Materials Spur Innovation
Lighter vehicles chase CAFE fuel standards with lighter, tougher materials
By Jim Lorincz
Materials suppliers to the US automotive industry, for both cars and trucks, carefully watch any news of changes in government-mandated Corporate Average Fuel Economy (CAFE) fuel standards. Every tenth of a point of mpg adds up, requiring vehicle manufacturers to find ways to lighten components and their suppliers to machine them. Lighter powertrains and bodies and chassis increase mpg. The materials of choice, both new and old, include compacted graphite iron (CGI), aluminum alloys, and proven standbys like powder metals (PM). New hybrid and electric vehicles (EV), for example, are seen as promising targets for aluminum extrusions and alloys.
Each of the materials brings its own unique benefits for making components lighter and stronger, but each poses its own special manufacturing characteristics that cutting tool manufacturers are continually challenged to meet for turning, milling, and drilling. Following are materials trends challenging cutting tool manufacturers and their customers:
CGI is lighter and stronger than grey or ductile iron for engine blocks, allowing thinner walls and higher temperatures and pressures in the combustion chamber to produce more power in a compact, lighter engine with less emission pollution. But CGI is highly abrasive to machine.
Aluminum alloys, especially high silicon-content aluminum, and composites are driving developments in PCD diamond-like coatings, diamond-etched inserts, and diamond-extended tools.
Longer warranties by car makers generally equate to tighter tolerances and better finishes especially for moving components, requiring less power to get up to speed faster and better finishes for axles, and bearing surfaces. The first inklings of that consideration were seen in the racing industry where speed is king and light weight and strength are valued.
Wherever the CAFE targets are finally set, and they do seem to change from day to day, the challenge to the cutting tool manufacturers, according to Jeff Bryant, North American Operations manager-GM, MAPAL Inc. (Port Huron, MI), is to go “lighter, stronger, and hold tighter tolerances—all at the same time.” And that’s for materials that are all considered more difficult to machine than grey cast iron or other traditional materials.
Bryant says the CAFE standards for 2012, set at 33.3 mpg (7.05 L/100 km) for cars and 25.4 mpg (9.25 L/100 km) for trucks, and for 2016 at 37.8 mpg (6.22 L/100 km)for cars and 28.8 mpg (8.16 L/100 km) for trucks, “represent quite a challenge. Auto manufacturers are tightening up overall, wanting smoother bores. You can’t have leaky valves any more on transmissions, and they’re looking at valve body control of 12 µm on cars, pushing that down into single digits in the next couple of years, farther than can be reliably measured on the shop floor.” For example, Bryant points out that controlling the casting is critical to meeting the part’s tolerance. “In other words, I can’t have a core hole that has a 30-µm tolerance without prequalifying that hole at some point.”
For drilling smaller-diameter holes, the majority of holes that are made, Mapal has developed a tool with a PCD head adhered on a solid-carbide tool. “Yes, it’s more expensive,” says Bryant, adding “a traditional tool that might cost $200 moves into the $1000 range. But when you’re drilling 29 holes per transmission case, for example, maximum production of 800 parts, or 25–30,000 holes per day, means the machine has to be shut down every day to change-out tools. In testing with the PCD tool, we’ve doubled the life of the tool so that the tool change is needed every two days, and we’re pretty sure that the next-generation tool will do 2000–5000 parts. Our target is to make a tool change only once a week. It all comes down to CPU [cost per unit] and with the doubling the life of the tool to extend the time needed for tool change, the CPU will be much lower.”
Don Graham and Chad Miller of Seco Cutting Tools Inc. (Troy, MI) point to several trends in the automotive industry: “As the government continues to squeeze producers of engines on emissions, CGI is recognized for its ability to withstand high pressures and temperatures in the combustion chamber, which is needed to eliminate emission pollution and makes it a good candidate to replace grey iron. Also, the electric car industry is using lighter-weight alloys, both for mpg, and on a smaller scale for components turbochargers, and crank and camshafts. The idea is that the lighter the material, the faster they can rev up. Think about a racing engine. They want the engine up to speed right now. With steel or cast-iron parts that have to spin, it takes a while for the rpms to get up.”
