Injection molding firm Proto Labs Inc. opened a $19 million manufacturing plant in Plymouth this week while also announcing that it acquired a 3-D printing firm that will add $10 million to its annual sales.

The $37 million acquisition of Raleigh, N.C.-based FineLine Prototyping Inc. gives Proto Labs 85 workers and its first presence in 3-D printing. 3-D printing is a manufacturing process that uses computers, software and automated machines that repeatedly deposit tiny layers of plastic until a 3-D product is formed.

FineLine makes goods for customers in medical, aerospace, computer, consumer and industrial products industries, and the company serves the same industries as Proto Labs. But Proto Labs is new to 3-D printing and is best known for plastic injection molding and highly technical metal and plastic milling jobs.

During an interview Thursday, CEO Vicki Holt said FineLine will continue to be based in Raleigh. FineLine President Rob Connelly said in a statement "It is a great cultural fit for FineLine."

The addition of FineLine lands in what has become a big month for Proto Labs, which has $163 million in annual sales. The company just opened its fifth Minnesota manufacturing plant Thursday, gaining its first location in Plymouth.

Proto Labs originally planned to spend $15 million to buy, renovate and equip an abandoned foundry on Plymouth's Niagara Lane. But manufacturing Vice President Mike Kenison said Thursday that the company will spend $19 million after all the construction, materials-recycling, power and equipment costs are tallied for the Plymouth Industrial Building.

The 1971 building has become a great new use for the community, said Holt while touring the cavernous space Thursday.

"What I love about this project is we took a building that had been empty for seven years. … We are bringing a lot of jobs to this area," she said.

Proto Labs also expanded into steel and rubber injection molding earlier this month, after adding $3 million worth of automated equipment at its Maple Plain headquarters.

Transferring to Plymouth

Beginning Monday, 175 workers will transfer from Maple Plain to the Plymouth site. By 2017, 25 more workers will transfer and 100 new workers will be hired for a total of 300 employees. Proto Labs already has 500 workers across Minnesota and 285 more worldwide.

This weekend, crews will install the first 160 computerized milling machines that precision-cut hefty blocks of steel, aluminum or plastic into exacting parts for product designers and manufacturers of medical equipment, airplanes, autos and consumer products.

Eventually the 166,300- square-foot Plymouth factory will house 350 computerized milling machines, and 25 injection molding presses. Maple Plain will keep about 75 milling machines and 155 injection molding presses. Newly freed-up space in Maple Plain will be converted from manufacturing space to offices, Holt said.

The space is needed because "we are growing about 25 percent a year," she said. "We're pleased to be moving into our new Plymouth building. The additional location will help us meet the high demand for our quick turn, custom parts business."

Meanwhile, FineLine uses 3-D printers and software manufactured by Concept Laser and 3-D Systems Corp. It does not use systems made by Eden Prairie-based Stratasys, one of the larger 3-D printing firms in the country.

Holt said that Proto Labs managers expect to have some conversations with Stratasys in the coming months or years. "We know the folks at Stratasys very well," she said.