Building It Better

ON THE COVER

building it better

Advanced alloys, plastics, and automated controls are speeding the production and raising the quality of manufactured goods.

By Michael Valenti, Senior Editor

A manufacturer that is unable or unwilling to improve its productivity will be left in the dust by its more nimble competitors. The iron law of industry buttresses the search for new ways to speed throughput and enhance finished quality.

Among the strategies that are improving manufacturing in the aluminum and automotive industries—to pick just two at the beginning of the alphabet—are advanced alloys, which can be more easily machined than their predecessors for faster production and longer tool life. There are also high-performance plastics that can be injection molded in a single piece to replace assemblies of several metal parts. Automated controls enhance the precision of what were once manual operations and make them safer.

A slight variation of an industrial material yielded major benefits for Siemens VDO Automotive Inc. of Chatham, Ontario. The company fabricates up to 10,000 automotive emission control valves daily, and does it more efficiently than it did in the past, now that it has switched the steel
alloy of the valve seats.

Steel Speeds Throughput

The valve seats are made by AAA Industries of Detroit. Siemens originally specified Type 416 stainless steel, made by Carpenter Technology Corp. of Reading, Pa., for the valve seats. The metal was easily machined, and possessed the wear, impact, and corrosion resistance required for its automotive job.

The finished seats were staked into cast-iron valve bases. This involved positioning each seat over the circular grooves of the cast-iron base. A multiton hydraulic press used a four-point tool to force the stainless steel seat to flow into the grooves of the base, forming a tight, nonwelded join.

However, Siemens machinists found that the Type 416 stainless steel did not flow properly into the cast-iron bases and caused two problems. After about every 100 staking operations, one of the two pins that support the base would break. Operators needed 20 minutes to stop the staking line and replace the pin. Also, the cast-iron valve bases cracked at times from the pressure applied while trying to stake the valve seat in the base.

A metallurgist from Carpenter Technology Corp. discussed the problem with Siemens and suggested switching from Type 416 to No. 5-F, a ferritic stainless steel that is easier to machine than Type 416 and has a hardness of approximately 200 Brinell.

This hydraulic press with staking tool is poised to squeeze a Carpenter No. 5-F stainless steel valve seat into the bottom of a cast iron base.

The alloy consists of a maximum of 0.1 percent carbon, 1 percent manganese, 0.06 percent phosphorus, 1 percent silicon, 13.5 percent chromium, and 0.5 percent nickel. It has a minimum of 0.3 percent sulfur, and the balance is iron.
Siemens conducted successful production trial runs using valve seats made of the new alloy, and found that the 5-F steel flowed much better into the base material during the staking operation. The OEM changed its specifications for the part so that AAA could make the switch.

AAA Industries in Detroit is using a Davenport multispindle screw machine to drill the tapered internal diameters on the stainless steel valve seats it manufactures for Siemens VDO Automotive Inc. of Chatham, Ontario.

AAA fashioned the valve seats on a Davenport multispindle screw machine. The valve seats typically measured a half-inch long by a half-inch wide.

Screw machine operators formed the valve seats, drilled their tapered internal diameters for the valve heads, and cut the parts to length before sending them to a chamfering machine. Because of its greater machinability, the No. 5-F stainless valve seats had a 30 micro finish, twice as smooth as the 60 micro finish obtained by the Type 416 valve seats. A better surface finish enhanced the seal between the valve seat and valve base, and thus the entire valve's performance.

In addition, doubling surface finish quality also doubled AAA's tool life, from daily replacement to every two days of service.

Plastic Simplifies Assembly

Replacing assembled metal parts with injection-molded plastic components often reduces the number of manufacturing steps and their related costs, as well as the weight of the finished product. For example, DaimlerChrysler reduced the cost of the fuel rails on its 2.7-liter V6 engines by 30 percent when it switched from steel to Fortron 1140L4 linear polyphenylene sulfide plastic, or PPS. The automaker earned most of those savings by consolidating seven separate components that made up its steel fuel rails into a single plastic component. The substitution also cut the weight of the rails by 25 percent.

DaimlerChrysler first incorporated the new fuel rails
on the engines powering its 2001 model year LH series
Intrepid and Concorde, and JR series Stratus and Sebring sedans. The rails are 10.5 inches, or almost 270 mm, long, and a half-inch, or 12.7 mm, in diameter. They have a wall thickness of 2.5 mm, about a tenth of an inch.

