Aircraft Parts Manufacturer Reaps Benefits of FMS
System delivers the ultimate in flexibility--lot sizes as small as one.
Aerospace suppliers are responding to fast-changing production rates with innovative new manufacturing technologies, assumption of new roles, and increased efficiencies.
The Piper Archer is powered by the 360-cubic-inch series Lycoming engine.
One such supplier, Kurt Manufacturing Co. of Minneapolis, MN, has implemented a flexible manufac turing system (FMS) for producing piston-driven aircraft engine crankcases in what it calls the "ultimate in flexibility"--the ability to run with lot sizes as small as one engine crankcase. In all, 24 different versions of these crankcases are produced quickly with minimal changeover and effort.
To ensure the highest level of quality, every tool, operation, and part is tracked by computer from process beginning to end. Utilizing a tool management system and a probing package to prevent errors that could occur in conventional machining operations, the system delivers a very high level of quality, with the advantages of short lead times and product mix flexibility.
More than half the world's general aviation fleet is powered by Lycoming.
This work cell, comprised of three Leblond Makino A77 machines with computer-controlled delivery vehicle and several support machines, operates 24 hours a day, seven days a week, employing four teams of eight operators, giving its customer Textron Lycoming the correct model and engine crankcase when required.
Focusing on expertise
Textron Lycoming manufactures piston aircraft engines in four, six, and eight cylinders from 100 to 400 horsepower. These engines are normally aspirated or fuel injected, with some engines turbo-charged and/or intercooled.
Over the past 70 years, Lycoming has produced more than 275,000 piston aircraft engines with a reputation for performance and reliability. From the World Aerobatic Championships in 1998 where Lycoming powered 24 of the 27 competing aircraft, to engines for the revolutionary Piper Malibu Mirage and the new family of Cessna aircraft, Textron Lycoming engines now dominate and power more than 85% of the new-generation piston engine powered aircraft produced worldwide.
To meet the needs of a world market with widely differing requirements and fluctuating demand, Howard Best, Textron Lycoming procurement team manager, said that his company looked both inward and outward for possible solutions.
"When we entered the 90s, we had to modernize our machining processes regardless of what the market might do," Best stated. "We were both a supplier of new engines and also had a large base of engines in use which required periodic refurbishing and rebuilding to stay certified. Much of our machining operations were designed in the late 70s and early 80s and we needed to stay competitive. Drawing on the Air Force's lean manufacturing initiatives of reorganizing facilities and processes to focus on core expertise, outsourcing appeared to be a viable option, especially after a thorough investigation of what suppliers offered."
In 1994, Best participated in a cost-analysis team to evaluate strategies for modernizing its machining operations and evaluate outside machining capabilities.
Best's team was given responsibility for crankcases, and other soft metal parts--all parts machined from castings. The team consisted of a manufacturing engineer, quality engineer, and procurement manager. The team visited up to 100 precision machining suppliers and received support from finance material planning, legal, and design engineering departments.
Driving the project
"We had to have a partner that could not only think big but act big because of the upfront technical requirements to design the process and capital equipment investment to implement the process," Best said.
New Kurt process machines crankcase halves in matching pairs with repeatable precision.
Kurt--which had long-term relationships with Honeywell on military projects and IBM on major computer programs, and a longtime supplier of airframe and flap control gearbox systems to Boeing--came to the table prepared to design a process that was completely new and different from anything it had done before. The $3.5 million capital expenditure for the complete cell was the largest for Kurt on a single project up to that time.
Nineteen-year Kurt veteran engineer Gary Stockwell was put in charge of the project, "and really put life into it," said Best. "He and his counterpart at Lycoming, Mike Cervinsky, traveled back and forth spending weeks at both Kurt and Lycoming plants designing the process, assembling the worker teams, acquiring the new machines, building the tooling, writing the computer programs, and proving out the process. Someone jokingly said Stockwell and Cervinsky were joined at the hip but that's what it took from the time the project started in mid-1995. We placed our first order with Kurt in January 1996 and had product delivery starting in August."
Cervinsky and Stockwell set an early target to design a process that would produce the finished machined crankcase halves in matching right and left pairs to satisfy the basic requirement of just in time. The batch processing method, which was previously used, produced only individual crankcase halves and lacked flexibility for inventory management. By employing a machining system that produced the crankcases in matching pairs with a tracking process that monitors every tool and each operation every step of the way, the highest quality level was achieved insuring that crankcase halves matched perfectly, eliminating later part matchup and assembly problems.