One material cited by Messrs Graham and Miller is titanium aluminide, an alloy developed by the aerospace industry in the 1970s that the industry walked away from because of cost and machinability. “The racing industry picked it up and uses it for push rods, valve stems, components, and it may make a comeback in automotive applications, although difficulty of machining will have to be addressed. Titanium aluminide has been talked about being used for turbochargers because of its ability to take high temperatures. It’s good in every aspect except machinability and cost. Sometimes they are called gamma titanium alloys.”
Graham illustrates the difficulty of machining different materials using a machinability rating: “One very soft steel, B1112 is the baseline, or 100 on the machinability rating scale. Anything easier to machine has a higher number; harder to machine, a lower number. Ductile iron might be 50–60, Inconel 718 would be a 15 or so, and titanium aluminide would have a rating of 5. If you use one insert, one drill, or one broach to make a part out of B1112 steel, you use two inserts for ductile iron, seven inserts for Inconel 718, and 20 inserts for titanium aluminide to make that same part.”
Seco Tools continues to position itself at the forefront of coating technology. “We’re always looking for ways to improve the integrity of micrograin carbide,” says Graham. “One example is our ability to coat with very thin, very hard, alternating layers of titanium aluminum nitride and titanium silicon nitride to improve integrity and cutting edge. These layers are just a few atoms thick on top of a substrate that has 2000 Vickers hardness, a 20% improvement.” Seco’s PVD-coated TH 1000 grade features the thin alternating layers for turning applications, and its CVD-coated TH 1500 features Duratomic coating. “We’re working at the atomic level on these coatings, and it won’t be long before everybody else is, too,” says Graham.
According to Rich Maton of Sumitomo Electric Carbide, “One of the biggest things we see, especially in the European markets is the use of CGI, which is lighter but more abrasive than ductile/nodular irons. BNS 800 is a solid CBN and BN 700 (tipped BN) are intended for turning and milling more-difficult-to-machine materials like CGI for engine blocks. For PM parts, CBN BN 7500 is used for turning shafts and gears. For aluminum, carbon fiber, and plastics parts, which we are seeing more of, DA1000 PCD tools are used for turning, drilling, and milling, especially for engine blocks and wheels. Aurora-coated drills, which are diamond-like carbon-coated, are intended for drilling on engine blocks and wheels. For bearing steel, Sumitomo’s coated CBN grades, including BNC100, BNC160, BNC200, and BNC300 are used for bearing races and similar applications.
“We’re starting to see aluminum blocks and aluminum-type applications where we would use DA 1000. These applications are quite different and range from machining aluminum to machining bronze or copper bushings, carbon fibers, those types of materials that are typically found in race cars. DA 800 can be used for cylinder bores, as well as hardened parts,” says Maton.
For grooving processes like aluminum wheels, for example, manufacturers want tooling with inserts that won’t move in the pocket. This is especially important as profiling passes are made, says Matt Schmitz of Iscar Metals Inc. (Arlington, TX), “so that the insert won’t draw out of the pocket and send a wheel flying. A new technique that is being used with PCD inserts is to produce a chipformer on the PCD using a laser for better chip control, so that aluminum wheels won’t be scratched or marred by long chips common to aluminum machining.”
Hassan Narasimhan, Iscar Metals’ national product manager-indexable milling, outlines a strategy for milling CGI at lower surface speeds because of its abrasiveness. “Our strategy is to reduce surface feet and use a cutter that has more flutes. CGI with more than 1–2% titanium reduces tool life dramatically. One solution is found in using a cutter with more flutes, as many as 22 flutes, to help increase feed rate and reduce cycle time.”
