3/15/2000 | 7 MINUTE READ

Cutting Tools for Powertrain Applications: A Quick Look At Some Recent Developme

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Whether you need to hard turn, precisely ream, run at high speeds, or produce plenty of aluminum parts with few tool changes, there is undoubtedly a product that will meet your specific requirements. Here are some details.


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The tool. Kyon 4400, an alumina/titanium-carbonitride ceramic coated with titanium nitride from Kennametal Inc., Metalworking Systems Div. (Raleigh, NC). All of which means that it is a ceramic with a hard coating for high wear resistance and long tool life. It can be used in place of cubic boron nitride tools.

What's it good for? According to Frank Battaglia, product manager, Kyon 4400 is engineered for hard turning operations of a variety of steels: 1050,1080, D2, D3, A2, A3 among them—above 45 and to the 60 Rockwell hardness vicinity. Parts including gears and carriers. Hardened shafts. Bearings. Some powder metal parts.

The fundamentals. Breaking down the chemistry, he says the substrate is "almost like a typical black ceramic." The substrate has a fine grain structure. This is important from the standpoint of achieving "virtually 100% density" after the powder has been sintered and pressed. The addition of the nitride improves the hot hardness of the tool. The coating is put on with physical vapor deposition (PVD). Battaglia explains that this approach is beneficial in that it provides a compressive stress on the insert. In effect, what happens is something that can be thought of as being akin to shrink wrapping: a shell is placed around the insert, then shrunk so that it compresses around the substrate. One benefit of this is that it helps resist crack formation. (An alternative deposition method used sometimes by cutting tool manufacturers is CVD—chemical vapor deposition. According to Battaglia, that's not used in this case because there is a concern with the increased temperature that's required for CVD: there could be some unwanted effects on the base material or embrittlement as a result. Additionally, he says that there is also a cracking problem that can occur with CVD: although the coating can be uniformly applied to the substrate, the coating cools more quickly than the base material, which can result in cracking.)

The shape. Generally, the geometry consists of simple shapes. Chip formation is not a problem in hard turning. The chips tend to fragment off. They are hard; they don't bend, they snap. It is worth noting, of course, that because this is hard turning, the amount of stock being removed tends to be small (e.g., the depth of cut on a 5120 steel drive gear is 0.005 in.), so the chips are generally fine (as in "particles."). There can be as many as eight cutting edges per insert.

The cutting conditions. "Generally, it's done dry," remarks Battaglia. The reason comes down to shock. Ceramics don't like shock. So if, for example, coolant was being used, and, for whatever reason (Murphy's Law) the coolant flow came to an end, there would be thermal shock. Or the same problem could occur if the tool comes out of the cut and gets struck by a cold blast of coolant.

Failure mode. Generally, it is a matter of tool wear. Since hard turning is meant to replace grinding, the surface finish and tolerance that are being generated are critical. So tool wear can necessitate a tool index or change.

Payback. The return on the investment is found in a consideration of the cost of grinding versus the cost of hard turning. Grinding, for a variety of reasons (e.g., speed of operation; coolant and swarf handling; wheel cost), can be an expensive operation. Hard turning can be faster, done dry, presenting no chip handling problems, and provides greater flexibility from the standpoint of a part modification requiring a different insert (as compared to getting a different grinding wheel).

Precise Reaming

The tool. BIFIX SR80 and SR81 indexable carbide reamers from Carboloy, a Seco Tools company (Detroit, MI). Which are tools that use a blade for cutting that offers two cutting edges; blades are available in three standard grades (H15—uncoated, for all materials requiring a sharp edge; CP20—a TiCN-coated blade applicable to materials other than aluminum; CM—an uncoated cermet optimized for steel). Optionally, they can be obtained in diamond versions.

What's it good for? According to Derek Giles of Carboloy, aluminum transmission valve bodies are a big application area. Cast iron gearbox bushings and bearings are other powertrain-related applications.

The fundamentals. There are three cermet pads on the reamer. Which helps contribute to precision reaming—from the standpoints of tolerance, size, straightness, and surface finish. The hole size tolerance that is provided ranges from 0.0003 to 0.0006 in. The surface finish is on the order of 10 microinch. What's important to note is that Giles argues that compared to other types of reamers, the BIFIX can be setup and dialed in to within millions in "a tenth of the time" of other reamers; "this is designed to be toolroom friendly." The clamping system is patented. A wide array of grades and sizes is available for as standards; there is a set of semi-standard reamer types, diameters, and blades, as well.

The shape. A blade held in a reamer body.

