chrringoftheprintingmachine:

Tony has always defended himself through evasive
manoeuvres, and never used shields.
Yet in Infinity War, he is using shields left and right. (The only time he shielded himself was in Iron Man 1, when he opened flaps in his gauntlet, and that was because he down low on power and couldn’t fly away.)

Tony realised that the team has lost a “shield”, so he took it upon himself to become one. He built a shield that could withstand the power of an Infinity Stone. Because he always knew the fight was coming, a bigger threat is on the horizon and he needed to be ready.

Meanwhile, Tony designed new shield for Cap (despite all the Civil War mess), new “magic” belt for Thor (despite not knowing whether Thor will return), ensured Hulkbuster was accessible to Bruce (despite Bruce being MIA) and built space-travel-safe spider-themed nano-suits for Peter (despite Peter not being an avenger yet).