Extending PCD to tuned cutting-tool geometries

  • 07-Aug-2009 08:56 EDT
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Veined PCD, made by sintering PCD into the carbide tool blank, yields more complex shapes. MegaDiamond

A potential drawback to traditional use of polycrystalline diamond (PCD) in cutting tools is that flat wafers are cut and brazed to the tool, limiting cutting-edge geometries. Not only that, the braze joint is close to the hot cutting surface and prone to failure, according to Scott Horman Product Engineering Manager for MegaDiamond.

One solution is to produce carbide tool blanks for routers and drills with complex geometries formed or pocketed into them. Diamond powder is filled into the pockets and sintered into PCD. Once fluted and sharpened, these hybrid tool blanks become complex-geometry cutting tools.

“A key point with these tools is that the braze joint is farther away from the cutting surface than with traditional PCD-edged tools,” reducing failures due to joint failure, said Horman.

MegaDiamond provides semi-finished tool blanks to partner companies who then flute and sharpen the tools to their finished geometry. These tools cost more than other solutions—sometimes many times more. The cost per part is likely to pencil out when the tool proves to cut faster and longer in a high volume operation. Precorp is another company that provides tool blanks for veined PCD tools.

Besides providing coated carbide and PCD-tipped tools, Unimerco is an end-supplier of veined PCD tools. Combining superior wear characteristics with tuned geometry provides the ultimate in both worlds—as long as the machine running the tool is rigid enough. In one application involving a stack of aluminum and carbon-fiber-reinforced plastics (CFRP), Unimerco provided a drill for combined drilling and countersinking in one operation using a veined PCD tool. The CFRP was 6.35 mm thick on aluminum whose thickness ranged from 6 to 16 mm. The customer demanded no exit burs and no delamination in addition to an accuracy to the H11 tolerance specification, which requires holes no larger than 75 micron from nominal diameter, and no smaller (0.0 micron) than nominal diameter. Tests showed a Cpk of just less than 4.0 against a requirement of 1.33. The company’s one-shot method replaced three drilling operations, delivering an 83% lower cost per hole despite the higher cost of the drill itself.

Jim Stead, Business Development Manager for Unimerco, is unequivocal about the future of PCD tools. “PCD can provide up to more than 30 times longer tool life over even our coated carbide tools. While the use of carbide is increasing [to meet increasing requirements for composites], the use of PCD tools of late is increasing even more. That trend is not going to change. The use of PCD tools is going to increase the most rapidly.”

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