At first it might seem that machining fiber-filled composites with hard cutting tools would be a recipe for disaster. Developers of cutting methods and tools for composites face all kinds of problems. A composite's fiber layers can delaminate from the machined surface; the fibers or other hard reinforcements are abrasive and reduce tool life considerably; and the combination of hard and soft materials that make up a composite complicates the best choice of tool and machining parameters.
What do I use then?
Diamond will interact with carbon in ferrous materials, so its use is largely restricted to nonferrous workpieces. Today, the automotive industry is the major user of diamond tools in machining components made of aluminum-silicon alloys--in particular the 300 series of aluminum alloys. Major applications for silicon-containing aluminum materials are in pistons, engine heads, blocks and manifolds, wheels, and transmission parts. Other significant applications for diamond tools are in machining graphite, carbon-carbon (C-C) composites, metal-matrix composites (MMC), and fiber reinforced plastics (FRPs).
Where do I find the tools?
PCD Inserts
Diamond Coated Inserts
What about speeds and feeds?
Speeds and feeds for machining composites with pcd
special thanks to SME for information on machining composites
Thursday, February 21, 2008
Turning Carbon Fiber Composites
Wednesday, January 30, 2008
Disadvantages of Diamond Coated Inserts
Probably the main weakness of thin-film diamond-coated inserts is lack of toughness. CVD diamond films are brittle when deposited on low cobalt substrates. These inserts are not always robust enough to endure high mechanical shock. They are not always the best choice for heavy metal removal and interrupted cutting.
As with most coated inserts, thin-film diamond-coated inserts are "throwaways." They cannot be reground.
Predicting the performance of CVD diamond inserts is still somewhat uncertain. Vagaries in cobalt distribution in the tungsten carbide substrate makes wear difficult to predict. Nevertheless, compared to non-diamond inserts, a tool-life increase of 10 to 50 times is common--depending, of course, on machining conditions and material.
At this time, diamond tools are limited to cutting only non-ferrous materials. However, experiments involving super-cold gases blown into the interface between a steel workpiece and a diamond tool are being conducted with encouraging results. It may be practical to cut ferrous materials with diamond in the near future.
By Chris Koepfer
Anatomy of a Diamond Coated Insert
A carbide insert is made from two main ingredients, carbide and cobalt, which are mixed together in various ratios and sintered. Carbide manufacturers guard their ratios and sintering process details the way chefs protect their recipes.
The carbide used in an insert is granular, although individual grains are very smallmany formulas call for grains in the single-digit micron range. By using different grain sizes specific cutting performance can be selected. For diamond coatings to adhere more firmly to the substrate, a larger grain carbide is usually specified so the surface has some roughness.
Cobalt is the "cement" that bonds the carbide grains. It gives the carbide its cutting characteristics of hardness and toughness.
The mixture of carbide and cobalt is pressed in a mold, giving it the shape of an insert. Chipbreakers and other performance enhancing bumps and valley are formed as part of the molding process. These pressings are then sintered. At high temperature, the cobalt flows around the carbide grains creating a strong and very hard bond.
Tuesday, December 11, 2007
Advantages of Diamond Coated Inserts
Accuracy: The diamond coating is very thin, but very hard, and tools don’t change significantly in size during their life. For instance, the radius on an endmill will change by about 10 microns (0.0004") from when new to the point that it is worn out.
Speed: Diamond tools can typically be run at two to three times the surface speed of carbide tools.
Dry cutting: Diamond tools can often convert an operation from wet to dry machining, providing a significant saving in overall machining costs.
Machining Ferrous Materials with Diamond
Why can't you machine ferrous metals with diamond?
Diamond is unaffected by almost every other chemical or compound in nature. One exception is hot iron. The carbon atoms in diamond will dissolve into the iron, quickly eroding the diamond surface. Iron wheels are used for polishing natural diamond.
