Tool temperature control

A method of manufacturing a workpiece comprising the steps of:

• providing a tool element having a tool surface, and a control surface opposite the tool surface;
• a thermal control structure defining a fluid chamber partially bounded by the control surface and a plurality of plates, the fluid chamber comprising a fluid inlet configured for the introduction of a heating/cooling fluid and a fluid outlet, the fluid chamber being defined by walls that diverge towards the control surface;
• and a thermal control assembly comprising a tube that extends from outside the fluid chamber, that defines the fluid inlet into the fluid chamber and that extends into the fluid chamber in a direction toward a central point of the control surface such that the tube directs fluid toward the central point of the control surface, the thermal control assembly containing an electrical resistive air heater configured to heat the heating/cooling fluid flowing into the fluid chamber, wherein the electrical resistive air heater is attached to the tube at a position outside the fluid chamber and has an output entering the tube;
• providing an opposing tool element,
• forming the workpiece between the tool element and the opposing tool element.