onboard preventative maintenance schedule adds another layer to easing maintenance,” Bullis said.

“It’s not uncommon for personnel to leave after a period of time. Replacement operators often do not receive formal training. Or worse, they’re taught bad habits.” Bullis shared. “Chose a CNC router manufacturer that can offer training services to new employees as staff is added, at any point in the future.”

Another tool to assist in training and safety is intelligent control systems for CNC routers that are intuitive, upgradeable and modern.

“Intelligent control systems can take over/manage some of the machine operational processes and notify personnel and action is needed,” Bullis said.

“It’s always best to consult company directives on safety,” continued Bullis. “The operator should wear eye and hearing protection, safety shoes and certainly no loose clothing —respirators and dust collection systems too.”