Valves Adapt to a Changing World
Eaton keeps ahead of the game as evolving requirements ensure that manufacturing engine valves is no longer an open and shut case.
By Bruce Morey
Nothing typifies the deceptively difficult task facing most automotive manufacturing engineers than making engine valves. "They basically look like a shiny nail," remarks Steve Havranek, manager for engineering and new programs for Eaton Corp. (Cleveland) at its Kearney, NE, manufacturing facility. However, the simplicity of valves belies the extreme environment they operate in. Creating a tight seal thousands of times per minute, exposed to hot, corrosive exhaust gases, engine valves today must withstand such abuse for well over 100,000 miles just to be competitive, let alone excel.
Manufacturing these "shiny nails" means using precisely engineered materials that are forged and ground to tolerances in the microns, followed by precise heat treating or coating. Some are made of multiple materials. The hottest applications—becoming more common—use valves that are drilled hollow and filled with liquid sodium. With valve design expertise dating to the 1930s, Eaton opened the Kearney plant in 1969 and has pumped out millions of precision pieces since. It currently delivers over 250,000 valves per day. "This is the largest valve plant in the world based on volume," states Havranek. Even as the Kearney plant has met the challenge of delivering durable valves, new challenges keep Eaton’s manufacturing engineers active. These challenges include competitive pressures, the rise of lean manufacturing, and the pressing need for better fuel economy.
Quality, Lean, and Agility
The fact that Kearney is the largest producer of valves may not always be a blessing. One issue is tracking quality of so many pieces. "We measure defects in parts per billion," explains Andy Strong, engineering supervisor at the Kearney plant. "These parts are so critical that if even one problem valve is shipped, it can shut an engine assembly plant down. That is not good for anyone."
Another development is that, unlike the heyday of single-piece mass production when Kearney was built, the automotive industry has embraced the lean revolution. As its automotive customers have adopted just-in-time inventory, large production runs of any single part are a thing of the past. Even though the amount of individual designs—part numbers—remain stable at about 90, some lot sizes have been cut to about 1/10th of what they were in the not-so-distant past. "Our customers are demanding smaller lots because they want to reduce their inventory," explains Strong. "Another factor affecting us is changing designs. Where valve designs remained stable for 10 years in the past, now they last maybe five to eight years, with more engineering change orders mixed in as well," he adds. In a sign of how much activity is going into engines today, the plant also produces more prototype parts than ever, usually in small lots of 50 or 100. These parts are used to verify new valve designs in new or different engine applications. "We do about 50 such jobs a year, much more than in the past."
To adapt to smaller lots and prototype runs, Strong first points out changes they made in moving from high-volume to low-volume lines. "We have lines where multiple machines perform identical operations, say valve-tip grinding," he explains. That was the norm. "We now, however, have lower-volume lines with less identical machines in a group, for example, valve-tip grinding, stem grinding, and seat grinding," he explains. He goes on to note that this move to splitting large lines into smaller, more lean-oriented ones is more the European philosophy. There are advantages to engineers like Strong in Eaton’s global footprint. He reports working with Eaton’s Machine Design and Process Development group that is part of the Valve and Valve Train Headquarters in Turin, Italy, in developing the plans to create nimble, lean-oriented production lines.
Like many other automotive operations, changes like this are not easy. Why? Valve manufacturing is capital intensive. The value of the existing plant needs to be carefully weighed against the value of any change, even as pressures mount. How well have they adapted? "Our changeover times have decreased substantially over the last five years," he states, citing one of the common lean measures for success.
Fuel Economy and Valve Engineering
The other trend pushing on them is the drive for better fuel economy, lower emissions, and the competitive drive for more durable and reliable engines. Automakers are building smaller engines that will increasingly use forced induction such as turbocharging or supercharging, as well as gasoline direct injection to replace port fuel injection. One effect on valve makers is the call for ever tighter tolerances. "It is common for tolerance specifications to be 9 or 10 µm, sometimes less," states Havranek. There is also pressure on ever better process capability. "The norm in production is often a Cpk of 1.0 for any dimension on the print, for Significant Characteristics most customers want 1.33 Cpk," he explains, referring to the process capability index (Cpk.) This is statistical measurement commonly specified in automotive production, derived from measuring identified Significant Characteristics. While the specification numbers are not increasing, what goes into them is becoming more stringent. As engine manufacturers are driving towards higher-quality engines, they are requiring more dimensions to be considered significant and controlled better on their valves—as many as 11 on a single valve, according to Havranek.
