The same investors who participated in the 2011 seed round are back. Downloads have topped 1 million.

Engineering collaboration community GrabCAD has raised $4 million in a Series A funding round. This comes six months after an initial angel funding round of $1.1 million. (See the GraphicSpeak article,“GrabCAD lands $1.1 million investment,” June 9, 2011.)

GrabCAD provides a home for mechanical engineers to share models, build portfolios, and seek projects or employment. It has more than 70,000 registered users, and has passed the 1 million download mark.

Lead investors in this round include venture capital firms Matrix Partners and Atlas Ventures. David Skok, a Matrix Partners general partner and former member of the Dassault Systèmes SolidWorks board of directors, will join the GrabCAD board of directors. Another investor of note in this round is former SolidWorks CEO John McEleney. All were involved in the angel round.

“Series A round” is the name typically given to a company’s first significant round of venture funding in the tech industry model of start-up company formation, after the initial (angel) round. The name refers to the class of preferred stock sold to investors in exchange for their investment.