A process is disclosed for producing metal-based, high-aspect-ratio microscale structures (HARMs), for example microchannels in a heat exchanger. The preferred manufacturing method operates in a continuous mode, and employs low-temperature rolling of metals. A process is disclosed for bonding metal microchannel sheets or plates to flat metal sheets or plates to form single-, double-, and multiple-layered microchannel structures. The process can operate at much lower temperatures than prior methods of compression microscale molding of metals, at room temperature or even lower.