Engine makers are also calling for valves to take ever-higher temperatures. Nickel-based alloys have long been the solution to such high-temperature designs. However, with the high cost of nickel, Eaton with a supplier partner developed Crutonite, a material that uses significantly less nickel than traditional high-temperature alloys with comparable strength, wear, and corrosion resistance, according to the company. Another is to use valves with precision-drilled hollow stems filled with sodium to dissipate far more heat than traditional solid valves. To meet increasing demand, the Kearney facility will begin delivering sodium-filled hollow stem valves. Commonly found in aircraft valves, internally-cooled, or sodium-cooled valves are effective at reducing valve temperatures. Eaton developed a laser welding process for high-volume manufacturing of hollow-stem valves with conventional equipment. The new valve design is not limited by size or stem diameter considerations, and offers up to 15% reduction in weight and up to a 65°C decrease in valve operating temperatures, according to the company. Kearney’s experience with hollow-stem valves mirrors the industry’s interest in fuel economy. Kearney delivered such valves in the early 1990s, and is scheduled to again deliver the valves starting in 2012.
Technology Advances and Opportunities
While responding to the changing demands of its customer base is changing how Eaton makes and delivers engine valves, the company is also taking advantage of technical opportunities as well. It may be well-situated to do this. Kearney Valve is largely self-sufficient in supplying its own tooling and engineering expertise.
Valves are typically forged from cut round stock, heat-treated, machined, ground, and finally chrome-coated or nitrided. Two-piece valves are friction-welded. All forge tooling used is cut within the plant. Hundreds of dies are produced each day to pump out more than 250,000 valves. Much of the forging equipment dates in some fashion back to when the original plant was built in 1969, as are many of the grinding machines. "We are experts in centerless grinding operations here with over 100 centerless grinders," remarks Strong.
Though the legacy of this equipment may date back more than 40 years, the manufacturing engineers and tradesmen at Kearney continually adapt it as new technology has evolved to improve it. Since the process and equipment is so unique, Kearney has maintained the expertise to adapt and improve its own equipment. Strong remarks that only on rare occasions is there a need to purchase commercial off-the-shelf equipment that fits their needs. "For example, we recently purchased a valve-seat grinder from a supplier, a machine specifically designed for the task," he notes. More often, however, they find it more advantageous to adapt, modify, or even create their own. This attitude does not strike one as "not invented here." Rather designing and building their own equipment means competitive advantage. It may also reflect the uniqueness of the process itself.
What opportunities exist for the future? Strong is quick to point out improved machining capabilities in the revolution in inexpensive and capable electronics. Servomotors have long replaced original stepper motors in grinding machine movements, for example, improving cycle time and quality. Automating the forging equipment is perhaps the most exciting advance. Taking advantage of this continuing electronics revolution, the Kearney team rebuilt about half of its existing presses using laser sensors, actuators, and computers. This both decreases cycle time and precisely controls the forging process. "This gives us enormous competitive advantage," says Havranek.
Another key growth area for electronics is in quality control. Here, Strong points to digital cameras as an especially useful tool. "Cameras are getting close to being micron-level inspection tools," he says, predicting that they will continue to improve even as cost comes down. The versatility of cameras is allowing them to think beyond simple metrology checks used to replace or enhance simpler gauges. One example is to use cameras to detect defects of characters forged onto faces of valves. These characters are used in identifying valves as exhaust or intake in the assembly process. In one example, if a D stamped onto the face looked more like an O, it was an indicator of problems in the forging process. "We use 18 different vision cameras in the plant today, but with the continuing improvements in cameras, it is hard to predict just how much more we will use them," he explains.
The Kearney plant was originally built not only to provide another source of engine valves, but also to develop a new concept in workforce and management relationships. Known as the Kearney philosophy, it started with 100 employees and avoided both unions and time clocks. It has grown to over 400 employees today, and the plant manager, R. Wayne Brantley, can point to impressive delivery statistics, such as 297 consecutive months without a customer disruption. "The challenge for us is to continue to anticipate customer needs and focus our investments to meet or exceed their expectations," he says." That is why programs like the new hollow-stem valve are going to be so important for us."
This article was first published in the 2011-2012 edition of the Motorized Vehicle Manufacturing Yearbook.