Cutters Compress To Effectively Machine Composites
The combined up-cut and down-cut spiral flutes on these cutters compress layered composites to prevent delamination during machining.
Designers are increasingly using carbon fiber reinforced plastic (CFRP) and other composite materials for critical aerospace, automotive and wind turbine components. They appreciate composites because those materials are strong, light and thermally stable. Machinists, on the other hand, sometimes struggle to effectively mill and drill composites because the materials possess atypical properties that require special machining practices.
For example, composites are highly abrasive, which means cutting tool life can be quite low. In addition, the low-thermal-conductivity materials do not produce sizeable chips that carry heat away from a workpiece during machining. Thus, the wrong tool (or a worn one) can cause the material’s resin to burn or melt, damaging what is often a costly workpiece at that stage of production. And because composites consist of layers of fibrous material bound by resin, they are prone to delamination and splintering as they are machined.
Onsrud Cutter, a member of the LMT Group, offers six-flute composites cutting tools with specific geometries and coatings to overcome these machining challenges. The company’s “compression cutters” have intersecting up-cut and down-cut spiral flutes that push individual composite layers together during machining to prevent the layers from separating from each other. This action prevents delamination from occurring at the outermost material layers. It also averts delamination of inner layers, which can be a less noticeable workpiece imperfection.
The tools feature high positive rake angles to deliver sharp, clean cuts that minimize heat to prevent resin from burning. Similarly, a full eccentric relief angle prevents the edges of a tool from rubbing as they cut to reduce machining heat. A diamond film (CVD) coating over a carbide tool substrate offers protection against the wear caused by highly abrasive composites, extending tool life.
The company currently offers these tools as customs, but a standard product line will be available in 2010. This standard line will initially be offered in 3/8- and 1/2-inch-diameter versions, but other sizes are likely to be added.
To make the transition to hard turning, you'll need to switch from carbide to CBN inserts, but that is easier (and more economical) than you might think. It's making the jump to much higher surface speeds that might scare you off. It needn't. Here's why.
One of the most common methods of tapping in use today on CNC machines is 'rigid tapping' or 'synchronous feed tapping.' A rigid tapping cycle synchronizes the machine spindle rotation and feed to match a specific thread pitch. Since the feed into the hole is synchronized, in theory a solid holder without any tension-compression can be used.
The right choices in tooling and technique can optimize the thread turning process.