Process and device for manufacturing hollow, internally cooled valves

A method for shaping a hollow valve preform a using a tapering machine having a matrix with a circular through opening that tapers from an outer diameter of the opening to a reduced cone inner diameter, and wherein the outer diameter is greater than or equal to an initial outer diameter of the valve preform, and the matrix reduced cone inner diameter is smaller than the initial outer diameter of the valve preform, and further including a pressing device and a pressing device controller that are configured for pressing the valve preform with a stem section thereof into the matrix with an oscillating motion, the method comprising the steps of:

• providing the valve preform with a head section and the hollow stem section having initial outer diameter,
• pressing the hollow stem section into the matrix with the initial outer diameter that is tapered to the reduced cone inner diameter as a result of pressing the initial outer diameter into the matrix,
• controlling the pressing device of the tapering machine with the pressing device controller in such a way that the valve preform with the stem section is pressed into the matrix with an oscillating force and/or an oscillating path;
• and
• providing a calibration mandrel which on a free end includes a calibration bulb;
• inserting the calibration bulb into the valve preform before the pressing step, and wherein after the pressing step, pulling, the calibration mandrel and out of the stem end to further reduce a wall thickness of the hollow stem section and to increase a length of the hollow stem section.