All in the Family

all in the family

Flexible machining systems give manufacturers a hedge on their bets.

By John DeGaspari, Associate Editor

A trend in machine tools, known as reconfigurable machining systems, has lately caught the attention of some manufacturers who need something that is more flexible than a dedicated line and produces goods faster than a shop of CNC machines.

The lines are called reconfigurable because they consist of modules and, once they are programmed, can be switched quickly to turn out different, but similar pieces from a family of products.

Proponents say that reconfigurable machining systems have carved out a niche between two other alternatives—dedicated transfer lines, which are optimized for producing large volumes of specific parts, and computer numerical control machine tools, which have a high degree of flexibility but are slower to finish products.

Reconfigurable machining systems have been developed for the automotive industry, for instance, as car companies have increasingly outsourced their production to tier one suppliers and demanded price reductions. Automotive parts manufacturers are being squeezed further because new products are introduced more frequently today and product development times are increasingly compressed. This has forced manufacturers to make major investments in lines with little or no security in terms of a program's volume or duration.

Faced with a difficult business environment, some manufacturers see reconfigurable machining systems as a way of adding flexibility to their operations and offsetting large initial investments of machine tools. Reconfigurable machining systems can be implemented gradually to match production requirements and adapted to manufacture a range of parts within a broad family.

The advantage of a dedicated transfer line is that it is optimized to produce a large quantity of a single component. This situation requires a major capital investment up front.
The line must be designed for a predicted peak volume, although the pattern of a product cycle is that it ramps up gradually to the peak period followed by a gradual decline. Even if the predicted peak production volumes are realized, a dedicated line remains underused during ramp-up and ramp-down.

A. Galip Ulsoy, chair of the Department of Mechanical Engineering at the University of Michigan in Ann Arbor and an ASME Fellow, sees the dedicated line as very lean and precise, because it incorporates only the operations necessary for the production of a particular item. "You don't have any operations that you don't need," said Ulsoy, who is also deputy director of the university's Engineering Research Center for Reconfigurable Machining Systems, which is funded by the National Science Foundation.

The linear rail ram unit is mounted in the machining cell. The cell houses three LRUs, each of which performs bolthole machining. The part gets refixtured as it moves from one ram unit to the next.

On the other hand, flexible systems for general-purpose production can be composed of CNC machine tools that are able to perform many different operations. Flexible
lines can machine a wide range of different parts, but are generally limited to much smaller production runs. Flexible systems may be used to catch overflow production,
Ulsoy said.

One study, conducted by the ERC for Reconfigurable Machining Systems in 1996, compared rough machining operations for a V6 cylinder head. The study compared the investment cost of an existing CNC-based machining system with three proposed reconfigurable machining systems, at three different production volumes of 600, 1,200, and 1,800 engine sets per day. It also included information about the cost of a 1,200-part-per-day dedicated transfer line producing the same part.

According to J. Patrick Spicer, who was involved with the project, the reconfigurable machining system produced significant savings compared with the CNC system because it used spindles more efficiently. The reconfigurable machining system cost about 10 percent less than the CNC system at 600 parts per day and 25 percent less at 1,800 parts per day. At 1,200 parts per day, the reconfigurable machining system cost about 25 percent less than the CNC system; the dedicated transfer line cost about 33 percent less than the CNC system and about 15 percent less than the reconfigurable machining system. The study considered only machines and tools, and did not include materials handling.

Reconfigurable machining systems incorporate elements of both dedicated transfer lines and flexible machining centers, according to Ulsoy. "It takes advantage of the efficiency of the dedicated system that is designed around a particular product, and it designs in more flexibility," he said. Reconfigurable machining systems have enough flexibility to produce different designs of similar parts, or parts within a family, enabling manufacturers to respond quickly to changing market conditions.

For example, a dedicated transfer line may produce one specific part at full capacity—say, 450 parts per hour. An alternative approach would be to build three reconfigurable lines, each with an hourly production capacity of 150 parts. As production volumes for one type of product fall off sufficiently, one of the lines can be pulled off the job and retooled for another. The reconfigurable machining strategy assumes that the components being machined, although different from each other, still fall within a common range or family.

Making the Connection

Tri-Way Manufacturing Technologies Corp., a machine tool builder in Windsor, Ontario, recently developed a reconfigurable machining system for Federal-Mogul, also in Windsor, which will use it to make automotive connecting rods. The system was developed under the Industrial Research Assistance Program of the National Research Council of Canada. IRAP also provided financial support and matched Tri-Way with AKG Associates, a Windsor consultant, and with the University of Windsor's Department of Industrial Engineering and Manufacturing Systems.

Until recently, Tri-Way was a unit of Federal-Mogul. At the time, the Tri-Way division comprised two units, a custom machine tool builder and a parts manufacturer. Federal-Mogul sold off the machine tool portion of Tri-Way, which is now developing the reconfigurable tooling, and retained the parts manufacturing division. The company began to develop the line about 18 months ago, when Federal-Mogul was competing for a contract to supply connecting rods for General Motors.

Tri-Way has completed one reconfigurable machining line, which it is now testing. It expects to deliver the system in the first quarter, to become operational by midyear, according to Zoran Jovanovic, Tri-Way's director of operations.

