Customized metal-spinning machines fix out-of-round engine lip skins

MJC Engineering is a custom machine tool builder in Huntington Beach, California, specializing in metal-spinning machines for applications such as sheet spinning, flow forming, wheel spinning, and rotary forging. Recently, the company was commissioned to build a series of metal-spinning machines for GKN for use at its plants in Camarillo, California, and Orangeburg, South Carolina. These machines are currently in use, producing lip skins for the engine housings on Boeing 777X and 737MAX aircraft. Using advanced computer numerical control (CNC) from Siemens and robotic handling technology, plus its proprietary servopump-controlled Green Power hydraulic power unit, the team at MJC Engineering solved an engineering challenge brought to them by GKN.

Finding a solution

The key to the solution was how to spin-form production run components out-of-round by 8.5" to 9" in various aluminum alloy blanks measuring up to 270" diameters and 5/8" thickness, while holding tight tolerances to be verified by thermo-imaging cameras and fed back by the CNC for accuracy tracking, plus integrate the heating torch for in-process adjustments. Carl Lorentzen, president, MJC Engineering, Per Carlson, vice-president and general manager, and Don Hebert, electrical engineer, were up to the task.

Each day at MJC, Lorentzen and his team combine metal-spinning with modern CNC controls and robotics to create state-of-the-art manufacturing processes producing laminar-flow lip skins for Boeing’s 737MAX and 777X aircraft. The lip skin is the highly engineered aerodynamic structure that makes up the leading edge of jet engine nacelles.

Metal-spinning is a forming process in which a blank of material is rotated on a spinning machine similar to a lathe. The blank of material is clamped onto a spin-forming mandrel and rotated by servo-controlled motors and drives. During rotation, heat is applied by a gas torch affixed to a robotic armature and a roller on the spinning machine makes contact with the part blank, forcing the part blank to flow over the spin-forming mandrel surface.

Spin-forming, like no other metalforming process, has the ability to form very large and thick plates quickly and accurately. Though highly efficient in operation, the 737MAX and 777X CNC metal-spinning machines built by MJC for GKN rely on the precise and consistent application of heat throughout the metalforming cycle. Even the slightest variation in heating would contribute to undesirable results in the formed part.

Until recently, manufacture of these lip skin components relied on human intervention to control the direct application of heat throughout the spin-forming cycle. While this method can produce functional parts, the associated variations in consistency created downstream difficulties and challenges in subsequent fabrication and assembly operations. In the past, lip skins were produced by other methods, including draw-forming, bulge-forming, and drop-hammering. The spin-forming and machining techniques now used at GKN have been found to reduce overall manufacturing time and tooling costs, while improving part consistency.

Robots bring consistency

In an effort to reduce variation in the CNC spin-forming process to support high-rate programs such as the 737MAX and 777X, GKN Camarillo joined forces with MJC Engineering to create an automated CNC solution consisting of robots that apply heat in a precise and consistent manner, tied directly to a program shaping the part. This careful interplay between the heating and spin-forming operations is made possible by the Siemens Sinumerik 840D sl CNC, which integrates and monitors every movement between the spinning machine controller and the heating robot controller, resulting in a smooth-flowing production scenario with perfect timing and high marks for efficiency, according to James O’Sullivan, GKN general manager.

Before this combination, variation in product output was much less predictable. Now, part heating difficulties and variations are a thing of the past, according to MJC’s Carlson.

“CNC spin-formed lip skins with automated robotic heating exit the process as consistently as a stack of quarters, to draw an analogy. The results are derived from straightforward mathematical computations made possible by modern CNC technology from Siemens,” Carlson says. “Variation is the number one contributor to low manufacturing yields and increased operating costs. Study your process, understand where variations occur, and then eliminate them with cost-effective solutions. The improvement literally catapults a production floor to new levels of manufacturing excellence. It certainly has at GKN.”

How it’s done

In operation, the machine, takes the overhead crane-loaded 270" diameter blank, fixes it to the tailstock of the machine and rotates it on a 150hp motor-driven spindle, then progressively applies heat via the gas torch on the robot arm. Raytek thermal imaging cameras closely monitor the heat readings across the entire surface to create multiple control cones. When inconsistencies are detected, heat is appropriately adjusted in real time by the controllers. The heated material is then formed over the mandrel into the desired size, with out-of-round conditions ranging from 8.5" to 9" typically. Siemens Simatic S7 PLC technology is onboard the machine, controlling the various mechanisms, while the CNC integrates and feeds back all data.

Solid Edge is the CAD program for the design of the lip skin, while Siemens NX CAM translates the design data into machine execution steps. Each MJC machine involved in this project also incorporates Sinamics drives and Simotics motors from Siemens.

As electrical engineer Don Hebert explains, “There are seven axes of motion controlled by the CNC. We created custom screens for teach-in and playback on the machine to facilitate faster commissioning and troubleshooting onsite for the GKN operators. Zone Pro and Spin CAD were used to create the tool paths. On the robot, there are 32 pre-programmed moves, fully integrated with the heating and thermal imaging processes. The robot runs with an external PLC through G-code on the CNC, which dictates the on/off heating and cooling controls, based upon feedback from the temp zones monitored.”

Carlson adds, “From the time we built the first machine for Camarillo to the latest machine in Orangeburg, we have transitioned to newer technology; that’s how fast things are moving.”

Lorentzen concludes, “When we were also able to provide our Green Power technology and, in the process, save the customer substantial energy costs, the advantages of this machine design ratcheted up to a great degree.”

Using Sinamics servo-pump technology, Green Power provides the exact hydraulic pressures required, offering the customer energy-savings up to 40%, compared to a conventional constant-on hydraulic pump motor manifold.

MJC Engineering & Technology Inc.

www.mjcengineering.com

Siemens Industry Inc.

Motion Control

Machine Tool Systems

www.usa.siemens.com/cnc