The cutting conditions. Oil or other lubricant is usually used to help with material removal.

Failure mode. It generally isn't breaking. "People rarely break them," notes Giles. Rather, it is a matter of what would be imperceptible flank wear in other operations (e.g., milling). These reamer blades don't wear out; they lose size. Since reaming is a final operation, it is critical that the size is maintained.

Payback. Largely in the area of the ease of setting up the tool for reaming. Time is money.

Faster Is Better

The tool. Two steel-turning grades from Sandvik Coromant (Fair Lawn, NJ), the GC4015 and the GC4035. Both are coated carbide grades: the coatings in both cases are Al203 topped with TiN.

What's it good for? According to Jogendra Saxena, project manager, Automotive Business, GC4015 is a wear-resistant grade for general steel turning applications in up to medium-hardness materials including steel forgings and hardened steels (25-45 HRC). It can perform jobs from roughing to finishing. Automotive applications include a variety of transmission shafts and components. GC4035 is for tougher jobs in steel (shafts, gear blanks), even workpieces that have interruptions; Saxena explains, "If you see chipping on GC4015, then GC4035 could be the answer."

The fundamentals. Key to both grades are the materials. The substrate is produced with what's called the "gradient sintering process." One of the benefits of this process is that various material constituents go to where they are required, such as cobalt being located where needed to improve toughness (e.g., the cutting edge); the cobalt helps prevent chipping, chip fracture thermal cracking, edge line fracture, and chip hammering. The coatings are applied in what's known as a "Medium Temperature" chemical vapor deposition process (MT-CVD). The process is performed at 1,200ºF; the standard CVD process is performed at 1,800ºF. The benefit of the lower heat is that the coating is not only more uniformly applied, but there's better adhesion to the substrate (there isn't a brittle zone between the two), improved wear resistance. The initial coating is Al2O3, which provides heat protection for the substrate; heat protection helps prevent tool failures from such things as cratering, plastic deformation, and flank wear. On top of that is a TiN coating, that not only provides a gold color to the insert, but provides lubricity that helps move the chip past the insert and minimizes the possibilities of cratering and built-up edges.

The shape. Standard insert geometries.

The cutting conditions. Saxena emphasizes the importance of going fast: high rpm, high feedrates. According to Sandvik, calculations indicate that when it comes to cost considerations, cutting speed has 23 times greater impact on cost per part than insert cost, and 37 times more than tool life, which is to say that rather than worrying about the cost of the carbide or trying to keep the tools from wearing won't result in the same kind of savings that boosting the cutting speed can do for a given machining operation. Saxena says that although the grades have good stability so far as coolant use goes, their recommendation is to perform dry machining (the thermal resistance provided by the materials facilitates this).

Failure mode. "If the setup is rigid, then the tools will wear over a period of time," Saxena says.

Payback. Factors including the previously mentioned effect of cutting speed on part cost and the ability to eliminate coolant come into play here.

Value from Diamonds

The tool. DA2200, a polycrystalline diamond (PCD) grade that has nearly the same high strength of cemented carbide from Sumitomo Electric (Mount Prospect, IL).

What's it good for? Wheel turning—both roughing and finishing. Milling—once again, both roughing and finishing—of blocks, cylinder heads, manifolds, transmission cases, bell housings, and other parts. It can also be used in drilling, end milling and reaming applications.

The fundamentals. DA2200 has a ultra-fine grain substrate that helps provide uncharacteristically high-strength and wear- and chipping-resistance. In one test, DA2200 was put up against cemented carbide in face milling an aluminum (Al-12%Si alloy) transmission case; the part geometry has severe interruptions. The PCD tool outlasted the carbide, 400 pieces to 40. Up against another tooling vendor's PCD in a test of face milling an aluminum (Al-7%Si alloy) cylinder head, the tool life was shown to be 1.6 times better. The cutters can be produced with high positive rakes, which contribute to smooth surfaces and reduced burrs. High edge strength means that feed per tooth can be comparatively heavy, so fewer inserts can be used in milling cutters than otherwise would be necessary. And because of the strength, it has applicability in roughing, which is not where PCD products are ordinarily found.

The shape. DA2200 lends itself to a variety of insert geometries for milling, turning, drilling, end milling, and reaming.

The cutting conditions. Wet or dry machining of aluminum can be performed.

Failure mode. Generally, it is wear (not the chipping or breakage more characteristic of PCD tools).

Payback. Long tool life, improved surface finish and reduced burring are all factors that contribute to lower piece-part costs.


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