Gun drilling operation for 0.1875´´ diameter oil passages in crankcase on one of the Makino A77's. This particular machine, on the day photographed, had a utilization time of 99.27% for 24 hours.
"The new process design concept grew out of a pre-80s FMS system Lycoming had been operating but with the creative use of 90s machining technology," said Best. "The original Lycoming cell consisted of two Kearney and Trecker model 800 machining centers, ten 4-axis CNC mills, and four other on-line index machines. Castings were loaded and shimmed by hand to machine tables. Tracks with chains moved parts from machine to machine and four huge computers operated the cell. It was a good system but it was slow by today's standards and it lacked flexibility. Everything was batch processing with 20 to 30 right crankcase halves machined first followed by 20 to 30 left crankcase halves. We carried a large inventory. The cell and finished inventory occupied five times the floor space in comparison to the new system at Kurt with its JIT features."
Designing the new process took several weeks with intensive analysis of many different approaches by both Kurt and Lycoming engineering teams.
Kurt workcell for producing Lycoming engine crankcases consists of these 3 Model A77 Leblond Makino machining centers. A computer controlled delivery vehicle moves the crankcase halves through the cell.
"We explored using vertical machines, extra long bed machines, the load/unload requirements, and secondary operations needed," said Gary Stockwell. "We analyzed the amount of operator intervention all of these approaches required. We examined carefully low to high tech solutions for just about every operation. We settled on the Leblond Makino A77's because they gave us the speed, accuracy, and tool change time needed."
Kurt's new system with three Leblond Makino A77 machining centers (2 range, 30 kW/40 HP, 30 min. rate, integral drive, under race cooling, CAT 50 V-flange) are equipped with twin pallet changers and capable of spindle speeds to 18,000 rpm. These machines have spindle lubricant temperature controller, random pallet selection for assignment of individual programs for each pallet, adaptive control and spindle load monitoring, as well as tool life monitoring. Geometric intelligence control enhances high feed rate machining by analyzing and optimizing the feed rate based on the program geometry. A combination of highly refined AC digital servos and proprietary software make it possible to feed at the fastest rates relative to machining conditions while maintaining the specified accuracy. According to Stockwell, more than 1300 different part features are computer monitored and controlled throughout the manufacturing cycle.
Geometric intelligence control provides for high feed rate machining in each of Kurt's Model A77 Leblond Makino machines. This feature analyzes and optimizes the feed rate based upon the program geometry. The machines have many features for high speed machining, including coolant temperature control. Kurt machines in the 14,000 speed range.
Kurt operates these machines in the 14,000 rpm range with workpiece accuracies to ±0.0025 in the X-Y-Z- axis. The real efficiencies for the Textron Lycoming crankcase application, according to Stockwell, is in the tool change time of just 2.0 sec. and chip-to-chip time of 5.0 sec. The machines employ automatic tool changers with 244 tool capacity with every end mill holder custom balanced. Castings are hydraulic clamped throughout the machining cycle for holding repeatability.
Starting with raw aluminum castings, a computer controlled delivery vehicle presents fixtured castings to the first available Makino machine. Each machine's custom program performs close tolerance three, four, and five axes operations including drilling, tapping and boring operations.
The FMS controller assures that the machines do not have to wait for parts as long as the operator loads a fixture and releases it to production so that the delivery vehicle will deliver it to the next available machine. The part is shuttled through seven different machining fixtures before it is finally complete. Parts are scheduled and run when they are needed. This enables both Kurt and Lycoming to minimize inventory and the associated costs. Because there is no setup time required, the cell can quickly respond to changes in quantity requirements.
Secondary and finishing operations are completed using dedicated drill tables, a gun drill, two radial drills, and a custom tooled Snyder line boring machine with the final machine sequences completed in the FMS. Once the parts are machined, hand deburred, studded, tumbled, deburred, and washed, they are inspected, boxed, and shipped to Lycoming's engine assembly line in the required configuration. In all, 20 different versions of these crankcases are produced with minimal changeover and effort. Quantities of different models usually range from a low of 2 to a high of 20 pair a week, which according to Best is the most efficient quantity for their use.
The best benefit of the new Kurt system was that "the machining process didn't have to be a struggle. We were able to achieve predictable and repeatable quality. That's really what the bottom line is these days."
For more information, call 763-572-1500 or go to www.kurt.com
Or write to, Kurt Manufacturing 5280 Main Street NE Minneapolis, Minnesota 55421.
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5280 Main Street NE
Minneapolis MN 55421