Americanmachinist 2108 Tough0101png00000001162

One tough exterior

Jan. 1, 2002
New cutting tool coating makes easy work of hardened materials.

New cutting tool coating makes easy work of hardened materials.

Due to a new coating and special geometries, OSG's Exocarb Max end mills handle depths of cut up to 20% of the tool's diameter.

For materials as hard as 60 Rc, OSG treats its Exocarb VX taps with a TiCN coating.

OSG's Exocarb SH-DRL drills feature a sharp, yet strong, cutting edge for machining parts with 70-Rc hardness ratings.

Most shop owners wince at the thought of milling hardened steels. The tools involved usually cost a little more as compared to standard ones, have shorter lives, and remove smaller amounts of material. However, a new coating, teamed with some special geometries, lengthens tool life and increases depths of cut on materials as hard as 60 Rc.

The coating is TiAlN based, but with some added chemicals. What makes it special is a bombarding process that better adheres the coating to the substrate. The resulting smooth surface reduces the friction coefficient, making tools more wear and heat resistant.

Called Exocarb Max, the coating comes from OSG Tap & Die of Glendale Heights, Ill., and is a variation of the company's existing TiAlN coating. But the new one, because of the adhesion process, is about 5 finer — 15 layers as compared to 18. This further enhances the smoothness of the tool's cutting surface.

Exocarb Max-coated end mills compliment OSG-developed high-efficiency-machining (HEM) techniques, which differ from high-speed machining (HSM).

Of the two techniques, says Jiro Osawa, OSG engineering manager, HEM for hard-milling involves deeper axial depths of cut. With HSM, feedrates and spindle speeds are high, but axial depths of cut are as little as 5% of the cutter's diameter for a ballnose end mill cutting hardened materials. According to Osawa, Exocarb Max-coated end mills, along with HEM techniques, let shops take axial depths of cut up to 20% of the tool's diameter. To support such a cut, he says, requires not only the new coating and HEM but also a strong tool.

OSG's end mills get their strength from a special geometry, one that includes, what the company refers to as, a "spiral gash." This creates a negative rake angle and an ample chip pocket on the cutter. The whole geometry makes for a sharp, yet strong, cutting edge. For even more strength at high feedrates, the endmills have thicker-than-average core diameters.

Taps and drills
In addition to hardmilling, OSG applies its HEM techniques, new coating process, and special geometries to tapping and drilling. The result is its line of Exocarb VX-OT taps for hardened materials up to 60 Rc and Exocarb SH-DRL drills for up to 70 Rc.

Although the coating process on OSG's taps and drills is the same one applied to end mills, the coating itself differs. That's because the new coating is good for non-continuous cutting, such as with an end mill, but unsuitable for continuous-cutting operations, where the cutting edges of the tool are in constant contact with the workpiece material. So for taps and drills, OSG applies a TiCN coating referred to as its V-Coating.

The TiCN coating covers taps comprised of a submicron-grain carbide. Like the Exocarb Max end mills, the taps have sharp, yet durable, cutting edges. Negative rake angles, eccentric reliefs, and thick core diameters make these edges possible.

OSG makes Exocarb SH-DRL drills from the hardest carbide it produces. Since shops drilling 70-Rc material can't increase speed, says Osawa, OSG improves the process by concentrating on the hardness of the drill's substrate and by adding a special drill point.

Again, like on its end mills, OSG uses a spiral gash on the drills. In this case, it eliminates the need for honing.

According to Osawa, carbide drills usually have honed cutting edges to prevent chipping. Because the new drills aren't honed, they have a sharper cutting edge for hardened materials. In addition, their core diameter is thicker and their helix angles are not as steep.

Steeper helix angles, such as 30° or 40°, make for a sharp cutting edge, says Osawa, but one too sharp for hard drilling. So, OSG uses a 12° helix angle on the SHDRL drills.

Diamond-coated tools

Exocarb diamond-coated drills and taps from OSG show little and uniform wear after machining over 100 holes in Al-SiC material at Ceramic Process Systems.

In addition to TiAlN-coated tools, OSG uses its adhesion process to cover tools with an ultrafine-diamond coating. These are the company's Exocarb Diamond end mills, taps, and drills for nonferrous materials.

One shop taking advantage of OSG's diamond-coated drills and taps is Ceramic Process Systems (CPS) in Chartley, Mass. It manufactures a part, made from an AI-SiC material, for an electronic-packaging aerospace application. This material has 63% silicon carbide (by volume), which suspends the SiC particles in an aluminum matrix. The shop found it impossible to machine holes using standard carbide drills and taps, mainly because the abrasive material quickly ruined tools.

To drill and tap, CPS had the portions of the part where holes went cast rich in aluminum. This worked well for high-volume processing, but it limited quick product development because tooling with core pins took longer to build.

Because of the Exocarb coating, along with enhanced geometries, CPS drills and taps over 150 holes in the Al-SiC material. This is quite an improvement considering the shop could barely finish one hole before switching to OSG tools.

"We have tried several CVD coating vendors in the past," says Kevin Fennessy of CPS, "and none of their tools were as successful as OSG's. A common problem with other vendors was peeling or flaking of the diamond coating, but the OSG tool shows uniform wear."

Latest from Cutting Tools

Dmitry Kalinovsky | Dreamstime
Kalinovsky | Dreamstime
Inovatools Eckerle & Ertel
Whether drilling, milling or grinding, application-optimized semi-standard and special tools from Inovatools make many machining operations more productive and efficient.