Proto Labs Inc., a quick-turn manufacturer of custom parts for product designers and manufacturers around the globe, raised nearly $70 million in an initial public offering late Thursday, selling 4.3 million shares of stock at $16 per share.

Proto Labs, the first initial public offering of the year among Minnesota companies, began trading Friday morning on the New York Stock Exchange under the ticker symbol PRLB. In early morning trading the stock was up more than $11 per share, to $27.49 per share. That is a more than 70 percent increase over its offering price.

The website IPOscoop.com, which tracks the performance of IPO offerings, had been estimating that the Proto Labs IPO would price in the range of $13 to $15 per share. The Proto Labs deal, which was said to be "oversubscribed" by interested investors, is the largest Minnesota-based IPO since AGA Medical Corp. raised $199 million in 2009.

The underwriters, including Piper Jaffray & Co. and Craig-Hallum Capital, plan to sell up to an additional 645,000 shares over the next 30 days.

Earnings at Proto Labs, a 12-year-old firm started by a Minnesota inventor, increased 63 percent in 2011 to $18 million on revenue that rose 52 percent to $99 million, according to documents filed with the Securities and Exchange Commission. The Maple Plain-based firm has doubled employment to 511 since 2008 and sold products in more than 50 countries.

Proto Labs, founded by Minnesota technologist Larry Lukis, also has acquired a 128,000-square-foot office and manufacturing facility in Rosemount for $4 million, on top of its three-building, 170,000-square-foot campus in Maple Plain, west of Minneapolis.

The company's shareholders include North Bridge Growth Equity (32 percent), Lukis (36 percent) and CEO Brad Cleveland (8 percent).

Eagan-based Private Capital Management, which owns about 17 percent of Proto Labs, was the first outside investor in the company in 2006. Brian Smith, president of Private Capital Management, a private money manager that oversees about $850 million in client money, is a Proto Labs board member.

Lukis, 63, co-founded the former LaserMaster, an innovator in laser printing, in 1985 and left to start what became Proto Labs in 1999, partly because he was frustrated with the quality of parts and service from vendors while at LaserMaster.

Cleveland, 52, came to Proto Labs in 2001 from Aero Met Corp, where he was a vice president of the laser-additive manufacturing subsidiary of MTS Systems.

The board includes Sven Wehrwein, 60, a veteran company director and financial executive who also served as a director of Compellent Technology and Synovis Medical. Those are local public companies that had good runs in recent years before being acquired by industry giants within the last year.

At least one other Minnesota company is pursuing an IPO. BioAmber, a Plymouth-based agricultural start-up, filed an initial registration statement hoping to raise $150 million on Nov. 14. BioAmber filed an amended registration statement on Feb. 3, an indication it's making progress on its offering.

The last Minnesota-based company to complete an IPO was Manny Villafaña's Kips Bay Medical, which priced on Feb. 11, 2011, selling 2.1 million shares at $8 per share and raising $16.5 million. Kips Bay closed Thursday at $1.41.

In 2010, two Minnesota companies completed IPOs: New Prague's Electromed and Minneapolis-based software company SPS Commerce.

Neal St. Anthony • 612-673-7144 • nstanthony@startribune.com • Patrick Kennedy • 612-673-7926 • pkennedy@startribune.com