Sitting on a pallet in Arlington lies a slab of aluminum, roughly six inches thick and 12 feet long.

It’s too heavy for the average person to pick up, and it doesn’t serve much purpose.

But in a process that takes about 20 days, AMT turns that long, heavy slab of metal into something useful: a part for a Boeing 737 aircraft.

In those 20 days, the Arlington company uses advanced machines to shave and compress the aluminum into a wing rib. Then it sends the newly shaped ribs to Skills Inc., another aerospace company in the Puget Sound region, for finishing work.

It’s a common routine. Small, medium and large aerospace companies pooling their specialties to build an airplane.

“Machining is the core of our business,” said Derick Baisa, business development manager for AMT.

The company, which employs 275 people, estimates it has 35,000 hours of machine capacity open to customers each year. And with the backing of its parent company, Senior LLC, AMT has its eye on adding even more advanced machines.

“We’re utilizing technology to keep ourselves competitive in a global marketplace,” said Mark Riffle, chief executive officer of AMT.

The company runs one 12-hour shift Friday through Sunday and two 10-hour shifts Monday through Thursday.

AMT’s Riffle is confident the company can keep up with Boeing’s planned production increase to 37 aircraft monthly on the 737. Boeing is also considering a bump up to 40 monthly, which would match Airbus’ expected pace. Riffle says AMT can handle that, too.

Supplying the 54 wing ribs needed for each Boeing 737 that rolls out of the Renton factory is a large part of AMT’s business. But the company also supplies parts — including a 777 pylon fairing and 747 mop sills — for each of Boeing’s jets.

“We have a lot of different capabilities,” Riffle said.

While many aerospace companies in the county and region have diversified their portfolios, AMT’s success ultimately is tied to Boeing’s. About 93 percent of the work the company performs ultimately is for Boeing aircraft, though only 44 percent goes directly to the jetmaker locally. Boeing supplier Spirit Aerosystems gets about 25 percent of AMT’s work.

Through Spirit, some AMT products will end up on Airbus’ A350 jet. The Arlington company also supplies Bombardier, the Canadian jet maker.

“We’re getting more and more into complex assembly work,” Baisa said.

For example, AMT won a contract with Boeing’s Winnipeg division to assemble the 787 mid-cage, he said.

With 180,000 square feet of manufacturing space in Arlington, AMT is poised for growth, its leaders said. The company plans $89 million in sales for this year, $93 million in 2011 and $103 million in 2012 just to keep up with its customers’ planned production increases. Those estimates don’t include new business that AMT’s Riffle would like to recruit.

“We’ve got good content on the right platforms for growth,” Riffle said.