The 416 stainless valve seats caused broken pins (center) on support bases (left) when staked in place by the four-point staking tool (right).

Each rail feeds gasoline to three cylinders. Fuel is sent to the rail through a stainless steel tube attached to the car's fuel line. The gas flows through the rail and flows into three injector ports. The cylindrical ports project upward at 0.75 inch and retain the fuel injector at each cylinder. The rail is attached to the intake manifold by means of two brackets.

When the fuel rails were made of steel, they consisted of a tubular body, to which three injector ports, two brackets, and an end cap were added. This entailed forming, brazing, flushing, and plating the rail's body. Machinists also had to stamp and form the ports and brackets before welding and brazing them to the body.

These numerous metalworking steps were eliminated by the PPS rail, which is injection molded and then deflashed inside and out by shot blasting, according to Mark Cerny, engineering supervisor in premium vehicle powertrain adaptation at DaimlerChrysler.

The PPS used in the fuel rails is made by Fortron Industries, a joint venture formed by Kureha Chemical Industry Co. Ltd. of Tokyo and Ticona, the Summit, N.J., technical polymers business of Celanese AG of Frankfurt, Germany.

DaimlerChrysler reduced the cost of fuel rails on its V6 engines 30 percent by injection molding them out of Fortron PPS plastic, rather than assembling them from metal parts.

Cerny said that DaimlerChrysler chose Fortron PPS because it has a track record in automobile engine and fuel line applications, in which the material replaced steel. "We also considered polyphthalamide and nylon, but PPS offered better dimensional stability in this part. That is exceptionally important, since the injectors must line up precisely with the engine cylinders," explained Cerny, who added that PPS also offered greater resistance to fuel permeation and more fuel flexibility than nylon. DaimlerChrysler is planning to introduce a flexible fuel vehicle with this fuel rail in the near future.

Branched PPS and a phenolic thermoset were other material candidates for the fuel rail project that were passed over because of their greater tendency to brittleness compared with linear PPS, according to Cerny.

Passing Grueling Tests

Like any new component, the Fortron PPS fuel rails were subjected to a grueling round of laboratory bench and field tests before earning a spot under the hood. The rails were pressure cycled at three times the normal service pressure of 58 psi, at temperatures ranging from well below zero to more than 200°F.

Before being field tested, the plastic rail had to pass bending fatigue, vibration, and impact tests, as well as prove chemically resistant to different fuel blends, transmission fluid, brake fluid, spray solvents, and battery acid. DaimlerChrysler tested the Fortron PPS fuel rails in more than 100 vehicles of its internal fleet over the course of 18 months. Standard part testing usually involves fewer than 30 vehicles. Because the fuel rail is a critical safety and emissions component, the automaker wanted to ensure the effectiveness of the plastic part by conducting additional testing.

The fuel rail molds were originally developed by Dana Corp. of Toledo, Ohio, under contract to Bosch USA of Farmington Hills, Mich. Bosch adds the injectors and supplies the finished rails to DaimlerChrysler.

The Dana engineers equipped the mold for the main rail body with a floating core pin because the body's far end is closed. This involved tightly mating the core pin and the sliding pins that project through the injector ports during molding to minimize flash, according to Dan Kreiman, an account manager and previously a product engineer at Dana.

Kreiman said that making the undercut for the O-ring in the stuffer pack where the metal fuel tube enters the rail was another exacting molding challenge. Other intricate areas were the corners around the mounting brackets and the quick-connect area at the open end. "We used long-term tooling maintenance, including closely monitoring the tool vents that direct the gases and molten plastic, to ensure the mold would be filled," Kreiman explained.

Ticona engineers worked closely with the Dana design team on the fuel rail project. For example, they performed finite element analyses to determine the appropriate wall thickness of the new rails. Ticona conducted mold flow analyses and made prototypes for trials at its Application Development Center in Auburn Hills, Mich., to aid Dana's tooling design. Once production began, Ticona helped Dana optimize fabrication.

Multi-Plastics Inc. of Saegertown, Pa., began molding the fuel rails during the third quarter of 2001. The Pennsylvania plastics manufacturer gives Dana the plastic components. Dana assembles them with a steel crossover to make a three-quarter plastic/one-quarter steel hybrid component that Bosch completes for DaimlerChrysler.

