Industrial giant Siemens' Healthineers unit made its debut on the Frankfurt stock exchange Friday after the group raised 4.2 billion euros in an initial public offering that came in at the lower end of expectations.

Healthineers, one of Siemens' largest and most valuable divisions, supplies hospitals around the world with everything from X-ray and MRI machines to lab diagnostics gear and robotic arms used in the operating theatre. It's in robust health, achieving an operating profit margin of around 18 percent last year and revenues of 13.8 billion euros ($17 billion), second only to Siemens' flagship but troubled power and gas unit.

In a statement late Thursday, Siemens said it had fixed the price for the sale of its 15-percent stake in Healthineers -- equivalent to 150 million shares -- at 28 euros per share, valuing the company at some 28 billion euros. It had earlier set a price range of 26 to 31 euros. The flotation comes as the sprawling Siemens conglomerate seeks to become more nimble in response to changing markets and stronger competition.