MJC Engineering, a custom machine tool builder in Huntington Beach, CA, specializes in metal-spinning machines for such applications as sheet spinning, flow forming, wheel spinning, and rotary forging. The company was commissioned to build a series of metal-spinning machines for GKN for use at its plants in Camarillo, CA and Orangeburg, SC. These machines produce lip skins for the engine housings on Boeing 777X and 737MAX aircraft. Using CNC from Siemens Industry (Elk Grove Village, IL) and robotic handling technology — in addition to its proprietary servopump-controlled Green Power™ hydraulic power unit that saves up to 40% on energy — the MJC team devised a unique solution to an engineering challenge brought to them by GKN.

The machine designed by MJC Engineering forms 270”-diameter aluminum sheets, typically 5/8” thick, into lip skins for the nacelles on the engines of Boeing 737MAX and 777X aircraft.

The key aspects of the solution comprised how to spin-form production-run components out-of-round by 8½" to 9" in various aluminum alloy blanks measuring up to 270" diameter and 5/8" thickness, while holding tight tolerances to be verified by thermo-imaging cameras and fed back by the CNC for accuracy tracking. The solution also had to integrate the heating torch for in-process adjustments.

Combining Old and New

Each day, the MJC team combines the same metal-forming process that has been around for millennia with modern CNC controls and robotics to create the state-of-the-art manufacturing process used to produce laminar flow lip skins for Boeing’s newest flagship 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.

Siemens Sinumerik 840D sl CNC — along with Sinamics drives, Simotics motors, and Simatic PLC — control the seven axes of motion on the machine and the 32 programmable movements of the robot, to which the heating torch is affixed.

Spin-forming, like no other metal-forming 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 and currently located at GKN, are reliant upon the precise and consistent application of heat throughout the metal-forming 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 upon human intervention to control the direct application of heat throughout the spin-forming cycle. While this method could certainly produce a functional part, the associated variations in part 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.

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. That solution is now a reality, and consists of robots that apply heat in a precise and absolutely consistent manner, tied directly to a program that shapes 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.