NEW PRODUCTION TECHNOLOGY MAKES TITANIUM ATTRACTIVE TO AUTOMAKERS.
The 2001 model Chevrolet Corvette Z06. One of the most advanced cars in production also sports the first mass-produced titanium exhaust systems.
For decades, titanium's strength and its immunity to corrosion have made it attractive to the automotive world. But cost, both in materials and processing, kept titanium off the road. Fortunately, new production techniques have overcome the hurdles, and one of the first cars to benefit will be the 2001 Chevrolet Corvette Z06.
The new Corvette will sport the first mass-produced titanium exhaust system developed by Titanium Metals Corp. (Timet), Morgantown, Pa., and Arvin Exhaust, Farmington Hills, Mich.
This exhaust system stems from Chevrolet's desire to increase the Corvette's horsepower-to-weight ratio. The titanium system is 18 lb. lighter than the previous year's exhaust, making it the single greatest area of weight reduction between the 2000 and 2001 models. The result of this weight reduction is a car that accelerates faster, handles better, and gets more miles to the gallon than just a year before.
In 1994, Timet developed a strategy to establish titanium as an accepted material for the passenger automobile industry, but that plan wasn't without its hurdles. The largest obstacle was bridging the gap between the company's aerospace and specialty metal orientation and its desire to be a company that could supply the high-volume, low-cost, auto industry. To accomplish that goal, two things had to happen. One, Timet had to find ways to reduce the cost of titanium, and two, it had to deliver a product that could be processed using existing machines and practices.
Cars cost about $5 per pound when it comes to raw metal," says Kurt Faller, Timet's director of international automotive applications. "Titanium, on the other hand, runs about $7 to $25 per pound depending upon a number of factors."
Those numbers can be deceiving however. Titanium has a lower density but a higher strength than steel. This means only about half as much titanium as steel is needed to produce the same object — including a car exhaust. In addition, the use of thicker steel and expensive corrosion-resistant coatings on exhaust systems have narrowed the price gap between titanium and stainless steel.
Timet used electron-beam melting furnances at its Morgan-town, Pa. facility to reduce production costs. "With electron-beam melting," says Faller, "you can use essentially any input stock. That's different than our premelting where you're generally dealing with virgin material or selected scrap materials. With electron-beam melting, you can utilize all kinds of machine turnings and all the aerospace byproducts. It allows us to get an input product at a much lower cost and, therefore, produce a lower-cost ingot product."
Electron beam melting also offers greater high-volume production efficiencies. "Electron-beam melting doesn't constrain us to a round ingot," Faller explains. "We pour the liquid metal into large molds and evacuate the bottom of the mold, whatever the shape may be. Electron-beam melting also allows the production of 64-in.-wide rectangular slabs, which is unique in the industry. This is a huge savings over the vacuum or premelt round ingot that has to go through a cooling step before you can reheat it to forge it into a flattened product." In addition, having fewer rolling steps slashes production costs.
The use of 64-in. slabs lets the titanium be worked on the same machines using the same processes as steel. "It's a tricky material to work with," says Earl Clip, Arvin product manager, "and trying to come up with an efficient system to create automobile exhaust components was a real discovery process."
What the two companies found during that process was that existing stainless steel stamping, bending, cold forming, and welding equipment could be made to accommodate titanium.
Discovery and development
Timet and Arvin worked on certain conditions of the titanium that allowed them to form it more readily. The two companies also developed new testing methods and computer models to determine the best material gauges and to produce the acoustic tuning of the exhaust system.
At the same time, Timet optimized a lower-cost grade of titanium it calls Timetal as well as a special conditioning process that speeds forming rates and minimizes production losses.
"Timetal," Faller explains, "is a different version of titanium than our usual industrial grade, but that difference is more of a purpose kind of difference than an actual alloy kind of difference."
Timetal can be rolled, formed, and fabricated on available high-volume machinery.
"Expensive new equipment is not required," Faller says. "However, special tooling is a necessity because of the metal's characteristics."
The future appears to hold more possibilities for titanium in the automotive market. Valve springs, shock center rods, rear sway bumper supports, sway-bar fittings, mufflers, door intrusion beams, exhaust pipes, lug nuts and studs, brake-caliper pistons, drive shafts, front bumper supports, connecting rods, wrist pins, retainers, and valves are all possible future applications of the metal.
"The Corvette and titanium are a natural fit — unique, technologically advanced, high performance, and top of the line," says Michael Daniel, Arvin's director of sales and marketing.
"We have limited experience in the automotive market," Faller admits. "This has been an ideal first platform for us. I'm much happier with the company getting into an exhaust application that supports a high-performance sportscar that is a 5,000 to 10,000 cars-per-year application as opposed to a Ford Explorer that may have hundreds of thousands of applications. This gets us ramped up."
Timet anticipates other automakers will convert to titanium exhaust systems on select production cars over the next two years.
Early automotive titanium use
The 2001 Chevrolet Corvette is not General Motors' first use of titanium in a passenger car. The Fire-bird II, a turbine-engined show car featured at the company's 1956 Motorama, had an all-titanium body. The car, styled by Harley Earl, was built to look like a military jet and had air intakes, a tail fin, and a cock-pit-like interior.
For economic reasons, the Firebird II was never put into production and not a single titanium component has been used in United States series automobile production until recently.