For aluminum alloys with high-silicon content, as high as 8%, or even 12%, Narasimhan says an uncoated insert typically used for aluminum machining will wear out quickly. “For applications where long tool life is desired, we recommend and use CVD diamond-coated inserts. Traditionally, tools with one PCD corner have been used. With this technology, we can coat pure CVD diamond on all of the cutting edges of the insert. For general roughing, the CVD diamond coating requires a specialized preparation of the carbide substrate, and it does offer a cost-effective coating for machining engine blocks.”
Chris Wills of Mitsubishi Materials USA Corp. (Fountain Valley, CA) says, “The automotive industry is held to a higher standard today, and cars are built so much better because of the alloys that are used. When you’re talking about engine parts for automotive, we’re normally talking about tooling for cylinder heads, cylinder blocks, crankshafts, camshafts, and connecting rods. We’ve developed a new grade MB4020 with a grain size of CBN with a higher shear angle via an edge preparation for machining PM metals, which are used on many engine parts, including pulleys, timing pulleys, and gears among others. Today, there is more CBN being used in milling machines, though turning is still the mainstay application volume. One important change is in machining valve intake and exhaust valve seats, which have different heat characteristics. PM cylinder liners are pressed into the lighter aluminum engine block, requiring machining of the two metals as part of the engine block using special holders but standard inserts.”
Troy Stashi, automotive industry and application specialist at Sandvik Coromant (Fair Lawn, NJ), says that in addition to stronger versions of cast iron and aluminum, “the use of composites is growing exponentially. The auto companies are doing R&D to manufacture engine blocks and different powertrain components out of basic composite materials, which are extremely abrasive and require different tools and tool geometries to machine effectively. With that being said, a lot of them are injection molded and there isn’t a lot of machining that has to be done on the composite side, milling, drilling, and some edging. We have a partnership with a company whose main business is tooling for composites. We’re developing diamond-vaned and diamond-coated tools, including drills and reamers that are designed specifically for fiber materials. When you drill a hole, you don’t get a lot of break-out on the back side. Right now, composites are being used for intake manifolds, door panels, and some companies are starting to produce structural pieces inside the doors and front frame.”
Sandvik Coromant is developing a full line of tools for the automotive industry in the next couple of years. “The technology in the auto industry is growing faster than any other market, and we are able to provide low-cost process capabilities and the engineering resources to be a true partner to develop the lowest cost per unit,” says Stashi. “The automotive industry has seen a big reduction in its engineering staffs. We are an engineering-based company, and we have the resources to provide solutions developed on the same flexible CNC machining centers the auto industry now uses.”
“The Detroit 3 and Japanese 3 are talking about light weight to get more power out of higher operating temperatures in the combustion chamber,” explains Miyuki Kato of OSG Tap and Die Inc. (Glendale Heights, IL). “Everything including blocks, heads, cranks, camshafts, and connecting rods has to operate in conditions of higher temperature and pressure. All powertrain manufacturers, and their machining-center suppliers, are going to MQL [minimum quantity lubrication], especially on crank lines and also for some use on CGI blocks.”
Kato says that the challenge to tooling companies is to work harder to achieve better CPU. “It makes us put a lot more effort into R&D for our drilling and tapping products. For example, the Mega Muscle drill with MQL can achieve cutting speeds of 100 m/min. Mega Muscle drill is a three-flute drill that is designed to drill at feed rates 1.5–2× faster than two-flute drills on rigid machines. “If the machine isn’t capable of feeding fast enough, the user can run at his usual feeds and speeds and improve the quality of finish and double the tool life,” Kato points out.
OSG’s WD1 coating for taps and drills is chrome-based and harder than TiAlN, specifically developed to resist the higher oxidation temperatures presented by difficult-to-machine materials. For applications like crankpin holes where deep holes are typically gundrilled, OSG has developed its super-long drills, EXOCARB-WDO-GDXL, capable of drilling 20–30×D, up to 40–50×D. “These drills can be used on regular machines, but do require a pilot hole. With a gundrill, the maximum you can feed is 1% of diameter per revolution. With our super-long drills, you can feed 2–6% of diameter.”
