STAHL SPECIALITY'S AGILE EVOLUTION
Advanced Machining Technology Helps Permanent Mold Caster Meet JIT Demands
As a QS9000-certified supplier, Stahl Specialty Company has taken the term full-service to heart. From initial design to delivery on the customer’s line, Stahl’s permanent mold aluminum castings, equipment and services are comprehensive. One reason Stahl can provide these products and services Just-In-Time (JIT) to customers including Bosch Braking Systems, Caterpillar, John Deere and General Motors is Stahl’s agile manufacturing processes.
In moving to the agile platform to support its production machinery business, Stahl has evolved from using custom-made, dedicated machinery to using high-speed machining technology.
Old and New Technology In Tandem
Stahl’s evolution to agile parts production began in 1969 when it first started using CNC machining centers alongside dedicated machinery that was custom-made by Stahl to perform several boring and drilling operations. As CNC technology continued to evolve and business increased, the benefits of adding more CNC technology became clear to Stahl.
"The flexibility and productivity provided by high-speed machining technology is beneficial to our production machinery department," says Ron Zara, Stahl’s manufacturing manager. "We switched over from a custom-made transfer line to 14 A77 high-speed horizontal machining centers from Makino. These machining centers are used to machine raw castings to customers’ tolerances and specifications."
"Product life cycles are shorter and JIT is pretty much status quo now in the industry," says Mike Duncan, Stahl engineering supervisor. "It used to be a part design would not change for 20 years. Now you either have to be agile or you do not get the job. This high-speed technology provides us the flexibility and quality levels necessary to respond quickly and efficiently."
Keeping Casting Volume High
Stahl’s production machinery department machines more than 40 percent of the castings poured in Stahl’s foundries, generating approximately 60,000 pounds of aluminum chips per week. According to Bill Hentschel, Stahl’s production machinery manager, flexibility is the key to delivering part volumes of this size.
"We might have 20 different flywheel housings in a part family being machined over a short period of time," says Hentschel. "With high-speed CNC, we just change over the tooling and the programming and we are ready to machine a different part number. It was somewhat of a paradigm shift on the shop floor going from multiple machines and set ups down to one machine and three set ups, but the learning process is fast. In fact, one operator can now handle the operations for two machines at once."
"With dedicated equipment, if one machine goes down, the whole line is down," says Zara. "If a high-speed machining center would go down, we would only lose a percentage of part volume. And, since multiple operations can be conducted on one machining center, part accuracy has improved for better Cpks overall."
This accuracy becomes more apparent by examining the machining of diesel flywheel housing. On the A77, roughing facemills need only take two passes before finishing operations begin. Finishing is done at 10,000 rpm utilizing solid carbide endmills and through-spindle coolant. 180 cubic inches per minute metal removal is reached on this aluminum casting and the entire flywheel housing application takes approximately 26 minutes to complete. Cited as instrumental to this application is the interpolated boring performed on the castings. The A77’s boring replaces the fixed boring previously done with a boring machine and vertical lathes.
"On the flywheel housings there are several boring operations to be performed, " says Hentschel. "Before the A77s we could not conduct boring on a machining center—too much chattering. Now we conduct all boring on the A77s, including a 20-inch diameter bore at a tolerance of 1 .0002 inches. Being able to interpolate a precision bore with standard tooling versus using a custom-made, fixed diameter boring bar has made a big difference around here. Special boring bars are hard to tool change. Also, using standard tooling and thread mill multiple holes without having to tool change is much more flexible."
One reason the A77s can interpolate boring is Makino’s proprietary Super Geometric Intelligence software, which compensates machine tool behavior on the fly, reducing tool path error. This allows accurate interpolations at high feed rates and boring operations at multiple diameters with a single end mill.
Agile Allows Tool room To Increase Focus
At first glance, it might seem that the teams making Stahl’s custom-designed dedicated machining equipment might be endangered by the evolution to agile manufacturing. However, as the production machinery department moves away from this equipment, the tooling department’s services are in greater demand—merely with a different focus. The tooling department’s shop floor perspective has proven invaluable to Stahl in quoting customer jobs.
"Advancements in machining center speed, flexibility and accuracy have made it impractical for my department to build off line, dedicated equipment," says Duncan.
Zara agrees noting, "transfer lines are white elephants around here now."
"If you have optimized the manufacturing equipment, you shift your focus to the off line processes," says Duncan. "We determine the best way to machine a casting. From how the part will be processed through the facility, to the work holding and tooling it will require. In a way we reverse engineer the process to determine the technologies needed to prove out on the shop floor. Agile manufacturing has provided us the ability to optimize non-cut time and any other operation that can be addressed more efficiently."
Fixturing was one non-cut time technology that was impacted positively by the switch to machining centers. "For most castings, we have been able to switch back to manual clamping," says Duncan. "We can get some good clamping on the A77s which allows us to get good cutting forces. Manual clamping also impacts non-cut time, reduces fixture cost and makes the fixtures simpler to use and clean. Manual fixtures do not have tubing or exposed clamps for chip accumulation on the fixture. And since manual fixtures do not have to be changed, there is less set up time."
A Continuing Evolution
Stahl Specialty plans on continually improving on its production machinery applications and cycle times through additional technology designed to optimize the agile process.
"To meet and exceed customer demands, you have to be prepared to do things differently," says Zara. "We continue to reevaluate our applications."
That reevaluation most recently resulted in Stahl replacing two CNC machines, and a battery of dedicated machines, with four more Makino A77 machining centers and a 12 pallet modular machining cell (MMC) for more efficient material handling. The MMC utilizes a rail-guided pallet shuttle to feed the machines consistently and assure optimum machine utilization. The MMC also provides more pallets per machine providing flexibility for the applications.
And upgrades will continue for Stahl as it has realized the key to being a full-service supplier means determining not just what services the customer needs, but the best way to deliver them.
Stahl Specialty Company is based in Kingsville, Missouri. For more information, contact Stahl at (816) 597-3322 or visit them at www.stahlspecialty.com.