This digitized duo involved the Flash of two worlds. Robotman* left behind his native Earth-Two after fighting alongside fellow All-Star Squadron members versus time travel tyrant Per Degaton. His fellow All-Star Steel had himself accidentally left his native world in 1942 during the Crisis on Infinite Earths, and ended up on Earth-One, where he retired as a superhero and became a soldier and wealthy industrialist. Robotman remained an active hero.
Another mechanized man who journeyed across the dimensional barrier, in the reverse direction, was the sentry from the 64th Century which Flash brought with him from Earth-One as he tracked down his foe Abra Kadabra, now battling Earth-Two's Flash in Keystone City! This sentry was never shown as leaving Earth-Two, and hence forth it is assumed that eventually that Earth's Flash, Jay Garrick, tracked it down and scrapped it for parts.
* It should be noted that a previously reference remark that Robotman, aka Paul Dennis, would never meet the Earth-One Paul Dennis Robotman, was referring to the second body Robotman built for himself after his first was destroyed, shortly before he journeyed to Earth-One for a couple decades. Plus the fact that the Robotman in the prime Earth-Two timeline faded from existence when the Robotman from a divergent timeline created by Per Degaton moved to prime universe Earth-One in the mid-1940's.