Kato points out that roll-form tapping is becoming more accepted by all powertrain manufacturers. “There aren’t any chips to contend with, and with our S-XPF Form Taps, tapping can be done about 50% faster. Form taps don’t have flutes, just small oil grooves and are consequently much stronger, and increasingly are being adopted for block, head, and other powertrain applications,” Kato explains.
According to Pat Labunski, manager proposal engineering, Ingersoll Cutting Tools (Rockford, IL), CGI is being used in thin-walled applications to reduce weight and is material that has a composition able to withstand higher compression ratios required of today’s engines. “Near-net shape casting has helped make CGI a more attractive and practical material for both gas and diesel engine blocks. Less material has to be machined off near-net shape castings, but with that comes thinner cross sections, and that’s where we see issues for conventional negative-style cutting tool geometries. Walls are less than a ¼" (6.35 mm) and some flanges getting down to 0.150" (3.8 mm) aren’t uncommon. Advancements in positive insert geometries, coating technology, and carbide upgrades have made it more cost-effective than in the past.”
Labunski points to a continuing trend toward PCD tooling and PCD guide-pad tooling in machining aluminum alloys. Applications include a wide variety of components in cylinder heads for milling, suspension components, steering knuckles, and manifold transmission cases. “For PCD use on aluminum and bimetal, we have developed a laser technique for putting a chipbreaker into the PCD intended to minimize edge build-up. It solves a lot of the issues with BUE, which can start to deteriorate the machined surface. The tool may be cutting to size, but the surface finish starts to deteriorate, affecting tool life and part quality.”
Mark Blosser, manager of solutions, Komet of America Inc. (Schaumberg, IL) sees increasing use of magnesium for transmission and suspension components and CGI for engine blocks and cylinder heads. “The trend is toward smaller engines that put out the same amount of horsepower, which leads in the direction of CGI. CGI, which is much stronger, allows weight reduction by reducing the wall thickness between the cylinders.” CGI is also being explored for other components like power steering pumps, not just for blocks and heads.
For boring, reaming, and tapping, principally with carbide tools, Komet has developed boring-specific inserts to be more aggressive with the feed rate at the lower sfm range for CGI. For aluminum alloys and composites, Komet has just purchased a European company that allows it to produce PCD tools with coatings down to 1-µm thickness to maintain a sharp cutting edge. “The thin diamond coating is the secret to keeping the edge as sharp as possible when machining aluminum alloys, Blosser concludes.”
As part of its continued global expansion, earlier this year, Emuge Corp. (West Boylston, MA) had a introduced a new line of High Performance JIS Taps for tapping applications at companies manufacturing products with Japanese-specified standards. The new Emuge JIS Line includes a selection of taps and cold-forming taps. Shank diameter and square dimensions are in accordance with Japanese standards, and all Emuge JIS taps are uniquely designed to produce threads with a JIS Class 2 tolerance.
“As part of our continued global expansion, Emuge wants to recognize and offer key standards, such as the unique specifications for Japanese automotive manufacturing. Manufacturers who need to produce threads according to Japanese standards now have another choice for taps,” explains Peter Matysiak, president. “To further support this expansion and provide information for manufacturers located in Japan, Emuge has opened a branch office in Yokohama City, Japan.”
The new high-quality Emuge JIS Taps include a variety of geometries and styles that will produce threads in materials ranging from steels, stainless, cast and nonferrous, to titanium and titanium alloys, nickel, and nickel-base and cobalt-base alloys. The surface of the taps are treated with titanium carbonitride or titanium nitride coating for a long tool life. For efficient chip evacuation and maximum lubrication, Emuge JIS taps are available with an internal coolant-lubricant supply exiting through the tap or in the flutes. ME
This article was first published in the September 2011 edition of Manufacturing Engineering magazine. Click here for PDF.