Drilling stack materials

The aircraft industry now has the means to precisely machine multilayer material combinations.

These combinations, called stack materials, include several thin layers of different materials. Aircraft skin, for example, could consist of titanium, aluminum and composite layers, according to Lee Coleman, automation division manager for Suhner Manufacturing Inc., Rome, Ga.

Such combinations may improve end products, but can cause headaches for aircraft manufacturers trying to drill through them, as each material in the stack requires its own parameters for optimal machining. If the materials are drilled with the wrong speed and feed rate, the process won’t produce clean holes, Coleman said.

That’s why the French firm Somex, a member of the Suhner group of companies, developed an alternative to the pneumatic drills commonly used in the aircraft industry. In addition to their considerable air consumption and noise emissions, these pneumatic drills have fixed spindle speeds and feed rates, so they can’t be adjusted to the different material conditions encountered while moving through stack materials.

By contrast, Coleman noted, Somex’s new L-MAX is a CNC drilling unit that can be programmed to run at different speeds and feeds for each material in a stack and drill holes that meet the aircraft industry’s stringent quality standards. The L-MAX “is your only option when you’re dealing with stack materials that need to be cleanly drilled,” he said.

The L-MAX features two servomotors that work in conjunction with each other, one that drives the spindle and another for the feed. The motors are connected to a control system that lets users regulate the speed and feed at any point during drilling operations.

Another key L-MAX feature is its “adaptive drilling” mode. In this mode, the drill automatically recognizes the transition from one material layer to another and matches the speed and feed to the new material conditions.

The portable L-MAX is designed to drill clean holes in stack materials. Image courtesy Somex.