Jeff Wiles, manufacturing engineer at Federal-Mogul's Windsor plant, expects the line to produce 115 pieces per hour net, with an annual output of roughly 690,000 pieces per year at full capacity. As product needs grow beyond that, the job will be moved to a dedicated transfer line that will become free in 2003. The transfer line has an annual production capacity of about 1.8 million parts.

Jovanovic said it would be more economical to retool the existing dedicated transfer line, which will provide efficient, high-volume production at peak demand, than to build a brand new transfer line for a job that won't reach full production for another three years. He said that using the reconfigurable line for interim production lets the company make use of an existing asset—the dedicated transfer line—that would otherwise have become redundant in a couple of years. After the switch is made, the reconfigurable machining system will be available for the next program.

Wiles believes that reconfigurable machining systems is an excellent concept for producing connecting rods—a business in which actual production volumes often fall short of customers' projections.

Tri-Way's reconfigurable machining system consists of five metal-cutting machines, or cells, each about 8 x 10 feet on a single base. Each cell consists of two or three workstations that perform different tasks. A workstation consists of a workholding fixture and linear rail ram unit, or LRU, which is the basic building block of the Tri-Way line. The LRU is the common element of all of the metal-cutting cells. It contains the spindle that holds the tool and is set on a pair of rails that allow it to move forward and back as the workpiece, which is held in the fixturing unit, is being machined. The entire line is composed of a succession of manufacturing cells, each devoted to a particular task that produces the connecting rod.

Ben Chouchaoui, president of Windsor Industrial Development Laboratory in Windsor, Ontario, which performed static and dynamic design analysis of the system for Tri-Way, said that the key advantage of the reconfigurable setup is its flexibility.

The LRU performs two different boring operations on the same tool, as the part changes from one work position to the second position.

Because of its building block design, an LRU can fit a variety of machining cells, he said. Its flexibility lies in the interchangeability among manufacturing units, which may result from potential maintenance or adjustment requirements. He added that the lab intends to add vertical rails to give the LRU a second degree of motion. Another idea is to mount a second spindle within the LRU casing, opening avenues for dual drilling operations. Design through analysis at Windsor Industrial enabled Tri-Way to study machine components before they were built as physical prototypes.

As a result of this design, an LRU can be pulled off one manufacturing line that is ramping down and added to another that is ramping up. Manufacturing cells can be duplicated to add capacity to an existing line as production requirements increase, Chouchaoui said.

LRUs can be retooled to produce different parts within a family. Tri-Way designed the LRUs and fixturing units so they could be altered to accommodate connecting rods for a range of engine sizes.

In developing reconfigurable machining, Tri-Way audited every connecting rod for which the company built machine tools over the previous 10 years, Jovanovic said. "We took the biggest and the smallest, and added 10 millimeters on each side," he said.

The reconfigurable machining system developed by Tri-Way consists of manufacturing cells that perform the required tasks to produce the connecting rods. Certain LRUs perform more than one operation. One machine performs rough grinding of the C-74 steel rod, followed by rough and semi-finish boring operations. The semi-finishing cell performs laser scribing of fracture notches in the crank bore.

Next, the part is moved to the bolt hole operation, where the holes are spot-faced, drilled, reamed, and tapped. The part then goes into a fracturing machine that separates the crank end of the rod into halves. The same station inserts bolts that hold the halves together. The part is sent into a washer and weight sorter, before it is packed and shipped.

The boring machine is an approximately 8-foot-square unit. The line is comprised of five metal-cutting machines performing different tasks.

Reconfigurable manufacturing lines don't use any more workers than a high-speed transfer line, said Jovanovic. The tasks that workers perform may be different, however. "The way we perceive this is to minimize the equipment," compared to a dedicated transfer line, he said. Human operators, who may also perform inspection functions while waiting for the machine to finish its operation, load parts manually. "We have come up with something that is very efficient," he said.

The system is scalable, in that work cells can be duplicated to increase production volume, said Jovanovic. It also can be changed over more easily than a dedicated transfer line to machine different connecting rods. "Lead time to bring a new product into the line is very short—much shorter than traditional lines, and much more economical," he said. "Once we tool up for a part, we can switch back and forth readily."

Introducing a new connecting rod into a line could take eight to 12 weeks, with forward planning, he said. Once that is done, switching from manufacturing one component to another can be accomplished within a half-hour.

Making the Right Decision

According to Ulsoy, manufacturers need to consider the product mix in determining which type of production line to invest in. Factors to be considered include product mix, the expected volumes for those products, and how long production is expected to last. "Based on those decisions, companies can then make the decision about buying dedicated capacity, a flexible line, or a reconfigurable line," he said.

Reconfigurable machining systems also present their own set of issues that need to be considered, he added. For example, changing a line to produce a different product may necessitate changing software and controllers. Once a company decides to make a change, it should be careful to avoid problems of quality or excess downtime.

"Any time you make changes to anything, you potentially introduce problems," Ulsoy said. "You have to make sure that any changes you make don't affect quality or throughput negatively. And, if they do, you have to be able to find the problems quickly and resolve them." He said that the ERC for Reconfigurable Manufacturing Systems has programs that address these issues.