Micro heat exchangers for controlling temperature of workpieces being joined by welding

A method, for controlling temperature of at least a first workpiece of multiple workpieces being welded together, comprising:

• positioning a first workpiece, of the multiple workpieces, and a micro heat exchanger adjacent each other, the micro heat exchanger comprising:
• a first heat-transfer fluid tube extending between a first fluid-tube inlet and a first fluid-tube outlet;
• and
• a second heat-transfer fluid tube, unconnected fluidly from the first heat-transfer fluid tube, extending between a second fluid-tube inlet and a second fluid-tube outlet,
• wherein:
• the first heat-transfer fluid tube is configured to receive heat-transfer fluid via the first fluid-tube inlet and channel heat-transfer fluid, from the first fluid-tube inlet, through a first heat-transfer fluid-tube section, and to the first fluid-tube outlet;
• the second heat-transfer fluid tube is configured to receive heat-transfer fluid via the second fluid-tube inlet and channel heat-transfer fluid, from the second fluid-tube inlet, through a second heat-transfer fluid tube section, and to the second fluid-tube outlet;
• positioning a second workpiece, of the multiple workpieces, adjacent the first workpiece;
• and
• passing a heat-transfer fluid through the first heat-transfer fluid tube or the second heat-transfer fluid tube, wherein the heat-transfer fluid is either:
• heated, thereby heating the first heat-transfer fluid tube or the second heat-transfer fluid tube and, by the first or second heat-transfer fluid tube, the first workpiece;
• or
• cooled in order to cool, by way of the first heat-transfer fluid tube or the second heat-transfer fluid tube, the first workpiece or material joining the first workpiece and the second workpiece while and/or immediately after welding the workpieces together.