Multi-Plastics pays particular attention to the seating of the injector port pins and the floating core pin in the mold. It also regularly measures the area around the O-ring undercut to monitor the integrity of the molding tool, according to Chuck Johnston, the operations manager. Johnston said his company also frequently cleans the injection-molding tools it uses to make the fuel rails in order to minimize flash from cropping up near the injector ports and the sealing surfaces within the tube core.

According to Cerny at DaimlerChrysler, "I'd like to change a lot of our fuel rails to plastic, but only if the right conditions exist for the switch from steel. For example, on four-cylinder vehicles, the fuel rails are located in front of the engine and are thus too exposed in case of an impact. But if an intake manifold protects the fuel rails, it should be possible to use plastic fuel rails in other sedans, and some trucks and Jeeps as well."

The high cost of tooling up to make plastic fuel rails is a barrier to their use, at least in established model lines. "However, the tooling cost might be more acceptable when the company introduces a new engine or vehicle design," Cerny said.

Kreiman noted that "it's more challenging to engineer plastics for automotive fuel systems because steel is more familiar to the auto industry," but suggested this may change as plastic fuel rails become better known. "Dana has had discussions with Bosch in Germany on European plastic fuel rail programs," he said.

Automating Aluminum Tapping

Advances in instrumentation and control technologies are enabling manufacturers to automate more and more operations, with increases in efficiency and productivity beyond human limits. Ormet Aluminum Mill Products Corp. in Wheeling, W.Va., recently upgraded the strip casting furnace operations at its coated aluminum and foil aluminum facility in Jackson, Mich., this way.

A strip casting furnace at Jackson already saved time compared to scalping and hot rolling processes, but company engineers believed they could do better in reducing metal waste and improving the uniformity of their aluminum casting. Their plan involved stepping up the flow rates of molten aluminum from Ormet's 60,000-pound-capacity gravity furnace to the company's continuous sheet caster.

Previously, workers adjusted a tap rod manually to control the discharge of molten aluminum from the furnace into the casting line. The arrangement was inefficient, and because the workers stood close to the molten metal, it posed a safety hazard.

Ormet contacted LMI Selcom of Detroit, a manufacturer of laser sensors, for a solution. LMI Selcom provided its gravity furnace tapout actuator combined with its SLS-5000 noncontact laser sensor for control of the mold and launder—that is, the channel that guides molten aluminum.

An air-cooled housing protects the SLS-5000 laser sensor from the intense heat it is exposed to one foot above the aluminum furnace's tapout box.

The actuator controls the rod in a furnace tap hole by means of an electric motor, thereby controlling the flow rate of the aluminum. Regulating the flow rate also reduces metal oscillation during casting, to minimize metal tension and cracking.

In case of emergency power loss or electric motor malfunction, LMI Selcom equips its automatic drive actuator with a pneumatic closing cylinder and pressurized accumulator tank to swiftly close the control rod.

The SLS-5000 laser sensor is mounted about one foot above the tapout box. It is enclosed in an air-cooled housing that protects the sensor from the intense heat. The instrument's diode emits a 50-kilohertz pulsed laser beam that contacts the surface of the molten metal and returns to the sensor. An on-board microprocessor uses triangulation to calculate the flow rate of the aluminum based on the reflected pulses of light.

An advantage of using a pulsed laser light over a continuous laser beam is that the intermittent beam adjusts for ambient light, according to Mike Snow, an LMI Selcom spokesman.
The actuator at the Jackson site receives data from the laser sensor and uses it to make the precise adjustments to the electric motor that are needed to ensure the desired flow rate of aluminum.

Although LMI Selcom has combined its tapout actuator and laser sensor three times previously, Snow said his company equipped the Ormet plant's actuator with a stronger electric motor than previous designs used. It is capable of delivering 220 pounds of force rather than 120 pounds. "We beefed up the motor to enhance the safety factor," Snow said.

According to Tim Bishop, senior electrical engineer at the Ormet facility, "Our caster operation is more uniform and our operators are very pleased with the performance of the system. A consistent flow rate has been assured and by eliminating overpours and shortpours, our overall productivity and quality have increased."